Crosslinked resin foam

Abstract

To provide a crosslinked resin foam capable of suppressing generation of harmful gases such as ammonia and excellent in foam property and shape stability.SOLUTION: A crosslinked resin foam obtained by crosslinking and foaming a resin composition comprising (A) a thermoplastic olefin resin and (B) a blowing agent, the crosslinked resin foam having a gel fraction of 35 to 85% and having a concentration of ammonium ions detected by ion chromatography of less than 1,000 μg per 1 g of the crosslinked resin foam.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a crosslinked resin foam. [Background technology]

[0002] Crosslinked resin foams obtained by forming a crosslinked structure (three-dimensional network structure) in a resin composition and foaming it have excellent properties such as light weight, heat insulation, and compressive stress due to their cellular structure, and can also be provided with desired water resistance, chemical resistance, etc. by selecting the type of resin and blowing agent. For these reasons, crosslinked resin foams are widely used in fields such as building materials, electronic products, automobiles, energy equipment, and medicine.

[0003] Azodicarbonamide (ADCA) is widely known as a blowing agent used in the production of crosslinked resin foams (see, for example, Patent Document 1). ADCA is a thermal decomposition type blowing agent that decomposes at around 200°C, generating a large amount of nitrogen gas to form a cellular structure in a resin composition. While ADCA has excellent foaming properties, its thermal decomposition generates gases such as carbon monoxide and ammonia in addition to nitrogen gas, and also produces sublimable decomposition residues such as cyanuric acid, which can easily cause problems such as environmental pollution, metal corrosion, foaming furnace contamination, and mold contamination. Therefore, blowing agent compositions have been proposed that reduce the amount of ADCA used by combining them with other blowing agents, while also incorporating a higher fatty acid salt to reduce corrosiveness. For example, Patent Document 2 discloses a blowing agent composition containing specific amounts of ADCA, p,p'-oxybis(benzenesulfonohydrazide) (OBSH), sodium bicarbonate or potassium bicarbonate, citric acid or a salt thereof, and a higher fatty acid salt, and an expandable thermoplastic polymer composition containing 0.01 to 0.2% by weight of this blowing agent composition. Patent Document 2 also discloses that by extruding this expandable thermoplastic polymer composition from a kneading extruder, a low-expansion sheet with an expansion ratio of 1.01 to 3 times can be obtained, and that this expandable thermoplastic polymer composition may contain a crosslinking agent or a crosslinking aid. Furthermore, crosslinked resin foams using other blowing agents instead of ADCA as the blowing agent have also been proposed. For example, Patent Document 3 discloses an invention of a method for producing a polyolefin resin foam, which comprises mixing raw materials containing a polyolefin resin, a crosslinking agent, sodium bicarbonate that decomposes upon heating to generate carbon dioxide gas and water vapor, and a water-absorbent resin, the content of the water-absorbent resin being set so that the water absorption capacity, determined based on the product of the water absorption capacity and the content of the water-absorbent resin, is 20 to 1,300 parts by mass per 100 parts by mass of the polyolefin resin, and then heating the mixture, and foaming the polyolefin resin with carbon dioxide gas generated by the decomposition of the sodium bicarbonate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-245251 [Patent Document 2] Japanese Patent Application Publication No. 11-021364 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-217639 Summary of the Invention [Problem to be solved by the invention]

[0005] If the amount of ADCA is reduced, as in the expandable thermoplastic polymer composition described in Patent Document 2, the expandability of the composition will be low, and the resulting foam will have a poor expansion ratio, as described above. Furthermore, the technology described in Patent Document 2 is premised on the use of ADCA, even if only in small amounts, and this may cause problems such as environmental pollution in the long term. Furthermore, the resin foam described in Patent Document 3 uses sodium bicarbonate as a blowing agent, as mentioned above. Sodium bicarbonate generates carbon dioxide gas and water vapor upon thermal decomposition. After foaming, the water vapor cools and turns into water, reducing the volume. This reduces the pressure inside the foam cells, causing shrinkage and deformation of the foam. To address this issue, the resin foam described in Patent Document 3 is formulated with a water-absorbing resin, which absorbs the water vapor generated by the thermal decomposition of sodium bicarbonate, thereby preventing the foam from shrinking. However, water-absorbing resins absorb rainwater and moisture, which can cause dewdrops to form on the foam surface and reduce its insulating properties.

[0006] An object of the present invention is to provide a crosslinked resin foam that is excellent in foaming properties and shape stability while suppressing the generation of harmful gases such as ammonia gas. [Means for solving the problem]

[0007] As a result of intensive studies aimed at solving the above problems, the present inventors have found that, even without using ADCA as a blowing agent, shrinkage, deformation, and the like of a crosslinked resin foam after production can be effectively suppressed by increasing the gel fraction of the crosslinked resin foam within a specific range. Based on these findings, the present inventors have conducted further studies and have now completed the present invention.

[0008] That is, the above problems were solved by the following means. [1] A crosslinked resin foam obtained by crosslinking and foaming a resin composition containing (A) a thermoplastic olefin resin and (B) a foaming agent, the crosslinked resin foam has a gel fraction of 35 to 85%, The crosslinked resin foam has an ammonium ion concentration of less than 1000 μg / 1 g of crosslinked resin foam as detected by ion chromatography. Cross-linked resin foam. [2] The crosslinked resin foam according to [1] above, having an expansion ratio of 7 times or more. [3] The crosslinked resin foam according to [1] or [2], wherein the crosslinked structure of the crosslinked resin foam is formed by the action of an organic peroxide in the resin composition and / or the action of electron beam irradiation. [4] The crosslinked resin foam according to any one of [1] to [3] above, wherein a siloxane compound is not included in the five types of outgassing that are extracted in large amounts when detected by gas chromatography mass spectrometry of the crosslinked resin foam. [5] The crosslinked resin foam according to any one of [1] to [4] above, wherein the (B) foaming agent contains an inorganic carbonate. [Effects of the Invention]

[0009] The crosslinked resin foam of the present invention is inhibited from generating harmful gases such as ammonia gas, and is excellent in foaming properties and shape stability. DETAILED DESCRIPTION OF THE INVENTION

[0010] The crosslinked resin foam of the present invention is a crosslinked resin foam obtained by crosslinking and foaming a resin composition containing (A) a thermoplastic olefin resin and (B) a blowing agent. The crosslinked resin foam has a gel fraction of 35 to 85%, and an ammonium ion concentration of less than 1000 μg / g of crosslinked resin foam as detected by ion chromatography. A preferred embodiment of the crosslinked resin foam of the present invention will be described.

[0011] [Resin composition] The resin composition used to form the crosslinked resin foam of the present invention (hereinafter also referred to as the "resin composition used in the present invention") contains (A) a thermoplastic olefin resin (also referred to as component (A)) and (B) a blowing agent (also referred to as component (B)). Components (A) and (B), as well as the optional components described below, may each be used alone or in combination of two or more. The resin composition preferably does not substantially contain ADCA as a foaming agent. That is, the content of ADCA in the resin composition is preferably 0.1% by mass or less, more preferably 0.01% by mass or less, even more preferably 0.001% by mass or less, and even more preferably 0.0001% by mass or less, and it is particularly preferred that the resin composition does not contain ADCA. The components contained in the resin composition used in the present invention will be described below.

[0012] ((A) Thermoplastic olefin resin) The resin composition used in the present invention contains (A) a thermoplastic olefin resin as a base resin. The thermoplastic olefin resin may be an olefin homopolymer or an olefin copolymer. An olefin homopolymer is a polymer of one type of olefin. An olefin copolymer is a copolymer of an olefin with another olefin, or a copolymer of an olefin with a compound other than an olefin that has a carbon-carbon double bond (e.g., a vinyl compound or a styrene compound). In other words, any polymer that contains an olefin component as a constituent is included in component (A).

[0013] Component (A) preferably contains (A-1) a resin selected from polyethylene and polypropylene (also referred to as component (A-1)). It is also preferable that component (A) is component (A-1). Component (A) may contain, together with component (A-1), a resin other than component (A-1). As the resin other than component (A-1), (A-2) a resin having a structure that stabilizes radicals (also referred to as component (A-2)) is preferred.

[0014] Component (A-1) is preferably a polyethylene resin. Examples of this polyethylene resin include low-density polyethylene and high-density polyethylene. Of these, low-density polyethylene is preferred. In the present invention, low-density polyethylene is polyethylene having a density of 860 kg / m 3 More than 940kg / m 3 The high-density polyethylene refers to polyethylene having a density greater than that of the low-density polyethylene. The low-density polyethylene may be what is known as "low-density polyethylene" or "ultra-low-density polyethylene" having long chain branches, or may be linear low-density polyethylene obtained by copolymerizing ethylene with a small amount of an α-olefin monomer.

[0015] Examples of the "radical-stabilizing structure" in component (A-2) include a double bond or a polar group. The polar group is a group containing a heteroatom (such as an oxygen atom, sulfur atom, or nitrogen atom), such as an ester group, an ether group, a thioester group, a thioether group, a carboxy group, a hydroxy group, an amino group, or an imino group. Specific examples of preferred components (A-2) include ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-vinyl acetate copolymers, polybutadiene compounds (preferably butadiene-based elastomers), and styrene-based elastomers. Among these, ethylene-vinyl acetate copolymers and butadiene-based elastomers are preferred. A butadiene-based elastomer is an elastomer containing a component derived from a butadiene compound. The butadiene compound includes not only butadiene itself, but also compounds in which one or more hydrogen atoms of butadiene have been substituted. For example, isoprene (2-methyl-1,3-butadiene) is a type of butadiene compound. A compound in which one or more hydrogen atoms of butadiene have been substituted is preferably a hydrocarbon. A preferred example of a butadiene-based elastomer is a 1,3-butadiene polymer, more preferably 1,2-polybutadiene.

[0016] When component (A) contains both component (A-1) and component (A-2), the content ratio of component (A-1) to component (A-2) is, on a mass basis, preferably component (A-1):component (A-2)=95:5 to 55:45, more preferably component (A-1):component (A-2)=90:10 to 60:40, and even more preferably component (A-1):component (A-2)=85:15 to 70:30.

[0017] The thermoplastic olefin resin can be synthesized by a conventional method, or a commercially available product can be used.

[0018] In the resin composition, the content of the component (A) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The content is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The content of the component (A) is preferably in the range of 10 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 30 to 70% by mass.

[0019] ((B) Foaming agent) The resin composition used in the present invention contains (B) a foaming agent. The foaming agent is preferably a thermally decomposable foaming agent. A thermally decomposable foaming agent is a foaming agent that decomposes upon heating to generate gas. From the viewpoint of environmental safety, the thermally decomposable foaming agent is preferably a foaming agent that does not generate ammonia or cyanuric acid upon thermal decomposition, and more preferably an inorganic foaming agent (preferably an inorganic carbonate) from the viewpoint of not inhibiting the crosslinking reaction. Examples of inorganic carbonates include potassium carbonate, sodium carbonate, sodium bicarbonate (baking soda), barium carbonate, magnesium carbonate, lithium carbonate, iron(II) carbonate, and silver(I) carbonate, with sodium bicarbonate being preferred. The foaming agent is commercially available. Commercially available inorganic carbonates include Uniform AZ P-4 (trade name) manufactured by Otsuka Chemical Co., Ltd.

[0020] From the viewpoint of enhancing the foamability of the resulting crosslinked resin foam, the resin composition preferably contains 10 parts by mass or more of component (B) per 100 parts by mass of component (A), more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 60 parts by mass or more. Furthermore, from the viewpoint of suppressing a decrease in the expansion ratio due to cell breakage, the content is preferably 200 parts by mass or less, more preferably 180 parts by mass or less, even more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less. The content of component (B) is preferably within a preferred range, from 10 to 200 parts by mass, more preferably 20 to 180 parts by mass, even more preferably 30 to 150 parts by mass, and even more preferably 60 to 120 parts by mass, per 100 parts by mass of component (A).

[0021] ((C) Foaming aid) The resin composition used in the present invention may contain (C) a foaming aid (also referred to as component (C)) to the extent that the effects of the present invention are not impaired. By blending the foaming aid into the resin composition, for example, it is possible to adjust the decomposition temperature of the foaming agent within an appropriate range and thereby promote the decomposition of the foaming agent. Examples of the foaming aid include metal oxides such as zinc oxide, metal fatty acid salts such as zinc stearate, urea, citric acid, p,p'-oxybisbenzenesulfonylhydrazide (OBSH), carbon black, antimony trioxide, decabromodiphenylene oxide, trimellitic anhydride, maleic anhydride, and benzotriazole. Of these, OBSH or citric acid is preferred as the foaming aid, as they do not inhibit the decomposition of component (B) and are safe for the environment and humans. The content of the component (C) is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 40 parts by mass or less, also preferably 20 parts by mass or less, also preferably 10 parts by mass or less, and may be 5 parts by mass or less, relative to 100 parts by mass of the content of the component (A). When the resin composition contains component (C), the content of the component (C) relative to 100 parts by mass of the content of the component (A) is usually 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more. The content of component (C) relative to 100 parts by mass of component (A) is preferably in the range of 0 to 100 parts by mass, more preferably 0.1 to 100 parts by mass, even more preferably 0.2 to 70 parts by mass, and still more preferably 0.3 to 40 parts by mass, and may be 0.3 to 20 parts by mass, 0.3 to 10 parts by mass, or 0.3 to 5 parts by mass.

[0022] The resin composition used in the present invention can be crosslinked and foamed to obtain the crosslinked resin foam of the present invention. The crosslinked structure can be formed using a crosslinking agent or by irradiation with an electron beam. Crosslinking by a crosslinking agent and electron beam crosslinking can also be combined. That is, the crosslinked structure of the crosslinked resin foam of the present invention can be formed by the action of an organic peroxide in the resin composition and / or the action of electron beam irradiation. The resin composition can also contain a crosslinking aid, a crosslinking-accelerating resin, etc.

[0023] ((D) Crosslinking Agent) The resin composition used in the present invention may contain (D) a crosslinking agent (also referred to as component (D)) to the extent that the effects of the present invention are not impaired. Examples of the crosslinking agent include radical generators, and organic peroxides are preferably used. The radical generator thermally decomposes to generate radicals, which act to abstract hydrogen from resin components, etc., creating reactive sites and forming a crosslinked structure. Furthermore, by using the radical generator in combination with a crosslinking aid described below, the generated radicals can cause an addition reaction of carbon-carbon unsaturated bonds, forming a crosslinked structure. As the radical generator, it is preferable to use organic peroxides such as 1,1-di(t-butylperoxy)cyclohexane, dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di-(t-butylperoxy)-3-hexyne, α,α'-bis(t-butylperoxydiisopropyl)benzene, t-butylperoxycumene, 4,4'-di(t-butylperoxy)valeric acid n-butyl ester, and 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane. Among these, when an inorganic carbonate that thermally decomposes at low temperatures is used as component (B), it is preferable to use an organic peroxide with a 1-minute half-life temperature (the temperature at which 50% of the organic peroxide decomposes when held at a predetermined temperature for 1 minute) of 165°C or less, and it is more preferable to use an organic peroxide with a temperature of 130°C or more and 165°C or less. When a blowing agent that thermally decomposes at low temperatures is used as component (B), by controlling the one-minute half-life temperature of the crosslinking agent within the above-mentioned preferred temperature range, both the foamability and the degree of crosslinking (crosslinking density) of the resulting crosslinked resin foam can be achieved within a preferred range. For example, when a crosslinking agent with a one-minute half-life temperature above 165°C is used, the decomposition temperature of the blowing agent falls below the crosslinking initiation temperature, making it difficult to achieve a high expansion ratio for the resulting crosslinked resin foam. Therefore, by controlling the one-minute half-life temperature below 165°C, even when the decomposition temperature of the blowing agent is low, the crosslinking agent decomposes before the blowing agent decomposes, forming a crosslinked structure, and then the foaming agent promotes expansion, resulting in a high expansion ratio foam. Furthermore, by controlling the one-minute half-life of the crosslinking agent to 130°C or higher, the crosslinking reaction during processing (before the crosslinking treatment) can be suppressed. Examples of such organic peroxides include 1,1-di(t-butylperoxy)cyclohexane (one-minute half-life temperature: 153.8°C). The content of component (D) is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of component (A). When the resin composition contains component (D), the content of component (D) per 100 parts by mass of component (A) is usually 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more. The content of component (D) relative to 100 parts by mass of component (A) is preferably in the range of 0 to 5.0 parts by mass, more preferably 0.1 to 5.0 parts by mass, even more preferably 0.2 to 4.0 parts by mass, and even more preferably 0.3 to 3.0 parts by mass.

[0024] ((E) Crosslinking aid) The resin composition used in the present invention may contain (E) a crosslinking aid (also referred to as component (E)) to the extent that the effects of the present invention are not impaired. Examples of the crosslinking aid include allyl compounds and polyfunctional vinyl compounds, and among these, polyfunctional acrylate compounds and / or polyfunctional methacrylate compounds and / or polyfunctional vinyl ether compounds are preferred. Specific examples include trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and divinylbenzene, with trimethylolpropane trimethacrylate being preferred. The polyfunctional vinyl compound preferably has two or more vinyl groups (including cases where the vinyl groups are contained as acryloyl groups or methacryloyl groups) in one molecule, more preferably three or more, and even more preferably three to six. The content of component (E) is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of component (A). When the resin composition contains component (E), the content of component (E) per 100 parts by mass of component (A) is usually 0.1 parts by mass or more, preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more. The content of component (E) relative to 100 parts by mass of component (A) is preferably in the range of 0 to 5.0 parts by mass, more preferably 0.1 to 5.0 parts by mass, even more preferably 0.2 to 4.0 parts by mass, even more preferably 0.3 to 3.0 parts by mass, and even more preferably 0.5 to 2.0 parts by mass.

[0025] (Other ingredients) In addition to the above components (A) and (B), the resin composition used in the present invention may contain other components such as dispersants, fillers, pigments, light stabilizers, heat stabilizers, lubricants, compatibilizers, antioxidants, flame retardants, and flame retardant assistants, as long as the effects of the present invention are not impaired.

[0026] [Method of producing resin composition] The resin composition used in the present invention can be obtained by melt-kneading and homogenizing the above-mentioned components (A) and (B), and, if necessary, the above-mentioned optional components, using a commonly used kneading device such as a batch kneader, a roll, a kneader, or a Banbury mixer, or a twin-screw extruder.

[0027] The resin composition used in the present invention may be a molded article obtained by molding the melt-kneaded product, which can be molded by various molding methods such as extrusion molding and press molding.

[0028] [Crosslinked resin foam] The crosslinked resin foam of the present invention is a crosslinked resin foam obtained by crosslinking and foaming the resin composition, wherein the crosslinked resin foam has a gel fraction of 35 to 85% and an ammonium ion concentration of less than 1000 μg / g of crosslinked resin foam as detected by ion chromatography. "Less than 1000 μg / g of crosslinked resin foam" means a concentration of less than 1000 μg per 1 g of crosslinked resin foam. In the present invention and this specification, the term "by crosslinking and foaming" means forming a crosslinked structure in the resin composition and then foaming the crosslinked product either simultaneously with the formation of the crosslinked structure or after the formation of the crosslinked structure. In the present invention, the crosslinked resin foam has, as described above, a specific feature that it is produced by crosslinking and foaming a resin composition, but this simply specifies the state of the crosslinked resin foam. That is, this specific feature further clarifies the structure and properties of the crosslinked resin foam.

[0029] The thermoplastic olefin-based resin contained in the crosslinked resin foam of the present invention is basically the same as that described in the resin composition above, and the content is also substantially the same. On the other hand, it differs from the resin composition in that the resin etc. forms a crosslinked structure. That is, in the crosslinked resin foam of the present invention, the term "thermoplastic olefin-based resin" is used to mean a state in which the resin (polymer) of the above component (A) is incorporated as a constituent component of the crosslinked body formed by the crosslinking reaction.

[0030] (gel fraction) The crosslinked resin foam of the present invention has a gel fraction of 35 to 85%. That is, the crosslinked resin foam of the present invention is a foam containing a polymer with a three-dimensional network structure that is insoluble in solvents and its swollen body (gel), and has a structure in which countless polymer chains are connected in a network-like manner. The gel fraction means "when a sample is extracted with xylene, the portion that remains unextracted is called the gel portion, and the ratio of the mass of this gel portion to the mass before extraction with xylene." In the present invention, the gel fraction can be measured by the following method. Each foam sample is cut to 1.00±0.050 g and its mass is measured (mass A). The sample is placed in a flask, 100 ml of xylene is added to the flask, and the solvent is boiled at 120°C for 24 hours ±5 minutes. The sample is then removed from the boiling solvent and the residue is dried in a vacuum oven at 80°C ±2°C under a negative pressure of at least 85 kPa for 24 hours. After cooling, the sample is measured to a maximum of 1 mg (mass B). The gel fraction (%) is calculated from the measured masses A and B using the following formula (1): Gel fraction (%) = {(mass B) / (mass A)} × 100 (Equation 1) When the gel fraction of the crosslinked resin foam of the present invention is less than 35%, the degree of crosslinking is too low to form a foam structure, or even if the degree of crosslinking is sufficient to form a foam structure, shrinkage is likely to occur after production. In particular, when sodium carbonate, an inorganic carbonate, is used as component (B), significant shrinkage may occur due to cooling of the water vapor generated by decomposition. In the crosslinked resin foam of the present invention, the gel fraction is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. Furthermore, the gel fraction is preferably 82% or less, more preferably 80% or less. A preferred range for the gel fraction is preferably 40 to 85%, more preferably 50 to 85%, even more preferably 50 to 82%, even more preferably 50 to 80%, and even more preferably 60 to 80%. By controlling the gel fraction within the preferred range, deformation and shrinkage of the crosslinked resin foam after foaming can be further suppressed while maintaining a high expansion ratio. Methods for increasing the gel fraction include, for example, using an organic peroxide with a one-minute half-life temperature of 165°C or less to cause a high-density crosslinking reaction, or controlling the amount of electron beam irradiation to cause high-density crosslinking.

[0031] (Apparent density) The shape of the crosslinked resin foam of the present invention is not particularly limited, and may be, for example, 1 to 20 mm in thickness and 200 kg / m in apparent density. 3 It can be made into the following sheet form. Apparent density is 25 to 200 kg / m 3 More preferably, it is 30 to 175 kg / m 3 The "apparent density" of the crosslinked resin foam of the present invention is a value calculated by dividing the mass of a test piece of the foam cut into a predetermined size (e.g., 10 cm × 10 cm) by the volume of the foam (volume including the cellular portion).

[0032] (Expansion ratio) In the crosslinked resin foam of the present invention, the expansion ratio is preferably 7 times or more, more preferably 10 times or more, more preferably 15 times or more, and even more preferably 20 times or more. From the viewpoint of preventing the foam from breaking during use or processing, the expansion ratio is preferably 50 times or less, and more preferably 40 times or less. Therefore, the preferred range of the expansion ratio is preferably 7 to 50 times, more preferably 10 to 50 times, even more preferably 15 to 40 times, and even more preferably 20 to 40 times. The expansion ratio can be calculated using samples before and after foaming treatment according to the following formula (Formula 2): For example, the resin composition can be used as the unfoamed sample, and a crosslinked resin foam can be used as the foamed sample. Expansion ratio = density of unexpanded sample / apparent density of expanded sample (Equation 2)

[0033] (ammonium ion concentration) The crosslinked resin foam of the present invention has an ammonium ion concentration of less than 1000 μg / 1 g of crosslinked resin foam as detected by ion chromatography. For example, when ADCA is used as a foaming agent, not only nitrogen gas but also ammonia gas is generated during thermal decomposition, and ammonia remains in the resulting crosslinked resin foam. Harmful substances remaining in the foam can cause metal corrosion, etc. The ammonium ion concentration of the crosslinked resin foam of the present invention, as detected by ion chromatography, is preferably 500 μg or less per 1 g of crosslinked resin foam, more preferably 200 μg or less per 1 g of crosslinked resin foam, and even more preferably 100 μg or less per 1 g of crosslinked resin foam. It is also more preferable that the ammonium ion concentration be suppressed to below the detection limit.

[0034] The ammonium ion concentration can be measured by the ion chromatography method specifically by the following procedure. Weigh approximately 1.0 g of the sample into a polypropylene container, add 40 mL of ultrapure water, then weight it down with wrap so that the sample does not float, cover it, and seal it. Perform extraction at 90 °C for 24 hours. After allowing it to cool, filter and dilute to prepare a sample solution. Measure the amount of ammonium ions in the sample solution by ion chromatography using an ICS-6000 manufactured by Thermo Scientific. By dividing the measured amount of ammonium ions (μg) by the weight (g) of the sample, the amount of ammonium ions per 1 g of the crosslinked resin foam can be calculated.

[0035] (Concentration of siloxane compound) Moreover, it is preferable that the crosslinked resin foam of the present invention substantially does not contain a siloxane compound. For example, when a silane-grafted polyolefin is used as the base resin of the resin composition and a crosslinked resin foam is produced using silane crosslinking, a material having siloxane bonds generated may volatilize and deposit on the substrate of electronic components or the like, causing contact failure or conduction failure. Therefore, it is preferable that the outgas detected by gas chromatography-mass spectrometry of the crosslinked resin foam does not contain a siloxane compound among the five compounds with a large extraction amount (the first to fifth compounds in order of decreasing extraction amount, excluding unidentified substances). Also, the content of the detected siloxane compound can be 100 μg or less / 1 g-crosslinked resin foam, 50 μg or less / 1 g-crosslinked resin foam, 10 μg or less / 1 g-crosslinked resin foam, and it is preferably substantially free of siloxane compounds.

[0036] The measurement of the siloxane compound can be performed, for example, by subjecting it to Head Space (HS)-GC / MS analysis under the following conditions. <Sample preparation> Enclose 100 mg of the sample in a glass vial, heat the enclosed sample under the following HS conditions to recover volatile components. The recovered volatile components are subjected to measurement under the following GC / MS conditions for detection. <HS conditions> Apparatus: HT3 HS Auto Sampler manufactured by TELEDYNE TEKMAR Heating condition: 200 °C, 60 minutes Measurement mode: Loop mode Carrier gas: He, original pressure 40 kPa GC transfer line: 220 °C Inlet temperature: 220 °C Injection method: Split 10 mL / min <GC / MS conditions> Apparatus: TRACE GC ULTRA / TRACE DSQ manufactured by Thermo Column: TR-5MS manufactured by Thermo, 3 m, 0.25 mm ID, 0.25 μm Temperature rising condition: Heat at 40 °C for 4 minutes, raise temperature at 20 °C / min, heat at 250 °C for 10 minutes and 30 seconds Ionization method: EI method Ion source temperature: 250 °C MS transfer line temperature: 250 °C Detection method: Scan (m / Z = 29 - 600)

[0037] [Method for manufacturing crosslinked resin foam] As the method for manufacturing the crosslinked resin foam of the present invention, there are a method of simultaneously (parallelly) performing the formation of the crosslinked structure of the resin composition and the foaming treatment, and a method of performing the foaming treatment after forming the crosslinked structure in the resin composition. An example of each of these methods will be described below. Each method described below may be used alone or in combination of two or more methods. In any method, the above-mentioned (D) crosslinking agent and (E) crosslinking assistant can be blended into the resin composition as necessary to form a stronger crosslinked structure.

[0038] <Method of simultaneously performing the formation of the crosslinked structure and the foaming treatment> The resin composition of the present invention is prepared by blending the above (D) crosslinking agent and, if necessary, the (E) crosslinking aid. The kneading during preparation is carried out at a temperature (approximately 100 to 130°C) at which the (D) crosslinking agent and the (B) foaming agent are unlikely to decompose. The resin composition can be in the form of pellets. The resulting resin composition is fed to an extruder and extrusion-molded at a resin temperature of approximately 100 to 130°C to obtain an unfoamed sheet having the desired thickness and width. This unfoamed sheet is placed in a heating and foaming furnace adjusted to approximately 180 to 230°C to cause a crosslinking reaction and foaming, thereby producing a sheet of the crosslinked resin foam of the present invention.

[0039] <Method of foaming treatment after crosslinked structure formation> The crosslinked resin foam of the present invention can be obtained by irradiating the resin composition with ionizing radiation to form a crosslinked structure, followed by heating to decompose the foaming agent and generate gas. The ionizing radiation that can be irradiated includes α-, β-, or γ-rays, electron beams, neutron beams, etc. The electron beam irradiation intensity may be such that the gel fraction of the resulting foam falls within the range of 35 to 85%, and the acceleration voltage is preferably 100 kV to 1000 kV, more preferably 400 kV to 1000 kV, and the absorbed dose is preferably 10 kGy to 300 kGy, more preferably 10 kGy to 100 kGy. [Example]

[0040] The present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these.

[0041] [Example of resin foam preparation] The materials used to prepare the resin foams of Examples 1 to 14 and Comparative Examples 1 to 6 are shown in Table 1 below. Details of the materials used are as follows.

[0042] <Raw materials used> (thermoplastic olefin resin) LDPE (low-density polyethylene, manufactured by Japan Polyethylene Corporation: Novatec (registered trademark) LD LC600A (product name), MFR 7.0 g / 10 min, density 0.918 g / cm3 ) Polybutadiene thermoplastic elastomer (ENEOS Materials Corporation: RB810 (product name), MFR 3.0 g / 10 min, density 0.901 g / cm 3 ) Ethylene-vinyl acetate copolymer (Mitsui-Dow Polychemicals: V523 (trade name), MFR 14 g / 10 min, density 0.960 g / cm 3 ) (foaming agent) Inorganic carbonate (sodium bicarbonate, Otsuka Chemical Co., Ltd.: AZ P-4 (product name)) ADCA (azodicarbonamide, manufactured by Otsuka Chemical Co., Ltd.: Uniform AZ VI50ST (product name)) (Crosslinking agent) 1,1-di(t-butylperoxy)cyclohexane (NOF Corporation: Perhexa (registered trademark) C (trade name), 1-minute half-life: 153.8°C) Dicumyl peroxide (NOF Corporation: Percumyl (registered trademark) D (trade name), 1-minute half-life: 175.2°C) (Crosslinking aid) TMPT: (trimethylolpropane triacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd.: NK Ester TMPT (trade name))

[0043] <Method of manufacturing foam> (Examples 1 to 11, Comparative Examples 1 to 5) The raw materials were mixed according to the composition shown in Table 1 below, melt-kneaded at 110°C using a 1-liter kneader, and the kneaded mixture was formed into a sheet using an open roll. After cooling, the sheet was cut and granulated using a pelletizer to obtain a resin composition (pellets). The obtained pellets were fed into an extruder set at a temperature of 100 to 120°C, molded into a sheet with a thickness of 2 mm, and then cut into a square with a width and length of 10 cm to prepare unfoamed sheets. These unfoamed sheets were then introduced into a hot air oven adjusted to 190°C, and crosslinking reaction and foaming treatment were carried out simultaneously at this high temperature to produce foams of Examples 1 to 11 and Comparative Examples 1 to 5.

[0044] (Examples 12 to 14, Comparative Example 6) The raw materials were mixed according to the composition shown in Table 1 below, melt-kneaded at 110°C using a 1-liter kneader, and the kneaded mixture was formed into a sheet using an open roll. After cooling, the sheet was cut and granulated using a pelletizer to obtain a resin composition (pellets). The resulting pellets were fed into an extruder set at 100-120°C and molded into a 2mm thick sheet, which was then cut into 10cm squares to produce unfoamed sheets. These unfoamed sheets were then irradiated with an electron beam (Condition 1: Acceleration voltage 750kV, Exposure dose 20kGy, Exposure method both sides, Exposure atmosphere air; Condition 2: Acceleration voltage 500kV, Exposure dose 10kGy, Exposure method both sides, Exposure atmosphere air) to promote a crosslinking reaction, and then introduced into a hot air oven adjusted to 200°C to promote a foaming treatment, producing foams for Examples 12-14 and Comparative Example 6.

[0045] [Performance evaluation] The foams (Examples 1 to 14 and Comparative Examples 1 to 6) produced as described above were used to carry out the following performance evaluations. The results of each test are shown in Table 1 below. The blend amounts in the table below are in parts by mass.

[0046] (Measurement of deformation and shrinkage of cross-linked foam) Each foam was left at room temperature for 24 hours and visually inspected for deformation. The shrinkage rate (%) of each foam was calculated using the following formula (3). The thickness of each foam was calculated as the arithmetic mean value of 10 measurements taken at 10 random locations. Shrinkage rate (%) = {(thickness of cross-linked foam immediately after foaming - thickness of cross-linked foam after 24 hours) / thickness of cross-linked foam immediately after foaming} × 100 (Equation 3) -Evaluation criteria- ○: Shrinkage rate is 0% or more and less than 3% △: Shrinkage rate is 3% or more and less than 8% ×: Shrinkage rate is 8% or more

[0047] (Gel fraction measurement) Each foam sample was cut to 1.00±0.050 g and its mass was measured (mass A). Each foam sample was placed in a flask, and 100 ml of xylene was added to the flask to completely immerse the sample. The solvent was boiled at 120°C for 24 hours±5 minutes. The sample was then removed from the boiling solvent and dried in a vacuum oven at 80°C±2°C under a negative pressure of at least 85 kPa for 24 hours. After cooling, the sample was measured to a mass of 1 mg (mass B). The gel fraction (%) was calculated from the measured masses A and B using the following formula (1): Gel fraction (%) = {(mass B) / (mass A)} × 100 (Equation 1)

[0048] (Foaming test) The density of each unfoamed sheet of Examples 1 to 14 and Comparative Examples 1 to 6, and each foam obtained by crosslinking and foaming the sheet (which was left at room temperature for 24 hours after production) was measured, and the expansion ratio was calculated using the following formula (2). Expansion ratio = density of unfoamed sheet / apparent density of foam (Equation 2) The apparent density of each foam of Examples 1 to 14 was 50 to 175 kg / m 3 was within the range.

[0049] (Quantitative analysis of ammonium ions) Approximately 1.0 g of each foam sample was weighed into a polypropylene container, 40 mL of ultrapure water was added, and the container was then weighted down with plastic wrap to prevent the sample from floating. The container was then sealed with a lid. Extraction was performed at 90°C for 24 hours, and the container was allowed to cool. After cooling, the container was filtered and diluted to prepare a sample solution. The amount of ammonium ions in the resulting sample solution was measured by ion chromatography using a Thermo Scientific ICS-6000. The amount of ammonium ions per gram of crosslinked resin foam was calculated by dividing the measured amount of ammonium ions (μg) by the weight of the sample (g). A detected ammonium ion concentration of less than 1000 μg / g of foam was evaluated as "Good," and a concentration of 1000 μg or more / g of foam was evaluated as "Poor."

[0050] (Quantitative Analysis of Siloxane Compounds) 100 mg of the sample was sealed in a glass vial, and the sealed sample was heated under the following HS conditions to recover volatile components. Subsequently, the recovered volatile components were analyzed under the following GC / MS conditions. In any of the foams, siloxane compounds were not detected. <HS Conditions> Apparatus: HT3 HS autosampler manufactured by TELEDYNE TEKMAR Heating conditions: 200 °C, 60 minutes Measurement mode: Loop mode Carrier gas: He, original pressure 40 kPa GC transfer line: 220 °C Inlet temperature: 220 °C Injection method: Split 10 mL / min <GC / MS Conditions> Apparatus: TRACE GC ULTRA / TRACE DSQ manufactured by Thermo Column: TR-5MS manufactured by Thermo, 30 m, 0.25 mm ID, 0.25 μm Temperature rising conditions: Heated at 40 °C for 4 minutes, temperature rising at 20 °C / min, heated at 250 °C for 10 minutes and 30 seconds Ionization method: EI method Ion source temperature: 250 °C MS transfer line temperature: 250 °C Detection method: Scan (m / Z = 29 - 600)

[0051]

Table 1-1

[0052]

Table 1-2

[0053] As is clear from Table 1, the foams of Comparative Examples 1, 2, and 4, which had a gel fraction of 30% or less, did not form a foamed structure due to insufficient crosslinking, and all had poor expansion ratios. The foam of Comparative Example 6, which had a gel fraction of more than 30% but less than 35%, was able to form a normal foamed structure due to the crosslinking structure, but shrunk immediately after production. Furthermore, the foam of Comparative Example 3, which had a gel fraction of more than 85%, did not form a normal foamed structure. Furthermore, ammonium ions were detected in the foam of Comparative Example 5, which used ADCA as a blowing agent, by ion chromatography analysis. In contrast, in the foams (Examples 1 to 14) that satisfied all of the requirements of the present invention, no harmful gases such as ammonia gas were detected, and the foaming properties and shape stability were excellent.

Claims

1. A crosslinked resin foam obtained by crosslinking and foaming a resin composition containing (A) a thermoplastic olefin resin and (B) a foaming agent, The crosslinked resin foam has a gel fraction of 35 to 85%. the crosslinked resin foam has an ammonium ion concentration of less than 1000 μg / 1 g of crosslinked resin foam as detected by ion chromatography; Cross-linked resin foam.

2. The crosslinked resin foam according to claim 1 , having an expansion ratio of 7 times or more.

3. 3. The crosslinked resin foam according to claim 1, wherein the crosslinked structure of the crosslinked resin foam is formed by the action of an organic peroxide in the resin composition and / or the action of electron beam irradiation.

4. 3. The crosslinked resin foam according to claim 1, wherein a siloxane compound is not included in five outgases extracted in large amounts when detected by gas chromatography mass spectrometry of the crosslinked resin foam.

5. The crosslinked resin foam according to claim 1 or 2, wherein the (B) blowing agent comprises an inorganic carbonate.

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