JP4330020B2 - Optical fiber and optical fiber core wire using the same - Google Patents

Description

  The present invention relates to an optical fiber and an optical fiber core using the optical fiber. In particular, the present invention relates to an optical fiber that suppresses an increase in transmission loss by optimizing the coating resin of the optical fiber.

  The optical fiber is manufactured by a method of immediately coating the glass optical fiber after drawing in order to prevent the strength deterioration of the optical fiber. Generally, two coating layers of a soft coating layer and a hard coating layer are provided. For the soft coating layer that directly covers the glass optical fiber, a soft resin having a Young's modulus of 3 MPa or less is used so that the influence of external force is not transmitted to the glass. On the other hand, a hard resin having a Young's modulus of 500 MPa or more is used for the hard coating layer applied on the soft coating layer in order to protect it from an external force.

In general, the optical fiber is further coated with an extrusion coating layer on the outer periphery of the optical fiber and used as an optical fiber cord or an optical fiber cable.
There are various types of optical fiber cables, but the optical fiber colored cores are coated with a colored layer on the outer periphery of the optical fiber. 2. Description of the Related Art Ribbon slot type optical fiber cables in which optical fiber tape cores are covered with a curable resin to form optical fiber tapes and the optical fiber tape cores are accommodated in cables are widely used.
In this specification, an optical fiber having a colored layer on the outer periphery is referred to as an optical fiber core.

  When optical fiber cords or optical fiber ribbons used in these optical fiber cords or optical fiber cables are immersed in water, peeling may occur between the layers of each coating layer or between the glass optical fiber and the soft coating layer. . This can cause microbending in the optical fiber and increase transmission loss.

For this reason, great efforts have been made to examine the material of each coating layer, and in particular to ensure sufficient adhesion between the soft coating layer and the glass optical fiber.
However, there is a limit to addressing the above-mentioned problems while balancing the adhesion at the interface of each layer as in the prior art.

As a method using these methods, for example, Patent Document 1 discloses a method of maintaining good transmission characteristics by defining the water absorption rate of a coating resin layer of an optical fiber.
Further, Patent Document 2 discloses a method for reducing the water absorption rate of the colored layer and reducing the amount of moisture reaching the optical fiber.

JP 2002-122761 A JP 2002-372655 A

However, according to the method described in Patent Document 1, the water absorption rate of the optical fiber is kept low by managing the storage state of the optical fiber, the foaming caused by the moisture contained in the coating is suppressed, the hydraulic characteristics, the low temperature Although the deterioration of characteristics is prevented, when an optical fiber is immersed in water, it cannot be an effective means for preventing an increase in loss due to microbending caused by moisture reaching the optical fiber.
Further, even with the method described in Patent Document 2, when the optical fiber is immersed in water, the moisture reaching the optical fiber cannot be completely blocked, so an increase in loss due to microbending occurs depending on the immersion conditions. Resulting in.
As described above, at present, no extremely effective means for suppressing an increase in transmission loss of an optical fiber has been obtained.

The present invention has been made to solve the above-mentioned problems, and the optical fiber according to claim 1 of the present invention comprises a soft coating layer having a Young's modulus of 3 MPa or less and a Young's modulus of 500 MPa or more on the outer periphery of the glass optical fiber. In the optical fiber coated with the hard coating layer, a water absorption adjusting additive is added to the base resin as the innermost soft coating layer among the soft coating layers, and the water absorption rate is added to the base resin. A polyol or polyol mixture having a molecular weight of 200 or more is used as an adjustment additive , and at least one of the soft coating layers is coated on the surface of the glass optical fiber, and the water absorption rate of the soft coating layer is determined from the inside by C _p1 , C _p2 ··· _{C pn,} radius _{r p1, r p2 ··· r pn} , C s1 water absorption of the hard coating layer from the _{inner, C} s2 ··· C _s When the radius was _{r s1, r s2 ··· r sn} , the sum of the water absorption and the radius of the product of the soft coating layer _{R p = C p1 × r p1} + C p2 × r p2 + ··· + C pn × The sum of the product of r _pn and the water absorption rate and the radius of the hard coating layer R _s = C _s1 × r _s1 + C _s2 × r _s2 +... + C _sn × r _sn satisfies the relationship of R _p > R _s Features.

According to the optical fiber according to claim 1 of the present invention thus formed, due to the expansion force of the soft coating layer, the peeling between the layers is suppressed without depending on the adhesiveness at the interface between the glass optical fiber and the soft coating layer, As a result, an increase in transmission loss due to microbending can be suppressed.
Further, according to the optical fiber of the present invention as described above, the water absorption rate in the soft coating layer can be easily increased, and the separation at the interface between the glass optical fiber and the soft coating layer is effective. Can be suppressed.

The optical fiber according to claim 2 of the present invention is the optical fiber according to claim 1, wherein the sum R _p of the product of the water absorption rate and the radius of the soft coating layer and the sum R _s of the product of the water absorption rate and the radius of the hard coating layer. The difference is 5 or more.
According to the optical fiber according to the second aspect of the present invention thus configured, it is possible to reliably obtain the effects of the optical fiber according to the first aspect.

An optical fiber according to a third aspect of the present invention is the optical fiber according to the first or second aspect, wherein the soft coating layer and the hard coating layer are each composed of one layer.
According to the optical fiber according to claim 3 of the present invention thus configured, an optical fiber in which an increase in transmission loss due to microbending is suppressed can be realized at low cost.

An optical fiber according to a fourth aspect of the present invention is characterized in that in the optical fiber according to the first or second aspect, the soft coating layer comprises two layers and the hard coating layer comprises one layer.
According to the optical fiber of the present invention, the transmission loss due to the microbend is relatively easy without adjusting the difference in water absorption between the second soft coating layer and the hard coating layer. It is possible to provide an optical fiber that suppresses the increase in.

The optical fiber according to claim 5 of the present invention is characterized in that the innermost soft coating layer of the soft coating layers has a thickness of 3 μm or more and 10 μm or less.
According to the optical fiber according to claim 5 of the present invention thus configured, an increase in transmission loss due to microbending can be suppressed, and a highly reliable optical fiber can be realized relatively easily and at low cost.

An optical fiber according to a sixth aspect of the present invention is the optical fiber according to any one of the first to fifth aspects, wherein polyethylene glycol is used as the polyol .
According to the optical fiber according to the sixth aspect of the present invention thus configured, the operational effects of the optical fiber according to the first aspect described above can be obtained with certainty.

An optical fiber colored core wire according to a seventh aspect of the present invention is characterized in that the optical fiber according to any one of the first to sixth aspects is coated with a colored layer.
An optical fiber ribbon according to claim 8 of the present invention is characterized in that a plurality of optical fiber colored cores according to claim 7 are arranged in parallel in a planar shape and collectively covered.
According to the optical fiber ribbon of claim 8 of colored optical fiber and the invention of claim 7 of the thus formed by the present invention, an optical fiber which can suppress an increase in transmission loss due to microbend A colored core and an optical fiber ribbon can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, even when an optical fiber is immersed in water and a water | moisture content permeate | transmits through a coating layer, peeling in a glass optical fiber and a soft coating layer interface can be suppressed. Thereby, the increase in the transmission loss by microbending can be suppressed.

Embodiments of the present invention will be described below. 1 and 2 are sectional views of one embodiment of the optical fiber of the present invention. In the optical fiber of the present invention, the outer periphery of the glass optical fiber 1 is coated with soft coating layers 2 and 3 having a Young's modulus of 3 MPa or less and a hard coating layer 4 having a Young's modulus of 500 MPa or more.
FIG. 1 shows that each of the soft coating layer and the hard coating layer consists of one layer, and FIG. 2 shows that the soft coating layer consists of two layers and the hard coating layer consists of one layer. The soft coating layer and the hard coating layer may be composed of any number of layers, but the number of layers is generally preferably small in consideration of manufacturing cost and yield.
As the soft coating layer and the hard coating layer in the optical fiber of the present invention, an ultraviolet curable resin composition (hereinafter simply referred to as UV resin) is mainly used. From the viewpoint of curing speed, a urethane-acrylate system or an epoxy-acrylate system is used. Those having the main component of these oligomers are optimal.

  As a result of intensive studies, the present inventors have suppressed the separation at the interface between the glass optical fiber and the soft coating layer when water has penetrated into the optical fiber, and makes it difficult to increase transmission loss due to microbending. It has been clarified that can be achieved by making the sum Rp of the product of the water absorption rate and the radius of the soft coating layer of the optical fiber larger than the sum Rs of the product of the water absorption rate and the radius of the hard coating layer. In order to achieve this, it is necessary to make the water absorption rate of the soft coating layer larger than that of the hard coating layer. For example, the water absorption amount of the soft coating layer is made higher than that of the hard coating layer, or the elution amount of the soft coating layer is increased. This can be realized by making it lower than the hard coating layer.

In addition, the following water absorption C prescribed | regulated by JISK7209A is employ | adopted for the water absorption of the optical fiber coating layer in this specification.
Water absorption C = (m ₂ −m ₁ ) / m ₁ × 100 (%) (1)
Here, m ₁ is the test piece mass (mg) before the immersion after the initial drying, and m ₂ is the test piece mass (mg) after the immersion. The sample was a film having a thickness of 35 μm, and the water immersion conditions were 60 ° C. × 24 hours.
Similarly, the amount of water absorption is a value represented by m ₂ −m ₁ in the equation (1).

This is presumed to be due to the following principle.
When moisture reaches the optical fiber, the following two actions compete.
One is the action of the coating layer expanding due to water absorption. At this time, the soft coating layer material and the hard coating layer material that are generally widely used in optical fibers have a smaller intermolecular density, so the water absorption can be greatly different. The water absorption amount of the coating layer is higher, and the expansion rate is larger. Therefore, the soft coating layer sealed with the hard coating layer receives compressive stress from the hard coating layer.

  The other is the action of the coating layer contracting due to elution. In general, in the covering material widely used for optical fibers, the amount of elution from the soft covering layer material is almost larger than that of the hard covering layer material for the same reason as described above. For this reason, the soft coating layer has a larger shrinkage rate due to the elution, and the hard coating layer is pulled inward. However, as described above, the soft coating layer is generally a soft material of 3 MPa or less, while the hard coating layer is a hard material of 500 MPa or more. Generate power. This is converted into a peeling force between the glass optical fiber and the soft coating layer. Peeling occurs when the peeling force exceeds the adhesive force between the glass optical fiber and the soft coating layer.

  Here, when the contraction force due to elution is won, peeling occurs between the glass optical fiber and the soft coating layer, and transmission loss due to microbending increases. Conversely, when the expansion force due to water absorption is won Therefore, it is considered that peeling between the glass optical fiber and the soft coating layer can be suppressed, and as a result, an increase in transmission loss due to microbending can be suppressed.

  In order to explain the above estimation in more detail, a method for estimating the stress acting between the glass optical fiber and the soft coating layer or between the soft coating layer and the hard coating layer will be described. The stress generated in the coating layer of the optical fiber can be estimated by assuming that the coating layer is an infinite-length thick double cylinder and considering the internal pressure generated there. The equation for determining the displacement of a thick double cylinder subject to internal and external pressure is given as follows.

Where u: radial displacement, E: relaxation elastic modulus of coating material, ν: Poisson's ratio, r _i : inner radius of cylinder, r _o : outer radius of cylinder, P _i : inner pressure applied to cylinder, P _o : External pressure applied to the cylinder.

Not as complex systems, when estimating the stress generated in the coating layer alone, (2) the formula, assuming that all stresses generated in the individual covering layer acts inside the interface, and P _o = 0.
Based on the above assumption, the equation (2) is transformed and converted into an equation for obtaining the internal pressure = the stress P _i at the interface as follows.

Whether the coating layer of the optical fiber is likely to cause delamination depends on the amount of radial displacement (u), relaxation elastic modulus (E), Poisson's ratio (ν), and design items (r _i , r _o, etc.). It can be estimated by calculating and substituting those numerical values into equation (3). That is, (3) if the P _i is a positive value determined by the equation, the internal pressure of the cylinder is subjected is the force interface tends to expand outward, a force trying to peel pull the interface. On the other hand, if it is negative, it can be estimated that a force that the interface tends to shrink inward, that is, compressive stress is about to work. Further, by comparing the magnitudes of the numerical values, it can be used as a guideline for determining which coating material is more likely to cause peeling.

Here, regarding the stress generated when the coating layer expands and contracts due to water absorption or elution, a two-layer coated optical fiber in which a soft coating layer is coated on the surface of the glass optical fiber and a hard coating layer is coated on the outer periphery thereof. Consider an example.
In the two-layer coated optical fiber, the stress at the interface generated between the soft coating layer and the hard coating layer can be expressed as follows using the equation (3).

Here, P _p is the stress generated at the inner interface of the soft coating layer, P _s is the stress generated at the inner interface of the hard coating layer, u _p is the radial displacement of the soft coating layer, and u _s is the hard coating layer radial displacement, the relaxation modulus of E _p soft covering layer, the relaxation modulus of E _s is hard layer, r _g is the radius of the glass optical fiber, r _p is the soft covering layers radius, r _s is hard layer The radius, ν _p is the Poisson's ratio of the soft coating layer, and ν _s is the Poisson's ratio of the hard coating layer. When the amount of displacement in the radial direction has a positive sign, it means that the radius increases, that is, expands outward, and when it has a negative sign, it means that the radius decreases, that is, contracts inward.
Here, the conditions necessary for compressive stress to act between the glass optical fiber and the soft coating layer are:
P _p + P _s <0 (6)
This is the case.

When estimating the stress generated between the glass optical fiber and the soft coating layer of water absorption, items except u _p or u _s is given as all constant value, it is yet all positive values. This is because the Poisson's ratio of most organic polymer materials is known not to exceed 0.5. Further, the respective roles of the soft covering layer and the hard layer, E _s is greater more than 100 times as compared to E _p. Therefore, P _p << P _s and u _s <0 is a necessary condition for compressive stress to act between the glass optical fiber and the soft coating layer.

Here, u _s is described in more detail as follows.
u _s = C _s · r _s −C _p · r _p (7)
Here, C _s and C _p are the expansion coefficients in the radial direction given by the water absorption rates of the hard coating layer and the soft coating layer, respectively, and are numbers proportional to the square root of the water absorption rate. This is because the amount of displacement in the longitudinal direction is negligibly small when the volume of the infinitely long thick cylinder = the volume of the small cross section of the coating layer is changed.
From the equation (7), the necessary condition for the compressive stress to act between the glass optical fiber and the soft coating layer is:
us = C _s · r _s −C _p · r _p <0, that is, C _s · r _s <C _p · r _p (8)
It is.

From the equation (8), in order to generate a compressive stress between the glass optical fiber and the soft coating layer, thereby suppressing the generation of peeling, the product of the water absorption rate of the soft coating layer and the radius of the soft coating layer is It has been derived that it is necessary to be larger than the product of the water absorption rate of the hard coating layer and the radius of the hard coating layer. From the above consideration, hereinafter, the product of the water absorption rate of the coating layer and its radius is defined as a stress index, and the stress indexes in the soft coating layer and the hard coating layer are described as R _p and R _s , respectively. In the calculation of the stress index, C _p and C _s are numerical values representing the water absorption of the soft coating layer and the hard coating layer in weight%, respectively, and r _p and r _s are the radii of the soft coating layer and the hard coating layer. Are given by the results calculated using the values expressed in μm respectively.

Furthermore, the inventors have conducted intensive studies on a method for adjusting the water absorption rate of the soft coating layer, and have come to find the following method.
When moisture penetrates into the soft coating layer, the moisture absorption rate of the soft coating layer can be maintained higher than that of the hard coating layer by retaining moisture in the soft coating layer. Therefore, the inventors focused on alcohols having a high affinity for water. A compound having an alcoholic hydroxyl group has a relatively high affinity for water compared to other compounds having a hydrophilic functional group, and has an affinity for the resin material constituting the coating layer by increasing the molecular weight of the main skeleton. Can be granted. On the other hand, since a compound having an alcoholic hydroxyl group is easily soluble in water, it can be an elution component. However, this can also be retained in the coating layer material by increasing the molecular weight of the main skeleton and increasing the entanglement with the coating layer material. Such compounds are collectively referred to as polyols, and examples include polyether polyols, polyester polyols, polycarbonate polyols, polycaprolactone polyols, and other polyols. These polyols can be used alone or in combination of two or more. There are no particular restrictions on the polymerization mode of the structural units of these polyols. Any of random polymerization, block polymerization and graft polymerization may be used. Furthermore, examples of the polyether polyol include polyethylene glycol, other polypropylene glycols, other polypropylene glycol-ethylene glycol copolymers, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, and polydecamethylene glycol. It can be used.

  Furthermore, from the viewpoint of keeping the water absorption rate high, a component having a plurality of alcoholic hydroxyl groups in one molecule is preferable because the water absorption rate can be kept high even with a small amount of addition to the base composition. From such a viewpoint, among the above-mentioned polyols, polyethylene glycol, other polypropylene glycols, other polypropylene glycol-ethylene glycol copolymers, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, which are listed as glycols, Polydecamethylene glycol and the like are suitable for the use of the present invention, and polyethylene glycol is most suitable for industrial use from the viewpoint of availability and price.

  About the addition amount of the above polyols, it is preferable to add 0.1 to 10 parts by weight with respect to 100 parts by weight of the base composition, and to change the water absorption by increasing the addition amount stepwise. Can do. Furthermore, in the case of polyhydric alcohols such as various glycols, an addition amount of 0.1 to 5 parts by weight has the effect of sufficiently increasing the water absorption rate. In addition, the addition amount of these polyols is required to reach a desired water absorption rate with an addition amount that does not impair the mechanical properties required for the resin layer that plays a role in coating and protecting the glass optical fiber. Since the optimum addition amount varies depending on the characteristics of individual optical fibers or resin materials, it is desirable to adjust according to individual cases.

  The effect of the polyol clarified in the present invention is higher when the molecular weight of the main chain is higher. As described above with reference to the figure, while the component having an alcoholic hydroxyl group increases the water absorption rate, the component itself becomes an elution component, increasing the elution amount, and peeling between the glass optical fiber and the soft coating layer. It can be a factor that generates force. As described above, an effect opposite to the desired effect can be avoided by increasing the molecular weight of the main chain of the polyol. This is because, when the molecular weight of the main chain is long, the entanglement with the polymer skeleton of the resin forming the coating layer increases, and it cannot be easily dissolved in water. That is, for the two competing effects, by increasing the molecular weight of the polyol, the amount of water absorption can be increased and the amount of elution can be greatly shifted downward.

The increase in the entanglement with the polymer skeleton as described above is effective for a polyol having a molecular weight of 200 or more, and more preferably 250 or more.
However, the effect that alcohol molecules such as polyol are retained on the polymer skeleton of the resin constituting the coating layer does not depend only on the molecular weight, and side chain functional groups exist in the structure of the alcohols, and they are covered with them. When the polymer skeleton of the layer resin interacts, it is sufficiently expected that alcohols having a molecular weight of 150 or less have an effect of increasing the water absorption rate.

  Further, as another method having an action of preventing peeling between the glass optical fiber and the soft coating layer, a plurality of the above soft coating layers are arranged, and the innermost soft coating layer (hereinafter referred to as a primary soft coating layer). ) And the glass optical fiber. Furthermore, even for the primary soft coating layer, the water absorption is adjusted by blending polyol or polyol mixture, and the peeling from the glass optical fiber is effectively suppressed by utilizing the compressive force from the hard coating layer. It is possible to give the effect to obtain.

  As the resin composition for forming the primary soft coating layer, UV resin is mainly used, and it is optimal to use a silane coupling agent in order to improve the adhesion between the glass optical fiber and the soft coating layer. It is. Here, examples of the silane coupling agent include aminopropyltriethoxysilane, mercaptopropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, and the like.

  Here, the advantage of disposing a resin having a high water absorption rate in the primary soft coating layer is that the primary soft coating layer has no difference in the water absorption rate between the second and subsequent soft coating layers and the hard coating layer. By adjusting the water absorption rate of the coating layer to be high, peeling of the glass optical fiber and the soft coating layer can be effectively suppressed. That is, an optical fiber in which an increase in transmission loss due to microbending is suppressed can be manufactured relatively easily without adjusting the difference in water absorption between the second and subsequent soft coating layers and the hard coating layer.

Further, it is desirable that the thickness of the primary soft coating layer is thinner than the total thickness of the second and subsequent soft coating layers. This is due to the following reason.
In order to improve the adhesion between the glass optical fiber and the primary soft coating layer, a silane coupling agent is known as the most effective technique. Silane coupling agents require a blending amount of a certain ratio or more with respect to the coating material constituting the soft coating layer in order to improve adhesion, but among the components constituting the soft coating layer, It is expensive and increases the material cost by blending the required amount. Furthermore, since the silane coupling agent itself binds to the resin component, the curability of the coating may be reduced, or the crosslink density may be reduced, which may impair reliability. However, by disposing the thickness of the primary soft coating layer thinner than the total thickness of the second and subsequent soft coating layers, it has good adhesion, keeps the cost low, and improves reliability. An optical fiber that can be secured can be formed. From such a viewpoint, the thickness of the primary soft coating layer is preferably 10 μm or less at maximum.

On the other hand, the peeling between the glass optical fiber and a soft coating layer is expressed by the sum R _p of water absorption and the radius of the product of the soft coating layer larger than the sum R _s of water absorption and the radius of the product of hard layer The action that can effectively suppress the increase in the thickness of the primary soft coating layer. Therefore, in order to provide a certain level of action and effect, the thickness of the primary soft coating layer is preferably 3 μm or more. Therefore, the suitable coating thickness of the primary soft coating layer is 3 μm or more and 10 μm or less.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[Example 1]
Optical fibers 1 to 6 shown in Table 1 were produced. These are single-mode optical fibers having a two-layer structure each having one soft coating layer and one hard coating layer as shown in FIG. For the soft coating layer 2 of each optical fiber, a combination of the base compositions shown in Table 1 in amounts (parts by weight) was used, and different polyols were added as water absorption adjusting additives. The amount of polyol added in Table 1 indicates the number of parts relative to the base composition 100. Further, a coating material having a water absorption rate of 2.0 was used for the hard coating layer 4. In the optical fiber, the outer diameter of the glass optical fiber 1 was about 125 μm, the outer diameter of the soft coating layer 2 was about 200 μm, and the outer diameter of the hard coating layer 4 was about 250 μm.

Furthermore, for these optical fibers, the peelability (peeling rate) between the glass optical fiber and the soft coating layer after the water immersion test, and the increase in transmission loss after being immersed in warm water at 60 ° C. for 15 days were evaluated. . Details of the evaluation conditions are shown below.
[Peeling ratio between glass optical fiber / soft coating layer]
5 cm is cut out from the fiber immersed in warm water of 60 ° C. for 60 days and observed with a microscope. The area of the peeled portion was obtained from the length and number of peeled portions with respect to the observation length, and the ratio to the total area of the optical fiber was defined as the peel rate (%). Since the peeled portion grows in a circle or an ellipse, the area was calculated in a circular shape or an ellipse shape according to the individual shape and integrated to obtain the area of the peeled portion.
[Increase in transmission loss after immersion at 60 ° C for 15 days]
It was immersed in warm water at 60 ° C. for 15 days, and the increase in transmission loss of the optical fiber after immersion relative to the transmission loss of the optical fiber before immersion was measured at a wavelength of 1550 nm.

  The evaluation results are shown in Table 1.

As is clear from Table 1, by mixing a small amount of polyols such as polyethylene glycol and polypropylene glycol, the water absorption rate in the soft coating layer of the optical fiber is adjusted as compared with the case where no polyol is blended, and the hard coating layer the water absorption was greater than that effectively glass optical fiber and a soft by the sum R _p of water absorption and the radius of the product of the soft coating layer larger than the sum R _s of water absorption and the radius of the product of hard layer It is possible to suppress peeling at the coating layer interface. On the other hand, alcohols and diols with low molecular weights have the effect of increasing the amount of water absorption, but on the other hand, they themselves become the elution components, making the elution amount of the soft coating layer extremely higher than that of the hard coating layer. As a result, an effect of promoting separation between the glass optical fiber and the soft coating layer is brought about.
Further, when paying attention to the molecular weight of the polyol, polypropylene glycol having a high molecular weight exhibits an effect equal to or higher than that of polyethylene glycols A and B having relatively low molecular weights. From these results, it is clear that the molecular weight of the polyol is one important factor in adjusting the water absorption rate of the soft coating layer.

[Example 2]
Next, optical fibers 7 to 10 shown in Table 2 were produced. These are single-mode optical fibers having a three-layer structure having two soft coating layers and one hard coating layer, as shown in FIG. For the primary soft coating layer 2, a combination of the base compositions shown in Table 2 in amounts (parts by weight) was used, and different polyols were added as water absorption adjusting additives. The amount of polyol added in Table 2 indicates the number of parts relative to the base composition 100. The same resin composition as the soft coating layer of the optical fiber 4 shown in Table 1 was used for the second soft coating layer 3 (hereinafter referred to as the secondary soft coating layer 3). Further, a coating material having a water absorption rate of 2.0 was used for the hard coating layer 4. In the optical fiber, the outer diameter of the glass optical fiber 1 is about 125 μm, the outer diameter of the primary soft coating layer 2 is about 130 μm, the outer diameter of the secondary soft coating layer 3 is about 200 μm, and the outer diameter of the hard coating layer 4 is The thickness was about 250 μm. Furthermore, for these optical fibers, the peelability between the glass optical fiber after the water immersion test and the soft coating layer under the same conditions as in Example 1 and the increase in transmission loss after 15 days of 60 ° C. hot water immersion were evaluated.

As is apparent from Table 2, the soft coating layer has two layers, a small amount of polyol such as polyethylene glycol is blended, and the sum R _p of the product of the water absorption rate and the radius of the soft coating layer is the water absorption rate of the hard coating layer. An optical fiber provided with a primary soft coating layer that has an effect of improving the adhesion between the soft coating layer and the glass optical fiber, which is greater than the sum of radius products R _s , has only one soft coating layer. As compared with the optical fiber, it is possible to effectively suppress the separation between the glass optical fiber and the coating layer.
On the other hand, alcohols and diols with low molecular weights have the effect of increasing the water absorption and improving the adhesion at the interface on the glass optical fiber. As a result, the elution amount of the layer is increased, and as a result, an effect of promoting separation between the glass optical fiber and the soft coating layer is brought about.

Also, Table 1, from Table 2, in order to prevent microbending of the optical fiber, the optical fiber the sum R _p of water absorption and the radius of the product of the soft covering layers of the hard coating layer water absorption and radius must be greater than the sum R _s of the product, the difference between the sum R _s of water absorption and the radius of the product of the sum R _p of water absorption and the radius of the product of the soft coating layer hard coating layer, is 5 or more More preferably.
Furthermore, the design values such as the thickness of the coating layer are the same, and in the optical fiber similar to the single mode optical fiber used in this example, peeling is suppressed by the water absorption rate regardless of the magnitude of the stress index. You can compare the magnitude of the effect. Therefore, it is possible to easily determine whether or not the material has an effect for suppressing the peeling with the result of the water absorption rate, without calculating the stress index. As an index for simple determination, in order to effectively suppress peeling, the difference between the sum of the water absorption rate of the soft coating layer and the sum of the water absorption rate of the hard coating layer is 0.5% by mass or more. It is desirable that

[Example 3]
Next, using the optical fiber 1, the optical fiber 4, and the optical fiber 7 shown in Table 1 and Table 2, three types of optical fiber colored cores shown in FIG. 3 (colored core wire 1, colored core wire 2, colored core) 4) and three types of optical fiber tape core wires shown in FIG. 4 (referred to as tape core wire 1, tape core wire 2, and tape core wire 3) were produced. Specifically, as shown in FIG. 3, a colored layer 5 made of an ultraviolet curable resin composition and having a thickness of about 5 μm is further provided on the hard coating layer 4 to form an optical fiber colored core wire (hereinafter simply referred to as a colored core wire). Further, as shown in FIG. 4, eight colored cores are arranged in parallel in a plane, and a tape layer 6 is applied thereto using an ultraviolet curable resin composition. An optical fiber ribbon (hereinafter simply referred to as a tape ribbon) was obtained. Eight colors (red, blue, white, green, yellow, purple, orange, gray) were used for identification, but these were all the same except for the pigment composition.
The colored core wire 1 and the tape core wire 1 have an optical fiber 1, the colored core wire 2 and the tape core wire 2 have an optical fiber 7, and the colored core wire 3 and the tape core wire 3 have an optical fiber. 4 was used.
For these colored core wires and tape core wires, the peelability between the glass optical fiber and the soft coating layer after the water immersion test under the same conditions as in Example 1, and the increase in transmission loss after 15 days of 60 ° C. hot water immersion. Evaluated. The test results are shown in Table 3.

As apparent from Table 3, the sum R _p of the product of the water absorption rate and the radius of the soft coating layer of the optical fiber is made larger than the sum R _s of the product of the water absorption rate and the radius of the hard coating layer, and the glass optical fiber and the soft coating For colored cores and tape cores using optical fibers with a soft coating layer that has the effect of improving the adhesion between the glass optical fiber and the soft coating layer. Can be suppressed.
On the other hand, in a colored core or a tape core using an optical fiber in which the sum R _p of the product of the water absorption rate and the radius of the soft coating layer of the optical fiber is smaller than the sum R _s of the product of the water absorption rate and the radius of the hard coating layer, Peeling between the glass optical fiber and the soft coating layer cannot be suppressed, and peeling occurs, causing an increase in transmission loss due to microbending.

  From the above results, it is clear that the separation between the glass optical fiber and the soft coating layer can be effectively suppressed in the colored core wire and the tape core wire using the optical fiber according to the present invention. It was. Further, it is clear that the effect of the present invention is very great also in the optical fiber cable using the tape core wire according to the present invention.

It is a schematic diagram which shows the optical fiber of this invention. It is a schematic diagram which shows the optical fiber of this invention. It is a schematic diagram which shows the optical fiber colored core wire of this invention. It is a schematic diagram which shows the optical fiber tape core wire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass optical fiber 2 (Primary) Soft coating layer 3 (Secondary) Soft coating layer 4 Hard coating layer 5 Colored layer 6 Tape layer

Claims (8)

In an optical fiber in which the outer periphery of a glass optical fiber is coated with a soft coating layer having a Young's modulus of 3 MPa or less and a hard coating layer having a Young's modulus of 500 MPa or more,
Among the soft coating layers, as an innermost soft coating layer, a water absorption adjusting additive is added to the base resin separately from the base resin, and a polyol having a molecular weight of 200 or more is used as the water absorption adjusting additive. Alternatively, use a polyol mixture,
At least one of the soft coating layers is coated on the surface of the glass optical fiber, and the water absorption rate of the soft coating layer from the inside is C _p1 , C _p2 ... C _pn , the radius is r _p1 , r _p2. r _pn, when the _C s1 water absorption hard layer from the _{inside, C} s2 ··· C _sn, the radius was _{r s1, r s2 ··· r sn} ,
The sum of the water absorption and the radius of the product of the soft coating layer _{R p = C p1 × r p1} + C p2 × r p2 + ··· + C pn × sum of water absorption and the radius of the product of _{r pn} and the hard coating layer R _s = C _s1 × r _s1 + C _s2 × r _s2 +... + C _sn × r _sn satisfies the relationship of R _p > R _s . 2. The light according to claim 1 , wherein the difference between the sum R _p of the product of the water absorption rate and the radius of the soft coating layer and the sum R _s of the product of the water absorption rate and the radius of the hard coating layer is 5 or more. fiber. 3. The optical fiber according to claim 1 , wherein each of the soft coating layer and the hard coating layer is a single layer . The optical fiber according to claim 1 or 2, wherein the soft coating layer comprises two layers, and the hard coating layer comprises one layer . 5. The optical fiber according to claim 1, wherein a thickness of an innermost soft coating layer of the soft coating layers is 3 μm or more and 10 μm or less . The optical fiber according to any one of claims 1 to 5, wherein polyethylene glycol is used as the polyol . An optical fiber colored core formed by coating the optical fiber according to any one of claims 1 to 6 with a colored layer. An optical fiber ribbon comprising a plurality of the optical fiber colored cores according to claim 7 arranged in parallel in a planar shape and covered in a lump.

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