GB2224972A - Resin laminate with superficial layer of metal foil coated with pigmented resin - Google Patents

Abstract

A resin laminate is made by pressing a stack of resin-impregnated papers, which stack has at one surface a metal foil whose outer surface is coated with pigmented resin. The resultant laminate is novel, as well as the method. By using a plate with a variegated surface texture to press the stack, a laminate with a variegated surface texture is formed. The texture imparted to the laminate may be microtexture (determining gloss level) or macrotexture.

Description

DECORATIVE STRUCTURE The present invention relates to a decorative resin laminate, which has a surface layer of metal foil or film coated with pigmented resin. The invention also relates to a method of making such a laminate.

Many buildings, especially industrial or commercial units, have a decorative exterior cladding. One conventional material for such cladding and which can be given a variety of surface textures has a surface consisting of melamine formaldehyde resin reinforced with cellulose fibers. In practice, ageing of this material when used externally causes breakdown of the interface between the resin and the reinforcement which is manifest in severe "fiber blooming" which gives a "grey" appearance to the surface, severely damaging the decorative effect.

Gloss values are significantly altered and a noticeable change in the colour of the surface is obvious. One other disadvantage of this construction of exterior panel is the poor dimensional stability of this product. The dimensions of the panel can alter by several percent when the humidity changes.

Another conventional decorative cladding material is aluminium sheeting. The decoration of aluminium sheeting is obtained by coating or painting the sheeting with a suitable covering or paint. The end result is a smooth surface of uniform gloss level. The surface may, however, be provided with a three-dimensional structure at the macroscopic level.

British Patent No. 1176904 discloses a laminate comprising a plurality of resin-bonded paper layers and a decorative surface layer of oxidised aluminium foil. The laminate, therefore, always has a metallic look. The laminate is weather-proof and corrosion resistant. The surface of the foil may be either smooth or suitably patterned to provide the desired decorative effect.

A method has now been devised for making a new resin laminate of the type comprising a plurality of resin-impregnated papers or sheets bonded together. The new laminate is suitable for exterior use and can provide a non-metallic look.

In one aspect, the invention accordingly provides a method for making a resin laminate. In the method, there is formed a stack of resin-impregnated sheets. As a surface sheet of the stack there is provided a metal foil whose outer face is coated with pigmented resin. The stack is then pressed together at elevated temperature so that the resin-impregnated sheets and the metal foil bond together.

The resulting panel has enhanced dimensional stability and resists warping when subjected to a relative humidity difference between opposite faces. The product is also relatively fire-proof and may be cold formed more readily than conventional laminate without breaking. The decorative appearance of the panel is retained well, compared with that of conventional resin cladding.

Moreover, by choice of appropriate pigments a wide variety of non-metallic surface colours may be provided. The process further has the advantages that it requires only starting materials which are available on the market at relatively low cost and that special plant such as the anodic oxidising bath of British Patent No. 1176904 is not required. As will be explained more fully hereinafter, an additional attraction of our new process is that it may be used to impart to the laminate surface any desired gloss level or gloss pattern and/or a three-dimensional decorative structure.

An additional advantage of the inventive process is that it may readily be used to form a laminate with a metal film applied to both faces. If the laminate is to be used as surface covering, only one of the metal films need have a pigmented resin coating but both metal films may be coated. The use of a sandwich construction with two outer metal films can enhance moisture or fire resistance if the laminate is installed in a location where both faces might be exposed to moisture or fire.

The product laminate is novel per se and the invention therefore includes a resin laminate having a superficial layer of metal foil coated with pigmented resin. The laminate optionally has a metal foil on its face opposite that to which the pigmented resin-coated foil is applied.

As stated above, the pigmented resin coating may be provided with any desired level of gloss by virtue of the process of the invention. Furthermore, the laminate surface may be provided with any desired macrotexture.

The gloss level of a surface is determined by the surface microtexture, i.e. fine structure not normally visible to the naked eye. The pigmented resin coating may be imparted with a desired gloss level in the inventive process by texturing the resin-contacting surface of the press or plate to match the microtexture (gloss) desired in the end product. For example, a highly polished plate results in a product with a high gloss level. Thus, in the method of the present invention the surface of a resin may be structured by applying to the resin a press or platen having a surface whose texture matches that which it is desired to apply to the resin.

The resin microtexture (gloss) is modified by applying the press at an elevated temperature at which the resin is deformable or plastic and under a pressure at which the surface texture is modified by the press. The resin is usually then cooled to a temperature at which the surface substantially retains the applied texture, and the press is withdrawn.

It will be understood that the resin must be deformable at an elevated temperature, e.g. at least 500C, but rigid (i.e. capable of retaining the applied surface texture) at ambient temperatures. Thus an amorphous resin having a glass transition temperature of above, for example, 500C would be suitable. Alternatively, a thermoset resin which cures under application of heat at a temperature of, for example, 500C or more could be used.

The resin selected would also be of a type suitable for forming a pigmented coating or lacquer. An exemplary resin is a urethane acrylic resin. It is contemplated that alternative coating resins would be polyvinylidene fluoride (PVF2), PVC plastisol (a plasticised PVC), polyester or urethane polyester.

The resin contains pigment of the desired colour or colours. The pigmenting of resins is a well understood technique which need not be described further here. The resin may be coated on the substrate at a conventional thickness, for example 15-30 ,um, or more.

The laminate preferably has areas of different gloss level, whereby an attractive decorative effect is achieved. Additionally or alternatively, the laminate surface may be provided with a macroscopic relief pattern. The relief pattern is embossed in the laminate during pressing, by the use of plate with a complementarily structured surface. Whereas gloss level is determined solely by the structure of the surface coating, any relief pattern must be embossed in the laminate itself.

In one preferred embodiment, the laminate surface has both a variegated gloss pattern and a three-dimensional macrostructure, i.e. relief pattern.

The areas of different gloss level and the elevated or depressed regions are preferably in register, for example as shown in the accompanying Figure. The Figure illustrates a laminate surface having regions 1 standing proud of the general plane 2 of the surface. The plane 2 of the surface is of high gloss appearance and the elevated areas 1 are of mat appearance. Typically, the separation between elevated regions 1 and depressed regions 2 in any laminate is 0.2 to 0.4 mm.

The metal foil is aluminium foil (e.g. on the order of 0.1 mm thick) in practice, but alternative malleable metals could be used, for example copper or copper alloy.

However, copper is not presently economic to use. For improved weather resistance, metal foil may be applied to both outer surfaces of the laminate, although only one surface of the laminate need be decorative when it is to be used as a covering.

The laminate may be any conventional resin laminate, for example. The laminate comprises a multiplicity of resin impregnated sheets or papers bonded together under pressure. Examples of suitable resins are phenolic, melamine or polyester resins. The aluminium or metal foil is desirably coated with an adhesive layer of resin on its inner surface to obtain good adhesion of the foil to the laminate. For example, phenolic butyrate resin may be used as adhesive if the laminate comprises phenolic resin.

Materials and procedures used in the preparation of laminates will be familiar to the reader and need not be discussed at length here.

In recent years there has been serious concern about the fire hazards associated with the use of plastics in buildings and public places. Plastics tend to be relatively flammable and a particular menace presented by plastics is the release of highly toxic fumes in fires.

Toxic fumes are a major cause of fire deaths in the United Kingdom. The laminate of the invention has been shown to be fire resistant and also releases less smoke and fumes.

The laminate has been subjected to the fire test specified in British Standard BS 476 and found to have low flame spread, even if the normal fire inhibitors are not incorporated in the laminate resin.

If only one face of the laminate will be exposed to fire it should be sufficient to coat only that face with resin-coated foil, for example if the laminate is applied to a concrete or other mineral substrate. However, especially if both faces of the laminate might be exposed to fire in use, a second metal foil may be adhered to the surface of the laminate opposite that having the pigmented resin-coated foil. The second metal foil may also be coated with pigmented resin, and generally will be if it is visible when the laminate is installed.

Having regard to its fire resistance, the inventive laminate is suitable as a cladding in locations where fire would present a serious danger, for example in underground railway systems. It is also known for modern buildings to include insulated panelling in their construction, for example opaque panelling may be used beneath windows. The use of a laminate of the invention over insulating plastics foam in such locations provides a relatively fire-resistant structure which will also be slow to release fumes.

A metal sandwich laminate (at least one of the metal foil layers of which may, optionally, have an outer coating of pigmented resin) is believed to be novel and is included in the invention, and the invention also encompasses the use of the inventive laminate as a cover for plastics insulating foam or other flammable material, e.g. such foam having one surface with the laminate adhered thereto.

The use of a sandwich construction enhances resistance to moisture as well as to fire and, as an additional benefit, improves the ability of the laminate to be cold formed into a curved shape without breaking or detrimental effects to the decorative surface. Normally, a resin laminate breaks if it is bent through only a small angle, but a foil sandwich construction can be bent through a larger angle without breaking and is more suitable for covering curved surfaces.

The invention includes a structure comprising laminate with a metal foil surface, especially a metal foil sandwich laminate, arranged in a curved configuration. In particular the invention includes such a structure having a generally curved substrate with whose shape the laminate generally conforms.

The conditions under which the texture (gloss and/or macroscopic structure) of the pigmented surface resin is modified must be carefully selected for optimum results.

For the texture of the press to be precisely imparted to the resin a suitable combination of pressure and temperature must be selected. The conditions must also be selected for the laminate resin to cure in an acceptable time. Thus combinations of relatively low pressure and temperature usually require an excessive laminate curing time. Likewise, to retain the imparted texture with precision the resin must be adequately cooled while still under pressure. However, in some instances, precise retention of the surface structure might not be required and it is therefore envisaged that the resin need not always be cooled before removal of the press.

Suitable conditions will vary from resin to resin, and can readily be selected by trial and error together with published data regarding the resin. If urethane acrylic resin is used, a pressing temperature of at least 800C and a pressure of 500 psi (3.45 MPa) produces suitable results. The resin is preferably cooled to below 500C, e.g. to 400C, before the press is removed.

Press plates may be prepared by etching and polishing, as is known. Suitable plates are widely available from manufacturers.

In the following Example, gloss units are determined in accordance with British Standard BS 3900 D5.

Example Aluminium foil covered laminate coated with urethane acrylic resin The product is a decorative exterior surfacing sheet which has controlled gloss and macrotexture characteristics. This can only be achieved by subjecting the surface of the product to controlled heat and pressure conditions during manufacture. The product is made from the following components: Surface layer: Urethane acrylic resin cured and pigmented to the required colour, coated to a depth of at least 20 pin.

Aluminium foil: 100 pm thick chromated aluminium foil. The reverse (inner) side of the foil has an adhesive coating of the order of 5-10 g/m2 of a phenolic butyrate resin.

Laminate: A multiplicity of phenolic resin impregnated papers.

Procedure The foil with its coating of pigmented cured urethane acrylic resin is bonded under heat and pressure to the multiplicity of resin impregnated papers. The coated surface of this assembly is pressed during manufacture against a prepared plate which has a specific engineered texture. This surface can be flat and glossy (highly polished) at one extreme or rough and heavily textured at the other. The characteristics of this plate are imparted to the surface of the coated laminate under heat and pressure. Cooling of the assembly to less than 500C under pressure is necessary to retain the imparted impression with precision.

The coated foil initially has a 600 gloss level of between 43 and 45 gloss units. Heating this foil to 1600C for one hour makes no significant change in the gloss level of the foil. By pressing the surface against a textured plate, this coating surface gloss level can be precisely altered. For example by pressing against a glossy plate a surface gloss of between 91-92 gloss units can be obtained. At the other extreme, by pressing against a plate with a mat finish a gloss of 10 to 10.5 gloss units is obtained. This variation in gloss can be achieved without chemical modification of the coating resin, which might be achieved by the addition of flattening agents. In addition one significant advantage in product gloss control can be achieved by this approach which is not possible by chemical modification of the coating varnish.A product surface with precise gloss changes is possible. For example a product was produced which had vertical stripes 1" (2.54 cm) wide of alternate high and low gloss levels. The high gloss areas had a gloss level of between 88.5 and 90.5 gloss units whereas the low gloss areas were in the region of 21.7 to 22.9 gloss units.

Unless careful control of the manufacturing conditions is achieved, precision in producing this gloss is not obtained. A minimum temperature is required to achieve enough plasticity (deformability), at a fixed pressure, to deform the coating into the required gloss condition. For example, in the stripe patterns mentioned above with high gloss readings of 88.5 to 90.5 and low gloss of 21.7-22.9, a pressure of 1400 psi (9.65 MPa) at a temperature of 1450C was used for 30 minutes before the assembly was cooled to less than 500C under pressure. The pressure was applied for 30 minutes to ensure curing and bonding integrity of the laminate. The same experiment repeated on another assembly at 1400 psi (9.65 MPa) and 500C for 30 minutes then cooled to below 400C before reducing the pressure, gave a product with a different appearance.The high gloss areas had a gloss level of 72.5 to 77 gloss units and the low gloss areas had a level of 62-65 units. The high pressure certainly deformed the coating from a gloss of 44-45 but without precision. The closeness of the gloss levels of 72 and 62 between the high and the low gloss areas makes the design effect on the product barely visible. The pressure during manufacture has a marked effect on the ability to give a precise gloss effect between the high and low gloss areas.

At a pressure of 500 psi (3.45 MPa) and 500C there was no visible high gloss/low gloss stripe effect in the product with gloss reading between 68 and 74 units being obtained. By increasing the temperature to 700C at this pressure more high gloss/low gloss definition is obtained. This definition was however lost when the product was manufactured at the lower pressure of 250 psi (1.72 MPa) at 700C. These results are shown in the table. At a temperature of over 800C at 500 psi (3.45 MPa) a product similar in appearance to that at 1400 psi (9.65 MPa) is obtained.

It is also important to cool the product before the pressure is reduced for precise transfer of the plate surface structure. The example shown in the table indicates that a significant change in gloss is produced between samples cooled at less than 500C before pressure reduction and those discharged from pressure hot. Results show that when the press is discharged at temperatures above 1000C the mat/gloss effect is barely visible in the resulting product.

Table PRESSURE TEMP. UNDER PRESSURE 600 GLOSS UNITS PSI (MPa) MAX OC MIN OC HIGH LOW 1400* (9.65) 145* 40 89-90 22-23 1400 (9.65) 50 40 73-77 62-65 500 (3.45) 110 40 92-93 19-20 500 (3.45) 110 110 53 50 500 (3.45) 80 40 88 32-35 500 (3.45) 80 80 73-75 42-43 500 (3.45) 70 40 82-87 48-65 500 (3.45) 50 40 68-74 68-74 250 (1.72) 70 40 43 42 250 (1.72) 145 40 Stripe effect patchy 0 FOIL AS RECEIVED 44 *Standard conditions for high pressure laminate.

In another experiment a product was produced with a surface gloss of 10 units and re-pressed using the mat-gloss plate. This did not produce a product with a uniform mat/gloss effect. In a further experiment a product with a gloss of 91 was treated in the same way and that also failed to produce a product with satisfactory appearance. These experiments show that the urethane acrylic resin has some thermoset properties.

Another advantage of making a laminate with a coated aluminium foil construction is the dimensional stability this product has to humidity changes. For example a 1 mm thick product has an ambient dimensional change of 0.01% in the length direction and 0.2% in the transverse direction when tested according to ISO 4586. Similar thickness high pressure laminate products have dimensional changes in the order of 0.3% and 0.6%. This is well illustrated by the example of a double sided compact board. This product can be subjected to a high humidity condition on one side of the board and a low humidity condition on the other face without any warp being produced in the board. A similar test carried out on standard melamine surfaced compact laminate produced a very warped board within a few days. The characteristic of low dimensional movement with humidity changes is important for a product which is going to be used in outdoor exposure.

Claims (22)

1. A method of forming a resin laminate, comprising: providing a stack of resin-impregnated sheets or papers, which stack has at a surface thereof a metal foil whose outer surface is coated with pigmented resin, applying to the stack a press under such conditions of elevated temperature and pressure as to bond together the sheets or papers and the metal foil, and withdrawing the press.

2. A method as claimed in claim 1, wherein the surface of the press which contacts the coated metal foil has a texture which it is desired to impart to the surface of the laminate and the press is applied under such conditions that the texture is imparted to the laminate, the pigmented resin and, appropriately, the laminate resin being deformable under the conditions used.

3. A method as claimed in claim 2, wherein the pigmented resin is cooled to a temperature at which it substantially retains the imparted texture before the press is withdrawn.

4. A method as claimed in claim 2 or claim 3, wherein the press surface which contacts the coated metal foil has at least two areas of different texture.

5. A method as claimed in claim 4, wherein the press surface has areas of different microtexture (i.e.

different gloss level) and areas of different macrotexture, and the areas of different microtexture are in register with the areas of different macrotexture.

6. A method as claimed in any one of the preceding claims, wherein the metal foil is aluminium foil.

7. A method as claimed in any one of the preceding claims, wherein the pigmented resin is a urethane acrylic resin and the press is applied at a temperature of at least 800C.

8. A method as claimed in claim 7, wherein the press is applied at a pressure of at least 500 psi (3.45 MPa).

9. A method as claimed in any one of the preceding claims, wherein the inner surface of the metal foil has an adhesive coating of resin.

10. A resin laminate having a superficial layer of metal foil coated on its outer surface with pigmented resin.

11. A laminate as claimed in claim 10, wherein the resin coating has at least two areas of different texture.

12. A laminate as claimed in claim 11, wherein the resin coating has areas of different microtexture (i.e.

different gloss level) and areas of different macrotexture, and the areas of different microtexture are in register with the areas of different macrotexture.

13. A laminate as claimed in any one of claims 10 to 12, wherein the pigmented resin is a urethane acrylic resin.

14. A laminate as claimed in any one of claims 10 to 13, wherein the resin of the laminate is a phenolic, melamine or polyester resin.

15. A laminate as claimed in any one of claims 10 to 14, which has a layer of metal foil, optionally coated with pigmented resin, at the surface of the laminate opposite said superficial layer of metal foil coated with pigmented resin.

16. A method of making a resin laminate substantially as hereinbefore described.

17. A resin laminate substantially as hereinbefore described other than with reference to prior art.

18. A resin laminate having a metal foil adhered to each face thereof, at least one of the metal foils having a pigmented resin coating on its outer face.

19. Plastics insulating foam or other flammable material having applied thereover a resin laminate as defined in any one of claims 11 to 15, 17 or 18.

20. A laminate as claimed in any claim 18 or claim 20 wherein the resin is substantially free of fire inhibitors.

21. A method of forming a resin laminate, comprising: providing a stack of resin-impregnated sheets or papers, which stack has at both surfaces a metal foil, applying to the stack a press under such conditions of elevated temperature and pressure as to bond together the sheets or papers and the metal foil, and withdrawing the press.

22. A structure comprising a laminate as claimed in claim 18, which laminate is at least partially in a curved shape.