Rubber foam and rubber foam with double-sided tape

Abstract

To provide a rubber foam having a good surface appearance.SOLUTION: A rubber foam is a foam of a composition containing EPDM, PE of the following blend ratio, a crosslinker, a crosslinking aid having double bonds, and a foamer. The blend ratio (EPDM / PE) is 95 / 5-70 / 30 (mass ratio).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a rubber foam and a method for producing a rubber foam. [Background technology]

[0002] Patent Document 1 discloses a method for producing a flame-retardant EPDM foam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-211119 Summary of the Invention [Problem to be solved by the invention]

[0004] In the production of EPDM foam, depending on the material used, air bubbles may occur immediately after molding, resulting in a poor appearance of the foam surface. The present disclosure has been made in view of the above-described circumstances, and has an object to provide a rubber foam having a good-looking surface. The present disclosure can be realized in the following forms. [Means for solving the problem]

[0005] [1] A rubber foam, which is a foam of a composition containing EPDM, PE in the following blend ratio, a crosslinking agent, a crosslinking aid having a plurality of double bonds, and a foaming agent. Blend ratio (EPDM / PE): 95 / 5 to 70 / 30 (mass ratio) [Effects of the Invention]

[0006] The rubber foam of the present disclosure has a good surface appearance. DETAILED DESCRIPTION OF THE INVENTION

[0007] Here, a preferred example of the present disclosure will be described. [2] Contains at least a nitrogen-based flame retardant, [1] The rubber foam according to [1], wherein the amount of the nitrogen-based flame retardant is 50 parts by mass or more and 150 parts by mass or less, relative to 100 parts by mass of the total amount of the EPDM and the PE. [3] Contains at least a phosphorus-based flame retardant, The rubber foam according to [1] or [2], wherein the amount of the phosphorus-based flame retardant is 1 part by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the total amount of the EPDM and the PE. [4] The rubber foam according to any one of [1] to [3], having a sulfur content of 1000 ppm or less. [5] A method for producing a rubber foam, comprising foaming and crosslinking a composition containing EPDM, PE in the blend ratio described below, a crosslinking agent, a crosslinking aid having a plurality of double bonds, and a foaming agent. Blend ratio (EPDM / PE): 95 / 5 to 70 / 30 (mass ratio)

[0008] The present disclosure will be described in detail below. In this specification, when a numerical range is indicated using "to" it is intended to include both the lower limit and the upper limit unless otherwise specified. For example, the expression "10 to 20" includes both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

[0009] 1. Rubber foam The rubber foam is a foam of a composition containing EPDM, PE in the blend ratio shown below, a crosslinking agent, a crosslinking aid having multiple double bonds, and a foaming agent. Blend ratio (EPDM / PE): 95 / 5 to 70 / 30 (mass ratio)

[0010] (1) Composition The composition contains EPDM (ethylene-propylene-diene rubber), PE (polyethylene) in the following blend ratio, a crosslinking agent, a crosslinking aid having multiple double bonds, and a foaming agent. The composition may contain at least one optional component selected from fatty acid esters, metal hydroxides, flame retardants, and foaming aids. Each component of the composition will be described below.

[0011] (1.1) EPDM EPDM is a rubber obtained by copolymerizing ethylene, propylene, and dienes. EPDM is prepared by copolymerizing an ethylene-propylene copolymer with a diene to introduce an unsaturated bond, which allows vulcanization with a vulcanizing agent. The diene is not particularly limited, but a non-conjugated diene is preferred, such as 5-ethylidene-2-norbornene, 1,4-hexadiene, or dicyclopentadiene. From the viewpoint of obtaining the properties of the rubber foam of the present disclosure, 5-ethylidene-2-norbornene is preferred as the diene. The content of dienes in EPDM (diene content) is not particularly limited, but from the viewpoint of the influence of the crosslinking (vulcanization) reaction and mechanical properties, the content of dienes is preferably from 4 to 17% by mass, more preferably from 7 to 15% by mass. The ethylene content of EPDM is not particularly limited, but from the viewpoints of heat resistance and permanent deformation resistance, the ethylene content is preferably from 40 to 80 mass %, more preferably from 45 to 60 mass %. The EPDM may be used alone or in combination of two or more.

[0012] (1.2)PE Examples of PE include low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, high-density polyethylene, and copolymers containing ethylene as a main component. Among these, low-density polyethylene is preferred from the viewpoint of dispersibility of the compound during kneading, and from the viewpoint of ensuring low permanent deformation of the foam. The density of the low-density polyethylene in the non-foamed state is preferably 0.910 g / cm.3 More than 0.940g / cm 3 More preferably, it is 0.915 g / cm or less. 3 More than 0.935g / cm 3 More preferably, it is 0.920 g / cm or less. 3 More than 0.930g / cm 3 The following is the result. The melt flow rate (MFR) of PE is not particularly limited. From the viewpoint of moldability, the MFR of PE is preferably 0.5 g to 30 g / 10 min as measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238.

[0013] The blend ratio of EPDM to PE (EPDM / PE) is preferably 95 / 5 or less by mass, more preferably 90 / 10 or less, and even more preferably 85 / 15 or less, from the viewpoint of suppressing air swelling after molding of the foam. The blend ratio of EPDM to PE (EPDM / PE) is preferably 65 / 35 or more by mass, more preferably 70 / 30 or more, and even more preferably 75 / 25 or more, from the viewpoint of suppressing poor expansion. That is, the blend ratio of EPDM to PE (EPDM / PE) is preferably 95 / 5 to 65 / 35 by mass, more preferably 90 / 10 to 70 / 30, and even more preferably 85 / 15 to 75 / 25. A blend ratio within this range suppresses warpage of the molded rubber foam, improves the appearance of the rubber foam, and suppresses defects such as pinholes.

[0014] (1.3) Fatty acid esters (optional ingredients) Fatty acid esters (RCOOR', where R and R' may be the same or different) have both hydrophilic and hydrophobic properties. It is thought that the fatty acid ester acts as a surfactant, reducing the aggregation of metal hydroxide and PE and acting as a dispersant in rubber (rubber foam). Examples of fatty acid esters include glycerin fatty acid esters, higher alcohol fatty acid esters, sorbitan fatty acid esters, propylene fatty acid esters, and n-butyl stearate. The fatty acid ester may be used alone or in combination of two or more. The fatty acid ester has a melting point of 50° C. or more and 80° C. or less, and is preferably at least one selected from the group consisting of glycerin fatty acid esters and higher alcohol fatty acid esters, from the viewpoint of ease of dispersion during kneading. Examples of glycerin fatty acid esters include glycerin monostearate, glycerin monobehenate, glycerin monooleate, glycerin monolaurate, stearin distearate, glycerin dibehenate, and glycerin dioleate. Examples of higher alcohol fatty acid esters include stearyl stearate, lauryl stearate, lauryl laurate, and stearyl behenate. The amount of fatty acid ester is not particularly limited. When the total of EPDM and PE is 100 parts by mass, the amount of fatty acid ester is preferably 1 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, from the viewpoint of uniformly dispersing the metal hydroxide and PE without aggregation. On the other hand, the amount of fatty acid ester is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 7.0 parts by mass or less, from the viewpoint of suppressing oil bleeding. From these viewpoints, the amount of fatty acid ester is preferably 1.0 part by mass or more and 10.0 parts by mass or less, more preferably 3.0 parts by mass or more and 8.0 parts by mass or less, and even more preferably 5.0 parts by mass or more and 7.0 parts by mass or less.

[0015] (1.4) Crosslinking agent The crosslinking agent is not particularly limited, and an organic peroxide-based crosslinking agent can be suitably used. It is preferable not to use a sulfur crosslinking agent containing sulfur as the crosslinking agent from the viewpoint of suppressing contamination of electronic substrates, etc. Examples of the sulfur crosslinking agent include sulfur and sulfur compounds. The crosslinking agent may be used alone or in combination of two or more. Examples of the crosslinking agent include 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, dicumyl peroxide, di-t-butylperoxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butylhydroperoxide, t-butylcumyl peroxide, benzoyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxin)hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-mono(t-butylperoxy)hexane, and α,α'-bis(t-butylperoxy-m-isopropyl)benzene. As the crosslinking agent, particularly preferred are diacyl peroxides such as 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, dicumylperoxide, di-t-butylperoxide, and di-t-butylperoxy-3,3,5-trimethylcyclohexane. The amount of crosslinking agent is not particularly limited. From the viewpoint of improving the crosslink density in the rubber foam 1, the amount of crosslinking agent is preferably 0.05 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, where the total amount of EPDM and EVA is 100 parts by mass. On the other hand, from the viewpoint of suppressing deterioration of the physical properties of the rubber foam 1 due to scission of the rubber main chain, the amount of crosslinking agent is preferably 10.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 2.0 parts by mass or less. From these viewpoints, the amount of crosslinking agent is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.5 parts by mass or more and 4.0 parts by mass or less, and even more preferably 1.0 parts by mass or more and 2.0 parts by mass or less. Commercially available crosslinking agents are often diluted with silica, clay, calcium carbonate, or the like and sold in powder form to improve dispersibility in the compound. When two or more crosslinking agents are used, the amount of the crosslinking agent mentioned above means the total amount.

[0016] (1.5) Crosslinking aid (co-crosslinking agent) The cross-linking aid has a plurality of double bonds. The cross-linking aid preferably has a plurality of carbon-carbon double bonds. The cross-linking aid preferably has conjugated double bonds. Specific examples of crosslinking aids include quinone dioxime compounds such as p-quinone dioxime, methacrylate compounds such as ethylene glycol dimethacrylate and polyethylene glycol dimethacrylate, allyl compounds such as diallyl phthalate and triallyl cyanurate, maleimide compounds, and divinylbenzene. In particular, allyl compounds having a plurality of carbon-carbon double bonds, such as diallyl isocyanurate and triallyl isocyanurate, and methacrylate compounds having a plurality of carbon-carbon double bonds, such as ethylene glycol dimethacrylate and polyethylene glycol dimethacrylate, are preferably used. The amount of the crosslinking aid is not particularly limited. When the total of EPDM and PE is taken as 100 parts by mass, the amount of the crosslinking aid is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, from the viewpoint of improving the crosslink density in the rubber foam. On the other hand, the amount of the crosslinking aid is preferably 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less, from the viewpoint of suppressing deterioration of the physical properties of the rubber foam. From these viewpoints, the amount of the crosslinking agent is preferably 0.5 parts by mass or more and 10.0 parts by mass or less, and more preferably 1.0 parts by mass or more and 5.0 parts by mass or less.

[0017] (1.6) Metal hydroxide (optional component) As the metal hydroxide, known metal hydroxides can be used. The metal hydroxide improves the flame retardancy of the rubber foam. As the metal hydroxide, one or more types selected from the group consisting of aluminum hydroxide, magnesium hydroxide, and calcium aluminate can be used. The amount of metal hydroxide is not particularly limited. When the total of EPDM and PE is taken as 100 parts by mass, the amount of metal hydroxide is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, from the viewpoint of ensuring adhesion of the rubber foam 1 to the pressure-sensitive adhesive layer 3. On the other hand, the amount of metal hydroxide is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less, from the viewpoint of improving the dispersibility of the filler. From these viewpoints, the amount of metal hydroxide is preferably 20 parts by mass or more and 100 parts by mass or less, more preferably 30 parts by mass or more and 90 parts by mass or less, and even more preferably 50 parts by mass or more and 80 parts by mass or less.

[0018] (1.7) Flame retardant (optional) The flame retardant is not particularly limited. One type of flame retardant may be used alone, or two or more types may be used in combination. The flame retardant improves the flame retardancy of the rubber foam. The flame retardant is preferably a non-halogen flame retardant. The composition preferably does not contain a halogen flame retardant. The non-halogen flame retardant is not particularly limited. Examples of the non-halogen flame retardant include nitrogen-based flame retardants and phosphorus-based flame retardants.

[0019] (1.7.1) Nitrogen-based flame retardants The nitrogen-based flame retardant is not particularly limited. Examples of nitrogen-based flame retardants include melamine-based flame retardants, triazine compounds, and guanidine compounds. Examples of melamine-based flame retardants include melamine, melamine melam melem, melamine cyanurate, melamine phosphate, melamine pyrophosphate, melamine polyphosphate, melamine melam melem polyphosphate, and melamine sulfate. Melamine cyanurate is preferred as the nitrogen-based flame retardant. Melamine cyanurate has the property of not impairing the processability of rubber compounds even when highly filled. The nitrogen-based flame retardants may be used alone or in combination of two or more. The amount of nitrogen-based flame retardant used is not particularly limited. When the total of EPDM and PE is 100 parts by mass, the nitrogen-based flame retardant is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 65 parts by mass or more, from the viewpoint of ensuring high flame retardancy. On the other hand, the nitrogen-based flame retardant is preferably 150 parts by mass or less, more preferably 110 parts by mass or less, and even more preferably 90 parts by mass or less, from the viewpoint of kneading processability and molding processability. Specifically, nitrogen-based flame retardants do not have the reinforcing properties of rubber like carbon black, and adding a large amount of them reduces durability and strength, so 150 parts by mass or less is preferred. Furthermore, if the viscosity of the composition increases, the foaming property is controlled and low density cannot be ensured, so 150 parts by mass or less is preferred. From these viewpoints, the amount of the nitrogen-based flame retardant is preferably 50 parts by mass or more and 150 parts by mass or less, more preferably 60 parts by mass or more and 110 parts by mass or less, and even more preferably 65 parts by mass or more and 90 parts by mass or less.

[0020] (1.7.2) Phosphorus-based flame retardants The phosphorus-based flame retardant is not particularly limited. Phosphorus-based flame retardants are not particularly limited as long as they contain phosphorus atoms in the molecule. Examples of phosphorus-based flame retardants include red phosphorus-based flame retardants (flame retardants containing red phosphorus) and phosphorus compounds. Known red phosphorus-based flame retardants can be used. Red phosphorus has attracted attention in recent years due to its flame retardancy, low smoke generation, and low toxic gas emissions. Red phosphorus generally promotes carbonization of the matrix, forming a surface carbonized layer that blocks oxygen and provides flame retardancy. Furthermore, a proposed mechanism is proposed in which phosphorus is converted via methanoic acid to polyphosphoric acid, and during this process, a protective coating is formed, blocking oxygen and providing flame retardancy. The flame retardant effect of red phosphorus is thought to be achieved through a combination of carbonization promotion and coating effect. Examples of red phosphorus that can be used include Hishiguard CP (manufactured by Nippon Chemical Industry Co., Ltd.), which is surface-treated with aluminum hydroxide or the like to have an average particle size of approximately 15 μm, and 1140T (manufactured by Rin Chemical Industry Co., Ltd.). In addition, in consideration of dispersibility in rubber, a masterbatch type (EVA, etc.) of red phosphorus can also be suitably used. Examples of phosphorus compounds include melamine polyphosphate, ammonium polyphosphate, phosphazene compounds, melamine pyrophosphate, phosphoric acid, melamine orthophosphate, melamine phosphate, piperazine orthophosphate, piperazine pyrophosphate, and piperazine polyphosphate. The phosphazene compound is preferably a cyclic phenoxyphosphazene represented by the following general formula: Examples of phosphorus compounds that can be used include ADK STAB EP-2500 and BUDIT 667 (Budenheim), and examples of phosphazenes that can be used include Rabitle FP-100 (Fushimi Pharmaceutical).

[0021] [ka] (wherein n represents an integer of 3 to 25.)

[0022] The amount of the phosphorus-based flame retardant, when used, is not particularly limited. When the total of EPDM and PE is 100 parts by mass, the phosphorus-based flame retardant is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, from the viewpoint of ensuring higher flame retardancy in a vertical combustion test. On the other hand, the phosphorus-based flame retardant is preferably 24 parts by mass or less, more preferably 22 parts by mass or less, and even more preferably 20 parts by mass or less, from the viewpoint of suppressing an increase in the viscosity of the compound (kneaded product) and controlling the foamability to obtain a low-density rubber foam. From these viewpoints, the amount of the phosphorus-based flame retardant is preferably 1 part by mass or more and 24 parts by mass or less, more preferably 5 parts by mass or more and 22 parts by mass or less, and even more preferably 10 parts by mass or more and 20 parts by mass or less. Nitrogen-based flame retardants and non-halogen flame retardants such as phosphorus-based flame retardants have a high flame retardant effect, but they do not provide as high an effect as halogen-based flame retardants, so it is preferable to use multiple types in combination.

[0023] The total amount of the metal hydroxide and the flame retardant is not particularly limited, but when the total amount of EPDM and PE is taken as 100 parts by mass, the total amount of the metal hydroxide and the flame retardant is preferably 170 parts by mass or more and 240 parts by mass or less, more preferably 160 parts by mass or more and 230 parts by mass or less, and even more preferably 150 parts by mass or more and 220 parts by mass or less, from the viewpoint of ensuring higher flame retardancy in a vertical combustion test.

[0024] (1.8) Foaming agents The foaming agent is not particularly limited. Known foaming agents such as organic foaming agents and inorganic foaming agents can be used. One foaming agent may be used alone, or two or more foaming agents may be used in combination. As the foaming agent, for example, at least one of dinitropentadienetetramine (DPT), azodicarbonamide (ADCA), 4,4'-oxybisbenzenesulfonylhydrazide (OBSH), and sodium hydrogen carbonate can be used. The amount of the foaming agent is not particularly limited. When the total amount of EPDM and PE is 100 parts by mass, the amount of the foaming agent is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 9 parts by mass or more, from the viewpoint of adjusting the amount of foaming gas to obtain a low-density rubber foam. On the other hand, from the viewpoint of ensuring appearance (defects such as cracks and pinholes), the amount of the foaming agent is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. From these viewpoints, the amount of the foaming agent is preferably 5 parts by mass or more and 35 parts by mass or less, more preferably 8 parts by mass or more and 30 parts by mass or less, and even more preferably 9 parts by mass or more and 25 parts by mass or less.

[0025] (1.9) Foaming aid (optional ingredient) The foaming aid is not particularly limited. A urea-based foaming aid is preferably used as the foaming aid. The urea-based foaming aid is one whose main component is urea, and examples thereof include Cellpaste K-5 and Cellpaste 101 manufactured by Eiwa Chemical Industry Co., Ltd. The main component refers to a substance whose content (mass%) is 90 mass% or more (100 mass% or less). The blending ratio of the urea-based foaming aid is preferably 1.0 parts by mass or more and 9.0 parts by mass or less, and more preferably 2.0 parts by mass or more and 8.0 parts by mass or less, per 100 parts by mass of the total of EPDM and PE, from the viewpoint of adjusting the decomposition initiation temperature of the foaming agent during foam molding.

[0026] (1.10) Paraffin-based process oil The composition may also contain a paraffinic processing oil. Commercially available paraffin-based process oils can be used, such as Diana Process Oils "PS-430," "PS-32," "PS-90," "PW-32," "PW-90," "PW-150," and "PW-380" manufactured by Idemitsu Kosan Co., Ltd. The amount of paraffinic process oil is not particularly limited. The paraffinic process oil ensures the cohesiveness of the compound during kneading and can improve the dispersibility of the filler in the clayey compound. From the viewpoint of kneading processability, the amount of paraffinic process oil is preferably 0 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, based on 100 parts by mass of the total of EPDM and PE. On the other hand, from the viewpoint of suppressing oil bleeding, the amount of paraffinic process oil is preferably 80 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less. From these viewpoints, the amount of paraffinic process oil is preferably 0 parts by mass or more and 80 parts by mass or less, more preferably 3 parts by mass or more and 30 parts by mass or less, and even more preferably 5 parts by mass or more and 10 parts by mass or less. A rubber foam containing paraffin-based process oil has poor flammability, so the amount of paraffin-based process oil is preferably small.

[0027] (1.11) Other ingredients The composition may contain, in addition to the above-mentioned EPDM, PE, fatty acid ester, crosslinking agent, crosslinking aid, metal hydroxide, flame retardant, blowing agent, and blowing aid, additives such as crosslinking accelerators (vulcanization accelerators), fillers, softeners, flame retardants, glass fibers, wood flour, fibers, dehydrating agents, antioxidants, antioxidants, various micro- and nanocapsules, pigments, colorants, mildew inhibitors, reinforcing materials (various carbon blacks), and expandable graphite. The additives may be used alone or in combination of two or more.

[0028] (1.11.1) Fillers The filler is not particularly limited, but examples thereof include inorganic fillers such as calcium carbonate (such as heavy calcium carbonate), magnesium carbonate, silicic acid and its salts, clay, talc, mica powder, bentonite, silica, alumina, aluminum silicate, acetylene black, furnace black, and aluminum powder; organic fillers such as cork; and other known fillers. These fillers may be used alone or in combination of two or more. Calcium carbonate, clay, and silica are preferably used. The blending ratio of the filler is not particularly limited, but is preferably 30 to 200 parts by mass, more preferably 50 to 900 parts by mass, per 100 parts by mass of the total of EPDM and PE.

[0029] (1.11.2) Softener The softener is not particularly limited. In the present disclosure, known softeners such as plasticizers, liquid paraffin, rosin, chroman resin, polybutene, and asphalt can be used. These softeners may be used alone or in combination of two or more. Petroleum oils and asphalts are preferably used. From the viewpoint of ensuring flexibility, kneading processability, and adhesiveness of the pressure-sensitive adhesive, the blending ratio of the softener is preferably, for example, 0 parts by mass or more and 100 parts by mass or less, and more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the total of EPDM and PE.

[0030] (2) Apparent density of rubber foam The apparent density of the rubber foam is set to 0.05 g / cm from the viewpoint of obtaining flexibility to ensure airtightness, watertightness, etc. 3 More than 0.3g / cm 3 Preferably less than 0.06 g / cm 3 More than 0.2g / cm 3 Less than 0.07 g / cm is more preferable. 3 More than 0.09g / cm 3 The following is even more preferred: The apparent density of the rubber foam is measured by a measurement method in accordance with JIS K 6767.

[0031] (3) Sulfur content of rubber foam 1 There are no particular limitations on the sulfur content of the rubber foam 1. From the viewpoint of suppressing contamination of electronic substrates and the like, the sulfur content is preferably 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 100 ppm or less. The sulfur content is measured in accordance with JIS-6233. The test piece is placed in a flask filled with hydrogen peroxide and burned. The organic matter is oxidized and the sulfur is converted to sulfuric acid. The solution is quantified using ion chromatography.

[0032] (4) Manufacturing method of rubber foam The method for producing a rubber foam is not particularly limited. The rubber foam can be produced, for example, by the following production method. The rubber foam can be produced by foaming and crosslinking a composition containing EPDM, PE in the blend ratio shown below, a crosslinking agent, a crosslinking aid having multiple double bonds, and a foaming agent. The order in which the raw materials (EPDM, PE, crosslinking agent, crosslinking aid, foaming agent) are compounded and kneaded is not particularly limited. A portion of each raw material may be kneaded in advance. Blend ratio (EPDM / PE): 95 / 5 to 55 / 45 (mass ratio)

[0033] (5) Uses of the rubber foam of this embodiment The rubber foam of this embodiment is fixed to an adherend using double-sided tape. Any double-sided tape can be used. It is preferable to use a butyl-based adhesive for the adhesive layers on both sides of the double-sided tape. Because the adhesive strength between the rubber foam of this embodiment and the butyl-based adhesive is relatively high, the adhesive strength between the rubber foam and the double-sided tape can be increased.

[0034] (6) Effects of the rubber foam of this embodiment The rubber foam of this embodiment has the effect of having a good surface appearance. The rubber foam of this embodiment causes little contamination to electronic substrates and the like. When the rubber foam of this embodiment contains a specified flame retardant, even if it does not contain a halogen-based flame retardant, it can achieve V0 passing based on the V0 standard, with a burning time of 50 seconds or less, in a test conforming to the vertical burning test based on the UL94 standard.

[0035] The effect of the rubber foam of this embodiment, that is, the rubber foam has a good surface appearance, will be described in detail. When an organic peroxide-based crosslinking agent is used instead of a sulfur crosslinking agent in a rubber foam made of EPDM and EVA (ethylene-vinyl acetate copolymer), the following problem occurs: Air is trapped near the surface of the rubber foam immediately after molding. This can cause dome-shaped bulges (air bulges, e.g., circular domes of 5 mm to 20 mm) to form on the surface of the rubber foam, resulting in poor surface appearance and reduced commercial value. The inventors investigated the cause and speculated that it is as follows: The temperature of the rubber foam immediately after molding is approximately 160°C, and it gradually cools naturally to room temperature. Immediately after molding, the rubber foam is high in temperature and soft, and it is believed that the foaming gas is uniformly dispersed throughout the rubber foam. As cooling progresses, cooling occurs first from the surface, making it difficult for the interior to cool. The melting point of EVA is lower than that of EPDM. Therefore, even when the rubber foam is cooled and the EPDM portion begins to solidify, there is a period when the EVA portion remains soft. It is presumed that during this time, the foaming gas is forced into and collects in the soft EVA portion. It is presumed that when the rubber foam is cooled to room temperature, the entire rubber foam cools and solidifies, leaving a dome-shaped bulge on the surface of the rubber foam. The rubber foam of this embodiment uses EPDM and PE. PE has a higher melting point than EVA, approximately 110 to 125°C, so immediately after molding, the foam solidifies with the gas in a homogenized state. Therefore, gas accumulation is less likely to occur in the rubber foam (air blistering is less likely to occur). Therefore, the rubber foam of this embodiment has a good surface appearance.

[0036] Here, we will explain the estimated mechanism by which a rubber foam containing a metal hydroxide exhibits flame retardancy conforming to the 94V-0 standard specified in UL-94. In this case, a metal hydroxide is compounded into the rubber foam. Metal hydroxides exhibit self-extinguishing properties due to their dehydration action, and exhibit high flame retardancy. Therefore, it is estimated that when a metal hydroxide is compounded, the rubber foam exhibits excellent flame retardancy due to the interaction of the metal hydroxides. Furthermore, when a metal hydroxide and a fatty acid ester are blended into a rubber foam, the metal hydroxide is dispersed well due to the action of the fatty acid ester, and it is presumed that the metal hydroxide effectively contributes to flame retardancy. Furthermore, when a flame retardant is compounded into the rubber foam, high flame retardancy is ensured even when the foam is highly expanded (low density). [Example]

[0037] The present invention will be explained in more detail below with reference to examples.

[0038] 1. Rubber Foam Preparation Various rubber foams were produced using the compounding ratios shown in Table 1-2. In Table 1-2, the details of the main raw materials are shown below. EPDM: Mitsui EPT4021 manufactured by Mitsui Chemicals, Inc. was used. PE: Novatec LD LJ802 manufactured by Japan Polyethylene Co., Ltd. Fatty acid esters: As the fatty acid ester, Rikemal SL-800 (stearyl stearate) manufactured by Riken Vitamin Co., Ltd. was used. Paraffin-based process oil (abbreviated as "paraffin-based oil" in the table): Diana Process PS-430 manufactured by Idemitsu Kosan Co., Ltd. was used. Crosslinking aid: Taik (triallyl isocyanurate (co-crosslinking sites: 3 locations), 2 parts by mass) manufactured by Mitsubishi Chemical Corporation was used. Crosslinking agent: In Examples 1-6 and Comparative Examples 1, 2, and 4, a mixture of 1.5 parts by mass of Perhexa 25B-40 (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) and 2.5 parts by mass of Perhexa C-40MB (1,1-di(t-butylperoxy)cyclohexane), both manufactured by NOF Corporation, was used. Tables 1 and 2 show the total amount of crosslinking agent. Foaming aid: A urea-based foaming aid (Cell Paste K-5, manufactured by Eiwa Chemical Industry Co., Ltd., 4.6 parts by mass) was used. Foaming agent: Azodicarbonamide (Vinifor AC#3W, manufactured by Eiwa Chemical Industry Co., Ltd., 15 parts by mass) was used. ·Metal hydroxide: The aluminum hydroxide used was C-301N (manufactured by Sumika Alchem ​​Co., Ltd.). Carbon black: Although carbon black is not listed in Tables 1 and 2, Asahi Carbon #50G (20 parts by mass) manufactured by Asahi Carbon Co., Ltd. was used in all of Examples 1-6 and Comparative Examples 1-4. Nitrogen-based flame retardants: Melamine cyanurate MC-4500 (manufactured by Nissan Chemical Industries, Ltd.) was used as the nitrogen-based flame retardant. Phosphorus-based flame retardants: As the phosphorus-based flame retardant, a red phosphorus-based flame retardant (special surface treatment coated red phosphorus 1140T, manufactured by Rin Chemical Industry Co., Ltd.) was used. In Table 1-2, "Total of flame retardants" represents the total of the blending ratio of aluminum hydroxide, the blending ratio of nitrogen-based flame retardants, and the blending ratio of phosphorus-based flame retardants.

[0039] Specifically, each rubber foam was produced as follows. <Examples 1-6> EPDM, PE, carbon black, paraffin-based process oil, flame retardant (nitrogen-based flame retardant, phosphorus-based flame retardant (1), or phosphorus-based flame retardant (2) as listed in Table 1), fatty acid ester, crosslinking aid, and metal hydroxide were all charged into a Banbury mixer, and the compound was discharged when the temperature reached 130°C. Next, a crosslinking agent, a foaming aid, and a foaming agent were added to the compound, and the mixture was kneaded with a mixing roll and extruded into a sheet. The sheet was set in a mold at 130°C and subjected to primary press molding for 15 minutes, and then secondary press molding was performed at 160°C for 15 minutes to crosslink and foam, thereby obtaining a rubber foam.

[0040] <Comparative Example 1> A rubber foam was produced in the same manner as in Example 1-6, except that PE was not used. <Comparative Example 2> Rubber foams were produced in the same manner as in Examples 1 to 6. In Comparative Example 2, the blend ratio of EPDM to PE (EPDM / PE) was 60 / 40, which is outside the range of rubber foams of the present disclosure. <Comparative Example 3> A rubber foam was produced in the same manner as in Examples 1 to 6, except that no crosslinking agent or crosslinking aid was used. In Comparative Example 3, crosslinking was carried out with sulfur. <Comparative Example 4> A rubber foam was produced in the same manner as in Example 1-6, except that no crosslinking aid was used.

[0041] Each rubber foam of Examples 1-6 is considered to have a closed-cell structure because it has a low water absorption rate of 1 to 5%. Rubber foams with a closed-cell structure generally have high water-stopping performance but poor adhesion (adhesion) to a pressure-sensitive adhesive layer. On the other hand, rubber foams with an open-cell structure (water absorption rate of 100 to 300%) generally have low water-stopping performance but high adhesion (adhesion) to a pressure-sensitive adhesive layer.

[0042] 2. Evaluation Method (1) Apparent density The apparent density was measured in accordance with JIS-K 6767.

[0043] (2) 50% compression load The compressive load of the rubber foam was measured in accordance with JIS-K 6767. The skin layer of the rubber foam was removed to prepare a 10 mm thick test piece. After that, using a compression tester, the test piece was compressed to 50% at a compression rate of 10 mm / min, and the compression load was measured after 10 seconds.

[0044] (3) Measurement of water absorption rate The water absorption rate of the rubber foam was measured in accordance with ASTM D 1056. The skin layer of the rubber foam was removed to prepare a test piece having a thickness of 12.5 mm and a size of 50 mm x 50 mm. After measuring the weight of the test piece, the test piece was immersed 50 mm below the water surface, left under a reduced pressure of 17 kPa for 3 minutes, and then immersed at atmospheric pressure for 3 minutes. After immersion, water droplets adhering to the surface were wiped off, and the weight of the test piece after immersion was measured and the water absorption rate was calculated using the following formula.

[0045]

number

[0046] (4) UL94 vertical flame test Rubber foams of each thickness were tested in accordance with the vertical burning test based on the UL94 standard. Burning times of 50 seconds or less were evaluated as V0 pass based on the V0 standard. Burning times of 250 seconds or less were evaluated as V1 pass based on the V1 standard.

[0047] (5) Sulfur content measurement test (total sulfur) The test was conducted in accordance with JIS-K6233:2016. The test piece was placed in a flask filled with hydrogen peroxide and burned. The organic matter was oxidized and the sulfur was converted to sulfuric acid. The solution was quantified using ion chromatography.

[0048] [Table 1]

[0049] [Table 2]

[0050] 3.Results The results are shown in Table 1-2. In Table 1-2, the A, B, C, and D in the column for the condition of the rubber foam (molded product) are as follows: <State of rubber foam (state of molded product)> A: No swelling due to air in the rubber foam. No warping, pinholes or cracks in the rubber foam. Good. B: No swelling due to air in the rubber foam. Slight warping and cracking in the rubber foam. No pinholes. C: There is swelling due to air in the rubber foam. There is a fair amount of warping, cracking, and pinholes in the rubber foam. D: Numerous air bubbles in the rubber foam. Many warps, cracks, and pinholes in the rubber foam. Many air bubbles.

[0051] In Table 1-2, A, B, C, and D in the overall judgment column have the following meanings: A:Good. B: Somewhat good. C: Somewhat bad. D: Sorry.

[0052] (1) Fulfillment status of each requirement in Examples 1-6 The compositions constituting the rubber foams of Examples 1 to 6 satisfy all of the following requirements (a) to (f). · Requirement (a): Contains EPDM. · Requirement (b): Includes PE. Requirement (c): Contains a crosslinking agent. Requirement (d): Contains a cross-linking aid having multiple double bonds. Requirement (e): Contains a foaming agent. Requirement (f): The blend ratio (EPDM / PE) is 95 / 5 to 70 / 30 (mass ratio).

[0053] (2) Fulfillment status of each requirement in Comparative Examples 1-4 In contrast, the rubber foam of Comparative Example 1-4 does not satisfy the following requirements. Comparative Example 1 does not satisfy requirement (b). Comparative Example 2 does not satisfy requirement (f). Comparative Example 3 does not satisfy requirements (c) and (d). Comparative Example 4 does not satisfy requirement (d).

[0054] (3) Results and Discussion The rubber foams of Examples 1 to 6 were confirmed to have good moldability, i.e., the rubber foams of Examples 1 to 6 were confirmed to have no swelling due to air in the rubber foam and to have a good surface appearance. The rubber foams of Examples 1 to 6 had short burning times in the vertical burning test based on the UL94 standard and had high flame retardancy. It was confirmed that the rubber foams of Examples 1 to 6 had a low sulfur content and caused little contamination to electronic substrates and the like. The rubber foams of Examples 1 to 6 were in good condition and were also evaluated as good overall. The rubber foams of Examples 1 to 6 had a low apparent density (0.05 g / cm 3 ~0.30g / cm 3 ) and has a closed cell structure (water absorption rate of 5% or less), which provides good water-stopping properties. In contrast, Comparative Example 1, which did not contain PE, was inferior to the Examples in the state of the rubber foam and the results of the vertical combustion test, and the overall evaluation was also inferior to the Examples. In Comparative Example 2, in which the blend ratio of EPDM and PE (EPDM / PE) was 60 / 40 and which was outside the range of the rubber foam of the present disclosure, the state of the rubber foam and the results of the vertical combustion test were inferior to those of the Examples, and the overall evaluation was also inferior to that of the Examples. Comparative Example 3, which was crosslinked with sulfur, received an inferior overall rating to Examples. Furthermore, it was confirmed that Comparative Example 3 had a high sulfur content and was likely to contaminate electronic substrates and the like. Comparative Example 4, which did not contain a cross-linking aid having a plurality of double bonds, had many air blisters in the molded article and was also evaluated poorly overall.

[0055] 4. Effects of the Example According to the above-described examples, it is possible to provide a rubber foam that has a good surface appearance, high flame retardancy, and causes little contamination of electronic substrates, etc. Furthermore, according to the examples, it is possible to provide a rubber foam that causes little swelling due to air.

[0056] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible.

Claims

1. A foam of a composition containing EPDM, PE in the following blend ratio, a crosslinking agent, a crosslinking aid having a plurality of double bonds, a foaming agent, and red phosphorus, The PE is at least one selected from the group consisting of low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, and high-density polyethylene. Blend ratio (EPDM / PE): 95 / 5 to 70 / 30 (mass ratio)

2. A foamed product of a composition containing EPDM, PE in the following blend ratio, a crosslinking agent, a crosslinking aid having a plurality of double bonds, a foaming agent, and a metal hydroxide, The PE is at least one selected from the group consisting of low-density polyethylene, linear low-density polyethylene, linear very low-density polyethylene, medium-density polyethylene, and high-density polyethylene. Blend ratio (EPDM / PE): 95 / 5 to 70 / 30 (mass ratio)

3. A rubber foam described in claim 1 or claim 2, wherein the composition contains a nitrogen-based flame retardant.

4. The rubber foam according to any one of claims 1 to 3, wherein a blend ratio (EPDM / PE) is 80 / 20 to 75 / 25 (mass ratio).

5. A rubber foam with double-sided tape, comprising a rubber foam described in any one of claims 1 to 4 and double-sided tape.

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