Foamable resin composition, foamed resin molded article, and method for producing the same

Abstract

To provide an expandable resin molded body which can be used instead of urethane foam, and which achieves thermoplastic property, low density, low hardness and low compressive set.SOLUTION: An expandable resin composition includes: 100 pts.mass of a total sum of a styrenic thermoplastic elastomer and a dynamic cross linking thermoplastic elastomer; the dynamic cross linking thermoplastic elastomer is included by 10-40 pts.mass; to the 100 pts.mass, a high temperature expandable micro capsule and a low temperature expandable micro capsule are in total, included in 25-50 pts.mass. A ratio of the low temperature expandable micro capsule in both the micro capsules is, 17-67%. The expandable resin composition including the same is configured so that, the high temperature expandable micro capsule is expanded however is not broken, and the low temperature expandable micro capsule is expanded and at least partially broken. The expandable resin composition has 0.3 or lower of a relative density, Asker C hardness of 45 or lower, and compressive set of 35% or lower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a foamable resin composition, a foamed resin molded article, and a method for producing the same. [Background technology]

[0002] Molded urethane foam is used as a cushioning material for vehicle console lids. Because urethane foam is expensive, the use of foamed thermoplastic resin as a replacement has been considered to reduce costs.

[0003] Patent Document 1 discloses a method of kneading a composition containing an olefin-based thermoplastic resin and thermally expandable microcapsules, and then adding a thermoplastic resin (such as a styrene-based elastomer) to form a foam.

[0004] Patent Document 2 discloses a foamable thermoplastic elastomer composition containing an olefin resin or rubber, thermally expandable microcapsules, a volatile composition (heptane, silica sol, etc.), and a thermoplastic resin (styrene elastomer, etc.).

[0005] Patent Document 3 discloses a foamed molded article obtained by foaming a foamable thermoplastic elastomer composition containing an olefin-based resin or rubber, thermally expandable microcapsules, silica sol, and a thermoplastic resin (such as a styrene-based elastomer). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-17103 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-192825 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-270157 Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the inventors' investigations, it was difficult to obtain properties equivalent to those of urethane foam (low specific gravity, low hardness, low compression set) simply by incorporating thermally expandable microcapsules into a thermoplastic resin and a styrene-based elastomer. This is thought to be due to the following reasons. (1) Urethane foams during the reaction process of polyol-isocyanate, which is liquid at low temperatures, making it easy to achieve high foaming and lowering its specific gravity. However, thermoplastic resins must be foamed in a molten state at high temperatures, making it difficult to achieve high foaming and lowering its specific gravity. (2) Thermoplastic resins are disadvantageous in terms of compression set properties when compressed under high temperature conditions.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoplastic foamed resin molded article that can be used as an alternative to urethane foam and that has a low specific gravity, low hardness and low compression set. [Means for solving the problem]

[0009] [1] A foamable resin composition comprising a total of 100 parts by mass of a styrene-based thermoplastic elastomer and a dynamically crosslinked thermoplastic elastomer, the amount of the dynamically crosslinked thermoplastic elastomer being 10 to 40 parts by mass, and a total of 25 to 50 parts by mass of high-temperature expandable microcapsules and low-temperature expandable microcapsules relative to the 100 parts by mass, with the proportion of low-temperature expandable microcapsules in both microcapsules being 17 to 67% by mass.

[0010] Here, high-temperature expandable microcapsules and low-temperature expandable microcapsules refer to microcapsules with a relatively high maximum expansion temperature and microcapsules with a relatively low maximum expansion temperature. The maximum expansion temperature is the temperature beyond which the shell breaks, the foaming component escapes, and the microcapsule shrinks.

[0011] [2] A method for producing a foamed resin molded product, characterized in that a foamable resin composition containing a styrene-based thermoplastic elastomer, a dynamically crosslinked thermoplastic elastomer, high-temperature expandable microcapsules, and low-temperature expandable microcapsules is molded at a temperature at which the high-temperature expandable microcapsules do not break but at least a portion of the low-temperature expandable microcapsules break.

[0012] [3] A foamed resin molded product comprising a styrene-based thermoplastic elastomer, a dynamically crosslinked thermoplastic elastomer, high-temperature expandable microcapsules, and low-temperature expandable microcapsules, wherein the high-temperature expandable microcapsules are expanded but not broken, and the low-temperature expandable microcapsules are expanded and at least some of the microcapsules are broken, and the foamed resin molded product has a specific gravity of 0.3 or less, an Asker C hardness of 45 or less, and a compression set (JIS K6400-4, Method A, compression rate 50%) of 35% or less.

[0013] [Effect] (A) The crosslinked rubber elasticity of the dynamically crosslinked thermoplastic elastomer blended into the styrene-based thermoplastic elastomer base resin makes the resin resistant to crushing at high temperatures, resulting in low compression set, and also suppresses sink marks (crushing due to shrinkage after molding) that tend to occur with high foaming and open cells during foam molding. The dynamically crosslinked thermoplastic elastomer is set to 10 to 40 parts by mass per 100 parts by mass in order to achieve low compression set and low hardness. If it is less than 10 parts by mass, the compression set becomes high, and if it exceeds 40 parts by mass, it is difficult to achieve low hardness.

[0014] (A) Generally, when foaming with thermally expandable microcapsules, only microcapsules that do not break during molding are used, which results in closed cells and makes the molded product hard. In contrast, in this proposal, by using high-temperature expandable microcapsules that do not break during molding in combination with low-temperature expandable microcapsules that break at least some of the cells during molding, not only do the high-temperature expandable microcapsules form closed cells, but the broken low-temperature expandable microcapsules also connect the cells together to form open cells, resulting in low hardness. The total amount of high-temperature expandable microcapsules and low-temperature expandable microcapsules is 25 to 50 parts by mass per 100 parts by mass, and the proportion of low-temperature expandable microcapsules in both microcapsules is 17 to 67% by mass in order to achieve a low specific gravity and low hardness. [Effects of the Invention]

[0015] According to the present invention, it is possible to obtain a thermoplastic foamed resin molded article having a low specific gravity, low hardness and low compression set, which can be used as an alternative to urethane foam. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a micrograph of the cross section of the foamed resin molded article of Example 3. [Figure 2] FIG. 2 is a micrograph of the cross section of the foamed resin molded article of Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1. Thermoplastic styrenic elastomer (TPS) Examples of TPS include, but are not limited to, those in which the hard segment is polystyrene or polypropylene and the soft segment is a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene-styrene block copolymer (SIS), or a hydrogenated styrene-ethylene-butylene-styrene block copolymer (SEBS) or a styrene-ethylene-propylene-styrene block copolymer (SEPS).

[0018] 2. Dynamically crosslinked thermoplastic elastomer (TPV: thermoplastic vulcanizate) Although there are no particular limitations on the TPV, examples include those in which the hard segment is a polyolefin (e.g., polypropylene) and the soft segment is an olefin-based crosslinked rubber (e.g., EPDM). Dynamic crosslinking is a process in which a thermoplastic resin and a rubber are melt-kneaded and simultaneously the rubber is crosslinked under shear, and is referred to as opposed to the usual process of statically crosslinking rubber.

[0019] 3. High-temperature expanding microcapsules and low-temperature expanding microcapsules Both the high-temperature expandable microcapsules and the low-temperature expandable microcapsules used as foaming agents are formed by enclosing a foaming component in a shell. The shell material is not particularly limited, but examples thereof include thermoplastic resins (e.g., acrylic resins). The foaming component is not particularly limited, but examples thereof include liquid hydrocarbons.

[0020] 4. Other ingredients The foamable resin composition and foamed resin molded article of the present invention may further contain other components, such as a filler, a colorant, and an antioxidant.

[0021] 5. Molding of foamed resin bodies The molding (foam molding) method is not particularly limited, but examples thereof include injection foaming, press foaming, extrusion foaming, and blow foaming.

[0022] 6. Uses of foamed resin molded products The use of the foamed resin molded article is not particularly limited, but suitable examples include cushioning materials for automobile interior parts (console lids, armrests, seats, etc.) and cushioning materials for furniture (chairs, etc.). [Example]

[0023] [Preparation of Foamable Resin Composition] Each of the foamable resin compositions of Samples 1 to 31 was prepared by blending the materials in the formulations shown in Tables 1 and 2 below (the blending values are in parts by mass). Samples 1 to 7 are a group of TPS blended with various blowing agents. Samples 8 to 13 are a group in which the blending ratio of TPS and TPV was changed and the blending ratio of high-temperature expandable microcapsules and low-temperature expandable microcapsules was constant. Sample 14 is a group in which high-temperature expandable microcapsules are blended with TPV. Samples 15 to 31 are a group in which the blending ratio of TPS and TPV is constant and the blending ratio of high-temperature expandable microcapsules and low-temperature expandable microcapsules is changed.

[0024] [Table 1]

[0025] [Table 2]

[0026] The details of each material used are as follows: For the TPS, we used Mitsubishi Chemical's Tefablock T3779B, an elastomer that uses styrene-based rubber (styrene-butadiene copolymer (SBC)) as the base polymer. For the TPV, ExxonMobil's Santoprene 8211-45, a polyolefin-based elastomer containing vulcanized EPDM, was used. The chemical foaming agent used (samples 1 and 2 only) was Eiwa Chemical Industry Co., Ltd.'s "Polythren EV306G," a chemical foaming agent based on azodicarbonamide (ADCA), which was made into a masterbatch with vinyl acetate (EVA). For the low-temperature expanding microcapsules, we used Matsumoto Yushi Pharmaceutical's product name "Microsphere F185EVA." This has an acrylic resin shell, a hydrocarbon foaming component, and EVA as a masterbatch. It has a foaming start temperature of 145-155°C and a maximum expansion temperature of 190-200°C. For the high-temperature expanding microcapsules, we used Matsumoto Yushi Pharmaceutical's Microsphere F190EVA, a product name. This has an acrylic resin shell, a different foaming component from the above hydrocarbons, and contains EVA as a master batch. It has a foaming start temperature of 160-170°C and a maximum expansion temperature of 210-220°C.

[0027] The combined mass parts a+b of the two blowing agents, low-temperature expandable microcapsules (a) and high-temperature expandable microcapsules (b), and the ratio a / (a+b) (mass%) of the low-temperature expandable microcapsules in the two blowing agents are shown in Tables 1 and 2.

[0028] [Molding of foamed resin moldings] Next, each of the prepared foamable resin compositions of Samples 1 to 31 was injected at a composition temperature of 230°C into a mold having a mold temperature of 60°C at an injection speed of 120 mm / sec (mold conditions: short shot method) to foam-mold a foamed resin molded body (test piece) with dimensions of 60 mm x 200 mm x thickness of 6 mm. That is, each of the foamable resin compositions of Samples 6 to 14 and 16 to 31, which used a combination of low-temperature expandable microcapsules and high-temperature expandable microcapsules, was foam-molded at a temperature at which the high-temperature expandable microcapsules did not break, but at least some of the low-temperature expandable microcapsules broke.

[0029] [Characteristics of foamed resin moldings] Next, the following properties were measured for each of the foamed resin molded articles of Samples 1 to 31. (1) Specific gravity The specific gravity was measured in accordance with JIS K7222.

[0030] (2) Asker C hardness The hardness was measured using an Asker C hardness tester in accordance with JIS K7312.

[0031] (3) Compression set In accordance with JIS K6400-4, the specimen was compressed to 50% of its original thickness using Method A (compression at 70°C) and left for 22 hours. After the specimen was released from compression and allowed to recover for 30 minutes, the thickness was measured and the compression set (CS) was calculated.

[0032] The foamed resin molded articles and the foamable resin compositions used therein of Samples 8 to 12, 18 to 20, 22 to 25, and 28 to 30, which had a specific gravity of 0.3 or less, an Asker C hardness of 45 or less, and a compression set of 35% or less, were positioned as Examples. The foamed resin molded articles and the foamable resin compositions used therein of the other samples were positioned as Comparative Examples.

[0033] As shown in the cross-sectional micrograph of FIG. 2, the foamed resin molded product of Sample 5 (Comparative Example 5) contained only closed cells (about 0.2 to 0.4 mm) formed by high-temperature expandable microcapsules. In contrast, the foamed resin moldings of the examples, as shown in the cross-sectional micrograph of Sample 10 (Example 3) in Figure 1, contained both closed cells (approximately 0.2 to 0.4 mm) formed by high-temperature expandable microcapsules and open cells (approximately 0.6 to 1.0 mm) formed by broken low-temperature expandable microcapsules.

[0034] The present invention is not limited to the above-described embodiments, and can be embodied by making appropriate modifications within the scope of the invention.

Claims

1. A foamable resin composition comprising a styrene-based thermoplastic elastomer and a dynamically crosslinked thermoplastic elastomer in a total amount of 100 parts by mass, wherein the dynamically crosslinked thermoplastic elastomer is 10 to 40 parts by mass, and wherein high-temperature expandable microcapsules and low-temperature expandable microcapsules are combined in an amount of 25 to 50 parts by mass relative to the 100 parts by mass, and the proportion of low-temperature expandable microcapsules in both microcapsules is 17 to 67% by mass.

2. A method for producing a foamed resin molded product, comprising molding an expandable resin composition comprising 100 parts by mass of a styrene-based thermoplastic elastomer and a dynamically crosslinked thermoplastic elastomer, the dynamically crosslinked thermoplastic elastomer being 10 to 40 parts by mass, and comprising 25 to 50 parts by mass of high-temperature expandable microcapsules and low-temperature expandable microcapsules in total relative to the 100 parts by mass, the proportion of low-temperature expandable microcapsules in both microcapsules being 17 to 67% by mass, at a temperature at which the high-temperature expandable microcapsules do not break but at least a portion of the low-temperature expandable microcapsules break.

3. A foamed resin molded article comprising a styrene-based thermoplastic elastomer, a dynamically crosslinked thermoplastic elastomer, high-temperature expandable microcapsules, and low-temperature expandable microcapsules, wherein the high-temperature expandable microcapsules are expanded but not broken, and the low-temperature expandable microcapsules are expanded and at least some of the microcapsules are broken, and the foamed resin molded article has a specific gravity of 0.3 or less, an Asker C hardness of 45 or less, and a compression set (JIS K6400-4, Method A, compression rate 50%) of 35% or less.

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