JPS63239139A - Coating material for optical glass fiber - Google Patents

Abstract

PURPOSE:To obtain the title material having excellent curability and fast coating property and capable of providing an optical fiber having low water absorption and excellent softness and long-period reliability with high productivity by composing the material out of a urethane (meth)acrylate oligomer, a reactive diluent consisting of a specified compd., and a photopolymerization initiator, etc. CONSTITUTION:An isocyanate compd. having >=2 isocyanate groups in one molecule is allowed to react with the polyether polyol having a tetramethyleneoxy bond in the molecule to form a urethane bond, and then a (meth)acryloyl group is introduced into both terminal groups of the molecule to obtain a urethane (meth)acrylate oligomer (A). From 3-90wt.% A component and (B) 70-10wt.% of the compd. (e.g., lauryltridecyl acrylate) contg. one polymerizable C=C bond in one molecule and having 23-35dyne/cm surface tension (at ordinary temp.) as the reactive diluent are mixed to obtain 100pts.wt. mixture, and 1-10pts.wt. (C) photopolymerization initiator (e.g., benzophenone) is incorporated into the mixture to obtain the title material having 500-10,000cp (at 25 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to materials for coating optical glass fibers for light transmission.

[Conventional technology]

Optical glass fibers (hereinafter simply referred to as optical fibers) used as optical transmission media usually have a diameter of 20 mm.
Since it is less than 0 μm and the material is brittle, scratches are likely to occur on the surface during manufacturing, cable production, and storage, and these scratches become a source of stress concentration, making it easy to damage when external stress is applied. The disadvantage is that the optical fiber may break.

For this reason, it is extremely difficult to use optical fiber as it is as a medium for optical transmission. Therefore, conventionally, attempts have been made to coat the surface of an optical fiber with a resin, thereby maintaining the initial strength immediately after manufacturing the optical fiber and producing an optical fiber that can withstand long-term use.

Examples of such resin coating materials include those using thermosetting resins such as silicone resin, epoxy resin, and urethane resin, and those using ultraviolet rays such as epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate. Those using curable resin are known.

[Problem that the invention seeks to solve]

However, the above-mentioned thermosetting materials require a long time to cure and dry, resulting in poor productivity for optical fibers, and lack of long-term reliability due to insufficient curing, which impairs the adhesion between the coating and the optical fiber. I don't like it. In addition, although the above-mentioned ultraviolet curing materials exhibit relatively good curing properties compared to thermosetting materials, they are still not sufficient, and it is important to improve the productivity of optical fibers by applying and curing them at high speeds. From the perspective of achieving this, it was still not satisfactory.

Moreover, the conventional UV-curable materials mentioned above have difficulty in coating (drawability) when applied at high speed, making it difficult to form a uniform film, which causes microbending and transmission loss. There was a problem in that it caused an increase in In addition, as a coating material that is directly attached to the surface of an optical fiber, it is desirable that the cured film has a high elongation and flexibility, not only at room temperature but also at low temperatures, and has a low tensile modulus. However, the tensile modulus of conventional UV-curable materials tends to increase significantly at low temperatures, and when the tensile modulus increases in this way, the surface of the optical fiber becomes susceptible to microscopic damage, so transmission at low temperatures is difficult. There was a risk that losses would increase.

Therefore, the present invention solves the above-mentioned conventional problems, improves the productivity of optical fibers by exhibiting excellent curing properties with ultraviolet rays and electron beams, and facilitates the production of uniform coatings with good coating properties at high speeds. The cured product has excellent elongation and flexibility, and has a low tensile modulus.
The present invention also aims to provide an industrially useful coating material for optical fibers that greatly contributes to improving the reliability of optical fibers, in which the increase in tensile modulus at low temperatures is suppressed.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors decided to use urethane (meth)acrylate oligomer as the main material of this type of coating material, while using a specific surface as a reactive diluent for this main material. When a tensile monofunctional compound is used, it cures quickly by irradiation with ultraviolet rays or electron beams, and can easily form a uniform coating with good coating properties on the optical fiber surface at high speed. This invention was developed based on the knowledge that it has excellent elongation and flexibility, has a small tensile modulus, and suppresses the increase in the tensile modulus at low temperatures.

That is, the present invention provides a room-temperature urethane (meth)acrylate oligomer containing one polymerizable carbon-carbon double bond in one molecule that acts as a reactive diluent for a) urethane (meth)acrylate oligomer and b) component a. The surface tension at 23-35 dyn
The present invention relates to an optical fiber coating material containing a compound in the range of e/am and C) a photopolymerization initiator as essential components.

In this specification, a (meth)acryloyl group refers to an acryloyl group and/or a methacryloyl group represented by the following formula; and/or methacrylate, respectively.

In addition, the number average molecular weight described in this specification refers to a value measured by gel permeation chromatography (GPC) using polystyrene as a standard.
Further, viscosity means a value measured with a Brookfield viscometer, and surface tension at room temperature means a value measured with a Wilhelmi set (CBVP type) surface tension meter at 25°C.

[Structure and operation of the invention]

The urethane (meth)acrylate oligomer used as component a in this invention has a urethane bond in its molecular skeleton, and has 2 or more (meth)acryloyl groups, usually up to 5, in the molecule, Particularly preferred is one having (meth)acryloyl groups at least at both ends of the molecule, and its molecular weight is not particularly limited, but usually has a number average molecular weight of 1°000 to io, ooo, preferably 1,000.
~7,000. Such oligomers are characterized by superior elongation and flexibility of cured products compared to other known (meth)acrylate oligomers.

This urethane (meth)acrylate oligomer can be obtained by various methods, but generally, various polyols are reacted with an isocyanate compound having two or more isocyanate groups in one molecule via the hydroxyl groups of the polyol. to form a urethane bond, and then introduce (meth)acryloyl groups to both ends of the molecule via the remaining isocyanate groups of the above compound that participate in this bond.

The above polyols include polyether polyols,
polyolefin polyol, polyester polyol,
Examples include polycarbonate polyols and polycaprolactone polyols, but polyether polyols are particularly suitable, and among them, it is most desirable to use polyether polyols having a tetramethyleneoxy bond in the molecule. Polyether polyols having tetramethyleneoxy bonds in the molecule include polytetramethylene glycol, tetrahydrofuran-propylene oxide copolymers, and addition polymerization of tetrahydrofuran and/or propylene oxide to polyhydric alcohols such as glycerin and trimethylolpropane. Among them, those having a number average molecular weight of about 800 to 6,000 are particularly preferably used.

As an isocyanate compound for reacting with such a polyol to form a urethane bond, after forming the urethane bond, a (meth)acryloyl group is formed via the remaining isocyanate group of this compound that participates in this bond. If necessary, those having two or more isocyanate groups in one molecule are used. Its molecular weight is usually in the range of about 100 to 1,000.

Such isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate,
naphthalene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, bis(
Methyl isocyanate) cyclohexane, dicyclohexylmethane diisocyanate, 1.6-hexane diisocyanate, and the like.

As a means for introducing a (meth)acryloyl group through the remaining isocyanate groups of the above-mentioned isocyanated metal participating in the urethane bond, an active hydrogen atom that reacts with this group and a (meth)acryloyl group are introduced into the above-mentioned isocyanate group. What is necessary is to react a compound having the following properties, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,
Examples include N-hydroxymethyl (meth)acrylamide, trimethylolpropane 7-(meth)acrylate, and the like.

The urethane (meth)acrylate oligomer as component a is usually prepared by first reacting a polyol with a predetermined amount of an isocyanate compound using the above-mentioned raw materials, and then forming a compound having an active hydrogen atom and a (meth)acryloyl group. It is synthesized by a method of reacting a predetermined amount of the above components, but in some cases, it can also be synthesized by a method of reacting the above three components at once.

In these synthesis methods, the amounts of each raw material component used include, for example, polytetramethylene glycol as the polyol, a diisocyanate compound having two isocyanate groups in one molecule as the isocyanate compound,
For example, when 2-hydroxyethyl acrylate is used as a compound having an active hydrogen atom and a (meth)acryloyl group, a diisocyanate compound and a 2-hydroxyethyl acrylate are used per mole of polytetramethylene glycol.
The proportion of hydroxyethyl acrylate is about 2 moles in each case.

In this invention, when using such urethane (meth)acrylate oligomers, only one type of oligomers having different number average molecular weights and material compositions may be used, or two or more types of oligomers may be used in combination. The mixing ratio at that time may be arbitrary.

In this invention, polymerizable carbon-carbon atoms in one molecule act as a reactive diluent for the oligomer used as component b.
Surface tension at room temperature containing one carbon double bond is 23~
Compounds in the range of 35 dyne/cm give good results in curing by ultraviolet rays or electron beam irradiation, and their low surface tension allows for excellent wettability on the optical fiber surface and good coating properties at high speeds. It provides good results and helps in forming a uniform film, and also greatly contributes to reducing the tensile modulus and preventing its increase at low temperatures.

In place of this b component, for example, the surface tension at room temperature is 35
By using a compound having one polymerizable carbon-carbon double bond in one molecule exceeding dyne/crn, it is possible to obtain some good results in preventing a decrease in the tensile modulus and an increase in the above-mentioned modulus at low temperatures. Even if it is possible to achieve this, the curing properties may be impaired, and the wettability to the optical fiber surface may not be improved, resulting in poor coating properties at high speeds, making it difficult to form a uniform coating. Therefore, it is possible to use additives such as fluorosurfactants and silicone leveling agents that have the effect of lowering surface tension, but in this case, the surface tension of the entire coating material can be lowered. However, due to poor compatibility between the additive and the resin component, the blended system becomes non-uniform, and the contact angle (θ) with quartz glass measured with a contact angle meter, which will be described later, increases. Almost no good results are obtained in improving coverage at high speeds.

In addition, in place of the above-mentioned components, the surface tension at room temperature is 30 d.
Aliphatic polybasic acid esters such as dioctyl phthalate and diisodecyl adipate, which are around yne/cm,
When plasticizers such as phthalate esters such as dioctyl phthalate and diisodecyl phthalate are used, the wettability to the optical fiber surface is improved and coating properties at high speeds are improved, and the tensile modulus of the cured product is reduced and Good results can be obtained in preventing the increase in the elastic modulus at low temperatures, but this may cause problems in the curing of the entire coating material, and the water absorption rate of the cured product will increase due to the plasticizer remaining in the cured product. However, since the heating loss increases due to a decrease in the gel fraction, problems remain in terms of the reliability of the optical fiber.

On the other hand, when the above-mentioned components of the present invention are used, the above-mentioned problems do not occur, especially without increasing the water absorption rate or decreasing the gel fraction. Since good results can be obtained in reducing the tensile modulus at low temperatures, it can greatly contribute to improving the productivity and reliability of optical fibers.

Component b exhibiting such performance has a surface tension of 23 to 35 dyne/am at room temperature, particularly preferably 28
~33 dyne/cm and contains one polymerizable carbon-carbon double bond in the molecule, any compound can be used, but in particular, a (meth)acryloyl group as the double bond can be used. Preferred are 2-ethylhexyl acrylate, nonylphenoxyethyl acrylate, stearyl acrylate, tridecyl acrylate, lauryl acrylate, lauryl tridecyl acrylate (mixed acrylate of lauryl and tridecyl), etc., which have a tensile modulus at low temperature. Long-chain alkyl acrylates represented by the following formula: % (wherein R is an alkyl group having 8 to 18 carbon atoms) are most preferred, as they give particularly good results in preventing an increase in . These b components may be used alone or in combination of two or more.

Note that compounds with a surface tension of more than 35 dyne/cs at room temperature will have the drawbacks mentioned above.
Compounds with less than ne/co+ are unsuitable for the present invention because their surface tensions are too low to cause problems such as the inability to uniformly coat the film to a certain thickness.

In this invention, the above-mentioned components a and b are used as curable components, and the ratio of each component is C
Ingredients are 30-90% by weight, preferably 40-80% by weight
Component b is 70 to 10% by weight, preferably 60 to 10% by weight.
It is preferable to adjust the amount to 20% by weight. If component b is too small, not only will it fail to function as a reactive diluent, but
This is undesirable because the surface tension of the coating material becomes high, making it impossible to improve the coating properties at high speeds, and making it impossible to suppress the increase in tensile modulus at low temperatures. Moreover, if the amount is too large, the elongation and flexibility of the cured product will decrease, which is also not preferable.

As the photopolymerization initiator used as component C in this invention, various kinds of initiators generally used as initiators and sensitizers for ultraviolet curable coatings can be used. For example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-methylbenzoin, benzophenone, Michler's ketone, benzyl, benzyl dimethyl ketal, benzyl diethyl ketal, anthraquinone, methylanthraquinone, 2,2-jethoxyacetophenone , 2-methylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,
Examples include anthracene, 1,1-dichloroacetophenone, methyl orthobenzoylbenzoate, and those used in combination with small amounts of sensitizing aids such as amines.

The amount of these photopolymerization initiators to be used is usually about 1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on a total of 1100 parts by weight of the C component and b component. If this amount is too small, the curability cannot be satisfied, and even if it is used in excess of a predetermined amount, no further improvement in the curing rate can be expected.

The optical fiber coating material of the present invention includes the above C components, b
The C component is an essential component, and if necessary, polymerizable carbon-carbon doubles are added as an optional component to adjust the flexibility and hardness of the cured film and the workability when coating optical fibers. Compounds that do not belong to the above-mentioned components and are low-viscosity liquid at room temperature and have one or more bonds, preferably one bond, acrylic resins, polyamide resins, polyester resins, polyether resins, polyurethane resins, polyamide-imide resins, silicone resins, and phenols. Various modified resins such as resins,
Furthermore, various additives such as antioxidants and polymerization inhibitors are added.
It is not limited to one type, and two or more types may be used in combination.

The amount of these optional components used is usually 30 parts by weight or less, preferably 2 parts by weight, based on 100 parts by weight of the total amount of components a and b.
It is 5 parts by weight or less. It is not preferable to use more than this because there is a possibility that the object of the present invention cannot be achieved.

Examples of compounds that do not belong to component b, which have one or more polymerizable carbon-carbon double bonds in the molecule and are liquid at room temperature with low viscosity, include phenoxyethyl acrylate and (meth)acrylate of tetrahydrofurfuryl alcohol caprolactone adduct. , N-vinylpyrrolidone, N-N-dimethylacrylamide, and the like.

From the viewpoint of coating workability, the overall viscosity of the optical fiber coating material of the present invention is preferably adjusted to a range of 500 to 10,000 centivoise (25° C.).

The optical fiber coating material of the present invention, which is constructed as described above, is coated on the surface of the optical fiber immediately after spinning by an appropriate means so that the thickness after curing is usually 10 to 100 μm, and then exposed to ultraviolet rays or electron beams. It may be cured by irradiating the material. After applying the inner layer coating in this manner, it is usually desirable to apply and cure an outer layer coating material which provides a cured coating that is harder and tougher than the coating material of the present invention.

Furthermore, by forming a tough coating such as a thermoplastic resin coating such as polyethylene or nylon as the outermost layer on the coating layer thus formed,
An optical fiber coating with even better fiber strength can be obtained.

〔Effect of the invention〕

As described above, in this invention, a urethane (meth)acrylate oligomer as the component a is used as the main material of the coating material, and a monofunctional polyester having a specific surface tension as the component described above is used as a reactive diluent for the urethane (meth)acrylate oligomer. By using a compound, it has excellent curability and can greatly contribute to improving the productivity of optical fibers, and it is also possible to easily form a uniform film with good coating properties at high speed, and the cured film can be easily formed. Microbending has excellent elongation and flexibility, low tensile modulus, and suppresses the increase in tensile modulus at low temperatures, and has low water absorption and high gel fraction. Industrially extremely useful light that can be used to manufacture optical fibers with high long-term reliability, which have little increase in transmission loss due to low temperature, low temperature increase, and increase in transmission loss due to water absorption, etc. A coating material for fibers can be provided.

〔Example〕

EXAMPLES Below, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight.

Example 1 Polytetramethylene glycol having a number average molecular weight of 2,000 (product name PTMG2000 manufactured by Sanyo Chemical Co., Ltd.
) 1 mol, tolylene diisocyanate 2 mol and dibutyltin dilaurate 200 ppm, 60-7
The reaction was carried out at 0°C for 2 hours. Then, 2 moles of 2-hydroxyethyl acrylate were added, and the reaction was continued until the characteristic absorption band of the isocyanate group at 2.270 cta-' disappeared from the infrared absorption spectrum.

Urethane acrylate oligomer 6 obtained in this way
0 parts, lauryl tridecyl acrylate (product name: LT manufactured by Osaka Organic Co., Ltd.) having a surface tension of 29 dyne/am at room temperature.
A) 40 parts, 3 parts of benzophenone and 1 part of diethylaminoethanol were mixed and dissolved to give a viscosity of 2.000.
A centiboise (25° C.) optical fiber coating material was obtained.

Example 2 60 parts of the urethane acrylate oligomer obtained in Example 1, 20 parts of the same lauryl tridecyl acrylate as in Example 1, and an acrylate of tetrahydrofurfuryl alcohol caprolactone adduct (Nippon Chemical Co., Ltd.) having a surface tension of 41 dyne/cm at room temperature were added. Product name: TC11O8) 20 manufactured by Yakusha
1 part, 3 parts of benzophenone, and 1 part of diethylaminoethanol were mixed and dissolved to obtain a coating material for optical fiber having a viscosity of 3,000 centivoise (25°C).

Example 3 1 mol of tetrahydrofuran-propylene oxide copolymer (trade name PPTG4000 manufactured by Hodogaya Chemical Co., Ltd.) having a number average molecular weight of 4,000 was placed in a 31 four-bottle flask equipped with a stirrer, a condenser, and a thermometer. 2 moles of diisocyanate and 200 pp of dibutyltin dilaurate
m was charged and reacted at 60 to 70°C for 2 hours. Next, 2 moles of 2-hydroxyethyl acrylate were added, and infrared absorption spectroscopy revealed that the isocyanate groups were 2,27
The reaction was continued until the characteristic absorption band of 0C11-' disappeared.

Urethane acrylate oligomer 6 obtained in this way
0 parts, stearyl acrylate (trade name 5A manufactured by Osaka Organic Co., Ltd.) with a surface tension of 31 dyne/am at room temperature.
30 parts, surface tension at room temperature 28 dyne/cm2
- 10 parts of ethylhexyl acrylate (trade name 2-EHA manufactured by Osaka Organic Co., Ltd.), 3 parts of benzophenone and 1 part of diethylaminoethanol were mixed and dissolved to give a viscosity of 2.
．． A coating material for optical fiber of 100 centivoise (25° C.) was obtained.

Example 4 To 70 parts of the urethane acrylate oligomer obtained in Example 3, 20 parts of lauryl tridecyl acrylate as in Example 1, 10 parts of tetrahydrofurfuryl alcohol caprolactone adduct acrylate as in Example 2, and 3 parts of benzophenone. and 1 part of diethylaminoethanol were mixed and dissolved to give a viscosity of 4,500 centiboise (
A coating material for optical fiber was obtained.

Comparative Example 1 To 60 parts of the urethane acrylate oligomer obtained in Example 1, 40 parts of acrylate of the same tetrahydrofurfuryl alcohol caprolactone adduct as in Example 2, 3 parts of benzophenone, and 1 part of diethylaminoethanol were mixed and dissolved. Viscosity 7.800 centipoise (25
℃) coating material for optical fiber was obtained.

Comparative Example 2 To 60 parts of the urethane acrylate oligomer obtained in Example 3, 40 parts of diisodecyl adipate having a surface tension of 31 dyne/cm at room temperature, 3 parts of benzophenone and 1 part of diethylaminoethanol were mixed and dissolved to give a viscosity of 5.
, 800 centivoise (25° C.) optical fiber coating material was obtained.

Comparative Example 3 60 parts of the urethane acrylate oligomer obtained in Example 3, 40 parts of acrylate of the same tetrahydrofurfuryl alcohol caprolactone adduct as in Example 2, and a silicone leveling agent (trade name Q8- manufactured by Dow Corning) were added.
778), 3 parts of benzophenone, and 1 part of diethylaminoethanol were mixed and dissolved to give a viscosity of 7.
A coating material for optical fibers having a temperature of 800 centiboines (25° C.) was obtained.

The following tests were conducted to examine the performance of each of the optical fiber coating materials of Examples 1 to 4 and Comparative Examples 1 to 3.

<Test Example 1> First, the surface tension and contact angle of each coating material were measured. The contact angle was determined using a contact angle meter manufactured by Kyowa Kagakusha, and the contact angle with respect to quartz glass was determined by the liquid drop method, and the value 30 seconds after dropping the liquid was determined as the above contact angle.

Next, each coating material was applied to a glass plate to a thickness of 0.25 fins, and then cured using a high-pressure mercury lamp (80w/cm). , gel fraction, tensile modulus and elongation were measured. The tensile modulus at low temperature (-40°C) was also measured in the same manner. The tensile modulus and elongation are based on JIS K-
7113, and the water absorption rate is JIS K-72.
It was carried out in accordance with 09. Furthermore, the gel fraction was extracted with methyl ethyl ketone for 5 hours using a Soxhlet extractor, and
After drying in a vacuum dryer at 00°C for 1 hour, the weight was measured and calculated using the following formula.

The results of these tests were as shown in the table below.

As is clear from the table above, Example 1 according to the present invention
Compared to the materials of Comparative Examples 1 to 3, the coating materials of ~4 had a faster curing speed, lower surface tension and lower contact angle, and had better wettability to the optical fiber surface, allowing for high-speed coating. It has been found that this gives good results in forming a very uniform coating. In addition, in the materials of Examples 1 to 4, the elongation of the cured material is large and the tensile modulus is small, and the increase in the tensile modulus at low temperatures is suppressed, and furthermore, the water absorption rate is low and the gel content is high. It is also clear that the materials of Comparative Examples 1 to 3 are inferior in any of these properties.

<Test Example 2> Each optical fiber coating material of Examples 1 to 4 and Comparative Examples 1 to 3 was applied as an inner layer onto the surface of an optical fiber having a diameter of 125 μm so that the diameter after coating was 250 μm,
After curing at a linear speed of 200 m/min using a 160 W/cm high-pressure mercury lamp, the outer layer material (Shore hardness D-60, tensile modulus 40 kg/mA, elongation 45%)
was coated so that the diameter after coating was 400 pm, and was cured at the same speed using the same high pressure mercury lamp as above.

The optical fiber coated body thus obtained was prepared in Example 1.
In the case of using the optical fiber coating material No. 4 to 4, the appearance after applying the inner layer coating is very good and the uniformity of the coating is excellent, so that the increase in transmission loss due to microbending is reduced. Not observed at all, and at low temperatures (−
Almost no increase in transmission loss was observed at 40''C) or after the optical fiber coating was immersed in water for 48 hours.

However, in the case of using the optical fiber coating material of Comparative Example 1.3, after the inner layer coating was applied, the appearance was poor and the surface condition was uneven, resulting in a significant increase in transmission loss due to microbending. was recognized. Furthermore, in the case where the optical fiber coating material of Comparative Example 2 was used, the transmission loss significantly increased after the optical fiber coating was immersed in water for 48 hours.

Claims (3)

[Claims] (1) a) Urethane (meth)acrylate oligomer and b) 1 that acts as a reactive diluent for component a above.
An optical glass fiber containing as essential components a compound containing one polymerizable carbon-carbon double bond in its molecule and having a surface tension in the range of 23 to 35 dyne/cm at room temperature, and c) a photopolymerization initiator. coating material. (2) An isocyanate compound in which the urethane (meth)acrylate oligomer as component a has two or more isocyanate groups in one molecule via the hydroxyl group of this polyol to a polyether polyol having a tetramethyleneoxy bond in the molecule. to form a urethane bond, and (meta) to both ends of the molecule via the remaining isocyanate groups of the isocyanate compound involved in this bond.
The coating material for an optical glass fiber according to claim (1), which is a urethane (meth)acrylate oligomer having an acryloyl group introduced therein. (3) The compound as component b is a long-chain alkyl acrylate represented by the following formula: CH_z=CHCOOR_1 (wherein R_1 is an alkyl group having 8 to 18 carbon atoms). ) or (2), the coating material for optical glass fibers.