JP2011094068A - Polypropylene-based resin composition for injection foam molding and injection foam molded article comprising the resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene-based resin composition for injection foam molding, from which an injection foam molded article having excellent lightness and good surface appearance is obtained because the resin composition is applicable to thin wall injection filling and has a high foaming magnification, and to provide an injection foam molded article comprising the resin composition. <P>SOLUTION: The polypropylene-based resin composition for injection foam molding contains following materials (A) to (C): (A) a polypropylene-based resin exhibiting strain hardening property and having a melt tension of 1-5 cN, (B) thermally expandable microcapsules having an expansion starting temperature of ≤190°C and a maximum expanding temperature of ≥210°C, and (C) a chemical foaming agent and/or a physical foaming agent. <P>COPYRIGHT: (C)2011,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 automotive parts and the like, lightweight and excellent polypropylene resin products are provided, and one of such products is an injection foam molded product of polypropylene resin.

  As a technique for obtaining a highly foamed polypropylene resin injection foam molded article, after injecting a resin containing a foaming agent into a mold space held so as to be mold-openable, the mold is opened to open the space. There is a so-called core back method (Moving Cavity method) in which resin is expanded to expand (for example, Patent Documents 1 and 2).

  In general, as a characteristic of a polypropylene resin used for injection foam molding, fluidity for filling a resin in every corner of a mold and foamability for foaming thereafter are required.

  However, the linear polypropylene resin usually used is crystalline and has a low melt tension, so that bubbles are easily broken and it is difficult to achieve high foaming. In addition, there was a tendency for appearance defects called silver streaks due to the foaming agent-derived gas to easily occur on the surface of the injection-foamed molded article.

  Examples of methods for increasing the melt tension of a polypropylene resin include a method of introducing a long chain branch by irradiating a non-crosslinked polypropylene resin with a radiation (Patent Document 3), a polypropylene resin, an isoprene monomer, and initiation of radical polymerization. A method of producing a modified polypropylene resin by melt-kneading an agent (Patent Document 4) has been proposed. Certainly, although this method yields an injection-foamed molded article with a high foaming ratio, the viscosity at the time of resin melting increases too much, making injection difficult, and it is a molding defect that is considered to result from imparting foamability. In some cases, a flow mark was generated and the surface appearance was deteriorated.

  On the other hand, as a foaming agent used for injection foam molding, there are a chemical foaming agent, a physical foaming agent, a thermally expandable microcapsule, and the like.

  The chemical foaming agent is premixed with resin and then supplied to the injection molding machine, and decomposes in the cylinder to generate a gas such as carbon dioxide. It is easy to handle and safe, and has the advantage of being able to obtain a high-magnification injection-foamed molded product. On the other hand, the above-mentioned silver streak is generated on the surface of the injection-foamed molded product. It is essential to use a so-called counter pressure method in which the resin is introduced into the mold while applying pressure to the mold with an inert gas or the like. Since the counter pressure uses high-pressure gas, peripheral equipment becomes expensive.

  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. Like chemical foaming agents, it is easy to obtain a high-magnification injection-foamed molded product, but it is necessary to take measures against the appearance of the injection-foamed molded product.

  The thermally expandable microcapsule is obtained by microcapsulating a volatile liquid foaming agent with a polymer having a gas barrier property. The liquid foaming agent is premixed with the resin and then supplied to the injection molding machine, and the liquid foaming agent encapsulated in the capsule is vaporized and swelled to obtain an injection foamed molded article. Since defects due to chemical foaming agents and physical foaming agent-derived gas do not occur, the appearance of the injection-foamed molded article is good, but the expansion ratio is limited due to the structure of the capsule, and a high-magnification injection-molded molded article I can't get it.

  As described above, it has been difficult to obtain an injection-foamed molded article having a good surface appearance at a high foaming ratio that has both flowability and foamability as resin characteristics necessary for injection-foaming molding. there were.

WO2005 / 026255 Japanese Patent Laid-Open No. 2004-082547 JP 2001-226510 A JP-A-9-188774

  An object of the present invention is a polypropylene-based resin composition for injection foam molding, which can obtain an injection foam molded article having excellent lightness and good surface appearance because it is capable of thin-wall injection filling and has a high expansion ratio. An object of the present invention is to provide an injection foam molded article comprising the resin composition.

  The inventors of the present invention added high-foaming by adding a polypropylene-based resin having a specific melt viscosity and melt tension suitable for injection foaming, a specific thermally expandable microcapsule, and a chemical foaming agent and / or a physical foaming agent. It has been found that an injection-foamed molded article that can be reduced in weight at a magnification and has a good surface appearance can be obtained at a low cost, and the present invention has been completed.

That is, this invention consists of the following structures.
[1] A polypropylene resin composition for injection foam molding comprising the following (A) to (C).
(A) a polypropylene resin that exhibits strain hardening and has a melt tension of 1 cN or more and 5 cN or less,
(B) a thermally expandable microcapsule having an expansion start temperature of 190 ° C. or lower and a maximum expansion temperature of 210 ° C. or higher;
(C) Chemical foaming agent and / or physical foaming agent.
[2] A modified polypropylene resin (A) in which the (A) polypropylene resin exhibits strain-hardening properties, has a melt tension of 1 cN or more and 5 cN or less, and a melt flow rate of 10 g / 10 min or more and less than 100 g / 10 min. 1) The polypropylene resin composition for injection foam molding according to [1].
[3] A modified polypropylene resin (A) in which the (A) polypropylene-based resin exhibits strain hardening, a melt tension is 5 cN or more, and a melt flow rate is 0.1 g / 10 min or more and less than 10 g / 10 min. -2) The polypropylene system for injection foam molding according to [1], comprising a linear polypropylene resin (A-3) having a melt flow rate of 10 g / 10 min to 100 g / 10 min and a melt tension of less than 1 cN. Resin composition.
[4] The modified polypropylene resin (A-1) or (A-2) is obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator [2] or [3] The polypropylene resin composition for injection foam molding according to [3].
[5] An injection foam molded article comprising the polypropylene resin composition for injection foam molding according to any one of [1] to [4].

  The polypropylene resin composition for injection foam molding of the present invention has a melt viscosity and melt tension suitable for injection foaming. Further, when an injection foam molded article is produced by using a thermally expandable microcapsule having a expansion start temperature of 190 ° C. or less and a maximum expansion temperature of 210 ° C. or more in combination with a chemical foaming agent and / or a physical foaming agent, It has a high expansion ratio and can reduce silver streak without using a counter pressure method. Therefore, the injection-foamed molded article made of the polypropylene resin composition for injection-foam molding of the present invention has a high foaming ratio and is excellent in light weight and has a good surface appearance.

  Embodiments of the present invention will be described below.

  The polypropylene resin composition for injection foam molding of the present invention comprises (A) a polypropylene resin that exhibits strain hardening and has a melt tension of 1 cN or more and 5 cN or less, (B) a specific thermally expandable microcapsule, and ( C) It comprises a chemical blowing agent and / or a physical blowing agent.

  The (A) polypropylene resin used in the present invention exhibits strain hardening and has a melt tension of 1 cN or more and 5 cN or less.

  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 polypropylene resin (A) exhibits strain-hardening properties and the melt tension is within the above range, the foaming ratio is a high foaming ratio of 2 times or more. An injection foam molded article having excellent surface smoothness can be obtained for the reason that silver streaks that occur due to easy bubble breaking are less likely to occur.

Melt tension was lowered at a piston descending speed of 10 mm / min from a die having a hole of φ1 mm and length of 10 mm at 200 ° C. using a capillograph (manufactured by Toyo Seiki Seisakusho) with an attachment for measuring melt tension. When the strand is taken up at 1 m / min and the take-up speed is increased at 40 m / min ² after stabilization, it means the take-up load of the pulley with a load cell when it breaks.

The polypropylene-based resin (A) may exhibit strain hardening and have a melt tension of 1 cN or more and 5 cN or less, but as one preferred embodiment,
(1) Modified polypropylene resin (A-1) that exhibits strain-hardening properties, has a melt tension of 1 cN or more and 5 cN or less, and a melt flow rate of 10 g / 10 min or more and less than 100 g / 10 min.

  The modified polypropylene resin (A-1) used in the present invention preferably has a melt flow rate of 10 g / 10 min or more and less than 100 g / 10 min, more preferably 15 g / 10 min or more and 60 g / 10 min or less. is there. The melt tension is 1 cN or more and 5 cN or less, preferably 1.5 cN or more and 4 cN or less, and exhibits strain hardening.

  When the melt flow rate is 10 g / 10 min or more and less than 100 g / 10 min, there is a tendency that an injection foam molded article having a high expansion ratio and uniform bubbles is obtained. Further, when the melt tension is 1 cN or more and 5 cN or less, the foaming ratio is 2 times or more, and an injection foam molded product having uniform fine cells can be obtained. A melt flow rate means what was measured under 230 degreeC and a 2.16kg load based on ASTMD-1238.

As another preferred embodiment of the polypropylene resin (A),
(2) A modified polypropylene resin (A-2) exhibiting strain hardening, a melt tension of 5 cN or more and a melt flow rate of 0.1 g / 10 min or more and less than 10 g / 10 min, and a melt flow rate of 10 g / 10 minutes or more and 100 g / 10 minutes or less, and what comprises linear polypropylene resin (A-3) whose melt tension is less than 1 cN is mentioned. The modified polypropylene resin (A-2) used in the present invention preferably has a melt flow rate of 0.1 g / 10 min or more and less than 10 g / 10 min, more preferably 0.3 g / 10 min or more and 9 g / min. 10 minutes or less. Further, the melt tension is preferably 5 cN or more, 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 compatibility with the linear polypropylene resin (A-3) described later is good, the foaming ratio is high, and the bubbles are uniform. There is a tendency that an injection foam molded article having good surface properties is obtained. In addition, transferability to the mold surface is good, and a beautiful surface appearance can be obtained. Moreover, when the melt tension is 5 cN or more, it is easy to obtain an injection-foamed molded article having uniform and fine bubbles twice or more.

  As a method for producing such modified polypropylene resins (A-1) and (A-2), for example, a linear polypropylene resin is irradiated with radiation, or a linear polypropylene resin, a conjugated diene compound, a radical Examples thereof include a method of melt-mixing a polymerization initiator. The modified polypropylene resins (A-1) and (A-2) obtained by these methods contain a branched structure or a high molecular weight component. Among these, in the present invention, the modified polypropylene resins (A-1) and (A-2) are obtained by melting and mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator. Polypropylene resin is preferred because it does not require expensive equipment and can be manufactured at low cost.

The raw material polypropylene resin used in the production of the modified polypropylene resins (A-1) and (A-2) is a linear polypropylene resin having a linear molecular structure, and is a normal polymerization. Obtained by polymerization in the presence of a catalyst system (eg Ziegler-Natta catalyst) obtained from a transition metal compound and an organometallic compound supported on a carrier. 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 characteristics of the polypropylene resin, are maintained. Examples of copolymerizable α-olefins include ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, and 3,4-dimethyl-1- butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, carbon number 2 or 4 to 12 of α- olefin, 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, Diene such as 6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate Butyl acrylate, 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.

  In addition, it is preferable that the melt flow rate of the linear polypropylene-type resin used for manufacture of modified polypropylene resin (A-1) is 30 g / 10min or more and 100 g / 10min or less. Within this range, it is easy to obtain a modified polypropylene resin (A-1) having a melt flow rate of 10 g / 10 min or more and less than 100 g / 10 min.

  Moreover, it is preferable that the melt flow rate of the linear polypropylene-type resin used for manufacture of modified polypropylene resin (A-2) is 5 g / 10min or more and 60 g / 10min or less. Within this range, it is easy to obtain a modified polypropylene resin (A-2) 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 use 1 type (s) or 2 or more types.

  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 the linear polypropylene-based resin may be melt-kneaded (stirred) and then the conjugated diene compound or the radical initiator. May be mixed at the same time or 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.

  Thus, the modified polypropylene resins (A-1) and (A-2) used in the present invention can be produced. The shape and size of the modified polypropylene resins (A-1) and (A-2) are not limited, and may be pellets.

  The linear polypropylene resin (A-3) preferably has a melt flow rate of 10 g / 10 min to 100 g / 10 min, more preferably 15 g / 10 min to 50 g / 10 min, and preferably a melt tension. Less than 1 cN. 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. It is possible to fill the mold with the molten resin at a low pressure, and there is a tendency that continuous and stable injection foam molding can be performed. If the melt tension is less than 1 cN, the transferability to the mold surface is good, and an injection foam molded article having a beautiful surface appearance tends to be obtained.

  Examples of the linear polypropylene resin herein include the same materials as those taken up as the raw material linear polypropylene resin used in the production of the modified polypropylene resin. 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.

  The mixing ratio of the modified polypropylene resin (A-2) and the linear polypropylene resin (A-3) is preferably 5 parts by weight or more and 50 parts by weight in the total of 100 parts by weight of the modified polypropylene resin (A-2). Parts by weight or less, more preferably 10 parts by weight or more and 45 parts by weight or less. Linear polypropylene resin (A-3) becomes like this. Preferably they are 50 to 95 weight part, More preferably, they are 55 to 90 weight part. 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 thermally expandable microcapsule (B) used in the present invention has an expansion start temperature of 190 ° C. or lower and a maximum expansion temperature of 210 ° C. or higher.

  The thermally expandable microcapsule (B) used in the present invention is obtained by microcapsulating a volatile liquid expanding agent with a polymer. In general, it can be produced by a method of suspension polymerization of a polymerizable mixture containing at least a swelling agent and a polymerizable monomer in an aqueous medium. As the polymerization reaction proceeds, a heat-expandable microcapsule having a structure in which an outer shell is formed by the produced polymer and an expansion agent is encapsulated in the outer shell is obtained.

  As the polymer forming the outer shell, generally, a thermoplastic resin having good gas barrier properties may be used. The polymer forming the outer shell softens when heated. As the liquid expansion agent to be included in the outer shell resin, it is only necessary to select one that becomes gaseous at a temperature below the softening point of the polymer.

  The expansion start temperature is a temperature at which the liquid foaming agent encapsulated in the thermally expandable microcapsule evaporates and expands, and the elastic modulus of the polymer forming the outer shell sharply decreases and the capsule begins to expand. It is.

  When the expansion start temperature is within this range, the polypropylene resin composition for injection foam molding of the present invention can be sufficiently foamed after being filled in the mold.

  The maximum expansion temperature is a temperature at which the diameter becomes maximum when the diameter is measured while heating the thermally expandable microcapsule from room temperature.

  When the maximum expansion temperature is within this range, the expansion of the heat-expandable microcapsule does not appear, and the injection-foaming moldability is not affected. Is obtained.

  Here, “slip” means that the elastic modulus of the outer shell resin rapidly decreases in the process of heat-melting and kneading, and the encapsulated vaporized expansion agent permeates through the microcapsule, thereby reducing the internal pressure of the microcapsule. It is a phenomenon in which it is crushed due to shortage and the magnification of the injection-foamed molded article is reduced. In particular, when molding is performed at a temperature higher than the maximum expansion temperature, capsule “sagging” proceeds, and as a result, there is a tendency that an injection foam molded article having a desired magnification cannot be obtained.

  The proportion of the thermally expandable microcapsule (B) used in the present invention is preferably 0.5 parts by weight or more and 30 parts by weight or less, more preferably 100 parts by weight of the polypropylene resin (A). Is 2 parts by weight or more and 20 parts by weight or less. If it is the said usage-amount, it exists in the tendency which does not inhibit the foaming property of the coexisting chemical foaming agent and / or physical foaming agent, and has the surface appearance favorable, and the injection-foaming molded object whose expansion ratio is 2 times or more. Moreover, short shot does not occur in the injection molding having a thin portion, and continuous and stable production can be performed.

  The chemical foaming agent and / or physical foaming agent (C) used in the present invention is not particularly limited as long as it can be used for general injection foam molding.

  The chemical foaming agent is mixed with the resin in advance and then supplied to the injection molding machine, and decomposes in the cylinder to generate a gas such as carbon dioxide. 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 chemical foaming agent is preferable because a normal injection molding machine can be used safely and uniform fine bubbles are easily obtained. Among the chemical foaming agents, inorganic chemical foaming agents are preferable. When these chemical foaming agents and / or physical foaming agents are used, foaming aids such as organic acids such as citric acid are used as necessary in order to stably and uniformly make the bubbles of the injection foam molded article. A nucleating agent such as an inorganic fine particle such as an agent, talc, or lithium carbonate may be added. Usually, the 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 viewpoints of handleability, storage stability, and dispersibility in polypropylene resin.

  What is necessary is just to set the usage-amount of the said chemical foaming agent and / or a physical foaming agent suitably according to 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 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 (A). Used in the range of By using in this range, an injection foam molded article having a foaming ratio of 2 or more can be obtained without inhibiting the foamability of the coexisting thermally expandable microcapsules. Further, an injection foam molded article having a good surface appearance can be obtained without using a counter pressure facility that is a measure for improving the surface appearance.

  The polypropylene resin composition for injection foam molding used in the present invention comprises the polypropylene resin (A), the thermally expandable microcapsule (B), and a chemical foaming agent and / or a physical foaming agent (C). The method for adjusting the polypropylene resin composition for injection foam molding is not particularly limited, and can be performed by a known method. For example, pellet-shaped resin is dry-blended using a blender, mixer, etc., melt-mixed, solvent The method of melt | dissolving in and mixing is mentioned. In the present invention, a method of subjecting a polypropylene resin (A), a heat-expandable microcapsule (B), and a chemical foaming agent and / or a physical foaming agent (C) to dry blending and then subjecting to injection foam molding has a heat history. This is preferable because it requires less and less decreases in melt tension.

  There are no particular restrictions on the method of adding the chemical foaming agent and / or physical foaming agent, and the raw material polypropylene resin (A), thermally expandable microcapsule (B), chemical foaming agent and / or physical foaming agent ( C) may be dry blended and supplied to an injection molding machine, or after a polypropylene resin (A) and a thermally expandable microcapsule (B) are supplied to an injection molding machine, a chemical foaming agent and / or physical A foaming agent (C) may be added.

  Further, if necessary, stabilizers such as thermoplastic elastomers, impact modifiers such as rubber, metal deactivators, fluorescent brighteners, metal soaps, and antacid adsorbents, as long as the effects of the present invention are not impaired. Crosslinkers, chain transfer agents, nucleating agents, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents and other additives 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, it is used in an amount of 0.01 to 40 parts by weight.

  The polypropylene resin composition for injection foam molding is supplied to an injection molding machine, injected into a mold and used for foam molding, and becomes an injection foam molding. 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 layer tends to be uniform fine bubbles, has excellent lightness, and has a good surface appearance. It is preferable because a molded body 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.

  The expansion ratio of the injection-foamed molded article of the present invention is preferably 2 to 5 times, more preferably 2.5 to 3 times. When the expansion ratio is less than 2 times, it is difficult to obtain light weight, and when it exceeds 3 times, the rigidity tends to be significantly reduced. As for the expansion ratio, a polypropylene resin composition obtained by removing a thermally expandable microcapsule, a chemical foaming agent and / or a physical foaming agent from a polypropylene resin composition for injection foam molding was injection molded under the same conditions as the injection foam molded article. It is a value obtained from the ratio of specific gravity with the non-foamed molded article.

  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): measured in accordance with 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 200 ° C., it was broken 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 melt tension, when the take-up speed is increased, the take-up load suddenly increases, and when the fracture is reached, “strain hardenability is shown: ○”, otherwise it is “ The strain hardening property is not shown: x ”.

(4) Injection-foaming moldability: defective molding products such as short shots when 20 shots are continuously formed, poor foaming (cell non-uniformity in the foam layer), burns due to decreased fluidity (due to increased injection pressure), etc. The obtained number was obtained 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) Silver streak: The surface of the bottom surface of the injection-foamed molded article was visually observed to investigate the occurrence of silver streak.
Silver streak is inconspicuous ... ○
Silver streak stands out ... ×
Next, polypropylene resins, thermally expandable microcapsules, and foaming agents used in Examples and Comparative Examples are shown below. In addition, about the thermally expansible microcapsule, what was used as the masterbatch was used for the purpose of the dispersibility improvement to a polypropylene resin composition.

(Polypropylene resin)
A-1: As a linear polypropylene resin, a hopper was prepared by mixing a mixture of 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 45 g / 10 min and 1.0 part by weight of t-butylperoxyisopropyl carbonate as a radical polymerization initiator. Is supplied to a 45 mmφ twin screw extruder (L / D = 40) at a rate of 70 kg / hour and melt-kneaded at a cylinder temperature of 200 ° C., and isoprene monomer is 0.3 kg / hour from a press-fitted portion provided in the middle using a metering pump. Modified polypropylene resin obtained by water-cooling and chopping the strands (melt flow rate 56 g / 10 min, melt tension 2 cN, showing strain hardening)
A-2: A mixture of 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 45 g / 10 min as a linear polypropylene resin and 0.7 parts by weight of t-butylperoxyisopropyl carbonate as a radical polymerization initiator, Modified polypropylene resin obtained in the same manner as MP-1 except that the supply amount was 0.7 kg / hour (melt flow rate 7 g / 10 min, melt tension 12 cN, showing strain hardening)
A-3: Linear polypropylene resin, propylene-ethylene block copolymer, melt flow rate 45 g / 10 min, melt tension less than 1 cN

(Thermal expansion microcapsule masterbatch)
B-1: Fine Cell Master MS405K (Daiichi Seika Kogyo Co., Ltd., Carrier Resin: LDPE, Microcapsule Concentration 40wt%, Microcapsule Used: Kureha Microsphere S2320 (Kureha, Foaming Start Temperature 180 ° C, Maximum Foaming Temperature 225 ° C))

(Foaming agent)
C-1: Foaming agent master batch (Polyslen EE275F manufactured by Eiwa Kasei Co., Ltd., decomposition gas amount 40 ml / g)

(Examples 1-4)
The polypropylene resin composition for injection foam molding was mixed at the composition ratio (parts by weight) shown in Table 1 and dry blended.

It is an injection molding machine of “MD350S-IIIDP type” (shutoff nozzle specification) manufactured by Ube Industries, Ltd., and the thermally expandable microcapsule masterbatch and chemical foaming agent and / or physics at a resin temperature of 220 ° C. and a back pressure of 15 MPa. After melt-kneading a polypropylene resin composition containing a foaming agent, it has a φ2 mm pin gate set at 45 ° C., and is composed of a fixed mold and a movable mold capable of moving forward and backward, 330 mm long × horizontal A mold having a box-shaped cavity (230 mm × 100 mm height) (standing wall portion: inclination 10 degrees, clearance 3 mm, bottom portion: clearance t ₀ = 1.3 mm) was injected and filled at an injection speed of 100 mm / sec. 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 foam molded body was taken out after cooling for 40 seconds. Table 2 shows the injection foamability and the properties of the obtained injection foam molding.

  The polypropylene resin composition for injection foam molding of the present invention is a polypropylene resin that exhibits strain hardening and has a melt tension of 1 cN or more and 5 cN or less. Good properties. Moreover, the box-shaped injection foam molded article obtained by such a molding method has a good surface appearance and a high foaming ratio (3 times).

(Reference example)
The polypropylene resin composition obtained by removing the foaming agent from the polypropylene resin composition for injection foam molding in Examples was injected and filled, and after cooling for 60 seconds, the 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 thermally expansible microcapsule and having increased the foaming agent. The results are shown in Table 2. Although a 3-fold foamed molded product was obtained, silver streaks occurred and the surface appearance deteriorated.

(Comparative Example 2)
It carried out like Example 2 except not using a foaming agent. The results are shown in Table 2. Compared to the examples, it is difficult to obtain the desired thickness of the injection-foamed molded article, and the expansion ratio is inferior. The surface tension of the injection-foamed molded article is deteriorated.

(Comparative Example 3)
It carried out like Example 4 except not having used a foaming agent. The results are shown in Table 2. Compared to the examples, it is difficult to obtain the desired thickness of the injection-foamed molded article, and the expansion ratio is inferior. The surface tension of the injection-foamed molded article is deteriorated.

(Comparative Example 4)
The linear polypropylene resin was used without using the modified polypropylene resin, and the same operation as in Example 1 was performed. The results are shown in Table 2. Compared to the examples, the injection foaming moldability is poor, and a large number of large voids are generated inside the injection foaming molded product. The expansion ratio is inferior.

  The injection-foamed molded article of the present invention is a thin-walled injection filling required for weight reduction by using a modified polypropylene resin having a melt viscosity and melt tension suitable for injection foaming, a thermally expandable microcapsule, and a foaming agent. It has a high expansion ratio and is excellent in light weight. In addition, a molded article having a good surface appearance can be obtained without requiring expensive equipment. The present invention can be widely used in automobile interior materials such as console boxes, luggage boxes, door trims, deck side trims, and instrument panels, food packaging containers, household appliance housings, and household goods boxes.

Claims (5)

A polypropylene resin composition for injection foam molding comprising the following (A) to (C).
(A) a polypropylene resin that exhibits strain hardening and has a melt tension of 1 cN or more and 5 cN or less,
(B) a thermally expandable microcapsule having an expansion start temperature of 190 ° C. or lower and a maximum expansion temperature of 210 ° C. or higher;
(C) Chemical foaming agent and / or physical foaming agent.   The modified polypropylene resin (A-1) in which the (A) polypropylene-based resin exhibits strain-hardening properties, has a melt tension of 1 cN or more and 5 cN or less, and a melt flow rate of 10 g / 10 min or more and less than 100 g / 10 min. The polypropylene resin composition for injection foam molding according to claim 1.   The modified polypropylene resin (A-2) in which the (A) polypropylene resin exhibits strain-hardening properties, the melt tension is 5 cN or more, and the melt flow rate is 0.1 g / 10 min or more and less than 10 g / 10 min. The polypropylene resin composition for injection foam molding according to claim 1, comprising a linear polypropylene resin (A-3) having a melt flow rate of 10 g / 10 min to 100 g / 10 min and a melt tension of less than 1 cN. .   The modified polypropylene resin (A-1) or (A-2) is obtained by melt-mixing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator. Polypropylene resin composition for injection foam molding.   An injection foam molded article comprising the polypropylene resin composition for injection foam molding according to any one of claims 1 to 4.