| JP3022268 | ADHESIVE COMPOSITE BODY |
| JP63303731 | INCOMBUSTIBLE LIGNEOUS COMPOSITE SHEET |
| JP03258538 | COMPOSITE AND ITS MANUFACTURE |
Desmet, Jan (Kozakstraat 56 Wevelgem, B-8560, BE)
| 1. | 1) A flexible layered sheet (1) comprising a veneer top layer (2) laminated with its underside (6) to a backing layer (3,15) which backing layer has a controlled moisture absorbing capacity. |
| 2. | A layered sheet (1) according to claim 1 wherein the veneer top layer (2) has a thickness of less than 0.25 mm. |
| 3. | A layered sheet (1) according to claim 1 wherein the veneer top layer (2) has a thickness of at least 0.25 mm and wherein said veneer layer in the layered sheet is broken up to a controlled extent into its fibers along their grain direction. |
| 4. | A layered sheet (1) according to claim 1 wherein the backing layer (3,15) comprises a resin impregnated fiber sheet. |
| 5. | A layered sheet according to any previous claim wherein said backing layer (3) comprises a moisture absorbing bottom layer (4) and a moisture repellent intermediate layer (5) between said bottom layer (4) and the veneer top layer (2) and which intermediate layer (5) sticks to the underside (6) of the top layer by means of a first interposed adhesive sublayer (8) and sticks to the upper side (7) of said bottom layer by means of a second interposed adhesive sublayer (10). |
| 6. | A layered sheet acc. to claim 5 wherein the intermediate layer (5) comprises a moisture repellent coating. |
| 7. | A layered sheet acc. to claim 5 wherein said intermediate layer (5) comprises a moisture barrier foil. |
| 8. | A layered sheet according to claim 7 wherein the barrier foil (5) is a metal foil. |
| 9. | A layered sheet according to claim 7 wherein the barrier foil (5) is a plastic foil. |
| 10. | A layered sheet according to claim 5 wherein the first sublayer (8) comprises a fibrous web (11) provided on both sides with an adhesive resin coating (12) respectively (13). 11) A layered sheet according to claim 8 wherein the adhesive surfaces of the first and second sublayer both facing the metal foil is of a similar composition. |
| 11. | A layered sheet according to claim 1 comprising a fire retardant agent. |
| 12. | A layered sheet according to claim 12 wherein the fire retardant agent is present at least in or near the underside (6) of the veneer top layer (2). |
| 13. | A backing layer (3) for use in a layered sheet (1) according to claim 1, comprising in combination a bottom layer (4) and a moisture repellent intermediate layer (5) with a second sublayer (10) interbetween said bottom layer and said intermediate layer and with a first sublayer (8) on top of said intermediate layer (5). |
| 14. | A layered sheet according to claim 1 wound up as a cylindrical coil wherein the grain direction in the veneer layer (2) is perpendicular to the winding axis of said coil. |
| 15. | The use of a flexible layered sheet (1) according to claim 1 as a wall paper whereby at least the wall is first coated with an adhesive comprising a dispersion of an acrylic polymer in water and whereby the sheet (1) is applied and sticked to the wall in a conventional manner. |
| 16. | The use of sheet (1) as in claim 15 wherein the wall paper is in the form of strips with a width of between 20 cm and 110 cm and the direction of the veneer grain is perpendicular to the width of the strips. |
Background art The British patent application GB 2 191 731A describes a wall covering that has a backing layer coated with adhesive to which is applied at least two areas of different material. The material of the areas may be of the same nature, but of different shapes, e. g. of sheetlike, threadlike or particulate shape. The areas may be strips or other forms or shapes and the material may be applied by hand or be drawn from a roll of sheet or be threads applied through a reed. The material may include amongst others wood veneer. From US patent 4 047 344 it is known to cover a wall with wood veneer made up of various lengths of veneer strips disposed end-to-end in parallel, diagonal rows over a wall surface. Thereby glue is used.
It is also known to produce a laminated flexible sheet wherein a wood veneer top layer is glued onto a paper base sheet. After the glueing operation the veneer structure is broken up. This renders the laminated sheet more flexible. This flexible veneer sheet is used to cover supporting surfaces or substrates with a rounded off, curved or any other shape. It is glued onto these surfaces with a polyvinylacetate adhesive, a contact adhesive or a urea-formaldehyde glue. However these types of glues have the disadvantage that they dry and thereby develop their effective adhesive force either very fast or very slowly. As a consequence, when they dry too fast, they do not leave enough freedom of handling time to apply the laminated sheets reliably and at a suitable speed as a wall covering. In addition, with the aforementioned glues a considerable pressure would generally be needed to stick this flexible sheet as a wall paper or onto another supporting surface.
Moreover, conventional glues for wall papers often contain a considerable amount of water or other solvent or diluent or dispersant for the active component of the adhesive or glue. This dissolving or dispersing agent can then generate an undesirable and uncontrollable swelling effect in the paper backing and/or in the veneer top layer. As a
result, upon development of the adhesive force through drying, the laminated sheet tends to shrink to an uncontrollable extent, in particular in the direction transverse to the wood grain of the veneer layer. This shrinking effect may produce small gaps or cracks between the edges of adjacent sheets after application to e. g. a wall.
Description of the invention It is now a general object of the invention to provide a flexible layered sheet with a wood veneer or similar woodlike top layer that can be applied in a usable manner as a wall covering, in particular with the conventional glue compositions available for that purpose.
It is a further object of the invention to provide such a flexible layered sheet that avoids any excessive swelling during and shortly after its application to a wall and that avoids in addition excessive subsequent shrinking after its application to any substrate or wall during drying of the glue.
It is still a further object to provide such a layered sheet that is particularly suitable for adhering to a wall using an acrylic dispersion glue. With the term wall or supporting substrate is meant any substrate that is suitable for painting or paper covering. Preferably said wall consists of wooden board, particle board, plywood, MDF, HDF, plasterboard, gypsum board, a plastered wall, plastic, ceramic, glass or metal plates.
According to the invention the above described drawbacks of the state of the art are avoided by providing a flexible layered sheet comprising a veneer or other thin woodlike top layer laminated with its underside to a backing layer which backing layer has a controlled moisture absorbing capacity. The invention is in particular applicable to flexible layered sheets wherein the veneer layer has a thickness of less than 0.25 mm. When the veneer top layer is relatively thick, e. g. at least as thick as 0.25 mm then the veneer layer in the layered sheet is broken up to a controlled extent into its fibers along their grain direction.
The feature of having a relatively thick veneer layer broken up to such a controlled extent is necessary to produce sufficient and controlled flexibility in the layered sheet, especially in the direction transverse to that grain direction. Indeed, the layered sheet according to the invention has to be applied by hand as conventional wallpaper and therefore requires considerable flexibility.
The terms"controlled moisture absorbing capacity"mean that, on the one hand sufficient penetration of the viscous glue composition, that is applied beforehand on the wall surface, is achieved through impregnation in the pores on the backside of the flexible layer upon normal pressing of the layered sheet by hand against the wall. The impregnation is sufficient when it produces a durable adhesive anchoring force of that backside to the wall surface upon natural drying. On the other hand it means that the moisture absorbing capacity according to the invention is limited and does not result in a substantial penetration of water or other solvent, diluent or dispersant component of the glue so as to reach and excessively moisten and swell the veneer top layer of the layered sheet.
In other words, according to the invention a barrier to such excessive penetration is built into the layered structure somewhere under the veneer top layer. This barrier could be in the form of a separate foil impermeable for water and/or other solvent. It could also be a hydrophobic, water repellent, oleophobic or solvent repellent intermediate layer.
Measures and means for realising a controlled moisture absorbing capacity in the backing layer are varied and often complementary to each other. According to the invention the backing layer generally comprises a resin impregnated thin woven, knitted, braided or nonwoven fiber sheet or a soft plastic foam layer. A properly resin impregnated sheet can on itself ensure a suitable controlled moisture absorbing capacity as defined above.
Preferably however said backing layer comprises a moisture absorbing bottom layer and a moisture repellent intermediate layer between said bottom layer and the veneer top layer and which intermediate layer sticks to both the underside of the top layer and the upper side of said bottom layer. Said intermediate layer is e. g. a separate moisture barrier foil such as a metal, e. g. an aluminium or a plastic foil or it comprises a moisture repellent coating.
The intermediate layer can stick to the underside of the top layer through interposition of a first suitable adhesive sublayer comprising e. g. a fibrous web provided on both sides with an adhesive coating. The intermediate layer can further stick to the upperside of said bottom layer by means of the interposition of a second adhesive sublayer.
Brief description of the drawings The invention and its characteristics and distinctive features will now be explained by the description of some examples and preferred embodiments and with reference to the accompanying drawings. It should be noted that these examples are not regarded as a
restriction of the scope of the invention. The drawings illustrate in an exploded view a cross section of how the layered sheet can be composed or built up.
Figure 1 shows a simple embodiment of the layered sheet according to the invention. It comprises a properly resin impregnated fiber sheet that largely ensures on itself the controlled moisture absorbing capacity.
Figure 2 relates to a preferred embodiment of the layered sheet 1. It comprises in essence a veneer top layer 2 sticked to a composite laminated backing layer 3 comprising on its turn the moisture repellent intermediate layer 5 and the moisture absorbing bottom layer 4.
Detailed description of the drawings In both embodiments of figure 1 and 2 the veneer top layer 2 can be as thin as 0.2 mm but can also have a thickness of about 0.6 mm and even up to 1 mm and any thickness interbeween. By using a thin veneer layer 2, i. e. with a thickness of less than 0.25 mm, it is not necessary to submit either this veneer layer separately or the layered sheet 1 to a flexing or tenderising operation (as described below) to increase its flexibility.
The veneer top layer 2 of the layered sheet 1 is a thin slice of wood, usually thinner than 1 mm. It can be obtained by different cutting processes. It can be sliced, stay-log or rotary cut according to the machines used for cutting. Once the veneer is cut into a thickness of usually 0.6 mm or less it has to be dried and packed so that it can be spliced into a face or layon in a size that will match almost the finished product size. According to the copending European patent application no. 01203592 of Applicant this layon or face is then sticked by lamination to a backing sheet 15 such as a paper or a fleece, i. e. a nonwoven fiber sheet 15 as shown in figure 1. In the case of a paper backing 15, the paper has received an impregnation with a thermosetting acrylic polymer and has been covered with a thermoplastic ethylacrylate-styrene resin coating 16 that is melting down when exposed to heat and so sticks to the underside 6 of the veneer under pressure (in a hot press). In case of a fleece or membrane or other nonwoven web 15 made of e. g. cellulose fibers and polyester fibers, the impregnation is made with a thermoplastic polyvinylacetate resin or such a resin in combination with a thermosetting acrylic polymer. Alternatively, the impregnation could be replaced by a glue coating 16 (eg. of polyvinylacetate, an acrylic polymer or a polyacrylate) that could be applied separately to the backing paper 15 or to the veneer sheet 2. In any case, the impregnation and/or coating with these resins or glues renders the backing sheet 15 less permeable to water. Indeed these resins have a moisture repellent character. It thereby thus limits the moisture absorption capacity of the
backing sheet 15 to a certain extent with the ultimate effect of less swelling of the veneer top layer during application on a wall and less shrinking afterwards. The non impregnated sheet 15 has preferably a weight of between 25 and 50 g/m2.
Once this lamination step is done, the combination of this paperbacking sheet 15 with the veneer sheet 2 will receive a treatment by which it will become flexible to a controlled extent. This treatment is in particular necessary when the veneer sheet 2 has a thickness over 0.25 mm. The combination of veneer sheet 2 with backing sheet 15 is therefore advanced as a laminate and perpendicular to the grain direction into a flexing machine.
That machine comprises two rollers with a relatively large diameter and a very tiny steel roller interposed between the larger ones e. g. similar to figure 5 of US patent 4047344.
The diameter of the steel roller defines the flexing radius. This radius amongst others allows to control the extent of breaking. This steel roller breaks up the wood fibers along their grain direction to a certain extent because of the adjustable flexing action and pressure produced by the tiny steel roller. In this way it reduces the bending modulus of the wood veneer layer on itself and of the laminate. This flexing process on a single non- laminated wood veneer layer is generally called"tenderising". Next to the fact that in this way the flexible veneer layer has no longer a tendency to irregularly and uncontrollably crack as with a plain non tenderised veneer sheet, it has the advantage that the laminate can also be bent easily e. g. around a corner (without cracking at the corner edge).
After this operation, the flexible layered sheet comprising the veneer top layer and the backing is cut to the desired size so that it can be used and applied as a wall covering.
The length of the sheet (in the direction of the grain) is preferably between 2.30 m and 3.00 m, i. e. the normal height of a room. The width of the wall paper strips will preferably be between 20 cm and 110 cm. The veneer top face may afterwards be polished or sanded, either before or after application to the wall or substrate.
For the application of veneer to cover a wall or other support its surface must be properly prepared as required in general for other good quality wallpaper. First of all the wall must be cleaned and made flat and smooth to remove all holes and bubbles. The wall will then receive in a conventional way a coating of well rolled-out glue smeared out in all directions. A sufficient thickness is needed. The glue is preferably an acrylic dispersion glue or similar.
The invention covers thus also the use of a flexible layered sheet 1 as a wallpaper whereby at least the wall surface 18 is first covered with an adhesive coating 17
comprising a dispersion of an acrylic polymer in water and whereby the flexible sheet 1 is applied and sticked with its bottom surface 9 to the wall in a conventional manner in the form of strips with any suitable length and width as described above. The flexible sheet of veneer can be used in a lot of possible ways to decorate a room. It can cover the walls from floor to ceiling or less or with a certain pattern such as so called marquetterie. The old style house can be imitated easily and there is no need for using panels or woodframes to produce a wood aspect look or design in rooms.
Once the layered sheet is fixed to the wall, the product can then be given its final look. It can be stained, coloured, painted, lacquered or the wood design can be given any wanted finish in the decoration of the wall. The veneer surface can also receive a painted decoration pattern. After a lacquering operation the veneer top surface can be washed easily.
With reference now to the preferred embodiment of figure 2, the control of moisture absorption is further improved by inserting in the laminate an express moisture repellent intermediate layer 5 between the veneer layer 2 and a bottom layer 4. Said bottom layer 4 has a certain moisture absorbing capacity. The bottom layer 4 can have about the same composition as layer 15 described above. The intermediate layer 5 can comprise a conventional moisture repellent coating. The layer 5 can also be a separate moisture barrier foil such as an aluminium or other metal foil with a thickness between 10 um and 30 um. A substantially water impermeable plastic foil such as a polyethylene film, or a plastic foil provided with a water impervious metal coating is also an option. The advantage of a metal foil, besides its barrier function, is also its non elastic nature that counteracts any tendency to extend with any swelling (due to any increase of humidity in the room) and even to shrink (as a consequence of decrease of humidity) With regard to methods of manufacturing the layered sheet 1, the intermediate layer 5 is preferably combined in a hot press with the veneer layer 2 and with the upper side 7 of the bottom layer 4 after interposition of a first adhesive sublayer 8 and a second adhesive sublayer 10. The first sublayer 8 can be a thin fibrous web 11 impregnated and provided on both sides with a thermoplastic or thermosetting adhesive coating 12, respectively 13.
The second adhesive sublayer 10 can have a thermoplastic or thermosetting composition as well. When a metal foil is used as a barrier 5 the adhesive layers 13, resp. 10 of the first, respectively second sublayer, both facing the metal foil will preferably have a similar composition, such as a thermosetting polyurethane.
It is of course possible to combine in advance the layers 4 and 5 in the suitable order with the sublayers 8 and 10 to form a separate backing layer 3 for use in the layered sheet 1.
The backing layer 3 can then thus be delivered as an intermediate product with the suitable moisture absorption capacity for combining it afterwards with the veneer top layer 2, e. g. in a hot press. Alternatively, as intermediate products, other laminated precombinations of the adhesive sublayers 8 and 10 with the other sheets can be prepared: eg. a precombination of sheets or layers 2,8 and 5 with a precombination of layers 10 and 4 or a precombination of 2 and 8 with a precombination of 5,10 and 4.
In case the veneer top layer has a thickness of at least 0.25 mm-eg. 0.6 mm-the different sheets and layers 2,8, 5,10 and 4 are laminated under suitable heat and pressure to form a layered stack 1 and cooled down. This stack is then passed through a flexing machine as described above whereby the fibers in the veneer top layer 2 are broken up to a controlled extent. This flexing treatment renders the layered sheet 1 sufficiently flexible to wind it up afterwards as a cylindrical coil, eg. on a mandrel with an outer diameter of at least 20 cm.
According to an aspect of the invention the grain direction in the veneer top layer 2 is thereby oriented perpendicular to the axis of the winding operation. This winding direction offers further the advantage of a substantially balanced flexibility in all directions in the plane of the flexible layered sheet 1 upon subsequent unwinding for application to a wall.
Indeed, it counteracts any possible tendency for the flexible layered sheet 1 to curl along its logitudinal edges parallel to the grain direction after tenderising when it would be wound up with the grain direction parallel to the axis of the winding or coiling operation.
The layered sheet 1 can further comprise fire retardant agents. Fire retardant agents can be added e. g. to the paints or varnish compositions for laquering. Such agents can also be incorporated in the web 15 or glue coating 16 (figure 1) or in the first sublayer 8 at least near the underside 6 of the veneer top layer 2 (figure 2). Upon lamination of both layers 2 and 15, respectively 2 and 8, the fire retardants can then penetrate more or less in said underside 6 by impregnation. Such agents can also be incorporated in the second sublayer 10 and/or the bottom layer 4 shown in figure 2.
EXAMPLE A cherry wood veneer face layer 2 with a thickness of 0,6 mm, a length of 2,7 m and a width of 0,6 m was laminated in a hot press with a backing layer 3 comprising a 12 um
thick aluminium foil 5, a first sublayer 8 comprising a thin paper web 11 comprising cellulose and polyester fibers (weight of about 30 g/m2) covered with an adhesive offering a good adhesive bond to the veneer such as eg. an acrylic polymer layer 12 with a weight of about 50 g/m2. The composition of layers 13 and 10 facing the foil 5 can be equal or similar to the adhesives used in packing bricks that contain an aluminium foil. The composition of layers 13 and 10 can also comprise a polyurethane with a weight of preferably at least 5 g/m2. The bottom layer 4 was a non woven paper web as, or very similar to the paper web 11. After laminating said backing to the veneer layer 2 in a hot press, and cooling it down it was flexed in a tenderising operation as described before. At the outlet end of the tenderising machine the layered sheet 1 was then coiled with an outer diameter of between about 20 and 30 cm and with the axis of the coil being perpendicular to the grain direction of the veneer. About 20 sheets with a length of 2,7 m could be stored concentrically inside one another and packed in a box with a square bottom surface (side of the square 35 cm). For sheets with a width of 0,6 m the height of the box is then about 70 cm.
A plastered wall was coated with a conventional acrylic dispersion glue in water and a couple of the flexible layered sheets with a width of 0,6 m were applied by hand as usual for wall coverings with their longitudinal edges closely side by side in a vertical direction.
No visible swelling was observed during the first days after application to the wall. After three months no cracks nor gaps were visible between the two adjacent sheets in their border area on the wall. This means that in any event any transverse swelling or shrinking of more than 0, 1% and even of more than 0,05% is not expected.
The use of the flexible layered sheet 1 as a wall paper implies also that it can be removed from the wall in a satisfactory manner when replacement is due. A removal test was carried out on a layered sheet 1 according to figure 2 three months after it had been applied to the wall. The wall paper was removed by a conventional steamer for that purpose. The heat was easily transmitted and spread through the aluminium foil 5 and the backing layer 4 towards the adhesive interface 17 with the wall. This interface was thereby softened and the wall paper detached from the wall by simply tearing it off. Removal by dry heat, eg. by a hot air blower is possible as well.
Having described the invention with reference to certain preferred embodiments it is clear that modifications of certain parameters and of the composition of the different layers 3 to 16 can be contemplated to achieve eg. a specifically desired flexibility and/or moisture absorption capacity of the layered sheet. In particular the nature of the wood and the
thickness of the veneer layer 2 can have a definite influence on the behaviour of the layered sheet 1 as a wall paper under different circumstances of temperature and humidity of the environment. Adjustment for some parameters has then to be carried out, taking account however of the basic principles as herein described.