JPH03165862A - Overroll coater - Google Patents

Abstract

PURPOSE:To prevent local change in the concn. of coating liquid of a liquid reservoir part by providing a cleaning roll for removing the coating liquid residual on a transfer roll adjacently thereto in an overroll coater. CONSTITUTION:After a coated film is formed on a base plate 2 by a transfer roll 1, the coating liquid 21 residual in the nontransferred part of the transfer roll 1 is moved to a first cleaning roll 6 from the transfer roll 1. The liquid transfer part of the first cleaning roll 6 is cleaned by a second cleaning roll 6'. The coating liquid 21 residual on the first cleaning roll 6 is moved on the second cleaning roll 6'. Thereby before the transfer roll 1 is reimmersed in a liquid reservoir part 10, the residual coating liquid is removed from the surface. Therefore transfer is performed in the same conditions at every one rotation by the transfer roll 1.

Description

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

[Conventional technology]? There are various types of coating equipment, and among them, there are many types of roll coaters, and the purposes range from printing to painting, coating with adhesives, forming special functional layers, and photolithography technology fields.

On the other hand, various methods have been proposed for forming the recording layer of an optical recording medium. For example, Te-Ter■. TeC, Te
A recording layer made of an inorganic thin film such as -Se, Sb-Se/Bi-Te, etc. can be 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 is high. There are also other problems.

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 spinner 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 an optical card.

In the dip coating method, the substrate is immersed in a 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. The pot life of the coating liquid must be long for repeated use.

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 equipment used is an over-roll coater, which is used for resist coating, etc. are doing the same.

[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 dripping 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 coating solution accumulates during continuous coating. This changes the concentration of the part and 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. This local density unevenness is caused by an increase in the concentration of the coating liquid in the non-transfer area of the transfer roll, and a change in the concentration of the coating liquid near the transfer roll in the liquid pool area. For this reason, the coating film formed by transfer is thin in the center and thick in the periphery.

An object of the present invention is to provide an overroll coater that can solve the problem of local density unevenness as described above, and also to provide an overroll coater that can successfully perform continuous production of optical recording layers. With the goal.

[Means to solve the problem]

The present invention provides an over-roll coater for forming a recording layer on the upper surface of a substrate for an optical recording medium, which is equipped with a cleaning roll adjacent to the transfer roll for removing residual coating liquid on the transfer roll. It is a roll coater.

According to the present invention, by providing a cleaning roll on the transfer roll of an over-roll coater and removing residual coating liquid from the non-transfer area of the transfer roll, it is possible to prevent changes in the concentration of the coating liquid in the liquid pool area. This is what I did.

Here, the coating liquid for forming an organic thin film is one in which organic substances (including organic metals, etc., but not completely inorganic substances) are used as one of the components.
A coating liquid for forming a thin film (recording layer) that contains organic substances, solvents,
The binder may also contain other ingredients.

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. 10% or less and a viscosity at 20° C. of 20 cps or less, which is particularly suitable when using an organic thin film type coating liquid.

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 means for conveying the substrate, and also includes a driving roll 4 for driving the conveyor belt. 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 5 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 the circulation means. That is, the coating liquid is supplied from the supply pipe 9 to the liquid reservoir 10 .

A discharge pipe 8 is provided at approximately the same height as the liquid level in the liquid reservoir, and the coating liquid discharged from this pipe goes to a tank. After the transfer roll 1 forms a coating film on the substrate 2, the remaining coating liquid 2L in the non-transfer portion of the transfer roll 1 moves from the transfer roll 1 to the first cleaning roll 6. The liquid transfer portion of the first cleaning roll is cleaned by the second cleaning roll 6', and the remaining coating liquid 2l on the first cleaning roll is transferred to the second cleaning roll 6'.

As a result, the residual coating liquid is removed from the surface of the transfer roll l before it is immersed in the liquid reservoir 10 again. This allows the transfer roll 1 to perform transfer under the same conditions every rotation.

FIGS. 4 and 5 show an example of a conventional over-roll coater, but this apparatus is not provided with a cleaning roll. In this case, the transfer roll 1 has a transfer portion l3 and a non-transfer portion 12 as shown in FIG. 5, and the concentration of the coating liquid on the non-transfer portion becomes thicker as coating continues.

By using such an overroll coater, a uniform coating film can be continuously obtained on a substrate on which guide grooves for optical discs are continuously formed. Furthermore, the cleaning effect can prevent precipitation of solids from the coating solution.

The number of cleaning rolls is not particularly limited. Further, a means for cleaning the cleaning roll with a solvent or a mechanism for removing ink from the cleaning roll using a blade or bar may be added.

For example, as shown in FIG. 3, the circulation means includes a tank 19 containing a stirrer 20 at the end of the discharge pipe 8, and the liquid passes through a bomb 18, a valve 17, and a filter 16 for sucking the coating liquid from the tank. The coating liquid may be supplied from the supply pipe 9 to the liquid reservoir. The arrangement of pumps, etc., the number of systems, etc. may be determined as appropriate.

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 discharge pipe of the circulation means may be connected to the coating liquid reservoir from above the roll.

The concentration of the coating liquid in the tank is detected in the circulation means,
A mechanism that can inject a highly concentrated coating liquid and a solvent into the tank 19 may also be used. In this case, it is better to simultaneously monitor the concentration of the coating liquid in the reservoir. In addition, if the temperature increases due to the circulation of the liquid, a cooling device may be attached.

The conveying direction of the substrate may be not only the forward rotating roll coating shown by the solid line arrow in FIG. 1, but also the reverse rotating roll coating shown by the broken line arrow.

A coating liquid suitable for forming the recording layer of an optical recording medium using the apparatus of the present invention contains a material that forms the recording layer of the optical recording medium.

For example, when using an organic dye, it may be one that has appropriate solubility in an organic solvent, such as cyanine dyes, merocyanine dyes, naphthoquinone dyes, anthraquinone dyes, triphenylmethane dyes, squarylium dyes,
Examples include phthalocyanine dyes, naphthalocyanine dyes, amine dyes, vorimethine dyes, azulene dyes, and metal complex dyes. 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 polymer binders such as vinyl resins such as polyvinyl chloride, vinyl chloride 10-vinyl acetate copolymer, and ethylene-vinyl acetate copolymer, acrylic resins, polyester resins, polyurethane resins, Polycarbonate or cellulose resins such as nitrocellulose or cellulose acetate, olefin resins such as polyethylene and polypropylene, thermoplastic resins such as polybutyral resins, as well as epoxy resins, acrylic polyol-based urethane resins, and unsaturated polyesters. Examples include polyester resins.

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, parts of the circulation system,
Any solvent that does not adversely affect the substrate, the recording layer shape, or its materials may be used. When using the above-mentioned organic dyes, ester solvents such as ethyl acetate and butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, acetone, and diacetone may be used. Ketone solvents such as alcohol, methanol, ethanol, iso-11 alcohol solvents such as brobyl alcohol, ether solvents such as methyl ethyl ether and diethyl ether, aromatic solvents such as toluene and xylene, dichloromethane,
Organic solvents such as halogenated carbon solvents such as dichloroethane and furan solvents such as tetrahydrofuran can be used alone or in combination. Among them, the boiling point is 70℃
As mentioned above, especially when using one having a temperature of 70 to 160°C, a uniform 0. A coating film before and after lIim can be easily formed, which is preferable. If a material with a boiling point of 70° C. or lower is 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.

[Example 1 Example 1 A recording layer of an optical recording medium was formed using the overroll coater shown in FIGS. 1 to 3. However, there were three cleaning rolls, and the cleaning roll furthest from the transfer roll was continuously cleaned with acetone.

The circulation system was adjusted to have a discharge rate of 300 mβ/min at the outlet of the supply port. A stirring means was used in the tank to make the concentration of the coating solution uniform.

Three parts by weight of the compound of the following structural formula (I) were mixed with methyl ethyl ketone (boiling point: 79.6°C) and cyclohexane (boiling point: 155°C).
The mixture was dissolved in 100 parts by weight of a 1:1 mixture at a temperature of 7° C. to prepare a coating solution. The viscosity of this coating liquid is I. It was 5 cps.

The over-roll coater was operated by supplying this coating liquid from the supply pipe.

The substrate was a polymethacrylate (PMMA) board with a length of 20 m, a width of 20 cm, and a thickness of 1.2 mm. Guide grooves for optical discs with a diameter of 13 cm were continuously molded at a pitch of 35 cm in the center using ultraviolet curing resin. I used something.

The diameter of the transfer roll was 18 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.

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 16.
8% ± 1.6%, center (center of optical disc) 17
．． 2%±1.3%, and the left side in the transport direction (5 cm from the center of the optical disc) was 17.0%±1.5%. It was ±1.0% within the same optical disc.

Comparative Example The same test as in Example 1 was conducted using the conventional over-roll coater shown in FIGS. 4 and 5. This device is not equipped with a cleaning roll.

1 4 The transmittance is 16.2% ± 4.2% on the right side in the conveyance direction after 40 cm from the start of coating, and 17.4% in the center.
±2.8%, 16.0% ±3 on the left side when facing the conveyance direction
．． 8%, and there was a variation of ±3.1% within the same optical disc.

From the Examples and Comparative Examples, it can be seen that the cleaning roll provides a coating film with little variation in transmittance, that is, with little unevenness in film thickness.

〔Effect of the invention〕

According to the over-roll coater of the present invention, since it is possible to continuously coat a long substrate while cleaning the transfer roll with a cleaning roll, it is possible to suppress local changes in the concentration of the coating liquid in the liquid pool, and also to prevent The density of the ink on the transfer roll, which had been getting darker, can now be kept constant.
Precipitation of solid content from the coating liquid can be prevented.

As a result, continuous production of the optical recording layer can be carried out well,
It is possible to provide an inexpensive optical recording medium.

[Brief explanation of the drawing]

Fig. 1 is a schematic side view of one example of the over-roll coater of the present invention, Fig. 2 is a schematic plan view thereof, Fig. 3 is a schematic diagram of its circulation system, and Fig. 4 is a conventional over-roll coater. FIG. 5 is a schematic side view of an example of a coater, and FIG. 5 is a schematic plan view thereof. 1: Transfer roll 2: Substrate 3: Conveyor belt 4: Drive roll 5: Backup roll 6, 6゛: Cleaning roll 7: Doctor bar 8: Discharge pipe 9: Supply pipe 0: Liquid reservoir ll: Liquid leakage prevention valve 2: (Transfer roll) Non-transfer part 3: (Transfer roll) Transfer part 4: Optical recording medium guide groove 15: Coating film 6: Filter 17: Valve 8: Bomb 19: Tank

Claims (1)

[Claims] 1. An over-roll coater for forming a recording layer on the upper surface of a substrate for an optical recording medium, which is provided with a cleaning roll adjacent to the transfer roll to remove residual coating liquid on the transfer roll. Features an over roll coater. 2. 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 overroll coater according to claim 1, characterized in that it is less than or equal to cps.