Foam molding

Abstract

Provided is a foam molding which uses a fluorine-free thermoplastic resin and allows for easy control of the degree of communication and easy adjustment of the permeability in the foam molding.　The present invention is a foam molding. The foam molding includes a foam comprising a thermoplastic resin composition containing a thermoplastic resin and a foam breaker. The difference (ΔHSP value) between the Hansen solubility parameter (δ) of the thermoplastic resin and the Hansen solubility parameter (δ) of the foam breaker is 15.0 or less.

Description

Foamed molded body

[0001] This invention relates to a foamed molded article.

[0002] Foamed molded products, especially foamed films, are being actively researched from the perspective of weight reduction. Among these, foamed films that form continuous holes (hereinafter referred to as continuous-hole films) can be given selective permeability by controlling the foam diameter, and are widely used in moisture-permeable waterproof membranes, internal pressure adjustment applications, and air filters (see, for example, Patent Document 1).

[0003] Patent Application No. 2019-559667

[0004] Perforated films used for moisture-permeable waterproof membranes and internal pressure regulation applications use polytetrafluoroethylene (PTFE) as a raw material. From the perspective of PFAS regulations, there is a demand for the development of perforated films using fluorine-free raw materials.

[0005] One foaming and communication technology involves physically foaming a thermoplastic resin composition containing a thermoplastic resin and a foam-de-foaming agent to produce a foamed molded article.

[0006] However, controlling the number of continuous pores (hereinafter referred to as "communication degree") in the molding technology of the foamed molded articles described above has been difficult. In particular, there were no clear criteria for selecting a defoaming agent with what chemical properties to have in order to obtain the desired degree of communication (moisture permeability and air permeability). For this reason, conventionally, it was necessary to explore through trial and error from a vast number of combinations of defoaming agent types, quantities, and molding conditions, which required a great deal of time and effort to obtain the optimal molded article.

[0007] Based on the above points, the objective is to provide a porous film using a fluorine-free thermoplastic resin. In this invention, we investigated the production of porous molded articles using the above raw materials and the correlation between the type of defoaming agent and the degree of porousness. This invention solves the above problems and provides a foamed molded article in which the degree of porousness can be easily controlled and the permeability can be easily adjusted.

[0008] The inventors diligently conducted research to provide a continuous-hole molded article using a fluorine-free thermoplastic resin and to clarify the correlation between the type of defoaming agent and the degree of continuity. As a result, they found that by reducing the ΔHSP value, which is the difference between the solubility parameter (δ) of the thermoplastic resin and the Hansen defoaming agent, it is possible to produce a foamed and continuous-hole molded article of the thermoplastic resin, and that continuous holes can be efficiently formed in the foamed molded article, thus completing the present invention.

[0009] The Hansen solubility parameter described here is an index of solubility proposed by Dr. Charles M. Hansen et al. It expresses solubility using three parameters: dispersion (δd), polarity (δp), and hydrogen bonding (δh). Substances with similar parameters are judged to have high solubility towards each other. The Hansen solubility parameter (δ) is expressed by the following formula (1).

[0010] δ = ((δd)) ２ + (δp) ２ + (δh) ２ ) ０．５ ......(1)

[0011] In other words, the present invention provides the following foamed molded articles: [1] A foamed molded article comprising a foam made of a thermoplastic resin composition containing a thermoplastic resin and a foam-breaking agent, wherein the difference (ΔHSP value) between the Hansen solubility parameter (δ) of the thermoplastic resin and the Hansen solubility parameter (δ) of the foam-breaking agent is 15.0 or less. [2] The foamed molded article according to [1], wherein the foamed molded article has a non-foamed surface layer on the surface of the foam. [3] The foamed molded article according to [1] or [2], wherein the foam has at least a plurality of foam cells a and one or more cavities b formed on the inner surface of the foam cells a. [4] The foamed molded article according to [3], wherein the average cell diameter of the foam cells a is 5 μm or more and 800 μm or less. [5] The foamed molded article according to [3] or [4], wherein the average diameter of the cavities b is 0.1 μm or more and 100 μm or less. [6] The foamed molded body according to any one of [2] to [5], wherein the foamed molded body is in the shape of a plate, a sheet, or a film, and the non-foamed skin layer has a sandwich structure in which the foamed layer is sandwiched in the thickness direction. [7] The humidity permeability of the foamed layer of the foamed molded body is 1000 g / m² / 24hrs or more and 10000 g / m² ２ [1] to [6] or less foamed molded article. [8] The foamed molded article according to any one of [1] to [7], wherein the defoaming agent is both or either a defoaming agent and a lubricant. [9] The foamed molded article according to any one of [1] to [8], wherein the thermoplastic resin is a polyester resin.

[10] The foamed molded article according to any one of [1] to [9], containing 0.01 parts by mass or more and 10 parts by mass or less of the defoaming agent per 100 parts by mass of the thermoplastic resin.

[11] The foamed molded article according to [8], wherein the defoaming agent is at least one selected from the group consisting of a silicone defoaming agent, a mineral oil defoaming agent, and a polyether defoaming agent.

[12] The foamed molded article according to any one of [3] to

[11] , wherein the average diameter of the cavity b is 1 / 2 or less of the average cell diameter of the foamed cell a.

[0012] According to the present invention, by controlling the ΔHSP value of the thermoplastic resin and the defoaming agent, a molded article with a desired degree of interconnectedness can be easily provided. In one embodiment, by adjusting the ΔHSP value within the range of the present invention, interconnectivity (moisture permeability and air permeability) can be increased. Furthermore, while ensuring interconnectivity, the foam cells can be made finer, thereby achieving a high level of both strength and functionality (selective permeability) in the molded article.

[0013] This is a schematic diagram of an apparatus for manufacturing the foamed molded article of the present invention by injection molding. This is a schematic diagram of an apparatus for continuously manufacturing the foamed molded article of the present invention by extrusion molding. These are cross-sectional views of the foamed portion of the foamed molded articles obtained in Examples 1 to 4 (Figures 3a to d) and Comparative Example 1 (Figure 3e).

[0014] The present invention will now be described in detail. First, in this specification, the notation "○○~△△" (where ○○ and △△ are numbers) indicates that it is ○○ or greater, and △△ or less. Furthermore, ○○ and △△ are not necessarily a fixed combination, but can be combined arbitrarily as ○○ or greater, and △△ or less, with the numerical value of "~" in the same item. Moreover, ○○ or greater means that it is the same as ○○ or greater than ○○, and △△ or less means that it is the same as △△ or less than △△.

[0015] [Foamed Molded Article] The foamed molded article according to this embodiment is a foamed molded article made of a thermoplastic resin composition containing a thermoplastic resin and a foam-breaking agent. Preferred types of thermoplastic resins include olefin resins, polyester resins, polyamide resins, polyvinyl chloride, polystyrene, and ABS resin. Polyester resins, in particular, have good affinity for foaming gases, allowing for a wide range of foaming gas options and making it easier to obtain a good foamed molded article, making them suitable for use.

[0016] (Structure of the foamed molded body) The foamed molded body according to this embodiment may have a non-foamed surface layer (non-foamed skin layer) on the surface of the foam. In this case, the non-foamed skin layer does not need to cover the entire surface of the molded body, but may cover only a part of it. Alternatively, the foamed molded body may not have a non-foamed skin layer and may be entirely made of foam. In this case, it may have skin layers (foamed skin layers) with different degrees of foaming. The shape of the foamed molded body may be a three-dimensional shape, but it can also be a shape unfolded in a planar manner, such as a plate, sheet, or film. The foamed skin layer may have at least one of the following characteristics compared to the foam: a smaller amount of foam cells a (described later), a smaller average cell diameter of foam cells a, a smaller amount of voids b (or no voids b), or a smaller average diameter of voids b.

[0017] When the foamed molded body is unfolded into the planar shape, the foamed molded body may have the non-foamed skin layer on at least one surface in the thickness direction, but it is preferable to have a sandwich structure with non-foamed skin layers on both sides. Alternatively, it may have the foamed skin layer on at least one surface, or it may have a sandwich structure with foamed skin layers on both sides.

[0018] The size of the foamed molded body described above is not particularly limited, but in the case of the planar structure described above, when manufactured by injection molding as described later, the thickness may be 5 mm or more, or 10 mm or more. Alternatively, the thickness may be 80 mm or less, or 50 mm or less. In this case, if the planar shape is rectangular, one side can be 200 mm to 3000 mm. On the other hand, when the foamed molded body is continuously manufactured using extrusion molding as described later, the thickness may be 0.05 mm or more, or 0.1 mm or more. In this case, the thickness may be 8 mm or less, 5 mm or less, or 2 mm or less. In this case, the width of the foamed molded body can be 20 mm to 3000 mm.

[0019] Such a foamed molded article can form a moisture-permeable, open-cell structure in the foam layer, thereby exhibiting moisture permeability and excellent lightweight properties in the foamed molded article (foam).

[0020] The foam described above has one or more foam cells a and one or more cavities b formed on the inner surface of the foam cells a, and may further have a continuous resin phase. The cavities b are holes between adjacent foam cells, and the foam can form a continuous cell body with the foam cells a and the one or more cavities b formed on the inner surface of the foam cells a. Here, the continuous resin phase refers to the region in the foam layer that does not have cavities b, which are formed by the cured thermoplastic resin composition.

[0021] The average cell diameter of the foam cells a is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 30 μm or more. The upper limit is preferably 800 μm or less, more preferably 500 μm or less, and even more preferably 250 μm or less. The upper limit is preferably 1 / 3 or less of the thickness, and more preferably 1 / 5 or less. If it exceeds the above, pinhole-like holes may form in the film or sheet, resulting in a poor appearance, or materials that should be prevented from permeating the film, etc., may leak easily. When the average cell diameter of the foam cells a is greater than or equal to the above, the internal pressure in the foamed molded body is high, and the pressure during the formation of the non-foamed skin layer is sufficient, so the appearance tends to improve. On the other hand, when the average cell diameter of the foam cells a exceeds 800 μm, the strength tends to decrease. Furthermore, by setting the cell diameter of the foam cells a within the above range, an open-cell body can be easily formed.

[0022] The average diameter of the aforementioned cavities b is preferably 0.1 µm or more, and more preferably 0.2 µm or more. The average diameter of cavities b is preferably 100 µm or less, more preferably 50 µm or less, still more preferably 10 µm or less, and particularly preferably 5 µm or less. This allows the aforementioned foamed layer to form an open-cell structure. By setting the average diameter of the aforementioned cavities b to be not less than the lower limit described above, air permeability and moisture permeability can be increased, making it easier to obtain appropriate air permeability and moisture permeability. When the average diameter of the aforementioned cavities b exceeds the upper limit described above, air permeability and moisture permeability become excessively high, which tends to result in reduced selective permeability and strength. In order to form stable communicating pores, the average diameter of cavities b is preferably not more than 1 / 2, more preferably not more than 1 / 3, and even more preferably not more than 1 / 5 of the average cell diameter of foamed cells a.

[0023] The thickness of the non-foamed skin layer is preferably 100 µm or more, and more preferably 200 µm or more. The thickness is preferably 800 µm or less, more preferably 600 µm or less, and even more preferably 400 µm or less. When the thickness of the non-foamed skin layer is not less than the value described above, a good appearance tends to be obtained. On the other hand, when the thickness of the non-foamed skin layer is not more than the value described above, the foamed molded product tends to be obtained with uniform foamed cells a. However, since the aforementioned foamed molded product cannot achieve a predetermined moisture permeability when a non-foamed skin layer is present, it is necessary to remove the non-foamed skin layer from the aforementioned foamed molded product to obtain the desired moisture permeability in the aforementioned foamed molded product.

[0024] The thickness of the foamed skin layer also preferably falls within the range described above. In addition, when the foamed molded product has a foamed skin layer, it is not always necessary to remove the foamed skin layer, and whether to remove it or not can be determined according to the purpose.

[0025] The moisture permeability of the foamed layer of the aforementioned foamed molded product is 20 g / m ２ / 24 hrs (moisture permeability per 1 m ２ of film per day) or more, and preferably 10000 g / m ２ / 24 hrs or less.

[0026] The moisture permeability of the aforementioned foamed molded product is preferably 1000 g / m ２The concentration is 24 hours or more, and more preferably 1500 g / m². ２ / 24hrs or more, more preferably 2000 g / m ２ / 24hrs or more, particularly preferably 3000 g / m ２ The humidity is 24 hours or more. Furthermore, the humidity permeability is preferably 10,000 g / m³. ２ The concentration is less than or equal to 24 hours, and more preferably 9500 g / m². ２ The concentration is less than or equal to 24 hours, and more preferably 9000 g / m². ２ The concentration is less than or equal to 24 hours, and is particularly preferably 8500 g / m². ２ The humidity is less than or equal to 24hrs. The above humidity can be obtained by removing the non-foamed skin layer from the foamed molded body, as described above, leaving only the foamed layer. Therefore, the humidity of the foamed molded body is, in other words, the humidity of the foamed layer. When the humidity of the foamed molded body (the foamed layer) is greater than or equal to the above, many open cells are formed, and the humidity tends to improve. When the humidity of the foamed molded body (the foamed layer) is less than or equal to the above, the selective permeability tends to improve. The humidity can be adjusted by the amount of foaming agent, the amount of defoaming agent, and the molding conditions, and it can also be adjusted by the thickness.

[0027] The foaming method for the foamed molded article described above is not particularly limited, but it is preferable to use a foaming method in which a high-pressure gas is impregnated into the resin composition and then the pressure is reduced (released). In particular, as a foaming method that can obtain molding cycleability, low cost, and homogeneous foaming, it is preferable to use a method in which a foamed molded article is obtained by melting and mixing a foaming agent and a thermoplastic resin composition as described later and expanding the cavity volume during injection molding. The foaming method will be specifically described below with reference to Figure 1.

[0028] Figure 1 is a schematic diagram illustrating an example of a method for manufacturing a foamed molded article according to this embodiment. As shown in Figure 1, the foaming method first involves injecting a molten thermoplastic resin composition together with a chemical blowing agent and / or a supercritical inert gas (hereinafter collectively referred to as the "blowing agent") into a cavity 3 formed by a plurality of clamped molds 1 and 2. Subsequently, by filling the cavity 3 with these, a non-foamed skin layer with a thickness of 100 to 800 μm is formed on the surface. At this timing, at least one mold 2 is moved in the mold opening direction, thereby expanding the volume of the cavity 3 (so-called core backing), which reduces the pressure inside the cavity, causing bubbles to form in the resin composition and obtaining a foamed molded article. More specifically, after filling the cavity 3 with the thermoplastic resin composition and the blowing agent, the mixture is cooled to a predetermined temperature to form a non-foamed skin layer on the surface of the thermoplastic resin composition filled in the cavity 3. When this non-foamed skin layer reaches a predetermined thickness (100 to 800 μm), the mold 2 is moved in the mold opening direction to expand the volume of the cavity 3. The thermoplastic resin composition and the foaming agent can be pre-mixed in the plasticizing region 4a of the injection molding machine 4 before filling the cavity 3.

[0029] Figure 2 is a schematic diagram illustrating an example of a continuous manufacturing method for sheet-shaped foamed molded articles. As shown in Figure 2, a resin mixture of a molten thermoplastic resin composition, a foaming agent, and a defoaming agent is extruded from a T-die 11 into a sheet. The resin mixture, which has foamed due to the release of pressure from extrusion into the atmosphere, is cooled by a chill roll 12. At this time, a back roll 13 may be used to adjust the thickness, take up the sheet, and flatten the sheet surface.

[0030] A chemical blowing agent refers to a gas component that acts as a foaming nucleus or a component added to the molten resin in the resin melting zone of a molding machine as a source of foaming nuclei. Specifically, the chemical blowing agent can be an inorganic compound such as ammonium carbonate, sodium bicarbonate, or azide compounds, or an organic compound such as azo compounds, sulfohydrazide compounds, or nitroso compounds. Examples of the above azide compounds include terephthalic azide and p-ter-butylbenz azide. Examples of the above azo compounds include diazocarbonamide (ADCA), 2,2-azoisobutyronitrile, azohexahydrobenzonitrile, and diazoaminobenzene, with ADCA being preferred. Examples of the above sulfohydrazide compounds include benzenesulfohydrazide, benzene 1,3-disulfohydrazide, diphenylsulfon-3,3-disulfonhydrazide, and diphenyloxide-4,4-disulfonhydrazide, while examples of the above nitroso compounds include N,N-dinitrosopentaethylenetetramine (DNPT).

[0031] When using a chemical blowing agent as a blowing agent, the chemical blowing agent can be prepared as a blowing agent masterbatch using a thermoplastic resin with a melting point lower than the decomposition temperature of the chemical blowing agent as the base material, in order to uniformly disperse the chemical blowing agent in the thermoplastic resin composition. The base thermoplastic resin is not particularly limited as long as its melting point is 120°C or lower than the decomposition temperature of the chemical blowing agent, and examples include olefin resins, polyester resins, polyamide resins, polyvinyl chloride, polystyrene, ABS resin, etc. In this case, the mixing ratio of the chemical blowing agent to the base thermoplastic resin is preferably 0.5 to 10% by weight of the chemical blowing agent per 100% by weight of the base thermoplastic resin. When the amount of chemical blowing agent is 0.5% by weight or more, sufficient blowing does not occur, and when the amount of chemical blowing agent is 10% by weight or less, bubbles are sufficiently formed, and physical properties such as strength and selective permeability tend to improve.

[0032] When using a supercritical inert gas as a blowing agent, carbon dioxide and / or nitrogen can be used as the inert gas. When using supercritical carbon dioxide and / or nitrogen as a blowing agent, the amount of the inert gas is preferably 0.05 to 30% by weight, and more preferably 0.1 to 10% by weight, per 100% by weight of the thermoplastic resin composition. When the amount of supercritical carbon dioxide and / or nitrogen is 0.05% by weight or more, a uniform and fine foam cell a tends to be obtained. When the amount of supercritical carbon dioxide and / or nitrogen is 30% by weight or less, the appearance of the surface of the foamed molded article tends to be excellent.

[0033] Furthermore, while supercritical carbon dioxide or nitrogen can be used individually as blowing agents, they can also be used as a mixture of supercritical carbon dioxide and nitrogen. For thermoplastic resin compositions, nitrogen is suitable for forming finer cells, while carbon dioxide allows for a relatively large gas injection rate, making it suitable for obtaining a higher foaming ratio. Therefore, when using supercritical carbon dioxide as a blowing agent, it can be mixed with the foamed molded product as desired, and the mixing ratio can be in the molar range of 1:9 to 9:1. From the viewpoint of uniform fine foaming, it is preferable to use supercritical nitrogen as a blowing agent for efficiently forming interconnected voids b on the inner surface of fine foamed cells a.

[0034] When the foaming method shown in FIG. 1 is used, the molten thermoplastic resin composition is injected into the cavity 3 together with the blowing agent, so the molten thermoplastic resin composition and the blowing agent can be mixed in the plasticizing region 4a of the injection molding machine 4. When the foaming method shown in FIG. 2 is used, the molten thermoplastic resin composition and the blowing agent can be mixed in the extruder 14. In particular, when supercritical carbon dioxide and / or nitrogen is used as the blowing agent, for example, a method in which gaseous carbon dioxide and / or nitrogen from a gas cylinder 5 is injected directly or after being pressurized by a booster pump 6 into the injection molding machine 4 or the extruder 14 can be employed. From the viewpoints of solubility, permeability and diffusibility into the molten thermoplastic resin composition, it is preferable that such carbon dioxide and / or nitrogen is in a supercritical state inside the molding machine. In one embodiment, a resin composition obtained by melt-kneading a thermoplastic resin and a foam-breaking agent using a kneader such as a co-rotating twin-screw extruder and pelletizing the resulting mixture with a strand cutter or the like can be used.

[0035] As used herein, the term "supercritical state" refers to a state where, when the temperature and pressure of a substance in which a gas phase and a liquid phase coexist are increased, the distinction between the gas phase and the liquid phase disappears in a certain temperature range and pressure range. The temperature and pressure in this state are referred to as critical temperature and critical pressure, respectively. In a supercritical state, a substance has the properties of both gas and liquid, and the fluid generated in a supercritical state is called a supercritical fluid. Such a supercritical fluid has a higher density than gas and lower viscosity than liquid, so it has the property of being extremely easy to diffuse in a substance. In one embodiment, this high diffusibility promotes the fine and uniform dispersion of the foam-breaking agent in the resin, contributing to efficient formation of fine communicating structures (cavities b).

[0036] <Thermoplastic resin composition> The foam molded article of the present invention is formed from a thermoplastic resin composition comprising a thermoplastic resin and a foam breaking agent as described above. The thermoplastic resin composition preferably contains 0.01 wt% or more and 10 wt% or less of the foam breaking agent based on 100 wt% of the thermoplastic resin. As used herein, the "thermoplastic resin composition" may consist of the thermoplastic resin and the foam breaking agent, and may also contain a crosslinking agent, additives and the like in addition to the thermoplastic resin and the foam breaking agent as described below. In the present specification, since the blending amount (content) of the crosslinking agent, additives and the like contained in the thermoplastic resin composition is small as described later, both cases are described by the same term "thermoplastic resin composition".

[0037] (Thermoplastic resin) The thermoplastic resin is preferably an olefin resin, a polyester resin, a polyamide resin, polyvinyl chloride, polystyrene, or an ABS resin. In particular, polyester resins can be suitably used.

[0038] The above polyester resin is a polymer synthesized from a dicarboxylic acid or an ester-forming derivative thereof, and a diol or an ester-forming derivative thereof. Representative examples of such polyester resins include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polyethylene-2,6-naphthalate (PEN). These polyesters have high heat resistance, mechanical properties, chemical resistance, and dimensional stability against moisture absorption. The pore size and other properties are not easily changed even when subjected to mechanical loads such as tension and compression or changes in temperature and humidity, so the foam molded article can maintain stable properties even when subjected to temperature and mechanical loads in various fields such as filters and waterproof and moisture-permeable membranes. Among them, polyethylene terephthalate is preferable from the viewpoints of the above properties, cost and the like.

[0039] Furthermore, these polyester resins may be copolymerized with other components, as long as the objectives of the present invention are not impaired. Specifically, examples of copolymerized components include isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid and its ester-forming derivatives as dicarboxylic acid components. Examples of diol components include ethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Polyoxyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol are also examples. The copolymerization amount is preferably 10 mol% or less per constituting repeating unit, more preferably 7 mol% or less, and even more preferably 5 mol% or less. The total amount of copolymerized dicarboxylic acid components and copolymerized glycol components is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less, when the total polyester is considered as 100% by mass. The copolymerized glycol components also include components that are by-products of polyester polymerization, such as diethylene glycol. Alternatively, homopolyesters such as polyethylene terephthalate may be blended with copolymerized polyesters. In this case, the amount of copolymerized component in the blended polyester resin composition is the same as described above.

[0040] One method for producing polyester resins is to first produce them by carrying out the aforementioned dicarboxylic acid or its synthesis reaction. In one embodiment, one method is to use a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as the main starting materials, carry out an esterification or transesterification reaction according to a conventional method, and then carry out a polycondensation reaction at high temperature and reduced pressure.

[0041] The intrinsic viscosity of the polyester resin is preferably in the range of 0.50 to 0.90 dl / g, and more preferably in the range of 0.55 to 0.85 dl / g, from the viewpoint of film-forming properties.

[0042] (Foam-Breaking Agent) The foamed molded article according to this embodiment consists of a thermoplastic resin composition containing a thermoplastic resin and a foam-breaking agent, as described above. The foam-breaking agent in this disclosure refers to an additive that, during foam molding, locally breaks or thins a part of the cell wall of a foam cell a, thereby forming a cavity b on the inner surface of the foam cell a and enabling adjacent foam cells a to communicate with each other. The foam-breaking agent is preferably both or either a defoaming agent and a lubricant. When the foam-breaking agent is both or either a defoaming agent and a lubricant, dispersing the foam-breaking agent in the molten thermoplastic resin can reduce the surface tension of the thermoplastic resin composition or increase its internal lubricity. This makes it possible to form an open-cell foamed article having foam cells a with arbitrary cavities b in the foamed layer described later when the foamed molded article is formed.

[0043] Focusing on their mode of action, antifoaming agents can be used that possess antifoaming, lubricating, plasticizing, and crystallinity-adjusting properties. These actions are thought to adjust the surface tension, molecular chain slipperiness, melt viscosity, and molecular aggregation state (crystalline state) of the thermoplastic resin composition from foaming to cooling and solidification, making it easier for parts of the cell walls to become locally weakened. As a result, it is thought that cavities b are formed in parts of the cell walls without crushing the entire foam cell a, thereby promoting communication between foam cells a.

[0044] Furthermore, specific compounds exemplified as defoaming agents include silicone compounds, oils, waxes, higher fatty acids, higher alcohols, metal soaps, polyethers, alkyl esters, aromatic esters, alkylamides, phosphate esters, sulfonic acid esters, carboxylate metal salts, phosphates, sulfonates, resins, inorganic particles, organic particles, and organic-inorganic composite particles. Of these, silicone-based, mineral oil-based, and polyether-based defoaming agents that can contribute to the formation of cavities b on the inner surface of foam cell a, as well as compounds that act as lubricants, are preferred.

[0045] The content of the defoaming agent is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and may also be 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, or 3 parts by mass or more, per 100 parts by mass of thermoplastic resin. The content of the defoaming agent is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and may also be 8 parts by mass or less, 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, per 100 parts by mass of thermoplastic resin. By adjusting the content of the defoaming agent, it is easier to form cavities b on the inner surface of the foam cells a, and it is easier to suppress a decrease in the strength of the foam, poor appearance, or bleed-out while increasing the communication between the foam cells a.

[0046] For substances exhibiting the aforementioned modes of action, various additives known as defoamers (for defoaming action), lubricants (for lubrication action), plasticizers (for plasticization action), and nucleating agents (for adjusting crystallinity) can be used. The defoaming agents will be described in detail below.

[0047] 1) Defoaming Agent The foamed molded article according to this embodiment may contain a defoaming agent as a defoaming agent. The defoaming agent is not particularly limited as long as it is a compound that can reduce the surface tension of the thermoplastic resin. The defoaming agent mainly consists of a substance with low surface tension, so it localizes in the foam film, penetrating or thinning the foam film and destroying the foam film. As a result, the defoaming agent is used to eliminate foam in paints and the like. The defoaming agent exhibits a similar effect in this embodiment. That is, the foamed molded article relates to a thermoplastic resin composition containing a defoaming agent as a defoaming agent, and in the process of forming foam cells a from a molten state, the foam cells a themselves are not destroyed during foaming, but only the cell walls of the foam cells a where the defoaming agent is present and have low surface tension are destroyed, thereby forming cavities b. As a result, the foamed molded article can form an open-cell body in which the foam cells a are continuously connected by the cavities b.

[0048] The above-mentioned defoaming agents can be conventionally known, and examples include silicone oil, silicone resin, silicone solution, silicone-free special defoaming agents, alkyl acrylate copolymer, alkyl methacrylate copolymer, alkyl vinyl ether, acrylic copolymer, defoaming polymer, polysiloxane, defoaming polysiloxane, polymethylalkylsiloxane, polyether-based, polyether-modified polysiloxane, paraffinic mineral oil, and the like. From the viewpoint of facilitating the formation of cavities b on the surface of the foaming cell a, which will be described later, silicone-based, mineral oil-based, and polyether-based defoaming agents are preferred. The above-mentioned defoaming agents may be used individually or in combination of two or more types.

[0049] When the above-mentioned foamed molded article contains an antifoaming agent as a defoaming agent, the amount of antifoaming agent added is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on 100% by mass of the thermoplastic resin, from the viewpoint of antifoaming effect and prevention of contamination by bleeding onto the surface of the foam. On the other hand, the amount of antifoaming agent added is preferably 10% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. When the antifoaming agent content is within the above range, sufficient communication can be achieved, the bubbles remain dense and communicate, the strength is high, and humidity control is possible.

[0050] 2) Lubricant The foamed molded article according to this embodiment may contain a lubricant as a foam-breaking agent. The lubricant is not particularly limited as long as it is a compound that exists in a molecular state in the thermoplastic resin and can enhance the internal lubricity of the thermoplastic resin. When added to a resin, the lubricant works as an internal lubricant to reduce friction between the resin particles, thereby improving the fluidity and release properties of the resin. The lubricant exhibits the same effect in this embodiment. That is, the foamed molded article relates to a thermoplastic resin composition containing a lubricant as a foam-breaking agent, and in the process of forming foam cells a from a molten state, the internal lubricity of the resin composition is enhanced, which can destroy the cell walls in areas where the viscosity is locally reduced, thereby forming cavities b. As a result, the foamed molded article can form an open-cell body in which the foam cells a are continuously connected by the cavities b.

[0051] As the above lubricants, conventionally known ones can be used, and examples include polyether compounds, hydrocarbon compounds, fatty acid compounds, fatty acid amide compounds, ester compounds, alcohol compounds, metal soap compounds, natural wax compounds, silicone compounds, and fluorine compounds. Specifically, liquid paraffin, synthetic paraffin, synthetic hard paraffin, synthetic isoparaffin, petroleum hydrocarbons, chlorinated paraffin, paraffin wax, microwax, low polymer polyethylene, fluorocarbon oil, fatty acid compounds with 12 or more carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid, and hexylamide, octylamide, stearylamide, palmitylamide, oleylamide, erucylamide, ethylenebisstearylamide, laurylamide, behenylamide, methylenebisstearylamide, ricinolamide, etc. with 3 to 30 carbon atoms. Examples of lubricants include saturated or unsaturated aliphatic amides and their derivatives, lower alcohol esters of fatty acids, polyhydric alcohol esters of fatty acids, polyglycol esters of fatty acids, fatty alcohol esters of fatty acids such as butyl stearate, hydrogenated castor oil, ethylene glycol monostearate, cetyl alcohol, stearyl alcohol, ethylene glycol, polyethylene glycol with a number average molecular weight of 200 to 10,000, polytetramethylene oxide glycol, polyglycerol, carnauba wax, candelilla wax, montan wax, dimethyl silicone, and silicone gum. Furthermore, examples of lubricants include metal soaps, which are metal salts composed of compounds having straight-chain saturated fatty acids, side-chain acids, and cinoleic acid, with the metal being at least one selected from the group consisting of Li, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn, and Pb. Among these, copolymerized polyethers are preferred as lubricants, and polytetramethylene oxide glycol is particularly preferred, from the viewpoint of their high effect in improving internal lubricity and facilitating the formation of open-cell structures.

[0052] When the above-mentioned foamed molded article contains a lubricant as a foam-breaking agent, the amount of lubricant added is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and preferably 10% by mass or less, and more preferably 8% by mass or less, based on 100% by mass of the thermoplastic resin. When the lubricant content is within the above range, the effect of creating a continuous cell body with internal lubricity is obtained, and the lubricant is dispersed and does not precipitate as powdery aggregates on the surface of the foamed molded article, resulting in a tendency for a superior appearance.

[0053] 3) Other defoaming agents In the foamed molded article according to this embodiment, a defoaming agent or a lubricant is particularly preferably used as a defoaming agent. Furthermore, in one embodiment, in addition to both or either a defoaming agent and a lubricant, a crystal nucleating agent, a plasticizer, etc., may be further included as a defoaming agent. A crystal nucleating agent is a compound that can increase the crystallinity of a thermoplastic resin. In the process of forming foamed cells a from the molten state of the thermoplastic resin composition, the crystal nucleating agent breaks the cell walls in the parts of the foamed cells a where the crystallinity has increased, forming cavities b, and these cavities b form an open-cell body in which the foamed cells a are continuously connected. Examples of crystal nucleating agents include organic carboxylic acid metal salts having 3 to 40 carbon atoms and inorganic particles, from the viewpoint of compatibility with thermoplastic resin compositions (including thermoplastic elastomers).

[0054] When the crystal nucleating agent is a metal salt of an organic carboxylic acid having 3 to 40 carbon atoms, it is preferable that the metal salt of the organic carboxylic acid having 3 to 40 carbon atoms is an alkali metal salt of an aliphatic, alicyclic, or aromatic carboxylic acid having 3 to 40 carbon atoms. Sodium, potassium, and lithium are preferred alkali metals, with sodium being particularly preferred.

[0055] Aliphatic carboxylic acids are compounds in which a carboxyl group is attached to a linear or branched aliphatic group, and may have other substituents such as unsaturated groups, alicyclic groups, aromatic groups, hydroxyl groups, or phosphate ester groups in part of the bond. Aliphatic carboxylic acids are more preferably compounds in which a carboxyl group is attached to a linear saturated aliphatic group. Among these, propionic acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, and montanic acid are preferred. Among alkali metal salts, sodium salts are particularly preferred from the viewpoint of solubility in polyester elastomers.

[0056] In metal salts of organic carboxylic acids having 3 to 40 carbon atoms, the organic carboxylic acid is preferably an aliphatic carboxylic acid metal salt having 3 to 20 carbon atoms, from the viewpoint of melting properties and compatibility with thermoplastic resins. Among these, aliphatic carboxylic acid metal salts having less than 14 carbon atoms are preferred because they can increase the number of crystal nuclei with a small amount of formulation.

[0057] When the nucleating agent is an inorganic particle, it can be used without particular limitation as long as it is an unmelted particle during the melting process and can serve as a nucleus for foaming during the cooling process. Examples of the above inorganic particles include hydroxides such as aluminum hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide; clay (especially hard clay); talc; silica; zeolites; alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate; metal oxides such as zinc oxide, titanium oxide, and alumina; metal powders such as iron powder, copper powder, aluminum powder, nickel powder, zinc powder, titanium powder, and alloy powders; mica; carbon particles; glass fiber; carbon tubes; layered silicates; and glass. Among these, talc or calcium carbonate are particularly preferred from the viewpoint of forming open-cell bodies.

[0058] When the foamed molded article contains a nucleating agent, the content of the nucleating agent is preferably 0.05 to 9.5% by weight per 100% by weight of the thermoplastic resin. When the content of the nucleating agent is 0.05% by weight or more per 100% by weight of the thermoplastic resin, nuclei can be effectively formed. When the nucleating agent is an organic carboxylic acid metal salt having 3 to 40 carbon atoms, and its content is 9.5% by weight or less per 100% by weight of the thermoplastic resin, the pseudo-crosslinking effect of the thermoplastic resin by the metal salt is appropriate, and the melt viscosity during foam molding does not become too high, resulting in good foam moldability and a tendency to obtain a low-density foamed product. When the nucleating agent is an inorganic particle, and its content is 9.5% by weight or less per 100% by weight of the thermoplastic resin, the specific gravity of the foamed molded article does not become too high, and the desired flexibility tends to be obtained.

[0059] A plasticizer is a compound that exists in a molecular state within a thermoplastic resin and reduces its viscosity. In the process of forming foam cells a from a molten thermoplastic resin composition, the plasticizer breaks the cell walls in the areas where the viscosity of the foam cells a has decreased, forming cavities b. These cavities b then form an open-cell body in which the foam cells a are continuously connected. Examples of plasticizers that can be used include the following compounds.

[0060] In other words, phthalate ester plasticizers such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate, diisodecyl phthalate, diundecyl phthalate, and diisononyl phthalate; phosphate ester plasticizers such as tricresyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, trimethyl phosphate, and tris-dichloropropyl phosphate; trimellitic acid ester plasticizers such as trioctyl trimellitic acid and tri-2-ethylhexyl trimellitic acid; dipentaerythritol ester plasticizers; dioctyl adipate, di-2-ethylhexyl adipate, diisobutyl adipate, dibutyl adipate, diisodecyl adipate, dibutyl diglycol adipate, di-2-ethylhexyl azelate, dioctyl sebacate, and methyl azelate. Examples of plasticizers include fatty acid ester plasticizers such as cyricinolate, pyromellitic acid ester plasticizers such as octyl pyromellitic acid ester, epoxidized plasticizers such as epoxidized soybean oil, epoxidized linseed oil, and epoxidized alkyl fatty acid esters, and polyether plasticizers such as adipic acid ether esters, polyether esters, and polyethers, as well as benzoate plasticizers such as diethylene glycol dibenzoate, polypropylene glycol dibenzoate, tripropylene glycol dibenzoate, dipropylene glycol dibenzoate, dibutylene glycol dibenzoate, neopentyl glycol dibenzoate, glyceryl tribenzoate, pentaerythritol tetrabenzoate, triethylene glycol dibenzoate, polyethylene glycol dibenzoate, and trimethylolethane tribenzoate. Among these, trimellitic acid ester plasticizers or pyromellitic acid esters are preferred as plasticizers.

[0061] When the foamed molded article contains a plasticizer, the content of the plasticizer is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 3% by mass or more, and on the other hand, preferably 10% by mass or less, based on 100% by mass of the thermoplastic resin. When the content of the plasticizer is within the above range, crystal nuclei can be effectively formed, and the cavity b described later does not become too large, thereby allowing the degree of air permeability to be controlled.

[0062] In the present invention, it is preferable to set the difference (ΔHSP value) between the Hansen solubility parameter (δ) of the thermoplastic resin used in the foam and the Hansen solubility parameter (δ) of the defoaming agent to 15 or less. The ΔHSP value is more preferably 13.5 or less, even more preferably 10 or less, particularly preferably 8 or less, and most preferably 5 or less. By setting the ΔHSP value to the above or less, communication pores can be efficiently formed, improving permeability such as moisture permeability. Even when the ΔHSP value is high, it may still promote the formation of communication pores and improve humidity permeability compared to the case without the defoaming agent. The reason why communication pores are efficiently formed by reducing the ΔHSP value is not clear, but it is thought that the defoaming agent is dispersed more uniformly and in a finer state in the thermoplastic resin, thus efficiently destroying the bubble partitions. However, the present invention is not limited by this assumption. The lower limit of the ΔHSP value is not limited, but it is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more.

[0063] On the other hand, the ΔHSP value may be greater than 8, and may also be greater than 10. By increasing the ΔHSP value, it may be possible to reduce the bubble diameter while increasing moisture permeability, thereby improving selective permeability and creating a molded body with superior strength.

[0064] (Other Components) The foamed molded article according to this embodiment may contain a crosslinking agent in the thermoplastic resin as needed, to the extent that it does not impair the effects of this embodiment. The crosslinking agent is not particularly limited as long as it is a crosslinking agent that reacts with hydroxyl groups and carboxyl groups in the thermoplastic resin. Examples of the crosslinking agent include epoxy crosslinking agents, carbodiimide crosslinking agents, isocyanate crosslinking agents, acid anhydride crosslinking agents, silanol crosslinking agents, melamine resin crosslinking agents, metal salt crosslinking agents, metal chelate crosslinking agents, and amino resin crosslinking agents. The crosslinking agent can be used alone or in combination of two or more types.

[0065] In this embodiment, the foamed molded article can be compounded with various additives in addition to the above-mentioned anti-foaming agent and crosslinking agent, depending on the purpose. The type of such additives is not particularly limited, and various additives commonly used in foam molding can be used. Specifically, examples of additives include known hindered phenol, sulfur, phosphorus, and amine antioxidants; light stabilizers such as hindered amines, as well as benzotriazole, benzophenone, benzoate, triazole, nickel, and salicyl types; lubricants; fillers; flame retardants; flame retardant aids; mold release agents; antistatic agents; molecular modifiers such as peroxides; metal deactivators; organic and inorganic nucleating agents; neutralizing agents; antacids; antibacterial agents; fluorescent whitening agents; organic and inorganic pigments; and organic and inorganic phosphorus compounds used for the purpose of imparting flame retardancy and thermal stability. The amount of additive can be appropriately selected within a range that does not impair the formation of bubbles, and the amount used for molding ordinary thermoplastic resins can be adopted.

[0066] The composition and composition ratio of the thermoplastic resin composition constituting the foamed molded article according to this embodiment can be determined, for example, from the proton integral ratio of 1H-NMR measured by dissolving the sample in a solvent such as deuterated chloroform.

[0067] This application claims the benefit of priority under Japanese Application No. 2025-053649, filed on 27 March 2025. The entire specification of Japanese Application No. 2025-053649 is incorporated herein by reference.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0069] The following raw materials were used in the following examples and comparative examples. <Thermoplastic resin> The following compounds were prepared as thermoplastic resins.

[0070] As the thermoplastic resin, polyethylene terephthalate (PET) pellets with an intrinsic viscosity of 0.75 were used.

[0071] <Anti-foaming agents> The following formulations were prepared as anti-foaming agents: (Anti-foaming agent a) Silicone-based anti-foaming agent (product name: "Floren AO-5", manufactured by Kyoeisha Chemical Co., Ltd.) ("Anti-foaming agent-1" in Table 1) (Anti-foaming agent b) Polyether-based anti-foaming agent (product name: "SN Deformer 265", manufactured by Sunopco Co., Ltd.) ("Anti-foaming agent-3" in Table 1) (Anti-foaming agent c) Mineral oil-based anti-foaming agent (product name: "Noptam 8034-F", manufactured by Sunopco Co., Ltd.) ("Anti-foaming agent-4" in Table 1) (Anti-foaming agent d) Polyether-based anti-foaming agent (product name: "SN Deformer 327", manufactured by Sunopco Co., Ltd.) ("Anti-foaming agent-2" in Table 1)

[0072] <Preparation of Foamed Molded Articles> First, the thermoplastic resin and the anti-foaming agent were put into a twin-screw extruder set to a predetermined cylinder temperature in the combination and ratio (weight %) shown in Table 1. The mixture was then kneaded in the twin-screw extruder so that the anti-foaming agent was dispersed in the molten thermoplastic resin, thereby obtaining a thermoplastic resin composition. Next, the thermoplastic resin composition extruded from the twin-screw extruder was cut into pellets using a strand cutter. Foamed molded articles were then produced using these pelletized thermoplastic resin compositions by applying the foaming method described later.

[0073] Specifically, using the apparatus shown in Figure 1, the foaming method employed a mold for producing flat plates, consisting of a fixed mold 1 and a movable mold 2, which could form a cavity with a width of 100 mm, a length of 100 mm, and a thickness of 2.0 mm when the mold was clamped, and a cavity with the same width and length but a thickness of 2.0 mm + core back amount (mm) when the core was pushed back in the mold opening direction. In this foaming method, the thermoplastic resin composition and supercritical nitrogen were injected into the plasticizing region 4a of an electric injection molding machine 4 having a mold clamping force of 1800 kN, a screw diameter of 40 mm, and a screw stroke of 180 mm, and injected into the mold without temperature control. Subsequently, when a non-foamed skin layer of 100 to 800 μm was formed in the thermoplastic resin composition by the external injection pressure and internal foaming pressure, the movable mold was moved in the mold opening direction by the length shown as the core back amount (mm) in Table 1, thereby expanding the cavity volume and obtaining a foamed molded body.

[0074] <Evaluation of Foamed Molded Articles> Test specimens were prepared by removing the non-foamed skin layer from the foamed molded articles, and the following various evaluations were performed on these test specimens (hereinafter also referred to as "test specimens").

[0075] (Thickness of the foamed molded body (foamed layer) after removal of the non-foamed skin layer) The thickness (mm) of the test specimen was measured with calipers. This thickness corresponds to the thickness of the foamed layer in the foamed molded body described above. The results are shown in Table 1.

[0076] (Average cell diameter of foam cell a and average diameter of cavity b) First, a cross-section was formed in the test specimen, and a cross-sectional photograph of the specimen was obtained by photographing the area near the center of the cross-section in the thickness direction of the molded body using a scanning electron microscope SU1510 (manufactured by Hitachi High-Technologies). Next, the cross-sectional photograph was processed to measure the equivalent circle diameter of at least 30 adjacent foam cells a as the cell diameter, and the first average value of the 30 equivalent circle diameters was calculated. The above operation was performed at three arbitrary locations, and the average of the first average values ​​obtained at these three locations was determined as the average cell diameter of foam cell a. Furthermore, circular or elliptical shapes with different contrasts on the surface of at least 90 (at least 30 × 3 locations) foam cells a observed in the above cross-sectional photograph were considered as cavities b, the number of cavities b observed from all of these foam cells a was determined, and the equivalent circle diameter of the cavities b was measured as the cavity diameter, and the average value of the equivalent circle diameter was calculated. This average value was taken as the average diameter of cavities b. The results are shown in Table 1.

[0077] (Humidity Permeability) A test specimen (foamed layer) with a diameter of φ70 mm and a thickness of 1 mm was cut from the central part in the thickness direction of the foamed molded body. Using this test specimen, humidity permeability (unit: g / m³) was determined by the A-1 method (calcium chloride method) of JIS L1099. ２ The measurement was taken over 24 hours. The results are shown in Table 1.

[0078] (HSP values) Based on the method described in "Hansen Solubility Parameters; Users Handbook (CRCPress, 2007)" by Charles M. Hansen, the ΔHSP values ​​were calculated using the computer software "Hansen Solubility Parameters in Practice (HSPiP)" under conditions of 25°C. The calculated ΔHSP values ​​for the thermoplastic resin and antifoaming agent are shown in Table 1.

[0079] (Example 1) A foamed molded article was obtained in the same manner as in <Preparation of Foamed Molded Article> above, except that 0.2% by weight of defoaming agent a was added to the thermoplastic resin and pelletized. The foamed molded article of Example 1 exhibited excellent moisture permeability and selective permeability. In the cross-sectional image (Figure 3a), a cavity b (black circle portion) was formed. (Example 2) A foamed molded article was obtained in the same manner as in Example 1 above, except that 0.2% by weight of defoaming agent b was added to the thermoplastic resin and pelletized. Although the foamed molded article of Example 2 had slightly lower moisture permeability, it provided a foamed molded article with fine foam cells and high strength. In the cross-sectional image (Figure 3b), a small amount of cavity b (black circle portion) was formed. (Example 3) A foamed molded article was obtained in the same manner as in Example 1 above, except that 0.2% by weight of defoaming agent c was added to the thermoplastic resin and pelletized. The foamed molded article of Example 3 exhibited excellent moisture permeability and selective permeability. In the cross-sectional image (Figure 3c), many cavities b (black circle portion) were formed. (Example 4) A foamed molded article was obtained in the same manner as in Example 1, except that 0.2% by weight of a foam-breaking agent d was added to the thermoplastic resin and pelletized. The foamed molded article of Example 4 had a humidity permeability of 3000 g / m³. ２ - The humidity permeability was 24 hours, which is lower than that of Examples 1 and 3, but higher than that of Comparative Example 1, indicating a certain degree of selective permeability. In the cross-sectional image (Figure 3d), cavities b were not clearly observed, but since the humidity permeability was higher than that of Comparative Example 1, it is thought that fine interconnected pores were formed. (Comparative Example 1) In Example 1, a foamed molded article was obtained in the same manner as in Example 1, except that a foam-destroying agent was not added to the thermoplastic resin. The foamed molded article of Comparative Example 1 had low humidity permeability, and cavities b were not observed in the cross-sectional image (Figure 3e). Furthermore, the foam cells were also coarse.

[0080]

[0081] <Discussion> According to Table 1, Comparative Example 1, which does not contain a foam-breaking agent, has a humidity permeability of 2500, while Examples 1 to 4, which contain a foam-breaking agent, all exceed this, indicating that the addition of a foam-breaking agent promotes the formation of interconnecting pores. Furthermore, Examples 1 and 3, which have relatively small ΔHSP values, show high humidity permeability, while Examples 2 and 4, with a ΔHSP value of 13.9, show lower humidity permeability. This suggests that as the ΔHSP value increases, the formation of cavities b or interconnecting pores becomes insufficient or finer, and the humidity permeability improvement effect tends to decrease. In particular, although it is difficult to clearly observe cavities b in Figure 3d in Example 4, the humidity permeability is higher than that of Comparative Example 1, suggesting that fine interconnecting pores at a level difficult to observe are formed. Therefore, it can be seen that even in the range of higher ΔHSP values, the humidity permeability improvement effect is achieved compared to the case without foam-breaking agent. From the above, the ΔHSP value, which is the difference between the solubility parameter (δ) of the thermoplastic resin and the Hansen defoaming agent, affects the formation state of the interconnected holes and the humidity permeability. When the ΔHSP value is relatively small, the defoaming agent acts more effectively, making it easier to form interconnected holes and resulting in a tendency for high humidity permeability. Although the example is a core-back molded product, it is considered that even if the apparatus shown in Figure 2 is used, for example, sheet-like foamed molded products with interconnected holes can be efficiently manufactured continuously.

[0082] According to the present invention, a thermoplastic resin composition comprising a thermoplastic resin and a foam-breaking agent and supercritical N ２ By melting and kneading these materials and then injection molding them, foamed molded products and foamed molded products having continuous holes can be provided.

[0083] 1. Fixed mold 2. Moving mold 3. Cavity 4. Injection molding machine 4a. Plasticizing area 5. Gas cylinder 6. Booster pump 7. Pressure control valve 11. T-die 12. Chill roll 13. Back roll 14. Extrusion molding machine

Claims

1. A foamed molded article, wherein the foamed molded article comprises a foam made from a thermoplastic resin composition containing a thermoplastic resin and a foam-breaking agent, and the difference (ΔHSP value) between the Hansen solubility parameter (δ) of the thermoplastic resin and the Hansen solubility parameter (δ) of the foam-breaking agent is 15.0 or less.

2. The foamed molded article according to claim 1, wherein the foamed molded article has a non-foamed surface layer on the surface of the foam.

3. The foamed molded article according to claim 1, wherein the foam has at least a plurality of foam cells a, and has one or more cavities b formed on the inner surface of the foam cells a.

4. The foamed molded article according to claim 3, wherein the average cell diameter of the foamed cells a is 5 μm or more and 800 μm or less.

5. The foamed molded article according to claim 3, wherein the average diameter of the cavity b is 0.1 μm or more and 100 μm or less.

6. The foamed molded body according to claim 2, wherein the foamed molded body is in the shape of a plate, a sheet, or a film, and has a sandwich structure in which the non-foamed skin layer sandwiches the foamed layer in the thickness direction.

7. The humidity permeability of the foam layer of the foamed molded body is 1000 g / m². ２ / 24hrs or more 10000g / m ２ The foamed molded article according to claim 1, wherein the temperature is 24 hours or less.

8. The foamed molded article according to claim 1, wherein the defoaming agent is both or either an antifoaming agent and a lubricant.

9. The foamed molded article according to claim 1, wherein the thermoplastic resin is a polyester resin.

10. The foamed molded article according to claim 1, wherein the foam-breaking agent is contained in an amount of 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the thermoplastic resin.

11. The foamed molded article according to claim 8, wherein the defoaming agent is at least one selected from the group consisting of silicone-based defoaming agents, mineral oil-based defoaming agents, and polyether-based defoaming agents.

12. The foamed molded article according to claim 3, wherein the average diameter of the cavity b is 1 / 2 or less of the average cell diameter of the foamed cell a.

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