JPH032364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an ethylene-vinyl acetate (EVA) copolymer.

It is known that the properties of ethylene-vinyl acetate polymers are determined by both the proportion of monomers used and the method of production. Copolymers with low vinyl acetate contents can therefore be produced economically, for example by high pressure polymerization. Copolymers with low vinyl acetate content and favorable properties can be produced particularly economically by common high pressure polymerization methods. The polymerization reaction is carried out at a pressure in the range 1000-2000 bar and a temperature in the range 150-280°C.

Increasing the amount of vinyl acetate added can reduce the polymerization temperature and pressure. At high vinyl acetate contents, it becomes difficult to produce high molecular weight copolymers due to the high temperatures at which bulk polymerization reactions occur.

Since copolymers containing more than 70% by weight of vinyl acetate are generally further processed in an aqueous dispersion, the copolymers are preferably prepared by emulsion polymerization. Products with relatively high ethylene contents can also be produced by emulsion polymerization. However, with increasing ethylene content, significant amounts of cross-linked polymer are produced, which can complicate subsequent processing.

Products with a vinyl acetate content of more than 30% by weight are produced by solution polymerization processes in the medium pressure range (100-400 bar). In this method, the polymerization temperature is below the softening range of the EVA-copolymer. High molecular weight, slightly branched products can thus be produced. The solvents used include tertiary-butanol or mixtures of tertiary-butanol, methanol and hydrocarbons in which the polymers are kept in solution even during the polymerization process.

The processes according to DE 1495767, which are polymerization processes carried out in tertiary-butanol as solvent, are therefore characterized by their favorable processability and exhibit particularly favorable rubber technology properties after vulcanization. Provides high quality rubber-like polymers.

However, for various applications it is desirable to increase the tensile strength of the vulcanized product without affecting the other advantageous properties of EVA-copolymers. These products are of particular use for the production of highly climate-resistant and heat-stable cables.

The polymerization reaction is carried out on the basis of a continuous solution polymerization in at least three autoclaves arranged in sequence at temperatures below 100 °C in the presence of radical-generating substances, in which 25-40% of the vinyl acetate used is converted. After that, 30-70% of the radical initiator used for the polymerization and 10-20% of the vinyl acetate used for the polymerization are introduced into the reaction mixture, and 30-80% of the total amount of vinyl acetate used It has now been found that EVA-copolymers can be produced which exhibit increased tensile strength in the vulcanized state by polymerizing until % conversion.

Post-addition of vinyl acetate as well as post-addition of activators are also effective in improving the tensile strength.

However, a combination of both methods is particularly effective.

Therefore, the present invention provides tertiary as a solvent.
A continuous solution polymerization process in connected multi-stage reaction chambers for producing ethylene-vinyl acetate copolymer in butanol, comprising at least three autoclaves arranged in sequence. conducted in 100 parts by weight of vinyl acetate,
50-200 parts by weight of tertiary-butanol, 40
~350 parts by weight of ethylene and 0.05 to 1.5 parts by weight of a radical initiator are continuously added to the monomers at a temperature of 50 to 100 °C and a pressure of 100 to 400 bar,
The mixture of solvent and radical initiator (in parts by weight) is added in such a way that most of the mixture (parts by weight) passes through all reaction chambers of the continuously connected multi-stage reaction chamber, however, only 25-40% of the vinyl acetate used is converted. After that, 30-70% of the radical initiator used for polymerization
% and 10-20% of vinyl acetate used for polymerization
is introduced into the reaction mixture and polymerized until 30 to 80% of the total amount of vinyl acetate used has been converted.

The post-addition of vinyl acetate and radical former can advantageously be combined.

Radical initiators (polymerization initiators) used as radical generating substances include, for example, organic peroxides,
Examples are benzoyl peroxide, lauroyl peroxide, peroxydicarbonates, dichlorobenzoyl peroxide, organic compounds such as α,α'-azodiisobutyric acid derivatives or α,α'-azodiisovaleric acid derivatives.

Free radical initiators with a half-life of less than 5 hours at 50°C are preferably used. Initiators such as these include, for example, peroxydicarbonates such as diisopropyl peroxydicarbonate, bis-(2-ethylhexyl)-peroxydicarbonate, bis-(4-tertiary-
butyl-cyclohexyl)-peroxydicarbonate, and ester or nitrile derivatives of azo-bis-isovaleric acid. Cyclohexyl peroxydicarbonate is particularly preferred.

The ethylene pressure during the polymerization reaction is preferably at least 50 bar, and the polymerization reaction is preferably between 100 and 400 bar.
It is carried out under pressure in an autoclave which acts as a bar reaction chamber.

The temperature is preferably in the range 60-80°C. There may be different temperatures in the individual reaction chambers of the cascade.

The solvent used for the process according to the invention is tertiary-butanol, optionally in combination with small proportions of other solvents. The proportion by weight of the solvent used is between 0.1 and 3 times the weight of the vinyl acetate used, and preferably between 0.5 and 2 times the weight of the vinyl acetate used.
For twice as long.

A standard stirrer-equipped autoclave with a volume ranging from 0.1 to 15 m ³ can be used as the reaction chamber. Larger autoclaves can also be used if technical prerequisites are met.
(The number of autoclaves arranged in sequence should be at least 3.) The post-addition of the monomer/solvent/radical initiator mixture is preferably carried out at the beginning of the multistage reaction chamber in which the reaction mixture is connected. This is done when passing through two autoclaves. 25-40% of vinyl acetate used
reacts after passing through the first two reaction chambers, when the radical initiator used for polymerization
Add 70% and 10-20% of vinyl acetate. The polymerization reaction is carried out in subsequent reaction chambers of connected multi-stage reaction chambers, with 30-80% of the total amount of vinyl acetate used;
The reaction is continued until 35-60% of the reaction has occurred.

The polymers produced by the method according to the invention can be vulcanized, for example with peroxides. They then exhibit increased tensile strength. The vulcanized products are also characterized by good extrudability. The vulcanized product is free of gel components and has a low second order transition temperature. They are used as films, coatings, for example for the production of coatings on cables,
It can then be used for the modification of other plastics such as cellulose esters or polyvinyl chloride.

The invention is illustrated by the following examples, in which the percentages are by weight.

Example 1 35.0 Kg/h of ethylene, 63.0 Kg/h of bipartite tertiary-butanol were continuously charged into a connected multi-stage reaction chamber consisting of four 200 liter high-pressure stirrer-equipped autoclaves arranged in sequence. and 1 part vinyl acetate, and 60 g/h of dicyclohexyl carbonate.

Furthermore, 9.45 Kg/h of tertiary-butanol/vinyl acetate mixture and 30 g/h of dicyclohexyl percarbonate are added to the middle of the connected multi-stage reaction chamber, i.e. between the second and third reactors, in other words: 13 of the total amount of vinyl acetate
% and 1/3 of the total amount of activator was introduced into the middle of the connected multi-stage reaction chambers.

Internal reactor temperatures were 65, 72, 70 and 72°C. The operating pressure was adjusted to 250 bar. After reaching equilibrium, samples were removed from the individual reactors through locks. Unused ethylene was carefully expanded and removed. A sample that does not contain gas is
They contained 10.7, 21.5, 33.7 and 38.6% solids. The vinyl acetate content of the isolated polymers was 44, 43, 46 and 45%.

Analysis of the data presented shows that 66.1% of the total amount of vinyl acetate was reacted and 27.5% of the total amount of vinyl acetate was reacted after - before addition.
It was shown that % reacted.

Example 2 A connected multistage reaction chamber according to Example 1 was continuously charged with 35.0 Kg/h of ethylene, 67.5 Kg/h of a mixture consisting of 2 parts of tertiary-butanol and 1 part of vinyl acetate, and 55 g/h. of tertiary-butyl perpivalate. However, no post-addition was performed. Internal reactor temperature is
73, 68, 73 and 65℃, and the reaction pressure is
It was 250 bar.

In sample collection carried out in the same manner as in Example 1,
Solids contents of 10.7, 21.9, 33.4 and 39.6% and vinyl acetate contents of 48, 47, 46 and 45% were shown. Therefore, 68.4% of the vinyl acetate used was reacted.

Example 3 The following components were mixed together in a laboratory kneader (filling basis 100%) by methods of the type commonly used in the rubber industry. The EVA copolymer used had a vinyl acetate content of 45% and a Mooney viscosity of 14.6.

EVA copolymer 100 parts Stearic acid 1 part Styrenated diphenylamine 1 part Carbon Black N550 40 parts Triallyl cyanurate (70%) 3.5 parts Bis-(tert-butylperoxyisopropyl)-benzene (40%) 4 parts 149.5 parts The mixture was pressure-vulcanized at 170 DEG C. for 20 minutes to give 4 mm thick pieces, from which standard rings were produced and tested according to DIN 52 502 and DIN 53 504. A tensile strength of 16.4 MPa and a Shore hardness of 72 were measured.

Example 4 The EVA copolymer used as in Example 2 containing 45% vinyl acetate and having a Mooney viscosity of 17.3 was mixed in an internal kneader as in Example 3; It was then further processed as described in the examples. A tensile strength of only 12.2 MPa and a Shore hardness of 67 were measured.

Claims (1)

[Scope of Claims] 1. A method for continuous solution polymerization in connected multistage reaction chambers for producing an ethylene-vinyl acetate copolymer in tertiary-butanol as a solvent, comprising: The process is carried out in at least three autoclaves arranged in series, containing 100 parts by weight of vinyl acetate, 50 to 200 parts by weight of tertiary-butanol, 40 to 350 parts by weight of ethylene and 0.05 to 1.5 parts by weight of radicals. The initiator is added at a temperature of 50 to 100 °C and a pressure of 100 to 400 bar in all reaction chambers of a multi-stage reaction chamber in which the majority of the monomer, solvent and radical initiator mixture (parts by weight) is connected. However, after 25-40% of the vinyl acetate used has been converted, 30-70% of the radical initiator used for the polymerization and 10-20% of vinyl acetate was introduced into the reaction mixture, and 30% of the total amount of vinyl acetate used
A process characterized by polymerizing until ~80% conversion. 2. Process according to claim 1, characterized in that the radical initiator used has a half-life of less than 5 hours at 50°C.