JP6835848B2 - Liquid purification method and porous membrane manufacturing method - Google Patents

Description

The present invention relates to a liquid purification method for purifying a viscous liquid and a method for producing a porous membrane that can be suitably used for the purification method.

Conventionally, various viscous liquids having a certain degree of viscosity have been used for various purposes. Such a viscous liquid tends to embrace the gas inside when it comes into contact with the gas by being agitated or moving in the pipe.
When a viscous liquid embraces a gas, it is difficult for the viscous liquid to be naturally degassed due to its viscosity, and bubbles are stably present.

For example, when the viscous liquid is a photoresist composition, the bubbles contained in the photoresist composition may cause coating unevenness or cause defects in the patterned film formed by using the photoresist composition. Or become.
For this reason, there is a demand for a method for satisfactorily removing air bubbles in a viscous liquid such as a photoresist composition.

As a method of removing air bubbles from a viscous liquid such as a photoresist composition, a method of supplying the viscous liquid to a substrate after passing it through a filter for removing foreign substances and air bubbles has been proposed (Patent Document 1). ).

Japanese Unexamined Patent Publication No. 2010-135535

However, Patent Document 1 does not specifically describe the material, shape, opening diameter, etc. of the filter. For example, when a well-known filter such as a non-woven fabric made of PTFE (polytetrafluoroethylene) fiber is applied to remove air bubbles, air bubbles in the liquid to be treated may rather be affected depending on the viscosity of the liquid and the method of passing the liquid through the filter. It may increase.

The present invention has been made in view of the above problems, and is a method for purifying a viscous liquid capable of satisfactorily reducing the number of bubbles in the viscous liquid, and a porous method preferably used as a filter in the production method. It is an object of the present invention to provide a method for producing a film.

The present inventors apply a varnish containing a resin component (A), particles (B), and a solvent (S) on a substrate, and a composite composed of the resin component (A) and particles (B). A porous film obtained by a production method including forming a film and removing particles (B) in the composite film, or a communication hole including a structure in which spherical pores or substantially spherical pores are mutually communicated with each other. We have found that the above problems can be solved by filtering a viscous liquid having a viscosity of 0.1 Pa · s or more using a filter containing a porous membrane having a viscosity, and have completed the present invention. Specifically, the present invention provides the following.

A first aspect of the present invention is a method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
The filter is
A varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a composite film composed of the resin component (A) and particles (B). ,
A method comprising removing particles (B) in a composite membrane and containing a porous membrane obtained by a production method comprising.

A second aspect of the present invention is a method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
The filter is
A method comprising a porous membrane having a communication hole including a structure in which spherical holes or substantially spherical holes communicate with each other.

A third aspect of the present invention is
A varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a composite film composed of the resin component (A) and particles (B). ,
A method for producing a porous membrane, which comprises removing particles (B) in a composite membrane.
This is a method in which the viscosity of the varnish is 2.0 Pa · s or more.

According to the present invention, there is provided a method for purifying a viscous liquid capable of satisfactorily reducing the number of bubbles in the viscous liquid, and a method for producing a porous membrane which is suitably used as a filter in the production method. Can be done.

≪First purification method≫
In the specification of the present application, the liquid purification method described below is referred to as a "first purification method".
Specifically, it is a method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
The filter is
A varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a composite film composed of the resin component (A) and particles (B). ,
A method comprising removing particles (B) in a composite membrane and containing a porous membrane obtained by a production method comprising.
The viscosity of the viscous liquid is a value measured at 25 ° C. using an E-type viscometer.

In the first purification method, a viscous liquid having a predetermined viscosity is filtered while reducing the number of bubbles contained in the viscous liquid by using a filter containing a porous film obtained through the above-mentioned predetermined steps. , Can be purified.
The porous membrane used in the first purification method has pores corresponding to the shape of the particles (B). Then, in the porous membrane, communication holes in which a large number of pores communicate with each other are formed due to the method for producing the porous membrane.

In the porous membrane provided with such communication holes, the opening of the front surface (first main surface) of the porous membrane and the back surface of the porous membrane (second main surface opposite to the first main surface) The opening of the surface) is communicated with the communication hole.
Such communication holes function as a flow path for flowing a fluid from the first main surface to the second main surface of the porous membrane when the porous membrane is used as a filter.

Although the reason is not clear, the inclusion of the characteristically shaped communication holes in the porous film prevents the bubbles from passing through the porous film, and also prevents the bubbles from passing through the porous film when the viscous liquid passes through the porous film. It is thought that the generation of gas and the growth of gas dissolved in the viscous liquid into bubbles are hindered, and as a result, the number of bubbles contained in the viscous liquid is reduced by filtering the viscous liquid using the porous film as a filter. Be done.
The porous membrane naturally also has a function of removing fine solid foreign substances. Therefore, according to the first purification method, not only the number of bubbles in the viscous liquid but also the number of solid foreign substances is reduced.

The porous membrane used as a filter preferably has a communication hole including a structure in which spherical pores or substantially spherical pores communicate with each other.
That is, it is preferable that at least substantially all of the pores in the porous membrane in the present invention are curved surfaces. In the specification of the present application, such a hole having a shape substantially close to a true sphere may be referred to as a "spherical hole", and a hole having a shape generally close to a true sphere is referred to as a "substantially spherical hole". I have something to write about.
In the present specification, substantially spherical is defined by the sphericity represented by the value obtained by dividing the major axis of spherical particles or pores by the minor axis.
A shape having a sphericity within 1 ± 0.3 and not being a sphere is defined as a substantially sphere. The sphericity of the spherical pores or substantially spherical pores contained in the porous membrane used in the first purification method is preferably 0.90 or more and 1.10 or less, and more preferably 0.95 or more and 1.05 or less.

From the viewpoint of easy filtration in a short time, the garley air permeability of the porous membrane is preferably, for example, 1000 seconds or less, more preferably 100 seconds or less, further preferably 50 seconds or less, and most preferably 20 seconds or less. The lower the value, the more preferable, so the lower limit is not particularly set, but for example, 1 second or more is preferable in that the number of bubbles can be easily reduced while maintaining the flow velocity of the viscous liquid passing through the porous membrane to some extent.

<Manufacturing method of porous membrane>
The porous membrane used as a filter in the first purification method is
A varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a composite film composed of the resin component (A) and particles (B). ,
It is produced by a method comprising a porous membrane obtained by a production method comprising removing particles (B) in the composite membrane.
Hereinafter, the step of forming the composite film is also referred to as a “composite film forming step”, and the step of removing the particles (B) from the composite film is also referred to as a “removal step”.

[Composite film forming process]
In the composite film forming step, a varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a coating film, and then a solvent (S) is applied from the coating film. It is removed to form a composite film composed of the resin component (A) and the particles (B).
Hereinafter, the components contained in the varnish, the method for producing the varnish, and the coating method will be described.

[Resin component (A)]
The resin component (A) is not particularly limited as long as it is a resin having sufficient mechanical strength and chemical resistance to be used as a filter.
The resin preferably used as the resin component (A) includes at least one resin selected from the group consisting of polyvinylidene fluoride, polyether sulfone, polyamic acid, polyimide, polyamide-imide precursor, and polyamide-imide. ..
When the resin component (A) contains a polyamic acid or a polyamide-imide precursor, the composite film or the porous film after removing the particles (B) is subjected to imidization treatment to obtain a polyamide. It is preferable to convert the acid or polyamide-imide precursor to polyimide or polyamide-imide, respectively.
Hereinafter, these resins will be described.

(Polyvinylidene fluoride)
The polyvinylidene fluoride is not particularly limited as long as it is soluble in the solvent used for varnish formation. The polyvinylidene fluoride may be a homopolymer or a copolymer (copolymer). Examples of the constituent unit to be copolymerized include ethylene, ethylene trifluoride, ethylene tetrafluoride, propylene hexafluoride, and the like, and the mass average molecular weight is, for example, about 10,000 or more and 5 million or less.

(Polyester sulfone)
The polyether sulfone is not particularly limited as long as it is soluble in the solvent used for varnish formation. The polyether sulfone can be appropriately selected depending on the intended use of the porous membrane to be produced, and may be hydrophilic or hydrophobic. Further, it may be an aliphatic polyether sulfone or an aromatic polyether sulfone. The mass average molecular weight is, for example, 5000 or more and 1,000,000 or less, preferably 10,000 or more and 300,000 or less.

(Polyamic acid)
As the polyamic acid, a product obtained by polymerizing an arbitrary tetracarboxylic dianhydride and a diamine can be used without particular limitation. The amount of the tetracarboxylic dianhydride and the diamine used is not particularly limited, but it is preferable to use 0.50 mol or more and 1.50 mol or less of the diamine with respect to 1 mol of the tetracarboxylic dianhydride, and 0.60 mol. It is more preferable to use 1.30 mol or less, and it is particularly preferable to use 0.70 mol or more and 1.20 mol or less.

The tetracarboxylic dianhydride can be appropriately selected from the tetracarboxylic dianhydrides conventionally used as synthetic raw materials for polyamic acids. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride, but from the viewpoint of the heat resistance of the obtained polyimide resin, the aromatic dianhydride is used. It is preferable to use a carboxylic dianhydride. As the tetracarboxylic dianhydride, one type may be used alone, or two or more types may be used in combination.

Preferable specific examples of the aromatic tetracarboxylic acid dianhydride include pyromellitic acid dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, and bis (2,3-dicarboxyphenyl). Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3', 4'- Biphenyltetracarboxylic acid dianhydride, 2,2,6,6-biphenyltetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2) , 3-Dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2- Bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, bis ( 3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic acid dianhydride, 4,4- (P-Phenylenedoxy) diphthalic hydride, 4,4- (m-Phenylenedoxy) diphthalic hydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5 , 8-Naphthalene tetracarboxylic acid dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10 -Perylene tetracarboxylic acid dianhydride, 2,3,6,7-anthracene tetracarboxylic acid dianhydride, 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride, 9,9-bisfluorene phthalate anhydride , 3,3', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride and the like. Examples of the aliphatic tetracarboxylic dianhydride include ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1,2, Examples thereof include 4,5-cyclohexanetetracarboxylic dianhydride and 1,2,3,4-cyclohexanetetracarboxylic dianhydride. Among these, 3,3', 4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoint of price, availability and the like. In addition, these tetracarboxylic dianhydrides may be used alone or in admixture of two or more.

The diamine can be appropriately selected from diamines conventionally used as a synthetic raw material for polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine, but an aromatic diamine is preferable from the viewpoint of heat resistance of the obtained polyimide resin. One of these diamines may be used alone, or two or more of these diamines may be used in combination.

Examples of the aromatic diamine include a diamino compound in which one phenyl group or two or more and ten or less phenyl groups are bonded. Specifically, phenylenediamine and its derivatives, diaminobiphenyl compounds and their derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindane and its derivatives, diaminotetraphenyl. It is a compound and its derivative, a diaminohexaphenyl compound and its derivative, and a cardo-type fluorinamine derivative.

The phenylenediamine is m-phenylenediamine, p-phenylenediamine or the like, and the phenylenediamine derivative is a diamine to which an alkyl group such as a methyl group or an ethyl group is bonded, for example, 2,4-diaminotoluene or 2,4-triphenylene. Diamine and the like.

In the diaminobiphenyl compound, two aminophenyl groups are bonded to each other. For example, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl and the like.

A diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other via another group. The bond is an ether bond, a sulfonyl bond, a thioether bond, a bond by an alkylene or a derivative group thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a ureylene bond and the like. The number of carbon atoms in the alkylene bond is about 1 or more and 6 or less. The derivative group of the alkylene group is an alkylene group substituted with one or more halogen atoms or the like.

Examples of diaminodiphenyl compounds include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylketone , 3,4'-Diaminodiphenylketone, 2,2-bis (p-aminophenyl) propane, 2,2'-bis (p-aminophenyl) hexafluoropropane, 4-methyl-2,4-bis (p) -Aminophenyl) -1-pentene, 4-methyl-2,4-bis (p-aminophenyl) -2-pentene, iminodianiline, 4-methyl-2,4-bis (p-aminophenyl) pentane, Bis (p-aminophenyl) phosphenyl oxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis (4-aminophenoxy) benzene, 1 , 3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl ] Sulphon, bis [4- (3-aminophenoxy) phenyl] sulphon, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane and the like can be mentioned.

Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferable from the viewpoint of price, availability, and the like.

The diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are both bonded via other groups. As the other group, a group similar to the diaminodiphenyl compound is selected. Examples of the diaminotriphenyl compound include 1,3-bis (m-aminophenoxy) benzene, 1,3-bis (p-aminophenoxy) benzene, 1,4-bis (p-aminophenoxy) benzene and the like. be able to.

Examples of diaminonaphthalene include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

Examples of aminophenylaminoindanes include 5- or 6-amino-1- (p-aminophenyl) -1,3,3-trimethylindanes.

Examples of diaminotetraphenyl compounds are 4,4'-bis (p-aminophenoxy) biphenyl, 2,2'-bis [p- (p'-aminophenoxy) phenyl] propane, 2,2'-bis [ Examples thereof include p- (p'-aminophenoxy) biphenyl] propane, 2,2'-bis [p- (m-aminophenoxy) phenyl] benzophenone and the like.

Examples of the cardo-type fluorene amine derivative include 9,9-bisaniline fluorene.

The number of carbon atoms of the aliphatic diamine is, for example, preferably 2 or more and 15 or less. Specific examples of the aliphatic diamine include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

The hydrogen atom of these diamines may be a compound substituted with at least one substituent selected from the group of halogen atom, methyl group, methoxy group, cyano group, phenyl group and the like.

The means for producing the polyamic acid is not particularly limited, and for example, a known method such as a method of reacting an acid or a diamine component in a solvent can be used.

The reaction of the tetracarboxylic dianhydride with the diamine is usually carried out in a solvent. The solvent used for the reaction between the tetracarboxylic dianhydride and the diamine is particularly limited as long as it is a solvent capable of dissolving the tetracarboxylic dianhydride and the diamine and not reacting with the tetracarboxylic dianhydride and the diamine. Not done. One type of solvent may be used alone, or two or more types may be used in combination.

Examples of solvents used in the reaction of tetracarboxylic acid dianhydride with diamine include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, Nitrogen-containing polar solvents such as N-diethylformamide, N-methylcaprolactam, N, N, N', N'-tetramethylurea; β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, Lactone-based polar solvents such as γ-caprolactone and ε-caprolactone; dimethylsulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellsolvate acetate, ethyl cell solve acetate Etc.; Examples thereof include phenolic solvents such as cresols and xylene-based mixed solvents.
One of these solvents may be used alone, or two or more of these solvents may be used in combination. The amount of the solvent used is not particularly limited, but it is desirable that the content of the polyamic acid produced is 5% by mass or more and 50% by mass or less.

Among these solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethyl are due to the solubility of the polyamic acid produced. A nitrogen-containing polar solvent such as formamide, N-methylcaprolactam, N, N, N', N'-tetramethylurea is preferable.

The polymerization temperature is generally −10 ° C. or higher and 120 ° C. or lower, preferably 5 ° C. or higher and 30 ° C. or lower. The polymerization time depends on the raw material composition used. The polymerization time is usually 3 Hr (hours) or more and 24 Hr or less.
As the polyamic acid, one type may be used alone, or two or more types may be used in combination.

[Polyimide resin]
The structure and molecular weight of the polyimide resin are not limited, and a known polyimide resin can be used. Regarding polyimide, the side chain may have a condensable functional group such as a carboxy group or a functional group that promotes a crosslinking reaction or the like during firing. When the varnish contains a solvent, a soluble polyimide resin that is soluble in the solvent used is preferable.

Use of a monomer to introduce a flexible bent structure in the main chain to obtain a solvent-soluble polyimide resin, such as ethirediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, Aliphatic diamines such as 4,4'-diaminodicyclohexylmethane; 2-methyl-1,4-phenylenediamine, o-trizine, m-trizine, 3,3'-dimethoxybenzidine, 4,4'-diaminobenzanilide, etc. Aromatic diamines; polyoxyalkylene diamines such as polyoxyethylene diamines, polyoxypropylene diamines, and polyoxybutylenediamines; polysiloxane diamines; 2,3,3', 4'-oxydiphthalic acid anhydrides, 3,4,3' , 4'-oxydiphthalic acid anhydride, 2,2-bis (4-hydroxyphenyl) propandibenzoate-3,3', 4,4'-tetracarboxylic acid dianhydride, etc. are effective. Also, the use of monomers having functional groups that improve solubility in solvents, such as 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl, 2-trifluoromethyl-1,4- It is also effective to use a fluorinated diamine such as phenylenediamine. Further, in addition to the monomer for improving the solubility of the polyimide resin, the same monomer as the monomer described in the column of polyamic acid can be used in combination as long as the solubility is not impaired.
As each of the polyimide resin and the monomer thereof, one type may be used alone, or two or more types may be used in combination.

There is no particular limitation on the means for producing the polyimide resin. For example, a known method such as a method for chemically imidizing or heat imidizing a polyamic acid can be used. Examples of such a polyimide resin include an aliphatic polyimide resin (total aliphatic polyimide resin) and an aromatic polyimide resin, and an aromatic polyimide resin is preferable. The aromatic polyimide resin is a polyimide resin obtained by ring-closing a polyamic acid having a repeating unit represented by the formula (1) by a thermal or chemical means, or a polyimide resin having a repeating unit represented by the formula (2). And so on. In the formula, Ar represents an aryl group. If the varnish contains a solvent, these polyimide resins may then be dissolved in the solvent used.

(Polyamide-imide resin and polyamide-imide precursor)
As the polyamide-imide resin, a known polyamide-imide resin can be used without being limited in its structure and molecular weight. The polyamide-imide resin may have a condensable functional group such as a carboxy group or a functional group that promotes a crosslinking reaction during firing in the side chain. When the varnish contains a solvent, a soluble polyamide-imide resin that is soluble in the solvent used is preferable.

The polyamide-imide resin is usually (i) a resin obtained by reacting an acid having a carboxy group and an acid anhydride group in one molecule such as trimellitic anhydride with diisocyanate, and (ii) trimellitic anhydride chloride. A resin or the like obtained by imidizing a precursor polymer (polyamide-imide resin precursor) obtained by reacting a reactive derivative of the above acid with a diamine can be used without particular limitation.

Examples of the acid or its reactive derivative include trimellitic anhydride, trimellitic anhydride such as trimellitic anhydride, trimellitic anhydride, and trimellitic anhydride.

Examples of the optional diamine include the diamines exemplified in the above description of the polyamic acid. In addition, diaminopyridine compounds can also be used.

The arbitrary diisocyanate is not particularly limited, and examples thereof include diisocyanate compounds corresponding to the above arbitrary diamines. Specific examples thereof include metaphenylene diisocyanate, p-phenylenediis diisocyanus, o-trizine diisocyanate, and p-phenylene. Diisocyanis, m-phenylenediisocyanis, 4,4'-oxybis (phenylisocyanide), 4,4'-diisocyanide diphenylmethane, bis [4- (4-isocyanene phenoxy) phenyl] sulfone, 2,2'-bis [4- ( 4-Isocyanisene phenoxy) phenyl] propane, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 3, Examples thereof include 3'-diethyldiphenyl-4,4'-diisocyanis, isophorone diisocyanis, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate and naphthalenedi isocyanate.

In addition to the above, compounds described as general formulas in JP-A-63-283705 and JP-A-2-198619 can also be used as the raw material monomer for the polyamide-imide resin. Further, the imidization in the above method (ii) may be either thermal imidization or chemical imidization. As the chemical imidization, a method such as immersing an unfired composite membrane formed by using a varnish containing a polyamide-imide precursor or the like in acetic anhydride or a mixed solvent of acetic anhydride and isoquinolin can be used. The polyamide-imide precursor can be said to be a polyimide precursor from the viewpoint of a precursor before imidization.

The polyamide-imide resin contained in the varnish includes (1) a polymer obtained by reacting an acid such as trimellitic anhydride with diisocyanate, and (2) a reactive derivative of the above acid such as trimellitic anhydride chloride. It may be a polymer obtained by imidizing a precursor polymer obtained by a reaction with a diamine. As used herein and in the claims, "polyamide-imide precursor" means a polymer before imidization (precursor polymer).
As each of the polyamide-imide resin and the polyamide-imide precursor, one type may be used alone, or two or more types may be used in combination. Further, regarding the polyamide-imide resin, each of the above-mentioned polymer, raw material monomer, and oligomer may be used alone or in combination of two or more.

[Particle (B)]
The material of the particles (B) is not particularly limited as long as it is insoluble in the solvent contained in the varnish and can be later removed from the composite film composed of the resin component (A) and the particles (B). It can be adopted. For example, inorganic materials include metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al ₂ O ₃ ), and organic materials include high molecular weight olefins (polypropylene, polyethylene, etc.), polystyrene, and acrylic resins (Al). Examples thereof include organic polymer fine particles such as methyl methacrylate, isobutyl methacrylate, polymethyl methacrylate (PMMA), etc.), epoxy resin, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, polyether and the like.

Among the materials of the particles (B), silica such as colloidal silica is preferable as the inorganic material, and acrylic resin, particularly PMMA, is preferable as the organic material. It is preferable to use spherical particles made of such a material as the particles (B) because it is easy to form fine pores having a curved surface on the inner surface in the porous film.

Further, the resin used as the material of the particles (B) may be appropriately selected from, for example, ordinary linear polymers and known depolymerizable polymers according to the purpose.
A normal linear polymer is a polymer in which the molecular chain of the polymer is randomly cleaved during thermal decomposition, and a depolymerizable polymer is a polymer in which the polymer is decomposed into monomers during thermal decomposition.
All of them can be removed from the composite membrane by decomposing them into monomers, low molecular weight substances, or CO _{2 when heated.}
The decomposition temperature of the resin used as the material of the particles (B) is preferably 200 ° C. or higher and 320 ° C. or lower, and more preferably 230 ° C. or higher and 260 ° C. or lower.
When the decomposition temperature is 200 ° C. or higher, film formation can be performed even when a high boiling point solvent is used for the varnish, and there is a wide range of selection of firing conditions when producing a polyimide resin or a polyamide-imide resin by firing.
Further, when the decomposition temperature is 320 ° C. or lower, the particles (B) can be eliminated from the composite film while suppressing the heat damage of the resin component (A) in the composite film.

Among the depolymerizable polymers, since the thermal decomposition temperature is low and the pores are easily handled, a homopolymer of methyl methacrylate or isobutyl methacrylate (polymethylmethacrylate or polyisobutylmethacrylate), or methyl methacrylate. Alternatively, a copolymer mainly composed of a unit derived from isobutyl methacrylate is preferable.

It is preferable to use particles (B) having a high sphericity ratio because it is easy to form pores having a preferable shape having a curved surface on the inner surface in the formed porous film.
The particle size (average diameter) of the particles (B) is, for example, preferably 800 nm or more and 3500 nm or less, more preferably 900 nm or more and 3000 nm or less, and particularly preferably more than 2000 nm and 2500 nm or less.
By using the particles (B) having such a particle size, communication holes in which pores having corresponding diameters communicate with each other are formed in the porous membrane. When a porous film having such communication holes is used, the viscous liquid can be filtered at a pressure such that the porous film does not break, and the filtration using the porous film makes it particularly easy to reduce bubbles in the viscous liquid.

The particle size distribution index (d25 / 75) of the particles (B) may be 1 or more and 6 or less, preferably 1.1 or more and 5 or less, and more preferably 1.2 or more and 4 or less. By setting the lower limit value to 1.1 or more, the particles (B) can be efficiently filled in the composite film, and therefore, the communication holes which are the flow paths of the viscous liquid are satisfactorily formed. Further, in the case of 1.6 or more, since pores of different sizes are formed in the porous membrane, the convection state of the viscous fluid at each pore during filtration changes variously. It is considered that such a change in the convection condition enhances the purification effect of the viscous liquid based on the adsorption by the inner wall surface of the hole.
Note that d25 and d75 are values of particle diameters in which the cumulative frequencies of the particle size distribution are 25% and 75%, respectively, and in the present specification, d25 is the larger particle size.

In the production method described later, when the composite film is formed as a two-layer laminated film, the particles (B1) used for the first varnish and the particles (B2) used for the second varnish are the same and are the same. It may be different.
In order to make the pores on the side in contact with the base material more dense, the particle size distribution index of the particles (B1) is preferably equal to or less than the particle size distribution index of the particles (B2).
Alternatively, the sphericity of the particle (B1) is preferably equal to or less than the sphericity of the particle (B2).
Further, the particle size (average diameter) of the particles (B1) is preferably smaller than the particle size of the particles (B2). In this case, it is easy to increase the strength of the porous film while making the opening ratio of the surface of the porous film high and uniform.

[Dispersant]
The varnish may further contain a dispersant together with the particles (B) for the purpose of uniform dispersion of the particles (B). Since the varnish contains a dispersant, the resin component (A) and the particles (B) can be mixed more uniformly, and the particles (B) can be uniformly mixed in the coating film formed by using the varnish. Can be distributed.
As a result, it is possible to provide a dense opening on the surface of the finally obtained porous membrane and to form a communication hole for efficiently communicating the front and back surfaces of the porous membrane so as to improve the air permeability of the porous membrane. ..

The dispersant is not particularly limited, and can be appropriately selected from known dispersants. Specific examples of suitable dispersants include palm fatty acid salt, castor sulfate oil salt, lauryl sulfate salt, polyoxyalkylene allylphenyl ether sulfate salt, alkylbenzene sulfonic acid, alkylbenzene sulfonate, alkyldiphenyl ether disulfonate, alkyl. Anionic surfactants such as naphthalene sulfonate, dialkyl sulfosuccinate salt, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salt, polyoxyethylene allylphenyl ether phosphate salt; oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl Cationic surfactants such as trimethylammonium chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, didecyldimethylammonium chloride; palm alkyldimethylamine oxide, fatty acid amidepropyldimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amide betaine type activity Amphoteric surfactants such as agents, alanine-type activators, lauryliminodipropionic acid; polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxy Nonionic surfactants of polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers such as ethylene polystyrylphenyl ether and polyoxyalkylene polystyrylphenyl ether, polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylene acidification Other polyoxyalkylene-based nonionic surfactants such as castor oil, polyoxyethylene hydrogenated castor oil, sorbitan lauric acid ester, polyoxyethylene sorbitan lauric acid ester, fatty acid diethanolamide; octyl stearate, trimethyl propantoridecano Fatty acid alkyl esters such as ate; polyether polyols such as polyoxyalkylene butyl ethers, polyoxyalkylene oleyl ethers, and trimethyl propanthris (polyoxyalkylene) ethers can be mentioned. Dispersants are not limited to these. Further, the dispersant may be used as a mixture of two or more kinds.

[Solvent (S)]
The type of the solvent (S) is not particularly limited as long as the resin component (A) can be dissolved and the particles (B) are not dissolved. Examples of the solvent (S) include the solvent exemplified as the solvent used for the reaction between the tetracarboxylic dianhydride and the diamine. The solvent (S) may be used alone or in combination of two or more.
When the resin component (A) is polyvinylidene fluoride, examples of the solvent include the above-mentioned nitrogen-containing polar solvent, lower alkyl ketones such as methyl ethyl ketone, acetone and tetrahydrofuran, and trimethyl phosphate and the like.
When the resin component (A) is polyether sulfone, the solvent used is diphenyl sulfone, dimethyl sulfone, dimethyl sulfoxide, benzophenone, tetrahydrothiophene-1,1-dioxide, 1,3-dimethyl-in addition to the above-mentioned nitrogen-containing polar solvent. Examples thereof include polar solvents such as 2-imidazolidinone.

[Other ingredients]
In addition to the above components, varnish is an antistatic agent, a flame retardant, a chemical imidizing agent, a condensing agent, for the purpose of antistatic, flame retardant, low temperature firing, mold release, and coating property improvement. Known components such as a release agent and a surface conditioner may be appropriately contained, if necessary.

[Varnish manufacturing method]
As described above, the varnish contains the resin component (A), the particles (B), and the solvent (S).
The method for producing the varnish is not particularly limited as long as the resin component (A) is dissolved in the solvent (S) and the particles (B) can be dispersed in the solvent (S).
For example, the monomer may be polymerized in the solvent (S) to generate the resin component (A), or the resin component (A) may be dissolved in the solvent (S).
When the resin component (A) is produced in the solvent (S), the polymerization reaction may be carried out in the presence of the particles (B) or in the absence of the particles (B).

The viscosity of the varnish is preferably 2.0 Pa · s or more. Such viscosity is a value measured at 25 ° C. using an E-type viscometer. When a porous film is formed using a varnish having a viscosity of 2.0 Pa · s or more, it is particularly easy to form a porous film that easily removes air bubbles in a viscous liquid.
The viscosity of the varnish has some influence on the dispersed state of the particles (B) in the coating film formed by using the varnish, and a porous film having communication holes having a shape that facilitates removal of air bubbles is formed. It is presumed.
The viscosity of the varnish is more preferably 2.0 Pa · s or more, and particularly preferably 2.3 Pa · s or more and 4.9 Pa · s or less. The viscosity of the varnish is preferably 2.0 Pa · s or more, more preferably 2.3 Pa · s or more, and 2.5 Pa · s or more, from the viewpoint of coatability and uniformity of the film thickness of the formed porous film. -S or more is particularly preferable.
The method for adjusting the viscosity of the varnish is not particularly limited, but the content of the resin component (A), the type of the resin component (A), the content of the particles (B), the particle size of the particles (B), and the solvent (S). It is preferable to adjust by changing at least one of the content and the type of the solvent (S).

The solid content concentration of the varnish is preferably 25% by mass or more. The solid content concentration of the varnish is particularly preferably 40% by mass or less.
By using a varnish having a solid content concentration of 25% by mass or more, it is particularly easy to form a porous film in which bubbles in a viscous liquid can be easily removed. Further, when the solid content concentration of the varnish is 40% by mass or less, the varnish can be easily applied to the substrate, and a porous film having a uniform film thickness can be easily formed.

Further, in the varnish, and the volume _{V A} of the resin component (A), the ratio _V A of the volume _{V B} of particles (B): is _{V B,} 15: _85~40: 60 is preferred. When the resin component (A) and the particles (B) are mixed in the varnish at a ratio within such a range, it is easy to uniformly disperse the particles (B) in the varnish while preventing the particles (B) from aggregating. , It is easy to form a porous film having a uniform opening on the surface.

[Composite film forming method]
The varnish produced by the method described above is applied onto the substrate to form a coating film containing the resin component (A), the particles (B), and the solvent (S). By heating the coating film to remove the solvent (S), a composite film composed of the resin component (A) and the particles (B) is formed.
The coating film is heated at 0 ° C. or higher and 120 ° C. or lower (preferably 0 ° C. or higher and 100 ° C. or lower) under normal pressure or vacuum, and more preferably 60 ° C. or higher and 95 ° C. or lower under normal pressure (preferably 0 ° C. or higher and 100 ° C. or lower) when removing the solvent (S). More preferably, it is carried out at 65 ° C. or higher and 90 ° C. or lower).
The coating film thickness is, for example, 1 μm or more and 500 μm or less, preferably 5 μm or more and 100 μm or less, and preferably 10 μm or more and 50 μm or less. A release layer may be provided on the substrate as needed.
Further, in the production of the composite film, a dipping step in a solvent containing water, a pressing step, and a drying step after the dipping step may be provided as arbitrary steps before the firing step described later.

The release layer can be produced by applying a release agent on a substrate and then drying or baking. As the release agent, known release agents such as alkyl phosphate ammonium salt type, fluorine type and silicone can be used without particular limitation.
When the composite film containing the resin component (A) and the particles (B) is peeled from the substrate after the solvent (S) is removed, a small amount of the release agent remains on the peeled surface of the composite film.
Since the remaining mold release agent may affect the wettability of the surface of the porous film and the mixing of impurities, it is preferable to remove it.

When the release layer is provided, the composite film peeled from the substrate is preferably washed with an organic solvent or the like. The cleaning method can be selected from known methods such as a method of immersing the composite membrane in the cleaning liquid and then taking it out, and a method of spraying the composite membrane with the cleaning liquid for shower cleaning.
Further, the composite membrane after washing is dried. As a drying method, known methods such as air-drying the washed composite membrane at room temperature and heating the composite membrane to an appropriate set temperature in a constant temperature bath can be applied without limitation. At the time of drying, for example, a method of fixing the end portion of the composite film to a SUS mold or the like to prevent deformation can be adopted.

On the other hand, when the substrate is used as it is without providing the release layer for forming the composite film, the step of forming the release layer and the step of cleaning the unfired composite film can be omitted.

When the composite film is formed as a two-layer laminated film, first, the first varnish is applied as it is on a substrate such as a glass substrate, and the temperature is 0 ° C. or higher and 120 ° C. or lower (preferably 0) under normal pressure or vacuum. The first composite film is formed by drying at a normal pressure of 10 ° C. or higher and 100 ° C. or lower (more preferably 10 ° C. or higher and 90 ° C. or lower). The film thickness of the first composite film is preferably 1 μm or more and 5 μm or less.

Subsequently, a second varnish is applied onto the first composite film, and similarly, 0 ° C. or higher and 80 ° C. or lower (preferably 0 ° C. or higher and 50 ° C. or lower), more preferably normal pressure of 10 ° C. or higher and 80 ° C. or lower. Drying is carried out at (more preferably 10 ° C. or higher and 30 ° C. or lower) to form a second composite film to obtain a composite film which is a two-layered laminated film. The film thickness of the second composite film is preferably 5 μm or more and 50 μm or less.

When the resin component (A) directly constitutes a porous film, the composite film obtained according to the above method is then subjected to a removal step described later.
When the resin component (A) contains a polyamic acid, a polyamide-imide precursor, or the like, if necessary, the composite film is fired before removing the fine particles (B) to be contained in the resin component (A). The polyamic acid or the polyamide-imide precursor may be converted into a polyimide resin or a polyamide-imide resin, respectively.

The firing temperature also differs depending on the structure of the polyamic acid or polyamide-imide precursor contained in the composite film and the presence or absence of a condensing agent. The firing temperature is usually preferably 120 ° C. or higher and 400 ° C. or lower, and more preferably 150 ° C. or higher and 375 ° C. or lower.

Baking does not necessarily have to be clearly separated from the drying process. For example, when firing at 375 ° C, the temperature is raised from room temperature to 375 ° C in 3 hours and then held at 375 ° C for 20 minutes, or the temperature is gradually raised from room temperature to 375 ° C in 50 ° C increments (each). A stepwise drying-thermal imidization method can also be used, such as holding for 20 minutes in steps) and finally holding at 375 ° C. for 20 minutes. At that time, a method may be adopted in which the end portion of the unfired composite film is fixed to a mold made of SUS or the like to prevent deformation.

The thickness of the composite film can be obtained by measuring and averaging the thicknesses of a plurality of locations with a micrometer or the like. The average thickness is preferably thin, for example, 1 μm or more, 5 μm or more and 500 μm or less, and 8 μm or more and 100 μm or less is more preferable.

[Removal process]
By selecting and removing the particles (B) from the composite film by an appropriate method, a porous film having micropores can be produced with good reproducibility.
For example, when silica is used as the fine particles, a porous membrane can be obtained by treating the composite membrane with low-concentration hydrogen fluoride water (HF) or the like to dissolve and remove silica from the composite membrane.
When the particles (B) are resin fine particles, the composite film is heated to a temperature equal to or higher than the thermal decomposition temperature of the resin fine particles and lower than the thermal decomposition temperature of the resin component (A) to obtain the resin fine particles. Can be decomposed and removed from the composite membrane.

When the porous film obtained after the removal step contains a polyamic acid or a polyamide-imide precursor as the resin component (A), the porous film is closed with the polyamic acid or the polyamide-imide precursor to form an imide ring. May be processed for this purpose.
Examples of such a treatment include the above-mentioned firing treatment.

[Chemical etching process]
The composite film or the porous film formed as described above may be further subjected to chemical etching. By performing chemical etching, the aperture ratio of the surface of the porous film can be increased. In particular, when the porous film is chemically etched, the plurality of pores derived from the particles (B) are well communicated with each other, and it is easy to form communication pores having a preferable shape.
The chemical etching method is not particularly limited, and for example, a conventionally known method can be used.

Examples of the chemical etching method include treatment with a chemical etching solution such as an inorganic alkaline solution or an organic alkaline solution. Inorganic alkaline solutions are preferred. As the inorganic alkali solution, for example, a hydrazine solution containing hydrazine hydrate and ethylenediamine, a solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, an ammonia solution, an alkali hydroxide. An etching solution containing hydrazine and 1,3-dimethyl-2-imidazolidinone as main components can be mentioned. Examples of the organic alkaline solution include primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; dimethylethanolamine. , Alcohol amines such as triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; alkaline solutions such as cyclic amines such as pyrrol and pyridin.

Pure water and alcohols can be appropriately selected as the solvent for each of the above solutions. It is also possible to use a solvent to which an appropriate amount of a surfactant is added. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

When chemical etching is performed, it is preferable to clean the porous film in order to remove excess etching solution components.
As the cleaning after the chemical etching, water washing alone may be used, but it is preferable to combine acid washing and / or water washing.

[Physical removal process]
The composite film or the porous film formed as described above may be physically removed separately from the chemical etching or together with the chemical etching.
Examples of the physical removal method include dry etching by plasma (oxygen, argon, etc.), corona discharge, or the like.
By such a method, the resin component (A) in the porous film is partially removed, and the same curing as the above-mentioned chemical etching can be obtained.

[Reburning process]
When a porous film is produced using a varnish containing a resin component (A) containing one or more selected from a polyimide resin, a polyamide-imide resin, a polyamic acid, and a polyamide-imide precursor, the surface of the porous film is organic. In order to improve the wettability to the solvent and remove the residual organic matter, the porous film may be obtained once and then fired again.
The firing conditions in the recalcination step are the same as the conditions for closing the polyamic acid or the polyamide-imide precursor to form an imide ring.

By the method described above, a porous membrane used as a filter in the first purification method is produced.

The obtained porous membrane has spherical pores having an average diameter of 800 nm or more and 3500 nm or less (preferably 900 nm or more and 3000 nm or less, more preferably more than 2000 nm and 2500 nm or less). The hole diameter of the portion (communication hole) in which the spherical pores are connected preferably includes a communication hole of 50 nm or more and 2000 nm or less, more preferably 500 nm or more and 1800 nm or less, and a communication hole of more than 1000 nm and 1300 nm or less. It is particularly preferable to include it. The average pore diameter of the communication holes measured by the porosimeter is preferably 500 nm or more and 2000 nm or less, more preferably 900 nm or more and 1800 nm or less, and further preferably 1000 nm or more and 1500 nm or less. The porosity of the obtained porous membrane is, for example, 50% or more and 90% or less, preferably 60% or more and 85% or less.

<Viscous liquid>
The viscous liquid may be a liquid having a viscosity of 0.1 Pa · s or more measured at 25 ° C. using an E-type viscometer and which does not dissolve or deteriorate the filter by contact for several minutes to 1 hour. There is no particular limitation.
In the above-mentioned viscous liquid, due to its viscosity, it is difficult for gas to be naturally released from the liquid, and bubbles are stably present.
Further, in the filtration operation, when the viscous liquid moves in the piping or the filter device, if a flow that entrains the gas is generated, bubbles may be generated in the viscous liquid.
However, when the viscous liquid is filtered using the porous membrane formed by the method described above, the number of bubbles in the viscous liquid can be effectively reduced.

Generally, the higher the viscosity of a liquid, the more difficult it is to remove air bubbles. However, in the first purification method, the viscosity measured by an E-type viscometer at 25 ° C. is 0.15 Pa · s or more, preferably 0.7 Pa · s or more, more preferably 1 Pa · s or more, still more preferably. It is particularly effective in reducing the number of bubbles in a viscous liquid of 1.5 Pa · s or more.
The upper limit of the viscosity of the viscous liquid is not particularly limited as long as it can be filtered by a filter, but is preferably 8.0 Pa · s or less, and more preferably 7.0 Pa · s or less.
If the viscosity is excessively high, it may be difficult to filter with a filter in the first place.

The first purification method is preferably used for purifying a liquid curable material used for forming an insulating film, an antireflection film, an adhesive layer, and a hard coat, for example. When the liquid curable material contains air bubbles, appearance defects occur in the formed insulating film, antireflection film, adhesive layer, hard coat and the like.
In particular, when the insulating layer, antireflection film, adhesive layer, hard coat, etc. are transparent layers, in a display device or an optical device including these layers, bubbles cause unwanted light scattering or refraction, and the device It may deteriorate the performance.

A photoresist composition is also preferable as a purification target by the first purification method. Bubbles in the photoresist composition become defects in the patterned film formed with the photoresist composition. Further, if air bubbles are present in the photoresist composition, when the photoresist composition is applied to the substrate, the air bubble portion remains in the coating film, causing coating unevenness such as thinning of the film thickness of the portion. Cheap.
The composition of the photoresist composition is not particularly limited, and may be a negative type or a positive type.

Further, as the purification target by the first purification method, a raw material chemical solution such as a resin solution used for the above-mentioned curable material or a photoresist composition is also preferable. In general, a high-concentration and highly viscous raw material chemical solution can be purified to effectively reduce the number of bubbles in the liquid.

<Specific liquid purification method>
In the first purification method, the viscous liquid described above is filtered using a filter containing a porous membrane produced by the method described above. In the first manufacturing method, the viscous liquid is permeated from one side of the filter to the other side. Such transmission is typically achieved by creating a differential pressure on one side and the other side of the filter.

Examples of the method of using the porous membrane as a filter in the first purification method include a method of using a flat porous membrane, a method of using a porous membrane processed into a pipe shape, and the like.
It is preferable that the pipe-shaped porous membrane has a pleated shape because the contact area between the viscous liquid and the filter increases. As will be described later, the porous membrane is appropriately sealed so that the supply liquid and the filtrate are not mixed.

Purification of the viscous liquid can be carried out by using the above-mentioned porous membrane without differential pressure, that is, by natural filtration by gravity, but it is preferable to carry out by differential pressure.
The method of generating the differential pressure is not particularly limited as long as it is a method of providing a pressure difference between one side and the other side of the porous membrane. As a method of generating the differential pressure, usually, pressure is applied to one side of the porous membrane (supply liquid side) (positive pressure), and one side of the porous membrane (filter liquid side) is negative pressure. Pressure reduction (negative pressure) and the like can be mentioned, and pressurization is preferable.

Pressurization is the application of pressure to the side (supply liquid side) of the polyimide-based resin porous membrane in which the liquid (sometimes referred to as “supply liquid” in the present specification) before permeating the porous membrane exists. is there. For example, it is preferable to apply pressure by utilizing the flow pressure generated by the circulation or delivery of the feed solution or by utilizing the positive pressure of the gas.
The flow pressure can be generated by, for example, an aggressive flow pressure addition method such as a pump (liquid feed pump, circulation pump, etc.). Specific examples of the pump include a rotary pump, a diaphragm pump, a metering pump, a chemical pump, a plunger pump, a bellows pump, a gear pump, a vacuum pump, an air pump, a liquid pump and the like.
The flow pressure may be, for example, the pressure applied to the porous membrane by the liquid when the liquid is permeated through the porous membrane only by gravity. It is preferable that the pressure is applied by the above-mentioned positive flow pressure application method.
The gas used for pressurization is preferably a gas that is inert or non-reactive with respect to the feed solution, and specific examples thereof include nitrogen, and rare gases such as helium and argon.
When the viscous liquid is an electronic material, particularly a liquid used in the manufacturing field such as a semiconductor, pressurization is preferable. In that case, the side that collects the liquid that has passed through the porous membrane may be at atmospheric pressure without decompression. As the pressurization, positive pressure by gas is preferable.
The pressurization may be performed via a pressurizing valve or a valve such as a pressurizing valve or a three-way valve.
The depressurization is the decompression on the side (filtrate side) that collects the liquid that has passed through the polyimide resin porous membrane. The depressurization may be, for example, decompression by a pump. It is preferable to reduce the pressure to vacuum.
When the feed fluid is circulated or pumped by a pump, the pump is usually arranged between the feed fluid tank (or circulation tank) and the porous membrane.

For pressurization, both the flowing pressure and the positive pressure of the gas may be used. Further, the differential pressure may be a combination of pressurization and depressurization. For pressurization, for example, both the fluid pressure and the depressurization may be used, both the positive pressure and the depressurization of the gas may be used, and the fluid pressure and the positive pressure and the depressurization of the gas are used. You may.
When the method of providing the differential pressure is combined, the combination of the flow pressure and the positive pressure of the gas and the combination of the flow pressure and the reduced pressure are preferable from the viewpoint of simplification of production and the like.

The pressure difference applied to the front and back of the porous membrane by providing the differential pressure is the film thickness, porosity or average pore size of the porous membrane used, or the desired degree of purification, flow rate, flow rate, or concentration of the feed solution. It may be set appropriately depending on the viscosity and the like.
In the case of the so-called cross-flow method (the supply liquid flows parallel to the porous membrane), the differential pressure is preferably 3 MPa or less, for example.
In the case of the so-called dead-end method (the supply liquid flows so as to intersect the porous membrane), the differential pressure is preferably 1 MPa or less, for example.
If the differential pressure is excessively high, bubbles may be generated in the viscous liquid during filtration. When the differential pressure is within the above range, it is easy to filter the viscous liquid without generating bubbles.
In these methods, the lower limit of the differential pressure is not particularly limited, and is, for example, 10 Pa.

The temperature during filtration may be appropriately set, for example, in the range of 0 ° C. or higher and 30 ° C. or lower, preferably 25 ° C. Regarding the filtration temperature, a temperature gradient may be provided by a time difference in filtration, or a temperature difference may be provided between the supply liquid side and the filtrate side.

In the first purification method, it is preferable to pre-wet the porous membrane with a liquid different from the viscous liquid before supplying the viscous liquid to the porous membrane. The pre-wetting improves the wettability between the viscous liquid and the porous membrane, is expected to improve the filtration rate of the viscous liquid, and enhances the effect of reducing air bubbles.
Examples of the liquid used for pre-wetting include alcohols such as methanol, ethanol and isopropyl alcohol, ketones such as acetone and methyl ethyl ketone, and water. When the viscous liquid contains an organic solvent, the liquid used for prewetting may be other organic solvent, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol-n-propyl ether, ethylene glycol mono. -N-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol mono Ethyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-n- (Poly) alkylene glycol monoalkyl ethers such as butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, (Poly) alkylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate; other ethers such as diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether and tetrahydrofuran; methyl ethyl ketone, cyclohexanone, 2 Ketones such as −heptanone and 3-heptanone; Lactate alkyl esters such as methyl 2-hydroxypropionate and ethyl 2-hydroxypropionate; ethyl 2-hydroxy-2-methylpropionate, methyl 3-methoxypropionate, 3 -Ethyl methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, ethyl ethoxyacetate, ethyl hydroxyacetate, methyl 2-hydroxy-3-methylbutanoate, 3-methyl-3-methoxybutyl ace Tate, 3-methyl-3-methoxybutyl propionate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl formate, isopentyl acetate, n-butyl propionate, ethyl butyrate, Other esters such as n-propyl butyrate, isopropyl butyrate, n-butyl butyrate, methyl pyruvate, ethyl pyruvate, n-propyl pyruvate, methyl acetoacetate, ethyl acetoacetate, ethyl 2-oxobutanoate; toluene, xylene Aromatic hydrocarbons such as: Organic solvents such as amides such as N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and the like. The liquid used for pre-wetting can be used alone or in combination of two or more.
The liquid used for pre-wetting is preferably a solvent containing at least one of the solvents contained in the viscous liquid, and more preferably the same solvent as the solvent contained in the viscous liquid.

The method of contacting the pre-wet liquid and the porous membrane before permeating the supply liquid is not particularly limited as long as it is a method capable of contacting the pre-wet liquid and the porous membrane.
A preferred method is a method of impregnating the inside of the porous membrane with the liquid for pre-wetting by immersing the porous membrane in the liquid for pre-wetting.
The contact between the pre-wet liquid and the porous membrane before permeating the viscous liquid may be performed by the above-mentioned differential pressure. The range of the differential pressure is, for example, about 1 KPa or more and 0.25 MPa or less. In particular, when the liquid for pre-wetting is infiltrated into the pores inside the porous membrane, the pre-wetting may be performed under pressure. When pressurizing, it is preferably performed in the range of 0.01 MPa or more and 0.25 MPa or less.

By filtering the viscous liquid using the porous membrane as a filter according to the method described above, it is possible to remove the bubbles in the viscous liquid while preventing the generation of bubbles during filtration.

In the first purification method, the porous membrane can be used, for example, as a filter medium or other filter medium, and specifically, it may be used alone or as another functional layer (membrane). May be given.
The porous membrane may be used as a membrane to be combined with other filter media, and may be used, for example, as a membrane used for a filter device or the like.
The functional layer that can be used in combination with the porous membrane is not particularly limited, and is, for example, a nylon membrane, a polytetrafluoroethylene (PTFE) membrane, a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) membrane, or these. Examples thereof include membranes having a chemical or physicochemical function, such as a membrane modified with.

≪Second purification method≫
The second purification method is a method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
A method in which the filter contains a porous membrane having communication holes including spherical holes or a structure in which substantially spherical holes communicate with each other.

The method for producing the porous membrane used as the filter in the second purification method is not particularly limited. Typically, the method described for the first production method produces a porous membrane containing the above-mentioned predetermined structure.

In the second purification method, the viscous liquid is filtered using a porous membrane having communication holes including spherical pores or a structure in which substantially spherical pores communicate with each other as a filter, thereby preventing the generation of bubbles during filtration. , The number of bubbles in the viscous liquid can be reduced.

The viscous liquid to be purified by the second purification method is the same as the method described for the first purification method.
Further, the method for filtering the viscous liquid in the second purification method is the same as the method described for the first purification method.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the Examples shown below.

In the examples, the following polyamic acid solutions, organic solvents, dispersants and fine particles were used. Regarding the particle size distribution index (d25 / 75) of each silica, the silica (1) is about 1.5 and the silica (2) is 1.6 or more.
-Polyamide acid solution: Reactant of pyromellitic acid dianhydride and 4,4'-diaminodiphenyl ether (organic solvent: N, N-dimethylacetamide)
-Organic solvent (1): N, N-dimethylacetamide (DMAc)
-Organic solvent (2): Gamma-butyrolactone-Dispersant: Polyoxyethylene secondary alkyl ether-based dispersant-Fine particles: Silica (1): Silica with an average particle size of 2500 nm
Silica (2): Silica etching solution with an average particle size of 3500 nm: Tetramethylammonium hydroxide (TMAH) 5% by mass solution of a mixture of isopropyl alcohol: water (mass ratio 6: 4)

[Example 1]
A dispersion of silica (1) (dispersion medium is DMAc) is added to the polyamic acid solution, and the organic solvents (1) and (2) are further added to the solvent composition of the entire varnish. Organic solvent (1): Organic solvent (2) Each was added so as to be 90:10, and the varnish was prepared by stirring. The volume ratio of polyamic acid to silica in the obtained varnish is 40:60 (mass ratio is 30:70), and the solid content concentration (concentration of polyamic acid and silica) is 33% by mass. The viscosity was 4.0 Pa · s.

The above varnish is applied to a base material, prebaked at 70 ° C. for 5 minutes, and then the unfired composite film is peeled off from the base material to obtain an unfired composite film, which is heat-treated (baked) at 400 ° C. for 15 minutes each. As a result, imidization was carried out to obtain a polyimide-fine particle composite film. The obtained polyimide-fine particle composite membrane was immersed in a 20% HF solution to remove fine particles contained in the membrane, followed by washing with water and drying to obtain a polyimide porous membrane.
Further, an etching solution was used to expand the opening diameter and communication holes on the surface of the polyimide porous film, and after washing and drying with water, heat treatment was performed again at 350 ° C. for 15 minutes. After reheating, a polyimide porous membrane 1 having a film thickness of about 40 μm, an air permeability of 20 seconds or less, a porosity of about 70%, and an average pore diameter of 2500 nm was obtained. The average diameter of the communication holes confirmed by the porosimeter was 1000 nm.

[Example 2]
A polyimide porous film 2 was obtained in the same manner as in Example 1 except that silica (2) was used instead of silica (1). The final varnish viscosity was 4.1 Pa · s. The polyimide porous membrane 2 had a film thickness of about 40 μm, an air permeability of 20 seconds or less, a porosity of about 70%, and an average pore diameter of 3500 nm. The polyimide porous membrane 2 had communication holes exceeding 1000 nm.

[Comparative Example 1]
A varnish was prepared in the same manner as in Example 1 except that the viscosity of the final varnish was adjusted to about 1.5 Pa · s. When an unfired composite film was formed using the varnish of Comparative Example 1, a polyimide porous film could not be formed because sea islands were generated after prebaking.

[Example 3]
Using the filter device provided with the polyimide porous film 1 obtained in Example 1 as a filter, the resist composition for the plating process (viscosity (25 ° C., E-type viscometer)) was used at room temperature under the conditions shown in Table 1. ): 3.9 Pa · s, manufactured by Tokyo Ohka Kogyo Co., Ltd., containing propylene glycol monomethyl ether acetate (PGMEA)) was filtered.
As the test apparatus, an apparatus having the following configurations 1) to 6) was used.
1) Resist liquid tank.
2) A liquid supply pipe that connects the resist liquid tank and the liquid supply port of the filter device.
3) A liquid supply pump installed in the middle of the liquid supply pipe for supplying liquid to the filter while generating a differential pressure (filtration pressure).
4) A filter device equipped with a filter.
5) Discharge liquid piping that connects the discharge port of the filter device and the resist liquid tank.
6) A three-way valve for sampling provided in the middle of the discharge liquid piping.
The filtration conditions are as shown in Table 1. Before starting the filtration, the filter was pre-wet by passing about 4 L of PGMEA through the filter under a pressurized condition of 0.02 MPa.

First, at the start of filtration, 0.5 L of the resist composition was passed through a filter in a filter device, and the resist composition that had passed through the filter was discarded.
Next, 2 L of the resist composition was supplied from the resist liquid tank toward the filter. The filtrate produced by the 2L liquid supply was collected in a resist liquid tank.
100 mL of the filtrate sample at the time of 2 L supply was collected from the three-way valve. This sample was designated as sample 1.
Then, 13 L of the resist composition was supplied to the filter device while circulating a circulation system including a resist liquid tank, a liquid supply pipe, a filter device, and a discharge liquid pipe for a part of the resist composition. 100 mL of the filtrate sample at the time of supplying 13 L (15 L in total) was collected from the three-way valve. This sample was designated as sample 2.

For Sample 1 and Sample 2, the reduction in the number of foreign substances and the reduction in the number of bubbles were evaluated according to the following methods.
First, after applying a sample of the resist composition on the wafer, a film having a film thickness of about 38 μm formed by prebaking the coating film at 140 ° C. for 300 seconds was observed with NSX-220 (manufactured by Rudolph). , The number of foreign substances and the number of bubbles per unit area were counted.
The same evaluation was performed on the resist composition before filtration.

As a result of the above evaluation, a reduction in the number of foreign substances was observed in Samples 1 and 2.
Further, in sample 1, the number of bubbles was reduced to 5% of the number of bubbles in the resist composition before filtration, and the number of bubbles in sample 2 was the same as that in sample 1.

[Comparative Example 2]
Filtration of the resist composition in the same manner as in Example 3 except that the filter is changed to a filter made of PTFE fiber having an average pore size of 1 μm (1000 nm) and the filtration conditions are changed to the conditions shown in Table 1. Processing was performed.
When the number of bubbles in the resist composition obtained after filtration was confirmed by the same method as in Example 3, it was confirmed that the number of foreign substances was reduced for Samples 1 and 2.
However, in sample 1, the reduction in the number of bubbles from the resist composition before filtration could not be confirmed, and in sample 2, the number of bubbles increased to about 100 times the number of bubbles before filtration.

The differential pressure (filtration pressure) was increased to 0.5 MPa, and the same test as in Comparative Example 2 was performed. In this test, an increase in the number of bubbles similar to that in Comparative Example 2 was confirmed even when the amount of liquid flowing was smaller than that in Comparative Example 2.

[Example 4]
Using the filter device provided with the polyimide porous film 1 obtained in Example 1 as a filter, the resist composition for the plating process (viscosity (25 ° C., E-type viscometer)) at room temperature under the conditions shown in Table 2. ): 1.0 Pa · s, manufactured by Tokyo Ohka Kogyo Co., Ltd., containing propylene glycol monomethyl ether acetate (PGMEA) and 3-methoxybutyl acetate (MA)) was filtered.
As the test apparatus, an apparatus having the following configurations 1) to 6) was used.
1) Resist liquid tank.
2) A liquid supply pipe that connects the resist liquid tank and the liquid supply port of the filter device.
3) A liquid supply pump installed in the middle of the liquid supply pipe for supplying liquid to the filter while generating a differential pressure (filtration pressure).
4) A filter device equipped with a filter.
5) Discharge liquid piping that connects the discharge port of the filter device and the resist liquid tank.
6) A three-way valve for sampling provided in the middle of the discharge liquid piping.
The filtration conditions are as shown in Table 2.

First, at the start of filtration, 0.5 L of the resist composition was passed through a filter in a filter device, and the resist composition that had passed through the filter was discarded.
Next, 12 L of the resist composition was supplied to the filter device while circulating a circulation system including a resist liquid tank, a liquid supply pipe, a filter device, and a discharge liquid pipe for a part of the resist composition. 100 mL of the filtrate sample at the time of 12 L supply was recovered from the three-way valve. This sample was designated as sample 3.

For sample 3, the reduction in the number of foreign substances and the reduction in the number of bubbles were evaluated in the same manner as in Example 3. Regarding the resist composition before filtration, the number of foreign substances and the number of bubbles were evaluated in the same manner as in Example 3.
As a result, a reduction in the number of foreign substances was observed in Sample 3.
Further, the number of bubbles in the sample 3 was reduced to about 6% of the number of bubbles in the resist composition before filtration, and the number of foreign substances was reduced to about 2% of the number of bubbles in the resist composition before filtration.

[Comparative Example 3]
The evaluation was carried out in the same manner as in Example 4 except that the filter in the test apparatus was changed to a PTFE non-woven fabric. Unlike Example 3, the number of bubbles in the sample was not reduced (about 80% of the number of bubbles in the resist composition before filtration remained), and the number of foreign substances was about 41% of the number of foreign substances in the resist composition before filtration. Was reduced only to.

Claims (5)

A method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
The filter
A varnish containing a resin component (A), particles (B), and a solvent (S) is applied onto a substrate to form a composite film composed of the resin component (A) and the particles (B). That and
It contains a porous membrane obtained by a production method comprising removing the particles (B) in the composite membrane.
A method in which the average particle size of the particles (B) is more than 2000 nm and 3500 nm or less. A method for purifying a liquid, which comprises filtering a viscous liquid having a viscosity of 0.1 Pa · s or more with a filter.
The filter
Containing a porous membrane having a communication hole including a structure in which spherical holes or substantially spherical holes communicate with each other,
A method in which the average diameter of the spherical holes or substantially spherical holes is more than 2000 nm and 3500 nm or less. The method according to claim 1 or 2, wherein the porous membrane has communication holes, and the average pore diameter of the communicating portions in the communication holes is 500 nm or more and 2000 nm or less. The method according to claim 1, wherein the particles (B) are removed by hydrofluoric acid. The method according to any one of claims 1 to 4, comprising a step of prewetting the filter with a liquid different from the viscous liquid before filtering the viscous liquid.