US3840428A - Base sheet for strippable wall covering and process for making - Google Patents

Abstract

A base sheet made on a paper machine for use in the manufacture of strippable wall coverings, the process of making it, and strippable wall coverings including it. The base sheet is characterized by having throughout a non-continuous membrane formed from a self-reactive vinyl acrylic terpolymer latex comprising butyl acrylate, vinyl acetate, and a self-reactive comonomer and having certain specified properties and characteristics.

Description

UNITED STATES PATENTS 3/1961 Maeder et a1 117/33 D United States Paten 11 1 1111 3,840,428 Ring et a1. 1 51 Oct. 8, 1974 [5 1 BASE SHEET FOR STRIPPABLE WALL 2,976,167 3/1961 Maeder et a1 117/161 COVERING AND PROCESS FOR MAKING 3,083,172 3/1963 260/29.6 3,144,380 8/1964 Drennan 162/164 [75] Inventors: Michael Ring, Warw1ck; Joseph F. 3,149,023 9/1964 Bodendorf e181. 162/135 Sheehey, South Glens Falls, both of 3,184,373 5/1965 Ar1edter..... 162/1'68 N.Y. 3,190,789 6/1965 Taylor 162/181 3,235,443 2/1966 Greenman et a1. 162/135 Asslgneei llltematlonal Paper Company New 3,275,469 9/1966 Streit 117/76 York, 3,275,469 9/1966 Streit 117/161 [22] Filed: June 2, 1972 [21] Appl. No.: 259,343 Primary Examiner-George F. Lesmes Assistant Examiner-William R. Dixon, Jr. Rained Apphcatlon Data Attorney, Agent, or Firm-Walt Thomas Zielinski [63] Continuation of Ser. No. 32,365, Apnl 27, I970, abandoned, which is a continuation-in-part of Ser. No. 803,523, Jan. 29, 1969, abandoned, which is a continuation-in-part of Ser. No. 531,317, Dec. 1, 1965, abandoned. ABSTRACT [52] US. Cl 162/146, 161/146, 161/232, A base sheet made on a paper machine for use in the 161/233, 161/251, 162/168, 162/184, 260/851 manufacture of strippable wall coverings, the process [51] Int. Cl D21h 5/12 of making it, and strippable wall coverings including [58] Field of Search 162/ 135, 168, 181; it. The base sheet is characterized by having through- 161/167, 232, 233, 251; 260/80, 81, 29.6; out a non-continuous membrane formed from a self- 117/161 A, 161 L, 161 LN, 161 VT, 155 R, reactive vinyl acrylic terpolymer latex comprising 155 L, 155 A butyl acrylate, vinyl acetate, and a self-reactive comonomer and having certain specified properties and [56] References Cited characteristics.

2 Claims, N0 Drawings This application is a continuation of U.S. Ser. No. 32,365, filed Apr. 27, 1970 and now abandoned, which was a continuation-in-part of U.S. Ser. No. 803,523, filed Jan. 29, 1969 and now abandoned. U.S. Ser.No. 803,523 was a continuation-in-part of U.S. Ser. No. 531,317, filed Dec. 1, 1965 and now abandoned.

This invention relates to strippable wall covering, that is, a wall covering-which, after having been hung on a wall for an extended period, may be readily pulled from the wall in large sheets, leaving the wall intact and clean, in condition for a subsequent application of another wall covering. More specifically, this invention relates to the base sheet used in the manufacture of strippable wall covering.

Customarily, a wall covering manufacturer applies a coating, or coatings, to a base sheet and prints a pattern thereon. This coated and printed sheet can be embossed. As is made clear in U.S. Pat. No. 3,212,957, issued Oct. 19, 1.965, the base sheet can also be combined with other. wall covering materials such as paper, cloth, wood veneer, plastics, etc., but, normally the side of the base sheet which is to be put in contact with the wall receives no further treatment other than the paste used in the hanging operation. (For a prepasted grade, the paste is applied by the wall covering manufacturer.) The base sheet is, then, the component of the complete construction which is principally responsible for the strippability of the wall covering.

It is a purpose of this development to provide a base sheet which meets all the requirements for manufacture and end use of a strippable wall covering. it is a further purpose to make such a base sheet from inexpensive materials on a conventional paper machine at a' high production rate.

It is advantageous for a wall covering to be readily strippable from a wall in continuous strips without damage to itself or to the wall surface; Upon stripping, such wall covering does not rupture, causing fragments of it to remain on the wall surface, nor does it cause fragments of the wall to be separated from the wall and be retained upon the wall covering. And, to obtain the desired strippability, the wall covering must bestronger than the adhesive bond between it and the wall when conventional wall covering adhesives, such as wheat paste, are used to make the wall covering adhere to the wall. Or, in other words, the wall covering must possess a high level of wet tensile strength and of wet edge tear strengh. See, for example, U.S. Pat. No. 3,212,957, issued Oct. 19, 1965. In addition, the side of the wall covering which is to be applied to the wall must have a high level of water resistance to prevent the penetration into it of water-based adhesives.

A strippable wall covering must also satisfy the requirements expected of conventional wall coverings. It must not slide nor sag on the wall. It must remain firmly and uniformly attached to the wall for extended periods. It must not curl when it is hung. It must possess the proper drape" and hang for ease of application.

Again, the base sheet of a strippable wall covering must be suitable for subsequent converting operations. In a typical wall covering manufacturing operation, the base sheet is coated with a ground coat"; this coating normally contains a pigment such as clay and a waterbased adhesive and is applied as an aqueous system and subsequently dried. The ground coat is normally printed and subsequently covered with an additional transparent coat of polyvinyl chloride or the like. Thus, the base sheet must have a smooth finish and be satisfactorily devoid of fuzz. It must readily accept a water-base coating; it must lend itself to a good bond with the ground coat. The base sheet must be sufficiently flexible, so that the dried ground coat does not crack when the coated sheet is folded. The base sheet must not contain materials which would cause discoloration or other undesirable change in the applied coatings upon aging. The degree of stretch of the base sheet must be limited lest it cause the problem of misregister in the printing operation on the ground coat. The base sheet must not curl excessively during a coating operation. It must accept deep embossing.

Then too, the wall covering must have high opacity to prevent show-through of a pattern of a material upon which may be applied and must retain a high proportion of this opacity when it is wet, to satisfy this requirement when the sheet is wetted at the time of application. The base sheet should have a high brightness so that it does not adversely affect the brightness of the finished wall covering and consequently its suitability for printing a pattern on a bright background. The wall covering is normally expected to be stain-resistant; the base sheet should not contain materials which will detract from this property.

Strippable wall coverings have previously been provided. These wall coverings, however, have disadvantages.

Strippable wall coverings have been prepared from vinyl films, coated with rubber-based pressure-sensitive adhesives. Vinyl film of sufficient weight in itself to be the covering is expensive; rubber-based pressuresensitive adhesives are many times more expensive than conventional wallpapaer adhesives. There is a further disadvantage of pressure-sensitive adhesives; A paperhanger must be able to move, or slide, paper laterally on a wall to align one strip with the strip which he has applied immediately before. With a pressuresensitive adhesive it is very difficult to achieve this lateral movement. Another disadvantage of pressuresensitive adhesives is their failure with age; the rubber component degrades through oxidation-Upon stripping a wall covering applied with such an aged adhesive, a considerable residue of the adhesive remains on the wall. This residue is very difficult to remove; normally an organic solvent is required for effective removal.

Strippable wall coverings have been made by laminating conventional hanging stock to woven textile scrim, or by forming a sheet of which scrim is an inte- 'gral part; the scrim provides the strength necessary for strippability. Such a material has certain disadvantages. The lamination process is normally slow; production of a sheet of which scrim is an integral part also is normally slow. The scrim is expensive. Unbleached scrim, which is less expensive than bleached scrim, contains objectionable dirt. The only embossing pattern readily usable is that which is imposed by the geometry of the scrim itself.' The surface irregularities caused by the scrim make uniform printing very difficult. In addition, scrim-containing papers are stiff. A paperhanger normally folds long strips of wall covering to facilitate handling and, when a scrim-containing sheet is folded,

' the coating frequently cracks, causing unsightly marks.

Strippable wall coverings have been made by applying a coating of polyvinyl chloride to a closely woven fabric. The principal disadvantage of such a product is the extremely high cost of the fabric. Because of'the texture of the fabric, printing is frequently a problem with such materials. Pasting of such wall coverings-is frequently a problem; the paste tends to fill the voids of the fabric instead of forminga film over the entire surface.

Strippable wall coverings have been made with base sheets containing long fibers of synthetic polymers in mixture with a major portion of conventional papermaking fibers, the whole fiber furnish being bonded together with a resin. The synthetic fibers, which may be up to an inch in length, provide the impression of a'fabric. These synthetic fibers cause many papermaking difficulties which make the production rate of such a sheet very slow. In addition, such fibers are very expensive.

The strippable wall covering basesheet of this invention is produced on conventional papermaking equipment and, broadly, the sheet is formed from a suspension of a mixture of conventional papermaking or cellulosic fibers, synthetic fibers (optional), and a filler or pigment; is partially dried; is saturated with a synthetic latex; and, is then dried to a moisture content normal for paper products. This sheet has been produced on a Roto-former machine, but it can be made on a Fourdrinier paper machine. The formed and partially dried sheet can be saturated with the synthetic latex on a conventional size press which is an integral part of the paper machine, but it can as well be saturated on other conventional saturating equipment which is either integral with the paper machine or separate from the paper machine.

In the product and process of the present invention, a variety of materials can be used. Thus, for example, strong, bleached cellulosic pulps of the type commercially available under the trademark Celgar or of the type reclaimed from waste polyethylene-coated (polybroke) paper used in the manufacture of milk cartons or the like can be resorted to for the papermaking fibers. The synthetic fibers, if used at all, can be rayon, nylon, Orlon, or Dacron and they can be used in amounts representing as much as 50 percent by weight of the fiber furnish in the base sheet of the present invention. As a filler or pigment, a titanium dioxide material such as the commercially available Titanox RA-SO can be used, as can any one of a number of others familiar to those skilled in the art.

It is distinctly useful to employ a wet strength agent such as one of the commercially available melamineformaldehyde resins, e.g., Parez Resin 607. And, if some of the Parez Resin 607 is used together wiht another melamine resin such as Parez Resin 613, a filler retention agent having additional advantageous properties is at work. The combination of a melamineformaldehyde resin (e.g., Parez Resin 607) and a highly reactive melamine resin of the methylated methylol melamine type (e.g., Parez Resin 613), have proven especially worthwhile and beneficial, provided both resins are added to the stock prior to the formation therefrom of a sheet.

So far as can be ascertained, the presence of the Parez Resin 607 when the sheet is formed from stock containing it insures a sufficient degree of wet strength in the sheet to permit complete submersion thereof, without disintegration, in a bath of the completed latex. And, upon subsequent drying of the sheet, the presence of ,Parez Resin 613 when the sheet is formed from stock containing it insures a reaction with the latex which produces a tough, non-continuous, water resistant membrane throughout the sheet. Thus, by adding the methylated methylol melamine to the stock at the wet end and the latex at the size press in the process of the present invention, there is achieved an in situ reaction between the melamine and latex which forms a three dimensional membrane throughout the sheet.'

the sheet and controls its strippability by permitting some, yet controlling the degree of, penetration into the sheet of the paperhangers paste.

By contrast, if the Parez Resin 613 were added to the latex emulsion at the size press, as is fairly conventional, rather than to the stock slurry from which the sheet is later formed, a water resistant skin or film would be formed on the surface of the sheet. This would prevent the proper adhesion of the wall paper paste to the sheet and the subsequent adhesion of the sheet to a wall. Clearly, then, the point of addition of the Pal-e2" Resin 613 is significant.

As for the correct synthetic latex to use in the process and product of the present invention, the work thus far undertakenhas centered in the area of the acrylic resins, particularly the self-crosslinking acrylic resins. The latter type of resins is discussedin the American Dyestuff Reporter for Mar. 5, 1962, as well as other articles in the technical literature which are available. These latter materials are produced by producing copolymers with crosslinking reactive groups constructed into the polymer backbone, so that the resin becomes self-reactive without resort to an-external crosslinking agent.

The common acrylic esters (methyl, butyl, etc.) are essentially non-reactive. In order to facilitate crosslinking, it is necessary to incorporate into the polymer a minor proportion of an appropriate functional monomer. These reactive monomer groups need not.necessarily be members of the acrylicfamily, are usually distributed randomly along the polymer chain, and permit crosslinking of adjacent chains and the formation of a threedimensional polymer network. They are made to react at the proper time either with the aid of an external crosslinking agent, the use of acid catalysis, and v curing or, if the necessary functionality has been built into the basic polymer, with the use of acid catalysis and curing only. See the American, Dyestuff Reporter for Sept. 2, 1963 at page 44.

To date, the best synthetic latex for the purposes of this invention, and the one which is clearly preferred, is a commercially available material which its manufacturer calls a self-reactive vinyl acrylic terpolymer latex and sells as an aqueous dispersion containing about 45 percent to 50 percent total solids and anionic or non-ionic surfactants. The use of the surface active agents to disperse the acrylic monomers therein during emulsion polymerization is said to result in a product ofsuperior chemical stability, particularly with respect of 3 to 4 minutes at 130C. is usually necessary to effect a complete cure. Oxalic or citric acid or ammonium salts of these are suitable catalysts for accelerating the curing.

More particularly, the preferred terpolymer em- 5 is in the range of about to 35 parts by weight, and 15 the proportion of self-reactive comonomer is in the range of about 1 to 10 parts by weight. Further, such terpolymer is characterized by a second order transition temperature (i.e., a temperature below which the polymer changes from a rubbery to a plastic material) of themagnitude of about -36C.; a tensile strength of the magnitude of about 240 psi and, after curing seconds at 130C., about 275 psi; and, an elongation of the magnitude of about 925 percent and, after curing 30 seconds at 130C., about 300 percent. Here, tensile and agitated at ambient temperature to achieve approximately 20 percent solids. Ammonium chloride, to serve as a curing aid, is added in aqueous solution. Then, the entire saturant is pumped to the size press pond and applied to the wall covering sheetin the conventional manner.

Attached Table 1 summarizes the data drawn from the preparation of three qualities of wall covering materials made in accordance with the present invention.

0 Such table, then, describes three examples of such coverings in' terms of both their constituents and their properties. It does not, of course, exhaust the possible combinations of ingredients which properly come within the scope of the present invention. Neither does it, for instance, limit the quantity of synthetic latex and curing aid which can be used. Indeed, it is to be clearly understood that the lower limit of such quantity is determined primarily by the strength requirements of the wall covering sheet being made and the upper limit is determined primarily by the application equipment available and the further handling of the sheet. If, for instance, it is desired to ground coat the sheet (cf., U.S. Pat. No. 3,212,957, column 2), care must be taken to avoid the use of so much of the synthetic latex as will 25 inhibit proper adhesion between the ground coat and Alum added tp pH approximately 4.5.

'Tensile Tester using 3 mil (approx.) films dried at 72F.

and elongatlon values were obta ned wlth-an lnstron sheet.

TABLE I High Medium Low White White White Grade Grade Grade BEATER FURNISH (Parts) Celgar" bleached kraft 46.5 Polybroke Pulp 46.5 Rayon l5 7 5 Parez Resin 613 1.5 1.3 1.3 Parez Resin 607 0.5 0.5 0,5 Titanox RA-50 12 5 3.5 Alum SATURANT o1 finished sheet) Terpolymer (Resyn 2873) 20 20 20 Ammonium Chloride 0.3 0.5 05

TEST RESULTS Dry Dry Wet Dry Wet Basis Wt. (24X36-500). lb 82 84.3 85.0

Cali er, mils 8.0 8.2 8.7 Mul en, psi 69.8 57.6 Tensile, lb/in. MD 44.2 50.0 19.0 37.6 19.4 CD 21.7 13.9 6.3 13.9 6.0 Stretch. MD 3.5 9.5 3.4 12.2 CD 9.1 14.6 8.5 18.5 Tear. 3 With Gr 153 134 142 Across Gr 159 208 202 Edge tear. g MD 5300 4700 6000 CD 6950 5600 5750 Fold MD 6100 2735 CD 525 Porosity, sec/100 cc 40 15 Brightness, F 81.5 72.5 67.9 W 82.1 72.1 67.8 Opacity, 91.4 94.1 91.8 lnk Penetration F 1000+ 1380 3600 w 3600+ 2700 What is claimed is:

l. A process for manufacturing a base sheet for strippable wall covering comprising the steps of (a) forming a paper sheet from cellulosic fibers and from about 0 percent to 50 percent by weight synthetic fibers filled with pigment in the presence of a filler retention agent comprising a melamine-formaldehyde resin and a methylated methylol melamine resin; (b) partially drying the formed paper sheet; saturating the formed 'paper sheet with not more than about 20 percent by weight of a self-reactive vinyl acrylic terpolymer latex comprising butyl acrylate, vinyl acetate, and a third monomer containing polyfunctional groups capable of crosslinking with similar groups in adjacent chains wherein the proportion of the butyl acrylate is in the range of about 65 to 85 parts by weight, the proportion of the vinyl acetate is in the range of about 15 to 35 parts by weight, and the proportion of the third monomer is in the range of about 1 to parts by weight and characterized by a second order transition temperature the process of claim 1.

Claims (2)

1. A PROCESS FOR MANUFACTURING A BASE SHEET FOR STRIPPABLE WALL COVERING COMPRISING THE STEPS OF (A) FORMING A PAPER SHEET FROM CELLULOSIC FIBERS FILLED FROM ABOUT 0 PERCENT TO 50 PERCENT BY WEIGHT SYNTHETIC FIBERS FILLED WITH PIGMENT IN THE PRESENCE OF A FILLER RETENTION AGENT COMPRISING A MELAMINEFORMALDEHYDE RESIN AND A METHYLATED METHYLOL MELAMINE RESIN; (B) PARTIALLY DRYING THE FORMED PAPER SHEET; (C) SATURATING THE FORMED PAPER SHEET WITH NOT MORE THAN ABOUT 20 PERCENT BY WEIGHT OF SELF-REACTIVE VINYL ACRYLIC TEROLYMER LATEX COMPRISING BUTYL ACRYLATE, VINYL ACETATE, AND A THIRD MONOMER CONTAINING POLYFUNCTIONAL GROUPS CAPABLE OF CROSSLINKING WITH SIMILAR GROUPS IN ADJACENT CHAINS WHEREIN THE PROPORTION OF THE BUTYL ACRYLATE IS IN THE RANGE OF ABOUT 65 TO 85 PARTS BY WEIGHT, THE PORPORTION OF THE VINYL ACETATE IS IN THE RANGE OF ABOUT 15 TO 35 PARTS BY WEIGHT, AND THE PORPORTION OF THE THIRD MONOMER IS IN THE RANGE OF ABOUT 1 TO 10 PARTS BY WEIGHT AND CHARACTERIZED BY A SECOND ORDER TRANSITION TEMPERATURE OF THE MAGNITUDE OF ABOUT -36*C., A TENSILE STRENGTH OF THE MAGNITUDE OF ABOUT 240 PSI, A TENSILE STRENGTH AFTER CURING 30 SECONDS AT 130*C. OF THE MAGNITUDE OF ABOUT 275 PSI, AN ELONGATION OF THE MAGNITUDE OF ABOUT 925 PERCENT, AND AN ELONGATION AFTER CURING 30 SECONDSS AT 130*C. OF THE MAGNITUDE OF ABOUT 300 PERCENT; AND, (D) DRYING THE SATURATED SHEET WHICH H REACT THE METHYLATED METHYLOL MELAMINE RESIN AND THE LATEX TO PRODUCE THE BASE SHEET WHICH HAS THROUGHOUT A NONCONTINUOUS MEMBRANE FORMED FROM THE LATEX.

2. A base sheet for strippable wall covering made by the process of claim 1.