Channel forming device, extrusion device, plastic sheet, foam sheet, plastic sheet manufacturing method, and foam sheet manufacturing method

Abstract

To provide a flow channel forming apparatus capable of improving the appearance of a molded article while obtaining a high expansion ratio.SOLUTION: The parallelism between the outer circumferential surface of the inner member and the inner circumferential surface of the outer member in the first section X1 having a length of 10 mm or more and 60 mm or less from the discharge port 40 serving as the flow path outlet along the extrusion central axis O1 is set to 1 mm or less and the parallelism with the extrusion central axis O1 of the other is set to 4.5 mm or more. Further, the narrowest portion where the gap between the outer peripheral surface of the inner member and the inner peripheral surface of the outer member is narrowest is provided in the range of O1 or less along the extrusion 1mm line upstream in the flow direction from the discharge port 40, and the second section X1 from the downstream end portion in the flow direction of the first section X2 to the discharge port 40 has the diameter-increasing region where the flow path is diameter-increased toward the discharge port 40, and the length Y1 along the direction orthogonal to the extrusion X1 line from the downstream end portion in the flow direction of the first section 10mm to the discharge port is equal to or less than the center line.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a flow path forming device, an extrusion device, a plastic sheet, a foamed sheet, a method for manufacturing a plastic sheet, and a method for manufacturing a foamed sheet. [Background technology]

[0002] Conventionally, a flow path forming device has been known which has an outer member having a through hole and an inner member which is placed in the through hole with a gap relative to the inner surface of the through hole, and in which the inner surface of the outer member and the outer surface of the inner member form a flow path whose cross-sectional shape is annular and perpendicular to the central extrusion axis. Conventionally, a flow path forming device has been known which has an outer member having a through hole and an inner member which is placed in the through hole with a gap at the inner peripheral surface of the through hole, and in which the inner peripheral surface of the outer member and the outer peripheral surface of the inner member form a flow path whose cross-sectional shape is annular and perpendicular to the central extrusion axis.

[0003] Patent Document 1 describes the flow path forming device as being attached to an extrusion device, which extrudes a molten plastic composition containing polylactic acid and carbon dioxide from the outlet of a flow path to form a foamed plastic sheet. Summary of the Invention [Problem to be solved by the invention]

[0004] However, there was a problem in achieving both a high expansion ratio and good appearance of the molded product. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a flow path forming device that includes an outer member having a through hole, and an inner member that is disposed in the through hole with a gap between it and the inner peripheral surface of the through hole, and that forms a flow path having an annular cross section perpendicular to an extrusion central axis by the inner peripheral surface of the outer member and the outer peripheral surface of the inner member, wherein, in a cross section that passes through the extrusion central axis and is parallel to the extrusion central axis, the outer peripheral surface of the inner member and the inner peripheral surface of the outer member are spaced apart from each other in a first section of the flow path that is 10 mm to 60 mm along the extrusion central axis upstream in a flow direction of a fluid flowing through the flow path from a flow path outlet. the parallelism with the extrusion central axis of one of the inner and outer members is 1 mm or less and the parallelism with the extrusion central axis of the other is 4.5 mm or more; the narrowest gap between the outer peripheral surface of the inner member and the inner peripheral surface of the outer member is located within a range of 1 mm or less upstream from the flow path outlet along the extrusion central axis in the flow direction; the second section of the flow path from the downstream end of the first section in the flow direction to the flow path outlet has a diameter that increases toward the flow path outlet, and the distance from the downstream end of the first section in the flow direction to the flow path outlet along the direction perpendicular to the extrusion central axis is 10 mm or less. [Effects of the Invention]

[0006] According to the present invention, it is possible to obtain a high expansion ratio and to improve the appearance of the molded article. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic diagram of an extrusion device to which the flow path forming device of the present embodiment is attached. [Figure 2] FIG. 2 is a cross-sectional view parallel to the extrusion central axis of the flow path forming device of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an extrusion device 110 to which a flow path forming device 5 of this embodiment is attached. The extrusion device 110 includes a first extruder 110a that performs a kneading process and a second extruder 110b that performs a foaming process. A flow path forming device 5 is attached to the downstream end of the second extruder 110b in the direction of movement of the plastic composition. The extrusion device 110 may further include devices that perform other processes.

[0009] The extrusion device 110 has a raw material mixing / melting area a, a compressible fluid supply area b, a kneading area c, and an extrusion area d. Each area is an example and can be set appropriately depending on the purpose. A static mixer, a filter, and other components may be added as appropriate.

[0010] In the raw material mixing / melting area a of the first extruder 110a, which performs the kneading process, the raw materials that make up the plastic composition are supplied by the metering feeders 1 and 2, heated, and melted. The number and order of the raw materials supplied by the metering feeders 1 and 2 can be freely changed.

[0011] The plastic composition is a material that constitutes a foamed plastic sheet (hereinafter simply referred to as a foamed sheet) formed using the flow path forming device 5. The plastic composition contains at least one type of plastic resin, preferably a filler (also referred to as a foam nucleus material) and a foaming agent, and may further contain other components as needed. Examples of other components include a crosslinking agent, a heat stabilizer, an antioxidant, a plasticizer, and a lubricant.

[0012] The plastic resin, which is one of the materials constituting the plastic composition, is not particularly limited and can be appropriately selected depending on the purpose. Examples of plastic resins include styrene-based homopolymers such as polystyrene and poly-p-methylstyrene; styrene-based copolymers such as styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-acrylonitrile-butadiene copolymer, styrene-acrylic acid copolymer, and styrene-methacrylic acid copolymer; styrene-based resins such as a mixture of polystyrene and polyphenylene oxide; and aliphatic polyester resins such as polylactic acid, polyglycolic acid, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-3-hydroxyvalerate), polycaprolactone, polybutylene succinate, and poly(butylene succinate-adipate). These may be used alone or in combination. The aliphatic polyester resin may be synthesized using an alcohol component or a derivative thereof and an acid component or a derivative thereof, or may be a commercially available product.

[0013] Among these, aliphatic polyester resins, which are polymeric materials with low environmental impact, are preferred, and polylactic acid, which is a carbon-neutral material and relatively inexpensive, is more preferred. Polylactic acid is also preferred because it has properties similar to conventionally used polystyrene resins and has a relatively higher melting point, toughness, chemical resistance, etc. than other biodegradable plastics.

[0014] Examples of polylactic acid include copolymers of D-lactic acid and L-lactic acid, homopolymers of either D-lactic acid (D-form) or L-lactic acid (L-form), and ring-opening polymers of at least one lactide selected from the group consisting of D-lactide (D-form), L-lactide (L-form), and DL-lactide. These may be used alone or in combination of two or more. The polylactic acid may be appropriately synthesized or commercially available.

[0015] The D-to-L ratio of lactic acid constituting the polylactic acid is not particularly limited, but it is preferable that either the D- or L-form of lactic acid constituting the polylactic acid accounts for 95 mol % or more of the polylactic acid. Polylactic acid consisting of only one of the D- or L-form optical isomers may also be used. Polylactic acid within this range has high crystallinity, and foamed sheets produced using such polylactic acid are expected to have good heat resistance and are suitable for food applications.

[0016] The content of the plastic resin in the plastic composition is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 90% by mass or more based on the total amount of the plastic composition. The method for measuring the plastic resin content is not particularly limited and can be selected appropriately depending on the purpose. For example, it can be measured by determining the weight percentage of the resin component from the ash content determined in accordance with JIS K7250-1.

[0017] The filler (hereinafter sometimes referred to as "foam nucleus material") is contained for the purposes of adjusting the foaming state (bubble size, amount, arrangement, etc.) of the plastic composition, reducing costs, and improving strength. The filler is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include inorganic fillers, organic fillers, etc. These may be used alone or in combination of two or more.

[0018] Examples of inorganic fillers include talc, kaolin, calcium carbonate, silicate minerals, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fibers, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, glass fibers, and carbon fibers. Among these, silicate minerals are preferred from the viewpoints of performance and cost. Alternatively, silica or fillers surface-treated with silica are also preferred because of their affinity with the compressible fluid described below.

[0019] Examples of organic fillers include naturally occurring polymers such as starch, cellulose, wood flour, soybean pulp, rice husks, and bran, sorbitol compounds, benzoic acid, metal phosphate ester salts, and rosin compounds. Among these, cellulose is preferred from the viewpoint of low environmental impact.

[0020] The blowing agent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the blowing agent include physical blowing agents such as hydrocarbons such as lower alkanes such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, ethers such as dimethyl ether, halogenated hydrocarbons such as methyl chloride and ethyl chloride, and compressible gases such as carbon dioxide and nitrogen (hereinafter sometimes referred to as "compressible fluids"). Among these, compressible gases such as carbon dioxide and nitrogen are preferred because they are odorless, safe to handle, and have a low environmental impact. By including a foaming agent, a foamed sheet with a high expansion ratio can be obtained.

[0021] In the raw material mixing and melting area a, the master batch (an intermediate resin composition containing at least a plastic resin and a crosslinking agent), filler, and other ingredients (such as the heat stabilizer, antioxidant, plasticizer, lubricant, etc. mentioned above) are supplied by the metering feeders 1 and 2.

[0022] In the compressible fluid supply area b, a compressible fluid is supplied to the molten plastic resin by a metering pump 3 as a compressible fluid supply unit, thereby plasticizing the molten plastic resin.

[0023] Carbon dioxide is a preferred compressive fluid. By impregnating molten plastic resin with the compressive fluid, it is possible to knead the plastic well even in a high-viscosity state. This allows the filler (foam nucleus material) to be uniformly dispersed in the plastic resin, resulting in the production of a foamed sheet with uniform and fine bubbles.

[0024] In this embodiment, the compressible fluid supplied in the compressible fluid supply area b is used as a foaming agent. By using the compressible fluid supplied in the compressible fluid supply area b as a foaming agent, kneading and foaming can be carried out in a single process, which is preferable as a manufacturing method from the viewpoint of reducing the environmental load.

[0025] In the kneading area c, the raw materials supplied in the raw material mixing / melting area a are kneaded at a temperature lower than the melting temperature of the plastic resin to obtain a plastic composition.

[0026] The plastic composition obtained by mixing in the mixing area c of the first extruder 110a is supplied to the extrusion area d of the second extruder 110b. In this extrusion area d, the plastic composition supplied from the first extruder 110a is further mixed. The set temperature of the extrusion area d is preferably set so that the temperature of the plastic composition when extruded from the flow path outlet of the flow path forming device 5 is lower than the melting point of the plastic composition.

[0027] By setting the temperature of the plastic composition when it is extruded from the flow path outlet of the flow path forming device 5 to a temperature lower than the melting point of the plastic composition, the viscosity of the plastic composition can be increased, thereby producing a foamed sheet with a high expansion ratio.

[0028] The plastic composition further kneaded in extrusion area d of the second extruder 110b is extruded into the flow path forming device 5. The plastic composition extruded into the flow path forming device 5 by the second extruder 110b passes through the flow path of the flow path forming device 5 and is foamed at the outlet of the flow path, thereby extruding a cylindrical foam sheet 4. The extruded foam sheet 4 is wound around a mandrel.

[0029] It is not necessary to adopt a take-up method in which the foam sheet is taken up at a speed faster than the extrusion speed. In this embodiment, the extruded foam sheet is stretched using a mandrel, but the stretching method and timing of the foam sheet are not limited. The extruded tubular foam sheet 4 may be cut open to form a flat sheet before being taken up, or the tubular foam sheet 4 may be cut open after being taken up to form a flat sheet.

[0030] The extrusion-molded foam sheet may be used as it is, or may be molded into a molded body (product) and used. The foam sheet made of the above-described plastic composition is excellent in moldability, heat resistance, heat insulation, and biodegradability, and is therefore suitable for use as a food container, tableware, etc. It is also suitable as a heat-resistant food container, but is not limited to such an application. The foam sheet may also be used as it is after printing, etc.

[0031] Examples of molded products (also referred to as manufactured goods, consumer goods, etc.) made from foam sheets include household goods such as containers, bags, packaging containers, trays, tableware, cutlery, stationery, and cushioning materials. The concept of molded products includes rolls of foam sheets that serve as intermediates for processing molded products. The concept of molded products also includes not only single molded products but also products made up of a combination of parts consisting of multiple molded products. An example of a product made up of a combination of parts consisting of multiple molded products is a combination of a handle made by molding a foam sheet and a tray made by molding a foam sheet.

[0032] The shape of the container formed from the foam sheet can be selected without any particular limitation. Examples include lidless containers such as trays, and containers whose openings are closed with shrink film, top seals, snap-on lids, etc. In addition, lids for containers whose openings are closed with snap-on lids, etc., can also be molded from the foam sheet. Examples of container lids obtained by molding the foam sheet include, but are not limited to, lids for beverage cups, lids for side dish containers, lids for soup containers, and lids for lunch boxes.

[0033] The material of the beverage cup to be covered by the molded lid is not particularly limited and may be paper, plastic, a composite material thereof, etc. Furthermore, examples of the beverage cup lid as a molded body include a lift-up lid, a drinking lid, a flat lid with a U-shaped notch, a flat lid with an X-shaped notch, a dome-shaped lid, etc., and the shape of the beverage cup lid as a molded body is not particularly limited.

[0034] Examples of bags obtained by molding the foam sheet include plastic shopping bags, shopping bags, garbage bags, etc. Examples of stationery obtained by molding the foam sheet include clear files, badges, etc.

[0035] Furthermore, the molded articles obtained by molding the foamed sheet can be used for purposes other than daily necessities, such as industrial materials, daily necessities, agricultural products, sheets for food, medicines, cosmetics, etc., and packaging materials.

[0036] The extrusion-molded foam sheet may be subjected to processing such as lamination or coating, as needed. The processing may be performed before or after winding of the foam sheet during production. The type of laminating film or coating agent and the processing method may be selected without particular limitation.

[0037] The molding method for the extrusion-molded foam sheet is not particularly limited and may be appropriately selected depending on the shape of the molded product to be obtained. When a molded product is obtained from a foam sheet by a thermoforming method, it is preferable to include a heating step and a thermoforming step. The thermoforming method may also include other steps, such as a demolding step of removing the molded product from the mold after the thermoforming step, a step of punching the molded product from the foam sheet before the heating step, and a step of cutting off excess parts such as burrs from the molded product removed from the mold.

[0038] The apparatus for producing a molded product in which the method for molding an extrusion-molded foamed sheet is carried out is not particularly limited and can be appropriately selected depending on the shape of the desired molded product, etc. The apparatus for producing a molded product from a foamed sheet by the thermoforming method has a heating means, a heat-molding means, and other means.

[0039] The heating step is a step of heating and softening the foamed sheet before molding it. The method of heating the foamed sheet in the heating step is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a method of heating the foamed sheet by arranging heating means above and below the foamed sheet or on either the upper or lower surface of the foamed sheet. The heating means is not particularly limited and can be appropriately selected from known heating elements depending on the purpose, and examples thereof include an electric heater, a heating plate, and an IR (infrared) heater.

[0040] When polylactic acid is used as the plastic resin, it is preferable to not promote crystallization of polylactic acid in the heating step but to promote crystallization of polylactic acid in the subsequent heat molding step in terms of improving heat resistance. Therefore, when polylactic acid is used as the plastic resin, the heating step is preferably a method that can heat the foamed sheet in a short time, and a heating method using IR (infrared) heaters placed above and below the foamed sheet is particularly preferable.

[0041] The heating temperature of the foamed sheet in the heating step is not particularly limited and can be appropriately selected depending on the purpose. When polylactic acid is used as the plastic resin, the heating temperature is preferably a temperature equal to or higher than the glass transition temperature of polylactic acid. Specifically, heating is more preferably performed at a temperature of 60°C or higher, and even more preferably at a temperature of 80°C or higher. Furthermore, if the foamed sheet is heated near the cold crystallization temperature of polylactic acid, crystallization will progress during the heating step. Therefore, the heating temperature of the foamed sheet in the heating step is preferably at most 110°C or lower, more preferably 100°C or lower.

[0042] The heating temperature means the temperature of the foamed sheet itself. The heating time of the foamed sheet in the heating step is not particularly limited and can be appropriately selected depending on the purpose. When polylactic acid is used as the plastic resin, the heating time is preferably within 15 seconds, more preferably within 10 seconds, and even more preferably within 5 seconds, from the viewpoint of preventing excessive crystallization.

[0043] The heat molding step is a step of molding the foamed sheet softened by the heating step using a mold, preferably a metal die, into the shape of a desired molded product. The molding method using a mold is not particularly limited, and any conventionally known thermoforming method for thermoplastic resins can be used, such as vacuum molding, pressure molding, vacuum-pressure molding, and matched mold molding.

[0044] When polylactic acid is used as the plastic resin, the matched mold molding method is particularly preferred from the viewpoint of promoting crystallization of the polylactic acid resin of the foam sheet during the molding process and improving heat resistance.

[0045] The mold temperature in the heat molding step is not particularly limited and can be appropriately selected depending on the purpose. When polylactic acid is used as the plastic resin, the heat molding step is preferably performed at a temperature close to the cold crystallization temperature of polylactic acid so that the crystallization of polylactic acid in the foamed sheet proceeds.

[0046] Here, "near the cold crystallization temperature of polylactic acid" means a temperature 20°C or lower than the cold crystallization temperature of polylactic acid. Specifically, the mold temperature in the heat molding step is preferably 100°C or higher and 120°C or lower, and more preferably 100°C or higher and 110°C or lower. By maintaining the mold temperature in the heat molding step at a temperature near the cold crystallization temperature of polylactic acid, a molded product with excellent heat resistance can be obtained.

[0047] The heat molding time in the heat molding step is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable to ensure a time sufficient for the foamed sheet to crystallize. When polylactic acid is used as the plastic resin, the heat molding time is more preferably 5 seconds or more, and even more preferably 7 seconds or more. When polylactic acid is used as the plastic resin, the heat molding time is preferably 10 seconds or less from the viewpoint of heat resistance.

[0048] Next, the flow path forming device 5, which is a characteristic feature of this embodiment, will be described. FIG. 2 is a cross-sectional view parallel to the extrusion central axis O1 of the flow path forming device 5 of this embodiment. The flow path forming device 5 has an outer member 10 having a through hole, and an inner member 20 disposed in the through hole with a gap between it and the inner peripheral surface 11 of the through hole. The inner peripheral surface 11 of the through hole of the outer member 10 and the outer peripheral surface 21 of the inner member 20 form a flow path 30 having an annular cross section perpendicular to the extrusion central axis O1.

[0049] In this embodiment, the gap between the inner circumferential surface of the through hole of the outer member and the outer circumferential surface of the inner member is narrowest in the discharge region up to a distance of 1 mm along the extrusion central axis O1 (X direction in the figure) from the discharge port 40, which is the flow path outlet from which the plastic composition of the flow path 30 is extruded. This narrows the cross-sectional area of ​​the flow path in the discharge region, allowing effective pressure to continue to be applied to the plastic composition until the plastic composition is discharged from the discharge port 40 (extrusion is completed), and suppresses foaming of the foaming agent in the flow path. This allows the foaming agent to foam after being discharged from the discharge port 40, resulting in a high expansion ratio.

[0050] In order to withdraw the foamed sheet without causing wrinkles or poor appearance, the opening angle 2θ of the discharge port 40 is preferably 90° or more and 180° or less, and particularly preferably 120° or more and 160° or less. The opening angle 2θ of the discharge port 40 is twice the angle θ between the direction of advance of the plastic composition at the discharge port 40 (discharge direction, see the arrow in FIG. 2 ) and the extrusion central axis O1. The direction of advance of the plastic composition at the discharge port 40 is parallel to the center line of the cross-sectional curve formed by the outer peripheral surface 21b of the inner member and the inner peripheral surface 11b of the through hole in the outer member at the discharge port 40, and faces downstream in the flow direction, in the cross section shown in FIG. 2 . This allows the extrusion-molded foamed sheet to be stretched efficiently, and allows the foamed sheet to be handled well after extrusion, allowing the foamed sheet to be withdrawn (wound up) while suppressing the occurrence of wrinkles and poor appearance.

[0051] In this embodiment, in a second section X2 from the discharge outlet 40 to a position 10 mm away in the X direction in the figure, the flow path 30 is shaped so that it moves away from the extrusion central axis O1 as it approaches the discharge outlet 40, so that the opening angle 2θ is 90° to 180°, and the annular flow path 30 is shaped so that it expands in diameter as it approaches the discharge outlet.

[0052] In the second section X2, in the cross section shown in FIG. 2, when the flow path shape was such that it moved away from the extrusion central axis O1 toward the discharge outlet 40 and the cross-sectional area of ​​the flow path in the discharge region up to a distance of 1 mm from the discharge outlet 40 along the extrusion central axis O1 (X direction in the figure) was narrowed, the appearance of the extruded foam sheet was poor.

[0053] The inside of the flow channel forming device 5 is difficult to observe, and the flow of the plastic composition within the flow channel 30 is a black box. However, based on speculation, it is believed that the following factors disrupted the flow of the plastic composition within the flow channel, resulting in poor appearance. Specifically, the flow channel shape in the second section X2, which moves away from the extrusion central axis O1 toward the discharge port 40, causes the plastic resin within the flow channel 30 to deform and undergo self-shearing. Furthermore, as described above, in order to achieve a high expansion ratio, narrowing the cross-sectional area of ​​the discharge region from the discharge port 40 to a distance of 1 mm along the extrusion central axis O1 (X direction in the figure) allows the plastic composition to be discharged from the discharge port 40 at a high shear and high linear velocity, subjecting the plastic composition to significant stress. The stress exerted on the plastic composition in the second section X2 and the discharge region disrupts the flow of the plastic composition as it is discharged from the discharge port 40, potentially resulting in poor appearance of the extrusion-molded foam sheet.

[0054] Therefore, in this embodiment, the appearance of the foamed sheet is suppressed by the following configuration: That is, a configuration is adopted in which stress is applied in advance to the plastic composition in the flow channel 30 in a first section X1 that is a distance of 10 mm or more and 60 mm or less along the extrusion central axis O1 from the discharge port 40, which is a flow channel outlet through which the plastic composition is extruded in the flow channel 30.

[0055] 2, the parallelism of the outer peripheral surface 21a of the inner member 20 to the extrusion central axis O1 in the first section X1 is set to 1 mm or less, and the parallelism of the inner peripheral surface 11a of the through hole of the outer member 10 to the extrusion central axis O1 is set to 4.5 mm or more. The parallelism of the outer peripheral surface 21a of the inner member 20 to the extrusion central axis O1 in this first section X1 is set to 1 mm or less to prevent unnecessary stress from being applied to the plastic composition in the flow path. On the other hand, the parallelism of the inner peripheral surface 11a of the through hole of the outer member in this first section X1 to the extrusion central axis O1 is set to 4.5 mm or more to apply appropriate stress to the plastic composition in the flow path passing through this first section X1.

[0056] In this way, by applying stress to the plastic composition in the flow path in advance in the first section X1, the shock at the outlet 40 is dispersed over time, suppressing disturbance of the flow of the plastic composition when it is discharged from the outlet 40 and suppressing deterioration of the appearance.

[0057] The parallelism to the extrusion central axis O1 is the difference between the longest and shortest distances along the direction perpendicular to the extrusion central axis O1 in the first section X1 relative to the extrusion central axis O1.

[0058] The parallelism of the outer peripheral surface 21a of the inner member 20 in the first section X1 can be found by using a three-dimensional measuring device to measure the outline of the outer peripheral surface 21a of the inner member 20 in the first section X1 and the central axis of the inner member 20 as the extrusion central axis O1. Here, if the central axis of the inner member 20 can be defined in the first section X1, it is done in the first section X1, but if this is not possible, several circles are defined on the outer peripheral surface 21b of the second section X2 as a substitute, and the straight line passing through the centers of those circles is taken as the extrusion central axis O1.

[0059] The parallelism of the inner peripheral surface 11a of the outer member 10 in the first section X1 can be measured in the same manner as the outer peripheral surface of the inner member. That is, it can be determined by measuring the outline of the inner peripheral surface 11a of the outer member 10 in the first section X1 and the central axis of the outer member 10 as the extrusion central axis O1 using a three-dimensional measuring device. Similarly, if the central axis of the outer member 10 cannot be defined in the first section X1, several circles can be defined on the inner peripheral surface 11b of the second section X2 as a substitute, and a straight line passing through the centers of those circles is defined as the extrusion central axis O1.

[0060] In Fig. 2, the inner circumferential surface 11a of the through hole in the outer member in the first section X1 is formed with an uneven shape, and the parallelism with respect to the extrusion central axis O1 is 4.5 mm or more. However, a monotonically decreasing or monotonically increasing taper is also acceptable. Furthermore, in the cross section shown in Fig. 2, the entire first section may be formed with a convex or concave curved surface, or a tapered surface may be combined with a straight portion to achieve a parallelism of 4.5 mm or more. However, a shape such as a spiral groove, which would cause the circularity of the inner member or the through hole in the outer member to be 1 or more in a cross section perpendicular to the extrusion central axis O1, is not preferred because it disrupts the flow of the plastic composition in the flow channel and makes it difficult to suppress deterioration in appearance.

[0061] In addition, the parallelism of the inner peripheral surface 11a of the outer member 20 in the first section X1 with respect to the extrusion central axis O1 may be 1 mm or less, and the parallelism of the outer peripheral surface 21a of the inner member 20 with respect to the extrusion central axis O1 may be 4.5 mm or more. However, it is preferable to set the parallelism of the outer peripheral surface 21a of the inner member 20 in the first section X1 to 1 mm or less. This is because the inner member 20 has a smaller diameter than the outer member 10. If the outer peripheral surface 21a of the inner member 20 in the first section X1 is given an uneven shape or the like to set the parallelism with respect to the extrusion central axis O1 to 4.5 mm or more, a narrow-diameter portion may be formed in the inner member 20, which may reduce its strength. This is because the flow path forming device is attached to the extruder in a cantilevered state, and a reduction in the strength of the inner member may cause the inner member 20 to bend and deform due to the gravity of the inner member 20, resulting in a deterioration in its posture. Furthermore, applying high pressure to the plastic composition in the flow paths in order to stabilize the quality of the foamed sheet and increase the production speed may also damage the inner member. Therefore, by setting the parallelism of the outer peripheral surface 21a of the inner member to the extrusion central axis O1 to 1 mm or less and the parallelism of the outer peripheral surface of the outer member to 4.5 mm or more throughout the entire first section X1, it is possible to suppress a decrease in strength of the inner member 20 and prevent deterioration of its posture due to gravity. This is also preferable because it allows a high pressure to be applied to the plastic composition in the flow channel, stabilizing the quality of the foamed sheet and increasing the production speed.

[0062] Furthermore, in this embodiment, the distance Y1 along the direction perpendicular to the extrusion central axis O1 from a position 10 mm in the X direction from the discharge port 40, which is the connecting point between the first section X1 and the second section X2, to the discharge port 40 is set to 10 mm or less, preferably 5 mm or less. This allows the diameter of the annular flow path 30 to gradually expand in the second section X2, reduces stress on the plastic composition in the second section X2 immediately before extrusion, and suppresses turbulence in the flow of the plastic composition when it is discharged from the discharge port 40, thereby suppressing deterioration in appearance.

[0063] Furthermore, by setting the distance Y1 to 10 mm or less, preferably 5 mm or less, it is possible to suppress the diameter of the inner member 20 from becoming thinner, thereby obtaining a foamed sheet with a desired circumferential length. Furthermore, by suppressing the diameter of the inner member 20 from becoming thinner, it is possible to suppress a decrease in the strength of the inner member 20. As a result, it is possible to suppress deterioration of the posture of the inner member 20 due to gravity. Furthermore, it is possible to increase the pressure applied to the plastic composition in the flow path, which stabilizes the quality of the foamed sheet and increases the production speed.

[0064] Furthermore, in this embodiment, the outer peripheral surface 21b of the inner member in the second section X2 and the inner peripheral surface 11b of the through hole in the outer member are curved so as to expand in diameter, making the flow path in the second section X2 rounded. This gradually changes the flow direction of the plastic composition in the second section X2 of the flow path, reducing stress on the plastic composition in the second section X2. This further reduces turbulence in the flow of the plastic composition when it is discharged from the discharge port 40, effectively preventing deterioration in appearance.

[0065] In the present embodiment, for the radius of curvature Ri of the curved surface of the outer peripheral surface 21b of the inner member 20 in the second section X2 in the cross section shown in FIG. 2, it is preferably 1 < Ri < 10, and more preferably 2 ≤ Ri ≤ 9. For the radius of curvature R0 of the curved surface of the inner peripheral surface 11b of the through hole of the outer member 10, it is preferably 1 < R0 < 10, and more preferably 2 ≤ R0 ≤ 9. Note that Ri and R0 may be the same or different. Also, it is most preferable that both the outer peripheral surface 21b of the inner member in the second section X2 and the inner peripheral surface 11b of the through hole of the outer member include curved surfaces, but a configuration having a curved surface with a radius of curvature of 1 to 10 on only one of the outer peripheral surface 21b of the inner member and the inner peripheral surface 11b of the through hole of the outer member is also acceptable.

[0066] In the present embodiment, in the second section X2, the outer peripheral surface 21b of the inner member and the inner peripheral surface 11b of the through hole of the outer member are in an R shape. However, in the cross section shown in FIG. 2, the outer peripheral surface 21b and the inner peripheral surface 11b may be curved surfaces such as a part of an ellipse or a parabola. In that case, it is preferable that the curvature in a minute section includes 1 < Ri < 10 and 1 < R0 < 10.

[0067] Also, it is not necessary for the entire flow path in the second section X2 to be curved, and a combination of a curved flow path and a straight flow path may be used. Examples of the combined flow path of a curved flow path and a straight flow path include a flow path composed of a straight flow path along the extrusion central axis O1 from the downstream end in the flow direction of the first section X1, a straight flow path along the discharge direction of the plastic composition from the discharge port, and a curved flow path connecting these straight flow paths, or a flow path having a straight flow path along the extrusion central axis O1 from the downstream end in the flow direction of the first section X1 and a curved flow path from the downstream end of this straight flow path to the discharge port.

[0068] In this embodiment, as described above, the gap between the inner circumferential surface of the through hole of the outer member and the outer circumferential surface of the inner member in the discharge region up to a distance of 1 mm from the discharge port 40 along the extrusion central axis O1 (X direction in the figure) is made narrowest, making it difficult for pressure in the flow path to escape. As a result, even if the distance Y1 is set to 10 mm or less and the flow path in the second section X2 is made rounded to make it easier for the plastic composition to flow in the flow path, pressure can be effectively applied to the plastic composition continuously, foaming of the blowing agent in the flow path can be suppressed, and a high expansion ratio can be obtained.

[0069] The gap between the inner circumferential surface of the through hole of the outer member 10 and the outer circumferential surface of the inner member 20 in the discharge region from the discharge port 40 to a distance of 1 mm along the extrusion central axis O1 (X direction in the figure) does not need to be constant in the range from X = 0 to X = 1 mm, as long as the narrowest part in the flow path forming device is present in this range. For example, the structure may be such that X = 0 is the narrowest, or such that X = 1 mm is the narrowest, or such that the edge at X = 0 is rounded. Furthermore, the inner circumferential surface of the through hole of the outer member 10 and the outer circumferential surface of the inner member 20 in this section may be either straight or curved in the cross section shown in FIG. 2, but is preferably curved.

[0070] In the present embodiment, the cross-sectional shape of the discharge port 40 perpendicular to the extrusion central axis O1 is preferably annular. By making the cross-sectional shape of the discharge port 40 perpendicular to the extrusion central axis O1 annular, thickness unevenness of the extrusion-molded tubular foamed sheet can be suppressed.

[0071] In this embodiment, the area extending from the discharge port 40 of the flow path 30 to a position 250 mm in the X direction (position X3 in FIG. 2 ) is annular, and the circularity of the inner circumferential surface 11 of the through hole of the outer member and the outer circumferential surface 21 of the inner member within that area is 1 mm or less. The flow path forming device 5 controls the temperature of the outer circumferential surface of the outer member using a heater or the like to maintain the molten state within the flow path 30. By setting the range where the circularity is 1 mm or less within the above range, the temperature of the plastic composition within the flow path 30 can be uniformly controlled. This allows the melting state and temperature of the plastic composition within the flow path 30 to be uniform in the circumferential direction. As a result, the plastic composition can be extruded uniformly from the discharge port 40 in the circumferential direction, suppressing uneven thickness and adverse effects on appearance.

[0072] Although the longer the range in which the circularity of the inner peripheral surface 11 of the through hole of the outer member and the inner peripheral surface of the inner member is 1 mm or less, the greater the effect, the greater the precision machining range, leading to increased manufacturing costs. Furthermore, the longer the overall length of the flow path forming device, the greater the weight of the flow path forming device and the worsening of its posture due to gravity. This is because the flow path forming device has a non-circular section of a certain length upstream of the circular section with a circularity of 1 mm or less in the direction of plastic composition flow. Therefore, the longer the circular section, the longer the length of the flow path forming device in the X direction, and the corresponding increase in weight of the flow path forming device. Because the flow path forming device is attached to the extruder in a cantilevered manner, increasing the length of the flow path forming device in the X direction may cause the flow path forming device to bend due to gravity, resulting in poor posture. Therefore, in this embodiment, the above range is set to a position 250 mm in the X direction from the discharge port 40, from the perspectives of manufacturing cost, the weight of the flow path forming device, and good extrusion molding. However, depending on the viscosity of the resin used and the production volume, the range where the circularity is 1 mm or less (circular section) may be 300 mm or 500 mm or more from the discharge port 40 in the X direction. From the viewpoint of stabilizing the melting state and temperature of the plastic composition, the range of circularity of 1 mm or less (circular section) is preferably 150 mm or more.

[0073] The roundness of the outer peripheral surface 21 of the inner member and the inner peripheral surface 11 of the through hole of the outer member up to 250 mm in the X direction from the discharge port 40 can be measured by a coordinate measuring machine or a roundness measuring device.

[0074] The material of the inner member 20 and the outer member 10 is not particularly limited and can be appropriately selected depending on the purpose. Examples include metal, carbon steel, chromium steel, nickel steel, nickel chromium steel, aluminum, plastic, stainless steel, pre-hardened steel, cemented carbide, and high-speed steel, such as S45C, S50C, S55C, A5052, SS400, SUS304, SUS316, SUS420, SKD11, SKH51, HPM-38, SCM415, SCM435, and SCM440. Other examples include hard chrome plating, electroless nickel plating, alumite treatment, black dyeing, Parkerization, carbide film formation, nitride film formation, oxide film formation, DLC treatment, silicone release treatment, fluorine release treatment, that is, coatings of Cr, Ni, Ni-P, amorphous alumina, crystalline alumina, zirconia, TiC, TiCN, TiN, WC, PTFE, ETFE, FEP, PCTFE, PFA, PVDF, composites of these, and composites of these with plastic functional aids.

[0075] The method for forming the inner member 20 and the outer member 10 is not particularly limited and can be appropriately selected depending on the purpose. Examples include cutting, rolling, electrical discharge machining, drawing, polishing, painting, vapor deposition, PVD, CVD, plating, thermal spraying, and etching. Among these, painting is particularly efficient for experimentally examining various embodiments, but it is also acceptable to mass-produce materials examined using painting using a different method. Dilution with a solvent is desirable as a painting method, but this is not a problem as long as it is processable. Using a paint that undergoes a reaction when baked is preferable in terms of durability, but this is not a limitation. It is preferable to roughen the base as much as possible to maintain adhesion of the paint, but this is not a limitation. In some cases, it is acceptable to intentionally form a composite state in which the base is exposed and a coating layer remains in the valleys.

[0076] The method for finishing the materials of the inner member 20 and the outer member 10 is not particularly limited and can be selected appropriately depending on the purpose, and examples include plasma treatment, ozone treatment, thermal aging treatment, chemical aging treatment, physical aging treatment, silane coupling treatment, glass coating, paper finishing, blast finishing, a combination of these, etc. For example, in the case of plating, these are intended to stabilize the number of cracks on the surface or to increase the width of the cracks, but are not limited to this, and may also be intended to control the surface roughness, the contact angle, or the rate of deterioration.

[0077] The method for forming the entire flow path forming device 5 is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a T-die, a flat die, a seamless die, a circular die, a single-heart die, a double-heart die, a spiral die, a bridge die, a spider die, a tournament die, a manifold die, a helical die, and a composite die thereof. Among these, from the viewpoint of forming a non-petroleum-derived foamed sheet using a compressible fluid, a seamless die is preferred, and a circular die is more preferred.

[0078] The following describes the evaluation tests conducted by the present inventors. The evaluation tests were conducted to evaluate the expansion ratio and appearance of foamed sheets extrusion-molded using the flow path forming devices of Examples 1 to 4 and Comparative Examples 1 to 3 described below.

[0079] Example 1 Example 1 is a flow channel forming device 5 having the cross-sectional shape shown in FIG. 2 , in which the shape of the inner circumferential surface 11a of the outer member and the shape of the outer circumferential surface 21a of the inner member in the first section X1 are interchanged, and the inner circumferential surface of the inner member is unevenly shaped with a parallelism of 4.5 mm. This flow channel forming device was attached to the extrusion device shown in FIG. 1 . Polylactic acid and filler were supplied at a total flow rate of 10 kg / hr. Polylactic acid A (Nature Works, 4032D, melting point 168°C) was supplied as the plastic resin at 9 kg / hr, magnesite (Konoshima Chemical Co., Ltd., MS-S, number-average particle diameter 1.2 μm) was supplied as the filler at 1 kg / hr, and carbon dioxide was supplied as the compressive fluid at 0.9 kg / h (equivalent to 10% by mass of the polylactic acid). The resulting mixture was kneaded to produce a polylactic acid composition as a plastic composition. The polylactic acid composition was then extruded from the discharge port 40 of the flow channel forming device 5 to obtain a foamed sheet. The temperatures in each zone were 190°C for the raw material mixing / melting area a and compressive fluid supply area b, 190°C for the kneading area c, and 170°C for the extrusion area d. The target thickness of the foamed sheet was 5 mm.

[0080] Example 2 In Example 1, the shapes of the inner member 20 and the outer member 10 in the first section X1 were interchanged, so that the flow path shape of the first section X1 was the same as the shape shown in Figure 2. In addition, in Example 1, the radii of curvature Ri and R0 of the curved portion of the flow path in the second section X2 and the distance Y1 in Figure 2 were shortened. Then, a polylactic acid composition was extruded in the same manner as in Example 1 to obtain a foamed sheet.

[0081] Example 3 In Example 2, the depth of the uneven shape on the inner peripheral surface of the outer member in the first section X1 was increased to change the parallelism to 6 mm, and the radii of curvature R0 and Ri of the curved portions of the flow path in the second section X2 were made the same. A foamed sheet was obtained by extruding a polylactic acid composition in the same manner as in Example 1.

[0082] Example 4 In Example 2, the depth of the uneven shape on the inner peripheral surface of the outer member in the first section X1, the shape of the curved portion of the flow path in the second section X2, and the distance Y1 in Figure 2 were set in the same manner as in Example 1, and a polylactic acid composition was extruded to obtain a foamed sheet.

[0083] (Comparative Example 1) The cross-sectional area of ​​the flow channel in the discharge region within 1 mm from the discharge port was set to be the same as the cross-sectional area of ​​the flow channel in the second section, and certain modifications were made to the flow channel shape of Example 1. Specifically, in Comparative Example 1, the second section X2 did not include a curved flow channel, and the second section X2 was formed so that the annular flow channel gradually expanded in diameter by bending from the first section X1. Furthermore, the flow channel shape was such that the parallelism of both the outer peripheral surface 21a of the inner member 20 and the inner peripheral surface 11a of the outer member 10 with respect to the extrusion central axis O1 in the first section X1 exceeded 10 mm. Furthermore, the flow channel shape was such that the distance Y1 shown in FIG. 2 exceeded 20 mm. A polylactic acid composition was then extruded in the same manner as in Example 1 to obtain a foamed sheet.

[0084] (Comparative Example 2) In Comparative Example 1, changes were made to the parallelism of the outer peripheral surface of the inner member and the inner peripheral surface of the outer member relative to the extrusion central axis O1 in the first section X1, the flow path shape of the second section X2, and the distance Y1 in Figure 2. The flow path in the second section X2 included a curved flow path with radii of curvature Ri and R0 similar to those in Example 1 (R0 was the same as in Example 1, and Ri was slightly larger than in Example 1). In Comparative Example 2, the distance Y1 shown in Figure 2 was 13 mm. Then, a foamed sheet was obtained by extruding a polylactic acid composition in the same manner as in Example 1.

[0085] (Comparative Example 3) In Comparative Example 2, the parallelism of the outer peripheral surface of the inner member and the inner peripheral surface of the outer member relative to the extrusion central axis O1 in the first section X1 and the shape of the flow path in the second section were changed. The flow path in the second section in Comparative Example 3 included a curved flow path with radii of curvature R0 and Ri similar to those in Example 2 (R0 was the same as in Example 2, and Ri was slightly larger than in Example 2). Then, a polylactic acid composition was extruded in the same manner as in Example 1 to obtain a foamed sheet.

[0086] Next, the expansion ratio and appearance of each foamed sheet were evaluated as follows, and the results are shown in the table below.

[0087] <Expansion ratio> The expansion ratio of the foamed sheet was determined as follows. -Calculation of bulk density and expansion ratio- The expansion ratio of the foam sheet was calculated using the following formula: The expansion ratio of the foam sheet can be calculated by dividing the density (true density ρ0) of the composition constituting the foam sheet by the bulk density (ρ1) based on the following formula (1). Expansion ratio = true density (ρ0) / bulk density (ρ1) Formula (1) The true density (ρ0) is the density of the plastic composition remaining as the final plastic composition, and the true density of polylactic acid is approximately 1.25 g / cm 3 is. The bulk density was measured as follows. Specifically, the foam sheet was left to stand for 24 hours or more in an environment adjusted to a temperature of 23°C and a relative humidity of 50%, and a 50 mm x 50 mm test piece was cut out. The cut test piece was subjected to a submerged weighing method using an automatic hydrometer (DSG-1, manufactured by Toyo Seiki Seisaku-sho, Ltd.) to determine the bulk density. The weight (g) of the foam sheet in air was precisely weighed, and then the weight (g) of the foam sheet in water was precisely weighed, and the bulk density was calculated using the following formula: Bulk density [g / cm 3 ] = sample weight in air [g] / {(sample weight in air [g] - weight in liquid [g]) × liquid density [g / cm 3 ]}

[0088] <Appearance> The appearance of the foamed sheet was evaluated as follows. Appearance evaluation was performed by analyzing the front and back surfaces of the resulting foam sheets using image processing and using a numerical index to quantify their poor appearance. The larger the size and width of solid foreign matter present on the sheet surface and the greater its contrast with the background, the worse the visual evaluation of the appearance tended to be. Therefore, approximately 100 samples were visually evaluated by humans in advance, and ranked from best to worst, with rank 100. An image processing algorithm was then fitted to achieve the highest degree of agreement and used for evaluation. While visual rankings are essentially acceptable for a few evaluations, this index was used given the need for thousands of evaluations and the need for reproducibility. This visual evaluation was not performed by foam sheet experts; it merely assessed whether the surface appeared clean or dirty to the average user, and did not involve any special technology. However, this evaluation was conducted because a product that did not appear clean would be deemed unsuitable for commercial release, and despite its simplicity, it is a crucial indicator.

[0089] [Evaluation criteria] The appearance of the foamed sheets obtained by the above-mentioned method was evaluated, with a rank of less than 8 being evaluated as ◎, a rank of 8 or more but less than 16 being evaluated as 〇, and other cases being evaluated as ×. Since market research and the like revealed that the evaluation ranks that could be used as products were 1 to 16, the evaluation rank of 16 was set as the threshold for the appearance evaluation. After the evaluation rank was determined by fitting using an image processing algorithm, the foamed sheets obtained were visually observed for confirmation. It was immediately apparent that samples with an appearance rating of 〇 (a rank of less than 16) were more aesthetically pleasing than any of the samples with an appearance rating of × (a rank of 16 or more).

[0090] [Table 1]

[0091] Table 1 above summarizes the results of the evaluation test. As shown in Table 1, the appearance evaluation of Comparative Examples 1 to 3 was rated as "X", with an evaluation rank of 16 or higher. This is thought to be because the stress applied to the plastic composition in the flow path in the first section X1 and the second section X2 was large, causing disturbance in the flow of the plastic composition in these sections, resulting in poor appearance of the foamed sheet.

[0092] In contrast, Examples 1 to 4 achieved high expansion ratios of 11 times or more, and the appearance was also evaluated as "good" or better. In particular, Example 2 achieved a high expansion ratio of 14 times or more, while also achieving an appearance evaluation of "Excellent," an excellent result. This is because, in Examples 1 to 4, the cross-sectional area of ​​the flow channel in the discharge region of 1 mm or less from the discharge port in the X direction is narrowest, allowing effective pressure to be applied to the plastic composition until the plastic composition is discharged from the discharge port 40 (extrusion is completed). Furthermore, the distance Y1 (see FIG. 2) is set to 10 mm or less, and the annular flow channel 30 is gradually expanded in the second section X2, and the flow channel in the second section is rounded. This suppresses pressure loss within the flow channel and maintains high pressure all the way to the discharge port. Therefore, the pressure on the plastic composition is rapidly reduced at the discharge port 40, allowing carbon dioxide to be effectively foamed, resulting in a foamed sheet with a high expansion ratio. In addition, in Examples 2 and 3 where the distance Y1 (see Figure 2) was 5 mm, the annular flow path 30 could be made to have a shape in which the diameter expanded more gradually in the second section X2, and the stress on the plastic composition within the flow path could be effectively reduced, which is thought to be why the appearance evaluation was "◎".

[0093] Furthermore, in Examples 1 to 4, the parallelism of either the inner circumferential surface 11a of the outer member or the outer circumferential surface 21a of the inner member with respect to the extrusion central axis O1 in the first section X1 was set to 1 mm or less. This is thought to have suppressed turbulence in the flow of the plastic composition in the flow channel compared to Comparative Examples 1 and 2, in which the parallelism of both the inner circumferential surface 11a of the outer member and the outer circumferential surface 21a of the inner member with respect to the extrusion central axis O1 in the first section X1 exceeded 1 mm. This is thought to have resulted in improved appearance.

[0094] 2 exceeds 10 mm, the diameter of the annular flow path increases more rapidly in the second section X2 than in Examples 1 to 3, in which the distance Y1 is 10 mm or less. As a result, the flow direction of the plastic composition is abruptly changed at the connection point between the first section X1 and the second section X2 (a position 10 mm from the discharge port in the X direction), and excessive stress is applied to the plastic composition, which is thought to have deteriorated the appearance.

[0095] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications and variations are possible within the spirit and scope of the present invention as set forth in the claims.

[0096] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) In a flow path forming device (5) having an outer member (10) having a through hole and an inner member (20) arranged in the through hole with a gap from the inner peripheral surface (11) of the through hole, the inner peripheral surface (11) of the outer member (10) and the outer peripheral surface (21) of the inner member (20) form a flow path (30) having an annular cross section perpendicular to the extrusion central axis (O1), the flow path (30) being formed by the inner peripheral surface (11) of the outer member (10) and the outer peripheral surface (21) of the inner member (20) in a first section (X1) of 10 mm or more and 60 mm or less along the extrusion central axis (O1) upstream in the flow direction of a fluid flowing in the flow path from an outlet of the flow path such as a discharge port (40). The parallelism of one of the peripheral surfaces 11a to the extrusion central axis O1 is 1 mm or less, and the parallelism of the other of the peripheral surfaces 11a to the extrusion central axis O1 is 4.5 mm or more, the narrowest gap between the outer peripheral surface of the inner member and the inner peripheral surface of the outer member is located within a range of 1 mm or less upstream from the outlet of the flow channel along the extrusion central axis in the flow direction, the second section X2 of the flow channel from the downstream end of the first section X1 in the flow direction to the outlet of the flow channel has an expanding diameter region in which the diameter of the flow channel expands toward the outlet of the flow channel, and the distance from the downstream end of the first section in the flow direction to the outlet of the flow channel along the direction perpendicular to the extrusion central axis O1 is 10 mm or less. This makes it possible to obtain a high expansion ratio and to improve the appearance of the molded product, as explained in the above evaluation test.

[0097] (Aspect 2) In the first aspect, in the entire first section, the parallelism between the outer peripheral surface 21 of the inner member 20 and the extrusion central axis O1 is 1 mm or less throughout the entire first section X1. As a result, as described in the embodiment, it is possible to prevent a decrease in strength of the inner member 20, which has a smaller diameter than the outer member 10, and to prevent the inner member from becoming unbalanced due to gravity.

[0098] (Aspect 3) In the first or second embodiment, the distance Y1 from the downstream end of the first section X1 in the flow direction to the flow path outlet such as the discharge port 40 along the direction perpendicular to the extrusion central axis O1 is 5 mm or less. This allows the flow path in the second section X2 to expand more gradually, further reducing stress on the fluid, such as the plastic composition, in the flow path in the second section X2, thereby suppressing turbulence in the flow path and improving the appearance of the extrusion-molded product.

[0099] (Aspect 4) In any of the first to third embodiments, the cross-sectional shape of the flow path outlet, such as the discharge port 40, perpendicular to the extrusion central axis O1 is annular. This can suppress unevenness in the thickness of the extrusion-molded cylindrical foamed sheet, as described in the embodiment.

[0100] (Aspect 5) In embodiment 4, the circularity of the outer peripheral surface 21 of the inner member 20 and the circularity of the inner peripheral surface 11 of the outer member 10 are 1 mm or less in at least the entire area of ​​250 mm or less upstream in the flow direction from the flow path outlet such as the discharge port 40 along the extrusion central axis O1. As a result, as described in the embodiment, the melting state and temperature of the fluid, such as the plastic composition, in the flow path can be made uniform in the circumferential direction, and the fluid can be pushed out uniformly in the circumferential direction, thereby suppressing unevenness in thickness and effects on appearance.

[0101] (Aspect 6) In any of the first to fifth embodiments, in a cross section passing through the extrusion central axis and parallel to the extrusion central axis, the second section X2 has a curved flow path in which the outer peripheral surface 21a of the inner member 20 and the inner peripheral surface 11a of the outer member 10 are curved. According to this, as described in the embodiment, the plastic composition in the flow path can be smoothly flowed into the discharge region inclined at a predetermined angle with respect to the extrusion central axis O1 to set the discharge angle such that the stretchability of the foamed sheet and the handleability of the molded product after extrusion molding can be obtained, thereby suppressing stress on the plastic composition in the flow path and suppressing deterioration in appearance.

[0102] (Aspect 7) In an extrusion apparatus having a flow path forming device 5 and extruding a fluid containing a foaming agent such as a plastic composition from a flow path outlet such as the discharge port 40 of the flow path forming device 5 to foam it, the flow path forming device 5 was any one of the flow path forming devices of embodiments 1 to 7. This makes it possible to obtain an extrusion molded product with a good appearance and a high expansion ratio, as explained in the embodiment.

[0103] (Aspect 8) In embodiment 7, the fluid comprises polylactic acid. As a result, as explained in the embodiment, it is possible to obtain a molded article that has a relatively higher melting point, toughness, chemical resistance, and the like than other biodegradable plastics.

[0104] (Aspect 9) In embodiment 7 or 8, the blowing agent is carbon dioxide. This makes it possible to improve safety and reduce the environmental load, as explained in the embodiment.

[0105] (Aspect 10) The plastic sheet is formed by the channel forming device of any one of the first to sixth embodiments. This makes it possible to obtain a plastic sheet with a high expansion ratio and good appearance.

[0106] (Aspect 11) The foamed sheet is formed by the extrusion apparatus of any of the seventh to ninth embodiments. This makes it possible to obtain a foamed sheet with a high expansion ratio and good appearance.

[0107] (Aspect 12) In the plastic sheet production method in which a plastic composition is extruded from the channel outlet of a channel forming device 5 to obtain a plastic sheet, the channel forming device 5 used was any one of the channel forming devices of embodiments 1 to 6. This makes it possible to obtain a plastic sheet with a high expansion ratio and good appearance.

[0108] (Aspect 13) In the method for producing a foamed sheet in which a fluid containing a foaming agent is extruded from a channel outlet of a channel forming device using an extruder to obtain a foamed sheet, the extruder of any one of Embodiments 7 to 9 was used. This makes it possible to obtain a foamed sheet with a high expansion ratio and good appearance. [Explanation of symbols]

[0109] 1: Fixed quantity feeder 2: Fixed quantity feeder 3: Metering pump 4: Foam sheet 5: Flow path forming device 10:Outer member 11: Inner surface of outer member 11a: Inner peripheral surface of the outer member of the first section 11b: Inner peripheral surface of the outer member of the second section 20: Inner member 21: Outer surface of inner member 21a: Outer surface of the inner member of the first section 21b: Outer surface of the outer member of the second section 30: Flow path 40:Discharge port 110: Extrusion device 110a: First extruder 110b: Second extruder A: Polylactic acid O1: Extrusion central axis X1: First section X2: Second section Y1: Distance from the discharge port to the downstream end of the first section in a direction perpendicular to the extrusion central axis a: Melting area b: Compressible fluid supply area c: Mixing area d: Extrusion area [Prior art documents] [Patent documents]

[0110] [Patent Document 1] Patent No. 7402439

Claims

1. an outer member having a through hole; an inner member disposed in the through hole with a gap between the inner member and an inner peripheral surface of the through hole; In a flow path forming device, a flow path having an annular cross-sectional shape perpendicular to an extrusion central axis is formed by the inner peripheral surface of the outer member and the outer peripheral surface of the inner member, in a cross section passing through the extrusion central axis and parallel to the extrusion central axis, in a first section of the flow path extending from a flow path outlet along the extrusion central axis to an upstream position of 10 mm or more and 60 mm or less, the parallelism of one of the outer peripheral surface of the inner member and the inner peripheral surface of the outer member with the extrusion central axis is 1 mm or less, and the parallelism of the other of the outer peripheral surface and the extrusion central axis is 4.5 mm or more, a location where the gap between the outer peripheral surface of the inner member and the inner peripheral surface of the outer member is narrowest is present within a range of 1 mm or less upstream from the flow channel outlet along the extrusion central axis in the flow direction, a second section of the flow path from a downstream end of the first section in the flow direction to the flow path outlet has an expanding region in which the flow path expands in diameter toward the flow path outlet, A flow path forming device, characterized in that the distance from the downstream end of the first section in the flow direction to the flow path outlet along a direction perpendicular to the extrusion central axis is 10 mm or less.

2. The flow path forming device according to claim 1 , A flow path forming device, characterized in that the parallelism between the outer peripheral surface of the inner member and the extrusion central axis is 1 mm or less throughout the entire first section.

3. The flow path forming device according to claim 1 , A flow path forming device, characterized in that the distance from the downstream end of the first section in the flow direction to the flow path outlet along a direction perpendicular to the extrusion central axis is 5 mm or less.

4. The flow path forming device according to claim 1 , A flow path forming device, characterized in that the cross-sectional shape of the outlet of the flow path, which is perpendicular to the extrusion central axis, is annular.

5. The flow path forming device according to claim 4, a flow path forming device characterized in that the circularity of the outer peripheral surface of the inner member and the circularity of the inner peripheral surface of the outer member are 1 mm or less at least in an entire region of 250 mm or less upstream from the flow path outlet along the extrusion central axis in the flow direction.

6. The flow path forming device according to claim 1 , In a cross section passing through the extrusion central axis and parallel to the extrusion central axis, The flow path forming device, wherein the second section has a curved flow path in which the outer peripheral surface of the inner member and the inner peripheral surface of the outer member are curved.

7. A flow path forming device is provided, An extrusion device that extrudes a fluid containing a foaming agent from a flow path outlet of the flow path forming device to foam mold the fluid, An extrusion device, comprising the flow path forming device according to claim 1 as the flow path forming device.

8. 8. The extrusion device according to claim 7, The extrusion device, wherein the fluid contains polylactic acid.

9. 8. The extrusion device according to claim 7, The extrusion device is characterized in that the foaming agent is carbon dioxide.

10. A plastic sheet formed by the flow path forming device according to claim 1.

11. A foamed sheet formed by the extrusion apparatus according to claim 7.

12. 1. A method for producing a plastic sheet by extruding a plastic composition from a flow channel outlet of a flow channel forming device to obtain a plastic sheet, comprising:

2. A plastic sheet manufacturing method, comprising using the flow path forming device according to claim 1 as the flow path forming device.

13. 1. A method for producing a foamed sheet by extruding a fluid containing a foaming agent through a flow path outlet of a flow path forming device using an extrusion device to obtain a foamed sheet, A method for producing a foamed sheet, comprising using the extrusion device according to claim 7 as the extrusion device.

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