Adhesive property modifiers and adhesives

Abstract

To provide a physical property improving agent for an adhesive which is capable of improving physical properties of the adhesive by being mixed into the adhesive.SOLUTION: A physical property improving agent for an adhesive is formed by combining core-shell type rubber particles and cellulose nanofiber, and is intended to improve physical properties of the adhesive. A mass ratio of the cellulose nanofiber to the core-shell type rubber particles (cellulose nanofiber / core-shell type rubber particles) is 0.05-0.3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a property modifier for adhesives and an adhesive containing the property modifier for adhesives. [Background technology]

[0002] Adhesive bonding offers the advantage of a uniform stress distribution across the entire coated joint, resulting in high specific strength. Due to these advantages and good bonding properties with various materials depending on the adhesive material, the use of adhesives is expanding in a wide range of fields, including general machine parts, industrial machine parts, vehicle parts, marine and aerospace parts, electronic and electrical components, building and civil engineering materials, consumer goods, and containers and packaging materials.

[0003] With this expansion, attempts are being made to improve the physical properties of existing adhesives according to their respective applications.

[0004] For example, Patent Document 1 discloses an epoxy resin product that overcomes various problems in conventional epoxy resin reinforcement by using an epoxy resin composition in which a core-shell polymer is dispersed in the epoxy resin as primary particles. It then provides various examples of epoxy resin products, such as structural adhesives (for the assembly of primary / secondary structural materials of vehicles and car bodies, civil engineering, and construction), heat-resistant adhesives (for aircraft and other applications requiring heat resistance), and adhesives with excellent low-temperature properties (adhesives requiring cold resistance). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-255822 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, Patent Document 1 does not evaluate the physical properties of the adhesive, particularly fatigue resistance. In addition to adhesive strength, fatigue life after bonding is expected to become increasingly important from an SDG perspective. Therefore, while the compositional design of the adhesive itself is important, having a property-improving material that can improve the physical properties of conventional adhesives would be beneficial from a practical standpoint, as it would reduce the cost associated with the above-mentioned compositional design.

[0007] Based on the above, the present invention aims to provide an adhesive property modifier that can improve the physical properties of an adhesive when mixed with the adhesive. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors have come up with the present invention described below and found that it can solve the problems. That is, the present invention is as follows.

[0009] [1] A property modifier for adhesives comprising a combination of core-shell type rubber particles and cellulose nanofibers, wherein the mass ratio of the cellulose nanofibers to the core-shell type rubber particles (cellulose nanofibers / core-shell type rubber particles) is 0.05 to 0.3. [2] The adhesive property modifier according to [1], wherein the degree of polymerization of the cellulose nanofiber is 100 to 1000. [3] The adhesive property modifier according to [1] or [2], wherein the average particle size (D50) of the core-shell type rubber particles is 100 to 300 nm. [4] The adhesive is an epoxy resin adhesive, as described in any one of [1] to [3]. [5] An adhesive comprising a physical property modifier for adhesives and a matrix resin as described in any one of [1] to [4]. [6] The adhesive according to [5], wherein the matrix resin is an epoxy resin. [7] The adhesive according to [5] or [6] further comprising a hardening agent. [8] The adhesive according to [7], wherein the mass ratio of the curing agent to the epoxy resin (curing agent / epoxy resin) is 0.25 to 0.8. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an adhesive property modifier that can improve the physical properties of an adhesive by being mixed with the adhesive. [Brief explanation of the drawing]

[0011] [Figure 1] This is an SEM image of the fracture surface of the adherend during a fatigue life test of an adhesive joint using the adhesive of Example 4. [Modes for carrying out the invention]

[0012] Hereinafter, one embodiment of the present invention (this embodiment) will be described.

[0013] [Property modifier for adhesives] The adhesive property modifier according to this embodiment comprises a combination of core-shell type rubber particles and cellulose nanofibers, and improves the physical properties of the adhesive. "Improving the physical properties of the adhesive" here means improving the mechanical properties of the adhesive (for example, at least one of adhesive fatigue life, adhesive strength, or impact strength) compared to an adhesive without the adhesive property modifier.

[0014] In this embodiment, when core-shell type rubber particles and cellulose nanofibers are combined and mixed into an adhesive, the cellulose nanofibers are thought to crosslink and bond the core-shell type rubber particles to the surrounding core-shell type rubber particles, thereby improving the mechanical properties of the adhesive, such as adhesive fatigue life, adhesive strength, or impact strength. Various adhesives can be used, but epoxy resin adhesives are preferred.

[0015] From the perspective of improving the physical properties as described above, the mass ratio of cellulose nanofibers to core-shell rubber particles (cellulose nanofibers / core-shell rubber particles) is set to 0.05 to 0.3, preferably 0.05 to 0.17, and more preferably 0.06 to 0.13. If the mass ratio is less than 0.05, useful cross-linking cannot be formed in the adhesive due to the small amount of cellulose nanofibers. If it exceeds 0.3, it becomes difficult to disperse the cellulose nanofibers in the adhesive, and excessive cellulose nanofibers will aggregate. Hereinafter, the core-shell rubber particles and cellulose nanofibers will be described in detail.

[0016] (Core-shell rubber particles) The core-shell rubber particles (hereinafter sometimes referred to as "CSR") according to this embodiment are particles having a particulate core portion mainly composed of an elastomer, a rubbery polymer, etc., and a polymer different from the core portion coating part or the whole of the core surface by a method such as graft polymerization.

[0017] As the polymer constituting the core portion of the core-shell rubber particles, a polymer composed of one or more selected from conjugated diene monomers, (meth)acrylate monomers, polysiloxane rubber, or a combination thereof can be used.

[0018] Examples of such conjugated diene monomers include butadiene, isoprene, chloroprene, etc. A polymer composed of these alone or in combination, or a cross-linked polymer may be used. Butadiene is particularly preferred in terms of being inexpensive and easy to polymerize. That is, it is preferable that the polymer is polymerized from a monomer containing butadiene as the core component.

[0019] The shell portion of the core-shell type rubber particles is preferably one that has affinity for the matrix resin in the adhesive. The shell portion may also have the function of chemically reacting with the matrix resin and forming a chemical bond. When the matrix resin is, for example, an epoxy resin, the polymer constituting the shell portion is preferably a polymer obtained by polymerizing one or more components selected from (meth)acrylic acid esters, aromatic vinyl compounds, and vinyl cyanide compounds, or a copolymer obtained by copolymerization, from the viewpoint of being inexpensive, having good graft polymerizability, and having affinity for epoxy resin.

[0020] The volume-average particle diameter (D50) of the core-shell type rubber particles is preferably 50 to 500 nm, more preferably 60 to 300 nm, even more preferably 80 to 250 nm, and most preferably 90 to 200 nm. A volume-average particle diameter of 50 to 500 nm results in good dispersibility of the core-shell type rubber particles in the matrix resin, facilitating crosslinking with the cellulose nanofibers described later, and thus making it easier to obtain an improvement in the adhesive properties. The volume-average particle size (D50) can be measured using a laser diffraction particle size distribution analyzer.

[0021] There are no particular restrictions on the method for producing core-shell type rubber particles, and known methods can be used. Furthermore, the core-shell type rubber particles may be extracted in a lump form, crushed into a powder, and applied to improve the physical properties of the adhesive according to this embodiment, or they may be applied in the form of a masterbatch dispersed in epoxy resin or the like without ever being extracted in a lump form.

[0022] Due to the ease of handling and dispersion of core-shell type rubber particles, it is preferable to use them in masterbatch form. Core-shell type rubber particles in masterbatch form can be produced, for example, by the method described in Japanese Patent Application Publication No. 2004-315572. Specifically, core-shell type rubber particles are produced using polymerization methods in an aqueous medium such as emulsion polymerization, dispersion polymerization, or suspension polymerization, and a suspension of dispersed core-shell type rubber particles is produced. Next, water and a partially soluble organic solvent (e.g., acetone, methyl ethyl ketone, etc.) are mixed with the produced suspension, and then a water-soluble electrolyte (e.g., an alkali metal salt such as sodium chloride or potassium chloride) is brought into contact with the suspension to separate the organic solvent layer from the aqueous layer, remove the aqueous layer, and produce an organic solvent in which core-shell type rubber particles are dispersed. After that, epoxy resin is mixed in, the organic solvent is removed, and a masterbatch in which core-shell type rubber particles are dispersed in epoxy resin is produced. As such a masterbatch in which core-shell type rubber particles are dispersed in epoxy resin, Kaneka Corporation's KaneAce (registered trademark) can be used.

[0023] (Cellulose nanofiber) The cellulose nanofibers (hereinafter sometimes referred to as "CNF") according to this embodiment are practical in terms of their chemical stability, thermal stability, and low cost compared to other nanofibers.

[0024] The average fiber diameter of cellulose nanofibers is preferably 1 to 100 nm, more preferably 5 to 80 nm, and even more preferably 10 to 50 nm, because if it is too thick or too thin, there is a risk of aggregation of cellulose nanofibers, deterioration of handling properties due to increased viscosity of the adhesive matrix, and difficulty in adsorption and crosslinking to the CSR surface. Furthermore, the average length of the cellulose nanofibers is preferably 0.5 to 100 μm, more preferably 1 to 50 μm, and even more preferably 1 to 30 μm, from the viewpoint of dispersibility in the adhesive, handling properties, and ease of crosslinking with CSR, similar to the fiber diameter. The average fiber diameter and length of cellulose nanofibers can be calculated from fiber diameter and length (n=20 or so) measured based on electron microscope images or atomic force microscope images taken at appropriate magnification.

[0025] Cellulose nanofibers can be produced using various manufacturing methods, but among them, mechanically defibrated cellulose nanofibers are preferred. Mechanically defibrated cellulose nanofibers are obtained by cutting raw material fibers to a predetermined length using a beater or refiner, and then fibrillating or micronizing (mechanically grinding) them using a high-pressure homogenizer, grinder, impact pulverizer, bead mill, etc.

[0026] On the other hand, there are chemically modified cellulose nanofibers that are manufactured through chemical modification. These chemically modified cellulose nanofibers are obtained by chemically treating the raw material fibers to make them easier to refine, and then further refining them by mechanical defibrillation. For example, when using chemically modified CNF such as TEMPO-oxidized CNF, metal ions contained in the salt may act as impurities. Examples of metal ions include sodium, aluminum, copper, and silver.

[0027] On the other hand, mechanically defibrated cellulose nanofibers do not undergo chemical modification during the miniaturization process and use only an aqueous medium. Therefore, they do not contain compounds that are likely to affect inorganic particles, and are chemically and thermally stable. For this reason, they can be considered more practical than chemically modified cellulose nanofibers. Furthermore, even when processed with a high-pressure homogenizer, mechanically defibrated cellulose nanofibers are less prone to a decrease in their degree of polymerization.

[0028] Here, the mechanically defibrated cellulose nanofiber has a content of 0.1% by mass or less of any one of sodium, aluminum, copper, and silver (preferably any two of each, more preferably any three of each), and it is preferable that the content is 0.01% by mass or less. The above content can be determined by elemental analysis using high-frequency inductively coupled plasma emission spectroscopy, EPMA using an electron beam microanalyzer, or X-ray fluorescence analysis, but it is preferable that the content is 0.1% by mass or less, and preferably 0.01% by mass or less, by at least one of the above methods.

[0029] Furthermore, the degree of polymerization of the mechanically defibrated cellulose nanofibers is preferably 100 to 1000, more preferably 550 to 900, and even more preferably 600 to 850. A degree of polymerization of 100 to 1000 allows for the production of cellulose nanofibers suitable for dispersibility and crosslinking in adhesives. The degree of polymerization is the number of glucose units, which are the smallest constituent units of cellulose, linked together, and is determined by the viscosity method using a copper ethylenediamine solution.

[0030] In this embodiment, the cellulose nanofiber may be in the form of a CNF dispersion obtained by mechanically defibrillating cellulose, or in the form of dried CNF (dried CNF) obtained by drying the CNF dispersion, and this can be applied as a material for improving the physical properties of adhesives.

[0031] One method for mechanically grinding cellulose, the raw material for cellulose nanofibers, to produce a CNF dispersion is to mechanically grind the pulp to a predetermined length using a beater or refiner, and then fibrillate or pulverize it using a high-pressure homogenizer, grinder, impact mill, bead mill, etc.

[0032] As cellulose, wood pulp with crystalline form I cellulose (cellulose type I), non-wood pulps such as cotton, linters, hemp, bacterial cellulose, and parenchyma cell fibers are used, as well as regenerated cellulose fibers with crystalline form II cellulose (cellulose type II) using N-methylmorpholine N-oxide / water solvent, copper ammonia complex, or sodium hydroxide / carbon disulfide as solvents. Because cellulose type II has a lower molecular weight and degree of crystallinity, its fibers are more easily cut than cellulose type I, and it also has lower heat resistance, so cellulose type I is the preferred material.

[0033] The aforementioned defibration method is preferably a method in which a cellulose-dispersed fluid (preferably a cellulose-water-dispersed fluid) is ejected through a 0.1 to 0.8 mm diameter injection nozzle at a high pressure of 100 to 245 MPa, causing it to collide with a hard object for impact, that is, a defibration method (WJ method) that utilizes the shear force, impact force, and cavitation of a water jet (WJ). With this method, unlike commercially available high-pressure homogenizers, it is possible to perform continuous high-pressure processing using not only the shear force that homogenizes the cellulose-dispersed fluid when it is released after passing it through a narrow channel at high pressure and low speed, but also the impact force from colliding with a hard object for impact and cavitation. In the WJ method, from the viewpoint of obtaining uniform nanofibers, it is preferable to perform repeated collisions, preferably 1 to 30 times, and more preferably 5 to 20 times, with one collision treatment considered as one pass.

[0034] Furthermore, because the WJ method does not require the use of acids or alkalis, it causes less damage to the molecular chains of cellulose, for example, resulting in CNF with high crystallinity. In the case of cellulose, the crystallinity for each pass (number of collisions) compared to untreated material ranges from 40% to 83%. A major advantage of the WJ method is that, unlike other physical grinding methods such as ball mills and disc mills, the crystallinity decreases over time.

[0035] Furthermore, the WJ method allows for the defibrillation of cellulose dispersion fluids with a high concentration of up to 30% by mass by impacting them against a hard impact material using a high-pressure jet treatment at 100-245 MPa through a 0.1-0.8 mm diameter injection nozzle. Compared to the commonly used 1-2% by mass nanofiberization process, the processing rate per solid content is dramatically improved, making it possible to obtain CNF dispersions at low cost, with low environmental impact, and high efficiency.

[0036] Dry CNF, for example, as a CNF dispersion, or a CNF dispersion mixed with appropriate organic components and stirred, undergoes a constant-rate drying period in a drying apparatus after a preheating period (a drying process in which the moisture content decreases at a constant rate over time when drying food under constant heating conditions), with a drying rate of 0.0002 to 0.5 kg / m³. 2 It can be obtained by performing the operation under the condition of [s].

[0037] In this case, the change in the mass of the wet material before drying with respect to time θ [s] is expressed as rm [kg / s], where rm = -dms / dθ. If the mass of the dry material is m [kg] and the mass of water is mw [kg], then ms = m + mw. Since m remains constant during the drying process, rm = -d(m + mw) / dθ = -dmw / dθ. Furthermore, the drying rate R is given by the area A [m²] over which evaporation occurs. 2 Using ] as the reference, R = -1 / A·dmw / dθ = rm / A [kg / m 2 It is represented as ·s].

[0038] Regarding the drying rate for cellulose nanofibers produced by the WJ method, the above range is 0.0002 to 0.5 [kg / m]. 2 If the value falls within the range of [s], it can be dispersed in the resin without causing strong aggregation during drying. On the other hand, if the drying rate is 0.0002 [kg / m³], 2 Below [s], dispersibility may decrease drastically. Drying speed 0.0002~0.5 [kg / m] 2The drying method for conditions within the range of [s] is not limited to any drying apparatus that can achieve the desired drying speed, and various commercially available drying apparatuses can be used. For example, not only spray drying apparatuses using the spray drying method, but also drying apparatuses using the vacuum drying method, airflow drying apparatuses using the airflow drying method, and fluidized bed drying apparatuses using the fluidized bed drying method can be considered.

[0039] Spray drying is a method of rapidly drying liquids or mixtures of liquids and solids (slurries) by spraying them into a gas to produce dried powders. Spray drying, also known as spray drying or spray drying, is preferred for drying materials that are easily damaged by heat, such as food and pharmaceuticals, and is used for drying products such as catalysts because the dried material has a stable particle size distribution.

[0040] Vacuum drying is a drying method performed under vacuum or reduced pressure. When atmospheric pressure decreases, the partial pressure of water vapor in the air decreases, lowering the boiling point of water and accelerating the evaporation rate, thus speeding up the drying of the object.

[0041] Airflow drying is a method of rapidly drying powdery, wet, muddy, or lumpy materials in seconds while they are suspended in a high-speed hot airflow of 300-600°C during transport. The hot air generally flows through the airflow drying tube at about 10-30 m / s, resulting in good heat transfer efficiency.

[0042] Fluidized bed drying is a method of drying powder by fluidizing it with a drying gas, utilizing the excellent mixability, gas contactability, and heat transfer properties of a fluidized bed. The material to be dried is introduced from one end of the fluidized bed and discharged from the outlet while floating and flowing. The movement speed and flow state of the material to be dried may be adjusted as needed, and partition plates may also be used.

[0043] For example, the spray dryer and its conditions for spray drying can be those described in Japanese Patent Publication No. 2019-131772 and Japanese Patent Publication No. 2019-131774, thereby producing a cellulose nanofiber additive in which the water content of the cellulose nanofibers is 10% by mass or less. Furthermore, the drying speed is 0.0002 to 0.5 kg / m 2 By adjusting the range to [s], the moisture content of the dry CNF can be reduced to 10% by mass or less.

[0044] By combining the above-described CSR and CNF such that their mass ratio (CNF / CSR) is in the range of 0.05 to 0.3, the adhesive property modifier according to this embodiment is produced.

[0045] Here, the manner in which CSR and CNF are combined is not particularly limited as long as their interaction is exhibited when CSR and CNF are mixed into the adhesive. Preferably, it is a combination of a masterbatch in which CSR powder and / or CSR is dispersed in epoxy resin, etc., and a CNF dispersion (preferably a CNF ethanol dispersion obtained by substituted ethanol in an aqueous CNF dispersion) or dried CNF. These may be pre-mixed when added to the adhesive, or they may be added simultaneously or sequentially to combine them when added to the adhesive. In other words, it is sufficient that CSR and CNF are ultimately mixed in the adhesive.

[0046] [glue] The adhesive according to this embodiment includes the aforementioned adhesive property modifier and matrix resin. That is, the adhesive according to this embodiment includes the aforementioned core-shell type rubber particles, cellulose nanofibers, and matrix resin. As the matrix resin, thermosetting resins are preferred, and examples include phenolic resins, urea resins, melamine resins, benzoguanamine resins, alkyd resins, unsaturated polyester resins, vinyl ester resins, diallyl(tere)phthalate resins, epoxy resins, silicone resins, urethane resins, furan resins, ketone resins, xylene resins, and thermosetting polyimide resins. These thermosetting resins can be used individually or in combination of two or more. In addition, small amounts of thermoplastic resins or monomers such as acrylic or styrene can be added as long as the properties of the thermosetting resin are not impaired.

[0047] Among the matrix resins mentioned above, epoxy resin is preferred. Compared to other resins, epoxy resin has a high affinity with the adhesive property modifier of this embodiment and also offers good versatility.

[0048] Examples of epoxy resins include bisphenol-type epoxy resins, novolac-type epoxy resins, resorcinol-type epoxy resins, phenol aralkyl-type epoxy resins, naphthol aralkyl-type epoxy resins, aliphatic polyepoxy compounds, alicyclic epoxy compounds, glycidylamine-type epoxy compounds, glycidyl ester-type epoxy compounds, monoepoxy compounds, naphthalene-type epoxy compounds, biphenyl-type epoxy compounds, epoxidized polybutadiene, epoxidized styrene-butadiene-styrene block copolymers, epoxy group-containing polyester resins, epoxy group-containing polyurethane resins, epoxy group-containing acrylic resins, stilbene-type epoxy compounds, triazine-type epoxy compounds, fluorene-type epoxy compounds, triphenolmethane-type epoxy compounds, alkyl-modified triphenolmethane-type epoxy compounds, dicyclopentadiene-type epoxy compounds, and arylalkylene-type epoxy compounds. Among these, bisphenol-type epoxy resins are preferred from the viewpoint of good affinity with the adhesive property modifier of this embodiment.

[0049] Examples of bisphenol-type epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD ​​type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydrogenated bisphenol F type epoxy resin, hydrogenated bisphenol AD ​​type epoxy resin, and tetrabromobisphenol A type epoxy resin, with bisphenol A type epoxy resin being preferred.

[0050] The matrix resin may also contain a curing agent. Examples of curing agents include amine-based curing agents, acid anhydride-based curing agents, amide-based curing agents, phenol-based curing agents, thiol-based curing agents, imidazole, boron trifluoride-amine complexes, guanidine derivatives, and the like.

[0051] When using epoxy resin as the matrix resin, it is preferable to use an amine-based curing agent. The amine-based curing agent may be at least one selected from the group consisting of aliphatic amines, alicyclic amines, modified aliphatic polyamines, modified alicyclic amines, and polyamidoamines, with polyoxyalkylenediamines such as polyoxypropylenediamine being preferred. A commercially available example of polyoxypropylenediamine is "JEFFAMINE D-230" (manufactured by Huntsman Japan Co., Ltd.).

[0052] The mass ratio of the curing agent to the epoxy resin (curing agent / epoxy resin) is preferably 0.25 to 0.8, more preferably 0.25 to 0.50, and even more preferably 0.28 to 0.30, from the viewpoint of curing speed.

[0053] Furthermore, a curing accelerator may be included as needed. The curing accelerator is not particularly limited as long as it is capable of reacting with epoxy groups, etc., and various known ones can be used. The matrix resin may contain various conventionally known additives as long as the effects of the present invention are not impaired. Examples include hydrolysis inhibitors, colorants, flame retardants, antioxidants, polymerization initiators, polymerization inhibitors, ultraviolet absorbers, antistatic agents, lubricants, mold release agents, defoamers, leveling agents, light stabilizers (e.g., hindered amines), antioxidants, inorganic fillers, organic fillers, and the like.

[0054] The adhesive according to this embodiment can be manufactured using the materials described above by various known methods. For example, one method involves thoroughly stirring a matrix resin, an adhesive property modifier, and optionally a curing agent, etc., under normal or reduced pressure using a stirrer such as a mixing mixer. Another method involves dissolving the matrix resin, an adhesive property modifier, and optionally a curing agent, etc., in various organic solvents and thoroughly stirring them using a stirrer such as a mixing mixer. Examples of organic solvents include cyclohexanenone and toluene. [Examples]

[0055] [Examples 1 to 3, Comparative Example 1] One of the following cellulose nanofibers A to C and core-shell rubber particles were combined as shown in Table 1 and used as a physical property improver for adhesives, and adhesives were prepared as follows. First, one of cellulose nanofibers A to C and core-shell rubber particles were added to bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation: jER828, epoxy equivalent 190) in the formulations shown in Table 1. Further, an amine-based curing agent (polyoxypropylene diamine, "JEFFAMINE D-230" manufactured by Huntsman Japan Co., Ltd.) was added in the formulation shown in Table 1, and it was stirred for 10 minutes under the conditions of 800 / 2000 rpm (rotation / revolution) using a rotation-revolution mixer (AR-100 manufactured by THINKY). Then, an adhesive was prepared by performing a defoaming treatment for 5 minutes under the conditions of 0 / 2000 rpm.

[0056] · Cellulose nanofiber A: FMa (dry CNF) manufactured by Sugino Machine Limited, degree of polymerization 200, average fiber diameter 20 nm, specific surface area 150 m 2 / g, type I crystal · Cellulose nanofiber B: WFo (dry CNF) manufactured by Sugino Machine Limited, degree of polymerization 650, average fiber diameter 20 nm, specific surface area 120 m 2 / g, type I crystal · Cellulose nanofiber C: IMa (dry CNF) manufactured by Sugino Machine Limited, degree of polymerization 800, average fiber diameter 20 nm, specific surface area 120 m 2 / g, type I crystal Note that all of cellulose nanofibers A to C correspond to mechanically defibrated cellulose nanofibers. · Core-shell rubber particles: Kane Ace (registered trademark) MX-153 manufactured by Kaneka Corporation (masterbatch containing 33% by mass of CSR), volume average particle diameter (D50) 100 nm

[0057] (Evaluation) The following evaluations were performed on the adhesives of each example and comparative example. The results are shown in Table 1. (1) Tensile shear adhesive strength The tensile shear bond strength was measured as follows, in accordance with the method specified in JIS K6850. First, adhesive was applied to one side of a test specimen (194 mm x 25 mm, 1.6 mm thick cold-rolled steel), and then it was bonded together with another test specimen (194 mm x 25 mm, 1.6 mm thick cold-rolled steel). Next, it was cured in an electric furnace at 70°C for 7.0 hours. This was used as the sample for measuring tensile shear adhesive strength. Tensile shear adhesive strength (unit: MPa) was measured using a universal material testing machine (Shimadzu Corporation, rated load 100 kN) at a temperature of 23°C, humidity of 50%, and a tensile speed of 0.5 mm / min. The number of samples (n) was 5, and the average was calculated.

[0058] (2) Fatigue life of adhesive joints The fatigue life of the adhesive joint was measured as follows, in accordance with the method specified in JIS K6864. First, the same samples used for measuring tensile shear bond strength were employed. The fatigue life of the bonded joints was measured using a hydraulic servo-type strength tester (Shimadzu Corporation, rated load 50kN) under conditions of 23°C and 50% humidity, with a maximum stress of 70% of the static strength, a frequency of 5Hz, a sinusoidal waveform, and a stress ratio of 0.1. The number of samples (n) was 5, and the average was calculated.

[0059] (3) Impact strength of adhesive The impact strength of the adhesive was measured as follows, in accordance with JIS K6855, under conditions of 23°C and 50% humidity. First, the adherends were JIS SS400, and their bonding surfaces were adjusted to Ra 1.6 μm by grinding and then degreased. Using fluororesin tape for control, the adhesive was applied to the adherends to a thickness of 0.16 mm, and the adherends were joined together. After that, curing was performed in an electric furnace at 70°C for 7.0 hours. An Izod impact tester (Impact Tester IT: Toyo Seiki Co., Ltd.) was used for the test, and an impact was applied at a position 9.0 mm above the end face of one of the adherends. The energy required to break the adhesive joint was measured from the change in angle of the impact hammer. The impact adhesive strength was calculated using the following formula. The number of samples (n) was 5, and the average was calculated. Equation: S = E / A Here, E is the impact absorption energy and A is the bonding area. The number of samples (n) was set to 5, and the average was calculated.

[0060] [Table 1]

[0061] [Examples 4, 5, Comparative Example 2] Adhesives were prepared in the same manner as in Example 2, except that the amount of CNF added was changed as shown in Table 2. The prepared adhesives were evaluated as described above. The fatigue life of the adhesive joints was evaluated with the maximum stress set to 90% of the static strength, and all other conditions as described above. The results are shown in Table 2.

[0062] [Table 2]

[0063] Here, Figure 1 shows the results of measuring the fracture surface of the bonded material using an electron microscope (JEOL Ltd., model name JSM-7001FD) when a fatigue life test of the bonded joint was performed using the adhesive prepared in Example 4. As shown in Figure 1, it can be observed that the CNF and the CSR dispersed in the epoxy are bonded in a cross-linking manner at the fracture surface. It is presumed that the cross-linking of the CNF and the CSR dispersed in the epoxy improves the interfacial adhesion between the materials and suppresses crack propagation. This is thought to improve the mechanical properties of the adhesive, such as adhesive fatigue life, adhesive strength, and impact strength.

Claims

1. An adhesive comprising an adhesive property modifier and a matrix resin, The aforementioned adhesive modifier consists of a combination of core-shell type rubber particles and cellulose nanofibers, and improves the physical properties of the adhesive. The mass ratio of cellulose nanofibers to the core-shell type rubber particles (cellulose nanofibers / core-shell type rubber particles) is 0.05 to 0.

3. An adhesive in which the degree of polymerization of the cellulose nanofiber is 600 to 850.

2. The adhesive according to claim 1, wherein the average particle size (D50) of the core-shell type rubber particles is 100 to 300 nm.

3. The adhesive according to claim 1 or 2, wherein the matrix resin is an epoxy resin.

4. Furthermore, the adhesive according to claim 3, further comprising a curing agent.

5. The adhesive according to claim 4, wherein the mass ratio of the curing agent to the epoxy resin (curing agent / epoxy resin) is 0.25 to 0.

8.

6. The adhesive according to claim 4, wherein the curing agent is an amine-based curing agent.

7. The adhesive according to claim 5, wherein the curing agent is an amine-based curing agent.

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