JPH0160072B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thixotropic ultraviolet curing adhesive composition which is rich in thixotropic properties and has improved sag, stringiness and flow (spreading) during coating operations. In recent years, as evidenced by the development trend of ultraviolet curable adhesives, the use of chemical reactions caused by ultraviolet light has become popular in photosensitive materials for copying, display materials, paints, inks, IC fields, etc., and is especially used in consumer equipment. printed wiring boards, conductor circuits, relays, etc.
Its use in sockets, etc. is attracting attention. For this reason, many types of photocurable resins have been developed, and many types of ultraviolet curable adhesive compositions having special physical properties depending on their uses have also been proposed.
Particularly in the production of the above-mentioned devices, it is desired that these compositions have special physical properties, ie, thixotropy, so that they can be applied automatically by automatic machines. Generally, a method using a so-called dispenser, in which the adhesive is applied by discharging the adhesive from a nozzle with a narrow tip, is often used as an adhesive application using an automatic machine. Application using this dispenser has the following advantages: (1) There is no stringing due to high-speed application, (2) constant and constant amount of application is possible, and (3) the adhesive applied to the object does not flow and spread. Characteristics such as not dripping are required. Conventionally, as the above-mentioned compositions having thixotropic properties, there have been ultraviolet curable adhesive compositions which have been given thixotropic properties by adding inorganic fillers such as magnesium silicate, aluminum silicate, bentonite, silica powder, asbestos, mica powder, etc. Are known. However, since this type of composition has thixotropic properties by adding an inorganic filler, the viscosity of the composition increases rapidly, extremely reducing coating workability. Because of this, the viscosity of the composition must be adjusted using low-viscosity substances such as solvents and reactive monomers, which causes an extreme decrease in the physical properties and performance of adhesives. An object of the present invention is to provide a thixotropic ultraviolet curable adhesive composition which is imparted with thixotropic properties and has improved application workability with a dispenser, and which overcomes all the drawbacks of the above-mentioned known techniques. In order to achieve the aforementioned object, according to the present invention:
In an ultraviolet curable adhesive composition comprising a (meth)acrylate oligomer or (meth)acrylate monomer and a photosensitizer that cures rapidly by ultraviolet rays, a combination of an imidazole compound and silica powder is added to the composition. It is characterized by the addition of the following additives. Typical examples of (meth)acrylate oligomers or (meth)acrylate monomers used as UV-curable base resins include neopentyl glycol diacrylate, diethylene glycol diacrylate, tetrahydrofurfuryl acrylate, tetraethylene glycol diacrylate, and polyethylene glycol. diacrylate,
2-2bis(4-acryloxydiethoxyphenyl)propane, epoxy acrylate, etc., and as photosensitizers, carbonyl compounds such as benzoin ethyl ether, benzoin methyl ether, benzoin isopropyl ether, anthraquinone, etc. Sulfur compounds such as nyl sulfide, dibenzoyl sulfide, tetramethylthiuram sulfide, and other anthracene compounds,
Examples include halogenated hydrocarbons. Further, imidazole compounds that can be used as additives in the present invention include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-ethylimidazole, 2-
heptadecylimidazole, 2-phenylimidazoline, 2-ethyl-4-methylimidazoline,
These include 2-heptadecyl imidazoline, 2,4-dimethylimidazole, and other imidazole derivatives. Some of these imidazole compounds are insoluble in the known ultraviolet curable adhesive compositions, but in this case, they can be dissolved in a solvent such as alcohol, acetone, benzene, etc., or added by heating. It may be added after melting. The present inventors discovered that simply adding only the imidazole compound to the known UV-curable adhesive composition did not provide the thixotropic properties that are the object of the present invention, and that adding only silica powder to the adhesive composition It was confirmed through various experiments that the desired thixotropy could not be obtained even if the viscosity increased significantly even if Further, the unique thixotropic properties of the present invention cannot be obtained even when an imidazole compound is combined with other inorganic powders such as magnesium silicate, aluminum silicate, bentonite, asbestos powder, mica powder, and talc. In this way, the present invention provides a desired effect by adding an additive consisting of a combination of an imidazole compound and silica powder to a known ultraviolet curable adhesive composition. The -OH group in and the imidazole compound form a hydrogen bond,
This is thought to be because a kind of structure is formed between the silica powders in the suspension. Also, the most effective is to add 0.1 to 15 parts by weight of an additive consisting of an imidazole compound and silica powder to 100 parts by weight of the ultraviolet curable adhesive composition. If the amount of this additive is small, the appropriate thixotropy in the application process, which is the objective of the present invention, cannot be obtained, and if it is too large, the physical properties of the adhesive after curing, that is, the irradiation with light, cannot be achieved sufficiently. Adhesive strength will decrease. In addition, the imidazole compound and silica powder used as additives are 0.1 to 10% for the former and 90 to 99.9% for the latter.
It is best to add it within the range of 100 to 100%, and as the amount of the imidazole compound decreases, the viscosity increase due to the silica powder increases, and the effect of the combination of the imidazole compound and the silica powder decreases. Furthermore, if the amount of imidazole compound increases, the hardness of the cured product decreases and sufficient strength cannot be obtained. Furthermore, generally known polymerization inhibitors may be added to the composition of the present invention. As described above, the present invention exhibits good thixotropic properties and achieves the objects of the present invention by adding additives consisting of an imidazole compound and silica powder to a generally known ultraviolet curable adhesive composition. . Example 1 A basic composition (1) was prepared by adding 2 g of benzoin ethyl ether to 100 g of various methacrylate oligomers or monomers shown in Table 1, and 1-benzyl-2-methylimidazole was added to the composition (1). The composition to which 0.4 g was added was designated as composition (2).
Composition (3) is obtained by adding 8 g of silica powder to composition (1), and composition (3) is obtained by adding 0.4 g of 1-benzyl-2-methylimidazole and 8 g of silica powder to composition (1). The viscosity and thixotropy of each of these compositions were measured. The thixotropy was expressed as a thixotropic coefficient. Viscosity measurement is made by Tokyo Keiki Co., Ltd.
Measurement was performed at 25°C using a BH type rotational viscometer with No. 7 rotor. Thixotropic coefficient is 2rpm/20rpm
It was determined by the ratio, and the viscosity was shown at 20 rpm. Example 2 A composition prepared by adding 2 g of benzoin ethyl ether to 100 g of 2-2-bis(4-acryloxydiethoxyphenyl)propane (monomer No. 1 of Example 1).
The viscosity and thixotropic coefficient of each composition were determined in the same manner as in Example 1 by adding additives in combination of 0.8 g of various imidazole compounds and 8 g of silica powder as shown in Table 2 to Composition 6 (same as Composition 1). Example 3 Out of the respective compositions shown in Example 1, the ejectability and fluidity of the composition added with only silica powder and the composition added with an additive made of a combination of an imidazole compound and silica powder from a dispenser was measured. Note that the discharge performance depends on the nozzle diameter.
Evaluation was made by measuring the time taken to discharge 5 mg of the composition under conditions of 0.5 mm air pressure of 5 kg/cm ² . The fluidity was determined by dropping each composition onto a glass plate and measuring the difference in diameter immediately after and 5 minutes later.

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[Table] As is clear from the above examples, in order to provide thixotropic properties while maintaining low viscosity, which is the objective of the present invention, an additive consisting of an imidazole compound and silica powder was added to a known ultraviolet curable adhesive composition. By adding it, unique properties not seen before can be obtained. That is, the viscosity and thixotropy can be freely adjusted by adjusting the respective addition ratios of silica powder and imidazole compound and the amounts added to the above-mentioned known ultraviolet curable adhesive composition depending on the application. For example, when applying with a dispenser, it is best to have a viscosity of 650 to 1100 poise (at 25°C) and a thixotropic coefficient of 6 to 8, which not only allows for quick dispensing, but also allows for stringing, quantitative application, and post-application. It has various characteristics such as no spreading and no sag, and will save labor as automation increases in the future.
There are great corporate values such as improved quality.

Claims (1)

[Claims] 1. Rapidly cures by ultraviolet rays (meth)
A thixotropic ultraviolet curable resin composition comprising an acrylate oligomer or a (meth)acrylate monomer and a photosensitizer, characterized in that an additive comprising a combination of an imidazole compound and silica powder is added to the composition. UV-curable adhesive composition. 2 0.1 to 15 parts by weight of an additive consisting of an imidazole compound and silica powder is added to 100 parts by weight of an adhesive composition consisting of a (meth)acrylate oligomer or a (meth)acrylate monomer and a photosensitizer. A thixotropic ultraviolet curable adhesive composition according to claim 1.