JPH0629302B2 - Polystyrene manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing high impact polystyrene (HIPS).

<Prior Art> In recent years, various synthetic resins have been used in large amounts in household appliances, vehicles such as automobiles, and many other fields. Depending on their respective applications, mechanical properties and thermal properties, and further, There is a strong demand for improvement of various characteristics such as appearance characteristics such as surface gloss of molded products.

Especially in the case of HIPS, the impact strength of the molded product is high,
In addition, high surface gloss is required, and from the viewpoint of operability during molding, high tensile strength and maximum elongation and good extrusion flowability are also required.

In general, in order to improve the impact strength of polystyrene, a method of graft-polymerizing a styrene monomer or a mixture of styrene and another monomer copolymerizable with styrene in the presence of butadiene rubber to obtain a resin having improved impact strength Has been developed and is being implemented industrially.

However, in this case, the use of polybutadiene having a high cis content (so-called high Cis-BR), which is usually commercially available as a butadiene-based rubber, not only has an insufficient effect of improving the impact strength, but also causes HIPS. However, there is a problem that the impact strength is reduced due to the coloring of the gel or the mixing of the gel component. On the other hand, when polybutadiene with a relatively high trans content (so-called low Cis-BR), which is synthesized and marketed with a lithium-based polymerization initiator, is used, the gel content is relatively low and the impact strength is considerably improved. In this case, in order to further improve the impact strength, it is necessary to increase the amount of polybutadiene used or the average molecular weight of polybutadiene. As a result, the gloss of HIPS is deteriorated and the surface smoothness is increased. In both cases, impact strength and appearance physical properties were not improved at the same time.

Recently, a method for producing HIPS with improved falling weight impact strength and Izod impact strength by slightly increasing the vinyl bond content in polybutadiene rubber obtained by a polymerization method using a lithium-based polymerization initiator, a so-called solution anion polymerization method, has been proposed. , Japanese Patent Publication No. 53-44188 and Japanese Patent Publication No. 58-4934.

Further, Japanese Patent Laid-Open No. 59-24711 discloses a method for producing a HIPS having improved impact resistance and surface gloss by using a butadiene rubber containing a tin-butadiene bond.

HIPS obtained by these manufacturing methods is the same as conventional HIP.
Although it shows a slightly different physical property value than S, further improvement is required from the viewpoint of the balance of practical physical properties required today.

<Problems to be Solved by the Invention> An object of the present invention is to solve the above problems, improve impact resistance and appearance characteristics at the same time, and increase tensile strength and elongation, and improve extrusion flowability. It is to provide a method of manufacturing HIPS.

<Means for Solving Problems> The inventors of the present invention have studied the molecular structure of the butadiene rubber used in the synthesis of HIPS, particularly the molecular weight distribution, the morphology of branching, the microbonding mode, and the relationship between the physical properties of the resulting HIPS. As a result of earnest studies, it was found that by using a butadiene-based polymer having a specific structure as the butadiene-based rubber, an impact-resistant polystyrene having desired performance can be obtained, and the present invention has been completed.

That is, the present invention provides a method for producing impact-resistant polystyrene by radically polymerizing butadiene-based rubber and styrene, wherein 1,3-butadiene or 1,3-butadiene and styrene are used as the butadiene-based rubber in the presence of an organolithium compound. Is polymerized or copolymerized, and a compound defined by the chemical formula R _l SiX _4-l (R = hydrocarbon group, Si = silicon atom, X = halogen atom, and 1 = 0 or 1) is added. A butadiene-based polymer having a branched polymer chain obtained by the reaction, wherein the 1,2-bond content based on the bound butadiene in the butadiene-based polymer is 8 to 14 mol% and the butadiene-based polymer is The amount of bound styrene in the coalescence is 15% by weight or less, and the ratio of the polymerization average molecular weight to the number average molecular weight is 1.08 to
1.60, the content of branched polymer chains is 50% by weight or more, the molecular length of branched polymer chains and the molecules of unbranched polymer chains measured by gel permeation chromatography (GPC) Using a butadiene-based polymer having a chain length ratio of 1.8 to 3.2, a Mooney viscosity of 35 to 50 at 100 ° C and a solution viscosity of 25 to 65 cps at a concentration of 5% by weight in styrene at 25 ° C, and producing polystyrene The present invention provides a method for producing impact-resistant polystyrene, which comprises polymerizing so that the content of a butadiene-based polymer in the composition is 5 to 15% by weight.

The butadiene-based polymer used as the butadiene-based rubber in the present invention is an organic lithium compound (polymerization initiator)
1,3-butadiene can be polymerized alone in the presence of
Butadiene having a branched polymer chain obtained by copolymerizing butadiene and styrene, and further reacting with a compound having the chemical formula of R _l SiX _4-l to react with the active polymerization end of this polymerization or copolymer It is a polymer.

Here, as the organic lithium compound used as the polymerization initiator, ethyl lithium, n-butyl lithium, n-
Hexyllithium, stearyllithium, allyllithium, cyclohexyllithium, phenyllithium, benzyllithium, tetramethylenedilithium, diphenylethylenedilithium, 1,20-dilithioeicosane, 1,4
-Dilithiocyclohexane and the like are exemplified, but alkyl lithium is particularly preferable and used. Such an organolithium compound is usually 0.5 to 100 g of 1,3-butadiene.
3 mmol is used.

In the present invention, in order to control the content of 1,2-bond based on the bound butadiene in the butadiene-based polymer, a Lewis basic compound may be allowed to coexist during the synthesis of the polymer.

Lewis basic compounds include dibutyl ether, tetrahydrofuran, ethylene glycol dimethyl ether,
Ethers such as ethylene glycol dibutyl ether, diethylene glycol dimethyl ether and diethylene glycol dibutyl ether, and tertiary amines such as triethylamine, tributylamine, N, N, N'N'-tetramethylethylenediamine are used. Also, it may be a mixture of two or more kinds. The amount used is not necessarily specified because it varies depending on the individual compound, but when typical tetrahydrofuran is used, it is 0.2 to 1.0 mol times that of the organolithium compound.

The basic component, 1,3-butadiene, is preferably used alone, but may optionally be used with styrene. However, even when styrene is used in combination, the amount used is such that the amount of bound styrene in the obtained butadiene-based polymer is 15% by weight or less, preferably 10% by weight or less. It is preferable in terms of product surface gloss.

In such a butadiene-based polymer, the average 1,2-bond content in the butadiene-based polymer needs to be in the range of 8 to 14 mol%, preferably 10 to 13 mol% based on the bound butadiene. When the 1,2-bond content is lower than this range, the surface gloss of the HIPS product is significantly deteriorated, while when it is higher than this range, irregular stripes may occur on the surface of the HIPS product. Or, 0.01mm ~
By creating foreign particles of about 0.2 mm in size,
Not preferable.

The control of the 1,2-bond content can be achieved by adjusting the kind and amount of the above-mentioned Lewis basic compound during (co) polymerization of 1,3-butadiene or a mixture of styrene and styrene. it can.

A 1,3-butadiene (co) polymer obtained by (co) polymerizing in the presence of the above organolithium compound and, if necessary, a Lewis basic compound, has the chemical formula of R ₁ SiX _4-l A butadiene-based polymer having a branched polymer chain can be obtained by reacting with a compound.
Here, R is a hydrocarbon group, Si is a silicon atom, X is a halogen atom, and l is 0 or 1.

The compound having the chemical formula of R _l SiX _4-l is selected from various compounds such as monomethyl silicon trichloride, monoethyl silicon trichloride, monophenyl silicon trichloride, silicon tetrachloride, silicon tetrabromide, silicon tetraiodide, etc. One kind or a mixture of two or more kinds can be used. In particular, it is preferable to use monomethyl silicon trichloride or silicon tetrachloride in terms of stability during synthesis of butadiene-based polymer and stability of butadiene-based polymer during HIPS production.

On the other hand, in the field of so-called solution anionic polymerization, it is known to use a halogen compound containing a metal atom other than silicon as a branching agent. For example, a butadiene-based compound containing a tin atom-containing compound such as tin tetrachloride is used. Synthesize rubber,
When it is used as a HIPS raw material, some branch breakage occurs when the rubber is dissolved in the styrene monomer, and the extent of this change changes due to subtle differences in the HIPS polymerization formulation.
This is not preferable in view of the object of the present invention because it causes difficulty in controlling the physical properties of PS.

In the synthesis of the butadiene-based polymer used in the present invention,
The addition timing of the compound having the chemical formula of R _l SiX _4-l depends on the butadiene monomer to be bonded in the butadiene-based polymer,
Alternatively, in some cases, the time when the polymerization proceeds to 75% to 95% of the amount of the mixture with the styrene monomer is preferably selected.

Further, the addition amount of the compound R ₁ SiX _4-l is preferably 0.50 to 0.90 g equivalent per 1 g equivalent of the active growth terminal of the butadiene-based polymer. The regulation of such addition timing and addition amount is for controlling the molecular weight distribution and branching morphology of the butadiene-based polymer. That is, when the polymerization of the butadiene monomer, or in some cases the copolymerization with the styrene monomer, is started and the polymerization reaction progresses to 75% to 95%, the compound R ₁ Si
X _4-l was added to cause a so-called coupling reaction to form a polymer chain having a star-shaped branched structure with a molecular weight of 4 times or 3 times depending on l = 0,1 After that, the polymerization reaction between the polymerization-promoting terminal and the residual monomer that are not involved in the coupling reaction is continued to substantially complete the polymerization reaction.

The molecular weight of the star-shaped branched polymer chain in the butadiene-based polymer synthesized in this way is about 2 to 3.7 times the molecular weight of the unbranched polymer chain. The ratio of the measured optical chain lengths is in the range of 1.8 to 3.2. When the ratio of the optical molecular chain length is smaller than this range, the impact strength of the HIPS product is lowered, while when the ratio of the molecular chain length is larger than this range, the HIPS product is The elongation is small, and both are not preferable in view of the object of the present invention. This value is particularly preferably 2.3 or more and 3.0 or less.

The butadiene-based polymer used in the present invention is 1,3
-For the active polymerization end of butadiene (copolymer), R _l
It is characterized by containing 50% by weight or more, particularly preferably 60% by weight or more, of a branched polymer chain obtained by reacting a compound having the chemical formula of SiX _4-l . If the content ratio is 50% by weight or more, HI is preferable in terms of impact strength and appearance physical properties.
Not only can PS be obtained, but good operability can be obtained during the production of HIPS. On the other hand, if the content is less than 50% by weight, the viscosity of the polymerization system when the butadiene polymer is mixed with a monomer such as styrene to produce a HIPS resin becomes high, and the resin machine Inconvenient situations such as deterioration of stability and reproducibility of physical properties occur.

The content of this branched polymer chain can be controlled by adjusting the amount ratio of the above organic lithium compound as the R _l SiX _4-l type compounds, the present invention R _l SiX _4-l type As the compound, a butadiene-based polymer synthesized by a method used in a ratio of 0.5 equivalent times or more and 0.9 equivalent times or less with respect to the organolithium compound is used.

The butadiene-based polymer used in the present invention is produced as described above and has various restrictions. Furthermore, it has a Mooney viscosity of 35 to 50 at 100 ° C. 5% by weight solution viscosity
It should be between 25 and 65 cps.

When the viscosity is lower than these ranges, that is, when the molecular weight is low, the impact strength of HIPS is low, or HIPS
If the stability and reproducibility of the physical properties of the resin deteriorate, or in extreme cases, a so-called salami type layer separation structure between the polystyrene phase and the rubber phase, which is a feature of HIPS, cannot be formed, and the surface of the molded product becomes uneven. The result is that an unsuitable resin is obtained in view of the object of the present invention, such as the occurrence of severe so-called fish eyes.

On the other hand, if the molecular weight exceeds the above range, that is, if the molecular weight is high, the external physical properties such as gloss of HIPS are deteriorated, or H
It becomes difficult to stir and mix in the equipment when IPS is synthesized, and HIP
The homogeneity of the quality of S products will not be maintained.

The butadiene-based polymer used in the present invention is
The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw /
The value of Mn) is in the range of approximately 1.08 to 1.60, preferably 1.10 to 1.40. The value of (Mw / Mn) is the same as the above R _l SiX _4-l
It is controlled by the amount of type compound added and the timing of addition. (M
It is practically difficult to control w / Mn) to be lower than the above range, while if it exceeds the above range, HI
The gloss of the PS product is deteriorated, which is not suitable for the purpose of the present invention.

The present invention is to produce HIPS by radically polymerizing such a butadiene-based polymer and styrene. The reaction ratio of the two is such that the content of the butadiene-based polymer in the obtained HIPS is 5 to 15% by weight. It is preferable that Content of butadiene-based polymer is 5% by weight
When the content is less than 1, the Izod impact strength is low, while when the content exceeds 15% by weight, the surface gloss decreases.

As the polymerization method, either a conventionally known bulk polymerization method or a bulk / suspension polymerization combined method is selected. For example, in the case of the bulk polymerization method, a butadiene-based polymer is dissolved in a styrene monomer, and a catalyst is added or a catalyst is added and heated to carry out the polymerization until a predetermined amount of styrene is reacted. In this case, a small amount of toluene, ethylbenzene, etc. should be added in order to avoid the situation that the viscosity of the polymerization system rises rapidly with the increase of the polymerization conversion rate, stirring becomes difficult, and the reaction becomes uncontrollable due to the rapid increase of the reaction rate. Can be added as a diluent, and these diluents are removed together with unreacted styrene monomer after the completion of polymerization under heating or reduced pressure conditions. In the case of the bulk / suspension polymerization combined use method, a butadiene-based polymer is dissolved in a styrene monomer and heated in the absence of a catalyst or in the presence of a catalyst to polymerize a part of the styrene monomer. The polymerized polymerization mixture is transferred into water in the presence of a suspension stabilizer or a surfactant, stirred and dispersed, and then the polymerization of styrene monomer is completed by the suspension polymerization method. It is performed by taking out particles, washing and drying.

Further, in the production method of the present invention, a part of the styrene monomer forming HIPS together with the butadiene-based polymer may be replaced with a monomer other than styrene which is radically copolymerizable with styrene. Monomers other than styrene include monovinyl aromatic hydrocarbons such as α-methylstyrene, p-methylstyrene, P-tert-butylstyrene, m-methylstyrene and vinylnaphthalene,
Alternatively, conjugated dienes such as butadiene and isoprene, or one or more kinds of monomers selected from acrylonitrile and methyl methacrylate are exemplified, and these are within a range of 50% by weight or less based on all monomers including styrene. Used.

The HIPS produced by the production method of the present invention is put to practical use as various products by a processing method such as injection molding or extrusion molding. It is also possible to mix an ultraviolet absorber, a lubricant, a release agent, a filler and the like.

The HIPS obtained by the method of the present invention thus obtained has an improved and improved balance between Izod impact strength and surface gloss as compared with the conventional so-called impact-resistant polystyrene, and has a large tensile strength and extrusion flowability. Is also an improvement. It is highly useful because it satisfies the physical property levels that are practically required when it is used for vehicle applications, home appliances and the like. In particular, it has been difficult to improve these characteristics at the same time by the conventionally known methods, and the manufacturing method of the present invention brings about remarkable progress in the HIPS manufacturing technology in the art. .

<Examples> The present invention will be described below with reference to Examples.

Examples 1 to 7 and Comparative Examples 1 to 6 An autoclave with a stirrer and a jacket having an internal volume of 10 was thoroughly internally replaced with dry nitrogen gas, and then dried cyclohexane 7,1,3-butadiene (variable amount) and optionally tetrahydrofuran ( (Variable amount) was added to adjust the internal temperature to 55 ° C. Next, n-butyllithium (variable amount) was added to initiate polymerization, and after about 150 minutes of reaction, silicon tetrachloride,
Alternatively, monomethyl silicon trichloride (variable amount) was added and reacted for 30 minutes. After that, 1,3-butadiene (variable amount) was further added and the reaction was carried out for about 60 minutes.

2,6-di-tert- as a stabilizer in the obtained polymer solution
Butyl-4-methylphenol (Sumitomo Chemical Industries, Ltd.
Iser (BHT) is added in an amount of 0.5 weight phr, and the solvent is distilled off by heating.
To obtain polybutadiene.

Add 8.5 parts by weight of these polybutadienes to 91.5 parts by weight of styrene monomer, stir and dissolve at room temperature, then add tert-
0.08 parts by weight of dodecyl mercaptan was added, and the mixed solution was heated in the absence of a catalyst at 120 ° C. for 4 hours with stirring to obtain a solution in which about 30% of styrene monomer was polymerized.

150 parts by weight of water per 100 parts by weight of the solution,
Aluminum hydroxide 0.2 part by weight, sodium dodecylbenzene sulfonate 0.02 part by weight, benzoyl peroxide 0.
3 parts by weight and 0.05 parts by weight of di-t-butyl peroxide were added, and polymerization was carried out at 80 ° C. for 4 hours, 100 ° C. for 3 hours, and 130 ° C. for 5 hours. The polymer was separated from the obtained polymer slurry liquid, washed with water and dried, and then a press sheet was prepared using an extruder and a compression molding machine and used for physical property evaluation.

The physical properties were evaluated by the methods described below.

Izod impact strength It carried out according to JIS K-6871.

Surface gloss It was performed according to JIS Z-8471.

Tensile Strength and Elongation It was carried out according to JIS K-6871.

Melt flow index It carried out according to JIS K-6870.

Surface condition of molded product Visual inspection was conducted to judge the test pieces with irregular stripes, foreign particles, fish eyes, etc. as “X” and those not found as “○”.

The structural analysis of polybutadiene was carried out by the method described below.

Average 1,2-bond content by infrared absorption spectroscopy.

Mooney viscosity Preheat for 1 minute using a Mooney viscometer set to 100 ° C.
The torque value after 4 minutes was read. (ML, 1 + 4,
100 ℃) Mw / Mn, the content of the branched polymer chains, and using the molecular chain length ratio Toyo Soda Ltd. HLC-802UR, 10 ³ as partition column, 10
Columns of ⁴ , 10 ⁶ and 10 ⁷ were selected and a diffractometer was used as the detector. The molecular weight distribution (Mw / Mn) of the polymer was measured at 40 ° C. using tetrahydrofuran (THF) as a developing solvent. In addition, the relative ratio of the heights of the peaks corresponding to the average molecular weights of the branched polymer chains and the unbonded polymer chains is taken as the weight ratio of the respective polymer chains. The chain content was calculated. Then, the loading time of the peak of each polymer chain was converted into the optical molecular chain length by comparing the loading time of standard polystyrene measured separately.

The solution viscosity was set to 25 ° C., and the viscosity was measured in a constant temperature soda using a B-type viscometer under the condition that the polybutadiene concentration in the styrene monomer was 5% by weight.

The results are shown in Table 1.

Comparative Examples 7 and 8 Using two types of commercially available polybutadienes A and B, HIPS was synthesized in the same manner as in Example 1 and the physical properties were measured.

The molecular weight distribution of polybutadiene A is a bimodal distribution having two peaks, and the optical molecular chain length ratio corresponding to the peak on the high molecular weight side and the peak on the low molecular weight side was 3.4. The peak on the high molecular weight side was regarded as a tetrafunctional branched polymer chain, and its content was calculated.

These results are also shown in Table 1.

As can be seen from Table 1, the HIPS (Examples 1 to 7) manufactured according to the manufacturing method of the present invention have high values of Izod impact strength and surface gloss, and also require practically tensile strength and melt flow index. In addition to satisfying the standards, the maximum elongation at break also showed a characteristically large value.

On the contrary, regardless of the production method of the present invention, for example, in Comparative Examples 2 and 5 in which polybutadiene having a low content of branched polymer chains is used, the elongation at break becomes a small value, and ， Izod impact strength is also low, which is not preferable.

In addition, in Comparative Example 3 using polybutadiene having a low solution viscosity, or Comparative Example 6 using polybutadiene having a remarkably small ratio of optical molecular chain lengths regardless of the method of the present invention, the value of Izod impact strength is also On the contrary, in Comparative Example 4 in which polybutadiene having a small solution viscosity and a high solution viscosity is used and Comparative Example 8 in which polybutadiene having a wide molecular weight distribution is used, the surface gloss is lowered, which is not preferable. In Comparative Example 4, the melt flow index also has a small value.

Further, in Comparative Examples 1 and 7 using polybutadiene having a 1,2 bond content of more than 14 mol%, although the value measured as the surface gloss is high, foreign particles and stripes are observed on the surface (Comparative Example 7). , And fish eyes were generated (Comparative Example 1), which are not preferable.

<Effects of the Invention> As described above, according to the present invention, a method for producing HIPS having improved impact resistance and appearance characteristics at the same time, large tensile strength and elongation, and good extrusion flowability is provided. Can be provided.

Claims (5)

[Claims] 1. A method for producing impact resistant polystyrene by radically polymerizing butadiene rubber and styrene, wherein 1,3-butadiene or 1,3-butadiene and styrene are used as the butadiene rubber in the presence of an organic lithium compound. Is polymerized or copolymerized, and a compound defined by the chemical formula R _l SiX _4-l (R = hydrocarbon group, Si = silicon atom, X = halogen atom, and 1 = 0 or 1) is added. A butadiene-based polymer having a branched polymer chain obtained by reacting, wherein the content of 1,2-bond based on the bound butadiene in the butadiene-based polymer is 8 to 14
Mol%, the amount of bound styrene in the butadiene-based polymer is 15% by weight or less, and the ratio of the weight average molecular weight to the number average molecular weight is 1.08.
~ 1.60, the content of branched polymer chains is 50% by weight or more, and the molecular length of branched polymer chains and unbranched polymer chains measured by gel permeation chromatography (GPC) The ratio to the molecular chain length is 1.8 or more and 3.2 or less, and the Mooney viscosity at 100 ° C is 35-50, in styrene at 25 ° C 5
Impact resistance characterized by using a butadiene-based polymer having a solution viscosity of 25 to 65 cps at a weight% concentration and polymerizing so that the content of the butadiene-based polymer in the produced polystyrene is 5 to 15% by weight Polystyrene manufacturing method. 2. The method for producing high impact polystyrene according to claim ₁ , wherein the compound defined by the chemical formula R ₁ SiX _4-l is either silicon tetrachloride or monomethyl silicon trichloride. 3. The butadiene-based polymer is a butadiene-based polymer having a ratio of a branched polymer chain to a molecular chain length of an unbranched polymer chain of 2.3 or more and 3.0 or less. The method for producing the impact-resistant polystyrene according to item 2. 4. The impact-resistant polystyrene according to claim 1, wherein the butadiene-based polymer is a butadiene-based polymer having a branched polymer chain content of 60% by weight or more and 95% by weight or less. Manufacturing method. 5. The method for producing impact-resistant polystyrene according to claim 1, wherein the butadiene-based polymer is a butadiene-based polymer having a ratio of the weight average molecular weight to the number average molecular weight of 1.10 to 1.40.