CA2072641A1 - Paper coating - Google Patents
Paper coatingInfo
- Publication number
- CA2072641A1 CA2072641A1 CA002072641A CA2072641A CA2072641A1 CA 2072641 A1 CA2072641 A1 CA 2072641A1 CA 002072641 A CA002072641 A CA 002072641A CA 2072641 A CA2072641 A CA 2072641A CA 2072641 A1 CA2072641 A1 CA 2072641A1
- Authority
- CA
- Canada
- Prior art keywords
- cationic
- weight
- pigment
- coating composition
- paper
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/36—Coatings with pigments
- D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
- D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Paper (AREA)
- General Preparation And Processing Of Foods (AREA)
- Non-Silver Salt Photosensitive Materials And Non-Silver Salt Photography (AREA)
- Medicinal Preparation (AREA)
- Wrappers (AREA)
- Making Paper Articles (AREA)
Abstract
There is disclosed an aqueous paper coating composition which comprises at least 45 % by weight of a particulate pigment dispersed with a dispersing agent, and an adhesive; characterised in that said dispersing agent comprises an anionic polyelectrolyte and a cationic polyelectrolyte, the cationic polyelectrolyte being present in an amount sufficient to render the particles cationic, in that said adhesive is a cationic or non-ionic adhesive and in that said particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said cationic polyelectrolyte. Also disclosed is a method for making the paper coating composition, a method for coating a paper with a paper coating composition and the resulting coated paper. The coated paper of the invention is particularly suited to recycling.
Description
Z1~7;~541.
PAPER COATING
This invention relates to a paper coating composition, a method for preparing a paper coating composition, a method for coating a paper with a paper coating composition and coated paper. This invention also relates to a paper recycling process in which a coated paper of the invention is employed as "broke" in a paper making process. "Broke" i~ the term used in the art for paper, cardboard, or the like which is to be recycled.
Calcium carbonate is known as a paper coating pigment and, because it normally carries a positive charge, it is conventionally dispersed with an anionic dispersing agent. Other paper coating pigments which carry a neutral or positive charge exist, such as gypsum, talc, calcined kaolin clay, and these must also be dispersed using an anionic dispersing agent. (These minerals are also recognised as having a deficiency in negative sites).
A full discussion of the constituents of paper coating compositions and of the methods of applying such compositions to paper i9 given in Chapter XIX, Volume III of the second edition of the book by James P. Casey entitled "Pulp and Paper: Chemistry and Technologyn. A further discussion is given in "An Operator's Guide to Aqueous Coating for Paper and Board", edited by T.W.R. Dean, The British Paper and Board Industry Federation, London, 1979.
DE-3707221 and EP-0307795 disclose a cationic pigment dispersion. The pigment is first given a protective colloid cover using a cationised polymer and then, under certain circumstances, i8 di~per~ed with a - cationic polymer. --TAPPI, vol. 65, no. 4, April 1982, pages 123-125, Atlanta, Georgia, U.S.A.; A.J. Sharpe, Jr. et al.:
"Improved Cationic Conductive Polymer Displays Wosl/08~1 PCT/CB90/01883 z~7~64~ -2-Outstanding Fflmability describes a polysalt formed from the interaction of a strongly cationic polymer, such a~ a poly(diallyl dimethyl ammonium chloride), and a weakly anionic polymer, ~uch as polyacrylic acid.
The thus-formed polysalt is added in substantial quantities (of the order of 50% by weight, based on the weight of the pigment) to a predispersed, low ~olids pigment slurry in order to provide a conductive coating ;j colour which is used to prepare a paper having a conductive surface.
~'.
According to a first aspect of the present invention there is provided an aqueou~ paper coating ; composition which comprises (i) at least 45% by weight ~:.
of a particulate inorganic pigment dispersed with a dispersing agent and (ii) an adhesive; characterised in that said dispersing agent comprises an anionic polyelectrolyte and a cationic polyelectrolye~ the cationic polyelectrolyte being present in an amount`
~; sufficient to render the pa,ticles cationic; in that said adhesive is a cationic or non-ionic adhesive; and in that said particulate pigment i~ one which i~ not ;3 capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said ~- cationic polyeletrolyte.
Z5 According to a second aspect of the present invention there is provided a method of coating a sheet member comprising the step of coating the sheet member with a paper coating composition in accordance with the first aspect of this invention.
According to a third aspect of the present invention, there is provided a coated paper produced by the method of the second aspect of this invention.
The particulate pigment used in the present invention is one which i8 not capable of being dispersed in water at high solids (~uch as greater than 60% by weight) and following vigorous mixing, (for example sufficient to dissipate at least 10kJ
of energy per kg of dry piqment), in the .
.; , W~3 91/08341 PCI/GB90/01883 2~264~
PAPER COATING
This invention relates to a paper coating composition, a method for preparing a paper coating composition, a method for coating a paper with a paper coating composition and coated paper. This invention also relates to a paper recycling process in which a coated paper of the invention is employed as "broke" in a paper making process. "Broke" i~ the term used in the art for paper, cardboard, or the like which is to be recycled.
Calcium carbonate is known as a paper coating pigment and, because it normally carries a positive charge, it is conventionally dispersed with an anionic dispersing agent. Other paper coating pigments which carry a neutral or positive charge exist, such as gypsum, talc, calcined kaolin clay, and these must also be dispersed using an anionic dispersing agent. (These minerals are also recognised as having a deficiency in negative sites).
A full discussion of the constituents of paper coating compositions and of the methods of applying such compositions to paper i9 given in Chapter XIX, Volume III of the second edition of the book by James P. Casey entitled "Pulp and Paper: Chemistry and Technologyn. A further discussion is given in "An Operator's Guide to Aqueous Coating for Paper and Board", edited by T.W.R. Dean, The British Paper and Board Industry Federation, London, 1979.
DE-3707221 and EP-0307795 disclose a cationic pigment dispersion. The pigment is first given a protective colloid cover using a cationised polymer and then, under certain circumstances, i8 di~per~ed with a - cationic polymer. --TAPPI, vol. 65, no. 4, April 1982, pages 123-125, Atlanta, Georgia, U.S.A.; A.J. Sharpe, Jr. et al.:
"Improved Cationic Conductive Polymer Displays Wosl/08~1 PCT/CB90/01883 z~7~64~ -2-Outstanding Fflmability describes a polysalt formed from the interaction of a strongly cationic polymer, such a~ a poly(diallyl dimethyl ammonium chloride), and a weakly anionic polymer, ~uch as polyacrylic acid.
The thus-formed polysalt is added in substantial quantities (of the order of 50% by weight, based on the weight of the pigment) to a predispersed, low ~olids pigment slurry in order to provide a conductive coating ;j colour which is used to prepare a paper having a conductive surface.
~'.
According to a first aspect of the present invention there is provided an aqueou~ paper coating ; composition which comprises (i) at least 45% by weight ~:.
of a particulate inorganic pigment dispersed with a dispersing agent and (ii) an adhesive; characterised in that said dispersing agent comprises an anionic polyelectrolyte and a cationic polyelectrolye~ the cationic polyelectrolyte being present in an amount`
~; sufficient to render the pa,ticles cationic; in that said adhesive is a cationic or non-ionic adhesive; and in that said particulate pigment i~ one which i~ not ;3 capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said ~- cationic polyeletrolyte.
Z5 According to a second aspect of the present invention there is provided a method of coating a sheet member comprising the step of coating the sheet member with a paper coating composition in accordance with the first aspect of this invention.
According to a third aspect of the present invention, there is provided a coated paper produced by the method of the second aspect of this invention.
The particulate pigment used in the present invention is one which i8 not capable of being dispersed in water at high solids (~uch as greater than 60% by weight) and following vigorous mixing, (for example sufficient to dissipate at least 10kJ
of energy per kg of dry piqment), in the .
.; , W~3 91/08341 PCI/GB90/01883 2~264~
sole presence of the cationic polyelectrolyte. This means that the pigment surface should have a neutral, or overall positive, charge. This i8 true of inorganic pigmentn such as calcium carbonate, calcium sulphste, talc and calcined kaolin clay, for example. Most preferably, the pigment i8 calcium carbonate, in any form, natural or synthetic. Most preferred is ground or crushed marble, but chalk, or precipitated calcium - carbonate (PCC) may also be used. In this respect, it should be noted that whilst raw chalk is capable of being dispersed using a cationic polyelectrolyte in the ; absence of vigorous mixing, this is not true if the chalk is subject to vigorous mixing. It i~ believed that this is because the vigorous mixing strips off the anionic aluminosiliceous layer normally present on raw chalk. In the absence of vigorous mixing, the aluminosiliceous layer is able to confer a negative charge on the surface of the chalk particlee and this enables dispersion by a cationic polyelectrolyte to be achieved.
~i It is preferred that the ground pigment has a particle size distribution such that at lea~t 50%
percent by weight has an equivalent spherical diameter smaller than two microns. More preferably, at least 60% percent by weight has an equivalent spherical diameter smaller than two microns. _ Ground marble for use in the present invention is preferably formed by crushing batches of marble in aqueous suspension in the absence of a chemical dispersing agent using a particulate grinding medium.
; Any agglomerates formed may be broken up by dewatering the suspension of ground marble, for example by filtration in the absence of a flocculating agent and ;~ then drying the pigment, and pulverising the dried product in a conventional mill.
The particulate pigment is dispersed with the .
.
WO91/0834l PCT/GB90/01883 2Q7~164~ r combination of an anionic polyelectrolyte and a cationic polyelectrolyte. Preferably, the anionic polyeletrolyte is a water-soluble vinyl polymer, an alkali metal or ammonium ~alt thereof or an alkali S metal or ammonium salt of polysilicic acid. Most ; preferably, the anionic polyeletrolyte is a poly(acrylic acid), a poly(methacrylic acid), a substituted poly~acrylic acid) or a substituted poly(methacrylic acid), or an alkali metal or ammonium 10 salt of any of these acids. The substituted poly(acrylic acid) may be a partially sulphonated polymer. An especially effective anionic polyelectrolyte is an alkali metal or ammonium salt of a copolymer of acrylic acid and a sulphonic acid 15 derivative of acrylic acid, in which the proportion of the sulphonic acid derivative monomer is preferably from 5% to 20% of the total number of monomer units.
The number average molecular weight of the anionic polyelectrolyte is preferably at lea~t 500, and ~i 20 preferably no greater than lO0,000. The amount u~ed is generally in the range of from about 0.01% to about 0.5% by weight based on the weight of dry pigment, preferably in the range of from about 0.1 to 0.2% by weight.
The cationic polyelectrolyte may be a water-soluble substituted polyolefine containing quaternary ammonium groups. The quaternary ammonium group~ may be in the linear polymer chain or may be in branche~ of the polymer chain. The number average molecular weight of the substituted polyolefine i8 preferably at least 1500 and preferably no greater than 1,000,000, and is more preferably in the range of from 50,000 to 500,000.
- The quantity required i~ generally in the range of from about 0.01% to about 1.5% by weight based on the weight of dry pigment. Advantageou~ results have been obtained when the substituted polyolefine is a poly .. .... , , ., .,, . . , . .. , , . . , , . , . .. .. . .. " . . . .. . ...... . . . . . .. . .. . . . . . . .. . ...
.
W 0 91/08341 `2~7~S41 P~rJGB90/01883 . .~
. (diallyl di(hydrogen or lower alkyl)ammonium salt).
The lower alkyl groups, which may be the same or different, may for example, have up to four carbon . atom~ and e~ch i~ preferably methyl. The ammonium ~alt ` 5 may be, for example, a chloride, bromide, iodide, ~S04-, CH3S04- or nitrite. Preferably the salt is a chloride.
Most preferably, the cationic polyelectrolyte is poly (diallyl dimethyl ammonium chloride). Alternatively, .~ the water-soluble substituted polyolefin may be the . 10 product of co-polymerising epichlorohydrin and an aliphatic secondary amine, said product having the ~-. formula .~--CEI2 c~2 C~2 ~
: 15 X' lR' l~
;: in which R and R', which may be the same of different, .i are each hydrogen or a lower alkyl group having from one to four carbon atom~, preferably methyl or ethyl `. and ~ i5 Cl-~ Hr~' I-~ EIS0~ C~3SO"- or nitrite. The preferred number average molecular weight of this epichlorohydrin product i5 in the range of from 50,000 ~ to 300,000.
: Alternatively, the cationic polyelectrolyte may be a water-soluble organic compound having a plurality of basic groups and preferably having a number average molecular weight of at least 10,000 and preferably no greater than 1,000,000. Most preferably, the number ~:: average molecular weight is at least 50,000. These : water-soluble organic compounds may be described as polyacidic organic bases, and are preferably compounds of carbon, hydrogen and nitrogen only and are free of other functional groups, such as hydroxy or carboxylic acid groups, which would increase their solubility in water and thus increase the likelihood of their being desorbed from the clay mineral in an aqueous suspension. Preferably, the organic compound is , ' ' .~
.
WO91/08~1 PCT/GB90/01883 ~Q7~641. ~ :--polyethyleneimine (PEI) having a number average molecular weight in the range 50,000 to l,000,000. A
further example of a water-soluble organic compound ~ which may be employed is a polyethylene diamine which .1 5 may be a copolymer of ethylene diamine with an ethylene dihalide or with formaldehyde.
: The cationic polyelectrolyte is employed in an : amount sufficient to render the mineral particles cationic. Experiments have shown that the zeta potential of the particles will normally be at least ~2~mV after treatment, typically in the range of from ~30 to ~40 mV and usually no greater than +50 to ~60mV.
These potentials have been measured using a dilute (0.02 weight %) solids suspension using a supporting lS electrolyte of potassium chloride (lO~M) with a "Pen Kem Laser Z" meter.
: The ratio of the weight of cationic polyelectrolyte to the weight of anionic polyelectrolyte used is preferably in the range of from 20 2:1 to 20:1, when the calcium carbonate is a ground marble.
According to a fourth aspect of the pre~ent invention, there is provided a process for preparing a paper coating composition comprising the steps of:
(i) dispersing in aqueous suspension a particulate pigment; and ~
(ii) combining the dispersed aqueous suspension with an adhesive and, if necessary, adjusting the dilution such that the particulate material constitutes at least 45% by weight of the composition;
characterised in that said pigment is dispersed using a dispersing agent comprising a combination of an anionic polyelectrolyte and a cationic polyelectrolyte;
in that said cationic polyelectrolyte is used in an amount sufficient to render the pigment particles cationic; in that said adhesive is a cationic or non-.~, .
: , :
~ ` ~'0 91/08341 PC~r/G B90/01883 2~2~
-ionic adhesive; and in that ~aid particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the ~ole presence of ~aid cationic polyeletrolyte.
In the method of the invention, it is normally the case that the raw pigment is received a~ a filter cake having a relatively high solids content. To thi~ i8 added the dispersing agent in order to provide a dispersed high solids slurry ~45-80% by weight ~olids) : 10 which may then be subjected to vigorou6 mixing. This slurry is then "made down" into a paper coating composition by dilution and addition of the required quantity of the cationic or non-ionic adhe~ive and other conventional paper coating composition adjuvants.
Preferably, the pigment is mixed with the anionic polyeletrolyte before mixing with the cationic polyelectrolyte. This appears to enable a more fluid suspension to be obtained at a higher solids concentration.
The aqueous dispersion of the pigment may also include other conventional paper coating composition adjuvants such as an insolubilising agent (e.g. a ` melamine formaldehyde re~in), a lubricant such as - calcium stearate and a catalyst to catalyze cross-linking of the cationic latex if present: a ~uitable such catalyst is sodium bicarbonate. The quantities of ; these adjuvants required are known to those skilled in the art.
The adhesive used in the present invention should be a non-ionic or a cationic adhesive. Such adhesives - contrast with the anionic adhesives which are normally used in paper coating compositions in which the pigment is anionic. Thus, cationic guar gum and cationic starch adhesives can be used as well as cationic or non-ionic latices. Such cationic and non-ionic adhesives are readily commercially available. The particular cationic or non-ionic adhesive used will ~ .
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..
~ WO91/08341 PCT/GB90/018X3 2Q7~641.
depend, for example, on the printing proce~a to be used, e.g. offset lythography requires the adhesive to be water-insoluble. For paper to be used in an offset printing technique, the amount of adhesive should ` 5 preferably be of the order of from 7 to 25~ by weight, based on the weight of pigment whil~t, for graw re printing paper, the adhesive should be used in an amount of 4-15% by weight, based on the weight of pigment. The precise quantity of adhesive required }0 will depend upon the nature of the adhesive and the material being coated, but this can readily be determined by the person skilled in the art.
The suspe~sion of the pigment for incorporation into the paper coating composition of the present invention should preferably be subjected to vigorous mixing before or after dispersion. Typically, the vigorous mixing should be sufficient to impart at least lOkJ energy per kg of pigment, and preferably no more than about 50kJ per kg. Normally, the amount of energy input will be in the range of from 18-36kJ per kg of pigment.
The coating composition may be coated on to a sheet member using normal paper coating machinery and under normal paper coating conditions. It has been found that the paper coated with a cationic composition in accordance with the present invention provides broadly similar results to that obtained with a conventional anionic system.
The coated paper of the present invention is of advantage when it is employed as "broke" or recycled paper in a paper making process. Commonly, large quantities of paper are recycled at the point of manufacture for one reason or another, and the advantages of the paper of the present invention in recycling are most important to the paper manufacturer.
Thus, in accordance with a fourth aspect of the present : ...
:~ WO 91tQ8341 PCI/GB90/01883 2~7:~641.
, 9 invention, there is provided a method for recycling paper including the step of reducing paper in accordance with the third aspect of the present invention to a fibrous recyclable state and incorporating said fibre in a paper-making composition.
Such a paper-making composition may include conventional paper-making pulp, such as a bleached sulphite pulp and, typically, the broke fibre and the . pulp will be employed in a ratio of from 10:90 to : 10 60: 40 .
~` Also included in the paper making composition will be a filler, for instance a calcium carbonate filler and also a retention aid. Since the broke fibre will include a proportion of calcium carbonate from the coating, it is possible to reduce the amount of calcium carbonate filler employed to give a total quantity of filler in the range of from 5 to 20 percent by weight of the total paper-making composition. The weight of dried broke added (fibre and filler) should preferably be in the range of from about 5 to 30 percent by weight of fihre.
It has been found that, when the broke fibre employed is derived from a coated paper in accordance with the present invention, this enables the amount of retention aid employed in the paper making composition to be reduced.
The present invention will now be illustrated by the following examples: -Three batches of raw cru~hed marble were ground in anaqueous suspension containing 30% by weight of dry solids and in the absence of chemical dispersing agent, by means of a particulate grinding medium. The duration of grinding wàs different in each case 50 as ~` 35 to yield three different ground products having p~rticle size distributions such that 50%, 68~ and 87 ~; .
~.
, .
:
WO91/08~1 PCT/GB90/01883 ,.,.~
2~7~ o-- ~y weight, respectively, had an equivalent spherical diameter smaller than 2 microns. In each case the suspension of ground marble wa~ dewatered by filtration in a tube pressure filter in the absence of a flocculating agent and the filter cake was dried and ; pulverised in a laboratory hammer mill.
Samples of each of the three ground marble powders were mixed with water and with two different dispersing ; age~ts by each of two different methods described below. The dispersing agents were:-(E) an anionic polyelectrolyte which was a sodium polyacrylate having a number average molecular weight of 4,000; and (F) a cationic polyelectrolyte which was a poly (diallyl dimethyl ammonium chloride) having a number average molecular weight of 50,000.
In each case the ratio of weight of (F) to the weight of (~) was 4:1 but the optimum total quantity of dispersing agents were determined for each ground marble powder and was found to differ in each case.
The two methods for preparing the aqueous suspension of the marble powders were:-(i) the powder was mixed with water containing the reguired quantity of (~) and after thorough mixing the required quantity of (F) was added, followed by further mixing; and (ii) the powder was mixed with water containing the required quantities of both (E) and (F) together.
In each case the viscosity of the suspension was measured by means of a Brookfield Vi~cometer at a spindle speed of lO0 rpm. and the percentage by weight of dr,v solids was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension wa~ then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were , .. . ~ ,.. , .. ... . . .. , . . .. , . ., ,, , . "=
- ` ;
. .~ . .
WO91/08~1 PCT/GB90/01883 1 1- 2Q7~
made. A graph was plotted of vi~cosity against percentage by weight of dry solids and the solids concentration for a suspension having a vi~cosity of 500 mPa.s was determined by interpolation.
The results obtained are set forth in Table I
below:-by wt. of dry solids for a % by wt. based on viscosity of % by wt. smaller wt. of dry 500 mPa.s than 2 microns marble of by method in marble ~E~ (F) (il (ii) 0.02 0.083 72.0 71.3 ; 15 ~8 0.075 0.289 71.4 65.6 87 0.166 0.65 64.6 60.3 These results show that fluid suspension can be obtained at a higher solids concentration by method (i) (mixing the powder firstly with the anionic polyelectrolyte and secondly with the cationic polyelectrolyte) than by method (ii) (mixing the powder with both dispersing agents together). This effect is more marked with finely ground marble powders than with a coarser product.
~XAMPI~ 2 - A further batch of finely ground marble powder was prepared by the process described in Example 1, the particle size distribution of the ground product being such that 87~ by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns.
Samples of this marble powder were incorporated - into paper coating compositions prepared according to , the followinq recipes:-. ~ .
. .~ .
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WO91/08341 PCT/GB90/018~3 Z07~Ç,4~.
IngredientParts by_weiqht ` Composition (a) Marble powder100 ~ Quaternary cationic :~. 5 acrylic latex12 ~' Cationic guar gum 0.5 Inqredient~Parts by weiqht 10 Composition (b) Marble powder 100 Quaternary cationic acrylic latex 8 Cationic starch 4 Three different compositions of type (b) were prepared containing the following three different cationic starches:- .
(i) a cationic starch of low degree of substitution (ii) another cationic starch of low degree of substitution (iii) a cationic starch of high degree of substitution The three compositions were identified as compositions (b)(i), (b)(ii) ant (b)(iii), respectively InqredientParts by wei~ht Composition (c) Marble powder 100 Styrene butadiene rubber latex 12 =
Sodium carboxymethyl cellulose 0.75 'i InqredientParts ~v ~eiaht Composition (d) Marble powder 100 Styrene butadiene ' rubber latex 8 Oxidi~ed starch 4 In the case of the cationic compositions (a) and (b) an aqueous suspension of the marble powder wa~ first prepared using as the dispersing agents 0.16% by - - ., . " ~ - , , , ~
~ 2C7~641 weight, based on the weight of dry marble, of anionic dispersing agent (E) and 0.65% by weight, based on the weight of dry marble, of cationic dispersing agent (F), by the method de~cribed under (i) in Example 1 ~bove.
In the case of the anlonic compositions (c) and (d) the marble powder was treated with 0.30~ by weight, based on the weight of dry marble, of dispersing agent (E) alone.
In addition there were added to each of compositions (a), (b), (c) and (d) 0.8 part by weight of a melamine formaldehyde resin, as an insolubilising agent, and 0.5 part by weight of calcium stearate. There was also added to each of the cationic compositions (a) and (b) 0.2 part by weight of sodium bicarbonate to catalyse the cross linking reaction of the cationic latex.
Each paper coating composition was diluted with water to give a high-shear viscosity as measured by a Ferranti-Shirley Viscometer at a shear rate of 12,800 s~
1 in the range 60-70 mPa.s if possible. The high-shear viscosities and the percentage by weight of solids in the diluted compositions are set forth in Table II
below.
Each composition was coated on to a lightweight offset base paper of substance weight 48 g~m~2 by means of a laboratory paper coating machine of the type described in British Patent Specification No. 1032536.
:, , The coated paper samples were then supercalendered under a pressure of lO00 psi ~6.89 MPa) and a temperature of 65C with lO passes through the nip of the calender rolls at a speed of 36m.min~1.
Each sample of calendered, coated paper wa~ tested ~- for gloss by the TAPPI Standard method, for smoothness by the Parker Print Surf at lO Rgf., for percentage reflectance to light of wavelength 457nm and for percentage opacity. In each case the determinations of gloss, smoothness, ~ reflectance and % opacity were ' .
... ... ... . ...
., ~
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WO91/08~1 PCT/GB90/01883 -:` 2Q7~41 `
obtained by coating samples of paper at a range of different coat weights, measuring these quantities for each coat weight, plotting a graph of the quantity against coat weight and interpolating to find the value of quantity for a coat weight of 8g.m~2. The results are set forth in Table II below:-TABL~ II
% by High ~ reflectance wt. of shear Gloss to light of dry viscosity (TAPPI 457nn.
ComPosition solids (mPa.s) units) Smoothness wavelength ~ oPacity (a) 62.0 62 45 0.7Z 78.1 90.1 (b)(i) 60.6 66 45 1.05 7-4 9 4 (b)(ii) 51.2 70 43 0.68 78.4 89.8 (b)(iii) 59 4 72 38 0.71 78.4 90.1 (c) 65.8 73 46 0.67 78.1 90.1 (d) 64.9 104 39 0.76 77-8 89.7 : .
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.. .
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W~91/08~1 PCT/GB90/01883 ,~
When the results for cationic composition (a) are compared with those for the corresponding anionic composition (c), and the results for the cationic compositions of type (b) are compared with those for 5 the corresponding anionic composition (d), it will be noted that the coated paper properties for a cationic system in accordance with the invention are broadly similar to those obtained with a conventional anionic system .
Samples of paper coated with the above coating compositions were used as recycled paper or "broke" in a paper making process. Bleached sulphite pulp was ; beaten in accordance with TAPPI Standard T200 to a degree of freeness of 45 SR or 270 Canadian Standard lS Freeness and paper ma~ing compositions were prepared consisting of suspensions in water of the following ingredients:-Inqredient Parts of weiqht Bleached sulphite pulp 70 Broke fibre 30 Calcium carbonate filler 50 Polyacrylamide retention aid 0.03 ` 25 The calcium carbonate filler had a particle size ;) distribution such that 43% by weight consisted of ` particles having an equivalent spherical diameter smaller than 2 microns. Since the broke çontained ``~ about 20~ by weight of inorganic filler material the quantity of fresh calcium carbonate filler added was reduced to give a total quantity of filler of 50 parts - by weight. Similarly the weight of dry broke added (fibre + filler) was such as to provide 30 parts by ` weight of fibre.
- The retention of the calcium carbonate filler in paper prepared from compo~itions containing broke which had been coated with each of the coating composition~
(a), (b)(ii), (c) and (d) above wa~ measured by means ,, ~ ';~'' ' .
:- . ' :
.
W091/08~1 PCT/GB90/018~3 2Q7~64~ - 16-of a retention jar with the stirrer set at speed 5 (lO50 rpm) and a stirring duration of 30 seconds. As a comparison the retention of the same calcium carbonate filler in a paper making composition containing no broke was also measured. The results are set forth in Table III below:-TABLB III
Broke containing % by wt. retention coatinq composition of calcium carbonate Non~ 74.3 (a) 83.9 (b)(ii) 79.2 (c) 49.8 lS (d) 46.2 These results show that although the incorporation into paper making composition of broke which has been coated with an anionic composition (c) and (d) reduces the retention of a calcium carbonate filler as compared with a paper ma~ing composition which contains no broke, the incorporation of broke coated with a cationic co~position actually improves the retention of the filler.
~XAMPI~ 3 A batch of raw cru~hed marble was ground by the method described in Bxample l above to give a ground product having a particle size distribution such that 60% by weigh~ consisted of particles having an equivalent spherical diameter smaller then 2 microns.
The suspension of ground marble was dewatered by means of a centrifuge and the centrifuge cake which contained 68% by weight of dry solids was used Sn the following experiments.
Samples of the centrifuge cake of ground marble were mixed first with an anionic dispersing agent, and then, -- after thorough mixing, with a cationic dispersing agent. In each ca~e a predetermined quantity of the anionic di~persing ~gent was used, but, for the :
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- 2C~7264~ -`
cationic dispersing agent, a small quantity of the dispersing agent was first added, the suspension was vigorously mixed for 1 minute, and the viscosity of the su~pension was mea~ured by meane of a Brookfield Viscometer at a spindle speed of 100 rpm. The amount of dispersing agent and the viscosity were recorded and a further small quantity of the dispersing agent was added and the procedure repeated. Further small increments of the dispersing agent were added until the viscosity of the suspension reached a minimum, at which point the total amount of the cationic dispersing agent which had been added was regarded as the optimum.
The dispersing agents were:-(G) an anionic polyelectrolyte which was a sodium 15 polyacrylate having a number average molecular weight of 70,000 (H) sodium silicate which is a sodium salt of a polysilicic acid and acts a~ an anionic dispersing agent;
(I) a cationic polyelectrolyte which was a poly (diallyl dimethyl ammonium chloride) having a number average molecular weight of 50,000.
(J) a cationic polyelectrolyte whlch was a ' polyethyleneimine.
When dispersing agent (J) was used it was also necessary to add sufficient sulphuric acid to adjust the pH to 7.8 since polyethyleneimines are sensitive to pH and do not act efficiently as dispersing agents at p~ values greater than 8.
As a comparison one sample of the centrifuge cake was t~eated with disper3ing agent (J) at p~ 7.8 alone, no anionic dispersing agent being used.
For each combination of disper~ing agents the percentage by weight of dry marble in the ~uspension, the minimum viscosity of the suspension and the quantities of anionic and cationic dispersing agent ::
.: . . ~ . .. ... .. . . ., . , _ j , . . . .. . . . . . . . . .....
;~
Wo91/08~1 PCT/GB90/01883 2C~6~
were recorded, and the results are set forth in Table IV below:-TABLE IV
Anionic Amount CAtionic Amount Minimum dispers- used dispers- used % by wt. viscos-ing (% by ing (~ by of dryity aqent wt.) agent wt.) solids ~mPa.s) G 0.10 I 0.48 67.23000 G 0.10 J 0.40 67.5 252 H 0.16 J 0.39 65.4 224 none - J 0.37 67.1>10,000 These results show that, in general, lower viscosities are obtainable with polyethyleneimine as the cationic dispersing agent, rather than with poly (di~llyl dimethyl ammonium chloride), but the use of the cationic dispersing agent must be preceded by the ~- addition of an anionic di~persing agent.
EXAMPT.R 4 A batch of marble flour having a particle size distribution such that substantially all of the particles passed through a No. 300 mesh British Standard sieve (nominal aperture 53 microns) was subjected to attrition grinding in a concentrated, deflocculated aqueous suspension, the quantities of marble flour, water and grinding sand being:-615g marble flour 330g water + anionic and cationic dispersing agents 1500g sand The grain size of the sand was smaller than No. 18 mesh ~ritish Standard sieve (nominal aperture 0.850mm) and larger than No. 30 mesh British Standard sieve (nominal aperture 0.500mm). The anionic disper~ing agent used was (E) and the cationic dispersing agent was (F), both as described in Example 1 above.
Portions of marble flour were ground using different ., .
. . ' . :
~ . ' ' ' ' ' ' : :, WO91/08~1 PCT/GB90/01883 -19- Z~
total quantities of (E) and (F) but in each case the weight ratio of (F):(E) was 4:l. In each case the grinding was continued for a time sufficient to dissipate in the ~u~pension 396 kJ of energy per kg of dry marble and in each case the product had a particle size distribution such that about 50% by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns. On completion of grinding the suspension of ground marble was separated from the sand and the viscosity of the suspension was measured by means of a ~rookfield Viscometer at a spindle speed of l00 rpm. The suspension was then diluted with a smaIl quantity of water and the viscosity was measured again. The percentage by weight , 15 of dry marble in the suspension was also determined by drying a ~nown small weight of the suspension and weighing the dried residue. The steps of diluting with water and measuring the viscosity and percentage by weight of dry marble were repeated several tLmes. A
graph was drawn of viscosity against percentage by weight of dry marble and the percentage by weight of dry marble in the suspension which had a viscosity of 500 mPa.s was found by interpolation. The results are set forth in Table V below:-TABLE V
Total % by % by wt. of dry wt. of marble for a % by wt. % by wt. dispersing viscosity of of (E) of (F) aqents 500 mPa.
0.05 0.20 0.25 63.9 0.06 0.24 0.30 64.5 ~` 0.07 0.28 0.35 65.0 EXAMPIæ 5 Further batche8 of the same marble flour as was uaed in Example 4 were ground by the method described in :~ .
, ..... ., ~ - - :
.. I' WO91/08~1 PCT/GB90!01883 ZC~72641.
Example 4, there being used as the anionic dispersing agent 0.07% by weight, based on the weight of dry marble, of (E), and as the cationic di~persing agent 0.28~ by weight, based on the weight of dry marble, of S one of a selection of poly (diallyl dimethyl ammonium chloridet polyelectrolytes of different molecular weights. In each case the percentage by weight of dry marble in a suspension having a viscosity of 500 mPa.s was measured as described in Example 4 above and the results are set forth in Table VI below:-~ABL~ VI
Number average ~ by wt. of dry molecular weight marble for a of cationic viscosity of disPersinq aqent 500 mPa.s 9,500 58.4 26,000 61.8 50,000 65.0 71,500 64.9 These results show that the poly (diallyl dimethyl ammonium chloride) should have a number average molecular weight of at least 50,000 if a marble suspension of acceptable fluidity is to be obtained.
~XAMPIE 6 A batch of raw crushed marble was ground by themethod described in Example l to give a ground product having a particle size distribution such that 60~ by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewatered by means of centrifuge and the centrifuge cake which contained 73%
by weight of dry solid~ was used in the following experiments:
Samples of the ground marble centrifuge cake were first mixed with 0.1% by weight, based on the weight of dry marble, of anionic dispersing agent ~ as described in Example 3 ~i.e. a sodium polyacrylate having a .
. .
WO91/08341 PCTtGB90/01883 2~64~
number average molecular weight of 70,000). After thorough mixing there was added to each sample of aqueous suspension of anionically dispersed ground marble a quantity of one of the four following cationic dispersing agents:-(I) a cationic polyelectrolyte which was apoly(diallyl dimethyl ammoniùm chloride) having a number average molecular weight of 50,000 - 100,000;
(J) a cationic polyelectrolyte which was a polyethyleimine;
(K) a polyethyleneimine of number average molecular weight lower than that of (J);
`~ (L) a polyethyleneimine of number average molecular weight lower than that of tR).
The quantity of each cationic dispersing agent was that which was found by experiment to give the lowest ` viscosity for a suspension of given solids content.
For dispersing agent (I) this quantity was found to be 0.45% by weight, based on the weight of dry marble, and for dispersing agents (J), (K) and (L) the quantity was found to be 0.40% by weight, based on the weight of dry marble.
In the case of the polyethyleneimine dispersing agents (J), (K) and (L) there was alRo added sufficient sulphuric acid to adjust the p~ to 7.8. In each case the viscosity of the suspensio~ was measured by means of a Brookfield Viscometer at a spindle speed of 100 rpm and the percentage by weight of dry solids in the suspension was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension was then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were made. The procedure of diluting the suspension and measuring the viscosity and percentage by weight of dry i" solids was repeated two or three tLmes and a graph was .. , . .. .... , . , ~ .. . .. ..
Wo91/08~1 PCT/GB90/01883 2C~7~G41 plotted of viscosity against percentage by weight o f dry solids. The solids concentration for a suspension having- a viscosity of 300 mPa. 8 was determined by interplotation and the results are set forth in TablQ
VII:-TABLE VII
Cationic % by weight of dry dispersing marble for a viscosity aqent of 300 mPa.s I 61.0 ; J 68.5 K 71.8 L 73.0 15 A batch of raw crushed marble was ground in an aqueous suspension containing 30~ by weight of dry solids and in the absence of chemical dispersing agent, by means of a particulate grinding medium to yield a ground calcium carbonate product of paper coating grade having a particle size distribution such that 90~ byweight of the particles had an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewàtered by filtration in the absence of a flocculating agent and the filter cake was dried and pulverised in a laboratory hammer mill.
Samples of the finely ground marble powder were mixed with water to form a suspension containing 60% by weight of dry solids and varying quantities of an anionic and of a cationic dispersing agent. The anionic dispersing agent was a 30dium polyacrylate dispersing agent having a number average molecular weight of 4000 and the cationic dispersing agent was a poly~(diallyl dimethyl ammonium chloride) having a number average molecular weight of about 50,000.
; 35 In each experiment the anionic dispersing agent was added first to the suspension of ground marble and the .:
' ' ' -- .
, W~9t/08~1 PCT/GB90/01883 2~7;~:641.
mixture stirred by 9,400 revolutions of an impeller rotating at l,420 rpm. The cationic dispersing agent was then added and the mixing procedure was repeated.
The visco~ity was measured immediately on completion of the second mixing procedure by means of a Brookfield Viscometer.
The results obtained are set forth in Table VIII
; below:
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-25- ;
These results show that the optimum dispersion was -- obtained when the ratio of the weight of cationic ~- dispersing agent to the weight of anionic dispersing r,!, agent was about 4:1. When the ratio was increased to 6.9:1 it was still possible to obtain a very fluid suspension but at the expense of a slightly higher dose of mixed dispersing agents.
~XAMPLE 8 A batch of raw crushed marble was ground in an aqueous suspension containing 30% of dry solids and in the absence of chemical dispersing agents by means of a particulate grinding medium to yield a ground product having a particle size distribution such that 78% by weight of the particles had an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewatered in the absence of a flocculating agent on a vacu~m drum filter to a dry solids content of 64~ by weight. Some of the filter cake thus formed was thermally dried and mixed back ` 20 with the moist filter cake to give a mixture having a dry solids content of 70% by weight.
This mixture was divided into three portions to be treated with cationic poly(diallyl dimethyl ammonium chloride) dispersing agents having three different number average molecular weights. ~ach of the three portions were further subdivided into three ~maller -:
portions which were treated with different doses of anionic dispersing agent (E) as described in Example 1.
In each case the anionic dispersing agent was added first to the cake of ground marble and well mixed therewith, and the cationic dispersing agent was then added and mixed in. The dose of the cationic dispersing agent used was in each case about 3.5 times - the dose of the anionic dispersing agent.
In each case the viscosity of the resultant suspension was measured by means of a Brookfield ., ~:
,:
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WO91/08~1 PCTtGB90/018~3 .:~.
2Q7 26 4~ -26-Viscometer at a spindle speed of lO0 rpm and the percentage by weight of dry solids was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension was then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were made. A graph was plotted of viscosity against percentage by weight of dry solids and the solids content for a suspension having a visc08ity of 300 mPa.s was determined by interpolation.
The results obtained are set forth in Table IX
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WO 91/08341 PCr/GB90/01883 -27- ~7~6~1 Table ~C
~ Mol wt % by ut Z by wt % by ut of dry :. dispersing dispersing dispersing 300 mPa.s ~i 100 000 o,074 o.265 66666~4~ 7l 200,000 000,1o755 '45 6677.. 9 500 000 0.100 o.360 68.
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~Q7~4~ -28-The results show that slightly more fluid suspensions for a given solid~ content were obtained when the cationic dispersing agent having a number average molecular weight of 500,000 was used.
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~i It is preferred that the ground pigment has a particle size distribution such that at lea~t 50%
percent by weight has an equivalent spherical diameter smaller than two microns. More preferably, at least 60% percent by weight has an equivalent spherical diameter smaller than two microns. _ Ground marble for use in the present invention is preferably formed by crushing batches of marble in aqueous suspension in the absence of a chemical dispersing agent using a particulate grinding medium.
; Any agglomerates formed may be broken up by dewatering the suspension of ground marble, for example by filtration in the absence of a flocculating agent and ;~ then drying the pigment, and pulverising the dried product in a conventional mill.
The particulate pigment is dispersed with the .
.
WO91/0834l PCT/GB90/01883 2Q7~164~ r combination of an anionic polyelectrolyte and a cationic polyelectrolyte. Preferably, the anionic polyeletrolyte is a water-soluble vinyl polymer, an alkali metal or ammonium ~alt thereof or an alkali S metal or ammonium salt of polysilicic acid. Most ; preferably, the anionic polyeletrolyte is a poly(acrylic acid), a poly(methacrylic acid), a substituted poly~acrylic acid) or a substituted poly(methacrylic acid), or an alkali metal or ammonium 10 salt of any of these acids. The substituted poly(acrylic acid) may be a partially sulphonated polymer. An especially effective anionic polyelectrolyte is an alkali metal or ammonium salt of a copolymer of acrylic acid and a sulphonic acid 15 derivative of acrylic acid, in which the proportion of the sulphonic acid derivative monomer is preferably from 5% to 20% of the total number of monomer units.
The number average molecular weight of the anionic polyelectrolyte is preferably at lea~t 500, and ~i 20 preferably no greater than lO0,000. The amount u~ed is generally in the range of from about 0.01% to about 0.5% by weight based on the weight of dry pigment, preferably in the range of from about 0.1 to 0.2% by weight.
The cationic polyelectrolyte may be a water-soluble substituted polyolefine containing quaternary ammonium groups. The quaternary ammonium group~ may be in the linear polymer chain or may be in branche~ of the polymer chain. The number average molecular weight of the substituted polyolefine i8 preferably at least 1500 and preferably no greater than 1,000,000, and is more preferably in the range of from 50,000 to 500,000.
- The quantity required i~ generally in the range of from about 0.01% to about 1.5% by weight based on the weight of dry pigment. Advantageou~ results have been obtained when the substituted polyolefine is a poly .. .... , , ., .,, . . , . .. , , . . , , . , . .. .. . .. " . . . .. . ...... . . . . . .. . .. . . . . . . .. . ...
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W 0 91/08341 `2~7~S41 P~rJGB90/01883 . .~
. (diallyl di(hydrogen or lower alkyl)ammonium salt).
The lower alkyl groups, which may be the same or different, may for example, have up to four carbon . atom~ and e~ch i~ preferably methyl. The ammonium ~alt ` 5 may be, for example, a chloride, bromide, iodide, ~S04-, CH3S04- or nitrite. Preferably the salt is a chloride.
Most preferably, the cationic polyelectrolyte is poly (diallyl dimethyl ammonium chloride). Alternatively, .~ the water-soluble substituted polyolefin may be the . 10 product of co-polymerising epichlorohydrin and an aliphatic secondary amine, said product having the ~-. formula .~--CEI2 c~2 C~2 ~
: 15 X' lR' l~
;: in which R and R', which may be the same of different, .i are each hydrogen or a lower alkyl group having from one to four carbon atom~, preferably methyl or ethyl `. and ~ i5 Cl-~ Hr~' I-~ EIS0~ C~3SO"- or nitrite. The preferred number average molecular weight of this epichlorohydrin product i5 in the range of from 50,000 ~ to 300,000.
: Alternatively, the cationic polyelectrolyte may be a water-soluble organic compound having a plurality of basic groups and preferably having a number average molecular weight of at least 10,000 and preferably no greater than 1,000,000. Most preferably, the number ~:: average molecular weight is at least 50,000. These : water-soluble organic compounds may be described as polyacidic organic bases, and are preferably compounds of carbon, hydrogen and nitrogen only and are free of other functional groups, such as hydroxy or carboxylic acid groups, which would increase their solubility in water and thus increase the likelihood of their being desorbed from the clay mineral in an aqueous suspension. Preferably, the organic compound is , ' ' .~
.
WO91/08~1 PCT/GB90/01883 ~Q7~641. ~ :--polyethyleneimine (PEI) having a number average molecular weight in the range 50,000 to l,000,000. A
further example of a water-soluble organic compound ~ which may be employed is a polyethylene diamine which .1 5 may be a copolymer of ethylene diamine with an ethylene dihalide or with formaldehyde.
: The cationic polyelectrolyte is employed in an : amount sufficient to render the mineral particles cationic. Experiments have shown that the zeta potential of the particles will normally be at least ~2~mV after treatment, typically in the range of from ~30 to ~40 mV and usually no greater than +50 to ~60mV.
These potentials have been measured using a dilute (0.02 weight %) solids suspension using a supporting lS electrolyte of potassium chloride (lO~M) with a "Pen Kem Laser Z" meter.
: The ratio of the weight of cationic polyelectrolyte to the weight of anionic polyelectrolyte used is preferably in the range of from 20 2:1 to 20:1, when the calcium carbonate is a ground marble.
According to a fourth aspect of the pre~ent invention, there is provided a process for preparing a paper coating composition comprising the steps of:
(i) dispersing in aqueous suspension a particulate pigment; and ~
(ii) combining the dispersed aqueous suspension with an adhesive and, if necessary, adjusting the dilution such that the particulate material constitutes at least 45% by weight of the composition;
characterised in that said pigment is dispersed using a dispersing agent comprising a combination of an anionic polyelectrolyte and a cationic polyelectrolyte;
in that said cationic polyelectrolyte is used in an amount sufficient to render the pigment particles cationic; in that said adhesive is a cationic or non-.~, .
: , :
~ ` ~'0 91/08341 PC~r/G B90/01883 2~2~
-ionic adhesive; and in that ~aid particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the ~ole presence of ~aid cationic polyeletrolyte.
In the method of the invention, it is normally the case that the raw pigment is received a~ a filter cake having a relatively high solids content. To thi~ i8 added the dispersing agent in order to provide a dispersed high solids slurry ~45-80% by weight ~olids) : 10 which may then be subjected to vigorou6 mixing. This slurry is then "made down" into a paper coating composition by dilution and addition of the required quantity of the cationic or non-ionic adhe~ive and other conventional paper coating composition adjuvants.
Preferably, the pigment is mixed with the anionic polyeletrolyte before mixing with the cationic polyelectrolyte. This appears to enable a more fluid suspension to be obtained at a higher solids concentration.
The aqueous dispersion of the pigment may also include other conventional paper coating composition adjuvants such as an insolubilising agent (e.g. a ` melamine formaldehyde re~in), a lubricant such as - calcium stearate and a catalyst to catalyze cross-linking of the cationic latex if present: a ~uitable such catalyst is sodium bicarbonate. The quantities of ; these adjuvants required are known to those skilled in the art.
The adhesive used in the present invention should be a non-ionic or a cationic adhesive. Such adhesives - contrast with the anionic adhesives which are normally used in paper coating compositions in which the pigment is anionic. Thus, cationic guar gum and cationic starch adhesives can be used as well as cationic or non-ionic latices. Such cationic and non-ionic adhesives are readily commercially available. The particular cationic or non-ionic adhesive used will ~ .
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~ WO91/08341 PCT/GB90/018X3 2Q7~641.
depend, for example, on the printing proce~a to be used, e.g. offset lythography requires the adhesive to be water-insoluble. For paper to be used in an offset printing technique, the amount of adhesive should ` 5 preferably be of the order of from 7 to 25~ by weight, based on the weight of pigment whil~t, for graw re printing paper, the adhesive should be used in an amount of 4-15% by weight, based on the weight of pigment. The precise quantity of adhesive required }0 will depend upon the nature of the adhesive and the material being coated, but this can readily be determined by the person skilled in the art.
The suspe~sion of the pigment for incorporation into the paper coating composition of the present invention should preferably be subjected to vigorous mixing before or after dispersion. Typically, the vigorous mixing should be sufficient to impart at least lOkJ energy per kg of pigment, and preferably no more than about 50kJ per kg. Normally, the amount of energy input will be in the range of from 18-36kJ per kg of pigment.
The coating composition may be coated on to a sheet member using normal paper coating machinery and under normal paper coating conditions. It has been found that the paper coated with a cationic composition in accordance with the present invention provides broadly similar results to that obtained with a conventional anionic system.
The coated paper of the present invention is of advantage when it is employed as "broke" or recycled paper in a paper making process. Commonly, large quantities of paper are recycled at the point of manufacture for one reason or another, and the advantages of the paper of the present invention in recycling are most important to the paper manufacturer.
Thus, in accordance with a fourth aspect of the present : ...
:~ WO 91tQ8341 PCI/GB90/01883 2~7:~641.
, 9 invention, there is provided a method for recycling paper including the step of reducing paper in accordance with the third aspect of the present invention to a fibrous recyclable state and incorporating said fibre in a paper-making composition.
Such a paper-making composition may include conventional paper-making pulp, such as a bleached sulphite pulp and, typically, the broke fibre and the . pulp will be employed in a ratio of from 10:90 to : 10 60: 40 .
~` Also included in the paper making composition will be a filler, for instance a calcium carbonate filler and also a retention aid. Since the broke fibre will include a proportion of calcium carbonate from the coating, it is possible to reduce the amount of calcium carbonate filler employed to give a total quantity of filler in the range of from 5 to 20 percent by weight of the total paper-making composition. The weight of dried broke added (fibre and filler) should preferably be in the range of from about 5 to 30 percent by weight of fihre.
It has been found that, when the broke fibre employed is derived from a coated paper in accordance with the present invention, this enables the amount of retention aid employed in the paper making composition to be reduced.
The present invention will now be illustrated by the following examples: -Three batches of raw cru~hed marble were ground in anaqueous suspension containing 30% by weight of dry solids and in the absence of chemical dispersing agent, by means of a particulate grinding medium. The duration of grinding wàs different in each case 50 as ~` 35 to yield three different ground products having p~rticle size distributions such that 50%, 68~ and 87 ~; .
~.
, .
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WO91/08~1 PCT/GB90/01883 ,.,.~
2~7~ o-- ~y weight, respectively, had an equivalent spherical diameter smaller than 2 microns. In each case the suspension of ground marble wa~ dewatered by filtration in a tube pressure filter in the absence of a flocculating agent and the filter cake was dried and ; pulverised in a laboratory hammer mill.
Samples of each of the three ground marble powders were mixed with water and with two different dispersing ; age~ts by each of two different methods described below. The dispersing agents were:-(E) an anionic polyelectrolyte which was a sodium polyacrylate having a number average molecular weight of 4,000; and (F) a cationic polyelectrolyte which was a poly (diallyl dimethyl ammonium chloride) having a number average molecular weight of 50,000.
In each case the ratio of weight of (F) to the weight of (~) was 4:1 but the optimum total quantity of dispersing agents were determined for each ground marble powder and was found to differ in each case.
The two methods for preparing the aqueous suspension of the marble powders were:-(i) the powder was mixed with water containing the reguired quantity of (~) and after thorough mixing the required quantity of (F) was added, followed by further mixing; and (ii) the powder was mixed with water containing the required quantities of both (E) and (F) together.
In each case the viscosity of the suspension was measured by means of a Brookfield Vi~cometer at a spindle speed of lO0 rpm. and the percentage by weight of dr,v solids was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension wa~ then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were , .. . ~ ,.. , .. ... . . .. , . . .. , . ., ,, , . "=
- ` ;
. .~ . .
WO91/08~1 PCT/GB90/01883 1 1- 2Q7~
made. A graph was plotted of vi~cosity against percentage by weight of dry solids and the solids concentration for a suspension having a vi~cosity of 500 mPa.s was determined by interpolation.
The results obtained are set forth in Table I
below:-by wt. of dry solids for a % by wt. based on viscosity of % by wt. smaller wt. of dry 500 mPa.s than 2 microns marble of by method in marble ~E~ (F) (il (ii) 0.02 0.083 72.0 71.3 ; 15 ~8 0.075 0.289 71.4 65.6 87 0.166 0.65 64.6 60.3 These results show that fluid suspension can be obtained at a higher solids concentration by method (i) (mixing the powder firstly with the anionic polyelectrolyte and secondly with the cationic polyelectrolyte) than by method (ii) (mixing the powder with both dispersing agents together). This effect is more marked with finely ground marble powders than with a coarser product.
~XAMPI~ 2 - A further batch of finely ground marble powder was prepared by the process described in Example 1, the particle size distribution of the ground product being such that 87~ by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns.
Samples of this marble powder were incorporated - into paper coating compositions prepared according to , the followinq recipes:-. ~ .
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WO91/08341 PCT/GB90/018~3 Z07~Ç,4~.
IngredientParts by_weiqht ` Composition (a) Marble powder100 ~ Quaternary cationic :~. 5 acrylic latex12 ~' Cationic guar gum 0.5 Inqredient~Parts by weiqht 10 Composition (b) Marble powder 100 Quaternary cationic acrylic latex 8 Cationic starch 4 Three different compositions of type (b) were prepared containing the following three different cationic starches:- .
(i) a cationic starch of low degree of substitution (ii) another cationic starch of low degree of substitution (iii) a cationic starch of high degree of substitution The three compositions were identified as compositions (b)(i), (b)(ii) ant (b)(iii), respectively InqredientParts by wei~ht Composition (c) Marble powder 100 Styrene butadiene rubber latex 12 =
Sodium carboxymethyl cellulose 0.75 'i InqredientParts ~v ~eiaht Composition (d) Marble powder 100 Styrene butadiene ' rubber latex 8 Oxidi~ed starch 4 In the case of the cationic compositions (a) and (b) an aqueous suspension of the marble powder wa~ first prepared using as the dispersing agents 0.16% by - - ., . " ~ - , , , ~
~ 2C7~641 weight, based on the weight of dry marble, of anionic dispersing agent (E) and 0.65% by weight, based on the weight of dry marble, of cationic dispersing agent (F), by the method de~cribed under (i) in Example 1 ~bove.
In the case of the anlonic compositions (c) and (d) the marble powder was treated with 0.30~ by weight, based on the weight of dry marble, of dispersing agent (E) alone.
In addition there were added to each of compositions (a), (b), (c) and (d) 0.8 part by weight of a melamine formaldehyde resin, as an insolubilising agent, and 0.5 part by weight of calcium stearate. There was also added to each of the cationic compositions (a) and (b) 0.2 part by weight of sodium bicarbonate to catalyse the cross linking reaction of the cationic latex.
Each paper coating composition was diluted with water to give a high-shear viscosity as measured by a Ferranti-Shirley Viscometer at a shear rate of 12,800 s~
1 in the range 60-70 mPa.s if possible. The high-shear viscosities and the percentage by weight of solids in the diluted compositions are set forth in Table II
below.
Each composition was coated on to a lightweight offset base paper of substance weight 48 g~m~2 by means of a laboratory paper coating machine of the type described in British Patent Specification No. 1032536.
:, , The coated paper samples were then supercalendered under a pressure of lO00 psi ~6.89 MPa) and a temperature of 65C with lO passes through the nip of the calender rolls at a speed of 36m.min~1.
Each sample of calendered, coated paper wa~ tested ~- for gloss by the TAPPI Standard method, for smoothness by the Parker Print Surf at lO Rgf., for percentage reflectance to light of wavelength 457nm and for percentage opacity. In each case the determinations of gloss, smoothness, ~ reflectance and % opacity were ' .
... ... ... . ...
., ~
:
WO91/08~1 PCT/GB90/01883 -:` 2Q7~41 `
obtained by coating samples of paper at a range of different coat weights, measuring these quantities for each coat weight, plotting a graph of the quantity against coat weight and interpolating to find the value of quantity for a coat weight of 8g.m~2. The results are set forth in Table II below:-TABL~ II
% by High ~ reflectance wt. of shear Gloss to light of dry viscosity (TAPPI 457nn.
ComPosition solids (mPa.s) units) Smoothness wavelength ~ oPacity (a) 62.0 62 45 0.7Z 78.1 90.1 (b)(i) 60.6 66 45 1.05 7-4 9 4 (b)(ii) 51.2 70 43 0.68 78.4 89.8 (b)(iii) 59 4 72 38 0.71 78.4 90.1 (c) 65.8 73 46 0.67 78.1 90.1 (d) 64.9 104 39 0.76 77-8 89.7 : .
. .
.. .
;:
W~91/08~1 PCT/GB90/01883 ,~
When the results for cationic composition (a) are compared with those for the corresponding anionic composition (c), and the results for the cationic compositions of type (b) are compared with those for 5 the corresponding anionic composition (d), it will be noted that the coated paper properties for a cationic system in accordance with the invention are broadly similar to those obtained with a conventional anionic system .
Samples of paper coated with the above coating compositions were used as recycled paper or "broke" in a paper making process. Bleached sulphite pulp was ; beaten in accordance with TAPPI Standard T200 to a degree of freeness of 45 SR or 270 Canadian Standard lS Freeness and paper ma~ing compositions were prepared consisting of suspensions in water of the following ingredients:-Inqredient Parts of weiqht Bleached sulphite pulp 70 Broke fibre 30 Calcium carbonate filler 50 Polyacrylamide retention aid 0.03 ` 25 The calcium carbonate filler had a particle size ;) distribution such that 43% by weight consisted of ` particles having an equivalent spherical diameter smaller than 2 microns. Since the broke çontained ``~ about 20~ by weight of inorganic filler material the quantity of fresh calcium carbonate filler added was reduced to give a total quantity of filler of 50 parts - by weight. Similarly the weight of dry broke added (fibre + filler) was such as to provide 30 parts by ` weight of fibre.
- The retention of the calcium carbonate filler in paper prepared from compo~itions containing broke which had been coated with each of the coating composition~
(a), (b)(ii), (c) and (d) above wa~ measured by means ,, ~ ';~'' ' .
:- . ' :
.
W091/08~1 PCT/GB90/018~3 2Q7~64~ - 16-of a retention jar with the stirrer set at speed 5 (lO50 rpm) and a stirring duration of 30 seconds. As a comparison the retention of the same calcium carbonate filler in a paper making composition containing no broke was also measured. The results are set forth in Table III below:-TABLB III
Broke containing % by wt. retention coatinq composition of calcium carbonate Non~ 74.3 (a) 83.9 (b)(ii) 79.2 (c) 49.8 lS (d) 46.2 These results show that although the incorporation into paper making composition of broke which has been coated with an anionic composition (c) and (d) reduces the retention of a calcium carbonate filler as compared with a paper ma~ing composition which contains no broke, the incorporation of broke coated with a cationic co~position actually improves the retention of the filler.
~XAMPI~ 3 A batch of raw cru~hed marble was ground by the method described in Bxample l above to give a ground product having a particle size distribution such that 60% by weigh~ consisted of particles having an equivalent spherical diameter smaller then 2 microns.
The suspension of ground marble was dewatered by means of a centrifuge and the centrifuge cake which contained 68% by weight of dry solids was used Sn the following experiments.
Samples of the centrifuge cake of ground marble were mixed first with an anionic dispersing agent, and then, -- after thorough mixing, with a cationic dispersing agent. In each ca~e a predetermined quantity of the anionic di~persing ~gent was used, but, for the :
. .
~,, . . _ . .. ... .. , . ... . ... . . . . . . . . . , ,, . , ~ . , .
., .:, `~
- 2C~7264~ -`
cationic dispersing agent, a small quantity of the dispersing agent was first added, the suspension was vigorously mixed for 1 minute, and the viscosity of the su~pension was mea~ured by meane of a Brookfield Viscometer at a spindle speed of 100 rpm. The amount of dispersing agent and the viscosity were recorded and a further small quantity of the dispersing agent was added and the procedure repeated. Further small increments of the dispersing agent were added until the viscosity of the suspension reached a minimum, at which point the total amount of the cationic dispersing agent which had been added was regarded as the optimum.
The dispersing agents were:-(G) an anionic polyelectrolyte which was a sodium 15 polyacrylate having a number average molecular weight of 70,000 (H) sodium silicate which is a sodium salt of a polysilicic acid and acts a~ an anionic dispersing agent;
(I) a cationic polyelectrolyte which was a poly (diallyl dimethyl ammonium chloride) having a number average molecular weight of 50,000.
(J) a cationic polyelectrolyte whlch was a ' polyethyleneimine.
When dispersing agent (J) was used it was also necessary to add sufficient sulphuric acid to adjust the pH to 7.8 since polyethyleneimines are sensitive to pH and do not act efficiently as dispersing agents at p~ values greater than 8.
As a comparison one sample of the centrifuge cake was t~eated with disper3ing agent (J) at p~ 7.8 alone, no anionic dispersing agent being used.
For each combination of disper~ing agents the percentage by weight of dry marble in the ~uspension, the minimum viscosity of the suspension and the quantities of anionic and cationic dispersing agent ::
.: . . ~ . .. ... .. . . ., . , _ j , . . . .. . . . . . . . . .....
;~
Wo91/08~1 PCT/GB90/01883 2C~6~
were recorded, and the results are set forth in Table IV below:-TABLE IV
Anionic Amount CAtionic Amount Minimum dispers- used dispers- used % by wt. viscos-ing (% by ing (~ by of dryity aqent wt.) agent wt.) solids ~mPa.s) G 0.10 I 0.48 67.23000 G 0.10 J 0.40 67.5 252 H 0.16 J 0.39 65.4 224 none - J 0.37 67.1>10,000 These results show that, in general, lower viscosities are obtainable with polyethyleneimine as the cationic dispersing agent, rather than with poly (di~llyl dimethyl ammonium chloride), but the use of the cationic dispersing agent must be preceded by the ~- addition of an anionic di~persing agent.
EXAMPT.R 4 A batch of marble flour having a particle size distribution such that substantially all of the particles passed through a No. 300 mesh British Standard sieve (nominal aperture 53 microns) was subjected to attrition grinding in a concentrated, deflocculated aqueous suspension, the quantities of marble flour, water and grinding sand being:-615g marble flour 330g water + anionic and cationic dispersing agents 1500g sand The grain size of the sand was smaller than No. 18 mesh ~ritish Standard sieve (nominal aperture 0.850mm) and larger than No. 30 mesh British Standard sieve (nominal aperture 0.500mm). The anionic disper~ing agent used was (E) and the cationic dispersing agent was (F), both as described in Example 1 above.
Portions of marble flour were ground using different ., .
. . ' . :
~ . ' ' ' ' ' ' : :, WO91/08~1 PCT/GB90/01883 -19- Z~
total quantities of (E) and (F) but in each case the weight ratio of (F):(E) was 4:l. In each case the grinding was continued for a time sufficient to dissipate in the ~u~pension 396 kJ of energy per kg of dry marble and in each case the product had a particle size distribution such that about 50% by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns. On completion of grinding the suspension of ground marble was separated from the sand and the viscosity of the suspension was measured by means of a ~rookfield Viscometer at a spindle speed of l00 rpm. The suspension was then diluted with a smaIl quantity of water and the viscosity was measured again. The percentage by weight , 15 of dry marble in the suspension was also determined by drying a ~nown small weight of the suspension and weighing the dried residue. The steps of diluting with water and measuring the viscosity and percentage by weight of dry marble were repeated several tLmes. A
graph was drawn of viscosity against percentage by weight of dry marble and the percentage by weight of dry marble in the suspension which had a viscosity of 500 mPa.s was found by interpolation. The results are set forth in Table V below:-TABLE V
Total % by % by wt. of dry wt. of marble for a % by wt. % by wt. dispersing viscosity of of (E) of (F) aqents 500 mPa.
0.05 0.20 0.25 63.9 0.06 0.24 0.30 64.5 ~` 0.07 0.28 0.35 65.0 EXAMPIæ 5 Further batche8 of the same marble flour as was uaed in Example 4 were ground by the method described in :~ .
, ..... ., ~ - - :
.. I' WO91/08~1 PCT/GB90!01883 ZC~72641.
Example 4, there being used as the anionic dispersing agent 0.07% by weight, based on the weight of dry marble, of (E), and as the cationic di~persing agent 0.28~ by weight, based on the weight of dry marble, of S one of a selection of poly (diallyl dimethyl ammonium chloridet polyelectrolytes of different molecular weights. In each case the percentage by weight of dry marble in a suspension having a viscosity of 500 mPa.s was measured as described in Example 4 above and the results are set forth in Table VI below:-~ABL~ VI
Number average ~ by wt. of dry molecular weight marble for a of cationic viscosity of disPersinq aqent 500 mPa.s 9,500 58.4 26,000 61.8 50,000 65.0 71,500 64.9 These results show that the poly (diallyl dimethyl ammonium chloride) should have a number average molecular weight of at least 50,000 if a marble suspension of acceptable fluidity is to be obtained.
~XAMPIE 6 A batch of raw crushed marble was ground by themethod described in Example l to give a ground product having a particle size distribution such that 60~ by weight consisted of particles having an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewatered by means of centrifuge and the centrifuge cake which contained 73%
by weight of dry solid~ was used in the following experiments:
Samples of the ground marble centrifuge cake were first mixed with 0.1% by weight, based on the weight of dry marble, of anionic dispersing agent ~ as described in Example 3 ~i.e. a sodium polyacrylate having a .
. .
WO91/08341 PCTtGB90/01883 2~64~
number average molecular weight of 70,000). After thorough mixing there was added to each sample of aqueous suspension of anionically dispersed ground marble a quantity of one of the four following cationic dispersing agents:-(I) a cationic polyelectrolyte which was apoly(diallyl dimethyl ammoniùm chloride) having a number average molecular weight of 50,000 - 100,000;
(J) a cationic polyelectrolyte which was a polyethyleimine;
(K) a polyethyleneimine of number average molecular weight lower than that of (J);
`~ (L) a polyethyleneimine of number average molecular weight lower than that of tR).
The quantity of each cationic dispersing agent was that which was found by experiment to give the lowest ` viscosity for a suspension of given solids content.
For dispersing agent (I) this quantity was found to be 0.45% by weight, based on the weight of dry marble, and for dispersing agents (J), (K) and (L) the quantity was found to be 0.40% by weight, based on the weight of dry marble.
In the case of the polyethyleneimine dispersing agents (J), (K) and (L) there was alRo added sufficient sulphuric acid to adjust the p~ to 7.8. In each case the viscosity of the suspensio~ was measured by means of a Brookfield Viscometer at a spindle speed of 100 rpm and the percentage by weight of dry solids in the suspension was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension was then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were made. The procedure of diluting the suspension and measuring the viscosity and percentage by weight of dry i" solids was repeated two or three tLmes and a graph was .. , . .. .... , . , ~ .. . .. ..
Wo91/08~1 PCT/GB90/01883 2C~7~G41 plotted of viscosity against percentage by weight o f dry solids. The solids concentration for a suspension having- a viscosity of 300 mPa. 8 was determined by interplotation and the results are set forth in TablQ
VII:-TABLE VII
Cationic % by weight of dry dispersing marble for a viscosity aqent of 300 mPa.s I 61.0 ; J 68.5 K 71.8 L 73.0 15 A batch of raw crushed marble was ground in an aqueous suspension containing 30~ by weight of dry solids and in the absence of chemical dispersing agent, by means of a particulate grinding medium to yield a ground calcium carbonate product of paper coating grade having a particle size distribution such that 90~ byweight of the particles had an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewàtered by filtration in the absence of a flocculating agent and the filter cake was dried and pulverised in a laboratory hammer mill.
Samples of the finely ground marble powder were mixed with water to form a suspension containing 60% by weight of dry solids and varying quantities of an anionic and of a cationic dispersing agent. The anionic dispersing agent was a 30dium polyacrylate dispersing agent having a number average molecular weight of 4000 and the cationic dispersing agent was a poly~(diallyl dimethyl ammonium chloride) having a number average molecular weight of about 50,000.
; 35 In each experiment the anionic dispersing agent was added first to the suspension of ground marble and the .:
' ' ' -- .
, W~9t/08~1 PCT/GB90/01883 2~7;~:641.
mixture stirred by 9,400 revolutions of an impeller rotating at l,420 rpm. The cationic dispersing agent was then added and the mixing procedure was repeated.
The visco~ity was measured immediately on completion of the second mixing procedure by means of a Brookfield Viscometer.
The results obtained are set forth in Table VIII
; below:
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WO 91/08341 PCT/GB90/Ol883 2~.7~4~
-25- ;
These results show that the optimum dispersion was -- obtained when the ratio of the weight of cationic ~- dispersing agent to the weight of anionic dispersing r,!, agent was about 4:1. When the ratio was increased to 6.9:1 it was still possible to obtain a very fluid suspension but at the expense of a slightly higher dose of mixed dispersing agents.
~XAMPLE 8 A batch of raw crushed marble was ground in an aqueous suspension containing 30% of dry solids and in the absence of chemical dispersing agents by means of a particulate grinding medium to yield a ground product having a particle size distribution such that 78% by weight of the particles had an equivalent spherical diameter smaller than 2 microns. The suspension of ground marble was dewatered in the absence of a flocculating agent on a vacu~m drum filter to a dry solids content of 64~ by weight. Some of the filter cake thus formed was thermally dried and mixed back ` 20 with the moist filter cake to give a mixture having a dry solids content of 70% by weight.
This mixture was divided into three portions to be treated with cationic poly(diallyl dimethyl ammonium chloride) dispersing agents having three different number average molecular weights. ~ach of the three portions were further subdivided into three ~maller -:
portions which were treated with different doses of anionic dispersing agent (E) as described in Example 1.
In each case the anionic dispersing agent was added first to the cake of ground marble and well mixed therewith, and the cationic dispersing agent was then added and mixed in. The dose of the cationic dispersing agent used was in each case about 3.5 times - the dose of the anionic dispersing agent.
In each case the viscosity of the resultant suspension was measured by means of a Brookfield ., ~:
,:
.
WO91/08~1 PCTtGB90/018~3 .:~.
2Q7 26 4~ -26-Viscometer at a spindle speed of lO0 rpm and the percentage by weight of dry solids was determined by completely drying a known weight of the suspension and weighing the dried residue. The suspension was then diluted with a small quantity of water and further determinations of viscosity and percentage by weight of dry solids were made. A graph was plotted of viscosity against percentage by weight of dry solids and the solids content for a suspension having a visc08ity of 300 mPa.s was determined by interpolation.
The results obtained are set forth in Table IX
bolow:-~,., ' :` .
~` .
:
: . , - . .
WO 91/08341 PCr/GB90/01883 -27- ~7~6~1 Table ~C
~ Mol wt % by ut Z by wt % by ut of dry :. dispersing dispersing dispersing 300 mPa.s ~i 100 000 o,074 o.265 66666~4~ 7l 200,000 000,1o755 '45 6677.. 9 500 000 0.100 o.360 68.
.. 500 000 0.125 0.450 67.6 :`
. .
. .
. i .
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W091/08~1 PCT~GB90/01883 .: .
~Q7~4~ -28-The results show that slightly more fluid suspensions for a given solid~ content were obtained when the cationic dispersing agent having a number average molecular weight of 500,000 was used.
. . , , . .
. . :
'' - ": .
Claims (18)
1. An aqueous paper coating composition which comprises (i) at least 45% by weight of a particulate inorganic pigment dispersed with a dispersing agent and (ii) an adhesive; characterised in that said dispersing agent comprises an anionic polyelectrolyte and a cationic polyelectrolye, the cationic polyelectrolyte being present in an amount sufficient to render the particles cationic; in that said adhesive is a cationic or non-ionic adhesive; and in that said particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said cationic polyeletrolyte.
2. A paper coating composition according to claim 1, wherein the pigment is selected from calcium carbonate, calcium sulphate, talc or a calcined kaolin-clay.
3. A paper coating composition according to claim 1, wherein the pigment is a calcium carbonate pigment.
4. A paper coating composition according to any preceding claim, wherein the number average molecular weight of the anionic polyelectrolyte is in the range of from 500 to 100,000.
5. A paper coating composition according to any preceding claim, wherein the anionic polyelectrolyte is employed in an amount in the range of from 0.01% to 0.5% by weight based on the weight of dry calcium carbonate.
6. A paper coating composition according to any preceding claim, wherein the cationic polyelectrolyte is a water-soluble substituted polyolefine containing quaternary ammonium groups.
7. A paper coating composition according to claim 6, wherein the number average molecular weight of the substituted polyolefine is in the range of from 1500 to 1,000,000.
8. A paper coating composition according to claim 6 or 7, wherein the amount of cationic polyelectrolyte employed is in the range of from 0.01% to 1.5% by weight based on the weight of dry calcium carbonate pigment.
9. A paper coating composition according to any one of claims 1 to 5, wherein the cationic polyelectrolyte is a water-soluble organic compound having a plurality of basic groups and a number average molecular weight in the range of from 10,000 to 1,000,000.
10. A paper coating composition according to claim 9, wherein the organic compound is polyethyleneimine having a number average molecular weight in the range of from 50,000 to 1,000,000.
11. A paper coating composition according to any preceding claim, wherein the ratio of the weight of cationic polyelectrolyte to the weight of anionic polyelectrolyte is in the range of from 2:1 to 20:1.
12. A process for preparing a paper coating composition comprising the steps of:
(i) dispersing in aqueous suspension a particulate pigment; and (ii) combining the dispersed aqueous suspension with an adhesive and, if necessary, adjusting the dilution such that the particulate material constitutes at least 45% by weight of the composition;
characterised in that said pigment is dispersed using a dispersing agent comprising a combination of an anionic polyelectrolyte and a cationic polyelectrolyte;
in that said cationic polyelectrolyte is used in an amount sufficient to render the pigment particles cationic; in that said adhesive is a cationic or non-ionic adhesive; and in that said particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said cationic polyeletrolyte.
(i) dispersing in aqueous suspension a particulate pigment; and (ii) combining the dispersed aqueous suspension with an adhesive and, if necessary, adjusting the dilution such that the particulate material constitutes at least 45% by weight of the composition;
characterised in that said pigment is dispersed using a dispersing agent comprising a combination of an anionic polyelectrolyte and a cationic polyelectrolyte;
in that said cationic polyelectrolyte is used in an amount sufficient to render the pigment particles cationic; in that said adhesive is a cationic or non-ionic adhesive; and in that said particulate pigment is one which is not capable of being dispersed in water at high solids, and following vigorous mixing, in the sole presence of said cationic polyeletrolyte.
13. A process according to claim 12, wherein the pigment is selected from calcium carbonate, calcium sulphate, talc or calcined kaolin clay.
14. A process according to claim 13, wherein the pigment is a calcium carbonate pigment
15. A process according to claim 12, 13 or 14, wherein the pigment is mixed with the anionic polyelectrolyte before mixing with the cationic polyelectrolyte.
16. A method of coating a sheet member comprising the step of coating the sheet member with a paper coating composition in accordance with any one of claims 1 to 11.
17. A coated paper whenever produced by the method of claim 16.
18. A paper making process in which a paper as claimed in claim 17 is recycled.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB898927536A GB8927536D0 (en) | 1989-12-06 | 1989-12-06 | Paper coating |
| GB8927536.6 | 1989-12-06 | ||
| US61344790A | 1990-11-13 | 1990-11-13 | |
| PCT/GB1990/001883 WO1991008341A1 (en) | 1989-12-06 | 1990-12-04 | Paper coating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2072641A1 true CA2072641A1 (en) | 1991-06-07 |
Family
ID=26296317
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002072641A Abandoned CA2072641A1 (en) | 1989-12-06 | 1990-12-04 | Paper coating |
Country Status (16)
| Country | Link |
|---|---|
| EP (1) | EP0504245B1 (en) |
| JP (1) | JPH05502484A (en) |
| CN (1) | CN1051826C (en) |
| AT (1) | ATE121149T1 (en) |
| AU (1) | AU647762B2 (en) |
| BR (1) | BR9007899A (en) |
| CA (1) | CA2072641A1 (en) |
| DE (1) | DE69018648T2 (en) |
| DK (1) | DK0504245T3 (en) |
| ES (1) | ES2070484T3 (en) |
| FI (1) | FI101091B (en) |
| GB (2) | GB8927536D0 (en) |
| NO (1) | NO180598C (en) |
| NZ (1) | NZ236353A (en) |
| WO (1) | WO1991008341A1 (en) |
| ZA (1) | ZA909749B (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9200683D0 (en) * | 1992-01-14 | 1992-03-11 | Univ Manchester | Improvements relating to materials |
| US5387826A (en) * | 1993-02-10 | 1995-02-07 | National Semiconductor Corporation | Overvoltage protection against charge leakage in an output driver |
| US5406140A (en) * | 1993-06-07 | 1995-04-11 | National Semiconductor Corporation | Voltage translation and overvoltage protection |
| AU5324896A (en) * | 1995-04-11 | 1996-10-30 | Columbia River Carbonates | Calcium carbonate pigments for coating paper and paper board |
| US5676748A (en) * | 1995-12-29 | 1997-10-14 | Columbia River Carbonates | Bulking and opacifying fillers for paper and paper board |
| AU5376396A (en) * | 1995-04-11 | 1996-10-30 | Columbia River Carbonates | Bulking and opacifying fillers for cellulosic products |
| US5676747A (en) * | 1995-12-29 | 1997-10-14 | Columbia River Carbonates | Calcium carbonate pigments for coating paper and paper board |
| WO1996032447A1 (en) * | 1995-04-11 | 1996-10-17 | Columbia River Carbonates | Bulking and opacifying fillers for paper and paper board |
| US5653795A (en) * | 1995-11-16 | 1997-08-05 | Columbia River Carbonates | Bulking and opacifying fillers for cellulosic products |
| EP0790135A3 (en) * | 1996-01-16 | 1998-12-09 | Haindl Papier Gmbh | Method of preparing a print-support for contactless ink-jet printing process, paper prepared by this process and use thereof |
| DE102005057836B3 (en) * | 2005-12-03 | 2007-03-08 | Corvus Beschichtungssysteme Gmbh | Adhesion-improving material, useful for paper and copying paper, comprises fixing agent and polycarboxylic acid as dispersant, also microcapsule coating mass containing it |
| JP2007163955A (en) * | 2005-12-15 | 2007-06-28 | Nippon Paper Industries Co Ltd | Transfer paper for electrophotography |
| JP5264661B2 (en) * | 2009-09-14 | 2013-08-14 | 北越紀州製紙株式会社 | Manufacturing method of coated paper for offset and gravure printing |
| DK2447328T3 (en) * | 2010-10-29 | 2015-03-09 | Omya Int Ag | A method for improving håndterligheden of calcium carbonate-containing materials |
| ES2456369T3 (en) | 2011-08-31 | 2014-04-22 | Omya International Ag | Hybrid of self-binding pigments |
| EP2565237B1 (en) * | 2011-08-31 | 2015-03-18 | Omya International AG | Process for preparing self-binding pigment particle suspensions |
| PT2662419E (en) | 2012-05-11 | 2015-10-07 | Omya Int Ag | Charge controlled phch |
| ES2547808T3 (en) * | 2012-05-11 | 2015-10-08 | Omya International Ag | Treatment of materials containing calcium carbonate for increased filler agent load on paper |
| FI126543B (en) * | 2013-05-17 | 2017-02-15 | Fp-Pigments Oy | A process for the preparation of an aqueous pigment-containing cationic high solids dispersion, an aqueous pigment dispersion and its use |
| CN109844005B (en) | 2016-08-24 | 2022-05-10 | 有机点击股份公司 | Bio-based polyelectrolyte complex compositions containing aliphatic compounds with increased hydrophobicity |
| WO2018038669A1 (en) * | 2016-08-24 | 2018-03-01 | Organoclick Ab | Bio-based polyelectrolyte complex compositions comprising non-water soluble particles |
| SE1651136A1 (en) | 2016-08-24 | 2018-02-25 | Organoclick Ab | Bio-based pec compositions as binders for fiber based materials, textiles, woven and nonwoven materials |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NZ223204A (en) * | 1987-01-21 | 1989-12-21 | Erba Farmitalia | Pyrazole derivatives and pharmaceutical compositions |
| GB8701491D0 (en) * | 1987-01-23 | 1987-02-25 | Ecc Int Ltd | Aqueous suspensions of calcium |
-
1989
- 1989-12-06 GB GB898927536A patent/GB8927536D0/en active Pending
-
1990
- 1990-12-04 JP JP3501306A patent/JPH05502484A/en not_active Expired - Lifetime
- 1990-12-04 ES ES91900880T patent/ES2070484T3/en not_active Expired - Lifetime
- 1990-12-04 DK DK91900880.5T patent/DK0504245T3/en active
- 1990-12-04 WO PCT/GB1990/001883 patent/WO1991008341A1/en active IP Right Grant
- 1990-12-04 AU AU69584/91A patent/AU647762B2/en not_active Ceased
- 1990-12-04 DE DE69018648T patent/DE69018648T2/en not_active Expired - Fee Related
- 1990-12-04 EP EP91900880A patent/EP0504245B1/en not_active Expired - Lifetime
- 1990-12-04 AT AT91900880T patent/ATE121149T1/en not_active IP Right Cessation
- 1990-12-04 BR BR909007899A patent/BR9007899A/en not_active IP Right Cessation
- 1990-12-04 ZA ZA909749A patent/ZA909749B/en unknown
- 1990-12-04 CA CA002072641A patent/CA2072641A1/en not_active Abandoned
- 1990-12-05 NZ NZ236353A patent/NZ236353A/en unknown
- 1990-12-06 CN CN90110340A patent/CN1051826C/en not_active Expired - Fee Related
-
1992
- 1992-04-07 GB GB9207583A patent/GB2253857B/en not_active Expired - Fee Related
- 1992-06-03 FI FI922555A patent/FI101091B/en active
- 1992-06-04 NO NO922206A patent/NO180598C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| NO180598B (en) | 1997-02-03 |
| JPH05502484A (en) | 1993-04-28 |
| DE69018648T2 (en) | 1995-08-10 |
| EP0504245A1 (en) | 1992-09-23 |
| GB2253857A (en) | 1992-09-23 |
| EP0504245B1 (en) | 1995-04-12 |
| DE69018648D1 (en) | 1995-05-18 |
| BR9007899A (en) | 1992-09-15 |
| FI101091B (en) | 1998-04-15 |
| NO180598C (en) | 1997-05-14 |
| GB2253857B (en) | 1993-08-04 |
| WO1991008341A1 (en) | 1991-06-13 |
| ES2070484T3 (en) | 1995-06-01 |
| FI922555A (en) | 1992-06-03 |
| CN1052912A (en) | 1991-07-10 |
| AU647762B2 (en) | 1994-03-31 |
| AU6958491A (en) | 1991-06-26 |
| NZ236353A (en) | 1993-01-27 |
| ZA909749B (en) | 1991-10-30 |
| FI922555A0 (en) | 1992-06-03 |
| CN1051826C (en) | 2000-04-26 |
| GB9207583D0 (en) | 1992-06-03 |
| ATE121149T1 (en) | 1995-04-15 |
| NO922206L (en) | 1992-06-30 |
| DK0504245T3 (en) | 1995-09-04 |
| GB8927536D0 (en) | 1990-02-07 |
| NO922206D0 (en) | 1992-06-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |