WO1996006142A1

WO1996006142A1 - Polyester based optical fiber coatings

Info

Publication number: WO1996006142A1
Application number: PCT/US1995/009674
Authority: WO
Inventors: James Ronald Snyder; George David Green; Alvin Charles Levy; Raymond John Swedo
Original assignee: Alliedsignal Inc.
Priority date: 1994-08-19
Filing date: 1995-08-01
Publication date: 1996-02-29
Also published as: TW343226B

Abstract

Optical fiber coatings may be prepared from compositions containing one or more vinyl ether polyester oligomers prepared by reacting an hydroxyl-terminated polyester or polyether, a polyol, and a hydroxy monovinyl ether, with one or more mono or multifunctional vinyl ether terminated monomers, which may be derived from esters or alcohols.

Description

POLYESTER BASED OPTICAL FIBER COATINGS Prior Art

This invention relates generally to the field of optical fibers and, more particularly, to the coatings applied to such fibers and the coated fibers.

Optical fibers have become commonplace in recent years because of their ability to handle large volumes of data transmitted over long distances. However, this is only possible because optical fibers have been developed which have extremely low transmission losses. These optical fibers are operated with light having wavelengths in the narrow regime between 0.6 and 1.6 microns to obtain the maximum transmission of light. Losses have been attributed to scattering of light, absorption, and imperfections called "microbending", which refers to scattering of light caused by small deformations of the fiber axis. Such microbending has been attributed to coating defects, thermal contraction and external stresses. It has been found desirable to coat glass fibers in order to protect them and to give strength to the fibers and to alleviate the losses assigned to microbending.

Properties of the coatings depend on the type used, but where two layers are employed, as is typical in the art, the inner layer should have a low modulus down to -40°C, be thermally and hydrolytically stable, have good adhesion to glass and not evolve hydrogen (which can react with the fiber and reduce light transmission). The outer layer of a two layer system serves to protect the fiber and the inner coating and thus must meet dififerent requirements. The outer layer should be tough and abrasion resistant, be thermally and hydrolytically stable and not evolve hydrogen.

In practice, the most commonly used coatings have been derived from acrylates, although silicones or rubber compounds have been employed. The most widely used acrylates are those which are capable of ultra-violet radiation curing at high speed since the coatings are normally applied immediately after the glass fiber has been drawn from the molten state and cooled to an appropriate temperature. Typical of such acrylates are multifunctional acrylate terminated monomers and oligomers. The outer coating are most often urethane-acrylate or epoxy-acrylate copolymers which also can be cured by ultra-violet radiation The acrylates have inherent disadvantages since they are considered to present health hazards and also tend to be brittle and to absorb moisture.

Examples of prior formulations include U.S. Pat. No. 4,472,019, in which a top coating is disclosed for fiber optic filaments. In commonly- assigned U.S. Pat. No. 4,682,851 an undercoating is described which is different from the outer coating of U.S. Pat. No. 4,472,019.

In U.S. Pat. No. 5,139,872 it was shown that vinyl ether urethane oligomers could be formulated to provide superior coatings for glass optical fibers, having higher cure speed, improved low temperature properties, improved moisture resistance, and lower toxicity compared to the acrylates heretofore used. While such vinyl ether urethane compounds have distinct advantages, further improvements in T_g, cure speed, hydrogen generation, and moisture sensitivity have been needed. We have now found that polyester based vinyl ether oligomers, such as those disclosed in U.S. Pat. No. 5,286,835, can provide the needed properties, as will be shown in the discussion below. .

Summary of the Invention

Fiber optic coatings may be prepared from compositions which employ vinyl ether polyester oligomers, along with mono or multifunctional vinyl ether terminated monomers, which may be derived from esters or alcohols.

The coating compositions include an effective amount of a photoinitiator to cause the vinyl ethers to react and produce the desired coatings.

In the formulas below, where a moiety may be di, tri or tetra valent, they are defined as, for example, alkyl, aryl, etc. which is to be understood as not implying a monovalent group, but a polyfunctional group having the general chemical nature indicated.

The vinyl ether polyester oligomers are obtained by reacting (i) a polybasic ester having the formula

wherein R₇ is chosen from the group consisting of phenyl and an alkyl group containing from 1 to 6 carbons, X_a, X_b, Y_a, and Y_b are radicals having a molecular weight of from 25 to about 500, each X_a, each X_b, each Y_a, and Y_b being independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, j is an integer from 0 to 2, z is an integer from 0 to 2, p is an integer from 0 to 2, V is an integer from 0 to 2, m is an integer from 0 to 100, and w is an integer from 0 to 2; and (ii) a hydroxy monovinyl ether having the formula

wherein R₁ and R₂ are monovalent radicals selected from the group consisting of hydrogen and alkyl groups having 1 to 10 carbon atoms Preferably, R₁ is an alkyl group having 1 to 4 carbon atoms and R₂ is hydrogen or R₁ is hydrogen and R₂ is an alkyl group having 1 to 4 carbon atoms Most preferably, both R₁ and R₂ are hydrogen. X_a is a divalent radical having a molecular weight in the range of from 25 to about 500 and is independently selected from the group consisting of alkylene, cycloalkylene, and alkylene ether radicals; and (iii) a polyol having the formula

wherein X_a and X_b are radicals having a molecular weight of from 25 to about 500, and each X_a and X_b is independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, m is an integer from 0 to 100, preferably 1 to 10, and w is an integer from 1 to 3 indicating the number of additional substituents of X_b .

The vinyl ether polyester oligomers are combined with one or more vinyl ether terminated ester monomers having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of Y ', Y' is a mono-, di-, tri-, or tetrafunctional radical having a molecular weight of 15 to 500 and is independently selected from the group consisting of alkylene, arylene, aralkylene, and cycloalkylene radicals, X_a is a divalent radical having a molecular weight of 25 to 500, each X_a being independently selected from the group consisting of alkylene or cycloalkylene radicals, and R₃ and R₄ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms

The formulation may also comprise one or more vinyl ether terminated monomers derived from an alcohol having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of D, R₅ and R₆ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms, preferably independently selected from the group consisting of hydrogen and methyl, and D is a mono-, di-, tri-, or tetravalent radical consisting of alkyl, cycloalkyl, or alkyl ethers having a molecular weight of 56 to 1000. Both the primary and secondary coatings formulations typically will include additives such as thermal oxidation, stabilizers, hydrogen stabilizers, light screens, color stabilizers, blocking agents, and coupling agents.

Primary optical fiber coatings generally will include oligomers having T_g equal to or less than -10°C while the oligomers used in secondary optical fiber coatings have a T_g equal to or greater than -10°C. The coating formulations will have a viscosity of about 100 to 10,000 cps (mPa•s) at their application temperature. As cured, the primary coating will have a Tg at or below O°C, a modulus of about 80-800 psi (551-5510 kPa) at room temperature and an elongation greater than 50%. The cure secondary coating will have a Tg greater than 50°C, a modulus of at least 50,000 psi (344,735 kPa) at room temperature and an elongation greater than 5%

Description of Preferred Embodiments

Advantages of Polyester Based Optical Fiber Coatings

The optical fiber coatings described in U.S. Pat. No. 5,139,872 have advantages over coatings derived from acrylates, particularly in cure speed, physical properties at low temperatures (i.e below 0°C), moisture resistance, and toxicity. By employing polyester-based vinyl ether oligomers rather than the vinyl ether oligomers based on urethanes of the '872 patent, we obtain further improved performance.

The polyester-based formulations cure more rapidly with a lower radiation dose required. In addition the polyester-based coatings can be cured at above ambient temperatures. Typically, glass fibers are drawn from heat- soften glass rod at a high speed in an elevated "draw tower". This means that the glass must be cooled rapidly from about 1800°F (982°C) so that the coatings can be applied and cured and the cooling is a critical factor in the design and operation of the draw towers. As the speed of drawing glass fibers is increased in a given tower, it is evident that the temperature of the fibers rises. Consequently, it is an important advantage if a coating formulation can be cured at higher temperatures with a lower radiation dose. Acrylate formulations require curing temperatures of about 50ºC. while the vinyl ether oligomers may be cured at fiber temperatures of up to about 150°C. As will be seen in the examples below the polyester-based vinyl ether formulations are clearly superior. This improvement in cure speed provides additional benefits. Since the polyester-based formulations cure more rapidly, the amount of photoinitiator used can be reduced, which as will be shown, has advantages in improved thermal stability, color, and, particularly, in reduced hydrogen generation, which is a major concern in optical fiber coatings. Finally, the polyester-based coatings of the invention are superior in having lower water absorption and extractables.

The formulations comprise (a) vinyl ether polyester oligomers, plus either or both of (b) vinyl ether terminated ester monomers and (c) vinyl ether terminated monomers derived from an alcohol.

(a) Ninyl Ether Polyester Oligomers

These oligomers are prepared by reacting (i) a polybasic ester (ii) a hydroxy monovinyl ether and (iii) a polyol.

(i) Polyesters

The polybasic esters useful in the invention may be described by the formula

wherein R₇ is chosen from the group consisting of phenyl and an alkyl group containing from 1 to 6 carbons, X_a, X_b, Y_a, and Y_b are radicals having a molecular weight of from 25 to about 500, each X_a, each X_b, each Y_a, and Yb being independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, j is an integer from 0 to 2, z is an integer from 0 to 2, p is an integer from 0 to 2, v is an integer from 0 to 2, m is an integer from 0 to 100, preferably 1 to 10, and w is an integer from 0 to 2 Preferred structures for X_a are independently selected from the group consisting of:

wherein q is an integer from 0 to 40, n is an integer from 2 to 20, E is chosen from the group consisting of bond, O, CH₂, S, SO₂, >C(CH₃)₂, and >C(CF₃)₂.

The preferred structure for X_b are those for X_a where V is 0 and where X_b is polyfunctional

C-(-CH₂-O)-_4,

R-C-(CH₂-O-)-₃ where R is 1-10 carbon alkyl.

Preferred structures for Y_a and Y_b are those independently selected from the group consisting of:

wherein n' is an integer between 0 and 20, E is chosen from the group consisting of bond, O, CH₂, S, SO₂, >C(CH₃)₂, and >C(CF₃)₂, and R_y is chosen from the group consisting of alkyl containing from 1 to 6 carbon atoms, and NO₂, and Y_b may additionally be chosen from the group consisting of:

(ii) Hydrpxyl Monovinyl Ethers

The vinyl ether terminated alcohols which are used in preparing the oligomeric esters of this invention have a structure corresponding to the adduct of an alkyne and a diol. However, these vinyl ether terminated alcohols also can be made in other ways, and the method of producing them is not part of this invention. The structure is illustrated by the formula

wherein R₁ and R₂ are monovalent radicals selected from the group consisting of hydrogen and alkyl groups having 1 to 10 carbon atoms. Preferably, R₁ is an alkyl group having 1 to 4 carbon atoms and R₂ is hydrogen or R₁ is hydrogen and R₂ is an alkyl group having 1 to 4 carbon atoms. Most preferably, both K₁ and R₂ are hydrogen. X_a is a divalent radical having a molecular weight in the range of from 25 to about 500 and is independently selected from the group consisting of alkylene, cycloalkylene, and alkylene ether radicals Preferred structures for X_a are the same as those listed for the polyester (i) above. (iii) Polyols

The polyols which may be used in the process of the invention include diols described above and higher polyols They may be generally described by the formula

wherein X_a and X_b are radicals having a molecular weight of from 25 to about 500, and each X_a and X_b is independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, m is an integer from 0 to 100, preferably 0 to 10, and w is an integer from 1 to 3 indicating the number of additional substituents of X_b. Preferred structures for X_a are the same as those listed for the polyester (i) above. The preferred structures for X_b are those for X_a plus

where R is 1-10 carbon alkyl.

Catalysts

The catalysts useful in preparing vinyl ether terminated polyester oligomers generally are transesterification catalysts. Examples of such catalysts include dibutyl tin diacetate, dibutyl tin dilaurate, titanium tetra isopropoxide, lead oxide, antimony oxide, manganese diacetate, cobalt diacetate hydrate, nickel diacetate hydrate, and lithium metal and mixtures thereof. The amount required will vary but generally will be about 0.005 to 0.5 wt.% based on oligomer product weight. Since the catalysts used for preparing the oligomers remain in the products, they are present during curing of the optical fiber coatings and may affect such curing although they are not the cationic initiators, which are discussed below. Accordingly, the catalysts should be selected taking such effects into account.

Reaction Conditions

Specific examples given below will provide typical conditions found useful in the process of forming vinyl ether terminated ester oligomers. More generally, the process may be described as a sequential one in which the molecular weight of the oligomers produced is adjusted by varying the initial ratio of the ester to the polyol and in which by-products are continually vaporized and removed. Preferably, the reaction conditions are adjusted so that neither the ester nor the polyol are removed.

There are two basic variations of the process. In one aspect, the process involves contacting of a vinyl ether-terminated polyester with a polyol, or alternatively, the reaction of a polyester with a hydroxy monovinyl ether to form the vinyl ether terminated polyester, followed by reaction with a polyol. A vinyl ether is produced by the chain extension reaction and separated immediately from the reacting mixture. An example employing a dibasic ester is as follows:

The reaction may be carried out in the liquid phase at temperatures in the range of about 50° to 250°C and at a vacuum selected to permit efficient removal of the hydroxy monovinyl ether by-product , typically about 0.01 to 200 torr (0.0013 to 26.7 kPa.abs ). In general, the reaction will require about 1 to 20 hours to complete, depending upon the temperature, concentrations, catalyst and other factors familiar to those skilled in the art.

In an alternative, the polybasic ester is chain extended with the polyol, followed by addition of a hydroxy monovinyl ether to cap the chain extended ester. This may be illustrated as follows:

The first step, chain extension, will be carried out in the liquid phase at temperatures of about 50° to 250°C and a vacuum selected to effectively remove alcohol (XOH), generally about 0.01 to 500 torr (0.0013 to 66.7 kPa.abs.). The reaction requires about 0.5 to 10 hours to complete, depending on the temperature, concentrations, catalyst, and other factors familiar to those skilled in the art. The alcohol formed as a by-product is continuously removed during the reaction.

The second step, end capping, will take place at temperatures of about 50° to 180°C and a vacuum selected to efficiently remove alcohol, generally about 0.01 to 500 torr (0.0013 to 66.7 kPa.abs ). The reaction requires about 0.5 to 10 hours to complete, depending on various factors as suggested above. Again, alcohol is removed as formed.

The objective of either reaction scheme is to provide a series of vinyl ether capped ester oligomers varying in molecular weight, viscosity, and reactivity. The molecular weight is generally controlled by the ratio of the ester to the polyol. As the mol ratio approaches 1.0/1.0 the molecular weight becomes undesirably high and consequently mol ratios of about 1.5/1 are preferred, however, only exactly equal amounts of the reactants are excluded and ratios between 1.5/1 and 1.0/1.0 may be used. As the mol ratio is raised still higher the product approaches a single molecule of the ester end capped with a vinyl ether (i.e. no polyol is present). Such materials are useful, but generally require the presence of higher molecular weight oligomers for most practical applications. Alternatively, increasing the polyol so that it is in excess of the ester, i.e. less than 1.0/1.0, will produce an oligomer terminated with hydroxyl groups, which must be terminated with a vinyl ether terminated ester.

(b) Ninyl Ether Terminated Ester Monomers

The vinyl ether polyester oligomers are combined with a vinyl ether terminated ester monomer having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of Y', Y' is a mono-, di-, tri-, or tetrafunctional radical having a molecular weight of 15 to 500 and is independently selected from the group consisting of alkyl, aryl, aralkyl, and cycloalkyl radicals, X_a is a divalent radical having a molecular weight of 25 to 500, each X_a being independently selected from the group consisting of alkylene or cycloalkylene radicals, and R₃ and R₄ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms.

Preferred compositions include those where X_a is the same as given above for polyesters of (a)(i), R₃ and R₄ are both hydrogen, and Y' is independently chosen from the group consisting of

^ R -

wherein n is an integer from 0 to 10, n' is an integer from 2 to 10, E is chosen from the group consisting of bond, O, CH₂, S, SO₂, >C(CH₃)₂, and >C(CF₃)₂, and R_y is chosen from the group consisting of alkyl containing from 1 to 6 carbon atoms, alkoxy containing 1 - 6 carbon atoms, and NO₂ (c) Vinyl Ether Terminated Monomer Derived from an Alcohol

The formulation also comprises a vinyl ether terminated monomer derived from an alcohol having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of D, R₅ and R₆ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms, preferably independently selected from the group consisting of hydrogen and methyl, and D is a mono-, di-, tri-, or tetravalent radical consisting of alkyl, cycloalkyl, or alkyl ethers having a molecular weight of 56 to 1000.

Preferred compositions include those where R₅ and R₆ are both hydrogen and D is (3

0

y

where n = 4 - 20

p= 0 - 10

E is bond, O, CH₂, S, SO₂, >C(CH₃)₂, >C(CF₃)₂ Formulation of Optical Coatings

As earlier discussed, optical coatings are usually applied in two layers, the inner having much different physical properties than the outer. The inner or primary coating is softer and more elastic than the outer or secondary coating, which is intended to provide a tough barrier able to protect the inner coating and the glass fiber beneath it. Although the formulations used by the present inventors are selected from the same families of vinyl ether compounds, as will be seen quite different properties can be obtained. It is an advantage to the formulator that both layers are chemically related.

The coatings provide an important funαion in protecting optical fibers as has been discussed earlier. In order to avoid damage to the fiber it is coated as soon as possible after it is drawn. In effect, this means that the coating formulations must be able to be applied readily and that after curing certain physical properties must be satisfied.

The coating formulations will include vinyl ether ester oligomers and one or both of the vinyl ether monomers derived from esters or alcohols as previously described. The oligomers should have a Tg which is suitable for the properties of the inner or outer layers. If used for the inner resilient layer, the Tg of the oligomers should be equal to or less than -10°C, while for the outer rigid layer, the Tg of the oligomers should be equal to or greater than -10°C

For coating, the liquid formulation should have a viscosity at the application temperature (about 20° to 100°C) of about 100 to 10,000 cps (mPa•s) for both the primary or inner layer and the secondary or outer layer. The coating should not be so fluid as to flow significantly before curing or so viscous as to be difficult to coat the fiber surface.

The cured coatings require certain physical properties consistent with their function. Thus, for the primary layer, the glass transition temperature (Tg) should be at or below 0°C and have a modulus of 80-800 psi (551-5510 kPa) at room temperature with an elongation greater than 50%. The secondary layer should have a cured Tg greater than 50°C, a cured modulus of at least 50,000 psi (344.7 MPa) at room temperature and an elongation greater than 5%. One familiar with the art will recognize that the primary coating is to remain easily deformed under stress even at low ambient temperatures so that it c an minimize the transfer of external forces to the glass fiber and thus limit the effect of "microbending" discussed earlier. The outer layer is seen to be much more rigid and provides protection to the inner layer and the glass fiber.

In general, the primary and secondary coating formulations will meet the requirements described above. Within the limits set by the properties needed for applying the coatings and the cured properties, the proportions of the oligomers and monomers can be varied widely, depending upon the properties of the oligomers. Thus, it is possible for the oligomers to make up only a minor fraction of the coating formulation, but up to nearly all may be oligomer. In addition to the oligomers, one or both of the types of vinyl ether monomers may be used in formulating the primary and secondary coatings.

An effective amount of a cationic photoinitiator is used to cause the vinyl ethers to react and produce the desired polymer. The recognized classes of cationic photoinitiators include various compounds which respond to irradiation by producing acid species capable of catalyzing cationic polymerization. See Crivello, Advances in Polymer Science, 62, p. 1-48 (1984) Onium salts of Group V, VI, and VIl elements are stated to be the most efficient and versatile of the cationic photoinitiators They generate strong Lewis acids which can promote cationic polymerization Curing of the vinyl ether compositions of the invention is not limited to a particular class of such photoinitiators, although certain types are preferred, including onium salts based on halogens and sulfur. More specifically, the onium salt photoinitiators described in Crivello's U.S. Pat. No. 4,058,400 and in particular iodonium and sulfonium salts of BF₄-, PF₆-, SbF₆-, and SO₃CF₃-. Preferred photoinitiators are triarylsulfonium salts, and diaryliodonium salts. Preferred anions are hexafluorophosphate and hexafluoroantimonate They are usually required in amounts from about 0.1 to 5 wt.% in the blended formula of vinyl ethers and epoxides. Preferred initiators include:

where X is SbF₆- or PF₆- Commercially available initiators include UNI-6974 (an SbF₆- salt) and UVI- 6990 (a PF₆- salt) supplied by Union Carbide. Other cationic photoinitiators are defined by the formulas

where y is 1 to 18

In addition to the principal ingredients discussed above, the formulations may also contain dyes, stabilizers, fillers, pigments, and antioxidants such as hindered phenols, wetting agents such as fluorosurfactants e.g. FC-430 from 3-M, photosensitizers such as benzophenone, thioxanthone, perylene and other components familiar to those skilled in the art

In addition to the principal ingredients discussed above, the formulations may also contain various stabilizers may be included as discussed in more detail below. They include thermal oxidation stabilizers, hydrogen stabilizers, light screens, color stabilizers, blocking stabilizers (slip agents), and coupling agents (adhesion promoters).

Thermal Oxidation Stabilizer The thermal oxidation stabilizer is present in the coating in an amount up to about 5 wt.%, preferably in the range of from about 0.25 wt.% to about 3.0 wt.% Examples are hindered phenolic antioxidants such as octadecyl 3-(3',5'-di-tertbutyl-4'-hydroxyphenyl)- propionate (Irganox 1076), tetrakis [methylene (3,5-di-tert-butyl-4-hydroxy- hydrocinnamate)]methane (Irganox 1010), and benzene propanoic acid, 3,5- bis(1,1-dimethylethyl)-4-hydroxy-,thiodi-2,1-ethanediyl ester (Irganox 1035) Examples of stabilizers which are not hindered phenolic antioxidants are Ν,Ν'- (2-naphthyl)-phenylenediam ine (AgeRite White) dilauryl thiopropionate (Irganox PS800), and p,p'-2-(2-phenylpropyldiphenylamine (Νaugard 445).

Hydrogen Stabilizer The hydrogen stabilizer may comprise one or more components chosen from the group consisting of hindered phenolic antioxidants, nitrogen-based stabilizers, aliphatic sulfides, aliphatic disulfides, aliphatic polysulfides, aromatic sulfides, aromatic disulfides, aromatic poly sulfides, mixed aliphatic/aromatic sulfides, mixed aliphatic/aromatic disulfides, mixed aliphatic/aromatic polysulfides, aliphatic nitro compounds, and aromatic nitro compounds.

Examples of hindered phenolic antioxidants are Irganox 1076, 1010, and 1035 (see list of hindered phenolic antioxidants under (d) above for chemical formulas). Examples of nitrogen-based stabilizers are phenothiazine, carbazole, and urethane proteαed hindered amine light stabilizers (HALS). Examples of aliphatic sulfides (R-S-R) are dodecyl sulfide, octyl sulfide, octadecyl sulfide, sec-octyl sulfide, t-butyl sulfide, dilauryl thiopropionate (Irganox PS800). Examples of aliphatic disulfides (R-S-S-R) are dodecyl disulfide, octyl disulfide, octadecyl disulfide, sec-octyl disulfide, and t-butyl disulfide. Examples of aliphatic polysulfides are di-octyl polysulf.de, di-t- dodecyl polysulfide, and di-t-nonyl polysulfide. Examples of aromatic sulfides (Ar-S-Ar) are phenyl sulfide, benzyl sulfide, tolyl sulfide, and 6-hydroxynaphthyl sulfide. Examples of aromatic disulfides (Ar-S-S-Ar) are phenyl disulfide, benzyl disulfide, tolyl disulfide, 6-hydroxynaphthyl disulfide, and a mixture of amylphenol disulfide polymers (Vultac 3, marketed by Atochem). Examples of aromatic polysulfides are benzyl trisulfide and phenyl trisulfide. Examples of mixed aliphatic/aromatic sulfides (Ar-S-R) are phenyl octyl sulfide, naphthyl octyl sulfide, and tolyl ethyl sulfide. Examples of mixed aliphatic/aromatic disulfides (Ar-S-S-R) are phenyl octyl disulfide, naphthyl octyl disulfide, and tolyl ethyl disulfide. Examples of aliphatic nitro compounds (R-NO₂) are nitro- methane, 2-nitro-2-methyl-1-propanol, and 2-nitro-2-methyl-1,3-propanediol Examples of aromatic nitro compounds (Ar-NO₂) are 5-nitroisophthalate esters.

Another type of hydrogen stabilizer which has been found especially effective may be generally characterized as transition metal salts of organic compounds. They are believed to have broad usefulness and are the subject of another patent application. These materials can act to decompose hydroperoxides believed to be associated with hydrogen generation, although their effectiveness may relate to other effects as well. Examples of these salts include naphthenate octoate, 2-ethyl hexanoate, and cyclohexane butyrate salts, plus acetyl acetonate complexes of cobalt, manganese, nickel, iron, copper and zinc.

The hydrogen stabilizers may be present in the coating at a range of 0 to 5 wt.%. Preferably, optical fiber coatings will include a mixture of hindered phenols, organics, sulfides or disulfides, and the organic salts of transition metals. Light Screen The light screen may be present in the coating at a range of 0 to 5 wt.%. Examples of light screens include aromatic esters such as Cyasorb 2908 (2,6-di(t-butyl)-p-hydroxy-benzoic acid, hexadecyl ester), aryl salicylate esters, and esters of 2-cyano-3,3-di-phenyl-acrylic acid

Color Stabilizer The color stabilizer may be present in the coating at a range of 0 to 5 wt.%. Examples of color stabilizers are carbamates such as N.K-dicarbomethoxybenzidine and blocked amines such as Tinuvin 440 (8-aceτyl-3-dodecyl-7,7,9,9-tttramethyl-1,3,8-triazaspiro(4,5)decane-2,4- dione).

Blocking Stabilizer The blocking stabilizer is present in the secondary coating only at a range of 0 to 5 wt.%. of the secondary coating. Examples of blocking stabilizers are carnauba wax, polyether silicone copolymers such as SF 1188, fluorinated copolymers, such as FC 430, micronized polyethylene waxes, and micronized celluloses.

Coupling Agent The coupling agent is used in the coating to promote adhesion of the coating with the substrate. In optical fiber coatings, coupling agents are used in the primary coating only and promote the adhesion of the primary coating with the glass fiber. Typical coupling agents are substituted trialkoxy silanes such as epoxypropyltrimethoxy silane, acryloxy- propyltrimethoxy silane, allytriethoxysilane, and epoxycyclohexylethyltri- methoxy silane.

Another coupling agent which has been found to be of particular usefulness is generally classified as vinyl ether urethane siloxanes. These compounds also have other uses and are the subject of another patent application. They may be prepared by reacting mono hydroxy vinyl ethers with an isocyanate-containing alkoxy silane. Examples of such compounds are those obtained by reacting isocyanoto propyl triethoxysilane with 4-hydroxy-butyl vinyl ether 2-hydroxyethyl vinyl ether and hydroxy methyl cyclohexyl methyl vinyl hers.

The coupling agent may be present in the coating at a range of from 0 to 5 wt.%.

Curing of Optical Coatings

The vinyl rther formulations of this invention may be cured or polymerized by methods known in the art. The resins may be radiation cured, as for example by being subjected to an electron beam of an energy in the range from about 50 up to perhaps 500 KeV with a dosage from about 0.1 to about 10.0 Mrads. Electron beam curing may be performed advantageously in the presence of an iodonium or a sulfonium salt to afford high speed cationic polymerization. Ultraviolet curing in the presence of an onium salt also may be used to produce cationic polymerization. The ultraviolet radiation from a mercury vapor lamp is commonly used.

In a typical application, the coatings of the invention are applied by drawing the glass fiber from a heated glass rod and then passing a glass fiber through a die which applies the coating formula. A glass rod is heated to a temperature which softens it so that it can be pulled into a thin fiber. After the hot fiber is cooled by air, it is coated with a primary vinyl ether formulation as described above and then cured by exposure to ultraviolet radiation. Thereafter, the secondary coating formulation is applied and cured in a similar manner. In some instances the curing of the primary coating is omitted and both coatings are applied before curing. Once the coatings have been applied and cured, the glass fibers are ready for use.

Example 1

A vinyl ether terminated polyester oligomer for use in a primary optical fiber coating was prepared by reacting 890 g of hydroxy butyl monovinyl ether (HBVE) with 4452 g of dimrthyl isophthalate (DMI) and 4056 g of polytetrahydrofuran diol (PolyTHF-250) and 600 g of bishydroxymethyltricyclodecane (BHTD) in a two-step procedure First, the DMI was reacted with the THF diol and BHTD at a temperature of 120°C and a vacuum of 300 torr (40 kPa) using 10 g of dibutyl tin diacetate (DBTDA) as a catalyst. After 3.3 hours, the HBVE was added and the reaαion carried out at 120°C with a vacuum of 190 torr (25.3 kPa). After 6 hours, the vacuum was reduced to less than 5 torr (0.67 kPa) and excess HBVE was removed by distillation. After cooling, the oligomer was available for use in a primary optical fiber coating, where it is designated VEX 8075-59 and may be represented by the following: HBVE-[(DMI)_x(PolyTHF-250)_y(BHTD)_z]DMI- HBVE where x, y, and z represent the molar proportions of the chain-extended polyester.

Example 2

A vinyl ether terminated polyester oligomer for use in a secondary optical fiber coating was prepared by reacting 2699 g of HBVE with 4526 g of DMI and 3050 g of bishydroxymethyltricyclodecane (BHTD) in a two-step procedure as in Example 1. First the DMI and BHTD were reacted at a temperature of 120°C and a vacuum of 300 torr (40 kPa) using 10 g of DBTBA catalyst. After 1.45 hours, the HBVE was added and the reaction carried out at 120°C with a vacuum of 105 torr (14 kPa). After 5.5 hours, the vacuum was reduced to less than 5 torr (0.67 kPa) and excess HBVE was removed by distillation. After cooling, the oligomer was available for use in a secondary optical fiber coating, where it is designated VEX 8075-63 and may be represented by the following: HBVE-[(D MI)_x(BHTD)_y] -DMI-HBVE where x and y represent the molar proportions of the chain-extended polyester.

Example 3

A fiber optic secondary (outer) coating was formulated as shown below:

(a) oligomer of Example 2 above

(b) reaction product of HBVE and dimethylisophthate (AlliedSignal)

(c) triaryl sulfonium salt (Union Carbide)

(d) 2 pph Irganox 1076 (Ciba-Geigy), 0.5 pph dodecyl sulfide, 0.0025 pph copper-2-ethylhexanoate, 0.1 pph SF-1188 (silicone-polyether copolymer, GE)

This formulation had a viscosity of 1560 cps @ 60°C. The formulation was coated on a glass plate with a 3 mil film applicator. The film was heated to 60°C and cured by exposure to a mercury arc lamp with a dose of ca. 100 mJ/cm ² in a nitrogen atmosphere. The cured film was removed from the glass plate for analysis. The results are summarized in Table A below.

Example 4

A fiber optic primary (inner) coating was formulated as shown below:

(a) oligomer of Example 1 above

(b) reaction product of HBVE and methyl benzoate (AlliedSignal)

(c) 2.0 pph Irganox 1076, 0.5 pph dodecyl sulfide, 0.5 pph CHMVE- silicone (reaction product of isocyanate propyl triethoxy silane with hydroxy methyl cyclohexylmethylvinyl ether), 0.0025 pph copper-2- hexyl hexanoate

This formulation had a viscosity of 980 cps @ 60°C The formulation was coated on a glass plate with a 6 mil film application. The film was heated to 60°C and cured by exposure to a mercury arc lamp with a dose of ca. 250 mJ/cm 2 in a nitrogen atmosphere. The cured film was removed from the glass plate for analysis. The results are summarized in Table A below

It can be seen that adjustment of the formulations which appear similar can actually produce quite different properties when cured The inner coating is soft and elastic as required for such coatings. The outer coating is much harder and will serve to proteα the inner coating and also has low water absorption. Example 5

It has been found that polyester-based formulations cure more rapidly than do urethane-based formulations. Two secondary coating compositions were prepared for comparison.

(a) reaction produα of polypropylene adipate

= 500, Witco Formrez 33- 225, 1.0 hydroxy equivalent) with modified MDI (BASF MP-102, 2 NCO equivalents) and 4-hydroxy methyl cyclohexyl methyl vinyl ether (CHMVE) (1.0 hydroxy equivalent) plus 12% 1,4-cyclohexane dimethanol divinyl ether (CHVE).

(b) reaction product of cyclohexane dimethanol vinyl ether (CHMVE) and dimethyl glutarate.

(c) 1,4-cyclohexane dimethanol divinyl ether

(d) 1 pph Irganox 1076 (Ciba-Geigy), 0.25 pph phenothiazine, 0.5 pph SF-1188 (silicone-polyether copolymer, GE).

(a) 2 pph Irganox 1076, 0.5 pph dodecyl sulfide, 0.0025 pph copper-2-ethyl hexanoate, 0.1 pph SF-1188.

The two formulations were spread on glass plates with a 3 mil thickness and then cured as in Examples 3 and 4 at room temperature and 60°C with the radiation dose being varied. The modulus of the cured fibers was measured with an Instron Model 4502. The results are tabulated below and plotted in

Figure 1.

Comparison of the results shows that the polyester-based formulation generally provides a higher modulus and requires a lower radiation dose to obtain a fully cured film. Also, the additional data for curing the polyester formulation at 80°C shows that fully cured films can be obtained at high temperatures with only a small radiation dose required.

Example 6

Polyester-based formulations have been found to have superior physical properties relative to urethane-based formulations. Two compositions were compared.

Urethane Formulations

Primary Coating Parts by Weight

VE 2010(a) 69%

Poly THF-DVE (b) 9%

(a) The reaction produα of Formrez 33-56, CHMVE, and MP-102

(modified MDI, BASF).

(b) The divinyl ether of poly THF-250 (BASF)

(c) Hexyl ethoxy vinyl ether

(d) 1.0 pph Irganox 1076, 0.25 pph phenothiazine

(a) 1.0 pph Irganox 1076, 0.25 pph phenothiazine, 0.5 pph SF-1 188.

(a) oligomer of HBVE, DMI, PolyTHF 250, PolyTHF 650, and BHTD with molar proportions of 6.0/25.02/17.41/0.64/3.97.

(b) 2.0 pph Irganox 1076, 0.5 pph dodecyl sulfide, 0.0025 pph copper-2- ethyl hexanoate, 0.5 pph CHMVE-silicone.

(a) oligomer of HBVE, DMI, and BHTD with molar proportions 2/3/2. (b) 2.0 pph Irganox 1076, 0.5 pph dodecyl sulfide, 0.0025 pph copper- 2-ethyl hexanoate, 0.1 pph SF-1188.

Example 7

The formulations of Example 6 were tested to compare their resistance to high temperature oxidation. First, by Thermal Gravimetric Analysis, the temperature of cured samples of the formulations were subjected to an increase of 5°C/min in air until the onset of oxidation was deteαed The results are shown in the following table.

The formulations were tested also by exposing cured samples to a temperature of 125°C in air for seven days and measuring the weight loss. The results were as follows:

It can be seen that the polyester-based coatings are more resistant to oxidation at high temperatures than are the polyurethane-based coatings.

Example 8

The polyester-based secondary formulations of Example 6 were tested again for high temperature oxidation resistance but the amount of photoinitiator was cut in half. This was possible since the polyester-based formulations cure very rapidly. The weight loss after exposure to 125°C in air was compared for samples of the secondary coatings of Example 6 with 0.8 pph and 0.4 pph of the photoinitiator UV1-6974. The results are as follows:

It can be seen that the curing speed of the polyester-based formulation makes it possible to improve the high temperature resistance of the coatings by reducing the amount of the photoinitiator used in curing. Example 9

Hydrogen generation is a recognized problem with optical fiber coatings. The high curing speed of polyester-based vinyl ether coatings makes it possible to reduce hydrogen generation by reducing the amount of the photoinitiator and the radiation dose, as will be seen in the following results with the polyester-based formulations of Example 6. The amount of hydrogen generated by exposing the cured coatings to 100°C for 24 hours are reported.

It can be seen that curing with a low radiation dose at a high temperature produces less hydrogen.

Example 10

Optical fiber coatings should be insensitive to moisture. However, increasing humidity results in an undesirable reduction in the modulus of the coatings. Cured films of the secondary coating formulations of Example 6 were exposed to humid air and the modulus measured as before. The results were as follows.

It can be seen that the polyurethane coatings suffered a larger loss of its modulus than did the polyester coating. Since the minimum value for the modulus of the secondary coating is about 50,000 psi (344.7 MPa), it is believed that the polyester coating would be satisfactory under humid conditions, while the polyurethane coating might not.

Example 11

Measurements were made on cured films of the coatings of Example 6 to compare the water absorbed and the extraαable liquids. The films were immersed in deionized water for 24 hours at room temperature, then patted dry with a cotton cloth to absorb excess water and weighed to determined water absorption. The films were dried in a dessicator to a constant weight to determine the amount of extraαable materials in the films The results are shown below.

It can be seen that the polyester coatings are superior to the polyurethane coatings.

Example 12

A primary (inner) coating for optical fibers was formulated as follows.

(a) oligomer HBVE-[(DMI)₃(THF-1000)₃]-DMI-HBVE

(b) ester monomer-reaction produα of HBVE and dimethyl isophthalate

(c) triaryl sulfonium salt (Union Carbide)

This formulation contained only two vinyl ether components and omitted alcohol-derived vinyl ester monomers. The viscosity was 11,652 cps (mPa•s) at 40°C and 3,737 cps (mPa•s) at 60°C. After curing, the T_g was -62.7°C, the modulus 569 psi (3923 kPa), and the elongation 54%.

Example 13

A secondary (outer) coating for optical fibers was formulated as shown below.

(a) oligomer HBVE-[(DMI)₂(BHTD)ι(HBPA)₁]-DMI-HBVE

where HBP A is hydrogenated bisphenol A

(b) ester monomer - reaction product of HBVE and dimethyl isophthalate (AlliedSignal)

(c) ester monomer - reaαion product of HBVE and trimethyltrimelitate (AlliedSignal)

(d) triaryl sulfonium salt (Union Carbide)

(e) Irganox 1076 (Ciba Geigy)

This formulation contained only ester monomers - again, alcohol-derived monomers were omitted. The viscosity was 1548 cps (mPa•s) at 60°C and 320 cps (mPa•s) at 80°C. After curing at 80°C with 200 mJ/cm², the T_g was 53°C, the modulus was 76,406 psi (526.8 MPa), and the elongation 13.9%.

Claims

1. A composition for coating optical fiber consisting essentially of the reaction product of

(a) a vinyl ether polyester oligomer consisting essentially of the reaction product of (i) a polybasic ester having the formula

wherein R₇ is chosen from the group consisting of phenyl and an alkyl group containing from 1 to 6 carbons, X_a, X_b, Y_a, and Y_b are radicals having a molecular weight of from 25 to about 500, each X_a, each Y_a, and Yb being independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, j is an integer from 0 to 2, z is an integer from 0 to 2, p is an interger from 0 to 2, V is an integer from 0 to 2, m is an integer from 0 to 100, preferably 1 to 10, and w is an integer from 0 to 2. and (ii) a hydroxy monovinyl ether having the formula

wherein R₁ and R₂ are monovalent radicals selected from the group consisting of hydrogen and alkyl groups having 1 to 10 carbon atoms. Preferably, R₁ is an alkyl group having 1 to 4 carbon atoms and R₂ is hydrogen or R₁ is hydrogen and R₂ is an alkyl group having 1 to 4 carbon atoms. Most preferably, both R₁ and R₂ are hydrogen. X_a is a divalent radical having a molecular weight in the range of from 25 to about 500 and is independently selected from the group consisting of alkylene, cycloalkylene, and alkylene ether radicals. and (iii) a polyol having the formula

wherein X_a and X_b are radicals having a molecular weight of from 25 to about 500, and each X_a and X_b is independently selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, m is an integer from 0 to 100, preferably 0 to 10, and w is an integer from 1 to 3 indicating the number of additional substituents of X_b. b) a vinyl ether terminated ester monomer having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of Y',

Y' is a mono-, di-, tri-, or trtrafunαional radical having a molecular weight of 15 to 500 and is independently selected from the group consisting of alkylene, arylene, aralkylene, and cycloalkylene radicals, X_a is a divalent radical having a molecular weight of 25 to 500, each X_a being independently selected from the group consisting of alkylene or cycloalkylene radicals, and R₃ and R₄ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms;

c) a vinyl ether terminated monomer derived from an alcohol having the formula

wherein w is an integer from 1 to 4 indicating the number of substituents of D, R₅ and R₆ are monovalent radicals which are independently selected from the group consisting of hydrogen and alkyl groups having 1-10 carbon atoms, preferably independently selected from the group consisting of hydrogen and methyl, and D is a mono-, di-, tri-, or tetravalent radical consisting of alkylene, cycloalkylene, or alkylene ethers having a molecular weight of 56 to 1000.

2. The composition of Claim 1 for a primary optical fiber coating wherein for the vinyl ether polyester oligomer of (a)

(i) the polybasic esters where

X_a is independently chosen from the group consisting of ^

where q = 0 to 40

X_b is either chosen from the same group as X_a where V is 0 and where X_b is polyfunαional from

C-(-CH₂-O)-4, R-C-(CH₂-O-)-₃

where R is 1-10 carbon alkyl.

Y_a is independently chosen from the group consisting of

j is 0-1

m is 0-50

w is 0 - 2

R₇ is CH₃

p is 0 - 2

z is 0 - 2

(ii) the hydroxy monovinyl ethers where

X_a is independently chosen from the group consisting of

where n is 2, 4, or 6

R₁ and R₂ are both hydrogen

(iii) the polyols where

X_a is independentiy chosen from the group consisting of

where q = 0 to 20

X_b is C₂H₅C(CH₂O-)₃

m is 0-20

w is 1 - 2

X_b is chosen from the same group as X_a where V is 0 and where X_b is polyfunctional from

C-(-CH₂-O)-₄,

R-C-(-CH₂-O-)-₃ where R is 1-10 carbon alkyl.

3. The composition of Claim 2 wherein for the vinyl ether terminated ester monomer of (b)

X_a is the same as in Claim 2 (a) (ii)

R₃ and R₄ are both hydrogen

Y is independently chosen from the group consisting of

-

wherein n is an integer from 0 to 10, n' is an integer from 2 to 10, E is chosen from the group consisting of bond, O, CH₂, S, SO₂, >C(CH3)₂, and >C(CF₃)₂, and R_y is chosen from the group consisting of alkyl containing from 1 to 6 carbon atoms, alkoxy containing 1 - 6 carbon atoms, and NO₂

4. The composition of Claim 2 wherein for the vinyl ether terminated monomer derived from an alcohol of (c)

R₅ and R₆ are both hydrogen

D is ^

where n = 4 - 20

p= 0 - 10

E is bond, O, CH₂, S, SO₂, >C(CH₃)₂, >C(CF₃)₂

5. The composition of Claim 1 for a secondary optical fiber coating wherein for the polyester oligomer of (a)

(i) the polybasic esters where

X_a is independently chosen from the group consisting of

where n is 2 or 4

R₇ is CH₃

R₁ and R₂ are H

(ii) the hydroxy monovinyl ethers where

X_a is independently chosen from the group consisting of

where n is 2, 4, or 6

R₁ and R₂ are both hydrogen

(iii) the polyols where

X_a is independently chosen from the group consisting of

6. The composition of Claim 5 wherein for the vinyl ether terminated ester monomer of (b)

X_a is the same as in Claim 5

R₃ and R₄ are both hydrogen

Y' is independently chosen from the group consisting of

wherein n' is an integer between 2 and 10, E is chosen from the group consisting of bond, O, CH₂, S, SO₂, >C(CH₃)₂, and >C(CF₃)₂, and R_y is chosen from the group consisting of alkyl containing from 1 to 6 carbon atoms, and NO₂

7. The composition of Claim 5 wherein for the vinyl ether terminated monomer derived from an alcohol of (c)

R₅ and R₅ are both hydrogen

D is ^

O

where n is an integer from 4 to 20

p is an integer from 0 to 10

E is bond, 0, CH₂, S, SO₂, >C(CH₃ )₂ , >C(CF₃)₂