RU2249016C2 - Method of producing urea-formaldehyde resin for manufacture of foamed plastics - Google Patents

Abstract

FIELD: polymer production.

SUBSTANCE: condensation of urea with formaldehyde is conducted at starting urea-to-formaldehyde molar ratio 1:(2.0-2.2) in several steps in a medium with variable acidity on heating in presence of modifying additive, namely aqueous solution of polyvinyl alcohol. As formaldehyde-containing component of condensation, urea-formaldehyde concentrate is utilized. Starting reaction mixture contains 54-60% total formaldehyde, 20-24% total urea, and water in balancing amount. Process is carried out in presence of viscosity adjuster: demineralized water and 1-3 wt parts modifier per 100 wt parts urea. Reaction mixture is first heated to 90±2°C at pH 7.5-8.5, kept for 20 min, and, after lowering temperature to 82-85°C, kept at pH 4.5-5.0 for 20-50 min and then neutralized to pH 7.5-6.0. After addition of additional urea to urea-to-formaldehyde molar ratio 1:1.5, reaction mixture is kept for further 60 min at 65-70°C.

EFFECT: eliminated production of waste water and increased productivity of equipment.

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Description

The invention relates to methods for producing urea-formaldehyde resins used for the manufacture of foam.

Currently, there remains an acute problem of creating resource and energy-saving technologies, in particular the use of heat-insulating materials for thermal insulation of buildings, equipment, refrigerators, etc. One of the first gas-filled plastics that found wide application for thermal insulation was foams based on urea-formaldehyde oligomers (CFD) . CFDs are the most economical starting material for foam production. Along with the positive properties, urea foams have several disadvantages, such as low mechanical strength, brittleness, and shrinkage during curing and drying. The production of urea-formaldehyde oligomers (resins) by traditional technology is associated with significant energy consumption for the concentration of the reaction mixture, as well as a large amount of formaldehyde-containing suprasmal waters, and the foams obtained on their basis do not fully satisfy the increasing requirements for formaldehyde emission.

There is a method of producing urea-formaldehyde resin for the manufacture of urea foam by co-condensing urea with formaldehyde in the presence of glycerol by heating to the boiling point of the resulting solution in a medium with variable acidity and a final molar ratio of formaldehyde: urea - 1.7 ÷ 1.8: 1 [A .F.Nikolaev. Synthetic polymers and plastics based on them. Chemistry, M., 1996, 78 pp. 391-392]. The disadvantages of this method is the significant content of free formaldehyde in the resin and the insufficient mechanical strength of the finished foam. Close to the solution of this problem is a method for producing a urea-formaldehyde resin by condensation of urea with formaldehyde, an aqueous solution of which was previously neutralized with ammonia water, in a medium with variable acidity when heated to a temperature of 60-95 ° C, vacuum drying, the introduction of a modifying additive in the form of an aqueous solution hydroxyl-containing polymer in an amount of 0.6-2.5 mass. parts per 100 parts of urea, post-condensation with an additional amount of urea to a final molar ratio of urea: formaldehyde 1: 1.2-1.6 [Application 96124470/04 Russia, cl. C 08 G 12/40, C 08 J 9/06, claimed December 27, 1996; published 27.1.99 // Patent No. 2115666]. The disadvantage of this method is its multi-stage and duration, which reduces the productivity of technological equipment, significant consumption of steam and electricity at the stage of cooking and vacuum drying of the resin.

The basis of the invention is the task of improving the method of producing urea-formaldehyde resin by reducing multi-stage and reducing the energy intensity of the process while improving the technical characteristics of the finished product (resin), as well as the physico-mechanical properties of the foam.

Physico-mechanical properties of the foam are shown in table 1.

The problem is achieved in that for the condensation of urea with formaldehyde in a medium with variable acidity when heated, according to the invention, urea-formaldehyde concentrate (CPK) is used as the main raw material component. The resin production process is carried out in the presence of a viscosity regulator and a modifying additive.

The essence of the proposed solution is the synthesis of urea-formaldehyde resin by condensation of CPA with the first portion of urea in the presence of a viscosity regulator — demineralized water, as well as a modifying additive in the form of an aqueous solution of polyvinyl alcohol at pH 7.5-8.5, for 20 minutes at a temperature of 90 ± 2 ° C. The initial molar ratio of urea to formaldehyde in this case is 1: 2.2-2.0, respectively. Then the mixture is cooled to 82-85 ° C with the introduction of a 20% solution of ammonium chloride, the pH is adjusted to 4.5-5.0 and incubated for 20-50 minutes until the resin coagulates. This is followed by neutralization of the reaction mass to a pH of 7.5-8.0 with simultaneous cooling to 70 ° C. When this temperature and pH are reached, a second portion of urea is introduced, a post-condensation step is carried out at 65-70 ° C for 60 minutes.

The use of KFK as a feedstock (according to TU U 6-05761614.005-96), which contains (% wt.) 54-60 "total" formaldehyde, 20-24 "total" urea, the rest is water, instead of 37% formalin, eliminates the stage of vacuum drying and thereby reduce the duration of the whole process of obtaining the resin. At the same time, the formation of tar waters is excluded, which is beneficial for environmental and economic reasons. The use of an aqueous solution of polyvinyl alcohol as a modifying additive makes it possible to obtain a foam with improved physical and mechanical properties and the absence of cracking.

The proposed method is illustrated by the following examples.

The applied skin contains 56.7% formaldehyde, 22.8% urea. Demineralized water is used to control the viscosity of the reaction mixture.

EXAMPLE 1

106 kg of CPA and 16.5 kg of demineralized water are loaded into a reactor V = 0.2 m ³ , pH 7.5-8.5 is adjusted using a 10% NaOH solution. After that, the first portion of urea is introduced in an amount of 33.1 kg, with the stirrer working, the mixture is heated to a temperature of 90 ± 2 ° C. Upon reaching a temperature of 40-50 ° C, a modifying additive — polyvinyl alcohol in the amount of 0.8 kg or one mass part per 100 mass parts of urea in the form of an aqueous solution — is loaded into the reactor. To prepare this solution, demineralized water is used in the same amount as water for the viscosity regulator (16.5 kg). At a temperature of 90 ° C, hold for 20 minutes. Upon completion of exposure in an alkaline medium, the reaction mass is cooled to 82-85 ° C and 0.5 dm ^{3 of a} 20% solution of NH ₄ Cl is introduced, the pH is set at 4.9. Polycondensation is carried out until the miscibility of the resin with cold water (t = 12 -15 ° C) in a ratio of 1: 8-10, respectively. The duration of this stage is 20-50 minutes depending on the temperature and the set pH level. After the miscibility of the resin with water reaches the desired limit, the contents of the reactor are neutralized with a NaOH solution to a pH of 7.5-8.0 in an amount of 0.4 dm ³ and the reaction mass is cooled to 70-75 ° C. Download the first portion of urea weighing 23 kg and carry out the stage of post-condensation for one hour at a temperature of 65-70 ° C. The final molar ratio of urea: formaldehyde is 1: 1.5, respectively. The finished resin is cooled to 25-30 ° C and poured into barrels.

EXAMPLE 2

The condensation conditions in example 1. The amount of the first portion of urea is 30.6 kg, the second is 25.5. The amount of modifying additive 1.6 kg or 2 mass parts per 100 mass parts of urea.

EXAMPLE 3

The condensation conditions in example 1. The amount of the first portion of urea is 36 kg, the second is 20. The amount of modifying additive is 2.4 kg or 3 parts by weight per 100 parts by weight of urea.

EXAMPLE 4

The process is carried out as in example 1. The amount of the first portion of urea is 33.1 kg, the second is 23. The amount of modifying additive is 0.8 kg, and polyvinyl alcohol is dissolved in the presence of 5.7 kg of urea, and the final molar ratio of urea: formaldehyde is 1: 1.4, respectively.

Comparative characteristics of the properties of the resins obtained by the proposed and known methods are presented in table 1.

Thus, by the proposed method, it is possible to obtain high-quality urea-formaldehyde resin for the production of foam, while the formation of wastewater is and the number of process steps is reduced.

Table 1
PHYSICAL AND MECHANICAL PROPERTIES OF FOAM Indicator Norm Prototype The proposed method Bending strength, MPa, not less 0.005-0.02 0,0405 0.144 Density, kg / m ³ 8-25 13.3 22.4

table 2
RESIN CHARACTERISTICS Names of indicators Prototype Examples 1 2 2 4 Mass fraction of solids, wt.% 56 63 62 62 63 The content of free formaldehyde, wt.% 0.25 0.19 0.20 0.17 0.11 VZ-4 viscosity (at 20 ° С), sec twenty 31 35 33 32 The concentration of hydrogen ions, pH 7.6 7.7 7.8 7.7 7.6 Gelatinization time at 100 ° С, sec 57 62 59 60 64

Claims (1)

A method of producing a urea-formaldehyde resin for the production of foam by condensation of a urea and a formaldehyde-containing component with an initial molar ratio of urea and formaldehyde of 1: (2.0-2.2) in several stages in a medium with variable acidity when heated, in the presence of a modifier - an aqueous solution of polyvinyl alcohol, characterized in that as a formaldehyde-containing component, a urea-formaldehyde concentrate is used containing 54-60 wt.% total formaldehyde, 20-24 wt.% total urea, the rest nd - water, the process is conducted in the presence of a viscosity regulator - demineralized water and 1-3 parts by weight modifier per 100 parts by weight urea, and at first the reaction mixture of urea, urea-formaldehyde concentrate and modifier is heated to 90 ± 2 ° C at pH 7.5-8.5, incubated for 20 minutes, reduce the temperature to 82-85 ° C and at pH 4.5-5, 5 are incubated for 20-50 minutes, then neutralized to a pH of 7.5-8.0, an additional amount of urea is introduced to a final molar ratio of urea and formaldehyde of 1: 1.5 and incubated for 60 minutes at 65-70 ° C.