JP5122760B2 - Polypropylene resin injection foam - Google Patents

Description

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

  In the injection foam molding of polypropylene-based resins, a core back foaming method (also referred to as a moving cavity method), which is performed by retreating a movable mold for the purpose of weight reduction, has been conventionally performed. However, a normal linear polypropylene resin is crystalline and has a low melt tension (melting tension), and bubbles are easily destroyed. As a result, an appearance defect called silver streak (or swirl mark) was likely to occur on the surface of the molded body, and voids were likely to be generated inside the molded body because the bubbles were uneven and large. Such a molding defect impairs surface smoothness and lowers rigidity, so it is difficult to increase the expansion ratio. As a result, the weight reduction was not sufficient. In particular, in a box-shaped injection-foamed molded article having a standing wall portion, which is difficult to achieve high foaming in the core back method, it was difficult to increase the weight reduction rate to 20% or more. In addition, the void as used in the present case is a coarse bubble generated by internal bubbles communicating with each other and substantially means a bubble having a diameter exceeding 1.5 mm.

  An injection foam molded article using a modified polypropylene resin in which a melt tension is increased by adding a crosslinking agent or a silane graft thermoplastic resin is disclosed (for example, Patent Document 1 and Patent Document 2). However, in this method, although a foamed molded article having a high expansion ratio can be obtained, the melt viscosity is significantly increased by the crosslinking reaction. In the case of injection molding having a thin portion with a mold cavity clearance of about 1 to 2 mm, which is necessary for weight reduction in the core back foaming method, there is a case where injection foam molding cannot be performed.

  In order to solve the above problem, a method using a non-crosslinked modified polypropylene resin, for example, a method using a modified polypropylene resin into which long chain branching is introduced by irradiation (Patent Document 3) has been proposed. ing. However, even in such modified polypropylene resin, the melt flow rate is only about 4 g / 10 min, the fluidity at the time of melting is low, and the above-mentioned mold cavity clearance is about 1-2 mm. In the injection molding having, it tends to be a short shot, and there is a problem in injection foaming moldability.

  Moreover, the method of making foamability and fluidity | liquidity compatible by blending a linear polypropylene resin with high fluidity | liquidity to a modified polypropylene resin is proposed (for example, patent document 4, patent document 5). However, the modified polypropylene tends to have a lower bulk density than the linear polypropylene, and the resin is classified or segregated in the hopper during resin transportation from the raw material storage tank to the molding machine, or causes poor dispersion in the molding machine. There is a possibility that the foaming property and the physical properties of the molded product may vary. Moreover, the cost increase by the said blending work process also arises. That is, there was a problem in productivity.

As described above, there has been no injection foam molded body made of a polypropylene resin excellent in injection foam moldability, light weight, rigidity, and productivity.
JP 61-152754 A Japanese Patent Laid-Open No. 7-109372 JP 2001-26032 A JP 2003-128854 A JP 2005-97389 A

  An object of the present invention is to provide an injection foam molded article excellent in injection foam moldability, light weight, rigidity and productivity.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention are excellent in injection foaming moldability, light weight, rigidity, and productivity by using a modified polypropylene resin having both foamability and fluidity. The present inventors have found that an injection-foamed molded article can be obtained and have completed the present invention.

  That is, the present invention supplies 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 properties, and a chemical foaming agent to an injection molding machine. Then, the present invention relates to an injection foam molded article which is injected into a mold and foam-molded.

  In a preferred embodiment, the modified polypropylene resin is obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. In another preferred embodiment of the present invention, the linear expanded polypropylene resin is a propylene-ethylene block copolymer. As another preferred embodiment, the injection foam molded article comprises 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. And the foaming ratio is 2 times or more and 10 times or less and the wall thickness is 30 mm or less. Is a box-shaped injection foam molded article comprising a bottom surface portion and a standing wall portion formed integrally with the bottom surface portion.

  The injection foam molded article of the present invention is excellent in injection foam moldability, light weight, rigidity and productivity, and particularly has sufficient light weight even in a box-shaped injection foam molded article.

  Embodiments of the present invention will be described below.

  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 5 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, an injection foam molded article having good fluidity and excellent surface smoothness can be obtained. Further, when the melt tension is 2 cN or more, an injection foamed molded article having uniform fine bubbles twice or more can be obtained.

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

  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.

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-olefin having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene and other cyclic olefins, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6 -Diene such as octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, acrylic Butyl Le, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene. Among these, ethylene and 1-butene are preferable in terms of improving cold brittleness resistance and low cost.

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

  The linear polypropylene resin used preferably has a melt flow rate of 30 g / 10 min or more and 100 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. Good. 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 0.1 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 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 polypropylene resin for injection foam molding used in the present invention can be obtained by mixing a modified polypropylene resin and a foaming agent. The mixing method is not particularly limited, and can be performed by a known method, for example, dry blending a pellet-shaped resin using a blender, mixer, etc., melt mixing, dissolving and mixing in a solvent, etc. Can be mentioned. 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 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 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. It is a thing. 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. These foaming agents include, for example, foaming aids such as organic acids such as citric acid and inorganic fine particles such as talc and lithium carbonate, in order to stably and uniformly make the foamed foam air bubbles. A nucleating agent such as 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 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin of the present invention. Used in range. 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 lubricant, a plasticizer, a filler, a reinforcing material, a pigment, a dye, a flame retardant, and an antistatic agent may be used in combination. Of course, these additives used as necessary are used within the range not impairing the effects of the present invention, but generally 0 parts by weight with respect to 100 parts by weight of the polypropylene resin composition of the present invention. 0.01 parts by weight or more and 10 parts by weight or less is used.

  Next, the method of injection foam molding will be specifically described. A known method can be applied as the molding method itself, and the molding conditions may be appropriately adjusted depending on the melt flow rate of the modified polypropylene resin, the type of foaming agent, the type of molding machine, or the shape of the mold. Usually, the resin temperature is 170 to 250 ° C., the mold temperature is 10 to 100 ° C., the molding cycle is 0.5 to 30 minutes, the injection speed is 10 to 300 mm / second, and the injection pressure is 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, and the foamed inner layer tends to become uniform fine bubbles at a high foaming ratio, and has excellent lightness and rigidity. It is preferable because a molded body is easily obtained.

  The foamed molded article of the present invention thus obtained has an average cell diameter of preferably 500 μm or less, more preferably 250 μm or less, and a thickness formed on the surface of at least one side of the foam layer, preferably 10 μm. And a non-foamed layer having a thickness 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, it may be difficult to obtain light weight.

  The expansion ratio of the foamed molded article of the present invention is preferably 2 to 10 times, more preferably 2.5 to 6 times, and the wall thickness is preferably 30 mm or less, more preferably 20 mm or less. If the expansion ratio is less than 2 times, it may be 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 article and the non-foamed molded article injected under the same conditions except that no chemical 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, and more preferably 25% or more.

ここで、Ｗ_Sは同じ剛性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にくい。

Here, W _S is the weight of the non-foamed injection molded body having the same rigidity, and W _E is the weight of the foam molded body. When the weight reduction rate is less than 20%, it is difficult to obtain a significant weight reduction that is a feature of the present invention.

  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 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-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) Productivity: When multiple types of polypropylene resin are used, the resin may be classified or segregated in the hopper during resin transport from the raw material storage tank to the molding machine, or it may cause poor dispersion in the molding machine. It was marked as x. On the other hand, in the case of one type, since there was no such problem, it was set as “◯”.

(5) Injection foaming 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.

(6) Surface smoothness: The degree of surface irregularities of the foam molded article was evaluated in the following three stages.
No surface irregularities ... ○
Some irregularities on the surface ... △
Many surface irregularities ...

(7) Foaming ratio: From a ratio of specific gravity to a bottom surface portion of a non-foamed molded body having a thickness of 3 mm (reference example) cut out from a bottom surface portion of the foam molded body including a non-foamed layer on the surface. Asked.

(8) 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.

(9) Internal void: A cross section obtained by cutting the bottom surface portion 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 ...

(10) Rigidity: Flexural modulus measured on a specimen cut to a width of 50 mm from the bottom surface of the foamed molded product so that the longitudinal direction of the specimen is perpendicular to the injection resin flow direction in accordance with JIS-K6911 ( The bending stiffness (G) was determined from the following equation using E) and the secondary moment of inertia (I).

ここで断面二次モーメント（Ｉ）は、試片の巾（ｂ）および厚み（ｈ）から次式で表される。

Here, the cross-sectional secondary moment (I) is expressed by the following equation from the width (b) and thickness (h) of the specimen.

（１１）軽量化率：軽量化率を求める発泡成形体の重量をＷ_E、後述の参考例にしたがって作製した、発泡成形体と同じ剛性Ｇを有する非発泡射出成形体の重量をＷ_Sをとして、次式から軽量化率Ｌを計算した。

(11) Weight reduction rate: The weight of the foam molded body for which the weight reduction ratio is determined is W _E , and the weight of the non-foamed injection molded body having the same rigidity G as that of the foam molded body prepared according to the reference example described below is W _S. As a result, the weight reduction rate L was calculated from the following equation.

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 propylene-ethylene block copolymer having a melt flow rate of 45 g / 10 min as a linear polypropylene resin, and t-butyl peroxyisopropyl carbonate as a radical polymerization initiator 7 parts by weight of the mixture 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. Modified polypropylene resin obtained by supplying water at a rate of 0.5 kg / hour, cooling the strands with water, and chopping (melt flow rate 16 g / 10 min, melt tension 6 cN, showing strain hardening)
MP-2: 100 parts by weight of a propylene-ethylene block copolymer having a melt flow rate of 100 g / 10 min as a linear polypropylene resin, and 2,5-dimethyl-2,5-di (t-butylperoxy) as a radical polymerization initiator ) A modified polypropylene resin obtained in the same manner as MP-1 except that a mixture of 2 parts by weight of hexane was supplied from a hopper at 20 kg / hour and the supply amount of isoprene monomer was 0.6 kg / hour. (Melt flow rate 25 g / 10 min, melt tension 5 cN, strain hardening)
MP-3: PF814 manufactured by Sun Allomer (homotype polypropylene, melt flow rate 3 g / 10 min, melt tension 10 cN, strain hardening)

(B) Linear polypropylene-based resin PP-1: J708UG manufactured by Prime Polymer Co., Ltd. (Propylene-ethylene block copolymer having a melt flow rate of 45 g / 10 min, melt tension 1 cN, no strain hardening property)
PP-2: PMD81M manufactured by Sun Allomer Co., Ltd. (Propylene-ethylene block copolymer having a melt flow rate of 100 g / 10 min, melt tension of 1 cN, no strain hardening property)

(C) Foaming agent BA-1: Chemical foaming agent master batch (Polyslen EE275 manufactured by Eiwa Kasei Co., Ltd., decomposition gas amount 40 ml / g)
BA-2: Carbon dioxide (purity 99% or more)

(Examples 1 and 2)
The modified polypropylene resin and the foaming agent were dry blended at a composition ratio shown in Table 1 to obtain a polypropylene resin composition for injection foam molding.

  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., 40 ° 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) A mold having a clearance of 3 mm and a bottom surface portion of clearance of 1.5 mm was injected and filled at an injection speed of 100 mm / second (injection process). Immediately after the completion of injection filling, the movable mold was retracted and foamed to a mold cavity clearance of 4.0 mm at the bottom part at a mold opening speed of 50 mm / sec (foaming step). After further cooling for 60 seconds, the foamed molded product was taken out (cooling step). Table 2 shows the injection foaming moldability and the properties of the obtained foamed molded article.

  Since the modified polypropylene resin of the present invention uses one kind of resin, there is no problem of classification and segregation due to a plurality of dry blends, and the productivity is excellent. In addition, since the fluidity is excellent, even when the mold cavity clearance at the time of injection filling is 1.5 mm, short shots at the time of continuous molding hardly occur and the injection foaming moldability is good. Further, the obtained box-shaped foamed molded article has almost no surface irregularities and is excellent in surface smoothness, has a foaming ratio exceeding 2 times, and has a high foaming ratio. The weight of the foamed molded product was 300 g. Despite the box-shaped foamed molded product, a weight reduction rate of 25% was achieved with respect to the non-foamed molded products having the same rigidity (Reference Examples 1 and 2).

(Reference Example 1)
In Example 1, linear polypropylene resin PP-1 was used instead of modified polypropylene resin MP-1, injection filling was performed without using a foaming agent, and the foaming step was omitted, after cooling for 60 seconds. The non-foamed molded body was taken out. At this time, the initial clearance of the mold bottom was 3 mm. The rigidity of the bottom surface portion of the obtained foamed molded product was 0.16 N · m ² , and the weight was 400 g.

(Reference Example 2)
In Example 2, linear polypropylene resin PP-2 was used instead of modified polypropylene resin MP-2, injection filling was performed without using a foaming agent, the foaming step was omitted, and cooling was performed for 60 seconds. The non-foamed molded body was taken out. At this time, the initial clearance of the mold bottom was 3 mm. The rigidity of the bottom surface portion of the obtained foamed molded product was 0.15 N · m ² , and the weight was 400 g.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that MP-3 was used as the modified polypropylene resin. The results are shown in Table 2. The injection foaming moldability was poor, and there were 6 short shots out of 20 shots.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that 30% of MP-3 was used as the modified polypropylene resin and 70% of PP-1 was used as the linear polypropylene resin. The results are shown in Table 2. Since a plurality of resins are used by dry blending, classification and segregation may occur during molding, which is problematic in productivity.

(Comparative Example 3)
It implemented like Example 1 except using PP-1 as a linear polypropylene resin instead of a modified polypropylene resin. The results are shown in Table 2. Many voids were generated inside the molded product foamed layer, the surface smoothness was poor, and a decent foamed product could not be obtained.

(Example 3)
0.75 parts of the chemical foaming agent BA-1 as a modified polypropylene resin and MP-1 as a foam nucleating agent were dry blended to obtain a polypropylene resin mixture for injection foam molding.

  The injection molding machine used in Example 1 was changed to a vent type specification, and further, carbon dioxide gas as a foaming agent could be supplied at a constant pressure using “CO2 gas supply device MAC-100” manufactured by Asahi Engineering Co., Ltd. . The amount of carbon dioxide dissolved in the molten resin was controlled by the carbon dioxide supply pressure as shown in Table 3. Other molding conditions were the same as in Example 1.

  Table 4 shows the injection foaming moldability and the obtained foam properties. Since the polypropylene resin of the present invention uses one kind of resin, there is no problem of classification and segregation due to a plurality of dry blends, and the productivity is excellent. Moreover, since it is excellent in fluidity | liquidity, the short shot at the time of continuous molding does not occur easily, and injection foaming moldability is favorable. In addition, the box-shaped foamed molding obtained by such a molding method has almost no surface irregularities and excellent surface smoothness, and has a foaming ratio exceeding 2 times and a high foaming ratio. The bubbles were fine and had a non-foamed layer (skin layer), and there were almost no voids inside the molded body. Despite the box-shaped foam molded article, a weight reduction rate of 25% was achieved with respect to the non-foamed molded article having the same rigidity.

(Comparative Example 4)
The same procedure as in Example 3 was performed except that 30% of MP-3 was used as the modified polypropylene resin and 70% of PP-1 was used as the linear polypropylene resin. The results are shown in Table 4. Since a plurality of resins are used by dry blending, classification and segregation may occur during molding, which is problematic in productivity.

  The injection foam molded article of the present invention is excellent in injection foam moldability, light weight, rigidity and productivity, and particularly has sufficient light weight in a box-shaped injection foam molded article. Therefore, it can be widely used for automobile interior materials such as luggage boxes, console boxes, tool boxes, building materials, food packaging containers, home appliance housings, daily miscellaneous goods boxes, and the like.

Claims (5)

A modified polypropylene resin having a melt flow rate of 15 g / 10 min or more and less than 50 g / 10 min, a melt tension of 5 cN or more and exhibiting strain-hardening properties, and a foaming agent are supplied to an injection molding machine, and then a mold An injection-foamed molded article characterized by being injected into a foam and molded by foaming. 2. The injection foam molded article according to claim 1, wherein the modified polypropylene resin is obtained by melt-kneading a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. The injection-foamed molded article according to claim 2, wherein the linear polypropylene resin is a propylene-ethylene block copolymer. The injection foam molded article has 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, and the foaming ratio is doubled The injection-foamed molded article according to any one of claims 1 to 3, which has a thickness of 10 times or less and a wall thickness of 30 mm or less. The said injection-foaming molded object is a box-shaped injection-foaming molded object which consists of a bottom face part and the standing wall part integrally formed with the bottom face part, The any one of Claims 1-4 characterized by the above-mentioned. Injection foam moldings.