NO179752B - Means for impregnating cellulosic fibrous materials - Google Patents

Abstract

Compositions for impregnating cellulose-containing fibre fabrics based on an aqueous solution of a partially alcohol-etherified melamine-formaldehyde condensate give very good results when impregnating fairly thick papers even without the additional use of organic solvents if they are prepared from a water-incompatible or only restrictedly water-compatible solution of a formaldehyde-melamine condensate having a molar ratio of formaldehyde to melamine of at least 4.5, which is predominantly or completely etherified with a water-soluble monohydric aliphatic alcohol, by reacting with at least 1 mol, per mol of melamine of the condensate, of a water-soluble di- or trihydric alcohol at about 50 to 100 DEG C at an acid pH until the formation of an unrestrictedly water-miscible state of the solution.

Description

The invention relates to an agent for impregnating cellulose-containing fiber materials based on an aqueous solution of a melamine-formaldehyde condensate that is at least partially etherified with alcohol, which is particularly suitable for impregnating thick paper with a high basis weight.

It is e.g. known from DE-OS 2005166 to prepare water-soluble etherified methylol melamines using a 2- or 3-hydric alcohol and a 1-hydric alcohol. The products serve particularly for textile equipment, as agents that provide grip when equipping materials made of synthetic fibers and as an additive product for adhesives.

It is also known from DE-AS 1932528 and DE-OS 3430248 to use aqueous or aqueous-alkaline solutions of melamine-formaldehyde pre-condensates for the impregnation of paper webs, which after drying are processed into layered press materials or used for the surface treatment of wood materials. The paper webs are not very thick, mostly approx. 0.1 mm thick, and can be further processed individually or by overlapping several layers. The quality of the impregnation resins, impregnation methods and further processing methods are numerous and have already reached a high degree of perfection.

The impregnation process is more difficult when thicker papers are used, e.g. such with thicknesses of 0.1 to 0.7 mm, as substrate. It is easy to realize that opposite requirements, such as thorough penetration and impregnation speed, are more difficult to fulfill with thicker papers and that special precautions are necessary to achieve split-free and elastic products. Therefore, organic solvents, e.g. methanol, ethanol or isopropanol, to achieve good and rapid penetration of the resin into the paper. The combined use of organic solvents has, among other things, the disadvantages are that, when dried, they burden the exhaust air and the environment and, in addition, constitute a loss of raw materials.

It was the basis of the present invention to provide means for impregnating cellulose-containing fibrous materials, which are also suitable for impregnating thicker carriers, especially thicker papers, also without the co-use of organic solvents such as alcohols, and still provide a good penetration of the impregnation resin in the paper at normal throughput speeds, causes little swelling of the paper with good adhesion to support materials, further a splitting resistance and sufficient elasticity of the impregnated paper with a good flatness as well as that it exhibits good varnish retention and sufficient durability for the impregnation solution.

It has now been found that an agent for impregnating cellulose-containing fiber materials based on an aqueous solution of a melamine-formaldehyde condensate which has been at least partially etherified with alcohol, to a large extent fulfills the stated task, when the agent is prepared by reacting

A - a solution which takes up at most 50% by weight, calculated on the amount of resin, of water without forming two phases, of a by reaction of its alkaline aqueous solution with methanol etherified melamine-formaldehyde condensate, where 4.5-6 hydrogen atoms in

the melamine is substituted with N-methoxymethyl groups, med

B - at least one mole, per moles of the condensate, of a water-soluble

2- or 3-hydric alcohol at 50-100°C at acidic pH until an unlimited water-miscible state occurs in the solution, in which the resin forms a clear solution with water in any mixing ratio.

The starting solution of the etherified melamine-formaldehyde condensate (A) can be prepared in a manner known per se, e.g. by condensation of one mole of melamine with at least 4.5 moles, preferred

5 to 10 mol of formaldehyde in alkaline, aqueous solution and subsequent etherification of the methylol groups in the condensate one or more times with an added excess of water-soluble, monovalent, aliphatic alcohol, especially methanol or ethanol, e.g. 10 moles of methanol per moles of melamine, in an acidic environment, e.g. at a pH value of 4 to 6.5. After partial distillation of the alcohol-water mixture, a water-incompatible product or a product that is only partially water-compatible, i.e. which takes up a maximum of 50% by weight of water calculated on the amount of resin, without forming two phases.

Of the etherified N-methylol melamines used in the production of the impregnating agent, hexakismethoxymethylmelamine has proven suitable.

The viscosity of the aqueous solutions of the etherified starting condensate (A) is advantageously 2500 to 7000 mPa.s, especially 3000 to 5000 mPa.s, measured in an approx. 95% solution (95% non-volatile components) according to DIN 53 018 (rotational viscometer).

The reaction of the etherified condensate solution with 2- and/or 3-valent alcohol (B) takes place while heating the solution to 50 to 100°C and preferably 70 to 95°C at an acidic pH value in the solution, preferably at a pH value of 3.0 to 6.5 and especially 3.5 to 5, whereby this is set by adding an inorganic acid such as hydrochloric, sulfuric or phosphoric acid or preferably an organic acid, especially a dicarboxylic acid such as maleic acid and preferably oxalic acid. Finally, a temperature must be reached at which the lower monoalcohol evaporates.

As water-soluble 2- or 3-hydric alcohols (B), water-soluble alcohols with 2 to 6 C atoms and preferably ethylene glycol, di- and triethylene glycol as well as glycerol are suitable for the reaction. But other water-soluble glycols are also suitable, e.g. polyethylene glycols, or triols, which during the reaction transfer the resin solution to an unlimited water-miscible state. The quantity of polyalcohol (B) for the turnover is at least 1 mol per moles of melamine in impregnation resin (A) in the solution to be reacted and advantageously 1 to 5 moles per moles of melamine. The turnover is advantageously carried out while stirring and for as long as the water incompatibility or the only limited water compatibility that exists to begin with has changed to an unlimited water miscibility resp. full water dilutability, which generally occurs in approx. 2 to 5 hours.

The unlimited water-miscible state of the impregnation resin solution is thus achieved at the time the resin forms a clear solution with water in any mixing ratio.

After achieving the unlimited water dilutability, the impregnation resin solution is cooled. The resulting impregnation resin solution shows after the reaction a clearly lowered viscosity compared to the starting solution, which is often only 1/4 to 2/3 of the viscosity value in the starting solution (in mPa.s).

The impregnation resin solutions according to the invention contain no added organic solvents such as monoalcohols, and therefore pose no burden on the environment during use.

For many applications, the agent can advantageously be added to wetting agents, mostly in an amount below 1% by weight, e.g. fatty alcohol ethoxylate or alkylphenyl ethoxylate or mixtures thereof.

Advantageously, the agent in the form of the impregnation solution to be used further contains an added, acid-acting curing agent of a known type, such as acids, ammonia or amine salts which are decomposable in the heat, of which p-toluenesulfonic acid and its amine salts, and preferably mixtures of morpholine and p-toluenesulfonic acid have proved particularly advantageous.

Advantageous agents in the form of impregnation solutions contain 0-100 parts by weight of water, 3-6 parts by weight of p-toluenesulfonic acid (50%) and 0.2 to 0.6 parts by weight of wetting agent per 100 parts by weight of the impregnation resin (approx. 80 by weight).

To increase durability, the funds or the impregnating agent solutions are also added up to approx. 2, preferably 0.1 to 1% by weight of magnesium chloride.

Especially for improving the paint's holding power and elasticity, it is also often advantageous to add resp. mixing the agents according to the invention with an aqueous dispersion of a polymer or copolymer of an acrylic or methacrylic acid ester, preferably in amounts of up to approx. 10% by weight of the agent, e.g. a copolymer based on N-butyl acrylate, acrylonitrile, methacrylic acid and methacrylamide.

When using the agents according to the invention, the impregnation solution advantageously exhibits a pH value of from 3 to 6.

The impregnation resin solutions according to the invention provide an advantageous impregnation of even thicker paper without the otherwise usual addition of alcohols such as isopropanol or of other organic solvents with good, uniformly maintained quality of the produced edge films. Furniture edges produced in this way are elastic, have little paper swelling and are also split-resistant. During the processing of the impregnation agent according to the invention, there is no environmental impact from organic solvents, and the amount of formaldehyde released is also reduced. The user can thus avoid exhaust gas cleaning and afterburning facilities.

Further advantages of the invention can be seen from the following examples and comparative tests which describe the invention. The parts and percentages stated therein are calculated by weight unless otherwise stated.

Example 1

In a 2-liter wooden-necked flask with stirrer, thermometer and reflux condenser, 400 g (1.14 mol calculated for melamine) of technical hexakismethoxymethylmelamine with a molar ratio of melamine:formaldehyde methoxyl groups = 1:5.7:5.2 = (viscosity: 4000 mPa.s) added 150 g (1.41 mol) diethylene glycol. After adding 0.2 g of oxalic acid, the mixture was heated to 90°C. A pH value of 4.2 was thereby set.

The reaction mixture was stirred at 90°C for so long that the water impurity at the start had changed to complete water dilutability. To achieve this, 1-2 hours were needed. After achieving the water dilutability, the reaction mixture was cooled to room temperature.

550 g of an impregnation resin solution according to the invention were obtained with the following properties: Non-volatile fractions (2 g sample, dried for 2 hours at 125°C) : 82.1%, viscosity: 740 mPa.s, water dilutability: 1: infinite .

Example 2

In a 2-liter wooden-necked flask with stirrer, thermometer and reflux condenser, 400 g (1.14 mol calculated on melamine) of technical hexakismethoxymethylmelamine with a molar ratio of melamine:formaldehyde:methoxyl groups = 1:5.7:5.2 (viscosity: 4,320 mPa.s) added 150 g (1.23 mol) triethylene glycol and heated to 90°C after addition of 0.2 g oxalic acid.

The reaction mixture was stirred at 90°C for such a long time that the water impurity from the start had changed to complete water dilutability. 4 hours were needed for this. After achieving water dilutability, the reaction mixture was cooled to room temperature.

550 g of an impregnation resin solution according to the invention were obtained with the following properties: Non-volatile components (2 g sample, dried for 2 hours at 125°C) : 82.2%, viscosity:

210 mPa.s, water dilutability: 1: infinite.

Example 3

In a 2-liter wooden-necked flask with stirrer, thermometer and reflux condenser, 400 g (1.14 mol calculated for melamine) of technical hexakismethoxymethylmelamine with a molar ratio of melamine: formaldehyde: methoxyl groups = 1 : 5.7 : 5.2 (viscosity: 4500 mPa.s) added 150 g (1.65 mol) glycerol and heated to 90°C after addition of 0.2 g oxalic acid.

The mixture was stirred at 90°C for such a long time that the initial water incompatibility had changed to complete water dilutability. 4 hours were needed for this. After achieving the water dilutability, the reaction mixture was cooled to room temperature.

550 g of an impregnation resin solution according to the invention were obtained with the following properties: Non-volatile fractions (2 g sample, dried for 2 hours at 125°C) : 75.2%, viscosity: 250 mPa.s, water dilutability: 1: infinite .

Application example 1

A mixture of 100 parts of the resin solution prepared according to example 2, 3 parts of a mixture of morpholine and p-toluenesulfonic acid (weight ratio 1:1) and 0.4 parts of a wetting agent solution (Kauropal<®> 930/931 in a mixture ratio of 2:1) had a pH value of 3.8. The gelation time was 5 min. The impregnation viscosity was 13 seconds run time in a 4 mm DIN cup at 25°C. The durability of the impregnation solution was at least 24 hours.

With the above-mentioned mixture, 150-280 g/m<2> heavy edge paper was impregnated. The paper is fed with resin to approx. 50%, i.e. is brought to a final weight of 225 and 420 g/m<2> respectively. The VC value (residual moisture) is thereby set to 2-4%.

The edges obtained have a thickness swelling in water of 13 and can be bent over a mandrel to approx. 6 mm without breakage.

Application examples 2 and 3 and comparison! causes 1 and 2

For comparison, for the impregnation of paper, impregnating agents with resin according to example 1 (application example 2 as well as application example 3 (with the addition of a commercially available acrylic dispersion)) were used, and without the addition of organic solvents, as well as a commercially available impregnating agent, which was prepared once during the addition of organic solvent (comparison experiment 1), once without the addition of organic solvent (comparison experiment 2). The impregnating agents and the properties of the impregnated papers appear in the following table.

The penetration time was determined as the time from application of a black paper web (120 g/m<2>, 40 mm diameter) to the impregnating solution (impregnating agent) until complete wetting. The paper swelling was determined in %, the thickness swelling being measured with a micrometer screw after 24 hours of storage in water. The elasticity was determined by bending the dried film around mandrels of decreasing diameter until the film broke.

The splitting strength was determined in a manual cutting test on the impregnated foils. Fracture perpendicular to the surface: good, fracture parallel to the surface: poor.

The table shows that the impregnation agents according to the invention exhibit satisfactory properties. If an acrylate dispersion is added (application example 3), a particularly good so-called lacquer holding capacity is achieved, i.e. that a coat of varnish on the foil does not sink in.

Claims (8)

1. Agent for the impregnation of cellulose-containing fibrous materials based on an aqueous solution of a melamine-formaldehyde condensate that is at least partially etherified with alcohol, characterized in that the agent is produced by reacting A - a solution that occupies at most 50% by weight, calculated on resin the amount, of water without forming two phases, of a melamine-formaldehyde condensate etherified by reaction of its alkaline, aqueous solution with methanol, where 4.5-6 hydrogen atoms in the melamine are substituted with N-methoxymethyl groups, with B - at least one moles, per moles of the condensate, of a water-soluble 2- or 3-hydric alcohol at 50-100°C at acidic pH until an unlimited water-miscible state occurs in the solution, in which the resin forms a clear solution with water in any mixing ratio. 2. Means according to claim 1, characterized in that the solution of the melamine-formaldehyde condensate is prepared by reaction with ethylene glycol, diethylene glycol, triethylene glycol or glycerol as 2- or 3-hydric alcohols. 3. Means according to claim 1 or 2, characterized in that the solution upon reaction with the water-soluble 2- or 3-hydric alcohol exhibits an acidic pH value of 3.0 to 6.5. 4. Agent according to one of claims 1 to 3, characterized in that it contains an added wetting agent. 5. Agent according to one of claims 1 to 4, characterized in that it contains an acidic-acting aminoplast curing agent. 6. Means according to claim 5, characterized in that it contains as curing agent p-toluenesulfonic acid or a mixture thereof with an amine, especially morpholine. 7. Agent according to one of claims 1 to 6, characterized in that it contains an aqueous dispersion of a polymer or copolymer of an acrylic or methacrylic acid ester. 8. Agent according to one of claims 1 to 7, characterized in that it contains magnesium chloride in an amount of up to 2, preferably 0.1 to 1.0% by weight.