Adhesive composition for inorganic fiber-reinforced composite materials

Abstract

To provide an adhesive composition containing cellulose nanofibers that can be used as an adhesive between inorganic fiber-reinforced composite materials such as CFRP. [Solution] An adhesive composition for inorganic fiber-reinforced composite materials comprising modified cellulose fibers having a modifying group and a resin. Preferably, the modified cellulose fibers having the modifying group are modified cellulose fibers having the modifying group via ionic bonds and / or covalent bonds.

Description

Technical Field

[0001] The present invention relates to an adhesive composition for inorganic fiber reinforced composite materials. Furthermore, the present invention relates to a method for bonding inorganic fiber reinforced composite materials using such an adhesive composition.

Background Art

[0002] In recent years, technologies with less environmental impact have come to the forefront. Under such a technological background, materials using cellulose fibers, which are biomass abundantly present in nature, have attracted attention.

[0003] Cellulose nanofibers are known as resin reinforcing fillers. For example, Patent Document 1 proposes using a resin composition containing cellulose nanofibers as an adhesive.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when such a resin composition is applied to bonding carbon fiber reinforced resins (CFRP), unexpectedly, material failure may occur. This is considered to be due to delamination occurring between layers.

[0006] Therefore, the present invention relates to providing an adhesive composition containing cellulose nanofibers that can be used as an adhesive for bonding inorganic fiber reinforced composite materials such as CFRP.

Means for Solving the Problems

[0007] The present invention relates to the following [1] to [8]. [1] A method for bonding inorganic fiber-reinforced composite materials together using a composition comprising modified cellulose fibers having modifying groups and a resin. [2] An adhesive composition for inorganic fiber-reinforced composite materials, comprising modified cellulose fibers having modifying groups and a resin. [3] The adhesive composition for inorganic fiber-reinforced composite materials according to [2], wherein the modified cellulose fibers having modifying groups are modified cellulose fibers having modifying groups via ionic bonds and / or covalent bonds. [4] The adhesive composition for inorganic fiber-reinforced composite materials according to [2] or [3], wherein the amount of modified cellulose fibers having a modifying group is 0.5 parts by mass or more and 100 parts by mass or less per 100 parts by mass of resin. [5] The adhesive composition for inorganic fiber-reinforced composite materials according to any one of [2] to [4] above, wherein the modifying group in the modified cellulose fiber having a modifying group is one or more selected from the group consisting of hydrocarbon groups and polymer groups. [6] An adhesive composition for inorganic fiber-reinforced composite materials according to any one of the above items [2] to [5], wherein the resin is a curable resin. [7] An adhesive composition for inorganic fiber-reinforced composite materials according to any one of the above items [2] to [6], wherein the inorganic fiber-reinforced composite material is a carbon fiber-reinforced composite material. [8] A method for manufacturing a structure, comprising the step of bonding inorganic fiber-reinforced composite materials together using an adhesive for inorganic fiber-reinforced composite materials described in any one of the above items [2] to [7]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an adhesive composition containing cellulose nanofibers that can be used as an adhesive between inorganic fiber-reinforced composite materials. [Modes for carrying out the invention]

[0009] As a result of diligent research by the inventors to solve the above problems, they discovered that by using modified cellulose fibers having modifying groups as cellulose nanofibers, delamination between layers of CFRP can be suppressed, and thus completed the present invention.

[0010] 1. Adhesive composition for inorganic fiber-reinforced composite materials The adhesive composition for inorganic fiber-reinforced composite materials of the present invention (hereinafter sometimes referred to as "adhesive composition") is made by compounding modified cellulose fibers having modifying groups with a resin. Although the mechanism by which the adhesive composition of the present invention exerts the above effects is not clear, it is presumed that by using a resin in which modified cellulose fibers having modifying groups are uniformly dispersed as an adhesive, the toughness of the resin is improved, which in turn improves the adhesive strength of the adhesive, and as a result, delamination between layers of CFRP can be suppressed.

[0011] [Modified cellulose fiber] The modified cellulose fiber in this invention is a cellulose fiber having a modifying group. The modifying group is preferably bonded to the glucose constituting the cellulose fiber via ionic bonds and / or covalent bonds (e.g., amide bonds), more preferably to some or all of the hydroxyl groups of the glucose, or to the carboxyl group obtained by converting the hydroxyl group of the glucose unit to a carboxyl group, and more preferably to the carboxyl group obtained by converting the group at the C6 position (-CH2OH) of the glucose unit to a carboxyl group.

[0012] [Modifying group] Modifying groups that modified cellulose fibers may have include, for example, one or more selected from the group consisting of (a) hydrocarbon groups and (b) polymer groups.

[0013] (a) hydrocarbon group The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group. Examples of unsaturated hydrocarbon groups include monovalent unsaturated hydrocarbon groups, such as chain-type unsaturated hydrocarbon groups and cyclic unsaturated hydrocarbon groups. From the perspective of improving the adhesion strength, the number of carbon atoms in the unsaturated hydrocarbon group is 2 or more, preferably 3 or more. From the perspective of the availability of raw materials, it is preferably 30 or less, more preferably 22 or less, still more preferably 18 or less, still more preferably 12 or less, and still more preferably 8 or less. The unsaturated hydrocarbon group may have substituents described later, and a part of the unsaturated hydrocarbon group may be substituted with a hydrogen nitride group. When introducing the unsaturated hydrocarbon group into the cellulose fiber using an amine compound, the number of unsaturated hydrocarbon groups per nitrogen atom is 1 to 3, and from the perspective of improving the adhesion strength, 2 is preferable.

[0014] From the perspective of enhancing the adhesion strength, the chain-type unsaturated hydrocarbon group is preferably a linear chain-type unsaturated hydrocarbon group. Specific examples of the chain-type unsaturated hydrocarbon group include, for example, a propenyl group, a butenyl group, an isobutenyl group, an isoprenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, and an octadecenyl group.

[0015] Examples of the cyclic unsaturated hydrocarbon group include an aryl group, an aralkyl group, and a heterocyclic aromatic hydrocarbon group. Examples of the aryl group include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a biphenyl group, a triphenyl group, a terphenyl group, and groups in which these groups are substituted with substituents described later. Examples of the aralkyl group include a benzyl group, a phenethyl group, a phenylpropyl group, a phenylpentyl group, a phenylhexyl group, a phenylheptyl group, a phenyloctyl group, and groups in which these groups are substituted with substituents described later. Examples of the heterocyclic aromatic hydrocarbon group include an imidazole group, a methylimidazole group, an ethylimidazole group, a propylimidazole group, a 2-phenylimidazole group, a benzimidazole group, and groups in which these groups are substituted with substituents.

[0016] From the viewpoint of enhancing the adhesive strength, the saturated hydrocarbon group is preferably a linear chain saturated hydrocarbon group. Examples of the chain saturated hydrocarbon group include a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, a pentyl group, a tert-pentyl group, an isopentyl group, a hexyl group, an isohexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, a dodecyl group, a tridecyl group, a tetradecyl group, an octadecyl group, a docosyl group, an octacosanyl group, and the like.

[0017] (b) Polymer group The polymer group in the present invention is a functional group containing a polymer structure. From the viewpoint of enhancing the adhesive strength, the formula weight (molecular weight) of the polymer group is preferably 100 or more, more preferably 200 or more, still more preferably 300 or more, still more preferably 500 or more, still more preferably 1,000 or more, still more preferably 1,500 or more. From the same viewpoint, it is preferably 1,000,000 or less, more preferably 100,000 or less, still more preferably 10,000 or less, still more preferably 7,000 or less, still more preferably 5,000 or less, still more preferably 4,000 or less, still more preferably 3,500 or less, still more preferably 2,500 or less.

[0018] From the viewpoint of enhancing the adhesive strength, the polymer group is preferably a functional group having a repeating structure linked by a structure having an oxygen atom, more preferably a functional group having a repeating structure linked by an oxygen atom such as a polyoxyalkylene structure or a polysiloxane structure, still more preferably having a polyoxyalkylene structure, and still more preferably an alkoxy polyoxyalkylene group.

[0019] From the viewpoint of increasing adhesive strength, the polyoxyalkylene structure is preferably a (co)polymer structure of one or more oxyalkylenes selected from oxyalkylenes having 2 to 8 carbon atoms, more preferably a (co)polymer structure of one or more oxyalkylenes selected from oxyalkylenes having 2 to 4 carbon atoms, even more preferably a (co)polymer structure of one or two oxyalkylenes selected from ethylene oxide (EO) and propylene oxide (PO), and even more preferably a copolymer structure (EO / PO copolymer structure) in which ethylene oxide and propylene oxide are polymerized randomly or in blocks.

[0020] An example of a copolymer structure in which ethylene oxide and propylene oxide are polymerized randomly or in a blocky manner is the following formula:

[0021] [ka]

[0022] (In the formula, R 1 represents a hydrogen atom, a hydrocarbon group having 1 to 6 carbon atoms, or a -CH2CH(CH3)NH2 group. EO and PO are present randomly or in a blocky arrangement, where a is a positive number representing the average number of moles of EO added, and b is a positive number representing the average number of moles of PO added. Examples of structures include those shown in ).

[0023] R 1 From the viewpoint of increasing adhesive strength, the alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group. From the viewpoint of increasing adhesive strength, a is preferably 1 or more, more preferably 3 or more, even more preferably 6 or more, even more preferably 11 or more, even more preferably 15 or more, even more preferably 20 or more, even more preferably 25 or more, and even more preferably 30 or more. From a similar viewpoint, it is preferably 100 or less, more preferably 70 or less, even more preferably 60 or less, even more preferably 50 or less, and even more preferably 40 or less.

[0024] From the viewpoint of increasing adhesive strength, b is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more. From a similar viewpoint, it is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, even more preferably 25 or less, even more preferably 20 or less, even more preferably 15 or less, and even more preferably 10 or less. In the above formula, a+b represents the average number of moles added in total of EO and PO, and from the viewpoint of increasing adhesive strength, it is preferably 4 or more, more preferably 6 or more, and even more preferably 8 or more, and from the same viewpoint, it is preferably 100 or less, and more preferably 70 or less.

[0025] The PO content (mol%) in the EO / PO copolymer structure can be calculated based on a and b above, specifically from b × 100 / (a ​​+ b). From the viewpoint of increasing adhesive strength, the PO content is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 7 mol% or more, even more preferably 10 mol% or more, and even more preferably 20 mol% or more. From a similar viewpoint, it is preferably 100 mol% or less, more preferably 90 mol% or less, even more preferably 85 mol% or less, even more preferably 75 mol% or less, even more preferably 60 mol% or less, even more preferably 50 mol% or less, even more preferably 40 mol% or less, and even more preferably 30 mol% or less.

[0026] (c) Further substituents The modifying group may have further substituents. Examples of substituents include alkoxy groups having 1 to 6 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, isopentyloxy, and hexyloxy; methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl, isobutoxycarbonyl, sec-butoxycarbonyl, and tert-butoxycarbonyl groups. Examples include alkoxy-carbonyl groups with 1 to 6 carbon atoms, such as t-butoxycarbonyl, pentyloxycarbonyl, and isopentyloxycarbonyl groups; halogen atoms such as fluorine, chlorine, bromine, and iodine atoms; acyl groups with 1 to 6 carbon atoms, such as acetyl and propionyl groups; aralkyl groups; aralkyloxy groups; alkylamino groups with 1 to 6 carbon atoms; dialkylamino groups with 1 to 6 carbon atoms in the alkyl group; and hydroxyl groups.

[0027] [Method for producing modified cellulose fibers] Modified cellulose fibers, that is, modified cellulose fibers having modifying groups, can be produced, for example, by introducing anionic groups into raw cellulose fibers to produce anionically modified cellulose fibers (Step 1), and then attaching modifying groups to the anionic groups of the anionically modified cellulose fibers (Step 2). The "anionically modified cellulose fibers" used in the present invention are cellulose fibers that have been anionically modified to contain anionic groups within the cellulose fibers.

[0028] (Process 1) Raw material: cellulose fiber As cellulose fibers used as raw materials for anion-modified cellulose fibers, natural cellulose is preferred from an environmental standpoint. Examples include wood pulp such as coniferous pulp and hardwood pulp; cotton pulp such as cotton linters and cotton lint; non-wood pulp such as straw pulp and bagasse pulp; and bacterial cellulose. One of these can be used alone or in combination of two or more.

[0029] The average fiber diameter of the raw cellulose fibers is not particularly limited, but from the viewpoint of handling and cost, it is preferably 5 μm or more, more preferably 7 μm or more, and from the same viewpoint, preferably 500 μm or less, more preferably 300 μm or less. The average fiber diameter of the raw cellulose fibers can be determined by the method described in the examples below.

[0030] Furthermore, while the average fiber length of the raw cellulose fibers is not particularly limited, from the viewpoint of availability and cost, it is preferably 5 μm or more, more preferably 25 μm or more, and from the same viewpoint, preferably 5,000 μm or less, more preferably 3,000 μm or less. The average fiber length of the raw cellulose fibers can be measured according to the method described in the examples below.

[0031] Method for introducing anionic groups Methods for introducing a carboxyl group as an anionic group into cellulose fibers include, for example, oxidizing the hydroxyl group of the cellulose fiber to convert it into a carboxyl group, or reacting the hydroxyl group of the cellulose fiber with at least one selected from the group consisting of compounds having a carboxyl group, acid anhydrides of compounds having a carboxyl group, and derivatives thereof.

[0032] One method for oxidizing the hydroxyl groups of cellulose fibers is described in Japanese Patent Publication No. 2015-143336 or Japanese Patent Publication No. 2015-143337, which involves reacting 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) as a catalyst with an oxidizing agent such as sodium hypochlorite and a bromide such as sodium bromide, using cellulose fibers as a raw material. By oxidizing cellulose fibers using TEMPO as a catalyst, the group (-CH2OH) at the C6 position of glucose in the cellulose fiber constituent units is selectively converted to a carboxyl group, thereby obtaining the aforementioned oxidized cellulose fibers. Methods for introducing sulfonic acid groups as anionic groups into cellulose fibers include adding sulfuric acid to the cellulose fibers and heating them. Methods for introducing ()phosphorous groups as anionic groups into cellulose fibers include mixing powder or aqueous solution of ()phosphorous or ()phosphorous derivatives with dry or wet cellulose fibers, or adding aqueous solution of ()phosphorous or ()phosphorous derivatives to a dispersion of cellulose fibers. When these methods are employed, dehydration and heat treatment are generally performed after mixing or adding powder or aqueous solution of ()phosphorous or ()phosphorous derivatives.

[0033] The anionic group content in anionically modified cellulose fibers is preferably 0.1 mmol / g or more, more preferably 0.4 mmol / g or more, even more preferably 0.6 mmol / g or more, even more preferably 0.7 mmol / g or more, and even more preferably 0.8 mmol / g or more, from the viewpoint of introducing stable modifying groups and increasing adhesive strength through the introduction of modifying groups. Furthermore, from the viewpoint of improving handling, it is preferably 3 mmol / g or less, more preferably 2.5 mmol / g or less, more preferably 2 mmol / g or less, more preferably 1.9 mmol / g or less, even more preferably 1.8 mmol / g or less, even more preferably 1.7 mmol / g or less, and even more preferably 1.5 mmol / g or less. Note that "anionic group content" refers to the total amount of anionic groups in the glucose constituting the cellulose fiber, and is specifically measured by the method described in the examples below.

[0034] (Process 2) The introduction of modifying groups to the anionic groups of anionic-modified cellulose fibers is achieved by reacting the anionic-modified cellulose fibers with a compound for introducing modifying groups to the anionic groups (referred to as the "modifying compound"). Methods for introducing the modifying groups include (1) introduction via ionic bonding, as described in Japanese Patent Publication No. 2015-143336, and (2) introduction via amide bonding, as described in Japanese Patent Publication No. 2015-143337. After the completion of step 2, post-treatment may be performed as appropriate to remove unreacted compounds, etc. Examples of post-treatment methods include filtration, centrifugation, and dialysis.

[0035] (Refining process) By refining the cellulose fibers at any stage of the modified cellulose fiber manufacturing method (for example, before step 1, before step 2, and after step 2), micrometer-scale cellulose fibers can be refined to a nanometer scale. This is preferable because reducing the average fiber diameter to nanometer size improves dispersibility.

[0036] For the micronization process, known micronization methods can be employed. For example, to obtain modified cellulose fibers with an average fiber diameter of nanometer size, a processing method using a grinder such as a muscoloider or a processing method using a high-pressure homogenizer in a medium can be carried out.

[0037] Examples of media include alcohols with 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as water, methanol, ethanol, propanol, and 1-methoxy-2-propanol (PGME); ketones with 3 to 6 carbon atoms, such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ketones with 2 to 4 carbon atoms, such as ethyl acetate and butyl acetate; saturated or unsaturated hydrocarbons with 1 to 6 carbon atoms; aromatic hydrocarbons such as benzene and toluene; halogenated hydrocarbons such as methylene chloride and chloroform; lower alkyl ethers with 2 to 5 carbon atoms; and polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide, and dimethyl sulfoxide. These can be used individually or in combination of two or more. The amount of media used should be an effective amount that can disperse the modified cellulose fibers, and it is preferable to use an amount of at least 1 mass, more preferably 2 mass, more preferably 500 mass, and more preferably 200 mass, relative to the modified cellulose fibers.

[0038] In addition to high-pressure homogenizers, other known dispersers can be suitably used in the micronization process. For example, dissociators, beaters, low-pressure homogenizers, grinders, mascolloiders, cutter mills, ball mills, jet mills, short-screw extruders, twin-screw extruders, ultrasonic stirrers, and household juicer mixers can be used. Furthermore, the solid content of the modified cellulose fibers in the micronization process is preferably 50% by mass or less.

[0039] (Short fiber treatment) In any step of the method for producing modified cellulose fibers, the cellulose fibers may be subjected to a short fiber treatment. The short fiber treatment can be carried out by subjecting the target cellulose fibers to one or more treatment methods selected from the group consisting of (i) alkali treatment, (ii) acid treatment, (iii) heat treatment, ultraviolet treatment, electron beam treatment, mechanical treatment, and enzymatic treatment.

[0040] [Properties of modified cellulose fibers] The main properties of the modified cellulose fibers in this invention are as follows:

[0041] (Crystal structure) From the viewpoint of improving adhesive strength, modified cellulose fibers having a cellulose type I crystalline structure are preferred. From the viewpoint of increasing adhesive strength, the degree of crystallinity of the modified cellulose fibers is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. Furthermore, from the viewpoint of raw material availability, it is preferably 90% or less, more preferably 85% or less, even more preferably 80% or less, and even more preferably 75% or less. In this specification, the degree of crystallinity of cellulose fibers is the degree of cellulose type I crystallinity calculated from the diffraction intensity value by X-ray diffraction, and can be measured, for example, according to the method described in Japanese Patent Application Publication No. 2024-067274. Cellulose type I refers to the crystalline form of natural cellulose, and the degree of cellulose type I crystallinity means the proportion of the crystalline region in the total amount of cellulose fibers. The presence or absence of a cellulose type I crystalline structure can be determined by the presence of a peak at 2θ = 22.6° in X-ray diffraction measurement.

[0042] (Average fiber diameter) Modified cellulose fibers are preferably those that have been micronized to a nanometer size. Therefore, the average fiber diameter of the modified cellulose fibers is preferably 1 nm or more, more preferably 2 nm or more, from the viewpoint of handling, availability, and cost, and preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, even more preferably 120 nm or less, and even more preferably 20 nm or less, from the viewpoint of improving handling, dispersibility, and adhesive strength.

[0043] (Average fiber length) From the viewpoint of improving adhesive strength, the average fiber length of the modified cellulose fibers is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. On the other hand, from the same viewpoint, it is preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and even more preferably less than 150 nm.

[0044] (Average aspect ratio) The average aspect ratio of the modified cellulose fibers is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoint of increasing adhesive strength, while from the viewpoint of increasing handling properties and adhesive strength, it is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less, even more preferably 100 or less, and even more preferably 70 or less. The average fiber diameter, average fiber length, and average aspect ratio of the modified cellulose fibers are determined by the method described in the examples below.

[0045] (Amount of modifying group attached and rate of introduction) From the viewpoint of increasing adhesive strength, the amount of modifying groups bound to the modified cellulose fibers is preferably 0.01 mmol / g or more, and from the same viewpoint, preferably 3.0 mmol / g or less. When any two or more modifying groups are simultaneously introduced into the modified cellulose fibers, the amount of modifying groups bound is preferably within the above range.

[0046] From the viewpoint of dispersibility in the resin, the introduction rate of modifying groups in modified cellulose fibers is preferably 10 mol% or more. When two or more arbitrary modifying groups are introduced simultaneously, it is preferable that the total introduction rate does not exceed the upper limit of 100 mol% while remaining within the above range.

[0047] The amount and rate of modification groups can be adjusted by the type and amount of modification compound added, the reaction temperature, the reaction time, the type of solvent, etc. The amount (mmol / g) and rate (mol%) of modification groups refer to the amount and percentage of modification groups introduced (bonded) to the anionic groups in the modified cellulose fibers. For example, when the anionic group is a carboxyl group, the amount and rate of modification groups in the modified cellulose fibers can be calculated using the method described in the examples below.

[0048] The amount of modified cellulose fibers in the composition of the present invention, when calculated in terms of blending amount, is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, more preferably 0.1% by mass or more, more preferably 1% by mass or more, and still more preferably 2% by mass or more, from the viewpoint of increasing adhesive strength, while from the viewpoint of handling properties, it is preferably 30% by mass or less, more preferably 20% by mass or less, more preferably 15% by mass or less, more preferably 10% by mass or less, more preferably 7% by mass or less, still more preferably 5% by mass or less, and still more preferably 3% by mass or less.

[0049] In this specification, "glucose portion" refers to the portion consisting of glucose units in various types of cellulose fibers. In the case of unmodified cellulose fibers, it refers to the entire glucose unit; in the case of anionically modified cellulose fibers, it refers to the entire glucose unit including the anionic group attached to the glucose unit; and in the case of modified cellulose fibers having a modifying group, it refers to the entire glucose unit excluding the modifying group attached to the glucose unit. That is, in this specification, glucose units also include glucose units in which a hydroxymethyl group has been converted to a carboxyl group.

[0050] 〔resin〕 The resins used in this invention are preferably resins that have adhesive properties on their own, or resins that exhibit adhesive properties when used in combination with a curing agent. The resins may be used individually or as a mixture of two or more resins.

[0051] Specific examples of resins include epoxy resins, urethane resins, acrylic resins, polyvinyl chloride resins, phenoxy resins, phenolic resins, urea resins, melamine resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins, and rubber-based resins.

[0052] Among resins, curable resins (e.g., epoxy resins, urethane resins, acrylic resins, phenoxy resins, phenolic resins, urea resins, melamine resins) are preferred from the viewpoint of increasing adhesive strength. Depending on the type of resin, photocuring and / or thermocuring treatment can be performed. Thermosetting resins are preferred as the resin used in the present invention.

[0053] [Other ingredients] The adhesive composition of the present invention may optionally contain components known in the field of adhesives, such as polymerization initiators, plasticizers, stabilizers, lubricants, surfactants, and inorganic / organic fillers. The amount of such components is not particularly limited, and appropriate amounts may be used as appropriate.

[0054] In the adhesive composition of the present invention, the mass ratio of modified cellulose fibers to resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and even more preferably 4 parts by mass or more, of 100 parts by mass of resin, from the viewpoint of adhesive strength. On the other hand, from the viewpoint of handling properties, the modified cellulose fibers are preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, of 100 parts by mass of resin.

[0055] [Method for manufacturing adhesive compositions] The adhesive composition of the present invention can be produced, for example, by mixing the modified cellulose fibers and the resin. Furthermore, a solvent, a curing agent, and other components may be mixed as needed. The method for mixing each component of the adhesive composition is not particularly limited and general methods include using a stirrer, ultrasonic homogenizer, high-pressure homogenizer, etc.

[0056] Examples of solvents that can be used during manufacturing include dimethylformamide, ethyl acetate, methyl methacrylate, ethanol, isopropanol, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide, tetrahydrofuran (THF), diester of succinic acid and triethylene glycol monomethyl ether, acetone, methyl ethyl ketone (MEK), acetonitrile, dichloromethane, chloroform, toluene, 1-methoxy-2-propanol (PGME), acetic acid, etc., and these can be used individually or in combination of two or more. When a solvent is used, the amount is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, per 100 parts by mass of resin, while preferably 5000 parts by mass or less, and more preferably 2000 parts by mass or less.

[0057] The adhesive composition of the present invention is liquid or solid (e.g., pelletized or powdered) at room temperature (25°C). In the case of solid form, it can be made into a paste, solution, or dispersion by adding an appropriate medium. It can also be heated to a liquid state as needed before use.

[0058] [Applicable to] The adhesive composition of the present invention is applied to bonding inorganic fiber-reinforced composite materials to each other. Examples of inorganic fiber-reinforced composite materials include carbon fiber-reinforced plastics and glass fiber-reinforced plastics. When bonding inorganic fiber-reinforced composite materials, it can be applied to bonding materials of the same type, or to bonding materials of different types.

[0059] 2. Method for bonding inorganic fiber-reinforced composite materials together The present invention provides a method for bonding inorganic fiber-reinforced composite materials together, using a composition comprising modified cellulose fibers having modifying groups and a resin. Examples of compositions comprising modified cellulose fibers having modifying groups and resins include the above-described adhesive composition for inorganic fiber-reinforced composite materials of the present invention. One embodiment of the bonding method of the present invention is a method in which the composition is applied to one or both of the target inorganic fiber-reinforced composite materials, bonded together, and the composition is cured, thereby achieving bonding between the inorganic fiber-reinforced composite materials.

[0060] 3. Manufacturing method of structures The manufacturing method for the structure of the present invention is a manufacturing method that includes a step of bonding inorganic fiber-reinforced composite materials together using the inorganic fiber-reinforced composite material adhesive of the present invention described above. Examples of structures referred to here include car bodies, aircraft wings, wind turbine propellers, drones, rockets, and ships. For example, a process for bonding inorganic fiber-reinforced composite materials together may involve applying the composition to one or both of the target inorganic fiber-reinforced composite materials, bonding them together, and then curing the composition. [Examples]

[0061] The present invention will be specifically described below with reference to examples. The following examples are merely illustrative of the present invention and do not imply any limitation. "Normal pressure" refers to 101.3 kPa, and "room temperature" refers to 25°C.

[0062] [Average fiber diameter and average fiber length of cellulose fibers and (shortened) anion-modified cellulose fibers] Deionized water was added to the cellulose fibers to be measured or a suspension containing the cellulose fibers to be measured to prepare a dispersion with a content of 0.01% by mass. This dispersion was measured using a wet dispersion type image analysis particle size distribution analyzer (Jusco International Co., Ltd., product name: IF-3200) under the following conditions: front lens: 2x, telecentric zoom lens: 1x, image resolution: 0.835 μm / pixel, syringe inner diameter: 6515 μm, spacer thickness: 500 μm, image recognition mode: ghost, threshold: 8, analysis sample volume: 1 mL, sampling: 15%. The length of the short axis when the cellulose fiber is approximated as a rectangle was defined as the fiber diameter, and the length of the long axis was defined as the fiber length. These values ​​were measured for 100 cellulose fibers, and the average value was calculated.

[0063] [Average fiber diameter and average fiber length of cellulose fibers after micronization treatment] Deionized water or N,N-dimethylformamide (DMF) was added to the cellulose fibers to be measured or a dispersion containing the cellulose fibers to be measured to prepare a dispersion with a content of 0.0001% by mass. This dispersion was dropped onto mica and dried to serve as an observation sample. The fiber height (difference in height between areas with and without fibers) of the cellulose fibers in the observation sample was measured using an atomic force microscope (AFM) (Digital Instruments, Nanoscope II Tappingmode AFM; probe used: Nanosensors, Point Probe (NCH)). In the microscope image where the cellulose fibers could be confirmed, 100 cellulose fibers were extracted, and the average fiber diameter was calculated from their fiber heights. The average fiber length was calculated from the distance in the direction of the fibers.

[0064] [Anionic group content of anionic-modified cellulose fibers] A 0.5 g dry weight of the cellulose fiber to be measured was placed in a beaker, and deionized water or a methanol / deionized water = 2 / 1 (volume ratio) mixed solvent was added to make a total volume of 55 mL. 5 mL of 0.01 M sodium chloride aqueous solution was then added to prepare a dispersion. The dispersion was stirred until the cellulose fiber was sufficiently dispersed. 0.1 M hydrochloric acid was added to the dispersion to adjust the pH to 2.5-3. Using an automatic titrator (Toa DKK Co., Ltd., AUT-701), 0.05 M sodium hydroxide aqueous solution was added dropwise to the dispersion with a waiting time of 60 seconds, and the conductivity and pH values ​​were measured every minute. Measurements were continued until the pH reached approximately 11, and a conductivity curve was obtained. The amount of sodium hydroxide titration was determined from this conductivity curve, and the anionic group content of the cellulose fiber was calculated using the following formula. Anionic group content (mmol / g) = [Titration volume of sodium hydroxide aqueous solution (mL) × Concentration of sodium hydroxide aqueous solution (0.05M)] / [Mass of cellulose fiber to be measured (0.5g)]

[0065] [Amount of modifying groups attached to and introduction rate of modified cellulose fibers] The amount of modifying groups attached to modified cellulose fibers was determined by the following IR measurement method, and the amount of attachment and the introduction rate were calculated using the following formula. Specifically, the IR measurement involved measuring the infrared absorption spectrum of the dried cellulose fibers to be measured using an infrared absorption spectrometer (IR) (Thermo Fisher Scientific, Nicolet 6700) by the ATR method, and the amount of attachment and the introduction rate of the modifying groups were calculated using formula A. The following shows the case where the anionic group is a carboxyl group, i.e., the case of oxidized cellulose fibers. The following "1720 cm" -1 The peak intensity is derived from the carbonyl group. For anionic groups other than carboxyl groups, the wavenumber value should be appropriately changed to calculate the amount of modifying group bonded and the introduction rate. <Formula A> Amount of modifying group attached (mmol / g) = a × (bc) ÷ b a: Carboxy group content of oxidized cellulose fibers (mmol / g) b: 1720 cm of oxidized cellulose fiber -1 Peak intensity c: Modified cellulose fiber 1720cm -1 Peak intensity <Formula B> Modification group introduction rate (mol%) = 100 × f / g f: Amount of modifying group attached (mmol / g) g: Carboxylate group content of oxidized cellulose fiber (mmol / g)

[0066] [Content of each ingredient] The content of each component other than water was calculated from the amount of each component used. Regarding the glucose content, it was calculated by assuming that all the anionically modified cellulose fibers and modifying compounds blended during the preparation of the modified cellulose fibers were ionically bonded, and considering the mass of the anionically modified cellulose fibers contained in the blended modified cellulose fibers as the mass of the glucose portion. Furthermore, the water content in the dispersions and suspensions was measured by Karl Fischer titration using a CA-200 manufactured by Mitsubishi Analytec Corporation. Furthermore, the solid content concentration in various cellulose fibers was calculated by measuring the water content in the sample using an infrared moisture meter (Shimadzu Corporation, MOC-120H) and taking the difference from 100% by mass. For 1 g of sample, the water content was measured every 30 seconds at a constant temperature of 150°C, and the value displayed when the mass decrease over 30 seconds was 0.1% or less was used.

[0067] [Measurement of electrical conductivity of filtrate] The electrical conductivity of the filtrate was measured using a compact electrical conductivity meter (LAQUAtwin EC-33B, manufactured by Horiba, Ltd.).

[0068] [Anionic modified cellulose fiber] As the raw material for component (A), anion-modified cellulose fiber 1 having the physical properties listed in Table 1 was used.

[0069] [Table 1]

[0070] Such anionically modified cellulose fibers 1 can be prepared, for example, by performing the following TEMPO oxidation treatment.

[0071] [TEMPO oxidation treatment] In a 2L PP beaker equipped with a mechanical stirrer and stirring blades, weigh out 20g of bleached kraft pulp fiber from coniferous trees (the raw material for natural cellulose fiber) and 1980g of deionized water, and stir at 25°C and 100rpm for 30 minutes. Next, add 0.26g of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO), 2.6g of sodium bromide, and 70.0g of 10.5% by mass sodium hypochlorite aqueous solution to the 20g of pulp fiber in this order. Then, perform pH stat titration using an automatic titrator and add 0.5M sodium hydroxide aqueous solution dropwise to maintain the pH at 10.5. The reaction is carried out at 25°C for 120 minutes with a stirring speed of 100rpm. Next, while stirring, add 0.01M hydrochloric acid to adjust the pH of the suspension to 2. Finally, filter out the solids by suction filtration. The solids are dispersed in deionized water, and the solids are filtered off by suction filtration. This process is repeated until the conductivity of the filtrate is 200 μS / cm or less. The resulting solids are then dehydrated to obtain anionically modified cellulose fibers.

[0072] [Shortened anionic modified cellulose fibers] To 227 g (75 g solid content) of the cake containing anionically modified cellulose fiber 1, deionized water was added until the solid content concentration reached 5% by mass from the values ​​shown in Table 1. The resulting suspension was stirred at 95°C for 12 hours to obtain an aqueous suspension of short-fiber anionically modified cellulose fibers. The obtained suspension was centrifuged using a high-speed refrigerated centrifuge (Koki Holdings Co., Ltd., CR21G III) at 25°C, 10,000 G, and for 1 minute to obtain 285 g (23.5% by mass solid content) of a dispersion of short-fiber anionically modified cellulose fiber 1 as a precipitate.

[0073] Example 1 [Preparation of adhesive composition] A dispersion of short-fiber anionic modified cellulose fibers 1 was added to 1-methoxy-2-propanol (PGME) to obtain a dispersion with a solid content of 2.0% by mass. To the obtained dispersion, amines (EO / PO amines) were added in the amounts shown in Table 2, and the mixture was stirred at 25°C for 1 hour to obtain a dispersion of modified cellulose fibers 1 having modifying groups via ionic bonding.

[0074] [Table 2]

[0075] The resulting dispersion of modified cellulose fiber 1 was mixed with epoxy resin in the mass ratio shown in Table 3 and stirred at 25°C for 1 hour. Next, the mixture was dispersed five times at 150 MPa using a high-pressure homogenizer (NanoVeta L-ES, manufactured by Yoshida Machinery Industry Co., Ltd.). Subsequently, PGME and water were removed from the dispersion of modified cellulose fiber 1 using an evaporator.

[0076] Evaporator conditions Water bath temperature: 75℃ Degree of pressure reduction (absolute pressure): 0-1 kPa Determination of distillation completion: This was determined when a mass reduction equivalent to the amount of water and organic solvents present occurred.

[0077] Next, the mixture after the distillation treatment was mixed with a curing agent and a curing accelerator in the mass ratios shown in Table 3. The mixture was then stirred for 3 minutes at 2,000 rpm at 25°C using an automatic orbital stirrer (Sinky Co., Ltd., Awatori Rentaro), followed by degassing for 2 minutes at 2,200 rpm at 25°C to obtain the adhesive composition.

[0078] Example 2 [Preparation of adhesive composition] The adhesive composition of Example 2 was obtained by performing the same procedure as in Example 1, except that epoxy resin, a curing agent, etc. were added to a dispersion of modified cellulose fiber 1 in the mass ratios shown in Table 3.

[0079] Comparative Example 1 [Preparation of Adhesive Composition] After mixing the epoxy resin, curing agent, and curing accelerator in the mass ratios shown in Table 3, the mixture was stirred for 3 minutes at 2,000 rpm at 25°C using an automatic orbital stirrer (Sinky Co., Ltd., Awatori Rentaro), followed by degassing for 2 minutes at 2,200 rpm at 25°C to obtain the adhesive compositions shown in Table 3.

[0080] Test Example 1 [Shear Bond Strength Test] Shear bond strength tests were performed on each of the above adhesive compositions according to the procedure shown below. [Preparation of test specimens] Two test plates were created by cutting a CFRP sheet (manufactured by Standard Test Piece Co., Ltd.: plain weave, glossy, thickness: 2 mm) to 100 mm x 25 mm. An adhesive composition was applied to one test plate, and a spacer with a diameter of 150 μm was placed between the two test plates. The other test plate was then bonded to the other test plate so that the short edges of both plates overlapped by an area of ​​12.5 mm × 25 mm. After removing the excess adhesive composition, the adhesive composition was allowed to cure by standing at 130°C in an air atmosphere for 2 hours to obtain the test specimen.

[0081] [Shear bond strength test] Each test specimen was pulled at a benchtop precision universal testing machine (Shimadzu Corporation, AGS-X) at a chuck distance of 111.5 cm and a pulling speed of 5 mm per minute under conditions of 25°C. The stress at which delamination occurred was read and defined as the yield point stress (MPa).

[0082] Table 3 shows the composition of the adhesive and the test results.

[0083] [Table 3]

[0084] From the above test results, the yield strength of the adhesive composition of the example was higher than that of the adhesive composition of the comparative example. Therefore, it was found that the adhesive composition of the present invention is excellent as an adhesive between inorganic fiber-reinforced composite materials.

[0085] Manufacturing Example 1 [Manufacturing of Micronized Modified Cellulose Fibers] After stirring the dispersion of modified cellulose fiber 1 at 25°C for 1 hour, the dispersion was subjected to five dispersion treatments at 150 MPa using a high-pressure homogenizer (NanoVeta L-ES, manufactured by Yoshida Machinery Industry Co., Ltd.) to obtain a dispersion of finely milled modified cellulose fibers. Table 4 shows the average fiber diameter and average fiber length of the micronized modified cellulose fibers.

[0086] [Table 4]

[0087] Manufacturing Example 2 [Manufacturing of Anionic Modified Cellulose Fiber 2] An adhesive composition similar to that in Examples 1 and 2 can be obtained by using anionically modified cellulose fiber 2, which has phosphoric acid introduced into it, instead of anionically modified cellulose fiber 1, which has a carboxyl group introduced into it. Such anionically modified cellulose fiber 2 can be prepared by the following phosphorylation treatment.

[0088] [Phosphorication treatment] To obtain chemically impregnated fibers, 100 parts by mass of bleached kraft pulp fibers from coniferous trees, which are used as the raw material for natural cellulose fibers, are impregnated with a mixed aqueous solution of ammonium dihydrogen phosphate and urea, and then pressed until the mixture contains 56 parts by mass of ammonium dihydrogen phosphate and 150 parts by mass of urea. The chemical-impregnated fibers are dried in a dryer at 105°C to evaporate the moisture. The fibers, from which the moisture has been evaporated, are heated in a forced-air dryer set to 140°C for 4 minutes. To 100 parts by mass of the obtained fibers, 10,000 parts by mass of deionized water are added, and the mixture is stirred to disperse the fibers. The solid components are then filtered off by suction filtration. To 100 parts by mass of solids in the filtered cake, 10,000 parts by mass of deionized water are added, and the mixture is stirred to disperse the fibers. The solids are then filtered off by suction filtration. To the resulting cake, 10,000 parts by mass of deionized water are added, and while stirring, a 1N sodium hydroxide aqueous solution is added dropwise to obtain a slurry with a pH of 12-13. Next, while stirring, 0.01M hydrochloric acid is added to adjust the pH of the suspension to 2. Then, the solid components are filtered off by suction filtration. The resulting cake is dispersed in deionized water, and the cake is filtered off by suction filtration. This process is repeated until the conductivity of the filtrate is 200 μS / cm or less. The resulting solid content is then dehydrated to obtain anionic modified cellulose fibers 2.

[0089] [Reagents and raw materials] In the above examples, the following reagents and raw materials were used without special purification. Resin: Epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER828, epoxy equivalent = 184-194, weight-average molecular weight = 370) Hardener: Dicyandiamide (DICY, manufactured by Mitsubishi Chemical Corporation) was used, which was pulverized using a mini blender (manufactured by Osaka Chemical Co., Ltd.). The curing accelerator used was 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (manufactured by Thermo Scientific), which was pulverized using a mini blender (manufactured by Osaka Chemical Co., Ltd.). PGME: 1-Methoxy-2-propanol (manufactured by Daicel Corporation) EO / PO amine: Methoxypoly(oxyethylene / oxypropylene)-2-propylamine (HUNTSMAN, Jeffermin M2070, Mw=2,000, EO:PO=31:10) [Industrial applicability]

[0090] The adhesive composition of the present invention can be used as an adhesive for composite materials reinforced with inorganic fibers such as carbon fibers.

Claims

1. A method for bonding inorganic fiber-reinforced composite materials using a composition comprising modified cellulose fibers having modifying groups and a resin.

2. An adhesive composition for inorganic fiber-reinforced composite materials, comprising modified cellulose fibers having modifying groups and a resin.

3. The adhesive composition for inorganic fiber-reinforced composite materials according to claim 2, wherein the modified cellulose fibers having modifying groups are modified cellulose fibers having modifying groups via ionic bonds and / or covalent bonds.

4. The adhesive composition for inorganic fiber-reinforced composite materials according to claim 2, wherein the amount of modified cellulose fibers having a modifying group is 0.5 parts by mass or more and 100 parts by mass or less per 100 parts by mass of resin.

5. The adhesive composition for inorganic fiber-reinforced composite materials according to claim 2, wherein the modifying group in the modified cellulose fiber having a modifying group is one or more selected from the group consisting of hydrocarbon groups and polymer groups.

6. The adhesive composition for inorganic fiber-reinforced composite materials according to claim 2, wherein the resin is a curable resin.

7. The adhesive composition for inorganic fiber-reinforced composite materials according to claim 2, wherein the inorganic fiber-reinforced composite material is a carbon fiber-reinforced composite material.

8. A method for manufacturing a structure, comprising the step of bonding inorganic fiber-reinforced composite materials together using the inorganic fiber-reinforced composite material adhesive described in claim 2.

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