JP2011074152A - Prefoamed particle and process for producing the same - Google Patents

Abstract

It is an object of the present invention to provide a method for suppressing a decrease in thermal fusion between expanded particles, thereby suppressing a decrease in mechanical strength of an in-mold foam molded product.
SOLUTION: In-mold foam molding having a foaming ratio of 5 to 60 times, a porosity of 10 to 30%, a sound absorption rate of 0.3 or more, a bending break point displacement of 10 mm or more, and a dimensional change rate of 1.5% or less. A method for producing pre-foamed particles used in the production of a body, comprising a foaming agent and having a mass ratio of 20/80 to 50/50 and derived from composite resin particles of polypropylene resin and polystyrene resin The above-mentioned problems are solved by a method for producing pre-expanded particles, characterized in that the pre-expanded particles are obtained by pre-expanding the particles and then preparing the residual foaming agent amount to be reduced to 0 to 3% by mass.
[Selection figure] None

Description

  The present invention relates to pre-expanded particles and a method for producing the same. More specifically, the present invention relates to pre-expanded particles for producing an in-mold foam molded product having specific physical properties and a method for producing the same. The pre-expanded particles of the present invention are suitable for uses that require shock absorption and sound absorption, for example, for the production of vehicle shock absorbers.

The in-mold foam molded body is used as a sound absorbing material by forming a void. An in-mold foam-molded article having a void is described in, for example, Japanese Patent Application Laid-Open No. 7-80873 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2008-239793 (Patent Document 2).
According to Japanese Patent Application Laid-Open No. 7-80873, pre-expanded particles are heated and foamed, and the particles are provided with a porosity derived from a space of 10 to 40% between the particles while thermally fusing between the particles. A method for obtaining an in-mold foam molded article is described.
Japanese Patent Application Laid-Open No. 2008-239793 discloses that the particle surface absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) is in the range of 0.1 to 2.5, and 100 parts by mass of the polyolefin resin component and 100 to styrene resin component. A method for obtaining an in-mold foam molded article having a porosity derived from a space of 5 to 50% of particles while thermally foaming pre-foamed particles containing 400 parts by mass and thermally fusing the particles together Is described.

Japanese Patent Laid-Open No. 7-80873 JP 2008-239793 A

  In order to increase the porosity of the in-mold foam molded product, it is necessary to suppress secondary foaming of the pre-foamed particles during molding. As a method of suppressing secondary foaming, there are a method of lowering the steam temperature during molding and a method of shortening the heating time. However, since both methods are methods in which the foaming pressure of the pre-foamed particles is lowered, there is a problem that the thermal fusion between the foamed particles is lowered, and the mechanical strength of the obtained in-mold foam molded product is lowered. It was.

  The inventors of the present invention have studied a method for suppressing a decrease in thermal fusion between foamed particles and thereby suppressing a decrease in mechanical strength of the in-mold foam molded product, and the amount of residual foaming agent is reduced. When the in-mold foam molded body is formed using the pre-expanded particles prepared as described above, the present invention has been found by surprisingly finding that the suppression is possible.

Thus, according to the present invention, a mold having a foaming factor of 5 to 60 times, a porosity of 10 to 30%, a sound absorption rate of 0.3 or more, a bending break point displacement of 10 mm or more, and a dimensional change rate of 1.5% or less. A method for producing pre-expanded particles used for the production of an inner foam molded article,
Foamable resin particles containing a foaming agent and having a mass ratio of 20/80 to 50/50 and derived from a composite resin particle of a polypropylene resin and a polystyrene resin are prefoamed, and then the amount of residual foaming agent is 0 to 3% by mass. A method for producing pre-expanded particles is provided, characterized in that the pre-expanded particles are obtained by preparing the particles so as to be reduced to a minimum.

  Further, according to the present invention, expandable resin particles derived from a composite resin particle of a polypropylene resin and a polystyrene resin containing a foaming agent and having a mass ratio of 20/80 to 50/50 are pre-foamed, and then the residual foam is formed. Pre-expanded particles obtained by adjusting the amount of the agent to 0 to 3% by mass, wherein the pre-expanded particles are 5 to 60 times expanded, 10 to 30% porosity, Pre-expanded particles for use in the production of in-mold foam molded articles having a sound absorption of 3 or more, a bending break point displacement of 10 mm or more and a dimensional change rate of 1.5% or less are provided.

  The present invention pre-foams expandable resin particles derived from composite resin particles of a polypropylene resin and a polystyrene resin containing a foaming agent and having a mass ratio of 20/80 to 50/50, and then the amount of residual foaming agent is reduced to 0. It is a method of obtaining pre-expanded particles by preparing to reduce to ˜3% by mass. The pre-expanded particles obtained by this method have an expansion ratio of 5 to 60 times, a porosity of 10 to 30%, a sound absorption rate of 0.3 or more, a bending break point displacement of 10 mm or more, and a dimension of 1.5% or less. An in-mold foam molded product with a change rate can be obtained efficiently.

Further, when the pre-expanded particles have a surface with an absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) of 0.1 to 2.5, it is possible to provide in-mold foam molding in which fusion between the expanded particles is more securely secured. .
Furthermore, if the in-mold foamed molded body is laminated with an exterior material made of nonwoven fabric or felt and used as an interior part for vehicles, it has shock absorption and noise reduction, and noise reduction due to excellent friction and force of the exterior material. Parts can be provided.

The pre-foamed particle production method of the present invention pre-foams expandable resin particles containing a foaming agent and derived from a composite resin particle of a polypropylene resin and a polystyrene resin, and then the amount of the remaining foaming agent is 0 to 3% by mass. And a step of preparing to reduce the amount.
The pre-expanded particles used in this step are obtained by pre-expanding expandable resin particles containing a foaming agent. Expandable resin particles used in the foaming step are obtained by impregnating resin particles with a foaming agent.

(1) Foaming agent Various known volatile foaming agents can be used as the foaming agent. For example, butane, pentane (normal pentane, isopentane alone or as a mixture, industrial pentane), petroleum ether, cyclohexane, cyclopentane, hexane and the like can be mentioned.
As content of a foaming agent, it is preferable that it is 7.5-13 mass% with respect to an expandable resin particle. When the content of the foaming agent is less than 7.5% by mass, the foamability of the foamable resin particles may be lowered. When the foamability is lowered, it becomes difficult to obtain low-bulk density pre-expanded particles having a high bulk ratio, and the in-mold foam-molded product obtained by molding the pre-expanded particles in the mold has a reduced fusion rate, resulting in resistance to resistance. Crackability may be reduced. On the other hand, when it exceeds 13% by mass, pre-expanded particles having a low bulk density of 65 times or more can be obtained. However, the bubble size in the pre-expanded particles tends to be excessive, and the moldability and the strength characteristics such as compression and bending of the obtained in-mold foam molded product may be deteriorated. A more preferable foaming agent content is in the range of 8.0 to 12.5% by mass.

  Further, a foaming aid may be used. Examples of the foaming aid include solvents such as toluene, xylene, ethylbenzene, cyclohexane, and d-limonene, and plasticizers (high boiling solvents) such as diisobutyl adipate, glycerin, diacetylated monolaurate, and coconut oil. In addition, as addition amount of a foaming adjuvant, 0.5-10 mass parts is preferable with respect to 100 mass parts of resin particles.

(2) Resin Particles The resin constituting the resin particles is not particularly limited as long as it is a resin that can form pre-foamed particles and can be subjected to in-mold foam molding. As the resin particles, composite resin particles of polypropylene resin and polystyrene resin are used. As composite resin particles of polypropylene resin and polystyrene resin, resin particles mixed with polypropylene resin and polystyrene resin, seed particles (micropellets) made of polypropylene resin are impregnated (absorbed) with styrene monomer Then, resin particles (hereinafter, also referred to as modified resin particles) obtained by polymerization are exemplified. Of the resin particles, modified resin particles are preferred. Hereinafter, the modified resin particles will be described.

  Examples of polystyrene resins include resins derived from styrene monomers. As the styrene monomer, any of styrene and substituted styrene (substituent includes lower alkyl, halogen atom (especially chlorine atom) and the like) can be used. Examples of the substituted styrene include chlorostyrenes, vinyltoluenes such as p-methylstyrene, and α-methylstyrene. Of these, styrene is preferred. The styrene monomer is a mixture of styrene and substituted styrene, a small amount of other monomers copolymerizable with styrene (for example, acrylonitrile, alkyl methacrylate ester (the alkyl portion has about 1 to 8 carbon atoms). ), Mono- or dialkyl maleates (alkyl moieties of about 1 to 4 carbon atoms), divinylbenzene, mono- or diacrylic or methacrylic esters of ethylene glycol, maleic anhydride, N-phenylmaleide, etc.) it can. In these mixtures, styrene preferably occupies a dominant amount (for example, 50% by mass or more).

It does not specifically limit as a polypropylene resin, A well-known resin can be used. Moreover, the polypropylene resin may be crosslinked. Examples thereof include polypropylene resins such as a propylene homopolymer, an ethylene-propylene random copolymer, a propylene-1-butene copolymer, and an ethylene-propylene-butene random copolymer.
Of the resin particles, modified resin particles are preferred. Hereinafter, the modified resin particles will be described.

The content of the polypropylene resin and the polystyrene resin constituting the modified resin particles is 20/80 to 50/50 in terms of the mass ratio of the polypropylene resin and the polystyrene resin.
When the content of the polystyrene resin is more than 20/80, the polystyrene resin component has high retention of the foaming agent, and thus it may be difficult to reduce the amount of the foaming agent of the pre-expanded particles. On the other hand, when the ratio is less than 50/50, the diffusibility of the foaming agent is high, so that it is difficult to increase the bulk density of the pre-expanded particles and the bulk density may be difficult to adjust.

  The average particle diameter of the modified resin particles is preferably 800 to 2400 μm. The modified resin particles having an average particle size of less than 800 μm are required to reduce the average particle size of the raw material polypropylene resin particles. In that case, the yield of polypropylene resin particles may deteriorate and the cost may increase. If it exceeds 2400 μm, the pre-expanded particles become too large, and the pre-expanded particles tend to have poor filling properties in the mold when forming an in-mold expanded molded article having a complicated shape. A preferable average particle diameter is 1200-2000 micrometers.

  Seed particles made of polypropylene resin can be obtained by a known method. For example, seed particles can be prepared by first melt-extruding a polypropylene-based resin using an extruder and granulating by underwater cutting, strand cutting, or the like. Usually, the shape of the polypropylene resin used is, for example, a true sphere, an elliptic sphere (egg), a cylinder, a prism, a pellet, or a granular.

  The polypropylene resin may contain a radical scavenger. The radical scavenger may be added to the polypropylene resin in advance, or may be added simultaneously with melt extrusion. The radical scavenger is preferably a compound having an action of scavenging radicals such as a polymerization inhibitor (including a polymerization inhibitor), a chain transfer agent, an antioxidant, a hindered amine light stabilizer, and the like, which is hardly soluble in water. .

As the polymerization inhibitor, t-butylhydroquinone, paramethoxyphenol, 2,4-dinitrophenol, t-butylcatechol, sec-propylcatechol, N-methyl-N-nitrosoaniline, N-nitrosophenylhydroxylamine, triphenyl Phosphite, tris (nonylphenyl phosphite), triethyl phosphite, tris (2-ethylhexyl) phosphite, tridecyl phosphite, tris (tridecyl) phosphite, diphenyl mono (2-ethylhexyl) phosphite, diphenyl monodecyl phosphite Phyto, diphenyl mono (tridecyl) phosphite, dilauryl hydrogen phosphite, tetraphenyl dipropylene glycol diphosphite, tetraphenyl tetra ( Rideshiru) phenol-based polymerization inhibitor such as pentaerythritol diphosphite, nitroso-based polymerization inhibitor, an aromatic amine-based polymerization inhibitor, a phosphite-based polymerization inhibitor, a thioether-based polymerization inhibitor, and the like.
Examples of chain transfer agents include β-mercaptopropionic acid 2-ethylhexyl ester, dipentaerythritol hexakis (3-mercaptopropionate), tris [(3-mercaptopropionyloxy) -ethyl] isocyanurate, and the like. Is done.

  Antioxidants include 2,6-di-t-butyl-4-methylphenol (BHT), n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythris Lithyl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 3,9-bis [2- {3- (3-t- Butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, distearyl pentae Thritol diphosphite, tris (2,4-di-t-butylphenyl) phosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, tetrakis (2,4-di-t -Butylphenyl) 4,4'-biphenylenediphosphonite, bis (2-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, 2,4,8,10-tetra-tert-butyl-6- [3- (3-methyl-4-hydroxy-5-t-butylphenyl) propoxy] dibenzo [d, f] [1,3,2] dioxaphosphine, phenyl-1-naphthylamine, octylated diphenylamine, 4,4-bis (α, α-dimethylbenzyl) diphenylamine, N, N′-di-2-naphthyl-p-phenylenediamine, etc. Nord antioxidants, phosphorus antioxidants, etc., an amine-based antioxidant may be exemplified.

Examples of hindered amine light stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and bis (1 , 2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate and the like.
As a usage-amount of a radical scavenger, it is preferable that it is 0.005-0.5 mass part with respect to 100 mass parts of polypropylene resins.

  Polypropylene resins include, in addition, nucleating agents such as talc, calcium silicate, synthetically or naturally produced silicon dioxide, ethylene bis stearamide, methacrylic acid ester copolymers, triallyl isocyanurate hexabromide, etc. In addition, a colorant such as carbon black, iron oxide, and graphite may be included.

Next, the seed particles are dispersed in an aqueous medium in a polymerization vessel, and polymerization is performed while impregnating the styrene monomer with the seed particles.
Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol).
Impregnation of the seed particles with the styrene monomer may be performed while polymerizing, or may be performed before the polymerization is started. Of these, it is preferable to carry out the polymerization. In addition, when superposing | polymerizing after impregnating, superposition | polymerization of the styrene-type monomer near the surface of a seed particle occurs easily. In addition, the styrene monomer not impregnated in the seed particles is easily polymerized alone. As a result, a large amount of fine particle polystyrene resin particles may be generated.

When impregnating while polymerizing, the seed particles in the case of calculating the above content are particles composed of a polypropylene resin, an impregnated styrene monomer, and an impregnated polystyrene resin that has already been impregnated. Means.
In order to maintain the content at 0 to 35% by mass, the styrenic monomer can be continuously or intermittently added to the aqueous medium in the polymerization vessel. In particular, it is preferable to gradually add the styrene monomer to the aqueous medium. For the polymerization of the styrene monomer, an oil-soluble radical polymerization initiator can be used. As this polymerization initiator, a polymerization initiator generally used for the polymerization of styrene monomers can be used. For example, benzoyl peroxide, lauroyl peroxide, t-butyl peroxy octoate, t-hexyl peroxy octoate, t-butyl peroxy benzoate, t-amyl peroxy benzoate, t-butyl peroxybivalate, t- Butyl peroxyisopropyl carbonate, t-hexyl peroxyisopropyl carbonate, t-butyl peroxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t- Examples thereof include organic peroxides such as butyl peroxybutane, di-t-hexyl peroxide, and dicumyl peroxide, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These oil-soluble radical polymerization initiators may be used alone or in combination.

Various methods can be used as a method of adding the polymerization initiator to the aqueous medium in the polymerization vessel. For example,
(1) A method in which a polymerization initiator is dissolved and contained in a styrene monomer in a container different from the polymerization container, and the styrene monomer is supplied into the polymerization container.
(2) A solution is prepared by dissolving a polymerization initiator in a part of a styrene monomer, a solvent such as isoparaffin, or a plasticizer. A method of simultaneously supplying this solution and a predetermined amount of a styrenic monomer into a polymerization vessel,
(3) A dispersion in which a polymerization initiator is dispersed in an aqueous medium is prepared. Examples thereof include a method of supplying the dispersion and the styrene monomer into the polymerization vessel.
The amount of the polymerization initiator used is usually preferably 0.02 to 2.0% by mass based on the total amount of styrene monomer used.

  It is preferable to dissolve a water-soluble radical polymerization inhibitor in the aqueous medium. The water-soluble radical polymerization inhibitor not only suppresses the polymerization of the styrene monomer on the seed particle surface, but also prevents the styrene monomer floating in the aqueous medium from being polymerized alone. This is because the generation of fine resin particles can be reduced.

As the water-soluble radical polymerization inhibitor, a polymerization inhibitor that dissolves 1 g or more in 100 g of water can be used. For example, thiocyanate such as ammonium thiocyanate, zinc thiocyanate, sodium thiocyanate, potassium thiocyanate, aluminum thiocyanate Nitrate, mercapto Ethanol, monothiopropylene glycol, thioglycerol, thioglycolic acid, thiohydroacrylic acid, thiolactic acid, thiomalic acid, thioethanolamine, 1,2-dithioglycerol, 1,3-dithioglycerol, etc. Water-soluble sulfur-containing organic compounds, may be mentioned addition of ascorbic acid, ascorbic acid sodium or the like. Of these, nitrite is particularly preferable.
As the usage-amount of the said water-soluble radical polymerization inhibitor, 0.001-0.04 mass part is preferable with respect to 100 mass parts of water of an aqueous medium.

  In addition, it is preferable to add a dispersant to the aqueous medium. Examples of such a dispersant include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose, magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, and magnesium phosphate. And inorganic dispersants such as magnesium carbonate and magnesium oxide. Of these, inorganic dispersants are preferred.

  When an inorganic dispersant is used, it is preferable to use a surfactant in combination. Examples of such surfactants include dodecyl benzene sulfonic acid soda and α-olefin sulfonic acid soda.

The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for suspension polymerization of styrene monomers.
Further, the shape of the stirring blade is not particularly limited, and specifically, a paddle blade such as a V-shaped paddle blade, a fiddler blade, an inclined paddle blade, a flat paddle blade, a pull margin blade, a turbine blade, a fan turbine blade, etc. Examples include a turbine blade and a propeller blade such as a marine propeller blade. Of these stirring blades, paddle blades are preferred. The stirring blade may be a single-stage blade or a multi-stage blade. A baffle may be provided in the polymerization container.

  The temperature of the aqueous medium when polymerizing the styrene monomer in the seed particles is not particularly limited, but is preferably in the range of −30 to + 20 ° C. of the melting point of the polypropylene resin used. More specifically, 100 to 160 ° C is preferable, and 110 to 150 ° C is more preferable. Furthermore, the temperature of the aqueous medium may be a constant temperature from the start to the end of the polymerization of the styrenic monomer, or may be increased stepwise. When raising the temperature of an aqueous medium, it is preferable to make it raise at the temperature increase rate of 0.1-2 degree-C / min.

  Furthermore, when using seed particles made of a crosslinked polypropylene resin, the crosslinking may be performed in advance before impregnating the styrene monomer, or the seed particles are impregnated with the styrene monomer. It may be performed during the polymerization, or may be performed after impregnating and polymerizing the styrene monomer in the seed particles.

  Examples of the crosslinking agent used for crosslinking the polypropylene resin include 2,2-di-t-butylperoxybutane, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy. An organic peroxide such as hexane may be mentioned. In addition, a crosslinking agent may be individual or may be used together 2 or more types. Moreover, the usage-amount of a crosslinking agent has preferable 0.05-1.0 mass part normally with respect to 100 mass parts of seed particles.

  Examples of the method of adding the crosslinking agent include a method of directly adding the crosslinking agent to the polypropylene resin, a method of adding the crosslinking agent after dissolving it in a solvent, a plasticizer or a styrene monomer, and a method of adding the crosslinking agent to water. The method of adding after dispersing in, etc. is mentioned. Among these, a method of adding a crosslinking agent after dissolving it in a styrene monomer is preferable.

(3) Impregnation with foaming agent The resin particles are impregnated with a foaming agent by a known method to form foamable resin particles.
The method of impregnating the resin particles with the foaming agent can be appropriately changed according to the type of the foaming agent. For example, a foaming agent is pressed into an aqueous medium in which resin particles are dispersed, and the resin particles are impregnated with the foaming agent. The resin particles are supplied to a rotary mixer, and the foaming agent is pressed into the rotary mixer. And a method of impregnating the resin particles with a foaming agent. The temperature at which the resin particles are impregnated with the foaming agent is usually preferably 50 to 90 ° C.

(4) Production of pre-expanded particles Pre-expanded particles can be obtained by heating the expandable resin particles impregnated with the foaming agent using a heating medium such as water vapor so as to foam to a predetermined bulk density.
The pre-expanded particles have a bulk ratio of 5 to 60 times (bulk density 0.016 to 0.2 g / cm ³ ). A preferred bulk multiple is 10 to 55 times, and a more preferred bulk multiple is 30 to 45 times. When the bulk multiple is larger than 60 times, the closed cell ratio of the pre-expanded particles is lowered, and the strength of the in-mold foam molded product obtained by foaming the pre-expanded particles may be lowered. On the other hand, if it is less than 5 times, the mass of the in-mold foam molded product obtained by foaming the pre-foamed particles may increase.

  The average particle diameter of the pre-expanded particles is preferably in the range of 2.00 to 7.00 mm. When the particle diameter of the pre-expanded particles is less than 2.00 mm, a slight gap (middle between the male and female of the mold is used to eliminate the filling failure of the expanded particles when the expanded particles are sucked and filled during in-mold expansion molding. Cracking), but pre-expanded particles may spill out from this gap. When the particle diameter of the pre-expanded particles exceeds 7.00 mm, when the foamed particles are sucked and filled at the time of in-mold foam molding, the thin portion of the molding die may be poorly filled. A more preferable particle diameter is in the range of 3.00 to 5.50 mm.

  The cell thickness of the pre-expanded particles is preferably in the range of 1.0 to 20.0 μm. More preferably, the range of 2.5-13.0 micrometers is preferable. When the cell thickness of the pre-expanded particles is less than 1.0 μm, the cell thickness is too thin, so that the foaming pressure of the pre-expanded particles becomes weak at the time of in-mold foam molding, and sufficient heat-fusibility cannot be obtained. There is. Furthermore, since the cell thickness of the foamed particles constituting the in-mold foam-molded product becomes too thin, the appearance and mechanical strength of the obtained foamed resin-molded product may be lowered. In addition, when the cell thickness of the pre-expanded particles exceeds 20.0 μm, the cell thickness is too thick, and the amount of heat for melting the surface of the pre-expanded particles is too large at the time of in-mold foam molding. In some cases, heat fusion cannot be obtained. In addition, water vapor during molding does not easily pass through the foamed particles, the crystallinity in the foamed particles cannot be sufficiently increased, and the heat resistance of the in-mold foam molded product may not be sufficiently exhibited. .

  The bubble diameter of the pre-expanded particles is preferably in the range of 5 to 1500 μm. When the cell diameter of the pre-expanded particles is less than 5 μm, the cell diameter may be too small, and the foaming pressure of the pre-expanded particles may be reduced during in-mold foam molding, and heat fusion between the pre-expanded particles may easily occur. . When the bubble diameter exceeds 1500 μm, the bubble diameter is too large, and the appearance and mechanical strength of the obtained in-mold foam-molded product may be inferior. A more preferable bubble diameter is in the range of 10 to 600 μm.

  The cell thickness of the pre-expanded particles is a measured value of the cell thickness of the outermost surface layer of the pre-expanded particles, and the bubble diameter is an average value of the bubble diameters measured from the surface layer to the inside. The cell thickness and the cell diameter can be measured from a photograph obtained by cutting the pre-foamed particles with a razor and photographing the cut surface with a scanning electron microscope.

  Here, when the pre-expanded particles are composed of the modified resin particles, the absorbance ratio of the surface portion of the pre-expanded particles can be 0.1 to 2.5. By using this absorbance ratio, the content ratio of the polypropylene resin and the polystyrene resin in the surface portion of the pre-expanded particles is optimized, and the pre-expanded particles are sufficiently expanded without contraction during in-mold foam molding. It can be expected that heat fusion is integrated with pressure. The absorbance ratio is more preferably 1.5 to 2.4. Furthermore, in the in-mold foam molded product obtained by in-mold foam molding from the pre-foamed particles having the above-mentioned absorbance ratio, the foam particles constituting the mold contain moderately polypropylene resin on the surface thereof. Excellent chemical resistance, impact resistance and heat resistance.

(5) Residual foaming agent amount preparation The obtained pre-expanded particles are adjusted so that the residual foaming agent amount contained therein is reduced to 0 to 3 mass%. When the amount of the remaining foaming agent is more than 3% by mass, the secondary foaming property of the pre-foamed particles becomes large when foam-molding in the mold, and it becomes difficult to obtain a surface with unevenness. A preferable amount of the remaining foaming material is 0 to 2.8% by mass. In addition, the amount of residual foaming agents of general pre-expanded particles is 3.1% by mass or more.

  The amount of the foaming agent is not particularly limited, but can be adjusted as follows, for example. That is, the pre-foamed particles immediately after the pre-foaming are left to stand at room temperature for about 12 hours for aging, then transferred to a tough cloth or the like (perforated plastic bag or the like), and heated at 60 ° C. in an oven or the like (hot air dryer or the like). (50-80 ° C.) for several hours to several days. As a result of heating, the amount of the remaining foaming agent in the pre-expanded particles can be reduced to 0.0 to 3.0% by mass. Instead of this method, after the pre-foamed particles immediately after the pre-foaming are transferred to tough cloth or the like, the amount of the remaining foaming agent in the foamed particles is 0.0 to It can be reduced to 3.0% by mass.

(In-mold foam molding process)
In the present invention, since the amount of the remaining foaming agent in the pre-foamed particles is adjusted to 0 to 3% by mass, the secondary foaming force of the foamed particles is suppressed. In-mold foam molding is molding that uses the secondary foaming power of pre-expanded particles, and is usually performed by introducing water vapor into the mold. The mold used in this step has an inner mold corresponding to the desired shape of the molded body. The introduction of water vapor can be performed by a known method.
Here, the range of various physical property values of the in-mold foam-molded product can be set by adjusting the pressure of water vapor and the introduction time of water vapor. For example, the pressure of water vapor is preferably 0.13 to 0.25 MPa. The introduction time is preferably 20 to 60 seconds.

(In-mold foam molding)
The in-mold foam molded product produced from the pre-expanded particles of the present invention has an expansion ratio of 5 to 60 times, a porosity of 10 to 30%, a sound absorption rate of 0.3 or more, a bending break point displacement of 1 mm or more, and 1 It has various physical properties with a dimensional change rate of 5% or less. When the expansion ratio is less than 5 times, the mass of the in-mold foam molded article is not preferable. When the ratio is larger than 60 times, the closed cell ratio of the pre-expanded particles is lowered, so that shrinkage occurs during in-mold molding, and a good in-mold foam molded article cannot be obtained. Further, when the porosity is less than 10% and the sound absorption coefficient is less than 0.3, sufficient sound absorption may not be obtained. If it is larger than 30%, the strength of the in-mold foam molded product may be lowered. When the bending break point displacement is less than 10 mm and the dimensional change rate is more than 1.5%, the strength is not sufficient.

(Use of in-mold foam moldings)
The in-mold foam molded product can be used for applications such as cushioning materials (cushion materials) for home appliances, electronic parts, various industrial materials, food containers, sound absorbing materials, drainage materials, and the like. Moreover, it can also be used suitably as interior materials for vehicles, such as a core material of a bumper for vehicles, and a door interior cushioning material.
In particular, by laminating with an exterior material, it can be used as an interior material for a vehicle that requires more sound absorption.

Examples of the exterior material include a fiber material and a porous film. Among these, a fiber material that can further reduce noise caused by rubbing is preferable.
Examples of the fiber material include felt and nonwoven fabric. The kind of fiber material can be selected according to the use for which the laminated body of this invention is used. For example, those generally used in the field of automobiles can be used as appropriate. Specifically, recycled materials (for example, crushed products of urethane, cotton, chemical fibers, etc.) such as felt (for example, cotton, chemical fibers, etc., which are solidified with PET), polyurethane foam, nonwoven fabric, etc. Can be enumerated with PET resin, defibrated fibers, animal and plant fiber materials, glass wool, asphalt foams, and the like.
Examples of the laminating method of the exterior material and the in-mold foam molded body include a laminating method using an adhesive, a laminating method by melting the exterior material and / or the in-mold foam molded body, and the like.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Various measurement methods in the following examples are described below.
(Average particle diameter of resin particles)
Using a vernier caliper (manufactured by Mitutoyo Corporation), the particle diameter of 10 modified resin particles is measured. The average particle diameter means the average of 10 measured values.

(Measurement method of polystyrene resin ratio of pre-expanded particles)
The absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) is measured as follows.
That is, the infrared absorption spectrum is obtained by performing ATR infrared spectroscopic analysis on the surface of 10 randomly selected pre-expanded particles. In the measurement of the surface, the ATR prism is closely attached to the surface of each pre-expanded particle.
An absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) is calculated from each infrared absorption spectrum, and the minimum absorbance ratio and the maximum absorbance ratio are excluded. The arithmetic average of the remaining 8 absorbance ratios is taken as the absorbance ratio (D ₆₉₈ / D ₁₃₇₆ )). The absorbance ratio is measured by using, for example, a measuring apparatus sold under the trade name “Fourier Transform Infrared Spectrophotometer MAGMA 560” from Nicolet (currently Thermofisher). The PS ratio (mass%) is calculated from the absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) based on a calibration curve prepared in advance using a standard product.

A standard sample is obtained by the following method. First, a total of 2 g of a polystyrene resin and a polypropylene resin having the same composition as those contained in the pre-expanded particles to be measured so that the composition ratio (polystyrene resin / polypropylene resin) is the following ratio is precisely weighed.
Composition ratio (PS / PP; mass ratio): 0/10 = PP resin only, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 8 / 2, 10/0 = PS resin only This is heated and kneaded under the following conditions with a small injection molding machine and molded into a cylindrical shape having a diameter of 25 mm and a height of 2 mm to obtain a standard sample.

In addition, as a small-sized injection molding machine, it can shape | mold on the following conditions, for example using the thing sold by CSI with the brand name "CS-183".
Injection molding conditions: heating temperature 200 to 250 ° C., kneading time 10 minutes The absorbance ratio of the standard sample of the above ratio was measured with the measuring device, and the polystyrene resin ratio (mass%) and the absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) A calibration curve can be obtained by graphing the relationship.
The polystyrene resin ratio (mass%) of the pre-expanded particles is calculated based on the calibration curve.

(Method for measuring bulk density of pre-expanded particles)
The bulk density of the pre-expanded particles is measured as follows.
First, the pre-expanded particles 500 cm ^3, filled into the graduated cylinder to the scale of 500 cm ^3. When the graduated cylinder is visually observed from the horizontal direction and any pre-expanded particles reach a scale of 500 cm ³ , the filling of the pre-expanded particles into the graduated cylinder is terminated at that point.
Next, the mass of the pre-expanded particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, and the mass is defined as W (g).
Then, the bulk density of the pre-expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500
The bulk foaming factor is the reciprocal of the bulk density.

(Measurement method of average particle diameter of pre-expanded particles)
Using a vernier caliper (manufactured by Mitutoyo Corporation), the particle diameter of 10 pre-expanded particles is measured. The average particle diameter means the average of 10 measured values.

(Measurement method of average cell diameter of pre-expanded particles)
The average cell diameter of the pre-expanded particles is measured according to the test method of ASTM D2842-69. Specifically, the pre-expanded particles are cut so as to be approximately bisected, and the cut surface is enlarged and photographed 15 times using a scanning electron microscope (trade name “JSM-6360LV” manufactured by JOEL). .
Next, the photographed image is printed on A4 paper, and a straight line having a length of 60 mm is drawn at an arbitrary location. The average chord length (t) of the bubbles is calculated from the number of bubbles existing on the straight line by the following formula. calculate.

Average string length t = 60 / (number of bubbles × photo magnification)
When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. Also, if some of the bubbles come into point contact with a straight line, this bubble is included in the number of bubbles, and if both ends of the straight line are located in the bubble without penetrating the bubbles Includes the bubbles in which both ends of the straight line are located in the number of bubbles.

Based on the calculated average chord length t, the bubble diameter is calculated by the following equation.
Bubble diameter (mm) D = t / 0.616
Furthermore, the bubble diameter is calculated in the same manner as described above at any five locations in the photographed image. The average bubble diameter is an arithmetic average value of these bubble diameters.

(Method for measuring cell thickness of pre-expanded particles)
About 10 arbitrarily selected from the pre-foamed particles, a razor blade is used to bisect each of the planes through the center of each particle, and the outermost layer portion of one of the cut surfaces is scanned with an electron microscope JSM-6360LV. Using (NEC Corporation), create an image magnified 500 times. Thereafter, using the length measurement function, a 15 dotted line is arbitrarily drawn on the outermost non-foamed layer, and the thickness is measured. Each image is measured in the same manner, and the average value for a total of 10 images is defined as the cell thickness.

(Measurement method of residual gas amount of pre-expanded particles (residual foaming agent amount))
The residual gas amount of the pre-expanded particles is measured as follows.
Pre-expanded particles are weighed in an amount of about 20 mg, set at the cracking furnace entrance of a pyrolysis furnace PYR-1A manufactured by Shimadzu Corporation, and purged with helium for about 15 seconds to discharge the mixed gas at the time of sample setting. After sealing, the sample was inserted into a 200 ° C. core, heated for 120 seconds to release the gas, and the released gas was quantified using a gas chromatograph GC-14B (detector: TCD) manufactured by Shimadzu Corporation. Get quantity. The measurement conditions were: Polapack Q (80/100) 3 mmf × 1.5 m manufactured by GL Sciences Inc., column temperature (100 ° C.), carrier gas (helium), carrier gas flow rate (1 ml / min), inlet temperature (120 ° C.) and detector temperature (120 ° C.).

(Measuring method of density of in-mold foam molding)
The density of the in-mold foam molded product is measured as follows.
Measured by the method described in JIS K7222: 2005 "Foamed plastics and rubbers-Measurement of apparent density".
A test piece of 50 cm ³ or more (100 cm ³ or more in the case of semi-hard and soft materials) is cut so as not to change the original cell structure of the material, its mass is measured, and the density is calculated by the following formula.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
A test specimen for measurement was cut from an in-mold foam molded article that had passed 72 hours or more after molding, and was subjected to atmospheric conditions of 23 ° C. ± 2 ° C. × 50% ± 5% or 27 ° C. ± 2 ° C. × 65% ± 5% for 16 hours That's what I left.
The expansion factor is the reciprocal of the density.

(Measurement method of sound absorption coefficient)
The sound absorption coefficient is measured in accordance with ISO 10534-2 (Determination of sound absorption coefficent and Impedance in impulse tubes Part 2: Transfer-function method) and ASTM E 1050.

That is, using a normal incidence sound absorption coefficient measurement system 4206 type acoustic impedance tube (manufactured by Bruel & Care) and measurement software MS1021 type (manufactured by Matsushita Techno Trading), measurement conditions are a temperature of 20 ° C., a sample thickness of 30 mm, and the back surface of the sample. A frequency range of 500 Hz to 6000 Hz is measured without an air layer.
The sound absorption rate T is evaluated according to the following criteria.
○: T ≧ 0.3; the adsorption rate is high and can be used practically.
X: T <0.3; the adsorption rate is low and cannot be used practically.

(Measurement method of porosity)
The porosity of the foamed molded product is measured according to the measuring method described in ASTM D2856-87. Specifically, five test pieces (cubes each having a side of 25 mm) made of a cut surface having no skin such as a molding surface with six surfaces were cut out from the foamed molded product, and the apparent volume of the test piece was measured using calipers. Measure W4. Next, the volume W5 of the test piece can be measured by an 1-1 / 2 atm method using an air comparison type hydrometer, and the porosity of the foamed molded product can be calculated based on the following formula. In addition, the air comparison type hydrometer can use what is marketed by Tokyo Science company by the brand name "1000 type | mold".
Porosity (%) of foam molded article = 100 × (W4−W5) / W4

(Measurement method of bending displacement at bending)
The bending strength is measured according to the method described in JIS K7221-2: 2006 “Hard foamed plastic—Bending test—Part 2: Determination of bending characteristics”. That is, using a Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.), the specimen size is 75 × 300 × 25 mm, the compression speed is 10 mm / min, the tip jig is a pressure wedge 10R, and a support base 10R. The distance between fulcrums is measured as 200 mm.

The breaking point displacement amount of bending is defined as the breaking point displacement point where the following phenomenon occurs in the bending test. The fracture detection sensitivity is set to 0.5%, and when the decrease exceeds the set value of 0.5% compared with the immediately preceding load sampling point, the immediately preceding sampling point is measured.
The bending break point displacement amount H is evaluated according to the following criteria.
○: H ≧ 10; good fusing property and practically usable.
X: H <10; Fusing property is insufficient and practical use is impossible.

(Measurement method of compressive strength)
The compressive strength is measured by the method described in JIS K7220: 2006 “Rigid foamed plastic-Determination of compression properties”. That is, using Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), the test specimen size is 50 × 50 × 25 mm, the compression speed is 10 mm / min, and the compression strength at 40% compression is measured.

(Measurement method of heating dimensional change rate)
The heating dimensional change rate is measured by the method B described in JIS K 6767: 1999 “Foamed Plastics—Polyethylene—Test Method”.
The test piece is 150 x 150 x original thickness (mm), and three straight lines are written in the center part in parallel with each other in the vertical and horizontal directions at intervals of 50 mm. After being left for 22 hours, it is taken out and left in a standard state for 1 hour, and then the vertical and horizontal line dimensions are measured by the following formula.

S = (L1-L0) / L0 × 100
In the formula, S represents a heating dimensional change rate (%), L1 represents an average dimension (mm) after heating, and L0 represents an initial average dimension (mm).
The heating dimensional change rate S is evaluated according to the following criteria.
○: 0 ≦ S <1.5; dimensional change rate is low, and dimensional stability is good.
X: S>1.5; dimensional change is remarkably seen and cannot be used practically.

(Measurement method of burning rate)
The burning rate is measured by a method in accordance with the US automobile safety standard FMVSS 302. The test piece is 350 × 100 × 12 mm, and the skin is present on at least two sides of 350 mm × 100 mm.
The evaluation method for the burning rate is “◯” when the burning rate is 80 mm / min or less, and “x” when the burning rate exceeds 80 mm / min.

Example 1
By supplying 100 parts by mass of a polypropylene-based resin (manufactured by Prime Polymer Co., Ltd., trade name “F-744NP”, melting point: 140 ° C.) to an extruder, melt-kneading, granulating pellets by strand cutting, ) Polypropylene resin particles were obtained.
The polypropylene resin particles at this time were adjusted to 56 mmg per 100 grains and an average particle diameter of about 1 mm.

  Next, 800 g of the polypropylene resin particles are put into a 5 L autoclave with a stirrer, and 2 kg of pure water, 20 g of magnesium pyrophosphate and 0.5 g of sodium dodecylbenzenesulfonate are added as an aqueous medium, and the mixture is stirred and suspended in the aqueous medium. Held for 10 minutes, and then heated to 60 ° C. to obtain an aqueous suspension.

Next, 400 g of styrene in which 0.8 g of dicumyl peroxide was dissolved in this suspension was dropped in 30 minutes. After dropping, the mixture was held for 30 minutes, and styrene was absorbed by the polypropylene resin particles.
Next, the temperature of the reaction system was raised to 140 ° C., which is the same as the melting point of the polypropylene resin particles, and maintained for 2 hours, and styrene was polymerized (first polymerization) in the polypropylene resin particles.

Next, the reaction liquid of the first polymerization is set to 120 ° C. that is 20 ° C. lower than the melting point of the polypropylene resin particles, and 1.5 g of sodium dodecylbenzenesulfonate is added to this suspension, and then the polymerization initiator is used. 800 g of styrene in which 3.6 g of dicumyl peroxide was dissolved was dropped over 4 hours, and polymerization (second polymerization) was performed while absorbing the polypropylene resin particles (PP resin / PS ratio = 40/60).
After the completion of the dropping, the mixture was held at 120 ° C. for 1 hour, then heated to 140 ° C. and held for 3 hours to complete the polymerization, and modified resin particles were obtained.

  Thereafter, the temperature of the reaction system was set to 60 ° C., and 20 g of tri (2,3-dibromopropyl) isocyanate (manufactured by Nippon Kasei Co., Ltd.) as a flame retardant and 2,3- 10 g of dimethyl-2,3-diphenylbutane (manufactured by Kayaku Akzo) was added, the temperature of the reaction system was raised to 130 ° C., and stirring was continued for 2 hours to obtain flame retardant modified resin particles. It was. Next, it was cooled to room temperature, and the resin particles were taken out from the 5 L autoclave. The average particle diameter of the modified resin particles was 1400 μm.

  2 kg of the modified resin particles and 2 L of water after taking out were again put into a 5 L autoclave with a stirrer, and 300 g of butane as a blowing agent was injected into the 5 L autoclave with a stirrer. After the injection, the temperature was raised to 70 ° C. and stirring was continued for 4 hours. Then, it cooled to normal temperature, took out from the 5L autoclave, and dehydrated and dried and obtained the expandable resin particle.

Next, the obtained expandable resin particles were pre-expanded to a bulk expansion ratio 40 times (bulk density 0.025 g / m ³ ) to obtain pre-expanded particles. And the light absorbency was measured using the obtained pre-expanded particle | grains, and the polystyrene-type resin ratio was computed. The pre-foamed particles after pre-foaming are allowed to stand at room temperature for about 12 hours for aging, then transferred to tough cloth, and annealed at 60 ° C. (50-80 ° C.) for several days in an oven (hot air dryer). The blowing agent was removed. The residual gas amount of the pre-expanded particles after removing the foaming agent was measured. In this example, the amount of residual gas in the pre-expanded particles was reduced to 0.0% by mass.

Next, the pre-expanded particles after removing the foaming agent are filled into a cavity of a molding die having a size of 400 mm × 300 mm × 30 mm, 0.16 MPa water vapor is introduced into the molding die for 60 seconds, and then It cooled until the maximum surface pressure of the foaming molding fell to 0.001 MPa, and the in-mold foaming molding was obtained. Under these molding conditions, an in-mold foam molded article having good voids in appearance and fusion was obtained.
For foam molding, a foam molding machine (manufactured by Sekisui Koki Co., Ltd., trade name “ACE-11QS”) was used.
And the density of the obtained in-mold foam-molded product, bending break point displacement, porosity, sound absorption rate, heating dimensional change rate, compressive strength, and combustion test were measured.

Example 2
An in-mold foam molded article was obtained in the same manner as in Example 1 except that the residual gas amount of the pre-foamed particles was 0.9 mass% and the heating time during foam molding was 50 seconds.
Example 3
An in-mold foam molded body was obtained in the same manner as in Example 1 except that the residual gas amount of the pre-foamed particles was 2.9% by mass and the heating time during foam molding was 30 seconds.

Example 4
An in-mold foam molded article was obtained in the same manner as in Example 1 except that the PP resin / PS ratio of the modified resin particles was 30/70 and the vapor pressure during foam molding was 0.14 Mpa. It was.
Example 5
The PP resin / PS ratio of the modified resin particles was 30/70, the residual gas amount of the pre-expanded particles was 2.7% by mass, the vapor pressure during foam molding was 0.14 Mpa, and the heating time The in-mold foam-molded article was obtained in the same manner as in Example 1 except that was changed to 30 seconds.

Example 6
An in-mold foam molded article was obtained in the same manner as in Example 1 except that the PP resin / PS ratio of the modified resin particles was 20/80 and the vapor pressure during foam molding was 0.13 Mpa. It was.
Example 7
The PP resin / PS ratio of the modified resin particles was set to 20/80, the residual gas amount of the pre-expanded particles was set to 2.8% by mass, the vapor pressure at the time of molding the foam was set to 0.13 Mpa, the heating time The in-mold foam-molded article was obtained in the same manner as in Example 1 except that was changed to 40 seconds.

Example 8
The PP resin / PS ratio of the modified resin particles was 50/50, the bulk foaming factor of the pre-foamed particles was 30 times (bulk density 0.033 g / m ³ ), and the vapor pressure during foam molding was An in-mold foam molded article was obtained in the same manner as in Example 1 except that the pressure was 0.17 Mpa.
Example 9
The PP resin / PS ratio of the modified resin particles was 50/50, the bulk expansion ratio of the pre-expanded particles was 30 times (bulk density 0.033 g / m ³ ), and the residual gas amount was 3.0 mass. %, A vapor pressure at the time of foam molding was set to 0.17 Mpa, and a heating time was set to 45 seconds.

Example 10
The bulk expansion ratio of the pre-expanded particles was 5 times (bulk density 0.200 g / m ³ ), the residual gas amount was 0.8% by mass, and the vapor pressure during molding of the foam was 0.15 MPa. Except that, an in-mold foam molded article was obtained in the same manner as in Example 1.
Example 11
The bulk expansion ratio of the pre-expanded particles was 60 times (bulk density 0.016 g / m ³ ), the residual gas amount was 0.7% by mass, the vapor pressure at the time of foam molding was 0.15 Mpa, An in-mold foam molded article was obtained in the same manner as in Example 1 except that the heating time was 30 seconds.

Example 12
An in-mold foam molded article was obtained in the same manner as in Example 1 except that the residual gas amount of the pre-foamed particles was 1.5% by mass and the vapor pressure during foam molding was 0.16 MPa. .
Example 13
An in-mold foam molded article was obtained in the same manner as in Example 1 except that the vapor pressure during foam molding was 0.12 MPa and the heating time was 30 seconds.

Comparative Example 1
2. The PP resin / PS ratio of the modified resin particles was 55/45, the bulk expansion ratio of the pre-expanded particles was 4.5 times (bulk density 0.21 g / m ³ ), and the residual gas amount was 3. An in-mold foam molded article was obtained in the same manner as in Example 1 except that the content was 2% by mass, the vapor pressure during foam molding was 0.17 MPa, and the heating time was 45 seconds.
Comparative Example 2
2. The PP resin / PS ratio of the modified resin particles was set to 60/40, the bulk foaming factor of the pre-foamed particles was 4.5 times (bulk density 0.21 g / m ³ ), and the residual gas amount was 3. An in-mold foam molded article was obtained in the same manner as in Example 1 except that the content was 3% by mass, the vapor pressure during foam molding was 0.17 MPa, and the heating time was 45 seconds.

Comparative Example 3
The PP resin / PS ratio of the modified resin particles was set to 10/90, the bulk expansion ratio of the pre-expanded particles was increased to 65 times (bulk density 0.015 g / m ³ ), and the residual gas amount was 3.3 mass. %, A foam pressure in the mold was obtained in the same manner as in Example 1, except that the vapor pressure during foam molding was 0.12 MPa and the heating time was 45 seconds.
Comparative Example 4
The PP resin / PS ratio of the modified resin particles was 16/84, the bulk expansion ratio of the pre-expanded particles was 65 times (bulk density 0.015 g / m ³ ), and the residual gas amount was 3.5 mass. %, A foam pressure in the mold was obtained in the same manner as in Example 1, except that the vapor pressure during foam molding was 0.12 MPa and the heating time was 45 seconds.

Comparative Example 5
In the same manner as in Example 1, except that the residual gas amount of the pre-expanded particles was 3.3% by mass, the vapor pressure during foam molding was 0.15 Mpa, and the heating time was 15 seconds. An inner foamed molded product was obtained.
Comparative Example 6
In the same manner as in Example 1, except that the residual gas amount of the pre-expanded particles was 3.2% by mass, the vapor pressure during foam molding was 0.15 Mpa, and the heating time was 35 seconds. An inner foamed molded product was obtained.

Comparative Example 7
In the same manner as in Example 1, except that the residual gas amount of the pre-expanded particles was 3.9% by mass, the vapor pressure at the time of foam molding was 0.12 Mpa, and the heating time was 30 seconds. An inner foamed molded product was obtained.
Comparative Example 8
The PP resin / PS ratio of the modified resin particles was set to 30/70, the residual gas amount of the pre-expanded particles was set to 3.5% by mass, the vapor pressure at the time of molding the foam was set to 0.12 Mpa, the heating time The in-mold foam-molded article was obtained in the same manner as in Example 1 except that was changed to 30 seconds.

Comparative Example 9
The PP resin / PS ratio of the modified resin particles was set to 20/80, the residual gas amount of the pre-expanded particles was set to 4.0% by mass, the vapor pressure at the time of molding the foam was set to 0.12 Mpa, the heating time The in-mold foam-molded article was obtained in the same manner as in Example 1 except that was changed to 30 seconds.
Comparative Example 10
The PP resin / PS ratio of the modified resin particles was 50/50, the bulk expansion ratio of the pre-expanded particles was 30 times (bulk density 0.033 g / m ³ ), and the residual gas amount was 3.8 masses. %, A foam pressure in the mold was obtained in the same manner as in Example 1 except that the vapor pressure at the time of molding the foam was 0.12 MPa and the heating time was 30 seconds.
Tables 1 and 2 show the ratios of the polypropylene resin and polystyrene resin, the properties of the pre-foamed particles, the molding conditions, and various measured values of the molded body of the resin raw materials of the above Examples and Comparative Examples.

  According to Tables 1 and 2, it can be seen that if the residual gas amount of the expanded particles is 3.0% by mass or less, an in-mold expanded molded article satisfying various physical property values can be obtained.

Claims (4)

For the production of in-mold foam molded articles with 5 to 60 times the expansion ratio, 10 to 30% porosity, 0.3 or more sound absorption rate, 10 mm or more bending break point displacement and 1.5% or less dimensional change rate A method of producing pre-expanded particles used,
Foamable resin particles containing a foaming agent and having a mass ratio of 20/80 to 50/50 and derived from a composite resin particle of a polypropylene resin and a polystyrene resin are prefoamed, and then the amount of residual foaming agent is 0 to 3% by mass. A method for producing pre-expanded particles, characterized in that the pre-expanded particles are obtained by preparing the particles so as to be reduced. The method for producing pre-expanded particles according to claim 1, wherein the pre-expanded particles have a surface with an absorbance ratio (D ₆₉₈ / D ₁₃₇₆ ) of 0.1 to 2.5.   The method for producing pre-expanded particles according to claim 1 or 2, wherein the in-mold foam-molded product is used as an interior part for a vehicle by being laminated with an exterior material made of a nonwoven fabric or felt.   Foamable resin particles containing a foaming agent and having a mass ratio of 20/80 to 50/50 and derived from a composite resin particle of a polypropylene resin and a polystyrene resin are prefoamed, and then the amount of residual foaming agent is 0 to 3% by mass. It is a pre-expanded particle obtained by preparing to reduce to 5 to 60 times, the expansion ratio is 5 to 60 times, the porosity is 10 to 30%, the sound absorption is 0.3 or more, 10 mm or more Pre-expanded particles used for the production of an in-mold expanded molded article having a bending break point displacement of 1.5% and a dimensional change rate of 1.5% or less.