GB1599875A

GB1599875A - Tissue laminates

Info

Publication number: GB1599875A
Application number: GB23637/77A
Authority: GB
Original assignee: Rohm and Haas Co
Current assignee: Rohm and Haas Co
Priority date: 1977-06-03
Filing date: 1977-06-03
Publication date: 1981-10-07
Also published as: FI781730A; SE7806457L; DE2823566A1; FR2392809A1; NL7805977A; BE867763A

Description

(54) TISSUE LAMINATES (71) We, ROHM AND HAAS COMPANY, a corporation organized under the laws of the State of Delaware, United States of America, of Independence Mall West, Philadelphia, Pennsylvania 19015, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention is concerned with tissue laminates and their production.

Laminates of this invention may for example be useful as domestic or industrial wipes, usually regarded as disposable. The invention is however concerned with any laminate of paper or non-woven or woven fabric of up to 30 gms/m2 weight, for example tissue paper or other thin paper or thin non-woven fabrics. This class of materials will hereinafter be called "tissue".

Tissue laminates are conventionally made by placing layers of tissue together, optionally interleaved with one or more layers of scrim, with a layer of adhesive between each pair of opposing faces then drying and curing the adhesive. As adhesive, about 10 g/m2 or more of thickened emulsion polymer is conventionally used and is applied by printing, spraying or other conventional techniques. During drying and curing the laminate is of course held together although sometimes the adhesive is partly pre-dried, this to avoid penetration and ultimately strike-through of the outer tissue layers by the adhesive. Strike-through is disadvantageous because the resulting laminate then loses the surface qualities of the outer tissue layers and instead aquires the feel and characteristics of the adhesive.

We have now found a method and product wherein such penetration and strike-through can be more successfully avoided and adhesion can be effected using lower quantities of adhesive polymer.

According to the invention there is provided a'laminate of two or more tissue layers optionally interleaved with one or more scrim layers adjacent tissue layers being bound together by 2 to 5 gms/m2 of crushed polymeric foam, the outer most layers being tissue layers.

Another embodiment of the invention provides a method of making a tissue laminate comprising two or more tissue layers, as hereinbefore defined, optionally interleaved with one or more scrim layers, which method comprises coating tissue and/or scrim, when present, with a polymeric foam, drying or substantially drying the foam before or after placing the layers together so that the outermost layers are tissue layers and, concurrently or separately, crushing and curing the foam, the amount of foam being sufficient to provide from 2 to 5 grams per square meter of polymer solids between adjacent tissue layers.

The polymer of the crushed foam may preferably be a polymer of at least two of the following monomers of which preferably at least one is a monomer which will carry into the polymer functional groups capable of crosslinking: (a) cr.p-ethylenically unsaturated acid which includes acrylic acid, methacrylic acid. ethacrylic acid, itaconic acid, aconitic acid, crotonic acid, citraconic acid, maleic acid, fumaric acid, -chloroacrylic acid, cinnamic acid and mesaconic acid;; (b) monomer of the formula

wherein R is hydrogen or alkyl, for example. lower alkyl of from 1-4 carbon atoms, and R' is a straight, branched or cyclic alkyl, alkoxyalkyl or alkylthioalkyl radical having from 1 to 20 carbon atoms, or cycloalkyl having from 5-6 carbon atoms, such as methyl, ethyl propyl, n-butyl, 2-ethylexyl, heptyl, hexyl, octyl, 2methyl-butyl, I-methyl-butyl, butoxybutyl, 2-methylpentyl, methoxymethyl, ethoxyethyl, isobutyl, ethylthioethyl, methylthioethyl, ethylthiopropyl, 6methylnonyl, decyl, dodecyl, tetradecyl or pentadecyl; R1 may also be ureido, hydroxy alkyl of from 1 to 5 carbon atoms, such as hydroxymethyl, hydroxyethyl.

hdroxypropyl, hedroxybutyl or hydroxypentyl, 2,3-epoxypropyl, amino (C1 to C5)- akyl,mono- or di-(C1 to C5)-alkyl or hydroxy (C1 to C5)-alkyl substituted amino (C to C5)-alkyl; (c) monomer of the formula

wherein R2 is hydrogen or methyl and R3 is halo such as chloro (C1 to C5)- alkanoyloxy such as acetoxy, cyano, formyl, phenyl, carbamoyl, N-hydroxymethyl carbamoyl, tolyl, methoxyethyl, methoxymethyl, 2,4-diamino-s-triazinyl (Cf to C5)- alkyl, or epoxy; and

wherein R4 is hydrogen or methyl;R5 and R6 are (Cl to C5)-alkoxy such as methoxy and ethoxy, or (C1 to C-alkanoyloxy such as acetoxy.

Examples of the specific monomers (b), (c) and (d) which may be employed are: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, isopentyl methacrylate, tert-pentyl methacrylate, hexyl methacrylate, cyclohexyl methacylate, 2-ethylbutyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decal methacrylate, lauryl methacrylate, kyristyl methacrylate, cetyl methacrylate, stearyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, tert-amyl acrylate, hexyl acrylate, octyl acrylate, 2ethylhexyl acrylate, vinyl acetate, tetradecyl acrylate, acrylamide, pentadecyl acrylate, styrene, pentadecyl methacrylate, vinyl toluene, methacrylamide, Nmethylolacrylamide, glycidyl methacrylate, methyl-aminoethyl methacrylate, tertbutylaminoethyl methacrylate, 6-(3-butenyl)-2,4-diamino-s-triazine, hydroxypropyl methacrylate, hydroxyethyl methacrylate, methacrylonitrile, methoxymethyl methacrylamide, N-methylol methacrylamide, acrolein, methacrolein, 3,4-epoxy-1butene, acrolein di-ethyl acetal, acrolein dimethyl acetal, allylidene diacetate, methallylidene diacetate. Also useful are the analogs of the methacrylic acid derivatives mentioned above with other unsaturated acids such as acrylic acids and itaconic acid, such acids themselves, dicarboxylic acids such as maleic acid and half esters and half amides thereof; vinyl ethers of glycols such as ethylene glycol are also included.

The crosslinkable addition polymerizable unsaturated monomers may have reactive polar groups selected from -OH, >

Such groups may be included as are mutually or self-crosslinkable, or separate crosslinking compounds such as triazineformaldehyde resin may be added.

Of course, water-sensitive materials such as isocyanates should not be used in aqueous systems unless they are blocked by reaction with a phenol group which protects the isocyanate groups until subsequent heating or the use of other reaction mechanisms such as the use of calcium, zinc, or tin compound catalyst convention in the art.

The preferred copolymers have a molecular weight of from 70,000 and 2,000,000 and preferably 250,000 to 1,000,000 and are made by emulsion copolymerization of the several monomers in the proper proportions. Conventional emulsion polymerization techniques are described in U.S. Patent Nos. 2,754,280 and 2,795,654. Thus, the monomers may be emulsified with an anionic, a cationic, or a nonionic dispersing agent, 0.05 to 10 percent thereof ordinarily being used on the weight of the total monomers. The acid monomer and many of the other functional or polar monomers may be soluble in water so that the dispersing agent serves to emulsify the other monomer or monomers. A polymerization initiator of the free radical type, such as ammonium or potassium persulfate, may be used alone or in conjunction with an accelerator, such as potassium metabisulfite or sodium thiosulfate.Organic peroxides, such as benzoyl peroxide and tert-butyl hydro-peroxide are also useful initiators. The initiator and accelerator, commonly referred to as catalyst, may be used in proportions of 0.1 percent to 10 percent each based on the weight of monomers to be copolymerized. The amount as indicated above, may be adjusted to control the intrinsic viscosity of the polymer. The temperature may be from room temperature to about 760"C.

The following is a list of some of the copolymers which may be employed in this invention. The copolymers have the following monomer compositions: 96EA/3.5AM/0.5AA; 96EA/4MOA; 94EA/5.5ALAC/AC/0.5AA; 94.5EA/5HEMA/0.5AA; 66EA/32.7MMA 1 .3MAA; 100EA; 83EA/15MMA.2AA; 83BA/1SAN/IAC/1AA: 65EA/25.5BA/4.5 AN/3.5AM/1.5IA; 86EA/10AN/4MOA, 83BA/l 4AN/l Ac/2AA; 68BA/28MMA/2Ac/2AN; 30BA/55EA/10MMA/3.5AN/O.SAc/lAA and 45BA/IOAN/40EA/4HEMA/IAA. The definitions of the abbreviations are: EA=ethyl acrylate; BA=butyl acrylate; MMA=methyl methacrylate; AA=acrylic acid; MAA=methacrylic acid; IA=itaconic acid; HEMA=hydroxyethyl methacrylate;AN=acrylonitrile; Ac=acrolein; ALACAC=allyl acetoacetate; MOA=acrylamide/N-methylol acrylamide (1:1) and AM=acrylamide.

The polymers above described are intended as exemplification of preferred polymers. Other suitable polymers are undoubtably available.

The latex when formulated, optionally with a foam stabilizer and suitable pigments, can readily be foamed. The polymer composition is preferably such that excessive thickening of the formulation is not encountered under the acid or alkaline conditions employed to assure the most efficient operation of the foam stabilizer.

Any of the standard or other useful techniques for applying foam may be employed. If a two-layer laminate is desired the foam would normally just be applied to one side of one tissue layer against which the other tissue layer will be placed. Often however tissue laminates have three or more fabric layers, the middle layer(s) often being scrim. In this case, for example with a three layer laminate, it is convenient to apply foam to both sides of the layer which is to be the middle layer.

This is possible even in the case of a layer of scrim which is a commonly used central reinforcing layer. Then the scrim, foam coated on both sides is sandwiched, before or after drying the foam as described below, between the outer tissue layers.

The latex which is to form the foam is preferaly initially foamed to a wet foam density of 0.5 to 0.05, preferably 0.5 to 0.1 grams per cubic centimeter, and is then applied to the substrate in a thickness such as will put 2 to 5 grams/sq. m of polymer solids on the substate. The density. of course, will vary with the presence or absence of pigments and fillers and their identity. The foam may then be dried without causing thermosetting, crosslinking or vulcanization for example by heating the foam-coated substrate at a temperature below that which causes thermosetting, crosslinking or vulcanization, for example for from 1 to 10 minutes at a temperature of from 100 to 175"C. preferably 120 to 150"C. In the case of some polymers a lower drying temperature, for example 80 to 1000C. is preferred to avoid premature crosslinking.This is followed, after having placed the desired number of tissue/scrim layers together, by crushing the laminate so that the foam is reduced to a thickness of between 5 percent and 25 percent of the original dry foam thickness. This is followed or accompanied by curing of the crushed foam. In general, the thickness of the dried foam prior to crushing may be substantially less than that of the wet foam, there at times being some shrinkage. This shrinkage may result in up to 30 percent of the thickness of the wet foam being lost during drying.

When we talk about dry or substantially dry we mean that the moisture content of the foam will be from 5 percent to 20 percent.

It is essential, we believe, to form a less dense foam then crush it since, if the initial foam is formed to the ultimate desired density by control of the amount of foaming agent or by means such as using a chemical blowing agent and restraining the expansion in order to get the final density, the walls or struts connecting the air spaces are relatively thick. A crushed foam, on the other hand. initially having expanded to a number of times its final thickness, has connecting walls or struts of a thin flexible nature. We have observed that as a result the crushed foam is much more flexible than a foam initially expanded only to the ultimate density. These foams are inherently opaque.

When pigmented compositions are contemplated, examples of the pigments that may be employed include clays, especially of the kaolin type, calcium carbonate, blanc fixe, talc, titanium dioxide, colored lakes and toners, ochre.

carbon black, graphite, aluminum powder flakes, chrome yellow, molybdate orange, toluidine red and copper phthalocycanines, such as i'Monastral" blue and green lakes. If dyed compositions are required, examples of dyes for acrylic film and foam include basic and dispersed dyes. Other composites could be made dyeable, if they are not already inherently so, through the use of additlves such as methyl cellulose, hydroxyl ethyl cellulose, and the like. Other dyes which could be used include acid dyes, vat dyes, direct dyes and fiber reactive dyes.

The laminate is formed by a multiplicity of layers of pieces of the tissue and optionally scrim for example, from 2 to 7 layers of the tissue and, when present, scrim with interposed foam layers being placed one upon the other. The tissue and, when present, scrim may be placed in a delibrately chosen orientation of the fill and weft of each layer to those in the other layers for the achievement of desired stretch properties. That is not to say that random placement is excluded; one may deliberately choose such a random arrangment and we mean to include this option as indeed a uniform arrangement is also included.

The foam coated tissue and/or, when present, scrim may be laminated to one another by applying pressures up to 300 PSI. Preferred ranges are 10 to 300 PSI, preferably 50 to 150 PSI. Temperatures may be from 1500 to 300"C. and most preferably 200 to 2500 C.

As to the rate of application of the polymer, as specified there must be 2 to 5 g of polymer solids per square meter between each adjacent tissue layer. It is not necessary to apply this amount of polymer between adjacent scrim and tissue layers. Rather a polymer coated scrim layer for interleaving between two tissue layers would comprise 2 to 5 g/sq meter of scrim-reinforced polymer foam.

Thus it is apparent that, the laminates of the invention may be made by (a) coating the desired tissues, and optionally scrim, with the appropriate amount of foam, (b) then (and/or later) drying or substantially drying the foam if necessary to increase foam stability before the layers are placed together or (c) placing the layers together and then drying the foam if predrying has not been effected, (d) crushing and (e) curing the foam. The crushing and curing may be carried out in a single application of heat and pressure, or in discrete steps or in one step wherein the heat and pressure are gradually increased. The heat and pressure applied at this stage will vary with the polymer but in general they will cause the foam to collapse and the polymer to flow around the fibres in the tissues or scrim and finally to cure.

It will be noted however that in all cases the initially applied foam is dried before crushing. It is also apparent that the drying, crushing and curing temperatues, times and pressures will vary with the polymer used. For drying the temperature must be low enough to avoid curing and the drying time will increase with decrease in temperature. For curing the temperature will be higher. For crushing the pressure will be sufficient to reduce the thickness of the dried foam to the degree above described. The combination of temperature, pressure and time must be sufficient to cause flow of the polymer to bond with the tissue/scrim layers. Strike through however, is generally avoided by the low level of polymer applied according to the invention rather than by control of temperature, time and pressure.

Some preferred embodiments of the invention will now be described in and by the following Examples which are given for the purposes of illustration only and in which all parts and percentages are by weight unless otherwise specified.

Example I An emulsion copolymer dispersion prepared from 25.5 parts of butyl acrylate.

65 parts of ethyl acrylate 4.5 parts of acrylonitrile and 3-5 parts of acrylamide is formulated in a ratio of 100 to 7.5 with 5.25 parts of water, 5 parts of 25% ammonium hydroxide, 10 parts of 33% ammonium stearate and 5.62 parts of Aerotex M3 melamine-formaldehyde resin. The ingredients are mixed, and foamed in a kitchen aid mixer (Model C) to a wet density of about 0.2 grams per c.c. The foam is then applied to a polypropylene scrim by passing it through a foam bank which is situated between two rollers to apply approximately 2.5 g/m2 solids.

The foam coated scrim is then dried in an oven at 1200C. for fifteen seconds after which lamination is effected by placing tissue paper on each side and pressing the sandwich together using a pressure of approximately 24 kg/cm2 for three seconds at 150"C. The composite is then cured for three minutes at 1500 C.

Example II Example I. is repeated except that lamination of the tissue paper to the foam coated polypropylene scrim is done prior to drying. The composite is dried for 1.5 minutes at 1200C.

Example III Example I. is repeated except that the composition of the copolymer is 48.25% ethyl acrylate, 48.25% butyl acrylate, 3% methylol acrylamide/methacrylamide solution and 0.5% itaconic acid.

Example IV Example II is repeated except that the composition of the copolymer is 48.25% ethyl acrylate, 48.25% butyl acrylate, 3% methylol acrylamide/methacrylamide solution and 0.5% itaconic acid.

All of these Examples yielded tissue laminates wherein the tissue and scrim layers were securely adhered to each other without strike through of the polymer to the outer tissue surfaces.

WHAT WE CLAIM IS: 1. A laminate of two or more tissue layers as hereinbefore defined, optionally interleaved with one or more scrim layers, adjacent tissue layers being bound together by 2 to 5 gms/m2 of crushed polymeric foam, the outermost layers being tissue layers.

2. A laminate as claimed in claim 1 which consists of two tissue layers interleaved with a single scrim layer.

3. A laminate as claimed in claim 1 or 2 wherein the polymer contains units of at least two of the following monomers: (a) ,-ethylenically unsaturated acid; (b) monomer of the formula:

wherein R is hydrogen or (C1-C4) alkyl, R' is an alkyl, alkoxyalkyl or alkylthioalkyl radical containing from 1 to 20 carbon atoms, C5 or C6 cycloalkyl, ureido, (C1-C5) hydroxyalkyl, 2,3 epoxypropyl, amino (C1-C5) alkyl, mono- or di-(C1-C5) alkyl or hydroxy (C1-C5) alkyl substituted amino (C1-C5) alkyl; (c) monomer of the formula: :

wherein R2 is hydrogen or methyl, R3 is halo, (C1-C5) alkanoyloxy, cyano, formyl, phenyl, carbamoyl, N hydroxymethyl carbamoyl, tolyl, methoxyethyl, methoxymethyl, 2,4 diamino-S-triazinyl (C1-C5) alkyl or epoxy; and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. formulated in a ratio of 100 to 7.5 with 5.25 parts of water, 5 parts of 25% ammonium hydroxide, 10 parts of 33% ammonium stearate and 5.62 parts of Aerotex M3 melamine-formaldehyde resin. The ingredients are mixed, and foamed in a kitchen aid mixer (Model C) to a wet density of about 0.2 grams per c.c. The foam is then applied to a polypropylene scrim by passing it through a foam bank which is situated between two rollers to apply approximately 2.5 g/m2 solids. The foam coated scrim is then dried in an oven at 1200C. for fifteen seconds after which lamination is effected by placing tissue paper on each side and pressing the sandwich together using a pressure of approximately 24 kg/cm2 for three seconds at 150"C. The composite is then cured for three minutes at 1500 C. Example II Example I. is repeated except that lamination of the tissue paper to the foam coated polypropylene scrim is done prior to drying. The composite is dried for 1.5 minutes at 1200C. Example III Example I. is repeated except that the composition of the copolymer is 48.25% ethyl acrylate, 48.25% butyl acrylate, 3% methylol acrylamide/methacrylamide solution and 0.5% itaconic acid. Example IV Example II is repeated except that the composition of the copolymer is 48.25% ethyl acrylate, 48.25% butyl acrylate, 3% methylol acrylamide/methacrylamide solution and 0.5% itaconic acid. All of these Examples yielded tissue laminates wherein the tissue and scrim layers were securely adhered to each other without strike through of the polymer to the outer tissue surfaces. WHAT WE CLAIM IS:

1. A laminate of two or more tissue layers as hereinbefore defined, optionally interleaved with one or more scrim layers, adjacent tissue layers being bound together by 2 to 5 gms/m2 of crushed polymeric foam, the outermost layers being tissue layers.

wherein R is hydrogen or (C1-C4) alkyl, R' is an alkyl, alkoxyalkyl or alkylthioalkyl radical containing from 1 to 20 carbon atoms, C5 or C6 cycloalkyl, ureido, (C1-C5) hydroxyalkyl, 2,3 epoxypropyl, amino (C1-C5) alkyl, mono- or di-(C1-C5) alkyl or hydroxy (C1-C5) alkyl substituted amino (C1-C5) alkyl; (c) monomer of the formula::

(d) monomer of the formula:

wherein R4 is hydrogen or methyl and R5 and R6 are (C1-C6) alkoxy or (C1-C5) alkanoyloxy.

4. A laminate as claimed in any of claims 1 to 3 wherein the polymer has a molecular weight of from 70,000 to 2,000,000 and is made by emulsion polymerization.

5. A laminate as claimed in claim I substantially as described in any of the foregoing examples.

6. A method of making a tissue laminate comprising two or more tissue layers, as hereinbefore defined, optionally interleaved with one or more scrim layers, which method comprises coating tissue and/or scrim, when present, with a polymer foam, drying or substantially drying the foam before or after placing the layers together so that the outermost layers are tissue layers and, concurrently or separately, crushing and curing the foam, the amount of foam being sufficient to provide from 2 to 5 grams per square meter of polymer solids between adjacent tissue layers.

7. A method as claimed in claim 6 wherein the laminate is crushed at a pressure of from 10 to 300 pounds per square inch and cured at a temperature of from 150 to 3000C.

8. A method as claimed in claim 6 or 7 as applied to the preparation of a laminate according to any of claims 1 to 5.

9. A laminate whenever prepared by a method according to claim 6.