JP2011213889A - Foamable resin composition and method for molding foam injection molded article using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamable resin composition from which a foam injection molded article excellent in rigidity and impact resistance can be obtained by foam injection molding, particularly core back molding, and a method for molding a foam injection molded article using the same.SOLUTION: The foamable resin composition contains 100 pts.wt. of a polypropylene-based resin, 5-10 pts.wt. of an ethylene-ethylene/butylene-ethylene block copolymer, and a foaming agent. The composition develops melt viscosity suitable for foaming in foam injection molding, and the resulting foam injection molded article has excellent impact resistance and rigidity as well as excellent appearance, retains excellent impact resistance and rigidity particularly even in a small thickness, and also has excellent lightness.

Description

  The present invention relates to a foamable resin composition and a method for molding an injection foam molded article using the same.

  Conventionally, in order to reduce the weight of automobiles, polypropylene-based resin foam molded products have been used as vehicle interior materials such as automobile door trims, and impact resistance and rigidity are required. This polypropylene resin foam molded article is manufactured by the core back method.

  The core back method is a method in which a fixed mold and a movable mold are clamped to fill a cavity formed between the mating surfaces of these molds with a foamable resin composition, and then the movable mold is moved backward to retract the cavity. This is a method of forming a foam having a desired shape by foaming a foamable resin composition while spreading.

  As a foamable resin composition used in the core back method, Patent Document 1 discloses (1) a melt flow rate of 10 g / 10 min or more and less than 50 g / 10 min, a melt tension of 2 cN or more, and strain hardening. Modified polypropylene resin, (2) (a) at least one thermoplastic rubber selected from (a) ethylene-α-olefin copolymer rubber and (b) alkenyl aromatic compound unit-containing rubber, (3) polyolefin wax And (4) a foamable resin composition comprising a foaming agent is disclosed.

  However, the injection-foamed molded product molded by the core back method using the foamable resin composition has a problem that the impact resistance and rigidity are low when the thickness is thin. The unit-containing rubber also has a problem that it has an odor.

JP 2008-290282 A

  The present invention provides a foamable resin composition capable of obtaining an injection foam molded article having excellent rigidity and impact resistance by injection foam molding, particularly a core back method, and a method for molding an injection foam molded article using the same. .

  The foamable resin composition of the present invention comprises 100 parts by weight of a polypropylene resin, 4 to 14 parts by weight of an ethylene-ethylene / butylene-ethylene block copolymer, and a foaming agent.

  The polypropylene resin is not particularly limited as long as it is conventionally used for injection foam molding, and examples thereof include a propylene homopolymer, a copolymer of propylene and another olefin, and the like. Even if it is used, 2 or more types may be used together. Further, the copolymer of propylene and other olefins may be any of a block copolymer, a random copolymer, and a random block copolymer.

  Examples of the olefin copolymerized with propylene include α such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene and 1-decene. -Olefin etc. are mentioned.

  The foamable resin composition of the present invention contains an ethylene-ethylene / butylene-ethylene block copolymer (CEBC). The ethylene-ethylene / butylene-ethylene block copolymer is a sandwich-type triblock copolymer represented by A-B-A, wherein A is an ethylene polymer block, and B is ethylene and butylene. And a random polymer block. The ethylene-ethylene / butylene-ethylene block copolymer is commercially available from JSR under the trade name “Dynalon 6200P”.

  As described above, since the foamable resin composition contains the ethylene-ethylene / butylene-ethylene block copolymer, in the random polymer block of ethylene and butylene, a part of the butylene portion is compatible with the polypropylene resin. When melted and part of the butylene portion is dispersed in the polypropylene resin, the foamable resin composition exhibits a melt viscosity and elongation viscosity suitable for foaming at the time of foaming, and is twice or more. The foamed molded product obtained by molding the foamable resin composition can be foamed at a high foaming ratio and has excellent impact resistance and rigidity.

  And since the foamable resin composition contains an ethylene-ethylene / butylene-ethylene block copolymer, it has a melt viscosity suitable for foaming as described above, and the foamable resin composition is While flowing in the cavity, the foaming gas leaks from the molten foamable resin composition, and the foaming gas enters between the cavity inner surface and the molten polypropylene resin to enter the surface of the injection foamed molded product. Irregularities and gas stains are not generated, and an injection foam molded product having an excellent appearance can be formed.

  In the ethylene-ethylene / butylene-ethylene block copolymer, the degree of polymerization of the ethylene polymer blocks on both sides is preferably 1000 to 2000, and the degree of polymerization of the random polymer block of ethylene and butylene is preferably 2000 to 3000. .

  And if there is little content of the ethylene-ethylene / butylene-ethylene block copolymer in a foamable resin composition, the impact resistance of the injection foam molded product obtained by foaming a foamable resin composition will fall. In many cases, since the rigidity of the injection-foamed molded article obtained using the foamable resin composition may be reduced, it is limited to 4 to 14 parts by weight with respect to 100 parts by weight of the polypropylene resin, 5 to 10 parts by weight is preferred.

  Furthermore, the foaming resin composition contains a foaming agent. The foaming agent is not particularly limited as long as it is conventionally used for injection foam molding, and examples thereof include sodium hydrogen carbonate and azodicarbonamide.

  When the content of the foaming agent in the foamable resin composition is small, the foamable resin composition may not foam. When the content is large, the foamable resin composition in which the foaming gas is melted in the course of injection foam molding. The surface of the injection-foamed molded product may be uneven due to the foam gas entering between the cavity inner surface and the molten polypropylene-based resin due to leakage from the object, so that 100 parts by weight of the polypropylene-based resin 1 to 7 parts by weight is preferable, and 2 to 5 parts by weight is more preferable.

  Next, the point which shape | molds an injection foam molded product by injection foam molding using a foamable resin composition is demonstrated. First, as shown in FIG. 1, a fixed mold 1 and a movable mold 2 are prepared as molds for injection foam molding, and the fixed mold 1 and the movable mold 2 are used as mold mounting frames (not shown) of an injection molding machine. ), The movable mold 2 is moved to the fixed mold 1 side, and the mold is clamped as shown in FIG.

  Thereafter, the foamable resin composition is injected and filled into the cavity 3 with a predetermined injection pressure through a gate (not shown) provided in the fixed mold 1. A skin layer 4 formed by cooling and solidifying a polypropylene resin is formed on a portion in contact with the inner surface of the cavity 3, that is, on the entire opposing surfaces 1 a and 2 a of the fixed mold 1 and the movable mold 2.

  Next, the width of the movable mold 2 between the opposed surfaces 1a and 2a of the movable mold 2 and the fixed mold 1 is set to a width interval corresponding to the thickness of the injection foam molded product A to be molded, as shown in FIG. If it is made to retreat until it becomes, the volume of the cavity 3 will increase, the inside of the cavity 3 will be pressure-reduced, and foaming gas, such as a carbon dioxide and nitrogen produced | generated when the foaming agent contained in the foamable resin composition decomposes | disassembles As a result, the foamable resin composition foams, and an injection foam molded article A having the core layer 5 made of the foamed resin covered with the skin layer 4 is obtained.

  However, the foamable resin composition of the present invention contains an ethylene-ethylene / butylene-ethylene block copolymer, and the foamable resin composition has an appropriate melt viscosity at the time of injection into the cavity 3 and filling. The cavity 3 formed by clamping the fixed mold and the movable mold 2 is uniformly filled without a gap.

  When the foamable resin composition is filled in the cavity 3, as described above, the skin layer 4 is formed by cooling and solidifying at the portion in contact with the cavity 3, but the foamable resin composition is made of ethylene- Since the ethylene / butylene-ethylene block copolymer is contained, the melt viscosity is increased, and the foaming gas contained in the foamable resin composition penetrates the skin layer 4 to form the skin layer 4 and the cavity. No leakage occurs between the inner surface and the surface of the resulting injection-foamed molded product A, and unevenness and dirt due to the leaked foaming gas do not occur.

Since the foamable resin composition of the present invention comprises a polypropylene resin containing an ethylene-ethylene / butylene-ethylene block copolymer, the cavity 3 when the foamable resin composition is injected and filled into the cavity 3 is used. Even if the thickness W ₀ , that is, the distance between the opposed surfaces 1a and 2a of the fixed mold 1 and the movable mold 2 is set small, and the thickness of the resulting injection foam molded product A is reduced, the injection foam molded product A is Excellent impact resistance and rigidity.

  The foamable resin composition of the present invention is characterized by containing a polypropylene resin, an ethylene-ethylene / butylene-ethylene block copolymer and a foaming agent, so that it has a melt viscosity and elongation suitable for foaming during injection foam molding. The injection foam molded product that expresses viscosity has an excellent appearance, and is excellent in impact resistance and rigidity, and particularly excellent in maintaining impact resistance and rigidity even when the expansion ratio is high. It has a light weight.

  And since the foamable resin composition of the present invention does not need to contain a compound containing a benzene ring and does not generate an odor due to the benzene ring, the resulting injection-foamed molded product does not generate an odor that pierces the nose. , Can be suitably used for various applications.

It is a vertical side view of the injection foam molding die. It is a vertical side view of the state which moved the movable mold | type back.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Examples 1-3, Comparative Examples 1-3, 5-6)
Predetermined amounts of polypropylene resin (trade name “AZ846E4” manufactured by Sumitomo Chemical Co., Ltd.), ethylene-ethylene / butylene-ethylene block copolymer (CEBC, manufactured by JSR, trade name “Dynalon 6200P”, ethylene polymer shown in Table 1 Degree of polymerization of block: 1300 to 1700, degree of polymerization of random copolymer block of ethylene and butylene: 2200 to 2800), styrene-ethylene-butylene-styrene copolymer (SEBS, trade name “DYNARON 8600P” manufactured by JSR) ), A foaming resin composition containing sodium hydrogen carbonate (trade name “Celmic 3274” manufactured by Sanwa Kasei Co., Ltd.) and a colorant (trade name “136B” manufactured by Tokyo Ink Co., Ltd.). Screw) and melt-kneaded at 200 ° C.

  On the other hand, a fixed mold 1 and a movable mold 2 as shown in FIG. 1 are prepared as injection molds, and the fixed mold 1 and the movable mold 2 are used as a mold mounting frame (not shown) of an injection molding machine. After mounting in a state of being opposed to each other, the movable mold 2 was moved to the fixed mold 1 side and clamped as shown in FIG. 1, and the fixed mold 1 and the movable mold 2 were heated to 50 ° C. and maintained.

Thereafter, the foamable resin composition melt-kneaded by the extruder as described above was injected and filled into the cavity 3 with a predetermined injection pressure through a gate (not shown) provided in the fixed mold 1. . The thickness W ₀ of the cavity 3 when the foamable resin composition was injected and filled into the cavity 3 was 1.2 mm.

Next, after leaving the cavity 3 to be filled with the foamable resin composition for 0.5 seconds, as shown in FIG. 2, the movable mold 2 is divided into the movable mold 2 and the fixed mold 1. The cavity 3 is retreated until the width between the opposing surfaces 1a and 2a reaches the width interval W ₁ shown in Table 1 corresponding to the thickness of the injection foam molded product A to be molded, and the volume of the cavity 3 is increased to increase the volume inside the cavity 3. The carbon dioxide gas produced by the decomposition of sodium hydrogen carbonate contained in the foamable resin composition is expanded by the decompression to generate bubbles in the foamable resin composition. Was formed, and a flat injection-molded foamed product A having a core layer 5 made of a foamed resin covered with the skin layer 4 was obtained.

(Comparative Example 4)
A predetermined amount of polypropylene resin (trade name “AZ846E4” manufactured by Sumitomo Chemical Co., Ltd.), ethylene-ethylene / butylene-ethylene block copolymer (CEBC, product name “Dynalon 6200P” manufactured by JSR) and a colorant shown in Table 1 A resin composition containing (trade name “136B” manufactured by Tokyo Ink Co., Ltd.) was supplied to an extruder and melt-kneaded at 200 ° C.

  On the other hand, a fixed mold 1 and a movable mold 2 as shown in FIG. 1 are prepared as injection molds, and the fixed mold 1 and the movable mold 2 are respectively attached to a mold mounting frame (not shown) of an injection molding machine. After mounting in an opposed state, the movable mold 2 was moved to the fixed mold 1 side and clamped as shown in FIG. 1, and the fixed mold 1 and the movable mold 2 were heated and maintained at 50 ° C.

  Thereafter, the resin composition melt-kneaded by the extruder as described above is injected into the cavity 3 with a predetermined injection pressure through a gate (not shown) provided in the fixed mold 1 and filled with resin. After completing the filling of the composition, it was allowed to stand for 25 seconds and cooled to obtain an injection molded product.

  For the injection-foamed molded products A obtained in Examples 1 to 3 and Comparative Examples 1 to 3 and 5 to 6 and the injection-molded products obtained in Comparative Example 4, bending elastic gradient, Charpy impact strength, low temperature falling ball impact resistance The side impact test and appearance were measured as follows, and the results are shown in Table 1.

(Bending elastic gradient)
A test piece having a plane rectangular shape of 50 mm long and 150 mm wide is cut out from the molded product, a load is applied to the central portion of the test piece, and the portion where the load is applied to the central portion of the test piece is before the load is applied to the test piece. The load when it was displaced by 10 mm from the position was measured.

(Charpy impact strength)
A test piece having a plane rectangular shape measuring 10 mm in length and 80 mm in width was cut out from the molded product, and a cut having a length of 10 mm and a depth of 2 mm was formed at the center of the test piece. Using a Charpy impact tester (trade name “DG-UB” manufactured by Toyo Seiki Seisakusho Co., Ltd.), the swing angle was measured according to JIS K7111-1 to measure the Charpy impact strength. In JIS K7111-1, the thickness of the test piece is 4 mm, but when the thickness is not 4 mm, the Charpy impact strength obtained by multiplying the coefficient (4 / thickness of the test piece (mm)) by the Charpy Impact strength was used.

(Low temperature falling ball impact resistance)
After the injection foam molded product is allowed to stand on a horizontal surface of a thermostatic chamber at −30 ° C., a 500 g iron ball naturally falls from the top surface of the injection foam molded product at a height of 10 cm from the top surface of the injection foam molded product. I let you. Visual observation of whether or not the injection foam molded product is cracked due to the fall of the iron ball, and if there is no crack in the injection foam molded product, the height position is further increased by 5 cm as the vertical height position. From the above, an iron ball was naturally dropped on the upper surface of the injection foam molded product, and whether or not the injection foam molded product was cracked was visually observed. The height position of the iron ball was increased in the above-described manner until a crack occurred in the injection foam molded product, and the height position where the crack occurred in the injection foam molded product was measured.

(Side test)
A weight having a weight of 21.9 kg was made to collide with one surface of the injection foam molded product at a speed of 4.4 m / sec to visually observe whether or not the injection foam molded product was cracked. When a crack occurred in the injection foamed molded product, the length of the crack was measured. In addition, when the crack has generate | occur | produced in the injection foaming molded article, Table 1 described the length of the crack.

(Appearance)
Whether or not the surface of the injection-foamed molded product has unevenness caused by the foaming gas leaking out of the molten foamable resin composition and entering between the cavity inner surface and the molten polypropylene resin. Visual observation was performed.

1 Fixed mold 2 Movable mold 3 Cavity 4 Skin layer 5 Core layer A Injection foam molded product

Claims (2)

A foamable resin composition comprising 100 parts by weight of a polypropylene resin, 4 to 14 parts by weight of an ethylene-ethylene / butylene-ethylene block copolymer and a foaming agent. In a cavity formed between the mating surfaces of the fixed mold and movable mold, 100 parts by weight of a polypropylene resin, 4 to 14 parts by weight of an ethylene-ethylene / butylene-ethylene block copolymer, and A method for molding an injection foam molded product, comprising filling a foamable resin composition containing a foaming agent and then foaming the foamable resin composition while expanding the cavity by retracting the movable mold.