JP2007015228A - Method for producing thermoplastic resin expanded particles, thermoplastic resin particles, thermoplastic resin expanded particles, and molded thermoplastic resin particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cut strands that can stably produce fine thermoplastic resin particles without causing cracks or chips even with a relatively hard thermoplastic resin having a tensile elastic modulus of 1600 MPa or more. It is an object of the present invention to provide a method and to provide fine thermoplastic resin particles having a uniform particle diameter, which are resin particles produced by the method.
SOLUTION: The method for producing thermoplastic resin particles of the present invention comprises extruding a molten thermoplastic resin as a plurality of strands into a gas phase from a die attached to an outlet of an extruder, and the strands in water. Is a method for producing resin particles by cutting the strands after cooling and solidifying by passing through the water, and the thermoplastic resin has a tensile modulus Y (MPa) of 1600 or more. In addition, it is characterized in that Z (MPa · mm) = X · Y determined by the diameter X (mm) of the obtained resin particles and the tensile elastic modulus Y satisfies a specific relationship.
[Selection] Figure 1

Description

  The present invention relates to a method for producing thermoplastic resin particles, the thermoplastic resin particles produced by the method, the thermoplastic resin foam particles obtained by foaming the thermoplastic resin particles, and the thermoplastic resin foam particles. The present invention relates to a foamed thermoplastic resin molded article that is attached or bonded.

  Conventionally, thermoplastic resin foam particle molded bodies made of thermoplastic resins such as polystyrene resins and polyolefin resins are known, and these molded bodies utilize their excellent flexibility and impact resistance, It is used as a shock-absorbing packaging material for fish boxes, a shock-absorbing packaging material for electrical products, an automobile energy absorbing material such as a bumper, and a heat insulating material. These molded products are generally filled with thermoplastic resin foam particles in a mold of any shape, and heated or fused by introducing steam or the like, or an adhesive between thermoplastic resin foam particles. Manufactured by adhering to each other.

The foamed particles used in the molded article are produced by granulating resin particles of an appropriate size, impregnating the resin particles with a foaming agent, and heating and foaming. As a means for producing the resin particles, a strand cut method is generally carried out in which resin particles having a uniform particle diameter can be mass-produced with an inexpensive apparatus. In the strand cutting method, as shown in FIG. 1, after melt-kneading the raw resin and various additives in the extruder, from a large number of holes formed in the die 2 installed at the outlet of the extruder 1, The molten thermoplastic resin is extruded as a plurality of strands 3, the strands 3 are cooled and solidified in water, dehydrated, sandwiched between take-up rollers 8 and fed to a pelletizer while being pulled at a constant speed. Then, the resin particles 5 are manufactured by cutting into an appropriate size (Patent Document 1, Patent Document 2).
The thermoplastic resin particles thus obtained can be used as a main raw material and a secondary raw material for resin processing, as well as foaming applications, or as a filler through secondary processing.

  On the other hand, in recent years, there has been an increasing demand for fine resin particles and ultralight resin particles. In other words, if small resin particles are used, small foam particles can be produced, and the small foam particles have excellent filling properties in the mold, so products for thin and small products that have been difficult until now are used. Development becomes possible. Further, by using fine resin particles as a raw material for extrusion molding, kneadability inside the extruder can be improved.

JP-A-61-215631 JP-A-9-174545

  However, in the above-described prior art, when trying to pelletize a relatively hard thermoplastic resin (tensile elastic modulus of 1600 MPa or more), the resin particles are cracked or chipped, and the resulting fine resin particles have uneven particle sizes. The problem of becoming occurred.

  The present invention solves the problems of the strand cutting method, and even if it is a relatively hard thermoplastic resin (tensile elastic modulus of 1600 MPa or more), it is possible to stably produce fine thermoplastic resin particles without causing cracks or chips. It is an object of the present invention to provide a strand cutting method capable of producing a resin, and to provide fine thermoplastic resin particles having a uniform particle diameter, which are resin particles produced by the method. Furthermore, an object of the present invention is to provide a thermoplastic resin foam particle obtained from the fine resin particles, and a thermoplastic resin foam particle molded body molded using the thermoplastic resin foam particles.

When the present inventors produce thermoplastic resin particles by the strand cut method, the resin particles are cracked or chipped, resulting in irregular particle sizes of the resulting resin particles. The present invention has been achieved by focusing on the point relating to the tensile modulus of the thermoplastic resin and the diameter of the strand.
According to this invention, the manufacturing method of the thermoplastic resin particle shown below is provided.
[1] By extruding molten thermoplastic resin as a plurality of strands into the gas phase from a die attached to the outlet of the extruder, immersing the strands in water, and passing through the water In the production method in which the strands are cut and solidified after cooling and solidification, the thermoplastic resin has a tensile modulus Y (MPa) of 1600 or more, and the diameter X (mm) of the obtained resin particles A method for producing thermoplastic resin particles, wherein Z (MPa · mm) = X · Y determined by the tensile elastic modulus Y satisfies the following formula (1):
300 <Z <4000 (1)
[2] The method for producing thermoplastic resin particles according to [1], wherein the strand is taken out from water to which a surfactant is added.
[3] Resin particles obtained by the method for producing thermoplastic resin particles according to [1] or [2], wherein an average particle weight of the resin particles is 1.0 mg or less. Thermoplastic resin particles.
[4] The above-mentioned [3], wherein the resin particles are cylindrical and the ratio L / D of the length (L) to the diameter (D) of the resin particles is more than 1 and 5 or less. Thermoplastic resin particles.
[5] A thermoplastic resin foamed particle, wherein the thermoplastic resin particle according to [3] or [4] is foamed to an apparent density of 10 to 600 g / L.
[6] A thermoplastic resin foamed particle molded article obtained by fusing or adhering a plurality of the foamed thermoplastic resin particles according to [5].

According to the method for producing thermoplastic resin particles of the invention according to claim 1 of the present invention, by improving the strand cut method, even a relatively hard thermoplastic resin (tensile elastic modulus of 1600 MPa or more) Fine thermoplastic resin particles can be produced stably without causing chipping.
According to the method for producing thermoplastic resin particles of the invention according to claim 2 of the present invention, by adding a surfactant to water, even a relatively hard thermoplastic resin (tensile elastic modulus of 1600 MPa or more), A stable mass production of fine thermoplastic resin particles can be achieved without fusing the strands together.
By using the thermoplastic resin particles of the invention according to claims 3 and 4 of the present invention, it is possible to obtain thermoplastic resin expanded particles capable of forming a molded thermoplastic resin expanded particle having excellent rigidity even in a shape having a thin wall portion. be able to. Further, by using the fine resin particles of the present invention as a raw material for extrusion molding, it becomes possible to improve the kneadability inside the extruder.
If the thermoplastic resin foamed particles of the invention according to claim 5 of the present invention are used, it is excellent in filling property in a narrow space in the mold, so that the foamed particles mutually It is possible to form a thermoplastic resin foamed particle molded body having an excellent appearance with few voids.
The thermoplastic resin foamed particle molded body of the invention according to claim 6 of the present invention is a foamed particle molded body having an excellent appearance with few voids between the foamed particles despite having a thin portion.

Hereinafter, the method for producing thermoplastic resin particles of the present invention, the thermoplastic resin particles obtained by the production method (hereinafter also simply referred to as “resin particles”), and the thermoplastic resin foam obtained by foaming the resin particles. Particles (hereinafter also simply referred to as “foamed particles”), thermoplastic resin foam particles obtained by molding the foamed particles (hereinafter also simply referred to as “foamed particle shaped bodies” or “molded bodies”).
The method of the present invention is a method for producing thermoplastic resin particles using a conventionally known strand cutting method. As shown in FIG. 1, a molten thermoplastic resin is removed from a die 2 attached to the outlet of an extruder 1. A plurality of strands 3 are extruded in the gas phase (usually in the atmosphere), the strands 3 are immersed in water 4, cooled and solidified by passing through the water 4, pulled up from the water, and dehydrated and dried. 7 is a method of obtaining resin particles 5 by cutting the strands 3 into an appropriate size.
The distance between the take-up roller unit 8 and the cutter blade 9 is slightly different depending on each pelletizer, but is usually 30 to 50 mm.

  The strand cut method is a conventionally known method, but the first feature of the present invention is that the tensile elastic modulus Y (MPa) of the thermoplastic resin used for the strand cut is 1600 MPa or more. The characteristic is that Z (MPa · mm) = X · Y determined by the diameter X (mm) of the obtained resin particles and the tensile elastic modulus Y must satisfy a specific relationship. That is, the first feature of the method of the present invention is to clarify that a relatively hard thermoplastic resin is an object of the present invention, and the second feature is the hardness of the thermoplastic resin and the diameter of the strand. The product has a specific range, and by combining the first feature with the second feature of the present invention, cracking or chipping of resin particles can occur even with a relatively hard thermoplastic resin. Therefore, it is possible to efficiently produce fine resin particles efficiently.

Next, the first feature of the method of the present invention will be described in detail.
In the present invention, the tensile elastic modulus Y (MPa) of the thermoplastic resin is 1600 MPa or more. A thermoplastic resin having a tensile elastic modulus Y (MPa) of 1600 MPa or more is a hard resin, and is suitable for obtaining a hard thermoplastic resin foam particle molded body, that is, a molded body that is lightweight and excellent in strength. However, due to its hardness, it was difficult to process into resin particles by pelletizing in the prior art, but according to the method of the present invention, resin particles can be easily obtained. In contrast, thermoplastic resins having a tensile modulus of less than 1600 MPa are unsuitable for applications that require hardness. From this viewpoint, the tensile modulus Y (MPa) is preferably 1800 MPa or more, and more preferably 2000 MPa or more.
The upper limit of the tensile elastic modulus Y (MPa) is usually 5000 MPa, and if it exceeds this, troubles such as chipping of the cutter occur, which may make it difficult to produce resin particles by the strand cutting method.

  The said tensile elasticity modulus Y (MPa) is a value about the thermoplastic resin as a raw material used for manufacture of a thermoplastic resin particle. When an additive for softening the resin is not added when the resin particles are produced, the tensile elastic modulus of the thermoplastic resin and the tensile elastic modulus of the thermoplastic resin particles show substantially the same value. In the present invention, as will be described later, various additives can be added to the thermoplastic resin, but in order to obtain a hard thermoplastic resin foam particle molded body, the tensile elastic modulus (MPa) of the thermoplastic resin particles is It is necessary to select the type and amount of the additive so that it does not fall below 1600 MPa. In addition, it is possible to prevent the tensile elastic modulus (MPa) of the thermoplastic resin particles from falling below 1600 MPa by conducting a preliminary experiment in advance.

The measurement of the tensile elastic modulus Y (MPa) in this specification shall be performed as follows.
After the thermoplastic resin is heated and compressed by sandwiching it in a steel plate for 5 minutes at a temperature of 220 ° C. and a pressure of 490 N / cm ^{2 with} a hot press, it is immediately moved between 30 ° C. cooling presses in a state of being sandwiched between the steel plates. By cooling, a sheet having a thickness of 1 mm is produced. The obtained sheet was subjected to a tensile test under the following conditions in accordance with JIS K7113 (1981) under an atmosphere at 23 ° C., and the tensile modulus was determined from the obtained chart according to JIS K7113 (1981). A value obtained by calculating Y (MPa) is employed. Moreover, what is necessary is just to measure similarly, when measuring a tensile elasticity modulus using a thermoplastic resin particle.
Test piece JIS No. 2 type test piece thickness 1 ± 0.1mm
Test speed 50mm / min
Distance between chucks 80mm
Measurement temperature 23 ℃

If the thermoplastic resin used in the method of the present invention has a tensile modulus of 1600 MPa or more, has a property of softening or flowing by heating and solidifying by cooling, and this property is repeatedly expressed, There is no question of structure or nature.
Examples of the thermoplastic resin include polylactic acid resin, polypropylene resin, polyethylene resin, polystyrene resin, acrylic resin, vinyl chloride resin, chlorinated polyethylene resin, ethylene-vinyl acetate copolymer resin, ethylene-vinyl. Alcohol copolymer resin, cellulose acetate resin, polyacetal resin, polyamide resin, polyarylate resin, thermoplastic polyurethane elastomer, liquid crystal polymer, polyether ether ketone, polysulfone, polyether sulfone, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyphenylene Ether resin, polyphenylene oxide, polyphenylene sulfide, polybutadiene, polymethylpentene resin, polyamic acid, thermoplastic polyimide, ionomer tree , Ethylene-ethyl acrylate resin, ethylene-methyl acrylate resin, styrene-methyl methacrylate resin, polyacrylonitrile-acrylic acid-styrene copolymer, acrylonitrile-styrene copolymer, polydicyclopentadiene, acrylonitrile-chlorinated polyethylene-styrene copolymer Examples thereof include a blend, an acrylonitrile-butadiene-styrene copolymer, a resin made of a fluororesin, and a blend resin of two or more of the above resins. The above-mentioned polylactic acid-based resin, polypropylene-based resin, polyethylene-based resin, and polystyrene-based resin are thermoplastic resins in which the proportion of structural units obtained from lactic acid exceeds 50 mol% in the resin. Similarly, the thermoplastic resin in which the proportion of structural units obtained from styrene exceeds 50 mol% in the resin is a polystyrene-based resin, and the proportion of structural units obtained from propylene exceeds 50 mol% in the resin. The thermoplastic resin is a polypropylene resin. For example, polylactic acid-based resins include homopolymers of lactic acid, copolymers of lactic acid and other monomers, and a copolymer resin in which the proportion of structural units obtained from lactic acid exceeds 50 mol%. Is included.
Even if these resins are blended, they can be used as long as the tensile elastic modulus is 1600 MPa or more.

Moreover, you may add coloring pigments or dyes, such as black, gray, brown, blue, green, etc. in the thermoplastic resin used by the method of this invention, for example. If colored resin particles made of a colored thermoplastic resin are used, colored thermoplastic resin products can be obtained, including colored thermoplastic resin expanded particles and thermoplastic resin expanded particle molded bodies.
Examples of the colorant include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments can be used.

  In addition, inorganic substances such as talc, calcium carbonate, borax, zinc borate, and aluminum hydroxide can be added to the thermoplastic resin in advance as a bubble regulator. When additives such as color pigments, dyes or inorganic substances are added to the thermoplastic resin, the additive can be supplied to the extruder as it is together with the thermoplastic resin, kneaded, and extruded as a strand. It is preferable to make a master batch of the additives in consideration of the above, and to supply the thermoplastic resin and the thermoplastic resin to an extruder and knead them. The amount of the color pigment or dye added varies depending on the color of the color, but usually it is preferably 0.001 to 5 parts by weight with respect to 100 parts by weight of the thermoplastic resin. Moreover, it is preferable that the addition amount of an inorganic substance shall be 0.001-5 weight part with respect to 100 weight part of thermoplastic resins, and also 0.02-1 weight part. By adding an inorganic substance to the thermoplastic resin, an effect of improving the expansion ratio can be obtained when the resin particles are expanded.

  In the method of the present invention, additives such as flame retardants, antistatic agents, weathering agents and thickeners can also be mixed. Assuming that the product is discarded after use, it is not preferable to add a high concentration of additives such as pigments and bubble regulators.

  The melting point of the thermoplastic resin used in the method of the present invention is not particularly limited, but preferably has a melting point that does not exceed a temperature at which it can be processed by a general-purpose extruder, and particularly preferably 350 ° C. or lower. Further, the melt mass flow rate (MFR) of the thermoplastic resin is preferably from 0.1 to 80 g / 10 minutes, particularly preferably from 0.5 to 30 g / 10 minutes. Melt mass flow rate (MFR) is measured in accordance with JIS K7210 (1999) by using condition code D in the case of polylactic acid resin, and condition code M in the case where the thermoplastic resin is polypropylene resin. In the case of polystyrene resin, it is a value measured using the condition code H.

Next, the second feature of the method of the present invention will be described.
In the method of the present invention, Z = X · Y (MPa · mm) determined by the diameter X (mm) and tensile elastic modulus Y (MPa) of the obtained resin particles needs to satisfy the following formula (1).
300 <Z <4000 (1)

  Z is an index representing the rigidity (hardness) of one strand. When this numerical value is small, that is, 300 or less, the rigidity of the strand becomes poor, and the strand is wound with a cutter and cut. The trouble of winding the strand around the take-up roller will occur. On the other hand, if Z is too large, that is, 4000 or more, the rigidity of the strands becomes too large, the strands overlap each other, the cut becomes unstable, and the resin particles are cracked or chipped. From such a viewpoint, the above Z is preferably 300 <Z <3000, and more preferably 300 <Z <2000.

  The diameter X (mm) of the resin particles means the diameter of the circle when the cross section of the strand is circular, the major axis when it is elliptical, and the maximum dimension when it is other shapes. . Here, the maximum dimension means the maximum value among the dimensions between both ends of the cross section in all directions of the cross section of the strand.

In the method of the present invention, the resin particle diameter X (mm) is preferably 0.1 to 2.0 mm, more preferably 0.1 to 1.0 mm, and still more preferably 0.1 to 0.7 mm.
There exists a possibility that Z may exceed the upper limit of (1) Formula as X (mm) exceeds 2.0 mm. On the other hand, if X (mm) is less than 0.1 mm, there is a possibility that resin particles cannot be produced.

  In order to produce resin particles having a diameter X within the above range, it is preferable to use a die in which resin passage holes having specific diameters are formed, and the diameter of the passage holes is preferably 0.1 to 3.0 mm. 0.1 to 2.0 mm is more preferable. If the diameter of the passage hole is outside the range of 0.1 to 3.0 mm, resin particles having a diameter X (mm) of 0.1 to 2.0 mm may not be manufactured.

  In consideration of productivity, the number of the resin passage holes, that is, the number of strands extruded from the die is preferably 2 to 10,000, more preferably 5 to 5,000, and still more preferably 40 to 500.

In the method of the present invention, it is preferable that the strand extruded from the extruder into the gas phase is guided into water to which a surfactant is added, and the strand is cooled and solidified by passing through water. If it does in this way, many strands which can manufacture the resin particle which satisfies the above-mentioned formula (1) can be extruded, and it can take up stably, ensuring high productivity. Next, the reason will be described in detail.
When trying to produce fine resin particles with the same amount of discharge by the strand cutting method, it is necessary to increase the take-up speed of the take-up roller and the cutting speed of the pelletizer, resulting in the ability of the pelletizer to increase. It becomes the driving | running in the place exceeding it, and it will become difficult to manufacture a fine resin particle stably. This can be solved by reducing the discharge amount, but the productivity of the resin particles is reduced. Therefore, in order to stably manufacture minute resin particles while ensuring high productivity, it is required to increase the opening area of the die by increasing the number of holes formed in the die.

  However, for example, when it is desired to halve the diameter of the strand, the number of holes needs to be quadrupled to maintain the opening area, so the strand can be stably extruded, but the spacing between adjacent holes Becomes shorter, and a new problem arises that the strands are easily fused. This problem can be solved by immersing the strands in water to which a surfactant has been added. That is, the strands are fused with each other when a strand extruded into the gas phase enters the water, and a kind of vibration phenomenon occurs. When the amplitude of the vibration overlaps, the strands are adjacent to each other before entering the water. This is because the strands come into contact with each other and fusion occurs. The present inventors have noticed this, and when the surface tension is lowered by using a surfactant, the vibration phenomenon of the strand is greatly reduced, and the fusion between the strands can be prevented. .

As long as the surfactant used in the method of the present invention has a lipophilic group and a hydrophilic group, the type thereof is not limited. However, when the strand is introduced into the pelletizer and cut, water attached to the strand is removed. A smaller amount is less likely to cause slippage on the take-up roller and improves productivity, so that the HLB is preferably 20 or less (1 to 20) in order to reduce adhering water.
In addition, HLB represents a balance between hydrophilicity and lipophilicity, and is a value obtained by setting the weakest hydrophilicity as 1, and the strongest hydrophilicity as 40. Specifically, HLB is described in the 61st page of “Chemistry of Dispersion / Emulsification System” 2nd edition (author: Fumio Kitahara, Kunio Furusawa) published on June 15, 1980, Engineering Books Co., Ltd. And according to the method submitted by Rideal.

The addition amount of the surfactant is preferably 0.001 to 0.1 parts by weight with respect to 100 parts by weight of water in the water tank. When the addition amount of the surfactant is less than 0.001 part by weight, strand fusion tends to occur. On the other hand, if the added amount exceeds 0.1 parts by weight, the amount of water adhering to the strand surface increases, and as a result, slipping easily occurs on the take-up roller, resulting in strand cut errors or the size of the resin particles obtained. It can cause unevenness.
The water temperature is preferably 0 to 60 ° C. When the temperature exceeds 60 ° C., the rapid cooling effect becomes poor, and when foamed particles are produced using the obtained resin particles, foamed particles having a very small cell diameter may be obtained, which may reduce in-mold moldability. . On the other hand, when the temperature is lower than 0 ° C., water begins to freeze, which is not preferable.

Surfactants that can be used in the method of the present invention include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants.
Examples of the anionic surfactant include fatty acid salt, alkyl sulfate ester salt, polyoxyethylene alkyl sulfate ester salt, alkylbenzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, alkyl Examples thereof include phosphates.
Examples of the cationic surfactant include quaternary ammonium salts and alkylamine salts.
Examples of the amphoteric surfactant include alkyl betaines and amine oxides.
The nonionic surfactant includes polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyethylene derivative, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester. , Polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkylalkanolamides, modified silicone oils obtained by imparting surfactant capabilities to silicone oils, and the like. Examples of such modified silicone oil include those obtained by substituting part of the methyl groups of siloxane oil such as dimethylpolysiloxane oil with organic functional groups to impart hydrophilicity, or by adding oxygen groups to the siloxane oil. And those having hydrophilic properties.
In any of the above surfactants, the alkyl moiety preferably has 10 to 30 carbon atoms, and the fatty acid moiety preferably has 10 to 30 carbon atoms.

  Among the above surfactants, nonionic surfactants are most preferred, and specifically, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene aoleyl ether, polyoxyethylene Nonionic surfactants such as higher alcohol ethers and modified silicone oils are exemplified. As the modified silicone oil, polyether-modified silicone oil (silicone polyether copolymer) is preferable.

  In the method of the present invention, in order to reduce the amount of the surfactant used, inorganic and organic auxiliaries (fusing prevention auxiliaries) can be added to the water in the water tank. Examples of the auxiliary agent include finely divided aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, kaolin, mica, clay, polyvinyl alcohol and the like. In addition, since the water tank may foam during long-time operation, an antifoaming agent such as silica or inorganic salt can be used in combination for the purpose of preventing this.

  If the above method is used, it becomes possible to extrude a large number of strands without fusing them. However, when water to which a surfactant is added is used as a cooling medium, the amount of water adhering to the strand tends to slightly increase when it is introduced into the pelletizer as compared with the case where no surfactant is used. In this case, as described above, the HLB of the surfactant can generally be dealt with. However, in order to reduce the amount of water adhering to the strand as much as possible, the second water tank is added after the water tank to which the surfactant is added. It is preferable to install. Since the purpose of the second water tank is to wash the surfactant adhering to the strands, water alone may be used, but in order to increase the purpose of washing, it is preferable to add a cleaning agent. As the cleaning agent, for example, when a water-soluble inorganic salt capable of breaking the micelle formed on the strand surface, a cationic surfactant or an anionic surfactant is used, the used surface activity is used. An inverse soap having a reverse performance to the agent (which can break micelles formed on the strand surface) is exemplified. Moreover, it is also preferable to use together the said water-soluble inorganic salt and reverse soap. The reverse soap having reverse performance means an anionic surfactant when a cationic surfactant is used, and a cationic when an anionic surfactant is used. Means a surfactant.

The water-soluble inorganic salt that is the cleaning agent is an inorganic salt that can dissolve at least 1 mg or more in 100 cc of water at 40 ° C., and at least one of the anion or cation of the inorganic salt is divalent or trivalent. Examples of the inorganic salt include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate. Such inorganic salt is used in an amount of about 0.0001 to 1 part by weight per 100 parts by weight of water.
The inverse soap is preferably used in an amount of 0.001 to 0.1 parts by weight per 100 parts by weight of water.
The washed strand or the strand that has not undergone the washing step is preferably cut after drying.

Next, the thermoplastic resin particles obtained by the method of the present invention will be described.
The thermoplastic resin particles of the present invention are resin particles obtained by the above-described method of the present invention, and could not be easily mass-produced by the conventional strand cutting method. It is. The tensile elastic modulus Y of the thermoplastic resin constituting the resin particles is 1600 MPa or more, and the average particle weight is usually 15 mg or less, preferably 10 mg or less, more preferably 0.01 to 1.0 mg. More preferably, it is 0.01-0.6 mg or less, Most preferably, it is 0.01-0.3 mg. In particular, resin particles having an average particle weight of 1.0 mg or less are used for the production of fine thermoplastic resin foam particles (hereinafter also simply referred to as foam particles), and the thin thermoplastic resin foam particles using the foam particles. It can be suitably used for the production of a molded body (hereinafter simply referred to as a foamed particle molded body or molded body). Specifically, although it depends on the expansion ratio, molding with a thickness of 5 mm or less is possible.
When the average particle weight is more than 15 mg, the foamed particles obtained are too large, and it is difficult to obtain a thin foamed particle molded body. On the other hand, when the average particle weight is less than 0.02 mg, the obtained foamed particles are too small and the resin particles may be easily blocked.

In the present specification, the average particle weight is measured as follows.
Ten resin particles are collected and measured with an electronic balance to a unit of 0.0001 g, and the arithmetic average value is adopted.

  The thermoplastic resin particles of the present invention are cylindrical in shape, and the ratio L / D of the length (maximum dimension in the extrusion direction) to the diameter (maximum dimension in the direction orthogonal to the extrusion direction) of the resin particles is 1. It is preferable that it is more than 5 or less. When the ratio L / D of the length to the diameter of the resin particles is 1 or less, the foamed particles obtained from the resin particles tend to be flat. From this viewpoint, 1.2 or more is more preferable, and 1.4 or more is more preferable. On the other hand, when the ratio L / D exceeds 5, the shape of the obtained expanded particles tends to be elongated. From this viewpoint, 4.5 or less is more preferable, and 3.5 or less is more preferable. In any case, when the foamed particle molded body is produced, there is a possibility that the filling rate of the foamed particles into the mold may be reduced, and in that case, the molded body obtained does not sufficiently fill the space between the foamed particles. There is a risk of it.

Next, the thermoplastic resin expanded particles of the present invention will be described.
The foamed thermoplastic resin particles of the present invention are obtained by foaming the resin particles and have an apparent density of 10 to 600 g / L. When the apparent density is less than 10 g / L, the expansion ratio is too high. As a result, the closed cell ratio of the expanded particles tends to decrease, and when the expanded particles are molded in-mold using the expanded particles, There is a risk of forming a foamed particle molded body having large shrinkage. When the apparent density exceeds 600 g / L, the expansion ratio is too low, and there is a possibility that the buffering property and heat insulating property of the obtained foamed particle molded body are too low.

When selecting a polylactic acid-based resin as the thermoplastic resin constituting the expanded particles, it is preferable to select a crystalline polylactic acid-based resin in consideration of the heat resistance of the finally obtained expanded particle molded body. In view of heat moldability, it is preferable to have the following thermal characteristics.
The polylactic acid resin preferably has an endotherm (R _endo ) of 5 J / g or more, more preferably 10 J / g or more, more preferably 15 J / g or more in differential scanning calorimetry at a heating rate of 2 ° C./min. Are more preferable, and those of 20 J / g or more are particularly preferable. When the endothermic amount is less than 5 J / g, the crystal component is too small, and there is a possibility that a foamed particle molded body having heat resistance and rigidity such as little deformation in a heating atmosphere cannot be obtained. On the other hand, the upper limit is that the amount of endotherm is preferably 50 J / g or less, since it may be difficult to handle, for example, it takes time and labor to crystallize if there are many crystal components, and the upper limit is preferably 40 J / g or less. Are more preferable, and those of less than 30 J / g are particularly preferable. In general, the endothermic amount is displayed as a negative value, but the endothermic amount is an absolute value.

  The endothermic amount (Rendo) in the differential scanning calorimetry of the polylactic acid resin is a value determined by heat flux differential scanning calorimetry described in JIS K7122 (1987) for the polylactic acid resin. However, 1 to 4 mg of polylactic acid resin is used as a test piece, and the condition adjustment of the test piece and the measurement of the DSC curve are performed according to the following procedure. The test piece was put in a container of a DSC apparatus, heated and melted to 200 ° C., kept at that temperature for 10 minutes, then cooled to 110 ° C. at a cooling rate of 2 ° C./min, kept at that temperature for 120 minutes, A DSC curve is obtained when heat-melting to a temperature about 30 ° C. higher than the end of the melting peak at a heating rate of 2 ° C./min after the heat treatment cooling to 40 ° C. at a cooling rate of 2 ° C./min.

Furthermore, in the case of polylactic acid-based resin expanded particles, those having the following thermal characteristics are preferable in consideration of the thermoformability.
In the polylactic acid-based resin expanded particles, the ratio (B _exo / B _endo ) of the calorific value (B _exo ) and the endothermic amount (B _endo ) in differential scanning calorimetry at a heating rate of 2 ° C./min is 0.02. Preferably, the endothermic amount (B _endo ) is 5 J / g or more. If the ratio (B _exo / B _endo ) is less than 0.02, crystallization is advanced and high temperature steam is required for heat forming, so a special molding machine with high mold clamping force is used. There is a risk of having to. In addition, the amount of steam required for in-mold molding is large, and productivity may be poor. From the above viewpoint, the ratio (B _exo / B _endo ) is more preferably 0.025 or more, and further preferably 0.03 or more. Usually, the upper limit is 1, but 0.6 or less is preferable.

In the case of polylactic acid-based resin expanded particles, the difference between the endothermic amount (B _endo ) and the exothermic amount (B _exo ) (B _endo -B _exo ) is preferably 0 J / g or more and less than 35 J / g. The difference (B _endo -B _exo ) is the endothermic amount (B _endo ), which is the energy absorbed when the crystalline part of the expanded particle melts at the time of temperature rise, and the expansion of the expanded particle prior to the melting of the crystal part at the time of temperature increase. This represents the difference in calorific value (B _exo ), which is the energy released by crystallization of the non-crystallized portion. The smaller the difference, the less the crystallization of the expanded particles. A larger value means that the crystallization of the expanded particles is progressing. When the difference (B _endo -B _exo ) is 35 J / g or more, secondary foaming of the foamed particles may deteriorate during in-mold molding, resulting in a foamed particle molded product having poor fusibility between the foamed particles. is there. On the other hand, if the difference (B _endo -B _exo ) is within the above range, molding becomes easy. From this viewpoint, it is more preferably 30 J / g or less, still more preferably 25 J / g or less. Note that the difference (B _endo -B _exo ) may be 0 J / g.

In the case of polylactic acid resin expanded particles, the endothermic amount (B _endo ) in differential scanning calorimetry at a heating rate of 2 ° C./min is preferably 5 J / g or more, more preferably 10 J / g or more, More preferably, it is 15 J / g or more, and particularly preferably 20 J / g or more. The larger the endothermic amount (B _endo ) is, the more the crystal component of the expanded particles is, and the higher the degree of crystallization, the more likely it is to be able to obtain an expanded particle molded body with excellent heat resistance. . On the other hand, the upper limit is that when there are many crystal components, high temperature steam is required when molding in the mold, and a special molding machine must be used. Therefore, the endothermic amount (B _endo ) is preferably 50 J / g or less, 40 J / g or less is more preferable, and less than 35 J / g is particularly preferable.

In addition, although it _{depends on} the endothermic amount (B _endo ) of the polylactic acid-based resin expanded particles, the calorific value (B _exo ) in differential scanning calorimetry at a heating rate of 2 ° C./min is preferably 1 J / g or more. A larger calorific value (B _exo ) means that even the crystalline foamed particles are not crystallized. When the calorific value (B _exo ) is less than 1 J / g, there is little crystalline component or crystallization has progressed too much, and when there is little crystalline component, heat resistance such as being easily deformed in a high-temperature atmosphere. It will be inferior. Moreover, when crystallization progresses too much, there exists a possibility that a high temperature steam may be required in order to improve the melt | fusion property between foaming particles at the time of in-mold shaping | molding. From this viewpoint, the calorific value (B _exo ) is more preferably 3 J / g or more, further preferably 5 J / g or more, and most preferably 8 J / g or more. On the other hand, since the energy required for crystallization may increase and the crystallization time may increase, the calorific value (B _exo ) is preferably 50 J / g or less, and 40 J / g or less. Is more preferable, and less than 30 J / g is particularly preferable.

The exothermic amount (B _exo ) and endothermic amount (B _endo ) of the expanded particles are values determined by heat flux differential scanning calorimetry described in JIS K7122 (1987). However, the test piece is 1 to 4 mg of expanded particles, and the condition adjustment and DSC curve measurement of the test piece are performed according to the following procedure.
A test piece is put into a container of a DSC apparatus, and a DSC curve is obtained when the temperature is raised from 40 ° C. to 200 ° C. at a heating rate of 2 ° C./min without heat treatment. The exothermic amount (B _exo ) of the expanded particles is defined as a point c where the exothermic peak departs from the low temperature side baseline of the DSC curve, and a point d where the exothermic peak returns to the high temperature side baseline. , And a value obtained from the area of the portion surrounded by the straight line connecting point c and point d and the DSC curve. Further, the endothermic amount (B _endo ) of the expanded particles is defined as a point e where the endothermic peak is separated from the low temperature side baseline of the endothermic peak of the DSC curve, and a point f where the endothermic peak returns to the high temperature side baseline. As a value obtained from the straight line connecting the point e and the point f and the area of the portion surrounded by the DSC curve. Examples of DSC curves showing the exothermic amount (Bexo) and endothermic amount (Bendo) of the expanded particles determined by a thermal flow rate differential scanning calorimeter are shown in FIGS.

Next, a method for producing the thermoplastic resin foamed particles by foaming the thermoplastic resin particles of the present invention will be described.
As a method for obtaining the expanded particles of the present invention, 1) According to the method of the present invention, a thermoplastic resin and a desired additive are supplied to an extruder and melt-kneaded, and then from a die attached to an outlet of the extruder, The thermoplastic resin is extruded into a gas phase as a plurality of strands, cooled and solidified by passing through the water, the strand is taken out from the water, and the strands are cut to obtain resin particles. It can be produced by a resin particle preparation step to be produced, 2) a foaming agent impregnation step in which a thermoplastic resin is impregnated with a foaming agent in an aqueous medium, and 3) a foaming step in which polylactic acid resin particles impregnated with the foaming agent are foamed. it can. Moreover, the resin particle containing a foaming agent is also producible by the foaming resin particle preparation process which combined said 1) and 2). 4) The foamable resin particle production step is an embodiment of the method of the present invention. A thermoplastic resin and a desired additive are supplied to an extruder and melt kneaded, and a physical foaming agent is press-fitted in the extruder. The molten thermoplastic resin is extruded as a strand containing a foaming agent into the gas phase from a die attached to the outlet of the substrate, and the strand is immersed in water and allowed to cool and solidify by passing through the water. By cutting the strand, the resin particles containing the foaming agent can be produced in only one step.

  First, 1) A resin particle production process for producing foaming resin particles will be described. 1) The resin particle production step is a step of producing resin particles by the method of the present invention described above. That is, it is a step of melt-kneading the thermoplastic resin with an extruder as described above, extruding it into a strand, and cutting it. When the thermoplastic resin has hygroscopicity such as a polylactic acid resin, the thermoplastic resin is used. It is preferable to dry in advance. When a resin containing a large amount of moisture is introduced into the extruder, bubbles that adversely affect the uniformity of the foamed foam bubbles when mixed with the resin particles, or melt-kneaded with an extruder There is a risk that the physical properties of the thermoplastic resin will deteriorate and the melt mass flow rate (MFR) will become extremely large. Therefore, the upper limit temperature of the extrusion temperature condition is set so that the MFR of the thermoplastic resin does not become extremely large. In addition, when the thermoplastic resin is a resin that easily deteriorates due to moisture, such as a polylactic acid-based resin, for example, an extruder with a vent port is used to suppress the deterioration, and the moisture is removed from the thermoplastic resin by vacuum suction. It is also preferable to adopt a method of removing.

  In addition, when the thermoplastic resin is a resin that is easily hydrolyzed, such as a polylactic acid resin, the obtained resin particles can be stored in an environment where hydrolysis does not proceed by avoiding high temperature and high humidity conditions. preferable.

  As mentioned above, although the resin particle preparation process was explained centering on the polylactic acid-based resin, resin particles used for foaming applications are manufactured by the same method for, for example, a polystyrene-based resin or the like except that it is easily hydrolyzed. be able to.

Next, the 2) foaming agent impregnation step in which the resin particles of the present invention are impregnated with the foaming agent will be described.
The foaming agent impregnation step includes a step of impregnating the foaming agent in a liquid phase and a step of performing in a gas phase. Among them, the obtained foamed particles are formed in a uniform cell shape, and thus the step is performed in a liquid phase. This is preferred. Specifically, it is preferable to impregnate thermoplastic resin particles with a foaming agent in an aqueous medium. That is, it is preferable to impregnate the resin particles with the foaming agent by placing the aqueous medium in a sealed container, adding the resin particles and the foaming agent to the aqueous medium, and stirring the mixture.

  As the aqueous medium, water is preferably used, and more preferably ion-exchanged water. However, it is not limited to water, and the resin particles can be dispersed without dissolving the resin particles. Any solvent or liquid that does not inhibit the above can be used. Examples of the aqueous medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.

  Examples of the blowing agent include conventionally known propane, isobutane, normal butane, isohexane, normal hexane, cyclobutane, cyclohexane, isopentane, normal pentane, cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, chlorofluoromethane, and trifluoro. Organic physics such as methane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane Examples include foaming agents and inorganic physical foaming agents such as nitrogen, carbon dioxide, argon, and air. Among them, inorganic physical foaming agents that do not destroy the ozone layer and are inexpensive are preferable, particularly nitrogen, air, and carbon dioxide. Is preferred. In the present invention, carbon dioxide is more preferable from the viewpoint of obtaining expanded particles having a smaller apparent density with respect to the amount of the foaming agent used. Two or more blowing agents such as carbon dioxide and isobutane can also be used.

Hereinafter, the method for impregnating the foaming agent will be specifically described in the case of using a polylactic acid resin among thermoplastic resins and using carbon dioxide as the foaming agent.
The impregnation amount of carbon dioxide is usually 2.5 to 30% by weight, preferably 3 to 20% by weight, and more preferably 5 to 15% by weight. If the amount of impregnation is too small, the polylactic acid resin particles may not be sufficiently foamed. On the other hand, if the amount of impregnation is too large, expandability and fusion during molding of the obtained foamed particles may be used. There is a risk that the property will be insufficient. This is presumably because the crystallization of the polylactic acid resin particles easily proceeds.

  The impregnation temperature of carbon dioxide is preferably 10 to 50 ° C, more preferably 20 to 40 ° C. In particular, the impregnation temperature when carbon dioxide is used as the foaming agent is more preferably (−0.6X + 50) or less, where the amount of carbon dioxide impregnation is (X wt%). When (−0.6X + 50) is exceeded, particularly in a polylactic acid resin having high crystallinity, an improvement in the expansion ratio may not be expected due to the extreme progress of crystallization. In addition, when the obtained expanded particles are molded in the mold, the expandability of the expanded particles and the possibility of fusion between the expanded particles may decrease, and the surface must be molded with high temperature steam. There is a risk of forming an in-mold expanded particle molded body having an uneven shape.

  Further, the pressure of carbon dioxide in the resin particle atmosphere in the carbon dioxide impregnation step into the polylactic acid-based resin particles varies depending on the apparent density (foaming ratio) of the target foamed particles, but is usually 0.05 to 0. The impregnation time is 0.2 to 5 hours.

The impregnation amount (% by weight) of carbon dioxide is determined by the following equation (2).
Carbon dioxide impregnation (wt%)
= {Weight of carbon dioxide impregnated in resin particles (g) × 100} / {weight of resin particles before carbon dioxide impregnation (g) + weight of carbon dioxide impregnated in resin particles (g)} (2)
The weight of the carbon dioxide impregnated in the resin particles in the formula (2) is obtained from the difference in weight of the resin particles before and after the carbon dioxide impregnation, and the weight measurement of the resin particles is measured to the order of 0.0001 g.

  The foaming agent impregnation step has been described with a focus on polylactic acid resin. However, except that it is easily hydrolyzed, for example, polystyrene resin can be impregnated with foaming agent in the same manner. it can.

Next, 3) a foaming step for foaming resin particles impregnated with a foaming agent will be described.
The foaming process is roughly divided into two methods. One is 3-1) Disperse the thermoplastic resin particles in a dispersion medium in the presence of a foaming agent in a closed container, and stir the contents while adjusting the temperature, and put the foaming agent in the resin particles. A so-called dispersion medium discharge foaming method in which a foaming agent impregnation step and a foaming step are performed in which the contents are impregnated and the contents are released into a region lower than the pressure of the sealed container and foamed, and the foaming step is performed. This is a method of heating and foaming thermoplastic resin particles. Among these, from the viewpoint of obtaining substantially spherical foamed particles efficiently, 3-2) a method of heating and foaming the foamable particles is preferable.

  3-2) As a method of heating and foaming the foamable thermoplastic resin particles, a conventionally known method can be adopted, but usually a method of filling foamable particles in a sealed container and introducing water vapor to foam is preferable. . Note that the airtight container is provided with an opening valve that slightly exhausts the internal heating medium, so that the atmosphere temperature in the airtight container can be easily maintained constant, and foam particles having a uniform density can be obtained. It is preferable because it is easy.

The atmospheric temperature at which the foamable thermoplastic resin particles impregnated with the foaming agent are heated, that is, the foaming temperature, varies depending on the type of the thermoplastic resin.
In the case of a polylactic acid-based resin, it is (Tg-50) ° C. to (Tg + 50) ° C., preferably (Tg−40) ° C. to (Tg + 40) ° C., of the thermoplastic resin.
In the case of polyolefin resin, it is (Tm-30) ° C to (Tm + 30) ° C, preferably (Tm-20) ° C to (Tm + 20) ° C of the thermoplastic resin. Tm is the melting point (° C.).
In the case of an aromatic polyester resin, it is (Tg-50) ° C. to (Tg + 50) ° C., preferably (Tg−40) ° C. to (Tg + 40) ° C., of the thermoplastic resin.
When the foaming temperature is lower than the above range, sufficient foaming hardly occurs, and when the foaming temperature is higher than the above range, the closed cell ratio of the foamed particles is lowered and it is difficult to obtain foamed particles exhibiting good moldability. . In the case of a polylactic acid-based resin, when carbon dioxide is used as a foaming agent, foaming is performed even at a temperature equal to or lower than the midpoint glass transition temperature by impregnating the foaming agent. The foaming temperature in this case is (Tg-30) ° C. to (Tg + 30) ° C., preferably (Tg−20) ° C. to (Tg + 20) ° C. of the thermoplastic resin. The Tg is the midpoint glass transition temperature.

  The above-mentioned midpoint glass transition temperature (Tg) is a value determined as the midpoint glass transition temperature of a DSC curve obtained by heat flux differential scanning calorimetry according to JIS K 7121 (1987). Note that the measurement conditions for determining the midpoint glass transition temperature are those described in JIS K7121 (1987) 3. Condition of test piece According to “When measuring glass transition temperature after performing a certain heat treatment” described in (3), put the test piece into a container of DSC apparatus and heating rate from 0 ° C. to 200 ° C. 10 When the temperature is raised at 0 ° C./min and dissolved by heating, immediately adjusted to 0 ° C. at a cooling rate of 10 ° C./min, and heated from 0 ° C. to 200 ° C. at a heating rate of 10 ° C./min. Is obtained from the DSC curve obtained.

  In the case of a polylactic acid-based resin, the obtained polylactic acid-based resin expanded particles are preferably stored under conditions that avoid hydrolysis under high temperature and high humidity conditions.

  As described above, the foaming process has been described mainly with respect to the polylactic acid resin. However, for example, polystyrene resin can be foamed by the same method except that it is easily hydrolyzed and is crystalline.

Next, the thermoplastic resin expanded particle molded body of the present invention will be described.
The foamed particle molded body of the present invention is obtained by filling the thermoplastic resin foamed particles of the present invention into a mold and heat molding. Since the fine foamed particles of the present invention are used, the foamed particle molded body is a thin-walled foamed particle molded body. In addition, it has excellent rigidity.

  The shape of the foamed particle molded body is not particularly limited, and examples of the shape include various shapes such as a container shape, a cylindrical shape, and a sheet shape.

  The thickness of the foamed particle molded body is preferably 1 to 10 mm, more preferably 1 to 7 mm, and still more preferably 1 to 5 mm.

If foamed bead molded article of the present invention consists of polylactic acid resin, the apparent density is preferably from 0.023 g / cm ³ or more, 0.03 g / cm ³ or more is more preferable. On the other hand, the upper limit is preferably 0.9 g / cm ³ or less, 0.6 g / cm ³ or less is more preferable.
Moreover, when this molded object consists of polypropylene resin, 0.02-0.6 g / cm < ³ > is preferable, as for the apparent density, 0.03-0.3 g / cm < ³ > is more preferable, 0.04-0 . ) G / cm ³ is more preferred.
Further, if the molded body is composed of an aromatic ester-based resin, the apparent density is preferably from 0.04~0.7g / cm ^3, more preferably 0.05~0.6g / cm ^3, 0.06 More preferably -0.5 g / cm ³ .
When the apparent density is less than the above range, the mechanical strength of the foamed particle molded body may be insufficient, and when it exceeds the above range, there is a possibility that characteristics of the foam such as light weight may be lost.

The apparent density of the foamed particle molded body is obtained by dividing the weight WM (g) of the foamed particle molded body by the volume VM (cm ³ ) obtained from the external dimension of the foamed particle molded body (WM / VM). .

The porosity of the foamed particle molded body of the present invention is usually 3% or less, more preferably 1% or less, and most preferably 0%, although it depends on the purpose. With such a configuration, the foamed particle molded body has few voids and excellent appearance.
When the foamed particle molded body is made of a polylactic acid-based resin, hydrolysis is suppressed as long as the porosity is used in a normal manner, and excellent biodegradability is exhibited in the soil after use. .
Further, the porosity when used as a sound absorbing member or a water permeable member is preferably 10 to 60%, more preferably 15 to 50%, and most preferably 0%.

The porosity is determined by the following method.
The porosity (%) of the foamed particle molded body is a scale in which the volume obtained from the outer dimensions (25 mm × 25 mm × 100 mm) of the test piece cut out from the foamed particle molded body is a (cm ³ ), and the sample is filled with alcohol. The true volume of the sample obtained from the increment of the scale when submerged in alcohol in the attached container is defined as b (cm ³ ), and is obtained from the following formula (3).
Porosity (%) = {1- (b / a)} × 100 (3)

Next, an in-mold molding method for molding a foamed particle molded body using the foamed particles of the present invention will be described.
In the in-mold molding method, it is preferable that the foamed particles are fused together by heating the foamed particles with a heating medium such as steam or hot air after filling the foamed particles in the mold. Thus, when heat-molded, the foamed particles are fused to each other to obtain an integrated foamed particle molded body. As a mold for molding in this case, a conventional mold or a steel belt used in a continuous molding apparatus described in JP-A No. 2000-15708 is used. As the heating means, steam is usually used, and the heating rate may be set to a temperature at which the surface of the expanded particles melts.

In the case of producing a foamed particle molded body, it is preferable to give a gas to the foamed particles provided in the mold by using an inorganic gas such as air, nitrogen, carbon dioxide or the like in advance. An organic gas such as butane can also be used. Of these, carbon dioxide is preferable because it requires less time to apply the internal pressure. By using the foamed particles with gas as the foaming particles for molding, secondary foaming properties such as a reduction in the gap between the foaming particles during molding, moldability such as the same shape as the mold, foaming obtained The recoverability of the particle compact is improved. The gas is preferably applied in the range of 0.3 to 4 mol / (1000 g expanded particles), more preferably 0.7 to 4 mol / (1000 g expanded particles).
The amount of gas (mol / 1000 g expanded particles) in the expanded particles is determined by the following equation (4).

Gas amount in expanded particles (mol / 1000 g expanded particles) =
{Gas increase (g) × 1000} / {Gas molecular weight (g / mol) × Foamed particle weight (g)} (4)

The gas increase amount (g) in the equation (4) is determined as follows.
Take out 500 or more foamed particles filled in the molding machine whose internal pressure is increased by applying gas, and move to a constant temperature and humidity chamber under atmospheric pressure at 23% and 50% relative humidity within 60 seconds. Then, place it on a balance in the constant temperature and humidity chamber, take out the foamed particles, and read the weight after 120 seconds. The weight at this time is defined as Q (g). Next, the foamed particles are allowed to stand for 240 hours in the same constant temperature and humidity room at 50% relative humidity and 23 ° C. atmospheric pressure. Since the high-pressure gas in the expanded particles permeates the bubble membrane and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and after 240 hours, the weight has reached equilibrium. stable. The weight of the expanded particles after 240 hours is measured in the same constant temperature and humidity chamber, and the weight at this time is defined as S (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and S (g) obtained by this measurement is defined as the gas increase amount (g) in the equation (4).

  As mentioned above, the in-mold molding method has been described with a focus on polylactic acid-based resins. However, except that it is easily hydrolyzed and crystalline, for example, polystyrene-based resins can be molded in the mold by the same method. Can do.

When manufacturing a foamed particle molded body, it is preferable to provide a curing step after performing in-mold molding. The curing temperature varies depending on the type of thermoplastic resin constituting the molded body.
In the case of a foamed molded article of polylactic acid-based resin, it is preferably maintained in an atmosphere at a temperature of [Tg + 2] to [Tg + 30] ° C. in the curing step. When the temperature of the curing process is less than [Tg + 2] ° C., it takes a long time to crystallize the polylactic acid resin, resulting in poor productivity, and further, there is no effect of improving the heat resistance of the foamed particle molded body. It becomes a foamed particle molded body having inferior properties. In this respect, the curing temperature is more preferably [Tg + 5] ° C. or higher, and further preferably [Tg + 7] ° C. or higher. Moreover, when it is higher than [Tg + 30] ° C., the foamed particle molded body is deformed, and it becomes difficult to obtain a good foamed particle molded body. In this respect, [Tg + 25] ° C. or lower is more preferable, and [Tg + 20] ° C. or lower is still more preferable.
In the case of a polyolefin resin foamed particle molded body, it is preferable to maintain the curing process in an atmosphere having a temperature of 40 to 100 ° C. When the temperature of the curing process is less than 40 ° C., the molded product has poor recoverability. In this respect, the curing temperature is more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher. On the other hand, when the temperature is higher than 100 ° C., the foamed particle molded body contracts, and it becomes difficult to obtain a good foamed particle molded body. In this respect, 100 ° C. or lower is more preferable, and 90 ° C. or lower is still more preferable.
In the case of a foamed particle molded body of an aromatic ester-based resin, it is preferable that the temperature of the curing process is maintained in an atmosphere having a temperature of [Tg + 2] to [Tg + 30] ° C. When the temperature of the curing process is less than [Tg + 2] ° C., it takes a long time to crystallize the aromatic ester resin, resulting in poor productivity, and further no effect of improving the heat resistance of the foamed particle molded body. A foamed particle molded body having poor heat resistance is obtained. In this respect, the curing temperature is more preferably [Tg + 5] ° C. or higher, and further preferably [Tg + 7] ° C. or higher. Moreover, when it is higher than [Tg + 30] ° C., the foamed particle molded body is deformed, and it becomes difficult to obtain a good foamed particle molded body. In this respect, [Tg + 25] ° C. or lower is more preferable, and [Tg + 20] ° C. or lower is still more preferable.

  Moreover, as time to hold | maintain under a specific atmosphere at a curing process, 1 hour or more is preferable from a viewpoint of a heat resistant improvement, 3 hours or more are preferable, and especially 5 hours or more are preferable. On the other hand, the upper limit is usually 36 hours or less from the viewpoint of the deformation and discoloration of the foamed particle molded body. From the above viewpoint and productivity balance, 24 hours or shorter is more preferable, and 12 hours or shorter is particularly preferable.

In the case of polylactic acid-based resin, if the relative humidity in the curing process is high, the foamed particle molded body is likely to be hydrolyzed, which may result in a polylactic acid-based resin expanded particle molded body having poor mechanical properties. Therefore, 40% RH or less is preferable. From the above viewpoint, 30% RH or less is more preferable, and 20% RH or less is more preferable. On the other hand, the lower limit of 0% RH is preferably 5% RH or more because there is a possibility that a special apparatus may be required to satisfy the condition.
Moreover, when the time of the whole curing process is 100%, from the above viewpoint, the time when the relative humidity exceeds 40 RH% is preferably 50% or less, and more preferably 25% or less.

  When curing, the foamed particle molded body may be in the form as it is, but if the temperature is high, the foamed particle molded body may be deformed. In such a case, it is preferable to fix the foamed particle molded body with a jig for fixing the shape.

Heating in the curing process is usually performed with hot air.
In the case of a polylactic acid-based resin expanded particle molded body, the heating in the curing step can also be crystallized on the basis of the midpoint glass transition temperature of the base resin. Obtainable. In this case, by heat curing, it is preferable to improve the heat resistance so that the absolute value of the heating dimensional change rate within 22 hours in an atmosphere of 90 ° C. is within 4%, more preferably within 3%. % Is more preferable. If the absolute value of the heating dimensional change rate exceeds 4%, the use range may be narrowed, such as being difficult to use in the field used near 90 ° C.

In the polylactic acid-based resin expanded particle molded body obtained by the curing step, the exothermic amount (bF _exo ) and endothermic amount (bF _endo ) of the expanded expanded particle body in differential scanning calorimetry at a heating rate of 2 ° C./min preferably the ratio of _(bF exo _/ bF _endo) is 0 to 0.20, the difference between the endothermic heat _{(bF endo)} and emitting heat _{(bF exo) (bF endo -bF} exo) is 15 J / g The above is preferable. When this condition is satisfied, crystallization of the polylactic acid-based resin proceeds and a foamed particle molded body having excellent heat resistance is obtained.

When the ratio (bF _exo / bF _endo ) exceeds 0.2, crystallization does not proceed, so that the heat resistance is low. From the viewpoint of improving the heat resistance, the ratio is more preferably 0.18 or less, further preferably 0.16 or less, further preferably 0.14 or less, and particularly preferably 0.
On the other hand, the lower limit is 0 because the calorific value (bF _exo ) when crystallization is completely promoted is 0.
Further, the difference (bF _endo -bF _exo ) between the endothermic amount (bF _endo ) and the calorific value (bF _exo ) of the obtained expanded foam molded body is 10 J / g or more from the viewpoint of improving practical heat resistance. Is more preferable, and 15 J / g or more is more preferable. On the other hand, the upper limit depends on the endothermic amount of the base resin, but is preferably 50 J / g or less, more preferably 40 J / g or less, and particularly preferably less than 30 J / g.

In the curing process of the in-mold polylactic acid resin expanded particle molded body, a molded body having a calorific value (aF _exo ) of the molded body before curing in differential scanning calorimetry at a heating rate of 2 ° C./min is 5 J / g or more. calorific value of the molded product after curing in differential scanning calorimetry in the case of curing, heating rate 2 ° C. / min and _{(bF exo)} and heating value of pre-cured _{(aF exo)} the ratio of _{(bF exo / aF} exo) Is preferably 0 to 0.7.
When the ratio (bF _exo / aF _exo ) between the calorific value (aF _exo ) of the molded body before the curing process and the calorific value (bF _exo ) of the molded body after the curing process exceeds 0.7, the mold is obtained. The expanded foam molded body has insufficient heat resistance. The lower limit of the ratio is more preferably 0.65 or less, more preferably 0.6 or less, since crystallization proceeds and the heat resistance is improved as the calorific value (bF _exo ) of the molded product is closer to 0 after the curing process. 0.55 or less is more preferable, and 0 is particularly preferable.

The measurement method of the calorific value _{(aF exo)} and the endothermic amount measurement method _{(aF endo),} and calorific value _{(bF exo)} and the endothermic amount _{(bF endo)} uses a sample taken from the mold PP bead molding Except for the above, it is the same as the method for measuring the calorific value (B _exo ) and the endothermic amount (B _endo ) described above.

  Hereinafter, the present invention will be described with reference to examples and comparative examples. However, the present invention is not limited to the examples.

Example 1
[Polylactic acid resin]
<Manufacture of resin particles>
An apparatus in which a die having a diameter of 0.8 mm for each circular hole, a number of holes of 275, and a minimum distance between the outer circumferences of the two closest circular holes (minimum distance between holes) of 1 mm is attached to the outlet of an extruder having an inner diameter of 65 mm. Using.
Add calcium stearate to crystalline polylactic acid (“Lacia H-100” manufactured by Mitsui Chemicals, Inc., tensile elastic modulus 2250 MPa, endotherm (R _endo ) 33 J / g) so that the content is 1000 ppm, After melt-kneading with the above extruder, each of the circular holes provided in the die is extruded into the atmosphere as a strand, and then each strand is placed in a water tank having a length of 1 m, a width of 0.4 m, and a depth of 1 m. The water is adjusted to 20 ° C. (water is accommodated up to a height of 900 mm in the water tank) and is cooled and solidified. The strand is pulled up from the water tank and at the same time the water adhering to the surface of the strand is blown off, and then the strand is pelletized. To obtain resin particles having an L / D of 1.2 and a resin particle weight (average particle weight) of 0.0040 mg. In addition, 0.005 parts by weight of (modified silicone oil (SR8410 manufactured by Toray Dow Corning Silicone)) as a surfactant per 100 parts by weight of water was added to the water in the water tank.

Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.
The endothermic amount (R _endo ) (J / g) was measured by the measurement method described above. As a measuring apparatus, a trade name “Q1000” manufactured by TA Instruments Inc. was used.

<Manufacture of expanded particles>
Into an autoclave having an internal volume of 5 L, 3000 mL of water and 1000 g of the above resin particles were added. 0.5 parts by weight of “PL-019” was added.

Next, after raising the temperature to 40 ° C., carbon dioxide (CO ₂ ) was press-fitted into the autoclave via a pressure control valve, adjusted to a pressure of 2 MPaG, and held for 2 hours. Next, after removing carbon dioxide from the autoclave, the expandable resin particles were taken out. The amount of carbon dioxide (CO ₂ ) impregnated in the foamable resin particles was 5.5 wt%.

  After filling the expandable resin particles impregnated with carbon dioxide into a sealed container with a pressure regulating valve, steam of 0.1 MPaG (101 ° C.) is introduced for 20 seconds, heated, expanded and foamed, and expanded particles. Got. The apparent density of the expanded particles was 84 g / L, calorific value (Bexo) 6 J / g, endothermic amount (Bendo) 33 J / g, ratio (Bexo / Bendo) 0.18, and difference (Bendo-Bexo) 27 J / g. It was.

  The exothermic amount (Bexo) and endothermic amount (Bendo) of the expanded particles were measured by the measurement method described above. As a measuring apparatus, a product name “DSC-50” manufactured by Shimadzu Corporation was used, and “analysis software was a partial area analysis program version 1.52 for Shimadzu Thermal Analysis Workstation TA-60WS”.

Example 2
[Polylactic acid resin]
Resin particles having an L / D of 1.2 and a resin particle weight (average particle weight) of 0.6077 mg were obtained in the same manner as in Example 1 except that the strand take-up speed was changed.
Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.
Further, the same operation as in Example 1 was performed except that carbon dioxide (CO ₂ ) was press-fitted into the autoclave through a pressure regulating valve, the pressure was adjusted to 2.0 MPaG, and the pressure was maintained for 2.5 hours. Expanded particles were produced. The apparent density of the expanded particles was 63 g / L, calorific value (Bexo) 5 J / g, endothermic amount (Bendo) 33 J / g, ratio (Bexo / Bendo) 0.15, difference (Bendo-Bexo) 28 J / g. It was.

Example 3
[Polylactic acid resin]
L / D1.2, resin particle weight (average particle weight) 5.8314 mg in the same manner as in Example 1 except that the circular hole of the die was changed as shown in Table 1 and the strand take-up speed was changed. Resin particles were obtained.
Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.
In addition, carbon dioxide (CO ₂ ) was press-fitted into the autoclave through a pressure regulating valve, adjusted so that the pressure became 2.5 MPaG, and the same operation as in Example 1 was performed except that the pressure was maintained for 4 hours. Manufactured. The apparent density of the expanded particles was 70 g / L, calorific value (Bexo) 4 J / g, endotherm (Bendo) 33 J / g, ratio (Bexo / Bendo) 0.12, and difference (Bendo-Bexo) 29 J / g. It was.

Comparative Example 1
[Polylactic acid resin]
Resin particles having an L / D of 1.2 and a resin particle weight (average particle weight) of 0.0012 mg were obtained in the same manner as in Example 1 except that the strand take-up speed was changed. Immediately a trouble of winding of the strand occurred and it was unstable, but a small amount of sample was obtained.

  Table 2 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.

Comparative Example 2
[Polylactic acid resin]
L / D1.2, resin particle weight (average particle weight) 9.4952 mg in the same manner as in Example 1 except that the circular hole of the die was changed as shown in Table 1 and the strand take-up speed was changed. Resin particles were obtained. The obtained resin particles were cracked and chipped.

  Table 2 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.

Example 4
[Polypropylene resin]
<Manufacture of resin particles>
Using the same apparatus as in Example 1, 100 parts by weight of the propylene homopolymer (tensile elastic modulus: 1760 MPa, melting point: 162 ° C., MFR: 60 g / 10 min) was used as the thermoplastic resin, and 100 parts by weight of the propylene homopolymer. After adding 0.005 parts by weight of zinc borate as a nucleating agent and melt-kneading both in the above extruder, each of the circular holes provided in the die is extruded as a strand into the atmosphere and carried out. The strand was cut with a pelletizer in the same manner as in Example 1 to obtain resin particles having L / D and resin particle weight (average particle weight) shown in Table 1. In addition, the modified silicone oil (SR8410 by Dow Corning Toray Co., Ltd.) was added to the water in the water tank as a surfactant in the same manner as in Example 1.

  Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.

<Manufacture of expanded particles>
Using the obtained resin particles, the following operations were performed to produce expanded particles.
In a 400 liter autoclave, 100 parts by weight of the resin particles, 220 parts by weight of water, 0.05 parts by weight of a surfactant (sodium dodecylbenzenesulfonate), 0.3 parts by weight of kaolin, 0.02 parts by weight of aluminum sulfate and foaming The mixture was charged with 1.5 parts by weight of dry ice as an agent, heated to 167 ° C. with stirring, and kept at that temperature for 15 minutes. Next, one end of the autoclave was opened to release resin particles and water to obtain expanded particles. In addition, discharge | release was performed supplying carbon dioxide gas in an autoclave so that the internal pressure of a container during discharge | release of a resin particle from an autoclave may be maintained at the internal pressure of a container. The foamed particles thus obtained were washed with water and centrifuged, and allowed to stand at atmospheric pressure for 24 hours, followed by curing, and then the apparent density of the foamed particles was measured. The results are shown in Table 1.

Example 5
[Polypropylene resin]
L / D 2.4, resin particle weight (average particle weight) 2.2568 mg in the same manner as in Example 1 except that the circular hole of the die was changed as shown in Table 1 and the strand take-up speed was changed. Resin particles were obtained.
Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.
Moreover, the same operation as Example 1 was performed except changing dry ice as a foaming agent into 2 weight part, and the expanded particle was manufactured. The apparent density of the expanded particles was 45 g / L.

Example 6
[Polypropylene resin]
L / D 2.4, resin particle weight (average particle weight) 13.6551 mg, in the same manner as in Example 1 except that the circular hole of the die was changed as shown in Table 1 and the take-up speed of the strand was changed. Resin particles were obtained.
Table 1 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.
Moreover, the same operation as Example 1 was performed except changing dry ice as a foaming agent into 2 weight part, and the expanded particle was manufactured. The apparent density of the expanded particles was 32 g / L.

Comparative Example 3
[Polypropylene resin]
Resin particles having L / D 2.4 and resin particle weight (average particle weight) of 0.0057 mg were obtained in the same manner as in Example 1 except that the strand take-up speed was changed. Immediately a trouble of winding of the strand occurred and it was unstable, but a small amount of sample was obtained.

  Table 2 shows Z = X · Y of the obtained resin particles, evaluation of occurrence of cracks in the resin particles, and evaluation of occurrence of winding of the pelletizer around the take-up roll.

Comparative Example 4
[Polypropylene resin]
L / D 2.4, resin particle weight (average particle weight) 26.4938 mg, in the same manner as in Example 1 except that the circular hole of the die was changed as shown in Table 1 and the strand take-up speed was changed. Resin particles were obtained. The obtained resin particles were cracked and chipped.

In Examples 1 to 4, which show examples in which resin particles were produced by the strand cutting method according to the method of the present invention, Z = X ·· in spite of being a thermoplastic resin having a tensile elastic modulus Y of 1600 MPa or more. Since Y satisfies the formula (1), small resin particles having a weight of less than 2.5 mg per resin particle can be produced with high productivity and without fusion between strands. .
In addition, when the surfactant was added to water, the strands were not fused even when the minimum distance between the circular holes of the die was very close to 1 mm.

  On the other hand, in Comparative Examples 1 and 3, since Z = X · Y was lower than the lower limit of the formula (1), the winding of the strand around the take-up roll occurred and the productivity was extremely poor. Met.

  On the other hand, in Comparative Examples 2 and 4, since Z = X · Y exceeded the upper limit of the formula (1), the resin particles were cracked and chipped, and the productivity was extremely poor. .

It is explanatory drawing of a strand cut method. It is drawing which shows an example of the DSC curve which shows the emitted-heat amount (Bexo) of a foamed particle calculated | required with a heat flow rate differential scanning calorimeter, and an endothermic amount (Bendo). It is drawing which shows an example of the DSC curve which shows the emitted-heat amount (Bexo) of a foamed particle calculated | required with a heat flow rate differential scanning calorimeter, and an endothermic amount (Bendo). It is drawing which shows an example of the DSC curve which shows the emitted-heat amount (Bexo) of a foamed particle calculated | required with a heat flow rate differential scanning calorimeter, and an endothermic amount (Bendo).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extruder 2 Die 3 Strand 4 Water 5 Resin particle 6 Guide roll 7 Dehydrator 8 Take-off roller 9 Cutter

Claims (6)

From the die attached to the outlet of the extruder, the molten thermoplastic resin is extruded into the gas phase as a plurality of strands, and the strands are immersed in water and allowed to cool and solidify by passing through the water. In the manufacturing method of cutting the strands to obtain resin particles, the thermoplastic resin has a tensile modulus Y (MPa) of 1600 or more, and the diameter X (mm) of the obtained resin particles and the tensile elasticity A method for producing thermoplastic resin particles, wherein Z (MPa · mm) = X · Y determined by the rate Y satisfies the following formula (1):
300 <Z <4000 (1)   2. The method for producing thermoplastic resin particles according to claim 1, wherein the strand is taken out from water to which a surfactant is added.   A thermoplastic resin particle obtained by the method for producing a thermoplastic resin particle according to claim 1 or 2, wherein an average particle weight of the resin particle is 1.0 mg or less.   The thermoplastic resin particles according to claim 3, wherein the resin particles are cylindrical and the ratio L / D of the length (L) to the diameter (D) of the resin particles is more than 1 and 5 or less. .   The thermoplastic resin foamed particles according to claim 3 or 4, which are foamed to an apparent density of 10 to 600 g / L.   A thermoplastic resin foamed particle molded body comprising a plurality of the foamed thermoplastic resin particles according to claim 5 fused or bonded together.

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