JPH0777643A - Glass fiber for light transmission and its production - Google Patents

Abstract

PURPOSE:To provide the glass fiber for light transmission having an excellent side pressure characteristic and transmission characteristic and the process for production of such glass fiber. CONSTITUTION:This glass fiber for light transmission which has at least >=2 layers of coatings on the outer periphery of the glass fiber 1 has a gap 1' between the glass fiber side innermost layer coating 2 and the glass fiber. The length in the outer peripheral direction of the glass fiber in the gap part at the section is 10 to 50% of the outer peripheral length of the glass fiber. A gap 1' is formable in the innermost coating layer 2' of the coating by applying and curing a resin or resin compsn. contg. 5 to 20% volatile or migratable non-gel component. The film thickness of the coating layer is particularly preferably made uneven to prevent the generation of the gap 1' uniform over the entire periphery of the glass fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission glass fiber used for optical communication and the like, and more particularly to an optical transmission glass fiber having excellent lateral pressure characteristics and transmission characteristics.

[0002]

2. Description of the Related Art A glass fiber for optical transmission has a problem in maintaining mechanical strength and transmission characteristics in a state of being drawn. That is, when a bending called microbending is applied to the optical fiber by an external force, the optical transmission characteristics deteriorate. Therefore, a coating of a polymer material is provided on the outer circumference of the glass fiber to improve mechanical strength and microbending resistance. This anti-micro-bending property is generally called lateral pressure property. The above-mentioned coating generally has a two-layer structure, and a relatively soft buffer layer is provided as an inner layer, and a hard protective layer is provided on the outer periphery thereof. As the coating material, an ultraviolet curable resin (abbreviated as UV resin) that can realize high-speed curing and is excellent in productivity is used. FIG. 2 shows a series of apparatus configurations for forming a UV resin coating in tandem after drawing an optical fiber. In FIG. 2, the optical fiber preform 4 heated and melted in the drawing furnace 5 is drawn into the glass optical fiber 1, and the resin coating device 6 is immediately added.
Then, the resin (composition) for coating the inner layer is applied, and then the coating layer is cured by the ultraviolet irradiation device 9. Further, after being introduced into the resin coating device 6 ′ and the ultraviolet irradiation device 9 ′ to form the outer coating layer, the resin coated optical fiber 11 is wound by the winding machine 12. In addition, 7 is an ultraviolet irradiation lamp, 8 is a cylindrical body, 1
0 indicates a reflecting mirror. Although not shown, a two-layer simultaneous coating and curing method in which the inner layer coating resin and the outer layer coating resin are simultaneously applied to the outer periphery of the glass optical fiber to form a coating layer, and then both layers are cured by UV irradiation may also be used. Glass fibers for optical transmission having a multilayer coating can be manufactured. In order to further increase the density of optical cables in the future, thinning of the fiber coating is required, but thinning of the coating is a major obstacle to maintaining lateral pressure characteristics. As a measure for satisfying these conflicting requirements, for example, Japanese Patent Laid-Open No. 63-168610.
It is proposed in the publication that a stress relaxation layer such as a void is provided between the glass fiber and the coating layer.

[0003]

However, it has been found that the presence of voids, as in the method proposed in the above publication, may reduce the adhesion between the glass and the coating layer.
When the adhesion between the glass and the coating is lost, for example, the glass may protrude from the coating or the glass may be broken in the connector. In addition, for example, the literature (1992 IWCS Proceeding p.428
~ 434, "Designand qualification of optical fiber
As described in "coating for ribbon fiber"), when such a fiber is used as a tape core wire, the glass fiber is moved by a small amount and the inter-fiber distance and the like are scattered ( There is a problem that a so-called "misalignment") and a batch fusion connection cannot be performed. The present invention intends to develop a novel coating layer structure that solves such a problem, and to provide a glass fiber for optical transmission which has excellent lateral pressure characteristics and transmission characteristics.

[0004]

The first object of the present invention for solving the above-mentioned problems is to provide a glass fiber for optical transmission which has a coating of at least two layers on the outer circumference of the glass fiber.
An optical transmission characterized by having a gap between the innermost layer coating on the glass fiber side and the glass fiber, and the length of the gap in the cross section in the glass fiber outer peripheral direction is 10 to 50% of the glass fiber outer peripheral length. Regarding glass fiber. In the present invention, the voids contain 5 to 20 volatile or migrating ungelled components as the innermost layer coating on the glass fiber side.
It is particularly preferable that the coating is formed between the glass and the innermost layer by coating the coating containing the content by weight. A second aspect of the present invention is that, when forming two or more layers of coating on the outer circumference of the glass fiber, the innermost layer of the coating is volatile or migrating in the innermost layer immediately after curing by applying a resin or a resin composition and then curing. Non-gel component is contained in an amount of 5 to 20% by weight, and a coating for the second and subsequent layers is formed simultaneously with the formation of the innermost layer or subsequent to the formation of the innermost layer, and then the innermost layer is formed. A void is generated between the innermost layer and the glass fiber by the volume change of the glass fiber, and the length of the void portion in the cross section in the glass fiber outer peripheral direction is 10 to 50% of the glass fiber outer peripheral length. The present invention relates to a method for manufacturing a glass fiber for optical fiber transmission.

[0005]

The present inventor can achieve both stress buffering property and adhesiveness by keeping the generation of voids between the glass and the coating layer within the range of 10 to 50% of the outer circumference of the glass and maintaining the adhesiveness with the coating layer for the rest. I thought. And as the method, the innermost layer is migrating immediately after curing, the volume change that occurs in the innermost layer after that by containing a certain amount of the volatile ungelled component, that is, volume reduction or swelling is used, and further the coating layer It was found that it is possible to always generate only within 50% of the outer circumference of the glass by intentionally deviating the thickness of the glass to prevent uniform generation of voids, and by setting the uneven thickness ratio to 5 to 25%. Came to.

The present invention will be specifically described with reference to FIG.
The above-mentioned "voids occur within the range of 10 to 50% of the glass outer circumference" means that the total outer circumference length of the glass fiber is L0 in the cross section of the glass fiber for optical transmission, and the length between the glass fiber and the innermost layer is When the length of the glass outer peripheral direction of the portion in which voids are generated is L, it means that 10≤ [L / L0] × 100≤50 (%). When the voids exceeding 50% are generated, the adhesion between the glass and the coating is lowered, and the above-mentioned glass protrusion and connection failure at the tape core wire occur. Further, if the void is less than 10%, the stress buffer layer expected between the glass and the coating resin layer does not function. Therefore, the voids in the present invention are preferably 10 to 50%, more preferably 20%.
~ 40%

The voids of the present invention are 10% to 50% on the outer circumference of the glass.
In order to obtain the generated coated fiber, first, as the resin or resin composition for coating the innermost layer, the volatile or migrating ungelled component content (ungelled fraction) immediately after coating and curing is 5 The innermost layer is formed using a resin or resin composition having a content of ˜20%. Here, the volatile or migratory non-gel component in the present invention means a low molecular weight compound which is not incorporated into the outermost periphery where the liquid resin composition is solidified by the curing reaction and the resin skeleton. If the ungelled component is less than 5%, the generation of voids does not fall within the scope of the present invention, and if it exceeds 20%, the curing of the resin becomes insufficient and the mechanical strength such as elastic modulus and elongation of the resin cannot be maintained, which is the worst case. In this case, a serious defect will occur in the glass fiber for optical transmission. A particularly preferred range of ungelled component is 7-15%. The ungelled fraction of the coating layer is measured by immersing the glass fiber coating for optical transmission in a methyl ethyl ketone solvent at 60 ° C. for 16 hours, extracting the so-called ungelled component with a solvent, and measuring the coating weight (W) of the sample. . Initial weight of sample is W0
Where, the ungelled portion is represented by the following equation. Ungelled fraction = [(W0-W) / W0] x 100 (%)

Further, in the present invention, the coating layer is not made to have a uniform thickness but is intentionally made uneven in thickness within the range of 5 to 25% so that voids are uniformly generated between the coating layer and the innermost layer on the outer periphery of the glass fiber. Can be prevented, and [L / L0] is 10 to 50
It can be%. The "uneven wall thickness ratio" in the present invention means
As shown in FIG. 3, when the maximum coating thickness of each portion is t1 and the minimum coating thickness is t2, the uneven thickness ratio = [(t1-t2) / t1] .times.100 (%). In the present invention, when the uneven thickness ratio is less than 5%, voids are uniformly generated, and it becomes difficult to control the voids to be within 50%. On the other hand, when the uneven thickness ratio exceeds 25%, extremely thin portions are formed in the inner layer or the outer layer, which adversely affects the transmission characteristics and the glass strength.

The operation of this structure will be described in more detail. A glass fiber drawn by a drawing device as shown in FIG. 2 is coated with a soft resin mixed with a volatile or migrating photoinitiator, a photopolymerizable monomer, or a relatively low molecular weight oil as an innermost layer. Then, the resin is cured, and a harder resin is applied and cured as a protective layer on the upper layer. At that time, in order to intentionally make the coating uneven in thickness, each resin coating device is arranged at a position displaced from the center of the glass base material (glass fiber), or the die of the coating device is made noncircular. A coated glass fiber of the inventive structure is obtained. That is, when the ungelled component contained in the innermost layer is transferred to the upper layer and volatilized, the volume of the innermost layer is reduced. In this case, comparing the adhesiveness to the layers on both sides of the innermost layer that is an organic layer, the inner side is an inorganic glass, and the other outer layer is an organic layer as well as the innermost layer, so the adhesiveness of the former glass Since it is overwhelmingly low, a gap is preferentially generated between the glass and the innermost layer. At that time, since the thickness of each layer is different in the circumferential direction, the locations where the voids are formed are biased, and once the voids are formed, the voids expand around the position. By the way, regardless of whether the driving force of the void generation is the volume decrease of the innermost layer or the swelling force of the outer layer, the phenomenon is that partial peeling occurs at the interface with the glass that was originally adhered. . From this fact, once delamination occurs, the residual stress is released from the delaminated part,
There is no more stress to enter the part that remains in close contact. This is called "relaxation of resin (stress) due to generation of voids", and the relaxation of the resin stops the expansion of voids. And, the condition limited to the present invention, that is, the uneven thickness ratio is 5 to
By setting the content to 25%, the outer circumference of the glass of the present invention is 10 to 5
It is possible to suppress the voids within the range of 0%. Also,
The mechanism of void generation is, as described above, in addition to the volume reduction of the innermost layer, the migrating ungelled component of the innermost layer migrates to the outer layer,
The outer layer is swollen by the ungelled component, and the outer layer spreads outward so as to separate the innermost layer from the glass during the swelling. Since the Young's modulus of the outer layer is usually 2 to 3 orders of magnitude higher than that of the innermost layer, the peeling force is large. Therefore, if the outer layer has uneven thickness, the swelling force is unevenly distributed, and there is a region where peeling easily occurs. Therefore, in the case of a coating layer structure of three or more layers, it can be said that a layer having a nonuniform thickness other than the innermost layer is a layer in contact with the innermost layer.

The resin used for the coating resin or resin composition of the innermost layer suitable for such a coating structure of the present invention is
An ultraviolet curable resin is preferable, and examples thereof include urethane acrylate resin, epoxy acrylate resin, silicon acrylate resin, and butadiene acrylate resin. The Young's modulus of the resin or resin composition is 0.0
It is preferably ⁵ to 0.20 kg / mm ² .

Examples of the ungelled component to be contained in the coating resin or resin composition for the innermost layer of the present invention include photoinitiators such as acetophenone type and benzyl ketal type, such as N-vinylpyrrolidone and dimethylacrylamide. Examples thereof include photopolymerizable monomers such as tetraethylene glycol diacrylate, and low molecular weight oils having a molecular weight of 5000 or less such as silicone oil and mineral oil. The thickness of the innermost layer is generally about 10 to 50 μm.

The resin used for the coating resin of the outer peripheral protective coating layer or the resin composition is preferably an ultraviolet curable resin, and examples thereof include urethane acrylate resin, epoxy acrylate resin, silicon acrylate resin and butadiene acrylate resin. The Young's modulus of the resin or resin composition is preferably 10 to 200 kg / mm ² . The thickness of the outer layer is generally about 10 to 50 μm.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. [Examples 1 to 3 and Comparative Examples 1 to 3] Using the drawing apparatus shown in FIG. 2, the optical fiber preform 1 was drawn in the drawing furnace 5 to form the glass optical fiber 1. The coating was performed by the resin coating device 6. Then, the coating resin is cured by the ultraviolet irradiation device 9 to obtain a glass fiber for optical transmission. At this time, a UV-curable urethane acrylate resin having a Young's modulus of 0.1 kg / cm ² that makes the non-gel component having migration property and volatility 6% or 10% after curing is used for the inner layer 2 and the Young layer is used for the outer layer. The outer diameter of the inner layer is 190 using UV-curable urethane acrylate resin with a rate of 80 kg / cm ^2.
μm, and the outer layer was coated so that the outer diameter was 250 μm. At that time, the uneven thickness ratio of each layer was changed as shown in Table 1 (Examples 1 to 3 and Comparative Example 1). The state of void formation one day after drawing was observed with a microscope. The results are also shown in Table 1. Also, as Comparative Examples 2 and 3, except that the inner layer 2 was made of a UV-curable urethane acrylate resin having a Young's modulus of 0.1 kg / cm ² , which had a migration-resistant and volatile ungelled component of 4% after curing. A coating was formed as in Example 1. No void was generated in the sample of Comparative Example 2.

[0014]

[Table 1]

The quality of the lateral pressure characteristics of each of the above coated optical fibers was examined. In the present invention, the fiber length was 5 km, the bobbin barrel diameter was 280 mmφ, and the tension was 100 g, and it was wound around the bobbin, and it was judged by the size of the transmission loss when measured within 30 minutes after the winding. The glass fiber has a glass outer diameter of 1
25 μm, MFD 9.5 μm, cutoff wavelength 1.2
It is a μm single mode fiber. Table 2 shows the measurement results
However, in the case of Comparative Example 2 in which no void is generated, 1.55
The transmission loss in μm was 0.45 dB / km, which was extremely inferior to the first and second embodiments of the present invention.

Using each of the coated optical fibers of Examples 1 to 3 and Comparative Examples 1 to 3, a 4-fiber ribbon was manufactured, and whether or not batch fusion splicing was possible was examined. The results are also shown in Table 2, but Comparative Example 2 was not acceptable.

[0017]

[Table 2]

In each of the above Examples and Comparative Examples, the tandem method in which the coating is sequentially formed from the inner layer has been described.
It goes without saying that the glass fiber for optical transmission of the present invention can also be manufactured by a method of simultaneously coating and curing multiple layers.

As explained above, the glass fiber for optical transmission of the present invention has excellent transmission characteristics, and at the same time can solve various problems caused when the adhesion between the glass and the coating is greatly reduced, and the lateral pressure characteristics can be solved. It has excellent transmission characteristics and is very advantageous in industry.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating an embodiment of the present invention.

FIG. 2 is a schematic explanatory view of the method of manufacturing the coated glass optical fiber (glass fiber for optical transmission) according to the present invention.

FIG. 3 is a schematic cross-sectional view for explaining the uneven thickness ratio of the coating in the present invention.

[Explanation of symbols]

1 glass optical fiber, 1'void, 2 inner layer, 3 outer layer, 4 optical fiber base material, 5 drawing furnace, 6 resin coating device, 6'resin coating device,
7 ultraviolet lamp, 8 cylindrical body, 9 ultraviolet irradiation device, 9'ultraviolet irradiation device, 10 reflecting mirror, 11 resin coated optical fiber, 12 winding machine.

Claims (7)

[Claims] 1. A glass fiber for optical transmission, which has a coating of at least two layers on the outer circumference of the glass fiber, has a gap between the glass fiber innermost layer coating and the glass fiber, The glass fiber outer peripheral length is 10 to 50 of the glass fiber outer peripheral length.
% Glass fiber for optical transmission. 2. The voids, as an innermost layer coating on the glass fiber side, contain 5 to 20% by weight of a volatile or migrating ungelled component.
2. The glass fiber for optical transmission according to claim 1, wherein the glass fiber is produced between the glass fiber and the innermost layer coating by coating the contained glass. 3. The glass fiber for optical transmission according to claim 1, wherein the thickness deviation of the innermost layer on the glass fiber side is 5 to 25%. 4. The optical transmission according to claim 1, wherein at least one layer of the outermost coating on the glass fiber side innermost layer has an uneven thickness ratio of 5 to 25%. For glass fiber. 5. The glass fiber for optical transmission according to claim 1, wherein the coating of two or more layers is made of an ultraviolet curable resin or an ultraviolet curable resin composition. 6. When forming a coating of two or more layers on the outer periphery of a glass fiber, the innermost layer of the coating is a volatile or migrating non-gel in the innermost layer immediately after curing by applying a resin or a resin composition and then curing it. The composition is formed so as to contain 5 to 20% by weight of the components, and a coating for the second layer and subsequent layers is formed at the same time as the formation of the innermost layer or subsequent to the formation of the innermost layer, and the volume change of the innermost layer thereafter. To generate a gap between the innermost layer and the glass fiber, and the length of the gap in the cross section in the glass fiber outer peripheral direction is 10 to 50% of the glass fiber outer peripheral length. Of manufacturing glass fiber for automobiles. 7. A coating resin or a resin composition is applied by removing the position of the glass fiber from the center of the die or by using an eccentric die to make the coating layer uneven in thickness and thereby control the generation of voids. The method for producing a glass fiber for optical transmission according to claim 6.