Mayland, Calum (89 Gateside Avenue, Haddington, East Lothian EH41 3JE, GB)
| 1. | A display sheet material that is intended to be affixed to a surface, which sheet material comprises a display face and a substrate layer, characterised in that the substrate layer comprises a fibrous web material that comprises a synthetic resin binder that comprises a polymer that comprises polymerized units derived from a monomer having low solubility in water. |
| 2. | A display sheet material according to Claim 1 in which the monomer having low solubility in water is selected from a, ßethylenically unsaturated compounds. |
| 3. | A display sheet material according to claim 1 or 2 in which the monomer having low solubility in water comprises a C12C30 hydrocarbyl chain. |
| 4. | A display sheet material according to claim 3 in which the monomer having low solubility in water comprises a C12C30 alkyl or alkenyl ester of acrylic or methacrylic acid. |
| 5. | A display sheet material according to any of claims 1 to 4 in which the monomer having low solubility in water is selected from primary alkenes, styrene, alkylsubstituted styrenes, vinyl esters of C4C30 carboxylic acids, vinyl halides, vinylidene halides, Nalkylsubstituted (meth) acrylamides, vinyl C3C3oalkyl ethers, vinyl aryl ethers, C1C30 alkyl esters of (meth) acrylic acid, C2C30alkenyl esters of (meth) acrylic acid, unsaturated vinyl esters of (meth) acrylic acid, multifunctional monomers, monomers derived from cholesterol, and mixtures of two or more monomers from the aforesaid compounds. |
| 6. | A display sheet material according to any of claims 1 to 5 in which the monomer having low solubility is selected from styrene, amethyl styrene, vinyl toluene, vinyl 2ethyl hexanoate, vinyl neodecanoate, vinyl chloride, vinylidene chloride, Noctyl acryamide, Noctyl maleic acid amide, stearyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2ethylhexyl (meth) acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, oleyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, pentaerythritol triacrylate and mixtures of two or more of the aforesaid compounds. |
| 7. | A display sheet material according to any of claims 1 to 6 in which the said polymer is a copolymer that comprises, in addition to the units derived from a monomer having low water solubility, units derived from a monomer having high solubility in water. |
| 8. | A display sheet material according to claim 7 in which the monomer having high solubility in water is selected from a, ßmonoethylenically unsaturated monomers containing at least one carboxylic acid group. |
| 9. | A display sheet material according to claim 8 in which the monomer having high solubility in water is selected from acrylic acid, methacrylic acid, acryloxypropionic acid, methacryloxypropionic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, monoalkyl maleates, monoalkyl fumarates, monoalkyl itaconates, acid substituted (meth) acrylates, sulfoethyl methacrylate, acid substituted (meth) acrylamides, basic substituted (meth) acrylates, basic substituted (meth) acrylamides, acrylonitrile, (meth) acrylamide, substituted (meth) acrylamide, (meth) acrolein, CiC8 alkyl (meth) acrylates and mixtures of two or more of the aforesaid compounds. |
| 10. | A display sheet material according to claim 3 or 4 in which the polymer is a copolymer that also comprises units derived from a C1C6 alkyl acrylate or methacrylate or from styrene. |
| 11. | A display sheet material according to claim 1 in which the polymer is a styreneacrylic copolymer. |
| 12. | A display sheet material according to any of claims 1 to 11 in which the fibrous web material comprises cellulose fibres. |
| 13. | A display sheet material according to claim 12, in which the cellulose fibres are wood pulp fibres, vegetable pulp fibres or a mixture thereof. |
| 14. | A display sheet material according to any of claims 1 to 13 in which the fibrous web material comprises cellulose fibres and synthetic fibres. |
| 15. | A display sheet material according to claim 14, in which the fibrous web material is a nonwoven web material. |
| 16. | A display sheet material according to claim 14, being a wallcovering material that comprises a decorative face and a substrate layer, characterised in that the substrate layer comprises a nonwoven web material that comprises cellulosic fibres, synthetic fibres and a synthetic resin binder that comprises a polymer that comprises polymerized units derived from a monomer having low solubility in water. |
| 17. | A display sheet material according to claim 14,15 or 16, which the fibrous web material comprises from 5 to 50% synthetic fibre, relative to the weight of total fibre content of said nonwoven web material. |
| 18. | A display sheet material according to claim 17 in which the fibrous web material contains from 10 to 35% synthetic fibre, relative to the weight of total fibre content of the said nonwoven material. |
| 19. | A display sheet material according to any of claims 1 to 14, in which the fibrous web material comprises 95100% cellulosic fibre, by weight of total fibre content, the balance, if any, being synthetic fibre. |
| 20. | A display sheet material according to any of claims 14 to 19, in which the synthetic fibre is polyester. |
| 21. | A display sheet material according to any of claims 1 to 20 in which the binder constitutes from 8 to 20% by weight of the said nonwoven web material in the finished product. |
| 22. | A display sheet material according to any of claims 1 to 21, in which the said fibrous web material has been made by a process wherein a synthetic resin binder is applied in the form of a water emulsion to a fibrous web material, wherein the said binder comprises a polymer that contains units derived from a monomer having low solubility in water. |
| 23. | A display sheet material according to any of claims 1 to 22 in which the said polymer is hydrophobic. |
| 24. | A display sheet material according to any of claims 1 to 23, wherein the display face is produced by printing, painting, embossing, coating, laminating or a combination of two or more such methods. |
| 25. | A display sheet according to any of claims 1 to 23, wherein the display face is produced by applying to a surface of the fibrous web material a vinyl or polyolefin layer, which vinyl or polyolefin layer bears the display face. |
| 26. | A display sheet material according to any of claims 1 to 23, in which the display face is produced by applying to a surface of the fibrous web material a glass fibre scrim or a textile fabric. |
| 27. | A display sheet material according to any of claims 1 to 26, wherein the display face is produced by printing and/or by embossing. |
| 28. | A process for the production of a display sheet material that is intended to be affixed to a surface, which process comprises applying a display face to a surface of a substrate, wherein the substrate comprises a fibrous web material that comprises a synthetic resin binder, wherein the said binder comprises a polymer that contains polymerised units derived from a monomer having low solubility in water. |
| 29. | A process according to claim 28, directed to the production of a display sheet material according to any of claims 2 to 27. |
| 30. | The use, in or as a sheet material that is intended to be affixed to a surface, of a fibrous web material that comprises a synthetic resin binder that comprises a polymer that comprises polymerized units derived from a monomer having low solubility in water. |
| 31. | The use according to claim 30 wherein the fibrous web material is as defined in any of claims 2 to 27. |
Background to the invention Traditional decorative wallcoverings (often called wallpapers) have utilized paper, nonwovens and sometimes textiles as the substrate web, which could be printed or coated to provide the decorative face.
A particular disadvantage of all such wallcoverings is the need to remove an old wallcovering before a new one can be applied. Traditional printed paper wallcoverings can be quite easily, if messily, removed by the application of water, which is readily absorbed into the paper and then softens the water-based adhesive so that the paper can be pulled or, if necessary, scraped off the wall.
With the advent of plastics-coated products, for example, the"Vinyls"or foam- coated materials, water can no longer penetrate the wallcovering so that stripping becomes difficult and even with the use of special stripping equipment is still seen as a major problem. In fact the need to strip old wallcoverings from the wall during redecoration is considered to be one of the main reasons why paint is still the preferred wall decoration material. Over the years, various wallcover base webs have been developed in an attempt to resolve the problem of stripping the wallcovering from the wall. These wallcoverings have generally been in one of two classes: pelable or strippable.
The pelable wallcovering is one in which a layer of the wallcovering is left behind
on the wall and this layer can serve as a surface to which the new covering is attached or paint applied. Essentially, the structure of the pelable wallcovering is such that it can be readily delaminated. US-A-4 101 359 (Faillot) describes such a construction. Two-phase wetlaid webs can also be made to be pelable if, during the web forming operation, the machine settings are controlled so as to limit the bond strength between the two phases. The disadvantages of a pelable wallcover are that, first, at some stage the layer (s) that have been left behind on the wall will have to be removed to provide a new, sound base and, second, if the peeling is imperfect then the layer that is intended to be left behind may need to be repaired or patched.
A preferred solution would be a fully strippable wallcovering in which the old wallcovering can be removed in its entirety without the application of water (or other solvents) and without the need to scrape material off the wall with the possibility of damaging the wall.
The creation of a strippable wallcovering has usually entailed the treatment of the substrate layer in such a way as to reduce the adhesion of the substrate to the wall in a controlled manner, so that, in the stripping process, the wall to substrate bond is easily broken but there is no tendency for the wallcovering to detach from the wall in other circumstances. An example of a material that is claimed to have strippability is disclosed in US-A-3 840 428 (Ring and Sheehey) according to which a wet-laid web containing melamine resins, which are added to the stock prior to formation, is treated with an acrylic/acetate synthetic latex. This results, it is suggested, in a melamine resin/latex reaction product in the form of a non- continuous film within the substrate that, in part, inhibits the penetration of the hanging adhesive into the product. The disadvantage of this material resides in the use of the melamine resins, which necessitates the use of acid conditions in the wet part of the wet lay machines that can lead to corrosion and environmental impact issues. Further, formaldehyde is an active component in the melamine resins and this material is best avoided in building materials because of the possible risks of long-term exposure to formaldehyde.
Another example of a strippable wallcover backing is disclosed in EP-A-0 118 221 (The Dexter Corporation). In this, the wallcover backing is treated with a fluorochemical (FC) complex that acts as an adhesive penetration inhibitor. This can be an effective material with low-strength adhesives and such FC-containing products are quite common but usually are only recommended for use with certain adhesives. There are issues with the use of the FC materials and other similar materials cited in this prior-art document, owing to excessive emission of volatile organic compounds during the impregnation process. The FC treatment is also quite costly.
Strippability would be a useful property not only of wallcoverings but also of other sheet materials, e. g. bills, posters, notices or placards, that are intended to be affixed to a surface, e. g. a surface of a panel, wall, fence, partition or billboard.
Summary of the invention.
In a first aspect, the present invention provides a fibrous web material for use as or in a sheet material that is intended to be affixed to a surface, which web material comprises a synthetic resin binder, wherein the said binder comprises a polymer that contains polymerized units derived from a monomer having low solubility in water. In general, such a polymer is hydrophobic. The expression"fibrous web material"includes papers and nonwoven web materials.
In a second aspect, the present invention provides a process for the manufacture of a fibrous web material for use as or in a sheet material that is intended to be affixed to a surface, wherein a synthetic resin binder is applied in the form of a water emulsion to a fibrous web material, wherein the said binder comprises a polymer that contains units derived from a monomer having low solubility in water.
In general, such a polymer is hydrophobic.
In a third aspect, the present invention provides a display sheet material that is intended to be affixed to a surface, being a sheet material that comprises a display face and a substrate layer, which substrate layer comprises a web material according to the first aspect of the invention or a web material produced by a
process according to the second aspect of the invention. The expression"display sheet material"includes a sheet material that is decorative and/or that presents viewable information; analogously, the expression"display face"includes a face or surface that is decorative and/or that presents viewable information. The expression"viewable information"is to be broadly construed to include, for example, pictures, text, lettering, symbols, signs and any combination thereof.
Thus, the expression"display sheet material"covers wallcoverings (including the materials often referred to as"wallpapers") and, for example, bills, notices, placards and posters (including advertising posters).
In a fourth aspect, the present invention provides a process for the manufacture of a display sheet material that is intended to be affixed to a surface, which comprises applying a display face to a surface of a substrate, wherein the said substrate comprises a web material according to the first aspect of the invention or a web material produced by the process according to the second aspect of the invention. The term"substrate"in this and similar contexts herein includes a backing or base sheet, layer, stratum or ply.
In a fifth aspect, the present invention provides the use, in or as a sheet material that is intended to be affixed to a surface, of a web material according to the first aspect of the invention or a web material produced by a process according to the second aspect of the invention.
Brief description of the Figures Figures 1-3 illustrate the strippability of various wallcoverings, including samples that are according to the present invention.
Description of exemplary embodiments.
The fibrous web material will, in general, comprise cellulose fibres. The preferred cellulose fibres are of natural origin, e. g. softwood and/or hardwood pulps, pulps derived from vegetable fibres such as abaca or sisal, or even unpulped vegetable
fibres treated so as to able to be formed into a wetlaid web. However, the cellulose content of the web may comprise man-made or regenerated cellulose fibres, e. g. rayon fibres. Mixtures of different cellulosic fibres may be used.
Although the fibre content of the fibrous web material may be entirely cellulosic, as in, for example, a 100% cellulosic paper, in certain preferred embodiments the fibre content comprises not only cellulose fibres but also other fibres, in general synthetic fibres, in particular organic synthetic fibres. In general, however, the content of cellulose fibres will not be less than 50% by weight of total fibre content; and in general the content of synthetic fibre will not be more than 50% by weight of total fibre content (and will in general constitute the balance, if any, of fibre content). Suitable synthetic fibres include polyester fibres, e. g. short cut polyester fibres. The fibre length and linear density of the polyester or other synthetic fibres should be chosen to give good web uniformity and will, typically, be in the range 5 to 20 mm and 1.0 to 6.0 denier (0.11 to 0.67 tex) respectively.
The invention thus relates, in certain preferred embodiments, to a nonwoven web of cellulosic and synthetic fibres that is treated with a synthetic resin binder, wherein the synthetic resin binder includes, as a starting material, a monomer having low water-solubility and thus has, in general, an inherently hydrophobic character. The term"nonwoven web"herein includes a manufactured sheet or other web material of directionally or randomly orientated fibres (which may be of natural and/or man-made origin and which may be staple or continuous filaments), bonded by friction and/or cohesion and/or adhesion. It includes but is not limited to nonwovens as defined according to ISO 9092: 1988 (cf. Larousse Dictionary of Science and Technology, 1995, p. 755).
The fibrous web will preferably have a synthetic fibre content from 5 to 50% by weight of total fibre content, e. g. 10 to 35%, with the balancing fibrous material being in general cellulosic, preferably wood pulp or vegetable fibres or a mixture thereof. Fibrous web materials that contain 95 to 100% cellulose fibres and 5 to 0% synthetic fibres (the percentages being by weight of the total fibre content) also
come into consideration. Such materials could be regarded as papers or synthetic-fibre-reinforced papers, as the case may be.
The fibrous web material may be produced by any suitable method, e. g. it may be wet-laid, dry-laid or spun-laid. A preferred fibrous web material is a wetlaid nonwoven and preferably comprises 18% polyester staple fibre and 82% softwood pulp.
Other constructions could be envisaged such as two-phase wet-formed webs or hydroentangled multi-layer webs comprising various combinations of wetlaid, drylaid and spunlaid webs. SMS nonwovens thus also come into consideration ("SMS"being a conventional acronym for a nonwoven composite that comprises layers of spunbonded (S), melt blown (M) and spunbonded (S) webs).
The fibrous web material will normally have a grammage of from 40 to 200 g/m2.
The synthetic resin binder comprises (for example, consists essentially of) a polymer containing units derived from a monomer having low water solubility, or a mixture of such polymers. The polymer may be selected from homopolymers and copolymers. The mixtures may comprise two or more homopolymers, two or more copolymers or at least one homopolymer and at least one copolymer. Suitable synthetic resin binders have been described in EP-A-0 710 675 (Rohm & Haas) and its counterpart United States Patent, No. 5 521 266 (Lau). Certain of the binders have also been disclosed by Johnny U and Willie Lau, "A New Class of Hydrophobic Acrylic Binders", INDEX 99 Congress. The teaching in each of those documents is incorporated herein by reference.
By low water solubility is meant a solubility in water at from 20° to 50°C of 200 millimoles/litre or less, preferably of 50 millimoles/litre or less. By high water solubility is meant a solubility in water at from 20° to 50°C of greater than 200 millimoles/litre.
In certain preferred binders, the monomer having low water solubility is selected from a, ß-ethylenically unsaturated compounds. In certain preferred binders, the monomer having low water solubility is selected from primary alkens, styrene, alkyl-substituted styrenes, vinyl esters of C4-C30 carboxylic acids, vinyl halides, vinylidene halides, N-alkyl-substituted (meth) acrylamides, vinyl C3-C3o-alkyl ethers, vinyl aryl ethers, C1-C30 alkyl esters of (meth) acrylic acid, C2-C3o-alkenyl esters of (meth) acrylic acid, unsaturated vinyl esters of (meth) acrylic acid, multifunctional monomers, monomers derived from cholesterol, and mixtures of two or more monomers from the aforesaid compounds. The expression" (meth) acrylic" is an abbreviation used herein to denote"acrylic or methacrylic". Similarly, " (meth) acrylate" denotes"acrylate or methacrylate".
Preferred monomers include styrene, a-methyl styrene, vinyl toluene, vinyl 2-ethyl hexanoate, vinyl neodecanoate, vinyl chloride, vinylidene chloride, N-octyl acryamide, N-octyl maleic acid amide, stearyl vinyl ether, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, lauryl (meth) acrylate, oleyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, pentaerythritol triacrylate and mixtures of two or more of the aforesaid compounds.
One class of preferred monomers having low water solubility are those which comprise a C12-C3o hydrocarbyl chain. Particularly preferred monomers are C12 -C30 alkyl or alkenyl esters of acrylic or methacrylic acid. Units derived from these monomers preferably constitute at least 40% by weight of the total monomeric units in the polymer (s) in the binder.
A further class of preferred binders are those which comprise a copolymer that contains, in addition to units derived from a monomer having low water solubility, units derived from a monomer having high solubility in water. The monomers having high solubility in water may be selected, typically, from a, (3- monoethylenically unsaturated monomers containing at least one carboxylic acid group. Preferred monomers that have high water solubility include acrylic acid, methacrylic acid, acryloxypropionic acid, methacryloxypropionic acid, itaconic acid,
maleic acid, maleic anhydride fumaric acid, crotonic acid, monoalkyl maleates, monoalkyl fumarates, monoalkyl itaconates, acid substituted (meth) acrylates, sulfoethyl methacrylate, acid substituted (meth) acrylamides, basic substituted (meth) acrylates, basic substituted (meth) acrylamides, acrylonitrile, (meth) acrylamide, substituted (meth) acrylamide, (meth) acrolein, C1-C8 alkyl (meth) acrylates and mixtures of two or more of the aforesaid compounds.
One class of particularly preferred binders are those based on polymers comprising a C12-C3o alkyl or alkenyl ester of acrylic or methacrylic acid, especially a lauryl, myristyl, palmityl, stearyl or oleyl ester, and also units derived from a C1-C6 alkyl or (meth) acrylate, e. g. butyl acrylate or methacrylate, or from styrene.
Certain preferred binders comprise a polymer that is sufficiently hydrophobic to give a Cobb value of 20 g/m2 or less, more preferably of 10 g/m2 or less and most preferably 5 g/m2 or less, when measured according to the Cobb test T441 om-90, Water absorptiveness, TAPPI Test Methods 1994-1995, TAPPI Press, Atlanta (1994), and/or a hydrostatic head value of at least 2 cm, more preferably at least 5 cm and most preferably at least 10 cm, when measured by the Hydrostatic Head Test, ERT 120.1-80, Nonwovens repellency, Edana Test Methods 1996. The test materials may be prepared by impregnating a carded polyester web of 33 g/m2 basis weight (grammage) with binder to 22% solids add-on based on fibre weight.
Preferred synthetic resins include certain Lipacryl and Primal products from Rohm & Haas. The method of manufacture of such resins is described in EP 0 710 675.
Binders that also come into consideration are based on styrene-acrylic copolymers e. g. such as those also available under the Primal trade mark (Rohm & Haas).
The synthetic resin binder, which is preferably applied to the formed and dried fibrous web, will preferably constitute from 8 to 20 % by weight, e. g. 12 to 18%, of the finished product. The synthetic resin is, in general, applied in the form of a
water emulsion and the treated fibrous web complex is dried. The preferred binder content is 15% of the finished product. The binder can be conveniently applied as a dilute water emulsion by spray or size press to the previously dried fibrous web.
Other additives may be included in the fibrous web material provided that they do not render it unsuitable for its intended use, e. g. use in or as a wallcovering material. A mineral filler, for example, might come into consideration if substrate opacity is to be improved. However, in many types of coated wallcovering, substrate opacity is not generally an important property.
The invention provides a wallcover substrate that can be provided with a decorative face-e. g. by coating, printing, painting, laminating, embossing or a combination of two or more such techniques-to provide a decorative wallcovering that is not restricted to the use of certain specific hanging procedures and that can be readily stripped from the wall when redecoration is required. Thus, the application of a decorative face to a surface of the fibrous web material of this invention, e. g. a nonwoven web material, may be effected in any suitable manner, e. g. by printing and/or coating, by conventional techniques including, for instance, extrusion lamination, solvent coating, water-coating or foam coating. The decorative face may bear a two-dimensional design, e. g. a repeating or random pattern of markings, or a three-dimensional design, e. g. as in a textured or embossed surface. In certain embodiments a vinyl or polyolefin layer may be applied to the fibrous web material by coating, e. g. with a vinyl plastisol, or by lamination. Other decorative facing materials that may be laminated to this substrate include other plastics materials, glassfibre scrims and fabrics, e. g. textile fabrics. The wallcovering may have a laminated or multi-layer construction, e. g. there may be one or more intermediate layers between the decorative face and the above-described substrate layer. Thus a printed design may be applied directly to the fibrous web substrate or to a layer or coating borne by the said substrate. In certain embodiments, a protective outer layer may be applied to the decorative face of the wallcovering. In other embodiments, the wallcovering substrate will be used as lining paper and a decorative face applied to it by painting.
The techniques described in the preceding paragraph may also be utilised to prepare other display sheet materials, including those that have a face which provides information instead of, or in addition to, decoration.
Advantages of the invention over the prior-art that can be achieved include the following. The wallcovering can be removed from the wall very easily no matter what conventional hanging technique has been used. (Prior-art materials are generally only strippable when specific hanging techniques or adhesives have been used. ) Analogous advantages can be achieved with other display sheet materials according to this invention. The product has a smoother surface than prior-art materials. When used as a base for foamed polymer coatings the foam is bulkier so that less polymer is required to give a given depth of foam. The environmental impact of the invention is much less than that of the prior-art materials. The wet and dry tensile strengths and dimensional stability are comparable to those achieved with conventional acrylic binders.
Examples The present invention is illustrated in and by the following examples. Percentages are by weight unless otherwise stated.
Cobb data Cobb data were determined by Cobb test T441 om-90, water absorptiveness, TAPPI Test Methods 1994-1995, TAPPI Press, Atlanta (1994).
Strippability test for wallcoverings Three test pieces, 300 mm (machine direction) by 200 mm are prepared from each sample. These are pasted to a"standard wall"which consists of a vertically mounted sheet of gypsum plasterboard.
For each test piece, a 300 mm (vertical) x 200 mm area is marked on the face surface of the plasterboard. Using a brush, the desired amount of wallpaper paste is applied as evenly as possible to the marked area (eg. about seven grams for an approximate 120g/m2 coverage of paste). The test piece is then applied to the pasted surface leaving a strip about 20 mm wide across the top of the test piece free of the surface. The test piece is then smoothed out using a blade type wallpaper applicator.
The test pieces are left on the substrate for 14 days. The test pieces are then removed from the substrate by gripping the unattached strip at the top of the sample and pulling downwards as near vertically as possible. The amount of material remaining on the"wall"is then estimated (minor residues are ignored) and expressed as a percentage of the original area pasted to the wall. This result is subtracted from 100% to give the strippability result.
Example 1 Wetlaid nonwoven webs having a nominal grammage (basis weight) of about 61 g/m2were produced from 18. 5% of 1.5 denier (0.167 tex) x 15mm polyester fibre
and 81.5% bleached softwood kraft pulp. Five different resin formulations were applied to these webs at the size press to give a final 15% resin content. Three were resins from Rohm & Haas all comprising units derived from lauryl methacrylate but with different glass transition temperatures (Tg) and crosslinking capabilities (see Table 1) and two were formulations containing Primal HA16, a commercial acrylic resin from Rohm & Haas. One of the HA16 treatments contained no other additive but the other contained 2% FC 280, a fluorochemical emulsion from the 3M company.
The self-crosslinking resin of Tg +28°C (see Table 1) was produced from the monomers lauryl methacrylate, methyl methacrylate, ethyl acrylate, butyl acrylate and styrene with the use of N-methyl acrylamide as a cross-linker. It has the commercial designation Primal (or Lipacry I TM) E-3690 (ex Rohm & Haas). The self-crosslinking resin of Tg + 12°C was produced with a lower level of styrene.
The non-self-crosslinking resin of Tg + 29°C is similar to the first resin of Tg + 28°C but without the N-methyl acrylamide.
The Cobb value results indicate the degree of water holdout (sizing) of the materials with a low number indicating a high degree of holdout. The strippability data indicate the amount of the wallcovering that could readily be removed from the wall. Two water based adhesives from Henkel were employed : Metylan TT, the stronger adhesive based on PVA and starch, and Metylan Spezial based on starch. Approximately 125g/m2 of adhesive was applied in each case.
The results are shown in Table 1. The Cobb data demonstrate the higher water holdout of the materials treated with the resins comprising units derived from lauryl methacrylate. The strippability results show that with the less demanding (weaker) adhesive, all materials performed well but with the stronger adhesive, the products containing the resins comprising units derived from lauryl methacrylate were to be preferred.
Table 1 Binder Type Tg+28°C Tg+12°C Tg+29°C HA16 HA16+ Self-Self-Not self-2% FC crosslinking crosslinking Crosslinking Grammage (g/m2) 59 60.5 64.2 60.7 60.2 Cobb value (q/m2) 3. 11 3. 04 4. 72 47. 58 8. 28 top side Cobb value (g/m2) 4.96 3.98 4.49 38.7 7.21 wire side Strippability (%) 75 60 93 5 10 Metylan# TT Strippability (%) 100 100 100 100 100 MetylanT" Spezial
Example 2 In this example, nonwoven webs with a similar fibre composition to that of Example 1 were impregnated with different amounts of the Primal# E-3690 self- crosslinking resin with a Tg of + 28°C (ref: Table 1). This resin had given good strippability and it had also been found that it gave a substrate with good dimensional stability. The hanging adhesive was MetylanT TT. The results in Table 2 show that optimum strippability was achieved at about 15% resin content.
Table 2 Grammage e (g/m2 Resin content (%) Strippability (% 111.0 7.3 65.8 58.9 11.7 95.0 66.4 15.1 100.0 122. 5 16. 9 100. 0
Example 3 A visual comparison of the strippability of various materials, including samples according to the present invention, is illustrated in Figure 1.
Figure 1 illustrates the strippability performance of a commercial PVC coated paper wallcovering using 175g/m2 of Metylan TM Spezial as the adhesive. The right- hand side of the Figure shows the residue after the wallcovering has been stripped and it can be seen that nearly all the paper substrate remains on the test wall.
Figure 2 illustrates the strippability performance of two similar nonwoven substrates with different resin treatments, again using 175g/m2 of Metylan TM Spezial as the adhesive. On the left-hand side of the Figure there are the two materials on the test wall. The upper sample is a material according to the present invention with an 18% polyester/82% softwood pulp nonwoven impregnated to give a 15% content of the Primal E-3690 resin of Example 1. The lower sample is a similar nonwoven but it has been impregnated to give a 15% content of a vinyl acetate resin (Raisiow 412) and 1% of fluorochemical. With this adhesive both materials show for practical purposes virtually 100% strippability, as can be seen from the right-hand side of the Figure.
Figure 3 shows the same wallcovering materials in the same juxtaposition as that in Figure 2. The difference is that 175g/m2 of a strong adhesive has been used (Tekfix 65, a PVA/starch adhesive from Tektura PLC). It can be seen from the right-hand side of Figure 3 that the material according to the present invention (upper sample) again demonstrates for practical purposes virtually 100% strippability. The lower sample, which is typical of the prior-art, demonstrates poor strippability.
It will, of course, be understood that the present invention has been described above purely by way of example and that modifications of detail can be made within the scope of the invention.