JP6333010B2 - Manufacturing method of sealing material - Google Patents

Description

  The present invention relates to a method for manufacturing a sealing material such as a gasket or packing.

  As a representative example of sealing materials such as gaskets and packings used in various applications, a rubber system obtained by crosslinking (vulcanizing) a rubber composition containing a rubber component and a crosslinking agent (vulcanizing agent) There is a sealing material. As the rubber component, for example, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR) depending on the application (application location) and required characteristics of the sealing material. ), Butyl rubber (IIR), fluorine rubber (FKM), silicone rubber (Q), and the like are used (for example, see Patent Documents 1 to 3).

  As the cross-linking agent, use of sulfur in addition to organic peroxide is conventionally known. However, when using sulfur, unlike the case of using organic peroxide, sufficient heat resistance cannot be imparted to the sealing material. There is a tendency. In addition, the use of sulfur has a problem of poor cleanliness. For example, the problem that the member adjacent to a sealing material corrodes by the sulfur component contained in a sealing material may arise. Therefore, it is preferable to use an organic peroxide as a crosslinking agent, particularly when heat resistance is required.

JP-A-9-157464 JP 2012-087254 A International Publication No. 2010/131559

  On the other hand, the conventional method for producing a sealing material by crosslinking a rubber composition containing an organic peroxide crosslinking agent has the following problems.

  [A] A rubber composition using an organic peroxide crosslinking agent generally starts crosslinking in a relatively short time from the start of mold molding and has a short flowable time in the mold. Since the cross-linking behavior is very long until the cross-linking is completed, it takes a long time for molding even though the cross-linking starts at an early stage.

  [B] In addition to the low molecular weight components (or low molecular weight components produced by the reaction thereof) originally contained in the rubber component of the raw material, the unreacted components (rubber components and crosslinking agents) are compared in the resulting sealing material. Easy to survive. As a result, it is difficult to obtain a sealing material excellent in low outgas characteristics (property of releasing low molecular weight components and unreacted components as gas). Sealing materials with poor low outgassing characteristics can contaminate objects in contact with them (typically the fluid to be sealed by the sealing material).

  Regarding the above problem [a], it is conceivable to increase the molding temperature (crosslinking temperature) in order to shorten the molding time (crosslinking time). It gets even faster.

  Further, as a method that can improve the problem [a], it is conceivable to add a large amount of a plasticizer to the rubber composition in order to increase the fluidity of the unvulcanized rubber composition in the mold. . However, the rubber composition containing a large amount of plasticizer has the following problems.

[A] The plasticizer or components derived from it are volatilized by heating during molding, resulting in mold contamination.
[A] The above volatile component adheres to the surface of the sealing material, resulting in a product defect (appearance defect or quality defect) such as giving uneven gloss to the surface.
[C] Because it contains a large amount of plasticizer not involved in crosslinking, the heat resistance of the sealing material is inferior compared to the case where no plasticizer is contained.
[D] By including a plasticizer or a component derived therefrom, it is difficult to obtain a sealing material excellent in low outgas characteristics, and an object that contacts the sealing material (typically, a fluid to be sealed by the sealing material) May contaminate.

  The present invention has been made in view of the above problems, and an object thereof is a method for producing a sealing material by crosslinking a rubber composition containing an organic peroxide as a crosslinking agent, which comprises a plasticizer. An object of the present invention is to provide a method capable of producing a sealing material excellent in low outgas characteristics with good moldability without using it.

The present invention provides the manufacturing method of the sealing material shown below.
[1] 100 parts by weight of a rubber component;
A composite cross-linking agent containing 0.5 to 5 parts by weight of an organic peroxide and a nitrooxide compound;
2 to 20 parts by weight of a liquid co-crosslinking agent that is at least one selected from the group consisting of trimethylolpropane trimethacrylate and trimethylolpropane triacrylate;
A step of cross-linking a rubber composition for a sealing material comprising:
A step of heat-treating the resulting crosslinked molded article;
The manufacturing method of the sealing material containing this.

[2] The production method according to [1], wherein the heat treatment time is 0.5 to 32 hours.
[3] The production method according to [1] or [2], wherein the content of the nitrooxide compound is in the range of 1 to 20% by weight of the content of the organic peroxide.

  [4] The production method according to any one of [1] to [3], wherein the rubber composition for a sealing material does not contain a plasticizer.

  [5] The method according to any one of [1] to [4], wherein the rubber component is at least one selected from the group consisting of ethylene-propylene-diene rubber, hydrogenated nitrile rubber, and fluororubber.

  According to the present invention, even when the rubber composition does not contain a plasticizer, and despite containing an organic peroxide as a cross-linking agent, a sealing material having excellent low outgas characteristics is obtained with good moldability. Can be manufactured. The method of the present invention is used in applications where low outgas characteristics are required [contamination (and degradation associated therewith) due to outgassing of a fluid (liquid, gas, etc.) to be sealed by a sealing material]. Suitable for manufacturing sealing materials.

Rubber composition for sealing material of Reference Example 1 and Comparative Reference Example 3 and rubber composition for sealing material obtained by adding a crosslinking retarder to the rubber composition for sealing material of Comparative Reference Example 3 (Rubber for sealing material of Comparative Reference Example 9) It is a figure which compares the crosslinking characteristic (crosslinking behavior) of a composition.

The manufacturing method of the sealing material according to the present invention is as follows:
(1) 100 parts by weight of rubber component [A], 0.5 to 5 parts by weight of an organic peroxide and a composite crosslinking agent [B] containing a nitrooxide compound, trimethylolpropane trimethacrylate and trimethylolpropane triacrylate A step of crosslinking and molding a rubber composition for a sealing material containing 2 to 20 parts by weight of a liquid co-crosslinking agent [C] that is at least one selected from the group consisting of: (crosslinking molding step); and (2) obtained Process for heat treatment of cross-linked molded product (heat treatment process)
including.

(1) Crosslinking molding process Examples of the rubber component [A] contained in the rubber composition for a sealing material to be crosslinked include ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), and nitrile rubber (NBR). Acrylonitrile butadiene rubber), hydrogenated nitrile rubber (HNBR; hydrogenated acrylonitrile butadiene rubber), butyl rubber (IIR), fluorine rubber (FKM), silicone rubber (Q), and the like. Among them, EPDM, HNBR, FKM, and the like are preferable because they have good characteristics as a rubber for a sealing material. The rubber component [A] may be used alone or in combination of two or more.

  EPDM is a rubber component that is excellent in heat resistance, chemical resistance, cleanliness, etc., and is cheaper than NBR, HNBR, FKM, Q, etc. It is. A rubber composition using EPDM as the rubber component [A] and using an organic peroxide as the cross-linking agent may be inferior in molding processability compared to NBR, Q, etc. (for example, the adhesiveness of the cross-linked molded product) However, when the cross-linked molded product is taken out, a part thereof adheres to the mold and contaminates the mold, which tends to occur more easily than NBR, Q, and the like. However, even in the case of using a rubber component that is not relatively high in moldability, such as EPDM, according to the present invention, the above-described problem of mold contamination is suppressed, and low outgas characteristics are achieved. An excellent sealing material can be manufactured.

  EPDM is a ternary copolymer composed of a structural unit derived from ethylene, a structural unit derived from propylene, and a structural unit derived from a diene monomer. In EPDM, the rubber properties can be controlled by adjusting the content ratio between the structural unit derived from ethylene and the structural unit derived from propylene. For example, when the ratio of the structural unit derived from ethylene is increased, the chemical resistance and the crystallinity (and hence the mechanical strength) of the rubber tend to increase. On the other hand, when the ratio of the structural unit derived from ethylene is increased, EPDM molding processability and fluidity tend to decrease.

  In order to improve the molding processability of EPDM and to produce a higher-quality sealing material, the content of the structural unit derived from ethylene in EPDM is preferably 65% by weight or less, and preferably 60% by weight or less. It is more preferable. If content of the structural unit derived from ethylene is 65 weight% or less, while being able to give favorable fluidity | liquidity to EPDM, favorable heat resistance and sealing property can be provided to a sealing material. On the other hand, when the content of the structural unit derived from ethylene is too low, the resulting sealing material has insufficient tensile strength. Therefore, the content of the structural unit derived from ethylene is preferably 45% by weight or more, and more preferably 50% by weight or more.

  Specific examples of the diene monomer constituting EPDM include 5-ethylidene-2-norbornene (ENB), dicyclopentadiene (DCPD), 1,4-hexadiene (1,4-HD), methyltetrahydroindene, 5-methylene- Non-conjugated diene monomers such as 2-norbornene, cyclooctadiene, dicyclooctadiene are included. Among these, it is preferable to use ENB and 1,4-HD because EPDM shows a good crosslinking rate (vulcanization rate) and is excellent in heat resistance of the obtained sealing material. From the viewpoint of superiority, it is more preferable to use ENB. Only one diene monomer may be used alone, or two or more diene monomers may be used in combination.

  The content of the structural unit derived from the diene monomer in EPDM is preferably 1% by weight or more, and more preferably 3% by weight or more from the viewpoint of improving the crosslinking rate and the molding processability of the rubber composition. Further, considering the ease of deterioration of the sealing material due to a large amount of double bonds remaining after crosslinking, the content of the structural unit derived from the diene monomer is preferably 12% by weight or less. % Or less is more preferable.

  Specific examples of commercially available EPDM products that can be used in the present invention include, for example, “EPT” manufactured by Mitsui Chemicals, “Esprene” manufactured by Sumitomo Chemical Co., Ltd., JSR ) "EP" manufactured by LANXESS, "KELTAN" manufactured by LANXESS Corporation.

  As will be described later, from the viewpoint of improving the molding processability of the rubber composition, the viscosity of the rubber composition is 60 in Mooney viscosity [ML (1 + 4) 100 ° C.] at 100 ° C. measured according to JIS K6300-1. The following is preferable. Accordingly, in order to realize a rubber composition having such a viscosity, the viscosity of the rubber component to be used is preferably 50 or less, more preferably 48 or less in Mooney viscosity [ML (1 + 4) 100 ° C.]. preferable.

  An oil-extended rubber component is commercially available as a low Mooney viscosity product, which contains a large amount of the oil component. The use of such a rubber component is not preferable because it may cause the problems [A] to [D] described in the section [Problems to be Solved by the Invention] as in the case of containing a plasticizer.

  The composite crosslinking agent [B] contains an organic peroxide as a crosslinking agent for crosslinking the rubber component [A] and a nitrooxide compound. By using the composite cross-linking agent, it is possible to appropriately delay the cross-linking start time, extend the flowable time in the mold, and shorten the time from the start of cross-linking to the completion of cross-linking. Such cross-linking properties can improve the molding processability of the rubber composition and make the rubber composition suitable for various molding methods, particularly injection molding. Moreover, shortening the time from the start of crosslinking to the completion of crosslinking leads to a reduction in molding time and a reduction in molding cost. The use of the composite cross-linking agent does not decrease the final cross-linking density of the obtained sealing material, so that a sealing material having a desired cross-linking density and exhibiting desired excellent characteristics can be obtained.

  The use of the composite cross-linking agent is advantageous for the suppression of the mold contamination problem described above, in combination with the use of a predetermined amount of other predetermined blending components [A] and [C].

  On the other hand, it is known to add a crosslinking retarder to the rubber composition in order to delay the crosslinking start time, but the conventionally used crosslinking retarder can delay the crosslinking start time, There is a problem that the final crosslink density of the obtained sealing material is lowered.

  As the organic peroxide, a conventionally known crosslinking agent can be used. For example, dicumyl peroxide, t-butyl dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide can be used. Oxide, t-butyl dicumyl peroxide, benzoyl peroxide, acetyl peroxide, isobutyryl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, 2,5-dimethyl -2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, α, α'-bis (t-butylperoxyisopropyl) benzene, t -Butylperoxyisopropyl carbonate, parachlorobenzoyl peroxide, t-butyl perben Zoate, 3,3,5-trimethylhexanone peroxide, n-butyl-4,4-bis (t-butylperoxy) valerate, di-sec-butylperoxydicarbonate, 1,1-di (t-butyl) Peroxy) cyclododecane and the like. An organic peroxide may be used individually by 1 type, and may use 2 or more types together. Among them, dicumyl peroxide, α, α′-bis (t-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, n-butyl-4,4 -Bis (t-butylperoxy) valerate or the like can be preferably used.

  The composite crosslinking agent is added to the rubber composition so that the content of the organic peroxide is 0.5 to 5 parts by weight with respect to 100 parts by weight of the rubber component, preferably 0.8 to 4.5 parts by weight. It is added to the rubber composition. The amount of the composite crosslinking agent added is, for example, about 1 to 20 parts by weight or about 1 to 15 parts by weight. By setting the content of the organic peroxide to 0.5 parts by weight or more with respect to 100 parts by weight of the rubber component, a sufficient crosslinking density can be obtained. Thereby, good rubber elasticity, hardness, mechanical strength, heat resistance, and sealing properties can be imparted to the sealing material. Further, setting the content of the organic peroxide to 0.5 parts by weight or more with respect to 100 parts by weight of the rubber component is also advantageous for suppressing the above-described problem of mold contamination.

  On the other hand, the content of the organic peroxide with respect to 100 parts by weight of the rubber component being 5 parts by weight or less can suppress or prevent foaming and stickiness from occurring in the obtained sealing material, and the heat resistance of the resulting sealing material. This is advantageous in that the property and the sealing property can be improved.

Specific examples of the nitrooxide compound include, for example,
2,2,6,6-tetramethylpiperidine-1-oxyl,
4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl,
4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl,
4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl,
2,2,5,5-tetramethylpiperidine-1-oxyl,
Bis (2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl) sebacate,
4,4 ′-[(1,10-dioxo-1,10-decandiyl) bis (oxy)] bis [2,2,6,6-tetramethyl] -1-piperidinyloxy,
2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl monophosphate,
3-carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl and the like.

  Among the above, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 2,2,6,6-tetramethylpiperidine-1-oxyl, 4,4 ′-[(1, 10-Dioxo-1,10-decandiyl) bis (oxy)] bis [2,2,6,6-tetramethyl] -1-piperidinyloxy is preferably used.

  The content of the nitrooxide compound in the composite crosslinking agent is preferably in the range of 1 to 20% by weight of the content of the organic peroxide, more preferably in the range of 2 to 15% by weight, and still more preferably It is in the range of 2.5 to 10% by weight. By setting the content of the nitrooxide compound within this range, it is possible to obtain a good effect of delaying the start of crosslinking and a shortening effect of the crosslinking time.

  The composite crosslinking agent may be composed only of an organic peroxide and a nitrooxide compound, but may contain other components such as a filler component. Examples of the filler component include inorganic pigments (calcium carbonate, silica, clay, talc, etc.), organic pigments, resin components, and the like. The form of the composite crosslinking agent is not particularly limited, and may be a molded body (for example, a granular shape, a pellet shape, a sheet shape, etc.) in addition to a liquid or a powder. A filler may be used individually by 1 type and may use 2 or more types together.

  Examples of commercially available composite cross-linking agents that can be used in the present invention include, for example, “Luperox DC40P-SP2” (organic peroxide: 40% by weight of dicumyl peroxide, nitrooxide compound, manufactured by Arkema Co., Ltd.) under the trade name. : 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl 2.4% by weight, balance: filler); “Luperox F40P-SP2” (organic peroxide: α, α′-bis ( t-butylperoxyisopropyl) benzene 40% by weight, nitrooxide compound 3.8% by weight, balance: filler); “Luperox 101XL45-SP2” (organic peroxide: 2,5-dimethyl-2,5-di ( t-butylperoxy) hexane 45% by weight, nitrooxide compound and filler).

  The rubber composition for a sealing material includes, as a co-crosslinking agent, a liquid co-crosslinking agent (co-crosslinking agent that is liquid at room temperature and normal pressure) [C] composed of trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, or a mixture thereof. Including. In conventional rubber compositions for sealing materials, sulfur, sulfur compounds, quinone dioxime, ethylene glycol dimethacrylate, divinylbenzene, diallyl phthalate, triallyl isocyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, 1 , 2-polybutadiene, metal methacrylate, metal acrylate, and the like have been used as co-crosslinking agents without particular distinction. In the present invention, in order to obtain a desired effect, the specific liquid co-crosslinking agent is used. It is necessary to use [C]. That is, by using a specific liquid co-crosslinking agent [C], in combination with the use of a predetermined amount of other predetermined blending components [A] and [B], the case where no plasticizer is contained. In addition, it is possible to obtain a good effect of delaying the crosslinking start time and a shortening effect of the crosslinking time, and it is possible to produce a sealing material excellent in low outgas characteristics with good moldability.

  In addition, by using a specific liquid co-crosslinking agent [C], the crosslinking rate of the rubber composition can be adjusted, and the properties of the sealing material (for example, elongation properties, heat resistance, sealing properties, mechanical strength) can be improved. You can also.

  On the other hand, when a solid co-crosslinking agent (a co-crosslinking agent that is solid at normal temperature and pressure) or a liquid co-crosslinking agent other than the specific liquid co-crosslinking agent [C] is used, the other ingredients specified in the present invention Even when [A] and [B] are used in a predetermined amount, the desired effect as described above cannot be obtained. The above-described effects exhibited by the present invention are considered to be due to the improvement of the fluidity of the rubber composition by using the specific liquid co-crosslinking agent [C], particularly the fluidity at the initial stage of molding.

  The content of the liquid co-crosslinking agent [C] in the rubber composition for a sealing material is 2 to 20 parts by weight, preferably 5 to 20 parts by weight, more preferably 5 to 10 parts by weight per 100 parts by weight of the rubber component. Part. Thus, in order to obtain the desired effect more effectively, the liquid co-crosslinking agent [C] is preferably added in a relatively large amount compared to the addition amount of the conventional co-crosslinking agent. No adverse effects (for example, inhibition of the crosslinking reaction, etc.) due to the addition of a large amount are observed, and a sealing material having a desired crosslinking density can be obtained. As the content of the liquid co-crosslinking agent [C] is larger within the above range, the desired effect can be obtained more effectively and the hardness and heat resistance of the sealing material can be further improved while maintaining good elongation characteristics. It is possible to increase. In contrast, a co-crosslinking agent such as triallyl isocyanurate is in a liquid state, but if added in a large amount, it causes self-polymerization and inhibits a normal crosslinking reaction.

  When the content of the liquid co-crosslinking agent [C] is less than 2 parts by weight or more than 25 parts by weight with respect to 100 parts by weight of the rubber component, the fluidity of an appropriate rubber composition necessary for molding with good processability (Especially, fluidity at the initial stage of molding) cannot be ensured, and it tends to be difficult to obtain a high-quality sealing material due to defects during molding. In addition, when the content of the liquid co-crosslinking agent [C] is less than 2 parts by weight or more than 25 parts by weight with respect to 100 parts by weight of the rubber component, sufficient elongation characteristics, heat resistance, seal Tend to be unable to impart properties and / or mechanical strength.

  The rubber composition for sealing material can contain other components [D] other than the above components [A] to [C] as necessary. Examples of other components include fillers (meaning including extender pigments and colored pigments), anti-aging agents, antioxidants, vulcanization accelerators, processing aids, stabilizers, tackifiers, and silane couplings. And additives such as additives, plasticizers, flame retardants, mold release agents, waxes and lubricants. An additive may be used individually by 1 type and may use 2 or more types together.

  Specific examples of fillers include carbon black, silica, alumina, zinc oxide, titanium dioxide, clay, talc, diatomaceous earth, barium sulfate, calcium carbonate, magnesium carbonate, calcium oxide, mica, graphite, aluminum hydroxide, aluminum silicate, hydro Includes talcite, granular or powdered resin, metal powder, glass powder, ceramic powder and the like.

  Specific examples of the antioxidant include phenol derivatives, aromatic amine derivatives, amine-ketone condensates, benzimidazole derivatives, dithiocarbamic acid derivatives, thiourea derivatives and the like. Specific examples of the vulcanization accelerator include thiuram, thiazole, sulfenamide, and thiourea compounds.

  When the rubber composition for sealing materials contains said additive, the content may be the quantity normally used in the said field | area.

  However, in view of the object of the present invention as described above, the content of the plasticizer is preferably as small as possible (for example, 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 100 parts by weight of the rubber component). 2 parts by weight or less, more preferably 1 part by weight or less), and it is very preferable not to contain a plasticizer. By using a rubber composition that does not contain a plasticizer, the problems [a] to [e] described in [Problems to be solved by the invention] can be solved, and the outgas derived from the plasticizer can be reduced. It is possible to produce a sealing material that can be suppressed and that exhibits good heat resistance and sealing properties.

  In addition, the rubber composition for a sealing material of the present invention contains other additives that can cause contamination to an object in contact with the sealing material, such as a mold release agent, a wax, a lubricant, a liquid processing aid, and the like. It is preferable to reduce the amount as much as possible (for example, 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 2 parts by weight or less, even more preferably 1 part by weight or less based on 100 parts by weight of the rubber component). More preferably, no additive is contained.

  In addition, the plasticizer here is a plasticizer in a narrow sense (phthalate ester, adipate, aliphatic dibasic ester, phosphate ester, citrate ester, trimellit plasticizer, etc.) In addition, oils (naphthenic process oil, paraffinic process oil, aromatic process oil, vegetable oil, epoxidized vegetable oil, etc.) are also included.

  The rubber composition for a sealing material of the present invention uniformly kneads a rubber component [A], a composite crosslinking agent [B], a liquid co-crosslinking agent [C], and other components [D] that are optionally added. Can be prepared. As the kneader, conventionally known ones such as a mixing roll, a pressure kneader, an internal mixer (Banbury mixer) can be used. At this time, components other than the components that contribute to the vulcanization reaction, such as the composite crosslinking agent and the liquid co-crosslinking agent, are first kneaded uniformly, and then the components that contribute to the vulcanization reaction are kneaded. You may make it do. The kneading temperature can be around room temperature, for example.

  The rubber composition for a sealing material preferably has a Mooney viscosity [ML (1 + 4) 100 ° C.] at 100 ° C. measured according to JIS K6300-1 of 60 or less, and more preferably 55 or less. By setting the content of the components [A] to [C] within the above predetermined range and adjusting the viscosity within this range, a rubber composition having good moldability, particularly easy injection molding is obtained. be able to. However, when the viscosity is excessively small, the fluidity of the rubber composition becomes too large, and a defect is likely to occur in the appearance and quality of the sealing material. Therefore, the Mooney viscosity [ML (1 + 4) 100 ° C.] of the rubber composition for sealing material is preferably more than 40, more preferably 42 or more, and further preferably 44 or more.

  In the cross-linking molding step, a cross-linked molded product is obtained by cross-linking the rubber composition for a sealing material as described above. As the crosslinking molding method, conventionally known methods such as injection molding, compression molding, and transfer molding can be adopted. However, in mass production of sealing materials, injection molding is advantageous from the viewpoint of shortening molding time and molding cost. It is. The temperature during crosslinking (crosslinking temperature) is, for example, about 100 to 200 ° C. (preferably 150 to 190 ° C., more preferably 160 to 180 ° C.), and the heating time (crosslinking time) is, for example, 0.5 to 120. About minutes.

(2) Heat treatment step This step is a step of heat-treating the crosslinked molded product obtained in the crosslinking molding step. By passing through this process, low molecular weight components (or low molecular weight components produced by reaction) originally contained in the rubber component of raw materials, unreacted components (rubber components and crosslinking agents), and further contained in plasticizers It is possible to obtain a sealing material in which the generation of outgas due to the low molecular weight component is suppressed. In addition, the crosslinking of the rubber composition has sufficiently progressed in the above-described crosslinking molding process (for example, when the crosslinking properties are measured by the die vulcanization test A method according to JIS K6300-2, The rubber composition (crosslinked molded product) has a torque value of about 92% or more, more typically about 95% or more of the maximum torque value.) Crosslinking does not proceed in this step, or However, the progress is slight.

  The temperature of heat processing is 150-300 degreeC normally, Preferably it is 150-280 degreeC. If the heat treatment temperature is excessively high, the resulting sealing material will be thermally deteriorated, the crosslinking density will be reduced, and the mechanical strength and heat resistance of the sealing material may be reduced. The heat treatment may be performed at a temperature higher than the temperature at the time of cross-linking molding.

  The heat treatment time is preferably 0.5 to 32 hours, although it depends on the temperature. When the heat treatment time exceeds 32 hours, low outgassing properties can be obtained, but the sealing material is thermally deteriorated, the crosslinking density is lowered, and the mechanical strength and heat resistance of the sealing material may be lowered. .

  The pressure at the time of heat treatment is usually lower than that of the above-described cross-linking molding step, and this is different from the above-mentioned cross-linking molding step in which heat treatment is performed under a corresponding pressure to perform molding. The pressure during the heat treatment can be, for example, normal pressure (or the vicinity thereof) or a pressure lower than normal pressure. In addition, when the time of the above-described cross-linking molding process is extended instead of the heat treatment in this step, scorching where cross-linking proceeds excessively occurs, and conversely, the cross-linking density decreases, and the mechanical strength and heat resistance of the sealing material are reduced. The nature will decline.

  Since the sealing material (for example, O-ring) obtained by the method of the present invention is excellent in low outgas characteristics, contamination of the fluid (liquid, gas, etc.) to be sealed by the sealing material due to outgas (and accompanying this). Suitable for applications where deterioration is to be suppressed. Such applications include, for example, battery applications that use a sealing material at sites that can come into contact with liquids such as electrolytes (lead storage batteries, lithium batteries, nickel batteries, redox flow batteries, sodium / sulfur batteries, alkaline secondary batteries, etc. ) And semiconductor manufacturing equipment applications. In addition, the sealing material obtained by the method of the present invention is less prone to problems due to the fluidity and crosslinking behavior of the rubber composition during the molding process. Therefore, the sealing material has excellent properties (elongation characteristics, hardness, heat resistance). , Sealing properties, mechanical strength, etc.) and good appearance quality.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1-5, Comparative Examples 1-4>
(1) Production of sealing material A rubber composition for a sealing material was prepared according to the following procedure, and then a sealing material was produced. First, according to the compounding composition shown in Table 1 (the unit of the compounding amount in Table 1 is parts by weight), a predetermined amount of rubber component (EPDM), anti-aging agent, processing aid and fillers 1 and 2 (Comparative Example 2). In -4, a plasticizer) was further kneaded with a pressure kneader. At this time, the rotation speed of the pressure kneader was 30 rpm, and the kneading time was the time required for the maximum temperature of the kneaded product to reach 120 ° C. After cooling, the obtained kneaded product was charged with the composite crosslinking agent or crosslinking agent and the liquid co-crosslinking agent 1, and kneaded with a pressure kneader to prepare a rubber composition for a sealing material.

  Next, the obtained rubber composition for sealing material was subjected to cross-linking molding using an injection molding machine under the conditions shown in Table 1, then placed in an oven and subjected to heat treatment under the conditions shown in Table 1 under normal pressure. As a result, an O-ring sealing material was obtained. However, in Comparative Examples 1 and 2, the heat treatment step was not performed.

The detail of each component used in the Example and the comparative example is as follows.
[1] EPDM: The content of structural units derived from ethylene is 56% by weight, the content of structural units derived from 5-ethylidene-2-norbornene, which is a diene monomer, is 5% by weight, and conforms to JIS K6300-1. An ethylene-propylene-diene rubber having a Mooney viscosity [ML (1 + 4) 100 ° C.] at 100 ° C. of 40 measured by
[2] Anti-aging agent: dimethylbenzyldiphenylamine,
[3] Processing aid: stearic acid,
[4] Filler 1: 2 types of zinc oxide,
[5] Filler 2: Furnace black,
[6] Plasticizer: paraffinic process oil,
[7] Composite crosslinking agent: “Luperox DC40P-SP2” manufactured by Arkema [Organic peroxide: 40% by weight of dicumyl peroxide, nitrooxide compound: 4-hydroxy-2,2,6,6-tetramethylpiperidine -1-oxyl 2.4% by weight, balance: filler (calcium carbonate and silica)],
[8] Crosslinking agent: dicumyl peroxide,
[9] Liquid co-crosslinking agent 1: trimethylolpropane trimethacrylate.

(2) Evaluation of sealing material [A] Normal properties of sealing material Using the same rubber composition as used in Examples and Comparative Examples, the same method was used for cross-linking molding and heat treatment, and the thickness was 2 mm according to JIS K6250. A sheet-like cross-linked molded article was produced. From this sheet-like cross-linked molded article, a dumbbell-shaped No. 3 type test piece was punched out in accordance with JIS K6251. This test piece was pulled at 500 mm / min, and the tensile strength and elongation at break were measured. Further, according to JIS K6253, the hardness of the sheet-like crosslinked molded product was measured with a type A durometer hardness tester. All these tests were conducted at a temperature of 25 ° C. The results are shown in Table 1.

[A] Low outgassing property of sealing material The amount of outgassing of the sealing material was measured by a thermal desorption method. Specifically, using a generated gas concentration introduction device (thermal desorption system manufactured by Shimadzu Corporation), about 0.3 g of a sample cut out from the sealing material is heated at 180 ° C. in an inert He gas stream, The outgas generated from the sample was collected and concentrated with an adsorbent (TENAX TA), and the gas re-desorbed at 280 ° C. was introduced into a gas chromatograph mass spectrometer (“GCMS-QP2010Plus” manufactured by Shimadzu Corporation). The amount of outgas (μg) generated from 1 g of the sample was measured. In the capillary column of the gas chromatograph mass spectrometer, “Rxi-1ms” (inner diameter: 0.25 mm × length: 60 m, film thickness: 0.25 μm, stationary phase: 100% polydimethylsiloxane) manufactured by Shimadzu Corporation is used. Using. And the low outgas property was evaluated according to the following evaluation criteria. The results are shown in Table 1.

A (good): Outgas amount is less than 10 μg / g,
B (slightly good): outgas amount of more than 10 μg / g and less than 20 μg / g,
C (slightly poor): outgas amount of more than 20 μg / g and less than 30 μg / g,
D (defect): Outgas amount exceeds 30 μg / g.

<Reference Examples 1-3 and Comparative Reference Examples 1-9>
(1) Production of sealing material A rubber composition for a sealing material was prepared according to the following procedure, and then a sealing material was produced. First, according to the blending composition shown in Table 2 (the blending amount unit in Table 2 is parts by weight), predetermined amounts of rubber component (EPDM), anti-aging agent, processing aid and fillers 1 and 2 (comparative reference example) In No. 8, a plasticizer) was further kneaded by a pressure kneader. At this time, the rotation speed of the pressure kneader was 30 rpm, and the kneading time was the time required for the maximum temperature of the kneaded product to reach 120 ° C. After cooling, the resulting kneaded product is charged with a composite crosslinking agent or crosslinking agent and a co-crosslinking agent shown in Table 2 (in addition, a crosslinking retarder in Comparative Reference Example 9), and kneaded with a pressure kneader. Thus, a rubber composition for a sealing material was prepared.

  Next, the obtained rubber composition for a sealing material was subjected to cross-linking molding at 170 ° C. using an injection molding machine (no heat treatment step was performed) to obtain a sealing material that was an O-ring.

  The details of each component other than the above [1] to [9] used in Reference Examples and Comparative Reference Examples are as follows.

[10] Liquid co-crosslinking agent 2: triallyl isocyanurate,
[11] Solid co-crosslinking agent: N, N′-m-phenylene dimaleimide,
[12] Crosslinking retarder: N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine.

(2) Evaluation of rubber composition for sealing material and sealing material The following items were measured and evaluated for the rubber composition for sealing material and the crosslinked molded product (sealing material) obtained. The results are shown in Table 2 (FIG. 1 for the following [A] v).

[A] Molding processability of rubber composition for sealing material i) Mooney viscosity The Mooney viscosity [ML (1 + 4) 100 ° C.] of the rubber composition for sealing material was measured according to JIS K6300-1.

ii) Burrs of the cross-linked molded product The burrs of the cross-linked molded product were observed visually, and the following criteria:
A (good): In mass production of cross-linked molded products, the burrs are thin and can be easily removed from the cross-linked molded products, and there is no burr of chatter and no sticking of burrs to the mold.
B (slightly bad): In mass production of cross-linked molded products, slight chatter is observed in burrs.
C1 (defect): In mass production of crosslinked molded products, considerable burr is observed in the burr.
C2 (Bad): In mass production of cross-linked molded products, when removing burrs, the burrs are thick enough to partially tear the product part together
C3 (defect): In mass production of cross-linked molded products, burr adhesion to the mold is recognized.
Evaluated according to. The defects of B and C1 to C3 are caused when the rubber composition has insufficient fluidity, or when the rubber composition has a crosslinking property suitable for molding (the crosslinking start time is appropriately delayed, but the crosslinking is completed from the start of crosslinking) This may occur in the case where it does not have the cross-linking property that the time until the time is short.

iii) Fluidity of rubber composition for sealing material The obtained cross-linked molded product was observed visually, and the following criteria:
A (good): In mass production of cross-linked molded products, there are no traces (including fogging of the cross-linked molded product surface) and dents (unevenness on the cross-linked molded product surface) that occur when flowing in the mold.
B (slightly poor): In mass production of a crosslinked molded product, the above-mentioned traces or dents may be slightly observed, or slight foaming may be observed in the crosslinked molded product.
C (defect): In mass production of a cross-linked molded product, the above-mentioned mark or dent is remarkably recognized, or the above-mentioned foaming is remarkably recognized
Evaluated according to. The above-mentioned marks, dents and foaming can all occur when the rubber composition has insufficient fluidity or is excessively high.

iv) Mold contamination The mold after taking out the cross-linked molded product is visually observed, and the following criteria:
A (good): In mass production of a cross-linked molded product, there is no dirt on the mold due to the cross-linked molded material.
B (slightly poor): In mass production of a cross-linked molded article, the contamination of the mold due to the cross-linked molded article material is clearly increased as compared to A (but not as much as C below),
C (defect): Adhesion of the crosslinked molded product to the mold is remarkable, and mass production of the crosslinked molded product is difficult.
Evaluated according to. Contamination of the mold with the cross-linked molding material can be caused by insufficient cross-linking reaction.

v) Crosslinking characteristics of rubber composition for sealing material Rubber composition for sealing material of Reference Example 1 and Comparative Reference Example 3 and rubber composition for sealing material of Comparative Reference Example 9 (Rubber composition for sealing material of Comparative Reference Example 3) In addition, JIS K6300- for a rubber composition obtained by adding 2 parts by weight of N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine as a crosslinking retarder to 100 parts by weight of a rubber component In accordance with No. 2, the crosslinking characteristics (crosslinking behavior) were measured by the die vulcanization test method A (170 ° C. × 30 minutes). The results are shown in FIG.

[A] Normal physical properties of the cross-linked molded product Using the same rubber composition as that used in the reference examples and comparative reference examples, the cross-linked molding was performed in the same manner, and a sheet-shaped cross-linked molded product having a thickness of 2 mm according to JIS K6250 Was made. From this sheet-like cross-linked molded article, a dumbbell-shaped No. 3 type test piece was punched out in accordance with JIS K6251. This test piece was pulled at 500 mm / min, and the tensile strength, elongation at break, and 100% tensile stress were measured. Further, according to JIS K6253, the hardness of the sheet-like crosslinked molded product was measured with a type A durometer hardness tester. All these tests were conducted at a temperature of 25 ° C.

[C] Compression set of crosslinked molded product According to JIS K6262, the compression set was measured using a wire diameter φ1.9 O-ring under conditions of 150 ° C. × 72 hours and a compression rate of 25%.

  As shown in the evaluation results shown in Table 2, the rubber compositions of Reference Examples 1 to 3 have appropriate fluidity and crosslinking characteristics suitable for molding processing (especially injection molding) even though they do not contain a plasticizer. Therefore, it was possible to produce a high-quality sealing material with good moldability. The obtained sealing material had excellent normal physical properties. Further, the sealing material comprising the rubber composition of Reference Example 1 has an excellent compression set (heat resistance and resistance) as compared with Comparative Reference Example 8 using a plasticizer and Comparative Reference Example 9 using a crosslinking retarder. It was confirmed to have a sealing property. From the viewpoint of heat resistance and sealing properties, the compression set is preferably 40% or less.

  On the other hand, since the rubber compositions of Comparative Reference Examples 1 and 2 using the liquid co-crosslinking agent 2 (triallyl isocyanurate) or the solid co-crosslinking agent have poor fluidity (high Mooney viscosity), a crosslinked molded product There were traces and dents that occurred when flowing in the mold. Further, the burr was thick due to poor fluidity. In the rubber composition of Comparative Reference Example 3 using only dicumyl peroxide instead of the composite crosslinking agent, Mooney viscosity was good, but clear chattering by scorch was confirmed in the burr. This means that scorch occurs also in the cross-linked molded product. In addition, the traces and dents were slightly generated.

  In this regard, as shown in FIG. 1, according to the rubber composition used in the present invention, it is possible to appropriately delay the crosslinking start time and to shorten the time from the start of crosslinking to the completion of crosslinking (FIG. 1). 1 “Reference Example 1”). When only dicumyl peroxide is used instead of the composite cross-linking agent, scorch (and chatter associated therewith) where cross-linking proceeds excessively during flow (see “Comparative Reference Example 3” in FIG. 1). Scorch can be suppressed by the addition of a crosslinking retarder, but in this case, it is difficult to complete the crosslinking reaction and the crosslinking density decreases (see “Comparative Reference Example 9” in FIG. 1). 1 that the rubber composition used in the present invention can moderately delay the crosslinking start time while ensuring the maximum torque (final crosslinking density) equivalent to that of Comparative Reference Example 3.

  In the rubber composition of Comparative Reference Example 4 in which the content of the liquid co-crosslinking agent 1 is small, the Mooney viscosity is high, the burr is slightly chattered, and the cross-linked molded product has a slight trace or dent. It has occurred. In the rubber composition of Comparative Reference Example 5 in which the content of the liquid co-crosslinking agent 1 is large, there is no problem with burrs, but the fluidity is too high, and the above traces and dents are remarkably generated in the crosslinked molded product.

  In the rubber composition of Comparative Reference Example 6 in which the content of the composite crosslinking agent was small, the crosslinking reaction was insufficient, so that burr adhesion was significant, resulting in significant mold contamination. Even in the rubber composition of Comparative Reference Example 7 in which the content of the composite cross-linking agent was large, burr adhesion was confirmed. Further, in the rubber composition of Comparative Reference Example 7, slight foaming was observed in the crosslinked molded product due to insufficient fluidity of the rubber composition and decomposition products of excess organic peroxide.

  In the rubber compositions of Comparative Reference Examples 8 and 9, the compression set was greatly deteriorated due to the influence of the plasticizer or the crosslinking retarder.

Claims (5)

100 parts by weight of a rubber component;
A composite cross-linking agent containing 0.5 to 5 parts by weight of an organic peroxide and a nitrooxide compound;
2 to 20 parts by weight of a liquid co-crosslinking agent that is at least one selected from the group consisting of trimethylolpropane trimethacrylate and trimethylolpropane triacrylate;
A step of cross-linking a rubber composition for a sealing material comprising:
A step of heat-treating the resulting crosslinked molded article;
The manufacturing method of the sealing material containing this.   The manufacturing method of Claim 1 whose time of the said heat processing is 0.5 to 32 hours.   The production method according to claim 1 or 2, wherein the content of the nitrooxide compound is in the range of 1 to 20% by weight of the content of the organic peroxide.   The said rubber composition for sealing materials is a manufacturing method of any one of Claims 1-3 which does not contain a plasticizer.   The manufacturing method according to any one of claims 1 to 4, wherein the rubber component is at least one selected from the group consisting of ethylene-propylene-diene rubber, hydrogenated nitrile rubber, and fluorine rubber.

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