JPH05318541A - Method for injection molding of plastic - Google Patents

Abstract

PURPOSE:To prevent the generation of molding inferiority such as the lowering of the strength and heat resistance due to the temp. rise of a resin material, appearance inferiority such as gas scorch or coloration, the burr in the boundary surface of a mold or the insufficient filling in a terminal part in the injection molding of plastic. CONSTITUTION:Gas is introduced into the cylinder of an injection molding machine at the time of injection molding to pressurize the cylinder and the flowability of a resin is enhanced to suppress the generation of molding inferiority. A gas vent spontaneously and forcibly removing the gas issued into a cavity is combined to still more enhance the suppressing effect of molding inferiority. A thermoplastic resin compsn. containing 10-90% of a compd. becoming gas at 40 deg.C under atmospheric pressure in a volume converted to room temp. and atmospheric pressure is injected into a mold cavity in such a state that the mold cavity is opened to the atmosphere or reduced in pressure and pressed by pressing force equal to or higher than pressure generating an air bubble.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin injection molding method. Due to the variety and excellent characteristics of thermoplastic resins, they are used in a wide range of fields from manufacturing of general machinery, transportation equipment, electric and electronic equipment, civil engineering construction, mining, agriculture, forestry and fisheries to sports and leisure products. There is.

When a thermoplastic resin is used, various molding methods such as extrusion molding, blow molding, rotary molding, pressure molding, press molding, and injection molding can be applied because of its good moldability. The most suitable molding method is selected and used from the application, cost, and production volume. Of these, injection molding is one of the widely used molding methods because it is suitable for mass production and is excellent in cost, strength of molded products, dimensional accuracy, and appearance.

[0003]

2. Description of the Related Art The injection molding method is generally a method of heating a thermoplastic resin in a cylinder to impart fluidity and applying a shearing force with a screw or the like to melt and agitate, and generally injection at high pressure (100 atm or more). It is formed by extrusion into the cavity of a mold that is closed by pressure. For this reason, the thermoplastic resin becomes a high temperature exceeding the heat resistant temperature of the resin in the cylinder or in the mold in whole or in part, which causes various undesirable reactions such as thermal decomposition, oxidative deterioration, and hydrolysis reaction. It is easy to cause side reactions.

Due to these reactions, the molded product has a decrease in strength, a decrease in heat resistance, a defective appearance such as gas burning and coloring,
This is a cause of molding defects such as burrs on the die boundary surface or insufficient filling due to short shots at the ends.
(Basics and applications of injection molding technology-Published by Japan Plastic Processing Technology Association) In order to prevent these, addition of various stabilizers such as phenol-based or hindered amine-based thermoplastic resins and phthalates have been conventionally applied to thermoplastic resins. Fluidity improver such as
There are many innovations such as resin modification and alloying, and many optimizations such as screw optimization and mold optimization have been made in the injection molding machine. There is a limit to improving the basic resin properties, and when used in a large amount with a fluidity improver, it causes a decrease in mechanical strength. there were. (Latest technology of polymer additives-issued by CMC)

On the other hand, in the past, at the time of molding, "introducing gas into the nozzle portion of a cylinder of an injection molding machine or into a mold cavity" (Japanese Patent Publication No. 57-14968), "using a foaming agent (Japanese Patent Publication No. 43- 16844), a method of foaming a molded product by 0.5% or more ”is publicly known, but in both cases, the defective appearance, which was a defect of the injection molded product of the thermoplastic resin, was caused by foaming the entire molded product or locally. This is an effective method to reduce sink marks that appear in uneven parts and ribs, and to reduce weight. However, molded products may cause deterioration in strength due to foaming and appearance defects such as flow marks due to gas. is there.

Incidentally, "a molding method in which a gas is not used or a foaming agent is used, injection molding is first performed with a partly opened mold and then compression molding is performed" (molding process 3 (6)
402 (1991)) is used for compact discs to improve the residual strain of molded products, and is also used for laminating with automobile seats for automobile interiors, but the improvement of molding fluidity is not always sufficient. is not.

[0007]

Focusing on the fact that the main cause of defective molding during injection molding of plastic is the lack of fluidity under temperature limitation due to the heat resistant temperature of the molten thermoplastic resin, The task is to measure the improvement.

[0008]

As a result of intensive studies on the method for solving the above-mentioned problems, the inventors of the present invention plasticized by introducing a gas into a thermoplastic resin at the time of injection molding. By finding that the fluidity is significantly improved, and combining it with the voluntary or forced removal of the gas released in the mold cavity,
It has become possible to improve the formability by avoiding a decrease in strength and a poor appearance, and has reached the present invention.

That is, (1) 10 to 90% by volume of a compound which becomes a gas body at atmospheric pressure and 40 ° C. converted to normal temperature and normal pressure.
The injection molding method, characterized in that the thermoplastic resin composition containing is injected into the mold cavity in a state where the mold cavity is opened to the atmosphere or depressurized, and is pushed with a pressing force higher than the pressure at which bubbles are generated. (2) The method of (1) above, wherein the gas is directly introduced into the cylinder of the injection molding machine,
(3) 10 to 90% by volume of gas converted into normal temperature and normal pressure in the cylinder of the injection molding machine with respect to the thermoplastic resin composition
The method according to (1) above, wherein an amount of the foaming agent that can be generated is used.

(Detailed Description) The thermoplastic resin used in the present invention is a synthetic resin having a property of softening by heating and being deformed by an external force, but retaining its shape when cooled, and having a specific melting point. With polyethylene (PE), polypropylene (PP), polybutene (P
B), polyamide (PA), polyethylene terephthalate (PET), polybutylene terephthalate (PB)
T), polyacetal (POM), polyacrylonitrile (PAN), polyphenylene sulfide (PPS)
Crystalline resin such as polystyrene (PS), ABS, polycarbonate (PC), A that does not have a specific melting point
S, polyphenylene ether (PPE), polyether ether ketone (PEEK), polyether ketone (P
There are many materials such as amorphous resin such as EK) and polyarylate (PAR), or liquid crystal resin, but the material is not limited to a specific thermoplastic resin such as a crystalline resin or an amorphous resin. Combine more than one type of thermoplastic resin, or use PPE / PS, PPE / PA, PBT / AB in advance.
It is also possible to combine two or more kinds of polymers such as S and PBT / PC and use them as a polymer composition as a polymer alloy. Among them, the thermoplastic resin used in the present invention is preferably an amorphous resin.

The term "amorphous" generally means that there is no definite melting point or measurable heat of fusion, but in the present invention, it includes those which show some crystallinity when slowly cooled, and the present invention Those exhibiting crystallinity may be included within the range of not significantly impairing the effect of. The glass transition temperature, melting point, and heat of fusion can be measured using a differential scanning calorimeter.

An example of this is PERKIN-ELMER
There is DSC-II manufactured by the company. Using this device, the heat of fusion heats the sample at a temperature above the expected melting point at a rate of 10 ° C per minute, then the sample is heated to 10 ° C per minute.
The temperature is lowered at a rate of 30 ° C., the temperature is cooled to 30 ° C., the temperature is left for about 1 minute, and then the temperature is raised again at a rate of 10 ° C. per minute. As the heat of fusion, the one that the value measured in the cycle of temperature increase and temperature decrease becomes constant within the experimental error range is adopted. The amorphous thermoplastic resin in the present invention is defined as one having a heat of fusion of less than 1 cal / g measured by the above method.

As the thermoplastic resin, a fibrous, granular or powdery organic or inorganic material, or a thermoplastic resin composition containing a filler in which two or more kinds of these are combined may be used. In addition, various additives such as flame retardants, antioxidants, UV inhibitors, colorants, fluidity improvers, crystallization nucleating agents, crystallization accelerators, release agents and stabilizers are added according to each purpose. It is also possible to use. Examples of the filler include glass fibers, carbon fibers, polyimide fibers, fibers such as alumina fibers, whiskers such as potassium titanate, silicon carbide, alumina, and silicon nitride, talc, clay, silica, mica, calcium carbonate, barium sulfate, and water. Examples thereof include granular and plate-shaped materials such as magnesium oxide, barium hydroxide, shirasu, and glass balloons.

Examples of the flame retardant include phosphoric acid esters such as diphenyl cresyl phosphate, chlorine compounds such as chlorinated paraffin, bromine compounds such as decapromodiphenyl ether, and antimony trioxide. Alkylphenols and thiopropionates are used as antioxidants, benzophenone derivatives and various salicylates are used as UV inhibitors, and pigments and dyes such as titanium oxide are used as colorants.

Phthalates are used as fluidity improvers, and liquid paraffins and higher fatty acids are used as lubricants.
Examples thereof include alcohols such as polyglycol and metal soaps such as calcium stearate. Sulfated aluminum, sodium phosphate, etc. are used as the crystallization nucleating agent, silicone compounds and waxes are used as the release agent, and various metal soaps and epoxy compounds are used as the heat stabilizer.

Next, the gas used in the present invention is a compound having a boiling point of 40 ° C. or less at 1 atm, that is, a compound which becomes a gas at atmospheric pressure and 40 ° C., preferably from the viewpoint of fire explosion and occupational health. Also, a gas that is less problematic in terms of environmental safety, corrosive to the injection molding machine, and less adversely affecting the individual thermoplastic resin is desirable.

Specifically, helium, argon, nitrogen,
Carbon dioxide, inorganic gases such as ammonia, methane, ethane, propane, butane, neopentane, ethylene, propylene, butene, pentene, hydrocarbons such as butadiene and mixtures thereof, chloromethane, chloroethane,
Examples thereof include chlorine compounds such as chlorobutane, fluorine compounds such as trichlorofluoromethane, amines such as methylamine, dimethylamine and trimethylamine.

Further, a gas generating agent (foaming agent) in the cylinder may be used. In this case, as a foaming agent, a carbon dioxide generating agent such as sodium bicarbonate, ammonium bicarbonate, sodium citrate or the like is used. Azodicarbonamide (ADC
A), p, p-oxybis (benzenesulfonylhydrazide) (OBSH), dinitrosopentamethylenetetramine (DPT), azobisformamide (ABF)
A), azobisisobutyronitrile (AIBN), p-
Examples thereof include toluenesulfonyl semicarbazide (TSSC) and trihydrazinotriazine (THT).

The gas or the foaming agent may be used alone or as a mixture of two or more kinds. The amount of gas to be added (when a foaming agent is used, the amount added is converted to the amount of gas generated in the cylinder) is 10 to 90 volumes with respect to the entire resin composition in normal temperature and pressure in the cylinder. %, Preferably 20 to 90% by volume, more preferably 20 to 60% by volume.

When a gas is used, it is desirable to introduce it into the melting zone of the cylinder while controlling the volume of the gas with a flow meter from a conduit equipped with a check valve. It is desirable to mix a predetermined amount with the resin composition and supply it into the cylinder, or to supply the predetermined amount quantitatively into the cylinder independently from a supply port separate from the resin composition. It is important not to let the gas introduced into the cylinder of the injection molding machine escape from the system from the nozzle or the like before the injection molding. Therefore, it is necessary to install a valve mechanism or the like at the tip of the nozzle.

It is another requirement of the present invention that the molded product is not substantially foamed.
Before injection-molding resin during injection molding, the gas inside the cavity of the mold is forcibly evacuated from the flow path of the gap while the mold is closed and the resin does not flow out from part of the mold cavity. Use a pump or the like to reduce the pressure and eliminate it, and forcibly eliminate the gas that is generated in the cavity by operating the vacuum pump during resin injection and during pressure retention, or combine injection molding and compression molding. At the time of injection molding, it is necessary to inject and degas the mold with the mold partially opened and then perform compression molding.

At this time, it is desirable that the fact that the weight of the molded product does not decrease by 0.5% or more with respect to the density when gas is not used is used as a standard that the gas has been removed and foaming has not occurred. It should be noted that there is no particular limitation on the type, type, complex combination, etc. of the injection molding machine.

The present invention will be described below with reference to examples, but the scope of the present invention is not limited thereby. Fineblowing (foaming agent manufactured by Mitsubishi Yuka, trade name) ADCA (azodicarbonamide), sodium citrate, and nitrogen gas were used as the foaming agent in each example.

【Example】

 Examples 1-1 to 1-4 and Comparative Example 1

[Table 1]

Polyethylene terephthalate resin reinforced with 30% glass fiber (Mitsubishi Petrochemical Remappet 330)
And the blowing agent or gas as shown in Table 1 of Japan Steel Works, Ltd. J
Using a -100 type injection molding machine, the end of a spiral so-called spiral die having a width of 8 mm and a thickness of 2 mm is 56
Reduced pressure to 0 Torr, molding temperature 265 ℃, mold temperature 90 ℃
Was molded, and its flow length was measured. Further, the specific gravity of the molded product and its physical properties were measured, and as comparative examples, the same procedure as in the example was carried out except that the foaming agent and gas were not used, and the comparison was made.
The results are shown in Table 1.

Examples 2-1 to 2-4 and Comparative Example 2

[Table 2]

Molding was carried out in the same manner as in Example 1 using polycarbonate (Iupilon S-2000 manufactured by Mitsubishi Gas Chemical Co., Ltd.) at the molding temperature of 290 ° C. and the mold temperature of 90 ° C.
The flow length was measured. The results are shown in Table 2.

Examples 3-1 to 3-4 and Comparative Example 3

[Table 3]

As shown in Table 3, polyphenylene ether (H-40 manufactured by Nippon Polyether) was used with a TU-15 type injection molding machine manufactured by Toyo Kikai Kinzoku Co., Ltd., and a bar flow metal having a width of 8 mm and a thickness of 0.5 mm was used. Type end with vacuum pump 560
Reduce the pressure to Torr, molding temperature 310 ℃, mold temperature 120
Molded at ° C. The results are shown in Table 3.

Example 4

[Table 4]

The same 30% glass fiber reinforced polyethylene terephthalate resin as in Example 1 was used, as shown in Table 4, using a 200T injection compression molding machine manufactured by Komatsu Ltd. to produce 200 × 15.
Use a box-shaped die with a thickness of 0 x 50 mm and a thickness of 3 mm to set the molding temperature to 2
Injection molding was performed at 60 ° C and a mold temperature of 80 ° C. Next, pressing was carried out at a pressing speed of 5 mm / s, and the conditions for full filling without generation of flash were selected. Comparative Example 4 was carried out in the same manner as in Example 4 except that the foaming agent was not added, and the molding conditions were compared with the specific gravity of the molded product. The results are shown in Table 4.

[0031]

From the results of Examples 1 to 3, the Example showed fluidity more than double that of the Comparative Example without causing deterioration of physical properties. Further, as is clear from Example 4, it was found that in injection compression molding, it is possible to perform molding under injection and compression conditions of 1/4 or less by using a foaming agent. In each of the examples, it was confirmed that the specific gravity of the molded product was 0.5% or less in terms of the foaming ratio (change in density of the molded product) despite the introduction of gas, and that substantially no foaming occurred.

Claims (4)

[Claims] 1. A thermoplastic resin composition containing 10 to 90% of a compound which becomes a gas at 40 ° C. at atmospheric pressure at room temperature and atmospheric pressure, with a mold cavity open to the atmosphere or a reduced pressure. The injection molding method is characterized in that the resin is injected into the mold cavity and is back-pressed with a pressing force equal to or higher than the pressure at which bubbles are generated. 2. A method according to claim 1, wherein the gas is introduced directly into the cylinder of the injection molding machine. 3. The volume of gas in a cylinder of an injection molding machine converted into normal temperature and normal pressure with respect to the thermoplastic resin composition is 10
The method of claim 1 wherein an amount of blowing agent capable of generating .about.90% is used. 4. The method according to claim 1, wherein an amorphous resin is used as the thermoplastic resin.