CS197063B1 - Process for the preparation of a phenol-formaldehyde resin of the resole type - Google Patents

Abstract

The invention relates to the preparation of a phenol-formaldehyde resin of the resole type, e.g. for gluing chipboard or plywood with high water resistance without pre-drying the applied resin, by a multi-stage reaction of phenol with formaldehyde in an alkaline environment.

Description

The present invention relates to the preparation of a phenol-formaldehyde resin of the resol type, for example for gluing particle board or plywood with high water resistance without pre-drying the deposited resin, via a multi-stage reaction of phenol with formaldehyde in an alkaline environment.

The resin prepared according to the invention has a minimum content of free phenol and formaldehyde and has a high reactivity. It is unlimited miscible with water.

For these properties, the resin according to the invention has advantageous use, for example, as a binder for the production of agglomerated wood-based materials, in particular for the manufacture of water-resistant plywood.

The disadvantages of commonly produced binders for these purposes are their low reactivity, considerable penetration into wood mass, high content of free / components (phenol, formaldehyde) detrimental to the working and environment, as well as short binder life. These drawbacks are largely eliminated by the resin of the invention. Meets the requirement of universal use as binders, eg for the production of plywood, fibreboard and particle board and the like, without

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197 063 demanding modifications to existing production facilities. The increased reactivity of the resin makes it possible to reduce the pressing temperatures up to 120 ° C while increasing the capacity of the production lines by 20%. The low penetration rate of the resin into the wood allows to reduce the specific consumption of resin in the seam joint by 40 g / m. An important feature of the proposed resin is a significant improvement in sanitary conditions. The emissions of pollutants during processing are minimized below the permissible limits, they are practically zero from finished products. The advantage of the proposed resin is its 3x longer lifetime compared to existing known types of phenol-formaldehyde resins for this purpose.

The preparation of the resin consists in reacting the phenol with formaldehyde in the presence of an alkali such as sodium hydroxide. The reaction proceeds in several stages. These reaction steps are not temperature and temperature controlled, respectively, in comparison with the known and described processes. the reaction time or viscosity of the end product, such as disclosed in patents dealing with the preparation of resol type phenol-formaldehyde resins (e.g. USSR 408 954, USSR 389 113, USSR 118 126, USSR 101 927, US 2,579,329, etc.). They are controlled so as to produce the desired substances in the reaction mixture so that the preparation of the phenol-formaldehyde resin according to the invention is not practically limited by the reaction temperature and reaction time and the viscosity of the product, but by the type of substances formed in the reaction mixture and their amounts. The type of substances and their amounts can be determined by gel chromatography, which separates the individual substances in the reaction mixture and determines their exact concentrations.

The first stage of the reaction is characterized mainly by the addition reaction of phenol with formaldehyde, where polycondensation reactions are undesirable and it is necessary to guide the reaction mechanism in such a way that the polycondensation reactions are suppressed as much as possible. In the first stage of the reaction, the free phenol reacts with formaldehyde to form predominantly phenol-alcohols. 1.5 to 2.8 moles of formaldehyde and 1.3 to 1.6 moles of hydroxide are metered in per 1 mol of phenol and water is metered in an amount corresponding to the desired viscosity of the mixture. The mixture is heated to 40 - 65 ° C, preferably to 55 - 57 ° C and maintained at this temperature until a reaction mixture of at most 5% by weight of phenol, at least 36% by weight of phenolalcohols and at most 10% by weight of condensation forms. products.

The second stage of the reaction is characterized by the condensation reaction of the substances formed in the reaction mixture and is conducted under conditions such that, in the final stage, the products of the condensation condensate are formed and disappeared, respectively. to a minimum, the substances formed in the first step of the reaction. The mixture is heated to a temperature of 70 ° C until boiling, in which the mixture condenses to a final state, characterized in that the free phenol content falls below 0.5% by weight, the phenol-alcohol content is less than 7.5% by weight, the content of condensation products constitutes at least 39% by weight. Upon reaching this state, the mixture is cooled and adjusted to the desired viscosity.

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Example:

200 g of phenol, 55 g of sodium hydroxide and 168 g of water were metered into the solution. 367 g of 37% formaldehyde were added to the mixture at 20-40 ° C. The mixture was heated to 54-57 ° C and maintained at this temperature until the phenol content was reduced to 1.8% by weight, the phenolalcohols were formed at 39.7% by weight, and the content of condensation products was 4.5% % by weight. Then the temperature was raised to 85-90 ° C and the mixture was maintained at that temperature until the phenol content dropped to 0.17% by weight, the phenol alcohol content dropped to 5.00% by weight, the condensation product content increased to 40.33% % by weight. The mixture was then cooled to room temperature.

The resulting product produced by the procedure of Example 1. had the following basic characteristics:

product dry matter (2 hours at 150 ° C) free phenol content (gas chromatograph) free formaldehyde content (potentiometrically) sodium hydroxide content

Viscosity at 20 ° C

Solubility in water

42.3% by weight 0.17% by weight 0.003% by weight 7.00% by weight

145 mPa. with unlimited

The composition of the reaction mixture is monitored by gel chromatography on a pre-calibrated system. The frequency of sampling and the number thereof cannot be accurately determined, since the rate of reaction in both steps depends on the molar ratio of phenol to formaldehyde used, the amount of sodium hydroxide diluted with water and, in particular, the temperature at which the reaction proceeds. E.g. in that particular case, in the first stage of the reaction, it was sufficient to take the first sample in 50 minutes and each subsequent sample in another 60 minutes. These parameters were achieved after 180 minutes of reaction. In the second step, the first sample was taken after 120 minutes and each subsequent after 60 minutes, and the parameters were achieved after 180 minutes of reaction in the second stage, i.e. a total of 360 minutes from the start of the reaction.

The collected sample cooled to room temperature was weighed in an amount of 1 - 1.3 g and shaken in a graduated flask with 6-8 ml of tetrahydrofuran, 80 - 100 microliters of glacial acetic acid was added, made up with tetrahydrofuran to a total volume of 10 ml.

5-6 g of a 3 A molecular sieve having a particle size of 1-3 mm were then added to the sample to drain the sample. Then, after removal of the molecular sieve, the sample was injected into the gel chromatograph at 200 microliters.

Samples were analyzed on a fully automated, continuously operating gel chromatograph. A Waters S column system (USA) was connected to the device. Column length

197,063 was 1.2 meters, 9 mm inside diameter. The columns were packed with polystyrene-divynylbenzene gel, particle diameter 35-75 microns, brand PORAGEL, respectively. STYREL.

Tetrahydrofuran was used as the eluent at 23 + 3 ° C at a flow rate of 0.5 ml per minute. Tetrahydrofuran was stripped of stabilizers, dried and pre-distilled before use.

The eluate composition was determined by a differential UV analyzer manufactured by ČSAV Praha at a wavelength of 254 manometers.

Claims (1)

SUBJECT OF THE INVENTION Process for the preparation of phenol-formaldehyde resins of the resolve type, for example for gluing particleboards or highly water-resistant plywood, characterized in that 1.5 moles of 2.6 moles of formaldehyde, 0.3 moles of 1.8 moles of sodium hydroxide are added per mol of phenol and water in an amount corresponding to the desired viscosity of the mixture, gradually increasing the temperature of the mixture to 40 - 65 ° C, preferably to 55 - 57 ° C, which is maintained until a reaction mixture of at most 5% phenol by weight, at least 36% by weight of phenol-alcohols and not more than 10% by weight of condensation products; the mixture is then heated to a temperature of 70 ° C until boiling until the product contains below 0.5% phenol, the phenol alcohol content is less than 7.5% by weight, and the condensation product content is at least 39% by weight.