CN114249996B - Coating composition and application thereof - Google Patents

Abstract

The invention discloses a coating composition, which comprises the following components: polymerized monomer, cross-linking agent, thickening agent, photoinitiator and deionized water; the water loss of the coating is less than 1wt%. Compared with the existing optical fiber water-blocking material, the coating is thinner, the weight of the optical cable can be greatly reduced, the core number of light is increased under the same weight, and the communication weight can be increased; the coating can be directly coated and cured by using the existing ink coloring equipment, and has the advantages of simple process, high curing speed and high production efficiency; the coating has the advantages of high water absorption rate, no excessive attenuation of optical fibers, no organic solvent, environmental friendliness, capability of still keeping an elastic film state after water absorption and expansion, no drop, strong water retention capacity and low water loss.

Description

Coating composition and application thereof

Technical Field

The invention relates to a water-blocking coating, in particular to an optical fiber water-blocking coating for a dry optical cable.

Background

The optical cable is a communication line which is formed by a certain number of optical fibers into a cable core in a certain mode, is externally coated with a sheath, and is also coated with an outer protective layer for realizing optical signal transmission. As is well known, water vapor is harmful to the optical cable, and the penetration of external moisture and humidity can cause the increase of the hydrogen loss of the optical cable, the strength of the optical fiber is damaged, and the service life and the transmission performance of the optical fiber of the optical cable are further affected. The traditional optical cable is characterized in that water-blocking factice is filled in an optical cable sleeve to isolate water from contacting with optical fibers, so that the effect of protecting the optical fibers by water and moisture is achieved. The material belongs to an oily material, the dead weight of the optical cable is overlarge due to large filling amount, the optical cable has large harm to the environment and is difficult to clean (particularly, the optical cable can be cleaned only by a solvent during connection), and at present, foreign optical cable factories are gradually eliminated and changed into dry optical cables. Compared with water-blocking ointment in the traditional optical cable, water-blocking materials such as water-blocking powder, water-blocking yarn or hot melt adhesive water-blocking ring are used in the dry-type optical cable sheath room, and the radial water-blocking effect of the sleeve is realized through the good water absorption expansion performance of the water-blocking materials. The water-blocking powder and the water-blocking yarn are easy to absorb moisture, the storage environment requirement is strict, the optical cable production accident can be caused when the powder falling phenomenon is serious, and the process requirement is high; the water blocking method of filling the hot melt adhesive water blocking ring in the outer sheath of the optical cable has low efficiency, complex process and poor water blocking effect. In the design and manufacture of the existing dry optical cable, water-blocking materials such as water-blocking ointment, water-blocking powder, water-blocking yarn, water-blocking tape and the like are basically filled or wound, and although the water-blocking materials can achieve a certain water-blocking effect, most of the materials are complex in manufacturing process, and the weight of the optical cable is too large due to the fact that the materials are thick.

The invention patent application of Chinese patent CN 1072454122A discloses a sodium acrylate water-absorbing resin solution and a PET fiber water-absorbing expansion water-blocking tape prepared by using the sodium acrylate water-absorbing resin solution, the water-blocking tape has good moisture absorption expansion performance, the water-absorbing expansion thickness can reach 12-16mm in 5min, but the water-blocking tape is prepared by high-temperature crosslinking copolymerization in a hot air high-temperature furnace, the preparation method is energy-consuming and the equipment is complex. In addition, the thickness of the PET fiber water-swelling water-blocking tape disclosed above is 40-100um, the product form is thicker, the diameter of the cross section of the optical cable is large, the thickness and weight of the PET fiber water-swelling water-blocking tape can increase the weight of the optical cable, and the manufacturing cost of the optical cable is directly influenced. The other background discussion about the preparation of the high water absorption expansion type water-blocking yarn for filling the optical cable or the electric cable can refer to Chinese patent application CN1208784C, which discloses a high water absorption expansion type water-blocking yarn for the optical cable or the electric cable, wherein the high water absorption expansion type water-blocking yarn is prepared by soaking a high water absorption material on fibers, then putting the high water absorption material into a drying tunnel, heating, drying and crosslinking, the high water absorption material is a compound of neutral acrylate or methacrylate, acrylate or methacrylate copolymer, polyethylene glycol and a crosslinking agent, and has the advantages of capability of absorbing and keeping a large amount of water, high expansion rate and good heat-resistant stability, but the treatment process is complex and the powder falling phenomenon is easy to occur. The traditional water-blocking materials filled or wound in the gaps of the optical cable cores, the reinforcing parts and the optical cable loose tubes contain water-absorbing polymers, and the traditional water-blocking materials can absorb water and expand when meeting water, so that gaps inside the optical cable cores or the loose tubes are full of water-blocking gel substances, water seepage channels and damage points are blocked, water and moisture cannot continuously permeate, and a water blocking effect is achieved. In patent documents, many existing water-blocking materials such as water-blocking yarns, water-blocking tapes or water-blocking powders which have excellent water-blocking performance, such as high expansion rate, high expansion speed and high water absorption rate and can meet the water-blocking requirement of optical fibers of optical cables have appeared, but the existing water-blocking materials can be directly coated on the surfaces of the optical fibers in a controllable mode, and the coating composition which can be radiation-cured into a uniform coating and has the water-blocking performance is rarely described in the documents, and foreign patent WO2019203639A1 relates to a radiation-curable coating composition for water-blocking of optical fibers, wherein the coating has a relatively large water absorption multiple, and the extrusion on the optical fibers can be caused by the excessive water absorption multiple, so that the optical fibers are seriously attenuated, and the optical fiber products are not accepted by the market. In addition, the existing optical fiber water-blocking paint has the following problems: 1. the construction operation is difficult to control, and the water-blocking effect is poor due to uneven coating thickness; 2. the stability of the coating is poor, and the phenomenon of raw material precipitation exists; 3. high water loss rate, poor water retention, easy contact of optical fiber with water, negative influence on optical signal transmission, etc. Therefore, there is an urgent need for a water blocking coating for optical fibers that can be directly applied to the optical fiber, can be UV cured to a thinner coating, and has excellent water retention properties and low optical fiber attenuation.

Disclosure of Invention

Aiming at the technical problems: 1. the water-blocking materials such as water-blocking ointment, water-blocking powder, water-blocking yarn, water-blocking tape and the like are basically filled or wound, the manufacturing process is complex, and the weight of the optical cable is too large due to the fact that the materials are thick; 2. the existing coating composition for blocking water of the optical fiber has a slow water absorption rate, and cannot absorb water in a short time when water invades, so that the water can enter the optical fiber to damage the optical fiber; 3. the existing coating for optical fiber group water has the problem of relatively serious optical fiber attenuation and is not accepted by the market; 4. the existing optical fiber water-blocking paint is difficult to coat due to the problem of viscosity during coating, is difficult to construct or has insufficient coating thickness and poor water-blocking effect; 5. the water-blocking paint has the problem of poor compatibility; 6. the invention provides a coating composition, which has poor water retention performance of an existing optical fiber water-blocking coating, and comprises the following components: polymerized monomer, cross-linking agent, thickening agent, photoinitiator and deionized water; the water loss of the coating is less than 3.5wt%.

As a preferable technical scheme, the polymerized monomer contains hydrophilic groups and/or acid ions.

In a preferred embodiment, the polymerized monomer is a mixture of a hydrophilic group-containing polymerized monomer and an acid ion-containing polymerized monomer, and the molar ratio is (0.5.

As a preferred technical scheme, the cross-linking agent is an acrylamide compound or an acrylate compound.

As another preferred technical solution, the cross-linking agent is a group consisting of at least two of acrylamide compounds, or a group consisting of at least one of acrylamide compounds and at least one of acrylate compounds.

As a preferable technical scheme, the functionality of the active group of the acrylamide compound or the acrylate compound is more than or equal to 2; the active group is selected from one or more of carbon-carbon double bonds, hydroxyl, carboxyl, amino, ester groups, ether groups and carbonyl groups.

In a preferred embodiment, the acrylamide compound is at least one selected from the group consisting of N, N-ethylenebisacrylamide, N-methylenebisacrylamide, N-hydroxyethylacrylamide, N-hydroxymethylacrylamide, diacetone acrylamide, N-p-hydroxyphenylacrylamide, and N, N-dibenzylacrylamide.

In a preferred embodiment, the acrylate compound is at least one selected from the group consisting of ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, 1, 3-butanediol diacrylate, 1, 4-butanediol diacrylate, 1,6 hexanediol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, ethoxylated hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate, ethoxylated pentaerythritol triacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, methyl ether diacrylate, neopentyl glycol diacrylate, glycerol-1, 3-diglycerol diacrylate, 1, 6-adipylbis [ oxy-2-hydroxy-3, 1-propanediyl ] diacrylate, pentaerythritol triacrylate, hexamethylene glycol diacrylate, bisphenol a diacrylate, and pentaerythritol tetraacrylate.

As a preferred embodiment, the coating composition further comprises a comonomer.

As a preferred embodiment, the coating composition further comprises a toner.

As a preferred embodiment, the coating composition further comprises a fluorescent whitening agent.

The second aspect of the invention also provides the use of a coating composition as described above in a dry optical cable.

Compared with the prior art, the invention has the following beneficial effects:

1. compared with optical fiber water-blocking materials (40-100 mu m) such as water-blocking yarns, water-blocking powder, water-blocking tapes, water-blocking factice and the like, the thickness of the water-blocking coating can reach below 10 mu m, more specifically below 6 mu m, and the preferred thickness can reach 4 mu m, so that the weight of the optical cable can be greatly reduced, and therefore, under the same weight, the number of cores of the optical fiber is increased, and the communication weight can be increased;

2. the water-blocking coating can be directly coated by using the existing ink coloring equipment and is cured into a water-absorbing coating through UV (ultraviolet), the process is simple, the coating thickness is uniform and controllable, the curing speed is high, and the production efficiency is high;

3. the water-blocking coating has a faster water absorption rate which is lower than 10s, more preferably lower than 7s, can absorb water rapidly under extreme conditions, and protects optical fibers from being influenced by water vapor;

4. the waterproof coating disclosed by the invention has the advantages of no organic solvent, higher production safety, environmental friendliness and no pollution;

5. the water-blocking coating disclosed by the invention keeps an elastic film state after water absorption and expansion, has good adhesion with an optical fiber, and cannot fall off;

6. the water loss rate of the water-blocking paint is lower than 3.5%, preferably lower than 2%, more preferably lower than 1%, and the water retention capacity is strong;

7. the water-blocking coating disclosed by the invention is good in stability, raw materials are not easy to separate out, the integrity of the coating is kept, and water vapor is prevented from entering;

8. the water-blocking coating disclosed by the invention keeps the water absorption rate of the coating to be 3-15 times, and more preferably 3-10 times under the synergistic action of all components, so that the optical fiber attenuation exceeding standard caused by excessive extrusion of the optical fiber after the coating coated on the optical fiber absorbs water can be avoided.

Drawings

To further illustrate the beneficial effects of the UV-curable water-blocking coating for dry-type optical fiber cables provided in the present invention, the accompanying drawings are provided, it is noted that the drawings provided in the present invention are only selected as individual examples in all the drawings and are not intended as a limitation of the claims, and all other corresponding diagrams obtained through the drawings provided in the present application should be considered within the protection scope of the present application.

FIG. 1 is an on-line construction process diagram of the UV curing water-blocking coating of the invention.

Detailed Description

The invention will be further understood by reference to the following detailed description of preferred embodiments of the invention and the examples included therein. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. To the extent that a definition of a particular term disclosed in the prior art is inconsistent with any definition provided herein, the definition of the term provided herein controls.

As used herein, a feature that does not define a singular or plural form is also intended to include a plural form of the feature unless the context clearly indicates otherwise. It will also be understood that the term "prepared from" \8230 ", as used herein, is synonymous with" comprising, "includes," "including," "has," "contains," and/or "contains," when used in this specification means that the composition, step, method, article, or device recited, but does not preclude the presence or addition of one or more other compositions, steps, methods, articles, or devices. Furthermore, the use of "preferred," "preferably," "more preferred," etc., when describing embodiments of the present application, is meant to refer to embodiments of the invention that may provide certain benefits, under certain circumstances. However, other embodiments may be preferred, under the same or other circumstances. In addition, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

In order to solve the above problems, the present invention provides a coating composition which can be directly applied to an optical fiber and cured by UV to form a water-absorbing and water-swellable coating, particularly suitable for use as a water blocking material for optical fibers in dry optical cables. The coating comprises the following components: polymerized monomer, cross-linking agent, thickening agent, photoinitiator and deionized water; the water loss of the coating is less than 3.5wt%.

In some preferred embodiments, the coating comprises the following components: 20 to 70 weight percent of polymerized monomer, 0.02 to 5 weight percent of cross-linking agent, 1 to 20 weight percent of thickening agent, 0.01 to 5 weight percent of photoinitiator and the balance of deionized water; as an example, the weight percentage of the polymerized monomer in the coating composition may be 20%,25%,30%,35%,40%,45%,50%,55%,60%,65%,70%, etc.; as an example, the weight percentage of the crosslinker in the coating composition can be 0.02%,0.06%,0.1%,0.2%,0.3%,0.4%,0.5%,0.6%,0.7%,0.8%,0.9%,1%,1.2%,1.4%,1.6%,1.8%,2%,2.2%,2.4%,2.6%,2.8%,3%,3.2%,3.4%,3.6%,3.8%,4%,4.2%,4.4%,4.6%,4.8%,5%, etc.; as an example, the weight percentage of the thickener in the coating composition can be 1%,2%,3%,4%,5%,6%,7%,8%,9%,10%,11%,12%,13%,14%,15%,16%,17%,18%,19%,20%, etc.; as an example, the weight percent of the photoinitiator in the coating composition can be 0.01%,0.06%,0.1%,0.2%,0.3%,0.4%,0.5%,0.6%,0.7%,0.8%,0.9%,1%,1.5%,2%,2.5%,3%,3.5%,4%,4.5%,5%, etc.

When the components are in the proportion range, the components can be matched synergistically, so that the water absorption rate of the prepared UV coating is controlled to be 3-15 times, and the UV coating has a high water absorption rate, good water retention performance, low optical fiber attenuation and an excellent water blocking effect.

Further preferably, the coating comprises the following components: 40 to 70 weight percent of polymeric monomer, 0.1 to 3 weight percent of cross-linking agent, 3 to 10 weight percent of thickening agent, 0.1 to 1 weight percent of photoinitiator, and the balance of deionized water. Wherein water is used as a part of the coating composition of the present invention to dissolve the polymerized monomer, the weight percentage of water in the coating composition is 20-70wt%, when the water content is too high, the water absorption performance of the coating is affected, the water absorption rate is too low, and when the water content is too low, the sodium acrylate cannot be completely dissolved, is dispersed in the coating in a granular form, and is not beneficial to use.

Polymerizing monomers

The term "polymerizable monomer" as used herein refers to a compound having hydrophilicity, being soluble in water, and being polymerized under specific conditions.

In some preferred embodiments, the polymerized monomer contains hydrophilic groups capable of polar interaction with water molecules and/or acid ions, which means that the polymerized monomer can be ionized in water. Examples of the hydrophilic group include a hydroxyl group, a carboxyl group, an amino group, and the like; examples of the acid ion include a carboxylate ion and a sulfonate ion.

In some preferred embodiments, the hydrophilic group-containing polymeric monomer is acrylic acid, and the acidic ion-containing polymeric monomer is sodium acrylate, from the viewpoints of compatibility of raw materials and curing speed of the coating material. The sodium acrylate in the present application may be commercially available or may be obtained by neutralizing a part of acrylic acid with sodium hydroxide.

In some preferred embodiments, the polymerized monomer is a mixture of acrylic acid and sodium acrylate in a molar ratio of (1. As an example, the molar ratio of acrylic acid to sodium acrylate can be 1,9, 1. The molar ratio of acrylic acid to sodium acrylate in the present invention can be characterized by the degree of neutralization, i.e., a portion of the acrylic acid is neutralized with sodium hydroxide, wherein the molar ratio of acrylic acid to sodium hydroxide is the degree of neutralization. The inventors found that if the neutralization degree is too low, the sodium acrylate content is relatively small, the water absorption rate is too low to meet the water blocking requirement, and if the neutralization degree is too high, the sodium acrylate content is relatively too high, the water absorption capacity of the coating is high, but the crosslinking degree is low, the curing speed is reduced, and the water swelling rate is too large, and the optical fiber is extruded. The coating composition is cured into a water-absorbing and water-swelling coating through UV, the water-absorbing rate of the coating composition is too low, when water invades, the coating composition cannot completely absorb water in a short time, and water can enter an optical fiber to damage the optical fiber, so that the higher the water-absorbing rate, the better the water-blocking effect. In addition, the requirement of the market on the attenuation coefficient of the optical fiber is not more than 0.200dB/km, the transmission of optical fiber signals is seriously hindered due to a larger attenuation coefficient, and the optical fiber is difficult to use, and the attenuation coefficient of a common optical fiber (which is not coated with water-blocking paint) is generally between 0.180dB/km and 0.190dB/km, so that external force (such as the coating of the water-blocking paint) is increased, and the increase value of the attenuation coefficient of the optical fiber is required to be less than 0.02dB/km, and more preferably less than 0.01dB/km to meet the use requirement of the market on the optical fiber. The coating is a water-absorbing swelling coating formed by directly coating a liquid coating on the surface of an optical fiber and curing, and the inventor researches and discovers that the optical fiber is extruded to bend due to overhigh water-absorbing rate and overlarge volume expansion, and light in the optical fiber is lost due to scattering to cause loss and influence the transmission of signals. In addition, the inventor researches and finds that the water absorption multiplying power is 3 times to meet the minimum water-blocking requirement of the optical fiber water-blocking coating, the water absorption multiplying power is too low, the volume expansion is not enough to fill gaps, and the water-blocking effect is poor. In order to ensure that the coating composition has a good water-blocking effect and simultaneously does not cause loss caused by extrusion of optical fibers, the water absorption rate of the water-blocking coating of the optical fibers needs to be controlled to be 3-15 times, so that the water-blocking requirement of the optical fibers is met, and other surrounding optical fibers are not attenuated caused by extrusion. As an example, the water absorption rate of the optical fiber water-blocking coating may be 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times, etc., and more preferably 3 to 10 times. It should be noted that, the water absorption rate and the water absorption rate are in positive correlation, the water loss rate and the water absorption rate are in positive correlation, and the higher the water absorption rate of the coating composition is, the better the water blocking effect is under the condition of meeting the low optical fiber attenuation.

The acrylic acid in the coating is neutralized to its salt by the use of an inorganic base, preferably sodium hydroxide (NaOH), but other inorganic bases, such as potassium hydroxide, which are also suitable for this purpose are not excluded.

Crosslinking agent

The term "crosslinking agent" herein may crosslink the monomers to form a network structure, changing the water-swelling properties of the coating.

In some preferred embodiments, the crosslinking agent is an acrylamide-based compound or an acrylate-based compound.

In other preferred embodiments, the crosslinking agent is an acrylamide-based compound.

In other preferred embodiments, the crosslinking agent is a group of at least two of acrylamide-based compounds, or at least one of acrylamide-based compounds and at least one of acrylate-based compounds.

In some preferred embodiments, the reactive group functionality of the acrylamide-based compound or acrylate-based compound is greater than or equal to 2; the active group is selected from one or more of carbon-carbon double bond, hydroxyl, carboxyl, amino, ester group, ether group and carbonyl group.

In some preferred embodiments, the acrylamide-based compound is selected from at least one of N, N-ethylenebisacrylamide (CAS number: 2959-58-3), N-methylenebisacrylamide (CAS number: 110-26-9), N-hydroxyethylacrylamide (CAS number: 7646-67-5), N-hydroxymethylacrylamide (CAS number: 924-42-5), diacetoneacrylamide (CAS number: 2873-97-4), N-p-hydroxyphenylacrylamide (CAS number: 34443-04-4), N-dibenzylacrylamide (CAS number: 57625-28-2); from the viewpoint of good compatibility of the coating composition and obtaining a low optical fiber attenuation coating composition, it is further preferable that the acrylamide-based compound is at least one selected from the group consisting of N, N-ethylene bisacrylamide, N-methylene bisacrylamide, N-hydroxyethyl acrylamide, and N-hydroxymethyl acrylamide.

In some preferred embodiments, the acrylate compound is selected from ethylene glycol diacrylate (CAS number: 2274-11-5), diethylene glycol diacrylate (CAS No.: 4074-88-8), propylene glycol diacrylate (CAS No.: 24493-53-6), 1, 3-butanediol diacrylate (CAS No.: 19485-03-1), 1, 4-butanediol diacrylate (CAS No.: 1070-70-8), 1, 6-hexanediol diacrylate (CAS No.: 13048-33-4), triethylene glycol diacrylate (CAS No.: 1680-21-3), tetraethylene glycol diacrylate (CAS No.: 17831-71-9), ethoxylated hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate (CAS No.: 28961-43-5), ethoxylated pentaerythritol triacrylate, trimethylolpropane diacrylate (CAS No.: 94108-97-1), trimethylolpropane triacrylate (CAS No.: 15625-89-5), methyl ether diacrylate, neopentyl glycol diacrylate (CAS No.: 2223-82-7), glycerol-1, 3-diglycerol diacrylate (CAS No.: 453: 6084-1), 1, 6-2-hydroxybis [ oxy ] -3-hydroxy bis [ CAS No. ] 3-4-045 ] diacrylate (CAS No.: 3-82-7), glycerol-1, 3-diglyceride diacrylate (CAS No.: 6084-1, 601, 6-2-hydroxy bis [ oxy ] -0458, 3 ] diacrylate, 3-045, 3,4, 3-4), at least one of pentaerythritol triacrylate (CAS number: 3524-68-3), hexamethylene glycol diacrylate, bisphenol A diacrylate, pentaerythritol tetraacrylate (CAS number: 4986-89-4); from the viewpoint of stability of the coating composition, it is more preferable that the acrylate compound is at least one selected from the group consisting of ethylene glycol diacrylate, triethylene glycol diacrylate, propylene glycol diacrylate, polyethylene glycol diacrylate, 1, 3-butanediol diacrylate, 1, 4-butanediol diacrylate, 1, 6-hexanediol diacrylate, and diethylene glycol diacrylate.

In the research of the inventor, the use amount of the cross-linking agent of more than 5wt% of the coating composition of the invention can cause poor compatibility of raw materials and the presence of insoluble particles in the coating, thereby causing large attenuation of optical fibers, whereas the use amount of the cross-linking agent of less than 0.02wt% of the coating composition of the invention can not achieve the cross-linking effect, and the water absorption rate and the speed can not reach the standard. For the selection of the cross-linking agent, the inventor finds that diacetone acrylamide, N-p-hydroxyphenyl acrylamide, N-dibenzyl acrylamide and the like which are used as the cross-linking agent of the invention are difficult to dissolve in the mixture of other components of the invention, which causes poor compatibility of the water-blocking coating composition, particles exist in the water-blocking coating, and the coating on the surface of the optical fiber causes uneven surface of the optical fiber to cause attenuation increase.

Based on the fact that the coating composition has a low water loss rate and good water retention performance is obtained, the cross-linking agent of the present invention is preferably selected from the group consisting of at least two of acrylamide compounds, or at least one of acrylamide compounds and at least one of acrylate compounds, and the inventors have studied that when the cross-linking agents are used in combination in the above manner, the coating composition of the present invention loses less than 3.5%, preferably less than 2%, more preferably less than 1%, of water after water absorption and swelling, and has more excellent water retention performance. It is to be noted that, when at least one of acrylamide compounds and at least one of acrylate compounds are used as the crosslinking agent of the present invention, in order not to affect the water blocking effect of the coating composition, in some preferred embodiments, the content of the acrylate compound is 1 to 30wt% of the crosslinking agent, and as an example, the weight percentage of the acrylate compound in the crosslinking agent may be 1%,3%,5%,7%,9%,10%,12%,14%,16%,18%,20%,22%,24%,26%,28%,30%, etc., more preferably 5 to 25wt%, and still more preferably 10 to 20wt%. The examples provided by the present invention (taking examples 1 to 3 as examples) further illustrate that when the difference in water absorption rate is small, and the group consisting of at least one of acrylamide compounds and at least one of acrylate compounds is used as the crosslinking agent of the present invention, and the content of the acrylate compound is preferably 1 to 30wt%, more preferably 5 to 25wt%, and even more preferably 10 to 20wt% of the crosslinking agent, the water loss rate of the coating is significantly lower, and the water retention performance is better.

Thickening agent

The term "thickener" is used herein to adjust the viscosity of the system to facilitate the application of the coating.

From the standpoint of good storage stability and workability, ensuring that the coating composition has a viscosity suitable for optical fiber coating applications, low toxicity, environmental friendliness, and good water retention properties of the coating, in some preferred embodiments, the thickener is selected from one or more of gelatin, a cellulose-based thickener, an aqueous polyurethane thickener, a hydrophobically modified polyether thickener, and a hydrophobically modified amino thickener.

The term "gelatin" herein is a class of macromolecular hydrocolloids; the term "cellulosic thickeners" is a class of water-soluble polymers that thicken by hydrating swollen long chains; the term "aqueous polyurethane thickener" (HEUR) is a kind of hydrophobic group modified ethoxy polyurethane water-soluble polymer, which is composed of three parts of hydrophobic group, hydrophilic chain and polyurethane group; the term "hydrophobically modified amino thickeners" (HEAT) are multi-branched, hydrophobic compounds made by grafting multiple hydrophobic groups onto an amino resin containing polyoxyethylene chains.

Examples of the cellulose-based thickener include starch, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, methyl hydroxyethyl cellulose, and ethyl hydroxyethyl cellulose.

As the aqueous polyurethane thickener (HEUR), BYK 425 produced by Pico chemistry, TEGO Visco plus 3010, TEGO Visco plus 3030, TEGO Visco plus 3060 and the like produced by Woodbis may be exemplified.

Examples of the hydrophobically modified polyether thickener (HMPE) include Aquaflow NLS 200, aquaflow NLS 210, aquaflow NLS 300, and the like, which are manufactured by ashland.

As the hydrophobically modified amino thickener (HEAT), optiflo H500 chemically produced in south germany can be exemplified.

In some preferred embodiments, the thickener is an aqueous polyurethane thickener.

In some preferred embodiments, the viscosity of the coating is preferably in the range of 40 to 1000cps, and too low a viscosity may result in insufficient coating thickness; when the viscosity is too high, the coating is not easy to coat, the surface of the material cannot be uniformly covered, the curing time is long, the coating is easy to crack after curing, the adhesive force is low, the viscosity of the coating composition needs to be reduced by heating, water can volatilize, and when the water volatilizes to a certain proportion, the solubility of the sodium acrylate in the system can be reduced, solid sodium acrylate particles can be separated out by crystallization, so that the product is deteriorated and cannot be used. As an example, the viscosity of the coating may be 40cps,80cps,100cps,150cps,200cps,250cps,300cps,350cps,400cps,450cps,500cps,550cps,600cps,650cps,700cps,750cps,800cps,850cps,900cps,950cps,1000cps, etc. Further, when the viscosity of the coating is preferably 400 to 600cps, the curable coating composition of the present invention has the best coating and curing effects, and can be applied under normal temperature conditions without heating.

Photoinitiator

A variety of free radical photoinitiators can be used in the coating compositions of the present invention, and the term "photoinitiator" herein is a class of compounds that can be excited by light or the action of light with the electrons of a sensitizing dye to generate free radicals that initiate polymerization of monomers, crosslinking, and curing. The photoinitiator can affect the polymerization degree of acrylic acid-sodium acrylate, the water absorption rate and water absorption rate of the coating can be reduced when the photoinitiator is used excessively, and when the content of the photoinitiator exceeds 5%, the water absorption rate of the coating composition is difficult to meet the water blocking requirement, the water absorption rate is too low, and the water blocking effect is not ideal in a stricter environment such as a low water content environment.

Starting from the class of polymerized monomers described herein, in some embodiments, the photoinitiator is a free radical photoinitiator.

Starting from the viewpoints of good stability, easy storage, good compatibility, no toxicity and no odor, in some preferred embodiments, the photoinitiator is selected from at least one of acylphosphine oxide photoinitiators, alkylbenzene ketone photoinitiators, benzophenone photoinitiators, benzil photoinitiators and thioxanthone photoinitiators.

As the acylphosphine oxide-based photoinitiator, bisacylphosphine oxide (BAPO) or monoacylphosphine oxide (MAPO); as bisacylphosphine oxide photoinitiators, there can be exemplified phenylbis (2, 4, 6-trimethylbenzoyl) phosphine oxide (819), bis (2, 4, 6-trimethylbenzoyl) - (2, 4-dipentyloxyphenyl) phosphine oxide, bis (2, 6-dimethoxybenzoyl) -2, 4-trimethylpentylphosphine oxide, etc.; as the monoacylphosphine oxide photoinitiator, 2,4,6 (trimethylbenzoyl) diphenylphosphine oxide (TPO), 2,4,6-trimethylbenzoyl ethoxyphenylphosphine oxide (TEPO), and the like can be exemplified.

Examples of the alkylbenzene photoinitiator include 1-hydroxycyclohexyl benzophenone (184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), 2-methyl-1- [4- (methylthio) phenyl ] -2- (4-morpholino) -1-propanone (907), 2-hydroxy-2-methyl-1- [4- (2-hydroxyethoxy) phenyl ] -1-propanone (2959), 1' - (methylenebis-4, 1-phenylene) bis [ 2-hydroxy-2-methyl-1-propanone ] (127), 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) butanone (369), 2- (4-methylbenzyl-2- (dimethylamino) -1- [4- (4-morpholino) phenyl ] -1-butanone, and 2-benzyl-2- (dimethylamino) -1- [3, 4-dimethoxyphenyl ] -1-butanone.

As the benzophenone-based photoinitiator, benzophenone (BP), 2,4, 6-trimethylbenzophenone, 4-methylbenzophenone, 2-methoxycarbonylbenzophenone, 4 '-bis (chloromethyl) -benzophenone, 4-chlorobenzophenone, 4-phenylbenzophenone, 4' -bis (dimethylamino) -benzophenone, 4 '-bis (diethylamino) benzophenone, methyl 2-benzoylbenzoate, 3' -dimethyl-4-methoxybenzophenone, 4- (4-methylphenylthio) benzophenone, 2,4, 6-trimethyl-4 '-phenylbenzophenone, 3-methyl-4' -phenylbenzophenone and the like can be exemplified.

Examples of the benzil photoinitiator include 2, 2-dimethoxy-2-phenylacetophenone (BDK) and 2, 2-dimethoxy-1, 2-diphenyl-ethanone.

Examples of the thioxanthone photoinitiator include 2-Isopropylthioxanthone (ITX).

In some preferred embodiments, in order to ensure that the coating has both a high water absorption rate and good curing properties, it is particularly suitable that the photoinitiator is a group of at least two of the above photoinitiators, preferably two, three, four, five, six, and more preferably two, three or four photoinitiators. In some preferred embodiments of the present invention, the photoinitiator is selected from the group consisting of at least two photoinitiators, wherein the photoinitiator comprises an alkyl benzophenone photoinitiator and one or two of a benzophenone photoinitiator, a benzil photoinitiator, and a thioxanthone photoinitiator. In some preferred embodiments of the present invention, the photoinitiator is selected from the group consisting of at least two photoinitiators, wherein the photoinitiator comprises an alkylbenzene photoinitiator in an amount of less than 70wt%, and wherein the alkylbenzene photoinitiator may be present in the photoinitiator in an amount of 30%,35%,40%,45%,50%,55%,60%,65%,70%, etc., by weight, as an example; more preferably, the ratio of the alkylbenzene ketone photoinitiator in the photoinitiator is 30-70 wt%; furthermore, the proportion of the alkylbenzene ketone photoinitiator in the photoinitiator is 40-60 wt%.

The inventors have experimentally proved that the coating has a faster water absorption rate than the same water absorption rate when one photoinitiator is used alone, a group of at least two photoinitiators is used as the photoinitiator of the present invention, and the proportion of the alkylbenzene ketone photoinitiator in the photoinitiator is less than 70 wt%. The examples provided by the present invention (taking example 1 (water absorption capacity is 9.8 times) and example 4 (water absorption capacity is 10 times) as examples) further illustrate that when the difference of the water absorption capacities is small, the water absorption rate of the coating is significantly increased when a group consisting of at least two photoinitiators is used as the photoinitiator of the present invention and the ratio of the alkyl ketone photoinitiator in the photoinitiator is less than 70wt%, more preferably 30 to 70wt%, and still more preferably 40 to 60wt%.

In some preferred embodiments, the coating further comprises a comonomer; further preferably, the coating also comprises 0 to 5 weight percent of comonomer; furthermore, the coating also comprises 0 to 1 weight percent of comonomer.

The inventor tries to add part of comonomer in the experimental process, the comonomer can improve the mechanical property of the coating after curing, but the introduction of the comonomer in a proportion of more than 5wt% can seriously affect the water absorption speed and the expansion ratio of the coating after curing. It should be noted that if a comonomer is added to the formulation, in order not to affect the water absorption rate and the expansion ratio of the coating after curing of the coating, the proportion of the added comonomer should not exceed 5wt%, preferably not exceed 3wt%, and further preferably not exceed 1wt%, and the proportion of the optional comonomer should be 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 0.6wt%, 0.8wt%.

Examples of the comonomer include at least one of hydroxyethyl acrylate, methoxy (polyethylene glycol) acrylate, ethoxy (polyethylene glycol) acrylate, 2- (2-ethoxyethoxy) ethyl acrylate, ethylene glycol methyl ether acrylate, diethylene glycol methyl ether acrylate, triethylene glycol methyl ether acrylate, tetramethylene glycol methyl ether acrylate, ethylene glycol ethyl ether acrylate, diethylene glycol ethyl ether acrylate, triethylene glycol ethyl ether acrylate, tetramethylene glycol ethyl ether acrylate, and diethylene glycol-2-ethylhexyl acrylate.

Starting with fiber identification, in some preferred embodiments, the coating further comprises a toner; further preferably, the coating further comprises 0.001 to 0.5wt% of a toner, illustratively, in an amount of 0.001%,0.003%,0.005%,0.007%,0.01%,0.02%,0.03%,0.04%,0.05%,0.06%,0.07%,0.08%,0.09%,0.1%,0.15%,0.2%,0.25%,0.3%,0.35%,0.4%,0.45%,0.5%, etc., by weight of the coating composition; furthermore, the paint also comprises 0.005-0.2 wt% of toner.

The term "toner" herein may be an organic toner, which is an organic mixture composed of hydrocarbons, or an inorganic toner, which is a metal-free, organic-free toner, primarily providing different colors to the system. Examples of the toner include titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine green, benzidine yellow, rubine 4B, permanent violet, and permanent red.

Starting with fiber identification on a multicore count, in some preferred embodiments, the coating further comprises an optical brightener; further preferably, the coating further comprises 0.001 to 0.125wt% of an optical brightener, as an example, in an amount of 0.001%,0.003%,0.005%,0.007%,0.01%,0.012%,0.015%,0.018%,0.02%,0.025%,0.03%,0.035%,0.04%,0.045%,0.05%,0.055%,0.06%,0.065%,0.07%,0.075%,0.08%,0.085%,0.09%,0.095%,0.1%,0.11%,0.125%, etc. by weight of the coating composition; further, the coating also comprises 0.0005 to 0.05 weight percent of fluorescent whitening agent.

Examples of the fluorescent whitening agent include stilbene fluorescent whitening agents, coumarin fluorescent whitening agents, azole fluorescent whitening agents, and dicarboximide fluorescent whitening agents; examples of the stilbene fluorescent whitening agent include triazine type stilbene, bisamide type stilbene, and triazole type stilbene; examples of the coumarin fluorescent whitening agents include 3-carboxycoumarin, 4-methyl-7-aminocoumarin, 3-phenyl-7-aminocoumarin, heterocyclic coumarin, and the like; examples of the azole fluorescent whitening agent include benzoxazole, benzimidazole, pyrazoline, and other heterocyclic azole fluorescent whitening agents; examples of the dicarboximide fluorescent whitening agents include phthalimide and naphthalimide.

The inventor finds that after the fluorescent whitening agent is added into the coating, the water-blocking coating has a fluorescent effect under the irradiation of ultraviolet light, and the multi-core optical fiber is easy to distinguish.

The invention also provides a preparation method of the coating, which comprises the following steps: firstly, dissolving weighed photoinitiator and cross-linking agent in acrylic acid, and adding a small amount of deionized water for dilution to prepare a component I; simultaneously dissolving sodium hydroxide into the rest deionized water to prepare a component II; then neutralizing the component I and the component II in a cold water bath (not higher than 35 ℃) to prepare an acrylic acid-sodium acrylate solution with a certain neutralization degree; adding a certain amount of thickening agent into the acrylic acid-sodium acrylate solution, and fully mixing to form the coating.

The invention also provides a using method of the UV curing water-blocking coating for the dry optical cable, which comprises the following steps: and (3) coating a liquid film with the thickness of 4-6 mu m on the surface of the optical fiber by dip-coating the water-blocking coating by using optical fiber ink coloring equipment, and curing the liquid film under the irradiation of a UV lamp to obtain the water-blocking coating. FIG. 1 shows a method of using the UV-curable water-blocking coating for dry optical cables according to the present invention.

Examples

The technical solution of the present invention is described in detail by the following examples, but the scope of the present invention is not limited to the examples. Unless otherwise specified, all the raw materials in the present invention are commercially available.

The following are the raw materials used in the examples:

a: polymerizing monomers

A1: acrylic acid

A2: acrylic acid sodium salt

B: crosslinking agent

B1: n, N-methylenebisacrylamide

B2: ethylene glycol diacrylate

B3: n, N-ethylene bisacrylamide

B4: triethylene glycol diacrylate

B5: propylene glycol diacrylate

B6: polyethylene glycol diacrylate

B7:1, 3-butanediol diacrylate

B8: n-hydroxyethyl acrylamide

B9: n-methylolacrylamide

B10: diethylene glycol diacrylate

B11: n-p-hydroxyphenyl acrylamide

C: thickening agent

C1：BYK 425

C2: carboxymethyl cellulose

C3：TEGO ViscoPlus 3010

C4：Optiflo H500

C5: methyl cellulose

C6：AquaflowNLS200

D: photoinitiator

D1:184 (1-Hydroxycyclohexylbenzophenone)

D2:1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone)

D3:819 (Phenylbis (2, 4, 6-trimethylbenzoyl) phosphine oxide)

D4: TPO (2, 4,6 (trimethylbenzoyl) diphenylphosphine oxide)

D5:2959 (2-hydroxy-2-methyl-1- [4- (2-hydroxyethoxy) phenyl ] -1-propanone)

D6:907 (2-methyl-1- [4- (methylthio) phenyl ] -2- (4-morpholinyl) -1-propanone

D7: BDK (2, 2-dimethoxy-2-phenyl acetophenone)

D8: ITX (2-isopropyl thioxanthone)

D9:127 (1, 1' - (methylenebis-4, 1-phenylene) bis [ 2-hydroxy-2-methyl-1-propanone ])

D10: BP (benzophenone)

E: comonomer

E1: acrylic acid hydroxy ethyl ester

E2: methoxy (polyethylene glycol) acrylate

The preparation method of each embodiment comprises the following steps: dissolving weighed photoinitiator D and cross-linking agent B (and comonomer E) in acrylic acid A1, and adding a small amount of deionized water to dilute to prepare a component I; simultaneously dissolving sodium hydroxide in the rest deionized water to prepare a component II; then neutralizing the component I and the component II in a cold water bath (not higher than 35 ℃) to prepare acrylic acid A1-sodium acrylate A2 solution; adding a thickening agent C into the acrylic acid A1-sodium acrylate A2 solution, and mixing to form a coating; wherein the amount of sodium hydroxide is determined according to the desired molar ratio of acrylic acid A1 to sodium acrylate A2.

The method of use of the embodiments includes the steps of: and (2) coating a liquid film with the thickness of about 5 mu m on the surface of the optical fiber in a dip-coating mode by using a coating composition prepared by mixing the components according to the proportion by using optical fiber coloring ink coloring equipment, and then curing by using a UV lamp to obtain the water-blocking coating for the optical fiber.

The coatings obtained in the embodiments are subjected to performance measurement, and the test contents comprise viscosity, water absorption rate, water retention performance and optical fiber attenuation, and the test method comprises the following steps:

1. and (3) viscosity measurement: the viscosity of the coating was measured in cps using a Bolefei rotary viscometer.

2. And (3) measuring the water absorption rate: (1) Coating a liquid film with the thickness of 5 +/-0.5 mu m on the surface of a clean glass plate, and curing by using a UV lamp; (2) Removing the cured coating film from the surface of the glass plate, placing the glass plate in a drying oven for 24 hours, weighing, and recording the weight as W1; (3) Completely immersing the placed coating film into normal-temperature deionized water for 2 hours; (4) Taking out the soaked coating film from the water, wiping off residual water drops on the surface by using dust-free paper, weighing, and recording the weight as W2; (5) calculating the water absorption capacity: (W2-W1)/W1.

3. And (3) measuring the water absorption rate: in a normal temperature environment, 2g of the cured coating film is weighed, 5g of deionized water is added, and the time required for completely absorbing the deionized water by the coating film is recorded.

4. And (3) water retention property measurement: placing the film after absorbing water in a normal-temperature drying oven for 24 hours, taking out the film, weighing the film as m2, recording the weight of the film after absorbing water as m1, and calculating the water loss rate: (m 1-m 2)/m 1.

5. Measuring the attenuation of the optical fiber; because the 1550nm wave band is sensitive to the influence of the bending loss of the optical fiber compared with other wave bands, the 1550nm wave band is selected for testing the attenuation condition of the optical fiber, one end of the optical fiber is connected to an optical fiber tester, 5 groups of optical fiber attenuation data at the 1550nm wave band are read, and the average value of the optical fiber attenuation data is obtained. And at the 1550nm waveband, the difference obtained by subtracting the attenuation coefficient of the common optical fiber which is not coated with the water-blocking paint from the attenuation coefficient of the optical fiber which is coated with the water-blocking paint is the increase value of the attenuation coefficient of the optical fiber.

Example 1

TABLE 1

Example 2

TABLE 2

Example 3

TABLE 3

Example 4

TABLE 4

Example 5

TABLE 5

Example 6

TABLE 6

Example 7

TABLE 7

Example 8

TABLE 8

Example 9

TABLE 9

As can be seen from tables 1 to 9, the UV coatings provided in examples 1 to 9 have a water loss rate of less than 0.8% and a good water retention property, and when the photoinitiator is introduced into the coating composition in the form of a group consisting of at least two photoinitiators, the coating has a faster water absorption rate without affecting other properties, and has an excellent optical fiber water blocking effect;

the water absorption multiplying power of the UV coating provided by the embodiment of the application is 3-10 times, the optical fiber attenuation increase value is lower than 0.01dB/km while the optical fiber water blocking requirement is met, the tolerance of common optical fiber attenuation is high, and the UV coating can be used for common optical fibers with wide optical fiber attenuation range;

the UV coating provided by the embodiment of the application keeps an elastic film state after water absorption and expansion, has good adhesion with the optical fiber and is not easy to drop.

Example 10

Watch 10

When the viscosity is controlled to achieve the purpose of convenient construction, the inventor researches and discovers that when the viscosity of the coating composition is too high, heating is needed to reduce the viscosity to facilitate coating, water is volatilized when the coating composition is heated, sodium acrylate is precipitated and formed into particles due to over-saturation of the coating composition, the coating on the surface of an optical fiber is uneven, the attenuation of the optical fiber is increased, and the product cannot be used. The use amount of the thickening agent influences the viscosity of the coating composition to a great extent, and the storage performance and the construction performance of the product are ensured to be improved under the condition of not reducing the water resistance performance by controlling the use amount of the thickening agent, so that the product can be cured at normal temperature without heating.

Example 11

The inventors tried to use diacetone acrylamide, N-p-hydroxyphenyl acrylamide, N-dibenzyl acrylamide as a crosslinking agent in the course of experiments, and found that there was a problem of poor compatibility, in the following formula B11: n-p-hydroxyphenyl acrylamide was used as an example, and the results are shown in Table 11.

TABLE 11

In this example, the inventors have observed that the incompatibility of the crosslinking agents results in the presence of particles in the water-blocking coating, and that the application of the coating to the surface of the optical fiber causes the surface of the optical fiber to be uneven, resulting in increased attenuation, and the product is unusable. Because the solubility of the cross-linking agent is limited, the cross-linking agent is not compatible under the mixing of other component types and contents, if the cross-linking agent is forcedly dissolved in the mixture of other components, a large amount of acid needs to be added, but the added acid can be neutralized by sodium hydroxide, the neutralization degree of acrylic acid-sodium acrylate is less than 10%, the water absorption rate can be reduced, and the water-blocking effect is not good, and the inventor researches and finds that the neutralization degree needs to be reduced to 5%, and the cross-linking agent can be dissolved by 0.02wt%. That is, when the degree of neutralization of acrylic acid-sodium acrylate of the present invention is 10% or more, the use of the above-mentioned crosslinking agent species is not soluble.

Example 12

TABLE 12

Example 13

Watch 13

Tables 12 and 13 show that the kind of the comonomer has little influence on the water absorption rate, and the increase of the comonomer content lowers the water absorption rate and the water absorption rate, and particularly, when the addition amount thereof exceeds 1wt%, the coating composition has difficulty in satisfying the basic water blocking requirement of the optical fiber; when the amount exceeds 5wt%, the water-blocking coating has substantially lost the water-absorbing ability. Examples 12 and 13 show mainly that the effect of the comonomer is consistent for formulations with different water absorption grades.

Example 14

TABLE 14 Effect of Water absorption Rate on attenuation of optical fiber after Cabling

Water absorption rate	Increase in attenuation coefficient of optical cable
		1 times of	0.001dB/km
3 times of	0.002dB/km
		5 times of	0.006dB/km
10 times of	0.010dB/km
		15 times of	0.020dB/km
20 times of	0.051dB/km
		30 times of	0.081dB/km
50 times of	0.102dB/km

The attenuation coefficient of the common optical fiber (without coating the water blocking paint) is generally between 0.180dB/km and 0.190dB/km, while the attenuation coefficient of the optical fiber is generally required not to exceed 0.200dB/km, and based on the attenuation coefficient of the common optical fiber, an external force (such as coating of the water blocking paint) is added, so that the increase value of the attenuation coefficient of the optical fiber is required to be less than 0.02dB/km, and more preferably less than 0.01dB/km, so as to be accepted by the market. In table 14, the increase of the attenuation coefficient of the optical fiber coated with the water blocking coating is the increase of the attenuation coefficient of the optical fiber compared with the optical fiber coated with no water blocking coating, and the data in the table show that when the water blocking coating is coated on the optical fiber, the water absorption rate is 1-15 times, the increase of the attenuation coefficient of the optical fiber is less than or equal to 0.02dB/km, and when the water absorption rate exceeds 15 times, the attenuation coefficient of the optical fiber is accelerated obviously, so that the product is not accepted by the market. To ensure that the optical fiber has a certain water-blocking effect and simultaneously avoid excessive attenuation, the water absorption multiple of the water-blocking coating needs to be controlled to be 3-15 times, and more preferably 3-10 times. In addition, from the aspect of controlling the attenuation of the optical fiber, the optical fiber water-blocking coating provided by the invention has higher tolerance to the common optical fiber, and can be used for the common optical fiber with wider range of optical fiber attenuation.

The foregoing examples are merely illustrative and serve to explain some of the features of the method of the present invention. The appended claims are intended to claim as broad a scope as can be conceived and the examples presented herein are merely illustrative of selected implementations in accordance with all possible combinations of examples. Accordingly, it is applicants' intention that the appended claims are not to be limited by the choice of examples illustrating features of the invention. Also, where numerical ranges are used in the claims, subranges therein are included, and variations in these ranges are also to be construed as possible being covered by the appended claims.

Claims (4)

1. A coating composition, characterized in that the coating comprises the following components: 20-70wt% of polymerized monomer, 0.02-5wt% of cross-linking agent, 1-20wt% of thickening agent, 0.01-5wt% of photoinitiator and the balance of deionized water; the coating composition has a water loss of less than 3.5wt%;

the polymerization monomer is a mixture of acrylic acid and sodium acrylate, and the molar ratio is (1);

the cross-linking agent is a group consisting of at least two of acrylamide compounds, or a group consisting of at least one of the acrylamide compounds and at least one of the acrylate compounds, and the content of the acrylate compounds is 1-30wt% of the cross-linking agent;

the active group functionality of the acrylamide compound or the acrylate compound is more than or equal to 2; the active group is selected from one or more of carbon-carbon double bond, hydroxyl, carboxyl, amino, ester group, ether group and carbonyl;

the coating also comprises 0.01 to 1 weight percent of comonomer;

the comonomer is at least one selected from hydroxyethyl acrylate, methoxy (polyethylene glycol) acrylate, ethoxy (polyethylene glycol) acrylate, 2- (2-ethoxyethoxy) ethyl acrylate, ethylene glycol methyl ether acrylate, diethylene glycol methyl ether acrylate, triethylene glycol methyl ether acrylate, tetramethylene glycol methyl ether acrylate, ethylene glycol ethyl ether acrylate, diethylene glycol ethyl ether acrylate, triethylene glycol ethyl ether acrylate, tetramethylene glycol ethyl ether acrylate and diethylene glycol-2-ethylhexyl acrylate.

2. The coating composition of claim 1, wherein the acrylamide compound is at least one selected from the group consisting of N, N-ethylenebisacrylamide, N-methylenebisacrylamide, N-hydroxyethylacrylamide, N-hydroxymethylacrylamide, diacetone acrylamide, N-p-hydroxyphenyl acrylamide, and N, N-dibenzylacrylamide.

3. The coating composition of claim 1, wherein the acrylate compound is at least one selected from the group consisting of ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, 1, 3-butanediol diacrylate, 1, 4-butanediol diacrylate, 1,6 hexanediol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, ethoxylated hexanediol diacrylate, ethoxylated trimethylolpropane triacrylate, ethoxylated pentaerythritol triacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate, methyl ether diacrylate, neopentyl glycol diacrylate, glycerol-1, 3-diglyceride diacrylate, 1, 6-hexanediylbis [ oxy-2-hydroxy-3, 1-propanediyl ] diacrylate, pentaerythritol triacrylate, hexamethylene glycol diacrylate, bisphenol a diacrylate, and pentaerythritol tetraacrylate.

4. Use of a coating composition according to any one of claims 1 to 3 in a dry optical cable.

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