DE3027203C1 - Process for the production of water-soluble binders for wood gluing - Google Patents

Description

According to this procedure, the decisive factor for weather resistance can be used The proportion of pheno / formaldehyde condensation products should be relatively large without the advantage of a reaction catalyzed with acidic hardeners, as is the case with urea resins is common to lose. The hardening process is technically more common Way, z. B. by catalytically acting weak acids or latent acids, under the action of heat to undertake.

The invention thus relates to a method for production of phenol / urea / melamine mixed condensates according to claim 1, which in particular characterized by the following steps: a) Making one with water unlimited miscible urea / formaldehyde resin (Al in a manner known per se, in the manner that initially in the alkaline medium urea with commercially available aqueous formaldehyde solution react with one another in a molar ratio of 1: 2-1: 4, preferably 1: 2.5-1: 3, then carried out the condensation in the acidic medium and then as much urea is added until a urea / formaldehyde molar ratio of 1: 1.0-1: 2.0, preferably 1: 1.3-1: 1.7 sets b) condensation of phenol and formaldehyde in resin A at 75-1000C, with a phenol / formaldehyde molar ratio of 1: 2.0-1: 3.0, preferably 1: 2.4-1: 2.7 is chosen using 0.25-0.40 moles, preferably 0.25-0.30 mol of NaOH per 1 mol of phenol and post-condensation of the urea / pheno-formaldehyde mixed condensate at 75-1000C up to a viscosity of 100-300 seconds flow time according to DIN 53211.

c) Production of a water-dilutable melamine / formaldehyde resin (B) in a melamine / formaldehyde molar ratio of 1: 1.3-1: 2.0, preferably 1: 1.4-1: 1.7, which in particular has a solids content of 55-70%.

Mixing and diluting the highly viscous urea / phenol / formaldehyde mixed condensate with the melamine resin B or a mixture of resin B with up to 60% by weight of resin A in such a way that in the mixed resin now obtained for 1 mol of urea 0.8-1.5 mol Melamine, 0.3-0.6 moles of phenol and 3.5-6.0 moles of formaldehyde are present.

Preferably elasticizing agents, such as. B.

Diethylene glycol, in amounts of 5-14%, based on the finished mixed resin, expediently by condensing into resin (A) or (B) or at the latest in the stage b added before the post-condensation.

The invention is illustrated in more detail by means of the following examples Example 1 Preparation of the urea / formaldehyde resin (A) 40.8 g of urea, 127.5 g of commercially available aqueous formaldehyde solution (40%) and 29.1 g of diethylene glycol were adjusted to a pH value of 8.5-9.0 with dilute sodium hydroxide solution and with stirring Reacted for 15 minutes at 900 ° C. Subsequently, dilute formic acid was added the pH of the reaction solution was lowered to 5.0-5.5 and then at 90 "C for 60 minutes condensed. After the reaction temperature had been lowered to 60 ° C., 19.2 g of urea were obtained added and adjusted to a pH of 8.5-9.0 with dilute sodium hydroxide solution after cooling to room temperature, the resin solution had a solids content of 50%.

Production of the melamine / formaldehyde resin (B) 126 g melamine, 120 g of commercially available aqueous formaldehyde solution (40%) and 26 g of water were diluted with Sodium hydroxide solution adjusted to a pH value of 9.0-10.0 and stirred for about 90 minutes heated at 900 C until diluted with a resin sample with 15 times the amount of water a turbidity occurred at 20O C. After cooling to room temperature, the Resin solution has a solids content of 63% and a viscosity according to DIN 53211 of 30 seconds.

94 g of phenol were added to 421 g of the urea / formaldehyde resin (A) and added 195 g of 40% strength commercially available aqueous formaldehyde solution. After heating to 900 ° C., 20.2 g of 50% strength sodium hydroxide solution were added with stirring and then the Reaction mixture at 90 "C up to a viscosity according to DIN 53211 of 100 seconds condensed 570 g of the melamine / formaldehyde resin (B) were then added and 130 ml of water were then removed from the resin solution by applying a vacuum.

The water-thinnable mixed resin thus obtained had a solids content of 63%, a viscosity of DIN 53 211 of 80 seconds and a content of free Formaldehyde of <0.5%.

Example 2 To 466 g of the urea / formaldehyde resin (A) were 94 g phenol and 195 g 40% strength commercial aqueous formaldehyde solution added. To 12.3 g of 50% sodium hydroxide solution were added to the heating to 90 ° C. while stirring the reaction mixture condenses to a viscosity according to DIN 53 211 of 230 seconds 102.5 g of urea / formaldehyde resin (A) and 509 g of melamine / Formaldehyde resin (B1 each produced according to Example 1, added by applying 184 ml of water were then removed from the resin solution by vacuum.

A water-dilutable resin solution with a solids content is obtained of 62.5%, a viscosity according to DIN 53 211 of 70 seconds and with a free Formaldehyde content of <0.5%.

Example 3 545.3 g of the urea / formaldehyde resin (A) were added 94 g of phenol and 195 g of 40% commercial aqueous formaldehyde solution to 90 ° C heated Then 12.6 g of 50% sodium hydroxide solution were added with stirring and condensed up to a viscosity according to DIN 53 211 of 250 seconds. After addition of 146.8 g of urea / formaldehyde resin (A) and 407.1 g of melamine / formaldehyde resin (B, ¢ each prepared according to Example 1, were the resin solution by applying Removed vacuum 213 g of water.

It became a water-thinnable resin solution with a solids content of 62.5%, a viscosity according to DIN 53211 of 75 seconds and a content of free Get formaldehyde of <0.5%.

Comparative Example A mixture of 421 g of the urea / formaldehyde resin (A) according to Example 1, 94 g of phenol, 195 g of 40% commercial aqueous formaldehyde solution, 20.2 g of 50% sodium hydroxide solution and 570 g of melamine / formaldehyde resin (B, according to Example 1 were condensed at 90 "C up to a viscosity according to DIN 53 211 of 40 seconds After removing 131 ml of water through Application of vacuum was made a resin solution obtained with a viscosity according to DIN 53 211 of 70 seconds, one Water dilutability of 1 0.8, a solids content of 62.5% and a content of free formaldehyde of 0.9%.

This resin solution only had a storage stability of about 2 weeks. After this time, the viscosity had increased so much that processing was impossible became.

The resins of Examples 1-3 were made under the following conditions and the comparative example in 16 mm thick chipboard (mainly softwood containing) used. The chipboard test was carried out in accordance with DIN 68 761, Sept. 1967.

Gluing: 12% resin, based on absolutely dry wood. 0.6% paraffin, based on absolutely dry wood hardener (aqueous ammonium chloride solution with 10% ammonium chloride and 8% ammonia): 9%, based on the resin solution. 170-175O pressing time: 3.5 min.

Compression pressure: 20 bar.

The chipboard test was carried out according to the known DIN regulations performed. The results are given in the table below: Example Comparative example 1 2 3 Density kg / m3 704 698 707 701 Flexural strength 21 -19 20 18 N / mm2 transverse tensile strength N / mm2 -V 20 1.01 0.98 0.96 0.85 V 100 0.49 0.45 0.43 0.32 Swelling 20OC% Q 2 2.5 2.6 2.1 2.9 Q 24 7.1 7.6 7.5 8.4 The specified key figures are mean values from approx. 40 individual samples.

Claims (3)

Claims: 1. Process for the production of water-soluble binders for gluing wood through condensation of urea, phenol and melamine with formaldehyde, which to 1 mole of urea 0.8-1.5 moles of melamine, 0.3-0.6 moles of phenol and 3.5-6.0 Moles of formaldehyde, if necessary with the use of elasticizing agents Means, d a d u r c h characterized in that a) in a known manner a water-dilutable Urea / formaldehyde resin in a molar ratio of 1: 1.0 to 1: 2.0 and produced b) in this solution phenol and formaldehyde using 0.25-0.40 mol Alkali, based on 1 mole of phenol, reacted, the phenol / urea mixed condensate thus obtained condensed up to a viscosity of 100 to 300 sec according to DIN 53 211 and c) then by one prepared in a manner known per se in a molar ratio of 1: 1.3-1: 2.0 Melamine / formaldehyde resin to a processable viscosity of 50-100 sec according to DIN 53 211 is diluted. .2. Method according to claim 1, characterized in that in addition to a melamine resin, the urea resin initially used as a diluent up to 60 wt .-% is used instead of the melamine resin. 3. The method according to claim 1 or 2, characterized in that up to 14% by weight of diethylene glycol, based on the finished binding agent, at the latest be added at the beginning of the phenol / formaldehyde condensation. The invention relates to a process for the production of in water Resins dissolved and further dilutable with water based on urea / melamine / phenol / formaldehyde mixed condensates for gluing wood, especially as a chipboard binder. It is known for the production of composite compositions from loose particles Use resin binder. For the production of chipboard e.g. provides the largest proportion of these binders represent urea / formaldehyde condensates, their Properties are sufficient for many purposes. For higher demands, e.g. B. for weatherproof chipboard, which is used, among other things, in the construction industry, the strength of the urea / formaldehyde condensates is insufficient. Properties, such as B. Boil resistance of the glue joint, were previously only hardened by alkaline Phenolic resins or amino resins with a certain proportion of phenolic resins achieved on the one hand through the connections between binder and material Side and the weather resistance of the products produced on the other hand Little is known. What is certain is that by simple mixtures of amino resins Weatherproof gluing cannot be achieved with phenolic resins. From DE-PS 8 75568 is known to condense melamine and phenol with formaldehyde and the aqueous solutions of the condensation products to form alkaline mixtures to unite. However, the resin sizes obtained according to this patent specification have no shelf life, so that they have to be subjected to spray drying. These resins have only a low water resistance and are therefore suitable for Manufacture of weatherproof chipboard not suitable. According to DE-AS 15 95 817, mixed condensates are formed by joint condensation a urea / formaldehyde precondensate with phenol, formaldehyde and optionally produced additional urea in the presence of a basic catalyst. These resins contain high levels of formaldehyde and are used as wood binders not suitable. According to DE-PS 20 20481, formaldehyde mixed condensates are made from melamine, Urea and phenol produced by first being known per se Way from melamine and / or urea and formaldehyde produces a condensate solution and the solution at a pH of 7.5-10 and at 45-100 C with little phenol as well optionally formaldehyde and optionally melamine-formaldehyde precondensates implements. These mixed condensates also do not yet satisfy all requirements for weatherproof wood binding agent, especially because of its low water thinnability of the resin solutions, because of the not optimal boiling resistance of the hardened resins and because of the caused by the relatively high content of urea resins high formaldehyde release from the finished chipboard. The water dilutability of condensation products with formaldehyde is inversely proportional to the degree of condensation, i.e. i.e., a high degree of condensation due to a low water dilutability. In addition, the viscosity of the resin solutions increases as the degree of condensation increases at. A high degree of cohesion always has a beneficial effect on the quality of the glue of the resins. The aim is to achieve the highest possible degree of condensation set a still acceptable water thinnability and viscosity. In essence, the water dilutability depends on the condensation the amine components influenced, so that a common condensation of all partners is inevitably determined by the decreasing water dilutability of the amine resins and the reaction must be terminated before z. B. the phenolic resin component has reached an effective high degree of condensation. It has now been found that a high degree of condensation is established can be if the reaction of phenol and formaldehyde initially in a still water-dilutable urea precondensate solution takes place in an alkaline medium. in the In contrast to the prior art, this process enables the phenol / formaldehyde reaction optimally, whereby the resin solutions retain their good water-thinnability. The highly viscous resins obtained in this way are then diluted with a melamine / formaldehyde precondensate.