JPH08333491A - Thermoplastic resin composition for high-speed molding - Google Patents

Abstract

PURPOSE: To obtain a thermoplastic resin compsn. which can reduce the cooling and solidifying time in high-speed molding for producing a high-precision molded item and thus can highten the molding cycle by compounding a thermoplastic resin. an inorg. filler, and a blowing agent each in a specified amt. CONSTITUTION: This compsn. is prepd. by compounding 65-95wt.% thermoplastic resin (e.g. PP) with 5-35wt.% inorg. filler (e.g. glass fiber) and a blowing agent (e. g. sodium dihydrogencitrate) in such a way that the amt. of the blowing agent compounded satisfies the conditions that the gauge pressure at the part corresponding to the center of gravity of the resulting molded item just after filling a mold in injection molding is 0. 5-20kg/cm<2> and that the relation: 5.0×10<-4> ×V>=Vg>=5.0×10<-2> ×V (wherein V is the vol. of the molded item; and Vg is that of the gas generated by blowing) is satisfied in the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin composition for molding at high speed a molded article of high dimensional accuracy manufactured by an injection molding method, a molding method and a molded article obtained by the method. Is.

[0002]

2. Description of the Related Art Generally, thermoplastic resins are used for automobile parts, home electric appliance parts, OA equipment parts, because of their good dimensional stability and moldability.
It has been widely used for furniture parts. Among them, for OA equipment chassis, which require particularly dimensional accuracy, rotary blades of air conditioners, vehicle mechanism parts, etc., thermoplastic resins such as talc, mica, fillers such as calcium carbonate, potassium titanate, and magnesium sulfate. Resin compositions containing whiskers, glass fibers, fibers having a large aspect ratio such as carbon fibers, and other inorganic fillers are used. The drawback of these thermoplastic resin compositions is that the time required for one molding step in injection molding is long.

Generally, the time required for one molding is called a molding cycle, which mainly consists of the following steps. First, the step of closing the mold attached to the molding machine, then the step of injection-filling the plasticized thermoplastic resin composition into this mold, and subsequently the thermoplastic resin composition filled in the mold A pressure-holding step of fully pushing to the end of the mold before solidification, a step of cooling and solidifying the thermoplastic resin composition filled in the mold, and a step of opening the mold and taking out a molded product in the mold, Mass production is achieved by a continuous operation in which these steps are sequentially executed. This molding cycle has a large impact on manufacturing costs as well as material costs. In other words, if the molding cycle is long, the number of moldings produced per unit time is small, but a certain amount of power and cooling water is required for the molding machine, and labor costs per man-hours involved in molding are also required. However, the manufacturing cost per final molded product becomes extremely high. Therefore, shortening the molding cycle is the most important issue for those who produce thermoplastic resin molded products,
Conventionally, various means such as the following have been taken.

From the injection molding machine side, improvement of injection rate, improvement of plasticizing ability, improvement of mold opening / closing speed, and further improvement of eject speed at the time of taking out a molded product have been attempted. From the mold side, development of hot runner system, examination of gas venting method, optimum design of mold material, cooling circuit, etc. have been carried out. Furthermore, recently, a gate cutting method for a resin to be supplied has been developed for a mold. However, from the molding material side, only high fluidization has been attempted from the past with the aim of increasing the speed at injection filling, and speaking of high-speed molding materials, it has become more popular as high-fluidity brands are shown. It was something that was done.

The improvement of the fluidity of these high-fluidity thermoplastic resin compositions is related to the content of various inorganic fillers added, the diameter and length of the fiber, but basically, It depends largely on the properties of the thermoplastic resin that is the matrix. In order to produce a high-fluidity brand in a thermoplastic resin, the molecular weight of the resin can be lowered in the polymerization stage, kneading with an extruder using a peroxide or a catalyst to lower the molecular weight, or liquid paraffin can be added to the thermoplastic resin. A method of adding a metal soap, a higher fatty acid, a higher aliphatic alcohol, a fatty acid amide, a fatty acid ester, or the like and blending them with a kneading extruder is used.

In injection molding using the thermoplastic resin composition highly fluidized in this manner, the injection speed into the mold in the injection filling process can be increased, but the injection filling process occupies the molding cycle. It takes only a short time and most of the time is spent in the cooling process. Therefore,
A new development from the thermoplastic resin side has been urgently required for shortening the molding cycle which is directly related to the manufacturing cost.

[0007]

DISCLOSURE OF THE INVENTION The present invention was developed for the purpose of shortening the time for cooling and solidification of the resin filled in the mold without requiring the fluidity of the resin to shorten the molding cycle at the time of injection molding. , To provide a completely new thermoplastic resin composition. That is, it is an object to provide a resin composition for promoting the solidification rate of the thermoplastic resin filled in the mold.

[0008]

[Means for Solving the Problems] The inventors of the present invention have earnestly studied the resin filling cooling and solidifying behavior in a mold, and have obtained the following findings. The plasticized thermoplastic resin filled in the mold by injection molding solidifies in a shape according to the shape of the mold cavity as cooling progresses. Here, the thermoplastic resin is
It is taken out of the mold after being cooled to a temperature at which its phase changes from a molten state to a solid state and its appearance does not change significantly over time. The temperature at the time of taking out from the mold may be higher or lower than the glass transition temperature. At this time, the specific volume is changed by the phase change inherent to each thermoplastic resin, the dimensional shrinkage due to the temperature decrease after the change to the solid state, and the presence or absence of the progress of crystallization due to the time-dependent temperature decrease are filled in the mold. The thermoplastic resin thus shrinks entirely. Due to this shrinkage, a space between the mold surface for promoting cooling and the thermoplastic resin molded product is delicately opened, and a heat insulating layer with a slight air layer is formed between the mold surface and the molded product. For this reason, the heat transfer coefficient from the high temperature thermoplastic resin molded product to the low temperature mold is remarkably lowered, and it takes a long time to take it out by cooling.

Based on the above findings, the present inventors have further studied a thermoplastic resin composition in which the molded product adheres to the mold as much as possible even when it is cooled and solidified, and the heat transfer efficiency is not lowered, and the present invention has been achieved. did.

That is, the first aspect of the present invention is that the thermoplastic resin 6
5 to 95% by weight, an inorganic filler 5 to 35% by weight, and a foaming agent are contained, and the amount of the foaming agent is the gauge pressure at the time of injection molding immediately after filling in a portion corresponding to the center of gravity of the molded article. A resin composition for high-speed injection molding, which is compounded so as to have a concentration of 0.5 to ²⁰ kg / cm ^2, and the second is a thermoplastic resin of 65 to 95% by weight, an inorganic filler of 5 to 35% by weight, and a foaming agent. For high-speed injection molding, wherein the amount of the foaming agent is such that the volume V _{G of the} gas body generated by foaming with respect to the volume V of the molded product is blended so as to satisfy the following relational expression in the mold. It is a resin composition. V _G = 5.0 × 10 ⁻⁴ × V to 5.0 × 10 ⁻² × V

A third aspect of the present invention is to inject the resin composition according to the first or second aspect of the invention into a mold, stop the injection before the resin is completely filled in the mold, and thereafter Is an injection molding method characterized by filling the inside of a mold by blowing a foaming agent, and a molded product obtained thereby.

The present invention will be described in detail below. The thermoplastic resin used in the resin composition of the present invention is not particularly limited, and examples thereof include polystyrene resin, ABS resin, AS resin,
Examples include general-purpose resins such as low-density polyethylene resin, high-density polyethylene resin, polypropylene resin, vinyl chloride resin, and engineering resins such as polyamide resin, polycarbonate resin, PBT resin, and polyacetal resin. Further, polymer alloys with these resins and various elastomers are also included.

The blending amount of the thermoplastic resin is 65% by weight or more and 95% by weight or less. If the blending amount of the thermoplastic resin is less than 65% by weight, when the resin composition is used, the other fillers are in an excessive proportion, the fluidity of the resin composition is lowered, and the injection filling speed into the mold is considerably high. descend. If the blending amount exceeds 95% by weight, a molded product that requires dimensional accuracy is less likely to eliminate the change in the specific volume of the thermoplastic resin itself, the shrinkage rate due to the temperature decrease of the molded product, or the dimensional shrinkage due to crystallization. Difficult to do. Therefore, the blending amount of the thermoplastic resin is 65% by weight or more and 95% by weight or less, preferably 75% by weight or more and 85% by weight or less.

The inorganic filler to be used in the present invention may be a general commercially available one used for ordinary thermoplastic or thermosetting resins, for example, various fillers such as talc, mica, calcium carbonate, and titanic acid. Various whiskers such as potassium and magnesium sulfate, as well as fibers having a large aspect ratio such as glass fibers and carbon fibers are included. These inorganic fillers have a particle diameter, a fiber diameter,
The fiber length, density, etc. are not particularly limited. It is preferable that these are treated with a surface treatment agent having an affinity with the thermoplastic resin to be blended, for example, a silane coupling agent.

The blending amount of the inorganic filler is 5% by weight or more and 35
% By weight or less. If it is less than 5% by weight, the blending ratio of the thermoplastic resin increases, and the specific volume change from the molten state to the solidified state in the mold, the shrinkage rate due to the temperature change of the molded product, or the dimensional shrinkage due to crystallization. It is difficult to obtain a molded product that requires a dimensional accuracy with a small degree of elimination. On the other hand, if the blending amount exceeds 35% by weight, the proportion of the filler in the thermoplastic resin composition becomes excessive, the fluidity at the time of molding is lowered, and not only a large pressure is required for injection filling into the mold, but also It is not preferable because the filling speed also decreases. Therefore, the content of the inorganic filler is 5% by weight or more and 35% by weight or less, and 15% by weight or less.
It is preferably not less than 25% by weight.

The most characteristic feature of the present invention is that, unlike the conventional injection molding, the filling pressure in the mold is obtained by using the foaming pressure of the foaming agent compounded in the thermoplastic resin composition. is there. Therefore, in the present invention, a small amount of a foaming agent is added to the resin composition.

The inventors of the present invention provided in-mold pressure sensors at several places of molds of various shapes and measured the pressure immediately after the resin containing the foaming agent was filled in the mold. As a result, they have found that the pressure immediately after filling of the mold part corresponding to the center of gravity of the molded product is closely related to the degree of adhesion of the resin to the mold. That is, the pressure of the portion immediately after being filled in the mold is 0.5 Kg / c.
When the amount of the foaming agent is less than m ² , the adhesion strength of the thermoplastic resin composition to the mold is weak, the dimensional shrinkage of the molded product is large, and the dimensional accuracy is lowered, and the resin is filled into the end of the mold. It is easy to become a so-called short shot. On the other hand, when the amount of the foaming agent is such that the pressure immediately after filling is 20.0 Kg / cm ² or more, the amount of the foaming agent blended in the thermoplastic resin composition is excessive, so that the cooling in the mold during molding is not possible. It takes a long time, and when it is taken out from the mold in a normal cooling time, so-called post-foaming occurs in which the molded product is deformed by the gas pressure inside the molded product, and the dimensional accuracy cannot be obtained. Therefore, one method of determining the amount of the foaming agent is to mix the foaming agent so that the pressure immediately after filling the mold at the portion corresponding to the center of gravity of the molded product during injection molding is 0.5 to ²⁰ kg / cm ^{2 in} gauge pressure. This significantly improves the adhesion of the molded product to the mold and significantly reduces the cooling time. Preferably, the composition is such that the pressure immediately after filling in the mold is 2.0 Kg / cm ² or more and 6.0 Kg / cm ² or less in gauge pressure.

The amount of foaming agent may also be determined as follows. That is, the foaming agent is blended so that the volume V _{G of the} gas body generated by foaming with respect to the volume V of the molded product satisfies the following relational expression in the mold. V _G = 5.0 × 10 ⁻⁴ × V to 5.0 × 10 ⁻² × V Specifically, at the time of injection molding of the thermoplastic resin composition, for a molded product volume V that is almost the same as the mold shape, , The volume V _{G of the} gas body generated by the foaming of the foaming agent is 0.05% by volume in the mold.
It is determined to be 5.0% by volume or less. This gas body volume is maintained under a predetermined filling pressure in the mold in a plasticizing temperature range corresponding to various thermoplastic resins. That is, the thermoplastic resin composition filled in the mold in the plasticization molding temperature range contains therein minute voids generated by the decomposition of the foaming agent, and the expansive force of the gas body caused by this is the plasticized heat. By adhering the plastic resin composition to the mold from the inside, cooling and solidification are promoted. The gas body volume is finally equal to the void volume in the cooled molding.

At the time of injection molding, the volume V _{G of the} gas body is 0.05% by volume with respect to the volume V of the molded product corresponding to the shape of the mold.
When the amount of the foaming agent is less than the above, the force for adhering the plasticized thermoplastic resin composition to the mold is weak, and it is possible to resist shrinkage of the thermoplastic resin composition constituting the molded product by cooling and solidification. However, it is not possible to form a gap between the mold surface and the molded product, and a heat insulating layer is formed. On the other hand, at the time of plasticizing molding, if the amount of the foaming agent is such that the volume V _{G of the} gas body exceeds 5.0% by volume with respect to the volume V of the molded product, the thermoplastic resin composition in the plasticized state in the mold is The pressure of the gas body becomes large, and after solidification by cooling, deformation due to so-called post-foaming from the inside of the molded product is likely to occur. Therefore, a long time is required for cooling during molding, which is not preferable. Therefore,
At the time of plasticizing, the foaming agent is mixed so that the volume V _G of the gas body due to the decomposition reaction with respect to the volume V of the molded product is 0.05 volume% or more and 5.0 volume% or less. Preferably 0.5
It is blended so as to be from volume% to 1.5 volume%.

The injection molding temperature may be appropriately set according to the characteristics of the resin and the molding machine. Generally, the plasticizing temperature of the resin can be set as a guide. Specifically, the plasticizing temperature is about 160 to 260 for polyethylene resin which is a general-purpose resin.
℃, polypropylene resin about 180 ~ 280 ℃, polystyrene resin about 190 ~ 280 ℃, ABS resin, A
The S resin has a temperature of about 190 to 280 ° C., the engineering resin polyamide resin has a temperature of about 250 to 300 ° C., and the polycarbonate resin has a temperature of about 260 to 300 ° C.
Injection molding is generally performed in such a temperature range,
It is possible to set it outside this range. In the case of a polymer alloy in which these resins are combined, the temperature in the intermediate region of the combination resin is set, and in the composition in which glass fiber is added to these thermoplastic resins, the temperature is higher by 5 to 10 ° C. than the above plasticization temperature. Is common.

Although the amount of the foaming agent is determined in this manner, specifically, injection molding is carried out on a trial basis by using several kinds of resin compositions in which the amount of the foaming agent is changed in advance, and the above mold filling is performed. The amount that satisfies the pressure condition immediately after or the volume condition of the gas body may be determined. It is preferable that the pressure is set so as to satisfy both the pressure condition immediately after the die filling and the volume condition of the gas body. The specific amount depends on the type of resin, type of foaming agent, injection molding conditions, type of mold, etc., but is generally 0.2.
The amount of the foaming agent used in the present invention is from 0.8 to 0.8% by weight, preferably from 0.4 to 0.6% by weight, and there is no particular limitation. If so, it can be used without problems. For example, an exothermic decomposition type foaming agent such as azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, or polycarboxylic acid salts such as sodium dihydrogen citrate, endothermic heat of sodium bicarbonate, sodium borohydride, etc. Examples include decomposable foaming agents, but the foaming agents are not limited to the above. Therefore, the gas bodies generated in the thermoplastic resin composition by the decomposition of the foaming agent are N ₂ , CO ₂ , H ₂ O and N.
Any material such as H ₃ and H ₂ that is in a gas state during injection molding can be used without particular limitation.

As the chemical foaming agent used in the present invention, a chemical foaming agent which improves the foaming state by adding a nucleating agent, a foaming auxiliary agent, a moisture absorption inhibitor, and other additives can be used. Among them, the foaming agent particularly recommended in the present invention is 10 to 20 ° C. from the lower limit plasticization temperature of the thermoplastic resin used in the present invention.
Those that undergo a decomposition reaction at a high temperature and exhibit an endothermic decomposition reaction are preferable. In the case where the decomposition reaction occurs below the plasticizing temperature of the thermoplastic resin, the gas body due to the decomposition reaction has already been dispersed during injection molding, and there is no adhesion effect of the thermoplastic resin composition to the mold due to gas pressure and cooling efficiency However, if the decomposition temperature is remarkably high, the decomposition reaction does not occur during molding, so that no gas is generated and the effect cannot be obtained.
Further, those which are accompanied by an exothermic reaction at the time of decomposition are recommended because those which are accompanied by an endothermic reaction at the time of decomposition are apt to cause the generated gas body to escape to the surface of the molded product and cause a defective appearance.

As the method for producing the thermoplastic resin composition of the present invention, the above compositions are directly blended using a tumbler, a Henschel mixer, etc., and a uniaxial or biaxial kneading extruder is used at a temperature not higher than the decomposition temperature of the foaming agent. It can be pelletized and manufactured using a kneader, ruder, or the like. At this time, pigments, colorants such as dyes, plasticizers, dispersants, release agents, antistatic agents,
Various additives such as flame retardants can also be added.

Further, the method for producing the thermoplastic resin composition of the present invention is not limited to the above, and it is pelletized by a so-called side-feed extrusion method in which only an inorganic filler and a foaming agent are blended at the discharge stage of a kneading extruder, Further, these can be separately manufactured as masterbatch pellets and can be manufactured in a pellet blend state in which the composition is directly blended with a thermoplastic resin.

A preferred method of molding the resin composition of the present invention thus obtained is to inject the resin composition into a mold,
The injection is stopped before the resin is completely filled in the mold, and thereafter the resin is filled by the foaming of the foaming agent. In the conventional injection molding, as described above, after the injection and filling into the mold, the pressure-holding step in which the thermoplastic resin composition filled in the mold is sufficiently pressed to the end of the mold before it is solidified is essential. . This is to prevent sink marks due to shrinkage of the resin during the cooling process and to prevent the cooling efficiency from decreasing. However, in order to maintain sufficient holding pressure, an injection molding machine with a large mold clamping pressure is required, which is not only a cost disadvantage, but also deteriorates the releasability of the molded product, which is not preferable for shortening the molding cycle. . In the present invention, such a pressure-holding step is unnecessary because the expansion of the foaming agent mixed in a small amount into the resin causes volume expansion after the completion of injection of the resin. Rather, the resin is not completely filled up to the inner end of the mold, that is, injection is stopped in the state of a short shot, and then the resin is completely filled in the mold by volume expansion due to foaming, while the injection nozzle is blocked. A molding method in which the resin is prevented from flowing back is preferable.
In the cooling process, the molded product is in close contact with the mold due to the volume expansion due to foaming, so the cooling efficiency is extremely high.

As described above, when the thermoplastic resin composition of the present invention is used to produce a molded product by an injection molding method, it is possible to remarkably shorten the time required for taking out from the mold by cooling and solidifying as compared with the conventional materials. , Productivity can be greatly improved.

[0027]

EXAMPLES The present invention will be described below with reference to examples. Example 1 AS resin (Lightac A-20
0: manufactured by Mitsui Toatsu Chemicals, Inc. 87.5% by weight, 77.5
%, 67.5% by weight, and glass fiber (ECS03 T-340 / P: manufactured by Nippon Electric Glass Co., Ltd.) as an inorganic filler in 10.0% by weight and 20.0% by weight, respectively.
30.0 wt% was compounded and the twin-screw kneading extruder (AS-3
0: Extruded using Nakatani Machine Co., Ltd. to produce glass fiber-containing AS resin composition pellets.

For each of the above glass fiber-containing AS resin compositions, a carbonate type foaming agent M. B. (EB-207:
20 wt% master batch manufactured by Eiwa Kasei Co., Ltd. was blended in a pellet blend of 2.5 wt% each. The thermoplastic resin composition thus blended was used in Example 1-1,
1-2 and 1-3.

Next, in order to evaluate these thermoplastic resin compositions of the present invention, an injection molding machine (J-100EP: manufactured by Japan Steel Works, Ltd.) having a mold clamping force of 150 t was used to evaluate each composition. Using, a flat plate having a length of 150 mm, a width of 50 mm, and a wall thickness of 2.5 mm having a film gate at one end in the longitudinal direction was formed. At this time, the resin temperature of the molding machine is 220 ° C,
The mold circulating water temperature is set to 20 ° C., and a crystal pressure transducer for plastic molding (615) is attached to the center of the flat mold.
7A: Nippon Kistler Co., Ltd. was installed and the pressure immediately after filling during molding was measured.

The flat plate thus formed was taken out while changing the cooling time, and the flat part was placed on the fulcrums with a width of 100 mm so that the central portion of the molded product coincided with the center of the fulcrums. It was left for 24 hours. Then, after confirming that the thickness of the central part of the molded product is within the specified range of 2.5 mm ± 0.1 mm, the molded product is formed between the fulcrum and the straight line connecting both longitudinal ends of the flat surface of the molded product. Bending was measured as the amount of deformation, which was the distance from the central portion on the plane where deformation was the most. Then, as the cooling time becomes longer, the deformation amount becomes smaller, and the cooling time at the time of molding until the deformation amount finally converges within ± 0.1 mm was obtained. In addition, a part of the flat plate of the molded product at this time is cut, and an electronic hydrometer (ED-120
T: Measure specific gravity using Mirage Trading Co., Ltd.
It was determined gas body volume / molding volume of (V _G / V) from the value. The results are shown in Table-1.

Comparative Example 1 AS resin (Lytac A-20 was used as the thermoplastic resin.
0: Mitsui Toatsu Chemical Co., Ltd.) 90.0% by weight, 80.0
Glass fiber (ECS03 T-340 / P: manufactured by Nippon Electric Glass Co., Ltd.) as an inorganic filler is added to each of 10% by weight and 70.0% by weight, respectively, 10.0% by weight, 20.0% by weight,
30.0 wt% was compounded and the twin-screw kneading extruder (AS-3
0: Extruded using Nakatani Machine Co., Ltd. to produce glass fiber-containing AS resin composition pellets. The thermoplastic resin composition produced in this manner was used as Comparative Example 2-1.
2-2 and 2-3.

With respect to the thermoplastic resin composition produced here, a flat plate molded article was prepared by using an injection molding machine in the same manner as in Example 1, and a sufficient holding pressure was applied immediately after filling at the time of molding to reduce the pressure at that time. After cooling, the cooling time at the time of molding until the flexural deformation amount after releasing falls within a specified range, and the specific gravity of the molded product were measured. The results are shown in Table-1.

Comparative Example 2 As a thermoplastic resin, AS resin (Lytac A-20
0: manufactured by Mitsui Toatsu Chemicals, Inc. 97.5% by weight, 58.5
Glass fiber (EC
S03 T-340 / P: manufactured by Nippon Electric Glass Co., Ltd., each containing no addition and 40.0% by weight, was extruded using a twin-screw kneading extruder (AS-30: manufactured by Nakatani Machinery Co., Ltd.). Pellets of AS resin composition without glass fiber and containing glass fiber were produced. For each of the above glass fiber-free and glass fiber-containing AS resin compositions, a carbonate-based foaming agent M. B. (EB-207: Eiwa Kasei Co., Ltd.
2.5 wt% each was blended in a pellet blend. The thermoplastic resin compositions thus blended are referred to as Comparative Examples 2-4 and 2-5.

Further, as the thermoplastic resin, AS resin (Lytac A-200: manufactured by Mitsui Toatsu Chemicals, Inc.) 79.0
20.0% by weight of glass fiber (ECS03 T-340 / P: manufactured by Nippon Electric Glass Co., Ltd.) as an inorganic filler was added to each of 7% by weight and 73.0% by weight, and the same as in Example 1. Was extruded using a twin-screw kneading extruder (AS-30: manufactured by Nakatani Kikai Co., Ltd.) to produce pellets of the glass fiber-containing AS resin composition. AS with this glass fiber
A carbonate-based foaming agent M. B.
(EB-207: manufactured by Eiwa Kasei Co., Ltd.) 0.5% by weight,
Azo-based foaming agent M. B. (EB-106: Eiwa Kasei Co., Ltd.
7.0% by weight was blended in a pellet blend. The thermoplastic resin composition thus blended was used in Comparative Example 2-
6 and 2-7.

With respect to the thermoplastic resin composition produced here, a flat plate molded product was prepared by using an injection molding machine in the same manner as in Example 1, and the pressure immediately after filling at the time of molding was measured, and the flexural deformation after release was performed. Cooling time during molding until the amount falls within the specified range,
And the specific gravity of the molded product was measured. The results are shown in Table-1.

Example 2 As a thermoplastic resin, polypropylene resin (Mitsui Noblen BJHH: manufactured by Mitsui Toatsu Chemicals, Inc.) 87.5% by weight, 77.5% by weight, 67.5% by weight, 77.5% by weight , 82.5% by weight, and glass fiber (ECS03 T-488 / P: manufactured by Nippon Electric Glass Co., Ltd.) as an inorganic filler in 10.0% by weight, 20.0% by weight and 3%, respectively.
0.0% by weight, talc (Wakida Industry Co., Ltd.) 20.0
%, And magnesium sulfate whiskers (Mosheiji: manufactured by Ube Industries, Ltd.) of 15.0% by weight, extruded using a twin-screw kneading extruder (AS-30: manufactured by Nakatani Machinery Co., Ltd.), and an inorganic filler Pellets of the contained polypropylene resin composition were produced.

For each of the polypropylene resin compositions containing an inorganic filler, a polycarboxylic acid salt type foaming agent M. B. (Activex 536: JM Hube
25% by weight masterbatch manufactured by Company r).
5 wt% each was blended in a pellet blend. The thermoplastic resin composition thus blended was used in Examples 3-1 and 3-
2, 3-3, 3-4, 3-5. Next, in order to evaluate these thermoplastic resin compositions of the present invention, a similar flat plate was formed from each composition by the same molding machine as in Example 1 under the same conditions. The molded flat plate was evaluated in the same manner as in Example 1. The results are shown in Table-2.

Comparative Example 3 As a thermoplastic resin, polypropylene resin (Mitsui Noblen BJHH: manufactured by Mitsui Toatsu Chemicals, Inc.) 90.0% by weight, 80.0% by weight, 70.0% by weight, 80.0% by weight , 85.0% by weight, glass fiber (ECS03 T-488 / P: manufactured by Nippon Denki Sangyo Co., Ltd.) as an inorganic filler in 10.0% by weight, 20.0% by weight, and 30.0% by weight, respectively.
0.0% by weight, talc (Wakida Industry Co., Ltd.) 20.0
%, And magnesium sulfate whiskers (Mosheiji: manufactured by Ube Industries, Ltd.) of 15.0% by weight, extruded using a twin-screw kneading extruder (AS-30: manufactured by Nakatani Machinery Co., Ltd.), and an inorganic filler Pellets of the contained polypropylene resin composition were produced. The thermoplastic resin composition thus blended was used as Comparative Examples 4-1, 4-2, 4-3, and 4.
-4 and 4-5. With respect to the thermoplastic resin composition produced here, a flat plate molded product was molded using an injection molding machine in the same manner as in Example 2, and sufficient pressure was applied immediately after filling during molding, and the pressure at that time was measured. The cooling time at the time of molding until the amount of flexural deformation after molding falls within a specified range, and the specific gravity of the molded product were measured. The results are shown in Table-2.

Comparative Example 4 Polypropylene resin (Mitsui Noblen BJHH: manufactured by Mitsui Toatsu Chemical Co., Ltd.) 97.5% by weight and 58.5% by weight as a thermoplastic resin, and glass fiber (ECS03 T as an inorganic filler) were used. -488 / P: manufactured by Nippon Electric Glass Co., Ltd., each containing no additive and 40.0% by weight, and a twin-screw kneading extruder (AS-30: Nakatani Machinery Co., Ltd.).
Extrusion was performed to produce pellets of polypropylene resin composition containing no glass fiber and containing glass fiber. For each of the glass fiber-containing polypropylene resin compositions, a polycarboxylic acid salt-based foaming agent M. B. (A
ctivex536: J. M. Huber Co., Ltd.)
Were blended in pellet blends at 2.5 wt% each.
The thermoplastic resin composition thus blended was used in Comparative Example 4
-6 and 4-7.

As the thermoplastic resin, polypropylene resin (Mitsui Noblen BJHH: Mitsui Toatsu Chemicals Co., Ltd.)
Glass fiber (ECS03 T-488 /) as an inorganic filler in each of 79.0% by weight and 73.0% by weight.
P: made by Nippon Electric Glass Co., Ltd. 20.0% by weight, 2
0.0 wt% was compounded and extruded using a twin-screw kneading extruder (AS-30: manufactured by Nakatani Machinery Co., Ltd.) in the same manner as in Example 1 to produce pellets of a glass fiber-containing polypropylene resin composition. . For each of the polypropylene resin compositions containing glass fiber, a carbonate type foaming agent M. B.
(EE-207: manufactured by Eiwa Kasei Co., Ltd.) 0.4% by weight,
Azo-based foaming agent M. B. (EE-106: Eiwa Kasei Co., Ltd.
7.0% by weight was blended in a pellet blend. The thermoplastic resin composition thus blended was used in Comparative Example 4-
8 and 4-9. With respect to the thermoplastic resin composition produced here, a flat plate molded article was prepared using an injection molding machine in the same manner as in Example 2, and the pressure immediately after filling during molding was measured, and the amount of flexural deformation after release was within a specified range. The cooling time at the time of molding and the specific gravity of the molded product were measured. Table of the results
It is shown in FIG.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

EFFECTS OF THE INVENTION The thermoplastic resin composition of the present invention can significantly shorten the solidification cooling time when various moldings which require particularly dimensional accuracy are manufactured by injection molding.
It is apparent from the examples that the productivity can be significantly improved and the manufacturing cost can be significantly reduced. Therefore, the thermoplastic resin composition of the present invention can be widely used for OA equipment chassis, rotary blades of various air conditioners, vehicle mechanical parts, instrument panel structural parts, and the like. In particular, it is effective for a molded product having a large wall thickness and a large content of an inorganic filler that requires rigidity and dimensional accuracy, and the molding cycle can be significantly shortened compared to conventional materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatake Misumi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (4)

[Claims] 1. A thermoplastic resin comprising 65 to 95% by weight, an inorganic filler 5 to 35% by weight, and a foaming agent, the amount of the foaming agent being within a mold in a portion corresponding to the center of gravity of the molded product during injection molding. The pressure immediately after filling is 0.5 to 20 in gauge pressure.
A resin composition for high-speed injection molding, which is compounded so as to be kg / cm ² . 2. A thermoplastic resin (65-95% by weight), an inorganic filler (5-35% by weight) and a foaming agent are contained, and the amount of the foaming agent depends on the volume V of the molded product of the gas body generated by foaming. A resin composition for high-speed injection molding, which is compounded so that the volume V _G satisfies the following relational expression in a mold. V _G = 5.0 × 10 ⁻⁴ × V to 5.0 × 10 ⁻² × V 3. The resin composition according to claim 1 or 2 is injected into a mold, the injection is stopped before the resin is completely filled in the mold, and thereafter the inside of the mold is formed by foaming of a foaming agent. An injection molding method, characterized in that it is filled in 4. A molded product having an expansion ratio of 0.05 to 5% obtained by the method of claim 3.