CA1049715A - Process for the preparation of paper sheets coupled to films of polymeric material - Google Patents
Process for the preparation of paper sheets coupled to films of polymeric materialInfo
- Publication number
- CA1049715A CA1049715A CA222,966A CA222966A CA1049715A CA 1049715 A CA1049715 A CA 1049715A CA 222966 A CA222966 A CA 222966A CA 1049715 A CA1049715 A CA 1049715A
- Authority
- CA
- Canada
- Prior art keywords
- fibrils
- weight
- panel
- process according
- thermoplastic polymer
- 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.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
- D21F11/02—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines of the Fourdrinier type
- D21F11/04—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines of the Fourdrinier type paper or board consisting on two or more layers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
- B32B5/24—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer
- B32B5/26—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer another layer next to it also being fibrous or filamentary
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B38/00—Ancillary operations in connection with laminating processes
- B32B38/16—Drying; Softening; Cleaning
- B32B38/164—Drying
- B32B2038/166—Removing moisture
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
- B32B2262/02—Synthetic macromolecular fibres
- B32B2262/0253—Polyolefin fibres
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
- B32B2262/06—Vegetal fibres
- B32B2262/062—Cellulose fibres, e.g. cotton
- B32B2262/067—Wood fibres
Landscapes
- Paper (AREA)
- Laminated Bodies (AREA)
- Wrappers (AREA)
Abstract
ABSTRACT OF DISCLOSURE
Products comprising cellulose paper sheets coupled to films of thermoplastic polymers are prepared by (a) forming a panel comprising at least two superimposed fibrous layers, one layer consisting, at least predominantly, of cellulose fibers and the other consisting, at least predominant-ly, of fibrils or microfibers of synthetic thermoplastic poly-mers, by successive stratification of pulp or aqueous dis-persions of said fibers and fibrils;
(b) reducing the water content of the panel, by suction and/or compression, until it is between 30% and 80% by weight;
(c) drying the panel to a moisture content of less than 0.5% by weight; and (d) heating the panel under pressure at a temperature higher than the softening temperature of the synthetic thermoplastic polymer.
Products comprising cellulose paper sheets coupled to films of thermoplastic polymers are prepared by (a) forming a panel comprising at least two superimposed fibrous layers, one layer consisting, at least predominantly, of cellulose fibers and the other consisting, at least predominant-ly, of fibrils or microfibers of synthetic thermoplastic poly-mers, by successive stratification of pulp or aqueous dis-persions of said fibers and fibrils;
(b) reducing the water content of the panel, by suction and/or compression, until it is between 30% and 80% by weight;
(c) drying the panel to a moisture content of less than 0.5% by weight; and (d) heating the panel under pressure at a temperature higher than the softening temperature of the synthetic thermoplastic polymer.
Description
~ ~049715 :
, , , . .. ,:, . -THE-PRIOR ART : : ~ -In the last years it has become common to use paper sheets :
coupled to pla~tic film, al80 Icnown aH "plasticized paper, " fGr packaging variou~ article~ . .
.:, . ' ~ . , .
. . .' 1 . ' .~ ;~
':' ~ '~
. ' ' . ' ,, : ` ' .', . . ,. : ~
I . .
., . . : - . . : . .. : : - . : . :
: - -. - . . ., . -., : , ~ '' - : ;~ ' ', - ' : . : : - . ' .
Such plasticed papers have been obtained by coupling, in general under pressure, a paper sheet to a film of ~;~olymeric material, after treating the paper sheet with adhesives, or one or both of the components with electrical discharges of the "corona" type, for promoting their mutual adhesion.
The process i~ rather complicated and requires separation of the forming equipment both for the paper sheet and the polymeric film. Moreover due to the extreme difficulty of obtaining by ext-rusion films of polymers with a high molecular weight, said process is limited to the use of polymers with a low molecular weight which yield however film~ of poor mechanical characteristics and scant "barrier" properties.
The process most comrrionly used by the Prior Art consists in conveying the paper sheet, treated superficially with a suitable adhesive, to the head of a polymer film extruder which covers the passing paper sheet with the polymer film which is made to adhere definitively by compression. The device illustrated on Figure 1 of the accompanying drawing exemplifies said process. In this drawing in (1) is represented the paper sheet feeding reel, ~ (2) is the adhesive containing vat, (3) is the dryer, (4) represents the extruder ., ;~l (5) the polymeric film, (6) the rolls for the compression and cooling of the ., coupled product, and in ~7) is shown the winding up reel for.the finished , I product. ;' Such a process offer~ considerable disadvantages due to the low extrusion speed of the film and to the relative ease with which the latter breaks leaving the p,aper uncovered, due to the thickness of the film.
` 25 Said drawbacks are increased whenever it is the question of pre-,~ paring multi-layer coupled product~, for instance socalled "sandwich" coup-ling~ in which the polymer film 1~ ~closed between two pap-r sheet~.
,' , ' ' .1 .'' . : '-~ ' ' ' -.
; . . .
10~971S
THE PRESENT INVENTION
An object of this invention is to provide a rapid and cheap process for preparing "plasticized paper" comprising cellulose paper coupled to ther-moplastic polymer films and having characteristics superior to those of the "plasticized papers" known heretofore.
This and other objects are accomplished by this invention in accordance with which the thermoplastic polymeric material is used in the form of fibrils dispersed in an aqueous medium.
By the term fibrils as used herein fibers (or fiber - like products) having a length comprised between 1 and 50 mm, an average (apparent) diameter ranging from l to 400 micron and a surface area (specific surface) larger than 1 m /g, are meant.
Said fibrils, which are in the art, may be prepared according to various different methods and are generally used in the manufacture of -synthetic paper. A process for preparing fibrils of polyolefinic material i9 :
described, f. i., in Italian Patent No. 947, 919, of Montedison.
According to that process, a solution of the olein polymer is extruded at a temperature above the boiling temperature of the solvent under normal conditions, and under autogenous pressure, or at pressure greater than the autogenous pressure, into a zone of lower pressure, and is then hit in an at least expanded state by a jet of high speed fluid which is at a temperature lower than the temperature of the solution, and has an agled direction with respect to the direction of extrusion of the solution.
Other methods ior obtaining fibrils of synthetic polymer, suited for manufacturing the coupled sheets of the present invention, are disclosed, I.i., in U.S. Patents No. 2, 999, 788 and No. 3, 40Z, 231, in British Patent No.
1, 262, 531 and in German Patent Publications DT-OS No. 1, 951, 576. 5 and D A S No. 1, 290, 040. ~-~,~,, _. , ., . . ' ` , . : .
The proce~s of the invention thus .comprise~. following baslc operat ions carried.out in the order stated:
(a) formation of a panel comprising at least two super-impoded fibrous layers, each consisting, at least pre-dominantly, respectively of cellulosic fibers and of fibrils of synthetic thermopla~tic polymers, obtained by success-ive stratification of aqueou~ pulp~ or dispersions of such fibers or fibrils;
(b) reduction of the content in water of the panel up to quantities comprised between 30% and 80% by weight of water, by ; su.ction and/or compression;
(c) drying the panel until attaining a content in humidity of le~
. than 0 . 5% by weight; and (d) heating the panel up to a temperature greater than the soften-ing temperature of the thermoplastic polymer, under pressure.
Between operation (b) and operation (c) there may be inserted a cold compression step for the panel at pre~sure~ comprised between 50 and 150 kg/sq. cm, which compression may be carried out"for instance between "hunlid" roll~ or presse~ in those cases in which it ia wished to obtain more compact papers and lower moisture contents before the drying.
For the preparation of the flbrous panel in step (a), there may be . used in the form of pulp or a~ueous dispersion, fibril~ made of any synthetic theremoplastic polymer with a softening temperature not exceeding Z50 C.
i Examples of suitable theremoplastic polymers are, in particular, polyolefins,~
especially low and high density polyethylene, polypropylene prevailingly ; consi~ting of isotactic macromolecules, ethylene/propylène copolymers with a predominant content of propyl~e, a~ well a~ polyarnides such as nylon 6, vinyl polymer~ such as polyvinyl chloride and polyvinyl acetate, polyacrylo-. . nitrile and the polyoxymethylenes.
_4_ ~ 1049715 Whellever pos9ible, and especially in order to improve the look-through and the penetration of the plastic layer into the cellulose without re- ¦
.; ducing the "barrier" property, it is prèferred to use mixtures of fibrils of the same polymer but with different thermoplastic characteristics; for instance in case of polyethylene fibrils, it i8 preferred to use an aqueous di6persion consisting of high-density polyethylene fibril~ mixed with low-density polyethylene fibrils.
Aqueous di~per~ons (or pulp9) of different thermoplastic polymer~ may in any case be used, provided said polymers are compatible with each other and have sufficiently close softening temperatures.
In the above-mentioned disper~ions there may also be present cellulosic fibers in quantities not exceeding 10% by weight on the total weight of the fibers.
In order to achieve in the finished product the greatest possible coherence between the cellulose fiber layer and the layer of the thermo-plastic polymer, it has proved to be quite effective to use, in the panel pre-'i paration step (a), thermopla~tic fibril~ with si~e~ distributed within rather ,1 wide intervals, preferably comprised between 0. 5 and 5 mm with regard to their length and between 3 micron and 60 micron as far as the diameter is concerned .
; Further preferred conditions to be applied in the preparation of the fibrous panel in operation or step (a) consist in the use of pulps or aqueous l dispersions of thermoplastic fibrils having a concentration in fibrils equàl to ;' 1. 5 - 2, 5 times the concentration of the cellulosic fibers in the agueou6 dispersions containing the cellulo~ic fibers at least predominantly.
s' In this way on the contact ~urfaces between the layers forming the panel the possibility for the fibers of each layer to penetrate in the fiber6 ofthe other layer ia increa~ed, with a considerable advantage for the mutual ~ ~ !
adhesion between the thermoplastic phase and the cellulosic phase in the end product.
The process, on the whole, is easily achieved with the devices commonly used in paper mill9, devices which comprise cellulose pulp beat-S ing machines and machines for the forming, drying and calandering of paper sheets .
The preparation of the multi-layer fibrous panel, according to step (a), may be carried out, for instance, by the ~uccessive deposition of the corresponding aqueous dispersions of the fibers on a filtering section, or by gathering on a common conveyor felt the fibrous pulps directly drawn from the respective aqueous dispersions by curved or flat table forming machines arranged in ~eries, according to processes known in the paper manufacturing art.
Step (b) for the elimination qf the excess water from the panel may be achieved by passing the panel over suction boxes and/or between pressing rollers. This operation promotes the phenomenon of the interpenetration of the two layèrs, made po~sible by the high content in water of the pulps, and facilitated by the disuniformity of sizes of the fibers, especially of the .
.l thermoplastic fibrila. ' ..
The drying of the panel in step (c) is conveniently carried out between cylinders maintained at increasing temperatures, but obviously lower : than the softening temperature of the thermoplastic polymer present in thepanel, and this drying must bring the content in water of the panel down to not more tha 0. 5% by weight, in order to avoid the formation of vapour 2S bubble~ inside the panel, during the 3ubsequent step (d) heating at high tem-perature. This latter operation, carried out under pressure, preferably compriaed between 30 and 100 kg/sq. cm, may be carried out between the rolls of a glazing machine~ and causes the melting of the thermoplastic iibril3 with tb orm3tion of a compact layer adhering to the cellDlollic layer. ¦
~- , .
If necessary, after the coupling achieved by this latter operation, the panel may be subjected, after cooling down, to operations for the superficial treatment of the cellulosic layer, such as calandering, coating glueing, etc. operations that are generally used for sheets of cellulose paper.
The pulps or aqueous dispersions, both of the cellu-losic fibers and of the thermoplastic fibrils, used for the pre- -paration of the starting panel~ may contain additives such as dyestuffs, pigments, inorganic fillers, antimildew agents, dis-persants, etc. The dispersions of cellulosic fibers may also contain fibers of a different nature, in quantities not ex~eeding 10% by weight with respect to the cellulose material, such as for instance rayon fibers, or fibers of cellulose acetate, nylon, polyvinyl alcohol and the likes.
It is essential for the process that the fi~rils of thermoplastic material be thoroughly and homogeneously dispersed ~-in water so as to form homogeneous and uniform layers. For this purpose it is necessary, in general, to add, auring their mixing with water, disperslng agents such as polyvinyl alcohol, anionic ,20 surfactan~s, urea resins, etc., or to submit the fibrils, before their use, to a superficial modification which will make them hydrodispersable. Such a modification may consist in coating the ~-fibrils with a dispersant, by dipping them into an aqueous solution of the dispersant and by successively dr~ing them.
; Such a method, wherein dispersants are used which consist of polyvinyl alcohol/aliphatic aldehydes Cl - C6 conden- -sates; is described in U.S. Patent No. 4,002,796 (Luciano Baldi et al) issued January 11, 1977.
The process according to this invention allows to '30~ obtain sheets of plasticized paper in which the resistance to ~, breakaway or "frilling" of the component layers is practically indeterminable in as much as this reslstance is greater than the j tearing resistance of the sheets themselves. A considerable .~ :
~ ~ - 7 -:. ~ .
.~ 1049715 a ~nta~e of this proc~ss consists in the fact that thcre a~ no limits to the speed of preparation of the sheets, since the resistance of thc cellulose support is never appreciably influenced by the presence of the thermoplastic material in any of the processing phases. It is thus possible to use the same cellulose compositions as well as the same operational speeds normally used for the preparation of sheets of common paper, speeds that are by far superior to those usable in the classical coupling or bonding processes.
By the process according to this invention, it is possible to prepare "sandwiched" couplings in which, for instance, the thermoplastic polymeric material in the form of a continuous film is enclosed between two or more sheets of paper or cellulosic cardboards.
In drawings which illustrate embodiments of this invention, Figure 2 represents a ~omplete diagram of the pre- -; paration of a-binary coupled sheet according to the invention.
Figure 3 is-a complete diagram for the preparation of a ternary cellulose/thermoplastic material/cellulose coupling.
In the diagram of Figure 2, there are shown the curved forming boxes (1) and (2~ which contain, respectively, the cellulose fiber pulps and the thermoplastic polymer fibril pulps;
the con~eyor felt (10) on which the cellulose fiber layer adheres, and, successively, by superimposition, the layer of thermoplastic fibrils; the suc~ion boxes (3); "wet" presses (4); the sets of drying cylinders (5); the heated "glazing" unit (6); the cooling rolls (~); the take-up reel for the coupled sheet (8), and the conveyor felts (9). In this diagram the position of the forming boxes may be inverted still obtaining the same results without :30 modifying the arrangement of the remaining equipment.
In the daigram of Figure 3 are represented: the curved forming boxes (l) and ~2), containing the cellulose fiber pulp; the flat table with inflow box (3), containing the fibrils of thermoplastic material, the suction boxes (4); the "wet" presses (5); the drying set (6); the heated "glazing" unit (7); the cold rollers (8); the take-up reel (9) and the conveyor or carrier felts (10).
The following examples are given to further illustrate the invention and are not intended as limiting.
In all of such examples, olefin polymer fibrils were utilized, prepared according to the technology illustrated in the above mentioned Italian Patent No. 947,919.
', ., .
. ' ~ .
_ g -, .: .. ' '' ' .... '' " .':,, ~' '' .. '~
~ ~ 1049715 Preparation of polyolefin fibrils A 50 liter autoclave, provided with heating chamber and stirrer, was fed with 2. 5 kg of high den~ity polyethylene (M. I. =5, Melting point =
135 C) and 1. 5 kg of kaolin, along with 35 liters of n-hexane. The mixture wa-S heated under the following conditions:
~: temperature = 180 C
total pressure (comprising an overpressure of nitrogen) = 15 kg/sq. cm.
until a ~olution of the polymer in the n-hexane was obtained.
Under such conditions, the mixture was ejected to the atmosphere, through a circular noz~le having 2 mm diameter, and was made to collide, at about 1 mm distance from the nozzle outlet, with a dry saturated steam jet, coming from a nozzle of 4 mm diameter and arranged at about 85 to the direction of ejection of the solution, at an impact speed of the steam of about l 15 470 m/sec. The fibrous product thus obtained was composed of individual J fibrils having length comprised between 0. 5~ and 5 mm, an average diameter i of between 15 and 45 micron, a surface area of 5 m ~g and containing abo~dt: :
30% by weight of kaolm.
'.1 ~ , ' ; I : Pr paration of the coupled sheet
, , , . .. ,:, . -THE-PRIOR ART : : ~ -In the last years it has become common to use paper sheets :
coupled to pla~tic film, al80 Icnown aH "plasticized paper, " fGr packaging variou~ article~ . .
.:, . ' ~ . , .
. . .' 1 . ' .~ ;~
':' ~ '~
. ' ' . ' ,, : ` ' .', . . ,. : ~
I . .
., . . : - . . : . .. : : - . : . :
: - -. - . . ., . -., : , ~ '' - : ;~ ' ', - ' : . : : - . ' .
Such plasticed papers have been obtained by coupling, in general under pressure, a paper sheet to a film of ~;~olymeric material, after treating the paper sheet with adhesives, or one or both of the components with electrical discharges of the "corona" type, for promoting their mutual adhesion.
The process i~ rather complicated and requires separation of the forming equipment both for the paper sheet and the polymeric film. Moreover due to the extreme difficulty of obtaining by ext-rusion films of polymers with a high molecular weight, said process is limited to the use of polymers with a low molecular weight which yield however film~ of poor mechanical characteristics and scant "barrier" properties.
The process most comrrionly used by the Prior Art consists in conveying the paper sheet, treated superficially with a suitable adhesive, to the head of a polymer film extruder which covers the passing paper sheet with the polymer film which is made to adhere definitively by compression. The device illustrated on Figure 1 of the accompanying drawing exemplifies said process. In this drawing in (1) is represented the paper sheet feeding reel, ~ (2) is the adhesive containing vat, (3) is the dryer, (4) represents the extruder ., ;~l (5) the polymeric film, (6) the rolls for the compression and cooling of the ., coupled product, and in ~7) is shown the winding up reel for.the finished , I product. ;' Such a process offer~ considerable disadvantages due to the low extrusion speed of the film and to the relative ease with which the latter breaks leaving the p,aper uncovered, due to the thickness of the film.
` 25 Said drawbacks are increased whenever it is the question of pre-,~ paring multi-layer coupled product~, for instance socalled "sandwich" coup-ling~ in which the polymer film 1~ ~closed between two pap-r sheet~.
,' , ' ' .1 .'' . : '-~ ' ' ' -.
; . . .
10~971S
THE PRESENT INVENTION
An object of this invention is to provide a rapid and cheap process for preparing "plasticized paper" comprising cellulose paper coupled to ther-moplastic polymer films and having characteristics superior to those of the "plasticized papers" known heretofore.
This and other objects are accomplished by this invention in accordance with which the thermoplastic polymeric material is used in the form of fibrils dispersed in an aqueous medium.
By the term fibrils as used herein fibers (or fiber - like products) having a length comprised between 1 and 50 mm, an average (apparent) diameter ranging from l to 400 micron and a surface area (specific surface) larger than 1 m /g, are meant.
Said fibrils, which are in the art, may be prepared according to various different methods and are generally used in the manufacture of -synthetic paper. A process for preparing fibrils of polyolefinic material i9 :
described, f. i., in Italian Patent No. 947, 919, of Montedison.
According to that process, a solution of the olein polymer is extruded at a temperature above the boiling temperature of the solvent under normal conditions, and under autogenous pressure, or at pressure greater than the autogenous pressure, into a zone of lower pressure, and is then hit in an at least expanded state by a jet of high speed fluid which is at a temperature lower than the temperature of the solution, and has an agled direction with respect to the direction of extrusion of the solution.
Other methods ior obtaining fibrils of synthetic polymer, suited for manufacturing the coupled sheets of the present invention, are disclosed, I.i., in U.S. Patents No. 2, 999, 788 and No. 3, 40Z, 231, in British Patent No.
1, 262, 531 and in German Patent Publications DT-OS No. 1, 951, 576. 5 and D A S No. 1, 290, 040. ~-~,~,, _. , ., . . ' ` , . : .
The proce~s of the invention thus .comprise~. following baslc operat ions carried.out in the order stated:
(a) formation of a panel comprising at least two super-impoded fibrous layers, each consisting, at least pre-dominantly, respectively of cellulosic fibers and of fibrils of synthetic thermopla~tic polymers, obtained by success-ive stratification of aqueou~ pulp~ or dispersions of such fibers or fibrils;
(b) reduction of the content in water of the panel up to quantities comprised between 30% and 80% by weight of water, by ; su.ction and/or compression;
(c) drying the panel until attaining a content in humidity of le~
. than 0 . 5% by weight; and (d) heating the panel up to a temperature greater than the soften-ing temperature of the thermoplastic polymer, under pressure.
Between operation (b) and operation (c) there may be inserted a cold compression step for the panel at pre~sure~ comprised between 50 and 150 kg/sq. cm, which compression may be carried out"for instance between "hunlid" roll~ or presse~ in those cases in which it ia wished to obtain more compact papers and lower moisture contents before the drying.
For the preparation of the flbrous panel in step (a), there may be . used in the form of pulp or a~ueous dispersion, fibril~ made of any synthetic theremoplastic polymer with a softening temperature not exceeding Z50 C.
i Examples of suitable theremoplastic polymers are, in particular, polyolefins,~
especially low and high density polyethylene, polypropylene prevailingly ; consi~ting of isotactic macromolecules, ethylene/propylène copolymers with a predominant content of propyl~e, a~ well a~ polyarnides such as nylon 6, vinyl polymer~ such as polyvinyl chloride and polyvinyl acetate, polyacrylo-. . nitrile and the polyoxymethylenes.
_4_ ~ 1049715 Whellever pos9ible, and especially in order to improve the look-through and the penetration of the plastic layer into the cellulose without re- ¦
.; ducing the "barrier" property, it is prèferred to use mixtures of fibrils of the same polymer but with different thermoplastic characteristics; for instance in case of polyethylene fibrils, it i8 preferred to use an aqueous di6persion consisting of high-density polyethylene fibril~ mixed with low-density polyethylene fibrils.
Aqueous di~per~ons (or pulp9) of different thermoplastic polymer~ may in any case be used, provided said polymers are compatible with each other and have sufficiently close softening temperatures.
In the above-mentioned disper~ions there may also be present cellulosic fibers in quantities not exceeding 10% by weight on the total weight of the fibers.
In order to achieve in the finished product the greatest possible coherence between the cellulose fiber layer and the layer of the thermo-plastic polymer, it has proved to be quite effective to use, in the panel pre-'i paration step (a), thermopla~tic fibril~ with si~e~ distributed within rather ,1 wide intervals, preferably comprised between 0. 5 and 5 mm with regard to their length and between 3 micron and 60 micron as far as the diameter is concerned .
; Further preferred conditions to be applied in the preparation of the fibrous panel in operation or step (a) consist in the use of pulps or aqueous l dispersions of thermoplastic fibrils having a concentration in fibrils equàl to ;' 1. 5 - 2, 5 times the concentration of the cellulosic fibers in the agueou6 dispersions containing the cellulo~ic fibers at least predominantly.
s' In this way on the contact ~urfaces between the layers forming the panel the possibility for the fibers of each layer to penetrate in the fiber6 ofthe other layer ia increa~ed, with a considerable advantage for the mutual ~ ~ !
adhesion between the thermoplastic phase and the cellulosic phase in the end product.
The process, on the whole, is easily achieved with the devices commonly used in paper mill9, devices which comprise cellulose pulp beat-S ing machines and machines for the forming, drying and calandering of paper sheets .
The preparation of the multi-layer fibrous panel, according to step (a), may be carried out, for instance, by the ~uccessive deposition of the corresponding aqueous dispersions of the fibers on a filtering section, or by gathering on a common conveyor felt the fibrous pulps directly drawn from the respective aqueous dispersions by curved or flat table forming machines arranged in ~eries, according to processes known in the paper manufacturing art.
Step (b) for the elimination qf the excess water from the panel may be achieved by passing the panel over suction boxes and/or between pressing rollers. This operation promotes the phenomenon of the interpenetration of the two layèrs, made po~sible by the high content in water of the pulps, and facilitated by the disuniformity of sizes of the fibers, especially of the .
.l thermoplastic fibrila. ' ..
The drying of the panel in step (c) is conveniently carried out between cylinders maintained at increasing temperatures, but obviously lower : than the softening temperature of the thermoplastic polymer present in thepanel, and this drying must bring the content in water of the panel down to not more tha 0. 5% by weight, in order to avoid the formation of vapour 2S bubble~ inside the panel, during the 3ubsequent step (d) heating at high tem-perature. This latter operation, carried out under pressure, preferably compriaed between 30 and 100 kg/sq. cm, may be carried out between the rolls of a glazing machine~ and causes the melting of the thermoplastic iibril3 with tb orm3tion of a compact layer adhering to the cellDlollic layer. ¦
~- , .
If necessary, after the coupling achieved by this latter operation, the panel may be subjected, after cooling down, to operations for the superficial treatment of the cellulosic layer, such as calandering, coating glueing, etc. operations that are generally used for sheets of cellulose paper.
The pulps or aqueous dispersions, both of the cellu-losic fibers and of the thermoplastic fibrils, used for the pre- -paration of the starting panel~ may contain additives such as dyestuffs, pigments, inorganic fillers, antimildew agents, dis-persants, etc. The dispersions of cellulosic fibers may also contain fibers of a different nature, in quantities not ex~eeding 10% by weight with respect to the cellulose material, such as for instance rayon fibers, or fibers of cellulose acetate, nylon, polyvinyl alcohol and the likes.
It is essential for the process that the fi~rils of thermoplastic material be thoroughly and homogeneously dispersed ~-in water so as to form homogeneous and uniform layers. For this purpose it is necessary, in general, to add, auring their mixing with water, disperslng agents such as polyvinyl alcohol, anionic ,20 surfactan~s, urea resins, etc., or to submit the fibrils, before their use, to a superficial modification which will make them hydrodispersable. Such a modification may consist in coating the ~-fibrils with a dispersant, by dipping them into an aqueous solution of the dispersant and by successively dr~ing them.
; Such a method, wherein dispersants are used which consist of polyvinyl alcohol/aliphatic aldehydes Cl - C6 conden- -sates; is described in U.S. Patent No. 4,002,796 (Luciano Baldi et al) issued January 11, 1977.
The process according to this invention allows to '30~ obtain sheets of plasticized paper in which the resistance to ~, breakaway or "frilling" of the component layers is practically indeterminable in as much as this reslstance is greater than the j tearing resistance of the sheets themselves. A considerable .~ :
~ ~ - 7 -:. ~ .
.~ 1049715 a ~nta~e of this proc~ss consists in the fact that thcre a~ no limits to the speed of preparation of the sheets, since the resistance of thc cellulose support is never appreciably influenced by the presence of the thermoplastic material in any of the processing phases. It is thus possible to use the same cellulose compositions as well as the same operational speeds normally used for the preparation of sheets of common paper, speeds that are by far superior to those usable in the classical coupling or bonding processes.
By the process according to this invention, it is possible to prepare "sandwiched" couplings in which, for instance, the thermoplastic polymeric material in the form of a continuous film is enclosed between two or more sheets of paper or cellulosic cardboards.
In drawings which illustrate embodiments of this invention, Figure 2 represents a ~omplete diagram of the pre- -; paration of a-binary coupled sheet according to the invention.
Figure 3 is-a complete diagram for the preparation of a ternary cellulose/thermoplastic material/cellulose coupling.
In the diagram of Figure 2, there are shown the curved forming boxes (1) and (2~ which contain, respectively, the cellulose fiber pulps and the thermoplastic polymer fibril pulps;
the con~eyor felt (10) on which the cellulose fiber layer adheres, and, successively, by superimposition, the layer of thermoplastic fibrils; the suc~ion boxes (3); "wet" presses (4); the sets of drying cylinders (5); the heated "glazing" unit (6); the cooling rolls (~); the take-up reel for the coupled sheet (8), and the conveyor felts (9). In this diagram the position of the forming boxes may be inverted still obtaining the same results without :30 modifying the arrangement of the remaining equipment.
In the daigram of Figure 3 are represented: the curved forming boxes (l) and ~2), containing the cellulose fiber pulp; the flat table with inflow box (3), containing the fibrils of thermoplastic material, the suction boxes (4); the "wet" presses (5); the drying set (6); the heated "glazing" unit (7); the cold rollers (8); the take-up reel (9) and the conveyor or carrier felts (10).
The following examples are given to further illustrate the invention and are not intended as limiting.
In all of such examples, olefin polymer fibrils were utilized, prepared according to the technology illustrated in the above mentioned Italian Patent No. 947,919.
', ., .
. ' ~ .
_ g -, .: .. ' '' ' .... '' " .':,, ~' '' .. '~
~ ~ 1049715 Preparation of polyolefin fibrils A 50 liter autoclave, provided with heating chamber and stirrer, was fed with 2. 5 kg of high den~ity polyethylene (M. I. =5, Melting point =
135 C) and 1. 5 kg of kaolin, along with 35 liters of n-hexane. The mixture wa-S heated under the following conditions:
~: temperature = 180 C
total pressure (comprising an overpressure of nitrogen) = 15 kg/sq. cm.
until a ~olution of the polymer in the n-hexane was obtained.
Under such conditions, the mixture was ejected to the atmosphere, through a circular noz~le having 2 mm diameter, and was made to collide, at about 1 mm distance from the nozzle outlet, with a dry saturated steam jet, coming from a nozzle of 4 mm diameter and arranged at about 85 to the direction of ejection of the solution, at an impact speed of the steam of about l 15 470 m/sec. The fibrous product thus obtained was composed of individual J fibrils having length comprised between 0. 5~ and 5 mm, an average diameter i of between 15 and 45 micron, a surface area of 5 m ~g and containing abo~dt: :
30% by weight of kaolm.
'.1 ~ , ' ; I : Pr paration of the coupled sheet
- 2~
~l In two separate vats were prepared two pulps respectively consistt-ing of - an aqueous mixture consisting of~ 10 g/lt of cellulose with a re-fining degree Sl~ = 35; 16% by weight of kaolin and 2% by weight of ~Aquapel" ( a glue for cellulo~e fibers);
.
;' ; -10-~:'t .;
11 . .
ll 1049715 . I
- an aqueous mixture consi6ting of: 15 g/lt of the poly-ethylene fibrils prepared a8 described above and which had been precoated with 0. 05% by weight of a dispersant consist^
ing of a polyvinyl alcohol/butyraldehyde condensate (4. 2 aldehyde groups/100 monomeric vinyl unitsJby dipping in an aqueous solution of the dispersant and subsequent drying.
The two pulp9 were conveyed to the corresponding curved forming boxes, obtaining at the rate of 25 mt/min. a panel consisting of one layer of cellulose fiber pulp about 2 mm thick, and, superimposed on it, a layer of polyethylene fibril pulp about 1 mm thick.
After passing over 3 suction boxes arranged in series, the panel showed a content in water of 80% by weight. Through two wet presses, exerting a pressure of 50 kg/sq. cm, the panel was then conveyed towards a battery of 17 drying cylinders of which the firstl¦6 were maintained at at . 15 temperature increasing from 90C to 110C, and caused drying of the panel to a residual humidity of about 0. 2Clo by weight, while the ~7th cylinder was maintained at a temperature of 125 C which induced an incipient melting of the outer polyethylene fibrils. :
Thereafter, the panel was passed between "glazer" rolls that were maintained at a temperature of 150 C and exerted a pressl~re of 80 kg/sq. cm, wherefore there occurred th~ transofrmation of the layer of fibrils into a translucid and compact polyethylene film of about 20 micron thickness ano which was adhered to the cellulose sheet. The characteristics of the coupled Z S ¦¦ p roduct ar umm~ ri~ed in T-ble 1.
' ' -11- ' : ' ' ' , ,," : . : . . -. . .
1~ 1049715 EXAMPLE Z
A binary coupling wa~ prepared by using, for the cellulose fiber layer, a cellulosic pulp similar to the one described in Example l, and for the thermoplastic material, an aqueous mixture of uncharged high density polyethylene fibril~ ~M.I. = 1.2, melting point = 135 C) with a fibril length . comprised between 1. 5 and 3. S mm and a fibril diameter between 15 and 40 and surface area of 6 m2/g. The concentration in f~bril~ was 20 g/lt and - the content of polyvinyl alcohol as a dispersant was 1% by weight.
'. The procedures and the equipment for the formation of the two-layer panel are similar to those de~cribed in Example 1, except that the first 16 cyclinders for the drying were maintained at temperatures increasing from 70 to 90C, while the seventeenth cylinder attained a temperature of 115C.
The temperature of the cylinders of the glazing unit was 175 C. The cnarsctcriotic f thc coupled product are recordod IA Table l.
' . . , ' . ' ' , ' .,,.
. .
" ''' :" ''" ,"' ,, , ,;~
~:, . . ..
~ . -12-......................... ~ ..
. ' ' .
A binary coupled sheet was prepared by starting from a mixture of cellulosic fiber~ similar to that in Example 1, and from an aqueou~ dis-persion of polypropylene fibers (isotacticity index = 92; M.I. at 260C = 10), melting point = 17 0C) having a diameter comprised between 15 and 3~ micron a length of between 1 and 4 mm, and a surface area of 7 m2/g, and which had " been coated superficially like the polyethylene fibrils of Example 1. The concentration of the polypropylene fibers in the aqueous dispersion was Z0 g/lt .
By using two curved-table forming boxes, arranged in series, the first containing the dispersion of polypropylene fibrils, the second containing the cellulose fiber dispersion, on a conveyor net running at 30 mt/min., there wa~ prepared a panel consiating of one ground layer of polypropylene fibrils, about I mm thick, and of a superimposed layer of cellulose fibers ; ~, about 2 mm thick.
Thi~ panel was passed over 3 suction boxes where the content 'il lS in water of the panel was reduced to 75%; it was then passed over "wet"
presses operating at 50 kg/sq. cm and finally was passed on 17 drying cylind-! ers or rolls of which the first 16 were operating at between 60 and 130C, ~' while the-seventeenth operated at 165C. After the passage between the rolls j ~ ~ of a glazing unit, kept at 198C anid exerting a pressure of 60 kg/sq.cm, the thus obtained coupled sheet was cooled down and wound up on reels. Its characteri~tic~ are given in Table I. . :
", . ~ '.
~ -13-!~ ' ' ~ . .
By means of a continuous coupling machine of the type illustrated in Figure 3 of the drawing, there was prepared a "sandwich" type coupled product consisting of two outer cellulose paper sheets and of an inner low density polyethylene film.
For this purpose there were used two pulps re~pectively consist-ing of:
- an aqueous mixture of cellulose fibers having a concentration in fibers of 10 grams/liter, and containing 18% by weight of kaolin and 2% by weight of "Aquapel ";
- an aqueous mixture containing 20 g/liter of low-density poly-ethylene fibrils (M.I. = 5, melting point = 115C) with a diameter comprised between 10 and 40 micron, a length of between 1. 5 and 5 mm, a surface area of 6 mZtg and coated with 0. 05% by weight of the same dispersant as in Example I.
The mixture of cellulose fibers were fed to the two curved-table forming boxes, while the polyethylene fibril mixture was fed to the flat-table with in-flow bo:c.
The triple-layer panel:cellulose/polyethylene/cellulo~e, which after passing over the suction boxes and between the "wet" presses exerting il 2~ a pressure of 50 kg/sq. cm, was then dried by pas~ing it over 7 drying rollers or cylinders, maintained at growing temperatures increasing from ~0 to 90 C until the moisture content of the "sandwich" was 0. 1% by weight.
-~- .` .
~` 25 '' ' ..
.' . 1 : :
`: 1049715 The melting of the intermediate layer of polyethylene fibrils was carried out successively by pa~sing the panel between the cylinders or rolllers of a glazing device, which rollers were maintained at 150C and exerted a pressure of 75 kg/sq. cm.
After cooling, the coupled sheet was wound on reel~ and atored.
Its characteristic~ are reported in Table I.
'.' .
., ,.; _ Following a traditional method of preparation, carried out on a ~ 10 device similar to that illu~trated in Figure l of the drawing, a binary coupl-; ' ing was prepared starting from a sheet of packing paper filled with 16% by weight of kaolin, and by low-density polyethylene granules having a M. I. = 8.
The paper sheet was fir~t impregnated with an adhesive consisting of a 0. 2% by weight solution of polyisocyanate in methylene chloride, and then wa~ dried and conveyed at a rate of 100 mt/min. to the head of a wormscrew extruder loaded with polyethylene granules, where it received on its surface the semi-molten polyethylene film, in the extrusion phase. ;
The coupled product thus obtained was passed between two cylinders exerting a pressure of 55 kg/sq. cm, one of the c~r1inders being ~,~ rubberized while the other o~e~was chromium-plated and serving to cool the ,1 polymer layer. The sheet wa~ then gathered on reels and ~tored. The 11 propl~rtil o be collplod ohoee are ~hl~wn in Tablc I.
'1 25 , ~-15-;, ,', , a il . . .
E ~ ~ o o ~ ~, ~ o In o o 1 Ln ~ ~
~ ~, ~ ~ ~ I~ 0 0 ~ o ln ~ O
e . _ .
~ ~ o o O O n O ~ O n o X O O "~ ~ ~ o o ~ ' U
r~ . .
O
E ~ ", ~ co o o u~ o ~ '-. ~L~
_~ . 1~ h ~ 1~ 0 o O o ~n Oo U') oo to ~ _, U
_ CO ~ CO ~ ~1 O ~ ~ ~ . . . h 1~ d' O
w E ~ , , V ~ :-~ -- ............................. . . ~ . .
¢ C E O ~ W
' E E `.................... ~ '~ E ~ a . . _ U U C C . ,~
.~ ~ ~ ...
O O D u~ h ~, ~ -- D ~ ~DU ,~ C a) h _~ a w^ ~ -- -- h h ~ ~ ~ :
ù E ~ ~C a ~ p~ P N ~a h ~ ~ -- -- h -- td ~d U .~ O
a ~ ? ~ a ~ a ~ r ~ S ~at L
- :
-15 a-,~ , .. . .
~l In two separate vats were prepared two pulps respectively consistt-ing of - an aqueous mixture consisting of~ 10 g/lt of cellulose with a re-fining degree Sl~ = 35; 16% by weight of kaolin and 2% by weight of ~Aquapel" ( a glue for cellulo~e fibers);
.
;' ; -10-~:'t .;
11 . .
ll 1049715 . I
- an aqueous mixture consi6ting of: 15 g/lt of the poly-ethylene fibrils prepared a8 described above and which had been precoated with 0. 05% by weight of a dispersant consist^
ing of a polyvinyl alcohol/butyraldehyde condensate (4. 2 aldehyde groups/100 monomeric vinyl unitsJby dipping in an aqueous solution of the dispersant and subsequent drying.
The two pulp9 were conveyed to the corresponding curved forming boxes, obtaining at the rate of 25 mt/min. a panel consisting of one layer of cellulose fiber pulp about 2 mm thick, and, superimposed on it, a layer of polyethylene fibril pulp about 1 mm thick.
After passing over 3 suction boxes arranged in series, the panel showed a content in water of 80% by weight. Through two wet presses, exerting a pressure of 50 kg/sq. cm, the panel was then conveyed towards a battery of 17 drying cylinders of which the firstl¦6 were maintained at at . 15 temperature increasing from 90C to 110C, and caused drying of the panel to a residual humidity of about 0. 2Clo by weight, while the ~7th cylinder was maintained at a temperature of 125 C which induced an incipient melting of the outer polyethylene fibrils. :
Thereafter, the panel was passed between "glazer" rolls that were maintained at a temperature of 150 C and exerted a pressl~re of 80 kg/sq. cm, wherefore there occurred th~ transofrmation of the layer of fibrils into a translucid and compact polyethylene film of about 20 micron thickness ano which was adhered to the cellulose sheet. The characteristics of the coupled Z S ¦¦ p roduct ar umm~ ri~ed in T-ble 1.
' ' -11- ' : ' ' ' , ,," : . : . . -. . .
1~ 1049715 EXAMPLE Z
A binary coupling wa~ prepared by using, for the cellulose fiber layer, a cellulosic pulp similar to the one described in Example l, and for the thermoplastic material, an aqueous mixture of uncharged high density polyethylene fibril~ ~M.I. = 1.2, melting point = 135 C) with a fibril length . comprised between 1. 5 and 3. S mm and a fibril diameter between 15 and 40 and surface area of 6 m2/g. The concentration in f~bril~ was 20 g/lt and - the content of polyvinyl alcohol as a dispersant was 1% by weight.
'. The procedures and the equipment for the formation of the two-layer panel are similar to those de~cribed in Example 1, except that the first 16 cyclinders for the drying were maintained at temperatures increasing from 70 to 90C, while the seventeenth cylinder attained a temperature of 115C.
The temperature of the cylinders of the glazing unit was 175 C. The cnarsctcriotic f thc coupled product are recordod IA Table l.
' . . , ' . ' ' , ' .,,.
. .
" ''' :" ''" ,"' ,, , ,;~
~:, . . ..
~ . -12-......................... ~ ..
. ' ' .
A binary coupled sheet was prepared by starting from a mixture of cellulosic fiber~ similar to that in Example 1, and from an aqueou~ dis-persion of polypropylene fibers (isotacticity index = 92; M.I. at 260C = 10), melting point = 17 0C) having a diameter comprised between 15 and 3~ micron a length of between 1 and 4 mm, and a surface area of 7 m2/g, and which had " been coated superficially like the polyethylene fibrils of Example 1. The concentration of the polypropylene fibers in the aqueous dispersion was Z0 g/lt .
By using two curved-table forming boxes, arranged in series, the first containing the dispersion of polypropylene fibrils, the second containing the cellulose fiber dispersion, on a conveyor net running at 30 mt/min., there wa~ prepared a panel consiating of one ground layer of polypropylene fibrils, about I mm thick, and of a superimposed layer of cellulose fibers ; ~, about 2 mm thick.
Thi~ panel was passed over 3 suction boxes where the content 'il lS in water of the panel was reduced to 75%; it was then passed over "wet"
presses operating at 50 kg/sq. cm and finally was passed on 17 drying cylind-! ers or rolls of which the first 16 were operating at between 60 and 130C, ~' while the-seventeenth operated at 165C. After the passage between the rolls j ~ ~ of a glazing unit, kept at 198C anid exerting a pressure of 60 kg/sq.cm, the thus obtained coupled sheet was cooled down and wound up on reels. Its characteri~tic~ are given in Table I. . :
", . ~ '.
~ -13-!~ ' ' ~ . .
By means of a continuous coupling machine of the type illustrated in Figure 3 of the drawing, there was prepared a "sandwich" type coupled product consisting of two outer cellulose paper sheets and of an inner low density polyethylene film.
For this purpose there were used two pulps re~pectively consist-ing of:
- an aqueous mixture of cellulose fibers having a concentration in fibers of 10 grams/liter, and containing 18% by weight of kaolin and 2% by weight of "Aquapel ";
- an aqueous mixture containing 20 g/liter of low-density poly-ethylene fibrils (M.I. = 5, melting point = 115C) with a diameter comprised between 10 and 40 micron, a length of between 1. 5 and 5 mm, a surface area of 6 mZtg and coated with 0. 05% by weight of the same dispersant as in Example I.
The mixture of cellulose fibers were fed to the two curved-table forming boxes, while the polyethylene fibril mixture was fed to the flat-table with in-flow bo:c.
The triple-layer panel:cellulose/polyethylene/cellulo~e, which after passing over the suction boxes and between the "wet" presses exerting il 2~ a pressure of 50 kg/sq. cm, was then dried by pas~ing it over 7 drying rollers or cylinders, maintained at growing temperatures increasing from ~0 to 90 C until the moisture content of the "sandwich" was 0. 1% by weight.
-~- .` .
~` 25 '' ' ..
.' . 1 : :
`: 1049715 The melting of the intermediate layer of polyethylene fibrils was carried out successively by pa~sing the panel between the cylinders or rolllers of a glazing device, which rollers were maintained at 150C and exerted a pressure of 75 kg/sq. cm.
After cooling, the coupled sheet was wound on reel~ and atored.
Its characteristic~ are reported in Table I.
'.' .
., ,.; _ Following a traditional method of preparation, carried out on a ~ 10 device similar to that illu~trated in Figure l of the drawing, a binary coupl-; ' ing was prepared starting from a sheet of packing paper filled with 16% by weight of kaolin, and by low-density polyethylene granules having a M. I. = 8.
The paper sheet was fir~t impregnated with an adhesive consisting of a 0. 2% by weight solution of polyisocyanate in methylene chloride, and then wa~ dried and conveyed at a rate of 100 mt/min. to the head of a wormscrew extruder loaded with polyethylene granules, where it received on its surface the semi-molten polyethylene film, in the extrusion phase. ;
The coupled product thus obtained was passed between two cylinders exerting a pressure of 55 kg/sq. cm, one of the c~r1inders being ~,~ rubberized while the other o~e~was chromium-plated and serving to cool the ,1 polymer layer. The sheet wa~ then gathered on reels and ~tored. The 11 propl~rtil o be collplod ohoee are ~hl~wn in Tablc I.
'1 25 , ~-15-;, ,', , a il . . .
E ~ ~ o o ~ ~, ~ o In o o 1 Ln ~ ~
~ ~, ~ ~ ~ I~ 0 0 ~ o ln ~ O
e . _ .
~ ~ o o O O n O ~ O n o X O O "~ ~ ~ o o ~ ' U
r~ . .
O
E ~ ", ~ co o o u~ o ~ '-. ~L~
_~ . 1~ h ~ 1~ 0 o O o ~n Oo U') oo to ~ _, U
_ CO ~ CO ~ ~1 O ~ ~ ~ . . . h 1~ d' O
w E ~ , , V ~ :-~ -- ............................. . . ~ . .
¢ C E O ~ W
' E E `.................... ~ '~ E ~ a . . _ U U C C . ,~
.~ ~ ~ ...
O O D u~ h ~, ~ -- D ~ ~DU ,~ C a) h _~ a w^ ~ -- -- h h ~ ~ ~ :
ù E ~ ~C a ~ p~ P N ~a h ~ ~ -- -- h -- td ~d U .~ O
a ~ ? ~ a ~ a ~ r ~ S ~at L
- :
-15 a-,~ , .. . .
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for preparing coupled cellulose paper sheets with film of thermoplastic polymeric material, which consists, in the given order, of the following operations:
(a) formation of a web comprising at least two superimposed fibrous layers, one layer consisting of at least 90% by weight of cellulosic fibers and the other of at least 90% by weight of fibrils of thermoplastic synthetic polymers having a surface area greater than 1 m2/g, said thermoplastic polymer having a softening temperature not exceeding 250°C, said web being formed by successive stratification of aqueous dis-persions of said fibers and fibrils, the fibrils being thoroughly and homogeneously dispersed in the water;
(b) reduction of the water content of the web to between 30% and 80% by weight, by means of suction and/or com-pression;
(c) drying of the web to a moisture content of less than 0.5% by weight; and (d) heating of the web under pressure at a tem-perature higher than the softening temperature of the thermoplastic polymer, so as to melt the fibrils and form a thermoplastic synthetic film having a value of the porosity to air of zero cm3/sec.
(a) formation of a web comprising at least two superimposed fibrous layers, one layer consisting of at least 90% by weight of cellulosic fibers and the other of at least 90% by weight of fibrils of thermoplastic synthetic polymers having a surface area greater than 1 m2/g, said thermoplastic polymer having a softening temperature not exceeding 250°C, said web being formed by successive stratification of aqueous dis-persions of said fibers and fibrils, the fibrils being thoroughly and homogeneously dispersed in the water;
(b) reduction of the water content of the web to between 30% and 80% by weight, by means of suction and/or com-pression;
(c) drying of the web to a moisture content of less than 0.5% by weight; and (d) heating of the web under pressure at a tem-perature higher than the softening temperature of the thermoplastic polymer, so as to melt the fibrils and form a thermoplastic synthetic film having a value of the porosity to air of zero cm3/sec.
2. The process according to claim 1, characterized in that between operations (b) and (c) there is introduced an operation in which the panel is subjected to cold compression at pressures comprised between 50 and 150 kg/sq. cm.
3. The process according to claim 1, characterized in that the fibrils of thermoplastic polymer have a length com-prised between 0.5 and 5 mm. and a diameter comprised between 3 and 60 micron.
4. The process according to claim 1, characterized in that the fibril concentration of the aqueous dispersion of thermo-??? tic polymer fibrils is 1.5-2.5 times the concentration of the cellulosic fibers in the aqueous dispersion consisting at least predominantly of the cellulosic fibers.
5. The process according to claim 1, characterized in that the thermoplastic polymer fibrils are of polyethylene fibrils.
6. The process according to claim 1, characterized in that the thermoplastic polymer fibrils are polypropylene fibrils.
7. The process according to claim 1, characterized in that the thermoplastic polymer is an ethylene/propylene copolymer in which propylene predominates.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT49607/74A IT1011142B (en) | 1974-03-25 | 1974-03-25 | PROCEDURE FOR PREPARING PAIRS OF PAPER SHEETS WITH POLYMERIC FILM |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1049715A true CA1049715A (en) | 1979-03-06 |
Family
ID=11271158
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA222,966A Expired CA1049715A (en) | 1974-03-25 | 1975-03-24 | Process for the preparation of paper sheets coupled to films of polymeric material |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS50130598A (en) |
| BE (1) | BE827071A (en) |
| CA (1) | CA1049715A (en) |
| DE (1) | DE2512921A1 (en) |
| ES (1) | ES435970A1 (en) |
| FR (1) | FR2265541B1 (en) |
| GB (1) | GB1500542A (en) |
| IT (1) | IT1011142B (en) |
| NL (1) | NL7503418A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2352103A1 (en) * | 1976-05-21 | 1977-12-16 | Solvay | SEPARABLE PAPER |
| JPS604319B2 (en) * | 1976-06-08 | 1985-02-02 | レンゴ−株式会社 | Paperboard-like synthetic pulp paper and its manufacturing method |
| SE442182B (en) * | 1976-06-05 | 1985-12-09 | Rengo Co Ltd | REINFORCED WELL PAPER JUST SET TO MANUFACTURE THE SAME |
| IT1085565B (en) * | 1977-05-09 | 1985-05-28 | Montedison Spa | PROCEDURE FOR PREPARING PACKAGING CARDBOARD, EQUIPPED WITH RESISTANCE TO HUMIDITY |
| IT1131836B (en) * | 1980-06-20 | 1986-06-25 | Montedison Spa | PROCEDURE FOR PREPARING MULTILAYER STRUCTURES FROM SHEETS CONTAINING SYNTHETIC FIBERS |
| IT1139131B (en) * | 1981-08-14 | 1986-09-17 | Montedison Spa | PROCEDURE FOR THE PREPARATION OF MULTI-LAYER FIBROUS STRUCTURES |
| FR2516107B1 (en) * | 1981-11-06 | 1985-06-28 | Du Pin Cellulose | PAPERS AND CARDBOARDS, METHOD AND DEVICE FOR MANUFACTURING |
| WO1984001176A1 (en) * | 1982-09-13 | 1984-03-29 | Eastman Kodak Co | Stratified composite paper product and a method of making same |
| US5204173A (en) * | 1990-11-29 | 1993-04-20 | Dvsg Holding Gmbh | Paperboard product and process |
| GB9702857D0 (en) * | 1997-02-12 | 1997-04-02 | Crompton J R Plc | Porous web material |
| ES2246125B2 (en) * | 2004-03-01 | 2006-11-16 | Fabrica Nacional De Moneda Y Timbre - Real Casa De La Moneda | SECURITY PAPER OR SPECIAL PAPER THAT INCLUDES HIGH RESISTANCE SYNTHETIC ELEMENTS AND PROCEDURE FOR OBTAINING SUCH PAPERS. |
-
1974
- 1974-03-25 IT IT49607/74A patent/IT1011142B/en active
-
1975
- 1975-03-21 NL NL7503418A patent/NL7503418A/en not_active Application Discontinuation
- 1975-03-24 GB GB12088/75A patent/GB1500542A/en not_active Expired
- 1975-03-24 DE DE19752512921 patent/DE2512921A1/en not_active Withdrawn
- 1975-03-24 FR FR7509052A patent/FR2265541B1/fr not_active Expired
- 1975-03-24 BE BE154659A patent/BE827071A/en unknown
- 1975-03-24 ES ES435970A patent/ES435970A1/en not_active Expired
- 1975-03-24 CA CA222,966A patent/CA1049715A/en not_active Expired
- 1975-03-25 JP JP50035016A patent/JPS50130598A/ja active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2265541B1 (en) | 1977-04-15 |
| JPS50130598A (en) | 1975-10-15 |
| ES435970A1 (en) | 1976-12-16 |
| DE2512921A1 (en) | 1975-10-09 |
| BE827071A (en) | 1975-09-24 |
| GB1500542A (en) | 1978-02-08 |
| FR2265541A1 (en) | 1975-10-24 |
| IT1011142B (en) | 1977-01-20 |
| NL7503418A (en) | 1975-09-29 |
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