JPH0380124A - Method for cleaning inside of glass pipe for optical fiber - Google Patents

Abstract

PURPOSE:To increase cleaning efficiency by coating the outside of a glass pipe with an etching resistant and thermally shrinkable tube, immersing the coated glass pipe in a glass etching soln. and cleaning the inside of the glass pipe. CONSTITUTION:A glass pipe is put in an etching resistant and thermally shrinkable tube of PVC resin, 'Teflon(R)' resin, PE resin, etc., having a slightly larger dimension, than the outside diameter and length of the glass pipe and the outside of the glass pipe is coated with the tube by heating. The glass pipe is then immersed in an HF soln. having 5-10% concn. or a mixed acid soln. contg. HF, HNO3, HCl, H2SO4 and NH4F for 30-120min and the inside of the glass pipe is uniformly etched to 5-100mum depth.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning the inner surface of a glass tube for optical fibers, and more specifically to a method for cleaning the inner surface of a glass tube for coating optical fibers for image guides.

[Prior art and its problems] In order to manufacture optical fibers for image guides, a core glass made of multi-component glass such as lead silicate glass formed into a round rod shape is inserted into a tubular cladding made of borosilicate glass or soda lime glass. After inserting it into glass, heating, stretching and convergence are repeated several times to form each piece to a diameter of 5 to 12 μm.

By the way, optical fibers for image guides are required to transmit optical information precisely and faithfully, so it is important that the glass used for this has no optical defects, but it is important that the glass used for this is free from optical defects. In the process of manufacturing borosilicate glass tubes and soda lime glass tubes, there is a problem in that various optical defect factors are likely to be formed on the inner surface of the tubes.

In other words, when manufacturing the above-mentioned glass tube, the glass is melted in a refractory melting kiln, cooled and supplied to a refractory sleeve, and the tube is drawn and formed by blowing air with a low-pressure blower. In this case, reaction products between the glass and the refractory are likely to precipitate on the inner surface of the glass tube, and bubble streaks are likely to occur due to foaming from the refractory. Also, in rare cases, fine metal rust or refractory pieces in the air supplied from a low-pressure blower may adhere to the inner surface of the glass tube. If a glass tube containing these reaction products, bubble streaks, and attached foreign matter is heated as a clad glass together with a core glass, devitrification and foaming will occur at the interface between the clad glass and the core glass, which will significantly deteriorate the quality of the optical fiber. Become.

From the above, in order to produce high-quality optical fibers, it is necessary to prevent devitrification and foaming from occurring at the interface between the clad glass and the core glass by removing reaction products, bubble streaks, and adhering foreign matter from the inner surface of the glass tube. However, for this purpose, it is effective to clean the glass tube with a glass-eroding solution.

However, in general, fine scratches such as roller scratches and cutting chute scratches are easily formed on the outer surface of glass tubes during the tube manufacturing process, and if a glass tube with such scratches is cleaned with a glass-eroding solution, the scratches will expand. However, in the subsequent process, problems arise in that foreign matter tends to adhere there and the appearance becomes poor.

[Objective of the Invention] The present invention has been made in view of the above circumstances, and is intended to remove reaction products, bubble streaks, or foreign matter adhering to the inner surface of a glass tube used as cladding glass for optical fibers. The purpose of this invention is to provide a method for cleaning.

[Structure of the Invention] The method of cleaning the inner surface of a glass tube for optical fiber according to the present invention includes coating the outer surface of the glass tube with a corrosion-resistant and heat-shrinkable tube, and then immersing the tube in a glass corrosive solution. It is characterized in that the inner surface of the glass tube is cleaned.

As the glass corrosive solution used in the present invention, hydrofluoric acid alone or a mixed acid solution of hydrofluoric acid, nitric acid, hydrochloric acid, sulfuric acid, or ammonium fluoride is suitable. The concentration is preferably 3 to 10%, and depending on the concentration, the glass tube is immersed for 30 to 120 minutes to uniformly erode the inner surface to a depth of 5 to 100 μm.

Further, the corrosion-resistant and heat-shrinkable tube has the property that it is not corroded by the above-mentioned glass-corrosive solution, and also has the property that it shrinks when heated. The tube has dimensions slightly larger than the outer diameter and length of the glass tube, and after pushing the glass tube into it,
When heated, it contracts and adheres tightly to the glass tube. Furthermore, it is desired that the tube be easily removable after cleaning the glass tube, and from the above point of view, specifically, polyvinyl chloride resin, Teflon resin, polyethylene resin, etc. are preferable, and the wall thickness of the tube is The thickness is preferably 0.3 mm or more to prevent scratches on the outer surface of the glass tube during handling after coating.

[Example code] The present invention will be explained below based on examples.

First, soda lime glass is drawn into a tube and cut into a tube with an outer diameter of 18φ, a wall thickness of 2.8mm, and a total length of 500mm.
A glass tube with dimensions of was fabricated. When the inner surface of this glass tube was observed using a polarizing microscope, the presence of reaction products with the refractory and minute cracks caused by the refractory were observed. After that, this glass tube was made into an outer diameter of 20φ and a wall thickness of 0.
Insert it into a polyvinyl chloride resin tube having dimensions of 5 mm and total length of 600 mm, place it in a hot air stove, and
The outer surface of the glass tube was coated with the tube by heating at 701°C.

Next, this glass tube was immersed in a mixed acid solution of 5% HF and 35% HNO at 25°C for 120 minutes to uniformly erode the inner surface of the glass tube to a depth of 50 μm. After washing with ethyl alcohol and further drying using an infrared heater, the inner surface was observed under a polarizing microscope, and the reaction products with the refractory and microbubble streaks were removed, and no trace of them was observed at all.

[Effects of the Invention] As described above, according to the method for cleaning the inner surface of a glass tube for optical fibers of the present invention, reaction products, bubble streaks, or attached foreign matter formed on the inner surface of a glass tube used for clad glass can be easily removed. Moreover, since the outer surface of the glass tube is covered with a corrosion-resistant and heat-shrinkable tube, it will not be corroded. Furthermore, since the outer surface is covered with a tube, it is possible to prevent the glass tube from being scratched during handling, and it can be efficiently cleaned by stacking multiple glass tubes and immersing them in an corrosive solution. is possible.

Claims (1)

[Claims] (1) An optical device characterized in that the outer surface of a glass tube is coated with a corrosion-resistant and heat-shrinkable tube, and then the inner surface of the glass tube is cleaned by immersing it in a glass-corrosive solution. A method for cleaning the inner surface of glass tubes for fibers.