JPWO2020170694A1 - Manufacturing method of thermoplastic resin foamed particles, and thermoplastic resin foamed particles - Google Patents

Abstract

In the production method of the present invention, carbon dioxide gas is used as a foaming agent for the purpose of obtaining thermoplastic resin foamed particles having at least a uniform cell structure at a high foaming ratio and at least improving the variation in the foaming ratio at a low foaming ratio. After heating and pressurizing the dispersion liquid of the resin particles (9), the dispersion liquid is applied from the squeezing plate 1 of the pressure-resistant container (7) to a low-pressure container under a lower pressure atmosphere than the internal pressure in the pressure-resistant container (7). It is emitted to (13) and collides with the curved surface (14a).

Description

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

As a prior art, the thermoplastic resin particles 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 the thermoplastic resin particles are subjected to a lower pressure than in the container. A method for producing foamed particles by releasing them into the atmosphere of the above and foaming them is known. Further, a method of dispersing the foaming agent in the container as needed is also known.

For example, Patent Documents 1 to 3 describe a technique for causing foamed particles to collide with a collision plate or a container wall from a discharge portion of a pressure-resistant container when the polyolefin-based resin particles are discharged into an atmosphere having a lower pressure than the inside of the container and foamed. Is disclosed. This reduces the variation in the expansion ratio of the foamed particles.

Patent No. 3963720 Patent No. 4747472 Patent No. 4818101

In general, foamed particles having a relatively low foaming ratio tend to have a large variation in the foaming ratio of the foamed particles. On the other hand, foamed particles having a relatively high foaming ratio tend to have a non-uniform cell structure. In the above-mentioned conventional technique, there is room for improvement in the above points.

One aspect of the present invention realizes a method for producing thermoplastic resin foamed particles in which at least the variation in the foaming ratio is improved at a low foaming ratio and at least the cell structure is uniform at a high foaming ratio, and the thermoplastic resin foamed particles. The purpose is.

In order to solve the above problems, the method for producing thermoplastic resin foamed particles according to one aspect of the present invention is to prepare a dispersion liquid by dispersing the thermoplastic resin particles in an aqueous dispersion medium in a pressure-resistant container. In the step, using carbon dioxide gas as a foaming agent, the dispersion is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles and pressurized, and then discharged under a lower pressure atmosphere than the internal pressure in the pressure-resistant container. This includes a foaming step of foaming, and the foaming step includes a collision step of causing the mixture to collide with a curved surface when the mixture in the pressure resistant container is discharged from the discharging portion.

Further, in order to solve the above-mentioned problems, the thermoplastic resin foamed particles according to one aspect of the present invention have a foaming magnification of 10 to 25 times, and the difference in cell diameter between the constituent particle cells is 70 μm or less. It is a composition.

According to one aspect of the present invention, at a low foaming ratio, at least the variation in the foaming ratio is improved, and at a high foaming ratio, thermoplastic resin foam particles having at least a uniform cell structure can be obtained.

It is a figure which shows the schematic structure of an example of the foaming apparatus used in the manufacturing method of the thermoplastic resin foamed particles which concerns on embodiment of this invention. It is a front view which shows the structure of the drawing machine used in the manufacturing method of the thermoplastic resin foam particle which concerns on embodiment of this invention. It is a front view which shows the structure of the modification of the diaphragm 1 shown in FIG. It is sectional drawing which shows the structure of the drawing machine used in the manufacturing method of the thermoplastic resin foam particle which concerns on embodiment of this invention.

An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope of the claims. Further, the technical scope of the present invention also includes embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments or examples. Further, by combining the technical means disclosed in each embodiment, new technical features can be formed. In addition, all the academic and patent documents described in the present specification are incorporated as references in the present specification. Further, unless otherwise specified in the present specification, "A to B" representing a numerical range is intended to be "A or more (including A and larger than A) and B or less (including B and smaller than B)".

1. 1. Method for Producing Thermoplastic Resin Foamed Particles According to the Present Invention As a result of diligent studies on the above-mentioned problems, the present inventor has made a member having a specific structure when the contents of the pressure-resistant container are discharged from the discharging portion. We have found a unique finding that, when foamed particles having a low foaming ratio are produced by collision, at least the variation in the foaming ratio is improved. Furthermore, we have independently found that when foaming particles with a high foaming magnification are produced, at least the cell structure becomes uniform. Then, the present inventor came to the present embodiment based on these findings.

That is, in the method for producing thermoplastic resin foam particles according to the present embodiment (hereinafter, simply referred to as this method), a dispersion liquid preparation in which the thermoplastic resin particles are dispersed in an aqueous dispersion medium in a pressure resistant container is prepared. In the step, using carbon dioxide gas as a foaming agent, the dispersion is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles and pressurized, and then discharged under a lower pressure atmosphere than the internal pressure in the pressure resistant container. This includes a foaming step of foaming, and the foaming step includes a collision step of causing the mixture to collide with a curved surface when the mixture in the pressure resistant container is discharged from the discharging portion.

2. 2. Material of Thermoplastic Resin Foaming 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 resins, polyester resins, polystyrene resins, polyphenylene ether resins, polyamide resins, and mixtures thereof. The thermoplastic resin is preferably a polyolefin-based resin or a polyester-based resin. Examples of the polyester-based resin include an aliphatic polyester resin, an aromatic polyester resin, and an aliphatic aromatic polyester resin. Specific examples of the polyester resin include polyhydroxy alkanoate, polybutylene succinate (PBS), poly (butylene adipate-co-butylene terephthalate) (PBAT), polyethylene terephthalate (PET) and the like. The polyhydroxy alkanoates are poly (3-hydroxybutyrate-3-hydroxyhexanoate) (PHBH), poly (3-hydroxybutyrate) (P3HB), and poly (3-hydroxybutyrate-co). -3-Hydroxyvariate) (PHBV), Poly (3-Hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), Poly (3-Hydroxybutyrate-3-hydroxyoctanoate), Poly At least one selected from the group consisting of (3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among these, polyolefin-based resins are preferably used. Hereinafter, embodiments in which a polyolefin-based resin is used as the base resin for the thermoplastic resin particles will be described. The base resin of the thermoplastic resin particles that can be used in this embodiment is not limited to the polyolefin-based resin.

2-1. Polyolefin-based resin The polyolefin-based resin used as the base resin for the polyolefin-based resin particles 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. 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 homopolymers; ethylene-propylene random copolymers, Α-Olefin-propylene random copolymers such as ethylene-propylene-1-butene random copolymers and propylene-1-butene random copolymers, and polypropylenes such as α-olefin-propylene block copolymers; propylene Homopolymers, other polyolefin homopolymers such as polybutene; and the like. These may be used alone or in combination of two or more.

Among these, the ethylene-propylene random copolymer, the ethylene-propylene-1-butene random copolymer, and the propylene-1-butene random copolymer show good foamability when they are used as foamed particles. , Suitable for use.

In addition to the polyolefin-based resin, the base resin of the polyolefin-based resin foamed particles is mixed with other thermoplastic resins such as polystyrene, polybutene, and ionomer as long as the characteristics of the polyolefin-based resin are not lost. May be.

Further, the polyolefin-based resin is usually melted by using an extruder, a kneader, a Banbury mixer, a roll, etc. so as to easily produce foamed particles, and has a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, etc. It is preferable to process the resin particles in advance. The resin particles are also referred to as pellets.

The weight of each polyolefin-based resin particle is preferably 0.1 to 30 mg, more preferably 0.3 to 10 mg.

2-2. Additives to be added to the polyolefin resin When adding an additive to the polyolefin resin, it is preferable to mix the polyolefin resin and the additive using a blender or the like before producing the polyolefin resin particles. Specific examples of the additive include a cell nucleating agent (also simply referred to as a nucleating agent). When a hydrocarbon-based foaming agent such as propane, butane, pentane, or hexane is used, the nucleating agent is an inorganic substance such as talc, silica, calcium carbonate, kaolin, titanium oxide, bentonite, barium sulfate, or the like. Nucleating agents are commonly used. The amount of the cell nucleating agent added varies depending on the type of the polyolefin resin used and the type of the cell nucleating agent, so it cannot be unconditionally specified, but it is approximately 0.001 part by weight or more with respect to 100 parts by weight of the polyolefin resin. It is preferably 2 parts by weight or less.

Further, in this method using carbon dioxide gas (carbon dioxide) as a foaming agent, it is preferable to use the inorganic nucleating agent and / or a hydrophilic substance. When water is used as a dispersion medium for an aqueous dispersion, the polyolefin resin is impregnated with water, and the impregnated water acts as a foaming agent together with other foaming agents or alone.

The hydrophilic substance acts to increase the amount of water impregnated in the polyolefin resin. Specific examples of the hydrophilic substance include inorganic substances such as sodium chloride, calcium chloride, magnesium chloride, borosand, and zinc borate; or glycerin, melamine, isocyanuric acid, melamine / isocyanuric acid condensate; polyethylene glycol, polyethylene oxide, and the like. Polyethers, adducts of polyethers to polypropylene, etc., and their polymer alloys; alkali metal salts of ethylene- (meth) acrylic acid copolymers, alkali metal salts of butadiene- (meth) acrylic acid copolymers, Examples thereof include alkali metal salts of carboxylated nitrile rubbers, alkali metal salts of isobutylene-maleic anhydride copolymers, polymers such as alkali metal salts of poly (meth) acrylic acid; and other organic substances. These hydrophilic substances may be used alone or in combination of two or more.

The amount of the hydrophilic substance added was 0. With respect to 100 parts by weight of the polyolefin resin. It is preferably 005 parts by weight or more and 2 parts by weight or less, and more preferably 0.005 parts by weight or more and 1 part by weight or less. By adjusting the type and amount of the hydrophilic substance, the average bubble diameter of the polyolefin resin foamed particles can be adjusted.

Furthermore, when producing polyolefin resin particles, if necessary, colorants, antistatic agents, antioxidants, phosphorus-based processing stabilizers, lactone-based processing stabilizers, metal deactivators, benzotriazole-based ultraviolet absorbers, and benzoate-based light Add additives such as stabilizers, hindered amine-based light stabilizers, flame retardants, flame retardant aids, acid neutralizers, crystal nucleating agents, and amide-based additives to the extent that the characteristics of the polyolefin-based resin are not impaired. be able to.

2-3. Foaming agent In this method, the foaming agent used in the foaming step is carbon dioxide gas (carbon dioxide). In addition, this method may be any method using carbon dioxide gas as a foaming agent, and a method in which carbon dioxide gas and a conventionally known foaming agent are used in combination is also included in the category of this method. As conventionally known foaming agents, volatile hydrocarbon-based foaming agents such as propane, isobutane, butane, pentane, and hexane, and inorganic gases such as air, nitrogen, and water can be used.

1-4. Dispersant and Dispersion Aid It is preferable to use water as the aqueous dispersion medium. A dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin or the like to water can also be used as an aqueous dispersant.

In the aqueous dispersion medium, it is preferable to use a dispersant in order to prevent fusion of the polyolefin-based resin particles. Specific examples of the dispersant include inorganic dispersants such as calcium tertiary phosphate, magnesium tertiary phosphate, titanium oxide, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. Among these, tricalcium phosphate, barium sulfate, and kaolin are more preferable because they can stably disperse an aqueous dispersion containing polyolefin-based resin particles in a pressure-resistant container even in a small amount.

Further, it is preferable to use a dispersion aid together with the dispersant. Specific examples of the dispersion aid include carboxylate types such as N-acylamino acid salt, alkyl ether carboxylate, and acylated peptide; alkyl sulfonate, alkylbenzene sulfonate, alkylnaphthalene sulfonate, and sulfosuccinate. Sulfate type such as acid salt; sulfate ester type such as sulfated oil, alkyl sulfate, alkyl ether sulfate, alkylamide sulfate; and alkyl phosphate, polyoxyethylene phosphate, alkyl allyl ether sulfate Phosphate ester type such as salt; and anionic surfactants such as. Further, as a dispersion aid, polyvalent salts such as maleic acid copolymer salt; polycarboxylic acid type polymer surfactant such as polyacrylic acid salt; and polystyrene sulfonate, naphthalsulfonic acid formalin condensate salt; etc. Anionic polymer surfactants can also be used.

As the dispersion aid, it is preferable to use a sulfonate-type anionic surfactant, and further, it is preferable to use one or a mixture of two or more selected from an alkyl sulfonate and an alkyl benzene sulfonate. .. Further, it is more preferable to use an alkyl sulfonate, and it is preferable to use an alkyl sulfonate having a linear carbon chain having 10 to 18 carbon atoms as a hydrophobic group, which adheres to the foamed particles of the polyolefin resin. It is particularly preferable because the dispersant can be reduced.

Then, in the embodiment of the present invention, one or more selected from tricalcium phosphate, magnesium tribasic phosphate, barium sulfate or kaolin as a dispersant and n-paraffin sulfonic acid sodium as a dispersant aid may be used in combination. Especially preferable.

3. 3. Each step of this method 3-1. Dispersion Liquid Preparation Step In the dispersion liquid preparation step, the above-mentioned polyolefin resin particles are dispersed in the above-mentioned aqueous dispersion medium in a pressure-resistant container to prepare a dispersion liquid.

The amount of the dispersant and the dispersion aid used varies depending on the type thereof or the type and amount of the polyolefin resin used. Usually, the dispersant is preferably blended in an amount of 0.1 parts by weight or more and 5 parts by weight or less, and preferably 0.2 parts by weight or more and 3 parts by weight or less with respect to 100 parts by weight of the aqueous dispersion medium. More preferred. The dispersion aid is preferably blended in an amount of 0.001 part by weight or more and 0.3 part by weight or less, and more than 0.001 part by weight and 0.1 part by weight or less with respect to 100 parts by weight of the aqueous dispersion medium. It is more preferable to do so. Further, in order to improve the dispersibility in the aqueous dispersion medium, the polyolefin-based resin particles are usually preferably used in an amount of 20 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of the aqueous dispersion medium. With the above configuration, the polyolefin-based resin particles can be stably dispersed in the aqueous dispersion medium in the pressure-resistant container.

3-2. Foaming step In the foaming step, carbon dioxide gas is used as a foaming agent to heat the dispersion liquid to a temperature equal to or higher than the softening temperature of the polyolefin resin particles and pressurize the mixture, and then the atmosphere is lower than the internal pressure in the pressure-resistant container. Foam by releasing below. 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, and the resin composition particles are impregnated with carbon dioxide gas as a foaming agent. After that, an inorganic gas is introduced into the pressure-resistant container to set the pressure in the pressure-resistant container to 0.6 to 5.0 MPa, and while maintaining this pressure, it is discharged into an atmosphere lower than the internal pressure in the pressure-resistant container. Foam by.

The temperature for heating the dispersion is not particularly limited as long as it is at least the softening temperature of the polyolefin-based resin particles, but is preferably at least the melting point of the polyolefin-based resin particles, and more preferably at least the melting point of + 5 ° C. The temperature for heating the dispersion is preferably a melting point of +20 ° C. or lower, more preferably a melting point of +15 ° C. or lower. For example, in the case of an ethylene-propylene copolymer having a melting point of 145 ° C., the heating temperature is preferably 145 to 165 ° C., more preferably 150 to 160 ° C. When the heating temperature is less than 145 ° C., the polyolefin-based resin particles are less likely to foam. Further, when the heating temperature exceeds 165 ° C., the mechanical strength and heat resistance of the obtained foamed particles are not sufficient, and the polyolefin-based resin particles tend to be easily fused in the pressure-resistant container.

The melting point of the polyolefin resin is raised from 40 ° C. to 220 ° C. at a rate of 10 ° C./min by a DSC (differential scanning calorimetry), cooled to 40 ° C. at a rate of 10 ° C./min, and then again. It is the temperature at the peak of the melting peak that appears when the temperature is raised to 220 ° C. at a rate of 10 ° C./min.

The inorganic gas is not particularly limited, but is mainly composed of nitrogen, air or these (usually 50% by volume or more, preferably 70% by volume or more), and is an inert gas such as argon, helium or xenone, water vapor, oxygen, etc. An inorganic gas containing a small amount of hydrogen, ozone, etc. (50% by volume or less, preferably 30% by volume or less) can be used, but nitrogen is preferable from the viewpoint of economy, productivity, environmental compatibility, etc., and is safe. , Air is more preferable from the viewpoint of economy.

The holding pressure due to the inorganic gas is not particularly limited, but is preferably 0.6 to 5.0 MPa, more preferably 1.0 to 3.5 MPa, as described above, from the viewpoint of improving the foaming ratio and reducing the variation in the foaming ratio. preferable. When the holding pressure is less than 0.6 MPa, the effect of introducing the inorganic gas is reduced, the foamed particles tend not to foam sufficiently, and it tends to be difficult to obtain foamed particles having a desired foaming ratio. There is. Further, when it exceeds 5.0 MPa, the bubbles of the obtained foamed particles become finer, the closed cell ratio decreases, and the shrinkage, shape stability, mechanical strength, and heat resistance of the molded product tend to be impaired. Since the introduction timing of the inorganic gas does not significantly affect the quality such as the magnification and the variation in magnification of the foamed particles, it may be any of before, during, and after heating in the pressure-resistant container.

The time from pressurizing with the inorganic gas to reaching a predetermined pressure until the polyolefin-based resin particles are released into the low-pressure atmosphere together with the aqueous dispersion medium is not particularly limited, but is 60 minutes from the viewpoint of improving productivity. It is preferably within or as short as possible. It is preferable that the pressure inside the container during discharge is maintained at the reached pressure.

Further, the low-pressure atmosphere in which the dispersion liquid is discharged may be an atmosphere having a pressure lower than the internal pressure in the pressure-resistant container, but an atmosphere having a pressure near the atmospheric pressure is usually selected. Further, the atmosphere means a space including a scattering locus of the released aqueous dispersion (foaming particles and aqueous dispersion medium), but generally refers to a pipe or duct-like space inside a device that is shielded from the outside air. ..

Here, in the method for producing the polyolefin-based resin foamed particles, the dispersion liquid (polyolefin-based resin particles and the aqueous dispersion medium) is preferably pressure-resistant after passing through a pressure-resistant container from the pressure-resistant container while maintaining the internal pressure of the pressure-resistant container. It is released into a low pressure atmosphere rather than the internal pressure of the container. Here, the diaphragm used in this method will be described below.

<Aperture board>
The drawing machine is generally used for adjusting the release time and making the foaming ratio uniform. In this method, a diaphragm with a cylinder having a cylinder attached to the orifice plate is used. As a result, the scattering angle of the released dispersion can be reduced. As a result, it is possible to foam the foamed particles having a uniform size and reduce the variation in magnification. As the orifice plate, an orifice type, a nozzle type, a venturi type and the like can be used, and these can also be used in combination. It is preferable to use an orifice type as the orifice plate. By using the orifice type, it is possible to obtain foamed particles having a simple structure, a constant outflow rate, a high magnification, and a small variation in magnification.

FIG. 2 is a front view showing the configuration of the diaphragm 1 used in this method. FIG. 3 is a front view showing a configuration of a modified example of the diaphragm 1 shown in FIG. FIG. 4 is a cross-sectional view showing the configuration of the diaphragm 1.

As shown in FIGS. 2 and 4, the diaphragm 1 includes a tubular body 2 and an orifice plate 3. The tubular body 2 has a cylindrical shape and is formed on the surface of the orifice plate 3 on the discharge side of the dispersion liquid. Further, the orifice plate 3 is formed with an orifice 5 through which the dispersion liquid passes. The tubular body 2 is arranged so that its inner side surface surrounds the orifice 5. More specifically, the center of the orifice 5 and the center of the cylinder 2 are in a positional relationship that substantially coincides with each other.

When using an orifice plate 3, the diameter _{h a} of the orifice 5 is not particularly limited, is preferably at least 6.0 mm, more preferably at least 7.0 mm, more 8.0mm is more preferable. The upper limit of the diameter h _a is not particularly limited. However, as the diameter h _a increases, the need for capacity for transporting expanded particles becomes high, the equipment cost becomes high.

The thickness of the orifice plate 3 is preferably 0.2 to 10 mm, more preferably 0.5 to 5 mm. If the thickness is less than 0.2 mm, the orifice plate 3 may be damaged due to the pressure at the time of discharge. On the other hand, if the thickness exceeds 10 mm, the expansion ratio of the obtained foamed particles decreases, it becomes difficult to obtain foamed particles having a desired foaming ratio, and the opened portion may be blocked by the resin. ..

Further, the tubular body 2 attached to the orifice plate 3 is integrally attached to the discharge side of the dispersion liquid in the orifice 5. The material of the cylinder 2 is not particularly limited, but generally metal is used. Further, the method of integrating the tubular body 2 and the orifice plate 3 is not particularly limited, and welding, fitting, screwing, bonding, or the like may be used. If necessary, the orifice plate 3 and the cylinder 2 may be manufactured as the same product.

Further, the opening area of the tubular body 2 on the opposite side of the orifice plate 3 can be appropriately set according to the size and length of the tubular body 2, and is generally 1.3 times or more the opening area of the orifice 5. Is. When the opening area of the tubular body 2 is less than 1.3 times the opening area of the orifice 5, the released foamed particles are likely to be aggregated or clogged. If the length of the cylinder 2 is short, the above-mentioned problem does not occur, but the effect of the cylinder 2 is less likely to occur.

The 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 referred to here is a through hole having a shape such as a circular, oval, rectangular or square inner side wall having a semicircle having a diameter added to two opposing sides. Means.

The tubular body 2 is not limited to the circular hole. As shown in FIG. 3, the tubular body 2 may have a slit shape 4. The tubular body 2 of the slit shape 4 referred to here means a through hole having a polygonal shape such as a rectangle, a square, a rhombus, a trapezoid, a parallelogram, another quadrangle, a triangle, a pentagon, or a hexagon.

Further, the shape of the tubular body 2 may be a prism or a columnar shape. In this case, the shape of the opening of the tubular body 2 is a slit shape 4 or a circular shape. Moreover, such a cylindrical body 2 has a width or minor axis _{H a} front (the side to release the dispersion liquid), 0.6 mm or more, preferably 1.2～25Mm, the cylindrical body 2 in the discharge direction The length M is 5 mm or more, preferably 5 to 300 mm. If the width or minor axis H _a slit-shaped 4 or circular front face of the cylindrical body is less than 0.6 mm, a slit or hole is easily clogged. When the length M of the cylinder 2 is less than 5 mm, the scattering locus of the released dispersion liquid is not different from the case where the diaphragm 1 without the cylinder 2 is used. Therefore, the effect of reducing the variation in magnification is weakened. If the length M is longer than 300 mm, the foamed particles may collide with each other inside the tubular body 2 and fuse with each other, making it impossible to obtain the foamed particles.

Further, the shape of the tubular body 2 may be a shape forming a part of a pyramid or a conical shape. In this case, the area of the portion of the tubular body 2 in contact with the orifice plate 3 is close to the opening area of the orifice 5. Then, the opening area of the cylinder 2 at the time when the dispersion liquid is discharged after passing through the cylinder 2 is wide. That is, the shape of the tubular body 2 is such that the opening area surrounded by the side wall of the tubular body 2 increases toward the discharge direction of the dispersion liquid.

Further, the diaphragm 1 with a cylinder may be provided with a cylinder 2 having the same number or less as the number of holes opened in the orifice 5 of the orifice plate 3. When there are a plurality of orifices 5 in the diaphragm 1, the production speed is increased, which is advantageous.

Next, refer to FIGS. 1 to 3 for how to obtain the slit shape 4 of the cylinder body 2 of the diaphragm 1 with a cylinder, the width or minor axis Ha _{a of the front surface of the circular shape, and the length M of the cylinder body 2.} I will explain. The dimension of the cylinder 2 is the inner diameter dimension of the cylinder.

First, the length M is defined as the distance from the portion of the tubular body 2 closest to the orifice plate 3 to the location farthest from the orifice plate 3 in the discharge direction of the dispersion liquid. The width H _a and height, if slit 4 is rectangular, it is long sides and short sides (the same in the case of a square). Also, if the slit 4 is trapezoidal, the dimensions of the larger of the base and height are the width H _a, the size of the smaller is the height. When the slit shape 4 has another shape, the length of the longest line segment among the line segments obtained by cutting an arbitrary straight line passing through the center of gravity of the slit shape 4 by the side of the slit shape 4 is set as the major axis, and the longest. _{Let the} short line segment be the minor axis Ha. Further, the cylindrical body 2 may be elliptical, the long axis and a width H _a or major axis, the minor axis and the height or minor axis H _a.

When two or more cylinders are provided on the diaphragm 1 with a cylinder, the slit shapes 4 or the circular shapes of the plurality of cylinders 2 may all have the same shape or all have different shapes. May be good. Further, a part may have the same shape and a part may have a different shape.

3-3. Collision Step In the present method, the foaming step includes a collision step in which the mixture in the pressure-resistant container is made to collide with a curved surface when the mixture is discharged from a discharge unit (for example, a drawing machine 1). The term "mixture" as used herein means a mixture of polyolefin resin particles impregnated with carbon dioxide gas as a foaming agent and a dispersion liquid. FIG. 1 is a diagram showing a schematic configuration of an example of an effervescent apparatus used in this method. As shown in FIG. 1, in this method, the effervescent apparatus includes a throttler 1 with a cylinder, a discharge pipe 6, a pressure resistant container 7, a valve 8, a low pressure container 13, and a collision plate 14. There is.

The discharge pipe 6 is a pipe that connects the pressure-resistant container 7 and the low-pressure container 13. A valve 8 is provided in the discharge pipe 6. The valve 8 is a valve for switching the opening and closing of the pressure resistant container 7. Further, the diaphragm 1 is arranged at the outlet of the discharge pipe 6. The discharge pipe 6 and the low pressure container 13 communicate with each other via the drawing disc 1. Further, the collision plate 14 is provided in the low pressure container 13 and is arranged so as to face the outlet of the drawing disc 1.

The pressure-resistant container 7 contains a dispersion liquid in which resin particles 9 made of a polyolefin resin are dispersed in an aqueous dispersion medium 10. The dispersion liquid heated and pressurized inside the pressure-resistant container 7 passes through the discharge pipe 6 by opening the valve 8 and is discharged into the low-pressure container 13 from the outlet of the drawing disc 1 to become foamed particles 11. In the collision step, the foamed particles 11 discharged from the outlet of the drawing disc 1 are made to collide with the collision plate 14.

In this method, the collision plate 14 is a member for changing the scattering direction of the foamed particles 11 emitted from the diaphragm 1. Normally, when the temperature becomes lower than the softening temperature of the resin particles 9 during foaming, the resin is cured and foaming is completed. However, it is considered that when the dispersion liquid in which the resin particles 9 are dispersed in the aqueous dispersion medium 10 is made to collide with the collision plate 14 as in this method, the temperature and humidity of the foaming atmosphere become more uniform. 11 Individuals foam uniformly, and the variation in foaming ratio becomes small. Here, in this method, the collision plate 14 has a curved surface 14a. In this method, the dispersion liquid discharged from the diaphragm 1 is made to collide with the curved surface 14a. The curved surface 14a is not particularly limited, but is preferably a concave curved surface recessed in the scattering direction of the dispersion liquid.

In this method, in particular, since the dispersion liquid is made to collide with the curved surface 14a, at least the variation in the foaming ratio can be further reduced when the foamed particles 11 having a low foaming ratio are produced. On the other hand, in the case of producing the foamed particles 11 having a high foaming ratio, it is possible to obtain the foamed particles 11 having at least a uniform cell structure. In general, the higher the expansion ratio of the produced foamed particles, the more non-uniform the cell structure of the produced foamed particles tends to be. The present inventor has found that the cell structure can be made uniform even when the foaming particle to be produced has a high foaming ratio by colliding the dispersion liquid with the curved surface 14a, and has arrived at the present method. The technical idea based on the knowledge of this method cannot be predicted from the conventional knowledge, but has been independently completed by the present inventors.

The "low foaming ratio" here means that the foaming ratio is 10 to 18 times, preferably 12 to 16 times, and the "high foaming ratio" means that the foaming ratio is 18 to 25 times, preferably 18 to 25 times. It means 20 to 22 times.

The radius of curvature of the curved surface 14a of the collision plate 14 is 500 to 1500 mm, preferably 800 to 1200 mm, more preferably 900 to 1100 mm, and even more preferably 1000 mm. When the radius of curvature of the curved surface 14a is less than 500 mm, the fluidity of the foamed particles deteriorates, which is not preferable. If the radius of curvature of the curved surface 14a exceeds 1500 mm, the effect of collision is weakened, which is not preferable.

The size of the collision plate 14 may be a size that allows the foamed particles 11 to collide with each other. Further, the distance L from the discharging portion (the tip of the drawing disc 1) to the collision plate 14 may be any distance as long as the foamed particles 11 can collide with each other. In order to produce the foamed particles 11 having a small variation in the foaming ratio and a uniform cell structure, the distance L is 50 mm ≦ L ≦ 600 mm, preferably 50 mm <D <400 mm, more preferably 50 mm <D <200 mm, and further. It is preferably 50 mm <D <100 mm. When the distance L is 50 mm or more, foaming can be performed without fusing the foamed particles 11 in the gap between the diaphragm 1 and the collision plate 14, which is preferable. Further, although there are differences depending on the heating and pressurizing conditions in the pressure-resistant container, when the distance L is 600 mm or less, the collision effect works sufficiently, and the magnification variation reduction effect and the cell structure homogenization effect become large, which is preferable. If the distance L to the collision plate 14 is too long, the foamed particles 11 will be cooled and difficult to foam by the time they collide, and it will be difficult to obtain a desired foaming ratio. Therefore, the distance L needs to be set according to the foaming atmosphere.

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

The collision angle θ of the foamed particles 11 with respect to the curved surface 14a may be any angle at which the foamed particles 11 can collide. In order to produce the foamed particles 11 having a small variation in the foaming ratio and a uniform cell structure, the collision angle θ is preferably 13 ° or more, more preferably 15 to 25 °, still more preferably 18 to 22 °. Is. As shown in FIG. 1, the collision angle θ referred to here is the tangent G and the axis R of the collision plate 14 in P, where P is the intersection of the axis R of the cylinder in the drawing disc 1 and the collision plate 14. It means the angle between and.

When the collision angle θ is 13 ° or more, the effect of the collision becomes strong and the effect of reducing the variation in the foaming magnification tends to be large, which is preferable. Further, when the collision angle θ is 15 to 25 °, the effect of reducing the variation in the foaming magnification is large, and the cells on the collision surface (curved surface 14a) are less likely to be miniaturized and the cell structure tends to be uniform, which is more preferable.

As described above, in the present method, the diameter _{h a} of the orifice 5 is preferably at least 6.0 mm. Generally, when preparing the foamed particles 11 short foamed to, measures to lot release the foam particles 11 with a larger opening area to increase the diameter h _a is taken. If released thus expanded beads 11 to increase the diameter h _a, the conventional methods (Patent Documents 1 to 3), the present inventors that variations in the expansion ratio is deteriorated is found. The present inventors have discovered that by the impact surface of the expanded particles 11 in the impingement plate 14 and the impingement plate 14, an orifice 5 having a large diameter (diameter h _a is 6.0mm or more) even for a short time foam using, We have independently found that the variation in foaming ratio can be significantly reduced. Therefore, this method is preferably applied in short-time foaming with a large diameter orifice.

The foamed particles from the dispersion liquid containing the polyolefin-based resin particles thus obtained have a foaming ratio of about 2 to 40 times, preferably 3 to 30 times. Further, the foamed particles have a closed cell ratio of about 80 to 100%, preferably 90 to 100%. Further, the foamed particles have an average bubble diameter of about 20 to 500 μm, preferably 100 to 400 μm.

If the foaming ratio is less than 2 times, the flexibility of the obtained molded product becomes insufficient, and if it exceeds 40 times, the mechanical strength, heat resistance, etc. of the obtained molded product become insufficient. Further, when the closed cell ratio is less than 80%, the secondary foaming force is insufficient, so that fusion failure occurs during molding, and the mechanical strength of the obtained molded product is lowered. Further, when the average bubble diameter is less than 20 μm, problems such as distortion of the shape of the obtained molded product occur, and when it exceeds 500 μm, the mechanical strength of the obtained molded product is lowered. Further, when the variation in the foaming ratio is 7% or less, the weight variation of the molded product is reduced and the product yield is improved.

Further, the polyolefin-based resin foamed particles have a closed cell ratio of 80% or more. Therefore, if necessary, the foamed particles are air-impregnated by treating them in a pressure-resistant container under heating and pressurization for a certain period of time, then filled in a molding die and steam-heated to perform foam molding in the heating die. You may manufacture the molded product according to the mold. The foam molded product thus obtained is excellent in flexibility and cushioning property, has a small dimensional shrinkage rate, and has a small shape deformation, so that the commercial value is extremely high.

In the foamed particles having a low foaming ratio of 10 to 18 times, at least the variation in the foaming ratio depends on the foaming conditions and the like, but is usually less than 10%, preferably 7.0% or less. It tends to be preferably 5.0% or less. When producing foamed particles having a low foaming ratio, the production method according to the present embodiment can obtain good foamed particles having a small variation in foaming ratio as compared with the conventional foaming method.

Further, in the foamed particles having a high foaming ratio of 18 to 25 times, at least the uniformity of the cell structure becomes good. More specifically, the cell diameter between the constituent particle cells, in other words, the difference between the minimum average cell diameter and the maximum average cell diameter in one foamed particle (hereinafter, may be simply referred to as a cell diameter difference) is 70 μm or less. Is. The cell diameter difference can be calculated, for example, as follows. First, the foamed particles are cut, and the cut surface is divided into four parts vertically and horizontally. Next, the average cell diameter is calculated for each of the four divided regions. Then, of the four calculated average cell diameters, the maximum value is the maximum average cell diameter, the minimum value is the minimum average cell diameter, and the difference between them is the cell diameter difference. The cell diameter difference is preferably 50 μm or less, and more preferably 30 μm or less. When the difference in cell diameter is 70 μm or less, the appearance of the product as a molded product is improved, which is preferable. The smaller the cell diameter difference, the more preferable.

That is, the polyolefin-based resin foamed particles according to the present embodiment satisfy the following (i) and (ii).

(I) The foaming ratio is 18 to 25 times.
(Ii) Of the four average cell diameters calculated in each of the regions where the cut surface of the foamed particles is divided into four, the difference between the minimum average cell diameter and the maximum average cell diameter is 70 μm or less.

As described above, conventional foamed particles having a relatively high foaming ratio tend to have a non-uniform cell structure. The polyolefin-based resin foamed particles according to the present embodiment are characterized in that the cell structure is uniform despite the high foaming ratio.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims, and the embodiment obtained by appropriately combining the technical means disclosed in each embodiment is also available. It is included in the technical scope of the present invention.

〔summary〕
The method for producing the thermoplastic resin foamed particles according to the first aspect of the present invention includes a dispersion liquid preparation step in which the thermoplastic resin particles (resin particles 9) are dispersed in an aqueous dispersion medium 10 in a pressure resistant container 7 to prepare a dispersion liquid. Using carbon dioxide gas as a foaming agent, the dispersion is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles and pressurized, and then under a lower pressure atmosphere than the internal pressure in the pressure resistant container 7 (low pressure container 13). ), Including a foaming step of foaming by discharging the mixture into the curved surface 14a when the mixture in the pressure resistant container 7 is discharged from the discharging unit (drawing machine 1). Including the process.

In the method for producing thermoplastic resin foamed particles according to the second aspect of the present invention, in the first aspect, 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 the third aspect of the present invention, in the first or second aspect, the collision angle θ of the mixture with respect to the curved surface 14a is 15 to 25 °.

The method for producing thermoplastic resin foamed particles according to the fourth aspect of the present invention is the collision step in any one of the first to third aspects, when the distance from the discharging portion (drawing machine 1) to the curved surface 14a is L. Then, the mixture is made to collide with the curved surface 14a with 50 mm ≦ L ≦ 600 mm.

In the method for producing thermoplastic resin foamed particles according to the fifth aspect of the present invention, in any one of the first to fourth aspects, the discharging unit (squeezing machine 1) includes an orifice 5 from which the mixture is discharged. diameter _{h a} of the orifice 5 is more than 6mm.

In the method for producing thermoplastic resin foamed particles according to the sixth aspect of the present invention, the foaming ratio of the foamed particles to be produced is 10 to 25 times in any one of the first to fifth aspects.

The thermoplastic resin foamed particles according to the seventh aspect of the present invention have a foaming ratio of 18 to 25 times, and the difference in cell diameter between the constituent particle cells is 70 μm or less.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention should not be construed as being limited to these Examples.

<Measurement of variation in foaming magnification of foamed particles>
1 kg of polyolefin resin foamed particles were added to a JIS Z8801 standard sieve (nominal dimensions 1, 1.18, 1.4, 1.7, 2, 2.36, 2.8, 3.35, 4, 4.75, It was sieved with 11 kinds of sieves of 5.6). The weight fraction Wi and the expansion ratio Ki of the polyolefin-based resin foam particles remaining on each sieve are measured, and the average expansion ratio Kav is calculated from the following formula (1).

次に重量分率Ｗｉ、発泡倍率Ｋｉおよび平均発泡倍率Ｋａｖを用いて式（２）

から発泡倍率の標準偏差δｍを計算し、式（３）

から倍率バラツキＲ（％）を求めた。なお、発泡倍率のバラツキは、１０％未満を合格レベルとした。

Next, the formula (2) is used using the weight fraction Wi, the foaming ratio Ki, and the average foaming ratio Kav.

Calculate the standard deviation δm of the foaming magnification from Eq. (3).

The magnification variation R (%) was obtained from. The variation in foaming ratio was set to less than 10% as the pass level.

The expansion ratio Ki of the polyolefin-based resin foam particles remaining on each sieve was determined as follows. First, the weight Gi of the polyolefin-based resin foam particles remaining on each sieve was accurately weighed to 0.001 g (rounded to the fourth decimal place). Next, from the scale raised when the weighed polyolefin-based resin foam particles having a known weight were submerged in water in a measuring cylinder containing 100 ml of water at 23 ° C., the volume of the polyolefin-based resin foam particles yi (cm ^3). ) Was read. Then, the weight Gi (g) of the polyolefin-based resin foamed particles ^{is divided by the volume y (cm 3} ) of the polyolefin-based resin foamed particles, and this is converted into g / L units to obtain the polyolefin-based resin foamed particles of each sieve. The apparent density di was obtained. Finally, the foaming ratio Ki = ds / di was determined from the ratio with the density ds (= 900 g / L) of the base resin.

<Evaluation of cell structure uniformity of foamed particles>
The foamed particles were cut almost in the center, being careful not to break the bubble film. With respect to the cut surface, the regions divided into four in the vertical and horizontal directions were observed with a microscope, and the average cell diameter in each region was calculated. For the average cell diameter, a line segment corresponding to a length of 1000 μm was drawn, and the number of bubbles n through which the line segment passed was measured. Then, the bubble diameter was calculated at 1000 / n (μm) from the number of bubbles n. The average cell diameter was calculated for each of the 30 foamed particles.

The minimum average cell diameter and the maximum average cell diameter were calculated for each of the 30 foamed particles. Then, based on the calculated difference between the minimum average cell diameter and the maximum average cell diameter (cell diameter difference), the cell structure uniformity was evaluated as follows. This evaluation was performed based on the average value of the cell diameters among the 30 foamed particles.

The difference between the minimum average cell diameter and the maximum average cell diameter is 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)
[Manufacturing of resin particles]
26 mmφ biaxial extrusion of ethylene-propylene random copolymer (density 0.90 g / cm ³ , ethylene content 3%, melting point 145 ° C, MI = 7.5 g / 10 minutes, flexural modulus 1000 MPa), which is a polyolefin resin. It was supplied to a machine [TEM26-SX manufactured by Toshiba Machine Co., Ltd.] and melt-kneaded. Then, it was extruded from a cylindrical die having a diameter of 1.2 mmφ, cooled with water, and cut with a cutter to obtain resin composition particles (pellets) (1.2 mg / grain) made of a columnar polyolefin resin. The melting point of the obtained resin particles was 145 ° C., and the density was 0.90 g / cm ³ measured by JIS K7112.

[Manufacturing of foamed particles]
100 parts by weight of the obtained resin particles, 0.5 part by weight of tertiary calcium phosphate [manufactured by Taihei Kagaku Sangyo Co., Ltd.] as a dispersant, and sodium alkylsulfonate (n-paraffin sulfonic acid soda) as a dispersion aid [Kao Co., Ltd. ), 0.03 part by weight of Latemul PS] was charged into the pressure-resistant container 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 charged, and the aqueous dispersion was heated to 151 ° C. while stirring in the pressure-resistant container 7. The pressure in the pressure-resistant container 7 at this time was about 1.7 MPa. Then, carbon dioxide gas was additionally press-fitted to increase the pressure to 2.2 MPa. After holding at the foaming temperature and foaming pressure for 20 minutes, the valve 8 at the bottom of the pressure-resistant container 7 is opened to discharge the aqueous dispersion liquid from the one-hole drawing machine 1 having an orifice 5 having _{a diameter ha of 8 mm to the low-pressure container 13.} did. Then, in the low-pressure container 13, the aqueous dispersion was made to collide with the curved surface 14a having a radius of curvature of 1000 mm to obtain polyolefin-based resin foam particles (collision step). In this collision step, the distance L between the diaphragm 1 and the collision plate 14 was set to 150 mm, and the collision angle θ was set to 18 °. Further, in Example 1, the target foaming ratio of the produced foamed particles was set to 14 times.

With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 2)
Effervescent particles were obtained in the same manner as in Example 1 except that the distance L between the diaphragm 1 and the collision plate 14 was set to 50 mm. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 3)
Effervescent particles were obtained in the same manner as in Example 1 except that the distance L between the diaphragm 1 and the collision plate 14 was set to 300 mm. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 4)
Foamed particles were obtained in the same manner as in Example 1 except that the distance L between the diaphragm 1 and the collision plate 14 was set to 600 mm and the target foaming magnification was set to 13 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 5)
Foamed particles were obtained in the same manner as in Example 1 except that the collision angle θ was set to 15 ° and the target foaming magnification was set to 13 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 6)
Effervescent particles were obtained in the same manner as in Example 1 except that the collision angle θ was set to 25 °. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 7)
Effervescent particles were obtained in the same manner as in Example 1 except that the target foaming ratio was set to 9 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 8)
Effervescent particles were obtained in the same manner as in Example 1 except that the target foaming ratio was set to 20 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 9)
Effervescent particles were obtained in the same manner as in Example 1 except that the distance L between the diaphragm 1 and the collision plate 14 was set to 5 mm. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 10)
Foamed particles were obtained in the same manner as in Example 1 except that the distance L between the drawing machine 1 and the collision plate 14 was set to 700 mm and the target foaming magnification was set to 13 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 11)
Foamed particles were obtained in the same manner as in Example 1 except that the collision angle θ was set to 13 ° and the target foaming magnification was set to 12 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Example 12)
Foamed particles were obtained in the same manner as in Example 1 except that the collision angle θ was set to 30 ° and the target foaming magnification was set to 14 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Comparative Example 1)
The aqueous dispersion was made to collide with a flat plate-shaped collision plate instead of the curved surface 14a, the collision angle θ was set to 20 °, the distance L between the diaphragm 1 and the collision plate 14 was set to 300 mm, and the target foaming. Foamed particles were obtained in the same manner as in Example 1 except that the magnification was set to 12 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

(Comparative Example 2)
Effervescent particles were obtained in the same manner as in Comparative Example 1 except that the target foaming ratio was set to 20 times. With respect to the obtained foamed particles, the variation in the foaming magnification was measured and the uniformity of the cell structure was evaluated.

Table 1 shows the evaluation results of the variation in the expansion ratio and the uniformity of the cell structure of the foamed particles of Examples 1 to 12 and Comparative Examples 1 and 2.

表１の結果から、実施例１〜１２の発泡粒子は、発泡倍率のバラツキが１０％以下であり、バラツキが良好であった。一方、比較例１の発泡粒子は、発泡倍率のバラツキが１０％を超え、バラツキが良好ではなかった。それゆえ、実施例１〜１２の発泡粒子は、比較例１の発泡粒子よりも発泡倍率のバラツキが低減されていることが分かった。また、実施例１〜７、９〜１２と比較例１との比較から、目標発泡倍率が１２〜１４倍程度の低発泡倍率で発泡粒子を製造した場合、曲面１４ａを有する衝突板１４を用いることにより、少なくとも発泡倍率のバラツキを低減できることが分かった。また、衝突角度については、衝突面が曲面であり、且つ衝突角度が１３°以上である場合、発泡倍率のバラツキが７％以下となり良好であることがわかった。

From the results in Table 1, the foamed particles of Examples 1 to 12 had a variation in the expansion ratio of 10% or less, and the variation was good. On the other hand, in the foamed particles of Comparative Example 1, the variation in the expansion ratio exceeded 10%, and the variation was not good. Therefore, it was found that the foamed particles of Examples 1 to 12 had a smaller variation in the foaming ratio than the foamed particles of Comparative Example 1. Further, from the comparison between Examples 1 to 7 and 9 to 12 and Comparative Example 1, when the foamed particles are produced at a low foaming ratio having a target foaming ratio of about 12 to 14 times, the collision plate 14 having the curved surface 14a is used. As a result, it was found that at least the variation in the foaming ratio can be reduced. Regarding the collision angle, it was found that when the collision surface is a curved surface and the collision angle is 13 ° or more, the variation in the foaming magnification is 7% or less, which is good.

Further, in Example 8, the foamed particles are produced at a high foaming ratio of about 20 times as the target foaming ratio. The produced foamed particles had (i) a foaming ratio of 20 times and (ii) an evaluation of cell structure uniformity of 4. That is, (ii) the difference between the minimum average cell diameter and the maximum average cell diameter was 70 μm or less.

On the other hand, in Comparative Example 2, when the foamed particles were produced at a high foaming ratio of about 20 times, the evaluation of the uniformity of the cell structure was 2. That is, the difference between the minimum average cell diameter and the maximum average cell diameter exceeded 70 μm.

From the comparison results between Example 8 and Comparative Example 2, when the foamed particles were produced at a high foaming ratio of about 20 times, the cell structure was at least uniform by using the collision plate 14 having the curved surface 14a. It was found that foamed particles could be obtained.

Further, from the comparison between Examples 1 to 4 and Examples 9 and 10, when the distance L between the diaphragm 1 and the collision plate 14 is 50 to 600 mm, the variation in the foaming ratio is further reduced and the cell structure is further reduced. Was also found to be uniform. Further, from the comparison between Examples 1, 5 and 6 and Examples 11 and 12, when the collision angle θ is 15 ° to 25 °, the variation in the foaming magnification is 5% or less, and the variation is very small. Moreover, it was found that the evaluation of the uniformity of the cell structure was 4 or more, and the cell structure was also uniform.

INDUSTRIAL APPLICABILITY The present invention can be suitably used for, for example, foamed particles used in the manufacture of cushioning packaging materials, physical distribution materials, heat insulating materials, civil engineering and building materials, automobile members, and the like.

1 Aperture board (release part)
2 Cylinder 3 Orifice plate 4 Slit shape 5 Orifice 6 Discharge pipe 7 Pressure-resistant container 8 Valve 9 Resin particles 10 Aqueous dispersion medium 11 Foam particles 14 Collision plate 14a Curved surface 13 Low-pressure container

Claims (7)

A dispersion preparation step in which thermoplastic resin particles are dispersed in an aqueous dispersion medium in a pressure-resistant container to prepare a dispersion, and a dispersion preparation step.
Using carbon dioxide as a foaming agent, the dispersion is heated to a temperature equal to or higher than the softening temperature of the thermoplastic resin particles, pressurized, and then foamed by being discharged under a lower pressure atmosphere than the internal pressure in the pressure-resistant container. Including the foaming process and
The foaming step is a method for producing thermoplastic resin foamed particles, which comprises a collision step of causing the mixture to collide with a curved surface when the mixture in the pressure-resistant container is discharged from a discharging portion. The method for producing thermoplastic resin foamed particles according to claim 1, wherein the collision angle of the mixture with respect to the curved surface is 13 ° or more. The method for producing thermoplastic resin foamed particles according to claim 1 or 2, wherein the collision angle of the mixture with respect to the curved surface is 15 ° to 25 °. When the distance from the emission part to the curved surface is L,
The method for producing thermoplastic resin foamed particles according to any one of claims 1 to 3, wherein in the collision step, the mixture is made to collide with the curved surface at 50 mm ≦ L ≦ 600 mm. The discharge section comprises an orifice in which the mixture is discharged.
The method for producing thermoplastic resin foamed particles according to any one of claims 1 to 4, wherein the orifice has a diameter of 6 mm or more. The method for producing thermoplastic resin foamed particles according to any one of claims 1 to 5, wherein the foamed particles to be produced have a foaming ratio of 10 to 25 times. The foaming ratio is 18 to 25 times,
Thermoplastic resin foamed particles having a difference in cell diameter of 70 μm or less between the constituent particle cells.

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