JP2020152781A - Method for producing foam molding - Google Patents

Abstract

To provide a method for producing a foam molding that has a high expansion ratio, includes fine cells, has a good appearance, and has a suppressed bad smell.SOLUTION: A method for producing a foam molding has the step (I) for foam molding a thermoplastic resin composition containing a thermoplastic resin (A), a nitrogen gas foaming agent (B) and a carbon dioxide gas foaming agent (C), with (mass of the foaming agent (B))/(mass of the foaming agent (C)) of 1/100 or more and less than 15/100.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a foam molded product, and more particularly to a method for producing a foam molded product of a thermoplastic resin composition.

Thermoplastic resins such as polypropylene are used in various fields.
In the field of automobile interior / exterior parts and the like, a foam molded product such as polypropylene may be used from the viewpoint of weight reduction, and as such a foam molded product, for example, Patent Document 1 describes polypropylene using a specific impact polypropylene. A polypropylene-based foamed molded article is disclosed, and Patent Document 2 also discloses a polypropylene-based expanded molded article in which the thermal resistance in the thickness direction and the heat capacity per unit area are within a specific range and satisfy a specific relationship. ..

As the foaming agent used for foam molding, various foaming agents such as a physical foaming agent such as carbon dioxide gas and a pyrolysis type foaming agent such as baking soda are known, and foaming by using a plurality of types of foaming agents in combination. Attempts have also been made to improve the molded product. For example, Patent Document 3 is a polyolefin-based resin-crosslinked foam containing a heat-generating decomposition type chemical foaming agent and a heat-absorbing decomposition type foaming agent and cross-linked by electron beam, and the foaming ratio of the foam is 10 to 50 times. , A polyolefin-based resin crosslinked foam having an average cell diameter of 0.6 to 1.5 mm is disclosed. Further, Patent Document 4 describes a thermoplastic resin composition for foam molding containing a thermoplastic resin, an azodicarboxylic amide having a predetermined particle size, a baking soda having a predetermined particle size, and a crystal nucleating agent. It is described that a molded product having fine cells can be produced by injection-foam molding a thermoplastic resin composition in which the mass ratio of azodicarboxylic amide / the baking soda is in the range of 100/25 to 15/100.

International Publication No. 2010/050509 International Publication No. 2016/068164 Japanese Unexamined Patent Publication No. 2000-007810 Japanese Unexamined Patent Publication No. 2018-135458

However, in the prior art, there is room for further improvement from the viewpoint of cell miniaturization and the appearance of the foamed molded product when the foaming ratio is increased. Further, in the technique described in Patent Document 4, the foaming ratio cannot be increased so much when aiming at the miniaturization of cells, and in addition, since azodicarbonamide is blended in a high proportion, carbon monoxide, ammonia, etc. are contained during the decomposition. There was room for further improvement in that a large amount of toxic and irritating gas was generated, which not only deteriorated the molding environment but also deteriorated the odor of the molded product itself.
Therefore, an object of the present invention is to provide a method for producing a foam molded product having a high foaming ratio, fine cells, a good appearance, and a suppressed odor.

As a result of diligent research by the present inventor, when nitrogen gas is used as the foaming gas when producing the foamed molded product, the cells become finer, but the appearance of the molded product tends to deteriorate and it is difficult to increase the foaming ratio. It was also found that when carbon dioxide is used as the foaming gas, the foaming ratio tends to increase, but the cell tends to grow. Then, based on this finding, by adding nitrogen gas and carbon dioxide gas in a specific ratio, even if the foaming ratio is increased, the cell is made finer while maintaining the good appearance of the molded product, and the ammonia odor is suppressed. We found that we could do it, and completed the present invention.

The present invention relates to the following [1] to [9].
[1]
The step (I) of foam-molding a thermoplastic resin composition containing a thermoplastic resin (A), a nitrogen gas-based foaming agent (B) and a carbon dioxide gas-based foaming agent (C) is included.
A method for producing a foamed molded product in which (mass of the foaming agent (B)) / (mass of the foaming agent (C)) is 1/100 or more and less than 15/100.

[2]
The foamed molded product of the above [1], wherein the foaming agent (B) is an organic foaming agent capable of generating nitrogen gas, and the foaming agent (C) is an inorganic foaming agent capable of generating carbon dioxide gas. Manufacturing method.

[3]
The total content of the organic foaming agent (B) and the inorganic foaming agent (C) in the thermoplastic resin composition is 0.5 to 10% by mass according to the above [1] or [2]. A method for producing a foam molded product.

[4]
The method for producing a foamed molded product according to the above [2] or [3], wherein the organic foaming agent (B) is an azodicarbonamide.

[5]
The method for producing a foamed molded product according to any one of [2] to [4] above, wherein the inorganic foaming agent (C) is baking soda.

[6]
The method for producing a foamed molded product according to any one of [1] to [5] above, wherein the thermoplastic resin (A) contains a propylene-based polymer.

[7]
The method for producing a foam molded product according to the above [1] to [6], wherein the step (I) is a step of injection-foaming the thermoplastic resin composition.

[8]
The method for producing a foamed molded product according to any one of [1] to [7], wherein in the step (I), the thermoplastic resin composition is foam-molded so that the foaming ratio is 2.0 times or more.

[9]
A foam molded product produced by any of the production methods [1] to [8].

According to the method for producing a foamed molded product of the present invention, it is possible to produce a foamed molded product having a high foaming ratio, fine cells, a good appearance, and an odor (ammonia odor) suppressed.

Hereinafter, the method for producing the foamed molded article of the present invention will be described in more detail.
The method for producing a foam molded article of the present invention is
The step (I) of foam-molding a thermoplastic resin composition containing a thermoplastic resin (A), a nitrogen gas-based foaming agent (B) and a carbon dioxide gas-based foaming agent (C) is included.
(Mass of the foaming agent (B)) / (mass of the foaming agent (C)) is 1/100 or more and less than 15/100.

<Thermoplastic resin composition>
The thermoplastic resin composition used in the present invention contains a thermoplastic resin (A), a nitrogen gas-based foaming agent (B), and a carbon dioxide gas-based foaming agent (C).

(Thermoplastic resin (A))
As the thermoplastic resin (A), various thermoplastic resins that can be used for foam molding can be used, and crystals of polyolefins (ethylene-based polymers, propylene-based polymers, etc.), polyethylene terephthalates, polyamides, polyacetals, etc. Examples thereof include sex polymer materials, polystyrene, polymethyl methacrylate, acrylonitrile, butadiene, styrene, polycarbonate and other non-crystalline polymer materials. These may be used alone or in combination of two or more. Among these, crystalline polymer materials, among them, polyolefins, particularly ethylene-based polymers and propylene-based polymers, are preferably used in terms of mechanical strength, moldability, and cost.

Impact polypropylene containing high molecular weight component (a1);
Among these thermoplastic resins, a propylene-based polymer, which is a high molecular weight component-containing impact polypropylene which is particularly preferably used (hereinafter, also referred to as “high molecular weight component-containing impact polypropylene (a1)”) is described in detail. Describe.

The high molecular weight component-containing impact polypropylene (a1) has a propylene / ethylene copolymer specified as a room temperature paraxylene-soluble component in an amount of 4.5 to 31.0% by mass, preferably 5 to 30% by mass, more preferably. Is 6 to 28% by mass.

The high molecular weight component-containing impact polypropylene (a1) contains 0.2 to 3.7% by mass of a propylene polymer component having an ultimate viscosity [η] of 6.0 to 20.0 dl / g in tetralin at 135 ° C. It preferably contains 0.5 to 3.5% by mass, more preferably 1.0 to 3.0% by mass. When the ultimate viscosity [η] is in this range, the foaming performance and injection moldability of the thermoplastic resin composition are good.

In the impact polypropylene (a1) containing a high molecular weight component, the propylene homopolymer portion and the polyethylene portion contained as necessary are insoluble in normal temperature paraxylene, and the propylene / ethylene random copolymer portion is soluble in normal temperature paraxylene. Is. It is preferable that the content of the room temperature para-xylene-soluble component in the impact polypropylene (a1) containing a high molecular weight component is in the above range because the balance between rigidity and impact resistance is excellent.

By containing a specific amount of a propylene polymer component (hereinafter, referred to as propylene polymer component (x)) having an ultimate viscosity [η] in the above range, which is contained in the high molecular weight component-containing impact polypropylene (a1). , It is preferable because a thermoplastic resin composition having high melt tension and adjusted viscous elastic properties can be obtained.

The ultimate viscosity [η] of the propylene polymer component (x) is 6.0 to 20.0 dl / g, preferably 6.5 to 19 dl / g, and more preferably 7.0 to 18 dl / g. When the ultimate viscosity [η] of the propylene polymer component (x) is in this range, the foaming performance and injection moldability of the thermoplastic resin composition are good.

The melt flow rate (MFR) of the high molecular weight component-containing impact polypropylene (a1) measured by ASTM D-1238 at 230 ° C. and a load of 2.16 kg is usually 35 to 190 g / 10 minutes, preferably 40 to 170 g / 10. Minutes, more preferably 45-150 g / 10 minutes.

The ultimate viscosity [η] of the propylene / ethylene copolymer specified as the room temperature paraxylene-soluble component in the high molecular weight component-containing impact polypropylene (a1) is usually 3.5 to 10 dl / g, preferably 3. It is 5-9 dl / g. The content of the propylene / ethylene copolymer specified as the room temperature paraxylene-soluble component in the high molecular weight component-containing impact polypropylene (a1) is 4.5 to 31.0% by mass, preferably 5 to 30. It is about% by mass, more preferably about 6 to 28% by mass. Further, the ethylene content in the propylene / ethylene copolymer is preferably 20 to 45% by mass, more preferably 25 to 40% by mass.

The propylene homopolymer portion contained in the room temperature para-xylene insoluble component in the impact polypropylene (a1) containing a high molecular weight component preferably has excellent stereoregularity. For example, the isotactic pentad fraction (mmmm fraction). However, it is preferably 95.0% or more, more preferably 97.0% or more. When the propylene homopolymer portion has such a high isotactic pentad fraction, it is possible to produce a foam molded product having high crystallinity of the resin and high rigidity.

The isotactic pentad fraction (mmmm fraction) is a value measured using ¹³ C-NMR, and indicates the abundance ratio of the isotactic chain in the polypropylene molecular chain in pentad units. , The fraction of the propylene monomer unit at the center of the chain in which five propylene monomer units are continuously mesobonded. Specifically, it is a value calculated as a fraction of the mmmm peak in the total absorption peak of the methyl carbon region observed in the ¹³ C-NMR spectrum.

The high molecular weight component-containing impact polypropylene (a1) may contain a branched olefin polymer in a proportion of usually 0.1% by mass or less, preferably 0.05% by mass or less. Since the branched olefin polymer acts as a nucleating agent for the high molecular weight component-containing impact polypropylene (a1), the isotactic pentad fraction of the propylene homopolymer portion can be increased and the moldability can be improved. Examples of such branched olefin polymers include 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, and 3-methyl-1. -A homopolymer of a branched olefin such as pentene or a copolymer containing the same can be used. Of these, 3-methyl-1-butene is preferred.

The production method of the high molecular weight component-containing impact polypropylene (a1) is not particularly limited, but is produced, for example, by the method described in [0041] to [0075] of International Publication No. 2010/050509. be able to.

The high molecular weight component-containing impact polypropylene (a1) may be used alone or in combination of two or more. It is preferable that the impact polypropylene (a1) containing a high molecular weight component satisfies the above range as a whole.

The impact polypropylene (a1) containing a high molecular weight component is
Impact polypropylene (a11) having an amount of propylene / ethylene copolymer specified as a room temperature paraxylene-soluble component of 5 to 30% by mass, and homopolypropylene containing a high molecular weight component satisfying the following (i) and (ii). (A12)
It may be composed of.
(I) Contains 5 to 30% by mass of a propylene homopolymer component having an ultimate viscosity [η] of 6.0 to 20 dl / g in tetralin at 135 ° C.
(Ii) Contains 70 to 95% by mass of a propylene homopolymer component having an ultimate viscosity [η] of 0.5 to 3.0 dl / g in tetralin at 135 ° C.

Impact polypropylene (a11);
The impact polypropylene (a11) has a propylene / ethylene copolymer specified as a room temperature paraxylene-soluble component in an amount of preferably 5 to 30% by mass, more preferably 8 to 27% by mass. In the impact polypropylene (a11), the propylene homopolymer portion and the polyethylene portion contained as needed are insoluble in normal temperature paraxylene, and the propylene / ethylene random copolymer portion is soluble in normal temperature paraxylene. When the content of the room temperature para-xylene soluble component in the impact polypropylene (a11) is in the above range, the balance between rigidity and impact resistance is excellent, which is preferable.

The melt flow rate (MFR) of the impact polypropylene (a11) measured by ASTM D-1238 at 230 ° C. and a load of 2.16 kg is preferably 50 to 200 g / 10 minutes, more preferably 55 to 150 g / 10 minutes. is there.

The propylene / ethylene copolymer specified as a room temperature paraxylene-soluble component in the impact polypropylene (a11) preferably has an intrinsic viscosity [η] of 3.5 to 10 dl / g, more preferably 3.5 to. It is 9 dl / g.

The content of the propylene / ethylene copolymer specified as the room temperature paraxylene-soluble component in the impact polypropylene (a11) is preferably about 5 to 30% by mass, more preferably about 8 to 27% by mass, and also. The ethylene content in the propylene / ethylene copolymer is preferably about 20 to 45% by mass, more preferably about 25 to 40% by mass.

The propylene homopolymer portion contained in the room temperature para-xylene insoluble component in the impact polypropylene (a11) preferably has excellent stereoregularity, and for example, the isotactic pentad fraction (mm mm fraction) is preferable. It is preferably 95.0% or more, more preferably 97.0% or more. When the propylene homopolymer portion has such a high isotactic pentad fraction, it is possible to produce a foam molded product having high crystallinity of the resin and high rigidity.

The MFR (230 ° C., load 2.16 kg) of the propylene homopolymer portion contained in the room temperature para-xylene insoluble component in the impact polypropylene (a11) is preferably 2 g / 10 minutes or more and 1000 g / 10 minutes or less, and more. It is preferably 50 g / 10 minutes or more and 500 g / 10 minutes or less, and more preferably 150 g / 10 minutes or more and 350 g / 10 minutes or less.

The impact polypropylene (a11) may contain the branched olefin polymer in a proportion of 0.1% by mass or less, preferably 0.05% by mass or less. Since the branched olefin polymer acts as a nucleating agent for the impact polypropylene (a11), the isotactic pentad fraction of the propylene homopolymer portion can be increased and the moldability can be improved. Examples of such branched olefin polymers include 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, and 3-methyl-1. -A homopolymer of a branched olefin such as pentene or a copolymer containing the same can be used. Of these, 3-methyl-1-butene is preferred.

The production method of the impact polypropylene (a11) is not particularly limited, but it can be produced, for example, by the method described in [0049] of International Publication No. 2010/050509.

The impact polypropylene (a11) may be used alone or in combination of two or more. When two or more kinds are used, it is preferable that impact polypropylene (a11) satisfies the above range as a whole.

High molecular weight component-containing homopolypropylene (a12);
The high molecular weight component-containing homopolypropylene (a12) is
(I) A propylene homopolymer component having an intrinsic viscosity [η] of more than 6.0 to 20 dl / g in tetralin at 135 ° C. (hereinafter referred to as “component (i)”) is preferably 5 to 30 mass by mass. %, More preferably 10 to 25% by mass,
(Ii) A propylene homopolymer component having an ultimate viscosity [η] of 0.5 to 3.0 dl / g in tetralin at 135 ° C. (hereinafter referred to as “(ii) component”) is preferably 70 to 95. It contains% by mass, more preferably 75 to 90% by mass.

The high molecular weight component-containing homopolypropylene (a12) achieved high melt tension and adjusted viscoelastic properties by containing the component (i), that is, the ultra-high molecular weight propylene-based polymer component in a specific amount. It is a linear propylene-based polymer.

The ultimate viscosity of the component (i) is preferably 6.0 to 20 dl / g, more preferably 7.0 to 18 dl / g. Further, the mass fraction of the component (i) in the high molecular weight component-containing homopolypropylene (a12) is more preferably 10 to 25% by mass.
When the component (i) is contained in the above ratio, the foaming performance and injection moldability of the thermoplastic resin composition are good.

The ultimate viscosity of the component (ii) is preferably 0.5 to 3.0 dl / g, more preferably 0.5 to 2.0 dl / g, and particularly preferably 0.5 to 1.5 dl / g. The mass fraction of the component (ii) is preferably 70 to 95% by mass, more preferably 75 to 90% by mass.

When the component (ii) is contained in the above ratio, the foaming performance and injection moldability of the thermoplastic resin composition are good.
The MFR of the high molecular weight component-containing homopolypropylene (a12) measured at 230 ° C. and a load of 2.16 kg is preferably 10 g / 10 minutes or less, more preferably 7 g, from the viewpoint of forming a homogeneous foam during high foaming. / 10 minutes or less.

The production method of the high molecular weight component-containing homopolypropylene (a12) is not particularly limited, but is produced, for example, by the method described in International Publication No. 2010/050509 [0058] to [0075]. be able to.

Ethylene / α-olefin copolymer rubber (a2);
The thermoplastic resin (A) is an ethylene / α-olefin copolymer (hereinafter referred to as “ethylene ・” together with various resins such as the high molecular weight component-containing impact polypropylene (a1) which is the base of the thermoplastic resin (A). It may also contain α-olefin copolymer rubber (a2) ”).

As the ethylene / α-olefin copolymer rubber (a2), those having excellent compatibility with various resins such as the high molecular weight component-containing impact polypropylene (a1) can be used without limitation, and ethylene and the number of carbon atoms can be used. A copolymer with an α-olefin having a value of 3 or more and 10 or less is preferable.

Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1 -Decenes, etc. can be mentioned. One type of α-olefin may be used alone, or two or more types may be mixed and used. Of these, 1-butene and 1-octene are particularly preferable.

The MFR of the ethylene / α-olefin copolymer rubber (a2) measured by ASTM D-1238 at 190 ° C. and a load of 2.16 kg is preferably 1 to 50 g / 10 minutes, more preferably 10 to 40 g /. It is 10 minutes. The density of the ethylene / α-olefin copolymer rubber (a2) is preferably 0.84 to 0.94 g / cm ³ , and more preferably 0.86 to 0.92 g / cm ³ .

The ethylene / α-olefin copolymer rubber (a2) may be used alone or in combination of two or more, but the ethylene / α-olefin copolymer rubber (a2) as a whole may be used as described above. It is preferred to meet the MFR and density.

The ethylene / α-olefin copolymer rubber (a2) can be produced by a conventionally known method, but various commercially available products can also be used. As commercially available products, Toughmer A series / H series manufactured by Mitsui Chemicals, Engage series manufactured by Dow Inc., Exact series manufactured by Exxon, etc. can be preferably used.

Highly fluid homopolypropylene (a3);
The thermoplastic resin (A) may contain high-fluidity homopolypropylene (a3) together with various resins such as the high molecular weight component-containing impact polypropylene (a1) which is the base of the thermoplastic resin (A). good.

The MFR of the highly fluid homopolypropylene (a3) measured by ASTM D-1238 at 230 ° C. and a load of 2.16 kg is preferably 200 to 1000 g / 10 minutes, more preferably 220 to 800 g / 10 minutes, and further. It is preferably 240 to 700 g / 10 minutes. When the MFR of the highly fluid homopolypropylene (a3) is within the above range, the MFR of the obtained thermoplastic resin composition can be improved, and the fluidity can be further improved.

(Nitrogen gas-based foaming agent (B))
Examples of the nitrogen gas-based foaming agent (B) include supercritical or gaseous nitrogen and an organic foaming agent capable of generating nitrogen gas. Examples of the organic foaming agent include organic foaming agents.
For example, N-nitroso compounds such as N, N'-dinitrosopentamethylene, N, N'-dinitrosopentamethylenetetramine;
Azo compounds such as azodicarboxylic amide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, barium azodicarboxylate;
Sulfonyl hydrazide compounds such as benzenesulfonylhydrazide, toluenesulfonylhydrazide, p, p'-oxybis (benzenesulphenylhydrazide), diphenylsulphon-3,3'-disulfonylhydrazide; and calcium azide, 4,4'-diphenyldisulfonyl. Examples of azide compounds such as azide and p-toluenesulfonyl azide include azo compounds, which have the advantages of being nonflammable and self-extinguishing among organic foaming agents, and do not burn even when brought close to a flame and are being stored. Azodicarboxylic amide is particularly preferable from the viewpoint of being widely used and easily available.

When the foaming agent (B) is in the form of particles, the average particle size D ₅₀ is not particularly limited, but is, for example, 10 μm or less, preferably 1 to 8 μm.
The average particle size D ₅₀ is the particle size at the time of 50% accumulation in the cumulative distribution based on the volume, and is the average particle size measured by a commercially available laser particle size distribution meter.
The foaming agent (B) may be blended in the form of a masterbatch in which the foaming agent (B) is kneaded into the resin when the thermoplastic resin composition is prepared.

(Carbon dioxide gas-based foaming agent (C))
Examples of the carbon dioxide gas-based foaming agent (C) include supercritical or gaseous carbon dioxide and an inorganic foaming agent capable of generating carbon dioxide gas, and examples of the inorganic foaming agent include carbon dioxide gas.
Examples thereof include baking soda (sodium hydrogen carbonate), sodium carbonate, ammonium hydrogen carbonate, ammonium carbonate and the like, and baking soda is particularly preferable from the viewpoint of being non-toxic, odorless, easy to handle and excellent in storage stability.

When the foaming agent (C) is in the form of particles, the average particle size D ₅₀ is not particularly limited, but is, for example, 10 μm or less, preferably 1 to 8 μm.
The average particle size D ₅₀ is the particle size at the time of 50% accumulation in the cumulative distribution based on the volume, and is the average particle size measured by a commercially available laser particle size distribution meter.
The foaming agent (C) may be blended in the form of a masterbatch in which the foaming agent (C) is kneaded into the resin when the thermoplastic resin composition is prepared.

<< Ratio of foaming agent >>
In the thermoplastic resin composition, the foaming agent (B) and the foaming agent (C) have a (mass of the foaming agent (B)) / (mass of the foaming agent (C)) of 1/100 or more, 15 It is contained in a ratio of less than / 100, preferably 4/100 to 13/100.
If this ratio is less than 1/100, the effect of miniaturizing the cells of the foamed molded product tends not to appear, and if this ratio exceeds 15/100, the appearance of the foamed molded product tends to deteriorate.

(Optional ingredient)
The thermoplastic resin composition may contain components that are usually contained in a thermoplastic resin composition for foam molding, particularly injection foam molding.
Examples of such optional components include inorganic fillers and various additives.

Inorganic filler;
The inorganic filler is not particularly limited, but for example, heavy calcium carbonate, light calcium carbonate, talc, glass fiber, magnesium carbonate, mica, kaolin, calcium sulfate, barium sulfate, titanium white, white carbon, carbon black, water. Aluminum oxide, magnesium hydroxide, clay, magnesium oxide, silicates, carbonates, plaster, wallanite, alumina, silica, calcium sulfate, carbon fiber, metal fiber, silica sand, zeolite, molybdenum, silica soil, sericite, Examples thereof include silas, calcium hydroxide sodium sulfate, bentonite, and graphite. These may be used alone or in combination of two or more. Of these, talc is the most preferred.

The average particle size D ₅₀ of the inorganic filler is not particularly limited, but is preferably 0.5 μm or more and 20 μm or less, and more preferably 1.0 μm or more and 15 μm or less.
The average particle size D ₅₀ is the particle size at the time of 50% accumulation in the cumulative distribution based on the volume, and is the average particle size measured by a commercially available laser particle size distribution meter.

Various additives;
The thermoplastic resin composition may contain various additives as long as its effect is not impaired. Examples of the additive include a crystal nucleating agent, an antioxidant, a hydrochloric acid absorber, a heat-resistant stabilizer, a weather-resistant stabilizer, a light stabilizer, an ultraviolet absorber, a lubricant, an antistatic agent, a flame retardant, a pigment, a dye, and a dispersant. Examples thereof include copper damage inhibitors, neutralizers, plasticizers, cross-linking agents, peroxides, weld strength improvers, natural oils, synthetic oils, waxes and the like.

The ratio of each component in the thermoplastic resin composition is appropriately set. Taking the case where the high-mass component-containing impact polypropylene (a1), the ethylene / α-olefin copolymer rubber (a2), and optionally the inorganic filler are used as an example, the total amount of these three components is used. When it is 100 parts by mass,
The blending amount of the high molecular weight component-containing impact polypropylene (a1) is usually 48 to 90 parts by mass, preferably 53 to 87 parts by mass, and more preferably 57 to 85 parts by mass;
The blending amount of the ethylene / α-olefin copolymer rubber (a2) is usually 10 to 30 parts by mass, preferably 13 to 27 parts by mass, and more preferably 14 to 25 parts by mass;
The blending amount of the inorganic filler is usually 0 to 22 parts by mass, preferably 0 to 20 parts by mass, and more preferably 1 to 18 parts by mass.

Further, the high molecular weight component-containing impact polypropylene (a1) is composed of the impact polypropylene (a11) and the high molecular weight component-containing homopolypropylene (a12), and the impact polypropylene (a11) and the high molecular weight component-containing homopolypropylene (a12) are formed. ), The ethylene / α-olefin copolymer rubber (a2), and optionally the inorganic filler are used as an example. When the total amount of these four components is 100 parts by mass,
The blending amount of the impact polypropylene (a11) is usually 46 to 88 parts by mass, preferably 50 to 84 parts by mass, and more preferably 54 to 82 parts by mass;
The blending amount of the high molecular weight component-containing homopolypropylene (a12) is usually 2 to 15 parts by mass, preferably 3 to 12 parts by mass, and more preferably 3 to 10 parts by mass;
The blending amount of the ethylene / α-olefin copolymer rubber (a2) is usually 10 to 30 parts by mass, preferably 13 to 27 parts by mass, and more preferably 14 to 25 parts by mass;
The blending amount of the inorganic filler is usually 0 to 22 parts by mass, preferably 0 to 20 parts by mass, and more preferably 1 to 18 parts by mass.

When the highly fluid homopolypropylene (a3) is used, the blending amount thereof is usually 5 to 25 parts by mass based on the above criteria.
The total content of the organic foaming agent (B) and the inorganic foaming agent (C) in the thermoplastic resin composition is a gas generated from the foaming agent, depending on the required properties of the foamed molded product to be produced. It is selected in consideration of the amount, the desired foaming ratio, and the like, but is preferably 0.5 to 10% by mass, and more preferably 1.0 to 5.0% by mass. When the content is in the above range, it is possible to obtain a foamed molded product having the same bubble diameter and uniformly dispersed bubbles.

<Preparation of thermoplastic resin composition>
The thermoplastic resin composition is prepared, for example, by mixing or melt-kneading each component with a mixing device such as a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, or an injection molding machine. Can be done. The mixing order of each component is arbitrary, and they may be mixed at the same time, or a multi-step mixing method such as mixing a part of the components and then mixing the other components may be adopted. As an example of the multi-step mixing method, first, components other than the foaming agent (B) and the foaming agent (C) (these may be master batches) are mixed to form a composition (hereinafter, "base"). A method of preparing the composition (also referred to as “composition”) and then mixing the base composition with the foaming agent (B) and the foaming agent (C) can be mentioned.

The foaming agent (B) itself may be mixed with the base composition or the thermoplastic resin (A), and a masterbatch of the foaming agent (B) may be mixed with the base composition or the thermoplastic resin (A). It may be mixed.

Similarly, the foaming agent (C) itself may be mixed with the base composition or the thermoplastic resin (A), and a masterbatch of the foaming agent (C) may be mixed with the base composition or the thermoplastic resin (A). It may be mixed with A).

The resin constituting the masterbatch may be the thermoplastic resin (A), or may be a resin different from the thermoplastic resin (A).
Specific examples of the method for preparing the thermoplastic resin composition include
(I) A method of dry-blending the thermoplastic resin (A) or the base composition with the foaming agent (B) and the foaming agent (C).
(Ii) A method of supplying the foaming agent (B) and the foaming agent (C) to the thermoplastic resin (A) or the base composition being melt-kneaded in a molding machine (preferably an injection molding machine).
(Iii) The thermoplastic resin (A) or the base composition is dry-blended with a part of the foaming agent (B) and the foaming agent (C), and then the obtained mixture is molded by a molding machine (preferably). , An injection molding machine) to supply the foaming agent (B) and the rest of the foaming agent (C) into the mixture while melting and kneading.

In the methods (i) and (iii), each component to be subjected to the dry blend is preferably in the form of pellets (in the case of the foaming agent (B) and the foaming agent (C), the pellet-shaped masterbatch). is there. Dry blending is usually done before feeding each component to a molding machine (preferably an injection molding machine).

Further, in the methods (ii) and (iii), the foaming agent (B) and / or the foaming agent (C) is added to the resin (that is, the thermoplastic resin (A) or the base resin) being melt-kneaded. As a method of supplying the foaming agent (that is, the foaming agent (B) and / or the foaming agent (C)) in a gas state or a supercritical state by making a hole in the heating cylinder of the injection molding machine. Can be mentioned as a method of pouring the resin into the resin being melt-kneaded.

<Foam molding of thermoplastic resin composition>
The method for producing a foam molded product of the present invention includes a step (I) of foam molding the thermoplastic resin composition.
The step (I) is preferably a step of injection-foaming the thermoplastic resin composition.
In injection foam molding, the thermoplastic resin composition is melt-kneaded under the condition that the thermoplastic resin (A) melts, injection-filled from the injection molding machine into the cavity of the mold, and then the volume of the cavity is increased. This is performed by foaming the thermoplastic resin composition to produce a foamed molded product.

The molding die used for injection foam molding is composed of a fixed mold and a movable mold, and these are preferably in a mold compaction state at the time of injection filling of the thermoplastic resin composition. Further, the volume of the cavity is generally increased by retracting the movable mold (core back) to expand the cavity, but it can also be increased by moving a part of the mold. In particular, it is preferable to move the movable mold after an appropriate time after injection filling to increase the cavity volume.

The initial position of the movable type is the position when the fixed type and the movable type are closest to each other and are in the mold clamping state to which the mold clamping force is applied. A cavity close to the product shape is formed at a place where the volume of the melt of the thermoplastic resin composition used for one molding has a volume substantially equal to the volume filled in the unfoamed state.

It is also possible to make the initial cavity volume narrower than the resin to be filled and expand it to the filling amount by resin pressure at the time of filling or by controlling the molding machine, and then expand the cavity volume and foam it. It is also possible to expand the initial cavity volume by making it wider than the resin to be filled, reducing the cavity volume during or after filling the resin, and then expanding the cavity volume in order to carry out this foam molding. It is one of the methods.

The expansion direction length at the start of injection formed between the fixed mold and the movable mold, that is, the cavity clearance (T ₀ ) of the mold at the start of injection is usually 0.7 mm or more and less than 1.5 mm, preferably 0. It is set in the range of 7. mm or more and 1.4 mm or less, more preferably 0.9 mm or more and 1.4 mm or less.

When the cavity clearance (T ₀ ) is equal to or higher than the above lower limit value, a sufficient cavity for injection filling can be secured, and the thermoplastic resin composition is introduced into the cavity due to an increase in viscosity or solidification of the thermoplastic resin composition. It is possible to prevent the inability to supply and fill sufficiently. Therefore, it is possible to reduce forcibly injection filling at high pressure in order to sufficiently fill the cavity with the thermoplastic resin composition, and burrs are generated due to the high injection filling pressure, and the resin composition is formed by the mold. It is possible to prevent the foaming from becoming defective due to rapid cooling and core backing without sufficient foaming.

The injection time of the thermoplastic resin composition into the cavity of the mold is not particularly limited, but is preferably 0.4 to 5.0 seconds, more preferably about 0.6 to 4.0 seconds. A delay time of 0 to 5 seconds, more preferably 0 to 3 seconds is provided after the injection is completed, and then the partition wall constituting the cavity is preferably set to 1 to 100 mm / sec, more preferably 1 to 1. It is desirable to expand the cavity volume by moving (core back) at 50 mm / sec. By providing this delay time, the thickness of the solid skin layer can be controlled, and when the delay time is lengthened, the solid skin layer can be made thicker, and as a result, mechanical properties such as rigidity can be improved. Here, it is desirable that the expansion ratio of the cavity volume is usually 1.9 to 6.0 times, preferably 2.0 to 5.0 times.

In the foaming for expanding the cavity volume performed in the present invention, the expansion ratio basically changes with the expansion rate of the cavity volume, but under the condition that the foaming gas is large, the expansion rate of the cavity is 1.9. It is possible to achieve a foaming ratio of 2.0 times or more even if it is doubled.

Further, the core back amount is preferably 2.0 to less than 4.0 mm, more preferably 2.2 to 3.5 mm. When the amount of core back is within the above range, a foam molded product having a small cell diameter can be manufactured. On the other hand, if the core back amount is larger than the above range, cracks may occur near the center of the foamed molded product.

Further, T ₀ and the ratio (T ₁ / T ₀₎ between the expansion direction length of the cavity of the section after the movable mold retracted (T ₁₎ is preferably 1.9 to 6.0, more preferably 2. It is 0 to 5.0. When T ₁ / T ₀ is at least the above lower limit value, the desired rigidity can be efficiently obtained.

The core moving speed at the time of core back varies depending on the thickness of the molded product, the type of resin, the type of foaming agent, the mold temperature, and the resin temperature, but is preferably about 1.0 to 50 mm / sec, for example. When the core moving speed is at least the above lower limit value, it is possible to prevent the resin from solidifying in the middle of the core back and not obtaining a sufficient foaming ratio. When the core moving speed is not more than the above upper limit value, it is possible to prevent the generation and growth of cells from following the movement of the core, causing the cells to break and not obtaining a molded product having a good appearance.

The temperature and mold temperature of the thermoplastic resin composition to be injected vary depending on the thickness of the molded product, the type of resin, the type and amount of foaming agent added, etc., but are the temperatures usually used for molding the thermoplastic resin composition. Is sufficient, and when a product having a thin product thickness and a product having a high foaming ratio is obtained, it is preferable to set the temperature higher than the normal mold temperature.
Specifically, the temperature of the thermoplastic resin composition to be injected is preferably 170 to 250 ° C, more preferably 180 to 230 ° C.

The temperature of the fixed mold and the movable mold at the time of injection is preferably 25 to 80 ° C, more preferably 30 to 70 ° C.
Moreover, the injection rate of the injection molding machine in the filling of the thermoplastic resin composition into the mold, is preferably 100~2,000cm ³ / sec, more preferably 200~1,500cm ³ / sec .. The injection pressure of the injection molding machine at this time is preferably 70 to 200 MPa, more preferably 80 to 160 MPa.

As described above, by filling the cavity with the thermoplastic resin composition at a time and then foaming it, the resin in the portion in contact with the mold solidifies faster than the resin inside, and the surface of the polypropylene-based foam molded product is formed. An unfoamed skin layer (solid skin layer) can be formed.

Further, even if some distribution occurs in the cell shape, cell density, and foaming ratio inside the foamed molded product, a molded product having a good appearance can be obtained due to the smoothness and rigidity of the solid skin layer. The thickness of this solid skin layer is not particularly limited, but is preferably 0.1 to 0.5 mm, more preferably 0.2 to 0.45 mm.

The timing at which the mold actually starts to open in the core back for forming the solid skin layer of the above thickness varies depending on the type of resin, the type of foaming agent, the mold temperature, and the resin temperature, but it is a normal thermoplastic resin composition. When a material is used, it is preferably more than 0 seconds and 5 seconds or less from the completion of injection filling, and more preferably more than 0 seconds and 3 seconds or less.

When the time from the completion of injection filling to the core back is at least the above lower limit value, a skin layer having a sufficient thickness can be generated, and when it is at least the above upper limit value, the solidification of the thermoplastic resin composition proceeds. It can be suppressed and a sufficient foaming ratio can be obtained.

The foaming ratio can be appropriately controlled by the resin temperature, injection speed, waiting time from the end of injection filling to the start of core back, the amount of core back, the core back speed, the cooling time after the end of core back, and the like. Further, the core back can be performed in several stages, whereby a foam molded product having a controlled cell structure and end shape can be obtained.

Further, in the present invention, a hot runner, a shut-off nozzle, a valve gate and the like used in ordinary injection molding can also be used. The valve gate and hot runner not only suppress the generation of waste resin such as the runner, but also have the effect of preventing the occurrence of defects in the foamed molded product in the next cycle by leaking the thermoplastic resin composition from the inside of the mold into the cavity. ..

Further, in the present invention, various steel materials used in general molds can be used on one side or both sides of the cavity of the mold, and the present invention is not particularly limited, but particularly from the general structural rolled steel material SS400 and the carbon steel steel material S45C. It is preferable to arrange a material having a low thermal conductivity in order to produce a foamed molded product having an excellent appearance, and the thermal conductivity is 0.18 to 40 W / m · K, preferably 0.18 to 36 W / m · K. It is more preferable to arrange a heat insulating layer of K, more preferably 0.18 to 33 W / m · K. It is desirable to use various heat-resistant resins and ceramics such as zirconia, alumina, and silicon nitride for this heat insulating layer. However, if the thermal conductivity is within the above range, it is one of the desirable forms to use a metal or the like containing a different element. The thickness of the heat insulating layer itself is not strict, but if it is in the form of a thin film of about 0.01 to 0.5 mm, the filled thermoplastic resin composition can be instantaneously delayed in cooling, and the foam molded product The appearance of the can be further improved. Even if a member having a thermal conductivity higher than the above is used on the cavity surface, it is also one of the desirable methods to use a member in which members are laminated to reduce the average thermal conductivity from the cavity surface layer to a depth of 5 mm. ..

After the completion of foaming, the foamed molded product may be taken out by cooling as it is, and the molding cycle may be shortened by controlling the contact state between the foamed molded product and the mold by slightly molding and promoting cooling. A foam molded product having a good dent and cell shape may be obtained.

In the method for producing a foamed molded product of the present invention, for example, a foamed molded product having a thickness of about 1.2 to 8 mm can be preferably obtained. When this foamed molded product has closed cells, the average cell diameter measured by the method adopted in the examples described later is about 0.01 to 0.20 mm, but depending on the shape of the molded product and the application, the number may be several. Even if the cell diameter is mm, the average cell diameter as a whole may satisfy the above value even if a part of the cells is communicated with each other.

[Foam molding]
The foamed molded product of the present invention can be produced by the production method of the present invention described above. The foamed molded product of the present invention is a foamed molded product of the thermoplastic resin composition, and the foaming ratio thereof is preferably 2.0. More than double. The lower limit of the foaming ratio is more preferably 2.2 times, still more preferably 2.4 times, from the viewpoint of rigidity improving effect and weight reduction. The upper limit of the foaming ratio is preferably 6 times, more preferably 5 times, from the viewpoint of preventing continuous foaming of the foam cells in the center of the molded body or cracking in the center of the molded body. This foaming ratio is confirmed at the site where the "post-foaming molded body thickness / pre-foaming resin filling thickness" ratio is the largest when injection molding is performed.

The foaming ratio is defined as follows.
Foaming ratio = ρ _s / ρ _f
[In the above formula, ρ _f is the apparent specific gravity of the foam molded product (the specific gravity of the composite of the solid skin layer and the foam layer).
ρ _s is the specific gravity of the foamed molded product that has been melted and then pressure-cooled (in the unfoamed state). ]
However, only when the molded body is a flat plate manufactured by injection foam molding.
Foaming ratio = T _f / T _s
[In the above formula, T _s is the thickness of the molded product (initial thickness of the cavity) obtained without expanding the cavity volume of the mold.
T _f is the actual thickness of the foamed part. ]
May be defined as.

Although the foamed molded product of the present invention has a high foaming ratio, the cells are fine, the appearance is good, and the odor of ammonia is suppressed.
In the foam molded product of the present invention, since the cell is fine, fracture (buckling) of the cell wall is suppressed, and the cell has a high closed cell property. Therefore, the foam molded product of the present invention has high compressive strength. Further, in the foam molded product of the present invention, the cell is fine, so that the cell uniformity is high. As described above, since the foam molded product of the present invention has high compressive strength and high cell uniformity, it can be applied to a large foam molded product that was conventionally impossible or difficult to mold.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
[Measurement or evaluation method]
The measurement or evaluation method of the foam molded product is as follows.
(Expansion ratio)
Since the shape of the foam molded product produced in Examples and the like was a flat plate, the foaming ratio was calculated by the following formula.
Foaming ratio = T _f / T _s
[In the formula, T _s is the initial cavity thickness (1.3 mm) and T _f is the actual thickness of the foamed part. ]

(Cell diameter)
The vicinity of the center of the foam molded product was cut in the thickness direction, and the obtained cross section was photographed with a stereomicroscope or the like. From the enlarged image, 10 or more cells existing in the plate thickness direction are picked up at almost regular intervals, the average diameter which is the average value of the major axis and the minor axis of each picked-up cell is calculated, and further, the average diameter of each cell is calculated. The average value of the average diameter was calculated and used as the cell diameter.

(Appearance (swirl mark, amount of streaks))
The molded product was visually observed, and the appearance of the molded product was evaluated by the amount of swirl marks and streaks.
The meanings of the symbols in Table 2 are as follows.
◯: No swirl marks or streaks were observed.
X: Swirl marks and / or streaks were observed.

(Appearance (Abata, surface deformation))
The molded product was visually observed, and the appearance of the molded product was evaluated based on the amount of avatar and the presence or absence of surface deformation. The meanings of the symbols in Table 2 are as follows.
◯: No deformation of the avatar and the surface of the molded product was observed.
Δ: Deformation of the avatar and the surface of the molded product was not observed, but slight waviness was observed on the surface.
X: Deformation of the avatar and / or the surface of the molded product was observed.

(Ammonia odor)
The presence or absence of ammonia odor during molding was confirmed at a distance of 50 cm from the color changing resin at the time of color change. The meanings of the symbols in Table 2 are as follows.
◯: There was no ammonia odor.
X: There was an ammonia odor.

[Preparation Example 1] (Preparation of Base Composition 1)
A composition having the composition shown in Table 1 (hereinafter referred to as “base composition 1”) was produced according to the description of Example 9 of International Publication No. 2010/050509.

[Example 1]
20% by mass of azodicarbonamide (hereinafter referred to as "ADCA"), which is a foaming agent, so that the amount of the foaming agent component is 0.1% by mass with respect to the base composition 1 obtained in Preparation Example 1. Including master batch (manufactured by Eiwa Kasei Kogyo Co., Ltd., POLYTHLENE® (Polyslen) EE206, hereinafter referred to as "azo-based foaming agent MB"), and the foaming agent component so as to be 2.5 parts by mass. , A master batch containing 50% by mass of a foaming agent, Boso (POLYTHLENE EE515 manufactured by Eiwa Kasei Kogyo Co., Ltd., hereinafter referred to as "Boso-based foaming agent MB") is dry-blended to form a thermoplastic resin composition. A product was obtained (the amount of the obtained composition is 100% by mass). Next, the obtained composition was put into a hopper of an injection molding machine and injection foam molded under the following conditions to obtain a foam molded product.
・ Equipment Injection molding machine: 350t injection molding machine (Ube Machinery Co., Ltd., MD350S-III)
Mold: 400 x 200 square sheet metal mold (center 1 point direct gate)
Cavity initial thickness (initial thickness is the distance between the cavity surface of the fixed mold and the movable mold before filling the resin composition): 1.3 mm,
Cavity material: SCM steel, foam molding conditions Injection temperature: 190 ° C
Mold temperature: 60 ° C
Injection rate: 255 cm ³ / s (rate of fire: 160 mm / s)
Initial filling thickness: 1.3 mm

Claims (8)

The step (I) of foam-molding a thermoplastic resin composition containing a thermoplastic resin (A), a nitrogen gas-based foaming agent (B) and a carbon dioxide gas-based foaming agent (C) is included.
A method for producing a foamed molded product in which (mass of the foaming agent (B)) / (mass of the foaming agent (C)) is 1/100 or more and less than 15/100. The foam molding according to claim 1, wherein the foaming agent (B) is an organic foaming agent capable of generating nitrogen gas, and the foaming agent (C) is an inorganic foaming agent capable of generating carbon dioxide gas. How to make a body. The foaming according to claim 1 or 2, wherein the total content of the organic foaming agent (B) and the inorganic foaming agent (C) in the thermoplastic resin composition is 0.5 to 10% by mass. A method for manufacturing a molded product. The method for producing a foamed molded product according to claim 2 or 3, wherein the organic foaming agent (B) is an azodicarbonamide. The method for producing a foamed molded product according to any one of claims 2 to 4, wherein the inorganic foaming agent (C) is baking soda. The method for producing a foamed molded product according to any one of claims 1 to 5, wherein the thermoplastic resin (A) contains a propylene-based polymer. The method for producing a foamed molded product according to any one of claims 1 to 6, wherein the step (I) is a step of injection-foaming the thermoplastic resin composition. The method for producing a foamed molded product according to any one of claims 1 to 7, wherein in the step (I), the thermoplastic resin composition is foam-molded so that the foaming ratio is 2.0 times or more. ..