OPTICAL FIBRE COATED WITH A POLYESTER COATING

Abstract

The present invention concerns an optical fibre comprising: an optical waveguide comprising a glass core surrounded by a glass cladding; a coating surrounding said optical waveguide comprising a cured polymer material comprising a polyester obtained by polymerization of a monomer selected from an acid, a triglyceride, or a mixture of triglycerides having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds. The present invention concerns also a method for coating an optical fibre with said polyester coating. The cured polymer material forming the coating can be prepared by curing the polyester of the invention either thermally or by radiation.

Claims

1. An optical fibre comprising: an optical waveguide comprising a glass core surrounded by a glass cladding; a coating surrounding said optical waveguide comprising a cured polymer material comprising a polyester obtained by polymerization of a monomer selected from an acid, a triglyceride, or a mixture of triglycerides having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds.

2. The optical fibre according to claim 1, wherein said cured polymer material is a thermally cured polymer material.

3. The optical fibre according to claim 1, wherein the monomer is a monocarboxylic acid.

4. The optical fibre according to claim 1, wherein the monomer is an acid selected from alpha-eleostearic acid, calendic acid, punicic acid or licanic acid.

5. The optical fibre according to claim 1, wherein the monomer is a triglyceride or a mixture of triglycerides containing at least 70 wt %, based on the total weight of said triglyceride or mixture of triglycerides, of C.sub.16-C.sub.24 aliphatic chains comprising at least two conjugated double bonds.

6. The optical fibre according to claim 1, wherein the polymerization is carried out in the presence of a catalyst selected from tin or titanium catalyst.

7. The optical fibre according to claim 1, wherein said coating is selected from: primary coating and single coating.

8. The optical fibre according to claim 1, wherein said coating is a primary coating which is surrounded by a secondary coating, said secondary coating comprising a polymer selected from: methacrylate polymer, acrylate polymer and mixtures thereof.

9. A method for coating an optical fibre comprising: providing an optical waveguide comprising a glass core surrounded by a glass cladding; applying a radiation curable coating composition on the cladding, said coating composition comprising a polyester obtained by polymerization of a monomer selected from an acid, a triglyceride, or a mixture of triglycerides having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds; curing said radiation curable coating composition so as to crosslink said polyester and to form the coating.

10. The method according to claim 9 wherein the polymerization is carried out in the presence of a catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0028] According to the invention, a coating for optical fiber can be obtained by polymerizing a monomer which is an acid, a triglyceride, or a mixture of triglycerides having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds. The Applicant has observed that monomers lacking chains with at least two conjugated double bonds are unsuitable for the purpose of the present invention, as the polyester derived from their polymerization is either not sufficiently crosslinkable or is crosslinkable only after curing times too long for a convenient industrial application.

[0029] Preferably, the acid having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds as monomer is a monocarboxylic acid.

[0030] The acid having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds as monomer suitable for the present invention can also be in form of salt or of salt mixture thereof.

[0031] For example, the acid having a C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds is alpha-eleostearic acid (-ESA; 9Z11E13E-18:3), calendic acid (8E10E12Z-18:3), punicic acid (9E11E13Z-18:3) or licanic acid (4-keto-octadeca-9,11,13-trienoic acid). Alpha-eleostearic acid is preferred.

[0032] In an embodiment of the invention, coating for optical fibres can be obtained from a monomer which is a triglyceride or a mixture of triglycerides comprising at least one C.sub.16-C.sub.24 aliphatic chains comprising at least two conjugated double bonds. Vegetable oils or seed oils can contain such triglycerides or mixture of triglycerides in an amount of from 30 wt % to 80 wt %.

[0033] Advantageously, the monomer suitable for the present invention is a triglyceride or mixture of triglycerides containing at least 70% by weight, based on the total weight of said triglyceride or mixture of triglycerides, of C.sub.16-C.sub.24 aliphatic chains comprising at least two conjugated double bonds. When the level of C.sub.16-C.sub.24 aliphatic chain comprising at least two conjugated double bonds in an oil is lower than 70 wt %, known techniques can be applied to concentrate the polyunsaturated conjugated part, e.g. by fractional crystallization.

[0034] Mixture of triglycerides having the above amount of C.sub.16-C.sub.24 aliphatic chains comprising at least two conjugated double bonds are commercially available, e.g. as tung oil, pomegranate seed oil, calendula oil, and their mixtures.

[0035] In the case of triglycerides or mixture thereof, C.sub.16-C.sub.24 aliphatic chain monomers according to the invention can also react with monomers having different aliphatic chains and being contained in the triglyceride or mixture thereof, resulting in polyester copolymer by-products. These by-products, if any, are generally present in negligible amounts not affecting the features and performance of the cured polymer material comprising the polyester according to the present invention.

[0036] The use of triglycerides as monomer can be advantageous with respect to the use of an acid as such in that the first is economically profitable.

[0037] To prepare the polyesters suitable for the coating of the present invention, the monomer can be polymerized using the techniques and the devices well known to the person skilled in the art. See, for example, C. Wang and S. Erhan, Journal of the American Oil Chemists' Society (JAOCS), Vol. 76, no. 10 (1999). The polymerization reaction of the monomer according to the invention is carried out, for example, in the presence of oxygen and heating at a temperature of from 150 C. to 300 C. in the absence of any polymerization initiator.

[0038] A catalyst, such as an acid catalyst, may be added. Examples of catalysts are: rare earth oxides, rare earth salts and transition metal salts, organometallics, and the like.

[0039] Preferably the catalyst of the present polymerization reaction is a tin or a titanium catalyst. Examples of preferred catalyst according to the invention are: metal oxyacid salts, or tin salts (such as tin tetrachloride), titanium tetrachloride, iodonium derivatives, palladium, platinum, rhodium and complexes thereof.

[0040] Preferably, the catalyst is used in an amount within the range of from 0.1 to 3 mol %, based on the total moles of acid present in the reaction mixture, when the acid is used as such, or from 0.1 to 0.8 mol % of monomer.

[0041] Preferably, the polymerization reaction is carried out at a pressure within the range from 1 atm to 4 atm.

[0042] Preferably, the reaction time is within the range from 0.015 hours to 2 hours.

[0043] Preferably, the polymerization reaction is carried out in the absence of any added solvent so as to avoid any contamination of the polymer coating applied on the optical waveguide.

[0044] The polyester suitable for the coating of the present invention is radiation curable. Radiation includes infrared radiation, thermal radiation, ultraviolet radiation, X-rays, electron beams, and the like. Thermal and UV radiation are preferred, the first being more preferred. Other curing method can be applied concurrently with the radiation curing.

[0045] According to a first preferred embodiment, the cured polymer material of the coating is obtained by thermally curing the present polyester. Thermal curing is preferably carried out at a temperature up to 300 C., more preferably within the range of 200 C. to 300 C. The reaction time can be from 0.1 to 2 minutes.

[0046] The curing of the polyester can take place also by crosslinking in the presence of oxygen. Oxygen can behave as crosslinking initiator or adjuster. Catalytic amounts of transition metal salts can be conveniently used to improve the crosslinking effect of oxygen. The desired final properties of the cured polymer can be adjusted by varying both the curing temperature and the curing time, as these two parameters influence the crosslinking density of the curing reaction and thus the degree of crosslinking of the polymer.

[0047] Optionally, curing of the polyester can be done in the presence of a radical thermal or redox initiator.

[0048] Preferably, thermal initiators having an activation temperature within the range of from 60 C. to 300 C. are used. Examples of thermal initiators that can be used for the purpose of the present invention are: 2,2-azobis(2-methylpropio-nitrile), meso-1,2-dibromo-1,2-diphenylethane, tetraalkyl-1,2-diphenylethanes.

[0049] When a thermal initiator is used, a thermocurable composition comprising a polyester and a thermal initiator is prepared, wherein said initiator is preferably present in an amount of from 0.3 wt % to 8 wt %, more preferably from 0.5 wt % to 5 wt %, based on the weight of the thermocurable composition.

[0050] According to a second preferred embodiment, the coating of the present invention is obtained by UV-curing the polyester, particularly in the presence of a photoinitiator. Conventional photoinitiators can be used in the present invention. Examples of suitable photoinitiators include benzophenone- and/or acetophenone derivatives, such as alpha-hydroxy alkylphenyl ketones, benzoin alkyl ethers and benzyl ketals, monoacylphosphine oxides, and bisacylphosphine oxides. Preferred photoinitiators are 1-hydroxy-cyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, and diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide.

[0051] When a photoinitiator is used, a UV-curable composition comprising a polyester and a photoinitiator is prepared, wherein said photoinitiator is present in an amount of from 0.3 wt % to 8 wt %, more preferably from 0.5 wt % to 5 wt %, based on the weight of the radiation curable composition.

[0052] Under certain reaction conditions, for example at a temperature of from 200 to 300 C., and in the presence of a radical thermal or redox initiator, the monomer suitable to obtain the coating of the present invention can be polymerized and cured in a single stage.

[0053] The radiation cured polymer material for the coating of the present invention can also include other conventional additives in effective amounts. For example, additives such as stabilizers, levelling agents, adhesion promoters, chain transfer agents, colorants including pigments and dyes, viscosity adjusters, wettability adjusters, adhesion promoters and the like can be used.

[0054] The cured polymer material suitable for the present invention can be prepared by mixing the components with any suitable method known in the art.

[0055] After curing, the polymers obtained have mechanical properties, elasticity and adhesion properties which make them suitable as coating layers for optical fibres. Particularly, the cured polymer materials according to the present invention have modulus of elasticity (E) and glass transition temperature which fulfil the requirements for use as primary coating layers, secondary coatings or single coating layers. Preferably, the coating materials of the present invention are used as primary coating layers and single coating layers.

[0056] When used as primary coating layer, the cured polymer material of the present invention preferably has a modulus of elasticity (E) at 25 C. of from 0.01 to 5 MPa, more preferably of from 0.05 to 5 MPa, and a glass transition temperature (Tg) of 20 C. at most, preferably of 30 C. at most.

[0057] When used as single coating layer, the cured polymer material of the present invention preferably has a modulus of elasticity (E) at 25 C. of from 20 to 100 MPa, more preferably of from 30 to 80 MPa, and a glass transition temperature (Tg) of 20 C. at most, preferably of 0 C. at most.

[0058] When used as secondary coating layer, the cured polymer material of the present invention preferably has a modulus of elasticity (E) at 25 C. of from 500 to 2000 MPa, and a glass transition temperature (Tg) greater than 50.

[0059] When the present polyester is used to form a primary coating on an optical fibre, a secondary coating surrounding said primary coating can also be applied using the polymer materials conventionally used in the art for the manufacturing of secondary coatings, for example a UV curable acrylate secondary coating.

[0060] A secondary coating usable in the fibre of the present invention in combination with a thermally curable primary coating can comprise a polymer selected from: methacrylate polymer, acrylate polymer and mixtures thereof. In particular, the secondary coating comprises urethane acrylate polymers which can be obtained, for instance, by radiation curing a radiation curable composition comprising an oligomer having a backbone derived from polypropylenglycol and a dimer acid based polyester polyol. A material suitable for the secondary coating of the optical fibre of the invention is disclosed in WO2012036546 or is marketed by DeSolite 3471-2-136.

[0061] The manufacturing of the coated optical fibre according to the present invention can be carried out according to known techniques. For example, after drawing of the optical waveguide a primary coating can be applied by passing the optical waveguide through a sizing die and a reservoir containing the curable polyester according to the present invention. When a thermally curable composition is used, the application can advantageously be done when the optical waveguide has a suitable temperature, e.g. from 150 C. to 300 C., so as to exploit the heat of the drawn optical waveguide to obtain the final cured polymer material. When a radiation curable polymer or composition is applied, the application step is followed by radiation curing (e.g. by UV or IR) of the applied composition so as to obtain the final polymer material. In the case of deposition of both a primary and a secondary coating, the latter is applied on the primary coating before or after the curing of the secondary coating (by techniques known as wet-on-dry or wet-on-wet deposition).

[0062] An optical fibre thus produced may be used in the production of optical cables. The fibre may be used either as such or in the form of ribbons comprising several fibres combined together by means of a common coating.

[0063] The present description shows only some embodiments of a coated optical fibre according to the invention. Suitable modifications can be made to these embodiments according to specific technical needs and application requirements without departing from the scope of the invention.

[0064] The following examples are provided to further illustrate the invention.

EXAMPLES

Synthesis of the Polyester

[0065] Polyester polymers according to the present invention were prepared using the following procedure. Tung oil, a triglyceride according to the invention containing -eleostearic acid (82 wt %), linoleic acid (8 wt %), palmitic acid (5 wt %, oleic acid (5 wt %, weight percentages referred to the weight of the oil) was heated up to 260 C. for 1 minute, in the presence of air. This procedure yielded a cured polyester homopolymer in the form of a film.

[0066] The modulus of elasticity (E) at 30 C., +25 C. and +100 C. and the glass transition temperature of each of the cured film as determined by means of dynamic mechanical analysis are compiled in Table 1. Comparative results obtained on films of commercial primary coating C1 (DP1014-XS by DSM) and single coating SC (3471-3-14 by DSM) compositions are also reported in Table 1. The curing conditions for the reference coating were as indicated by the supplier.

TABLE-US-00001 TABLE 1 Curing Tg ( C.) conditions E (MPa) on-set Sample no. ( C. - min) 30 C. +25 C. +100 C. point 1 679 1.05 0.55 41.18 C1 33.33 0.882 1.12 46.7 SC 1300 200 <3 5

[0067] As shown by the above results, the cured polymers based on the polyesters according to the present invention have adequate mechanical properties for use as primary coating for optical fibres.