JPH0788902A - Injection molding method for polyolefin resin - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an injection molding method of a polyolefin resin capable of stably injection-molding a molded product having high product surface gloss and appearance without deteriorating industrial productivity. To do. [Structure] In a method for injection molding a polyolefin resin, the inner surface of an injection molding die has a thermal conductivity of 1 × 1.
A coating layer made of a resin having a thickness of 0 to ⁴ to 30 × 10 ⁻⁴ cal / cm · sec · ° C., a melting point or a softening point of 150 ° C. or higher, and a surface gloss of 60% or higher was provided with a thickness of 5 to 1,000 μm. An injection molding method for a polyolefin resin, comprising:

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to injection of a polyolefin-based resin having a high product surface gloss and appearance, which can be used for molding daily sundries, household appliances, interior parts and exterior parts of automobiles and the like. The present invention relates to a molding method.

[0002]

2. Description of the Related Art Conventionally, when injection molding of a polyolefin resin, particularly a polyolefin resin composition containing a mixture of an inorganic filler, a rubber component, etc. is performed, the gloss of the surface of the molded article cannot be obtained. There is a problem that the surface smoothness is inferior and the appearance such as generation of flow marks is inferior. Therefore, as a method for improving the gloss and appearance (surface smoothness, flow mark) of the surface of the molded product in such a case, there is a method of finishing the surface of the mold with higher accuracy. There was a limit to improving the gloss and appearance of the surface of the molded product by performing the surface finishing of. In addition, in order to improve the gloss and appearance of the surface of a molded product, it is usually possible to improve the temperature by supplying a resin with a high temperature for injection molding or by setting a high temperature for the injection molding die. Has been done. However, the method of setting the temperature of the resin to be injection-molded high cannot be expected to make a dramatic improvement, and the method of setting the temperature of the injection-molding mold to be high increases the cooling time of the mold accordingly. This is not preferable because it leads to a reduction in productivity industrially. On the other hand, as a method for solving these problems and imparting excellent gloss and appearance, it is known to provide a coating layer of a low thermal conductivity substance on the inner surface of the mold. However, also in this case, it was not possible to stably injection-mold a molded product having high product surface gloss and appearance.

[0003]

Therefore, an object of the present invention is to provide a polyolefin capable of stably injection-molding a molded product having a high product surface gloss and appearance without causing a decrease in industrial productivity. An object of the present invention is to provide an injection molding method for resin.

[0004]

Means for Solving the Problem [Outline of the Invention] The inventors of the present invention have conducted various studies in order to solve the above problems, and as a result, have found that the inner surface of a mold for injection molding has a specific physical property. By providing a coating layer made of a resin with a specific thickness, it was found that a molded product having high product surface gloss and appearance can be stably molded without causing a decrease in productivity, thus completing the present invention. It has come to do. That is, the polyolefin resin injection molding method of the present invention is a method of injection molding a polyolefin resin, wherein the thermal conductivity is 1 × 10 ⁻⁴ to 30 × 10 ⁻⁴ cal on the inner surface of the injection molding die. / Cm ・ sec ・ ° C,
It is characterized in that a coating layer made of a resin having a melting point or softening point of 150 ° C. or higher and a surface gloss of 60% or higher is provided with a thickness of 5 to 1,000 μm.

[Detailed Description of the Invention] [I] Raw Material (1) Polyolefin Resin The polyolefin resin used as a raw material in the polyolefin resin injection molding method of the present invention includes:
Ethylene homopolymers such as low-pressure polyethylene, medium-pressure polyethylene, high-pressure polyethylene, and linear low-density polyethylene, or ethylene resins such as ethylene / propylene copolymers, propylene homopolymers such as stereoregular polypropylene, or And other α-olefin resins such as propylene-based resins such as propylene / ethylene copolymer, stereoregular poly-1-butene, and stereoregular poly-4-methyl-1-pentene. Among these, ethylene homopolymers, ethylene-based resins such as ethylene / propylene copolymers, propylene homopolymers, or propylene-based resins such as propylene / ethylene copolymers are preferably used. In the polyolefin-based resin injection molding method of the present invention, the effect of the present invention can be remarkably exhibited particularly when the polyolefin-based resin used as a raw material contains an inorganic filler or a rubber component.

(2) Compounding agent (a) Inorganic filler As the inorganic filler to be added to the polyolefin resin, calcium oxide, magnesium oxide, silica, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, Basic magnesium carbonate, calcium carbonate, barium sulfate, talc, clay, mica, zeolite, fibrous potassium titanate, fibrous magnesium oxalphate, fibrous aluminum borate and other whiskers, carbon fiber, glass fiber and the like. it can. The blending amount of the inorganic filler is the polyolefin resin 10
The effect of the present invention can be remarkably exhibited when the amount is generally 1 to 60 parts by weight, preferably 20 to 60 parts by weight, relative to 0 parts by weight.

(B) Rubber component As a rubber component to be blended with the polyolefin resin,
Ethylene / propylene copolymer rubber (EPM), ethylene / 1-butene copolymer rubber, ethylene / propylene / 1-
Polyolefins such as butene copolymer rubber, ethylene / propylene / non-conjugated diene copolymer rubber (EPDM), ethylene / 1-butene / non-conjugated diene copolymer rubber, ethylene / propylene / 1-butene / non-conjugated diene copolymer rubber Examples thereof include rubber and styrene-based rubber such as styrene / butadiene copolymer. Among these rubber components, ethylene / propylene copolymer rubber (EPM), ethylene / propylene
It is preferable to use a polyolefin rubber such as propylene / non-conjugated diene copolymer rubber (EPDM). These rubber components have a Mooney viscosity (ML) measured at 100 ° C.
_{1 + 4} ) is usually 10 to 200, preferably 30 to 150
Those in the range of are used. The amount of the rubber component is generally 1 to 4 with respect to 100 parts by weight of the polyolefin resin.
0 parts by weight, preferably 10 to 40 parts by weight,
The effect of the present invention can be remarkably exhibited.

(C) Additives In the polyolefin resin of the present invention, a pigment and a pigment dispersant for coloring are usually used in many cases, but in order to further improve the performance, in addition to the above components, an oxidation agent is added. Inhibitor,
An antistatic agent, a light stabilizer, an ultraviolet absorber, a neutralizing agent, a metal corrosion inhibitor, a lubricant, a flame retardant, a nucleating agent, a dispersant, a processability stabilizer, a fluidity improver and the like can be added.

[II] Injection Molding In the polyolefin resin injection molding method of the present invention, the structure of the mold used is most characterized. (1) Mold for injection molding (a) Mold The mold used in the method of the present invention is formed from at least an upper mold and a lower mold so that the mold can be opened after injection molding. A cavity is formed when they are fitted together. A product is molded by injecting the polyolefin resin into the cavity. The upper mold and the lower mold are formed by using a metal such as steel or an alloy containing iron as a main component, an aluminum alloy, a zinc alloy as a main material.

(B) Covering Layer The mold used in the method of the present invention is formed on the inner wall surfaces of the upper mold and the lower mold on the cavity side when the upper mold and the lower mold are combined. A resin coating layer having the following physical properties is formed.

The coating layer formed on the inner wall surfaces of the upper mold and the lower mold is a resin having the following physical properties. Resin physical properties Thermal conductivity Thermal conductivity is 1 × 10 ⁻⁴ to 30 × 10 ⁻⁴ cal / cm · s
ec · ° C., preferably 1 × 10 ^{−4 to} 5 × 10 ⁻⁴ cal /
cm · sec · ° C. If the thermal conductivity is out of the above range, high gloss and high appearance cannot be achieved. Melting point or softening point 150 ° C. or higher, preferably 150 to 2
It is at 60 ° C. High gloss when the melting point is less than the above range,
High appearance cannot be achieved. Surface gloss Surface gloss is 60% or more, preferably 80% or more. If the surface gloss is less than the above range, high gloss and high appearance cannot be achieved. The surface gloss is measured according to JIS-Z.
It can be measured according to 8741 (reflection angle 60 degrees).

Resin thickness The resin thickness is 5 to 1,000 μm, preferably 50 to 50
The thickness is 0 μm. If the resin wall thickness is less than the above range, high gloss and high appearance cannot be achieved, and if it exceeds the above range, cooling takes time and productivity is reduced.

Resins Specific examples of the resin having the above physical properties include polyethylene terephthalate, polytetrafluoroethylene, polycarbonate, nylon and the like.

Formation of coating layer The coating layer is formed by spraying the resin on the inner surface of the mold or by adhering a film of these resins to the inner surface of the mold.

(2) Injection Molding (a) Preparation of Raw Material The above-mentioned raw material polyolefin resin or the polyolefin resin is mixed with an inorganic filler and / or a rubber component. Kneading is performed in order to perform particularly sufficient mixing. The kneading is a conventional kneading machine,
For example, kneading is performed using an extruder, a Banbury mixer, a super mixer, a roll, a Brabender plastograph, a kneader or the like. It is preferable to knead using an extruder, especially a twin-screw extruder. The above kneading is generally performed under normal pressure,
It is carried out under the condition of a temperature of 180 to 260 ° C, preferably 190 to 230 ° C. (b) Injection molding Molding is performed using an injection molding machine. Injection molding is generally performed at a resin temperature of 180 to 250 ° C. and 300 to 1,300.
The injection pressure is kg / cm ^{2, and} the mold temperature is 20 to 60 ° C.

[III] Injection-Molded Product (1) Physical Properties The injection-molded product obtained by the method of the present invention has a product surface gloss of 50% or more, preferably 80% or more, and a good or very good product surface appearance. It is also possible to obtain a product having a high flexural modulus in which an inorganic filler is blended in a high concentration. (2) Uses The injection-molded product thus obtained can be used as an injection-molded product for various purposes. Specifically, automobile exterior parts such as automobile bumpers, mat guards, side moldings, wheel caps, spoilers, vehicle interior parts such as instrument panels, levers, knobs, linings, pots, vacuum cleaners, washing machines, Examples include home electric appliances parts such as refrigerators, lighting equipment, and audio equipment, and daily sundries such as color boxes and storage cases.

[0017]

EXAMPLES The injection molding method for polyolefin resin of the present invention will be described in detail below with reference to experimental examples. [I] Evaluation Method The physical properties in the examples and comparative examples were evaluated by the methods described below. (1) Surface gloss: measured according to JIS-Z8741. (2) Surface appearance: Measured visually. The criteria are as follows. ◎: Very good ○: Good ×: Poor XX: Very bad (3) Flexural modulus: 23 according to JIS-K7203
It was measured at a temperature of ° C.

[II] Experimental Example (1) Examples 1-2, 5-6 and 8 Examples 1-2, 5-6 and 8 were resin compositions obtained by kneading the raw materials shown in Table 1. At the time of injection molding using, the cavity surface of the mold has a wall thickness of 500 μm, a thermal conductivity of 3 × 10 ⁻⁴ cal / cm · sec · ° C., and a melting point of 25.
Using a mold provided with a coating layer made of a polyethylene terephthalate resin (PET) film having a surface gloss of 95% at 4 ° C. or more, under a condition of a resin temperature of 200 ° C., an injection pressure of 500, and a mold temperature of 40 ° C., 120 mm × 120 mm x 3 mm
A sheet of t was injection molded. The results are shown in Table 1.

(2) Examples 3 to 4, 7 and 9 In Examples 3 to 4, 7 and 9, when the resin composition obtained by kneading the raw materials shown in Table 1 was used for injection molding, The surface of the mold cavity has a wall thickness of 300 μm and a thermal conductivity of 2
× 10 ^-4 cal / cm · sec · ° C, softening point 240 ° C,
Using a mold provided with a coating layer made of a polycarbonate resin (PET) film having a surface gloss of 95%, under the same conditions as in the above example, 120 mm × 120 mm × 3 mm
A sheet of t was injection molded. The results are shown in Table 1.

(3) Comparative Examples 1 to 4 and 9 Comparative Examples 1 to 4 and 9 were used to mold the mold cavity when injection molding was performed using the resin composition obtained by kneading the raw materials shown in Table 1. Using a mold obtained by subjecting the tee surface to a mirror surface and performing a chrome plating treatment, under the same conditions as in the above-mentioned example, 120 mm
A sheet of × 120 mm × 3 mmt was injection molded. The results are shown in Table 1.

(4) Comparative Examples 5-8 In Comparative Examples 5-8, when the resin composition obtained by kneading the raw materials shown in Table 1 was used for injection molding, the surface of the cavity of the mold was Thermal conductivity of 5.9 × 10 with a wall thickness of 100 μm
^-4 cal / cm.sec..degree. C., melting point 327.degree. C., using a mold provided with a coating layer made of Teflon resin sprayed with a surface gloss of 10%, under the same conditions as the above examples, 120 mm ×
A 120 mm × 3 mmt sheet was injection molded. The results are shown in Table 1.

[0022]

[Table 1]

[0023]

The polyolefin resin injection molding method of the present invention allows stable injection molding of a molded product having high product surface gloss and appearance without causing industrial productivity deterioration.

Claims (2)

[Claims] 1. A method for injection molding a polyolefin resin, wherein the inner surface of an injection molding die has a thermal conductivity of 1 ×.
^{10 -4 ~30 × 10 -4 cal /} cm · sec · ℃, melting point or softening point of 0.99 ° C. or higher, provided the coating layer surface gloss is formed of 60% of the resin thickness of 5~1,000μm An injection molding method for a polyolefin resin, comprising: 2. The inorganic filler is blended in an amount of 1 to 60 parts by weight and / or a rubber component in a proportion of 1 to 40 parts by weight, based on 100 parts by weight of the polyolefin resin. Injection molding method for polyolefin resin.