JPH05220442A - Method for forming protective film - Google Patents

Abstract

PURPOSE:To form a protective film having extremely uniform thickness by almost horizontally rotating the protective film forming surface of a base material and supplying a protective film forming substance to the rotating surface from a nozzle at a predetermined jet speed to form a liquid film and subsequently curing the liquid film. CONSTITUTION:In forming a protective film 7 on the protective film forming surface of a base material 1 by a spin coating method, said protective film forming surface is almost horizontally rotated and a liquid protective film forming substance whose viscosity is adjusted to 20cps or less is supplied to the rotating surface from a nozzle at a jet speed of 110cm/sec or less to form a liquid film which is, in turn, cured to form the protective film 7. As mentioned above, the viscosity at the time of coating of the curable resin used in the formation of the protective film 7 is set to 20cps or less. When said viscosity is higher than 20cps, the thickness control of the protective film becomes hard. When the jet speed of the curable resin is higher than 110cm/sec, coating irregularity is generated and non-uniformity is generated in the thickness of the protective film 7.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a protective film. More specifically, the present invention relates to a method of forming a hard protective film on the surface of a synthetic resin substrate such as an optical disc to prevent scratches.

[0002]

2. Description of the Related Art In recent years, an optical recording medium such as a write-once type or a rewritable type has attracted attention as a large capacity memory.
An optical recording medium has a recording layer on which a signal is recorded, which is formed on one surface of a transparent substrate. Recording and reproduction are usually performed by converging laser light from the opposite side (hereinafter, substrate side). Therefore, the substrate side is used while being exposed to the atmosphere,
Dust may adhere and cause scratches.

A transparent resin substrate such as polycarbonate is usually used as a substrate, but the surface hardness of the transparent resin substrate is lower than that of metal and the like, and the substrate is easily scratched by physical impact. The generation of scratches hinders recording and reproduction with laser light. Therefore, a method is known in which a transparent resin film having a relatively high hardness such as an ultraviolet curable resin is formed as a protective film on the substrate side to protect the substrate.

[0004]

A spin coating method is generally used as a method for forming a protective film. However, when the spin coating method is used, the thickness of the protective film formed may vary depending on the coating conditions. Uniformity may occur. Further, if the range in which the thickness of the protective film is not uniform is not sufficiently smaller than the laser beam diameter (about 1 mm) on the protective film, recording and reproduction may be adversely affected. In the worst case, a focus error and a tracking error may occur, which may cause servo misalignment and operation stop. The present invention has been made in view of these facts, and an object thereof is to make the film thickness of the protective film uniform.

[0005]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that the problem can be solved by making the spin coat condition a special condition, Has been completed. The gist of the present invention is to form a protective film by spin coating.
The surface of the base material on which the protective film is to be formed is rotated substantially horizontally and rotated, and a liquid protective film-forming substance having a viscosity of 20 centipoises or less is rotated 110 cm from the nozzle.
Is supplied at a jet speed of not more than / sec to form a liquid film, and then
A method for forming a protective film is characterized in that the liquid film is cured.

The present invention will be described in more detail below by taking an optical recording medium as an example. The structure of the optical recording medium is shown in FIG.
2 is roughly classified into an air sandwich structure method as shown in FIG. 2, a whole surface contact bonding method as shown in FIG. 2 and a single plate coating method as shown in FIG. The present invention can be applied to any of these structures. In the figure, 1 is a substrate, 2 is a recording layer,
3 is a spacer, 4 is an air layer, 5 is an adhesive layer, 6 is a protective layer,
Reference numeral 7 indicates a protective film (overcoat layer).

In the present invention, the substrate 1 (base material) is
A resin substrate made of polycarbonate resin, acrylic resin, polystyrene resin, polymethylmethacrylate resin or the like is used. As the recording layer 2, any layer structure generally used for publicly known optical recording can be used. For example,
A write-once recording layer made of a low melting point metal such as Te. Further, for example, TbFe, TbFeCo, TbCo, Dy
Amorphous magnetic alloy of rare earth and transition metal such as FeCo, Mn
An example of the magneto-optical recording layer is a polycrystalline perpendicular magnetization film such as Bi or MnCuBi. A single layer may be used as the magneto-optical recording layer, or a single layer such as GdTbFe / TbFe may be used.
Recording layers of more layers may be stacked.

Normally, in the case of the write-once type (drilling type), as shown in FIG. 1, an air sandwich type in which a spacer 3 is formed so as to form an air layer 4, and a magneto-optical recording type is illustrated. As shown in FIG. 2, a bonding type in which two substrates are bonded by an adhesive layer 5 or a recording layer 2 as shown in FIG.
It is used as a coating type in which the surface of the protective layer 6 is coated. The present invention is applicable to any type of medium.

In the present invention, as a protective film forming substance for forming the protective film 7, a so-called hard coat agent made of a curable resin such as an energy ray (for example, ultraviolet ray) curable type or a thermosetting type is used. As the energy ray (for example, ultraviolet ray) curable resin, a resin composed of a compound having a single or a plurality of acrylate or methacrylate groups, for example, a resin mainly containing epoxy acrylate or urethane acrylate is preferably used. In addition, as the thermosetting resin, silicon-based resin, epoxy-based resin, titanium-based resin, or the like is used.

In the present invention, the viscosity of the curable resin used for forming the protective film 7 at the time of application is 20 cP (centipoise) or less, preferably 1 to 5 cP. When the viscosity is higher than 20 cP, it becomes difficult to control the thickness of the protective film, which is not preferable. The viscosity is preferably adjusted to the above viscosity by diluting the curable resin with a solvent before use. further,
The spin coating conditions for applying the curable resin include:
The surface on which the protective film is formed is rotated substantially horizontally, and the jetting linear velocity from the coating nozzle is 110 cm / sec or less, preferably 10 to 10.
A curable resin is supplied and applied at a rate of 110 cm / sec. When the jet linear velocity is higher than 110 cm / sec, coating unevenness occurs and the thickness of the protective film becomes uneven, which is not preferable. Other conditions for the spin coating are not particularly limited, but generally the inner diameter of the coating nozzle is 0.5 to
2.0 mm, substrate rotation speed during coating 300-2000 rpm,
It is preferably carried out in the range of 400 to 1000 rpm.

The protective film of the present invention is usually used for forming the protective film 7 on the substrate opposite to the recording layer of the disk (base material) substrate, and the protective layer on the recording layer as shown in FIG. Of course, it may be used for forming 6. For the liquid film curing conditions after the liquid film is formed, a curing method suitable for each coating agent may be used. For example, energy curing type, that is, ultraviolet curing type is irradiated with ultraviolet rays, and electron beam curing type is irradiated with electron beam. For example, a method of irradiating and heat-treating if it is a thermosetting type is adopted.

The thickness (after curing) of the protective film formed is usually preferably 0.5 to 100 μm, more preferably 1 to 50 μm. Furthermore, 1 to 20μ
About m 2 is preferable, and if it is thicker than this, deformation of the substrate may occur due to the influence of shrinkage of the protective film, and measures must be taken for this. If it is too thin, durability deteriorates.

Although the above description has been made with reference to an optical recording medium, the present invention is applicable to other optical products such as plastic lenses,
Of course, it is also useful for forming a protective film for other articles.

[0014]

EXAMPLES Examples of the present invention will be described below, but the scope of the present invention is not limited by the following examples unless the gist thereof is exceeded. The present inventors conducted a detailed study on the spin coating method and found the relationship between spin coating conditions and film thickness unevenness. As a simple evaluation method of the film thickness unevenness, a visual method, particularly a method of observing the cleanliness of the coating boundary line on the inner peripheral portion of the disk is easy. However, as a final evaluation, the focus error signal and the tracking error signal should be measured by the inspection drive.

Spin coating conditions include those relating to the material to be coated, those relating to the coating nozzle, and those relating to the spinner (rotating body). Related to the material is the viscosity of the material. A nozzle inner diameter is related to the coating nozzle. When the spin coater applies a material having low viscosity, about 1 mm is suitable. When the ejection linear velocity is constant, the larger the nozzle inner diameter, the larger the coating amount per unit time.

Next, regarding the distance between the substrate and the nozzle, if this is too small, turbulence will occur in the flow of the coating agent, and if it is too large, scattering of the coating agent will increase. The nozzles can be moved from the inner circumference to the outer circumference, from the outer circumference to the inner circumference again to the outer circumference, or after applying only the inner circumference to the outer circumference by centrifugal force of rotation. There is. Especially when the coating agent is diluted with a solvent,
In some cases, the solvent volatilizes to some extent when the substrate is thinly spread by rotation, and the film thickness distribution during coating may be determined. The application time is determined by the speed and distance traveled by the nozzle. Further, the coating agent consumption amount is determined by the coating time and the coating amount per unit time.

The condition related to the spinner is the rotation speed. In the case of spin coating, in order to make the film thickness uniform, it is often the case that the coating is applied at a certain rotation speed and then rotated at a higher rotation speed for a while, and the excess coating material is shaken off. However, when the solvent-diluting type coating agent is used, the coating film thickness after coating most depends on the rotation speed during coating.

The present inventors tried coating by changing the nozzle inner diameter, the coating time, the ejection linear velocity, and the rotation speed during coating among the above conditions, and observed the coating film thickness unevenness. As a result, it was found that the occurrence of film thickness unevenness depends only on the jet linear velocity and not on the nozzle inner diameter, the coating time, and the rotation speed. Specifically, it was confirmed that when the viscosity of the coating agent was 5 cP and the ejection linear velocity was 110 cm / s as a boundary, the film thickness unevenness did not occur below that, and the film thickness unevenness occurred above that.

EXAMPLE An inorganic write-once recording layer was formed on a polycarbonate substrate, and the opposite surface was spin-coated with an ultraviolet curable resin under various conditions. First, the fixed conditions are shown below. Coating material viscosity: 5 cP Shaking off speed: 1000 rpm Shaking off time: 10 seconds Coating nozzle height: 1.2 mm Coating direction: outer circumference → inner circumference → outer circumference

With respect to the above conditions, the following conditions were individually changed, and it was confirmed whether or not the film thickness unevenness occurred. The coating time was the time at which the coating amount was 10 g under each condition. (1) Nozzle inner diameter 1.12, 0.90 mm (2) Coating amount 6, 8, 10 g (3) Coating rotation speed 400, 600 rpm (4) Discharge linear velocity 60, 80, 100, 110, 12
The results of 0,140 cm / sec are shown in Table 1.

[0021]

[Table 1]

From the above, it can be seen that the presence or absence of uneven coating on the inner circumference depends only on the discharge linear velocity, and does not depend much on the inner diameter of the nozzle, the coating amount, and the number of revolutions. The occurrence of coating unevenness greatly depends on the discharge linear velocity, so even if for some reason, you change certain conditions, adjust the other conditions so that the discharge linear velocity does not exceed the specified value, and avoid coating unevenness. it can.

[0023]

According to the method of the present invention, a protective film having an extremely uniform film thickness is formed. Therefore, when applied to an optical recording medium or the like, optical distortion is small and scratches are prevented from being practically used. A very suitable protective film can be obtained.

[Brief description of drawings]

FIG. 1 Sectional view

FIG. 2 is a sectional view.

FIG. 3 is a sectional view.

[Explanation of symbols]

 1 Substrate 7 Protective film

Claims (4)

[Claims] 1. When forming a protective film by a spin coating method, the base material on which the protective film is formed is rotated with its surface on which the protective film is formed being substantially horizontal, and the rotating surface is prepared to have a viscosity of 20 centipoise or less. A method for forming a protective film, which comprises supplying a liquid protective film-forming substance from a nozzle at a jet speed of 110 cm / sec or less to form a liquid film, and then curing the liquid film. 2. The method for forming a protective film according to claim 1, wherein the number of revolutions of the substrate is 300 to 2000 rpm. 3. The method for forming a protective film according to claim 1, wherein the liquid protective film forming substance is an ultraviolet curable resin. 4. The method for forming a protective film according to claim 1, wherein the inner diameter of the nozzle is 0.5 to 2 mm.