JP2012082857A - Outer film for heat insulator, and heat insulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outer film for a heat insulator with superior water vapor barrier properties.SOLUTION: The outer film for a heat insulator includes repeating units represented by the following formulae (1), (2) and (3), and the content of a repeating unit containing a 2,6-naphthylene group is 40 mol% or more relative to the total amount of all of the repeating units: -O-Ar-CO- (1), -CO-Ar-CO- (2), -O-Ar-O-(3) (wherein Arrepresents a 2,6-naphthylene group, a 1,4-phenylene group or a 4,4'-biphenylene group; and Arand Arindependently represents a 2,6-naphthylene group, a 1,4-phenylene group, a 1,3-phenylene group or a 4,4'-biphenylene group, wherein each of hydrogen atoms contained in the group represented by Ar, Aror Armay be substituted by a halogen atom, an alkyl group or an aryl group).

Description

  The present invention relates to an exterior film for a heat insulator composed of liquid crystal polyester. Moreover, this invention relates to the heat insulating body which uses this exterior film for heat insulating bodies.

  2. Description of the Related Art As a heat insulator for a cooling / cold insulation device / container such as a refrigerator, a freezer, a low-temperature container, a portable cooler, etc., a core material wrapped with an exterior film is known. This exterior film is required to have a water vapor barrier property in order to prevent water vapor from entering the outer film and thereby reducing the heat insulation property of the heat insulator. Therefore, a liquid crystal polyester film has been studied as the exterior film because it has excellent water vapor barrier properties. For example, Patent Document 1 discloses that a liquid crystal polyester composition film having a liquid crystal polyester as a continuous phase and a copolymer having a functional group that reacts with the liquid crystal polyester as a dispersed phase is used as an exterior film for an insulator. As the liquid crystalline polyester, 60 mol% of repeating units derived from p-hydroxybenzoic acid, 15 mol% of structural units derived from terephthalic acid, 5 mol% of structural units derived from isophthalic acid, and 4 , 4-dihydroxybiphenyl having 20 mol% structural units, p-hydroxybenzoic acid-derived repeating units 73 mol%, and 6-hydroxy-2-naphthoic acid-derived repeating units 27 mol % Are specifically disclosed.

Japanese Patent Laid-Open No. 11-60758

  An object of the present invention is to provide an exterior film for a heat insulator that is made of liquid crystal polyester and that is excellent in water vapor barrier properties.

  In order to achieve the object, the present invention comprises a repeating unit represented by the following formula (1), a repeating unit represented by the following formula (2), and a repeating unit represented by the following formula (3). And a heat-insulating exterior film comprising a liquid crystal polyester having a content of repeating units containing 2,6-naphthylene groups and not less than 40 mol% based on the total amount of all repeating units.

—O—Ar ¹ —CO— (1)
—CO—Ar ² —CO— (2)
—O—Ar ³ —O— (3)

(Ar ¹ represents a 2,6-naphthylene group, a 1,4-phenylene group or a 4,4′-biphenylylene group. Ar ² and Ar ³ are each independently a 2,6-naphthylene group, 1,4 Represents a -phenylene group, a 1,3-phenylene group or a 4,4'-biphenylylene group, wherein the hydrogen atoms in the group represented by Ar ¹ , Ar ² or Ar ³ are each independently a halogen atom or an alkyl group; Alternatively, it may be substituted with an aryl group.)

  Moreover, this invention provides the heat insulating body formed by wrapping a core material with the said exterior film for heat insulating bodies.

  The exterior film for a heat insulator of the present invention is excellent in water vapor barrier properties, and by using this, a heat insulator excellent in heat insulation durability can be obtained.

  The liquid crystalline polyester constituting the heat insulating body exterior film of the present invention is a polyester that exhibits optical anisotropy when melted, and may be referred to as a repeating unit represented by the following formula (1) (hereinafter referred to as a repeating unit (1)). ), A repeating unit represented by the following formula (2) (hereinafter sometimes referred to as repeating unit (2)), and a repeating unit represented by the following formula (3) (hereinafter referred to as repeating unit (3)) There is a).

—O—Ar ¹ —CO— (1)
—CO—Ar ² —CO— (2)
—O—Ar ³ —O— (3)

(Ar ¹ represents a 2,6-naphthylene group, a 1,4-phenylene group or a 4,4′-biphenylylene group. Ar ² and Ar ³ are each independently a 2,6-naphthylene group, 1,4 -Represents a phenylene group, a 1,3-phenylene group or a 4,4'-biphenylylene group, wherein the hydrogen atom in the group represented by Ar ¹ , Ar ² or Ar ³ is independently a halogen atom or a carbon number (It may be substituted with an alkyl group of 1 to 10 or an aryl group of 6 to 20 carbon atoms.)

As said halogen atom, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are mentioned. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butyl group, n-hexyl group, 2-ethylhexyl group, An n-octyl group and n-decyl group are mentioned, The carbon number is 1-10 normally. Examples of the aryl group include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 1-naphthyl group, and a 2-naphthyl group, and the number of carbon atoms is usually 6 to 20. . When the hydrogen atom is substituted with these groups, the number is usually 2 or less for each group represented by Ar ¹ , Ar ² or Ar ³ , and preferably 1 It is as follows.

The repeating unit (1) is a repeating unit derived from a predetermined aromatic hydroxycarboxylic acid. As the repeating unit (1), Ar ¹ is preferably a 2,6-naphthylene group, that is, a repeating unit derived from 6-hydroxy-2-naphthoic acid is preferable.

The repeating unit (2) is a repeating unit derived from a predetermined aromatic dicarboxylic acid. As the repeating unit (2), Ar ² is a 2,6-naphthylene group, that is, a repeating unit derived from 2,6-naphthalenedicarboxylic acid, and Ar ² is a 1,4-phenylene group, Repeating units derived from terephthalic acid are preferred.

The repeating unit (3) is a repeating unit derived from a predetermined aromatic diol. As the repeating unit (3), Ar ³ is a 1,4-phenylene group, that is, a repeating unit derived from hydroquinone, and Ar ³ is a 4,4′-biphenylylene group, that is, 4,4′-. Repeating units derived from dihydroxybiphenyl are preferred.

Content of repeating unit containing 2,6-naphthylene group in liquid crystalline polyester, that is, repeating unit (1) in which Ar ¹ is 2,6-naphthylene group, repeating unit in which Ar ² is 2,6-naphthylene group (2) and the total content of the repeating unit (3) in which Ar ³ is a 2,6-naphthylene group is the total amount of all repeating units (the mass of each repeating unit constituting the liquid crystal polyester is expressed by the formula of each repeating unit) By dividing by the amount, the substance amount equivalent amount (mole) of each repeating unit is obtained, and the sum thereof is 40 mol% or more. By forming a liquid crystal polyester having such a predetermined repeating unit composition into a film, a liquid crystal polyester film having excellent water vapor barrier properties can be obtained. The content of the 2,6-naphthylene group is preferably 50 mol% or more, more preferably 60 mol% or more, and further preferably 70 mol% or more.

  In the liquid crystal polyester, the content of the repeating unit (1) is preferably 30 to 80 mol%, more preferably 40 to 70 mol%, still more preferably 45 to 65 mol, based on the total amount of all repeating units. The content of the repeating unit (2) is preferably 10 to 35 mol%, more preferably 15 to 30 mol%, still more preferably 17.5 to 27.27%, based on the total amount of all repeating units. The content of the repeating unit (3) is preferably 10 to 35 mol%, more preferably 15 to 30 mol%, still more preferably 17.5 to the total amount of all repeating units. 27.5 mol%. The liquid crystal polyester having such a predetermined repeating unit composition has an excellent balance between heat resistance and moldability. In addition, it is preferable that content of a repeating unit (2) and content of a repeating unit (3) are substantially equal. The liquid crystalline polyester may have repeating units other than the repeating units (1) to (3) as necessary, but the content thereof is usually 10 mol with respect to the total amount of all repeating units. % Or less, preferably 5 mol% or less.

A typical example of a liquid crystal polyester having high heat resistance and high melt tension is a repeating unit (1) in which Ar ¹ is a 2,6-naphthylene group, that is, 6-hydroxy-2-hydroxy, based on the total amount of all repeating units. The repeating unit derived from naphthoic acid is preferably 40 to 74.8 mol%, more preferably 40 to 64.5 mol%, still more preferably 50 to 58 mol%, and Ar ² is a 2,6-naphthylene group. The repeating unit (2), that is, a repeating unit derived from 2,6-naphthalenedicarboxylic acid, is preferably 12.5 to 30 mol%, more preferably 17.5 to 30 mol%, still more preferably 20 to 25 a mole%, repeating units Ar ² is 1,4-phenylene group (2), i.e., repeating units derived from terephthalic acid, preferably 0.2 to 15 mol%, more preferably 0. 12 mol%, more preferably has 2 to 10 mol%, the repeating units Ar ³ is 1,4-phenylene group (3), i.e., a repeating unit derived from hydroquinone, preferably 12.5 to 30 mol %, More preferably 17.5 to 30 mol%, still more preferably 20 to 25 mol%, and the content of the repeating unit (2) in which Ar ² is a 2,6-naphthylene group is such that Ar ² is The total content of the repeating unit (2) which is a 2,6-naphthylene group and the repeating unit (2) wherein Ar ² is a 1,4-phenylene group is preferably 0.5 mol times or more, more preferably It is 0.6 mol times or more.

  The liquid crystalline polyester is a monomer that gives a repeating unit (1), that is, a predetermined aromatic hydroxycarboxylic acid, a monomer that gives a repeating unit (2), that is, a monomer that gives a predetermined aromatic dicarboxylic acid, and a repeating unit (3) That is, a predetermined aromatic diol is combined with the total amount of monomers having 2,6-naphthylene groups, that is, the total amount of 6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid and 2,6-naphthalenediol. The polymer can be produced by polymerization (polycondensation) so as to be 40 mol% or more based on the total amount of all monomers. In that case, the aromatic hydroxycarboxylic acid, the aromatic dicarboxylic acid, and the aromatic diol may be independently replaced by a part or all of the polymerizable derivatives thereof. Examples of polymerizable derivatives of a compound having a carboxyl group such as an aromatic hydroxycarboxylic acid and an aromatic dicarboxylic acid include those obtained by converting a carboxyl group into an alkoxycarbonyl group or an aryloxycarbonyl group, and a carboxyl group as a haloformyl. And a group formed by converting a carboxyl group into an acyloxycarbonyl group. Examples of polymerizable derivatives of hydroxyl group-containing compounds such as aromatic hydroxycarboxylic acids and aromatic diols include those obtained by acylating a hydroxyl group and converting it to an acyloxyl group.

  Moreover, it is preferable to manufacture liquid crystalline polyester by melt-polymerizing a monomer and solid-phase-polymerizing the obtained polymer (prepolymer). Thereby, liquid crystalline polyester with high heat resistance and high melt tension can be manufactured with good operability. Melt polymerization may be carried out in the presence of a catalyst. Examples of this catalyst include metal compounds such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, , N, N-dimethylaminopyridine, N-methylimidazole, and the like, and nitrogen-containing heterocyclic compounds are preferably used.

  The liquid crystal polyester has a flow initiation temperature of preferably 280 ° C. or higher, more preferably 290 ° C. or higher, further preferably 295 ° C. or higher, and usually 380 ° C. or lower, preferably 350 ° C. or lower. As the flow start temperature is higher, the heat resistance and melt tension are more likely to be improved. However, if the flow start temperature is too high, a high temperature is required for melting, and thermal deterioration tends to occur during molding.

The flow start temperature is also called flow temperature or flow temperature, and is 4 ° C / min under a load of 9.8 MPa (100 kg / cm ² ) using a capillary rheometer having a nozzle having an inner diameter of 1 mm and a length of 10 mm. This is a temperature at which the melt viscosity shows 4800 Pa · s (48,000 poise) when the heated melt of liquid crystal polyester is extruded from the nozzle at a temperature rising rate, and is a measure of the molecular weight of the liquid crystal polyester (Naoyuki Koide) Ed., “Liquid Crystal Polymer—Synthesis / Molding / Application—”, CMC, June 5, 1987, p. 95).

  The liquid crystal polyester may be blended with other components as necessary to form a composition. Examples of other components include fillers, thermoplastic resins other than liquid crystal polyesters, and additives. The ratio of the liquid crystal polyester in the entire composition is preferably 80% by mass or more, and more preferably 90% by mass or more.

  Examples of fillers include glass fibers such as milled glass fibers and chopped glass fibers, potassium titanate whiskers, alumina whiskers, aluminum borate whiskers, silicon carbide whiskers, silicon nitride whiskers, and other metal or non-metallic whiskers. , Glass beads, hollow glass spheres, glass powder, mica, talc, clay, silica, alumina, potassium titanate, wollastonite, calcium carbonate (heavy, light, colloidal, etc.), magnesium carbonate, basic magnesium carbonate, sodium sulfate , Calcium sulfate, barium sulfate, calcium sulfite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium silicate, silica sand, quartz, quartz, titanium oxide, zinc oxide, iron oxide graphite, molybdenum, asbestos, silica alumina Fiber , Alumina fibers, gypsum fibers, carbon fibers, carbon black, white carbon, diatomaceous earth, bentonite, sericite, Shirasu and graphite are mentioned, it is also possible to use two or more of them, if necessary. Among these, glass fiber, mica, talc and carbon fiber are preferably used.

  The filler may be surface-treated as necessary, and examples of the surface treatment agent include reactivity such as a silane coupling agent, a titanate coupling agent, and a borane coupling agent. Examples include coupling agents and lubricants such as higher fatty acids, higher fatty acid esters, higher fatty acid metal salts, and fluorocarbon surfactants.

  Examples of thermoplastic resins other than liquid crystal polyesters include polycarbonate, polyamide, polysulfone, polyphenylene sulfide, polyphenylene ether, polyether ketone, and polyetherimide resin.

  Examples of additives include mold release improvers such as fluororesins and metal soaps, nucleating agents, antioxidants, stabilizers, plasticizers, lubricants, anti-coloring agents, coloring agents, ultraviolet absorbers, antistatic agents, Examples include lubricants and flame retardants.

  By forming the liquid crystal polyester thus obtained or a composition thereof into a film, a liquid crystal polyester film that becomes the heat insulating body exterior film of the present invention can be obtained. Examples of the film forming method include an extrusion molding method, a press molding method, a solution casting method, and an injection molding method, and the extrusion molding method is preferable. Examples of the extrusion molding method include a T-die method and an inflation method. In the T-die method, uniaxial stretching or biaxial stretching may be performed.

  The draw ratio (draft ratio) of the uniaxially stretched film is usually 1.1 to 40, preferably 10 to 40, and more preferably 15 to 35. The draw ratio in the MD direction (extrusion direction) of the biaxial film is usually 1.2 to 40 times, and the draw ratio in the TD direction (direction perpendicular to the extrusion direction) of the biaxial film is usually 1.2 to 20 times. Is double. The stretch ratio in the MD direction of the inflation film (drawdown ratio = bubble take-off speed / resin discharge speed) is usually 1.5 to 50, preferably 5 to 30, and the stretch ratio of TD of the inflation film (blow ratio = bubble). (Diameter / annular slit diameter) is usually 1.5 to 10, preferably 2 to 5.

  The thickness of the liquid crystal polyester film is preferably 5 to 100 μm, more preferably 10 to 75 μm, and still more preferably 15 to 75 μm. If it is too thin, the strength will be insufficient, and if it is too thick, the flexibility will be insufficient.

The liquid crystal polyester film thus obtained is excellent in water vapor barrier properties by being composed of the liquid crystal polyester having the predetermined repeating unit composition, and is used as an exterior film for a heat insulator of the present invention. Temperature 40 ° C. and water vapor permeability, measured at a relative humidity of 90% for the exterior film is preferably 0.1g / m ² · 24h or less, and more preferably not more than 0.05g / m ² · 24h.

  A laminated film obtained by laminating a plurality of liquid crystal polyester films or laminating another film such as a thermoplastic resin film on the liquid crystal polyester film is also used as the exterior film for an insulator of the present invention. Moreover, in order to further improve the water vapor barrier property on the liquid crystal polyester film or the laminated film, a laminated film obtained by providing a water vapor barrier layer or other functional layers is also used as the exterior film for a thermal insulator of the present invention. Used.

  The heat insulator of the present invention is obtained by wrapping the core material with the heat insulating film for heat insulator of the present invention. At that time, it is preferable that the inside of the exterior film (inside where the core material exists) is evacuated to be in a reduced pressure state because the heat insulation and heat insulation properties are improved. Typically, the vacuum insulator is formed by cutting an exterior film into a predetermined size and shape, wrapping a core material with the film, adhering or fusing the periphery of the film, and then opening the film from the opening of the film. The inside (the inside where the core material is present) is vacuumed to obtain a vacuum, and then the opening of the film is sealed.

  Examples of the core material include fine powders such as alumina, silica, pearlite, calcium silicate compact, urethane foam, carbon foam, phenol foam, and phenol-urethane foam. Among these, resin foams such as urethane foam, phenol foam, and phenol-urethane foam are preferable. Moreover, it is preferable that this resin foam has an open cell inside.

  The heat insulating body of the present invention thus obtained has excellent heat insulation durability because the core material is wrapped in the heat insulating body outer film of the present invention having excellent water vapor barrier properties. For example, a refrigerator, a freezer It is used as a thermal insulator for equipment and containers for cooling and cooling such as low temperature containers and portable coolers. Moreover, it is used also as a heat insulator of industrial facilities, such as a reactor, a tank, and piping.

[Measurement of flow start temperature]
Using a flow tester (“CFT-500 type” manufactured by Shimadzu Corporation), about 2 g of the sample was filled into a capillary rheometer equipped with a die having an inner diameter of 1 mm and a length of 10 mm, and 9.8 MPa (100 kgf / The sample was extruded while melting at a temperature rising rate of 4 ° C./min under a load of cm ² ), and a temperature at which the melt viscosity was 4800 Pa · s (48000 poise) was measured.

[Evaluation of water vapor barrier properties]
In accordance with JIS K7126 (A method: differential pressure method), a gas permeability / moisture permeability measuring device (“GTR-10X” from GTR Tech Co., Ltd.) under conditions of a temperature of 40 ° C. and a relative humidity of 90% The transmittance was measured.

Production Example 1
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas introduction tube, a thermometer and a reflux condenser, 1033.499 g (5.5 mol) of 6-hydroxy-2-naphthoic acid and 2,378 of 2,6-naphthalenedicarboxylic acid 0.33 g (1.75 mol), 83.07 g (0.5 mol) of terephthalic acid, 272.52 g of hydroquinone (2.475 mol: 0.225 based on the total amount of 2,6-naphthalenedicarboxylic acid and terephthalic acid) Molar excess), 1226.87 g (12 mol) of acetic anhydride, and 0.17 g of 1-methylimidazole as a catalyst, and after replacing the gas in the reactor with nitrogen gas, stirring at room temperature under a nitrogen gas stream To 145 ° C. over 15 minutes and refluxed at 145 ° C. for 1 hour. Next, while distilling off by-product acetic acid and unreacted acetic anhydride, the temperature was raised from 145 ° C. to 310 ° C. over 3 hours and 30 minutes, held at 310 ° C. for 3 hours, then the contents were taken out and cooled to room temperature did. The obtained solid was pulverized to a particle size of about 0.1 to 1 mm with a pulverizer, then heated from room temperature to 250 ° C. over 1 hour in a nitrogen atmosphere, and increased from 250 ° C. to 310 ° C. over 10 hours. Solid state polymerization was performed by warming and holding at 310 ° C. for 5 hours. After solid state polymerization, the mixture was cooled to obtain a powdery liquid crystal polyester. In this liquid crystal polyester, 55 mol% of the repeating unit (1) in which Ar ¹ is a 2,6-naphthylene group and Ar ² is a 2,6-naphthylene group in terms of the total amount of all repeating units ( 2) 17.5 mol%, Ar ² is a repeating unit (2) having a 1,4-phenylene group, 5 mol%, and Ar ³ is a repeating unit (3) having a 1,4-phenylene group, 22. 5%, and the flow start temperature was 333 ° C.

Production Example 2
In the same reactor as in Production Example 1, 911 g (6.6 mol) of p-hydroxybenzoic acid, 274 g (1.65 mol) of terephthalic acid, 91 g (0.55 mol) of isophthalic acid, 4,4′-dihydroxybiphenyl 409 g (2.2 mol), 1235 g of acetic anhydride (12.1 mol), and 0.17 g of 1-methylimidazole as a catalyst were added, and the gas in the reactor was replaced with nitrogen gas, followed by stirring under a nitrogen gas stream While raising the temperature from room temperature to 150 ° C. over 15 minutes, the mixture was refluxed at 150 ° C. for 1 hour. Then, after adding 1.7 g of 1-methylimidazole, the temperature was raised from 150 ° C. to 320 ° C. over 2 hours and 50 minutes while distilling off by-product acetic acid and unreacted acetic anhydride, and an increase in torque was observed. At that time, the contents were removed and cooled to room temperature. The obtained solid was pulverized to a particle size of about 0.1 to 1 mm with a pulverizer, then heated from room temperature to 250 ° C. over 1 hour in a nitrogen atmosphere, and increased from 250 ° C. to 285 ° C. over 5 hours. Solid state polymerization was performed by warming and holding at 285 ° C. for 3 hours. After solid state polymerization, the mixture was cooled to obtain a powdery liquid crystal polyester. In this liquid crystal polyester, 60 mol% of the repeating unit (1) in which Ar ¹ is a 1,4-phenylene group, 15 mol% of the repeating unit (2) in which Ar ² is a 1,4-phenylene group, and Ar ² is The repeating unit (2) which is a 1,3-phenylene group has 5 mol% and the repeating unit (3) whose Ar ³ is a 4,4′-biphenylylene group has 20%, and its flow initiation temperature is 327 ° C. there were.

Example 1
The liquid crystalline polyester obtained in Production Example 1 was granulated with a twin screw extruder ("PCM-30" by Ikegai Co., Ltd.), pelletized, and then supplied to a single screw extruder (screw diameter 50 mm). It was melted, extruded from a T die (lip length: 300 mm, lip clearance: 1 mm, die temperature: 350 ° C.) and cooled to obtain a liquid crystal polyester film having a thickness of 25 μm. The liquid crystal polyester film has a water vapor permeability of 0.011 g / m ² · 24 h, and is excellent in water vapor barrier properties as an exterior film for a heat insulator.

Comparative Example 1
A liquid crystal polyester film having a thickness of 25 μm was obtained in the same manner as in Example 1 except that the liquid crystal polyester obtained in Production Example 2 was used in place of the liquid crystal polyester obtained in Production Example 1. The water vapor permeability of the liquid crystal polyester film is 0.343 g / m ² · 24 h, and the water vapor barrier property is insufficient as an exterior film for a heat insulator.

Claims (5)

It has a repeating unit represented by the following formula (1), a repeating unit represented by the following formula (2), and a repeating unit represented by the following formula (3), and includes a 2,6-naphthylene group. An exterior film for a heat insulator comprising a liquid crystal polyester having a repeating unit content of 40 mol% or more based on the total amount of all repeating units.
—O—Ar ¹ —CO— (1)
—CO—Ar ² —CO— (2)
—O—Ar ³ —O— (3)
(Ar ¹ represents a 2,6-naphthylene group, a 1,4-phenylene group or a 4,4′-biphenylylene group. Ar ² and Ar ³ are each independently a 2,6-naphthylene group, 1,4 Represents a -phenylene group, a 1,3-phenylene group or a 4,4'-biphenylylene group, wherein the hydrogen atoms in the group represented by Ar ¹ , Ar ² or Ar ³ are each independently a halogen atom or an alkyl group; Alternatively, it may be substituted with an aryl group.) The exterior film for a heat insulating body according to claim 1, wherein the water vapor permeability measured at a temperature of 40 ° C. and a relative humidity of 90% is 0.1 g / m ² · 24 h or less.   A heat insulator formed by wrapping a core material with the exterior film for a heat insulator according to claim 1 or 2.   The heat insulator according to claim 3, wherein an inner side of the heat insulating film is in a reduced pressure state.   The heat insulator according to claim 3 or 4, wherein the core material is a resin foam.