JPH0676504B2 - Soft foamable resin composition for injection molding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a foamed resin composition suitable for injection molding which is imparted with air quality, flexibility and heat resistance.

[Prior Art and Problems] In recent years, thermoplastic elastomers having excellent moldability have attracted attention in fields such as automobile interior parts and home electric appliance parts.

As these thermoplastic elastomers, various elastomers such as polyolefin-based, polyurethane-based, polyester-based, polystyrene-based, and polyvinyl chloride-based elastomers have been developed and are now on the market.

Of these, polystyrene-based (SIS, SBS, SEBS, SEPS, etc.) elastomers are particularly good in terms of the balance of flexibility and heat resistance. However, it is insufficient from the viewpoint of molding processability, and it is necessary to add a molding process improving material. The addition of this improving material improves the workability and mechanical strength.
However, flexibility decreases. To prevent this,
At present, a large amount of a rubber softening agent is added to increase flexibility.

These compositions are disclosed, for example, in JP-A-58-206644 and JP-A-58-206644.
-222143, 60-86154, 61-28548 and the like.

Since a large amount of a softening agent is added to these molded products in order to ensure flexibility, bleeding out to the molded products is severe, which causes stickiness to be severe, and coloring with pigments etc. is performed before molding. When used as a product, the product value is lost due to the stickiness of the surface. Further, although the molded product was painted to eliminate stickiness, the paintability was poor even when it was painted, and there was a problem in the adhesiveness of the paint after aging.

Also in terms of moldability, the stickiness causes poor releasability from the mold. Further, although these molded products have no problem in flexibility (hardness), they do not have sufficient feel (feeling) and cannot be used in products requiring both flexibility and feel.

The inventors of the present invention have the above-mentioned drawbacks in that the amount of the softening agent added is minimized and the inside of the composition is foamed so that the conventional softening agent is added in a large amount to the unfoamed product (hereinafter, elastomer solid System) and a composition suitable for injection molding in which the bleeding of the softening agent on the surface of the product and the coating property or the moldability are improved.

[Means for Solving the Problems] The present invention addresses the above problems by blending a polystyrene-based thermoplastic elastomer and a modifier (a polyolefin-based resin as a processability improver and a softening agent as a flexibility-imparting agent). The solution was to obtain an injection foam moldable composition.

That is, the present invention provides a basic polymer 40-70 which is (A) a thermoplastic block copolymer having a block of a vinyl aromatic compound such as polystyrene at the terminal and having polybutadiene, polyisoprenes or polyolefins in the intermediate main chain. % By weight (B) 10 to 40% by weight of polyolefin resin (C) 5 to 25% by weight of softening agent for rubber (D) chemical foaming agent 0.2 per 100 parts by weight of (A) + (B) + (C) The soft foamable resin composition for injection molding composed of ˜3 parts by weight solved the above-mentioned drawbacks.

The feature of the present invention is that the addition amount of the softening agent is small, and
By foaming, the bleed of the softening agent is trapped in the foaming cell and does not move to the surface, and stickiness is suppressed for the amount of the softening agent added.

Furthermore, when injection-foam molding is performed, the surface becomes slightly rough, so that the contact area between the molded product and the mold surface is reduced, and there is no problem with releasability. Moreover, since the stickiness is drastically reduced, molding with a colored material is possible, and painting is not particularly required. Further, even when considering painting, problems such as paintability and adhesiveness of paint are eliminated.
In particular, the injection-foam molded product has a better feel than the elastomer solid-based molded product, and in addition, it is possible to satisfy the two characteristics of flexibility.

The basic polymer of the component (A) in the present invention is XY-
This refers to an X type block copolymer, where X is a block of a vinyl aromatic compound typified by polystyrene, which has a glass transition point at room temperature or higher and can be a physical crosslinking point at room temperature or lower.

Y represents a block in which a diene or a hydrogenated polyolefin thereof such as ethylene / butylene or ethylene / propylene forms a rubber phase.

The weight average molecular weight of this basic polymer is 25,000 to 220,00.
The styrene content is preferably in the range of 0 to 40% (by weight).

Examples of such a polymer having a microscopic two-phase form include, for example, "Califlex TR1107" (Y component polybutadiene) and "Califlex TR1111" (Y component polyisoprene) marketed by Shell Chemical Co., Ltd. ), Product name "SIS-5000" (Y component polyisoprene) marketed by Nippon Synthetic Rubber Co., Ltd., "Quintac 3435" (Y component polyisoprene) marketed by Nippon Zeon Co., Ltd., etc. As for the Y component as a polyolefin-based product, Shell Chemical Co., Ltd. puts it on the market under the product name “Clayton G1652” (Y
Component ethylene-butylene polymer) and the like.
These polymers may be blended alone or in a mixed system. It is preferable that the low hardness Y component is mixed with a basic polymer of polyisoprene.

The blending amount is 40 to 70% by weight of the total blending amount, preferably
50 to 70% by weight. When it is less than 40% by weight, the feel and flexibility are lost, and when it exceeds 70% by weight, the mechanical properties are deteriorated and the molding processability is also problematic.

The polyolefin resin as the component (B) of the present invention includes ethylene, propylene, butene-1, pentene-1, hexene-1,
It is a crystalline resin obtained by polymerizing α-olefin such as 4-methylpentene-1 by a conventional method in the form of a homopolymer or a copolymer. Among these, particularly preferred as the component (B) are crystalline propylene-ethylene random or block copolymers, or high-pressure low density polyethylene (hereinafter LDPE) and linear low-density polyethylene (hereinafter L-LDPE). ).

The MFR (melt flow rate) of these polymers is 1
-100 g / 10 min (ASTM D-1238, 230 ° C, 2.16 kg), preferably 10-100 g / 10 min. If the MFR is less than 1, it will adversely affect the filling property into the details during injection foam molding, resulting in MF.
When R is 100 or more, shearing is less likely to occur at the time of granulating the composition by an extruder, a kneader, etc., and the dispersibility of the polymer is deteriorated, and finally it becomes difficult to maintain fine bubbles in the foamed molded product. These polymers may be used alone or in a mixed system. The compounding amount is 10 to 40% by weight, preferably 10 to 35% by weight, based on the total compounding amount. 10% by weight
In the following, problems will occur in moldability and mechanical properties will deteriorate. If it is less than 40% by weight, the feel and flexibility will be lost.

The non-aromatic mineral oil or liquid or low molecular weight synthetic softening agent is suitable as the softening agent for rubber of the component (C) in the present invention. Generally, a process oil used for softening, increasing the volume and improving the processability of rubber, or a mineral rubber softening agent called extender oil is a mixture of an aromatic ring, a naphthene ring and a paraffin chain. The paraffinic chain has more than 50% of the total number of carbons in the paraffin chain.
30-45% are naphthenic, and have 30 aromatic carbons
More than% is considered aromatic.

The mineral oil-based rubber softening agent used in the present invention is preferably a naphthene-based or paraffin-based one in the above categories. Aromatic compounds having an aromatic carbon number of 30% or more are not preferable in terms of dispersibility with the component (A). The properties of these softening agents for non-aromatic rubbers have a kinematic viscosity of 2 at 98.9 ° C.
~ 40cst, pour point -10 ~ -35 ℃, and flash point 170 ~
Indicates 300 ° C.

As the synthetic softening agent, polybutene, low molecular weight polybutadiene and the like can be used, but the above-mentioned mineral oil type softening agent for rubber gives better results.

The compounding amount of this rubber softening agent is 5 to 25% by weight of the total compounding amount.
And preferably 5 to 20% by weight. If it is 5% by weight or less, no effect is exhibited in terms of feel and flexibility, and if it is 25% by weight or more, mechanical properties are deteriorated and bleeding out of the softening agent occurs.

The chemical foaming agent of the component (D) in the present invention may be either an inorganic or organic decomposable foaming agent. Examples of the inorganic decomposing type foaming agent include sodium bicarbonate, ammonium carbonate, ammonium nitrite, sodium borohydride and the like. Examples of organic decomposing type blowing agents include azido compounds such as azodicarbonamide, azobisformamide, isobutyronitrile and diazoaminobenzene, N, N'-dinitroso pentamethylenetetramine, N, N'-dimethyl, N,
Examples thereof include nitroso compounds such as N'-dinitroterephthalamide. Furthermore, as a decomposition aid for these foaming agents, generally known inorganic zinc stearate, zinc acetate, etc., organic glycerin, diethylene glycol, etc., and a mixed system may be used. Also, a mixed system of an organic foaming agent and an inorganic foaming agent may be used.

To satisfy both the surface condition and the uniformity of foam cells,
A mixed system of organic / inorganic foaming agents is preferred. In particular, as the organic foaming agent, the product name "Vinihol AC # 3" marketed by Eiwa Kasei Co., Ltd., and as the inorganic foaming agent, the product name "hydrocerol" marketed by Mitsubishi Yuka Co., Ltd. Mixtures of "compounds" are preferred.

The amount of these decomposable foaming agents used is the amount of components (A) + (B)
+ (C) 100 parts by weight, 0.2 to 3 parts by weight, preferably 0.5 to 2 parts by weight. When the amount is 0.2 parts by weight or less, the foaming ratio is low, so that air and flexibility cannot be obtained. When the amount is 3 parts by weight or more, no independent cells are formed and continuous cells are formed, and mechanical properties are remarkably deteriorated. The surface condition of is poor.

To prepare a soft foamable resin composition for injection molding comprising the above components (A), (B), (C) and (D), for example, a single-screw extruder, a twin-screw extruder, a Banbury internal A method using a general melt-kneader such as a mixer or various kneaders can be adopted.

Regarding the method of adding the component (D), the composition consisting of the components (A), (B) and (C) is prepared by the kneading machine, and then chemically foamed through a spreading oil (such as liquid paraffin). Can be dry-blended to give a soft foamable resin composition for injection molding.

In addition to the above components (A), (B), (C), and (D), various additives, such as antioxidants, lubricants, colorants, ultraviolet absorbers, antistatic agents, and dispersants, if necessary. It is also possible to add a copper damage inhibitor or the like.

[Examples] The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. In addition, in these Examples and Comparative Examples, injection foam molding conditions and test methods are as follows.

Injection foam molding conditions Molding Machine; shutoff screw-line injection molding machine having a nozzle (UBE MAX D150-10) cylinder temperature: 220 ° C. (maximum) Injection pressure: 700 kg / cm ² Injection speed: 46cm ³ / sec molded article shape; 16 x 16 cm 5 mmt foam flat plate product 16 x 16 cm 3 mmt elastomer solid product Test method The above molded product was used as the test sample.

(1) Hardness (degree) JIS K6301 A type (2) Tensile strength (kg / cm ² ) and elongation (%) JIS K6301 test pieces were prepared using a No. 3 dumbbell.

(3) Tear strength (kg / cm ² ) A JIS K6301 test piece was prepared using a B-shaped dumbbell.

(4) Compression set (%) JIS K6301 70 ° C × 22 hours, the residual strain rate after 25% deformation was determined. A circular dumbbell was used to prepare the test piece.

(5) Foaming ratio It was determined by the specific gravity ratio of the foamed molded product of the same composition and the elastomer solid molded product by the underwater substitution method.

(6) Stickiness of the surface of the molded product The molded product immediately after molding was overlaid, and a load of 100 gr / cm ² was applied to the molded product, and the product was allowed to stand in a 23 ° C x 60RH% constant temperature room for 240 hours, and then judged by the separation property of the molded product.

(7) Appearance of molded product Surface smoothness, flash due to foaming agent, color unevenness, etc. were visually evaluated.

(8) Uniformity of foamed cells The center of the molded product was cut out and the uniformity of the cells was evaluated by a microscope.

(9) Coating performance Coating was performed 24 hours after molding, and the coating performance was evaluated for the following items.

1) Goggle tape test After 24 hours of coating, based on JIS D0202, a safety razor blade was used to divide 10 × 10 mm into 100 pieces, and the pieces were peeled in a direction perpendicular to the surface with cellophane tape having a width of 12 mm, and the number of non-peelings was measured. .

2) Heat resistance test The coated product was left in a gear oven at 100 ° C for 240 hours, and 1 hour after taking it out, a scoring tape test was conducted.

The components used in the examples and comparative examples are as follows.

Ingredients (A) (A-1) SIS-5000 Brookfield viscosity manufactured by Japan Synthetic Rubber Co., Ltd .; 150 cp in 25 wt% toluene solution
s (25 ° C) (A-2) Shell Chemical Co. KRATON G-1652 Brookfield viscosity; 550 cp in 20 wt% toluene solution
s (25 ℃) Component (B) (B-1) Ube Industries' LDPE J3524 density 0.924, MFR90gr / 10 minutes (230 ℃, 2.16kg or less) (B-2) Ube Industries L-LDPE JL2516 density 0.916, MFR42gr / 10 minutes (B-3) Ube Industries Co., Ltd. Propylene-ethylene random copolymer J315GY Ethylene content 3%, MFR15gr / 10 minutes Component (C) (C-1) naphthenic rubber softener Fuji Fujisan Co., Ltd. Fuccol FLEX # 2050N Kinematic viscosity 9.42cst (98.9 ° C) Carbon type analysis C _N = 39.0 wt% C _P = 55.0 wt% (C-2) Olefinic rubber softener Idemitsu Kosan Diana Process Oil PW-90 Kinematic viscosity 11.25 cst (98.9 ° C) Carbon type analysis C _N = 29.0% by weight C _P = 71.0% by weight Component (D) (D-1) Organic foaming agent Vinehole AC # 3 manufactured by Eiwa Chemical Co., Ltd. Main component: Azodicarbonamide Molecular weight = 116 Decomposition temperature = 208 ° C Evolved gas amount = 200ml / gr (0 ° C, 1 atm) In fin. Viscosity = 1 to 35μ True specific gravity = 1.65 (D-2) Inorganic foaming agent Hydrocerol compound manufactured by Mitsubishi Yuka Co., Ltd. Component: Sodium bicarbonate / citric acid mixture Decomposition temperature = 168 to 210 ° C. Generated gas amount = 90 cc / gr Average particle size = 100μ Examples 1 to 6 and Comparative Examples 1 to 6 The above components were mixed in the proportions shown in Table 1 with an antioxidant, a UV inhibitor and a coloring pigment, and the component (C) was mixed with a V-type blender.
Was mixed until it was sufficiently impregnated with the component (A), and kneaded and granulated at 190 ° C. using a single-screw kneader to obtain a composition pellet. 1 part by weight of liquid paraffin was added to the pellets as an extending oil of a foaming agent, and after blending, a foaming agent of the component (D) shown in Table 1 was added and blended, and injection foam molding was performed under the above conditions. A test piece was prepared by using the above, and various tests were conducted by the above method. The results are shown in Tables 1-1 and 1-2.

[Effects of the Invention] By injection-foaming the composition of the present invention, a feeling not obtained with an elastomer solid injection-molded product,
A molded product having flexibility can be obtained. In addition, the softening agent does not easily bleed out, resulting in good coatability.
There are no problems with paint adhesion. Further, since there is no stickiness, the need for coating is eliminated, and the final product can be obtained by coloring the composition with a pigment and molding.
It is very economically advantageous. Also in terms of moldability, there was a problem in mold releasability from the mold in the injection molding of the elastomer solid system, but in the composition of the present invention, there is little tackiness and the effect due to some roughening of the surface due to foaming. Therefore, there is no problem in moldability. In addition, since a clear skin layer is formed even when molding is carried out under the generally used thermoplastic resin injection foam molding conditions, the molded product does not lose its shape. The molded product using the composition of the present invention is suitable for use in automobile interior parts, home electric appliance parts and the like, which require air feel and flexibility.

Claims (1)

[Claims] 1. A backbone polymer, which is a thermoplastic block copolymer having (A) a block of a vinyl aromatic compound such as polystyrene at the end and polybutadiene, polyisoprenes or polyolefins in the intermediate main chain, 40 to 70% by weight. % (B) Polyolefin resin 10 to 40% by weight (C) Rubber softening agent 5 to 25% by weight (D) Chemical blowing agent 0.2 to 100 parts by weight of the above (A) + (B) + (C) A soft foamable resin composition for injection molding comprising 3 parts by weight.