GB2344061A

GB2344061A - Repositionable/slippable self-adhesive articles

Info

Publication number: GB2344061A
Application number: GB9825950A
Authority: GB
Inventors: William Britton
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-11-26
Filing date: 1998-11-26
Publication date: 2000-05-31
Anticipated expiration: 2018-11-26
Also published as: GB9825950D0; GB2344061B

Abstract

A self-adhesive article 1 is capable of being placed against a surface and repositioned or slid on that surface, provided that not more than a certain degree of pressure is applied to the article during positioning. The article 1, which may be a wall covering, has a substrate 2 having an adhering surface 3 coated with an adhesive layer 5 bearing microparticles 6. The minimum thickness of the adhesive layer is not greater than the upper limit of the range of microparticle diameters to ensure that at least some portions of microparticles protrude from the layer 5. An optional moisture barrier layer 10 may be provided to inhibit water penetration into the article, this layer may be formed from polyvinylidene chloride or polyvinylidene fluoride. The article may also bear printing 8 and a release layer 9.

Description

REPOSITIONABLE AND/OR SLIPPABLE SELF-ADHESIVE ARTICLES This invention relates to articles having adhesives thereon which allow the articles to be positioned on a surface prior to final adhesion, and in particular, but not exclusively, to articles designated for use as slippable, repositionable self-adhesive wallcoverings.

Conventional self-adhesive sheets, such as selfadhesive wallcoverings, are 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.

US patent application serial no. 08/933,164, filed 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.

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 adhesive from the wall surface.

According to a first aspect of the present invention, there is provided an article including: i) a substrate having an adhering surface and a non-adhering surface; ii) an adhesive layer including a substantially evenly-distributed adhesive covering at least a portion of said adhering surface, the adhesive layer being provided with 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 adhesive in the adhesive layer has a minimum thickness which 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 clothbacked 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. Where the substrate includes paper containing cellulose, it is highly advantageous to provide an additional moisture barrier layer in the article; especially when the article is intended for use in regions of variable ambient humidity. This is even more important where this variable humidity tends to be relatively high, since the cellulose component of paper tends to swell upon absorption of moisture and to shrink upon evaporation of absorbed moisture, which respectively leads to bubbling or cracking of the substrate once firmly adhered in position, e. g. as a sheet of wallpaper firmly adhered to a wall. The moisture barrier layer may be situated on or over the non-adhering surface of the substrate, or may, where a paper/PVC composite substrate is used, be situated between the paper and PVC components of the substrate. In some embodiments of the present invention, a moisture barrier layer may alternatively or additionally be situated on the adhering surface of the substrate, so as to provide resistance against moisture penetration from this side of the substrate, caused, for example, by wall dampness where the article is used as a wallcovering. It is to be noted that while PVC tends to be splash resistant, it does not make an effective moisture barrier, since a significant amount of water penetration is still achievable through a vinyl layer.

The provision of a moisture barrier layer bonded or otherwise associated with a paper-based component of the substrate can be particularly advantageous in the production of repositionable and/or slippable selfadhesive wallcoverings. Repositionable wallcoverings demonstrate a low degree of tack prior to the application of a substantial amount of pressure, and may therefore be lightly adhered to a wall and subsequently peeled off and repositioned prior to the application of the required degree of pressure, for example by way of a squeegee, needed to achieve permanent adhesion. 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 E500 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. However, 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.

Preferred materials for the moisture barrier layer include polyvinylidenes, such as polyvinylidene chloride (polyvinyl dichloride or PVDC) and polyvinylidene fluoride (polyvinyl difluoride or PVDF).

Other suitable materials for the moisture barrier layer may be formed 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 filmforming 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 filmforming 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.

At present, the use of PVDF as a moisture barrier layer appears interesting, since a layer thereof has a relatively low coefficient of friction as well as being a good moisture barrier. It is envisaged that the optional release layer mentioned above may be formed of PVDF instead of silicone, thereby providing a good release layer with a low coefficient of friction combined with excellent moisture retardation properties. Another possibility would be to include PVDF or the like in any inks used in forming the optional layer of printing. In this way, the optional layer of printing can provide, in a single layer, the functions of providing decoration, moisture retardation and release. However, other materials, such as a combination of PVDC and silicones, may provide similar benefits.

The adhesive layer contains adhesive that exhibits high adhesion. Preferably, it exhibits a tack of greater than about lOg/cm2 and less than about 1000g/cm2, and in some embodiments from about 100g/cm2 to about 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 0.5 pounds per lineal inch, more preferably greater than about 1.0 pounds per lineal inch, and most preferably greater than about 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, 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 rheology modifying agents, antioxidants, tackifiers, adhesives, plasticisers, and fillers.

The adhesive layer preferably has a thickness less than about 0.01 inch, more preferably less than about 0.005 inch, and most preferably about 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 80 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 Scotchlite"glass bubbles" (3M Co., St. Paul, Minn.), Dualitew hollow spheres (Pierce & Stevens Corp., Buffalo, NY), Q-CEL'"extendospheres" (PQ Corp., Valley Forge, PA), extendospheres "BUBBLECUP" (PA Industries, Inc., Chattanooga, TN), and Expancelw microspheres (Expancel Inc., Diluth, GA).

Scotchlite Kl"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/cm2.

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 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 particulary 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 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 80psi or above, and even more preferably 100 or even 130psi. Commerciallyavailable hollow glass microparticles are available with breaking points of 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 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 patters, 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.

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 the present invention; FIGURE 2 is a cross-section through a second embodiment of the present invention; FIGURE 3 is a cross-section through a third embodiment of the present invention; FIGURE 4 is a cross-section through a fourth embodiment of the present invention; and FIGURE 5 is a cross-section through a fifth embodiment of the present invention.

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 on 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 0.01 inch, more preferably less than about 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 350 F. For example, a rubber resin can be used as the hot melt adhesive.

Conventional pressure-sensitive adhesives can be used in both 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, maleic acid, maleic 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.

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 RevacrylT 620 (Harco Ltd.), Kratonw D-1107 and Kraton D-1102, block copolymers of styrene-butadiene styrene, styrene-isoprene-styrene, styrene-ethylene-butylene-styrene, and styrene-ethylenepropylene (Shell Chemical Co., Houston, TX). Kraton D-1107 and Kraton D-1102 may be used in combination.

Permanent adhesives for use in the invention are well-known and include adhesives commercially sold as H2179-01 (Findley Adhesives Inc., Wauwatosa, WI) and LHM 2512 (Imperial Adhesives).

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 PICCOLYTETM (Hercules, Wilmington, DE) or hydrocarbon resins from the Cs-C9 oil refining stream such as ESCOREZTM (Exxon, Houston, TX) and WINGTACKTM (Goodyear, Akron, OH).

In the embodiment of Figure 1, 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 8, 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 onto 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. W 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 8, 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 addition to or in place of a silicone-based release layer 9, a moisture barrier layer 10 may be provided, as shown in Figure 3. 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 cellulosecontaining 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 4.

Some embodiments of the invention may include a moisture barrier 10 on either side of the substrate 2, as shown in Figure 5. 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.

When articles such as those described above 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.

All patents, applications, publications, and test methods mentioned herein are hereby incorporated into the present application by reference.

Claims

CLAIMS:

1. An article including: i) a substrate having an adhering surface and a non-adhering surface; ii) an adhesive layer including a substantially evenly-distributed adhesive covering at least a portion of said adhering surface, the adhesive layer being provided with 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 adhesive in the adhesive layer has a minimum thickness which 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 those parts of the microparticles which form said protrusions 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 nonadhering 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, wherein a further moisture barrier layer is additionally situated on the non-adhering surface of the substrate.

21. An article as claimed in any one of claims 14 to 20, wherein the moisture barrier layer is formed from polyvinylidene chloride (PVDC).

22. An article as claimed in any one of claims 14 to 20, wherein the moisture barrier layer is formed form polyvinylidene fluoride (PVDF).

23. An article as claimed in any preceding claim, wherein said microparticles are selected from the group consisting of hollow microparticles and solid microparticles.

24. 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.

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

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

27. An article as claimed in claim 26, wherein said microparticles have diameters from 5 to 200 microns.

28. An article as claimed in claim 26, wherein said microparticles have diameters from 60 to 100 microns.

29. An article as claimed in claim 26,27 or 28, wherein said microparticles have an average diameter of around 80 microns.

30. An article as claimed in any preceding claim, wherein said microparticles have a breaking point of 80psi or above.

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

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

33. An article as claimed in claim 31 wherein said adhesive is removable by heat.

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

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

36. A method according to claim 34 or 35, wherein the second surface of the substrate is provided with coating including a moisture barrier layer.

37. A method according to claim 34,35 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 34 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 34 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 34 to 39, wherein the first surface of the substrate is additionally provided with a coating including a moisture barrier layer.

41. An article substantially as hereinbefore described with reference to the accompanying drawings.

42. A method substantially as hereinbefore described with reference to the accompanying drawings.