JPH0453824B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical fiber having a primary or buffer coating and a top coating, in which the top coating composition uses a radiation-curable coating composition for optical fibers having specific properties. Here, the buffer coating between the glass fiber and the top coating is also treated as a primary coating. If this buffer coating is defined as a primary coating, the top coating may be defined as a secondary coating. Optical glass fibers are becoming increasingly important for communication purposes, and the use of glass fibers requires protection of the glass surfaces from moisture and abrasion. This is accomplished by coating the glass fibers immediately after molding. Although solvent solution coating and extrusion are used, these problems have been overcome to a large extent by the use of ultraviolet light curable coating compositions. One problem that arises from the use of coatings that are bonded to the glass surface of optical fibers is that
There is a problem with microbending of the fiber caused by deviations in response to temperature changes between the glass and the coating. This is particularly noticeable in extremely low temperature environments. A solution to this problem is to select a primary coating with a very low modulus, and UV-curable compositions with this low modulus have been developed. No. 170,148 (filing date:
July 18, 1980, Inventor: Robert E. Ansel) and U.S. Patent Application No. 398,161 (Filing date:
July 19, 1982 Inventor: Robert E. Ansel, O.
Ray Cutler, Elias P. Moscovis). In order to provide the desired low modulus for the primary coating, the hardness and toughness desired for the coating in contact with the glass must be sacrificed. It is desirable to apply a secondary coating over the primary coating to increase the hardness and toughness of the exposed coating surface. It is an object of the present invention to provide an optical fiber having such a configuration. The present invention provides an optical fiber having a primary or buffer coating and a top coating, wherein the top coating is (1) a diethylenically terminated polyurethane based on a diisocyanate having an average molecular weight of 400 to 5000; and (2) A radiation-curable composition containing a liquid radiation-curable monoethylenically unsaturated monomer whose homopolymer has a glass transition temperature of 55°C or higher has a modulus at room temperature of 40,000 to 40,000.
The present invention provides an optical fiber characterized by being a cured product having a strength of 200,000 psi. To explain in more detail about diacrylate-terminated polyurethane, it has a molecular weight of 400 to 5000,
It is preferably produced by placing an acrylate functional end group on a diisocyanate terminated compound of 800-2500. Although several methods of preparation are used, the diisocyanate-terminated compound is the reaction product of an organic diisocyanate and an aliphatic molecule having two isocyanate-reactive hydrogen atoms. Hydrogen atoms are e.g. OH, SH or
given by the NH ₂ group. These diisocyanate-terminated reaction products are 2
Contains ~10, preferably 2-4 urethane and/or urea groups. Preferably, the aliphatic group is a simple alkanediol such as 1,6-hexanediol, and the aliphatic group is selected from polyether, polyester and polyether-ester groups. Examples of polyether groups are tetramethylene glycol, polyester groups due to the ester reaction product of 2 moles of ethylene glycol and 1 mole of adipic acid, and polyester groups due to the ester reaction product of 2 moles of diethylene glycol and 1 mole of adipic acid. It is a polyether-ester group. Suitable diisocyanates are aliphatic or aromatic, such as isophorone diisocyanate, 2,4-toluene diisocyanate and its isomers. Toluene diisocyanate is preferred, and materials of this type are known in the art. Diacrylate termination of diisocyanates is accomplished in a variety of ways. That is, a high molecular weight diisocyanate is first produced and then it is reacted with a 2 molar proportion of hydroxyalkyl acrylate to attach one unsaturated group to each isocyanate group. These hydroxyalkyl acrylates have alkyl having 2 to 6 carbon atoms, such as hydroxyethyl acrylate, hydroxypropyl acrylate. Alternatively, hydroxyalkyl acrylate is first reacted with 1 mole of low molecular weight diisocyanate, and then the resulting unsaturated monoisocyanate 2
1 mole of dihydroxy compound giving the desired molecular weight are reacted. Both methods are known in the art. Urea groups may be introduced into the polyurethane by reaction of 1 mole of the diisocyanate described above with 1 mole of hydroxyethyl acrylate to give an unsaturated urethane product containing one unreacted isocyanate group. A polyurea polyurethane having two terminal acrylate groups is then obtained by reacting 2 moles of this monoisocyanate with 1 mole of a diamine such as butylene diamine. Urea-containing diacrylates are described in detail in US Pat. No. 4,097,439. An excellent method of reducing coating viscosity while increasing radiation cure rate is to use radiation curable monoethylenically unsaturated liquid monomers having a T _g of about 55° C. or higher. T _g indicates the glass transition temperature of the homopolymer made from that monomer. Examples of high T _g monomers used here are dimethylacrylamide, N-vinylpyrrolidone,
isobornyl acrylate, acrylic acid and dicyclopentenyl acrylate. N-vinylpyrrolidone is preferred because it has a low viscosity and at the same time increases cure speed. Although it is known that N-vinylpyrrolidone and, to a lesser extent, other exemplary monomers, can reduce the viscosity and improve cure speed of radiation-curable coatings, relatively large amounts of high T _g monomers is not known to increase the hardness of a coating composition while maintaining the general toughness and moderate modulus of the cured coating. Thus, N-vinylpyrrolidone and the other listed high T _g monomers simultaneously achieve several commercially important objectives. The radiation curable compositions used in the top coating of the optical fibers of the present invention contain from 5 to 40% by weight of the composition up to a molecular weight of 1000 to impart significant hardness and great physical toughness to the coating. Preferably, diethylenically unsaturated esters of diglycidyl ethers of bisphenols (preferably bisphenol A) of 400 or less are incorporated.
Preferred ethylenic groups that can be UV cured are acrylate groups. The diglycidyl ether of bisphenol preferably used has a 1,2-epoxy equivalent weight of about 2.0, although anything above about 1.4 is useful.
This simply means that the desired diglycidyl ether may be in a mixture with a monoglycidyl ether that reduces the epoxy equivalent weight. These diglycidyl ethers, if of low molecular weight, can be used to form diacrylates (by addition to form hydroxyacrylates). These are used in combination with diacrylate terminated polyurethanes to provide medium modulus coatings with good hardness and toughness as described above. The term "bisphenol" refers to a pair of phenol groups linked through an intermediate divalent group, usually an alkylene group. When the phenolic OH group in each phenol moiety of bisphenol is in the para position and 2,2-propylene is used as the intermediate divalent group, the product is known as bisphenol A and is industrially It's being used. The hardness of the top coating is further determined by the fact that 5 to 30% by weight of the coating composition has a molecular weight of about 300 or less;
Improvements can also be made by the inclusion of diacrylate esters of polyether glycols, such as triethylene glycol diacrylate or tetraethylene glycol diacrylate. If a diacrylate ester is used, additionally 1 to 15% by weight of triacrylate;
For example, it is preferred to include trimethylolpropane triacrylate or pentaerythritol triacrylate. The effect of the inclusion of diacrylate esters of polyether glycols is that rapid curing is obtained when radiation-curable coatings are applied. The diacrylate esters of polyether glycols used herein have low viscosities and are fast to radiation cure, especially with ultraviolet light, without significantly sacrificing the hardness and toughness provided by the main components of the composition. . Ultraviolet light is preferred, so acrylic unsaturation is best, but as the radiation changes, the nature of the unsaturation used will also change. Examples of other useful ethylenically unsaturated components include methacrylates, itacones, crotons, allyls, and vinyls. These can be obtained, for example, when methacrylic unsaturation is used, by reaction of isocyanate functions with 2-hydroxymethacrylate. Allyl unsaturation is introduced using allyl alcohol instead of hydroxyacrylate. Vinyl unsaturation can be introduced using hydroxybutyl vinyl ether instead of hydroxyacrylate. Therefore, although acrylate unsaturation has been described as a preferred example, other radiation-curable monoethylenically unsaturated groups can also be used in place of the methacrylic unsaturation example. The radiation used for curing when coating an optical fiber is appropriately selected depending on the photoinitiator used. Visible light can also be used with suitable photoinitiators. Examples of these are camphorquinone and coumarin, used together with tertiary amines such as triethanolamine. Diphenylbenzoylphosphine oxide is useful in the ultraviolet and near ultraviolet regions. When ultraviolet light is used, the coating composition typically includes a ketonic photoinitiator, such as about 3% diethoxyacetophenone. Other photoinitiators are also known, such as acetophenone, benzophenone, m-chloroacetophenone, propiophenone, thioxanthone, benzoin, benzyl, anthraquinone. Photoinitiators may be used alone or in mixtures and are present in amounts up to about 10% of the coating composition. Various amines such as dimethylamine can also be present, but are not specifically required here. The radiation curable coating used in this invention exhibits unique effects when applied as a top coat on buffer coated optical fiber. The coating compositions have excellent hardness and toughness that make them useful as optical fiber top coats, regardless of the radiant energy used for curing. Once cured, the coating used in the present invention typically operates between 40,000 and 200,000 psi (2812 and 14,062 psi) at room temperature.
Kg/cm ² ). This is too hard to serve as a coating in direct contact with the glass surface of the optical fiber. Therefore, the buffer coating used must have a modulus of about 15,000 psi (1054 kg/cm ² ) or less as measured at room temperature. Most radiation curable coatings have very high modulus and are too brittle for use in the present invention. Modifying these brittle coatings to make them less brittle results in a loss of strength. Thus, coatings having a combination of hardness and toughness while having a normal modulus are suitable for use for the specific purposes of the present invention. The table shows some examples of coating compositions that can be used in the present invention.

[Table] Component 1 is an adduct of 2 moles of 2-hydroxyethyl acrylate and 1 mole of diisocyanate-terminated polyurethane.
20% isomer) and polyoxytetramethylene glycol produced as a polyether diol with a molecular weight of 600 to 800 by polymerization of tetrahydrofuran. The polyurethane produced by acrylation of this diisocyanate has a molecular weight of about 1900 and contains an average of 5 to 6 urethane groups per molecule. As component 1, du Pont product Adiprene L
-200 may also be used. Component 2 is a diacrylate ester of diglycidyl ether of bisphenol A and has an average molecular weight of about 390. As component 2, Shell's product DRH370 may be used. Component 3 is tetraethylene glycol diacrylate. Component 4 is triethylene glycol diacrylate. Component 5 is trimethylolpropane triacrylate. Component 6 is benzyl dimethyl ketal used as a photoinitiator. Component 7 is a phenothiazine. Component 8 is benzophenone. Component 9 is 2-hydroxy-4-n-octoxybenzophenone, and this compound acts as a light stabilizer. Component 10 is dimethylamine. Component 11 is N-vinylpyrrolidone. It is even more preferred to use small amounts of adjuvants. One function, although not an essential function, of such adjuvants is to provide surface lubricity. In composition example 1, 0.01
% petrolactam, and silicone oil was used in composition examples 2 to 6. Composition Example 2 contains 0.2% of Dow Corning's fluid DC37 and 0.4% of the same fluid DC190.
%It was used. Composition Examples 3 and 5 used the same fluid but increased the DC190 to 0.6%. Composition Examples 4 and 6 used 0.07% DC57 along with 0.13% DC190. Composition Example 6 further contains 0.2% N-β-(N-
Vinyl-benzylamino)ethyl-6-aminopropyltrimethoxysilane was used as the monohydrochloride. The coating compositions listed above were used as top coats for buffer coated glass fibers according to the invention. The buffer coated optical fiber has a diameter of approximately 125 microns and was buffer coated to a thickness of 125 microns using the low modulus buffer coating described in the aforementioned US patent application Ser. No. 170,148. Specifically, this buffer coating contains 4 moles of 4,
4'-methylene bis(cyclohexyl isocyanate) is reacted with 2 moles of polyoxypropylene glycol having a molecular weight of 1000, and then 2 moles of 2-
reacted with hydroxyethyl acrylate, and further with 1 mol of polyoxypropylene having a molecular weight of 230,
It was prepared by reacting in the presence of 3.4 moles of N-vinylpyrrolidone and 917 moles of phenoxyethyl acrylate. This mixture is UV cured on a newly prepared optical fiber with 3% by weight of diethoxyacetophenone. The top coat shown in the table was applied to the buffer-coated glass fiber at a thickness of 125 microns and passed through two series 10 inch (25.4 cm) medium pressure mercury vapor lamps (300 watts) at 1.5 m/s.
The following results were obtained by passing the The properties recorded were measured on a free film approximately 75 microns thick.

【table】

[Table] Composition Examples 3 and 4 were omitted because they showed results equivalent to those obtained in Composition Examples 1 and 2. In the results of these experiments, the results of Examples 1 and 2 are of course satisfactory, but the results of Example 3
and 4 are even better, and the results are remarkable. That is, the viscosities of Examples 3 and 4 are lower than those of Examples 1 and 2, respectively, and are therefore more satisfactory. At the same time, it cures quickly, has a low coefficient of thermal expansion below T _g , and has low strain when the glass fiber is placed at low temperatures.

Claims (1)

[Scope of Claims] 1. An optical fiber having a primary or buffer coating and a top coating, wherein the top coating comprises (1) a diethylenically terminated polyurethane based on a diisocyanate having an average molecular weight of 400 to 5000; and ( 2) A cured product having a modulus at room temperature of 40,000 to 200,000 psi of a radiation-curable composition containing a liquid radiation-curable monoethylenically unsaturated monomer whose homopolymer has a glass transition temperature of 55°C or higher. An optical fiber characterized by: