FIELD OF THE INVENTION
[0001] This invention relates to a spin-coating apparatus for preparing optical discs.
BACKGROUND OF THE INVENTION
[0002] Hitherto, a spin-coating method has been widely used for preparing optical discs.
The spin-coating method comprises the steps of dropping a coating liquid onto a central
part of a rotating substrate, spreading the liquid outward by centrifugal force to
form a coating film on the substrate, splashing off excess of the liquid from the
edge of the substrate, and then drying the coating film by evaporating the solvent.
Examples of optical discs prepared by the spin-coating method are: an optical disc
of CD-R type comprising a disc-shaped transparent substrate (hereinafter referred
to as "disc substrate" or simply "substrate"), a recording dye layer, a light-reflecting
layer, and a protective layer overlaid in order; an optical disc of DVD-R type formed
by combining a multi-layered composite (comprising a disc substrate, a recording dye
layer, a light-reflecting layer, and if desired, a protective layer overlaid in order)
and another disc substrate (protective substrate) with an adhesive so that the recording
layer may be placed inside; and an optical disc of DVD-R type formed by combining
a pair of the multi-layered composites with an adhesive so that each recording layer
may be placed inside. In preparing these optical discs, the recording dye layer and
the protective layer are often formed by the spin-coating method. In Japanese Patent
Publication No. 7(1995)-118094, the preparation process of CD-R type optical discs
is described in detail.
Moreover, US Patent Serial No. 5,002,008 discloses a coating apparatus for applying
a resist or developing solution to a semiconductor wafer and wherein said apparatus
comprises a plurality of specially-designed nozzles. The spin-coating method is generally
performed by means of an apparatus described below.
[0003] A spin-coating apparatus generally comprises an applying device, a spinner head,
a round guard wall and an exhaust system. The applying device comprises a nozzle equipped
with a pressure tank and a regulating valve for adjusting the amount of a drop of
the coating liquid which is given through the nozzle onto the surface of a disc substrate.
The spinner head is placed below the applying device to hold the substrate horizontally
with a detachable mount, and is rotatable around its axis by means of a driving motor.
In the apparatus, the coating liquid is dropped from the nozzle onto the rotating
substrate horizontally held on the spinner head, and then spread outward to form a
coating film on the substrate. The excess of the liquid is splashed off from the edge
of the substrate by centrifugal force, and then the coating film is dried by evaporating
the solvent. In order to shield the surroundings from the thus splashed excess liquid,
the guard wall is provided around the spinner head and the wall has an opening on
its top. In the exhaust system, air is introduced from the opening on the top, made
to flow over the surface of the substrate, and then exhausted from a space below the
spinner head. Since the exhaust system has an exhaust fan and a regulating valve for
adjusting the amount of the exhausted air, the conditions for drying the coating film
can be easily varied by adjusting the amount of the exhausted air (i.e., by adjusting
the flow rate of the air).
[0004] The nozzle of the applying device is generally made of stainless steel. However,
if the coating liquid is a dye solution for preparing a recording dye layer, the nozzle
of stainless steel exhibits a small contact angle to the solution. This means that
the surface of the nozzle is well wetted with the solution and therefore that the
solution well attaches onto the pointed end (leading end) of the nozzle. As shown
in Figure 5, the solution thus attaching onto the pointed end is liable to easily
dry to deposit a solid dye (sediment 53) while the apparatus is continuously used
for a long time. Tne sediment formed at the pointed end often causes troubles. For
example, the sediment may fall onto the substrate to damage a formed film, and further
it may choke the nozzle to prevent the coating liquid from dropping smoothly. In order
to avoid these troubles, some known apparatuses are equipped with cleaning means by
which the pointed end of the nozzle is washed and dried. However, the apparatus having
the cleaning means requires a complicated system. In practice, the pointed end of
the nozzle is regularly cleaned while the production line is stopped at regular intervals.
However, the regular stoppage of the production line lowers the production efficiency,
and further film-forming errors are liable to occur while the line is repeatedly stopped
and resumed.
SUMMARY OF THE INVENTION
[0005] Accordingly, it is an object of the present invention to provide a spin-coating apparatus
in which the coating liquid hardly attaches onto the pointed end of the nozzle and
hence which can be continuously used for forming a coating film for a long time. In
the spin-coating apparatus of the invention, the coating liquid is prevented from
attaching onto the pointed end of the nozzle without either providing the cleaning
means or stopping the production line at regular intervals.
[0006] The inventors had studied about the nozzle of the applying device, and found the
following fact. If the pointed end of the nozzle has a surface made of polytetrafluoroethylene
(Teflon), the coating liquid hardly attaches onto the end. Consequently, the apparatus
having such nozzle can keep producing optical discs efficiently for a long time without
the troubles.
[0007] The present invention resides in a spin-coating apparatus for preparing optical discs,
comprising
an applying device equipped with a nozzle having a pointed end for giving a dye solution
onto a disc-shaped transparent substrate,
a spinner head which is placed below the applying device to keep the substrate horizontally
and which is rotatable around its axis,
a guard wall provided around the spinner head which has an opening on its top and
keeps therewithin the coating liquid which is given onto the rotating substrate on
the spinner head, spreads outward, and then splashes around the substrate, and
an exhaust system in which air is introduced from the opening, made to flow over the
substrate, and then exhausted from a space below the spinner head;
wherein the nozzle is made of stainless steel, and its surface of the wall is
covered with polytetrafluoroethylene at least at the pointed end and is characterised
in that said coverage is on the inside and outside walls following the pointed end
at a length of longer than 1 mm.
[0008] Preferred embodiments of the invention are as follows.
(1) The coverage of the stainless steel with polytetrafluoroethylene extends to a
length of longer than 5 mm, preferably longer than 10 mm.
(2) The whole surface of the nozzle is completely covered with polytetrafluoroethylene.
BRIEF DESCRIPTION OF DRAWINGS
[0009]
Figure 1 shows a schematic sectional view of a spin-coating apparatus of the invention.
Figure 2 shows schematic views of an applying device of the invention. In Figure 2,
(a) is a plan view and (b) is a front elevation.
Figure 3 shows a schematic sectional view of an example of the nozzle having the pointed
end which is covered with polytetrafluoroethylene
Figure 4 shows a partial schematic sectional view of an optical disc comprising a
disc-shaped transparent substrate, a recording dye layer, a light-reflecting layer,
and a protective layer overlaid in order.
Figure 5 is a schematic view showing a solid dye (sediment) deposited at the pointed
end of a known nozzle.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The spin-coating apparatus of the invention comprises an applying device, a spinner
head, a guard wall and an exhaust system. The applying device has a specific nozzle.
Referring to the attached drawings, the spin-coating apparatus of the invention is
described below in detail.
[0011] Figure 1 shows a schematic sectional view of a spin-coating apparatus of the invention.
As shown in Figure 1, the spin-coating apparatus 10 comprises applying device 11,
spinner head 13, guard wall 15 and exhaust system 18. The applying device 11 comprises
nozzle 12 equipped with a pressure tank (not shown in the figure) and a regulating
valve (not shown in the figure) for adjusting the amount of a drop of coating liquid
which is given through the nozzle 12 onto the surface of the disc substrate 1. In
the apparatus 10, the applying device 11 can be moved from a waiting position to the
predetermined position over the substrate 1 by means of a handling mechanism (not
shown in the figure). The spinner head 13 is placed below the applying device 11 to
hold the substrate 1 horizontally with detachable mount 14, and is rotatable around
the axis with a driving motor (not shown in the figure). In the process for forming
a coating film, the coating liquid is dropped from the nozzle 12 of the applying device
11 onto the rotating substrate 1 horizontally supported by the spinner head 13, and
then spread outward by centrifugal force to form a coating film on the substrate 1.
The excess of the liquid is splashed off from the edge of the substrate 1, and the
coating film is dried by removing the solvent. In order to keep the surroundings from
the thus splashed liquid, the guard wall 15 is provided around the spinner head 13
and the wall has an opening 16 on its top position. The excess liquid collected on
the guard wall 15 is introduced into the drain 17. In the exhaust system 18, air is
aspirated from the opening 16, made to flow over the surface of the substrate 1, and
then exhausted from a space below the spinner head 13. Since the exhaust system 18
has an exhaust fan 19 and a regulating valve (not shown in the figure) for adjusting
the amount of the exhausted air, the conditions for drying the coating film can be
easily varied by adjusting the amount of the exhausted air (i.e., by adjusting the
flow rate of the air).
[0012] The applying device having the specific nozzle is described below in detail.
[0013] Figure 2 shows schematic views of an applying device of the invention. In Figure
2, (a) is a plan view and (b) is a front elevation. Figure 3 also shows a schematic
sectional view of a preferred example of the nozzle. In the nozzle 22 of the applying
device 21 according to the invention, the pointed end and both the inside and the
outside within not less than 1 mm of the pointed end have surface made of polytetrafluoroethylene.
Typical examples of the nozzle preferably used for the invention are: a nozzle in
which the pointed end and the body within not less than 1 mm of the pointed end are
made of polytetrafluoroethylene; and a nozzle (shown in Figure 3) in which the pointed
end 23 and both of the inner wall surface 24 and the outer wall surface 25 within
not less than 1 mm of the pointed end are covered with polytetrafluoroethylene. The
former nozzle is, for example, prepared in the following manner. First, the nozzle
body except for the end part is beforehand made of stainless steel. After that, the
end part (the pointed end and the body within not more than 5 mm of the pointed end)
is made of polytetrafluoroethylene. This structure is practically preferred in consideration
of strength of the nozzle. In the nozzle shown in Figure 3, the pointed end and the
nozzle body within not less than 10 mm of the pointed end are preferably covered with
polytetrafluoroethylene. More preferably, the whole surface of the nozzle is completely
covered with polytetrafluoroethylene. The thickness of the coating polytetrafluoroethylene
covering layer is not particularly restricted, but usually in the range of 5 to 500
µm. As described above, the body of the nozzle is preferably made of stainless steel.
The inner diameter of the nozzle generally is in the range of 0.5 to 1.0 mm.
[0014] The following is a detailed description of the process for preparing optical discs
employing the spin-coating apparatus having the applying device equipped with the
nozzle of the invention.
[0015] A typical optical disc prepared in the process is shown in Figure 4. The disc 40
in Figure 4 comprises a disc-shaped transparent substrate 1, a recording dye layer
2, a light-reflecting layer 3, and a protective layer 4 overlaid in this order.
[0016] Examples of materials for the substrate include polycarbonate, acrylic resins such
as polymethyl methacrylate, vinyl chloride resins such as polyvinyl chloride and vinyl
chloride copolymer, epoxy resins, amorphous polyolefins, and polyesters. These materials
can be employed in combination, if desired. Polycarbonate is most preferred from the
viewpoints of humidity resistance, dimensional stability and economical cost.
[0017] On the surface of the substrate, a pregroove for tracking or giving address signals
is preferably formed. The pregroove is preferably formed directly on the surface of
the substrate when the substrate is molded from polymer material (such as polycarbonate)
by injection or extrusion. The pregroove preferably has a depth in the range of 0.01
to 0.3 µm and a half-width of 0.2 to 0.9 µm.
[0018] The recording dye layer is formed on the disc substrate in the following manner by
means of the spin-coating apparatus of the invention.
[0019] First, the disc substrate 1 is installed on the mount 14 of the spinner head 13 shown
in Figure 1. The substrate 1 is horizontally kept on the spinner head 13. The coating
liquid supplied from the pressure tank (not shown in the figure) is introduced to
the regulating valve (not shown in the figure) so that the amount may be adjusted
to the predetermined volume, and then dropped through the nozzle 12 onto the central
part of the substrate 1. As described above, since the nozzle 12 of the invention
has the surface of polytetrafluoroethylene at the pointed end and on the inside and
the outside walls within not less than 1 mm from the pointed end, the coating liquid
hardly adheres to the end. Therefore, the coating film can be smoothly formed without
troubles caused by the deposited dye. The coating liquid is generally prepared by
dissolving a dye in a proper solvent in an amount of 0.01 to 15 wt.%, preferably 0.1
to 10 wt.%, more preferably 0.5 to 5 wt.%, further preferably 0.5 to 3 wt.%.
[0020] In the apparatus, the spinner head 13 is made to rotate at a high speed by a driving
motor. The coating liquid is dropped onto the central part of the rotating substrate
1, spread outward to the edge of the substrate 1, and then splashed off from the edge
by centrifugal force. The splashed liquid bumps on the guard wall 15 to gather in
a gutter provided at the foot of the wall, and the gathered liquid is removed through
the drain 17. During or after the procedure for forming the coating film, the film
is dried. The coating film (dye recording layer) generally has a thickness of 20 to
500 nm, preferably 50 to 300 nm.
[0021] The dyes used for the recording dye layer are not particularly restricted. Examples
of the dyes include cyanine dye, phthalocyanine dye, imidazoquinoxaline dyes, pyrylium/thiopyrylium
dyes, azulenium dyes, squalilium dyes, metal complex dyes such as Ni complex and Cr
complex, naphthoquinone dyes, anthraquinone dyes, indophenol dyes, indoaniline dyes,
triphenylmethane dyes, merocyanine dyes, oxonol dyes, aminium/diimmonium dyes, and
nitroso compounds. Preferred are cyanine dye, phthalocyanine dye, azulenium dyes,
squalilium dyes, oxonol dyes, and imidazoquinoxaline dyes.
[0022] Examples of the solvent used for the coating liquid for the dye recording layer include
esters such as butyl acetate and cellosolve acetate; ketones such as methyl ethyl
ketone, cyclohexanone and methyl isobutyl ketone; chlorinated hydrocarbons such as
dichloromethane, 1,2-dichloroethane and chloroform; amides such as dimethylformamide;
hydrocarbons such as cyclohexane; ethers such as tetrahydrofuran, diethyl ether and
dioxane; alcohols such as ethanol, n-propanol, isopropanol, n-butanol, and diacetone
alcohol; fluorine atom-containing solvents such as 2,2,3,3-tetrafluoropropanol; and
glycol ethers such as ethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether
and propyleneglycol monomethyl ether. These solvents can be employed in combination
in consideration of the solubility of the used dye. Preferred are fluorine atom-containing
solvents such as 2,2,3,3-tetrafluoropropanol.
[0023] The coating liquid may contain, if desired, not only an anti-fading agent and a binder
but also auxiliary additives such as an oxidation inhibitor, a UV absorber, a plasticizer
and a lubricant.
[0024] Examples of the anti-fading agents include nitroso compounds, metal complex compounds,
diimmonium salts and aminium salts. Those examples are described in Japanese Patent
Provisional Publications No. H2(1990)-300288, No. H3(1991)-224793 and No. H4(1992)-146189.
[0025] Examples of the binders include natural-origin polymers such as gelatin, cellulose
derivatives, dextran, rosin and rubber; hydrocarbon polymer resins such as polyethylene,
polypropylene, polystyrene and polyisobutyrene; vinyl polymers such as polyvinyl chloride,
polyvinylidene chloride, and vinyl chloride-vinyl acetate copolymer; acrylate polymers
such as polymethyl acrylate and polymethyl methacrylate; polyvinyl alcohol, chlorinated
polyethylene; epoxy resins; butyral resins, rubber derivatives, and thermosetting
resins such as prepolymers of phenol-formaldehyde. The binder is generally used in
an amount of not more than 20 weight parts, preferably not more than 10 weight parts,
more preferably not more than 5 weight parts based on 100 parts of the dye.
[0026] The substrate may have an undercoating layer on its surface on the recording layer
side, so as to enhance surface smoothness and adhesion and to keep the dye recording
layer from deterioration.
[0027] Examples of the material for the undercoating layer include polymers such as polymethyl
methacrylate, acrylate-methacrylate copolymer, styrene-maleic anhydride copolymer,
polyvinyl alcohol, N-methylolacrylamide, styrene-vinyltoluene copolymer, chloro-sulfonated
polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester,
polyimide, vinyl acetate-vinyl chloride copolymer, ethylene-vinyl acetate copolymer,
polyethylene, polypropylene and polycarbonate; and surface treating agents such as
a silane-coupling agent. The undercoating layer can be formed by applying a coating
solution (in which one or more of the above-mentioned materials are dissolved or dispersed)
onto the surface of the substrate by the known coating methods such as spin-coat,
dip-coat, and extrusion-coat. The undercoating layer generally has a thickness of
0.005 to 20 µm, preferably 0.01 to 10 µm.
[0028] On the dye recording layer, the light-reflecting layer is placed so as to enhance
the light-reflection in the course of reproduction of information. The light-reflecting
material to be used for the formation of the light-reflecting layer should show a
high reflection to the laser light. Examples of the light-reflecting materials include
metals and sub-metals such as Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re,
Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po,
Sn, and Bi. Stainless steel film is also employable. Preferred light-reflecting materials
are Cr, Ni, Pt, Cu, Ag, Au, Al and stainless steel film. These materials can be employed
singly, in combination, or in the form of alloy. Au, Ag and their alloys are particularly
preferred. The light-reflecting layer can be formed on the recording layer by vacuum
deposition, sputtering, or ion-plating. The thickness of the light-reflecting layer
generally is 10 to 800 nm, preferably 20 to 500 nm, more preferably 50 to 300 nm.
[0029] On the light-reflecting layer, a protective layer can be placed so as to protect
the recording layer from chemical deterioration or physical damage. The protective
layer can be also placed on the substrate on the face not having the recording layer
so as to enhance the scratch resistance and the moisture resistance of the disc. The
protective layer can be formed of inorganic materials such as SiO, SiO
2, MgF
2, SnO
2, and Si
3N
4; or organic materials such as thermo-plastic resins, thermosetting resins, and UV
curable resins.
[0030] The protective layer can be formed on the light-reflecting layer and/or the substrate
by laminating a film of plastic material with an adhesive. The inorganic material
can be also placed on the light-reflecting layer and/or the substrate by vacuum deposition
or sputtering. Otherwise, the organic polymer material can be coated in the form of
a solution containing the polymer material and dried to give the protective layer.
For example, the UV curable resin is dissolved in a solvent and coated on the light-reflecting
layer and/or the substrate, and cured by applying ultra-violet rays to the coated
solution. The coating solution may include various additives such as an anti-static
agent, an oxidation inhibitor, and a ultra-violet absorber. The protective layer generally
has a thickness of 0.1 to 100 µm.
[0031] In the process for producing an optical disc, the undercoating layer and/or the protective
layer may be formed by means of the spin-coating apparatus of the invention in the
manner described above for forming the recording dye layer.
Example and Comparison Example
[Comparison Example 1]
[0032]
[0033] The cyanine dye having the above formula was dissolved in 2,2,3,3-tetrafluoropropanol
to give a coating solution for preparing a recording dye layer (dye content: 2.65
% wt./vol.).
[0034] Independently, a polycarbonate transparent substrate (diameter: 120 mm, thickness:
1.2 mm, Panlight AD5503 (trade name), available from Teijin Limited) was prepared.
The substrate had a spirally formed pregroove (track pitch: 1.6 µm, width: 0.5 µm,
depth: 0.17 µm) which was produced by the injection molding.
[0035] The coating solution was then applied onto the substrate surface having the pregroove
thereon by means of a conventional spin-coating apparatus comprising an applying device
equipped with a stainless steel nozzle (inner diameter: 0.8 µm). The rotation of the
spinner head was varied from 300 r.p.m. to 2000 r.p.m., to form a recording dye layer
(thickness at the groove: approx. 200 nm). The conditions for forming the layer were
as follows:
room temperature and humidity: 23°C and 50%RH,
temperature of the solution: 23°C,
temperature of the substrate: 23°C, and
flow rate of the air: 0.8 m/second.
[0036] On the coated dye layer, a light-reflecting layer (thickness: 100 nm) of gold was
provided by sputtering. Subsequently, a UV curable photopolymer (UV curable agent:
SD-220, available from Dainippon Ink & Chemicals, Inc.) was coated on the light-reflecting
layer by means of the conventional spin-coating apparatus. The rotation of the spinner
head was varied from 300 r.p.m. to 2,000 r.p.m. to give a coated layer. The coated
layer was irradiated with ultra-violet rays for curing to form a protective layer
(thickness: 8 µm).
[0037] Thus, an optical disc of CD-R type comprising the substrate, the dye recording layer,
the light-reflecting layer and the protective layer overlaid in order was produced.
[Example 1]
[0038] The procedure of Comparison Example 1 was repeated except for using the spin-coating
apparatus of the invention (shown in Figure 1) comprising an applying device equipped
with a nozzle (material of the body: stainless steel, inner diameter: 0.8 µm) having
the whole wall surface completely covered with polytetrafluoroethylene, in place of
the above conventional apparatus. Thus, an optical disc of CD-R type was produced.
[Evaluation of Spin-Coating Apparatuses]
[0039] After 300 discs were continuously produced in accordance with Comparison Example
1, a deposited solid dye (sediment 53) was observed at the pointed end of the nozzle
as shown in Figure 5. In contrast, the nozzle employed in Example 1, no sediment was
observed even after 300 discs were continuously produced. Consequently, it was confirmed
that 300 discs of high quality were continuously produced without any trouble by means
of the apparatus of the invention.