Cationically photocurable adhesive, camera module or in-vehicle optical sensor, and method for producing the same

Abstract

To provide a cationically photocurable adhesive, a cured product of which has a low linear expansion coefficient and a low storage elastic modulus.SOLUTION: Disclosed is a cationically photocurable adhesive which is characterized by containing (A) an epoxy compound, (B) an oxetane compound, (C) a silane coupling agent, (D) a photoacid generator, and (E) silica, and which is also characterized in that the silica (E) has a BET specific surface area of 5-25 m2 / g and (D90 - D10) / D50 of 0.7 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a photocationically curable adhesive. [Background technology]

[0002] In camera modules for vehicles and smartphones, photocationically curable adhesives are used to fix components such as lenses and imaging elements. Known photocationically curable adhesives include those that contain a compound having a cationic polymerizable group, such as an epoxy compound or an oxetane compound, a photoacid generator as a polymerization initiator, a silane coupling agent for improving adhesion, and silica as a filler (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-69039 A Summary of the Invention [Problem to be solved by the invention]

[0004] The photocationically curable adhesive used for fixing the components of the camera module as described above is required to fix the components with high dimensional accuracy and to prevent the components from being displaced or dislodged due to thermal and mechanical effects associated with changes in the usage environment. Therefore, the photocationically curable adhesive is required to have a low linear expansion coefficient, a low storage modulus, and excellent flexibility after curing. However, although the linear expansion coefficient decreases when the blending ratio of the filler is increased, the storage modulus increases and flexibility is lost, making it difficult to achieve both of these physical properties. Therefore, the object of the present invention is to provide a photocationically curable adhesive having a low linear expansion coefficient and a low storage modulus of the cured product. [Means for solving the problem]

[0005] The present inventors have conducted extensive research to achieve the above object, and as a result have found that the storage modulus is reduced when a silica filler having a highly uniform particle size distribution is used, which has led to the completion of the present invention.

[0006] That is, the present invention includes (A) an epoxy compound, (B) an oxetane compound, (C) a silane coupling agent, (D) a photoacid generator, and (E) silica, wherein the (E) silica has a BET specific surface area of ​​5 to 25 m 2 / g, and (D90-D10) / D50 is 0.7 or less.

[0007] The amount of the (E) silica blended is preferably 100 parts by mass or more and 200 parts by mass or less, based on 100 parts by mass of the total amount of the (A) epoxy compound and the (B) oxetane compound.

[0008] The present invention also includes a camera module or an on-vehicle optical sensor that includes a cured product of the photocationically curable adhesive. The present invention also includes a method for manufacturing a camera module or an on-vehicle optical sensor that includes a step of bonding components of a camera module together and / or a step of bonding a camera module to a housing using the photocationically curable adhesive. Effect of the Invention

[0009] According to the present invention, it is easy to obtain a photocationically curable adhesive having a low storage modulus while decreasing the linear expansion coefficient of the cured product by increasing the mixing ratio of silica as a filler. As a result, it is easy to suppress the displacement or dislocation of parts in a camera module or an on-vehicle optical sensor. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an example of an on-vehicle optical sensor in which the photocationically curable adhesive of the present invention can be used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the gist of the present invention.

[0012] (A) Epoxy compound The photocationically curable adhesive of the present invention contains an epoxy compound (A). The epoxy compound (A) can be used without any particular limitation as long as it has one or more epoxy groups in the molecule. By containing such an epoxy compound, it becomes possible to fix parts, etc. by curing the photocationically curable adhesive through a polymerization reaction. The epoxy compound (A) preferably has two or more epoxy groups in the molecule. By having two or more epoxy groups in the molecule, it becomes easy to increase the strength of the cured product of the photocationically curable adhesive.

[0013] The structure of the epoxy compound (A) is not particularly limited, but it is preferably an alicyclic epoxy compound having an alicyclic structure and an epoxy group, and more preferably an alicyclic epoxy compound having an epoxy group (alicyclic epoxy group) composed of two adjacent carbon atoms and an oxygen atom that constitute an alicyclic ring. By including such a compound, rigidity is imparted to the cured body of the photocationically curable adhesive, and as a result, volume expansion due to heat is suppressed, making it easy to lower the linear expansion coefficient.

[0014] When the alicyclic epoxy compound has two or more epoxy groups in the molecule, all of the epoxy groups may be alicyclic epoxy groups, or the compound may have both alicyclic epoxy groups and non-alicyclic epoxy groups. However, it is preferable that the compound has two or more alicyclic epoxy groups in the molecule, and it is particularly preferable that all of the epoxy groups are alicyclic epoxy groups.

[0015] The alicyclic epoxy compound may be used alone or in combination of two or more, but it is preferable to use both the alicyclic epoxy compound represented by the following general formula (1) and another alicyclic epoxy compound. This allows a flexible skeleton to be appropriately introduced into the rigid molecular structure, making it easy to reduce the storage modulus while keeping the linear expansion coefficient of the cured body of the photocationically curable adhesive low.

[0016] [ka]

[0017] In the general formula (1), R 1 represents an alkylene group having 4 to 8 carbon atoms, and n represents an integer of 1 to 5.

[0018] The blending ratio of the alicyclic epoxy compound represented by the general formula (1) and the other alicyclic epoxy compound is not particularly limited, but the mass ratio of the other alicyclic epoxy compound:alicyclic epoxy compound represented by the general formula (1) is preferably within a range of 1:1 to 6:1, and more preferably within a range of 2:1 to 3:1. This makes it easy to adjust the linear expansion coefficient and storage modulus of the cured body in a well-balanced manner.

[0019] Examples of the other alicyclic epoxy compounds include alicyclic epoxy compounds represented by the following general formula (2) or (3).

[0020] [ka]

[0021] In the general formula (2), X represents a single bond, an ether bond (-O-), a thioether bond (-S-), or an alkylene group having 1 to 3 carbon atoms.

[0022] [ka]

[0023] R in general formula (3) 2 represents an alkylene group having 1 to 3 carbon atoms.

[0024] Examples of the alicyclic epoxy compounds include CELLOXIDE 8000, CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2083, CELLOXIDE 2085, EPOLEAD GT401, and EHPE3150 manufactured by Daicel Corporation; and TTA21, TTA22, TTA26, and TTA3150 manufactured by Sun Chemical Co., Ltd.

[0025] The photocationically curable adhesive of the present invention may contain a bisphenol-type diglycidyl ether as the epoxy compound (A). By containing such an epoxy compound with a long molecular chain, it becomes easy to adjust the crosslink density after curing of the photocationically curable adhesive, lower the linear expansion coefficient of the cured body, and lower the storage modulus.

[0026] The molecular weight of the bisphenol diglycidyl ether is not particularly limited, but from the viewpoint of the linear expansion coefficient of the cured body, it is preferably 300 or more and 1200 or less, more preferably 300 or more and 1000 or less, even more preferably 300 or more and 800 or less, and particularly preferably 300 or more and 600 or less.

[0027] Examples of such bisphenol diglycidyl ethers include jER806, jER806H, jER807, jER825, jER827, jER828, jER828EL, jER828US, jER828XA, and jER834 manufactured by Mitsubishi Chemical Corporation; YD-8125 and YDF-8170C manufactured by Nippon Steel Chemical & Material Co., Ltd.; and Epicron 830, Epicron 830-S, Epicron 835, Epicron 840, Epicron 840-S, Epicron 850, Epicron 850-S, and Epicron 850-LC manufactured by DIC Corporation.

[0028] (A) The epoxy compound may be used alone or in combination of two or more kinds, but it is preferable to include both an alicyclic epoxy compound and a bisphenol diglycidyl ether. This makes it easy to adjust the physical properties such as the linear expansion coefficient, storage modulus, and glass transition temperature of the cured body of the photocationically curable adhesive. The blending ratio of the alicyclic epoxy compound and the bisphenol diglycidyl ether is not particularly limited, but the mass ratio of the alicyclic epoxy compound:bisphenol diglycidyl ether is preferably within the range of 1:1 to 6:1, and more preferably within the range of 3:1 to 4:1. This makes it easy to adjust the linear expansion coefficient, storage modulus, and glass transition temperature of the cured body to values ​​desired for the photocationically curable adhesive used in a camera module or an in-vehicle optical sensor.

[0029] (B) Oxetane Compound The photocationically curable adhesive of the present invention contains an oxetane compound (B). The oxetane compound (B) can be used without any particular restrictions as long as it has one or more oxetane groups in the molecule. Since the propagation reaction rate of an oxetane compound is faster than that of an epoxy compound, the photocationically curable adhesive contains an oxetane compound, so that the polymerization reaction when curing the photocationically curable adhesive can proceed efficiently. This reduces the brittleness peculiar to epoxy resins, and makes it possible to improve flexibility and toughness.

[0030] (B) Examples of the oxetane compound include 3-ethyl-3-hydroxymethyloxetane (oxetane alcohol) (e.g., OXT-101 manufactured by Toagosei Co., Ltd.), xylylene bisoxetane (e.g., OXT-121 manufactured by Toagosei Co., Ltd.), oxetanyl silsesquioxetane (e.g., OXT-191 manufactured by Toagosei Co., Ltd.), 3-ethyl-3-phenoxymethyloxetane (e.g., OXT-211 manufactured by Toagosei Co., Ltd.), Examples of such oxetanes include 2-ethylhexyloxetane (e.g., OXT-212 manufactured by Toagosei Co., Ltd.), 3-ethyl-3-(cyclohexyloxy)methyloxetane (e.g., OXT-213 manufactured by Toagosei Co., Ltd.), 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane (e.g., OXT-221 manufactured by Toagosei Co., Ltd.), and phenol novolac oxetane (e.g., PHOX manufactured by Toagosei Co., Ltd.). These may be used alone or in combination of two or more.

[0031] The amount of the oxetane compound (B) in the photocationically curable adhesive of the present invention is not particularly limited, but in consideration of the balance between the curing speed and the physical properties of the cured body, the mass ratio of the epoxy compound (A) to the oxetane compound (B) is preferably within a range of 4:1 to 20:1, and more preferably within a range of 8:1 to 10:1.

[0032] (C) Silane coupling agent The photocationically curable adhesive of the present invention contains a silane coupling agent (C). By containing a silane coupling agent (C), the adhesiveness of the photocationically curable adhesive can be improved. The silane coupling agent (C) is not particularly limited and a known one can be used. For example, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. can be used. From the viewpoint of affinity with the epoxy compound (A) and the oxetane compound (B), it is particularly preferable to use 3-glycidoxypropyltrimethoxysilane. These may be used alone or in combination of two or more.

[0033] The amount of the silane coupling agent (C) in the photocationically curable adhesive of the present invention is not particularly limited, but in order to ensure high adhesion, the amount is preferably 0.5 parts by mass or more and 5.5 parts by mass or less, more preferably 1.0 parts by mass or more and 5.0 parts by mass or less, and even more preferably 1.5 parts by mass or more and 4.5 parts by mass or less, per 100 parts by mass of the total amount of the epoxy compound (A) and the oxetane compound (B).

[0034] (D) Photoacid generator The photocationically curable adhesive of the present invention contains a photoacid generator (D). The photoacid generator (D) generates an acid when exposed to energy rays or radiation, and is blended in the photocationically curable adhesive of the present invention as a polymerization initiator.

[0035] (D) The photoacid generator is not particularly limited and may be a known one, for example, an onium salt that releases a Lewis acid upon irradiation with energy rays. The onium salt may be a salt of a cation and an anion.

[0036] Examples of the onium salt include sulfonium salts. The cation may be a compound having a sulfonio group. The sulfur atom constituting the sulfonio group is preferably bonded to an aromatic ring. The aromatic ring may be substituted with a fluorine atom, ethylene glycol, or the like. Examples of the cation include compounds represented by the following formulas (4a) and (4b).

[0037] [ka]

[0038] The anion of the onium salt has the general formula: LM b Z c - L is a metal or a metalloid, and examples of such elements include B, P, As, Sb, Fe, Sn, Bi, Al, Ca, In, Ti, Zn, Sc, V, Cr, Mn, and Co. M is a halogen atom, and examples of such elements include F, Cl, Br, and I. b is an integer of 3 to 6. Z is a functional group containing a halogen atom, and examples of such elements include CF3, C2F5, C3F7, and C6F5. c is an integer of 0 to 4.

[0039] As the anion of the onium salt, for example, tetrakis(pentafluorophenyl)borate (B(C6F5)4) is used in terms of sensitivity and availability. - ), tetrakis(3,5-difluoro-4-methoxyphenyl)borate, tetrafluoroborate (BF4 - ), tris(pentafluoroethyl)trifluorophosphate (PF3(C2F5)3 - ), hexafluorophosphate (PF6 - ), hexafluoroantimonate (SbF6 - ), hexafluoroarsenate (AsF6 - ), hexachloroantimonate (SbCl6 - ) etc.

[0040] Examples of the photoacid generator (D) include the compounds represented by the following (5a), (5b), (5c), (5d), (5e), ​​and (5f).

[0041] [ka]

[0042] The amount of the photoacid generator (D) in the photocationically curable adhesive of the present invention is not particularly limited, but is preferably 0.5 to 5.5 parts by mass, more preferably 1.0 to 5.0 parts by mass, and even more preferably 1.5 to 4.5 parts by mass, relative to 100 parts by mass of the total amount of the epoxy compound (A) and the oxetane compound (B). When the amount of the photoacid generator (D) is within the above range, the photocationic polymerization reaction tends to proceed smoothly with short-term ultraviolet irradiation.

[0043] (E) Silica The photocationically curable adhesive of the present invention contains (E) silica, and the (E) silica has a BET specific surface area of ​​5 to 25 m 2 The composition is characterized in that the ratio of (D90-D10) / D50 is 0.7 or less. By including such silica, the storage modulus of the cured product of the photocationically curable adhesive can be reduced. The reason for this is unclear, but the present inventors consider it as follows.

[0044] That is, when (E) silica is blended, it is possible to reduce the proportion of resin components (polymers of epoxy compounds and oxetane compounds) with a relatively large linear expansion coefficient and lower the linear expansion coefficient of the cured body of the photocationically curable adhesive, but on the other hand, the storage modulus increases due to the increase in the relatively hard silica components. Here, (D90-D10) / D50 is an index showing the uniformity of particle size distribution, and the smaller this value, the higher the uniformity of the particle size distribution. The (E) silica blended in the photocationically curable adhesive of the present invention has a small (D90-D10) / D50 of 0.7 or less and a high uniformity of particle size distribution. In such a silica with a high uniformity of particle size distribution, the BET specific surface area, which is a parameter correlated with particle size, is 25 m 2 / g or less means that there is little fine powder with a significantly small particle size. And because the particle size distribution is highly uniform and there is little fine powder, the silica is less likely to become densely packed, and the BET specific surface area is 25m 2 / g or less, the amount of resin that interacts with the silica surface is small, so it is assumed that the free resin area in the cured body of the photocationically curable adhesive increases, making it easier to relieve stress when stress is applied. Furthermore, the particle size distribution is highly uniform and the BET specific surface area is 5m 2 / g or more means that there is little coarse powder with a significantly large particle size. Since coarse powder has a large volume, stress is concentrated in the area where the coarse powder is present when stress is applied, which can cause an increase in the storage modulus. However, when the particle size distribution is highly uniform and the BET specific surface area is 5 m 2 It is presumed that such stress concentration is unlikely to occur when the BET specific surface area of ​​(E) silica is 5 to 25 m / g or more. 2 / g and (D90-D10) / D50 is 0.7 or less, the storage modulus will be lower than when other silica is used, even if the proportion of silica in the photo-cationically curable adhesive is the same, and as a result, it is presumed that it will be easier to provide a photo-cationically curable adhesive with a low linear expansion coefficient and a low storage modulus.

[0045] (E) The BET specific surface area of ​​silica is 5m2 / g or more, and 2 / g or more, and 2 / g or more is more preferable, and 8m 2 It is more preferable that the viscosity is 25m / g or more. 2 / g or less, and 2 / g or less, and 2 / g or less is more preferable, and 13m 2 / g or less is more preferable. By having the BET specific surface area in the above range, it becomes easy to reduce the storage modulus of the cured body of the photocationically curable adhesive. The BET specific surface area is a specific surface area measured by the BET method.

[0046] (E) silica has a (D90-D10) / D50 of 0.7 or less, preferably 0.6 or less, more preferably 0.5 or less. By having (D90-D10) / D50 in the above range, it becomes easy to reduce the storage modulus of the cured body of the photocationically curable adhesive. The lower limit of (D90-D10) / D50 is not particularly limited, but is generally 0.2 or more, particularly 0.3 or more.

[0047] D10, D50 and D90 in this specification are the particle sizes at which the volume accumulation is 10%, 50% and 90% in the particle size distribution curve obtained by laser diffraction method. Specifically, 100mg of silica is dispersed in 40ml of water, and dispersed with a homogenizer at an output of 40W for 10 minutes to obtain a sample, and the particle size distribution of the sample is measured using a laser diffraction type particle size distribution measuring device, and D10, D50 and D90 can be obtained from the obtained particle size distribution curve.

[0048] The D50 of (E) silica is preferably 0.05 μm or more, more preferably 0.15 μm or more, and even more preferably 0.25 μm or more, and is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.50 μm or less.

[0049] The shape of the (E) silica is not particularly limited, but it is preferably spherical. Being spherical makes it possible to ensure high fluidity without increasing the viscosity even when highly loaded with silica. In the present invention, "spherical" means that the shapes of 1000 or more silica particles are observed with a scanning electron microscope (SEM), and the sphericity of each particle is measured, and the average is 0.9 or more. Sphericity is calculated as 4π×(area) / (perimeter) 2 The sphericity can be measured using an image processing program (for example, AnalySIS manufactured by Soft Imaging System GmbH).

[0050] It is preferable that the (E) silica is independent. Being independent means that the (E) silica exists as a single particle and is unlikely to form aggregates, which makes it easier for the silica to exist independently in the photocationically curable adhesive without agglomeration, and stress concentration is unlikely to occur, making it easier to reduce the storage modulus of the cured product of the photocationically curable adhesive. In the present invention, being independent means that (BET specific surface area) / (calculated value of specific surface area) is in the range of 0.85 to 1.35. The calculated value of the specific surface area can be calculated by 6 / (density×D50), and the density of silica is 2.2 g / cm. 3 It is calculated as follows.

[0051] (E) Silica is independent and spherical, and is particularly preferably independent spherical silica.

[0052] The amount of silica (E) in the photocationically curable adhesive of the present invention is not particularly limited, but is preferably 100 parts by mass or more, more preferably 125 parts by mass or more, and even more preferably 150 parts by mass or more, relative to 100 parts by mass of the total amount of epoxy compound (A) and oxetane compound (B). By setting the amount of silica (E) in the above range, it is easy to make the linear expansion coefficient low. In addition, it is preferably 200 parts by mass or less, more preferably 185 parts by mass or less, and even more preferably 170 parts by mass or less, relative to 100 parts by mass of the total amount of epoxy compound (A) and oxetane compound (B). By setting the amount of silica (E) in the above range, it is easy to improve the workability during use by suppressing the increase in viscosity and increasing fluidity while maintaining a low linear expansion coefficient, and to adjust the physical properties to values ​​desirable for a photocationically curable adhesive used in a camera module or an on-vehicle optical sensor.

[0053] The method for producing (E) silica is not particularly limited, and it may be produced by a dry method or a wet method. The BET specific surface area and (D90-D10) / D50 can be adjusted by controlling the reaction conditions during production or the classification conditions after production.

[0054] The dry method is a method in which silica powder is generated by burning a silicon compound and grown in and near the flame. Examples of the dry method include the method described in WO2020 / 175160. In the dry method, the BET specific surface area and particle size distribution can be adjusted by adjusting the flame combustion conditions, cooling conditions, and heat removal amount. As for the flame combustion conditions, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced by controlling the amount of oxygen in the entire flame to be large. As for the flame cooling conditions, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced by controlling the flame cooling rate to be slow. By reducing the amount of heat removal, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced. After obtaining silica by the dry method, the BET specific surface area and particle size distribution may be adjusted to a desired range by sieving or air classification.

[0055] As a wet method, for example, the sol-gel method described in WO2018 / 096876 can be mentioned. In the sol-gel method, silicon alkoxide is hydrolyzed and polycondensed in a reaction medium consisting of water containing a catalyst and an organic solvent to generate a silica sol, which is then gelled, and the generated solid is taken out and dried to generate a silica powder. In the sol-gel method, the BET specific surface area and particle size distribution can be adjusted by the reaction temperature, reaction liquid concentration, drop speed of the reaction liquid, etc. For example, by lowering the reaction temperature, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced. By lowering the reaction liquid concentration, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced. By slowing down the drop speed of the reaction liquid, the BET specific surface area can be reduced and (D90-D10) / D50 can be reduced. After obtaining silica by a wet method, the BET specific surface area and particle size distribution may be adjusted to a desired range by sieving or air classification.

[0056] Commercially available silica may be used as is, or the BET specific surface area and particle size distribution of the commercially available silica may be adjusted to a desired range by sieving or air classification.

[0057] The (E) silica may be surface-treated with a surface treatment agent such as a silane coupling agent. When the surface treatment is performed, it may be performed by a known method using a known surface treatment agent.

[0058] (Other ingredients) The photocationically curable adhesive of the present invention may contain components other than (A) the epoxy compound, (B) the oxetane compound, (C) the silane coupling agent, (D) the photoacid generator, and (E) silica, as long as the effects of the present invention are not impaired. Examples of the other components include fillers other than silica, thermal cationic polymerization initiators, curing accelerators, flame retardants, rubber particles, thickeners, defoamers, leveling agents, antioxidants, and colorants.

[0059] (Physical properties of cured bodies of photocationically curable adhesives) The storage modulus of the cured product of the photocationically curable adhesive of the present invention is preferably 10 GPa or less, more preferably 9 GPa or less, even more preferably 8 GPa or less, and particularly preferably 7 GPa or less. By lowering the storage modulus of the cured product, it is possible to increase the flexibility of the adhesion site, and when fixing the parts of a camera module or an in-vehicle optical sensor, it is easy to reduce the mechanical influence caused by changes in the usage environment and to suppress the parts from being displaced or coming off. The lower the storage modulus of the cured product of the photocationically curable adhesive of the present invention, the more preferable it is, but it is generally 4 GPa or more, particularly 5 GPa or more.

[0060] The linear expansion coefficient of the cured product of the photocationically curable adhesive of the present invention is preferably 60 ppm / K or less, more preferably 50 ppm / K or less, and even more preferably 45 ppm / K or less. By reducing the linear expansion coefficient of the cured product, it becomes easier to reduce the thermal expansion / contraction caused by temperature changes at the adhesion site during the manufacture of a camera module or an on-board optical sensor, or when the sensor is subjected to thermal effects caused by changes in the usage environment, thereby suppressing the displacement or dislocation of parts. The linear expansion coefficient of the cured product of the photocationically curable adhesive of the present invention is preferably as low as possible, but is generally 30 ppm / K or more, particularly 35 ppm / K or more.

[0061] The cured product of the photocationically curable adhesive of the present invention preferably has a glass transition temperature of 130° C. or higher, more preferably 140° C. or higher, and even more preferably 150° C. or higher. By setting the glass transition temperature of the cured product within the above range, the expected performance can be exhibited even under conditions of high temperature in the external environment. The glass transition temperature of the cured product of the photocationically curable adhesive of the present invention is generally 250° C. or lower, particularly 200° C. or lower. The glass transition temperature is mainly adjusted by the structure and compounding ratio of the epoxy compound and the oxetane compound.

[0062] As described above, the photocationically curable adhesive of the present invention can reduce the storage modulus of the cured product. Therefore, by increasing the silica content and decreasing the linear expansion coefficient, it becomes easy to reduce the storage modulus and increase the degree of freedom in designing the components other than (E) silica, and it becomes easy to adjust the physical properties of the photocationically curable adhesive to the desired range.

[0063] (Method of manufacturing photocationic curing adhesive) The method for producing the photocationically curable adhesive of the present invention is not particularly limited, and it can be produced by mixing each component by a known method using a blender, mixer, etc. During the mixing, each component may be added to a mixer or the like at the same time and mixed, or each component may be added to a mixer or the like sequentially and mixed. The order of addition in this case is not particularly limited. Furthermore, the mixing may be performed under heating, or under an adjusted atmosphere such as an inert gas atmosphere, if necessary.

[0064] (Applications of photocationic curing adhesives) The photocationically curable adhesive of the present invention can reduce the storage modulus, and in particular, can reduce the linear expansion coefficient and the storage modulus, so that it can be suitably used in camera modules for vehicles and smartphones, which require high dimensional accuracy, for bonding and fixing their components. Similarly, it can be suitably used in an on-vehicle optical sensor equipped with a camera module, for bonding between the camera module and the housing. By using the photocationically curable adhesive of the present invention for fixing components in a camera module or bonding between the camera module and the housing, it is easy to reduce the effects of changes in the usage environment and to suppress the displacement or dislocation of components. In addition, the low linear expansion coefficient also makes it easy to improve the dimensional accuracy when fixing components during manufacturing.

[0065] (Camera modules and automotive optical sensors) A camera module and an on-vehicle optical sensor for which the photocationically curable adhesive of the present invention can be suitably used will be described with reference to FIG.

[0066] An in-vehicle optical sensor is mounted on a vehicle to detect information such as surrounding obstacles. Information obtained by an in-vehicle optical sensor is used to warn the driver and control the vehicle, and therefore high reliability is required. As shown in FIG. 1, an in-vehicle optical sensor 1 generally has a camera module, which is composed of components such as a lens 2, a lens barrel 3, an image sensor 5, a seal glass 4, and a circuit board 6, fixed to a housing 7. The photocationically curable adhesive of the present invention can be suitably used when bonding these components together or when fixing the camera module to the housing 7.

[0067] The lens 2 is fixed to the inside of the lens barrel 3 using an adhesive. If the lens is misaligned, the resolution, angle of view, optical axis, flange back, etc. may be shifted, which may cause a decrease in optical performance. Therefore, it is required to fix the lens with high dimensional accuracy during manufacturing, and it is required to prevent the lens from being misaligned or coming off due to thermal and mechanical influences accompanying environmental changes during use. The photocationically curable adhesive of the present invention has a small storage modulus and excellent flexibility, and a low linear expansion coefficient, so it can be suitably used for bonding lenses and lens barrels that require such characteristics.

[0068] The lens barrel 3 and the circuit board 6 on which the image sensor 5 is mounted are fixed using an adhesive. If a positional deviation occurs between the lens barrel and the circuit board, a positional deviation will occur between the lens and the image sensor, which may cause an optical axis deviation or a focus deviation. Therefore, during manufacturing, it is required to fix the lens barrel and the circuit board with high dimensional accuracy, and during use, it is required to prevent positional deviation or dislocation between the lens barrel and the circuit board due to thermal and mechanical influences accompanying environmental changes. The photocationically curable adhesive of the present invention has a small storage modulus and excellent flexibility, and a low linear expansion coefficient, so it can be suitably used for bonding a lens barrel and a circuit board, which require such characteristics.

[0069] The imaging element 5 mounted on the circuit board 6 is fixed to the circuit board 6 using an adhesive. If the imaging element is misaligned on the circuit board, the lens and the imaging element will be misaligned, which may cause optical axis misalignment and focus misalignment. Therefore, during manufacturing, it is required to fix the imaging element on the circuit board with high dimensional accuracy, and during use, it is required to prevent misalignment and dislocation between the imaging element and the circuit board due to thermal and mechanical effects associated with environmental changes. The photocationically curable adhesive of the present invention has a small storage modulus and excellent flexibility, and a low linear expansion coefficient, so it can be suitably used for bonding imaging elements and circuit boards that require such characteristics.

[0070] A seal glass 4 may be placed between the lens 2 and the image sensor 5 to protect the image sensor. The seal glass 4 is fixed to the inside of the lens barrel 3 using an adhesive. If the seal glass is displaced or removed, the protection function of the image sensor is reduced, causing damage to the image sensor. The seal glass may also have an optical filter function. An example of an optical filter is an infrared cut filter for removing specific frequency components. If the infrared cut filter is displaced or removed, appropriate filtering cannot be performed, and color tone abnormalities occur. Therefore, it is required to prevent the seal glass from being displaced or removed due to thermal and mechanical effects associated with environmental changes during use. The photocationically curable adhesive of the present invention has a small storage modulus and excellent flexibility, and a low linear expansion coefficient, so it can be suitably used for bonding seal glass and a lens barrel, which require such characteristics.

[0071] By storing the camera module in the housing 7, the camera module is protected from external impacts during distribution and use, and can be easily attached to a vehicle or the like. When storing the camera module in the housing, the outside of the lens barrel of the camera module and the housing are fixed using an adhesive. If a positional shift or dislocation occurs between the camera module and the housing, when the camera module is mounted on a vehicle or the like and used, it causes an error in identifying the size of the imaged object and the distance to the object. In addition, the camera module may not be sufficiently protected from external impacts during distribution and use. Therefore, it is required to fix the camera module and the housing with high dimensional accuracy during manufacturing, and it is required to prevent positional shifts and dislocations between the camera module and the housing due to thermal and mechanical effects associated with environmental changes during distribution and use. The photocationically curable adhesive of the present invention has a small storage elastic modulus and excellent flexibility, and a low linear expansion coefficient, so it can be suitably used for bonding a camera module and a housing that require such characteristics.

[0072] The method of bonding and fixing components in a camera module or bonding a camera module and a housing using the photocationically curable adhesive of the present invention is not particularly limited. It can be performed by a known method. For example, it can be performed by applying the photocationically curable adhesive to the bonding surface of the bonding object, placing it on the bonding surface of another bonding object, and then irradiating ultraviolet rays to cure the photocationically curable adhesive. The ultraviolet irradiation may be performed by first irradiating low-intensity ultraviolet rays to temporarily fix the object, and then irradiating high-intensity ultraviolet rays to permanently fix the object. Thereafter, heat curing may be performed to promote post-curing and release thermal distortion caused by ultraviolet irradiation to increase adhesive strength. The heat curing conditions are not particularly limited, but can be, for example, 50 to 150°C for 0.5 to 5 hours. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Various materials used and physical property measurement conditions are described below.

[0074] (A) Epoxy compound A-1: Celloxide 2021P (alicyclic epoxy compound corresponding to general formula (3), manufactured by Daicel Corporation) A-2: Celloxide 2081 (alicyclic epoxy compound corresponding to general formula (1), manufactured by Daicel Corporation) A-3: jER828 (bisphenol diglycidyl ether, manufactured by Mitsubishi Chemical Corporation) (B) Oxetane Compound ·B-1:OXT-101 (manufactured by Toagosei Co., Ltd.) (C) Silane coupling agent C-1: 3-Glycidoxypropyltrimethoxysilane (D) Photoacid generator D-1: The following compound D-1

[0075] [ka]

[0076] (E) Silica E-1: Silica produced by the method described in Example 9 of WO2020 / 175160 (BET specific surface area: 9 m 2 / g, D50: 0.37 μm, (D90-D10) / D50: 0.58) E-2: Sunseal SS-01 (Tokuyama, BET specific surface area: 15m 2 / g, D50: 0.16 μm, (D90-D10) / D50: 0.58) E-3: Sunseal SS-03 (Tokuyama, BET specific surface area: 11m 2 / g, D50: 0.33 μm, (D90-D10) / D50: 0.43) E-4: Sunseal SS-04 (Tokuyama, BET specific surface area: 8m 2 / g, D50: 0.41 μm, (D90-D10) / D50: 0.39) E-5: Silica produced by the method described in Comparative Example 4 of Japanese Patent No. 6901853 (BET specific surface area: 16 m 2 / g, D50: 0.18 μm, (D90-D10) / D50: 0.92) ·E-6: Sanshiru SS-07 (manufactured by Tokuyama, BET specific surface area: 4 m 2 / g, D50: 0.72 μm, (D90 - D10) / D50: 0.43)

[0077] <Measurement of D10, D50, and D90> For a sample obtained by dispersing 100 mg of silica in 40 ml of water and subjecting it to ultrasonic irradiation of about 40 W for 10 minutes, the particle size distribution was measured using a laser diffraction scattering type particle size distribution analyzer (manufactured by Beckman Coulter, Inc.: LS13 320). In the obtained volume frequency distribution of particle sizes (particle size distribution), the particle size at which the cumulative value of the volume frequency becomes 10% from the smaller particle size side was defined as D10, the particle size at which the cumulative value becomes 50% was defined as D50, and the particle size at which the cumulative value becomes 90% was defined as D90.

[0078] <Measurement of BET Specific Surface Area> The BET specific surface area was determined by the BET method (nitrogen adsorption one-point method) using a rapid surface area measuring device (manufactured by Shibata Scientific Technology Ltd.: SA-1000). For the measurement, 2 g of a powder sample was used, which had been previously dried at 100 °C for 1 hour in a nitrogen gas flow.

[0079] <Measurement of Sphericity> The sphericity was measured by observing 1000 silica particles with a scanning electron microscope (SEM), measuring the sphericity for each particle, and obtaining the average value. The measurement was performed using an image processing program (AnalySIS manufactured by Soft Imaging System GmbH), and the sphericity was calculated by 4π×(area) / (perimeter length) 2 as calculated.

[0080] <Measurement of Linear Expansion Coefficient> The photocationically curable adhesive prepared in the examples and comparative examples was poured into a PTFE mold capable of producing a block-shaped cured body, and then irradiated with ultraviolet light from the top and bottom for 5 minutes each, and then heated at 100°C for 1.5 hours to cure. This was polished and shaped to produce a cured body of 12 mm x 6 mm x 5.5 mm. The obtained cured body was measured by a compression load method using a thermomechanical analyzer (NETZSCH: TMA4000SE) with a sample length of 12 mm, a load of 10 g, and a heating rate of 5°C / min from 40°C to 300°C. The linear expansion coefficient was calculated from the slope of the change in linear expansion coefficient from 50°C to 100°C (region below the glass transition temperature).

[0081] <Measurement of storage modulus> The photocationically curable adhesives prepared in the examples and comparative examples were poured into a PTFE mold capable of producing a rectangular cured body, and then irradiated with ultraviolet light from the top and bottom for 5 minutes each, and then heated at 100°C for 1.5 hours to cure. This was polished and shaped to produce a cured body of 25mm x 5mm x 1mm. The obtained cured body was measured in tensile measurement mode using a dynamic viscoelasticity measuring device (NETZSCH: DMA 242 E Artemis) with a sample length (chuck distance) of 10mm, a frequency of 1Hz, and a heating rate of 3°C / min from 0°C to 300°C. The storage modulus was obtained as a value at 25°C.

[0082] <Measurement of glass transition temperature> The photocationically curable adhesive prepared in the examples and comparative examples was poured into a PTFE mold capable of producing a rectangular cured body, and then irradiated with ultraviolet light from the top and bottom for 5 minutes each, and then heated at 100°C for 1.5 hours to cure. This was polished and shaped to produce a cured body of 25mm x 5mm x 1mm. The obtained cured body was measured in tensile measurement mode using a dynamic viscoelasticity measuring device (NETZSCH: DMA 242 E Artemis) with a sample length (chuck distance) of 10mm, a frequency of 1Hz, and a heating rate of 3°C / min from 0°C to 300°C. The glass transition temperature was obtained as the peak temperature of the loss tangent given by the loss modulus / storage modulus.

[0083] <Measurement of elongation rate> The photocationically curable adhesives prepared in the examples and comparative examples were poured into a PTFE mold capable of producing a dumbbell-shaped cured body, and then irradiated with ultraviolet light from above for 5 minutes. Then, with a weight placed on top, the cured body was heated at 100°C for 1.5 hours to obtain a cured body with a thickness of 0.2 mm, which is the same as the dimensions of a dumbbell test piece as specified in JIS K7161-2 5A. A tensile break test was performed on the obtained cured body using a precision universal testing machine (Shimadzu Corporation: AUTOGRAPH AG-X plus 50kN) under conditions of a chuck distance of 50 mm and a tensile speed of 10 mm / min. The elongation rate (%) was calculated from the formula (stroke amount until breakage / gauge distance) x 100.

[0084] Example 1 (A) 50 parts by mass of A-1, 20 parts by mass of A-2, and 20 parts by mass of A-3 as epoxy compounds, (B) 10 parts by mass of B-1 as oxetane compound, (C) 3.0 parts by mass of C-1 as silane coupling agent, (D) 3.0 parts by mass of D-1 as photoacid generator, and 160 parts by mass of E-1 as silica were measured and mixed to obtain a photocationically curable adhesive. The physical properties of the silica used and the evaluation results of the physical properties of the cured body of the photocationically curable adhesive are shown in Table 1.

[0085] [Examples 2 to 4, Comparative Examples 1 and 2] A photocationically curable adhesive was produced in the same manner as in Example 1, except that the type of silica was changed as shown in Table 1. Table 1 shows the evaluation results of the physical properties of the silica used and the physical properties of the cured product of the photocationically curable adhesive.

[0086] [Table 1]

[0087] The evaluation results showed that (E) the BET specific surface area of ​​silica is 5 to 25 m 2 / g, and Examples 1 to 4 in which (D90-D10) / D50 is 0.7 or less are compared with Comparative Example 1 in which the silica has a (D90-D10) / D50 of more than 0.7, and the silica has a BET specific surface area of ​​5 m 2 / g, the thermal expansion coefficient was almost the same, but the storage modulus was lower. This means that the photo-cationically curable adhesive of the present invention can easily achieve both a low thermal expansion coefficient and a low storage modulus. [Explanation of symbols]

[0088] 1. Automotive optical sensors 2 Lenses 3. Telescope tube 4. Sealing Glass 5. Image sensor 6 Circuit Board 7. Cabinet

Claims

1. (A) an epoxy compound, (B) an oxetane compound, (C) a silane coupling agent, (D) a photoacid generator, and (E) silica; The silica (E) has a BET specific surface area of ​​5 to 25 m ２ / g, (D90-D10) / D50 is 0.7 or less, Photocationic curing adhesive.

2. 2. The photocationically curable adhesive according to claim 1, characterized in that the amount of the (E) silica is 100 parts by mass or more and 200 parts by mass or less when the total amount of the (A) epoxy compound and the (B) oxetane compound is 100 parts by mass.

3. A camera module or an on-vehicle optical sensor comprising a cured product of the photocationically curable adhesive according to claim 1 or 2.

4. A method for manufacturing a camera module or an on-vehicle optical sensor, comprising a step of bonding components of a camera module together and / or a step of bonding a camera module to a housing using the photocationically curable adhesive according to claim 1 or 2.

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