IT201800007353A1 - Process for the production of fiber cement sheets with printed surface patterns and printed fiber cement sheets obtained with this process - Google Patents

Description

DESCRIPTION

Field of application

In its more general aspect, the present invention refers to the sector of the production of fiber cement sheets.

In particular, the present invention relates to a process for the production of fiber cement sheets bearing printed surface patterns and printed fiber cement sheets obtained in this way.

Known art

As is known, fiber cement sheets are products widely used as building materials, in particular for the cladding of internal and external facades of buildings.

In order to protect these materials from potential damage during transport or installation as well as from defects caused by weather and humidity, it is known to apply one or more layers of coating to the outer surface during their production. The surface coating of the fiber cement slabs may be desirable not only for the above reasons but also for aesthetic reasons, for example to impart an attractive exterior appearance to the consumer, by imparting a desired decorative, advertising and / or identifying pattern on the surface of the slab.

In this regard, it is known that the ink jet printing technique with water or solvent based pigment compositions allows to apply decorative motifs on a support directly without the need to use masks. Although inkjet printing is widely used for the application of decorative patterns on the surfaces of ceramic and glass products, this technique still does not provide satisfactory results when applied directly to the surface of fiber cement plates. This is due to the heterogeneous composition and intrinsic surface roughness of the fiber cement which leads to the dispersion of the ink in the product structure and therefore to poor print quality.

Application WO 2016/146423 describes a process for the production of fiber cement products suitable for ink jet printing. To overcome the drawback of poor printing quality that occurs when ink jet printing is carried out directly on the surface of the plate, application WO 2016/146123 proposes to previously coat the surface of the fiber cement plate with one or more layers of a thermosetting material comprising a pigment and an acrylic polymer in which the pigment volume concentration (intended as volume of pigment / volume of solids x 100) is greater than 40%. In this way, according to the application WO 2016/146123, a fiber cement product is obtained which is suitable for the subsequent printing of desired decorative motifs by means of an ink jet since the coating with the above thermosetting material increases the surface porosity of the plate allowing capturing the ink composition and avoiding its dispersion.

However, the process described in application WO 2016/146423, in addition to the quantity of pigment necessary for the actual printing process, requires the use of significant additional quantities of pigment in the formation of the coating base necessary to obtain a sufficiently homogeneous surface. and high porosity for carrying out the meeting jet printing. Therefore, the aforementioned procedure disadvantageously involves significant additional costs in relation to the use of pigments which in themselves also have relatively high costs.

The main purpose of the present invention is to provide a process for the production of printed fiber cement plates which allows to print decorative motifs directly on the surface of the plates while maintaining a good print quality, so as to overcome the drawbacks previously mentioned with reference to the known art.

A further object of the present invention is to provide a process as above which can be carried out on an industrial scale with relatively low costs.

Summary of the invention

These purposes are achieved primarily by a process for the production of a molded fiber cement plate, the process comprising the steps of:

- apply an ink print comprising at least one inorganic pigment on a surface of a fiber cement plate so as to form a predetermined decorative pattern printed on said surface of the fiber cement plate,

- applying on said printed surface of the fiber cement plate at least one layer of a first polymerizable transparent coating composition, the first composition comprising at least one isocyanate monomer and a polyol,

- polymerizing or crosslinking said first composition obtaining at least a first layer of transparent polyurethane-based coating on said printed surface of said fiber cement plate.

According to an embodiment of the invention, the aforementioned process further comprises the step of applying on said at least one first coating layer a second radiation-curable transparent coating composition, said second coating composition comprising an aliphatic acrylate urethane oligomer, a multifunctional acrylate or methacrylate, an isocyanate and a photoinitiator,

- hardening said second coating composition by radiation obtaining a second transparent and hard coating layer on said at least one first coating layer.

Preferably, the second composition comprises an acrylate containing at least one polymerizable unsaturated group per molecule.

According to another embodiment of the invention, the aforementioned process further comprises the step of applying on said second transparent coating layer a third radiation curable transparent coating composition, said third coating composition comprising a polyurethane acrylate and a photoinitiator and being able to form, after hardening, a glossy or matte finish,

- hardening said third coating composition by radiation obtaining, after a possible further surface finishing, a third layer of glossy or opaque coating on said second coating layer.

The aforementioned purposes are also achieved by a fiber cement plate comprising a decorative pattern applied directly to one of its surfaces by printing an ink comprising at least one inorganic pigment and at least a first transparent coating layer applied to said decorative pattern, said first coating layer. comprising a polyurethane polymer obtained by polymerization or crosslinking of a composition obtained by mixing at least one isocyanate and a polyol.

According to an embodiment of the invention, the fiber cement plate also comprises a second coating layer obtained by hardening a composition comprising a polyurethane acrylate and an isocyanate, said second coating layer being applied on said first coating layer.

According to a further embodiment of the invention, the fiber cement slab further comprises a third layer of glossy or opaque coating obtained by hardening a composition comprising a polyurethane acrylate suitable for giving a glossy or matt finish after hardening, said third layer of coating being applied on said second coating layer.

Further features and advantages of the present invention will emerge from the detailed description and the following example which are provided for indicative and non-limiting purposes.

Detailed description

In this description, the indication of numerical ranges includes all the values and fractions included in the respective ranges as well as the end values.

The terms "predetermined" or "default" as used in this description when referring to one or more parameters or properties generally indicate that the desired value (s) of such parameters or properties have been defined or determined in advance, i.e. prior to beginning of the process for the production of printed plates which are characterized by one or more of these parameters or properties.

The term "fiber cement slab" as used in the present description refers to a flat, usually rectangular element in the form of a slab, panel or plate made of a material comprising synthetic and / or natural fibers and cement. The fiber cement slab has two opposing main surfaces or faces of larger area and can be used for the cladding of interior and exterior facades of buildings or constructions.

The fiber cement slab can be obtained with processes which are conventional in themselves and which involve the production of a mixture comprising water, fibers and cement followed by a hardening process. The fibers can be natural organic fibers (typically cellulose fibers) or synthetic organic fibers such as, by way of example and not limiting, polyvinyl alcohol, polyacrylonitrile, polypropylene, polyamide, polyester, polycarbonate, polyethylene, etc.). The cementitious material or cement can be, by way of example and not limited to, Portland cement, cement with a high content of alumina, iron Portland cement, trass cement, slag cement, gypsum, calcium silicates etc. The mixture may contain further additives such as anti-foaming agents, flocculants or other additives, for example pigments to obtain a so-called mass-colored product.

The mixture comprising fibers and cement is pressed and hardened in a conventional manner, for example by air hardening or by thermal hardening, for example by autoclave treatment under pressure at relatively high temperatures and in the presence of water vapor.

At the end of the hardening, a fiber cement product is obtained which has a significant moisture content, usually between 10% and 15% by weight on the weight of the dry product where by weight of the dry product we mean the weight of the product when subjected to drying at 105 ° C in a ventilated oven until a constant weight is obtained. The fiber cement product is cut to a predetermined length to form fiber cement slabs of predetermined dimensions.

In the present description, the term "pigment" means an insoluble dry substance, usually pulverized, which when suspended in a liquid carrier becomes an ink, paint, etc. Typically, pigments consist of fine solid particles which improve the appearance providing color and / or the properties of an ink or varnish that comprise them. Inorganic pigments are used in the present invention, i.e. mineral coloring compounds usually consisting of oxides and / or metal salts. Inorganic pigments can be pigments capable of diffusing light and providing whiteness (white) to the ink (or varnish) and / or pigments capable of selectively absorbing light and providing a color to the ink or varnish. By way of non-limiting indication, white pigments include antimony pigments such as antimony oxide, lead pigments such as carbonate and lead oxide, titanium pigments such as titanium oxide and zinc pigments such as zinc oxide. By way of non-limiting indication, the colored pigments can be chosen from oxides, hydroxides and salts of cobalt, copper, chromium, iron, lead, cadmium, manganese, aluminum, carbon (for example carbon black) etc. depending on the color chosen.

In the present invention, the ink (or paint) comprises at least one pigment suspended in a liquid vehicle which can be a water-based or solvent-based vehicle. Therefore, a water-based ink identifies an ink comprising at least one pigment in a colloidal suspension in water. The solvent of water-based inks can be water alone or water as the main solvent together with one or more other co-solvents. Typically, these co-solvents are volatile organic compounds such as, but not limited to, ethanol, ethyl acetate, ethylene glycol, glycol esters, hexane, isopropanol, methanol, methyl ethyl ketone, propyl acetate, white spirit, propyl alcohol, toluene, xylene etc. The solvent-based ink instead refers to an ink comprising at least one pigment in a colloidal suspension in a solvent other than water. The main solvent in solvent-based inks can typically be selected from volatile organic solvents such as, by way of example but not limited to, ethanol, ethyl acetate, ethylene glycol, glycol esters, hexane, isopropanol, methanol, methyl ethyl ketone, propyl acetate , white spirit, propyl alcohol, toluene, xylene etc.

In the process according to the invention, a pre-established decorative pattern is created directly on a surface of a fiber cement plate by printing an ink comprising at least one inorganic pigment.

This step can be carried out by means of any known printing process based on ink jet using an ink comprising one or more inorganic pigments suspended in a liquid carrier which is preferably a water-based liquid carrier. The ink composition can be suitably formulated by a person skilled in the art, in particular in terms of viscosity, to have characteristics suitable for ink jet printing. Furthermore, the choice of the pigments and their dimensions, the choice of the liquid carrier and of other possible components of the composition as well as of the respective ratios can be determined by a person skilled in the art on the basis of his own knowledge and according to contingent and specific needs.

The composition of the ink may include in addition to at least one pigment and a liquid carrier, additional components such as wetting agents, dependent agents, defoaming agents, humectants, rheology control agents, pH control agents, biocides, etc.

The ink can be applied on the fiber cement plate in an amount that is preferably between 1 g / m <2> and 10 g / m <2>, more preferably between 4g / m <2> and 8 g / m <2>, in particular 6 g / m <2>.

After the ink has been applied by printing onto the surface of a fiber cement plate, it is dried preferably by applying heat (for example by heating or applying infrared (IR) rays) or other systems known to those skilled in the art. conventional selves.

Subsequently, in accordance with the present invention, the application of at least one layer of a first polymerizable transparent coating composition, the first composition comprising at least one isocyanate and a polyol, is provided on the surface of the fiber cement plate bearing the already printed decorative pattern. , followed by the polymerization or crosslinking of said first composition obtaining at least a first layer of transparent polyurethane-based coating on the printed surface of said fiber cement plate.

The contemplated isocyanates of the present invention include all aliphatic or cycloaliphatic isocyanates, preferably diisocyanates. By way of non-limiting example, the aliphatic diisocyanates can be selected from hexamethylene 1,6 diisocyanate, 2-methylpentamethylene 1,5-diisocyanate and their mixtures while the cycloaliphatic diisocyanates can be selected from isophorone diisocyanate and cyclohexane 1,4 diisocyanate and their mixtures. .

Preferably, the isocyanates are not used in their monomer form but in the form of pre-polymers (or otherwise called oligomers) of isocyanates, isocyanurates, allophanates or biuretics.

Preferably, the isocyanate components used to form the first composition are selected from poly (hexamethylene) diisocyanate (CAS 28182-81-2), poly (isophorone diisocyanate) (CAS 53880-05-0) and their mixtures.

In one embodiment, the isocyanate components used to form the first composition are poly (hexamethylene) diisocyanate (CAS 28182-81-2) and poly (isophorone diisocyanate) (CAS 53880-05-0) mixed together in a ratio that varies between 1: 1 and 5: 1.

The isocyanates preferably have an NCO content of from 26.5 to 16% by weight, more preferably between 20 and 24% by weight and a viscosity at 60 ° preferably lower than 1000 mPa, more preferably lower than 500 mPa.

Preferably, the content of isocyanates in the first composition is between 1 and 50% by weight on the weight of the first composition, in particular between 10% and 30% by weight on the weight of the first composition.

As polyols it is possible to use, for example, polyether polyols, polyester polyols and alcohols with a low molecular weight. Preferably, the polyols have a molar functionality from 1.5 to 5, preferably from 2 to 5 and an OH number between 100 and 950, preferably between 100 and 500.

Preferably, the polyols include polyether polyols, polyester polyols and low molecular weight alcohols.

The polyether polyols are prepared by known procedures usually by catalytic addition reaction of alkylene oxides, in particular ethylene oxide and / or propylene oxide with polyfunctional alcohols such as dihydric alcohols (diols) such as ethylene glycol, propylene glycol or butanediols, trihydric alcohols (triols) such as glycerol or trimethylpropane, and alcohols with greater functionality such as pentaerythritol, sugar alcohols such as sucrose, glucose or sorbitol etc.

As low molecular weight alcohols it is possible to use for example dihydric, trihydric or tetrhydric alcohols such as ethanediol, propane 1,2 and 1,3 diol, diethylene glycol, dipropylene glycol, butane 1,4 diol, hexane 1,6 diol, glycerol and / or pentaerythritol.

Suitable polyester polyols include hydroxyl-terminated reaction products of polyalcohols such as ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, butanediol, furan dimethanol, cyclohexane dimethanol, glycerol, trimethylol propane or pentaerythritol and mixtures thereof, especially polycarboxylic acids, or their ester-forming derivatives, for example heptanoic acid, octanioic acid, nonanioic acid, decanioic acid, succinic acid, glutaric acid, adipic acid or their dimethyl esters, phthalic anhydride or diethyl terthalate. Polyesters obtained from the polymerization of lactones, for example caprolactone, with a polyol can also be used.

Preferably, the polyol content is between 50% and 90% by weight on the weight of the first composition, in particular between 50% and 80% by weight on the weight of the first composition.

Further components such as liquid carriers, catalysts and / or crosslinkers can be used for the first composition.

The liquid carrier is preferably water-based and is preferably water or alternatively a mixture comprising water and an organic co-solvent selected for example from the organic solvents indicated above.

The catalyst is selected from the compounds usually used in the formation of polyurethanes such as organic compounds of tin, zinc, titanium, zirconium, aluminum, iron and / or bismuth and / or strongly basic amines such as triethylamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, 1,2 dimethylimidazole , dimethylcyclohexylamine and dimethylbenzylamine.

Preferably, the catalyst selected is dimethylcyclohexylamine. The amount of catalyst added is preferably between 1 and 2.5% by weight on the weight of the first composition.

The crosslinker can consist of and alkyl silanes, preferably alkyl silanes containing epoxide group.

Preferably, the crosslinker is selected from 3- (glycidoxypropyl) trimethoxysilane (CAS: 2530-83-8).

The amount of crosslinker added is preferably between 1 and 2.5% by weight of the weight of the first composition.

Auxiliary components such as surfactants, lubricants, stabilizers, viscosity regulators etc. conventional per se can also be added to form the first composition.

For example, the first composition may contain silicones, in particular polysiloxanes such as polydimethylsiloxane as surface additives to provide good wetting properties and avoid crater formation by reducing the surface tension in the coating layer. The first composition is obtained by mixing the aforementioned components which can be added individually or as pre-mixes which contain some of them to form the first final composition. Subsequently, the first composition is applied to the surface of the fiber cement plate bearing the previously printed decorative pattern.

The application of the first composition on the printed surface of the fiber cement slab can be carried out with conventional techniques known to the skilled in the art such as spraying, application with knife, roller application, curtain coating, brushing, dipping. and their combinations.

Preferably, the first composition is applied to the printed surface of the fiber cement slab by spraying.

The first composition can be applied on the printed surface of the fiber cement slab in an amount which is preferably between 20 g / m <2> and 100 g / m <2>, more preferably between 40 g / m <2> and 80 g / m <2>.

After application of a layer, the first composition is made to polymerize or crosslink in a conventional manner, for example by heating to a temperature below 100 ° C, obtaining a transparent coating layer based on polyurethane. The operations of applying the first composition and subsequent polymerization can be repeated in sequence in the case of making several layers of the first transparent polyurethane-based coating.

Preferably, the aforesaid operations of applying the first composition and subsequent polymerization are repeated (for example from 2 to 5 times) so as to form a plurality of layers of the first transparent polyurethane-based coating.

Preferably, the overall thickness of the at least one layer of transparent polyurethane-based coating is between 0.01 and 1 mm.

It has been surprisingly found that by coating the surface of a fiber cement plate bearing a previously printed decorative pattern with at least one transparent layer based on polyurethane, a strong and lasting fixing of the ink forming this previously printed decorative pattern is obtained, thereby avoiding the its dispersion and thus obtaining a good and homogeneous print quality over the entire surface of the printed fiber cement plate.

Even without wanting to be bound to any scientific theory, it is believed that the above beneficial effect may be due to the ability of the polyurethane polymeric layer to partially penetrate into the pores of the concrete slab around the areas affected by the presence of the ink. of printing by fastening strongly to the fiber cement plate and constituting a sort of “sealant” for the ink, preventing its dispersion from the areas where it has been applied.

In addition, the transparent polyurethane-based layer also constitutes a protective layer for the pattern printed directly on the surface of the plate, making it visible from the outside at the same time.

Thereafter, the process according to the invention may comprise the step of applying on the at least one first transparent coating layer a second transparent coating composition which can be cured by radiation, the second composition comprising an aliphatic urethane acrylate oligomer, an acrylate or multifunctional methacrylate, an isocyanate and a photoinitiator.

The aliphatic urethane acrylate oligomers are conventional per se and can be obtained by reaction of a multifunctional acrylate (e.g. 1.6 hexanediol diacrylate, hydroxyethyl acrylate and trimethylol propane triacrylate) with a polyether or polyester aliphatic urethane.

The multifunctional acrylate or methacrylate preferably comprises at least two polymerizable unsaturated groups per molecule and can have a molecular weight between 170 and 1000. By way of non-limiting example, the multifunctional acrylate can be selected from the group consisting of ethylene glycol di (meta ) acrylate, 1.6 hexadiol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, tetraethylene glycol diacrylate, dipropylene glycol diacrylate (oxybis (methyl-2,1-ethanediyl) diacrylate) and mixtures thereof. Preferably, the multifunctional acrylate or methacrylate is 1.6 hexadiol diacrylate.

Preferably, in the second composition, the aliphatic acrylate urethane oligomer and the multifunctional acrylate or methacrylate are each present in an amount ranging from 1% to 20% by weight of the weight of the second composition and preferably in a ratio between them. : 2 and 2: 1.

The second composition may further comprise an unsaturated aliphatic urethane acrylate in an amount preferably comprised between 0.1% and 2% by weight on the weight of the composition.

Unsaturated aliphatic urethane acrylate can be obtained, for example, by the reaction of a multifunctional acrylate containing at least three polymerizable groups per molecule with an aliphatic urethane.

The isocyanate can be an aliphatic or cycloaliphatic isocyanate, preferably diisocyanate. Examples of suitable isocyanates are the compounds illustrated above with reference to the first clear coating composition.

Preferably, the isocyanate comprises or consists of poly (hexamethylene) diisocyanate (CAS 28182-81-2).

Preferably, the amount of isocyanate in the second composition is between 80% and 99% by weight on the weight of the composition.

The second composition further comprises a polymerization photoinitiator. In this regard, the second composition can be polymerized (cured) preferably by ultraviolet (UV) radiation although other radiations can be used in combination with other photoinitiators.

The photoinitiator, together with the oligomers, provides the radiation curable compositions with good cure rate when the compositions are applied to the fiber cement sheet and exposed to radiation, without causing premature gelation or hardening of the compositions. Further important features for the photoinitiator are that the photoinitiator must not interfere with optical clarity or cause yellowing of the cured coatings and that the photoinitiator is thermally stable. UV curable photoinitiators are known in the art and can be employed in the second radiation curable composition used in the present invention. Examples of photoinitiators suitable for use in the second composition of the present invention include, but are not limited to, benzoin or its alkyl ethers such as benzophenones, phenylmethylketone (acetophenone), substituted acetophenones, acyl phosphine oxides and the like. Specific photoinitiators suitable for use in the second composition of the present invention include the following: hydroxycyclohexylphenyl ketone; hydroxymethylphenylpropanone; dimethoxyphenyl acetophenone; 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propanone-1; 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one; 1- (4-dodecyl) -2-hydroxy-2-methylpropan-1-one; 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone; diethoxyacetophenone; 2,2-di-sec-butoxyacetophenone; diethoxyphenyl acetophenone; diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide; bis (2,6-dimethoxybenzoyl) (2,4,4-trimethylpentyl) phosphine oxide; bis (2,4,6-trimethylbenzoyl) phenyl phosphine oxide; ethyl-2,4,6-trimethylbenzoyl phenyl phosphine; and their mixtures.

Preferably, the photoinitiator is diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide.

The photoinitiator is included in the second radiation curable composition in an amount effective to promote radiation polymerization of the composition. Preferably, the photoinitiator is included in an amount of from about 0.1% by weight to about 5% by weight by weight of the second radiation curable coating composition.

The second composition is preferably solid (solvent-free) or alternatively can comprise an inert solvent. In case it comprises a solvent, representative solvents include ester solvents, e.g. ethyl acetate, butyl acetate and the like, ketone solvents, e.g. acetone, methyl isobutyl ketone, methylethyl ketone and the like, alcohols, e.g. butyl alcohol and the like and aromatic solvents, e.g. toluene xylene and the like. The quantity of solvent in the second composition can be chosen by the person skilled in the art according to specific needs, such as for example the method of application of the second composition.

The second clear coat composition may also include other conventional additives. For example, it may contain polymeric coating surface enhancing agents, flow improvers, antioxidants, stabilizers, etc. per se known to those skilled in the art.

The second clear coat composition can be applied to the first polyurethane-based clear coat layer by any conventional coating method as known in the art. Suitable methods include, for example, spraying, knife application, roller application, curtain coating, brushing, dipping and combinations thereof.

Preferably, the second composition is applied to the first polyurethane-based transparent coating layer by roller application.

The second composition can be applied on the first polyurethane-based transparent coating layer in an amount that is preferably between 5 g / m <2> and 50 g / m <2>, more preferably between 10g / m <2 > and 30 g / m <2>.

Once applied, the second coating composition can be cured by irradiation with ultraviolet rays as is known to those skilled in the art. In this regard, the irradiation is continued until the end of the polymerization, with preferred exposure times typically lower than 300 seconds. Curing temperatures can vary from room temperature to the heat distortion temperature of the substrate.

An ultraviolet light source having a wavelength range between about 1800 Angstrom and 4500 Angstrom is preferred for hardening the second composition. For example, sunlight, mercury lamps, arc lamps and the like can be used.

At the end of the hardening, a second layer of hard and transparent coating is obtained on the at least one first layer of transparent coating which exhibits considerable adhesion, as well as providing adequate characteristics of mechanical resistance, in particular resistance to removal of the layers, to cutting and to scratches, as will be illustrated in the examples, thereby adequately protecting the first coating layer and the underlying printed decorative pattern.

Preferably, the overall thickness of the second hard and transparent coating layer is comprised between 0.01 and 1 mm.

Thereafter, the process according to the invention may comprise the step of applying on the at least one second hard and transparent coating layer a third coating composition which can be cured by radiation, the third composition comprising an aliphatic acrylate urethane, a (meta) multifunctional acrylate comprising at least two polymerizable unsaturated groups per molecule and a photoinitiator to give, after hardening, a glossy or matte finish.

The aliphatic acrylate urethane oligomer can be obtained by reaction of a multifunctional acrylate (for example 1.6 hexanediol diacrylate, hydroxyethyl acrylate and trimethylol propane triacrylate) with an aliphatic urethane based on polyether or polyester.

The multifunctional acrylate or methacrylate comprising at least two polymerizable unsaturated groups per molecule has a molecular weight between 170 and 1000. It can be chosen for example among the compounds mentioned above in relation to the multifunctional acrylate or methacrylate of the second coating composition.

Preferably, the multifunctional acrylate or methacrylate is 1.6 hexadiol diacrylate.

Preferably, in the third composition, the aliphatic acrylate urethane oligomer and the multifunctional acrylate or methacrylate are each present in an amount comprised between 10 and 50% by weight of the weight of the second composition and in a ratio between them preferably comprised between 1: 2 and 2: 1.

The third composition further comprises a polymerization photoinitiator. In this regard, the third composition can be polymerized (cured) preferably by ultraviolet (UV) radiation although other radiations can be used in combination with other photoinitiators.

The photoinitiator can be selected for example from the photoinitiator compounds mentioned above with reference to the second coating composition. For example, a preferable photoinitiator is diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide.

The photoinitiator is included in the second radiation curable composition in an amount effective to promote radiation polymerization of the composition. Preferably, the photoinitiator is included in an amount of from about 0.1% by weight to about 5% by weight by weight of the third radiation curable coating composition.

The third composition is preferably solid (solvent-free) or alternatively it can comprise an inert solvent selected for example from those indicated above for the second composition.

The third coating composition may also include other conventional additives. For example, it may contain polymeric coating surface enhancing agents, flow improvers, antioxidants, stabilizers, etc. per se known to those skilled in the art.

The third coating composition can be applied to the second hard and clear coating layer by any conventional coating method as known in the art. Suitable methods include, for example, spraying, knife application, roller application, curtain coating, brushing, dipping and combinations thereof.

Preferably, the third composition is applied to the second hard and transparent coating layer by roller application.

The third composition can be applied on the second hard and transparent coating layer in an amount which is preferably between 5 g / m <2> and 50 g / m <2>, more preferably between 10g / m <2> and 30 g / m <2>, in particular 10-15 g / m <2>.

Once applied, the third coating composition can be cured by irradiation with ultraviolet rays as is known to those skilled in the art.

At the end of hardening, a third layer of coating is obtained on the second layer of transparent and hard coating which provides, possibly after further surface finishing, a glossy or matte surface finish.

Preferably, the overall thickness of the third coating layer is comprised between 0.01 and 1 mm.

EXAMPLE 1

Fiber cement sheets were produced in a conventional manner and hardened in an autoclave. The moisture content of the fiber cement sheets after hardening was 10-15%.

The fiber cement plates were subjected to a conventional ink jet printing on one of their surfaces with a water-based ink comprising inorganic pigments so as to form a decorative pattern printed on one surface of each fiber cement plate.

The ink was applied in an amount of 6 g / m <2> and dried after application by heat.

Subsequently, a first water-based composition containing the components (with the exception of the aqueous balancing solvent) and the relative concentration ranges indicated in Table 1 below was applied to the printed surface of each fiber cement slab.

Table 1

The first composition was applied on the printed surface of each fiber cement slab by spraying in an amount of 50 g / m <2> and was then cross-linked by heating at a temperature below 100 ° C, obtaining a first layer of transparent coating at polyurethane base on the printed surface of each fiber cement slab.

Subsequently, a second solid composition (i.e. without added solvent) containing the components and relative concentration ranges indicated in Table 2 below was applied to the first transparent coating layer of the printed surface of each fiber cement plate.

Table 2

The second composition was applied on the first transparent coating layer of the printed surface of each fiber cement slab by roller application in an amount of 30 g / m <2> and was then hardened by UV irradiation, obtaining a second layer of clear and hard coating on the first coating layer of the printed surface of each fiber cement slab.

Subsequently, a third solid composition (i.e. without added solvent) containing the components and relative concentration ranges indicated in Table 3 below was applied to the second transparent and hard coating layer of the printing surface of each fiber cement plate.

Table 3

The third composition was applied on the second coating layer of the printed surface of each fiber cement slab by roller application in an amount of 12 g / m <2> and was then cured by UV irradiation, obtaining a third coating layer opaque on the second coating layer of the printed surface of each fiber cement slab.

EXAMPLE 2

The printed and coated sheets obtained in accordance with Example 1 have been tested for their properties of adhesion and resistance to the separation of the layers, resistance to scratches and resistance to the formation of stains and resistance to atmospheric agents.

The adhesion and resistance to separation of the layers was assessed using the ISO 2409: 2013 & ISO 16276-2: 2007 / ASTM3359-97 standards. In particular, the samples were subjected to the application of a pressure-sensitive tape and subsequent removal of the tape on specific areas on which X-cuts (X-cut test) and lattice cuts (grid) with 6 longitudinal parallel cuts had been made. and transversal according to (cross-cut test) and in specific areas without prior cuts. The cuts were made to a depth such as to reach the substrate (slab).

The results of adherence on areas not subject to shear were evaluated on a scale from 0 to 4 where 0 = very good; 1 = good; 2 = moderate; 3 = poor; 4 = unusable.

The results of resistance to separation in areas where X-cut tests have been made were evaluated on a scale from 0 to 5 where 0 = no removal; 1 = traces of removal along incisions or at their intersection; 2 = jagged removal along incisions up to 1.6 mm on either side; 3 = jagged removal along most incisions up to 3.2mm on either side; 4 = removal from most of the X area under the tape; 5 = removal beyond the area of the X.

The results of resistance to separation in areas on which cross-cut tests were made were evaluated on a scale from 0 to 5 with reference to the percentage of surface area of the lattice in which the flaking occurred. 0 = no removal; 1 = less than 5%; 2 = 5- <15%; 3 = 15-35%; 4 => 35-65%; 5 => 65%.

The results of the aforementioned tests conducted on test samples of plates according to the invention are shown in Table 4 below:

Table 4

It can be noted that the sheets according to the invention have good excellent adhesion properties of the layers and good properties of resistance to separation of the same in cutting conditions.

Scratch resistance was carried out according to the DIN55656 method (equivalent to the ISO1518-1: 2011 standard). In this respect, a 1 mm diameter tungsten carbide tip was used to scratch (scuff) test plate samples at a predefined constant pressure. The presence of a visible mark on the surface indicates a lack of scratch resistance. The results are classified into 3 classes as follows: OK = no visible sign; Marked (M) = presence of a visible mark and NO OK = deep cut in the coating layer.

The results of the aforementioned tests conducted on test samples of plates according to the invention are shown in Table 5 below: Table 5

It can be noted that the sheets according to the invention have excellent scratch resistance characteristics even in conditions of relatively high applied pressure (for example 24N).

The resistance to the formation of stains was assessed by pouring one of the following products onto a specific area of the samples of the test plates and letting these products stay on the samples for 5 minutes and 1 h before their removal.

The products are as follows: mustard, ketchup, vinegar, olive oil, whitening product, wine, muriatric acid.

No stains were detected on the test plate samples by the aforementioned products either after standing for 5 minutes or after standing for 1 hour.

The test of resistance to atmospheric agents was carried out with the QUV test (Accelerated weathering test) according to the standard UNE-EN 1062-11: 2003. In particular, in accordance with ASTM G154, the test plate samples were subjected to accelerated aging cycles by irradiation with UV lamps (UVB-313 lamps) consisting of:

- dry irradiation phase lasting 4 hours (60 ± 3 ° C); - condensation phase lasting 4 hours (50 ± 3 ° C).

After 1000 h and 1768 h of exposure, color, luster and defects present in the test samples were evaluated.

No color change or loss of luster was found in the test samples either after 1000 h of exposure or after 1768 h of exposure.

Furthermore, no chalking, embrittlement, blistering, cracking and flaking defects were found in the test samples both after 1000 h of exposure and after 1768 h of exposure.

Furthermore, no hazing was found in the test samples after 1000 h of exposure while a slight clouding was found in the test samples after 1768 h of exposure.

To the process according to the invention, in order to meet contingent and specific needs, a person skilled in the art will be able to make numerous changes and variations, all of which are included in the scope of the protection of the attached claims.

Claims (10)

CLAIMS 1. Process for the production of a printed fiber cement slab, the process comprising the steps of: - apply an ink jet print comprising at least one inorganic pigment on a surface of a fiber cement plate so as to form a predetermined decorative pattern printed on said surface of the fiber cement plate, - applying on said printed surface of the fiber cement plate at least one layer of a first polymerizable transparent coating composition, the first composition comprising at least an isocyanate and a polyol, -polymerizing or crosslinking said first composition obtaining at least a first layer of transparent polyurethane-based coating on said printed surface of said fiber cement plate. 2. A process according to claim 1, further comprising the step of applying on said at least one first transparent coating layer a second radiation curable coating composition, said second coating composition comprising an aliphatic urethane acrylate oligomer, a (meth) acrylate multifunctional, an isocyanate and a photoinitiator, - hardening said second coating composition by radiation obtaining a second transparent and hard coating layer on said at least one first coating layer. The process according to claim 2, further comprising the step of applying on said second coating layer a third radiation curable coating composition, said third coating composition comprising an aliphatic urethane acrylate, a multifunctional (meth) acrylate comprising at least two groups polymerizable unsaturated molecules and a photoinitiator to give, after hardening, a glossy or matte finish, - hardening said third coating composition by radiation obtaining, after a possible further surface finishing, a third layer of glossy or opaque coating on said second coating layer. 4. Process according to any one of the preceding claims, in which in the first composition said at least one isocyanate is present in an amount comprised between 1% and 50% by weight of the weight of the first composition, preferably between 10% and 30%, and is selected preferably between poly (hexamethylene) diisocyanate (CAS 28182-81-2), poly (isophorone diisocyanate) (CAS 53880-05-0) and their mixtures and said polyol is present in an amount comprised between 50% and 90% by weight on the weight of the first composition and is preferably selected from polyether polyols, polyester polyols and alcohols with a low molecular weight. 5. Process according to any one of the preceding claims, wherein said first composition is applied on the printed surface of the fiber cement plate in an amount which is comprised between 20 g / m <2> and 100 g / m <2>, preferably between 40 g / m <2> and 80 g / m <2>. Process according to any one of the preceding claims, wherein in the second composition said aliphatic acrylate urethane oligomer is present in an amount comprised between 1% and 20% by weight on the weight of the second composition; said (meth) acrylate has a molecular weight comprised between 170 and 1000, is present in the second composition in an amount comprised between 1% and 20% by weight on the weight of the second composition and is preferably 1.6 hexadiol diacrylate; and said isocyanate is present in an amount comprised between 80% and 99% by weight of the weight of the second composition and is preferably hexamethylene diisocyanate. 7. Process according to any one of the preceding claims, wherein said second composition further comprises an unsaturated aliphatic urethane acrylate in an amount preferably comprised between 0.1% and 2% by weight on the weight of the second composition. 8. Process according to any one of the preceding claims, wherein the second composition is applied on the first transparent coating layer based on polyurethane in an amount comprised between 5 g / m <2> and 50 g / m <2>, preferably between 10 g / m <2> and 30 g / m <2>. Process according to any one of the preceding claims, wherein in the third composition the aliphatic urethane acrylate oligomer and the multifunctional acrylate or methacrylate are each present in an amount comprised between 10 and 50% by weight of the weight of the third composition and in a ratio between them preferably comprised between 1: 2 and 2: 1. Process according to any one of the preceding claims, wherein the third composition is applied on the second hard and transparent coating layer in an amount preferably comprised between 5 g / m <2> and 50 g / m <2>, more preferably between 10 g / m <2> and 30 g / m <2>, in particular 10-15 g / m <2>. 1 1. Fiber cement slab obtainable by the process according to any one of the preceding claims.