JP2017094538A - Method for manufacturing heat insulative food container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a heat insulative food container which can manufacture a heat insulative food container having excellent heat insulation property while suppressing poor molding and poor appearance.SOLUTION: A method for manufacturing a heat insulative food container which includes a step of melting a resin composition containing polyolefin and a polylactic acid, and impregnating the resin composition with a fluid in a supercritical state to prepare a molten resin, a step of injecting the molten resin to fill a cavity in a mold with the injected molten resin, and moving a part of the mold and expanding a capacity of the cavity before solidification of the molten resin filled in the cavity completes, where the cavity has a distance between a resin injection port and a cavity terminal of 250 mn or less, and an average distance between mold gaps in the cavity when filled with the molten resin of 0.4 mm or more and 3.5 mm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a heat insulating food container.

Thermal insulation is required for containers of instant foods such as instant ramen, instant soup, instant coffee, etc. that are poured by hot water and foods that are supposed to be heated in a microwave oven. Foamed molded products not only have excellent heat insulation properties because they contain bubbles, but also have features such as being lightweight and reducing the amount of materials used, making them suitable for food containers with heat insulation properties. However, it has not been put into practical use yet.

A foam-molded article can be produced by molding a resin composition filled in a mold while foaming. Known foaming methods include, for example, a method of decomposing a foaming agent in a resin composition and a method of injecting a gas into the resin composition. In recent years, a supercritical fluid is injected into the resin composition. A way to do this is also being considered. In addition, it is known to use, for example, injection molding for molding the resin composition. About the manufacturing method of such a general foaming molded article, it is disclosed by patent documents 1-4, for example.

Japanese Patent Laid-Open No. 2002-067111 JP 2003-231148 A Japanese Patent No. 5283710 JP 2010-173238 A

In order to put the foam-molded product into practical use as a heat-insulating food container, there is room for improvement in the suppression of molding defects and appearance defects and the improvement of heat insulation.

The present invention has been made in view of the above situation, and provides a method for producing a heat-insulating food container capable of producing a heat-insulating food container having excellent heat insulation properties while suppressing molding defects and appearance defects. Objective.

The inventors of the present invention first focused on using, as a food container, a foam molded article produced by a method of injection molding a molten resin containing a fluid in a supercritical state. Then, various investigations were made on methods for improving the heat insulating properties required for food containers. When a combination of polyolefin and polylactic acid was used as the resin material used for the molten resin, a large number of fine bubbles were uniformly formed inside the molded product. I found out that I can do it. In addition, before the molten resin filled in the cavity in the mold finishes solidifying, the part of the mold is moved to expand the volume of the cavity, thereby further increasing the amount of foaming and foam molding. It has also been found that the heat insulation of the product can be improved. On the other hand, it has been found that increasing the amount of foaming tends to cause defective molding and poor appearance. Therefore, as a result of diligent investigations on how to suppress these defects, the distance from the resin injection port to the end of the cavity and the average distance between the mold gaps in the cavity when filling with molten resin are controlled within a specific range. I found that it was extremely important. From the above, the present invention has been completed by reaching a method capable of producing a foamed molded article having excellent heat insulation that can be used as a heat insulating food container with high productivity.

The method for producing a heat-insulating food container of the present invention includes a step of melting a resin composition containing polyolefin and polylactic acid, impregnating the resin composition with a fluid in a supercritical state, and preparing a molten resin, and the melting Injecting resin to fill the cavity in the mold, and before the molten resin filled in the cavity finishes solidifying, moving a part of the mold to enlarge the volume of the cavity; The cavity has a distance from the resin inlet to the end of the cavity of 250 mm or less, and the average distance of the mold gap in the cavity when filling the molten resin is 0.4 mm or more and 3.5 mm or less It is characterized by being.

The resin composition preferably further contains a layered silicate.

According to the method for producing a heat-insulating food container of the present invention, in the injection molding using a supercritical fluid as a foaming agent, a heat-insulating food container having excellent heat insulation is produced while suppressing molding defects and appearance defects. it can.

It is a schematic diagram explaining an example of the method of manufacturing a foaming molded article using a supercritical injection molding apparatus. FIG. 2 is a schematic cross-sectional view showing an enlargement of the cavity periphery of the mold of FIG. 1 in order to explain the core back, where (a) shows the initial state before the core back, and (b) shows the state after the core back. Indicates the extended state. It is a figure explaining the shortest distance when reaching the cavity end through the inside of the cavity from the resin inlet, (a) is provided with the resin inlet at the center of the bottom of the cavity for the plate-like foam molded product (B) shows the case where a resin injection port is provided on the side surface of the cavity for the plate-like foam molded article, and (c) shows the cavity for the cup-like foam molded article. The case where the resin injection port is provided in the center of the bottom surface of FIG. 4D shows the case where the resin injection port is provided on the side surface of the cavity for the cup-shaped foam molded product. FIG. 2 is a schematic cross-sectional view showing an enlargement of the cavity periphery of the mold of FIG. 1 in order to explain the dimensions of each part of the mold. It is an example of the cup-shaped foaming molded product (heat-insulating food container) manufactured by this invention. It is the cross-sectional schematic diagram which expanded and showed a part of foaming molded product (heat-insulating food container) manufactured by this invention. It is the cross-sectional schematic diagram which showed the shape of the foaming molded article produced in the Example and the comparative example.

The method for producing a heat-insulating food container of the present invention includes a step of melting a resin composition containing polyolefin and polylactic acid, impregnating the resin composition with a fluid in a supercritical state, and preparing a molten resin, and the melting Injecting resin to fill the cavity in the mold, and before the molten resin filled in the cavity finishes solidifying, moving a part of the mold to enlarge the volume of the cavity; The cavity has a distance from the resin inlet to the end of the cavity of 250 mm or less, and the average distance of the mold gap in the cavity when filling the molten resin is 0.4 mm or more and 3.5 mm or less It is characterized by being.

In the step of preparing the molten resin, the molten resin composition is impregnated with a supercritical fluid (hereinafter also referred to as “supercritical fluid”). First, the resin composition will be described in detail below.

The resin composition contains polyolefin and polylactic acid. What has a thermoplastic resin as a main component is used suitably. Since polyolefin and polylactic acid are incompatible polymers that do not dissolve each other, even if mixed, they do not dissolve each other and an interface is formed. Therefore, in foaming using a supercritical fluid, the interface can be used as a foaming origin (foaming nucleus).

As the polyolefin, it is preferable to use one or both of polypropylene and polyethylene. The melt mass flow rate (MFR) of polypropylene is preferably 5 to 100 g / 10 minutes, more preferably 10 to 50 g / 10 minutes. The MFR of polypropylene is a value measured according to JIS K7210 at a temperature of 230 ° C. and a load of 21.2 N. The MFR of polyethylene is preferably 5 to 100 g / 10 minutes, more preferably 10 to 50 g / 10 minutes. The MFR of polyethylene is a value measured at a temperature of 190 ° C. and a load of 21.2 N in accordance with JIS K7210.

The polyolefin may contain only polypropylene and / or polyethylene, but may contain other polyolefins other than polypropylene and polyethylene.
Examples of the other polyolefin include an α-olefin homopolymer, an ethylene-propylene copolymer, an ethylene-α olefin copolymer, and a propylene-α olefin copolymer. Examples of the α-olefin include 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, and 3-ethyl-1. -C4-C12 alpha olefins, such as -pentene, 1-octene, 1-decene, and 1-undecene, are mentioned.

The melt viscosity (220 ° C.) of the polyolefin is preferably 150 Pa · S or more and 400 Pa · S or less. A more preferable lower limit of the melt viscosity of the polyolefin is 200 Pa · S, and a more preferable upper limit is 300 Pa · S. The melt viscosity can be measured using, for example, “Flow Tester CFT-500D” manufactured by Shimadzu Corporation. Specifically, the resin to be measured is heated to a predetermined temperature and fluidized, and is extruded from the cylinder with a piston having a predetermined surface pressure of 1 MPa through a capillary die (inner diameter φ1 mm, length 10 mm). The viscosity characteristics can be evaluated by the time taken.

The content of the polyolefin with respect to the entire resin composition is preferably 30% by weight or more and 80% by weight or less. When the content is less than 30% by weight, the fluidity and solidification rate of the resin composition may be lowered, and the moldability may be deteriorated. When the content exceeds 80% by weight, the foaming property is deteriorated, the surface of the obtained heat insulating food container is uneven, the appearance is impaired, and the resin composition is mixed with the supercritical fluid. The composition may be difficult to impregnate with the supercritical fluid. The minimum with more preferable content with respect to the whole resin composition of polyolefin is 35 weight%, and a more preferable upper limit is 70 weight%.

The polylactic acid is a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a copolymer of L-lactic acid and D-lactic acid, or a mixture thereof. The crystallinity of the polylactic acid obtained can be adjusted by the enantiomeric ratio of lactic acid, the method of copolymerizing enantiomers (random, block, graft, etc.), the method of adding a crystal nucleating agent, and the like.

The polylactic acid preferably has a melt viscosity (220 ° C.) of 150 Pa · S or more and 400 Pa · S or less. A more preferable lower limit of the melt viscosity of the polylactic acid is 200 Pa · S, and a more preferable upper limit is 300 Pa · S. The melt viscosity of the polylactic acid can be measured in the same manner as the melt viscosity of the polyolefin.

It is preferable that content with respect to the whole resin composition of the said polylactic acid is 3 to 40 weight%. When the content is less than 3% by weight, foaming of the molten resin may be insufficient. When the said content exceeds 40 weight%, the fluidity | liquidity of a resin composition and the solidification speed | rate may fall, and a moldability may worsen. The minimum with more preferable content with respect to the whole resin composition of the said polylactic acid is 8 weight%, and a more preferable upper limit is 30 weight%.

By setting the content of the polyolefin and the content of the polylactic acid within the range of 3% by weight to 40% by weight, the fluidity of the resin composition can be adjusted and the moldability can be improved.

The difference in melt viscosity between the polyolefin and polylactic acid is preferably 200 Pa · S or less. When the melt viscosity difference is 200 Pa · S or less, both components are easily mixed. A more preferable upper limit of the difference in melt viscosity is 150 Pa · S.

As a method of mixing incompatible polymers, a method of forming a chemical bond between the two components or a method of forming a cross-linked structure between the same polymers may be used. Foam molding using polylactic acid In the case of obtaining a product, for example, reaction extrusion (reactive processing) in which kneading is performed while synthesizing polylactic acid using a synthesis catalyst such as a metal complex, a radical generator, or the like may be used. When the interface between polyolefin and polylactic acid acts as a foam nucleus, unlike the reaction extrusion in which kneading is performed while synthesizing polylactic acid, there is no need to add a synthesis catalyst, a radical generator or the like to the resin composition. . In addition, as reaction extrusion of polylactic acid, for example, tin 2-ethylhexanoate is used as a synthesis catalyst, an antioxidant (for example, “Irganox 1010” from Ciba Specialty Chemicals) is added, and L-lactide is added. Method of reacting ε-caprolactone; Method of reacting polylactic acid and polyethylene glycol using a radical generator such as dicumyl peroxide; Polycarbonate and polybutylene adipate terephthalate (PBAT) using poly (lactic acid) using a radical generator And polycaprolactone (PCL), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA) and the like.

As the resin composition, a mixture of polyolefin, polylactic acid and a modified polyolefin containing a carbonyl group in the molecule is suitably used. By adding a modified polyolefin containing a carbonyl group, the polyolefin and polylactic acid can be made compatible and the dispersibility can be improved. As a result, a large number of fine bubbles (foamed particles having a small particle diameter) can be uniformly present inside the molded product, and a heat insulating food container excellent in properties such as heat insulating properties, strength and light weight can be manufactured. .

Examples of the modified polyolefin containing a carbonyl group in the molecule include those obtained by addition reaction of an unsaturated carboxylic acid, an ester of an unsaturated carboxylic acid, or an anhydride of an unsaturated carboxylic acid to the polyolefin. . Examples of the unsaturated carboxylic acid include maleic acid, fumaric acid, and itaconic acid. Examples of the unsaturated carboxylic acid ester include maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, and fumaric acid monomethyl ester. Examples of the unsaturated carboxylic acid anhydride include itaconic anhydride and maleic anhydride. As the modified polyolefin containing a carbonyl group in the molecule, maleic anhydride-modified polyolefin, glycidyl methacrylate-modified polyolefin and the like are preferably used. The modified polyolefin containing a carbonyl group in the molecule may be used alone or in combination of two or more.

The modified polyolefin containing a carbonyl group in the molecule may be a copolymer of an olefin and a vinyl monomer. As a copolymer of an olefin and a vinyl monomer, for example, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) ethyl acrylate copolymer, and ethylene- (meth) acrylate methyl copolymer Etc. The (meth) acrylic acid may be either acrylic acid or methacrylic acid.

The MFR of the modified polyolefin containing a carbonyl group in the molecule is preferably 0.1 to 100 g / 10 minutes, more preferably 0.3 to 50 g / 10 minutes. MFR is a numerical value measured according to JIS K7210 at a temperature of 230 ° C. and a load of 21.2 N.

The content of the modified polyolefin containing a carbonyl group in the molecule with respect to the entire resin composition is preferably 1% by weight or more and 20% by weight or less. Within this range, an interface is formed between the incompatible polyolefin and polylactic acid, and the dispersibility of both components can be effectively improved. When the content is less than 1% by weight, foaming of the molten resin may be insufficient. When the content exceeds 20% by weight, generation of odor, coloring, deterioration of moldability, increase in water absorption, and the like may be caused. The more preferable lower limit of the content of the modified polyolefin containing a carbonyl group in the molecule with respect to the entire resin composition is 3% by weight, and the more preferable upper limit is 12% by weight.

The resin composition preferably contains a layered silicate. When mixing the polyolefin, polylactic acid, and modified polyolefin containing carbonyl group, if the shear force during mixing is insufficient, the dispersibility of polyolefin and polylactic acid can be improved by adding layered silicate. The foam nuclei can be highly dispersed in the resin composition.

Examples of the layered silicate include pyrophyllite, talc, kaolin (kaolinite), montmorillonite, fisheye stone, margarite, prenite, mica (mica) and the like, and in particular, talc, kaolin, montmorillonite, Mica (mica) is preferably used. The said layered silicate may be used independently and may use 2 or more types together.

The content of the layered silicate with respect to the entire resin composition is preferably 10% by weight or more and 40% by weight or less. If the content is less than 10% by weight, the effect of improving the shearing force during mixing may not be sufficiently obtained. When the said content exceeds 40 weight%, the moldability of a resin composition may fall. The minimum with more preferable content with respect to the whole resin composition of the said layered silicate is 15 weight%, and a more preferable upper limit is 35 weight%.

The resin composition may contain a filler other than the layered silicate. Examples of fillers composed of inorganic materials include metal oxides (magnesium oxide, calcium oxide, etc.), graphite, carbon black, molybdenum disulfide, tungsten disulfide, calcium carbonate, silica, silica gel, zeolite, boron nitride, and alumina. Etc. can be used. Examples of fillers composed of organic materials include fluorine resins such as polytetrafluoroethylene (PTFE), ultrahigh molecular weight polyethylene, electron beam cross-linked polyethylene, aromatic polyamide, aliphatic polyamide, silicon carbide, acrylic resin, and phenol. Resin, melamine resin, etc. can be used. Although the compounding quantity of fillers other than a layered silicate is not specifically limited, For example, it is set as the range which does not exceed 1 weight% with respect to the whole resin composition.

As the supercritical fluid impregnated in the resin composition, for example, a supercritical fluid of an inert gas such as carbon dioxide, nitrogen, argon, helium or the like is used. Of these, carbon dioxide or nitrogen supercritical fluid is preferable, and nitrogen supercritical fluid is more preferable. The supercritical fluid can be generated by a conventionally known supercritical fluid generator.

The filling amount of the supercritical fluid is preferably 0.05% by weight to 1.0% by weight with respect to the resin composition. When the filling amount is less than 0.05% by weight, the molten resin may not be sufficiently foamed. If the filling amount exceeds 1.0% by weight, the present invention forms a thin foamed molded product, and thus the appearance may be impaired due to surface swelling or the like.
The filling amount of the supercritical fluid can be calculated by the following equation (1).
Supercritical fluid filling amount (unit:% by weight) = [(supercritical fluid flow rate × supercritical fluid inflow time × conversion factor 27.8) ÷ resin composition weight] × 100 (1)

The molten resin is preferably a single-phase solution of the resin composition and the supercritical fluid. A single-phase solution can be produced by injecting a supercritical fluid into a molten resin composition under high pressure and further stirring.

In the present invention, injection molding is performed in which the molten resin is injected and filled into a cavity in a mold. In injection molding, a molten resin containing supercritical fluid is filled into a mold cavity, and then cooled and solidified, so that foam molding of precise shapes and various shapes according to the shape of the cavity in the mold. Product can be manufactured. In addition, when the molten resin containing the supercritical fluid is decompressed during injection molding, the supercritical fluid undergoes a phase transition to the gas, so that the molten resin is foamed and a foamed molded product containing fine bubbles is obtained. . The amount of bubbles can be increased by allowing a large number of foaming origins (foaming nuclei) to exist uniformly in the molten resin.

In the present invention, before the molten resin filled in the cavity is solidified, a step of moving a part of the mold to enlarge the volume of the cavity (hereinafter also referred to as “core back”) is performed. By forcibly expanding the cavity in a state where a part or all of the molten resin is melted, a rapid pressure decrease is caused and the amount of foaming can be greatly increased. Thereby, a bubble can be formed over the whole inside of the molten resin with which the cavity was filled. The mold usually has a male mold having a convex shape and a female mold having a concave shape, and a gap formed in a state where the male mold and the female mold are fitted becomes a cavity filled with a molten resin. . When enlarging the volume of the cavity, at least a part of the male mold and / or the female mold is moved. When the male mold is the movable side and the female mold is the fixed side, the entire male mold is moved. It is preferable to move to enlarge the volume of the cavity.

The core back is preferably started immediately after completion of filling of the molten resin into the cavity (0 seconds after completion of filling) to within 5 seconds after completion of filling. The moving speed of the mold (core back speed) is preferably 0.1 mm / second or more. The amount of expansion of the gap distance of the mold due to the core back (core back amount) is preferably 0.1 mm or more, and more preferably 0.5 mm to 10 mm.

The production of the molten resin containing the supercritical fluid and the molding while foaming the molten resin are performed using, for example, a supercritical injection molding apparatus in which an injection molding machine and a supercritical fluid generator are connected. be able to. Examples of the supercritical injection molding apparatus include a MuCell injection molding machine (“MuCell” is a registered trademark of Trexel.co. Ltd).

FIG. 1 is a schematic view for explaining an example of a method for producing a foam molded article using a supercritical injection molding apparatus. In the supercritical injection molding apparatus 20 shown in FIG. 1, an injection molding machine including a hopper 21, a heating cylinder 22, a screw 23 and an injection nozzle 24 is added to a cylinder 25, a supercritical fluid generator 26 and an injection controller 27. A critical fluid generator is connected.

The hopper 21 includes a container for storing the charged resin material, and an appropriate amount of the resin material is dropped into the heating cylinder 22 through an openable opening at the bottom of the container. Examples of the resin material charged into the hopper 21 include pellets of a resin composition prepared by melt-kneading a mixture of a plurality of raw materials using an extruder. The extruder is not particularly limited, and various types of single-screw or multi-screw extruders can be used. For example, a twin-screw extruder having a set temperature of 200 ° C. or higher is preferable. As a kneading method, all the raw materials may be kneaded at once, or after kneading any raw material, the remaining raw materials may be added and kneaded. The heating cylinder 22 can heat the inside of the cylindrical space and can melt the resin material.

The cylinder 25 is filled with an inert gas serving as a raw material for the supercritical fluid. The inert gas is sent from the cylinder 25 to the supercritical fluid generator 26 and becomes a supercritical fluid. The supercritical fluid is introduced into the heating cylinder 22 from the supercritical fluid generator 26 via the injection controller 27. The injection control unit 27 controls the filling amount of the supercritical fluid into the resin material melted in the heating cylinder 22.

The screw 23 is configured to be movable while rotating in the heating cylinder 22 and pushes it toward the tip of the heating cylinder 22 while mixing the molten resin material and the supercritical fluid. By this mixing, a single-phase melt of molten resin material and supercritical fluid (molten resin containing supercritical fluid) is formed. The molten resin containing the supercritical fluid is pushed out by the screw 23 and conveyed to the injection nozzle 24 side, and is injected from the injection nozzle 24 into the mold 30 by an appropriate amount.

The mold 30 includes a male mold 31 having a convex shape and a female mold 32 having a concave shape, and a cavity 33 is formed between the male mold 31 and the female mold 32. The molten resin injected from the injection nozzle 24 passes through the runner 34 and is filled into the cavity 33 from a resin injection port (hereinafter also referred to as “gate”). Due to the pressure loss in the mold 30, the supercritical fluid undergoes phase transition to gas when the critical pressure is reached, and bubbles are generated in the molten resin. Furthermore, as shown in FIG. 2, the pressure reduction is accelerated by retracting the male mold 31 before the cooling and solidification of the molten resin proceeds, and performing the core back to expand the cavity 33, and the melting in the cavity 33 is performed. Promotes resin foaming. FIG. 2 is a schematic cross-sectional view showing the periphery of the cavity of the mold in FIG. 1 in order to explain the core back, (a) shows the initial state before the core back, (b) The expanded state after the core back is shown.

The mold 30 is preferably one having a hot runner attached thereto. The hot runner is a system that heats all or part of the runner (resin flow path) 34 from the injection nozzle 24 to the cavity 33 to a temperature higher than the melting point of the resin to be used. By providing the hot runner, solidification of the molten resin can be delayed when the molten resin is poured from the gate to the end of the cavity. Therefore, solidification of the molten resin before completion of filling can be more reliably prevented.

In the present invention, the cavity 33 has a distance of 250 mm or less from the resin inlet to the end of the cavity. Thereby, in this invention which shape | molds a thin foam molded article, generation | occurrence | production of unfilling can be suppressed and favorable moldability can be ensured. The number of resin injection ports leading to one cavity 33 may be one or two or more, but when there is one resin injection port, the design criteria for the cavity 33 of the present invention The advantage of adopting is great. “Cavity end” means the part of the cavity 33 farthest from the resin injection port, and “Distance from the resin injection port to the end of the cavity” means the distance from the resin injection port to the cavity 33 (flow of molten resin). This means the shortest distance (the length of the flow path of the molten resin flowing in the cavity 33) when reaching the end of the cavity through the path. FIG. 3 is a diagram for explaining the shortest distance when reaching the end of the cavity from the resin injection port through the inside of the cavity, and (a) shows the resin injection port at the center of the bottom surface of the cavity for the plate-like foam molded product. (B) shows the case where a resin injection port is provided on the side surface of the cavity for the plate-like foam molded product, and (c) shows the cup-shaped foam molding. The case where the resin injection port is provided in the center of the bottom of the product cavity is shown, and (d) shows the case where the resin injection port is provided on the side surface of the cavity for the cup-shaped foam molded product. . In FIG. 3, “G” represents the position of the resin injection port, and the dotted arrow represents the flow path of the molten resin. From the viewpoint of manufacturing a food container of a general size, a preferable lower limit of the distance from the resin inlet to the end of the cavity is 20 mm. A preferable upper limit of the distance from the resin inlet to the cavity end is 150 mm. If the distance is too large, foaming may proceed excessively at the end of the cavity, and excessive foaming causes a decrease in mold transferability (deterioration in appearance) and a decrease in strength. Further, when the injection speed is increased in order to suppress excessive foaming, the flow resistance value is increased, which causes inconveniences such as reduction in the number of molds taken and shortening of the mold life.

4 is an enlarged schematic cross-sectional view showing the periphery of the cavity of the mold shown in FIG. 1 in order to explain the dimensions of each part of the mold. In the cavity 33 that defines the shape of the foam molded product 10, the distance between the molds 30 (the distance between the male mold 31 and the female mold 32) B shown in FIG. 4 defines the thickness of the foam molded product 10. In the present invention, the average distance of the mold gaps in the cavity 33 when filling the molten resin (before the core back) is set to 0.4 mm or more and 3.5 mm or less. When the distance between the mold gaps in the cavity 33 is not constant, the average distance between the mold gaps can be calculated by dividing the volume of the mold gap in the cavity 33 by the area where the male mold 31 and the female mold 32 face each other. . When the average distance between the mold gaps is less than 0.4 mm, a foam layer having a sufficient thickness is formed inside the molded product while forming a non-foamed layer substantially free of bubbles on the surface of the molded product. I can't. For this reason, the heat insulation effect by a bubble cannot fully be acquired and favorable heat insulation cannot be obtained. The average distance between the mold gaps is preferably 0.6 mm or more. On the other hand, if the average distance between the mold gaps exceeds 3.5 mm, the cooling and solidification time becomes longer. Therefore, the operation of taking out the molded product from the mold 30 and the foaming residue (foaming power remains and the resin The foamed molded product 10 may be deformed due to insufficient solidification), and it is relatively easy to cause foaming of the molten resin. Therefore, there are few advantages of adopting the mold configuration of the present invention. Become. The average distance between the mold gaps is preferably 3.0 mm or less. According to the present invention, even if the wall thickness is reduced, it is possible to suppress the occurrence of swelling of the surface and poor foaming, so that it is possible to produce a foamed molded article 10 that is lighter and has better heat insulation than conventional ones. The shortest distance between the mold gaps is preferably 0.2 mm or more. When the shortest distance between the mold gaps is less than 0.2 mm, a foam layer having a sufficient thickness is formed inside the molded product while forming a non-foamed layer substantially free of bubbles on the surface of the molded product. There are times when you can't.

The shape of the foam molded product (heat insulating food container) produced in the present invention is not particularly limited, but a cup shape composed of a side surface and a bottom surface is suitable. FIG. 5 is an example of a cup-shaped foam-molded product (heat-insulating food container) produced according to the present invention. When manufacturing the cup-shaped foam molded article 10, the resin inlet may be provided at a position in contact with the side surface or at a position in contact with the bottom surface, but is preferably provided at a position in contact with the bottom surface. Accordingly, the molten resin can be diffused throughout the cavity 33 at a uniform and uniform speed from the resin injection port, so that molding defects and foaming defects can be more effectively prevented.

In the cup-shaped foam molded article 10, the angle formed between the side surface and the bottom surface is preferably 5 ° or more, and preferably less than 90 °. A more preferable lower limit of the angle formed by the side surface and the bottom surface is 45 °. Moreover, it is preferable that the height from a bottom face is 5 mm or more, and it is preferable that it is 60 mm or less. A more preferable lower limit of the height from the bottom surface is 10 mm. Furthermore, it is preferable that there are straight portions on each of the side surface and the bottom surface, and the length of the straight portions is preferably 5 mm or more, and preferably 30 mm or less. A more preferable lower limit of the length of the straight portion is 10 mm. If the shape of the cup-shaped foamed molded article 10 is within the above-described preferable range, the effects of the present invention that suppress molding defects and foaming defects are sufficiently exhibited.

FIG. 6 is a schematic cross-sectional view showing an enlarged part of a foam molded product (heat insulating food container) manufactured according to the present invention. The foam molded article 10 shown in FIG. 6 has a structure in which a foam layer 12 is sandwiched between skin layers (outer skin layers) 11 located on the surface of the foam molded article 10. The foam layer 12 refers to a region including a large number of bubbles (foamed particles) in the resin, and the skin layer 11 refers to a region not including the bubbles in the resin. The foam molded article 10 has high strength due to the presence of the skin layer 11 on the surface, and the surface thereof is smooth. The foamed molded article 10 is excellent in heat resistance because the foam layer 12 is present in the center portion, so that not only the weight can be reduced but also heat cannot be transmitted. In addition, the foam molded product 10 shown in FIG. 6 is an example of the foam molded product (heat-insulating food container) manufactured by this invention. The structure of the foam molded product (heat insulating food container) produced by the present invention is not limited to the three-layer structure of skin layer 11 / foam layer 12 / skin layer 11.

The foamed layer 12 preferably has 100 or more foamed particles in the range of 1 mm × 1 mm of the foamed layer 12 when the cross section of the foamed molded article 10 is observed, and an average of 100 arbitrarily selected foamed particles The particle diameter is preferably 100 μm or less. The foamed particles can be measured with a scanning electron microscope (SEM). For example, “S-4800” manufactured by Hitachi High-Technologies Corporation can be used.

The foamed molded product (heat-insulating food container) produced according to the present invention may be decorated with patterns, colors, letters, etc. on the surface thereof. When applying such decoration, a pigment filler, a color master batch, or the like may be added to the resin composition.

The heat resistance of the heat-insulating food container produced according to the present invention is 7.4 S2029 7.4 heat resistance test (display heat resistance temperature 120 ° C.), 7.10 microwave high frequency suitability test, and 7.11 microwave oven durability. Complies with sex test. Therefore, the heat insulation food container manufactured by this invention can be used for the heating or cooking by a microwave oven.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples.

Example 1
50% by weight of polypropylene (PP), 20% by weight of polylactic acid (PLA), 10% by weight of modified polyolefin containing a carbonyl group in the molecule and 20% by weight of talc are dry blended, and a twin-screw extruder (manufactured by Nippon Steel Works) , “TEX30”) was kneaded at a temperature setting of 220 ° C. to obtain a pellet-shaped foaming resin composition. The obtained foaming resin composition was a resin composition in which polylactic acid particles were dispersed in polypropylene. The sources and physical properties of each material are as shown in Table 1 below.

Next, the obtained pellet-shaped foaming resin composition was put into an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) equipped with a supercritical generator. While the foaming resin composition was melted in a heating cylinder set at a temperature of 200 ° C., a supercritical fluid of nitrogen (N ₂ ) was mixed under conditions of a filling amount of 0.2 wt% and a filling pressure of 16 MPa. The filling amount (unit:% by weight) of the supercritical fluid is calculated by the above formula (1).

The molten resin obtained by mixing the supercritical fluid was injected from the resin injection port (gate) into the cavity in the mold under the conditions of an injection speed of 80 mm / second and a screw back pressure of 15 MPa. The opening shape of the gate was circular, and its diameter A (see FIG. 4) was φ3.0 mm. The mold temperature was 60 ° C. The average distance between the mold gaps in the cavity before the core back was 1.2 mm.

Further, immediately after the filling of the molten resin into the cavity was completed (0 seconds after the filling was completed), the core back was performed. Specifically, the foaming of the molten resin was promoted by retracting the male mold by 3 mm and expanding the volume of the cavity. By completing the solidification of the molten resin, a foam molded product used as a heat-insulating food container was obtained.

The foam molded product produced in Example 1 had a cup shape composed of the bottom and side surfaces shown in FIG. FIG. 7 is a schematic cross-sectional view showing the shape of the foam molded product produced in the examples and comparative examples, and shows a cross section when viewed from the direction of the arrow in FIG. As shown in FIG. 7, the obtained foamed molded product had a cup shape in which the angle formed between the side surface and the bottom surface was 70 °. Further, the distance from the gate to the end of the cavity in the cavity before the core back was 78.3 mm. Since the gate is in a position where the gate is in contact with the center 41 of the bottom surface of the foam molded product and the cavity end is in a position in contact with the end portion 42 on the side surface of the foam molded product, the distance from the gate to the cavity end in the cavity is This was equivalent to the sum of the radius of the bottom surface of the molded product and the length of the straight portion of the side surface. Further, as shown in FIG. 6, the foam molded article 10 had skin layers 11 on both surfaces of the foam layer 12.

(Examples 2-8 and Comparative Examples 1-6)
As shown in Table 2 below, the resin material blended into the foaming resin composition, the material of the supercritical fluid, the average distance between the mold gaps in the cavity before the core back, and the distance from the gate to the end of the cavity in the cavity A heat-insulating food container was produced in the same manner as in Example 1 except that was changed.

Regarding the blending of the resin material, in Example 6, 50% by weight of polyethylene (PE), 20% by weight of polylactic acid, 10% by weight of modified polyolefin containing a carbonyl group in the molecule, and 20% by weight of talc were blended. . In Example 7, 25% by weight of polypropylene, 25% by weight of polyethylene, 20% by weight of polylactic acid, 10% by weight of modified polyolefin containing a carbonyl group in the molecule, and 20% by weight of talc were blended. In Comparative Example 4, 70% by weight of polypropylene, 10% by weight of modified polyolefin containing a carbonyl group in the molecule, and 20% by weight of talc were blended. In Comparative Example 5, 70% by weight of polylactic acid, 10% by weight of modified polyolefin containing a carbonyl group in the molecule, and 20% by weight of talc were blended. In Comparative Example 6, 70% by weight of polyethylene, 10% by weight of modified polyolefin containing a carbonyl group in the molecule, and 20% by weight of talc were blended. The sources and physical properties of polyethylene used in Examples 6 and 7 and Comparative Example 6 are as shown in Table 1 above.

Further, the average distance between the mold gaps in the cavity before the core back was adjusted by changing the position of the male mold before the core back. The distance from the gate to the end of the cavity in the cavity was adjusted by changing the lengths of the straight portions of the bottom surface and the side surface of the foam molded article shown in FIG.

(Evaluation of foam molded products)
About the foam-molded article produced by the Example and the comparative example, (1) heat resistance, (2) heat insulation, (3) moldability, and (4) external appearance were evaluated with the following method. The results are shown in Table 2 below.

(1) After placing the foamed molded product in a heat-resistant 110 ° C. drying oven for 5 minutes, the presence or absence of deformation was visually confirmed. The case where deformation was not confirmed was marked with ◯ (passed), and the case where deformation was confirmed was marked with x (failed).

(2) After spraying a black body spray ("THI-1B", manufactured by TASCO JAPAN Co., Ltd.) on the heat insulating foamed molded product, the solvent contained in the black body spray is used indoors for 12 hours to 24 hours. A cup-shaped measurement sample that was dried and colored black was prepared. Then, 100 ml of boiling hot water was put into the measurement sample, and after 3 minutes, the infrared radiation thermometer (“Nippon Avionics” manufactured by Nippon Avionics Co., Ltd.) was adjusted. TVS-200 ").
The case where the measured surface temperature was 60 ° C. or lower was rated as “◎”, the case where it was higher than 60 ° C. and lower than 65 ° C. was marked as “◯”, and the case where it was higher than 65 ° C. was marked as “x”.

(3) Moldability For each of the Examples and Comparative Examples, 100 injection moldings were performed to produce 100 foam molded products. Those satisfying both of the following two criteria were evaluated as ◯ (passed), and those satisfying either one or both were evaluated as x (failed).
-In 100 injection moldings, no unfilling occurred (visual confirmation).
-The molten resin could be cooled and solidified within 45 seconds in a 60 ° C mold.

(4) Appearance For each of the examples and comparative examples, 100 injection moldings were carried out to produce 100 foam molded products. The surface of the obtained foamed molded product is visually confirmed, and the case where no swelling or wrinkle is observed in all the foamed molded products is indicated as ◯ (pass), and one or more foamed molded products have blisters or wrinkles. The case was marked with x (failed).

10 Foamed product 11 Skin layer (outer layer)
DESCRIPTION OF SYMBOLS 12 Foam layer 20 Supercritical injection molding apparatus 21 Hopper 22 Heating cylinder 23 Screw 24 Injection nozzle 25 Cylinder 26 Supercritical fluid generating part 27 Injection control part 30 Mold 31 Male mold 32 Female mold 33 Cavity 34 Runner 41 Bottom center 42 Side End of

Claims (2)

Melting a resin composition containing polyolefin and polylactic acid, and impregnating the resin composition with a fluid in a supercritical state to prepare a molten resin;
Injecting the molten resin to fill the cavity in the mold, and moving the part of the mold to expand the volume of the cavity before the molten resin filled in the cavity is solidified And
The cavity has a distance from the resin inlet to the end of the cavity of 250 mm or less,
The method for producing a heat-insulating food container, wherein an average distance between mold cavities in the cavity when the molten resin is filled is 0.4 mm or more and 3.5 mm or less. The said resin composition contains layered silicate further, The manufacturing method of the heat insulating food container of Claim 1 characterized by the above-mentioned.

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