Adhesive composition

Abstract

To provide an adhesive composition having sufficient adhesive force.SOLUTION: An adhesive composition contains a clathrate composed of a cyclodextrin derivative and a guest compound, an epoxy resin and a photoacid generator, wherein the cyclodextrin derivative has an alkoxy group, and a substituted or unsubstituted amino group, and the guest compound has a substituted or unsubstituted amino group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive composition.

Background Art

[0002] Articles in which two members having different coefficients of linear expansion are joined by an adhesive are known. For example, articles in which different types of materials such as a plastic lens having an aspherical surface and a glass lens having a spherical or aspherical surface, which are used as an optical system, are adhered. In this case, in order to relieve the stress caused by the difference in the coefficients of linear expansion of the two, it is common to use an adhesive having a low elastic modulus such as rubber. However, generally, an adhesive having a low elastic modulus has a low adhesive strength and is likely to peel off. Conventionally, as an adhesive for adhering a plastic lens and a glass lens, an epoxy adhesive or a silicone-based adhesive capable of obtaining a high adhesive strength higher than the stress caused by the difference in the coefficient of linear expansion has been used (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, for example, in optical devices and the like, the shapes of articles in which two members having different coefficients of linear expansion are adhered are various, and it has been difficult to obtain sufficient adhesive strength with epoxy adhesives or silicone-based adhesives in some cases. Generally, epoxy adhesives are hard and brittle. Therefore, when adhering dissimilar materials such as "plastic and glass" or "plastic and metal", or glasses having different coefficients of linear expansion even with the same type of material, the stress caused by the difference in the coefficient of linear expansion cannot be relieved, and peeling or crack generation on the adhesive surface may cause a decrease in the adhesive strength.

Means for Solving the Problem

[0005] The adhesive composition of the present invention comprises an inclusion compound composed of a cyclodextrin derivative and a guest compound, an epoxy resin, a photoacid generator, and is characterized in that the cyclodextrin derivative has an alkoxy group and a substituted or unsubstituted amino group, and the guest compound has a substituted or unsubstituted amino group. and the cyclodextrin derivative is a β-cyclodextrin derivative, the guest compound is 1-adamantylamine, the content of the photoacid generator is 2.5 parts by mass or more and 8.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin

Advantages of the Invention

[0006] The adhesive composition of the present invention has sufficient adhesive strength.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0008] ≪Adhesive Composition≫ The adhesive composition of the present invention contains an inclusion compound composed of a cyclodextrin derivative and a guest compound, an epoxy resin, and a photoacid generator. The cyclodextrin derivative has an alkoxy group and a substituted or unsubstituted amino group, and the guest compound has a substituted or unsubstituted amino group.

[0009] ​Generally, the photoacid generator used in epoxy UV adhesives is composed of a light-absorbing part and an acid-generating part. A general photoacid generator is an onium salt having a sulfonium ion or an iodonium ion as a cation part. In these onium salts, the photoacid generator absorbs light and then decomposes to generate an acid by extracting hydrogen from the photoacid generator itself. The generated acid coordinates with the epoxy resin and undergoes a nucleophilic attack of the next epoxy to generate an oxonium cation which is the true active species of cationic polymerization, and then the ring-opening polymerization of the epoxy resin proceeds. As will be described later, the adhesive composition of the present invention contains an inclusion complex to relieve stress and improve the impact resistance of the cured product, and the inclusion complex has an amino group. The present inventor has found that a part of the acid generated from the photoacid generator changes at least a part of the amino group of the inclusion complex into an ammonium salt, and the remaining acid causes the epoxy resin to undergo ring-opening polymerization and cure.

[0010] <Inclusion complex> The inclusion complex is a supramolecular inclusion complex composed of a cyclodextrin derivative and a guest compound.

[0011] Examples of the cyclodextrin derivative include α-cyclodextrin derivative, β-cyclodextrin derivative, γ-cyclodextrin derivative and the like. When the guest compound is adamantylamine, a β-cyclodextrin derivative is preferable as the cyclodextrin derivative.

[0012] The cyclodextrin derivative has an alkoxy group and a substituted or unsubstituted amino group. Generally, since the supramolecular inclusion complex composed of cyclodextrin and a guest compound undergoes chemical bonding in a hydrophilic polymer, the cyclodextrin is modified with a hydroxyl group and has poor compatibility with an epoxy resin. However, in the present invention, at least a part of the hydroxyl groups of cyclodextrin is substituted with an alkoxy group and a substituted or unsubstituted amino group, thereby improving the compatibility with the epoxy resin. The cyclodextrin derivative is preferably a compound in which a plurality of the hydroxyl groups of cyclodextrin are substituted with alkoxy groups. The alkoxy group is not particularly limited, but from the viewpoint of compatibility with the epoxy resin, a methoxy group is preferred. The substituted or unsubstituted amino group is not particularly limited, but from the viewpoint of reactivity with the epoxy resin, an unsubstituted amino group is preferred.

[0013] The guest compound has a substituted or unsubstituted amino group. The substituted or unsubstituted amino group is not particularly limited, but from the viewpoint of reactivity with the epoxy resin, an unsubstituted amino group is preferred. As the guest compound, adamantylamine such as 1-adamantylamine is preferred.

[0014] The content of the inclusion complex is preferably 1 part by mass or more and 2.5 parts by mass or less with respect to 100 parts by mass of the epoxy resin. If the content of the inclusion complex is 1 part by mass or more, the stress relaxation effect by the inclusion complex can be sufficiently obtained, and the impact resistance of the cured product can be sufficiently obtained. On the other hand, if the content of the inclusion complex is 2.5 parts by mass or less, a sufficient number of amino groups can be changed to ammonium salts with a photoacid generator, and curing inhibition is less likely to occur.

[0015] <Epoxy resin> The adhesive composition of the present invention contains an epoxy resin (prepolymer) as the main component. The epoxy resin may be any material that undergoes a polymerization reaction and cures by the acid generated by a photoacid generator, and is not particularly limited. Examples of the epoxy resin include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin and bisphenol F-type epoxy resin, novolak-type epoxy resins such as novolak epoxy resin and cresol novolak epoxy resin, biphenyl-type epoxy resin, stilbene-type epoxy resin, triphenolmethane-type epoxy resin, alkyl-modified triphenolmethane-type epoxy resin, triazine nucleus-containing epoxy resin, dicyclopentadiene-modified phenol-type epoxy resin, and other epoxy resins. Among them, from the viewpoint of adhesive strength, it is preferable to use an epoxy resin having a rigid structure such as a biphenyl skeleton, a bisphenol skeleton, or a stilbene skeleton in the main chain. In particular, it is preferable to use a bisphenol-type epoxy resin, and among them, it is preferable to use a bisphenol F-type epoxy resin. This is because the bisphenol (F-type) epoxy resin has the characteristics of high mechanical strength, good chemical resistance, high curability, small free volume, and thus small hygroscopicity due to the high crosslinking density.

[0016] <Photoacid generator> The adhesive composition of the present invention contains a photoacid generator. Examples of the photoacid generator include onium salts having a sulfonium ion such as triphenylsulfonium hexafluorophosphate or an iodonium ion such as diphenyliodonium hexafluorophosphate as the cation part. Among them, triarylsulfonium salts are preferred.

[0017] The ratio of the content mass of the photoacid generator to the content mass of the inclusion complex in the adhesive composition (content mass of photoacid generator / content mass of inclusion complex) is preferably 1.25 or more and 4 or less. If this ratio is 1.25 or more, when the adhesive composition is cured, it is difficult for the amino group of the inclusion complex to inhibit curing. On the other hand, if this ratio is 4 or less, it is difficult for unreacted photoacid generator to remain. Therefore, when the adherend is glass, there is no risk that the glass itself will become brittle due to acid and be easily broken. Also, when the adherend is a metal such as iron or aluminum, there is no risk of corrosion (rust) occurring due to the strong acid generated from the photoacid generator.

[0018] The content of the photoacid generator is preferably 2.5 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by mass of the epoxy compound. When the content of the photoacid generator is within this range, the amino group that binds to the inclusion complex is changed to an ammonium salt, and the remaining acid causes the epoxy resin to undergo ring-opening polymerization and cure, thereby obtaining sufficient adhesive strength. If the content of the photoacid generator is 2.5 parts by mass or more, the ring-opening polymerization of the epoxy resin proceeds sufficiently, and uncured portions are less likely to occur. On the other hand, if the content of the photoacid generator is 6.0 parts by mass or less, when the adherend is glass, there is no risk that the glass itself will become brittle due to acid and be easily broken, and when the adherend is a metal such as iron or aluminum, there is no risk of corrosion (rust) occurring due to the strong acid generated from the photoacid generator.

[0019] <Method for producing the adhesive composition> The method for producing the adhesive composition of the present invention is not particularly limited, but for example, it can be produced as follows.

[0020] First, the supramolecular inclusion complex can be produced in powder form by stirring a cyclodextrin derivative and a guest compound in water, for example, at a molar ratio of 1:1, and drying the filtrate.

[0021] Subsequently, the supramolecular inclusion complex and the photoacid generator are put into the same container, and then the epoxy resin is added. After gently stirring the added materials with a spatula, centrifugation is performed to uniformly disperse the supramolecular inclusion complex and the photoacid generator in the epoxy resin. For centrifugation, for example, a small ultracentrifuge ("CS150GX" manufactured by Hitachi Koki Co., Ltd.) can be used. The composition after centrifugation can be mixed and defoamed to produce an adhesive composition. For mixing and defoaming, for example, a planetary rotation device ("AR-100" manufactured by Shinchi Co., Ltd.) can be used. In this embodiment, an ultracentrifuge is used for mixing and dispersing the supramolecular inclusion complex and the photoacid generator in the epoxy resin. However, the mixing method is not particularly limited as long as the supramolecular inclusion complex and the photoacid generator can be mixed into the epoxy resin.

[0022] ≪Cured Product≫ The cured product of the present invention is obtained by curing the adhesive composition of the present invention and has crosslinking points formed by the inclusion complex. Further, in the cured product of the present invention, at least a part of the amino group of the inclusion complex, that is, the amino group of the cyclodextrin derivative or the amino group of the guest compound, has been changed to an ammonium salt by the acid generated from the photoacid generator.

[0023] FIG. 1 is a conceptual diagram showing an example of a crosslinked portion of a cured product obtained by curing the adhesive composition of the present invention. FIG. 2 is a conceptual diagram explaining the high elastic modulus and high fracture energy state exhibited by the cured product of the present invention. In FIGS. 1 and 2, 1 is a cyclodextrin derivative, 2 is a guest compound (1-adamantylamine in this example), 3 is a crosslinking point by non-covalent bond, 4 is a chain polymer, and 5 is a crosslinking point by covalent bond. As shown in FIG. 1, the crosslinking point 3 by non-covalent bond is formed by a supramolecular inclusion complex composed of a cyclodextrin derivative 1 and a guest compound 2. Further, as shown in FIG. 2, in the cured product of the present invention, a three-dimensional network structure is formed in which the chain polymers 4 are crosslinked by the crosslinking point 3 by non-covalent bond and the crosslinking point 5 by covalent bond.

[0024] In conventional cured products, in order to enhance mechanical strength and the like, a three-dimensional network structure is formed in which chain-like polymers are cross-linked by cross-linking points formed by covalent bonds. When stress is applied to a conventional cured product, the stress tends to concentrate on short portions (cross-linking points formed by covalent bonds) of the three-dimensional network, so that damage is likely to occur. And once the bond of the cross-linking point formed by covalent bond is cut, it does not return to its original state, so the fracture energy is low.

[0025] The cured product of the present invention has cross-linking points 3 formed by non-covalent bonds in addition to cross-linking points 5 formed by covalent bonds. Therefore, as shown in Fig. 2(a), when an external force is applied, the cyclodextrin derivative 1, which is the host compound, detaches from the guest compound 2, and has the effect of alleviating stress concentration. Further, as shown in Fig. 2(b), when the external force is removed, the detached cyclodextrin derivative 1 and the guest compound 2 become a supramolecular inclusion complex again, and form cross-linking points 3 formed by non-covalent bonds. Thus, since the cross-linking points 3 formed by non-covalent bonds have a buffering action, it becomes a cured product having a high elastic modulus and a high fracture energy. That is, it becomes a cured product in which the fracture energy is increased and the adhesive force is improved while having an elastic modulus equivalent to that of a conventional epoxy adhesive.

[0026] ≪Article≫ The adhesive composition of the present invention can be suitably used as an adhesive for articles such as optical elements, and can be used, for example, for adhering members having different linear expansion coefficients such as a plastic lens and a glass lens.

[0027] The article of the present invention has a first member, a second member, and an adhesive portion that adheres the first member and the second member, and the adhesive portion has a cured product of the present invention. It is preferable that the first member and the second member have different coefficients of linear expansion. FIG. 3 is a schematic cross-sectional view showing an example of an optical element which is one aspect of the article of the present invention. The optical element in FIG. 3 has a plastic lens 11 as the first member and a glass lens 12 as the second member, and has an adhesive portion 13 obtained by curing the adhesive composition of the present invention in the gap and the outer peripheral surface between the plastic lens 11 and the glass lens 12. This optical element can be used as a lens constituting a part of an optical system of an imaging device such as, for example, an interchangeable lens of a single-lens reflex camera, a compact digital camera, and a smartphone.

Examples

[0028] Next, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples. The compounds and evaluation methods used in the Examples and Comparative Examples are as follows.

[0029] <Compound> [Epoxy resin] Bisphenol F type epoxy resin [Photoacid generator] Triarylsulfonium·PF6 salt (CPI-110P / manufactured by San-Apro)

[0030] <Synthesis of supramolecular inclusion complex> Among the hydroxyl groups of β-cyclodextrin, 20 were substituted with methoxy groups and 1 was substituted with an amino group. The β-cyclodextrin derivative and the guest compound 1-adamantylamine were placed in a 50 mL eggplant flask containing a stir bar at a molar ratio of 1:1, and water was added. After heating and stirring using a hot water bath, the obtained solution was removed from the hot water bath and returned to room temperature (25 ° C), and then filtration was performed. The obtained filtrate was dried to obtain a supramolecular inclusion complex.

[0031] <Evaluation method> [Curing property evaluation] To evaluate the curability of the adhesive, the adhesive composition was placed in a container with a volume of 5 cm 3Put it into a syringe and set it on a dispenser coating device ML-808GX (manufactured by Musashi Engineering). The needle attached to the syringe was a metal needle 23G (manufactured by Musashi Engineering), and the coating amount was adjusted according to the air pressure and time of the dispenser.

[0032] After applying the adhesive composition on the glass substrate, EXECURE-H-1VC (manufactured by HOYA) was used as the UV light source, and it was irradiated at an illuminance of 300 mW for 30 seconds to cure the adhesive composition. After curing, by Fourier transform infrared spectroscopy, the absorption at 915 cm showing epoxy groups -1 and the intensity ratio of the peak derived from the aromatic ring (1607 cm -1 ) were defined as the reaction rate, and the curability was evaluated. When the reaction rate was 95% or more, it was designated as "A", and when it was less than that, it was designated as "NG".

[0033] [Breaking Energy Evaluation] Regarding the breaking energy of the adhesive composition, dynamic viscoelasticity measurement (DMA) was performed. As the measurement sample, a film with a width of 5.0 mm and a thickness of 100 μm was prepared, and the area of the stress-strain diagram was taken as the breaking energy. The measurement conditions were a tensile speed of 0.0175 mm / second and an ambient temperature of 25°C. When the breaking energy was 0.5 MJ / m 3 or more, it was designated as "A", and when it was 0.2 MJ / m 3 or more and less than 0.5 MJ / m 3 it was designated as "B", and when it was less than 0.2 MJ / m 3 it was designated as "C". A and B were regarded as good products, and C was regarded as a defective product.

[0034] [Adhesion Evaluation] The adhesion evaluation when bonding a plastic lens and a glass lens was performed by compression shear adhesion. As the test pieces for evaluation, the following plastic plate and glass plate were used. Plastic plate: A flat cycloolefin polymer (trade name: Zeonex / manufactured by Nippon Zeon) of a plastic lens material with a length and width of 20 mm × 20 mm and a thickness of 2 mm Glass plate: A glass plate of the same size with a coating film of an inner surface antireflection paint (GT-7II) made by Canon Optron formed in advance on the bonding side surface of the glass lens material After bonding a plastic plate and a glass plate so that the thickness of the adhesive becomes 0.5 mm, the compressive shear adhesive strength was measured. When the adhesive strength was 7.0 MPa or more, it was designated as "A", when it was less than 7.0 MPa and 5.0 MPa or more, it was designated as "B", and when it was less than 5.0 MPa, it was designated as "C". A and B were regarded as good products, and C was regarded as defective products.

[0035] <Example 1> 1 part by mass (1.0 g) of the supramolecular inclusion complex and 2.5 parts by mass (2.5 g) of the photoacid generator were put into a 100 ml tube for a centrifuge, and then 100 parts by mass (100 g) of the epoxy resin was put into the same tube. After gently stirring using a spatula, the tube was set in a small ultracentrifuge ("CS150GX" manufactured by Hitachi Koki Co., Ltd.). In order to uniformly disperse the supramolecular inclusion complex and the photoacid generator in the epoxy resin, centrifugation was performed at 13,000 rpm for 1 hour. After the centrifugation, mixing and defoaming were performed for 3 minutes using a planetary rotation device ("AR-100" manufactured by Shinki) to obtain an adhesive composition. The evaluation results are shown in Table 1.

[0036] <Examples 2 to 4> An adhesive composition was produced and evaluated in the same manner as in Example 1, except that the formulation was changed as shown in Table 1. The results are shown in Table 1.

[0037]

Table 1

[0038] As shown in Table 1, in Examples 1 and 2, good results were obtained for all of curability, fracture energy, and adhesive strength.

[0039] In Example 3, good results were obtained for curability and fracture energy, but the adhesive strength was inferior to that of Example 1. This is presumably because the addition amount of the photoacid generator was slightly large, and the remaining acid attacked the glass, causing partial cohesive failure of the glass itself during the adhesive strength evaluation.

[0040] In Example 4, the curability was a good result, but the breaking energy and adhesive strength were inferior to those in Example 1. This is presumably because the addition amount of the clathrate was small and the effect of the clathrate was not as pronounced as in Example 1.

Explanation of Symbols

[0041] 1: Cyclodextrin derivative, 2: Guest compound, 3: Crosslinking point by non-covalent bond, 4: Chain polymer, 5: Crosslinking point by covalent bond, 6: Lens barrel, 11: Plastic lens, 12: Glass lens, 13: Adhesive part

Claims

1. An inclusion compound comprising a cyclodextrin derivative and a guest compound, an epoxy resin, a photoacid generator, and containing wherein the cyclodextrin derivative has an alkoxy group and a substituted or unsubstituted amino group, and the guest compound has a substituted or unsubstituted amino group, the cyclodextrin derivative is a β-cyclodextrin derivative, the guest compound is 1-adamantylamine, and an adhesive composition characterized in that the content of the photoacid generator is 2.5 parts by mass or more and 8.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin.

2. The adhesive composition according to claim 1, characterized in that the ratio of the content of the photoacid generator to the content of the inclusion compound is 1.25 or more and 4 or less.

3. The adhesive composition according to claim 1 or 2, characterized in that the content of the inclusion compound is 1 part by mass or more and 2.5 parts by mass or less with respect to 100 parts by mass of the epoxy resin.

4. The adhesive composition according to any one of claims 1 to 3, characterized in that the content of the photoacid generator is 2.5 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by mass of the epoxy resin.

5. The adhesive composition according to any one of claims 1 to 4, characterized in that the epoxy resin is a bisphenol type epoxy resin.

6. The adhesive composition according to any one of claims 1 to 5, characterized in that the cyclodextrin derivative is a compound in which at least a part of the hydroxyl groups of cyclodextrin is substituted with the alkoxy group or the amino group.

7. The adhesive composition according to any one of claims 1 to 6, characterized in that the alkoxy group is a methoxy group.

8. The adhesive composition according to any one of claims 1 to 7, characterized in that the amino group is an unsubstituted amino group.

9. A cured product obtained by curing the adhesive composition according to any one of claims 1 to 8, having crosslinking points formed by the inclusion compound, and the inclusion compound having an ammonium salt.

10. An article having a first member, a second member, and an adhesive portion for adhering the first member and the second member, wherein the adhesive portion has the cured product according to claim 9.

11. The article according to claim 10, wherein the first member is a plastic lens and the second member is a glass lens.

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