SPECIFICATIONRegistered debossed decorative thermoset plasticslaminatesThis invention relates to registered debossed decorative thermoset plastics laminates and more especially to debossed decorative thermoset plastics laminates wherein the debossed areas of the decorative surface of the laminates exhibit a different col ourtothe non-debossed areas.
Decorative high-pressure thermoset plastics laminates have been known and used for many years as durable, aesthetically pleasing, surfacing materials for a variety of applications, such as wall claddings, table and counter tops and bathroom and kitchen work surfaces.
Generally, the method for forming such a laminate comprises consolidating to a unitary structure, by means of heat and pressure, an assembly comprising, in superimposed relationship:(i) a core layer- usually comprising a plurality of thermosettable phenol-formaldehyde resin impregnated kraft paper sheets;(ii) a decorative layer - conventionally comprising a printed or plain-coloured opaque highly filled alpha-cellulose paper sheet impregnated with a col ourless thermosettable melamine resin composition and which serves not only to provide a decorative affect to the product laminate but also, because of its opacity, to maskthe dark brown colour of the core layer and further, it prevents bleed through of the phenolic resin from the core to the surface layer; and(iii) an optional substantially transparent wear layer- conventionally comprising a colourless high quality alpha cellulose paper sheet impregnated with a colourless melamine resin composition (an overlay) and which, in the product laminate, serves to protect the decorative sheet from wear and damage whilst enabling the decorative sheet to be viewed therethrough. Customarily the overlay makes little, if any, contribution to the decorative effect of the product laminate.
Customarily the pressures and temperatures employed to consolidate an assembly to provide a highpressure thermoset plastics laminate are in the range 55 to 120 Kg/cm2 and 11 0 C to about 1 550C respectively.
Such laminates are available in a variety of surface textures such as 'glossy', 'suede' or'matte' and these surface textures may be provided by consolidating the assembly with the decorative surface associated with a press-plate of corresponding surface finish or by the use of a removable film or sheet having the desired surface finish positioned intermediate the decorative surface and the press-plate during the consolidation.
More recently, there has been a demand for laminates exhibiting deeply debossed (having a hill-tovalley depth of about 0.02mm or greater) surfaces and closely approaching in appearance natural materials such as leather, slate or weathered timber and fashioned materials such as woven cloths and fabrics. In order that laminates closely approach such materials in appearance, it is highly preferable not only that they exhibit appropriate debossed and non-debossed areas but also that the debossed portions of the laminates should exhibit a different col ourtothe non-debossed portions. (Such laminates currently being known as debossed registered laminates).
In the production of such deeply debossed registered laminates one approach has been to use etched or engraved metal plates orthermoset resin plates, having a surface complementarytothat desired in the product laminate, in assocation with an opaque decorative sheet bearing a printed pattern which corresponds to the colour variation required in the different portions of the laminate.
However, this technique has proved to be unsatisfactory in practice, more especially as it requires considerable skill and time in preparing the assembly so as to ensure registration between the printed pattern on the decorative sheet and the contured pattern on the press-plate.
Various attempts to overcome this problem have been proposed (see for example U.S. Patents 3373068,3732137 and 3814647) but some of these whilst successfully overcoming the problems encountered in the conventional technique, have their own drawbacks in that they require special materials or techniques or are expensive to operate.
In French Patent Publication No. 2330538 a method of ensuring register of colour and embossment is related wherein a high-pressure decorative laminate is prepared by pressing against a sculptured press-plate an assembly comprising an overlay sheet having therebeneath an impregnated opaque print sheet having thereon a coating containing a high flow melamine resin and pigment. During the pressing operation the resin coating flows laterally from the high-pressure areas to the low-pressure areas with the result that the underlying opaque print sheet is visible through the overlay sheet in the high-pressure areas while the pigment coating masks the print sheet in the low-pressure areas.
In French Patent Publication No. 2283312 there is disclosed a method of preparing high-pressure laminates having embossment and colouration in register wherein an overlay sheet is impregnated with a pigmented resin composition and then used in a conventional assembly atop of a conventional melamine resin impregnated opaque print sheet of contrasting colourtothat of the pigmented resin composition which gives rise to the variation in colour desired.
These two latter techniques have in common the requirement to use conventional opaque decorative sheets and to employ a flowable pigmented melamine resin composition as opposed to the conventionally employed non-pigmented resins and the use of such pigmented resins may of itself give rise to problems of formulation and stability.
The above related techniques require essentially the presence of an opaque filled decorative sheet which may be printed or plain coloured.
We have found that decorative plastics laminates having debossed and non-debossed portions and wherein the debossed portions exhibit a darker colour than the non-debossed portions (i.e. laminates which exhibit registered debossment and colourcontrast) may be produced satisfactorily without theuse of a conventional opaque highly filled decorativepaper sheet.
When one or a stack of conventional thermosettable phenolic resin kraft paper sheets is heatedunder pressure the degree of consolidation increases with the applied pressure up to a limiting value and due to the nature of the resin and paper the higher the degree of consolidation the darker the colourofthe consolidated assembly.
Thus, if a press-plate having a pressing surface in the form of a grid is used to consolidate an assembly of thermosettable phenolic resin impregnated paper sheets, then the consolidated thermoset laminate produced exhibits a grid pattern corresponding to that of the press-plate with the debossed grid lines darker than the non-debossed intervening areas.
This effect is due to those portions of the press-plate comprising the grid members applying a higher pressure to and thus imparting a higher degree of consolidation and hence a darker colourto those parts of the assembly which were associated with those portions of the press-plate intermediate of the grid members.
In order that this effect may be utilised to provide decorative laminates comprising one or a plurality of thermoset phenolic resin impregnated paper sheets surfaced with a plurality of other sheets or layers it is, of course, necessarythatthe surfacing sheets or layers should not be opaque. For example, when said other sheets or layer comprise a paper sheet(s) impregnated with a thermoset resin composition, the paper sheet(s) and the said composition together must not contain sufficient opacifying filler that, in conjunction, they mask the difference in colour between the debossed (darker) and non-debossed (lighter) portions ofthethermosetphenolic resin impregnated paper sheet(s).
It is an object of this invention to provide a decorative plastics laminate having a decorative surface comprising debossed and non-debossed areas and wherein the debossed areas exhibit a darker colour than the non-debossed areas and which laminate does not comprise a conventional opaque highly filled decorative paper sheet.
It is a further object of this invention to provide a method for preparing a decorative plastics laminate having debossed and non-debossed areas and comprising at least one transparent noble thermoset resin impregnated paper surfacing sheet and at least one thermoset phenolic resin impregnated kraft paper sheet, said laminate being characterised in that those portions of the said kraft paper sheet underlying the debossed areas have a greater degree of consolidation and hence a darker colour than those portions of the said kraft paper sheet underlying the non-debossed areas of the laminate and wherein said kraft paper is visible through the transparent surfacing sheet.
According to one aspect of the invention a decorative thermoset plastics laminate having registereddebossment and colour contrast comprises, insuperimposed relationship:(a) at least one thermoset phenolic resin impregrated kraft paper sheet; (b) at least one transparent noble thermoset resin impregnated paper sheet; said laminate being characterised in that the decorative surface thereof comprises debossed and non-debossed areas of contrasting colour wherein the colour contrast is a consequence of those portions of the phenolic resin impregnated kraft paper sheet underlying the debossed area having a greater degree of consolidation and darker colour than those portions of said kraft paper sheet underlying the non-debossed areas and wherein the, or uppermost, phenolic resin impregnated kraft paper sheet is visible through the noble resin impregnated paper sheet(s).
According to a second aspect of the invention a decorative thermoset plastics laminate having registered debossment and colour contrast is prepared by a method comprising: (A) Forming an assembly consisting essentially of:(i) a stack comprising in superimposed relationship:(a) at least one thermosettable phenolic resin impregnated kraft paper sheet; and(b) at least one noble thermosettable resin impregnated paper sheet which said impregnated sheet when in the thermoset state is substantially transparent;(ii) a press-plate, at least that surface of the press-plate adjacent to the noble resin impregnated paper sheet having a relief surface comprised of high areas and low areas; (B) Applying heat and pressure to the assembly so as to convert said stack to a decorativethermoset plastics laminate having a decorative surface comprising debossed and non-debossed areas of contrasting colour corresponding to said high and low areas of said plate respectively; and wherein those portions of the said phenolic resin impregnated kraft paper sheet underlying the debossed areas are consolidated to a greater degree and a darker colour than those portions underlying the non-debossed areas.
The thermosettable phenolic resin impregnated kraft paper sheets are preferably those paper sheets known for use in the production of conventional high-pressure thermoset decorative laminates, they may be bleached or coloured if desired. Suitably they are prepared in a known manner wherein a web of the paper is impregnated with a solution or dispersion of a thermosettable phenolic resin composition in a suitable solvent, the web is then dried to a desired volatile content and cut into sheets of the desired size.
Still more preferably the thermosettable phenolic resins used to impregnate some or all of the kraft paper core sheets are those resins useful in the production of post-formable laminates as these facilitate the production of laminates according to the invention having a depth of debossment of about 0.02mm or greater. We prefer that laminates according to the invention exhibit a depth of embossment of at least 0.02mm and still more preferably a depth of embossment greater than 0.5mm.
The noble thermosettable resins employed are suitably those known for use in the conventional production of high-pressure decorative plastics laminates. (By "noble thermosettable resins" we mean those resins which on conversion from the thermosettable to the thermoset state show no significant darkening in colour). Such resins include, for example, polyester resins, melamine-formaldehyde resins, urea-formaldehyde resins, melamine-ureaformaldehyde resins, benzoguanamineformaldehyde resins, acetoguanamineformaldehyde resins and apoxy resins. We prefer to employthermosettable melamine-formaldehyde resins and when the depth of debossment is about 0.02mm or more, we, more preferably, employ those melamine-formaldehyde resin compositions known for use in the production of post-formable laminates.
The noble resin impregnated paper sheets suitably comprise those unfilled papers customarily employed to provide the wear layers of conventional decorative laminates. The sheets may comprise unfilled kraft papers which may be bleached or coloured provided that the thermoset noble resin impregnated sheets prepared therefrom are transparent; but we prefer to employ high quality unfilled alpha-cellulose paper sheets.
Preferably the sheets are prepared in a conventional manner by impregnation of a web of the paper with a solution or dispersion in a suitable solvent of the chosen noble thermosettable resin composition and then, after drying to a required volatile content, the web is cut into sheets of the desired size. Optionally, the web, and consequently the sheets cut therefrom may be coloured or printed over all, or part hereof, with a desired pattern or legend - provided that in the product laminate the noble resin impregnated sheets are substantially transparent and the phenolic resin impregnated kraft papers may be viewed therethrough. The web may be dyed or coloured during the course of its manufacture, or it may be printed, by silk-screen or gravure techniques or otherwise, subsequent to its manufacture, but, preferably, prior to its impregnation.When a plurality of such sheets is employed they may be the same or different; for example, when two such sheets are used the first may be cut from a coloured resin impregnated web whilst the second may be cut from a colourless web, or, both may be cut from colourless, or the same, or differently, coloured webs.
Optionally further paper sheets may be employed in the formation of the stack and hence the product laminate if required.
Thus, for example, a non-impregnated un-filled bleached kraft paper sheet, optionally carrying a coloured coating, may be positioned between the uppermost of the phenolic resin impregnated kraft paper sheets and the lower most of the un-filled noble resin impregnated paper sheets. It is, of course, necessary when such a further sheet or sheets are employed that in the product laminate said sheet is substantially transparent so that at least the uppermost phenolic resin impregnated kraft paper sheet is visible therethrough in order to retain this essential characteristic of the product laminate.
The press-plate employed in the process of our invention may be any such plate known for use in the production of decorative laminates and bearing a relief surface comprised of high and low areas. If desired, both major surfaces of the plate may be provided with a relief pattern (which patterns may be the same or different) and an assembly formed with a stack of paper sheets associated with each of the major surfaces. The plate may comprise any suitable material; thus it may be an etched, engraved or electroformed metal plate or it may be a thermoset plastics laminate (optionally surfaced with a metal foil).
If the press-plate employed is so contoured as to provide areas of intermediate height thereon, then those portions of the phenolic resin impregnated kraft paper corresponding to those areas will be consolidated to a degree, and exhibit a colour, intermediate those of the portions of the sheets corresponding to the high and low areas. Accordingly, a product laminate produced from such a plate will exhibit colours, the darkness of which will be dependent upon the depth of debossment at any particular areas, with, of course, the most deeply embossed areas being the darkest in colour.
Whilst a laminate according to the invention may exhibit a wide range of debossed patterns, we prefer the patterns to be bold, that is, where the debossed portions may be distinguished from a viewing distance of a metre or more.
We prefer to position a release sheet in the assembly between the press-plate and the outermost noble resin impregnated paper sheet. The release sheet may be any of those known for use in the production of decorative plastics laminates and suitably is a texturing release sheet which serves the double purposes of imparting a desired surface finish to the product laminate as well as ensuring separation of the press-plate from the product laminate.
The consolidation of the stack by heat and pressure is suitably carried out by pressures of from 10 to 120Kg/cm2 and preferably at a pressure of 40 to 60Kg/cm2 and more preferably at a pressure of about 50 Kg/cm2. These pressure conditions relate to the average pressure exerted on the press-plate, the high areas of the plate will, of course, exert a higher pressure on the stack than this whilst the low areas will exert a lesser pressure.
The temperature employed is suitably in the range of from about 11 00C to about 1 60"C and the stack should be held at this temperature for from about 5 to 50 minutes.
It is within the scope of the invention to provide decorative thermoset laminates which comprise, additionally, a supporting substrate such as a lignocellulosic panel (e.g. plywood or chipboard), a metal sheet or a plaster-board or asbestos based board.
For example, a decorative thermoset laminate comprising a pre-formed chipboard panel may be prepared according to the invention by positioning a chipboard panel adjacent that phenolic resin impregnated kraft paper sheet distant from the noble resin impregnated sheet(s) and consolidating to a unitary assembly the stack so formed.
The following examples are given so that the invention may be more clearly understood.
EXAMPLE 1A stack was formed comprising (a) 5 kraft paper core sheets impregnated with a conventional post formable thermosettable phenolic resin composition; (b) a kraft paper core sheet impregnated with a conventional thermosettable phenolic resin composition; (c) a first, colourless, un-filled alpha cellulose paper sheet impregnated with a non-pigmented postformablethermosettable melamine resin composition; (d) a second colourless alpha cellulose paper sheet impregnated with a non-pigmented postformable thermosettable melamine resin composition.
Atexturing release sheet comprising a composite aluminium foil-paper web was positioned with the aluminium surface adjacent the second alpha cellulose paper sheet and a press-plate, having a relief surface complementary to a panel of ceramic tiles and comprising a plurality of thermoset phenolic resin impregnated kraft paper sheets, was situated with the relief surface adjacent the paper web com ponentofthetexturing release sheet.
The assembly thus formed was then heated under pressure of 50 Kg/cm2 in a hydraulic press to a temperature of 140"C for about 25 minutes to cure the resin compositions and render the melamine resin impregnated sheets transparent. The press was then opened and the press-plate and release sheet stripped off. The decorative thermoset plastics laminate thus formed had a relief surface substantially the same in appearance as the panel of ceramic tiles used to prepare the press-plate. The debossed areas of the laminate (corresponding to the grout lines between the ceramic tiles) being dark brown in colour and the non-debossed areas which correspond to the original tiles being light brown in colour.
The depth of debossment, i.e. the difference in height between the bottom of the debossed portions and the top of the non-debossed portions was about 1 .0mum.
EXAMPLE2Example 1 was repeated in all respects except that orange dyed non-filled alpha cellulose paper sheets impregnated with a colourless melamine resin composition were used in place of the colourless sheets used in that Example. The consolidation under heat and pressure rendered the dyed sheets transparent and the product laminate was similar in appearance to that of Example 1 except that the debossed areas exhibited a dark orange brown colour whilst the non-debossed areas exhibited a lighter orange colour.
EXAMPLE3 Astackwasformed as related in Example 1 but with the addition of an unfilled non-impregnated bleached kraft paper sheet carrying a coating of a yellow coloured melamine resin composition between the uppermost phenolic resin impregnated kraft paper sheet and the first melamine resin impregnated alpha cellulose sheet.
The stack was consolidated as related in Example 1 to cause the coated bleached kraft paper sheets to become transparent, the resins to cure and to provide a decorative thermoset plastics laminate exhibiting dark green-brown debossed areas and light yellow-green non-debossed areas corresponding in distribution to the grout lines and the tiles of the original ceramic tile panel respectively.
EXAMPLE 4A stack was prepared comprising in order:- (a) 7kraft paper core sheets each being impregnated with a conventional thermosettable phenolic resin composition; (b) a yellow coated bleached kraft paper as used in Example 3; (c) a first un-filled alpha cellulose paper sheet bearing a screen printed design in a blue colour and impregnated with a colourless melamine resin composition; and (d) a second un-filled alpha cellulose paper sheet bearing a screen printed dot pattern in a white colour. (Both sheets (c) and (d) were positioned with their printed surfaces towards the bleached kraft paper sheet.) The coating on sheet (b) and the printings on sheets (c) and (d) were such that in the product laminate all the sheets were substantiallytransparent and the uppermost phenolic resin impregnated kraft was visible therethrough.
The stack was pressed employing an etched metal press-plate having high, low and intermediate areas in an abstract pattern using the same conditions of temperature and pressure as related in Example 1.
The decorative thermoset plastics laminate produced exhibited a vari-coloured appearance; some positions exhibiting a yellowigreen others a yellow and others a yellow-brown background to the white dot pattern; however, the deepest embossed portions corresponding to the high areas of the plate exhibited a darker colour than all other areas and those areas corresponding to the high areas of the plate exhibited the lightest colouration.
EXAMPLE 5A stack comprising (a) a single kraft paper core sheet impregnated with a conventional thermosettable phenol-formaldehyde resin and (b) a single colourless alpha cellulose overlay paper sheet impregnated with a conventional melamine-formaldehyde resin composition, was consolidated by means of heat and pressure using conventional polymeric release sheets and a metal press-plate bearing a raised emblem. The release sheets were removed to leave a decorative laminate suitable for cladding vertical surfaces and exhibiting the debossed emblem in a dark brown colour on a lighter brown nondebossed background. The depth ofdebossmentof the emblem was about 0.01 mm.
EXAMPLE 6A stack comprising (a) a single kraft paper core sheet impregnated with a conventional thermosettable phenol-formaldehyde resin; (b) a conventional thermosettable melamine-formaldeyde resin impregnated un-filled kraft paper sheet; and (c) a conventional thermosettable melamine4ormaldehyde resin impregnated high quality unfilled alpha cellulose overlay paper sheet, was consolidated as in Example 5 to provide a decorative laminate exhibiting a brown debossed emblem on a dark cream background. The depth of debossment was about 0.02mm and the laminate was especially useful as a vertical cladding material.
EXAMPLE 7A stack was prepared comprising in order:- (a) a supporting substrate being a chipboard panel; (b) 2 kraft paper core sheets each impregnated with a conventional phenolic resin composition; (c) 2 unfil led alpha cellulose paper sheets each printed in a 'cloud' pattern with a transparent coral coloured ink; (d) a paper-aluminium foil composite release sheet.
The stack was pressed employing a metal pressplate having high areas and low areas, and having the appearance of a brick panel with the high areas corresponding to the pointing between the bricks.
After consolidation the release sheet was stripped off to provide a self-supporting decorative laminate useful as a structural element having the appearance of a panel of red-brown bricks having intermediate pointing of a dark brown colour and debossed about 0.8mm below the surface of the 'bricks'. (The depth of debossment achieved in the product laminate being constituted in part by deformation of the surface of the supporting substrate.)EXAMPLE 8Example 7 was repeated in all respects except that a plywood panel was employed in place of chipboard as a supporting substrate.
The product laminate obtained was similar in appearance to that of Example 7.
EXAMPLES 9 to 11 Example 7 was repeated except that in each ofExample 9 to 11, seven (7) kraft core sheets instead of the two of that example were employed and the supporting substrates were:Example No. Substrate9 a 20 gauge steel plate10 a 25mm proprietary plaster board11 an 8mm proprietary asbestos boardThe product from each example was useful as a construction of cladding panel exhibiting a brick panel appearance of red-brown bricks surrounded by dark brown pointing.