WO2018003811A1 - ミラブル型シリコーンゴム組成物、ミラブル型シリコーンゴムスポンジ及び該スポンジの製造方法 - Google Patents
ミラブル型シリコーンゴム組成物、ミラブル型シリコーンゴムスポンジ及び該スポンジの製造方法 Download PDFInfo
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- E—FIXED CONSTRUCTIONS
- E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
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Definitions
- the present invention relates to a millable silicone rubber composition, a millable silicone rubber sponge, and a method for producing the sponge by continuous foaming.
- Silicone rubber sponge is a sponge with excellent physical properties such as excellent heat resistance, cold resistance, electrical insulation, flame retardancy, etc. unique to silicone rubber, and low compression set. Silicone rubber sponges having such characteristics are used for OA equipment, automobiles, building materials and the like to promote low thermal conductivity and light weight.
- Silicone rubber sponges are produced by various methods such as silicone rubber molding / crosslinking methods and foaming methods, depending on the application.
- foaming methods there is a method of obtaining a sponge by blending thermally expandable resin fine particles (thermally expandable microcapsules) encapsulating a solvent in a rubber composition.
- the solvent in the heat-expandable microcapsule evaporates with heating, and the heat-expandable microcapsule expands.
- the particle diameter of the expanded thermally expandable microcapsule becomes the size of the sponge cell.
- the crosslinking agent used in the silicone rubber sponge can be selected from addition crosslinking agents and organic peroxide crosslinking agents.
- addition crosslinking agents in general, in the case of atmospheric hot-air crosslinking (HAV: Hot Air Vulcanization, hereinafter abbreviated as HAV), an addition crosslinking agent with good surface crosslinking is selected, and in the case of mold crosslinking, an organic peroxide is selected.
- HAV Hot Air Vulcanization
- Patent Document a method using a polyhydric alcohol, an inorganic acid salt, a metal soap, an organic tin compound, or the like as a foaming agent.
- Patent Document 3-5
- an already-expanded microballoon is added to the addition-crosslinking liquid silicone, a liquid or an ionic substance is used as a foaming agent, and a step of heating (curing) the silicone rubber;
- JP-A-8-012888 Japanese Patent Laid-Open No. 8-012795 Japanese Patent Laid-Open No. 2001-220510 JP 2002-070838 A JP 2001-295830 A
- the present invention uses a thermally expandable microcapsule as a foaming agent and can set a wide density from a low foaming ratio to a high foaming ratio, but has a low compression set and does not impair the physical properties inherent to silicone rubber.
- Another object of the present invention is to provide a silicone rubber sponge having a highly fine foamed uniform fine cell structure and a method for producing the same.
- the inventors of the present invention blended solvent-encapsulated non-expanded microcapsules that thermally expand and contract at a specific temperature with respect to the thermosetting millable silicone rubber composition.
- the millable silicone rubber can be used as a foamed sponge only by performing a general HAV process.
- the millable silicone rubber sponge manufactured by this method has a wide range of densities from low foaming ratio to high foaming ratio, is highly elastic, and the surface smoothness of the skin layer
- the present invention was completed by discovering that the silicone rubber sponge had excellent dimensional accuracy after foaming and had a uniform fine cell structure. That is, the present invention provides the following millable silicone rubber sponge and a method for producing the same.
- ⁇ 2> The method for producing a millable silicone rubber sponge according to ⁇ 1>, wherein the heat treatment is performed with atmospheric hot air.
- ⁇ 3> ⁇ E> ⁇ 1> or ⁇ 2>, wherein the amount of gas generated by the continuous foaming agent of component (E) is 100 cc or more with respect to a total of 100 g of component (A) and component (B) A method for producing a millable silicone rubber sponge.
- the foaming agent is at least one selected from azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, and hydrazodicarbonamide, according to any one of ⁇ 1> to ⁇ 3> Method for producing a millable silicone rubber sponge.
- D The millable according to any one of ⁇ 1> to ⁇ 4>, wherein the curing agent is a dialkyl organic peroxide and the crosslinking initiation temperature (6-minute half-life temperature) is 135 to 180 ° C. Type silicone rubber sponge manufacturing method.
- (D) curing agent organic peroxide 0.01 to 20 parts by mass with respect to 100 parts by mass of component (A) Foaming agent: high-temperature decomposition of a solid having a decomposition start temperature of 180 ° C. or higher Type organic foaming agent that begins to decompose after curing of component (A)
- An organopolysiloxane having a polymerization degree of 3,000 or more and having at least two alkenyl groups in one molecule is represented by: 100 parts by mass (B) reinforcing silica (A) 10 to 100 parts by mass with respect to 100 parts by mass of component (C) Thermally expandable microcapsules having an expansion start temperature of 90 to 150 ° C., contracted by 20% or more from the maximum expansion volume by heating at 200 ° C. for 5 minutes, and a contraction temperature of 200 ° C. or higher. 0.1 to 20 parts by mass with respect to part (D) Curing agent: Organic peroxide having a crosslinking initiation temperature of 100 to 180 ° C.
- Foaming agent Solid high-temperature decomposable organic foaming agent having a decomposition start temperature of 180 ° C. or more (A) 0.1-30 parts by mass with respect to 100 parts by mass of component (C) Expansion start temperature of component ⁇ ( D) Component crosslinking initiation temperature ⁇ Millable silicone rubber composition, which is a decomposition starting temperature of shrinkage temperature ⁇ (E) component of the C) component.
- the production method of the present invention a wide range of densities can be set from a low foaming ratio to a high foaming ratio, the elasticity is high, and the surface smoothness of the skin layer and the dimensional accuracy after foaming are excellent. It is possible to produce a silicone rubber sponge having a uniform and fine cell structure. Therefore, the silicone rubber sponge of the present invention is useful for sponge rolls, belts, sheets and the like.
- FIG. 2 is an enlarged photograph of a sponge cross section of Example 1.
- the present invention comprises alkenyl group-containing organopolysiloxane (A), reinforcing silica (B) for imparting strength to silicone rubber, specific heat-expandable microcapsules (C) for forming sponge cells, and component (A).
- A alkenyl group-containing organopolysiloxane
- B reinforcing silica
- C specific heat-expandable microcapsules
- component (A) component
- a millable silicone rubber composition containing a curing agent (D) for curing and a solid high-temperature decomposable foaming agent (E) that generates gas after the silicone rubber cures to foam the sponge cell. It is characterized by.
- the thermally expandable microcapsule of component (C) expands at 90 to 150 ° C. and foams in components (A) and (B).
- the curing agent of component (D) generates radicals at a temperature of 120 to 170 ° C., crosslinks component (A), and a sponge cell is formed.
- the shrinkage of the thermally expandable microcapsule of component (C) is started at 180 to 210 ° C., and a gap is created between the outer shell resin and the sponge cell of the shrinkable thermally expandable microcapsule. Furthermore, when the temperature range of 180 to 250 ° C.
- the foaming agent of component (E) is decomposed to generate a large amount of gas, and is discharged outside the sponge while foaming the sponge cell.
- Oxygen penetrates into the sponge to oxidize and deteriorate the residual resin of the thermally expandable microcapsule of component (C) that has shrunk.
- the organopolysiloxane of component (A) has the following average composition formula (I) R 1 a SiO 4-a / 2 (I) [In formula (I), R 1 represents the same or different monovalent hydrocarbon group, and a represents a positive number of 1.95 to 2.04. ] An organopolysiloxane having a polymerization degree of 3,000 or more and having at least two alkenyl groups in one molecule.
- examples of R 1 include the same or different monovalent hydrocarbon groups having preferably 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms.
- alkyl groups such as methyl group, ethyl group, propyl group, butyl group, hexyl group and dodecyl group, cycloalkyl groups such as cyclohexyl group, alkenyl groups such as vinyl group, allyl group, butenyl group and hexenyl group
- Aryl groups such as phenyl group and tolyl group, and aralkyl groups such as ⁇ -phenylpropyl group.
- R 1 in which some or all of the hydrogen atoms bonded to the carbon atoms are replaced with halogen atoms.
- examples include chloromethyl group and trifluoropropyl group.
- R 1 a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable, and in particular, a methyl group in R 1 is preferably 80% or more, and more preferably 95% or more.
- a is a positive number of 1.95 to 2.04, and this organopolysiloxane is substantially linear, but is branched as long as the rubber elasticity of the cured silicone rubber sponge is not impaired. May be.
- the organopolysiloxane may have a molecular chain end blocked with a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a trivinylsilyl group, or the like. It is necessary to have at least two alkenyl groups, specifically, 0.001 to 5%, particularly 0.05 to 0.5% of R 1 is an alkenyl group, particularly a vinyl group. preferable.
- the component (A) organopolysiloxane is alkalinized by hydrolytic condensation of one or more selected organohalosilanes or cyclic polysiloxanes (such as siloxane trimers or tetramers). Alternatively, it can be obtained by ring-opening polymerization using an acidic catalyst, which is basically a linear diorganopolysiloxane, but may be partially branched. Further, it may be a mixture of two or more different molecular structures.
- the degree of polymerization of the organopolysiloxane is 3,000 or more, and the upper limit is preferably 100,000, and the range is preferably 6,000 to 10,000.
- the degree of polymerization is a value obtained as an average degree of polymerization from a polystyrene-equivalent number average molecular weight in gel permeation chromatography (GPC) analysis using toluene as a developing solvent.
- GPC gel permeation chromatography
- the reinforcing silica (B) is a component necessary for improving the processability, mechanical strength, etc. of the silicone rubber sponge, and the specific surface area is preferably 50 m 2 / g or more, preferably from 100 to 400 m. 2 / g is more preferable.
- the reinforcing silica include fumed silica (dry silica) and precipitated silica (wet silica). Of these, fumed silica (dry silica) is preferable.
- the reinforcing silica as the component (B) may be those obtained by hydrophobizing these surfaces with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. These silicas may be used alone or in combination of two or more.
- the amount of reinforcing silica added is 10 to 100 parts by weight, preferably 10 to 70 parts by weight, particularly preferably 20 to 50 parts by weight, based on 100 parts by weight of the organopolysiloxane of component (A).
- the addition amount of the reinforcing silica is less than 10 parts by mass, it is too small to obtain a sufficient reinforcing effect, and if it exceeds 100 parts by mass, the processability of the silicone rubber sponge is deteriorated or the physical properties of the resulting silicone rubber sponge are reduced. The properties may be deteriorated, and the viscosity of the silicone rubber composition before cross-linking may become very high, making it difficult to make a sponge.
- thermoplastic resin such as polyvinylidene chloride, polyacrylonitrile, and a copolymer of vinylidene chloride / acrylonitrile as an outer shell, and a solvent (hydrocarbon solvent such as isobutane, isopentane and n-hexane). What is comprised and included is mentioned.
- thermoplastic resin in the outer shell is softened by heat, and the thermally expandable microcapsule expands in a balloon-like shape by vaporizing the solvent contained therein almost simultaneously (hereinafter expanded).
- Thermally expandable microcapsules are called resin microballoons). Therefore, when the silicone rubber composition containing this is heated and cured, a silicone rubber sponge having spherical sponge cells formed by resin microballoons is obtained.
- unexpanded thermally expandable microcapsules are included in the silicone rubber composition.
- Polyacrylonitrile that exhibits high hardness and strength at room temperature so that the outer shell of the unexpanded thermally expandable microcapsule is not destroyed even when the silicone rubber composition containing the capsule is kneaded with two rolls or the like It is preferable to use a resin, a vinylidene chloride / acrylonitrile copolymer resin, or the like.
- the molecular weight of the polyacrylonitrile resin and the vinylidene chloride / acrylonitrile copolymer resin is preferably 500,000 to 5,000,000, and more preferably 1,000,000 to 2,000,000.
- the molecular weight is a value obtained as a number average molecular weight in terms of polystyrene in gel permeation chromatography (GPC) analysis using THF as a developing solvent.
- GPC gel permeation chromatography
- the solvent encapsulated in the unexpanded thermally expandable microcapsule is preferably a linear or branched aliphatic hydrocarbon having 3 to 8 carbon atoms or an alicyclic hydrocarbon having 3 to 8 carbon atoms, Specific examples include isobutane, isopentane, n-hexane, and cyclohexane, and a mixture thereof may be used.
- the unexpanded thermally expandable microcapsule preferably contains 10 to 30% by mass of a solvent based on the total mass of the thermally expandable microcapsule.
- the expansion start temperature and maximum expansion of the thermally expandable microcapsule can be adjusted by adjusting the softening point of the thermoplastic resin of the outer shell and the boiling point of the solvent.
- the diameter can be adjusted arbitrarily.
- the volume of the resin microballoon after expansion can be arbitrarily adjusted by adjusting the amount of the solvent contained and the particle diameter before expansion of the thermally expandable microcapsule. Therefore, cell foaming due to abnormal foaming or outgassing, and cracking of the sponge can be prevented, and a silicone rubber sponge excellent in surface smoothness of the skin layer can be easily obtained.
- the “particle diameter before expansion” of the thermally expandable microcapsule is the thermal expansion before expansion, measured as a weight average value (or median diameter) using a particle size distribution measuring apparatus such as a laser diffraction method.
- the particle diameter before expansion is preferably 10 to 70 ⁇ m. If the particle diameter before expansion is smaller than 10 ⁇ m, the solvent to be included is reduced, and a desired sponge foaming ratio may not be obtained. If it exceeds 70 ⁇ m, the sponge cell becomes a coarse sponge.
- the “expansion start temperature” and the “expansion end temperature” of the thermally expandable microcapsule are values determined by the following procedure. (1) The thermally expandable microcapsules before expansion in a glass bottle are heated for 5 minutes in a dryer at each temperature (60 to 250 ° C.) and then allowed to cool at room temperature for 30 minutes. (2) The size (particle diameter) of the thermally expandable microcapsules before and after heating (expansion) is measured with an optical microscope. The size at this time is a value obtained by measuring the size of an arbitrary number of microcapsules and calculating an average value thereof. (3) The expansion ratio is calculated from the particle diameter before expansion and the particle diameter after expansion.
- the expansion ratio is a ratio of the volume calculated from the particle diameter after expansion when the volume calculated from the particle diameter before expansion is 1.
- the “expansion start temperature” of the thermally expandable microcapsule was the heating temperature for 5 minutes when the expansion ratio became 5 times or more.
- the expansion start temperature is 90 to 150 ° C., preferably 100 to 140 ° C., and more preferably 110 to 130 ° C.
- the expansion start temperature is less than 90 ° C., the timing of foaming is too early and the thermoplastic resin in the outer shell of the resin microballoon shrinks before crosslinking of the silicone rubber composition, so a uniform cell cannot be obtained, Moreover, there exists a possibility that the high temperature compression set of the sponge obtained may become large.
- the expansion start temperature exceeds 150 ° C., the heat-expandable microcapsule expands after the silicone rubber composition is cross-linked, and foaming starts. Therefore, the expansion ratio does not increase, and a large pinhole is generated and the appearance is very high. It becomes a bad sponge.
- the “expansion end temperature” of the thermally expandable microcapsule is the heating temperature for 5 minutes when the expansion ratio reaches the maximum (maximum expansion ratio). Also called “expansion temperature”.
- the maximum expansion ratio is preferably 20 times or more and 150 times or less, and more preferably 30 times or more and less than 120 times. When the maximum expansion ratio is less than 20 times, a sufficient foaming ratio cannot be obtained. When the maximum expansion ratio exceeds 150 times, the thickness of the thermoplastic resin of the outer shell becomes thin, and before the silicone rubber composition is crosslinked during expansion. The cell easily breaks, making it difficult to obtain a uniform and fine cell.
- the size of the thermally expandable microcapsule (resin microballoon) at the expansion end temperature is “maximum expansion diameter”, and the volume of the thermally expandable microcapsule (resin microballoon) at the expansion end temperature calculated from the maximum expansion diameter. Is defined as “maximum expansion volume”.
- the heating temperature at which the resin microballoon contracts by 20% from the maximum expansion volume is This is referred to as “shrink temperature”.
- shrink temperature the heating temperature at which the resin microballoon contracts by 20% from the maximum expansion volume.
- the shrinkage of the resin microballoon due to heating depends on the properties of the thermoplastic resin of the outer shell, but in the present invention, the shrinkage temperature is 200 ° C. or higher, preferably 190 ° C. or higher, more preferably 180 ° C. or higher.
- foaming is performed using a thermally expandable microcapsule, and after the component (A) is crosslinked by the component (D), the foam cell is made highly foamed using the foaming agent of the component (E).
- Resin microballoons need to shrink quickly after silicone rubber crosslinking. Therefore, a resin microballoon that contracts greatly when it is continuously heated in the air at a contraction temperature of 200 ° C. or higher is preferable.
- the thermoplastic resin of the outer shell is high and the shrinkage temperature of the resin microballoon is high, the thermoplastic resin of the outer shell remains without shrinking, and the sponge cell cannot be foamed by the foaming agent. Since it becomes an independent bubble, it is not preferable.
- the thermally expandable microcapsule of the present invention is one that shrinks 20% or more from the maximum expansion volume when the thermally expandable microcapsule that has reached the maximum expansion ratio is heated at 200 ° C. for 5 minutes, more preferably It shrinks 30% or more.
- the volume shrinkage ratio is as follows. When the thermally expandable microcapsules having the maximum expansion ratio are placed in a glass bottle and the volume of the thermally expandable microcapsule in the glass bottle is 100, the glass bottle is placed in a dryer at 200 ° C. for 5 minutes. The ratio of the volume which occupies for the glass bottle of the shrinkable thermally expansible microcapsule after heating is shown. For example, when the volume of the thermally expandable microcapsule in the glass bottle shrinks to 70 after heating at 200 ° C. for 5 minutes, the shrinkage rate is 30%.
- Component (C) is blended in an amount of 0.1-20 parts by weight, preferably 0.3-10 parts by weight, more preferably 1.0-5. 0 parts by mass.
- a sufficient foaming ratio cannot be obtained, and when it exceeds 20 parts by mass, the rubber elasticity of the silicone rubber sponge is lacking. The molded product tends to be damaged, and the resin component remaining in the rubber increases, so that the mechanical strength is greatly reduced.
- the (D) component curing agent is a component for curing the (A) component organopolysiloxane.
- an organic peroxide is used as the curing agent for the component (D). Any organic peroxide may be used as long as it can cure the component (A), but the thermally expandable microcapsule of the component (C) needs to start crosslinking (curing) of the component (A) after expansion. Therefore, organic peroxides such as peroxyesters, peroxyketals, dialkyl peroxides, and hydroperoxides that can cure component (A) by heating at 100 to 180 ° C. for about 3 minutes as the crosslinking initiation temperature. Things are preferred.
- dialkyl organic peroxides having a crosslinking initiation temperature (6-minute half-life temperature) of 135 to 180 ° C.
- the addition crosslinking type curing agent using platinum as a catalyst generates a skin layer on the surface of the silicone rubber sponge in the HAV initial stage, which makes it difficult to make the sponge cell open. Inappropriate.
- alkyl organic peroxide examples include 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane ( Dialkyl type, 160 ° C.), 2,5-dimethyl-2,5-di- (t-butylperoxy) -3-hexyne (dialkyl type, 174 ° C.), di-t-butyl peroxide (dialkyl type, 167 ), Dicumyl peroxide (dialkyl type, 154 ° C.), cumyl-t-butyl peroxide (dialkyl type, 148 ° C.), and the like.
- a dialkyl peroxide having a temperature of 180 ° C., more preferably 140 to 170 ° C., and even more preferably 150 to 165 ° C. is preferable in view of the stability of the organic peroxide.
- These organic peroxides may be used singly or in combination of two or more.
- the blending amount of the organic peroxide which is the curing agent of the component (D) is 0.01 to 20 parts by mass, preferably 0.5 to 15 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). It is. If the amount of the organic peroxide is less than 0.1 parts by mass, the component (A) cannot be sufficiently cured, and if it exceeds 20 parts by mass, there is no particular effect, and a curing agent. Heating for a long time is required to remove unreacted substances and decomposition residues, which may adversely affect the physical properties of the resulting silicone rubber.
- the component (E) foaming agent is a gas generating component for making a hole in the cell wall after forming the sponge cell, and has a role different from that of the component (C) solvent-derived gas component that forms the sponge cell. It is. Therefore, in the present invention, a solid high-temperature decomposition type organic foaming agent (gas generating agent) having a decomposition start temperature of 180 ° C. or higher is used as the foaming agent for the component (E).
- the component (E) needs to start generating gas at a temperature higher than the temperature at which the organopolysiloxane of the component (A) starts to cure.
- the component (E) is limited to a solid high-temperature decomposable organic foaming agent having a decomposition start temperature of 180 ° C. or higher.
- the decomposition start temperature (gas generation temperature) of the component (E) foaming agent is 180 ° C. or higher, preferably 190 ° C. or higher, more preferably 200 ° C. or higher.
- the type of the foaming agent is not particularly limited as long as the decomposition start temperature is 180 ° C. or higher.
- solid high-temperature decomposition type organic foaming agent examples include azodicarbonamide (decomposition start temperature of pure product 210 ° C.), urea-containing azodicarbonamide (decomposition start temperature 190 ° C. of purity 95%), N, N′— Examples thereof include dinitrosopentamethylenetetramine (decomposition start temperature of pure product 205 ° C.), hydrazodicarbonamide (decomposition start temperature of pure product 245 ° C.) and the like.
- the addition amount of the foaming agent for component (E) is 0.1 to 30 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 2 parts per 100 parts by weight of component (A). 0.0 to 10 parts by mass. If the amount added is less than 0.1 parts by mass, the generated gas pressure and gas amount are insufficient, and the sponge cannot be foamed. If it exceeds 30 parts by mass, the physical properties of the silicone rubber due to the decomposition residue of the foaming agent It may cause worsening of.
- the amount of gas generated by the decomposition of the component (E) foaming agent needs to be approximately the same volume or more as the silicone rubber sponge.
- the gas generation amount (theoretical gas generation amount) of the component (E) is required to be 100 cc or more, preferably 300 cc or more, with respect to 100 g in total of the organopolysiloxane (A) and the reinforcing silica (B). More preferably, it is 500 cc or more.
- the amount of gas generated is about 200 cc per gram, so 0.5 g or more of a pure product of azodicarbonamide is required for 100 g of component (A) + (B). It is a calculation.
- the components (C) to (E) are used in order to enable a series of reaction processes of the foaming mechanism of the millable silicone rubber composition to be performed in one step. It is preferable to use a component such that (C) component expansion start temperature ⁇ (D) component crosslinking start temperature ⁇ (C) component shrinkage temperature ⁇ (E) component decomposition start temperature. Also, (C) Component shrinkage temperature ⁇ (E) Component decomposition start temperature may be sufficient. By satisfying these conditions, a series of reaction processes of the foaming mechanism of sponge cell formation and continuous foaming can be performed in one step of atmospheric hot air crosslinking.
- the silicone rubber composition of the present invention may contain the following components in addition to the above components as long as the effects of the present invention are not impaired.
- the dispersing agent examples include alkoxysilane, diphenylsilanediol, carbon functional silane, silanol group-blocked low molecular weight siloxane and the like.
- the silanol group-blocked low molecular siloxane at both ends is specifically a dimethylpolysiloxane having both ends silanol groups and a viscosity at 23 ° C. of 10 to 100 mm 2 / s, preferably 20 to 40 mm 2 / s.
- Examples include siloxane.
- Semi-reinforcing or non-reinforcing fillers include pulverized silica, diatomaceous earth, metal carbonate, clay, talc, mica, Examples thereof include titanium oxide.
- the platinum complex for example, chloroplatinic acid isopropyl alcohol etc.
- a titanium oxide for example, a baking mica, aluminum hydroxide etc.
- the flame retardant is useful for producing a flame retardant sponge.
- Thermal conductivity imparting agent pulverized quartz, zinc oxide, aluminum oxide, metallic silicon powder, silicon carbide, fiber, which are generally added to impart thermal conductivity to the silicone rubber composition Carbon fiber and the like.
- Conductivity imparting agent examples include conductive carbon and conductive metal oxide fine particles (conductive zinc oxide fine particles, conductive titanium oxide fine particles, conductive tin-antimony oxide fine particles). In this invention, it can also be set as a conductive sponge by adding this electroconductivity imparting agent.
- the silicone rubber composition of the present invention may contain a heat-resistant additive, an antioxidant, a processing aid and the like. Further, ferrite powder or the like may be blended in the silicone rubber composition of the present invention to enable molding by high frequency dielectric heating.
- the method for producing the silicone rubber composition of the present invention is not particularly limited, and examples thereof include a method of kneading a predetermined amount of each component described above with a two roll, kneader, Banbury mixer or the like. If necessary, heat treatment (kneading under heating) may be performed. Specifically, the base rubber composition is obtained by first kneading and heat-treating the component (A), the component (B), and other components added as necessary. Next, a method of adding the components (C), (D), and (E) after cooling the base rubber composition is exemplified.
- the heat treatment temperature and time for obtaining the base rubber composition are not particularly limited, but the heat treatment temperature is, for example, 100 to 250 ° C., and the heat treatment time is 30 minutes to 5 hours.
- the manufacturing method of the millable silicone rubber sponge of the present invention includes a step of heat-treating the above-described silicone rubber composition at 200 ° C. or higher.
- the heat treatment is preferably performed at 200 to 400 ° C. for 1 minute to 1 hour, more preferably at 220 to 250 ° C. for 10 to 30 minutes.
- a silicone rubber sponge having a high reaming rate can be obtained by such one step.
- the heat treatment may be performed in several steps as long as it includes a heat treatment at 200 ° C. or higher.
- a first heat treatment is performed on the silicone rubber composition at 80 to 200 ° C., particularly 100 to 200 ° C. for 1 minute to 1 hour.
- the thermally expandable microcapsule of component (C) expands and the organopolysiloxane of component (A) is cured, so the primary heat treatment is also referred to as an expansion / curing step.
- the silicone rubber composition that has undergone the first heat treatment is subjected to a second heat treatment at 200 to 400 ° C. for 0.5 to 24 hours.
- the foaming agent of component (E) is decomposed, so this secondary heat treatment is also referred to as a foaming step.
- post-curing at 200 to 250 ° C. for about 10 minutes to 10 hours may be performed in addition to the heat treatment step described above.
- the millable silicone rubber sponge of the present invention can remove the foaming agent, the decomposition residue of the curing agent and the thermoplastic resin residue of the outer shell of the thermally expandable microcapsule by a high temperature treatment such as post cure.
- the heat treatment in the manufacturing method of the millable silicone rubber sponge of the present invention is atmospheric pressure hot air crosslinking (HAV) because it is necessary to increase the open cell ratio of the sponge cell.
- HAV atmospheric pressure hot air crosslinking
- the normal-pressure hot air crosslinking may be performed in a batch manner or a continuous manner.
- the composition of the present invention molded by an arbitrary method may be placed in a batch dryer and subjected to atmospheric pressure hot air crosslinking, and the composition of the present invention is molded by extrusion molding. May be put into a continuous dryer by means of a belt conveyor or the like and subjected to normal pressure hot air crosslinking.
- Atmospheric pressure hot air crosslinking also includes a powder curing method in which foaming is performed in heated glass beads. In addition, this is not the case when there is sufficient space inside the mold cross-linking and an escape path for the (E) component foaming gas is secured.
- the silicone rubber sponge of the present invention obtained by the above-described production method is characterized by an open cell ratio of 20% or more, preferably 20 to 100%, more preferably 25 to 100%.
- the open cell ratio is measured by the following method.
- Open cell ratio (%) [(mass of absorbed sponge ⁇ mass of sponge) / specific gravity of water] / [(1 ⁇ (specific gravity of sponge / specific gravity of rubber before foaming)) ⁇ (mass of sponge / specific gravity of sponge) ] X 100
- the specific gravity of water was 1.00.
- the expansion ratio of the silicone rubber sponge of the present invention obtained by the above production method is preferably 110 to 1,000%, particularly preferably 120 to 500%.
- the expansion ratio is a value calculated by the specific gravity of rubber before foaming / specific gravity of sponge ⁇ 100 (%), and the specific gravity is a value measured by the method described in JIS K 6268: 1998.
- the silicone rubber sponge produced by the production method of the present invention has a sponge cell aspect ratio of 1.0 to 1.3, preferably 1.0 to 1.2, and an average cell diameter of 250 ⁇ m.
- the thickness is preferably 30 to 200 ⁇ m.
- the optical microscope was used for the measurement of the aspect-ratio and average cell diameter of sponge cell in this invention. Specifically, cells on an arbitrary cut surface of the sponge were observed with an optical microscope, an arbitrary number of cell diameters were measured, and an average cell diameter was calculated as an average value.
- the cells on an arbitrary cut surface of the sponge are observed with an optical microscope, and the major axis and minor axis of an arbitrary number of cells are measured, and the average value of values obtained by dividing the major axis of the cell by the minor axis.
- the cell aspect ratio was calculated as follows.
- Such a silicone rubber sponge is useful for producing an electrophotographic image forming member (in particular, a fixing member, a driving roll, a paper supply / discharge roll, a pressure pad, etc.) having at least one layer made of the sponge.
- the fixing member include a single-layer fixing roll having one layer made of the sponge, a multi-layer fixing roll having two or more layers made of the sponge, a fixing belt, and a fixing pad.
- the multi-layer fixing roll include a multi-layer fixing roll to which a surface layer releasing agent such as a PFA tube is bonded, and a multi-layer fixing roll for a toner melt fixing application including a solid rubber layer, a sponge layer, and a toner release layer. It is done.
- the drive roll is a belt drive roll.
- the silicone rubber sponge of the present invention is also used as a sponge gasket and protective cushioning material for seats, space sponges, sound absorbing sponges and flame retardant sponges for transport equipment such as automobiles, railway vehicles, aircraft and ships. it can.
- Base rubber composition 1 100 parts by weight of dimethylpolysiloxane having both ends blocked with dimethylvinylsilyl groups and an average degree of polymerization of about 8,000 having 10 methylvinylsiloxane units; 40 parts by mass of dry silica Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) with a BET surface area of 200 m 2 / g, and 5 parts by mass of dimethylpolysiloxane having silanol groups at both ends and a viscosity of 29 mm 2 / s (23 ° C.) And heat-treated at 180 ° C. for 2 hours to prepare a base rubber composition 1.
- Base rubber composition 2 > 100 parts by mass of dimethylpolysiloxane having both ends blocked with trimethylsilyl groups and having an average degree of polymerization of about 6,000 having 15 methylvinylsiloxane units, and dry silica Aerosil 200 (Nippon Aerosil (Japan Aerosil)) having a BET surface area of 200 m 2 / g
- a base rubber composition 2 was prepared by blending 15 parts by mass with a kneader and heat treating at 180 ° C. for 2 hours.
- C Thermally expandable microcapsule>
- C1 Thermally expandable microcapsule encapsulating polyacrylonitrile resin (molecular weight 1,200,000) as an outer shell and isobutane 10% by mass and isopentane 10% by mass as solvent
- C2 polyacrylonitrile resin (molecular weight 1,200,000)
- C3 Polyacrylonitrile resin (molecular weight 1,200,000) as the outer shell, encapsulating 10% by mass of isobutane and 5% by mass of isopentane as the solvent
- C4 Thermally expandable microcapsule encapsulated with polyacrylonitrile resin (molecular weight 1,200,000) as outer shell and 10% by mass of isopentane and 18% by mass of n-hexane
- C5 vinylidene chloride Copolymer tree of acrylonitrile Thermally expandable microcapsules containing fat (molecular weight 1,500,000) as outer shell and 25% by mass of isobutane as solvent (for comparative example
- ⁇ (D) component curing agent>
- D1 2,5-Dimethyl-2,5-di- (t-butylperoxy) hexane (6 minutes half-life temperature: 160 ° C.)
- D2 Dicumyl peroxide (6 minutes half-life temperature 154 ° C)
- D3 Cumyl-t-butyl peroxide (6 minutes half-life temperature 148 ° C)
- D4 Bis (2,4-dichlorobenzoyl) peroxide (6-minute half-life temperature 99 ° C.) (for comparison)
- Addition Addition curing agent C-25A (platinum catalyst) / C-25B (organohydrogenpolysiloxane) (for comparison) (All are manufactured by Shin-Etsu Chemical Co., Ltd., and the base rubber composition is cured in about 30 seconds at 120 ° C.)
- ⁇ (E) component a continuous foaming agent>
- E1 Azodicarbonamide (pure product, decomposition start temperature 210 ° C.)
- E2 Urea-containing azodicarbonamide (purity 95%, decomposition start temperature 190 ° C.)
- E3 N, N′-dinitrosopentamethylenetetramine (pure, decomposition start temperature 205 ° C.)
- E4 hydrazodicarbonamide (pure product, decomposition start temperature 245 ° C.)
- E5 Azobisisobutyronitrile (decomposition start temperature 107 ° C.) (for comparison)
- E6 Urea and organozinc-containing azodicarbonamide (purity 88%, decomposition start temperature 140 ° C.) (for comparison)
- -Average cell diameter The cell in the arbitrary cut surface of sponge was observed with the optical microscope, the cell diameter was measured, and the average value was computed.
- Cell aspect ratio A cell on an arbitrary cut surface of a sponge was observed with an optical microscope, the major axis and minor axis of the cell were measured, and the average value of values obtained by dividing the major axis of the cell by the minor axis was calculated. .
- -Open cell rate The open cell rate of the sponge was calculated according to the following procedure.
- Open cell ratio (%) [(mass of absorbed sponge ⁇ mass of sponge) / specific gravity of water] / [(1 ⁇ (specific gravity of sponge / specific gravity of rubber before foaming)) ⁇ (mass of sponge / specific gravity of sponge) ] X 100
- the specific gravity of water was 1.00.
- the base rubber composition 1 is 145 parts by mass
- the thermal expansion microcapsule (C1) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 7.0 parts by mass of azodicarbonamide (theoretical gas generation amount 1,400 cc) as a foaming agent (E1) were added and mixed in a two-roll mill, and 9 mm thick uncrosslinked rubber A composition sheet was prepared. Next, this uncrosslinked rubber composition sheet having a thickness of 9 mm was subjected to atmospheric pressure hot air crosslinking for 30 minutes in a hot air dryer at 230 ° C. to obtain a silicone rubber sponge.
- FIG. 1 is an enlarged photograph of the cross section of the sponge of Example 1. It was revealed that the sponge of Example 1 had a uniform microstructured cell.
- Example 2 For 145 parts of base rubber composition 1, 2.3 parts by mass of thermally expandable microcapsules (C2), 1.2 parts by mass of dicumyl peroxide as a curing agent (D2), and as a foaming agent (E2) A sponge was produced in the same manner as in Example 1 by adding and mixing 3.5 parts by mass of urea-containing azodicarbonamide (theoretical gas generation amount: 690 cc) with a two-roll mill. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- Example 3 145 parts by mass of base rubber composition 1, 3.0 parts by mass of thermally expandable microcapsules (C3), 1.8 parts by mass of cumyl-t-butyl peroxide as a curing agent (D3), and a continuous foaming agent As (E3), 4.5 parts by mass of N, N′-dinitrosopentamethylenetetramine (theoretical gas generation amount 1,100 cc) was added and mixed in a two-roll mill, and a sponge was produced in the same manner as in Example 1. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- Example 4 2.3 parts by mass of thermally expandable microcapsules (C4) and 2,5-dimethyl-2,5-di- (t-butylperoxy as a curing agent (D1) with respect to 145 parts by mass of base rubber composition 1 ) 1.5 parts by mass of hexane and 7.0 parts by mass of azodicarbonamide (theoretical gas generation amount 1,400 cc) as a foaming agent (E1) were added and mixed in a two-roll mill. To make a sponge. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- Example 5 The base rubber composition 1 is 145 parts by mass, the thermal expansion microcapsule (C1) is 3.0 parts by mass, and the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 3.0 parts by mass of hydrazodicarbonamide (theoretical gas generation amount 530 cc) as a foaming agent (E4) were added and mixed in a two-roll mill, and a sponge was obtained in the same manner as in Example 1. Produced. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- Example 6 For 115 parts by mass of base rubber composition 2, 2.3 parts by mass of thermally expandable microcapsules (C1) and 2,5-dimethyl-2,5-di- (t-butylperoxy as a curing agent (D1) ) 1.2 parts by mass of hexane and 6.0 parts by mass of azodicarbonamide (theoretical gas generation amount: 1,000 cc) as a foaming agent (E1) were added and mixed in a two-roll mill, and a sponge was used in the same manner as in Example 1. Was made. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- the base rubber composition 1 is 145 parts by mass
- the thermal expansion microcapsule (C1) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 1.5 parts by mass of azobisisobutyronitrile (theoretical gas generation amount 200 cc) as a foaming agent (E5) were added and mixed in a two-roll mill, and the same as in Example 1 Thus, a sponge was produced. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- the base rubber composition 1 is 145 parts by mass
- the thermal expansion microcapsule (C5) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 3.0 parts by mass of azodicarbonamide (theoretical gas generation amount: 600 cc) as a foaming agent (E1) were added and mixed in a two-roll mill, and a sponge was obtained in the same manner as in Example 1.
- Table 2 the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- the base rubber composition 1 is 145 parts by mass
- the thermal expansion microcapsule (C1) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 7.0 parts by mass of urea and organozinc-containing azodicarbonamide (theoretical gas generation amount: 1,000 cc) as a continuous foaming agent (E6) were added and mixed in a two-roll mill.
- the base rubber composition 1 is 145 parts by mass
- the thermal expansion microcapsule (C6) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butylperoxy ) 1.5 parts by mass of hexane and 3.6 parts by mass of azodicarbonamide (theoretical gas generation amount 720 cc) as a foaming agent (E1) were added and mixed in a two-roll mill, and a sponge was produced in the same manner as in Example 1. However, a large pinhole having a diameter of 1 to 3 mm was generated inside the sponge, resulting in a sponge with poor appearance. Thereafter, the results of evaluating the sponge in the same manner as in Example 1 are shown in Table 2.
- Comparative Example 4 and Comparative Example 7 using the thermally expandable microcapsules having the expansion start temperature of the component (C) outside the range specified in the present invention sponge cracks and pinholes occurred, and the open cell ratio was low.
- Comparative Example 3 using an addition crosslinking agent as the component (D) the sponge was not cured.
- Comparative Example 6 using an organic peroxide crosslinking agent in which the crosslinking initiation temperature of the component (D) is lower than the expansion initiation temperature of the component (C) the sponge is formed from the inside. It was torn and the open cell rate was low.
- Comparative Example 1 in which a foaming agent having a decomposition start temperature of the component (E) lower than the expansion start temperature of the component (C) is used, the cell opening ratio is low, the cell aspect ratio is large, and A sponge with spherical cells could not be obtained. Further, even when the decomposition start temperature of the component (E) is higher than the thermal expansion start temperature of the component (C), the decomposition start temperature of the component (E) is lower than the crosslinking start temperature of the component (D). In Comparative Example 5 using the continuous foaming agent, a dome-shaped crack occurred in the sponge. On the other hand, it was found that the sponges of Examples 1 to 6 using each component in the temperature range specified in the present invention had a uniform fine cell structure with high open cell foam.
- the base rubber composition 1 is 145 parts by mass
- the thermally expandable microcapsule (C1) is 3.0 parts by mass
- the curing agent (D1) is 2,5-dimethyl-2,5-di- (t-butyl per Only 1.5 parts by mass of oxy) hexane was added and mixed in a two-roll mill, and a sponge not containing a continuous foaming agent was produced in the same manner as in Example 1.
- the photograph of the obtained sponge was compared with Example 1.
- the completed sponge was cut into a diameter of 29 mm and a thickness of 12.5 mm, and the compression set was measured by the method described in JIS K 6262: 2013 (180 ° C., 25% compression, 22 hours). The results are shown in Table 3.
- Example 6 With respect to 145 parts by mass of base rubber composition 1, 3.0 parts by mass of thermally expandable microcapsule (C1), 1.5 parts by mass of curing agent (D1), 7.0 parts by mass of foaming agent (E1) ( In addition to the composition of Example 1 above, in order to make the sponge flame-retardant, Crystallite VX-S (Tatsumori) is a crystalline silica having 0.6 parts by mass of 5% isopropyl chloroplatinate alcohol solution and an average particle diameter of 4 ⁇ m.
- the sponge flame immediately disappeared after removal of the burner, and the resulting sponge was UL 94 HF-1.
- it carried out similarly to the method mentioned above, and measured the hardness (Asker C) and open-cell rate of the obtained sponge. Further, the density of the obtained sponge was measured according to JIS K6268. The results are shown in Table 5.
- Example 9 A silicone rubber sponge was obtained in the same manner as in Example 6 except that the same amount of the components other than the continuous foaming agent (E1) was added in the components of Example 6 above. Thereafter, the obtained silicone rubber sponge was post-cured at 230 ° C. for 2 hours. The obtained sponge was tested in a sponge UL flame resistance test (ASTM D 4986). As a result, glowing combustion was continued after removing the burner, and combustion was continued for 10 seconds or more. The burning rate was 36 mm / min, there were no burning drops, and the resulting sponge was UL 94 HBF. Furthermore, the results of evaluating the sponge in the same manner as in Example 6 are shown in Table 5.
- a silicone rubber sponge having a uniform fine cell structure with high open-cell foam and small compression set can be obtained simply by atmospheric pressure hot air crosslinking (HAV). It turns out that it is possible to obtain.
- HAV atmospheric pressure hot air crosslinking
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Abstract
Description
上記の熱膨張性マイクロカプセルを多量に配合することにより、シリコーンゴムスポンジの低比重化も可能であるが、得られたシリコーンゴムスポンジは、熱膨張性マイクロカプセルの樹脂成分がゴム内に残るため、得られるスポンジの硬度が非常に高くなり、ゴム弾性が低下してしまう。そのため、シリコーンゴムスポンジの圧縮永久ひずみが大きくなり、厚いスポンジを作りにくいという問題がある。
即ち、本発明は、以下のミラブル型シリコーンゴムスポンジ及びその製造方法等を提供するものである。
下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮する熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤であり、(A)成分の硬化後に分解開始するもの (A)成分100質量部に対して0.1~30質量部
を含有するシリコーンゴム組成物を、200℃以上で熱処理することを特徴とする、連泡率が20%以上のミラブル型シリコーンゴムスポンジの製造方法。
熱処理を常圧熱風により行うことを特徴とする<1>記載のミラブル型シリコーンゴムスポンジの製造方法。
<3>
(E)成分の連泡化剤が発生するガス量が、(A)成分と(B)成分の合計100gに対して100cc以上であることを特徴とする<1>又は<2>に記載のミラブル型シリコーンゴムスポンジの製造方法。
(E)連泡化剤が、アゾジカルボンアミド、N,N’-ジニトロソペンタメチレンテトラミン及びヒドラゾジカルボンアミドから選ばれる少なくとも1種である<1>~<3>のいずれか1項に記載のミラブル型シリコーンゴムスポンジの製造方法。
<5>
(D)硬化剤が、ジアルキル系の有機過酸化物であり、架橋開始温度(6分間半減期温度)が135~180℃である<1>~<4>のいずれか1項に記載のミラブル型シリコーンゴムスポンジの製造方法。
<6>
下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮する熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤であり、(A)成分の硬化後に分解開始するもの (A)成分100質量部に対して0.1~30質量部
を含有するシリコーンゴム組成物の熱処理物たるミラブル型シリコーンゴムスポンジであって、
連泡率が20%以上であり、
セルのアスペクト比が1.0~1.3であり、かつ
平均セル径が250μm以下である
ことを特徴とするミラブル型シリコーンゴムスポンジ。
<7>
<6>に記載のミラブル型シリコーンゴムスポンジからなるベルト状成形物。
<8>
<6>に記載のミラブル型シリコーンゴムスポンジからなるシート状成形物。
<9>
<6>に記載のミラブル型シリコーンゴムスポンジからなるスポンジロール状成形物。
<10>
<6>に記載のミラブル型シリコーンゴムスポンジからなる輸送機用保護緩衝材。
<11>
下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮し、収縮温度が200℃以上の熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:架橋開始温度が100~180℃の有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤 (A)成分100質量部に対して0.1~30質量部
を含み
(C)成分の膨張開始温度<(D)成分の架橋開始温度<(C)成分の収縮温度≦(E)成分の分解開始温度であることを特徴とするミラブル型シリコーンゴム組成物。
まず、本発明のミラブル型シリコーンゴム組成物及びミラブル型シリコーンゴムスポンジの構成成分と本発明の製造方法について説明する。
まず、(C)成分の熱膨張性マイクロカプセルが90~150℃で膨張し、(A)及び(B)成分中で発泡する。
次に、120~170℃の温度で(D)成分の硬化剤がラジカルを発生し、(A)成分を架橋し、スポンジセルが形成される。
その後、180~210℃で(C)成分の熱膨張性マイクロカプセルの収縮が開始され、収縮した熱膨張性マイクロカプセルの外殻樹脂とスポンジセル間に隙間が生まれる。
さらに、180~250℃の温度領域に達すると(E)成分の連泡化剤が分解して多量のガスを発生させ、スポンジセルを連泡化させながらスポンジ外部に排出されると共に、外部より酸素がスポンジ内に侵入することにより、収縮した(C)成分の熱膨張性マイクロカプセルの残渣樹脂を酸化劣化させる。連泡化によって、スポンジ内部の残渣樹脂をすべて酸化劣化させることで、耐熱性が損なわれることなく、シリコーンが本来有する耐熱性を有したシリコーンゴムスポンジを得ることができる。さらに、これら一連の反応をHAVという一工程で実施可能とするものである。
(A)成分のオルガノポリシロキサンは下記平均組成式(I)
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]で表される、1分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサンである。
また、このオルガノポリシロキサンの重合度は3,000以上であり、その上限は100,000であることが好ましく、さらにその範囲は6,000~10,000であることが好ましい。ここで、重合度は、トルエンを展開溶媒としたゲルパーミエーションクロマトグラフィ(GPC)分析におけるポリスチレン換算の数平均分子量から平均重合度として求めた値である。
(B)成分の補強性シリカは、シリコーンゴムスポンジの加工性、機械的強度等を良好にするために必要な成分であり、比表面積が50m2/g以上であることが好ましく、100~400m2/gであることがより好ましい。この補強性シリカとしては煙霧質シリカ(乾式シリカ)、沈殿シリカ(湿式シリカ)が例示され、このうち煙霧質シリカ(乾式シリカ)が好ましい。また、(B)成分の補強性シリカは、これらの表面をオルガノポリシロキサン、オルガノポリシラザン、クロロシラン、アルコキシシラン等で疎水化処理したものでもよい。これらのシリカは1種単独で用いても2種以上併用してもよい。
この補強性シリカの添加量は、(A)成分のオルガノポリシロキサン100質量部に対して10~100質量部であり、好ましくは10~70質量部、特に好ましくは20~50質量部である。この補強性シリカの添加量が、10質量部未満では少なすぎて十分な補強効果が得られず、100質量部より多くするとシリコーンゴムスポンジの加工性が悪くなったり、得られるシリコーンゴムスポンジの物理特性が低下することがあり、また架橋前のシリコーンゴム組成物の粘度が非常に高くなり、スポンジ化が難しくなるおそれがある。
(C)成分の、膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮する熱膨張性マイクロカプセルは、本発明のスポンジにセルを形成させるための成分である。
このような熱膨張性マイクロカプセルは、ポリ塩化ビニリデン、ポリアクリロニトリル及び塩化ビニリデン・アクリロニトリルのコポリマー等の熱可塑性樹脂を外殻とし、溶剤(イソブタン、イソペンタン及びn-ヘキサン等の炭化水素系溶媒)を内包して構成されるものが挙げられる。(C)成分の熱膨張性マイクロカプセルは、熱によって外殻の熱可塑性樹脂が軟化し、ほぼ同時に内包された溶剤が気化することによって熱膨張性マイクロカプセルがバルーン状に膨らむ(以下、膨張した熱膨張性マイクロカプセルを樹脂マイクロバルーンという)。したがって、これを含むシリコーンゴム組成物を加熱して硬化すると、内部に樹脂マイクロバルーンによって形成される球状のスポンジセルを有するシリコーンゴムスポンジとなる。
また、未膨張の熱膨張性マイクロカプセルに内包される溶剤は、炭素数3から8の直鎖状もしくは分岐状脂肪族炭化水素、又は炭素数3から8の脂環式炭化水素等が好ましく、具体的にはイソブタン、イソペンタン、n-ヘキサン、及びシクロヘキサン等が挙げられ、これらの混合物であってもよい。未膨張の熱膨張性マイクロカプセルは、熱膨張性マイクロカプセルの全質量のうち、10~30質量%の溶剤を含むものが好ましい。
そのため、異常発泡やガス抜けによるセルの破泡、スポンジの割れを防止でき、スキン層の表面平滑性に優れたシリコーンゴムスポンジを容易に得ることが可能となる。
(1)ガラス瓶に入れた膨張前の熱膨張性マイクロカプセルを各温度(60~250℃)の乾燥器で5分間加熱した後、常温にて30分間放冷する。
(2)加熱(膨張)前後の熱膨張性マイクロカプセルの大きさ(粒子径)を光学顕微鏡でそれぞれ測定する。このときの大きさは、任意の数のマイクロカプセルの大きさを測定し、その平均値として算出した値である。
(3)膨張前の粒子径と膨張後の粒子径から膨張倍率を計算する。具体的には、膨張倍率は、膨張前の粒子径から算出した体積を1とした場合の膨張後の粒子径から算出した体積の比である。
(4)以上の手順より得られた温度(5分間加熱温度)と膨張倍率の関係をプロットすると、温度の上昇に伴い膨張倍率は上昇し、ある温度において膨張倍率が極大値をとり、その後膨張倍率が減少する。
本発明において、膨張開始温度は90~150℃であり、100~140℃であることが好ましく、110~130℃であることがより好ましい。
なお、膨張終了温度における熱膨張性マイクロカプセル(樹脂マイクロバルーン)の大きさを「最大膨張径」、該最大膨張径から算出される膨張終了温度における熱膨張性マイクロカプセル(樹脂マイクロバルーン)の体積を「最大膨張体積」と定義する。
加熱による樹脂マイクロバルーンの収縮は外殻の熱可塑性樹脂の特性に依存するが、本発明では収縮温度が200℃以上、好ましくは190℃以上、さらに好ましくは180℃以上である。
体積収縮率は、最大膨張倍率となった熱膨張性マイクロカプセルをガラス瓶に入れ、ガラス瓶に占める熱膨張性マイクロカプセルの体積を100としたときに、該ガラス瓶を乾燥器にて200℃で5分間加熱した後の収縮した熱膨張性マイクロカプセルのガラス瓶に占める体積の割合を示している。例えば、200℃で5分間加熱した後、熱膨張性マイクロカプセルのガラス瓶に占める体積が70に収縮した場合、収縮率は30%である。
(D)成分の硬化剤は、(A)成分のオルガノポリシロキサンを硬化させるための成分である。(D)成分の硬化剤として、本発明では有機過酸化物を使用する。有機過酸化物の種類は(A)成分を硬化させ得るものであればよいが、(C)成分の熱膨張性マイクロカプセルが膨張後に(A)成分の架橋(硬化)を開始する必要があるため、架橋開始温度として100~180℃にて3分程度の加熱で(A)成分を硬化させることが可能なパーオキシエステル、パーオキシケタール、ジアルキルパーオキサイド、ハイドロパーオキサイドのような有機過酸化物が好ましい。特にジアルキル系の有機過酸化物であり、架橋開始温度(6分間半減期温度)が135~180℃である有機過酸化物が好ましい。
また、本発明では白金を触媒として使用する付加架橋系の硬化剤は、シリコーンゴムスポンジ表面のスキン層をHAV初期段階で生成してしまい、スポンジセルを連泡化することがむずかしくなってしまうため不適当である。
(E)成分の連泡化剤は、スポンジセル形成後にセル壁に穴を開けるためのガス発生成分であり、スポンジセルを形成させる(C)成分の溶剤由来のガス成分とは役割が異なるものである。そのため、(E)成分の連泡化剤として、本発明では分解開始温度が180℃以上の固体の高温分解型有機発泡剤(ガス発生剤)を使用する。(E)成分は(A)成分のオルガノポリシロキサンが硬化開始する温度よりも高い温度でガスを発生し始める必要がある。即ち、(D)成分の有機過酸化物が分解及び架橋開始するよりも高い温度で(E)成分が分解してガスを発生させる必要がある。そのため(E)成分は、分解開始温度が180℃以上の固体の高温分解型有機発泡剤に限られる。(E)成分の連泡化剤の分解開始温度(ガス発生温度)は、180℃以上、好ましくは190℃以上、さらに好ましくは200℃以上である。連泡化剤の種類は、分解開始温度が180℃以上であれば特に限定されるものではない。固体の高温分解型有機発泡剤の具体例としては、アゾジカルボンアミド(純品の分解開始温度210℃)、尿素含有アゾジカルボンアミド(純度95%の分解開始温度190℃)、N,N’-ジニトロソペンタメチレンテトラミン(純品の分解開始温度205℃)、ヒドラゾジカルボンアミド(純品の分解開始温度245℃)等が挙げられる。
(C)成分の膨張開始温度<(D)成分の架橋開始温度<(C)成分の収縮温度<(E)成分の分解開始温度
となるようなものを用いることが好ましい。
また、
(C)成分の収縮温度≦(E)成分の分解開始温度
であってもよい。
これらの条件を満たすことによって、スポンジセル形成と連泡化という発泡メカニズムの一連の反応過程が、常圧熱風架橋という一工程で実施可能となる。
本発明のシリコーンゴム組成物は、以上の成分の他に本発明の効果を阻害しない範囲で、以下の成分を配合してもよい。
分散剤としては、アルコキシシラン、ジフェニルシランジオール、カーボンファンクショナルシラン、両末端シラノール基封鎖低分子シロキサン等が挙げられる。ここで、両末端シラノール基封鎖低分子シロキサンとしては、具体的には、両末端シラノール基を有し、23℃における粘度が10~100mm2/s、好ましくは20~40mm2/sのジメチルポリシロキサンが挙げられる。
半補強性ないし非補強性の充填材としては、粉砕シリカ、ケイソウ土、金属炭酸塩、クレー、タルク、マイカ、酸化チタンなどを挙げることができる。
難燃剤としては、一般的に難燃化のために添加される白金錯体(例えば、塩化白金酸イソプロピルアルコールなど)、酸化チタン、焼成マイカ、水酸化アルミニウム等が挙げられる。本発明では、難燃剤を多量に添加してもスポンジ成形に悪影響を与えることがなく、良好な微細スポンジを得ることが出来るため、該難燃剤は難燃スポンジの作製に有用である。
熱伝導性付与剤としては、一般的にシリコーンゴム組成物に熱伝導性を付与するために添加される粉砕石英、酸化亜鉛、酸化アルミニウム、金属珪素粉末、炭化珪素、繊維状カーボンファイバー等が挙げられる。
導電性付与剤としては、導電性カーボンや導電性金属酸化物微粒子(導電性酸化亜鉛微粒子、導電性酸化チタン微粒子、導電性スズ-アンチモン酸化物微粒子)等が挙げられる。本発明では、該導電性付与剤を添加することにより導電スポンジとすることもできる。
このような1工程により、高連泡率のシリコーンゴムスポンジを得ることができる。
1)シリコーンゴム組成物(以下、「発泡前ゴム」という)及びシリコーンゴムスポンジ(以下、「スポンジ」という)の比重と質量を測定する。
なお、比重の測定はJIS K 6268:1998記載の方法によって行い、ただし、比重測定時の水中に浸漬する時間は5秒以内とする。
2)水を入れた容器に、スポンジを水に沈むように配置し、該容器ごと真空容器に入れ、真空容器内を10mmHg以下に減圧する。
3)真空容器内を常圧に戻した後に5分間放置してスポンジに吸水させる。
4)吸水したスポンジの質量を計量する。
次に、下記計算式に従って連泡率を求める。
なお、上記式において、水の比重は、1.00とした。
定着部材の例としては、該スポンジからなる層を1層有する単層の定着ロール、該スポンジからなる層を2層以上有する複層定着ロール、定着ベルト、定着パッド等が挙げられる。複層定着ロールとしては、PFAチューブ等の表層離型剤を接着させた複層定着ロール並びにソリッドゴム層、該スポンジからなる層及びトナー離型層からなるトナー溶融定着用途の多層定着ロールが挙げられる。
駆動ロールの例としては、ベルト駆動ロールが挙げられる。
また、本発明のシリコーンゴムスポンジは、自動車、鉄道車両、航空機、船舶などの輸送機用、宇宙用、建築用のスポンジガスケット及び保護緩衝材、座面スポンジ、消音スポンジや難燃スポンジとしても利用できる。
両末端がジメチルビニルシリル基で封鎖され、10個のメチルビニルシロキサン単位をもつ平均重合度が約8,000であるジメチルポリシロキサン100質量部、
BET表面積200m2/gの乾式シリカAerosil200(日本アエロジル(株)製)40質量部、及び
両末端にシラノール基を有し、粘度29mm2/s(23℃)のジメチルポリシロキサン5質量部をニーダーで配合し、180℃で2時間熱処理しベースゴム組成物1を作製した。
両末端がトリメチルシリル基で封鎖され、15個のメチルビニルシロキサン単位をもつ平均重合度が約6,000であるジメチルポリシロキサン100質量部、及び
BET表面積200m2/gの乾式シリカAerosil200(日本アエロジル(株)製)15質量部をニーダーで配合し、180℃で2時間熱処理しベースゴム組成物2を作製した。
C1:ポリアクリロニトリル樹脂(分子量1,200,000)を外殻とし、イソブタン10質量%及びイソペンタン10質量%を溶剤として内包する熱膨張性マイクロカプセル
C2:ポリアクリロニトリル樹脂(分子量1,200,000)を外殻とし、イソペンタン25質量%を溶剤として内包する熱膨張性マイクロカプセル
C3:ポリアクリロニトリル樹脂(分子量1,200,000)を外殻とし、イソブタン10質量%及びイソペンタン5質量%を溶剤として内包する熱膨張性マイクロカプセル
C4:ポリアクリロニトリル樹脂(分子量1,200,000)を外殻とし、イソペンタン10質量%及びn-ヘキサン18質量%を溶剤として内包する熱膨張性マイクロカプセル
C5:塩化ビニリデン・アクリロニトリルのコポリマー樹脂(分子量1,500,000)を外殻とし、イソブタン25質量%を溶剤として内包する熱膨張性マイクロカプセル(比較例用)
C6:ポリアクリロニトリル樹脂(分子量1,200,000)を外殻とし、n-ヘキサン18質量%を溶剤として内包する熱膨張性マイクロカプセル(比較例用)
ここで、分子量は、THFを展開溶媒としたゲルパーミエーションクロマトグラフィ(GPC)分析におけるポリスチレン換算の数平均分子量として求めた値である。また、各溶剤の量は、マイクロカプセル全体の量を100としたときの質量%である。
D1:2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン(6分間半減期温度:160℃)
D2:ジクミルパーオキサイド(6分間半減期温度154℃)
D3:クミル-t-ブチルパーオキサイド(6分間半減期温度148℃)
D4:ビス(2,4-ジクロロベンゾイル)パーオキサイド(6分間半減期温度99℃)(比較用)
付加:付加硬化剤C-25A(白金触媒)/C-25B(オルガノハイドロジェンポリシロキサン)(比較用)
(いずれも信越化学工業(株)製、120℃において約30秒でベースゴム組成物を硬化する)
E1:アゾジカルボンアミド(純品、分解開始温度210℃)
E2:尿素含有アゾジカルボンアミド(純度95%、分解開始温度190℃)
E3:N,N’-ジニトロソペンタメチレンテトラミン(純品、分解開始温度205℃)
E4:ヒドラゾジカルボンアミド(純品、分解開始温度245℃)
E5:アゾビスイソブチロニトリル(分解開始温度107℃)(比較用)
E6:尿素及び有機亜鉛含有アゾジカルボンアミド(純度88%、分解開始温度140℃)(比較用)
・硬さ:JIS S 6050:2008規定のアスカーC硬度を測定した。
・発泡倍率:以下の各例における未架橋ゴム組成物シートの比重(発泡前ゴム比重)及びポストキュアー後のシリコーンゴムスポンジの比重(スポンジ比重)をそれぞれ測定した。なお、比重の測定はJIS K 6268:1998記載の方法によって行った。そして、下記式より発泡倍率を算出した。
[計算方法:発泡前ゴム比重/スポンジ比重×100(%)]
・セルの状態:異常発泡、割れ、スキン層状態を観察した。目視にて異常発泡又は割れがないことが確認され、かつスキン層の表面平滑性に優れるものを「良好」と評価した。
・平均セル径:スポンジの任意の切断面にあるセルを光学顕微鏡にて観察し、セル径を測定し、平均値を算出した。
・セルのアスペクト比:スポンジの任意の切断面にあるセルを光学顕微鏡にて観察し、セルの長径及び短径をそれぞれ測定し、セルの長径を短径で割った値の平均値を算出した。
・連泡率:スポンジの連泡率を以下の手順で算出した。
1)以下の各例における未架橋ゴム組成物シート(発泡前ゴム)及びポストキュアー後のシリコーンゴムスポンジ(スポンジ)の比重と質量を測定した。
なお、比重の測定はJIS K 6268:1998記載の方法によって行い、ただし、比重測定時の水中に浸漬する時間は5秒以内とした。
2)水を入れた容器に、スポンジを水に沈むように配置し、該容器ごと真空容器に入れ、真空容器内を10mmHg以下に減圧した。
3)真空容器内を常圧に戻した後に5分間放置してスポンジに吸水させた。
4)吸水したスポンジの質量を計量した。
そして、下記式により連泡率を算出した。
連泡率(%)=[(吸水したスポンジの質量-スポンジの質量)/水の比重]/[(1-(スポンジの比重/発泡前ゴムの比重))×(スポンジの質量/スポンジの比重)]×100
なお、上記式において、水の比重は、1.00とした。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E1)としてアゾジカルボンアミド7.0質量部(理論ガス発生量1,400cc)を2本ロールミルにて添加混合し、9mm厚の未架橋ゴム組成物シートを作製した。
次にこの9mm厚の未架橋ゴム組成物シートを230℃の熱風乾燥器で30分間常圧熱風架橋させてシリコーンゴムスポンジを得た。
その後、得られたシリコーンゴムスポンジを230℃で2時間のポストキュアーを行った。得られたスポンジのセルの状態を上記のようにして確認・評価し、スキン層をとり除いた後に、スポンジの硬さ、発泡倍率、平均セル径、セルのアスペクト比(真球性)及び連泡率を上記のようにして調べた。評価結果を表2に示す。
また、図1は実施例1のスポンジの断面の拡大写真である。実施例1のスポンジは、均一な微細構造セルを有していることが明らかとなった。
ベースゴム組成物1を145部に対し、熱膨張性マイクロカプセル(C2)2.3質量部、硬化剤(D2)としてジクミルパーオキサイド1.2質量部、及び連泡化剤(E2)として尿素含有アゾジカルボンアミド3.5質量部(理論ガス発生量690cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C3)3.0質量部、硬化剤(D3)としてクミル-t-ブチルパーオキサイド1.8質量部、及び連泡化剤(E3)としてN,N’-ジニトロソペンタメチレンテトラミン4.5質量部(理論ガス発生量1,100cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C4)2.3質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E1)としてアゾジカルボンアミド7.0質量部(理論ガス発生量1,400cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E4)としてヒドラゾジカルボンアミド3.0質量部(理論ガス発生量530cc)を2本ロールミルにて添加混合し実施例1と同様にスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物2を115質量部に対し、熱膨張性マイクロカプセル(C1)2.3質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.2質量部、及び連泡化剤(E1)としてアゾジカルボンアミド6.0質量部(理論ガス発生量1,000cc)を2本ロールミルにて添加混合し実施例1と同様にスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E5)としてアゾビスイソブチロニトリル1.5質量部(理論ガス発生量200cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤として付加架橋硬化剤C-25A0.7質量部及びC-25B3.0質量部、並びに連泡化剤(E5)としてアゾビスイソブチロニトリル1.5質量部(理論ガス発生量200cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジを作製した。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤として付加架橋硬化剤C-25A0.7質量部及びC-25B3.0質量部、並びに連泡化剤(E1)としてアゾジカルボンアミド1.5質量部(理論ガス発生量300cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジの作製を試みたが、アゾジカルボンアミドが付加架橋阻害物となってしまいスポンジを得ることができなかった。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C5)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E1)としてアゾジカルボンアミド3.0質量部(理論ガス発生量600cc)を2本ロールミルにて添加混合し、実施例1と同様にしてスポンジの作製を試みたが、架橋後に連泡化することができず、アゾジカルボンアミドの発生ガスによって内部よりスポンジが大きく割れてしまった。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、並びに連泡化剤(E6)として尿素及び有機亜鉛含有アゾジカルボンアミド7.0質量部(理論ガス発生量1,000cc)を2本ロールミルにて添加混合し、実施例1と同様にスポンジの作製を試みたが、スポンジが内部よりドーム状に膨らんで破裂してしまった。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D4)として低温分解型の有機過酸化物であるビス(2,4-ジクロロベンゾイル)パーオキサイド1.0質量部、及び連泡化剤(E1)としてアゾジカルボンアミド3.0質量部(理論ガス発生量600cc)を2本ロールミルにて添加混合し、実施例1と同様にスポンジ作製を行ったが、スポンジの内部に長さ0.5~3cm、幅0.5~2mmの裂け目が数多く発生し外観不良のスポンジとなった。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C6)3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサン1.5質量部、及び連泡化剤(E1)としてアゾジカルボンアミド3.6質量部(理論ガス発生量720cc)を2本ロールミルにて添加混合し、実施例1と同様にスポンジ作製を行ったが、スポンジの内部に直径1~3mmの大きなピンホールが発生し外観不良のスポンジとなった。その後、実施例1と同様にしてスポンジを評価した結果を表2に示す。
(D)成分として付加架橋剤を用いた比較例3では、スポンジが硬化しなかった。また、有機過酸化物架橋剤であっても、(D)成分の架橋開始温度が(C)成分の膨張開始温度より低い有機過酸化物架橋剤を用いた比較例6では、スポンジが内部から裂けてしまい、連泡率も低かった。
(E)成分の分解開始温度が(C)成分の膨張開始温度より低い連泡化剤を用いた比較例1では、連泡率が低く、セルのアスペクト比も大きく、高連泡化した真球状のセルを有するスポンジが得られなかった。また、(E)成分の分解開始温度が(C)成分の熱膨張開始温度より高い連泡化剤であっても、(E)成分の分解開始温度が(D)成分の架橋開始温度より低い連泡化剤を用いた比較例5では、スポンジにドーム状の割れが生じてしまった。
一方、本願発明で規定する温度範囲の各成分を用いた実施例1~6のスポンジは、高連泡化した均一な微細セル構造を有することがわかった。
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)を3.0質量部、硬化剤(D1)として2,5-ジメチル-2,5-ジ-(t-ブチルパーオキシ)ヘキサンを1.5質量部のみを2本ロールミルにて添加混合し、連泡化剤を含まないスポンジを実施例1と同様にして作製した。得られたスポンジの写真を実施例1と比較した。また、出来上がったスポンジを直径29mm、厚さ12.5mmに切りだし、JIS K 6262:2013記載の方法(180℃、25%圧縮、22時間)により圧縮永久ひずみを測定した。結果を表3に示す。
直径6mm×長さ300mmのアルミニウム芯金の外周に、実施例1又は比較例2で作製したスポンジによって被覆された、外径30mm×長さ250mmの単層シリコーンゴムスポンジロールを作製した。このロールを直径26mmまで研磨した後、付加架橋型一液型シリコーンゴム接着剤KE-1884(信越化学工業社製)にて内面を処理した膜厚50μmのフッ素PFAチューブを研磨後のロールに被覆し、150℃で30分加熱硬化し、更に200℃で4時間ポストキュアーし、外径26mm×長さ250mmのPFA樹脂被覆シリコーンゴムスポンジ定着ロールを作製した。
このようにして得られた定着ロールの23℃雰囲気での外径をレーザー変位計(CMOSレーザーアプリセンサIL-S100+アンプユニットIL-1000(キーエンス社製))を用いて測定した。また、上記で得られた定着ロールを200℃の熱風乾燥器に15秒間入れた後の空気膨張した定着ロールの外径を同様に測定した。
それぞれの外径及びこれらから算出した外径変化率を表4に示す。実施例1の組成物を使用した定着ロールは外径変化率が約2%であったが、比較例2の組成物を使用した定着ロールでは外径変化率が約5%と定着ロールの外径が大きく膨らんでいる状態であった。比較例2の組成物を使用した定着ロールでは、使用する場合に文字かすれ等の定着不良が発生するおそれがある程の外径変化であった。
〔実施例6〕
ベースゴム組成物1を145質量部に対し、熱膨張性マイクロカプセル(C1)3.0質量部、硬化剤(D1)1.5質量部、連泡化剤(E1)7.0量部(以上実施例1組成)に加え、スポンジを難燃化させるために5%塩化白金酸イソプロピルアルコール溶液を0.6質量部、平均粒子径4μmの結晶性シリカであるクリスタライトVX-S(龍森製)60質量部及び比表面積30m2/gの酸化チタンであるスーパータイタニアF-2(昭和電工社製)7質量部を2本ロールミルにて添加混合し、3mm厚の未架橋ゴム組成物シートを作製した。
次にこの3mm厚の未架橋ゴム組成物シートを230℃の熱風乾燥器で30分間常圧熱風架橋させて6mm厚のシリコーンゴムスポンジを得た。その後、得られたシリコーンゴムスポンジを230℃で2時間のポストキュアーを行った。
得られたスポンジをスポンジUL耐炎性試験(ASTM D 4986)にて試験を行った結果、バーナー除去後にスポンジの炎が直ちに消え、得られたスポンジはUL 94 HF-1であった。
また、上述した方法と同様にして、得られたスポンジの硬さ(アスカーC)及び連泡率を測定した。さらに、得られたスポンジの密度をJIS K6268により測定した。その結果を表5に示す。
上記の実施例6の成分において、連泡化剤(E1)以外の成分を全て同量添加して、実施例6と同様の方法でシリコーンゴムスポンジを得た。その後、得られたシリコーンゴムスポンジを230℃で2時間のポストキュアーを行った。
得られたスポンジをスポンジUL耐炎性試験(ASTM D 4986)にて試験を行った結果、バーナー除去後にグローイング燃焼を続け、10秒以上燃焼継続した。燃焼速度は36mm/分で燃焼滴下物は無く、得られたスポンジはUL 94 HBFであった。さらに、実施例6と同様にしてスポンジを評価した結果を表5に示す。
Claims (11)
- 下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮する熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤であり、(A)成分の硬化後に分解開始するもの (A)成分100質量部に対して0.1~30質量部
を含有するシリコーンゴム組成物を、200℃以上で熱処理することを特徴とする、連泡率が20%以上のミラブル型シリコーンゴムスポンジの製造方法。 - 熱処理を常圧熱風により行うことを特徴とする請求項1記載のミラブル型シリコーンゴムスポンジの製造方法。
- (E)成分の連泡化剤が発生するガス量が、(A)成分と(B)成分の合計100gに対して100cc以上であることを特徴とする請求項1又は2に記載のミラブル型シリコーンゴムスポンジの製造方法。
- (E)連泡化剤が、アゾジカルボンアミド、N,N’-ジニトロソペンタメチレンテトラミン及びヒドラゾジカルボンアミドから選ばれる少なくとも1種である請求項1~3のいずれか1項に記載のミラブル型シリコーンゴムスポンジの製造方法。
- (D)硬化剤が、ジアルキル系の有機過酸化物であり、架橋開始温度が135~180℃である請求項1~4のいずれか1項に記載のミラブル型シリコーンゴムスポンジの製造方法。
- 下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮する熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤であり、(A)成分の硬化後に分解開始するもの (A)成分100質量部に対して0.1~30質量部
を含有するシリコーンゴム組成物の熱処理物たるミラブル型シリコーンゴムスポンジであって、
連泡率が20%以上であり、
セルのアスペクト比が1.0~1.3であり、かつ
平均セル径が250μm以下である
ことを特徴とするミラブル型シリコーンゴムスポンジ。 - 請求項6に記載のミラブル型シリコーンゴムスポンジからなるベルト状成形物。
- 請求項6に記載のミラブル型シリコーンゴムスポンジからなるシート状成形物。
- 請求項6に記載のミラブル型シリコーンゴムスポンジからなるスポンジロール状成形物。
- 請求項6に記載のミラブル型シリコーンゴムスポンジからなる輸送機用保護緩衝材。
- 下記(A)~(E)成分
(A)下記平均組成式(I):
R1 aSiO4-a/2 (I)
[式(I)中、R1は同一又は異種の1価炭化水素基を示し、aは1.95~2.04の正数を示す。]
で表される、一分子中にアルケニル基を少なくとも2個有する重合度3,000以上のオルガノポリシロキサン 100質量部
(B)補強性シリカ (A)成分100質量部に対して10~100質量部
(C)膨張開始温度が90~150℃であり、200℃で5分間の加熱により最大膨張体積から20%以上収縮し、収縮温度が200℃以上の熱膨張性マイクロカプセル (A)成分100質量部に対して0.1~20質量部
(D)硬化剤:架橋開始温度が100~180℃の有機過酸化物 (A)成分100質量部に対して0.01~20質量部
(E)連泡化剤:分解開始温度が180℃以上の固体の高温分解型有機発泡剤 (A)成分100質量部に対して0.1~30質量部
を含み
(C)成分の膨張開始温度<(D)成分の架橋開始温度<(C)成分の収縮温度≦(E)成分の分解開始温度であることを特徴とするミラブル型シリコーンゴム組成物。
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WO2020053826A1 (en) | 2018-09-13 | 2020-03-19 | 3M Innovative Properties Company | Foam compositions and methods of making same |
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