JP6294040B2 - Styrenic resin particles, expandable particles, expanded particles and expanded molded articles - Google Patents

Description

  The present invention relates to styrenic resin particles, expandable particles, expanded particles, and expanded molded articles. More specifically, the present invention is a styrenic resin particle, expandable particle, expanded particle, which can be molded with a small amount of steam and can give a foamed molded article excellent in mechanical strength (bending strength, compressive strength, etc.) The present invention relates to a foam molded article.

Conventionally, foamed molded articles are light weight and excellent in heat insulation and mechanical strength, and thus have been used for transport packing materials such as fish boxes and food containers, cushioning materials, and the like. Among them, in-mold foam molded articles produced using foamable particles as raw materials are often used because of the advantage that a desired shape is easily obtained.
Expandable styrene resin particles are widely used as expandable particles, which are raw materials for producing expanded molded articles. For example, expanded molded articles are obtained as follows. That is, expandable particles such as expandable styrene resin particles are heated with steam and pre-expanded to obtain expanded particles (pre-expanded particles). The obtained pre-expanded particles are filled into the mold cavity. Next, a foamed molded article can be obtained by integrating the pre-expanded particles by heat-sealing while pre-expanding the filled pre-expanded particles with steam. In recent years, a reduction in the amount of heavy oil required for generating steam with a boiler or the like has been demanded from the viewpoint of energy saving, and there is a demand for expandable styrene resin particles capable of producing a foamed molded article with a small amount of steam.

In general, the foamed molded article obtained by the above method has pre-expanded particles integrated by heat fusion, so that the strength of the fused surface is weaker than the portion other than the fused surface. This weakness of the fused surface leads to the disadvantage of inferior mechanical strength. In particular, when molding is performed with a small amount of steam, the strength of heat-sealing between the pre-expanded particles tends to be inferior, and as a result, a foamed molded product having sufficient mechanical strength is often not obtained. Therefore, it is desired to provide a foamed molded article having improved mechanical strength.
From the viewpoint of reducing the amount of steam, Japanese Patent Application Laid-Open No. 2011-26508 (Patent Document 1) proposes expandable styrene resin particles capable of providing a foamed molded article excellent in appearance and fusion with a small amount of steam. Yes.

JP 2011-26508 A

  Even with the technique described in the above publication, a foamed molded article having sufficient mechanical strength can be obtained with energy saving. However, from the viewpoint of further improving energy saving, it has been desired to provide a foamed molded article having mechanical strength (bending strength, compressive strength, etc.) while maintaining moldability even with a smaller amount of steam.

  The inventor of the present invention reviewed the glass transition temperature of the styrene resin particles in order to improve the mechanical strength of the foamed molded product. As a result, it was found that the styrene-based resin particles capable of imparting excellent mechanical strength to the foamed molded article can be provided even with a small amount of steam because the glass transition temperature at the center is lower than the overall glass transition temperature, and the present invention has been achieved. It was.

Thus, according to the present invention, styrene resin particles containing a resin component derived from a monofunctional acrylate ester,
The styrene resin particles have a central glass transition temperature that is 2 to 5 ° C. lower than the entire glass transition temperature.

  According to this invention, the expandable particle | grains containing the said styrene resin particle and a foaming agent are provided. Furthermore, according to this invention, the expanded particle obtained by making the said expandable particle expand is provided. Moreover, according to this invention, the foaming molding obtained by carrying out the foam molding of the said foaming particle is provided.

According to the present invention, it is possible to provide styrene-based resin particles, expandable particles, and expanded particles that can provide expanded molded articles having excellent mechanical strength even with a small amount of steam. The inventor believes that this effect is exhibited when the glass transition temperature at the center is lower than the entire glass transition temperature. The foamed molded article having excellent mechanical strength of the present invention can improve bending strength, compressive strength, etc. while maintaining energy saving during molding.
Even if the foamed molded product of the present invention is thinner than the conventional foamed molded product, the same mechanical strength can be obtained. Therefore, the amount of styrene resin particles that are raw materials can be reduced. Transportation costs can be reduced by reducing the weight of the foamed molded product.

When (1) the styrene resin particles have a glass transition temperature of the surface layer that is 5 to 20 ° C. higher than the entire glass transition temperature,
(2) A monofunctional methacrylic acid ester or α-methylstyrene having a resin component derived from a monofunctional acrylate ester having a C 1-10 alkyl group in the center and a surface layer having a C 1-10 alkyl group When including a resin component derived from
(3) When the monofunctional acrylic ester is butyl acrylate and the monofunctional methacrylate is methyl methacrylate,
(4) If the surface layer is any one having a Z average molecular weight of 700,000 to 2,000,000, resin particles capable of providing a foamed molded article having more excellent mechanical strength with energy saving can be provided.

It is a photograph of a sectional view of a foaming fabrication object before and behind measurement of glass transition temperature Tg of a central part.

(Styrene resin particles)
(1) Constituent Component The styrene resin particles have a glass transition temperature at the center that is 2 to 5 ° C. lower than the entire glass transition temperature. Because the glass transition temperature at the center is low, the amount of heat applied to the expandable particles is small when the styrene resin particles are impregnated with a foaming agent to form expandable particles, and the expandable particles are expanded to form expandable particles. Even (even if the amount of steam is small), it is possible to obtain expanded particles having a desired magnification. There are various methods for lowering the glass transition temperature at the center, and one method is to adjust the position of the resin constituting the styrene resin particles. For example, the styrenic resin particles of the present invention contain a resin component derived from a monofunctional acrylate ester. By including a large amount of this resin component in the center, the glass transition temperature of the center can be lowered. .

  Here, the glass transition temperature of the styrene homopolymer is 100 ° C., and among the monofunctional acrylate ester, homopolymer glass of methyl acrylate, ethyl acrylate, n-propyl acrylate and butyl acrylate, and octyl acrylate. The transition temperatures are 6 ° C, -24 ° C, -48 ° C, -55 ° C, and -65 ° C, respectively. With reference to such a glass transition temperature, the selection, content and location of the monofunctional acrylate may be adjusted so that the desired energy saving and mechanical strength can be obtained. Monofunctional acrylic acid esters are preferably methyl acrylate, ethyl acrylate, and butyl acrylate. Here, from the viewpoint of compatibility, the resin component derived from the monofunctional acrylate ester is preferably present in the styrene resin particles in the form of a copolymer with a styrene monomer.

Moreover, it is preferable that a styrene-type resin particle has a glass transition temperature of the surface layer 5-20 degreeC higher than the whole glass transition temperature. By having such a surface layer, it is possible to provide styrene-based resin particles that can provide a foamed molded article having higher mechanical strength while maintaining energy saving. The inventor believes that this is due to the following reason. That is, the heat resistance of the styrenic resin particles decreases when the styrenic resin particles are in direct contact with the high-temperature mold during the production of the foam molded article. Moreover, heat resistance falls also when the plasticizer and solvent which were used at the time of manufacture of a styrene-type resin particle localize on a surface layer. This decrease in heat resistance leads to a decrease in the mechanical strength of the foam molded article, which can be suppressed by increasing the glass transition temperature of the surface layer.
There are various methods for raising the glass transition temperature of the surface layer, and one method is to adjust the position of the resin constituting the styrene resin particles. For example, the glass transition temperature of the surface layer can be increased by including a large amount of a resin component derived from monofunctional methacrylate and α-methylstyrene in the surface layer. Among the monofunctional methacrylic acid esters, the glass transition temperatures of homopolymers of methyl methacrylate and α-methylstyrene are 105 ° C. and 180 ° C., respectively. With reference to such a glass transition temperature, the selection of the monofunctional methacrylate ester and α-methylstyrene, the content thereof and the location thereof may be adjusted so as to obtain the desired energy saving and mechanical strength.

  In the present specification, the central portion means within about 30% of the radius from the center of the styrenic resin particles, and the surface layer means within about 20% of the radius from the surface. Further, the glass transition temperatures of the central portion and the surface layer are difficult to measure from the styrene resin particles because they are very small, and thus are measured through a foamed molded product that is foamed to a predetermined multiple. That is, the glass transition temperature of the surface layer from the product obtained by thinly peeling the surface layer of the foam molded product, and the glass transition temperature of the center portion from the material obtained by hollowing out the center of the fused foam particles constituting the foam molded product, respectively. It is regarded as the glass transition temperature of the surface layer and the center of the resin particle. In addition, the glass transition temperature of the whole styrene-type resin particle is substantially in agreement with the glass transition temperature of the whole foaming molding.

The styrene resin particles contain a resin component derived from a styrene monomer. The styrene monomer is not particularly limited, and any known monomer can be used. For example, styrene, vinyl toluene, chlorostyrene, ethyl styrene, isopropyl styrene, dimethyl styrene, bromostyrene, and the like can be given. These styrenic monomers may be one kind or a mixture of plural kinds. A preferred styrenic monomer is styrene.
The styrene resin particles may contain a resin component derived from a polyfunctional vinyl monomer copolymerizable with the styrene monomer. The polyfunctional vinyl monomer is preferably a monomer having 2 to 15 vinyl groups from the viewpoint of improving foam moldability of the foam molded article. Resin particles containing a resin component derived from such a polyfunctional vinyl monomer having a specific number of vinyl groups can provide a foamed molded article having more excellent mechanical strength. Specific polyfunctional vinyl monomers include bifunctional monomers such as divinylbenzene, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, ethoxylation Trifunctional monomers such as trimethylolpropane trimethacrylate and ethoxylated isocyanuric acid triacrylate are exemplified. The polyfunctional vinyl monomer may be used alone or in combination.

The ratio of the resin component derived from the styrene monomer constituting the styrene resin particles, the resin component derived from the monofunctional acrylate ester, the resin component derived from the monofunctional methacrylate and α-methylstyrene is 1: 0.005. The range is preferably 0.1: 0 to 1.0 (mass ratio).
When the proportion of the resin component derived from the monofunctional acrylate is less than 0.005, it is necessary to maintain a high vapor pressure during foam molding in order to obtain a foam molded article having a desired strength, which may be inferior in energy saving. is there. If it is more than 0.1, the strength of the foamed molded product may be lowered.
When the ratio of the monofunctional methacrylate ester and the resin component derived from α-methylstyrene is more than 1.0, a good foamed molded article may not be obtained with a low molding vapor pressure.
A more preferable ratio is in the range of 1: 0.01 to 0.08: 0.05 to 0.8, and a further preferable ratio is in the range of 1: 0.01 to 0.05: 0.1 to 0.6. is there.

Moreover, it is preferable that the ratio for which the component copolymerized with the styrene-type monomer accounts for 70 mass% or more in the resin component derived from monofunctional acrylate ester. On the other hand, the ratio of the component copolymerized with the styrenic monomer in the resin component derived from monofunctional methacrylate and α-methylstyrene is preferably 50% by mass or more.
The ratio of the resin component derived from the monomer substantially matches the ratio of the monomer as the raw material. Furthermore, the resin component derived from the monofunctional acrylate ester and the monofunctional methacrylic acid ester and α-methylstyrene are used in the obtained styrene resin particles, and the types of monomers used are: The remaining monomer can be discriminated by qualitative analysis by gas chromatography.

The styrene resin particles may contain components other than the resin component.
Examples of the other components include resin components such as polyolefin resins such as polyethylene and polypropylene, polycarbonate resins, and polyesters.
In addition, within the range that does not impair the physical properties, flame retardants, flame retardant aids, plasticizers, lubricants, anti-binding agents, fusion accelerators, anti-static agents, spreading agents, bubble regulators, crosslinking agents, fillers, Additives such as colorants may be included.
As flame retardants, tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, tetrabromobisphenol A-bis (2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A- Examples thereof include bis (2,3-dibromopropyl ether).

Examples of the flame retardant aid include organic peroxides such as 2,3-dimethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, dicumyl peroxide, and cumene hydroperoxide. .
Examples of the plasticizer include glycerin fatty acid esters such as phthalic acid ester, glycerin diacetomonolaurate, glycerin tristearate and diacetylated glycerin monostearate, and adipic acid esters such as diisobutyl adipate.
Examples of the lubricant include paraffin wax and zinc stearate.
Examples of the binding inhibitor include calcium carbonate, silica, zinc stearate, aluminum hydroxide, ethylene bis stearamide, tricalcium phosphate, dimethyl silicon and the like.

Examples of the fusion accelerator include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, stearic acid sorbitan ester, and polyethylene wax.
Examples of the antistatic agent include polyoxyethylene alkylphenol ether, stearic acid monoglyceride, polyethylene glycol and the like.
Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.
Examples of the bubble regulator include methacrylic acid ester copolymer, ethylene bis stearamide, polyethylene wax, ethylene-vinyl acetate copolymer, and the like.

(2) Glass transition temperature of styrene-based resin particles The glass transition temperature at the center is preferably 2 to 5 ° C lower than the entire glass transition temperature. When the difference in glass transition point is less than 2 ° C., the energy-saving foaming property may be insufficient. If it is 5 ° C. or higher, the mechanical strength may be insufficient.
The glass transition temperature of the surface layer is preferably 5 to 20 ° C. higher than the entire glass transition temperature. If the difference in glass transition point is less than 5 ° C, the mechanical strength may be insufficient. When the temperature is 20 ° C. or higher, the energy-saving foamability may be insufficient. The glass transition temperature of the surface layer is more preferably 5 to 15 ° C. higher than the entire glass transition temperature.
In addition, it is preferable that the glass transition temperature of the whole styrene-type resin particle is 95-99 degreeC, the glass transition temperature of surface layer is 100-120 degreeC, and the glass transition temperature of center part is 90-97 degreeC. The overall glass transition temperature can be measured from the styrene resin particles themselves. Moreover, it can also measure from the site | part cut out arbitrarily of the foaming molding.

(3) Z-average molecular weight of surface layer The surface layer preferably has a Z-average molecular weight of 700,000 to 2,000,000. The surface layer here means the same surface layer as the glass transition point, and the Z average molecular weight is measured by GPC method by thinly peeling the surface layer of the foamed molded product, similarly to the measurement of the glass transition point. can get. When the Z average molecular weight is less than 700,000, the mechanical strength may be insufficient. When it is larger than 2 million, the fusion property between the expanded particles constituting the expanded molded article is lowered, and as a result, the mechanical strength may be lowered. The Z average molecular weight of the surface layer is more preferably in the range of 800,000 to 1,800,000, still more preferably in the range of 800,000 to 1,500,000. The Z average molecular weight of the entire styrene resin particles is preferably in the range of 600,000 to 1,000,000. The surface layer preferably has a Z-average molecular weight of 100,000 to 500,000 larger than the whole.
The overall Z average molecular weight can be measured from the styrene-based resin particles themselves, and almost coincides with the overall Z average molecular weight of the foam molded article.

(4) Shape of styrene resin particles The shape of the styrene resin particles is not particularly limited. For example, spherical shape, cylindrical shape, etc. are mentioned. Of these, a spherical shape is preferable. The average particle diameter of the styrene-based resin particles can be appropriately selected depending on the application. For example, those having an average particle diameter of 0.2 mm to 5 mm can be used. In consideration of the filling ability into the mold, the average particle diameter is more preferably 0.3 mm to 2 mm, and still more preferably 0.3 mm to 1.4 mm.

(Method for producing styrene resin particles)
The method for producing styrene resin particles is not particularly limited. For example, resin particles can be obtained by absorbing and polymerizing a monomer mixture containing a styrene monomer into seed particles made of a styrene resin.
(1) Seed particles Seed particles produced by a known method can be used. For example, (i) a styrene resin is melt-kneaded with an extruder, extruded into a strand, and the strand is cut. (Ii) An aqueous medium, a styrenic monomer and a polymerization initiator are fed into an autoclave, and the styrene monomer is suspended and polymerized while heating and stirring in the autoclave to produce seed particles. (Iii) Aqueous medium and styrenic resin particles are fed into the autoclave, and the styrenic resin particles are dispersed in the aqueous medium, and then the styrene monomer is continuously added while heating and stirring the autoclave. Alternatively, the polymer is supplied intermittently and polymerized in the presence of a polymerization initiator while allowing the styrene resin particles to absorb the styrene monomer. Examples thereof include a seed polymerization method for producing seed particles.
In addition, the resin particles can be used for part or all of the seed particles. In the case of using a recovered product, production of seed particles by an extrusion method is suitable.

  The average particle size of the seed particles can be adjusted as appropriate according to the average particle size of the resin particles. For example, when obtaining resin particles having an average particle diameter of 1 mm, it is preferable to use seed particles having an average particle diameter of about 0.7 mm to 0.9 mm. Furthermore, the weight average molecular weight of the seed particles is not particularly limited, but is preferably 100,000 to 700,000, and more preferably 150,000 to 500,000.

(2) Impregnation step Each monomer is absorbed by the seed particles by supplying a monomer mixture into a dispersion obtained by dispersing the seed particles in an aqueous medium.
Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol).

  Each monomer to be used may contain a polymerization initiator. The polymerization initiator is not particularly limited as long as it is conventionally used for monomer polymerization. For example, benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, lauryl peroxide, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl Organics such as carbonate, t-butyl peroxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate Examples thereof include peroxides, azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile, and the like. Among these initiators, in order to reduce the residual monomer, it is preferable to use two or more different polymerization initiators having a decomposition temperature of 80 to 120 ° C. to obtain a half-life of 10 hours. In addition, a polymerization initiator may be used independently or 2 or more types may be used together.

  A suspension stabilizer may be included in the aqueous medium to stabilize the dispersion of monomer droplets and seed particles. The suspension stabilizer is not particularly limited as long as it is conventionally used for monomer suspension polymerization. Examples thereof include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate, magnesium pyrophosphate, magnesium oxide, and hydroxyapatite. And when using a sparingly soluble inorganic compound as said suspension stabilizer, it is preferable to use an anionic surfactant together, and as such anionic surfactant, for example, fatty acid soap, N-acylamino acid or its Salts, carboxylates such as alkyl ether carboxylates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl sulfoacetates, sulfonates such as α-olefin sulfonates; higher alcohol sulfuric acid Ester salts, secondary higher alcohol sulfates, sulfates such as alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, etc .; phosphates such as alkyl ether phosphates, alkyl phosphates, etc. Is mentioned.

(3) Polymerization process Although a polymerization process changes with monomer types to be used, a polymerization initiator seed | species, a polymerization atmosphere seed | species, etc., it is normally performed by maintaining 70-130 degreeC heating for 3 to 10 hours. The polymerization step may be performed while impregnating the monomer.
In the polymerization step, the total amount of monomers used may be polymerized in one stage, or may be polymerized in two or more stages (including polymerization during the production of seed particles). It is easier to adjust the positions of the resin component derived from the monofunctional acrylate ester and the resin component derived from the monofunctional methacrylic acid ester and α-methylstyrene when divided into two or more stages. Furthermore, adjustment is easier if it is divided into three or more stages. When polymerizing in two or more stages, the impregnation process is usually performed in two stages. The polymerization temperature and time of the polymerization process divided into two or more steps may be the same or different. The polymerization process is preferably in three stages.

When performed in three stages, it is preferable to adjust the polymerization process as follows.
First, a monofunctional acrylic acid ester (with a styrene monomer if necessary) is absorbed into seed particles of a styrene resin and polymerized in the seed particles (first step).
Next, the particles obtained through the first step are polymerized while absorbing the styrene monomer (second step).
Further, the particles obtained through the second step are polymerized while absorbing the monofunctional methacrylic acid ester and α-methylstyrene (with a styrene monomer as required) (third step). The third step is an optional step.

  In the third step, it is preferable to carry out while maintaining the polymerization conversion rate of the seed particles in the range of 75% by mass or more and less than 100% by mass. When the polymerization conversion rate is within this range, it is possible to easily adjust the position of the resin component derived from the monofunctional acrylic ester, the resin component derived from the monofunctional methacrylate and α-methylstyrene. A preferable polymerization conversion rate is in the range of 80 to 98% by mass, and a more preferable range is 80 to 97% by mass.

  Moreover, it is preferable that the usage-amount of the styrene-type monomer used at a 2nd process is 10 mass% or more with respect to the monomer whole quantity used at a 1st process-a 3rd process. When the amount is less than 10% by mass, a resin component derived from a monofunctional acrylate ester is included up to the surface layer of the particle, or a resin component derived from a monofunctional methacrylate ester and α-methylstyrene is included up to the center of the particle. Therefore, it may be difficult to obtain styrene resin particles having energy-saving moldability and high mechanical strength.

(Expandable particles)
The expandable particles are particles obtained by impregnating the styrene resin particles with a foaming agent.
(1) Foaming agent The foaming agent is not particularly limited, and any known foaming agent can be used. In particular, a gaseous or liquid organic compound having a boiling point equal to or lower than the softening point of the styrene resin 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. Low boiling point ether compounds such as alcohols, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, halogen-containing hydrocarbons such as trichloromonofluoromethane, dichlorodifluoromethane, inorganic gases such as carbon dioxide, nitrogen, ammonia, etc. Can be mentioned. These foaming agents may be used alone or in combination of two or more. Among these, it is preferable to use hydrocarbons from the viewpoint of preventing the destruction of the ozone layer and from the viewpoint of quickly replacing with the air and suppressing the time-dependent change of the foamed molded product. Of the hydrocarbons, hydrocarbons having a boiling point of −45 to 40 ° C. are more preferable, and propane, n-butane, isobutane, n-pentane, isopentane and the like are more preferable.

  Furthermore, it is preferable that content of a foaming agent is the range of 2-12 mass%. If it is less than 2% by mass, a foamed molded article having a desired density may not be obtained from the expandable particles. In addition, since the effect of increasing the secondary foaming power at the time of in-mold foam molding is reduced, the appearance of the foam molded article may not be good. When the amount is more than 12% by mass, the time required for the cooling step in the production process of the foamed molded product becomes long, and the productivity may decrease. A more preferable content of the blowing agent is 3 to 10% by mass.

(2) Method for producing expandable particles Expandable particles can be obtained by impregnating the above styrene resin particles with a foaming agent. The impregnation may be performed wet simultaneously with the polymerization (for example, the third step), or may be performed wet or dry after the polymerization. When it is carried out in a wet manner, it may be carried out in the presence of a suspension stabilizer and a surfactant exemplified in the polymerization step.
The impregnation temperature of the foaming agent is preferably 60 to 120 ° C. When the temperature is lower than 60 ° C., the time required for impregnating the resin particles with the foaming agent becomes long, and the production efficiency may decrease. On the other hand, when the temperature is higher than 120 ° C., the resin particles may be fused to generate bonded particles. A more preferable impregnation temperature is 70 to 110 ° C.
A foaming aid may be used in combination with a foaming agent. Examples of the foaming aid include isobutyl adipate, toluene, cyclohexane, and ethylbenzene.

(Foamed particles)
The expanded particles are obtained by expanding the expandable particles to a desired bulk density using water vapor or the like. The foamed particles can be used as they are for applications such as cushioning fillers, and can be used as a raw material for foam molded articles for foaming in the mold. In the case of the raw material of the foam molded article, the expanded particles are generally referred to as pre-expanded particles, and the expansion to obtain the expanded particles is generally referred to as pre-expanded.
The bulk density of the expanded particles is preferably in the range of 0.01 to 0.04 g / cm ³ . When the bulk density of the expanded particles is less than 0.01 g / cm ³ , shrinkage may occur in the foamed molded product to be obtained next, and the appearance may be deteriorated. In addition, the heat insulation performance and mechanical strength of the foamed molded product may deteriorate. On the other hand, when the bulk density is larger than 0.04 g / cm ³ , the lightweight property of the foamed molded product may be lowered.
In addition, it is preferable to apply powder metal soaps such as zinc stearate to the surface of the expandable particles before foaming. By applying, the bonding between the foamed particles can be reduced in the foaming process of the foamable particles.

(Foamed molded product)
The foamed molded product can be used, for example, for containers for food and industrial products, packaging materials for fish, agricultural products, etc., heat insulating materials for floor insulation, embankment materials, tatami core materials, and the like. The foamed molded product can take a shape corresponding to the intended use. According to the present invention, it is possible to provide a foamed molded product having a bending strength increased (improved) by about 10% if the thickness is the same as that of a conventional foamed molded product, and about 5% lighter if the bending strength is the same. A foamed molded article can be provided.
The density of the foam molded article is preferably in the range of 0.01 to 0.04 g / cm ³ . When the density of the foamed molded product is smaller than 0.01 g / cm ³ , the foamed molded product may shrink and the appearance may be deteriorated. In addition, the heat insulation performance and mechanical strength of the foamed molded product may deteriorate. On the other hand, when the density is larger than 0.04 g / cm ³ , the lightweight property of the foamed molded product may be lowered.

The foam molded article can be obtained, for example, by the following method.
By filling the expanded particles in a closed mold having a large number of small holes and heating and foaming with a heat medium (for example, pressurized water vapor) to fill the voids between the expanded particles and fuse the expanded particles to each other A foamed molded product can be produced by integrating the components. At that time, the density of the foamed molded product can be adjusted, for example, by adjusting the filling amount of the foamed particles in the mold.

  Heating foaming can be performed, for example, by heating with a heat medium of 110 to 150 ° C. for 5 to 50 seconds. Under these conditions, good fusing property between the particles can be ensured. More preferably, the heat foaming can be performed by heating for 10 to 50 seconds with a heat medium of 90 to 120 ° C. In the present invention, heating foaming is performed under a pressure of the heat medium forming vapor pressure (gauge pressure) of 0.03 to 0.05 MPa, which is lower than a general vapor pressure (for example, 0.06 to 0.08 MPa). Can do. Therefore, a foamed molded product can be produced with a small amount of steam.

  The foamed particles may be aged, for example, at normal pressure before molding the foamed molded product. The aging temperature of the expanded particles is preferably 20 to 60 ° C. When the aging temperature is low, the aging time of the expanded particles may be long. On the other hand, if it is high, the foaming agent in the foamed particles may dissipate and the moldability may deteriorate.

  Hereinafter, specific examples of the present invention will be described by way of examples. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples. In the following, “part” and “%” are based on mass unless otherwise specified.

<Polymerization conversion>
The method for measuring the amount of monomer contained in seed particles in the middle of nuclear polymerization (hereinafter referred to as growing particles) refers to those measured in the following manner.
That is, the growing particles are taken out from the dispersion, and the water adhering to the surface is wiped off with gauze. 0.08 g of growing particles are collected, and the collected growing particles are dissolved in 24 mL of toluene to prepare a toluene solution. Next, 10 mL of a Wis reagent, 30 mL of a 5% by mass potassium iodide aqueous solution and 30 mL of a 1% by mass starch aqueous solution are added to the toluene solution. The result obtained by titrating the obtained solution with an N / 40 sodium thiosulfate solution is defined as a titration constant (mL) of the sample. The Wies reagent is obtained by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 L of glacial acetic acid. On the other hand, 10 mL of a Wis reagent, 30 mL of a 5% by mass potassium iodide aqueous solution and 30 mL of a 1% by mass starch aqueous solution are added to 24 mL of toluene without dissolving the growing particles. The obtained solution was titrated with a N / 40 sodium thiosulfate solution to obtain a blank titration constant (mL).
From the obtained droplet constant, the amount of unreacted monomer in the growing particles is calculated based on the following formula.
Amount of monomer (% by mass) in growing particles =
0.1322 × (blank drop constant−sample drop constant) / sample drop constant Further, the polymerization conversion is calculated by the following equation.
Polymerization conversion rate (%) =
100 × (sample mass−monomer amount of growing particles) / sample mass

<Z average molecular weight: Mz>
The surface layer Z average molecular weight of the resin particles is measured from the surface layer of the foam molded article. That is, since the foam molded body is obtained by pre-foaming resin particles and molding in-mold, the resin particle surface layer corresponds to the foam molded body surface layer, and the Z average molecular weight of the resin particle surface layer is Z of the foam molded body surface layer. Corresponds to the average molecular weight. The overall Z average molecular weight of the resin particles is measured from the resin particles themselves.
A foam molded body having a density of 0.0166 g / cm ³ was dried at 50 ° C. for 24 hours, and then ham slicer (Fujishima Koki Co., Ltd .: FK-18N type) was used to form 0.2 to 0.00 from the surface of the foam molded body. Cut at a depth of 3 mm to obtain a surface GPC measurement sample. The surface layer of the foamed molded product corresponds to a portion having a radius of about 20% from the surface of the styrene resin particles. As the whole GPC measurement sample, resin particles themselves are used. The Z average molecular weight of the sample is measured using the following GPC (gel permeation chromatography). In addition, Z average molecular weight means the polystyrene conversion Z average molecular weight.

  3 mg of the above sample is dissolved in 10 mL of tetrahydrofuran (THF) (completely dissolved), and measured by filtration through a non-aqueous 0.45 μm chromatodisc. The weight average molecular weight of the sample is obtained from a standard polystyrene calibration curve that has been measured and prepared in advance. The chromatographic conditions are as follows.

・ Device: High-speed GPC device ・ Product name: HLC-8320GPC EcoSEC-WorkStation (built-in RI detector) manufactured by Tosoh Corporation
・ Analysis conditions Column: TSKgel SuperHZM-H × 2 (4.6 mm ID × 15 cmL × 2)
Guard column: TSK guard column Super HZ-H x 1 (4.6 mm ID x 2 cm L)
Flow rate: Sample side 0.175 ml / min, Reference side 0.175 ml / min
Detector: Built-in RI detector Concentration: 0.3 g / L
Injection volume: 50 μL
Column temperature: 40 ° C
System temperature: 40 ° C
Eluent: THF

(Create a calibration curve)
Standard polystyrene samples for calibration curves include standard polystyrene samples having a weight-average molecular weight of 500, 2630, 9100, 37900, 102000, 355000, 3840000, and 5480000 as trade name “TSK standard POLYSTYRENE” manufactured by Tosoh Corporation, and Showa Denko. A standard polystyrene sample having a weight average molecular weight of 1030000 with a trade name “Shodex STANDARD” manufactured by the company is used.
The method of creating a calibration curve is as follows. First, the standard polystyrene samples for calibration curves are group A (with a weight average molecular weight of 1030000), group B (with a weight average molecular weight of 500, 9100, 102000, and 3480000) and group C (with a weight average molecular weight of 2630, 37900). 355,000 and 5480000). 5 mg of a standard polystyrene sample belonging to group A having a weight average molecular weight of 1030000 is weighed and then dissolved in 20 mL of THF, and 50 μL of the resulting solution is injected into the sample side column. Standard polystyrene samples belonging to group B having weight average molecular weights of 500, 9100, 102000, and 3480000 are weighed 10 mg, 5 mg, 5 mg, and 5 mg, respectively, dissolved in 50 mL of THF, and 50 μL of the resulting solution is injected into the sample side column. . Standard polystyrene samples having a weight average molecular weight of 2630, 37900, 355000, and 5480000 belonging to group C were weighed 5 mg, 5 mg, 5 mg, and 1 mg, respectively, dissolved in 40 mL of THF, and 50 μL of the resulting solution was injected into the sample side column. . A calibration curve (tertiary equation) is prepared from the retention time of these standard polystyrene samples with a data analysis program GPC workstation (EcoSEC-WS) dedicated to HLC-8320GPC, and this is used as a calibration curve for polystyrene-equivalent weight average molecular weight measurement.

<Glass transition temperature>
The central part for measurement is an arbitrary part of a foam molded product having a density of 0.0166 g / cm ³ , and the foam molded body is dried at 50 ° C. for 24 hours, and then a ham slicer (Fujishima Koki Co., Ltd .: FK-18N type). And slice at a depth of 0.2 to 0.3 mm. Next, the diameter of the arbitrarily selected particle is measured on the sliced product, and the center of the particle and the center of the wire are penetrated through the center of the particle using a wire on a cylinder having an outer diameter of 30% of the diameter. And take a sample. On the other hand, the surface layer sample for measurement is obtained in the same manner as the Z-average molecular weight measurement. In addition, the glass transition temperature of the whole styrene resin particle | grains extract | collects the arbitrary locations of a foaming molding, and measures it as a sample.
(Sample processing)
A sample collected by the above method is dissolved in THF, impurities are filtered, and then reprecipitated in methanol. The precipitate is dried at 90 ° C. for 2 hours to obtain 6.5 ± 0.5 mg of a sample for measuring the glass transition temperature.
(Glass transition temperature measurement method)
Inflection point measurement is performed in accordance with JIS K7121 plastic transition temperature measurement method.
Measuring device: differential scanning calorimeter device DSC 6220 type (manufactured by SII Nanotechnology)
Sample amount: 6.5 ± 0.5 mg
Nitrogen gas flow rate: 20 mL / min
Measurement start / end temperature: -20 ° C to 70 ° C

<Bulk density of pre-expanded particles>
The bulk magnification of the pre-expanded particles is measured according to JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. Specifically, first, Wg is collected using pre-expanded particles as a measurement sample, and this measurement sample is naturally dropped into a measuring cylinder. The volume Vcm ³ of the measurement sample dropped into the graduated cylinder is measured using an apparent density measuring instrument based on JIS K6911. By substituting Wg and Vcm ³ into the following formula, the bulk density of the pre-expanded particles is calculated.
Bulk density of pre-expanded particles (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)

<Density of foam molding>
The mass (a) and volume (b) of a test piece (example 75 × 300 × 30 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).

<Average maximum bending strength>
The average maximum bending strength of the foam is measured according to the method described in JIS A9511. Specifically, the average maximum bending strength of the foam is measured according to the method described in JIS A9511: 1999 “Foamed plastic heat insulating material”. Specifically, a rectangular parallelepiped test piece having a length of 75 mm × width of 300 mm × thickness of 30 mm is cut out from a foam having a density of 16.7 kg / m ³ . Thereafter, this test piece was subjected to a bending strength measuring instrument (trade name “UCT-10T” manufactured by Orientec Co., Ltd.) under the conditions of a compression speed of 10 mm / min, a distance between fulcrums of 200 mm, a pressure wedge 10R and a support base 10R. Measure with Five test pieces are prepared, the maximum bending strength is measured for each test piece as described above, and the arithmetic average thereof is defined as the average maximum bending strength.
Maximum bending strength measurement condition Load (fs%) Start point = 0.0, End point = 20.0, Pitch = 0.2 (fs%)
Evaluation: Average maximum bending strength is 0.32 MPa or more: ○
Less than 0.32 MPa: ×
<Compressive strength>
The average maximum bending strength of the foam is measured according to the method described in JIS A9511. Specifically, the compressive strength of the foam is measured according to the method described in JIS A9511: 1999 “Foamed plastic heat insulating material”. Specifically, a rectangular parallelepiped test piece having a length of 100 mm × width of 100 mm × thickness of 30 mm is cut out from a foam having a density of 16.7 kg / m 3. Thereafter, this test piece is measured under the conditions of a compression speed of 10 mm / min and a compression jig R10 cm using a bending strength measuring instrument (trade name “UCT-10T” manufactured by Orientec Co., Ltd.). Five test pieces are prepared, and the 5% compressive strength is measured for each test piece as described above, and the arithmetic average is obtained.
Evaluation: Compressive strength is 0.10 MPa or more: ○
Less than 0.10 MPa: ×

  Examples are shown below, but the present invention is not limited to these examples.

Example 1
(Manufacture of seed particles)
Into a polymerization vessel equipped with a stirrer having an internal volume of 100 L, 40000 parts by mass of water, 100 parts by mass of magnesium pyrophosphate as a suspension stabilizer and 5.0 parts by mass of sodium dodecylbenzenesulfonate as an anionic surfactant are stirred and stirred with 40000 styrene. After adding 144.0 parts by mass of benzoyl peroxide and 28.0 parts by mass of t-butyl peroxybenzoate as a polymerization initiator and a polymerization initiator, the temperature was raised to 90 ° C. to polymerize. And it hold | maintained at this temperature for 6 hours, and also, after heating up to 125 degreeC, it cooled after 2 hours, and obtained the styrene-type resin particle (a).
The styrene resin particles (a) were sieved to obtain styrene resin particles (b) having a particle diameter of 0.5 to 0.71 mm as seed particles.

Next, 2340 g of seed particles of styrene resin (average particle diameter 0.63 mm; b) having a weight average molecular weight of 250,000, 30 g of magnesium pyrophosphate, and 10 g of sodium dodecylbenzenesulfonate are placed in a polymerization vessel equipped with a stirrer with an internal volume of 25 L. Was heated to 72 ° C. while stirring to prepare a dispersion.
Subsequently, a solution prepared by dissolving 45.9 g of benzoyl peroxide and 6.1 g of t-butylperoxybenzoate in a mixture of 850 g of styrene and 150 g of n-butyl acrylate was supplied to the dispersion while stirring.

And it maintained for 60 minutes, after supplying the said solution in a dispersion liquid (1st process).
Thereafter, while the temperature of the dispersion was raised to 88 ° C. over 60 minutes, 2660 g of styrene was charged into the polymerization vessel at a constant rate, and the reaction was carried out while absorbing the seed particles (second step).
Next, while maintaining the dispersion at 88 ° C., 500 g of styrene, 3500 g of methyl methacrylate, and 0.6 g of divinylbenzene were dissolved at a constant rate into the polymerization vessel over 90 minutes, and polymerized while being absorbed by the seed particles. Reaction was performed (third step). The polymerization conversion rate in the third step was maintained at 85 to 98%.

After the third step, the dispersion was further heated to 120 ° C. and held for 60 minutes to react unreacted monomers. The glass transition temperature of the entire styrene resin particles obtained was 97 ° C. Furthermore, Mz of the entire styrene resin particles was 650,000.
Next, the dispersion is kept at 100 ° C., and then 80 g of cyclohexane, 70 g of diisobutyl adipate and 700 g of normal butane are pressed into the polymerization vessel and held for 3 hours, whereby normal butane is contained in the resin particles. Was impregnated. Thereafter, the inside of the polymerization vessel was cooled to 25 ° C. to obtain expandable particles.

Polyethylene glycol was applied as an antistatic agent to the surface of the expandable particles. Thereafter, zinc stearate and hydroxystearic acid triglyceride were further applied to the surface of the expandable particles. After coating, the expandable particles were left in a thermostatic chamber at 13 ° C. for 5 days. The expandable particles were heated and pre-expanded to a bulk density of 0.0166 g / cm ³ to obtain pre-expanded particles. Pre-expanded particles were aged at 20 ° C. for 24 hours.
Next, the pre-expanded particles were filled in a mold and heated and foamed at a vapor pressure of 0.05 MPa to obtain a foamed molded product having a length of 400 mm × width of 300 mm × thickness of 30 mm. After the foamed molded product was dried in a drying chamber at 50 ° C. for 6 hours, the density was measured and found to be 0.0166 g / cm ³ (16.6 kg / m ³ ). The foamed molded article was excellent in appearance without shrinkage. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 101 ° C. and 1.3 million. The glass transition temperature at the center of the foamed molded product (resin particles) was 95 ° C. The bending strength of this foamed molded product was excellent at 0.330 MPa. In addition, the cross-sectional photograph of the foaming molding before and behind acquisition of the sample for the glass transition temperature and Mz measurement of a center part is shown to Fig.1 (a) and (b).

(Example 2)
A foamed molded article was obtained in the same manner as in Example 1, except that 100 g of styrene and 3900 g of methyl methacrylate were used instead of 500 g of styrene, 3500 g of methyl methacrylate, and 0.5 g of divinylbenzene. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 102 ° C. and 1.15 million. The glass transition temperature at the center of the foamed molded product (resin particles) was 95 ° C. Furthermore, the glass transition temperature and Mz of the entire resin particles were 98 ° C. and 630,000. The bending strength of this foamed molded product was excellent at 0.340 MPa.
(Example 3)
A foamed molded article was obtained in the same manner as in Example 1 except that only 4000 g of methyl methacrylate was used instead of 500 g of styrene, 3500 g of methyl methacrylate, and 0.5 g of divinylbenzene. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 104 ° C. and 750,000. The glass transition temperature at the center of the foamed molded product (resin particles) was 96 ° C. Furthermore, the glass transition temperature and Mz of the entire resin particles were 99 ° C. and 670,000. The bending strength of this foamed molded product was excellent at 0.347 MPa.

Example 4
A foamed molded article was obtained in the same manner as in Example 1, except that styrene 500 g, α-methylstyrene 1000 g was used instead of styrene 500 g, methyl methacrylate 3500 g, and divinylbenzene 0.5 g. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 115 ° C. and 740,000. The glass transition temperature at the center of the foamed molded product (resin particles) was 96 ° C. Further, the glass transition temperature and Mz of the entire resin particles were 99 ° C. and 680,000. The bending strength of this foamed molded product was excellent at 0.355 MPa.
(Example 5)
A foam molded article was obtained in the same manner as in Example 1 except that 500 g of styrene, 3500 g of methyl methacrylate, and 1.2 g of divinylbenzene were used instead of 500 g of styrene, 3500 g of methyl methacrylate, and 0.5 g of divinylbenzene. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 102 ° C. and 1.87 million. The glass transition temperature at the center of the foamed molded product (resin particles) was 95 ° C. Furthermore, the glass transition temperature and Mz of the entire resin particles were 97 ° C. and 670,000. The bending strength of this foamed molded product was excellent at 0.352 MPa.

(Comparative Example 1)
A foamed molded article was obtained in the same manner as in Example 1, except that styrene 4000 g was used instead of 500 g of styrene, 3500 g of methyl methacrylate, and 0.5 g of divinylbenzene. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 96 ° C. and 630,000. The glass transition temperature at the center of the foamed molded product (resin particles) was 96 ° C. Further, the glass transition temperature and Mz of the entire resin particles were 97 ° C. and 640,000. The bending strength of the foamed molded product was inferior at 0.310 MPa.
(Comparative Example 2)
A foamed molded article was obtained in the same manner as in Example 1 except that 2000 g of styrene and 2000 g of α-methylstyrene were used instead of 500 g of styrene and 3500 g of methyl methacrylate. The glass transition temperature and Mz of the surface layer of the obtained foamed molded product (resin particles) were 124 ° C. and 1.12 million. The glass transition temperature at the center of the foamed molded product (resin particles) was 95 ° C. Furthermore, the glass transition temperature and Mz of the entire resin particles were 101 ° C. and 650,000. The bending strength of this foamed molded product was inferior at 0.297 MPa.
The results of Examples 1 to 5 and Comparative Examples 1 and 2 are summarized in Table 1.

  From Examples 1 to 5 and Comparative Examples 1 and 2, it can be seen that a foam molded article having improved mechanical strength can be obtained even with a small amount of steam by having a glass transition temperature that is 2 to 5 ° C. lower than the center. .

Claims (8)

It is a styrene resin particle containing a resin component derived from a monofunctional acrylate ester,
The styrenic resin particles have a central glass transition temperature that is 2 to 5 ° C. lower than the entire glass transition temperature.   The styrenic resin particles according to claim 1, wherein the styrenic resin particles have a surface glass transition temperature that is 5 to 20 ° C higher than the entire glass transition temperature.   The center part includes a resin component derived from a monofunctional acrylate ester having an alkyl group having 1 to 10 carbon atoms, and the surface layer is derived from a monofunctional methacrylate ester or α-methylstyrene having an alkyl group having 1 to 10 carbon atoms. The styrenic resin particles according to claim 2, comprising the following resin component. The styrenic resin particles according to claim 3 , wherein the monofunctional acrylic ester is butyl acrylate, and the monofunctional methacrylic ester is methyl methacrylate. The styrenic resin particles according to any one of claims 2 to 4, wherein the surface layer has a Z average molecular weight of 700,000 to 2,000,000.   Expandable particles comprising the styrenic resin particles according to any one of claims 1 to 5 and a foaming agent.   Expanded particles obtained by expanding the expandable particles according to claim 6.   A foam-molded product obtained by foam-molding the foamed particles according to claim 7.