HRP950615A2 - Modified melamine resins and their use for manufacturing post-formed laminates - Google Patents

Description

Laminates of melamine resin on the basis of impregnated papers have a wide range of applications as surfaces for decoration and protection, due to their properties to retain permanent color, due to wear resistance, resistance to chemicals, resistance to high temperature and due to surface strength.

Layered, printed materials of this type, which are obtained by impregnating a carrier base made of textile, paper or glass wool with aqueous solutions of melamine-formaldehyde-precondensate and finally drying and hardening at temperatures above 100°C, are described for example in EP-A- 0 077 067. EP-B1-0 268 809 describes foils made of melamine resin, which are obtained by coating paper with at least 70% by weight of an aqueous solution of methyletherized melamine resin.

The disadvantage of these well-known melamine resins and melamine resin laminates is that they shrink a lot during hardening, that their mechanical properties, such as resistance to boiling water, in many cases are not good enough, that, above all, they are quite fragile, and that they do not possess properties that enable subsequent shaping.

From US 4,424,261 it is known that the use of hydroxylalkyl-melamine as a modifying agent for melamine-formaldehyde-resins affects the improvement of the subsequent molding properties. The disadvantage of these modifying agents is their instability, and thus handling them is more difficult, since they are quite prone to cross-linking. Other modifying agents, such as for example guanamines, which enable the post-forming properties of the resins, are described in EP-Al-0 561 432. Guanamines, especially those with aromatic nuclei such as benzoguanamine, are not sufficiently resistant to light, as a result of which the modified resins easily turn yellow. Furthermore, the low solubility of guanamine in the reaction medium has a bad effect on the resin production process.

For this reason, it was necessary to find a modifying agent for melamine resins, which would not have the disadvantages of the previously known modifying agents and which would significantly improve the subsequent molding properties, without reducing their resistance to boiling water.

Thus, it was unexpectedly discovered that such melamine resins can be obtained by combining certain polyalcohols and dicyandiamide as modifying agents.

The subject of this invention are accordingly modified melamine-formaldehyde-resins, which are characterized by the fact that they consist of formaldehyde-condensate, melamine and a modifying agent and a combination

a) 5 to 25 wt.%, in relation to melamine, dicyandiamide and

b) 8 to 30 wt.%, relative to melamine, of a water-soluble polyalcohol with at least two hydroxylalkyl groups, whereby the molar ratio of formaldehyde to melamine is 1.2 to 2.5.

The melamine resins of the present invention are modified by combining dicyandiamide with polyalcohols containing at least two hydroxyl-alkyl groups.

Polyalcohols, which have at least two hydroxyl-alkyl groups, are compounds in which the hydroxyl-alkyl groups are attached to an aliphatic, cycloaliphatic or heterocyclic core structure. As aliphatic core structures are meant linear or branched C1 to C10 alkyl groups, which can also be substituted with carbonyl-, amino- or (C1-C6)-alkyl groups. As a cycloaliphatic core structure, C5 to C8 cycloalkyl groups come into consideration, which can also have other substituents, such as carbonyl groups, in addition to hydroxyl alkyl groups. The heterocyclic core structure can have heteroatoms such as N, O or S in cycles 1 to 3, as well as other substituents, such as carbonyl residues. The share of alkyl hydroxyl-alkyl groups amounts to 1 to 6 carbon atoms.

Polyalcohols of the formula are recommended

[image]

or the rest of the formula

[image]

and R2 is a linear or branched (C1 to C4)-alkyl radical.

In formula Ib) R 3 , R 4 and R 5 mean a linear or branched (C 1 to C 6 ) alkyl residue, which can also be substituted with the following hydroxyl group.

R3, R4 and R5 can be the same or different.

R 3 can furthermore be a cycloalkyl residue with 6 carbon atoms.

The polyalcohols trimethylolpropane, trimethylolethane, trihydroxyethyl isocyanurate, neopentylglycol, 1,4-dimethylolcyclohexane, 4-methyl-2,4-pentanediol, 1,6-hexanediol, 3-methyl-1, 3, 5-pentanetriol and 2, 2, 4-trimethyl-1,3-pentanediol.

Polyalcohols can be added as a single compound or as a mixture of several polyalcohols. The amount of polyalcohol in the melamine resin according to this invention is about 8 to 30% by weight, in relation to the melamine used. It is recommended to use 12 to 22 wt.% polyalcohol.

According to this invention, polyalcohols are used in combination with dicyandiamide as a modifying agent for melamine-formaldehyde-resins. The amount of dicyandiamide is about 5 to 25 wt.%, compared to the melamine used, and about 8 to 18 wt.% is recommended. The molar ratio of formaldehyde to melamine for resins to be modified is 1.2:1 to 2.5:1. It is recommended to use formaldehyde and melamine in a molar ratio of 1.4 to 2.0:1.

Melamine-formaldehyde-resins modified according to this invention are obtained by condensing melamine with formaldehyde in a known manner in an aqueous solution and adding polyalcohol and dicyandiamide components with mixing before or during condensation in the above-mentioned quantity. Polyalcohol and dicyandiamide components can be added as a mixture or as individual components. A ready mixture consisting of melamine, formaldehyde, dicyandiamide and polyalcohol can be used for the production of resins according to this invention.

The next subject of this invention is therefore the use of a mixture of formaldehyde, melamine, 5 to 25 wt.%, relative to melamine, dicyandiamide and 8 to 30 wt.% relative to melamine, to a water-soluble polyalcohol with at least two hydroxylalkyl groups, which contains formaldehyde and melamine in a molar ratio of 1.2 to 2.5, for the production of modified melamine-formaldehyde resins.

To speed up the reaction in the modification of melamine resins with the combination according to this invention, common catalysts, such as p-toluenesulfonic acid, can be added in amounts of about 0.1 to 1% by weight, relative to the total amount of melamine resin.

Salts, which can undergo hydrolysis, of weak to strong carbonic acids, sulfonic acids or mineral acids, for example diethanolamine acetate, morpholine, diethanolamine, ethanolamine hydrochloride, ethylenediamineacetate, ammonium rhodanide, ammonium lactate, ethylenediaminephosphate or dimethylethanolamine salts of p-toluenesulfonic acid, can also be added to the resins. in order to speed up the hardening without jeopardizing the elasticity of the resins.

During the production of resins, additional modifying agents, caprolactam or aromatic sulphonic acid amides, such as p-toluene-sulfonamides, can be added. As a rule, condensation of resins continues until the limited possibility of dilution with water.

Modified melamine-formaldehyde resins are particularly suitable for the production of decorative surfaces and protective surfaces with excellent properties that enable subsequent shaping. The production of preliminary products (films) for decorating surfaces and protective surfaces is done by impregnating paper or fabric threads. Paper threads (fibers) are usually made of decorative paper or thick paper. The fabric threads preferably consist of wool, fabric or a base made of glass-, carbon-, ceramic- or aramid fibers. According to the requirements for the properties of the laminates produced in this way, a mixture of different fibers, unidirectional endless fibers or multiple layers of the same or different reinforcing threads can be used.

The impregnation of these threads (strips) with modified melamine-formaldehyde resins is done, for example, by dipping or spraying and finally by kneading or scraping to the desired resin content of the films. The resin content primarily depends on the desired properties of films or laminates as well as the type of fiber reinforcement, and is usually from 30 to 60%, compared to the supporting (base) material that is impregnated with resin.

Depending on the viscosity and consistency of the melamine resin, impregnation usually occurs at temperatures from around 20 to 60°C. In order to prevent the melamine resin from coming out of the supporting (base) material, after impregnation at 80 to 160°C, the films are dried to a certain remaining moisture content, whereby the easy-flowing impregnation resin reacts depending on the temperature and the length of the heat treatment more or less due to partial hardening and cross-linking.

In this state, the film is suitable for storage and transport at room temperature. Several layers of impregnated thick and decor paper are pressed at a temperature of 120 to 180°C under a pressure of 25 to 100 bar to form a laminate. Based on its excellent properties that enable subsequent shaping, the laminate can be shaped to the desired shape by further cross-linking the melamine resin at temperatures from 80 to 180°C under pressure.

Laminates obtained from resins modified according to this invention have above all a high resistance to boiling water as well as improved surface elasticity, so that small bending radii can be achieved without cracking.

Example 1

In a tank with a stirrer and reflux cooling device, 126 parts (1 mol) of melamine, 137.5 parts (1.65 mol) of a 36% formaldehyde solution, 20 parts (0.15 mol) of trimethylpropane, 17.5 parts of (0.21 mol) of dicyandiamide and 66 parts of deionized water at 90°C and with a pH value of 9.5-10 (supported by sodium hydroxide) to a water dilution of about 1.2 (at 20°C), (1 .0 parts by volume (resin): 1.2 parts by volume (H2O)).

Example 2 to 4

Analogous to example 1, other modified melamine resins are produced. The proportion of melamine was 126 parts (1 mol), the proportion of 36% formaldehyde was 137.5 parts (1.65 mol). 66 parts of deionized water were used. The polyalcohol used, its proportion, as well as the proportion of dicyandiamide can be seen from Table 1.

Table 1

[image]

Comparative example V1:

Analogously to example 1, a melamine resin was produced with 37.5 parts (0.28 mol) on trimethylpropane, but without dicyandiamide.

Example 5

The resins from examples 1 to 4 as well as from example V1 are catalyzed with 0.2% by weight of hardener EC15 (Chemie Linz Castellanza) for 20 minutes at a cloud point of 100°C. Finally, the decor paper as well as the thick paper, which functioned as the base paper (core), is impregnated. Decor paper (95 g/m2) contains 55% by weight of resin and 6% by weight of volatile components (compared to impregnated paper), basic paper (80 g/m2) contains 47% by weight of resin and also 6 wt% of volatile constituents (in relation to impregnated paper).

One layer of impregnated decor paper and 3 layers of base paper are then pressed together with a pressure of 30 bar at a temperature of 175°C for 20 seconds.

Laminates thus obtained are tested with regard to their possibility of subsequent formation and their resistance to boiling water. The results can be seen in Table 2.

Table 2

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(*) The smallest diameter at which the laminate can be bent around a metal cylinder, heated to 160°C, without cracking.

Claims (7)

1. Modified melamine-formaldehyde resins, characterized in that they consist of condensate from formaldehyde, melamine and modifying agents containing a compound of a) 5 to 25 wt.% in relation to melamine, dicyandiamide and b) 8 to 30 wt.% in relation to melamine, water-soluble polyalcohols of the formula R1-(R2OH)3 Ia or HOR4-R3-R5OH Ib where in formula Ia R1 denotes the rest of the formula C-(CH2)n-CH3 with n equal to 0 to 3 IIa or the rest of the formula [image] and R2 is a straight or branched (C1 to C4) alkyl residue, and in formula Ib R3 denotes a cycloalkyl residue with 6 carbon atoms or R3, as R4 and R5 of a straight or branched (C1 to C6) alkyl residue, which can be substituted with additional by a hydroxyl group if necessary, wherein R 3 , R 4 and R 5 may be the same or different, and the molar ratio of formaldehyde to melamine is 1.2 to 2.5. 2. Modified melamine-formaldehyde resin according to claim 1, characterized in that the modifying agent consists of a compound of a) 8 to 18 wt.% in relation to melamine, dicyandiamide and b) 12 to 22 wt.% in relation to melamine, a water-soluble polyalcohol of formula Ia or Ib. 3. Modified melamine-formaldehyde resin according to claim 1, characterized by the fact that trimethylolpropane, trimethylolethane, trihydroxyethyl isocyanurate, neopentylglycol, 1,4-dimethylolcyclohexane, 4-methyl-2,4-pentanediol, 1,6-hexanediol, can be used as polyalcohol. 3-methyl-1,3,5-pentanediol or 2,2,4-trimethyl-1,3-pentanediol or their mixtures. 4. Modified melamine-formaldehyde resins according to claim 1, characterized in that they contain formaldehyde and melamine in a molar ratio of 1.4:1 to 2:1. 5. Use of a mixture of formaldehyde, melamine, 5 to 25 wt.%, in relation to melamine, dicyandiamide and 8 to 30 wt.%, in relation to melamine, of a water-soluble polyalcohol of the formula Ia or Ib, according to claim 1, characterized in that it contains formaldehyde and melamine in a molar ratio of 1.2:2.5, and is used for the production of modified melamine-formaldehyde resins. 6. Melamine resin laminates, characterized in that they consist of long sheets of paper or fabric impregnated with modified melamine resins according to claim 1. 7. Process for the production of melamine resin laminates, indicated by the fact that the roll of paper or fabric is impregnated with a modified melamine resin of condensate of formaldehyde, melamine and a modifying agent, which contains a compound of, linked to an aliphatic, cycloaliphatic or heterocyclic group, a) 5 to 25 wt.% in relation to melamine, dicyandiamide and b) 8 to 30 wt.% in relation to melamine, water-soluble polyalcohol formula Ia or Ib, according to claim 1, and the molar ratio of formaldehyde to melamine is 1.2:2.5, and that the films obtained during impregnation are pressed into a laminate, they are partially dried if necessary, reshaped and fully hardened.