JPH0372649B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to styrene-butadiene rubber (hereinafter referred to as
It is related to the manufacturing method of "SBR"),
Specifically, it relates to a method for producing SBR with a wide distribution of styrene reaction amounts. SBR is widely used as a material for industrial rubber products such as tire leads, belts, and packing. However, the manufacturing method is generally an emulsion polymerization method using water as a medium, and most of industrially manufactured SBR belongs to the above method.
The manufacturing technology for emulsion polymerization SBR involves introducing the entire required amount of styrene and butadiene monomers into a polymerization reactor from the beginning to start polymerization, and stopping the reaction when the reaction rate reaches approximately 60%. Then,
By collecting unreacted monomers, the desired
A common method is to obtain SBR. In such a polymerization method, the polymerization reaction of styrene and butadiene is almost ideal copolymerization, and the compositional distribution of styrene and butadiene in the polymer is narrow and the bonding state is almost random. This fact is also clear from the fact that the product of the reactivity ratios γ ₁ and γ ₂ of butadiene and styrene monomers is 1.08, which is close to 1. This is said to be hardly affected by changing the amount of emulsifier or molecular weight regulator used. By the way, emulsion polymerization by the conventional method described above
When SBR is used, for example, in tire treads, its performance is not sufficient, and improvements have been desired for some time. As a result of intensive studies in view of the above circumstances, the present inventors found that a special SBR produced by a specific method has excellent rubber physical properties, and completed the present invention. That is, the gist of the present invention is a method for producing styrene-butadiene rubber by an emulsion polymerization method using a radical initiator, the method comprising using 1,3-butadiene monomer alone or containing 1,3-butadiene monomer of 86
A pre-polymerization step in which a mixed monomer of 1,3-butadiene and styrene is polymerized in an amount of % or more by weight, and a styrene monomer or styrene and 1,3-butadiene is added to the polymer obtained in the pre-polymerization step. a second stage polymerization step in which a mixed monomer is added to continue the polymerization reaction, and the amount of styrene monomer added in the second stage polymerization step is equal to the total monomer amount including unreacted monomers in the first stage polymerization step. A method for producing styrene-butadiene rubber, characterized in that the concentration in the body is 36% by weight or more, and the average amount of bound styrene in the obtained styrene-butadiene rubber is 15 to 50% by weight. The method of the present invention will be explained in detail below. The method of the present invention is a method of polymerizing styrene and butadiene monomers using a radical initiator by an emulsion polymerization method, and its greatest feature is that the polymerization reaction is carried out in two stages. That is, the amounts of styrene and 1,3-butadiene to be used are appropriately selected depending on the composition of the target polymer, but in the present invention, the polymerization reaction is divided into a first stage polymerization reaction and a second stage polymerization reaction, and a single The main point is to add the required total amount of the polymer in two stages. In the method of the present invention, first, in the first stage polymerization step, 1,3-butadiene monomer alone or a mixed monomer of 1,3-butadiene and styrene having a 1,3-butadiene monomer content of 86% by weight or more is used. A polymerization reaction is carried out, and then a styrene monomer alone or a mixed monomer of styrene and 1,3-butadiene is added to the obtained polymer to continue the reaction in the latter polymerization step. Due to this two-step reaction, the distribution of the reaction amount of styrene is wider than in the conventional method in which the entire amount of monomer required is subjected to the polymerization reaction from the beginning.
You can get SBR. The thus obtained styrene has a wide reaction amount distribution.
SBR exhibits superior tire performance compared to conventional SBR. In the present invention, it is necessary to keep the amount of styrene reacted in the first stage polymerization step within a certain range. That is, in the first stage polymerization step, butadiene monomer is used alone, or the butadiene monomer concentration in the mixed monomer of butadiene and styrene is 86% by weight or more, and the amount of polybutadiene rubber or reacted styrene is 10% by weight or less. It produces SBR of low-reactivity styrene. In addition, in the latter polymerization step, styrene monomer alone or a mixed monomer of styrene and butadiene is added to the polymerization system so that the styrene monomer concentration in the monomer is 36% by weight or more. It is preferable to produce SBR with a content of 30% by weight or more, and by doing so, an SBR with a wider distribution of styrene reaction amount can be obtained. In addition, SBR with a constant styrene reaction amount distribution
However, if the absolute amount of the styrene-butadiene polymer constituting the tire is uneven, sufficient effects cannot be expected from the viewpoint of improving tire performance.
Therefore, it is preferable to keep the absolute amount of the polymer constituting the styrene reaction amount distribution within a certain range. In order to satisfy this condition, the polymerization reactions in the first and second polymerization steps must be carried out so that the proportion of the styrene-butadiene copolymer that reacts in the second polymerization step in the resulting SBR is 20 to 80% by weight. You need to choose a rate. Further, the polymerization reaction rate is preferably 70% or less based on the total styrene-butadiene monomer added to the polymerization system in order to suppress the formation of gel components and obtain SBR with excellent processability. In addition, if the average amount of bound styrene is lower than 15% by weight, SBR has a wide distribution of styrene reaction amount.
It is difficult to manufacture the rubber, and if the content exceeds 50% by weight, sufficient elasticity as a rubber cannot be obtained, so the content is preferably in the range of 15 to 50% by weight. Therefore, the target average amount of bound styrene is
The amount of styrene and butadiene monomer added can be adjusted by appropriately selecting the amount of styrene and butadiene monomers added, but the following relationship generally exists between the average amount of bound styrene (BS) of the SBR of the present invention and the styrene-butadiene monomer composition. To establish. BS<(0.79A-2.0) (All units are weight %) In the above formula, A means the weight % of the styrene monomer in all the monomers added to the polymerization reaction system. Therefore, such a relationship indicates that when producing SBR having the same average amount of bound styrene compared to SBR produced by a conventional method, the SBR produced by the present invention has a large amount of styrene monomer. It suggests that you need a body. Further, the Mooney viscosity is preferably ML ₁₊₄ =20 to 150 from the viewpoint of the physical properties and processability of the rubber. If it exceeds 150, the processability of the rubber will deteriorate, and if it is less than 20, the physical properties of the rubber, especially the tensile strength and dynamic properties, will deteriorate. In the case of the method of the present invention, since the first stage polymerization step and the second stage polymerization step are carried out continuously, the polymer with a low styrene content or polybutadiene produced in the first stage polymerization step tends to have a low molecular weight. It is preferable to adjust the molecular weight of each component by adding the components separately at a later stage, which particularly improves wear resistance. In the method of the present invention, the polymerization reaction of styrene and butadiene monomers is carried out in two stages as described above. It can be determined according to the method of The amount of water used in the polymerization reaction is 100 to 250 parts by weight, preferably 150 to 200 parts by weight, per 100 parts by weight of monomer.
Selected from a range of parts by weight. As the emulsifier, anionic surfactants such as fatty acid soap, rosin acid soap, naphthalene sulfonic acid sodium formalin condensate, and sodium alkylbenzene sulfonate, or nonionic surfactants such as polyoxyethylene alkyl ether are used. It will be done. These emulsifiers are used in appropriate combinations, and the amount thereof is usually 2 to 8 parts by weight per 100 parts by weight of the monomer as a total amount of emulsifiers.
The emulsifier may be added all at once to the polymerization reaction system in the first stage polymerization process, but by dividing it into parts, it can be used as an emulsifier for the monomers added in the second stage polymerization process, and then added to the polymerization system together with the monomers in the second stage polymerization process. It can also be added. Potassium persulfate is used as a polymerization initiator in the so-called hot rubber formulation in which polymerization is carried out at high temperatures of 30 to 60°C, and the amount used is usually 100% of the monomer.
It is 0.03 to 3.0 parts by weight per part by weight. Also 0-20
In so-called cold rubber formulations in which polymerization is carried out at low temperatures of 0.degree. C., redox initiators called sulfoxylate formulations are generally used. As the redox initiator, a combination of an organic peroxide such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, para-menthane hydroperoxide, etc. and ferrous sulfate is used. The amount of organic peroxide and ferrous sulfate used is 100% of the monomer.
Per weight part, 0.01~0.1 weight part, 0.005~
It is 0.07 part by weight. In sulfoxylate formulations,
It is chelated with sodium ethylenediaminetetraacetate and added with a reducing agent such as sodium formaldehyde sulfoxylate. The amount of reducing agent used in this case is usually 0.01 to 100 parts by weight of monomer.
It is 0.5 part by weight. Electrolytes such as potassium chloride and tripotassium phosphate are used to prevent gelation of latex.
It is usually used in an amount of 0.2 to 0.5 parts by weight per 100 parts by weight of the monomer. The molecular weight can be adjusted by using t-dodecyl mercaptan,
This is carried out by adding t-nonylmercaptan to the polymerization system, and the amount used is usually selected from the range of 0.05 to 0.5 parts by weight per 100 parts by weight of the monomer. Further, in the first stage polymerization step, an aromatic nitro compound such as nitrobenzene may be added in order to improve linearity. The amount used is usually 0.03 to 1 part by weight per 100 parts by weight of the monomer. The polymerization reaction is stopped by adding an appropriate amount of a polymerization terminator such as diethylhydroxylamine or dithiocarbamate to the reaction system. After the reaction has stopped, unreacted monomers are collected and removed.
Obtain SBR latex. The obtained SBR latex is solidified by adding salt and an acid such as sulfuric acid, and then washed with water, dehydrated, and dried to form a solid.
Can be SBR. Incidentally, during this coagulation, an oil masterbatch or a carbon masterbatch can also be directly produced by co-coagulating with process oil or carbon black. The SBR of the present invention manufactured as described above is
Particularly preferred SBRs of the present invention, which are characterized by a broader styrene reaction amount distribution than those of conventional methods, have a characteristic glass transition temperature. In other words, in the case of SBR, the glass transition point is
It is known that the amount of styrene reacted and the microstructure of the butadiene unit have an effect. on the other hand,
It is known that in emulsion polymerization using a radical initiator, the microstructure of the butadiene unit takes a certain reaction form as long as the polymerization conditions such as the polymerization temperature are the same.
Emulsion polymerized SBR polymerized with trans-1,4
Butadiene is present in the proportions of 76%, cis-1,4-butadiene 7% and 1,2-butadiene 16%. Therefore, the glass transition point of emulsion polymerized SBR is
It is determined by the amount of styrene reacted, and generally the glass transition point increases as the amount of styrene reacted increases.
From this, it is understood that SBR, which has a wide distribution of styrene reaction amount, has a wide peak temperature width of the glass transition point or multiple glass transition points when measured using a differential calorimeter (DSC). However, as shown in the Examples below, the particularly preferred SBR of the present invention has such a characteristic glass transition point. According to the method of the present invention explained above, rubber physical properties,
In particular, SBR with improved wear resistance and wet skid resistance, which are important physical properties for tire performance (particularly for tread tires), is produced. Conventionally, these two performances have been in a trade-off relationship, and it has been considered virtually impossible to improve both performances at the same time, so the method of the present invention is revolutionary. SBR with such performance can be used for tire treading, etc. without being blended with other rubber components, but the method of the present invention requires a dry blending process that requires a large amount of energy and equipment. It also has significant advantages such as not having to EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, in the following Examples and Comparative Examples, unless otherwise specified, parts indicate parts by weight. Example 1 According to the basic polymerization recipe shown in Table 1, a two-stage polymerization reaction was carried out using a polymerization reactor with a capacity of 100. First, 63.6 parts of 1,3-butadiene and 0.15 parts of t-dodecyl mercaptan as a molecular weight regulator were added to a polymerization reactor, and the first stage polymerization reaction was started at 10°C. When the reaction rate reached 40%, 36.4
of styrene was added to the polymerization reactor to continue the second stage polymerization reaction. When the reaction rate of all monomers reached 60%, 0.05 part of diethylhydroxyamine was added to the polymerization reactor to stop the subsequent polymerization reaction. Next, after recovering unreacted monomers according to a conventional method, 20 parts of highly aromatic process oil was emulsified and added, and the mixture was further coagulated to form crumbs, which were then dehydrated and dried to form oil-extended SBR. Obtained. The above oil-extended SBR was treated with a Banbury mixer according to the formulation shown in Table 2, and then heated at 145°C.
Vulcanized rubber compound 1 was obtained by vulcanization treatment for 30 minutes. The glass transition point of the vulcanized rubber compound was measured by DSC, and the results are shown in Table 4, and the measurement chart is shown in FIG. Note that the measurement conditions are as follows. Equipment: PerkinElmer DSC- Sensitivity: 2m cal/sec Heating rate: 20°C/min Chart speed: 40mm/min Cooling means: Use of liquid nitrogen In addition, the above oil-extended SBR was mixed with the compounding treatment shown in Table 3. The mixture was treated using a B-type Banbury mixer and a 6-inch roll according to the method, and then vulcanized at 145° C. for 60 minutes to obtain vulcanized rubber compound 2. The rubber physical properties of the vulcanized rubber compound were measured, and the results are shown in Table 5. Example 2 61.2 parts of 1,3-butadiene and 0.14 parts of t-
The polymerization reaction was carried out in the same manner as in Example 1, except that the first stage polymerization reaction was started using dodecyl mercaptan, and when the reaction rate reached 49%, 38.8 parts of styrene was added to continue the second stage polymerization reaction. Obtained oil exhibition SBR. The obtained oil-extended SBR was used to obtain vulcanized rubber compounds 1 and 2 similar to those in Example 1, and the glass transition point and rubber physical properties of these were measured under the same conditions as in Example 1. are shown in Tables 4 and 5 and Figure 1. Example 3 An oil-extended SBR was obtained by conducting a polymerization reaction in the same manner as in Example 1, except that t-dodecylmercaptan was added to the polymerization reactor in two stages. That is, in this example, 0.092 part of t-dodecylmercaptan was used in the first stage polymerization reaction, and 0.048 part was added together with styrene in the second stage polymerization reaction. Using the obtained oil-extended SBR, vulcanized rubber compounds 1 and 2 similar to those in Example 1 were obtained, and the glass transition point and rubber physical properties of these were measured under the same conditions as in Example 1. are shown in Tables 4 and 5 and Figure 1. Comparative Example A polymerization reaction was carried out in the same manner as in Example 1, except that 71 parts of 1,3-butadiene, 29 parts of styrene, and 0.124 parts of t-dodecyl mercaptan were added to the polymerization reactor and the polymerization reaction was carried out in one stage. and obtained oil-extended SBR. Using the obtained oil-extended SBR, vulcanized rubber compounds 1 and 2 similar to those in Example 1 were obtained, and the glass transition point and rubber physical properties of these were measured under the same conditions as in Example 1. are shown in Tables 4 and 5 and Figure 1.

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【table】 [Brief explanation of drawings]

FIG. 1 shows a chart of the glass transition point measurements of the oil-extended SBRs obtained in Examples 1 to 3 and Comparative Examples using a differential calorimeter. In the figure, a is Example 1, b is Example 2, c is Example 3, and d
is an oil-extended SBR obtained in a comparative example, T _G indicates the glass transition point, and ΔT indicates the peak temperature width of the glass transition point.

Claims (1)

[Scope of Claims] 1. A method for producing styrene-butadiene rubber by emulsion polymerization using a radical initiator, the method comprising: 1,3-butadiene monomer alone or 1,3-butadiene monomer;
1,3- with a butadiene monomer content of 86% by weight or more
A pre-polymerization step in which a mixed monomer of butadiene and styrene is polymerized, and a styrene monomer alone or a mixed monomer of styrene and 1,3-butadiene is added to the polymerization reaction product obtained in the pre-polymerization step. The amount of styrene monomer added in the latter polymerization step is 36 as the concentration in the total monomers including unreacted monomers in the first polymerization step. % by weight or more, and the average amount of bound styrene in the obtained styrene-butadiene rubber is 15 to 50% by weight. 2. The method according to claim 1, characterized in that the proportion of the styrene-butadiene copolymer reacted in the latter polymerization step in the styrene-butadiene rubber is 20 to 80% by weight based on the total polymer. Method.