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

Abstract

The present invention addresses the problem of providing a cationically photocurable adhesive, a cured product of which has a low linear expansion coefficient and a low storage elastic modulus. 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.

Description

Photocationic curing adhesive, camera module or in-vehicle optical sensor, and method for manufacturing the same

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

[0002] In camera modules for vehicles, smartphones, etc., photocationically curable adhesives are used to fix components such as lenses and image sensors. Known photocationically curable adhesives include those containing a compound having a cationically 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 (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2022-69039

[0004] Photocationically curable adhesives used to fix components of camera modules such as those described above are required to fix components with high dimensional accuracy and to prevent displacement or detachment of components due to thermal and mechanical influences associated with changes in the usage environment. Therefore, photocationically curable adhesives are required to have a low linear expansion coefficient, a low storage modulus, and excellent flexibility after curing. However, while increasing the filler content reduces the linear expansion coefficient, it has been difficult to achieve both of these physical properties, as this increases the storage modulus and results in a loss of flexibility. Therefore, an object of the present invention is to provide a photocationically curable adhesive that has a low linear expansion coefficient and a low storage modulus after curing.

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

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

[0007] When the total amount of the epoxy compound (A) and the oxetane compound (B) is taken as 100 parts by mass, the blending amount of the silica (E) is preferably 100 parts by mass or more and 200 parts by mass or less.

[0008] The present invention also includes a camera module or an on-vehicle optical sensor containing 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, the method including 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.

[0009] The present invention makes it easy to obtain a photocationically curable adhesive that has a low storage modulus while maintaining a low coefficient of linear expansion of the cured product by increasing the proportion of silica as a filler, which makes it easy to prevent component displacement or detachment in camera modules and on-board optical sensors.

[0010] FIG. 1 is a schematic diagram of an example of an on-vehicle optical sensor that can use the photocationically curable adhesive of the present invention.

[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 implemented with any modifications within the scope of the gist of the present invention.

[0012] (A) Epoxy Compound The photocationically curable adhesive of the present invention contains (A) an epoxy compound. The (A) epoxy compound can be used without 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 cure the photocationically curable adhesive through a polymerization reaction and fix components, etc. The (A) epoxy compound preferably has two or more epoxy groups in the molecule. By having two or more epoxy groups in the molecule, it becomes easier 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 product of the photocationically curable adhesive, and as a result, thermal volume expansion 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]

[0017] In addition, 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 general formula (1) to the other alicyclic epoxy compound is not particularly limited, but the mass ratio of the other alicyclic epoxy compound to the alicyclic epoxy compound represented by 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, which makes it easy to adjust the linear expansion coefficient and storage modulus of the cured product 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]

[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]

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

[0024] Examples of 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 diglycidyl ether as the epoxy compound (A). By containing such an epoxy compound with a long molecular chain, the crosslink density of the photocationically curable adhesive after curing can be adjusted, and the linear expansion coefficient of the cured product and the storage modulus can be easily reduced.

[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 from 300 to 1,200, more preferably from 300 to 1,000, even more preferably from 300 to 800, and particularly preferably from 300 to 600.

[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 Epiclon 830, Epiclon 830-S, Epiclon 835, Epiclon 840, Epiclon 840-S, Epiclon 850, Epiclon 850-S, and Epiclon 850-LC manufactured by DIC Corporation.

[0028] The (A) epoxy compound may be used alone or in combination of two or more types, but it is preferable to use both an alicyclic epoxy compound and a bisphenol diglycidyl ether. This makes it easy to adjust the physical properties of the cured product of the photocationically curable adhesive, such as the linear expansion coefficient, storage modulus, and glass transition temperature. The blending ratio of the alicyclic epoxy compound to the bisphenol diglycidyl ether is not particularly limited, but the mass ratio of the alicyclic epoxy compound to the bisphenol diglycidyl ether is preferably within a range of 1:1 to 6:1, and more preferably within a range of 3:1 to 4:1. This makes it easy to adjust the linear expansion coefficient, storage modulus, glass transition temperature, and other properties of the cured product to values ​​desirable for a 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 any compound having one or more oxetane groups in the molecule without any particular limitations. Oxetane compounds have a faster propagation reaction rate than epoxy compounds, so including an oxetane compound in the photocationically curable adhesive allows the polymerization reaction to proceed efficiently when the photocationically curable adhesive is cured. This reduces the brittleness inherent 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 terms of the balance between the curing speed and the physical properties of the cured product, the mass ratio of the epoxy compound (A):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 (C) silane coupling agent. By including a (C) silane coupling agent, the adhesive properties of the photocationically curable adhesive can be improved. The (C) silane coupling agent is not particularly limited and known substances 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 (A) epoxy compound and the (B) oxetane compound, it is particularly preferable to use 3-glycidoxypropyltrimethoxysilane. These may be used alone or in combination of two or more types.

[0033] The amount of (C) silane coupling agent in the photocationically curable adhesive of the present invention is not particularly limited, but in order to ensure high adhesion, it 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, relative to 100 parts by mass of the total amount of (A) epoxy compound and (B) oxetane compound.

[0034] (D) Photoacid Generator The photocationically curable adhesive of the present invention contains (D) a photoacid generator. The (D) photoacid generator 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] The photoacid generator (D) 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 onium salts 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 cations include compounds represented by the following formulas (4a) and (4b):

[0037]

[0038] The anion of the onium salt has the general formula: LM ｂ Z ｃ － L is a metal or a semimetal, and examples thereof 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 thereof 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 thereof include CF ３ , C ２ F ５ , C ３ F ７, C ６ F ５ and the like. c is an integer of 0 to 4.

[0039] As the anion of the onium salt, for example, tetrakis(pentafluorophenyl)borate (B(C ６ F ５ ) ４ － ), tetrakis(3,5-difluoro-4-methoxyphenyl)borate, tetrafluoroborate (BF ４ － ), tris(pentafluoroethyl)trifluorophosphate (PF ３ (C ２ F ５ ) ３ － ), hexafluorophosphate (PF ６ － ), hexafluoroantimonate (SbF ６ － ), hexafluoroarsenate (AsF ６ － ), hexachloroantimonate (SbCl ６ － ) etc.

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

[0041]

[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 this 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 present invention is characterized in that the ratio (D90-D10) / g and (D50) / g are 0.7 or less. By including such silica, it is possible to reduce the storage modulus of the cured product of the photocationically curable adhesive. The reason for this is not clear, but the present inventors believe it to be as follows.

[0044] That is, when silica (E) 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 thereby lower the linear expansion coefficient of the cured product of the photocationically curable adhesive, but on the other hand, an increase in the relatively hard silica component results in an increase in the storage modulus. 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 silica (E) blended in the photocationically curable adhesive of the present invention has a small (D90-D10) / D50 of 0.7 or less, and has a highly uniform particle size distribution. In such silica with a highly uniform particle size distribution, the BET specific surface area, a parameter correlated with particle size, is 25 m ２ / g or less means that there is little fine powder with an extremely small particle size. Since the particle size distribution is highly uniform and there is little fine powder, the silica is less likely to be densely packed, and the BET specific surface area is 25 m ２ / g or less, the amount of resin that interacts with the silica surface is small, so it is presumed that the free resin area in the cured product of the photocationically curable adhesive increases, and stress is more easily alleviated when stress is applied. Furthermore, the particle size distribution is highly uniform, and the BET specific surface area is 5 m 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 exists 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 or more, 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 silicas are used, even if the proportion of silica in the photocationically curable adhesive is the same, and as a result, it is presumed that it will be easier to provide a photocationically curable adhesive with a low linear expansion coefficient and a low storage modulus.

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

[0046] The (D90-D10) / D50 of (E) silica is 0.7 or less, preferably 0.6 or less, and more preferably 0.5 or less. When (D90-D10) / D50 is in the above range, it becomes easy to reduce the storage modulus of the cured product of the photocationically curable adhesive. Although there are no particular restrictions on the lower limit of (D90-D10) / D50, it is generally 0.2 or more, and particularly 0.3 or more.

[0047] In this specification, D10, D50, and D90 are particle sizes at which the cumulative volume is 10%, 50%, and 90%, respectively, in a particle size distribution curve obtained by laser diffraction. Specifically, 100 mg of silica is dispersed in 40 ml of water, and the dispersion is dispersed for 10 minutes using a homogenizer at an output of 40 W to obtain a sample. The particle size distribution of the sample is measured using a laser diffraction particle size distribution analyzer, 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 (E) silica is not particularly limited, but is preferably spherical. By being spherical, the viscosity is less likely to increase even when silica is highly loaded, and high fluidity can be ensured. In the present invention, "spherical" means that the shapes of 1,000 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. The sphericity is calculated as 4π x (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. This makes it easier for the silica to exist independently in the photocationically curable adhesive without agglomeration, making stress concentration less likely to occur, and 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 the ratio (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 x D50), and the density of silica is 2.2 g / cm. ３ It is calculated as follows.

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

[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 the epoxy compound (A) and the oxetane compound (B). By setting the amount of silica (E) in this range, it becomes easy to achieve a low linear expansion coefficient. Furthermore, 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 the epoxy compound (A) and the oxetane compound (B). Setting the amount of silica (E) in this range makes it possible to maintain a low linear expansion coefficient while suppressing an increase in viscosity and increasing fluidity, thereby improving workability during use, and facilitating adjustment to desirable physical properties for a photocationically curable adhesive used in a camera module or an on-board 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 produced by burning a silicon compound and grown in or near the flame. Examples of dry methods include the method described in WO 2020 / 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. The flame combustion conditions can be controlled to increase the oxygen content of the entire flame, thereby reducing the BET specific surface area and (D90-D10) / D50. The flame cooling conditions can be controlled to slow the flame cooling rate, thereby reducing the BET specific surface area and (D90-D10) / D50. The BET specific surface area can be reduced and (D90-D10) / D50 can be reduced by reducing the heat removal amount. 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] An example of a wet method is the sol-gel method described in WO 2018 / 096876. The sol-gel method involves hydrolyzing and polycondensing silicon alkoxide in a reaction medium consisting of water and an organic solvent containing a catalyst to produce a silica sol, which is then gelled. The resulting solid is then removed and dried to produce a silica powder. In the sol-gel method, the BET specific surface area and particle size distribution can be adjusted by adjusting the reaction temperature, reaction solution concentration, and reaction solution drop rate. For example, lowering the reaction temperature can reduce the BET specific surface area and (D90-D10) / D50. Lowering the reaction solution concentration can reduce the BET specific surface area and (D90-D10) / D50. Slowing the reaction solution drop rate can reduce the BET specific surface area and (D90-D10) / D50. 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 may be used after adjusting the BET specific surface area and particle size distribution to desired ranges by sieving or air classification.

[0057] The silica (E) 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 using a known surface treatment agent by a known method.

[0058] (Other Components) 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 other components include fillers other than silica, thermal cationic polymerization initiators, curing accelerators, flame retardants, rubber particles, thickeners, antifoaming agents, leveling agents, antioxidants, and colorants.

[0059] (Physical properties of cured body of photocationically curable adhesive) The cured body of the photocationically curable adhesive of the present invention preferably has a storage modulus of 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 reducing the storage modulus of the cured body, it is possible to increase the flexibility of the adhesive site, and when fixing components of a camera module or an on-board optical sensor, it is possible to mitigate the mechanical effects associated with changes in the usage environment and easily suppress displacement or detachment of the components. The lower the storage modulus of the cured body of the photocationically curable adhesive of the present invention, the better, but it is generally 4 GPa or more, particularly 5 GPa or more.

[0060] The cured product of the photocationically curable adhesive of the present invention preferably has a linear expansion coefficient of 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, thermal expansion / contraction caused by temperature changes at the bonded site is reduced during the manufacture of camera modules or on-board optical sensors, or when exposed to thermal effects caused by changes in the usage environment, making it easier to suppress misalignment or detachment of parts. The lower the linear expansion coefficient of the cured product of the photocationically curable adhesive of the present invention, the better, but it 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 external environments. 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 structures and compounding ratios 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. This makes it easier to lower the storage modulus while decreasing the linear expansion coefficient by increasing the silica content, and also increases the degree of freedom in designing components other than (E) silica, making it easier to adjust the physical properties of the photocationically curable adhesive to desired ranges.

[0063] (Method for producing photocationically curable adhesive) The method for producing the photocationically curable adhesive of the present invention is not particularly limited, and the adhesive can be produced by mixing the components by a known method using a blender, mixer, or the like. During the mixing, the components may be added simultaneously to a mixer or the like and mixed, or the components may be added sequentially to a mixer or the like and mixed. The order of addition is not particularly limited. Furthermore, the mixing may be carried out under heating, or in a controlled atmosphere such as an inert gas atmosphere, if necessary.

[0064] (Uses of Photo-Cationic Curable Adhesive) The photo-cationic curable adhesive of the present invention can have a low storage modulus, and in particular, a low coefficient of linear expansion and a low storage modulus. Therefore, it can be suitably used for bonding and fixing components in camera modules for in-vehicle applications, such as smartphones, which require high dimensional accuracy. Similarly, it can be suitably used for bonding the camera module to a housing in an in-vehicle optical sensor equipped with a camera module. By using the photo-cationic curable adhesive of the present invention to fix components in a camera module or to bond the camera module to a housing, it is possible to mitigate the effects of changes in the usage environment and easily prevent component misalignment or detachment. Furthermore, the low coefficient of linear expansion also makes it easy to improve dimensional accuracy when fixing components during manufacturing.

[0065] (Camera Module and On-Vehicle Optical Sensor) 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] Automotive optical sensors are installed in vehicles to detect information such as surrounding obstacles. Information obtained by automotive optical sensors is used to issue warnings to the driver and control the vehicle, so high reliability is required. As shown in FIG. 1 , an automotive optical sensor 1 generally comprises a camera module, which is composed of components such as a lens 2, a lens barrel 3, an imaging element 5, a seal glass 4, and a circuit board 6, and is 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 misaligns, the resolution, angle of view, optical axis, flange back, etc. may shift, which can cause a decrease in optical performance. Therefore, it is necessary to fix the lens with high dimensional accuracy during manufacturing, and during use, it is necessary to prevent the lens from shifting or becoming detached due to thermal and mechanical influences associated with environmental changes. The photocationically curable adhesive of the present invention has a small storage modulus, excellent flexibility, and a low linear expansion coefficient, and therefore can be suitably used for bonding lenses and lens barrels that require such properties.

[0068] The lens barrel 3 and the circuit board 6 on which the image sensor 5 is mounted are fixed using an adhesive. Misalignment between the lens barrel and the circuit board can result in misalignment between the lens and the image sensor, potentially causing optical axis misalignment and focus shifts. Therefore, during manufacturing, it is necessary to fix the lens barrel and the circuit board with high dimensional accuracy, and during use, it is necessary to prevent misalignment or separation between the lens barrel and the circuit board due to thermal and mechanical influences associated with environmental changes. The photocationically curable adhesive of the present invention has a low storage modulus, excellent flexibility, and a low linear expansion coefficient, making it suitable for use in bonding lens barrels and circuit boards where these properties are required.

[0069] The imaging element 5 mounted on the circuit board 6 is fixed to the circuit board 6 using an adhesive. Misalignment of the imaging element on the circuit board can result in misalignment between the lens and the imaging element, potentially causing misalignment of the optical axis or focus. Therefore, during manufacturing, it is necessary to fix the imaging element to the circuit board with high dimensional accuracy, and during use, it is necessary to prevent misalignment or separation between the imaging element and the circuit board due to thermal and mechanical influences associated with environmental changes. The photocationically curable adhesive of the present invention has a low storage modulus, excellent flexibility, and a low linear expansion coefficient, making it suitable for use in bonding imaging elements and circuit boards, which require such properties.

[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. Misalignment or detachment of the seal glass reduces the protective function of the image sensor, causing damage to the image sensor. The seal glass may also function as an optical filter. Examples of optical filters include infrared cutoff filters designed to remove specific frequency components. Misalignment or detachment of the infrared cutoff filter prevents proper filtering and results in color anomalies. Therefore, it is necessary to prevent misalignment or detachment of the seal glass due to thermal and mechanical effects associated with environmental changes during use. The photocationically curable adhesive of the present invention has a low storage modulus, excellent flexibility, and a low linear expansion coefficient, making it suitable for use in bonding seal glass and lens barrels, which require these properties.

[0071] Enclosing the camera module in the housing 7 protects the camera module from external impacts during distribution and use and facilitates installation in vehicles, etc. When the camera module is housed in the housing, the exterior of the camera module's lens barrel is fixed to the housing using an adhesive. Misalignment or detachment between the camera module and the housing can cause errors in determining the size of an imaged object and the distance to the object when the camera module is mounted on a vehicle or other device for use. Furthermore, the camera module may not be adequately protected from external impacts during distribution and use. Therefore, it is necessary to fix the camera module and the housing with high dimensional accuracy during manufacturing, and it is necessary to prevent misalignment or detachment between the camera module and the housing due to thermal and mechanical influences associated with environmental changes during distribution and use. The photocationically curable adhesive of the present invention has a low storage modulus, excellent flexibility, and a low linear expansion coefficient, making it suitable for use in bonding camera modules and housings where such properties are required.

[0072] The photocationically curable adhesive of the present invention can be used to bond and fix components in a camera module or to bond a camera module to a housing, without any particular limitations. Known methods can be used. For example, the photocationically curable adhesive can be applied to the bonding surface of an object to be bonded, then placed on the bonding surface of another object to be bonded, and then irradiated with ultraviolet light to cure the photocationically curable adhesive. UV irradiation may be performed by first irradiating the object with low-intensity UV light to temporarily fix the object, and then irradiating with high-intensity UV light to permanently fix the object. Subsequently, thermal curing may be performed to promote post-cure and relieve thermal distortion caused by UV irradiation, thereby increasing adhesive strength. The conditions for the thermal curing are not particularly limited, but may be, for example, 50 to 150°C for 0.5 to 5 hours.

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

[0074] (A) Epoxy compounds 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 compounds B-1: OXT-101 (manufactured by Toagosei Co., Ltd.) (C) Silane coupling agents C-1: 3-glycidoxypropyltrimethoxysilane (D) Photoacid generator D-1: Compound D-1 shown below

[0075]

[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 (manufactured by Tokuyama, BET specific surface area: 15 m ２ / g, D50: 0.16 μm, (D90-D10) / D50: 0.58) E-3: Sunseal SS-03 (manufactured by Tokuyama, BET specific surface area: 11 m ２ / g, D50: 0.33 μm, (D90-D10) / D50: 0.43) E-4: Sunseal SS-04 (manufactured by Tokuyama, BET specific surface area: 8 m 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: Sunseal 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> 100 mg of silica was dispersed in 40 ml of water and irradiated with ultrasonic waves at about 40 W for 10 minutes to obtain a dispersed sample, and the particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (LS13 320, manufactured by Beckman Coulter, Inc.). In the obtained volume frequency distribution of particle sizes (particle size distribution), the volume frequencies were accumulated from the smallest particle size, and the particle size at which the cumulative value reached 10% was defined as D10, the particle size at which the cumulative value reached 50%, and the particle size at which the cumulative value reached 90% was defined as D90.

[0078] <Measurement of BET Specific Surface Area> The BET specific surface area was determined by the BET method (single-point nitrogen adsorption method) using a rapid surface area analyzer (SA-1000 manufactured by Shibata Scientific Co., Ltd.) 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] <Confirmation of Sphericity> The sphericity was determined by observing the shapes of 1,000 silica particles with a scanning electron microscope (SEM), measuring the sphericity of each particle, and calculating the average value. The measurement was performed using an image processing program (AnalySIS manufactured by Soft Imaging System GmbH). The sphericity was calculated as 4π × (area) / (perimeter). ２ It was calculated by:

[0080] <Measurement of Linear Expansion Coefficient> The photocationically curable adhesives prepared in the Examples and Comparative Examples were poured into a PTFE mold capable of producing a block-shaped cured product, and then irradiated with ultraviolet light from both the top and bottom for 5 minutes each, followed by heat treatment at 100°C for 1.5 hours to cure. This was then polished and shaped to obtain a cured product measuring 12 mm x 6 mm x 5.5 mm. The obtained cured product was measured using a thermomechanical analyzer (NETZSCH: TMA4000SE) by the compression load method, 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 (the 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 product, and then irradiated with ultraviolet light from both the top and bottom for 5 minutes each, followed by heat treatment at 100°C for 1.5 hours to cure. This was then polished and shaped to produce a cured product measuring 25 mm x 5 mm x 1 mm. The resulting cured product was measured in tensile measurement mode using a dynamic viscoelasticity measuring device (NETZSCH: DMA 242 E Artemis) with a sample length (chuck distance) of 10 mm, a frequency of 1 Hz, 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] <Glass Transition Temperature> The photocationically curable adhesives prepared in the Examples and Comparative Examples were poured into a PTFE mold capable of producing a rectangular cured product, and then irradiated with ultraviolet light from both the top and bottom for 5 minutes each, followed by heat treatment at 100°C for 1.5 hours to cure. This was then polished and shaped to produce a cured product measuring 25 mm x 5 mm x 1 mm. The resulting cured product was measured in tensile measurement mode using a dynamic viscoelasticity measuring device (NETZSCH: DMA 242 E Artemis) with a sample length (chuck distance) of 10 mm, a frequency of 1 Hz, 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 ratio.

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

[0084] Example 1 A photocationically curable adhesive was obtained by measuring and mixing (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. The physical properties of the silica used and the evaluation results of the physical properties of the cured product of the photocationically curable adhesive are shown in Table 1.

[0085] Examples 2 to 4, Comparative Examples 1 and 2 Photocationically curable adhesives were 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 physical properties of the silica used and the evaluation results of the physical properties of the cured product of the photocationically curable adhesive.

[0086]

[0087] Regarding the evaluation results, (E) the BET specific surface area of ​​the silica is 5 to 25 m ２ / g, and Examples 1 to 4 in which (D90-D10) / D50 is 0.7 or less are the same as Comparative Example 1 in which the silica has a (D90-D10) / D50 of more than 0.7, and the same as Comparative Example 1 in which the silica has a BET specific surface area of ​​5 m ２ / g, the thermal expansion coefficient was almost the same as that of Comparative Example 2, which had a storage modulus of less than 1 / g. 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.

[0088] REFERENCE SIGNS LIST 1 In-vehicle optical sensor 2 Lens 3 Lens barrel 4 Seal glass 5 Imaging element 6 Circuit board 7 Housing

Claims

1. A composition comprising (A) an epoxy compound, (B) an oxetane compound, (C) a silane coupling agent, (D) a photoacid generator, and (E) silica, wherein the silica has a BET specific surface area of ​​5 to 25 m ２ / g, and (D90-D10) / D50 are 0.7 or less.

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