JP5628553B2 - Thermoplastic elastomer composition for injection foam molding and injection foam molded article comprising the resin composition - Google Patents

Description

  The present invention relates to a thermoplastic elastomer composition for injection foam molding and an injection foam molding using the same.

  Foam is widely used in members that require shock absorbing performance and cushioning properties such as cushioning materials such as electronic devices and furniture, automobile interior materials, food packaging materials, and the like. Among them, a thermoplastic elastomer foam is suitably used for applications that require cushioning and flexibility.

  For example, Patent Document 1 proposes a method of mixing a polyolefin resin with a thermoplastic elastomer. However, the polyolefin used here uses a polyolefin with low fluidity in order to obtain a high expansion ratio. Specifically, a non-foamed sheet impregnated with a high-pressure gas and then foamed or extruded. Only the embodiment of the foam sheet is described. Patent Document 2 discloses extrusion molding of a mixture of a thermoplastic elastomer and a long-chain branched polypropylene. Although it is suggested that the present invention can be applied to injection foaming, it is presumed that the polypropylene resin having a melt flow rate of 2 to 4.1 described in the document has poor fluidity. In particular, when a high expansion ratio is obtained by mixing with a thermoplastic elastomer having poor foamability, it is necessary to increase the polypropylene resin ratio. In such a case, it is presumed that the fluidity is particularly poor. Further, when such a resin is used, the mold transferability at the time of injection molding tends to be inferior, and is not suitable for injection foam molding that requires fluidity at the time of injection filling and transferability of a fine pattern of the mold. .

  Patent Document 3 discloses a resin composition pellet having a melt flow rate of 50 g / 10 min comprising 50% by weight of a hydrogenated styrene copolymer and 50% of a propylene resin having a high melt flow rate, and a melt flow rate. It is disclosed to injection foam molding a mixture of long chain branched polypropylene of 3.5 g / 10 min. However, when using a long-chain branched polypropylene resin, not only the fluidity when injecting the molten resin is insufficient, but a high injection pressure is generated, and the load is more than necessary. The mold transferability tends to be inferior, and a flow mark tends to occur on the surface of the molded body, which tends to impair the appearance.

Japanese Patent Laid-Open No. 2001-348452 Japanese Patent Laid-Open No. 9-296063 JP 2003-41039 A

  An object of the present invention is to provide a thermoplastic elastomer composition for injection foam molding that can provide an injection foam molded article having a high expansion ratio, good mold transferability, and excellent soft feeling.

  By mixing a specific polypropylene-based resin with a specific thermoplastic elastomer, the present inventors achieve both fluidity and foamability during injection filling, excellent mold fine pattern transferability, and elastomer foaming. It has been found that an injection foam molded article having a soft feeling peculiar to the body can be obtained, and the present invention has been completed.

That is, this invention consists of the following structures.
[1] A thermoplastic elastomer (A) having a melt flow rate of 1 g / 10 min to 80 g / 10 min and a type A hardness of 50 to 90 wt% to 50 wt% to 97 wt%,
The modified polypropylene resin (B) satisfying any of the following requirements (a) to (e) and exhibiting strain-hardening properties: 3% by weight or more and 50% by weight or less [(A) and (B ) Is 100% by weight], a thermoplastic elastomer composition for injection foam molding.
(B) Melt flow rate 4.5 g / 10 min or more and less than 10 g / 10 min, Melt tension 5 cN or more (b) Melt flow rate 10 g / 10 min or more and less than 30 g / 10 min, Melt tension 2 cN or more (C) Melt flow rate 30 g / 10 min or more and less than 50 g / 10 min, Melt tension 1 cN or more (2) Melt flow rate 50 g / 10 min or more and 100 g / 10 min or less, Melt tension 0.3 cN or more (e) Melt flow rate 100 g / 10 min or more 250 g / 10 min or less, melt tension 0.3 cN or more [2] thermoplastic elastomer (A) having a melt flow rate of 1 g / 10 min or more and 80 g / 10 min or less, and a type A hardness of 50 or more and 90 or less 50 wt% or more 95% by weight or less,
The modified polypropylene resin (B) satisfying any one of the following requirements (a) to (d) and exhibiting strain-hardening properties comprises 5% by weight or more and 50% by weight or less [(A) and (B ) Is 100% by weight], a thermoplastic elastomer composition for injection foam molding.
(B) Melt flow rate 4.5 g / 10 min or more and less than 10 g / 10 min, Melt tension 5 cN or more (b) Melt flow rate 10 g / 10 min or more and less than 30 g / 10 min, Melt tension 2 cN or more (C) Melt flow rate 30 g / 10 min or more and less than 50 g / 10 min, melt tension 1 cN or more (2) melt flow rate 50 g / 10 min or more and 100 g / 10 min or less, melt tension 0.3 cN or more
[3] The thermoplastic elastomer composition for injection foam molding according to [1] or [2], wherein the thermoplastic elastomer (A) is an olefin-based thermoplastic elastomer.
[4] An injection foam molded article obtained by injection foaming the thermoplastic elastomer composition for injection foam molding according to any one of [1] to [3].
[5] The injection foam molded article according to [4], wherein the foaming ratio of the injection foam molded article is more than 2 times and 10 times or less, and the type A hardness is 30 or more and 80 or less.
[6] The injection foam molding thermoplastic elastomer composition and the foaming agent according to any one of [1] to [3] are supplied to an injection molding machine, and then injected into a mold for foam molding. A method for producing a foamed molded product.
[7] A mold including a fixed mold and a movable mold capable of moving forward and backward at an arbitrary position is used, and after completion of injection, the movable mold is moved backward to foam. [6] The manufacturing method of the foaming molding of description.

  Since the thermoplastic elastomer composition for injection foam molding of the present invention contains a specific polypropylene-based resin in a specific thermoplastic elastomer, the thermoplastic elastomer composition has excellent foamability and can be highly foamed. Therefore, it is possible to obtain an injection-foamed molded article having a soft feeling and a high expansion ratio.

Furthermore, the thermoplastic elastomer composition for injection foam molding of the present invention has excellent fluidity. Therefore, the thin-wall filling property is good, and it is possible to obtain a light-weight injection-foamed molded article by thinning the mold clearance during injection filling.
That is, the thermoplastic elastomer composition for injection foam molding of the present invention is excellent in mold transferability because it is highly fluid and highly foamable. Therefore, it is possible to obtain an injection foam molded article that has a high foaming ratio, has a soft feeling, is reduced in weight, and has excellent mold transferability.

  The thermoplastic elastomer composition for injection foam molding of the present invention comprises a specific thermoplastic elastomer and a polypropylene resin in a specific ratio.

  The thermoplastic elastomer (A) used in the present invention has a melt flow rate of 1.0 g / 10 min to 80 g / 10 min, preferably 5 g / 10 min to 70 g / 10 min. When the melt flow rate of the thermoplastic elastomer is within the above range, the fluidity is ensured, and injection filling can be performed without imposing an excessive load on the molding machine or the mold, and there is no gloss unevenness or flow mark. An injection foam molded body having a hardness can be obtained.

  Here, the melt flow rate (hereinafter sometimes abbreviated as “MFR”) conforms to the provisions of Method A described in JIS K7210 (1999), and uses a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho). It is a value converted from the amount of resin extruded from a die at a constant time under a load of 2.16 kg at 230 ° C. to the amount extruded in 10 minutes. The fixed time is 120 seconds when the melt flow rate exceeds 0.5 g / 10 minutes and 1.0 g / 10 minutes or less, and when the melt flow rate exceeds 1.0 g / 10 minutes and 3.5 g / 10 minutes or less. Is 30 seconds when it exceeds 3.5 g / 10 minutes and 10 g / 10 minutes or less for 60 seconds, 10 seconds when it exceeds 10 g / 10 minutes and 25 g / 10 minutes or less, and it exceeds 25 g / 10 minutes and 100 g / 10 If it is less than 5 minutes, it is 5 seconds, and if it exceeds 100 g / 10 minutes, it is 3 seconds. Three pieces cut out at the predetermined time are collected and the average value is calculated. If three pieces cannot be collected in one measurement, the measurement is continued until three pieces can be collected. If the melt flow rate measured in a certain number of seconds is not in the corresponding range, the measurement is performed again in the number of seconds corresponding to the melt flow rate.

The thermoplastic elastomer (A) used in the present invention has a type A hardness of 50 or more and 90 or less, preferably 50 or more and 80 or less. When the type A hardness is in the above range, it is easy to obtain a product having a good balance such as cushioning properties and heat resistance of the obtained injection foam molded article.
Here, the type A hardness means a value measured by a type A durometer hardness test in an environment of 23 ° C. according to JIS K6253.

  Examples of the thermoplastic elastomer (A) used in the present invention include an ethylene-α-olefin copolymer, a propylene-α-olefin copolymer, an ethylene-propylene-diene copolymer, an ethylene-vinyl acetate copolymer, and a polybutene. Olefin-based elastomers such as chlorinated polyethylene; styrene-isobutylene-styrene copolymers, styrene-isobutylene copolymers, styrene-butadiene-styrene copolymers, styrene-isoprene-styrene copolymers, and hydrogenated products thereof Styrenic elastomers such as; polyester-based elastomers; polyamide-based elastomers; polyurethane-based elastomers, and mixtures of these and polyolefin-based resins such as polypropylene and polyethylene by means of polymerization, blending, melt-kneading, etc. Etc.

  These thermoplastic elastomers are not particularly limited as long as they have the above-mentioned properties, and can be used alone or in combination of two or more, but the modified polypropylene resin (B) described later can be used. From the viewpoint of easy dispersibility and desired hardness and relatively low cost, an ethylene-α-olefin copolymer or a mixture of these with a polyolefin resin is preferred.

Further from the viewpoint of dispersibility and desired hardness can be easily obtained with respect to the polypropylene, the density of the thermoplastic elastomer (A) is preferably from 0.85 g / cm ³ or more 0.880 g / cm ³ or less, 0.855 g / cm ³ or more and 0.875 g / cm ³ or less are more preferable.

  The modified polypropylene resin (B) used in the present invention has strain hardening property, and the lower limit of the melt flow rate is 4.5 g / 10 minutes, preferably 5 g / 10 minutes, and more preferably 10 g / 10. Minutes are preferred. The upper limit of the melt flow rate is 250 g / 10 minutes, preferably 200 g / 10 minutes, and more preferably 100 g / 10 minutes.

  The effect of the strain-hardening property of the modified polypropylene resin (B) used in the present invention is that the internal bubbles (cells) are hard to break during the injection foam molding, and the injection with high expansion ratio is excellent in transferability. A foam molded article is obtained.

Here, “strain hardening” is defined as an increase in viscosity with an increase in the stretching strain of the melt, and is usually determined by the method described in JP-A-62-1121704 (ie, It can be determined by plotting the relationship between the extensional viscosity measured by a commercially available rheometer and time).
In addition, for example, strain hardening can be determined from the fracture behavior of the melt strand at the time of melt tension measurement. That is, when the take-up speed is increased, the melt tension increases abruptly, and when cutting, strain hardening is exhibited.

If the melt flow rate of the modified polypropylene resin (B) is less than 4.5 g / 10 minutes, the fluidity is insufficient, and the molding machine and the mold are unnecessarily burdened, and the injection foam has a complicated shape. In a molded body or a large injection foam molded body, it is difficult to fill the resin into every corner of the mold, and short shot defects tend to occur. Furthermore, the transferability of a fine pattern applied to the mold is deteriorated, a desired shape cannot be obtained, and uneven gloss and flow marks tend to occur on the surface of the molded product. If the melt flow rate exceeds 250 g / 10 min, the metering process may not be stable.
Here, the melt flow rate means a value measured in the same manner as the melt flow rate of the thermoplastic elastomer.

  The melt tension (melt tension) of the modified polypropylene resin (B) in the present invention is a physical property that can serve as an index of foaming properties, but the appropriate value depends on the melt flow rate, and the lower the melt flow rate, the more necessary it is. The melt tension tends to be high.

In the present invention, a melt tension value suitable for foaming is shown according to the melt flow rate of the modified polypropylene resin. That is, the modified polypropylene resin (B) of the present invention has a melt tension that satisfies any of the following (A) to (E).
(A) When the melt flow rate is 4.5 g / 10 min or more and less than 10 g / 10 min, the melt tension is 5 cN or more, preferably 7 cN or more.
(B) When the melt flow rate is 10 g / 10 min or more and less than 30 g / 10 min, the melt tension is 2 cN or more, preferably 3 cN or more.
(C) When the melt flow rate is 30 g / 10 min or more and less than 50 g / 10 min, the melt tension is 1 cN or more, preferably 1.5 cN or more.
(2) When the melt flow rate is 50 g / 10 min or more and 100 g / 10 min or less, the melt tension is 0.3 cN or more, preferably 0.6 cN or more.
(E) When the melt flow rate exceeds 100 g / 10 min and is 250 g / 10 min or less, the melt tension is 0.3 cN or more, preferably 0.5 cN or more.

  When the melt flow rate and melt tension of the modified polypropylene resin (B) are within the above ranges, the resin has a good balance between fluidity and foamability, and internal bubbles (cells) are difficult to break during injection foam molding. It is easy to obtain an injection foam molded article with high foaming ratio with excellent transferability, and also prevents foam breakage at the molten resin flow tip during injection foam molding, making it difficult for silver streak to occur and a beautiful surface An injection foam molded article having an appearance is obtained. Polypropylene resins with a high melt flow rate and high melt tension as described above tend to affect performance such as foamability, fluidity, and transferability, that is, they tend to greatly affect the performance of the entire composition even in small amounts. It is in.

Here, the melt tension is equipped with an attachment for measuring melt tension, using a capillograph (manufactured by Toyo Seiki Seisakusho) having a 10 mmφ cylinder with an orifice having an inner diameter of 1 mmφ and a length of 10 mm at the tip. Pull down the strand discharged from the die when the piston descends at ℃, 10mm / min on a pulley with a load cell 350mm below and pull it at a speed of 1m / min. After stabilization, increase the pulling speed at 40m / min ² The load applied to the pulley with a load cell when the strand breaks. If the strand does not break, the melt tension is the load at which the load applied to the pulley with the load cell does not increase even if the take-up speed is increased.

  As modified polypropylene resin (B) resin which has the above characteristics, what has a branched structure or a high molecular weight component is mentioned, for example. As a method for producing such a modified polypropylene resin (B), for example, radiation is applied to a linear polypropylene resin, or a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator are melt mixed. The method is mentioned.

  In the present invention, those having a branched structure are particularly preferred. As a method for producing the same, a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator is expensive. It is preferable because it can be manufactured at low cost by not requiring it.

  The linear polypropylene resin used in the production of the modified polypropylene resin (B) is a polypropylene resin having a linear molecular structure, specifically, a propylene homopolymer and a block copolymer. A polymer and a random copolymer, which are crystalline polymers. As a copolymer of propylene, a copolymer containing propylene in an amount of 75% by weight or more is preferable in that the crystallinity, rigidity, chemical resistance, etc., which are characteristics of the polypropylene resin, are maintained.

The copolymerizable α-olefin is ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene. , 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene and the like, such as α-olefins having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,11,8,13, 6] Cyclic olefins such as -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene Such as dienes, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, Examples thereof include vinyl monomers such as butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and divinyl benzene. These may be used alone or in combination of two or more.
Among these, ethylene and 1-butene are preferable from the viewpoints of improving cold brittleness resistance and low cost.

Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2,4-hexadiene, and the like. These may be used alone or in combination of two or more.
Of these, butadiene and isoprene are particularly preferable because they are inexpensive and easy to handle and the reaction easily proceeds uniformly.

  The addition amount of the conjugated diene compound is preferably 0.01 parts by weight or more and 20 parts by weight or less, and more preferably 0.05 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. If the addition amount of the conjugated diene compound is less than 0.01 parts by weight, the effect of the modification may be difficult to obtain, and if the addition amount exceeds 20 parts by weight, the effect is saturated and may not be economical. .

  Monomers copolymerizable with the conjugated diene compounds, such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, acrylic acid Metal salts, metal methacrylate salts, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid esters such as 2-ethylhexyl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid 2 -You may use together methacrylic acid esters, such as ethylhexyl and stearyl methacrylate.

  The radical polymerization initiator generally includes peroxides, azo compounds, and the like, but those having a capability of extracting hydrogen from a polypropylene resin or the conjugated diene compound are preferable. Generally, ketone peroxides, peroxyketals, hydroperoxides are used. Organic peroxides such as oxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters are listed. Among these, those having particularly high hydrogen abstraction ability are preferable, for example, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane. N-butyl 4,4-bis (t-butylperoxy) valerate, peroxyketals such as 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5- Diacyl peroxides such as dimethyl-2,5-di (t-butylperoxy) -3-hexyne and dialkyl peroxides such as benzoyl peroxide Oxide, t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate Peroxyesters such as 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. It is done. These may be used alone or in combination of two or more.

  The addition amount of the radical polymerization initiator is preferably from 0.01 to 10 parts by weight, more preferably from 0.05 to 4 parts by weight, based on 100 parts by weight of the linear polypropylene resin. If the addition amount of the radical polymerization initiator is less than 0.01 parts by weight, the effect of the modification may be difficult to obtain. If the addition amount exceeds 10 parts by weight, the effect of the modification is saturated and economical. It may not be.

  The equipment for reacting the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator includes a kneading machine such as a roll, a kneader, a Banbury mixer, a Brabender, a single screw extruder, a twin screw extruder, and a biaxial surface. An updater, a horizontal stirrer such as a two-shaft multi-disc device, a vertical stirrer such as a double helical ribbon stirrer, and the like. Among these, it is preferable to use a kneader, and an extruder is particularly preferable from the viewpoint of productivity.

There is no particular limitation on the order and method of mixing and kneading (stirring) the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator. After mixing the linear polypropylene resin, the conjugated diene compound and the radical polymerization initiator, they may be melt-kneaded (stirred), or after melt-kneading (stirred) the polypropylene resin, the conjugated diene compound or radical initiator is added. At the same time or separately, they may be mixed in a lump or divided.
The temperature of the kneading (stirring) machine is preferably 130 ° C. or more and 300 ° C. or less in that the linear polypropylene resin melts and does not thermally decompose. The kneading (stirring) time is generally preferably 1 to 60 minutes.

  There is no restriction | limiting in the shape and magnitude | size of the modified polypropylene resin (B) obtained in this way, A pellet form may be sufficient.

  The method for mixing the thermoplastic elastomer (A) and the modified polypropylene resin (B) is not particularly limited, and can be performed by a known method. Examples of the mixing method include methods such as dry blending both pellets using a blender, a mixer, etc., melt mixing, and dissolving and mixing in a solvent. In the present invention, a method of dry blending and then subjecting to injection foam molding is preferable because it requires less heat history and decreases the melt tension of the modified polypropylene resin (B).

  The thermoplastic elastomer composition for injection foam molding of the present invention comprises a thermoplastic elastomer (A) of 50 to 97% by weight and a modified polypropylene resin (B) of 3 to 50% by weight. [The total amount of (A) and (B) is 100% by weight], preferably 50% to 95% by weight of the thermoplastic elastomer (A) and 5% by weight of the modified polypropylene resin (B). More preferably 50 wt% or less, more preferably 55 wt% or more and 90 wt% or less of the thermoplastic elastomer composition (A), 10 wt% or more and 45 wt% or less of the modified polypropylene resin (B), Preferably, the thermoplastic elastomer composition (A) contains 55 wt% or more and 82 wt% or less, and the modified polypropylene resin (B) contains 18 wt% or more and 45 wt% or less.

  When the blending ratio of the thermoplastic elastomer (A) and the modified polypropylene resin (B) is within the above range, it has fluidity suitable for use in injection foam molding and melt tension for preventing bubble breakage. It becomes a composition, and an injection foam molded article that is light in weight, has a good transferability at a high expansion ratio, and has an excellent soft feeling.

  The foaming agent used in the present invention is not particularly limited as long as it can be usually used for injection foam molding, such as a chemical foaming agent and a physical foaming agent.

  A chemical foaming agent decomposes | disassembles and generate | occur | produces gas, such as a carbon dioxide gas, It can supply to an injection molding machine, after previously mixing with the said resin. Examples of the chemical foaming agent include inorganic chemical foaming agents such as sodium bicarbonate and ammonium carbonate, and organic chemical foaming agents such as azodicarbonamide and N, N′-dinitrosopentamethylenetetramine. These may be used alone or in combination of two or more.

  A physical foaming agent is injected into a molten resin in a cylinder of a molding machine as a gaseous or supercritical fluid, dispersed or dissolved, and functions as a foaming agent by being released from pressure after being injected into a mold. Is. Examples of the physical blowing agent include aliphatic hydrocarbons such as propane and butane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, halogenated hydrocarbons such as chlorodifluoromethane and dichloromethane, nitrogen, carbon dioxide gas, Inorganic gas such as air can be used. These may be used alone or in combination of two or more.

  Among these foaming agents, an ordinary injection molding machine can be used safely, and uniform fine bubbles are easily obtained. As a chemical foaming agent, an inorganic chemical foaming agent is used, and as a physical foaming agent, nitrogen, carbonic acid is used. Inorganic gases such as gas and air are preferred.

These foaming agents include, for example, foaming aids such as organic acids such as citric acid, talc, and lithium carbonate, in order to stably and uniformly make the bubbles of the injection foam molded article. A nucleating agent such as inorganic fine particles may be added.
Usually, the inorganic chemical foaming agent is used by preparing a masterbatch of a polyolefin resin having a concentration of 10 to 50% by weight from the viewpoint of handleability, storage stability, and dispersibility in a thermoplastic elastomer composition. It is preferable.

What is necessary is just to set the usage-amount of the foaming agent in this invention suitably by the foaming magnification of the injection foaming molding obtained, the kind of foaming agent, and the resin temperature at the time of shaping | molding.
For example, in the case of an inorganic chemical foaming agent, usually, it is preferably 0.5 parts by weight or more and 20 parts by weight or less, more preferably 1 part by weight or more with respect to 100 parts by weight of the thermoplastic elastomer composition for injection foam molding. It is used in the range of 15 parts by weight or less. By using the inorganic chemical foaming agent in the above range, it is economically easy to obtain an injection foam molded article having a foaming ratio of 2 times or more and uniform fine bubbles. In the case of a physical foaming agent, the injection is carried out in the range of 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, with respect to 100 parts by weight of the polypropylene resin of the present invention. Used by supplying to a molding machine.

  As for the method of adding the foaming agent, a thermoplastic elastomer composition for injection foam molding, which is dry blended with a chemical foaming agent, or a material impregnated with a physical foaming agent may be supplied to an injection molding machine in advance. After the thermoplastic elastomer composition for injection foam molding other than the foaming agent is supplied to the injection molding machine, the foaming agent may be added from the middle of the molding machine cylinder.

  In the present invention, if necessary, fluidity improvers such as lubricants, polyolefin waxes, antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, as long as the effects of the present invention are not impaired. Stabilizer, light stabilizer, fluorescent brightener, metal soap, antacid adsorbent stabilizer, cross-linking agent, chain transfer agent, nucleating agent, plasticizer, filler, reinforcing material, pigment, dye, flame retardant, electrification You may use together additives, such as an inhibitor. Of course, these additives used as needed are used within a range not impairing the effects of the present invention, but with respect to 100 parts by weight of the thermoplastic elastomer composition for injection foam molding of the present invention, Preferably, it is used in 0.01 parts by weight or more and 40 parts by weight or less.

  The thermoplastic elastomer composition for injection foam molding of the present invention obtained as described above is injection foamed into an injection foam molded article.

Next, the manufacturing method of the injection foaming molding of this invention is demonstrated concretely.
A known method can be applied to the production method itself, and the molding conditions may be appropriately adjusted depending on the melt flow rate of the thermoplastic elastomer composition for injection foam molding, the type of foaming agent, the type of molding machine, or the shape of the mold.

  In the case of the thermoplastic elastomer composition for injection foam molding of the present invention, the resin temperature is 170 to 250 ° C., the mold temperature is 10 to 100 ° C., the molding cycle is 1 to 60 minutes, the injection speed is 10 to 300 mm / second, and the injection pressure is 10 to 10. It is preferable to carry out under the condition of 200 MPa.

  There are various methods of foaming in the mold, and among these, a mold composed of a fixed mold and a movable mold that can be moved forward and backward at an arbitrary position is used. The so-called core back method (moving cavity method), which causes the mold to recede, forms a non-foamed layer on the surface, the foamed layer tends to become uniform fine bubbles, has excellent lightness and good softness. It is preferable because a simple injection foamed molded product is easily obtained. As a method of retracting the movable mold, it may be performed in one stage, or may be performed in two or more stages, and a process for stopping the movable mold in each stage is added, or the speed is continuously changed. May be moved backward, and the moving speed may be adjusted as appropriate.

  In addition, by introducing a thermoplastic elastomer composition for injection foam molding into the mold while pre-pressing the inside of the mold with an inert gas or the like, the so-called counter pressure method is used in combination, resulting in silver streak. Since the surface appearance defect of an injection foaming molding can be reduced, it is preferable.

  The clearance of the mold when injection-filling the molten mixture of the thermoplastic elastomer composition for injection foam molding and the foaming agent of the present invention is preferably 1.0 mm or more and 3.0 mm or less. It is preferably 2 mm or more and 2.5 mm or less. When the mold clearance is within the above range, it is easy to obtain an injection foamed molded article having a high foaming ratio and excellent in lightness.

The injection-foamed molded article of the present invention thus obtained has fine bubbles, is excellent in lightness, and is excellent in soft feeling. Specifically, the injection-foamed molded article of the present invention preferably has a foaming ratio of more than 2 times and 10 times or less, a type A hardness of 30 or more and 80 or less, and a foaming ratio of 2.5. It is preferable that the hardness is not less than 10 times and not more than 10 times, and the type A hardness is 40 or more and 75 or less.
Here, the method for measuring the type A hardness of the injection-foamed molded article is the same as that for the thermoplastic elastomer.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples.

  In the examples and comparative examples, the test methods and criteria used in various evaluation methods are as follows.

(1) Melt flow rate (MFR):
MFR is a resin that is extruded from a die under a load of 230 ° C. and 2.16 kg using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho) in accordance with the provisions of Method A described in JIS K7210 (1999). It was set as the value converted into the amount extruded from the amount for 10 minutes.
The fixed time is 120 seconds when the melt flow rate exceeds 0.5 g / 10 minutes and 1.0 g / 10 minutes or less, and when the melt flow rate exceeds 1.0 g / 10 minutes and 3.5 g / 10 minutes or less. Is 30 seconds when it exceeds 3.5 g / 10 minutes and 10 g / 10 minutes or less for 60 seconds, 10 seconds when it exceeds 10 g / 10 minutes and 25 g / 10 minutes or less, and it exceeds 25 g / 10 minutes and 100 g / 10 If it is less than 5 minutes, it is 5 seconds, and if it exceeds 100 g / 10 minutes, it is 3 seconds.
Three pieces cut out at the predetermined time are collected and the average value is calculated. If three pieces cannot be collected in one measurement, the measurement is continued until three pieces can be collected. If the melt flow rate measured in a certain number of seconds is not in the corresponding range, the measurement is performed again in the number of seconds corresponding to the melt flow rate.

(2) Melt tension:
Melt tension is equipped with an attachment for measuring melt tension, using a capillograph (manufactured by Toyo Seiki Seisakusho) having a 10 mmφ cylinder with an inner diameter of 1 mmφ and a length of 10 mm at the tip. taken up at 1 m / min over a strand discharged from the die when the lowered at a rate of 10 mm / min load cell with pulley under 350 mm, when increasing the take-off speed at 40 m / min ² after stabilization, the strands The load applied to the pulley with a load cell when ruptures.
When the strand does not break, it means the load at which the load applied to the pulley with a load cell does not increase even if the take-up speed is increased.

(3) Strain hardenability:
When the take-up speed is increased at the time of the above melt tension measurement, the take-up load increases rapidly, and when it reaches breakage, it indicates “strain hardenability”, otherwise it indicates “no strain hardenability”. did.

(4) Type A hardness:
In accordance with JIS K6253, a type A durometer hardness test was performed, and the hardness at 23 ° C. was measured.

(5) Injection pressure:
The peak pressure during injection filling was evaluated as one of the indicators of resin fluidity. At this time, if the injection pressure is high, it can be said that the fluidity is poor. Note that ◎ to Δ were judged to be practically acceptable levels.
Injection pressure is 130MPa or less ...
Injection pressure exceeds 130 MPa and 145 MPa or less.
Injection pressure is over 145 MPa and 150 MPa or less.
Injection pressure exceeds 150 MPa

(6) Foaming ratio:
The thickness is calculated by measuring the thickness of the bottom surface portion of the box-shaped injection-foamed molded article and dividing the thickness by the cavity clearance t ₀ in the mold-clamped state of the part.

(7) Internal void:
A cross section of the bottom portion of the box-shaped injection-foamed molded body cut in the thickness direction was observed, and the presence or absence of voids having a diameter of 1.5 mm or more was examined in the foam layer.
No voids are observed ... ○
Things with voids ... ×

(8) Mold transferability:
The transfer state of the cross-shaped marking line provided at a position 25 mm inside from the center of the short side of the bottom surface of the molded body was visually confirmed for any 10 molded products and evaluated as follows.
Less than 4 pieces of missing part
5 or more with some missing lines ... △

(9) Flow mark:
A flow mark (ring-shaped pattern generated concentrically around the gate) appearing on the surface of the injection-foamed molded body was visually observed and evaluated according to the following criteria.
The flow mark is inconspicuous ...
The flow mark stands out ...

Next, resin materials and foaming agents used in Examples and Comparative Examples are shown below.
(A) Thermoplastic elastomer TP-1: ethylene-propylene copolymer (Dow Chemical Japan, Versify 3401 (type A hardness 72, density 0.86 g / cm ³ , MFR (230 ° C.) 8 g / 10 min))
TP-2: Ethylene-1-butene copolymer (Dow Chemical Japan, Engage 7447 (Type A hardness 57, density 0.87 g / cm ³ , MFR (230 ° C.) 11 g / 10 min))
(B) Modified polypropylene resin MP-1: 100 parts by weight of a propylene homopolymer having a melt flow rate of 45 g / 10 min as a linear polypropylene resin, and t-butyl peroxyisopropyl carbonate 0.6 as a radical polymerization initiator A mixture of parts by weight is supplied from a hopper to a 45 mmφ twin-screw extruder (L / D = 40) at 70 kg / hour and melt-kneaded at a cylinder temperature of 200 ° C. and a rotational speed of 150 rpm. By supplying 0.8 parts by weight (at 0.56 kg / hr) of isoprene monomer as a compound using a metering pump, melt-kneading in the twin screw extruder, and cooling and shredding the extruded strand. The obtained modified polypropylene resin (melt flow rate 6 g / 10 min, melt tension 12 cN, showing strain hardening)
MP-2: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 0.65 parts by weight and the amount of isoprene monomer supplied was changed to 0.5 parts by weight. Resin (melt flow rate 25 g / 10 min, melt tension 4.7 cN, showing strain hardening)
MP-3: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 0.4 parts by weight and the amount of supplied isoprene monomer was changed to 0.4 parts by weight. Resin (melt flow rate 43 g / 10 min, melt tension 1.9 cN, showing strain hardening)
MP-4: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 0.4 parts by weight and the amount of supplied isoprene monomer was changed to 0.35 parts by weight. Resin (melt flow rate 62 g / 10 min, melt tension 1.1 cN, showing strain hardening)
MP-5: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 1.0 part by weight and the amount of supplied isoprene monomer was changed to 0.3 part by weight. Resin (melt flow rate 56 g / 10 min, melt tension 4.8 cN, showing strain hardening)
MP-6: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 1.4 parts by weight and the amount of isoprene monomer supplied was changed to 0.25 parts by weight. Resin (melt flow rate 175 g / 10 min, melt tension 1.9 cN, showing strain hardening)
MP-7: Modified polypropylene obtained in the same manner as MP-1 except that the blending amount of t-butylperoxyisopropyl carbonate was changed to 1.4 parts by weight and the amount of supplied isoprene monomer was changed to 0.22 parts by weight. Resin (melt flow rate 207 g / 10 min, melt tension 1.2 cN, showing strain hardening)
MP-8: The melt flow rate of the propylene homopolymer used was changed to 15 g / 10 min, the blending amount of t-butylperoxyisopropyl carbonate was changed to 0.7 parts by weight, and the amount of supplied isoprene monomer was changed to 2.0 parts by weight. Except for this, a modified polypropylene resin obtained in the same manner as MP-1 (melt flow rate 3 g / 10 min, melt tension 17 cN, showing strain hardening)
PP-1: Commercially available linear polypropylene (propylene-ethylene block copolymer, melt flow rate 45 g / 10 min, melt tension 0.2 cN, no strain hardening)
PP-2: Commercially available linear polypropylene (propylene homopolymer, melt flow rate 3 g / 10 min, melt tension 1.9 cN, no strain hardening)
(C) Foaming agent BA-1: Chemical foaming agent master batch (Polyslen EE275F manufactured by Eiwa Kasei Co., Ltd., decomposition gas amount 40 ml / g)

Example 1
The thermoplastic elastomer and the modified polypropylene resin were dry blended at a composition ratio shown in Table 1 to obtain a thermoplastic elastomer composition for injection foam molding.
An electric injection molding machine (Ube Industries Co., Ltd.) having a core back function and a shut-off nozzle with a mold clamping force of 350 tons obtained by adding 8 parts by weight of the chemical foaming agent BA-1 to 100 parts by weight of the composition. )), And after being melt-kneaded at a cylinder temperature of 200 ° C. and a back pressure of 15 MPa, it is composed of a fixed mold set at 30 ° C. and a movable mold capable of moving forward and backward, 330 mm long × 230 mm wide × height An injection speed of 100 mm in a mold having a 100 mm box-shaped cavity (standing wall part: tilt 10 degrees, clearance 3 mm, bottom part: clearance t ₀ = 2.0 mm) and having a φ2 pin gate at the center of the bottom part Injection filling at / second. After completion of the injection filling, the movable mold was retracted so that the bottom surface portion had a desired thickness (foaming ratio), and the resin in the cavity was foamed. After completion of foaming, the injection foamed molded article was taken out after cooling for 100 seconds. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 2)
An injection-foamed molded article was obtained in the same manner as in Example 1 except that the ratio of the thermoplastic elastomer and the modified polypropylene resin was as shown in Table 1 and the expansion ratio was 4 times.
Table 1 shows the physical properties of the obtained injection-foamed molded article.

Example 3
An injection foam molded article was obtained in the same manner as in Example 1 except that the ratio of the thermoplastic elastomer and the modified polypropylene resin was as shown in Table 1 and the expansion ratio was 2.3 times.
Table 1 shows the physical properties of the obtained injection-foamed molded article.

Example 4
An injection foam molded article was obtained in the same manner as in Example 1 except that the ratio of the thermoplastic elastomer and the modified polypropylene resin was as shown in Table 1 and the expansion ratio was 2.3 times.
Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 5)
An injection-foamed molded article was obtained in the same manner as in Example 1 except that the thermoplastic elastomer was changed to TP-2 and the ratio of the modified polypropylene resin was changed as shown in Table 1.
Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 6)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-2. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 7)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-3. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 8)
An injection foam molded article was obtained in the same manner as in Example 1 except that the thermoplastic elastomer was changed to TP-2, the modified polypropylene resin was changed to MP-4, and the respective ratios were as shown in Table 1. Table 1 shows the physical properties of the obtained injection-foamed molded article.

Example 9
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-5. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 10)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-5 and the mixing ratio was as shown in Table 1. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 11)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-6. Table 1 shows the physical properties of the obtained injection-foamed molded article.

(Example 12)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was changed to MP-7. Table 1 shows the physical properties of the obtained injection-foamed molded article.

  The thermoplastic elastomer composition for injection foam molding of the present invention exhibits excellent fluidity and can be molded with a relatively small injection pressure. In addition, since it has excellent foaming properties, there are no voids in the interior, no surface irregularities, excellent mold transferability, no voiding expansion ratio of 2.3 to 4 times, and type A hardness is A box-shaped injection foam molded article having 42 to 75 bottom portions was obtained.

(Comparative Example 1)
An injection foam molded article was obtained in the same manner as in Example 1 except that the modified polypropylene resin was not used and the expansion ratio was 2.3 times. Table 1 shows the physical properties of the obtained injection-foamed molded article.
The injection pressure at the time of molding was high and the load on the machine was large, and the obtained injection-foamed molded article had voids inside. Moreover, many small dents were seen on the surface of the molded body, and the appearance was not good.

(Comparative Example 2)
Except that the modified polypropylene resin was not used and the thermoplastic elastomer was changed to TP-2, molding was carried out in the same manner as in Example 1, but the injection pressure became too high and the machine stopped due to overload. It was impossible to mold.

(Comparative Example 3)
An injection foam molded article was obtained in the same manner as in Example 1 except that the ratio of the thermoplastic elastomer and the modified polypropylene resin was as shown in Table 1. Table 1 shows the physical properties of the obtained injection-foamed molded article.
The obtained molded body was as hard as 90 or more in hardness, and the flow mark was conspicuous.

(Comparative Example 4)
Injection was carried out in the same manner as in Example 1 except that the thermoplastic elastomer was changed to TP-2, the modified polypropylene resin was changed to commercially available linear PP (PP-1), and the respective ratios were as shown in Table 1. A foamed molded product was obtained. Table 1 shows the physical properties of the obtained injection-foamed molded article.
The resulting injection-foamed molded article had a foaming factor of 2.1 and voids therein, and it was difficult to increase the foaming factor further.

(Comparative Example 5)
An injection foam molded article was obtained in the same manner as in Example 3 except that the modified polypropylene resin was changed to commercially available linear PP (PP-2). Table 1 shows the physical properties of the obtained injection-foamed molded article.
Not only is the injection pressure high during molding and the load on the machine is large, the resulting injection foamed molded article has a foaming ratio of 2.3 times and voids inside, and it is difficult to further increase the foaming ratio. The mold transferability was also inferior.

(Comparative Example 6)
An injection foam molded article was obtained in the same manner as in Example 2 except that the modified polypropylene resin was changed to MP-8. Table 1 shows the physical properties of the obtained injection-foamed molded article.
The injection pressure was higher than that of Example 2, the moldability of the obtained injection foam molded article was inferior, and the flow mark was conspicuous.

Claims (7)

A thermoplastic elastomer (A) having a melt flow rate of 1 g / 10 min to 80 g / 10 min, a type A hardness of 50 to 90, 50% to 97% by weight;
The modified polypropylene resin (B) satisfying any of the following requirements (a) to (e) and exhibiting strain-hardening properties: 3% by weight or more and 50% by weight or less [(A) and (B ) Is 100% by weight], a thermoplastic elastomer composition for injection foam molding.
(B) Melt flow rate 4.5 g / 10 min or more and less than 10 g / 10 min, Melt tension 5 cN or more (b) Melt flow rate 10 g / 10 min or more and less than 30 g / 10 min, Melt tension 2 cN or more (C) Melt flow rate 30 g / 10 min or more and less than 50 g / 10 min, melt tension 1 cN or more (2) melt flow rate 50 g / 10 min or more and 100 g / 10 min or less, melt tension 0.3 cN or more
(E) Melt flow rate exceeding 100 g / 10 min and 250 g / 10 min or less, melt tension 0.3 cN or more A thermoplastic elastomer (A) having a melt flow rate of 1 g / 10 min to 80 g / 10 min and a type A hardness of 50 to 90 wt% to 95 wt%;
The modified polypropylene resin (B) satisfying any one of the following requirements (a) to (d) and exhibiting strain-hardening properties comprises 5% by weight or more and 50% by weight or less [(A) and (B ) Is 100% by weight], a thermoplastic elastomer composition for injection foam molding.
(B) Melt flow rate 4.5 g / 10 min or more and less than 10 g / 10 min, Melt tension 5 cN or more (b) Melt flow rate 10 g / 10 min or more and less than 30 g / 10 min, Melt tension 2 cN or more (C) Melt flow rate 30 g / 10 min or more and less than 50 g / 10 min, melt tension 1 cN or more (2) melt flow rate 50 g / 10 min or more and 100 g / 10 min or less, melt tension 0.3 cN or more   The thermoplastic elastomer composition for injection foam molding according to claim 1 or 2, wherein the thermoplastic elastomer (A) is an olefinic thermoplastic elastomer.   An injection foam molded article obtained by injection foaming the thermoplastic elastomer composition for injection foam molding according to any one of claims 1 to 3.   The injection-foamed molded article according to claim 4, wherein the expansion ratio is more than 2 times and 10 times or less, and the type A hardness is 30 or more and 80 or less. Foam injection molding thermoplastic elastomer composition according to claim 1 and a foaming agent is supplied to an injection molding machine, then, characterized by injection to be foam molded in a mold, foaming Manufacturing method of a molded object. The mold according to claim 6, wherein a mold composed of a fixed mold and a movable mold capable of moving forward and backward at an arbitrary position is used, and after completion of injection, the movable mold is moved backward to foam. A method for producing a foam molded article.