JPWO2009060792A1 - Polypropylene-based resin composition for foam molding and foam-molded product obtained by foaming the resin composition - Google Patents

Abstract

Foam molding that is excellent in fluidity and foamability, and can be molded with a large mold, especially in application to injection foam molding, and can provide an injection foam molded body with improved surface appearance, especially the flow mark on the surface of the molded body. Propylene molded resin composition and foamed molded article comprising the resin composition. It comprises a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more, and exhibiting strain hardening, and a foaming agent (C). And a foamed molded article comprising the resin composition.

Description

  The present invention relates to a polypropylene resin composition for foam molding and a foam molded article using the same, and more particularly 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. As a polypropylene resin product, there is a polypropylene foam resin molded product obtained by foaming a polypropylene resin. Polypropylene-based resin foam moldings are made by sandwiching an extruded foam sheet obtained by melting and mixing a mixture of a polypropylene-based resin and a foaming agent with an extruder and extruding them under atmospheric pressure. The resin foam pre-expanded particles are filled in a mold having a desired shape and heated with steam, etc., so that the pre-expanded particles are fused to form a molded body. Has been applied. 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, the characteristics of the resin used for injection foam molding are required to satisfy both the fluidity for filling the resin in every corner of the mold and the foamability for foaming thereafter.

  Polypropylene resin injection foam moldings are required to be lightweight, thin, and highly rigid moldings when used as automobile parts, especially as large moldings such as console boxes, luggage boxes, door trims, and tool boxes. However, in this case, in order to easily cause molding defects such as short shots during molding, it is necessary to increase the fluidity of the raw material resin to be used.

  Moreover, since normal linear polypropylene resin is crystalline and has low melt tension (melting tension), bubbles are easily destroyed. As a result, an appearance defect called silver streak tends to occur on the surface of the molded body, and voids are easily generated inside, making it difficult to increase the expansion ratio.

  As a method for increasing the melt tension of a polypropylene resin, for example, a crosslinking agent or a silane graft thermoplastic resin is added (Patent Documents 2 and 3), and long-chain branching is introduced by irradiating a non-crosslinked polypropylene resin with radiation. A method (Patent Document 4), a method of manufacturing a modified polypropylene resin by melting and kneading a polypropylene resin, an isoprene monomer, and a radical polymerization initiator (Patent Document 5) have been proposed. Although a foamed molded article having a high foaming ratio can be obtained by this method, the viscosity at the time of resin melting is excessively increased, making injection molding difficult, and molding defects considered to be caused by imparting foamability. In some cases, a flow mark was generated and the surface appearance was deteriorated. In particular, this tendency was prominent in molding with a large die, such as short shot due to insufficient fluidity.

As described above, it is difficult to obtain a polypropylene resin for injection foam molding that achieves both good fluidity and foamability for injection foam molding using a large mold, including countermeasures for the above-mentioned appearance defects. there were.
WO2005 / 026255 JP 61-152754 A Japanese Patent Laid-Open No. 7-109372 JP 2001-226510 A JP-A-9-188774

  The object of the present invention is a polypropylene resin composition for foam molding, which is excellent in fluidity and foamability, has a low resistance during extrusion and injection and has a good surface appearance, and foam molding comprising the composition. In particular, a polypropylene resin composition for injection foam molding that can be molded with a large mold and has a good surface appearance without a flow mark, and the resin composition It is providing the injection-foaming molding which consists of.

  As a result of intensive studies, the present inventors have found that a polypropylene resin composition for injection foam molding comprising a predetermined linear polypropylene resin, a modified polypropylene resin, and a foaming agent can solve the above problems, It has been found that a polypropylene resin composition comprising a modified polypropylene resin having a predetermined property can be suitably used as a resin composition for foam molding, and has completed the present invention.

  That is, the first of the present invention is a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more and exhibiting strain hardening, and a foaming agent (C ) -Containing polypropylene resin composition for foam molding.

As a preferred embodiment,
(1) A modified polypropylene resin having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more and exhibiting strain hardening (50 parts by weight or more and 95 parts by weight or less of polypropylene resin) B) 5 parts by weight or more and 50 parts by weight or less (however, the total of the polypropylene resin and the modified polypropylene resin (B) is 100 parts by weight) and the foaming agent (C).
(2) The polypropylene resin is a linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min and a melt tension of 2 cN or less.
(3) The modified polypropylene resin (B) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound.
The present invention relates to the polypropylene resin composition for foam molding described above.

  2nd of this invention is related with the foaming molding formed by foaming the polypropylene resin composition for foam molding of the said description.

  A third aspect of the present invention is a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more, and exhibiting strain hardening, and a foaming agent (C). The present invention relates to a polypropylene resin composition for injection foam molding comprising:

As a preferred embodiment,
(1) A linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min, a melt tension of 2 cN or less, and a melt flow rate of 10 g / 10 Min. To less than 30 g / 10 min., Modified polypropylene resin (B) having a melt tension of 5 cN or more and exhibiting strain-hardening properties, 5 parts by weight or more and 50 parts by weight or less (provided that the linear polypropylene resin (A) is modified) The total of the quality polypropylene resin (B) is 100 parts by weight), (C) comprises a foaming agent,
(2) The modified polypropylene resin (B) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound.
The present invention relates to the polypropylene resin composition for injection foam molding described above.

  A fourth aspect of the present invention relates to an injection foam molded article obtained by foaming the above-described polypropylene resin composition for injection foam molding.

  Since the polypropylene resin composition for foam molding of the present invention is excellent in fluidity and foamability, it can be suitably used particularly for injection foam molding, and particularly enables molding with a large mold. And the injection-foaming molded object which consists of this resin composition becomes a thing with a favorable surface appearance without a flow mark by high foaming magnification.

  Embodiments of the present invention will be described below.

  The polypropylene resin composition for foam molding of the present invention comprises a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more and exhibiting strain hardening. And a foaming agent (C).

  A preferred embodiment is a modified polypropylene resin (B) having 50 to 95 parts by weight of a polypropylene resin, a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more, and exhibiting strain hardening. ) 5 to 50 parts by weight (however, the total of the polypropylene resin and the modified polypropylene resin (B) is 100 parts by weight) and the foaming agent (C).

In another preferred embodiment, the polypropylene resin is a linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min and a melt tension of 2 cN or less.
The polypropylene resin composition for foam molding of the present invention is a modified polypropylene resin obtained by melting and mixing a modified polypropylene resin (B) with a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. It is preferable that it is a resin.

  The polypropylene resin composition for injection foam molding of the present invention comprises a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more, and exhibiting strain hardening. And a foaming agent (C).

  Preferably, a linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min, a melt tension of 2 cN or less, a melt flow rate of 10 g / 10 min to 30 g / 10 min, Is 5 cN or more and comprises a modified polypropylene resin (B) exhibiting strain hardening and a foaming agent (C).

  The modified polypropylene resin (B) used in the present invention has a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, preferably 12 g / 10 min or more and 20 g / 10 min or less, and a melt tension of 5 cN. As described above, it is preferably 7 cN or more and exhibits strain hardening. When the melt flow rate is 10 g / 10 min or more and less than 30 g / 10 min, an injection foam molded article having a beautiful surface appearance without a flow mark can be obtained. Further, when the melt tension is 5 cN or more, the foaming ratio is 2 times or more, and an injection foam molded product having uniform fine bubbles can be obtained.

  Here, the melt flow rate is based on ASTM D-1238 and measured under a load of 230 ° C. and 2.16 kg. Made from a die having a hole with a diameter of φ1 mm and a length of 10 mm at 230 ° C., the strand lowered at a piston lowering speed of 10 mm / min is drawn at 1 m / min. When increased, it refers to the take-up load of the pulley with 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.

  Examples of the modified polypropylene resin (B) used in the present invention include a method of irradiating a linear polypropylene resin with radiation, or a method of melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. And a modified polypropylene-based resin containing a branched structure or a high molecular weight component, obtained by Among these, a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound is preferable because it can be produced at low cost without requiring expensive equipment.

  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 1, peroxyesters such as 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, di-t-butylperoxyisophthalate A seed | species or 2 or more types is mentioned.

  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.

  The linear polypropylene resin (A) used in the present invention preferably has a melt flow rate of 10 g / 10 min or more and 150 g / 10 min or less, more preferably 15 g / 10 min or more and 50 g / 10 min or less. The melt tension is preferably 2 cN or less, more preferably 1 cN or less. When the melt flow rate is in the range of 10 g / 10 min or more and 150 g / 10 min or less, when producing an injection-foamed 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. Further, since the bubbles are not easily destroyed during foaming, a foamed molded article having a beautiful surface appearance can be obtained. 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 linear polypropylene resin (A) here is a polypropylene resin having a linear molecular structure, and is obtained from a usual polymerization method, for example, a transition metal compound supported on a carrier and an organometallic compound. Obtained in the presence of a catalyst system such as a Ziegler-Natta catalyst. 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, such as α-olefins having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,11,8,13, 6] Cyclic olefins such as -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene Such as dienes, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, Examples thereof include vinyl monomers such as butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and divinyl benzene. Among these, ethylene and 1-butene are preferable in terms of improving cold brittleness resistance and low cost. The shape and size of the linear polypropylene resin (A) and modified polypropylene resin (B) of the present invention are not limited, and may be pellets.

  In the present invention, the modified polypropylene resin (B) exhibits its effect even when used alone, but can be used in combination with the linear polypropylene resin (A) when applied to injection foam molding. preferable. When the linear polypropylene resin (A) and the modified polypropylene resin (B) are used in combination, the linear polypropylene resin is contained in a total of 100 parts by weight of the linear polypropylene resin (A) and the modified polypropylene resin (B). (A) is 50 to 95 parts by weight, preferably 60 to 90 parts by weight. The modified polypropylene resin (B) is 5 to 50 parts by weight, preferably 10 to 40 parts by weight. When the blending amount is as described above, there is a tendency that an injection foam molded article having a fine surface appearance and having a flow mark of 2 times or more having uniform fine bubbles can be provided at low cost.

  The mixing method of the linear polypropylene resin (A) and the modified polypropylene resin (B) is not particularly limited, and can be performed by a known method. For example, the pellet-shaped resin is dried using a blender, a mixer, or the like. Examples of the method include blending, melt mixing, and dissolving and mixing in a solvent. In the present invention, the method of dry blending and then subjecting to injection foam molding is preferable because it requires less heat history and decreases the melt tension.

  The foaming agent (C) 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 premixed with the resin and then supplied to an extruder or an injection molding machine, and decomposes in a 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 an extruder or an injection molding machine as a gaseous or supercritical fluid, dispersed or dissolved, and foamed by being released from pressure after being injected into a mold. It functions as an agent. 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, ordinary extruders and injection molding machines can be used safely, and uniform fine bubbles are easily obtained. As chemical foaming agents, inorganic chemical foaming agents, and as 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 foamed foam air bubbles. A nucleating agent such as fine particles may be added. Usually, the inorganic chemical foaming agent is preferably used as 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 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 final product, the kind of foaming agent, and the resin temperature at the time of shaping | molding. For example, usually, 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, more preferably 1 part by weight, in 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 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. These additives used as necessary are used within a range not impairing the effects of the present invention, but the total of the linear polypropylene resin (A) and the modified polypropylene resin (B). The amount is preferably 0.01 parts by weight or more and 10 parts by weight or less based on 100 parts by weight.

  The polypropylene resin composition for foam molding of the present invention can be suitably used for foam molding such as extrusion foam molding and injection foam molding.

  The polypropylene resin composition for injection foam molding of the present invention can be suitably used for injection foam molding.

  Next, an injection foam molding method according to one embodiment of the present invention will be described in detail. A known method can be applied to the injection foam molding method itself, and the molding conditions may be appropriately adjusted depending on 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 carried out 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 120 minutes, an injection speed of 10 to 300 mm / second, and 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) in which the foam is made to recede forms a non-foamed layer on the surface, the foamed layer tends to become uniform fine bubbles, and a foam molded article excellent in lightness can be easily obtained. This is preferable. 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.

  By using a so-called counter pressure method that introduces a polypropylene resin composition for injection foam molding into the mold while pre-pressing the inside of the mold with an inert gas or the like, surface appearance defects due to silver streaks are reduced. This is preferable because it can be performed.

  In this way, the injection foam molded article of the present invention can be obtained.

  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 a value obtained from the ratio of the specific gravity of the injection foam molded product and the non-foam molded product injected under the same conditions except that no foaming agent is added to the polypropylene resin composition for injection foam molding. .

  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 filling property: The number of short shots when 20 shots were continuously formed (number of defects) 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 (flow mark): The flow mark appearing on the surface of the foamed molded product was evaluated by visually observing the position where the flow mark was generated from the molded product gate part and its conspicuousness, and evaluated in the following three stages.

The flow mark did not stand out ...
The flow mark is slightly noticeable ...
The flow mark was conspicuous ...
(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) Internal void: A cross section obtained by cutting the bottom surface of the foamed molded body in the thickness direction was observed, and the presence or absence of bubbles having a size of 1 mm or more in the foamed layer was examined.

No internal voids ...
Something ...
(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 is set to 60 ° 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. Moreover, the fluidity | liquidity improvement rate with respect to the comparative example 2 (example which used the conventional modified polypropylene resin) was calculated | required.

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

(A) Linear polypropylene resin PP-1: propylene / ethylene block copolymer, melt flow rate 45 g / 10 min, melt tension 1 cN or less)
PP-2: propylene / ethylene block copolymer, melt flow rate 100 g / 10 min, melt tension 1 cN or less (B) Modified polypropylene resin MP-1: polypropylene having a melt flow rate of 50 g / 10 min as a linear polypropylene resin A mixture of 100 parts by weight of homopolymer and 0.5 parts by weight of t-butyl peroxyisopropyl carbonate as a radical polymerization initiator is fed from a hopper to an 80 mmφ twin screw extruder (L / D = 40) at 180 kg / hour. Modified polypropylene obtained by melt-kneading at a cylinder temperature of 200 ° C., supplying isoprene monomer at a rate of 0.9 kg / hour using a metering pump from a press-fitting portion provided in the middle, and cooling and chopping the strands with water. Resin (melt flow rate 14 g / 10 min, melt tension 12cN, shows the strain hardening property)
MP-2: a mixture of 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 50 g / 10 min as a linear polypropylene resin and 0.7 parts by weight of t-butylperoxyisopropyl carbonate as a radical polymerization initiator, an isoprene monomer A modified polypropylene resin obtained in the same manner as MP-1 except that the supply amount was 1.2 kg / hr (melt flow rate 20 g / 10 min, melt tension 11 cN, showing strain hardening)
MP-3: A mixture of 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 50 g / 10 min as a linear polypropylene resin and 0.7 parts by weight of t-butyl peroxyisopropyl carbonate as a radical polymerization initiator is supplied from a hopper. It is supplied to a 45 mmφ twin-screw extruder (L / D = 40) at 50 kg / hour, melt-kneaded at a cylinder temperature of 200 ° C., and isoprene monomer is supplied at 0.5 kg / hour using a metering pump from a press-fitting portion provided in the middle. Modified polypropylene resin obtained by feeding at a speed, water-cooling and chopping the strands (melt flow rate 7 g / 10 min, melt tension 10 cN, showing strain hardening)
(C) Foaming agent C-1: Chemical foaming agent master batch (Polyslen EE275F manufactured by Eiwa Kasei Co., Ltd., Decomposition gas amount 40 ml / g)
(Examples 1-3)
A linear polypropylene resin (A), a modified polypropylene resin (B), and a foaming agent (C) are added so as to have a composition ratio shown in Table 1 and dry blended, and a polypropylene resin composition for injection foam molding. Got.

  After melt-kneading the resin composition containing the blowing 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., 30 ° 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) The mold having a clearance of 3 mm and a bottom surface portion: clearance t0 = 1.5 mm) was injection-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 foamed molded product was taken out after cooling for 60 seconds. Table 2 shows the evaluation of the obtained foamed molded product.

  Since the polypropylene resin composition for injection foam molding of the present invention is excellent in fluidity, the fluidity improvement rate is 4 to 12%, short shots during continuous molding hardly occur, and injection filling properties are good. there were. Moreover, the foaming ratio of the bottom part of the foamed molded product was 3 times, and a product with a high foaming ratio was obtained, and the flow mark on the surface of the molded product was not conspicuous.

(Comparative Example 1)
The same procedure as in Examples 1 and 2 was performed except that the modified polypropylene resin (B) was not used. The results are shown in Table 2. Compared to the examples, a desired foaming ratio was not obtained, and a molded article having internal voids was obtained.

(Comparative Example 2)
The same procedure as in Examples 1 and 2 was carried out except that MP-2 was used for the modified polypropylene resin (B). The results are shown in Table 2. Although a molded product having a desired expansion ratio was obtained as compared with the examples, the flow marks on the surface were conspicuous.

  Since the polypropylene-based resin composition for foaming of the present invention has high fluidity at the time of melting and high melt tension, by using the resin composition particularly for injection foam molding, thin-wall molding with a large mold can be performed. It is possible to obtain an injection-foamed molded article having an improved surface appearance, particularly a flow mark on the surface of the molded article. 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.

Claims (9)

  For foam molding comprising a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more and exhibiting strain hardening, and a foaming agent (C) Polypropylene resin composition.   Modified polypropylene resin (B) 5 having a polypropylene resin of 50 parts by weight or more and 95 parts by weight or less, a melt flow rate of 10 g / 10 minutes or more and less than 30 g / 10 minutes, a melt tension of 5 cN or more, and exhibiting strain-hardening properties. 2. The polypropylene resin for foam molding according to claim 1, comprising a part by weight and 50 parts by weight or less (provided that the total of the polypropylene resin and the modified polypropylene resin (B) is 100 parts by weight) and a foaming agent (C). Composition.   The polypropylene resin composition for foam molding according to claim 2, wherein the polypropylene resin is a linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min and a melt tension of 2 cN or less. .   The modified polypropylene resin (B) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. Polypropylene resin composition for foam molding.   The foaming molding formed by foaming the polypropylene-type resin composition for foam molding as described in any one of Claims 1-4.   Injection foam molding comprising a modified polypropylene resin (B) having a melt flow rate of 10 g / 10 min or more and less than 30 g / 10 min, a melt tension of 5 cN or more and exhibiting strain hardening, and a foaming agent (C). Polypropylene resin composition.   50 to 95 parts by weight of a linear polypropylene resin (A) having a melt flow rate of 10 g / 10 min to 150 g / 10 min, a melt tension of 2 cN or less, and a melt flow rate of 10 g / 10 min to 30 g. / 10 minutes or less, 5 to 50 parts by weight of a modified polypropylene resin (B) having a melt tension of 5 cN or more and exhibiting strain hardening (however, the linear polypropylene resin (A) and the modified polypropylene resin) The polypropylene resin composition for injection foam molding according to claim 6, comprising a resin (B) in a total of 100 parts by weight) and (C) a foaming agent.   The injection foam molding according to claim 6 or 7, wherein the modified polypropylene resin (B) is a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. Polypropylene resin composition.   An injection foam molded article obtained by foaming the polypropylene resin composition for injection foam molding according to any one of claims 6 to 8.