RU2761276C1 - Polyurethane composition for articles with increased frost resistance and method for production thereof - Google Patents

Abstract

FIELD: polymers.

SUBSTANCE: present invention relates to a group of inventions: a polyurethane composition for articles with increased frost resistance and a method for manufacturing a polyurethane composition for articles with increased frost resistance. The composition comprises the components in a ratio, molar fractions: polyurethane prepolymer based on mixtures of polyethers with a molecular weight of 1,000 to 2,000 - 1.0; mixture of 2,4- and 2,6-toluylenediisocyanates - 1.9 to 2.2, amine hardener - 0.85 to 0.95. The content of isocyanate groups in the composition is 3.3÷5.7 wt.% at a stoichiometric concentration of the amine hardener of 85÷95 wt.%. The amine hardener constitutes a eutectic mixture of bi-, tri- and greater functionality amines. The method includes three stages: first stage - the raw materials, polyethers with a molecular weight of 1,000 to 2,000 are heated until complete melting, followed by loading into a prepolymer synthesis reactor, wherein, prior to the synthesis of the prepolymer, the polyethers are dried under a vacuum at a temperature of 80÷95°C until a moisture content of no more than 0.08 wt.% at Pres = 10÷20 mm Hg is reached, followed by cooling the polyethers to a temperature of 50÷60°C, then the calculated amount of 2,4- and 2,6-toluylenediisocyanate with a certain isocyanate index is loaded into the cooled mixture of polyethers with a working stirrer in two or three passes; second stage - synthesis of the prepolymer under a vacuum (Pres = 10÷20 mm Hg) at a temperature of 80÷85°C for 30÷40 minutes, controlling the end of the reaction by sampling for the content of NCO groups; third stage - the hardener heated to 85°C is introduced into the resulting prepolymer with heavy stirring, wherein the stoichiometric concentration of the amine hardener can amount to 85-95 wt.%.

EFFECT: production of a polyurethane composition with a high level of physical and mechanical properties: increased frost resistance, wear resistance, resistance to cyclic loads, low indicators of water absorption and residual deformation, and articles made thereof are suitable for operation under heavy loads, in operating conditions with a large temperature difference, during work in an aggressive environment.

7 cl, 1 tbl, 6 ex

Description

The claimed group of inventions - POLYURETHANE COMPOSITION FOR PRODUCTS OF INCREASED FROST RESISTANCE AND THE METHOD OF ITS PRODUCTION relate to polyurethane elastomers of increased frost resistance and to methods of their production by injection technology and can be used in mechanical engineering, oil and gas industry.

At present, frost-resistant polyurethane compositions described in patents are known, for example, RU 2298568 C1, C08L75 / 04 (54) FROST-RESISTANT POLYURETHANE COMPOSITION, where a frost-resistant polyurethane composition for products is patented, containing urethane prepolymers based on 2,4-toluene diisoxymethanate 1400 and based on 2,4-toluene diisocyanate and oligobutadienediol with a molecular weight of 2000, hardener - 3,3'-dichloro-4,4'-diaminodiphenylmethane, non-volatile solvent hardener consisting of plasticizer - 2,6-diethylhexylsebacate and polytetramethylene oxide diol 1000 with the following ratio of components, parts by weight:

A prepolymer based on 2,4-toluene diisocyanate and polytetramethylene oxide diol with a molecular weight of 1400 - 100

A prepolymer based on 2,4-toluene diisocyanate and oligobutadienediol with a molecular weight of 2000 - 120-160

3,3'-Dichloro-4,4'-diaminodiphenylmethane - 7-9

- 2,6-Diethylhexylsebacate - 35-45

Polytetramethylene oxide diol with a molecular weight of 1000 - 70-80.

And a polyurethane composition patented as a polyurethane composition for articles obtained by casting (RU 2323237 C1, 04/27/2008, C08L 75/04) is a prototype containing a polyurethane prepolymer based on a polyether with a molecular weight of 1000-2000 and 2,4-toluene diisocyanate, amine hardener, plasticizer.

The disadvantages of these compositions are the insufficient quality of the products obtained, which limits the possibility of their use during operation under conditions of a large temperature difference, as well as the low manufacturability of the manufacturing process due to the increased time of its carrying out.

The closest of the identified technical solutions is a solution patented as a polyurethane composition RU 2404215. The present invention relates to a polyurethane composition for articles obtained by casting.

The polyurethane composition contains, by weight: 100 - polyether with molecular weight 1000-2000, 150-350 - 2,3-toluene diisocyanate, 1-95 - amine hardener, 10-35 - plasticizer, 1-20 - fluoroligomeric alcohol with molecular weight weighing 1000-5000 and 5-100 - polyol with a molecular weight of 1200-3500. The content of NCO-groups in the composition is 4.09-6.5%. The elastomers obtained from this composition have high durability, high strength characteristics and frost resistance, allowing the products obtained from them to be used under high loads, under operating conditions with a large temperature difference, when operating in an aggressive environment.

The disadvantage of this composition is the use of plasticizers, which migrate to the surface with a temperature drop, resulting in a deterioration in the quality of the resulting products and a decrease in their durability.

The technical result of the claimed invention is to obtain a polyurethane composition, achieved due to the additional introduction into the composition of a eutectic mixture of amines of bi-, tri- and higher functionality and a polyol with a molecular weight of 2000, as well as the use of the following ratios between the components, make it possible to obtain a polyurethane composition with a high level physical and mechanical properties - increased frost resistance, wear resistance, resistance to cyclic loads, low rates of water absorption and permanent deformation, and products made from it are suitable for work under heavy loads, under operating conditions with a large temperature difference, when working in an aggressive environment.

DESCRIPTION OF THE CLAIMED COMPOSITION

A polyurethane composition for products with increased frost resistance, containing a polyurethane prepolymer based on mixtures of polyethers, molecular weight 1000-2000 and mixtures of 2,4- and 2,6-toluene diisocyanates, additionally contains a eutectic mixture of amines of bi-, tri- and higher functionality at the following ratio of components, mole fractions:

- 1.0 - simple polyester or a mixture of simple polyethers with molecular weight 1000-2000,

- 1.9-2.2 - a mixture of 2,4- and 2,6-toluene diisocyanates,

- 0.85-0.95 - amine hardener (eutectic mixture of amines).

The content of isocyanate groups (NCO-groups) in the composition is 3.3-5.7% of the mass.

The stoichiometric concentration of the amine hardener - eutectic mixture of amines can be 85-95% by weight, while the content of NCO-groups in the composition is 3.3-5.7% by weight.

Polytetramethylene glycol or a mixture of polytetramethylene glycol and polypropylene glycol can be used as polyether.

A eutectic mixture of bi-, tri- and higher functionality amines was used as an amine hardener.

The addition of bi-, tri- and higher functionality amines and a polyol with a molecular weight of 2000 to the composition of the eutectic mixture of amines, as well as the use of the above ratios between the components, make it possible to obtain a polyurethane composition with a high level of physical and mechanical properties - increased frost resistance, wear resistance, resistance to cyclic loads, low rates of water absorption and permanent deformation, and products made from it are suitable for work under heavy loads, in operating conditions with a large temperature difference, when working in an aggressive environment.

The ratio of the components used to prepare the polyurethane composition may vary within the stated ratios and depends on the requirements for the product. If the ratio between the components was violated (went beyond the stated limits) the level of physical and mechanical characteristics of the polyurethane elastomer ceases to meet the required parameters.

Stoichiometric concentration of amine hardener - eutectic mixture of amines can be 85-95% of the mass.

These ranges are optimal and are due to the fact that when the concentration of the eutectic mixture of amines outside the specified range, the physicomechanical properties of the composition may deteriorate, because at the same time, the relative elongation and permanent deformation increase, and the tensile strength and abrasion resistance also decrease.

The content of isocyanate groups (NCO-groups) in the composition can be 3.3-5.7% by weight, while the percentage of NCO-groups is selected depending on the type of product that needs to be made, the requirements for this product and on the expected conditions its exploitation.

Outside the stated range of the content of NCO-groups in the composition, there is a deterioration in the physical and mechanical properties of the polyurethane elastomer: hardness, ultimate strength, elongation, permanent deformation, wear resistance, resistance to cyclic loads, water absorption, frost resistance.

Control over the content of isocyanate groups is carried out in accordance with the method for determining NCO-groups, given, for example, in TU-38-103137-78 for urethane prepolymer SKU-PFL-100.

The table (see Appendix) shows the main physical and mechanical properties of the polyurethane composition with different percentage of NCO-groups.

The claimed polyurethane composition can be processed into finished products by the free casting method, both in batch and continuous schemes.

Example 1: Polyurethane composition for products with increased frost resistance, containing: 1.0 mol of polytetramethylene glycol polyether with a molecular weight of 1000, 1.9 mol of a mixture of 2,4- and 2,6-toluene diisocyanate (ratio 50:50 parts by weight), 0.85 ÷ 0.95 mol of amine hardener (eutectic mixture of amines). In this case, the content of NCO-groups in the composition is 4.3-5.7% of the mass.

Example 2: Polyurethane composition for products with increased frost resistance, containing a mixture of polytetramethylene glycol and polypropylene glycol polyesters with a molecular weight of 1000 (ratio 85:15 parts by weight) and 1.9 mol of a mixture of 2,4- and 2,6-toluene diisocyanate (ratio 50: 50 parts by weight), 0.85 ÷ 0.95 mol of an amine hardener (eutectic mixture of amines). In this case, the content of NCO-groups in the composition is 4.3-5.7% of the mass.

Example 3: Polyurethane composition for products with increased frost resistance, containing polyether polytetramethylene glycol with a molecular weight of 2000 and 2.2 mol of a mixture of 2,4- and 2,6-toluene diisocyanate (ratio 50:50 parts by weight), 0.85 ÷ 0 , 95 mol of amine hardener (eutectic mixture of amines). In this case, the content of NCO-groups in the composition is 3.3-4.3% of the mass.

Example 4: Polyurethane composition for products with increased frost resistance, containing a mixture of polyesters of polytetramethylene glycol with a molecular weight of 1000 and polytetramethylene glycol with a molecular weight of 2000 (85:15 weight ratio) and 2.2 mol of a mixture of 2,4- and 2,6-toluene diisocyanate (ratio 50:50 parts by weight), 0.85 ÷ 0.95 mol of amine hardener (eutectic mixture of amines). In this case, the content of NCO-groups in the composition is 3.3-5.7% of the mass.

Example 5: Polyurethane composition for products with increased frost resistance, containing a mixture of polyesters of polytetramethylene glycol with a molecular weight of 2000 and polypropylene glycol with a molecular weight of 1000 (ratio 85:15 parts by weight) and 2.2 mol of a mixture of 2,4- and 2,6-toluene diisocyanate (ratio 50:50 parts by weight), 0.85 ÷ 0.95 mol of amine hardener (eutectic mixture of amines). In this case, the content of NCO-groups in the composition is 3.3-4.7% of the mass.

In addition to the components included in the claimed composition of the composition, dyes can also be included in the composition of the urethane composition.

METHOD FOR PRODUCING POLYURETHANE COMPOSITION FOR PRODUCTS WITH INCREASED FROST RESISTANCE

Problems arising in the manufacture of a polyurethane composition for products of increased frost resistance can be called: low processability of the process due to the increased time of its implementation, as well as the complication of the technological cycle due to the introduction of additional stages.

Known methods for the manufacture of products from polyurethane compositions, for example, the method described in patent RU 2400361, which includes the preparation and pouring of the polyurethane composition into a preheated mold, setting the mold with the polyurethane composition into a thermal oven for polymerization, and removing the part from the mold and exposure of the part, where a polyurethane composition is used with a content of isocyanate groups in an amount of 4.09-6.5%, and after installing the mold with a polyurethane composition in a thermal furnace, it is heated and further held at a temperature of 110-120 ° C for 0 , 5-2 hours, after holding the mold with the polyurethane composition in a thermal oven and before removing the part from the mold, direct pressing of the polyurethane composition in the mold is carried out using a hydraulic press at a temperature of 110-120 ° C, a pressure of 20-120 atm for 7-10 minutes , and the holding of the part after removing it from the mold is carried out in a thermal furnace at a temperature of 110-1 20 ° C for 8-16 hours, and after removing from the mold and holding the part in a thermal furnace, the part is machined.

The disadvantage of this method of manufacturing products is the complication of the technological cycle due to the introduction of an additional stage of pressing, as well as due to changes in the design of the mold for the implementation of direct pressing.

The closest is the method described in patent (19) RU (11) 2323237 (13) C1 (51) IPC C08L75 / 04 (2006.01) (54) FROST-RESISTANT POLYURETHANE COMPOSITION FOR PRODUCTS OBTAINED BY THE MOLDING METHOD. Preparation of prepolymer SKU-PFL-100 with terminal isocyanate groups is carried out by reacting polytetramethylene oxide diol with MM 1000 and 2,4-toluene diisocyanate taken in double excess with respect to stoichiometry. The molecular weight of the prepolymer, calculated from the content of NCO groups, is 1400.

The preparation of the named prepolymer is carried out with stirring and a temperature of 60-80 ° C for 3-4 hours. 15-20 minutes before the end of the synthesis, the evacuation is started at a residual pressure of 10-15 mm Hg. Art.

To obtain a polyurethane composition, preliminary with stirring, evacuation at a residual pressure of not more than 10 kPa and heating to 70 ÷ 80 ° C, a liquid hardener is prepared - a mixture of Diamet "X", plasticizer DEGS and polyfurite with MM 1000. Then the prepared hardener is mixed with prepolymers.

The mixing of the prepolymer and the hardener is carried out with stirring and evacuation at a temperature of 30-40 ° C. After stirring for 10-15 minutes, the prepared reaction mixture is poured into a slot-type mold and cured at 80 ° C for 3 days. After removal from the mold, the polyurethane elastomer sample is kept for 10 days at 20 ° C. Then its physical and mechanical characteristics are determined.

The choice of the number of parts by weight for the polyurethane composition is made by calculation, based on the molar ratios and molecular weights of the components of the curing system. The mass parts of the plasticizer are calculated based on the specified mass content of it in the composition.

The disadvantage of this method is the absence of a drying stage for polyesters, which can lead to the production of low-quality products, as well as a long synthesis time (3-4 hours) and curing of products in the form (3 days), which means low manufacturability of the manufacturing process due to the increased time its implementation and deceleration of the turnover of forms.

TECHNICAL RESULT

The claimed invention proposes a simpler, in comparison with the known, method for the production of frost-resistant polyurethanes, where there is no need for direct pressing of products and where the time for the synthesis and curing of products in the form is reduced.

DESCRIPTION OF THE CLAIMED METHOD

The method of obtaining a polyurethane composition for products of increased frost resistance (hereinafter referred to as the method) consists in preparing the equipment, in the preparation of raw material components, in the synthesis of a prepolymer followed by its evacuation and in the interaction of the prepolymer with an amine hardener - a eutectic mixture of amines. From the obtained composition by the casting method, finished products are obtained.

Before starting the synthesis, in order to bring the casting machine into working condition, it is necessary to set the preset temperature using the appropriate regulators:

- on the tank, pump and feed line of the prepolymer line - 60 ÷ 80 ° C;

- on the tank, pump and feed pipe of the crosslinker line - 100 ÷ 120 ° C.

The preparation of raw materials consists in heating it to the temperature required by the process technology followed by loading into the prepolymer synthesis reactor (polytetrate methylene glycol or a mixture of polytetrat methylene glycol and polypropylene glycol is heated at a temperature of 60 ÷ 80 ° C for 16 ÷ 24 hours; 2,4- and 2,6-toluene diisocyanate heated at a temperature of 40 ÷ 60 ° C until complete melting; the hardener in the form of a eutectic mixture of amines is heated at a temperature of 80 ÷ 110 ° C until complete melting, after which it is thoroughly mixed until the product is completely homogenized).

Before synthesis, polyesters, due to the high reactivity of isocyanates with respect to water, are dried under vacuum (Growth = 10–20 mm Hg) at a temperature of 80–95 ° C. The moisture content in polyesters used for the synthesis of polyurethanes should not exceed 0.08% of the mass.

To achieve this indicator, the drying process is monitored by analyzing polyester samples for moisture content in accordance with GOST 14870-77 (p. 2 Method for determining water with Fischer's reagent). When the desired result is obtained, the polyester is cooled to a temperature of 50 ÷ 60 ° C.

In the cooled mixture of polyesters while the mixer is running, the calculated amount of 2,4- and 2,6-toluene diisocyanate is loaded in 2-3 steps. The isocyanate index, depending on the required physical and mechanical properties of polyurethane, is taken equal to 1.9 ÷ 2.2.

The synthesis of the prepolymer under vacuum (P _rest = 10 ÷ 20 mm Hg) is carried out at a temperature of 80 ÷ 85 ° C for 30 ÷ 40 minutes, after which a sample is taken for the content of NCO-groups and upon reaching the value of NCO _fact. close to NCO _theor. the vacuum is turned on, controlling the end of the reaction by sampling for the content of NCO groups.

Obtaining a polyurethane composition consists in the interaction of a prepolymer with a eutectic mixture of amines, where a hardener heated to 85 ° C is introduced into the prepolymer with vigorous stirring. The stoichiometric concentration of the eutectic mixture of amines can be 85 ÷ 95% of the mass. The resulting mass is poured into a casting mold preheated to 110 ÷ 120 ° C with an applied anti-adhesive layer. In this case, the viability (time of gelation and loss of fluidity) of the reaction mixture at a temperature of 80 ÷ 85 ° C is 15 ÷ 20 minutes.

The inventive method is performed using the following equipment:

- a reactor for drying polyesters and synthesizing a prepolymer, closed with a lid with a feed opening and connected to a vacuum line, where the lid closes a heated vessel with a stirrer;

- prepolymer unit, including a heated container with a stirrer, closed with a lid with a loading opening, connected to a heated supply pipeline and to a vacuum line;

- a sampler for taking samples of polyester and prepolymer;

- stapler unit, including a heated container with a stirrer, closed with a lid with a loading opening, connected to a heated supply pipeline;

- a mixing head consisting of a mixing chamber with agitators.

Filled with the polyurethane composition obtained according to the claimed method, the molds are fed into a heating cabinet and kept at 100–120 ° C for 16–24 hours for final polymerization.

In order to accelerate the turnover of molds, it is allowed to remove products from the molds after 2 ÷ 3 hours from the moment of pouring. Further temperature control of products is carried out on special stands. At the end of the curing process, the products are removed from the oven, cooled to ambient temperature, subjected to mechanical treatment and kept at ambient temperature for 10-14 days for the final structuring of the polymer and a set of optimal physical and mechanical parameters.

EXAMPLE OF PERFORMANCE OF THE METHOD FOR OBTAINING A POLYURETHANE COMPOSITION FOR EXAMPLE 2.

Before the start of the synthesis, the casting machine was brought into working condition, with the help of the appropriate regulators, the preset temperature was set:

- on the tank, pump and feed line of the prepolymer line - 60 ÷ 80 ° C;

- on the tank, pump and feed pipe of the crosslinker line - 100 ÷ 120 ° C.

A mixture of polytetratemethylene glycol and polypropylene glycol with a molecular weight of 1000 was heated at a temperature of 60 ÷ 80 ° C in a heating cabinet for 16 ÷ 24 hours and loaded into the container of the prepolymer unit of the filling machine; 2,4- and 2,6-toluene diisocyanate was heated in a heating cabinet at a temperature of 40 ÷ 60 ° C until complete melting; The hardener in the form of a eutectic mixture of amines was heated in a heating cabinet at a temperature of 80 ÷ 110 ° C until complete melting, after which it was thoroughly mixed until the product was completely homogenized using a stirrer and loaded into the container of the crosslinker unit of the filling machine.

Before synthesis, the polyesters were dried under vacuum (Height = 10–20 mm Hg) at a temperature of 80–95 ° C for 1 hour.

Control over the drying process was carried out by analyzing polyester samples for moisture content in accordance with GOST 14870-77 (p. 2 Method for determining water by Fisher's reagent). The moisture content in polyesters did not exceed 0.08% of the mass. After obtaining the desired result, the polyester was cooled to a temperature of 50 ÷ 60 ° C.

In the cooled mixture of polyesters with the stirrer running, the calculated amount of 2,4- and 2,6-toluene diisocyanate was loaded in 2-3 steps in a ratio of 50:50 (%). The isocyanate index was taken to be 1.9.

The synthesis was carried out at a temperature of 80 ÷ 85 ° C for 30 ÷ 40 minutes, after which a sample was taken for the content of NCO groups. The content of NCO-groups in the composition was 4.3-5.7% of the mass.

The synthesis of the prepolymer under vacuum (P _rest = 10–20 mm Hg) was carried out for 40–60 minutes at a temperature of 80–85 ° C, controlling the end of the reaction by sampling for the content of NCO groups. The content of NCO-groups in the composition was 4.3-5.7% of the mass.

The hardener and prepolymer heated to 85 ° C were fed to the mixing head using metering pumps through heated hoses and the reaction components were thoroughly mixed. The stoichiometric concentration of the amine hardener - eutectic mixture of amines was 85%. The resulting mass was poured into a casting mold preheated to 110 ÷ 120 ° C with an applied anti-adhesion layer, in parallel, a slotted mold was poured to obtain standard samples for determining elastic strength properties. In this case, the viability (time of gelation and loss of fluidity) of the reaction mixture at a temperature of 80 ÷ 85 ° C was 15 ÷ 20 minutes.

The molds filled with the polyurethane composition were placed in an oven and kept at 100–120 ° C for 16–24 hours for final polymerization. In order to accelerate the turnover, the products were removed from the molds after 2 ÷ 3 hours from the moment of pouring. Further thermostating of the products was carried out on special stands. At the end of the curing process, the products were removed from the oven, cooled to ambient temperature, subjected to mechanical treatment and kept at ambient temperature for 10-14 days for the final structuring of the polymer and a set of optimal physical and mechanical parameters.

After the specified time, the obtained samples were tested to determine the elastic strength properties in tension according to GOST 270-75, Shore A hardness according to GOST 263-75, tear resistance according to GOST 262-93, and glass transition temperature on the Marey device.

The following values were obtained:

• conditional tensile strength - 35.3 MPa;

• relative elongation at break - 344%;

• hardness Shore A - 85 conventional units;

• tear resistance - 80 N / mm;

• glass transition temperature - -40 ° C.

The results of the tests carried out showed that the samples meet the technical requirements imposed on them.

Products from the claimed composition can be used in mechanical engineering and the gas and oil industry.

The elastomers obtained from the claimed composition have high durability and high strength characteristics, allowing the products obtained from them to be used under heavy loads, under operating conditions with a large temperature difference (from -60 ° C to + 80 ° C), when operating in an aggressive environment.

The main physical and mechanical properties of a polyurethane composition with a different percentage of NCO groups.

Table.

Indicator name Content of NCO-groups,% wt. 3.3-4.3 4.3-5.7 Tensile strength, MPa thirty 34 Elongation at break,% 450 300 Shore A hardness, conventional units 75 85 Tear resistance, N / mm 70 80 Glass transition temperature, ° С -60 -40

Claims (11)

1. Polyurethane composition for products with increased frost resistance, containing a polyurethane prepolymer based on mixtures of polyethers with molecular weight 1000-2000 and mixtures of 2,4- and 2,6-toluene diisocyanates, an amine hardener - a eutectic mixture of bi-, tri- and higher functionality amines with the following ratio of components, mole fractions: - 1.0 - a mixture of polyethers of molecular weight 1000-2000, - 1.9 ÷ 2.2 - a mixture of 2,4- and 2,6-toluene diisocyanates, - 0.85 ÷ 0.95 - eutectic mixture of amines, where the content of isocyanate groups in the composition is 3.3 ÷ 5.7% of the mass. at a stoichiometric concentration of the amine hardener - 85 ÷ 95% of the mass. 2. Composition according to claim 1, characterized in that polytetramethylene glycol with a molecular weight of 1000 is used as the polyether. 3. Composition according to claim 1, characterized in that a mixture of polytetramethylene glycol and polypropylene glycol with a molecular weight of 1000 is used as the polyether. 4. A composition according to claim 1, characterized in that polytetramethylene glycol with a molecular weight of 2000 is used as the polyether. 5. Composition according to claim 1, characterized in that the polyether is a mixture of polyesters - polytetramethylene glycol with a molecular weight of 2000 and polytetramethylene glycol with a molecular weight of 1000. 6. Composition according to claim 1, characterized in that the polyether is a mixture of polyesters - polytetramethylene glycol with a molecular weight of 2000 and polypropylene glycol with a molecular weight of 1000. 7. The method of manufacturing a polyurethane composition for products with increased frost resistance consists of three stages: the first consists in the fact that the raw material - polyethers of molecular weight 1000-2000 are heated to complete melting, followed by loading into the prepolymer synthesis reactor, where the polyesters are dried before the prepolymer synthesis under vacuum at a temperature of 80 ÷ 95 ° C until reaching at Growth. = 10 ÷ 20 mm Hg. Art. the moisture content is not more than 0.08% wt., after which the polyesters are cooled to a temperature of 50 ÷ 60 ° C, and then the calculated amount of 2,4- and 2,6-toluene diisocyanate is loaded into the cooled mixture of polyesters with the mixer in operation in two or three steps with a certain isocyanate index (selected depending on the type of product that needs to be manufactured, the requirements for this product and on the expected conditions of its operation) and then the second stage is carried out - the synthesis of the prepolymer under vacuum (Height = 10 ÷ 20 mm Hg) at a temperature of 80 ÷ 85 ° C for 30 ÷ 40 minutes, controlling the end of the reaction by sampling for the content of NCO-groups, the third stage - obtaining a polymer consists in the fact that a hardener heated to 85 ° C is introduced into the obtained prepolymer with vigorous stirring, while stoichiometric concentration of amine hardener - eutectic mixture of amines can be 85-95% of the mass.

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