FIELD OF THE INVENTION The present invention relates to wallcoverings and apparatus and methods for covering walls therewith. In particular, though not exclusively, the invention relates to pre-pasted wallcoverings, such as pre-pasted wallpaper.

BACKGROUND OF THE INVENTION Traditionally, wallcoverings such as wallpaper have been applied to walls by a process of manually coating a surface of the covering with a liquid adhesive paste (e.g. wallpaper paste) and then simply hanging the pasted wallcovering on a wall surface. More recently, pre-pasted wallcoverings have been available. These products comprise a wallcovering pre-pasted with a dry adhesive which removes the somewhat messy process of manually applying a liquid adhesive paste. However, pre-pasted wallcoverings are not without their problems.

The adhesive on the back of pre-pasted wallcovering must be 'activated' (liquefied) before applying the wallcovering to walls. This is generally done using water. Activation may be done by soaking the wallcovering in water. A sponge saturated with water can be used or pieces of the wallcovering may be soaked in a tray/bath of water for several seconds. A piece of wallpaper soaked in a bath of water is the common way to achieve adhesive activation. Traditionally, pre-pasted wallcovering requires at least three separate steps to prepare and apply to a wall:

Immersion of the pre-pasted wallcovering in a water reservoir; then,

Setting aside of the wallcovering to allow the paste to be activated prior to being applied on to the wall; and then,

Hanging of the wet, pre-pasted wallcovering on a wall.

These steps involve specialist tools, a long preparation prior to applying the wallcovering on a wall, and professional expertise for good results. When applying a wallcovering directly from a water bath to a wall, one should typically place the water bath in position at the base of the wall. This is messy, prone to accidents and most inconvenient to users. The other disadvantages of this approach include:

Long drying times: a minimum of 2 days, longer if conditions are especially humid or cold; Potential for damage/deformation of the wet wallcovering during preparation/application; Potential for damage to the wall due to excessive moisture being present; Damage to carpets or floors immediately below a wall due to water dripping from wet wallcoverings;

Potential damage to decorator's clothes due to contact with wet adhesive paste.

The invention aims to provide an improved wallcovering, system and apparatus and methods for applying wallcovering to walls therewith.

SUMMARY OF THE INVENTION

At its most general, the invention implements the idea of preparing a wall surface directly by applying (e.g. spraying) the wall surface with an aqueous activator solution and hanging a dry pre-pasted wallcovering directly on to the prepared wall surface. When applying the pre-pasted wallcovering on to the prepared (e.g. coated/sprayed) area of the wall, the water present in the aqueous film on the wall may activate the dry, pre-pasted adhesive on the wallcovering turning it from a dry coating to a wet paste coating. The activator solution desirably has a viscosity exceeding that of pure water, natural water, or tap water. The adhesive activator preferably comprises a water-based rheology control additive, which preferably is able to form a layer of aqueous film upon a wall surface when applied there. The adhesive activator may be colloidal. For example, the adhesive activator may comprise microscopically dispersed insoluble particles that are suspended throughout water to form a fluid having viscosity exceeding that of water. The adhesive activator solution may be prepared in the form of a colloid in order to make a substantially homogeneous fluid structure. For example, the rheology control additive may comprise insoluble particles (e.g. starch particles) which may be substantially uniformly dispersed through the colloid and thereby be less prone to aggregation and sedimentation. This helps make a volume of the adhesive activator solution more uniform in its properties throughout that volume so that all parts of the volume have substantially the same viscosity, and other properties. Also, in examples of the invention in which the adhesive activator solution is applied by a spray device (e.g. an atomiser), this reduces the chance of blockage of the sprayer/atomizer nozzle by aggregated particles. The enhanced viscosity of the adhesive activator solution (e.g. colloid) promotes the retention of the adhesive activator solution on the top/outer surface of a wall onto which it is deposited, and reduces the chance of the solution flowing down the wall (under gravity) or penetrating into the wall. It thus requires the use of less volume of adhesive activator solution (e.g. quantity per unit area of wall) to hang wallpaper and concurrently less potential for running down a wall and damaging a carpet or floor at the base of the wall. The adhesive activator solution is preferably arranged to substantially hold this moisture on the surface of the wall for an extended time after being sprayed on the wall. Furthermore, the adhesive activator solution is preferably arranged such that the solution does not substantially penetrate in to the wall. Addition of a rheology control additive (e.g. starch particles) increases the fluid viscosity and may raise the fluid surface tension of the adhesive activator solution. Once sprayed on wall, it preferably gives activator droplets the property of 'hold out', whereby they remain either substantially static or only very slowly moving, rather than quickly soaking into the wall surface or quickly flowing down the wall surface. The viscosity of the activator solution reduces, inhibits or suppresses the running of the solution down the surface of a prepared wall and thereby retains the activator in the intended position on the wall surface. It also assists in preventing the solution from penetrating the wall such, ensuring that it is not necessary to apply a large volume of solution to the wall per unit area. This viscosity enhancement also suppresses penetration of the water-based activator (and the water within it) significantly in to the pores, cracks and microscopic openings within the surface of a wall, potentially causing water damage to it. This also promotes the concentration/retention of the adhesive activator solution upon/at the wall surface enabling a muchmore effective interface between the wall surface and the adhesive of the wallcovering once activated, i.e. migration of the activated adhesive into the pores of the wall surface is greatly reduced.

The adhesive activator may include a colour indicator arranged to act as a visual indication chemical to indicate, by its colour, where it has been applied to a wall surface by changing the appearance of a differently-coloured, wall immediately after application to indicate the uniformity of coverage there. The colour indication is preferably fugitive, i.e. after initially indicating a given colour, this visibly fades to (or at least towards) a substantially white/whiter or colourless/less-colourful appearance (based on the visible spectrum of 400-800 nm). This helps minimise any possibility of the visual appearance of the wallcovering being affected once applied.

In a first aspect, the invention may provide a wallcovering apparatus for applying a wallcovering to a wall surface, comprising a wall cover sheet pre-pasted with a water-activable dry adhesive layer upon a surface thereof, a water-based activator fluid having a viscosity exceeding the viscosity of water and applicable to at least partially coat a said wall surface, wherein the dry adhesive layer is arranged to moisten from contact with the activator fluid thereby to be activated to form an aqueous adhesive layer upon the surface of the wall cover sheet and upon the coated parts of the wall surface concurrently.

The viscosity of the activator fluid may be less than about 50000 mPas, or less than about 5000 mPas, or preferably between about 30mPas and about 2500 mPas. Preferably the viscosity of the activator fluid is between about l OOmPas and about 2000 mPas. More preferably, the viscosity of the activator fluid is between about 200 mPas and about 1700 mPas. These ranges of viscosity have been found to be particularly (surprisingly) effective at enabling ease of application of the aqueous activator to a wall surface and at the same time be sufficiently viscous to suppress penetration (soaking-in) of pores of the wall surface, and be predominantly retained at the wall surface without significantly 'running' down the wall.

The activator fluid may comprise a starch solution, such as a potato starch solution (e.g. modified potato starch). The solution may comprise starch in water in a concentration range of concentration of up to about 4 w%. For example, the range may be between about 0.5% and about 4% weight per unit volume of the solution. For example, the range may be between about 0.5% and about 3% weight per unit volume of the solution, or between about 0.5% and about 2.5% weight per unit volume of the solution. More preferably, the concentration may be between about 1 .0% and about 2.0% weight per unit volume of the solution. Yet more preferably, the concentration may be between about 1 .5% and about 1 .9% weight per unit volume of the solution. For example, a viscosity of about 50K mPas of activator fluid may be achieved using about 4w% of starch solution at a temperature of about 18°C, and is relatively less flowable. Consequently, an activator fluid at this concentration level is more difficult to be atomized in some devices than in other devices and may be more suitable for use in high- powered sprayer devices such as are readily available to the skilled person. Increasing or reducing the temperature of the activator fluid may typically result in change on viscosity.

The starch may be a biocide dried onto a flake. The careful addition of fluid rheology modifiers (e.g. starch) also has been found to significantly improve the control of the fluid rheology under the shear forces that apply to the adhesive activator solution within a spray nozzle of atomiser nozzle in those circumstances when it is applied to a wall by a sprayer/atomiser, or the like.

The spray/atomization shear forces are found to induce some shear thinning within the adhesive activator fluid when suitable a concentration of fluid rheology modifier is employed. This causes the activator fluid viscosity to fall under the atomization/sprayer shear force and thus become more flowable. The fluid viscosity will then recover to its original value once shear is removed - i.e. when upon the wall surface.

Examples of suitable rheology modifiers found to have this property include: any type of starch, cellulose ethers (carboxymethylcellulose (CMC), methylcellulose (MC) and derivatives, hydroxyethylcellulose (HEC) and derivatives, hydroxylpropyl cellulose (HPC), and ethylcellulose (EC), acrylic polymers, polyvinyl alcohol, proteins, latex. The rheology modifier may alternatively, or additionally, include any one or more of the following constituents, selected from any one or more of the following four catalogues:

1 . Inorganic rheology controller such as a clay or a silica.

2. Organic rheology modifier such as a cellulosic, a starch, a polyacrylate, a polyurethane, a latex or a polyvinyl alcohol.

3. Associative rheology modifiers adapted to thicken by non-specific interactions of hydrophobic end-groups of a thickener molecule both with themselves and with components of the physical network (such as: hydrophobically modified polyether; hydrophobically modified polyurethane).

4. Non-associative rheology modifiers adapted to thicken by an entanglement of water- soluble, high molecular weight polymer chains (e.g. alkali swellable emulsion).

These rheology modifiers may be used instead of, or to supplement, the starch additive as desired.

The activator fluid preferably comprises a fugitive colour indicator. This may comprise an indicator including a dye or pigment (i.e. it is possible for the colour change material to be insoluble and delivered as part of a dispersion rather than, or in addition to, a solution) being a first colour when in a liquid phase with the activator fluid and a subsequent second colour different to the first colour (or substantially colourless) before or by/when in the dried phase with the activator when subsequently dried. Thus, the user is able to see where activator has or has not been applied to a wall, due to the colour of the activator, and can act accordingly to ensure that an even and/or accurate application of activator solution is applied. The subsequent fading of the colour of the activator prevents interference (e.g. staining or 'see- through' discolouration) or damage to the colour effect of the wallcovering. The dye or pigment may be substantially colourless or white when in the dried phase. The dye is preferably arranged to react with a component of the ambient air to form the second colour. For example, the component of air may be oxygen or carbon dioxide. Examples of suitable dyes such as would be readily available to the skilled person can be found in the following references:

[1 ] Kolthoff, I.M.; Acid-Base Indicators (Macmillan, New York, 1937).

[2] Kolthoff, I.M, Stenger, V.A.; Volumetric Analysis Vol. I & II (Interscience, New York, 2 ^nd Edition, 1942).

[3] Bates, R.G.; Determination of pH (Wiley & Sons, New York, 1954).

[4] Bishop, E.; Indicators (Pergamon Press, Oxford, 1972).

[5] Green, F.J.; The Signa-Aldrich Handbook of Stains, Dyes and Indicators (Aldrich, Milwaukee, Wisconsin, 1990).

Preferred indicators include: phenolphthalein; thymolphthalein; o-cresolphthalein and ethyl bis(2,4-dinitrophenyl)acetate. The reason is that they all have a first colour in a basic pH condition and become colourless when pH reduced. Thus, interference or damage to the colour effect of the wallcovering is prevented. Also, these indicators have a modest transition pH range (7.5~10.5), which allows indicators to introduce the first colour with presence of a relatively small alkali change and then turn colourless by reaction with carbon dioxide in air. The fugitive colour indicator may comprise, for example, phenolphthalein plus sodium hydroxide for colour indication. The dye may be photo-unstable or photo-sensitive such that the colour of the dye is reduced of lost upon exposure to light, such as Ultra-Violet light, visible light or Infra-red light. The dry adhesive layer is preferably arranged to swell from contact with the activator fluid thereby to form a gel rendering the wall cover sheet slippable on a said coated wall surface.

The pre-pasted adhesive may comprise a blend of water soluble polymers, which may be either modified poly (acrylic acid) sodium salt or polyacrylic acid / poly acrylamide copolymer. Preferably the pre-paste may comprise polyacrylic acid / poly acrylamide copolymer as this has been found to provide a better combination of swell, wet tack, slip/slide and final adhesion.

Preferably, the pre-pasted adhesive (such as one selected from the above list) is arranged to swell to form a gel after contact with the adhesive activator solution. Once dried the adhesive (e.g. polymer) preferably forms an adhesive bond between the substrate (e.g. paper) of the wallpaper construction and the wall. The viscosity of the gel, when formed in this way, may be related to:

i. The quantity of adhesive from the wallpaper;

ii. The quantity of water available from the activator solution;

iii. The molecular chain length of the polymer(s) used in the adhesive;

iv. The degree of hydrolysis of the polymer(s) used in the adhesive;

v. The blend of polymers used in the adhesive (if blended).

Preferably, the coat weight of pre-paste adhesive on the pre-pasted wallcovering of preferred embodiments of the invention is from about 4 gsm (gsm= g/m ² ) to about 6 gsm. For example, optimal gel properties (e.g. swelling) may be achieved by employing any one or more of the following:

i. Providing the adhesive coat weight of pre-pasted wallpaper to between about 4 gsm and about 6 gsm. Nevertheless an adhesive coat weight of pre-pasted wallpaper of between 2- 3gsm also works, but is not optimal.

ii. Providing the degree of hydrolysis to make the polymer more water soluble - preferably in the range from about 75% to about 85%.

iii. Providing the blend of acrylic copolymers so that the molecular weight is higher.

The wallcovering apparatus may include an activator fluid applicator for use in applying the activator fluid to a said wall surface, comprising an atomiser arranged for holding a quantity of the water-based activator fluid and operable to form a directed spray of activator fluid from a said quantity thereof. The viscosity of the activator is most preferably within one of the stated ranges identified above, to enable effective atomisation and the formation of activator droplets of suitable size possessing the desired surface energy to enhance adhesion to the wall surface to which they are applied in use. The wall surface may typically be a skimmed plaster wall surface, an emulsion-coated wall surface, or a primer-coated wall surface, or may be coated otherwise. Of course, the activator fluid may be applied to a wall by other means, such as by brush, roller or the like. The activator fluid applicator may be a brush, a roller or a foam pad (e.g. suitable for applying aqueous solution to a wall - such as a paint brush, roller or pasting brush).

It is contemplated that this invention may be made and sold in the form of a pack or kit of parts comprising the wallcovering described above. For example, the invention in a second aspect may provide a kit of parts for a wallcovering apparatus for applying a wallcovering to a wall surface, the kit comprising a wall cover sheet pre-pasted with a water-activable dry adhesive layer upon a surface thereof, an activator material arranged for mixing with water to form a water-based activator fluid having a viscosity exceeding the viscosity of water and applicable to coat a said wall surface, an activator fluid applicator for use in applying the activator fluid to a said wall surface, comprising an atomiser arranged for holding a quantity of the water-based activator fluid and operable to form a directed spray of activator fluid from a said quantity thereof, wherein the dry adhesive layer is arranged to moisten from contact with the activator fluid thereby to be activated to form an aqueous adhesive layer upon the surface of the wall cover sheet and upon the coated parts of the wall surface concurrently. The adhesive activator may be formulated in powder form and packed in container (e.g. a small sachet) for sale. In that case, the kit of parts may comprise instructions for preparing the adhesive activator solution (e.g. addition of water) to the desired viscosity, such as a viscosity within a range of viscosity as described above. However, in the alternative, the adhesive activator may be prepared as a fluid, e.g. in colloid form. The atomiser may comprise an air-inclusion nozzle. The air-inclusion nozzle may comprise one or more air-intake openings in communication with an intermediate nozzle/tunnel of the air-inclusion nozzle for conveying activator fluid. The air-inclusion nozzle may comprise a Venturi. This may be arranged to cause air to be sucked in though the air-intake openings such that air and activator fluid mix in the nozzle. This aerated activator fluid may then be sprayed from/through an outlet orifice of the nozzle.

The atomiser may comprise a nozzle (known as a 'flat fan nozzle': see Table 4 below) arranged to spray a flat sheet, or fan, of liquid and produce a flat fan spray pattern. Such spray patterns have been found to be particularly advantageous in directing the activator uniformly and accurately only to those areas of the wall requiring treatment. This helps prevent overspray of an adjacent area, such as area of wall cover that may already have been installed, doorframes, etc. The flat-sheet structure of sprayed liquid may be formed by providing a nozzle having an elliptical fluid outlet orifice. The flat-sheet structure of sprayed liquid may be formed by providing a nozzle having a round fluid outlet orifice (circular or elliptical) arranged to direct output fluid flow to impinge upon a deflective surface that is oblique to the axis of fluid flow from the outlet orifice (i.e. not 'face-on'). This 'deflection' type flat fan nozzle produces the flat fan pattern/structure in the sprayed fluid by deflecting the fluid stream against the deflective surface after it has exited from the nozzle orifice. The deflective surface may be a curved deflective surface. The impact of the fluid on the deflection surface causes the desired atomisation and the geometry of the surface shapes the resulting spray into a flat fan pattern. This means that the nozzle orifice can remain circular, rather than being elliptical as is the case with standard flat fan nozzles. A benefit of this is that a circular orifice is less prone to wear and clogging. The atomiser may include a flat fan nozzle that is also an air-inclusion nozzle. This combination has been found to provide maximum spray accuracy and cleanliness.

The activator material may comprise a modified potato starch solution. The activator material may comprise an indicator including a dye or pigment (i.e. it is possible for the colour change material to be insoluble and delivered as part of a dispersion rather than, or in addition to, a solution) being a first colour when in a liquid phase with the activator fluid and a subsequent second colour different to the first colour (or substantially colourless) before or by/when in the dried phase with the activator when subsequently dried. The dye is preferably substantially colourless or white when in the dried phase. The dye or pigment may be arranged to react with a component of the ambient air to form the second colour. The dry adhesive layer may be arranged to swell from contact with the activator fluid thereby to form a gel rendering the wall cover sheet slippable on a said coated wall surface.

In a third aspect, the invention may provide a method for covering a wall a wall surface, comprising, providing a wall cover sheet pre-pasted with a water-activable dry adhesive layer upon a surface thereof, applying to the wall surface a water-based activator fluid having a viscosity exceeding the viscosity of water, therewith to at least partially coat the wall surface, and placing the surface of the wall cover sheet in contact with the activator fluid upon the wall surface thereby to be activating the dry adhesive layer to moisten to form an aqueous adhesive layer upon the surface of the wall cover sheet and upon the coated parts of the wall surface concurrently. The method may include applying the fluid activator to the wall surface as an atomised spray.

The activator fluid preferably comprises an indicator including a dye or pigment (i.e. it is possible for the colour change material to be insoluble and delivered as part of a dispersion rather than, or in addition to, a solution) being a first colour when in a liquid phase with the activator fluid and a subsequent second colour different to the first colour (or substantially colourless) before or by/when in the dried phase with the activator when subsequently dried, wherein the method preferably includes placing the surface of the wall cover sheet in contact with the activator fluid upon the wall surface while the indicator dye or pigment is the first colour.

The term 'about' when used in this specification refers to a tolerance of ±10%, of the stated value, i.e. about 50% encompasses any value in the range 45% to 55%, In further embodiments 'about' refers to a tolerance of ±5%, ±2%, ±1 %, ±0.5%, ±0.2% or ±0.1 % of the stated value.

There now follows a description of a preferred embodiment of the invention with reference to the accompanying drawings. This embodiment is intended to illustrate one implementation of the invention but is not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows schematically a cross-sectional view of two pre-pasted wallcoverings;

Figure 2 schematically shows a wallcovering apparatus in use, whereby a wall surface is prepared by an activator solution prior to application of a pre-pasted wallcovering of a type shown in Figure 1 ;

Figure 3 schematically shows application of a pre-pasted wallcovering to the prepared wall surface shown in Figure 2;

Figure 4 schematically shows, in cross-section, the interface between the prepared wall surface and wallcovering of Figure 3, via the activated adhesive layer of the wallpaper;

Figure 5 shows the relationship between activator composition and viscosity;

Figure 6 shows a graph of Peel strength comparing an example of the present invention to other wallpapers;

Figure 7 illustrates in cross-section, an air-inclusion nozzle of an atomiser for mixing air bubbles in to sprayed activator fluid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, like items are assigned like reference symbols. Figure 1 shows schematically a cross-sectional view of two pre-pasted wallcoverings (1 , 2). A first wallcovering 1 is a pre-pasted wallpaper and a second wallcovering 2 is a pre-pasted lining paper. Each wallcovering comprises a non-woven fabric substrate web 3 such as a paper material (other non-woven materials are possible) to one surface of which is bonded a pre-pasted dry adhesive coating layer 4 which is arranged to be activated into a fluid adhesive by application of water, such as the water contained within an adhesive activator fluid as discussed below. This completes the structure of the lining paper 2, whereas the wallpaper further comprises a decorative layer 5 printed (or otherwise coated or bonded) to the surface of the fabric substrate opposite to the one baring the pre-pasted adhesive layer 4. This may be a patterned, textured or designed layer applied by conventional printings, screen printings, digital printing, flexo, inkjet, flocking, coating, lamination techniques or other potential techniques known in the art. In general, the substrate material of any embodiment may be any suitably dimensionally stable substrate, and is not limited to a non-woven fabric substrate. For example, in other embodiments, the substrate material could be nonwoven, woven fabric or a synthetic material film. In preferred embodiments, the substrate material may preferably be other than paper, which has a relatively high wet expansion rate potentially resulting in bubbling paper or overlapped edges at joint. Nevertheless, a paper substrate may be used if desired. As one example of the method of manufacture of such a wallcovering, the following outline is provided. A wet acrylate adhesive paste may be initially coated on to a non-woven substrate 3 (e.g. about 85 gsm, such as wetlaid nonwoven) at a density of twenty grams per square metre. A rotary screen cylinder (e.g. 80 mesh) may be used for this purpose and operated at a machine speed of about 60 metres/minute, for example. The pre-pasted substrate that results may then be dried at about 135°C. This provides either a pre-pasted lining paper or, if a wallpaper is being manufactured then a subsequent printing step may follow. In the printing step, the pre-pasted substrate is initially pre-conditioned in an oven at about 120°C to adjust the moisture content of the substrate and release tension. The preconditioned substrate may then be printed (e.g. with plastisol) by a rotary screen printing method and then pre-gelled at about 165°C. This product may then be finally cured at about 200°C in an oven for about 40 to 50 seconds (e.g. 42 seconds). The result is a patterned, pre-pasted wallpaper 1 .

Figure 2 schematically shows a wallcovering apparatus 6 for applying a wallcovering to a wall surface such as a skimmed plaster wall 10. The apparatus comprises a wallpaper sheet 1 as shown in Figure 2, including a non-woven substrate 3 pre-pasted with a water-activable dry adhesive layer 4. In addition, the apparatus includes a water-based activator fluid 8 having a viscosity exceeding the viscosity of water and applicable to coat a said wall surface.

An activator fluid applicator 7 is included for use in applying the activator fluid to a wall surface. The activator fluid applicator comprises a hand-held pump-action atomiser having a fluid chamber part (e.g. bottle) arranged for holding a charge/quantity of the water-based activator fluid, and a trigger-actuated atomiser pump head detachably attached to the top opening of the fluid chamber. It is to be understood that the activator fluid applicator may be other than a hand-held atomiser, and may be, for example, a larger apparatus comprising a larger fluid chamber part arranged to be rested on a floor/ground surface and to be pressurised by a pump attached to the fluid chamber part. In that case, the atomiser/sprayer may be hand-held and in fluid communication with the fluid chamber via a hose or pipe or the like. The atomiser pump of the present embodiment is in fluid communication with the fluid chamber and its contents via a fluid flow tube 13 and is operable, by pump-action of the atomiser trigger, to draw fluid from within the fluid chamber along the fluid flow tube and to deliver it to the atomiser pump head where it is formed into a directed spray 9 of atomised activator fluid for coating the skimmed plaster surface of the wall 10. In this way, a substantially non-drip coating of activator fluid 1 1 may be applied to the wall surface 10 in preparation for applying the pre-pasted wallpaper 1 thereto.

The fluid applicator may be a pump-action atomiser bottle such as is well known the fields of domestic cleaning applications and the like. Other known fluid atomisers such as are readily available to the skilled person, may be used of course, as discussed above. Indeed, the invention is not limited to the use of an atomiser/sprayer and so in yet further embodiments, the fluid applicator may be a brush or roller for applying the activator fluid manually without atomisation/spraying. The dry adhesive layer 4 is arranged to moisten from contact with the substantially non-drip activator fluid layer 1 1 formed on the surface of the wall 10, as shown in Figure 2, thereby to be activated to form an aqueous adhesive layer 12 upon the surface of the wallpaper sheet 3 and upon the coated parts of the wall surface 10 concurrently as shown in Figure 4.

Adhesive Activator. The adhesive activator may be a preparation of modified potato starch solution. Spraying of the activator solution on to a wall surface forms a layer of activator solution film on the wall. The higher viscosity of activator solution, relative to water, maintains a hydrous environment at the outermost surface on the wall. This higher viscosity is especially beneficial to the application of pre-pasted wallpaper on porous wall surfaces (e.g. skimmed plaster wall). Once the pre-pasted wallpaper is applied onto the sprayed area, placing the pre-pasted adhesive in direct contact with the hydrous activator film, the pre-pasted adhesive will seek out water from activator solution film and swell to form a gel, such as shown as item 12 in Figure 4. The gel has a viscosity which is low enough to permit the wallpaper to be moved by sliding across the wall surface to align the paper upon the wall as desired. This gel, when dry, forms into a continuous dry film, and therefore provide the bond between the wallpaper and wall. Viscosities of adhesive activator solution were measured as a function of varying concentrations (additive weight per volume of solution) of rheology control additive using a Brookfield DV3T viscometer. The results are shown in Figure 5 and are tabulated below in Table 1 .

Table 1

Concentration Viscosity Spindle Speed Torque Temperature

(w/v) (cP) No. (rpm) (%) (°C)

0.0% 0 - - - -

0.5% 36 RV-2 250 22.7% 17.4

1 .0% 80 RV-2 250 49.8% 17.2

1 .5% 226 RV-2 90 50.5% 17.5

2.0% 1680 RV-3 30 49.4% 18.8

2.5% 3433 RV-5 60 51 .5% 18.8

3.0% 25150 RV-5 8 50.4% 18.4

4.0% 45545 RV-6 1 1 50.1 % 18.3

The concentration levels (w/v) of rheology control additive (modified potato starch, in this case, added to tap water) are shown in the first column of Table 1 . The resulting measured viscosity is shown in the second column of Table 1 . Three of these eight samples (Table 1) of adhesive activator solution having 2%, 1 % and 0% (w/v) concentration of rheology control additive respectively, were sprayed onto a wall surface (on a freshly skimmed plaster wall of the same type/structure in each case) and left exposed for a succession of different time periods before a pre-pasted wall-covering was applied to the pre-sprayed wall surface. This was done to test how the application of the rheology control additive effected moisture retention times at the pre-sprayed wall surface. The results showed that one layer of uniform spraying with a 1 % (w/v) concentration of adhesive activator could hold a sufficient film of moisture at the wall surface for about 3 minutes. That film of moisture was sufficient, after the 3 minutes of exposure. To activate the pre-pasted adhesive on the wallcovering to permit the wallcovering to adhere and hang upon the wall. When the concentration increased to 2% (w/v), this moisture holding time increased to 8 minutes, and a pre-pasted wallcovering could still successfully adhere to the pre-sprayed wall surface.. However, when the wall was pre-sprayed with tap water (0% (w/v) concentration level) the water merely soaked into the wall structure quickly and sufficient moisture could only be held for about 60 second even when the wall surface was saturated with water. After that time, re- spraying was required. The Atomization efficiency of each non-zero concentration level of activator fluid shown in Table 1 , was evaluated using a hand-held squeezed spray bottle and pumped sprayer. The tests were based on these three types of sprayer illustrated in Table 2 (see page 20), and the results are given in Table 2.

Atomization of an adhesive activator using a pumped-type sprayer with a flat fan type nozzle (second image of standard flat fan) has been tested as indicated in Table 2 (see page 20). The test was based using commercially available sprayers obtained from a DIY store. However, these results are only intended to illustrate the principle of atomisation variation according to differing sprayer types, and should not be considered as limiting. Indeed, a more powerful industrial type or electrically-powered spry gun may equally be used according to the invention if desired. These results are based on three common types of sprayer which are widely available in DIY stores. If a different or modified atomizer is used, or a powered sprayer is used, the atomization of adhesive activator fluid having higher concentration levels (e.g. about or beyond 4%) is possible, and a higher viscosity of the adhesive activator fluid is possible (e.g. above 50000mPas).

It is advantageous to apply the activator fluid only to the intended treatment area, and to avoid contaminating the area beside the target area with "overspray", or build-up activator solution on the floor below the target area. This is to preferable to protect e.g. an area of wall covering that may already have been installed, or a doorframe, a window, a window frame, etc.

To reduce or substantially prevent overspray, embodiments of the invention may employ an atomiser (item 7, Fig, 1 ) for use in spraying the activator fluid comprising an air-inclusion nozzle 15, such as is schematically illustrated in Figure 7. The air-inclusion nozzle comprises one or more air-intake openings (17), at a side thereof, in communication with a tapered intermediate nozzle/tunnel (16) of the air-inclusion nozzle for conveying activator fluid. During the spraying operation of the air-inclusion nozzle, activator fluid firstly enters a tapered intermediate nozzle/tunnel (16) which accelerates the activator fluid and projects the flow in to a tapered opening of a Venturi (18). This creates a vacuum that causes air to be sucked in though the side air-intake openings (17). Air and activator fluid are caused to mix in the nozzle body (18) and this aerated activator fluid is then sprayed through an elliptical nozzle orifice (19 e.g. flat fan orifice). Sprayed activator fluid thereby is caused to contain air bubbles (20) and produces a flat fan shape of spray effect have been found to be particularly advantageous in directing the activator uniformly only to those areas of the wall requiring treatment. Also the included air in the sprayed droplets acts as shock absorber to minimize the sprayed activator fluid splashing back and building up on the floor below the target area. This improves cleanliness. A flat fan nozzle may be used that is also an air-inclusion nozzle. This combination has been found to provide maximum spray accuracy and cleanliness.

The viscosity of the activator fluid is preferably less than about 50000 cP (1 cP = 1 mPa-s), or preferably between about 30cP and about 2500 cP. Preferably the viscosity of the activator fluid is between about 100 cP and about 2000 cP. The Applicant has found that the optimum range for viscosity of activator solution to be between 200-1700 mPas. This viscosity permitted the most effective spraying of fluid activator solution from an atomiser spray bottle such as is readily available. It also produced an aqueous film (item 1 1 , Fig.3) upon a vertical wall which did not significantly run down the wall surface, did not significantly soak into the pores of the wall surface (e.g. a very porous skimmed plaster surface), and thereby stayed available on the surface to activate the pre-paste adhesive layer on the wallcovering (item 4, Fig.3). It was found through experiments by the Applicant that the spraying of water alone onto a wall surface is very often wholly insufficient to effectively activate the pre-paste adhesive layer. Retention of the water at the wall surface was poor in porous walls which tended to soak-up pure water intended for the pre-pasted layer of the wallpaper. The running-down of water was high in non-porous walls, again, this reduced the amount of water available for the pre-pasted layer of the wallpaper and in both cases water damage to the wall/floor was increased. The adhesive of the pre-pasted wallcovering may be a modified poly (acrylic acid) sodium salt, or may be another adhesive compound. For example, the pre-pasted adhesive preferably comprises a blend of water soluble polymers, which may be either modified poly (acrylic acid) sodium salt or polyacrylic acid / poly acrylamide copolymer. Preferably the pre-paste may comprise polyacrylic acid / poly acrylamide copolymer as this has been found to provide a better combination of swell, wet tack, slip/slide and final adhesion. The pre-pasted adhesive may be activated through absorbing the water from within the aqueous film 1 1 formed on the wall 10 by the super water absorption nature of the polyacrylate species. The pre-pasted adhesive layer 4 may absorb sufficient water in few second and swell to form a hydro gel. On other hand, the pre-pasted adhesive may be activated by seeking out water from the activator solution 1 1 and swelling to form a hydro gel. The gel, in either case, will dry to form into a continuous dry film, and become the bond between the wallpaper and wall.

The pre-pasted adhesive is arranged to swell to form a gel after contact with the adhesive activator solution. Once dried the adhesive (e.g. polymer) preferably forms a cohesive bond between the substrate (e.g. paper) of the wallpaper construction and the wall. The viscosity of the gel, when formed in this way, may be related to:

i. The quantity of adhesive from the wallpaper;

ii. The quantity of water available from the activator solution;

iii. The molecular chain length of the polymer(s) used in the adhesive;

iv. The degree of hydrolysis of the polymer(s) used in the adhesive;

v. The blend of polymers used in the adhesive (if blended).

For example, optimal gel properties (e.g. swelling) may be achieved by employing any one or more of the following:

i. Increasing the adhesive coat weight of pre-pasted wallpaper to between about 4 gsm and about 6 gsm. Nevertheless an adhesive coat weight of pre-pasted wallpaper of between 2-3 gsm also works, but is not optimal.

ii. Altering the degree of hydrolysis to make the polymer more water soluble - preferably in the range from about 75% to about 85%.

iii. Altering the blend of acrylic copolymers so that the molecular weight is higher.

The adhesive activator may be applied to a wall in relatively much lower quantities than would be the case were the viscosity of the solution not controlled. This reduces the cost and working time required to decorate a room. This is connected with the formation of a gel-state material (item 1 1 , Fig.3) on the surface of the wall that helps to retain moisture on the surface, preventing it from penetrating the wall. Water that has penetrated a wall cannot contribute to the adhesion of the wallpaper. In Table 3, the results of experiments by the Applicant are presented. In these experiments, a one metre-squared area of wall was sprayed with either tap water, or with an aqueous activator solution as shown in Figure 2. A pre-pasted wallpaper of standard size was then applied to the prepared wall. The minimum amount of activator (water, or aqueous solution) required to retain the wallpaper on the wall was determined by trial and error in each case. Two different wall types were considered:

(1) a skimmed plaster wall which had been pre-coated with a standard wall primer paint;

(2) a bare skimmed plaster wall which had no pre-coating at all.

Table 3

Wall Type Water as Activator Activator solution

Primer-coated wall 182 mL/n 176 mL/n

Skimmed plaster wall 432 ml_/n 170 ml_/n One can see that on all wall types tested, the present invention required less activator to be applied to the wall to achieve successful wallpaper hanging. Most notably, when applied to a bare, skimmed plaster wall, over 2.5 times the amount of activator was required when water alone was applied in conjunction with existing pre-pasted wallpapers. This is because, once applied on the porous wall surface, such as skimmed plaster wall, the quick water adsorption of the wall competes with the pre-pasted adhesive for water at the wall surface. This results in insufficient activation of pre-pasted adhesive. Also, it has been found that entrapped bubbles or raised up edges were formed at/under the test wallpaper after it had dried. When applying only water alone as the activating agent, an existing pre-pasted wallpaper product was used that had 12gsm of pre-pasted adhesive coated on the back of the product. This was 4x (four times) pre-paste adhesive than was found to be necessary to provide in the pre-pasted paper (item 1 , or 2, Figs.1 to 3) of the present invention used in conjunction with the aqueous solution activator. This shows that these existing pre-pasted wallcoverings require a much larger amount of adhesive to be able to ensure that the wall-covering product will actually adhere/hang to a wall when activated with water alone as described above. According to the invention, lesser application of pre-pasted adhesive and activator solution will save capital costs to produce the product. Furthermore, this reduction in adhesive quantity has a further practical advantage in making the dry-stripping of wallpaper easier. Dry-stripping is the process of removing existing wallcoverings prior to applying a new wallcovering and is usually done manually by peeling the existing wallcovering from the wall by force. Over-adhesion of wallcoverings usually requires scraping implements to be used to scrape a wallcovering from a wall surface, and this is very labour intensive and very often damages the wall surface. Preferably, the coat weight of pre-paste adhesive on the pre- pasted wallcovering of preferred embodiments of the invention is from about 4gsm to about 6gsm. Peel Strength Test:

A pre-pasted wallpapers (item 1 , Fig.2) was bonded on to walls (item 10, Fig.4) comprising:

(1) a bare skimmed plaster wall (12.5mm plaster board) which had no pre-coating at all; (2) a skimmed plaster wall which had been pre-coated with a US-standard wall primer paint ('Roman' brand, popular in USA);

(3) a skimmed plaster wall which had been pre-coated with a UK-standard wall primer paint ('Johnson's' brand, popular in UK).

This was done by spraying the aqueous activator solution (item 9, Fig.2) onto each wall surface and applying a pre-pasted wallpaper of the present invention to that surface, as is shown schematically in figures 2 to 4. For comparison, an existing pre-pasted wallpaper product was also applied on the same type of wall surfaces which had been prepared by spraying tap water, as adhesive activator, onto the wall surfaces. As an additional comparison, samples of standard wallpaper were also prepared on the same surfaces by directly pasting wall-paper paste onto the wallpaper and applying that to the walls, in the old-fashioned way, as control. The prepared samples are allowed to dry for 4 days before a peel strength test was applied. During the peel strength tests, a given wallpaper sample was peeled backwards at a 180 degree angle at a speed of 152.4mm per minute peel strength in compliance with the ASTMD903-98 standard. The results are shown in Figure 6. Figure 6 compares peeling strength among an example of paste-on-wall wallpaper, an embodiment of the present invention and an example of pre-pasted product, when these wallcoverings are delaminated from a skimmed plaster wall or a coated wall. Figure 6 illustrates that wallpaper samples prepared by the methods of applying liquid adhesive paste adhesive upon non-pre-pasted paper and spraying the aqueous activator solution upon a wall surface (see Figs. 2 to 4) substrate have very similar peel strength of strength about 0.0035- 0.0061 KgF/mm. However, the force required to peel the existing pre-pasted wall- paper product, activated by pure water sprayed upon a wall, is about 7 times higher (0.03-0.039 KgF/mm). This shows that the pre-pasted wallpaper activated by the aquesous activator solution of the present invention has the same dry strippability as old-fashioned paste-on-wall wallpaper, and much better than the existing pre-pasted wallpapers.

Colour indicator.

The colour indicator may be a type of Acid-Base indication chemical with alkaline additive (e.g. NaOH). The chemistry involved has been well described in technical publications, for example see: Hand Book of Acid-Base Indicators (Sabnis, R.; CRC Press, 2007). In the solution state, the colour indicator may be arranged to introduce a primary colour to the sprayed area on wall. This primary colour indicates to the decorator whether or not an even and full coat of activator solution has been sprayed to a particular area. The indicator is arranged to react with a component of air (e.g. 0 ₂ or C0 ₂ ), which turns it to a secondary colour (or colourless) and does not interfere with the adhesion of the wallpaper to the wall. The time required to allow the activator's colour to fade is variable according to the activator concentration and the amount applied to a wall surface (e.g. activator layer thickness). As an example, when spraying 341 ml_ of 2% (weight/vol.) activator solution on 1 m ² of wall surface area (which corresponds to 6.8gsm of dry activator material upon the surface), the time required for the fugitive colour indicator to substantially totally fade from pink to colourless was found to be not less than 5 minutes and 34 seconds.

The time required to achieve a substantially full colour fade is found to be variable according to the pH value of activator solution or the quantity of alkali addition. For example, using Phenolphthalein as a colour indicator, the colour-transition pH value is 8.2. More alkali can result in a strongly-coloured basic activator solution which requires a longer time to react with ambient carbon dioxide in order to reach the necessary colour-transition pH value. Other options include, but are not limited to, addition of a basic buffering agent or slow release vehicle containing alkali or buffering agent.

As an example, Phenolphthalein (colour indicator) powders may be contained in the activator during its production/formulation. Sodium hydroxide may also be added in the formulation to maintain the activator solution an alkaline condition (pH>8.3). This time indicator solution shows a pinkish colour. After spraying this activator on a wall surface, carbon dioxide in the air is found to dissolve into the activator solution and this leads to the pH falling below its colour change threshold (pH<8.2), which turns indicator colourless:

OH-(aq) + CO _z (g)→ C0 ₃ ^2" (aq) + H ⁺ (aq) Alternatively, the colour indicator may be a photo-unstable compound or photo sensitive dye, such that colour is lost on exposure to light or specific frequency of electro-magnetic radiation.

Various photo-unstable or photo-sensitive compounds may be used in this application. One possible type is a photochromic chemical, which is able to reversibly transform its chemical species between two forms by the absorption of electromagnetic radiation. For example, under UV radiation (250-380 nm), spiropyran can transform its structure into colour emitting merocyanin-form. Another example is a phosphorescent pigment, such as zinc sulphide, calcium sulphide and strontium aluminate. These materials may be charged in normal (visible) light, and then glow and slowly fade out (few minutes to several hours) in darkness.

The present invention provides a pre-pasted wallcovering and an adhesive activator designed to apply directly to wall surfaces to efficiently activate the dry-adhesive of the pre-pasted covering with reduced cost effort and with greater ease of stripping at a later date. Hanging of wallcoverings may simply be done by spraying activator solution on a wall surface and applying wallcovering sheets to the sprayed area. This hanging method has eliminated the need for applying traditional wet wallpaper paste. Thus decoration becomes much cleaner. In preferred embodiments, a spray bottle is the only tool required to install wallpaper and no professional skills and tools (e.g. water reservoir for pre-pasted wallpaper; or roller, tray, bucket and paste table for paste-on-wall wallpaper) are required. Of course, the aqueous activator solution may be applied to a wall by other means, such as by brush, roller or the like. Colour indication chemicals within the activator, may indicate to a decorator whether or not an even and full coat of activator has been coated/sprayed to a particular area. This colour indication is helpful to applying an activator layer of even coverage thereby to save a material and effort from unnecessarily re-coating/spraying the same area. The activator preferably is a rheology controller in nature. Thus, after coating/spraying activator on a wall and applying the pre-pasted wallcovering thereto, the activated adhesive will form an aqueous film and swell to a layer of gel. The gel will permit the wallcovering to be moved by sliding across the wall to align. This coat/spray-on-wall and hanging method not only provides better adherence of wallcovering on a wall, but also does not compromise the dry strippability of the wallcovering.

Spraying Pattern: To prevent overspray of an adjacent area, such as area of wall cover that may already have been installed, doorframes, etc., it is advantageous to apply the activator only to the intended treatment area. Nozzles that spray a flat sheet of liquid and produce a flat fan spray pattern have been found to be particularly advantageous in directing the activator uniformly only to those areas of the wall requiring treatment. The pattern is formed by providing an elliptical exit orifice for forming a fan-shaped spray structure, or by providing an exit orifice (e.g. round) arranged for directing output liquid on to a deflective surface that is tangential/oblique to the liquid flow from the exit orifice. In the elliptical orifice type fan nozzle (e.g. without a deflection surface), the pattern spray out of the exit orifice is directed in line with the flow axis of the outlet orifice (i.e. the outlet pipe). The deflection type nozzle produces the flat fan pattern by deflecting the fluid stream against the deflection (e.g. curved) surface after it has exited from the nozzle orifice. Examples are given in Table 4 (see page 20).

The examples and embodiments of the invention described above are presented to aid an understanding of the general inventive concept of the present invention, and are not intended to limit the scope of the invention, e.g. as is defined by the claims. Variations, modifications and equivalents to the stated examples, such as will be readily apparent to the skilled person are encompassed within the scope of the invention.

Table 2

4.0% 49700 None atomization None atomization None atomization

Table 4

SUBSTITUTE SHEET RULE 26