EP1518024B2 - Prepreg - Google Patents

Abstract

A pre-impregnate (I) is prepared by impregnation of a raw paper with a thermally cross-linkable combination (II) comprising a formaldehyde-free resin solution and a polymer dispersion in a mix ratio (solids:solids) of 45:55-10:90 with a residual moisture content of 2-3 wt.% whereby the dried pre-impregnate (I) has a degree of cross-linking of 10-85%. An independent claim is included for a process for the preparation of the preimpregnate (I) by impregnating raw paper with the combination (II) and drying.

Description

The invention relates to prepregs, a process for their preparation and decorative coating materials obtainable therefrom.

Decorative coating materials, so-called decor papers or decorative films, are preferably used for surface coating in furniture production and interior design, especially for laminate flooring. These decorative films are resin-impregnated and optionally subsequently surface-treated paper webs that are decorative printed or unprinted and in a no longer reactivated under pressure and heat condition. Depending on the type of impregnation process, a distinction is made between thermosetting decorative films with impregnated core (offline process) and decorative films based on prepregs (on-line process), on which subsequently a finish coating can be carried out. This creates a decorative film that has a finished surface.

Decorative films based on prepregs are already more or less deeply soaked within the paper machine, immediately after sheet formation and drying, with a resin mixture, depending on the basis weight of the base paper. After drying and smoothing, usually also within the paper machine, the paper or the film must be crosslinked and thus be gap-resistant, so that during the subsequent processing steps of the finish coating and lamination on corresponding carrier no fiber separation occurs within the decorative film. In addition, the prepregs for further processing high coverage and surface quality, good printability in rotogravure, good paintability (high paint level), good flatness and bondability with chipboard and MDF boards (medium-density fiberboard) required.

The thermally crosslinkable impregnating resins commonly used for the preparation of prepregs are water-dilutable, formaldehyde-containing resin solutions based on urea, melamine or phenolic resins. Since their sole use leads to relatively brittle products, these resin solutions are generally used in combination with water-dilutable, thermally crosslinkable polymer dispersions based on acrylic acid, acrylic acid ester, styrene, butadiene, vinyl acetate or acrylonitrile.

In the case of prepregs, the resin absorption can be between 5 and 35% by weight, with the proportion of resin solutions generally penetrating deeper into the base paper than the proportion of polymer dispersions. The latter are more or less rich on the top and bottom of the paper and ensure good smoothability and thus printability and Oberfilächendichtigkeit and thus paintability (paint level) of the papers. In contrast, the resin solutions are intended to ensure the good gap strength and flatness of the prepreg by crosslinking the fiber-resin composite during further processing.

The penetration depth of polymer dispersions can be increased by various additives, for example by water-soluble polymers based on polyvinyl alcohols, gelatin, starches, cellulose derivatives, alginates and mixtures thereof ( EP 0739 435 B1 ), Maleic acid copolymers ( EP 0 223 922 A1 ) or a copolymer of (meth) acrylamide and (meth) acrylic acid ( DE 197 28 250 A1 and DE 197 584 79 A1 ).

Partially used in the preparation of the prepregs using o.g. Additives completely dispensed with the use of classical formaldehyde-containing resin solutions. These then formaldehyde-free prepregs, however, are limited in their gap strength, flatness and printability.

By using a thermally curable, formaldehyde-free resin solution, the first at a heat treatment of the prepreg over a period of about 40 seconds at about 132 ° C according to DE 101 34 302 C1 largely crosslinked (degree of crosslinking of at most 85%), these disadvantages are avoided. The resin solution used for this purpose, its production and possible uses, inter alia for the impregnation of papers for decorative applications, are in the DE 197 35 959 A1 described. A disadvantage is that such until hot compression on the carrier material (eg chipboard) as the last further processing step completely unvemetztes prepreg according to DE 101 34 302 C2 until then has no better or even worse internal strengths than known formaldehyde-free or -contaminated prepregs. In particular, it has up to the hot pressing a poorer surface impermeability and thus poorer paint (lower paint level) and a poorer flatness during the lamination (bonding) than previously known formaldehyde-free and -containing pre-impregnate.

The invention is therefore an object of the invention to provide teilvemetzten prepregs that largely avoid the disadvantages mentioned at the end of the paper machine and as far as possible by high surface quality, good printability and higher splitting strength than known formaldehyde-free or prepregs, good paintability (high paint level) , good flatness and bondability with conventional adhesives Characterized in the subsequent processing stages and thus are almost equivalent in properties off-line impregnated papers.

This object is achieved by a formaldehyde-free prepreg having the features of claim 1. Further advantageous embodiments will become apparent from the dependent claims.

In procedural terms, the object is achieved by a method according to claim 8, wherein advantageous further embodiments are specified in the corresponding subclaims.

The prepreg according to the invention is obtainable by impregnating a base paper with a Impregnating combination containing a thermally curable, formaldehyde-free resin solutions and a thermally crosslinkable polymer dispersion. The impregnated base paper is dried and smoothed. The smoothing is expediently carried out within the paper machine used to produce the prepreg. The degree of crosslinking of the prepreg is at least 10% and at most 85%. The impregnated base paper has a residual moisture of 2 to 3 wt .-%.

The degree of crosslinking is analogous to that in the DE 101 34 302 C1 test method described by punching an area of 100 cm ² in a pre-impregnate, weighed and kept in water at a temperature of 60 ° C for 15 minutes, rinsed, dried in an oven at 130 ° C and weighed again. From the weight difference and the known order of the impregnating resin or the impregnating combination (eg 12 g / m ² dry with a 60 g / m ² pre-impregnate), the soluble fraction of the polymer or polymers can be determined. The degree of crosslinking in% is then 100 - soluble fraction in%.

The invention also provides a process for producing thermally partially crosslinked, formaldehyde-free prepregs within the paper machine and their use as decorative coating materials. According to the invention, prepregs are understood to mean partially impregnated papers in the formaldehyde-free resin solutions in combination with polymer dispersions. The proportion of the impregnating components is from 5 to 35% by weight, preferably from 10 to 30% by weight, based on the weight of the raw paper.

The residual moisture content of the prepreg is between 1.5 and 3% by weight. At residual moisture contents of more than 3.5% by weight, the prepreg can adhere to machine parts, for example to the calender rolls of the paper machine.

• A) mindestens ein durch radikalische Polymerisation erhältliches Polymerisat, das weniger als 5 Gew.-% einer α, β-ethylenisch ungesättigten Mono- oder Dicarbonsäure einpolymerisiert enthält,
• B) mindestens ein durch radikalische Polymerisation erhältliches Polymerisat, das mehr als 15 Gew.-% einer α, β-ethylenisch ungesättigten Mono- oder Dicarbonsäure einpolymerisiert enthält, und
• C) mindestens ein Alkanolamin mit mindestens zwei Hydroxylgruppen.

Suitable for impregnation formaldehyde-free resin solutions are those in the DE 197 35 959 A1 containing polymer compositions containing

• A) at least one polymer obtainable by free-radical polymerization and containing less than 5% by weight of an α, β-ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form,
• B) at least one polymer obtainable by free-radical polymerization which contains more than 15% by weight of an α, β-ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form, and
• C) at least one alkanolamine having at least two hydroxyl groups.

According to a particularly preferred embodiment, for impregnating the base paper, a resin can be used which contains the aforementioned components B) and C), but not the component A). Such resins are in the DE 197 35 959 A1 disclosed.

The inventive water-dilutable impregnating mixture from o.g. Formaldehyde-free resin solutions A) + B) + C) or B) + C) and commonly used polymer dispersions is applied to at least one side of the paper web, then dried to a residual moisture content of 2 to 3 wt .-% and then smoothed. The impregnated base paper is thereby partially crosslinked, the degree of crosslinking depending on the mixing ratio of the impregnating combination between at least 10% and max. 85% In the subsequent processing steps, such as printing, painting and laminating, this partially crosslinked prepreg is sufficiently flexible. It is particularly advantageous for the quality of the prepreg if the residual moisture is already set in the paper machine ("on-line"). Under a paper machine is understood in accordance with the general use of the word, the plant for papermaking, starting from the screening of the pulp suspension to the rolling up of the base paper.

The mixing ratio between formaldehyde-free resin solution (I) and polymer dispersion (II) is (solid: solid), 45:55 to 30:70. Mixture ratios of 35:65 to 30:70 are particularly preferred, since prepregs which have been produced with impregnation combinations having these mixing ratios are particularly easy to print and are sufficiently flexible.

The concentration of the impregnating mixture according to the invention, which contains further additives if required, can be up to 50% by weight. The impregnating combination according to the invention can be applied online to the paper web in an amount of between 5 and 35% by weight, preferably between 10 and 30% by weight, based on the basis weight of the base paper. As application devices, all commonly used within the paper machine units can be used, preferably roller application devices, such as size press or film press.

Surprisingly, it has been found that prepregs according to the invention already have better properties than previously known formaldehyde-containing and formaldehyde-free prepregs with regard to printability and surface strength (Tesafestigkeit) immediately after the paper machine. At the same time they retain a high surface density (high paint level) and dimensional stability / flatness, the formaldehyde-free uncrosslinked prepregs according to DE 101 34 302 C1 , so impregnated with the above-mentioned formaldehyde-free resin solutions according to DE 197 35 959 A1 do not own after the paper machine. In the case of the last-mentioned prepreg, partial crosslinking takes place only at the end of the entire process chain of further processing, ie hot-pressing.

These outstanding properties of the prepreg according to the invention are achieved by the combination of resin solutions and polymer dispersions in a certain mixing ratio, in which an optimum between penetrating and film-forming properties of the individual components in the impregnation of the base paper and the already within the paper machine, probably by synergy effects and temperature influence, has largely reached its final state.

The prepreg according to the invention is thus significantly more universally applicable in the further processing steps and is not subject to any technological limitations with respect to various process parameters, such as speed, temperature and pressure. In particular, the prepregs according to the invention can be prepared so that they have high flexibility, dimensional stability and good barrier properties against water and solvents and can be used in particular as a base material for high-quality specialty papers, such as printing and advertising media, decorative wall materials, abrasive papers, adhesive tapes or floor coverings.

Particularly good pre-impregnate qualities could be achieved if the degree of crosslinking of the prepreg is more than 50%, preferably 70% or more.

The raw papers to be impregnated according to the invention are those which are described, inter alia, in the patents EP 0223 922 A1 . EP 0870 872 A1 and DE 101 34 302 A1 are described. Likewise, the impregnation, drying and smoothing methods used in the documents cited and in the trade journal " Wochenblatt für Papierfabrikation "No. 6 (2000), pp. 350 to 355 described in detail and known prior art.

The following examples illustrate the invention. All quantities are based on the solids or solids content, unless stated otherwise.

Example 1 (comparison)

According to the invention, a raw paper of 20% pine sulfate pulp and 80% eucalyptus pulp was produced. The freeness was 30 ° SR (Schopper-Riegler). The additives used were 25% titanium dioxide and 4% formaldehyde-free wet strength agent on dry pulp. This raw paper without engine sizing and with a basis weight of 48 g / m ² was impregnated on both sides in a laboratory size press with a formaldehyde-free resin solution of about 30% solids content of modified polyacrylic acid and a polyhydric alcohol (Acrodur 950 L Fa. BASF) and then at dried at different temperatures within about 18 seconds to a residual moisture content of about 2%.

The amount applied after drying was 10 g / m ² .

Table 1 shows the degrees of crosslinking of the prepregs dried at different temperatures. This is followed by partial cross-linking of the prepregs up to about 30%, with drying conditions customary in the paper machine (up to 110 ° C., drying time about 300 seconds).

Example 2 (Inventive prepreg)

The base paper from Example 1 was impregnated by means of a laboratory size press with the impregnating mixture according to the invention from a formaldehyde-free resin solution (Acrodur 950 L) and a styrene-acrylate dispersion (Acronal 305 D from BASF) in a ratio of 35:65 (solid: solid) and dried at temperatures of about 110 ° C to a residual moisture content of about 2% within about 18 seconds.

The order amount was about 12 g / m ² . The degree of crosslinking of the prepreg according to the invention was about 70%. Thus, the addition of polymer dispersion to the resin solution significantly increases the degree of crosslinking.

Example 3 (comparison)

The base paper from Example 1 was produced by means of a laboratory size press with a commonly used impregnation mixture for classic prepregs of formaldehyde-free styrene-acrylate dispersion (Acronal 305) and formaldehyde-containing resin solution (Urecoll TS) in the ratios 70:30 (A) and 90:10 (B) ( solid calculated) and then dried analogously to Example 2. The order amount was in each case about 13 g / m ² .

The degree of crosslinking of the classical prepreg was 76% (A) or 84% (B) and is thus significantly higher than that of prepregs according to the invention with proportions of formaldehyde-free resin solutions according to Examples 1 and 2

Example 4

The Vorimprägnate prepared according to Example 1 to 3 were under constant conditions in a Smoothed laboratory calender. The paper properties achieved are summarized in Table 2.

In comparison to conventionally used formaldehyde-containing or low-formaldehyde prepregs (Comparative Examples 3 A and 3 B), the formaldehyde-free prepreg according to the invention (Example 2) has a significantly better nip strength and printability. The paint level remains at a high level of quality, while the flatness gets a little worse.

In contrast to the formaldehyde-free prepreg according to Example 1, the prepreg of the invention (Example 2) is characterized by improved surface impermeability and thus significantly higher paint level, lower color penetration (pinhole test) and better printability and higher flatness.

The significantly better properties of the thermally partially crosslinked prepreg according to the invention are caused by the combination of resin solution and polymer dispersion in a certain range of the mixing ratios and the resulting higher levels of crosslinking than with the resin solution alone. <b><u> Table 1 </ u></b> Degree of crosslinking of prepregs after different thermal treatment (contact drying) Drying temperature, ° C 95 100 105 110 Degree of crosslinking,% 0 11.3 18.6 30.5 Impregnation with formaldehyde-free resin solution. Acrodur 350 L, 30% lg) Order about 10 g / m ² Comparison of the properties of different prepregs, smoothed comparisons Inventive prepreg paper feature Example 3 (A) Example 3 (B) example 1 Example 2 area based size, g / m ² about 60 about 60 about 60 about 60 Order quantity, g / m ² about 13 about 13 about 10 about 12 Degree of crosslinking,% (110 ° C, <20 seconds) about 76 about 84 about 30 about 70 Water absorption, g / m ² 17.0 20.0 37.8 23.0 Porosity after Bendtsen, ml / min 37.1 36.0 250 14.5 Smoothness to Bekk, s 296 310 285 320 Flatness, s 14 5 6 10 Splitting strength / Tesatest 3 5 1 1 Paint level / shine, % 84.6 82.1 21.0 81.8 Pinhole Test 1 1 4 2 Printability (aqueous intaglio printing) 3 3 4 1 Formaldehyde emission, mg HCO / m ² .h about 0.7 approx. 0.35 (low in formaldehyde) <0.2 (free of formaldehyde) <0.2 (formaldehyde-free) Grade 1 = very good Grade 5 = very bad

Claims (14)

1. A prepreg, obtainable by impregnating a base paper with a thermally cross-linkable impregnation combination which contains a formaldehyde-free resin solution and a polymer dispersion, characterized in that the mixing ratio between the resin solution and the polymer dispersion in the impregnation combination amounts to from 45 : 55 to 30 : 70 (solid : solid), the residual moisture amounts to from 2 to 3% by weight, and, after drying, the prepreg has a degree of cross-linking of at least 10% and at most 85%.
2. A prepreg according to Claim 1, wherein the resin solution contains:

   a) a polymer which is obtainable by radical polymerization and which contains, polymerized in, less than 5% by weight of an α-, β-ethylene-unsaturated mono- or dicarboxylic acid,

   b) a polymer which is obtainable by radical polymerization and which contains, polymerized in, more than 15% by weight of an α-, β-ethylene-unsaturated mono-or dicarboxylic acid, and

   c) an alkanolamine with at least two hydroxyl groups.
3. A prepreg according to one of Claims 1 and 2, characterized in that the polymer dispersion is constituted on the basis of acrylic acid, acrylic acid ester, styrene, butadiene, vinyl acetate or acrylonitrile.
4. A prepreg according to any one of Claims 1 to 3, characterized in that the mixing ratio between the resin solution and the polymer dispersion in the impregnation combination amounts to from 35 : 65 to 30 : 70.
5. A prepreg according to any one of Claims 1 to 4, characterized in that the proportion of the impregnation components in the paper amounts to between 5 and 35% by weight with respect to the weight per unit area of the base paper.
6. A prepreg according to any one of Claims 1 to 5, characterized in that the drying takes place to a residual moisture of from 2 to 3% by weight, and degrees of cross-linking of at least 50%, and preferably at least 70%, are achieved.
7. A prepreg according to any one of Claims 1 to 6, characterized in that the prepreg is a decorative prepreg or a decorative coating material.
8. A method of producing a prepreg, comprising the steps:

   a) impregnating a base paper with a thermally cross-linkable impregnation combination which contains a formaldehyde-free resin solution and a polymer dispersion, wherein the mixing ratio between the resin solution and the polymer dispersion in the impregnation combination amounts to from 45 : 55 to 30 : 70 (solid : solid), and

   b) drying the impregnated base paper, so that the impregnation combination has a degree of cross-linking of at least 10% and at most 85% and a residual moisture of from 2 to 3% by weight.
9. A method according to Claim 8, characterized in that the resin solution contains:

   a) a polymer which is obtainable by radical polymerization and which contains, polymerized in, less than 5% by weight of an α-, β-ethylene-unsaturated mono- or dicarboxylic acid,

   b) a polymer which is obtainable by radical polymerization and which contains, polymerized in, more than 15% by weight of an α-, β-ethylene-unsaturated mono-or dicarboxylic acid, and

   c) an alkanolamine with at least two hydroxyl groups.
10. A method according to one of Claims 8 to 9, characterized in that the drying is carried out at at least 100°C.
11. A method according to any one of Claims 8 to 10, characterized in that during the impregnation the mixing ratio between the resin solution and the polymer dispersion in the impregnation combination amounts to from 35 : 65 to 30 : 70.
12. A method according to any one of Claims 8 to 11, characterized in that during the impregnation the proportion of the impregnation components in the paper amounts to between 5 and 35% by weight with respect to the weight per unit area of the base paper.
13. A method according to any one of Claims 8 to 12, characterized in that the drying takes place in the paper-making machine.
14. A method according to any one of Claims 8 to 13, characterized in that the impregnation combination, the resin solution and/or the polymer dispersion are applied to the base paper by means of a roller-application apparatus, preferably a glue press or film press.