SE457966B - IMPREGNATED PAPER CONTAINING A PRE-CONDENSATED BETWEEN PHENOL AND FORMAL HYDRADE AND PROCEDURES FOR ITS PREPARATION - Google Patents

Description

_._,, »of 457 966 10. 15. 20. 25. 30. 35. f 2 the stability is correspondingly shortened. The invention also has for its object to enable an increase in the curing speed without the properties of the impregnated paper otherwise deteriorating.

These purposes are achieved in the manner set out in the patent claims.

According to the invention, a carbonate of the type described in more detail below is used as a hardener for the phenolic resin in the impregnated paper. The carbonate additive has been found to give a considerable shortening of the pressing times during lamination without the storage stability being significantly impaired. _ Nor are the properties of the paper adversely affected, but laminate is obtained with the same quality as when no carbonate additive was used. The advantages of the additive are best utilized if it is made directly to the impregnation solution and if the conditions during drying are chosen so that carbon dioxide bubbles are released in the film, since a film with high formability is then obtained.

When applying the invention, normal phenolic resins or phenol-modified resins can be used for paper impregnation, for example resins with a formaldehyde / phenol molar ratio of about 1.0 to 3.0.

The carbonate is suitably added to the impregnation solution containing the resin. This can be done by bubbling gaseous carbon dioxide or adding a substance that releases carbon dioxide when heated. Solid carbonates can also be added directly to the impregnation solution or added in the form of solutions. Particularly preferred are carbonate additives which, in connection with drying, have the ability to give rise to carbon dioxide evolution, either by decomposition of the carbonate alone or by reaction with another substance. Soluble carbonates are preferred. Hydrocarbonates, such as sodium bicarbonate, have proven to be particularly useful. Normal additives such as release agents, waxes, wetting agents, etc. can also be included.

After impregnation of the paper web, it can be dried in the usual way by heating in air to temperatures between about 150 and 200 ° C. With the additive according to the invention, the drying time can generally be shortened by the resin curing faster to the desired degree of pre-curing. The conditions 10. 15. 20. 25. 457 966 -___ s during drying are preferably chosen so that a carbon dioxide evolution from the carbonate is obtained, which can be determined by the film then becoming more opaque than otherwise. In addition to the choice of carbonate, the pH of the impregnation solution and the drying temperature. the temperature is used to influence gas evolution.

After possible intermediate storage in the usual way, the dried paper can be used in normal applications. Lamination against other materials and / or of several paper layers with each other normally takes place in presses at pressures between 5 and 20 kp / cm2 and temperatures between 90 and 180 ° C. As mentioned, the required time for final curing of the resin can be reduced by means of the invention, often to about half the time.

The press times can, for example, be between 20 seconds and 15 minutes depending on conditions.

A preferred application for the paper according to the invention is as a surface processing film on wood-based materials and especially as a molded film.

Example 1% sodium bicarbonate is charged to a conventional phenolic resin for paper impregnation, which is pre-adjusted to pH 9.5. In other respects, dyes, wetting agents and release agents are used in the usual way. The resin is impregnated on a H0 g / m2 absorbent kraft paper, dried in the drying zones of the impregnating machine at temperatures between 16006 and 18000 to a storage stable film with a total weight of 120 g / m2 and a residual moisture of 5-3 1- This_film was then pressed on a bed - hot plywood in hot press at a press temperature of 13500 and a pressure of lü00-1800 kPa. The press time was only U min. against normally about 7 min.

Claims (8)

10. 15. 20. 25. 30. 35. 457 966 * in Patent Claims 1. l. Impregnated paper containing a precondensate between phenol and formaldehyde, characterized in that the resin contains bubbles of free carbon dioxide. Impregnated paper according to claim 1, characterized in that it comprises an addition of carbonate or carbon dioxide. c k - 3. Impregnated paper n a t thereof, that the carbonate 4. U. Impregnated paper n a t thereof, that the carbonate Impregnated paper according to claim 2, characterized in that it is a bicarbonate. according to claim 2, k ä n n e t e c k - is sodium bicarbonate. according to claim 2, characterized in that the amount of carbonate added to the resin is between 0.1 and 10% by weight. ' Impregnated paper according to claim 5, characterized in that the amount is between 0.5 and 5% by weight. Process for the preparation of impregnated paper containing a precondensate between phenol and formaldehyde, by impregnating a paper with an aqueous impregnation solution of a phenol / formaldehyde precondensate with subsequent drying and partial curing of the precondensate, characterized in that a carbonate is added to the impregnation solution and the drying is carried out under conditions which lead to the release of bubbles containing carbon dioxide in the resin. 8. A method according to claim 7, characterized in that carbonate is formed in situ in the impregnation solution by bubbling carbon dioxide gas.