EP2050870A1 - Method of manufacturing a decorative sheet of paper with reduced resin-absorbing capacity. - Google Patents

Abstract

Sheet of decorative stationery, impregnated with thermosetting resin, contains 5 - 50 wt.% decorative particles and/or colored pigments or organic and/or opaque fillers particularly titanium dioxide has degree of absorption of water (COBB 60) at most = 40% mass of sheet. Independent claims are also included for making said sheet of stationery; and laminated panel decorated with the sheet.

Description

The invention relates to a decorative paper sheet impregnable by a thermosetting resin. This sheet is used in the manufacture of laminated decorative panels or profiles. The invention also relates to the decorative sheets impregnated with a thermosetting resin as well as the panels or laminated decorative profiles comprising it and the processes for producing the sheets.

For many years, laminated decorative panels or profiles have been used as materials in homes, commercial and industrial premises. Typical applications of such laminates are furniture coatings, table tops, chairs and the like, or floor coatings such as flooring-like coatings.

There are two main types of decorative "laminates": so-called high-pressure "laminates" and so-called "low-pressure" laminates.

The so-called high pressure decorative laminates are produced from a core made of resin-impregnated sheets. These sheets are generally made of kraft paper and have been impregnated with a thermosetting resin, most often a phenolic resin.

After impregnating the resin sheets, they are dried, cut, and stacked on top of one another. The number of sheets in the stack depends on the applications and varies between 3 and 9, but can be higher.

Then placed on the pile of sheets constituting the soul, a decorative sheet. In general, there is placed above the decorative sheet, a protective sheet cover, called "overlay", devoid of pattern and transparent in the final laminate, to improve the abrasion resistance of the laminate.

The stack of impregnated sheets is then placed in a laminating press, the trays of which are provided with a sheet which confers the surface state of the laminate. Then, the cell is densified by heating, at a temperature of the order of 110 ° C. to 170 ° C., and by pressing, at a pressure of the order of 5.5 MPa to 11 MPa, for approximately 25 to 60 minutes. minutes, to obtain a unitary structure.

This structure is then fixed on a base support, for example by gluing it to said support such as a panel of agglomerated particles, especially agglomerated wood particles.

The so-called low-pressure decorative laminates are produced using only a decorative sheet impregnated with thermosetting resin, and possibly an overlay sheet, which is laminated directly on the base support such as a panel during a short cycle, the temperature being the order of 160 to 175 ° C and the pressure of 1.25 MPa to 3 MPa.

The impregnable decorative sheet used for the manufacture of laminates is generally a sheet of paper made on a paper machine and which comprises cellulose fibers and possibly synthetic fibers, the cellulose fibers being distributed, by weight, between 40 to 100% preferably from 80 to 100%, short fibers and from 0 to 60%, preferably 0 to 20%, long fibers, 0.2 to 1% by dry weight relative to the sheet, preferably 0.4 to 0.5%, of a wet strength agent, and 5 to 50%, by dry weight with respect to the sheet, of decorative particles, for example iridescent pigments, and / or of pigmentary or organic dyes, and / or opacifying fillers such as titanium dioxide, especially rutile type, said opacifying filler such as titanium dioxide being preferably in amounts of at least 15%, generally between about 15 to 40% relative to the weight of the sheet . It may also contain other additives usually used in paper industry and in particular retention agents or specific agents such as alkaline products to control characteristics such as postforming.

These decorative sheets do not contain a bonding agent or are subjected to any surface treatment because they must be very absorbent of the thermosetting resin they will be impregnated. You can also print a decor on this sheet, for example an imitation wood or any other fantasy decor.

This sheet is then impregnated with a thermosetting resin but thermally stable (not yellowing), most often with melamine-formaldehyde resins or urea-formaldehyde resins, or sometimes benzoguanamine-formaldehyde resins, resins of unsaturated polyester. In a second step, the impregnated sheet is heated and the resin is partially crosslinked (thermoset) so that the resin is no longer in a sticky state and the sheet is manipulable. Such a decorative sheet impregnated with partially crosslinked resin is called, in terms of occupation, "decorative film" or "decorative film" or "melamine film".

This second step is generally carried out by bringing the sheet to temperatures of about 110 to 140 ° C and is controlled, so that the resin during the final lamination of the decorative film flows well into the sheet, by measuring the volatile rate remaining in the movie decor. Indeed, this decor film then comprises a certain percentage, of the order of 5 to 8%, of volatile products (solvent water of the resin, water resulting from the chemical condensation of the resin, residual formaldehyde, other residual products. ..). These volatiles represent the compounds that will be removed during the total crosslinking of the resin, during the lamination of the decor film.

The resin, once fully thermoset after lamination, will provide surface resistance to the final laminate (abrasion resistance, soil resistance, water vapor and chemical agents such as solvents, acids and bases, etc ...).

Moreover, this sheet, once laminated, must have a very high resistance to light because it is exposed almost permanently to light radiation by its use of surface covering; the compounds that constitute it must therefore be selected so as to obtain this light-fastness, preferably greater than or equal to 6 on the blue scale according to ISO 4586-2.16.

In addition, this sheet must make it possible to obtain an opaque decor film after lamination. It is indeed important that we do not see the base support and / or sheets of kraft paper on which or we have laminated the impregnated decorative sheet, through said sheet, so that there is no interference with the decor of the sheet. It must therefore have a decorative sheet giving the most opacity possible.

In the case of a white decoration, for which a very white opacifying filler such as titanium dioxide is used, it is then necessary to use large quantities of fillers such as titanium dioxide (about 40% by weight relative to the leaf) to obtain this opacity. Indeed, after impregnation and stratification, only titanium dioxide brings opacity because, because the cellulose has a refractive index close to that of the resin, the cellulose fibers are made transparent, and that all more than the amount of resin is important.

It is therefore necessary to put as much charge as titanium dioxide but this is expensive and unfavorable to the mechanical characteristics of the sheet.

To reduce the cost of the decorative film, it is sought to minimize the amount of resin absorbed by the sheet while retaining the mechanical and surface resistance to the decorative laminate thermoset resin brings it.

This problem is particularly important in the case of panels or low-pressure laminated decorative profiles because the impregnated decorative sheet is directly laminated on the support panel.

In the patent application EP 0 677 401 these problems have been addressed by providing a decorative sheet having a bonding agent and preferably creating an absorption gradient of the thermosetting resin, so that the upper part of the sheet is richer in resin than the lower part. internal to the laminate. The bonding agent, thanks to its hydrophobic effect, prevents the impregnating resin from penetrating completely into the sheet. The agent gluing is added in bulk or on the surface and differentially or by forming two jets, the lower jet comprising the bonding agent.

However it has been noted that this latter solution is difficult to implement, does not always allow a uniform creep of the resin in the sheet and may cause appearance defects of the laminate decorative panel, especially in the case of low laminated decorative panels pressure.

The invention aims to solve these problems and therefore aims to provide a decorative paper sheet used in decorative laminates, said sheet leading to a high opacity of the final decorative laminate and to obtain a decorative laminate without appearance defects.

The Applicant has found that the object of the invention is achieved if the paper sheet has a value of COBB ₆₀ degree of water absorption of the sheet, determined according to ISO 535, lower than the basis weight of the sheet and this at most 40% while the sheets according to the prior art and without bonding agent being composed substantially of cellulose fibers, always have a COBB ₆₀ degree of water absorption equal to or greater than their basis weight.

It thus appears that the wettability of the sheet is maintained and therefore that the thermosetting resin is evenly distributed in the sheet and that furthermore the absorption capacity of the thermosetting resin sheet is reduced.

More specifically, the invention provides a decorative papermaking sheet impregnable by a thermosetting resin comprising from 5 to 50% by dry weight relative to the sheet of decorative particles and / or of pigmentary or organic dyes and / or opacifying fillers, in particular titanium dioxide, characterized in that the value of COBB ₆₀ water absorption degree of the sheet, determined according to ISO 535 (water, 1 minute, 23 ° C) is lower than the basis weight of the sheet and this is at most 40%, and more particularly at least 5%.

Preferably, the value of the degree COBB ₆₀ is 10 to 35% less than the weight of said sheet.

In an advantageous embodiment, the sheet comprises a composition of at least one hydrophilic polymer. The hydrophilicity of the composition may be derived from the chemical nature of said polymer itself or emulsifying agents when said polymer is a water-insoluble polymer used in the form of an aqueous dispersion.

The hydrophilic nature of said composition or said polymer is therefore controlled (neither too high nor too low) so as to reduce the degree of COBB ₆₀ of water absorption according to the limits mentioned above, namely a decrease of plus 40% of the basis weight of said sheet.

The hydrophilic character of said composition or of said polymer also makes it possible to reduce the COBB ₆₀ degree of water absorption of the sheet, determined according to the ISO 535 standard (water, 1 minute, 23 ° C.) and at most 35 % with respect to COBB ₆₀ degree of water absorption of the same sheet not containing said composition or said polymer, preferably at least 5%.

The present invention therefore also provides a decorative papermaking sheet that can be impregnated with a thermosetting resin comprising from 5 to 50% of decorative particles and / or of pigmentary and / or organic dyes or opacifying fillers, in particular titanium dioxide, by dry weight per relative to the sheet, characterized in that it comprises a composition of at least one hydrophilic polymer and the COBB ₆₀ degree of water absorption of the sheet, determined according to the ISO 535 standard is lower than plus 35% relative to COBB ₆₀ degree of water absorption of the same sheet not containing said polymer (s).

Preferably, the basis weight of the sheet containing said polymeric composition is 50 to 150 g / m ² , preferably 60 to 100 g / m ² .

In one particular case, the sheet comprises from 4 to 20% by weight of said polymer (s) relative to the sheet, in particular from 2 to 10 g / m ² by dry weight of said polymer (s). ).

Preferably, said composition comprises a non-water-soluble polymer in aqueous dispersion.

More preferably, said non-water-soluble polymer is a hydrophilic polymer. As water-insoluble polymer, there may be mentioned polymers chosen from vinyl acetate polymers and in particular copolymers of vinyl acetate and butyl acetate, copolymers of vinyl acetate and ethylene or copolymers of acrylic esters, in particular copolymers of ethyl acetate of acrylonitrile and methacrylate, or mixtures thereof. Other non-hydrosoluble polymers of hydrophilic nature known as binder, although it is not according to the present invention of the desired technical effect, may be compatible with the application according to the present invention, especially if they do not alter the good light resistance of the decorative laminate, which is preferably greater than or equal to 6 on the blue scale according to the ISO - 4586-2.16 standard.

It is also possible to use a polymeric composition comprising, in admixture, an aqueous dispersion of a non-water-soluble polymer and an aqueous solution of a water-soluble polymer, in particular a polyvinyl alcohol polymer.

More particularly, the composition may comprise 80 to 95% by dry weight of a water-insoluble polymer and 5 to 20% by dry weight of water-soluble polymer. Said polymer water-soluble can help improve the uniformity of the appearance and water vapor resistance of the final panel and reduce the time of impregnation of the sheet by the thermosetting resin.

Said polymer is advantageously introduced into the sheet by an impregnation process, in particular by means of a gluing press containing said polymer in an aqueous medium. Any other means of application allowing good penetration of the sheet by the polymer can also be used. The treatment composition may also contain additives which are customary in the paper industry, in particular viscosity-regulating agents and anti-foam agents.

The dry extract of the composition and its viscosity are adjusted by those skilled in the art depending on the means of application used and the amount of said polymer to be introduced into the sheet.

Optionally said polymer can be added in bulk, in the chest of a paper machine.

Preferably, the opacifying fillers are titanium dioxide pigments and they are present at a level of 20 to 45% by dry weight of the sheet, more particularly from 30 to 40%. Other white fillers can be used, such as kaolin or talc, or in addition to titanium dioxide or mixed with pigment dyes.

• des fibres cellulosiques et éventuellement des fibres synthétiques, les fibres de cellulose se répartissant en poids entre 40 à 100 %, de préférence 80 à 100 %, en fibres courtes et entre 0 à 60 %, de préférence 0 à 20 %, en fibres longues,
• 0,2 à 1 %, de préférence 0,4 à 0,5 %, d'un agent de résistance humide en poids sec par rapport à la feuille.

In one embodiment, the paper sheet according to the invention comprises:

• cellulosic fibers and optionally synthetic fibers, the cellulose fibers being distributed in weight between 40 to 100%, preferably 80 to 100%, in short fibers and between 0 to 60%, preferably 0 to 20%, in long fibers. ,
• 0.2 to 1%, preferably 0.4 to 0.5%, of a wet strength agent on a dry weight basis with respect to the sheet.

The invention also provides a decorative papermaking sheet impregnated with a partially crosslinked thermosetting resin (decor film) which is characterized in that it comprises said decorative sheet with said polymer and which it contains in thermosetting resin at most 50%, preferably at least 40%, more preferably at least 45% by weight based on the weight of the resin-impregnated sheet, including volatile compounds.

The impregnated decorative sheet according to the invention may also be characterized in that it contains in thermosetting resin at most 50%, preferably at least 40%, more preferably at least 45%, by weight relative to the weight of the sheet impregnated with resin, including volatile compounds and a titanium dioxide content of less than 40% by dry weight of the sheet, preferably less than 35%, and having an opacity identical to that of a decorative sheet of the same basis weight before impregnation with said resin and containing a titanium dioxide of at least 40% by dry weight of the sheet and more than 50% of said resin based on the weight of the resin-impregnated sheet, including volatile compounds.

In particular, the thermosetting resin is chosen from melamine-formaldehyde resins, urea-formaldehyde resins or from benzoguanamine-fomialdehyde resins, unsaturated polyester resins or their mixtures.

• sur une machine à papier, on forme une feuille, à partir d'une suspension aqueuse de fibres de cellulose et éventuellement de fibres synthétiques, et 5 à 50 % en poids sec par rapport à la feuille de particules décoratives et/ou de colorants pigmentaires ou organiques et/ou de charges opacifiantes, en particulier du dioxyde de titane et éventuellement d'autres additifs usuellement employés pour ces feuilles,
• on l'essore, et éventuellement on la sèche,
• on imprègne la feuille formée, à l'aide d'une presse encolleuse, par une composition en milieu aqueux contenant un ou plusieurs desdits polymères,
• on essore et on sèche la feuille.

The subject of the present invention is also a process for the wet manufacture of said decorative sheet which is characterized in that it comprises the following steps:

• on a paper machine, a sheet is formed from an aqueous suspension of cellulose fibers and optionally synthetic fibers and 5 to 50% by dry weight relative to the sheet of decorative particles and / or pigment dyes or organic and / or opacifying fillers, in particular titanium dioxide and optionally other additives usually used for these sheets,
• it is wrung out, and eventually dried,
• the formed sheet is impregnated with a sizing press by a composition in an aqueous medium containing one or more of said polymers,
• we drain and dry the sheet.

• sur une machine à papier, on forme une feuille, à partir d'une suspension aqueuse de fibres de cellulose et éventuellement de fibres synthétiques, ces fibres se répartissant entre 40 à 100 %, de préférence 80 à 100 %, en fibres courtes et entre 0 à 60 %, de préférence 0 à 20 %, en fibres longues, 0,2 à 1 %, de préférence 0,4 à 0,5 %, d'un agent de résistance humide en poids sec par rapport à la feuille, et 5 à 50 % en poids sec par rapport à la feuille de particules décoratives et/ou de colorants pigmentaires ou organiques et/ou de charges opacifiantes, en particulier du dioxyde de titane et éventuellement d'autres additifs usuellement employés pour ces feuilles,
• on l'essore, et éventuellement on la sèche,
• on imprègne la feuille formée, à l'aide d'une presse encolleuse, par 4 à 20 % en poids sec par rapport à la feuille, notamment 2 à 10 g/m² en poids sec, d'une composition en milieu aqueux contenant un ou plusieurs desdits polymères, l'extrait sec de la composition étant notamment compris entre 5 et 20 % en poids,
• on essore et on sèche la feuille.

In one particular case, the method comprises the following steps:

• on a paper machine, a sheet is formed from an aqueous suspension of cellulose fibers and optionally of synthetic fibers, these fibers being distributed between 40 to 100%, preferably 80 to 100%, in short fibers and between 0 to 60%, preferably 0 to 20%, of long fibers, 0.2 to 1%, preferably 0.4 to 0.5%, of a wet strength agent by dry weight relative to the sheet, and 5 to 50% by dry weight relative to the sheet of decorative particles and / or of pigmentary or organic dyes and / or opacifying fillers, in particular titanium dioxide and optionally other additives usually used for these sheets,
• it is wrung out, and eventually dried,
• the sheet formed is impregnated with a sizing press by 4 to 20% by dry weight relative to the sheet, in particular 2 to 10 g / m ² by dry weight, of a composition in an aqueous medium containing one or more of said polymers, the dry extract of the composition being in particular between 5 and 20% by weight,
• we drain and dry the sheet.

According to a particular case, the invention also provides a method for manufacturing a decorative sheet impregnated with a partially crosslinked thermosetting resin (decorative film) which is characterized in that a paper sheet as described above is used, that the 'we said film is impregnated with a thermosetting resin and that the resin is partially crosslinked, the content of volatile compounds being between 5 and 8% by weight of the sheet.

The invention also relates to a laminated decorative panel or profile which is characterized in that it comprises as a decorative sheet a sheet as described above.

In particular, this laminated decorative panel or profile is a low pressure laminate that can be conventionally produced as described in the introduction.

The invention therefore makes it possible to reduce the demand for thermosetting resin and to improve the opacity of the decorative film while maintaining satisfactory properties for the final laminate, as shown by the following nonlimiting examples:

EXAMPLES EXAMPLE 1 COMPARATIVE WITNESS:

• Step 1: A sheet of control paper is produced according to the prior art:
  On a Foudrinier-type paper machine, a sheet of paper is produced by mass mixing, with a suspension of cellulose fibers in an aqueous medium, 0.5% with respect to the sheet of a wet-strength agent (a resin polyamide-polyamine-epichlorohydrin), titanium dioxide pigments in amounts such that they are present at about 40% in the paper. The titanium dioxide content is determined by the ash content at 800 ° C., titanium dioxide being the only inorganic compound, therefore incombustible in the paper, apart from residues in the pulp (in very small quantities). The sheet is formed and dried.
• Step 2: Using a laboratory impregnator, the sheet is impregnated with a mixture of thermosetting resins (urea-formaldehyde, melamine-formaldehyde) in aqueous solution. The resin is then partially cross-linked (thermoset) to obtain a resin with a level of volatile compounds of 6.5% by weight.
  The rate of volatiles is determined by heating the resin impregnated sheet at 160 ° C for five minutes, it corresponds to the ratio of the difference between the weight of the sheet at the exit of the oven and its weight before entering the oven. relative to the weight of the sheet before entering the oven.
• Step 3: A laminate is made in the laboratory by applying the resulting sheet to a particle board and subjecting the assembly to a temperature of 180 ° C for one minute at a pressure of 2.5 MPa.

EXAMPLE 2 COMPARATIVE:

• Step 1: a sheet of base paper is taken up according to step 1 of example 1, but it is impregnated with an aqueous composition comprising a polymer of hydrophobic nature, used in the form of a stable aqueous dispersion. . It is a copolymer of butyl acrylate and styrene. The solids content of this composition is 10% by weight.
  The sheet is dried.
  Steps 2 and 3 are carried out as in Example 1.
  When proceeding to step 2 of impregnation with the thermosetting resin, the sheet impregnates poorly and after step 3 it is found that the resulting laminate has a speckled appearance.
  The COBB ₆₀ water absorption rate of the leaf increased from 73 g / m ² to 29 g / m ² , a decrease of 60%; it is clearly inferior to that of the control sheet and is therefore too weak for the sheet to impregnate properly and to produce decorative panels of correct appearance.

EXAMPLE 3

• Step 1: a sheet of base paper is taken up according to step 1 of example 1 but is impregnated with a press-sizing agent with an aqueous composition comprising a mixture of an aqueous dispersion of a water-insoluble polymer with a character hydrophilic, known as a binder, and a solution of polyvinyl alcohol. The water-insoluble polymer is a copolymer of vinyl acetate and ethylene. The solids content of this composition is 10% by weight. The solids content of this composition comprises 10% by weight of said water-soluble polymer and 90% by weight of said water-insoluble polymer.
  The sheet is dried.
  Then proceed to step 2 of impregnation with the thermosetting resin and in step 3 of lamination as in Example 1.

EXAMPLE 4

• Step 1: a sheet of base paper is taken up according to step 1 of example 1, but is impregnated with a press-sizing agent with an aqueous composition comprising a polymer of hydrophilic nature, known as a binder, used in the form of a stable aqueous dispersion. This polymer is a copolymer of vinyl acetate and butyl acetate. The solids content of this composition is 10% by weight.
  The sheet is dried.
  Then proceed to step 2 of impregnation with the thermosetting resin and in step 3 of lamination as in Example 1.

EXAMPLE 5

• Step 1: a sheet of base paper is taken up according to step 1 of example 1 but is impregnated with a press-sizing agent with an aqueous composition comprising a mixture of an aqueous dispersion of a water-insoluble polymer with a character hydrophilic, known as binder and an aqueous solution of polyvinyl alcohol. This non-water-soluble polymer is a copolymer of acrylic esters (copolymers of ethyl acetate, acrylonitrile and a methacrylate). The solids content of this composition is 10% by weight.
  The solids content of this composition comprises 10% by weight of said water-soluble polymer and 90% by weight of said water-insoluble polymer.
  The sheet is dried.
  Then proceed to step 2 of impregnation with the thermosetting resin and in step 3 of lamination as in Example 1

COMPARATIVE EXAMPLE 6

• Step 1: a sheet of base paper is taken up according to step 1 of example 1, but it is impregnated with a press-sizing agent with an aqueous composition comprising a very hydrophilic polymer. It is a poly (vinyl alcohol) in aqueous solution. The solids content of this composition is 10% by weight.
  The sheet is dried.
  Steps 2 and 3 are carried out as in Example 1.
  In this example, the demand for resin could not be reduced. The degree of COBB ₆₀ water absorption of the sheet is greater than its basis weight and increased with respect to the COBB ₆₀ degree of the control.

Results:

The data and test results relating to these Examples 1 to 6 are presented in Table 1.
These examples show that at titanium dioxide content per constant square meter, the papers impregnated with a polymer decreasing the COBB ₆₀ degree of water absorption of the sheet, determined according to ISO 535, at most 40% relative to the basis weight of the sheet, and more particularly than at most 35% relative to COBB ₆₀ degree of water absorption of the same sheet not yet impregnated with said polymer, have a decreased resin demand compared to untreated control paper and that their opacity on laminated panel is greater than the control and that the appearance of the laminate obtained is not impaired.

EXAMPLE 7 WITNESS and EXAMPLE 8

Example 8 is carried out according to Example 3 with the same aqueous composition of the copolymer hydrophilic vinyl acetate and ethylene and the polymer poly (vinyl alcohol).
Control Example 7 is a paper made under the conditions of Example 1.
The data and test results for these examples are presented in Table 2,
Furthermore, it has been verified that the abrasion resistance of the laminate according to Example 8 treated with a hydrophilic polymer is not or very little impaired. It is also verified that there is no cracking on the surface of the laminate and that the laminate has good resistance to pulling.
Example 8 treated with a hydrophilic polymer shows that the resin demand is decreased for the sheet treated with a hydrophilic polymer relative to the untreated sheet, the opacity having been further improved.
The comparison of Example 8 treated with the hydrophilic polymer with Control Example 7 shows that comparable basis weight is less titanium dioxide per square meter while having a comparable opacity.
The treatment with the hydrophilic polymer thus makes it possible to reduce the resin demand of a sheet and the titanium dioxide content while obtaining a decorative film having good opacity after lamination and a laminate of uniform appearance. In addition, the surface resistance characteristics of the laminate have remained at a good level.

DESCRIPTION AND CONDITIONS OF REALIZATION OF THE TESTS:

• Le grammage des feuilles est déterminé selon la norme ISO 536 après conditionnement selon la norme ISO 187. Il s'agit du grammage de la feuille traitée par ledit polymère mais avant imprégnation de la résine.
• Le degré d'absorption d'eau, noté COBB₆₀, est déterminé selon la norme ISO 535 (1 minute, eau, 230°C).
• Le Delta (COBB₆₀ -Grammage), exprimé en pour cent, correspond à la différence entre le degré COBB₆₀ d'un échantillon et le grammage du même échantillon, divisée par ce grammage.
• Le Delta (COBB₆₀ - Témoin), exprimé en pour cent, correspond à la différence entre le degré COBB₆₀ d'un échantillon, avant et après traitement avec ledit polymère, divisée par le degré COBB₆₀ de la feuille non traitée (témoin).
• La reprise est la reprise sèche c'est-à-dire la quantité de la composition dudit polymère dont a été imprégnée la feuille et exprimée en poids sec de la composition (en gramme) par mètre carré de la feuille.
• La perméabilité à l'air, méthode porosité Gurley, est déterminée selon la norme ISO 5636-5R (1990).
• La demande en résine est la quantité de résine thermodurcissable nécessaire à introduire dans la feuille pour obtenir, après stratification sur panneau, un test au graphite supérieur ou égal à 4,5. Cette demande est exprimée en pour cent et représente le rapport du poids de résine thermodurcissable absorbée au poids de la feuille imprégnée de la résine, la résine contenant 6,5% de volatils.
• La teneur en cendres à 800°C est déterminée selon la norme française NF-Q-03.047 (Nov. 1971). Les tests suivants sont réalisés sur le film décor (feuille imprégnée de résine) stratifié sur un panneau de particules :
• Le test au graphite est réalisé comme suit : on mélange du graphite en poudre avec une huile de façon à former une pâte. On étale cette pâte sur la face apparente du film décor. On nettoie ensuite le panneau avec une éponge humide imprégnée d'un détergent. On compare la surface nettoyée avec une échelle témoin. L'échelle va de 1 à 6, 1 étant la plus basse note. On estime que la note minimale acceptable est de 4,5.

Ce test au graphite permet d'apprécier la porosité du film décor après stratification et donc sa résistance à la salissure. Cette caractéristique dépend de plusieurs paramètres dont le taux de volatils dans la résine, la stratification, la feuille décorative. La présente invention fournit des stratifiés présentant une note d'au moins 5 sur l'échelle du Test au graphite.

• L'opacité est déterminé sur la face apparente du film décor comme suit : sur un spectrophotomètre ELREPHO 2000, sous l'illuminant C et sous un angle d'observation de 10 degrés, on mesure le coefficient de réflexion du film décoratif stratifié R₀ et le coefficient de réflexion R_∞ de quatre films stratifiés sur le panneau qui donnent une opacité totale. L'opacité de l'échantillon est donnée par le rapport entre ces deux coefficients R₀ / R_∞ et est exprimée en pour cent. La présente invention fournit des feuilles décoratives présentant une opacité supérieure ou égale à environ 90%.
• L'aspect du stratifié est apprécié visuellement selon une échelle de 1 à 5, la note 1 correspondant à un aspect très mauvais (moucheté) et la note 5 a un aspect parfaitement uniforme. La présente invention fournit des stratifiés d'aspect avec une note supérieure ou égale à 3,5.
• La tenue lumière, réalisée selon la norme 1S0 4586-2.16 selon l'échelle des bleus. La présente invention fournit des feuilles décoratives qui une fois stratifiées présente une tenue à la lumière supérieure ou égale à 6 sur l'échelle des bleus.
• Le test à la vapeur d'eau, réalisé selon la norme BS 7331 selon une échelle de notes de 1 à 5, la note 1 correspondant à la présence de cloques et la note de 5 à aucune altération. La présente invention fournit des feuilles décoratives avec une note supérieure ou égale à 3.
• Le test aux fissurations, réalisé selon la nonne NF-B-51281 : après un vieillissement accéléré à 70°C pendant 24 heures, on regarde si des fissurations sont apparues.
• Le test à l'arrachage, réalisé selon la norme NF-B-51283.
• La résistance à l'abrasion TABER du stratifié, déterminée selon la norme NF-EN-483-2.

La résistance à l'abrasion des stratifiés selon l'invention n'est pas altérée ou très peu altérée. H n'apparaît pas de fissurations à leur surface et ils ont une bonne résistance à l'arrachage. TABLEAU 1 Exemple 1 comparatif (témoin) Exemple 2 comparatif Exemple 3 Exemple 4 Exemple 5 Exemple 6 comparatif reprise (g/m²) 0 6 4,5 5 5 5,2 grammage (g/m²) 72 78 76,5 77 77 77,2 épaisseur (µm) 86 88 90 87,5 86,5 2 Porosité Gurley (s) 20 81 77 36 52 21 COBB₆₀ (g/m²) 73 29 52 48 50 80 Delta (COBB₆₀ - grammage) (%) +1,3 -62,8 -32,0 -37,7 -35,0 +3,6 Delta (COBB₆₀ - Témoin) (%) 0 -60 -28,7 -34,2 -31,5 +9,5 Taux de TiO2 (g/m²) 29,5 29,5 29,5 29,5 29,5 29,5 Taux de cendres (%) 41 37,8 38,5 38,3 38,3 38,2 Demande de résine (%) 53 43 49 46 49 53 Teste au graphite (face décor) 4,5 5 5 5 5 5 Opacité sur panneau (%) 90,5 96,3 93,2 94,5 93,5 - Aspect du stratifié 4 2 4 3,5 4 - Tenue lumière ≥ 6 ≥ 6 ≥ 6 ≥ 6 ≥ 6 - Résistance à la vapeur d'eau 5 3 4 3 4 - TABLEAU 2 Exemple 7 (témoin) Exemple 8 Reprise (g/m²) 0 0 5,6 Grammage (g/m²) 80 74,7 78,9 Epaisseur (µm) 118 115 111 Porosité Gurley moyenne(s) 16 12,3 30 Taux de cendres (%) 40 34,2 32,7 Taux de dioxyde de titane (g/m²) 32 25,5 25,8 Demande en résine (%) 55 55 49 Opacité sur panneau 90 87,9 89,9

• The grammage of the sheets is determined according to the ISO 536 standard after conditioning according to the ISO 187 standard. It is the grammage of the sheet treated by said polymer but before impregnation of the resin.
• The degree of water absorption, noted COBB ₆₀ , is determined according to ISO 535 (1 minute, water, 230 ° C).
• The Delta (COBB ₆₀ -Frame), expressed in percent, is the difference between the COBB ₆₀ degree of a sample and the basis weight of the same sample, divided by that basis weight.
• The Delta (COBB ₆₀ - Control), expressed in percent, is the difference between the COBB ₆₀ degree of a sample, before and after treatment with said polymer, divided by the COBB ₆₀ degree of the untreated sheet (control) .
• The recovery is the dry recovery that is to say the amount of the composition of said polymer which has been impregnated the sheet and expressed in dry weight of the composition (gram) per square meter of the sheet.
• The air permeability, Gurley porosity method, is determined according to ISO 5636-5R (1990).
• The resin demand is the amount of thermosetting resin required to be introduced into the sheet to obtain, after panel lamination, a graphite test greater than or equal to 4.5. This demand is expressed in percent and represents the ratio of the weight of thermosetting resin absorbed to the weight of the sheet impregnated with the resin, the resin containing 6.5% volatiles.
• The ash content at 800 ° C. is determined according to the French standard NF-Q-03.047 (Nov. 1971). The following tests are performed on the decor film (resin impregnated sheet) laminated on a particle board:
• The graphite test is carried out as follows: graphite powder is mixed with an oil so as to form a paste. This paste is spread on the apparent face of the decor film. The panel is then cleaned with a damp sponge impregnated with a detergent. The cleaned surface is compared with a control scale. The scale goes from 1 to 6, 1 being the lowest note. It is estimated that the minimum acceptable score is 4.5.

This graphite test makes it possible to assess the porosity of the decorative film after lamination and thus its resistance to soiling. This characteristic depends on several parameters including the rate of volatiles in the resin, the stratification, the decorative sheet. The present invention provides laminates having a rating of at least 5 on the graphite test scale.

• The opacity is determined on the apparent face of the decorative film as follows: on an ELREPHO 2000 spectrophotometer, under the illuminant C and at an observation angle of 10 degrees, the reflection coefficient of the laminated decorative film R ₀ is measured and the reflection coefficient R _∞ of four films laminated on the panel which give total opacity. The opacity of the sample is given by the ratio between these two coefficients R ₀ / R _∞ and is expressed in percent. The present invention provides decorative sheets having an opacity greater than or equal to about 90%.
• The appearance of the laminate is assessed visually on a scale of 1 to 5, the score 1 corresponding to a very bad appearance (speckled) and the score 5 has a perfectly uniform appearance. The present invention provides appearance laminates with a rating greater than or equal to 3.5.
• The light behavior, carried out according to the standard 1S0 4586-2.16 according to the blue scale. The present invention provides decorative sheets which when laminated has a light resistance greater than or equal to 6 on the blue scale.
• The water vapor test, carried out according to BS 7331 according to a scale of scores from 1 to 5, the note 1 corresponding to the presence of blisters and the grade of 5 to no alteration. The present invention provides decorative sheets with a rating greater than or equal to 3.
• The crack test, carried out according to the standard NF-B-51281: after an accelerated aging at 70 ° C for 24 hours, it is examined whether cracks have appeared.
• The peel test, carried out according to standard NF-B-51283.
• The TABER abrasion resistance of the laminate, determined according to standard NF-EN-483-2.

The abrasion resistance of the laminates according to the invention is not impaired or very little altered. There are no cracks on their surface and they have good resistance to pulling. <u> TABLE 1 </ u> Comparative Example 1 (control) Comparative Example 2 Example 3 Example 4 Example 5 Comparative Example 6 recovery (g / m ² ) 0 6 4.5 5 5 5.2 grammage (g / m ² ) 72 78 76.5 77 77 77.2 thickness (μm) 86 88 90 87.5 86.5 2 Porosity Gurley (s) 20 81 77 36 52 21 COBB ₆₀ (g / m ² ) 73 29 52 48 50 80 Delta (COBB ₆₀ - basis weight) (%) 1.3 -62.8 -32.0 -37.7 -35.0 3.6 Delta (COBB ₆₀ - Witness) (%) 0 -60 -28.7 -34.2 -31.5 9.5 TiO2 content (g / m ² ) 29.5 29.5 29.5 29.5 29.5 29.5 Ash rate (%) 41 37.8 38.5 38.3 38.3 38.2 Resin Request (%) 53 43 49 46 49 53 Graphite test (face decoration) 4.5 5 5 5 5 5 Panel opacity (%) 90.5 96.3 93.2 94.5 93.5 - Aspect of laminate 4 2 4 3.5 4 - Holding light ≥ 6 ≥ 6 ≥ 6 ≥ 6 ≥ 6 - Resistance to water vapor 5 3 4 3 4 - Example 7 (control) Example 8 Resumption (g / m ² ) 0 0 5.6 Weight (g / m ² ) 80 74.7 78.9 Thickness (μm) 118 115 111 Average Gurley Porosity 16 12.3 30 Ash rate (%) 40 34.2 32.7 Titanium dioxide content (g / m ² ) 32 25.5 25.8 Demand in resin (%) 55 55 49 Panel opacity 90 87.9 89.9

Claims (15)

Process for the wet production of a decorative sheet, characterized in that it comprises the following steps: - On a paper machine, the sheet is formed from an aqueous suspension of cellulose fibers and optionally synthetic fibers, and 5 to 50% of decorative particles and / or pigmentary or organic dyes and / or fillers opacifying agents, in particular titanium dioxide, in dry weight with respect to the sheet and optionally other additives usually used for these sheets, - it is wrung out, and eventually it is dried, the sheet formed is impregnated with a composition in an aqueous medium comprising at least one polymer of hydrophilic nature, - Sore and dry the sheet. Process according to Claim 1, characterized in that the said polymer is introduced into the sheet by an impregnation process using a gluing press. Process according to Claim 1, characterized in that the water absorption value COBB ₆₀ of the sheet, determined according to ISO 535, is less than the basis weight of said sheet and not more than 40%. Process according to Claim 2, characterized in that the sheet formed is impregnated with the aid of said sizing press by 4 to 20% by dry weight relative to the sheet, in particular between 2 to 10 g / m ² in dry weight of said composition containing said hydrophilic polymer, the solids content of the composition being between 5 and 20% by weight. Process according to claim 3, characterized in that the value of said degree COBB ₆₀ is at least 5% less than the grammage of said sheet. Process according to claim 5, characterized in that the value of said degree COBB ₆₀ is 10 to 35% less than the basis weight of said sheet. Process according to one of the preceding claims, characterized in that the sheet is formed from an aqueous suspension of cellulose fibers and optionally of synthetic fibers, these fibers being distributed between 40 and 100%, preferably 80 to 100% , in short fibers and between 0 and 60%, preferably 0 to 20%, long fibers, 0.2 to 1%, preferably 0.4 to 0.5%, of a wet strength agent in dry weight compared to the sheet, and 5 to 50% by dry weight relative to the sheet of decorative particles and / or pigmentary or organic dyes and / or opacifying fillers, in particular titanium dioxide and optionally other additives usually used for these sheets . Method according to any one of the preceding claims, characterized in that the basis weight of the sheet is 50 to 150 g / m ² , preferably 60 to 100 g / m ² . Process according to any one of the preceding claims, characterized in that the composition comprises a water-insoluble polymer of hydrophilic nature. Process according to any one of the preceding claims, characterized in that the composition comprises two hydrophilic polymers comprising from 80 to 95% by dry weight of a non-water-soluble polymer, and 5 to 20% by dry weight of a polymer. water-soluble. Process according to claim 10, characterized in that said water-soluble polymer is polyvinyl alcohol. Process according to one of Claims 9 to 11, characterized in that the said hydrophilic non-water-soluble polymers are chosen from vinyl acetate polymers, vinyl acetate copolymers, acrylic ester copolymers, and their mixtures. Process according to Claim 12, characterized in that the said polymers are chosen from copolymers of vinyl acetate and of butyl acetate, the copolymers of vinyl acetate and of ethylene and the copolymers of ethyl acetate, acrylonitrile and methacrylate. Process according to any one of the preceding claims, characterized in that the opacifying fillers are titanium dioxide pigments and are present at a level of 20 to 45% by dry weight relative to the weight of the sheet. Process according to any one of the preceding claims, characterized in that the content of titanium dioxide is 30 to 40% by dry weight relative to the weight of the sheet.