JP2021157860A - Insulation paste - Google Patents

Abstract

To provide a technique for improving the strength of an insulation paste and improving the thermal dimensional stability of it.SOLUTION: An insulation paste has microfibrous cellulose, thermosetting resin, and a curing agent. The microfibrous cellulose has following characteristics: (A) it has a number average fiber diameter of 2 nm or more and 500 nm or less, (B) it has an average aspect ratio of 10 or more and 1000 or less, (C) it includes a cellulose I-type crystal structure, (D) it includes anionic functional groups, and (E) some or all of the anionic functional groups described in (D) have predetermined organic onium ions bound thereto.SELECTED DRAWING: None

Description

The present invention relates to an insulating paste.

In recent years, cellulose nanofibers have been known as a material having excellent transparency and heat resistance (for example, Patent Document 1).

As a material using such cellulose nanofibers, Patent Document 1 discloses a thermosetting resin composition containing fine fibrous cellulose and polyetheramine.

JP-A-2018-44096

However, when the thermosetting resin of Patent Document 1 is used as the insulating paste, there is room for improvement in strength and dimensional stability with respect to heat. Therefore, it has been desired to develop an insulating paste having excellent strength and dimensional stability against heat.

The present invention has been made to solve the above problems, and can be realized as the following forms.

(1) According to one embodiment of the present invention, an insulating paste containing fine fibrous cellulose, a thermosetting resin, and a curing agent is provided. In this insulating paste, the fine fibrous cellulose is characterized by satisfying the following conditions (A) to (E).
(A) Number average fiber diameter is 2 nm or more and 500 nm or less (B) Average aspect ratio is 10 or more and 1000 or less (C) Cellulose I-type crystal structure (D) Anionic functional group (E) The above (D). The organic onium ion represented by the following formula (1) is bonded to a part or all of the anionic functional groups of.

〔前記式（１）中、Ｍは窒素原子又はリン原子を示し、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４は、炭素数１以上２０以下の直鎖もしくは分岐のアルキル基、アレーン基、又はアリル基を示す。〕

[In the above formula (1), M represents a nitrogen atom or a phosphorus atom, and R ¹ , R ² , R ³ , and R ⁴ are linear or branched alkyl groups having 1 or more and 20 or less carbon atoms, arene groups, or Shows an allyl group. ]

According to this form of the insulating paste, it is excellent in strength and dimensional stability against heat.

(2) In the insulating paste of the above form, ^{at least one of R 1} , R ² , R ³ , and R ⁴ in the above formula (1) may have 6 or more carbon atoms.

According to this form of insulating paste, it is more excellent in strength.

(3) In the insulating paste of the above form, the anionic functional group may be a carboxy group.

According to this form of insulating paste, it is easy to introduce anionic functional groups into the fine fibrous cellulose.

(4) In the insulating paste of the above form, the thermosetting resin may contain an epoxy resin.

According to this form of the insulating paste, the dispersibility with the fine fibrous cellulose is improved.

(5) In the insulating paste of the above form, the solid content concentration of the fine fibrous cellulose may be 0.05% by mass or more and 3.0% by mass or less.

According to this form of insulating paste, it is excellent in handleability and thickening.

(6) According to another embodiment of the present invention, there is provided a resin composition prepared from the insulating paste of the above embodiment.

The present invention can be realized in various forms, for example, in an aspect such as a method for producing an insulating paste.

The figure explaining the measuring method of a fiber diameter.

A. Insulating Paste The insulating paste according to the embodiment of the present invention is an insulating paste containing fine fibrous cellulose, a thermosetting resin, and a curing agent, and the fine fibrous cellulose is as follows. It is characterized in that the conditions (A) to (E) are satisfied.

(A) The number average fiber diameter is 2 nm or more and 500 nm or less (B) The average aspect ratio is 10 or more and 1000 or less (C) Cellulose I-type crystal structure (D) Anionic functional group (E) (D). The organic onium ion represented by the following formula (1) is bonded to a part or all of the anionic functional groups.

〔式（１）中、Ｍは窒素原子又はリン原子を示し、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４は、炭素数１以上２０以下の直鎖もしくは分岐のアルキル基、アレーン基、又はアリル基を示す。〕

[In formula (1), M represents a nitrogen atom or a phosphorus atom, and R ¹ , R ² , R ³ , and R ⁴ are linear or branched alkyl groups, arene groups, or allyls having 1 to 20 carbon atoms. Indicates a group. ]

In the present specification, the organic onium ion described in the above formula (1) is also simply referred to as "organic onium ion".

The insulating paste of the present embodiment has excellent strength and dimensional stability against heat. The mechanism that exerts such an effect is not clear, but the following estimation mechanism can be considered. That is, since the fine fibrous cellulose can be sufficiently hydrophobized, it is considered that the fine fibrous cellulose can be dispersed in the solvent without agglutination, and as a result, the fine fibrous cellulose is excellent in dispersibility. Further, since the molecular weight of the organic onium ion represented by the above formula (1) is relatively small, it does not act as a plasticizer, so that it is considered to be excellent in strength and dimensional stability with respect to heat.

[Fine fibrous cellulose]
The fine fibrous cellulose satisfies the following conditions.

<Number average fiber diameter>
The number average fiber diameter of the fine fibrous cellulose is 2 nm or more and 500 nm or less, preferably 2 nm or more and 150 nm or less, more preferably 2 nm or more and 100 nm or less, and particularly preferably 3 nm or more and 80 nm or less. If the number average fiber diameter is less than 2 nm, the fine fibrous cellulose is dissolved, so that a three-dimensional network of the fine fibrous cellulose is not formed in the solvent, and there is a possibility that high strength cannot be obtained. On the other hand, even when the number average fiber diameter exceeds 500 nm, the fine fibrous cellulose may settle. The maximum fiber diameter is preferably 1000 nm or less, and particularly preferably 500 nm or less, in terms of dispersibility of the fine fibrous cellulose.

The number average fiber diameter and the number average fiber length of the fine fibrous cellulose can be measured by, for example, the following methods. That is, after preparing an aqueous dispersion of fine cellulose having a solid content of 0.05 to 0.1% by mass, the dispersion is cast on a carbon film-coated grid that has been hydrophilized to generate transmission electrons. Use as a sample for observation with a microscope (TEM).

FIG. 1 is a diagram illustrating a method for measuring a fiber diameter. The fiber diameter can be determined by measuring the distance between two intersections of a line orthogonal to the longitudinal direction of one fiber F and the outer periphery of the fiber. That is, it can be obtained by measuring the distance between the point P1 and the point P2 shown in FIG. The fiber length is obtained by measuring the length of the fiber in which the entire fiber is shown in the observation image. When measuring the length of a fiber, if the fiber has a bend, for example, if there is one bend point, the total value of the length from one end to the bend point and the length from this bend point to the other end. Let be the fiber length. Observe at least 25 fibers having a fiber diameter and a fiber length. Further, when a fiber having a large fiber diameter is contained, a scanning electron microscope (SEM) image of the surface cast on the glass may be observed. Then, observation by an electron microscope image may be performed at a magnification of 5000 times, 10000 times, or 50,000 times depending on the size of the constituent fibers. From the fiber diameter and fiber length data thus obtained, the number average fiber length and the number average fiber diameter are calculated.

<Average aspect ratio>
The average aspect ratio of the fine fibrous cellulose is 10 or more and 1000 or less, preferably 100 or more, and more preferably 200 or more. If the average aspect ratio is less than 10, the surface charge is reduced, which may cause a problem that high strength cannot be obtained.

The average aspect ratio of the fine fibrous cellulose is calculated by the following formula using the number average fiber diameter and the number average fiber length obtained according to the method described above.
Average aspect ratio = number average fiber length [nm] / number average fiber diameter [nm]

<Cellulose type I crystal structure>
The fine fibrous cellulose is a fiber obtained by refining a naturally-derived cellulose raw material having an I-type crystal structure. That is, in the process of biosynthesis of natural cellulose, nanofibers called microfibrils are formed almost without exception, and microfibrils are multi-bundle to form a higher-order solid structure.

The fact that the cellulose constituting the fine fibrous cellulose has an I-type crystal structure means that, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, 2 theta = 14 to 17 ° and 2 theta = 22 to 23. It can be identified by having typical peaks at two positions near °.

<Anionic functional group>
The fine fibrous cellulose has an anionic functional group. In the present specification, the anionic functional group refers to a functional group in which more than half of hydrogen ions are dissociated in water at pH 7. The anionic functional group is not particularly limited, and examples thereof include a carboxy group, a phosphoric acid group, and a sulfuric acid group. As the anionic functional group, a carboxy group is preferable because it is easy to introduce the anionic functional group into the fine fibrous cellulose.

The method for introducing a carboxy group into the fine fibrous cellulose is not particularly limited, and is selected from the group consisting of (i) a compound having a carboxy group, an acid anhydride of a compound having a carboxy group, and derivatives thereof. Examples thereof include a method of reacting at least one kind with a hydroxyl group of fine fibrous cellulose, and (ii) a method of converting the hydroxyl group of fine fibrous cellulose into a carboxy group by oxidizing the hydroxyl group.

The compound having a carboxy group is not particularly limited, and examples thereof include acetic acid halide. Examples of the halogenated acetic acid include chloroacetic acid, bromoacetic acid, iodoacetic acid and the like.

The acid anhydride of the compound having a carboxy group is not particularly limited, but is, for example, an acid of a dicarboxylic acid compound such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Anhydrides can be mentioned.

The derivative of the compound having a carboxy group is not particularly limited, and examples thereof include an imide of an acid anhydride of a compound having a carboxy group, a derivative of an acid anhydride of a compound having a carboxy group, and the like.

The imide of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include an imide of a dicarboxylic acid compound such as maleimide, succinateimide, and phthalateimide.

The derivative of the acid anhydride of the compound having a carboxy group is not particularly limited, but for example, at least a part of the hydrogen atom of the acid anhydride of the compound having a carboxy group is a substituent (for example, an alkyl group, a phenyl group, etc.). Examples are those replaced with. The acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include dimethylmaleic anhydride, diethylmalic anhydride, diphenylmaleic anhydride and the like.

The method for oxidizing the hydroxyl group of the fine fibrous cellulose is not particularly limited, and examples thereof include a method in which an N-oxyl compound is used as an oxidation catalyst and an copolymer is allowed to act on it.

As a method for introducing a carboxy group into fine fibrous cellulose, a method of oxidizing the hydroxyl group of cellulose is preferable because the selectivity of the hydroxyl group on the fiber surface is excellent and the reaction conditions are mild. Hereinafter, fine fibrous cellulose in which a carboxy group is introduced by oxidation of a hydroxyl group is also referred to as "oxidized cellulose".

The method for introducing a phosphoric acid group into the fine fibrous cellulose is not particularly limited, and examples thereof include the following methods. That is, (i) a method of mixing a powder or an aqueous solution of phosphoric acid or a phosphoric acid derivative with a dry or wet cellulose fiber raw material, and (ii) a method of mixing a dispersion liquid of a phosphoric acid fiber raw material with a phosphoric acid or a phosphoric acid derivative. Examples thereof include a method of adding an aqueous solution. In these methods, generally, after mixing or adding a powder or an aqueous solution of phosphoric acid or a phosphoric acid derivative, dehydration treatment, heat treatment and the like are performed. By doing so, a phosphoric acid ester is formed by dehydration reaction of a compound containing a phosphoric acid group or a salt thereof at the hydroxyl group of the glucose unit constituting cellulose, thereby forming the hydroxyl group of the glucose unit constituting cellulose. A phosphate group or a salt thereof is introduced. Here, the phosphoric acid or the phosphoric acid derivative is not particularly limited, and examples thereof include at least one compound selected from oxo acids containing a phosphorus atom, polyoxo acids, and derivatives thereof.

The content of the anionic functional group with respect to the content of the fine fibrous cellulose (content of the anionic functional group [mmol] / content of the fine fibrous cellulose [g]) is not particularly limited, but the content of the fine fibrous cellulose is not particularly limited. From the viewpoint of excellent dispersibility, it is preferably 1.0 mmol / g or more and 3.0 mmol / g or less, more preferably 0.5 mmol / g or more and 2.5 mmol / g or less, and further preferably 1.5 mmol. / G or more and 2.0 mmol / g or less.

The amount of anionic functional groups can be measured as follows.

For example, the measurement method when the anionic functional group is a carboxy group is shown below. That is, after preparing 60 ml of a 0.5 to 1% by mass slurry from the fine fibrous cellulose whose dry mass has been precisely weighed, the pH is adjusted to about 2.5 with a 0.1 M aqueous hydrochloric acid solution. Then, the electric conductivity is measured by dropping a 0.05 M aqueous sodium hydroxide solution. The measurement is continued until the pH reaches about 11. From the amount of sodium hydroxide (V [ml]) consumed in the neutralization step of a weak acid whose electrical conductivity changes slowly, the amount of carboxy group C can be determined according to the following formula.
C [mmol / g] = V [ml] x (0.05 / cellulose mass [g])

The measurement method when the anionic functional group is a carboxymethyl group is shown below. That is, after preparing a 0.6 mass% slurry from the fine fibrous cellulose whose dry mass has been precisely weighed, a 0.1 M hydrochloric acid aqueous solution is added to adjust the pH to 2.4. Then, the electric conductivity is measured until the pH reaches 11 by dropping a 0.05 N aqueous sodium hydroxide solution. The amount of carboxy group C is determined from the amount of sodium hydroxide consumed in the neutralization step of a weak acid whose electrical conductivity changes slowly according to the above formula. Then, the amount of carboxymethyl group Cm can be determined according to the following formula.
Cm [mmol / g] = (162 × C) / (1-58 × C) × 1000

[Organic onium ion]
The organic onium ion of this embodiment is the onium ion represented by the above formula (1). The organic onium ion is not particularly limited.

Examples of the organic onium ion containing an alkyl group include tetramethylammonium ion, tetraethylammonium ion, tetrabutylammonium ion, tetrahexylammonium ion, tetraoctylammonium ion, tetradecylammonium ion, and tetradodecylammonium ion. Examples of the organic onium ion containing an alkyl group include trimethyldodecylammonium ion, trimethyltetradecylammonium ion, trimethyloctadecylammonium ion, tributyldodecylammonium ion, and trioctylmethylammonium ammonium ion. Examples of the organic onium ion containing an alkyl group include octyldimethylethylammonium ion, dodecyldimethylethylammonium ion, and didecyldimethylammonium ion. Examples of the organic onium ion containing an alkyl group include tetraethylphosphonium ion, tetrabutylphosphonium ion, and tetraoctylphosphonium ion. Examples of the organic onium ion containing an alkyl group include tributylmethylphosphonium ion, tributyldodecylphosphonium ion, tributyltetradecylphosphonium ion, tributylhexadecylphosphonium ion, trihexyltetradecylphosphonium ion and the like.

Examples of the organic onium ion containing an arene group include benzyltrimethylammonium ion, benzyltributylammonium ion, benzyldimethyldodecylammonium ion, benzyldimethyltetradecylammonium ion, benzyldimethyloctadecylammonium ion and the like. Examples of the organic onium ion containing an arene group include benzyldimethylphenylammonium ion, triethylphenylammonium ion, dimethylphenylammonium ion and the like. Examples of the organic onium ion containing an arene group include tetraphenylphosphonium ion, benzyltriphenylphosphonium ion, methyltriphenylphosphonium ion, ethyltriphenylphosphonium ion, butyltriphenylphosphonium ion, tetradecyltriphenylphosphonium ion and the like. Can be mentioned.

Examples of the organic onium ion containing an allyl group include diallyldimethylammonium ion and allyltriphenylphosphonium ion.

From the viewpoint of achieving better strength in the organic onium ion, ^{at least one of R 1} , R ² , R ³ , and R ⁴ preferably has 6 or more carbon atoms. Further, from the viewpoint of realizing more excellent strength of the organic onium ion, ^{it is preferable that all of R 1} , R ² , R ³ and R ⁴ have 6 or more carbon atoms, and all of them have 8 or more carbon atoms. Is more preferable. Further, as for the organic onium ion, ^{it is more preferable that all of R 1} , R ² , R ³ , and R ⁴ are alkyl groups having 7 or more and 10 or less carbon atoms. Specifically, the organic onium ion preferably contains at least one of a tetraoctyl ammonium ion and a tetraoctyl phosphonium ion. Further, from the viewpoint of achieving more excellent strength, ^{the sum of the carbon numbers of R 1} , R ² , R ³ , and R ⁴ is preferably 50 or less, more preferably 45 or less, and 40 or less. It is more preferable to have.

The amount of organic onium ions blended per 1 g of fine fibrous cellulose is not particularly limited, but the amount of organic onium ions is preferably 1.0 mmol or more, more preferably 1.5 mmol or more, with respect to 1 g of fine fibrous cellulose. It is preferable, and 1.8 mmol or more is more preferable. By doing so, it is possible to suppress the aggregation of the fine fibrous cellulose in the solvent, so that the storage stability is improved. Further, the amount of organic onium ion is preferably 3.0 mmol or less, more preferably 2.5 mmol or less, still more preferably 2.2 mmol or less with respect to 1 g of fine fibrous cellulose. By doing so, it is possible to suppress the action of the organic onium ion as a plasticizer, so that high strength can be realized.

[Thermosetting resin]
The insulating paste of this embodiment contains a thermosetting resin. In the present specification, the thermosetting resin is a counter-concept of a thermoplastic resin, and means a resin that is irreversibly cured by heat. The thermosetting resin is not particularly limited, but for example, urethane resin, epoxy resin, phenol resin, melamine resin, urea resin, unsaturated polyester resin, polyester resin, silicone resin, polyimide resin, furan resin, urea resin, and polyimide. Examples thereof include resins, diallyl phthalate resins, vinyl ester resins, oxetane resins, and silicon resins. These thermosetting resins may be used alone or in combination of two or more. From the viewpoint of improving the dispersibility with the fine fibrous cellulose, it is preferable to use at least one of the urethane resin and the epoxy resin among these thermosetting resins, and it is more preferable to use the epoxy resin.

The urethane resin is a resin produced by condensation of a polyisocyanate containing an isocyanate group and a polyol containing a hydroxyl group.

The polyol is not particularly limited, but for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butanediol, 2 , 2'-Dimethyl-1,3-propanediol, diethylene glycol, triethylene glycol, 1,5-pendamethylene glycol, dipropylene glycol, neopentyl glycol, 1,6-hexamethylene glycol, cyclohexane-1,4-diol , Cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, 2-butene-1,4-diol, 2,2,4-trimethyl-1,3-pentanediol and other diols, trimethylolpropane and the like. Examples thereof include triol, tetraol such as pentaerythritol, and hexaol such as dipentaerythritol. These may be used alone or in combination of two or more.

The polyisocyanate is not particularly limited, but for example, 2,4-tolylene diisocyanate, dimeric of 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate. Aromatic diisocyanate compounds such as isocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 3,3'-dimethylhiphenyl-4,4'-diisocyanate; hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine Aliphatic diisocyanate compounds such as diisocyanate and diisocyanate dimerate; isophorone diisocyanate, 4,4'-methylenebis (cyclohexylisocyanate), methylcyclohexane-2,4- (or 2,6) diisocyanate, 1,3- (isocyanatemethyl) cyclohexane Such as alicyclic diisocyanate compounds and the like. These polyisocyanates may be used alone or in combination of two or more. Further, a chain extender or the like may be used if necessary.

The epoxy resin is not particularly limited, and known epoxy resins can be used, and examples thereof include the epoxy resins shown below. These epoxy resins may be used alone or in combination of two or more. These epoxy resins are thermosetting resin prepolymer epoxy compounds, and by using a curing agent, a cured epoxy resin which is a cured product of the epoxy resin can be obtained.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin and other bisphenol type epoxy resins, phenol novolac type epoxy resin, cresol novolac type epoxy resin and the like. Examples thereof include novolak type epoxy resins, aromatic epoxy resins such as trisphenol methanetriglycidyl ether, and water additives and brominated products thereof. In addition, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, bis (3,4) -Epoxycyclohexyl) adipate, bis (3,4-epoxycyclohexylmethyl adipate, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 2- (3,4-epoxycyclohexyl-5,5-spiro-3) , 4-Epoxycyclohexanone-meth-dioxane, alicyclic epoxy resin such as bis (2,3-epoxycyclopentyl) ether and the like can be mentioned.

Examples of the epoxy resin include diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, and diglycidyl ether of polyethylene glycol. Glycidyl ether, diglycidyl ether of polypropylene glycol, polyoxyalkylene glycol containing an alkylene group having 2 to 9 carbon atoms (preferably 2 to 4), polyglycidyl ether of a long chain polyol containing polytetramethylene ether glycol, and the like. Examples include aliphatic epoxy resins. In addition, glycidyl ester type epoxy such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, diglycidyl-p-oxybenzoic acid, glycidyl ether-glycidyl ester of salicylate, and dimer acid glycidyl ester. Examples thereof include resins and hydrogenated products thereof. In addition, triglycidyl isocyanurate, N, N'-diglycidyl derivative of cyclic alkylene urea, N, N, O-triglycidyl derivative of p-aminophenol, N, N, O-triglycidyl derivative of m-aminophenol, etc. Examples thereof include glycidylamine type epoxy resins and hydrogenated products thereof. Further, examples thereof include a copolymer of glycidyl (meth) acrylate and a radically polymerizable monomer such as ethylene, vinyl acetate and (meth) acrylic acid ester.

[Curing agent]
The insulating paste of this embodiment contains a curing agent. The curing agent is not particularly limited, and for example, the same curing agent as that has been used so far in the technical field of thermosetting resin can be used. Examples of the curing agent include amines such as aliphatic amines and aromatic amines, polyamide resins, tertiary and secondary amines, imidazoles, polyethercaptans, acid anhydrides, dicyandiamides, and polyisocyanates. The amount of the curing agent added can be appropriately selected according to the desired physical properties, and for example, in the insulating paste, it can be in the range of 0.1% by mass or more and 50% by mass or less.

[Manufacturing method of insulating paste]
The method for producing the insulating paste of the present embodiment is not particularly limited, and for example, it can be produced by mixing fine fibrous cellulose, a thermosetting resin, and a curing agent. Here, the thermosetting resin before curing is generally insoluble in water but soluble in an organic solvent. Therefore, the oil-based fine fibrous cellulose dispersion has good compatibility with the thermosetting resin. Therefore, the fine fibrous cellulose and the thermosetting resin can be uniformly mixed.

The organic solvent refers to an organic compound that is a liquid other than water and is a liquid at 25 ° C. and 1 atm. As the organic solvent, an organic solvent used in the process for producing fine fibrous cellulose, which will be described later, may be used. The organic solvent is not particularly limited, but for example, methanol, ethanol, isopropyl alcohol, 2-butanol, 1-pentanol, octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, stearyl alcohol, glycerin, ethylene glycol, propylene glycol, etc. Examples thereof include alcohols such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 2-methyl-1-propanol and glycerin. Examples of the organic solvent include acetic acid, propionic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearer, oleic acid, linolenic acid, lactic acid, benzoic acid, succinic acid, and maleic acid. , Carous acids such as fumaric acid, and hydrocarbons such as hexane, heptane, octane, decane, and liquid paraffin. Examples of the organic solvent include aromatic hydrocarbons such as toluene, xylene, ethylbenzene and naphthalene, amides such as dimethylsulfoxide, dimethylformamide, dimethylacetamide and acetanilide, acetone, methylethylketone, diethylketone and methylisobutylketone. Examples thereof include ketones such as cyclohexanone and benzophenone, and halogens such as methylene chloride, chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethylene. Examples of the organic solvent include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butyrate, di2-ethylhexyl adipate and diisononyl adipate. , Diisodecyl adipate, di2-ethylhexyl sebacate, di2-ethylhexyl azelaine, bis 4-cyclohexene-1,2-dicarboxylic acid (2-ethylhexyl), tricresyl phosphate, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester , Polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters and other esters, polyethylene glycol, polytetramethylene oxide, polyoxyethylene alkyl ethers and other polyethers, polydimethylsiloxane and other silicone oils, etc. Can be mentioned. Examples of the organic solvent include dimethyl sulfoxide, acetonitrile, propionitrile, ester oil, light oil, kerosene, crude oil, salad oil, soybean oil, castor oil, triglyceride, polyisoprene, fluorine-modified oil and the like. These may be used alone or in combination of two or more. Further, instead of the organic solvent, an organic medium containing a reactive functional group may be used. Examples of the organic medium include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, and 2-hexyl acrylate. Ethylhexyl, 2-ethylhexyl methacrylate, nonanediol diacrylate, phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, phenylglycidyl ether acrylate, hexamethylene diisocyanate urethane prepolymer, phenylglycidyl ether acrylate toluenediisocyanate urethane prepolymer, Pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, ethylene glycol diglycidyl ether, diethylene glycol Diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, glycerin diglycidyl ether, trimethylpropan triglycidyl ether, polyethylene glycol diglycidyl ether, chlorostyrene, methoxystyrene, butoxystyrene, vinyl benzoic acid, etc. Can be mentioned. The organic solvent may be used alone or in combination of two or more.

The solid content concentration of the fine fibrous cellulose in the insulating paste of the present embodiment is preferably 0.05% by mass or more and 3.0% by mass or less, preferably 0.1% by mass or more, from the viewpoint of excellent handleability and thickening. 3.0% by mass or less is more preferable, and a range of 1.0% by mass or more and 2.0% by mass or less is further preferable.

[Other additives]
The insulating paste of the present embodiment preferably contains an aminosilane coupling agent in order to improve the adhesion to the substrate. The aminosilane coupling agent is not particularly limited, and for example, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-( Examples thereof include 2-aminoethyl) aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropylmethyldimethoxysilane, and 3-anilinopropyltrimethoxysilane. The content of the aminosilane coupling agent is preferably in the range of 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the insulating paste solid content of the present embodiment.

The insulating paste of the present embodiment may contain additives such as a dehydrating agent, a leveling agent, a thickener, and an ultraviolet absorber, if necessary. Examples of the dehydrating agent include methyl orthoformate, ethyl orthoformate, methyl orthoacetate, ethyl orthoacetate and the like. Examples of the leveling agent include various polyether-modified silicone oils.

Examples of the base material to which the insulating paste of the present embodiment is applied include metals such as iron, stainless steel, aluminum, alumite, and duralamine; metal oxides such as iron oxide, ferrite, alumina, and zinc oxide; mortar and slate. , Concrete, glass, ceramic and other inorganic substrates; wood, plywood; thermosetting resin, thermoplastic resin, FRP and other resins are exemplified. Examples of the shape of the base material include a plate shape, a block shape, a film shape, a particle shape, and a powder shape.

[Manufacturing method of fine fibrous cellulose]
The method for producing the fine fibrous cellulose of the present embodiment is not particularly limited, but the production method having the following steps (1) to (4) is preferable because it can be produced more efficiently.
Step (1): After dispersing the cellulose fiber having a cellulose type I crystal structure in water, the hydroxyl group of the cellulose fiber is converted into a substituent having a carboxy group. Step (2): Dispersion medium of the cellulose fiber Step (3): Step of adding organic onium ions to the cellulose fibers after the replacement (4): Nano of the cellulose fibers to which the organic onium ions are bound in the organic solvent. Defibering process

<Process (1)>
The step (1) is a step of converting the hydroxyl group of cellulose having a cellulose I-type crystal structure into a substituent having a carboxy group by oxidation or the like. Here, examples of the substituent having a carboxy group include a carboxy group, a carboxy base, a carboxyalkyl group and the like.

Cellulose As the cellulose having a type I crystal structure, natural cellulose is generally used. Here, the natural cellulose means purified cellulose isolated from the biosynthetic system of cellulose such as plants, animals, and bacterial gels. More specifically, natural cellulose is isolated from coniferous pulp, broadleaf pulp, cotton linter, cotton lint and other cotton pulp, straw pulp, bagas pulp and other non-wood pulp, bacterial cellulose (BC), and squirrel. Examples include cellulose and cellulose isolated from seaweed. Among the natural celluloses, softwood pulps, hardwood pulps, cotton linters, cotton lint and other cotton pulps, straw pulps, bagas pulps and other non-wood pulps are preferable. It is preferable that the natural cellulose is subjected to a treatment for increasing the surface area such as beating because the reaction efficiency can be increased and the productivity can be increased.

Examples of the cellulose in which the hydroxyl group on the surface of the cellulose fiber is converted into a substituent having a carboxy group include oxidized cellulose, carboxymethyl cellulose, polyvalent carboxymethyl cellulose, and salts thereof. Among these, cellulose oxide using an N-oxyl compound as an oxidizing agent, which has excellent selectivity of hydroxyl groups on the fiber surface and mild reaction conditions, is preferable. The method for obtaining oxidized cellulose using an N-oxyl compound as an oxidizing agent will be described in detail below.

(Oxidation process)
The cellulose oxide contains the natural cellulose, an N-oxyl compound, and an oxidation treatment in the presence of an oxidizer to obtain a cellulose fiber containing a carboxy group.

The dispersion medium of cellulose in the oxidation reaction is water, and the concentration of cellulose in the reaction aqueous solution is arbitrary as long as the concentration allows sufficient diffusion of cellulose. Generally, it is about 5% by mass or less of the reaction aqueous solution, but the reaction concentration can be increased by using an apparatus having a strong mechanical stirring force.

Examples of the N-oxyl compound include compounds having a nitrox radical, which is generally used as an oxidation catalyst. The N-oxyl compound is preferably a water-soluble compound, more preferably a piperidine nitroxyoxy radical, and 2,2,6,6-tetramethylpiperidinooxy radical, 4-acetamido-2,2,6. , 6-Tetramethylpiperidinooxy radicals are particularly preferred. The addition of the N-oxyl compound can be exemplified as an amount equivalent to the amount of the catalyst, and is preferably added to the reaction aqueous solution in the range of 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l.

The cooxidant is not a substance that directly oxidizes the hydroxyl group of cellulose, but a substance that oxidizes an N-oxyl compound used as an oxidation catalyst. Examples thereof include hypohalous acid or a salt thereof, hypohalogenic acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, a perorganic acid and the like. These may be used alone or in combination of two. Among these, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are preferable. When the sodium hypochlorite is used, it is preferable to proceed the reaction in the presence of an alkali metal bromide such as sodium bromide in terms of reaction rate. The amount of the alkali metal bromide added is about 1 to 40 times the molar amount, preferably about 10 to 20 times the molar amount of the N-oxyl compound.

The pH of the reaction aqueous solution is preferably maintained in the range of about 8 to 11. The temperature of the aqueous solution is arbitrary at about 4 to 40 ° C., but the reaction can be carried out at room temperature (25 ° C.), and no particular temperature control is required.

Generally, in order to obtain the desired amount of carboxy groups and the like, the degree of oxidation is controlled by the amount of the copolymer added and the reaction time.

(Reduction process)
The cellulose fibers after the oxidation treatment are preferably reduced with a reducing agent. As a result, some or all of the aldehyde group and the ketone group are reduced and returned to the hydroxyl group. The carboxy group is not reduced. The total content of the carbonyl groups (aldehyde group and ketone group) of the oxidized cellulose by the reduction is preferably 0.3 mmol / g or less, and particularly preferably 0.1 mmol / g or less. As a result, the decrease in the molecular weight of the fine fibrous cellulose is suppressed, and the thickening effect in the solvent can be maintained for a long period of time. Here, the total content of the carbonyl group (aldehyde group and ketone group) is calculated by the semicarbazide method described later. By setting the carbonyl group to 0.5 mmol / g or less, the generation of aggregates due to long-term storage can be suppressed, and the viscosity can be suppressed from significantly decreasing with the passage of time. As the reducing agent used in the reduction reaction, general ones can be used, but LiBH ₄ , NaBH ₃ CN, and NaBH ₄ are preferable. Among these, NaBH ₄ is particularly preferable from the viewpoint of cost and availability.

The amount of the reducing agent for reducing cellulose converted to a substituent having a carboxy group is preferably 0.1 to 20% by mass, particularly preferably 3 to 10% by mass, as a reference. The reaction conditions are room temperature (25 ° C.) or a temperature slightly higher than room temperature, and the reaction is carried out for 10 minutes to 10 hours, preferably 30 minutes to 2 hours.

The total content of carbonyl groups (aldehyde group and ketone group) is measured by the semicarbazide method, for example, as follows. That is, first, exactly 50 ml of a 3 g / l aqueous solution of semicarbazide hydrochloride adjusted to pH = 5 with a phosphate buffer solution is added to the dried sample, the sample is sealed, and then shaken for two days. Then, 10 ml of this solution is accurately collected in a 100 ml beaker, 25 ml of 5N sulfuric acid and 5 ml of a 0.05 N potassium iodate aqueous solution are added, and then the mixture is stirred for 10 minutes. Then, immediately after adding 10 ml of a 5 mass% potassium iodide aqueous solution, titration is performed with a 0.1 N sodium thiosulfate solution using an automatic titrator. From the titration amount and the like, the amount of carbonyl group in the sample can be determined according to the following formula. Semicarbazide reacts with an aldehyde group or a ketone group to form a Schiff base (imine), but does not react with a carboxy group. Therefore, it is considered that only the amount of the carbonyl group can be quantified by the above measurement.
Carbonyl group amount [mmol / g] = (DB) × f × (0.125 / w)
D: Sample titration [ml]
B: Titration of blank test [ml]
f: Factor of 0.1N sodium thiosulfate solution w: Sample amount [g]

<Process (2)>
In the step (2), first, the cellulose fibers after the above treatment are washed with an acid to convert the carboxy group introduced in the step (1) into an acid type. Then, after purifying by repeating filtration and washing with water as appropriate, solid-liquid separation is performed by a centrifuge or the like. Then, after repeatedly washing the cellulose with an organic solvent, the solvent is replaced with an organic solvent from water.

(acid)
The above-mentioned acid keeps the cellulose fiber aqueous dispersion liquid acidic, and the type of the acid is not particularly limited. Examples of the acid include inorganic acids such as hydrochloric acid, nitrate, sulfuric acid, phosphoric acid, acetic acid and hydrogen peroxide, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, sodium sebacate, stearic acid, maleic acid and succinic acid. Examples thereof include organic acids such as acids, tartaric acids, fumaric acids and gluconic acids. Hydrochloric acid is preferably used as the acid because it is possible to avoid deterioration and damage of the cellulose fibers due to the acid and the waste liquid treatment is easy.

<Process (3)>
The step (3) is a step of adding the organic onium ion represented by the above formula (1) to the oxidized cellulose after the dispersion medium substitution. As a result, the organic onium ion represented by the above formula (1) is bonded to the carboxy group of the above-mentioned oxidized cellulose, and the cellulose is made into a lipophilic oil. The above reaction is carried out in an organic solvent.

<Process (4)>
The step (4) is a step of nano-defibrating the cellulose fibers after oil-forming in an organic solvent. Examples of the disperser used for the nano-defibration include a homomixer under high-speed rotation, a high-pressure homogenizer, an ultra-high-pressure homogenizer, an ultrasonic dispersion treatment, a beater, a disc-type refiner, a conical-type refiner, a double-disc-type refiner, and a grinder. And so on. By using these devices having a strong beating ability, it is possible to make the device finer, so that more efficient and advanced downsizing becomes possible. As the disperser, for example, a screw type mixer, a paddle type mixer, a disper type mixer, a turbine type mixer or the like may be used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. In the example, "%" means a mass standard unless otherwise specified.

First, prior to the preparation of Examples and Comparative Examples, cellulose fibers A1 to A4 for Examples and cellulose fibers A5 and A6 for Comparative Examples were prepared according to the following Production Examples 1 to 6.

[Production Example 1: Preparation of Cellulose Fiber A1 (for Examples)]
To 2 g of softwood pulp, 150 ml of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) were added, and the mixture was sufficiently stirred and dispersed. Then, the reaction was started by adding a 13% sodium hypochlorite aqueous solution to 1.0 g of softwood pulp so that the amount of sodium hypochlorite was 5.2 mmol / g. Since the pH decreases as the reaction progresses, the reaction was carried out while dropping a 0.5 N sodium hydroxide aqueous solution so as to maintain the pH at 10 to 11 until no change in pH was observed. This reaction time was 120 minutes. After completion of the reaction, the reaction was neutralized by adding 0.1N hydrochloric acid, solid-liquid separated by a centrifuge, and then pure water was added to adjust the solid content concentration to 4%. Then, the pH of the slurry was adjusted to 10 with a 24% aqueous sodium hydroxide solution. After the temperature of the slurry was adjusted to 30 ° C., a reduction treatment was carried out by adding 0.2 mmol / g of sodium borohydride to the cellulose fibers and reacting the slurry for 2 hours. After the reaction, the pH was adjusted to 2 or less by adding 0.1N hydrochloric acid, and then filtration and washing with water were repeated for purification to obtain cellulose fiber A1.

[Production Example 2: Preparation of Cellulose Fiber A2 (for Examples)]
Cellulose fiber A2 was obtained by the same method as the method for preparing cellulose fiber A1 except that the amount of the sodium hypochlorite aqueous solution added was 12.0 mmol / g with respect to 1.0 g of softwood pulp.

[Production Example 3: Preparation of Cellulose Fiber A3 (for Examples)]
After putting 100 g of softwood pulp in a mixed solution of 435 g of isopropanol (IPA), 65 g of water and 9.9 g of sodium hydroxide, the mixture was stirred at 30 ° C. for 1 hour. After adding 23.0 g of an IPA solution of 50% monochloroacetic acid to this slurry, the temperature was raised to 70 ° C., and then the reaction was carried out for 1.5 hours. The obtained reaction product was washed with 80% methanol, then replaced with methanol, and then dried to obtain cellulose fibers A3.

[Production Example 4: Preparation of Cellulose Fiber A4 (for Examples)]
A phosphorylating agent was prepared by dissolving 20 g of urea, 12 g of sodium dihydrogen phosphate dihydrate, and 8 g of disodium hydrogen phosphate in 20 g of water. Then, 20 g of softwood pulp (NBKP) crushed with a household mixer was spray-sprayed on the phosphorylating agent while stirring with a kneader to obtain phosphorylating agent-impregnated pulp. Next, the phosphorylated pulp was obtained by heat-treating the phosphorylated agent-impregnated pulp in a blower dryer equipped with a damper heated to 140 ° C. for 60 minutes. Water was added to the obtained phosphorylated pulp to adjust the solid content concentration to 2%, and the pulp was stirred and mixed to uniformly disperse the pulp, and then filtration and dehydration were repeated twice. Then, water was added to the obtained recovered pulp to obtain a solid content concentration of 2%. Then, while stirring, a 1N aqueous sodium hydroxide solution was added little by little to obtain a pulp slurry having a pH of 12 to 13. Subsequently, this pulp slurry was filtered, dehydrated, and then water was further added to repeat the operations of filtration and dehydration twice. Then, it was replaced with methanol and dried to obtain cellulose fiber A4.

[Production Example 5: Preparation of Cellulose Fiber A5 (for Comparative Example)]
A dispersion having a pulp concentration of 2% was prepared by dispersing 50 g of softwood bleached kraft pulp (NBKP) in 4,950 g of water. Cellulose fiber A5 was obtained by treating this dispersion with Serendipitter MKCA6-3 (manufactured by Masuyuki Sangyo Co., Ltd.) 30 times.

[Production Example 6: Preparation of Cellulose Fiber A6 (for Comparative Example)]
Regenerated cellulose was used instead of the raw material coniferous pulp, and the amount of sodium hypochlorite aqueous solution added was 27.0 mmol / g with respect to 1.0 g of regenerated cellulose. Cellulose fiber A6 was prepared in the same manner.

Using the above cellulose fibers, each characteristic was evaluated according to the following evaluation method.

<Crystal structure>
The diffraction profile of the cellulose fiber was measured using an X-ray diffractometer (RINT-Ultima3, manufactured by Rigaku Co., Ltd.). If typical peaks are observed at two positions, 2 theta = 14 to 17 ° and 2 theta = 22 to 23 °, the crystal structure (I-type crystal structure) is evaluated as "yes", and these If at least one of the peaks was not seen, it was evaluated as "none".

<Measurement of carboxy group amount>
After preparing 60 ml of an aqueous cellulose dispersion in which 0.25 g of the above cellulose fibers was dispersed in water, the pH was adjusted to about 2.5 with a 0.1 N hydrochloric acid aqueous solution. Then, the electric conductivity was measured by dropping a 0.05 M aqueous sodium hydroxide solution. The measurement was continued until the pH reached 11. The amount of carboxy group was determined based on the following formula using the amount of sodium hydroxide (V) consumed in the neutralization step of the weak acid in which the change in electrical conductivity was gradual.
Amount of carboxy group [mmol / g] = V [ml] x (0.05 / mass of cellulose [g])

<Measurement of carboxymethyl group amount>
After preparing the above cellulose fibers into a 0.6% by mass slurry, a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.4. Then, the electric conductivity was measured by dropping a 0.05 N aqueous sodium hydroxide solution. The measurement was continued until the pH reached 11. After measuring the amount of carboxy groups from the amount of sodium hydroxide consumed in the neutralization step of a weak acid whose electrical conductivity changes slowly, the amount of carboxymethyl groups can be calculated based on the following formula.
Carboxymethyl group amount [mmol / g] = (162 × C) / (1-58 × C) × 1000
C: Amount of carboxy group [mmol / g]

<Measurement of phosphate group amount>
The cellulose fibers were diluted with ion-exchanged water so as to have a solid content concentration of 0.2% by mass, treated with an ion-exchange resin, and then the amount of phosphate groups was measured by titration with an alkali. In the treatment with an ion exchange resin, a strongly acidic ion exchange resin (manufactured by Organo Corporation, Amber Jet 1024) per volume was added to a slurry containing 0.2% fine cellulose fibers, and then shaken for 1 hour. .. Then, the resin and the slurry were separated by pouring this suspension onto a mesh having a mesh size of 90 μm. In the titration using alkali, the change in the value of electrical conductivity exhibited by the aqueous dispersion was measured while adding a 0.1 N aqueous sodium hydroxide solution to the aqueous dispersion of fine cellulose fibers after ion exchange. That is, the value obtained by dividing the amount of alkali [mmol] added until the value of electrical conductivity became the smallest by the solid content [g] in the slurry to be titrated was defined as the amount of phosphoric acid groups [mmol / g].

<Measurement of carbonyl group amount>
Approximately 0.2 g of the above-mentioned cellulose fiber was precisely weighed, and exactly 50 ml of a 3 g / l aqueous solution of semicarbazide hydrochloride adjusted to pH = 5 with a phosphate buffer solution was added thereto, and the mixture was sealed and shaken for 2 days. Next, 10 ml of this solution was accurately collected in a 100 ml beaker, 25 ml of 5N sulfuric acid and 5 ml of a 0.05 N potassium iodate aqueous solution were added, and the mixture was stirred for 10 minutes. Then, 10 ml of a 5 mass% potassium iodide aqueous solution was added, and the sample was immediately titrated with a 0.1 N sodium thiosulfate solution using an automatic titrator. The total content of the aldehyde group and the ketone group) was determined.
Carbonyl group amount [mmol / g] = (DB) × f × (0.125 / w)
D: Sample titration [ml]
B: Titration of blank test [ml]
f: Factor of 0.1N sodium thiosulfate solution w: Sample amount [g]

The evaluation results of the above-mentioned plurality of cellulose fibers are shown below.

[Example 1]
(Preparation of modifier)
Tetraoctylammonium bromide (manufactured by Tokyo Kasei Co., Ltd.) was dissolved in ethanol to 0.1 N, and then an ion exchange resin (manufactured by Tokyo Kasei Co., Ltd., Amberlite IRN78) in an amount of 5 times that of tetraoctylammon bromide was added. After that, it was stirred with a shaker overnight. Then, the ion exchange resin was removed by filtration to obtain a 0.1N tetraoctylammonium hydroxide ethanol solution.

(Preparation of insulating paste)
The water contained in the cellulose fibers was replaced with MEK by repeating the methanol washing in which methanol was added to the cellulose fibers A1 and filtering, and then the methyl ethyl ketone (MEK) washing was repeated. Then, a 0.1N tetraoctylammonium hydroxide ethanol solution having the same amount as the carboxy group amount of MEK and the cellulose fiber was added to the cellulose fiber A1 substituted with MEK, and then diluted to a cellulose concentration of 1%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose MEK dispersion.

Bisphenol A (manufactured by DIC, EPICLON 850S) is added to the above-mentioned fine fibrous cellulose MEK dispersion, and then MEK and ethanol are distilled off by a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.) to remove the dispersion solvent from bisphenol. Replaced with A. Then, bisphenol A and dicyandiamide (Ajinomoto Co., Inc., Amicure AH-154) were added as a curing agent, and then T.I. K. By stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), an insulating paste in which the cellulose fiber concentration, the modifier concentration, the thermosetting resin concentration, and the curing agent concentration were adjusted as shown in the table below was obtained. ..

[Examples 2, 5-11, 13, 14, Comparative Examples 4-6]
A fine fibrous cellulose MEK dispersion and an insulating paste were prepared in the same manner as in Example 1 except that the blending amount and composition were changed as shown in the table below.

[Example 3]
Water was added to the cellulose fiber A3 to dilute it to a solid content of 1%, and then T.I. K. While stirring with a homomixer (manufactured by PRIMIX Corporation) at 8000 rpm for 10 minutes, 1N hydrochloric acid was added until the pH of the solution became 2. Then, it was filtered and washed thoroughly with water. Next, the acid-type cellulose fiber A3 was prepared by repeatedly washing with methanol and then washing with MEK to prepare the acid-type cellulose fiber A3 in which the solvent was replaced with MEK. MEK and a 0.1N tetraoctylammonium hydroxide ethanol solution equal to the amount of carboxy groups of the cellulose fibers were added to the acid-type cellulose fibers A3, and the mixture was diluted to a cellulose concentration of 1%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose MEK dispersion.

After adding modified bisphenol A (EPICLON 850S manufactured by DIC) to this fine fibrous cellulose MEK dispersion, the dispersion solvent is modified by distilling off MEK and ethanol with a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.). It was replaced with bisphenol A. Then, bisphenol A and dicyandiamide (Ajinomoto Co., Inc., Amicure AH-154) were added as a curing agent, and then T.I. K. By stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), an insulating paste in which the cellulose fiber concentration, the modifier concentration, the thermosetting resin concentration, and the curing agent concentration were adjusted as shown in the table below was obtained. ..

[Example 4]
The fine fibrous cellulose MEK dispersion and the insulating paste were prepared in the same manner as in Example 3 except that the cellulose fiber A4 was used instead of the cellulose fiber A3.

[Example 12]
After repeating the methanol washing in which methanol was added to the cellulose fiber A2 and filtered, the water contained in the cellulose fiber was replaced with MEK by further repeating the methyl ethyl ketone (MEK) washing. Then, a 0.1N tetraoctylammonium hydroxide ethanol solution having the same amount as the carboxy group amount of MEK and the cellulose fiber was added to the cellulose fiber A2 substituted with MEK, and then diluted to a cellulose concentration of 1%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose MEK dispersion.

After adding a polyol (Aimflex 318A, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) to the above fine fibrous cellulose MEK dispersion, the MEK and ethanol are dispersed by distilling off MEK and ethanol with a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.). The solvent was replaced with polyol. Then, after adding a polyol and polyisocyanate (Aimflex 318B, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a curing agent, T.I. K. By stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), an insulating paste in which the cellulose fiber concentration, the modifier concentration, the thermosetting resin concentration, and the curing agent concentration were adjusted as shown in the table below was obtained. ..

[Comparative Example 1]
Water and a 24% aqueous sodium hydroxide solution are added to the cellulose fiber A2 so that the amount is equal to the amount of carboxy groups of the cellulose fiber, diluted to a cellulose concentration of 1%, and then a high-pressure homogenizer (sugino machine). A fine fibrous cellulose aqueous dispersion was obtained by treating once at a pressure of 100 MPa using Starburst (manufactured by the same company). Water was distilled off by drying this fine fibrous cellulose aqueous dispersion by freeze-drying, and then diluted with MEK so that the solid content became 1%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst). However, since the cellulose fibers settle in the MEK, the fine fibrous cellulose MEK dispersion has not been prepared.

[Comparative Example 2]
Methanol was added to the cellulose fiber A5 and then filtered. Then, after repeating the methanol washing and further repeating the MEK washing, the mixture was diluted with MEK so that the solid content became 1%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst). However, since the cellulose fibers settle in the MEK, the fine fibrous cellulose MEK dispersion has not been prepared.

[Comparative Example 3]
After distilling off water by drying the cellulose fiber A6 by freeze-drying, MEK and a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equal to the amount of carboxy groups of the cellulose fiber were added, and the cellulose concentration was 1. Diluted to%. Then, it was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst) to obtain a fine fibrous cellulose MEK dispersion.

After adding modified bisphenol A (EPICLON 850S manufactured by DIC) to this fine fibrous cellulose MEK dispersion, the dispersion solvent is modified by distilling off MEK and ethanol with a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd.). It was replaced with bisphenol A. Then, bisphenol A and dicyandiamide (Ajinomoto Co., Inc., Amicure AH-154) were added as a curing agent, and then T.I. K. By stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), an insulating paste in which the cellulose fiber concentration, the modifier concentration, the thermosetting resin concentration, and the curing agent concentration were adjusted as shown in the table below was obtained. ..

[Comparative Example 7]
An insulating paste was prepared in which the polyol concentration was adjusted to 59% and the polyisocyanate concentration was adjusted to 41%.

Each characteristic was evaluated according to the following evaluation method using the above insulating paste or the like.

<Measurement of number average fiber diameter and aspect ratio>
The number average fiber diameter and fiber length of the cellulose fibers in the fine fibrous cellulose MEK dispersion were observed using a transmission electron microscope (TEM, JEM-1400 manufactured by JEOL Ltd.). That is, the number average fibers were cast by the above-mentioned method using a TEM image (magnification: 10000 times) negatively stained with 2% by mass uranyl acetate after casting each cellulose fiber on a carbon film-coated grid that had been hydrophilized. The diameter and number average fiber length were calculated. Furthermore, using these values, the aspect ratio was calculated according to the following formula.
Aspect ratio = number average fiber length [nm] / number average fiber diameter [nm]

<Evaluation of dispersion stability>
The fine fibrous cellulose MEK dispersion was transferred to a test tube and allowed to stand overnight (10 hours), and then the dispersed state of the cellulose fibers in the test tube was visually observed and evaluated according to the following evaluation criteria.
◯: Cellulose fibers were uniformly dispersed in the fine fibrous cellulose MEK dispersion liquid.
X: Cellulose fibers were settled in the fine fibrous cellulose MEK dispersion.

<Evaluation of strength>
A resin composition was obtained by pouring the insulating paste between two iron plates and then heating and drying at 150 ° C. for 1 hour. After cutting out the resin composition into a dumbbell type according to JIS K6251, the elastic modulus (E) [MPa] was measured using a universal testing machine (manufactured by Instron Japan Co., Ltd., type 5581).

Further, the strength improvement rate [%] is calculated by using the elastic modulus (E) of the resin composition in which the fine fibrous cellulos is compounded, the elastic modulus (E _{Blank) of the resin alone, and the following formula.} bottom. From the calculated strength improvement rate, the strength was evaluated based on the following criteria.
Strength improvement rate [%] = (E / E _Blank ) x 100-100
⊚: 10% or more ○: less than 10% 5% or more Δ: less than 5% 2.5% or more ×: less than 2.5

<Evaluation of dimensional stability>
A resin composition was obtained by pouring the insulating paste between two iron plates and then heating and drying at 150 ° C. for 1 hour. After cutting out a test piece from the resin composition according to JIS K7197, the coefficient of linear expansion (CTE) was measured using a thermomechanical analyzer TMA (TMA8311 manufactured by Rigaku Co., Ltd.).

Further, dimensional stability [%] is used by using the coefficient of linear expansion (CTE) of the resin composition in which the fine fibrous cellulos is compounded, the coefficient of linear expansion (CTE _{Blank) of the resin alone, and the following formula.} Was calculated. From the calculated dimensional stability, the dimensional stability was evaluated based on the following criteria. The smaller the value of the coefficient of linear thermal expansion, the more thermally stable it is. Therefore, the smaller the value of dimensional stability, the higher the stability.
Dimensional stability [%] = CTE / CTE _Blank x 100
⊚: Less than 30% ○: 30% or more and 40% or more Δ: 40% or more and less than 50% ×: 50% or more

The test results are shown below.

※１ ＨＵＮＴＳＭＡＮ社製、ＪＥＦＦＡＭＩＮＥ Ｍ−２００５、分子量：２０００
※２ ＨＵＮＴＳＭＡＮ社製、ＪＥＦＦＡＭＩＮＥ Ｍ−２０７０、分子量：２０００
※３ ＭＥＫ分散物を調製できないので、測定不可
※４ ＭＥＫに溶解しているため、測定不可

* 1 HUNTSMAN, JEFFAMINE M-2005, molecular weight: 2000
* 2 HUNTSMAN, JEFFAMINE M-2070, molecular weight: 2000
* 3 Cannot be measured because MEK dispersion cannot be prepared. * 4 Cannot be measured because it is dissolved in MEK.

From the above results, the following was found. That is, it was found that Examples 1 to 14 were superior in strength improvement rate and dimensional stability with respect to heat as compared with Comparative Examples 1 to 7. In Comparative Example 1, it is considered that the MEK dispersion could not be prepared because the fine fibrous cellulose aggregated in the solvent due to insufficient hydrophobicity of the modifier. In Comparative Example 2, it is considered that the MEK dispersion could not be prepared because the fine fibrous cellulose aggregated in the solvent due to the absence of the modifier. For Comparative Example 3, an insulating paste was obtained. However, in Comparative Example 3, since the fine fibrous cellulose did not have a crystal structure, the strength was not improved and the dimensional stability against heat was not improved.

Further, in Comparative Examples 5 and 6, an insulating paste was obtained, but the molecular weight of the modifier polyetheramine was very large. Therefore, since the polyether amine acts as a plasticizer, the expected strength and dimensional stability with respect to heat have not been improved.

On the other hand, since the modifier used in the examples contains quaternary onium ions, it is possible to sufficiently hydrophobize the cellulose fibers. Therefore, in the examples, the insulating paste could be prepared as a result of the fine fibrous cellulose being dispersed in the solvent without agglutination. Further, since the modifier used in the examples contains quaternary onium ions, the plasticity of the modifier is low because the molecular weight of the modifier is relatively small. As a result, it was found that the examples were excellent in strength improvement and dimensional stability against heat.

Here, Examples 1 to 4 are the results of using different cellulose fibers. Examples 2, 5 to 11 are the results of using different modifiers. Examples 2 and 12 are the results of using different thermosetting resins. Examples 2, 13 to 14 are the results in which the cellulose fiber concentrations are different from each other.

Since the insulating paste of the present invention is excellent in strength improvement and dimensional stability against heat, it can be suitably used in the field of, for example, electronic materials.

The present invention is not limited to the above-described embodiment, and can be realized with various configurations within a range not deviating from the gist thereof. For example, the embodiment corresponding to the technical feature in each embodiment described in the column of the outline of the invention, the technical feature in the embodiment may be used to solve a part or all of the above-mentioned problems, or the above-mentioned above. It is possible to replace or combine them as appropriate to achieve some or all of the effects. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

P1 ... Point P2 ... Point F ... Fiber

Claims (6)

An insulating paste containing fine fibrous cellulose, a thermosetting resin, and a curing agent.
The fine fibrous cellulose is an insulating paste characterized by satisfying the following conditions (A) to (E).
(A) Number average fiber diameter is 2 nm or more and 500 nm or less (B) Average aspect ratio is 10 or more and 1000 or less (C) Cellulose I-type crystal structure (D) Anionic functional group (E) The above (D). The organic onium ion represented by the following formula (1) is bonded to a part or all of the anionic functional groups of.

[In the above formula (1), M represents a nitrogen atom or a phosphorus atom, and R ¹ , R ² , R ³ , and R ⁴ are linear or branched alkyl groups having 1 or more and 20 or less carbon atoms, arene groups, or Shows an allyl group. ] The insulating paste according to claim 1, wherein at least one of ^{R 1} , R ² , R ³ , and R ^{4 in} the formula (1) has 6 or more carbon atoms. The insulating paste according to claim 1 or 2, wherein the anionic functional group is a carboxy group. The insulating paste according to any one of claims 1 to 3, wherein the thermosetting resin contains an epoxy resin. The insulating paste according to any one of claims 1 to 4, wherein the solid content concentration of the fine fibrous cellulose is 0.05% by mass or more and 3.0% by mass or less. A resin composition prepared from the insulating paste according to any one of claims 1 to 5.

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