Resin foam sheet

Abstract

To provide a resin foam sheet having superior water repellency.SOLUTION: Provided is a resin foam sheet obtained by foaming a composition containing a polyolefin-based resin and silicone, the resin foam sheet having a contact angle with water of 120° or more. The resin foam sheet may have a 50% compressive stress strain of 40 kPa or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present technology relates to a resin foam sheet.

Background Art

[0002] Conventionally, resin foam sheets have been used in various applications because they are excellent in cushioning, heat insulation, water repellency, moisture resistance, etc. Here, in recent years, since resin foam sheets are also used in devices that require high water repellency performance such as smartphones and wearable terminals, there is a situation where water repellency performance is particularly required.

[0003] On the other hand, for example, in Patent Document 1, a polyethylene-based resin foam sheet is proposed, which has a glossiness of 10 or less on at least one surface (however, the glossiness is the glossiness measured according to the method described in JIS K7105) and a water contact angle of 85 degrees or more. Further, for example, in Patent Document 2, a foamed resin tube is proposed, which includes a tube body and a surface layer disposed on the outer surface side of the tube body, and the water contact angle with respect to the surface layer is 120° or more, and no dew condensation occurs on the outer surface of the surface layer until drain water at a temperature of 10°C flows for 15 minutes in an environment of a temperature of 25°C and a humidity of 90%. Furthermore, for example, in Patent Document 3, a foam sheet is proposed, which has an average bubble diameter of 40 to 200 μm and a 50% compression strength B of 25 to 800 kPa after 3 hours have elapsed since the start of compression.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventionally, although technologies related to resin foam sheets with improved water repellency have been developed, there is no resin foam sheet that satisfies as a sealing material, and there is a situation where the development of the above-described technologies is not sufficient.

[0006] Therefore, the main object of the present technology is to provide a resin foam sheet excellent in water repellency.

Means for Solving the Problems

[0007] In the present technology, a polyolefin resin, silicone, a resin foam sheet obtained by foaming a composition containing the same, and a resin foam sheet having a contact angle of 120° or more between the resin foam sheet and water is provided. The resin foam sheet according to the present technology may have a 50% compression stress strain of 40 kPa or less. The composition may contain a petroleum resin. In addition, the present technology also provides a sealing material including the resin foam sheet.

Brief Description of the Drawings

[0008] [Figure 1] It is a diagram for explaining dimensions in a U-shaped water stop test. [Figure 2] It is a diagram for explaining the evaluation of water stoppage performance.

Modes for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments for carrying out the present technology will be described. The embodiments described below show an example of a typical embodiment of the present technology, and any of the embodiments can be combined. Further, the scope of the present technology is not construed narrowly by these.

[0010] 1. Resin Foam Sheet The resin foam sheet according to the present technology is formed by foaming a resin composition. The resin composition contains a polyolefin-based resin and silicone. Further, the resin composition may contain a foaming agent, a crosslinking agent, and the like. Furthermore, the contact angle between the resin foam sheet according to the present technology and water is 120° or more.

[0011] Generally, when using a resin foam sheet as a sealing material, flexibility and continuity are in an inverse relationship. That is, in order to improve the followability to the adherend by softening, if the followability is insufficient, water leakage occurs from the interface between the resin foam sheet and the adherend. On the other hand, one of the methods of softening is a method of making cells continuous. However, when the cells are made continuous, water easily propagates inside the resin foam sheet, resulting in internal water leakage. In addition, in order to enhance the water repellency performance, it is necessary to improve the contact angle (water repellency) with water. Simply making the cells finer and continuous does not satisfy the predetermined water repellency performance with a contact angle of about 100°. Although the cells can be made finer to improve the contact angle, it becomes hard, and the man-hours of the step of defoaming the cells (defoaming step) are difficult to perform, and uniform defoaming is also difficult.

[0012] In contrast, the resin foam sheet according to the present technology has excellent water repellency by adopting the above configuration. Hereinafter, each component will be described in detail.

[0013] (1) Polyolefin-based resin The polyolefin-based resin is a resin having an olefin component unit as a main component. A resin having an olefin component unit as a main component is a resin containing 50% by mass or more of an olefin component unit. In the present technology, the content of the olefin component unit in the resin is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and it is particularly preferable that the resin component is composed only of a polyolefin-based resin.

[0014] The polyolefin resin preferably contains ethylene vinyl acetate copolymer (hereinafter also referred to as "EVA") and / or polyethylene. It is particularly preferable that the polyolefin resin in the present technology contains both EVA and polyethylene from the viewpoints of adjusting the degree of crosslinking and melt viscosity to obtain a good foam, imparting heat resistance, and preventing settling after foam collapse. The polyolefin resin may contain resin components other than EVA and polyethylene.

[0015] [EVA] The vinyl acetate content in the EVA is not particularly limited. From the viewpoint of improving flexibility, the vinyl acetate content, as measured in accordance with JIS K 6924-1, is preferably 5% by mass or more, and more preferably 10% by mass or more, where the mass of the EVA is taken as 100% by mass. Furthermore, from the viewpoint of preventing excessive crosslinking, the upper limit is preferably 40% by mass or less, and more preferably 30% by mass or less.

[0016] From these viewpoints, the content of vinyl acetate is preferably 5% by mass to 40% by mass, and particularly preferably 10% by mass to 30% by mass.

[0017] The melt flow rate (MFR) of the EVA is not particularly limited. From the viewpoint of moldability, the MFR of the EVA is measured in accordance with JIS K6924-1 at 190°C under a load of 2.16 kg. The lower limit is preferably 0.1 g / 10 min or more, more preferably 0.3 g / 10 min or more, and even more preferably 0.5 g / 10 min or more. The upper limit is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, and particularly preferably 5.0 g / 10 min or less.

[0018] From these viewpoints, in terms of moldability, the MFR of EVA is preferably 0.1 g / 10 min to 20 g / 10 min, more preferably 0.3 g / 10 min to 10 g / 10 min, and particularly preferably 0.5 g / 10 min to 5.0 g / 10 min, as measured in accordance with JIS K6924-1 at 190°C under a load of 2.16 kg.

[0019] From the perspective of flexibility in the foaming process, the lower limit of the EVA content is, for example, more than 0 parts by mass, preferably 10 parts by mass or more, particularly preferably 30 parts by mass or more, based on 100 parts by mass in total of the polyolefin resin. Also, from the perspective of preventing excessive crosslinking, the upper limit of the EVA content is, for example, less than 100 parts by mass, preferably 70 parts by mass or less, particularly preferably 50 parts by mass or less.

[0020] From these perspectives, the EVA content is, for example, more than 0 parts by mass and less than 100 parts by mass, preferably 10 parts by mass to 70 parts by mass, particularly preferably 30 parts by mass to 50 parts by mass.

[0021] [Polyethylene] Examples of the polyethylene include low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), etc. These polyethylenes may be used alone or in combination of two or more.

[0022] LDPE is usually a polyethylene formed by randomly branching and bonding ethylene repeating units. MDPE is a polyethylene with fewer branched bonds than low density polyethylene. HDPE is a polyethylene formed by linearly bonding ethylene repeating units with almost no branches. LLDPE is a polyethylene obtained by copolymerizing ethylene without long chain branches and an α-olefin. Examples of the α-olefin include propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, 4-methyl-1-pentene, etc.

[0023] In this technology, among these polyethylenes, it is particularly preferable to use LDPE from the perspectives of flexibility, cushioning property, processability, productivity, weight reduction, etc.

[0024] From the viewpoint of moldability, the MFR of polyethylene is a value measured at 190 °C and 2.16 kgf in accordance with JIS K7210-1. The lower limit is preferably 0.1 g / 10 min or more, more preferably 0.3 g / 10 min or more, and particularly preferably 0.5 g / 10 min or more. The upper limit is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, and particularly preferably 5.0 g / 10 min or less.

[0025] From these viewpoints, the MFR of polyethylene is a value measured at 190 °C and 2.16 kgf in accordance with JIS K7210-1, and is preferably 0.1 g / 10 min to 20 g / 10 min, more preferably 0.3 g / 10 min to 10 g / 10 min, and particularly preferably 0.5 g / 10 min to 5.0 g / 10 min.

[0026] From the viewpoints of flexibility and weight reduction, the lower limit of the polyethylene content is more than 0 parts by mass, preferably 30 parts by mass or more, and particularly preferably 50 parts by mass or more, with respect to 100 parts by mass in total of the polyolefin resin. The upper limit is, for example, 100 parts by mass or less, preferably 90 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0027] From these viewpoints, the polyethylene content is more than 0 parts by mass and 100 parts by mass or less, preferably 30 parts by mass to 90 parts by mass, and particularly preferably 50 parts by mass to 70 parts by mass, with respect to 100 parts by mass in total of the polyolefin resin.

[0028] [Other polyolefin resins] The polyolefin resins other than the above EVA and the above polyethylene are not particularly limited, and examples thereof include a polypropylene homopolymer, an ethylene-propylene copolymer, an ethylene-1-butene copolymer, an ethylene-propylene-1-butene copolymer, an ethylene-(4-methyl-1-pentene) copolymer, and an ethylene-acrylate copolymer. These polyolefin resins may be used alone, or two or more thereof including the above EVA and the above polyethylene may be used in combination.

[0029] From the viewpoints of heat resistance, processability, etc., it is preferable that the above polyolefin resin contains a polyethylene resin, but it may also contain a polypropylene resin. The polypropylene resin is a polymer containing structural units derived from propylene in one molecule, and examples thereof include a polypropylene homopolymer, an ethylene-propylene copolymer, and an ethylene-propylene-1-butene copolymer. These polypropylene resins may be used alone or in combination of two or more including EVA and polyethylene.

[0030] [Petroleum resin] In the present technology, it is preferable that the composition containing a polyolefin resin and silicone contains a 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.

[0031] Examples of the petroleum resin include an aliphatic petroleum resin (C5 petroleum resin), an aromatic petroleum resin (C9 petroleum resin), an aliphatic / aromatic petroleum resin (C5 / C9 petroleum resin), and an alicyclic petroleum resin (hydrogenated petroleum resin). The aliphatic petroleum resin (C5 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 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 petroleum resin) is a synthetic resin obtained by copolymerizing a raw material obtained by blending the above C5 fraction and C9 fraction.

[0032] From the viewpoint of the foam-breaking property of the resin foam sheet according to the present technology, the petroleum resin is particularly preferably a C9 hydrogenated petroleum resin.

[0033] From the viewpoints of odor, hue, thermal stability, weather resistance, and compatibility with polyolefin resins, a hydrogenated petroleum resin is preferred. A hydrogenated petroleum resin is a resin obtained by adding hydrogen to unsaturated double bonds present in a 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.

[0034] From the viewpoint of improving foamability, the content of the petroleum resin is preferably at least 2.0 parts by mass, more preferably at least 3.0 parts by mass, particularly preferably at least 4.0 parts by mass, based on 100 parts by mass in total of the polyolefin resin. Also, the upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, particularly preferably less than 10 parts by mass.

[0035] From these viewpoints, the content of the petroleum resin is preferably 2.0 parts by mass to 20 parts by mass, more preferably 3.0 parts by mass to 15 parts by mass, particularly preferably 4.0 parts by mass or more and less than 10 parts by mass, based on 100 parts by mass in total of the polyolefin resin.

[0036] [Other Components] In addition, the resin foam sheet according to the present technology may contain other resins, thermoplastic elastomers, thermosetting elastomers, etc. within a range that does not impair the object and effects of the present technology, in addition to the polyolefin resin. Examples of resins other than the polyolefin resin include thermoplastic resins such as polystyrene resins, polyamide resins, and polyester resins. Examples of thermoplastic elastomers include olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. Examples of thermosetting elastomers include synthetic rubbers such as ethylene propylene rubber (EPDM) and natural rubber.

[0037] (2) Silicone The resin foam sheet according to the present technology contains silicone. As the silicone, for example, polyorganosiloxane and the like can be preferably used. Here, polyorganosiloxane has a siloxane bond as the main chain and an organic group in the side chain. Examples of the organic group include a methyl group, a vinyl group, an ethyl group, a propyl group, a phenyl group, and the like. Specific examples of polyorganosiloxane include dimethylpolysiloxane, methylethylpolysiloxane, methyloctylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, methyl(3,3,3-trifluoropropyl)polysiloxane, and the like.

[0038] Silicone 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 preferably used in the form of silicone gum.

[0039] In the present technology, the silicone is preferably used as a masterbatch in which the silicone is dispersed in the above-described resin component. By using the masterbatch, the dispersibility in the resin component can be improved. In the present technology, for example, a masterbatch composed of low-density polyethylene (LDPE) and silicone gum made of dimethylpolysiloxane can be used in an arbitrary ratio.

[0040] The content of silicone is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, particularly preferably 0.1 parts by mass or more, with respect to a total of 100 parts by mass of the polyolefin-based resin. The upper limit is preferably 10 parts by mass or less, more preferably 7.0 parts by mass or less, still more preferably 5.0 parts by mass or less, even more preferably 4.0 parts by mass or less, particularly preferably 3.0 parts by mass or less, and more particularly preferably 2.5 parts by mass or less.

[0041] From these viewpoints, the silicone content is 0.05 parts by mass to 10 parts by mass, more preferably 0.07 parts by mass to 7.0 parts by mass, and particularly preferably 0.1 parts by mass to 5.0 parts by mass with respect to 100 parts by mass in total of the polyolefin resin.

[0042] (3) Blowing agent The blowing agent is not particularly limited, but is preferably a thermal decomposition type blowing agent that decomposes by heat to generate gas. As the thermal decomposition type blowing agent, an organic blowing agent or an inorganic blowing agent can be used.

[0043] Examples of the organic blowing agent include azodicarbonamide (ADCA), barium azodicarboxylate, azobisisobutyronitrile (AIBN), azocyclohexylnitrile, N,N'-dinitrosopentamethylenetetramine, 4,4'-oxybisbenzenesulfonylhydrazide, toluenesulfonyl semicarbazide, and the like. Examples of the inorganic blowing agent include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, sodium nitrite, ammonium nitrite, sodium borohydride, sodium monosodium citrate anhydride, and the like. The blowing agent may be used alone or in combination of two or more.

[0044] In the present technology, among the above blowing agents, from the viewpoint of obtaining a foam with a large amount of gas and a high expansion ratio, it is preferable to use azo compounds such as ADCA, barium azodicarboxylate, and AIBN, and nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, and it is particularly preferable to use ADCA.

[0045] The content of the blowing agent is preferably 5.0 parts by mass or more, more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more with respect to 100 parts by mass in total of the polyolefin resin. The upper limit is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and still more preferably 25 parts by mass or less.

[0046] The content of the foaming agent is preferably 5.0 parts by mass to 35 parts by mass, more preferably 10 parts by mass to 30 parts by mass, and particularly preferably 15 parts by mass to 25 parts by mass with respect to 100 parts by mass in total of the polyolefin resin.

[0047] (4) Crosslinking agent The crosslinking agent is used to impart an arbitrary crosslinked structure to the resin foam sheet according to the present technology. Examples of the crosslinking agent include organic peroxides such as dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis-tert-butylperoxyhexane, and 1,3-bis-tert-butylperoxy-isopropylbenzene.

[0048] The resin foam sheet according to the present technology may adopt an electron beam crosslinked structure formed by electron beam crosslinking in addition to the chemical crosslinked structure containing the above crosslinking agent. As the crosslinked structure of the polyolefin resin foam, it is particularly preferable to adopt a chemical crosslinked structure from the viewpoint of the ease of continuous cell formation during foaming.

[0049] The content of the crosslinking agent has a lower limit value that is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and particularly preferably 1.0 part by mass or more with respect to 100 parts by mass in total of the polyolefin resin. Also, the upper limit value is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and particularly preferably 1.5 parts by mass or less.

[0050] From these viewpoints, the content of the crosslinking agent is preferably 0.1 part by mass to 3.0 parts by mass, more preferably 0.5 part by mass to 2.0 parts by mass, and particularly preferably 1.0 part by mass to 1.5 parts by mass with respect to 100 parts by mass in total of the polyolefin resin.

[0051] (5) Other additives Various additives can be added to the above composition as needed. These optional additives are not particularly limited, and examples include foaming aids, lubricants, internal lubricants, cell nucleating agents, cell nucleation assisting agents, weathering agents, antioxidants, shrinkage preventers, crystal nucleating agents, heat stabilizers, antistatic agents, conductivity imparting agents, flame retardants, flame retardant aids, inorganic fillers, colorants (pigments, dyes, etc.), particles encapsulating liquefied gas, surfactants, vulcanizing agents, surface treatment agents, and the like. The above optional additives may be used alone or in combination of two or more.

[0052] Regarding the content of other additives, based on 100 parts by mass in total of the polyolefin resin, the lower limit is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and particularly preferably 0.5 part by mass or more. Also, the upper limit is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, and particularly preferably 3.0 parts by mass.

[0053] From these viewpoints, the content of other additives is preferably 0.1 part by mass to 10 parts by mass, more preferably 0.3 part by mass to 5.0 parts by mass, and particularly preferably 0.5 part by mass to 3.0 parts by mass based on 100 parts by mass in total of the polyolefin resin.

[0054] 2. Method for manufacturing resin foam sheet The method for manufacturing the resin foam sheet according to the present technology is not particularly limited. For example, a method can be adopted in which a foaming agent is added to a polyolefin resin and silicone, and further, a crosslinking agent and other additives are optionally added and mixed, and then foaming molding is performed. Preferably, the method for manufacturing the polyolefin resin foam can 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.

[0055] In the present technology, among these, from the viewpoint of the ease of occurrence of continuous cell formation during foaming, the long-length foaming method using chemical crosslinking is particularly preferable. Hereinafter, each manufacturing method will be described in detail.

[0056] [Long-strip Foaming Method Using Chemical Crosslinking] (1) Kneading Step A polyolefin resin, a petroleum resin, a crosslinking agent, a foaming agent, silicone, and, if necessary, any additives are kneaded using a single-screw extruder, a 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 "mother board"). Kneading and extrusion can be carried out collectively by an extruder. In order to perform uniform kneading, it is preferable to perform extrusion after previously mixing each component.

[0057] (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°C to 250°C (above the decomposition start temperature of the foaming agent and the crosslinking agent) for 5 minutes to 20 minutes to be foamed, thereby obtaining a resin foam. In addition, when using a device in which a heating device such as an oven and a transport device are integrated, the mother board can be continuously processed.

[0058] (3) Forming Step The resin foam sheet obtained in the foaming step can be directly subjected to the defoaming step described later, but it is also possible to subject it to the defoaming step described later after performing a forming step of forming it into a desired form by slicing or the like as necessary.

[0059] (4) Defoaming Step A compression treatment is performed on the resin foam sheet obtained through the foaming step and, if necessary, the forming step by passing it between two rolls rotating in different directions to obtain an open-cell foam. This step is a step of rupturing closed cells to make the closed cells of the polyolefin resin foam into open cells (continuous) by performing a compression treatment of passing the resin foam between two rolls rotating in different directions. Here, the compression conditions (compression ratio, peripheral speed ratio of the rolls) at each compression treatment can be appropriately set according to the degree of continuous foaming.

[0060] [Long-strip Foaming Method Using Electron Beam Crosslinking] (1) Kneading Step A polyolefin resin, a petroleum resin, a crosslinking agent, a foaming agent, silicone, and, if necessary, any additives are kneaded using a single-screw extruder, a twin-screw extruder, etc., and a resin composition (master sheet) having a predetermined shape such as a sheet shape is extruded. Kneading and extrusion can be carried out in one batch by an extruder. In order to perform uniform kneading, it is preferable to perform extrusion after previously mixing each component.

[0061] (2) Crosslinking step The master sheet obtained in the kneading step is crosslinked. As the crosslinking method, a method of crosslinking with ionizing radiation such as an electron beam or a γ-ray can be used. As the crosslinking method, crosslinking by electron beam irradiation (electron beam crosslinking) is preferable. This is because electron beam crosslinking can achieve refinement of cells formed in the foam and can control the cell diameter within a predetermined range. Electron beam crosslinking can be carried out using an electron beam irradiator. Incidentally, if necessary, a crosslinking agent such as the above-mentioned organic peroxide may be blended and chemical crosslinking may be used in combination.

[0062] The irradiation dose of the electron beam is preferably 1.0 Mrad to 10.0 Mrad (10 kGy to 100 kGy). If the irradiation dose is less than 1.0 Mrad, good foaming may not occur in the foaming step described later. If the irradiation dose exceeds 10.0 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 sheet, etc., and is not particularly limited.

[0063] (3) Foaming step The crosslinked master sheet obtained in the crosslinking step is heated at 120°C to 250°C (above the decomposition temperature of the foaming agent and the crosslinking agent) for 5 to 20 minutes while being transported in a heating device such as an oven to obtain a resin foam sheet. When using a device in which a heating device such as an oven and a transport device are integrated, the master sheet can be continuously processed.

[0064] (4) Molding step The resin foam sheet obtained in the foaming step can be directly subjected to the defoaming step described below, or it can also be subjected to the defoaming step after performing a forming step of forming it into a desired form by slicing or the like as necessary.

[0065] (5) Defoaming step The resin foam sheet obtained through the foaming step and, if necessary, the forming step is subjected to a compression treatment by passing it between two rolls rotating in different directions to obtain an open-cell foam. Since the details of this step are the same as those of the defoaming step in the long-length foaming method using chemical crosslinking described above, the description is omitted here.

[0066] [One-step block foaming method] (1) Kneading step A polyolefin resin, a petroleum resin, a crosslinking agent, a foaming agent, silicone, and, if necessary, any additives are melt-kneaded at a temperature below the decomposition temperature of the foaming agent using a kneading device such as an extruder, a Banbury mixer, a kneader, or a roll to obtain a foamable resin composition.

[0067] (2) Foaming step The foamable 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 the crosslinking of the crosslinking agent and the decomposition of the foaming agent. Then, the mold is opened and depressurized to obtain a resin foam.

[0068] (3) Forming step The resin foam obtained in the foaming step is, if necessary, subjected to ear cutting, slicing, etc. to form it into a desired form to obtain a resin foam sheet.

[0069] (4) Defoaming step The resin foam sheet obtained through the foaming step and, if necessary, the forming step is subjected to a compression treatment by passing it between two rolls rotating in different directions to obtain an open-cell foam. Since the details of this step are the same as those of the defoaming step in the long-length foaming method using chemical crosslinking described above, the description is omitted here.

[0070] [Two-stage Block Foaming Method] (1) Kneading Process A polyolefin resin, a petroleum resin, a crosslinking agent, a foaming agent, silicone, and, if necessary, any additives are melt-kneaded at a temperature below the decomposition temperature of the foaming agent using a kneading device such as an extruder, a Banbury mixer, a kneader, or a roll to obtain a foamable resin composition.

[0071] (2) Primary Foaming Process The foamable resin composition obtained in the kneading process is filled into the molding space of the primary mold and heated under pressure. This decomposes part of the crosslinking agent, or part of the crosslinking agent and the foaming agent. Then, the pressure is released, and the foamable resin composition intermediate is taken out. The heating temperature is usually determined in the range of 120 to 160 °C, and the heating time is usually in the range of 10 to 60 minutes.

[0072] (3) Secondary Foaming Process The foamable resin composition intermediate obtained in the primary foaming process is placed in the molding space of the secondary mold, heated under normal pressure to cause secondary foaming, and then the resin foam is taken out from the secondary mold.

[0073] (4) Molding Process The resin foam obtained in the foaming process is, if necessary, subjected to ear cutting, slicing, etc. to be molded into a desired form to obtain a resin foam sheet.

[0074] (5) Defoaming Process The resin foam sheet obtained through the foaming process and, if necessary, the molding process is subjected to a compression treatment of passing between two rolls rotating in different directions to obtain an open-cell foam. Since the details of this process are the same as those of the defoaming process in the long-length foaming method using chemical crosslinking described above, the description is omitted here.

[0075] 3. Physical Properties of the Resin Foam Sheet Hereinafter, the physical properties of the resin foam sheet according to the present technology will be described in detail.

[0076] (1) Contact Angle The contact angle between the resin foam sheet according to the present technology and water is 120° or more, preferably 123° or more, more preferably 125° or more, still more preferably 126° or more, even more preferably 129° or more, and particularly preferably 130° or more, from the viewpoint of obtaining the required water-stopping property.

[0077] (2) Cell number The cell number of the resin foam sheet according to the present technology is preferably 20 cells / 25 mm or more, more preferably 25 cells / 25 mm or more, and particularly preferably 27 cells / 25 mm or more.

[0078] In the present technology, the cell number is counted as the number of cells per 25 mm (n = 5 average value). The upper limit value of the above cell number is not particularly limited, but is, for example, 100 cells / 25 mm or less. From the viewpoint of water-stopping property, the above cell number is preferably 20 cells / 25 mm to 100 cells / 25 mm. Note that "cell" means the pore part in the foam and is synonymous with "bubble".

[0079] (3) Density The lower limit of the density of the resin foam sheet according to the present technology is preferably 20 kg / m 3 or more, more preferably 25 kg / m 3 or more, and particularly preferably 30 kg / m 3 or more. Also, the upper limit is preferably 100 kg / m 3 or less, more preferably 70 kg / m 3 or less, and particularly preferably less than 50 kg / m 3 .

[0080] From these viewpoints, the density is preferably 20 kg / m 3 to 100 kg / m 3 , more preferably 25 kg / m 3 to 70 kg / m 3 , and still more preferably 30 kg / m 3 or more and less than 50 kg / m 3 . By setting the density within the above range, the polyolefin-based resin foam can be lightened.

[0081] (4) Compressive stress strain From the viewpoint of obtaining the required resilience, the compressive stress of the resin foam sheet according to the present technology is preferably 40 kPa or less, more preferably 30 kPa or less, still more preferably 20 kPa or less, and particularly preferably 10 kPa or less at 50% compression. By setting the compressive stress at 50% compression to 40 kPa or less, a resin foam sheet with more excellent water repellency can be obtained.

[0082] Also, it is preferably 18 kPa or less, more preferably 13 kPa or less, still more preferably 10 kPa or less, and particularly preferably 8 kPa or less at 25% compression. Further, it is preferably 15 kPa or less, more preferably 13 kPa or less, still more preferably 10 kPa or less, and particularly preferably 6 kPa or less at 10% compression. The lower limit of the compressive stress of the resin foam sheet according to the present technology is not particularly limited, but in any case of compression, it is usually 0.1 kPa or more.

[0083] (5) Adhesiveness From the viewpoint of obtaining the required adhesive force, the adhesiveness of the resin foam sheet according to the present technology is preferably 5 N or more, more preferably 10 N or more, and particularly preferably 13 N or more. The upper limit value of the adhesiveness of the resin foam sheet according to the present technology is not particularly limited, but for example, it is 30 N or less.

[0084] (6) Water stoppage property The resin foam sheet according to the present technology can be used as a sealing material (water-stopping material). When used as a sealing material, the resin foam sheet according to the present technology is formed into a thickness and shape (for example, string shape) according to the application by punching or the like. The resin foam sheet according to the present technology preferably has a holding time value of 100 mmAq water pressure of 30 minutes or more, more preferably 9 hours or more, and particularly preferably 24 hours or more.

[0085] 4. Applications of the resin foam sheet The resin foam sheet according to the present technology can be used for various applications in all fields by taking advantage of its high quality. Specifically, for example, sealing materials, shock absorbers, buffers, sound absorbers, heat insulators, heat retainers, etc. can be mentioned.

Example

[0086] Hereinafter, the present technology will be described in more detail based on examples. Note that the examples described below show an example of a typical example of the present technology, and the scope of the present technology is not construed narrowly thereby.

[0087] <Experimental Example> In this experimental example, each resin foam sheet was produced and their physical properties were examined.

[0088] (1) Raw materials · Polyolefin resin 1: Ethylene vinyl acetate copolymer (EVA) (vinyl acetate content 19% by mass, density 941 kg / m 3 , MFR 2.5 g / 10 min) · Polyolefin resin 2: Low density polyethylene (LDPE) (density 924 kg / m3, MFR 3.0 g / 10 min) · Petroleum resin: C9 hydrogenated petroleum resin (partially hydrogenated type, softening point 90 °C) · Foaming agent: Azodicarbonamide (ADCA) · Crosslinking agent: Dicumyl peroxide (DCP) · Silicone masterbatch: 50:50 masterbatch of silicone gum made of dimethylpolysiloxane and LDPE (manufactured by Shin-Etsu Chemical Co., Ltd., product name: X-22-2125H)

[0089] (2) Manufacture of resin foam sheet The raw materials were mixed at the blending ratios shown in Table 1 below, and a resin foam was obtained by a long foam method using chemical crosslinking. In the foam breaking process, a compression treatment was performed by passing the molded body between two rolls rotating in different directions. The obtained resin foam was sliced to 5 mm, and each physical property was measured and evaluated.

[0090] (3) Evaluation For each of the manufactured foams, each evaluation was performed using the following method.

[0091] [Contact Angle] The contact angle was measured 30 seconds after a small amount (about 0.01 g) of pure water was dropped from a syringe onto the resin foam sheet in accordance with JIS R 3257 6. Static Method.

[0092] [Cell Count] The cell count was measured in accordance with the procedure described in the cell counting procedure specified in Appendix A of JIS K6767:1999.

[0093] [Density] The density was measured in accordance with JIS K6767:1999.

[0094] [Expansion Ratio] The expansion ratio was calculated based on the measured density and the following formula. Expansion ratio (times) = 1000 / density (kg / m 3 )

[0095] [Compression Stress Strain] The compression stress strain was measured in accordance with JIS K6767:1999.

[0096] [Adhesion] The adhesion was evaluated by performing the peel test described below. A crosslinked polyolefin foam sheet (width 25 mm × length 150 mm × thickness 5 mm) was adhered to a SUS plate with a double-sided tape (manufactured by Nitto Denko Corporation, No. 516). At this time, a PET film was sandwiched at the peeling start position between the crosslinked polyolefin foam sheet and the double-sided tape and adhered. The crosslinked polyolefin foam sheet was peeled off at a peeling rate of 300 mm / min from the peeling start position, and the peel strength was measured. The crosslinked polyolefin foam sheet was evaluated for each case where the cell surface and the skin surface were adhered. The peel strength was taken as the average value of the three measurement results.

[0097] [Water Stop Property] The U-shaped water-stop test described below was conducted for evaluation. Samples (each resin foam sheet) for water-tightness measurement, which were created by punching a sealing material with a thickness of 5 mm into a U-shape according to the dimensions shown in Fig. 1, were sandwiched between two acrylic resin plates 20, 20 with a compression ratio of 50% as shown in Fig. 2. In this state, water was injected into the U-shaped sample 10 so that the water pressure became 100 mAq, and the time during which the 100 mmAq water pressure was maintained was measured. A holding time of 24 hours or more was rated as "pass: ○", and less than 24 hours was rated as "fail: ×".

[0098] (4) Results The results are shown in Table 1 below.

[0099]

Table 1

[0100] (5) Discussion As shown in Table 1 above, in Examples 1 to 4, the contact angle was 120° or more, the water-tightness was excellent, and there were no problems with other physical properties. On the other hand, Comparative Example 1, which did not contain silicone and had a contact angle of 120° or less, was inferior in water-tightness compared to Examples 1 to 4.

[0101] Therefore, it was found that a resin foam sheet obtained by foaming a composition containing a polyolefin-based resin and silicone, and having a contact angle of 120° or more between the resin foam sheet and water, was excellent in water-tightness.

Claims

1. A resin foam sheet obtained by foaming a composition containing a polyolefin resin and silicone, wherein the contact angle between the resin foam sheet and water is 120° or more. Resin foam sheet.

2. The resin foam sheet according to claim 1, wherein the 50% compression stress strain is 40 kPa or less.

3. The resin foam sheet according to claim 1, wherein the composition contains a petroleum resin.

4. A sealing material comprising the resin foam sheet according to any one of claims 1 to 3.

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