EP0118552A1

EP0118552A1 - Stratified composite paper product and a method of making same

Info

Publication number: EP0118552A1
Application number: EP19830903065
Authority: EP
Inventors: Barry W. Crouse; Frank L. Wells
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1982-09-13
Filing date: 1983-09-12
Publication date: 1984-09-19
Also published as: WO1984001176A1

Abstract

Un produit de papier composite stratifié (8) qui est sensiblement imperméable au liquide et au gaz comprend: une couche intérieure (2) composée principalement de fibres cellulosiques de papeterie (3), directement contiguës à chaque face de la couche intérieure (2), une couche intermédiaire (4) contenant des fibres de résine thermoplastique (5) entremêlées à des fibres cellulosiques de papeterie (3), et directement contiguë à chaque zone intermédiaire (4), une couche extérieure continue fortement adhésive (9) d'une résine thermoplastique. Ce produit de papier est particulièrement utile en tant que base de papier aussi bien pour des éléments d'enregistrement d'image que pour des éléments photographiques récepteurs d'image. Le produit est préparé avantageusement par un procédé consistant à faire écouler des bouts de fibres cellulosiques (100) et de fibres de résine thermoplastique (101) dans une zone de formage de bande (106) de manière à former une bande composite (108) possédant des couches extérieures de fibres de résine thermoplastique (5). Après séchage, la bande composite (108) est soumise à une température et/ou une pression suffisantes pour fondre les couches extérieures en des couches continues de résine thermoplastique (9).A laminated composite paper product (8) which is substantially impermeable to liquid and gas comprises: an inner layer (2) mainly composed of cellulosic stationery fibers (3), directly contiguous to each face of the inner layer (2), an intermediate layer (4) containing fibers of thermoplastic resin (5) intermingled with cellulosic stationery fibers (3), and directly contiguous to each intermediate zone (4), a continuous highly adhesive outer layer (9) of a resin thermoplastic. This paper product is particularly useful as a paper base for both image recording and photographic image receiving elements. The product is advantageously prepared by a process consisting in flowing ends of cellulosic fibers (100) and of thermoplastic resin fibers (101) in a strip forming zone (106) so as to form a composite strip (108) having outer layers of thermoplastic resin fibers (5). After drying, the composite strip (108) is subjected to a temperature and / or a pressure sufficient to melt the outer layers into continuous layers of thermoplastic resin (9).

Description

STRATIFIED COMPOSITE PAPER PRODUCT AND A METHOD OF MAKING SAME

The present invention relates to a stratified composite paper product composed partly of cellulose and partly of synthetic resin materials . In a particular aspect, it relates to a stratified composite paper product having outer synthetic resin strata, which product is useful as a support for image-recording elements. This invention also relates to a method of making such a paper product.

There have been many attempts to improve the characteristics of paper, such as dry and wet strength, flexibility, hydrophobicity and liquid impermeability. Attempts to improve paper strength have included making sheet materials out of a mixture of cellulosic or other vegetable fibers and synthetic resin fibers, as described, for example, in U. S. Patent 2,526,125. In seme cases, synthetic resin fibers have been pressed between sheets of cellulosic fibers to provide a web of substantially mixed fibers, which web also has some layer structure to it.

A common method of making a continuous laminated web of cellulosic and polymeric materials i_s n extrusion coating process. As is generally known, this process typically includes extrusion of a molten synthetic resin through an extruder die onto a moving cellulosic web. After extrusion (sometimes called resin coating) , the resulting composite web is cooled and subjected to compression to increase interlayer adhesion.

In order to increase productivity in making such composite webs, the trend in the art has been to increase coating speed and to reduce the thickness of

OMPI synthetic resin applied. Both of these changes, however, have given rise to an increased tendency for inadequate adhesion between cellulosic and resin strata in the composite. The deleterious effects of inadequate interlayer adhesion are well recognized and include delamination, irregular edges after cutting operations and reduced hydrophobicity and liquid and gas impermeability. The problem of inadequate adhesion is particularly serious when the paper product is used as a support for coating of a composite layer photosensitive composition.

Attempts to improve interlayer adhesion have met with varying degrees of success. Perhaps the simplest way to improve such adhesion is to raise the resin extrusion temperature. However, as this temperature approaches the degradation temperature of the resin, the resin begins to break down thereby causing objectionable odors and discoloration. Degradation products may also adversely affect subsequent coatings, e.g. photosensitive coatings, and destabilize the resulting composite structure, reducing its useful life.

Another common way of improving interlayer adhesion is to treat the surface of the cellulosic substrate prior to resin coating to alter surface characteristics. Typically, the cellulosic substrate is subjected to corona discharge prior to resin coating to improve the interlayer adhesion. This technique, however, requires complex manufacturing equipment and substantial operational expense and adds yet another tedious and time-consuming step in the process of making composite structures . Corona discharge also causes some degradation of the cellulosic materials and can result in shortened

OMPI useful life for certain resin-coated paper products . In addition, extreme care must be taken to make sure the treatment is uniformly applied lest objectionable surface characteristics be developed. This additional care results in considerable manufacturing expense.

Another surface treatment technique known in the art involves the application of a primer layer on the cellulosic surface before resin coating. Such primers, however, are generally very expensive, and careful selectivity is required in the conditions of their use. In addition, application of such primers typically requires wetting of the cellulosic substrate, which in turn can make low strength substrates difficult to handle and weaken high strength substrates .

It is the object of this invention to make a stratified composite paper product containing cellulosic and synthetic resin materials, having improved interlayer adhesion and permanence (i.e. longer product life) . It is also an object of this invention to provide an improved method of preparing such a paper product, which method avoids conventional extrusion coating operations and the problems attendant thereto.

In accordance with this invention, there is provided a stratified composite paper product which is substantially impermeable to liquids and gases . This paper product comprises (1) an interior stratum consisting essentially of cellulosic papermaking fibers; (2) directly contiguous to each face of the interior stratum, an intermediate stratum containing intermingled thermoplastic resin fibers and cellulosic papermaking fibers; and (3) directly contiguous to each of the intermediate strata, a

OMPI strongly adhering, continuous outer stratum of a thermoplastic resin.

The stratified composite paper product has improved interlayer adhesion between cellulosic and the synthetic resin strata and less likely to suffer delamination during its useful life. Furthermore, the paper product of this invention has improved permanence, meaning that the materials making up the various strata are less likely to degrade during its useful life because they have not been subjected to high extrusion temperatures.

The invention also provides a method for the preparation of the stratified composite paper product described above. This method comprises the steps of: (A) simultaneously flowing an aqueous slurry of cellulosic papermaking fibers and at least one aqueous slurry of thermoplastic resin fibers into a web-forming zone to form therein a stratified composite web comprising an interior stratum consisting essentially of cellulosic papermaking fibers, an intermediate stratum contiguous to each face of the interior stratum composed of intermingled thermoplastic resin fibers and cellulosic papermaking fibers, and an exterior stratum contiguous to each of the intermediate strata consisting essentially of thermoplastic resin fibers; (B) rendering the web substantially dry; and (C) subjecting the web to heat sufficient to fuse each exterior strata into a strongly adhering continuous layer of thermoplastic resin to each intermediate stratum.

The novel method provide significant manufacturing advantages and results in an improved stratified paper product. The method can be practiced using conventional papermaking equipment (e.g. a Fourdrinier machine) which has been suitably

'OMFI modified. The paper product can be used as a support material immediately after manufacture thereby eliminating the need for the extrusion coating operation. The avoidance of extrusion coating significantly reduces manufacturing costs, and eliminates resin degradation which can occur at high extrusion coating temperatures. Hence, the method of this invention, produces a product that has improved permanence, i.e. extended useful life, with improved interlayer adhesion, thereby obviating the need for any surface treatment (e.g. corona discharge) or expensive primer layers.

The stratified composite paper product described hereinabove is particularly useful as a support having thereon at least one image-recording layer or at least one photosensitive silver halide emulsion layer.

Considering the major differences in physical and chemical properties between a slurry of cellulosic fibers and a slurry of thermoplastic resin fibers (e.g. differences in drainage rates and sheet-forming characteristics) , it was unexpected and surprising to find that a composite product comprised of both types of fibers and having the desired stratified arrangement could be formed in a single web-forming step. In particular, the ability of the process to provide a sufficiently uniform distribution of thermoplastic resin fibers on each face of the composite to yield the desired continuous fused outer layers, while at the same time providing a sufficiently high concentration of cellulosic fibers in the interior of the composite to yield a stratified composite product having characteristics much like those of conventional extrusion-coated paper products, is a result that would not have been expected.

FIG. 1 is a partial, sectional view of a stratified composite product prepared by the method of this invention but prior to the fusing step. FIG. 2 is a partial, sectional view of a stratified composite paper product of this invention prepared by subjecting the stratified composite product of FIG. 1 to the fusing step.

FIG. 3 is a schematic diagram illustrating a preferred embodiment of the method of this invention. The stratified composite paper product of this invention is substantially impermeable to liquids and gases . As used throughout this specification and in the claims, the term "substantially impermeable" refers to the capability of such paper product to resist physical permeation by most commonly encountered liquids and gases .

Liquid permeability of a substrate is typically characterized for paper substrates by a test known as the Cobb Test. This is a standard test which includes the steps of: (1) conditioning and weighing a sample of the substrate; (2) wetting the sample with 100 milliliters of water for 2 minutes; and (3) determining the weight gain of the sample. Further details of this test are described in TAPPI T441 os-77. Gas permeability of a substrate is typically characterized for paper substrates by a test known as the Sheffield Test. This is a standard test which includes measuring the air resistance of a substrate sample when it is subjected to a 1.5 psi (77.6 mm Hg) air column. Further details of this test are described in TAPPI U.M. 524.

Typically, the paper product of this invention has a liquid permeability of less than 10 grams per square meter, and preferably of zero, as

OMPI easured by the Cobb Test described hereinabove . Also, these products typically have a gas permeability of less than about 20 milliliters per minute as determined with a 1.5 inch (3.8 cm.) I.D. orifice plate, and preferably of zero, as measured by the Sheffield Test described hereinabove.

The paper product of this invention has outer thermoplastic resin layers which are highly hydrophobic, i.e. the resin layers have a high tendency to repel water. This hydrophobicity can be conveniently determined by measuring the receding water contact angle, O_R, established between a droplet of distilled water and the surface of any of the resin layers. Methods for determining O_R are well known. A suitable method is the Sessile drop method described in Physical Chemistry of Surfaces by A. W. Adamson (published by Interscience Publishing Corp., 1967, pp. 352-375). Although the 0_R can be lower, typically the 0_R of the paper products of this invention, as determined by the Sessile drop method, is greater than about 75°, and preferably greater than about 80°. More preferably the 0-, is greater than about 90°.

The amount of thermoplastic resin incorporated into the paper products of this invention can vary widely as long as the requisite requirements of liquid and gas impermeability are met. Typically, the amount of resin is within the range of from about 10 to about 70 percent, based on total solids weight (i.e. including cellulosic materials and any additives). However, preferably the amount of resin is within the range of from about 30 to about 70 percent, and more preferably, from about 40 to about 60 percent, based on total solids weight. The amount of cellulose is typically within the range of from about 30 to about 90 percent, based on total solids weight. However, preferably the amount of cellulose is within the range of from about 30 to about 70 percent, and more preferably, from about 40 to about 60 percent, based on total solids weight.

Another way of characterizing the amounts of resin and cellulose in the described paper product is a weight ratio of resin to cellulose. This ratio is typically in the range of from about 1:4 to about 2:1, and preferably from about 1:3 to about 1:1. In addition, the thickness of the outer thermoplastic resin layers can vary greatly depending upon the resins used and the product end use, as long as the paper product has the desired liquid and gas impermeabilities. Each outer resin layer can be of the same thickness or one can be thicker than the other, as desired.

The paper product of this invention has an interior stratum consisting essentially of cellulosic papermaking fibers. Typically, there are few, if any, resin or other noncellulosic fibers in the interior stratum. The cellulosic papermaking fibers therein are tightly packed together in the form of a sheet material. The types of cellulosic fibers useful in making the paper product of this invention are well known and are made, for example, by extensive "refining" of bleached sulfite wood cellulosic paper stocks to a desired fiber length and surface area. Such paper stocks can comprise hardwood or softwood fibers or mixtures of both. They can be treated in any suitable way prior to being formed into a stratum of a stratified composite web. Various additives can be incorporated into the cellulosic stratum if desired. Such additives include sizing agents, wet or dry strength agents, fillers, brighteners, opacifiers, pigments, antioxidants , dispersing aids, antifoamers, biocides and retention/drainage aids. For example, it may be useful in some instances to include a dispersing aid, such as clay, in the slurry of cellulosic fibers from which the interior stratum is formed.

The interior stratum of the paper product can be a single layer or be composed of a plurality of substrata, each having the same or different types of cellulosic papermaking fibers in order to provide particular desirable characteristics. Preferably, the interior stratum is a single layer . The average thickness of the interior stratum can vary widely, but typically, it is within the range of from about 25 to about 350 micrometers. The stratum thickness can also vary within this range throughout a given sample of paper product.

The thermoplastic resins useful in preparing the paper products of this invention are generally synthetic resins which can be rendered soft or moldable with appropriate heat. Any suitable thermoplastic resin or mixture thereof can be used in the practice of this invention as long as it is capable of being formed into fibers and such fibers can be fused with heat and/or pressure. Typical useful thermoplastic resins include polyesters (e.g. polyesters formed from a diol and dicarboxylic acid or ester or anhydride derivative thereof, etc.); acrylic resins (e.g. poly(methyl methacrylate) , etc.); polyvinyl esters (e.g. polyvinyl acetate, polyvinyl propionate, etc.); polyvinylarenes (e.g. polystyrene, etc.); polyvinyl halides (e.g. polyvinyl chloride, etc.); polyvinyl alcohol; polyolefins , and others known in the art. The preferred thermoplastic resins are polyolefins. As used in this specificati.on and in the claims, the term "polyolefin" refers, first of all, to a homopolymer of an α-olefin having from 2 to 8 carbon atoms, such as ethylene, propylene, butylene, isobutylene, isoprene, amylene, etc., which can be halo-substituted (e.g. chloro, bromo, etc.) if desired. The term also refers to copolymers of two or more of the described α-olefins including what are sometimes called polyallomers; and to copolymers prepared primarily (greater than about 50 weight percent) from one or more of the described α-olefins and one or more ethylenically unsaturated monomers copolymerizable with α-olefins, including but not limited to vinyl esters, ethylenically unsaturaced carboxylic acids and esters and amides thereof, styrene, vinyl amides and the like.

Preferably, polyethylene or polypropylene is used in the paper products of this invention, with polyethylene being more preferred. These resins typically have a density in the range of from about 0.90 to about 0.98 grams per cubic centimeter and a melting point in the range of from about 105° to about 135°C. The thermoplastic resins described herein are either readily available commercially or can be prepared by well known condensation or additive polymerization methods. For example, the polyolefins can be prepared by conventional addition polymerization methods using a Ziegler catalyst. Any compatible mixture of thermoplastic resins can be used in the practice of this invention, including mixtures of two or more different types of resins (e.g. a mixture of a polyvinylarene and a polyolefin) , and mixtures of two or more resins of

O PI -li¬ the same type (e.g. a mixture or blend of two or more polyolefins) .

Either or both of the described outer thermoplastic resin layers can also contain various additives, including pigments, opacifiers, antioxidants, stabilizers, UV absorbers, plasticizers, brighteners, antistatic agents, dispersing aids, lubricants, etc. which do not adversely affect the properties desired for the present invention. For example, it may be useful in some instances to include a dispersing aid, such as clay, in the slurry of resin fibers from which each resin layer is formed. Typically, the resin layers also contain transparent or colored pigments, but preferably they contain white opacifying pigments, such as titanium dioxide (either rutile or anatase) , zinc oxide, talc, calcium carbonate, alumina, etc. in an amount in the range of from about 5 to about 25 percent, based on the total weight of resin in the paper product. Any other additives to such resins are generally present in an amount up to about 3 percent, based on total weight of resin.

In the composite paper product, the outer thermoplastic resin layers can be composed of the same thermoplastic resin or mixture of resins, or each layer can be a different resin or mixture. For example, one of the outer layers can consist essentially of a first thermoplastic resin and the other outer layer can consist essentially of a second thermoplastic resin of composition different than the first resin. Preferably, both outer resin layers are of the same composition and therefore can be formed from the same slurry of resin fibers. Additionally, the types and amounts of additives can be the same or different for the respective resin layers. As is the case with the interior cellulosic stratum, each outer thermoplastic resin layer can be a single continuous layer or a composite of two or more substrata of the same or different resins . Preferably, each outer resin layer is a single continuous layer .

The average thickness of each outer thermoplastic resin layer can vary widely, but typically it is within the range of from about 25 to about 350 micrometers. Layer thickness can also vary within these limits throughout a given sample of paper product.

Between the aforesaid interior stratum and each of the continuous outer layers is an intermediate stratum containing intermingled thermoplastic resin fibers and cellulosic papermaking fibers. Both of these types of fibers have been described hereinabove. Typically, an intermediate stratum has more thermoplastic resin fibers near the outer resin layer and more cellulosic fibers near the interior stratum. In other words, there is generally a gradient of resin fibers decreasing from near the outer layer towards the interior stratum and a gradient of cellulosic fibers increasing towards the interior stratum. Each intermediate stratum can also contain the various additives which can be found in either the interior stratum or the continuous outer resin layers. The thickness of each intermediate stratum can vary greatly but is typically within the range of from about 10 to about 50 micrometers throughout a given sample of paper product.

If desired, the paper product of this invention can have additional layers on either or both outer faces of the outer resin layers . Such additional layers include, but are not limited to,

TURE OMPI antistatic layers, backing layers, antihalation layers, subbing layers, protective layers, pigmented layers and the like.

The method provided by the present invention for making the composite paper product utilizes conventional papermaking equipment. This equipment can be easily modified to accommodate multi-ply paper webs. The paper product of this invention is prepared from two or more aqueous slurries, i.e. an aqueous slurry for each type of fiber to be included in the paper product. For example, if three different paper stocks and two different thermoplastic resins are to be incorporated as distinct layers into the paper product, a total of five aqueous slurries are used. In one embodiment, a photographic paper base is prepared with two aqueous slurries, one containing cellulosic fibers and the other containing polyolefinic fibers, whereby each outer resin layer is of the same composition. In another, more preferred embodiment, a photographic paper base is prepared with three aqueous slurries, one containing cellulosic fibers and the other two containing polyolefinic fibers of the same composition. In this embodiment, however, the slurries can have different consistencies (i.e. different percent solids) . All of these slurries are typically prepared using refining techniques well known in the papermaking art. Generally, for the cellulosic slurry, raw paper stock is dispersed in an aqueous medium with a refiner or other suitable equipment. Conventional additives (e.g. pigments, strengthening agents, fillers, brighteners, etc.) can be incorporated into the slurries as desired. For the synthetic resin slurry, the synthetic resin is usually purchased in fibrous form having suitable

OMPI fiber length and dispersed in an aqueous medium along with pigments or other desired additives.

Once the slurries have been prepared and their components have been uniformly admixed, they are delivered simultaneously to a web-forming zone to be formed into a stratified composite web. Such a web is multi-ply, meaning that it has three or more layers, at least one layer corresponding to each slurry delivered to the zone. Slurry delivery can be accomplished by any suitable means. For example, it can be accomplished by pumping the slurries to a plurality of conventional headboxes situated on suitable papermaking equipment (e.g. a Fourdrinier machine) in such a manner as to deliver the slurries substantially simultaneously to a web-forming wire. Preferably, the slurries are pumped to a single headbox and delivered simultaneously to the web-forming zone with that headbox. Such a headbox has a main chamber divided into a plurality of subchambers by a dividing means. Each subchamber communicates with or is connected to the web-forming zone so that a specific slurry can flow to the zone simultaneously with the others but with minimal mixing of the slurries. In a preferred embodiment of this invention, cellulosic and thermoplastic resin fiber slurries are simultaneously delivered to a "slice opening" and onto a web-forming wire with a single headbox. For example, one such headbox useful in the practice of this invention is the Strata-Flo Converflo™ headbox, commercially available from Beloit Corporation, Beloit, Wisconsin. The cellulosic slurry is delivered by a first subchamber of such a headbox and the thermoplastic resin fiber slurry is divided and delivered through second and third

CMPI subchambers on opposite sides of the first subchamber. Alternatively, separate resin slurries can be delivered through the second and third subchambers. This provides a web having an interior stratum (also known as a layer) predominantly of cellulosic fibers and strata of thermoplastic resin fibers on either side of the interior stratum. As there is some intermingling of cellulosic and thermoplastic resin fibers between such strata, an intermediate stratum (could also be called a zone) containing intermingled resin and cellulosic fibers is formed between the interior stratum and each outer resin stratum.

The composite multi-ply web is formed from dilute aqueous slurries, e.g. typically from about 0.3 to about 3 percent of fibers by weight, in accordance with conventional papermaking techniques, and the water is drawn off through the web-forming wire to yield a laminate structure which still has a substantial water content. Accordingly, the web must be rendered substantially dry prior to carrying out further steps of the manufacturing process. This can be done with conventional papermaking pressing or drying techniques or a combination thereof. xt may be advantageous in some instances for the cellulosic and thermoplastic resin slurries to have different consistencies. That is, the percentages, by weight, of fibers for the respective slurries may differ. For example, it may be advantageous for the thermoplastic resin slurry for one or both outer resin fiber strata to have a higher fiber weight percent (i.e. a higher consistency) than the cellulosic fiber slurry. It may also be advantageous for each resin layer to be formed from separate slurries having different consistencies .

OMPI For example, in a preferred embodiment of this invention, a composite multi-ply web is preferred from a single cellulosic fiber slurry and two thermoplastic resin slurries. As the thermoplastic resin slurries are delivered to the web-forming zone and the multi-ply web is formed on the papermaking wire, one of the resin slurries is located "above" the cellulosic slurry and the other is located "below" it. The consistency of the slurry "below" the cellulosic slurry is lower than the consistency of the cellulosic slurry, which in turn is lower than the consistency of the upper most resin slurry.

The substantially dry stratified composite web is then subjected to heat and/or pressure sufficient to fuse the exterior thermoplastic resin fibers into strongly adhering continuous resin layers. This fusing step can be done in any suitable manner which does not degrade the resin or cellulose. For example, fusing can be accomplished by heat alone, e.g. by heating a polyolefin-containing web to a temperature in the range of from about 110 to about 135°C with infrared radiation from suitable infrared heaters. This heating can be preceded or followed by calendering the web under controlled temperature and pressure conditions. Alternatively and preferably, the fusing is accomplished by running the web through a series of heated calender rolls (i.e. a calender stack) under controlled temperature and pressure conditions. Generally, fusing thermoplastic resin fibers into a continuous film by calendering can be accomplished with widely varying temperatures and pressures. For example, as the temperature is increased, generally less pressure is necessary for

OMPI fusing.

Preferably, calendering is accomplished at a temperature greater than the glass transition temperature and less than the melting temperature of all of the thermoplastic resins being used in a particular composite paper product. For the typical thermoplastic resins described hereinabove as useful in the practice of this invention, the useful temperature range is from about 90 to about 135°C. For polyolefins, the preferred calendering temperature is in the range of from about 110 to about 130°C. Preferably, the calendering pressure for any thermoplastic resin is in the range of from about 35 to about 210 kilonewtons per linear meter. Most preferably, the pressure is relatively low, for example, from about 40 to about 70 kilonewtons per linear meter, for calendering webs containing polyolefins where high opacity is desired. In a preferred embodiment, the opaque paper product described hereinabove is provided by calendering the dry composite web under temperature and pressure conditions controlled to maintain the desired opacity.

After the fusing step, the resulting stratified composite paper product can be treated further or coated with any desired coating composition. For example, subbing, antistatic, antihalation, protective, image-recording layers can be applied to either or both sides of the paper product. Either surface of the paper product can be treated (e.g. corona, electron bombardment, plasma, etc.) prior to such coating to improve adhesion. In a preferred embodiment, the paper product is coated with one or more image-recording compositions, such as photosensitive silver halide emulsions. Referring to the drawings, FIG. 1 is an

-&URE exaggerated partial sectional view of stratified composite web 1_ which has not yet been subjected to the fusing step of the method of this invention. Web 1_ comprises interior stratum 2 which consists essentially of cellulosic papermaking fibers represented by the numeral 3_. Directly contiguous to each face of interior stratum 2_ is intermediate stratum 4 composed of intermingled thermoplastic resin fibers represented by the numeral 5_ and cellulosic papermaking fibers represented by the numeral 3_. Directly contiguous to each of intermediate strata 4 is exterior stratum 7_ composed of thermoplastic resin fibers represented by the numeral 5_. FIG. 2 is an exaggerated partial sectional view of a stratified composite paper product of this invention which results when web 1_^ of FIG. 1 is subjected to the fusing step described hereinabove in relation to the process of this invention. Composite paper product 8_^ comprises interior stratum 2_ composed predominantly of cellulosic papermaking fibers represented by the numeral 3_. Directly contiguous to each face of interior stratum 2 is intermediate stratum 4 composed of intermingled thermoplastic resin fibers represented by the numeral 5_ and cellulosic papermaking fibers represented by the numeral 3_. Directly contiguous to each of intermediate strata 4 is strongly adhering, continuous outer layer 9 of a thermoplastic resin. FIG. 3 is a schematic illustration of a preferred embodiment of the method of this invention. In this method, aqueous slurry 100 of cellulosic papermaking fibers and aqueous slurry 101 of thermoplastic resin fibers are prepared and delivered to single headbox 102. Cellulosic slurry 100 is delivered to web-forming zone 106 through subchamber 103 while resin slurry 101 is delivered to zone 106 through subchambers 104. Both slurries are then formed into stratified composite 108 on web-forming wire 110 which is part of Fourdrinier web-forming equipment 112. This web is then subjected to pressing with pressing rolls 114 and drying in drying zone 116. Subsequent to drying, the web is subjected to calendering under controlled temperature and pressure conditions to fuse the outer resin fiber layers with calender stack 118 and becomes paper product 119 which is wound up on take up roll 120 for storage or subsequent treatment.

The paper product of the present invention can be used in a variety of ways, such as packaging for foods, cardboard, paper board, shipping containers, bags, etc. In a preferred embodiment, this paper product is useful as a support material for image-recording elements. Such elements are known in the art and generally include a support having thereon one or more image-forming or image-receiving layers as well as any additional layers desired.

Typical image-forming elements of this invention include photographic (both positive and negative working) , photothermographic, thermographic and radiographic elements and diffusion or image transfer film units. Preferably, the paper products are used in what are known in the art as photographic papers useful in preparing reflection prints. The characteristics and components of such elements and papers, including image-forming materials, are known in the art. One reference summarizing much of this art is Research Disclosure, publication 17643, pp. 22-31, December, 1978 (published by Industrial

OMPI Opportunities, Ltd., Homewell, Havant Hampshire P09 1EF, United Kingdom).

Typical image-receiving elements of this invention are elements which "receive" an image which has been previously formed elsewhere, such as on an image-forming element. Such "receivers" as they are sometimes called can be used in integral intake transfer film units or two-sheet instant film products including those sometimes called "peel apart" products as well as in the products described in U. S. Patents 4,296,195 (issued October 20, 1981 to Bishop et al) and 4,297,432 (issued October 27, 1981 to Bowman et al) .

The following example is included to further illustrate the invention.

A stratified composite paper was prepared in the following manner using conventional Fourdrinier papermaking equipment fitted with a Strata-Flo

TM

Converflo headbox manufactured by the Beloit

Corporation, Beloit, Wisconsin.

An aqueous slurry of hardwood kraft cellulosic fibers was prepared having 0.4 percent solids. The fines fraction of the fibers was believed to be about 20%. A yellow dye was added to the slurry to allow easy identification of cellulosic layers in the composite paper. An aqueous slurry of polyethylene fibers was also prepared having 0.4 percent polyethylene solids and 10% clay (based on polyethylene weight) . The two slurries were then fed to the paper-forming wire of the papermaking

ItlVf equipment via the Strata-Flo Converflo headbox with the cellulosic slurry directed to a central chamber of the headbox and two portions of the polyethylene slurry directed respectively to two chambers one on each side of the central chamber .

OMFI The resulting multi-ply web formed on the paper-forming wire and subsequently dried was substantially like the web illustrated in FIG. 1. The weight ratio of polyolefin to cellulose in the web was about 1:1.

Samples of the multi-ply web so prepared were calendered under controlled temperature and pressure conditions to fuse the outer resin fiber layers. In one instance, the calendering was done with a four-roll calender stack having a calender surface temperature of about 55°C and providing a maximum loading of about 87 kilonewtons of pressure per linear meter. The resulting stratified composite paper product was substantially like the element illustrated in FIG. 2 and had surface characteristics (e.g. hydrophobicity and liquid and gaseous impermeability) similar to those of a conventional resin-extruded paper product.

Claims

CLAIMS:

1. A stratified composite paper product which is substantially impermeable to liquids and gases, said product comprising (1) an interior stratum consisting essentially of cellulosic papermaking fibers; (2) directly contiguous to each face of said stratum, an intermediate stratum containing intermingled thermoplastic resin fibers and cellulosic papermaking fibers; and (3) directly contiguous to each of said intermediate strata, a strongly adhering, continuous outer layer of a thermoplastic resin.

2. The paper product of claim 1 wherein, each of said outer layers consists essentially of a polyolefin.

3. The paper product of claim 2 wherein said polyolefin is polyethylene.

4. The paper product of claim 1 wherein one of said continuous outer layers consists essentially of a first thermoplastic resin and the other of said continuous outer layers consists essentially of a second thermoplastic resin of different composition than said first resin.

5. The paper product of claim 1 having liquid and gas permeabilities of zero as measured by the Gobb and Sheffield tests, respectively.

6. The paper product of claim 1 exhibiting a receding contact angle of greater than about 75° as measured between a droplet of distilled water and the outer surface of either one of said outer resin layers.

7. The paper product of claim 1 wherein each of said outer resin layers contains a pigment.

8. The paper product of claim 7 wherein said pigment is a white opacifying pigment.

9. The paper product of claim 1 having from about 10 to about 70 percent of thermoplastic resin based on total dry product weight.

10. A method for the preparation of a substantially liquid and gas impermeable, stratified composite paper product, which method comprising the steps of:

(A) simultaneously flowing an aqueous slurry of cellulosic papermaking fibers and at least lυ one aqueous slurry of thermoplastic resin fibers into a web-forming zone to form therein a stratified composite web comprising an interior stratum consisting essentially of cellulosic papermaking fibers, an intermediate stratum directly contiguous 5 to each face of said stratum containing intermingled thermoplastic resin fibers and cellulosic papermaking fibers, and an exterior stratum directly contiguous to each of said intermediate strata consisting essentially of thermoplastic resin fibers; 0 (B) rendering said web substantially dry; and

(C) subjecting said web to heat sufficient to fuse each of said exterior strata into a strongly adhering continuous layer of 5 thermoplastic resin.

11. The method of claim 10 wherein said flowing step (A) is accomplished with a single headbox having a main chamber divided into subchambers by dividing means, each of said 0 subchambers communicating with said web-forming zone.

12. The method of claim 11 wherein said cellulosic slurry is delivered to said web-forming zone through a first subchamber, and said resin slurry is delivered to said web-forming zone through 5 second and third subchambers on opposite sides of

OMPI said first subchamber .

13. The method of claim 12 wherein the consistency of said thermoplastic resin slurry is greater than the consistency of said cellulosic slurry.

14. The method of claim 13 wherein said cellulosic slurry is delivered to said web-forming zone through a first subchamber and first and second thermoplastic resin slurries are delivered to said θ web-forming zone through second and third subchambers, respectively, on opposite sides of said first subchamber.

15. The method of claim 14 wherein said cellulosic and resin slurries have mutually 5 different consistencies.

16. The method of claim 10 wherein said fusing step is accomplished by calendering said web at a temperature and pressure sufficient to fuse each of said exterior strata into a strongly 0 adhering continuous layer of thermoplastic resin.

17. The method of claim 10 wherein each of said outer layers consists essentially of a polyolefin.

18. The method of claim 17 wherein said 5 polyolefin is polyethylene.

19. The method of claim 10 wherein said paper product comprises about 10 to about 70 percent of thermoplastic resin based on total dry product weight. 0

20. A stratified composite paper product according to Claim 1 having coated thereon at least one image-recording layer.

21. A stratified composite paper product according to claim 1 having coated thereon at least one photosensitive silver halide emulsion layer .

-glRE

OMPI