JPH0330609B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing chloroprene rubber having excellent low-temperature properties. The polymer of 2-chlorobutadiene-1,3 (hereinafter referred to as chloroprene) is inherently crystalline, and when left at low temperatures for a long time, the degree of crystallinity increases, resulting in an increase in hardness and permanent deformation. Unfavorable properties such as increase in Therefore, in order to suppress the crystallinity of chloroprene polymers, methods of polymerizing chloroprene at higher temperatures than usual, methods of polymerizing chloroprene at higher temperatures than usual, and polymerization of 2,3-dichlorobutadiene-1,3 (hereinafter referred to as 2,3-DCB), styrene, acrylonitrile, etc. A method of copolymerizing monomers and chloroprene has been employed so far. However, polychloroprene obtained by the former method of polymerization at high temperatures lacks stability during storage, while in the latter method of copolymerization, monomers other than 2,3-DCB such as styrene and acrylonitrile are used. Since the polymerization rate is extremely slow compared to chloroprene, the copolymerizability is poor and the effect of inhibiting crystallization is small. Therefore, at present, as crystal-resistant chloroprene rubber, 2,3
-Copolymers of DCB and chloroprene are the most common. On the other hand, in addition to crystallinity, the glass transition temperature (hereinafter referred to as Tg) is a factor that determines the low-temperature properties of elastomers such as chloroprene rubber. When the atmospheric temperature is gradually lowered, the hardness and elastic modulus of an elastomer rapidly increase at a temperature near Tg, and the state transitions from a rubber state to a glass state, and when the temperature drops below Tg, it can no longer be used as an elastomer. become unable. That is, Tg can be said to be the lower limit temperature at which the elastomer can be used. In the case of chloroprene rubber, Tg is also closely related to the low temperature embrittlement temperature. In recent years, as the number of export destinations for automobiles has expanded, the conditions for their use have also expanded, and for cold regions, there is a strong demand for improved cold resistance of chloroprene rubber used as parts. In this case, in addition to crystallinity, Tg or low-temperature embrittlement temperature has come to be considered important as a measure for evaluating the cold resistance of chloroprene rubber. However, conventional copolymers of chloroprene and 2,3-DCB tend to have a higher Tg than chloroprene homopolymers, although their crystallinity at low temperatures is improved. As a result of various studies on methods for suppressing the increase in Tg and improving crystallization resistance, the present inventor found that
This led to the present invention. The present invention provides a method for producing a copolymer of chloroprene and 2,3-DCB by emulsion polymerization.
This is a method for producing chloroprene rubber, characterized by carrying out polymerization while continuously adding 3-DCB to a polymerization system under specific conditions. For more details, see 2.
In producing a chloroprene copolymer containing 2 to 15 mol% of 3-DCB by emulsion polymerization, the compositions of chloroprene and 2,3-DCB are 0.7 to 6.0 mol% and 94.0 to 99.3 mol%, respectively. The monomer mixture is emulsified to initiate polymerization, and ACx/t mol per minute per 100 mol of total monomers (here, A is a constant of 0.015 to 0.019, and C is the conversion rate (%) when polymerization is stopped. ), x is the amount (mol%) of 2,3-DCB in the monomer mixture initially emulsified, and t is the polymerization time (minutes).
3- Polymerization is carried out while continuously adding DCB, and 60
This is a method for producing chloroprene rubber, characterized in that polymerization and addition of 2,3-DCB are stopped at a conversion rate of ~80%. The amount of 2,3-DCB in the copolymer of chloroprene and 2,3-DCB is preferably 2 to 15 mol%.
If it is less than 2 mol%, the ability to suppress crystallization is low;
If it exceeds 15 mol%, the Tg will become high even if this method is used. The amount of 2,3-DCB in the copolymer is determined primarily by the composition of the monomer mixture of chloroprene and 2,3-DCB that is initially emulsified. If the amount of 2,3-DCB in the monomer mixture is 0.7-6 mol%, then 2-15 mol% 2,3-DCB in the copolymer
A chloroprene copolymer containing the following can be obtained. The amount of 2,3-DCB that is continuously added to the polymerization system is determined by the composition of the monomer mixture that is initially emulsified and the polymerization time. That is, for 100 moles of the initially emulsified monomer mixture,
ACx/tmol. Here, A is a constant of 0.015 to 0.019, C is the conversion rate (%) when polymerization is stopped,
x is 2,3 in the monomer mixture to be initially emulsified.
- DCB amount (mol %), t is polymerization time (minutes). If the addition rate of 2,3-DCB is outside this range, the effect of the present invention of suppressing the increase in Tg will be lost. The polymerization time is almost the same whether 2,3-DCB is added continuously or not if other conditions are the same, so if you measure the polymerization time in advance, you can Addition rate
ACx/tmol/min can be determined. The polymerization method of the above monomer mixture may be generally known methods, such as long chain alkyl mercaptans such as n-dodecylmercaptan, tert-dodecylmercaptan, n-octylmercaptan, diisopropylxanthogen disulfide, diethylxanthogen disulfide, etc. The emulsification is carried out using a well-known method together with a molecular weight regulator such as a dialkylxanthogen disulfide, and polymerization is initiated using an inorganic peroxide such as potassium persulfate. As an emulsifier, a water-soluble alkali salt of rosin acid such as disproportionated rosin, raw rosin, polymerized rosin, or a carbon number of 12 or more
Water-soluble alkali salts of 20 saturated or unsaturated fatty acids and water-soluble alkali salts of naphthalenesulfonic acid formalin condensates are used. At the same time as starting the polymerization, 2,3-DCB is continuously added to the polymerization system at a constant rate. At this time, the polymerization temperature is preferably 10 to 60°C. If the temperature is lower than 10°C, the crystallinity of the chloroprene polymer will increase, and 60
If the temperature exceeds .degree. C., the crystallinity will be good, but other physical properties will be unfavorable, such as poor stability of the resulting chloroprene rubber. 2,3-DCB added during polymerization may be added as is, but 2,3-DCB with a molecular weight regulator dissolved therein may be added as is.
Addition of 3-DCB, a solution of 2,3-DCB or 2,3-DCB with a molecular weight regulator dissolved in it diluted with an inert solvent such as benzene, or an emulsion of these with an appropriate emulsifier. It is also possible to do so. When a conversion of 60 to 80% is reached, a polymerization terminator such as phenothiazine is added to stop the polymerization, and at the same time, the addition of 2,3-DCB is also stopped. The conversion rate at which polymerization is stopped is preferably 60% or more from the viewpoint of productivity, and if it exceeds 80%, branched polymers and gel polymers will be produced, and the physical properties of the chloroprene rubber will deteriorate. After stopping the polymerization, the obtained latex was
After removing unreacted monomers by steam stripping, the mixture is freeze solidified and dried to obtain chloroprene rubber chips. The present invention will be explained below with reference to Examples, but it is not limited to these Examples. Examples 1 to 3 and Comparative Examples Using a reactor with a capacity of 10, 4000 g of a monomer mixture having the composition shown in Table 1 was mixed with 10 g of n-dodecyl mercaptan and 160 g of potassium salt of disproportionated rosin, 28 g. The sodium salt of naphthalene sulfonic acid formalin condensate, 8 g of caustic soda, and 4000 g of distilled water were emulsified, and polymerization was carried out at 40° C. in a nitrogen atmosphere using potassium persulfate as an initiator. In Examples 1 to 3, 2,3-DCB was added to the polymerization system at the addition rate shown in Table 1 simultaneously with the start of polymerization. When the conversion rate reached 70%, an emulsion of phenothiazine and para-tert-butylcatechol was added to stop the polymerization, and in Examples 1 to 3, the addition of 2,3-DCB was also stopped at the same time. For comparison, Table 1 also shows examples in which polymerization was carried out in the same manner except that 2,3-DCB was not added during polymerization. Polymerization time was approximately 210 minutes in all cases. After removing unreacted monomers from the obtained latex by a conventional stripping method, chips of chloroprene rubber were obtained by a conventional freeze-coagulation drying method. The Mooney viscosity of the obtained chloroprene rubber is
ML ₁₊₄ (100℃) was 45-50. The amount of 2,3-DCB in the obtained chloroprene rubber was determined by elemental analysis. The results are shown in Table 1.

【table】

[Table] Next, "Skyprene B-30" (trade name manufactured by Toyo Soda Kogyo Co., Ltd.), which is a homopolymer product of chloroprene rubber and chloroprene obtained in Examples 1 to 3 and comparative examples, is shown in Table 2. Knead with a roll according to the recipe, 150℃
Press vulcanization was performed for 30 minutes.

[Table] Storage modulus E′ and loss modulus of the obtained vulcanized rubber
The temperature dependence of E'' and loss tangent tan δ was measured using a Rheovibron DDV-B model manufactured by Toyo Baldwin Co., Ltd. The measurement frequency was 11 Hz, and the temperature measurement range was -70 to 0 °C. The table shows the peak temperature of E″ corresponding to Tg of each chloroprene rubber vulcanizate. In the method of the present invention, 2,3-DCB
It is clear that the increase in Tg is suppressed even when copolymerized with Table 3 also shows that E′ is 100MPa.
It also shows the temperature at which it occurs. As is clear from Table 3, it is clear that the chloroprene rubber obtained by the method of the present invention retains its rubber-like properties even at lower temperatures than the comparative example.

【table】

[Table] A compound of the chloroprene rubber obtained in Example 2 and Comparative Example and "Skybrene B-30" was kneaded with a roll according to the formulation shown in Table 4, and the compound was kneaded at 150°C.
Vulcanized for 30 minutes. The obtained vulcanized rubber was heated to zero ambient temperature.
It was maintained at 0.degree. C. and the change in hardness (JIS-A) with the holding time was measured. The results are shown in FIG. 1st
As is clear from the figure, it is clear that the chloroprene rubber produced by the method of the present invention has excellent crystallization resistance.

【table】 [Brief explanation of the drawing]

FIG. 1 shows the change in hardness (JIS-A) of each chloroprene rubber vulcanizate at 0°C with time. 1 shows the results of the chloroprene sole rubber, 2 shows the rubber of the comparative example, and 3 shows the results of the rubber obtained in Example 2.

Claims (1)

[Claims] 1 A 2-chlorobutadiene-1,3 (hereinafter referred to as chloroprene) copolymer containing 2 to 15 mol% of 2,3-dichlorobutadiene-1,3 (hereinafter referred to as 2,3-DCB) is produced by emulsion polymerization. During production, a monomer mixture containing 2,3-DCB and chloroprene having a composition of 0.7 to 6.0 mol% and 94.0 to 99.3 mol%, respectively, is emulsified and polymerization is initiated.
Furthermore, ACx/t mol per minute per 100 mol of total monomers (where A is a constant of 0.015 to 0.019, C is the conversion rate (%) when polymerization is stopped, and x is the monomer mixture to be emulsified first) Polymerization was carried out while continuously adding 2,3-DCB to the polymerization system at a rate of 60 to Polymerization at 80% conversion and 2,3
- A method for producing chloroprene rubber, characterized in that the addition of DCB is stopped.