WO2025203712A1 - Regenerated perfluoro (co)polymer production method and regenerated material production method - Google Patents

Abstract

[Problem] To provide a method for producing a regenerated perfluoro (co)polymer wherein the crosslinking site of a crosslinked perfluoro (co)polymer that has been crosslinked is regenerated, the regenerated perfluoro (co)polymer production method making it possible to sufficiently regenerate a crosslinking site using a simple method while preventing a reduction in the mass of the perfluoro (co)polymer when regenerating the crosslinking site. [Solution] A regenerated perfluoro (co)polymer production method including a step for heat-treating, in an inert gas atmosphere, a crosslinked perfluoro (co)polymer obtained by crosslinking a perfluoro (co)polymer having a crosslinking site, and thereby regenerating the crosslinking site.

Description

Method for producing recycled perfluoro(co)polymer and method for producing recycled material

The present invention relates to a method for producing recycled perfluoro(co)polymers and a method for producing recycled materials.

Sealing materials have traditionally been used in a wide variety of applications, and one example of an application that places the greatest strain on sealants is the use of sealants in semiconductor manufacturing equipment.

Cross-linkable fluoroelastomers such as fluoroelastomers (FKM) and perfluoroelastomers (FFKM) are used as such sealing materials, as they offer excellent plasma and radical resistance. FFKM is particularly popular when high temperatures or harsh chemicals are used.

Sealing materials made from crosslinkable fluoroelastomers such as those described above are typically made by blending the crosslinkable fluoroelastomer with additives such as a crosslinking agent or crosslinking aid to produce an elastomer composition, which is then molded and crosslinked to form the sealing material.

As with general molded products, the above-mentioned sealing materials sometimes require disposal of molding scraps (burrs), defective products, and used molded products. However, the excellent properties of cross-linked fluoroelastomers can actually hinder chemical processing, and they produce corrosive decomposition products when burned, making thermal recycling difficult. Therefore, until now, they have been disposed of by landfilling, etc.

However, in recent years, with growing awareness of environmental protection through measures such as reducing landfill volume and making effective use of resources, there has been a demand for the development of methods to reuse crosslinked fluoroelastomers that have previously been discarded.

As a method for reusing such crosslinked fluoroelastomers, for example, Patent Document 1 discloses a method for decrosslinking a crosslinked fluoropolymer in a supercritical fluid or subcritical fluid of a compound having active hydrogen.
Furthermore, Patent Document 2 discloses a method of heat treating vulcanized fluororubber in air.

Japanese Patent Application Laid-Open No. 2007-63334 Japanese Patent Application Publication No. 61-69805

However, the method described in Patent Document 1, which uses a supercritical fluid or a subcritical fluid, is not easy to process and cannot be carried out simply, so there is room for improvement.
Furthermore, as a result of intensive studies by the present inventors, it has been found that the method described in Patent Document 2 does not sufficiently devulcanize the vulcanized fluororubber (regenerate crosslinking sites), and that the heat treatment causes decomposition of the vulcanized fluororubber, resulting in a large mass loss rate of the fluororubber before and after the heat treatment.

The present invention was made in light of the above, and aims to provide a method for producing a recycled perfluoro(co)polymer that regenerates the crosslinking sites of a crosslinked crosslinked perfluoro(co)polymer. The objective of the method is to provide a method for producing a recycled perfluoro(co)polymer that can sufficiently regenerate crosslinking sites in a simple manner while suppressing the mass loss of the perfluoro(co)polymer when regenerating the crosslinking sites.

As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration examples, and have completed the present invention.
An example of the configuration of the present invention is as follows.

[1] A method for producing a regenerated perfluoro(co)polymer, comprising the step of heat-treating a crosslinked perfluoro(co)polymer, formed by crosslinking a perfluoro(co)polymer having crosslinking sites, in an inert gas atmosphere to regenerate the crosslinking sites.

[2] The method for producing a recycled perfluoro(co)polymer described in [1], wherein the crosslinking site is a nitrile group.

[3] The method for producing recycled perfluoro(co)polymers according to [1] or [2], wherein the inert gas is at least one selected from nitrogen gas, argon gas, and helium gas.

[4] A method for producing a recycled perfluoro(co)polymer according to any one of [1] to [3], wherein the perfluoro(co)polymer having crosslinking sites is a (co)polymer that does not contain a carbon-hydrogen bond in the main chain of the (co)polymer.

[5] A method for producing a recycled material, comprising a step of crosslinking a recycled material-forming material containing a recycled perfluoro(co)polymer obtained by the method for producing a recycled perfluoro(co)polymer described in any one of [1] to [4].

[6] The method for producing recycled materials described in [5], wherein the recycled material-forming material further contains a crosslinking agent.

[7] The method for producing recycled materials described in [5] or [6], wherein the recycled material-forming material further contains an uncrosslinked perfluoro(co)polymer.

[8] The method for producing recycled materials described in [7], wherein the content of the recycled perfluoro(co)polymer in the recycled material-forming material is 0.5 parts by mass or more per 100 parts by mass of uncrosslinked perfluoro(co)polymer.

[9] The method for producing recycled materials described in any one of [5] to [8], wherein the recycled material is a sealing material.

According to the present invention, when regenerating the crosslinking sites of a crosslinked crosslinked perfluoro(co)polymer, the crosslinking sites of the crosslinked perfluoro(co)polymer can be sufficiently regenerated by a simple method while suppressing the mass loss of the perfluoro(co)polymer when regenerating the crosslinking sites.
In this way, the crosslinking sites of the crosslinked perfluoro(co)polymer can be sufficiently regenerated while suppressing mass loss, and therefore, even when the resulting recycled perfluoro(co)polymer is used, a molded article (regenerated material) can be formed that has physical properties (hardness, tensile strength, elongation at break, compression set, and plasma resistance) comparable to those when a virgin product (uncrosslinked perfluoro(co)polymer) is used.
Therefore, the recycled material can be suitably used as a sealing material for semiconductor manufacturing equipment, a sealing material for plasma processing equipment, etc.

<Production method for recycled perfluoro (co)polymer>
The method for producing a recycled perfluoro(co)polymer (hereinafter also referred to as "the recycled product") according to the present invention (hereinafter also referred to as "the method for producing the recycled product") includes a step of heat-treating a crosslinked perfluoro(co)polymer (hereinafter also referred to as "the recycled product") in an inert gas atmosphere, in which a perfluoro(co)polymer having crosslinking sites is crosslinked, thereby regenerating the crosslinking sites.

Whether or not crosslinking sites have been regenerated in the regenerated product can be determined, for example, by using FT-IR to measure the amount of crosslinking sites in the regenerated product and the amount of crosslinking sites in the obtained regenerated product.
The method for producing the recycled product is preferably a method in which the content of crosslinking sites in the resulting recycled product is preferably 150% or more, more preferably 200% or more, when the content of crosslinking sites in the recycled product is taken as 100%, because the recycled product obtained can be used to easily form a recycled material having desired physical properties.
The content of the crosslinking sites can be measured using FT-IR, specifically by the method described in the examples below.

Furthermore, in view of the fact that the method for producing the recycled product can easily form a recycled material having desired physical properties using the obtained recycled product, it is desirable that the mass reduction rate due to the heat treatment, specifically the mass reduction rate represented by the following formula (1), is preferably 2% or less, more preferably 1% or less.
Mass reduction rate (%) = [(mass of recycled product - mass of main recycled product) / mass of recycled product] x 100 ... (1)

<Recycled products>
The recycled product is a crosslinked perfluoro(co)polymer obtained by crosslinking a perfluoro(co)polymer having crosslinking sites (hereinafter also referred to as "uncrosslinked perfluoro(co)polymer"). Examples of the recycled product include crosslinked perfluoro(co)polymers contained in (unused) molded products such as sealing materials formed using conventional uncrosslinked perfluoro(co)polymers (virgin products), scraps (burrs) generated during the production of such molded products, defective products, used molded products, etc.
Examples of the used compacts include not only those used in semiconductor manufacturing equipment but also those used in chemical plants, various industrial equipment, and the like.
In the method for producing the recycled product, the raw material to be subjected to the heat treatment may be the crosslinked perfluoro(co)polymer itself, the (unused) molded body, the scraps (burrs) or defective products, or the used molded body.

The crosslinked perfluoro(co)polymer in the recycled product is a crosslinked product obtained by crosslinking the following uncrosslinked perfluoro(co)polymer (virgin product) by a conventionally known method.
The conventionally known method includes crosslinking using a crosslinking agent, and the crosslinking agent may be appropriately selected depending on the uncrosslinked perfluoro(co)polymer to be used, and examples thereof include peroxide-based crosslinking agents, bisphenol-based crosslinking agents, triazine-based crosslinking agents, oxazole-based crosslinking agents, imidazole-based crosslinking agents, thiazole-based crosslinking agents, amidoxime-based crosslinking agents, and amidrazone-based crosslinking agents. In other words, the recycled product may include a crosslinked perfluoro(co)polymer having at least one crosslinked structure selected from crosslinked structures derived from these crosslinking agents and intermediate structures when forming these crosslinked structures (e.g., amidine structure when forming an oxazole structure).
The degree of crosslinking in the recycled product is not particularly limited, and it is sufficient if the degree of crosslinking is the same as that when forming a molded product such as a sealing material.

[Uncrosslinked perfluoro (co)polymer]
The uncrosslinked perfluoro(co)polymer is a perfluoro(co)polymer having crosslinking sites before crosslinking, and can also be called a "virgin product."
The uncrosslinked perfluoro (co)polymer is preferably a perfluoroelastomer (FFKM).
The FFKM is not particularly limited, but is preferably a polymer that does not contain a hydrogen atom (carbon-hydrogen bond) in the polymer main chain (excluding the terminals), and specifically includes a tetrafluoroethylene (TFE)-perfluorovinyl ether copolymer having a crosslinking site, and is preferably a copolymer that contains a constitutional unit derived from TFE and a constitutional unit derived from a perfluorovinyl ether, and further contains a constitutional unit derived from a crosslinking site-containing monomer, as necessary.

Suitable examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) and perfluoro(alkoxyalkyl vinyl ether).

The perfluoro(alkyl vinyl ether) may be a compound in which the alkyl group has, for example, 1 to 10 carbon atoms. Specific examples include perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether), with perfluoro(methyl vinyl ether) being preferred.

The perfluoro(alkoxyalkyl vinyl ether) may be a compound in which the group bonded to the vinyl ether group (CF ₂ ═CFO—) has, for example, 3 to 15 carbon atoms, and specific examples include the following compounds:
CF ₂ =CFOCF ₂ CF(CF ₃ )OC _n F _2n+1
CF ₂ =CFO(CF ₂ ) ₃ OC _n F _2n+1
CF ₂ =CFOCF ₂ CF(CF ₃ )O(CF ₂ O) _m C _n F _2n+1
CF ₂ =CFO(CF ₂ ) ₂ OC _n F _2n+1
In these formulas, n is independently 1 to 5, for example, and m is 1 to 3, for example.

The crosslinking site refers to a site capable of undergoing a crosslinking reaction, and examples thereof include a nitrile group, a halogen atom (e.g., I, Br), and a perfluorophenyl group. Of these, a nitrile group is preferred because it enhances the effects of the present invention.

Examples of crosslinking site monomers having a nitrile group as a crosslinking site include nitrile group-containing perfluorovinyl ethers, and specific examples include the following compounds.
CF ₂ ═CFO(CF ₂ ) _n OCF(CF ₃ )CN (n is, for example, 2 to 4)
CF ₂ ═CFO(CF ₂ ) _n CN (n is, for example, 2 to 12)
CF ₂ ═CFO[CF ₂ CF(CF ₃ )O] _m (CF ₂ ) _n CN (n is, for example, 1 to 4, m is, for example, 1 to 5)
CF ₂ ═CFO[CF ₂ CF(CF ₃ )O] _n CF ₂ CF(CF ₃ )CN (n is, for example, 0 to 4)
CF ₂ ═CF(CF ₂ ) _n CN (n is, for example, an integer of 1 to 8)
CF ₂ ═CFCF ₂ (OCF ₂ ) _n CN (n is, for example, an integer of 0 to 5)
CF ₂ ═CFCF ₂ (OCF(CF ₃ )CF ₂ ) _m —CN (m is, for example, an integer of 0 to 5, and n is, for example, an integer of 0 to 5)
CF ₂ ═CF(OCF ₂ CF(CF ₃ )) _m O(CF ₂ ) _n —CN (m is, for example, an integer of 0 to 5, and n is, for example, an integer of 1 to 8)
CF ₂ ═CF(OCF ₂ CF(CF ₃ )) _m —CN (m is, for example, an integer of 1 to 5)
CF ₂ ═CFOCF ₂ (CF(CF ₃ )OCF ₂ ) _n CF(—CN)CF ₃ (n is, for example, an integer of 1 to 4)
CF ₂ ═CFO(CF ₂ ) _n OCF(CF ₃ )—CN (n is, for example, an integer of 2 to 5)
CF ₂ ═CF(OCF ₂ CF(CF ₃ )) _n OCF ₂ CF(CF ₃ )—CN (n is, for example, an integer of 1 or 2)
CF ₂ ═CFO(CF ₂ CF(CF ₃ )O) _m (CF ₂ ) _n —CN (wherein m is, for example, an integer of 0 to 5, and n is, for example, an integer of 1 to 3)
CF ₂ ═CFO(CF ₂ CF(CF ₃ )O) _m CF ₂ CF(CF ₃ )—CN (m is an integer of 0 or more)
_CF2 =CFOCF( _CF3 ) _CF2O ( _CF2 ) _n -CN (n is an integer of 1 or more)
CF ₂ =CFOCF ₂ OCF ₂ CF(CF ₃ )OCF ₂ -CN

Examples of crosslinking site-containing monomers that have halogen atoms as crosslinking sites include halogen-containing perfluorovinyl ethers, specifically compounds in which the nitrile groups in the specific examples of nitrile-containing perfluorovinyl ethers mentioned above are replaced with halogen atoms. Furthermore, examples of crosslinking site-containing monomers that have halogen atoms include the compounds described in WO 2009/119409, JP 2002-97329 A, and JP 2008-56739 A.

In FFKM, the content of TFE-derived structural units is preferably 50.0 to 79.9 mol%, the content of perfluorovinyl ether-derived structural units is preferably 20.0 to 46.9 mol%, and the content of crosslinking site-containing monomer-derived structural units is preferably 0.1 to 2.0 mol%.

<Heat treatment conditions, etc.>
The heat treatment in this method for producing recycled products is characterized by being carried out in an inert gas atmosphere.
By carrying out the heat treatment under an inert gas atmosphere, it is possible to suppress decomposition of the recycled product when obtaining a recycled product from the recycled product, thereby suppressing mass loss, and furthermore, it is possible to easily obtain a recycled product with a large amount of regenerated crosslinking sites.

Specific examples of the inert gas include nitrogen gas, argon gas, and helium gas, and among these, nitrogen gas is preferred.
The inert gas may be used alone or in combination of two or more.
The inert gas is preferably a gas that does not contain oxygen or a gas that contains a small amount of oxygen, in order to more effectively exhibit the effects of the present invention.
As for the gas containing a small amount of oxygen, since a high oxygen content makes it easier for the thermal decomposition of the product to be recycled to proceed, it is desirable that the oxygen content be less than 5% by volume, more preferably 3% by volume or less, and even more preferably 1% by volume or less, of the total.

The temperature and time for the heat treatment are not particularly limited as long as they are such that crosslinking sites are regenerated in the regenerated product.
The temperature during the heat treatment is usually a temperature exceeding the temperature at which the uncrosslinked perfluoro(co)polymer (virgin product) is crosslinked by a conventionally known method, and is preferably 300 to 400°C, more preferably 320 to 390°C, and even more preferably 350 to 380°C.
The time for the heat treatment varies depending on the heat treatment temperature, but is preferably 30 minutes to 5 hours, more preferably 1 to 3 hours.
The pressure during the heat treatment is not particularly limited, but it is preferable to carry out the heat treatment under normal pressure.

<Recycled material manufacturing method>
The method for producing a recycled material according to the present invention (hereinafter also referred to as the "method for producing the recycled material") includes a step of crosslinking a recycled material-forming material including the recycled product obtained by the method for producing the recycled product.
In this method for producing recycled materials, recycled products obtained by heat treatment in an inert gas atmosphere are used, making it possible to form recycled materials that are particularly superior in plasma resistance compared to, for example, recycled products obtained by heat treatment in air.

<Recycled material forming material>
The recycled material-forming material is not particularly limited as long as it contains the recycled product, and may be a material consisting essentially of the recycled product alone, but may also contain other components that have been conventionally known and have been incorporated into molded products such as sealing materials, if necessary.
Examples of such other components include uncrosslinked perfluoro(co)polymers (virgin products); crosslinking agents; crosslinking aids; ethylenically unsaturated bond-containing compounds; reactive organosilicon compounds having two or more hydrosilyl groups in the molecule; perfluoropolyethers; non-adhesive agents such as fluorinated oils; catalysts; polyol-based compounds; (co)polymers other than the above-mentioned perfluoro(co)polymers (e.g., fluororesins); acid acceptors such as magnesium oxide and calcium hydroxide; organic pigments such as anthraquinone-based pigments, perylene-based pigments, and dioxazine-based pigments; processing aids; vulcanization accelerators; antioxidants; antioxidants; inorganic fillers; and organic fillers.
The other components may each be used alone or in combination of two or more.

[This recycled product]
The recycled product used for the recycled material-forming material may be one type or two or more types.
Considering the balance between environmental protection, effective utilization of resources, and the ease of forming a recycled material having the desired physical properties, the amount of the recycled product used is preferably 0.5 to 60% by mass, more preferably 1 to 50% by mass, and even more preferably 10 to 40% by mass, relative to 100% by mass of the recycled material-forming material.
Furthermore, when an uncrosslinked perfluoro(co)polymer is used as the recycled material-forming material, the amount of this recycled product used is preferably 0.5 parts by mass or more, more preferably 0.5 to 90 parts by mass, even more preferably 1 to 80 parts by mass, and particularly preferably 10 to 70 parts by mass, per 100 parts by mass of uncrosslinked perfluoro(co)polymer, from the viewpoint of being able to easily form a recycled material having the desired physical properties.

[Uncrosslinked perfluoro (co)polymer]
It is preferable to use an uncrosslinked perfluoro(co)polymer (virgin product) as the recycled material-forming material, since it is possible to easily obtain a recycled material-forming material with excellent moldability and to easily form a recycled material having the desired physical properties (hardness, tensile strength, elongation at break, compression set, and plasma resistance).
Examples of the uncrosslinked perfluoro(co)polymer include the same (co)polymers as the uncrosslinked perfluoro(co)polymers described in the section on the recycled product.
The uncrosslinked perfluoro(co)polymer may be a perfluoro(co)polymer having a crosslinking site different from the crosslinking site contained in the recycled product used in the recycled material-forming material, but it is preferable to use a perfluoro(co)polymer having a crosslinking site similar to the crosslinking site contained in the recycled product used in the recycled material-forming material.

When an uncrosslinked perfluoro(co)polymer is used as the recycled material-forming material, the amount of the uncrosslinked perfluoro(co)polymer used is preferably 40 to 99.5% by mass, more preferably 50 to 99% by mass, and even more preferably 50 to 90% by mass, relative to 100% by mass of the recycled material-forming material, in order to facilitate the formation of a recycled material with the desired physical properties.

[Crosslinking agent]
The recycled material-forming material can be crosslinked without using a crosslinking agent, but it is preferable to use a crosslinking agent appropriate for the type of recycled product or uncrosslinked perfluoro(co)polymer used in the recycled material-forming material, since this allows for sufficient crosslinking and makes it easy to form a recycled material that is well-balanced and excellent in hardness, tensile strength, elongation at break, and tensile stress at 100% elongation (100% Mo).

The crosslinking agent can be any conventionally known crosslinking agent, such as those described in Japanese Patent No. 5278312, and is not particularly limited. Specific examples include peroxide-based crosslinking agents, bisphenol-based crosslinking agents, triazine-based crosslinking agents, oxazole-based crosslinking agents, imidazole-based crosslinking agents, thiazole-based crosslinking agents, amidoxime-based crosslinking agents, and amidrazone-based crosslinking agents.

Peroxide-based crosslinking agents include, for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, t-butyldicumyl peroxide, benzoyl peroxide, 2,5-dimethyl-2,5-(t-butylperoxy)hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and t-butylperoxyisopropyl. Examples include propyl carbonate, di-(4-t-butylcyclohexyl) peroxydicarbonate, p-chlorobenzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, t-butylperoxybenzene, and t-butylperoxymaleic acid.

Examples of bisphenol-based crosslinking agents include bisphenol AF and bisphenol S.

Examples of triazine crosslinking agents include 2,4,6-trimercapto-1,3,5-triazine, 2-hexylamino-4,6-dimercaptotriazine, 2-diethylamino-4,6-dimercaptotriazine, 2-cyclohexylamino-4,6-dimercaptotriazine, 2-dibutylamino-4,6-dimercaptotriazine, 2-anilino-4,6-dimercaptotriazine, and 2-phenylamino-4,6-dimercaptotriazine.
The triazine crosslinking agent may also be a compound that can act as a catalyst to form a triazine ring using only the nitrile groups contained in the recycled product or the uncrosslinked perfluoro(co)polymer, such as an organic tin compound such as tetraphenyltin or triphenyltin.

Examples of oxazole-based crosslinking agents include 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BOAP), 4,4'-sulfonylbis(2-aminophenol), and 9,9-bis(3-amino-4-hydroxyphenyl)fluorene.

Examples of imidazole crosslinking agents include 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis[3-amino-4-(N-methylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-ethylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-propylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-perfluorophenylamino)phenyl]hexafluoropropane, and 2,2-bis[3-amino-4-(N-benzylamino)phenyl]hexafluoropropane.

Examples of thiazole-based crosslinking agents include 2-mercaptobenzothiazole and dibenzothiazyl disulfide.

When a crosslinking agent is used in the recycled material-forming material, the amount of crosslinking agent used is preferably 0.2 to 4 parts by mass, and more preferably 0.2 to 2.5 parts by mass, per 100 parts by mass of the recycled product and uncrosslinked perfluoro(co)polymer combined, in order to ensure that the crosslinking reaction proceeds sufficiently and to easily form a recycled material that is well-balanced in terms of hardness, tensile strength, elongation at break, and 100% Mo.

[Crosslinking aid]
In the recycled material-forming material, the crosslinking agent may be used alone, but when a crosslinking agent such as the peroxide-based crosslinking agent is used, it is preferable to use a crosslinking aid, which may be selected from known crosslinking aids depending on the type of crosslinking agent.

For example, examples of crosslinking aids used when a peroxide-based crosslinking agent is used include triallyl isocyanurate; triallyl cyanurate; trimethallyl isocyanurate; triallyl formal; triallyl trimellitate; N,N'-m-phenylene bismaleimide; dipropargyl terephthalate; diallyl phthalate; tetraallyl terephthalamide; polyfunctional (meth)acrylates such as ethylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate; and other compounds (polyfunctional monomers) capable of co-crosslinking by radicals; metal salts of higher carboxylic acids; polyhydric alcohol (meth)acrylates; and metal (meth)acrylic acid salts.
Among these, triallyl isocyanurate is preferred because it has excellent reactivity, excellent heat resistance, and can easily produce a sealing material with high hardness and high modulus.

When a cross-linking aid is used in the recycled material-forming material, the amount of cross-linking aid used is preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the recycled product and uncross-linked perfluoro(co)polymer combined, in order to ensure that the cross-linking reaction proceeds sufficiently and to easily form a sealing material that is well-balanced in terms of hardness, tensile strength, elongation at break, and 100% Mo.

When a crosslinking agent and crosslinking aid are used in the recycled material-forming material, the mass ratio of the content of crosslinking aid to the content of crosslinking agent in the recycled material-forming material (crosslinking aid content/crosslinking agent content) is preferably 1 or more, more preferably 2 or more, and preferably 30 or less, more preferably 20 or less, in order to allow the crosslinking agent to react in the right amount and easily form a recycled material that exhibits the desired physical properties.

[Ethylenically unsaturated bond-containing compound]
Examples of the ethylenically unsaturated bond-containing compound include compounds described in WO 2022/065054, JP 2003-183402 A, and JP 11-116684 A.

[Reactive organosilicon compounds]
Examples of the reactive organosilicon compound include compounds similar to the organosilicon compounds described in JP-A Nos. 2003-183402 and 11-116684.

[catalyst]
Examples of the catalyst include the same catalysts as those described in JP-A Nos. 2003-183402 and 11-116684.

[Organic pigments]
Examples of the organic pigment include organic pigments similar to those described in International Publication No. 2016/043100, Japanese Patent No. 4720501, International Publication No. 2004/094527, Japanese Patent No. 5278312, and the like.

[Filling material]
Examples of the inorganic filler include particulate (powdered) inorganic materials such as carbon black, silica, barium sulfate, titanium oxide, and aluminum oxide.
Examples of the organic filler include particulate (powdered) organic materials such as fluororesins such as PTFE, PFA, FEP, ETFE, and PVDF, polyethylene, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyetherketone, silicone resin, and melamine resin.

[Method for preparing recycled material]
The recycled material-forming material can be prepared by mixing (kneading) the recycled product with the other components as required.
When mixing the recycled product with the other components, the order of mixing is not particularly limited, and they may be mixed (kneaded) sequentially in any order, or they may be mixed (kneaded) all at once, but it is preferable to mix (knead) them sequentially so that each component is uniform.

For the mixing (kneading), a conventionally known mixer (kneader) can be used, and examples thereof include an open roll, a Banbury mixer, a twin-screw roll, and a kneader.
Furthermore, during the mixing (kneading) process, the components may be mixed (kneaded) under heating or cooling, as required, depending on the mixer (kneader) used.

<Step of cross-linking recycled material-forming material>
The method for producing the present recycled material is not particularly limited as long as it includes a step of crosslinking the recycled material-forming material.

When forming recycled materials from the recycled material-forming material, it is preferable to carry out a separating process in order to improve the efficiency of the forming process and reduce the defect rate. This separating process is usually carried out using a roll or the like, and is usually also a process in which the recycled material-forming material is preliminarily formed into a sheet.

The sheet obtained in the separating step is preferably preformed into the shape of the desired recycled material before the crosslinking step.
This preforming may involve directly forming the desired recycled material shape from the sheet obtained in the separating process, or the sheet obtained in the separating process may be cut or extruded to form a rope-like shape (which also has the same meaning as a ribbon-like or noodle-like shape), and the resulting rope-like material may then be formed into the desired recycled material shape.

The crosslinking step more preferably includes a primary crosslinking step and a secondary crosslinking step.
The crosslinking step is preferably carried out using a preformed body having the desired recycled material shape obtained by the preforming step.

The primary crosslinking step is preferably a step of heating and pressurizing a preformed body of the desired recycled material shape obtained by the preforming step. A specific example is a step of placing the preformed body in a mold and crosslinking it using a heating press or the like under a pressure of about 2 to 15 MPa at a temperature of, for example, 150 to 200°C for, for example, about 5 minutes to 1 hour.

The secondary crosslinking step is preferably a step of heating the molded body obtained in the primary crosslinking step, and specifically includes a step of heating the molded body at normal pressure to reduced pressure using various ovens, preferably a vacuum oven, at a temperature of, for example, 150 to 300°C for 1 to 48 hours, more preferably 3 to 24 hours.
This secondary crosslinking process accelerates crosslinking, and even if unreacted components remain after the primary crosslinking process, the unreacted components can be decomposed and evaporated, resulting in the formation of a recycled material that emits less gas.

In the manufacturing method of this recycled material, a step of irradiating with radiation (radiation irradiation step) may be carried out after the crosslinking step, as this makes it easier to suppress cracks that may occur in the recycled material in a plasma atmosphere, etc. The recycled material obtained through this radiation irradiation step can be said to be a radiation-treated product.

The radiation to be irradiated in the radiation irradiation step is not particularly limited, and examples thereof include X-rays, gamma rays, electron beams, proton beams, neutron beams, heavy particle beams, alpha rays, and beta rays. Among these, gamma rays and electron beams are preferred.
The radiation to be irradiated may be one type alone or two or more types.

When irradiating with radiation, it is desirable to irradiate so that the absorbed dose is preferably 1 to 120 kGy, more preferably 20 to 100 kGy. Irradiation with such an amount of radiation can reduce unreacted components that can become particles or released gases, and can easily form recycled materials that are excellent in plasma resistance, crack resistance, etc., without excessively lowering the molecular weight of the recycled product and uncrosslinked perfluoro(co)polymer.
The radiation irradiation step may be carried out in two or more stages by changing the conditions.

Radiation may be performed in air, but the presence of oxygen during irradiation can inhibit the crosslinking reaction, potentially reducing the mechanical strength of the resulting recycled material and causing the surface of the recycled material to become sticky. For this reason, it is preferable to perform the radiation irradiation process in an atmosphere of an inert gas such as nitrogen or argon.

<Recycled material>
The recycled material obtained by this recycled material manufacturing method is not particularly limited, but can be used, for example, as gaskets or packings for various components, and can be particularly suitably used as a sealing material for semiconductor manufacturing equipment or a sealing material for plasma processing equipment, and particularly as a sealing material for driving parts such as gate valves used in the openings of plasma processing chamber units.
The recycled material is preferably a sealing material, and examples of the sealing material include O-rings, square rings, gaskets, packing, oil seals, bearing seals, and lip seals.
The shape of the recycled material may be appropriately selected depending on the intended use.

The semiconductor manufacturing equipment is not limited to equipment specifically used to manufacture semiconductors, but broadly includes all manufacturing equipment used in the semiconductor field, which requires a high level of cleanliness, such as equipment used to manufacture liquid crystal panels and plasma panels. Specific examples include the equipment described in Patent Publication No. 5278312.

The IRHD of the recycled material measured in accordance with JIS K 6253-2:2012 is preferably 45 or more, more preferably 50 or more.
The tensile strength of the recycled material, measured by the method described in the examples below, is preferably 7 MPa or more, more preferably 8 MPa or more.
The elongation at break of the recycled material, measured by the method described in the examples below, is preferably 120% or more, and more preferably 130% or more.
The mass loss rate of the recycled material measured by the method described in the examples below is preferably 5% or less, more preferably 3% or less, and the lower limit is not particularly limited, but is, for example, 0%.

Next, the present invention will be explained in more detail using examples, but the present invention is not limited to these.

<Crosslinked perfluoro(co)polymer (recycled product)>
The crosslinked perfluoro (co)polymers (products to be recycled) used in the following examples and comparative examples are as follows:
"Crosslinked perfluoro(co)polymer-1": 100 parts by mass of a perfluoroelastomer (PFE131T [manufactured by 3M], a perfluoro(co)polymer in which the crosslinking site is a nitrile group) and 0.5 parts by mass of an oxazole-based crosslinking agent (BOAP, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, manufactured by Tokyo Chemical Industry Co., Ltd.) were kneaded using an open roll, and the resulting bulk elastomer composition was filled into an O-ring-shaped mold and press-molded at 180°C for 30 minutes using a compression vacuum press under a pressure of 5 MPa (primary crosslinking), and then the press-molded sheet was heated in an oven at 250°C for 24 hours (secondary crosslinking) to produce a molded product (O-ring) (corresponding to an unused or used molded product).
"Crosslinked perfluoro(co)polymer-2": 100 parts by mass of a perfluoroelastomer (Tecnoflon PFR94 [manufactured by Solvay], a perfluoro(co)polymer in which the crosslinking site is a halogen atom), 1 part by mass of TAIC (manufactured by Mitsubishi Chemical Corporation, triallyl isocyanurate), and 0.5 parts by mass of Perhexa 25B (manufactured by NOF Corporation) were kneaded using an open roll, and the resulting bulk elastomer composition was filled into an O-ring-shaped mold and press-molded using a compression vacuum press at 170°C for 10 minutes under a pressure of 5 MPa (primary crosslinking), and then the press-molded sheet was heated in an oven at 200°C for 4 hours (secondary crosslinking) to produce a molded product (O-ring) (corresponding to an unused or used molded product).

[Example 1]
The crosslinked perfluoro(co)polymer-1 (the product to be recycled) was placed in a KDF-75Plus manufactured by Yamato Scientific Co., Ltd., and heat-treated at 380°C and 1 atmosphere for 1 hour in a nitrogen atmosphere to obtain a recycled perfluoro(co)polymer-1 (the recycled product).

[Example 2]
A recycled perfluoro(co)polymer-2 (recycled product) was obtained in the same manner as in Example 1, except that the crosslinked perfluoro(co)polymer-2 (recycled product) was used instead of the crosslinked perfluoro(co)polymer-1.

[Example 3]
The crosslinked perfluoro(co)polymer-1 (the product to be recycled) was placed in a KDF-75Plus manufactured by Yamato Scientific Co., Ltd., and heat-treated at 370°C and 1 atmosphere for 1 hour in a helium gas atmosphere to obtain a recycled perfluoro(co)polymer-3 (the recycled product).

[Example 4]
The crosslinked perfluoro(co)polymer-1 (the product to be recycled) was placed in a KDF-75Plus manufactured by Yamato Scientific Co., Ltd., and heat-treated at 370°C and 1 atmosphere for 1 hour in an argon gas atmosphere to obtain a recycled perfluoro(co)polymer-4 (the recycled product).

[Comparative Example 1]
The crosslinked perfluoro(co)polymer-1 (the product to be recycled) was placed in a KDF-75Plus manufactured by Yamato Scientific Co., Ltd. and heat-treated in air at 380°C and 1 atmosphere for 1 hour to obtain a recycled perfluoro(co)polymer-c1 (the recycled product).

[Comparative Example 2]
A recycled perfluoro(co)polymer-c2 (recycled product) was obtained in the same manner as in Comparative Example 1, except that the crosslinked perfluoro(co)polymer-2 (recycled product) was used instead of the crosslinked perfluoro(co)polymer-1.

<Content of cross-linking sites>
The content of crosslinking sites in the crosslinked perfluoro(co ⁾ polymer (recycled product) and the recycled perfluoro(co)polymer (recycled product) was measured using an FT-IR (HYPERION 3000, manufactured by Bruker) under the conditions of a resolution of 4 cm, a scan number of 32, transmission mode, and a measurement range of 400 to 4000 ^cm . The results are shown in Table 1.
Specifically, the content of crosslinking sites (nitrile groups) was determined by dividing the maximum intensity obtained by connecting the intensities from 2230 to 2290 cm ⁻¹ as the baseline by the intensity at 2500 cm ⁻¹ obtained by connecting the intensities from 2200 to 2700 cm ⁻¹ as the baseline. However, if the calculation result (content of crosslinking sites (nitrile groups)) was less than 0.01, the content of crosslinking sites (nitrile groups) was determined to be 0.01.

In the column for Example 2 in Table 1 below, the content of crosslinked sites is marked as "-", but in Example 2, it is believed that the crosslinked sites (C=C bonds) on the right side of the formula below have been sufficiently regenerated.

<Mass reduction rate>
The mass of the crosslinked perfluoro(co)polymer (recycled product) used in the above Examples or Comparative Examples before heat treatment was measured, and the mass of the resulting recycled perfluoro(co)polymer (recycled product) was also measured.
The mass loss rate (%) was calculated using the following formula: The results are shown in Table 1.
Mass reduction rate (%) = [(mass of recycled product - mass of recycled product) / mass of recycled product] x 100

<Uncrosslinked perfluoro (co)polymer (virgin product)>
The uncrosslinked perfluoro(co)polymers (virgin products) used in the following examples and comparative examples are as follows:
"Uncrosslinked perfluoro (co)polymer-1": PFE131T (manufactured by 3M)
"Uncrosslinked perfluoro (co)polymer-2": Tecnoflon PFR94 (manufactured by Solvay)

[Example 5]
A bulk elastomer composition was obtained by kneading 60 parts by mass of uncrosslinked perfluoro(co)polymer-1 (virgin product), 40 parts by mass of recycled perfluoro(co)polymer-1 (recycled product), and 0.5 parts by mass of an oxazole-based crosslinking agent (BOAP, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, manufactured by Tokyo Chemical Industry Co., Ltd.) using an open roll.
The obtained bulk elastomer composition was filled into an O-ring-shaped mold and press-molded using a compression vacuum press at 180°C for 30 minutes under a pressure of 5 MPa (primary crosslinking). The press-molded sheet was then heated in an oven at 250°C for 24 hours (secondary crosslinking) to obtain a molded product (O-ring).

[Comparative Examples 3 to 4]
In Example 5, a molded body was obtained in the same manner as in Example 5, except that (co)polymers of the types and amounts (numbers, parts by mass) shown in Table 2 were used as the uncrosslinked perfluoro(co)polymer and the recycled perfluoro(co)polymer.

[Example 6]
A bulk elastomer composition was obtained by kneading 60 parts by mass of uncrosslinked perfluoro(co)polymer-2 (virgin product), 40 parts by mass of recycled perfluoro(co)polymer-2 (recycled product), 10 parts by mass of PTFE particles (Lubron L5 (manufactured by Daikin Industries, Ltd.)), 0.5 parts by mass of Perhexa 25B (manufactured by NOF Corporation), and 1 part by mass of TAIC (triallyl isocyanurate, manufactured by Mitsubishi Chemical Corporation) with an open roll.
The obtained bulk elastomer composition was filled into an O-ring-shaped mold and press-molded using a compression vacuum press at 170°C for 10 minutes under a pressure of 5 MPa (primary crosslinking). The press-molded sheet was then heated in an oven at 200°C for 4 hours (secondary crosslinking) to obtain a molded product (O-ring).

[Comparative Examples 5 to 6]
In Example 6, a molded body was obtained in the same manner as in Example 6, except that (co)polymers of the types and amounts (numbers, parts by mass) shown in Table 2 were used as the uncrosslinked perfluoro(co)polymer and the recycled perfluoro(co)polymer.

<IRHD>
The hardness of the obtained molded body was measured at 23° C. using an IRHD hardness measuring device in accordance with JIS K 6253-2: 2012. The results are shown in Table 2.

<Tensile strength and elongation at break>
The obtained molded article (O-ring) was stretched at 500 mm/min, and the tensile strength and elongation at break were measured using a Schopper tensile tester at 23° C. The results are shown in Table 2.

<Compression set>
The compression set of the sealing material was determined in accordance with JIS K 6262:2013.
The obtained molded body was kept at 200°C for 72 hours at a compression ratio of 25%, and then the pressure was released and the molded body was allowed to cool at the standard temperature of the test room for 30 minutes, after which the thickness of the molded body was measured.
The obtained molded body was kept at 260°C for 72 hours at a compression ratio of 20%, and then the pressure was released and the molded body was allowed to cool at the standard temperature of the test room for 30 minutes, after which the thickness of the molded body was measured.
The compression set (CS) was calculated based on the following formula: The results are shown in Table 2.
Compression set rate (%) = {(h0 - h1) / (h0 - h2)} x 100
[h0: thickness of the molded body before compression (mm), h1: thickness of the molded body after cooling for 30 minutes (mm), h2: thickness (height) of the spacer (mm)]

<Mass reduction rate (plasma resistance)>
The plasma resistance (mass reduction rate) of the obtained molded body was measured as follows. The results are shown in Table 2.
A fluorine radical exposure test was conducted in which the obtained molded body (O-ring) was exposed to fluorine radicals generated from _NF3 by remote plasma under the following conditions. The mass of the molded body (O-ring) was measured before and after the test, and the mass loss rate was calculated according to the following formula to evaluate plasma resistance. It can be said that the smaller the mass loss rate, the better the plasma resistance.
Mass reduction rate (%) = {(mass before test - mass after test) / (mass before test)} × 100

(conditions)
・Plasma source: Remote plasma source ・Plasma output: 5000W
Gas flow rate: NF ₃ : 1.5 SLM, argon : 1.5 SLM
・Vacuum level: 7torr
Test temperature: 250°C
・Exam time: 5 hours

In Example 5, a molded article having the same IRHD and elongation at break as in Comparative Example 4, which used only virgin products, was obtained, and a molded article having a smaller compression set and excellent plasma resistance (low mass loss rate) compared to Comparative Example 3 was obtained.
Furthermore, in Example 6, a molded article having the same IRHD and tensile strength as Comparative Example 6, which used only virgin products, was obtained. Compared to Comparative Example 5, the molded article had a smaller compression set when maintained at 200°C for 72 hours at a compression ratio of 25%, and was excellent in plasma resistance (having a smaller mass loss rate).

Claims (9)

A method for producing a regenerated perfluoro(co)polymer, comprising the step of heat-treating a crosslinked perfluoro(co)polymer, formed by crosslinking a perfluoro(co)polymer having crosslinking sites, in an inert gas atmosphere to regenerate the crosslinking sites. The method for producing recycled perfluoro(co)polymers according to claim 1, wherein the crosslinking sites are nitrile groups. The method for producing recycled perfluoro(co)polymers according to claim 1, wherein the inert gas is at least one selected from nitrogen gas, argon gas, and helium gas. The method for producing recycled perfluoro(co)polymers according to claim 1, wherein the perfluoro(co)polymer having crosslinking sites is a (co)polymer that does not contain carbon-hydrogen bonds in the main chain of the (co)polymer. A method for producing recycled materials, comprising a step of crosslinking a recycled material-forming material containing a recycled perfluoro(co)polymer obtained by the method for producing recycled perfluoro(co)polymer described in any one of claims 1 to 4. The method for producing recycled materials according to claim 5, wherein the recycled material-forming material further contains a crosslinking agent. The method for producing recycled materials described in claim 5, wherein the recycled material-forming material further contains an uncrosslinked perfluoro(co)polymer. The method for producing recycled materials described in claim 7, wherein the content of the recycled perfluoro(co)polymer in the recycled material-forming material is 0.5 parts by mass or more per 100 parts by mass of uncrosslinked perfluoro(co)polymer. The method for manufacturing recycled materials described in claim 5, wherein the recycled material is a sealing material.