阅读说明：本技术 热塑性树脂发泡颗粒的制造方法、及热塑性树脂发泡颗粒 (Method for producing thermoplastic resin foamed particles, and thermoplastic resin foamed particles ) 是由 早瀬勇贵 于 2020-01-21 设计创作，主要内容包括：本发明的目的是得到：在低发泡倍率情况下,至少发泡倍率的不均匀得到改善,且在高发泡倍率情况下,至少泡室结构均匀的热塑性树脂发泡颗粒。本发明的制造方法使用二氧化碳气体作为发泡剂,将树脂颗粒(9)的分散液加热加压,然后,将该分散液从耐压容器(7)的节流盘1排向比耐压容器(7)内的内压低的气氛下的低压容器(13),从而其与曲面(14a)碰撞。(The purpose of the invention is to obtain: at a low expansion ratio, at least unevenness of the expansion ratio is improved, and at a high expansion ratio, at least cell structure-uniform thermoplastic resin expanded particles. The production method of the present invention uses carbon dioxide gas as a foaming agent, heats and pressurizes a dispersion of resin particles (9), and then discharges the dispersion from a throttle disk 1 of a pressure-resistant container (7) into a low-pressure container (13) in an atmosphere lower than the internal pressure of the pressure-resistant container (7), so that the dispersion collides with a curved surface (14 a).)

1. A method for producing thermoplastic resin foamed particles, comprising:

a dispersion preparation step of preparing a dispersion by dispersing thermoplastic resin particles in an aqueous dispersion medium in a pressure-resistant vessel; and

a foaming step of heating and pressurizing the dispersion to a temperature equal to or higher than a softening temperature of the thermoplastic resin particles using carbon dioxide gas as a foaming agent, and then discharging the heated dispersion into an atmosphere lower than an internal pressure of the pressure-resistant container to foam the thermoplastic resin particles,

wherein the foaming step includes a collision step of causing the mixture in the pressure-resistant container to collide with a curved surface when the mixture is discharged from the discharge portion.

2. The method for producing thermoplastic resin expanded particles according to claim 1,

the mixture has a collision angle of 13 ° or more with respect to the curved surface.

3. The method for producing thermoplastic resin expanded particles according to claim 1 or 2, wherein,

the mixture has an angle of impingement of 15 to 25 with respect to the curved surface.

4. The method for producing thermoplastic resin expanded particles according to any one of claims 1 to 3, wherein,

a distance from the discharge portion to the curved surface is L,

in the collision process, the mixture collides with the curved surface in a mode that L is more than or equal to 50mm and less than or equal to 600 mm.

5. The method for producing thermoplastic resin expanded particles according to any one of claims 1 to 4,

the discharge portion is provided with a choke for discharging the mixture,

the aperture of the throttling opening is more than 6 mm.

6. The method for producing thermoplastic resin expanded particles according to any one of claims 1 to 5, wherein,

the foaming ratio of the produced foaming particles is 10 to 25 times.

7. A thermoplastic resin foamed particle is provided,

the foaming ratio is 18 to 25 times,

the difference between cell diameters of the cells constituting the expanded thermoplastic resin beads is 70 μm or less.

Technical Field

The present invention relates to a method for producing thermoplastic resin foamed particles, and thermoplastic resin foamed particles.

Background

As a conventional technique, a method for producing expanded beads is known in which thermoplastic resin beads are dispersed in an aqueous dispersion medium in a pressure-resistant container, heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin and pressurized, and then expanded by discharging the thermoplastic resin beads into an atmosphere lower in pressure than the container. Further, a method of dispersing a foaming agent in a container as needed is also known.

For example, patent documents 1 to 3 disclose techniques for causing expanded particles to collide with a collision plate or a container wall from a discharge portion of a pressure-resistant container when the polyolefin resin particles are discharged to an atmosphere lower in pressure than the container interior and expanded. This can reduce the unevenness in the expansion ratio of the expanded beads.

(Prior art document)

Patent document 1: japanese patent No. 3963720

Patent document 2: japanese patent No. 4747472

Patent document 3: japanese patent No. 4818101

Disclosure of Invention

(problems to be solved by the invention)

In general, expanded beads having a lower expansion ratio tend to have a more uneven expansion ratio. On the other hand, expanded beads having a higher expansion ratio tend to have a more uniform cell structure. The above-described prior art has room for improvement in the above respects.

An object of one aspect of the present invention is to achieve: a process for producing expanded thermoplastic resin particles which, at a low expansion ratio, are improved in at least unevenness of the expansion ratio and, at a high expansion ratio, have a uniform cell structure; and thermoplastic resin foamed particles.

(means for solving the problems)

In order to solve the above problems, a method for producing thermoplastic resin foamed particles according to one aspect of the present invention includes: a dispersion preparation step of preparing a dispersion by dispersing thermoplastic resin particles in an aqueous dispersion medium in a pressure-resistant vessel; and a foaming step of heating and pressurizing the dispersion to a temperature equal to or higher than a softening temperature of the thermoplastic resin particles using carbon dioxide gas as a foaming agent, and then discharging the heated dispersion to an atmosphere lower than an internal pressure of the pressure-resistant container to foam the thermoplastic resin particles, wherein the foaming step includes a collision step of colliding a mixture in the pressure-resistant container with a curved surface when the mixture is discharged from a discharge portion.

In order to solve the above problems, the thermoplastic resin expanded beads according to one aspect of the present invention have an expansion ratio of 10 to 25 times, and the difference between cell diameters of cell cells constituting the thermoplastic resin expanded beads is 70 μm or less.

(effect of the invention)

According to one aspect of the invention, it is possible to obtain: at a low expansion ratio, at least unevenness of the expansion ratio is improved, and at a high expansion ratio, at least cell structure-uniform thermoplastic resin expanded particles.

Drawings

Fig. 1 is a schematic configuration of an example of a foaming apparatus used in the method for producing thermoplastic resin foamed particles according to the embodiment of the present invention.

Fig. 2 is a front view of a throttle disk used in the method for producing thermoplastic resin foamed particles according to the embodiment of the present invention.

Fig. 3 is a front view of a modified example of the throttle plate 1 shown in fig. 2.

Fig. 4 is a structural sectional view of a throttle disk used in the method for producing thermoplastic resin foamed particles according to the embodiment of the present invention.

< description of reference >

1 throttle disk (discharge part)

2 barrel

3 throttle plate

4 long and narrow shape

5 throttle orifice

6 discharge piping

7 pressure-resistant container

8 valve

9 resin particles

10 aqueous dispersion medium

11 expanded particles

14 collision board

14a curved surface

13 Low pressure vessel

Detailed Description

An embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to the embodiments described below, and various modifications can be made within the scope shown in the specification. Further, embodiments and examples obtained by appropriately combining technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. Further, the technical means disclosed in the respective embodiments can be appropriately combined to form new technical features. All academic and patent documents cited in the present specification are incorporated herein by reference. In the present specification, "a to B" indicating a numerical range means "a is not less than a (including a and greater than a) and not more than B (including B and less than B)" unless otherwise specified.

1. Method for producing thermoplastic resin expanded beads of the present embodiment

The present inventors have conducted extensive studies to solve the above problems, and as a result, have found that when contents in a pressure-resistant container are discharged from a discharge portion and collide with a member having a specific structure, foamed particles having a low expansion ratio can be produced, and at least unevenness in the expansion ratio can be improved. And, it was found alone that at least the cell structure can be made uniform when expanded beads of high expansion ratio are produced. The present inventors have completed the present embodiment based on these findings.

That is, the method for producing thermoplastic resin expanded beads according to the present embodiment (hereinafter, simply referred to as the present method) includes: a dispersion preparation step of preparing a dispersion by dispersing thermoplastic resin particles in an aqueous dispersion medium in a pressure-resistant vessel; and a foaming step of heating and pressurizing the dispersion to a temperature equal to or higher than a softening temperature of the thermoplastic resin particles using carbon dioxide gas as a foaming agent, and then discharging the heated dispersion to an atmosphere lower than an internal pressure of the pressure-resistant container to foam the thermoplastic resin particles, wherein the foaming step includes a collision step of colliding a mixture in the pressure-resistant container with a curved surface when the mixture is discharged from a discharge portion.

2. Material of thermoplastic resin foamed particles

The base resin of the thermoplastic resin particles used in the present embodiment is not particularly limited as long as it is a generally known foamable thermoplastic resin. Examples of the thermoplastic resin include polyolefin-based resins, polyester-based resins, polystyrene-based resins, polyphenylene ether-based resins, polyamide-based resins, and mixtures thereof. The thermoplastic resin is preferably a polyolefin resin or a polyester resin. Examples of the polyester resin include aliphatic polyester resins, aromatic polyester resins, and aliphatic aromatic polyester resins. Specific examples of the polyester resin include polyhydroxyalkanoate, polybutylene succinate (PBS), poly (butylene adipate-co-terephthalate) (PBAT), polyethylene terephthalate (PET), and the like. In addition, the polyhydroxyalkanoate is at least 1 selected from the group consisting of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly (3-hydroxybutyrate) (P3HB), poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly (3-hydroxybutyrate-co-3-hydroxyoctanoate), poly (3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among these, polyolefin resins are preferably used. Hereinafter, an embodiment in which a polyolefin resin is used as a base resin of the thermoplastic resin particles will be described. However, the base resin of the thermoplastic resin particles usable in the present embodiment is not limited to the polyolefin resin.

2-1. polyolefin-based resin

The polyolefin resin is a resin containing 50% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more of olefin units as a base resin of the polyolefin resin particles. Specific examples of the polyolefin-based resin include polyethylenes such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and low-molecular-weight polyethylene; propylene homopolymer; polypropylene-based polymers such as an α -olefin-propylene random copolymer, e.g., an ethylene-propylene random copolymer, an ethylene-propylene-1-butene random copolymer, and an α -olefin-propylene block copolymer; other polyolefin homopolymers such as propylene homopolymer and polybutene; and the like. These may be used alone or in combination of 2 or more.

Among these, the ethylene-propylene random copolymer, the ethylene-propylene-1-butene random copolymer, and the propylene-1-butene random copolymer are preferable because they exhibit good foamability when formed into foamed particles.

In addition, other thermoplastic resins than the polyolefin-based resin, for example, polystyrene, polybutene, and ionomer, may be mixed in the base resin within a range not affecting the properties of the polyolefin-based resin.

For the purpose of producing expanded beads, it is generally preferable to melt the polyolefin resin by an extruder, kneader, banbury mixer, roll or the like and to process the melted polyolefin resin into resin beads having a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape or the like. In addition, the resin particles are also referred to as small pellets.

The polyolefin resin particles are contained in an amount of 0.1 to 30mg, preferably 0.3 to 10mg, per particle.

2-2 additives to polyolefin resins

When the additive is added to the polyolefin-based resin, the polyolefin-based resin and the additive are preferably mixed with each other using a stirrer or the like before the polyolefin-based resin pellets are produced. Specific examples of the additives include Cell nucleating agents (nucleating agents for short). When an alkane blowing agent such as propane, butane, pentane or hexane is used, an inorganic nucleating agent such as talc, silica, calcium carbonate, kaolin, titanium oxide, bentonite or barium sulfate is generally used as the nucleating agent. The amount of the cell nucleating agent to be added varies depending on the kind of the polyolefin resin used and the kind of the cell nucleating agent, and cannot be determined uniformly, but is preferably about 0.001 parts by weight or more and 2 parts by weight or less based on 100 parts by weight of the polyolefin resin.

In the method, carbon dioxide gas (carbon dioxide) is used as the blowing agent, and the inorganic nucleating agent and/or the hydrophilic substance is preferably used. When water is used as a dispersion medium of the aqueous dispersion, the polyolefin resin is impregnated with water, and the impregnated water functions as a foaming agent together with or separately from other foaming agents.

The hydrophilic substance is used to impregnate the polyolefin resin with more moisture. Specific examples of the hydrophilic substance include inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borax, and zinc borate; alternatively, glycerin, melamine, isocyanuric acid, a melamine-isocyanuric acid condensate; polyethers such as polyethylene glycol and polyethylene oxide, adducts obtained by adding polyethers to polypropylene, and polymer mixtures thereof; polymers such as alkali metal salts of ethylene- (meth) acrylic acid copolymers, alkali metal salts of butadiene- (meth) acrylic acid copolymers, alkali metal salts of carboxylated nitrile rubbers, alkali metal salts of isobutylene-maleic anhydride copolymers, and alkali metal salts of poly (meth) acrylic acid; and the like. These hydrophilic substances may be used alone or in combination of 2 or more.

The amount of the hydrophilic substance added is preferably 0.005 to 2 parts by weight based on 100 parts by weight of the polyolefin resin. More preferably 0.005 to 1 part by weight. The average cell diameter of the polyolefin resin expanded beads can be adjusted by adjusting the type and amount of the hydrophilic substance.

In addition, in the production of the polyolefin resin pellets, additives such as a coloring agent, an antistatic agent, an antioxidant, a phosphorus-based treatment stabilizer, a lactone-based treatment stabilizer, a metal deactivator, a benzotriazole-based ultraviolet absorber, a benzoate-based light stabilizer, a hindered amine-based light stabilizer, a flame retardant aid, an acid neutralizer, a crystal nucleating agent, and an amide-based additive may be added as needed within a range that does not affect the properties of the polyolefin resin.

2-3. foaming agent

In the method, the blowing agent used in the foaming step is carbon dioxide gas (carbon dioxide). The method may be a method using carbon dioxide gas as a blowing agent, and a method using carbon dioxide gas in combination with a conventionally known blowing agent is also included in the scope of the method. As the conventionally known blowing agents, volatile alkane blowing agents such as propane, isobutane, butane, pentane and hexane, and inorganic gases such as air, nitrogen and water can be used.

1-4 dispersing agent and dispersing auxiliary agent

As the aqueous dispersion medium, water is preferably used. A dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water can also be used as the aqueous dispersant.

In order to prevent the polyolefin resin particles from being fused to each other, a dispersant is preferably used in the aqueous dispersion medium. Specific examples of the dispersant include inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, titanium oxide, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. Of these, tricalcium phosphate, barium sulfate, and kaolin are preferred because even when used in small amounts, the aqueous dispersion containing the polyolefin resin particles in the pressure vessel can be stably dispersed.

In addition, a dispersing aid is preferably used together with the dispersant. Specific examples of the dispersing aid include: carboxylate types such as N-acylamino acid salts, alkyl ether carboxylate salts, acylated peptides, etc.; sulfonate types such as alkylsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, and sulfosuccinates; sulfuric acid ester types such as sulfated oils, alkyl sulfates, alkyl ether sulfates, and alkylamide sulfates; and phosphate ester types such as alkyl phosphate, polyoxyethylene phosphate, and alkyl allyl ether phosphate; and the like anionic surfactants. In addition, as the dispersing aid, there can be used: a maleic acid copolymer salt; polycarboxylic acid high-molecular surfactants such as polyacrylate; and, polystyrene sulfonate, naphthalenesulfonic acid formalin condensate salt; and multivalent anionic polymeric surfactants.

As the dispersing aid, a sulfonate type anionic surfactant is preferably used, and further, a mixture of 1 or 2 or more selected from alkyl sulfonate and alkyl benzene sulfonate is preferably used. Further, the use of an alkylsulfonate, particularly an alkylsulfonate having a linear carbon chain of 10 to 18 carbon atoms as a hydrophobic group, is more preferable because the use of such an alkylsulfonate can reduce the amount of a dispersant adhering to the expanded particles of the polyolefin resin, and therefore, such an alkylsulfonate is particularly preferable.

In the embodiment of the present invention, it is particularly preferable to use 1 or more selected from tricalcium phosphate, trimagnesium phosphate, barium sulfate, and kaolin as the dispersant in combination with sodium n-paraffin sulfonate as the dispersion aid.

3. The process steps

3-1 preparation of Dispersion

In the dispersion preparation step, the polyolefin resin particles are dispersed in the aqueous dispersion medium in a pressure-resistant vessel to prepare a dispersion.

The amounts of the dispersant and the dispersing aid used vary depending on the kind thereof, or the kind and the amount of the polyolefin resin used. In general, the amount of the dispersant used is preferably 0.1 part by weight or more and 5 parts by weight or less, and more preferably 0.2 part by weight or more and 3 parts by weight or less, based on 100 parts by weight of the aqueous dispersion medium. The amount of the dispersion aid used is preferably 0.001 parts by weight or more and 0.3 parts by weight or less, and more preferably 0.001 parts by weight or more and 0.1 parts by weight or less, based on 100 parts by weight of the aqueous dispersion medium. In order to improve the dispersibility of the polyolefin resin particles in the aqueous dispersion medium, the amount of the polyolefin resin particles to be used is preferably 20 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of the aqueous dispersion medium. With this configuration, the polyolefin resin particles can be stably dispersed in the aqueous dispersion medium in the pressure-resistant vessel.

3-2. foaming step

In the foaming step, the dispersion is heated to a temperature equal to or higher than the softening temperature of the polyolefin resin particles using carbon dioxide gas as a foaming agent, pressurized, and then discharged into an atmosphere having a pressure lower than the internal pressure in the pressure-resistant container to foam. More specifically, in the foaming step, the dispersion is heated to a temperature equal to or higher than the softening temperature of the polyolefin resin composition to impregnate the resin composition particles with carbon dioxide gas as a foaming agent. Then, an inorganic gas is introduced into the pressure-resistant container so that the pressure in the pressure-resistant container is 0.6 to 5.0MPa, and the pressure is maintained, and the contents are discharged into an atmosphere lower than the internal pressure in the pressure-resistant container to foam.

The heating temperature of the dispersion is not particularly limited as long as it is not lower than the softening temperature of the polyolefin resin particles. The polyolefin resin particles preferably have a melting point of not less than the melting point of the polyolefin resin particles, and more preferably have a melting point of not less than +5 ℃. The heating temperature of the dispersion is preferably a melting point +20 ℃ or lower, and more preferably a melting point +15 ℃ or lower. For example, in the case of an ethylene-propylene copolymer having a melting point of 145 ℃, the heating temperature is 145 to 165 ℃, and more preferably 150 to 160 ℃. When the heating temperature is less than 145 ℃, the polyolefin resin particles are less likely to foam. When the heating temperature exceeds 165 ℃, the mechanical strength and heat resistance of the resulting expanded beads are insufficient, and the polyolefin resin beads tend to be easily fused together in the pressure-resistant container.

The melting point of the polyolefin resin is: the peak temperature of the melting peak appeared when the temperature was raised from 40 ℃ to 220 ℃ at a rate of 10 ℃/min, then cooled to 40 ℃ at a rate of 10 ℃/min, and then raised to 220 ℃ again at a rate of 10 ℃/min using DSC (differential scanning calorimeter).

The inorganic gas is not particularly limited, and nitrogen, air, or an inorganic gas mainly containing these (usually 50% by volume or more, preferably 70% by volume or more) and containing a small amount (50% by volume or less, preferably 30% by volume or less) of an inert gas such as argon, helium, or xenon, or a water vapor, oxygen, hydrogen, ozone, or the like can be used. Nitrogen gas is preferred from the viewpoint of economy, productivity, environmental suitability, and the like, and air is more preferred from the viewpoint of safety and economy.

The holding pressure of the inorganic gas is not particularly limited, but is preferably 0.6 to 5.0MPa, more preferably 1.0 to 3.5MPa, as described above, from the viewpoint of increasing the expansion ratio and reducing the unevenness of the expansion ratio. If the holding pressure is less than 0.6MPa, the effect of introducing the inorganic gas is reduced, and the expanded beads tend to be insufficiently expanded, and it tends to be difficult to obtain expanded beads having a desired expansion ratio. When the holding pressure exceeds 5.0MPa, the cells of the obtained expanded beads become fine, the closed cell ratio is reduced, and the molded article tends to shrink, thereby impairing the shape stability, mechanical strength and heat resistance. The timing of introduction of the inorganic gas does not greatly affect the expansion ratio of the expanded beads and the quality such as the unevenness of the expansion ratio, and may be performed before, during or after heating in the pressure-resistant vessel.

The time from when the pressure of the inorganic gas is increased to a predetermined pressure to when the polyolefin-based resin particles are discharged to a low-pressure atmosphere together with the aqueous dispersion medium is not particularly limited, but is preferably 60 minutes or less or as short as possible from the viewpoint of improving productivity. The pressure in the container during the discharge is preferably maintained at the above-mentioned reached pressure.

The pressure of the low-pressure atmosphere to which the dispersion is discharged may be lower than the internal pressure of the pressure-resistant container, and an atmosphere having a pressure near atmospheric pressure is usually selected. In addition, the atmosphere means: the space including the trajectory of scattering of the discharged aqueous dispersion (foamed particles and aqueous dispersion medium) is generally a pipe, a tube, and the inside of the apparatus isolated from the outside air.

Among these, in the method for producing expanded polyolefin resin particles, it is preferable that the dispersion (the polyolefin resin particles and the aqueous dispersion medium) is passed from the pressure-resistant container through a throttle disk while maintaining the internal pressure of the pressure-resistant container, and then discharged into an atmosphere lower than the internal pressure of the pressure-resistant container. The throttle disk used in the present method will be described below.

< throttle disk >

The orifice plate is generally used to adjust the discharge time and to uniformize the expansion ratio. The method uses a throttle plate with a cylinder, which is formed by arranging a cylinder on a throttle plate. This can reduce the angle of scattering of the discharged dispersion. As a result, expanded beads having a uniform size can be expanded, and variation in the magnification can be reduced. As the throttle plate, a throttle type, a nozzle type, a venturi type, or the like can be used, and these may be used in combination. Preferably, a throttle die is used as the throttle plate. By using the orifice type, a fixed outflow rate can be maintained by a simple structure, and expanded beads with a high magnification and less variation in magnification can be obtained.

Fig. 2 is a front view of the structure of the throttle disk 1 used in the present method. Fig. 3 is a front view of a modified example of the throttle plate 1 shown in fig. 2. Fig. 4 is a structural sectional view of the orifice plate 1.

As shown in fig. 2 and 4, the throttle disk 1 includes a cylindrical body 2 and a throttle plate 3. The cylindrical body 2 is cylindrical and is formed on the surface of the throttle plate 3 on the dispersion liquid discharge side. The orifice plate 3 forms an orifice 5 through which the dispersion passes. The cylinder 2 is arranged with its inner side surrounding the throttle orifice 5. A more specific positional relationship is that the center of the orifice 5 substantially coincides with the center of the cylinder 2.

If the throttle plate 3 is used, the aperture h of the throttle orifice 5_aThe thickness is not particularly limited, but is preferably 6.0mm or more, more preferably 7.0mm or more, and still more preferably 8.0mm or more. In addition, the bore h_aThe upper limit of (b) is not particularly limited. However, the bore h_aThe larger the required capacity to transport the expanded particles, the higher the equipment cost.

The thickness of the throttle plate 3 is preferably 0.2 to 10mm, and more preferably 0.5 to 5 mm. If the thickness is less than 0.2mm, the throttle plate 3 may be damaged by the pressure during discharge. On the other hand, if the thickness exceeds 10mm, the expansion ratio of the obtained expanded beads may decrease, it may be difficult to obtain expanded beads having a desired expansion ratio, and the resin may block the open pore portion.

The cylinder 2 attached to the throttle plate 3 is integrally attached to the throttle plate 3 on the dispersion discharge side of the throttle orifice 5. The material of the cylindrical body 2 is not particularly limited, and metal is generally used. The method of integrating the cylinder 2 and the throttle plate 3 is not particularly limited, and welding, fitting, screwing, bonding, or the like can be employed. The throttle plate 3 and the cylinder 2 may be integrally manufactured as necessary.

The opening area of the cylindrical body 2 on the side opposite to the throttle plate 3 may be set as appropriate depending on the size and length of the cylindrical body 2, and may be generally 1.3 times or more the opening area of the throttle orifice 5. If the opening area of the cylinder 2 is less than 1.3 times the opening area of the orifice 5, the discharged expanded beads are likely to be aggregated and clogged. If the length of the cylindrical body 2 is short, the above-described problem does not occur, but it is difficult to exhibit the effect of the cylindrical body 2.

The front shape of the cylinder 2 shown in fig. 2 is not limited to a cylinder, and may be a circular hole including a part of a circle or an ellipse. The circular hole here means a through hole having an inner wall in the following shape or the like: a circle, an ellipse, a rectangle, or a shape obtained by adding a semicircle with the diameter of the side to each of two opposite sides of the square.

The cylinder 2 is not limited to a circular hole. The barrel 2 may also be elongated 4, as shown in fig. 3. The cylinder 2 of the elongated shape 4 here means: the through-hole has a polygonal shape such as a rectangle, a square, a rhombus, a trapezoid, a parallelogram, other quadrangle, a triangle, a pentagon, or a hexagon.

The shape of the cylindrical body 2 may be a prism or a cylinder. In this case, the shape of the opening of the cylindrical body 2 is a narrow and long shape 4 or a circular shape. The width or short diameter H of the front surface (dispersion liquid discharge side) of the cylindrical body 2 is set to be larger than that of the front surface_aIs 0.6mm or more, preferably 1.2 to 25mm, and the length M of the cylinder 2 in the discharge direction is 5mm or more, preferably 5 to 300 mm. Narrow shape 4 of cylinder or round front width or front minor axis H_aIf the thickness is less than 0.6mm, the elongated portion or the hole tends to be clogged. When the length M of the cylinder 2 is less than 5mm, the scattering trajectory of the discharged dispersion is not different from that in the case of using the orifice 1 without the cylinder 2. Therefore, the effect of reducing the unevenness of magnification is reduced. If the length M is longer than 300mm, the expanded beads may collide with each other and be fused inside the cylindrical body 2, and the expanded beads may not be obtained.

The shape of the cylindrical body 2 may be a part of a pyramid or a cone. In this case, the area of the portion of the cylinder 2 in contact with the throttle plate 3 is made close to the opening area of the throttle orifice 5. Also, the opening area of the cylinder 2 corresponding to the point where the dispersion passes through the cylinder 2 and is discharged is relatively large. That is, the shape of the cylinder 2 is: the opening area surrounded by the side wall of the cylindrical body 2 increases toward the discharge side of the dispersion.

In the cylindrical orifice disk 1, the cylindrical body 2 can be provided in the number of openings of the orifice 5 of the orifice plate 3 or less. The plurality of orifices 5 of the throttle disk 1 is advantageous because the production speed is increased.

Next, referring to fig. 1 to 3, the narrow shape 4 or the circular front width or the front short diameter H of the cylindrical body 2 of the cylindrical orifice plate 1 will be described_aAnd a method of determining the length M of the cylinder 2. The size of the cylinder 2 is the inner diameter size of the cylinder.

First, the length M is a distance from a portion of the cylinder 2 closest to the throttle plate 3 to a portion of the cylinder 2 farthest from the throttle plate 3 in the discharge direction of the dispersion liquid. In addition, if the elongated shape 4 is rectangular, the width H_aAnd the height is the long side and the short side (if square, the long and short sides are the same). In addition, if the elongated shape 4 is a trapezoid, the larger of the base and the height is the width H_aThe smaller dimension is the height. In addition, when the long and narrow shape 4 is another shape, the length of the longest line segment among line segments cut by the sides of the long and narrow shape 4 on an arbitrary straight line passing through the center of gravity of the long and narrow shape 4 is defined as the major axis, and the length of the shortest line segment is defined as the minor axis H_a. When the cylinder 2 is oval, the major axis is defined as the width H_aOr major axis and minor axis as height or minor axis H_a。

When more than 2 cylinder bodies are arranged on the throttle disk 1 with the cylinder, the long and narrow shapes 4 or the circular shapes of the cylinder bodies 2 can be completely the same or completely different. Alternatively, some of the cylinders may have the same shape and the other may have different shapes.

3-3. Collision step

In the method, the foaming step includes a collision step of causing the mixture in the pressure-resistant container to collide with a curved surface when the mixture is discharged from a discharge portion (for example, a throttle plate 1). The term "mixture" as used herein means: the polyolefin resin particles are impregnated with carbon dioxide gas as a blowing agent, and then mixed with the dispersion. FIG. 1 is a schematic configuration of an example of a foaming apparatus used in the method. As shown in fig. 1, the foaming apparatus of the present method includes: a throttle disk with a cylinder 1, a discharge pipe 6, a pressure vessel 7, a valve 8, a low pressure vessel 13, and a collision plate 14.

The discharge pipe 6 is a pipe connecting the pressure vessel 7 and the low pressure vessel 13 to each other. The discharge pipe 6 is provided with a valve 8. The valve 8 is a valve for switching the opening and closing of the pressure-resistant container 7. The throttle disk 1 is provided at the outlet of the discharge pipe 6. The discharge pipe 6 and the low-pressure tank 13 communicate with each other through the orifice 1. The collision plate 14 is provided in the low pressure tank 13 and faces the outlet of the throttle disk 1.

Resin particles 9 containing a polyolefin resin are dispersed in an aqueous dispersion medium 10 to form a dispersion, and the dispersion is contained in a pressure-resistant container 7. The dispersion heated and pressurized in the pressure-resistant vessel 7 flows through the discharge pipe 6 by opening the valve 8, and is discharged from the outlet of the orifice plate 1 into the low-pressure vessel 13 to become the expanded beads 11. In the collision step, the foamed beads 11 discharged from the outlet of the orifice 1 collide with the collision plate 14.

In this method, the collision plate 14 is a member that changes the scattering direction of the foamed particles 11 discharged from the orifice 1. In general, when the temperature becomes equal to or lower than the softening temperature of the resin particles 9 during foaming, the resin is cured and foaming is terminated. However, it is considered that the reason why the temperature and humidity of the foaming atmosphere in the present method are more uniform is that when the resin particles 9 are dispersed in the aqueous dispersion medium 10 to form a dispersion and the dispersion is collided with the collision plate 14, the foamed particles 11 are uniformly foamed and the variation in the expansion ratio can be reduced. In the present method, the collision plate 14 has a curved surface 14 a. In this method, the dispersion discharged from the orifice 1 is caused to collide with the curved surface 14 a. The curved surface 14a is not particularly limited, and is preferably a concave curved surface that is concave in the dispersion scattering direction.

In the method, particularly, since the dispersion is caused to collide with the curved surface 14a, it is possible to at least further reduce the unevenness of the expansion ratio in the production of the expanded particles 11 having a low expansion ratio. On the other hand, in the production of expanded beads 11 having a high expansion ratio, expanded beads 11 having a uniform cell structure can be obtained. In general, the higher the expansion ratio of the produced expanded beads, the more uneven the cell structure of the produced expanded beads tends to be. The present inventors have found that the dispersion liquid collides with the curved surface 14a, whereby the cell structure can be made uniform even if the expansion ratio of the foamed particles to be produced is high, and thus completed the present method. The technical idea based on the knowledge of the method is unpredictable by the prior art and is independently accomplished by the present inventors.

The term "low expansion ratio" as used herein means an expansion ratio of 10 to 18 times, preferably 12 to 16 times, and the term "high expansion ratio" means an expansion ratio of 18 to 25 times, preferably 20 to 22 times.

The curvature radius of the curved surface 14a of the collision plate 14 is 500 to 1500mm, preferably 800 to 1200mm, more preferably 900 to 1100mm, and still more preferably 1000 mm. If the radius of curvature of the curved surface 14a is less than 500mm, the flowability of the expanded beads is poor, which is not preferable. If the radius of curvature of the curved surface 14a exceeds 1500mm, the collision effect is reduced, which is not preferable.

The size of the collision plate 14 may be a size that allows collision of the foamed particles 11. The distance L from the discharge portion (the front end of the throttle plate 1) to the collision plate 14 may be a distance that allows the foamed particles 11 to collide. In order to produce expanded beads 11 having a uniform cell structure with little variation in expansion ratio, the distance L is 50mm L600 mm, preferably 50mm D400 mm, more preferably 50mm D200 mm, and still more preferably 50mm D100 mm. When the distance L is 50mm or more, the expanded beads 11 are preferably not fused to each other in the space between the throttle disk 1 and the collision plate 14 during foaming. The distance L varies depending on the heating and pressurizing conditions in the pressure vessel, but a distance L of 600mm or less is preferable because the collision effect is sufficient, the effect of reducing the unevenness of magnification and the effect of uniformizing the cell structure are large. If the distance L to the collision plate 14 is too long, the expanded beads 11 are cooled before the collision and are difficult to expand, and it is difficult to obtain a desired expansion ratio. Therefore, the distance L needs to be set appropriately according to the foaming atmosphere.

The material of the collision plate 14 is not particularly limited, and may be metal, plastic, rubber, felt, ceramic, or wood.

The collision angle θ of the expanded beads 11 with respect to the curved surface 14a may be an angle at which the expanded beads 11 can collide. In order to produce expanded beads 11 having a uniform cell structure with little unevenness in expansion ratio, the collision angle θ is preferably 13 ° or more, more preferably 15 to 25 °, and still more preferably 18 to 22 °. As shown in fig. 1, the collision angle θ here means: when the intersection point between the axis R of the cylindrical body of the throttle disk 1 and the impingement plate 14 is P, the angle formed by the tangent G at the point P on the impingement plate 14 and the axis R.

When the collision angle θ is 13 ° or more, the collision effect is strong, and the effect of reducing the unevenness of the foaming ratio is large, which is preferable. Further, when the collision angle θ is 15 to 25 °, the effect of reducing the unevenness of the foaming ratio is large, and the cells that have come into contact with the collision surface (curved surface 14a) tend not to be easily miniaturized and the cell structure tends to be uniform, which is preferable.

As described above, in the present method, the bore h of the choke 5_aPreferably 6.0mm or more. In general, when the expanded beads 11 are produced by expanding in a short time, it is preferable to increase the diameter h_aAnd the opening area is increased to discharge more foaming particles 11. When the aperture h is increased in this way_aThe present inventors have found that the conventional methods (patent documents 1 to 3) cause the expansion ratio to be deteriorated when the expanded beads 11 are discharged. The present inventors have found that, when the impact plate 14 is used as the impact surface of the impact plate 14 that receives the expanded beads 11, the choke 5 (i.e., the diameter h) having a large diameter is used_a6.0mm or more) in a short time, the unevenness of the expansion ratio can be remarkably reduced. Thus, the present method is preferably suitable for short-time foaming using a large-bore orifice.

The expansion ratio of the expanded beads obtained from the dispersion containing polyolefin resin particles thus obtained is about 2 to 40 times, preferably 3 to 30 times. The expanded beads have a closed cell content of about 80 to 100%, preferably 90 to 100%. The average cell diameter of the expanded beads is about 20 to 500 μm, preferably 100 to 400 μm.

When the expansion ratio is less than 2 times, the flexibility and the like of the obtained molded article are insufficient, and when it exceeds 40 times, the mechanical strength, the heat resistance and the like of the obtained molded article are insufficient. When the closed cell content is less than 80%, the 2-pass foaming power is insufficient, and therefore, fusion failure occurs during molding, and the mechanical strength and the like of the obtained molded article are deteriorated. When the average cell diameter is less than 20 μm, the shape of the obtained molded article may be deformed, and when it exceeds 500 μm, the mechanical strength of the obtained molded article may be lowered. When the unevenness of the expansion ratio is 7% or less, the weight unevenness of the molded article is less likely to occur, and the yield of the product is improved.

The polyolefin resin foamed particles have an independent cell content of 80% or more. Therefore, if necessary, the expanded beads are treated under heat and pressure for a certain period of time in a pressure-resistant container to be impregnated with air, and then filled into a molding die and steam-heated to be foam-molded in the heating die, thereby producing a molded article having a cavity shape. The foamed molded article thus obtained is excellent in flexibility and cushioning properties, and has a small dimensional shrinkage and a small deformation in shape, and therefore has an extremely high commercial value.

In addition, in the low expansion ratio expanded beads having an expansion ratio of 10 to 18, although the unevenness of the expansion ratio depends on the expansion conditions and the like, at least the unevenness of the expansion ratio tends to be usually less than 10%, preferably 7.0% or less, and more preferably 5.0% or less. When expanded beads having a low expansion ratio are produced, the production method of the present embodiment can produce good expanded beads having less unevenness in expansion ratio than the conventional expansion method.

Further, the expanded beads having a high expansion ratio of 18 to 25 times have a good uniformity of cell structure. More specifically, the difference between the cell diameters of the particle cells constituting the expanded particles, in other words, the difference between the minimum average cell diameter and the maximum average cell diameter (hereinafter, also simply referred to as cell diameter difference) of 1 expanded particle is 70 μm or less. The cell diameter difference can be calculated, for example, as follows. First, the foamed particles were cut, and the cut section was divided into 4 parts, upper, lower, left, and right. Next, the average cell diameter of each of the 4 regions was calculated. Then, of the calculated 4 average cell diameters, the maximum value was defined as the maximum average cell diameter, the minimum value was defined as the minimum average cell diameter, and the difference therebetween was defined as the cell diameter difference. The cell diameter difference is preferably 50 μm or less, more preferably 30 μm or less. The difference in cell diameter is preferably 70 μm or less because the molded article has good product appearance. The smaller the cell diameter difference, the more preferable.

That is, the polyolefin resin foamed particles of the present embodiment satisfy the following (i) and (ii).

(i) The foaming ratio is 18 to 25 times,

(ii) among the average cell diameters obtained by dividing the cut cross section of the foamed particles into 4 regions and calculating the average cell diameters for the 4 regions, the difference between the minimum average cell diameter and the maximum average cell diameter is 70 μm or less.

As described above, conventional expanded beads having a high expansion ratio tend to have an uneven cell structure. The polyolefin resin expanded beads of the present embodiment are characterized by a high expansion ratio and a uniform cell structure.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the specification, and embodiments obtained by appropriately combining technical means disclosed in the embodiments are also included in the technical scope of the present invention.

[ conclusion ]

The method for producing thermoplastic resin foamed particles according to embodiment 1 of the present invention includes: a dispersion liquid preparation step of preparing a dispersion liquid by dispersing thermoplastic resin particles (resin particles 9) in an aqueous dispersion medium 10 in a pressure-resistant container 7; and a foaming step of heating the dispersion to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles using carbon dioxide gas as a foaming agent, pressurizing the dispersion, and then discharging the dispersion into an atmosphere (low-pressure container 13) lower than the internal pressure of the pressure-resistant container 7 to foam the dispersion, wherein the foaming step includes a collision step of causing the mixture in the pressure-resistant container 7 to collide with the curved surface 14a when the mixture is discharged from a discharge portion (throttle plate 1).

In the method for producing thermoplastic resin foamed particles according to mode 1, mode 2 of the present invention, the collision angle θ of the mixture with respect to the curved surface 14a is 13 ° or more.

In the method for producing thermoplastic resin foamed particles according to mode 3 of the present invention according to mode 1 or 2, an impact angle θ of the mixture with respect to the curved surface 14a is 15 to 25 °.

In the method for producing thermoplastic resin expanded beads according to mode 4 of the present invention according to any one of modes 1 to 3, the distance from the discharge portion (throttle disk 1) to the curved surface 14a is L, and in the collision step, the mixture is caused to collide with the curved surface 14a so that L is 50mm or more and 600mm or less.

In the method for producing thermoplastic resin expanded beads according to mode 5 of the present invention according to any one of modes 1 to 4, the discharge portion (orifice plate 1) includes an orifice 5 through which the mixture is discharged, and the diameter h of the orifice 5_aIs more than 6 mm.

In the method for producing thermoplastic resin expanded beads according to mode 6 of the present invention according to any one of modes 1 to 5, the expansion ratio of the produced expanded beads is 10 to 25 times.

The thermoplastic resin expanded beads of embodiment 7 of the present invention have an expansion ratio of 18 to 25 times, and the difference between cell diameters of cell cells constituting the thermoplastic resin expanded beads is 70 μm or less.

(examples)

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

< measurement of non-uniformity of expansion ratio of expanded particles >

1kg of expanded polyolefin resin beads were sieved through a standard sieve (11 sieves having sizes commonly referred to as 1, 1.18, 1.4, 1.7, 2, 2.36, 2.8, 3.35, 4, 4.75 and 5.6) according to Japanese Industrial Standard (JIS) Z8801. The weight fraction Wi and the expansion ratio Ki of the polyolefin resin expanded particles remaining on each sieve were measured, and the average expansion ratio Kav was calculated by the following formula (1).

Kav ═ Σ (Ki × Wi) · formula (1)

(i denotes sieves)

Next, using the weight fraction Wi, the expansion ratio Ki and the average expansion ratio Kav, the following equation (2) was used

σm＝[∑{Wi×(Kav-Ki)²}]^1/2The type (2)

(i denotes sieves)

The standard deviation δ m of the foaming ratio was calculated by the following equation (3)

Magnification unevenness R (%) (σ m/Kav). times.100. formula (3)

The magnification unevenness R (%) is obtained. The unevenness of the expansion ratio was at an acceptable level of less than 10%.

The foaming ratio Ki of the polyolefin resin foamed particles remaining on each screen was determined as follows. First, the weight Gi of the polyolefin resin expanded beads remaining on each sieve was precisely weighed to the order of 0.001g (the number of 4 th positions after decimal point was rounded). Subsequently, the polyolefin resin foamed particles weighed to a known weight were immersed in 100ml of water at 23 ℃ in a measuring cylinder. The volume yi (cm) of the polyolefin resin expanded beads was read from the scale of the rise of the liquid surface³). Then, the volume yi (cm) of the expanded polyolefin resin particles is divided by the weight Gi (g) of the expanded polyolefin resin particles³) The quotient was converted to g/L units, and the apparent density di of the polyolefin resin expanded beads on each sieve was determined. Finally, the ratio of the density ds of the base resin (900 g/L), i.e., the expansion ratio Ki (ds/di), was determined.

< evaluation of cell structure uniformity of expanded beads >

Sufficient care was taken not to break the bubble film, cutting the expanded beads substantially centrally. The cut section was divided into 4 regions, i.e., upper, lower, left, and right regions, and the average cell diameter was calculated for each region. With respect to the average cell diameter, a line segment corresponding to a length of 1000 μm was drawn, and the number n of bubbles passed through by the line segment was measured. Then, the cell diameter was calculated at 1000/n (. mu.m) from the number of cells n. The average cell diameter of each of 30 expanded particles was calculated.

The minimum average cell diameter and the maximum average cell diameter of each of 30 expanded particles were calculated. Then, based on the difference between the minimum average cell diameter and the maximum average cell diameter (cell diameter difference), cell structure uniformity was evaluated as follows. The evaluation was made based on the average value of the cell diameter difference between 30 expanded particles.

Difference between minimum average cell diameter and maximum average cell diameter

Less than 30 μm: 5

30 μm or more and less than 60 μm: 4

60 μm or more and less than 90 μm: 3

90 μm or more and less than 120 μm: 2

120 μm or more: 1

(example 1)

[ production of resin particles ]

An ethylene-propylene random copolymer (density: 0.90 g/cm) was added as a polyolefin resin³The resulting mixture was fed to a 26mm phi biaxial extruder (TEM 26-SX, Toshiba mechanical Co., Ltd.) having an ethylene content of 3%, a melting point of 145 ℃, an MI of 7.5g/10 min and a flexural modulus of elasticity of 1000MPa, and melt-kneaded. Then, the pellets were extruded from a cylindrical die having a diameter of 1.2 mm. phi., cooled with water, and then cut with a cutter to obtain cylindrical resin composition pellets (pellets) (1.2 mg/pellet) containing a polyolefin resin. The melting point of the obtained resin pellets was 145 ℃ and the density measured in accordance with JIS K7112 was 0.90g/cm³。

[ production of expanded beads ]

100 parts by weight of the obtained resin particles, 0.5 part by weight of tricalcium phosphate (manufactured by taiping chemical industries, ltd.) as a dispersant, and sodium alkylsulfonate (sodium n-alkanesulfonate sodiu) as a dispersion aidm n-paraffinfin sulfonate (Laemeul PS, manufactured by Kao corporation) 0.03 parts by weight, was added to the pressure-resistant vessel 7 of the apparatus shown in FIG. 1 together with 200 parts by weight of water. Then, 3.5 parts by weight of carbon dioxide gas was added to the reaction solution, and the temperature was raised to 151 ℃ while stirring the aqueous dispersion in the pressure resistant vessel 7. The pressure in the pressure-resistant vessel 7 at this time was about 1.7 MPa. Then, carbon dioxide gas was additionally introduced thereinto under pressure to raise the pressure to 2.2 MPa. After the mixture is kept at the foaming temperature and the foaming pressure for 20 minutes, the valve 8 at the lower part of the pressure-resistant container 7 is opened to allow the aqueous dispersion to have a diameter h_aThe single orifice throttle disk 1 with 8mm throttle orifice 5 drains to the low pressure reservoir 13. Then, the aqueous dispersion was allowed to collide with a curved surface 14a having a curvature radius of 1000mm in the low-pressure vessel 13, thereby obtaining polyolefin resin foamed particles (collision step). In this collision step, the distance L between the throttle disc 1 and the collision plate 14 is 150mm, and the collision angle θ is 18 °. In example 1, the target expansion ratio of the expanded beads produced was 14 times.

For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 2)

Expanded beads were obtained in the same manner as in example 1, except that the distance L between the throttle disk 1 and the collision plate 14 was 50 mm. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 3)

Expanded beads were obtained in the same manner as in example 1, except that the distance L between the throttle disk 1 and the collision plate 14 was 300 mm. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 4)

Expanded beads were obtained in the same manner as in example 1, except that the distance L between the throttle disk 1 and the collision plate 14 was 600mm and the target expansion ratio was 13 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 5)

Expanded beads were obtained in the same manner as in example 1, except that the collision angle θ was 15 ° and the target expansion ratio was 13. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 6)

Expanded particles were obtained in the same manner as in example 1, except that the collision angle θ was 25 °. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 7)

Expanded beads were obtained in the same manner as in example 1, except that the target expansion ratio was 9 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 8)

Expanded beads were obtained in the same manner as in example 1, except that the target expansion ratio was 20 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 9)

Expanded beads were obtained in the same manner as in example 1, except that the distance L between the throttle disk 1 and the collision plate 14 was 5 mm. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 10)

Expanded beads were obtained in the same manner as in example 1, except that the distance L between the throttle disk 1 and the collision plate 14 was 700mm and the target expansion ratio was 13 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 11)

Expanded beads were obtained in the same manner as in example 1, except that the collision angle θ was 13 ° and the target expansion ratio was 12. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

(example 12)

Expanded beads were obtained in the same manner as in example 1, except that the collision angle θ was 30 ° and the target expansion ratio was 14. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

Comparative example 1

Expanded beads were obtained in the same manner as in example 1, except that the aqueous dispersion was allowed to collide with a flat-plate-shaped collision plate, instead of colliding with the curved surface 14a, the collision angle θ was 20 °, the distance L between the throttle disk 1 and the collision plate 14 was 300mm, and the target expansion ratio was 12 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

Comparative example 2

Expanded beads were obtained in the same manner as in comparative example 1, except that the target expansion ratio was 20 times. For the obtained expanded beads, the unevenness of expansion ratio was measured, and the uniformity of cell structure was evaluated.

The results of evaluating the unevenness of expansion ratio and the uniformity of cell structure of the expanded beads of examples 1 to 12 and comparative examples 1 and 2 are shown in table 1.

(Table 1)

From the results shown in table 1, the expanded beads of examples 1 to 12 had a degree of unevenness of expansion ratio of 10% or less, and the degree of unevenness was good. On the other hand, the expanded beads of comparative example 1 had a degree of unevenness of expansion ratio exceeding 10%, and the degree of unevenness was not good. Therefore, it is understood that the expanded beads of examples 1 to 12 have a reduced degree of unevenness in expansion ratio as compared with the expanded beads of comparative example 1. Further, by comparing examples 1 to 7, 9 to 12 and comparative example 1, it is understood that when expanded beads are produced at a low expansion ratio of about 12 to 14 times the target expansion ratio, the use of the collision plate 14 having the curved surface 14a can at least reduce the unevenness of the expansion ratio. In addition, regarding the collision angle, if the collision surface is a curved surface and the collision angle is 13 ° or more, the degree of unevenness in expansion ratio is good and 7% or less.

In example 8, expanded beads were produced at a high expansion ratio of about 20 times the target expansion ratio. The expanded beads produced had (i) an expansion ratio of 20 times and (ii) cell structure uniformity evaluation of 4. That is, (ii) the difference between the minimum average cell diameter and the maximum average cell diameter is 70 μm or less.

On the other hand, in comparative example 2, expanded beads were produced at a high expansion ratio of about 20 times the target expansion ratio, and the uniformity of cell structure was evaluated as 2. That is, the difference between the minimum average cell diameter and the maximum average cell diameter exceeds 70 μm.

As a result of comparing example 8 and comparative example 2, it is understood that when expanded beads are produced at a high expansion ratio of about 20 times the target expansion ratio, expanded beads having a uniform cell structure can be obtained at least by using the collision plate 14 having the curved surface 14 a.

Further, by comparing examples 1 to 4 and examples 9 and 10, it is understood that when the distance L between the throttle disk 1 and the collision plate 14 is 50 to 600mm, the unevenness of the expansion ratio can be reduced and the cell structure can be made uniform. Further, by comparing examples 1, 5 and 6 with examples 11 and 12, it is understood that when the collision angle θ is 15 ° to 25 °, the unevenness of the expansion ratio is low and 5% or less, and the uniformity of the cell structure is evaluated to be 4 or more, that is, the cell structure is uniform.

(availability in industry)

The present invention is suitably applicable to, for example, expanded beads used for the production of cushioning packaging materials, materials for logistics, heat insulating materials, civil engineering and construction parts, automobile parts, and the like.