RU2844882C1 - Method of preparing a rubber mixture - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of preparing partially vulcanised rubber mixtures based on ethylene propylene diene rubber for producing heat-shielding and heat-absorbing materials for operation at high-temperature heating. Method of producing a partially vulcanised rubber mixture based on ethylene-propylene rubber SKEPT-40 includes steps of introducing into rubber a vulcanising group and a crystalline hydrate – calcium chloride dihydrate or citric acid monohydrate, wherein vulcanising group is introduced at temperature of rubber 90-100 °C, curing mixture for 25 minutes, and crystalline hydrate is added when degree of vulcanisation of mixture is 65 % of optimum and mixing rubber mixture under same conditions for 3 minutes, with following ratio of components of mixture, pts. wt.: SKEPT-40 rubber 100; zinc oxide 5; stearine 1; sulphur 2; white soot BS-120 30; altax 0.5; dithiomorpholine 1.5; thiuram D 0.75; technical carbon P-803 2; crystalline hydrate 20-30.

EFFECT: high resistance to thermal aging during high-temperature heating of heat-shielding and heat-absorbing materials based on ethylene propylene diene rubber.

1 cl, 1 tbl, 6 ex

Description

The invention relates to methods for preparing rubber mixtures based on ethylene propylene diene rubber for obtaining heat-protective and heat-absorbing materials for operation under high-temperature heating, which can be used in the creation of protective polymer coatings, for example, in mechanical engineering, hydrocarbon extraction and transportation, construction and aircraft manufacturing.

A method for producing heat-accumulating material is known (patent RU 2161174, IPC C09K 5/06, C08G 18/83, C08L 75/04, C08K 3/24, published 27.12.2000), in which hydroxyl-containing oligodiene TsKDP-N, polyisocyanate, glycerin, tertiary amine and aluminum nitrate nonahydrate are thoroughly mixed for 30 minutes. Then they are poured into a mold and kept at room temperature (17-25 ^o C) for 3 days. The finished samples are removed from the mold using a knife.

The disadvantage of this method is the lack of the ability to form a protective coating with the material together with the protected surface under vulcanization conditions, and the impossibility of realizing the protective effect under high-temperature exposure without combustion and open flame.

The closest method is to obtain a rubber mixture including crystalline hydrates of salts by mechanical mixing followed by vulcanization of the composition, where ethylene propylene rubber is used as a polymer binder (The influence of heat absorption modifiers on the characteristics of composite elastomer materials / M.Kh. Wu, A.N. Gaidadin, I.P. Petryuk, K.D. Pham, H.S. Abzal'dinov // Industrial production and use of elastomers. - 2021. - No. 1. - P. 16-22).

The disadvantage of the method is the partial dehydration of crystalline hydrates during the production and vulcanization of the rubber mixture (composition). An additional disadvantage is the low strength values of the composition, including crystalline hydrates, which is associated with a change in the acid-base parameters of the mixture.

The objective of the present invention is to develop a method for producing a rubber mixture filled with crystalline hydrates of salts for use in the production of heat-absorbing and heat-protective materials.

The technical result consists in increasing the resistance to thermal aging during high-temperature heating of heat-protective and heat-absorbing materials based on ethylene propylene diene rubber.

The specified technical result is achieved in a method for producing a partially vulcanized rubber mixture based on ethylene-propylene rubber SKEPT-40, which includes introducing a vulcanizing group and a crystal hydrate - calcium chloride dihydrate or citric acid monohydrate - into the rubber, wherein the rubber is fed into a rubber mixer, where it is subjected to preliminary plasticization, after which the temperature of the mixing chamber is increased to 90 ° C and simultaneously the rotation speed of the rotors of the rubber mixer is increased to 60 rpm, maintaining fluctuations in the maximum permissible temperature in the range of 90-100 ° C, zinc oxide, stearin, sulfur, white carbon, altax, dithiodimorpholine, thiuram D, carbon black are added one after another, the mixture is vulcanized when mixed under the specified conditions for 25 minutes, ensuring a degree of vulcanization of the mixture of 65% of the optimum, and the crystal hydrate is introduced upon reaching the specified degree of crosslinking of the mixture and The rubber mixture is mixed under the same conditions for 3 minutes, with the following ratio of mixture components, mass parts:

SKEPT-40 rubber 100 zinc oxide 5 stearin 1 sulfur 2 white carbon black BS-120 30 Altax 0.5 dithiodimorpholine 1.5 thiuram D 0.75 carbon black P-803 2 crystal hydrate 20-30

The method ensures the preservation of the integrity of the crystal hydrates during the manufacture of the composition and during its vulcanization. At the same time, vulcanization of the composition on the protected surface is ensured.

The rubber mixture based on ethylene-propylene rubber is prepared in a rubber mixer; during the reaction mixing, the temperature of the mixing chamber is maintained in the range of 90-100°C and at the same time the rotation speed of the rubber mixer rotors is ensured to be up to 60 rpm. The vulcanization process of the rubber mixture begins during mixing. Crystal hydrates of salts are introduced into the composition when the degree of its vulcanization (crosslinking) reaches at least 65% of the optimum. As a result, the time of exposure of the crystalline hydrate to the conditions of manufacturing the rubber mixture is reduced, and the presence of a network of cross-links prevents the loss of crystalline water and preserves the efficiency of the crystalline hydrate. Partial vulcanization during mixing also helps to reduce the vulcanization time of the composition during manufacturing on the protected surface, prevents the loss of crystalline water and deterioration of the structure of the material after vulcanization.

A significant reduction in the loss of crystallization water is associated with an increase in the shear modulus of the composition as a result of partial vulcanization. An increase in the shear modulus of the composition leads to an increase in the pressure of the polymer medium on the crystal hydrate particles, thereby preventing the dehydration process, which, as is known, depends on external pressure.

The proposed method uses the following components.

Ethylene propylene diene rubber SKEP-40 containing dicyclopentadiene as a diene copolymer (TU 2294-087-05766563-2010).

Vulcanizing group, including:

vulcanizing agents – sulfur (GOST 127.4-93), dithiodimorpholine (TU 2478-033-05807983-2002);

vulcanization accelerators - thiuram D (TU 6-14-943-79), altax (TU 6-14-851-86);

vulcanization activators – zinc oxide (GOST 202-84), stearin (GOST 6484-96).

Fillers: white carbon black BS-120 (GOST 18307-78), technical carbon P-803 (GOST 7885-86).

Typical crystalline hydrates used are calcium chloride dihydrate CaCl ₂ 2Н ₂ О (GOST R 55973-2014), citric acid monohydrate C ₆ H ₈ O ₇ Н ₂ О (GOST 908-2004). Other types of crystalline hydrates can also be used.

The vulcanization process parameters are determined according to GOST 12535-84 "Rubber mixtures. Method for determining vulcanization characteristics on a vulcameter". The deformation and strength characteristics of samples are determined according to GOST 270-75 "Rubber. Method for determining elastic-strength properties under tension", GOST 263-75 "Rubber. Method for determining hardness according to Shore A". Resistance to high-temperature heating is determined according to GOST 9.024-74.

The method for obtaining a rubber mixture containing crystalline hydrates of salts is carried out as follows.

The rubber is fed into a rubber mixer, for example, a Brabender 0.1 micro mixer, and is plasticized for two minutes at a temperature of 50°C and a rotor speed of 13 rpm. After which the temperature of the mixing chamber is increased to 90°C and simultaneously the rotor speed of the rubber mixer is increased to 60 rpm. The maximum permissible temperature fluctuations are maintained within the range of 90-100°C. Then the remaining ingredients are added one by one in the following order: zinc oxide, stearin, sulfur, white carbon, altax, dithiodimorpholine, thiuram D, carbon black. The mixture is mixed under the specified conditions for 25 minutes. This mixing time ensures a vulcanization (crosslinking) degree of the mixture of at least 65%. Then the crystal hydrate is added to it and the final mixing stage is carried out under the same conditions for 3 minutes.

The examples given below illustrate, but do not limit, the essence of the proposed invention.

Example 1. SKEPT-40 rubber was loaded into a rubber mixer at a rate of 100 parts by weight. The temperature of the mixing chamber was maintained at 50°C and the rotor speed was 13 rpm. The plasticization time was 2 minutes, after which the temperature was increased to 90°C and at the same time the rotor speed of the rubber mixer was increased to 60 rpm. Then the remaining ingredients were added one after another in the following order: zinc oxide (5 parts by weight), stearin (1 part by weight); sulfur (2 parts by weight); white carbon BS-120 (30 parts by weight), altax (0.5 parts by weight), dithiodimorpholine (1.5 parts by weight); thiuram D (0.75 parts by weight), carbon black P-803 (2 parts by weight). The maximum permissible temperature fluctuations were maintained within the range of 90-100°C. Then the rubber mixture was mixed for 25 minutes. This mixing time ensures a vulcanization (crosslinking) degree of the mixture of at least 65%. Then calcium chloride dihydrate was loaded at the rate of 20 parts by weight of rubber. Mixing was continued under the same conditions for 3 minutes.

The prepared rubber mixture was used to vulcanize test samples. Residual vulcanization of the rubber mixture was carried out at a temperature of 150°C for 10 minutes.

Example 2. A rubber mixture was prepared according to example 1 with a loading of calcium chloride dihydrate at a rate of 30 parts by weight.

Example 3. A rubber mixture was prepared according to example 1, replacing calcium chloride dihydrate with citric acid monohydrate, loading citric acid monohydrate at a rate of 20 parts by weight.

Example 4. A rubber mixture was prepared according to example 1, replacing calcium chloride dihydrate with citric acid monohydrate, loading citric acid monohydrate at a rate of 30 parts by weight.

Example 5 (control). The control rubber mixture was prepared according to example 1 without adding crystal hydrates.

Example 6 (prototype). 100 parts by weight of SKEPT-40 rubber were loaded into a rubber mixer. The temperature of the mixing chamber was maintained at 50 °C and the rotor speed was 13 rpm. The plasticization time was 2 minutes. Then the remaining ingredients were added one after another in the following order: zinc oxide (5 parts by weight), stearin (1 part by weight); sulfur (2 parts by weight); white carbon BS-120 (30 parts by weight), altax (0.5 parts by weight), dithiodimorpholine (1.5 parts by weight); thiuram D (0.75 parts by weight), carbon black P-803 (2 parts by weight) and calcium chloride dihydrate at the rate of (20 parts by weight). The temperature of the mixing chamber was maintained at 50 °C and the rotor speed was 13 rpm. The rubber mixture was then mixed for 28 minutes.

After the rubber mixture was prepared, the test samples were vulcanized. The rubber mixture was vulcanized at 150 °C for 27 minutes.

As can be seen from the data presented in the table, the rubber compounds obtained by the proposed method surpass the prototype in technical parameters. The conventional tensile strength increases by 3.65 times from 4.3 to 15.5 MPa. At the same time, the resistance to high-temperature heating increases significantly. Thus, the change in the conventional tensile strength during thermal aging at 200°C for 24 hours for the prototype is minus 62%, and for the rubber compounds obtained by the proposed method, this indicator changes in the range from minus 28 to minus 50%.

Table

Names of indicators Examples 1 2 3 4 5 (counter) According to the prototype Crystal hydrate content, mass parts – calcium chloride dihydrate CaCl ₂ ·2Н ₂ О 20 30 - - - 20 – citric acid monohydrate C ₆ H ₈ O ₇ H ₂ O - - 20 30 - _ Conditional tensile strength, MPa 15.7 14.3 14.1 13.7 11.7 4.3 Relative elongation at break, % 510 530 550 570 560 645.2 Shore A hardness, conventional units 64 60 65 62 67 58 Resistance to thermal aging by change in conventional tensile strength, %, at 200 °C for 24 hours minus
50 minus
35 minus
40 minus
28 minus
86 minus
62 Resistance to thermal aging by change in relative elongation at break, %, at 200°C for 24 hours minus
55 minus
65 minus
60 minus
65 minus
88 minus
77

The change in relative elongation at break during thermal aging at 200°C for 24 hours for the prototype is minus 77%, and for rubber mixtures obtained by the proposed method, this indicator changes in the range from 55 to 65%.

Thus, the method for producing a rubber mixture based on ethylene-propylene rubber SKEPT-40, including introducing a vulcanizing group into the rubber at a rubber temperature of 90-100 °C, vulcanizing the mixture for 25 minutes, upon reaching a degree of crosslinking of the mixture of at least 65% of the optimum, introducing a crystal hydrate - calcium chloride dihydrate or citric acid monohydrate, mixing the rubber mixture under the same conditions for 3 minutes, with the declared ratio of the mixture components, ensures an increase in the resistance to thermal aging during high-temperature heating of heat-shielding and heat-absorbing materials based on ethylene-propylene diene rubber.

Claims (2)

A method for producing a partially vulcanized rubber mixture based on ethylene-propylene rubber SKEPT-40, including introducing a vulcanizing group and a crystal hydrate - calcium chloride dihydrate or citric acid monohydrate - into the rubber, characterized in that the rubber is fed into a rubber mixer, where it is subjected to preliminary plasticization, after which the temperature of the mixing chamber is increased to 90 ° C and simultaneously the rotation speed of the rotors of the rubber mixer is increased to 60 rpm, maintaining fluctuations in the maximum permissible temperature in the range of 90-100 ° C, zinc oxide, stearin, sulfur, white carbon, altax, dithiodimorpholine, thiuram D, carbon black are added one after another, the mixture is vulcanized when mixed under the specified conditions for 25 minutes, ensuring a degree of vulcanization of the mixture of 65% of the optimum, and the crystal hydrate is introduced when the specified degree of crosslinking of the mixture is achieved and the rubber mixture is mixed under the same conditions for 3 minutes, with the following ratio of mixture components, mass parts: SKEPT-40 rubber 100 zinc oxide 5 stearin 1 sulfur 2 white carbon black BS-120 30 Altax 0.5 dithiodimorpholine 1.5 thiuram D 0.75 carbon black P-803 2 crystal hydrate 20-30