JPH03165860A - Roll coater - Google Patents

Abstract

PURPOSE:To form a uniformly coated film even by the coating liquid having a low viscosity by providing a plurality of circulation routes of coating liquid to a roll coater between a tank for supplying the coating liquid to the liquid reservoir part of the roll coater and this liquid reservoir part. CONSTITUTION:When a base plate 2 is sent by a carrier belt 3, coating liquid on a transfer roll 1 is transferred thereon and a coated film 15 is formed on the base plate 2. A backing-up roll 6 is provided to the position opposite to the transfer roll 1 via the carrier belt 3. When the transfer roll 1 is rotated, coating liquid is applied to the transfer roll 1 from the coating liquid reservoir part 10 formed between the transfer roll 1 and a doctor bar 7 and furthermore applied to the base plate 2. While the transfer roll 1 is rotated and coating is performed, the coating liquid is circulated by a plurality of circulating means.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a roll coater, which is one type of coating device, and specifically relates to an over-roll coater for coating and forming a recording layer of an optical recording medium on the upper surface of a substrate. .

[Conventional technology] There are various types of conventional coating equipment, including many types of roll coaters, and their purposes range from printing to painting, adhesive coating, formation of special functional layers, and photolithography technology fields. etc. over a wide range of areas.

On the other hand, various methods have been proposed for forming the recording layer of an optical recording medium. For example, Te-TeOz, TeC, Te
A recording layer made of an inorganic thin film such as -Se, Sb-Se/Bi-Te, etc. is formed by vacuum evaporation, sputtering, etc., but in this case, the manufacturing cost is high, the setting of manufacturing conditions is complicated, and the toxicity of the material etc. There is also the problem of

On the other hand, optical recording media manufactured by coating have many advantages such as not only easy manufacture but also low equipment and running costs. Especially dyes,
It is advantageous for forming thin films made of organic substances such as pigments and resins. For this reason, the subinner method, dip coating method, etc. are often used.

However, in the Sviner method, the amount of coating liquid removed to areas other than the substrate is greater than the amount of coating liquid used to form a thin film, resulting in waste of the coating liquid. Further, the film thickness tends to be thicker at the outer peripheral part of the substrate than at the inner peripheral part, making it difficult to obtain a uniform film thickness. Furthermore, if dust or foreign matter adheres to the substrate, radial streaks will occur from that area to the outer periphery, and film thickness unevenness will occur at the concave and convex portions of the light guide groove provided on the substrate. The disadvantage is that it is easy to occur. Furthermore, this method is not suitable for cases where the guide grooves are not concentric or spiral, such as in optical cards.

In the dip coating method, the substrate is immersed in the coating solution for forming a thin film and then pulled up to apply the coating, so it requires a much larger amount of coating solution than is actually applied, and it requires repeated application of the same coating solution. For use, the pot life of the coating solution must be long.

Therefore, large-scale equipment is required to keep the composition of a large amount of coating liquid constant at all times. Furthermore, since the pulling speed of the substrate must be slowed down to obtain a uniform film thickness, there is a drawback that the working efficiency is extremely low.

In order to solve these problems, a method for forming an optical recording layer using a roll coater has been proposed in JP-A-63-44337. This is a method in which a coating liquid is supplied to a cylindrical roll and brought into contact with the substrate to form a uniform film thickness of 1 μm or less. The principle is the same as that of an over-roll coater.

[Problem to be solved by the invention]

However, in the above proposal, since the substrate to be coated is not a long sheet, uneven film thickness occurs on each substrate at the initial stage of coating, and blurring of the coating liquid occurs at the end of coating. This becomes more noticeable as the viscosity of the coating liquid decreases.

Therefore, the substrate needs to be larger than the effective recording area for the optical recording medium, and the area other than the effective recording area is wasted. To solve this problem, forming continuous grooves and forming a continuous recording layer using a long sheet can be considered, but with an over-roll coater like the one proposed above, the liquid pools of the coating solution are removed while coating continues. The concentration changes, which affects the film thickness.

Currently, an over-roll coater has been developed that can circulate the coating liquid in the liquid pool, but this causes local unevenness in the concentration of the coating liquid at the boundary between the transfer area and the non-transfer area of the transfer roll. However, it does not prevent the formation of uneven film thickness in the coated film.

[Means to solve the problem]

The present invention is a roll coater for coating a recording layer of an optical recording medium on a substrate, and the present invention provides a roll coater for coating a recording layer of an optical recording medium on a substrate, and a plurality of rollers are provided between a tank for supplying a coating liquid to a liquid reservoir of the roll coater and the liquid reservoir. This is a roll coater characterized by having a coating liquid circulation path.

According to the present invention, the coating solution is formed by circulating the coating solution in the coating solution reservoir of the (over) roll coater using a plurality of circulation systems and keeping the coating solution at a constant concentration. This makes it possible to control the thickness of the film at a constant level. Further, the present invention is particularly suitable for long sheet substrates, which are effective when the coating liquid has a low viscosity. A plurality of optical recording media or grooves corresponding to a plurality of optical recording media can be continuously formed on the long sheet substrate, and high productivity can be expected.

Here, the organic thin film forming coating liquid means a coating liquid for forming a thin film (recording layer) containing an organic substance (including organic metals, etc., but not completely inorganic substances) as one of its components. This coating solution may contain the above-mentioned organic substance, solvent, binder, and other components.

Although there is a coating method in which a binder or the like is added to the coating solution, the coating solution for forming the recording layer of an optical recording medium is sometimes coated with a low viscosity without adding a binder. It is particularly suitable when using an organic thin film forming coating liquid with a viscosity of 10% or less and a viscosity of 20 cps or less at 20°C.

Representative embodiments of the present invention will be described in detail with reference to FIGS. 1 to 3.

As shown in FIG. 1, this apparatus has a conveyor belt 3 as a means for conveying the substrate, a drive roll 4 that drives the conveyor belt, and a support roll 5 that supports the conveyor belt.
Equipped with A transfer roll 1 is disposed close to the conveyor belt, and when the substrate 2 is conveyed by the conveyor belt, the coating liquid on the transfer roll is transferred to form a coating film 15 on the substrate. A backup roll 6 is provided at a position facing the transfer roll via the conveyor belt.

As the transfer roll 1 rotates, a coating liquid is applied onto the transfer roll from a liquid reservoir 10 formed between the transfer roll and the doctor blade 7, and is also applied onto the substrate. While the transfer roll is rotating and coating is being performed, the coating liquid is circulated by a plurality of circulation means.

As shown in FIG. 3, the number of circulation means is four here, but the number is not limited to this.

The discharge pipe 8 is installed at approximately the same height as the liquid level of the liquid reservoir 10.
is discharged. The concentration of the liquid in the tank is kept uniform by the stirring means 20. The liquid in the tank is circulated through bombs 18 to 18.
Depending on ゜゜゛, valve 17~17''', filter 16~
16゜゜゜ and then from the supply pipe 9 to 9゜゜゛ to the liquid reservoir 10
is supplied to

Figure 2 shows the roll coater viewed from above.
When the coating liquid is transferred from the transfer roll 1 to the substrate 2 provided with the guide groove 14 of the optical disc, a coating film 15 is formed on the substrate, and the coating liquid remains in the non-transfer part l2 of the transfer roll, but the coating liquid remains in the transfer part. The coating liquid is removed from 13. Conventionally, the coating liquid on the non-transfer area had a tendency to become thicker as the transfer roll continued to rotate, but in the present invention, the liquid is discharged by the discharge pipe 8-8゜゜゜ and the liquid is supplied by the supply pipe 9-9''゜. Concentration remains constant.

As shown in FIGS. 2 and 3, it is preferable to arrange the supply pipes and the discharge pipes alternately, but they may also be arranged one above the other in the same position. The circulation pump is preferably one without pulsating flow, and the circulation rate is preferably 9200 ml/min or less per bomb. Alternatively, a bomb may be provided in the middle of the discharge pipe and the discharge may be performed by suction. The filter has a bore diameter of 0.
A thickness of 20 to 1.0 μm is preferable. This filter allows the coating solution to be reused.

Although a roll coater using a doctor bar is shown here, a doctor roll type one may also be used.

In that case, the supply pipe and the discharge pipe may be connected to the coating liquid reservoir from above the roll.

It is also possible to adopt a mechanism in which the concentration of the coating liquid in the tank is detected in the circulation system and the highly concentrated coating liquid and solvent can be injected into the tank 19. In this case, it is better to simultaneously monitor the concentration of the coating liquid in the reservoir. Further, when the temperature increases due to the circulation of the liquid, a cooling device may be attached.

The direction of conveyance of the substrate may be in the forward direction with respect to the transfer roll, as shown by arrow A in FIGS. 1 and 2, or in the opposite direction, as shown by arrow B.

A coating liquid suitable for forming a recording layer of an optical recording medium using the apparatus of the present invention contains a material that forms the recording layer of an optical recording medium. Examples of organic dyes that can be used as materials include those that have appropriate solubility in organic solvents, such as cyanine dyes, merocyanine dyes, naphthoquinone dyes, anthraquinone dyes, triphenylmethane dyes, and squarylium dyes. , phthalocyanine dyes, naphthalocyanine dyes, amine dyes, vorimethine dyes, azulene dyes, metal complex dyes, and the like. In addition, inorganic water-soluble materials, alkoxides, etc. can also be used.

These may be used alone or in combination, and other additives may be added. Examples of additives include polymeric binders such as vinyl resins such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, acrylic resins, polyester resins, polyurethane resins, polycarbonates, etc. Cellulose resins such as nitrocellulose or cellulose acetate, olefin resins such as polyethylene and polypropylene, thermoplastic resins such as polybutyral resin, and thermosetting resins such as epoxy resins, acrylic polyol urethane resins, and unsaturated polyesters. Can be mentioned.

In addition, durability-modifying additives such as various surfactants, dispersants, ultraviolet absorbers, visible light absorbers, and antioxidants may be added.

The solvent used in the coating solution is a roll coater, circulation system parts,
Any solvent may be used as long as it does not adversely affect the substrate, the recording layer formation, or its materials. When using the above-mentioned organic dyes, ester solvents such as ethyl acetate and butyl acetate, methyl ethyl ketone, ethyl isobutyl ketone, acetone, dichloromethane, etc. Ketone solvents such as acetone alcohol, alcohol solvents such as methanol, ethanol, and isobrobyl alcohol, ether solvents such as methyl ethyl ether and diethyl ether, aromatic solvents such as toluene and xylene, and halogenated solvents such as dichloromethane and dichloroethane. Organic solvents such as carbon-based solvents and furan-based solvents such as tetrahydrofuran can be used alone or in combination. Among them, if you use one with a boiling point of 70°C or higher, especially 70 to 160°C, a uniform 0.1μ
A coating film of around m can be easily formed, which is preferable. Boiling point is 70℃
If the following materials are used, unevenness tends to occur during the drying process.

In addition to inorganic materials such as glass and ceramics, the substrate is made of
In addition to various organic compound sheets, sheets whose surfaces have been modified with photocurable materials, thermosetting materials, etc., and sheets with light guide grooves formed therein can also be used.

In particular, the present invention is effective when a recording layer is coated using a roll on the upper surface of a substrate where density unevenness is likely to occur in the liquid pool.

[Examples] Example 1 A recording layer of an optical recording medium was formed using the overroll coater shown in FIGS. 1 to 3.

For the coating solution, 2.5 parts by weight of organic dye ethyl violet (manufactured by Eastman Kodak) was dissolved in 100 parts by weight of a 1:1 mixture of methyl ethyl ketone (boiling point 79.6°C) and cyclohexane (boiling point 12-155.7°C). (viscosity 1.5 cps) was used.

The substrate used was a polymethacrylate (PMMA) plate with a length of 20 m, a width of 20 cm, and a thickness of 1.2 mm, on which guide grooves for optical discs with a diameter of 13 cm were continuously molded at a pitch of 35 cm using ultraviolet curing resin. .

The diameter of the transfer roll was 12 cm, the rotation speed was 2 m/min in the forward rotation to match the feed speed of the conveyor belt, and the interval between the transfer roll and the conveyor belt was 0.8 mm.

The bore diameter of the filter was 0.2 μm, and the circulation pump was adjusted to 100 ml/min at the outlet of the supply pipe. A stirring means (stirring bar) was rotated in the tank to make the concentration of the coating solution uniform.

After applying the coating solution to the substrate under these conditions and drying it, we examined the transmittance at 550 nm in the effective optical recording area and center of the coating film, and found that the transmittance was stable up to about 40 cm from the start of coating. However, after that, the right side (5 cm from the center of the optical disc) when facing the transport direction was 17.
5% ± 1.5%, center (center of optical disc) 18
．． 2%±1.8%, and 18.0%±1.4% on the left side in the transport direction (5 cm from the center of the optical disc). It was ±1.0% within the same optical disc. Further, there was no dust or foreign matter on the coated surface.

Example 2 Organic dye IR-820 (manufactured by Nippon Kayaku Co., Ltd.) 2 was used in the coating solution.
．． 5 parts by weight of diacetone alcohol (boiling point 167.9
°C) dissolved in 100 parts by weight (viscosity 3.8 cps
) was used.

The substrate used was polycarbonate (PC), which was formed by continuous pressure molding so that the guide groove for the optical disk had no steps.

The rest was the same as in Example 1, and the transmittance of the coating film was 830.
When measured in nm, the transmittance was not stable until about 40 cm from the start of coating, but after that, the transmittance was 22.4% ± 1.7% on the right side in the conveyance direction, and 22.8% in the center.
±1.2%, 22.1% ±1 on the left side in the transport direction
．． It was 6%. Within the same optical disc, it was ±1.1%. Further, there was no dust or foreign matter on the coated surface.

Comparative Example The same test as in Example 2 was conducted using the conventional over-roll coater shown in FIGS. 4 to 6.

This device has only one circulatory system.

The transmittance is 22.7% ± 4.2% on the right side in the conveyance direction and 24.6% in the center after 40 cm from the start of coating.
±4.7%, 21.6% ±3 on the left side in the transport direction
．． 8%, and there was a variation of ±29% within the same optical disc.

From the Examples and Comparative Examples, it can be seen that by circulating the coating liquid pool in a plurality of circulation systems, a coating film with less variation in transmittance, that is, less unevenness in film thickness, can be obtained.

[Effects of the Invention] According to the over-roll coater of the present invention, a more uniform coating film can be obtained even with a low-viscosity coating liquid. Additionally, since there are more filters in the circulation system, the life of the filters can be extended and the amount of dirt on the coating solution can be reduced.

Furthermore, since the long sheet is suitable as a coated substrate, it is suitable for continuous production and contributes to the provision of inexpensive optical recording media.

[Brief explanation of the drawing]

1 5 A schematic side view of an example, FIG. 2 is a schematic plan view thereof, FIG. 3 is a schematic diagram of its circulation system, FIG. 4 is a schematic side view of an example of a conventional over-roll coater, and FIG. The figure is a schematic plan view thereof, and FIG. 6 is a schematic diagram of its circulatory system. l: Transfer roll 3: Conveyor belt 5: Support roll 7: Doctor bar 8~8'': Discharge pipe 0: Liquid reservoir 2: Non-transfer area 4: Guide groove 6~16'': Filter 8~l8゜゜゜: Bump 20: Stirring bar 9~9゜゜゜: Supply pipe 1: Leak prevention valve 3: Transfer section 5: Coating film 7~17''゜: Valve 9: Tank 2: Substrate 4: Drive roll 6: Backup roll

Claims (1)

[Scope of Claims] 1. A roll coater for coating and forming a recording layer of an optical recording medium on a substrate, between a tank for supplying a coating liquid to a liquid reservoir of the roll coater and the liquid reservoir. A roll coater characterized by having a plurality of coating liquid circulation paths. 2. The roll coater according to claim 1, wherein the roll coater is an over-roll coater for coating and forming a recording layer on the upper surface of the substrate. 3. The roll coater according to claim 1, wherein the substrate is a long sheet substrate. 4. The coating liquid is an organic thin film forming coating liquid, has a solid content concentration of 10% or less, and has a viscosity of 20% at 20°C.
The roll coater according to any one of claims 1 to 3, wherein the roll coater is less than or equal to cps.