CA2359565A1

CA2359565A1 - Wall coverings

Info

Publication number: CA2359565A1
Application number: CA002359565A
Authority: CA
Inventors: William Britton
Original assignee: Individual
Current assignee: SPECIALITY COATINGS GROUP Ltd
Priority date: 1998-11-26
Filing date: 1999-11-25
Publication date: 2000-06-02
Also published as: EP1135447A2; WO2000031201A2; WO2000031201A3; AU1286900A

Abstract

This invention provides a self-adhesive article which is capable of being placed against a surface and repositioned or slid on that surface provided that not more than a predetermined degree of pressure is applied to the article during positioning. The article, such as a wall covering, has an adhering surface coated with an adhesive layer bearing microparticles. An optional moisture barrier layer is provided so as to inhibit the effects of water penetration into the article. A method of producing such an article is also provided.

Description

Wallcoverinas The present invention relates mainly to wallcoverings, though is applicable to other types of covering, and is concerned particularly, although not exclusively, with self-adhesive wallcoverings.
The invention is of particular relevance to wallcoverings comprising self-adhesive sheets made from a substrate, such as paper, or a layer of polyvinyl chloride (PVC) or the like bonded to a layer of paper, coated with an adhesive. Positioning such sheets on surfaces, however, is often quite difficult because the sheets cannot be moved once they initially touch the surface. The adhesive that is conventionally employed prevents such movement even after application of only minimal pressure to the sheet. This is particularly troublesome when the sheets are being used as a wallcovering, because it is difficult to ensure that each sheet is correctly positioned on a wall. In other words, such sheets are not truly repositionable once applied to a surface.
US Patent No. 3,331,729 describes an adhesive bonding product having microspheres sparsely, but uniformly, distributed over a pressure sensitive adhesive layer.
The object containing the adhesive can be positioned on the surface to be adhered to prior to pressing against the object to make a firm bond.
Similarly, US Patent No. 4,556,595 describes a pressure sensitive adhesive sheet having non-adhesive solid microparticles distributed over the surface of the adhesive layer.
Adhesive sheets made according to these patents, however, have no adhesive characteristics when initially applied to a surface. They only adhere to the surface upon application of substantial pressure, which strongly binds the sheet to the surface. The sheet cannot thereafter be repositioned. For this reason, it is very difficult for one person to align such sheets by him- or herself. Also, uniformly distributing microparticles on the surface of adhesive sheets as described in these patents is extremely difficult.
International patent application WO 98/20086, with a priority date of 8th November 1996, discloses removable articles which include a base layer having an adhering surface and a non-adhering surface; a first adhesive layer covering at least a portion of the adhering surface; and a low tack adhesive layer covering at least a portion of the base adhesive layer.
The low tack adhesive layer contains an adhesive and microparticles. Preferably, the microparticles cause the low tack adhesive layer to have a surface for adhering that is not flat. Once the article has been positioned, it can be adhered to the surface by applying sufficient pressure to fracture the microparticles and/or drive microparticles in the low tack adhesive layer into the base adhesive layer, thereby bringing adhesive in the first adhesive layer into contact with the substrate's adhering surface.
The adhesive in the first adhesive layer leaks, or viscously flows, through holes formed in the low tack layer in the spaces previously occupied by the microparticles.
International patent application W099/14041, having a priority date of 18th September 1997, discloses an article comprising: (a) a base layer having a substrate-facing surface and a non-adhering surface; (b) a continuous first adhesive layer which covers said substrate-facing surface of said base layer, said first adhesive layer having a substrate-facing surface and a base layer-facing surface and comprising a first adhesive; and (c) a second slidable spacing layer which covers and is non-removably adhered to a portion of said substrate-facing surface of said first adhesive layer, said second layer having a substrate-facing surface and a first adhesive layer-facing surface; and wherein a portion of said substrate-facing surface of said second layer extends further, as measured perpendicularly from said base layer, from said base layer than does said substrate-facing surface of said first adhesive layer.
US Patent No. 5,487,929 discloses a repositionable wall covering having a work surface covered with a tacky, discontinuous layer of pressure sensitive adhesive (PSA). A pattern of projections without adhesive having a height greater than or equal to the thickness of the adhesive is provided.within the discontinuities. After the wall covering is placed in the desired location, increased pressure on the decorative side of the wall covering causes deformation of the decorative sheet and/or sufficient compression of the projections to cause a significant area of the PSA to contact the wall surface to provide final adhesion. The discontinuities in the adhesive layer enable reduced surface contact between the PSA layer and the wall to provide temporary adhesion until a quantity of pressure is applied sufficient to deform the wall covering so a greater surface area of the PSA
makes contact with the surface of application.
US Patent No. 5,639,539 discloses a releasable wallcovering and method of manufacture. The wall covering has a reinforcing substrate or backing layer with a surfacing layer formed of a polymer coating overlying a front surface of the backing layer. A
layer of printing is applied to the surfacing layer, and a transparent top coat layer extends substantially over the entire printed area. A PSA layer underlies a rear surface of the backing layer to secure the wall covering to the wall, while allowing it to be repositionable upon installation and releasable after extended use. The pressure sensitive layer contains tacky polymeric microspheres to facilitate easy release of the wallcovering from the wall surface.
According to a first aspect of the present invention, there is provided an article including: a substrate having an adhering surface and a non-adhering surface; at least a portion of said adhering surface being covered by adhesive, substantially evenly distributed thereon, said adhesive being provided with substantially inelastic, frangible microparticles each having a diameter which falls within a given range of diameters, the range being defined inclusively between a lower limit and an upper limit; wherein the thickness of the adhesive at its thinnest point is not greater than the upper limit of the range of microparticle diameters.
The substrate may be, for example, a sheet, mirror panel, lightweight artificial brick, panel, tile, picture, poster, sticker, wall hanging, decorative applique, appliance panel, cabinet finish, insulation panel, billboard, display or any other article which can be adhered to a surface. The main field of use envisaged for the present invention is in interior decorating, and preferred articles therefore include wallcoverings, wall trim and shelf or drawer liners.
Accordingly, the invention is hereinbelow described with particular relevance to these particular articles, but is not intended necessarily to be limited thereto.
An optional layer of printing may be applied over the non-adhering surface of the substrate.

Alternatively or in addition, an optional release layer of_ silicone or other suitable material may be applied over the non-adhering surface or over the layer of printing. The release layer is useful where the article, after manufacture, is wound into rolls, e.g.
if the article is a length of wallcovering. The release layer reduces the likelihood of adhesion between the non-adhering surface of the substrate and the adhering surface when the article is rolled up on itself .
The substrate may be made. of paper, cloth, tape, foil, laminate, synthetic materials or any other suitable material. For wallcoverings, a paper/PVC
laminate (known in the art as a 'vinyl sheet') having PVC as one surface and paper as another opposite surface is particularly preferred, although cloth-backed vinyl may also be used. Generally, the PVC
surface forms the non-adhering surface and the paper surface the adhering surface, although in some embodiments the surfaces may be reversed.
Alternatively, it is envisaged that the substrate may be a synthetic paper such as calendered polypropylene or the like, which has the advantage of being inherently moisture resistant.
The adhesive layer contains adhesive that exhibits high adhesion. Preferably, it exhibits a tack of greater than about 10 6 kg/m2 (lOg/cm2) and less than about.l0 9 kg/mz (1000g/cm2), and in some embodiments from about 10 5 kg/m2 (100g/cmz) to about 3 x 10 5 kg/m 2 (300g/cm2) .
The adhesive is preferably capable of strongly adhering the substrate to the surface to be adhered to. As diluted in the layer, the adhesive preferably exhibits a peel value greater than about 87.5 N/m (0.5 pounds per lineal inch) more preferably greater than about 175 N/m (1.0 pounds per lineal inch), and most preferably WO 00!31201 PCT/GB99/03943 greater than about 350 N/m (2.0 pounds per lineal inch). The adhesive can be removable, for example, by peeling without any treatment. The adhesive can also be a "non-removable" or "permanent" adhesive, only removable by wetting, scraping, heating or steaming.
The adhesive used in the adhesive layer is preferably pressure sensitive. Other adhesives may, however, be used. For example, a wettable adhesive might be used which adheres to a wetted surface.
In currently-preferred embodiments, the adhesive is either a hot melt adhesive or an acrylic adhesive.
This allows the adhesive layer to be applied evenly to the adhering surface of the substrate.
In addition to the adhesive, the adhesive layer can contain other materials such as rheology modifying agents, antioxidants, tackifiers, adhesives, plasticisers, and fillers.
The adhesive layer preferably has a thickness less than about 2.5 x 10 4m (0.01 inch), more preferably less than about 1.25 x 10 4m (0.005 inch), and most preferably about 2.5 x 10-5m (0.001 inch). A
particularly preferred thickness is around 20 to 40 microns, although ranges of up to 10 to 200 microns or even 5 to 300 microns are envisaged.
The microparticles included in the adhesive layer may be hollow, solid, or a combination thereof. The microparticles can be breakable or non-breakable upon application of pressure to the article. The microparticles can also be collapsible (without breaking) upon application of pressure to the article, or non-collapsible. Preferred are microparticles that are breakable, and non-collapsible.
The microparticles can be made of any material having the appropriate size and other desired characteristics. For example, the microparticles can be made of glass, silica, clay, urea-formaldehyde resin, acrylate polymer, acrylate copolymer, rubber, foamed organic polymers, polytetrafluoroethylene, phenolic resin, calcium carbonate, aluminum hydroxide, ferrous oxide, or styrene resin. Hollow glass microspheres are preferred.
The microparticles can be of any diameter less than about 500 microns (i.e., 0.02 inch). Preferably, a mixture of microparticles have diameters less than about 200 microns (i.e., 0.008 inch) is used. In one embodiment, the microparticles are microspheres having mixed diameters ranging between 5 and 200 microns inclusive. In another embodiment, a diameter range between 60 and 100 microns is used. We have found that a mixture of microparticles having an average diameter of around 65 microns is convenient and effective.
Advantageously, the thickness of the adhesive layer measured at its thinnest point is less than the diameter of the largest microparticles. This has the effect of ensuring that at least some microparticles are of large enough size so as to project from the adhesive layer or to ensure that this layer is provided with relatively low-tack projections.
Suitable microparticles are commercially available, and include ScotchliteTM "glass bubbles" (3M
Co., St. Paul, Minn.), DualiteTM hollow spheres (Pierce & Stevens Corp., Buffalo, NY), Q-CELTM "extendospheres"
(PQ Corp., valley Forge, PA), extendospheres "BUBBLECUP" (PA Industries, Inc., Chattanooga, TN), and ExpancelT'' microspheres (Expancel Inc., Diluth, GA).
ScotchliteTj' K1 "glass bubbles" (3M Corp., St. Paul, MN) are particularly preferred. These microspheres have mixed diameters of less than around 200 microns and a typical density of about 0.12 g/cmz.
The microparticles may either be premixed with the adhesive prior to application to the non-adhering surface of the substrate or, preferably, may be applied _g_ onto the adhesive layer after this has been applied to the substrate. This may be done by a number of methods, including scattering the microparticles over the adhesive or dipping the adhesive-covered surface of the substrate into a supply of microparticles. At present, however, the preferred method is to spray the microparticles onto the adhesive layer after this has been applied to the substrate. Where the microparticles are premixed with the adhesive, each microparticle, including those which protrude from the surface of the adhesive layer relatively remote from the substrate, will generally be coated in adhesive.
This means that the surface of the adhesive/
microparticle layer remote from the substrate will have a degree of tackiness, enabling the article to be easily positioned on a surface yet remain repositionable by being peeled off and reapplied. It is, however, preferred to spray microparticles onto the surface of the adhesive layer remote from the substrate once the adhesive layer has been applied. The microparticles thus deposited on the surface of the adhesive layer will tend to become partially embedded and adhered to the adhesive layer, but are themselves generally free of adhesive where they protrude from the surface of this layer. This is particularly the case where a proportion of the microparticles have average diameters greater than the thickness of the layer of applied adhesive. The advantage hereby conferred is that the adhesive/microparticle layer is "slippable", i.e. the adhesive/microparticle layer exhibits very little or no tack on the surface remote from the substrate, and the article may therefore be repositioned by sliding, as opposed to being peeled off and replaced, before a gentle degree of pressure disturbs the microparticles so as to release an amount of adhesive thereby temporarily to hold the article to _g_ a wall or the like.
In preferred embodiments, where the microparticles are hollow and breakable, application of a relatively low localised pressure to the article will tend to displace some of the microparticles so as to allow an amount of adhesive to be released. The microparticles preferably have a breaking point of 552 kN/m2 (80psi) or above, and even more preferably 690 kN/m2 or even 897 kN/m2 (100 or even 130psi). Commercially-available hollow glass microparticles are available with breaking points of 1725 kN/m2 (250psi) and over. In order to fracture these microparticles and thereby to release the adhesive contained in the adhesive layer, a pressure greater than the breaking point of the microspheres is applied to the non-adhering surface of the substrate once the article is its final position.
This pressure may be applied, for example, by way of a squeegee or the like.
Selecting microparticles with a relatively high breaking point allows a substrate to be coated on its adhering surface with adhesive and microparticles, and then subsequently to be further processed, for example by the addition of a printing layer, a release layer or a moisture barrier, without disturbing the adhesive layer. This is because, in general, printing rollers and the rollers used for applying other layers during manufacture tend not to apply a localised pressure of greater than 449 kN/m2 (65psi). This enables the article to be manufactured and sold in different stages of readiness. For example, an article such as a roll of wallcovering may be produced by applying all the necessary layers to a substrate in a single run through the relevant production apparatus for sale direct to an end-user. Alternatively, the substrate bearing only the adhesive/microparticle layer and an optional moisture barrier may be produced and sold to a wholesaler or other intermediary for printing and the application of an optional release layer before the wholesaler or intermediary then sells the article to the end-user.
By producing the article in several stages of completeness, e.g. ready for use or ready for printing, significant commercial advantages can be achieved. For example, instead of manufacturing a substrate, sending it to a printworks for printing, then applying the adhesive layer and the optional coatings, it is possible to manufacture an article consisting solely of the substrate and the adhesive layer which is ready for printing and/or coating, and which may be produced in bulk and sold in the form of blank rolls or sheets to a wholesaler. The wholesaler will then be able to print his or her own desired pattern or colouring on the article before passing this on to a retailer. In other words, the manufacturer of the article itself need not limit him or herself to the production of articles having particular colours or patterns, and can save on manufacturing costs by not printing or coating the paper him or herself. Alternatively, the manufacturer may choose to print and coat the article, but this is optional.
The invention also provides a method of manufacturing a self-adhesive surface-covering article, the article having an adhering surface and a non-adhering surface, the method comprising coating said adhering surface with adhesive and substantially inelastic, frangible microparticles, wherein the microparticles have diameters falling within a range defined inclusively by an upper limit and a lower limit, and wherein the thickness of the adhesive at its thinnest is not greater than the upper limit of the range of microparticle diameters.
A problem with cellulose-containing substrates, even when coated with PVC, is that PVC, while being splash-resistant, is not in fact waterproof, and will over time permit the passage of water vapour and moisture. This moisture is then absorbed by the paper component of the sheet of wallcovering, causing cellulose contained within the paper component to expand and the wallcovering to bubble (due to one surface thereof being substantially immovably bonded to a wall, for example), especially in conditions of relatively high humidity. On the other hand, should the ambient humidity drop, then water is evaporated out from the cellulose fibres of the paper component, causing these to shrink and the wallcovering to crack.
US Patent No. 5,639,539 discloses a releasable wallcovering and method of manufacture. The wall covering has a reinforcing substrate or backing layer with a surfacing layer formed of a polymer coating overlying a front surface of the backing layer. A
layer of printing is applied to the surfacing layer, and a transparent top coat layer extends substantially over the entire printed area. A PSA layer underlies a rear surface of the backing layer to secure the wall covering to the wall, while allowing it to be repositionable upon installation and releasable after extended use. The pressure sensitive layer contains tacky polymeric microspheres to facilitate easy release of the wallcovering from the wall surface.
However, it has been found that the base layer expands and contracts with increasing and decreasing humidity, particularly after the article has been applied to a substrate. This creates many problems such as, for example, separation of the base layer from the adhesive.
JS Patent No. 5,441,784 discloses a paper-based self-adhesive wallcovering including a moisture-resistant elastomeric barrier layer, the properties of which are chosen so as to accommodate contraction and/or expansion of cellulose fibres in the wallcovering.
Particularly with articles such as are described above the expansion and/or contraction of the cellulose fibres is undesirable, since it can cause bubbling of e.g. a wallcovering (when the adhesive may not be sufficiently strong to resist this), and shrinkage can leave gaps between adjacent rolls of e.g. wallcovering.
Thus, specific embodiments of the invention aim to provide a wallcovering in which such expansion and/or contraction is minimised or eliminated.
According to a second aspect of the present invention, there is provided a wallcovering including:
i) a paper-containing, generally laminar substrate having first and second surfaces; and ii) a moisture barrier layer disposed on one or other or both of said first and second surfaces or therebetween.
The invention is particularly useful when used as the basis for a self-adhesive wallcovering or the like (for example, wall trim and shelf or drawer liners).
Hitherto, self-adhesive wallcoverings such as those described above, have tended to be successful only in regions of relatively constant low humidity, such as regions of the United States. This is because moisture absorption by and/or evaporation from the cellulose component of the paper tends to lead respectively to bubbling or cracking of the substrate, mainly as a result of the substrate being firmly adhered on one surface to a wall or the like.
Consequently, in countries with variable and sometimes relatively high humidity, such as the United Kingdom, these self-adhesive wallcoverings tend to give unsatisfactory performance. It should be noted that this problem can also affect conventional non-self-adhesive wallcoverings.
As well as paper, the substrate may include cloth, tape, foil, laminate, vinyls or any other suitable material. For wallcoverings, a paper/PVC laminate (known in the art as a 'vinyl sheet') having PVC as one layer and paper as another layer is particularly preferred.
The moisture barrier layer may be made of any suitable moisture retardant material, such as plastics, acrylics and/or synthetic/natural resins. A variety of combinations of barrier and protective and release-treated coatings and adhesives and modified adhesives may be used. In general most of the coatings may be obtained from emulsions or solutions of the following types: emulsion copolymers of vinylidene chloride and one or more acrylic esters, copolymers of styrene and one or more acrylic esters, plasticised polyvinyl acetate, vinyl acetate copolymers, acrylic ester polymers or copolymers and copolymers of butadiene with styrene, acrylonitrile or methyl methacrylate, solutions or dispersions of water soluble polyesters, water-dispersible polyurethanes, and the like.
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 may be used, mention is made of 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 the first coating (after drying) may be given a lightweight coating of a release agent such as a wax or silicone emulsion. In addition there may be used for the coatings certain mixtures of synthetic emulsions with other materials such as are described in Parkinson et al's UK Patent 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, the polymer being present in an amount of the total dry weight content of between 45 and 95 percent, a polysaccharide which is only partially soluble in cold water in an amount of between 1 to 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 UK Patent No. 1 157 040 is a polyvinyl acetate to give 10 percent of plasticiser on polymer weight the plasticiser being di-isobutyl phthalate.
Also useful, and preferred, are water-dispersible resins of the type described in German Published Patent Application Nos. 2141805 and 2141807 and US Patent Nos.
3,905,929 and 5,043,381. Particularly preferred materials for the moisture barrier layer include polyvinylidenes such as polyvinylidene chloride (polyvinyl dichloride or PVDC) and/or polyvinylidene f luoride (polyvinyl dif luoride or PVDF) .
The moisture barrier layer may be disposed on or in the substrate in a number of different ways, depending on the requirements of the resulting wallcovering. In general, when a wallcovering is adhered to a wall, the greatest exposure to ambient humidity and moisture is from the exposed surface of the wallcovering, i.e. that which is remote from the wall. Accordingly, one embodiment of the present invention provides a wallcovering having a substrate bearing a moisture barrier layer on the surface which is intended to face away from the wall once the wallcovering has been adhered in place. Particularly where the substrate takes the form of a composite or laminate of cellulose-based paper and another material, such as PVC or other appropriate vinyls as, for example, in a vinyl sheet, it may be advantageous to provide the moisture barrier layer between the paper component and the other material. In a vinyl sheet, for example, the substrate may then be formed as a layer of cellulose-based paper bottommost, followed by a moisture barrier layer, and then a layer of PVC or the like over the top. In these embodiments, it is envisaged that the wallcovering is adhered to a wall with the vinyl surface facing away from the wall.
Alternatively or in addition, the moisture barrier layer may be disposed on the surface of the substrate which will eventually face the wall once the wallcovering has been put into position. This helps to prevent moisture ingress caused by damp in the wall.
This embodiment of the present invention is particularly useful in the production of repositionable and/or slippable self-adhesive wallcoverings.
In order for the wallcovering to be successfully peeled off without delaminating, the paper component of the substrate needs to have a minimum internal bond strength. This represents the resistance to separation of the cellulose fibres making up the paper, and is related to the fibre density and manufacturing techniques used. Generally, the greater the fibre density, the greater the internal bond strength, but papers with high fibre densities are correspondingly significantly more expensive than papers with low fibre densities and consequent low internal bond strengths.
For example, cheap paper with a relatively low internal bond strength can be bought for around ~500 per tonne, but tends to delaminate or otherwise become separated from itself when peeled away from even a relatively low tack adhesive layer. Paper with relatively high internal bond strength is commercially available and is more resistant to such delamination, but is significantly more expensive, at around ~2000 per tonne.

Sheet materials in the past have relied on the paper manufacturers to add resins, binders, latex fillers etc in order to increase the bonding of the paper fibres during the paper making process. Bond strength of paper is very important in the wall covering industry. In traditional pre-pasted wall coverings, high bond strength is vital to ensure easy removability. Otherwise, the paper will simply separate from itself, i.e. delaminate. Traditional methods have again relied upon the paper maker increasing the bond strength during manufacture.
However, this approach has disadvantages at least in respect of cost, as explained above.
Bond strength is particularly important to self-adhesive products. Without sufficient bond strength the sheet material separates or delaminates upon attempted repositioning of the sheet. Once this occurs the material is then useless.
Thus, embodiments of this invention aim to provide products suitable for use with an adhesive system that requires a threshold internal bond strength to perform its intended function and in particular to achieve that threshold by the application of one or more coatings to a paper which is naturally of a lower threshold.
According to a third aspect of the present invention there is provided a wallcovering comprising a generally laminar substrate having at least one paper-containing layer strengthened by a coating of polymeric or resinous material disposed thereon.
The coating may be of natural or synthetic material.
The coating, which is arranged to enhance the apparent bond strength between paper fibres, may be selected from a group comprising natural or synthetic resins, polyvinyl alcohols, natural or synthetic waxes, acrylic ester copolymers, vinyl acetate copolymers, styrene and butadiene copolymers, polyvinylidene chloride, polyesters, polyurethanes, polyethylenes, vinyls, latex emulsions and the like.
The coating may be disposed on a wall-facing surface of said layer. Alternatively or in addition the coating may be disposed on an outward-facing surface of the said layer. The coating may be disposed between adjacent paper-containing layers in the substrate.
This aspect of the present invention is not limited to moisture-retardant layers to enhance internal bond strength, but is currently envisaged to extend to the use of layers which do permit the passage of moisture whilst still enhancing the apparent internal bond strength of the paper-containing component of the substrate. Where a moisture permeable layer is used, it is advantageous to provide an additional, moisture-retardant layer between the paper containing component of the substrate and the surface or surfaces of the wall covering which will eventually be exposed to ambient humidity once the wall covering has been adhered to a wall.
Thus, by applying a moisture barrier of the type outlined hereinbefore, it is possible significantly to increase the apparent internal bond strength of a paper-based substrate without significantly increasing the cost thereof.
The present invention may contain any combination of the features and limitations referred to herein, except such combinations in which the features are mutually exclusive.
For a better understanding of the present invention, and to show how it may be carried into effect, reference shall now be made, by way of example, to the accompanying drawings, in which:
FIGURE 1 is a cross-section through a first embodiment of thepresent invention;

FIGURE 2 is a cross-section through a second embodiment of thepresent invention;

FIGURE 3 is a cross-section through a third embodiment of thepresent invention, depicting a moisture barri er layer;

FIGURE 4 is a cross-section through a fourth embodiment of thepresent invention, also showing a moisture barri er layer;

FIGURE 5 is a cross-section through a fifth embodiment of thepresent invention, showing a moisture barrier layer applied the self-adhesive sheet of to figures 1 and 2;

FIGURE 6 is a cross-section of a sixth embodiment of the present in vention showing a further moisture barrier layer applied the sheet of Figures 1 and to 2;

FIGURE 7 is a cross-section of a seventh embodiment of thepresent invention showing a further moisture barri er layer plied to the sheet of Figures ap 1 and 2;

FIGURE 8 is a cross-section of an eighth embodiment of thepresent invention showing a sheet with a strengt hening disposed thereon; and coat Figure 9 is a cross-section of a ninth embodiment of the present invention also showing a strengthening coat.
In the Figures, which are necessarily schematic and not to scale, like reference numerals will be used for like features.
In Figure 1, there is shown a cross-section through an article 1 which includes a substrate 2 having an adhering surface 3 and a non-adhering surface 4. Such articles include, for example, wall covering, wall trim, and liners. Substrates include, but are not limited to, paper, cloth, tape, foil or laminates. The substrate may be coated with, for example ink, wax, foil, or combinations thereof.
Coatings can be used to provide decorative wall covering sheets containing printed matter on the non-adhering surface of the substrate material.
The substrate in these sheets can be conventional wallcovering substrate, such as a coated paper. Such coated papers are well known, the coating being made from e.g., pigment and latex binder. The pigments can be, e.g., clay and calcium carbonate. One commercially-sold paper of this type is identified as C2170-084 sold by Monadnock Paper Mills, Inc.
(Bennington, NH). An adhesive layer 5 is disposed on the adhering surface 3 of the substrate 2. The adhesive layer contains microparticles 6, preferably hollow glass microspheres, which cause the adhesive layer to have a contoured, non-flat, surface 7 for contacting a surface to be adhered to. Although the preferred embodiment of this invention involving a repositionable/slippable sheet is discussed in detail below, the same teachings can be applied by those skilled in this art to other articles.
The adhesive layer 5 preferably has a rough, or contoured, surface 7 caused by protuberance of the microparticles 6. This lowers the surface area of the adhering surface that contacts the surface to be adhered to and can cause the adhesive layer to exhibit low or substantially no tack. Thus, the thickness of the adhesive layer 5 at any point can vary depending or the diameter of any microparticle 6 present at that point. The thickness of the adhesive layer, measured at the thickest point, is preferably less than about 2.5 x 10-'gym (0.01 inch), more preferably less than about 1.25 x 10-9m (0.005 inch). The thickness of the adhesive layer 5 measured at the thinnest point is preferably less than the diameter of the largest microparticles 6.
In a preferred embodiment, the adhesive layer 5 is applied as an acrylic adhesive or as a dispersion of a hot melt adhesive at elevated temperature, such as 177°C (350°F). For example, a rubber resin can be used as the hot melt adhesive.
Conventional pressure-sensitive adhesives can be used in the adhesive layer 5. These can be chosen from among, for example, acrylic adhesives, and rubber resin adhesives.
Acrylic adhesives include, for example, homopolymers, copolymers or crosslinked copolymers of at least one acrylic or methacrylic component, for example acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert.-butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, undecyl acrylate or lauryl acrylate, or as a comonomer, a carboxyl-containing monomer such as (meth)acrylic acid, itaconic acid, crotonic acid, malefic acid, malefic anhydride or butyl maleate, a hydroxyl-containing monomer such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate or allyl alcohol, an amido-containing monomer such as (meth)acrylamide, N-methyl(meth)acrylamide or N-ethyl(meth)acrylamide, a methylol group-containing monomer such as N-methylol(meth)acrylamide or dimethylol(meth)acrylamide, an amino-containing monomer such as aminoethyl(meth)acrylate, dimethylaminoethyl(meth)acrylate or vinylpyridine, or a non-functional monomer such as ethylene, propylene, styrene or vinyl acetate.
Rubber adhesives include, for example, natural rubber, isoprene rubber, styrene-butadiene rubber, styrene-butadiene block copolymer, styrene-isoprene block copolymer, butyl rubber, polyisobutylene, silicone rubber, polyvinyl isobutyl ether, chloroprene rubber and nitrile rubber.

i~VO 00/31201 PCT/GB99/03943 Pressure sensitive adhesives are preferred.
Suitable pressure sensitive adhesive for use in the invention are commercially available. Preferred commercially available pressure sensitive adhesives for use in the adhesive layer contain RevacrylTM 620 (Harco Ltd. ) , KratonT'f D-1107 and KratonT'~ D-1102, block copolymers of styrene-butadiene styrene, styrene-isoprene-styrene, styrene-ethylene-butylene-styrene, and styrene-ethylenepropylene (Shell Chemical Co., Houston, TX). KratonT'' D-1107 and KratonT" D-1102 may be used in combination.
Permanent adhesives for use in the invention are well-known and include adhesives commercially sold as HM585 from H.B. Fuller, Inc.
Tackifying agents may be added if desired. Such agents are well known in the art. Typical commercially available agents include polyterpenes with ring and ball softening point from 85-115°C, such as AONESTERTM
(Arizona Chemical, Panama City, FL) and PICCOLYTE''' (Hercules, Wilmington, DE) or hydrocarbon resins from the CS-C9 oil refining stream such as ESCOREZTM (Exxon, Houston, TX) and WINGTACKT" (Goodyear, Akron, OH).
In the embodiment of Figure l, the microparticles 6 are premixed with the adhesive prior to the adhesive layer 5 being applied to the substrate 2. This means that substantially all of the microparticles 6 which cause projections in the surface 7 of the adhesive layer 5 are themselves covered by a thin layer of adhesive, providing a degree of initial tackiness.
Alternatively, as shown in Figure 2, the microspheres can be deposited on the adhesive layer 5 after this layer 5 has been applied to the substrate 2.
This may be done by spraying the microparticles 6 or_to the adhesive layer 5, or by any other suitable means.
Because the microparticles 6 have not been premixed with adhesive, the microparticles 6 which project from the surface 7 of the adhesive layer 5 will tend to be substantially free of adhesive. This has the potentially desirable effect of providing a substantially tack-free surface 8, which allows the article to be slid freely over a surface to which it is to be adhered, at least until gentle pressure is applied, for example by hand. This is especially desirable when the article is a sheet of patterned wallcovering, since it then becomes easy to ensure that the patterns on adjoining sheets are correctly matched prior to final adhesion.
If desired, the adhesive layer 5 can be covered with a release layer comprising, for example, a coating containing silicone, or with a peelable release layer, such as silicone coated papers. Such layers are well known in this art. UV 9300 (GE Silicones, Waterford, NY) is one commercially available release layer.
Similarly, as shown in Figures 1 and 2, the non-adhering layer of the substrate 2, which may optionally be provided with a layer of printing 4a, may be covered with a release layer 9 and/or a peelable layer. Such layers are conventionally applied, and act to reduce and stabilise unwind tension.
In Figure 3, there is shown a cross-section through a wallcovering 1 in the form of a sheet which includes a paper-containing substrate 2. Substrates include, but are not limited to, paper, cloth, tape, foil or laminates. The substrate may be coated with, for example ink, wax, foil, or combinations thereof.
Coatings can be used to provide decorative wall covering sheets containing printed matter on the substrate material.
The substrate in these sheets can be conventional wallcovering substrate, such as a coated paper. Such coated papers are well known, the coating being made from e.g., pigment and latex binder. The pigments can be, e.g., clay and calcium carbonate.
A coating l0a of PVDC or PVDF or other suitable material is applied to the surface of the substrate 2 which will be exposed to ambient conditions once the wallcovering 1 has been put in place on a wall or the like. This coating l0a may be selected so as to act as a moisture barrier layer, an internal bond strength enhancer for the substrate 2, a release layer or any combination thereof. An optional coating lOb of the same or a similar material may be provided on the other surface of the substrate 2.
Alternatively, as shown in Figure 4, a wallcovering 1 in the form of a sheet may be fabricated from a substrate including a paper-based layer 2a and a vinyl or similar layer 2b, the layers 2a and 2b being separated by a coating 10 of PVDC or PVDF or other suitable material. This coating 10 may be selected so as to act as a moisture barrier layer and/or an internal bond strength enhancer for the paper-based substrate layer 2a.
Figure 5 shows the article of Figures 1 and 2 together with a moisture barrier. The moisture barrier 10 may be made of PVDC, PVDF or any other suitable material, and serves to prevent ingress of ambient moisture into cellulose-based parts of the substrate 2 from the exposed surface of the article. By preventing absorption and evaporation of moisture from any cellulose-based parts of the substrate, bubbling and cracking of the substrate 2 over time is much inhibited. PVDF is interesting for use as a moisture barrier layer, since this material has good moisture retardation properties as well as having a low coefficient of friction, and is therefore useful as a combined moisture barrier layer and release layer 10,9.
A further development is to use inks based on PVDC
and/or PVDF to produce a combined printed layer, moisture barrier and, in the case of PVDF, release layer 8,9,10.
Where the substrate 2 is formed as a cellulose-containing composite or laminate, e.g. a paper/PVC
vinyl sheet, it is possible to include a moisture barrier layer 10 between the cellulose-based layer 11 and the non-cellulose-based layer 12 of the substrate 2, as shown in Figure 6.
Some embodiments of the invention may include a moisture barrier 10 on either side of the substrate 2, as shown in Figure 7. By providing a moisture barrier 10 on the adhering surface 3 of the substrate as well as on the non-adhering surface 4, ingress of moisture through the adhesive layer 5 into the substrate 2 is additionally inhibited. This is useful where the article is a wallcovering to be applied to a wall which is subject to damp.
Figures 8 and 9 show, in cross section, a paper based wall covering 1 having a coating 12 of bond-enhancing substance disposed on an upper surface of substrate 2. In the case of Figure 8 the coating 12 is substantially even, whereas in the case of Figure 9 the coating is substantially uneven. These two Figures illustrate the fact that the coatings do not reside simply on the surface of the sheet material. Rather, the coatings become absorbed into the cellulose fibres in the substrate 2 and lock them together. Gains in internal bond strength are variable dependent upon at least the following factors, namely absorbability, quantity of coating used, number of coats (or layers) and the strength of substance (such as resin) used.
Absorbability varies, as can be seen from Figures 8 and 9.
A variety of materials can be used for the bond enhancing coating including (but not limited to) natural or synthetic resins, polyvinyl alcohols, natural or synthetic waxes, acrylic ester copolymers, vinyl acetate copolymers, styrene and butadiene copolymers, polyvinylidene chloride, polyesters, polyurethanes, polyethelenes, vinyls, latex emulsions and the like.
The following samples were prepared using various materials and the bond strength was tested as N/25mm at 90° peel angle.
SAMPLE SERIES H SERIES I
A (base value -no coating) 4.4 19.6 B 5.9 23.0 C 7.8 24.0 D 4.5 21.1 E 7.5 26.5 Series H represents a very inexpensive paper sheet with a naturally low internal bond strength. Series I
represents a very expensive, high internal bond strength sheet.
B represents one coat of an acrylic ester/natural wax mixture at 5.5gsm coating weight.
C represents one heavy coat of an acrylic ester/
natural wax mixture at 11.2gsm.
D represents two coats of an acrylic ester/natural wax mixture at 5.5gsm and 3.lgsm.
E represents two heavy coats of an acrylic ester/
natural wax mixture at 11.2gsm and 8.2gsm.
As can be seen from these results, a dramatic increase of up to 77% in the internal bond strength has been achieved in the inexpensive sheet. One can also see frcm comparing sample C to sample E that once a threshold has been obtained additional coatings or heavier coatings do not apparently result in higher internal bonding of the cellulose fibres. Also, relevant gains have been achieved in the expensive sheets, though not apparently to the extent of those achieved with the inexpensive sheets. Significant increases in the internal strength of paper-based substrates can be achieved, without requiring saturation of the substrate.
In general, when articles such as those described above in relation to Figures 1-9 are applied to a surface, the surface is in contact with the low tack or tack-free surface 7 of the adhesive layer 5. The overall low tack of this layer allows the sheet to be easily moved or repositioned. Where, as is currently preferred, the surface 7 exhibits substantially no tack (e.g. the embodiment of Figure 2), then the article is said to be "slippable". In other words, the article can be placed against a surface and slipped or slid freely about this surface, provided that not enough pressure is applied to as significantly to displace or fracture the microparticles 6. For example, wallcoverings having a printed surface can be easily moved to obtain registration of the print pattern.
Pressure may then be applied by hand to a portion of the article, usually by way of the exposed topside of the article, in order to break a proportion of the microparticles 6 dispersed in or on the adhesive layer 5 or to drive a proportion of the microparticles 6 thereinto. If a low degree of pressure is applied, such as normally occurs when pressing with the hand, the adhesive layer 5 can primarily hold the article in place while the rest of the article is positioned.
Once the rest of the article is positioned, higher pressure can be applied, such as with a squeegee, so as further to fracture and/or displace the microparticles 6 and thereby to allow adhesive layer 5 to strongly adhere the article to the surface. Use of a removable adhesive, as opposed to a permanent adhesive, allows the sheet to he removed without wetting, scraping or steaming at a later date, if desired.
The articles of the present invention can be made by conventional means. In one manufacturing process, a roll provides a substrate, preferably having a print on the top side of the substrate. The substrate is fed through various idler and tensioning rollers, as is well known by those skilled in the art, where an adhesive material, optionally premixed with microparticles, is applied. The adhesive material is dispersed on the bottom side of the substrate. An adhesive application roller or slot die may be used to apply a controlled and evenly distributed amount of the adhesive along the bottom surface of the substrate.
Alternatively or in addition, suitable microparticles can be applied, for example by spraying means, to the surface of the adhesive after it has been applied to the substrate.

Claims

CLAIMS:

1. An article including:
a substrate having an adhering surface and a non-adhering surface;
at least a portion of said adhering surface being covered by adhesive, substantially evenly distributed thereon, said adhesive being provided with substantially inelastic, frangible microparticles each having a diameter which falls within a given range of diameters, the range being defined inclusively between a lower limit and an upper limit;
wherein the thickness of the adhesive at its thinnest point is not greater than the upper limit of the range of microparticle diameters.

2. An article as claimed in claim 1, wherein said microparticles are substantially all coated with said adhesive.

3. An article as claimed in claim 1, wherein parts of at least some of the microparticles protrude from said adhesive and are substantially free of said adhesive.

4. An article as claimed in claim 1, 2 or 3, wherein said adhesive is a permanent adhesive.

5. An article as claimed in claim 1, 2 or 3, wherein said adhesive is removable by wetting, scraping or steaming.

6. An article as claimed in any preceding claim, wherein said substrate is selected from the group consisting of paper, vinyl, fabric, polymer and combinations thereof.

7. An article as claimed in any preceding claim, wherein said substrate is formed from composite of a paper layer and a vinyl layer.

8. An article as claimed in any preceding claim, wherein the substrate is formed from calendered polypropylene or other synthetic papers.

9. An article as claimed in any preceding claim, wherein at least a portion of said non-adhering surface of said substrate is provided with at least one coating.

10. An article as claimed in claim 9, wherein said coating includes a printed pattern.

11. An article as claimed in claim 9 or 10, wherein said coating is selected from the group consisting of ink, wax, foil, and any combination thereof.

12. An article as claimed in claim 9, 10 or 11, wherein at least a portion of said coating includes a release layer.

13. An article as claimed in claim 12, wherein said release layer is a silicone-based material.

14. An article as claimed in any preceding claim, wherein the article includes at least one moisture barrier layer.

15. An article as claimed in claim 14, wherein said moisture barrier layer is situated on the non-adhering side of the substrate.

16. An article as claimed in claim 14, wherein said moisture barrier layer is situated directly on the non-adhering surface of the substrate.

17. An article as claimed in claim 15 depending from claim 9, wherein said moisture barrier layer is situated within or forms a part of said coating but is not situated directly on the non-adhering surface of said substrate.

18. An article as claimed in claim 14 depending from claim 9, wherein said moisture barrier layer is situated over said coating.

19. An article as claimed in claim 14 depending on claim 7, wherein said moisture barrier layer is situated between said vinyl layer and said paper layer.

20. An article as claimed in claim 14 or claim 15, wherein the moisture barrier layer is situated on the non-adhering surface of the substrate.

21. An article as claimed in any of claims 14 to 20 wherein the moisture barrier layer is selected from a group comprising natural or synthetic resins, polyvinyl alcohols, natural or synthetic waxes, acrylic ester copolymers, vinyl acetate copolymers, styrene and butadiene copolymers, polyvinylidene chloride, polyesters, polyurethanes, polyethylenes vinyls, latex emulsions.

22. An article as claimed in any one of claims 14 to 21, wherein the moisture barrier layer is formed from polyvinylidene chloride (PVDC).

23. An article as claimed in any one of claims 14 to 21, wherein the moisture barrier layer is formed form polyvinylidene fluoride (PVDF).

24. An article as claimed in any preceding claim, wherein said microparticles are hollow.

25. An article as claimed in any preceding claim, wherein said microparticles are comprised of material selected from the group consisting of glass, silica, clay, urea-formaldehyde resin, acrylate polymer, acrylate copolymer, rubber, foamed organic polymers, polytetrafluoroethylene, phenolic resin, calcium carbonate, aluminum hydroxide, ferrous oxide or styrene resin.

26. An article as claimed in any preceding claim, wherein said microparticles are hollow glass spheres.

27. An article as claimed in any preceding claim, wherein said microparticles have diameters equal to or less than about 500 microns.

28. An article as claimed in claim 27, wherein said microparticles have diameters from 5 to 200 microns.

29. An article as claimed in claim 27, wherein said microparticles have diameters from 60 to 100 microns.

30. An article as claimed in claim 27, 28 or 29, wherein said microparticles have an average diameter of around 65 microns.

31. An article as claimed in any preceding claim, wherein said microparticles have a breaking point of 552 kN/m2 (80psi) or above.

32. An article as claimed in any preceding claim, wherein said adhesive comprises an acrylic or a hot melt adhesive.

33. An article as claimed in any preceding claim, wherein said adhesive comprises a pressure sensitive adhesive.

34. An article as claimed in claim 32 wherein said adhesive is removable by heat.

35. A method for manufacturing the article of claim 1, the method including the steps of:
i) providing a substrate having opposed first and second surfaces;
ii) coating the first surface of said substrate with an adhesive layer, premixed with microparticles.

36. A method for manufacturing the article of claim 1, the method including the steps of:
i) providing a substrate;
ii) coating the first surface of the substrate with an adhesive layer; and iii) spraying or otherwise applying a layer of microparticles over an exposed portion of said adhesive layer.

37. A method according to claim 35 or 36, wherein the second surface of the substrate is provided with a coating including a printed pattern.

38. A method according to any one of claims 35 to 37, wherein the second surface of the substrate is provided with a coating including a release layer.

39. A method according to any one of claims 35 to 38, wherein the second surface of the substrate is provided with a coating including a moisture barrier layer.

40. A method according to any one of claims 35 to 39, wherein the first surface of the substrate is provided with a coating including a moisture barrier layer.

41. A method of manufacturing a self-adhesive surface-covering article, the article having an adhering surface and a non-adhering surface, the method comprising coating said adhering surface with adhesive and substantially inelastic, frangible microparticles, wherein the microparticles have diameters falling within a range defined inclusively by an upper limit and a lower limit, and wherein the thickness of the adhesive at its thinnest point is not greater than the upper limit of the range of microparticle diameters.

42. A method according to claim 41 comprising applying to said adhering surface an adhesive which has been pre-mixed with said microparticles.

43. A method according to claim 41 comprising the steps of i) applying said adhesive to said adhering surface and, subsequently, ii) coating said adhesive with said microparticles.

44. A method according to any of claims 41-43 comprising the further step of coating said article with a moisture barrier.

45. An article according to any of claims 1 to 34 wherein the substrate has at least one paper-containing layer strengthened by a coating of polymeric or resinous material disposed thereon.

46. A method as claimed in any of claims 34 to 43 comprising strengthening a paper-containing layer of the substrate with a coating of polymeric or resinous material thereon

47. A wallcovering including:
i) a paper-containing, generally laminar substrate having first and second surfaces; and ii) a moisture barrier layer disposed on one or other or both of said first and second surfaces or therebetween.

48. A wallcovering as claimed in claim 47, wherein said substrate is formed from at least first and second layers, the first layer being formed from a synthetic material containing no cellulose, and the second layer being a cellulose-based paper-containing layer.

49. A wallcovering as claimed in claim 47 or 48, wherein said moisture barrier is disposed between said first and second surfaces.

50. A wallcovering as claimed in claim 47, 48 or 49, wherein said moisture barrier layer includes polyvinylidene chloride (PVDC).

51. A wallcovering as claimed in any of claims 47 to 50, wherein said moisture barrier layer includes polyvinylidene fluoride (PVDF).

52. A wallcovering as claimed in claim 51, wherein said moisture barrier layer is disposed on one or other of said surfaces.

53. A wallcovering according to claim 47, wherein said substrate has a cellulose-based paper-containing layer; and disposed thereon is a polymeric or resin-based strengthening layer bonded to said substrate so as to increase the apparent internal bond strength of the substrate.

54. A wallcovering as claimed in claim 53, wherein said strengthening layer includes polyvinylidene chloride (PVDC).

55. A wallcovering as claimed in claim 53 or 54, wherein said strengthening layer includes polyvinylidene fluoride (PVDF).

56. A wallcovering comprising a generally laminar substrate having at least one paper-containing layer strengthened by a coating of polymeric or resinous material disposed thereon.

57. A wallcovering as claimed in claim 56 wherein the coating is selected from a group comprising natural or synthetic resins, polyvinyl alcohols, natural or synthetic waxes, acrylic ester copolymers, vinyl acetate copolymers, styrene and butadiene copolymers, polyvinylidene chloride, polyesters, polyurethanes, polyethylenes vinyls, latex emulsions.

58. A wallcovering as claimed in claim 56 or 57 wherein the coating is disposed on a wall-facing surface of said layer.

59. A wallcovering as claimed in any of claims 56 to 58 wherein the coating is disposed on an outward-facing surface of said layer.

60. A wallcovering as claimed in any of claims 56 to 59 wherein the coating is disposed between adjacent paper-containing layers in said substrate.

61. A wallcovering as claimed in any of claims 56 to 60 wherein said coating comprises a moisture barrier.

62. A wallcovering as claimed in any of claims 56 to 60 wherein said wallcovering comprises an article according to any of claims 1 to 33.

63. A method of manufacturing a wall covering, the method comprising strengthening a paper-containing layer of said wallcovering with a coating of polymeric or resinous material.

64. An article substantially as herein described with reference to the accompanying drawings.

65. A wallcovering substantially as herein described with reference to the accompanying drawings.

66. A method of manufacture, the method being substantially as herein described with reference to the accompanying drawings.