WO2000053666A1

WO2000053666A1 - Sheet prepreg

Info

Publication number: WO2000053666A1
Application number: PCT/NL2000/000112
Authority: WO
Inventors: Maurits Frederik Hendrik Van Tol; Karel Franciscus Hubertus Bonekamp; Wouter Heinen
Original assignee: Dsm N.V.
Priority date: 1999-03-05
Filing date: 2000-02-23
Publication date: 2000-09-14
Also published as: AU2832300A; NL1011468C2

Abstract

Sheet prepreg comprising one or more layers of a carrier sheet, which carrier has been impregnated with an as yet uncured resin, the carrier containing a meltable polymer that has been mixed with cellulose or regenerated cellulose or mixtures or combinations thereof and that the elongation at break of the prepreg and of the separate, impregnated carrier sheet is higher than 2 %.

Description

SHEET PREPREG

The invention relates to a sheet prepreg comprising one or more layers of a carrier sheet, which carrier has been impregnated with an as yet uncured resin. Sheet prepregs comprising a number of stacked carriers of alpha cellulose impregnated with the reaction product of formaldehyde and melamine are disclosed, for instance, in US-A-3730828. According to said patent, first paper is impregnated with a melamine- formaldehyde resin. Then a prepreg is made by drying a few layers of this impregnated paper and stacking them on top of one another. The resin is then cured in a press at a pressure of, for instance, 6 MPa and at a temperature of approximately 150°C, yielding a sheet product. The reaction between formaldehyde and melamine in the sheet product thus obtained is complete at the temperature used (completely cured) . The sheet products described in said patent specification appear to have good postforming properties. Postforming is here understood to mean that the sheet product can be bent at an elevated temperature which is between 160 and 180°C. It is possible to bend the sheet product to some degree along one axis (the so-called 2D deformation, yielding 2D moulded articles) without the sheet product breaking and/or cracking.

A disadvantage is that, starting from a prepreg according to US-A-3730828, it is not possible to obtain sheet products which can be bent along two (or more) mutually intersecting axes to form complex shapes without breaking or cracking (the so-called 3D deformation, yielding 3D moulded articles) . Complex shapes may be considered to be, for instance, a saddle- type pattern, a small tub, a hemisphere, a sickle pattern or a satchel . The object of this invention is to provide a prepreg with which complex shapes can be obtained and/or covered.

This object is achieved with a prepreg containing one or more layers of a porous carrier sheet, which porous carrier sheet has been impregnated with an as yet uncured resin, the carrier containing a meltable polymer mixed with cellulose or regenerated cellulose or mixtures or combinations thereof. The ratio of meltable polymer to cellulose or regenerated cellulose is determined by the final use and may vary within very broad limits. The meltable polymer content may, for instance, be between 1 and 99 wt.%. As cellulose, use is preferably made of wood or paper pulp, more m particular kraft paper pulp. Regenerated cellulose is understood to be treated cellulose. This treatment implies that the cellulose is converted into a soluble cellulose derivative (usually the xantagonate) , which derivative is converted into fibres, for instance via a spinning process, following which an acid is used to convert these fibres into regenerated cellulose fibres. From these regenerated cellulose fibres then for instance a woven or non-woven porous carrier can be prepared.

Preferably a cellulose ester or a mixture of several cellulose esters, more preferably a mixture of cellulose esters containing celluloseacetate and more m particular cellulose acetate is used as the meltable polymer. A cellulose acetate containing carrier is understood to be a carrier containing cellulose acetate of which between 0.01 and 3 (degree of substitution) of the OH groups of the monomer units are acetylated, such as cellulose monoacetate, cellulose diacetate, cellulose triacetate as well as mixtures or combinations of these acetates. Preferably, the degree of substitution is between 2 and 3.

The carrier on the basis of a cellulose acetate may also contain a plasticizer. If a plasticizer is used, this plasticizer can together with the cellulose acetate be spun into fibres, which fibres can then be converted into a plasticizer containing carrier. It is also possible to treat cellulose acetate fibres with plasticizer and then convert them into a plasticizer containing carrier. A third option is subsequent treatment of the cellulose acetate containing carrier with plasticizer. As the plasticizer use can be made of all plasticizers known for cellulose acetates, such as for instance triacetine, triethylcitrate, diethylcitrate, N-methyl-o,p-toluene sulphonamide, phosphates and phthalates, in particular diethylphthalate. The advantage of adding a plasticizer is that the glass transition temperature of the cellulose acetate carrier can be controlled.

The elongation at break of the separate porous carrier sheet and of the prepreg obtained is higher than 2%, preferably higher than 5%, and in particular higher than 10%. The elongation at break is measured at a temperature that is virtually the same as the temperature at which the carrier or the prepreg is processed into a sheet product . It has been found that, starting from the prepreg according to the invention, sheet products can be made in the most diverse shapes without any cracks being formed in the sheet product during deformation.

Sheet products are now possible with shapes involving local stretching of the prepregs from 10% to more than 400% during the shaping. Objects in which the required maximum deformation is lower than 10%, too, can be coated better with the sheet product according to the invention than with sheet products on a paper basis. Example are some so-called softline panels, 3D-shaped panels with round edges and/or corners, and/or gradually inclining surfaces or contours.

A further advantage is that the further curing of the resin and the deformation can be performed in one step. This is in contrast to the method described in the above-mentioned US-A-3730828 where, starting from the prepreg, two steps are necessary to obtain a shaped final product.

An additional advantage is that the prepreg can be processed by a multiplicity of techniques, as a result of which the optimum technique can always be used for each final product .

Yet another advantage is that, starting from the prepregs according to the invention, both 2D and 3D objects can be coated, so that it is possible to obtain identical designs on both objects, for instance the design of a 3D kitchen cabinet and a 2D laminate floor. Starting from the prepreg according to the invention it is furthermore possible to make sheet products which are bent, for instance along one axis, to form an acute angle. Starting from the known prepregs based on a paper carrier, this is impossible.

JP-A-7002119 discloses a prepreg consisting of a carrier of a polyamide non-woven material and a carrier of kraft paper, which carriers have separately been impregnated with a melamine-formaldehyde resin and have then been stacked. An impregnated polyamide non- woven carrier as a rule has an elongation at break of more than 2%. However, impregnated kraft paper has an elongation at break of less than 2%, as a result of which the elongation at break of the prepreg as a whole is less than 2%.

A porous polymer carrier sheet containing a meltable polymer is understood as meaning any polymer carrier having a high degree of porosity. The porosity of the polymer carrier is essential for obtaining the advantageous properties of the prepreg as described above. As a result of the high porosity, the polymer carrier sheet can be filled homogeneously with the resin. Preferably, the porosity is obtained m the form of microscopically small, mutually communicating cavities and there are preferably few larger cavities and holes present. Larger cavities and holes result m loss of resin during further processing to give the prepreg its final shape. Preferably, the porosity is sufficiently high so that at least 30% by volume of the final moulded article consists of resin.

The porous polymer carrier containing a meltable polymer will preferably be a woven or non-woven polymer sheet, an open polymer foam sheet or a microporous membrane. Preferably, the fibres of the non- woven have a diameter of less than 0.1 mm. Non-wovens with fibres that have a very small diameter are also referred to as open films. This class of non-wovens has, as a result of the small thread diameter, few larger meshes and many microscopically small, mutually communicating cavities. Polymer foams have mutually communicating cavities. The cavities preferably have a diameter of less than 1 mm. Larger cavities may occasionally be present m the foam provided more than

80% by volume of the cavities have said smaller diameters .

The polymer carrier containing porous cellulose acetate can for instance be prepared by pouring a solution of a cellulose acetate m acetone into stirred ethanol. This results m the formation of fibres of a cellulose acetate. The length and diameter of these fibres can be controlled by, among other things, changing the concentration of the cellulose acetate m acetone or adjusting the stirring speed during addition of the cellulose solution to the ethanol. The cellulose acetate fibres that are formed can subsequently be added to paper pulp and be converted m a known way into a porous, cellulose acetate containing paper carrier.

Another preparation method is converting a cellulose acetate solution m acetone via a spinneret into cellulose acetate threads, with the acetone evaporating. Chopping the threads into pieces and adding these to paper pulp, followed by upgrading, yields a porous, cellulose acetate containing paper carrier.

Instead of chopping up the threads, it is also possible to convert the threads m a known way into wovens and non-wovens and use these as porous carrier. It is also possible to add cellulose acetate fibres not to kraft paper pulp but to commercially available, wholly or partly regenerated celluloses. These regenerated celluloses are known, for instance, under the generic names viscose and rayon or under the brand name Lyocell® (an Acordis product) . Wholly or partly regenerated celluloses are prepared by modifying cellulose, which is the main component of among other things wood pulp, and rendering it soluble by for instance turning it into a cellulose xantagonate. Contrary to cellulose itself, these cellulose xantagonates are capable of being dissolved and spun, so that threads can be obtained. These threads can be regenerated m an acid environment, so that threads of regenerated cellulose are obtained. These threads can subsequently be converted into fibres and be added, for instance, to paper pulp or be converted into a web, such as a woven or a non-woven.

The porous, polymer carrier may m principle be any porous, polymer carrier which contains a meltable polymer and which meets the requirement that the impregnated carrier has an elongation at break, measured under the processing conditions, of more than 2%. Porous carriers such as wovens or non-wovens may for instance be prepared from the cellulose acetates already referred to, but also for instance from polyethylene; polypropylene; polystyrene; ethylene-propylene copolymers; EPDM; polyamides, such as, for instance, nylon 6,6 or nylon 6; ethylcellulose; SMA/SAN; polyesters, such as, for instance, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) ,- polyethers or mixtures thereof . As the porous polymer carrier, the above-mentioned polymers can be used as a woven or non-woven, open film or as an open polymer foam. The polymer may have both polar and apolar properties. As a result of making use of suitable wetting agents, the desired degree of impregnation of the polymer sheet by the resin can be obtained. As a rule, all the wetting agents known to one skilled m the art can be used. Examples of wetting agents are PAT

523W, PAT^® 959 (PAT^® is a Wύrtz brand name) , Nonidet^® P40 (Nonidet P40 is a Sigma Chemie brand name) and Ammol N (Amino1 is a Chem-Y brand name) .

The resin with which the carrier is impregnated may m principle be any known resin and may moreover contain a reactive or non-reactive solvent. It is also possible for the resin to consist of polymerizable monomers. Examples are thermosettmg resins or elastomeπc resins which resins can be cured via an ionic, radical, oxidation, addition or condensation mechanism or which cure via a combination of these mechanisms, such as for instance the so- called dual curing.

Examples of resins that cure via an oxidation mechanism are alkyd resins. Usually, however, cationically and/or radically curing resms are used and/or resins that cure via a condensation or addition reaction.

Cationically or radically curing resins can cure according to a homopolymerization or a copolymerization reaction. Radically curing resins can contain unsaturated monomers and/or groups which contain, inter alia, (meth) acrylate, itaconate, maleate, fumarate, styrene, fumaramide, maleamide, maleimide, vmylether, allylether and/or vinyl ester groups. Examples are the acrylate resms .

Cationically curing resms can contain monomers and/or groups which contain polymeπzable groups, such as for instance epoxy, glycidyl, cycloaliphatic epoxide, vinyl ether, vinyl ester, allyl ether, allyl ester, propenyl ether, butenyl ether, vinyl acetate, oxetane, cyclic carbonate and/or dioxalane groups. Examples are epoxy resms.

Examples of resms that cure via an addition or condensation mechanism are ammoplastic resms, phenol -formaldehyde resms (PF resms) and/or two- component resms consisting of hydroxyl-functional polymers or oligomers and isocyanate- functional oligomers or polymers and/or alkylated melamine resms. Preferably, an ammoplastic resin is used.

As the ammoplastic use can be made of compounds of formaldehyde with, for instance, urea, melamine, acetoguanamme or benzoguanam e, or mixtures or combinations of these. Preferably, melamine is used because of the superior mechanical properties of the final product . The aminoplastic resin can be prepared in a process known to one skilled in the art by reaction of, for instance, melamine and/or urea with formaldehyde in water. Optionally, the urea and/or the melamine can be partially replaced by, for instance, phenol, but this may have adverse effects on the colour. Modifiers, such as sorbitol, ε-caprolactam, ethylene glycol , polyethylene glycol, polypropylene glycol, hydroxy- functional polyesters, hydroxy-functional acrylates, trioxitol, toluene sulphonamide, and benzo- and acetoguanamine can also be added.

It is also possible to use resin mixtures or resin combinations that can cure according to different mechanisms, such as for instance a mixture of a melamine-formaldehyde resin and an acrylate-functional resin, for impregnation of the carrier. It is possible for these resins to be prepared and/or cured in the presence of a catalyst and/or initiator that is specific to each resin system, as known to one skilled in the art.

Mechanical properties that are suitable for practical use are achieved if 10-70% by weight of porous polymer and 90-30% by weight of resin are used. The resin may contain the known pigments, colorants and/or fillers such as for instance known from the paper industry. Examples include titanium dioxide, iron oxide, clay, glass, lime, carbon, silica or metal particles. It has been found, however, that the best results are achieved in the absence of fillers or at any rate with less fillers than has been customary so far. The filler to resin weight ratio is preferably between 0:1 and 0.5:1. These ratios relate to the cured final sheet product .

The prepreg is made under the conditions which are already known for making prepregs based on a paper carrier, as described, for instance, m the above- mentioned US-A-3730828 or JP-A-7002119. The viscosity of the resm used for the impregnation can be influenced by, among other things, varying the nature and the amount of solvent. As yet uncured ammoplastic resm such as melamine formaldehyde resm is for instance dissolved m water and preferably has a viscosity of 1- 1000 mPa.s. Preferably, solvents are used m which the polymer carrier does not dissolve or swell . The temperature during the impregnation is typically between 15 and 60 °C and for practical reasons is often room temperature. Higher temperatures are less practical because then the resm might wholly or partially cure during the impregnation. The pressure during the impregnation is not critical and for practical reasons is as a rule atmospheric.

The carriers impregnated m this way can optionally be dried until a certain residual volatility is reached. For melamine-formaldehyde (MF) and PF resms this residual volatility is the prepreg' s mass loss at 160°C for 7 minutes. The residual volatility of the prepreg usually lies between 2 and 20%. The elongation at break of the prepreg as used m the description is defined as the elongation at break at a residual volatility of about 6 to 7% and measured at a temperature that is close to the product's processing temperature .

Drying preferably takes place at a temperature of 80-160°C if melamine formaldehyde resm (MF resm) is used. Higher temperatures are less practical because the drying times then become too short, resulting m a process that is difficult to control . The temperature will m practice also be determined by the type of resm and the type of oven. The optionally dried carriers can be stacked to form a multi -layer prepreg. In principle, as many sheets can be stacked as is needed to obtain the desired thickness and/or strength, for instance for self-supporting 2D and 3D moulded articles such as lamp shades and (corrugated) sheeting for interior and exterior use. For laminate application on a substrate the number of carrier sheets is usually 100 or lower, m particular 10 or lower, and preferably 5 or lower.

The prepreg may optionally also comprise layers of a non-porous polymer besides the porous polymer carriers, provided these polymers also have an elongation at break that is higher than or equal to that of the prepreg.

The prepregs can be processed into a shaped final product by first deforming the prepreg and then curing the intermediate product formed or by combining the deformation and curing operations m one step. Resm curing can for instance be realized by heating the prepreg, optionally at elevated pressure, up to a temperature at which the resm cures. An example is the curing of an MF resm. If the resm contains polymeπzable groups that can react by means of a radical mechanism, such as for instance a resm containing unsaturations, the resm can be cured by treating the prepreg with an electron beam, or irradiating the prepreg with ultraviolet or ionizing radiation. If a prepreg contains a resm that cures via a radical mechanism, it may be advantageous to add a radical initiator. The radical initiator will fully or partly disintegrate into radicals that can start the polymerization reaction. Examples of well-known radical initiators are peroxides from the Tπgonox® series (produced by AKZO-NOBEL) . To accelerate the initiation of the polymerization, an accelerator can be added to the resm. Examples of well-known accelerators are cobalt complexes. The polymerization of resm that cures according to a cationic mechanism and that has been impregnated m a carrier can be initiated by the addition of a cationic initiator, The surface of the final product can be prepared as desired using techniques known to one skilled the art. A high-gloss surface can for instance be obtained by using for instance a polishing plate m the press, a polishing membrane or a polished mould. An embossed surface can be obtained by using, for instance, an etched or engraved plate m the moulding operation, or applying an embossed membrane or an embossed mould. Patterns can be provided m a similar way. It is also possible, for instance, to use films between the pressing plate or membrane and the moulded article. These films, turn, can also be smooth, matt or have the desired pattern or relief. Optionally, such films may also be used as a membrane

Deforming, optionally m combination with curing, can be performed by means of bending, embossing,

3D deformation such as 3D pressing, stamping, pneumatic stretching or mechanical stretching.

The deformation temperature will depend on the yield stress of the prepreg. The yield stress is the stress at which the material begins to flow. In principle, said temperature may be between room temperature and 200°C.

The shaped product obtained m this way can be used as a final product or as a protective layer around an object having a core material of, for instance, wood, wood-based fibre materials such as the well-known MDF (Medium Density Fibreboard) and HDF (High Density Fibreboard) materials, metal, glass or plastic, for instance polyethylene, polypropylene, ABS, polyester, polyamide, MF resms, PF resms and epoxy resms or composite objects.

The invention also relates to objects provided with a top layer obtained from a sheet prepreg bent along two (or more) mutually intersecting axes (3D objects) .

Examples of 3D final products of the shaped product are serving trays, washing-up basins, crockery, lamp shades, (corrugated) sheeting, doors, kitchen worktops, furniture, wall panels. Examples of final products where the shaped product is used as a protective layer for a wooden or wood-based core are worktops with a 3D structure and/or, for instance, an acute angle, (kitchen) cupboards, panels with a 3D structure, for instance on the basis of milled MDF board, window frames, laminated flooring with a 3D structure (for instance with upright edges) , skirting boards, etc.. Examples of articles m which the shaped product serves as a protective layer for a plastic core are bumpers, petrol tanks, helmets, garden furniture, chairs, worktops or car bodywork components.

The invention relates particular to sheet prepregs that provide objects having a 3D structure that are based on milled MDF or HDF board with a top layer. These laminated MDF or HDF boards can be produced m one process step, for instance m an -mould lamination process .

The sheet products according to the invention can also be used m flat applications (2D applications) such as laminate flooring, interior door panels, wall panels, table tops, etc., and m postforming applications.

Surprisingly, it has been found that when a cellulose diacetate is used as the meltable polymer, preferably a cellulose diacetate with a degree of substitution between 2 and 3, its processing into laminate, including for instance printing, impregnation, processing and moulding properties, proceeds better than with the current commercial decorative paper. Moreover, after pressing to form LPL (Low Pressure Laminate) or HPL (High Pressure Laminate) the surface properties, such as water absorption, dimensional stability and the suitability for the application of patterns and/or embossing will be better than those of the known commercial decorative paper.

The top layer may be glued to the core material. Another possibility is for the shaped product to be applied to the core while the resin is still incompletely cured. The resin then serves as a glued joint when it is subsequently cured.

The invention will be elucidated by means of the following, non-limiting examples. Examples I up to and including IV and example VIII relate to flat 2D moulded articles on MDF. Examples III up to and including VIII relate to 3D moulded articles on MDF.

Prepregs from example VIII were further subjected to in- mould lamination carried out in two ways.

Example 1

Preparation of resin

In a reactor, 48 parts of water and 131 parts of formalin (30 wt% formaldehyde in water treated with 50 wt% NaOH to adjust its pH to 9.3) were added to 100 parts of melamine. The F/M ratio of the resin was 1.65 (F/M ratio is the molar formaldehyde-melamine ratio) . The melamine-formaldehyde condensation reaction was performed at 95 °C and this temperature was maintained until the water dilutability of the resin at 20°C was 1.5 g of resin per g of water. The water dilutability is the amount (g) of water which can be added to a resm solution (g) at 20°C before the solution becomes turbid. Using a 50 wt% p-toluene sulphomc acid solution (catalyst) the resm pH was adjusted to 7.5 at 20°C to make the solution suitable for further processing.

Preparation of sheet product

The carrier used was a so-called wet-laid non-woven on the basis of 90 wt% cellulose acetate fibres (degree of substitution 2.45) and 10 wt% kraft paper pulp, with 10 wt% diethyl phthalate (DEP) homogeneously distributed m this cellulose acetate/kraft paper pulp combination as plasticizer. Such a wet-laid non-woven is prepared by passing a paper pulp of kraft paper fibres with the cellulose acetate (CD) fibres dispersed m it over a filter, the resulting filter cake being dried to yield a carrier sheet . The CD fibres were made by pouring a solution of CD m acetone into stirred ethanol. The morphology of the CD fibres is comparable to that of the paper fibres. After filtration (during which sheet formation occurs) of the aqueous CD/kraft paper pulp, the filter cake was dried. The weight of the dried carrier sheet is about 160 g/m². A carrier sheet measuring 20 by 20 cm was impregnated at room temperature with the above-mentioned resm solution, to which 0.5 wt% PAT^® TD80 (a Wύrtz product) had been added for wetting purposes and 0.2 wt% PAT ® 523/W (a Wϋrtz product) for mould release purposes. After about a mmute, the resm- impregnated sheet was removed from the impregnation equipment and the excess resm was removed with the aid of a wringer. The sheet was dried m a circulatmg-air oven for 8 minutes at 100°C. See Table 1. Characterization of the prepreg

Resin content : the resin content of the prepreg was determined by weighing the prepreg and the polymer carrier and was 138%. The resin content is defined as :

(g (prepreg) -g (carrier) ) /g (carrier) ,

g (prepreg) and g (carrier) are the weights of the prepreg and of the polymer carrier, respectively.

Residual volatility: the residual volatility was determined by measuring the weight loss after further drying and curing of the prepreg for 7 minutes in an oven at 160 °C and was 6.0 wt%. The residual volatility is defined as:

(g (before) -g (after) ) /g (before) ,

g (before) and g (after) are the weights of the prepreg before and after the treatment at 160°C, respectively. See Table 1.

Elongation at break and tensile strength The elongation at break and tensile strength of the prepreg were measured on test specimens (measuring 50.0 x 4.0 x 0.43 mm) using a Standard Zwick tensile tester at 140°C and 160°C according to ISO 527- 2, 5A (1993) . The deformation rate was 100 mm/min. For the results, see Table 4.

2D pressing on a flat substrate :

One sheet of the prepreg based on CD/kraft paper with 10 wt% DEP measuring 20 x 20 cm was pressed on a flat Medium Density Fiberboard (MDF) panel into a laminate using the following low-pressure lamination method: The MDF panel with the prepreg on top of it is placed the press (of the type Fontijne TP400) following which the press is closed and its pressure raised to 2 MPa . Only the upper mould half - which was fitted with a polishing plate - was heated and the temperature is 140°C. These conditions were maintained for 3 minutes and then the press was opened and the laminate taken out. For the pressing conditions see Table 1. After cooling the laminate could be characterized .

Characterization of the 2D laminate

- In the first place the laminate was assessed visually, also with the aid of a light microscope. The laminate looked good. At microscale the structure was rather fine, resembling that of paper.

- In addition, it was subjected to a few standard tests, specifically the stammg test and the Kiton test. These are well-known tests the world of MF resm laminates, which are used to check whether the laminate surface is closed and whether the resm is adequately cured. Below a brief description will be given together with the results. - The stammg test used here is derived from EN 438-2 and is based on stammg of the laminate surface with a neutral solution of an intensive colorant m an organic solvent (ethanol, methanol and a small amount of surfactant) . This solution has a strongly wetting and staining effect.

The result of the test was expressed m a rating ranging from 1 to 5, with 1 standing for: very good (no discoloration) and 5 for: very poor (very strong discoloration) . The score of the above-mentioned laminate was 1. The Kiton test is based on stammg with an aqueous sulphuric acid solution of an intensive colorant. This test, too, is derived from EN 438-2. The result of this test is expressed m the same numerical values. In this test, too, the laminate was found to be very good: 1. For the results of the sta mg test and the Kiton test, see Table 5.

Example II

The process of Example 1 was repeated, but as the porous film use was now made of a wet -laid non-woven on the basis of 80 wt% CD and 20 wt.% kraft paper pulp with 10 wt% DEP homogeneously distributed m it as plasticizer. The weight was about 160 g/m². Table 1 shows the resm content, the residual volatility content, and the conditions under which the prepreg was pressed on MDF. Table 4 shows the elongation at break of the prepreg at the stated test temperature. Table 5 gives the characterization of the laminate.

Example III (code KB664-G)

As basic material use was now made of a hand-made, wet-laid non-woven on the basis of 80% cellulose diacetate fibres (degree of substitution 2.45) and 20% paper pulp (50% hardwood /50% softwood) with 7.5% DEP homogeneously distributed m this combination. The cellulose diacetate (CD) fibres were obtained by spinning from a solution of CD m acetone. After the spinning process these CD fibres were chopped into pieces and added to the paper pulp for further refining. After sufficient refining the slurry, being a blend of CD fibres and paper fibres, was filtered through a screen and dried. The weight of the carrier sheet is 105 g/m². Using the method described m Example I, this carrier sheet was then processed into a prepreg and a flat laminate, see Tables 1 and 5.

3D pressing on a 3D shaped substrate using the membrane pressing technique:

Two sheets of the prepreg described above m III, based on CD/paper with 7.5% DEP and measuring 20 x 20 cm, were pressed together on a MDF panel with 3D shape obtained by milling measuring 12 x 12 cm. The thickness of the MDF was 18 mm. 3D shaping of such panels can take place by providing, for instance, flat MDF boards with internal grooves of random shape by means of milling. These grooves may be round or straight, but they may also be acute-angled. The outer circumference of such panels, too, can m such a way be provided with a shape milled out m the straight saw- cut .

Pressing took place m a so-called membrane press. In this type of press, the upper (and sometimes also the lower) mould half consists among other things of a rubber membrane which can be pressurized by means of (heated) air or liquid. These presses are used mainly for coating said 3D panels with thermoplastic films or veneer. The press used m the following examples has one upper 2 mm silicon rubber membrane, which is forced against the edge of a slightly concave metal upper mould. This upper mould has a temperature of 180°C. The required pressure is obtained by means of nitrogen at a temperature of 175 °C. When all material is removed from the membrane and a vacuum is drawn, the membrane comes into contact with the hot metal upper mould and is then rapidly (preferably withm 30 seconds) brought at the required temperature. The temperature at the membrane bottom is then 175-178°C. The lower mould half is flat and is not heated. After the two mould halves have been closed, a vacuum can be created at the bottom of the membrane. This, therefore, is the place where the workpiece is located. The process then carried out is as follows.

In the opened press, with the membrane forced against the hot upper mould, the following are successively placed on the lower mould half: a flat pad, the 3D panel (with the side to be laminated facing upwards) and 2 prepregs. The pad is about 5 mm thick and should be slightly smaller than the panel, so that the bottom edge of the panel can also be properly coated. If the panel sides must also be coated, the prepregs should project some distance outside the edges of the panel . After introduction of these materials, the press is closed and a vacuum is drawn in the compartment containing the panel . At the same time the hot nitrogen is used to apply a pressure of 12 bar to the silicon membrane. These conditions are maintained for 6 minutes, following which the pressures are released and the press is opened. For the pressing conditions see Table 2. The laminate was characterized after cooling.

Characterization of the 3D laminate The laminate was assessed mainly for deformation and bonding, both of the internal milled parts and of the external edges. For good deformation the laminate should fully follow the structure of the panel while being completely forced against it in all corners, without any cracking. Furthermore, all parts of the laminate should of course be properly bonded. This was tested by means of a sharp knife that was used to try and remove the laminate. In addition, the appearance was assessed and a staining test was carried out (see Example I) . The appearance of the laminate is good and it has a glossy surface. Deformation and bonding are complete in the internal deep parts. The internal part was subjected to a staining test. The surface is fairly closed, its rating being 3. The results are presented in Table 6.

Example IV (code KB664-H)

The same process as in Examples I and III was repeated, but now with a wet-laid non-woven on the basis of 80% cellulose diacetate fibres (degree of substitution 2.45) and 20% paper pulp (50% hardwood / 50% softwood) with 12.5% DEP homogeneously distributed in this combination. The basic weight also was 105 g/m². Table 1 presents the resin content and the residual volatility content of the prepreg and the 2D pressing conditions on MDF. Table 2 presents the resin content and the residual volatility content of the prepreg and the 3D pressing conditions on MDF. Tables 5 and 6 give the characterization of the 2D and the 3D laminate, respectively. The 3D lamination involved the pressing together of 2 prepregs.

Example V (code KB678-A) The same process as in Example III was repeated, but now with a hand-made, wet -laid non-woven on the basis of 75% cellulose diacetate fibres (degree of substitution 2.45) and 25% paper pulp (50% hardwood / 50% softwood) with 10% N-ethyl , -o,p-toluene sulphonamide (Ketjenflex-8 from AKZO) homogeneously distributed in this combination. The fibres used (CD + paper) had previously been refined for 30 minutes. The basic weight of the non-woven was 160 g/m². Table 2 presents the resin content and the residual volatility content of the prepreg and the 3D pressing conditions on MDF. Table 6 gives the characterization of the laminate. One prepreg was pressed on MDF.

Example VI (code KB678-B) The same process as in Example III was repeated, but now with a hand-made, wet -laid non-woven on the basis of 75% cellulose diacetate fibres (degree of substitution 2.45) and 25% paper pulp (50% hardwood / 50% softwood) with 10% N-ethyl , -o,p-toluene sulphonamide (Ketjenflex-8 from AKZO) homogeneously distributed in this combination. The fibres used (CD + paper) had now previously been refined for 90 minutes. The basic weight of the non-woven was 160 g/m². Table 2 presents the resin content and the residual volatility content of the prepreg and the 3D pressing conditions on MDF. Table 6 gives the characterization of the laminate. One prepreg was pressed on MDF.

Example VII (code KB676-B)

The same process as in Example III was repeated, but now with a hand-made, wet -laid non-woven on the basis of 75% cellulose diacetate fibres (degree of substitution 2.45) and 25% paper pulp (50% hardwood / 50% softwood) . The fibres used (CD + paper) had previously been refined for 90 minutes. No plasticizer was present. The basic weight was 160 g/m². Table 2 presents the resin content and the residual volatility content of the prepreg and the 3D pressing conditions on MDF. Table 6 gives the characterization of the laminate.

One prepreg was pressed on MDF. Example VIII (code KB672-B3)

The same process as m Examples I and III was repeated, but now with a wet-laid non-woven, made on a pilot paper line, on the basis of 75% cellulose diacetate fibres (degree of substitution = 2.45) and 25% paper pulp (60% hardwood / 40% softwood) with 9.6% DEP homogeneously distributed m this combination. This non- woven contained 20% filler (70% Tι0₂ / 30% FeO) on the basis of the non-filled non-woven weight and was of a light brown colour. The basic weight was 160 g/m². Table

1 presents the resm content and the residual volatility content of the prepreg and the 2D pressing conditions on MDF. The 2D laminate is characterized m Table 5. Table

2 presents the res content and the residual volatility content of the prepreg and the 3D pressing conditions on

MDF. Before actual 3D pressing the non-coated MDF panel was preheated for 4 minutes at a pressure of 10 bar with the heated membrane (150°C) . Then the membrane was heated again against the hot upper mould (170°C) and the laminate was pressed. Table 6 presents the characterization of the 3D laminate. In the machine direction (MD) of the carrier the elongation was insufficient and lower than m the direction perpendicular to this (cross direction, CD) . In the cross direction sufficient elongation was obtained. One prepreg was pressed on MDF.

3D pressing on a core material m a 3D shaped metal compression mould ( -mould lamination) During pressing according to this method the core is not yet fully cured and post-formable under the pressing conditions. Curing also takes place, both of the core and of the 3D shaped top layer. Examples of core materials are: 1) wood powder impregnated with phenol -formaldehyde resin which is not yet fully cured

2) wood chips impregnated with phenol -formaldehyde resin which is not yet fully cured 3) several stacked kraft papers, impregnated with phenol -formaldehyde resin which is not yet fully cured, the papers having been cut so that upon stacking a three-dimensional surface structure is obtained. Prepregs obtained in Example VIII were pressed according to the following two methods.

A) At a high pressure and with a long cycle time (high pressure laminate, long cycle time = HPL long cycle) . The process used was as follows: Into the opened, cold press the following were successively placed on the flat lower mould half: a decorative paper impregnated with melamine-formaldehyde resin, several - to obtain the proper thickness - kraft papers impregnated with phenol - formaldehyde resins, cut so that on the upper side a three-dimensional surface is formed (core material 3), and a prepreg according to example VIII. The core part of the laminate may thus also consist of one of the above-mentioned core materials 1 or 2 ; further, the number of decorative papers and/or prepregs according to example may of course also be higher than

1.

After introduction of the entire package, the upper 3D shaped metal mould half was lowered so that the mould was closed. While the moulding pressure was stepwise increased, heating up to a temperature of 160°C now took place. The pressure eventually amounted to 80 bar. These conditions were maintained for a few minutes, upon which cooling under pressure took place. At a temperature of 70°C the pressure was fully released. At a temperature of about 30 °C the press was opened and the laminate taken out. The total cycle time was 30 minutes. The characterization of the laminate is given Table 7. For the moulding conditions, see Table 3.

B) At a high pressure and with a short cycle time (high pressure laminate, short cycle time = HPL short cycle) . In this method, use was made of a press that already had a temperature of 140°. The process used was as follows: into the opened press the following were successively placed on the flat lower mould half: a decorative paper impregnated with melamine-formaldehyde res , an MDF or HDF core that had already to some extent been given the desired shape (consisting for instance of core material 1 or 2) and a prepreg according to example VIII.

The number of decorative papers (for coating the flat side) and/or prepregs according to example VIII (for the coating of the 3D shaped and optionally also the flat side) may of course also be higher than 1. After introduction of the entire package, the upper 3D shaped metal mould half was lowered and the mould was thus closed and brought at a pressure of 40 bar. After 3 minutes the pressure was released, the press was opened and the moulded article taken out. After cooling, the characteristics of the laminate were determined, see Table 7. For the pressing conditions, see Table 3.

Comparative Experiment A

The same process as m Example I, Example III and Examples VIII -A and B (codes A-A and A-B, respectively) was used, but this time with a decorative paper (80 g/m²) which had been impregnated with MF resm and processed into a prepreg. The elongation at break was only 0.8%. See Tables 1 - 7 for further conditions and results. Table 1: Laminate preparation conditions (2D, on flat MDF)

Table 2 : Conditions of laminate preparation using a membrane press (3D, on 3D-shaped MDF)

Table 3 : Conditions of laminate preparation using 3D in-mould lamination (HPL, long & shor cycle)

Table 4 : Elongation at break and tensile strength of prepregs

Table 5: Characterization of the 2D laminates (flat on MDF)

Table 6: Characterization of the 3D laminates (membrane pressing on 3D shaped MDF)

Table 7, Characterization of the 3D in-mould laminates (HPL, long & short cycle)

Claims

1. Sheet prepreg comprising one or more layers of a porous carrier sheet, which porous carrier sheet has been impregnated with an as yet uncured resm, characterized that the carrier contains a meltable polymer which has been mixed with cellulose or regenerated cellulose or mixtures or combinations thereof.

2. Sheet prepreg according to claim 1, characterized that a cellulose ester, preferably several esters and more m particular cellulose acetate is used as the meltable polymer

3. Sheet prepreg according to claim 2, characterized that the cellulose acetate that is used has a degree of substitution of between 0.01 and 3.

4. Sheet prepreg according to claim 3, characterized that the cellulose acetate that is used has a degree of substitution of between 2 and 3.

5. Sheet prepreg according to claims 1-4, characterized that kraft paper pulp is used as cellulose .

6. Sheet prepreg according to any one of claims 1-5, characterized that the elongation at break of the impregnated carrier sheet and of the prepreg is higher than 2%.

7. Sheet prepreg according to claims 1- 6, characterized m that the resm is an ammoplastic resm.

8. Sheet prepreg according to claim 7, characterized that the ammoplastic resm is melamine formaldehyde resm.

9. Sheet prepreg according to claims 1-8, used m self-supporting moulded articles.

10. Sheet prepreg according to claims 1-8, used in sheet products that can be deformed along two or more mutually intersecting axes.

11. Object provided with a top layer obtained from a sheet prepreg according to claims 1-8 which has been deformed along two or more mutually intersecting axes.

12. Sheet prepreg according to claims 1-8 which provides objects with 3D structures based on milled MDF or HDF board with a top layer.

13. Sheet prepreg according to claims 1-8 which provides objects with 2D structures with a laminate top layer.

14. Sheet prepregs and objects as follows from the description and the examples.