US3132042A

US3132042A - Manufacture of cellulosic product

Info

Publication number: US3132042A
Application number: US176554A
Authority: US
Inventors: Robert E Weber
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1962-03-01
Filing date: 1962-03-01
Publication date: 1964-05-05
Anticipated expiration: 1981-05-05

Description

May 5, 1964 R. E. WEBER I MANUFACTURE oF cELLULosIc PRODUCT Filed March l, 1962 k QQU MQQ @S QR 2Q@ .ISQQ Q QS h6 X065 uw Qw El QQSQ Numwmw@ 3 ethyl, propyl and butyl acrylates; and esters of secondary alkanols such as isopropyl acrylate and isobutyl acrylate.

Examples of mono-unsaturatedl ethylenic carboxylic acids are: acrylic acid, methacrylic acid, itaconic acid, aconitic acid, maleic acid, fumarie acid, and the like.

Examples of'hardening monomers for use in the tri- Y polymer are: the alkyl'rnethacrylates such as the methyl, ethyl, and propyl.

Typical interpolymer or copolymer systems of the first emulsion include:

Techniques for polymerizing the foregoing monomers into'the copolymer are further illustrated in Patents Nos. 2,795,564; 2,760,886; 2,790,736; and 2,790,735. The C0- polymer dispersions which may contain -50% resin solids may be made by any of the known emulsion copolymerization procedures, preferably by mixing the several monomers in the desired proportions into an aqueous solution of an anionic or a nonionic dispersing or emulsifying agent. Specific examples of suitable anionic and nonionic emulsifying orvdispersing agents andl catalysts are set forth hereinafter and are designated in the patents mentioned above.

A second emulsion includes the polymerized hardening monomer. acrylate. The solids content of such dispersion also is suitably in the range of Btl-50% resin solids.

The two emulsions are mixed together to form the binder and then combined with other constituents of the top coating composition as described hereinafter.

In addition to hardness, the composite binder must impart other desirable characteristics to the coating such as a suitable minimum film-forming temperature, coales.- cence and drying at conventional temperatures utilized in Such monomer preferably is methyl methpapermaking and coating operations, a capacity for application at high speeds common to a papermaking machine, suitable viscosity at relatively high solids, ,and maximum bonding to the prime coated web; and it must itself bond well to the pigment particles of the top coating.

I' have found that, if at least 50% by weight of the solids content of the binder mixture is produced from polymerized hardening monomer introduced bythe second emulsion, the results desired may be achieved-that is, a paper gloss of atleast 87 and a coating which maybe easily supercalendered at normal temperatures and pressures. The polymerized hardening monomer may form 65% by weight of the binder; yabove about this limit dif mits the use of the relatively large quantity of the polymerized hardening monomer in the coating composition. This factor, and the effect of the underlying prime coat, provides for the achievement of the desired coating, comparable to a cast coated sheet.

The top coating composition, it has been found, is `sensitive to the introduction, as already noted, of adhesive materials. In some instances, as in reverse roll coating operations, it is desirable to employ a coating of relatively highl solids; a suspending or thickening agent is then employedf-such should, however, be present only in trace quantity-4M to 0.3% on the weight of the pigment to avoid lossr'of gloss. Agents such as the watersensitive gums including the gel forming synthetic hydrophilic colloids, typical of which is carboxypolymethylene, a vinyl polymer with active carboxyl groups and a commercial form of which is Carbopol 934, a synthetic polycarboxylic acid and a product of B. F. Goodrich Chemical Company; Acrysol thickeners such as an aqueous solution of sodium polyacrylalte serve the purpose when introduced in about the same small proportion. The thickener must be such that it Ywill maintain the ingredients of the coating composition suspended in stable condition under the action 0f high shearing stresses exerted by coating equipment during the formation of the coating and in its application to the prime coated web.

The invention will be more fully understood by reference to the following detailed description, examples, and accompanying drawings wherein:

FIG. 1 is a ow'diagramillgustrating the steps 0f producing coated paper in accordance 'with this invention; and

IFIG. 2 is a diagrammatic and greatly enlarged representation of a section of coated paper of the present invention illustrating a web coated on one side.

The product is produced on a papermlaking machine in accordance with a preferred embodiment of the invention as illustrated inthe flow diagram, FIG. l. While coating on one side only of the |web is illustrated, it will be understood that it is conventional to apply coating to both sides of the paper. The web 10 (FIG. 2) is formed in conventional manner (step 1) and dried (step 2), and `a prime coat A12 is applied (step 3) thereto. This prime coat lpenetrates the Aweb interstices, Vand the adhesive of Ithe prime coat bonds the particles of pigment to each other as well as to the cellulosic paper fibers. The prime coated yweb is then dried (step 4) in the continuous operation of the paperrrnaking machine. Such operation is conventional. The formationof the web and drying of the web (steps 1 and 2) are optional in the process of the invention as they may take place independently of the coati-n-g steps.

yIt is also conventional to double coat'webs yon each side. The `dried prime coated web in this instance has a second coat 14 applied thereto as illustrated by step 5. Such second coat might, of course, be applied on an olfftihe-machine ooater after the prime coat has been dried, the web rolled up, and cooled.

As indicated in the drawing, the coating composition. t

of step 5 includes an admixture of the soft interpolymer mer with yother coating composition constituents. The

top coat is dried on the prime coated web (step 6) and then is supercalenderedy (step 7). Such supercalendering is necessary to raise Ythe gloss to desired levels.

The nal step 8 of printing the supercalendered paper is voptional as indioated'in the drawing; printing paper,

v however, isv the desired objective of the process of inven- In theffollowing examples which are illustrative of the present invention, the parts are by dry weight runless otherwise noted.

Example I i -In a preferred specific embodiment the invention is practiced by treating a relatively heavy basis weight paper with a first coat, followed by the high gloss coating. The

coating Vapplications may be by on-or-off the machinesheet or web. 3 Speed lof formation is about 1000 feet per Y minute.

l This web is then coated on its opposed sides with a coating `composition compounded by-conventional meth- Y ods androf a lformulation such as:

Clay (premium predispersed kaolin) l 100 Starch (white dextrin) 22 Sodium hexamet-aphosphate 0.1 Sodium hydroxide 0.1 Water to give solids of'55%.

'The viscosity of such coating is about 40 poises at 50 C. 'Dhslcoating composition is applied to the web by a pounds per side in some applications but `then the binder Y (starch)Y content of the coating is preferably increased to about 35% based on the weight lof the clay. VThe important function of this base or prime coat is to penetrate theweb and to provide 'a kind of tie ply'to the paper `web `for the ltop coat as Well as lto impart strength to the sheet.

The basecoated web is ydried to a Water content of or lessbefore application of the top coat. The following formulation may be employed forl the top coat, the

quantities being von a dry weight basis;

Clay (premium predispersed haolinL 100 Titanium dioxide 20 Acrylic homopolymer (polymethyl methacrylate) 11.2 Acrylic interpo lymer L V7.

(Ethyl acrylate-83) (Methyl methacrylate--13) (Methacrylic acid-4) (Tie-i+1) Thickening yagent (high mol.A Wgt.` polyacrylic acid)4 Y 0.148 Sodulm-` hexametaphosphate'. 0.16 Sodium hydroxide 0.11 Water'suiicient to make solids of 64.9%.

p r v d '1.8 poises at 50 C. lat 100 rpm. With t6-'spindle (1180 ceutipoises). i f l Coat weight, 13 pounds perside.V Y a rlhe prime coated web to which this top coat is applied has abasis Weight of about 64 po unds (25" x 38 x 500 sheets); y

'.Io prepare the`top coat formulation; the thickener is dis-solved in Kwaterto provide a clear solution; this solution is` added to a kneader, 'and the dispersant, sodium hexametaphosphate,fintroduced. `The pigment is then `60 added to the solution to form a' slurrywhile stirring at v.room temperature; the slurry is opaque and creamy and Y preferably as much as possible of the pigment (clay and Vtitanium dioxide) is added atthis time-usually enough 'to malte the solids content Vofthe slurry about 1,5% by Weight@ Sodium hydroxide in af Vsolution form (1 -5%) is then .added to neutralize the mentioned thickener-i-this Yalkali addition helps Ito thicken thefslurry and aids in dryingfwof inlc subsequently applied tothe ltinished paper. The /remainingwater and pigment are thenl added and Vmixingcontinues for 20 to 30y minutes. Thebinder is dryer.

The tripolymer aqueous dispersion is obtained by the emulsion polymerization of a mixture of 83 parts by Weight of ethyl acrylate, 13 parts by Weight ofmethyl methacrylate,A and 4 parts of methacrylic acid in about 100 partsof water in the presence of about 6 parts of a t-octylphenoxypolyethoxy ethanol containing about 30 oxyethylene units and small amounts of ammonium persulfate and sodium hydrosulite as catalyst. After polymerization, the pH is adjusted to about 6.5. The T1 ofV such interpolymer is about 1 C. A similar commercial emulsion suitablefor the purpose is provided as Rhoplex B15-by Rohm & Haas Company, Washington Square, Philadelphia 5, Pennsylvania. coat formulation given above except for an acrylic interploymer of S5 parts of ethyl acrylate, 10 parts of methyl methacrylate and 5 parts of acrylic acid having a Ti of about -5 C., similar results areobtained.

The dspersion of the hardening monomer is formed by the emulsion polymerization of about parts by Weight of methylmethacrylate in about 100 parts of water in the presence of about 5 parts of sodium lauryl sulfate and small amounts of potassium persulfate and sodium meta-bisulte as catalyst. After polymerization, alkali,

such as sodium hydroxide, is added to Vadjust the pH to` about 8.5.

These two emulsions are' mixed at roorn temperature and combined in the coating composition as `described above. Y

The Weight of `top coating applied to each side maybe about 13 pounds per side for the 50-p'ound uncoated sheet. The top coating is applied in excess to the Web and subjected to the action of a rod rotating reversely to web movement to remove the excess While the web is supported on a backing roll.

. Wetting of the prime coat by the aqueous top coat composition causes the two coatings to become intimately united.

The Web with the prime and top coats thereon is dried at about 350 F. air temperature in a high velocity air Such drying 'is an important Vstep vto `achieve adequate'bonding of the top coating. The drying temperature may suitably be as loW as 300 F. but should not exceed 450 F. air temperature. -Too low a temperature of drying as Well as too high a rate of drying at a high temperature tends to result in poor bonding of pigment in the top coating and of poor top coat bonding'to the calendering operation has 'a normal range of 140-160 F. `Supercalendering pressure was also normal; the pressurerange was about 1000 pounds per lineal inch and may range from as low as 350 pounds to 2000 pounds per lineal inch depending on calender roll diameter. With the coated web sheet moistureis not critical forsupercalendering.V Ai gloss of 87D orM above can be obtained with less uthan 1% moisture inthe sheet, butsomefmois- ,ture will increase gloss byaV point'ortwof- The sheet, however, lis calendered without external moisture application. Y t V The totalbasis Weight of this sheet was about pounds per ream (25 x 38k x 500 sheets). f'

Paper gloss'aftersupercalendering Was89,.2 on 'the Wireand ,89.9 on the felt side-using a 775 instrument.

Such gloss meter is a conventional device commonlyemployed in gloss measurements.

Tests on the Vpaper made `as described gave optimum half-tone and letter pressjpick values. i

Also, with the same top Example 1I The procedure of Example I is followed, substituting for the quantity of interpolymer 8.42 parts by weight and for the homopolymer 10.28 parts by weight. This is about a 45 to 55 ratio. The quality of the coated paper is similar to that attained in accordance with Example I.

Example IV The procedure of Example `I is followed except that equal parts by weight of the interpolymer and hornopolymer are employed, 9.35 by weight of each on a dry basis.

Example V The procedure of Example I is followed except that the top coating compositionist- Clay (premium predispersed kaolin) 100 Acrylic homopolymer (methyl methacrylate) 10.8 Acrylic interpolymer (Example I) 7.2

Thickening agent (carboxypolymethylene) 0.148

Sodium hexametaphosphate 0.16

Sodium hydroxide 0.11

Water to make solids of 60.9%. v

Viscosity 2450 centipoises at 50 C.

The top coat weight per side is 13.3 pounds. The

basis'weight of such finished coated sheet is about 90 pounds.

Such sheet, when supercalendered at normal temperatures and pressures, had a paper gloss on each side of 87.4.

It will be noted that the effect of eliminating the titanium dioxide is to slightly reduce the gloss.

' Example VI The procedure of Example I is followed except that the top coating composition is:

Clay (premium predispersed kaolin) 90 Titanium dioxide Rhoplex B--a 46% solids aqueous emulsion, a

commercial product of Rohm & Haas-solida-- 7.5 Rhoplex B-85-a 38% solids, a commercial product of Rohm & Haas-solids 7.5 Thickening agent (Carbopol 934) a synthetic polycarboxylic acid, a product of B. F. Goodrich Chemical Co 0.156 Sodium hexametaphosphate 0.1 Sodium hydroxide 0.0611 Water to make solids of 65%. Viscosity, 1110 centiposises at 50 C. pH 6.7

The results of such top coat application are similar to thoseof Example I; on supercalendering gloss levels-*f 89-91 were obtained. Half-tone valuesand print values were optimum. I

However, it is to be noted that lessjalkali Was included and the composition was slightly acid-this leads to slower speedof ink drying.v However, the commercial binder products'work as well on the alkaline side When employed in the composition as indicated inthe following example.

S Example VII The procedure of Example Il is followed except that the top coating composition contains:

Clay (premium predispersed kaolin) 100 Rhoplex B-15-a 46% solids aqueous emulsion, a

commercial product of Rohm & Haas Company-solids 10 Rhoplex B-85--a 38% solids aqueous emulsion-a commercial product of Rohm & Haas Company-solids l 5 Thickening agent (Carbopol 934) 0.148

Sodium hexametaphosphate 0.10

Sodium hydroxide 0.11

Water to make solids of 65%.

Viscosity, 1200 centipoises at 50 C.

pI-I i 7.5

Upon supercalendering a web with the above noted top coating at a top coating weight of about 10 pounds per side, a paper gloss of 89-90 is achieved.

In the finished coating the soft copolymer or interpolymer tends to surround the pigment particles and to retain them positioned with a degree of plasticity to give a smooth surface on supercalendaring.l The admixed hard polymer particles dispersed throughout the coating v are oflesser effect in aiding the retention of the pigment particles, and the hard polymer would itself be quite ineffective as the sole binder material. However, when well dispersed in the coating, the hard particles, when present as described, achieve a high gloss and the overall sheet gloss is'uniform and high, in excess of 87 as already noted. The flow of the softer, more thermoplastic'material under supercalendering pressures and temperatures aids the attainment of this high uniform gloss; in the appropriate proportion the thermoplastic softer material is not adversely aected by the calender temperature and pressure, and picking at the calender is avoided.

Similarly, the picking factor is excellent when the paper is subjected to tacky letterpress or oifset inks. The smooth gloss surface exhibits high ink holdout characteristic of coatings formulated with al1 soft copolymer or interpolymer as binder.

Print test results on the high gloss paper produced in accordance with the invention are comparable to results achieved with a high quality cast coated paper. Four- .color reproductions, monotone half-tones and gloss instrument measurements made on commercially produced prints indicated that the paper quality is comparable for the cast coated and machine produced paper of this Vinvention. Ink drying and coating pick even using inks which were quite tacky were entirely satisfactory. Registry in the printing operation'was also good. f

The specific embodiments described have all included a thickener inthe top coating in what is substantially trace amounts. The thickener is employed for the purpose of achieving optimum rheological properties in the coating for blade, rod, and reverse roll coating applications. It may be eliminated when-the coating is applied by other methods such as dipping ork air knif Y The clay and other pigments may be any conventional material which is well dispersed in the .composition to provide for adequate coating application, drying and supercalendering.

Theweb itself suitably has a basis weight (25" x 38 x 500 sheets) ofat least 40 pounds uncoated and about 70 pounds coated; usually the upper limit of the coated sheet `is a basis weight of about 120 pounds. Conventionally,

the type of printing paper under consideration is coated on both sides and has a basis weight of 80 to about 100 pounds;l

v While the prime `coat need not contain pigment, it is highly desirable that a considerable quantity of clay be tion by weight on a dry-basis. Clay in the prime coat not only provides for increased Yadherence of the top coating, but the clay is receptive to the action of polar groups in the top coating' to further improve adhesion.

It will be understood that this invention is susceptible tomodiiication in order to adapt to different usages and conditions4 and, accordingly, it is desired to comprehend such modifications withinthe invention as 4may fall within the scope of theappended claims.

.What is` claimed is:

1. A coated and supercalendered printing paper having a paper gloss in excess of 87 and comprising a web of cellulosic iibers, atop coating on saidweb'having the noted gloss characteristic, said toplcoating including a soft acrylic interpolymer having a specific adherence to polar groups yand having a Tivalue of between about ;--l0 C. and +10 C., a pigment, and methyl meth- .acrylate physically admixed with the interpolymer and pigment and present in the top coating to at least the same extent by weight as the interpolymer, Vand a prime coat Y containing a major proportion by weight of a pigment and an adhesive which has a specific adherence to said web and to said top coat, said prime coat penetrating, coatingand bonding the fibers of the web and providing ajsmooth surface to which the top coat is bonded, the top coat being thereby bonded to the web, said top coat lbeing present on said web inra greater proportion by Weight than said prime coat. y f 2,. t A coated and supercalendered paper product having p a paper gloss in excess of 87 comprisinga web of cellulrosic fibers, a prime coat containing an adhesive having a specic adherence to said vfibers, said prime coat pene- `trating and coating said web and bonding fibers of the web together, and a top coating on said prime coated web, said top coating'comprising: v

(a) a inely divided pigment having a 'predominant acid or amide to the extent of between about 0.5% to about 7.0% by weight and Vselected frein the group consisting of methacrylic acid, acrylic acid, itaconic acid, `maleic acid, fumarie acid, or amides of these acids and With a small proportionof an alkyl methacrylate; and

. v(l2) a homopolymer which includes methyl meth- Y acrylate hardening monomer, said methyl meth- Y acrylate being present to the extent of between (c) applying a top lcoating to said prime .coating which fis compatible with and bonds to the` adhesive-con- `Staining prime coating; f` (al) vapplying said top coating in theform of an aqueous dispersion containing a pigment and a binder to the Y 'extentl of about l2 to v25% by weight of the pigment, said binder containing a physical admixture of ,(1) an interpolymer which has' adherence to (2) a methyl methacrylatehomopolynier present to at least the same extent by Weight as the interpolymer and which homopolymer normally has little adherence to cellulose;

(e) drying the web with the top coating'thereon at a temperature in the range of about 225-450f F.; and

(f) supercalendering the web'under elevated tempera- `ture to a paper gloss'of at least 87.

4. A method of producing a supecalendered coated paper having a paper gloss `in excess of 87, thel said `method comprising the steps oft.'v

(a) coating a relatively heavy basis Weight web of cellulosic fibers with a prime coating composition containing an adhesive having a specific adherence to polar groups to impregnate and bind the fibers together and to provide a smooth coated surface on said web; i

(b) drying the coated web;

(c) applying a top coating to said prime-coating which is compatible with and bonds to the adhesive-containing prime coating; n

(d)applying said top coating in the form of an aqueous vdispersion containing a pigment and a binder to the extent of about l2 to 25% by weight of the pigment, said binder containing a physical admixture of (l) an interpolymer which has adherence to cellulose and has a T1 value of between about Y -10 C. and +10" C.; and

v(2) a methyl methacrylate homopolymer present to at least the same Vextent by weight as the interpolymer and which homopolymer normally has little adherence to cellulose; f

(e) drying the web with high velocity heated air at a temperature of between about 3D0-450 F.; and

(f) supercalendering the web under elevated temperature `to a paper gloss of -at least 87.

5. A method of producing a supercalenderedcoated paper having aV paper gloss in excess of 87, the said method comprising the steps of:

(a) coating a relatively heavy basis weight web of cellulosic fibers with a prime coating` composition containing an adhesive having a speciiic adherence to polargroups to impregnate and bind the iibers to-A is compatible with and bonds to the adhesive-containing prime coating; (d) applying said top` coating in the form of an aqueous dispersion containing a pigment and a binder to theextent of about 12 to 25% by weight of the pigment, said binder containing a physical admixture of (l) an interpolymer which has adherence to cel-V Y lulose and has a T1 value of between aboutr -10 C. and +10 C.; and V(2) a methyl methacrylate `homopolymer present to at least the sameextent by weight asV the interpolymer and which homopolymer normally has littleV adherence to cellulose;

V(e) drum drying the web with the top coating thereon ata temperature inthe range of about Z-325 F.;

and (f) supercalendering the web' under elevated temperature to a-paper gloss of at least 87.

f 6. A method ofrproducing a supercalendered coated comprising the steps of:

celluloseV and has a Ti value of between abouti.'

(a) coating a relatively heavy basis Weight web of cellulosic fibers with a prime coating composition 9 containing an adhesive Vhaving a speciiic adherence i Y to polar groups to impregnate and bind the fibers saidgweb; i

'(b)' drying the coated web;

together and to provide a smooth coatedsurface on 1 l (c) applying a top coating to said prime coating which is compatible with and bonds to the adhesive-containy ing prime coating;

n (d) applying said'top coating in the form of an aqueous l2 (e) drying the web with the top coating thereon at a temperaturein the range of about 225-45G F.;

, and A n Y (f) supercalendering the web under'elevated temperature to a paper gloss of at least 87.

t References Cited'in the le of this patent UNITED STATES PATENTS 2,776,236 Staehle4 Jan. l, 1957 2,790,735 McLaughlin et al.V Apr. 30, 1957 3,081,198 Miller v Mar. 12, 1963 OTHER REFERENCES Y Acrylic Resins (Horn), published by Reinhold, 1960,

interpolymer and which homopolymer normally 15 page 30- has little adherence to cellulose;

Claims

2. A COATED AND SUPERCALENDERED PAPER PRODUCT HAVING A PAPER GLOSS IN EXCESS OF 87 COMPRISING A WEB OF CELLULOSIC FIBERS, A PRIME COAT CONTAINING AN ADHESIVE HAVING A SPECIFIC ADHERENCE TO SAID FIBERS, SAID PRIME COAT PENETRATING AND COATING SAID WEB AND BONDING FIBERS OF THE WEB TOGETHER, AND A TOP COATING ON SAID PRIME COATED WEB, SAID TOP COATING COMPRISING: (A) A FINELY DIVIDED PIGMENT HAVING A PREDOMINANT PORTION OF CLAY; AND (B) A BINDER COMPRISING FOR EACH 100 PARTS OF CLAY BETWEEN ABOUT 12 AND 25 PARTS BY WEIGHT OF AN ADMIXTURE OF (1) AN INTERPOLYMER HAVING A T1 VALUE OF BETWEEN ABOUT -10*C. AND +10*C. WHICH INCLUDES A WATER-INSOLUBLE COPOLYMER OF AT LEAST ONE LOWER ALKYL ACRYLATE IN WHICH THE ALKYL GROUP HAS FROM 1 TO 4 CARBON ATOMS WITH AN ACID OR AMIDE TO THE EXTENT OF BETWEEN ABOUT 0.5% TO ABOUT 7.0% BY WEIGHT AND SELECTED FROM THE GROUP CONSISTING OF METHACRYLIC ACID, ACRYLIC ACID, ITACONIC ACID, MALEIC ACID, FUMARIC