JPH0365533A - Method for coating optical fiber - Google Patents

Abstract

PURPOSE:To suppress eccentricity by regulating the ratio of a straight length in a nozzle part to a nozzle inside diameter of a pressurizing type die and viscosity of a coating material at a prescribed temperature and shearing rate within a specific range. CONSTITUTION:A coating material 6 is fed from a pressurized vessel 7 through a pipeline 8 under pressure to a nozzle part 5 of a pressurizing type die constructed of an upper holder 1, a lower holder 2, a nozzle 3 mounted therein and a nipple 4. The coating material having a viscosity (mu) within the range expressed by the formula at 25 deg.C and a shearing rate I(sec<-1>) is pressed into the nozzle part at a ratio of the straight length L(mm) thereof to the nozzle inside diameter 2R0(mm) under a pressure P(kg/cm<2>) applied thereto and a fiber having an outside diameter 2Ri(mm) before coating is then drawn and passed therethrough at a take-off speed Vf(m/min) to form a coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of coating a cladding material in the production of quartz-core or plastic-core optical fibers, and in particular to a method of coating a cladding material by passing the fiber through a pressurized die. The present invention relates to a coating method for optical fibers.

[Conventional technology]

Optical fiber A method in which a quartz base material is heated and melted, thinned to form a fiber, and this fiber is continuously coated with a cladding material, or a thermoplastic is melt-spun to form a fiber, and a cladding material is continuously applied to this fiber. A commonly used method for coating materials is to pass the fiber through an open, non-pressurized die and coat the fiber.

However, in this method, as the moving speed of the fiber increases, the shear rate of the coating material on the fiber surface increases, which causes a sliding phenomenon between the fiber and the coating material in the die, causing the coating layer to deteriorate. It became impossible to form the fiber, and it was not possible to perform fiber coating at high speed. In addition, since the outer diameter of the coating layer is determined only by the inner diameter of the die nozzle,
It was difficult to perform coating while keeping the outer diameter of the coating layer within a target value.

In order to solve these problems and perform coating, a method has been proposed in which coating is applied by drawing fibers through a pressurized die that has a sealed structure in which a nozzle and a nipple are integrated into the die body.

In this method, a coating material is press-fitted into a pressurized die through a supply port, and the fibers passing through a nozzle are coated. In this method, by applying pressure to the coating material in the die and extruding it, it is possible to avoid the slipping phenomenon seen in open die coating, and therefore, high-speed coating is possible. Furthermore, by adjusting the pressure applied to the die,
It becomes possible to perform coating while keeping the outer diameter of the coating layer within a target value.

[Problem to be solved by the invention]

However, this pressurized die coating method has a major drawback in that the pressure H applied to the die tends to cause the flow of the coating material within the die to be uneven, which tends to cause eccentricity of the core material.

This eccentricity not only causes a decrease in optical performance due to deflection in clad material coatings, but also has a negative effect on the specularity of the cut surface of the core material in crimp coatings, so it affects the transmission performance of optical fibers. If the eccentricity is significant, it may lead to damage to the core due to contact with the upper nipple. For these reasons, preventing core eccentricity is an important issue in pressurized die coating.

In order to prevent this eccentricity in pressurized coating, there are methods such as rotating the exit nozzle part around the axial direction of the fiber, making a part of the coating material flow upward from the nipple part, and creating a gas flow passage. Various attempts have been made to hold the fiber at the nozzle axis and suppress eccentricity by applying pressure and causing the fiber to flow in the opposite direction to the direction in which the fiber travels, but none of these methods have been effective in preventing eccentricity. It is not a suitable method.

The present invention aims to provide a method for uniformly and stably coating an optical fiber by uniformizing the flow of the coating material within the die to prevent eccentricity of the core material in fiber coating using a pressurized die. .

[Means to solve the problem]

The present invention has been made in view of the above problems, and its gist is to apply a pressure higher than atmospheric pressure to a pressurized die equipped with a nozzle and a nipple to inject a liquid plastic coating material into the pressurized die. In this method, the fiber is supplied and the fiber is passed through a nozzle at the tip and a coating material is applied to the fiber. (mm) ratio and temperature 25℃, shear rate 1
Viscosity μ (voids) of coating material in sec-'
A method for coating an optical fiber, characterized in that the coating is performed in a range of .

Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1 is a cross-sectional view of a pressurized die according to the present invention;
FIG. 2 is a detailed view of the pressurized die nozzle section, and FIG. 3 is a sectional view of an open die showing one of the conventional methods.

In FIG. 1, the pressurized die consists of an upper holder 1, a lower holder 2, and a nozzle 3 and a nipple 4 installed inside them. be pumped.

This pressure coating method applies a certain pressure to the coating material inside the die and extrudes it from the nozzle part 5 to coat the material, so it is possible to prevent coating failure due to slippage, which is the case with non-pressure dies during high-speed coating. The coating material follows the fibers closely.

However, this pressurizing force caused non-uniform flow of the coating material in the nozzle, causing eccentricity of the optical fiber core.

The inventors of the present invention conducted extensive studies to prevent such fiber eccentricity, and as a result, they came up with the present invention.

As shown in Fig. 2, a pressurized die with a nozzle inner diameter of 2Ro and a nozzle straight length of L was heated at 25°C and at a shear rate/
Viscosity μ at 5ec-’ (hereinafter abbreviated as viscosity μ)
A coating material is press-fitted by applying a pressure P, and a fiber having an outer diameter of 2 Ri before coating is drawn through at a take-up speed Vf to form a coating layer. At this time, the factors that affect the fiber eccentricity are: - In addition to the pressure P applied to the die, - the viscosity μ of the coating material, - the nozzle inner diameter 2Ro, - the straight length of the nozzle part, and - the moving speed Vf of the fiber. However, as a result of coating examination, it became clear that
Furthermore, the effect is as follows: - nozzle inner diameter 2Ro, - slit thickness Ro-Ri formed by nozzle inner diameter 2Ro and fiber diameter 2Ri, and - pressurizing force P. The larger the eccentricity, the more the fiber speed Vf.

It was confirmed that the larger the viscosity μ of the coating material and the nozzle straight length L1, the more effective it is to suppress eccentricity.

These matters are considered as follows.

That is, if we consider the velocity distribution V of the coating material in the radial direction inside the nozzle as shown in Figure 4 (r is an arbitrary radius), the velocity V of the coating material is determined by the velocity generated by the movement of the fiber (=v, ) and the pressing force. It is given by the sum of the resulting velocities (=V,), and various velocity distribution patterns are formed depending on the values taken by Vf, P, L, μ, Ro, etc. in the above equation.

FIG. 5 is a diagram showing a representative pattern of speed distribution. The pattern indicated by a indicates a velocity distribution pattern when Vf, μ, and L are large, and the pattern indicated by an opening indicates a velocity distribution pattern when the values of P and 2Ro are large. Streamline showing the maximum velocity in the mouth pattern (the pressure is minimum at this streamline)
is separated from the fiber surface, a force F is generated from the fiber surface toward this streamline, making it extremely unstable to keep the fiber axially centered, resulting in eccentricity.

On the other hand, in pattern A, the speed of the coating material is maximum at the fiber surface, all the force F is directed toward the fiber surface, that is, the axis, and the fiber can stably pass through the axis, so eccentricity does not occur.

These are in good agreement with the coating study results, and from the above, it is clear that increasing the coating material viscosity μ and the straight length of the nozzle part is effective in suppressing eccentricity in pressurized die coating. .

Figure 6 shows the coating material viscosity μ on the vertical axis (logarithmic axis) and L
It is a graph showing a good coating area as a model based on the coating results, with the /2Ro ratio taken on the horizontal axis. The shaded area is a good area, and the ■ zone is an area where eccentricity occurs. In the figure, it can be seen that increasing the A-line viscosity μ and the L/2Ro ratio is advantageous for eccentricity.

However, beyond a certain range the viscosity μ and L/2R.

When the ratio is on the lower side, areas with coating unevenness occur due to insufficient discharge of the coating material, as shown in Figure 6 (d). This can be explained by the fact that due to excessive flow resistance in the nozzle, the velocity distribution of the coating material becomes as shown in FIG. 8, making it difficult for the coating material to follow the fibers.

As a result of a coating study, it became clear that the coating unevenness can be divided into a good area and an area with coating unevenness, with the boundary being .

That is, coating with the L/2Ro ratio and the viscosity μ of the coating material within the following ranges can be an effective means for suppressing eccentricity and coating unevenness and performing uniform fiber coating.

FIG. 7 shows a cross-sectional view of the coated fiber in each region in FIG. 6, where a represents the coating state of the r zone, b represents the good region, and C represents the coating state of the ■ zone. 9 is a core material, and 10 is a coating layer.

The coating method according to the present invention involves a process in which a quartz-based base material is heated and melted, thinned into fibers, and then coated continuously, or a thermoplastic is melt-spun to form fibers, and this fiber is continuously coated. It is suitable for use in coating processes etc. It is also possible to apply a process of further coating these core/cland coated fibers with a protective layer.

As a coating material, the polymer is made into a liquid plastic by containing a solvent in which the polymer is soluble, and the solvent is removed by heating and drying after coating. It is made of plastic, and after coating, it is irradiated with ultraviolet rays and polymerized.
A method of obtaining fibers is effective.

Polymers of the coating material used in the present invention include polymethacrylic esters or polyacrylic esters such as polymethyl methacrylate and polymethyl acrylate, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, polyfluorinated Vinyl, polyfluoroalkyl methacrylate, polyfluoroalkyl acrylate, etc. are effective.

Also,? For treatment, methyl ethyl ketone setone,
Ketones such as cyclohexane, esters such as ethyl acetate and methyl acetate, aromatic hydrocarbons such as henzene, xylene and toluene, alcohols such as methanol, ethanol and isopropyl alcohol, and mixed solvents thereof can be used.

Monomers include methyl (meth)acrylate, ethyl (meth)acrylate, vinyl acetate, styrene, vinyl chloride, vinylidene chloride, vinyl fluoride, fluorinated acrylate,
Examples include fluorinated methacrylate.

The fiber dimensions applicable to the present invention generally include a core diameter (2Ri) of 0, 15 to 2 mmφ, a coating thickness (
R-Ri) is 5 to 500-, but especially 2Ri is 0
, 2 to 1 φ, and R-Ri is 5 to 50-.

Furthermore, the method according to the present invention provides a fiber moving speed vr
It is particularly effective at speeds of 5 to 70 m/min, but it is also applicable at higher speeds of 100 to 200 m/min. It was revealed that preventing eccentricity is beneficial when the fiber moving speed Vf is high, but in order to avoid coating failure due to slipping on the fiber surface, the value of the pressurizing force P is set to be higher than that at low speeds. Since it is necessary to increase the displacement, eccentricity tends to occur, and in order to prevent this, the method of the present invention moves to the right even at high speeds.

FIG. 9 shows a nozzle shape that can be used in the present invention.

The shape of the fiber prosthesis is tapered as shown in A, mouth, and C.
Either a flat shape or a reverse tapered shape is possible, and the fiber exit shape can be any of the tapered shape, flat shape, and reverse tapered shape shown in 2, E, and F. Furthermore, these straight lines may be used as smooth I-output lines, and any combination of the shapes of the inlet and outlet portions described above is possible.

Coatings were applied at fiber speeds of 5-70 m/min. Methacrylic resin 0, 3 as core fiber
Immediately after coating, the coating film was polymerized and cured using a Toshiba ultraviolet lamp to form a fiber.

The results of these experiments are shown in Table 1.

The viscosity of the coating material is 25°C and a shear rate of 1.
sec"' value (measured with a cylindrical rotational viscometer)
shows.

[Specific Examples] The present invention will be further explained below with reference to Examples and Comparative Examples.

Examples 1 to 5 Comparative Examples 1 to 4 Methyl methacrylate monomer was used as the coating material, polytetrafluoropropyl methacrylate was used as the thickener, and Irgacure 651 (photosensitizer manufactured by Chiha Geigy) was added to give various viscosities. Liquid brass tink is prepared, and it is applied with a pressure of 1 to 4 kg/cJ using a pressurizing die shown in Fig. 1.

Table 1 [Effects of the Invention] As explained above, according to the present invention, a coated optical fiber that is stable in the longitudinal direction of the fiber and free from eccentricity and coating rings can be manufactured without requiring any special additional equipment or skill. I can do it.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a pressurized die used in the method of the present invention, Fig. 2 is a detailed sectional view of the nozzle part of the pressurized die, Fig. 3 is a sectional view of an open die showing the conventional method, and Fig. 4. is a model diagram showing the velocity distribution in the nozzle, Figures 5 and 8 are model diagrams showing the velocity distribution pattern, Figure 6 is a graph showing a model area for good coating, and Figure 7 is a model diagram showing the velocity distribution pattern. FIG. 6 is a cross-sectional view of the fiber showing the coating state in each region, and FIG. 9 is a view showing the shapes of the nozzle inlet and outlet. l... Upper holder 2... Lower holder 3.
... Nozzle, 5... Nozzle part, 7... Pressurized container, 9... Core material, 4... Nipple, 6... Coating material, 8... Pipeline, 10... coating layer.

Claims (1)

[Claims] 1. A liquid plastic coating material is supplied into a pressurized die equipped with a nozzle and a nipple by applying a pressure higher than atmospheric pressure, and the fiber is drawn through the nozzle at the tip. This is a method of applying a coating to the inner diameter of the narrowest part of the tip channel, that is, the inner diameter of the nozzle 2.
Nozzle straight length L relative to Ro (mm)
(mm) ratio and temperature 25℃, shear rate 1s
An optical fiber coating method characterized by coating the viscosity μ (poise) of the coating material at ec^-^1 within the range of ▲numerical formula, chemical formula, table, etc.▼.