WO2004074577A1

WO2004074577A1 - Prepreg

Info

Publication number: WO2004074577A1
Application number: PCT/EP2004/001393
Authority: WO
Inventors: Arnold Holger; Reinhardt Bernd
Original assignee: AHLSTROM OSNABRÜCK GmbH
Priority date: 2003-02-24
Filing date: 2004-02-13
Publication date: 2004-09-02
Also published as: EP1518024B1; EP1518024B2; BRPI0407760B1; CA2518942A1; DE502004001322D1; ATE338167T1; DE10307966B4; BRPI0407760A; ES2271845T3; EP1757731A2; EP1518024A1; EP1757731A3; ES2271845T5; DE10307966A1; CA2518942C; DE10307966C5

Abstract

Disclosed are prepregs which can be obtained by impregnating a raw paper with a thermally crosslinkable impregnation combination, and methods for the production thereof. The impregnation combination contains a thermally crosslinkable, formaldehyde-free resin solution and a polymer dispersion. The mixing ratio between the resin solution and the polymer dispersion in the impregnation combination ranges between 45:55 and 10:90 (solid:solid). After drying, the prepreg has a degree of crosslinking of no less than 10 percent but no more than 85 percent and a residual moisture of 2 to 3 percent by weight. The inventive prepregs are provided with better properties than previously known formaldehyde-containing and formaldehyde-free prepregs regarding printability and surface bonding strength (ripping resistance) as early as the moment the prepregs leave the paper machine while maintaining great surface density (great ability to receive lacquer) and dimensional stability/flatness.

Description

prepreg

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

Decorative coating materials, so-called decorative papers or decorative foils, are preferably used for surface coating in furniture manufacture and in interior construction, especially for laminate floors. These decorative films are impregnated with synthetic resin and, if necessary, subsequently surface-treated paper webs, which are decoratively printed or unprinted and in a state which can no longer be reactivated under pressure and heat. Depending on the type of impregnation process, a distinction is made between thermosetting decorative films with a fully impregnated core (offline process) and decorative films based on pre-impregnated materials (online process), on which a finish coating can then be carried out. This creates a decorative film that has a finished surface. Decorative films based on pre-impregnates are already soaked with a resin mixture within the paper machine, immediately after sheet formation and drying, depending on the mass per unit area of the base paper. After drying and smoothing, usually also within the paper machine, the paper or film must be cross-linked and therefore gap-proof, so that no fiber separation occurs within the decorative film in the subsequent processing steps of the finish coating and lamination on the appropriate carrier. In addition, the pre-impregnates for further processing require high opacity and surface quality, good printability in rotogravure printing, good varnishability (high varnish level), good flatness and bondability with chipboard and MDF (medium density fibreboard).

The thermally crosslinkable impregnating resins which are usually used for the production of pre-impregnates are water-thinnable, 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 pre-impregnates, the resin absorption can be between 5 and 35% by weight, the proportion of resin solutions generally penetrating deeper into the base paper than the proportion of polymer dispersions. The latter accumulate more or less on the top and bottom of the paper and ensure good smoothness and thus printability as well as surface tightness and thus varnishability (varnish level) of the paper. The resin solutions, on the other hand, are intended to ensure the good splitting strength and flatness of the pre-impregnate by crosslinking the fiber-resin composite during the further processing processes.

The penetration depth of polymer dispersions can be increased by various additives, such as, for example, by water-soluble polymers on the basis of polyvinyl alcohols, gelatin, starches, cellulose derivatives, alginates and their mixtures (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).

In some cases, the pre-impregnates are manufactured using the above-mentioned. Additives completely dispense with the use of classic resin solutions containing formaldehyde. However, these pre-impregnates, which are then free of formaldehyde, are limited in their splitting strength, flatness and printability.

These disadvantages are avoided by using a thermally curable, formaldehyde-free resin solution, which largely crosslinks only after heat treatment of the pre-impregnate over a period of about 40 seconds at about 132 ° C. according to DE 101 34 302 C1 (degree of crosslinking of at most 85%). The resin solution used for this, its production and possible uses, including for impregnating papers for decorative applications are described in DE 197 35 959 A1. It is disadvantageous that such a pre-impregnate according to DE 101 34 302 C2, which is completely uncrosslinked up to hot compression on the carrier material (e.g. chipboard) as the last further processing step, does not have any better or even worse internal strengths than known pre-impregnated formaldehyde-free or containing. In particular, up to hot pressing, it has poorer surface tightness and therefore poorer painting (lower paint level) and poorer flatness during lamination (bonding) than previously known formaldehyde-free and containing pre-impregnates.

The invention is therefore based on the object of providing partially crosslinked pre-impregnates which largely avoid the disadvantages mentioned at the end of the paper machine and, if possible, have high surface quality, good printability and higher splitting resistance than known pre-impregnates containing or containing formaldehyde, good paintability (high level of lacquer) , good flatness and stickability with common adhesives in the subsequent processing stages and are virtually equivalent in their properties to off-line impregnated papers.

This object is achieved by a formaldehyde-free prepreg with the features according to claim 1. Further advantageous embodiments result from the subclaims.

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

The prepreg according to the invention can be obtained by impregnating a base paper with an impregnation combination which contains a thermally curable, formaldehyde-free resin solution 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 pre-impregnate is at least 10% and at most 85%. The impregnated base paper has a residual moisture of 2 to 3% by weight.

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

The invention also relates to a method for producing thermally partially crosslinked, formaldehyde-free pre-impregnates within the paper machine and their use as decorative coating materials. According to the invention, prepregs are partially impregnated papers with formaldehyde-free resin solutions in combination with polymer dispersions Roger that. The proportion of the impregnation components is 5 to 35% by weight, preferably 10 to 30% by weight, based on the weight of the base paper.

The residual moisture of the pre-impregnate is between 1.5 to 3% by weight. At residual moisture levels of more than 3.5% by weight, the pre-impregnate can adhere to machine parts, for example to the smoothing rollers of the paper machine.

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

A) at least one polymer which can be obtained by free-radical polymerization and contains less than 5% by weight of an α, /? - 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 a, / J-ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form, and

C) at least one alkanolamine with at least two hydroxyl groups.

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

The water-dilutable impregnation mixture of the above-mentioned formaldehyde-free resin solutions A) + B) + C) or B) + C) and customarily used polymer dispersions is applied to at least one side of the paper web, then dried to a residual moisture of 2 to 3% by weight and then smoothed. The impregnated base paper is thus partially cross-linked, the degree of cross-linking depending on the mixing ratio of the impregnation combination between at least 10% and max. Is 85%. In the subsequent processing steps,. such as printing, varnishing and laminating / gluing, this is only partially cross-linked pre-impregnate sufficiently flexible. It is particularly advantageous for the quality of the pre-impregnate if the residual moisture is already set in the paper machine (“on-line”). Under a paper machine, in accordance with the general use of the word, the plant for paper production, starting with sieving the fiber suspension understood until the base paper is rolled up.

The mixing ratio between formaldehyde-free resin solution (I) and polymer dispersion (II) can be 49:51 to 10:90 (solid), preferably 45:55 to 20:80. Mixing ratios of 35:65 to 30:70 are particularly preferred, since pre-impregnates combined with impregnation combinations. these mixing ratios were produced, are particularly easy to print and are sufficiently flexible.

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

Surprisingly, it was found that the pre-impregnates according to the invention immediately after the paper machine have better properties than previously known formaldehyde-containing and formaldehyde-free pre-impregnates with regard to printability and surface strength (tesa strength). At the same time, however, they retain a high level of surface tightness (high paint level) and dimensional stability / flatness, which formaldehyde-free, uncrosslinked pre-impregnates according to DE 101 34 302 C1, i.e. impregnated with the above formaldehyde-free resin solutions according to DE 197 35 959 A1, do not have after the paper machine. With the latter pre-impregnate, the partial crosslinking takes place only at the end of the entire process chain of further processing, i.e. hot pressing. These outstanding properties of the pre-impregnate according to the invention are achieved by the combination of resin solutions and polymer dispersions in a specific mixing ratio, in which there is an optimum between the penetrating and film-forming properties of the individual components when impregnating the base paper, and this already within the paper machine, presumably through synergy effects and temperature influence, largely reached its final state.

As a result, the prepreg according to the invention can be used significantly more universally in the further processing steps and is not subject to any technological restrictions with regard to various process parameters, such as speed, temperature and pressure. In particular, the pre-impregnates according to the invention can be produced in such a way that they have a high degree of flexibility, dimensional stability and good barrier properties against water and solvents and can be used in particular as a base material for high-quality special papers, such as printing and advertising media, decorative wall materials, sanding papers, adhesive tapes or floor coverings.

Particularly good pre-impregnate qualities could be achieved if the degree of cross-linking of the pre-impregnate is more than 50%, preferably 70% and more.

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

The following examples illustrate the invention. Unless otherwise stated, all quantities relate to the solids or solids content. Example 1 (comparison)

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

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

Table 1 shows the degrees of crosslinking of the pre-impregnates dried at different temperatures. This is followed by a partial crosslinking of the pre-impregnates up to about 30% under drying conditions customary in the paper machine (up to 110 ° C., drying time approx. 14 seconds at 300 m / min).

Example 2 (He in improper pre-impregnation)

The base paper from Example 1 was impregnated by means of a laboratory size press with the impregnation mixture according to the invention consisting of 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) and at temperatures dried from about 110 ° C to a residual moisture of about 2% within about 18 seconds.

The amount applied was about 12 g / m ² . The degree of crosslinking of the prepreg according to the invention was approximately 70%. Accordingly, 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 processed using a laboratory size press with a commonly used impregnation mixture for classic pre-impregnates made from formaldehyde-free styrene-acrylate dispersion (Acronal 305) and formaldehyde-containing resin solution (Urecoll TS) in a ratio of 70:30 (A) and 90:10 (B) ( calculated) impregnated and then dried analogously to Example 2. The application quantity was approx. 13 g / m ^{2 in} each case.

The degree of crosslinking of the classic pre-impregnate was 76% (A) or 84% (B) and is therefore significantly higher than that of pre-impregnates according to the invention with proportions of formaldehyde-free resin solutions according to Examples 1 and 2

Example 4

The pre-impregnates prepared according to Examples 1 to 3 were smoothed under constant conditions in a laboratory calender. The paper properties achieved are summarized in Table 2.

Compared to the formaldehyde-containing or low-formaldehyde-containing pre-impregnates (comparative examples 3 A and 3 B) which are usually used, the formaldehyde-free pre-impregnate according to the invention (Example 2) has significantly better splitting resistance and printability. The paint level remains at a high quality level, while the flatness is somewhat worse.

In contrast to the formaldehyde-free pre-impregnate according to Example 1, the pre-impregnate according to the invention (Example 2) is characterized by an improved surface tightness and thus significantly higher lacquer level, less color penetration (pinhole test) and better printability and higher flatness.

The significantly better properties of the thermally partially crosslinked pre-impregnate 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 degrees of crosslinking than with the resin solution alone.

Table 1

Degree of crosslinking of pre-impregnates after different thermal treatment (contact drying)

Impregnation with formaldehyde-free resin solution Acrodur 350 L, 30%) application approx. 10 g / m ²

Table 2 Comparison of the properties of different prepregs, smoothed

Compare Vorim rä nat according to the invention

Grade 1 = very good Grade 5 = very bad

Claims

Expectations

1. Preimpregnate, obtainable by impregnating a base paper with a thermally cross-linkable impregnation combination that is formaldehyde-free

Contains resin solution and a polymer dispersion, characterized in that the mixing ratio between resin solution and polymer dispersion in the impregnation combination is 45:55 to 10:90 (solid), the residual moisture is 2 to 3 wt .-% and the pre-impregnation after drying one Networking degree of at least 10% and at most 85%.

2. The pre-impregnate according to claim 1, wherein the resin solution contains:

a) a polymer obtainable by free-radical polymerization which contains less than 5% by weight of an o,? -ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form,

b) a polymer obtainable by free-radical polymerization which contains more than 15% by weight of an α, /? - ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form, and

c) an alkanolamine with at least two hydroxyl groups.

3. Preimpregnate according to one of claims 1 and 2, characterized in that the polymer dispersion is based on acrylic acid, acrylic acid ester, styrene, butadiene, vinyl acetate or acrylonitrile.

4. Preimpregnate according to one of claims 1 to 3, characterized in that the mixing ratio between resin solution and polymer dispersion in the impregnation combination is 35:65 to 30:70.

5. Preimpregnate according to one of claims 1 to 4, characterized in that the proportion of the impregnating components in the paper is between 5 and 35% by weight based on the weight per unit area of the base paper.

6. Preimpregnate according to one of claims 1 to 5, characterized in that the drying takes place up to a residual moisture content of 2 to 3% by weight and degrees of crosslinking of at least 50%, preferably at least 70% are achieved.

7. pre-impregnate according to one of claims 1 to 6, characterized in that the pre-impregnate is a decorative pre-impregnate or decorative coating material.

8. A method of making a pre-impregnate comprising the steps of:

a) impregnating a base paper with a thermally cross-linkable impregnation combination which contains a formaldehyde-free resin solution and a polymer dispersion, the mixing ratio between resin solution and polymer dispersion in the impregnation combination being 45:55 to 10:90 (solid), and

b) drying the impregnated base paper so that the impregnation combination has a degree of crosslinking of at least 10% and at most 85% and a residual moisture of 2 to 3% by weight.

9. The method according to claim 8, characterized in that the resin solution contains:

a) a polymer obtainable by free-radical polymerization which contains less than 5% by weight of a, β-ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form,

b) a polymer which can be obtained by free-radical polymerization and contains more than 15% by weight of a, β-ethylenically unsaturated mono- or dicarboxylic acid in copolymerized form, and

c) an alkanolamine with at least two hydroxyl groups.

10. The method according to any one of claims 8 to 9, characterized in that the drying is carried out at at least 100 ° C.

11. The method according to any one of claims 8 to 10, characterized in that the impregnation, the mixing ratio between resin solution and polymer dispersion in the impregnation combination is 35:65 to 30:70.

12. The method according to any one of claims 8 to 11, characterized in that when impregnating the proportion of impregnating components in the paper is between 5 and 35 wt .-% based on the basis weight of the base paper.

13. The method according to any one of claims 8 to 12, characterized in that the drying takes place in the paper machine.

14. The 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 device, preferably a size or film press.