JP2002348397A - Production method for lightweight molded item - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily producing a lightweight molded item having a good external appearance. SOLUTION: This method for producing a lightweight molded item comprises blending (A) a blowing agent masterbatch prepared by mixing 50-95 mass% thermoplastic rubber having a melt viscosity (at 190 deg.C and a shear rate of 100s<-1> ) of 10<1> -10<5> Pa s with 50-5 mass% blowing agent with (B) a thermoplastic resin having a melt viscosity lower than that of the thermoplastic rubber and heating the resultant blend to a temperature higher than the melting point of the thermoplastic resin to thereby foam and simultaneously mold the blend.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily producing a lightweight molded article having a good appearance.

[0002]

2. Description of the Related Art Conventionally, resin foams have been used in various applications for the purpose of weight reduction, heat insulation and sound absorption of molded articles. However, in the conventional foam molding method, when the expansion ratio is increased or the injection speed is decreased, a silver mark is generated on the surface of the molded product due to the foaming gas, and there is a problem that the appearance is deteriorated. .
As a means for solving this problem, a counter pressure method has been proposed in which an inert gas is injected into a cavity of a mold, an internal pressure is applied to suppress foaming by a foaming agent, and then the volume of the cavity is enlarged and foamed. . However, in this method, it is necessary to devise equipment, a mold, and the like, so that there is a problem that the cost is increased. Further, in this method, there is a problem that the diameter of the foamed particles is large, and the strength of the molded product is reduced. As a countermeasure against these problems, there has been proposed a method of increasing the melt viscosity by kneading an elastomer or the like with a resin. However, elastomers (rubbers) with large melt viscosities
In the case of using, the dispersibility in resin is poor, and the appearance and physical properties of a molded article are deteriorated, so that the melt viscosity of an elastomer (rubber) that can be used is limited. In addition, a resin having good fluidity has a problem that the melt viscosity is too low and the dispersibility of the rubber is deteriorated.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light-weight molded article which does not generate silver and has a good appearance.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a masterbatch in which a foaming agent is dispersed in an elastomer (rubber) having a high melt viscosity is used. Without using a special molding method such as a counter pressure method, it is possible to obtain a light-weight molded article having no appearance of silver and having a good appearance, and a moderately uniform foamed particle diameter without coarsening. I found that. The reason why the foamed particle diameter is not coarsened and is moderately uniform is that since the rubber having a high melt viscosity is finely dispersed in the foam, the overall melt viscosity is also high, and the gas is discharged outside the foam. This is probably due to less leakage. It is presumed that the reason why the rubber having a high melt viscosity is finely dispersed is that the foaming agent is finely dispersed in the rubber, and the gas generated at the time of kneading promotes the dispersion of the rubber. The present invention has been completed based on such findings. That is, the present invention provides (A) a temperature of 190 ° C. and a shear rate of 100 ° C.
a foaming agent masterbatch obtained by kneading 50 to 95% by mass of a thermoplastic rubber having a melt viscosity of 10 ¹ to 10 ⁵ Pa · s at s ⁻¹ and 50 to ⁵ % by mass of a foaming agent; After blending a thermoplastic resin having a lower melt viscosity than a thermoplastic rubber, the mixture is heated to a temperature not lower than the melting temperature of the thermoplastic resin, foamed with a foaming agent, and shaped to produce a lightweight molded article. Provide a method.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic rubber compounded in the blowing agent masterbatch used in the present invention has a melt viscosity of 10 ¹ to 10 ⁵ Pa at a temperature of 190 ° C. and a shear rate of 100 s ⁻¹ .
・ S. When the melt viscosity is less than 10 ¹ Pa · s, it is not possible to prevent the occurrence of silver in the lightweight molded article (foam molded article), and the foam cell diameter is large and irregular. On the other hand, when the melt viscosity is 10 ⁵
If it exceeds Pa · s, the thermoplastic resin of component (B)
Dispersion of the foaming agent master batch becomes poor, and the appearance and physical properties of the foamed molded article are deteriorated. This melt viscosity can be measured using a conical disk rheometer such as a Weisenberg Gregoniometer.

Examples of the thermoplastic rubber include known styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and amide-based thermoplastic elastomers. Styrene-based thermoplastic rubbers include styrene-butadiene block copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB, SEBC), styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene -Butadiene-styrene block copolymer (SE
BS), styrene-isoprene block copolymer (SI
R), hydrogenated styrene-isoprene block copolymer (SEP), styrene-isoprene-styrene block copolymer (SIS), hydrogenated styrene-isoprene-
Styrene block copolymer (SEPS), butadiene-
Acrylonitrile-styrene-core shell rubber (AB
S), methyl methacrylate-butadiene-styrene-
Core shell rubber (MBS), methyl methacrylate-butyl acrylate-styrene-core shell rubber (MA
S), octyl acrylate-butadiene-styrene-
Core shell rubber (MABS), alkyl acrylate-
Core-shell type particle-like elastic materials such as butadiene-acrylonitrile-styrene-core-shell rubber (ABS), butadiene-styrene-core-shell rubber (SBR), and siloxane-containing core-shell rubber such as methyl methacrylate-butyl acrylate-siloxane; Modified rubber and the like can be mentioned. Examples of the olefin-based thermoplastic elastomer include ethylene-propylene rubber (EPR) and ethylene-butene copolymer (EB
R), ethylene propylene diene rubber (EPDM), the hard phase is polypropylene or polyethylene and the soft phase is EP
M, EPDM, and the like, such as Sumitomo TPE, Mirastomer (manufactured by Mitsui Chemicals, Inc.), and Thermolan (manufactured by JSR). Examples of the polyester-based thermoplastic elastomer include Hytel (manufactured by DuPont) and Belprene (manufactured by Toyobo Co., Ltd.) in which the hard phase is polyester and the soft phase is polyether or polyester. As the amide-based thermoplastic elastomer, Vestamid whose hard phase is polyamide and whose soft phase is polyether or polyester.
(Manufactured by Huls), Relax A (manufactured by Ems) and the like. Among them, ethylene-butene copolymer and SEBS are particularly preferably used. These thermoplastic rubbers can be used alone or in combination of two or more.

As the blowing agent, thermal decomposition of azodicarboxylic amide, a mixture of sodium bicarbonate and citric acid, oxybisbenzenesulfonyl hydrazide, benzenesulfonyl hydrazide, P-toluenesulfonyl hydrazide, diazoaminobenzene, azobisisobutyronitrile, etc. One or two or more selected from a type chemical blowing agent can be used. In the foaming agent masterbatch of the component (A), the compounding amount of the foaming agent is 5 to 50% by mass of the total amount of the thermoplastic rubber and the foaming agent, but is 10 to 30% by mass.
Is preferred.

The thermoplastic resin of the component (B) has a lower melt viscosity than the thermoplastic rubber of the component (A). When the melt viscosity of the thermoplastic resin is higher than the melt viscosity of the thermoplastic rubber in the component (A), when the resin flows,
The thermoplastic rubber containing a low-viscosity foaming agent is exposed on the surface, and poor appearance (silver) occurs due to the foaming gas. Examples of the thermoplastic resin include polyolefin resins such as polypropylene and polyethylene, polystyrene resins, polycarbonate resins, polyacetal resins, polyester resins, polyamides, and the like. These can be used alone or in combination of two or more.
The use ratio of the component (A) to the component (B) is usually 99 to 1% by mass of the component (B) with respect to 1 to 99% by mass of the component (A), but preferably 2 to 60% by mass of the component (A). The component (B) is 98 to 40% by mass relative to the mass%.

In the present invention, in addition to the components (A) and (B), an inorganic filler, an antioxidant, a nucleating agent, a plasticizer, a release agent, Fuel,
Additives such as flame-retardant aids, pigments, dyes, carbon black and antistatic agents can be blended, and each of these can be used alone or in combination of two or more. . The lightweight molded article of the present invention can be produced by a molding method such as an injection molding method, an extrusion molding method, and a blow molding method. As the injection molding method,
There are a short shot foam injection molding method and an injection molding method in which foaming is performed by a core back after a full shot. The lightweight molded article of the present invention has an expansion ratio of about 1.2 to 5 times, but in the case of the latter injection molding method, the expansion ratio is 2 to 5 times.
It can be easily doubled, and the occurrence of silver in the molded product is small. In the latter injection molding method, foaming is performed by filling a cavity of a mold with a molten resin obtained by heating and melting a blend of the component (A) and the component (B), and then increasing the volume of the cavity. This is done by moving the mold in the direction. In this injection molding method, if the volume of the cavity is the same, silver is less likely to occur as the injection speed increases. In the present invention, the cavity is large like a large molded product, it takes time for the resin containing the foaming agent to fill the cavity, and even in a case where silver is easily generated in known foam molding, generation of silver is prevented. be able to.

[0010]

Next, the present invention will be described in more detail by way of examples.
As will be explained, the present invention is in no way limited by these examples.
Not something. Example 1 Temperature 190 ° C. and shear rate 100 s^-1Melt viscosity at
Is 1000 Pa · s rubber (ethylene-butene copolymer
Body) 90 parts by weight and a blowing agent (azodicarboxylic acid amide)
10 parts by weight are kneaded at 100 ° C with a twin-screw kneader and foamed.
An agent masterbatch was obtained. This masterbatch 20 weight
Part, temperature 190 ° C. and shear rate 100 s ^-1Dissolution in
Melt viscosity is 2.1 × 10^TwoPa · s and MI (Meltoy
Index) is 80 weight of 60g / 10min polypropylene
And dry blending the blended product with a mold.
Filled, foamed by injection molding at a resin temperature of 200 ° C
Obtained the form. MI is in accordance with JIS K7210.
Based on the value measured at a temperature of 230 ° C and a load of 21.18N
The same applies to the following. The mold size is 4
20mm x 100mm, mold cavity depth
Is 2 mm before filling with the blend,
After filling the material, the cavity depth will be 4mm
The mold was retracted. In addition, injection molding
Injection speed of 105mm / sec, 210mm / sec
c, under three conditions of 420 mm / sec. Foam molding
The appearance of the body was visually determined. In addition, injection speed 210mm
/ Sec cut out the inside of the foam molded body obtained
The state of the particles was observed with an electron microscope. These results
It is shown in Table 1.

Comparative Example 1 In Example 1, the temperature was 190 ° C. and the shear rate was 100 s.
Rubber melt viscosity 1000 Pa · s at ^-1 - instead of (ethylene-butene copolymer), the melt viscosity at 190 ° C. and a shear rate of 100s ^-1 is 2 Pa · s LD
Example 1 except that PE (low density polyethylene) was used.
A foam molded article was manufactured in the same manner as described above, and the same evaluation was performed. Table 1 shows the results. Comparative Example 2 82 parts by weight of polypropylene having an MI of 60 g / 10 min and a temperature of 190 ° C. and a shear rate of 100 s ⁻¹ were used in Example 1.
Was melt-kneaded in a twin-screw kneader with 18 parts by weight of a rubber (ethylene-propylene copolymer) having a melt viscosity of 8 Pa · s. 80 parts by weight of this kneaded material and 20 parts by weight of the foaming agent master batch obtained in Comparative Example 1 were dry-blended,
A foam molded article was manufactured in the same manner as in Example 1, and the same evaluation was performed. Table 1 shows the results. In Comparative Example 2, silver was hardly developed when the injection speed was 420 mm / sec. This is because the foaming gas was filled faster than the speed at which the foamable gas diffused to the resin surface. By being taken inside.

[0012]

[Table 1]

Example 2 Biaxial kneading of 80 parts by weight of rubber (SEBS) having a melt viscosity of 10,000 Pa · s at a temperature of 190 ° C. and a shear rate of 100 s ⁻¹ and 20 parts by weight of a foaming agent (a mixture of sodium bicarbonate and citric acid). The mixture was kneaded at 100 ° C. by a machine to obtain a foaming agent master batch. 15 parts by weight of this master batch,
A melt viscosity at a temperature of 190 ° C. and a shear rate of 100 s ⁻¹ is 3.6 × 10 ² Pa · s, MI (melt index) is 30 g / 10 min, and 85 parts by weight of polypropylene are dry-blended. Fill the mold,
A molded article was obtained by injection molding at a resin temperature of 200 ° C. The size of the mold is 420 mm x 100 mm,
The depth of the cavity of the mold was 2 mm before filling the blend, and after filling the blend, the mold was retracted so that the depth of the cavity was 4 mm. Also,
In the injection molding, the injection speed of the blend is set to 420 mm / sec.
Performed as c. As in Example 1, the appearance of the foamed molded article was visually determined. The foamed article expanded 2.5 times, and had a good appearance without silver or the like on the surface of the molded article.

Comparative Example 3 85 parts by weight of polypropylene used in Example 2 having an MI of 30 g / 10 min, a temperature of 190 ° C. and a shear rate of 100 s ^−1.
Having a melt viscosity of 10,000 Pa · s (SEB
S) 18 parts by weight were melt-kneaded with a biaxial kneader to obtain a kneaded product. Next, 80 parts by weight of EVA (ethylene-vinyl acetate copolymer) having a melt viscosity of 5 Pa · s at a temperature of 190 ° C. and a shear rate of 100 s ⁻¹ and 20 parts by weight of a blowing agent (a mixture of sodium bicarbonate and citric acid) 10 with twin-screw kneader
The mixture was kneaded at 0 ° C. to obtain a foaming agent master batch. 15 parts by weight of this foaming agent master batch and 85 parts by weight of the above kneaded material were dry-blended and injection-molded in the same manner as in Example 2 to obtain a foamed molded product. In the obtained foamed molded article, the rubber was not finely dispersed, a visually confirmable gel was present, silver was remarkable, and the appearance of the foamed molded article was poor.

[0015]

According to the present invention, a lightweight molded article having a good appearance can be easily produced. It is generally said that the injection speed should be increased in order to suppress silver due to foam decomposition gas. The present invention is characterized in that it can be set by setting a wider range of conditions for this injection speed and appearance than a commercially available foaming agent masterbatch, and improves production stability with respect to appearance. is there.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) B29K 105: 04 B29K 105: 04 C08L 101: 00 C08L 101: 00 (72) Inventor Manabu Nomura Ichihara-shi, Chiba 1 Anesaki Beach 1F Term (Reference) 4F074 AA13 AA24 AA26 BA03 BA13 BA14 BA17 BA18 CA24 CA26 CC04X CC05Z CC22X 4F206 AA03 AA45 AB02 AG20 AH48 JA04 JF01 JF04 JN33

Claims (5)

[Claims] (A) temperature 190 ° C. and shear rate 100
a foaming agent masterbatch obtained by kneading 50 to 95% by mass of a thermoplastic rubber having a melt viscosity of 10 ¹ to 10 ⁵ Pa · s at s ⁻¹ and 50 to ⁵ % by mass of a foaming agent; After blending a thermoplastic resin having a lower melt viscosity than a thermoplastic rubber, the mixture is heated to a temperature equal to or higher than the melting temperature of the thermoplastic resin, foamed by a foaming agent, and shaped to produce a lightweight molded body. Method. 2. A lightweight molded article having an expansion ratio of 1.2 to 5
The production method according to claim 1, wherein the production method is doubled. 3. A method for producing a lightweight molded article, comprising: an injection molding method;
2. An extrusion molding method or a blow molding method.
Or the production method according to 2. 4. A cavity of a mold is filled with a molten resin obtained by heating and melting a blend of the component (A) and the component (B) in an injection molding method, and then the volume of the cavity is increased. 4. The method according to claim 3, further comprising the step of moving the mold in the direction. 5. The method according to claim 1, wherein the thermoplastic resin is a polyolefin.