JP2012072314A - Styrenic resin foamed body, foamable styrenic resin particle, and method of producing the styrenic resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a styrenic resin foamed body having sufficient strength even in low density.SOLUTION: The styrenic resin foamed body includes: air bubbles each surrounded with a foam film consisting of a styrenic resin; and a scale-like silicate lying in the foam film. The foam film has an average foam film thickness of 0.2-2.0 μm, and the scale-like silicate has a thickness of 0-50% of the average foam film thickness.

Description

  The present invention relates to a styrene resin foam, expandable styrene resin particles, and a method for producing the same. More specifically, the present invention relates to a styrene resin foam excellent in bending strength, an expandable styrene resin particle that can be used for the production of the foam, and a method for producing the expandable styrene resin particle.

Styrenic resin foams are generally foamed by heating and foaming expandable styrene resin particles with steam or the like to form pre-expanded particles, which are filled into a closed mold having a large number of small holes, and heated again with pressurized steam or the like. It is manufactured by foaming, filling gaps between the foamed particles, and fusing the foamed particles together, then cooling and taking out from the mold.
The expandable styrene resin particles are usually produced by suspending and polymerizing a styrene monomer in water and impregnating with a foaming agent, or as disclosed in Japanese Patent Publication No. 49-2994 (Patent Document 1). The styrene resin particles are produced by a method of suspending styrene resin particles in water, supplying a styrene monomer continuously or intermittently thereto for polymerization, and impregnating with a foaming agent (seed polymerization method). Furthermore, it is manufactured by melting a styrene resin in an extruder, kneading a foaming agent, and then extruding it into a heated heating medium from a mold having small holes and cutting it into particles.

The styrene resin foam is used as, for example, a heat insulating material, a buffer material, or a structural member. In such applications, high strength is required for the styrene resin foam. Conventionally, foams having a density of about 10 to ³⁰ kg / m ³ are frequently used for styrene resin foams, but from the viewpoint of resource saving, styrene resin foams that can maintain strength even when the density is further reduced. Is desired.
Therefore, a low-density, high-strength styrene resin foam has been conventionally demanded, and measures for increasing the strength are considered.

  For example, Japanese Examined Patent Publication No. 57-34296 (Patent Document 2) obtains a styrene resin foam in which a large number of fine bubbles are formed by containing a specific thiourea compound in a styrene resin particle together with a foaming agent. A method is described. Japanese Patent Publication No. 55-49631 (Patent Document 3) contains a specific thiodipropionic acid ester or thiodibutyric acid ester together with a predetermined foaming agent in a styrene resin particle, A method for obtaining a styrene resin foam in which a large number of air bubbles are formed is described.

Japanese Patent Publication No.49-2994 Japanese Patent Publication No.57-34296 Japanese Patent Publication No.55-49631

The above method aims to increase the number of bubble films and improve the strength of the foam by making the bubbles finer. However, when the cell diameter is reduced by the above-described method or the like, the styrene resin foam has a property that the strength rapidly decreases as the density decreases, and the conventional method does not provide sufficient strength.
Therefore, it has been desired to provide a styrene resin foam having a sufficient strength even when the density is low.

The inventor of the present invention has a low density by a styrene resin foam containing a bubble film having a specific range of average cell thickness and a flaky silicate having a specific thickness located in the cell membrane, Surprisingly, it has been found that a styrene resin foam having sufficient strength can be provided, and the present invention has been achieved.
Thus, according to the present invention, comprising bubbles surrounded by a bubble film made of styrenic resin, and scaly silicate located in the bubble film,
The cell membrane has an average cell thickness of 0.2 to 2.0 μm;
There is provided a styrenic resin foam in which the scaly silicate has a thickness of more than 0% and less than 50% of the average bubble film thickness.

Moreover, according to the present invention, there is provided a method for producing expandable styrene resin particles used for producing the styrene resin foam,
Styrenic resin particles dispersed in an aqueous medium in a reaction vessel are impregnated with a styrenic monomer after impregnated with a styrenic monomer seed particle, or polymerized while impregnating the styrenic resin particles. Obtaining a step;
Impregnating the styrenic resin particles with a foaming agent or impregnating the foaming agent during polymerization of the styrenic monomer,
The impregnation and polymerization of the styrenic monomer are performed in a reaction vessel maintained at an oxygen concentration of 15% by volume or more,
The styrenic monomer is supplied into the aqueous medium so that the amount of the styrenic monomer in the styrenic growing resin particles from the beginning of impregnation of the styrenic monomer to the end of polymerization is 40% by mass or less. A method for producing expandable styrene resin particles is provided.
Moreover, according to this invention, the expandable styrene resin particle obtained by said manufacturing method is provided.

According to the present invention, it is possible to provide a styrenic resin foam that is excellent not only in foam moldability but also in bending strength even when the density is lowered. The inventor believes that this is because the cell membrane is reinforced with scaly silicate.
In addition, when the flaky silicate has an aspect ratio of 10 to 1000 and the styrene resin foam has a density of 10 to ³⁰ kg / m ³ , the foam moldability is excellent even when the density is lowered, and the bending strength is higher. It is possible to provide a styrenic resin foam having excellent resistance.
Furthermore, when the scaly silicate is natural mica, synthetic mica or sericite, it is possible to provide a styrenic resin foam having excellent foam moldability and superior bending strength even when the density is reduced.

The inventor of the present invention reviewed the structure of the foam as described below in order to lower the density and increase the strength of the styrene resin foam (hereinafter also referred to as a foam).
That is, the strength of the foam is generally greatly influenced by the bubble diameter, the bubble film thickness, the bubble density, the open cell ratio, and the foam density forming the foam. Among them, it has been conventionally considered that increasing the number of bubble films by reducing the bubble diameter (making fine bubbles) is effective in improving the strength.
However, when the bubble diameter is reduced, the bubble film thickness is reduced, and the bubbles are torn by heating during molding, so that the moldability and strength are easily lowered. Thus, it was very difficult to achieve both low density and high strength.
Therefore, as a result of investigation by the present inventors, the average bubble film thickness was adjusted to 0.5 to 2.0 μm, and the thickness of the flaky silicate present in the bubble film was larger than 0% of the bubble film thickness, and 50 It was found that a foam having a very low decrease in bending strength even when the density was decreased can be obtained by adjusting the content to less than%.

(Foam)
The foam of the present invention includes bubbles surrounded by a bubble film made of a styrene resin having an average cell thickness of 0.5 to 2.0 μm.
When the average cell thickness is less than 0.5 μm, the cell membrane is easily broken at the time of molding and the strength is lowered, and the foam tends to shrink. Furthermore, when it is larger than 2.0 μm, the number of bubbles in the foam becomes too small, and the strength may be lowered. The average cell thickness is preferably 0.7 to 1.5 μm.

The foam preferably has a density of 10 to ³⁰ kg / m ³ . By having the density in this specific range, a foam having higher bending strength can be provided. A more preferable density is 12.5 to 20.0 kg / m ³ .
The foam can be used for applications such as cushioning materials (cushion materials) such as 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 or a door interior cushioning material.

(1) Styrenic resin The foam includes a bubble film made of a styrene resin. The styrene resin is not particularly limited, and for example, a styrene monomer such as styrene, α-methyl styrene, paramethyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, i-propyl styrene, dimethyl styrene, bromo styrene, or the like. Examples thereof include a polymer or a copolymer thereof. The styrene resin preferably contains 50% by mass or more of a component derived from styrene, and more preferably consists of polystyrene.

  The styrene resin may be a copolymer of a styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. In the case of a copolymer, it is preferable that a component derived from a styrene monomer occupies a main component (50% by mass or more, preferably 80% by mass or more, more preferably 99.8 to 99.9% by mass). Examples of such vinyl monomers include alkyl (meth) acrylates having 1 to 8 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate, (meth) In addition to acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate and ethyl fumarate, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate, maleic anhydride, N-vinylcarbazole and the like can be mentioned.

(2) Scale-like silicate Scale-like silicate has a relative thickness that is greater than 0% of the average bubble film thickness and 50% or less, thereby realizing low density and high strength. When the thickness of the scaly silicate is 50% or more of the average cell thickness, the cell membrane is easily broken at the time of foam molding, the foam moldability is lowered, it is difficult to reduce the density, and the strength is also lowered.
Furthermore, the scaly silicate preferably has an aspect ratio of 10 to 1000. By having an aspect ratio in this range, low density and high strength can be realized. When the aspect ratio is less than 10, the effect of adding scaly silicate may be lowered. On the other hand, when the aspect ratio is larger than 1000, the bubble film is easily broken during foam molding. For this reason, foam moldability is lowered, making it difficult to reduce the density, and the strength may also be lowered.

Examples of scaly silicate include natural mica, synthetic mica, and sericite. Unlike natural mica, synthetic mica is an artificially produced mica having a composition in which all —OH groups in the crystal structure of natural mica are substituted with —F groups, and KMg ₃ AlSi ₃ O ₁₀ F ₂ is the ideal composition.
The surface of the scaly silicate may be coated with a metal oxide. Examples of such metal oxides include titanium oxide and iron oxide. Specific examples of the scaly silicate having a surface coated include natural mica or synthetic mica whose surface is coated with titanium oxide, and natural mica or synthetic mica whose surface is coated with iron oxide.

The content of the metal oxide is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and particularly preferably 30 to 60% by mass in the scale-like silicate whose surface is coated with the metal oxide.
Further, the surface of the scaly silicate is preferably treated with a silane coupling agent, a titanium coupling agent, or another surface treatment agent for the purpose of improving the compatibility with the styrene resin.
The content of scaly silicate is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass. If it is less than 3% by mass, the effect is low, and if it is more than 20% by mass, foam moldability and strength may be lowered.

  Furthermore, if the specific thickness of the scaly silicate is thin, it may be crushed before the foam is produced, and the foam may not exhibit the desired strength. On the other hand, if it is thick, the foam film of the foam is easily broken, and it may be difficult to obtain a foam with a high expansion ratio. Therefore, the thickness of the scaly silicate is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. In addition, the thickness of the scaly silicate is preferably 0.01 μm or more, more preferably 0.03 μm or more, and even more preferably 0.05 μm or more.

(3) Production method of foam For example, the foam is obtained by impregnating a styrene resin particle with a foaming agent to obtain a foamable styrene resin particle, and then prefoaming the foamable styrene resin particle. After being obtained, it can be produced by filling it into a mold and heating and foaming.
Expandable styrene resin particles are, for example,
(I) Styrenic resin seed particles (hereinafter referred to as seed particles) are dispersed in an aqueous medium, and a styrene monomer is continuously or intermittently supplied thereto, and suspension polymerization is performed in the presence of a polymerization initiator, and a foaming agent. Particles obtained by so-called seed polymerization method, or (ii) a styrenic monomer is continuously or intermittently supplied into an aqueous medium and subjected to suspension polymerization in the presence of a polymerization initiator, and a foaming agent The particle | grains obtained by the method of impregnating, what is called suspension polymerization method, etc. can be used.

In particular, the seed polymerization method is preferable for obtaining a foam having an average cell diameter in a specific range according to the present invention because the cell diameter is easier to prepare than that obtained by the suspension polymerization method.
The expandable styrene resin particles obtained by the seed polymerization method can be manufactured through the following steps, for example.
(A) Styrenic resin by impregnating a styrenic resin seed particle containing scaly silicate dispersed in an aqueous medium in a reaction vessel with a styrenic monomer, or polymerizing while impregnating. Step of obtaining resin particles (B) Step of impregnating styrene resin particles with foaming agent or impregnating foaming agent during polymerization of styrenic monomer Preparation to an average cell thickness of 0.5 to 2.0 μm is as follows: For example, a method for selecting the type of surfactant, a method for adding an additive having an effect of preparing bubbles (for example, stearate, sulfur compound, low molecular weight polyethylene), and a polymerization temperature are prepared. Method, method of selecting the type of polymerization initiator, method of selecting the type of blowing agent, method of adjusting the impregnation amount of the blowing agent, and seed polymerization method, the monomer supply rate is adjusted. The method or the like, can be carried out by a method commonly used in the bubble preparation of styrenic resin foam.

(A) Seed particles As the monomer for obtaining seed particles, any of the styrenic monomers and vinyl monomers mentioned in the section of the foam can be used. When the styrene-based weight average molecular weight of the styrene resin constituting the seed particles is small, the mechanical strength of the foam obtained by foaming the expandable styrene resin particles may be lowered. On the other hand, if it is large, the foamability of the expandable styrene resin particles may be lowered. A preferable average molecular weight is 120,000 to 600,000.

  If the particle diameter of the seed particles is within a narrow range, the particle diameter of the expandable styrene resin particles can be well aligned. In view of this, it is possible to use, as seed particles, particles prepared by once sieving the particles obtained by the suspension polymerization method so that the particle diameter is in the range of ± 20% of the average particle diameter. When seed particles are obtained by the bulk polymerization method, pellets having a desired particle size can be used. Therefore, according to the seed polymerization method, expandable styrene resin particles having a desired particle size range according to the application can be produced with a yield of almost 100%. For example, particles classified as 0.3 to 0.5 mm, 0.5 to 0.7 mm, 0.7 to 1.2 mm, 1.2 to 1.5 mm, 1.5 to 2.5 mm are desired. It can be selected according to the average particle diameter of the expandable styrene resin particles.

The seed particles preferably contain a styrene resin and a scaly silicate.
Moreover, it is preferable that seed particle | grains contain beforehand the quantity of scaly silicate contained in a foam. For example, it is preferable to use seed particles containing 1.2 to 40% by mass of flaky silicate. When the scale-like silicate in the seed particles is less than 1.2% by mass, the strength improvement may not be remarkable. Moreover, when it exceeds 40 mass%, it may become difficult to manufacture seed particles. As for content of the scale-like silicate in a seed particle, it is more preferable that it is 3-30 mass%.

(B) Aqueous medium Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, a lower alcohol).
(C) Styrenic monomer As the styrenic monomer, the styrenic monomer mentioned in the column of the foam can be used. Moreover, you may add the vinyl monomer quoted in the column of the said foam to the styrene-type monomer.

(D) Polymerization initiator As the polymerization initiator, any radical-generating polymerization initiator used in usual suspension polymerization of styrene can be used. For example, benzoyl peroxide, lauryl peroxide, t-butyl peroxybenzoate, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butyl peroxybutane, Organic peroxides such as t-butylperoxy-3,3,5-trimethylhexanoate and di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile Is mentioned. These polymerization initiators may be used alone or in combination of two or more. In order to adjust the molecular weight and reduce the residual monomer, the polymerization temperature is in the range of 50-80 ° C to obtain a half-life of 10 hours, and the decomposition temperature is in the range of 80-120 ° C It is desirable to use a polymerization initiator in combination.

(E) Use amount of seed particles The use amount of seed particles is preferably 10 to 90 mass%, more preferably 15 to 50 mass%, based on the total amount of resin particles at the end of polymerization. When the amount of seed particles used is less than 10% by mass, it is difficult to control the polymerization rate of the particles to an appropriate range when supplying the styrene monomer, and the resulting particles have a high molecular weight or a large amount of fine powder is generated. Doing so is disadvantageous industrially, such as a reduction in production efficiency. On the other hand, if it exceeds 90% by mass, it is difficult to obtain excellent foam moldability.

(F) Other components A suspension stabilizer may be used to stabilize the dispersibility of the styrene monomer droplets and seed particles.
Examples of the suspension stabilizer include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly soluble inorganic compounds such as tricalcium phosphate and magnesium pyrophosphate. Here, when a poorly soluble inorganic compound is used, an anionic surfactant is usually used in combination.

  The anionic surfactant functions as an auxiliary stabilizer for stabilizing the dispersion by the suspension stabilizer, and is obtained by being partially dissolved or entrained in the styrene polymer particles. This may affect the size of the bubble diameter in the foam. Therefore, what is necessary is just to select the kind of anionic surfactant so that it may fall in the range of a desired bubble film thickness.

  Examples of the anionic surfactant include fatty acid soaps, N-acyl amino acids or salts thereof, carboxylates such as alkyl ether carboxylates, alkylbenzenesulfonates such as calcium dodecylbenzenesulfonate and sodium dodecylbenzenesulfonate, alkyls Sulfonates such as naphthalene sulfonate, dialkyl sulfosuccinate, alkyl sulfoacetate, α-olefin sulfonate, higher alcohol sulfate, secondary higher alcohol sulfate, alkyl ether sulfate, polyoxy Examples thereof include sulfuric acid ester salts such as ethylene alkylphenyl ether sulfate, and phosphoric acid ester salts such as alkyl ether phosphoric acid ester salts and alkyl phosphoric acid ester salts.

  Furthermore, in order to adjust the average cell diameter of the foam obtained by foaming the expandable styrene resin particles, 5-10 minutes before the end of the seed polymerization, immediately after the end of the seed polymerization, or on the styrene resin particles After impregnating the foaming agent, the cell preparation agent may be added to the styrene resin particles so as to be 0.01 to 0.8% by mass. Examples of such foam preparation agents include stearates such as ethylene bis stearic acid amide, triglycerin fatty acid esters, and the like.

(G) Polymerization conditions The polymerization is usually carried out by maintaining heating at 60 to 150 ° C for 1 to 10 hours, although it varies depending on the monomer species, polymerization initiator species, polymerization atmosphere species, and the like.
Examples of the polymerization atmosphere include an atmosphere in which the oxygen concentration in the reaction vessel during the polymerization reaction is maintained at 15% by volume or more. This particular oxygen concentration is useful when the foam contains scaly acid salts. That is, when the oxygen concentration is less than 15% by volume, a large amount of scaly silicate tends to be contained on the surface of the expandable styrene resin particles. Therefore, when pre-expanded particles obtained by pre-expanding expandable styrenic resin particles are secondarily expanded, bubbles on the surface of the pre-expanded particles may be broken by scaly silicate. As a result, high foaming magnification of the foam may be hindered. In addition, it is impossible to obtain a foaming pressure for sufficiently preliminarily fusing the pre-expanded particles by fusing, resulting in inadequate heat fusing integration between the expanded particles. The mechanical strength of the resulting foam may be reduced. A more preferable oxygen concentration is in the range of 15 to 21% by volume.

The amount of the styrene resin seed particles used and the total amount of the styrene monomer supplied to the dispersion are 3 to 10 masses per 100 parts by mass of the styrene resin particles from which the scaly silicate contained in the seed particles is obtained. It is preferable to prepare so that it may become the range of a part.
In addition, the styrene monomer should be supplied to the aqueous medium so that the amount of the styrene monomer in the styrene-based growing resin particles from the beginning of impregnation of the styrene monomer to the end of polymerization is 40% by mass or less. Is preferred. By maintaining this amount of styrene monomer during polymerization, the average cell thickness desired by the present invention can be obtained.

(H) Styrenic resin particles The particle diameter of the styrene resin particles is preferably 0.3 to 2.0 mm from the viewpoint of filling into the mold of pre-expanded particles described later, More preferably, it is 1.4 mm.
Furthermore, if the styrene-based weight average molecular weight (Mw) of the styrene resin constituting the styrene resin particles is small, the mechanical strength of the foam obtained by foaming the expandable styrene resin particles may decrease. . On the other hand, if it is large, the foamability of the expandable styrenic resin particles is lowered, and a foam having a high expansion ratio may not be obtained. A preferable weight average molecular weight is 100,000 to 700,000 suitable for ordinary foam molding, and more preferably 150,000 to 400,000. Moreover, it is preferable to prepare the weight average molecular weight of the seed particles in a range suitable for the above foam molding.

  In order to adjust the weight average molecular weight to a range suitable for ordinary foam molding, it is important to make the polymerization initiator work efficiently. To prevent unnecessary decomposition and generate radicals throughout the polymerization process, In the distribution, polymerization temperature program, and seed polymerization method, it is preferable to further adjust and control the monomer supply rate, the polymerization rate during polymerization, and the like.

(I) Impregnation step The impregnation with the foaming agent may be performed on the particles after the polymerization of the styrene monomer, or the growing particles may be impregnated with the foaming agent. Impregnation during the polymerization can be performed by a method of impregnation in an aqueous medium (wet impregnation method). The impregnation after polymerization can be carried out by a wet impregnation method or a method of impregnation in the absence of a medium (dry impregnation method). Moreover, it is preferable to perform the impregnation in the middle of polymerization normally in the latter stage of polymerization.

Examples of the blowing agent include readily volatile compounds having a boiling point equal to or lower than the softening point of the polymer, such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, and petroleum ether. Hydrocarbons such as acetone, methyl ethyl ketone, alcohols such as methanol, ethanol, isopropyl alcohol, low boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, HCFC-141b, HCFC- 142b, HCFC-124, HFC-134a, HFC-152a and other halogen-containing hydrocarbons, carbon dioxide, nitrogen, ammonia and other inorganic gases. 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 change with time of the foam. Of the carbon hydrogen, it is more preferable to use butane.
The amount of the foaming agent used is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass with respect to 100 parts by mass of the expandable styrene resin particles.

(J) Others A solvent or a plasticizer may be added to the expandable styrene resin particles.
Examples of the solvent include aromatic organic compounds such as styrene, toluene, ethylbenzene, and xylene, cyclic aliphatic hydrocarbons such as cyclohexane and methylcyclohexane, ethyl acetate, and butyl acetate.
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.

When the content of the solvent and the plasticizer in the expandable styrene resin particles is small, the effect of adding the solvent and the plasticizer may not be exhibited. On the other hand, when the content is large, the foam obtained using the expandable styrene-based resin particles may be contracted or melted to deteriorate the appearance. The preferable content is 0.1 to 1.5% by mass, and more preferably 0.2 to 1.0% by mass, based on the total amount of the expandable styrene resin particles.
The impregnation with the solvent and the plasticizer can be performed on the particles after the polymerization of the styrenic monomer or the growing particles. Further, a solvent or a plasticizer may be added to the seed particles in advance.

  When the impregnation temperature of the solvent and the plasticizer into the styrene resin particles, seed particles or growing particles is low, the impregnation takes time, and the production efficiency of the expandable styrene resin particles may be lowered. On the other hand, when it is high, coalescence of the expandable styrene resin particles may occur in a large amount. The impregnation temperature is preferably 60 to 120 ° C, more preferably 70 to 100 ° C.

Furthermore, the expandable styrenic resin particles of the present invention contain other additives such as a foam cell nucleating agent, a filler, a flame retardant, a flame retardant aid, a lubricant, and a colorant within a range that does not impair the physical properties. You may go out. Other additives can be included in the expandable styrene resin particles in the same manner as the solvent and plasticizer.
Examples of the flame retardant include tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, and the like. And when there is little content of the flame retardant in an expandable styrene resin particle, the flame retardance of the foam obtained using an expandable styrene resin particle may become inadequate. On the other hand, in many cases, the moldability of the expandable styrene resin particles may decrease. The content of the flame retardant is preferably 0.5 to 1.5% by mass.

  Moreover, as a flame retardant adjuvant, the organic peroxide like a dicumyl peroxide is mentioned, for example. And when there is little content of a flame retardant adjuvant in an expandable styrene-type resin particle, the effect which added the flame retardant adjuvant may not express. On the other hand, in many cases, the foam moldability of the expandable styrene resin particles may be lowered. The content of the flame retardant aid is preferably 0.05 to 0.5% by mass.

(K) Pre-expanded particles The expandable styrene-based resin particles are pre-expanded particles having a large number of small holes by being pre-expanded with water vapor or the like in a pre-foaming machine. The bulk magnification of the pre-expanded particles is in the range of 30 to 100 times. When the bulk expansion ratio of the pre-expanded particles is larger than 100 times, the resulting foam may shrink and the appearance may be deteriorated. In addition, the thermal insulation performance and mechanical strength of the foam may decrease. On the other hand, when the bulk density is less than 30 times, not only the lightness of the foam is lowered, but also the effect of adding scaly silicate may be reduced.

(L) Molding of foam The pre-expanded particles are filled into a closed mold having a large number of small holes, and again heated and foamed with pressurized steam or the like to fill the gaps between the pre-expanded particles and A foam can be manufactured by fusing. At that time, the density of the foam can be adjusted, for example, by adjusting the filling amount of the pre-expanded particles in the mold.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited by these Examples. Various measurement methods in the examples are described below.
<Thickness of scaly silicate>
Examples of methods for measuring the average particle size of the flaky silicate include a method for obtaining an average particle size by a microtrack laser diffraction method or a micro sieve mesh sieve method, a method for obtaining by observation with an electron microscope, and the like. Although there is a difference in the particle diameter depending on the measurement method, the micro sieve mesh sieve method and the electron microscope are close to the actual particle diameter, and the micro track laser diffraction method is slightly larger than the actual particle diameter. The average particle diameter in the present specification is measured by a microtrack laser diffraction method from the viewpoint of ease of measurement and high reproducibility.

  The aspect ratio of the scaly silicate is measured under observation with a scanning electron microscope (Hitachi High-Technologies scanning electron microscope S-2400, hereinafter referred to as SEM). Specifically, the sample fixed on the SEM sample stage is increased from the direction of the cleaved surface (smooth surface) or laminated cross section (fracture surface) by increasing the observation magnification up to the maximum when one particle enters the field of view. Capture images (shoot). Next, the sample stage is rotated to capture (capture) an image from a direction different from the previous direction. From the image (photograph) thus obtained, the maximum length of the cleavage plane and the thickness of the laminated section are measured. Divide the measured value of the cleavage plane by the measured value of the laminated cross section to obtain the aspect ratio for each sample. This operation is performed on 100 mica flakes arbitrarily extracted. The average value of 100 aspect ratios is defined as the aspect ratio of the present specification.

<Styrene monomer amount>
The method for measuring the amount of styrene monomer in styrene resin growing particles (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 the 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 the Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight 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 (milliliter) of the sample. The Wis reagent is obtained by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.

On the other hand, without dissolving the growing particles, 10 ml of Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution are added to 24 ml of toluene. The resulting solution was titrated with a N / 40 sodium thiosulfate solution to give a blank titration (in milliliters).
From the obtained droplet constant, the amount of styrene monomer in the growing particles is calculated based on the following formula.
Amount of styrenic monomer in the growing particles (% by mass)
= 0.1322 × (blank drop constant−sample drop constant) / sample drop constant

<Weight average molecular weight>
A weight average molecular weight means the styrene conversion weight average molecular weight measured in the following ways.
That is, 30 mg of styrene resin is dissolved in 10 ml of chloroform. The resulting solution is filtered through a non-aqueous 0.45 μm chromatographic disk, and the average molecular weight is measured under the following conditions using a chromatograph.
Gas chromatograph: Product name “Detector 484, Pump 510” manufactured by Water
Column: Showa Denko Corporation trade name “Shodex GPC K-806L (φ8.0 × 300 mm)” Column temperature: 40 ° C.
Carrier gas: Chloroform Carrier gas flow rate: 1.2 ml / min injection / pump temperature: room temperature detection: UV254 nm
Injection amount: Standard polystyrene for 50 microliter calibration curve: Trade name “shodex” manufactured by Showa Denko KK Weight average molecular weight: 1030000 Polystyrene

<Scaly silicate content>
The foamable styrene resin particles are treated at 150 ° C. for 3 hours to dissipate the foaming agent. Place 1.0 g (mass of sample before ashing) of the residue after dissipation into a magnetic crucible with a capacity of 30 mL. The residue is incinerated by heating at 550 ° C. for 5 hours in an electric furnace (muffle furnace STR-15K (made by Isuzu)). The magnetic crucible is allowed to cool to room temperature (25 ° C.) in a desiccator. The mass of the sample after ashing in the magnetic crucible after standing to cool is measured. By substituting the mass of the sample before and after ashing into the following equation, the scaly silicate content (parts by mass) relative to 100 parts by mass of the styrene resin is calculated.
Scale-like silicate content (parts by mass) = Sample mass after ashing / Sample mass before ashing

<Bulk multiple>
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)
The bulk multiple is the reciprocal of the bulk density.

<Foam density>
The mass (a) and the volume (b) of a test piece (example 75 × 300 × 35 mm) cut out from a foam (after molding and dried at 40 ° C. for 20 hours or more) are 3 significant digits or more, respectively. And the density of the foam (kg / m ³ ) is determined by the formula (a) / (b).

<Bending strength>
A rectangular parallelepiped test piece having a length of 200 mm, a width of 75 mm and a thickness of 30 mm is cut out from a foam having a density of 16 kg / m ³ . And the bending strength of this test piece is measured according to JIS A-9511 at a span of 100 mm and a head speed of 10 mm / min. The case where the obtained bending strength is 0.12 MPa or more is evaluated as ◯ evaluation (good strength), and the case where it is less than 0.12 MPa is evaluated as x evaluation (strength failure).

<Average bubble film thickness>
The thickness of the bubble film is measured from a scanning electron micrograph of the cut surface of the foam. The number of measurements is 50, and the average is the average bubble film thickness.

<Moldability>
The case where the adhesive strength between the pre-expanded particles is weak and the shape cannot be maintained as a foam is indicated as x, and the case where the shape can be maintained is indicated as ◯.

<Comprehensive evaluation>
For foams having a good evaluation of formability and bending strength, the overall evaluation is good. For foams that have at least one evaluation of x, the overall evaluation is x.

Example 1
8000 parts by mass of a styrene resin (A) having a weight average molecular weight of 250,000 in terms of styrene (MS-100 manufactured by Sekisui Plastics Co., Ltd.) and a silane coupling agent (silane coupling agent KBE-503 manufactured by Shin-Etsu Chemical Co., Ltd.) in advance. 2,000 parts by weight of natural mica (A-61 manufactured by Yamaguchi Mica Kogyo Co., Ltd.) having a thickness of 0.3 μm and an aspect ratio of 170 was supplied to a twin screw extruder and melt kneaded at 230 ° C. for extrusion. Extruded into a strand from the machine, this strand is cut into predetermined lengths, and cylindrical styrene resin seed particles containing 20% by mass of flaky silicate (diameter: 1.0 mm, length: 1.5 mm) Was made.

Next, 2,000 parts by weight of water, 500 parts by weight of seed particles, 6 parts by weight of magnesium pyrophosphate, and 0.3 parts by weight of calcium dodecylbenzenesulfonate are supplied to a polymerization vessel equipped with a stirrer and heated to 70 ° C. while stirring. A dispersion was prepared.
Subsequently, 4.5 parts by mass of benzoyl peroxide and 1.1 parts by mass of t-butylperoxybenzoate were dissolved in 200 parts by mass of styrene monomer, and all the styrene monomer was supplied to the dispersion while stirring.

  Then, 30 minutes after supplying the styrene monomer into the dispersion, the dispersion was heated to 90 ° C., and 1300 parts by mass of the styrene monomer was further added to the dispersion at a constant supply rate over 3.5 hours. After supplying all the styrene monomers, the mixture was heated to 125 ° C. and allowed to stand for 2 hours, and then cooled to obtain styrene resin particles (B). When the amount of styrene monomer in the growing styrene-based resin growing particles was measured every 10 minutes from the start of supplying the styrene monomer into the dispersion, the maximum value was 22.5% by mass. The weight average molecular weight was 311,000.

  Next, after the dispersion liquid in which the styrene resin particles (B) are dispersed is heated to 70 ° C., 23.4 parts by mass of tetrabromocyclooctane as a flame retardant and 5.4 parts by mass of dicumyl peroxide as a flame retardant aid. Was supplied to the dispersion, and the polymerization vessel was sealed and heated to 90 ° C. Subsequently, 162 parts by mass of butane was pressed into the polymerization vessel and held for 6 hours. After impregnating butane into the styrene resin particles (B), the polymerization vessel was cooled to 30 ° C. and foamed. Styrenic resin particles were obtained. The obtained expandable styrene resin particles had a natural mica content of 5.0% by mass.

After applying polyethylene glycol as an antistatic agent to the surface of the expandable styrene resin particles, zinc stearate and hydroxystearic acid triglyceride were applied to the surface of the expandable styrene resin particles. In addition, each of zinc stearate and hydroxystearic acid triglyceride was prepared to be 0.05% by mass in the expandable styrene resin particles.
Thereafter, the expandable styrenic resin particles were left in a thermostatic chamber at 13 ° C. for 5 days. Then, the expandable styrene resin particles were heated and pre-expanded to a bulk density of 16.0 kg / m ³ to obtain pre-expanded particles. The 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 to obtain a plate-like foam having a length of 400 mm × width of 300 mm × thickness of 30 mm. The average bubble film thickness was 1.1 μm.

(Example 2)
A styrene-based resin foam was obtained in the same manner as in Example 4 except that scaly silicate having a thickness of 0.40 μm and an aspect ratio of 120 was used. The content of natural mica was 4.9% by mass. The maximum value of the amount of styrene monomer during polymerization was 21.0% by mass. The average cell thickness of the foam was 1.0 μm.
(Example 3)
A styrene resin foam was obtained in the same manner as in Example 1 except that N-pentane was used instead of butane as the foaming agent. The content of natural mica was 4.9% by mass, and the maximum value of the amount of styrene monomer during polymerization was 21.5% by mass. The average cell thickness of the foam was 1.7 μm.

(Comparative Example 1)
A styrene-based resin foam was obtained in the same manner as in the Examples except that no scaly silicate was added. The average cell thickness of the foam was 1.0 μm. However, it was inferior in bending strength.
(Comparative Example 2)
A styrene resin foam was obtained in the same manner as in the example except that a scaly silicate having a thickness of 0.8 μm and an aspect ratio of 69 was used. The average cell thickness of the foam was 1.0 μm. However, it was inferior in moldability and bending strength.
Table 1 summarizes various measured values of the foam.

  From Table 1, a styrene resin foam containing a bubble film having an average bubble film thickness in a specific range and a scale-like silicate having a specific thickness located in the bubble film has sufficient strength even if the density is low. It was found that

Claims (5)

Comprising bubbles surrounded by a bubble film made of styrene resin, and scaly silicate located in the bubble film,
The cell membrane has an average cell thickness of 0.2 to 2.0 μm;
The styrenic resin foam, wherein the scaly silicate has a thickness of more than 0% and not more than 50% of the average bubble film thickness. The styrenic resin foam according to claim 1, wherein the scaly silicate has an aspect ratio of 10 to 1000, and the styrenic resin foam has a density of 10 to ³⁰ kg / m ³ .   The styrenic resin foam according to claim 1 or 2, wherein the scaly silicate is natural mica, synthetic mica, or sericite. It is the manufacturing method of the expandable styrene resin particle used for manufacture of the styrene resin foam as described in any one of Claims 1-3,
Styrenic resin particles dispersed in an aqueous medium in a reaction vessel are impregnated with a styrenic monomer after impregnated with a styrenic monomer seed particle, or polymerized while impregnating the styrenic resin particles. Obtaining a step;
Impregnating the styrenic resin particles with a foaming agent or impregnating the foaming agent during polymerization of the styrenic monomer,
The impregnation and polymerization of the styrenic monomer are performed in a reaction vessel maintained at an oxygen concentration of 15% by volume or more,
The styrenic monomer is supplied into the aqueous medium so that the amount of the styrenic monomer in the styrenic growing resin particles from the beginning of impregnation of the styrenic monomer to the end of polymerization is 40% by mass or less. A process for producing expandable styrenic resin particles.   Expandable styrenic resin particles obtained by the production method according to claim 4.