Fluororubber adhesive composition

Abstract

[Problem] To provide a fluororubber adhesive composition that does not impair the inherent heat resistance, chemical resistance, weather resistance, and flame retardancy of fluororubber, and exhibits excellent adhesion and tack. [Solution] A fluororubber adhesive composition is made by blending an acrylic adhesive with a modified fluororubber having a mulli viscosity ML1+10 (121°C) of 10-80 containing unsaturated bonds or unsaturated bonds and functional groups. The acrylic adhesive contains an acrylic copolymer with a glass transition temperature Tg below 20°C. The acrylic adhesive is used at a ratio of 10-400 parts by weight relative to 100 parts by weight of the modified fluororubber.

Description

[Technical Field]

[0001] This invention relates to a fluororubber adhesive composition. More specifically, it relates to a fluororubber adhesive composition that does not impair the heat resistance, chemical resistance, weather resistance, flame retardancy, etc., inherent in fluororubber, and exhibits excellent adhesion and tack. [Previous Technology]

[0002] Conventionally, adhesives have generally been resin-based adhesives such as vinyl acetate resin, ethylene-vinyl acetate copolymer resin, vinyl chloride resin, epoxy resin, urethane resin, styrene resin, acrylic resin, polyamide resin, cyanoacrylate, cellulose resin, silane-based adhesives, and silica-based adhesives, or rubber-based adhesives such as nitrile rubber, styrene-butadiene rubber, and chloroprene rubber. As heat-resistant adhesives, acrylic adhesives and silica adhesives are generally available; however, acrylic adhesives have worse heat resistance than silica adhesives, and silica adhesives have lower bond strength than acrylic adhesives. Therefore, adhesives other than silica-based adhesives are difficult to use for long-term heat-resistant applications above 175°C, and silica adhesives are unsuitable for use in electronic components from a contamination perspective.

[0003] While fluoropolymers or fluororubbers exhibit excellent heat resistance, long-term resistance to chemicals, weathering, and friction at temperatures above 175°C, they generally cannot be used alone as adhesives or bonding agents due to their lack of tack and bonding properties. Fluororubbers, when not cross-linked, may exhibit some tackiness but lack bonding properties. This uncross-linked fluororubber develops tackiness through defluorination and hydrogenation using alkali, thus achieving bonding. However, because it is not cross-linked, it lacks strength, solvent resistance, chemical resistance, liquid resistance, pressure resistance, and bonding strength under heat, thereby limiting its applications.

[0004] Furthermore, although general fluororubber can improve its strength, solvent resistance, chemical resistance, liquid resistance, pressure resistance, and adhesion strength under heating by crosslinking with polyols, polyamines, peroxides, etc., it still lacks adhesiveness and adhesion after crosslinking, even though the glass transition temperature Tg is below room temperature. Therefore, crosslinked fluororubber is generally not usable as an adhesive.

[0005] Furthermore, in the crosslinking of fluororubber with polyols such as bisphenol A (BFA) or amines such as difunctional polyamine compounds, defluorination and hydrogenation will occur without divalent metal oxides such as magnesium oxide or calcium hydroxide, leading to the formation of carbon-carbon unsaturated bonds. Therefore, divalent metal oxides such as magnesium oxide or calcium hydroxide are necessary during crosslinking. However, divalent metal oxides harden quickly due to moisture absorption, and there is still a problem that they cannot be stored in sheets for a long time. In addition, calcium hydroxide hardens quickly, and when made into adhesives soluble in organic solvents, it gels quickly and becomes unusable. Furthermore, the addition of large amounts of inorganic substances such as calcium hydroxide and magnesium oxide leads to loss of adhesion and further reduces the adhesion after crosslinking.

[0006] Furthermore, the crosslinking of peroxides in fluororubber requires the isolation of oxygen through pressure or other means to achieve crosslinking. Since exposed parts or parts that oxygen can penetrate will not undergo crosslinking, problems such as adhesion of uncrosslinked parts or decreased liquid resistance may occur. Moreover, in production, since crosslinking is achieved in a short time by isolating air (oxygen), it is necessary to make the crosslinking process rapid. When dissolving the rubber components in organic solvents to prepare adhesives, rapid gelation makes them difficult to use. During solvent drying, the peroxide compounds are deactivated due to exposure to air, which also leads to insufficient crosslinking.

[0007] General fluororubber systems can be crosslinked using acid acceptors and crosslinking agents, but they cannot be crosslinked using epoxy resins, which have excellent heat resistance, water resistance, and can improve adhesion strength. Here, even if epoxy resin and polyamine are added to general fluororubber, although the epoxy resin will react with the polyamine, the crosslinking density of the fluororubber will not increase, thus failing to achieve improved adhesion and liquid resistance.

[0008] Patent Document 1 discloses an adhesive composition containing a fluorinated oligomer with a weight average molecular weight (Mw) of 3500 or higher, an ionic compound, and an acrylic polymer. While the inclusion of the acrylic polymer improves adhesion, the poor compatibility between the fluorinated oligomer and other polymers such as the acrylic polymer leads to a problem where the fluorinated oligomer migrates to the surface after coating or drying, resulting in reduced surface adhesion. The migration state of the fluorinated oligomer to the surface changes depending on the storage time and ambient temperature, thus the adhesion does not stabilize, and in cases of cross-linking, the adhesion further decreases.

[0009] Patent Document 2 discloses an adhesive that uses a fluorinated copolymer as the main component. This fluorinated copolymer is synthesized by copolymerizing perfluoroalkyl (meth)acrylate monomers, alkyl (meth)acrylate monomers, hydroxyl-containing acrylic monomers, and carboxyl-containing acrylic monomers. However, the adhesiveness is not high, and the bonding strength is also low, leading to degradation after prolonged exposure to high temperatures, resulting in a continued problem of reduced adhesion. [Prior Art Documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent No. 7,177,581 [Patent Document 2] Japanese Unexamined Patent Publication No. 2004-292529 [Patent Document 3] Japanese Unexamined Patent Publication No. 2009-108287 [Patent Document 4] Japanese Unexamined Patent Publication No. 2014-105268 [Patent Document 5] Japanese Patent No. 3,327,447 [Patent Document 6] Japanese Patent No. 3,975,249 [Patent Document 7] Japanese Unexamined Patent Publication No. 2002-030263 [Patent Document 8] Japanese Unexamined Patent Publication No. Sho 59-059764 [Patent Document 9] Japanese Unexamined Patent Publication No. Hei 2-245046 [Summary of the Invention]

[0011] [Problem to be Solved by the Invention] The object of the present invention is to provide a fluororubber adhesive composition that does not impair the inherent heat resistance, chemical resistance, weather resistance, and flame retardancy of fluororubber, and also exhibits excellent adhesion and bonding properties. [Means for Solving the Problem]

[0012] The object of this invention is achieved by means of a fluororubber adhesive composition, which is formed by blending an acrylic adhesive with a modified fluororubber having a Mooney viscosity (ML1+10) of 10 to 80 (121°C) having unsaturated bonds or functional groups such as unsaturated bonds and carboxyl groups. The acrylic adhesive contains an acrylic copolymer with a glass transition temperature (Tg) below 20°C. [Effects of the Invention]

[0013] The fluororubber adhesive composition of the present invention is a modified fluororubber with unsaturated bonds (and functional groups such as carboxyl groups) combined with an acrylic adhesive. This achieves the excellent effect of allowing the fluororubber to exhibit a low level of tackiness, similar to commercially available acrylic or silicone adhesives, without compromising the modified fluororubber's excellent adhesion (heat resistance), chemical resistance, weather resistance, and flame retardancy after prolonged heating. This is believed to be due to the fact that the fluorinated compound does not copolymerize with the acrylic compound, allowing the degree of tackiness to be adjusted by adding an acrylic adhesive. Furthermore, the fluororubber is miscible with the acrylic adhesive, thus providing an adhesive with superior heat resistance and adhesion compared to an acrylic adhesive alone.

[0014] Generally speaking, when fluororubber is blended with acrylic rubber or acrylic adhesive and dissolved in a solvent, the solution will undergo layer separation. Therefore, even if coating is applied, the coating surface will be uneven and the thickness will be uneven after drying, making it impossible to use it effectively as an adhesive tape or adhesive sheet. However, by alkali-modifying the fluororubber and blending it with acrylic adhesive, layer separation of the solution can be prevented, the unevenness of the coating surface can be eliminated, and it can be used effectively as an adhesive tape or adhesive sheet.

[0015] Therefore, by using modified fluororubber that decomposes, de-molecularizes, and imparts functional groups to uncrosslinked fluororubber with inorganic or organic bases to achieve adhesiveness and bonding properties, it is possible to achieve good compatibility with acrylic adhesives, so that the coating surface will not separate even when mixed, thus achieving an excellent effect.

[0016] Even without adding commonly used acid acceptors to the modified fluororubber, co-crosslinking of the modified fluororubber and the acrylic adhesive can be achieved by using crosslinking agents commonly used in acrylic adhesives, resulting in higher adhesion and bonding strength. Therefore, since inorganic fillers such as acid acceptors are not necessarily required, the adhesion will not deteriorate due to the addition of fillers, and the adhesion can be improved by adding crosslinking agents. Furthermore, if acid acceptors are not added, there will be no hardening degradation caused by acid acceptors, and there will be no significant decrease in adhesion with heating. Moreover, even if other adhesives are added, the compatibility remains good, no layer separation occurs, and the coating becomes uniform after drying.

[0017] To date, no adhesive has been found that offers better heat resistance than acrylic adhesives, higher adhesion strength than silicone adhesives, no silicone contamination, and high heat resistance. However, the fluororubber adhesive composition of this invention provides an adhesive that meets these requirements. Specifically, for example, when a steel ball with a diameter of 4.8 mm is placed on an adhesive surface formed by a 30-degree angle, it exhibits adhesion to the extent that the steel ball will not roll.

[0018] Since the fluororubber adhesive composition is viscous at room temperature, it can be laminated with the substrate at room temperature. The viscousness and adhesion can be further improved by oven heating treatment. Furthermore, since the fluororubber is modified to a lower molecular weight, it can seamlessly cover the unevenness of the substrate, such as the pattern unevenness of electronic substrates, and the adhesion strength is high.

[0019] When difluororubber is not cross-linked with polyamines or polyols, cross-linking will not occur without divalent metal oxides such as magnesium oxide or acid acceptors such as calcium hydroxide or hydrotalcite. However, since these particles are large, adhesives containing these particles may produce particles larger than the coating thickness, resulting in reduced adhesion, bonding, and heat resistance. Furthermore, these particles are prone to detaching from the adhesive surface, which can cause contamination in semiconductor applications due to particle shedding from inorganic fillers. The fluororubber adhesive composition of the present invention modifies the fluororubber and imparts functional groups, thereby eliminating the need to add divalent metal oxides such as magnesium oxide or calcium hydroxide and hydrotalcite. The cross-linking agent such as epoxy resin and the modified fluororubber will still directly undergo a cross-linking reaction, and there will be no contamination caused by particles from the adhesive surface.

[0020] Furthermore, even without the use of environmentally harmful bisphenol AF, the modified fluororubber is cross-linked by epoxy resin, resulting in fewer reactive gases during the heating of the laminate and preventing foaming of the laminate.

Implementation Method

[0021] As a fluororubber, highly fluorinated elastic copolymers can be used, such as two or more elastic copolymers of vinylidene fluoride, hexafluoropropylene, pentafluoropropylene, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, fluoroethylene, perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(propyl vinyl ether), etc., preferably vinylidene fluoride-hexafluoropropylene copolymers, especially vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymers, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-perfluoro(alkyl vinyl ether) terpolymers.

[0022] Furthermore, Patent Document 3 has proposed an adhesive composition composed of a fluororubber polymer that cannot be cross-linked with peroxide, a fluororubber polymer that can be cross-linked with peroxide, and a peroxide. Although this adhesive composition has excellent heat resistance and solvent resistance, it has no adhesiveness at room temperature, and the peroxide is deactivated by oxygen in the air and does not sufficiently induce a cross-linking reaction. Therefore, although this adhesive composition without acrylic adhesive can adhere to surfaces such as glass, for example, when a steel ball with a diameter of 4.8 mm is placed on a 30-degree inclined plane, the steel ball will roll.

[0023] Fluororubber can be manufactured as a latex by aqueous emulsion polymerization or aqueous suspension polymerization. In aqueous emulsion polymerization, either a water-soluble peroxide alone, or a redox system composed of a water-soluble peroxide and a water-soluble reducing agent, can be used as the reaction initiator system. Examples of water-soluble peroxides include ammonium persulfate, potassium persulfate, and sodium persulfate, while examples of water-soluble reducing agents include sodium sulfite and sodium bisulfite. In this case, pH adjusters (buffers) such as sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate, and potassium dihydrogen phosphate can be used as stabilizers for the aqueous emulsion.

[0024] Fluorinated carboxylate salts are generally used as emulsifiers in emulsion polymerization, and CF3CF2CF2O[CF(CF3)CF2O]nCF(CF3)COONH4 (n: 1 or 2) is preferred. These emulsifiers are used as an aqueous solution of about 1 to 30% by weight, preferably about 5 to 20% by weight. If the amount of emulsifier is less than this, the monomer and the resulting copolymer cannot be uniformly dispersed in the aqueous medium; if it is too much, it becomes economically unfavorable.

[0025] The copolymerization reaction is carried out at a temperature of about 20~80°C, preferably about 25~60°C. If the polymerization temperature is too high, problems such as foaming may occur during molding and processing. In addition, the polymerization pressure is generally carried out at about 5 MPa or less.

[0026] In the presence of the emulsifier shown in the aforementioned general formula, vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene are copolymerized in an aqueous medium. The copolymerization reaction in the aqueous medium can also be carried out as a suspension polymerization method, but emulsion polymerization is preferred to obtain the desired average emulsion particle size. The emulsion polymerization reaction is carried out under the following conditions: a water-soluble inorganic peroxide such as ammonium persulfate, or a redox system of the peroxide and a reducing agent, is used as a catalyst; the reaction is carried out at a ratio of approximately 0.001 to 0.2% by weight relative to the total weight of water added; in the presence of a commonly used surfactant as an emulsifier; a pressure of approximately 0 to 10 MPa, preferably approximately 0.5 to 4 MPa; and a temperature of approximately 0 to 100°C, preferably approximately 20 to 80°C. It is preferable to supply the fluorinated olefin mixture in batches so that the reaction pressure remains within a fixed range. Furthermore, to adjust the pH within the polymerization system, buffering electrolytes such as sodium monohydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate, or sodium hydroxide, can be added. Additionally, chain transfer agents such as ethyl malonate, acetone, and isopropanol can be used as appropriate.

[0027] The polymerization reaction is also affected by various polymerization conditions, and it generally takes about 1 to 15 hours to complete, which is not much different from the case when using ammonium perfluorooctanoate emulsifier. After the reaction is completed, the obtained aqueous emulsion can be condensed to form a polymer by adding aqueous solutions of potassium aluminum sulfate, sodium chloride, or calcium chloride, followed by washing and drying to obtain a fluorinated copolymer.

[0028] Here, fluorinated surfactants are widely used as surfactants in the emulsion polymerization of fluorinated monomers. Among them, perfluorooctanoic acid (PFOA) or its salts are known to be surfactants with excellent monomer emulsifying properties or latex stability. However, perfluorinated chemicals are difficult to decompose in the natural environment, and it has recently been found that perfluorinated compounds with 8 carbon atoms, represented by PFOA, have significantly stronger residual effects in the human body. Furthermore, due to its excellent affinity for rubber, PFOA tends to adhere to or remain in the fluororubber formed after the coagulation of rubber latex obtained by emulsion polymerization, and there is a strong desire to reduce this amount.

[0029] Regarding this requirement, as a means of imparting environmental decomposability to fluorinated emulsifiers, it is considered that a hydrogenated portion be incorporated into the perfluorinated hydrophobic group of the surfactant compound. In fluororubber latex, by using perfluoroalkyl alkylphosphonates CnF2n+1CmH2mP(O)(OM1)(OM2) as emulsifiers, PFOA countermeasures are achieved even without using fluorinated surfactants.

[0030] When using perfluoroalkyl alkylphosphonates, they are obtained by reacting perfluoroalkyl alkylphosphonic acid (CnF2n+1CmH2mP(O)(OH)2) (n: an integer from 2 to 6, m: an integer from 1 to 3) with an alkali metal hydroxide or ammonia. Using an equal molar amount of alkali metal hydroxide or ammonia relative to the perfluoroalkyl alkylphosphonic acid results in a single salt, while using twice the molar amount results in a disalt. Generally, a theoretical molar number or higher must be used; using an equal molar amount but less than twice the molar amount results in a mixture of single and disalts.

[0031] Because these perfluoroalkyl phosphonates have linear fluoroalkyl groups, their solubility in water is better than that of fluoropolyether-type emulsifier compounds with equivalent emulsifying properties. Furthermore, because their adhesion to the resulting fluororubber is lower than that of PFOA, the residual emulsifier content in the fluororubber obtained by coagulating the fluororubber latex through emulsification polymerization using methods such as salting out, acid precipitation, and mechanical stirring can be significantly reduced. The emulsification polymerization reaction of the fluorinated monomer using this emulsifier is carried out using the same method as when using PFOA emulsifier.

[0032] The emulsification polymerization reaction is carried out using water-soluble inorganic peroxides such as ammonium persulfate, or their redox system with a reducing agent, as a catalyst. To adjust the pH within the polymerization system, buffering electrolytes such as phosphates (Na₂HPO₄, NaH₂PO₄, KH₂PO₄, etc.) or borates (Na₂B₂O₇, etc.), or NaOH, may be added. The emulsification polymerization reaction uses approximately 0.001 to 10% by weight of emulsifier relative to water, preferably approximately 0.01 to 5% by weight, and is carried out under pressure at approximately 30 to 120°C for approximately 1 to 48 hours.

[0033] Furthermore, for the purpose of further improving adhesion, it is preferable to use modified fluororubber with a weight average molecular weight (Mw) of 300,000 or less. Also, a glass transition temperature (Tg) of 20°C or less is preferred. If fluororubber within this range is used, it can exhibit adhesion through the modification described later, and can be dissolved in solvents for coating.

[0034] Furthermore, Patent Document 4 discloses an easy-to-adhere composition containing hydroxyl-containing resins such as acrylic resin and fluororesin, wax and polyisocyanate compound, and Patent Document 5 discloses an adhesive for vinylidene fluoride resin, which is composed of soft fluororesin, acrylic resin, vinylidene fluoride resin, polyisocyanate and organic solvent. Although these compositions will bond during the crosslinking reaction, they have no adhesion after the crosslinking reaction. Although they can be used in coatings or adhesives, they cannot be used as adhesives.

[0035] The molecular weight, molecular weight distribution, and mucilage of fluororubber can be controlled by adjusting conditions such as the degree of polymerization, alkali content, denaturation temperature, and time. The weight-average molecular weight Mw is measured by gel permeation chromatography and converted based on a calibration curve made using standard polystyrene.

[0036] Fluororubber can be modified into a modified fluororubber using known modification methods before use. The modification of fluororubber can be achieved by using inorganic or organic bases, preferably organic bases, through partial defluorination and hydrogenation reactions to introduce unsaturated bonds (Patent Documents 6-7). Through this modification treatment, HF is removed from the fluoropolymer backbone to form carbon-carbon unsaturated bonds. The molecular weight of the fluoropolymer decreases through chain scission reactions, allowing for rapid decomposition, molecular weight reduction, and the introduction of functional groups, thereby obtaining a modified fluororubber with adhesiveness and bonding properties. Since inorganic base modification results in minimal penetration of the rubber even at room temperature or after heating, it is preferable to use organic bases that allow penetration of the fluororubber latex at room temperature. With organic bases, the fluororubber is uniformly modified, resulting in a modified fluororubber with enhanced adhesiveness.

[0037] Modified fluororubber has unsaturated bonds and functional groups such as carboxyl groups at the ends. Therefore, by adding a crosslinking agent, the crosslinking agent will react and crosslink with the substrate to be bonded, thereby improving adhesion, durability, liquid resistance, solvent resistance, and bonding strength under heating. Thus, it can be used as an adhesive that utilizes the characteristics of fluororubber.

[0038] Furthermore, by partially defluorinating hydrogen, unsaturated bonds are formed in the main chain. After the chain-breaking reaction, functional groups such as carboxyl groups are formed at the ends of the molecular chain through an oxidation reaction. This allows for cross-linking with cross-linking agents such as epoxy resins, diamine compounds, and polyamine compounds in the absence of acid acceptors. The number of functional groups formed by denaturation is not particularly limited.

[0039] Higher denaturation temperatures result in more polymers and lower denaturation temperatures result in more low-molecular-weight compounds. In the case of inorganic base denaturation, fluororubber will not be denatured unless heated to above 40°C. In the case of organic base denaturation, it becomes difficult to control the molecular weight above 40°C, so the process is carried out at approximately 5-35°C. In the case of organic base denaturation, if the denaturation temperature is below room temperature, time is required until the denaturation stabilizes. Within the range of 20-30°C (room temperature), denaturation can be carried out stably in a short time. Shorter denaturation times result in greater deviations in the denatured state, while longer times result in smaller deviations. More denaturant leads to more low-molecular-weight compounds; therefore, the denaturation temperature and amount of denaturant should be adjusted according to the necessary molecular weight. The heating and drying temperature after denaturation and cleaning is about 60~150℃, preferably about 80~120℃. If it is lower than this, the adhesion will deteriorate due to insufficient drying and solvent residue when stacking adhesive sheets, caused by foaming and low molecular weight residue. If it is higher than this, there will be more cross-linking and polymerization, which will lead to a decrease in adhesion.

[0040] As an organic base, at least one of the following can be used: 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN), tetramethylammonium hydroxide, tetramethylammonium hydroxide, tetrabutylphosphonium hydroxide, etc. As an inorganic base, examples include potassium hydroxide, sodium hydroxide, lithium hydroxide, etc., which are dissolved in water and then mixed with fluororubber.

[0041] The modified fluororubber is a type of rubber with a mulley viscosity ML1+10 (121°C) of 10 to 80, preferably 10 to 50, obtained according to JIS K6300-1 (2013) of ISO 289:12005, a weight average molecular weight Mw of 1.0 × 10⁵ to 3.0 × 10⁵, and a number average molecular weight Mn of 0.3 × 10⁵ to 7.0 × 10⁵. If the mulley viscosity is higher than this, there is no adhesiveness; if it is lower than this, it contains liquid substances due to decomposition during modification, which may contaminate the adhered material or impair the adhesiveness. Here, the measurement of the muni viscosity was performed according to JIS K6300-1 (2013) corresponding to ISO 289:12005, using a muni viscometer SMV-201 (manufactured by Shimadzu Corporation), under the conditions of a temperature of 121°C, a preheating time of 1 minute, and a rotor rotation time of 10 minutes.

[0042] The mulley viscosity ML1+10 (121°C) of fluororubber is subject to decomposition due to denaturation. Therefore, compared with the undeniable mulley viscosity, a reduction of 15-70 is acceptable, preferably a reduction of 20-70. This enhances adhesiveness.

[0043] After salting out or condensing, the modified fluororubber latex or solution can be easily and cost-effectively washed with water to remove components other than the fluororubber, thus forming a non-polluting adhesive that can be used in electronic components, semiconductor components, etc. This is because the fluororubber undergoes prepolymerization (partial cross-linking) by heating and drying the moisture, thereby imparting adhesiveness.

[0044] As an acrylic adhesive, in addition to acrylic monomers and methacrylate monomers, acrylate monomers and methacrylate monomers containing highly crosslinking functional groups can also be used. For example, monomers without functional groups, such as ethyl acrylate (EA), butyl acrylate (BA), and methyl methacrylate (MMA), can be copolymerized with at least one monomer containing highly crosslinking functional groups, such as methacrylic acid (MAA) or monobutyl fumarate (MBF).

[0045] As a monomer that does not contain functional groups, specifically, components that easily adjust the overall Tg of the adhesive layer to a suitable range include (meth)acrylates containing alkyl groups (excluding ethyl methacrylate and methyl methacrylate). Examples include ethyl acrylate, methyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, propyl methacrylate, pentyl methacrylate, hexyl methacrylate, vinyl acetate, vinyl propionate, styrene, and (meth)acrylonitrile. Preferably, at least one of ethyl acrylate, butyl methacrylate, acrylonitrile, methyl acrylate, 2-ethylhexyl methacrylate, and vinyl acetate can be selected. By using these, it becomes easier to adjust the peel force from the adhered material and easier to adjust the overall Tg of the adhesive layer to a suitable range.

[0046] As a monomer containing a highly crosslinkable functional group, such as a monomer having a carboxyl group, hydroxyl group, amino group, acetoacetoxy group, epoxy group, etc., from the point of view of general applicability, it is preferable to cite a monomer containing at least one of a carboxyl group and a hydroxyl group, and more preferably a monomer containing a carboxyl group.

[0047] As a monomer of the carboxyl group, examples include unsaturated carboxylic acids such as (meth)acrylic acid (methacrylic acid and / or acrylic acid), fumaric acid, maleic acid, itconic acid, crotonic acid, trimellitic acid, and benzopyrene, such as monomethyl itconic acid, monobutyl itconic acid, monobutyl fumarate, and 2-acryloxyethyl phthalic acid, and unsaturated tricarboxylic acid monoesters such as 2-(meth)acryloxyethyl trimellitic acid and 2-(meth)acryloxyethyl benzopyrene, such as carboxyethyl methacrylate and carboxypentyl methacrylate, etc.

[0048] These monopolymer systems are used in proportions of 30 to 95.5% by weight of monomers without highly crosslinking functional groups and 0.5 to 70% by weight of monomers with highly crosslinking functional groups. The more low molecular weight monomers such as ethyl acrylate are used, the better the compatibility with modified fluororubber tends to be. The degree of crosslinking can be adjusted by copolymerizing monomers with highly crosslinking functional groups. While increasing the degree of crosslinking can lead to increased bonding strength and improved liquid resistance, it also results in decreased adhesion. Therefore, the copolymerization ratio is adjusted according to the application.

[0049] The synthesis of acrylic copolymers is carried out by polymerizing the monomers in the presence of a polymerization initiator. The polymerization method is not particularly limited, and conventionally known methods can be used, such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Solution polymerization is preferred due to its simplicity. When using solution polymerization as the polymerization method, the reaction solvent can be, for example, ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether, etc. These reaction solvents can be used alone or in combination of two or more.

[0050] There are no particular limitations on the polymerization initiator; free radical polymerization initiators, anionic polymerization initiators, cationic polymerization initiators, etc., can be used. Among them, thermal free radical polymerization initiators are also suitable. Examples of thermal free radical polymerization initiators include organic peroxides and azo compounds. Examples of organic peroxides include 1,1-bis(trihexylperoxy)-3,3,5-trimethylcyclohexane, trihexylperoxytert-valerate, tributylperoxytert-valerate, 2,5-dimethyl-2,5-bis(2-ethylhexylperoxy)hexane, trihexylperoxy-2-ethylhexanoate, tributylperoxy-2-ethylhexanoate, tributylperoxyisobutyrate, tributylperoxy-3,3,5-trimethylhexanoate, tributylperoxylaurate, etc. Examples of azo compounds include azobisisobutyronitrile and azobiscyclohexaneformitrile. These polymerization initiators can be used alone or in combination of two or more.

[0051] Among the obtained acrylic copolymers, those with a Tg of 20°C or below, preferably 0°C or below, can be used as acrylic adhesives. By using a Tg, the adhesion at room temperature is improved.

[0052] Furthermore, the weight average molecular weight (Mw) of the acrylic copolymer is preferably about 100,000 to 1,000,000, and more preferably about 300,000 to 500,000. The weight average molecular weight (Mw) can be adjusted by polymerization conditions, such as the type or amount of polymerization initiator, polymerization temperature, monomer concentration, etc. If it is lower than this range, the strength will decrease and foaming will occur after lamination. If it is higher than this, the compatibility with modified fluororubber will deteriorate, the liquid will undergo layer separation, and the surface adhesion will disappear.

[0053] Furthermore, the lower the weight average molecular weight (Mw) of the acrylic copolymer, the better the adhesion. If it exceeds 1,000,000, the adhesion will still disappear even if the Tg is below 20°C. As long as it is not acrylic rubber but acrylic adhesive, commercially available products can be used directly. Examples include Arontack S-1511X, S-3403, and S-3452YKF from Toa Synthetic Products, Cybinol AT-193, AT-D40, AT-D50, AT-D45, AT-191, AT-260NT, ATR-1, ATR-373, and ATR-347 from SAIDEN Chemicals, CT-5030 from DIC, and Nissetsu KP-2500 from Nippon Carbide Industries.

[0054] Furthermore, Patent Document 8 discloses a heat-sensitive adhesive composed of a fluorinated thermoplastic rubber including acrylic polymers, but this heat-sensitive adhesive is not the adhesive used in commercially available adhesive tapes. Since acrylic polymers are rubbery, they have almost no adhesiveness. Although it can be used as a heat-sensitive adhesive, it cannot be used as a pressure-sensitive adhesive pressed at room temperature. If a crosslinking agent is added to this adhesive and crosslinking is performed before bonding, the adhesiveness and bonding properties will disappear. Therefore, if it is not applied to the bonding surface before crosslinking, the desired bonding properties cannot be obtained. Also, Patent Document 9 discloses a rubber composition, which is formed by combining a specific blend of fluororubber and acrylic rubber with organic peroxides, etc. Similar to the invention described in Patent Document 8, the molded article obtained from the disclosed rubber composition is rubbery and is not the adhesive used in commercially available adhesive tapes. It has almost no adhesiveness at room temperature and cannot be used as a pressure-sensitive adhesive.

[0055] Since any of these inventions are based on fluororubber combined with rubber-like acrylic polymers, they cannot achieve the adhesiveness that this invention aims to achieve. Although they can adhere to surfaces such as glass, in cases where the rubber surface is formed into a 30-degree angle and a steel ball with a diameter of 4.8 mm is placed, the steel ball will roll.

[0056] The acrylic adhesive is blended in a ratio of 10 to 400 parts by weight, preferably 25 to 250 parts by weight, relative to 100 parts by weight of modified fluororubber. If the blending amount is less than this, the adhesion will decrease; on the other hand, if the amount is more than this, the heat resistance or solvent resistance will deteriorate. The degree of adhesion can be adjusted according to the amount of acrylic adhesive. By blending the acrylic adhesive into the modified fluororubber, it becomes possible to adjust the desired adhesion and bonding properties that cannot be obtained by the modified fluororubber alone.

[0057] As a blending method, a common practice is to dissolve the modified fluororubber in a solvent and then blend it with a solution-polymerized acrylic adhesive solution by stirring. Alternatively, methods such as latex modification of the fluororubber with an alkali followed by mixing the latex with the acrylic adhesive can be used, or methods such as mixing solid modified fluororubber with a solvent-free acrylic adhesive using rollers or a kneader can be employed.

[0058] By further adding a crosslinking agent to the fluororubber composition, the terminal functional groups of the prepolymerized fluororubber react with the crosslinking agent, and then the crosslinking agent reacts and crosslinks with the substrate, thereby improving the durability, liquid resistance, and chemical resistance.

[0059] As a crosslinking agent, there are no particular limitations as long as it can be cured by heat treatment. One or more thermosetting resins such as epoxy resin, phenolic resin, xylene resin, guanidine resin, diallyl phthalate resin, vinyl ester resin, unsaturated polyester resin, furan resin, polyimide resin, polyamine ester resin, cyanate ester resin, maleimide resin, benzocyclobutene resin, butadiene resin, aromatic diamine compounds, and aliphatic diamine compounds can be used. From the viewpoint of reactivity, heat resistance, and adhesion to the substrate, epoxy resin is preferred. From the viewpoint of service life, aromatic diamine compounds are preferred. Since epoxy resins and aromatic diamine compounds not only improve adhesion to the substrate but also achieve cross-linking reactions with modified fluororubber and acrylic adhesives, they contribute to improved adhesion to modified fluororubber and acrylic adhesives in the cured adhesive composition. This also enhances the compatibility in the coating solution and improves the solvent resistance, chemical resistance, water resistance, and water vapor resistance of the dried coating film. As long as cross-linking agents such as epoxy resins are used, the cross-linking reaction will occur even in the presence of oxygen and air. Therefore, even without using pressure to isolate air and oxygen for the cross-linking reaction, cross-linking can still be achieved through coating and oven drying, allowing it to bond with the target material.

[0060] Examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin; phenolic resins such as cresol varnish type epoxy resin; phenolic resins such as bisphenol A varnish type epoxy resin; alicyclic epoxy resins; aliphatic chain epoxy resins; dipyropropyl ethers of biphenol; dipyropropyl ethers of naphthalene glycol; dipyropropyl ethers of phenols; dipyropropyl ethers of alcohols; and their alkyl-substituted derivatives and hydrides, etc. Cresol varnish type epoxy resin is preferred. One type of epoxy resin can be used alone, or two or more types can be used in combination.

[0061] As polyamine compounds, 4,4'-methylbis(2-ethyl-6-methylaniline), diaminodiphenylamine, diaminodiphenylmethane, m-phenylenediamine, diethylenetriamine, triethylenetetramine, isophorone diamine, etc., can be used. From the viewpoints of adhesive liquid life, adhesive sheet life, and heat resistance, aromatic diamine compounds are better than aliphatic compounds.

[0062] The crosslinking agent is used in a ratio of 1 to 50 parts by weight, preferably 4 to 20 parts by weight, relative to 100 parts by weight of modified fluororubber. By combining with a thermosetting resin, adhesion, bonding to the substrate, solvent resistance, and durability will increase. If the amount is less than this, the bonding strength will decrease, and the liquid resistance and durability will decrease. If the amount is more than this, the compatibility will deteriorate, the adhesion will disappear, and the material will harden.

[0063] As a crosslinking curing catalyst, imidazole compounds such as 2-methylimidazolium, 2-ethyl-4-methylimidazolium, 2-undecylimidazolium, 2-heptadecylimidazolium, 2-phenylimidazolium, 1-benzylimidazolium, 1-benzyl-2-methylimidazolium, 2,4-diamino-6-[2-methylimidazoline-(1)]-ethyl, s-triazine, etc. are used. The curing catalyst is used at a ratio of 0.1 to 5 parts by weight, preferably 0.2 to 2.5 parts by weight, relative to 100 parts by weight of modified fluororubber. If the proportion of curing catalyst is less than this, the curing of fluororubber will be slower and the crosslinking will be less. Conversely, if the curing catalyst is used at a higher proportion, the stability of the adhesive organic solvent solution will decrease over time due to the increased curing speed of fluororubber, the adhesion will decrease due to the decreased storage stability of the coated sheet, and the adhesion will decrease due to the increased crosslinking density or catalyst residue. Depending on the type of epoxy resin or the adjustment of the curing speed, there are also cases where heat treatment is used instead of a catalyst.

[0064] Without prejudice to the purpose of the present invention, in order to adjust the adhesion and bonding properties, tackifying resins, plasticizers, liquid rubbers, liquid resins, fillers, etc., may be appropriately added or used in the fluororubber adhesive composition. Here, depending on the heating temperature and heating time after bonding to the other material, there may be a situation where the adhesive strength increases and the adhesive is transferred to the other material. Therefore, in order to prevent such transfer, the amount of crosslinking agent may be reduced or appropriately added, and plasticizers, liquid rubbers, liquid resins, etc. may be used.

[0065] As a tackifying resin, examples include rosin ester tackifying resins with a hydroxyl value of less than 40 mg KOH / g, terpene resins, terpene phenol resins, coumarin indole resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5~9 copolymer petroleum resins.

[0066] Examples of plasticizers include phthalate plasticizers, fatty acid diester plasticizers, trimellitic acid ester plasticizers, epoxy plasticizers, phosphate ester plasticizers, ether plasticizers, polyester plasticizers, chlorine plasticizers, etc.

[0067] As liquid rubbers, examples include isoprene, 1,4-polybutadiene, NBR, HNBR, etc., with a viscosity of 10~100,000 mPa·s.

[0068] Examples of liquid resins include terpene resins, epoxy resins, polyamide resins, acrylic resins, 1,2-polybutadiene, polyether polycarbonate, polyethylene glycol, etc., with a viscosity of 10 to 100,000 mPa·s.

[0069] As fillers, known materials can be used, such as metal hydroxides like aluminum hydroxide and magnesium hydroxide, or metal oxides like aluminum oxide, antimony oxide, tin oxide, titanium oxide, and manganese oxide, as well as inorganic fillers, reinforcing materials, various organic flame retardants, and inorganic flame retardants like silicon oxide, calcium silicate, aluminum silicate, calcium carbonate, silicon nitride, aluminum nitride, boron nitride, talc, mica, and kaolin. When the maximum particle size of the filler is larger than the coating thickness of the adhesive, unevenness will occur on the coating sheet, so the adhesion can be adjusted by matching the particle size with the filler amount. To improve adhesion, it is preferable to add less than 3% of the filler, or none at all.

[0070] Any solvent used as a component of a fluororubber adhesive may be used without particular restriction, as long as it is an organic solvent that can dissolve the fluororubber. Examples include ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, di-n-propyl ketone, diisobutyl ketone, phorone, isophorone, cyclohexanone, and cyclohexanone; aromatic hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; and alcohol solvents such as ethanol, 2-propanol, n-butanol, pentanol, and heptanol. These solvents may also be used as mixed solvents of two or more types.

[0071] Examples of suitable substrates for fluororubber adhesive compositions include reinforcing films such as polyimide films, polyetheretherketone films, polyphenylene sulfide films, aromatic polyamide (aramid) films, polyethylene naphthalate films, liquid crystal polymer films, polyethylene terephthalate films, polyethylene films, polypropylene films, TPX films, fluoropolymer films, copper, silver, gold, tin, aluminum, indium, or alloys thereof. There are also cases where metals, release films, peel-off films, or release papers are coated and then adhered to the reinforcing film or metal for transfer printing.

[0072] The resin material constituting the substrate film may be mixed with antioxidants, ultraviolet absorbers, plasticizers, pigments, dyes, and various additives as necessary. Known or conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and primer coating may also be applied. Such surface treatments can, for example, improve the adhesion (anchoring of the adhesive layer) between the substrate film and the adhesive layer. The thickness of the substrate film is typically used in the range of 5 to 200 μm, and preferably in the range of 10 to 100 μm. A substrate film thickness within this range is preferable due to its excellent adhesion to and peelability from the adhered material.

[0073] As an adhesive coating method, for example, the concentration of the solid component is adjusted to 10-50% by weight, preferably 15-40% by weight, and then coated to a thickness of 5-200 μm after drying. As a coating method, in addition to roller coating, die coating, and doctor blade coating, partial coating by screen printing, dispenser, or inkjet printing can also be performed. The coating liquid is adjusted to a viscosity suitable for each coating method. For example, the viscosity for roller coating is preferably 500-5000 mPa·s, and the concentration of the solid component is adjusted appropriately according to the air temperature or liquid temperature. For example, an organic solvent solution of the above adhesive composition is prepared, coated onto a resin film layer such as polyimide to form an adhesive layer, and then dried at approximately 50-200°C for approximately 1-15 minutes to obtain an adhesive film. When acrylic adhesives contain low molecular weight compounds, foaming may occur when heated after lamination. Therefore, in such cases, the drying temperature after coating can be increased to 200°C.

[0074] The bonding can be performed according to the JISZ0237 2009 Test Method for Adhesive Tapes and Sheets, corresponding to ISO 29862:2007, 29863:2007, and 29864:2007, using a roller or roller laminator, at room temperature or with heating to achieve adhesion. Furthermore, in a treatment using heated air at approximately 150-200°C for approximately 10 seconds to 3 hours under vacuum or heat pressure (oven crosslinking), further treatment at approximately 150-200°C for approximately 1 minute to 15 hours can further improve adhesion. After bonding, even without pressure, heating in an oven or similar environment at approximately 80-200°C for approximately 1 minute to 24 hours can also improve adhesive strength. [Example]

[0075] Next, embodiments of the present invention will be described.

[0076] Reference Example 1 [Preparation of Fluororubber Latex] 15 kg of water and 2.5 g of emulsifier (Neos product FS-1110) were added to a 30 L stainless steel pressure vessel equipped with a stirrer. The internal space was then fully purged with nitrogen. 1,285 g of vinylidene fluoride [VdF] and 1,831 g of hexafluoropropylene [HFP] were then introduced, raising the temperature inside the reaction vessel to 70 °C. The pressure inside the reactor at 70 °C was 3.09 MPa.

[0077] Using the same weight ratio of VdF / HFP mixed gas as initially introduced, pressurize until the internal pressure reaches 24 kgf / cm² G. Then, pressurize 10 g of diethyl malonate to raise the internal temperature to 80°C. Initiate the polymerization reaction by pressing an aqueous solution of polymerization initiator (5 g of ammonium persulfate dissolved in 150 g of water) into the autoclave. At the point where the internal pressure drops to 2.842 MPa, pressurize the same VdF / HFP mixed gas in batches until the internal pressure reaches 2.94 MPa. Repeat this process whenever the internal pressure drops to 2.842 MPa until the internal pressure reaches 2.94 MPa. After the polymerization reaction begins, the batch addition of the mixed gas is stopped 3 hours after the first addition. The batch addition of the VdF / HFP mixed gas of the same composition is then stopped. Subsequently, the unreacted gas in the autoclave is flushed to stop the reaction, resulting in an aqueous emulsion (fluororubber latex). The fluororubber latex yield is 23 kg (solid component concentration 32%, solid fluororubber 7,310 g).

[0078] [Modification of fluororubber] 1 kg of fluororubber latex was stirred at a liquid temperature of 25°C, while 40 g of a 10% by weight sodium lauryl solution at a liquid temperature of 25°C was added dropwise. The latex was stirred at 100 rpm, and 119.2 g of a DBU aqueous solution containing 19.2 g of DBU at a liquid temperature of 25°C was added simultaneously. The mixture was then stirred at 100 rpm for 5 hours at room temperature to modify the fluororubber.

[0079] [Salting out of fluororubber] While stirring 3 kg of a 20% by weight NaCl aqueous solution at 400 rpm, the above modified fluororubber latex solution was added dropwise and stirred for 5 minutes to achieve micro-dispersion. Then, 5 L of water was added and stirred for 5 minutes. After standing for 3 minutes, the fluororubber was allowed to precipitate. The supernatant was removed to perform salting out of the modified fluororubber latex solution.

[0080] [Water washing of fluororubber] Repeat 5 times by adding 5L of water, stirring at 400rpm for 5 minutes, letting stand for 2 minutes, washing the modified fluororubber with water to allow it to precipitate and removing the supernatant, then repeat 5 times by adding 5L of water, stirring at 400rpm for 30 minutes, letting stand for 2 minutes, washing the modified fluororubber with water to allow it to precipitate and removing the supernatant.

[0081] [Drying of Fluororubber] The obtained modified fluororubber was washed and placed on a mesh at a height of less than 30 mm, and dried in an oven at 80°C for 15 hours. The modified fluororubber after drying had a Muney viscosity ML1+10 (121°C) of 10 and a weight average molecular weight Mw of 200,000.

[0082] Reference Example 2 In Reference Example 1, no modification step of fluororubber was performed. The unmodified fluororubber after drying had a Muney viscosity ML1+10 (121°C) of 50 and a weight average molecular weight Mw of 500,000.

[0083] Reference Example 3: 100g of dried, unmodified fluororubber obtained in Reference Example 2 was mixed with 900g of methyl isobutyl ketone and 100g of 20% potassium hydroxide solution. The mixture was stirred at 60°C and 100rpm for 8 hours. Then, 9% sulfuric acid was added dropwise until the pH reached 3, thereby modifying the fluororubber. The modified fluororubber solution was then added dropwise to ethanol while stirring. Following this, the mixture was washed with water and dried in the same manner as in Reference Example 1. The dried fluororubber had a Muney viscosity ML1+10 (121°C) of 30 and a weight-average molecular weight Mw of 300,000.

[0084] Reference Example 4 [Preparation of Acrylic Adhesive Solution] 49 parts by weight of ethyl acrylate, 49 parts by weight of butyl acrylate, 1 part by weight of monobutyl fumarate, and 150 parts by weight of ethyl acetate were added to a reaction vessel equipped with a stirring blade, thermometer, nitrogen inlet pipe, and cooler. The mixture was stirred at 150 rpm and purged with nitrogen for 30 minutes. Then, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (2,2'-Azobisisobutyronitrile) was added as a polymerization initiator. The liquid temperature was maintained at approximately 65°C for 6 hours to prepare an acrylic adhesive solution with a solid content concentration of 40% by weight. The weight average molecular weight (Mw) was 220,000, and the Tg was -43°C.

[0085] Reference Example 5: In Reference Example 4, 99 parts by weight of ethyl acrylate were used instead of butyl acrylate to prepare an acrylic adhesive solution with a solid content concentration of 40% by weight. The weight average molecular weight (Mw) was 110,000, and the Tg was -18°C.

[0086] Example 1 100 parts by weight of modified fluororubber obtained in Reference Example 1 250 parts by weight of acrylic adhesive solution obtained in Reference Example 4 (equivalent to 100 parts by weight of solid components) 8 parts by weight of o-cresol phenolic varnish type epoxy resin (DIC Corporation product N-695) 0.5 parts by weight of imidazole curing catalyst (Shikoku Chemical product Curezol 2E4MZ) 684 parts by weight of butyl acetate The above components were dissolved to obtain a fluororubber composition.

[0087] Example 2 In Example 1, the amount of acrylic adhesive solution was changed to 125 parts by weight (equivalent to 50 parts by weight of solid components), and the amount of butyl acetate was changed to 559 parts by weight.

[0088] Example 3 In Example 1, the amount of acrylic adhesive solution was changed to 1000 parts by weight (equivalent to 400 parts by weight of solid components), and the amount of butyl acetate was changed to 1430 parts by weight.

[0089] Example 4 In Example 1, the same amount (100 parts by weight) of the modified fluororubber obtained in Reference Example 3 was used as the fluororubber.

[0090] Example 5 In Example 1, the same amount (250 parts by weight; 100 parts by weight relative to the solid content) of the acrylic adhesive solution obtained in Reference Example 5 was used as the acrylic adhesive solution, and the amount of butyl acetate was changed to 684 parts by weight.

[0091] Example 6 In Example 1, 1.4 parts by weight of 4,4'-methylenebis(2-ethyl-6-methylaniline) (KUMIAI Chemical Industry Product CureHard MED-J) was used, and the amount of butyl acetate was changed to 690 parts by weight.

[0092] Example 7 In Example 2, o-cresol phenolic varnish-type epoxy resin and imidazole curing catalyst were not used, and the amount of butyl acetate was changed to 750 parts by weight.

[0093] Example 8 In Example 1, the amount of acrylic adhesive solution was changed to 500 parts by weight (equivalent to 200 parts by weight of solid components), the amount of o-cresol phenolic varnish epoxy resin was changed to 20 parts by weight, and the amount of butyl acetate was changed to 982 parts by weight.

[0094] Comparative Example 1 In Example 1, modified fluororubber was not used, and the amount of butyl acetate was changed to 552 parts by weight.

[0095] Comparative Example 2 In Example 1, the same amount (250 parts by weight; 100 parts by weight of solids) of unmodified fluororubber obtained in Reference Example 1 was used instead of modified fluororubber.

[0096] Comparative Example 3 The unmodified fluororubber obtained in Reference Example 2 consisted of 100 parts by weight of calcium hydroxide (Omi Chemical Industry Co., Ltd. Caldic ♯1000), 3 parts by weight of magnesium oxide (Kyowa Chemical Industry Co., Ltd. MgO ♯30), 6 parts by weight of vulcanizing agent (DuPont's Currative ♯30), 6 parts by weight of crosslinking accelerator (Beikō Chemical Industry Co., Ltd. BTPPC; 0.4 parts by weight of benzyltriphenylphosphonium chloride), and 461 parts by weight of butyl acetate. The fluororubber composition was obtained by dissolving the above components.

[0097] Comparative Example 4 In Example 1, the same amount (100 parts by weight) of acrylic rubber (Unimatec product PA522HF) was used instead of acrylic adhesive solution, and the amount of butyl acetate was changed to 834 parts by weight.

[0098] Comparative Example 5 In Example 1, acrylic adhesive solution was not used, and the amount of butyl acetate was changed to 434 parts by weight.

[0099] The fluororubber compositions obtained in the above embodiments and comparative examples were used as adhesives for adhesive solution solubility tests, curing tests, solvent resistance tests, adhesive evaluation, initial adhesion evaluation, and adhesion tests after heat resistance tests. For the solvent resistance test, adhesive evaluation, initial adhesion evaluation, and adhesion tests after heat resistance tests, the fluororubber composition was coated onto a 25 μm thick polyimide film (Toray DuPont product Kapton EN), and the solvent was dried at 140°C for 5 minutes to create an adhesive sheet with a coating thickness of 50 μm for use. Adhesive solution solubility test: After dissolving each component of the composition, visually confirm the solubility state after standing at room temperature for 3 hours to check for layer separation. If no layer separation is observed, it is judged as having compatibility and rated as ○. If layer separation is observed, it is judged as having no compatibility and rated as ×. Curing test: Coat the fluororubber composition onto the release film (Nitoflon No. 900UL, Nitto Denko Products), dry the solvent at 140°C for 5 minutes to form a thickness of 50μm, vacuum dry at room temperature for 1 hour, and then peel off the release film. Use an ENEOS Materials Co., Ltd. Curelastometer to test according to JIS K corresponding to ISO 6502-2:2018. 6300-2, For adhesive sheets made of 5 overlapping sheets with a thickness of 250μm, a torsional vibration parallel plate vulcanization test is performed at 170℃, and the change in torque is measured. Since the torque value increases as crosslinking progresses, if an increase in torque value is observed after 100 minutes, it is judged that crosslinking has occurred and is rated ○; if no increase in torque is observed, it is judged that crosslinking has not occurred and is rated ×. Solvent resistance test: The adhesive sheet is immersed in methyl ethyl ketone for 5 minutes at room temperature. Visual inspection is used to confirm whether the adhesive is dissolved by methyl ethyl ketone. If it is not dissolved, the fluororubber is judged to have crosslinked and is rated ○; if it is dissolved, the fluororubber is judged not to have crosslinked and is rated ×. Adhesion evaluation: According to JIS Z0237 (tilting ball adhesion test) corresponding to ASTM D3121. Using double-sided tape, adhere the film side of the adhesive sheet to a 30-degree angled surface. Place steel balls No. 5 (4.8mm diameter), No. 13 (10.3mm diameter), No. 19 (15.1mm diameter), No. 25 (19.8mm diameter), and No. 32 (25.4mm diameter) on the surface. Observe whether they roll. If they do not roll, rate it as ○, and if they roll, rate it as ×. The larger the steel ball that does not roll, the higher the adhesion. Initial adhesion evaluation: According to JIS Z0237 corresponding to ISO 29862:2007, use methyl ethyl ketone to bond a 0.2mm thick SUS430 plate and a 0.After degreasing, a 2mm thick aluminum plate was laminated with a 25μm thick polyimide film (Kapton EN) using roller lamination at room temperature. A 90° peel test was then performed (test environment: 23℃±2℃, 50%RH±10%RH; test piece shape: 10mm wide), and the peel strength was measured. Higher peel strength indicates higher adhesion, with 0.3N / mm or higher being preferred. Adhesion evaluation after heat resistance test: According to JIS Z0237 corresponding to ISO 29862:2007, roller lamination was performed at 100℃ to laminate with a 25μm thick polyimide film (Kapton EN). A 90° peel test was then performed at 150℃ or 200℃ for 250 hours, 500 hours, and 1000 hours, and the peel strength was measured. Higher peel strength indicates higher heat resistance, with 0.3N / mm or higher being preferred.

[0100] The results obtained are shown in Tables 1-2 below. Furthermore, as an adhesion evaluation test, for each comparative example, the film side of the adhesive sheet was further attached to an inclined plane with a 5-degree angle using double-sided tape, and a No. 5 (4.8 mm in diameter) steel ball was placed to confirm whether it would roll.

[0101] Based on the results of the above examples and comparative examples, the following conclusions can be drawn. (1) In the examples using modified fluororubber, the adhesion, bonding, and heat resistance were high. It was found that the more acrylic adhesive used, the higher the adhesion and bonding tended to be (Examples 1-3). (2) Compared to the case of using inorganic base to modify fluororubber, the case of using organic base to modify fluororubber could achieve high adhesion and bonding (Examples 1, 4). (3) It was found that the lower the glass transition temperature of the acrylic adhesive, the higher the adhesion tended to be (Examples 1, 5). (4) When more diamine compounds were added, the adhesion decreased slightly, but the heat resistance increased (Examples 1, 6). (5) When no crosslinking agent was used, or when the amount of crosslinking agent increased, the adhesion tended to decrease (Examples 1-2, 7-8). (6) In the case of acrylic adhesive that did not contain fluororubber, although adhesion was found, the bonding strength after the heat resistance test was lower (Comparative Example 1). (7) When using unmodified fluororubber, the initial bond strength or tackiness is low. Also, the solvent resistance is poor (Comparative Example 2). (8) When using components composed of commonly used ingredients as fluororubber components, although cross-linking occurs, the initial bond strength is low and the tackiness is low (Comparative Example 3). (9) When acrylic rubber is used instead of an acrylic adhesive, the initial bond strength is low and no tackiness is observed (Comparative Example 4). (10) When no acrylic adhesive is used, the initial bond strength is low and the tackiness is low (Comparative Example 5).

[0102] As the results above show, some of the comparative examples exhibited low adhesion, weak bond strength during room temperature bonding, and poor heat resistance, rendering them unusable as adhesives for demonstrating heat resistance. [Industrial Applicability]

[0103] The fluororubber adhesive composition of the present invention can be effectively used in tapes, adhesives, electronic parts, automotive parts, industrial parts, as well as in chemical plants, shock absorbers, vibration damping plates, heat insulation materials, solar cell panels, etc.

Claims

1. A fluororubber adhesive composition comprising an acrylic adhesive blended with a modified fluororubber having a mulli viscosity ML1+10 (121°C) of 10 to 50 having unsaturated bonds or unsaturated bonds and functional groups, wherein the acrylic adhesive contains an acrylic copolymer having a glass transition temperature Tg below 0°C.

2. The fluororubber adhesive composition of claim 1, wherein the functional group of the modified fluororubber is a carboxyl group.

3. The fluororubber adhesive composition as requested in item 1, wherein the fluororubber is an alkali-modified fluororubber, and the alkali-modified fluororubber has a mulli viscosity ML1+10 (121℃) after alkali modification that is 20~70 lower than that before alkali modification.

4. The fluororubber adhesive composition of claim 1, wherein the weight average molecular weight (Mw) of the modified fluororubber is 300,000 or less.

5. The fluororubber adhesive composition of claim 1, wherein the weight average molecular weight Mw of the acrylic copolymer is 100,000 to 1,000,000.

6. The fluororubber adhesive composition of any one of claims 1 to 5, wherein 10 to 400 parts by weight of acrylic adhesive are incorporated relative to 100 parts by weight of modified fluororubber.

7. The fluororubber adhesive composition of claim 1, wherein, relative to 100 parts by weight of modified fluororubber, it further contains 1 to 50 parts by weight of crosslinking agent.

8. The fluororubber adhesive composition of claim 7, wherein the crosslinking agent is a curing resin and / or an aromatic polyamine.

9. The fluororubber adhesive composition of claim 7 or 8, wherein, relative to 100 parts by weight of modified fluororubber, imidazole is used as a crosslinking curing catalyst and contains 0.1 to 5 parts by weight of imidazole.

10. The fluororubber adhesive composition of claim 7, wherein no acid acceptors are added.

11. An adhesive sheet comprising laminating a fluororubber composition as claimed in claim 1 onto one or both sides of a substrate.

12. The fluororubber adhesive composition of claim 1, wherein when a steel ball with a diameter of 4.8 mm is placed on an adhesive surface formed with an angle of 30 degrees, the steel ball has adhesive properties that prevent the steel ball from rolling.