Resin foam and seal member

Abstract

To provide a resin foam having a good appearance.SOLUTION: A resin foam is made by foaming a resin composition including a polyolefin resin and a petroleum resin. The resin foam may include a polyethylene resin as a polyolefin resin, and contains less than 29 pts.mass of the polyethylene resin with respect to a total of 100 pts.mass of the polyolefin resin.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a resin foam and a sealing member.

Background Art

[0002] Patent Document 1 describes a polyolefin-based resin continuous foam. The polyolefin-based resin continuous foam is obtained by heating a molded body obtained by adding a resin composition under normal pressure to cause crosslinking and foaming. The resin composition contains an ethylene-vinyl acetate copolymer, low-density polyethylene, dicumyl peroxide, an azodicarbonamide-based foaming agent, a silicone-based surfactant, and an antifoaming agent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the resin foam, a configuration with good appearance is required. An object of the present disclosure is to obtain a resin foam with good appearance. The present disclosure can be realized in the following forms.

Means for Solving the Problems

[0005] 〔1〕A resin foam obtained by foaming a resin composition containing a polyolefin-based resin and a petroleum resin, wherein the polyolefin-based resin may include a polyethylene-based resin, and the polyethylene-based resin is less than 29 parts by mass with respect to a total of 100 parts by mass of the polyolefin-based resin.

Effects of the Invention

[0006] According to the present disclosure, a resin foam with good appearance can be obtained.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0008] Here, desirable examples of the present disclosure are shown. 〔1〕It is formed by foaming a resin composition containing a polyolefin resin and a petroleum resin, The polyolefin resin may include a polyethylene resin, A resin foam in which the polyethylene resin is less than 29 parts by mass with respect to a total of 100 parts by mass of the polyolefin resin. 〔2〕The resin foam according to 〔1〕, having a cell number of 30 cells / 25 mm or more based on JIS K6400-1:2004. 〔3〕The resin foam according to 〔2〕, having a cell number of 60 cells / 25 mm or less based on JIS K6400-1:2004. 〔4〕A sealing member including the resin foam according to any one of 〔1〕 to 〔3〕.

[0009] Hereinafter, the present disclosure will be described in detail. In this specification, for a description using "-" for a numerical range, unless otherwise specified, it includes the lower limit value and the upper limit value. For example, in the description of "10-20", both the lower limit value "10" and the upper limit value "20" are included. That is, "10-20" has the same meaning as "10 or more and 20 or less". Also, in this specification, the upper limit value and the lower limit value of each numerical range can be arbitrarily combined.

[0010] 1. Resin Foam The resin foam of the present disclosure is formed by foaming a resin composition containing a polyolefin resin and a petroleum resin.

[0011] The resin composition may contain a silicone resin, a foaming agent, and a crosslinking agent (vulcanizing agent). Hereinafter, each component of the resin composition will be described.

[0012] (1) Polyolefin resin The polyolefin resin preferably contains an ethylene vinyl acetate copolymer (EVA). The polyolefin resin may contain only EVA, but preferably contains EVA and a polyolefin resin other than EVA. The polyolefin resin other than EVA may include a polyethylene resin.

[0013] EVA is a polymer containing a structural unit derived from ethylene and a structural unit derived from vinyl acetate in the molecule. The content of vinyl acetate in EVA is not particularly limited. From the viewpoint of improving flexibility, when the mass of EVA is 100% by mass, the content of vinyl acetate is preferably 5% by mass or more, more preferably 10% by mass or more. From the viewpoint of preventing excessive crosslinking, the content of vinyl acetate is preferably 40% by mass or less, more preferably 30% by mass or less. From these viewpoints, the content of vinyl acetate is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less. The content of vinyl acetate is based on JIS K 6924-1.

[0014] The melt flow rate (MFR) of EVA is not particularly limited. From the viewpoint of moldability, the value measured at 190°C and a load of 2.16 kg in accordance with JIS K7210-1 is preferably 0.1 g / 10 min - 20 g / 10 min, more preferably 0.3 g / 10 min - 10 g / 10 min, and even more preferably 0.5 g / 10 min - 5.0 g / 10 min.

[0015] When the total amount of the polyolefin resin is 100 parts by mass, the content of EVA is preferably 70 parts by mass or more, more preferably 75 parts by mass or more, and still more preferably 80 parts by mass or more, from the viewpoint of flexibility in the foaming process. From the viewpoint of preventing excessive crosslinking, the content of the above EVA is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, and still more preferably 85 parts by mass or less. From these viewpoints, the content of the above EVA is preferably 70 parts by mass or more and 95 parts by mass or less, more preferably 75 parts by mass or more and 90 parts by mass or less, and still more preferably 80 parts by mass or more and 85 parts by mass or less.

[0016] The polyolefin resin other than EVA is preferably at least one selected from the group consisting of polyethylene resins (excluding EVA) and polypropylene resins. The polyolefin resin other than EVA may be blended as a resin contained in the masterbatch. The masterbatch is, for example, a petroleum resin masterbatch containing a petroleum resin, a silicone masterbatch containing a silicone resin, a blowing agent masterbatch containing a blowing agent, and the like.

[0017] The polyethylene resin (excluding EVA) is preferably at least one selected from the group consisting of low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-propylene-1-butene copolymer, ethylene-(4-methyl-1-pentene) copolymer, and ethylene-acrylic acid ester copolymer. These polyethylene resins may be used alone or in combination of two or more. The polyethylene resin (excluding EVA) is preferably polyethylene, which is a polymer having a structure in which ethylene is polymerized.

[0018] Low-density polyethylene is usually formed by randomly branching and bonding repeating units of ethylene. From the perspective of moldability, the melt flow rate (MFR) measured at 190 °C and 2.16 kgf in accordance with JIS K7210-1 is preferably 0.1 g / 10 min - 20 g / 10 min, more preferably 0.3 g / 10 min - 10 g / 10 min, and even more preferably 0.5 g / 10 min - 5.0 g / 10 min.

[0019] Linear low-density polyethylene is a copolymer of ethylene without long-chain branches and an α-olefin. The α-olefin is preferably at least one selected from the group consisting of propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0020] Polypropylene-based resin is a polymer containing structural units derived from propylene in one molecule and is formed by polymerizing a monomer component containing propylene. The polypropylene-based resin may be a homopolymer of propylene or a copolymer of propylene and an olefin other than propylene (excluding ethylene). Also, the polypropylene-based resin may be used alone or in combination of two or more.

[0021] From the perspective of adjusting the degree of crosslinking and melt viscosity for obtaining a good foam and preventing sagging after foam breaking, the polyolefin-based resin preferably contains EVA and a polyethylene-based resin, and more preferably contains EVA and low-density polyethylene.

[0022] The content of the polyethylene-based resin is less than 29 parts by mass, preferably 25 parts by mass or less, and more preferably 20 parts by mass or less, when the total amount of the polyolefin-based resins is 100 parts by mass, from the viewpoint of improving the appearance, reducing the resin strength and enhancing the foam-breaking property. Incidentally, the content of the polyethylene-based resin may be 0 parts by mass. From the viewpoint of enhancing the water-stopping property, the content of the above polyethylene-based resin is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more. From these viewpoints, the content of the polyethylene-based resin is less than 29 parts by mass when the total amount of the polyolefin-based resins is 100 parts by mass, preferably 5 parts by mass or more and less than 29 parts by mass, more preferably 10 parts by mass or more and 25 parts by mass or less, and still more preferably 15 parts by mass or more and 20 parts by mass or less.

[0023] (2) Petroleum resin The petroleum resin is obtained by polymerizing a fraction containing unsaturated hydrocarbon monomers by-produced by thermal decomposition of petroleum naphtha or the like. The petroleum resin is preferably at least one selected from the group consisting of aliphatic petroleum resins (C5-based petroleum resins), aromatic petroleum resins (C9-based petroleum resins), aliphatic / aromatic petroleum resins (C5 / C9-based petroleum resins), and alicyclic petroleum resins (hydrogenated petroleum resins). The aliphatic petroleum resin (C5-based petroleum resin) is a synthetic resin obtained by polymerizing the refined components of the C5 fraction of petroleum naphtha cracked oil. The aromatic petroleum resin (C9-based petroleum resin) is a synthetic resin obtained by polymerizing the refined components of the C9 fraction of petroleum naphtha cracked oil. The aliphatic / aromatic petroleum resin (C5 / C9-based petroleum resin) is a synthetic resin obtained by copolymerizing a raw material in which the above C5 fraction and C9 fraction are blended. From the viewpoint of compatibility with the polyolefin-based resin, the petroleum resin is particularly preferably a C9-based hydrogenated petroleum resin.

[0024] From the viewpoints of odor, hue, thermal stability, weather resistance, and compatibility with the polyolefin-based resin, the petroleum resin is preferably a hydrogenated petroleum resin. The hydrogenated petroleum resin is a resin obtained by adding hydrogen atoms to the unsaturated double bonds present in the petroleum resin. As the hydrogenated petroleum resin, either a fully hydrogenated type hydrogenated petroleum resin with a hydrogenation rate of 90% or more or a partially hydrogenated type hydrogenated petroleum resin with a hydrogenation rate of less than 90% can be used.

[0025] Examples of commercially available C9 hydrogenated petroleum resins include Alcon P-90, Alcon P-100, Alcon P-115, Alcon P-125, Alcon P-140, Alcon M-90, Alcon M-100, Alcon M-115, Alcon M-135 (manufactured by Arakawa Chemical Industries, Ltd.), etc. Examples of commercially available C5 hydrogenated petroleum resins include East Tack C115W (manufactured by Eastman Chemical Company), etc. Examples of commercially available C5 / C9 hydrogenated petroleum resins include dicyclopentadiene / aromatic copolymerized hydrogenated petroleum resins such as Imarve S-100, Imarve S-110, Imarve P-100, Imarve P-125, Imarve P-140 (manufactured by Idemitsu Kosan Co., Ltd.), etc. Note that the numbers at the end of the above product names are catalog values indicating the softening point (°C) of the petroleum resin. From the viewpoint of handleability, the softening point of the petroleum resin is preferably greater than 90°C, more preferably 100°C or higher, and even more preferably 110°C or higher. The upper limit of the softening point is not particularly limited, but from the viewpoint of easy availability, it may be, for example, 140°C or lower. The difference in the softening point does not significantly affect the properties of the resin foam, but a petroleum resin with a low softening point may cause blocking, etc., where a powder becomes a lump during transportation, storage, etc. In that regard, if the softening point is within the above range, the petroleum resin is easy to handle. The petroleum resin may be used alone or in combination of two or more.

[0026] From the viewpoints of improving the foam-breaking property and making the cells finer, the content of the petroleum resin is preferably 2.0 parts by mass or more, more preferably 3.0 parts by mass or more, and still more preferably 4.0 parts by mass or more with respect to 100 parts by mass in total of the polyolefin resin. From the viewpoints of improving the foam-breaking property and making the cells finer, the content of the petroleum resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 8.0 parts by mass or less. From these viewpoints, the content of the petroleum resin is preferably 2.0 parts by mass or more and 20 parts by mass or less, more preferably 3.0 parts by mass or more and 10 parts by mass or less, and still more preferably 4.0 parts by mass or more and 8.0 parts by mass or less. Further, even when the content of the petroleum resin is 8 parts by mass or less or 6 parts by mass or less, the improvement of the foam-breaking property and the refinement of the cells can be achieved.

[0027] (3) Silicone resin As the silicone resin, for example, polyorganosiloxane or the like is preferable. Here, polyorganosiloxane has a siloxane bond as the main chain and an organic group in the side chain, and the organic group is preferably one or more selected from the group consisting of, for example, a methyl group, a vinyl group, an ethyl group, a propyl group, and a phenyl group.

[0028] As the polyorganosiloxane, one or more selected from the group consisting of dimethylpolysiloxane, methylethylpolysiloxane, methyloctylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, and methyl(3,3,3-trifluoropropyl)polysiloxane are preferable.

[0029] The silicone resin can be used in the form of silicone gum, silicone powder, silicone oil, or silicone resin. Among these, from the viewpoint of being less likely to cause blooming, it is preferable to use it in the form of silicone gum.

[0030] The content of the silicone resin is preferably more than 0 parts by mass, more preferably 1.0 part by mass or more, and still more preferably 1.5 parts by mass or more, based on 100 parts by mass in total of the polyolefin resin, from the viewpoint of improving the water-stopping property by imparting water repellency. The content of the above silicone resin is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 5 parts by mass or less, from the viewpoint of dispersibility in the polyolefin resin. From these viewpoints, the content of the above silicone resin is preferably more than 0 parts by mass and 10 parts by mass or less, more preferably 1.0 part by mass or more and 7 parts by mass or less, and still more preferably 1.5 parts by mass or more and 5 parts by mass or less.

[0031] (4) Foaming agent The foaming agent is not particularly limited, but a thermal decomposition type foaming agent that decomposes by heat to generate gas is preferable. As the thermal decomposition type foaming agent, an organic foaming agent or an inorganic foaming agent is preferable.

[0032] As the organic foaming agent, at least one selected from the group consisting of azodicarbonamide (ADCA), barium azodicarboxylate, azobisisobutyronitrile (AIBN), azocyclohexylnitrile, N,N'-dinitrosopentamethylenetetramine, 4,4'-oxybisbenzenesulfonylhydrazide, and toluenesulfonyl semicarbazide is preferable.

[0033] As the inorganic foaming agent, at least one selected from the group consisting of ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, sodium nitrite, ammonium nitrite, sodium borohydride, and monosodium anhydrous citrate is preferable.

[0034] The foaming agent may be used alone or in combination of two or more. Among the above, azo compounds such as azodicarbonamide (ADCA), barium azodicarboxylate, and azobisisobutyronitrile, and nitroso compounds such as N,N'-dinitrosopentamethylenetetramine are preferable because they can form fine bubbles, and azodicarbonamide is particularly preferable.

[0035] The foaming agent is preferably 5 parts by mass - 35 parts by mass, more preferably 10 parts by mass - 30 parts by mass, and still more preferably 15 parts by mass - 25 parts by mass with respect to 100 parts by mass in total of the polyolefin resin.

[0036] (5) Crosslinking agent The crosslinking agent is not particularly limited. Organic peroxides such as dicumyl peroxide (DCP), 2,5 - dimethyl - 2,5 - bis - tertiary butyl peroxyhexane, and 1,3 - bis - tertiary peroxy - isopropylbenzene are preferred.

[0037] (6) Other components The resin composition may contain, if necessary, additives such as fillers (calcium carbonate, etc.), foaming aids (zinc stearate, urea - based foaming aids, etc.), dispersants (polyethylene - based waxes, etc.), crosslinking aids, antioxidants, pigments, plasticizers, thermally expandable particles, and functional agents (e.g., flame retardants). These additives may be used alone or in combination of two or more. Also, the composition may contain polymers such as modifiers other than the above - mentioned polymers (hereinafter also referred to as other polymers) as long as the effects of the present disclosure are not significantly inhibited.

[0038] 2. Structure of the resin foam The cell structure of the resin foam is not particularly limited. The resin foam preferably has an open-cell structure. As will be described later, the resin foam having an open-cell structure can be obtained by rupturing the cell membranes to connect the cells of the resin foam. When the resin foam has an open-cell structure, the physical properties of the following resin foam are measured using a sample that has undergone the defoaming process described later. The conditions of the defoaming process can be appropriately changed according to the required physical properties. However, the physical properties of the following resin foam are, for example, the measured values measured using a sample obtained by repeatedly performing a compression treatment of passing between two rolls rotating in different directions in the defoaming process until the resilience resistance disappears. Pinch the molded body after passing through the roll with your finger, confirm the resilience resistance by touch, and confirm that there is no resilience resistance. If there is a resilience resistance, put it into the roll again.

[0039] (1) Cell count The resin foam of the present disclosure preferably has a cell count of 30 cells / 25 mm or more, more preferably 35 cells / 25 mm or more, and even more preferably 40 cells / 25 mm or more, as measured based on the cell counting procedure described in JIS K6400-1:2004 Annex A (specified). The above cell count is preferably 60 cells / 25 mm or less, more preferably 55 cells / 25 mm or less, and even more preferably 50 cells / 25 mm or less. In the present disclosure, a cell means a pore portion in the foam. The cell count is the number of cells per 25 mm of the sample piece, counted based on the above JIS K6400-1:2004.

[0040] (2) Density The density of the resin foam is preferably 15 kg / m 3 or more and 50 kg / m 3 or less, more preferably 20 kg / m 3 or more and 40 kg / m 3 or less, and even more preferably 25 kg / m 3 or more and 35 kg / m 3 or less. The above density is the apparent density measured according to JIS K6767:1999. By setting the density within the above range, the resin foam can be lightened.

[0041] (3) 50% Compressive Stress When the compressive stress of the resin foam is measured according to the test method of "Compressive Stress - Strain" in JIS K6767:1999 (when compressed by 50%, corresponding to ISO 3386-1), it is preferably 30 kPa or less, more preferably 20 kPa or less, and still more preferably 10 kPa or less. The lower limit of the compressive stress of the resin foam is not particularly limited, but is usually 0.1 kPa or more. Note that the compressive stress of the above resin foam can be adjusted, for example, by changing the blending ratio of the petroleum resin in the resin composition, the degree of cell communication, etc.

[0042] (4) Compression Set When the compression set of the resin foam is measured according to the test method of "Compression Set" in JIS K6767:1999 (measurement of the thickness 24 hours after the end of compression, corresponding to ISO 1856), it is preferably 5.0% or less, more preferably 2.5% or less, still more preferably 1.5% or less, and particularly preferably 1.0%. The lower limit of the compression set of the resin foam is not particularly limited, but is usually 0.1% or more.

[0043] (5) Water Resistance and Applications The resin foam is suitable as a sealing member. Examples of the sealing member include a water sealing material. When used as a water sealing material, the resin foam is formed into a thickness and shape (e.g., string shape) according to the application by punching or the like and then used. The resin foam preferably has a holding time of 100 mmAq water pressure of 30 minutes or more, more preferably 9 hours or more, and still more preferably 24 hours or more as described later. The holding time of 100 mmAq water pressure is the time when a water resistance measurement sample 1 created by punching a 10 mm thick water sealing material into a U shape with the dimensions shown in FIG. 1 is sandwiched between two acrylic resin plates 2 in a compressed state with a predetermined compression ratio (e.g., 50%, 60%, 70%) as shown in FIG. 2, and water is injected into the U-shaped test sample 1 to a water pressure of 100 mmAq and the 100 mmAq water pressure is maintained. Note that the applications of the resin foam are not limited to water sealing materials, and it can be widely used in various sealing members, cushioning materials, heat insulating materials, adsorbents, building members, automotive members, daily necessities, etc.

[0044] 3. Manufacturing Method of Resin Foam The manufacturing method of the resin foam is not particularly limited. For example, a method can be adopted in which a foaming agent is added to a polyolefin resin, and further, a crosslinking agent and other additives are optionally added and mixed, and then foaming molding is performed. Preferably, the manufacturing method of the polyolefin resin foam may be any of the following two-stage block foaming method, one-stage block foaming method, long-length foaming method using chemical crosslinking, and long-length foaming method using electron beam crosslinking. Among these, the block foaming method is preferable, and the two-stage block foaming method is more preferable in that a resin foam with a relatively large thickness can be manufactured, and the compression ratio can be increased in the defoaming process described later due to the large thickness.

[0045] <Two-Stage Block Foaming Method> The two-stage block foaming method includes, for example, the following steps (1)-(4). (1) Kneading Step The above-mentioned polyolefin resin, petroleum resin, crosslinking agent, foaming agent, silicone resin (optional component), additive (optional component), and filler and auxiliary agent required as appropriate are melt-kneaded at a temperature below the decomposition temperature of the foaming agent by a kneading device such as an extruder, Banbury mixer, kneader, or roll to obtain a foamable resin composition.

[0046] (2) Primary Foaming Step The foamable resin composition obtained in the kneading step is filled into the molding space of the primary mold and heated under pressure. Thereby, a part of the crosslinking agent, or a part of the crosslinking agent and the foaming agent is decomposed. Then, the pressure is released, and the foamable resin composition intermediate is taken out. The heating temperature is usually determined in the range of 130°C - 150°C, and the heating time is usually in the range of 25 - 70 minutes.

[0047] (3) Secondary Foaming Step The intermediate of the foamed resin composition obtained in the primary foaming step is placed in the molding space of the secondary mold, heated under normal pressure for secondary foaming, and then the resin foam is taken out from the secondary mold.

[0048] (4) Cell-breaking step The resin foam obtained in the secondary foaming step is subjected to a compression treatment by passing it between two rolls rotating in different directions to obtain a closed-cell resin foam. This step is a step of rupturing the cell membrane and connecting the cells of the resin foam by performing a compression treatment in which the resin foam is passed between two rolls rotating in different directions. Here, the compression conditions (compression ratio, peripheral speed ratio of the rolls) and the number of compression treatments at each compression treatment can be appropriately set according to the degree of cell connection. For example, the compression treatment is preferably performed repeatedly a plurality of times.

[0049] <One-step block foaming method> The one-step block foaming method includes, for example, the following steps (1)-(3). (1) Kneading step The above-mentioned polyolefin resin, petroleum resin, crosslinking agent, foaming agent, silicone resin (optional component), additive (optional component), and filler and auxiliary agent required as appropriate are melt-kneaded at a temperature below the decomposition temperature of the foaming agent by a kneading device such as an extruder, Banbury mixer, kneader, or roll to obtain a foamed resin composition.

[0050] (2) Foaming step The foamed resin composition obtained in the kneading step is filled into a mold, sealed, and heated for a predetermined time under pressure (heated at a temperature above the decomposition temperatures of the foaming agent and the crosslinking agent) to cause crosslinking of the crosslinking agent and decomposition of the foaming agent. Then, the mold is opened and depressurized to obtain a resin foam.

[0051] (3) Cell-breaking step The resin foam obtained in the foaming step is subjected to a compression treatment by passing it between two rolls rotating in different directions to obtain a closed-cell resin foam. For details, the description of the cell-breaking step in the two-step block foaming method is incorporated herein by reference.

[0052] <Long-strip Foaming Method Using Chemical Crosslinking> The long-strip foaming method includes, for example, the following steps (1)-(3). (1) Kneading step The above-mentioned polyolefin resin, petroleum resin, crosslinking agent, foaming agent, silicone resin (optional component), additive (optional component), and filler and auxiliary agent required as appropriate are kneaded with a single-screw extruder, twin-screw extruder, etc. and extruded into a sheet shape to extrude a foaming resin composition having a predetermined shape such as a sheet (hereinafter referred to as a mother board).

[0053] (2) Foaming step While transporting the mother board obtained in the kneading step in a heating device such as an oven, it is heated at 120-250 °C (above the decomposition temperature of the foaming agent and crosslinking agent) for 5-20 minutes to foam, thereby obtaining a resin foam. In addition, it is preferable to use a device in which a heating device such as an oven and a transport device are integrated, since the mother board can be continuously processed.

[0054] (3) Defoaming step A compression treatment is performed by passing the resin foam obtained in the foaming step between two rolls rotating in different directions to obtain a continuous bubble resin foam. For details, the description of the defoaming step in the two-stage block foaming method is incorporated by reference.

[0055] <Long-strip Foaming Method Using Electron Beam Crosslinking> The long-strip foaming method using electron beam crosslinking includes, for example, the following steps (1)-(4). (1) Kneading step The above-mentioned polyolefin resin, petroleum resin, foaming agent, silicone resin (optional component), foaming agent (optional component), crosslinking agent (optional component), additive (optional component), and filler and auxiliary agent required as appropriate are kneaded with a single-screw extruder, twin-screw extruder, etc. and extruded into a resin composition having a predetermined shape such as a sheet (hereinafter referred to as a mother board). Kneading and extrusion can be performed in one batch by an extruder. In order to perform uniform kneading, it is preferable to perform extrusion after previously mixing each component.

[0056] (2) Crosslinking step The master batch obtained in the kneading process is crosslinked. As the crosslinking method, a method of crosslinking with ionizing radiation such as electron beams or γ-rays is preferred. The crosslinking method is preferably crosslinking by electron beam irradiation (electron beam crosslinking). This is because electron beam crosslinking can achieve refinement of cells formed in the foam and control the cell diameter within a predetermined range. Electron beam crosslinking can be performed using an electron beam irradiator. Incidentally, if necessary, a crosslinking agent such as the aforementioned organic peroxide may be blended and chemical crosslinking may be used in combination. The irradiation dose of the electron beam is preferably 4.0 Mrad - 8.0 Mrad (40 kGy - 80 kGy). If the irradiation dose is less than 4.0 Mrad, good foaming may not occur in the subsequent foaming process. If the irradiation dose exceeds 8.0 Mrad, the crosslinking is strong and the resin becomes hard, so there is a concern that cracks may occur during foaming. The acceleration voltage of the electron beam may be appropriately adjusted according to the thickness of the master batch and the like, and is not particularly limited.

[0057] (3) Foaming process The crosslinked master batch obtained in the crosslinking process is heated at 120 - 250 °C (above the decomposition temperature of the foaming agent and the crosslinking agent) for 5 - 20 minutes while being transported in a heating device such as an oven to obtain a resin foam by foaming. Incidentally, it is preferable to use a device in which a heating device such as an oven and a transport device are integrated because the master batch can be continuously processed.

[0058] (4) Defoaming process The resin foam obtained in the foaming process is subjected to a compression process of passing between two rolls rotating in different directions to obtain an open-cell resin foam. For details, the description of the defoaming process in the two-stage block foaming method is incorporated.

[0059] 4. Effects of this embodiment In the resin foam of this embodiment, the content of the polyethylene-based resin is less than 29 parts by mass when the total of the polyolefin-based resins is 100 parts by mass. By setting such an upper limit for the content of the polyethylene-based resin, pinholes and the like are less likely to occur in the resin foam, the moldability is good, and the appearance is good. In addition, since pinholes and the like are less likely to occur in the resin foam, the sealing performance can be improved. Moreover, by setting the upper limit of the content of the polyethylene-based resin as described above, in the resin foam, the resin strength is reduced (in particular, the skin becomes soft), and the foamability is enhanced. Since the resin foam has good foamability, the flexibility can be suitably improved by forming a closed-cell structure. Therefore, when the resin foam is used as a sealing member, the adhesiveness to the adherend is increased, and the sealing performance can be improved. In particular, since the resin foam has good foamability, the number of compression treatments can be reduced when making the cells continuous to the same extent in the foaming process. Moreover, since the cells of the resin foam of the present embodiment are refined, when the resin foam is used as a sealing member, a gap is less likely to be formed between the resin foam and the adherend. Therefore, when the resin foam is used as a sealing member, the inflow of water, air, etc. from between the sealing member and the adherend can be suppressed, and the sealing performance can be improved.

[0060] Moreover, when the resin composition contains a silicone resin, the water-stopping property is good. It is presumed that the water-repellency of the resin foam is increased by the silicone resin, and the water-stopping property is improved.

Examples

[0061] Hereinafter, it will be described more specifically by way of examples. 1. Preparation of resin foam Resin foams of Examples 1-5 and Comparative Example 1 were prepared at the compounding ratios shown in Table 1. In Table 1, the compounding ratios represent the compounding ratios (parts by mass) when the total of the polyolefin-based resins is 100 parts by mass. In Table 1, the details of the main raw materials are shown below.

[0062]

Table 1

[0063] · Polyolefin-based resin 1: Ethylene vinyl acetate copolymer (EVA) (vinyl acetate content 15% by weight, density 936 kg / m 3, MFR 1.5 g / 10 min), additive is calcium carbonate, manufactured by Tosoh Corporation, Ultra Senn (registered trademark) 630 · Polyolefin resin 2: Low-density polyethylene (LDPE) (density 924 kg / m 3 , MFR 3.0 g / 10 min), Suntech TM-LD (registered trademark) F2225.4, manufactured by Asahi Kasei Corporation · Petroleum resin masterbatch (petroleum resin / polyolefin resin 3): A masterbatch of petroleum resin and low-density polyethylene (LDPE) in a ratio of 1:1 (mass ratio), C9 hydrogenated petroleum resin (partially hydrogenated type), softening point 90°C, manufactured by Arakawa Chemical Industries, Ltd., Alcon M-90 · Silicone masterbatch (silicone resin / polyolefin resin 4): A masterbatch of low-density polyethylene (LDPE) and silicone gum composed of dimethylpolysiloxane in a ratio of 1:1 (mass ratio), manufactured by Shin-Etsu Chemical Co., Ltd., X-22-2125H · Blowing agent masterbatch (ADCA / polyolefin resin 5): A masterbatch of azodicarbonamide (ADCA) and low-density polyethylene (LDPE) in a ratio of 3:2 (mass ratio), manufactured by Yonghe Chemical Industry Co., Ltd. · Filler: Calcium carbonate (CaCO3), manufactured by Maruo Calcium Co., Ltd., Snow Light SSS · Crosslinking agent: Dicumyl peroxide (DCP), manufactured by Kayaku Akzo Corporation, PERKADOX (registered trademark), BC-FF · Urea: Manufactured by Yonghe Chemical Industry Co., Ltd., Cellpaste (registered trademark) 101 · Blowing aid: Zinc stearate (ZnSt), manufactured by Tannan Chemical Industry Co., Ltd. · Dispersant: Polyethylene wax, manufactured by Sanyo Chemical Industries, Ltd., Sun Wax 131-P

[0064] In Table 1, for the "petroleum resin masterbatch", the blending ratios of "petroleum resin (C9 hydrogenated petroleum resin)" and "polyolefin resin 3 (LDPE)" are shown in parentheses. The fact that the value in the column of "polyolefin resin 3 (LDPE)" in Example 1 is "0.00" indicates that the petroleum resin is not made into a masterbatch. For the "silicone masterbatch", the blending ratios of "silicone resin (silicone gum)" and "polyolefin resin 4 (LDPE)" are shown in parentheses. For the "foaming agent masterbatch", the blending ratios of "ADCA" and "polyolefin resin 5 (LDPE)" are shown in parentheses.

[0065] The raw materials were mixed at the blending ratios described in Table 1, and a resin foam was obtained by the two-stage block foaming method described in the embodiment. In addition, the heating temperature in the secondary foaming process was 167°C in Examples 1-5 and Comparative Example 1.

[0066] In the foam breaking process, a compression treatment in which the molded body was passed between two rolls rotating in opposite directions was repeated until the repulsive resistance disappeared. Specifically, using 10-inch mixing rolls, the molded body was passed between two rolls rotating in opposite directions by the method described in the embodiment. The molded body after passing through the rolls was pinched with fingers, and the repulsive resistance was confirmed by touch. If there was a repulsive resistance, it was put back into the rolls again. If there was no repulsive resistance, the obtained resin foam was sliced into 10 mm and evaluated by the evaluation method described below. In addition, for Examples 1, 3-5 and Comparative Example 1, the vicinity of the core part (position about 5 cm from the surface) of the resin foam was sliced and taken out. For Example 2, the vicinity of the skin part (position about 1 cm - 2 cm from the surface) of the resin foam was sliced and taken out.

[0067] 2. Evaluation method (1) Density (apparent density) Density (kg / m 3 ) was measured as the apparent density based on JIS K6767:1999.

[0068] (2) 50% compression stress The 50% compression stress (kPa) was measured in accordance with the test method of "compression stress - strain" in JIS K6767:1999 (at 50% compression, corresponding to ISO 3386-1). A low 50% compression stress is one of the indicators of high flexibility of the resin foam.

[0069] (3) Compression set The compression set (%) was measured in accordance with the test method of "compression set" in JIS K6767:1999 (measurement of the thickness 24 hours after the end of compression, corresponding to ISO 1856).

[0070] (4) Cell number The cell number (pieces) was counted based on JIS K6400-1:2004 as the number of cells per 25 mm of the sample piece.

[0071] (5) Water stoppage property Using the evaluation method described in the embodiment, the retention time of 100 mmAq water pressure in the resin foam was measured. The compression ratio of the resin foam during measurement was 50%. Based on the retention time of 100 mmAq water pressure, the water stoppage property of the resin foam was evaluated according to the following criteria. A: The retention time of 100 mmAq water pressure is 24 hours or more. B: The retention time of 100 mmAq water pressure is less than 24 hours.

[0072] (6) Defoaming (foam breaking) times In the foam breaking process, the number of times of compression treatment of the molded body was defined as the defoaming (foam breaking) times. That is, using the method described in the embodiment, the molded body was passed between two rolls (roll size: 10 inches) that rotate in different directions, and the molded body after passing through the rolls was pinched with fingers, and the rebound resistance was confirmed by touch. The input to the rolls was repeated until the rebound resistance disappeared, and the number of compression treatments performed until it was determined that there was no rebound resistance was counted. The defoaming times were evaluated according to the following criteria. A: 40 times or less. B: More than 41 times and less than 45 times. C: 45 times or more.

[0073] (7) Appearance (Moldability) The appearance (moldability) of the resin foam was visually confirmed and evaluated according to the following criteria. A: There are no pinholes or the like, or the number of pinholes or the like is small, and the appearance is good. B: Many pinholes or the like are observed, and the appearance is poor.

[0074] 3. Results The results are shown in Table 1. In Examples 1-5, the evaluation of the appearance (moldability) was "A". In Comparative Example 1, the evaluation of the appearance (moldability) was "B". Examples 1-5 satisfy the following requirements (a) and (b). In contrast, Comparative Example 1 does not satisfy requirement (b). By satisfying the following requirements (a) and (b), Examples 1-5 had a relatively low content of low-density polyethylene in the resin composition, no pinholes or the like, or a small number of pinholes or the like, and it is considered that the appearance was good. Requirement (a): It is a resin foam obtained by foaming a resin composition containing a polyolefin resin and a petroleum resin. Requirement (b): The polyolefin resin contains less than 29 parts by mass of the polyethylene resin with respect to 100 parts by mass in total of the polyolefin resins.

[0075] The "number of defoaming times" decreases in the order of Comparative Example 1, Example 5, Example 4, and Example 3 to 45 times, 41 times, 34 times, and 31 times. Also, the "number of cells" increases in the order of Comparative Example 1, Example 5, Example 4, and Example 3 to 34 times, 36 times, 37 times, and 45 times. These are considered to be due to the fact that the content of low-density polyethylene in the resin composition decreases in the order of Comparative Example 1, Example 5, Example 4, and Example 3 to 35.72 parts by mass, 28.50 parts by mass, 23.50 parts by mass, and 18.50 parts by mass.

[0076] 4. Effects of the Examples According to the above examples, pinholes or the like were less likely to occur in the resin foam, the moldability was good, and the appearance was good. Also, pinholes or the like were less likely to occur in the resin foam, and the sealing property could be improved. Further, in the resin foam, the foam-breaking property was enhanced. Moreover, by manufacturing using raw materials with the same formulation as in Example 3 and existing equipment, a resin foam exhibiting the same physical properties as in Example 3 could be mass-produced.

[0077] The present disclosure is not limited to the embodiments described in detail above, and various modifications or changes are possible.

Claims

1. The foam is formed by foaming a resin composition containing a polyolefin resin and a petroleum resin, The polyolefin resin may include a polyethylene resin. The resin foam comprises less than 29 parts by mass of polyethylene-based resin per 100 parts by mass of the total of the polyolefin-based resins.

2. The resin foam according to claim 1, having a cell number based on JIS K6400-1:2004 of 30 cells / 25 mm or more.

3. The resin foam according to claim 2, having a cell number based on JIS K6400-1:2004 of 60 cells / 25 mm or less.

4. A sealing member comprising the resin foam according to claim 1 .

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