JP2024057640A - Photocurable gasket resin composition - Google Patents

Abstract

[Problem] To provide a photocurable gasket resin composition that has good workability even without containing a silica component, has good curability and low moisture permeability, and can be used as a cured in place gasket (CIPG) that easily ensures stable sealing properties. [Solution] The photocurable gasket resin composition contains acryloyl-terminated polyisobutylene, C8-18 monofunctional alkyl (meth)acrylate monomer, polyethylene powder, calcium carbonate, polyfunctional thiol, and a photopolymerization initiator, and is characterized by not containing a silica component. [Selected Figures] None

Description

The present invention relates to a photocurable gasket resin composition suitable as a resin for on-site formed gaskets that cures with light such as ultraviolet light.

Sealants (gaskets) are used for various purposes in electronic devices such as liquid crystal devices, battery units such as solar cells and fuel cells, and optical communication units such as optical fibers. For example, in precision electronic devices, they are used to protect the parts stored inside the device from external dust and moisture, and in battery units, they provide a gas barrier to prevent the leakage of fuel gas and oxygen gas, and to prevent the intrusion of external moisture.

Recently, there has been a demand for advanced sealing functions to improve reliability, and cured-in-place gaskets (CIPGs), in which an uncured liquid is applied to the area to be sealed and then cured, are becoming more common. CIPGs are viscous fluids before curing, so in order to improve their flow properties, various inorganic fillers are often blended into the composition. In particular, fumed silica, which improves thixotropy and prevents sagging after application, is used in many compositions (for example, Patent Document 1).

Currently, there are few problems with the availability of fumed silica in the domestic market, but many of its suppliers are overseas manufacturers, and the market share of the top three overseas manufacturers is said to be at about 80%. In recent years, sudden production halts and logistics delays due to infectious disease epidemics such as COVID-19, energy issues caused by overseas conflicts, and even trade restrictions due to intensifying conflicts between countries have led to situations in which supply chains have been suddenly disrupted, something that would have been unthinkable a few years ago. From the perspective of BCP, it has become an important issue to consider alternative materials, especially for raw materials that are mainly produced overseas. Regarding CIPG, there are cases where a composition with the same level of physical properties without containing fumed silica is required, leaving room for improvement.

Patent No. 6865792

The present invention aims to provide a photocurable gasket resin composition that has good workability even without silica components, has good curing properties, and can be used as a CIPG that has low moisture permeability and can easily ensure stable sealing properties after curing.

In order to solve the above problems, the invention described in claim 1 provides a photocurable gasket resin composition that contains acryloyl-terminated polyisobutylene (A), C8-18 monofunctional alkyl (meth)acrylate monomer (B), polyethylene powder (C), calcium carbonate (D), multifunctional thiol (E), and photopolymerization initiator (F), and is characterized by not containing any silica component.

The invention described in claim 2 provides the photocurable gasket resin composition described in claim 1, characterized in that (D) is surface-treated light calcium carbonate and has an average particle size of 10 to 500 nm.

The invention described in claim 3 provides a photocurable gasket resin composition according to claim 1 or 2, characterized in that the blending amount of (D) is 3 to 40% by weight based on the total solid content of the composition.

The invention described in claim 4 provides a photocurable gasket resin composition according to claim 1 or 2, characterized in that the amount of (C) is 5 to 35% by weight based on the total solid content of the composition.

The invention described in claim 5 provides a photocurable gasket resin composition according to claim 1 or 2, characterized in that (B) contains an alicyclic skeleton (meth)acrylate (b1) and a linear alkyl (meth)acrylate (b2).

The present invention has good workability even without the silica component, good curing properties, and the cured product has low moisture permeability and stable sealing properties, making it useful as a photocurable resin composition for CIPG.

The present invention will be described in detail below.

The composition of the present invention is composed of acryloyl-terminated polyisobutylene (A), C8-12 monofunctional alkyl (meth)acrylate monomer (B), polyethylene powder (C), calcium carbonate (D), polyfunctional thiol (E), and photopolymerization initiator (F). In this specification, (meth)acrylate includes both acrylate and methacrylate. Also, "silica-free" means that silica components are not intentionally blended to achieve a specific purpose, and does not mean that even trace amounts of silica components contained in each blended component are excluded, and refers to the amount of silica blended being 5% by weight or less, typically 1% by weight or less.

The acryloyl-terminated polyisobutylene (A) of the present invention is a base oligomer constituting a gasket resin, and is not particularly limited as long as it is a polymer having a polyisobutylene skeleton containing a -[ _CH2C ( _CH3 ) ₂ ]- unit. It is an excellent polymer that has high curability by irradiation with light, excellent heat resistance and weather resistance, a large tensile breaking strain compared to oligomers having a butadiene skeleton, and also has high gas barrier properties and low water vapor permeability.

The viscosity of (A) at 23°C measured with an E-type viscometer is preferably 100 to 10,000 Pa·s, more preferably 500 to 5,000 Pa·s, and particularly preferably 1,000 to 4,000 Pa·s. A viscosity of 100 Pa·s or more ensures sufficient cohesive strength, while a viscosity of 10,000 Pa·s or less makes it easier to adjust the viscosity to suit workability. A commercially available product is EP400V (product name: manufactured by Kaneka Corporation, acryloyloxy groups at both ends, viscosity 3,500 Pa·s/23°C).

The amount of (A) is preferably 10 to 55% by weight, more preferably 15 to 50% by weight, and particularly preferably 20 to 48% by weight, based on the total solid content, in consideration of the balance between the moisture permeability of the cured product and the properties of the composition. By making it 10% by weight or more, sufficient gas barrier properties and low moisture permeability can be ensured, and by making it 55% by weight or less, it is easy to adjust the viscosity to suit workability.

The monofunctional alkyl (meth)acrylate monomer (B) used in the present invention is blended to dilute (A) and at the same time improve photocuring reactivity. The alkyl number is C8 to 18, preferably C8 to C16, and more preferably C8 to C14. If it is less than C8, the flexibility of the cured product may decrease, and if it is more than C18, the curability tends to decrease. In particular, to improve the sealability, it is preferable to contain a C8 to 18 (meth)acrylate (b1) with an alicyclic skeleton having high rigidity and/or a linear alkyl (meth)acrylate (b2) with a good balance between curability and flexibility.

The ratio of (B) to the total solid content is preferably 5 to 50% by weight, more preferably 10 to 45% by weight, and particularly preferably 15 to 42% by weight. By making it 5% by weight or more, sufficient curing properties can be ensured, and by making it 50% by weight or less, sufficient gas barrier properties and low moisture permeability can be ensured.

Examples of (b1) include dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, adamantanyl (meth)acrylate, and cyclohexyl (meth)acrylate, and may be used alone or in combination of two or more. Among these, dicyclopentenyl-based (meth)acrylates are preferred, as they can increase the elastic modulus of the cured film.

Examples of (b2) include 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, and stearyl (meth)acrylate, which may be used alone or in combination of two or more. Among these, n-octyl acrylate is preferred because it has a low Tg and good compatibility with (A).

When (b1) and (b2) are used in combination, the ratio of (b1) to the total amount of (B) is preferably 30 to 95% by weight, more preferably 40 to 80% by weight, and particularly preferably 50 to 70% by weight. By setting it to 30% by weight, sufficient rigidity can be ensured, and by setting it to 95% by weight or less, sufficient gas barrier properties and low moisture permeability can be ensured.

The polyethylene powder (C) used in the present invention is blended for the purpose of suppressing stickiness of the cured coating surface and reducing the dynamic friction coefficient. In terms of excellent wear resistance and self-lubrication, it is preferable to use ultra-high molecular weight polyethylene with a molecular weight of 1 million to 7 million. In addition, in order to make the unevenness of the cured surface finer, the average particle size is preferably 10 to 50 μm, and more preferably 15 to 40 μm (Coulter counter method).

The amount of (C) is preferably 5 to 35% by weight, more preferably 8 to 30% by weight, and particularly preferably 10 to 25% by weight, based on the total solid content. By making it 5% by weight or more, sufficient slipperiness can be ensured, and as a result, the dynamic friction coefficient can be reduced, and by making it 35% by weight or less, appropriate hardness and distortion characteristics can be ensured. An example of a commercially available product is Mipelon (product name: ultra-high molecular weight polyethylene, manufactured by Mitsui Chemicals, Inc.).

The calcium carbonate (D) used in the present invention is blended in for the purpose of imparting thixotropy to the composition. In CIPG, which forms a sealing layer on a component, it is necessary to apply a liquid resin to a height that is useful as a sealing material and to maintain that shape until it hardens, and this can be achieved by blending (D) into the liquid composition to impart thixotropy. There are two types of calcium carbonate: light calcium carbonate, which is chemically produced, and heavy calcium carbonate, which is physically crushed and broken into pellets. Light calcium carbonate is preferred because it has uniform particle size and shape and contains fewer impurities.

The (D) is preferably surface-treated in terms of compatibility with the (A) to (C) components and excellent thixotropy even at low viscosity. For example, surface treatment with a fatty acid can be used. The BET specific surface area is preferably 5 to 50 m ² /g, more preferably 10 to 40 m ² /g, and particularly preferably 15 to 35 m ² /g. By making it 5 m ² /g or more, sufficient thixotropy can be imparted, and by making it 50 m ² /g or less, sufficient viscosity increase can be suppressed. The BET specific surface area is measured according to the JPCS test method established by the Japan Light Calcium Carbonate Industry Association.

The average primary particle diameter of (D) is preferably 10 to 500 nm, more preferably 20 to 300 nm, and particularly preferably 20 to 150 nm. By adjusting the amount within this range, sufficient thixotropy can be imparted even with a small amount. The average particle diameter was measured by observation with a scanning electron microscope. Commercially available products include Hakuenka CC (product name: manufactured by Shiraishi Kogyo Co., Ltd., fatty acid surface-treated light calcium carbonate, average primary particle diameter 50 nm, BET specific surface area 26 ^m2 /g), etc.

The amount of (D) is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, and particularly preferably 15 to 30% by weight, based on the total solid content. By making it 3% by weight or more, it is possible to impart sufficient thixotropy, and by making it 40% by weight or less, it is easy to control the viscosity to a level suitable for workability.

The multifunctional thiol (E) used in the present invention is blended for the purpose of improving the photocurability of the composition. Since an enethiol reaction that can suppress the inhibition of curing by oxygen is possible, the reactivity is improved and the elongation of the cured film can also be improved. For example, bifunctional thiols include 1,4 bis (3-mercaptobutyryloxy) butane and tetraethylene glycol bis (3-mercaptopropionate), trifunctional thiols include 1,3,5 tris (3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6-trione and trimethylolpropane tris (3-mercaptopropionate), and tetrafunctional thiols include pentaerythritol tetrakis (3-mercaptobutyrate) and pentaerythritol tetrakis (3-mercaptopropionate), and these can be used alone or in combination of two or more. Of these, secondary multifunctional thiols that have a good balance between reactivity and storage stability are preferred.

The amount of (E) is preferably 0.5 to 5% by weight, more preferably 0.8 to 3% by weight, and particularly preferably 1.0 to 2.0% by weight, based on the total solid content. The amount is preferably 1 to 8 parts by weight, more preferably 2 to 5 parts by weight, based on 100 parts by weight of radically polymerizable components. By keeping the amount within this range, the photoreaction can be improved and a sufficient elongation rate of the cured film can be ensured. A commercially available product is Karenz MT-BD1 (product name: 1,4 bis (3-mercaptobutyryloxy) butane, manufactured by Showa Denko KK).

The photopolymerization initiator (F) used in the present invention generates radicals when irradiated with ultraviolet light or an electron beam, and these radicals trigger the polymerization reaction. General-purpose photopolymerization initiators such as benzyl ketal, acetophenone, and phosphine oxide types can be used. By arbitrarily selecting the light absorption wavelength of the polymerization initiator, it is possible to impart curability over a wide wavelength range from the ultraviolet region to the visible light region. Specifically, benzyl ketals include 2.2-dimethoxy-1.2-diphenylethan-1-one, α-hydroxyacetophenones include 1-hydroxy-cyclohexyl-phenyl-ketone and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, α-aminoacetophenones include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, and acylphosphine oxides include 2.4.6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2.4.6-trimethylbenzoyl)-phenylphosphine oxide, which can be used alone or in combination of two or more.

Among the (F) above, it is preferable to use an α-hydroxyacetophenone type that is less prone to yellowing, and examples of commercially available products include Omnirad 127, 184, and 2959 (product names: manufactured by IGM Resins). The amount of (B) added per 100 parts by weight of the radically polymerizable component is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 8 parts by weight.

In the present invention, it is preferable to further blend an antioxidant. The antioxidant is a compound that efficiently traps radicals and can improve storage stability. Examples of antioxidants include hindered phenols, hindered amines, phosphorus, and sulfur-based antioxidants, which can be used alone or in combination of two or more. Among these, it is preferable to include a hindered phenol or hindered amine. When blending an antioxidant, the blending amount relative to the total solid content is preferably 0.5 to 5 wt%, and more preferably 1 to 4 wt%. By keeping it within this range, storage stability can be further improved. Commercially available products include Irganox 1010 (product name: manufactured by BASF Japan, hindered phenol) and Tinuvin 249 (product name: manufactured by BASF Japan, hindered amine).

If necessary, additives such as silane coupling agents, colorants, thermal polymerization initiators, defoamers, flame retardants, leveling agents, dispersants, polymerization inhibitors, phosphate esters, and organic fine particles can also be used in this composition.

The photocurable gasket resin composition of the present invention is used by applying it onto a member and then curing it by irradiation with light such as ultraviolet light to form a sealing layer. Known light sources such as high pressure mercury lamps, medium pressure mercury lamps, low pressure mercury lamps, metal halide lamps, xenon lamps, LED lamps, and electrodeless ultraviolet lamps can be used as light sources, and examples of ultraviolet irradiation conditions include an irradiation intensity of 50 mW/ ^cm2 to 3,000 mW/ ^cm2 and an integrated light quantity of 500 mJ/ ^cm2 to 10,000 mJ/ ^cm2 .

The moisture permeability of the sealing layer obtained by curing the photocurable gasket resin composition of the present invention at 60°C and 90% RH according to JIS Z0208 is preferably 40 g/ ^m2 ·24h or less, and more preferably 30 g/ ^m2 ·24h or less. If the cured product is within this range, the permeation of moisture and foreign matter from the sealing layer can be suppressed, and the cured product can be used sufficiently as a CIPG.

The present invention will be described in detail below based on examples and comparative examples, but these are specific examples and are not intended to be limiting. Unless otherwise specified, measurements were performed under conditions of room temperature of 25°C and relative humidity of 65%.

Examples 1 to 7
As the (A) there was used EPION EP400V (trade name: acryloyl-terminated polyisobutylene, manufactured by Kaneka Corporation), as the (b1) there was used FA-512AS (trade name: dicyclopentenyloxyethyl acrylate, manufactured by Hitachi Chemical Co., Ltd.), as the (b2) there was used NOAA (trade name: n-octyl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.), as the (C) there was used Mipelon XM-200 (trade name: Mitsui Chemicals, Inc., average molecular weight 2 million, average particle size as measured by the Coulter counter method 30 μm), as the (D) there was used Hakuenka CC (trade name: light calcium carbonate with fatty acid surface treatment, average primary particle size 4 0 nm), (E) Karenz MT-BD1 (product name: Showa Denko K.K., 1,4-bis(3-mercaptobutyryloxy)butane), (F) Omnirad 184 (product name: IGM Corporation, α-hydroxyacetophenone type), and as antioxidants Tinuvin 249 (product name: BASF Japan Ltd., hindered amine type) and Irganox 1010 (product name: BASF Japan Ltd., hindered phenol type) were mixed in the formulation shown in Table 1 until uniformly dissolved to prepare the photocurable gasket resin compositions of Examples 1 to 7.

Comparative Examples 1 to 4
In addition to the materials used in the examples, UV-3700B (product name: urethane acrylate, Mw 38000, manufactured by Mitsubishi Chemical Corporation) was used as an acrylic oligomer. The photocurable gasket resin compositions of Comparative Examples 1 to 4 were prepared by stirring until uniformly dissolved in the formulation shown in Table 2.

Table 1

Table 2

The evaluation method was as follows:

Viscosity/TI value: Using a cone-plate viscometer RE-215R manufactured by Toki Sangyo Co., Ltd., measurements were taken at 25±1°C with a cone angle of 3°×R7.7 and rotation speeds of 10 rpm and 1 rpm, and the ratio of these values was taken as the thixotropic value (TI value). If the viscosity was outside the measurement range, the rotation speed was lowered from 1 rpm to 0.1 rpm so that the viscosity was within the measurable range from 10 rpm, and the ratio of this value to the viscosity value measured at one-tenth the rotation speed was taken as the TI value.
The TI value was evaluated as follows: less than 1.5 was x, 1.6 to 2.5 was ◯, and more than 2.5 was ⊚.

Surface curability: The composition prepared above was filled to the brim into a dedicated mold (made of PP, 6 mmT, Φ26 mm) and cured using a UV irradiation device UV LIGHT HAMMER 6D bulb manufactured by FUSIONUV System under conditions of an irradiation intensity of 300 mw/ ^cm2 and an accumulated light quantity of 6,000 mJ/ ^cm2 . The tackiness of the surface was evaluated by touching with a finger. A mark of O was given when there was no tackiness, and a mark of × was given when tackiness remained.

Compression set: The composition prepared above was applied to a release PET film to a thickness of 2 mm, and cured using a UV irradiation device UV LIGHT HAMMER 6D bulb manufactured by FUSIONUV System under conditions of irradiation intensity 300 mw/cm ² and cumulative light amount 6,000 mJ/cm ^2. This was cut into a width of 5 mm x length of 15 mm, compressed and fixed between SUS plates with a 1 mm spacer, and aged at 80° C. for 16 hours. After removing from the test piece after a predetermined time, those with large cracks or those with three or more cracks of 1 mm or more were rated as ×, those with less than two cracks less than 1 mm in length were rated as ◯, and those without cracks were rated as ◎.

Moisture permeability: Measurement was performed according to JIS Z0208. The UV irradiation conditions were 300 mw/ ^cm2 irradiation intensity and 6,000 mJ/ ^cm2 cumulative light quantity using the above irradiation device, and the measurement conditions were 60°C/90% RH environment in which a 1 mm thick sample was left for 24 hours, and the moisture permeability was calculated from the weight change. The evaluation was as follows: less than 30 g/ ^m2 ·24h = ◎, 30-40 g/ ^m2 ·24h = ○, and more than 40 g/ ^m2 ·24h = ×.

Example evaluation results <br/> Table 3

Comparative Example Evaluation Results <br/> Table 4

The examples were excellent with no problems in terms of TI value, surface hardening, compression set, or moisture permeability.

On the other hand, Comparative Example 1 not containing (C) had poor surface curing properties, Comparative Example 2 not containing (D) had a low TI value and also had poor surface curing properties, Comparative Example 3 not containing (E) had poor compression set, and Comparative Example 4 using a binder other than (A) had high moisture permeability, all of which were not suitable for the present invention.

Claims (5)

A photocurable gasket resin composition comprising acryloyl-terminated polyisobutylene (A), C8-18 monofunctional alkyl (meth)acrylate monomer (B), polyethylene powder (C), calcium carbonate (D), multifunctional thiol (E), and photopolymerization initiator (F), and containing no silica component. The photocurable gasket resin composition according to claim 1, characterized in that (D) is surface-treated light calcium carbonate and has an average particle size of 10 to 500 nm. The photocurable gasket resin composition according to claim 1 or 2, characterized in that the amount of (D) is 3 to 40% by weight based on the total solid content of the composition. The photocurable gasket resin composition according to claim 1 or 2, characterized in that the amount of (C) is 5 to 35% by weight based on the total solid content of the composition. 3. The photocurable gasket resin composition according to claim 1, wherein the (B) contains an alicyclic skeleton (meth)acrylate (b1) and a linear alkyl (meth)acrylate (b2).