CS229417B1 - A method for producing urea-formaldehyde condensates releasing a very small amount of formaldehyde - Google Patents

Abstract

The subject of the invention is a method for producing urea-formaldehyde condensates which release a very small amount of formaldehyde when applied in the wood and furniture industry. Products glued with these condensates release 10 mg of formaldehyde/100 g abs. of dry particleboard according to the internationally valid FESYP methodology, which is based on the extraction of formaldehyde from the product with toluene and its subsequent determination according to known methods. The production method is based on the addition of formaldehyde and urea in dilute solutions at a basic molar ratio of urea and formaldehyde of 1:1.6 to 1:2.2. This pre-condensate is subjected to condensation in a pressure continuous device at pH 6.2 to the required degree, which is proportional to the viscosity of the product. In the second stage, the product is modified by continuous addition of urea and adjustment of the pH with alkali metal hydroxides to a value of 7 to 8.5. The amount of urea dosed is such that the resulting molar ratio of urea to formaldehyde is 1:1.1 to 1:1.6. This adjustment takes place at a temperature of 30 to 90 °C and a pressure of 2 to 20 kPa. The resulting product achieves very good reactivity in tests with ammonium chloride and releases a small amount of formaldehyde. Products glued with this product meet the requirements of hygiene authorities for use in the construction of residential buildings and similar equipment.

Description

229417 2

The present invention provides a process for the production of urea-formaldehyde nutrients which, when applied as adhesives in wood and non-wood industries, releases only a very small amount of formaldehyde.

According to current processes, urea-formaldehyde adhesives are produced in the presence of inorganic or organic acids at a base molar ratio of urea to formaldehyde of 1: 1.8 to 1: 2. The product is further treated with urea addition and a final 1: 1.2 to 1: 1.8 ratio. The process may be one- or multi-stage, wherein the condensation takes place at temperatures up to 100 ° C and at atmospheric pressure and the treatment of the adhesive called modification is carried out at temperatures up to 70 ° C under reduced pressure.

The process can be either discontinuous or continuous. These processes are protected by patents in a relatively large amount, e.g., NSR Pat. 2207921, 2243857, Jap. pat. 74-18925.Niektoré čs. patents and AO e.g. 206,094, AO 209 101 and A0 206 068 protect procedures that operate under quite different conditions. The condensation is carried out at a temperature of 102 to 150 ° C and a pressure of 0.002 to 0.5 MPa continuously or discontinuously at a basic molar ratio of urea and formaldehyde of 1: 1.5 to 1: 2.2 and further treated with subsequent addition of urea at temperatures up to 60 ° C and under reduced pressure to a final molar ratio of urea to formaldehyde of 1: 1.1 to 1: 1.85. The process may be performed either single or multi-step.

Methods of producing urea-formaldehyde adhesives protected by said MS. The author's certificates have provided the product with good physical-mechanical properties when applied as wood-based adhesives. According to the internationally valid FESYP method, their properties are classified in group E-2, ie that chipboard glued with these adhesives releases up to 30 mg of formaldehyde per 100 g of absolutely dry chipboard after their extraction with toluene composites of the above method. . I consider the increasing demands for chipboard and the environment to be also high. Adhesive is required which when applied. for particle board, I release at most 10 mg of formaldehyde per 100 g of particleboard, i.e. that classed into class E-1, it would be possible for UF-bonded products to approach this value as much as possible.

It is an object of the present invention to provide a continuous process for the production of urea-formaldehyde resins in dilute solutions.

The urea-formaldehyde precondensate is prepared in a separate stirred apparatus from 20 to 36 wt. preferably 30 wt. and solid urea, at a urea / formaldehyde ratio of 1: 1.6 to 1: 2.2, preferably 1: 1.95. The pH of the precondensate is treated with alkali metal, alkaline earth metal, ammonia and alkaline-reactive organic hydroxides. The precondensate is first condensed in a flow device at a temperature of 102 to 150 ° C and a pressure of 0.002 to 0.5 MPa to a condensation step which corresponds to a viscosity of 20 to 100 mPa.s, preferably 50 to 60 mPa.s.

The condensate thus produced is condensed in the second portion of the flow device at a temperature of 30 to 90 ° C and a pressure of 2 to 20 kPa, and evaporation of the urea-formaldehyde final molar ratio of 1: 1.1 to 1: 1.6 is advantageously effected with the addition of urea solution1: 1.15 and with the addition of alkali to adjust the pH of the resin solution to 7 to 8.5.

The dry weight of the resin solution is 45-60% by weight. preferably 55 wt.

According to the present invention, a resin suitable as an adhesive for the wood industry is obtained, which upon application releases 10 mg of formaldehyde per 100 g of particleboard according to the FESYP method. Reactivity (gelling time) with ammonium chloride according to a generally known methodology (15% ammonium chloride) is up to 65 s at 100 ° C. This high reactivity makes it possible to reduce pressing times, possibly to reduce the molding temperatures of chipboard manufacturers, resulting in improved economics and increased equipment and energy savings.

Claims (1)

EXAMPLE 22.8 nP of an aqueous solution of formaldehyde having a concentration of 30% by weight is metered into a stirred apparatus with the possibility of heating or cooling with a shake, 15 l of 10% sodium hydroxide are added and the pH is adjusted to 5.2-5. 4, and 400 kg of solid urea are added. The pH of the solution after the addition of urea is 6.3. After dissolution, the pre-condensate temperature is 15 ° C. This precondensate with a urea-formaldehyde molar ratio of 1: 1.95 is metered in at 6 µm to the first reaction stage where condensation takes place at 120 ° C and 0.3 MPa. The product of the first reaction stage with a viscosity of 60 mPa.s, at 50 ° C and 10 kPa pressure, is continuously withdrawn into the second reaction stage. there is no need for condensation and modification by the addition of 2 np / h of a 50% urea solution and 18 of 110% sodium hydroxide. From the second reaction step, the product is continuously withdrawn and has a solids content of 50 to 55% by weight. and a viscosity of 400 mPa.s after cooling to 20 ° C. The condensation product thus prepared releases 10 mg of formaldehyde when applied in the production of chipboard and load of 100 kg / np chips, with 0.1 µg of formaldehyde per g of cured adhesive, according to the valid state-of-the-art methodology. The reactivity of the produced condensate is 53 s / 100 ° C, BEFORE THE INVENTION OF THE INVENTION The method for producing urea-formaldehyde condensates releasing very small amounts of formaldehyde used in the wood and furniture industry, characterized in that the urea and formaldehyde are condensed together in dilute 20 to 20% formaldehyde solutions. 36% by weight, preferably 30% by weight, at a basic molar ratio of urea to formaldehyde of 1: 1.6 to 1: 2.2, wherein the pH of the solution is 3.0 to 6.9, temperature 20 to 50 ° C, this precondensate is then treated in the first reaction stage at a temperature of 102 to 150 ° C and a pressure of 0.01 to 0.5 MPa up to a viscosity of 20 to 100 mPa · s / 20 ° C, preferably up to a viscosity of 50 to 70 mPa · s / 20 ° C, the condensate is then further processed in a second reaction step at a temperature of 30 to 90 ° C and a pressure of 2 to 20 kPa to a dry matter content of 45 to 65% by weight of the simultaneous evaporation of the product and with the addition of urea so as to result in The urea mole-to-formaldehyde mole ratio was 1: 1.1 to 1: 1.6, with the pH of this solution being adjusted to 7 to 8.5 with alkali metal, alkaline earth, or ammonia hydroxides.