DESCRIPTION PHOTOSENSITIVE RESIN COMPOSITION AND PHOTOSENSITIVE MATERIAL USING THE SAME TECHNICAL FIELD The present invention relates to a highly sensitive photosensitive material used for manufacturing print circuit boards, developing a high productivity, and to a photosensitive resin composition used therein.

BACKGROUND ART In manufacturing print circuit boards, photosensitive material such as a dry film resist or the like are generally used. As the electric and electronic technologies continuously call for a higher density of print circuits, the photosensitive materials are required to become proportionately sensitive, so as to provide a higher resolution. It has been reported (U. S. Patent No.

3,479,185) that a photosensitive material containing a photoinitiator, 2- (2-chlorophenyl)-4, 5-diphenylimidazole dimer (hereinafter referred to as"B-CIM"), as expressed Compound (2), provides the highest level of resolution.

Compound (2)

Another photoinitiator, hexaarylbisimidazole (hereinafter referred to as"HABI") which is of the same type of compound with B-CIM is also commercially used in manufacturing dry film resists.

However, in case of a photosensitive material using B-CIM as a photoinitiator compound, the photoinitiator separates from it, and suspends in a developing solution as a fine particulate matter, which tends to deposit on the surface of a circuit board, interfering the lithographic pattern formed, on the circuit board, thereby making itself one of the major causes of defects on finished products, such as a disconnected circuit or a short circuit.

In order to avoid the problem mentioned above, it was necessary to renew the developing solution more frequently than desirable and, also, to wash a resist substrate very thoroughly. Thus, operation efficiency was poor.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a

compound belonging to the HABI type initiator compounds excellent in resolution, which hardly forms a particulate matter in a developing solution and has a more satisfactory sensitivity than conventional ones.

The present inventors have synthesized a plurality of compounds belonging to the HABI type group of compounds in search for an initiator which hardly forms a particulate matter in a developing solution, and have carried out tests by preparing a photosensitive resin composition and a photosensitive material to compare the action in a developing solution. As the result, the present inventors have discovered that the following Compound (1), Compound (1) i. e., 2- (2-chlorophenyl)-4, 5-bis (4-methoxyphenyl) imidazole dimer, has a high sensitivity and hardly forms a particulate matter in a developing solution, since it has a remarkably higher solubility in a resin composition as compared with a compound having a similar structure.

The present invention has been accomplished on the basis of this discovery.

Thus, the present invention provides a photosensitive resin composition comprising (A) a binder polymer having a carboxyl group, (B) a photopolymerizable compound having an ethylenic unsaturated group, and (C) a photoinitiator compound identified as Compound (1), as a photoinitiator, and also provides a photosensitive material characterized by the use of such a photosensitive resin composition.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 illustrates a UV ray-absorption spectrum of the compound prepared in Example 1 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The photoinitiator compound of the present invention is highly soluble in a resin composition and, therefore, hardly forms a particulate matter, which tends to deposit on the resist substrate, and yet has a higher sensitivity, as compared with conventional B-CIM.

In the present invention, examples of (A) a polymer having carboxyl groups include copolymers of methacrylic acid with styrene, alkyl or substituted alkyl acrylate, methacrylate or the like. The average molecular weight of the copolymers is preferably 10,000 to 100,000.

In the present invention, examples of (B) a compound having a polymerizable ethylenic unsaturated group

include a vinyl monomer or the like. Examples of a monofunctional vinyl monomer include monoacrylate or monomethacrylate, and examples of a difunctional vinyl monomer include diacrylate or dimethacrylate, and examples of a polyfunctional vinyl monomer include compounds obtained by reacting an a, -unsaturated carboxylic acid with a polyhydric alcohol or a glycidyl group-containing compound.

In the present invention, a blending amount of the component (A) is preferably 0.6 to 4 times the amount by weight of the component (B).

In the present invention, a blending amount of the photoinitiator compound (C) is preferably 0.005 to 0.15 time the amount by weight of the total weight of the component (A) and the component (B).

The photosensitive resin composition of the present invention may further contain an N, N'-tetraalkyl-4,4'- diaminobenzophenone such as N, N'-tetraethyl-4,4'- diaminobenzophenone, an N-aryl-a-amino acid such as N- phenylglycine, or the like as an additive, and may further contain a heat polymerization inhibitor, an adhesiveness-imparting agent, a colorant or the like, if necessary.

The photosensitive material of the present invention is prepared by coating a solution of the photosensitive resin composition of the present invention as a liquid resist on the surface of a metal as a substrate, and by

drying the coated layer to form a photosensitive layer.

A print circuit board can be produced by printing a device pattern on the photosensitive material by means of lithography technique and, then, processing by etching, plating or the like. Also, the photosensitive material of the present invention may be produced by coating the solution of the photosensitive resin composition of the present invention on a polymeric film such as polyethylene terephthalate by a well known method, drying to form a dry film and, then, laminating the dry film on the surface of a metal as a substrate to form a photosensitive layer.

In order to make a solution which can be easily coated, the photosensitive resin composition of the present invention may be diluted with a solvent such as acetone, methyl cellosolve, methyl ethyl ketone, toluene, methanol, propylene glycol monoethyl ether, dimethylformamide or the like, or a mixture solvent thereof. The coating can be carried out with a roll coater, an air knife coater, a bar coater, a spin coater or the like. The drying is carried out at a temperature of 60 to 130°C. After drying, the photosensitive layer preferably has a thickness of 5 to 100 um.

Light exposure of the photosensitive layer is carried out by light generated from a light source such as a high pressure mercury lamp. Development of the exposed photosensitive layer is carried out by using an

alkaline aqueous solution of sodium carbonate or other water-soluble alkaline materials. Etching and plating can be carried out by the conventional methods. The subsequent step of removing the light-cured part of the photosensitive layer can be carried out by using a strong alkaline aqueous solution.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention is more concretely illustrated with reference to Examples.

EXAMPLE 1 2- (2-chlorophenyl)-4, 5-bis (4-methoxyphenyl) imidazole dimer as a photoinitiator compound of the present invention was synthesized in accordance with the method disclosed in JP-B-5-60570, and was obtained as a yellow brown powder. An ultraviolet (W) ray-absorption spectrum of the obtained powder in acetonitrile is illustrated in Fig. 1.

The maximum absorption wavelength of the UV ray- absorption spectrum was 234 nm. This compound provided a pale greenish radical coloration as irradiated to ultraviolet rays.

Methacrylic acid, ethyl methacrylate and styrene were copolymerized to produce a carboxyl group-containing copolymer material having a molecular weight of 60,000.

Having 100 g of this copolymer as the Component (A), the Component (B) and the solvents were blended therewith as shown in the following Table 1, to obtain a solution of a

photosensitive resin composition.

Table 1 Components Names of materials g Component A Carboxyl group-containing compound 100 Tetradecaethylene glycol diacrylate (manufactured by Shinnakamura Kagaku 25 Component B K. K.) Tetramethylolmethane triacrylate (manufactured by Shinnakamura Kagaku 75 K.K.) 2-Methoxyethanol 108 Solvent Toluene 87 6.4 g of the photoinitiator compound of the present invention and 25 g of acetone were added to the above obtained solution in the dark. The compound added was easily dissolved. This solution was coated on a glass fiber-epoxy resin board laminated with a copper sheet (manufactured by Sumitomo Bakelite Co., Ltd.) with a bar coater, and was dried in an oven at 100°C for 10 minutes to form a photosensitive layer having a thickness of 20 um. The coated substrate was heated on a hot plate, and a PET film (manufactured by Toray Industries, Inc.) with a thickness of 25 um was suction-adhered thereon under vacuum to produce a photosensitive material with having a resist layer.

A Stoufer 21 gradation step tablet (manufactured by Electrophotographic Association) was placed as a negative on the above produced photosensitive material, and a quartz glass plate (manufactured by Seiko Tokushu Glass K. K.) of 2.3 mm in thickness was further placed thereon

and was further suction-adhered under vacuum to completely adhere the negative and the photosensitive material, which were then exposed to light from a parallel light-exposing apparatus (manufactured by Ushio Inc.) having a high pressure mercury lamp at 600 mj/cm After peeling off the PET film, the photosensitive material was dipped and shaken in 500 cc of a 1% sodium carbonate aqueous solution at 20°C for 90 seconds, and consequently the unexposed part could be easily dissolved and removed. The thickness of the light-cured layer formed on the coated substrate was measured with a contact type film thickness measuring apparatus (manufactured by Tokyo Seimitsu Co., Ltd.). As a reference example, a photosensitive resin composition containing B-CIM was prepared in the same manner as above, and the photosensitive resin composition was coated on a substrate in the same manner as above to form a light- cured layer which was then subjected to the same measurement as mentioned above. The layer's thickness of each step of the gradation step tablet was measured, and the highest step number of the gradation step tablet retaining at least 50% of the maximum layer thickness was made as an index for a sensitivity, as shown in the following Table 2.

Table 2 Compound Number of steps B-CIM 1 Compound prepared in Example 1 8 As the result, it was proved by the difference in the step numbers shown in Table 2 that the photosensitive composition and the photosensitive material prepared by using the photoinitiator compound of the present invention had a remarkably high sensitivity.

Consequently, in order to prepare a photosensitive material having the same degree of sensitivity as a photosensitive material using B-CIM, it was necessary to reduce an amount of the photoinitiator of the present invention to be dissolved to around one eighth of B-CIM.

EXAMPLE 2 and COMPARATIVE EXAMPLE 1 Photosensitive resin compositions were prepared by using 5.0 g of the photoinitiator compound of the present invention (Example 2) and 5.0 g of B-CIM (manufactured by Hodogaya Chemical Co., Ltd.) (Comparative Example 1), respectively, in the same manner as in Example 1. The photoinitiator compound of the present invention was easily dissolved, but it was necessary for dissolving B- CIM to stir for 30 minutes. Each of the photosensitive resin compositions thus prepared was coated on a total of 44 sheets of slide glass (manufactured by Matsunami Glass Kogyo K. K.) with a bar coater in such an amount as to provide a dry solid content of 0.1 g per sheet, and was

dried in an oven at 110°C for 10 minutes to form a photosensitive layer. On the other hand, a developing solution was prepared in two 200 ml beakers, by putting 150 ml of a 1% sodium carbonate aqueous solution in each of the beakers placed in a water bath controlled at 40°C, stirring by means of a compressed air blown therein and maintaining the temperature at 40°C. All the 44 sheets of slide glass with the photosensitive layers formed, containing the photoinitiator compound of the present invention, were dipped in one beaker with the developing solution in it, 4 sheets at one time and 11 times with 5 minutes intervals, and the photosensitive material, or resist layer formed, on each sheet of the slide glass was developed by dissolving. Another 44 sheets of slide glass with the photosensitive layers formed, containing B-CIM, were dipped in the other beaker with the developing solution in it, in the same manner as mentioned above, and the photosensitive material, or resist layer formed, on each sheet of the slide glass was developed by dissolving.

Each of the developing solutions became a cloudy suspension. The cloudy suspension was allowed to stand at room temperature for 3 days and was then decanted to recognize a white precipitate at the bottom of the beaker containing each of the developing solutions. The precipitate was dispersed in 3 ml of distilled water added, and the dispersion was decanted, thereby removing

the white matter, but fine sand-like particulate matter was still deposited on the bottom of each beaker. The amount of the deposited matter in each beaker was visually compared, and it was observed that an amount of the deposited matter in the beaker containing the photoinitiator compound of the present invention was notably smaller than that in the beaker containing B-CIM.

Each beaker was dried with the deposited matter intact to remove water. Then, 0.4 ml of tetrahydrofuran was added to each beaker to extract each initiator compound from the sand-like particulate matter remained.

2 pi of each of the extracted solutions was poured into a three dimensional liquid chromatography L7000 (manufactured by Hitachi Ltd.) equipped with Inertsil ODS-2 (reverse phase column, manufactured by Gaschro Kogyo K. K.), and a peak light absorbancy of each of the initiator compounds was determined from data obtained by monitoring at a wavelength of 277 nm. The light absorbancy thus determined and evaluated are shown in Table 3 as an index for an amount of the particulate matter formed.

Table 3 Light Photoinitiator compound absorbancy (Abs.) Example 2 Compound prepared in Example 1 0.03 Comparative B-CIM 0.33 Example1

It was proved from the difference in the light absorbancy values that an amount of the fine sand-like particulate matter formed from the photosensitive material prepared by using the photoinitiator compound of the present invention be much smaller than that formed on the photosensitive material prepared by using B-CIM in the same amount.

INDUSTRIAL APPLICABILITY The photosensitive resin composition of the present invention hardly forms a particulate matter in a developing solution, and yet has a high sensitivity.

The photosensitive material of the present invention does not cause a disconnected circuit, a short circuit or the like due to the particulate matter formed in a developing solution in manufacturing print circuit boards, and provides a satisfactory resist pattern with a satisfactory operation efficiency.