JPH0618960B2 - Styrene resin composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a styrene resin composition suitable for injection blow molding.

(Prior Art) It is known to add a higher fatty acid or a metal salt of a higher fatty acid to a styrene resin to improve the releasability during molding. Particularly, in injection blow molding, it is said that the use of higher fatty acid or its metal salt is effective in releasing at high temperature. (Japanese Patent Publication No. 47-37493, Japanese Patent Publication No. 57-42654) (Problems to be solved by the invention) However, in injection blow molding, not only the mold release defect and the defect phenomenon of uneven thickness due to mold release defect but not the problem of injection blow molding Improving the waist strength of a molded product by molding and making the molded product opaque are weight problems.

For example, in the case of hollow molded products such as lactic acid bacterium beverage containers, if the waist strength is insufficient, it is easy to receive the load in the tank when empty-shipping from the molding process to the filling process or when storing the molded products. Containers with low waist strength are not preferred because they tend to deform and cause troubles during the filling process.

Further, in the above-mentioned lactic acid bacterium beverage container or the like, it is usual to print the product name or the like on the outer surface of the container, but if the transparency is strong, the print does not appear, and the contents are too visible to make it look comfortable.

Therefore, it is necessary to increase the opacity of the container as much as possible.

In addition, the injection blow molding is not performed continuously for 24 hours, the molding is interrupted midway, and when the resin is heat lapped and the molding is started next time, the resin accumulated in the cylinder of the molding machine and thermally deteriorated causes black spots in the molded product. There is also a defective molding phenomenon called a black spot that appears.

(Means for Solving Problems) As a result of intensive research to solve the above-mentioned problems of releasability, uneven thickness, waist strength, and prevention of black spots, the rubber volume Average particle size (dv) is 1.0 to 45 μm, rubber concentration (C
r) is 2.0 to 4.5% by weight, and a rubber-modified polystyrene-based resin or a rubber-modified polystyrene-based resin in the range of dv × Cr = 4 to 18 and a transparent polystyrene-based resin not modified with rubber are mixed and homogenized. By using the resin mixture that becomes, the waist strength of the molded product and the opacity of the molded product are improved,
Further, by adding a specific amount of two or more higher fatty acids having different carbon numbers of 4 or more and one or more metal salts of higher fatty acids to the resin or the resin mixture, uneven thickness and mold release which are problems in injection blow molding can be obtained. The inventors have found that the defective molding phenomenon such as defectiveness and black spots can be improved, and arrived at the present invention.

That is, the present invention, the rubber concentration (Cr) in the resin mixture obtained by mixing and homogenizing the rubber-modified polystyrene-based resin or the rubber-modified polystyrene-based resin and the transparent polystyrene-based resin that has not been modified with rubber is 2.0 to 4.5% by weight. Yes, the volume average rubber particle diameter (dv) of the rubber is 1.0 to 4.5 μm, the value of dv × Cr is within the range of 4 to 18, and the resin or resin mixture 1
0.1 to 0.4 parts by weight of two or more higher fatty acids having different carbon numbers of 4 or more per 00 parts by weight, and the total amount is 0.3 to 0.8
The present invention provides a styrenic resin composition, characterized by containing 0.05 to 0.15 part by weight of one or more higher fatty acid metal salts.

For example, in injection blow molding, the volume average rubber particle size (dv) is
A resin having a rubber concentration (Cr) of 2.0 to 4.5% by weight at 1.0 to 4.5 μm and dv × Cr = 4 to 18 is suitable.

When the volume average rubber particle diameter (dv) is less than 1.0 μm, or when the rubber concentration (Cr) is less than 2.0% by weight, or when the volume average rubber particle diameter (dv) is 1.0 to 4.5 μm and the rubber concentration ( Cr)
Is 2.0 to 4.5% by weight but dv × Cr is less than 4, various problems occur. Specifically,
First, because the opacity of the molded product is insufficient, when printed on the outer surface of the molded product, the printing does not look good. Secondly, since the elastic strength of the molded product is low, the molded product is easily broken by a compressive force applied to the molded product during printing, idling or storage.

Also, when the volume average rubber particle diameter (dv) exceeds 4.5 μm, or when the rubber concentration (Cr) exceeds 4.5% by weight, or when the volume average rubber particle diameter (dv) is 1.0 to 4.5 μm, and the rubber Although the concentration (Cr) is 2.0 to 4.5% by weight, various inconveniences occur even when dv × Cr exceeds 18. Specifically, firstly, the molded product becomes soft and easily deformed by an external force. Secondly, since the fluidity of the resin becomes low and the molded product deteriorates, defective phenomena such as uneven thickness are likely to occur.

That is, only when the volume average rubber particle diameter (dv) and the rubber concentration (Cr) are within the range described in the claims, opacity,
A resin composition having a well-balanced waist strength and moldability of the molded product can be obtained.

The present invention not only determines the range of the volume average rubber particle diameter (dv) and the rubber concentration (Cr), but also the combination of the two, dv × Cr is 4.0 to 1
The resin in the range of 8 has been found to be excellent in opacity and waist strength, and this industrial advantage is great.

To mix and homogenize the rubber-modified polystyrene resin and the rubber-unmodified transparent polystyrene-based resin, once mix the rubber-modified polystyrene resin and the rubber-unmodified transparent polystyrene-based resin with a tumbler or the like, and then use an extruder or the like. It is preferable to knead, but the resin to be mixed may be directly charged into the hopper of the injection blow molding machine, and the adjusting method of the present invention is not limited.

The rubber-modified polystyrene resin used in the present invention is prepared by dissolving a predetermined amount of synthetic rubber in a vinyl aromatic compound monomer or a mixture of a vinyl aromatic compound monomer as a main component and a vinyl compound monomer copolymerizable therewith. And produced by a method of polymerizing a monomer. Preferred examples of the vinyl aromatic compound monomer include styrene, P-methylstyrene and P
-Tertiary butyl styrene, α-methyl styrene and the like, and examples of vinyl compound monomers copolymerizable therewith include unsaturated carboxylic acids such as acrylic acid and methacrylic acid and esters thereof. can give. Examples of the synthetic rubber include polybutadiene and a random or block copolymer of butadiene containing 50% by weight or more of butadiene and another copolymerizable monomer. Examples of the monomer that can be used for copolymerization with butadiene include vinyl aromatic compounds such as styrene and α-methylstyrene, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and their esters, acrylonitrile and methacrylic acid. Examples thereof include vinyl cyan compounds such as ronitrile. Other synthetic rubbers include polyisoprene, polychloroprene, and terpolymers of ethylene-propylene-diene monomer.

Further, the transparent polystyrene-based resin which is not modified with rubber used in the present invention is styrene, P-methylstyrene, P
A vinyl compound which is copolymerizable with an aromatic vinyl compound such as tertiary butyl styrene or α-methyl styrene, or has an aromatic vinyl compound as a main component, for example acrylic acid or methacrylic acid. It is obtained by copolymerizing unsaturated carboxylic acids and their esters, etc., but the component ratio is the same as the ratio of the components other than the rubber component of the rubber-modified polystyrene resin to be blended. It is preferable.

Next, the mixing ratio of the rubber-modified polystyrene-based resin and the transparent polystyrene-based resin not modified with rubber is such that the values of dv, Cr and dv × Cr in the resin composition after mixing are within the range specified in the present invention. If there is, it is not particularly particular.

Furthermore, in addition to the opacity and waist strength of the molded product, in order to improve defective phenomena such as uneven thickness due to poor release, biting into the mold, and black spots due to interruption / restart of molding, the volume average rubber particle diameter and rubber With respect to 100 parts by weight of the polystyrene resin or the resin mixture, which is the concentration, 0.3 to 0.8 parts by weight of two or more higher fatty acids having 4 or more carbon atoms different from each other in the range of 0.1 to 0.4 parts by weight are added, and It has been found to be effective to add 0.05 to 0.15 part by weight of one or more metal salts of higher fatty acids.

When the difference in carbon number between the two types of higher fatty acids is 3 or less, there is no difference in the effect from the case where one type of higher fatty acid is added, and there is little improvement effect on biting into the mold, uneven thickness and generation of black spots. Further, when the addition amount of each is less than 0.1 parts by weight, the effect of the combined use is small. If it exceeds 0.4 parts by weight, the effect corresponding to the amount added is not exhibited and it is not practical.

In addition, when two or more higher fatty acids and a metal salt of one or more higher fatty acids are used in combination, the release of the molded product is good during injection blow molding, the uneven thickness of the molded product is small, and the occurrence of black spots is suppressed. Is done. The addition amount of the metal salt of higher fatty acid at that time is 0.05 to 0.15 parts by weight with respect to 100 parts by weight of the polystyrene-based resin or the resin mixture. If the addition amount is less than 0.05 parts by weight, the addition effect is not obtained, and if the addition amount exceeds 0.15 parts by weight. It is not practical because it does not have the effect of matching the added amount.

The higher fatty acid used in the present invention refers to a monocarboxylic acid having 10 or more carbon atoms and 1 or less unsaturated number in the main chain, but having a carbon number of 10 to 24 from the viewpoint of compatibility with the resin. Is preferred.

Examples include stearic acid (18 carbon atoms), behenic acid (22 carbon atoms), oleic acid (18 carbon atoms, 1 unsaturation), and erucic acid (22 carbon atoms, 1 unsaturation).

The metal salt of higher fatty acid used in the present invention is the metal salt of higher fatty acid described above, and although it is not specified depending on the kind of metal, aluminum, calcium, magnesium, zinc or the like is usually used. These higher fatty acids and metal salts of higher fatty acids are rubber-modified polystyrene resins and /
Alternatively, it may be added during the polymerization of a transparent polystyrene resin that is not modified with rubber, or may be added during the preparation of medium impact polystyrene. In the present invention, the timing of addition of these additives and the method of addition are not limited at all. .
It is also possible to add additives such as colorants, antistatic agents and inorganic fillers which are usually added to styrene resins.

(Examples) The effects of the present invention will be described below with reference to examples, but the present invention is not limited to the examples.

First, in Experiments Nos. 1 to 10, the effects of additives such as higher fatty acids and metal salts of higher fatty acids on the poor molding phenomenon were investigated.

Volume average rubber particle diameter (dv) of rubber is 2.0 μm, rubber concentration (Cr)
Of 3.0% by weight (dv x Cr = 6.0) was added to the rubber-modified polystyrene, mixed with a blender in a blender, and then kneaded with an extruder to homogenize the rubber-modified polystyrene and the various additives. Created a pellet. Injection blow molding is performed with this pellet, uneven thickness, defective release,
The defective molding phenomenon such as black spots was investigated. Table 1 shows the formulations of the additives, and Table 3 shows the data of the molding failure phenomenon in each formulation. Experiment Nos. 1 to 6 are examples, and Experiments Nos. 7 to 10 are comparative examples.

Next, in Experiment Nos. 11 to 18, when the volume average rubber particle diameter (dv) and the rubber concentration (Cr) of the rubber of the rubber-modified polystyrene were variously changed (Table 2), the rubber-modified polystyrene and the additive were used. The physical properties of the resin composition obtained by mixing and homogenizing were investigated.

That is, 0.2 parts by weight of behenic acid, 0.2 parts by weight of stearic acid and 0.1 parts by weight of zinc stearate were mixed with 100 parts by weight of a rubber-modified polystyrene resin in a golender and kneaded with an extruder to prepare a pellet. A three-stage plate and a lactic acid bacterium beverage container were molded using each sample thus prepared, and the opacity, compressive strength and mouth strength were evaluated. Experiment Nos. 11 to 14 are examples, and Experiment Nos. 15 to 15 are
18 is a comparative example.

In Experiment No. 19, the physical properties of the resin composition obtained by mixing and homogenizing the transparent polystyrene not modified with rubber, the rubber modified polystyrene, and the additive were evaluated. In this case, 50 parts by weight of the rubber-modified polystyrene used in Experiment No. 14, 50 parts by weight of transparent polystyrene not modified with rubber and a predetermined amount of additives were mixed in a blender and kneaded in an extruder to prepare a pellet. did. The additive formulation and evaluation method are the same as in Experiment Nos. 11-18.

Table 2 shows the volume average rubber particle diameter (dv) and rubber concentration (C of the rubber of the rubber-modified polystyrene resin used in Experiment Nos. 11 to 19).
r) and the product of both (dv × Cr) are shown.

Further, Table 4 shows the opacity in Experiment Nos. 11 to 19,
The data of compression strength and mouth strength are shown.

In the additive formulations of Experiment Nos. 11 to 19, 0.2 parts by weight of behenic acid, 0.2 parts by weight of stearic acid, and 0.1 parts by weight of zinc stearate were added to 100 parts by weight of (rubber-modified) polystyrene.

Specific evaluation methods for uneven thickness, mold releasability, black spots, opacity, waist strength, etc. in the above test will be described below.

Evaluation method Each sample is manufactured by Sumitomo Heavy Industries, Ltd., injection blow molding machine; Nepiomat 260/700 50S, internal volume 6
Mold 5ml lactic acid bacteria beverage container (12 bottles), (cylinder temperature 230 ℃, injection pressure 140kg / cm ² , injection time)
0.8 seconds, core temperature 110 ℃, blown air pressure 6kg / c
m ² ) The evaluation was performed by the following method.

Unequal wall thickness: For each sample, after continuous 100-shot molding, one molding surface of the reversing mold, in this case, the upper rotation surface (takes 12 pieces)
More continuous 5 shots, totaling 60 pieces, were collected. Since this molded product has a cylindrical part around it, It was placed on a horizontal iron plate (6.3 S or less) having a length of 300 mm, and one end thereof was gradually lifted to obtain the height at which the molded product rolled out. A molded product with a small uneven thickness begins to roll when lifted a little, whereas a molded product with a large uneven thickness has its center of gravity deviated, so the molded product will not roll unless one end of the iron plate is lifted high.

In this way, the rolling height of each molded product was obtained.

Releasability: The releasability of the molded product from the hollow mold is determined by checking the ratio of the molded products that did not fall normally when each molded product was ejected by pressurized air and separated from the mold. Evaluated.

Black dots: After molding the sample for measuring uneven thickness, turn off the power of the molding machine with the resin remaining in the hopper and cylinder, turn it off after leaving it for 18 hours, then turn on the power of the molding machine again. As a result, the temperature was raised for 2 hours. After confirming that the temperature of the cylinder, hot runner, etc. was sufficiently constant, blanking was performed for 5 shots, 10 shots were immediately molded, and among the 120 moldings obtained, the number of moldings with black spots was counted, The occurrence rate was shown.

Opacity: The opacity of each sample was evaluated by making a flat plate having a thickness of 1 mm by injection molding and examining the total light transmittance thereof. The molding temperature was 220 ° C and the mold temperature was 40 ° C. The results are shown in Table 4.

Waist strength: The strength of the aforementioned lactic acid bacterium beverage container was measured. Strength was examined in two ways. First, the compressive strength is the compression jig of the compression tester which is a flat plate, and the flat plate is pressed against the container to perform compression, and the load when the container is broken is defined as the compressive strength.

The other one is the mouth strength. The compression jig of the compression tester is used as a weight, and the weight is set so that the weight hits the weld line of the container at a right angle to perform compression. It was considered as strength. The results are summarized in Table 4.

(Effects of the Invention) As is clear from the above results, the resin composition of the present invention has good mold releasability and few molding defects such as black spots and uneven thickness,
Excellent opaqueness and waist strength of molded products.

By using these resin compositions, it is possible to suppress the injection blow molded product from being caught in the mold, uneven thickness, and black spots, and to increase the opacity of the hollow molded product to give a high-grade feeling, and the hollow strength of the hollow molded product. Can be improved, and its practical value is obviously high.

Claims (1)

[Claims] 1. A rubber concentration (Cr) in a resin mixture obtained by homogenizing a rubber-modified polystyrene-based resin or a rubber-modified polystyrene-based resin and a transparent polystyrene-based resin that has not been modified with rubber is 2.0 to 4.5% by weight. , The volume average particle diameter (dv) of the rubber is 1.0 to 4.5 μm, and the value of dv × Cr is 4 to 18
0.1 to 0.4 parts by weight of two or more higher fatty acids each having 4 or more different carbon numbers with respect to 100 parts by weight of the resin or resin mixture, and a total amount of 0.3 to 0.8 parts by weight, A styrene-based resin composition comprising 0.05 to 0.15 part by weight of one or more metal salts.