CS206094B1 - Method of making the high reactive ureaformaldehyde condensates releasing small quantities of the formaldehyde - Google Patents

Description

The invention provides a process for the production of reactive urea-formaldehyde nutrients which, when used as adhesives in the wood and furniture industry, release only a small amount of formaldehyde.

According to the prior art, urea-formaldehyde adhesives are prepared in the presence of organic or inorganic acids and the basic molar ratio of urea to formaldehyde is 11: 8 to 1: 2.2. The product is further adjusted by adding urea to a molar ratio of urea: formaldehyde of 1: 1.3 to 1: 1.8. The free formaldehyde in the base resin is 0.5 to 8% by weight. (NSR Pat. 2,207,921, 2,243,857, Jap. Pat. 74-18,925). It is also known from the patent literature to add other formaldehyde-reducing substances in the resin, such as: ketones (Jap. Pat. 74-38 511), vegetable oils (Jap. Pat. 70-16 592) and others.

For practical use, however, it is very important that the resulting resin, which is used as a binder in the wood and furniture industry, releases only a minimum amount of formaldehyde when applied in order to exhibit high reactivity and good shelf life.

The formaldehyde released is generally detected from an ammonium chloride-cured glue (15% aqueous solution, 1% ammonium chloride per glue mass), which, after milling 206 094, is purged with dry hot air. The formaldehyde is absorbed in cold water and determined by the titration method. (State Examination Methodology No. 216 at SDVU Bratislava).

The urea-formaldehyde resins produced so far release the resins. in tests 4-6 mg formaldehyde / 1 g cured adhesive. The latest resins specially modified (Jap. Pat. 74-18925) below 1 mg formaldehyde / 1 g cured adhesive.

The prior art processes for the production of urea-formaldehyde resins were discontinuous and the free formaldehyde content was reduced by the addition of a urea solution, according to a relatively complicated dispenser scheme, generally in two and more stages. The adhesives produced were not characterized by high reactivity and the actual finishing was difficult to handle and to consume energy. At the same time, the reactivity of the adhesive is a decisive parameter for the production capacity of wood-chip boards in the wood industry. The reactivity of discontinuously produced adhesives was not less than 85 seconds at 100 ° C with 15% ammonium chloride in an amount of 1% by weight of the adhesive according to the above technology.

SUMMARY OF THE INVENTION The present invention relates to a process for the production of urea-formaldehyde resins at a temperature of 102 to 150 ° C and a pressure of 0.002 to 0.5 MPa in a continuous flow device in the presence of 0.01 to 0.5% by weight of organic or inorganic acids. the ratio of urea to formaldehyde feedstock is 1: 1.8 to 1: 2.2, preferably 1: 1.95. The urea-formaldehyde precondensate is prepared beforehand in a separate agitator, and at a pH of 5-8, the organic or anaerganic acid is pumped into the pressure reactor where the first condensation stage takes place.

In the second reaction step, further condensation of the added urea takes place, which is added in the form of a solid or aqueous solution at a pressure of 2 to 20 kPa and a temperature of 30 to 90 ° C, a pH of 7 to 9, preferably 8.2. 50 to 75% by weight. The components are metered continuously into the second stage, the pH being adjusted by the addition of alkali metal hydroxides, e.g. sodium hydroxide. The total amount of urea dosed is such that the resulting molar ratio of urea to formaldehyde is in the range of 1: 1.1 to 1: 1.29.

The object of the present invention is obtained by a simple resin technology suitable as an adhesive for the wood and furniture industry which releases below 1 mg of formaldehyde / lg of cured adhesive, its reactivity (gelling time) at 100 ° C with 15% ammonium chloride (1%) per glue mass) is below 70 seconds. This increased reactivity makes it possible to shorten the pressing times or to reduce the molding temperatures of the manufacturers of particle board (DTD) and furniture, thereby enabling the production of DTD and / or PCBs to be increased. energy saving.

The production of the animal according to the invention utilizes an exothermic reaction of urea and formaldehyde, making the production less energy intensive compared to the known processes, and in the technology the solid urea is metered into the aqueous formaldehyde solution.

206 094

Sulfur saves the energy needed to evaporate water, which is more than 20% of the total energy requirement.

Example

Dispense into a stirred tank equipped with a cooling jacket

20.08% aqueous solution of formaldehyde at a concentration of 37% by weight, add 20 l of 10% sodium hydroxide to adjust the pH, which after treatment is in the range of 7 to 8.5, and add 8 400 kg of solid urea. After dissolution, 10% formic acid is added in an amount such that the pH is in the range 5-7.9. The precondensate thus prepared (molar ratio of urea to formaldehyde of 1: 1.95) is metered in at 6 nm / h to the first reaction stage, where a condensation reaction takes place at a temperature of 125 ° C and a pressure of 0.3 MPa. The product of the first reaction stage with a viscosity of 20 to 80 mPas is continuously withdrawn to the second reaction stage, where further condensation takes place by adding 1.9 nP / h of 50% urea solution and 18 L of 10% sodium hydroxide solution at 55 ° C. and a pressure of 10.5 kPa, from the second reaction step, the product is continuously withdrawn on dry matter, from 67 to 1% by weight, a viscosity of 700 cps, a free formaldehyde content of 0.29% by weight, the reactivity of 62 ^to DWS / Lo DEG C. and cooled to 20 ° 0th After curing, the product releases 0.45 mg of formaldehyde / g of cured adhesive.

Claims (3)

OBJECT OF THE INVENTION A process for the production of highly reactive urea-formaldehyde condensates releasing a small amount of formaldehyde for use in the wood and furniture industry, characterized in that urea and formaldehyde are continuously condensed in the first reaction stage in a molar ratio of 1: 1.8 to 1: 2.2 at temperature 100 to 150 ° C, a pressure of 0.002 to 0.5 MPa in the presence of 0.01 to 0.5% by weight of organic or inorganic acids and in the second stage condensed and concentrated at a pressure of 2 to 20 kPa, a temperature of 30 to 90 ° C to a dry matter content of 50 to 75% by weight with continuous addition of urea so that the resulting molar ratio of urea to formaldehyde is 1: 1.1 to 1: 1.29 and with the addition of an alkali metal hydroxide solution, preferably sodium hydroxide at pH 7 to 9. 2. The method according to claim 1, characterized in that a precondensate previously prepared in a separate mixing apparatus by dissolving the solid urea in an aqueous formaldehyde solution is used. 3. The method of claim 1, wherein a solution of urea previously prepared by dissolving solid urea in water is used.