JPH0468251B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a silica glass optical transmission body, and more particularly to a manufacturing method for a silica glass optical transmission body that has excellent heat resistance and radiation resistance. [Conventional technologies and their problems] There has been a strong effort to develop optical transmission bodies with excellent radiation resistance to enable communication in high-temperature and radiation environments or to monitor inside nuclear reactors. It is requested. A quartz glass optical transmitter (hereinafter referred to as an "optical transmitter"), which is made by drawing a quartz base material and applying a precoat layer to it, is generally extremely superior to multi-component glass optical transmitters. Although it is expected to meet the above-mentioned demands because of its high radiation resistance, it has not yet been able to satisfy the requirements because there is no precoat layer that has both heat resistance and radiation resistance. The present inventors have been conducting intensive research to develop an optical transmitter with a precoat layer that has excellent heat resistance and radiation resistance. Based on this new idea, we continued our research on the formation of a precoat layer of wholly aromatic polyimide and discovered the following problems. That is, when coating a quartz glass core with a wholly aromatic polyimide, the wholly aromatic polyimide is coated while being dissolved in a solvent, then passed through a heating furnace to remove the solvent, and then hardened by a ring-closing reaction (imidization). )
Adopt a method to do so. However, in this method, dehydration occurs during ring closure, and since solvent removal also occurs at the same time, foaming tends to occur. In particular, this foaming is more likely to occur as the heating temperature during curing is higher and as the polyimide layer is thicker. Foaming not only causes poor appearance, but also reduces strength and may adversely affect the properties required as an optical transmission material. For this reason, it is necessary to apply a coating to prevent foaming. However, if the thickness of the coating layer is made thinner to prevent foaming, the strength will decrease and uneven thickness will occur.On the other hand, if the thickness is increased, foaming will occur more easily.If the heating temperature is lowered to prevent this, curing will be slow. It has been found that sagging occurs, resulting in poor appearance. [Problems to be Solved by the Invention] Therefore, the problems to be solved by the present invention are to solve the problems that arise when manufacturing a silica glass optical transmission body having a precoat layer of the above-mentioned wholly aromatic polyimide. More specifically, the objective is to develop a new method that can form a precoat layer of sufficient thickness on a quartz glass core while preventing foaming. [Means for solving the problem] This problem can be solved by forming a precoat layer made of wholly aromatic polyimide by coating it at least twice so that the total thickness of the layer is at least 5 μm, and by coating the precoat layer made of wholly aromatic polyimide at least twice. Baking the layers
This can be solved by performing the process at a low temperature of around 200℃. In order to improve the heat resistance and radiation resistance of this type of precoat layer-equipped silica glass optical transmitter, the present inventor came up with a completely new idea of using a wholly aromatic polyamide as a precoat layer. When the precoat layer was formed using
As already mentioned above, new problems have arisen, namely the occurrence of foaming during baking of the coating layer and the difficulties associated with thick coatings to avoid this. In order to solve the above-mentioned difficulties that newly arise when forming this wholly aromatic polyimide as a precoat layer, we continued our research and found that the process was repeated multiple times at least twice so that the total thickness of the entire layer was at least 5 μm. A pre-coat layer is formed by coating, and even if the inner layer within the outermost layer is baked at a low temperature of about 200℃, a layer that is sufficiently satisfactory as a pre-coat layer is formed, and foaming is effectively prevented. It turns out it can be done. At a baking temperature of around 200°C, the closure reaction of fully aromatic polyimide is about 50 to 70%, so it is in a so-called half-baked state, but when forming at least two or more layers of precoat, it can be used as an inner layer. Even with this degree of baking (ring closure rate), the entire precoat layer of the silica glass optical transmission body has sufficiently satisfactory characteristics. This point can also be said to be a new discovery of the present invention. It is well known in the electric wire industry that magnet wires are coated with polyimide varnish many times as an insulating layer and then baked. Baking is usually carried out at a high temperature of 400°C or higher, which is common knowledge in the industry.
Therefore, in the present invention, the method of baking wholly aromatic polyimide in a semi-hardened state (semi-baked state) is itself a completely new method that has not been seen in the common sense of those skilled in the art. I can do it. [Function and structure of the invention] In the present invention, in the method for manufacturing a silica glass optical transmission body having a precoat layer made of polyimide, (a) using a wholly aromatic polyimide as the polyimide; ) The pre-coat layer must be formed by coating at least twice, with a total thickness of at least 5 μm, and (c) The pre-coat layer within the outermost layer must be baked at 200°C.
The basic gist is to create a semi-hardened state at the front and back. By using these three technical means in combination, in other words, by adopting the means (b) and (c) above when forming a precoat layer made of wholly aromatic polyimide on quartz glass,
Surprisingly, without any foaming,
Even if the inner coating layer is semi-cured,
The entire precoat layer is a layer having sufficient practical characteristics as a precoat layer for a silica glass optical transmission body. At this time, as shown in the examples and comparative examples below,
For example, from the comparison between Example 1 and Comparative Example 1, 1
When semi-cured only once (Comparative Example 1), the effect as a pre-coat layer is poor, and when half-baked, the pre-coat layer lacks strength, whereas in Example 1, it has sufficient strength and no foaming. A precoat layer is formed. Further, when comparing Examples 1 and 2 with Comparative Examples 1 and 2, even if the coating is applied twice, foaming occurs when the inner layer is baked at 400° C. or higher. To explain the method of the present invention with reference to the drawings, a core 3 is created by drawing a quartz glass base material 1 while melting it in a melting furnace 2 according to a conventional method. The solution is passed through a first-stage die 4 to form a first-stage coating layer 5, and then passed through a first-stage curing furnace 6.
The precoat layer 7 is cured at about 200° C. and then passed through a wholly aromatic polyimide solvent solution through the second die 8 to form the second coating. A coating layer is formed and similarly cured in the second stage curing furnace 9. Although FIG. 1 shows a case in which the final curing is performed using a curing furnace 10, this curing furnace 10 is not necessarily necessary. This curing furnace 1
0, the curing in the curing furnace 9 is as follows:
Semi-cure at around 200℃. After curing, it is wound up by a winding machine 11. In this drawing, coating is performed in three stages, but the present invention is not necessarily limited to two stages, and can also be performed in two or four or more stages. In this case, the necessary number of dies and hardening furnaces may be provided and the material may be passed through these. As the wholly aromatic polyimide used in the present invention, the following can be exemplified as preferable. That is, the following general formula (However, R ₁ and R ₂ in the formula are the same or different,
An aliphatic, alicyclic, aromatic or heterocyclic tetravalent organic group having about 4 to 50 carbon atoms, preferably 6 to 20 carbon atoms, containing at least 30 mol% of an imide group represented by Preferably used. As this imide group, an imide group of polyimide is used, which is produced by reacting a diamine or diisocyanate with a tetracarboxylic acid or a derivative thereof, and then heating the obtained polyamic acid to convert it into polyimide. .
Examples of the diamine in this case include m-phenylenediamine, p-phenylenediamine, 2,
2'-bis(4-aminophenyl)propane, 4,
4'-Di-aminodiphenyl methane, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4' diaminodiphenyl ether,
2,6-diaminopyridine, bis(4-aminophenyl)diethylsilane, bis(4-aminophenyl)diphenylsilane, benzidine, 3,3'-
Dichlorobenzidine, 3,3'-dimethoxybenzidine, bis(4-aminophenyl)ethylphosphine oxide, 4,4'-diaminobenzophenone, bis(4-aminophenyl)phenylphosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, aminophenyl)-
N-butylamine, bis(4-aminophenyl)
-N-methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, N-(3-aminophenyl)-4-aminobenzamide, 4-aminophenyl-3-aminobenzoate , 2,4-bis(β-amino-t-butyl)toluene, bis-(p-β-amino-t-
butylphenyl) ether, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, m-xylylenediamine, p-xylylenediamine, bis( Preferred examples include 4-aminophenyl)-N-phenylamine and mixtures of two or more thereof. Examples of the diisocyanate include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate,
Cyclobutene 1,3-diisocyanate, cyclohexane-1,3 and 1,4-diisocyanate, 1,3 and 1,4-phenylene diisocyanate, 2,4 and 2,6-tolylene diisocyanate, and two or more of these An example is a mixture of Examples of the tetracarboxylic acid or its derivative used in the present invention include pyromellitic dianhydride, 2,3,6,7-naphthalene-tetracarboxylic dianhydride, 1,
2,5,6-naphthalene-tetracarboxylic acid anhydride, 3,4,9,10-pyrylenetetracarboxylic acid dianhydride, naphthalene-
1,2,4,5-tetracarboxylic acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride , 2,3,6,7-tetrachloronaphthalene-1,4,5,8,-tetracarboxylic acid dianhydride, phenanthrene-
1,8,9,10-tetracarboxylic acid dianhydride, pyridine-2,3,5,6-tetracarboxylic acid dianhydride, benzene-1,2,
3,4-tetracarboxylic acid dianhydride,
Preferred examples include thiophene-2,3,4,5-tetracarboxylic acid dianhydride and mixtures of two or more thereof. As the polyimide used in the present invention, a normal polyimide is used, and more specifically, an imide group represented by the above general formula (1) is substantially
A polyimide containing 100 mol% is used. As a specific example, for example, U.S. Patent Specification No.
Polyimides described in US Patent No. 2710853, US Patent No. 2712543, US Patent No. 2731447, US Patent No. 2880230, US Pat.
Examples include the polyamideimides described in No. 4329397, etc., and the polyesterimides described in No. 4329397. These are usually coated in the form of a solvent solution and cured by a curing process, usually by heating, to form the desired polyimide. The solvent used at this time may be any solvent as long as it can dissolve each of the above components. The final thickness of the precoat layer made of wholly aromatic polyimide in the present invention is at least 5 μm as a whole. When forming the final thickness, this is divided into at least two times. The optical transmission body of the present invention includes various optical transmission bodies, such as optical fibers for communication, optical fibers for illumination, and multiple optical fibers used as image transmission bodies such as fiberscopes. [Effects of the Invention] In the present invention, the polyimide precoat layer is coated at least twice,
Moreover, since the inner layer is half-baked, foaming that occurs when forming a thick precoat layer can be prevented, and since the inner layer has a predetermined thickness as a whole, there is almost no decrease in mechanical strength. Further, no foaming occurs, and no sagging or poor appearance occurs due to this. <Example> The present invention will be specifically described below with reference to Examples. Examples 1 to 2 A precoat layer was formed by a two-stage coating method on a light transmitting body for illumination according to the method shown in FIG. 1 and the conditions shown in Table 1. Note that the curing furnace 10 was not used. The results are also listed in Table 1.
However, "Pyralin" in Table 1 indicates the trade name of a wholly aromatic polyimide manufactured by DuPont.

【table】

[Table] Comparative Examples 1 to 2 Testing was carried out under the conditions shown in Table 2 without using the second-stage coating of the apparatus shown in FIG. The results are shown in Table 2.

[Table] As is clear from the above examples and comparative examples,
When the coating was applied in two stages, no foaming occurred and the appearance was good.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing the method of the present invention. 1... quartz glass base material, 2... melting furnace, 3...
Core, 4... First stage die, 5... First stage coating layer, 6... First stage curing furnace, 7... Precoat layer, 8... Second stage die, 9... Second stage hardening furnace, 10...Final hardening furnace, 11
... Winding bobbin.

Claims (1)

[Claims] 1. A method for manufacturing a silica glass-based optical transmitter having a precoat layer made of polyimide, using wholly aromatic polyimide as the polyimide, and coating the precoat layer with a total thickness of at least 5 μm or more at least twice. Along with forming
A method for manufacturing a silica glass optical transmission body, characterized in that the internal coating layer is baked in a low temperature range of about 200°C.