WO2000053668A1

WO2000053668A1 - Sheet prepreg containing carrier sheets and as yet uncured resin

Info

Publication number: WO2000053668A1
Application number: PCT/NL2000/000114
Authority: WO
Inventors: Maurits Frederik Hendrik Van Tol; Karel Franciscus Hubertus Bonekamp; Jan Jacob Hendrik Nusselder
Original assignee: Dsm N.V.
Priority date: 1999-03-05
Filing date: 2000-02-23
Publication date: 2000-09-14

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 being a porous carrier sheet on the basis of a fibrous cellulose acetate and that the elongation at break of the prepreg and of the separate impregnated carrier sheet is higher than 2 %.

Description

SHEET PREPREG CONTAINING CARRIER SHEETS AND AS YET

UNCURED RESIN

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 and 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 the above-mentioned patent 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 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 more complex shapes can be obtained and/or covered.

This object is achieved with a prepreg consisting of one or more layers of a carrier sheet, which carrier has been impregnated with an as yet uncured resin, the carrier being a porous carrier sheet that contains a fibrous cellulose ester, preferably several esters, and more m particular cellulose acetate. Preferably, fibrous cellulose acetate is used of which between 0.01-3 (degree of substitution) of the OH groups of the monomer units are acetylated, such as cellulose monoacetate, cellulose diacetate and cellulose triacetate as well as mixtures or combinations of these acetates. Preferably, the degree of substitution is between 2 and 3.

As carrier use is made m particular of fibrous cellulose diacetate, with the cellulose diacetate having the form of fibre bundles, the so- called CD tow, and with the individual fibres having a diameter of less than 100 μ, preferably less than 50 μ. The diameter of the individual fibres is more than 1 μ.

It is also possible to use fibrous cellulose acetate m the form of yarns . These yarns can be prepared on the basis of CD tow. Bundles of yarns can also be used.

The carrier on the basis of a fibrous cellulose acetate will preferably also contain a plasticizer. This plasticizer can be spun together with the cellulose acetate into fibres, which fibres can then be converted into a plasticizer containing carrier. It is also possible for cellulose acetate fibres to be treated with plasticizer and subsequently be converted 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 triacetme, triethylcitrate, diethylcitrate, N-methyl-o,p-toluene sulphonamide , phosphates and phthalates, m 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 prepreg and of the separate impregnated carrier is higher than 2%, preferably higher than 5%, and m 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 m the most diverse shapes without cracks being formed m the sheet product during deformation.

Sheet products are now possible with shapes involving local stretching of the prepregs from 10% to more than 100% during the shaping. Objects m 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 softlme 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 m one step. This is m contrast to the method described m 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 into an acute angle, for instance along one axis. Starting from the known prepregs based on a paper carrier, this is impossible.

A porous carrier sheet is understood as meaning any carrier having a high degree of porosity. The porosity of the carrier is essential for obtaining the advantageous properties of the prepreg as described above. As a result of the high porosity, the carrier sheet can, as it were, be almost homogeneously filled 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 holes result m loss of resin during the 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 carrier can for instance be a woven or non-woven carrier sheet, an open foam carrier sheet or a microporous membrane. Preferably, the fibres of the non-woven have a diameter of less than 0.1 mm. Non-wovens having very small -diameter fibres 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 .

The porous carrier sheet may have both polar and apolar properties. As a result of making use of suitable wetting agents, the desired degree of impregnation of the carrier 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^8" 523 , PAT^® 959 (PAT^* is a urtz brand name) , Nonidet^" P40 (Nonidet^" P40 is a Sigma Chemie brand name) and Amino1 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 polymeπzable monomers. Examples are thermosettmg resins or elastomeric resins, which resins can be cured via an ionic, radical, oxidation, addition or condensation mechanism or cure via a combination of these mechanisms, such as for instance m the so-called dual -curing .

Examples of resins that cure via an oxidation mechanism are alkyd resins. Usually, however, cationically and/or radically curing resins 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, malei ide, vmylether, allylether and/or vinyl ester groups. Examples are the acrylate resins.

Cationically curing resins can contain monomers which contain polymerizable 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 resins .

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

Compounds of formaldehyde with, for instance, urea, melamine, acetoguanamme or benzoguanamme, or mixtures or combinations of these, can be used as the ammoplastic. Preferably, melamine is used because of the superior mechanical properties of the final product

The ammoplastic resm can be prepared a process known to one skilled the art by reaction of, for instance, melamine and/or urea with formaldehyde 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, tπoxitol, toluene sulphonamide, and benzo- and acetoguanam e can also be added.

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

Mechanical properties that are suitable for practical use are achieved if 10-70% by weight of porous carrier and 90-30% by weight of resm are used. The resm may contain the known fillers and/or colorants such as lime, clay, glass, carbon, silica, titanium dioxide or metal particles. It has been found, however, that the best results are achieved m the absence of fillers or at any rate with less fillers than has been customary so far. The filler to resm weight ratio preferably lies 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. The viscosity of the resin used for the impregnation can be influenced by, for instance, varying the nature and the amount of the solvent . As yet uncured ammoplastic resm such as melamine-formaldehyde resm is for instance dissolved 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 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 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% and measured at a temperature that is close to the product's processing temperature. Drying preferably takes place at a temperature of 100- 160 °C if 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 carrier 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, 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 the number of carrier sheets is usually 100 or lower, preferably 10 or lower, and m particular 5 or lower. The prepreg may optionally comprise layers of a polymer besides the porous 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 the 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 polymerizable 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 for instance 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 m 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 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 moulding. These films, m turn, can also be smooth, matt or have the desired pattern or relief. Optionally, such films may also be used as a membrane.

The deformation, optionally combination with the curing, can for instance be performed by means of bending, embossing, 3D deforming such as 3D pressing, stamping, pneumatic stretching or mechanical stretching. The temperature during the deformation 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 or wood-based material such as the well- known MDF (Medium Density Fiberboard) and HDF (High Density Fiberboard); metal; glass; plastic, for instance polyethylene, polypropylene, ABS, polyamide, polyester and MF, PF and epoxy resms or combinations of these. The invention also relates to an object provided with a top layer comprising 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 and 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 or HDF board, window frames, laminated flooring with a 3D structure (for instance with upright edges) , skirting boards, etc.. Examples of objects in which the shaped product serves as a protective layer for a plastic core are bumpers, petrol tanks, helmets, garden furniture, furniture, worktops or car bodywork components.

The invention relates in particular to sheet prepregs that provide objects with a 3D structure based on milled MDF or HDF board with a top layer. These laminated MDF or HDF boards can be produced in one process step, for instance in an in-mould lamination process . The sheet products according to the invention can also be used in flat applications (2D applications) such as laminate flooring, interior door panels, wall panels, table tops, etc., and in post- forming applications. Surprisingly, it has been found that when a cellulose diacetate is used as 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 at least as good as 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 relief 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 resm is still incompletely cured. The resm then serves as a glued joint when it is subsequently cured. The invention will be elucidated by means of the following, non-limiting examples.

Example 1

Preparation of resin

In a reactor, 48 parts of water and 131 parts of formalin (30 wt . % formaldehyde 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 resm was 1.65 (F/M ratio is the molar formaldehyde-melamine ratio) . The condensation reaction was performed at 95°C until the water dilutability of the res at 20°C was 1.5 g of resm 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 . % para-toluene sulphonic acid solution 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 wet-laid non-woven on the basis of 100 wt . % cellulose diacetate (CD) m the form of fibres with 10 wt . % diethyl phthalate (DEP) homogeneously distributed m it as plasticizer. The CD fibres were made by pouring a solution of CD acetone into stirred ethanol . A wet-laid non-woven is prepared by passing a dispersion of CD fibres m water over a filter, the resulting filter cake being dried to yield a carrier. The morphology of the resulting CD fibres is fine and comparable to that of paper fibres paper pulp. The weight of the dried film this example was 80 g/m².

For 2D pressing a sheet measuring 20 x 20 cm was used. For 3D pressing a circular sheet having a diameter of 21 cm was used.

The sheets were impregnated at room temperature with the above-mentioned resm solution, to which 0.5 wt.% PAT° TD80 (from urtz) had been added for wetting purposes and 0.2 wt.% PAT^® 523/ (from Wurtz) for mould release purposes. After 30 seconds the resm- impregnated sheet was removed from the impregnation equipment and the excess resm was removed with the aid of a wringer. The sheets were dried m a circulatmg-air oven for 8 minutes at 100°C. See Tables la and lb.

Characterization of the prepreg

Resm content : the resm content of the prepreg was determined by weighing the prepreg and the carrier and was 138%. The res content is defined as:

(g (prepreg) -g (carrier) ) /g (carrier) , g (prepreg) and g (carrier) are the weights of the prepreg and of the carrier, respectively. See Tables la and lb.

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

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

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

See Tables la and lb.

Elongation at break and tensile strength

The elongation at break and tensile strength were measured on test specimens (measuring 50 x 4.0 x

0.52 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/mm. For the results, see

Table 2.

- 2D pressing on a flat substrate: One sheet of the prepreg based on CD non- woven 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 was placed m the press (of the type Fontijne TP400) following which the press was 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 was 140 °C. These conditions were maintained for 3 minutes and then the press was opened and the laminate removed. After cooling the laminate could be characterized .

- 3D pressing

To assess the eventual deformation of the prepreg, a pattern of small squares was pencilled on it. A circular sheet of the prepreg based on CD non-woven with 10 wt.% DEP with a diameter of 21 cm was pressed on so-called REMEL (REinforced MELamme) Sheet Moulding Compounds (SMC) . These are thin (thickness approx. 3 mm) glass mats filled with partly cured MF resm.

First of all a prepreg was clamped above the bottom of a mould shaped like a round tub. A number of stacked and preheated REMEL SMCs was placed on top of the clamped prepreg. The SMC inlay is about 60% relative to the mould surface area. The final moulding was formed by means of flow moulding, which involves the moulding sheets flowing out into the mould, filling it so that the final moulded article is obtained. The prepreg was drawn over the REMEL core like a skin. During this process, deformation, curing and gluing of the prepreg with the layer below it took place m one step. Pressing took place at 140°C and 160°C at a pressure of 10 MPa (High Pressure Laminate = HPL) using the following pressing cycle: placing m the mould, closing and pressurizing, deaeratmg (after 25 seconds) , reclosmg and repressurizmg, maintaining this pressure for some time (at 140°C: 315 seconds, at 160°C: 155 seconds) , after which the press could be opened and the moulded article taken out. After cooling the laminate could be characterized. Characterization of the 2D laminate (see Table 3a)

- The laminate was assessed visually as well as with the aid of a light microscope.

The laminate looked good and was homogeneous on macro scale. The laminate surface was smooth and closed.

- In addition, the laminate was subjected to a few standard tests, more specifically the staining test and the Kiton test. These are well-known tests m 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 is given together with the results.

- The staining test used here is derived from EN 438-2 and is based on staining 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 is 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, very good.

- The Kiton test is based on staining 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.

Characterization of the 3D laminate (see Table 3b)

- Pressing at 140°C:

The prepreg was uniformly drawn around the REMEL core. The surface was fairly smooth and looked closed. Result of staining test : 4 Result of Kiton test : 4

- Pressing at 160°C: The deformation of the prepreg is good. The surface was smooth and further looked closed. Result of staining test : 1 Result of Kiton test : 2

Example II

In this example use was made of a dry-laid non-woven based on 100% cellulose diacetate tow. Tow is made on a large scale by spinning a solution of cellulose diacetate m acetone, after which the acetone is evaporated. Tow is a bulk product used for instance m cigarette filters.

Tow fibres were processed into a non-woven. After the tow had been cut into pieces of approximately 5 cm long, the material was carded so that a felt-like mat was obtained. Several of these mats were stacked m different directions of orientation and needle-bonded to form a multilayer mat, which was subsequently calendered at elevated temperature.

This produces an extremely attractive and very strong non-woven film. Afterwards, 10% DEP was added as a plasticizer via spraying from a solvent . The film weighed about 150 g/m².

- 2D pressing took place m the same way as m Example 1. For further data and results, see Tables la, 2 and

3a. - 3D pressing

The film was impregnated with MF resin of pH 8.0. The prepreg obtained upon drying was pressed in one pass on a core of phenol formaldehyde resin (PF) filled with wood fibres. This was done in a 3D shaped aluminium mould. The pressed product has the shape of a plate with a hemisphere punched into it. Pressing took place at a pressure of 6 MPa for 15 minutes at 140°C. Under these conditions good curing of both the core and the laminate was achieved.

Tables lb, 2 and 3b present the conditions and results.

Comparative Experiment A

The same process as in Example 1 was used, but now use was made of a decorative paper (80 g/m²) . See Tables la, lb, 2, 3a and 3b for further conditions and results .

Table la: Laminate preparation conditions, 2D LPL on MDF

Table lb: Laminate preparation conditions, 3D HPL on Remel/PF wooden core

Table 2 : Elongation at break and tensile strength of prepregs

1) 400% is the maximum elongation that can be measured in the tensile tester

Table 3a: Characterization of the 2D laminates LPL on MDF

Table 3b: characterization of the 3D laminates HPL on REMEL / PF core

Claims

1. Sheet prepreg comprising one or more layers of a carrier sheet, which carrier has been impregnated with an as yet uncured resin, characterized in that the carrier is a porous carrier sheet containing a fibrous cellulose ester, preferably several esters and more in particular cellulose acetate.

2. Sheet prepreg according to claim 1, characterized in that the porous carrier sheet is based on cellulose acetate with a degree of substitution of between 0.01 and 3.

3. Sheet prepreg according to claims 1-2, characterized in that the fibrous cellulose acetate has the form of fibre bundles.

4. Sheet prepreg according to any one of claims 1-3, characterized in that the porous carrier is a woven or non-woven sheet, an open foam sheet or a microporous membrane.

5. Sheet prepreg according to any one of claims 1-4, characterized in that the elongation at break of the impregnated carrier sheet and of the prepreg is higher than 2%.

6. Sheet prepreg according to claims 1-5, characterized in that the resin is an aminoplastic resin.

7. Sheet prepreg according to claim 6, characterized in that the aminoplastic resin is melamine- formaldehyde resin.

8. Sheet prepreg according to claims 1-7, used in self-supporting moulded articles.

9. Sheet prepreg according to claims 1-7, used in sheet products that can be deformed along two or more mutually intersecting axes.

10. Object provided with a top layer obtained from a sheet prepreg according to claims 1-7 which has been deformed along two or more mutually intersecting axes.

11. Sheet prepreg according to claims 1-7 which provides objects with 3D structures based on milled MDF or HDF board with a top layer.

12. Sheet prepreg according to claims 1-7 which provides objects with 2D structures with a laminate top layer.

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