CS238448B1 - Process for the production of phenol formaldehyde adhesives - Google Patents

Abstract

A method of producing phenol-formaldehyde adhesives based on the reaction of phenol and formaldehyde in a dilute aqueous solution, where alkali metal hydroxide or alkaline earth metal hydroxide is used as a catalyst. The amount of hydroxide used is divided into two, which creates conditions for good control of the chemical condensation reaction and finally helps to reduce the content of unwanted monomers by disproportionation. The molar ratio of phenol and formaldehyde ranges from 1:1.5 to 2.5, alkali metal hydroxide or alkaline earth metal hydroxide 0.42 mole per mole of phenol, after the addition and condensation, the second part of the hydroxide is added in an amount of 0.51 to 1.2:1 and the adhesive is cooled. The adhesive is intended for gluing agglomerated materials in the woodworking industry,

Description

The invention solves the preparation of a tenolic adhesive intended primarily for gluing wood-based materials, agglomerated materials such as particle board and fibreboard of emission class E-1 according to the internationally valid FESYP methodology.

The preparation conditions are chosen such that the adhesives achieve a very low content of free monomers, i. j. phenol and formaldehyde.

A phenolic adhesive for the production of agglomerated materials according to AO 197 063 is currently being produced.

The solution proposed by us differs from the above and represents novelty and greater effect.

According to the proposed process for preparing the adhesive, the reaction of phenol and formaldehyde is carried out in the presence of alkaline catalysts, preferably sodium hydroxide. The preparation itself takes place in two stages and two levels of alkali content using the disproportionation effect.

In the first step, the phenol is reacted with formaldehyde at a molar ratio of 1: 1.5-2.5 (phenol: formaldehyde) preferably 1: 1.97 in the presence of an alkali metal hydroxide and an alkaline earth hydroxide, for example sodium hydroxide. The molar ratio of sodium hydroxide to phenol is 0.1 to 0.5 preferably 0.42: 1 and the addition of water in a molar ratio to phenol 0.2: 1 to 8: 1 preferably 1.8: 1 at a temperature of 20 to 75 Preferably 55 ° C. The addition reaction lasts from 0.5 to 6 hours, optimally 2.5 hours. During this time, the phenolic alcohols are formed in the reaction mixture.

In the second step, the condensation reaction of the resulting substances takes place after the previous addition. The condensation is carried out at a temperature of 75 to 105 ° C, preferably 80 to 90 ° C, until the final viscosity of the reaction mixture measured on the Ford Cup no. 4 at 20 ° C will be from 20 to 450 seconds, preferably 45 to 60 seconds. The reaction mixture is then cooled to a temperature of 20 to 75 ° C, preferably 40 ° C, and a second portion of sodium hydroxide catalyst is added in an amount to a final molar ratio of alkali to phenol of 0.51: 1 to 1.2: 1, preferably 0, 6: 1. The addition of the second part of sodium hydroxide reduces the free formaldehyde content to the desired value due to disproportionation. After cooling to 20 ° C, a phenolic adhesive is obtained having a free monomer content below 0.01% by weight of formalin and below 0.1% by weight of phenol.

Example

1500 kg of phenol, 525 kg of water and 600 kg of NaOH in the form of a 44% aqueous solution were metered into a reactor equipped with an efficient stirrer, with the possibility of cooling or heating. The temperature in the reactor rises to about 60 ° C. Cooling is switched on and the mixture is cooled to 48-51 ° C and started to be added from a measuring cup of formalin at a rate of 30-45 l / min. i.e., all 2550 kg of formalin was dosed in 1 to 1.5 hours. The temperature during the formalin dosing should not exceed 60 ° C and is optimally maintained at 54 to 56 ° C. After the addition of formalin, the temperature of the reaction mixture is maintained at 54 to 56 ° C for 2.5 to 3 hours. Then, by turning on heating, we raise the temperature in the reactor to 85-88 ° C and condense until the viscosity of the reaction mixture reaches 55 with Ford 4/20 ° C, cool rapidly and add a second portion of sodium hydroxide t while cooling. j. 240 kg of a 44% aqueous solution. After cooling to 25 ° C, the adhesive is pumped into storage containers.

The resulting product after analysis had 0.05% by weight of formalin and 0.015% by weight of phenol. The methodology used for the determination of the monomer content complies with the requirements of the State Testing Office no. 216 at the State Wood Research Institute, Bratislava.

Claims (1)

SUBJECT Process for producing phenol-formaldehyde adhesives by the reaction of phenol and phenol-formaldehyde, characterized in that 1.5 to 2.5 moles of formaldehyde, preferably 1.97 moles, 0.1 to 0.5 moles, are added per mole of phenol with preferably 0.42 molar parts of alkali metal hydroxide or alkaline earth metal hydroxides, 0.2 to 8 molar parts, preferably 1.8 molar parts of water, the mixture is added in the first step at a temperature of 20 to 75 ° C, preferably 55 ° C for 0.5 to 6 h, preferably 2.5 h, this reaction mixture is further condensed in the second step of the invention at a temperature of 75 to 105 ° C, preferably 85 ° C, until the viscosity of the reaction mixture measured by a Ford cup no. 4 at 20 ° C reaches 20 to 400 s, preferably 45 to 60 s, and is rapidly cooled to 20 to 75 ° C, preferably 40 to 50 ° C, and a second portion of the alkali metal hydroxide or hydroxide is added of alkaline earth in an amount to a final molar ratio of alkali to phenol of 0.51 to 1.2: 1, preferably 0.8: 1, after the disproportionation and cooling to 20 to 40 ° C, the adhesive production is terminated.