RU2230076C1 - Urea-formaldehyde resin production process - Google Patents

Abstract

FIELD: polymer production. SUBSTANCE: water-soluble urea-formaldehyde resins suitable as binding substances and glues for gluing wood, in manufacture of wood chipboards and heat-insulation materials are prepared via condensation of urea-formaldehyde concentrate with urea introduced portionwise in presence of buffer agent (borax or trisodium phosphate) or aqueous methanol. Condensation is conducted at heating in variable-acidity aqueous solution followed by post-condensation with additional urea and second portion of buffer agent. Viscosity regulator is added in two steps: before the first urea charge in amount 0.5 to 30% and after termination of condensation in the resin cooling step in amount 0.1 to 35% per 100% of urea-formaldehyde concentrate. EFFECT: optimized synthesis conditions, improved quality of resins and enhanced their water-miscibility. 1 tbl, 3 ex

Description

The invention relates to methods for producing water-soluble urea-formaldehyde resins used as binders and adhesives for gluing wood, in the manufacture of chipboard, fiberboard and MDF and thermal insulation materials.

In the synthesis of the latter using urea-formaldehyde concentrate, a significant drawback of the resins under consideration is the reduced miscibility with water, which prevents the production of products with the necessary thermophysical characteristics.

A known method of producing urea-formaldehyde resin from urea-formaldehyde concentrate containing 55% of “total” formaldehyde and 21% of “total” urea [RU No. 2059663, cl. C 08 G 12/12, 1996]. It involves adding to the urea-formaldehyde concentrate a first portion of urea in order to achieve a molar ratio of formaldehyde: urea (F: K) = 2.0: 1.0, heating the reaction mixture at 40 ° C for two hours, introducing a 10% acetic solution acid to reduce the pH of the mixture to 5.2 and conduct acid condensation at 90 ° C until a viscosity of 1000 MPa · s is reached. After this, the pH of the reaction mass is set at 7.5, a second portion of urea is introduced, and the pre-condensation process is completed within one hour at 60 ° C.

The disadvantages of this method include the increased viscosity of the urea-formaldehyde resin at the stage of acid condensation due to the high temperature of the process, the reduced reactivity of the finished urea-formaldehyde resin, characterized by the “gelatinization time” indicator, the difficulty in controlling the resin synthesis process.

Known [RU No. 2136703, class. C 08 G 12/12, 12/40 // C 08 L 61/24; 09/10/1999] a method for producing a urea-formaldehyde resin by condensation of a urea-formaldehyde concentrate with urea in several stages in a solution with variable acidity in the presence of a buffer additive introduced in the last stage of the process. In this case, a product containing 54.7 wt.% Of “total” formaldehyde, 23.6 wt.% Of “total” urea and 21.7 wt.% Water, modified 1-15 wt.% Damage and 1- 5 wt.% Triazinones.

The synthesis of urea-formaldehyde resin is carried out by condensation of a urea-formaldehyde concentrate with a first portion of urea in the presence of a viscosity regulator of the addition of demineralized water or a 5% aqueous solution of methanol with a pH of 7.5-9.0, for 10 minutes at 90 ° C with a pH of the reaction mixture 7 , 6-8.8 to achieve a molar ratio of F: K = 2.0: 1.0. At the end of the alkaline stage, the mixture is rapidly cooled to (80 ± 2) ° С, an acidic agent is introduced to lower the pH to 5.0 or less, acid condensation is carried out at (81 ± 2) ° С before the resin coagulation begins, alkalization and the simultaneous introduction of a second portion of urea and a buffer additive and the completion of pre-condensation at (66 ± 2) ° C for 30 minutes.

The disadvantage of this technical solution is that the urea-formaldehyde concentrate used, with a low content of impurities (methanol, formate, etc.), has increased reactivity, especially at the stage of acid condensation, which makes it difficult to control the process of obtaining highly viscous resin at low pH values. In addition, the resulting resin is characterized by reduced miscibility with water.

The closest in technical essence can be considered a method [RU No. 2174523, cl. C 08 G 12/12] for the preparation of urea-formaldehyde resin by condensation of a urea-formaldehyde concentrate containing 0.02-0.2 wt.% A buffer additive with the first portion of urea in the presence of a viscosity regulator — demineralized water or an aqueous solution of methanol with a pH of 7.5– 9.0, for 10 minutes at (88 ± 3) ° С and pH 7.6-9.0 until the molar ratio Ф: К = 2: 1 is reached. At the end of the alkaline stage, the reaction mass is rapidly cooled to (80 ± 2) ° С, an acidic agent is introduced in order to lower the pH to 4.0-5.0, and acid condensation is carried out at (80 ± 3) ° С for 20-50 minutes before the coagulation of the resin, simultaneous injection of a second portion of urea and 0.02-0.20 wt.% buffer additives per urea-formaldehyde concentrate and completion of the condensation at (65 ± 2) ° C for 30 minutes.

As in the case of other known methods, the resulting resin has insufficient solubility in water, which narrows the scope of its application.

An object of the invention is to optimize the synthesis of low molar urea-formaldehyde resins while improving their quality and, above all, increasing miscibility with water.

The problem is achieved in that in the known method in order to increase the miscibility of the resin with water, the introduction of a viscosity regulator — demineralized water or an aqueous solution of alcohol — is carried out in two steps: in the urea-formaldehyde concentrate at the alkaline stage before loading the first portion of urea and after completion of the condensation in the cooling process resins respectively.

The essence of the proposed technical solution is the synthesis of urea-formaldehyde resins by condensation of a urea-formaldehyde concentrate, which is an aqueous composition containing 41.5-59.2 wt.% Of “total” formaldehyde and 20.5-26.0 wt.% Of “total” urea molar ratio (3.2-5.4): 1, respectively, with the first portion of urea in the presence of the first portion of a buffer additive of borax or trisodium phosphate and a viscosity regulator - demineralized water or an aqueous solution of methanol, when heated in an aqueous solution with alternating acidity followed by post-condensation of the resulting product with an additional amount of urea and the introduction of a second portion of a buffer additive at the initial and final molar ratio of urea and formaldehyde of 1: (1.9-2.1) and 1: (1.02-1.7), respectively and cooling the finished resin, and the viscosity regulator is introduced in two stages: before loading the first portion of urea in the amount of 0.5-30 wt.% and after completion of the condensation at the stage of cooling the resin in the amount of 0.1-35 wt.% per 100 wt.% urea-formaldehyde concentrate.

A distinctive feature of the proposed technical solution is that the resin viscosity regulator is introduced into the reaction mixture in two stages: before loading the first portion of urea and after completion of the condensation during cooling, respectively.

The invention is illustrated by the following examples: urea-formaldehyde concentrate is used in the form of an aqueous composition containing 41.5-59.2 wt.% Of “total” formaldehyde and 20.5-26.0 wt.% Of “total” urea. The molar ratio of urea: formaldehyde is 1: 3.2-5.4.

To neutralize and acidify the reaction mixture, aqueous solutions of sodium hydroxide, formic acid, ammonium chloride and other bases and acids are used.

Comparative characteristics of resins made according to the proposed method and the prototype are presented in the table.

Example 1

4600 kg of urea-formaldehyde concentrate containing 55.0 wt.% Of “total” formaldehyde, 22.1 wt.% Of “total” urea and 22.4 wt.% Water (molar formaldehyde: urea ratio = 4) are loaded into a 10 m ³ reactor 98: 1). 4.6 kg of borax or trisodium phosphate and 230 kg of demineralized water are added to it. The contents of the reactor are heated to 30-40 ° C, the pH of the reaction mixture should be 8.5 ± 0.3. If the pH does not match this value, it is brought to the required level by the addition of a small amount of a 10% sodium hydroxide solution.

After that, the first portion of urea is fed into the reactor until the molar ratio of urea: formaldehyde = 1.0: 2.0 is reached. The condensation solution is heated to 90 ° C with vigorous stirring and kept at this temperature for 10 minutes. Upon completion of alkaline condensation, the temperature of the reaction mixture is reduced to 80 ± 2 ° C and 35 kg of a 10% solution of ammonium chloride are introduced into the reactor from the measuring device in order to lower the pH. The end of the polycondensation is determined by the technological sample: 3 cm ^{3 of the} reaction mixture are added to a beaker with 50 cm ^{3 of} water cooled to 12-14 ° C. Condensation is stopped after the appearance of stable turbidity or small coagulation. Its duration depends on temperature and steady-state pH.

Upon completion of the acidic stage of polycondensation, the contents of the reactor are neutralized with a 10% solution of sodium hydroxide to a pH of 7.2-7.8, adding it from the measuring device in an amount of about 35 kg, and a second portion of urea is introduced to achieve the desired molar ratio of formaldehyde to urea, and also 4.6 kg of borax or trisodium phosphate.

The temperature of the reaction mixture spontaneously decreases to 66 ± 2 ° C and is maintained at this level for 30 minutes. A second portion of the viscosity regulator is added to the finished resin - demineralized water in an amount of 850 kg, cooled to 20-25 ° C and pumped to a container for storage.

Example 2

The condensation conditions of example 1.

At the stage of alkaline condensation, after loading of the urea-formaldehyde concentrate, 540 kg of demineralized water were introduced into the reactor, and after additional condensation, 540 kg was added before cooling of the resin.

Example 3

The condensation conditions of example 1.

Instead of demineralized water, a 5% aqueous solution of methanol was used.

From the description of the invention and the table it can be seen that according to the claimed technical solution, it is possible to obtain high-quality urea-maldehyde resins with the necessary set of performance indicators: miscibility with water, viscosity, gelatinization time, free formaldehyde content.

Claims (1)

A method of producing a urea-formaldehyde resin by condensation of a urea-formaldehyde concentrate, which is an aqueous composition containing 41.5-59.2 wt.% Of "total" formaldehyde and 20.5-26.0 wt.% Of "total" urea in their molar ratio (3 , 2-5,4): 1, respectively, with the first portion of urea in the presence of the first portion of a buffer additive - borax or trisodium phosphate and a viscosity regulator - demineralized water or an aqueous solution of methanol, when heated in an aqueous solution with variable acidity followed by post-condensation the resulting product with an additional amount of urea and the introduction of a second portion of a buffer additive at an initial and final molar ratio of urea and formaldehyde of 1: (1.9-2.1) and 1: (1.02-1.7), respectively, and cooling the finished resin , characterized in that the viscosity regulator is introduced in two stages: before loading the first portion of urea in an amount of 0.5-30 wt.% and after completion of the condensation at the stage of cooling the resin in an amount of 0.1-35 wt.% per 100 wt.% urea-formaldehyde concentrate.

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