FIELD OF THE INVENTION

The present invention relates to an improved method for the production of elements intended for the cladding of surfaces in the building industry. More particularly, the invention relates to the production of protection elements, such as plinths and bumpers/fenders which are suitable for use in hygienically sensitive areas, such as in the food industry, in the pharmaceutical industry, in hospitals, or in clean rooms, such as, for example, also in the electronics industry. The invention is also suitable for the manufacture of special cladding elements, such as decorative construction elements, more particularly special floor and wall tiles. The invention also comprises certain of the possible products which may be manufactured by this method.

BACKGROUND OF THE INVENTION

It is known to apply protection elements such as plinths and bumpers/fenders in the places where walls and floors merge into one another. These elements may mechanically protect the bottom part of the walls, and indirectly the walls above them, against knocks and bumps by trolleys, carts, forklifts, pallet trucks, pump trucks or pallet trucks, also known as trans pallet trucks, or also by mobile equipment or furniture, such as serving trolleys or hospital beds. Especially the corners of passages are very vulnerable, and in those locations such protection is therefore very important.

The more traditional plinths, usually made of wood, plastic or light metal, cannot be used in many environments because they are not providing sufficient sturdiness and/or wear resistance, easily deform, do not comply with the hygiene requirements, or do not show the appropriate aesthetic look.

Firmer shock plinths may be made of concrete, but this material is relatively brittle and crumbles easily, usually has a certain porosity and is not water repellent, whereby these shock plinths are also from a hygienic point of view undesirable.

For this reason, such concrete bumpers/fenders are often provided with a metal coating on the outside, at least partially, but preferably over the entire visible surface. Stainless steel is often used in this context, because it confers a more hygienic and aesthetic view and also maintains this for a long time period. To improve the adhesion of the steel outer layer to the concrete, the metal coating may for a better anchoring be shaped so that it grips around the concrete core and/or an edge thereof may be incorporated into the concrete core. German Patent Specification DE 4340953 C1 describes such an embodiment, wherein a filling part consisting of polystyrene foam is used to decrease the weight of the product. To improve the adhesion of the steel outer layer to the concrete, the metal layer may also be glued. Such plinths are amongst others described in Belgian Patent Specification BE 1017613 A6. This additional metal coating is, however, cumbersome to apply.

DE 2619058 A1 describes a similar embodiment with a core of polyurethane (PU) foam. This foam may be given an appropriate firmness and elasticity to support the outer metal layer, to protect it against deformation upon impact, and even to provide it with a certain cushioning and flexibility.

Also DE 29904194 U1 describes a plinth or base frame wherein a metal cover is glued to a PU rigid foam core.

This additional metal coating represents in all described applications a significant additional cost in terms of materials and requires additional steps in the manufacturing process.

In addition, the lap joints of the plinths, i.e. the sides where two consecutive plinths approach each other, still remain in most of these models uncovered, so that they are still pretty roughly and imprecisely finished. When installing the bumpers/fenders, this leads to wider joints, which is undesirable because dirt more readily settles in those locations and because they require more material for being filled.

An additional disadvantage is that the decorative possibilities of these known bumpers/fenders still remain quite limited. These capabilities may be extended by additionally painting of the protection elements, which however means yet again a further treatment and additional raw material use. Certain floors like epoxy floors, may also be raised up to on the concrete bumper/fender, with decorative and technical advantages, but also this requires an additional treatment.

Plinths on the basis of less brittle materials than concrete have also been developed. The core of such plinths may use plastics as a binding agent, preferably supplemented with one or more filling materials. The binding agents are preferably polymeric resins which cure by cross-linking, so that they form a solid three-dimensional molecular structure. In this way they offer a good adhesion to the filling materials, and a solid structure. Preferably, these resins are also water-repellent, so that the plinths may also comply with the hygienic requirements.

EP 848 120 A1 discloses a solid plinth formed from a composite material consisting of silicon particles coated with a polyester binder, to which a dye may be added. A disadvantage of this embodiment is that a smooth outer surface is difficult to achieve because of the particles in the mass. If a high gloss, good colouring, and/or other additional properties are to be given to the plinths by additives, then high amounts of these additives are necessary to achieve the desired result in this embodiment. The properties of the core and of the surface may also not be influenced independently of each other.

At the outer sides which are intended for remaining visible, these plinths, therefore, may be further provided with an upper layer. This layer may also consist of plastic, because of good chemical and water repellent properties, and which may be given a certain decorative effect by means of a pigment. In order to increase the wear resistance of the plinths, a very strong cross-linking polymeric resin is preferably also used for the top layer, so that ultimately a surface with high hardness is obtained.

NL 1006957 describes a bumper/fender which is produced by first laying a prefabricated fiber-reinforced synthetic resin profile in pre-formed mould, or by making therein a top layer of a fibre reinforced coating. This top layer is made of a food-safe coating consisting of polyester resin mixed and filled up with fibres and/or glass fleece, produced to meet a particular impact strength. After the production of the top layer, the mould is filled with a composition consisting of very fine gravel parts, or other filling materials, and a polyester resin or other synthetic resin. Also accessories such as inside and outside corners and end pieces are described. NL 1006957 is not concerned with the compatibility between the binders of the top layer and of the core, nor with the adhesion between the core and the top layer of the bumper/fender.

DE 3145334 A1 describes a stairs step which is produced by applying on a glass plate a thin layer of a mixture on the basis of a resin "Feinschichtharz Nr. 325 ", which at 20°C ambient temperature has a gelation time of eight to twelve minutes, within which time the layer must have been applied. About 20 minutes, at the latest two hours, after the application of the thin layer on the glass, into the mould is poured the material for the filling layer, which is based on a polyester resin, and which is subsequently allowed to polymerize. The inventors have found that the adhesion between the core and the top layer of DE 3145334 may be further improved.

It is also not obvious how such plinths having both a core and a top layer on the basis of synthetic material may be produced in a simple way. It is important in this respect that the top layer is attached as tight as possible to the material of the core. And from an aesthetic point of view, it is also desirable to obtain very smooth outer surfaces. In addition, the upper layer with its high hardness also raises a problem of high brittleness, so that at the moment of mounting, wherein at times a pry bar must be used due to the weight element to be installed, there is a risk that flakes of the upper layer desquamate whereby the aesthetic effect is lost. The brittleness of both the upper layer and the core raises furthermore an additional problem that at unequal shrinkage of coating and core cracking may arise, making the product as such no longer useful and often must be disposed of as waste.

Thus, there remains a need for a simple process for the production of such cladding elements, wherein the top layer has a good adhesion with the core of the element, as well as to plinths or other cladding elements of which the plastic top layer and/or the core is less brittle than what so far is known in the art.

The present invention has as the object to avoid or at least alleviate the problems described above, and/or provide improvements in general.

SUMMARY OF THE INVENTION

According to the invention, there is provided an improved method for the production of elements for the cladding of floors or walls based on polymer resins, and in an improved cladding element as defined in any of the claims attached hereto.

The invention provides more particularly a method for the production of an article for the cladding of floors or walls, comprising the steps of:

a) applying a gel coat layer, based on a curing polymer resin, on the inside of a mould in order to obtain a coated mould,

b) introducing into the core of the' coated mould of step a) a filling composition which is based on a curing polymer resin supplemented with at least one mineral filler,

wherein the curing polymer resins of step a) and step b) are of the same chemical family of curable polymeric resins, and

wherein the gel coat layer in the coated mould of step a) is only cured partially before the coated mould of step a) is subjected to step b),

characterized in that the curing polymer resin of step a) is cured only until the gel coat layer is at most touch dry, before the coated mould of step a) is subjected to step b). We have found that the method according to the present invention is extremely simple, and moreover, provides without any layer of glue an exceptionally good adhesion between the gel coat upper layer and the core of the produced product. We have also found that by an appropriate selection of the raw materials, and by addition and appropriate selection of additives, initiators, accelerators and/or retarders, the course of the curing of the resins of step a) and step b) may be set independently from each other, so that they optimally meet the stated requirements and, at the same time may be adjusted to each other to be able to produce a product with the desired properties in a simple and fast way, and this with relatively little human intervention.

In another embodiment, the present invention provides an element for the cladding of floors or walls which may be produced by the method according to the present invention, and which consists of a core of a composition which is based on unsaturated polyester resin, supplemented with at least one mineral filler material, at least partially surrounded by an outer layer based on a gel coat, which is also based on unsaturated polyester resin, and which element is selected from a decorative wall tile or floor tile and a plinth or bumper/fender, wherein in the case of the decorative floor tile or wall tile at least one dye or pigment has been added to the gel coat, and/or whereby to at least one surface of the mould at least partly a varying relief shape is given, and wherein in the case of the plinth or bumper/fender, and optionally also to the decorative wall or floor tile, to the polymer resin of the core and/or of the top layer at least 0.5% and at most 20% by weight is added, expressed on the basis of the total amount of polymer resin in the top layer or in the core, of an unsaturated polyester resin which is characterized by an elongation at break after curing of the resin and tested according to ISO 527 of at least 4.0%.

The inventors have found that, by the addition of at least one pigment, or by giving one of the surfaces intended for remaining visible a further shape which deviates from a planar surface, and most preferably by a combination of the two characteristics, exceptional decorative 1

and/or functional effects may be obtained. Moreover, these components are not subject to rotting and/or corrosion, ensuring their longer life time.

In this way, for example, decorative wall tiles and floor tiles may be produced, which are highly resistant to the influence of weather conditions, especially to acid rain, but also to UV radiation, biological wear, and other chemical influences. Such floor tiles and wall tiles are also very easy to maintain and to clean because they are highly resistant to a wide range of detergents and surfactants, and to the other additives which are used in cleaning products. The water-repellent characteristics of the gel coat upper layer play an important role. Because of their high hardness, they may also easily be cleaned with a high-pressure water lance, without this leading to scratching and/or loss of gloss: The decorative possibilities are very broad, because the choice of pigments which may be added to the gel coat layer is virtually unlimited. These floor tiles and wall tiles thus offer an important alternative for the cladding of floors or walls, especially exterior floors and exterior walls, and by their extraordinary mechanical properties, especially impact strength and chemical resistance, they are in many aspects better than many of the other alternatives that are offered for floor or wall cladding.

These construction elements are therefore particularly suitable for cladding large outdoor floors around, or the exterior walls of buildings which are larger than typical in a residential context, such as public service and/or industrial buildings, and wherein said decorative elements by their appearance, luster, and persistence may significantly increase the appearance or the prestige of the clad building and/or its environment, and may guarantee this effect for a long time.

The plinths or bumpers/fenders according to the present invention have the advantage that they run less risk of damage during assembly, because the gel coat upper layer has some flexibility, is less brittle, and contains less residual stress. When mounting with a tool, flakes will therefore less easily desquamate, making sure the aesthetic and hygienic effect is better preserved. The products produced according to this method are also easy to repair, with a simple polyester kit having the appropriate colour.

DETAILED DESCRIPTION

In the context of the present invention, with the prefix "poly-" a quantity greater than 1 is meant. If only integers are applicable, "poly" means the same as "two or more" or "at least two (2)".

In this document, all percentages are by weight, unless indicated otherwise.

In principle, a wide variety of thermosets or thermosetting polymers or polymer resins may be used within the framework of the present invention. Alkyd resins, phenol formaldehyde (PF) resins, diallyl phthalate (DAP) resins, melamine-formaldehyde (MF) resins, polyester resins, and urea-formaldehyde (UF) resins are possible.

The inventors however prefer to use unsaturated polyesters, because these resins take up virtually no moisture, may even be water repellent, are good cold and heat resistant, are well resisting to acids, oxidizing agents and dilute alkalis, are good resisting to sunlight, are very wear resistant, are highly pressure-resistant, may give a high gloss, and are not affected by bacteria and fungi. Moreover, they are easy to handle, the curing reaction is easy to start and the reaction rate is easy to steer, and this within a wide temperature range which is easy to reach and typically includes the normal ambient temperature and/or room temperature. The inventors have also found that the cured polyester based bumpers/fenders have an impact resistance that is twice as high as concrete. An additional advantage is that these polyesters also undergo a slight shrinkage during curing, rendering the demoulding of the products much easier.

In another embodiment according to the present invention, the curing polymer resin of step a) and step b) belong to the family of unsaturated polyester polymer resins, and wherein preferably for the curing reaction a vinyl monomer has been incorporated, more preferably styrene. Unsaturated polyesters are curing polymer resins. Generally, they are copolymers obtained by the polymerisation of one or more polyols, usually diols, such as monoethylene glycol (MEG), with unsaturated dicarboxylic acids such as maleic acid or fumaric acid, and/or the anhydrides thereof. Hereby also partially saturated and/or aromatic acids and/or their anhydrides may be used, such as the various forms of phthalic acid or phthalic acid anhydride. The double bond of the unsaturated polyesters reacts during curing with a vinyl monomer, usually styrene, so that a three-dimensional cross-linked structure is formed. The cross-linking is usually set in motion by an exothermic reaction in which an organic peroxide may be used as an initiator, often also called less accurately the catalyst, such as methyl ethyl ketone peroxide, benzoyl peroxide or dibenzoyi peroxide. The initiator usually acts by releasing a free radical which initiates the polymerization or chain reaction.

As vinyl monomer usually styrene, a-methyl styrene, para- or meta-styrene, divinyl benzene, diallyl phthalate and prepolymers thereof, diallyl isophthalate, diallyl terephthalate, or prepolymers thereof, N-vinyl pyrrolidone, triallyl cyanurate, diallyl melamine, or the like, alone or in mixtures with each other are being used. Other vinyl monomers which may be used are the alkyl-styrenes, and other allyl, acrylate or methacrylate esters.

Suitable unsaturated polyesters are commercially offered by many companies, and are available in a wide range of properties. Such polyesters are also commercially available in mixtures with styrene so that they may immediately be used as a binder in the step b) of the method according to the present invention.

A gel coat layer within the context of the present invention is preferably a gel coat layer based on a polyester, such as obtained by the esterification of a polyvalent carboxylic acid with a polyol, which means a chemical substance having at least two hydroxyl (OH) groups.

The polyvalent carboxylic acid of the polyester resin of the gel coat layer or of the core of the article may be aliphatic or aromatic. The applicants prefer to use a polyester formed from an aromatic polyvalent carboxylic acid. Suitable candidates are, for example, phthalic acid, also called orthophthalic acid, isophthalic acid and/or terephthalic acid, but also acids with several benzene nuclei are possible. The applicants prefer a gel coat which is based on orthophthalic acid, most preferably based primarily on orthophthalic acid.

There are many polyols which may be used in the polyester according to the present invention. Suitable are, for example, ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,3-butanediol, ,4-butanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, and bis- ^-hydroxypropyl)ether of bisphenol A. The applicants prefer a polyol which has only two hydroxyl functions per molecule. Suitable candidates are available in large numbers, such as ethylene glycol, mono-ethylene glycol, ethylene glycol oligomers such as diethylene glycol, triethylene glycol, and tetraethylene glycol, ,2-propanediol, 1 ,3-propanediol or oligomers thereof, such as dipropylene glycol and other polypropylene glycols, 1 ,2-butanediol, 2,3-butanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,8-octanediol, 1 ,3- butanediol, ,2-pentanediol, 2-methyl-2,4-pentanediol, neopentyl glycol, bisphenol A, the bis-( -hydroxypropyl)ether of bisphenol A, and others.

Together with a divalent carboxylic acid, a divalent polyol gives a so-called "linear" polyester. This avoids excessive cross-linking, such that the viscosity of the polyester is kept quite low, so that the substance which contains the polyester is sufficiently well spreadable or sprayable, or that it flows sufficiently easily enough before the curing step, so that a good adaptation to the mould, or a good filling of the given space, may readily be achieved, with a minimum of effort. The applicants prefer a gel coat which is primarily based on a resin made from virtually pure isophthalic acid together with neopentyl glycol.

In the manufacture of the unsaturated polyester, often unsaturated carboxylic acids are used. Suitable are ethylene-like α,β- unsaturated dicarboxylic acids, for example maleic acid, fumaric acid, citraconic acid, itaconic acid, mesaconic acid and the like, or the anhydrides thereof. In the production of the unsaturated polyester, often also saturated carboxylic acids are used. Suitable are (ortho-)phthalic acid, or its anhydride, tetrahydrophthalic acid (or its anhydride), hexahydrophthalic acid (or its anhydride), isophthalic acid, terephthalic acid, adipic acid and succinic acid or butanoic divalent acid.

As chain terminators monohydric alcohols or acids may be used in the production of the polyester monomers which may be used as raw materials in the present invention. In addition, these components may be used either straight chained or branched. Also useful are polyhydric alcohols, such as glycerine, trimethylolpropane, pentaerythritol or the like, for obtaining, where possible, already some cross-linking in the monomer.

The polyesters are often offered as a solution in a liquid vinyl monomer, preferably styrene. The formulation is subsequently diluted, also called "modified" by the addition of dicyclopentadiene (DCPD). This DCPD provides additional cross-linking of the finally cured polymer, and because the reagent is a liquid, it allows to use less styrene for reaching the same low viscosity for the gel coat, in order to allow proper processing. For the gel coat, the applicants thereby prefer sometimes a "preaccelerated" version of this gel coat, wherein an amount of catalyst is added to obtain a faster curing reaction. As the catalyst, methyl ethyl ketone peroxide (MEKP) is preferably used, but other peroxides such as acetyl acetone peroxide (AAP) are suitable. Before the curing begins, this gel coat preferably has a viscosity of 2000 to 30000, preferably from 5000 to 25000, more preferably of from 8000 to 20000, and most preferably from 10000 to 18000 centipoise (cPs) at 20°C, measured according to NFT 51 210, with a Brookfield RVF 100 meter, using a No. 5 spindle at 20 revolutions per minute. Suitable versions are available as gel-coat HPH 6098 ST Paraf. from Ferro Plastics Europe, but also as polyester gel coat GC 875 9270 from Nord Composites.

As the binder for the filling composition of step b) the applicants prefer that these belong to the same chemical family as the resin which acts as the binder in the gel coat. The applicants thereby thus prefer to also use a polyester, preferably an unsaturated polyester. These products are typically offered as a solution in styrene monomer, which is liquid and may easily be pumped. Suitable products are for example VIAPAL VUP 4778/55 available from Cytec Surface Specialties GmbH, with approximately 44 wt% styrene, Distriton 110 mod available from Lonza SpA, and ENYDYNE ® D 20-321 from Cray Valley. The applicants prefer to use resins from the family Resin Poliplast R 96 Carlo Ricco' & F.lli S.p.A. (30-34% styrene), or Distitron® available from Polynt S.p.A. (34-39% styrene). Not "preaccelerated" versions are for example available as Resin Poliplast R 96.02 Carlo Ricco' & F.lli S.p.A. (30-34% styrene), or Distitron® 110 V3W available from Polynt S.p.A. (34-39% styrene). These resins have been modified with dicyclopentadiene (DCPD), and are thus even more chemically and thermo-mechanically resistant. Therewith the styrene content may also be kept somewhat lower, which is favourable for the industrial hygiene at the workplace. These products are offered in a version with already 25-50% styrene by weight, preferably 30-40% by weight, so that they are ready for the curing reaction, when necessary after introduction of a suitable catalyst. The applicants prefer the uncoloured version of these products, so that he himself may mix in the suitable dyes or pigments, as desired. The applicants also prefer the non-"preaccelerated" versions, because these are more stable during transport and storage, and because the curing reaction may be better controlled by the separate dosing in of the reaction accelerator.

The applicants preferably use as the principal resin a polyester resin having, prior to the curing reaction, a viscosity at 25°C of 100-600 mPa.s, more preferably of 200-500 mPa.s, more preferably of 250-460 mPa.s, yet more preferably of about 300-400 mPa.s, and most preferably of about 320-360 mPa.s. In addition, the polyester resin composition contains preferably 25-50% by weight of styrene, more preferably 30-40 wt%, and yet more preferably 31-33 wt% styrene.

For accelerating the curing reaction frequently an accelerator is used. Suitable are, for example, the salts of cobalt, manganese, vanadium and iron, β-diketones selected from derivatives of acetyl acetone, derivatives of aceto acetamide, and esters of aceto acetic acid, but also tertiary aromatic amines such as, for example, dimethyl aniline, dimethyl-p-toluene, diethyl aniline, phenyl diethyl aniline, phenyl-diethanol amine, and the like. These are typically used in concentrations of 0.05-1.0 parts by weight per hundred parts of resin. With metal components thus usually only the concentration of the metal is intended.

As the reaction accelerator or accelerator the applicants preferably use cobalt, more preferably a cobalt compound, more preferably an organometallic cobalt compound. Particularly suitable is cobalt octanoate, containing cobalt at 6% by weight, which is effective in small amounts, such as from 0.10-0.30 wt%, preferably 0.15-0.20% by weight, based on the resin. The applicants have found that this accelerator is very suitable in these concentrations, together with 1.0-3.0 wt% MEKP initiator, preferably 1.5-2.5% by weight of MEKP.

The cross-linking or curing reaction with unsaturated polyester resins is preferably a free radical polymerization reaction. This reaction is preferably initiated by an initiator, also called curing agent, a.k.a. hardener or catalyst. As initiator for the curing reaction, preferably peroxides are used, often a combination of several peroxides, more preferably organic peroxides because they are less volatile, and because they may often be supplied as a liquid. Suitable are, for example, hydrogen peroxide, benzoyl peroxide, lauryl peroxide, dicumyl peroxide, p-tertiary butyl perbenzoate, acetyl acetone peroxide (AAP), methyl isobutyl ketone peroxide, and the like. The applicants prefer to use methyl ethyl ketone peroxide (MEKP). MEKP gives a reliable performance at ambient temperature and at room temperature. The MEKP is normally supplied as a 30-40 wt% solution in a suitable solvent such as, for example, dimethyl phthalate ester. In addition, preferably, a phlegmatiser is added, which is a substance which stabilizes the relatively unstable peroxide during storage and for transport and handling, until it is expected to carry out its action. As a phlegmatiser, for example, 2,2,4-trimethyl-1 ,3-pentanediol diisobutyrate, also known as TXIB, may be used. Also other organic compounds having little to no of the relatively less stable -CH ₂ - groups may be used. The initiator brings the advantage that the cross-linking or curing reaction may be initiated at ambient and/or room temperature. As a result, extremely high temperatures are avoided, which could otherwise lead to discolouration, and even to a loss of the chemical and mechanical properties of the product.

The applicants prefer to use in the gel coat layer a high concentration of gel coat, such as at least 60 wt% based on the total gel coat layer, preferably at least 70 wt%, still more preferably at least 80 wt%, preferably at least 90 wt%, more preferably at least 95 wt%, still more preferably at least 98 wt%. The applicants prefer to use no or very little fillers in the gel coat layer, because thereby a smoother outer surface of the cladding element is obtained. Preferably the applicants add a pigment to the gel coat layer.

The applicants prefer to provide in the gel coat layer also a curing agent or initiator, as explained above. Preferably, the applicants prefer the methyl ethyl ketone peroxide as the sole curing agent. This curing agent is preferably used as a 30-40 wt% solution in 40-50 wt% dimethyl phthalate, along with a 10-20% TXIB as phlegmatiser or stabilizer. A suitable curing agent solution is, for example, available as Andonox KP-100 of the company Norac ANDOS AB. Curing agent concentrations referred to in this document are intended to be the concentrations of the curing agent solution, including the solvent and stabilizer, and any other ingredients of the solution.

The applicants prefer to apply the curing agent in a concentration of 1.0-5.0% by weight of the gel coat layer, preferably 1.2- 4.0% by weight, more preferably 1.4-3.0% by weight, even more preferably 1.5-2.5% by weight, and yet more preferably 1.8-2.2 wt%, typically about 2.0 wt%, and this on the basis of the weight of the total amount of resin, including the other monomers such as the vinyl monomer and/or DCPD, in the gel coat layer.

In the filling composition for the core, which is applied in step b), the applicants prefer to use a composition which is also based on unsaturated polyester resin as a binder, together with at least one mineral filler.

The selection of the binding material for the composition which is intended for the in step b) filling of the core of the coated mould according to the present invention is already described above. The binding material belongs to the same chemical family of curing polymer resins as the polymer resin chosen for the gel coat, it is preferably also an unsaturated polyester polymer resin. Preferably, a vinyl monomer is also mixed in, more preferably also styrene.

The applicants prefer to use in step b) a composition comprising as binder 10-30 wt% polyester resin, more preferably 12-25 wt%, still more preferably 15-20 wt%, and most preferably from about 17 wt% polyester resin.

The applicants use in the composition of step b) also preferably at least one initiator or curing agent. This brings the benefits which were also cited for the gel coat layer. Preferably a peroxide is used, more preferably an organic peroxide, such as those already mentioned above. Most preferably, the applicants use methyl ethyl ketone peroxide, preferably in solution, together with a stabilizer. Here, too, concentrations of curing agent referred to in this document are meant to be the concentrations of the curing solution, including the solvent and stabilizer, and any other eventual ingredients of the solution.

In this composition, the applicants prefer as the curing agents methyl ethyl ketone peroxide (MEKP) together with yet another peroxide. Preferably, we use cumyl hydroperoxide as a second curing agent. These curing agents are preferably used as a 25-40% solution in dimethyl phthalate, wherein the MEKP preferably constitutes 27-37 wt%, and cumyl hydroperoxide possibly constitutes 6-7 wt% of the solution, together with a 10- 20% phlegmatiser or stabilizer, which could be, for example, methyl benzoate. A suitable curing solution is for example available as Andonox KP-LE of the company Syrgis Performance Initiators AB. The applicants like to use for the core an initiator having a somewhat lower activity, which gives rise to a lower exotherm upon curing, such that the risk of stress, shrinkage and cracking decreases, which is especially important for thicker objects, such as the core of the elements which may be produced by the method according to the present invention. These initiators are preferably used in conjunction with cobalt-based accelerators, such as those which have already been discussed above.

In an embodiment of the method according to the present invention, the gel coat layer in step a) and/or the filling composition for the core in step b) further comprises at least one initiator, preferably an organic peroxide, more preferably methyl ethyl ketone peroxide (MEKP).

The applicants like to apply the curing agent in a concentration of 1.0-5.0 wt% of the composition of step b), preferably 1.2- 4.0 wt%, more preferably 1.4-3.0 wt%, even more preferably 1.5-2.5 wt% , and even more preferably 1.8-2.2 wt%, typically about 2.0 wt%, and this on the basis of the weight of the total amount of resin, including the other monomers such as the vinyl monomer and/or DCPD, which is introduced into the composition.

In particular, in the composition of step b) the applicants like to use an accelerator, preferably a cobalt accelerator, preferably an organic salt of cobalt, more preferably cobalt octanoate. A suitable accelerator is for example Accelerator NL-49P available from Akzo Nobel Polymer Chemicals BV. This is a solution of cobalt(ll)-2-ethyl- hexanoate into an aliphatic ester, which contains about 1 wt% cobalt, or 5- 10 wt% cobalt(ll)-2-ethyl-hexanoate, which may also be called cobalt octanoate. Typically as aliphatic ester for this cobalt salt is used TXIB, which was already described above. Another suitable accelerator is for example EGECat Cobalt 1% available from EGE KIMYA AS in Turkey. This comprises 0.9-1.1% by weight of cobalt metal dissolved in a hydrocarbon solvent.

In an embodiment according to the present invention, the gel coat layer in step a) and/or the filling composition for the core in step b) further comprises an accelerator for the curing reaction, preferably an organometallic compound, more preferably an organic cobalt salt, still more preferably cobalt octanoate.

In the composition for the filling of the core in step b), applicants prefer to use a significant amount of filler material. This provides important mechanical properties to the core, and is also more readily available than the binder, so that the products of the process according to the present invention may be provided for many applications, and may offer therein an economically valuable alternative when compared to other products which are produced on a different base.

As filling material a wide range of possible candidates may be designated as being suitable. In principle all solids on which the binder is prepared to adhere could be used as granulate, including recycled plastics.

The applicants however prefer to use at least partially mineral filler material, most preferably only mineral filling material, mainly because this is chemically less active, usually even inert, and hence there is no influence on the cross-linking of the filler material and/or curing reaction. In addition, mineral fillers usually have a lower porosity than for example plastics, whereby they take up less of the binding agent and the amount of resin does not have to be increased to compensate for such absorption. An additional advantage is the generally common availability of suitable mineral fillers.

In another embodiment of the method according to the present invention, the mineral filler in step b) is selected from the list consisting of quartz, preferably quartz grains, more preferably quartz grains having an average particle size in the range of 1 to 3 mm, more preferably dried grains of quartz, sand, preferably sand which was sieved, washed and dried, and mixtures or combinations thereof:

The applicants have found that a combination of a first filler, which comprises larger grains, with a second filler having a finer grain size, gives a very good degree of filling, and yet allows to limit the amount of polymer resin which is required as the binder. The applicants prefer that the smaller grains are selected such that they fit into the spaces of a stacking of the larger grains, so that they at least partly fill the spaces between the large grains with filler material, and that there is therefore less binder material is required. Therefore, the applicants prefer to use a mixture of a first filler with grains which have an average diameter in the range of 0.5- 5 mm, preferably at least 1.0 mm, and also preferably not more than 4 mm, more preferably not more than 3 mm, with a second filler with fine grains having an average diameter in the range of 50-500 pm, preferably 100- 400 μιτι, more preferably 150-350 pm, more preferably 200-300 pm and at still more preferably 235-280 pm.

The applicants prefer to use a mixture comprising 56 parts by weight of quartz grains having an average particle diameter in the range of 1 to 3 mm, and 32 parts by weight of quartz sand with a mean particle diameter (D50) of about 260 pm.

As first filler, many suitable candidates are available. The applicants prefer to use EIFEL quartz, 1-3 mm, , available from EUROTREX. As second filler a whole range of suitable candidates are also available. Applicants prefer to use M32 quartz sand, available from SIBELCO.

The applicants have found that the filling properties of the filler material may be further improved by the addition of a third filler with an even smaller grain size, which is suitable for also filling the smaller spaces between the grains of the second filler. The inventors prefer the third filler having an average grain diameter (D50) in the range of 5-200 pm, preferably 10-100 pm, more preferably 20-70 pm and even more preferably 30-50 pm. Many suitable filler powders are available. The applicants prefer therefore to use dolomite, which consists for about 99 wt% of calcium magnesium carbonate CaMg(C0 ₃ ) ₂ , such as dolomite powder Microdol A 70 available from OMYA Benelux. This powder also has the advantage that it also serves as a pigment, and makes the colour of the composition lighter, which is favourable in order to have no effect on the colour which the gel coat layer brings.

The applicants prefer to use a mixture of about 56 parts of the dried silica 1-3 (for example 1-3 EIFEL quartz) with about 33 parts of treated sand (for example, M32 SIBELCO quartz sand) in which further approximately 11 parts of dolomite powder (at example OMYA Microdol A70) is incorporated.

In order to more easily remove the product from the mould after the curing of the gel coat layer and the composition in the core, the inventors prefer that the mould be rubbed in with an external release agent or a release wax (also called "mould release agent" or "mould release wax"). In one embodiment of the method according to the present invention, the mould is, before the application of the gel coat layer in step a), rubbed in with a release agent (mould release agent, release wax). This release wax is preferably polished into the mould, as this gives a smoother outer surface of the produced article, which increases the aesthetic appearance, but also the hygienic aspect of the object.

Many substances and compositions are suitable as a release agent. The applicants prefer to use silicone-free formulations, to avoid unwanted colour effects on the cured gel coat layer. Better are versions with little or ho own colour, preferably transparent, and having a colour of not more than 6 Gardner (ASTM D 1544-80), and more preferably not more than 4 Gardner, because they do not materially affect the colour of the product. The applicants prefer to use a hydrocarbon mixture, or a derivative thereof. Very suitable are, for example, hydrogenated petroleum distillates, preferably the heavier fractions having a boiling point of at least 140°C, and preferably also having a flash point (closed cup) of at least 24°C. These heavier fractions impose lesser requirements relating to industrial hygiene and safety.

However, we prefer to use at least partially fractions which are not too heavy, preferably the "middle distillate" fractions, also known as kerosene or diesel oil types. Heavier fractions, such as waxes, may then be dissolved therein. Even more suitable are those fractions which are also desulphurized down to a low content of sulphur, such as at most 50 ppm by weight, preferably at most 30 ppm by weight, and even more preferably at most 10 ppm by weight.

Thereby they also offer a better chemical resistance, and higher resistance to discolouration, usually yellowing, and they are also suitable for food contact. The inventors prefer to use Ce-Sense Slip-X10 available from Brands Structural Products (NL).

The release agent may be applied by hand or by spraying. Preferably, the release agent is first left to dry before it is polished to a high gloss. On new or cleaned moulds, the material is preferably thinly applied 2-3 times to obtain a good coverage and a uniform thickness. The applicants prefer that this external release agent is applied in a very homogeneous thin layer with a very smooth top surface. This ensures that the top surfaces of the product of the method which were in contact with a wall of, the mould, obtain a very smooth aspect, and even become glossy.

In addition, also an internal release agent may be used. Many materials are suitable for this. The applicants prefer ADDITIV MIKON® INT-250 from MLJNCH-CHEMIE, to be used as an additional ingredient in the gel coat layer. In another embodiment of the method according to the present invention, the gel coat layer in step a) is applied by means of a technique selected from the list of spreading, for example, with a brush and/or roller and/or a soft cloth, spraying, and combinations thereof. The applicants prefer to use spraying with a spray gun under pressure.

The resins which are used in the context of the present invention may also be mixtures of two or more resins having different properties. In this case, the above description of the resins holds for the principal resin in such a mixture.

In an embodiment of the method according to the present invention, the gel coat layer in step a) and/or the filling composition for the core in step b) further comprises at least 0.5% and at most 20% by weight, expressed on the basis of the total amount of polymer resin in the top layer or in the core, of an unsaturated polyester resin which is characterized by an elongation at break after curing of the resin and tested according to ISO 527 of at least 4.0%.

Preferably, the elongation at break of this additional unsaturated polyester resin, after curing of the resin and tested according to ISO 527, is at least 5.0%, more preferably at least 10%, even more preferably at least 20%, preferably at least 30%, more preferably at least 40%, and still more preferably at least 45%. If necessary, this resin may be chosen so that the elongation at break is not more than 100%, preferably not higher than 75%, and more preferably not higher than 60%. In this way, the risk is reduced that the hardness would be reduced. The resin is usually obtained by making the polyester chain somewhat longer, preferably by incorporation of longer polyol monomers, preferably polyol monomers of which the chains are not strictly linear, but exhibit angles. Thus, one may, for example, instead of using only mono-ethylene glycol, also use oligomers thereof, preferably those which contain one or more ether functions as part of the chain. Thus, one may for example use triethylene glycol or tetraethylene glycol in the production of these polyesters. Also, one may start from a mixture of polybasic carboxylic acids, or produce polyesters with longer chain lengths, in order to obtain a polyester which will form less crystalline and more amorphous regions, so that the cured resin exhibits a certain degree of elasticity.

The inventors preferably use for the core not more than 15% by weight of this additional polyester resin, and this primarily because the hardness of the final product should not decrease too much. More preferably, the inventors use a maximum of 10% by weight, even more preferably at most 5% by weight, and even more preferably at most 3% by weight of this additional resin, and this relative to the total amount of resin which is used in the filling composition of the core.

In the gel coat layer, the inventors preferably use not more than 16% by weight of this additional polyester resin. More preferably, the inventors use a maximum of 12% by weight, even more preferably at most 9% by weight, and yet more preferably at most 7% by weight of this additional resin, and this relative to the total amount of resin which is used in the filling composition of the gel coat layer. The inventors preferably use in the gel coat layer at least 2% by weight, more preferably at least 3% by weight and even more preferably at least 4% by weight, expressed on the same basis. This quantity has been found to be sufficient for giving the desired properties to the gel coat top layer. As discussed later, this additional resin may also be used as pre-mixed.

The inventors have found that this additive gives a higher elasticity to the cured gel coat layer and/or to the cured core. This offers several advantages. The addition to the core offers the advantage that residual stresses are reduced which may arise from differences in shrinkage in the core itself, due to possible local differences in composition, but also between the core and the gel coat layer. The stresses may be reduced, and less likely lead to cracks, so that there are much less end-products which have to be rejected or further treated to remain useful.

This addition of the additional polyester resin also has the advantage that, when installing the cladding element, which, depending on its size, may have a considerable weight, and, therefore, often has to be placed with the help of mechanical tools such as a crowbar, there is less risk for desquamation of the gel coat layer, so that the aesthetic effect is better preserved, and fewer elements turn useless during the installation and must be replaced and/or discarded.

In one embodiment of the method according to the present invention, the gel coat layer further contains a substance which is selected from a dye, a pigment, a filler, paint chips, metal flakes, and combinations thereof. For example, the gel coat layer may be pigmented with a wide choice of pigments, in every available colour, for example, with each of the available RAL colours. Without the addition of a dye optionally also a transparent version is possible.

In an embodiment of the method according to the present invention, the partial curing of the gel coat layer comprises the retention of the coated mould in an environment with a temperature in the range of from 10°C to 50°C, preferably at least 15°C and more preferably at least 18°C, and optionally not more than 35°C, preferably at most 30°C, even more preferably at most 25°C, and still more preferably at most 23°C. The storage preferably occurs for a period of time of at least 2 minutes, preferably at least 5 minutes, even more preferably at least 10 minutes, and yet more preferably at least 15 minutes. Optionally, the retention takes no longer than 24 hours, preferably no longer than 18 hours, more preferably no longer than 12 hours, and even more preferably at most 6 hours.

In an embodiment of the method according to the present invention, the filling composition for step b) is obtained by first dry blending the mineral filler material, if present with other dry ingredients of the filling composition, followed by the injection of the curable polymer resin, preferably as a mixture which possibly shortly before the injection was mixed with the initiator and/or with at least one and preferably all of the other liquid ingredients of the filling composition, and subsequently mixing the liquid and the solid ingredients of the filling composition, preferably by means of a worm wheel or an Archimedes screw which brings the filling composition during the mixing at or above the coated mould. The applicants have found that this step is very easy to carry out and may readily be automated. The applicants have found that suitable machines are offered to execute this step. The applicants prefer to use a mixing machine which is derived from the type Perfecta, available from the company ADM Monobloc (DE).

In an embodiment of the method according to the present invention, as part of step b), after the insertion of the filling composition in the core of the coated mould, the mould is being vibrated, possibly in more than one cycle, each time with an interval, between which the mould may be transferred to a different location, and wherein preferably the vibration occurs at a frequency of a number of cycles per minute which is in the range of 10 to 600 cycles per minute, and this for a total vibration time which is in the range of 15 seconds to 2 minutes. This additional feature provides for a good filling of the core volumes, by a thorough deaeration of the filling composition under curing. It also improves the adhesion between the two components of the product, namely the gel coat layer and the composition which fills the core of the coated mould.

In an embodiment of the method according to the present invention, as part of step b), upon introduction of the filling composition into the core of the coated mould, the amount of introduced filling composition is accurately proportioned and limited in such a way that it fills, if present after shaking, at least 100 % of the remaining free volume of the mould and up a maximum of 105% of that remaining free volume.

In another embodiment, the present invention provides a product which may be produced according to the method which constitutes an embodiment of the present invention.

Thus, the present invention provides an element for the cladding of floors or walls which may be produced by the method according to any one of the preceding claims, and which consists of a core of a composition which is based on unsaturated polyester resin, supplemented with at least one mineral filler material, at least partially surrounded by an outer layer based on a gel coat, which is also based on unsaturated polyester resin, and which element is selected from a decorative floor tile or wall tile, and a plinth or bumper/fender, wherein in the case of the decorative floor- or wall tile, to the gel coat at least one dye or pigment has been added, and/or to at least one surface of the mould at least partly a varying relief shape is given, and wherein in the case of the plinth or bumper/fender, but optionally also to the decorative floor tile or wall tile, at least 1.0% and at most 18% by weight is added to the polymer resin of the core and/or of the top layer, expressed on the basis of the total amount of polymer resin in the top layer or in the core, of an unsaturated polyester resin which is characterized by an elongation at break after curing of the resin and tested according to ISO 527 of at least 4.0%. The preferred embodiments of the present inventors have already been explained above in this document.

The element according to the present invention with this additional resin brings the advantage that less residual stresses remain after curing and the consequent shrinkage. That way there is less risk of cracking, and thus indirectly of inferior and even potentially useless end products.

The inventors find t possible to use this additional resin only in the core or only in the gel coat layer. Yet, they prefer to use this additional resin in both, i.e. in both the core as well as in the gel coat top layer. In this way, all the advantages afforded by this additional resin may be achieved together.

In a specific embodiment of the present invention, it provides a plinth or bumper wherein the gel coat layer also comprises at least 0.5% and at most 20% by weight, expressed on the basis of the total amount of polymer resin in the top layer or in the core, of an unsaturated polyester resin which is characterized by an elongation at break after curing of the resin and tested according to ISO 527 of at least 4.0%. Preferred embodiments of this additional resin have already been explained earlier in this document. This plinth or bumper/fender brings the advantage that it gives less risk for desquamation of the gel coat layer when installing it by means of mechanical devices. It leads to less damage, better preservation of the aesthetic characteristics of the product after installation, and a lower risk of rejected elements which need to be replaced and/or discarded.

This additional resin may be blended into the ordinary resin. Preferably, the inventors use for the gel coat layer a pre-mixed blend with 5% weight of the additional resin. Such a polyester resin is, for example, based on isophthalic acid and neopentyl glycol and a flexible isophthalic resin. A suitable mixture is for example available as GC 875, Gel Coat ISO-NPG, NTG 193A from the company Nord Composites. For the core, the inventors prefer to use a pre-blended resin with 10-20% weight of the additional resin, and they themselves prefer to mix this mixture in a ratio of 20 parts by weight of the mixture with 80 parts by weight of the main resin for the filling composition of the core. Another suitable resin is available as VIAPAL UP 179 MT/57 from the company Cytec Surface Specialties.

The element according to the present invention may also be clad with a metal cladding, preferably a stainless steel cladding. This cladding may be mechanically anchored to the element by, for example, providing edges which grip around the element. The cladding may also be chemically anchored to the element, such as by gluing. As a glue the applicants prefer to use a glue based on modified silane (SiH4) compounds. The glue adhesion is subsequently achieved because water, for example originating from air humidity, reacts with the silane compounds and thereby achieves polymerization, and preferably also cross-linking. Such adhesives are also called SMP (Silyl Modified Polymer), also known as MS-polymer (Modified Silane Polyether).

EXAMPLE

A stainless steel mould for a plinth is polished with a layer of Ce-Sense Slip-X10 obtained from Brands Structural Products. With a soft cloth, this release is wax very thoroughly spread into all irregularities and corners of the mould, and the wax is additionally polished until the wax layer provides a very smooth inner surface. Into the polished mould is subsequently applied a gel coat layer, by means of a spray gun. The gel coat layer contains 98 wt% polyester gel coat GC 875 9270 obtained from Nord Composites (FR), in which was added 2.0 wt% Andonox KP-100 obtained from Norac ANDOS AG.

The coated mould is stored during 20 minutes in an environment with a temperature of 20°C to partially cure the gel coat layer. Subsequently, the core of the mould is filled with a filling composition.

The following solid materials are mixed in the indicated quantities by weight:

• 56 parts of quartz grains EIFEL QUARTZ 1-3 from EUROTREX

• 32 parts silica sand of M32 from SIBELCO

• 12 parts dolomite powder Microdol A 70 from OMYA

In order to prepare the filling composition for the core, this solid mixture was blended in a ratio of 79/21 with a polyester resin binder, consisting of 96 wt% Poliplast R 96.02 obtained from Carlo Ricco' & F.lli S.p.A. (IT), wherein as hardener 2.0 wt% Andonox KP-LE obtained from Syrgis Performance Initiators AB (SE) and as accelerator 2.0 wt% Accelerator NL-49P obtained from Akzo Nobel Polymer Chemicals BV (NL) were added.

The core of the coated mould was filled with a slight excess of the filling composition, and immediately vibrated to promote a good filling and to obtain a good deaeration of also the core of the product. The filled mould was allowed to further react by storage at about 18°C during a period of about 2 hours.

The product was subsequently removed from the mould, which was easily possible thanks to the small shrinkage inherent with the use of the polyester binder. The product exhibited very smooth surfaces where the product had been in contact with a wall of the mould.

Now that the present invention has been fully described, the skilled person will realize that the invention may be carried out with a wide range of parameters within what is claimed, without, however, departing from the spirit and scope of the invention. As is understood by those skilled in the art, the general invention as defined by the claims, includes other preferred embodiments which may not be specifically named.