Structural adhesive composition

Abstract

To provide a structural adhesive composition that balances applicability at a room temperature with flow water pressure resistance (shower resistance) in an uncured state.SOLUTION: A structural adhesive composition comprises an epoxy resin and a curing agent for the epoxy resin as its basic composition, while comprising hydrophilic silica and a glycol compound as its essential components.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a structural adhesive composition used for structural bonding of body panels of automobiles and industrial vehicles, and in particular to a structural adhesive composition that can be applied at room temperature and has water flow resistance (shower resistance) in an uncured state. [Background technology]

[0002] In recent years, there has been active development of technologies for reducing the weight of vehicles, with the aim of improving the fuel efficiency of automobiles and other vehicles, with the ultimate goal of curbing global warming and protecting the global environment. As a means of reducing weight, for example, thinner steel plates and the introduction of lightweight materials such as aluminum and resin have been promoted for the body panels of automobiles and other vehicles. On the other hand, there is also a demand for increasing the rigidity of the vehicle body in order to improve driving performance, handling performance, collision safety, etc. In order to increase the rigidity of the vehicle body, conventionally, thickening of structural members and the installation of reinforcing plates have been carried out, but thickening of structural members and the installation of reinforcing plates lead to an increase in the weight of the vehicle body, which is contrary to the goal of reducing the weight of automobiles.

[0003] Therefore, the use of a joining technique that combines structural adhesives with spot welding (weld bond method) is becoming more widespread as a technology that can both reduce the weight of the vehicle body and improve its rigidity. "Structural adhesives" refer to reliable adhesives (JIS K 6800) that can withstand heavy loads for long periods of time. This structural adhesive is used in the body processing and assembly processes, and because thermosetting adhesives that harden when heated are preferred in terms of toughness, thermosetting adhesives are generally used (applied) in the body processing. Furthermore, from the perspective of reducing labor and costs, the thermosetting adhesives applied in the body processing are generally cured by utilizing the heat of a paint drying oven at the same time as the electrodeposition coating is baked in the paint drying oven in the subsequent electrodeposition coating process. Here, in the electrodeposition coating process carried out after the body coating process, a washing process of the body is generally provided as a pretreatment for the surface treatment (electrodeposition coating) for the purpose of rust prevention. Therefore, thermosetting adhesives, which are applied to designated areas of the vehicle body during the bodywork process and hardened using the heat of the paint drying oven after electrodeposition coating, are in an unhardened state during cleaning treatment and electrodeposition coating.

[0004] For this reason, uncured adhesive applied in the body process may be torn or broken by the force of the water flow (shower) or splashes of running water in the cleaning process, which is performed as a pretreatment for electrodeposition coating during the electrodeposition coating process, and may be scattered, deformed (misaligned), or leaked (detached). If uncured adhesive is scattered by the pressure of the running water in the cleaning process, it may adhere to the surface of the body and contaminate the surface, causing poor painting or contaminating the electrodeposition liquid (treatment liquid). Furthermore, if uncured adhesive is significantly deformed by the pressure of the running water in the cleaning process, it may cause problems such as the sealer not adhering to the base during the subsequent sealer application process. In particular, when applying adhesive in the car body process, from the standpoints of bonding strength, rust prevention, and control of the application state, it is preferable to apply the adhesive over the entire joint so widely that it overflows from the edges of structural members such as steel plates, in order to ensure a uniform and wide bonding surface.However, if the adhesive overflows from the joint area of the steel plates, it is prone to scattering, deformation, leakage, etc. due to the pressure of running water during the cleaning process in the electrodeposition coating process.

[0005] To prevent adhesive scattering, deformation, and runoff due to the water pressure during cleaning, it is conceivable to design the viscosity characteristics of structural adhesives to be high around 40°C, the ambient temperature during cleaning. However, the viscosity of the epoxy resin-based adhesives used in this type of adhesive is temperature-dependent (thermosensitive), and viscosity fluctuates significantly with temperature. Therefore, increasing the viscosity around 40°C also increases the viscosity at room temperature. Therefore, conventionally, adhesives with high viscosity at room temperature have been applied by heating the adhesive applicator to increase the temperature and lower the viscosity (thinning the adhesive), thereby ensuring ease of application. In other words, conventionally, adhesives designed to have high viscosity around 40°C to ensure water pressure resistance (shower resistance) have been heated to lower the viscosity before application. However, this heating process during application increases energy consumption and costs.

[0006] Here, Patent Document 1 describes a rubber composition containing a main epoxy resin that is liquid at 20°C and is synthesized using bisphenol as a raw material, a solid rubber component that is at least one selected from NBR and SBR and does not react with the main epoxy resin, and a latent curing agent for epoxy resin that is activated by heating, and the composition has a shear rate of 15.5 sec according to JIS-K2220. -1 The apparent viscosity measured under the conditions of 20 ) is in the range of 200 to 500 Pa·s, and the apparent viscosity (V 40 ) at 20°C (V 20 ) ratio (V 20 / V 40 ) is in the range of 2.0 or more and less than 3.0. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-253131 Summary of the Invention [Problem to be solved by the invention]

[0008] The technology of Patent Document 1 reduces the temperature sensitivity of viscosity by blending a solid rubber component consisting of at least one selected from NBR and SBR that does not react with the main epoxy resin. However, there is a limit to the amount of solid rubber component that can be blended without inhibiting the crosslinking reaction of the epoxy resin, which limits how high the viscosity can be at around 40°C.

[0009] Therefore, an object of the present invention is to provide a structural adhesive composition that is compatible with both ease of application at room temperature and resistance to water flow pressure (shower resistance) in an uncured state. [Means for solving the problem]

[0010] The structural adhesive composition of the present invention as claimed in claim 1 is basically composed of an epoxy resin and a curing agent for the epoxy resin, and contains hydrophilic silica and a glycol compound as essential components. As the epoxy resin, general-purpose epoxy resins such as bisphenol A type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins can be used. The curing agent may be any agent having an active group that reacts with an epoxy group, and for example, an imidazole compound such as dicyandiamide is used. The hydrophilic silica is not subjected to a surface treatment to add an organic group or the like to its hydrophilic surface (silanol group), and includes fused silica, spherical silica, amorphous silica, crystalline silica, and the like. As the glycol-based compound, for example, a polyalkylene glycol-based compound such as polyalkylene glycol or its derivative (such as a polyalkylene glycol-based nonionic surfactant) can be used. Polyalkylene glycol is a concept that includes polyoxyalkylene glycol, and is an oligomer obtained by addition polymerization of an alkylene oxide (such as ethylene oxide, propylene oxide, or butylene oxide) to an alcohol, and for example, diol-type polyethylene glycol, polypropylene glycol, or the like is used.

[0011] The glycol compound of the structural adhesive composition of the invention according to claim 1 is a polyalkylene glycol compound.

[0012] The amount of hydrophilic silica in the structural adhesive composition of the invention of claim 1 is preferably 3 parts by mass or more and 25 parts by mass or less, more preferably 5 parts by mass or more and 20 parts by mass or less, and even more preferably 5 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the epoxy resin.

[0013] The amount of the glycol-based compound in the structural adhesive composition of the invention of claim 1 is preferably in the range of 1 part by mass or more and 8 parts by mass or less, more preferably 1 part by mass or more and 6 parts by mass or less, and even more preferably 2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the epoxy resin.

[0014] The glycol-based compound in the structural adhesive composition of the invention of claim 1 is preferably blended in an amount of 10 parts by mass or more and 50 parts by mass or less, more preferably 15 parts by mass or more and 45 parts by mass or less, and even more preferably 20 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the hydrophilic silica.

[0015] Request 1 The amount of hydrophilic silica in the structural adhesive composition of the present invention is preferably 1 part by mass or more and 8 parts by mass or less, more preferably 1 part by mass or more and 6 parts by mass or less, and even more preferably 2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the entire composition.

[0016] Request 1 The amount of the glycol-based compound in the structural adhesive composition of the present invention is preferably in the range of 0.5 parts by mass or more and 6 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less, and even more preferably 0.6 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the entire composition. The above numerical values are approximate rather than strict, and are naturally approximate values that include errors due to measurement, etc., and do not deny the possibility of errors of several tens of percent.

[0017] The structural adhesive composition of the present invention according to claim 2 further contains an elastomer component. The elastomer component is a concept that includes rubber components, and liquid or solid rubber (nitrile rubber, styrene-butadiene rubber), urethane elastomer, core-shell type rubber particles, etc. can be used, and they may be incorporated into the epoxy resin in advance.

[0018] The elastomer component of the structural adhesive composition of the invention according to claim 3 is a core-shell type rubber particle. The core-shell rubber particles (CSR particles) are particulate materials having a rubbery core layer and a shell layer covering the rubbery core layer. Materials for forming the core layer and shell layer are not particularly limited, as long as the core layer contains a rubber component and the shell layer covering the rubbery core layer is made of a non-elastic polymer material that does not exhibit rubber elasticity. The core layer, the shell layer, or both the core layer and the shell layer may be crosslinked (e.g., ionically or covalently), or the shell layer may be grafted to the core layer. [Effects of the Invention]

[0019] According to the structural adhesive composition of the present invention, the epoxy resin-based structural adhesive composition, whose basic composition is an epoxy resin and a curing agent for the epoxy resin, contains hydrophilic silica and a glycol-based compound such as polyalkylene glycol as essential components, thereby reducing the temperature dependence of viscosity. Therefore, even if the uncured adhesive has a high viscosity that is resistant to scattering, deformation (displacement), and spillage (detachment) due to the water pressure during cleaning performed under atmospheric conditions around 40°C, the low temperature dependence of viscosity keeps the viscosity increase at room temperature low, ensuring ease of application at room temperature. In other words, it is possible to achieve both ease of application at room temperature and resistance to water pressure (shower resistance) during the cleaning process in the uncured state.

[0020] According to the structural adhesive composition of the invention of claim 1, the glycol-based compound is a polyalkylene glycol-based compound, and therefore has good compatibility with epoxy resins, making it possible to form a homogeneous coating film without poor dispersion.

[0021] In the structural adhesive composition according to the invention of claim 1, the hydrophilic silica is preferably blended in an amount within the range of 3 to 25 parts by mass per 100 parts by mass of the epoxy resin. Here, if the amount of hydrophilic silica is too much, dispersibility will decrease, resulting in a decrease in coating workability, while if the amount of hydrophilic silica is too little, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependency of viscosity will not be sufficiently obtained. If the amount of hydrophilic silica is within the range of preferably 3 to 25 parts by mass per 100 parts by mass of epoxy resin, temperature dependency can be reduced while ensuring ease of application, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass per 100 parts by mass of epoxy resin.

[0022] In the structural adhesive composition according to the invention of claim 1, the glycol compound is preferably blended in an amount within the range of 1 to 8 parts by mass per 100 parts by mass of the epoxy resin. Here, if there is too much glycol-based compound, the viscosity of the material will be reduced, resulting in reduced sagging properties, while if there is too little glycol-based compound, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependence of viscosity will not be fully achieved. If the amount of the glycol compound is within the range of preferably 1 to 8 parts by mass per 100 parts by mass of the epoxy resin, sagging properties can be ensured while temperature dependency can be reduced, more preferably 1 to 6 parts by mass, and even more preferably 2 to 5 parts by mass per 100 parts by mass of the epoxy resin.

[0023] In the structural adhesive composition according to the invention of claim 1, the glycol compound is preferably blended in an amount within the range of 10 to 50 parts by mass per 100 parts by mass of hydrophilic silica. Here, if the amount of glycol-based compound is too large relative to the hydrophilic silica, the content of glycol-based compound in the composition will be high, resulting in a low viscosity of the material and reduced sagging resistance and resistance to running water pressure (shower resistance).On the other hand, if the amount of glycol-based compound is too small, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependence of viscosity will not be fully obtained. If the blending amount of the glycol-based compound is within the range of 10 to 50 parts by mass per 100 parts by mass of the hydrophilic silica, it is possible to ensure dripping resistance and resistance to running water pressure (shower resistance) while reducing temperature dependency. More preferably, the blending amount of the glycol-based compound is within the range of 15 to 45 parts by mass, and even more preferably 20 to 40 parts by mass or less per 100 parts by mass of the hydrophilic silica.

[0024] Request 1 According to the structural adhesive composition of the present invention, the hydrophilic silica is preferably blended in an amount within the range of 1 to 8 parts by mass per 100 parts by mass of the structural adhesive composition. Here, if the amount of hydrophilic silica is too much, dispersibility will decrease, resulting in a decrease in coating workability, while if the amount of hydrophilic silica is too little, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependency of viscosity will not be sufficiently obtained. The amount of hydrophilic silica blended is preferably within the range of 1 to 8 parts by mass per 100 parts by mass of the structural adhesive composition. 、Tu This makes it possible to reduce temperature dependency while ensuring fabric workability. More preferably, the amount of hydrophilic silica blended is within the range of 1 to 6 parts by mass, and even more preferably 2 to 5 parts by mass, per 100 parts by mass of the structural adhesive composition.

[0025] Request 1 According to the structural adhesive composition of the present invention, the glycol compound is preferably blended in an amount within the range of 0.5 to 6 parts by mass per 100 parts by mass of the structural adhesive composition. Here, if there is too much glycol-based compound, the viscosity of the material will be reduced, resulting in reduced sagging properties, while if there is too little glycol-based compound, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependence of viscosity will not be fully achieved. The amount of the glycol compound blended is preferably within the range of 0.5 to 6 parts by mass per 100 parts by mass of the structural adhesive composition. 、Chu More preferably, the amount of the glycol compound is in the range of 0.5 to 5 parts by mass, and even more preferably 0.6 to 5 parts by mass, per 100 parts by mass of the structural adhesive composition.

[0026] The structural adhesive composition of the invention of claim 2 further contains an elastomer component, which imparts flexibility to the coating film formed from the epoxy resin, thereby improving the toughness of the coating film in addition to the effect of claim 1.

[0027] According to the structural adhesive composition of the invention of claim 3, the elastomer component is a core-shell type rubber particle, and is therefore not miscible with the epoxy resin. In addition to the effect of claim 2, this composition can improve the toughness of the coating film without reducing the properties of the epoxy resin, such as heat resistance. DETAILED DESCRIPTION OF THE INVENTION

[0028] [Embodiment Mode] A structural adhesive composition according to an embodiment of the present invention will be described below. The structural adhesive composition of this embodiment is a thermosetting epoxy resin-based structural adhesive composition whose basic composition is an epoxy resin and a curing agent for the epoxy resin, i.e., whose basic composition is an epoxy oligomer having two or more epoxy groups (oxirane rings) in the molecule and a curing agent component having active hydrogen and catalytic action. The structural adhesive composition according to this embodiment contains an epoxy resin, a curing agent, hydrophilic silica, a glycol-based compound, core-shell rubber particles as an elastomer component, a reactive diluent, a filler, and the like.

[0029] Here, the epoxy resin may generally be a compound having two or more epoxy groups, and examples thereof include epoxy compounds having a bisphenyl group such as bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AD type, bisphenol AF type, and biphenyl type; epoxy compounds such as polyalkylene glycol type and alkylene glycol type; bifunctional glycidyl ether type epoxy resins such as epoxy compounds having a naphthalene ring and epoxy compounds having a fluorene group; novolac type epoxy resins such as phenol novolac type and orthocresol novolac type; polyfunctional glycidyl ether type epoxy resins such as tetraphenylolethane type; glycidyl ester type epoxy resins of synthetic fatty acids such as dimer acid; and N,N,N',N'- Examples of epoxy resins include aromatic epoxy resins having a glycidylamino group, such as tetraglycidyldiaminodiphenylmethane (TGDDM), tetraglycidyl-m-xylylenediamine, triglycidyl-p-aminophenol, and N,N-diglycidylaniline; trishydroxyphenylmethane epoxy resins; epoxy compounds having a tricyclodecane ring (e.g., epoxy compounds obtained by polymerizing dicyclopentadiene with a cresol such as m-cresol or a phenol, followed by reaction with epichlorohydrin); trishydroxyphenylmethane epoxy resins; sorbitol epoxy resins; polyglycerol epoxy resins; glycidyl ester epoxy resins; heterocyclic epoxy resins; diarylsulfone epoxy resins; pentaerythritol epoxy resins; and trimethylolpropane epoxy resins. Among these, bisphenol A and bisphenol F epoxy resins, which are general-purpose epoxy resins that allow for easy adjustment of the viscosity of the composition, are preferred. Bisphenol A type epoxy resins and the like can be used in liquid to solid forms depending on the molecular weight, but those that are liquid to semi-solid at room temperature are preferred, and those that are liquid at room temperature are particularly preferred in terms of ease of handling and application workability at room temperature. General-purpose epoxy resins that are liquid at room temperature usually have a number average molecular weight of about 300 to 1,000.The epoxy equivalent is preferably in the range of 150 to 600 g / eq, more preferably in the range of 180 to 300 g / eq. The epoxy equivalent means the number of grams of resin containing 1 gram equivalent of epoxy groups (unit: g / eq).

[0030] Furthermore, modified epoxy resins such as urethane-modified epoxy resins, dimer acid-modified epoxy resins, and rubber-modified epoxy resins can also be used as epoxy resins. The structure of the urethane-modified epoxy resin is not particularly limited as long as it is a resin having a urethane bond and two or more epoxy groups in the molecule. However, because it allows for efficient introduction of a urethane bond and an epoxy group into one molecule, a resin obtained by reacting a urethane bond-containing compound having an isocyanate group with a hydroxyl group-containing epoxy compound is preferred. Rubber-modified epoxy resins have two or more epoxy groups, and examples of the rubber skeleton include polybutadiene, acrylonitrile butadiene rubber (NBR), and butadiene-acrylonitrile rubber (CTBN). The epoxy resins can be used alone or in combination of two or more. The epoxy resin preferably has a viscosity in the range of 5,000 to 30,000 mPa·s / 25°C, and more preferably in the range of 10,000 to 20,000 mPa·s / 25°C. Within this range, dripping is unlikely to occur during application, the desired viscosity characteristics can be easily adjusted, and the viscosity of the composition can be made high under the ambient temperature conditions of the cleaning process (around 40°C).

[0031] The curing agent may be any of those typically used for curing epoxy resins, i.e., those having an active group that reacts with an epoxy group, and examples thereof include imidazole compounds such as dicyandiamide, polyaminoamide, 4,4'-diaminodiphenyl sulfone and 2-n-heptadecylimidazole, organic acid hydrazide compounds such as adipic acid dihydrazide, stearic acid dihydrazide, isophthalic acid dihydrazide, dibasic acid hydrazide and isophthalic acid dihydrazide, urea compounds such as N,N-dialkyl urea derivatives and N,N-dialkyl thiourea derivatives, acid anhydrides such as tetrahydrophthalic anhydride, semicarbazide, cyanoacetamide, Examples of suitable curing agents include diaminodiphenylmethane, aliphatic and aromatic tertiary amines, polyamines, amine compounds such as isophoronediamine and m-phenylenediamine, aminotriazoles such as 3-amino-1,2,4-triazole, N-aminoethylpiperazine, melamines, guanamines such as acetoguanamine and benzoguanamine, guanidines, dimethylureas, boron trifluoride complex compounds, boron trichloride complex compounds, Lewis acid complexes, polymercaptan, liquid phenols such as trisdimethylaminomethylphenol, polythiols, triphenylphosphine, ketimine compounds, sulfonium salts, onium salts, and phenol novolac resins. These may be used alone or in combination of two or more. Among these, from the viewpoint of ease of blending, dispersion-type latent curing agents that are activated by heat, such as dicyandiamide, imidazole compounds, and organic acid hydrazides, are preferred. Dicyandiamide (including derivatives such as polyepoxide addition modified products, amidation modified products, Mannich modified products, and Michael addition modified products) is more preferred from the viewpoints of adhesive strength, storage stability, etc. Dicyandiamide is one in which the curing agent component is dissolved and activated by heat, and epoxy resins can be cured at temperatures of 160 to 180°C. The amount of the curing agent to be added is determined based on the amine equivalent and epoxy equivalent, for example, in the case of an amine such as dicyandiamide. For example, the curing agent is blended in an amount of 1 to 20 parts by mass, preferably 2 to 15 parts by mass, and more preferably 5 to 10 parts by mass, per 100 parts by mass of the total amount of the epoxy resin.

[0032] Furthermore, when carrying out the present invention, a curing accelerator may be blended to accelerate the chemical reaction between the epoxy resin and the curing agent by shortening the curing time or lowering the curing temperature. For example, urea-based, imidazole-based, amine-based, triphenylphosphine, etc. can be used. The amount of such a curing accelerator to be added is preferably within the range of 1 to 10 parts by mass, more preferably 1 to 8 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the total amount of the epoxy resin. Within this range, the curing acceleration effect can be obtained without impairing viscosity characteristics or adhesiveness.

[0033] The hydrophilic silica is silica that has not been surface-treated (i.e., the silanol groups on the surface have not been substituted or coupled with organic silane compounds or the like, or the silanol groups on the surface have not been modified (reacted) with organic groups such as alkyl groups or carboxyl groups), and for example, amorphous dry silica, specifically fine particle fumed silica (flame-processed silica), is suitable. Hydrophilic silanol groups (Si-OH) are present on the surface of such hydrophilic silica. Preferably, the average primary particle size measured by the laser diffraction / scattering method is in the range of 5 to 40 nm, and the specific surface area measured by the BET method is 50 to 450 m. 2 / g, more preferably 300 to 450m 2 / g, more preferably 350 to 450 m 2 / g range is used.

[0034] Examples of glycol-based compounds include glycols such as diethylene glycol, dipropylene glycol, and poly(oxy)alkylene glycol, and glycol derivatives (such as polyalkylene glycol-type nonionic surfactants), and poly(oxy)alkylene glycol-based compounds are preferred. Examples of poly(oxy)alkylene glycols include polyethylene glycol (molecular formula: H[OHCH] n OH) and polypropylene glycol (molecular formula: H[OCH3] nOH), etc. can be used, preferably in liquid or paste form, and more preferably in liquid form due to its compatibility with epoxy resins. The polyethylene glycol used has an average molecular weight of, for example, 200 to 4,000, preferably 200 to 2,000, more preferably 200 to 700. The polypropylene glycol used has an average molecular weight of, for example, 400 to 3,000, preferably 1,000 to 2,000. Examples of polyalkylene glycol compounds that can be used include polyethylene glycols and polypropylene glycols manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Tokyo Chemical Industry Co., Ltd., Sigma-Aldrich, Dow Chemical, Sanyo Chemical Industries, Ltd., and Nacalai Tesque, Inc.

[0035] By blending these hydrophilic silicas with glycol-based compounds, the silanol groups (Si-OH groups) on the surface of the particulate hydrophilic silica interact (hydrogen bond) with the polar groups (OH groups, hydrophilic groups, etc.) of the glycol-based compound to form a three-dimensional network structure, imparting high structural viscosity. This reduces the temperature dependency of the composition's viscosity, and even if the viscosity is increased at ambient temperatures (around 40°C) during the cleaning process, the viscosity at room temperature can be kept low. This makes it possible to improve the water pressure resistance in the uncured state without compromising application workability at room temperature. In particular, polyalkylene glycol-based compounds, whose polyalkyl chains have good compatibility with epoxy resins and do not phase separate in the epoxy resin, can be dispersed without agglomeration in the epoxy resin, imparting strong structural viscosity through the construction of a weak three-dimensional network structure (silica-polyalkylene glycol-silica) formed by hydrogen bonds without impairing coating workability. In other words, polyalkylene glycol-based compounds possess both a miscible portion (polyalkyl chain) that is compatible with epoxy resins and a polar portion (hydroxyl group, etc.) that interacts with the silanol groups of hydrophilic silica, thereby forming a three-dimensional network structure through interaction with the hydrophilic silica, and these are dispersed in the epoxy resin. This allows for high structural viscosity without impairing the homogeneity of the coating film.

[0036] The amount of hydrophilic silica is preferably 3 to 25 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the total epoxy resin, and is preferably 1 to 8 parts by mass, more preferably 1 to 6 parts by mass, and even more preferably 2 to 5 parts by mass, per 100 parts by mass of the total composition. If the amount of hydrophilic silica is too much, the dispersibility will decrease, which will result in a decrease in application workability and a decrease in the adhesive strength of the cured product (adhesive).On the other hand, if the amount of hydrophilic silica is too little, the effect of imparting structural viscosity will not be obtained, and the effect of reducing the temperature dependency of viscosity will not be sufficiently obtained. Within the above range, structural viscosity can be imparted by combining with the glycol compound while ensuring ease of application, and the temperature dependency of viscosity can be effectively reduced.

[0037] The glycol compound is preferably blended in an amount of 1 to 8 parts by mass, more preferably 1 to 6 parts by mass, and even more preferably 2 to 5 parts by mass, per 100 parts by mass of the total epoxy resin. The glycol compound is preferably blended in an amount of 0.5 to 6 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 0.6 to 5 parts by mass, per 100 parts by mass of the total composition. The glycol compound is preferably blended in an amount of 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, and even more preferably 20 to 40 parts by mass, per 100 parts by mass of the hydrophilic silica. If there is too much glycol-based compound, the viscosity of the material will be low, resulting in reduced sagging and resistance to running water pressure (shower resistance), while if there is too little glycol-based compound, the effect of imparting structural viscosity will not be obtained, and the effect of the temperature dependency of viscosity will not be fully achieved. Within the above range, sufficient structural viscosity can be imparted by combining with hydrophilic silica while ensuring sagging properties, and the temperature dependency of viscosity can be effectively reduced.

[0038] The glycol compound is preferably blended in an amount within a range of 10 to 50 parts by mass, more preferably within a range of 20 to 40 parts by mass, per 100 parts by mass of hydrophilic silica. If the amount of glycol-based compound is too large relative to the hydrophilic silica, the content of glycol-based compound in the composition will be high, resulting in a low viscosity of the material and reduced sagging properties. On the other hand, if the amount of glycol-based compound is too small, the effect of imparting structural viscosity will not be obtained, and therefore the effect of reducing the temperature dependency of viscosity will not be sufficiently obtained. Within the above range, sufficient structural viscosity can be imparted while ensuring sagging properties, and the temperature dependency of viscosity can be effectively reduced.

[0039] Furthermore, the structural adhesive composition of this embodiment contains core-shell rubber particles. The incorporation of the core-shell rubber particles can impart flexibility to the epoxy resin, thereby improving the peel strength and shear strength of the cured adhesive, thereby making it tougher. In other words, the incorporation of the core-shell rubber particles can alleviate stress generated in the cured adhesive, thereby improving the durability of the cured adhesive.

[0040] Here, the core-shell rubber particles (CSR) are particles having a structure with at least two layers, a rubbery core layer and a shell layer. The core layer of a core-shell rubber particle (hereinafter sometimes simply referred to as "CSR") refers to the inner part of the CSR, and is capable of forming an internal domain of the CSR, in which a rubbery polymer is arranged. This core layer may be made of any rubbery substance, and is typically a crosslinked rubber, i.e., an elastomer, whose main component is butadiene, acrylic, silicone, or the like. For example, it is preferably made of a polymer obtained by polymerizing a conjugated diene and / or a lower alkyl acrylate, a copolymer obtained by copolymerizing these with a copolymerizable monomer, or a polysiloxane rubber, and further preferably is insoluble in epoxy resin.

[0041] Examples of conjugated dienes include butadiene, isoprene, and chloroprene. Among these, butadiene is particularly preferred because it is available at low cost, the resulting polymer has good rubber properties, and is easy to polymerize. Examples of lower alkyl acrylates include ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-ethylhexyl acrylate. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred because the resulting polymers have good rubber properties and are easy to polymerize. Examples of monomers copolymerizable with conjugated dienes or alkyl acrylates include aromatic vinyls such as styrene, vinyl toluene, vinyl naphthalene, and α-methyl styrene; aromatic vinylidenes; vinyl cyanides and vinylidene cyanides such as acrylonitrile and methacrylonitrile; alkyl methacrylates such as methyl methacrylate and butyl methacrylate; aromatic (meth)acrylates such as benzyl (meth)acrylate, phenoxyethyl acrylate, ethyl (meth)acrylate, and butyl methacrylate; vinyl acetate; and vinyl chloride.

[0042] It is also possible to copolymerize monomers having functional groups such as epoxy groups, carboxyl groups, hydroxyl groups, amino groups, etc. For example, examples of monomers having epoxy groups include glycidyl methacrylate, examples of monomers having carboxyl groups include methacrylic acid, acrylic acid, maleic acid, itaconic acid, etc., and examples of monomers having hydroxyl groups include 2-hydroxymethacrylate, 2-hydroxyacrylate, etc.

[0043] Furthermore, as components constituting the core, crosslinkable monomers (multifunctional monomers) such as divinylbenzene, butanediol di(meth)acrylate, triallyl (iso)cyanurate, allyl (meth)acrylate, diallyl itaconate, and diallyl phthalate, as well as grafting monomers having two or more unsaturated sites with unequal reactivity, at least one of which is non-conjugated, such as diallyl maleate, monoallyl fumarate, and allyl methacrylate, can be used. When such crosslinkable monomers or grafting monomers are used in small amounts, preferably 10% by weight or less of the total core-shell rubber particles, interlayer bonding is achieved, making the particles less susceptible to deformation even when heated. Furthermore, silicone rubber can also be used as a monomer copolymerizable with conjugated dienes or alkyl acrylates. In addition, instead of or in combination with such a monomer copolymerizable with a conjugated diene or alkyl acrylate, a polysiloxane rubber composed of alkyl- or allyl-disubstituted silyloxy units such as dimethylsilyloxy, methylphenylsilyloxy, diphenylsilyloxy, etc. When using such a polysiloxane rubber, it is preferable to introduce a crosslinked structure into the polysiloxane in advance, as necessary, by using a polyfunctional alkoxysilane compound in combination during polymerization or by subjecting a silane compound having a vinyl-reactive group to a radical reaction. The rubber core layer is preferably made of a material having a glass transition point (Tg) of -20°C or lower, because this reduces the elastic modulus at low temperatures and increases the peel strength. The glass transition point (Tg) is the temperature at which tan δ peaks in dynamic viscoelasticity measurements.

[0044] On the other hand, the shell layer of CSR is formed on the outer part of the core, usually forming the outermost part of the CSR, and has affinity (compatibility) with epoxy resins. The material constituting this shell layer is not particularly limited as long as it is a material that does not exhibit rubber elasticity, but for example, an acrylic copolymer, specifically a polymer formed by polymerizing methyl methacrylate and / or styrene monomers, or a copolymer formed by copolymerizing these with a copolymerizable monomer, is preferred. These materials are inexpensive, and can enable both good graft polymerization properties and affinity with epoxy resins, and have good adhesive strength over a wide temperature range.

[0045] Examples of monomers copolymerizable with methyl methacrylate or styrene include alkyl acrylates such as ethyl acrylate and butyl acrylate, alkyl methacrylates such as ethyl methacrylate and butyl methacrylate, aromatic vinyls such as vinyl toluene, α-methylstyrene, monochlorostyrene, 3,4-dichlorostyrene and bromostyrene, aromatic vinylidenes, vinyl cyanides such as vinyl acetate, vinyl chloride, acrylonitrile and methacrylonitrile, and vinyl polymerizable monomers such as vinyl cyanide, etc. Among these, ethyl acrylate or acrylonitrile is preferred. Furthermore, it is also possible to modify the surface of the shell layer with an epoxy group and / or a functional group reactive with an epoxy group, such as a carboxyl group, hydroxyl group, or amino group, by copolymerizing a monomer having an epoxy group and / or a functional group reactive with an epoxy group, as a monomer copolymerizable with methyl methacrylate or styrene. For example, an example of a monomer having an epoxy group is glycidyl methacrylate, an example of a monomer having a carboxyl group is methacrylic acid, acrylic acid, maleic acid, itaconic acid, and an example of a monomer having a hydroxyl group is 2-hydroxymethacrylate, 2-hydroxyacrylate, and the like.

[0046] In addition, when chemical reactivity of the shell layer during epoxy resin curing is required, copolymers obtained by copolymerizing one or more components selected from the group of monomers consisting of (meth)acrylic acid esters having reactive side chains such as hydroxyalkyl (meth)acrylates and epoxyalkyl (meth)acrylates, epoxyalkyl vinyl ethers, (meth)acrylamides (including N-substituted monomers), α,β-unsaturated acids, α,β-unsaturated acid anhydrides, and maleimide derivatives are more preferred. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, styrene, α-methylstyrene, (meth)acrylonitrile, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, glycidyl vinyl ether, (meth)acrylamide, maleic anhydride, and maleimide. Furthermore, reactivity can be enhanced by incorporating reactive groups that react with epoxy resins and curing agents, such as glycidyl groups provided by monomers such as glycidyl methacrylate, into the shell layer.

[0047] Furthermore, the shell layer is preferably grafted and / or crosslinked to the core layer, and a crosslinking monomer or grafting monomer can be used in an amount of 10% by weight or less as a monomer copolymerizable with methyl methacrylate or styrene. This is because interlayer bonding is achieved and the particles are less likely to deform even when heated. Examples of the crosslinking monomer include aromatic divinyl compounds such as divinylbenzene, and alkane polyol polyacrylates such as hexanediol diacrylate, butylene glycol dimethacrylate, and norbornene dimethylol dimethacrylate. Examples of the grafting monomer include unsaturated carboxylic acid allyl esters such as allyl methacrylate. The shell layer is preferably made of a substance having a glass transition point (Tg) of 50° C. or higher, because this allows for high adhesive strength to be obtained at high temperatures.

[0048] There are no particular restrictions on the manufacturing method of such CSR, and commercially available products can be used. CSR may be added in powder form, or in the form of a masterbatch in which CSR is blended and dispersed in an epoxy resin (for example, at a concentration of 10 to 60 wt%, preferably 25 to 40 wt%).

[0049] The CSR is preferably blended in an amount of 3 to 20 parts by mass, more preferably 3 to 15 parts by mass, and even more preferably 5 to 10 parts by mass, per 100 parts by mass of the epoxy resin. If the amount of CSR blended is too high, dispersibility decreases, making application workability difficult, while if the amount is too low, the cured product (adhesive) cannot be sufficiently toughened. Within the above range, the adhesive strength of the cured adhesive can be increased while ensuring ease of application.

[0050] The core / shell ratio (weight ratio) of CSR is preferably in the range of 50 / 50 to 95 / 5, and more preferably in the range of 60 / 40 to 90 / 10. If the core / shell ratio (weight ratio) exceeds 50 / 50 and the ratio of the core layer decreases, the viscosity of the composition may decrease. On the other hand, if the ratio of the shell layer decreases and exceeds 95 / 5, it becomes difficult to obtain primary particles, which reduces handleability and may prevent stable physical properties from being obtained. Furthermore, the CSR preferably has a primary average particle size measured by laser diffraction / scattering within the range of 50 nm to 1000 nm. If the average particle size is too small, it will aggregate, increasing viscosity and making it difficult to handle, while if the average particle size is too large, it will not be able to sufficiently toughen the cured product (adhesive). If the particle size is within the above range, the effect of improving the toughness of the cured product can be achieved without impairing handleability or application workability.

[0051] Furthermore, the structural adhesive composition according to this embodiment contains a reactive diluent. The reactive diluent is an epoxy-based diluent containing an epoxy group, i.e., a monoepoxide containing one epoxy group per molecule, which is incorporated into the molecule through a chemical reaction during curing. Specifically, monofunctional diluents such as n-butanol glycidyl ether, butyl glycidyl ether, butylphenyl glycidyl ether, hexyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, tetrahydrofurfuryl glycidyl ether, furfuryl glycidyl ether, trimethoxysilyl glycidyl ether, other higher alcohol glycidyl ethers, and methacrylic acid glycidyl esters can be used, as well as multifunctional diglycidyl ethers such as 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, and dimer acid diglycidyl esters. The viscosity can be adjusted by adding such a reactive diluent.

[0052] The reactive diluent is preferably blended in an amount of 5 to 30 parts by mass, more preferably 8 to 25 parts by mass, and even more preferably 10 to 20 parts by mass, relative to 100 parts by mass of the epoxy resin. Within the above range, a viscosity adjusting effect can be obtained without impairing sagging properties.

[0053] Furthermore, the structural adhesive composition according to the present embodiment contains a filler, such as calcium carbonate (e.g., heavy calcium carbonate), talc, magnesia, calcium silicate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, alumina, zircon, graphite, barium sulfate, clay, mica, kaolin, wollastonite, mica, feldspar, syenite, chlorite, bentonite, montmorillonite, barite, dolomite, quartz, diatomaceous earth, calcium silicate, aluminum silicate, barium carbonate, magnesium carbonate, zinc carbonate, textile fiber, glass fiber, and aramid. Examples of suitable materials include pulp, boron fiber, carbon fiber, phosphate, silica such as crystalline silica, amorphous silica, fused silica, fumed silica, calcined silica, precipitated silica, and pulverized (finely powdered) silica, pyrophyllite, silica sand, cristobalite, cellulose, cement, and resin powders such as polyethylene, calcium oxide, iron oxide, zinc oxide, titanium oxide, barium oxide, magnesium oxide, titanium dioxide, hollow inorganic beads such as hollow ceramic beads and hollow glass beads, hollow organic beads made of polyester resin, glass beads, silver powder, metal powder, and bitumen. These may be used alone or in combination of two or more, but calcium carbonate, particularly heavy calcium carbonate, is preferred from the standpoint of dispersibility, etc. By blending such fillers, it is possible to improve mechanical strength, adjust viscosity, reduce shrinkage on curing, and so on.

[0054] The filler is preferably blended in an amount of 5 to 100 parts by mass, more preferably 10 to 95 parts by mass, and even more preferably 20 to 95 parts by mass, relative to 100 parts by mass of the epoxy resin. Within the above ranges, it is possible to improve strength and reduce cure shrinkage without impairing application workability or adhesive strength. When the filler is particulate, the average particle size measured by a laser diffraction / scattering method is preferably in the range of 0.05 to 500 μm, more preferably 0.1 to 50 μm, and even more preferably 1 to 10 μm. If the particle size is within the above range, it is possible to improve strength and reduce cure shrinkage without impairing handleability such as dispersibility, ease of application, etc.

[0055] In the present embodiment, solid hydrophilic silica such as fumed silica and liquid glycol compounds have the functions of viscosity adjustment (thickening) and imparting thixotropy (thixotropy), but in order to improve viscosity adjustment (thickening) and thixotropy (thixotropy) from the viewpoints of handleability, application workability, prevention of sagging, smooth application, etc., it is also possible to blend in thixotropic agents (thixotropy-imparting agents, thixotropy-imparting agents) such as hydrophobic silica, carbon black such as Ketjenblack, colloidal calcium carbonate (fine calcium carbonate), and sepiolite. These solid thixotropic agents can be used alone or in combination of two or more.

[0056] The solid thixotropic agent is preferably blended in an amount within the range of 3 to 20 parts by mass relative to 100 parts by mass of the epoxy resin, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass. Within the above ranges, it is possible to improve handleability, application workability, drip prevention, smooth application, and the like, without impairing adhesive strength. Furthermore, it is preferable to use solid particles of the thixotropic agent having an average particle size in the range of 0.01 to 0.1 μm as measured by a laser diffraction / scattering method, which allows for improvements in handling, application workability, prevention of sagging, smooth application, etc., without impairing adhesive strength.

[0057] When carrying out the present invention, various additives may be further blended as necessary, such as blocked isocyanates as flexibility-imparting agents and acrylic resins as adhesion improvers for improving adhesion. Other additives that may be blended include pigments, dyes, colorants, antifoaming agents, leveling agents, tackifiers (adhesion promoters), flame retardants, catalysts, plasticizers, reaction retarders, antioxidants, antioxidants, coupling agents, antistatic agents, conductivity-imparting agents, lubricants, sliding-imparting agents, ultraviolet absorbers, surfactants, dispersants, dispersion stabilizers, dehydrating agents, crosslinking agents, rust inhibitors, and solvents.

[0058] The structural adhesive composition according to the present embodiment is prepared by homogeneously mixing and stirring these components using a known mixer / disperser or kneader, such as a planetary mixer, Disper (Dissolver), Henschel mixer, kneader, roll mill, homogenizer, intermixer, kneader, roll, or the like.

[0059] The structural adhesive composition according to the present embodiment thus prepared is applied to the objects to be joined by a known method, such as spraying using a pump or the like, applying with a gun, brushing, etc. When the objects to be joined are car bodies, the adhesive composition is applied to the joining points of the car bodies by spraying using a pump or the like, applying with a gun, etc. in a car body manufacturing process, etc. In particular, the structural adhesive composition of this embodiment contains hydrophilic silica and a glycol-based compound as essential components, which interact to form a three-dimensional network structure, imparting structural viscosity and reducing the temperature dependency of viscosity. Therefore, even if the adhesive is set to a high viscosity that is resistant to scattering, spillage, deformation, etc. due to the pressure of flowing water at the ambient temperature (around 40°C) during the cleaning process, it will have a viscosity suitable for application at room temperature when shear forces are applied, and it will have good dischargeability when applied using a pump or the like, resulting in good application workability.

[0060] The vehicle body to which the structural adhesive composition has been applied in the vehicle body process is then subjected to a cleaning process in the subsequent electrodeposition coating process. According to the structural adhesive composition of this embodiment, even in an uncured state, the combination of hydrophilic silica and glycol-based compound imparts structural viscosity, which increases the viscosity after application, making the composition less susceptible to scattering, flowing out, deformation, etc., even when subjected to the flowing water pressure of the cleaning process. After the structural adhesive composition is applied and the vehicle body is washed during the painting process, it is further subjected to electrodeposition coating and then baked in a paint drying oven (for example, at a temperature of about 160°C to 215°C for about 20 to 60 minutes). The structural adhesive composition applied to the vehicle body is then heat-cured simultaneously with the baking of the electrodeposition coating. In the structural adhesive composition of this embodiment, the incorporation of core-shell rubber particles as the elastomer component ensures that the cured adhesive exhibits high toughness and achieves good adhesive strength. In particular, in this embodiment, the elastomer component is core-shell rubber particles, so that the elastomer component (rubber component) of the rubber particles is unlikely to dissolve and remain in the epoxy resin phase after curing. This prevents the deterioration of the physical properties of the epoxy resin (heat resistance, elastic modulus, etc.) that would occur if the elastomer component remained dissolved in the epoxy resin phase, and makes it easy to design the cured adhesive to have the desired properties.

[0061] Thus, the structural adhesive composition of this embodiment, which has an epoxy resin and a curing agent as its basic components and contains hydrophilic silica and a glycol-based compound as essential components, can reduce the temperature dependency (temperature sensitivity) of the viscosity. Even if the composition is set to a high viscosity that is resistant to scattering, flowing out, deformation, etc. due to the pressure of flowing water at the ambient temperature during the cleaning process (around 40°C), the viscosity can be made suitable for application at room temperature when shear forces are applied. This is because, as mentioned above, by combining hydrophilic silica with a glycol-based compound, a three-dimensional network structure is formed by hydrogen bonding between the silanol groups (Si-OH groups) on the surface of the hydrophilic silica and the polar groups of the glycol-based compound, thereby imparting high structural viscosity. In other words, in the structural adhesive composition of this embodiment, structural viscosity is imparted by the blending of hydrophilic silica and glycol-based compounds, so that the viscosity has little temperature dependency, and even if the viscosity is high at the ambient temperature during cleaning (around 40°C), the viscosity can be reduced during application when shear forces are applied, resulting in a viscosity suitable for application at room temperature, i.e., a moderate viscosity that does not cause discharge defects at a specified discharge pressure during application even at room temperature. Therefore, it is possible to achieve both ease of application at room temperature and resistance to running water pressure (shower resistance) in the uncured state.

[0062] In particular, structural viscosity is imparted by a combination of hydrophilic silica and a glycol-based compound. Because these compounds do not react with epoxy resins, they do not inhibit the crosslinking or curing of the epoxy resin, and can increase the viscosity at ambient temperatures during cleaning (around 40°C). This improves water pressure resistance in the uncured state. Therefore, even if the structural adhesive composition is applied so that it overflows beyond the desired bonding site to ensure a wide bonding surface, the excess portion is less likely to scatter, flow, or deform under the water pressure during cleaning. Furthermore, this composition achieves both ease of application at room temperature and water pressure resistance (shower resistance) in the uncured state without compromising the physical properties (heat resistance, elastic modulus, etc.) of the epoxy resin.

[0063] Thus, according to the structural adhesive composition of this embodiment, structural viscosity is imparted by the blending of hydrophilic silica and glycol-based compounds, so that even in an uncured state, after application, the adhesive has a high viscosity that can withstand the pressure of flowing water in an atmosphere of around 40°C during the car body washing process and prevent scattering, outflow, deformation, etc. due to the pressure of flowing water, and when applied under shear force, the viscosity becomes suitable for application at room temperature.

[0064] Preferably, the structural adhesive composition of this embodiment is prepared by mixing the above-mentioned materials so that the viscosity (apparent viscosity) at 40°C measured according to JIS-K2220 at a shear rate of 15.5 / s is 110 Pa·s or more and 300 Pa·s or less. If the viscosity is within this range, even in the uncured state, scattering, outflow, deformation, etc. due to the pressure of running water during the cleaning process can be effectively prevented. More preferably, the viscosity is 110 Pa·s or more and 250 Pa·s or less.

[0065] Even when the structural adhesive composition of this embodiment has a high viscosity of 110 Pa·s or more and 300 Pa·s or less at 40°C, measured at a shear rate of 15.5 / s according to JIS-K2220, the ratio of the viscosity at 20°C to the viscosity at 40°C is 3.0 or less, due to the structural viscosity imparted by the combination of hydrophilic silica and glycol-based compound. Furthermore, the thixotropic index (Ti value) is 2.5 or more, i.e., the ratio of the viscosity measured at a shear rate of 15.5 / s (40°C) to the viscosity measured at a shear rate of 62 / s (40°C). This allows for good dischargeability from the applicator during application, providing excellent application workability, even at room temperature, and preventing splashing, spillage, deformation, and the like due to the pressure of running water, even in the uncured state.

[0066] Thus, the structural adhesive composition of this embodiment has a high viscosity at 40°C, preventing splashing, spillage, deformation, etc., caused by running water pressure in the uncured state. However, the viscosity is low during application under shear forces, and the composition does not need to be heated during application; it discharges well from a discharge device at room temperature, ensuring ease of application. This eliminates the need for heating or preheating equipment for application and pre-curing (curing), allowing application using existing equipment, reducing equipment costs. Furthermore, complicated processes such as heating during application, pre-heating, and cooling after heating are unnecessary, eliminating the need for time and effort without increasing costs or labor. Furthermore, while epoxy resins tend to foam when pseudo-cured by pre-heating, the elimination of the need for such pre-heating eliminates concerns about internal foaming and a decrease in adhesive strength.

[0067] Furthermore, hydrophilic silica and glycol-based compounds that can impart structural viscosity are inexpensively available materials, so they can be applied at low cost while achieving both ease of application at room temperature and resistance to running water pressure (shower resistance) in an uncured state.

[0068] Here, examples of the structural adhesive composition according to the embodiment of the present invention will be described. The structural adhesive compositions according to the present examples were prepared according to the blending compositions shown in Table 1. The blending amounts in Table 1 are in parts by mass.

[0069] [Table 1]

[0070] As shown in Table 1, the structural adhesive composition of this example contains a bisphenol A epoxy resin (general-purpose epoxy resin) that is liquid at room temperature, an epoxy resin with dispersed core-shell rubber particles (rubber component: PBR, CSR content: 33%, epoxy resin: bisphenol A, epoxy equivalent: 270 g / eq), dicyandiamide as a curing agent, urea as a curing accelerator, hydrophilic silica, liquid polyethylene glycol (average molecular weight 200) and / or liquid polypropylene glycol (average molecular weight 2000), which are polyalkylene glycol compounds, blocked isocyanate (block urethane resin) as a flexibility-imparting agent, monofunctional reactive glycidyl ether as a reactive diluent, heavy calcium carbonate (hydrophobic) as a filler, colloidal calcium carbonate as a thixotropic agent, and calcium oxide as a moisture absorbent.

[0071] That is, in this example, bisphenol A type epoxy resin was used as the epoxy resin, dicyandiamide was used as the epoxy resin curing agent, urea was used as its curing accelerator, core-shell type PBR particles were used as the elastomer component, fumed silica was used as the hydrophilic silica, polyethylene glycol and / or polypropylene glycol was used as the liquid polyalkylene glycol, blocked isocyanate (block urethane resin) was used as the flexibility imparting agent, monofunctional reactive glycidyl ether was used as the reactive diluent, heavy calcium carbonate was used as the thixotropic agent, and calcium oxide was used as the moisture absorbent.

[0072] The structural adhesive compositions of the present examples were prepared by blending various materials in the amounts shown in Table 1 and mixing them at room temperature using a high-speed mixer. As shown in Table 1, although the polyalkylene glycol blend differs between Examples 1 to 3, the blend amounts of the other materials were the same. For comparison, a composition according to Comparative Example 1 was also prepared. As shown in Table 1, Comparative Example 1 was prepared using the same blending materials as those in the examples, except that no polyalkylene glycol was blended.

[0073] Here, for the compositions of the examples and comparative examples prepared with each of these formulations, the material viscosity was measured to evaluate the dischargeability during application and resistance to running water pressure, and the peel strength was measured to evaluate the adhesive strength. The viscosity of the material was measured using a rheometer with a φ5 mm parallel plate as the jig at a shear rate of 15.5 s -1 , 62s -1 The viscosity (specifically, the viscosity 11 seconds after the viscosity stabilized) was measured under the conditions of 1) and 2) at temperatures of 20°C and 40°C. Furthermore, the viscosity-temperature characteristic value and the thixotropic index (Ti value), which are indicators of temperature dependency, were determined from various measurements of the material viscosity. The viscosity-temperature characteristic value, which is an index of temperature dependence, was -1 The material viscosity at 20°C measured at a shear rate of 15.5 s -1 The viscosity is the ratio of the viscosity at 20°C to the viscosity at 40°C measured at 20°C divided by the viscosity at 40°C. The Ti value is measured at a shear rate of 15.5 s at a temperature of 40°C. -1 The material viscosity measured at a shear rate of 62 s at a temperature of 40°C -1 This is the value divided by the material viscosity measured at a shear rate of 62 s -1 Viscosity at a shear rate of 15.5 s -1 is the ratio of viscosity at

[0074] The dischargeability during application was evaluated using the temperature dependency and Ti value as indicators, and the resistance to water pressure was evaluated using the viscosity at 40°C and Ti value as indicators. Temperature-dependent characteristic values (shear rate 15.5 s -1The smaller the ratio (material viscosity at 20°C / material viscosity at 40°C when measured at 20°C), the smaller the difference between the viscosity at 40°C and that at 20°C, and the smaller the temperature dependency. Therefore, even if the viscosity characteristics at around 40°C are set high to ensure resistance to flowing water pressure in the cleaning process where the ambient temperature is around 40°C, the viscosity does not become too high when applied at room temperature, and good dischargeability can be achieved when applied using a pump or the like. Therefore, if this characteristic value is 3.0 or less, the dischargeability is judged to be good and is rated as O, and if it exceeds 3.0, it is rated as X.

[0075] Furthermore, the larger the Ti value, the greater the structural viscosity, and the better the dischargeability and ease of application when external force is applied, but the viscosity increases after application, improving resistance to running water pressure. Therefore, if this Ti value is 2.5 or more, it is judged that the dischargeability and resistance to running water pressure are good and is evaluated as O, and if it is 2.5 or less, it is evaluated as X. Furthermore, since the higher the viscosity at 40°C, the better the resistance to water flow pressure, if the viscosity at 40°C was 100 Pa·s or higher, it was judged to have good resistance to water flow pressure and was rated as O, and if it was less than 100 Pa·s it was rated as X.

[0076] Furthermore, a peel strength evaluation test was also carried out to evaluate adhesiveness. Peel strength was measured in accordance with JIS K6854, using T-type peel adhesive strength (peel strength in a 90° peel test). Test specimens were prepared by using two 200 mm × 25 mm × 0.8 mm SPCC-SD steel plates bent at a 90° angle at a length of 150 mm. After degreasing, the adhesive composition was applied to a 50 mm long section, joined together, and heated at 170°C for 20 minutes to cure the adhesive composition. The adhesive composition thickness of the test specimen was 0.15 mm. The test specimens prepared in this manner were placed in a tensile tester (Shimadzu Autograph) and pulled at a temperature of 20°C and a pulling rate of 200 mm / min to measure the peel strength (N). A peel strength of 100 N / 25 mm or more was considered sufficient for the peel strength required of a structural adhesive, and a peel strength of 100 N / 25 mm or more was evaluated as "good."

[0077] If all of the above evaluation tests were rated as ◯, the dischargeability, water flow resistance, and adhesiveness were all good and the product was judged as passing (◯ or ◎), and if even one of the results was rated as ×, the product was judged as failing (×). Products that were particularly excellent in dischargeability and water flow resistance were judged as ◎.

[0078] As shown in Table 1, in Examples 1 to 3, all of the adhesives have a high viscosity of 100 Pa·s or more at 40°C, and a Ti value of 2.5 or more, so that they exhibit high viscosity characteristics at an ambient temperature of approximately 40°C during the cleaning process after application to steel plates, etc. as structural adhesives for car bodies in vehicle production line processes such as automobiles. On the other hand, since the viscosity ratio of the viscosity at 20°C to the viscosity at 40°C is 3.0 or less, viscosity fluctuations due to temperature changes are suppressed and temperature dependence is small, and since the Ti value is 2.5 or more, the increase in viscosity when applied at room temperature is kept low.

[0079] In contrast, Comparative Example 1, which does not contain liquid polyalkylene glycol, has a low viscosity of 61 Pa·s at 40°C. Furthermore, the viscosity ratio of the viscosity at 20°C to the viscosity at 40°C is high at 3.6, resulting in high temperature dependency and a low Ti value of 1.9.

[0080] Furthermore, from a comparison with Comparative Example 1, it is clear that the high viscosity at 40°C, small (low) temperature dependency, and high Ti value of Examples 1 to 3 are due to the combination of hydrophilic silica and polyalkylene glycol.

[0081] Therefore, the structural adhesive compositions of Examples 1 to 3 have a high viscosity of 100 Pa·s or higher at 40°C and a Ti value of 2.5 or higher, ensuring water pressure resistance (shower resistance) that prevents the adhesive from scattering, shifting (misalignment), or running off even when subjected to water pressure during cleaning in an uncured state. Even when the viscosity is increased at the ambient temperature during the cleaning process (i.e., approximately 40°C), the viscosity ratio of the 20°C viscosity to the 40°C viscosity is 3.0 or less, and the Ti value is 2.5 or higher, resulting in a low temperature dependency of the viscosity. This prevents viscosity increases during application at room temperature, providing viscosity characteristics suitable for application at room temperature, i.e., dischargeability that does not cause discharge problems in application equipment. Furthermore, the adhesive is less likely to sag after application, improving workability. Dragging resistance also ensures good adhesion to adherends and shape retention in the uncured state.

[0082] Therefore, while ensuring dischargeability such as spraying during application, flowing water pressure resistance (shower resistance) is ensured, which makes it difficult for the adhesive to scatter, shift (misalign), or flow out even when subjected to the flowing water pressure of a cleaning process in an uncured state, and it is possible to achieve both dischargeability such as spraying during application and flowing water pressure resistance in an uncured state during the cleaning process after application. This makes it possible to prevent coating defects and contamination of the electrodeposition solution due to scattering, loss, deformation, etc. of the uncured adhesive composition during the cleaning process. Furthermore, in this example, a polyalkylene glycol compound was used as the glycol compound, which had good compatibility with the epoxy resin, resulting in good coating workability without poor dispersion and a homogeneous coating film.

[0083] In contrast, Comparative Example 1, which does not contain liquid polyalkylene glycol, has a low viscosity of 61 Pa·s at 40°C, and such a low viscosity does not provide sufficient resistance to the pressure of running water during cleaning treatment, resulting in frequent scattering, displacement (misalignment), and outflow of the adhesive composition, leading to coating defects and contamination of the electrodeposition liquid. Furthermore, the viscosity ratio of the 20°C viscosity to the 40°C viscosity is high at 3.6, making it highly temperature-dependent, and the Ti value is low at 1.9, resulting in poor discharge properties for spraying and the like when applied at room temperature.

[0084] Furthermore, the adhesive compositions of Examples 1 to 3, incorporating core-shell rubber particles (CSR), exhibit sufficiently high peel strength after heating and complete curing under typical baking conditions for electrodeposition coating of car bodies, and also exhibit good peel adhesion strength and toughness. Furthermore, because the rubber particles are core-shell type, the rubber component does not dissolve and remain in the epoxy resin phase, so the cured product exhibits a high elastic modulus and the heat resistance of the epoxy resin is maintained. Therefore, high adhesive strength is maintained even in environments with high moisture content, resulting in high adhesive reliability. Furthermore, Examples 1 to 3 demonstrate good mechanical properties as an adhesive, even when containing hydrophilic silica and liquid polyalkylene glycol. Furthermore, compositions with such high peel strength are also capable of dispersing internal stresses caused by differences in thermal expansion coefficients.

[0085] In addition, the structural adhesive composition of the above example is a heat-curing, one-component adhesive. In particular, because the curing agent for the epoxy resin is dicyandiamide, a latent curing agent, it has high storage stability even when stored at room temperature, and its one-component structure saves storage space. In particular, the structural adhesive composition of this example exhibits minimal viscosity fluctuation over time, even when stored for long periods of time, allowing it to maintain a predetermined viscosity, resulting in high storage stability. This is thought to be due to the fact that viscosity fluctuation with temperature is kept low, even when the viscosity characteristics are high at the ambient temperature (near 40°C) in the electrodeposition coating process, which includes a cleaning step. Furthermore, the rubber particles are core-shell type, which means they have low reactivity with the epoxy resin, which minimizes viscosity increases due to dissolution of the rubber component in the epoxy resin. Furthermore, heating is not required during preparation of the adhesive composition, preventing the curing reaction from progressing.

[0086] In the above examples, the CSR-dispersed epoxy resin was added in the form of a masterbatch, in which CSR was blended and dispersed in the epoxy resin. This eliminates the need for the complicated mixing process required when powdered CSR is added, and the composition can be easily prepared. Furthermore, this CSR-dispersed epoxy resin maintains the inherent properties of the epoxy resin and exhibits high toughness. Furthermore, the core-shell rubber particles enable the composition to achieve viscosity characteristics that are easy to apply and less likely to drip, even without the need to blend large amounts of a thixotropic agent other than hydrophilic silica.

[0087] As explained above, the structural adhesive composition of the above embodiment is an epoxy resin-based structural adhesive composition whose basic composition is an epoxy resin and a curing agent for the epoxy resin, and contains hydrophilic silica and a glycol-based compound as essential components.

[0088] Therefore, according to the structural adhesive composition of the above embodiment, the inclusion of hydrophilic silica and a glycol-based compound results in the formation of a three-dimensional network structure between the silanol groups (Si-OH groups) on the surface of the hydrophilic silica and the polar groups of the glycol-based compound, thereby imparting high structural viscosity. This reduces the temperature dependency of the viscosity of the composition, and even if the viscosity is increased at around 40°C, the increase in viscosity at room temperature is suppressed. Therefore, when applying the adhesive at room temperature, it can be discharged well from the coating equipment, and even if the discharge rate during application is changed, stable application quality can be obtained, ensuring stable application workability at room temperature. Furthermore, even after application, it is less likely to drip, and has high shape retention and adhesion to the adherend. Furthermore, in the subsequent washing process in an atmosphere of around 40°C, the viscosity increases and even in the uncured state, it has high resistance to running water pressure, i.e., high resistance to running water pressure (shower resistance), and can prevent splashing, outflow, deformation, etc. In particular, polyalkylene glycol compounds have good compatibility with epoxy resins, and can form a three-dimensional network structure through hydrogen bonds with the silanol groups of the hydrophilic silica while remaining compatible with the epoxy resin, thereby imparting strong structural viscosity without causing poor dispersion.

[0089] Furthermore, because the adhesive composition has high resistance to flowing water pressure during cleaning (flowing water pressure resistance), and the uncured adhesive composition is unlikely to be scattered by flowing water pressure during cleaning, it is possible to widen the application area at the joint site or increase the application thickness. That is, even if the adhesive composition protrudes from the joint edge by widening the application area at the joint site or increasing the application thickness, the excess adhesive composition is unlikely to be scattered by flowing water pressure during cleaning, and there is no risk of it adhering to the vehicle body and causing poor painting, contamination of pre-paint treatment liquids (electrodeposition liquids, etc.), or poor processing in the subsequent sealer application process. Furthermore, because the adhesive composition has such high viscosity at temperatures around 40°C, it is easy to remove the excess adhesive composition that protrudes from the joint site even in its uncured state. Removing the excess adhesive composition also prevents the adhesive composition from being scattered and adhering to the vehicle body, causing poor painting, contaminating pre-paint treatment liquids, or poor processing in the subsequent sealer application process.

[0090] In the structural adhesive composition of the above embodiment, if the hydrophilic silica is blended in the range of 3 to 25 parts by mass per 100 parts by mass of epoxy resin, temperature dependency can be reduced while ensuring ease of application.Furthermore, if the glycol-based compound is blended in the range of 1 to 8 parts by mass per 100 parts by mass of epoxy resin, temperature dependency can be reduced while ensuring sagging properties.

[0091] Furthermore, if the hydrophilic silica is in the range of 1 to 8 parts by mass per 100 parts by mass of the structural adhesive composition, temperature dependency can be reduced while ensuring ease of application.Furthermore, if the glycol-based compound is blended in the range of 0.5 to 6 parts by mass per 100 parts by mass of the structural adhesive composition, temperature dependency can be reduced while ensuring sagging properties.

[0092] In addition, if the glycol compound is blended in the range of 10 to 50 parts by mass per 100 parts by mass of hydrophilic silica, the temperature dependency can be reduced without reducing dripping properties or resistance to running water pressure (shower resistance).

[0093] Furthermore, the structural adhesive composition of the above embodiment contains an elastomer component, which imparts flexibility to the coating film formed from the epoxy resin, thereby improving the toughness of the coating film. In particular, because the elastomer component is a core-shell type rubber particle, the rubber component is unlikely to dissolve and remain in the epoxy resin phase after curing, which makes it unlikely to cause a decrease in the performance of the epoxy resin, such as heat resistance, and elastic modulus. Therefore, mechanical properties can be stabilized.

[0094] The structural adhesive composition of the present embodiment can be used, for example, as an adhesive for structural members (e.g., made of metal materials, organic / polymeric materials such as plastics, inorganic materials such as concrete, etc.) in the fields of automobiles and other vehicles (bullet trains and electric trains), civil engineering, architecture, electronics, ships, aircraft, and the aerospace industry. In this case, high bonding strength to the structural parts can be ensured by using spot welding or the like (weld bond method) with electrodes or the like. The structural adhesive composition can also be used as an adhesive for medical, general office, and electronic materials (e.g., interlayer adhesives for multilayer substrates such as build-up substrates, die bonding agents, semiconductor adhesives such as underfills, BGA reinforcing underfills, and mounting adhesives such as anisotropic conductive films (ACFs) and anisotropic conductive pastes (ACPs)), making it applicable in a wide range of fields. In addition to its use as an adhesive, the epoxy resin composition can also be used in general-purpose articles, such as paints, coatings, molding materials (including sheets, films, FRP, etc.), insulating materials (including printed circuit boards, wire coatings, etc.), and sealants (e.g., potting, dipping, and transfer mold sealing for capacitors, transistors, diodes, light-emitting diodes, ICs, and LSIs; potting sealing for COB, COF, and TAB of ICs and LSIs; underfill for flip chips; and sealing for mounting IC packages such as QFP, BGA, and CSP). Because of its excellent water pressure resistance, it is particularly useful for bonding components that will be exposed to running water after application to the adherend.

[0095] When practicing the present invention, the composition, ingredients, blending amounts, preparation methods, etc. of other parts of the structural adhesive composition are not limited to those of the above embodiment. Furthermore, the numerical values given in the embodiments and examples of the present invention do not all indicate critical values, and some numerical values indicate suitable values for implementation, so slight changes to the above numerical values do not negate the implementation.

Claims

1. An epoxy resin-based structural adhesive composition having as its basic composition an epoxy resin and a curing agent for the epoxy resin, Contains hydrophilic silica and a glycol-based compound as essential components, the glycol-based compound is a polyalkylene glycol-based compound, and is blended in an amount within a range of 1 to 8 parts by mass relative to 100 parts by mass of the epoxy resin, and is blended in an amount within a range of 10 to 50 parts by mass relative to 100 parts by mass of the hydrophilic silica, and is further blended in an amount within a range of 0.5 to 6 parts by mass relative to 100 parts by mass of the structural adhesive composition; the hydrophilic silica is blended in an amount within a range of 3 to 25 parts by mass relative to 100 parts by mass of the epoxy resin, and is blended in an amount within a range of 1 to 8 parts by mass relative to 100 parts by mass of the structural adhesive composition; The structural adhesive composition is characterized in that the curing agent is blended in an amount within the range of 1 to 20 parts by mass per 100 parts by mass of the epoxy resin.

2. 2. The structural adhesive composition according to claim 1, further comprising an elastomer component.

3. 3. The structural adhesive composition according to claim 2, wherein the elastomer component is a core-shell type rubber particle.

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