JP4963266B2 - Polypropylene resin injection foam - Google Patents

Description

  The present invention relates to an injection foam molded body made of a polypropylene resin.

  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.

  In the case of using an injection-foamed molded article of polypropylene resin as an automobile part, it is often required to have high rigidity and high impact resistance. Moreover, since it becomes easy to raise | generate molding defects, such as a short shot, when it becomes the large component, it is necessary to raise the fluidity | liquidity of raw material resin to be used, maintaining the above-mentioned physical property as much as possible.

  As a method for improving the 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. Moreover, in order to improve fluidity | liquidity, using processing aids, such as a fluidity improver, is mentioned.

  In order to improve both impact resistance and fluidity, there is a technique in which an olefinic thermoplastic elastomer and a polyolefin wax are applied to a thermoplastic resin (for example, Patent Documents 1 and 2). In these documents, a flexible olefinic thermoplastic elastomer foam is provided which has a crosslinkable olefin copolymer rubber as a main component and has improved fluidity by adding a polyolefin wax. However, since the rubber component is the main component in this document, the balance between impact resistance and rigidity is poor.

An example of adding an elastomer and a polyolefin wax to a thermoplastic resin has been reported as described above. In particular, in an injection foamed molding mainly composed of a polyolefin resin, the injection foamability is maintained, and a large mold is used. No investigation has been made so far to obtain an injection-foamed molded article having good flowability for molding and sufficient impact resistance required for the aforementioned parts.
Japanese Patent Laid-Open No. 2005-220229 JP 2006-307069 A

  The purpose of the present invention is excellent in fluidity, in particular, can be molded by a large mold, and can be injection-filled with a thin wall and has a high expansion ratio, so it has excellent light weight, impact resistance and surface properties. It is to provide a good polypropylene-based resin injection foam molded article.

  The present inventors have used specific polypropylene resins, thermoplastic rubbers, and polyolefin waxes, while maintaining the melt viscosity and melt tension suitable for injection foam molding, and in which the rubber component is uniformly dispersed. A polypropylene resin composition for foam molding is obtained. By using the polypropylene resin composition for injection foam molding, it is possible to significantly reduce the weight at a high expansion ratio, impact resistance, and surface properties. The inventors found that a good injection-foamed molded article can be obtained and completed the present invention.

  That is, the present invention provides (1) a modified polypropylene resin having a melt flow rate of 10 g / 10 min or more and less than 50 g / 10 min, a melt tension of 2 cN or more, and exhibiting strain hardening, (2) (a) ethylene-α -Supplying at least one thermoplastic rubber selected from olefin copolymer rubber and (b) alkenyl aromatic compound unit-containing rubber, (3) polyolefin wax, and (4) blowing agent to an injection molding machine. Then, the present invention relates to an injection foam molded article obtained by injection molding into a mold and foam molding.

As a preferred embodiment,
(1) The modified polypropylene resin is obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound.
(2) The α-olefin component of the (a) ethylene-α-olefin copolymer rubber is 1-hexene or 1-octene.
(3) The (b) alkenyl aromatic compound unit-containing rubber is styrene-ethylene-butene-styrene rubber (SEBS).
(4) The polyolefin wax is a polyethylene wax produced using a metallocene catalyst.
(5) The foaming ratio is 2 times or more and 10 times or less, having a foam layer having an average cell diameter of 500 μm or less and a non-foam layer having a thickness of 10 μm or more and 1000 μm or less formed on at least one surface of the foam layer. ,
The present invention relates to the injection-foamed molded article described above.

  The injection-foamed molded article of the present invention has a high foaming ratio by using a polypropylene resin, a specific thermoplastic rubber and a polyolefin wax that have high fluidity during melt molding and high melt tension. It is excellent in light weight and has good impact resistance and surface appearance. In addition, by using the polypropylene resin, the thermoplastic rubber, and the polyolefin wax, since the thin injection filling property is good, it is particularly easy to obtain a large molded body.

  Embodiments of the present invention will be described below.

  The feature of the polypropylene resin injection foamed molded article of the present invention is that a modified polypropylene resin having a specific melt flow rate and melt tension, a specific thermoplastic rubber and an olefin wax are used.

  The modified polypropylene resin used in the present invention has a melt flow rate of 10 g / 10 min or more and less than 50 g / 10 min, preferably 15 g / 10 min or more and 40 g / 10 min or less, and a melt tension of 2 cN or more, preferably It is 4 cN or more and exhibits strain hardening. When the melt flow rate is 10 g / 10 min or more and less than 50 g / 10 min, a foamed molded product having a high expansion ratio and uniform bubbles can be obtained. When the melt tension is 2 cN or more, the foaming ratio is 2 times or more, and a foamed molded product having uniform fine cells 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. The melt tension is a capillograph (manufactured by Toyo Seiki Seisakusho) with an attachment for measuring the melt tension. 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.

  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. The modified polypropylene resin exhibits strain-hardening properties, and when the melt tension is high, a foamed product with a high foaming ratio of 2 times or more can be obtained, and it is easy to break the foam at the molten resin flow tip during injection molding. For this reason, a foam molded article having excellent surface smoothness can be obtained for the reason that silver streak that occurs is less likely to occur.

  Examples of a 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 radical polymerization initiator, and a conjugated diene compound. It is done. 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 radical polymerization initiator, and a conjugated diene compound can be manufactured at low cost by not requiring expensive equipment. It is preferable from the point. Moreover, in the range which does not impair the effect of this invention, in view of the improvement of cost and fluidity | liquidity, you may dilute to the said modified polypropylene resin using a general purpose linear polypropylene resin.

The raw polypropylene resin used in the production of the modified polypropylene resin is a linear polypropylene resin having a linear molecular structure, and is a normal polymerization method, for example, a transition metal compound supported on a carrier. And polymerization in the presence of a catalyst system (eg Ziegler-Natta catalyst) obtained from an organometallic compound. 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. 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-olefins having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 Cyclic olefins such as ^3,6 ] -4-dodecene, 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 , 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.

  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 linear polypropylene resin used preferably has a melt flow rate of 30 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 10 g / 10 min or more and less than 50 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, 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. 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. 1 type or 2 types or more can be used.

  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 apparatus for reacting the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator includes a roll, a kneader, a Banbury mixer, a Brabender, a single screw extruder, a kneader such as a twin screw extruder, a twin screw, etc. Examples of the surface renewal machine include a horizontal stirrer such as a biaxial multi-disk device, and a vertical stirrer such as a double helical ribbon stirrer. 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-based resin, the conjugated diene compound, and the radical polymerization initiator may be mixed and then melt-kneaded (stirred). After the polypropylene-based resin is melt-kneaded (stirred), the conjugated diene compound or the radical initiator may be mixed. They may be mixed simultaneously 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.

  In this way, the modified polypropylene resin 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 thermoplastic rubber used in the present invention is one or more selected from ethylene-α-olefin copolymer rubber and alkenyl aromatic compound unit-containing rubber.

  The ethylene-α-olefin copolymer rubber is a rubber composed of ethylene and an α-olefin having 4 to 20 carbon atoms. 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-1-pentene, Examples include 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. 1-butene, 1-hexene and 1-octene are preferred.

The density of the ethylene-α-olefin copolymer rubber is 0.85 to 0.885 g / from the viewpoint of enhancing the dispersibility of the modified polypropylene resin and the impact strength of the resulting resin composition. it is preferably cm ^3, and more preferably from 0.85~0.88g / cm ^3, more preferably from 0.855~0.875g / cm ^3.

  The 190 ° C. MFR of the ethylene-α-olefin copolymer rubber is usually from 0.1 to 30 g / 10 minutes, preferably from 0.5 to 20 g, from the viewpoint of fluidity during molding and impact strength. / 10 minutes.

  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 include a catalyst obtained by combining a metallocene compound coordinated with a group having an alumoxane or a boron compound, a so-called metallocene catalyst.

  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.

  As the alkenyl aromatic compound unit-containing rubber, for example, a block copolymer comprising a vinyl aromatic compound polymer block and a conjugated diene polymer block, and a double bond of a conjugated diene portion of the block copolymer is hydrogenated. The block polymer in which the double bond of the conjugated diene part of the block copolymer comprising a vinyl aromatic compound polymer block and a conjugated diene polymer block is hydrogenated is preferable. More preferably, it is a block polymer in which the double bond of the conjugated diene portion of the block copolymer is hydrogenated by 80% or more, and more preferably, the double bond of the conjugated diene portion is hydrogenated by 85% or more. Block polymer.

  More specifically, examples of the alkenyl aromatic compound unit-containing rubber include styrene-ethylene-butene-styrene rubber (SEBS), styrene-ethylene-propylene-styrene rubber (SEPS), and styrene-butadiene rubber (SBR). ), Block copolymers such as styrene-butadiene-styrene rubber (SBS), styrene-isoprene-styrene rubber (SIS), or block copolymers obtained by hydrogenating these rubber components.

  Examples of the method for producing the 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.

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

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

  The MFR at 230 ° C. of the alkenyl aromatic compound unit-containing rubber is preferably 1 to 15 g / 10 minutes, and more preferably 2 to 13 g / 10 minutes.

  The polyolefin wax used in the present invention is composed of an α-olefin copolymer having 2 to 20 carbon atoms, is a solid at normal temperature, and becomes a low viscosity liquid at 80 to 120 ° C. For example, a polyethylene wax, a polypropylene wax, etc. are mentioned. Examples of the α-olefin include propylene having 3 carbon atoms, 1-butene having 4 carbon atoms, 1-pentene having 5 carbon atoms, 1-octene having 8 carbon atoms, and preferably carbon atoms. An α-olefin having a number of 3 to 12, more preferably propylene, 1-butene, 1-hexene, and 4-methyl-1-pentene.

  A known method is used for the production of the polyolefin wax. For example, a metallocene catalyst comprising a metallocene compound of a transition metal selected from Group 4 of the periodic table and an organoaluminum oxy compound and / or an ionized ionic compound is used. Manufactured using.

  Among these, it is preferable to use a polyethylene wax containing an ethylene monomer, such as an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms. It is preferable to use what was manufactured using the catalyst.

The polyethylene wax preferably has a number average molecular weight of 1000 to 5000, more preferably 2000 to 4000. The density is preferably 870 to 960 kg / m ³ , the melting point is preferably 80 to 140 ° C., and more preferably the melting point is in the range of 90 to 120 ° C. If a polyethylene wax satisfying the above is used, a molded article having a great improvement in fluidity and a good surface appearance tends to be obtained.

  The polypropylene resin composition for injection foam molding used in the present invention can be obtained by mixing a modified polypropylene resin, a thermoplastic rubber, and a polyolefin wax.

  The mixing ratio of the modified polypropylene resin, the thermoplastic rubber, and the polyolefin wax used in the present invention is preferably 110 parts by weight or more and 95 parts by weight or less of the modified polypropylene resin in a total of 110 parts by weight. Preferably they are 80 to 90 weight part. The thermoplastic rubber is preferably 5 to 40 parts by weight, more preferably 10 to 20 parts by weight. The polyolefin wax is preferably 3 to 20 parts by weight, more preferably 4 to 10 parts by weight. If it is the said compounding quantity, it exists in the tendency for the foaming molding which has a foaming magnification of 2 times or more which has a uniform fine bubble. In addition, short shots do not occur in molding with thin portions, large molding is possible, continuous stable production is possible, and foam molded articles with good impact resistance tend to be provided at low cost. .

  The mixing method of the modified polypropylene resin, the thermoplastic rubber, and the polyolefin wax is not particularly limited, and can be performed by a known method. For example, dry blending a pellet-shaped resin using a blender, a mixer, etc., melt mixing Or a method of 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 injection foam molding. A mixture of modified polypropylene resin, thermoplastic rubber, and polyolefin wax may be mixed with a foaming agent and supplied to an injection molding machine, or a mixture of modified polypropylene resin, thermoplastic rubber, and polyolefin wax may be injection molded. A foaming agent may be added after feeding to the machine.

  The foaming agent that can be 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. The chemical foaming agent is usually mixed with the polypropylene resin composition for injection foam molding before being 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, normal injection molding machines can be used safely, and uniform fine bubbles are easily obtained. Chemical foaming agents are inorganic chemical foaming agents, physical foaming agents are nitrogen and carbon dioxide. Inorganic gas such as air is preferable. Add foaming aids such as organic acids such as citric acid and nucleating agents such as inorganic fine particles such as talc and lithium carbonate as necessary to make the foamed foams stable and uniform fine. May be. Usually, the inorganic chemical foaming agent is prepared from a polypropylene base for injection foam molding by preparing a masterbatch of polyolefin resin having a concentration of 10 to 50% by weight from the viewpoints of handleability, storage stability and dispersibility in polypropylene resin. It is preferably added to the resin composition and used.

  What is necessary is just to set the usage-amount of the said foaming agent suitably with the foaming magnification of the final product, 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 parts by weight or more and 20 parts by weight or less, and more preferably 1 part by weight with respect to 100 parts by weight of the polypropylene resin composition for injection foam molding of the present invention. It is used in the range of 10 parts by weight or more and 10 parts by weight or less. By using in this range, it is easy to economically obtain a foamed molded article having a foaming ratio of 2 times or more and uniform fine cells.

  Further, if necessary, as long as the effects of the present invention are not impaired, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, antacid adsorption An additive such as a stabilizer such as an agent, a crosslinking agent, a chain transfer agent, a nucleating agent, 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 necessary are used within a range not impairing the effects of the present invention, but preferably in 100 parts by weight of the polypropylene resin composition for injection foam molding of the present invention. 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 manufacturing method itself, and the molding conditions may be appropriately adjusted depending on the MFR 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, forms a non-foamed layer on the surface, the foamed layer tends to become uniform fine bubbles, has excellent lightness, and balance between rigidity and impact resistance Is preferable because it is easy to obtain a foamed molded article. 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 the injection-foamed molded article of the present invention thus obtained, the thermoplastic rubber component is preferably uniformly dispersed in a range of 0.1 to 5 μm, more preferably 0.2 to 3 μm. The injection foam molded article preferably has an average cell diameter of 500 μm or less, more preferably 200 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 foamed molded article of the present invention is preferably 2 times or more and 10 times or less, more preferably 2.5 times or more and 6 times or less. 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 a value obtained from the ratio of the specific gravity of the foamed molded product and the non-foamed molded product injected under the same conditions except that no foaming agent is added to the polypropylene resin composition for injection foam molding.

  Furthermore, the weight reduction rate L shown by the following formula of the foamed molded product of the present invention is preferably 20% or more, more preferably 25% or more.

ここで、Ｗ_Ｓは同じ剛性、具体的には曲げ弾性勾配を有する非発泡射出成形体の重量、Ｗ_Ｅは前記発泡成形体の重量である。軽量化率が２０％未満の場合には本発明の特徴である大幅な軽量化が得られない傾向にあるといえる。

Here, W _S is the weight of the non-foamed injection molded article having an elastic gradient bending the same rigidity, specifically, W _E is the weight of the foamed molded product. 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: 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 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) Surface appearance: The degree of the surface appearance of the foamed molded product was evaluated in the following three stages.
Good mold transfer and glossy ...
Good mold transfer, but not glossy ... △
Mold transferability is poor and gloss is not shining ...

  (6) Foaming ratio: A specimen including a non-foamed layer on the surface was cut out from the bottom part of the foam molded article, and the ratio of specific gravity to the bottom part of a separately produced non-foamed molded article having a thickness of 3 mm (Reference Example 1). I asked for it.

  (7) Average cell diameter, non-foamed layer thickness: It was determined from a micrograph of a cross section obtained by cutting the bottom surface of the 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) Internal Void: A cross section obtained by cutting the bottom surface of the foamed molded product in the thickness direction was observed, and the presence or absence of a void having a size of 1 mm or more in the foamed layer was examined.
No internal voids ... ○
Something ...

  (9) 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 is set to 30 ° C., the cavity clearance is 2 mm, the width is 20 mm, and the maximum flow length is 2000 mm. The flow length of the injection molded product taken out by injection filling at an injection speed of 60 mm / second and an injection pressure of 70 MPa was measured using the above bar flow mold.

(10) Impact resistance: Test pieces in compliance with JIS-K7211 of (that cut out 4cm square specimen from the formed body bottom) to determine the 50% breaking energy _{E 50} at room temperature (23 ° C.).

(11) weight ratio: weight W _E of the foamed molded to obtain the weight reduction rate _was prepared according to Reference Example described below, the weight W _S unfoamed injection molded article having the same bending elasticity gradient and this advance The weight reduction ratio L was calculated from Equation 1 in advance.

次に、実施例、比較例で使用したポリプロピレン系樹脂、発泡剤を以下に示す。

Next, polypropylene resins and foaming agents used in Examples and Comparative Examples are shown below.

(A) Modified polypropylene resin MP-1: 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 50 g / 10 min as a linear polypropylene resin, and t-butylperoxyisopropyl carbonate 0.7 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 50 kg / hour and melt-kneaded at a cylinder temperature of 200 ° C., and isoprene monomer is metered from a press-fitting part provided in the middle. Modified polypropylene resin (melt flow rate 30 g / 10 min, melt tension 4 cN, showing strain hardening)

(B) Rubber TP-1: Ethylene-1-octene copolymer rubber (Dow Chemical Japan Engage 8200 (density 0.87 g / cm ³ , MFR (190 ° C.) 5 g / 10 min))
TP-2: Styrene-ethylene-butene-styrene rubber (SEBS) (Taftec H1062 manufactured by Asahi Kasei Chemicals Co., Ltd. (density 0.89 g / cm ³ , MFR (230 ° C.) 4.5 g / 10 min, styrene pigment 18% by weight))

(C) Polyolefin wax EW-1: Polyethylene wax produced from a metallocene catalyst having a molecular weight of 2900, a density of 912 kg / m ³ , a softening point of 104.5 ° C., and a melting point of 102 ° C. (Excellex 30200BT manufactured by Mitsui Chemicals)

(D) Foaming agent Chemical foaming agent master batch (Polyslen EE275 manufactured by Eiwa Kasei Co., Ltd., decomposition gas amount 40 ml / g)

(Examples 1-3)
The modified polypropylene resin, olefinic thermoplastic rubber and polyolefin wax are composition blended as shown in Table 1, and 7.5 parts by weight of a foaming agent is added and dry blended to obtain a polypropylene resin composition for injection foam molding. It was.

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) In 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 / 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 foamed molded product 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 foam molded article.

  The polypropylene resin composition for injection foam molding of the present invention was excellent in fluidity, hardly caused short shots during continuous molding, and had good injection filling properties. Further, the foaming ratio of the bottom portion of the obtained foamed molded article was 3 times, the surface was glossy (shiny), and the surface appearance was good. 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 molded body. Moreover, the impact resistance was good, and a weight reduction rate of 30% was achieved with respect to the non-foamed molded body having the same rigidity despite the box-shaped foamed molded body.

(Reference example)
In Examples, the non-foamed molded article was taken out after injection-filling without using a modified polypropylene resin and a foaming agent and cooling for 60 seconds. 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 having used polyolefin wax. The results are shown in Table 2. Compared to the examples, the impact resistance is excellent, but the fluidity and surface appearance are inferior.

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

  The injection-foamed molded article of the present invention is capable of thin-wall injection filling necessary for significant weight reduction by using a polypropylene-based resin having high fluidity during melt molding and high melt tension. Good injection foaming moldability with large molds. In addition, since it has a high expansion ratio, it has good lightness and impact resistance. The present invention can be widely used for automobile interior materials such as luggage boxes, console boxes, tool boxes, etc., as well as food packaging containers, home 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 (6)

  (1) A modified polypropylene resin having a melt flow rate of 10 g / 10 min or more and less than 50 g / 10 min, a melt tension of 2 cN or more, and exhibiting strain hardening, (2) (a) an ethylene-α-olefin copolymer At least one thermoplastic rubber selected from a combined rubber and (b) an alkenyl aromatic compound unit-containing rubber, (3) a polyolefin wax, and (4) a foaming agent are supplied to an injection molding machine, and then in the mold Injection molded foam obtained by injection and foam molding.   The injection-foamed molded article according to claim 1, wherein the modified polypropylene resin is obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound.   The injection-foamed molded article according to claim 1, wherein the α-olefin component of the (a) ethylene-α-olefin copolymer rubber is 1-hexene or 1-octene.   The injection-foamed molded article according to claim 1, wherein the (b) alkenyl aromatic compound unit-containing rubber is styrene-ethylene-butene-styrene rubber (SEBS).   The injection-foamed molded article according to claim 1, wherein the polyolefin wax is a polyethylene wax produced using a metallocene catalyst.   It has a foaming layer having an average cell diameter of 500 μm or less and a non-foamed layer having a thickness of 10 μm or more and 1000 μm or less formed on at least one surface of the foam layer, and a foaming ratio of 2 to 10 times The injection foam molded article according to any one of claims 1 to 5.

Images