JP2010106093A - Injection foam molding polypropylene-based resin composition and injection foam molded product composed of the resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene-based resin injection foam molded product having excellent lightweight properties and good impact resistance since the resin has good flowability, enables thin wall injection filling, and has a high expansion ratio. <P>SOLUTION: The injection foam molding polypropylene-based resin composition comprises (1) a linear polypropylene-based resin having a melt flow rate of 10 g/10 min to 100 g/10 min and a melt tension of not more than 2 cN, (2) a modified polypropylene-based resin having a melt flow rate of 0.1 g/10 min to less than 10 g/10 min, a melt tension of not less than 5 cN and exhibiting strain-hardening properties, (3) at least one thermoplastic rubber selected from (a) ethylene-α-olefin copolymer rubbers and (b) alkenyl aromatic compound unit-containing rubbers, and (4) a blowing agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Polypropylene resin has good physical properties and moldability, and its use range is rapidly expanding as an environmentally friendly material. In particular, for automobile parts and the like, lightweight and excellent polypropylene resin products are provided. One such product is a polypropylene resin injection foam molding.

  As a technology for highly foaming polypropylene-based resin, a resin containing a foaming agent is injection-molded in a mold space that is held so that the mold can be opened, and then the mold is opened to expand the space. There is a so-called core back method (moving cavity method) for foaming (for example, Patent Document 1).

  In general, as a characteristic of polypropylene resin used for injection foam molding, both the fluidity for filling the resin in every corner of the mold and the foamability for foaming after filling, and a console box, Injected foam molded articles used as automobile parts such as luggage boxes, door trims, and tool boxes are required to be lightweight and thin and to have a good balance between rigidity and impact resistance.

  Normally used linear polypropylene resins are crystalline and have low melt tension, so that bubbles are easily destroyed, and as a result, appearance defects called silver streaks are likely to occur on the surface of the molded body. Furthermore, voids are likely to be generated inside, and it has been difficult to increase the expansion ratio, that is, to increase the expansion.

  Therefore, as a method for increasing the melt tension of the polypropylene resin, for example, a crosslinking agent or a silane-grafted thermoplastic resin is added (Patent Documents 2 and 3). A method of introducing a modified polypropylene resin (Patent Document 5), a method of introducing a modified polypropylene resin by melting and kneading a polypropylene resin, an isoprene monomer, and a radical polymerization initiator are proposed. Certainly, although this method can produce an injection foam molded article with a high expansion ratio, the viscosity at the time of resin melting increases too much, making injection molding difficult, and molding defects considered to result from imparting foamability. A certain flow mark was generated, and the surface appearance sometimes deteriorated. In particular, this tendency was prominent in molding with a large die, such as short shot due to insufficient fluidity.

  As a method for improving impact resistance, a method has been proposed in which an amorphous rubber-like substance is added to a polypropylene resin by blending or multistage polymerization (for example, Patent Documents 6 to 10). However, with this method, although impact resistance is high, the dispersibility of the rubber component to be added is poor and molding is poor, or the foaming property of the resin is not sufficient, and the injection foaming has a high foaming ratio of 2 times or more. It was difficult to obtain a product having both these physical properties, such as being unable to obtain a molded product.

As described above, injection foam molded products that have both flowability and foamability as resin characteristics required for injection foam molding, can be significantly reduced in weight at high expansion ratios, and have good impact resistance. It was difficult to obtain at a low cost.
WO2005 / 026255 JP 61-152754 A Japanese Patent Laid-Open No. 7-109372 JP 2001-226510 A JP-A-9-188774 Japanese Patent Laid-Open No. 2004-082547 JP 2002-11748 A JP 2004-189911 A JP 2005-324429 A JP 2002-283382 A

  An object of the present invention is a polypropylene resin composition for injection foam molding, which is excellent in light weight and has good impact resistance, because of its thin foam filling and high foaming ratio, and the resin composition. It is to provide an injection foam molded article.

  The inventors of the present invention have a polypropylene resin composition for injection foam molding comprising a specific polypropylene resin, a thermoplastic rubber, and a foaming agent, which maintains a melt viscosity and melt tension suitable for injection foaming, and has a high foaming ratio. It was possible to reduce the weight, and because the thermoplastic rubber component was uniformly dispersed, it was found that an injection-foamed molded article having good impact resistance was obtained at low cost, and the present invention was completed.

  That is, the first of the present invention is (1) a linear polypropylene resin having a melt flow rate of 10 g / 10 min to 100 g / 10 min and a melt tension of 2 cN or less, and (2) a melt flow rate of 0.1 g / min. (3) (a) ethylene-α-olefin copolymer rubber, or (b) a modified polypropylene resin having a melt tension of 5 cN or more and a strain tension of 10 g or more and less than 10 g / 10 min. The present invention relates to a polypropylene resin composition for injection foam molding comprising at least one thermoplastic rubber selected from alkenyl aromatic compound unit-containing rubber, and (4) a foaming agent.

As a preferred embodiment,
[1] The modified polypropylene resin is obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator.
[2] The α-olefin component of the (a) ethylene-α-olefin copolymer rubber is one or more selected from 1-butene, 1-hexene, and 1-octene.
[3] The (b) alkenyl aromatic compound unit-containing rubber is styrene-ethylene-butene-styrene rubber (SEBS).
The present invention relates to the polypropylene resin composition for injection foam molding described above.

  A second aspect of the present invention relates to an injection foam molded article comprising the above-described polypropylene resin composition for injection foam molding.

  The polypropylene resin composition for injection foam molding of the present invention contains a polypropylene resin having a high melt flowability and a high melt tension, and an ethylene-α-olefin copolymer rubber or alkenyl aromatic compound unit. By using at least one thermoplastic rubber selected from rubbers and a foaming agent, the dispersion of the rubber into the polypropylene resin becomes good, and an injection foam molded article with good impact resistance can be obtained. In addition, an injection foamed molded article made of the resin composition has a high foaming ratio and is excellent in lightness.

  Embodiments of the present invention will be described below.

  The polypropylene resin composition for injection foam molding of the present invention comprises two types of polypropylene resins having specific melt flow rate and melt tension, thermoplastic rubber, and a foaming agent.

  The polypropylene resin used in the present invention has a melt flow rate of 10 g / 10 min to 100 g / 10 min and a linear polypropylene resin (1) having a melt tension of 2 cN or less and a melt flow rate of 0.1 g / 10. It comprises a modified polypropylene resin (2) having a melt tension of 5 cN or more and a strain hardening property.

  The linear polypropylene resin (1) has a melt flow rate of 10 g / 10 min to 100 g / 10 min, preferably 15 g / 10 min to 50 g / 10 min, and a melt tension of 2 cN or less, preferably 1 cN. It is as follows. When the melt flow rate is in the range of 10 g / 10 min or more and 100 g / 10 min or less, when producing an injection foam molded article, the mold cavity clearance is relatively small even in molding having a thin part of about 1 to 2 mm. The molten resin can be filled into the mold at a low pressure, and continuous and stable molding can be performed. Moreover, if the melt tension is 2 cN or less, the transferability to the mold surface is good, and a foamed molded article having a beautiful surface appearance can be obtained.

The melt flow rate is a value measured under a load of 2.16 kg at 230 ° C. in accordance with ASTM D-1238. Used, a strand lowered at a piston descending speed of 10 mm / min was taken out at 1 m / min from a die having a hole of φ1 mm and a length of 10 mm at 230 ° C., and the take-up speed was increased at 40 m / min ² after stabilization. Sometimes, it refers to the take-up load of the pulley with a load cell when it breaks.

The linear polypropylene resin here is a polypropylene resin having a linear molecular structure, and is a normal polymerization method, for example, a catalyst system obtained from a transition metal compound and an organometallic compound supported on a carrier. (Eg, Ziegler-Natta catalyst) in the presence of polymerization. Specific examples include propylene homopolymers, block copolymers, and random copolymers, 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 the characteristics of a 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, α-olefin having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene and other cyclic olefins, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6 -Diene such as octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, acrylic Butyl Le, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene. Among these, ethylene and 1-butene are preferable in terms of improving cold brittleness resistance and low cost.

  Specific examples of linear propylene resins obtained by polymerizing these monomers include propylene homopolymers, propylene-ethylene random copolymers, propylene-ethylene block copolymers, and the like. It is preferable to use a propylene-ethylene block copolymer from the viewpoint of easily imparting properties.

  The modified polypropylene resin (2) used in the present invention has a melt flow rate of 0.1 g / 10 min or more and less than 10 g / 10 min, preferably 0.3 g / 10 min or more and 8 g / 10 min or less. The tension is 5 cN or more, preferably 8 cN or more, and exhibits strain hardening. When the melt flow rate is 0.1 g / 10 min or more and less than 10 g / 10 min, the dispersibility in the linear polypropylene resin (1) is good, the foaming ratio is high, the bubbles are uniform, and the surface property is high. A good foamed molded product of the present invention is obtained. In addition, transferability to the mold surface is good, and a beautiful surface appearance can be obtained. In addition, when the melt tension is 5 cN or more, an injection foam molded article having uniform fine bubbles of 2 times or more can be obtained.

  Strain hardenability is defined as an increase in viscosity with an increase in the stretching strain of a melt. Usually, the method described in JP-A-62-1121704, that is, an extensional viscosity measured by a commercially available rheometer, This can be determined by plotting the time relationship. Further, for example, strain hardening can be determined from the breaking behavior of the molten 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. When the modified polypropylene resin exhibits strain-hardening properties and the melt tension is high, an injection-foamed molded product with a high expansion ratio of 2 times or more can be obtained, and bubbles are broken at the molten resin flow tip during injection molding. An injection foam molded article excellent in surface smoothness can be obtained for the reason that silver streaks that occur due to the tendency to be difficult occur.

  Examples of the method for producing such a modified polypropylene resin include a method of irradiating a linear polypropylene resin with radiation, or melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator. Can be mentioned. The modified polypropylene resin obtained by these methods contains a branched structure or a high molecular weight component. Among these, in the present invention, a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator can be produced at low cost by not requiring expensive equipment. It is preferable from the point. Examples of the raw linear polypropylene resin used in the production of the modified polypropylene resin (2) include the same as the linear polypropylene resin (1).

  The linear polypropylene resin used for the production of the modified polypropylene resin (2) preferably has a melt flow rate of 5 g / 10 min or more and 60 g / 10 min or less. Within this range, it is easy to obtain a modified polypropylene resin having a melt flow rate of 0.1 g / 10 min or more and less than 10 g / 10 min.

  Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2,4-hexadiene, and these may be used alone or in combination. May be. Among 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 amount is less than 0.01 parts by weight, the effect of the modification may be difficult to obtain, and if the amount exceeds 20 parts by weight, the effect is saturated, which 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, metal acrylate Salt, metal methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, and other acrylic esters, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-methacrylic acid 2- Methacrylic acid esters such as ethylhexyl and stearyl methacrylate may be used in combination.

  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. Of these, those having particularly high hydrogen abstraction ability are preferred, such as 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, Peroxyketals such as n-butyl 4,4-bis (t-butylperoxy) valerate, 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-dimethyl Diacyl peroxides such as dialkyl peroxides such as -2,5-di (t-butylperoxy) -3-hexyne and benzoyl peroxides 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 can be used alone or in combination of two or more.

  The addition amount of the radical polymerization initiator is preferably 0.01 parts by weight or more and 10 parts by weight or less, more preferably 0.05 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. If the amount is less than 0.01 part by weight, the effect of reforming may be difficult to obtain, and if the amount exceeds 10 parts by weight, the effect of reforming may be saturated and not economical.

  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, a kneader is preferably used, 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. The linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator may be mixed and then melt-kneaded (stirred), or after the polypropylene resin is melt-kneaded (stirred), the conjugated diene compound or radical initiator may be mixed simultaneously. Alternatively, they may be mixed separately, collectively or divided. The temperature of the kneading (stirring) machine is preferably 130 to 300 ° C. in that the linear polypropylene resin melts and does not thermally decompose. The time is generally preferably 1 to 60 minutes.

  In this manner, the modified polypropylene resin (2) used in the present invention can be produced. There is no restriction | limiting in the shape and magnitude | size of a modified polypropylene resin, A pellet form may be sufficient.

  The mixing ratio of the linear polypropylene resin (1) and the modified polypropylene resin (2) is preferably 50 parts by weight or more and 95 parts by weight or less of the total 100 parts by weight of the linear polypropylene resin (1). Yes, more preferably 55 parts by weight or more and 90 parts by weight or less. The modified polypropylene resin (2) is preferably 5 to 50 parts by weight, more preferably 10 to 45 parts by weight. There exists a tendency which can provide the injection-foaming molded object which is the foaming magnification 2 times or more which has the uniform fine cell as it is the said compounding quantity at low cost.

  The thermoplastic rubber (3) used in the present invention is at least one selected from (a) an ethylene-α-olefin copolymer rubber or (b) an alkenyl aromatic compound unit-containing rubber. By using these thermoplastic rubbers, compatibility with the polypropylene resin is improved.

  (A) The ethylene-α-olefin copolymer rubber used in the present invention is composed of ethylene and an α-olefin having 4 to 20 carbon atoms, and examples of the α-olefin having 4 to 20 carbon atoms used include: 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl- Examples include 1-pentene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, and the like. These may be used alone or in combination of two or more. Preferably, it is one or more selected from 1-butene, 1-hexene, and 1-octene.

(A) The density of the ethylene-α-olefin copolymer rubber is usually 0.85 g / in, from the viewpoint of enhancing the dispersibility of the polypropylene resin and the impact strength of the obtained injection foamed molded article. preferably cm ³ or more 0.885 g / cm ³ or less, and more preferably not more than 0.85 g / cm ³ or more ～0.88G / cm ^3, more preferably 0.855 g / cm ³ or more 0.875g / Cm ³ or less.

  (A) The melt flow rate at 190 ° C. of the ethylene-α-olefin copolymer rubber is 0.1 g / 10 min or more and 30 g / 10 min or less from the viewpoint of fluidity at the time of molding and impact strength. Is more preferably 0.5 g / 10 min or more and 20 g / 10 min or less. Within the range, the compatibility with the polypropylene resin tends to be good.

  (A) As a manufacturing method of ethylene-alpha-olefin type copolymer rubber, the manufacturing method by a well-known polymerization method is mentioned using a well-known polymerization catalyst. Known polymerization catalysts include, for example, a Ziegler-Natta catalyst system comprising a vanadium compound, an organoaluminum compound and a halogenated ester compound, or at least one cyclopentadienyl anion skeleton on a titanium atom, a zirconium atom or a hafnium atom. Examples thereof include a so-called metallocene catalyst system in which a metallocene compound coordinated with a group having an alumoxane or boron compound is combined.

  Known polymerization methods include, for example, a method of copolymerizing ethylene and α-olefin in an inert organic solvent such as a hydrocarbon compound, and a method of copolymerizing in ethylene and α-olefin without using a solvent. Can be mentioned.

  Examples of the (b) alkenyl aromatic compound unit-containing rubber used in the present invention include, for example, a block copolymer comprising a vinyl aromatic compound polymer block and a conjugated diene polymer block, and a conjugated diene portion of the block copolymer. Examples include a block polymer in which a double bond is hydrogenated. Preferably, a double bond in a conjugated diene portion of a block copolymer comprising a vinyl aromatic compound polymer block and a conjugated diene polymer block is hydrogen. A block polymer that is added, more preferably a block polymer in which 80% or more of the double bond of the conjugated diene portion of the block copolymer is hydrogenated, and still more preferably a conjugate of the block copolymer. It is a block polymer in which 85% or more of the double bonds in the diene part are hydrogenated.

  More specifically, styrene-ethylene-butene-styrene rubber (SEBS), styrene-ethylene-propylene-styrene rubber (SEPS), styrene-butadiene rubber (SBR), styrene-butadiene-styrene rubber (SBS). ), Block copolymers such as styrene-isoprene-styrene rubber (SIS), or block copolymers obtained by hydrogenating these rubber components. Among them, it is preferable to use styrene-ethylene-butene-styrene rubber (SEBS) because the compatibility with the polypropylene resin is good.

  Examples of the method for producing the (b) alkenyl aromatic compound unit-containing rubber include a method in which an alkenyl aromatic compound is bonded to an olefin copolymer rubber or a conjugated diene rubber by polymerization, reaction, or the like.

  (B) The molecular weight distribution of the alkenyl aromatic compound unit-containing rubber is a molecular weight distribution (Mw) determined from a weight average molecular weight (Mw) and a number average molecular weight (Mn) measured by a GPC (gel permeation chromatography) method. / Mn: Q value) is preferably 2.5 or less, and more preferably 2.3 or less.

  (B) The content of the vinyl aromatic compound contained in the alkenyl aromatic compound unit-containing rubber is preferably 10% by weight to 20% by weight, and more preferably 12% by weight to 19% by weight.

  (B) The melt flow rate at 230 ° C. of the alkenyl aromatic compound unit-containing rubber is preferably 1 g / 10 min or more and 15 g / 10 min or less, more preferably 2 g / 10 min or more and 13 g / 10 min or less. When the molecular weight distribution and the melt flow rate are within the above ranges, the compatibility with the polypropylene resin tends to be good.

  (3) The mixing ratio of the thermoplastic rubber used in the present invention is thermoplastic with respect to the polypropylene resin, that is, a total of 100 parts by weight of the linear polypropylene resin (1) and the modified polypropylene resin (2). The rubber is preferably 3 to 40 parts by weight, more preferably 5 to 20 parts by weight. If it is the said compounding quantity, it exists in the tendency for the injection foaming molded object which has a uniform fine cell and whose expansion ratio is 2 times or more. In addition, short shots do not occur in molding having a thin portion, continuous stable production can be performed, and an injection foam molded article having good impact resistance can be provided at low cost.

  The foaming agent (4) 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.

  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. Physical foaming agents 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, air, etc. Inorganic gas. You may use these individually or in mixture of 2 or more types.

  Among these foaming agents, a normal injection molding machine can be used safely, and uniform fine bubbles are easily obtained. As chemical foaming agents, inorganic chemical foaming agents, physical foaming agents, nitrogen, Inorganic gases such as carbon dioxide and air are preferred. These foaming agents include, for example, foaming aids such as organic acids such as citric acid and inorganics such as talc and lithium carbonate, in order to stably and uniformly make the bubbles of the injection foam molded article. A nucleating agent such as fine particles may be added. In general, the inorganic chemical foaming agent is preferably 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 polypropylene resin. .

  What is necessary is just to set the usage-amount of the said foaming agent suitably with 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, it is preferably in the range of 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin. Used in. By using in this range, it is easy to economically obtain an injection foam molded article having a foaming ratio of 2 times or more and uniform fine bubbles.

  The polypropylene resin composition for injection foam molding used in the present invention can be obtained by mixing the above (1) to (4).

  The method for mixing (1) linear polypropylene resin, (2) modified polypropylene resin, (3) thermoplastic rubber, and (4) foaming agent is not particularly limited and can be performed by a known method, for example, Examples of the method include dry blending a pellet-shaped resin 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 preferred because it requires less heat history and decreases the melt tension.

  The polypropylene resin composition for injection foam molding is supplied to an injection molding machine, injected into a mold, and used for foam molding. Regarding the method of adding the foaming agent, the foaming agent may be dry blended in advance with the polypropylene resin composition for injection foam molding and supplied to the injection molding machine, or the polypropylene resin for injection foam molding other than the foaming agent. After supplying the composition to the injection molding machine, a foaming agent may be added.

  Furthermore, if necessary, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, light stabilizers, fluorescent brighteners, metal soaps, antacid adsorption, as long as the effects of the present invention are not impaired. An additive such as a stabilizer such as an agent, a crosslinking agent, a chain transfer agent, a nucleating agent, a lubricant, a plasticizer, a filler, a reinforcing material, a pigment, a dye, a flame retardant, and an antistatic agent may be used in combination. 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 polypropylene resin composition for injection foam molding of the present invention, Preferably, 0.01 parts by weight or more and 10 parts by weight or less are used.

  Next, the manufacturing method of an injection foaming molding is demonstrated concretely. A known method can be applied to the production method itself, and the molding conditions may be appropriately adjusted according to the melt flow rate of the polypropylene resin, the type of foaming agent, the type of molding machine, or the shape of the mold. Usually, in the case of polypropylene resin, it is performed under conditions such as a resin temperature of 170 to 250 ° C., a mold temperature of 10 to 100 ° C., a molding cycle of 1 to 60 minutes, an injection speed of 10 to 300 mm / second, an injection pressure of 10 to 200 MPa. There are various methods for foaming in the mold. Among them, a mold composed of a fixed mold and a movable mold capable of moving forward and backward at an arbitrary position is used. The so-called core back method (moving cavity method), which causes the foam to recede, has a non-foamed layer formed on the surface, the foamed inner layer tends to become uniform fine bubbles, is lightweight and has excellent impact resistance. It is preferable because a foamed molded product is easily obtained. As a method for retracting the movable mold, it may be performed in one step, may be performed in multiple steps of two or more steps, and the speed of retraction may be adjusted as appropriate.

  In addition, by using a so-called counter pressure method in which a polypropylene resin composition for injection foam molding is introduced into the mold while pre-pressing the inside of the mold with an inert gas or the like, poor surface appearance due to silver streak Can be reduced, which is preferable.

  In the injection-foamed molded article of the present invention thus obtained, the thermoplastic rubber component is uniformly dispersed with a particle size of 0.1 μm to 5 μm, preferably 0.2 μm to 3 μm. The injection foam molded article preferably has an average cell diameter of 500 μm or less, more preferably 250 μm or less, and a thickness formed on at least one surface of the foam layer, preferably 10 μm or more and 1000 μm or less. Has a non-foamed layer of 100 μm or more and 500 μm or less.

  When the average cell diameter of the foam layer exceeds 500 μm, excellent rigidity may not be obtained. If the thickness of the non-foamed layer is less than 10 μm, the rigidity tends to decrease, and if it exceeds 1000 μm, the lightness may be difficult to obtain.

  The expansion ratio of the injection-foamed molded article of the present invention is preferably 2 to 10 times, more preferably 2.5 to 6 times. If the expansion ratio is less than 2 times, it is difficult to obtain light weight, and if it exceeds 10 times, the rigidity tends to be significantly reduced. The expansion ratio is obtained from the ratio of the specific gravity of the resin composition obtained by removing the foaming agent from the polypropylene resin composition for injection foam molding and the non-foam molded article obtained by injection molding under the same conditions as the injection foam molded article. Value.

  Furthermore, the weight reduction rate L shown by the following formula of the injection foam molded article of the present invention is preferably 20% or more, and more preferably 25% or more.

Here, W _S is the weight of a non-foamed injection molded body having the same rigidity, specifically, a bending elastic gradient, and W _E is the weight of the injection foam molded body. When the weight reduction rate is less than 20%, it can be said that the significant weight reduction characteristic of the present invention tends not to be obtained.

  The present invention will be described in more detail with reference to the following 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) of polypropylene resin: Measured according to ASTM 1238 at a temperature of 230 ° C. and a load of 2.16 kg.

(2) Melt tension: A capilograph (manufactured by Toyo Seiki Seisakusho) with an attachment for measuring melt tension was used. When a strand lowered at a piston descending speed of 10 mm / min was drawn at 1 m / min from a die having a hole of φ1 mm and a length of 10 mm at 230 ° C., it broke when the take-up speed was increased at 40 m / min ² after stabilization. The take-up load of the pulley with the load cell at that time was taken as melt tension.

  (3) Strain hardenability: When measuring the above-mentioned melt tension, when the take-up speed is increased, the take-up load suddenly increases, and when it reaches breakage, it indicates “strain hardenability”; It does not show sex ".

(4) Injection foam moldability: The number of short shots (number of defects) when 20 shots were continuously molded was determined and evaluated in the following three stages.
The number of defects is 0 ...
The number of defects is 1-2.
The number of defects is 3 or more.

  (5) Foaming ratio: The specimen including the non-foamed layer on the surface was cut out from the bottom surface portion of the injection-foamed molded body, and the specific gravity of the non-foamed molded body (Reference Example 1) having a thickness of 3 mm separately produced was It was calculated from the ratio.

(6) Internal Void: A cross section obtained by cutting the bottom surface portion of the injection-foamed molded body in the thickness direction was observed, and the presence or absence of voids having a size of 1 mm or more in the foam layer was examined.
No internal voids ... ○
Something ...

  (7) Average cell diameter, non-foamed layer thickness: It was determined from a micrograph of a cross section obtained by cutting the bottom surface portion of the injection foamed molded product in the thickness direction. The average cell diameter was an average value of 20 arbitrarily selected. The non-foamed layer was an average value of the movable mold side and the fixed mold side.

  (8) Fluidity: After melt-kneading the resin composition not containing the blowing agent at a resin temperature of 200 ° C. and a back pressure of 5 MPa, the cavity clearance set at 30 ° C. is 2 mm, the width is 20 mm, and the maximum flow length is Using a 2000 mm bar flow mold, the flow length of the injection molded body taken out by injection filling at an injection speed of 60 mm / second and an injection pressure of 70 MPa was measured.

(9) Impact resistance: 50% fracture energy E ₅₀ at normal temperature (23 ° C.) of a test piece (4 cm square test piece cut out from the bottom of the molded body) was determined in accordance with JIS-K7211 (1976). .

(10) Weight reduction rate: The weight of the injection-foamed molded product for which the weight-reduction rate is determined is W _E , and the weight of the non-foamed injection-molded product having the same rigidity G prepared according to a reference example described later is previously set as W _S. The weight reduction ratio L was calculated from Equation 1 in advance.

  Next, raw materials such as polypropylene resins, thermoplastic rubbers and foaming agents used in Examples and Comparative Examples are shown below.

(A) Linear polypropylene resin PP-1: Propylene-ethylene block copolymer, MFR 45 g / 10 min, melt tension 1 cN or less

(B) Modified polypropylene-based resin MP-1: As linear polypropylene-based resin, 100 parts by weight of polypropylene homopolymer having an MFR of 50 g / 10 min, and 0.7 parts by weight of t-butylperoxyisopropyl carbonate as a radical polymerization initiator Is fed from a hopper to a 45 mmφ twin screw extruder (L / D = 40) at a rate of 50 kg / hour, melt-kneaded at a cylinder temperature of 200 ° C., and isoprene monomer from a press-fitted portion provided in the middle using a metering pump Modified polypropylene resin obtained by supplying water at a rate of 0.5 kg / hr, water cooling and chopping the strand (MFR 7 g / 10 min, melt tension 12 cN, showing strain hardening)

(C) Thermoplastic rubber TP-1: Ethylene-1-butene copolymer rubber (Dow Chemical Japan, Engage 7447 (density 0.87 g / cm ³ , MFR (190 ° C.) 5 g / 10 min))
TP-2: ethylene-1-octene copolymer rubber (Dow Chemical Japan, engage 8200 (density 0.87 g / cm ³ , MFR (190 ° C.) 5 g / 10 min))
TP-3: Styrene-ethylene-butene-styrene rubber (SEBS) (manufactured by Asahi Kasei Chemicals Corporation, Tuftec H1062 (density 0.89 g / cm ³ , MFR (230 ° C.) 4.5 g / 10 min, styrene content 18% by weight) )
TP-4: Polypropylene reactor TPO having an ethylene-propylene copolymer content of 80% by weight (manufactured by Sun Allomer, MFR 0.6 g / 10 min)

(D) Foaming agent Chemical foaming agent master batch (Polyslen EE275F manufactured by Eiwa Kasei Co., Ltd., decomposition gas amount 40 ml / g)

(Examples 1-5)
The polypropylene resin composition for injection foam molding was mixed at the composition ratio shown in Table 1 and dry blended.

After melt-kneading the resin composition containing the foaming agent at a resin temperature of 200 ° C. and a back pressure of 5 MPa using an injection molding machine of “MD350S-IIIDP type” (shutoff nozzle specification) manufactured by Ube Industries, Ltd., 60 ° C. A box-shaped cavity having a pin gate of φ2 mm and configured to be a fixed type and a movable type that can be moved forward and backward (vertical wall portion: vertical wall portion: 10 ° inclination) Into a mold having a clearance of 3 mm and a bottom surface portion: clearance t ₀ = 1.5 mm), injection filling was performed at an injection speed of 100 mm / second. After the injection filling was completed, the movable mold was retracted so that the foaming ratio of the bottom surface portion was 3, and the resin in the cavity was foamed. After completion of foaming, the injection foamed molded article was taken out after cooling for 60 seconds. Table 2 shows the injection foam moldability and the surface properties and physical properties of the obtained injection foam molded article.

  Since the polypropylene resin composition for injection foam molding of the present invention is excellent in fluidity, even when the mold cavity clearance during injection filling is 2 mm or less, short shots do not easily occur during continuous molding, and injection foam molding. Good properties. In addition, the box-shaped injection foamed molding obtained by such a molding method has almost no surface irregularities and excellent surface smoothness, has a foaming ratio of 3 times (bottom surface part), and has a high foaming ratio. Is. The average cell diameter was about 200 μm, and it had a non-foamed layer (skin layer) of 300 μm, and there was almost no void inside the injection foam molded article. In addition, the impact resistance was improved, and a weight reduction rate of 30% was achieved with respect to the non-foamed molded body having the same rigidity in spite of the box-shaped injection foamed molded body.

(Reference example)
In Examples, a polypropylene resin composition for injection foam molding excluding a foaming agent was injection-filled, and after cooling for 60 seconds, a non-foamed molded article was taken out. At this time, by changing the clearance of the initial mold bottom surface, molded bodies having different bottom wall thicknesses were obtained.

(Comparative Example 1)
It carried out like Example 1 except not using a modification polypropylene resin and using only PP-1 as a linear polypropylene resin. Many voids were generated inside the injection-foamed molded article, making foam molding difficult.

(Comparative Example 2)
It carried out like Example 1 except not having used thermoplastic rubber. The results are shown in Table 2. Compared to the examples, the impact resistance is inferior.

(Comparative Example 3)
It implemented like Example 1 except having used reactor TPO (TP-4) instead of the thermoplastic rubber. The results are shown in Table 2. Compared with Examples, the fluidity and impact resistance are inferior.

  The injection-foamed molded article of the present invention is capable of thin-wall injection filling necessary for weight reduction by using a modified polypropylene resin having high melt flowability suitable for injection foaming and high melt tension. In addition, although it has a high expansion ratio, it is excellent in light weight and has good impact resistance. The present invention can be widely used for automobile interior materials such as luggage boxes, console boxes, and tool boxes, as well as food packaging containers, household appliance housings, daily miscellaneous goods boxes, and the like.

It is the figure which showed the relationship between the molded object weight of the non-foaming injection molded object in a reference example, and the rigidity of the test piece cut out from the bottom face part.

Claims (5)

  (1) A linear polypropylene resin having a melt flow rate of 10 g / 10 min to 100 g / 10 min and a melt tension of 2 cN or less, and (2) a melt flow rate of 0.1 g / 10 min to less than 10 g / 10 min. A modified polypropylene resin having a melt tension of 5 cN or more and exhibiting strain hardening, (3) (a) an ethylene-α-olefin copolymer rubber, or (b) an alkenyl aromatic compound unit-containing rubber. A polypropylene resin composition for injection foam molding comprising at least one selected thermoplastic rubber and (4) a foaming agent.   The polypropylene resin composition for injection foam molding according to claim 1, wherein the modified polypropylene resin is obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator.   The polypropylene system for injection foam molding according to claim 1, wherein the α-olefin component of the (a) ethylene-α-olefin copolymer rubber is one or more selected from 1-butene, 1-hexene and 1-octene. Resin composition.   The polypropylene resin composition for injection foam molding according to claim 1, wherein the (b) alkenyl aromatic compound unit-containing rubber is styrene-ethylene-butene-styrene rubber (SEBS).   An injection foam molded article comprising the polypropylene resin composition for injection foam molding according to any one of claims 1 to 4.

Images