GB2079630A - Improvements in and relating to removable wallpaper - Google Patents

Abstract

Self-stripping wallpaper has over its rear face a substantially continuous coated film of at least one polymeric material selected from vinyl and vinylidene polymers, polyamides polychloroprene and celluloric derivatives at a coating weight of 2-10g/m<2>, the paper or, in the case of a laminated construction, the rear layer thereof, having far its fibre conent 0 - 50% by weight of synthetic thermoplastic polymer the fibres of which when present are at least partially welded together, the balance being cellulosic fibre. The fibre may include e.g. kaolin filler. The polymeric material of the coating not itself being a wallpaper adhesive, is desirably cured or cross-linked; this condition may be arrived at during the welding together of any thermplastic fibre content.

Description

SPECIFICATION Improvements in and relating to removable wallpaper The present invention relates to removable wallpaper, i.e. to wallpaper having the characteristic of being easily detachable from the wall to which it is bonded, without the necessity of scraping, either with or without a preliminary wetting of the paper. Detaching may easily be carried out manually, and in the dry state, by simple lifting of an edge of the paper in question and by pulling with a force of a few tens of grams/cm.

Current techniques for producing removable wallpaper consist essentially in suitably treating the surface to be stuck to the wall so as to avoid strong adhesion; or in manufacturing two-layer paper in order to achieve easy separation between the printed outer layer and the inner layer which remains adherent to the wall, so leaving the wall ready for a new application; or in manufacturing two-layer or multilayer paper characterized by the rear-most layer, intended for adhesion to the wall, containing synthetic fibres welded together, in amounts generally comprised between 50 and 90% of the fibre content of the layer.

The pretreatment of the surface to be bonded to the wall is generally expensive due to the labour and the materials required, while the use of two-layer papers, separable from each other, does not represent a complete solution of the problem of removability of the wallpaper since, after a few successive applications, it is necessary in any case to remove the accumulated deposit from the wall by means of an expensive manual scraping operation.

Even the use of synthetic fibres in multi-layer papers, concentrated in high amounts in the wall-contacting layer, does not represent a good solution since, after the welding together of the thermoplastic fibres, the adhesion of the layer containing them to the superimposed layer becomes so low that, during stripping, breakages with separation of the layers from each other are very frequent.

It is an object of the present invention to provide wallpaper which is cleanly and easily removable from a wall surface, characterized in that it consists of, or comprises, as a layer intended for adhesion to the wall, a sheet of cellulosic fibres, optionally blended with thermoplastic fibres at least partially thermowelded to one another, and in that it contains, on the surface intended for adhesion, a coating in the form of a substantially continuous film prepared from a polymeric material as described more specifically hereinafter.

Such wallpaper may be of the 'single-layer' type, i.e. of the type consisting of only one sheet of homogeneous composition, or it may be of the 'multi-layer' type, i.e. of the type consisting of two or more sheets laying one upon the other and of different composition.

Preferably, the sheet constituting such single-layer paper, or, in the case of multi-layer paper, the sheet that constitutes the layer intended for adhesion to the wall, contains up to 20% by weight of synthetic fibre composed of at least one thermoplastic polymer, calculated on the blend of such fibre with the cellulosic fibre.Amounts of such synthetic fibre up to 50% by weight may be present in such sheet; it is preferable, however, to limit the use of the higher amounts of synthetic fibre to multi-layer papers, where they are useful in the deep hot embossing of such paper, and optionally to limit such use to the sheet or layer intended for printing, while it is preferable to use, in the sheet which is intended for adhesion to the wall, amounts of synthetic thermoplastic fibre not exceeding 20%, and preferably ranging from 5 to 20% by weight referred to their blend with the cellulosic fibre.

As mentioned hereinbefore, the thermoplastic synthetic fibre contained in the single-layer paper sheet, or in the layer which is intended for the adhesion to the wall (in the case of the multi-layer paper), has the individual fibres at least partially welded to one another by thermal treatment. Such treatment may be effected by heating the sheet or the layer at a temperature at least equal to the melting temperature of the polymer constituting such fibres.

In the case of a multi-layer paper, the layer or layers which are not intended for the adhesiion to the wall may consist only of cellulose fibres, or only of synthetic fibres (whether thermoplastic or not), or of blends of such fibres in any desired ratio, such synthetic fibres optionally being welded to one another.

The polymeric material forming the coating on the paper surface intended for adhesion to the wall may be a vinyl or vinylidene polymer, a polyamide, polychloroprene or a cellulose derivative. Such polymer, at the time of coating, may or may not be in the cross-linked form, but it should be preferably in the cross-linked or cured form in the finished wallpaper.

Vinyl or vinylidene polymers suitable for forming the aforesaid coating are for example: polyvinyl alcohol, polyvinyl chloride, polystyrene, polyvinylidene chloride, polyacrylonitrile, the polymethacrylates and polyacrylates of methyl, ethyl, propyl, isopropyl, butyl and isobutyl alcohols, copolymers of the acrylates and methacrylates of methyl, ethyl, propyl, isopropyl, butyl and isobutyl alcohols with acrylonitrile, acrylic or methacrylic acid, acrylamide or mixtures thereof, and copolymers of the corresponding vinyl or vinylidene monomers with ethylene, constaining up to 50% by moles of copolymerized ethylene. Examples of derivatives of suitable cellulose are: cellulose acetate, nitrate, acetate-butyrate and xanthogenate (viscose).

The polymeric coating, which suitably has a weight of from 2 to 10 gum2, preferably from 3 to 6 gim2 can be prepared by deposition, onto the surface intended for adhesion to the wall, as an aqueous dispersion or of latex, or as a solution, in a suitable (organic) solvent, of the aforesaid polymeric material. The polymer concentration in aqueous dispersion is preferably not lower than 10% by weight, and even more preferably it ranqes from 25 to 60% by weight. The concentration of the polymer in organic solvent solution is preferably not higher than 5% by weight.

Generally, it is preferable to effect the application of the coating in a size-press, during the manufacture of the paper in continuous operation using a conventional paper machine, when the sheet leaves the first dry end at 90-100% humidity.

Such coating may also be carried out on the finished paper, before, during or after any printing operation.

When the coating is effected during a printing operation, the roller utilized for such purpose should advantageously be scored, with a suitable number of scorings per centimetre and suitable depth to allow the deposition of the desired coating.

Should the sheet or the layer intended to adhere to the wall contain thermoplastic synthetic fibres, the application of the coating is preferabltyeffected prior to the welding of the fibres. In such case, after the coating has been applied, the sheet or layer is heated at a temperature at least equal to the melting temperature of the polymer constituting the fibre. During this heating step, if the polymer constituting the coating is crosslinkable, it is possible also to procure the cross-linking of the polymer, according to the requirement for the particular type of polymer, using if appropriate specific cross-linking agents and/or catalytic systems previously added to the latex or to the polymeric solution utilised.

In the absence of thermoplastic fibres, the coating may simply be dried at a temperature generally of 90 to 1 1 5"C, or it may be brought to a higher temperature in order to achieve, if appropriate, the curing of the constituent polymer.

Though it is preferable, it is not essential that the polymer, after having been applied to the paper surface, should be cured, except in the case that it is too tacky.

Thus, the invention in one aspect consists in wallpaper comprising, at east on the side intended for adhesion to the wall, a layer of fibrous material containing 50-100% by weight of cellulosic fibre and 50-0% by weight by synthetic fibre of at least one thermoplastic polymer, the synthetic fibres being at least partially thermowelded to one another, and in which the surface intended to face the wall has a coating in the form of a substantially continuous film, weighing from 2 to 20 gum2, consisting of at least one polymeric material selected from vinyl and vinylidene polymers, polyamides, polychloropropene and cellulosic materials.

It is a further object of this invention to provide a process for making the above-defined wallpaper, comprising: (a) preparing a sheet consisting of or comprising, as a layer intended for adhesion to the wall, a layer of fibrous material of which 50-100% by weight is cellulosic and 50-0% by weight is synthetic fibrous material composed of at last one thermoplastic polymer, (b) coating the surface of such sheet or layer, which is intended for adhesion to the wall, with an aqueous emulsion or dispersion, or a solution in a suitable solvent, of at least one polymeric material selected from vinyl and vinylidene polymers, polyamides, polychloroprene and cellulosic materials, in such amounts as to obtain on such surface a substantially continuous coating of dry weight from 2 to 10 glum2, (c) drying such coating or, if such sheet or layer contains thermoplastic synthetic fibres, (d) heating such sheet or layer at a temperature at least equal to the melting temperature of the thermoplastic polymer constituting such fibres, to weld at least a part of such fibres to one another.

The preparation of the sheets, which may be single-layer or multi-layer, according to step (a), may be effected with conventional paper-making techniques, using flat table machines, or with cylindrical moulds, or with machines of the combined type, starting from aqueous dispersions of the fibrous material. Fillers, pigments, glues, resinous materials, such as, for example, urea-melamine-formaldehyde resins, and in general the additives usually employed in the making of paper may be present in such aqueous dispersions, mixed with the fibrous material, and by consequence also in the sheets so prepared.

As thermoplastic polymers constituting the synthetic fibres contained in the sheets, or- in the case of multi-layer paper, in the layers, whether or not intended for the adhesion to the wall - there may be mentioned by.way of example, olefinic polymerics particularly polyethylene, polypropylene, and ethylenepropylene copolymers; polyamides, vinyl polymers, polyester resins, acrylic polymers, polyethers, copolymers formed by the monomers corresponding to such polymers, and the mixtures of such polymers and/or copolymers. Generally, all the thermoplastic polymers capable of melting at temperatures lower than that at which substantial deterioration of the mechanical properties of cellulose occurs, are employable.

The fibres formed of such polymers or copolymers, suitable for the purposes of the present invention, may be fibres of the conventional type in the form of staple fibres, obtained by extrusion of the polymeric materials in the molten state, or by wet or dry spinning. However, it is preferable to use fibres in the form of fibrils orfibrids having a surface area of at least 1 m2/g.

Such fibrils or fibrids are well known as possible substitutes for cellulose in the making of paper or of related materials. Generally they have a length ranging from 1 to 10 mm, and a mean (apparent) diameter ranging from 1 to 500 microns. They can be prepared according to various methods, which are described, for example, in British patents Nos. 868,651; 1,287,917; 891,943; 891,945; 1,262,531; 1,355,912 and 1,355,913; in German patent applications Nos. 2,208,553 and 2,343,543; in US patents Nos. 3,770,856; 3,750,383 and 3,808,809; in Belgian patent No. 789,808; in French patent No.2,176,858, and in italian patents Nos. 997,919 and 1,030,809.

Conventional fibres of thermoplastic polymers in the form of staple fibres may be, however, utilized in admixture with cellulose and with such fibrils.

Inorganic fillers, such as, for example, kaolin, silica, titanium dioxide, talc and the like, in amounts up to 60% by weight may be present, in the incorporated state, in such fibres and fibrils.

As cellulose fibres it is possible to utilize all those conventionally employed in the paper industry for the making of paper, paperboard and similar products. Mixtures of coniferous and hardwood cellulose are preferred.

The drying step (c) is preferably effected in a continuous paper machine under conventional conditions. If synthetic fibres are present, the welding of the same and the optional cross-linking of the polymer or copolymer film applied to the surface intended for the adhesion to the wall may be carried out by raising the temperature up to a suitable value by means of radiant heating panels immediately before glazing (if effected). In the absence of synthetic fibres or fibrils, the optional thermal cross-linking of the polymer or copolymer of the coating may be carried out by suitably raising the temperature of the drying rollers.

The wallpapers forming the object of the present invention are generally subjected to embossing processes, which suitably are effected directly in the printing machine, when the papers in question do not contain thermoplastic fibres, or after the printing operation, in embossing machines of the kind generally 'used in the manufacture of vinyl wallpapers, when the presence of the synthetic fibres in such wallpapers may permit, depending on the operative thermal conditions, the procurement of more or less deep and moisture-resistant embossings. Once obtained, the wallpaper according to this invention can be made to adhere to wall surfaces by means of wallpaper adhesives generally, preferably in the form of aqueous solutions or dispersions, such as, for example, animal glues, glues based on amides or on carboxymethylcel lulose, and latices of synthetic resins, etc.

The following Examples are given to illustrate the present invention, without being however a limitation of the wider scope thereof.

Example 1 In a paper mill pulper, there were pulped together, after having been introduced in the given order: 300 kg of bleached coniferous cellulose,100 of or bleached hardwood cellulose and 100 kg of high-density polyethylene fibrils (melting temperature 135 C) having a weighted average length of 1.5 mm, a mean diameter of 16 microns and a surface area of 6 m2/g.

By means of double-disk refiners the aqueous fibre pulp, at a concentration of 3.5% by weight, was refined up to 30 Shopper-Riegel (S.R.), then treated with colophony resin (glue), with 2% by weight of titanium dioxide, and finally with aluminium sulphate to bring the pH to 5.

A preliminary glueing test revealed a Cobb value of 16 gim2 in 60 seconds. Employing such pulp and using a flat table continuous paper machine a paper was prepared, one surface of which was treated, in a size-press, with a latex of 25% by weight of a tetrapolymer composed of butyl acrylte, styrene, methylol-derivative of methacrylamide and methacrylic acid (Crilat DR-1465 produced by the Applicants).

The weight of the paper, after drying, was 140 g!m2; the weight of the polymeric coating was 3.5 g/m2. The paper was successively rotogravure printed, heated at a temperature of 145"C and embossed between water-cooled embossing rollers.

A paper removability test was carried out on a paper sample glued onto a Kraft paper sheet by means of a wallpaper paste based on carboxymethylcellulose; the force necessary to effect the detaching 72 hours after glueing was measured by means of a dynamometer. Detaching was almost complete, without tearing, and the force required was from 50 to 120 g/cm.

Example 2 The procedure of Example 1 was followed, but using a pulp containing only 5% of polyethylene fibrils. The cellulosic fibre content was increased to 95%, leaving the ratio between the cellulose types unaltered. The amount of tetrapolymer deposited on the surface was 5 gim2. Detachment from the Kraft paper was complete and the force required was 60-130 grams per linear centimeter.

Exmple 3 The preparation described in Example 1 was repeated, with the modification that the treatment in the size-press was effected by employing a latex of polyvinylidene chloride instead of the acrylic copolymer. The amount of dry polymer deposited on the surface of the wall-facing layer was 3.5 git2. The detaching force from the Kraft paper was now 100-120 grams per linear centimetre, and the detachment was complete, without tearing.

Example 4 Into a paper mill pulper there were introduced in the given order: 60 kg of bleached coniferous cellulose, 30 kg of bleached hardwood cellulose and 10 kg of high-density polyethylene fibrils similar to those of Example 1. By means of a pair of cone-shaped refiners working in series, the fibre pulp, dispersed in water at 2.5% concentration was refined up to 28 Shopper-Riegel. After addition of the aqueous solution of amide and melamine resin (glues), the pulp was diluted to 1% and discharged into a machine chest wherein it was brought to pH with aluminium sulphate. Into a similar pulper there were introduced 60 kg of bleached coniferous cellulose and 40 kg of the same high-density polyethylene containing, incorporated therein, 30% by weight of kaolin powder.After having been brought to a concentration of 2.5% in water, this fibre pulp wa.s refined hv means of a Dair of cone-shaped refiners arranged in series up to 28 Shopper-Riegel. After addition of 5% by weight of kaolin preliminarily dispersed in water, and of sodium resinate (glue), the pulp was poured into a second machine chest wherein it was diluted to 1% and brought to pH 5 with aluminium sulphate.

Using a continuous machine equipped with two round (cylindrical?) moulds, there was manufactured a two-layer paper (each layer weighing 60 glum2) and the layers were disposed so that the size-press applied acrylic polymer latex (as in Example 1) only to the surface of the layer containing 10% of polyethylene fibrils.

The weight of the coating of dry acrylic polymer so deposited was 4 g/m2.

The manufactured paper was then printed in a conventional manner on the surface of the layer containing 40% of polyethylene fibrils, whereupon it was heated to a temperature of 160"C in order to melt the fibrils and, at the same temperature, was embossed in a conventional manner.

The force required to effect detachment from the Kraft paper, measured after 96 hours from pasting as in Example 1,was 60-125 grams per centimetre; the detachment was complete and without tearing.

Example 5 Using a flat table continuous machine, a paper was manufactured which contained 45% wlw of high-density polyethylene fibrils similar to those of Example 1, but containing incorporated therein 30% of kaolin, 5% w/w of bleached wood pulp, and 50% of cellulose (bleached conifer and hardwood cellulose in a ratio of 60/40) (dry weight).

The paper, sized in the mass, contained also 5 parts of kaolin powder for 100 parts of fibre, added as external filler in admixture with the fibres. During the manufacture, the usual surface sizing in a size-press with amide resin was carried out. From the machine reel there were obtained four paper reels of reduced size, three of which were utilized for treating a surface of the respective paper with the latex of the tetrapolymer: butyl acrylate - styrene - methacrylamide - methacrylic acid as used in Example 1, but at the different concentrations set out below. The coating operation was effected with the air-blade technique under similar operative conditions for all the three papers, except for the polymer concentration of the latex.

The air blade slit was 0.2 mm and the air pressure 0.05 kg/cm2. The feed rate of the paper was 10 m/min., and the drying oven temperature 1 20"C. After drying, all four papers were heated at 145"C and then embossed in a conventional manner.The paper removability measurements were effected as described in Example 1, with the following results: Polymer Concentration Weight of the Detaching Force in the Latex Polymeric Coating from KraftPaper 1%1 film2) (g/cm) 0 0 Not measurable due to tea rings 5.87 1 Not measurable due to tearings 11.75 2 180 (no tearing) 23.50 4 90 (no tearing) Example 6 The same paper, prepared as described in Example 5, was coated on one surface in a size-press, with a latex containing 45% by weight of polymethylmethacrylate, instead of with the tetrapolymer used in such Example. The coating operation was effected by means of a T.H. Dixon Engineering machine, model 160, operating with a pressure between the rol!ers of 3.6 kg/cm, a feed rate of the paper of 20 m/min. and a drying oven temperature of 120 C. The dry weight of the coating was 3.5 g/m2. Part of the paper was then brought to a temperature of 1455C.

The results of the removability tests, carried out as described in Example 1, as well as the characteristics of the paper as such (without coating) heated at 145'C, of the paper provided with a coating but dried only at 1 20'C, and of the paper which was coated and heated to 145"C, are set out in the following Table.

Paper With Paper With Paper Coating Coating Treatment As Such Dried Treated at 120 C at 145 C Detaching force Not measur- 200 120 (g/cm) able due to tearing Cobb absorbance, at 60 seconds 15.7 10.3 7.0 (g of absorbed water) mZ mo Dennison waxes, (No.) 8 14 23 Permeability to air (Bendtsen) (cc/min.) 400 105 15 Example 7 The procedure described in Example 5 was repeated, but excluding the polyethylene fibrils and using as fibre a mixture consisting of 5% by (dry) weight of wood pulp, 57% by weight of conniferous cellulose and 38% by weight of hardwood celulose.

By carrying out a treatment outside the machine with the latex of tetrapolymer described in Example 1, an amount of 3.1 g/m2 of such tetrapolymer deposited onto the paper surface intended for the adhesion to the wall. The coating operation was conducted under the same operative conditions specified in Example 6.

Checks carried out on the paper as such, on the paper coated and dried at 1200C and on that coated and treated at 145"C gave the following results: Paper with Paper with Paper Coating Coating Treatment As Such Dried Treated at 120"C at 145"C Cobb absorbance, at 60 seconds (g/m2) 14.5 11.5 8.5 Dennison waxes (No.) 16 18 26 Permeability to air (Bendtsen) (cc/min.) 240 25 15 Detaching force from Kraftpaper(g/cm) Tearing 250 160

Claims (13)

1. Wallpaper comprising, as a layer intended for adhesion to a wall, a sheet of fibrous material containing 50-100% by weight of cel lulosic fibres and 50-0% by weight by synthetic fibres of at least one thermoplastic polymer, based on the total of these fibres, such synthetic fibres being at least partially welded to one another, the surface of said sheet being provided with a coating in the form of a substantially continuous film, weighing from 2 to 10 g/m2, comprising at least one polymeric material selected from vinyl and vinylidene polymers, polyamides, polychloroprene and cellulosic derivatives.

2. Wallpaper according to Claim 1, in which the synthetic fibres are in the form of fibrils having a surface area of at least 1 m2/g.

3. Wallpaper according to Claim 1 or 2, in which the coating has a weight ranging from 3 to 6 g/m2.

4. Wallpaper according to Claim 1,2 or 3, in which the polymeric material comprises polyvinyl alcohol, polyvinyl chloride, polystyrene, polyacrylonitrile, polymethacrylate or polyacrylate of methyl, ethyl, propyl, isopropyl, butyl or isobutyl alcohol, or a copolymer of an acrylate or methacrylate of methyl, ethyl, propyl, isopropyl, butyl or isobutyl alcohol with acrylonitrile, acrylic or methacrylic acid, acrylamide or mixtures of such monomers, or a copolymer of such acrylates or methacrylates with ethylene, containing up to 50 mole % of copolymerized ethylene.

5. Wallpaper according to any of Claims 1 to 3, in which the polymeric material comprises cellulose ar:etate nitrate. acetate-butvrate or xanthoqenate.

6. Wallpaper according to any of the foregoing Claims in which synthetic fibres in said sheet are present in an amount not exceeding 20% by weight in the blend with the cellulose fibres.

7. Wallpaper according to any foregoing claim in which the polymeic material of said coating is not rendered tacky by aplication of water.

8. Wallpaper according to Claim 1, substantially as hereinbefore exemplified.

9. Wallpaper according to any foregoing Claim, in the form of a roll 50-55 cm wide and at least 5 m long.

10. A process for manufacturing wallpaper according to Claim 1, comprising: (a) preparing a sheet comprising, as a layer intended for adhesion to a wall, fibrous material of which 50-100% by weight is cellulosic fibre and 50-0% by weight is synthetic fibre of at least one thermoplastic polymer, (b) applying to the surface of said layer an aqueous latex or dispersion, or a solution in a suitable solvent of at least one polymeric material selected from vinyl and vinylidene polymers, polyamides, polychloroprene and cellulosic derivatives, in such amount as to obtain on said surface a substantially continuous coating of 2 to 10 glum2 dry weight, and (c) drying such coating, or, if said layer contains thermoplastic synthetic fibres, (d) heating said layer at a temperature at least equal to the melting temperature of the thermoplastic polymer constituting such fibres, to melt and weld at least a part of such fibres to one another.

11. A process according to Claim 10, in which the aqueous latex or dispersion has a polymer concentration not lower than 10% by weight.

12. A process according to Claim 11, in which the aqueous latex or dispersion has a polymer concentration ranging from 25 to 60% by weight.

13. A process for manufacturing wallpaper according to Claim 10, substantially as hereinbefore exemplified.