JP4935273B2 - Method for producing polyimide-coated fiber - Google Patents

Description

  The present invention relates to a method for producing a polyimide-coated fiber in which a traveling fiber is coated with a polyimide resin.

  There is known a polyimide-coated fiber that can be used at a high temperature by coating a fiber with a polyimide resin. As a coating method for coating a linear body such as a fiber with a polyimide resin, for example, a method described in Patent Document 1 is also known.

In this polyimide resin coating method, as shown in FIG. 5, a supply device 101 for supplying a polyimide resin, a coating device 102 for coating the linear body 100 with a polyimide resin delivered from the supply device 101, and a coated polyimide Using a curing furnace 103 for curing the resin, a gas supply device 104 for sending an inert gas into the curing furnace 103, and a device including a winder (not shown), the temperature of the curing furnace 103 is set to 500 ° C. or more, The linear body 100 is covered with a polyimide resin by setting the inside of the curing furnace 103 as an inert gas atmosphere.
Japanese Unexamined Patent Publication No. 63-1489 (FIG. 5)

  By the way, in this polyimide-coated fiber, the polyimide resin is coated on the fiber by a solvent-removing and polyimide-forming curing reaction from a polyimide resin having excellent heat resistance. However, since the polyimide resin contains a large amount of solvent at the time of this coating, sufficient heating is required to heat and remove the solvent and cure. That is, the quality of the resulting polyimide coating is affected by the degree of cure and the amount of residual solvent. For this reason, in order to obtain a good covering state, it is necessary to cure under optimum temperature conditions.

  However, the conventional apparatus is not configured to promote efficient volatilization and curing of the solvent. For this reason, when a polyimide resin is coated on a fiber that is easily affected by characteristics due to external stress, the coated surface state may become viscous due to poor curing, and the fiber transmission characteristics may be poor. This is because a single curing furnace (limited curing region) cannot be cured at a high temperature at the time of polyimide curing, that is, it cannot be cured (temperature addition) so that residual solvent does not remain. The polyimide coating will be formed with insufficient. In addition, bubbles may be generated by the residual solvent, which may cause poor appearance and deterioration of fiber characteristics.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a polyimide-coated fiber that does not adversely affect fiber transmission characteristics, can realize a good coating state without delaying the production speed, and does not cause poor appearance. Is to provide.

The polyimide-coated fiber manufacturing method of the present invention is a polyimide curing step in which a drawn glass fiber is coated with a polyimide resin and cured, and most of the solvent contained in the polyimide resin is suppressed in a state where curing of the polyimide resin is suppressed. A volatilization process for volatilizing, a temporary curing process for volatilizing the remaining solvent and accelerating the curing of the polyimide resin, and after the temporary curing, volatilizing so that almost no remaining solvent remains, and curing the polyimide resin And a main curing process that accelerates the process to complete, and the treatment in each of the processes is performed using different curing furnaces, and the heating temperature in each of the curing furnaces is increased in the order of the processes. It is characterized by having a temperature gradient .

  In the method for producing a polyimide-coated fiber of the present invention, it is preferable that the heating temperature in each of the curing furnaces is given a temperature gradient so that the incoming line side is low and the outgoing line side is high.

  In the method for producing a polyimide-coated fiber of the present invention, it is preferable that the curing furnace used in the main curing process has an inert gas atmosphere in the furnace and an oxygen concentration in the furnace of 100 ppm or less.

  In the method for producing a polyimide-coated fiber of the present invention, the polyimide curing step is preferably performed by repeating the series of processes at least twice.

  According to the present invention, since the solvent can be sufficiently evaporated, it is possible to provide a method for producing a polyimide-coated fiber that does not adversely affect fiber transmission characteristics and does not cause poor appearance.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
(First embodiment)
FIG. 1 shows a coating apparatus for carrying out a method for producing a polyimide-coated fiber according to a first embodiment of the present invention. This polyimide-coated fiber coating apparatus 10 includes a coating apparatus 11 and a first curing. A furnace 12, a second curing furnace 13, a third curing furnace 14, and a guide roller 15 for guiding the fiber between these curing furnaces 12, 13, 14 are provided. The coating apparatus 11 coats the polyimide resin on the running glass fiber 1 after drawing. The 1st-3rd hardening furnaces 12-14 heat a polyimide resin, and are comprised with an electric furnace. In addition, as a 1st hardening furnace used as a volatilization process, the hot stove which has the intake / exhaust which can collect | recover a volatile component is preferable.

Among these, in the 1st hardening furnace 12, as described in [Table 1], the volatilization process which is the first process is performed among polyimide hardening processes. That is, in order to volatilize most of the solvent such as N-methyl-2-pyrrolidone contained in the polyimide resin in a state in which the curing of the polyimide resin is suppressed (this is called a “volatilization process”), a predetermined set temperature is set. it is intended to heat to T _1.
In the next curing process, the curing process is divided into two in order to cure efficiently in stages so that the solvent does not remain in the polyimide resin. For this reason, in the second curing furnace 13, the first half curing process (this is referred to as “temporary curing process”) is performed. This process is a process for volatilizing the remaining solvent and promoting the curing of the polyimide resin. Therefore, heating to a predetermined set temperature T _2. On the other hand, in the third curing furnace 14, the latter half of the curing process is performed (this is referred to as “main curing process”). This process is a process for volatilizing the remaining solvent so that it hardly remains, and for promoting the complete curing of the polyimide resin. Therefore, heating to a predetermined set temperature T _3. In these curing oven 12 to 14, the value of the setting temperature _T 1 through T ₃ becomes successively higher. That is, each curing furnace is set to a gradually higher temperature (T ₁ <T ₂ <T ₃ ).

  Moreover, in these 1st-3rd hardening furnaces 12-14, the temperature gradient is given to the inside of each furnace for each hardening furnace, and the solvent contained much in a polyimide resin is efficiently by stepwise temperature addition. The polyimide-coated fiber 2 is manufactured by curing.

For this reason, a temperature gradient of 50 ° C. is given in the first curing furnace 12. That is, in the first curing oven 12, to set the temperature in the curing oven top is the incoming line side T ₁ -25 ° C., the temperature in the curing oven bottom is outgoing line side T _{1 +} 25 ° C..

On the other hand, a similar temperature gradient, that is, a temperature gradient of 50 ° C. is also given in the second curing furnace 13. That is, the temperature at the upper part on the incoming line side is set to T ₂ -25 ° C., and the temperature at the lower part on the outgoing line side is set to T ₂ + 25 ° C.

Further, a temperature gradient of 50 ° C. is similarly applied in the third curing furnace 14. That is, the temperature at the upper part on the incoming line side is set to T ₃ -25 ° C., and the temperature at the lower part on the outgoing line side is set to T ₃ + 25 ° C. In the third curing furnace 14, it is preferable to supply an inert gas (for example, N ₂ ) into the furnace in order to prevent inflow of oxygen or the like.

Next, the manufacturing method of the polyimide coated fiber of this embodiment is demonstrated.
First, the glass fiber 1 after drawing is coated with a polyimide resin by a coating apparatus 11 as shown in FIG. Next, the coated bare fiber 1 sequentially passes through the first curing furnace 12, the second curing furnace 13, and the third curing furnace 14. At this time, the curing furnaces 12 to 14 have a temperature gradient between the curing furnaces so that the temperature rises in the order of the processes. Further, even in each furnace, temperature gradients are provided at the upper part (the incoming line side of the bare fiber 1) and the lower part (the outgoing line side of the bare fiber 1). Therefore, heat treatment can be performed in which the heating temperature gradually increases as it passes through the first curing furnace 12 to the third curing furnace 14. Thereby, volatilization and hardening of an efficient solvent can be aimed at. As a result, a good polyimide-coated fiber with no residual solvent is obtained.

  Therefore, in the polyimide curing step, (I) a volatilization process for volatilizing the solvent, (II) a temporary curing process for curing the solvent, and (III) a main curing process are performed using separate curing furnaces 12 to 14. Can be sufficiently heated and cured. In other words, the polyimide resin can be efficiently cured step by step, and the residual solvent can be eliminated. Thereby, the favorable polyimide covering fiber 2 which prevented generation | occurrence | production of a bubble is obtained. If these bubbles are mixed in, the cladding may be distorted and a lateral pressure or the like may be generated in the fiber, which may deteriorate the transmission characteristics.

  Moreover, in the present embodiment, not only is the temperature gradient provided so that the set temperatures of the respective curing furnaces 12 to 14 are sequentially increased, but also inside the furnaces of the respective curing furnaces 12 to 14, respectively, than the incoming line side. A temperature gradient with a high outgoing line is provided. For this reason, further effective volatilization / curing of the solvent can be promoted, the residual solvent can be eliminated, and an even better polyimide-coated fiber can be obtained.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals to avoid redundant description.
FIG. 2 shows a coating apparatus 20 for carrying out the method for producing a polyimide-coated fiber according to the second embodiment of the present invention. In this polyimide-coated fiber coating apparatus 20, the polyimide coating process and the polyimide curing process are repeated three times for convenience, the first to third coating apparatuses 21 to 23, the first curing furnace 24, and 25, a second curing furnace 26, a third curing furnace 27, and guide rollers 15, 28, and 29 that guide the travel of the bare fiber 1 between these curing furnaces 24 to 27.

  The 1st-3rd coating apparatuses 21-23 are comprised from three things in order to make polyimide coating finally in a thick state by apply | coating a polyimide resin to 3 layers. That is, since these coating devices 21 to 23 completely remove the solvent in each of the curing furnaces 24 to 27 that pass after the polyimide application, each of the devices 21 to 23 applies the polyimide resin relatively thinly to ensure the solvent. Can be evaporated.

The first to third curing furnaces 24 to 27 have the same configuration as that of the first embodiment, and are each configured by an electric furnace that heats the polyimide resin from T ₁ to T ₃ . However, in the present embodiment, unlike the first embodiment, the first curing furnace is composed of two things, but both have the same temperature setting. The first curing furnace 24 is used only for the volatilization process in the first layer, and the first curing furnace 25 is used for the volatilization process in the second layer and the third layer. To do.

In the third curing furnace 27 as the final curing furnace, an inert gas (for example, N ₂ ) is supplied into the furnace by a supply device (not shown) in order to prevent oxidation of the polyimide resin due to the inflow of oxygen. That is, in the present embodiment, the interior of the final curing furnace 27 is set to an inert gas atmosphere in order to prevent oxidative degradation of the polyimide resin. By supplying this inert gas, the inside of the third curing furnace 27 is brought to an oxygen concentration of 100 ppm or less.

Next, a method for producing a polyimide-coated fiber according to this embodiment will be described with reference to FIGS.
[1] First, as shown in FIG. 2, the glass fiber 1 immediately after drawing is coated with a first layer of polyimide resin by the first coating device 21 (first step S1). [2] Next, the coated fiber sequentially passes through the first curing furnace 24, the second curing furnace 26, and the third curing furnace 27. Here, as described above, in the curing furnaces 24, 26, and 27, a temperature gradient is provided between the curing furnaces, and further, a temperature gradient is provided at the upper part and the lower part in each furnace. Accordingly, heat treatment is performed such that the heating temperature gradually increases as it passes through the first curing furnace 24 to the third curing furnace 27 (second step S2 to fourth step S4). In this way, the first layer of polyimide resin is fully cured in the third curing furnace 27, which is the final curing furnace (fourth step S4).

[3] Thereafter, the guide path of the guide roller 29E is changed to the upward direction as viewed in the figure, and further passes through the guide rollers 28B and 28C, and then the polyimide resin which becomes the second layer in the second coating device 22 (5th step S5). [4] Next, similarly to the previous time, heat treatment is performed so that the heating temperature gradually increases through the second curing furnace 26 and the third curing furnace 27 (sixth step S6 to S6). Eighth step S8). In this way, the second-layer polyimide resin is fully cured in the third curing furnace 27 as the final curing furnace (eighth step S8).
[5] After that, similarly, the guide path of the guide roller 29E changes the traveling path upward as viewed in the figure, and the third layer is subjected to the same coating and curing process as the second layer ( Ninth step S9 to twelfth step S12). In this way, if the third-layer polyimide resin is main-cured in the third curing furnace 27 as the final curing furnace with respect to the fiber core wire 2 (12th step S12), it passes through the guide roller 29E. Later, it is moved to the traveling path in the right direction in the figure, and finally wound up by a winder not shown.

  Therefore, according to the present embodiment, as shown in FIG. 3, the process is repeated three times (first step S1 to twelfth step S12), and the coating layer is thickened to improve the strength. In addition, by performing this process a plurality of times, it is possible to freely increase the region where the curing process is performed, so that the manufacturing speed can be increased. Furthermore, good coating eccentricity can be obtained by increasing the thickness.

Further, in the present embodiment, in the third curing oven 27 which is the final curing oven, for supplying an inert gas (e.g., N ₂₎ in the furnace, good polyimide coating surface. As a result, it is possible to prevent the application of non-uniform stress due to the viscosity of the coating surface generated during degradation due to oxidation, that is, the fiber cores 2 are bundled together. Therefore, the polyimide-coated fiber 2 having good transmission characteristics with reduced transmission loss can be obtained.

Example 1 will be described with reference to FIGS. 2 and 3.
In this example, a polyimide-coated fiber coating apparatus shown in FIG. 2 was used to coat a fiber having a pure quartz core and a fluorine-added cladding in the same manner as in the second embodiment. . That is, the above-mentioned fiber having an outer diameter of 125 μm was coated with three layers of polyimide to produce a polyimide-coated fiber having an outer diameter of 170 μm. Piline PI-2525 was used as the polyimide resin. The curing temperatures were 200 to 250 degrees for the first curing furnaces 24 and 25, 250 to 300 degrees for the second curing furnace 26, and 450 to 500 degrees for the third curing furnace 27. Moreover, N ₂ which is an inert gas was fed into the third curing furnace 27 which is the final heating furnace, and the inside of the furnace was made an N ₂ gas atmosphere.

Under such conditions, the N ₂ flow rate was changed, the final furnace oxygen concentration was changed as shown in Table 2 below, and the fiber transmission loss at each oxygen concentration was measured and compared. As a result, a graph as shown in FIG. 4 was obtained.

  FIG. 4 shows that the fiber coated by the method of the present invention provides a good fiber with low transmission loss. In particular, as shown in Table 2, it was confirmed that by setting the oxygen concentration to 100 ppm or less, a further excellent fiber with lower transmission loss can be obtained.

Next, Example 2 will be described with reference to FIG.
In this example, as in Example 1, the polyimide-coated fiber was coated on the fiber by the same method as in the second embodiment using the polyimide-coated fiber coating apparatus shown in FIG.
In particular, in this example, in order to confirm the effect of thickening the coating portion coated with polyimide, two types of polyimide-coated fibers with outer diameters of 160 μm and 170 μm were manufactured, and the frequency of disconnection due to load load (1% elongation) was determined. An experiment was conducted to compare them. The results are shown in [Table 3].

  From the results of [Table 3], it was found that the disconnection frequency can be reduced by increasing the thickness.

  The present invention is not limited to the embodiment described above, and can be implemented in various forms without departing from the gist of the present invention.

  According to the method for producing a polyimide-coated fiber of the present invention, a good coating state can be realized without adversely affecting the fiber transmission characteristics and without delaying the production speed, and an appearance defect can be caused. This has the effect of producing a non-polyimide coated fiber, and is useful for fibers used at high temperatures.

It is explanatory drawing which shows the principal part of the fiber manufacturing apparatus with which the manufacturing method of the polyimide coating fiber which concerns on the 1st Embodiment of this invention is used. It is explanatory drawing which shows the principal part of the fiber manufacturing apparatus with which the manufacturing method of the polyimide coating fiber which concerns on the 2nd Embodiment of this invention is used. It is a flowchart which shows the manufacturing method of the polyimide coating fiber which concerns on the 2nd Embodiment of this invention. It is a correlation diagram of the transmission loss which shows the experimental result which concerns on Example 1 of this invention, and oxygen concentration in a final curing furnace. It is explanatory drawing which shows the coating part and hardening part of the manufacturing apparatus of the conventional polyimide coating fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass fiber 2 Polyimide coated fiber 10, 20 Coating apparatus of polyimide coated fiber 11 Coating apparatus 12, 24, 25 First curing furnace 13, 26 Second curing furnace 14, 27 Third curing furnace 15, 28, 29 Guide rollers 21-23 First to third coating devices

Claims (4)

In the polyimide curing process in which the drawn glass fiber is coated with a polyimide resin and cured,
A volatilization process that volatilizes most of the solvent contained in the polyimide resin while suppressing the curing of the polyimide resin, a temporary curing process that volatilizes the remaining solvent and accelerates the curing of the polyimide resin, and after temporary curing, And a main curing process that volatilizes the remaining solvent so that it hardly remains and accelerates the curing of the polyimide resin to be complete.
The process in each of the processes is performed using different curing furnaces, and the heating temperature in each of the curing furnaces has a temperature gradient so as to increase in the order of the processes . Production method. 2. The method for producing a polyimide-coated fiber according to claim 1, wherein the heating temperature in each of the curing furnaces has a temperature gradient such that the incoming line side is low and the outgoing line side is high. Curing oven used in the curing process, the inside of the furnace with an inert gas atmosphere, the polyimide coated fiber according to claim 1 or 2, characterized in that the oxygen concentration in the furnace and 100ppm or less Production method. The said polyimide hardening process repeats the said series of processes at least twice or more , The manufacturing method of the polyimide coated fiber of any one of Claim 1 to 3 characterized by the above-mentioned.

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