WALLPAPER
United States Patent 3620366
This invention provides a wallpaper having a decorative surface and coated on the back surface thereof with a coating of a permanently tacky pressure sensitive adhesive, the decorative surface being coated with a protective coating of a synthetic resin. The pressure-sensitive adhesive coating and the synthetic resin are so chosen that the protective coating of the synthetic resin on the decorative surface acts as a release coat for the adhesive. 7 Claims, No Drawings
US Patent References:
Method of removably mounting sheet material
Johnson - February 1939 - 2147817
Wallpaper roll
Yates et al. - August 1945 - 2383637
Color-changing pressure-sensitive adhesive indicator tapes
Crone et al. - February 1963 - 3078182
Self-adhesive decorative surface covering material
Silman - April 1964 - 3130113
Acrylate-polystyrene pressure sensitive adhesive tape
Webber - March 1967 - 3307963
Method of removably mounting sheet material
Johnson - February 1939 - 2147817
Wallpaper roll
Yates et al. - August 1945 - 2383637
Color-changing pressure-sensitive adhesive indicator tapes
Crone et al. - February 1963 - 3078182
Self-adhesive decorative surface covering material
Silman - April 1964 - 3130113
Acrylate-polystyrene pressure sensitive adhesive tape
Webber - March 1967 - 3307963
Inventors:
Norman, Parkinson (Coventry, GB2)
Christine Mary, Blakely Easton (nr. Woodbridge, GB2)
Robert Francis, Russell (Wellingborough, GB2)
Christine Mary, Blakely Easton (nr. Woodbridge, GB2)
Robert Francis, Russell (Wellingborough, GB2)
Application Number:
04/886350
Publication Date:
11/16/1971
Filing Date:
12/18/1969
View Patent Images:
Export Citation:
Assignee:
Scott Bader Company Limited (Wallaston, Wellingborough)
Primary Class:
Other Classes:
427/210, 428/343, 428/352, 427/208
International Classes:
C09J7/04; D21H27/20; D21H27/18; C09J7/04
Field of Search:
117/68.5,122P,122PF,76A 161/406,167 206/59
US Patent References:
| 3312563 | Decorative adhesive sheet material with a chlorinated vinyl polymerpolyester resin blend primer | April 1967 | Rusch | |
| 3336153 | Fire-retardant tape utilizing an intumescent coating | August 1967 | Juda | |
| 3423276 | DECORATIVE COVERING FOR DASHBOARD PANELS AND METHOD OF APPLYING SAME | January 1969 | Eckenroth | |
| 3502497 | PRESSURE-SENSITIVE ADHESIVE PRODUCT | March 1970 | Crocker | |
| 3510342 | ADHESIVE-REPELLING SURFACE COATINGS | May 1970 | Demmig et al. |
Primary Examiner:
William, Martin D.
Assistant Examiner:
Bernard, Pianalto D.
Attorney, Agent or Firm:
Jones & Lockwood
Parent Case Data:
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of our copending application Ser. No. 823,180 filed 8th May 1969 and now abandoned and entitled "Improvements in or relating to Wallpapers."
Claims:
1. A roll of wallpaper for application to a wall to be decorated, said wallpaper consisting essentially of a paper substrate weighing between about 75 grams and about 250 grams per square meter, a decorative surface on said paper substrate, a transparent flexible protective and release layer on said decorative surfaces, said layer weighing between about 10 grams and about 20 grams per square meter and comprising a synthetic resin material, and a permanently tacky pressure sensitive adhesive on the surface of said paper substrate opposite said decorative surface, said adhesive being adapted to affix said wallpaper to said wall and being present in an amount of between about 10 grams and about 40 grams per square meter, said roll including a plurality of turns of said wallpaper, the protective layer on one turn contacting the pressure-sensitive adhesive on an adjacent turn, and the protective layer on said one turn being readily separable from the pressure-sensitive adhesive on said adjacent turn, whereby said roll may be unrolled with delamination of said wallpaper.
2. A roll of wallpaper according to claim 1, in which said synthetic resin material comprises the residue obtained by drying an emulsion of copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers, acrylic ester copolymers, copolymers of styrene and butadiene, copolymers of styrene and acrylonitrile, or copolymers of styrene and methyl methacrylate.
3. A roll of wallpaper according to claim 1, in which said protective and release layer comprises a synthetic polymer or copolymer having a minimum film-forming temperature below about 20° C. in admixture with a release agent of natural waxes, synthetic waxes or silicones.
4. A roll of wallpaper according to claim 3, in which said protective and release layer comprises a copolymer of about 50 percent by weight of styrene and about 50 percent by weight of butyl acrylate in admixture with a silicone material.
5. A roll of wallpaper according to claim 1, in which said protective layer comprises a copolymer of between about 60 percent and about 75 percent by weight of vinylidene chloride and between about 40 percent and about 25 percent by weight of ethyl acrylate, and in which said permanently tacky pressure-sensitive adhesive comprises a copolymer of 2-ethylhexyl acrylate and methyl methacrylate containing at least 80 percent by weight of 2-ethyl hexyl acrylate, the weight of said adhesive on said opposite surface lying in the range of from about 14 to about 19 grams per square meter.
6. A roll of wallpaper according to claim 1, wherein said pressure-sensitive adhesive comprises the residue obtained by an emulsion of natural and synthetic rubbers, polyisobutylene, polyvinyl alkyl ethers, vinyl acetate copolymers, acrylic ester polymers or acrylic ester copolymers.
7. A roll of wallpaper according to claim 1, in which said protective coating comprises a first layer of a synthetic resin material on said paper substrate, said synthetic resin material being copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers, acrylic ester copolymers, copolymers of styrene and butadiene, copolymers of styrene and acrylonitrile or copolymers of styrene and methyl methacrylate, and a second layer on said first layer of a release agent of natural waxes, synthetic waxes or silicones, the coating weight of said release agent lying in the range of between about 1 gram and about 5 grams per square meter.
2. A roll of wallpaper according to claim 1, in which said synthetic resin material comprises the residue obtained by drying an emulsion of copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers, acrylic ester copolymers, copolymers of styrene and butadiene, copolymers of styrene and acrylonitrile, or copolymers of styrene and methyl methacrylate.
3. A roll of wallpaper according to claim 1, in which said protective and release layer comprises a synthetic polymer or copolymer having a minimum film-forming temperature below about 20° C. in admixture with a release agent of natural waxes, synthetic waxes or silicones.
4. A roll of wallpaper according to claim 3, in which said protective and release layer comprises a copolymer of about 50 percent by weight of styrene and about 50 percent by weight of butyl acrylate in admixture with a silicone material.
5. A roll of wallpaper according to claim 1, in which said protective layer comprises a copolymer of between about 60 percent and about 75 percent by weight of vinylidene chloride and between about 40 percent and about 25 percent by weight of ethyl acrylate, and in which said permanently tacky pressure-sensitive adhesive comprises a copolymer of 2-ethylhexyl acrylate and methyl methacrylate containing at least 80 percent by weight of 2-ethyl hexyl acrylate, the weight of said adhesive on said opposite surface lying in the range of from about 14 to about 19 grams per square meter.
6. A roll of wallpaper according to claim 1, wherein said pressure-sensitive adhesive comprises the residue obtained by an emulsion of natural and synthetic rubbers, polyisobutylene, polyvinyl alkyl ethers, vinyl acetate copolymers, acrylic ester polymers or acrylic ester copolymers.
7. A roll of wallpaper according to claim 1, in which said protective coating comprises a first layer of a synthetic resin material on said paper substrate, said synthetic resin material being copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers, acrylic ester copolymers, copolymers of styrene and butadiene, copolymers of styrene and acrylonitrile or copolymers of styrene and methyl methacrylate, and a second layer on said first layer of a release agent of natural waxes, synthetic waxes or silicones, the coating weight of said release agent lying in the range of between about 1 gram and about 5 grams per square meter.
Description:
This invention relates to wallpaper.
Wallpaper is normally adhered to walls with an aqueous paste of a water soluble cellulosic material, such as carboxy methyl cellulose. This paste has first to be made from the dry powder and is then brushed on to the back of strips of paper, which are then placed in position on the wall. This process is both time consuming and also requires considerable dexterity to prevent damage to the wet paper whilst being applied to the wall. One modification of this method is to apply the adhesive to the paper in the manufacturing stage so that it can be reactivated by wetting with water, but this does not obviate the need for wetting out and handling large sheets of wet wallpaper.
In addition to the above application problems with conventional wallpaper it is also difficult to remove old paper from walls prior to redecorating. This is usually done by wetting the paper with water, to soften the adhesive, and then scraping the paper from the wall. In the case of paper coated with a protective plastic covering the latter may be made so that it can be removed first by stripping off as a sheet to enable the water to wet out the paper. An alternative method is to prepare wallpaper using easily delaminatable base paper, which may be made on a twin wire paper machine. Here the print and ground coat of the old paper may then be peeled from the wall leaving a thin layer of the base paper which is a suitable base on to which the new paper may be applied. Such paper, is however, difficult to produce and is expensive.
It is an object of the invention to provide a wallpaper which will not require pasting before applying to a wall and which will not require scraping from the wall when it is desired to redecorate.
According to one aspect of the present invention we provide a wallpaper comprising a paper substrate having a decorative surface and coated on the back surface thereof with a coating of a permanently tacky pressure-sensitive adhesive, the decorative surface being coated with a protective coating of a synthetic resin, the pressure-sensitive adhesive coating and the synthetic resin coating being so chosen that the protective coating of synthetic resin on the decorative surface acts as a release coat for the adhesive.
According to another aspect of the present invention we provide a process for the manufacture of wallpaper which comprises coating a paper substrate having a decorative surface on the decorative surface with a synthetic resin and then coating the back surface of the paper with a pressure-sensitive adhesive, the pressure-sensitive adhesive coating and the synthetic resin coating being so chosen that, in the finished wallpaper, the coating of synthetic resin on the decorative surface acts as a release coat for the adhesive. In a particularly preferred process one or both of the coatings are applied by means of the air knife doctor technique.
The purpose of the pressure-sensitive adhesive is to enable the paper to be stuck to the wall and yet to permit removal of the paper by merely pulling the paper from the wall. Although the coating of pressure-sensitive adhesive should be such as to provide an adhesive to wall bond of sufficient strength for the paper to remain in position without spontaneous peeling for the useful life of the wallpaper, yet the adhesive strength of the adhesive to wall bond should not be greater than either the cohesive strength of the adhesive or the adhesive to paper bond, and these, in turn, should preferably not be greater than either the laminar or tear strength of the paper. The object of these requirements is to ensure that the paper can be removed from the wall before redecoration without delaminating or tearing, and to leave as little adhesive as possible on the wall. However, it is also necessary that, after the wallpaper has been reeled up after manufacture but before use, the adhesive layer should not pull off any of the printed surface of the paper or transfer onto that surface upon unreeling, thus the force necessary to separate on unreeling should be less than the forces necessary to cause delamination of the coating on the printed paper or for pulling away of the ground and print coats from the base paper.
These properties may be achieved by using a variety of combinations of protective coatings, which we shall sometimes hereinafter refer to as supercoats, and adhesives. For instance the supercoat may be obtained from emulsions of the following types: emulsion copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers or copolymers and copolymers of butadiene with styrene, acrylonitrile or methyl methacrylate. Suitable acrylic esters include the alkyl acrylates and methacrylates, such as methyl acrylate, ethyl acrylate, propyl acrylate, iso-propyl acrylate, butyl acrylate, t-butyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethyl hexyl acrylate, decyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and the like. The vinylidene chloride/acrylic ester copolymers may contain up to 75 percent by weight of vinylidene chloride; thus copolymers of 60 to 75 percent by weight of vinylidene chloride and 25 to 40 percent by weight of ethyl acrylate and especially a copolymer of 70 percent vinylidene chloride and 30 percent ethyl acrylate in emulsion form are useful. Such vinylidene chloride copolymers have a minimum film-forming temperature greater than room temperature (i.e. greater than 20° C.) and exhibit a glass transition temperature of at least 25° C. Similarly emulsion copolymers of styrene and one or more acrylic esters, for example a copolymer containing 40 to 60 percent by weight of styrene and 40 to 60 percent by weight of butyl acrylate can also be used. A preferred copolymer emulsion is a copolymer of equal parts by weight of styrene and butyl acrylate. In such styrene/acrylic ester copolymers, the greater the styrene content the greater the proportion of long chain alkyl ester that is necessary in the acrylic ester component in order to provide the desirable value for the minimum film-forming temperature of greater than 20° C. As an example of another copolymer that we may use we may mention a copolymer of 60-40 percent by weight of methyl methacrylate and 40-60 percent by weight of ethyl acrylate. A release agent such as a wax or silicone emulsion, may be added to the polymer or copolymer emulsion, particularly when the minimum film-forming temperature of the polymer or copolymer is less than about 20° C. In an alternative procedure the decorative surface may be given a first coating of one of the polymers or copolymers described above and then this first coating (after drying) may be given a lightweight coating of a release agent such as a wax or silicone emulsion. Typically the lightweight coating may be applied so as to give a coating weight of between about 1 and about 5 grams per square meter, for example 2 grams per square meter. In addition there may be used for the supercoat certain mixtures of synthetic emulsions with other materials such as are described in our U.K. Pat. No. 1,157,040 which discloses a transparent coating composition for application to a base material of wallpaper to give a matt finish comprising a synthetic polymer, capable of giving a transparent flexible nonblocking film, in the form of an emulsion or latex, said polymer being present in an amount of the total dry weight content of between 45 and 95 percent, a polysaccaride which is only partially soluble in cold water in an amount of between 1 and 40 percent of the total dry weight content and a mineral filler in an amount of between 1 and 30 percent of the total dry weight content. A typical synthetic polymer emulsion for use in the transparent coating composition of our U.K. Pat. No. 1,157,040 is a polyvinyl acetate emulsion at 55 percent solids content plasticized to give 10 percent of plasticizer on polymer weight the plasticizer being di-iso-butyl phthalate.
The coating weight of the supercoat needed to provide the desired properties in the end products may vary from paper to paper, but it is essential to apply sufficient to form a continuous coating on the decorative surface which is substantially free of "pinholes." Generally speaking satisfactory results can be obtained on nonembossed papers using coating weights of between about 10 and 20 grams per square meter for this protective supercoat. Also, higher coating weights may be needed for a supercoat on an embossed paper than for a paper that is only printed even though made from the same paper substrate.
The permanently tacky pressure-sensitive material may be any material which will give adequate adhesion to the wall and yet will permit both easy unreeling of the rolls and removal of the paper from walls by peeling. Materials which may be used include synthetic and natural rubbers (usually compounded with a tackifying resin), polyisobutylene, polyvinyl alkyl ethers and vinyl acetate copolymers and acrylic ester polymers and copolymers thereof. These adhesives may be applied in the form of solvent based solutions or emulsions though clearly the use of the emulsion form is advantageous due to the cost and fire hazards associated with the use of solvents.
The preferred adhesive is an acrylic ester polymer or copolymer emulsion because of the superior resistance to degradation and consequent freedom from changes in adhesive properties on ageing. Typical emulsions suitable for use to obtain in the adhesive coating include emulsions of copolymers of 2-ethyl-hexyl acrylate and/or heptyl acrylate and methyl methacrylate containing at least 80 percent (and preferably at least 90 percent) by weight of 2-ethyl-hexyl acrylate and/or heptyl acrylate and of copolymers of vinyl acetate and 2-ethyl-hexyl acrylate and/or heptyl acrylate containing 30 to 95 percent by weight of the acrylic ester.
The paper used for the substrates may be composed of bound fibers of many substances in sheet form. While the most common paper used is made from mechanical pulp, or groundwood, that made from chemical pulp may also be used but, where greater strength is required, these fibers may be partly or wholly replaced with stronger fibers made from materials such as are used for making textiles. Such fibers may be derived from regenerated cellulose, e.g. rayon or cellulose acetate, may be entirely synthetic in nature, e.g. polyamide and polyester fibers, or they may be inorganic fibers such as glass. An alternative method to obtain greater strength is to impregnate paper with resins such as styrene-butadiene or acrylic ester copolymer emulsions. Generally speaking papers suitable for the manufacture of wallpaper weigh between 75 and 250 grams per square meter.
The paper substrate is printed or otherwise decorated, for example by embossing so as to provide a decorative surface.
It cannot be overemphasized that the correct balance of properties, as described previously, must be obtained for each combination of paper, supercoat and adhesive, and it does not necessarily follow that any supercoat of the types mentioned will combine with every one of the described adhesives to produce wallpaper meeting the requirement of this invention. Moreover, the amount of adhesive applied will have a profound influence on both the adherence of the paper to the wall and the tendency of the adhesive to pull away the printed surface of the wallpaper on unreeling. Generally speaking we have found that satisfactory results are obtained with adhesive coating weights of between about 10 and about 40 grams of adhesive per square meter, and especially between about 15 and about 30 grams per square meter. The amount needed will depend on the paper substrate used, an embossed paper generally requiring a greater coating weight of adhesive than an unembossed paper.
The invention is illustrated by the following examples in which parts are by weight.
EXAMPLE 1
A roll of printed wallpaper made using as a substrate a paper derived from mechanical pulp or groundwood weighing 77 grams per square meter and known in the trade as Common Stainers was coated on the printed surface with a resin emulsion containing 50 percent solids of a copolymer of 70 weight percent vinylidene chloride and 30 weight percent ethyl acrylate using the air knife doctor technique and dried in a tunnel dryer at 100° C. The coating weight of this supercoat was found to be 16 grams per square meter.
The paper was then coated on its other or back surface with an adhesive consisting of a 50 percent solids synthetic resin emulsion of a copolymer containing 95 percent 2-ethyl hexyl acrylate and 5 percent methyl methacrylate at a variety of coating weights using the same coating and drying techniques as described above in the preceding paragraph.
Paper was coated with 12, 14, 19, 25 and 30 grams per square meter of dry adhesive. Each sample was reeled up and part of each unreeled and applied to a wall.
After storing the remainders of the samples under their own weight for a period of four weeks they were unreeled. The reels coated with 12, 14 and 19 grams per square meter unwound very easily, the one coated with 25 grams per square meter showed some resistance to unwinding but the printed surface was not damaged and the one having the highest coating weight (i.e., 30 grams per square meter) showed slight damage to the printed surface, caused by the supercoat sticking to the adhesive. Of the samples of paper applied to walls the adhesion of the one coated with 12 grams per square meter of adhesive was clearly inadequate whereas the others were all adequately stuck and were easy to peel off after remaining in position for 6 months. The example shows that, using the paper, resins and conditions described the optimum coating weight for the permanently tacky pressure sensitive adhesive of the example is around 14-19 grams per square meter.
EXAMPLE 2
The same paper as was used in example (I) was coated on the printed side, using the same method as described in that example with a resin emulsion containing 50 percent solids of a copolymer of equal parts by weight of butyl acrylate and styrene. Before coating, this emulsion had added to it a silicone release system consisting of a mixture of 9 parts of Midland Silicones MS2218 silicone dispersion and 1.8 parts of Midland Silicones N2250 catalyst; this mixture was added to 100 parts of the styrene/butyl acrylate copolymer dispersion. The coating weight applied was 15 grams per square meter. According to the manufacturers' literature, Midland Silicone MS2218 silicone dispersion is a 40 percent solids aqueous dispersion of silicone material whilst Midland Silicones N2250 catalyst contains 20 percent active material.
The paper was then coated on its other or back surface with a 50 percent solids synthetic resin emulsion containing 95 percent 2-ethyl hexyl acrylate and 5 percent methyl methacrylate using the same coating and drying method as was used for the coating on the printed side.
Using this system it was found that paper coated with around 15 grams per square meter of dry adhesive both gave adequate adhesion to a wall and yet was easy to peel off after remaining in position for 6 months and moreover could be unreeled without damaging the printed surface after standing stacked in rolls for a period of 4 weeks.
EXAMPLE 3
Wallpaper was prepared and tested exactly as described in example (2) except that in this case the pressure-sensitive adhesive coating used on the back surface was obtained from a 50 percent solids copolymer emulsion containing 90 percent 2-ethyl-hexyl acrylate and 10 percent of methyl methacrylate. In this case it was found that in order to obtain satisfactory adhesion of the paper to walls it was necessary to use a coating weight of around 25 grams per square meter.
EXAMPLE 4
Wallpaper was prepared and tested exactly as in example (I) except that the synthetic resin emulsion used for the supercoat had a 50 percent solids content of a copolymer containing 85 parts of vinyl acetate and 15 parts of 2-ethyl-hexyl acrylate. It was found that satisfactory adhesion and release properties were obtained with an adhesive coating weight of around 15 grams per square meter.
EXAMPLE 5
A roll of printed wallpaper, the paper substrate of which contained 70 percent rayon fibers and 30 percent groundwood, and weighed 100 grams per square meter was coated and tested exactly as in example (2) with the same supercoat and adhesive emulsion systems on the printed surface and the back surface respectively. The amount of adhesive required to obtain adequate adhesion and unreeling properties was again around 20 grams per square meter. This paper was exceptionally strong making stripping from walls even more easy than with other examples described in this specification.
EXAMPLE 6
Wallpaper was prepared and tested as described in example (2) except that in this case the pressure-sensitive adhesive coating used on the back surface was obtained from a 50 percent solids copolymer emulsion containing 65 percent 2-ethyl-hexyl acrylate and 35 percent of vinyl acetate. In this case it was found that in order to obtain both satisfactory adhesion of the paper to wall and unreeling properties, it was necessary to use a coating weight of around 30 grams per square meter.
EXAMPLE 7
The same wallpaper that was used in example (1) was coated on the printed side with the same mixture of the styrene/butyl acrylate copolymer and silicone release system that was used for the supercoat in example (2) under the same conditions.
A solution having a solids content of 20 percent was prepared by dissolving 80 parts by weight of a high molecular weight polyvinyl isobutyl ether, 20 parts by weight of a low molecular weight polyvinyl isobutyl ether and 5 parts by weight of ester gum in a sufficient amount of a mixture of equal parts by weight of acetone and toluene. This solution was then applied to the back surface of the wallpaper by the air knife doctor technique and dried at 100° C. The coating weight of the dried adhesive was found to be 25 grams adhesive per square meter. The product showed satisfactory adhesion and release properties.
EXAMPLE 8
A solution was prepared by dissolving 100 parts by weight of milled pale crepe rubber, 75 parts by weight of poly-β-pinene resin (m.p. 70° C.), 5 parts by weight of petroleum oil and 2 parts by weight of polymerized trimethyldihydroquinoline in sufficient solvent naphtha to give a solids content of 20 percent. The same wallpaper that was used in example (1) was given a protective coating on the printed side in the same way as in example (7). The back surface of the wallpaper was then coated with the rubber solution described above by the air knife doctor technique and then dried at 140° C. The coating weight for the adhesive coating was found to be 35 grams per square meter. The adhesion of the paper to wall surfaces and the unreeling properties were satisfactory.
Wallpaper is normally adhered to walls with an aqueous paste of a water soluble cellulosic material, such as carboxy methyl cellulose. This paste has first to be made from the dry powder and is then brushed on to the back of strips of paper, which are then placed in position on the wall. This process is both time consuming and also requires considerable dexterity to prevent damage to the wet paper whilst being applied to the wall. One modification of this method is to apply the adhesive to the paper in the manufacturing stage so that it can be reactivated by wetting with water, but this does not obviate the need for wetting out and handling large sheets of wet wallpaper.
In addition to the above application problems with conventional wallpaper it is also difficult to remove old paper from walls prior to redecorating. This is usually done by wetting the paper with water, to soften the adhesive, and then scraping the paper from the wall. In the case of paper coated with a protective plastic covering the latter may be made so that it can be removed first by stripping off as a sheet to enable the water to wet out the paper. An alternative method is to prepare wallpaper using easily delaminatable base paper, which may be made on a twin wire paper machine. Here the print and ground coat of the old paper may then be peeled from the wall leaving a thin layer of the base paper which is a suitable base on to which the new paper may be applied. Such paper, is however, difficult to produce and is expensive.
It is an object of the invention to provide a wallpaper which will not require pasting before applying to a wall and which will not require scraping from the wall when it is desired to redecorate.
According to one aspect of the present invention we provide a wallpaper comprising a paper substrate having a decorative surface and coated on the back surface thereof with a coating of a permanently tacky pressure-sensitive adhesive, the decorative surface being coated with a protective coating of a synthetic resin, the pressure-sensitive adhesive coating and the synthetic resin coating being so chosen that the protective coating of synthetic resin on the decorative surface acts as a release coat for the adhesive.
According to another aspect of the present invention we provide a process for the manufacture of wallpaper which comprises coating a paper substrate having a decorative surface on the decorative surface with a synthetic resin and then coating the back surface of the paper with a pressure-sensitive adhesive, the pressure-sensitive adhesive coating and the synthetic resin coating being so chosen that, in the finished wallpaper, the coating of synthetic resin on the decorative surface acts as a release coat for the adhesive. In a particularly preferred process one or both of the coatings are applied by means of the air knife doctor technique.
The purpose of the pressure-sensitive adhesive is to enable the paper to be stuck to the wall and yet to permit removal of the paper by merely pulling the paper from the wall. Although the coating of pressure-sensitive adhesive should be such as to provide an adhesive to wall bond of sufficient strength for the paper to remain in position without spontaneous peeling for the useful life of the wallpaper, yet the adhesive strength of the adhesive to wall bond should not be greater than either the cohesive strength of the adhesive or the adhesive to paper bond, and these, in turn, should preferably not be greater than either the laminar or tear strength of the paper. The object of these requirements is to ensure that the paper can be removed from the wall before redecoration without delaminating or tearing, and to leave as little adhesive as possible on the wall. However, it is also necessary that, after the wallpaper has been reeled up after manufacture but before use, the adhesive layer should not pull off any of the printed surface of the paper or transfer onto that surface upon unreeling, thus the force necessary to separate on unreeling should be less than the forces necessary to cause delamination of the coating on the printed paper or for pulling away of the ground and print coats from the base paper.
These properties may be achieved by using a variety of combinations of protective coatings, which we shall sometimes hereinafter refer to as supercoats, and adhesives. For instance the supercoat may be obtained from emulsions of the following types: emulsion copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticized polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers or copolymers and copolymers of butadiene with styrene, acrylonitrile or methyl methacrylate. Suitable acrylic esters include the alkyl acrylates and methacrylates, such as methyl acrylate, ethyl acrylate, propyl acrylate, iso-propyl acrylate, butyl acrylate, t-butyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethyl hexyl acrylate, decyl acrylate, dodecyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and the like. The vinylidene chloride/acrylic ester copolymers may contain up to 75 percent by weight of vinylidene chloride; thus copolymers of 60 to 75 percent by weight of vinylidene chloride and 25 to 40 percent by weight of ethyl acrylate and especially a copolymer of 70 percent vinylidene chloride and 30 percent ethyl acrylate in emulsion form are useful. Such vinylidene chloride copolymers have a minimum film-forming temperature greater than room temperature (i.e. greater than 20° C.) and exhibit a glass transition temperature of at least 25° C. Similarly emulsion copolymers of styrene and one or more acrylic esters, for example a copolymer containing 40 to 60 percent by weight of styrene and 40 to 60 percent by weight of butyl acrylate can also be used. A preferred copolymer emulsion is a copolymer of equal parts by weight of styrene and butyl acrylate. In such styrene/acrylic ester copolymers, the greater the styrene content the greater the proportion of long chain alkyl ester that is necessary in the acrylic ester component in order to provide the desirable value for the minimum film-forming temperature of greater than 20° C. As an example of another copolymer that we may use we may mention a copolymer of 60-40 percent by weight of methyl methacrylate and 40-60 percent by weight of ethyl acrylate. A release agent such as a wax or silicone emulsion, may be added to the polymer or copolymer emulsion, particularly when the minimum film-forming temperature of the polymer or copolymer is less than about 20° C. In an alternative procedure the decorative surface may be given a first coating of one of the polymers or copolymers described above and then this first coating (after drying) may be given a lightweight coating of a release agent such as a wax or silicone emulsion. Typically the lightweight coating may be applied so as to give a coating weight of between about 1 and about 5 grams per square meter, for example 2 grams per square meter. In addition there may be used for the supercoat certain mixtures of synthetic emulsions with other materials such as are described in our U.K. Pat. No. 1,157,040 which discloses a transparent coating composition for application to a base material of wallpaper to give a matt finish comprising a synthetic polymer, capable of giving a transparent flexible nonblocking film, in the form of an emulsion or latex, said polymer being present in an amount of the total dry weight content of between 45 and 95 percent, a polysaccaride which is only partially soluble in cold water in an amount of between 1 and 40 percent of the total dry weight content and a mineral filler in an amount of between 1 and 30 percent of the total dry weight content. A typical synthetic polymer emulsion for use in the transparent coating composition of our U.K. Pat. No. 1,157,040 is a polyvinyl acetate emulsion at 55 percent solids content plasticized to give 10 percent of plasticizer on polymer weight the plasticizer being di-iso-butyl phthalate.
The coating weight of the supercoat needed to provide the desired properties in the end products may vary from paper to paper, but it is essential to apply sufficient to form a continuous coating on the decorative surface which is substantially free of "pinholes." Generally speaking satisfactory results can be obtained on nonembossed papers using coating weights of between about 10 and 20 grams per square meter for this protective supercoat. Also, higher coating weights may be needed for a supercoat on an embossed paper than for a paper that is only printed even though made from the same paper substrate.
The permanently tacky pressure-sensitive material may be any material which will give adequate adhesion to the wall and yet will permit both easy unreeling of the rolls and removal of the paper from walls by peeling. Materials which may be used include synthetic and natural rubbers (usually compounded with a tackifying resin), polyisobutylene, polyvinyl alkyl ethers and vinyl acetate copolymers and acrylic ester polymers and copolymers thereof. These adhesives may be applied in the form of solvent based solutions or emulsions though clearly the use of the emulsion form is advantageous due to the cost and fire hazards associated with the use of solvents.
The preferred adhesive is an acrylic ester polymer or copolymer emulsion because of the superior resistance to degradation and consequent freedom from changes in adhesive properties on ageing. Typical emulsions suitable for use to obtain in the adhesive coating include emulsions of copolymers of 2-ethyl-hexyl acrylate and/or heptyl acrylate and methyl methacrylate containing at least 80 percent (and preferably at least 90 percent) by weight of 2-ethyl-hexyl acrylate and/or heptyl acrylate and of copolymers of vinyl acetate and 2-ethyl-hexyl acrylate and/or heptyl acrylate containing 30 to 95 percent by weight of the acrylic ester.
The paper used for the substrates may be composed of bound fibers of many substances in sheet form. While the most common paper used is made from mechanical pulp, or groundwood, that made from chemical pulp may also be used but, where greater strength is required, these fibers may be partly or wholly replaced with stronger fibers made from materials such as are used for making textiles. Such fibers may be derived from regenerated cellulose, e.g. rayon or cellulose acetate, may be entirely synthetic in nature, e.g. polyamide and polyester fibers, or they may be inorganic fibers such as glass. An alternative method to obtain greater strength is to impregnate paper with resins such as styrene-butadiene or acrylic ester copolymer emulsions. Generally speaking papers suitable for the manufacture of wallpaper weigh between 75 and 250 grams per square meter.
The paper substrate is printed or otherwise decorated, for example by embossing so as to provide a decorative surface.
It cannot be overemphasized that the correct balance of properties, as described previously, must be obtained for each combination of paper, supercoat and adhesive, and it does not necessarily follow that any supercoat of the types mentioned will combine with every one of the described adhesives to produce wallpaper meeting the requirement of this invention. Moreover, the amount of adhesive applied will have a profound influence on both the adherence of the paper to the wall and the tendency of the adhesive to pull away the printed surface of the wallpaper on unreeling. Generally speaking we have found that satisfactory results are obtained with adhesive coating weights of between about 10 and about 40 grams of adhesive per square meter, and especially between about 15 and about 30 grams per square meter. The amount needed will depend on the paper substrate used, an embossed paper generally requiring a greater coating weight of adhesive than an unembossed paper.
The invention is illustrated by the following examples in which parts are by weight.
EXAMPLE 1
A roll of printed wallpaper made using as a substrate a paper derived from mechanical pulp or groundwood weighing 77 grams per square meter and known in the trade as Common Stainers was coated on the printed surface with a resin emulsion containing 50 percent solids of a copolymer of 70 weight percent vinylidene chloride and 30 weight percent ethyl acrylate using the air knife doctor technique and dried in a tunnel dryer at 100° C. The coating weight of this supercoat was found to be 16 grams per square meter.
The paper was then coated on its other or back surface with an adhesive consisting of a 50 percent solids synthetic resin emulsion of a copolymer containing 95 percent 2-ethyl hexyl acrylate and 5 percent methyl methacrylate at a variety of coating weights using the same coating and drying techniques as described above in the preceding paragraph.
Paper was coated with 12, 14, 19, 25 and 30 grams per square meter of dry adhesive. Each sample was reeled up and part of each unreeled and applied to a wall.
After storing the remainders of the samples under their own weight for a period of four weeks they were unreeled. The reels coated with 12, 14 and 19 grams per square meter unwound very easily, the one coated with 25 grams per square meter showed some resistance to unwinding but the printed surface was not damaged and the one having the highest coating weight (i.e., 30 grams per square meter) showed slight damage to the printed surface, caused by the supercoat sticking to the adhesive. Of the samples of paper applied to walls the adhesion of the one coated with 12 grams per square meter of adhesive was clearly inadequate whereas the others were all adequately stuck and were easy to peel off after remaining in position for 6 months. The example shows that, using the paper, resins and conditions described the optimum coating weight for the permanently tacky pressure sensitive adhesive of the example is around 14-19 grams per square meter.
EXAMPLE 2
The same paper as was used in example (I) was coated on the printed side, using the same method as described in that example with a resin emulsion containing 50 percent solids of a copolymer of equal parts by weight of butyl acrylate and styrene. Before coating, this emulsion had added to it a silicone release system consisting of a mixture of 9 parts of Midland Silicones MS2218 silicone dispersion and 1.8 parts of Midland Silicones N2250 catalyst; this mixture was added to 100 parts of the styrene/butyl acrylate copolymer dispersion. The coating weight applied was 15 grams per square meter. According to the manufacturers' literature, Midland Silicone MS2218 silicone dispersion is a 40 percent solids aqueous dispersion of silicone material whilst Midland Silicones N2250 catalyst contains 20 percent active material.
The paper was then coated on its other or back surface with a 50 percent solids synthetic resin emulsion containing 95 percent 2-ethyl hexyl acrylate and 5 percent methyl methacrylate using the same coating and drying method as was used for the coating on the printed side.
Using this system it was found that paper coated with around 15 grams per square meter of dry adhesive both gave adequate adhesion to a wall and yet was easy to peel off after remaining in position for 6 months and moreover could be unreeled without damaging the printed surface after standing stacked in rolls for a period of 4 weeks.
EXAMPLE 3
Wallpaper was prepared and tested exactly as described in example (2) except that in this case the pressure-sensitive adhesive coating used on the back surface was obtained from a 50 percent solids copolymer emulsion containing 90 percent 2-ethyl-hexyl acrylate and 10 percent of methyl methacrylate. In this case it was found that in order to obtain satisfactory adhesion of the paper to walls it was necessary to use a coating weight of around 25 grams per square meter.
EXAMPLE 4
Wallpaper was prepared and tested exactly as in example (I) except that the synthetic resin emulsion used for the supercoat had a 50 percent solids content of a copolymer containing 85 parts of vinyl acetate and 15 parts of 2-ethyl-hexyl acrylate. It was found that satisfactory adhesion and release properties were obtained with an adhesive coating weight of around 15 grams per square meter.
EXAMPLE 5
A roll of printed wallpaper, the paper substrate of which contained 70 percent rayon fibers and 30 percent groundwood, and weighed 100 grams per square meter was coated and tested exactly as in example (2) with the same supercoat and adhesive emulsion systems on the printed surface and the back surface respectively. The amount of adhesive required to obtain adequate adhesion and unreeling properties was again around 20 grams per square meter. This paper was exceptionally strong making stripping from walls even more easy than with other examples described in this specification.
EXAMPLE 6
Wallpaper was prepared and tested as described in example (2) except that in this case the pressure-sensitive adhesive coating used on the back surface was obtained from a 50 percent solids copolymer emulsion containing 65 percent 2-ethyl-hexyl acrylate and 35 percent of vinyl acetate. In this case it was found that in order to obtain both satisfactory adhesion of the paper to wall and unreeling properties, it was necessary to use a coating weight of around 30 grams per square meter.
EXAMPLE 7
The same wallpaper that was used in example (1) was coated on the printed side with the same mixture of the styrene/butyl acrylate copolymer and silicone release system that was used for the supercoat in example (2) under the same conditions.
A solution having a solids content of 20 percent was prepared by dissolving 80 parts by weight of a high molecular weight polyvinyl isobutyl ether, 20 parts by weight of a low molecular weight polyvinyl isobutyl ether and 5 parts by weight of ester gum in a sufficient amount of a mixture of equal parts by weight of acetone and toluene. This solution was then applied to the back surface of the wallpaper by the air knife doctor technique and dried at 100° C. The coating weight of the dried adhesive was found to be 25 grams adhesive per square meter. The product showed satisfactory adhesion and release properties.
EXAMPLE 8
A solution was prepared by dissolving 100 parts by weight of milled pale crepe rubber, 75 parts by weight of poly-β-pinene resin (m.p. 70° C.), 5 parts by weight of petroleum oil and 2 parts by weight of polymerized trimethyldihydroquinoline in sufficient solvent naphtha to give a solids content of 20 percent. The same wallpaper that was used in example (1) was given a protective coating on the printed side in the same way as in example (7). The back surface of the wallpaper was then coated with the rubber solution described above by the air knife doctor technique and then dried at 140° C. The coating weight for the adhesive coating was found to be 35 grams per square meter. The adhesion of the paper to wall surfaces and the unreeling properties were satisfactory.