JPH0723239B2 - High-speed coating method for optical fiber coated with UV curable resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for coating an optical fiber,
More specifically, it relates to a method of coating an optical fiber at a high speed with an ultraviolet curable resin.

2. Description of the Related Art In the process of coating an optical fiber with an ultraviolet (hereinafter abbreviated as UV) curable resin, the UV curable resin is known to be easy to coat because it is cured only by irradiating it with UV light. For this reason, such a UV-curable resin-coated fiber is widely used (for example, Kokubu et al. “Design of UV-curable resin-coated optical fiber tape”, 1984, IEICE Communications Division National Conference, 476). However, almost no studies have been conducted on a method for producing a UV-curable resin-coated optical fiber by rapidly curing the UV-curable resin during coating. Therefore, the conventional optical fiber coating method has serious problems such as a long coating process and a high manufacturing cost.

On the other hand, the UV curing reaction has been theoretically studied as one of general chemical reactions. This type of reaction is called a radical reaction, and the following equation (for example, Tsuruta et al., “Polymer Constitution” Kagaku Dojin, 1966) is known as an equation expressing the change of the material monomer concentration [M] with respect to time t. .

[I] = [I ₀ ] exp (−k _d t) (2) where k _d : light absorption coefficient of photoinitiator k _p : rate constant of growth reaction k _t : rate constant of termination reaction f: light Initiation efficiency L: UV intensity [I]: Concentration of photoinitiator [I ₀ ]: Initial concentration of photoinitiator [M] = [M ₀ ] at time t = 0 according to formulas (1) and (2).
Solving as (M ₀ monomer initial concentration) gives the following equation.

From the above formula (3), it is possible to know the time change of the monomer concentration [M] of the UV curable resin, that is, the amount of change in concentration from the initial monomer concentration due to curing. However, the parameters k _d , k _p , k _t, and f necessary for obtaining the value of the monomer concentration are material-dependent amounts and change with changes in the coating material. Usually, the above parameter values for coating materials that are commercially available are not known.

Furthermore, equation (3) only shows the change in monomer concentration. The characteristics of a resin occur due to curing, but the relationship between the characteristics required for a coated optical fiber and the degree of resin curing is
It is unknown in equation (3).

Further, when coating the optical fiber, the necessary curing conditions vary depending on the coating layer, but the effect of thickness is not expressed in the formula (3). Therefore, the requirements for high speed coating are unknown.

As described above, in the generally known general reaction formula,
The conditions required to cure the UV curable resin at high speed were not clear. Therefore, high-speed coating cannot be performed,
There was a problem that the manufacturing cost was high.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the conventional method for coating an ultraviolet curable resin-coated optical fiber, the conditions necessary for curing the ultraviolet curable resin at high speed have not been clarified. Therefore, there is a problem that the coating cannot be performed at high speed and the manufacturing cost is high.

Therefore, the present invention intends to provide a method for producing a coated fiber at a high speed by clarifying the conditions necessary for curing the ultraviolet curable resin at a high speed.

Means for Solving the Problems That is, according to the present invention, in a method of coating an optical fiber with an ultraviolet curable resin that absorbs and cures ultraviolet rays, the optical absorption coefficient α of the ultraviolet curable resin having a coating thickness h and the resin Using two constants k _d and C obtained by measuring the Young's modulus of
formula A high-speed coating method for an ultraviolet-curable resin-coated optical fiber is provided, in which the ultraviolet light intensity L ₀ and the ultraviolet light irradiation time t satisfying the above are obtained, and coating is performed with the ultraviolet light intensity L ₀ and the ultraviolet light irradiation time t. It

Action In FIG. 1 showing a model of optical fiber coating with UV curable resin, the UV curable resin 1 having a thickness h is moving at a speed v in the z-axis direction. The UV curing resin 1 is irradiated with UV light L ₀ from below over a range of length 1. At this time, if the light absorption coefficient of the UV curable resin is α, the in-resin light intensity L is L = L ₀ e ^−αx (4). Here, the reflection on the resin surface was ignored. Formula (3)
And from the formula (4), the saturation rate S of the cured product is Becomes The characteristics of the UV curable resin having the thickness h cannot be expressed as a constant value because the degree of curing differs in the cross section, but it is considered appropriate to find the average value of the saturation rate. The average value S of S can be expressed by the following equation.

However, this integral cannot be analytically obtained, but if it is approximated by e ^{−αx / 2 ≈1} −αx / 2 (αx / 2 << 1), the following equation is obtained.

Next, consider the items to be evaluated as the characteristics of the resin after curing. Formula (6) shows the ratio of the product after curing, and the conventional gel fraction is known as an evaluation method corresponding to this. This is a value obtained by extracting the uncured portion from the product for a certain period of time with a solvent and obtaining the ratio of the remaining curing agent.

On the other hand, when it is used as a coating agent for optical fibers, its mechanical and microbend resistance properties are known to largely depend on the Young's modulus of the coating material (for example, Kokubu et al. “UV curable resin coated optical fiber tape Design ”1984 National Conference of the Communication Division of the Institute of Electronics and Communication Engineers, 476). Therefore, it is possible to adopt Young's modulus as the characteristic of the cured resin. In order to examine which of the gel fraction and Young's modulus is suitable, the light intensity L ₀ for irradiation was changed and the values of both characteristics were measured.

FIG. 2 shows the measurement results of the above UV light intensity L ₀ and the above-mentioned characteristics of the cured resin. The thickness of the resin is 0.25 mm. The Young's modulus E is expressed as E ∞ when a sufficiently large L ₀ is irradiated, and is dimensionlessly shown by the ratio E / E ∞. As is clear from FIG. 2, both properties show a tendency toward saturation monotonically with increasing L ₀ , but the gel fraction tends to saturate earlier than Young's modulus. In particular, in the range where L ₀ is small, Young's modulus better represents the degree of curing. Although the reason for this is not clear, it is considered that the Young's modulus can be measured as a small value because the resin is not completely cured in the range where L ₀ is small even if it is not extracted with a solvent.

From the above results, it can be judged that it is appropriate to adopt the Young's modulus which is closely related to the characteristics of the optical fiber and which can well express the degree of curing, as the value indicating the degree of curing.

Next, the validity of the equation (6) when Young's modulus is adopted as a value representing hardening is examined.

Using 5 kinds of resins shown in Table 1, Young's modulus which changes curing conditions was measured. Resins A1 to A3 are soft materials for primary coating, and B1 and B2 are hard materials for secondary coating. The sample size was a rectangle of 60 mm × 10 mm, and Young's modulus was measured at a gauge length of 25 mm and a pulling speed of 1 mm / min. First, apply UV resin on the glass surface and apply UV light.
It was cured by passing it through L _{0 at} a constant speed v. Speed v
And the irradiation time t are changed to measure the resin.
The results for A1 to A3 are shown in FIG. 3, and the results for B1 and B2 are shown in FIG.

Each measurement point is an average value of five measurement values, and the horizontal axis is shown in seconds (s). Further, in both figures, using Eq. (6), assuming that E / E∞ =, the parameters k _d and C were determined so as to best match the measurement results, and the calculated results are also shown. The values of the obtained parameters k _d and C are shown in Table 1.

As is clear from FIGS. 3 and 4, it can be seen that the equation (6) agrees well with the measured value when the parameters k _d and C are appropriately set. Conversely, if this measurement is performed, the parameters k _d and C that define the curing rate of the resin can be obtained. In order to determine k _d and C from the equation (6), it is sufficient in principle to have two different values, but when the two values are close, the root is likely to include an error in the equation. Therefore, it is desirable to obtain the values of the above parameters with as many measurement points as possible.

Next, the dependence of the resin thickness on the Young's modulus will be examined. The results of measuring the Young's modulus of the resins A1 and B1 while changing the resin thickness h are shown in FIG. Further, the results of calculating the thickness dependence from the equation (6) using the values of k _d and C already obtained are also shown in FIG. From this result, it is understood that using the obtained k _d and C, the equation (6) well expresses the experimental value even when the thickness h is changed.

Similarly, the Young's modulus of the sample cured by changing the UV light intensity L ₀ was measured. The measurement results are shown in FIGS. 6 and 7.
The resin thickness h and irradiation time t are A1; 0.25 mm, 0.3 seconds, A2; 0.25 mm, 1.5 seconds, A3; 0.2 mm, 2.3 for each sample, respectively.
Seconds, B1; 0.25 mm, 3 seconds, B2; 0.25 mm, 3 seconds. In the figure,
The results of calculating the L ₀ dependency from the equation (6) using the values of k _d and C already obtained are also shown. From this result, it is understood that using the obtained k _d and C, the equation (6) well expresses the experimental value even when the UV light intensity L ₀ is changed.

As described above, it was found that if the formula (6) representing the curing rate of the UV curable resin was derived and the Young's modulus was adopted as the characteristic representing the curing rate, this was in good agreement with the calculation formula.
Therefore, this equation can be used to determine the curing conditions. By further transforming equation (6), Becomes

Here, η represents the unsaturation rate, and η = 1-E / E∞, (E / E
∞ =).

It is necessary to sufficiently study the appropriate value of the unsaturated ratio η. If η is made extremely small, the time required for curing becomes long and it is not possible to achieve high speed. On the other hand, when η is large, the uncured portion remains used, and there is a possibility that reliability problems such as aging may occur.

Therefore, it is considered that a lot of tests are required and sufficient time is required to sufficiently confirm the proper value of η. Currently, a heat cycle test of a coated optical fiber manufactured with an appropriate value η = 0.1 from the already obtained results is being carried out, but no particular problem has appeared.

In the above description, the wavelength of light is not specified for the light absorption coefficient α. The wavelength λ of the light effective for curing the resin is 0.3
It is about 0.4 μm, and a value for this wavelength range is used as the light absorption coefficient α.

As described above in detail, if the resin constant and the curing conditions are determined so that η = 0.1 and Equation (7) is satisfied, the Young's modulus required as a coating material can be cured in a state of 90% or more saturation. . In the prior art, such a condition was completely unknown.

Example Hereinafter, an example of a high-speed coating method for an ultraviolet-curing resin-coated optical fiber according to the present invention will be described.

Example 1 The results of calculating the regions of UV light intensity L ₀ and irradiation time t satisfying the formula (7) based on the measured values shown in Table 1 for the resins A1 and A2 are shown by hatching in FIG. Although any combination of L ₀ and t within this region may be adopted as the curing condition, in order to cure at a high speed, that is, the irradiation time t
It can be seen that L ₀ needs to be increased in order to shorten.

L ₀ is a value on the resin surface, and is about 50 mW / mm ² in a commercially available UV light lamp. It is also possible to use a high-power lamp, but a strong UV light lamp also emits a large amount of infrared rays, so the temperature of the resin rises during coating, and there is a risk of resin deterioration. In order to avoid this, if the condition of L ₀ <50 mW / mm ² is set as shown in FIG.
For A1, t = 0.105 seconds and for A2, t = 0.31 seconds. If you use a commercially available UV light lamp with irradiation length 1 of 250 mm,
The coating linear velocity v (= l / t) is v = 143 m / min for resin A1, A2
It is possible to cure at v = 48 m / min.

When coating experiments were performed on both resins under these conditions, properly coated fibers were obtained.

In this way, the UV light intensity and irradiation time t depend on the characteristics of the resin.
Can be determined. Since L ₀ can be set large and t can be set small within a possible range, high-speed coating is possible. Therefore, the coated optical fiber having a clear curing rate can be manufactured at high speed, that is, with a small processing cost and economically.

Example 2 The same resins A1 and A2 as in Example 1 were subjected to higher speed coating. Two identical UV light lamps were arranged side by side, and the equivalent irradiation length was l = 500 mm, which was twice as long as that in the case of Example 1. The output of each lamp was L ₀ = 50 mW / mm ² . Since 1 was doubled, the coating linear velocity v was also doubled. That is, a coating experiment was performed at a high speed of v = 286 m / min for resin A1 and v = 96 m / min for A2.

As a result, a good coated fiber was obtained as in Example 1. Also in this example, it was confirmed that the coated fiber having a well-defined curing rate can be manufactured at high speed and economically as in the case of Example 1.

Example 3 An experiment was conducted in which an optical fiber was coated with a UV curable resin to a thickness h of 0.2 mm. The conditions were set such that the UV light intensity L ₀ = 50 mW / mm ² was irradiated onto the resin surface with one UV light lamp having an irradiation length of 1 = 300 mm.

As an example of high-speed curing, if the linear velocity v is 50 m / min and 100 m / min, the irradiation time t is t = 1 / v = 0.36 seconds and 0.18 seconds, respectively. Further, if the unsaturation rate is η = 0.1, then equation (7)
The area of k _d and C that satisfies is represented by the upper part of the curve in FIG. 9 indicated by hatching.

The values of k _d and C for the five types of UV curable resins shown in Table 1 are shown in Table 9.
Plotted in the figure. From this result, 100m under the above irradiation conditions
It is understood that when coating at a high speed of not less than / min, the resins A1, A2 and B1 can be cured with the unsaturation rate η <0.1, but the resins A3 and B2 cannot be cured.

In FIG. 9, the light absorption coefficient α is shown as a parameter, but α varies depending on the resin. Therefore, the corresponding calculated value should be obtained by substituting the corresponding α, but it can be seen from FIG. 9 that the α dependence is small. Therefore, if the calculated value for the larger value of α (α = 4 in FIG. 9) is adopted so as to satisfy the severe condition, the safety setting can be made.

In this way, a resin suitable for the set curing conditions can be selected. From FIG. 9, resin B1 was selected and cured at a coating linear velocity v = 100 m / min. As a result, a good coated fiber was obtained. The coated fiber thus obtained has a stable curing property because it has a clear curing rate under constant UV light irradiation conditions.

Example 4 In order to confirm the effect of implementation more quantitatively, the transmission loss of the coated optical fiber obtained by the coating experiment was evaluated.

FIG. 10 shows a cross-sectional view of the manufactured optical fiber tape.
Reference numeral 11 is a graded index type multimode optical fiber, which is a standard fiber having a core diameter / outer diameter of 50/125 μm and a relative refractive index difference of 1%. Resin 12 was used as the primary coating for 12 and resin B1 was used as the coating for the second layer as 13. The coatings 12 and 13 were applied at the same time as the drawing of the optical fiber, and the outer diameter of 13 was 0.2 mm, which was used as the strand. The coated wire speed is 100 m / min. Reference numeral 14 is a tape coating for collectively covering the 10 cores in a tape shape.

FIG. 11 shows the measurement results of the irradiation time t dependence of the Young's modulus ratio E / E∞ of the resin used for the tape coating 14. Also, in equation (6)
E / E ∞ = and set the constant k to best represent the measurement result.
_The results of calculating the Young's modulus ratio by setting _d and C are also shown in FIG. The obtained constants are k _d = 0.6S ^-1 , C = 4.1m
It is m (mJ) ^-1/2 . Further, the light absorption coefficient α = 2 mm ⁻¹ .
A tape coating 14 was formed using this resin to obtain the optical fiber tape shown in FIG. Its dimensions are 2.1 mm width and thickness
It is 0.3 mm. The tape coating 14 coats the circumference of the 10-fiber optical fiber, and the thickness h varies depending on the location, but at most h = 0.15 mm.

When a resin having a UV irradiation length of 1 = 350 mm is used and the resin 14 is coated at 100 m / min, the irradiation time t is 0.21 seconds. At this time, in order to set η = 0.1, it is necessary to set L ₀ > 55 mW / mm ² from the equation (7). In order to examine the influence of the unsaturation rate η = 0.1, the coating was performed at 100 m / min under the condition of L ₀ = 55 mW / mm ² , and the 10-fiber optical fiber tape shown in FIG. 10 was manufactured for 1 km.

Figure 12 shows the histogram of the measurement results of loss change due to tape coating, using the optical loss of the strand as the standard. 0.85 μm and 1.3
When 10 cores were measured at both wavelengths of μm, the average change was 0.02 dB / Km, which was a small value within the measurement error.

Then put this fiber optic tape in a constant temperature bath, -40 to +
The change in optical loss was measured in the temperature range of 60 ° C. Figure 13 shows the change based on the optical loss at 20 ° C. Loss change is −40
Although it tends to increase a little at ℃, it is ± 0.05 dB in average value.
It was a small value within / Km.

As described above, according to the method of the present invention, the UV light irradiation conditions can be determined so that the resin can be coated at a high speed according to the characteristics of the resin, and thus a coated optical fiber having stable characteristics can be manufactured at a high speed.

EFFECTS OF THE INVENTION As is clear from the above description, according to the high-speed coating method for an ultraviolet-curing resin-coated optical fiber according to the present invention, high-speed coating can be realized with a constant curing rate according to the characteristics of each ultraviolet-curing resin. it can. Therefore, the processing cost can be reduced, and the coated fiber having stable characteristics can be manufactured because the curing rate is constant. That is, a high quality and low cost coated fiber can be provided. Therefore,
The high-speed coating method for an ultraviolet-curing resin-coated optical fiber according to the present invention can be utilized over a wide range.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a cured state of a UV curable resin, and FIG. 2 is a diagram showing a measurement result of characteristics of the cured resin with respect to an irradiated UV light intensity L ₀ . FIG. 4 and FIG. 4 are views comparing the Young's modulus of the resin cured by changing the irradiation time t with a constant UV light intensity L ₀ , with respect to the measured value and the calculated value, and FIG. 5 is cured. It is the figure which compared the thickness dependence of the Young's modulus of the resin with the measured value and the calculated value, and FIGS. 6 and 7 show the UV light intensity dependence of the Young's modulus of the cured resin by the measured value and the calculated value. FIG. 8 is a diagram for comparison, FIG. 8 is a diagram showing a setting method of UV light irradiation time t and intensity L ₀ , and FIG. 9 is a setting range of parameters k _d and C under constant UV light irradiation conditions. FIG. 10 is a cross-sectional view of the optical fiber tape, and FIG. 11 is a view showing characteristics of the resin used for the coated fiber. , FIG. 12 is a histogram showing the results of measurement of the optical loss change due to the production of coated fiber, FIG. 13 is a diagram showing the temperature change test results of the coated fiber produced. (Main reference numbers) 1 ... UV curable resin, 11 ... Optical fiber, 12 ... UV curable resin for primary coating, 13 ... UV curable resin for protective coating, 14 ... UV curable resin for tape coating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Hokari, 162 Shirahone, Shirahoji, Tokai-mura, Naka-gun, Ibaraki Prefecture, Nippon Telegraph and Telephone Corporation, Ibaraki Electro-Communications Research Laboratory (72) Inventor Sadano Hadano, Naka, Ibaraki Prefecture 162 Shirahone, Shirokata, Tokai-mura, Gunma, Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A method for coating an optical fiber with an ultraviolet curable resin that absorbs and cures ultraviolet light, wherein an ultraviolet curable resin having a light absorption coefficient α and a coating thickness h is applied to an ultraviolet light intensity L ₀ and an ultraviolet light irradiation time t. Let E be the Young's modulus of the resin film cured by, and let E∞ be the Young's modulus of the resin film cured with a sufficiently large ultraviolet light intensity L ₀ or a sufficiently long ultraviolet light irradiation time t, and ultraviolet rays with different E / E∞. Light intensity L
Select at least two combinations of ₀ and ultraviolet light irradiation time t, and Using the two constants k _d and C determined from A high-speed coating method for an ultraviolet-curable resin-coated optical fiber, which comprises coating with an ultraviolet light intensity L ₀ and an ultraviolet light irradiation time t satisfying the above condition.