JPH08134321A - Resin composition for gas-assisted injection molding - Google Patents

Abstract

PURPOSE: To provide a resin composition for gas-assisted injection molding having a specific composition and giving molded products of well-balanced toughness and impact resistance because it has satisfactory moldability with no blister and reduced gas leak on gas injection molding. CONSTITUTION: This composition is obtained by formulating (A) 0.02-3 pts.wt. of an organic compound promoting crystallization to 100 pts.wt. of the total of the following components (B) through (E):(B) 60-80wt.% of a crystalline ethylene-propylene block copolymer of 4-10wt.% ethylene content, 3-30g/10min. melt index, and more than 90% content insoluble in boiling n-heptane, (C) 3-15wt.% of rubber selected from ethylene-propylene rubber, ethylene-butene-1 rubber, styrene-butadiene rubber and styrene-butadiene block copolymer rubber, (D) 13-23wt.% of tale of 0.5-3μm average particle size and (E) 1-18wt.% of fibrous magnesium oxysulfate of 0.1-1.5μm fiber diameter and 70-150 aspect ratio wherein the total of the components (D) and (E) is 15-25wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene material suitable for a gas-assisted injection molding method and a method for producing a gas-assisted injection-molded article using the material, which is suitable for interior parts for automobiles.

[0002]

2. Description of the Related Art A gas assisted injection molding method is a method of injecting nitrogen gas into a molten resin filled in a mold, and instead of maintaining the pressure by the resin, efficiently maintaining the pressure from the inside by sinking or sinking. Can be prevented. Other than that, by actively providing a hollow part to reduce the weight, and by arranging the gas channel as a gas guide path, a reinforcement effect can be obtained in addition to the resin flow support effect. It has the effect of improving rigidity (for example, Japanese Patent Publication No. 48-41).
No. 262, Japanese Examined Patent Publication No. 57-14968, JP-A-3-47.
No. 171).

On the other hand, polypropylene-based materials are widely used for automobile parts because they are inexpensive and have a good balance of impact resistance, rigidity and heat resistance. In particular, a resin composition obtained by combining polypropylene and ethylene / propylene rubber, ethylene / butene-1 rubber, styrene / butadiene rubber with talc or fibrous magnesium oxysulfate has a good balance of impact resistance, rigidity and heat resistance. It is known as an important material that can be easily taken (for example, Japanese Patent Publication No. 60-3414 and Japanese Patent Publication No. 61-14).
No. 68, Japanese Patent Publication No. 4-80060, Japanese Patent Publication No. 4-6310
No. 0, Japanese Patent Publication No. 6-27237).

A combination of this gas-assisted injection molding method and the above polypropylene-based material is applied to, for example, automobile parts such as a center cluster, a meter cluster, a trunk board, and an instrument panel. However, it is in the category of new technology to obtain a molded product by combining these two, and the parties are focusing on solving each new problem. One of the major problems among them is, for example, when an instrument panel, which is a large part of automobile parts, is molded with polypropylene material, gas leaks into the resin part around the gas inlet and gas channel. As a result, thinning and swelling due to gas occur, and the impact resistance of that part is reduced, and the commercial value is lost.

The leakage of the injected gas into the peripheral resin portion and the resulting swelling phenomenon are particularly caused when the hollow ratio is increased with an insufficient amount of resin (so-called loose short shot state) to fill the mold cavity, If the molded product is thin and has a large area, and the gas inlet is smaller than that area, or if the gas channel is long and slender, the amount of injected gas to fill the mold cavity before the molten resin solidifies The pressure may be increased and a required amount of gas may be rapidly fed or the gas pressure may be continuously applied for a long time, so that the leakage of gas into the peripheral resin portion and the bulging phenomenon are likely to occur in the molded product.

It is difficult to eliminate these defective phenomena only by molding conditions, and improvement in terms of materials is desired. In the case of a material that is not suitable for gas-assisted injection molding, at the same time when gas is injected, it also flows into the surrounding area and causes gas leakage to the flat surface portion. When the midway portion is closed by fusion of the resins, the gas at the tip portion remains without being collected, and eventually bulges when the mold is opened (pressure release). However, if the material is ideal, it is expected that the gas that has been press-fitted will flow along the rib structure portion of the mold, will not cause gas leakage to the flat surface portion, and will not close the gas flow path, and therefore will not swell.

The resin composition disclosed in Japanese Patent Publication No. 6-27237 is a material resin composition for ordinary injection molding, and can be improved in rigidity, reduced in specific gravity and reduced in weight, and is a large interior component for automobiles. It is a suitable material for However, since this material is not intended to be used for gas-assisted injection molding, its technical perfection is insufficient.

The present inventor has previously found an effective method for solving such a defective phenomenon, and for example, Japanese Patent Application No. 5-289.
No. 143 and Japanese Patent Application No. 6-20524. The resin compositions proposed in these have been developed for the purpose of being used for gas-assisted injection molding, and there are no problems in gas-assisted molding, but the mechanical properties of the material for large interior parts for automobiles, etc. Further improvement in rigidity and reduction in specific gravity and weight are desired.

[0009]

DISCLOSURE OF THE INVENTION The present invention has the mechanical characteristics of a material such as high rigidity, low specific gravity, and light weight, which are required for large interior parts for automobiles such as an instrument panel, and has a gas assist function. It is intended to provide a composite polypropylene resin composition suitable for molding.

[0010]

That is, the present invention is as follows.
(A) Ethylene content 4-10% by weight, MFI 3-3
Crystalline ethylene / propylene block copolymer 6 having 0 g / 10 minutes and a boiling n-heptane insoluble content of 90% by weight or more
0-80% by weight, (b) ethylene-propylene rubber,
3-15 wt% of at least one rubber selected from ethylene / butene-1 type rubber, styrene / butadiene type rubber, and styrene / butadiene block copolymer type rubber,
(C) Talc 13 to 23 having an average particle size of 0.5 to 3 μm
%, And (d) 1 to 8% by weight of fibrous magnesium oxysulfate having a fiber diameter of 0.1 to 1.5 μm and an aspect ratio of 70 to 150, and the sum of (c) and (d) is 15 to 25% by weight. % Component to 100 parts by weight,
(E) A resin composition containing 0.01 to 3 parts by weight of an organic compound having a crystallization-accelerating action, and having a crystallization start temperature of 75 when the molten mixture is cooled at a rate of 150 ° C./min. A resin composition for gas-assisted injection molding having a temperature of not less than 0 ° C.

Further, in the present invention, after the melt of the resin composition for gas-assisted injection molding is injected and injected into the mold cavity, the gas is injected alone or together with the melt while press-fitting to form the mold cavity. It is a method for manufacturing a molded body by a gas assist injection molding method that includes a filling step.
The component (a) is a crystalline ethylene / propylene block copolymer and has an ethylene content of 4 to 4 from the viewpoint of impact resistance.
10% by weight, more preferably 5 to 8% by weight, MFI is 3
-30 g / 10 minutes, more preferably 5-15 g / 10
And boiling n-heptane insoluble matter (a value that is an index of crystallinity and is also called isotactic index value or II) have a value of 90% by weight or more, more preferably 95% by weight or more in view of rigidity and hardness. Is.

Component (a) MFI (JIS-K721
The selected range of the melt flow index value (measured at 0, 230 ° C., 2.16 kg load) is not only for the moldability and impact resistance but also for the injection gas at the time of gas injection molding which is the object of the present invention. Leakage and swelling caused by it are reduced. In particular, the lower the MFI, the less leakage and swelling of the injected gas. Therefore, the MFI of less than 3 g / 10 min is mixed with a small amount of the MFI of more than 30 g / 10 min to obtain the total MFI. A combination of a plurality of crystalline ethylene / propylene block copolymers having a ratio of 3 to 30 g / 10 minutes can also be used in the present invention.

Component (b) is an ethylene / propylene-based rubber.
Rubber, ethylene / butene-1 type rubber, styrene / butadiene
Rubber, styrene / butadiene block copolymer
It is at least one kind of rubber selected from among the rubber. this
These rubbers are used to improve the impact resistance of molded products.
It In the case of rubber that is generally expressed by Mooney viscosity,
Mooney viscosity (JIS-K6300, ML _{1 + 4}10,
40 to 200 is preferable for 0 ° C), especially for large molded products.
50-150 is preferable. Also, styrene and butadiene
For rubber represented by MFI such as block copolymer rubber
If it is MFI, 0.1-10g / 10min is preferable.
Yes. Styrene / butadiene rubber, styrene / butadiene
The amount of bound styrene in block copolymer rubber is 10-6
0%, especially 15-40%, the target improvement in moldability
It is suitable for the balance with the physical properties of products and
Minutes better than ropylene rubber and ethylene butene-1 rubber
It has excellent dispersibility and is effective for improving paintability and adhesiveness.
It To improve light resistance, 95% or more of the residual unsaturated bonds
Hydrogenated is particularly preferable. Also, gas injection
The leakage of the injected gas during shaping and the resulting swelling phenomenon
High melt viscosity as much as possible from the viewpoint of reducing
(That is, those with high Mooney viscosity or MFI
Those with small values) are effective.

The component (c) is talc, which is most preferably used as a component for improving the dimensional accuracy, lowering the coefficient of linear expansion, and improving the rigidity and heat resistance of the product without impairing the moldability. Average particle size of this talc (JIS
-The value measured by Z8901) is preferably 0.5 to 3 μm in terms of the balance between dispersibility and rigidity improvement, and particularly 0.7
˜2 μm is preferred. A material having a whiteness of talc (Hunter-type whiteness value according to JIS P8123) of 80 to 95 is more preferable, and a whiteness of 80 to 93 is more preferable as a material which hardly causes swelling.

Component (d) is a fibrous magnesium oxysulfate having a fiber diameter of 0.1 to 1.5 μm, preferably 0.1 to 1 μm, and an aspect ratio of 70 to 150, which is injected from talc during gas injection molding. There is little gas leakage and swelling caused by it, and the rigidity and heat resistance of the product can be increased with a small amount, which is a preferable material for weight reduction. This magnesium oxysulfate is represented by MgSO ₄ .5Mg (OH) ₂ .3H ₂ O, and is commercially available, for example, under the trade name Mosheiji (manufactured by Ube Chemical Industry Co., Ltd.).

These (a), (b), (c), (d)
The preferable mixing ratio of each of and the reasons therefor will be described. The crystalline ethylene / propylene block copolymer (a) needs to be contained in an amount of 60 to 80% by weight.
This range is a value that satisfies both the rigidity and impact resistance of the product. If it is less than 60% by weight, the flexural modulus of the molded product will be low, and if it exceeds 80% by weight, the impact resistance strength at low temperature will not increase. .

The rubber component (b) must be contained in an amount of 3 to 15% by weight. This amount is necessary to improve the impact resistance strength of the crystalline ethylene / propylene block copolymer (a), especially at low temperatures, but if it is less than 3% by weight, the impact resistance strength at low temperatures is increased. On the other hand, if it exceeds 15% by weight, the flexural modulus of the molded product becomes too low. It is necessary to contain 13 to 23% by weight of talc (c).
If it is less than 13% by weight, the rigidity of the product is not sufficient, and as the amount increases, the weight of the product becomes heavier and the impact resistance strength decreases, so that the content is preferably 23% by weight or less.

The fibrous magnesium oxysulfate (d) must be contained in an amount of 1 to 8% by weight. When the content is 1% by weight or more, the dimensional stability and the rigidity of the product can be increased, which is effective in reducing the weight. It is possible to replace talc (c), but when the amount exceeds 8% by weight. The decrease in impact strength, deformation of molded products and dimensional anisotropy become noticeable. That is, the percentage of these four components in the present invention is (a) / (b) / (c) / (d) = 60-80 /
3 to 15/13 to 23/1 to 8% by weight, and the sum of (c) and (d) is 15 to 25% by weight. Preferably (a) / (b) / (c) / (d) = 65-78 / 5-1
1/15 to 20/2 to 6% by weight and the sum of (c) and (d) is 17 to 24% by weight.

The component (e) is an organic compound capable of increasing the crystallization initiation temperature of the polypropylene resin when the molten mixed resin composition comprising the above four components is rapidly cooled, and is substantially the component ( It is an organic compound having an action of promoting crystallization of the crystalline resin of a). Typical compounds having such an action are described in, for example, Plastics, Vol. 43. No11. It is as described and cited on page 113, is usually called a nucleating agent, and is generally processed into powder and is commercially available.

Of these in the present invention, preferably,
Examples thereof include metal salts of organic carboxylic acids, dibenzylidene sorbitol compounds (commonly known as DBS, substituted DBS), metal salts of aromatic phosphoric acid, and aluminum salts of aromatic carboxylic acids. Among them, the aromatic phosphoric acid metal salt and the aromatic carboxylic acid aluminum salt are most effective in the present invention because the effect can be improved by adding a small amount. Specific examples of the aromatic phosphoric acid metal salt include sodium salt, potassium salt and lithium salt of bis (4-t-butylphenyl) phosphoric acid, 2,2′-
Methylene-bis (4,6-di-t-butylphenyl) phosphoric acid sodium salt, potassium salt, magnesium salt and the like, as well as 2,2'-ethylidene-bis (4,6-di-
Examples thereof include sodium salt, potassium salt and lithium salt of t-butylphenyl) phosphoric acid. Among them, sodium salt of 2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphoric acid is more preferable.

Specific examples of the aluminum salt of aromatic carboxylic acid include aluminum-di-pt-butyl-monohydroxy-benzoic acid. In the present invention,
By accelerating the crystallization rate of the crystalline resin with these compounds, it is possible to reduce the leakage of the injected gas during gas injection molding and the swelling phenomenon caused thereby. More specifically, the resin composition of the present invention is melted at 150 ° C./mi.
When n is cooled at a rapid cooling rate corresponding to the cooling rate in the mold at the time of actual injection molding, the crystallization start temperature can be increased to 75 ° C. or higher. Any compound that has is extremely effective in suppressing the leakage and swelling phenomenon of the injected gas, which is the main object of the present invention. It is preferable that the amount of the compound exhibiting such an effect is as small as possible, but the amount is 0.01 with respect to 100 parts by weight of the total of (a), (b), (c) and (d). ~ 3 parts by weight, more preferably 0.0
3 to 1 part by weight, most preferably 0.05 to 0.5 part by weight. These compounds (e) may be used alone or in combination.

As a compounding method, upon use in injection molding, the materials (a) / (b) / (c) / (d) and (e) may be simply dry-blended, but those materials may be used in advance. It is preferable to use a material obtained by uniformly melt-kneading the material (usually pelletized) for molding. In addition to this, it is preferable to add 0.1 to 0.3 parts by weight of magnesium stearate or aluminum stearate to the above components at the time of melt kneading in order to uniformly disperse each component. The melt-kneading method may be a generally used extruder.

The physical properties of the resin composition thus obtained are preferably MFI of 3 to 25 g / 10 min, more preferably 4 to 15 g / 10 min, preferably 23 ° C. Izod value (ASTM D256). Is 10 kg / cm / cm
Or more, more preferably 15 kg · cm / cm or more, 23
The value of the flexural modulus at ℃ (ASTM D790) is preferably 20000 kg / cm ² or more, more preferably 230.
00 kg / cm ² or more, particularly preferably 25000 kg
If it is / cm ² or more, practically sufficient product performance can be obtained.

That is, (a) consisting of the above-mentioned mixing ratio.
A resin composition comprising at least 5 components of / (b) / (c) / (d) / (e), the melt of which is 150 ° C. /
When cooled at a rate of min, the crystallization start temperature is 7
The composition having a temperature of 5 ° C. or higher can reduce the leakage of the injected gas during the gas injection molding and the swelling phenomenon caused by the injection in the production of the hollow molded article injection molded product using the gas assist injection molding method. The product has practically sufficient moldability and product physical properties.

Next, a method for measuring the crystallization start temperature of the resin composition, which is defined in the present invention, will be described. The measuring device is, for example, a product of Perkin Elmer, and the model is DS
C-7 can be used. The temperature raising / lowering speed of this measuring machine is 0.1
It is possible in the range of 0.1 to 200 ° C./min in the step of ° C., and the transition temperature (Inse
t) can be measured with an accuracy of 156.5 ± 0.2 ° C. The sample to be used for measurement is from a resin composition homogeneously melt-kneaded containing the above-mentioned constituents, which is heated to form a film having a thickness of several μm, or a sliced product having a similar thickness. 0.5 ± 0.2 mg is collected and used. The sample heating rate is 200 ° C./min, and
Hold at 0 ° C. (at which time the sample is in the molten state) and hold for 3 minutes. Then, it is cooled at a rate of 150 ° C./min. The crystallization start temperature under this condition is determined. Regarding the method of obtaining the crystallization start temperature (Onset value), JIS-
K7121 (Section 9-2). The variation in the measured crystallization initiation temperature of the resin composition of the present invention thus obtained is obtained within a range of ± 1.5 ° C.

In addition to the above, the composition of the present invention can exhibit the same performance even if the component (b) is reduced by newly adding a polyethylene resin in an amount of 1/2% by weight or less of the component (b). . Further, addition of fine powder of calcium silicate or wollastonite (proposed in Japanese Patent Application No. 6-20524) effectively reduces the blistering phenomenon during gas injection molding. In addition, heat stabilizers, light stabilizers for the purpose of improving the processability and performance of resins,
Lubricants, colorants and the like can be added within a range that does not impair the intended effect of the present invention.

Next, a method for manufacturing the gas-assisted injection molded article will be described. The gas-assisted injection molding method for plastics is not limited to the patent documents cited in the section of the conventional technology,
There are many publications on it. For example, in recent years, Polyfile, Vol. 28 No. 9 P. 37-3
9 (1991), Plastic Age, Vol. 38
No. 10 P. 132-138 (1992), synthetic resin, Vol. 37 No. 5P. 48-52 (199
1), Industrial Materials, Vol. 42 No. 9 P. 65-
73 (1994).

The injection molding method comprises the steps of injecting a molten resin into a mold cavity attached to a molding machine, cooling it, and taking out a molded body. In this process, the high temperature resin is solidified to form a molded product, but in this process, the volume shrinkage of the resin occurs and as a result, the molded product is dented or warped. In order to prevent this, in the usual injection molding method, there is a step of further pushing the molten resin at the end of the injection step (this is called pressure holding).

The gas-assisted injection molding method is to inject a pressurized gas into the molten resin in a mold, replace this pressure with a holding pressure, and perform cooling during that period. Further, as described in the above-mentioned literature, it is also positively attempted to obtain a molded product having a hollow portion in an intended portion by slightly reducing the resin injected and injected into a mold. The injection method and amount of molten resin and gas in gas-assisted injection molding are as follows: Inject the same amount of resin as the space of the mold cavity and press in an amount of gas that is commensurate with the volume contraction when the resin solidifies. ,
Some even inject less resin than the space of the mold cavity and spread and shape with gas to increase the hollow rate.

Further, there are three types of positions and methods for injecting the gas into the nozzle of the molding machine, the runner, and the mold cavity, which are selected depending on the product shape and purpose. The timing of gas injection is performed at the same time as or after the completion of resin injection. Injecting gas before the completion of injection can improve the hesitation mark,
The method of delaying the timing from the completion of injection is effective in thickening the solidified resin layer and preventing puncture of the resin layer due to gas pressure. The pressure of the injected gas is higher than the internal pressure of the resin. These molten resins, gas injection method and amount thereof, and position and timing of gas injection are controlled and adjusted. In the present invention, the resin composition of the present invention is molded by using the general gas-assisted injection molding method described in the above literature.
The resin composition of the present invention is particularly useful for positively molding a molded product having a hollow portion.

[0031]

EXAMPLE A gas-assisted injection molding machine used was a molding machine (a modified SG220 manufactured by Sumitomo Heavy Industries) capable of injecting and recovering an arbitrary amount and pressure of nitrogen gas from a nozzle. The model die used for the evaluation of the appearance of the molded product has a width of 500 x a length of 200 x a thickness of 3.2 (unit: mm) shown in Fig. 1.
Using a mold for injection molding in which a product drawing (volume = 345 cm ³ ) having a rib structure with a diameter of 13φ and a length of 420 was engraved in the central part of the flat plate, a molded body was molded under the following molding conditions.

The cylinder temperature of the injection molding machine is 190/2.
10/220/230 ° C (nozzle part), screw rotation is 20% of maximum rotation speed, mold set temperature is variable, resin filling speed is 35% of maximum speed, and nitrogen gas injection timing is
A predetermined amount (variable) of resin was injected into the mold and immediately thereafter.
The pressure was 175 kg / cm ² · G, and the injection time was used as a variable. The time (pressure holding time) until the gas was recovered from the nozzle portion after injecting a predetermined amount of nitrogen gas was used as a variable. Cooling time from resin injection to product removal is 80 seconds,
The rest was 15 seconds.

These molding conditions are intentionally prepared under conditions where swelling is likely to occur, and the larger the swelling test condition (by rank), the more severe the condition. Table 1 summarizes the conditions (variable part only). Sampling for judging the appearance of products (occurrence of swelling) was made 10 when the mold temperature was stable, and the rate (%) of swelling of this molded product was expressed as an evaluation point. It should be noted that the evaluation of the leak of the injected gas (gas leak) is not particularly described because it has a substantially proportional relationship with the occurrence of swelling. In addition, the MFI value described below is JI.
It is a melt flow index value measured by S-K7210, 230 degreeC, and a 2.16 kg load.

[0034]

[Table 1]

[0035]

Examples 1 to 7, Comparative Examples 1 to 5 As the crystalline polypropylene of the component (a), MFI = 7, II = 92, ethylene / propylene block polymer (PP1) having an ethylene content of 7% by weight, MFI = 7, II = 97, ethylene-propylene block polymer (PP2) having an ethylene content of 7% by weight was used. As the rubber of the component (b), a hydrogenated styrene / butadiene block copolymer system rubber having a styrene content of 20% by weight and MFI = 0.5 (Tuftec H1071 manufactured by Asahi Kasei Kogyo Co., Ltd.) (SB
1), propylene content 42% by weight, Mooney viscosity =
120 ethylene / propylene copolymer rubbers (trade name: Dutraral CO059 manufactured by Enchem Co., Ltd.) (EP
1) was used. The talc of component (c) has a whiteness of 8
7. Talc (T-3) having an average particle size of about 2 μ was used. As the fibrous magnesium oxysulfate as the component (d), magnesium oxysulfate (MOS) having a fiber diameter of 0.5 μm and an aspect ratio of 100 was used.

Table 2 shows the blending ratio of PP / rubber / talc / MOS. In addition, 0.3 parts by weight of Irganox B215 (manufactured by Ciba-Geigy) and magnesium stearate were added to 100 parts by weight of PP / rubber / talc / MOS in total, and in Example 3, a phosphorus-based nucleating agent was used. Nucleating agent 2,2'-methylene-bis (4,6-
0.3 part of sodium salt of di-t-butylphenyl) phosphoric acid (trade name mark NA-11 manufactured by ADEKA ARGUS CORPORATION) was added. In addition, regarding other examples, aluminum-di-pt-butyl-monohydroxy-benzoic acid (ALPTBB manufactured by Shell Chemical Co., Ltd.), which is an aluminum-based nucleating agent, is used.
0.3 part by weight of A) was added.

These were previously stirred and mixed by using a Henschel mixer, and then melt-kneaded and pelletized by using a twin-screw kneading extruder so as to have a uniform composition. The general physical properties of this composition are shown in Table 3. Further, these materials were subjected to gas injection molding using a model mold, and the result of the swelling test and the crystallization start temperature (Onset value) measured by cutting out from the molded product are shown in Table 3 together. . As a result, it can be seen that the bending rigidity was improved, and if the crystallization start temperature of the resin composition was higher than 75 ° C., the defective phenomena such as leakage and swelling of the injected gas were remarkably improved.

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

Examples 8 to 15 and Comparative Examples 6 to 8 As polypropylene, PP1 and PP2 described in Example 1 were used as the rubber, and as the rubber, the propylene content was 50% by weight and the Mooney viscosity was 80. Company product name
Dutral CO058) (EP2) was used. As talc, talc of T-1 to T-7 having different whiteness was used. As the fibrous magnesium oxysulfate, the same MOS as in Example 1 was used. The polypropylene of Example 12 was PP2, and the others were PP1 including Comparative Examples. The composition (blending ratio) of these materials is PP / EP2 / talc / MOS
= 69/8/20/3. In the same manner as in Example 1, 0.3 parts by weight of Irganox B215 and magnesium stearate were added. Further, in the examples, 0.2 part by weight of ALPTBBA and 0.1 part by weight of Mark NA-11 were added as a nucleating agent. The comparative example is a system containing no nucleating agent. This composition was subjected to gas injection molding using a model mold, and the results of its swelling test and the physical properties of the molded products are shown in Table 4. As a result, it can be seen that talc having a lower degree of whiteness has less defective phenomena such as leakage or swelling of the injected gas. However, on the other hand, the rigidity becomes low. P that has a high II value for polypropylene
P2 gives better results.

[0041]

[Table 4]

[0042]

Examples 16 to 20 The crystalline polypropylene of the component (a) has an ethylene content of 6.5% by weight and MFI =
An ethylene / propylene block polymer (PP3) of 8.5 and II = 97 was used. SB1 and butene-1 content as rubber is 20% by weight, MFI = 1.0 ethylene-butene-1 copolymer rubber (Nippon Synthetic Rubber product name
EBM2011P) (EB1) was used. Talc is T-
The same MOS as in Example 1 was used as 3 talc as the fibrous magnesium oxysulfate. The blending ratios of these are shown in Table 5. In addition to this, Irganox B215
And 0.3 parts of aluminum stearate were added. Further, in the examples, ALPTBBA was set to 0.
Added 3 parts. These were previously stirred and mixed by using a Henschel mixer, and then melt-kneaded and pelletized by using a twin-screw kneading extruder so as to have a uniform composition. Table 6 shows the mechanical properties of molded articles of this composition and the results of the swelling test in gas injection molding using a model mold. From this result, it is understood that if the ratio of the fibrous magnesium oxysulfate is increased, the rigidity can be increased, but the impact resistance is lowered, so that it is necessary to balance the two.

[0043]

[Table 5]

[0044]

[Table 6]

[0045]

[Example 21, Comparative Example 9] The resin composition described in Example 17 and Comparative Example 9 was dug into a gas channel for gas injection molding with substantially the same design and dimensions as the actual passenger car instrument panel product shape. Instrument
Gas injection molding was performed using a panel gas injection molding die (ZAS type). As molding conditions, the cylinder temperature is 200/210/220/230/220 ° C (nozzle part), the screw rotation is 52 rpm, and the mold set temperature is 4
The temperature was 0 ° C., the resin filling rate was 60%, the injection time was 10 seconds, and the nitrogen gas was injected immediately after the injection of a predetermined amount of resin into the mold. The pressure was 185 kg / cm ² · G, and the injection time was 10 seconds. After injecting a predetermined amount of nitrogen gas, the time (pressure holding time) until the gas is collected from the nozzle is 2
It was set to 5 seconds. The cooling time from resin injection to product removal was 50 seconds. With respect to the appearance of each of the 20 molded articles thus obtained, the system using the resin composition of Example 17 had little gas leakage and practically no problem, but Comparative Example 9 was used. All of the systems had a large gas leak area, and swelling was observed at 5 to 8 points, and they could not be put to practical use as products.

[0046]

The resin composition of the present invention does not cause a swelling phenomenon even in gas injection molding under a wide range of molding conditions.
In addition, a product that causes little gas leakage and has no problem in practical use is obtained, and is suitable as a gas injection molding material.
That is, in the production of a hollow-molded product injection molded product using the hollow-molded product injection molding method, it is possible to reduce the leakage of the injected gas during gas injection molding and the swelling phenomenon resulting therefrom, and the product is practically sufficient. It is possible to obtain a product having excellent moldability and a good balance of rigidity and impact resistance.

[Brief description of drawings]

FIG. 1 is a top view and a side view of a gas-assisted injection-molded article used in Examples and Comparative Examples of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C08L 21/00 LBF

Claims (2)

[Claims] 1. (a) An ethylene content of 4 to 10% by weight,
Crystalline ethylene / propylene block copolymer 60 to 80% by weight having an MFI of 3 to 30 g / 10 minutes and a boiling n-heptane insoluble content of 90% by weight or more, (b) ethylene / propylene rubber, ethylene / butene-1. System rubber, styrene
At least one rubber selected from butadiene rubber and styrene-butadiene block copolymer rubber 3 to
15% by weight, (c) 13 to 23% by weight of talc having an average particle diameter of 0.5 to 3 μm, and (d) fiber diameter of 0.1 to 1.
(E) crystals with respect to 100 parts by weight of a component of 5 μm and 1 to 8% by weight of fibrous magnesium oxysulfate having an aspect ratio of 70 to 150, and the total of (c) and (d) is 15 to 25% by weight. A resin composition containing 0.01 to 3 parts by weight of an organic compound having a crystallization promoting action, and when the molten mixture is cooled at a rate of 150 ° C / min, the crystallization start temperature is 75 ° C or higher. Resin composition for gas-assisted injection molding. 2. A mold cavity is prepared by injecting a melt of the resin composition for gas-assisted injection molding according to claim 1 into a mold cavity and then continuously injecting a gas body alone or together with the melt while press-fitting. A method for manufacturing a molded body by a gas-assisted injection molding method, which includes a filling step.