JPH04327218A - Melt-spinning apparatus for molten pitch - Google Patents

Abstract

PURPOSE:To stably produce a carbon fiber having uniform fiber diameter in high efficiency using a molten pitch raw material by placing a thin heat- insulation layer at the lower side face of a nozzle plate and heating the nozzle plate from the outer circumference as well as from the center. CONSTITUTION:A thin heat-insulation layer having a thickness of <=20mm is formed on the lower side face of a nozzle plate 4 of a molten pitch spinning apparatus. The nozzle plate has a heater 2 at the center and a spinning cylinder 8 provided with a hot-air supplying function at the outlet side of the spinning nozzle. The nozzle plate is heated from outside as well as from the center and hot air is supplied from the spinning nozzle toward the lower face of the nozzle plate. A carbon fiber having uniform fiber diameter can be produced under stable melt-spinning condition in high efficiency using a molten pitch raw material.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a melt-pitch spinning apparatus for producing pitch-based carbon fibers, and particularly for efficient melt-spinning under stable conditions to produce pitch-based carbon fibers with uniform diameter. The present invention relates to a melt spinning apparatus that can be easily implemented.

0002

2. Description of the Related Art Carbon fibers have excellent strength and elastic modulus, and are therefore used in various fields as reinforcing fibers for high-performance composite materials. Among them, pitch-based carbon fibers are less expensive as raw materials than polyacrylonitrile-based fibers, and have a high carbonization yield, resulting in a high elastic modulus of the produced fibers, so their uses are gradually expanding. ing.

By the way, pitch-based carbon fibers are produced by performing melt pitch spinning followed by infusibility treatment and carbonization treatment, but the most important thing to pay attention to at this time is the melt spinning process. That is, since the quality and performance of pitch-based carbon fibers are mostly determined by the quality of the melt-spinning process, most of the improvement techniques have focused on the melt-spinning process.

[0004] In particular, the fiber diameter distribution (variation), which is one of the important qualities of pitch-based carbon fibers, is an important control item when producing a large number of fibers using a multi-hole nozzle. In other words, for carbon fibers that are often handled as fiber bundles such as 1K to 12K (K = 1000 fibers), it has been confirmed that when the dispersion in fiber diameter increases, the strength of the fiber bundle decreases significantly. The permissible value for the fiber diameter distribution is 5 to 6% in terms of coefficient of variation.

[0005] When melt-spinning pitch-based carbon fiber,
Normally, a nozzle plate with 500 to 1000 nozzles is used, and pitch-based raw materials (particularly mesophase pitch) melted at high temperature and pressure are discharged from the nozzles and drawn in air to form fine fibers. The dimensional accuracy and temperature distribution of each nozzle are factors that determine the fiber diameter distribution at time.

Among these, the dimensional accuracy of each nozzle directly affects the fiber diameter distribution, and the diameter of the nozzle ranges from 0.1 to 0.
It is very small at 3mm, and there is a limit to machining accuracy, so it is difficult to improve the accuracy beyond the current level. Furthermore, the temperature distribution within the nozzle plate also has a large effect on the viscosity of the molten pitch raw material discharged from each nozzle, and therefore has a close relationship with the fiber diameter distribution.

[0007] In particular, the melt viscosity of mesophase pitch changes significantly depending on the temperature, so even a slight temperature variation of, for example, 3 to 5°C can cause the viscosity to change significantly, and the difference in flow resistance when ejected from each nozzle causes the fiber to This causes the diameter distribution to widen. Incidentally, the present inventors have confirmed that when the temperature of mesophase pitch changes by 3°C, the fiber diameter increases or decreases by about 8% due to the accompanying increase or decrease in viscosity.

[0008] The diameter of the nozzle plate in a normal melt spinning apparatus is generally about 200 to 300 mm, and the external heater is usually provided on the outer circumferential side of the nozzle plate, so the nozzle plate has a considerable temperature in the central direction. This creates a gradient, which causes variations in fiber diameter.

[0009] Several methods have therefore been proposed to reduce the temperature distribution of the nozzle plate. For example, JP-A-62-62916 discloses a method of suppressing heat radiation from the nozzle plate surface by providing a heat insulating layer on the front side of the nozzle plate excluding the nozzle openings.

However, this method focuses on keeping the nozzle discharge surface at a high temperature by suppressing heat radiation from the nozzle plate surface, and although temperature variations are somewhat alleviated by suppressing heat radiation, the nozzle It is not possible to sufficiently eliminate the temperature gradient that occurs toward the center of the plate.

[0011] Also, in Japanese Patent Application Laid-open No. 19412/1983,
Disclosed is a heat-retaining cylinder arranged in front of the nozzle plate, and a hot gas flow is evenly sprayed from the heat-retaining cylinder toward the center of the nozzle plate, thereby maintaining the temperature of the entire nozzle plate uniformly. has been done. However, this thermal cylinder has a complicated and large-scale structure.
There are problems with equipment costs and operability. Moreover, considering the stability of spinning, it is known that if excessive heat is applied in the spinning tube where the spun product is drawn, the pitch will become too soft and yarn breakage will easily occur. The above adaptation is thought to be difficult. Furthermore, even with this method, it is not possible to eliminate the temperature gradient that occurs from the outer circumferential side of the nozzle plate toward the center.

0012

SUMMARY OF THE INVENTION The present invention has been made by focusing on the problems of the prior art as described above, and its purpose is to reduce the temperature from the outer circumferential side of the nozzle plate toward the center using a simple structure. Melted pitch that eliminates gradients and maintains a uniform temperature across the nozzle plate, which allows efficient production of homogeneous pitch-based carbon fibers with a small fiber diameter distribution without causing yarn breakage during the spinning process. The purpose is to provide a spinning device.

[0013]

[Means for Solving the Problems] The structure of the melt pitch spinning apparatus according to the present invention that can solve the above problems is that in the melt pitch spinning apparatus equipped with a heat insulating material layer, the heat insulating material layer is provided at least on the nozzle plate. The thickness is 20m
m or less, a heater is provided in the center of the nozzle plate, and a spinning tube with a hot air supply function is arranged on the outlet side of the spinning nozzle, and the above-mentioned heat insulating material layer By placing a heat radiation suppression plate such as aluminum foil underneath, the heat radiated from the bottom surface of the heat insulating material layer can be suppressed due to changes in emissivity, making it possible to reduce heat radiation even more efficiently. It becomes possible to maintain a more uniform temperature, further suppressing variations in fiber diameter, and further increasing spinning stability.

[0014]

[Function] The structure and effects of the present invention will be explained below with reference to the drawings, but the present invention is not limited to what is shown in the drawings, and may be modified as appropriate within the scope of the spirit described above. Of course, it is also possible to implement the system with design changes, and all of these are included in the technical scope of the present invention.

FIG. 1 is a schematic vertical cross-sectional view of the main parts illustrating a molten pitch spinning apparatus according to the present invention, in which 1 is a spin block constituting a molten pitch tank, 2 is an external heater, 3 is a filter, and 4 is a A nozzle plate having a large number of discharge nozzles N, 5 a central heater, 6 a heat insulating layer, 7 a heat radiation suppressing plate, 8 a spinning tube, 9 a spun fiber, and 10 a winding roll.

As shown in the figure, the present invention is different from the conventional example in that the spin block 1, nozzle plate 4, etc. are heated by an external heater 2, and melt spinning is performed while heating the melt pitch P to an appropriate temperature. does not change. However, in the present invention, as a means for eliminating the temperature gradient from the outer periphery toward the center of the nozzle plate 4, a center heater 5 is attached to the center of the nozzle plate 4 so that the nozzle plate 4 can be heated from the center as well. I have to.

Moreover, the lower surface side and center part of the nozzle plate 4 excluding the part where the discharge nozzle group N is opened, the spin block 1, the external heater 2, and the center heater 5
A heat insulating material layer 6 is also provided on each lower surface side to prevent heat dissipation toward the lower surface from which the molten pitch is discharged. As a result, the entire nozzle plate 4 is maintained at a uniform temperature due to the heating from the outer circumferential side and the central direction by the external heater 2 and the central heater 5 and the heat dissipation prevention effect by the heat insulating layer 6.

Furthermore, below the nozzle plate 4, etc.,
A spinning tube 8 equipped with a hot air supply mechanism is provided, and by sending warm air from the spinning tube 8 at a temperature of about room temperature to 80° C. to maintain the lower temperature of the nozzle plate 4 at a lower temperature, spinning can be carried out. The structure is such that the material is slowly cooled to lower its temperature, thereby allowing smooth spinning and winding without causing yarn breakage.

The heat insulating material layer 6 used in the present invention has the function of suppressing heat dissipation from the nozzle plate 4 and maintaining a uniform temperature of the entire nozzle plate 4 as described above, and also functions to maintain a uniform temperature of the nozzle plate 4 as a whole. Although it exhibits the effect of suppressing the temperature rise on the lower side, it has become clear that the thickness t should be suppressed to 20 mm or less for the reasons described later.

That is, since the heat insulating material layer 6 cannot be provided in front of the N group of discharge nozzles on the nozzle plate 4, it is impossible to prevent heat dissipation from this part downward. Therefore, as the heat insulating layer 6 becomes thicker, the recess 11 formed in front of the discharge nozzle group becomes deeper, making it difficult for warm air blown from above the spinning tube 8 to reach into the recess 11. , it becomes difficult to lower the temperature of this part, and thread breakage is more likely to occur in this part. However, if the heat insulating material layer 5 is kept thin, the warm air can be sufficiently distributed inside the recess 11 and the temperature of this area can be lowered reliably.
The problem of thread breakage is also solved.

[0021] As described above, in the present invention, since a relatively thin heat insulating material layer 6 is used, depending on the type of heat insulating material, the effect of preventing heat dissipation may be insufficient. Therefore, in consideration of this, a heat radiation suppression plate 7 such as aluminum foil is provided on the lower surface side of the insulation layer 6, and the radiation heat from the lower surface of the insulation layer 6 is reduced due to the lower emissivity. , heat dissipation can be further suppressed, which is extremely effective in carrying out the present invention.

[0022]

【Example】

Example 1 Using mesophase pitch with 100% anisotropic phase as a raw material, melt spinning was carried out using a melt spinning device equipped with a nozzle plate with a nozzle diameter (diameter) of 0.15 mm, a land length of 0.30, and a nozzle number of 500. went. The nozzle plate is equipped with an external heater on the outer periphery and a central heater in the center so that it can be heated from the outer periphery and the center. A silica-based heat insulating material layer with a thickness of 15 mm was pasted on. Further, aluminum foil was attached to the lower side of the heat insulating material layer.

[0023] The heating temperature of both the external heater and the central heater is set to 345°C to heat the nozzle plate, and a spinning cylinder is disposed at the bottom of the nozzle plate, and the heating temperature is set to 45°C at the bottom of the nozzle plate. Pitch was melt-spun while supplying hot air at a flow rate of 30 liters per minute, and fibers with a fiber diameter of 10.5 μm were wound up at a rate of 350 m/min.

When the fiber diameter distribution of each bundle of 500 fibers obtained was examined, the coefficient of variation was as small as 2.51, indicating that the fiber diameter distribution was narrow and homogeneous.

Example 2 Mesophase pitch with 100% anisotropic phase was used as a raw material, and a melt spinning device equipped with a nozzle plate having a nozzle diameter (diameter) of 0.20 mm, a land length of 0.40, and 250 nozzles was used. Melt spinning was performed. The nozzle plate is equipped with an external heater on the outer periphery and a central heater in the center so that it can be heated from the outer periphery and the center. A silica-based heat insulating material layer with a thickness of 20 mm was pasted on. Further, aluminum foil was attached to the lower side of the heat insulating material layer.

[0026] The heating temperature of both the external heater and the central heater is set to 342°C to heat the nozzle plate, and a spinning cylinder is disposed at the bottom of the nozzle plate, and the heating temperature is set to 50°C at the bottom of the nozzle plate. Pitch was melt-spun while supplying warm air at a flow rate of 40 liters per minute, and fibers with a fiber diameter of 11.8 μm were wound at a rate of 300 m/min.

When the fiber diameter distribution of each bundle of 250 fibers obtained was examined, the coefficient of variation was as small as 3.24, indicating that the fiber diameter distribution was sufficiently small and homogeneous.

Comparative Example 1 Mesophase pitch with 100% anisotropic phase was used as a raw material, and a melt spinning device equipped with a nozzle plate having a nozzle diameter (diameter) of 0.15 mm, a land length of 0.30, and 500 nozzles was used. Melt spinning was performed. The nozzle plate is equipped with an external heater on the outer periphery and a central heater in the center so that it can be heated from the outer periphery and the center. A silica-based heat insulating material layer with a thickness of 35 mm was pasted on. Further, aluminum foil was attached to the lower side of the heat insulating material layer.

Then, the heating temperature of both the external heater and the central heater is set to 345°C to heat the nozzle plate, and a spinning cylinder is disposed at the bottom of the nozzle plate, and the heating temperature is set to 200°C at the bottom of the nozzle plate. Pitch was melt-spun while supplying hot air at a flow rate of 40 liters per minute, and fibers with a fiber diameter of 10.8 μm were wound up at a rate of 300 m/min.

When the fiber diameter distribution of each bundle of 500 fibers obtained was examined, the coefficient of variation was as large as 9.37, and the fiber diameter distribution was extremely wide.

Comparative Example 2 Mesophase pitch with 100% anisotropic phase was used as a raw material, and a melt spinning device equipped with a nozzle plate having a nozzle diameter of 0.20 mm, a land length of 0.40, and 250 nozzles was used. Melt spinning was performed. The nozzle plate is equipped with an external heater on the outer periphery and a central heater in the center so that it can be heated from the outer periphery and the center. A silica-based heat insulating material layer with a thickness of 50 mm was pasted on. Further, aluminum foil was attached to the lower side of the heat insulating material layer.

[0032] The heating temperature of both the external heater and the central heater is set to 345°C to heat the nozzle plate, and a spinning tube is disposed at the bottom of the nozzle plate, and the heating temperature is set to 150°C at the bottom of the nozzle plate. Pitch was melt-spun while supplying hot air at a flow rate of 40 liters per minute, and fibers with a fiber diameter of 12.6 μm were wound at a rate of 250 m/min.

[0033] However, in this melt spinning process, yarn breakage frequently occurred and stable spinning properties could not be obtained. Furthermore, when the fiber diameter distribution of the obtained fibers was examined, the coefficient of variation was as large as 10.38, and the fiber diameter distribution was extremely wide and non-uniform.

[0034]

[Effects of the Invention] The present invention is constructed as described above, and it is possible to eliminate the temperature gradient in the nozzle plate and keep the temperature of the entire nozzle group as uniform as possible, and furthermore, it is possible to maintain the temperature of the entire nozzle group as uniform as possible. Since the carbon fibers are uniformly and slowly cooled by hot air immediately after being discharged, pitch-based carbon fibers with less variation in fiber diameter can be produced smoothly and efficiently without causing yarn breakage or the like.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional explanatory diagram of a main part showing an embodiment of the present invention.

[Explanation of symbols]

1 Spin block 2 External heater 3 Filter 4 Nozzle plate 5. Central heater 6 Insulation material (layer) 7 Heat radiation suppression plate 8 Spinning tube 9 Spun fiber 10 Take-up roll 11 Recessed part P Melt pitch N Nozzle

Claims (2)

[Claims] [Claim 1] In a melt pitch spinning apparatus equipped with a heat insulating material layer, the heat insulating material layer provided at least on the nozzle plate has a thickness of 20 mm or less, and a heater is provided in the center of the nozzle plate, and the spinning nozzle exit side is provided with a heater. A melt spinning device for melt pitch, characterized in that a spinning tube equipped with a hot air supply function is arranged. 2. The melt spinning apparatus according to claim 1, further comprising a heat radiation suppressing plate provided on the lower surface of the heat insulating layer.