US3850673A

US3850673A - Flexible sheet material

Info

Publication number: US3850673A
Authority: US
Inventors: S Nelson
Original assignee: Makin J & J Ltd
Current assignee: Makin J & J Ltd; Makin J & J Ltd gb
Priority date: 1967-03-04
Filing date: 1972-02-23
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

A readily strippable wall covering which comprises a wall covering sheet including a fibrous backing surface. A material comprising a wax-aluminum-protein-rosin complex in water is disposed on the fibrous backing surface in the form of a plurality of discontinuous portions incompletely covering the fibrous backing surface for reducing the susceptibility of the wall covering to adhere to a wall upon the subsequent application of a water-based adhesive to the material prior to positioning the wall covering on a wall such that the subsequently applied adhesive can be directly applied against the fibrous backing surface between the discontinuous portions, and the amount of the material applied to the fibrous backing surface is within the range of 2 gm/sq. meter to 12 gm/sq. meter to partially reduce a direct bonding between the adhesive and the fibrous backing surface.

Description

Nelson 1' 3,856,673 1 1 Nov. 26, 11974 1 1 FLEXIBLE SHEET MATERIAL [75] Inventor: Stanley Nelson, New Mills, near Stockport, England [73] Assignee: J & J. Makin Limited, Rochdale,

Lancashire, England 22 Filed: Feb. 23, 1972 211 App]. No.: 228,512 1 Related U.S. Application Data [63] Continuation-impart of Scr. No. 709,537, March 1,

1968, abandoned.

[30] Foreign Application Priority Data Mar. 4, 1967 Great Britain 10357/67 Mar. 18, 1967 Great Britain 12828/67 [52] U.S. Cl 117/76 A, 106/133, 106/134,

[56] References Cited UNITED STATES PATENTS 2,402,351 6/1946 Smith et a1 106/134 2,940,196 6/1960 Schor 3.076.588 2/1963 Conway ct all... 3,146,142 8/1964 Maly 156/91 10/1965 Lcfebvre 117/122 3,259,507 7/1966 Smith 3,366,525 1/1968 Jackson 156/197 3,438,794 4/1969 Ritson et 106/194- FOREIGN PATENTS OR APPLlCATlONS 15,518 3/1906 Great Britain 106/134 ,4/1940 Great Britain 162/172 Primary ExaminerWi1liarn D. Martin Assistant ExaminerM. R. Lusignan [57] ABSTRACT A readily strippable wall covering which comprises a wall covering sheet including a fibrous backing surface. A material comprising a wax-aluminum'proteinrosin complex in water is disposed on the fibrous backing surface in the form of a plurality of discontinuous portions incompletely covering the fibrous backing surface for reducing the susceptibility of the wall covering to adhere to a wall upon the subsequent application of a water-based adhesive to the material prior to positioning the wall covering on a wall such that the subsequently applied adhesive canbe directly applied against the fibrous backing surface between the discontinuous portions, and the amount of the material applied to the fibrous backing surface is within the range of2 gm/sq. meter to 12 gm/sq. meter to partially reduce a direct bonding between the adhesive and the fibrous backing surface.

13 Claims, 2 Drawing Figures PATENTELNUVZBIBM 3,850,673 SHEET 10F 2 INVENTOR:

PATEmmuvzslm N GE INVENTOR:

FLEXIBLE SHEET MATERIAL This is a continuation in-part application of the copending patent application Ser. No. 709,537, filed Mar. 1, 1968, now abandoned.

The present invention relates to a dry-strippable wall covering and to a method of manufacturing same.

Hitherto a water based adhesive has been used to apply a wall covering to a wall. When the time has come to remove the wall covering from the wall it has been necessary to apply water or steam to the wall covering to loosen the hold of the adhesive. Thereafter once the adhesive hold has been loosened it has been possible to scrape the wall covering from the wall.

Clearly a disadvantage with this known form of wall covering is that its removal from a wall is tedious and time consuming and therefore expensive.

In order to overcome the above problems various kinds of dry-strippable wall covering have previously been proposed.

One known dry-strippable wall covering consistsof two sheets namely a backing sheet and a facing sheet weakly adhered to the backing sheet. To apply the wall covering to a wall, the composite sheet is glued to the wall using a waterbased adhesive. When it is desired to remove the wall covering, the facing sheet is stripped from the backing sheet leaving the backing sheet attached to the wall. Clearly a major disadvantage with this known type of strippable wall covering is that the backing sheet remains on the wall.

Other forms of dry-strippable wall coverings are known. For example, it has been proposed to use a pressure sensitive adhesive on a wall covering. This suffers from the disadvantages that it renders the wall covering both expensive to produce and difficult to apply.

Again, it has been proposed to apply a continuous coating or film to the reverse or working side of a wall covering. With this form of covering it has been found that if a commercially available water based adhesive strippable wall covering.

It is one object of the present invention to provide a flexible sheet material for attachment to a relatively rigid surface which is readily strippable therefrom subity with the adhesive as compared to the untreated surface.

It is still another object of the present invention to provide a wall covering which is ultimately to be drystrippable from a wall to which the wall covering has been applied using a watenbased adhesive.

sequent to the attachment, a surface of which material has been treated to modify its susceptibility to adhere to the material surface of a substance which reduces its susceptibility to adhere to the relatively rigid surface.

It is another object of the present invention to provide a flexible sheet material for attachmentto a relatively rigid surface which is readily strippable therefrom subsequent to the attachment, the rear surface of which material has been treated by the application thereto of a substance exhibiting a reduced compatibil- It is also an object of the present invention to provide a dry-strippable wall covering which can be applied to a wall using any commercially available waterbased adhesive. I

It is a still further object of the present invention to provide a dry-strippable wall covering which can be drystripped from a wall, leaving a clean base for receiving a further wall covering.

It is still another object of the present invention to provide a dry-strippable wall covering to which an adhesive can be applied only when it is desired to hang the wall covering, and not in the factory of the paper manufacturer.

The substance which reduces the susceptibility of the material surface to adhere to the relatively rigid surface may be applied initially in liquid form over the entire surface of the sheet material.

' Alternatively the substance may be applied initially in liquid form or other form in a discontinuous coating to the surfuace of the sheet material.

In this embodiment of the present invention the substance is preferably applied as a pattern over the whole of the sheet. Although the substance may be applied as a regular or irregular pattern, preferably a broken pattem is applied such as a micro-dot patern, which may become irregular once the substance is applied, for instance due to the nature or properties of the sheet material and/or the substance. This is particularly the case where the surface, to which the substance is applied is fibrous, e.g., paper, since the substance may be absorbed into the fibers with consequent spreading or migration of the substance. Where the surface is fibrous therefore, the treated surface may comprise some fibers or parts of fibers having the substance absorbed thereon and other fibers or parts of fibers which do not have the substance absorbed thereon.

The present invention is particularly applicable to flexible sheet material bearing decorative, advertising or instructional matter.

As previously stated, the present invention has particular application to wall-coverings.

It is yet a further object of the'present invention to provide a readily strippable flexible wall-covering, the rear surface of which has been: treated by the application thereto of a substance of reducingits susceptibility to adhere to a wall surface on the application of an ad- Ihesive prior to offering the wall-covering up to thewall ble flexible sheet material which comprises printing or otherwise applying decorative, advertising or instructional matter to the material and treating only part of the rear surface of the material to reduce its susceptibility to adhere to a relatively rigid surface when adhesive is applied thereto prior to offering up the material to the surface.

The material may be treated before or after printing or otherwise applying decorative, advertising or instructional matter to the materialv Many methods may be used to apply the substance, which is in the liquid or semi-liquid form, to the surface to be treated, e.g., printing, coating, spraying, immersing or impregnating techniques. Specific methods which have been found to be particularly useful include application by gravure roll, size press, air knife, roller coating and spraying. Silk screen printing, preferably without a stencil, may also be used, for example, where the surface to be treated is relatively small.

Where the surface to be treated is a comparatively rough surface, e.g., the reverse side of the wallpaper, the substance may be applied to only parts of the surface by applying the material by means of a kiss coating method, by which the substance is applied only to the raised portions of the surface. When the adhesive is ap.

plied, therefore, it adheres to only those parts of the surface to which the substance has not been applied, i.e., the sunken parts of the surface. Any similar method may be used in which the surface is not completely sealed by the material.

The substance which may be used and the amounts used depend upon the surface being treated, the nature of the rigid surface to which the treated material is to be attached and the adhesive to be used. Examples of types of materials which may be used, however, include lattices, water-repellant inks, lacquers, silicones, and synthetic resins. It has been found that, using a vinylidene chloride copolymer as the substance, quantities between 3 and 12 grms/sq. meter are suitable for an 18 02. wallpaper that is to be adhered to a surface using a cellulose type adhesive.

The substance is generally one which will result in a water-and/or chemical-resistant finish being formed on at least a part of the surfaces to be adhered together.

Where the adhesive to be used is a water-based adhesive the substance used may be, e.g., a water-repellant material and this material may range from slightly water-repellent to extremely water-repellant.

The amount of substance utilized depends upon the properties of the surface being treated, the adhesive to be used, the properties of the surface to which the treated material is to be adhered and the particular substance used.

The weight of the substance applied to the surface may also vary depending on the method of application, e.g., it has been found that more material is used when aqueous systems are used than when organic solvent systems are used.

Generally the amount of the substance utilized where the surface being treated is a fibrous material such as the reverse side of a wallpaper, is in the range of from 2 to l2gms./sq. meter of surface although the workable range for each particular substance may not extend over the whole of this range and will vary with the properties of the surface to be treated, the adhesive to be used, the properties of the surface to which the treated material is to be adhered, and the method of application of the substance to the surface being treated.

One class of materials which have been found to be particularly useful are polyvinylidene chloride polymers/copolymers which generally may be used in both aqueous and organic solvent systems.

These polyvinylidene chloride polymers have been found to be of particular use when applied to a part of the non-design side of wallpaper to produce a wallpaper which is readily strippable. These materials are particularly preferred where the adhesive used in adhering the paper to the wall is of'the cellulose type. Examples of polyvinylidene chloride polymers which have been found to be useful are Polidene 91 I sold by Scott Bader (this material may generally be used on paper surface in amounts of between 8 and IZgm/sq. meter, optimally 10 gm/sq meter); Ixan 82A marketed by Solvay et Cie. and lxan SGA marketed by Solvay et Cie (these last two materials may generally be used on a paper surface in amounts of between 2 and 5 gm/sq. meter optimally 3gm/sq meter).

Further materials which have been found to be useful particularly for applying to the reverse side of wallpaper to produce an easily strippable wallpaper, are polyvinyl chloride resins whose films have low water vapour permeability, low water absorption and excellent toughness and flexibility. The resins are desirably unplasticized and are preferably copolymers with for ex ample one or more of the following:- vinyl acetate, vinyl alcohol and a dicarboxylic acid, such as maleic acid. Particular resins which have been found to be of special use for example, in treating the reverse side of wallpaper are Vinylite VYHH, Vinylite VAGH, and Vinylite VMCI-I, all of which are sold by Bakelite Limited, of 1218 Grosvenor Gardens, London, SW1. All three of these substances may generally be used on a paper surface in amounts of from 3 to 7 gm/sq. meters.

A further group of compounds which have been found to be of use in the present invention are nitrocel lulose resins whose films have low water absorption, ex cellent toughness and flexibility. The nitrocellulose resin is preferably unplastizised. When used on the reverse side of wall papers and other materials which are printed or will subsequently be printed, eg., labels, it is desirable that the resin has a high nitrogen content since printing inks may contain methylated spirits which may dissolve low nitrogen content nitrocellulose resins. One nitrocellulose resin which has been found to be of particular use especially in coating the reverse side of wallpaper is a mixture of percent of DI-IX 30/50 Industrial Nitrocellulose sold by Imperial Chemical Industries Limited, and 25 percent of /170 Industrial Nitrocellulose sold by Imperial Chemical Industries Limited. This material may generally be used on a paper surface in an amount of from 3 to 7 gm/sq. meter.

A still further group of compounds found to be useful are products sold under the trade name of Mystolene by Catamance Ltd., Bridge Road East, Welwyn Garden City, Hertforshire. Examples of such compounds are Mystolene PP/2R, and Mystolene MAS.

These materials may generally be applied to a paper surface in concentrations of 0.2 to 10 percent based on the weight of dried fiber. Optimum concentrations were found to be 6 percent using type PP/2R and 1.5 percent using type MAS, although the quality of the material effects these figures in some degree.

According to the present invention, there is provided a method of manufacturing a dry-strippable wall covering from a fibrous sheet material comprising treating the surface fiber of the fibrous sheet material with a freely flowing aqueous dispersion including:

paraffin waxes having melting points falling within the temperature range of 44- 60C;

a natural wood rosin;

an acid protein colloid as emulsion stabilizer;

an aluminum salt of a low molecular weight aliphatic carboxylic acid;

the ratio by weight of said paraffin waxes to rosin being from :1 to 1:4, and

subjecting the so treated backing material to a curing process wherein the treated surface of the fibrous sheet material attains a temperature above the melting points of the paraffin waxes present in the dispersion and which process ensures that the residual moisture content of the fibrous sheet material is from 5 to 12 percent.

Preferably the paraffin waxes have an oil content of less than 2 percent, usually less than 1 percent by weight.

The term natural wood rosin as used herein includes all rosins obtainable from wood. The natural wood rosin used is preferably of the best grade, for example, WW.

The acid protein emulsion stabilizer is preferably ani" mal glue which has been dimerized.

Examples of aluminum salts which may be used in the dispersions are aluminum acetate and especially aluminum formate. When the dispersion is made up with hard water, it has been found that some of the aluminum salt content may be wasted owing to its reacting, possibly in the form of a chelating agent, with the ions in the hard water. It has been found that no or very little aluminum formate is lost in this way and, therefore,

the use of dispersion containing aluminum formate is preferred.

The solids content of the dispersion conveniently has a controlled particle size of less than 2p. and preferably less than in. i

The total moisture content is calculated by determining the weight of moisture present in the fibrous material, e.g., by heating to dryness, and expressing this weight as a percentage of the weight of the sample originally, i.e., when moist under ambient conditions.

The dispersion which reduces cohesive strength of .the bond between the backing surface of the fiber and the subsequently applied water-based adhesive is applied initially in liquid form over the entire backing sur face of the fibrous sheet material. The effect of the reduced bond strength is to reduce the tensile strength required to dry-strip the wall-covering ata later date.

Normally the treated surface has a low 3 minute Cobb value usually below 15. A low Cobbvalue alone, however, is not sufficient to render a material drystrippable.

spreading or migration of the complex, though some penetration into the fibrous sheet material may occur resulting in that portion being wasted. This waste of dispersion may be reduced or eliminated by a sizing process or the like as hereinafter described. The treated surface therefore comprises some fibers or parts of fibers having the complex absorbed thereon and other fibers or parts of fibers which do not have the complex absorbed thereon.

Certain fibers exhibit a property known as preferential absorption which indicates that they have a tendency to adsorb more of an applied material, such as a sizing material, than other fibers. Clearly fibers exhibiting preferential absorption" together with fibers not exhibiting this property may both be found in a single sheet of fibrous material.

According to a further embodiment of the present invention there is provided a method of adhering a flexible sheet material to a relatively rigid surface so as to enable the material to be subsequently readily stripped therefrom, comprising treating "part of the rear surface of the material to reduce its compatability with the ad hesive as compared to the untreated surface, prior to application of the sheet material to the relatively rigid surface.

The present invention is applicable to any type of adhesive for example, a cellulose type or other waterbased adhesive provided it is chosen having regard to the particular treatment which the surface to be ad hered has been subjected to. Adhesives which have The effect of the treatment of the present invention is to render the adhesive bond between the treated surface and the surface to which it is adhered weaker than the bond holding the flexible surface together. As applied to'the case of, e.g., wallpaper, this means that when the treated wallpaper is applied to a wall, the adhesive bond between the wallpaper, and the wall is weaker than the bond between the fibers of the wallpaper. A piece of wallpaper thus may be readily removed from the wall. a

The invention is particularly applicable to wall coverings bearing or intended to bear decorative, advertising or instructional matter.

Many methods may be used to apply the aqueous dispersion to the fibrous backing surface to be treated, e.g., roller coating, spraying, contact coatingor preferably air-knife coating.

When the fibrous surface to be treated is comparatively rough, while the aqueous dispersion is applied to the whole surface to be treated only part of the surface is in fact treated.

The present invention will now be further described with reference to the following examples. Application weights and application concentrations given in the followingexamples are weights or concentrations of the substance, which reduces the susceptibility of the surface to adhere, retained on the surface being treated.

EXAMPLE 1 A polyvinylidene chloride copolymer sold by Scott 5 Bader under the trade name Polidene 911 and having a high vinylidene chloride content and the following characteristics:

approx. 0.25;; Specific gravity 25l25 C. 1.27

was thickened slightly by the addition of a 10 percent solution of polyvinyl alcohol and applied to the back of an 18 02. wallpaper by (a) gravure and, (b) plain roller systems to produce when dry a discontinuous coating. Weights of substance applied ranged from 5 gm/sq meter to 25 gm/sq meter. Application weights of 7 gm/sq meter and below did not have the desired effect, and the areas were 100 percent stuck. Application weights of l2 gm/sq meter and above, again did not have the desired effect, and the areas did not stick. Application weights between 8 gm/sq meter and 12 gm/sq meter, however, resulted in a paper which was at least 50 percent coated and which when used with a cellulose type wallpaper adhesive, adhered to a wall sufficiently for normal purposes but was easily removable when necessary. The optimum application weight by these methods was found to be 10 gm/sq meter. These weights and limits could vary with different substances and types of papers, and are also to some extent depen dent on the types of coatings and/or embossings which may be used.

EXAMPLE 2 A solution of a polyvinylidene chloride copolymer resin with a high vinylidene chloride content and marketed by Solvay Cie. under the trade name lxan WN. 82A was dissolved in a mixture of equal parts of acetone and toluene, to give a solid content of 20 percent, and was then applied to the back of an 18 02 wallpaper by a gravure system to produce when dry a discontinuous coating. Various weights were applied and it was found that the application weights of between 2 gms/sq meter and 5 gms/sq meter resulted in a paper which when used with a cellulose type wallpaper adhesive, adhered to a wall sufficiently for normal purposes but was easily removable when necessary. The best results were LII achieved using an application weight at 3 gms/sq meter. Using the gravure-solvent system of this example the close tolerances which were required could be achieved and slight variations could also be achieved by adjustmentof the concentrate on the machine. Such adjustment is not possible in an aqueous system because any alteration of the viscosity-concentration also alters the degree of penetration which should remain fixed to impart the desired properties to the finished sheet.

EXAMPLE 3 A solution of a polyvinylidene chloride copolymer resin with a medium vinylidene chloride content and marketed by Solvay et Cie under the trade name lxan S.G.A. was dissolved in a mixture of equal parts of acetone and toluene, to give a solids content of 20 percent, and was then applied to the back of an 18 02. wallpaper by a gravure sustem to produce when dry a discontinuous coating. Various weights were applied and it was found that application weights of between 2 gms/sq meter and 5 gms/sq meter resulted in a paper which when used with a cellulose type wallpaper adhesive, adhered to a wall sufficiently for normal purposes but was easily removable when necessary. The best results were achieved using an application weight of 3 gm/sq meter. Using the gravure-solvent system of this example the close tolerance which were required could be achieved and slight variations could also be achieved by adjustment of the concentrate on the machine. Such adjustment is not possible in an aqueous system because any alteration of the viscosity-concentration also alters the degree of penetration which should remain fixed to impart the desired properties to the finished sheet.

EXAMPLES 4 to 7 The materials set forth in Table 1 below were each made up as a 20 percent solution in 50/50 mixture or Acetone/Toluene and the resulting lacquers applied to the reverse side of both 18 oz. and 22 02. wallpapers by the gravure process. Application weights were varied by altering the concentration of the lacquer solutions and it was found that application weights of from 3 to 7 gm/sq meter resulted in a paper which when used with a cellulose type wallpaper adhesive (for example Polycel or Lapcel) adhered to a wall sufficiently for normal purposes but was easily removable when necessary. Application weights of below 3 gms./sq meter resulted in a paper which was not easily strippable and application weights of above 7 gms./sq. meter resulted in the paper not adhering sufficiently to the wall.

TABLE l Example N0.

Material used. Details of composition TABLE I -Continued Nitrocellulose EXAMPLES 8 and 9 The materials set forth in Table II were each applied as an aqueous system to the reverse side of both 18 oz. 20 and 22 02. wallpapers using (i) an air knife application. and (ii) a roller coating application. Various application concentrations based on the weight of dried fibers were tried and a range of 0.2 to 10.0 percent was found to result in wallpapers which when used with a cellulose 2 5 type adhesive adhered to a wall surface sufficiently for normal purposes but which were easily removable when necessary. 6 percent was found to be the optimum concentration with type PP/ZR and 1.5 percent with type MAS but actual figures depend on quality of Mystolene usedAll percentages are solid contents.

TABLE n bereceived only on the raised portions of the surface.

- sive to be used by the paper-hanger.

Example Material used Details of composition No.

8 Mystolene PP/ZR A wax-aluminium-protein rosin complex in water.

An acid dispersion of metallic salts, oxides and mineral and synthetic waxes in water. Solids content minimum 21%.

9 Mystelene MAS In all the foregoing examples it may be desirable to heat the treated sheetmaterial to dry or cure the treating substances, prior to rolling or otherwise storing the sheet material. 1

For example where a contact coating method is used on a comparatively rough surface the dispersion may According to a first preferred embodiment of the present invention there is provided a method of manufacturing a dry-strippable wall covering from a fibrous sheet material comprising treating the surface fibers of the fibrous sheet material with a freely flowing aqueous dispersion including paraffin waxes having melting points falling within the temperature range of 45- 60C,

anatural wood rosin,

dimerized animal glue as emulsion stabilizer,

aluminum formate,

the ratio by weight of said paraffin waxes to rosin being 1:2, and

subjecting the so treated backing material to a curing process wherein the treated surface of the fibrous sheet material attains a temperature of from 60 to C, which process insures that the residual moisture content of the fibrous sheet material is from 8 to 10 percent.

According to a second preferred embodiment of the present invention, there is provided a method of manufacturing a dry-strippable wall covering from a fibrous sheet material comprising treating the surface fibers of the fibrous sheet material with a freely flowing aqueous dispersion including paraffin waxes having melting points falling within the temperature range of 45- 60C,

, a natural wood rosin,

dimerized animal glue as emulsion stabilizer. aluminum formate, the ratio by weight of said paraffin being 9:1, and

subjecting the so treated backing material to a curing process wherein-the treated surface of the fibrous sheet material attains. a temperature of from 60 to 80C, which process insures that the residual moisture content of the fibrous sheet material is from 8 to 10 percent.

With the above and other objects and examples in view, the present invention will be clearly understood in connection with the accompanying drawings, in which: i

FIG. 1 illustrates diagrammatically one method, according to the present invention, of treating a flexible sheet material to render it more readily strippable; and

waxes to rosin FIG. 2 illustrates diagramatically a second method according to the present invention.

Referring now to the drawings, and more particularly to FIG. 1, plain paper is unwound from a storage reel 10 and is passed over guide andsupport rollers 12 to a treating station 14, where it is passed between a nip formed by an engraved roller 16, .and a backing roller 18. The roller 16, which has an engraved pattern of micro-dots thereon, rotates with a lower portion thereof in a reservoir 20 of substance, e.g., Ixan S.G.A. to be applied to the paper. The engraved rollerl6 picks up the substance in the cavities thereof, excess substance being removed by a doctor blade 22. Additional sub- Ill stance is stored in a tank 24 and is continuously circulated between the reservoir 20 and the tank 24 through

conduits

26 and 28, by means of a pump 30. After being treated, the paper is passed through a drying chamber 32, in which the temperature is preferably above 60C and is ideally at approximately 80C. After drying, the treated paper is passed around

coolling rollers

34, 36 and is then wound on a take-up reel 38. Drive for the paper may be supplied by rollers 40, 42 which form a nip drive.

Referring now to FIG. 2, plain paper is again drawn from a storage reel 10 and is passed over rollers 12 to a treating station 14. At the treating station l4 a plain application roller 44 rotates with its lower portion in a reservoir of the treating substance, for example Mystolene PP/2R and PP/W. The roller 44 picks up the treat ing substance on its surface. The substance is applied to the paper as it comes in contact with the paper sur face of the roller 44. The paper is then passed over a backing roller 46, while an air knife doctor 48 removes any excess of the treating substance from the paper, the excess being led back to the reservoir. The paper is then passed over a vacuum belt 50 and through a drying chamber 32.

The remainder of the treatment, including the temperature with the drying chamber 32, is as described in connection with FIG. 1, like reference characters being used to denote like elements shown in FIG. 1.

In the curing or heating process it is desirable that the surface of the treated fibrous sheet attains a temperature of at least 60C and preferably 80C. It is essential, however, that the temperature is at least several degrees, preferable more than lC, above the melting point of the waxes present in the dispersion. During the curing process all the moisture must not be driven from the material and the finished moisture content must lie within the range 5 percent to 12 percent and preferably within the range 8 percent to 10 percent.

The speed at which the material is passed through the dryer depends upon the dryer temperature. It has been found that the above conditions can be obtained with a sheet flow-through speed of approximately 400 ft/min with an air temperature of 150C and a web bulb temperature of at least 80C. The above quoted speed is i only approximate however, and must be regulated to maintain the desired finished moisture content. The approximate treatment time is l min.

In certain types of dryers it has been found necessary to introduce steam in order to maintain the wet bulb temperature above 80C.

After curing the treated sheet material is wound onto a take-up reel 26, drive for the material being supplied by drive rollers 28 and 30.

Referring now to FIG. 2 there are shown a plurality of fibers randomly arranged on the surface of a sheet of fibrous material. A plurality of zones are defined between the fibers and within the confines of some of the zones discrete particles of cured MYSTOLENE can be seen.

It will be appreciated from FIG. 2 that the treatment is not a coating but more a surface fiber treatment analogous to paper sizing (e.g., internal rosin sizing).

The treated surface has a controlled water repellency and would typically have a 3 minute COBB value of 15.

perature of 60C. Curing was effected for approxi- (BSS 2644 I955, TAPPI standard PT 15 1954). The treated surface allows a subsequently applied aqueous adhesive controlled adhesion to the fibrous surface. In

practice the controlled water repellency of the treated surface means that the surface has controlled wettability with respect to the aqueous adhesive.

The dispersions may generally be applied to the fibrous sheet material from 3 gm/sq. meter to 9 gm/sq. meter. The optimum concentration being an application weight to average 5 gm/sq. meter of cured dispersion using Mystolene type PP/2R although as previously mentioned the quality of the fibrous sheet material affects these figures in some degree.

Any type of aqueous based wall-covering adhesive for example, a cellulose-type adhesive may be used. Adhesives which have been found to be of particular use are, SOLVITE, POLYCELL or LAPCELL (Registered Trade Marks). POLYCELL is a mixture of carboxy methyl cellulose and methyl cellulose; the others are of similar compositions.

The effect of the treatment of the invention is to render the cohesive strength of the bond between the treated surface and'the adhesive weaker than the cohesive strength of the fibrous sheet material. A strip of wall-covering thus may be readily drystripped from the wall, either as a complete strip or in several large sectrons.

It has been found that the pre-surface size pressed paper can advantageously be used with the method of the invention. The pre-surface sizing can conveniently be applied on a size press of a paper making machine. Advantageously the fibrous web produced on the paper-making is sized at an approximate moisture content of 15 percent, typically with a starch size.

By pre-surface sizing the fibrous material less of the relatively expensive dispersion may be used since the size pressing holds the dispersion on the surface of and discourages penetration thereof into the fibrous material. Alternatively the same weight of the material applied would give an increased strippability relative to an unsized fibrous sheet. Since it is only the surface dispersion which is effective, the pre-surface sizing re duces or prevents any of the expensive dispersion penetrating beyond the surface of the fibrous material.

The freely flowing aqueous dispersion used includes paraffin waxes having melting points falling within the temperature range of 45 60C, a natural wood rosin, an acid protein colloid stabilizer as emulsion stabilizer and aluminum salt of a low molecular weight aliphatic carboxylic acid, the ratio by weight of said paraffin waxes to rosin being from 10:1 to 1:4.

The invention will now be further described with reference to the following specific examples. Application weights and application concentrations given in the following examples are weights or concentrations of the complex, which reduces the susceptibility of the surface to adhere, retained on the surface being treated.

EXAMPLE 10 The material set out in Table III was applied, as a freely flowing aqueous dispersion, to the reverse side of a 20 inch wide strip of fibrous sheet material by air knife coating. The treated sheet was then passed into a multi-chamber tunnel dryer having an air temperature of about 150C and a wet bulb temperature of C. The surface of the sheet material attained a temmately 1 minute and the final moisture content of the sheet material was 8 percent.

TABLE III Example Material used Details of composition No.

l MYSTOLENE An aqueous dispersion including PP/2R paraffin waxes having melting points falling within the temperature range of 4560C a natural wood rosin. dimerized animal glue as emulsion stabilizer and aluminium formate, The ratio by weight of the paraffin waxes to rosin is 1:2

EXAMPLE 1 l The material set out in Table IV was applied as a freely flowing aqueous dispersion to the reverse side of a 20 inch wide strip of wall covering having a fibrous backing surface. The treated sheet was then'cured under the conditions specified in Example 10.

paraffin waxes having melting points falling within the temperature range of 45-60C, a natural wood rosin, dimerized animal glue as emulsion stabilizer and aluminium acetate. The ratio by weight of the paraffin waxes to rosin was 9:1.

After curing, the treated surface was coated with SOLVITE (Registered Trade Mark) a commercially available water-based, cellulose-type adhesive, and the wall covering applied to a wall. After the adhesive had been allowed to' dry, the wall covering was drystripped, in a single piece, from the wall by a force of 1,000 gm applied evenly across the 20 inch wide wall covering. It will be appreciated that by varying. the strength of the dispersion or by varying the strength of the adhesive, the force required to dry-strip the material fromthe wall may be controlled. It has been found desirable to make the force required greater than 500gm/20 inch width of paper and preferably not more 1,000 gm/20 inch width. Below 500 gm the bond holding the wall covering to the wall is too weak for practical purposes and above 1,000 gm the bond is of such a strength that weak papers may not be removed from the wall in a single piece. Clearly if a stronger wall cov-' ering is used, such as a vinyl coated covering, the bond between the wall covering and wall may be increased.

lt will be readily apparent to those skilled in the art that various modifications or alterations may be effected to the invention set forth herein without departing from the spirit and scope of the invention as set forth in the appended claims.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense. I

I claim:

l. A readily strippable wall covering comprising a wall covering sheet including a fibrous backing surface, coated with the dried residue of an aqueous dispersion comprising a wax-a]uminum-protein-rosin complex in water disposed on said fibrous backing surface in the form of a plurality of discontinuous portions incompletely covering said fibrous backing surface being adapted to receive a water-based adhesive such that the adhesive can be directly applied against said fibrous backing surface between said discontinuous portions, said wax being a paraffin wax having a melting point in the range between 45C. and C., the aluminum component being an aluminum salt of a low molecular weight aliphatic carboxylic acid, the protein being an acid protein colloid and said rosin being a natural wood rosin, the ratio by weight of said paraffin wax to said rosin being from 10:1 to 1:4,

the amount of said material applied to said fibrous backing surface being within the range 2 gm/sq. meter to '12 gm/sq. meter to partially reduce a direct bonding between said adhesive and said fibrous backing surface, and the residual moisture content of the fibrous sheet material being from 5 to 12 percent. 2. A readilystrippable wall covering according to claiml wherein the amount of said complex applied to said range 3 to 7 gm/sq meter to partially reduce a direct bonding between said adhesive and fibrous backing surface.

3. The wall covering of claim 1 wherein said waxaluminum-protein-rosin complex comprises paraffin waxes having melting points falling within the temperature range of 45 to 60C,

a natural wood rosin,

an acid protein colloid as emulsion stabilizer,

an aluminum salt of range molecular weight aliphatic carboxylic acid,

the ratio by weight of said paraffin waxes to resin being from 10:1 to 1:4,

said wall covering having a residual moisture content of the fibrous sheet material from 5 to 12 percent.

4. The wall covering of claim 3 having a residual moisture content of the fibroussheet material from 8 to 10 percent.

5. The wall covering of claim 3, wherein the amount of said complex on said fibrous backing averages 5 gm/sq meter.

6. The wall covering of claim 3, wherein said acid protein colloid is dimerized animal glue.

7. The wall covering of claim 3, wherein said parafiin waxes used have an oil content of less than 2 percent by weight.

8. The wall covering of claim 3, wherein said fibrous backing surface contains a sizing means for the latter disposed between the latter and'said wax-aluminum-protein-rosin complex.

9. The wall covering of claim 1 wherein said waxaluminum-protein-rosin-complex comprises paraffin waxes having melting points falling within the temperature range of 45 to 60C a natural wood rosin,

dimerized animal glue as emulsionstabilizer, aluminum formate,

the ratio by weight of said paraffin waxes to resin being 1:2,

said wall covering having a residual moisture content of the fibrous sheet material from 8 to 10 percent.

10. The wall covering of claim 9, wherein the amount of said complex on said wall covering averaging 5 gm/sq meter.

11. The wall covering of claim 9,

wherein the backing surface of said fibrous sheet material contains a sizing material.

13. The wall covering of claim 12, wherein the amount of said complex on said wall covering averages

Claims

1. A READILY STRIPPABLE WALL COVERING COMPRISING A WALL COVERING SHEET INCLUDING A FIBROUS BACKING SURFACE COATED WITH THE DRIED RESIDUE OF AN AQUEOUS DISPERSION COMPRISING A WAX-ALUMINUM-PROTEIN-RESIN COMPLEX IN WATER DISPOSED ON SAID FIBROUS BACKING SURFACE IN THE FORM OF A PLURALITY OF DISCONTINUOUS PORTIONS INCOMPLETELY COVERING SAID FIBROUS BACKING SURFACE BEING ADAPTED TO RECEIVE A WATERBASED ADHESIVE SUCH THAT THE ADHESIVE CAN BE DIRECTLY APPLIED AGAINST SAID FIBROUS BACKING SURFACE BETWEEN SAID DISCONTINUOUS PORTIONS, SAID WAX BEING A PARAFFIN WAX HAVING A MELTING POINT IN THE RANGE BETWEEN 45*C. AND 60*C., THE ALUMINUM COMPONENT BEING AN ALUMINUM SALT OF A LOW MOLECULAR WEIGHT ALIPHATIC CARBOXYLIC ACID, THE PROTEIN BEING AN ACID PROTEIN COLLOID AND SAID ROSIN BEING A NATURAL WOOD ROSIN, THE RATIO BY WEIGHT OF SAID PARAFFIN WAX TO SAID ROSIN BEING FROM 10:1 TO 1:4, THE AMOUNT OF SAID MATERIAL APPLIED TO SAID FIBROUS BACKING SURFACE BEING WITHIN THE RANGE 2 GM/SQ. METER TO 12 GM/SQ. METER TO PARTIALLY REDUCE A DIRECT BONDING BETWEEN SAID ADHESIVE AND SAID FIBROUS BACKING SURFACE, AND THE RESIDUAL MOISTURE CONTENT OF THE FIBROUS SHEET MATERIAL BEING FROM 5 TO 12 PERCENT.

2. A readily-strippable wall covering according to claim 1 wherein the amount of said complex applied to said fibrous backing surface being within the range 3 to 7 gm/sq meter to partially reduce a direct bonding between said adhesive and fibrous backing surface.

3. The wall covering of claim 1 wherein said wax-aluminum-protein-rosin complex comprises paraffin waxes having melting points falling within the temperature range of 45* to 60*C, a natural wood rosin, an acid protein colloid as emulsion stabilizer, an aluminum salt of range molecular weight aliphatic carboxylic acid, the ratio by weight of said paraffin waxes to resin being from 10:1 to 1:4, said wall covering having a residual moisture content of the fibrous sheet material from 5 to 12 percent.

4. The wall covering of claim 3 having a residual moisture content of the fibrous sheet material from 8 to 10 percent.

7. The wall covering of claim 3, wherein said paraffin waxes used have an oil content of less than 2 percent by weight.

8. The wall covering of claim 3, wherein said fibrous backing surface contains a sizing means for the latter disposed between the latter and said wax-aluminum-protein-rosin complex.

9. The wall covering of claim 1 wherein said wax-aluminum-protein-rosin complex comprises paraffin waxes having melting points falling within the temperature range of 45* to 60*C a natural wood rosin, dimerized animal glue as emulsion stabilizer, aluminum formate, the ratio by weight of said paraffin waxes to resin being 1:2, said wall covering having a residual moisture content of the fibrous sheet material from 8 to 10 percent.

11. The wall covering of claim 9, wherein the backing surface of said fibrous sheet material contains a sizing material.

12. The wall covering of claim 1 wherein said wax-aluminum-protein-rosin complex comprises paraffin waxes having melting points falling within the temperature range of 45* to 60*C, a natural wood rosin, a dimerized animal glue as emulsion stabilizer, aluminum formate, the ratio by weight of said paraffin waxes to resin being 9:1, said wall covering having a residual moisture content of the fibrous sheet material from 8 to 10 percent.

13. The wall covering of claim 12, wherein the amount of said complex on said wall covering averages 5 gm/sq meter.