JPH02123172A - Ultraviolet-curing coating composition in low-viscosity liquid form - Google Patents

Abstract

PURPOSE: To provide a quickly curable coating composition to form a thin and scratch-resistant coating film, which contains a poly(meth)acrylate, carboxylic acid containing (metha)acrylic unsaturation and diol-di(metha)acrylate at specific ratio.

CONSTITUTION: This coating composition contains (A) 30-50% (to total weight of polymerizing materials) of one kind or more of poly(meth)acrylates containing at lest 2.4 of (metha)acrylate groups per molecule (example: trimethylolpropane triacrylate), (B) 5-15% of a carboxylic acid having (metha)acrylic unsaturation, (C) 20-40% of a 4-8C diol-di(meth)acrylate and (D) at least one kind of photopolymerization initiators, and has 15-50 centipoise of viscosity.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to ultraviolet curable coating compositions that can be applied by spin coating, have a high viscosity and are cured to provide scratch resistance. The present invention is an optical disc having a surface configured to suitably reflect light rays. The cured coating of the present invention provides a thin overcoat that is scratch resistant to the structured surface of the disk.

BACKGROUND OF THE INVENTION Ultraviolet curable coatings based on materials with acrylate end groups are well known. However, prior to the present invention, it has not been possible to provide rapidly curing thin coatings that are reasonably resistant to scratching from normal operations. This suggests that the viscosity of the acrylate-functional material that cures to provide the desired scratch resistance is too high to be used to form thin films formed by the known method of spin-coating under consideration. .

More specifically, the flat-surfaced polycarbonate disk is provided with a very thin metal surface, for example by vapor deposition of aluminum. The aluminum deposited surface can be formed by laser roughening selected portions thereof, or the like. As a result, the light beam is reflected in a predetermined manner by the flat aluminum deposited surface, but scattering occurs at this roughened area. In this way, the aluminum deposited surface has an optical image that can be used to generate electronic messages. The surfaces of these structures carry information that can be used for all kinds of purposes, for example for reproducing acoustic images.

Scratching on this aluminum deposited surface will alter the desired optical image, so the surface must be protected. In the present invention, the aluminum deposited surface is protected by coating the surface, and the protective coating must be extremely thin and scratch resistant.

Spin coating can be used to provide desired thin films because it provides greater control over the deposited thickness. However, in spin coating, the coating composition that is applied and spread onto the disk by centrifugal force is approximately
It should have a low viscosity, less than 0 centipoise. This is much lower than the viscosities used in roller, brush or spray applications.

Films that form when the viscosity is less than about 15 centipoise are unsatisfactory because the coating does not have good integrity when spreading.

In preferred practice, it is desirable to use a coating with a viscosity of 20 to 35 centipoise. The viscosities shown herein are measured at 25°C. Films produced by spin-coating coatings having the intended and required viscosity range from about 0.1 to about 0.3 mil. Organic solvents cannot be used to dilute the composition to the desired viscosity, since using organic solvents results in undesirable volatile content. Also,
Substantial loss of material can occur during and after curing, changing the properties of the cured coating. the result,
The compositions under consideration should be substantially free of organic solvents and have very low and narrow range viscosities.

[Means and effects for solving the problems] The present invention provides a liquid coating composition containing at least one poly(meth)acrylate having an average of at least 2.4 (meth)acrylate groups per molecule. 30% to about 50% and about 5 carboxylic acids having (meth)acrylic acidic unsaturation
% to about 15% and about 20% to about 40% of 04-C8 diol di(meth)acrylate, preferably 1,6-hexanediol diacrylate or dimethacrylate,
UV-curable coatings having the required low viscosity by incorporating at least one photoinitiator that renders the composition sensitive to UV radiation, i.e., curable upon exposure to radiation in or near the UV range. The proportion of said diol di(meth)acrylate is from about 15 to about 50 centipoise, preferably from 20 to 35 centipoise.
The proportions stated herein, including in the claims featuring viscosities in the centipoise range, are by weight relative to the total weight of the polymerizable material, unless otherwise specified.

It is well known that the term "(meth)acrylate" refers to acrylic acid or methacrylic acid esters. It is well known that the term poly(meth)acrylate also represents a large number of these groups.

Epoxy di(meth)acrylate, especially with a molecular weight of about 60
from about 1% to about 12%, preferably from 3% to 7% diacrylate of diglycidyl ether of bisphenol less than 0
It is also preferable to have This is an optional ingredient that acts to strengthen the coating.

As is well understood in the art, acrylates cure more quickly than methacrylates and are superior for this reason.

More specifically regarding poly(meth)acrylates having an average of at least 2.4 (meth)acrylate groups per molecule, these compounds preferably include trimethylolpropane triacrylate, various polyacrylates and polymethacrylates. They can also be used and replaced in whole or in part by the preferred triacrylates. Therefore, trimethylolpropane triacrylate is preferred, but
Useful polyacrylates and polymethacrylates having an average of at least about 2.4 unsaturated groups per molecule also include propoxylated glycerol triacrylate or pentaerythritol triacrylate or tetraacrylate. Although less preferred, the corresponding methacrylates can also be used.

Up to about 6 acrylate groups per molecule can be used, such as in the case of glucose hexaacrylate.

In more detail about the preferred trimethylolpropane triacrylate, trimethylolpropane can be completely or nearly completely acrylated. It is convenient to use trimethylolpropane which has been acrylated to provide an average of about 28 acrylate groups per molecule. It is understood that the term trimethylolpropane triacrylate also covers incompletely acrylated materials such as those mentioned above, as coatings can be produced that are reasonably scratch resistant. The available trimethylolpropane triacrylates are those with an average of 2.4 to 2.8 acrylate groups per molecule; these are preferred due to their effectiveness.

Although trimethylolpropane triacrylate or other similar polyacrylates or methacrylic acids provide considerable strength and abrasion resistance, a greater amount of this exemplary poly(meth)acrylate component than is used herein If this method is used, it will not be possible to obtain the low viscosity required by the present invention. Although trimethylolpropane triacrylate and similar poly(meth)acrylates are considered components that reduce coating viscosity, the viscosity required in this invention can be achieved by conventional methods using large proportions of trimethylolpropane triacrylate. Much lower viscosity than can be provided.

Another necessary factor in the compositions of the present invention is the presence of about 5% to about 15% carboxylic acid having (meth)acrylic acidic unsaturation. These acids are important to obtain a cured coating that has strong adhesion to the underlying substrate. Carboxylic acids with (meth)acrylic acidic unsaturation are used to provide this adhesion.

Acrylic acid itself is particularly preferred, but methacrylic acid can also be used.

Carboxyl-functional C1-CB alkylene esters and the corresponding amides of acrylic acid are also conceivable. Suitable esters include β-carboxyethyl acrylate. A suitable amide includes N-ε-carboxyhexyl acrylamide. The corresponding methacrylates and methacrylamides are also useful.

In the present invention, it is essential to use C4-C8 diol di(meth)acrylate, preferably from about 20% to about 40% of 1,6-hexanediol diacrylate. Other C4-C8 diol di(meth)acrylates, e.g. 1
, 4-butanediol diacrylate-1 or dimethacrylate or 1°8-octanediol dimethacrylate can also be used. A preferred diacrylate is 1,6-hexanediol diacrylate, which is particularly useful in providing the low viscosity necessary for this invention. This diol di(meth)acrylate is used in the present invention to adjust the viscosity of the composition to a specific range.

In the earlier work of A. Frank Lea, U.S. Pat. was a secondary issue.

Nevertheless, UV curable coatings similar to those contemplated in the present invention have been disclosed.

However, in Leo's invention it was not possible to use a very large proportion of diol di(meth)acrylate, which is essential to the invention.

The purpose of using diol diacrylates in the Leo disclosure was to improve limited flexibility. Large amounts of diol diacrylate components could not be used in the Leo patent because such large amounts were inconsistent with the pre-required high hardness and abrasion resistance. Although relatively low viscosities have been desired for some time, the even lower viscosities required to achieve cured thicknesses of about 0.1 to about 0.3 mils are more consistent with the average per molecule disclosed by Leo. polyacrylates or polymethacrylates having at least 24 unsaturated groups with at least 70%.

The photoinitiators used in the present invention are aryl ketones, which are well known for UV curing of (meth)acrylate functional materials. They are shown in the examples and are merely of background interest. Substituted acetophenones, especially those that are hydroxy-substituted, are particularly effective. A number of substituted acetophenones are described in U.S. Pat.
No. 284.485 and No. 4,318,791.

These photoinitiators are usually about 0.1% to IO%,
More specifically, it is used in an amount of 1% to 6%.

Although ultraviolet light has been used, this term is used in a narrow sense to
The wavelength may be approximately 400 na+. This term broadly refers to wavelengths of light in the near-ultraviolet visible region that are known to be useful for radiation curing of C(meth)acrylate functional materials due to the presence of an aryl ketone photoinitiator. Also includes.

Eboxy di(meth)acrylate, especially with a molecular weight of about 60
Approximately 1% diglyndyl ether of bisphenols less than 0
It is also preferred to have up to about 12%, preferably between 3% and 7%. This is an optional ingredient mentioned above. When used, this optional component is included in the calculation as part of the component having at least 2.4 (meth)acrylate groups per molecule.

Another optional ingredient that further increases scratch resistance by reducing surface tension without leaching from the coating is
silicone dicarbinol diurethane di(meth)acrylate, which ranges from about 0.5% to about 2.5% of the composition;
used in an amount of %. These compounds are based on organopolysiloxanes containing two substituents, each having a carbinol end group. The carbinol group starts from an organopolysiloxane with dihydroxy end groups, which is alkoxylated with ethylene oxide or propylene oxide to form the alkylene oxide portion of the molecule.
Provided by making 0% (haze formation).

The carbinol functionality thus provided is reacted with an organic diisocyanate, such as 2.44 toluene diisocyanate or isophorone diisocyanate, and a hydroxy-functional acrylate, such as 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate, to form an organopolysiloxane. A diacrylate functional diurethane derivative of cicarbinol is produced.

The order of the above reactions can be changed. The silicone sicarbinol is reacted with an excess of diisocyanate and then hydroxyacrylate, or the hydroxyacrylate is pre-reacted in a ratio of 1 mole of diisocyanate to form an unsaturated monoisocyanate, which is combined with sicarbinol, isocyanate and carbinol. It is also possible to react in stoichiometric amounts relative to functionality.

Commercially available organopolysiloxanes with conventional carbinol end groups are methyl or phenyl substituted (methyl substitution is preferred and used in the examples). The molecular weight of these carbinol-terminated organopolysiloxanes ranges from about 600 to about io,000.

The initial poly(methyl or phenyl)siloxane is dihydroxy terminated and these hydroxy end groups are pre-reacted with a monoepoxide such as propylene oxide or butylene oxide to provide terminal carbinol groups. This terminal carbinol group is then reacted with a sufficient amount of ethylene oxide or propylene oxide (alkylene oxide) to form a reacted alkylene oxide of about 200
~70%, preferably reacted ethylene oxide 40
% to 60% and is converted to urethane acrylate to form the polyethoxylate used in the present invention. A common commercially available material is polymethylpolysiloxane, which is ethoxylated to an ethylene oxide content of about 50% and has a number average molecular weight of 2000 to 6.
000.

A small amount of sowbornyl acrylate is used to increase flexibility,
It is also possible to enhance the liquid nature of the composition or one of its components.

The invention is illustrated as follows.

The ingredients shown in the table below (typically at a temperature of about 40°C)
Two coating formulations are provided by mixing with heating to ensure dissolution.

Table Example 1 Example 2 Epoxide diacrylate (1) 6.0
6.0 Trimethylolpropane triacrylate (2) 40.5
40.51.6-hexanediol diacrylate 32.0
32.0 Acrylic acid 10
．． 7β-carboxyethyl acrylate - 1
0.7 Silicone dicarbinol diurethane di(meth)acrylate 0.3 0
．． 3 Photopolymerization initiator (4) 4.
24 4.24 Stabilizer (5)
0.02 0.02 Evening Rockyur (Da
rocure) 1.173 (6) 4.2
4 4.24 Ultraviolet blocker (7)
2.0 2.0 (1) Bisphenol A with a molecular weight of 390 reacted with 2 moles of acrylic acid
diglycidyl ether.

(2) A material having an average of 2.8 acrylate groups per molecule was used.

(3) Dihydroxy-functional polymethylpolysiloxane with up to 50% ethylene oxide polyethoxylated and a molecular weight of 6000 (Dow Corning)
KAI Q4-3687 manufactured by Nlng) was reacted with 1 mole of inphorone diisocyanate and 1 mole of 2-hydroxyethyl acrylate per hydroxy group to form cicarbinol diurethane silicone diacrylate. I tried to do this.

(4) 1-hydroxycyclohexylphenyl ketone.

This photoinitiator is manufactured by Ciba Geig.
y), Ardsley, New York to Irgacure (
Irgacure) 1.84.

(5) 2,6-di-tert-butyl-4-methylphene,
Nord.

(6) Darocur 1173 is E-M Company
, Hawthorne, New York, and is the compound 2-hydroxypropylphenone.

(7) Bis(1,2,2,6,6,-pentamethyl-4-piperidinyl) sebacate.

The components listed in footnotes (5), (6) and (7) above are common additives used in UV-curable coatings.

The viscosity of the above formulation was approximately 30 when measured at 25°C.
centipoise, which was separately deposited onto a separate aluminized polycarbonate disc and then spun to distribute the deposited composition over the disc surface. When this is done, the coating spreads over the disk surface to form a smooth, thin coating. The resulting wet coating is then heated between 200 and 400
Curing was carried out by exposure to ultraviolet light using a lamp emitting most of the radiation in the nn+ range. The exposure used provided a dose of 0.5 Joule/cJ;
This produces a smooth coating that is approximately 0.2 mil thick, has strong adhesion to the aluminized polycarbonate surface, and has satisfactory scratch resistance.

Claims (15)

[Claims] (1) A low viscosity liquid ultraviolet curable coating composition having a viscosity in the range of 15 to 50 centipoise, comprising one or more polyesters having an average of at least 2.4 (meth)acrylate groups per molecule. about 30% to about 50% (meth)acrylate, about 5% to about 15% carboxylic acid having (meth)acrylic acidic unsaturation, and C_4 to C_8.
from about 20% to about 40% diol di(meth)acrylate and at least one photoinitiator that imparts sensitivity to ultraviolet radiation to the composition, said proportions being based on the total weight of the polymerizable material. and the proportion of said diol di(meth)acrylate is such that it gives a certain viscosity. (2) The ultraviolet curable coating composition according to claim 1, wherein the poly(meth)acrylate is trimethylolpropane triacrylate. (3) Claim 1, wherein the carboxylic acid is acrylic acid.
The ultraviolet curable coating composition described in . (4) The ultraviolet curable coating composition of claim 1, wherein said composition has a viscosity of 20 to 35 centipoise. 5. The ultraviolet curable coating composition of claim 1, wherein the poly(meth)acrylate component has from about 1% to about 12% epoxy di(meth)acrylate. 6. The ultraviolet curable coating composition of claim 1, wherein the carboxylic acid is a carboxyl-functional C_1-C_6 alkylene ester of acrylic acid or an amide of acrylic acid. (7) A low viscosity liquid ultraviolet curable coating composition having a viscosity in the range of 20 to 35 centipoise, the trimethylolpropane triacrylate having an average of at least 2.4 (meth)acrylate groups per molecule. , about 5% to about 15% acrylic acid, about 20% to about 40% 1,6-hexanediol diacrylate, and at least one photoinitiator that imparts sensitivity to ultraviolet light to the composition. A composition comprising: wherein said proportion is based on the total weight of the polymerizable material, and wherein said proportion of diol diacrylate is such as to give a specified viscosity. 8. The ultraviolet curable coating composition of claim 7, wherein the trimethylolpropane triacrylate has an average of about 2.8 acrylate groups per molecule. 9. The ultraviolet curable coating composition of claim 7, wherein the polyacrylate component comprises 3% to 7% diacrylate of diglycidyl ether of bisphenol. (10) Polyoxyethylene methyl or ethoxy group 4
formed from a phenyl-substituted polysiloxane that is ethoxylated to contain from 0% to 80% and has a molecular weight of about 600
8. The ultraviolet curable coating composition of claim 7, having from about 0.5% to about 2.5% silicone dicarbinol diurethane di(meth)acrylate of ~10,000. (11) The ultraviolet curable coating composition according to claim 7, wherein the photopolymerization initiator is an aryl ketone photopolymerization initiator. 12. An optical disk coated with an ultraviolet cured coating of the composition of claim 1, wherein the thickness of said cured coating ranges from about 0.1 to about 0.3 mil. (13) An optical disc, characterized in that the composition according to claim 1 is applied to the central part of the disc, the disc is then rotated to diffuse the coating on the disc, and the coating is cured by ultraviolet rays. Manufacturing method. 14. The method of claim 13, wherein the composition has a viscosity of 20 to 35 centipoise. 15. The method of claim 13, wherein the disk is an aluminized disk.