JP6081266B2 - Foam molding - Google Patents

Description

  The present invention relates to a foam molded article. More specifically, the present invention relates to a foamed molded article that is composed of a composite resin of a polyolefin-based resin and a polystyrene-based resin and has an improved appearance beauty.

A foam molded article comprising a polyolefin resin and a polystyrene resin as a base resin, and composed of fused foam particles, combines the excellent elasticity of a polyolefin resin with the excellent rigidity of a polystyrene resin. It is used as a cushioning material for automobiles and packaging.
In addition to the mechanical properties such as elasticity and rigidity, the foam molded body is required to improve the appearance and beauty in order to increase the commercial value. A foamed molded article is obtained by foam-molding pre-expanded particles. In order to improve the appearance beauty of the foam-molded body, a technique that focuses on the shape of the pre-expanded particles is disclosed in JP 2011-52167 A (Patent Document 1). )It is described in. In this publication, it is said that a foamed molded product having an L * value of 85 or more can be obtained by setting the average cell diameter of the pre-expanded particles and the number of pinholes within a specific range. Note that pinholes are bubbles that are significantly larger than the surrounding bubbles in the cross-section of the pre-foamed particles, and the L * value is an index indicating the degree of whiteness.

JP 2011-52167 A

  Even in the above publication, the appearance and beauty are not sufficient, and further improvement is required.

  The inventor of the present invention examined the reason why sufficient appearance beauty was not obtained in the above publication. As a result, it has been found that the average particle diameter, the average cell diameter and the cell diameter variation of the expanded particles constituting the expanded molded article have a great influence on the appearance beauty. In addition, although the said gazette does not specify the average particle diameter of the foam particle which comprises a foaming molding, the inventor of this invention has acquired the knowledge that it is remarkably larger than 4 mm. Specifically, in the example of the above publication, 30 parts by weight of polyethylene seed particles of about 1 mg / grain are impregnated with 17.5 to 30 parts by weight of styrene to obtain modified particles. The foamed molded product is obtained by pre-foaming and then foam molding. Under such conditions, the average particle diameter of the expanded particles constituting the expanded molded body is over 4 mm. Furthermore, the inventor believes that the absence of a description of the average particle size in the above publication means that the above publication does not contemplate the relationship between the average particle diameter and the appearance beauty.

  Thus, according to the present invention, there is provided a foam-molded article comprising 100 parts by weight of a polyolefin resin and 140 to 400 parts by weight of a polystyrene resin as a base resin and composed of fused foam particles. The foamed particles have an average particle diameter of 1 to 4 mm, and the foamed molded product has an average cell diameter of 0.05 to 0.25 mm and a cell diameter variation of 0 to 0.5 on the cut surface. There is provided a foam-molded article characterized by comprising bubbles.

According to the present invention, it is possible to obtain a foamed molded article having improved appearance and beauty.
Further, according to the present invention, the foam molded article has a whiteness with an average L * value of 95 or more on the surface and a variation between L * values of 0 to 0.5. It is possible to obtain a foamed molded article with improved appearance and beauty.

It is a figure which shows the setting condition of the particle circumcircle at the time of measuring the average particle diameter of the foaming particle which comprises a foaming molding. It is an electron micrograph of the surface layer part used when measuring the average cell diameter of a foaming molding. It is an enlarged electron micrograph of FIG. It is a figure explaining the setting procedure of a measurement point in the measuring method of L * value.

The foamed molded article of the present invention is composed of foamed particles containing a polyolefin resin and a polystyrene resin as a base resin and fused.
The foamed molded product can be used for applications such as cushioning materials (cushion materials) for home appliances, electronic parts, various industrial materials, food containers and the like. Moreover, it can also be suitably used as an impact energy absorbing material such as a vehicle bumper core material and a door interior cushioning material.
(Average particle size)
The fused foam particles have an average particle diameter of 1 to 4 mm. When the average particle diameter is less than 1 mm, the retention of the foaming agent may be reduced, and the foamed particle life (moldability) may be reduced. When it is larger than 4 mm, the appearance beauty may be deteriorated. A more preferable average particle diameter is 1.5 to 3.5 mm.

(Bubble diameter)
The foamed molded product has an average cell diameter of 0.05 to 0.25 mm at its cut surface. If the average bubble diameter is smaller than 0.05 mm, the bubble film may be broken by heating during molding, leading to poor appearance and poor physical properties. When it is larger than 0.25 mm, the appearance beauty may be deteriorated. A more preferable average cell diameter is 0.05 to 0.2 mm.
The foamed molded product has a bubble diameter variation of 0 to 0.5 on its cut surface. When the bubble diameter variation is larger than 0.5, the appearance beauty may be deteriorated.
Moreover, it is preferable that an average bubble diameter is a value of 1.0 to 6.5% of an average particle diameter. By setting the value within this range, it is possible to provide a foamed molded article with improved appearance and beauty.

(Pentane content)
The foamed molded article preferably has a pentane content of 1% by weight or less (the lower limit is 0% by weight). By reducing the pentane content, the compression strength of the foamed molded product can be improved.
In particular, pentane has various structural isomers. Among them, the foamed molded article preferably has a normal pentane content of 0.5% by weight or less (the lower limit is 0% by weight). By reducing the normal pentane content, the compression strength of the foamed molded product can be improved.

(L * value)
In the present specification, the L * value means whiteness, and the higher the value, the closer to the color of the foamed molded article using only polystyrene as the base resin. Therefore, the foam molded body having a high L * value can be easily replaced with a use in which the foam molded body using only polystyrene as the base resin is used.
The average value of L * values on the surface of the foamed molded article is preferably 95 or more (the upper limit is 100). A foamed molded product having an average L * value of 95 or more is a foamed molded product with extremely high appearance and beauty.
Furthermore, the variation between L * values is preferably 0 to 0.5. When the variation between the L * values is 0 to 0.5, it is possible to provide a foamed molded article having improved appearance beauty over the entire surface.
Here, the surface of the foamed molded product in calculating the L * value means a contact surface that is molded in contact with the inner surface of the mold during in-mold molding.

(Foaming multiple)
The foamed molded product preferably has a multiple of 5 to 70 times (density 0.014 to 0.2 g / cm ³ ). When the multiple is larger than 70 times, the strength of the foamed molded product may be lowered. On the other hand, if it is less than 5 times, the weight of the foamed molded product may increase. A more preferable multiple is 10 to 60 times.

(Base resin)
It does not specifically limit as polyolefin-type resin, A well-known resin can be used. The polyolefin resin may be cross-linked. For example, polyethylene resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers And polypropylene resins such as propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. In the above example, low density is preferably 0.91~0.94g / cm ^3, more preferably 0.91~0.93g / cm ^3. High density is preferably 0.95~0.97g / cm ^3, more preferably 0.95~0.96g / cm ^3. The medium density is an intermediate density between these low density and high density.

  Examples of polystyrene resins include polystyrene, substituted styrene polymers (substituents include lower alkyl, halogen atoms (especially chlorine atoms), etc.), other monomers based on styrene and copolymerizable with styrene. And a copolymer thereof. The main component means that styrene accounts for 70% by weight or more of the total monomers. Examples of the substituted styrene include chlorostyrenes, vinyltoluenes such as p-methylstyrene, and α-methylstyrene. Other monomers include substituted styrene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, alkyl acrylate ester, alkyl methacrylate ester, mono- or dialkyl maleate, divinylbenzene, mono- or di-ethylene glycol ( Examples include (meth) acrylic acid ester, polyethylene glycol dimethacrylate, maleic anhydride, N-phenylmaleide and the like. In the examples, alkyl means alkyl having 1 to 8 carbon atoms.

The base resin includes 100 parts by weight of a polyolefin resin and 140 to 400 parts by weight of a polystyrene resin. When there is more content of polystyrene-type resin than 400 weight part, the crack resistance of a foaming molding may fall. On the other hand, when the amount is less than 140 parts by weight, the crack resistance is greatly improved, but the rigidity may be lowered. The content of the preferred polystyrene resin is 150 to 360 parts by weight.
The base resin may contain a resin other than the polyolefin resin particles and the polystyrene resin. Examples of the other resins include acrylic resins derived from acrylic monomers such as acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, alkyl acrylate ester, and alkyl methacrylate ester.

(Method for producing foamed molded article)
The foam molded body is obtained by impregnating resin particles with a foaming agent to obtain foamable particles, foaming the foamable particles to obtain prefoamed particles, and foaming the prefoamed particles in a mold.
(1) Resin particles The resin particles for forming the pre-expanded particles may be resin particles containing a base resin in which a polyolefin resin and a polystyrene resin are simply mixed. Resin particles are preferred.
Polyolefin modified styrene resin particles (also referred to as modified resin particles) can be obtained by adding a styrene monomer to an aqueous medium in which polyolefin resin particles are dispersed and held for polymerization. A method for producing the modified resin particles will be described below.
Polyolefin resin particles for producing modified resin particles can be obtained by a known method. For example, after melt-extruding a polyolefin-based resin using an extruder, the polyolefin-based resin particles can be produced by granulation by underwater cutting, strand cutting, or the like. The polyolefin-based resin particles can take, for example, shapes such as a true sphere, an oval sphere (egg), a columnar shape, a prismatic shape, a pellet shape, and a granular shape. Hereinafter, the polyolefin resin particles are also referred to as micropellets.

  The polyolefin resin particles may contain a radical scavenger. The radical scavenger may be added to the polyolefin resin in advance, or may be added simultaneously with melt extrusion. As the radical scavenger, 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 difficult to dissolve in water, is preferable. .

  Polymerization inhibitors include 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 Phenol-based polymerization inhibitor such tridecyl) 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 and the like Lumpur antioxidants, phosphorus antioxidants, amine antioxidants and the like.

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.
The amount of the radical scavenger used is preferably 0.005 to 0.5 parts by weight with respect to 100 parts by weight of the polyolefin resin particles.

Polyolefin resin particles include, in addition, nucleating agents such as talc, calcium silicate, calcium stearate, synthetically or naturally produced silicon dioxide, ethylene bis stearamide, methacrylic ester copolymers, hexabromocyclododecane, etc. Further, it may contain a flame retardant such as triallyl isocyanurate hexabromide.
Next, the micropellets are dispersed in an aqueous medium in a polymerization vessel and polymerized while impregnating the styrenic monomer into the micropellets.
Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol).

A solvent (plasticizer) such as toluene, xylene, cyclohexane, ethyl acetate, dioctyl phthalate, or tetrachloroethylene may be added to the styrene monomer.
The amount of the styrene monomer used is 140 to 400 parts by weight with respect to 100 parts by weight of the polyolefin resin particles. More preferably, it is 150-360 weight part. The amount used corresponds substantially to the content of the polyolefin resin and the polystyrene resin constituting the foamed molded product.
When the amount of the styrene monomer used exceeds 400 parts by weight, the polystyrene resin particles may be generated without being impregnated with the polyolefin resin particles. In addition, not only the crack resistance of the foamed molded product is lowered, but also the chemical resistance may be lowered. On the other hand, if it is less than 140 parts by weight, the ability to hold the foaming agent of the expandable particles may be lowered. If it falls, it will become difficult to make it highly foamed. In addition, the rigidity of the foamed molded product may be reduced.

The impregnation of the polyolefin resin 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. When the polymerization is performed after impregnation, polymerization of the styrene monomer near the surface of the polyolefin resin particles tends to occur, and the styrene monomer not impregnated in the polyolefin resin particles is polymerized alone. In some cases, a large amount of fine particle polystyrene resin particles are produced.
When the impregnation is carried out while polymerizing, the polyolefin resin particles for calculating the content are particles composed of a polyolefin 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 weight, 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.

  An oil-soluble radical polymerization initiator can be used for the polymerization of the styrene monomer. 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,
(A) 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.
(B) A solution is prepared by dissolving the 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 styrenic monomer into the polymerization vessel,
(C) 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 a polymerization vessel.

In general, the polymerization initiator is preferably added in an amount of 0.02 to 2.0% by weight based on the total amount of the 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 surface of the polyolefin resin particles, but also prevents the styrene monomer floating in the aqueous medium from being polymerized alone. This is because the generation of fine particles can be reduced.

  As the water-soluble radical polymerization inhibitor, a polymerization inhibitor that can dissolve 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, and 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 weight part is preferable with respect to 100 weight part of water in 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, hydroxyapatite, calcium carbonate, Examples thereof include inorganic dispersants such as magnesium phosphate, 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 micropellet is not particularly limited, but it is within the range of −30 to + 20 ° C. of the melting point (measured by DSC method) of the polyolefin resin to be used. Is preferred. More specifically, 70-140 degreeC is preferable and 80-130 degreeC 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 particles made of a crosslinked polyolefin resin, the crosslinking may be performed in advance before impregnating the styrene monomer, or while impregnating and polymerizing the styrene monomer in the micropellet. Or after impregnating and polymerizing a styrenic monomer in a micropellet.

Examples of the crosslinking agent used for crosslinking the polyolefin 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 weight part normally with respect to 100 weight part of polyolefin resin particles (micro pellet).
Examples of the method of adding the crosslinking agent include a method of directly adding to the polyolefin resin particles, a method of adding the crosslinking agent after dissolving it in a solvent, a plasticizer or a styrene monomer, and a method of dispersing the crosslinking agent in water. The method of adding above etc. are mentioned. Among these, the method of adding after dissolving a crosslinking agent in a styrene-type monomer is preferable.
Modified resin particles are obtained by the above method.

(2) Expandable particles Expandable particles can be obtained by a method of impregnating resin particles with a foaming agent in an aqueous medium (wet impregnation method) or a method of impregnation in the absence of a medium (dry impregnation method). it can. In the former case, the monomer polymerization step and the foaming agent impregnation step during the production of the resin particles may be performed simultaneously.
The foaming agent is not particularly limited, and any known foaming agent can be used. Particularly, a gaseous or liquid organic compound having a boiling point equal to or lower than the softening point of the polystyrene resin and normal pressure is suitable. For example, hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, petroleum ether, ketones such as acetone and methyl ethyl ketone, methanol, ethanol, isopropyl alcohol, etc. Examples include alcohols, low boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether, and inorganic gases such as carbon dioxide, nitrogen, and ammonia. These foaming agents may be used alone or in combination of two or more. Among these, use of a hydrocarbon having a boiling point of −45 to 40 ° C. is preferable from the viewpoint of quickly replacing with air and suppressing the change with time of the foamed molded article, and pentane is more preferable.

  The amount of pentane contained in the expandable particles is preferably 7.5 to 11.0% by weight. If the pentane content is less than 7.5% by weight, the foamability of the foamable 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 foam-molded product obtained by molding the pre-expanded particles in the mold has a low fusion rate, and the appearance is beautiful. And crack resistance may be reduced. On the other hand, if it exceeds 11.0% by weight, the bubble size in the pre-foamed particles tends to be excessive, and the moldability and the strength properties such as compression and bending of the resulting foamed molded product may be reduced. . A more preferable content ratio of pentane is in the range of 8.5 to 10.0% by weight.

(3) Pre-expanded particles The pre-expanded particles can be obtained by heating the expandable particles using a heating medium such as water vapor and pre-expanding to a predetermined bulk density as necessary.
The pre-expanded particles preferably have a bulk ratio of 5 to 70 times (bulk density of 0.014 to 0.2 g / cm ³ ). When the bulk multiple is larger than 70 times, the closed cell ratio of the pre-expanded particles is lowered, and the strength of the foamed molded product obtained by foaming the pre-expanded particles may be lowered. On the other hand, if it is less than 5 times, the weight of the foamed molded product obtained by foaming the pre-foamed particles may increase. A more preferable bulk factor is 10 to 60 times.
The expandable particles before pre-expansion can be stored in a refrigerated or frozen state. Specifically, the storage temperature is preferably 5 ° C. or lower, more preferably −5 ° C. or lower, and further preferably −15 ° C. or lower.

(4) Manufacturing method of foamed molded body Preliminary foamed particles are filled in a mold of a foam molding machine, and then heated and subjected to secondary foaming so that the prefoamed particles are fused and integrated to have a desired shape. A foamed molded product can be obtained. As the foam molding machine, an EPS molding machine used when producing a foam molded body from polystyrene resin pre-expanded particles can be used.

Hereinafter, although an example is given and explained further, the present invention is not limited by these examples.
(Bulk multiple of pre-expanded particles)
The weight (a) of about 5 g of pre-expanded particles is weighed at the second decimal place. Next, weighed pre-expanded particles into a 500 mL graduated cylinder with a minimum memory unit of 5 mL, and this is a circular resin plate slightly smaller than the caliber of the graduated cylinder, with a width of about 1.5 cm and a length at the center. Apply a pressing tool on which a rod of about 30 cm is fixed upright, read the volume (b) of the pre-expanded particles, and calculate the bulk density (g / cm ³ ) of the pre-expanded particles according to the formulas (a) / (b). Ask. The bulk multiple is the reciprocal of the bulk density, that is, the formula (b) / (a).

(Multiple and density of foamed molded product)
The weight (a) and volume (b) of a test piece (example 75 × 300 × 35 mm) cut out from a foamed molded product (after being molded and dried at 40 ° C. for 20 hours or more) each have three or more significant figures. Then, the density (g / cm ³ ) of the foamed molded product is obtained by the formula (a) / (b). The multiple is the reciprocal of the density, that is, the formula (b) / (a).

(Average particle diameter of foamed particles constituting the foamed molded product)
The particle diameter (mm) of 20 foam particles continuous from the surface of the foam-molded product is measured, and the arithmetic average of these 20 particles is taken as the average particle diameter of the surface of the foam-molded product. Since the foamed particles are deformed in the foamed molded article, the diameter of the particle circumscribed circle is defined as the particle diameter as shown in FIG.

(Average cell diameter and bubble variation of foamed molded product)
A scanning electron microscope JSM-6360LV (manufactured by NEC Corporation) is used as a measuring device. An image obtained by cutting the surface portion of the foamed molded product in the vertical direction and enlarging the surface layer portion of the foamed particles from 20 times to 100 times using a scanning electron microscope for 10 continuous foam particles from the surface layer. Shoot.
Next, 10 images are printed one by one on A4 paper (see FIG. 2). From the printed image, the bubble diameter (μm) of each of 10 continuous bubbles that are in contact with the outermost layer is measured (see FIG. 3). The arithmetic average of the obtained 100 bubble diameters is defined as the average bubble diameter of the bubbles on the surface of the foam molded body. Further, the arithmetic average of the five large bubble diameters including the maximum bubble diameter out of the 100 bubble diameters is defined as the maximum bubble diameter (μm), and the five small bubbles including the minimum bubble diameter are selected from the 100 bubble diameters. The arithmetic average of the bubble diameter is defined as the minimum bubble diameter (μm). Next, bubble variation (d) = (bc) / a is calculated from the average bubble diameter (a), the maximum bubble diameter (b), and the minimum bubble diameter (c). When the value of bubble variation (d) is less than 0.5, it is judged as ◯, and when 0.5 or more, it is judged as ×.

(Fusability)
A 300 mm long and 5 mm deep cut line is placed on the surface of a 400 mm long, 300 mm wide, 30 mm high rectangular shaped foam molded body by a cutter, and the foam molded body is divided into two along this cut line. . Then, on the divided surface of the foam molded body, the number of expanded particles (a) broken in the expanded particles and the number of expanded particles (b) broken at the interface between the expanded particles were measured, and based on the following formula: To calculate the fusion rate.
Fusing rate (%) = 100 × (a) / [(a) + (b)]

(L * value and variation of foam molding)
As an evaluation of the hue, the L * value on the surface of the foamed molded product was measured by a reflection method in accordance with JIS Z8722: 2000 “Color Measurement Method-Reflection and Transmission Object Color”, a color meter (MINOLTA (currently CONICA MINOLTA). ), Model: CR-300). The measurement area was 8 mmφ, 25 points on the surface of the molded body of 400 × 300 mm were measured, and the arithmetic average was taken as the L * value. Further, the standard deviation σ of 25 points is regarded as a variation in L * value, and when this value is less than 0.5, it is judged as ◯, and when 0.5 or more, it is judged as ×. Standard alignment is performed using a standard white plate calibration plate (Y: 94.3, x: 0.3144, y: 0.3208).
The 25 points are set in 5 rows x 5 rows at intervals of 60 mm from the center of the 400 x 300 mm foamed molded body, as shown in FIG. In the figure, ◯ means a measurement point, and ● means a measurement point at the center of the molded body.

(Foaming agent content of foamed molded product)
20 mg is cut out from the foamed molded product and collected to obtain a measurement sample. This measurement sample was set at the entrance of a pyrolysis furnace (manufactured by Shimadzu Corporation, trade name: PYR-1A) and left in a nitrogen atmosphere for 15 seconds to set the measurement sample in the pyrolysis furnace. Replace the entrained gas with nitrogen. Next, after sealing the measurement sample, it was supplied into a core maintained at 200 ° C. and heated for 60 seconds to release the foaming agent component. The released foaming agent component was then gas chromatographed (Shimadzu Corporation). (Product name: GC-14B, Detector: FID), a foaming agent component chart was obtained under the following conditions, and foaming was performed from the chart based on a previously measured calibration curve of the foaming agent component. The foaming agent content (% by mass) in the conductive resin particles is calculated. The measurement conditions were as follows: Column: GL Sciences, trade name “Polapack Q” (80/100) (φ3 mm × 1.5 m), column temperature: 70 ° C., detector temperature: 110 ° C., inlet temperature: 110 ° C. Carrier gas: nitrogen, carrier gas flow rate: 1 mL / min. The foaming agent content (% by mass) is measured by gas chromatography.

(Measurement method of compressive strength)
The 25% compressive strength of the foam molded article is measured according to the method described in JIS A9511: 1995 “Foamed Plastic Insulating Material”. That is, using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), the specimen size is 50 mm × 50 mm × 50 mm, the compression speed is 10 mm / min, and the compression strength at 25% compression is measured.

Example 1
(Manufacture of polyethylene resin particles for seed polymerization)
Ethylene-vinyl acetate copolymer resin particles (manufactured by Asahi Kasei Chemicals Corporation, product name “Suntech EF0510”, melt flow rate 1.1 g / 10 min, density 0.92 g / ml, melting point 105 ° C., ethylene content 95% by weight) Extrusion was performed with an extruder, and the obtained extrudate was cut in a water flow to obtain 800 μg / grain of substantially spherical polyethylene resin particles for seed polymerization. In addition, 0.5 part by weight of talc was added to 100 parts by weight of the seed polymerization polyethylene-based resin particles as a bubble regulator during granulation.

(Manufacture of composite resin particles)
Put 14 kg of the above-mentioned polyethylene resin particles for seed polymerization into a 100 L pressure vessel with a stirrer, add 45 kg of pure water, 315 g of magnesium pyrophosphate and 1.6 g of sodium dodecylbenzenesulfonate as an aqueous medium and stir in the aqueous medium. Suspended and held for 10 minutes, and then heated to 60 ° C. to obtain an aqueous suspension. Next, 6.0 kg of styrene in which 7.2 g of dicumyl peroxide was dissolved in this suspension was added dropwise over 30 minutes. After dropping, the mixture was held for 30 minutes, and styrene was absorbed by the polyethylene resin particles. After absorption, the temperature was raised to 130 ° C. at a rate of 1 ° C./min, and polymerization was carried out at this temperature for 12 hours. Thereafter, the temperature was lowered to 90 ° C., 11.4 g of sodium dodecylbenzenesulfonate was added to this suspension, and then 39.9 g of benzoyl peroxide and 3.2 g of t-butylperoxybenzoate were used as polymerization initiators. 5 kg of styrene monomer in which 102.2 g of dicumyl peroxide was dissolved as a crosslinking agent was added dropwise over 1.5 hours. Next, 13.8 kg of a styrene monomer in which 105 g of ethylene bis fatty acid amide (manufactured by Kao Corporation: Kao Wax EBFF) was dissolved was dropped over 1.5 hours. After completion of the dropping, the mixture was held at 90 ° C. for 1 hour, then heated to 143 ° C. at a rate of 1 ° C./minute, held for 2 hours and 30 minutes to complete the polymerization, and cooled to room temperature at a rate of 1 ° C./minute. Composite resin particles were obtained.

(Manufacture of expandable particles)
100 parts by weight of the composite resin particles, 0.02 parts by weight of sodium dodecylbenzenesulfonate, 0.03 parts by weight of polyoxyethylene laurylamine, and 100 parts by weight of water are charged into a 100 L pressure vessel with an agitator, and the mixture is sealed and stirred. The temperature was raised to 70 ° C. After confirming the temperature rise at 70 ° C., 10 parts by weight of isopentane was added as a foaming agent, maintained at 70 ° C. for 4 and a half hours, and then cooled to 25 ° C. or lower to obtain expandable particles. The expandable particles were taken out, immediately cooled with cold water of 12 ° C. or lower, dehydrated while maintaining the expandable particle temperature at 15 ° C. or lower, and stored in a freezer set at −20 ° C. for 72 hours. The pentane content of the expandable particles was 6.5%.

(Manufacture of pre-expanded particles)
The above expandable particles are put into a batch type foaming machine (SKK-70, manufactured by Sekisui Koki Co., Ltd.), and heating is started while introducing steam at a setting of a gauge pressure of 0.05 MPa. About 0.1 g / cm ³ ) of pre-expanded particles were obtained. A gauge pressure means the pressure on the basis of atmospheric pressure.
(Manufacture of foam moldings)
The obtained pre-expanded particles were allowed to stand at room temperature for 24 hours, and then filled in a molding die having a size of 400 mm × 300 mm × 30 mm, and using a steam with a gauge pressure of 0.10 MPa, heating time: (1 ) Die heating for 10 seconds, (2) One heating for 30 seconds, (3) Reverse one heating for 10 seconds, (4) Double-side heating for 30 seconds, (5) Heat retention for 10 seconds, and then the molding surface pressure is 0 By cooling until the pressure decreased to 0.0 MPa, a foamed molded article having a multiple of 10 times (density 0.1 g / cm ³ ) was taken out. The obtained foamed molded article was dried for about 24 hours in a drying chamber at 60 ° C.

Example 2
A foamed molded article was produced in the same manner as in Example 1 except that 8 parts by weight of isopentane was added as a foaming agent to produce expandable particles.
Example 3
Foam molded body in the same manner as in Example 1 except that 11 parts by weight of isopentane was added as a foaming agent to produce foamable particles and that the foam was pre-foamed 20 times in bulk (density 0.05 g / cm ³ ). Manufactured.
Example 4
A foamed molded article was produced in the same manner as in Example 1 except that 5 parts by weight of isopentane and 3 parts by weight of normal pentane were added as foaming agents to produce foamable particles.

Example 5
(Manufacture of polyethylene resin particles for seed polymerization)
Linear low density polyethylene resin particles (manufactured by Nippon Polyethylene Co., Ltd., product name “NF-444A”, melt flow rate 2.0 g / 10 min, density 0.912 g / cm ³ , melting point 121 ° C.) are extruded using an extruder. The obtained extrudate was cut in a water stream to obtain 400 μg / grain of substantially spherical polyethylene resin particles for seed polymerization. In addition, 0.5 part by weight of talc was added to 100 parts by weight of the seed polymerization polyethylene-based resin particles as a bubble regulator during granulation.

(Manufacture of composite resin particles)
Put 7.7 kg of the above-mentioned polyethylene resin particles for seed polymerization into a 100 L pressure vessel with a stirrer, add 45 kg of pure water, 315 g of magnesium pyrophosphate and 1.5 g of sodium dodecylbenzenesulfonate as an aqueous medium, and stir the aqueous medium The suspension was suspended for 10 minutes and then heated to 60 ° C. to obtain an aqueous suspension. Next, 3.3 kg of styrene in which 9 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 polyethylene resin particles. After absorption, the temperature was raised to 135 ° C. at a rate of 1 ° C./min, and polymerization was carried out at this temperature for 2 hours. Thereafter, the temperature was lowered to 115 ° C., 11.4 g of sodium dodecylbenzenesulfonate was added to the suspension, and then 20 kg of styrene in which 105 g of t-butylperoxybenzoate was dissolved as a polymerization initiator was added over 3 hours. It was dripped. Next, 6.6 kg of a styrene monomer in which 350 g of ethylene bis fatty acid amide (manufactured by Kao Corporation: Kao Wax EBFF) was dissolved was dropped over 1 hour. After holding at 115 ° C. for 1 hour and 30 minutes, the temperature is raised to 140 ° C. at a rate of 1 ° C./minute and held for 3 hours to complete the polymerization, and then cooled to room temperature at a rate of 1 ° C./minute to obtain composite resin particles. It was.

(Manufacture of foamable particles to foamed molded products)
Except that the composite resin particles obtained above were used and 11 parts by weight of isopentane was added as a foaming agent to produce foamable particles and that the foam was pre-foamed to 25 times the bulk factor (density 0.04 g / cm ³ ). Produced a foamed molded article in the same manner as in Example 1.

Example 6
(Manufacture of polyethylene resin particles for seed polymerization)
By extruding ethylene-vinyl acetate copolymer resin particles (manufactured by Nippon Polyethylene Co., Ltd., LV-115) with an extruder, and cutting the resulting extrudate in a water stream, 400 μg / grain for substantially spherical seed polymerization. Polyethylene resin particles were obtained. In addition, 0.5 part by weight of talc was added to 100 parts by weight of the seed polymerization polyethylene-based resin particles as a bubble regulator during granulation.

(Manufacture of composite resin particles)
Place 10.5 kg of the above-mentioned polyethylene resin particles for seed polymerization into a 100 L pressure vessel equipped with a stirrer, add 45 kg of pure water, 315 g of magnesium pyrophosphate, and 1.6 g of sodium dodecylbenzenesulfonate as an aqueous medium, and stir the aqueous medium. The suspension was suspended for 10 minutes and then heated to 60 ° C. to obtain an aqueous suspension. Next, 4.5 kg of styrene in which 5.4 g of dicumyl peroxide was dissolved in this suspension was added dropwise over 30 minutes. After dropping, the mixture was held for 30 minutes, and styrene was absorbed by the polyethylene resin particles. After absorption, the temperature was raised to 130 ° C. at a rate of 1 ° C./min, and polymerization was carried out at this temperature for 1 hour and 45 minutes. Thereafter, the temperature was lowered to 90 ° C., 11.4 g of sodium dodecylbenzenesulfonate was added to this suspension, and then 39.2 g of benzoyl peroxide and 4.9 g of t-butylperoxybenzoate were used as polymerization initiators. 6.2 kg of styrene dissolved with 98.7 g of dicumyl peroxide as a crosslinking agent was added dropwise over 2 hours. Next, 13.8 kg of styrene monoer in which 175 g of ethylenebisfatty acid amide (manufactured by Kao Corporation: Kao Wax EBFF) was dissolved was dropped over 2 hours. After completion of the dropping, the mixture is held at 90 ° C. for 1 hour, then heated to 143 ° C. at a rate of 1 ° C./minute, held for 2 hours to complete the polymerization, and cooled to room temperature at a rate of 1 ° C./minute to obtain a composite resin. Particles were obtained.

(Manufacture of foamable particles to foamed molded products)
Except that the composite resin particles obtained above were used and 8 parts by weight of isopentane was added as a foaming agent to produce foamable particles, and that the foam was prefoamed to 10 times the bulk (density 0.10 g / cm ³ ). Produced a foamed molded article in the same manner as in Example 1.

Example 7
A foamed molded article was produced in the same manner as in Example 6 except that 10 parts by weight of isopentane was added as a foaming agent to produce expandable particles.
Example 8
Expanded molded body in the same manner as in Example 6 except that 11 parts by weight of isopentane was added as a foaming agent to produce expandable particles and that the foam was pre-foamed 20 times in bulk (density 0.05 g / cm ³ ). Example 9 which produced
Example 10 A foamed molded article was produced in the same manner as in Example 6 except that 8 parts by weight of isopentane was added as a foaming agent to produce foamable particles.
Expanded molded article in the same manner as in Example 5 except that 8 parts by weight of isopentane was added as a foaming agent to produce expandable particles and pre-foamed to a bulk multiple of 10 times (density 0.1 g / cm ³ ). Manufactured.

Comparative Example 1
A foamed molded article was produced in the same manner as in Example 1 except that 14 parts by weight of isopentane was added as a foaming agent to produce expandable particles.
Comparative Example 2
A foamed molded article was produced in the same manner as in Example 1 except that 2 parts by weight of isopentane and 9 parts by weight of normal pentane were added as foaming agents to produce foamable particles.
Comparative Example 3
Expanded molded body in the same manner as in Example 5, except that 16 parts by weight of isopentane was added as a foaming agent to produce expandable particles, and pre-foamed to a bulk multiple of 40 times (density 0.025 g / cm ³ ). Manufactured.

Comparative Example 4
Foam molded body in the same manner as in Example 6 except that 14 parts by weight of isopentane was added as a foaming agent to produce foamable particles and the foam was pre-foamed 20 times in bulk (density 0.05 g / cm ³ ). Tables 1 and 2 summarize the production conditions and measurement results of the above Examples and Comparative Examples. In Tables 1 and 2, PS means polystyrene, PO means polyolefin, i-n5 means isopentane, and nn5 means normal pentane.

  From the examples and comparative examples, the foamed particles have an average particle diameter of 1 to 4 mm, and the foamed molded product has an average cell diameter of 0.05 to 0.25 mm and air bubbles of 0 to 0.5 on the surface thereof. It can be seen that a foamed molded article having bubbles having diameter variation has both a high L * value (high appearance beauty) and a high compressive strength.

Claims (2)

  A foamed molded article comprising 100 parts by weight of a polyolefin-based resin and 140 to 400 parts by weight of a polystyrene-based resin as a base resin and composed of fused foam particles, wherein the fused foam particles are 1 to 4 mm. The foamed molded article is provided with bubbles having an average cell diameter of 0.05 to 0.25 mm and a cell diameter variation of 0 to 0.5 on the cut surface. Foam molded body.   2. The foamed molded product according to claim 1, wherein the foamed molded product has a whiteness with an average L * value of 95 or more on the surface and a variation between L * values of 0 to 0.5.