JPS6237042B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for producing polychloroprene in the presence of tetraalkylthiuram disulfides. Chloroprene homopolymers and copolymers have a variety of uses, such as as adhesive materials or elastomers. The chloroprene used as adhesive material is preferably a homopolymer, which is used in the form of a solution in an organic solvent, for example for bonding leather, rubber, plastics, wood and metals. They often contain auxiliary substances and additives such as terpene resins or modified terpene/phenolic resins. Both chloroprene homopolymers and chloroprene copolymers are used as elastomers. They have good resistance to oils, solvents and fats and high flame resistance. Among the chloroprene copolymers, those modified with sulfur are of particular interest because of their useful properties which allow for a wide range of pear applications. Their excellent millability and ability to be vulcanized without the addition of thiourea promoters must be recognized as particularly valuable properties, which make these special polymers suitable for use in conical belts and pneumatic bellows. making it a preferred material for the manufacture of articles required to withstand such high dynamic loads. It is known to produce homopolymers and copolymers of chloroprene in alkaline aqueous emulsions in the presence of emulsifiers and activators (Houben et al.
Weyl, Methoden der organischen Chemie,
Thieme Verlag Stuttgart, vol.XV/1,
(See Makromolekulare Stoffe, pp. 101 et seq.). An important auxiliary material for the production of chloroprene polymers is tetraalkylthiuram disulfide.
These are used as polymerization terminators, which improve the storage stability of adhesives and serve as peptizers for sulfur-modified polycloprenes. For these purposes, the tetraalkylthiuram disulfide is usually added after the polymerization is complete and before post-treatments such as peptization or finishing treatments. However, the finishing treatments of polychloroprene latexes, such as freeze-coagulation and drying processes to form solid rubber, are then highly unsatisfactory for ecological and economic reasons. Addition of a tetraalkylthiuram disulfide dispersion to a polychloroprene latex causes variations in the properties of the product due to the non-uniform distribution of the dispersion in the latex. For example, this leads to an undesirable decrease in the stability against hair agglomeration during storage of the finished adhesive solution. If a tetraalkylthiuram disulfide is initially added as a molecular weight regulator in the aqueous emulsion polymerization of, for example, chloroprene and sulfur, a significantly larger amount of promoter will achieve a certain degree of conversion than if it were not present. (DE-OS 2645920, p. 4). To solve this problem, the use of selected emulsifier systems and the additional use of secondary and/or tertiary aliphatic amines have been proposed. The addition of amines, which is itself undesirable, causes excessively rapid hardening of the rubber and significant discoloration. If tetraethylthiuram disulfide is added at the beginning of the reaction for the production of sulfur-modified polychloroprene, it results in poor storage stability, which manifests as an increase in viscosity during several weeks of storage (German Patent Application No. 1271405). , Example 2B). The object of the present invention is to use tetraalkylthiuram disulfides in such a way that the above-mentioned disadvantages are avoided and improved products are obtained economically. Surprisingly, it has been found that this problem is solved by adding the tetraalkylthiuram disulfide during the reaction and within a certain range of monomer conversion. In the case of adhesives, storage-stable products with much less variation in product properties and a distinctly lighter color are obtained. In the case of sulfur-modified polychloroprene, products are obtained which are light in color and have very good curing properties and good aging properties, such as low compression set and advantageous mechanical properties of the vulcanizate after aging. Addition of amine can be omitted. The present invention therefore comprises polymerizing chloroprene, optionally sulfur and optionally monomers copolymerizable with chloroprene - or more, in an alkaline aqueous emulsion at a temperature of 5 to 50° C. with the addition of a tetraalkylthiuram disulfide. In producing polychloroprene, the total amount of monomers is 100
Monomer conversion of 1.5×10 ^-2 to 4×10 ^-4 mol of tetraalkylthiuram disulfide per g
Add at 56-74% and continue polymerization for an additional 3-10%
% Continuing method. More advantageous properties are obtained in the process of the invention, especially when the thiuram disulfide is added in the form of a solution in an organic solvent, and it is particularly advantageous to add it in the form of a solution in chloroprene. The monomer conversion rate when adding the solution depends on the reaction temperature. Addition of thiuram disulfide solution results in a monomer conversion of 58-64% when the reaction temperature is 45°C and a monomer conversion of 62-68% when the reaction temperature is 25°C.
It has been found advantageous to carry out the reaction at a reaction temperature of 10 DEG C. with a monomer conversion of 66-72%. As a general rule, the higher the reaction temperature, the earlier the thiuram disulfide must be added. Examples of suitable comonomers, especially for sulfur-modified polychloroprenes, are styrene, acrylonitrile, 1-chlorobutadiene and 2,3
-dichlorobutadiene, which can be added in amounts up to a total of 10% by weight, based on the total amount of monomer. For the production of sulfur-modified polychloroprene, for example, 0.4 to 0.7 g of sulfur per 100 g of monomer is introduced into the polymerization reaction. Polymerization can be carried out continuously or batchwise, with continuous methods being preferred. A cascade of stirred vessels can then be used, the tetraalkylthiuram disulfide solution being introduced into the last vessel. The polymerization is carried out by known methods, which are described in German Patent Publications No. 3002711, No. 3002734 and No. 3002734.
Particularly suitable are those described in No. 2650714. One particularly suitable tetraalkylthiuram disulfide is tetraethylthiuram disulfide (TETD), which is generally added as a 5-50% by weight solution. The latex can be processed, for example, by freeze-coagulation using the method described in DE 26 45 921. In Examples 1 to 11 below, water was used as the catalyst.
Potassium persulfate 10g and sodium-β in 490g
- A solution of 0.2 g of anthraquinone sulfonate is used. Example 1 Production of polymer latex (comparative example) 970 g of 2-chloroprene and 30 g of 2,3,-dichlorobutadiene, 55 g of 70% by weight disproportionated resin acid,
It is emulsified in 1500 g of water to which are added 5 g of naphthalene sulfonic acid/formaldehyde condensate sodium salt, 5 g of sodium hydroxide, 3 g of anhydrous sodium pyrophosphate, 5 g of triisopropanolamine and 12 g of a sulfur dispersion (50% by weight). The emulsion is purged with nitrogen, heated to 50°C and started by adding the catalyst solution. During the polymerization process, a catalyst solution is further added at such a rate that the temperature of the reaction mixture does not rise above 50°C. After a monomer conversion of 65%, the polymerization is stopped using 1 g of phenothiazine and excess monomer is removed by steam distillation under reduced pressure. A latex with a solids content of 26.5-27.0% by weight is obtained. 18 ml of catalyst solution was consumed. Example 2 Preparation of Polymer Latex (Comparative Example) The procedure is the same as in Example 1, except that 3.0 g of TETD was added to the reaction mixture before the start of the reaction. To obtain 65% monomer conversion, 46 ml of catalyst solution was required to accelerate the reaction. Example 3 Preparation of Polymer Latex (Inventive Example) The procedure was the same as in Example 1, but in addition, 10 g and 20 g of TETD (a and b, respectively) dissolved in 20 g and 40 g of chloroprene, respectively, were added. Monomer conversion into reaction solution61
% when added and then polymerization monomer conversion 66%
Continue until. The subsequent finishing treatment is carried out as in Example 1. Catalyst consumption was 17ml. Examples 4-8 (Storage Stability) Latexes are peptized with various amounts of TETD and n-dibutylamine for 4 hours at 45°C, and samples are finished with TETD as a stabilizer. Mooney viscosity of polymer sample to DIN53
Measured by 523. The samples are stored at 70° C. for 3 days to measure the viscosity. The viscosity is then measured again. The smaller the difference in viscosity (ΔML) between the two measurements, the more stable the product. In the following table, all amounts of TETD added indicate solid weight.

Table: Example 9 Polymer Color The polymer latexes made in Examples 4, 7 and 8 are frozen on a chill roll and dried.
Rubber made according to the invention then has a bright natural color. To assess the color, the polymer is dissolved in toluene (20% by weight), a 1 mm thick film is cast from this solution, and after the film has dried the color is recorded on a specimen card RAL.
(Ausschusses f¨ur Lieferbedingungen und
G¨utesicherung beim Deutschen
Normenauschuss (DNA), 6Frankfurt/
M.1Gutleutstr.163-167). Polymer Examples Polymer Color according to RAL 4 ^* 1024 7 1002 8 1001 (*) Comparative Example This table clearly shows that the invention gives a lighter colored rubber (than Example 4) . Example 10 Compression Set (CS) Compression set or pressure residual deformation is measured according to DIN 53 517. This test serves to examine the behavior of an elastomer under constant deformation and indicates what percentage of deformation remains in the sample due to compression at a given time after pressure release. The values are determined on vulcanizates made from polymer/carbon black and cured at 150°C according to ISO standard 2475. The compression set should be as low as possible.

Table Example 11 Response of vulcanizates to aging Test mixtures of polymers were made according to ISO standards and at 150°C in three stages (20, 40 and 60
Cures in minutes). The strength and elongation are determined according to DIN 53 455 and also the loss of strength and elongation after hot air aging at 120° C. for 7 days.

Table: Examples 10 and 11 show that the vulcanizate of the polymer of Example 7 according to the invention has a considerably improved compression set and a more favorable response to aging than that of Comparative Example 4. There is. Example 12 Preparation of polymer latex (comparative example) 55 g of disproportionated resin acid (solids content 70%), 5 g of the sodium salt of naphthalene sulfonic acid/formaldehyde condensation product, 6 g of sodium hydroxide and n
-Water with 1.26g of dodecyl-mercaptan added
Emulsify 1000g of chloroprene in 1500g. A 3% by weight aqueous solution of formamidine sulfuric acid is used as a catalyst. Start by purging the emulsion with nitrogen, heating to 50°C and adding the catalyst solution. During the polymerization process, a catalyst solution is further added at a rate that does not cause the temperature of the reaction mixture to exceed 45°C. After 65% monomer conversion, the reaction is stopped with 1 g of phenothiazine and excess monomer is separated by steam distillation under reduced pressure. A 30% by weight aqueous dispersion of TETD was added to this latex.
34 g is added, the PH is lowered to 6.0 and the polymer is frozen on a chill roll and dried. The Mooney viscosity (ML-4') of the polymer is 108 ME. Example 13 Preparation of Polymer Latex (Comparative Example) An emulsion is prepared according to Example 12 and 0.8 g of potassium persulfate and 0.05 g of sodium anthraquinone-2-sulfonate are added as accelerators. The reaction starts at a reaction temperature of 15°C. The temperature of the reaction mixture is lowered to 10°C by external cooling and a 3% by weight solution of formamidine sulfinic acid is added at such a rate that the reaction temperature does not rise above 12°C. After 80% monomer conversion, the reaction is stopped as described in Example 12 and the product is worked up after addition of 42 g of TETD dispersion. The Mooney viscosity (ML-4') of the polymer is 95ME. Example 4 Production of polymer latex (example of the present invention) The procedure is the same as in Example 12, except that 25 g of chloroprene is used.
At 62% monomer conversion, 5 g of TETD dissolved in the solution is introduced into the reaction vessel and the polymerization is continued until 66% monomer conversion. Work-up is carried out as in Example 12, but without post-addition of TETD. A polymer with a Mooney viscosity (ML-4') of 104ME is obtained. Example 15 Preparation of Polymer Latex (Example of the Invention) The procedure is the same as in Example 13, except that 6.4 g of TETD dissolved in 25 g of chloroprene are introduced into the reaction vessel at 72% monomer conversion and then at 79% monomer conversion. Polymerization continues until Work-up is carried out as in Example 13, but without post-addition of TETD.
A polymer with a Mooney viscosity (ML-4') of 92ME is obtained. Example 16 (Polymer Color) The dry polymers according to Examples 12-15 are dissolved in toluene (20% by weight). A film with a thickness of 1 mm is cast from this solution. After drying these films, their colors are recorded on specimen cards (RAL).
Lieferbedingungen und G¨utesicherung beim
Deutschen Normenausschuss (DNA), 6000
Frankfurt/Main, 1 Gutelautstrasse 163～
167). Polymer Examples Polymer color according to RAL 12 ^* 1015 Pale ivory 14 9001 Cream color 13 ^* 1014 Ivory 15 9001 Cream color (*) Comparative example From the table it can be seen that the adhesive obtained according to the invention is substantially light colored. One thing is clear. Example 17 (Storage Stability) The spreadability and ease of processing of an adhesive solution is highly dependent on the viscosity of the adhesive, especially when using mechanical equipment. To ensure uniform processability and strength of the adhesive, it is necessary that the viscosity of the adhesive remain substantially constant during storage. These properties are suitably tested by measuring the viscosity stability and normal stress ratio (NZ) of the adhesive solution. A. Preparation of the adhesive solution: In a wide-necked 250 g flask with a screw cap, 33 g of polymer are dissolved in 117 g of a solvent mixture consisting of ethyl acetate/65-96°C petroleum hydrocarbons and toluene in a weight ratio of 2:2:1. Dissolve while stirring. The polymer is cut into strips approximately 5 mm in diameter and dissolved by rotating the closed flask at a speed of 300 revolutions per minute for 16 hours. B. Measurement of the viscosity of adhesives using the Breckfield rotational viscosity system: After the preparation of the solution, the used solvent mixture was further added to adjust the viscosity at 23 °C to 10 Pa.s by the Bruckfield viscometer LVT, and then for 6 months. Observe the solution over a period of time. Measurements are based on DIN53 019, January 1979 edition. Viscoelastic measurements of the solution according to method B were carried out at a storage temperature of 23°C.
After various storage times. The results obtained should remain as constant as possible. Significant deviations in both directions are undesirable. Measurements are made on adhesive materials made with various TETD contents according to Examples 13-15.

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Claims (1)

[Scope of Claims] 1. Polymerization of chloroprene, optionally sulfur, and optionally one or more monomers copolymerizable with chloroprene in an alkaline aqueous emulsion at a temperature of 5 to 50°C with the addition of tetraalkylthiuram disulfide. In the method for producing polychloroprene, when the monomer conversion is 56 to 74% during the polymerization process, 1.5 x 10 ^-2 to 4 x 10 ^-4 mol of tetraalkyl per 100 g of total monomer content at the start of polymerization. A process characterized in that thiuram disulfide is added and the polymerization is then continued for a further 3-10%. 2. A process according to claim 1, which comprises adding the tetraalkylthiuram disulfide in the form of a solution in an organic solvent. 3. The method according to claim 2, wherein the organic solvent comprises chloroprene. 4. The method of claim 1, wherein the tetraalkylthiuram disulfide comprises tetraethylthiuram disulfide. 5. A method according to claim 1, which comprises adding 0.4 to 0.7% by weight of sulfur, based on the monomers, for the production of sulfur-modified polychloroprene. 6 As comonomers, styrene, acrylonitrile, 1
2. A process according to claim 1, which comprises adding -chlorobutadiene and 2,3-dichlorobutadiene.