JP5367997B2 - Method for producing expandable styrene resin particles - Google Patents

Description

  The present invention relates to a method for producing expandable styrene resin particles. Specifically, it is possible to obtain a foamed styrene-based molded article having excellent moldability, and a spherical foamable styrene-based resin using columnar styrene-based resin particles obtained by granulation after melting and kneading with an extruder. The present invention relates to a method for producing particles.

  Styrenic foam made of expandable styrenic resin particles is a structure in which a large number of well-shaped cells are gathered, so it has excellent buffering and heat insulation properties, such as buffer materials for electrical appliances, food cold boxes, It is used in many fields such as thermal insulation for housing. As methods for producing such expandable styrenic resin particles, the following methods and the like have been conventionally known.

  (1) A production method involving a polymerization reaction in which resin particles are obtained by suspension polymerization of a styrene monomer together with various additives, and further, expandable styrene resin particles are obtained by impregnation with a foaming agent.

  (2) A production method that does not involve a polymerization reaction in which a styrene polymer is granulated together with various additives to a desired size by an extruder or the like, and further impregnated with a foaming agent to obtain expandable styrene resin particles.

  On the other hand, in recent years, with increasing interest in environmental conservation, attempts to recover and reuse styrene-based foams that have been widely used are expanding. Recycling methods include heat recovery by incineration, recycling as polystyrene after heat shrinkage, etc., but it is very meaningful to recycle again into expandable styrene resin particles aiming at a recycling type recycling system. And interest is growing.

  In the regeneration to such a styrene-based foam, since it is necessary to granulate a polymer as a starting material, the production method (2) is often used. In addition, the production method (2) has a lower production efficiency than the method (1), but it can be said to be a production method with high utility value because various components can be mixed.

And rollers to draw the strands by an extruder, if granulated by cutting with a pelletizer, the resin particles are not only becomes cylindrical, stretched in a direction pulling the resin to draw the strands in the molten state In addition, since the resin is rapidly cooled and solidified for cutting, the stretched force remains as internal strain in the granulated resin particles. Therefore, in the production of expandable styrene resin particles, if the columnar resin particles are impregnated with a foaming agent at a high temperature, the resin softens, resulting in stress relaxation and large shrinkage in the stretching direction, that is, the length direction. There was a problem of becoming flat particles.

  As a method of reducing internal strain that remains in the granulated resin particles, spherical resin particles are obtained by simultaneously extruding from an extruder without cutting the strand, and then cut into a foaming agent. There has been proposed a production method for obtaining expandable styrene resin particles by impregnating styrene (see Patent Document 1). However, this method is difficult to make fine adjustments of extrusion, cutting, and cooling, and it is easy to cause a decrease in productivity. The resin pressure in the extrusion die fluctuates, so that there are many miscuts, and the particle size is difficult to stabilize.

  In addition, a production method has been proposed in which expandable styrene resin particles are obtained by impregnating a styrene resin particles obtained by non-stretching heat melting with a foaming agent (see Patent Document 2). Although this method has the advantage of reducing internal strain, it is difficult to directly reduce the particle size to a size suitable for the expandable styrene resin particles. In order to reduce the particle size, a separate process is required, so that the productivity is low and the particle size tends to be uneven.

In addition, a production method has been proposed in which foaming thermoplastic resin particles are obtained by melt-kneading a thermoplastic resin and a foaming agent, then extruding from a die head and then immediately cooling the particles obtained by immediate cutting (patent) Reference 3). According to this method, the residual stress in the resin particles is relaxed, and it is possible to directly produce foamable thermoplastic resin particles, but it is difficult to suppress foaming when granulating. After all, there were problems with productivity and yield. Further, when melted and rapidly solidified in a short time, the quality of the foamed resin becomes unstable, the cells of the obtained foam are non-uniform, and it is difficult to obtain a molded product having a beautiful appearance.
JP-A-4-325534 JP-A-6-87973 JP-A-6-32932

  In view of the situation as described above, the present invention uses a cylindrical styrene resin particle obtained by granulation after melting and kneading with an extruder capable of obtaining a foamed styrene molded article having excellent moldability. Another object of the present invention is to provide a method for producing spherical expandable styrene resin particles.

  As a result of extensive studies to solve the above problems, it is possible to produce expandable styrene resin particles having excellent moldability by adopting the following configuration.

  That is, the present invention has the following configuration.

1). A method of producing expandable styrene resin particles in which cylindrical styrene resin particles obtained by melting and kneading styrene resin after granulation are dispersed in an aqueous medium and impregnated with a foaming agent. systems added foaming agent the length direction of the resin particles after heat shrunk until 5 to 50%, and wherein the impregnating method of expandable styrene resin particles.

2). The method for producing expandable styrene resin particles according to 1) , wherein the columnar styrene resin particles before heat shrinkage have a length / diameter ratio of 0.8 or more and 3.0 or less.

3). The styrene resin, characterized in that it contains recycled styrenic resin recovered more than 50 wt%, 1) or 2) The method of producing expandable styrene resin particles according to.

  The expandable styrene resin particles obtained by the production method of the present invention are spherical, and an expanded styrene molded article having excellent moldability can be obtained.

  The method for producing expandable styrene resin particles of the present invention is a foaming property in which cylindrical styrene resin particles obtained by melting and kneading granulated styrene resin are dispersed in an aqueous medium and impregnated with a foaming agent. A method for producing styrene-based resin particles, in which a lengthwise direction of cylindrical styrene-based resin particles is thermally shrunk to 5% or more and 50% or less, and then a foaming agent is added and impregnated.

  Examples of the monomer composition constituting the styrene resin particles include styrene and various substituted styrenes such as α-methylstyrene, chlorostyrene, paramethylstyrene, and t-butylstyrene. Or it is comprised from 2 or more types. Examples of components that can be copolymerized with the constituent monomer components include acrylic acid and methacrylic acid esters such as methyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate, acrylonitrile, dimethyl fumarate, and ethyl fumarate. Use a composition containing one or more of these various monomers, and a composition containing a polyfunctional monomer such as divinylbenzene or alkylene glycol dimethacrylate. Can do.

  Examples of the method for producing the styrene resin particles of the present invention include a method of directly obtaining polymer particles by suspension polymerization, bulk polymerization, emulsion polymerization or the like, and reused foam molding recovered after being used for the original purpose. It can be obtained by dissolving the body with a volume reducer or the like.

  The cylindrical styrenic resin particles can be obtained by a so-called strand cutting method in which a styrenic resin is drawn in a strand shape through an extruder with a die head having a small hole, and is cut into a desired size with a pelletizer having a rotary cutter. .

  In the present invention, columnar styrene resin particles for obtaining expandable styrene resin particles by adding and impregnating a foaming agent are obtained by drawing the styrene resin into strands through an extruder equipped with a die head having small holes. It can be obtained by cutting with a pelletizer having a rotary cutter. In the present invention, cylindrical styrene resin particles are used that are thermally contracted so that the length direction is 5% or more and 50% or less. This heat shrinkage is preferably 5% or more and 30% or less. If the shrinkage rate is too small, the internal strain is not sufficiently relaxed, causing a sudden change when the foaming agent is added, and the resulting expandable styrenic resin particles are flattened. Since the relaxation is too large, the resulting expandable styrene resin particles tend to be flat or egg-shaped.

  In the present invention, the method for thermally shrinking the cylindrical styrene resin particles produced by an extruder is not particularly limited, but it may be a method of heating in a gas phase by a fluid dryer or a dispersion in an aqueous medium. And the method of heating in the liquid phase, and the latter method is particularly preferable because it is easy to produce expandable styrene resin particles with a series of apparatuses.

As a method of heat shrinking, for example, a cylindrical styrene resin can be maintained at or above its glass transition temperature. When the glass transition temperature is maintained above the glass transition temperature, the temperature is not particularly limited, but it is preferable to maintain the temperature within the range of glass transition temperature to glass transition temperature + 30 ° C., more preferably glass transition temperature to glass transition temperature + 25 ° C.
Although there is no restriction | limiting in particular as time to hold | maintain to the temperature more than a glass transition temperature, 60 minutes or less, Furthermore, 20 minutes or less, More preferably, 5 minutes or less are preferable. If a predetermined temperature equal to or higher than the glass transition temperature is reached, the next operation may be started immediately.

  After adding the foaming agent, it is preferable to keep the glass transition temperature or higher. As the temperature at that time, the above temperature range is preferable. The holding time is preferably 1 hour to 10 hours, more preferably 2 hours to 8 hours.

  In addition, although a glass transition temperature can be measured by a well-known method, it can be measured, for example using a differential scanning calorimeter.

  The columnar styrenic resin particles before heat shrinkage of the present invention preferably have a length / diameter ratio of 0.8 or more and 3.0 or less, more preferably 0.9 or more and 2.5 or less. When the ratio is too small, the resulting expandable styrene resin particles tend to be flat, and when the ratio is too large, it tends to be an egg type.

  Since the cylindrical styrene resin particles of the present invention draw the molten resin in a strand shape, the cut surface may be elliptical. The diameter in the case of an ellipse can be expressed as an average value of the major axis and the minor axis of the ellipse.

  As an aqueous medium in which the styrene resin particles of the present invention are dispersed, water containing a dispersant can be used. The dispersant here is a dispersant generally used for suspension polymerization of a styrene monomer, for example, a polymer dispersant such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, such as calcium phosphate, hydroxyapatite, A poorly water-soluble inorganic salt such as magnesium pyrophosphate can be used. When a poorly water-soluble inorganic salt is used, it is preferable to use an anionic surfactant such as α-olefin sodium sulfonate or dodecylbenzene sodium sulfonate because it is effective in increasing dispersion stability.

  The blowing agent used in the present invention is a readily volatile organic compound having a boiling point equal to or lower than the softening point of the polymer. Examples of such blowing agents include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, and alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane.

  These foaming agents can be used alone or in combination of two or more. Of these easily volatile organic compounds, butane or pentane is preferable, and pentane is more preferable.

  The amount used is preferably 2 to 12 parts by weight, more preferably 3 to 8 parts by weight, per 100 parts by weight of the styrenic resin. If it is 2 parts by weight or less, it is difficult to obtain the foaming force after forming the expandable styrene resin particles, and if it is 12 parts by weight or more, the foaming force becomes excessive and the suspension stability in the impregnation step is lowered.

  In the styrene resin in the present invention, various additives such as a plasticizer, a flame retardant, and a cell regulator generally added when producing expandable styrene resin particles can be used. Examples of the plasticizer include stearic acid triglyceride, palmitic acid triglyceride, lauric acid triglyceride, stearic acid diglyceride, stearic acid monoglyceride and other fatty acid glycerides, palm oil, palm oil, palm kernel oil and other vegetable oils, dioctyl adipate, dibutyl sebacate And aliphatic hydrocarbons such as liquid paraffin, and organic aromatic hydrocarbons such as toluene and ethylbenzene. These may be used in combination.

  Examples of the flame retardant include halogen-based flame retardants, and specific examples include hexabromocyclododecane, tetrabromobisphenol A and diallyl ether, and monochloropentabromocyclohexane. Examples of the air conditioner include aliphatic bisamides such as methylene bis stearic acid amide and ethylene bis stearic acid amide, polyethylene wax, and the like.

  The foamable styrenic resin particles thus obtained are spherical, and a foamed styrenic molded article excellent in moldability can be obtained.

  Examples and Comparative Examples are given below, but the present invention is not limited thereby. In addition, among the operation, measurement, and evaluation methods, items other than those described above were performed as follows.

<Manufacture of cylindrical styrene resin particles by an extruder>
A 50 mmφ single screw extruder was charged with a styrene resin obtained by dissolving and crushing a foam molded product obtained from a foamable styrene resin commercially available as a homopolymer not crosslinked with styrene. Then, after being melted by heating, it was extruded into a strand shape from a die having small holes, quenched in water, and then cut with a pelletizer to obtain cylindrical styrene resin particles.

  It was 102 degreeC when the glass transition temperature of the cylindrical styrene-type resin particle obtained here was measured using the differential scanning calorimeter (DSC5200) by Seiko Denshi Kogyo.

<Measurement of resin particle size>
As the size, 20 grains were randomly selected from each sample, measured using a caliper capable of measuring up to 1/100 mm, and calculated as a number average value.

Example 1
In a reactor equipped with a stirrer, 200 parts by weight of pure water, 0.6 parts by weight of tribasic calcium phosphate, 0.012 parts by weight of sodium α-olefin sulfonate, 1 part by weight of sodium chloride, and a cylindrical shape having the size shown in Table 1 100 parts by weight of styrene resin particles were added, and the temperature was increased under stirring. In order to thermally contract the cylindrical styrene resin particles in a heated aqueous medium, the first temperature rise is about 120 ° C. at a rate of about 1.5 ° C./minute, and then cooled to 95 ° C. After that, 6 parts by weight of pentane (a mixture of normal 80% by weight and iso 20% by weight) was added.

  Table 1 shows the size of the cylindrical styrenic resin particles before the temperature increase and immediately before the addition of pentane. After adding pentane, impregnation was performed at 120 ° C. for 5 hours by raising the temperature again. After impregnation, after cooling to room temperature, it was taken out from the reactor, washed, dehydrated and dried to obtain expandable styrene resin particles.

  The obtained expandable styrenic resin particles were pre-foamed at a bulk magnification of 50 times with a pressure type pre-foaming machine (manufactured by Daikai Kogyo Co., Ltd., BHP), and then cured and dried by allowing to stand at room temperature for 1 day. Subsequently, the obtained styrene-based resin pre-expanded particles were subjected to a foam-molded product with a 300 × 450 × 20 (t) mm size mold using a molding machine (manufactured by Daisen Industry, KR-57). Evaluation was performed using the obtained expandable styrene resin particles and the foamed molded article, and the results shown in Table 2 were obtained.

(Example 2)
The columnar styrene resin particles having the sizes shown in Table 1 were used, except that the first temperature was raised to 110 ° C. at a rate of about 1.5 ° C./min, then cooled to 95 ° C. and pentane was added. In the same manner as in Example 1, expandable styrene resin particles were obtained, and the results shown in Table 2 were obtained.

(Example 3)
The columnar styrene resin particles having the sizes shown in Table 1 were used, except that the first temperature was raised to 120 ° C. at a rate of about 1.5 ° C./min, then cooled to 95 ° C. and pentane was added. In the same manner as in Example 1, expandable styrene resin particles were obtained, and the results shown in Table 2 were obtained.

(Examples 4 to 5)
The columnar styrene resin particles having the sizes shown in Table 1 were used, except that the first temperature was raised to 105 ° C. at a rate of about 1.5 ° C./min, then cooled to 95 ° C. and pentane was added. In the same manner as in Example 1, expandable styrene resin particles were obtained, and the results shown in Table 2 were obtained.

(Comparative Example 1)
Using columnar styrene resin particles of the size shown in Table 1, the first temperature rise was raised to 120 ° C at a rate of about 1.5 ° C / minute, held for 3 hours, and then cooled to 95 ° C. Expandable styrene resin particles were obtained in the same manner as in Example 1 except that pentane was added, and the results shown in Table 2 were obtained.

(Comparative Examples 2-3)
Example 1 except that the columnar styrene resin particles having the sizes shown in Table 1 were used, and the first temperature was raised to 95 ° C. at a rate of about 1.5 ° C./min, and then pentane was added immediately. In the same manner as above, expandable styrene resin particles were obtained, and the results shown in Table 2 were obtained.

Claims (3)

A method of producing expandable styrene resin particles in which cylindrical styrene resin particles obtained by melting and kneading styrene resin after granulation are dispersed in an aqueous medium and impregnated with a foaming agent. systems added foaming agent the length direction of the resin particles after heat shrunk until 5 to 50%, and wherein the impregnating method of expandable styrene resin particles. The method for producing expandable styrene resin particles according to claim 1 , wherein the columnar styrene resin particles before heat shrinkage have a length / diameter ratio of 0.8 to 3.0. . The styrene resin, characterized in that it contains recycled styrenic resin recovered more than 50 wt%, the production method of the expandable styrene resin particles according to claim 1 or 2.