JP2020007547A - Polypropylene injection foam molding - Google Patents

Abstract

To provide a polypropylene resin composition capable of being molded into an injection foam molding which is excellent in impact resistance and has a good foaming state even at a high expansion ratio.SOLUTION: The polypropylene resin composition contains a modified polypropylene resin (A) being a modified propylene-ethylene random copolymer, and a polypropylene resin (B) having a lower melt tension than the modified polypropylene resin (A). The content of an ethylene component in the component (A) is 1 wt.% or more and 7 wt.% or less. The content of the component (A) is 1-49 wt.% and the content of the component (B) is 51-99 wt.% based on 100 wt.% of the total of the component (A) and the component (B).SELECTED DRAWING: None

Description

  The present invention relates to an injection foamed molded article having a high expansion ratio using a polypropylene resin composition.

  Polypropylene resins have good physical properties and moldability, and the range of use thereof is rapidly expanding as an environmentally friendly material. In particular, for automotive parts and the like, lightweight and highly rigid polypropylene resin products are provided. One such product is an injection foamed molded article of a polypropylene resin. Among them, automobile parts are known to be a field where weight reduction is particularly required. In order to reduce the weight, it is effective to set the expansion ratio of the injection foam molded article to a high expansion ratio.

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

  However, the linear polypropylene resin generally used has a low impact resistance, so that the foam is apt to be broken, and it has been difficult to apply it to an application in which the impact resistance is emphasized. In addition, there was a tendency for poor foaming to occur, which was visually judged to be inferior in the cell state. In particular, when trying to obtain an injection foamed molded article having a high expansion ratio, the tendency of the foam to be easily broken and the tendency to determine that the cell state is inferior were remarkable.

  In order to improve them, for example, the following proposals have been made.

  Patent Literature 1 discloses that a composition containing (A) a linear polypropylene-based resin and (B) a modified polypropylene-based resin having a strain-hardening property and a foaming agent is injection-molded into a mold. And a molded article obtained by the method are disclosed, and it is described that a high expansion ratio is possible and the surface appearance is good. However, only the polypropylene homopolymer was used as the base resin for modifying the component (B), and the improvement in impact resistance was insufficient.

  Patent Document 2 discloses a method for producing (A) a modified polypropylene resin obtained by melt-kneading (a) a polypropylene resin, (b) an isoprene monomer, and (c) a radical polymerization initiator. It is described that the obtained (A) exhibits strain hardening properties and may be used for foam molding. However, there is no description about injection foam molding, and in that case, there is no description or suggestion about the impact resistance or the cell state when foamed, so application to injection foam molding is not easily conceived, The effect of applying it was also unclear. In addition, there is no description of using the component (A) in combination with an unmodified polypropylene resin.

  Patent Document 3 discloses a method of foaming (A) a modified polypropylene resin obtained by melt-kneading (a) a polypropylene resin, (b) an isoprene monomer, and (c) a radical polymerization initiator. A method for producing a molded article is disclosed, and it is described that a foam molded article having good heat resistance and excellent expansion ratio can be obtained. However, there is no description about injection foam molding, and in that case, there is no description or suggestion about the impact resistance or the cell state when foamed, so application to injection foam molding is not easily conceived, The effect of applying it was also unclear. In addition, there is no description of using the component (A) in combination with an unmodified polypropylene resin.

  Patent Literature 4 discloses that (A) a modified polypropylene resin obtained by melt-kneading (a) a polypropylene resin, (b) a monomer such as isoprene, and (c) a radical polymerization initiator is foamed. The disclosed foam sheet is described as having a small drawdown during heating and an excellent closed cell rate. However, there is no description about injection foam molding, and there is no description or suggestion about the impact resistance and the cell state when foamed, so that application to injection foam molding is not easily conceived, and when applied, The effect was completely unknown. In addition, there is no description of using the component (A) in combination with an unmodified polypropylene resin.

  Patent Document 5 discloses a method of injection foaming a composition containing (A) a modified polypropylene resin exhibiting strain hardening property and (C) a foaming agent into a mold, and molding obtained by the method. The article discloses that the foam has good foam moldability and excellent rigidity. Although a propylene-ethylene block copolymer is used as the base resin for the modification, there is no description or suggestion of the impact resistance, and the effect when applied to an application that emphasizes impact resistance is completely unknown. Was. In addition, there is no description of using the component (A) in combination with an unmodified polypropylene resin.

  As described above, it has been difficult to obtain a polypropylene-based resin composition that achieves both impact resistance and a cell state when expanded, in a polypropylene-based resin composition for injection foam molding. In particular, this was remarkable when trying to obtain an injection foamed molded article having a high expansion ratio.

JP 2005-224963 A JP 09-188729 A JP-A-09-188774 JP 2001-139716 A JP 2007-130992 A

  An object of the present invention is a polypropylene-based resin composition that can provide a high-expansion-ratio polypropylene-based injection-foamed molded article having excellent impact resistance and a favorable foaming state.

  The present invention is as follows.

  It contains a modified polypropylene resin (A) that is a modified propylene-ethylene random copolymer and a polypropylene resin (B) having a lower melt tension than the modified polypropylene resin (A). The content of the ethylene component is 1% by weight or more and 7% by weight or less, and the content of the component (A) is 1 to 49% by weight based on 100% by weight of the total of the components (A) and (B). A polypropylene-based resin composition having a component content of 51 to 99% by weight.

  ADVANTAGE OF THE INVENTION The polypropylene resin composition of this invention is excellent in impact resistance, and can provide the injection foaming molded article of a high expansion ratio which has a favorable foaming state. Therefore, the polypropylene-based injection-foamed molded article comprising the polypropylene-based resin composition of the present invention can be suitably used for applications such as interior and exterior materials for automobiles.

Relationship between melt flow rate (MFR) and melt tension (MT) of modified propylene-ethylene random copolymer (AR)

Hereinafter, embodiments of the present invention are as follows.
1) containing a modified polypropylene resin (A) that is a modified propylene-ethylene random copolymer and a polypropylene resin (B) having a lower melt tension than the modified polypropylene resin (A);
The content of the ethylene component in the component (A) is 1% by weight or more and 7% by weight or less,
A polypropylene resin composition wherein the content of the component (A) is 1 to 49% by weight and the content of the component (B) is 51 to 99% by weight based on 100% by weight of the total of the components (A) and (B). object.
2) The polypropylene resin composition according to 1), wherein the modified polypropylene resin (A) has a melt flow rate measured at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more and less than 100 g / 10 min.
3) The polypropylene resin composition according to 1) or 2), wherein the melt flow rate of the polypropylene resin (B) measured at 230 ° C. under a load of 2.16 kg is 1 g / 10 min or more and less than 100 g / 10 min. .
4) The melt tension of the modified polypropylene resin (A) measured at a temperature of 200 ° C., a piston descending speed of 10 mm / min, and a take-off speed of 3 m / min is 0.2 gf or more and 20 gf or less 1) to 3). The polypropylene resin composition according to any one of the above.
5) The melt tension of the polypropylene resin (B) measured at a temperature of 200 ° C., a piston descending speed of 10 mm / min, and a take-off speed of 3 m / min is less than 0.2. The polypropylene resin composition according to one of the above.
6) The polypropylene resin composition according to any one of claims 1) to 5), wherein the modified polypropylene resin (A) is a conjugated diene-modified polypropylene resin.
7) The polypropylene resin composition according to 6), wherein the conjugated diene is isoprene.
8) A molded article obtained by injection-molding the polypropylene resin composition according to claim 1.
9) A foam molded article obtained by subjecting the polypropylene resin composition according to claim 1 to injection foam molding.
The present invention relates to a polypropylene resin composition. The polypropylene resin composition of the present invention comprises a modified polypropylene resin (A) which is a modified propylene-ethylene random copolymer and a polypropylene resin (B) having a lower melt tension than the modified polypropylene resin (A). ), The content of the ethylene component in the component (A) is 1% by weight or more and 7% by weight or less, and the content of the component (A) is 100% by weight in total of the components (A) and (B) Is 1 to 49% by weight, and the content of the component (B) is 51 to 99% by weight.

<Modified polypropylene resin (A)>
The modified polypropylene resin (A) of the present invention has a melt flow rate measured at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more and less than 100 g / 10 min, 200 ° C., piston descending speed. It is a modified propylene-ethylene random copolymer having a melt tension of 0.2 gf or more and 20 gf or less measured at a speed of 10 mm / min and a take-up speed of 3 m / min.

  When the melt flow rate of the component (A) is less than 1 g / 10 minutes, the flowability of the resin composition is insufficient and molding defects such as short shots and deterioration of mold transferability in injection foam molding with a large mold are caused. Poor surface properties may occur. If the melt flow rate of the component (A) is 100 g / 10 minutes or more, the mixing with the component (B) may be insufficient, or the impact resistance of the injection foam molded article may be insufficient. The melt flow rate of the component (A) is preferably 20 g / 10 min or more and less than 100 g / 10 min when emphasis is placed on the mold transferability and the surface properties of the molded body, and when the impact resistance of the molded body is emphasized. Is preferably 1 g / 10 min or more and less than 20 g / 10 min.

  Here, the melt flow rate (hereinafter, may be abbreviated as “MFR”) is based on JIS K7210: 1999, using a melt indexer F-F01 (manufactured by Toyo Seiki Seisaku-sho, Ltd.) at 230 ° C. 2. A value obtained by converting the amount of resin extruded from a die for a certain time under the condition of a load of 16 kg into the amount of resin extruded for 10 minutes. This converted value was calculated by an MFR automatic calculation process (method B). The calculation formula is as follows. This method was applied even when the melt flow rate exceeded 50 g / 10 minutes.

MFR (g / 10 min) = (427 × Lxρ) / t
L (interval of test conditions): 3 (cm)
ρ (melt density at the test temperature): a value (g / cm 3) calculated by the following formula by the cutting method, but when the cutting method is impossible, 0.75 (g / cm 3) is set. /(0.711xL)
m: mass (g) of the sample flowing out of the piston after the piston moves in the interval L, which is measured by a cutting method.
L: Same as the above interval t (interval moving time): Actual measured value (second)
That is, when the cutout method can be applied, it may be calculated by the following formula.

MFR (g / 10 minutes) = (600 × m) / t
When the melt tension of the component (A) is less than 0.2 gf, the melt tension of the resin composition cannot be sufficiently ensured, and the thermoformability (drawdown property, deep drawability) and the film moldability (neck-in property) ) And foaming failure of foam cells during foam molding may cause molding failure. When the melt tension of the component (A) is larger than 20 gf, molding failure may occur.

  In the present application, the melt tension (hereinafter sometimes abbreviated as “MT”) is measured as follows. Attachment for melt tension measurement, 200 ° C., piston descending speed 10 mm using a Capillograph (manufactured by Toyo Seiki Seisakusho Co., Ltd.) having a φ10 mm cylinder with a φ1 mm or 10 mm long orifice at the tip. The load applied to the pulley with a load cell was measured over time while the strand discharged from the die when the wire was lowered at a rate of 3 m / min was taken out at a speed of 3 m / min. The maximum value and the minimum value of the load obtained after the deflection of the load was approximately stabilized were measured, and the average value thereof was defined as the melt tension. The measurement was impossible when the strand was broken, and the melt tension was set to 0 when the load on the pulley with the load cell was too low to be detected.

  Melt tension represents the tension required to deform the molten resin, whereas melt flow rate is a measure of the fluidity of the molten resin, so they are different concepts.

  The modified polypropylene resin (A) of the present invention is a modified propylene-ethylene random copolymer (AR). The copolymer (AR) is not particularly limited as long as it satisfies the MFR and MT. For example, a propylene-ethylene random copolymer is reacted with a conjugated diene compound to form a propylene-ethylene random copolymer. It may be a conjugated diene-modified polypropylene resin (A1) which can be obtained by introducing a branched structure and increasing the molecular weight thereof, or a polymer having a long chain branched structure by monomer polymerization. The conjugated diene-modified polypropylene-based resin (A1) obtained by reacting the conjugated diene compound melts the propylene-ethylene random copolymer (a), the radical polymerization initiator (b) and the conjugated diene compound (c). Those obtained by mixing are preferred. This molten mixture is excellent in that it does not require expensive equipment and can be manufactured at low cost.

  As shown in FIG. 1, the copolymer (AR) is superior in the melt tension in the same MFR region as compared with the modified propylene-ethylene block copolymer (AB). For example, around the MFR 40, MT (AR)> MT (AB). Therefore, it is excellent in processability such as thermoformability (drawdown characteristics, deep drawability), film moldability (neck-in), and foam moldability (foam cell stability).

  Further, the copolymer (AR) has the same melt tension in the same MFR region as the modified propylene homopolymer (AH), but the copolymer (AR) is higher than the homopolymer (AH). This is also characterized by excellent mechanical properties, for example, impact resistance. As will be described later, the foam molded article has excellent impact resistance.

  As described above, the copolymer (AR) is characterized in that both processability and mechanical properties can be achieved. In particular, when applied to foam molding, a foam molded article having a high expansion ratio and excellent impact resistance can be obtained.

<Propylene-ethylene random copolymer (a)>
The propylene-ethylene random copolymer (a) used to obtain the modified polypropylene-based resin (A) is composed of a linear polymer mainly composed of propylene and a comonomer mainly composed of ethylene randomly. It is a propylene-based polymer as it is polymerized. In the present invention, the propylene-ethylene random copolymer (a) is a random copolymer (a1) containing propylene as a main component and ethylene as a comonomer, and / or propylene as a main component, ethylene and a carbon number of 4 to 10. A mixture containing a random copolymer (a2) containing an α-olefin as a comonomer as an essential component and an optional propylene homopolymer (a3) may be used.

  The propylene-ethylene random copolymer (a) is preferably a copolymer containing a propylene component of 51% by weight or more. The contained copolymer is more preferable, 70% by weight or more is further preferable, and 80% by weight or more is particularly preferable.

  Further, the propylene-ethylene random copolymer (a) preferably contains 1 to 7% by weight of an ethylene component from the viewpoint of impact resistance and the like, and contains 1.5 to 5% by weight of an ethylene component. Are more preferable, and those containing 2 to 3.5% by weight are even more preferable.

  The propylene-ethylene random copolymer (a) may be a copolymer of a monomer copolymerizable with propylene in addition to propylene and ethylene. Examples of such a monomer copolymerizable with propylene include, for example, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl 4 to 12 α-olefins such as -1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene and 1-decene; cyclopentene, norbornene, tetracyclo [6,2,11,8,13, Cyclic olefins such as 6] -4-dodecene; 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene Diene such as vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, acrylic acid Chill, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, vinyl monomers such as divinylbenzene; and the like. These may be used alone or in combination of two or more. Of these, α-olefins are preferred, and 1-butene is more preferred, from the viewpoints of improving cold resistance and inexpensiveness.

Commercial products of the propylene-ethylene random copolymer (a) include, for example, J226T (MFR = 20), J229E (MFR = 50), J-721GR (MFR = 11), J-721 manufactured by Prime Polymer Co., Ltd. 2021GR (MFR = 22), J-2023GR (MFR = 22), J-2041GA (MFR = 22), J-3021GR (MFR = 33), F227D (MFR = 7), F219DA (MFR = 8), F329RA ( MFR = 25), F-744NP (MFR = 7)
And the like.

<Radical polymerization initiator (b)>
The radical polymerization initiator (b) used to obtain the modified polypropylene resin (A) generally includes a peroxide, an azo compound and the like, and includes a propylene-ethylene block copolymer (a) and a conjugated diene. Those having the ability to abstract hydrogen from compound (c) are preferred. Although not particularly limited, examples thereof include organic peroxides such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxydicarbonate, and peroxyester.

  Among them, those having a particularly high hydrogen abstracting ability are preferable. For example, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane , N-butyl 4,4-bis (t-butylperoxy) valerate, peroxyketals such as 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- Dialkyl peroxides such as dimethyl-2,5-di (t-butylperoxy) -3-hexyne, and diacyl peroxides such as benzoyl peroxide Oxide, t-butyl peroxy octate, t-butyl peroxy isobutyrate, t-butyl peroxy laurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxy isopropyl carbonate And peroxyesters such as 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate. Can be These may be used alone or in combination of two or more.

  The amount of the radical polymerization initiator (b) used for obtaining the modified polypropylene resin (A) is 0.05 parts by weight or more based on 100 parts by weight of the propylene-ethylene random copolymer (a). It is preferably at most 10 parts by weight, more preferably at least 0.2 part by weight and at most 5 parts by weight. If the amount of the radical polymerization initiator is less than 0.05 parts by weight, the modification may be insufficient. If the amount exceeds 10 parts by weight, the molecular chain scission takes precedence over the modification, and the desired modification may be obtained. Quality effect may not be obtained.

<Conjugated diene compound (c)>
Examples of the conjugated diene compound (c) used for obtaining the modified polypropylene resin (A) include, for example, butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2, 4-hexadiene and the like. These may be used alone or in combination. Of these, butadiene and isoprene are preferred because they are inexpensive, easy to handle, and the reaction can easily proceed uniformly.

  The addition amount of the conjugated diene compound (c) is preferably 0.01 to 5 parts by weight, and more preferably 0.05 to 2 parts by weight, based on 100 parts by weight of the propylene-ethylene random copolymer (a). Parts or less are more preferred. If the amount of the conjugated diene compound is less than 0.01 part by weight, the modification may be insufficient, and if it exceeds 5 parts by weight, the fluidity may be insufficient.

  In producing the modified polypropylene resin (A), a monomer copolymerizable with the conjugated diene compound may be used in combination with the conjugated diene compound. Such copolymerizable monomers include, for example, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, acrylic acid Metal salts, metal methacrylates, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylates such as stearyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid 2 -Methacrylic esters such as ethylhexyl and stearyl methacrylate.

<Conditions for producing modified polypropylene resin (A)>
When producing the modified polypropylene resin (A), the amount of the radical polymerization initiator (b) to be added is 0.1 to 10 times the weight of the conjugated diene compound (c). Then, the melt flow rate of the conjugated diene-modified polypropylene resin (A1) can be relatively easily adjusted to a range of 1 or more and less than 80. The addition amount of the radical polymerization initiator (b) is preferably 0.5 times or more and 7.5 times or less, more preferably 0.75 times or more and 5 times or less, of the addition amount of the conjugated diene compound (c). It is.

  In order to obtain the modified polypropylene resin (A), a device for reacting the propylene-ethylene random copolymer (a), the radical polymerization initiator (b), and the conjugated diene compound (c) includes a roll, Kneaders such as co-kneaders, Banbury mixers, Brabenders, single-screw extruders, twin-screw extruders, etc. Horizontal stirrers, such as horizontal stirrers such as twin-screw renewers, and twin-screw multi-disc units, and vertical stirrs such as double-helical ribbon stirrers Machine. Of these, a kneader is preferably used, and an extruder is particularly preferred from the viewpoint of productivity.

  Order or method of mixing and kneading (stirring) propylene-ethylene random copolymer (a), radical polymerization initiator (b), and conjugated diene compound (c) to obtain modified polypropylene resin (A) Is not particularly limited. After mixing the propylene-ethylene block copolymer (a), the radical polymerization initiator (b), and the conjugated diene compound (c), the mixture may be melt-kneaded (stirred), or the propylene-ethylene block copolymer (a ), The radical polymerization initiator (b) and the conjugated diene compound (c) may be mixed simultaneously or separately, collectively or separately. The temperature of the kneading (stirring) machine is preferably from 130 to 300 ° C. in that the propylene-ethylene block copolymer (a) melts and does not thermally decompose. The kneading (stirring) time is generally preferably 1 to 60 minutes.

  As described above, the modified polypropylene resin (A) can be produced. The shape and size of the manufactured modified polypropylene resin (A) are not limited, and may be pellets.

<Polypropylene resin (B)>
The polypropylene resin (B) of the present invention has a melt flow rate measured at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more and less than 100 g / 10 min. However, the modified propylene-based copolymer is not included in the category of the polypropylene-based resin (B).

  When the melt flow rate of the component (B) is less than 1 g / 10 min, and when the clearance of the mold cavity has a thin portion of, for example, about 1 to 2 mm at the time of manufacturing an injection-molded article, melting is performed at a relatively low pressure. In some cases, it becomes difficult to fill the resin with the resin, and it may not be possible to continuously perform stable injection molding. If the melt flow rate of the component (B) is 100 g / 10 minutes or more, the injection molding tends to be unstable due to excessive fluidity. The melt flow rate of the component (B) is more preferably 3 g / 10 min or more and 70 g / 10 min or less, and even more preferably 5 g / 10 min or more and less than 70 g / 10 min. The measurement conditions for the melt flow rate are the same as those described above.

<Polypropylene resin composition>
The polypropylene resin composition of the present invention is a combination of the above-mentioned modified polypropylene resin (A) and polypropylene resin (B). The polypropylene-based resin composition of the present invention can provide an injection-molded foam having excellent impact resistance and a favorable foamed state. In order to obtain such an injection foam molded article, both components are blended so that the content of the component (B) is larger than the content of the component (A). Specifically, the content of the component (A) is 1 to 49% by weight and the content of the component (B) is 51 to 99% by weight based on 100% by weight of the total of the components (A) and (B). . In this range, it is possible to obtain an injection-molded foam having excellent impact resistance and a favorable foamed state. From the viewpoint of impact resistance, the content of the component (A) is preferably 1 to 25% by weight, more preferably 3 to 25% by weight, and still more preferably 5 to 20% by weight.

  Further, the suitable range of the MFR and the content of the component (A) may vary depending on the MFR of the component (B). For example, when the MFR of the component (B) is less than 8 g / 10 min, the MFR of the component (A) is preferably 20 g / 10 min or more, more preferably 40 g / 10 min or more from the viewpoint of fluidity. When the MFR of the component (A) is less than 20 g / 10 minutes, problems such as deterioration of mold transferability may occur due to insufficient fluidity. When the MFR of the component (B) is less than 8 g / 10 minutes as described above, the amount of the component (A) is preferably 5 to 49% by weight, more preferably 10 to 35% by weight.

  The melt flow rate of the polypropylene resin composition of the present invention is not limited, but is preferably 8 g / 10 min or more and less than 80 g / 10 min. This melt flow rate is measured under the conditions described above. When the melt flow rate of the polypropylene resin composition is within this range, the polypropylene resin composition has fluidity suitable for injection foam molding, and a molded article having high impact resistance after injection foam molding. Obtainable.

  The melt flow rate of the polypropylene resin composition is a value measured after sufficiently melting and kneading each component, and the melt flow rate of each of the conjugated diene-modified polypropylene resin (A) and the polypropylene resin (B) is shown. And it can be easily adjusted depending on the amount of each component.

<Blowing agent (C)>
The polypropylene resin composition of the present invention usually contains a foaming agent. The foaming agent that can be used in the present invention can be used without any particular limitation as long as it can be generally used for injection foam molding, and may be any of a chemical foaming agent and a physical foaming agent.

  The chemical foaming agent is mixed with a resin component in advance and then supplied to an extruder or an injection molding machine, and is decomposed in a cylinder to generate a gas such as carbon dioxide gas. The chemical foaming agent is not particularly limited, and examples thereof include inorganic chemical foaming agents such as sodium bicarbonate and ammonium carbonate, and organic chemical foaming agents such as azodicarbonamide and N, N'-dinitrosopentamethylenetetramine. Can be These may be used alone or in combination of two or more.

  The physical foaming agent is injected or dispersed or dissolved as a gaseous or supercritical fluid into the molten resin in the cylinder of the extruder or injection molding machine, and after being injected into the mold, the pressure is released. Functions as a foaming agent. The physical blowing agent is not particularly limited, for example, aliphatic hydrocarbons such as propane and butane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, halogenated hydrocarbons such as chlorodifluoromethane and dichloromethane, and nitrogen. , Carbon dioxide, and inorganic gases such as air. These may be used alone or in combination of two or more.

  Among these foaming agents, those which can be safely used in ordinary extruders and injection molding machines, and which can easily obtain uniform fine bubbles, include inorganic chemical foaming agents as chemical foaming agents and nitrogen as physical foaming agents. , Carbon dioxide, and inorganic gases such as air are preferred. These foaming agents include, as necessary, a foaming aid such as an organic acid such as citric acid, talc, and lithium carbonate in order to stably and uniformly make the cells of the injection foam molded article fine. A nucleating agent such as inorganic fine particles may be added. Usually, the inorganic chemical foaming agent is prepared from a master batch of a polyolefin resin having a concentration of the foaming agent of 10 to 75% by weight in view of handleability, storage stability and dispersibility in a polypropylene resin. It is preferred to use

  The amount of the foaming agent used in the present invention can be appropriately set depending on the expansion ratio of the final product, the type of the foaming agent, and the resin temperature during molding. For example, the inorganic chemical foaming agent preferably ranges from 0.5 part by weight to 30 parts by weight, more preferably from 1 part by weight to 20 parts by weight, based on 100 parts by weight of the polypropylene resin composition of the present invention. Used in. By using the inorganic chemical foaming agent in this range, an injection foam molded article having a foaming ratio of 2 times or more and uniform fine cells can be obtained economically and easily. On the other hand, the physical foaming agent is injected in an amount of preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polypropylene resin composition. It is supplied to a molding machine and used.

<Other additives>
The polypropylene-based resin composition of the present invention may be a high-density polyethylene-based resin in addition to a polypropylene-based resin that does not correspond to any of the component (A) and the component (B), as long as the effects of the present invention are not impaired. Resins, high-pressure low-density polyethylene-based resins, linear low-density polyethylene-based resins, ethylene-α-olefin copolymers, olefin-based elastomers, styrene-based elastomers, and may further contain other thermoplastic resins .

  Further, the polypropylene-based resin composition of the present invention, if necessary, as long as the effects of the present invention are not impaired, an antioxidant, a metal deactivator, a phosphorus-based processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, Stabilizers such as fluorescent whitening agents, metal soaps, antacid adsorbents, crosslinking agents, chain transfer agents, nucleating agents, plasticizers, lubricants, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. May further be added.

<Injection foam molding>
The present invention also relates to an injection-molded foam of the polypropylene-based resin composition.

  The expansion ratio of the injection foamed molded article of the present invention is preferably 1.5 times or more and 8 times or less, more preferably 2 times or more and 5 times or less, and most preferably 2 times or more and 4 times or less. If the expansion ratio is less than 2 times, it tends to be difficult to obtain lightness, and if it exceeds 8 times, the rigidity tends to decrease significantly.

<Injection foam molding method>
The injection foam molding method that can be used for producing the injection foam molded article of the present invention is not particularly limited, and a known method can be applied. Specific molding conditions at that time can be appropriately determined in consideration of the melt flow rate, the melt tension, the type of a molding machine, the shape of a mold, and the like of the polypropylene resin composition. As an example, the resin temperature is preferably 170 to 300 ° C, more preferably 190 to 270 ° C, and the mold temperature is preferably 10 to 100 ° C, more preferably 20 to 80 ° C. Further, it is preferable to perform the molding under the conditions of a molding cycle of 1 to 120 minutes, an injection speed of 10 to 300 mm / sec, an injection pressure of 10 to 200 MPa, and the like.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.
In Examples and Comparative Examples, test methods and determination criteria used for various evaluation methods are as follows.

(1) Melt flow rate (MFR)
In accordance with JIS K7210: 1999, the amount of resin extruded from the die at a constant time under a condition of 230 ° C. and a load of 2.16 kg using a melt indexer F-F01 (manufactured by Toyo Seiki Seisaku-sho, Ltd.) was 10 It was converted to the amount of resin extruded per minute. The predetermined time is 60 seconds when the melt flow rate is 3.5 g / 10 min or more and less than 10 g / 10 min, 30 seconds when the melt flow rate is 10 g / 10 min or more and less than 25 g / 10 min, and 25 g / 10 min or more. The duration was 15 seconds for less than 50 g / 10 minutes, 5 seconds for 50 g / 10 minutes or more and less than 100 g / 10 minutes, and 3 seconds for 100 g / 10 minutes or more.

(2) Melt tension (MT)
Attachment for melt tension measurement, 200 ° C., piston descending speed 10 mm using a Capillograph (manufactured by Toyo Seiki Seisaku-sho, Ltd.) having a φ10 mm cylinder with a φ1 mm or 10 mm long orifice at the tip. The load applied to the pulley with a load cell was measured with time while the strand discharged from the die when the wire was lowered at a rate of 3 m / min was drawn on a pulley with a load cell below 370 mm or 520 mm at a speed of 3 m / min. The maximum value and the minimum value of the load obtained after the deflection of the load was approximately stabilized were measured, and the average value thereof was defined as the melt tension. The measurement was impossible when the strand was broken, and the melt tension was set to 0 when the load on the pulley with the load cell was too low to be detected.

(3) DuPont Impact Test Using a DuPont impact tester (manufactured by Yasuda Seiki Seisaku-Sho, Ltd.), a 50% breaking height was determined by the staircase method using a constant drop weight, and the energy value was calculated from the load at that time. The falling load was set to 300 g, 700 g, or 1000 g, and the calculation of the energy value was performed according to JIS-K-711.

(4) Visual Evaluation of Cell State of Foam Using an injection molding machine (MD350S-IV, manufactured by Niigata Machine Techno), the resin composition is completely filled in the following mold under the following molding conditions. Injection molded with minimum filling pressure.
・ Resin temperature: 200 ° C
・ Mold temperature: 40 ° C
・ Injection speed: 100mm / sec
-Die used: Box mold with 1 point pin gate at the bottom center, bottom shape: 190 mm x 190 mm, side shape (trapezoidal shape): 190 mm (bottom side) to 220 mm (opposite bottom side) x 100 mm, but only the bottom is core-backed, No side back core cavity clearance t0: 1.5mm
・ Cavity clearance t1: 2.1 mm
-Cavity clearance t2: Set foaming ratio set to 3 or 2 times Injection foaming molding when the foaming ratio was set to 3 times was performed in the following procedure.

  A composition containing a foaming agent is supplied to an injection molding machine set at a predetermined cylinder temperature, melted and kneaded at an appropriate back pressure, and then a mold having a cavity clearance t0 at a bottom surface temperature adjusted to a predetermined temperature. During this, injection filling was performed at a predetermined injection speed. Immediately after the injection filling was completed (the setting holding time was 0 second), the movable mold was retracted to the cavity clearance t1 on the bottom portion, and the resin in the cavity was foamed (first foaming step). Next, after maintaining a predetermined set time (6 seconds) in the state of the clearance t1 at the bottom surface of the mold, the movable mold is again moved to the cavity clearance t2 at the bottom portion so that the molded body has a desired thickness (expansion ratio). Then, foaming was performed again (second foaming step). After completion of the foaming, the foamed resin was cooled and solidified, and the injection foamed molded product was taken out.

Injection foam molding when the expansion ratio was set to 2 times was carried out in the same manner as above, except that the cavity clearance t2 was changed.
In collecting the molded product, four shots after purging (material switching) were discarded and the following seven shots were collected in order to guarantee the stability of the injection state. The appearance of the molded article was visually observed. The foaming state was evaluated according to the following criteria.
：: Good foaming property among test samples Δ: Intermediate between と and ×: Poor foaming property among test samples

<Preparation of conjugated diene-modified polypropylene resin>
(Production Example 1)
According to Table 1, (a) 100 parts by weight of an ethylene / propylene random polymer (a-1) having a content of an ethylene component of 2.5% by weight as a linear polypropylene-based resin having a melt flow rate of 50 g / 10 min. (B) t-butyl peroxyisopropyl monocarbonate as a radical polymerization initiator using a metering pump at 1.1 parts by weight (at a rate of 0.77 kg / hr) of a 46 mmφ twin screw extruder (L / L D = 62), melt-kneaded at a cylinder temperature of 200 ° C., and (c) an isoprene monomer as a conjugated diene compound and 0.36 parts by weight (0. At a rate of 252 kg / hr) and melt-kneaded in the twin-screw extruder to pelletize the conjugated diene-modified polypropylene resin (A-1). It was. MFR = 40 g / 10 min.

(Production Example 2)
According to Table 1, (a) an ethylene / propylene block polymer (a-2) having a melt flow rate of 45 g / 10 min as a linear polypropylene resin, and (c) a supply amount of isoprene as a conjugated diene compound at 0.43 parts by weight. Conjugated diene-modified polypropylene-based resin (A-2) was obtained in the same manner as in Production Example 1 except that the above was changed. MFR = 40 g / 10 min.

(Production Example 3)
According to Table 1, the supply amount of (a) a polypropylene homopolymer (a-3) having a melt flow rate of 45 g / 10 min as a linear polypropylene resin and (c) a supply amount of isoprene as a conjugated diene compound were changed to 0.42 parts by weight. A conjugated diene-modified polypropylene-based resin (A-3) was obtained in the same manner as in Production Example 1 except for the above. MFR = 40 g / 10 min.

(Production Example 4)
According to Table 1, a conjugated diene-modified polypropylene-based resin (A-4) was obtained in the same manner as in Production Example 3, except that the supply amount of isoprene as the conjugated diene compound was changed to 0.40 parts by weight. . MFR = 60 g / 10 min.

(Production Example 5)
According to Table 1, (a) an ethylene / propylene random copolymer (a-5) having a melt flow rate of 25 g / 10 min and an ethylene content of 15% by weight as a linear polypropylene resin, and (b) radical polymerization initiation Conjugated diene was prepared in the same manner as in Production Example 1 except that t-butyl peroxyisopropyl monocarbonate was changed to 1.0 part by weight as the agent and the supply amount of isoprene was changed to 0.40 part by weight as the (c) conjugated diene compound. A modified polypropylene resin (A-5) was obtained. MFR = 3 g / 10 min.

<Polypropylene resin>
Table 2 shows the propylene-ethylene block copolymer used as the polypropylene resin (B).

(Examples 1 to 4)
<Preparation of polypropylene resin composition and injection foam molded article>
A conjugated diene-modified polypropylene resin (A), a polypropylene resin (B), a foaming agent (C), and a color masterbatch as a colorant (D) are dry-blended to produce a resin composition, and injection foam molding is performed. Was served.

  Table 3 shows the types and amounts (parts by weight) of (A) and (B). In addition to (A) and (B) (a total of 100 parts by weight), the resin composition used here is 6 parts by weight of EE25C (manufactured by Eiwa Chemical Co., Ltd.) as (C) and Dye Color PP-M77255 (black) as (D). ) (Manufactured by Dainichi Seika) in an amount of 3 parts by weight. Table 3 shows the obtained results.

<Evaluation of foamability of injection foamed molded article>
The above-mentioned injection foam molding was evaluated in accordance with the items of the foamability evaluation described above.

(Comparative Examples 1 to 8)
Dry blending, injection foam molding, and evaluation were performed in the same manner as in Example 1 using the types and composition ratios shown in Table 3. Table 3 shows the obtained results.

  Comparative Example 1 is a case in which (A) is not used and foaming ratio is set to 2 and 3 times foaming. However, it can be seen that foaming properties are insufficient when 3 times foaming is performed and satisfactory foaming cannot be performed. Impact resistance could not be evaluated because a foam worthy of evaluation was not obtained.

  Further, a case where double foaming is set as the foaming ratio is described, but double foaming itself is possible without using (A), but Examples 1 to 4 and Comparative Examples 2 to 4 and 6 ( It can be seen that, in the case of using A), foaming can be doubled, and the foamability tends to be excellent. It can be seen that Examples 1 to 4 tend to be excellent in impact resistance in addition to foamability.

  From Comparative Examples 2 to 6, even when using a modified block polymer or propylene homopolymer, double foaming or triple foaming is possible if conditions are selected. In comparison, it can be seen that the impact resistance in double foaming and triple foaming is inferior.

  As seen in Examples 1 to 4 of the present invention, when (A) a modified product of a random polypropylene resin having an ethylene component content of 1% by weight or more and 7% by weight or less was used as a comparative example. It can be seen that foamability and impact resistance tend to be improved as compared with properties 2 to 8.

Claims (9)

It contains a modified polypropylene resin (A) that is a modified propylene-ethylene random copolymer and a polypropylene resin (B) having a lower melt tension than the modified polypropylene resin (A),
The content of the ethylene component in the component (A) is 1% by weight or more and 7% by weight or less,
A polypropylene resin composition wherein the content of the component (A) is 1 to 49% by weight and the content of the component (B) is 51 to 99% by weight based on 100% by weight of the total of the components (A) and (B). object.   2. The polypropylene resin composition according to claim 1, wherein the modified polypropylene resin (A) has a melt flow rate measured at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more and less than 100 g / 10 min.   3. The polypropylene resin composition according to claim 1, wherein the polypropylene resin (B) has a melt flow rate measured at 230 ° C. and a load of 2.16 kg of 1 g / 10 min or more and less than 100 g / 10 min. 4.   The melt tension of the modified polypropylene resin (A) measured at a temperature of 200 ° C., a piston descending speed of 10 mm / min, and a take-off speed of 3 m / min is 0.2 gf or more and 20 gf or less. The polypropylene-based resin composition according to any one of the preceding claims.   The melt tension of the polypropylene-based resin (B) measured at 200 ° C, a piston descending speed of 10 mm / min, and a take-up speed of 3 m / min is less than 0.2, according to any one of claims 1 to 4. A polypropylene-based resin composition.   The polypropylene resin composition according to any one of claims 1 to 5, wherein the modified polypropylene resin (A) is a conjugated diene-modified polypropylene resin.   The polypropylene resin composition according to claim 6, wherein the conjugated diene is isoprene.   A molded article obtained by injection molding the polypropylene resin composition according to claim 1.   A foam molded article obtained by subjecting the polypropylene resin composition according to claim 1 to injection foam molding.