JP7231691B2 - Method for producing expandable thermoplastic resin particles - Google Patents

Description

The present invention relates to a method for producing expandable thermoplastic resin particles.

BACKGROUND ART Conventionally, a bead foaming method has been used as one of the methods for obtaining foamed moldings of thermoplastic resins. In this method, for example, thermoplastic resin particles are first obtained by suspension polymerization, then impregnated with a foaming agent to form expandable thermoplastic resin particles, and the particle size is adjusted by drying and sieving. Such expandable thermoplastic resin particles are heated and softened with water vapor or the like to reduce the viscosity of the expandable thermoplastic resin particles, and the impregnated foaming agent is volatilized to form a large number of air bubbles in the resin particles. Pre-expanded particles are obtained by expanding to the expansion ratio (pre-expanding step). The obtained pre-expanded particles are filled in a mold, and the pre-expanded particles are fused together with water vapor or the like (molding step) to obtain a foamed article (see, for example, Patent Documents 1 and 2). .

However, since this conventional method is a discontinuous production method and utilizes suspension polymerization, thermoplastic resin particles having a wide particle size distribution can be obtained. Therefore, it is necessary to go through the particle size adjustment process as described above, and there are problems such as complication of the process, an increase in cost due to it, environmental problems due to waste water treatment associated with suspension polymerization, and a deterioration in yield. In addition, when it is desired to impart high heat insulating performance and high flame retardancy to a foamed molded product with high functionality, there is a problem that there are many restrictions when adding raw materials necessary for high functionality.

Therefore, thermoplastic resin is put into an extruder, melted and kneaded with a foaming agent and other additives, extruded in a foamed or unfoamed state through a small hole in a die installed after the extruder, and cut with a rotary cutter or the like. A method for obtaining expanded resin particles or unexpanded expandable resin particles has been proposed (see, for example, Patent Document 3). According to this method, thermoplastic resin particles having a small diameter and a uniform particle size distribution can be produced continuously and economically. There is also the advantage that there are less restrictions on the solid additives to be added.

Such a method is broadly classified into a hot cut method and a cold cut method depending on the timing of cutting the resin into particles. In the hot-cut method, a molten resin is extruded into a pressurized cooling liquid through a small hole in a die, and at the same time, the resin is cut with a rotating cutter or the like to be granulated and solidified by cooling to obtain expandable thermoplastic resin particles. On the other hand, in the cold cut method, a strand is obtained by extruding a molten resin into the air through a small hole of a die, and then cooling and solidifying the strand with a cooling liquid using a cutter to obtain expandable thermoplastic resin particles. The hot-cut method tends to be superior to the cold-cut method in terms of filling the pre-expanded particles into a molding die and the surface properties and strength of the expanded molded product in that spherical particles can be obtained.

In such a hot cut method, in Patent Document 4, when extruding the foaming agent-containing molten resin into the cooling liquid, the shear rate and melt viscosity of the molten resin when passing through the small hole land portion of the die are set to a specific range. It is disclosed that by controlling the particle diameter within the range, it is possible to produce expandable thermoplastic resin particles that are perfectly spherical in shape, uniform in particle size, and capable of producing expansion molded articles with excellent mechanical strength.

In Patent Document 5, a step of supplying a thermoplastic resin to a resin supply device equipped with a granulation die and melt-kneading it;
forming a foaming agent-containing resin by injecting a foaming agent into the thermoplastic resin while moving the thermoplastic resin toward the granulating die;
and obtaining expandable thermoplastic resin particles by cutting the foaming agent-containing resin discharged from a nozzle formed on the resin discharge surface of the granulating die with a cutter in a cooling medium. A method for producing particles, comprising:
The die temperature at a position 2 to 3 mm away from the resin ejection surface of the granulation die in contact with the cooling medium in the direction opposite to the ejection direction of the foaming agent-containing resin is minus the Vicat softening temperature of the thermoplastic resin. An expandable thermoplastic resin characterized by obtaining expandable thermoplastic resin particles while controlling the temperature so that the temperature of the cooling medium is in the range of 30 ° C. to +20 ° C. and the temperature of the cooling medium is in the range of 10 to 60 ° C. A method of making particles is disclosed.

In Patent Document 6, a step of supplying a thermoplastic resin to a resin supply device equipped with a granulation die having at least a die body having a resin discharge surface and melt-kneading the resin, and a step of injecting a foaming agent into the thermoplastic resin to form a foaming agent-containing resin while moving the mold toward the die body; and cutting in a cooling medium to obtain expandable thermoplastic resin particles, wherein the temperature of the die body is 115° C. higher than the molten resin temperature of the foaming agent-containing resin. A method for producing expandable thermoplastic resin particles is disclosed, which is characterized by obtaining expandable thermoplastic resin particles while controlling the temperature to be in the range of up to 200°C higher.

In Patent Document 7, a die having a plurality of die holes and an extruder for supplying molten resin to the die are provided, the die has a diverter valve, and the diverter valve is supplied from the extruder. A molten polystyrene-based resin containing a foaming agent is produced by using an underwater cut-type granulator having a first flow path for supplying the molten resin to the die hole and a second flow path for discharging the molten resin to the outside of the machine. A preparatory step is performed in which the extruder is supplied to the die while being discharged out of the machine through the second flow path, and after the preparatory step, the flow path of the molten polystyrene resin is switched to the first flow path. A method for producing expandable polystyrene resin particles, wherein the resin pressure of the molten polystyrene resin before switching to the first flow path is 10% after switching. A method for producing polystyrene-based expandable resin particles is disclosed, characterized in that the preparatory step is carried out as described above.

Japanese Patent Application Laid-Open No. 2001-164025 JP-A-4-91141 Japanese Patent Publication No. 2005-534733 WO2005/028173 JP 2009-292015 A JP 2010-179627 A JP 2012-207093 A

When producing expandable thermoplastic resin particles by the hot cut method, a molten resin containing a blowing agent is extruded through a small hole of a die into a cooling medium and cut by a cutter in the cooling medium to obtain expandable resin particles. there is Therefore, since the die surface is in contact with the cooling medium, heat is removed from the die surface by the cooling medium, causing the resin to solidify in the small holes of the die and clogging the small holes. It is an issue. If the small holes are clogged, not only does the production efficiency of the resin particles decrease, but the resin discharge amount per small hole varies, and the shape of the particles tends to be uneven. There was a risk that uniform particle size distribution and shape, which are merits, could not be maintained. In addition, if the production is continued with the pores clogged, the pores tend to become clogged with the lapse of time, which tends to further reduce the production efficiency and deteriorate the particle shape. In order to solve this problem, technical improvements have been made as in Patent Documents 4 to 7, but none of them are sufficient.

Specifically, Patent Document 3 describes the control of the die plate temperature and the temperature of polystyrene containing a blowing agent. However, in this technique, the small holes of the die are clogged, making it difficult to continuously produce expandable thermoplastic resin particles having a spherical shape and a uniform particle size. Specifically, in the manufacturing method of Patent Document 4, it is difficult to obtain a state in which the small holes of the die are not clogged, and continuous production is impossible.
Specifically, in the manufacturing method of Patent Document 5, since the die temperature drop due to the influence of the cooling medium is immediately fed back to the die temperature control, it is necessary to design a special die, and there is a problem in versatility. .
Specifically, in the manufacturing method of Patent Document 6, in order to prevent clogging of the small holes of the die, the temperature of the die is excessively increased to induce deterioration/decomposition of the thermoplastic resin and the release of additives such as flame retardants. There was a risk of mold corrosion due to disassembly, and there was a problem with maintenance and maintenance of the equipment.
Specifically, in the production method of Patent Document 7, immediately after the start of granulation, the closed state of the small holes of the die is relatively good, but 24 hours after the start of the granulation process, the state is already declining, and continuous production I had a sexual problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing expandable thermoplastic resin particles that enables continuous and stable production of expandable thermoplastic resin particles having a uniform shape.

The present inventors have made intensive studies to solve this problem, and found that the above problem can be solved by controlling the opening ratio of the small holes of the die immediately after the start of operation in the hot cut method, and completed the present invention. reached.

That is, the present invention is a method for producing expandable thermoplastic resin particles, in which a foaming agent-containing thermoplastic resin melt is extruded into pressurized water from a die having a plurality of small holes, and immediately thereafter cut into particles by a rotating cutter. The die has an effective aperture ratio of 90% or more at the start of operation (here, at the start of operation, when 5 minutes have passed since the start of cutting the expandable thermoplastic resin particles in the pressurized water). The present invention relates to a method for producing expandable thermoplastic resin particles (hereinafter sometimes referred to as “the method for producing expandable thermoplastic resin particles of the present invention”).

In the method for producing expandable thermoplastic resin particles of the present invention, the shear rate of the blowing agent-containing thermoplastic resin melt when passing through the small hole land portion of the die after the start of operation is It is preferably 0.5 to 0.9 times the shear rate.

In the method for producing expandable thermoplastic resin particles of the present invention, the shear rate of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die at the start of operation is preferably 13000 sec ⁻¹ or more. .

In the method for producing expandable thermoplastic resin particles of the present invention, the thermoplastic resin is preferably a styrene resin.

In the method for producing expandable thermoplastic resin particles of the present invention, it is preferable that the diameter of the pores is 0.5 mm to 1.0 mm.

In the method for producing the expandable thermoplastic resin particles of the present invention, the sphericity of the expandable thermoplastic resin particles is preferably 0.92 or more.

In the method for producing the expandable thermoplastic resin particles of the present invention, the sphericity of the expandable thermoplastic resin particles is preferably 0.95 or more.

The present invention also relates to a method for producing expandable thermoplastic resin particles, in which a foaming agent-containing thermoplastic resin melt is extruded into pressurized water through a die having a plurality of small holes, and immediately thereafter cut into particles by a rotating cutter. and a method for producing expandable thermoplastic resin particles, wherein the expandable thermoplastic resin particles have a sphericity of 0.92 or more.

The present invention also relates to a method for producing expandable thermoplastic resin particles, in which a foaming agent-containing thermoplastic resin melt is extruded into pressurized water through a die having a plurality of small holes, and immediately thereafter cut into particles by a rotating cutter. and a method for producing expandable thermoplastic resin particles, wherein the expandable thermoplastic resin particles have a sphericity of 0.95 or more.

According to the present invention, expandable thermoplastic resin particles having a uniform spherical shape can be stably produced continuously for a long period of time.

Sectional view showing the configuration near the exit of the die used in the embodiment of the present invention Cross-sectional view showing an enlarged vicinity of a small hole in the die of FIG.

The present invention will be described in detail below. The present invention relates to the production of expandable thermoplastic resin particles by extruding a foaming agent-containing thermoplastic resin melt from a die having a plurality of small holes into pressurized water and then cutting the melt with a rotary cutter to form particles and solidify by cooling. Regarding the method. A blowing agent-containing thermoplastic resin melt contains a thermoplastic resin, a blowing agent, and optionally other additives.

(Thermoplastic resin)
The thermoplastic resin used in the present invention is not particularly limited, but for example, polystyrene (PS), styrene-acrylonitrile copolymer (AS), styrene-(meth)acrylic acid copolymer (heat-resistant PS) , styrene-(meth)acrylic acid ester copolymer, styrene-butadiene copolymer (HIPS), N-phenylmaleimide-styrene-maleic anhydride three-dimensional copolymer, alloy of it with AS (IP), etc. Styrene-based resins; vinyl-based resins such as polymethyl methacrylate, polyacrylonitrile-based resins, and polyvinyl chloride-based resins; polypropylene, polyethylene, ethylene-propylene copolymers, ethylene-propylene-butene terpolymers, cycloolefin-based ( Co) polyolefin resins such as polymers and rheology-controlled polyolefin resins by introducing branched structures and crosslinked structures into these; polyamide resins such as nylon 6, nylon 66, nylon 11, nylon 12, and MXD nylon; polyethylene Polyester-based resins such as terephthalate, polybutylene terephthalate, polyarylate, and polycarbonate, aliphatic polyester-based resins such as polylactic acid; polyphenylene ether-based resins (PPE), modified polyphenylene ether-based resins (modified PPE), polyoxymethylene-based resins, engineering plastics such as polyphenylene sulfide-based resins, polyphenylene sulfide-based resins, aromatic polyether-based resins, and polyether ether ketone resins; These may be used alone or in combination of two or more.

Among these thermoplastic resins, styrene-based resins are preferable because they are relatively inexpensive, can be molded with low-pressure steam or the like without using a special method, and can provide high shock-absorbing and heat-insulating effects.

(styrene resin)
The styrenic resin used in the present invention includes not only styrene homopolymer (styrene homopolymer), but also styrene, other monomers copolymerizable with styrene, or their It may be copolymerized with a derivative. However, the brominated styrene/butadiene copolymer described later is excluded.

Other monomers copolymerizable with styrene or derivatives thereof include, for example, methylstyrene, dimethylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and styrene derivatives such as trichlorostyrene; polyfunctional vinyl compounds such as divinylbenzene; (meth)acrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate compounds; vinyl cyanide compounds such as (meth)acrylonitrile; diene compounds such as butadiene or derivatives thereof; unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride; N-methylmaleimide, N-butylmaleimide, and N-alkyl-substituted maleimide compounds such as N-cyclohexylmaleimide, N-phenylmaleimide, N-(2)-chlorophenylmaleimide, N-(4)-bromophenylmaleimide, and N-(1)-naphthylmaleimide. . These may be used alone or in combination of two or more.

The styrenic resin used in the present invention is not limited to the aforementioned styrene homopolymer and/or copolymers of styrene and other monomers copolymerizable with styrene or derivatives thereof. A homopolymer of the above-mentioned other monomers or derivatives, or a blend with a copolymer thereof may be used as long as the effect is not impaired.

The styrene resin used in the present invention may be blended with, for example, diene rubber-reinforced polystyrene, acrylic rubber-reinforced polystyrene, and/or polyphenylene ether resin.

Among the styrene resins used in the present invention, it is relatively inexpensive, can be foam-molded with low-pressure steam or the like without using a special method, and has an excellent balance of heat insulation, flame retardancy, and cushioning properties. Styrene homopolymers, styrene-acrylonitrile copolymers, or styrene-butyl acrylate copolymers are preferred.

(foaming agent)
The foaming agent used in the present invention is not particularly limited, but hydrocarbons having 3 to 6 carbon atoms are desirable, and more desirable, from the viewpoint of good balance between foamability and product life, and easy to achieve high magnification when actually used. is a hydrocarbon having 4 to 5 carbon atoms. If the number of carbon atoms in the foaming agent is 3 or more, the volatility of the foaming agent becomes low, and when the foaming agent is made into expandable styrene-based resin particles, it becomes difficult for the foaming agent to dissipate. It is preferable because it remains at a low level, it becomes possible to obtain sufficient foaming power, and it becomes easy to increase the magnification. Further, when the number of carbon atoms is 6 or less, the boiling point of the foaming agent is not too high, so that sufficient foaming power can be easily obtained by heating during preliminary foaming, and high foaming tends to be easily achieved. Examples of hydrocarbons having 3 to 6 carbon atoms include hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, normal hexane, and cyclohexane. These may be used individually by 1 type, and may be used in combination of 2 or more type.

Blowing agents other than hydrocarbons may also be used. For example, ethers such as dimethyl ether and diethyl ether, alcohols such as methanol and ethanol, carbon dioxide gas, nitrogen, water, and the like can be used. These foaming agents may be used alone or in combination of two or more. Moreover, you may use together with the said hydrocarbon.

The amount of the foaming agent to be added can be increased or decreased depending on the target expansion ratio. A range of to 9 parts by weight is more preferred. If the amount of foaming agent added is less than 2 parts by weight, the desired expansion ratio may not be obtained. If the amount of the foaming agent added is 15 parts by weight or less, the extruder or die pressure for dissolving the foaming agent in the thermoplastic resin, or a cooling medium for suppressing foaming of the thermoplastic resin after being discharged from the die. pressure can be set low, and as a result, equipment can be inexpensive and lead to stable production. Further, when the amount is 15 parts by weight or less, the production time (molding cycle) for producing the thermoplastic resin foam molded article is shortened, so that the production cost tends to be low. (Flame retardants)
In the present invention, a flame retardant may be used to impart flame retardancy to the thermoplastic foam. The flame retardant used in the present invention is not particularly limited, and any flame retardant conventionally used for thermoplastic resin foam molded articles can be used. Specific examples include halogen-based flame retardants, phosphorus-based flame retardants, and non-halogen-based flame retardants such as nitrogen-containing compounds. Among these, when a styrene resin is used as the thermoplastic resin, a brominated flame retardant having a high flame retardancy-imparting effect is desirable. Brominated flame retardants used in the present invention include, for example, 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane (also known as tetrabromobisphenol A -bis (2,3-dibromo-2-methylpropyl ether)), or 2,2-bis [4- (2,3-dibromopropoxy) -3,5-dibromophenyl] propane (also known as tetrabromobisphenol A - Brominated bisphenol compounds such as bis(2,3-dibromopropyl ether)), tetrabromocyclooctane, tris(2,3-dibromopropyl) isocyanurate, brominated styrene/butadiene block copolymer, brominated random Brominated butadiene/vinyl aromatic hydrocarbon copolymers such as styrene/butadiene copolymers or brominated styrene/butadiene graft copolymers (for example, disclosed in JP-T-2009-516019), and the like. be done. These brominated flame retardants may be used alone or in combination of two or more.

The brominated flame retardant is easy to control to the desired expansion ratio, and from the viewpoint of the balance of flame retardancy and the like when adding a radiation heat transfer inhibitor described later, the bromine content in 100% by weight of the expandable thermoplastic resin particles is preferably 0.8% by weight or more, and more preferably 5.0% by weight or less. When the bromine content is 0.8% by weight or more, the effect of imparting flame retardancy tends to increase, and when it is 5.0% by weight or less, the strength of the obtained resin foam molding tends to increase. The bromine content is more preferably blended into the expandable thermoplastic resin particles so as to be 1.0 to 3.5% by weight.

(Heat stabilizer)
In the present invention, decomposition and deterioration of the thermoplastic resin and the flame retardant during the production process can be suppressed by using a heat stabilizer in combination. The heat stabilizer in the present invention can be used in combination as appropriate depending on the type and content of the thermoplastic resin, foaming agent, and additive used.

As the heat stabilizer used in the present invention, a hindered amine compound, a phosphorus compound, a phenolic stabilizer, or an epoxy compound is desirable because the weight loss temperature in the thermogravimetric analysis of the brominated flame retardant-containing mixture can be arbitrarily controlled. . A heat stabilizer can be used individually by 1 type or in combination of 2 or more types. These heat stabilizers can also be used as light stabilizers as described later.

(radical generator)
In the present invention, by further containing a radical generator, it is possible to express high flame retardancy by using it in combination with a brominated flame retardant.

The radical generators in the present invention are used in combination according to the type of thermoplastic resin used, the type and content of the foaming agent, the type and content of the radiation heat transfer inhibitor, and the type and content of the brominated flame retardant. be able to.

Examples of the radical generator used in the present invention include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, and poly-1,4- isopropylbenzene and the like. A radical generating agent can be used individually by 1 type or in combination of 2 or more types.

(Radiation heat transfer inhibitor)
In the present invention, a radiation heat transfer inhibitor may be used in order to impart high heat insulating performance to the foam obtained from the expandable thermoplastic resin particles. The term "radiation heat transfer inhibitor" as used herein refers to a substance having properties of reflecting, scattering or absorbing light in the near-infrared or infrared region. For example, carbon materials such as graphite, graphene, carbon black, carbon nanotubes, activated carbon, expanded graphite, aluminum compounds such as aluminum and aluminum oxide, zinc compounds such as zinc aluminate, magnesium compounds such as hydrotalcite, silver and titanium compounds such as titanium, titanium oxide and strontium titanate.

(Other additives)
Further, as long as the effects of the present invention are not impaired, it is optionally selected from the group consisting of processing aids, light-resistant stabilizers, nucleating agents, foaming aids, antistatic agents, and colorants such as pigments. It may contain one or more other additives.

Processing aids include sodium stearate, magnesium stearate, calcium stearate, zinc stearate, barium stearate, liquid paraffin, and the like.

Examples of light-resistant stabilizers include hindered amines, phosphorus-based stabilizers, epoxy compounds, phenol-based antioxidants, nitrogen-based stabilizers, sulfur-based stabilizers, and benzotriazoles.

Nucleating agents include inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, calcium carbonate, sodium hydrogen carbonate, or talc, methyl methacrylate copolymers, or ethylene- Polymer compounds such as vinyl acetate copolymer resins, olefin waxes such as polyethylene wax, or fatty acid bisamides such as methylenebisstearylamide, ethylenebisstearylamide, hexamethylenebispalmitamide, or ethylenebisoleic acid amide. mentioned.

As the foaming aid, a solvent having a boiling point of 200° C. or less under atmospheric pressure can be desirably used, and examples thereof include aromatic hydrocarbons such as styrene, toluene, ethylbenzene, or xylene; ; acetic acid esters such as ethyl acetate and butyl acetate;

As the antistatic agent and colorant, those used in various resin compositions can be used without particular limitation.

These other additives can be used individually by 1 type or in combination of 2 or more types.

(Method for producing expandable thermoplastic resin particles)
The foaming agent-containing thermoplastic resin melt in the production method of the present invention is produced by supplying raw materials such as a thermoplastic resin, a foaming agent, and other additives to an extruder and melt-kneading them in the extruder. .

As the extruder used in the present invention, a general extruder can be used, and specific examples include a single-screw extruder, a twin-screw extruder, and a tandem extruder. Examples of the tandem extruder include one in which two single-screw extruders are connected, and one in which a single-screw extruder is connected to a twin-screw extruder. In addition, the extruder may be used in combination with a second kneading device such as a static mixer or a stirrer without a screw.

The timing for injecting the foaming agent in the present invention is not particularly limited, but it is preferable to inject the foaming agent as soon as possible after the raw resin has reached a molten or semi-molten state in the extruder. The later the injection timing, the more likely the foaming agent is evenly dispersed in the raw material resin and extruded before it is dissolved. It may lead to deterioration.

According to the production method of the present invention, the foaming agent-containing thermoplastic resin melt in which the foaming agent and other additives are dissolved or uniformly dispersed in the thermoplastic resin in the extruder is attached to the tip of the extruder. The die is extruded into a pressurized cooling medium, such as water, through a plurality of small holes in its face. Immediately after being extruded, the melt is cut with a rotary cutter to be granulated and solidified by cooling.

FIG. 1 is a cross-sectional view showing the configuration near the exit of a die used in an embodiment of the present invention, and FIG. 2 is an enlarged view showing the vicinity of a small hole in the die of FIG. A face 11 of the die 10 has a large number of small holes 12 through which the molten material exits. These small holes 12 communicate with a resin passage 13 inside the die, and the resin passage 13 further communicates with an exit at the tip of the extruder. That is, the melt formed in the extruder passes through the resin passage 13 in the die 10 from the tip of the extruder, reaches the small hole 12, and is extruded from the small hole 12 into the pressurized cooling water.

The small holes of the die in the present invention preferably have a diameter of 0.5 to 1.0 mm. When the diameter is 0.5 mm or more, clogging of the small holes tends to occur with difficulty, and stable continuous production tends to be possible. If the diameter is 1.0 mm or less, the pre-expanded particles obtained by pre-expanding the expandable particles can be made smaller, and the filling of the expanded particles into the molding die tends to be improved. It tends to have better fusion bondability. Incidentally, the diameter of the small hole is indicated by symbol b in FIG.

In addition, the length of the small-hole land portion in which the small holes are formed on the face surface 11 of the die (reference numeral a in FIG. 2) is preferably 2 to 10 mm. If the thickness is less than 2 mm, the pressure resistance performance of the die may deteriorate. In addition, the flow of the resin in the small holes may be disturbed, and the particle shape and size may become non-uniform. If it exceeds 10 mm, the resin pressure in the small holes increases, and the operation itself may become difficult. The small hole land portion means a region in which a small hole having the above diameter is formed, and the length of the small hole land portion corresponds to the length of the small hole having the above diameter.

In the manufacturing method of the present invention, the effective opening ratio of the small holes of the die at the start of operation is controlled to 90% or more. By setting the effective opening ratio at the start of the operation to 90% or more, it is possible to continuously produce expandable thermoplastic resin particles having a uniform particle size in a spherical shape for a long time, and the productivity is excellent, and the obtained foamed When the thermoplastic resin particles are pre-expanded, the expansion ratio is sufficiently high, and when the pre-expanded particles are fused to obtain a foam-molded article, the fusion rate of the foam-molded article is at a sufficient level. to reach Preferably, the effective aperture ratio is 95% or more, more preferably 98% or more.

If the effective aperture ratio at the start of operation is less than 90%, the effective aperture ratio tends to further decrease over time. In general, when the effective open area ratio decreases, the amount of resin discharged per small hole increases unless the amount of resin discharged from the extruder is changed. In order to keep the weight constant, it is necessary to increase the number of rotations of the cutter. As a result of intensive studies by the present inventors, it was surprisingly found that increasing the number of rotations of the cutter in order to keep the weight of each expandable thermoplastic resin particle constant when the effective aperture ratio is lowered further increases. It has been found that the effective aperture ratio is lowered. For this reason, in order to carry out continuous and stable production, it is desirable not to increase the number of rotations of the cutter as much as possible during production. It has been found that it is important to control to 90% or more.

The effective aperture ratio of the small holes means the ratio of the small holes that effectively discharge the resin to the total number of small holes of the die, and is calculated by the following formula (1).

Effective aperture ratio (%) = h/H x 100 (1)
h: Number of small holes that effectively discharge resin (pieces)
H: total number of small holes in the die (pieces)
Incidentally, all the small holes in the die exclude small holes which are previously embedded in the die with pins or the like and which are closed structurally so as not to discharge the resin.
Also, the number h of small holes through which the resin is effectively discharged is calculated by the following equation (2).

h={q/(N×n×W×60)}×10 ⁶ (2)
q: total discharge from the die (kg/hr)
N: rotation speed of rotary cutter (rpm)
n: Number of blades of rotary cutter (sheets)
W: Grain weight (mg).

Furthermore, in the present invention, when the shear rate of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die at the start of operation is A, after that, when passing through the small hole land portion of the die The shear rate of the foaming agent-containing thermoplastic resin melt is reduced to 0.5 to 0.9 times that of A (the shear rate at this time is the foaming agent By adjusting the shear rate B of the contained thermoplastic resin melt, the expandable thermoplastic resin particles can be stably and continuously produced while ensuring an effective open area ratio of 90% or more, and a higher expansion ratio and melting can be achieved. The present inventors have found that it is possible to produce expandable thermoplastic resin particles that are pre-expanded particles with high adhesion.

The start of operation is defined as 5 minutes after the start of cutting the expandable thermoplastic resin particles in pressurized water, and the grain weight and operating conditions of the expandable thermoplastic resin particles obtained at that time From this, the effective opening ratio of the small holes at the start of operation is calculated, and the shear rate A of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die at the start of operation is calculated. In the present invention, the effective open area ratio may be controlled to 90% or more after 5 minutes from the start of cutting of the expandable thermoplastic resin particles in pressurized water, and the same conditions may be maintained continuously. However, the conditions such as the shear rate may be changed after the operation is started. In the embodiment in which expandable resin particles are produced by reducing the shear rate as described above, the shear rate may be changed at any time after the start of operation. It is preferable to change the shear rate until the expandable thermoplastic resin particles are extruded in a weight corresponding to 10% by weight when the total amount (kg/hr) of the thermoplastic resin melt is 100% by weight. .

As a method for changing the shear rate of the foaming agent-containing thermoplastic melt when passing through the small hole land portion of the die, after starting the production of expandable thermoplastic resin particles, the amount of resin discharged per small hole The shear rate can be changed by changing . Specifically, a change from a high shear rate to a low shear rate can be achieved by reducing the raw material feed rate to the extruder per hour after starting to produce expandable thermoplastic resin particles.

In the present invention, the timing for evaluating the shear rate B of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die immediately after the start of production is changed from the discharge amount at the start of operation, Defined as after at least 5 minutes. From the particle weight of the expandable thermoplastic resin particles and the operating conditions at that time, the effective opening ratio of the small pores is calculated, and the shear rate B is calculated. Depending on the structure of the melt extruder, the time required for the conditions of the melt extruder and the die to stabilize will differ. may be evaluated.

In the present invention, the time for evaluating the shear rate C of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die after 48 hours from the start of production is defined as 48 hours after the start of production. . From the grain weight of the expandable thermoplastic resin particles and the operating conditions at that time, the effective opening ratio of the small pores is calculated, and the shear rate C is calculated.

In the present invention, the shear rate of the melt when passing through the small hole land portion of the die is calculated by the following equation (3). τ=4×Q/(π×r ³ ) (3)
τ: shear rate (sec ⁻¹ )
Q: Resin volume discharge amount per effective small hole (cm ³ /sec)
π: circular constant r: pore radius (cm).

From the above formula (3), the shear rate is proportional to the resin volume discharge amount per effective small hole, and is inversely proportional to the three small hole radii. Here, the effective small hole means a small hole that effectively discharges resin (that is, a small hole that is not clogged with resin), and the above Q is expressed by the following equation (4). be.

Q=total resin volume discharge rate from the die (cm ³ /sec)/number of small holes (h) for effectively discharging resin (4).

In the manufacturing method of the present invention, the method for increasing the effective opening ratio at the start of operation to 90% or more is not particularly limited. That is, when the effective aperture ratio is 100%, the shear rate of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die is 13000 sec ^-1 or more, more preferably 15000 sec ^-1 or more. , the number of small holes and the extruder feed rate.

In the production method of the present invention, immediately after the blowing agent-containing thermoplastic resin melt is extruded into the pressurized water through the small holes of the die, it is cut into short pieces by a rotary cutter to form spheres in the liquid. Solidification takes place. This forms expandable thermoplastic resin particles.

In the production method of the present invention, the temperature of the molten resin immediately before being extruded from the die is preferably Tg + 40 ° C. or higher, where Tg is the glass transition temperature of the resin in a state not containing a foaming agent. Tg+110°C is more preferable, and Tg+60°C to Tg+90°C is even more preferable. In the case of styrene homopolymer, the Tg is about 100°C, so the preferred temperature range is 140°C to 210°C, and the more preferred range is 160°C to 190°C.
If the temperature of the molten resin immediately before being extruded from the die is Tg + 40 ° C. or higher, the viscosity of the extruded molten resin is low, clogging of small holes is less likely to occur, and the effective opening ratio of small holes is less likely to decrease. It is possible to avoid distorted or uneven shape of the expandable styrene resin particles to be obtained. On the other hand, if the temperature of the molten resin immediately before it is extruded from the die is Tg+110° C. or less, the extruded molten resin is easily solidified, is less likely to wrap around the rotary cutter, and can be stably cut.

The cutting device for cutting the molten resin extruded by the pressurized water in the production method of the present invention is not particularly limited, but for example, it is cut by a rotating cutter that contacts the die to be made into small spheres, and foamed in the pressurized cooling water. a device that is transported to a centrifugal dehydrator for dehydration/aggregation, and the like.

The conditions of the pressurized water should be adjusted according to the type and content of the thermoplastic resin, foaming agent, and additives used. conditions are preferred.

Specifically, the temperature of the pressurized water is preferably 40°C to 80°C. If the temperature of the pressurized water is lower than 40° C., the die may be cooled excessively and the outlet of the small holes may be clogged with molten resin. On the other hand, if the temperature of the pressurized water exceeds 80° C., the molten resin may not be completely solidified in the pressurized water and may foam. In the case of styrene homopolymer, the temperature condition of the pressurized water is preferably 45°C to 75°C, more preferably 50°C to 65°C.

The pressure condition of the pressurized water is not particularly limited, but it is preferable to adjust the true density of the expandable thermoplastic resin particles obtained to be 0.8 times or more the true density of the raw material thermoplastic resin. When it is 0.8 times or more the true density of the raw material, the density of the expandable thermoplastic resin particles obtained is sufficiently high, so that the transportation cost per unit volume of the expandable thermoplastic resin particles can be suppressed.

When a styrene homopolymer is used as the thermoplastic resin, the density of the resulting expandable styrene resin particles is preferably 950 kg/m ³ to 1050 kg/m ³ , more preferably 1000 to 1050 kg/m ³ . Adjust pressure. Incidentally, the true density of styrene homopolymer is 1000 to 1050 kg/m ³ . Although it depends on the type of foaming agent used, when butane or pentane is used as the foaming agent, it is preferably 0.6 to 2.0 MPa, more preferably 0.7 to 1.7 MPa, and still more preferably 0.8 MPa. ~1.5 MPa.

Since the production method of the present invention can produce expandable thermoplastic resin particles while maintaining an extremely high effective open area ratio, it is possible to obtain expandable thermoplastic resin particles having an excellent shape. The sphericity of the expandable thermoplastic resin particles is preferably 0.92 or more, preferably 0.94 or more, and more preferably 0.95 or more. When the sphericity is within the above range, the fusion bondability is excellent. The sphericity referred to here will be described in detail in Examples.

Pre-expanded particles can be obtained by subjecting the expandable thermoplastic resin particles obtained as described above to a pre-expanding step. In this step, heated steam or the like is used to soften the expandable thermoplastic resin particles and at the same time volatilize the foaming agent in the particles to form a large number of cells in the particles to form pre-expanded particles. Specific conditions for the pre-foaming step can follow conventionally known conditions. The expansion ratio of the pre-expanded particles in this step can be appropriately selected, but according to the production method of the present invention, a relatively high expansion ratio can be achieved. Specifically, an expansion ratio of 70 times (cc/g) or more, further 80 times (cc/g) or more can be achieved.

After the obtained pre-expanded particles are aged for a certain period of time, they are further subjected to a molding step, whereby a foamed molded article can be produced. In this step, the pre-expanded particles are filled in a mold of a predetermined shape, steam is introduced into the mold to further expand the pre-expanded particles in the mold, and the pre-expanded particles are fused together. to form a foam molded body having a predetermined shape. Specific conditions for the molding process can follow conventionally known conditions. According to the manufacturing method of the present invention, specifically, a fusion rate of 70% or more, preferably 90% or more can be achieved.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

[Measurement of grain weight]
Using an electronic balance capable of measuring up to 0.01 mg, the weight of 100 expandable thermoplastic resin particles randomly sampled was measured, and the particle weight was calculated by the following formula.

Particle weight (mg)=[weight of 100 resin particles (mg)]/100.

[Calculation of effective aperture ratio of small holes]
The effective aperture ratio of small pores was calculated by the following formula.

Effective aperture ratio (%) = h/H x 100
h: Number of small holes that effectively discharge resin (pieces)
H: Total number of small holes in the die (pieces)
Incidentally, all the small holes in the die exclude small holes which are previously embedded in the die with pins or the like and which are closed structurally so as not to discharge the resin. Also, the number h of small holes through which the resin is effectively discharged was calculated by the following formula.

h (pieces) = {q/(N x n x W x 60)} x 10 ⁶
q: total discharge from the die (kg/hr)
N: rotation speed of rotary cutter (rpm)
n: Number of blades of rotary cutter (sheets)
W: Grain weight (mg).

[Calculation of shear rate]
The shear rate when the blowing agent-containing thermoplastic resin melt passed through the small hole land was calculated by the following formula.

τ=4×Q/(π×r ³ )
τ: shear rate (sec ⁻¹ )
Q: Resin volume discharge amount per effective small hole (cm ³ /sec)
π: circumference ratio r: small hole radius (cm)
Incidentally, Q was calculated from the following formula.

Q=total volume discharge from the die (cm ³ /sec)/number of small holes (h) effectively discharging resin.

[Maximum expansion ratio of pre-expanded particles]
The expandable thermoplastic resin particles were put into a pre-expanding machine, and steam of 0.1 MPa was introduced into the pre-expanding machine to expand them to obtain pre-expanded particles. Foaming was performed by changing the steam introduction time at intervals of 90 seconds to 30 seconds, and the expansion ratio was measured for each steam introduction time, and the highest expansion ratio was taken as the maximum expansion ratio of the pre-expanded particles. The steam introduction time was changed until shrinkage of the expanded particles (decrease in expansion ratio) due to overheating was confirmed. The expansion ratio was calculated by the following formula after putting the pre-expanded particles into a graduated cylinder so that the volume was 2000 cc, measuring the weight.

Expansion ratio (cc/g)=2000 cc/[weight of pre-expanded particles (g)].

[Measurement of fusion rate]
The thermoplastic resin foam molded product was split at the center and the total number of particles in the cross section was counted. Next, the number of particles (the number of broken particles) in which the particles were cracked and the bubbles inside were confirmed was counted and calculated by the following formula.

Fusion rate (%)=number of broken particles/total number of particles×100.

[Measurement of sphericity]
Using a microscope [manufactured by Keyence Corporation, VHX-900], the diameter of the expandable thermoplastic resin particles in three directions perpendicular to each other is measured, and the longest diameter is Dn (mm), and the next longest diameter is Ln ( mm), and the shortest diameter was Wn (mm). Ten particles were measured, D (mm), L (mm) and W (mm) were calculated from the arithmetic mean values, and the longest diameter D (mm) was taken as the maximum diameter. Next, L/D, W/D, and W/L were calculated, and the arithmetic mean value was taken as the degree of sphericity.

(Example 1)
[Production of expandable thermoplastic resin particles]
Polystyrene [manufactured by PS Japan Co., Ltd., 680] 93.3 parts by weight as a thermoplastic resin, graphite [manufactured by Marutoyo Casting Co., Ltd., flake graphite SGP-40B] 4 parts by weight, and a brominated flame retardant [Daiichi Kogyo Seiyaku Co., Ltd., SR-130] 2.5 parts by weight, stabilizer [ADEKA Co., Ltd., LA-57] 0.1 part by weight, stabilizer [ADEKA Co., Ltd., PEP-36] 0.1 part by weight is supplied to a co-meshing twin-screw extruder [manufactured by KraussMaffei Berstorff GmBH] with a total feed rate of 234.6 kg / hr and a diameter of 60 mm, and after the raw material feed section of the twin-screw extruder Melt-kneading was carried out at a cylinder temperature of 165°C. From the middle of the twin-screw extruder, mixed pentane [normal pentane (manufactured by SK Sangyo Co., Ltd.) 80% by weight and isopentane (manufactured by SK Sangyo Co., Ltd.) 20% by weight with respect to 100 parts by weight of the thermoplastic resin melt 4.8 parts by weight of the mixture] and 2.2 parts by weight of isobutane [manufactured by Mitsui Chemicals, Inc.] were injected.

After that, through a gear pump set at 170 ° C. connected to the tip of the twin screw extruder, a screen changer, and a diverter valve, 168 small holes with a diameter of 0.65 mm and a land length of 5.0 mm were connected downstream of the diverter valve. A blowing agent-containing thermoplastic resin melt having a resin temperature of 170° C. was extruded into pressurized water at a temperature of 65° C. and 1.4 MPa through a die set at 240° C. at a discharge rate of 251 kg/hr. The extruded blowing agent-containing thermoplastic resin melt is granulated and cooled to solidify by cutting the melt using a rotating cutter having 12 blades at 1362 rpm in a chamber filled with pressurized water. did.

Five minutes after the start of cutting the melt, the grain weight of the expandable thermoplastic resin particles was measured and found to be 1.55 mg. This point was defined as the start of operation, and the effective opening ratio of the small holes at the start of operation was calculated from the grain weight obtained. The calculated shear rate A of the plastic composition was 15947 sec ⁻¹ .

After confirming that the effective opening ratio of the small holes was 90% or more, the discharge rate was changed to 168 kg/hr without changing the supply ratio of each raw material.

Immediately after starting production was defined as 5 minutes after changing the discharge amount, and the particle weight of the obtained expandable thermoplastic resin particles was 1.05 mg. In addition, the small pore opening ratio immediately after the start of production was 97%, and the shear rate B of the blowing agent-containing thermoplastic melt immediately after the start of production was 10803 sec ^-1 .

As a result of evaluating the expandable thermoplastic resin particles after production for 48 hours after changing the discharge rate to 168 kg/hr, the grain weight of the obtained expandable thermoplastic resin particles was 1.05 mg, and the sphericity was was 0.95. Further, the effective opening ratio of small pores was maintained at 97%, and the shear rate C of the blowing agent-containing thermoplastic melt was 10803 sec ^-1 . After 0.08 parts by weight of zinc stearate was dry-blended with the resulting expandable thermoplastic resin, the mixture was stored at 15°C.

[Production of pre-expanded particles]
The expandable thermoplastic resin particles were put into a pre-expanding machine, and steam of 0.1 MPa was introduced into the pre-expanding machine to expand them to obtain pre-expanded particles having a maximum expansion ratio of 81 times.

[Preparation of foam molded product]
The obtained pre-expanded particles with an expansion ratio of 81 times were filled in a mold for in-mold molding attached to a styrene foam molding machine, and 0.04 MPa steam was introduced for 15 seconds to expand in the mold. The mold was cooled by spraying hot water at 50°C for 5 seconds. After holding the thermoplastic resin foam-molded product in the mold until the pressure of the thermoplastic resin foam-molded product pushing the mold reaches 0.015 MPa (gauge pressure), remove the thermoplastic resin foam-molded product. Thus, a rectangular parallelepiped thermoplastic resin foam molded product (length 450 mm×width 450 mm×thickness 50 mm) was obtained. The fusion rate of the molding was 90%.

(Example 2)
Expandable thermoplastic resin particles were obtained in the same manner as in Example 1, except that the discharge rate during production was changed from 168 kg/hr to 140 kg/hr and the cutter rotation speed was changed from 1362 rpm to 1119 rpm.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

(Example 3)
Expandable thermoplastic resin particles were obtained in the same manner as in Example 1, except that the discharge rate during production was changed from 168 kg/hr to 130 kg/hr and the cutter rotation speed was changed from 1362 rpm to 1050 rpm.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

(Example 4)
Expandable thermoplastic resin particles were obtained in the same manner as in Example 1, except that the discharge rate during production was changed from 168 kg/hr to 200 kg/hr and the cutter rotation speed was changed from 1362 rpm to 1600 rpm.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

(Example 5)
Expandable thermoplastic resin particles were obtained in the same manner as in Example 1 except that the discharge rate of 251 kg/hr at the start of operation was maintained during production without changing the discharge rate. Since the discharge amount was not changed, the start of operation and immediately after the start of production were taken as the same time.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

(Comparative example 1)
The discharge rate at the start of operation was changed from 251 kg/hr to 153 kg/hr, and the cutter rotation speed was changed from 1362 to 1850 rpm. Expandable thermoplastic resin particles were obtained in the same manner as in Example 5, except that the temperature was also maintained.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

(Comparative example 2)
Example 1 except that the discharge rate at the start of operation was changed from 251 kg/hr to 200 kg/hr, the cutter rotation speed was changed from 1362 to 2000 rpm, and the discharge rate during production was changed from 168 kg/hr to 153 kg/hr. Expandable thermoplastic resin particles were obtained in the same manner as above.

Using the obtained expandable thermoplastic resin particles, pre-expanded particles and an expanded molded article were produced in the same manner as in Example 1.

From the above results, in Examples 1 to 5, compared to Comparative Examples 1 and 2, the opening ratio of the small holes can be stably maintained for a long time, the expansion ratio of the pre-expanded particles is high, and the fusion rate of the molded body is also high. It turns out to be expensive. Furthermore, it can be seen that Examples 1 to 4 have a higher molding fusion rate than Example 5. Furthermore, it can be seen that Examples 1 to 3 have a higher sphericity than Examples 4 and 5 and Comparative Example 2, and a higher maximum expansion ratio and a higher fusion rate of molded bodies.

10 die 11 face 12 small hole 13 resin passage a length of small hole land b diameter of small hole

Claims (7)

A method for producing expandable thermoplastic resin particles, comprising extruding a foaming agent-containing thermoplastic resin melt from a die having a plurality of small holes into pressurized water and then cutting the molten resin with a rotary cutter to form particles,
The die has an effective aperture ratio of 90% or more at the start of operation (here, at the start of operation, when 5 minutes have passed since the start of cutting the expandable thermoplastic resin particles in the pressurized water). ,
The method for producing expandable thermoplastic resin particles, wherein the shear rate of the foaming agent-containing thermoplastic resin melt when passing through the small hole land portion of the die at the start of operation is 15000 sec ^-1 or more (however, the die The temperature is controlled so as to be 115° C. or more higher than the resin temperature of the foaming agent-containing thermoplastic resin melt). The method for producing expandable thermoplastic resin particles according to claim 1, wherein the temperature of the pressurized water is 45°C to 80°C. 3. The method according to claim 1 or 2, wherein the temperature of the foaming agent-containing thermoplastic resin melt immediately before being extruded from a die is Tg+40° C. or higher (Tg is the glass transition temperature of the resin in the absence of the foaming agent). A method for producing expandable thermoplastic resin particles. The expandable thermoplastic according to any one of claims 1 to 3, wherein the expansion ratio of the pre-expanded particles obtained by pre-expanding the expandable thermoplastic resin particles is 80 times (cc/g) or more. A method for producing resin particles. The method for producing expandable thermoplastic resin particles according to any one of claims 1 to 4, wherein the thermoplastic resin is a styrenic resin. The method for producing expandable thermoplastic resin particles according to any one of claims 1 to 5, wherein the diameter of the pores is 0.5 mm to 1.0 mm. The method for producing expandable thermoplastic resin particles according to any one of claims 1 to 6, wherein the expandable thermoplastic resin particles have a sphericity of 0.92 or more.

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