JP7344825B2 - adhesive composition - Google Patents

Description

The present invention relates to adhesive compositions.

Conventionally, it has been known to use fine fibrous cellulose as an adhesive (for example, Patent Document 1). Patent Document 1 discloses an adhesive composition containing fine fibrous cellulose and polyetheramine.

Japanese Patent Application Publication No. 2018-44097

However, although the adhesive composition described in Patent Document 1 has excellent heat resistance, there is room for improvement in adhesive strength. Therefore, it has been desired to develop an adhesive composition that has excellent heat resistance and adhesive strength.

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 adhesive composition containing fine fibrous cellulose and a matrix resin is provided. In this adhesive composition, the fine fibrous cellulose is characterized in that it satisfies the following conditions (A) to (E).
(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 has a type I crystal structure (D) It has an anionic functional group (E) The description in (D) above An organic onium ion represented by the following formula (1) is bonded to some 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 a linear or branched alkyl group having 1 to 20 carbon atoms, an arene group, or Indicates an allyl group. ]

The adhesive composition of this form has excellent heat resistance and adhesive strength.

(2) In the adhesive composition of the above embodiment, at least one of R ¹ , R ² , R ³ , and R ⁴ in the formula (1) may have 6 or more carbon atoms.

According to the adhesive composition of this form, it has excellent heat resistance and even more excellent adhesive strength.

(3) In the adhesive composition of the above embodiment, the anionic functional group may be a carboxy group.

According to this form of adhesive composition, it is easy to introduce anionic functional groups into fine fibrous cellulose.

(4) In the adhesive composition of the above embodiment, the matrix resin may contain at least one selected from the group consisting of epoxy resin, urethane resin, acrylic resin, acid vinyl resin, and hydrocarbon resin.

According to the adhesive composition of this form, it has more excellent heat resistance and even more excellent adhesive strength.

(5) In the adhesive composition of the above embodiment, the matrix resin may contain at least one of an epoxy resin and a urethane resin.

The adhesive composition of this form has excellent compatibility with fine fibrous cellulose.

(6) In the adhesive composition of the above form, the solid content concentration of the fine fibrous cellulose is 0.05% by mass or more and 3.0% by mass with respect to the total solid content of the matrix resin and the fine fibrous cellulose. It may be less than % by mass.

The adhesive composition of this form has excellent handling properties and thickening properties.

(7) In the adhesive composition of the above form, the content of the anionic functional group relative to the content of the fine fibrous cellulose (content of anionic functional group [mmol]/content of the fine fibrous cellulose [g ]) may be 1.0 mmol/g or more and 3.0 mmol/g or less.

The adhesive composition of this form has particularly excellent adhesive strength.

Note that the present invention can be realized in various forms, such as a writing instrument using an adhesive composition, a method for manufacturing an adhesive composition, and the like.

The figure explaining the measuring method of a fiber diameter.

A. Adhesive composition The adhesive composition which is one embodiment of the present invention is an adhesive composition containing fine fibrous cellulose and a matrix resin, and the fine fibrous cellulose contains the following (A). It is characterized by satisfying the conditions from (E).

(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 has type I crystal structure (D) It has an anionic functional group (E) The method described in (D) An organic onium ion represented by the following formula (1) is bound to part or all of the anionic functional group.

〔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 represent a linear or branched alkyl group having 1 to 20 carbon atoms, an arene group, or an allyl group. Indicates the group. ]

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

The adhesive composition of this embodiment has excellent heat resistance and adhesive strength. In this specification, adhesion refers to a phenomenon in which surfaces of substances that are in contact with each other are bonded together through an adhesive. For example, the adhesive may be broken as a factor that may cause the bond to be broken. However, by increasing the strength of the adhesive after solidification, the breakage of the adhesive is suppressed, and as a result, the adhesive strength is improved. In the adhesive composition of this embodiment, the fine fibrous cellulose hydrophobized with organic onium ions acts as a filler in the adhesive composition, and as a result, the adhesive strength is increased by improving the strength of the adhesive. It is considered that this has improved. On the other hand, when fine fibrous cellulose hydrophobized with polyether amine is used, polyether amine has a high molecular weight and high plasticity, so polyether amine cancels the effect of fine fibrous cellulose as a filler. It is considered that the adhesive strength as expected cannot be obtained.

[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, particularly preferably 3 nm or more and 80 nm or less. If the above-mentioned number average fiber diameter is less than 2 nm, the fine fibrous cellulose will dissolve and a three-dimensional network of the fine fibrous cellulose will not be formed in the solvent, and there is a possibility that adhesive strength will not be ensured. On the other hand, when the number average fiber diameter exceeds 500 nm, there is also a risk that fine fibrous cellulose will settle. Further, the maximum fiber diameter is preferably 1000 nm or less, particularly preferably 500 nm or less, from the viewpoint of excellent adhesive strength.

The number average fiber diameter and number average fiber length of the fine fibrous cellulose can be measured, for example, by the following method. That is, after preparing an aqueous dispersion of fine cellulose with a solid content of 0.05 to 0.1% by mass, the dispersion was cast onto a grid coated with a hydrophilic carbon membrane and subjected to transmission electron Use as a sample for observation with a microscope (TEM).

FIG. 1 is a diagram illustrating a method for measuring fiber diameter. The fiber diameter can be determined by measuring the distance between two intersections between a line perpendicular to the longitudinal direction of one fiber F and the outer periphery of the fiber. That is, it can be determined by measuring the distance between points P1 and P2 shown in FIG. The fiber length is determined by measuring the length of the fiber in which the entire fiber is visible in the observed image. When measuring the length of a fiber, if there is a bend in the fiber, for example, if there is one bending point, the total value of the length from one end to the bending point and the length from this bending point to the other end. Let be the fiber length. Note that the fiber diameter and length of at least 25 fibers are observed. In addition, when fibers with a large fiber diameter are included, a scanning electron microscope (SEM) image of the surface cast onto glass may be observed. Then, observation using an electron microscope image may be performed at a magnification of 5,000 times, 10,000 times, or 50,000 times depending on the size of the constituent fibers. From the data on the fiber diameter and fiber length obtained in this way, the number average fiber length and 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, there will be a problem that the surface charge will decrease and adhesive strength cannot be ensured.

The average aspect ratio of the fine fibrous cellulose is calculated by the following formula using the number average fiber diameter and 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 above-mentioned fine fibrous cellulose is a fiber obtained by refining a naturally derived cellulose raw material having a type I crystal structure. That is, in the process of biosynthesis of natural cellulose, first, almost without exception, nanofibers called microfibrils are formed, and when the microfibrils become multi-bundled, they form a higher-order solid structure.

The cellulose constituting the above-mentioned fine fibrous cellulose has a type I crystal structure, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, 2 theta = around 14 to 17 degrees and 2 theta = 22 to 23 degrees. It can be identified because it has typical peaks at two positions around .

<Anionic functional group>
The fine fibrous cellulose has an anionic functional group. In this specification, an anionic functional group refers to a functional group from which more than half of the hydrogen ions are dissociated in water at pH 7. Examples of the anionic functional group include, but are not limited to, a carboxy group, a phosphoric acid group, a sulfuric acid group, and the like. 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 carboxyl group into the fine fibrous cellulose is not particularly limited, but for example, (i) a compound selected from the group consisting of a compound having a carboxyl group, an acid anhydride of a compound having a carboxyl group, and a derivative thereof; Examples include a method of reacting at least one type with the 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 it.

The above-mentioned compound having a carboxyl group is not particularly limited, but includes, for example, halogenated acetic acid. Examples of the halogenated acetic acid include chloroacetic acid, bromoacetic acid, and iodoacetic acid.

The acid anhydride of the above-mentioned compound having a carboxyl group is not particularly limited, but examples include acids of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Examples include anhydrides.

The derivative of the compound having a carboxyl group is not particularly limited, and examples thereof include imidized acid anhydrides of compounds having a carboxyl group, derivatives of acid anhydrides of compounds having a carboxyl group, and the like.

The imidized product of an acid anhydride of a compound having a carboxyl group is not particularly limited, and examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalic acid imide.

The acid anhydride derivative of a compound having a carboxyl group is not particularly limited, but for example, at least some of the hydrogen atoms of the acid anhydride of a compound having a carboxyl group are substituents (e.g., alkyl group, phenyl group, etc.). Examples include those replaced with . The acid anhydride of the compound having a carboxyl group is not particularly limited, and examples thereof include dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, and the like.

The method for oxidizing the hydroxyl groups of the fine fibrous cellulose is not particularly limited, but includes, for example, a method in which an N-oxyl compound is used as an oxidation catalyst and a co-oxidizing agent is used.

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

Further, the method for introducing phosphoric acid groups into the fine fibrous cellulose is not particularly limited, and examples thereof include the following method. That is, (i) a method of mixing a powder or aqueous solution of phosphoric acid or a phosphoric acid derivative into a dry or wet cellulose fiber raw material; (ii) a method of mixing a powder or an aqueous solution of phosphoric acid or a phosphoric acid derivative into a dispersion of a cellulose fiber raw material; Examples include a method of adding an aqueous solution. In these methods, dehydration treatment, heat treatment, etc. are generally performed after mixing or adding powder or aqueous solution of phosphoric acid or phosphoric acid derivatives. By doing this, a phosphate group-containing compound or its salt undergoes a dehydration reaction with the hydroxyl group of the glucose unit constituting cellulose to form a phosphoric acid ester, and the hydroxyl group of the glucose unit constituting cellulose A phosphate group or a salt thereof is introduced. Here, the phosphoric acid or phosphoric acid derivative is not particularly limited, but includes, for example, at least one compound selected from oxo acids, polyoxo acids, and derivatives thereof containing a phosphorus atom.

The content of anionic functional groups relative to the content of fine fibrous cellulose (content of anionic functional groups [mmol]/content of fine fibrous cellulose [g]) is not particularly limited, but it has excellent adhesive strength. , 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, still more preferably 1.5 mmol/g or more and 2.0 mmol/g or more. It is 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 fine fibrous cellulose whose dry mass has been precisely weighed, the pH is adjusted to about 2.5 with a 0.1M aqueous hydrochloric acid solution. Thereafter, electrical conductivity is measured by dropping a 0.05M aqueous sodium hydroxide solution. Measurements are continued until the pH is approximately 11. From the amount of sodium hydroxide (V [ml]) consumed in the neutralization stage of the weak acid where the electrical conductivity changes slowly, the amount of carboxy groups C can be determined according to the following formula.
C [mmol/g] = V [ml] × (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% by mass slurry from fine fibrous cellulose whose dry mass was precisely weighed, a 0.1M aqueous hydrochloric acid solution was added to adjust the slurry to pH 2.4. Thereafter, the electrical conductivity is measured until the pH reaches 11 by dropping a 0.05N aqueous sodium hydroxide solution. The amount of carboxy groups C is determined from the amount of sodium hydroxide consumed in the neutralization stage of the weak acid in which the electrical conductivity changes slowly according to the above formula. Thereafter, the carboxymethyl group amount Cm can be determined according to the following formula.
Cm [mmol/g] = (162 x C) / (1-58 x C) x 1000

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

Examples of organic onium ions containing an alkyl group include tetramethylammonium ion, tetraethylammonium ion, tetrabutylammonium ion, tetrahexylammonium ion, tetraoctylammonium ion, tetradecylammonium ion, and tetradodecylammonium ion. Furthermore, examples of organic onium ions containing an alkyl group include trimethyldodecyl ammonium ion, trimethyltetradecylammonium ion, trimethylocdadecylammonium ion, tributyldodecyl ammonium ion, trioctylmethylammonium ammonium ion, and the like. Examples of the organic onium ion containing an alkyl group include octyldimethylethylammonium ion, dodecyldimethylethylammonium ion, didecyldimethylammonium ion, and the like. Furthermore, examples of the organic onium ion containing an alkyl group include tetraethylphosphonium ion, tetrabutylphosphonium ion, tetraoctylphosphonium ion, and the like. 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 organic onium ions containing an arene group include benzyltrimethylammonium ion, benzyltributylammonium ion, benzyldimethyldodecylammonium ion, benzyldimethyltetradecylammonium ion, benzyldimethyloctadecylammonium ion, and the like. Furthermore, examples of the organic onium ion containing an arene group include benzyldimethylphenylammonium ion, triethylphenylammonium ion, dimethylphenylammonium ion, and the like. Further, examples of organic onium ions containing an arene group include tetraphenylphosphonium ion, benzyltriphenylphosphonium ion, methyltriphenylphosphonium ion, ethyltriphenylphosphonium ion, butyltriphenylphosphonium ion, tetradecyltriphenylphosphonium ion, etc. can be mentioned.

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

In the organic onium ion, from the viewpoint of achieving better adhesive strength, at least one of R ¹ , R ² , R ³ , and R ⁴ preferably has 6 or more carbon atoms. Further, in the organic onium ion, from the viewpoint of achieving better adhesive strength, it is preferable that R ¹ , R ² , R ³ , and R ⁴ all have 6 or more carbon atoms. Further, in the organic onium ion, R ¹ , R ² , R ³ , and R ⁴ are all preferably alkyl groups having 7 or more and 10 or less carbon atoms. Specifically, the organic onium ion preferably includes at least one of a tetraoctyl ammonium ion and a tetraoctylphosphonium ion. Further, from the viewpoint of achieving better adhesive 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 that

The amount of organic onium ions per gram of fine fibrous cellulose is not particularly limited, but it is preferably 1.0 mmol or more, more preferably 1.5 mmol or more, per 1 g of fine fibrous cellulose. Preferably, 1.8 mmol or more is more preferable. By doing so, it is possible to suppress the fine fibrous cellulose from agglomerating in the solvent, thereby improving storage stability. Further, the amount of organic onium ions per 1 g of fine fibrous cellulose is preferably 3.0 mmol or less, more preferably 2.5 mmol or less, and even more preferably 2.2 mmol or less. By doing so, it is possible to suppress the organic onium ions from acting as a plasticizer, thereby achieving high adhesive strength.

[Matrix resin]
The adhesive composition of this embodiment contains a matrix resin. The matrix resin is not particularly limited as long as it can be used as an adhesive, and may be a monomer, oligomer, or polymer, and the polymer may be a homopolymer or a copolymer. . Moreover, these may be one type or a combination of multiple types.

The above-mentioned matrix resin is not particularly limited, but examples thereof include polycondensation resins, polyaddition polymerization resins, addition condensation resins, and addition polymerization resins. Polymer resins and addition polymer resins are preferred.

The polyaddition polymer resin is not particularly limited, and examples thereof include urethane resins, epoxy resins, aldehyde resins, ketone resins, and the like.

Examples of the addition polymer resin include, but are not particularly limited to, acrylic resins, acid vinyl resins, vinyl chloride resins, vinylidene chloride resins, hydrocarbon resins, and copolymers thereof. Examples of the acrylic resin include, but are not limited to, acrylic resins such as polyacrylic esters and polymethacrylic esters, and copolymers thereof. The acid vinyl resin is not particularly limited, but includes, for example, acrylic-styrene copolymer, acrylic-vinyl acetate copolymer, acrylic-vinyl chloride copolymer, acrylic-ethylene copolymer, polyvinyl acetate, and vinyl acetate copolymer. Examples include vinyl chloride copolymer, vinyl acetate-ethylene copolymer, vinyl acetate-styrene copolymer, and the like. Examples of the vinyl chloride resin include, but are not limited to, polyvinyl chloride, vinyl chloride-acrylic copolymer, vinyl chloride-ethylene copolymer, vinyl chloride-styrene copolymer, and the like. Examples of the hydrocarbon resin include, but are not limited to, polyethylene, polypropylene, polybutadiene, chloroprene, polystyrene, polyisobutylene, styrene-butadiene copolymer, polyacrylonitrile, acrylonitrile-butadiene copolymer, fluororesin, silicone resin, etc. Can be mentioned. In addition to these, synthetic resins modified with inorganic components may also be used, such as ceramic modified fluororesins, ceramic modified urethane resins, ceramic modified acrylic resins, and the like. Additionally, composite resins containing two or more different types of polymers within the particles may be used, such as urethane/acrylic, epoxy/acrylic, silicone/acrylic, polyester/acrylic, fluororesin/acrylic, colloidal silica/acrylic, Examples include nitrocellulose/acrylic, melamine resin/acrylic, and the like.

The polycondensation resins mentioned above are not particularly limited, but examples include amide resins, imide resins, alkyd resins, phthalic acid resins, fatty acid-modified phthalic acid resins, phenol-modified phthalic acid resins, unsaturated polyester resins, and polycarbonates. .

Examples of the addition condensation resin include, but are not particularly limited to, phenol resins, urea resins, urea melamine resins, and the like.

The matrix resin of this embodiment may contain at least one selected from the group consisting of epoxy resin, urethane resin, acrylic resin, acid vinyl resin, and hydrocarbon resin from the viewpoint of compatibility with fine fibrous cellulose. is preferable, and it is particularly preferable to contain at least one of an epoxy resin and a urethane resin.

In the adhesive composition of this embodiment, the solid content concentration of the fine fibrous cellulose is 0.05% by mass based on the total solid content of the matrix resin and the fine fibrous cellulose from the viewpoint of handling property and thickening property. The range is preferably 3.0% by mass or less, and more preferably 1.0% by mass or more and 2.0% by mass or less.

The total solid content of the matrix resin and fine fibrous cellulose in the adhesive composition of this embodiment is not particularly limited, but is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. .

[Other additives]
The adhesive composition of the present embodiment may contain optional components, as necessary, within a range that does not impede the effects of the present invention. The adhesive composition of this embodiment includes, for example, a hydrolysis inhibitor, a colorant, a flame retardant, an antioxidant, a polymerization initiator, a polymerization inhibitor, an ultraviolet absorber, an antistatic agent, a lubricant, a mold release agent, Antifoaming agents, leveling agents, light stabilizers (for example, hindered amines, etc.), antioxidants, conductivity imparting agents, sliding properties imparting agents, surfactants, catalysts, curing accelerators, inorganic fillers, organic fillers, etc. be able to. These additives can be added in steps (2) to (4) described later, but it is better to add them after preparing the adhesive composition described later, so that they can be adjusted according to the intended use of the adhesive. preferred for.

Furthermore, a non-reactive solvent may be added to the adhesive composition of this embodiment as necessary. The non-reactive solvent is not particularly limited, but includes, for example, aliphatic hydrocarbon solvents such as hexane and mineral spirits; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; ester solvents such as butyl acetate; methanol, butanol, etc. Alcohol solvents; aprotic polar solvents such as dimethylformamide, dimethylsulfoxide, and N-methylpyrrolidone; These solvents may be used alone or in combination.

[Method for preparing adhesive composition]
The adhesive composition of this embodiment can be prepared by homogeneously kneading the above-mentioned fine fibrous cellulose, matrix resin, and, if necessary, various additive components. Examples of the kneading machine used in this case include a disper, a planetary mixer, a kneader, a Henschel mixer, a roll, and an extruder. Further, the prepared adhesive composition can be applied to a substrate to be adhered by a conventional method such as spraying, sealer gun, brush coating, or the like.

[Method for producing fine fibrous cellulose]
The method for producing fine fibrous cellulose of the present embodiment is not particularly limited, but a production method having the following steps (1) to (4) is preferred because it can be produced more efficiently.
Step (1): Dispersing cellulose fibers having a cellulose I type crystal structure in water, and then converting the hydroxyl groups of the cellulose fibers into substituents having carboxy groups Step (2): Dispersion medium for the cellulose fibers Step (3): Adding organic onium ions to the cellulose fibers after the above substitution Step (4): The cellulose fibers to which the organic onium ions have been bonded are nano-sized in the organic solvent. Defibration process

<Step (1)>
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, and a carboxyalkyl group.

Natural cellulose is generally used as cellulose having a cellulose I type crystal structure. Here, natural cellulose means purified cellulose isolated from cellulose biosynthetic systems such as plants, animals, and bacterially produced gels. More specifically, natural cellulose includes softwood pulp, hardwood pulp, cotton pulp such as cotton linters and cotton lint, non-wood pulp such as straw pulp and bagasse pulp, bacterial cellulose (BC), and those isolated from ascidians. cellulose isolated from seaweed, cellulose isolated from seaweed, etc. Among natural celluloses, preferred are softwood pulp, hardwood pulp, cotton pulp such as cotton linters and cotton lint, and non-wood pulps such as straw pulp and bagasse pulp. The above-mentioned natural cellulose is preferable because the reaction efficiency and productivity can be increased by subjecting it to a treatment to increase its surface area, such as beating.

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

(Oxidation treatment process)
Cellulose fibers containing carboxy groups can be obtained by oxidizing the oxidized cellulose with the natural cellulose, an N-oxyl compound, and a co-oxidizing agent.

The dispersion medium for cellulose in the above oxidation reaction is water, and the concentration of cellulose in the aqueous reaction solution is arbitrary as long as it 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 a device with strong mechanical stirring force.

Examples of the N-oxyl compound include compounds having a nitroxy radical that are generally used as oxidation catalysts. The above N-oxyl compound is preferably a water-soluble compound, and among them, piperidine nitroxyoxy radical is more preferable, such as 2,2,6,6-tetramethylpiperidinooxy radical, 4-acetamide-2,2,6 ,6-tetramethylpiperidinooxy radical is particularly preferred. The N-oxyl compound may be added in an amount equivalent to the catalyst amount, preferably in the range of 0.1 to 4 mmol/l, more preferably in the range of 0.2 to 2 mmol/l, to the aqueous reaction solution.

The above-mentioned co-oxidizing agent is not a substance that directly oxidizes the hydroxyl groups of cellulose, but a substance that oxidizes the N-oxyl compound used as an oxidation catalyst. Examples include hypohalous acid or its salt, halous acid or its salt, perhalous acid or its salt, hydrogen peroxide, perorganic acid, and the like. These may be used alone or in combination of two types. Among these, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are preferred. When using the above sodium hypochlorite, it is preferable to proceed with 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, preferably about 10 to 20 times, the amount of the N-oxyl compound.

The pH of the aqueous reaction solution is preferably maintained in the range of about 8-11. Although the temperature of the aqueous solution is arbitrary at about 4 to 40°C, 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, etc., the degree of oxidation is controlled by the amount of co-oxidant added and reaction time.

(Reduction treatment process)
The cellulose fibers after the oxidation treatment are preferably reduced with a reducing agent. As a result, some or all of the aldehyde groups and ketone groups are reduced and returned to hydroxyl groups. Note that the carboxy group is not reduced. The total content of carbonyl groups (aldehyde groups and ketone groups) in the oxidized cellulose resulting from the reduction is preferably 0.3 mmol/g or less, particularly preferably 0.1 mmol/g or less. Thereby, the molecular weight reduction 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 carbonyl groups (aldehyde groups and ketone groups) is calculated by the semicarbazide method described below. In addition, by controlling the carbonyl group to 0.5 mmol/g or less, it is possible to suppress the generation of aggregates due to long-term storage, and it is possible to suppress the viscosity from decreasing significantly over time. In addition, as the reducing agent used in the above-mentioned reduction reaction, it is possible to use a general one, but preferably LiBH ₄ , NaBH ₃ CN, and NaBH ₄ are mentioned. Among these, NaBH ₄ is particularly preferred from the viewpoint of cost and availability.

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

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

<Step (2)>
As step (2), first, the cellulose fibers after the above treatment are washed with acid to convert the carboxy groups introduced in step (1) into acid form. Thereafter, after purification by repeating filtration and water washing as appropriate, solid-liquid separation is performed using a centrifuge or the like. Thereafter, after repeatedly washing the cellulose with an organic solvent, solvent replacement is performed from water to an organic solvent.

(acid)
The above-mentioned acid keeps the cellulose fiber aqueous dispersion acidic, and the type of acid is not particularly limited. Examples of acids include inorganic acids such as hydrochloric acid, nitric acid, 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 include organic acids such as acid, tartaric acid, fumaric acid, and gluconic acid. It is preferable to use hydrochloric acid as the acid because deterioration and damage to cellulose fibers caused by acids can be avoided and waste liquid treatment is easy.

<Step (3)>
Step (3) is a step of adding organic onium ions represented by the above formula (1) to the oxidized cellulose after the dispersion medium has been replaced. As a result, the organic onium ions represented by the above formula (1) bond to the carboxy groups of the oxidized cellulose, thereby making the cellulose lipophilic. Note that the above reaction is performed in an organic solvent.

<Step (4)>
Step (4) is a step of nanofibrillating the lipophilized cellulose fibers in an organic solvent. Examples of the dispersion machine used for the above nano-fibrillation include a homomixer under high-speed rotation, a high-pressure homogenizer, an ultra-high-pressure homogenizer, an ultrasonic dispersion treatment, a beater, a disc refiner, a conical refiner, a double disc refiner, and a grinder. etc. By using these devices with strong beating ability, it becomes possible to make the material finer, thereby enabling more efficient and advanced downsizing. In addition, as the above-mentioned dispersing machine, for example, a screw type mixer, a paddle mixer, a disperser type mixer, a turbine type mixer, etc. may be used.

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

First, prior to producing Examples and Comparative Examples, cellulose fibers A1 to A4 for Examples and cellulose fibers A5 and A6 for Comparative Examples were prepared according to Production Examples 1 to 6 below.

[Production Example 1: Preparation of cellulose fiber A1 (for example)]
150 ml of water, 0.25 g of sodium bromide, and 0.025 g of TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) were added to 2 g of softwood pulp, and the mixture was thoroughly stirred and dispersed. Thereafter, the reaction was started by adding a 13% aqueous sodium hypochlorite solution such that the amount of sodium hypochlorite was 5.2 mmol/g per 1.0 g of softwood pulp. Since the pH decreased as the reaction progressed, a 0.5N aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10 to 11, and the reaction was allowed to proceed until no change in pH was observed. The reaction time was 120 minutes. After the reaction was completed, the mixture was neutralized by adding 0.1N hydrochloric acid, followed by solid-liquid separation using a centrifuge, and then pure water was added to adjust the solid content concentration to 4%. Thereafter, the pH of the slurry was adjusted to 10 with a 24% aqueous sodium hydroxide solution. After the temperature of the slurry was set to 30°C, reduction treatment was performed by adding 0.2 mmol/g of sodium borohydride to the cellulose fibers and reacting for 2 hours. After the reaction, the pH was adjusted to 2 or less by adding 0.1N hydrochloric acid, and then purified by repeating filtration and water washing to obtain cellulose fiber A1.

[Production Example 2: Preparation of cellulose fiber A2 (for example)]
Cellulose fiber A2 was obtained in the same manner as the preparation method of cellulose fiber A1, except that the amount of sodium hypochlorite aqueous solution added was 12.0 mmol/g per 1.0 g of softwood pulp.

[Production Example 3: Preparation of cellulose fiber A3 (for example)]
After putting 100 g of softwood pulp into 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 a 50% monochloroacetic acid IPA solution to this slurry, the temperature was raised to 70° C., and the mixture was reacted for 1.5 hours. Cellulose fiber A3 was obtained by washing the obtained reaction product with 80% methanol, then replacing it with methanol, and drying it.

[Production Example 4: Preparation of cellulose fiber A4 (for example)]
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. Thereafter, phosphorylating agent-impregnated pulp was obtained by spraying 20 g of softwood pulp (NBKP) ground with a household mixer onto the phosphorylating agent while stirring with a kneader. Next, the phosphorylated pulp was obtained by heat-treating the phosphorylating agent-impregnated pulp for 60 minutes in a blow dryer equipped with a damper heated to 140°C. After adding water to the obtained phosphorylated pulp to make the solid content concentration 2%, stirring and mixing to uniformly disperse the pulp, the operations of filtration and dehydration were repeated twice. Next, water was added to the recovered pulp to give a solid content concentration of 2%. Thereafter, a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a pulp slurry with a pH of 12 to 13. Subsequently, this pulp slurry was filtered and dehydrated, then water was further added and the operations of filtration and dehydration were repeated twice. Thereafter, cellulose fiber A4 was obtained by drying after substitution with methanol.

[Production Example 5: Preparation of cellulose fiber A5 (for comparative example)]
A 2% pulp concentration dispersion 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 30 times with Serendipitor MKCA6-3 (manufactured by Masuko Sangyo Co., Ltd.).

[Production Example 6: Preparation of cellulose fiber A6 (for comparative example)]
The method for preparing cellulose fiber A1 was the same as the method for preparing cellulose fiber A1, except that regenerated cellulose was used instead of the raw material softwood pulp, and the amount of sodium hypochlorite aqueous solution was 27.0 mmol/g per 1.0 g of regenerated cellulose. Cellulose fiber A6 was prepared in the same manner.

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

<Crystal structure>
The diffraction profile of the cellulose fibers was measured using an X-ray diffraction device (RINT-Ultima 3, manufactured by Rigaku Corporation). If typical peaks are seen at two positions, around 2 theta = 14 to 17 degrees and around 2 theta = 22 to 23 degrees, the crystal structure (type I crystal structure) is evaluated as "present", and these When at least one of the peaks was not observed, it was evaluated as "none."

<Measurement of carboxy group amount>
After preparing 60 ml of a cellulose aqueous dispersion in which 0.25 g of the above cellulose fibers were dispersed in water, the pH was adjusted to about 2.5 with a 0.1N aqueous hydrochloric acid solution. Thereafter, electrical conductivity was measured by dropping a 0.05M aqueous sodium hydroxide solution. Measurements were continued until the pH reached 11. In the neutralization stage of the weak acid in which the electrical conductivity changes slowly, the amount of carboxy groups was determined based on the following formula using the amount (V) of sodium hydroxide consumed.
Carboxy group amount [mmol/g] = V [ml] × (0.05/cellulose mass [g])

<Measurement of carboxymethyl group amount>
After preparing the cellulose fibers into a 0.6% by mass slurry, a 0.1M aqueous hydrochloric acid solution was added to adjust the slurry to pH 2.4. Thereafter, electrical conductivity was measured by dropping a 0.05N aqueous sodium hydroxide solution. Measurements were continued until the pH reached 11. After measuring the amount of carboxy groups from the amount of sodium hydroxide consumed in the neutralization stage of a weak acid where the 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: Carboxy group amount [mmol/g]

<Measurement of phosphate group amount>
The cellulose fibers were diluted with ion-exchanged water to a solid content concentration of 0.2% by mass, treated with an ion-exchange resin, and then the amount of phosphoric acid groups was measured by titration with an alkali. In the treatment with ion exchange resin, 1/10 of the volume of strongly acidic ion exchange resin (manufactured by Organo, Amber Jet 1024) was added to the slurry containing 0.2% fine cellulose fibers, and the mixture was shaken for 1 hour. . Thereafter, the resin and the slurry were separated by pouring this suspension onto a mesh with openings of 90 μm. In the titration using an alkali, a 0.1N aqueous sodium hydroxide solution was added to the ion-exchanged fine cellulose fiber aqueous dispersion, and the change in the electrical conductivity value of the aqueous dispersion was measured. That is, the value obtained by dividing the amount of alkali [mmol] added until the electrical conductivity value 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 fibers were accurately weighed, and to this was added exactly 50 ml of a 3 g/l aqueous solution of semicarbazide hydrochloride adjusted to pH=5 with a phosphate buffer, the mixture was tightly stoppered, and the mixture was shaken for two days. Next, 10 ml of this solution was accurately taken into a 100 ml beaker, 25 ml of 5N sulfuric acid and 5 ml of a 0.05N potassium iodate aqueous solution were added, and the mixture was stirred for 10 minutes. Thereafter, 10 ml of 5% by mass potassium iodide aqueous solution was added, and immediately titrated with 0.1N sodium thiosulfate solution using an automatic titrator. From the titration amount, etc., the amount of carbonyl groups in the sample was determined according to the following formula: The total content of aldehyde groups and ketone groups) was determined.
Carbonyl group amount [mmol/g] = (DB) x f x (0.125/w)
D: Titration amount of sample [ml]
B: Titration amount of blank test [ml]
f: Factor of 0.1N sodium thiosulfate solution w: Sample amount [g]

The evaluation results of the above 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 a concentration of 0.1N, and then an ion exchange resin (manufactured by Tokyo Kasei Co., Ltd., Amberlite IRN78) was added in an amount five times that of tetraoctylammonium bromide. Afterwards, the mixture was stirred overnight using a shaker. Thereafter, the ion exchange resin was removed by filtration to obtain a 0.1N tetraoctylammonium hydroxide ethanol solution.

(Preparation of adhesive composition)
After repeating methanol washing in which methanol was added to the cellulose fibers A1 and filtering them, water contained in the cellulose fibers was replaced with MEK by repeating methyl ethyl ketone (MEK) washing. Thereafter, a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the carboxyl group content of MEK and cellulose fibers was added to the MEK-substituted cellulose fiber A1, and then diluted to a cellulose concentration of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion. After adding bisphenol A (EPICLON 850S, manufactured by DIC Corporation) to the above fine fibrous cellulose MEK dispersion, MEK and ethanol were distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.) to convert the solvent into bisphenol A. Replaced with Furthermore, after adding bisphenol A and dicyandiamide (manufactured by Ajinomoto Co., Ltd., Amicure AH-154) as a curing agent, T.I. K. The adhesive composition was prepared by stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX) so that the cellulose concentration, modifier concentration, matrix resin concentration, and curing agent concentration became the values shown in the table below. Obtained. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 150° C. for 1 hour to harden the adhesive composition. .

[Examples 2, 5-11, 15, 16, Comparative Examples 4-6]
A fine fibrous cellulose MEK dispersion, an adhesive composition, and a test piece were prepared in the same manner as in Example 1, except that the blending amount, composition, etc. were changed as shown in the table below.

[Example 3]
After adding water to cellulose fiber A3 and diluting it to a solid content of 1%, T. K. While stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), 1N hydrochloric acid was added until the pH of the solution became 2. Thereafter, it was filtered and thoroughly washed with water. Next, after repeated washing with methanol, the fibers were further washed with MEK to produce acid type cellulose fiber A3 in which the solvent was replaced with MEK. MEK and a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the amount of carboxy groups in the cellulose fibers were added to the acid type cellulose fiber A3, and the fiber was diluted to a cellulose concentration of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion.

After adding bisphenol A (manufactured by DIC Corporation, EPICLON 850S) to this fine fibrous cellulose MEK dispersion, MEK and ethanol were distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.) to convert the solvent into bisphenol A. Replaced with Furthermore, after adding bisphenol A and dicyandiamide (manufactured by Ajinomoto Co., Ltd., Amicure AH-154) as a curing agent, T.I. K. The adhesive composition was prepared by stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX) so that the cellulose concentration, modifier concentration, matrix resin concentration, and curing agent concentration became the values shown in the table below. Obtained. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 150° C. for 1 hour to harden the adhesive composition. .

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

[Example 12]
After repeating methanol washing in which methanol was added to the cellulose fiber A2 and filtering it, methyl ethyl ketone (MEK) washing was further repeated to replace water contained in the cellulose fiber with MEK. Thereafter, a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the carboxyl group content of MEK and cellulose fibers was added to the MEK-substituted cellulose fiber A2, and then diluted to a cellulose concentration of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion. After adding toluene to the fine fibrous cellulose MEK dispersion, MEK and ethanol were distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.), thereby replacing the solvent with toluene. Furthermore, after adding toluene and polyvinyl acetate (manufactured by Denki Kagaku Kogyo Co., Ltd., Denkasakunol SN-10) as a matrix resin, T. K. By stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX), an adhesive composition was obtained in which the cellulose concentration, modifier concentration, and matrix resin concentration were adjusted to the values shown in the table below. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 150° C. for 1 hour to harden the adhesive composition. .

[Example 13]
After repeating methanol washing in which methanol was added to the cellulose fiber A2 and filtering it, methyl ethyl ketone (MEK) washing was further repeated to replace water contained in the cellulose fiber with MEK. Thereafter, a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the carboxyl group content of MEK and cellulose fibers was added to the MEK-substituted cellulose fiber A2, and then diluted to a cellulose concentration of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion. After adding an acrylic monomer (Metallock Y610A, manufactured by Cemedine Co., Ltd.) to the above fine fibrous cellulose MEK dispersion, MEK and ethanol are distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.) to remove the solvent from the acrylic monomer. system monomer. Furthermore, after adding an acrylic monomer and an acrylic curing agent (Metallock Y610B, manufactured by Cemedine), T.I. K. The adhesive composition was prepared by stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX) so that the cellulose concentration, modifier concentration, matrix resin concentration, and curing agent concentration became the values shown in the table below. Obtained. In addition, a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm was used as an adherend, and the adhesive composition was cured by leaving it at room temperature (25°C) for 1 hour. Got a piece.

[Example 14]
After repeating methanol washing in which methanol was added to the cellulose fiber A2 and filtering it, methyl ethyl ketone (MEK) washing was further repeated to replace water contained in the cellulose fiber with MEK. Thereafter, a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the carboxyl group content of MEK and cellulose fibers was added to the MEK-substituted cellulose fiber A2, and then diluted to a cellulose concentration of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion. After adding a polyol (Aimflex 318A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to the above-mentioned fine fibrous cellulose MEK dispersion, MEK and ethanol were distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.) to remove the solvent. Substituted with polyol. Furthermore, after adding polyol and polyisocyanate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Aimflex 318B) as a curing agent, T.I. K. The adhesive composition was prepared by stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX) so that the cellulose concentration, modifier concentration, matrix resin concentration, and curing agent concentration became the values shown in the table below. Obtained. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 80° C. for 2 hours to harden the adhesive composition. .

[Comparative example 1]
Add water and a 24% aqueous sodium hydroxide solution to the cellulose fiber A2 in an amount equal to the amount of carboxy groups in the cellulose fiber, dilute it to a cellulose concentration of 1%, and then use a high-pressure homogenizer (Sugino Machine). A fine fibrous cellulose aqueous dispersion was obtained by treating the mixture once at a pressure of 100 MPa using a vacuum cleaner (Starburst, manufactured by Co., Ltd.) at a pressure of 100 MPa. This fine fibrous cellulose aqueous dispersion was dried by freeze-drying to remove water, and then diluted with MEK to a solid content of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst). However, since cellulose fibers precipitated in MEK, it was not possible to prepare a fine fibrous cellulose MEK dispersion.

[Comparative example 2]
After adding methanol to cellulose fiber A5, it was filtered. After repeating methanol washing, MEK washing was repeated, and then diluted with MEK to a solid content of 1%. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Sugino Machine Co., Ltd., Starburst). However, since cellulose fibers precipitated in MEK, it was not possible to prepare a fine fibrous cellulose MEK dispersion.

[Comparative example 3]
After distilling off water by drying cellulose fiber A6 by freeze-drying, MEK and a 0.1N tetraoctylammonium hydroxide ethanol solution in an amount equivalent to the carboxy group weight of the cellulose fiber were added to bring the cellulose concentration to 1. It was diluted to %. Thereafter, the mixture was treated four times at a pressure of 100 MPa using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose MEK dispersion. After adding bisphenol A (manufactured by DIC Corporation, EPICLON 850S) to this fine fibrous cellulose MEK dispersion, MEK and ethanol were distilled off using a rotary evaporator (manufactured by Tokyo Rikakiki Co., Ltd.) to convert the solvent into bisphenol A. Replaced with Furthermore, bisphenol A and dicyandiamide (manufactured by Ajinomoto Co., Ltd., Amicure AH-154) as a curing agent were added, and T.I. K. The adhesive composition was prepared by stirring at 8000 rpm for 10 minutes using a homomixer (manufactured by PRIMIX) so that the cellulose concentration, modifier concentration, matrix resin concentration, and curing agent concentration became the values shown in the table below. Obtained. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 150° C. for 1 hour to harden the adhesive composition. .

[Comparative example 7]
An adhesive composition prepared to have a resin concentration of 20% was obtained by adding polyvinyl acetate to toluene. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 150° C. for 1 hour to harden the adhesive composition. .

[Comparative example 8]
An adhesive composition was obtained in which the concentration of an acrylic monomer (Metallock Y610A, manufactured by Cemedine) was 50%, and the concentration of an acrylic curing agent (Metallock Y610B, manufactured by Cemedine) was 50%. In addition, a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm was used as an adherend, and the adhesive composition was cured by leaving it at room temperature (25°C) for 1 hour. Got a piece.

[Comparative Example 9]
An adhesive composition was obtained in which the polyol concentration was 59% and the polyisocyanate concentration was 41%. In addition, a test piece was obtained by using a cold-rolled steel plate with a thickness of 1.6 mm, a width of 25 mm, and a length of 100 mm as an adherend and heating it at 80° C. for 2 hours to harden the adhesive composition. .

Using the above-mentioned adhesive composition etc., each characteristic was evaluated according to the following evaluation method.

<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, after each cellulose fiber was cast onto a carbon film-coated grid that had been made hydrophilic, the number-average fibers were determined by the method described above using a TEM image (magnification: 10,000 times) negatively stained with 2% by mass uranyl acetate. The diameter and number average fiber length were calculated. Further, 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]

<Measurement of dispersion stability>
The fine fibrous cellulose MEK dispersion was transferred to a test tube, left to stand overnight, and the state of dispersion of cellulose fibers in the test tube was visually observed and evaluated using the following evaluation criteria.
Good: Cellulose fibers were uniformly dispersed in the fine fibrous cellulose MEK dispersion.
×: Cellulose fibers were sedimented in the fine fibrous cellulose MEK dispersion.

<Evaluation of adhesive strength>
Using a universal testing machine (manufactured by Instron Japan, model 5581), the above test piece was tested at 2.5 mm/min. in an atmosphere at 23°C. The tensile shear adhesive strength (S23) was measured under the following conditions. From the tensile shear adhesive strength of the resin composited with fine fibrous cellulose (S23) and the tensile shear adhesive strength of the matrix resin alone (S _Blank 23), use the following formula to calculate the tensile shear adhesive strength improvement rate. [%] was calculated. The calculated tensile shear adhesive strength improvement rate was evaluated based on the following criteria.
Tensile shear adhesive strength improvement rate [%] = (S23/S _Blank 23×100) -100
◎: 40% or more ○: Less than 40% 30% or more △: Less than 30% 20% or more ×: Less than 20

<Evaluation of heat resistance>
Using a universal testing machine (manufactured by Instron Japan, model 5581), the above test piece was tested at 2.5 mm/min. in an atmosphere at 23°C. The tensile shear adhesive strength was measured under the following conditions. Using the following formula, the tensile shear adhesive strength retention rate [% ] was calculated. The calculated tensile shear adhesive strength retention rate was evaluated based on the following criteria.
Tensile shear adhesive strength maintenance rate [%] = 100-[{(S23)-(S80)}/(S23)×100]
◎: 95% or more ○: Less than 95% 90% or more △: Less than 90% 80% or more ×: Less than 80

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分散物を調整できないので、測定不可
※４ ＭＥＫに溶解しているため、測定不可

*1 Manufactured by HUNTSMAN, JEFFAMINE M-2005, molecular weight: 2000
*2 Manufactured by HUNTSMAN, JEFFAMINE M-2070, molecular weight: 2000
*3 MEK dispersion cannot be adjusted, so measurement is not possible *4 It is dissolved in MEK, so measurement is not possible

From the above results, we found the following. In other words, in Examples 1 to 16, compared to Comparative Examples 1 to 9, it was found that the adhesive strength was improved by blending fine fibrous cellulose, and the retention rate of adhesive strength was high even under high heat. . In Comparative Example 1, the dispersibility was low due to insufficient hydrophobicity of the modifier, and as a result, it is thought that the MEK dispersion could not be prepared. It is thought that in Comparative Example 2, the fine fibrous cellulose aggregated due to the absence of a modifier, and as a result, the MEK dispersion could not be prepared. In Comparative Example 3, the cellulose fibers were dispersed in the solvent without agglomerating. However, in Comparative Example 3, the adhesive strength did not improve because the cellulose fibers did not have a crystalline structure, and the adhesive strength retention rate was low even under high heat.

Further, in Comparative Examples 4 and 5, it was possible to prepare an adhesive composition, but the molecular weight of the polyether amine as a modifier was very large. Therefore, since the polyetheramine acts as a plasticizer, the expected improvement in adhesive strength was not observed in Comparative Examples 4 and 5.

Here, Examples 1 to 4 are results using different cellulose fibers. Examples 2 and 5 to 11 are the results using different modifiers. Examples 2, 12 to 14 are results using different matrix resins. Examples 2, 15 and 16 have different cellulose fiber concentrations.

Since the adhesive composition of the present invention has excellent heat resistance and adhesive strength, it can be used, for example, as an adhesive in technical fields such as the aerospace field, electronics, civil engineering, and architecture, as well as in automobiles, Suitable for use in adhesives for on-vehicle devices.

The present invention is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and examples that correspond to the technical features in each form described in the summary column of the invention may be used to solve some or all of the above-mentioned problems, or to solve the above-mentioned problems. In order to achieve some or all of the effects, it is possible to replace or combine them as appropriate. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

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

Claims (7)

An adhesive composition containing fine fibrous cellulose and a matrix resin,
An adhesive composition, wherein the fine fibrous cellulose satisfies the following conditions (A) to (E).
(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 has a type I crystal structure (D) It has an anionic functional group (E) The description in (D) above An organic onium ion represented by the following formula (1) is bonded to some 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 a linear or branched alkyl group having 1 to 20 carbon atoms, an arene group, or Indicates an allyl group. ] The adhesive composition 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 adhesive composition according to claim 1 or 2, wherein the anionic functional group is a carboxy group. Any one of claims 1 to 3, wherein the matrix resin contains at least one selected from the group consisting of epoxy resin, urethane resin, acrylic resin, acid vinyl resin, and hydrocarbon resin. The adhesive composition according to item 1. The adhesive composition according to any one of claims 1 to 4, wherein the matrix resin contains at least one of an epoxy resin and a urethane resin. A solid content concentration of the fine fibrous cellulose is 0.05% by mass or more and 3.0% by mass or less with respect to the total solid content of the matrix resin and the fine fibrous cellulose. The adhesive composition according to any one of claims 1 to 5. The content of the anionic functional group relative to the content of the fine fibrous cellulose (content of anionic functional group [mmol]/content [g] of the fine fibrous cellulose) is 1.0 mmol/g or more.3. The adhesive composition according to any one of claims 1 to 6, characterized in that it has a content of 0 mmol/g or less.

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