JPS6150488B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to impact-resistant rubber-modified styrenic resin compositions with high gloss and excellent appearance. Conventionally, compositions obtained by polymerizing styrene in the presence of polybutadiene with a high content of 1,4-cis bonds have been known as styrenic resin compositions having high gloss and impact resistance. For example, Japanese Patent Application Publication No. 1973-
86444 etc. However, although these prior art compositions do have a high luster, they have a technical drawback in that they exhibit a pearl-like appearance when closely observed. In other words, the compositions of the prior art have an appearance defect phenomenon in which when a fluorescent light or the like is projected onto the flat surface of the molded product, the outline becomes blurred and a slight rainbow color appears, giving it a pearl-like appearance. This improvement was requested. The object of the present invention is to provide a rubber-modified styrenic resin with high gloss that improves this phenomenon of poor appearance. In order to achieve this objective, the present inventor used polybutadiene having a specific structure as a rubber-like elastic body in a rubber-modified styrenic resin composition, and imparted a specific structure to the soft component in the composition. They discovered that this is effective and completed the present invention. In order to achieve the object of the present invention, in the rubber-modified styrenic resin, as described in the claims, the structure of polybutadiene, which is a rubber-like elastic body,
The particle size of rubber particles (hereinafter referred to as soft component particles) produced by graft polymerization of a monomer such as styrene to the rubber-like elastic body and R R = g ₁ - g ₂ /r ( The symbols will be described later.) It is necessary to specify the values of each of them, and the object of the present invention cannot be achieved if any one of these requirements is missing. This will be explained in more detail below. The method for producing the resin composition of the present invention includes the following steps, as long as the above-mentioned characteristics are satisfied:
Any known polymerization method can be used, such as emulsion polymerization, bulk polymerization, bulk-suspension two-stage polymerization, etc., but preferably bulk polymerization or bulk polymerization in which styrene is polymerized in the presence of a rubber-like elastomer is preferred. - Suspension two-stage polymerization method is applied. As an example, the bulk-suspension two-stage mass method will be explained. First, the polybutadiene of the present invention is added to styrene and heated to 60 to 80°C to dissolve it. It is preferable that this dissolution be as uniform as possible. then 90-120
Bulk polymerization is carried out at °C with stirring until the polymerization rate of styrene is 10-40%. This step will be referred to as a "prepolymerization step," and in the prepolymerization step, the rubber-like elastic body is dispersed into particles under the action of stirring. After the preliminary polymerization step is completed, the mixture is suspended in an aqueous phase containing tertiary calcium phosphate or the like as a suspending agent to carry out suspension polymerization. Usually, polymerization is carried out until the polymerization rate approaches 100%. The step after this preliminary polymerization will be referred to as the "main polymerization step." If necessary, a "post-heating step" may be carried out following the main polymerization step, in which heating is continued after the amount of monomer is reduced. The slurry thus obtained is dehydrated, the beads are separated, dried, and pelletized in an extrusion process. When the polymerization is completely completed, the soft component is dispersed as particles in the hard phase of the styrene polymer in the composition, and this soft component is combined with the rubber-like elastic body graft-copolymerized with styrene. It is made up of encapsulated styrenic polymer. In order to achieve the object of the present invention, it is necessary that the average particle size of the soft component be in the range of 0.5 to 1.5 microns. If the average particle size is less than 0.5μ, the resin composition will have poor impact resistance, and if the average particle size exceeds 1.5μ, the resin composition will have poor gloss. Here, the average particle diameter is the one obtained by taking an electron micrograph of the resin using an ultrathin section method, measuring the particle diameters of 200 to 500 soft component particles in the photograph, and averaging them by weight according to the following formula. Weight average diameter=ΣnD ⁴ /ΣnD ³ where n is the number of particles of the soft component having a particle diameter D. The average particle diameter range specified in the present invention can be achieved by appropriately determining the stirring conditions in the prepolymerization step. In other words, increasing the number of stirrings by the stirring blade will reduce the average particle size, and decreasing the number of stirrings will increase the average particle size, so by selecting an appropriate number of stirrings, the desired average particle size can be achieved. It can be achieved. In order to achieve the object of the present invention, it is necessary that R defined by the following formula satisfy 0.5<R<5.0. R=g ₁ −g ₂ /r where g ₁ is the methyl ethyl ketone (MEK) insoluble content (weight percentage) after heating the composition in nitrogen at 300° C. for 5 hours, and it is encapsulated in a rubber-like elastic body. This means the content of soft components including monovinyl aromatic polymers. g ₂ is the methyl ethyl ketone (MEK) insoluble content (weight percentage) of the composition, meaning the content of soft components without encapsulation of monovinyl aromatic polymers. r is the rubbery elastic weight percentage of the composition. Therefore, R is considered to be a measure indicating the ratio of the monovinyl aromatic polymer encapsulated in the rubbery elastic body to the rubbery elastic body. Whether R is 0.5 or less or 5.0 or more, the appearance of the composition deteriorates. When R is between 0.7 and 2.0, the appearance of the composition is particularly good, which is preferable. R referred to in the present invention is determined as defined above, and the MEK insoluble content in the definition is the weight percentage of the substance insoluble in methyl ethyl ketone, and is determined as follows. In other words, 2.0g of the resin composition
Pour into 50ml of MEK and leave under reflux for 5 hours.
After cooling, the insoluble matter is centrifuged, the solution is removed by decanting, the solution is dried, and the insoluble matter is weighed. Weight of insoluble matter
If xg, the MEK insoluble content is determined by the following formula. MEK insoluble matter content = x/2.0×100 The range of R specified in the present invention is determined by adjusting the operating conditions such as polymerization temperature and initiator used in each production method when producing a polymer by a known method. This can be achieved by establishing the following. Usually this is adjusted by selecting a suitable temperature in the after-heating step and/or by adding crosslinking aids such as peroxides. That is, the higher the temperature in the post-heating step, the smaller R will be, and when an organic peroxide is added in this step, the larger the amount of organic peroxide decomposed, the smaller R will be. Alternatively, R can also be adjusted by the polymerization temperature and decomposition amount of the initiator in the main polymerization step. That is, the lower the polymerization temperature and the greater the amount of decomposition of the initiator, the greater R becomes. This R is thought to be correlated with the amount of monovinyl aromatic polymer that is not chemically bonded to the rubber encapsulated in the soft component, and the behavior of the rubber particles when molding the resin composition is affected by this R. Since it changes depending on R, it is presumed that the appearance also changes. The rubber-like elastic body used in the present invention has 10 to 25 mol% of 1,2-vinyl bonds and 25 to 45 mol% of 1,4-cis bonds.
The essential requirements are a microstructure defined by mole percent, 30 to 65 mole percent 1,4-trans bonds, and a solution viscosity of 30 to 60 centistokes. Rubber-like elastic bodies outside this range, such as cis 1,4
- High cis polybutadiene with a bond of 90 mol% or more,
When using polybutadiene with a solution viscosity of more than 60 centistokes, polybutadiene with a solution viscosity of less than 30 centistokes, styrene-butadiene copolymer rubber (SBR), etc., the resulting resin composition has poor gloss, appearance, and impact resistance. This is because it is significantly inferior to a resin composition using polybutadiene, which is a constituent element of the present invention. That is, if the 1,2-vinyl bond content is less than 10 mol%, the appearance of the composition will be poor, and if it exceeds 25 mol%, the impact resistance of the composition will decrease. If the content of 1,4-cis bonds is less than 25 mol%, the impact resistance will decrease;
Exceeding this will deteriorate the appearance. Furthermore, if the solution viscosity is less than 30 centistokes, the impact resistance will decrease, and if it exceeds 60 centistokes, the appearance will deteriorate. The solution viscosity referred to in the present invention was measured as follows. In other words, 2.5g of rubbery polymer and 47.5g of styrene.
This is the solution viscosity measured using an Ubbelohde viscometer at 30°C. The microstructure of polybutadiene referred to in the present invention is determined as follows. That is ^, polybutadiene is dissolved in carbon disulfide, and the infrared absorption spectrum of ^the solution is measured ^. , 4-cis bonds, the Morello method [D.Morero et al. Chim.e Ind.,
41 , 758 (1959)]. The polybutadiene used in the present invention is produced by polymerizing 1,3-butadiene using a known method, for example, using an organolithium catalyst as disclosed in JP-A-53-130793. The monovinyl aromatic monomer used in the present invention is styrene alone or a mixture of styrene and another vinyl monomer that can be copolymerized with styrene. Examples of other vinyl monomers that can be copolymerized with styrene include acrylonitrile, methyl methacrylate, α-methylstyrene, and nuclear-substituted monobromstyrene. The proportion of these monomers is usually 30% by weight or less, preferably 10% by weight or less of the total monomers. Appearance of the resin composition of the present invention (prevention of pearl pattern)
There is a clear difference compared to the prior art, and the gloss is significantly improved. Since the resin composition of the present invention has both high gloss and high impact resistance, it has extremely high utility value in industrial fields such as electrical equipment and miscellaneous goods. Specifically, it can be suitably used for housings for televisions, radios, cleaners, etc., kitchen utensils, various containers, etc. This will be explained in detail below using examples. Note that unless otherwise specified, "parts" represent parts by weight. Example 1 A Manufacture of resin composition In a polymerization tank with internal volume 120 with stirring, Asaprene 700x (manufactured by Asahi Kasei Corporation) 7 parts styrene 93 parts tertiary dodecyl mercaptan 0.5 parts (Here, Asaprene 700x contains 17 moles of 1,2-vinyl bond) %, 1,4-cis bond 38 mol%, 1,4
- It has a microstructure of 45 mol% trans bonds and a solution viscosity of 45 centistokes. ) and heated at 65°C for 5 hours with stirring to form a homogeneous solution. After that, the temperature was raised at a stirring speed of 250 rpm, and preliminary polymerization was carried out at 110° C. for 7 hours to give a styrene polymerization rate of 30%. Then, the following aqueous phase was prepared in a polymerization tank with an internal volume of 300 and equipped with a stirrer, and the polymerization mixture obtained in the above prepolymerization was added and dispersed in the form of particles. Water 150 parts Tertiary calcium phosphate 3 parts Sodium dodecylbenzenesulfonate 0.02 parts Add benzoyl peroxide to this suspension.
0.20 part of dicumyl peroxide and 0.02 part of dicumyl peroxide were added thereto, and main polymerization was carried out at 90°C for 5 hours and then at 130°C for 2 hours. The obtained suspended particles are separated, dried, and the suspended particles
Irganox as an antioxidant per 100 parts
0.3 part of 1076 was added and extruded using an extruder to form pellets. The average particle size of the soft component particles dispersed in this resin composition was 1.0 μm, and R was 1.1. B Evaluation Using this pellet, test pieces for measuring impact resistance and gloss were made by injection molding, and the following measurements were made. The results are summarized in Table-1. (1) Impact resistance measurement 1/4 on a square plate of 50m/m x 50m/m x 2.5m/m
It is expressed as the energy required to destroy 50% of the test piece when a constant load is dropped from above using a striking center of inch radius. Fracture energy (Kg・cm) = Load drop Height (cm) x Load (Kg) (2) Gloss measurement A square plate of 140 m/m x 80 m/m x 4 m/m was glossed using the JISK8741 method. It was measured. (3) Measurement of appearance Using the square plate described in (2) above, visual judgment was made according to the following criteria. Rating: 1...There is no pearl-like appearance defect, and when the fluorescent light is photographed, the outline of the fluorescent light is not blurred. 2...The above phenomenon is almost absent. Or slightly recognized. 3...The above phenomenon is clearly observed. Comparative Examples 1 to 6 According to Example 1, except that the raw material rubber-like elastic body and the stirring number in the prepolymerization step were changed as shown in Table 1.
A resin composition was obtained. These pellets were injection molded in the same manner as above to make test pieces, and impact resistance, gloss, and appearance were measured. Comparative Examples 1, 2, and 3 have poor appearance, while Comparative Examples 4 and 6
had low impact resistance, and Comparative Example 5 had poor appearance and impact resistance, both of which were inferior in performance to the resin composition of the present invention.

【table】

[Table] Examples 2 to 4 Resin composition pellets were obtained in accordance with Example 1, except that the monomers as raw materials and the stirring number in the prepolymerization step were changed as shown in Table 2. These pellets are made with impact resistance, gloss,
The appearance was measured. Comparative Examples 7 and 8 Resin composition pellets were obtained in accordance with Example 2, except that the number of stirrings in the prepolymerization step was changed as shown in Table 2. These pellets were injection molded in the same manner as above to prepare test pieces, and impact resistance, gloss, and appearance were measured. Comparative Example 7 had poor gloss, and Comparative Example 8 had poor impact resistance. In both cases, the particle size of the soft component is outside the scope of the present invention.

[Table] Examples 5 and 6 Resin composition pellets were obtained according to Example 1 except that the conditions of the main polymerization step and the post-heating step were changed as shown in Table 3. These pellets were injection molded into test pieces in the same manner as above, and impact resistance, gloss, and appearance were measured. Comparative Examples 9 and 10 In the same manner as in Example 5, a resin composition in which R was outside the range of the present invention was produced. The results are shown in Table-3.
Both Comparative Examples 9 and 10 had poor appearance.

【table】

Claims (1)

[Scope of Claims] 1. A resin composition obtained by dissolving 1 to 10 parts by weight of a rubbery elastic material in 90 to 99 parts by weight of a monovinyl aromatic monomer and polymerizing the mixture, wherein (a) the rubbery elastic material is 1,2-vinyl bond 10-25 mol%, 1,4-cis bond 25-45 mol%, 1,4
- having a microstructure of 30 to 65 mol% trans bonds and a solution viscosity of 30 to 60 centistokes; (b) soft component particles dispersed in the composition (the rubbery elastomer is a monovinyl aromatic rubber-like particles produced by graft polymerization with a monomer) have an average particle size of 0.5 to 1.5μ, (c) R defined by the following formula satisfies 0.5<R<5.0, R=g _{1 -g2} /r (However, _g1 : Insoluble content of methyl ethyl ketone after heating the composition in nitrogen at 300°C for 5 hours _g2 : Insoluble content of methyl ethyl ketone in the composition r: Rubber-like content in the composition (elastic weight percentage).