JP2018145344A - Production method of foamable thermoplastic resin particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing foamable thermoplastic resin particles having excellent productivity.SOLUTION: A method of producing foamable thermoplastic resin particles includes: a melting and kneading step of charging a thermoplastic resin in an extruder to melt and knead; and a granulating step of extruding a melt obtained by adding a foaming agent to the thermoplastic resin from a die having a plurality of small holes into pressurized cooling water followed by particulating by cutting the melt immediately after the extrusion, in which a step of selecting a part of foamable thermoplastic resin particles obtained by the granulating step as remelting foamable thermoplastic resin particles to remelt and knead by mixing in the range of 1 to 30 pts.wt. relative to 100 pts.wt of the thermoplastic resin in the melting and kneading step is included.SELECTED DRAWING: None

Description

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

  In-mold foam moldings using foamable thermoplastic resin particles are applicable to shapes having complex shapes such as irregularities, and are therefore used in a wide range of applications such as various containers, cushioning materials, and building materials.

  The method for producing expandable thermoplastic resin particles includes a suspension polymerization method in which a monomer component is suspended in an aqueous medium and polymerized to form resin particles, and then impregnated with a foaming agent to obtain expandable thermoplastic resin particles. Examples thereof include a melt-kneading method in which a thermoplastic resin is melt-kneaded using an extruder and then cut into particles. Among them, the thermoplastic resin composition is melted with an extruder, the foaming agent is press-kneaded into the melt of the thermoplastic resin composition, extruded through a die having small holes, into pressurized circulating water, and simultaneously cut with a rotary cutter. At the same time, the method of cooling and solidifying with pressurized circulating water (melt extrusion method) can easily produce good expandable particles, and is therefore employed in the production of various expandable resin particles.

  However, in the melt extrusion method, when extruding a molten resin containing a foaming agent from a die and simultaneously cutting and granulating with a rotary cutter, if the water pressure, water temperature, and molten resin temperature are poorly adjusted, distortion occurs. In some cases, expandable resin particles having shape defects such as dents and dents may occur. Moreover, since the die front end surface is in contact with the pressurized circulating water, the die opening ratio changes during continuous production, which also affects the particle weight of the resulting expandable resin particles. Since the range of the particle weight recognized as a product is determined, expandable resin particles whose particle weight is outside the range are treated as non-standard products. . If foamable resin particles with shape defects or foamable resin particles whose particle weight is outside the specified range are used for in-mold foam molding, the surface properties of the resulting in-mold foam may deteriorate or mechanical strength may be reduced. May be damaged. Therefore, these expandable resin particles cannot be used for in-mold molding and must be disposed of as non-standard products. Although such non-standard foamable resin particles have defects in shape and particle weight, they are not inferior in physical properties derived from components such as flame retardants and thermoplastic resins, so they are disposed of from the viewpoint of yield. That is not desirable.

  In recent years, recycling of waste resin has been actively carried out due to increased environmental protection. For example, Patent Documents 1 and 2 disclose that a styrene-based resin is recovered from a foamed molded article of waste, the foamable particles are regenerated by a melt extrusion method, and used again for the production of a foamed molded article. . However, Patent Documents 1 and 2 recycle the styrene resin recovered from the foamed molded article, but do not reuse the non-standard foamable resin particles themselves that are produced in the manufacturing process. Also from the viewpoint of such a social environment, a method that can effectively utilize non-standard expandable resin particles generated in the production process is desired.

JP 2003-306571 A JP 2004-115690 A

  An object of this invention is to provide the manufacturing method of a foamable thermoplastic resin particle with sufficient productivity.

  In the melt kneading method, it is preferable to suppress an increase in temperature of the thermoplastic resin during melt kneading in order to reduce decomposition and deterioration of the flame retardant and the like when the thermoplastic resin charged in the extruder is melt kneaded. Therefore, a plasticizer is generally added to the thermoplastic resin to lower the melt viscosity of the thermoplastic resin. However, when an additive such as a plasticizer is added, the balance of the foaming characteristics and the fusion characteristics of the expandable resin particles tends to be impaired. Therefore, the present inventors paid attention to the plasticizing action of the foaming agent contained in the foamable resin particles, and re-introduced the foamable resin particles obtained in the production process into the extruder as a plasticizer, together with the thermoplastic resin. It has been found that, by melt-kneading, the increase in the temperature of the molten resin during melt-kneading in the stage before the foaming agent press-in can be effectively suppressed, and the present invention has been completed.

  That is, the present invention includes a melt-kneading step in which a thermoplastic resin is introduced into an extruder and melt-kneaded, and a melt obtained by adding a foaming agent to the thermoplastic resin from a die having a plurality of small holes into pressurized cooling water. In the method for producing expandable thermoplastic resin particles, including the granulation step of cutting and granulating the melt extruded from the die immediately after the extrusion, the foamable thermoplastic obtained in the granulation step Part of the resin particles are selected as remeltable foamable thermoplastic resin particles, and the remeltable foamable thermoplastic resin particles are 1 to 30 parts by weight with respect to 100 parts by weight of the thermoplastic resin in the melt-kneading step. And a method for producing expandable thermoplastic resin particles, which includes a step of mixing and remelting and kneading within the range (hereinafter, sometimes referred to as “method for producing expandable resin particles of the present invention”). .

  In the method for producing expandable resin particles of the present invention, the remeltable expandable thermoplastic resin particles are foamable thermoplastic resin particles having a shape defect, and / or expandable thermoplastic resin whose particle weight is out of a specified range. Preferably it contains particles.

  In the method for producing expandable resin particles of the present invention, the expandable thermoplastic resin particles are preferably expandable polystyrene resin particles.

  In the process for producing expandable resin particles of the present invention, the remeltable expandable thermoplastic resin particles preferably contain 1 to 8% by weight of a foaming agent.

  According to the method for producing expandable resin particles of the present invention, by using the expandable resin particles obtained in the production process as a plasticizer, the melt resin temperature in the melt-kneading step can be used without using an additive such as a plasticizer. Can be suppressed.

  According to the process for producing expandable resin particles of the present invention, since non-standard products of expandable thermoplastic resin particles generated in the production process can be effectively used, the yield is improved and it is economical.

  The method for producing expandable resin particles of the present invention includes a melt-kneading step in which a thermoplastic resin is put into an extruder and melt-kneaded, and a melt containing a foaming agent in the thermoplastic resin is formed from a die having a plurality of small holes. In a method for producing expandable thermoplastic resin particles, including a granulation step of extruding into pressurized cooling water and cutting and granulating the melt extruded from a die immediately after extrusion, the granulation step is obtained in the above granulation step. A part of the expandable thermoplastic resin particles is selected as remeltable expandable thermoplastic resin particles, and the remeltable expandable thermoplastic resin particles are 1 in 100 parts by weight of the thermoplastic resin in the melt kneading step. It includes a step of mixing and remelting and kneading within a range of ˜30 parts by weight.

  By mixing a part of the foamable thermoplastic resin particles obtained in the granulation step as it is into the thermoplastic resin and remelting and kneading, it is possible to melt and knead while keeping the resin temperature of the thermoplastic resin low. By the foaming agent contained in the foamable thermoplastic resin particles, the thermoplastic resin is plasticized, and an increase in the molten resin temperature in the melt-kneading process until the foaming agent is press-fitted can be suppressed. Therefore, it is not necessary to further add an additive such as a plasticizer in order to suppress an increase in the molten resin temperature. Moreover, since a thermal decomposition of a flame retardant can be suppressed effectively when a flame retardant is included, the expandable thermoplastic resin particle excellent in the flame retardance can be obtained. Furthermore, by using foamable thermoplastic resin particles having shape defects such as distortion and dent, which are usually treated as non-standard products, and foamable thermoplastic resin particles whose particle weight is outside the specified range as a plasticizer, Yield can be improved.

<Melting and kneading process>
The thermoplastic resin used in the process for producing expandable resin particles of the present invention can contain a known thermoplastic resin, such as 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 Styrenic resin such as alloy (IP) with AS; vinyl resin such as polymethyl methacrylate, polyacrylonitrile resin and polyvinyl chloride resin; polypropylene, polyethylene, ethylene-propylene copolymer, ethylene-propylene -Polynes such as butene terpolymers and cycloolefin (co) polymers Fin resins and polyolefin resins whose rheology is controlled by introducing a branched structure or a crosslinked structure into them; polyamide resins such as nylon 6, nylon 66, nylon 11, nylon 12, MXD nylon; polyethylene terephthalate, polybutylene terephthalate, Polyarylate, polyester resins such as polycarbonate, aliphatic polyester resins such as polylactic acid; polyphenylene ether resin (PPE), modified polyphenylene ether resin (modified PPE), polyoxymethylene resin, polyphenylene sulfide resin, polyphenylene Examples include engineering plastics such as sulfide resins, aromatic polyether resins, and polyether ether ketone resins. These may be used singly or in combination of two or more. Among these, styrene resins are preferred because they are inexpensive and easy to foam.

  In the process for producing expandable resin particles of the present invention, various additives can be added to the thermoplastic resin as necessary. Examples include flame retardants, heat stabilizers, radical generators, processing aids, weathering stabilizers, nucleating agents, foaming aids, antistatic agents, radiation heat transfer inhibitors, and colorants. . These additives can be used alone or in combination of two or more.

  As the flame retardant, it is preferable to use a brominated flame retardant from the viewpoint of low environmental problems and high flame retardancy imparting effect. 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-methyl) Propyl ether)), or 2,2-bis [4- (2,3-dibromopropoxy) -3,5-dibromophenyl] propane (also known as: tetrabromobisphenol A-bis (2,3-dibromopropyl ether)) Brominated bisphenol compounds such as brominated bisphenol compounds, brominated styrene / butadiene block copolymers, brominated random styrene / butadiene copolymers, or brominated styrene / butadiene graft copolymers. Examples thereof include polymers (for example, disclosed in JP-T-2009-516019). Although brominated flame retardants are prone to thermal decomposition, according to the present invention, the thermoplastic resin and other components can be melt-kneaded while suppressing an increase in the molten resin temperature. -Deterioration is suppressed and the foamable thermoplastic resin particles obtained can exhibit good flame retardancy.

  The radiation heat transfer inhibitor is a substance that can suppress radiant heat transfer among the heat transfer mechanism transmitted through the foam molded body, and in the foam molded body of the same resin, foaming agent, cell structure, density, By adding a radiant heat transfer inhibitor, a substance having an effect of lowering the thermal conductivity can be used as compared with an additive-free system. Specifically, it may be a substance having a property of reflecting, scattering, and absorbing light in the near infrared or infrared region (for example, a wavelength range of about 800 to 3000 nm). For example, aluminum such as aluminum and aluminum oxide Compounds, zinc compounds such as zinc aluminate; magnesium compounds such as hydrotalcite; silver compounds such as silver: titanium compounds such as titanium, titanium oxide, strontium titanate; stainless steel, nickel, tin, silver, Heat-reflecting agents such as copper, bronze, shirasu balloon, ceramic balloon, microballoon, pearl mica, and carbon compounds such as carbon black, graphite, graphene, activated carbon; barium sulfate, strontium sulfate, calcium sulfate, mercalite, halotristone , Alumite, iron alumite, etc. Antimony compounds such as antimony trioxide, antimony oxide, and anhydrous zinc antimonate; metal oxides such as tin oxide, indium oxide, zinc oxide, and indinium tin oxide; ammonium, urea, imonium, aminium, cyanine And heat ray absorbers such as polymethine, polymethine, anthraquinone, dithiol, copper ion, phenylenediamine, phthalocyanine, benzotriazole, benzophenone, oxalic anilide, cyanoacrylate, and benzotriazole. These radiation heat transfer inhibitors may be used alone or in combination of two or more. A carbon-based compound is preferable from the viewpoint of an excellent balance between the thermal conductivity reduction effect and cost, and graphite, graphene, activated carbon, and titanium oxide are more preferable. Graphite and graphene are particularly preferable because the effect of reducing the thermal conductivity is exhibited with a relatively small amount.

  The melt-kneading step in the process for producing expandable resin particles of the present invention only needs to include an operation of melt-kneading the thermoplastic resin with an extruder, and a single extruder may be used, or a plurality of extruders may be connected. And may be melt-kneaded. Alternatively, melt kneading may be performed by using at least one extruder and a kneading apparatus such as a static mixer or a stirrer not having a screw.

  As an extruder, a well-known extruder can be used, for example, a single screw extruder or a twin screw extruder can be used. When using a twin screw extruder, the screw rotation direction may be the same or different. When two or more extruders are used, it is preferable to adopt a tandem type in which extruders are connected in series. For example, a single screw extruder-single screw extruder, a twin screw extruder-single screw extruder, and the dispersibility of a foaming agent and an additive is good. The configuration of the adopted twin screw extruder-single screw extruder is preferable.

  In the process for producing expandable resin particles of the present invention, a foaming agent is pressed into a molten thermoplastic resin. Although it does not specifically limit as a foaming agent, The balance of foamability and product life is good, and a hydrocarbon type foaming agent is preferable from a viewpoint of being easy to make high magnification when actually used, and a C4-C6 hydrocarbon is especially preferable. More preferred. When the carbon number of the foaming agent is 4 or more, the volatility is low and the foaming agent is less likely to dissipate from the foamable thermoplastic resin particles. A sufficient foaming force can be obtained, and high magnification is easy, which is preferable. Moreover, since the boiling point of a foaming agent is not too high as carbon number is 6 or less, it becomes easy to obtain sufficient foaming force by the heating at the time of preliminary foaming, and it becomes the tendency for high foaming to be easy. Examples of the hydrocarbon having 4 to 6 carbon atoms include hydrocarbons such as 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. The blowing agent is preferably a hydrocarbon having 4 to 5 carbon atoms.

  The addition amount of the foaming agent is preferably 4 to 10 parts by weight, more preferably 4.5 to 9 parts by weight, and still more preferably 5 to 8 parts by weight with respect to 100 parts by weight of the thermoplastic resin. If it is the said addition amount, the balance of foaming speed and foaming power will be good, and it will be easy to make high magnification stably. When the addition amount is 4 parts by weight or more, since the foaming force necessary for foaming is sufficient, high foaming becomes easy, and it is easy to produce a thermoplastic resin foam molded article having a high foaming ratio of 50 times or more. Further, when the addition amount is 10 parts by weight or less, the flame retardancy is improved and the production time (molding cycle) for producing the foamed molded product is shortened, so that the production cost can be reduced.

  The foaming agent may be press-fitted into the thermoplastic resin melted in the extruder, and when a kneading device such as a static mixer or a stirrer having no screw is provided in the extruder, the foaming agent is extruded from the extruder. You may press-fit into the molten thermoplastic resin until it knead | mixes with the said kneading apparatus.

  The set temperature in the melt-kneading step may be appropriately set according to the thermoplastic resin to be used, but is preferably 100 ° C to 250 ° C. If the set temperature is 250 ° C. or lower, it is difficult for the brominated flame retardant to decompose, it becomes possible to obtain the desired flame retardancy, and it is necessary to add the flame retardant excessively in order to impart the desired flame retardancy There is an effect that there is no. On the other hand, when the set temperature is 100 ° C. or higher, the load on the extruder or the like is reduced and the extrusion becomes stable.

<Granulation process>
The process for producing expandable resin particles of the present invention involves extruding a thermoplastic resin melt containing a foaming agent obtained in the melt-kneading step from a die having a plurality of small holes into pressurized cooling water and immediately after extrusion. The melt is cut into particles.

  The die used in the method for producing expandable resin particles of the present invention can be any known die without particular limitation as long as it is a die having a plurality of small holes. For example, the diameter is preferably 0.3 mm to 2.0 mm, A die having a small hole of 0.4 mm to 1.0 mm is more preferable.

  In the process for producing expandable resin particles of the present invention, the temperature of the melt of the foaming agent-containing thermoplastic resin immediately before being extruded from the die is Tg, which is the glass transition temperature of the thermoplastic resin in a state not containing the foaming agent. Tg + 40 ° C. or more is preferable, Tg + 40 ° C. to Tg + 100 ° C. is more preferable, and Tg + 50 ° C. to Tg + 70 ° C. is more preferable.

  When the temperature of the melt of the foaming agent-containing thermoplastic resin immediately before being extruded from the die is Tg + 40 ° C. or higher, the viscosity of the melt of the extruded foaming agent-containing thermoplastic resin is lowered, and small holes may be clogged. The foamable resin particles obtained due to the decrease in the aperture ratio of the small pores are less likely to be deformed. On the other hand, if the temperature of the melt of the foaming agent-containing thermoplastic resin immediately before being extruded from the die is Tg + 100 ° C. or less, the extruded foaming agent-containing thermoplastic resin is likely to solidify and foam. It is suppressed. In addition, the viscosity of the extruded foaming agent-containing thermoplastic resin does not become too low and can be stably cut by a rotary cutter, and the extruded foaming agent-containing thermoplastic resin is less likely to be wound around the rotary cutter.

  Other extrusion conditions such as the shear rate and discharge rate of the melt of the foaming agent-containing thermoplastic resin can be appropriately set according to various thermoplastic resins.

  The cutting device for cutting the foaming agent-containing thermoplastic resin extruded in the pressurized cooling water is not particularly limited. For example, the cutting device is cut by a rotary cutter substantially in contact with the die slip to be spheronized, and the pressurized cooling water is used. And a device that is transported to a centrifugal dehydrator without defoaming and dewatered and collected. Various conditions such as the rotating cutter speed, the pressure of the pressurized cooling water, and the water temperature can be appropriately set according to various thermoplastic resins.

<Selection and remelting process of resin particles for remelting>
In the process for producing the expandable resin particles of the present invention, the remeltable foamable thermoplastic resin particles are selected from the expandable thermoplastic resin particles obtained in the granulation step and mixed into the thermoplastic resin in the melt kneading step. Melt again.

  The foamable thermoplastic resin particle for remelting is not particularly limited as long as it is a foamable thermoplastic resin particle obtained in the granulation step, but from the viewpoint of productivity, the foamable thermoplastic resin particle having a shape defect or It is preferable to use expandable thermoplastic resin particles whose particle weight is outside the specified range. The shape defect is not particularly limited as long as it is inferior in foamability, and examples thereof include distortion and dent. Further, the prescribed range of the particle weight is a range that is appropriately set for each foamable resin particle that is a desired final product, and is determined in consideration of the filling property and foamability during molding.

  Expandable thermoplastic resin particles that have shape defects or whose particle weight falls outside the specified range are unsuitable for in-mold foam molding, but are composed of the same components as the raw materials. However, the physical properties of the desired foamable thermoplastic resin particles are not impaired. In addition, since it contains a foaming agent, the thermoplastic resin as a raw material can be plasticized and melt-kneaded while suppressing an increase in the resin temperature before the foaming agent is press-fitted.

  As the foamable thermoplastic resin particles for remelting used in the remelting process, the foamable thermoplastic resin particles obtained in the production process of the present invention may be used as they are, but from the viewpoint of backflow suppression and plasticization. The foaming agent content is preferably 1 to 8% by weight in 100% by weight of the foamable thermoplastic resin particles.

  In the remelting step in the production method of the present invention, the remeltable foamable thermoplastic resin particles are mixed and remelted so as to be in the range of 1 to 30 parts by weight with respect to 100 parts by weight of the thermoplastic resin. If it is the said range, the foaming agent contained in the foamable thermoplastic resin particle for remelting can act as a plasticizer of a thermoplastic resin, can suppress a rise in molten resin temperature, and also suppress backflow. And can be melt-kneaded. In addition, the influence of deterioration of the thermoplastic resin due to remelting of the foamable thermoplastic resin particles hardly occurs. Preferably it is 2-25 weight part, More preferably, it is 5-20 weight part.

<Post-processing>
The foamable thermoplastic resin particles obtained by the production method of the present invention can be dehydrated and dried after the granulation step, classified with a sieve or the like, and coated with a modifier such as an antistatic agent or an antiblocking agent. A known method can be applied to these steps.

Claims (4)

A melt-kneading step in which a thermoplastic resin is put into an extruder and melt-kneaded,
Extruding a melt obtained by adding a foaming agent to the thermoplastic resin from a die having a plurality of small holes into pressurized cooling water,
Immediately after the extrusion, including a granulation step of cutting and granulating the melt extruded from the die,
In the method for producing expandable thermoplastic resin particles,
A part of the foamable thermoplastic resin particles obtained in the granulation step is selected as remeltable foamable thermoplastic resin particles, and the remeltable foamable thermoplastic resin particles are selected as the thermoplastic resin in the melt kneading step. Including mixing and remelting and kneading within a range of 1 to 30 parts by weight with respect to 100 parts by weight,
A method for producing expandable thermoplastic resin particles.   The foamable thermoplastic resin particles according to claim 1, wherein the remeltable foamable thermoplastic resin particles include foamable thermoplastic resin particles having a shape defect and / or foamable thermoplastic resin particles whose particle weight is out of a specified range. For producing porous thermoplastic resin particles.   The method for producing expandable thermoplastic resin particles according to claim 1 or 2, wherein the expandable thermoplastic resin particles are expandable polystyrene resin particles.   The method for producing expandable thermoplastic resin particles according to any one of claims 1 to 3, wherein the remeltable expandable thermoplastic resin particles contain 1 to 8 wt% of a foaming agent.