JP2020193283A - Adhesive composition and method for producing the same - Google Patents

Abstract

To provide an adhesive composition containing cellulose nanofiber, the adhesive composition having improved dispersibility of the cellulose nanofiber and having strong adhesive strength.SOLUTION: An adhesive composition contains a core-shell composite particle 10 containing an adhesive component as a core material 2 and cellulose nanofiber 1 as a coating material.SELECTED DRAWING: Figure 1

Description

The present invention relates to an adhesive composition containing cellulose nanofibers and a method for producing the same.

In recent years, active attempts have been made to utilize a material (for example, cellulose nanofiber) obtained by refining cellulose fibers in wood to the order of nanometers on at least one side of the structure as a new functional material. There is.
As one of the utilization examples of cellulose nanofibers, it has been proposed to use a resin composition containing cellulose nanofibers as an adhesive (for example, Patent Documents 1 to 3). As an effect of adding cellulose nanofibers, improvement of adhesive strength derived from the crystallinity of cellulose nanofibers is expected.

Patent Document 1 discloses a technique for adding water-based cellulose nanofibers to the same water-based adhesive composition. Patent Document 2 discloses a technique for defibrating cellulose into cellulose nanofibers in an epoxy adhesive. Here, the cellulose nanofibers of Patent Documents 1 and 2 are all water-based. On the other hand, the adhesive itself is hydrophobic (even if it is a water-based adhesive, the adhesive component is hydrophobic only because it is latex). Therefore, the cellulose nanofibers may not be sufficiently dispersed.
Further, Patent Document 3 discloses a technique of adding cellulose nanofibers that have been made into oil by modifying with polyetheramine as an adhesive composition. Although the dispersibility in the adhesive composition is improved to some extent by the oil-forming property, there are problems that the dispersibility is still insufficient and the production of cellulose nanofibers becomes complicated.

Japanese Patent No. 6361123 Japanese Unexamined Patent Publication No. 2016-138220 JP-A-2018-44097

The present invention has been made in view of the above circumstances, and is an adhesive composition containing cellulose nanofibers, which can sufficiently disperse cellulose nanofibers and has strong adhesive strength. The purpose is to provide.

In order to solve the problem, the adhesive composition according to one aspect of the present invention contains core-shell type composite particles containing an adhesive component as a core material and cellulose nanofibers as a coating material.
The cellulose nanofibers preferably have an anionic functional group, and the anionic functional group is more preferably a carboxy group.
Further, the method for producing an adhesive composition, which is one aspect of the present invention, includes a step of preparing a cellulose nanofiber dispersion liquid, a step of adjusting a solution containing an adhesive component, and the above-mentioned cellulose nanofiber dispersion liquid and the above-mentioned adhesive component. Including the step of mixing the containing solutions to form an emulsion.

According to one aspect of the present invention, it is possible to provide an adhesive composition containing cellulose nanofibers, which can sufficiently disperse cellulose nanofibers and has strong adhesive strength.

It is sectional drawing of the core-shell type composite particle which concerns on embodiment of this invention. It is the schematic of the manufacturing procedure of the adhesive composition which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
However, in each of the figures described below, the parts corresponding to each other are designated by the same reference numerals, and the description of the overlapping parts will be omitted as appropriate. Further, the present embodiment exemplifies a configuration for embodying the technical idea of the present invention, and does not specify the material, shape, structure, arrangement, dimensions, etc. of each part to the following. The technical idea of the present invention may be modified in various ways within the technical scope specified by the claims stated in the claims.

<Core-shell type composite particles>
The adhesive composition of the present embodiment contains core-shell type composite particles in which the core material is coated with a coating material. In the present embodiment, the coating refers to a case where 80% or more, preferably 90% or more of the surface area of the core material is coated.
FIG. 1 is a schematic cross-sectional view of a core-shell type composite particle. The adhesive composition of the present embodiment containing the core-shell type composite particles 10 containing the adhesive component as the core material 2 and the cellulose nanofibers (hereinafter, also referred to as CNF) 1 as the coating material is the core-shell type composite particles 10. It takes a single form or a form in which the core-shell type composite particles 10 are dispersed in a solvent, a binder, or the like.
Further, the method for producing the adhesive composition of the present embodiment includes a step of preparing a CNF dispersion (first step), a step of adjusting a solution containing an adhesive component (second step), the CNF dispersion and the above. A step (third step) of mixing a solution containing an adhesive component to form an emulsion is included.

FIG. 2 is a schematic view of the manufacturing procedure of the adhesive composition. In the method for producing an adhesive composition of the present embodiment, as shown in FIG. 2, the CNF dispersion liquid 101 and the adhesive component-containing solution 102 are mixed, and in the third step, an appropriate emulsification treatment is performed to contain the adhesive component. An O / W type pickering emulsion in which the cellulose nanofibers 1 are adsorbed is formed at the droplet interface of the solution 102 to form a core-shell type composite particle dispersion liquid 103.
The emulsification treatment method can be selected from known methods such as stirring, ultrasonic waves, homogenizer, and microreactor. The core-shell type composite particle dispersion 103 can be used as it is as the adhesive composition 104, but it may be purified and solvent-substituted and dispersed in the dispersion medium (solvent or binder) 20 as necessary.

Here, the O / W type emulsion is also referred to as an oil droplet type in water (Oil-in-Water), in which water is a continuous phase and oil is dispersed as oil droplets therein.
In the present embodiment, by adopting the cellulose nanofiber 1 as the coating material of the core-shell type composite particles, the cellulose fiber 1 can be uniformly or substantially uniformly dispersed in the adhesive composition 104. Therefore, even when the adhesive composition of the present embodiment is actually used as an adhesive and solidified, the state in which CNF is uniformly dispersed in the system can be maintained.

<Cellulose nanofiber>
The cellulose nanofiber 1 is not particularly limited, but preferably has an anionic functional group on the crystal surface. The content of the anionic functional group is preferably 0.1 mmol or more and 5.0 mmol or less per 1 g of cellulose. The type and method of introducing the anionic functional group introduced into the crystal surface of cellulose are not particularly limited, but a carboxy group or a phosphoric acid group is preferable. A carboxy group is preferable because of the ease of selective introduction into the surface of the cellulose crystal.
Further, the cellulose nanofiber 1 preferably has a fiber shape derived from a microfibril structure. Specifically, the cellulose nanofiber 1 is fibrous, has a number average minor axis diameter of 1 nm or more and 1000 nm or less, a number average major axis diameter of 50 nm or more, and a number average major axis diameter of several average minor axis. It is preferably 5 times or more the diameter. Further, the crystal structure of the cellulose nanofiber 1 is preferably cellulose type I.

<Manufacturing method of cellulose nanofiber dispersion (first step)>
Next, a method for producing a cellulose nanofiber dispersion liquid, which corresponds to the first step of the production method, will be described. Specifically, it is a step of defibrating a cellulose raw material in a solvent to obtain a CNF dispersion.

First, various cellulose raw materials are dispersed in a solvent to prepare a suspension. The concentration of the cellulose raw material in the suspension is preferably 0.1% or more and less than 10%. If it is less than 0.1%, the solvent becomes excessive and the productivity is impaired, which is not preferable. If it is 10% or more, the suspension rapidly thickens with the defibration of the cellulose raw material, which makes uniform defibration difficult, which is not preferable. The solvent used for preparing the suspension preferably contains 50% or more of water. When the proportion of water in the suspension is 50% or less, the dispersion of cellulose nanofibers 1 is inhibited in the step of defibrating the cellulose raw material described later in a solvent to obtain a cellulose nanofiber dispersion liquid. Moreover, as a solvent contained other than water, a hydrophilic solvent is preferable. The hydrophilic solvent is not particularly limited, but alcohols such as methanol, ethanol and isopropanol and cyclic ethers such as tetrahydrofuran are preferable. If necessary, the pH of the suspension may be adjusted in order to improve the dispersibility of cellulose and the cellulose nanofibers 1 produced. The alkaline aqueous solution used for pH adjustment includes sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and hydroxide. Examples thereof include organic alkalis such as an aqueous solution of benzyltrimethylammonium. An aqueous sodium hydroxide solution is preferable from the viewpoint of cost and the like.

Subsequently, the suspension is subjected to a physical defibration treatment to refine the cellulose raw material. The method of physical defibration treatment is not particularly limited, but is limited to high pressure homogenizer, ultrahigh pressure homogenizer, ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer. , Mechanical processing such as underwater facing collision. By performing such a physical defibration treatment, the cellulose in the suspension is finely divided, and a dispersion liquid of the finely divided cellulose can be obtained until at least one side of the structure is on the order of nanometers. Further, the number average minor axis diameter and the number average major axis diameter of the obtained cellulose nanofiber 1 can be adjusted according to the time and number of physical defibration treatments at this time.
As described above, a cellulose dispersion (CNF dispersion) finely divided until at least one side of the structure is on the nanometer order is obtained. The obtained dispersion can be used as it is, or after being diluted, concentrated, etc., as a stabilizer for an O / W type emulsion described later.

Since the cellulose nanofiber 1 usually has a fiber shape derived from a microfibril structure, the cellulose nanofiber 1 used in the production method of the present embodiment preferably has a fiber shape within the range shown below. That is, the shape of the cellulose nanofiber 1 is preferably fibrous. Further, the fibrous cellulose nanofiber 1 may have a number average minor axis diameter of 1 nm or more and 1000 nm or less, preferably 2 nm or more and 500 nm or less in the minor axis diameter. Here, if the number average minor axis diameter is less than 1 nm, a highly crystalline rigid CNF fiber structure cannot be obtained, and stabilization of the emulsion and a polymerization reaction using the emulsion as a template cannot be carried out. On the other hand, if it exceeds 1000 nm, the size becomes too large to stabilize the emulsion, and it becomes difficult to control the size and shape of the obtained core-shell type composite particles 10. The number average major axis diameter is not particularly limited, but is preferably 5 times or more the number average minor axis diameter. If the number average major axis diameter is less than five times the number average minor axis diameter, the size and shape of the core-shell type composite particles 10 cannot be sufficiently controlled, which is not preferable.

The number average minor axis diameter of CNF fibers is determined as an average value obtained by measuring the minor axis diameter (minimum diameter) of 100 fibers by observation with a transmission electron microscope or observation with an atomic force microscope. On the other hand, the number average major axis diameter of CNF fibers is determined as an average value obtained by measuring the major axis diameters (maximum diameters) of 100 fibers by observation with a transmission electron microscope or observation with an atomic force microscope.

The type and crystal structure of cellulose that can be used as a raw material for the cellulose nanofiber 1 are not particularly limited. Specifically, as a raw material composed of cellulose type I crystals, for example, in addition to wood-based natural cellulose, non-wood-based natural cellulose such as cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, squirrel cellulose, and baronia cellulose Can be used. Furthermore, rayon fibers composed of cellulose type II crystals and regenerated cellulose typified by cupra fibers can also be used. From the viewpoint of easy material procurement, it is preferable to use wood-based natural cellulose as a raw material. The wood-based natural cellulose is not particularly limited, and those generally used for producing cellulose nanofibers such as softwood pulp, hardwood pulp, and waste paper pulp can be used. Softwood pulp is preferred because of its ease of purification and miniaturization.

Further, the CNF raw material is preferably chemically modified. More specifically, it is preferable that an anionic functional group is introduced on the crystal surface of the CNF raw material. This is because the introduction of the anionic functional group on the surface of the cellulose crystal facilitates the penetration of the solvent between the cellulose crystals due to the osmotic effect, and facilitates the miniaturization of the cellulose raw material.
The type and method of introducing the anionic functional group introduced into the crystal surface of cellulose is not particularly limited, but a carboxy group or a phosphoric acid group is preferable. A carboxy group is preferable because of the ease of selective introduction into the surface of the cellulose crystal.

The method for introducing a carboxy group into the fiber surface of cellulose is not particularly limited. Specifically, for example, carboxymethylation may be carried out by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a high-concentration alkaline aqueous solution. Further, a carboxy group may be introduced by directly reacting cellulose with a carboxylic acid anhydride compound such as maleic acid or phthalic acid gasified in an autoclave. Furthermore, in the presence of N-oxyl compounds such as TEMPO, which have high selectivity for oxidation of alcoholic primary carbon while maintaining the structure as much as possible under relatively mild water-based conditions, an copolymer is used. You may use the method used. Oxidation using an N-oxyl compound is more preferable for selectivity of the carboxy group introduction site and reduction of environmental load.

Here, examples of the N-oxyl compound include TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyradic) and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-. Oxil, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetamide-2,2 Examples thereof include 6,6-tetramethylpiperidin-N-oxyl. Among them, TEMPO having high reactivity is preferable. The amount of the N-oxyl compound used may be an amount as a catalyst and is not particularly limited. Usually, it is 0.01 to 5.0% by mass with respect to the solid content of the wood-based natural cellulose to be oxidized.

Examples of the oxidation method using the N-oxyl compound include a method in which wood-based natural cellulose is dispersed in water and subjected to an oxidation treatment in the presence of the N-oxyl compound. At this time, it is preferable to use a copolymer together with the N-oxyl compound. In this case, in the reaction system, the N-oxyl compound is sequentially oxidized by the copolymer to form an oxoammonium salt, and the cellulose is oxidized by the oxoammonium salt. According to this oxidation treatment, the oxidation reaction proceeds smoothly even under mild conditions, and the efficiency of introducing carboxy groups is improved. When the oxidation treatment is carried out under mild conditions, it is easy to maintain the crystal structure of cellulose.

Examples of the cooxidant include halogen, hypohalogenate, subhalogenic acid and perhalogenate, or salts thereof, halogen oxides, nitrogen oxides, peroxides, etc., if it is possible to promote the oxidation reaction. , Any oxidizing agent can be used. Sodium hypochlorite is preferable because of its availability and reactivity. The amount of the copolymer used may be an amount capable of promoting the oxidation reaction, and is not particularly limited. Usually, it is 1 to 200% by mass with respect to the solid content of the wood-based natural cellulose to be oxidized.

Further, at least one compound selected from the group consisting of bromide and iodide may be further used in combination with the N-oxyl compound and the copolymer. As a result, the oxidation reaction can proceed smoothly, and the efficiency of introducing the carboxy group can be improved. As such a compound, sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable from the viewpoint of cost and stability. The amount of the compound used may be any amount capable of promoting the oxidation reaction and is not particularly limited. Usually, it is about 1 to 50% by mass with respect to the solid content of the wood-based natural cellulose to be oxidized.

The reaction temperature of the oxidation reaction is preferably 4 to 80 ° C, more preferably 10 to 70 ° C. If it is less than 4 ° C., the reactivity of the reagent decreases and the reaction time becomes long. If the temperature exceeds 80 ° C., the side reaction is promoted, the sample becomes low in molecular weight, the highly crystalline rigid CNF fiber structure collapses, and the sample cannot be used as a stabilizer for O / W type emulsions.
The reaction time of the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxy groups, and the like, and is not particularly limited, but is usually 10 minutes to 5 hours.

The pH of the reaction system during the oxidation reaction is not particularly limited, but 9 to 11 is preferable. When the pH is 9 or more, the reaction can proceed efficiently. If the pH exceeds 11, side reactions may proceed and the decomposition of the sample may be promoted. Further, in the oxidation treatment, the pH in the system is lowered due to the formation of carboxy groups as the oxidation progresses. Therefore, it is preferable to keep the pH of the reaction system at 9 to 11 during the oxidation treatment. Examples of the method of keeping the pH of the reaction system at 9 to 11 include a method of adding an alkaline aqueous solution according to the decrease in pH.

Examples of the alkaline aqueous solution include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide aqueous solution. Organic alkali and the like. An aqueous sodium hydroxide solution is preferable from the viewpoint of cost and the like.
The oxidation reaction with the N-oxyl compound can be stopped by adding an alcohol to the reaction system. At this time, it is preferable to keep the pH of the reaction system within the above range.
As the alcohol to be added, low molecular weight alcohols such as methanol, ethanol and propanol are preferable in order to terminate the reaction quickly, and ethanol is particularly preferable from the viewpoint of safety of by-products produced by the reaction.

The reaction solution after the oxidation treatment may be subjected to the miniaturization step as it is, but in order to remove catalysts such as N-oxyl compounds, impurities and the like, cellulose oxide contained in the reaction solution is recovered and washed with a washing solution. Is preferable. The recovery of cellulose oxide can be carried out by a known method such as filtration using a glass filter or a nylon mesh having a pore size of 20 μm. Pure water is preferable as the cleaning liquid used for cleaning the oxidized cellulose.
When the obtained TEMPO-oxidized cellulose is defibrated, cellulose single nanofibers (CSNF) having a uniform fiber width of 3 nm can be obtained. When CSNF is used as a raw material for the cellulose nanofiber 1 of the core-shell type composite particles 10, the particle size of the obtained O / W type emulsion tends to be uniform due to its uniform structure.

As described above, the CNF used in the present embodiment can be obtained by a step of oxidizing the cellulose raw material and a step of making it finer and dispersing and liquefying it. The content of the carboxy group to be introduced into CNF is preferably 0.1 mmol / g or more and 5.0 mmol / g or less, and more preferably 0.5 mmol / g or more and 2.0 mmol / g or less. Here, if the amount of the carboxy group is less than 0.1 mmol / g, the solvent entry action due to the osmotic effect does not work between the cellulose microfibrils, so that it is difficult to make the cellulose fine and uniformly disperse it. In addition, if it exceeds 5.0 mmol / g, cellulose microfibrils become low in molecular weight due to side reactions associated with chemical treatment, so that a highly crystalline and rigid CNF fiber structure cannot be obtained, and the O / W type emulsion is stable. It cannot be used as an agent.

<Adhesive composition>
Subsequently, the adhesive composition of the present embodiment will be described. However, the adhesive composition of the present embodiment is not limited to the embodiments described below, and various modifications are made within the technical scope specified by the claims described in the claims. be able to.
The adhesive component that can be used in the present embodiment is not particularly limited, and may be a monomer, an oligomer, or a polymer. Further, these may be one type or a plurality of types may be used in combination.
In the second step of the manufacturing method, the solution containing the adhesive component is prepared by dissolving or dispersing the adhesive component in an organic solvent. The emulsion forming step of the third step is carried out in the same manner as described above. After forming the emulsion, the organic solvent may be removed from the core-shell type composite particles by drying by a known method such as heat treatment or decompression treatment.
The method of solidifying the adhesive composition is roughly classified into a method of hardening by a chemical reaction and a method of solidifying by a non-chemical reaction such as cooling from a dried or melted state.

(Adhesive component that solidifies other than chemical reaction)
Examples of the adhesive component that solidifies other than the chemical reaction used in the present embodiment include an adhesive component of a thermoplastic resin adhesive such as vinyl acetate, vinyl chloride, styrene, acrylic, and saturated polyester, and chloroprene rubber. , Nitrile rubber-based, butyl rubber-based, SBR-based and other synthetic rubber-based elastomers are exemplified.
The thermoplastic resin adhesive is used as a water volatilization type adhesive or a heat melting type adhesive. When used as a water volatilization type, the core-shell type composite particles obtained up to the third step may be used as they are, or may be purified by centrifugation or the like and then dispersed in water for use. When used as a heat-melting type, the core-shell type composite particles obtained up to the third step may be purified and dried by centrifugation or the like and used as a powder, or the same or different adhesive as the core material. It may be used after being dispersed in. When CNF is mixed with a resin, the dispersibility may be poor, but in the present embodiment, since it is a coating material for core-shell type composite particles, the particles are dispersed and the CNF is also uniformly dispersed.

Synthetic rubber-based elastomers are mainly dispersed in organic solvents and are used as adhesive components of organic solvent volatilization type. When used as an organic solvent volatilization type, the core-shell type composite particles obtained up to the third step can be purified by centrifugation or the like and then dispersed in an organic solvent for use.

(Adhesive component that solidifies by chemical reaction)
Examples of the adhesive component solidified by the chemical reaction used in the present embodiment include an adhesive component of a thermosetting resin adhesive such as an epoxy-based, urethane-based, unsaturated polyester-based, or acrylic-based adhesive.
The adhesive component of the thermosetting resin adhesive is composed of a plurality of components and is solidified by performing a curing reaction after applying the adhesive.
In the adhesive composition of the present embodiment, a plurality of adhesive components may be contained as the core material, or one adhesive component of the adhesive may be contained in the core material to prepare core-shell type composite particles. An adhesive composition can also be obtained by dispersing core-shell type composite particles using another adhesive component as a binder. In the latter case, it is possible to liquefy the two-component adhesive into one solution.

For example, when an adhesive component of an epoxy-based adhesive is used, a core-shell type composite particle is formed using an adhesive component composed of a curing agent such as amine as a core material, and this is dispersed in an epoxy oligomer to form an adhesive composition. It can be a thing. When an adhesive component of a urethane-based adhesive is used, a core-shell type composite particle is formed using an adhesive component composed of a curing agent such as isocyanate as a core material, and this is dispersed in a binder such as a polyol to form an adhesive composition. It can be a thing. When the adhesive component of an acrylic adhesive is used, a core-shell type composite particle is formed using the adhesive component consisting of an initiator and a curing agent as a core material, and this is dispersed in a binder such as an acrylic monomer or an acrylic oligomer. It can be an adhesive composition.

The adhesive composition of the present embodiment may contain various known additives depending on its use. For example, antioxidants, colorants, flame retardants, antioxidants, polymerization initiators, polymerization inhibitors, UV absorbers, antistatic agents, lubricants, mold release agents, defoamers, leveling agents, light stabilizers ( For example, hindered amines), antioxidants, conductivity-imparting agents, slide-imparting agents, surfactants, catalysts, curing accelerators, inorganic fillers, organic fillers and the like.

<Use of adhesive composition>
In the adhesive composition of the present embodiment, it is desirable to perform pressure bonding at the time of use. By performing the pressure treatment, the core-shell type composite particles are disintegrated and preferably exhibit an adhesive effect. The pressurizing conditions are selected according to the type of adhesive used.

Hereinafter, the present embodiment will be described in detail based on Examples, but the technical scope of the present invention is not limited to these Examples.
[Manufacturing Example 1]
(First step: Step to obtain cellulose nanofiber dispersion)
(TEMPO oxidation of wood cellulose)
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, a solution prepared by dissolving 0.7 g of TEMPO and 7 g of sodium bromide in 350 g of distilled water was added, and the mixture was cooled to 20 ° C. To this, 450 g of an aqueous sodium hypochlorite solution having a density of 1.15 g / mL and 2 mol / L was added dropwise, and the oxidation reaction was started. The temperature in the system was always kept at 20 ° C., and the decrease in pH during the reaction was kept at pH 10 by adding a 0.5 N aqueous sodium hydroxide solution. When the total amount of sodium hydroxide added reached 3.50 mmol / g with respect to the mass of cellulose, about 100 mL of ethanol was added to stop the reaction. Then, filtration washing with distilled water was repeated using a glass filter to obtain oxidized pulp.

(Measurement of carboxy group content of oxidized pulp)
The oxidized pulp and reoxidized pulp obtained by the above TEMPO oxidation were weighed by 0.1 g in terms of solid content mass, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. Then, the amount of carboxy groups (mmol / g) was determined by a conductivity titration method using a 0.5 M aqueous sodium hydroxide solution. The result was 1.6 mmol / g.

(Defibration treatment of oxidized pulp)
1 g of the oxidized pulp obtained by the above TEMPO oxidation was dispersed in 99 g of distilled water and finely divided with a juicer mixer for 30 minutes to obtain a CNF aqueous dispersion A1 having a CNF concentration of 1%. As a result of putting the CNF aqueous dispersion A1 in a quartz cell having an optical path length of 1 cm and measuring the spectral transmission spectrum using a spectrophotometer (manufactured by Shimadzu Corporation, "UV-3600"), the CNF aqueous dispersion A1 is high. Showed transparency. The number average minor axis diameter of CNF contained in the CNF aqueous dispersion A1 was 3 nm, and the number average major axis diameter was 1110 nm. Furthermore, as a result of steady-state viscoelasticity measurement using a rheometer, the CNF aqueous dispersion A1 showed thixotropic property.

[Example 1]
(Second step: Preparation of the adhesive component-containing solution)
A solution of the adhesive component was prepared by dissolving 50 parts by mass of vinyl acetate resin (Denkasakunor SN-10 manufactured by Denki Kagaku Kogyo Co., Ltd.) in 50 parts by mass of toluene.
(Third step: emulsion formation)
To 90 parts by mass of the CNF aqueous dispersion A1 obtained in Production Example 1, 10 parts by mass of the solution of the adhesive component obtained in the second step was added. The shaft of the ultrasonic homogenizer was inserted from the upper part of the liquid surface, and the ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was in the form of a cloudy emulsion. When one drop of the mixed solution was dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, it was confirmed that innumerable emulsion droplets of about several μm were generated and dispersed and stabilized as an O / W type emulsion. Was done.

The obtained dispersion was treated with a centrifugal force of 75,000 g for 5 minutes to obtain a sediment. The supernatant was removed by decantation to collect the sediment, and the mixture was repeatedly washed with pure water using a PTFE membrane filter having a pore size of 0.1 μm. The purified / recovered product thus obtained was redispersed at a concentration of 20% to obtain an adhesive composition.
Further, when the obtained recovered product was adjusted to a concentration of 1% with pure water and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), the average particle size was 2.1 μm.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 24 hours to obtain a test piece.

<Evaluation of stability of adhesive composition>
The adhesive composition was transferred to a 20 ml glass bottle and allowed to stand overnight. After that, it was confirmed whether or not the adhesive composition changed in the glass bottle.
◯: No change ×: Change (Details of change are shown in Table 1 described later)
<Evaluation of adhesive strength>
Using a small tabletop tester (manufactured by Shimadzu Corporation, EZ-LS), the tensile shear adhesive strength of the test piece was measured at 2.5 mm / min in an atmosphere of 23 ° C.

[Example 2]
(Second step: Preparation of the adhesive component-containing solution)
A ditrill rubber-based adhesive (manufactured by 3M Ltd., industrial adhesive EC776) was used as a solution of the adhesive component.
(Third step: emulsion formation)
To 90 parts by mass of the CNF aqueous dispersion A1 obtained in Production Example 1, 10 parts by mass of the solution of the adhesive component obtained in the second step was added. The shaft of the ultrasonic homogenizer was inserted from the upper part of the liquid surface, and the ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was in the form of a cloudy emulsion. When one drop of the mixed solution was dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, it was confirmed that innumerable emulsion droplets of about several μm were generated and dispersed and stabilized as an O / W type emulsion. Was done.

The obtained dispersion was treated with a centrifugal force of 75,000 g for 5 minutes to obtain a sediment. The supernatant is removed by decantation to collect the sediment, and then using a PTFE membrane filter with a pore size of 0.1 μm, pure water is used, followed by a pure water / MEK = 80/20 solution, and MEK in that order. It was changed and washed. The purified / recovered product thus obtained was redispersed in MEK at a concentration of 20% to obtain an adhesive composition.
Further, when the obtained recovered product was adjusted to a concentration of 1% with pure water and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), the average particle size was 5.6 μm.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 1 hour to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Example 3]
(Second step: Preparation of the adhesive component-containing solution)
An epoxy resin curing agent (manufactured by Mitsubishi Chemical Corporation, jER Cure ST13) was used as a solution of the adhesive component.
(Third step: emulsion formation)
To 90 parts by mass of the CNF aqueous dispersion A1 obtained in Production Example 1, 10 parts by mass of the solution of the adhesive component obtained in the second step was added. The shaft of the ultrasonic homogenizer was inserted from the upper part of the liquid surface, and the ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was in the form of a cloudy emulsion. When one drop of the mixed solution was dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, it was confirmed that innumerable emulsion droplets of about several μm were generated and dispersed and stabilized as an O / W type emulsion. Was done.

The obtained dispersion was treated with a centrifugal force of 75,000 g for 5 minutes to obtain a sediment. The supernatant is removed by decantation to collect the sediment, and then using a PTFE membrane filter with a pore size of 0.1 μm, pure water is used, followed by a pure water / MEK = 80/20 solution, and MEK in that order. It was changed and washed. The purified / recovered product thus obtained was redispersed in MEK at a concentration of 20%. Further, 40 parts by mass of a bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., jER282) was added to 100 parts by mass of the obtained MEK dispersion to obtain an adhesive composition.

Further, when the recovered product obtained by the above centrifugation was adjusted to a concentration of 1% with pure water and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), the average particle size was 7. It was 5 μm.
A steel sheet having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 2 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Example 4]
(Second step: Preparation of the adhesive component-containing solution)
An acrylic adhesive (Metal Lock Y610A, manufactured by Cemedine Co., Ltd.) was used as a solution of the adhesive component.
(Third step: emulsion formation)
To 90 parts by mass of the CNF aqueous dispersion A1 obtained in Production Example 1, 10 parts by mass of the solution of the adhesive component obtained in the second step was added. The shaft of the ultrasonic homogenizer was inserted from the upper part of the liquid surface, and the ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was in the form of a cloudy emulsion. When one drop of the mixed solution was dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, it was confirmed that innumerable emulsion droplets of about several μm were generated and dispersed and stabilized as an O / W type emulsion. Was done.

The obtained dispersion was treated with a centrifugal force of 75,000 g for 5 minutes to obtain a sediment. The supernatant is removed by decantation to collect the sediment, and then using a PTFE membrane filter with a pore size of 0.1 μm, pure water is used, followed by a pure water / MEK = 80/20 solution, and MEK in that order. It was changed and washed. The purified / recovered product thus obtained was redispersed in MEK at a concentration of 20%. Further, 20 parts by mass of an acrylic adhesive curing agent (Metal Lock Y610B, manufactured by Cemedine Co., Ltd.) was added to 100 parts by mass of the obtained MEK dispersion to obtain an adhesive composition.

Further, when the recovered product obtained by the above centrifugation was adjusted to a concentration of 1% with pure water and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), the average particle size was 4. It was 3 μm.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at 50 ° C. for 24 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Example 5]
(Second step: Preparation of the adhesive component-containing solution)
A solution of the adhesive component was prepared by dissolving 50 parts by mass of a one-component urethane adhesive (KU928X, manufactured by Konishi Co., Ltd.) in 50 parts by mass of toluene.
(Third step: emulsion formation)
To 90 parts by mass of the CNF aqueous dispersion A1 obtained in Production Example 1, 10 parts by mass of the solution of the adhesive component obtained in the second step was added. The shaft of the ultrasonic homogenizer was inserted from the upper part of the liquid surface, and the ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was in the form of a cloudy emulsion. When one drop of the mixed solution was dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, it was confirmed that innumerable emulsion droplets of about several μm were generated and dispersed and stabilized as an O / W type emulsion. Was done.

The obtained dispersion was treated with a centrifugal force of 75,000 g for 5 minutes to obtain a sediment. The supernatant was removed by decantation to collect the sediment, and the mixture was repeatedly washed with pure water using a PTFE membrane filter having a pore size of 0.1 μm. The purified / recovered product thus obtained was redispersed in water at a concentration of 20% to obtain an adhesive composition.
Further, when the recovered product obtained by the above centrifugation was adjusted to a concentration of 1% with pure water and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.), the average particle size was 2. It was 2 μm.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at 50 ° C. for 3 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 1]
50 parts by mass of vinyl acetate resin (Denkasakunor SN-10 manufactured by Denki Kagaku Kogyo Co., Ltd.) was dissolved in 50 parts by mass of toluene to prepare an adhesive composition.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 24 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 2]
A nitrile rubber adhesive (manufactured by 3M Ltd., industrial adhesive EC776) was used as an adhesive composition.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 1 hour to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 3]
100 parts by mass of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., jER282) and 50 parts by mass of epoxy resin curing agent (manufactured by Mitsubishi Chemical Co., Ltd., jER Cure ST13) were mixed to obtain an adhesive composition.
A steel sheet having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 2 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 4]
An acrylic adhesive (Metal Lock Y610A, manufactured by Cemedine Co., Ltd.) and 100 parts by mass of a curing agent (Metal Lock Y610B, manufactured by Cemedine Co., Ltd.) were mixed to prepare an adhesive composition.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at 50 ° C. for 24 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 5]
A one-component urethane adhesive (KU928X, manufactured by Konishi Co., Ltd.) was used as an adhesive composition.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at 50 ° C. for 3 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.

[Comparative Example 6]
After dissolving in 20 parts by mass of vinyl acetate resin (Denkasakunor SN-10 manufactured by Denki Kagaku Kogyo Co., Ltd.) and 80 parts by mass of toluene, 20 parts by mass of CNF aqueous dispersion A1 of Production Example 1 is mixed to form an adhesive composition. I made it a thing.
A steel plate having a thickness of 1 mm, a width of 15 mm, and a length of 50 mm was used as an adherend, and the adhesive composition was cured under pressure at room temperature for 24 hours to obtain a test piece. Each characteristic of the obtained adhesive composition and test piece was evaluated in the same manner as in Example 1.
The evaluation results using the above examples and comparative examples are summarized in Table 1.

Examples 1 to 5 showed higher adhesive strength as compared with the case of the adhesive alone of Comparative Examples 1 to 5. Further, in Comparative Examples 3 and 4, the stability of the adhesive composition was poor, whereas in Examples 3 and 4, the stability of the adhesive composition was good.
Further, Comparative Example 6 was a case where the adhesive and CNF were simply mixed instead of the core-shell type composite particles using CNF as a coating material, but the CNF was not uniformly dispersed and became an agglomerate. Therefore, the adhesive strength was not improved.

1 Cellulose nanofiber 2 Core material 10 Core shell type composite particles 20 Dispersion medium (solvent or binder)
101 Cellulose nanofiber aqueous dispersion 102 Adhesive component-containing solution 103 Core-shell type composite particle dispersion 104 Adhesive composition

Claims (4)

The core material contains core-shell type composite particles coated with a coating material,
An adhesive composition, wherein the core material contains an adhesive component, and the coating material contains cellulose nanofibers. The adhesive composition according to claim 1, wherein the cellulose nanofibers have an anionic functional group. The adhesive composition according to claim 2, wherein the anionic functional group is a carboxy group. A method for producing an adhesive composition, which comprises producing the adhesive composition according to any one of claims 1 to 3.
The process of preparing the cellulose nanofiber dispersion and
The process of adjusting the solution containing the adhesive component and
A step of mixing the cellulose nanofiber dispersion liquid and a solution containing the adhesive component to form an emulsion, and
A method for producing an adhesive composition, which comprises.

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