JPH0976362A - Manufacture of polyimide tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation foreign matters and the deterioration of a core body and to have a good appearance without swelling, etc., in a method in which the solution of a polyimide precursor is applied uniformly on the peripheral surface of the core body, and the film is heated to make a tube. SOLUTION: In a method for making a polyimide tube including a process in which the solution of a polyimide precursor is applied on the peripheral surface of a core body 1, and after the core body being heated until the film 4 has at least strength as a tube, the tube is removed from the core body 1, (A) the core body 1 having a form in which a projection spreading smoothly from the peripheral surface to the bottom part of a cylinder is formed, and a recession 3 is formed in the middle part of the projection, or (B) the core body 1 having a form in which the bottom part of the cylinder is flat or recessed, and a sharp edge is formed from the peripheral surface to the bottom part of the cylinder is used, and after the peripheral surface of the core body 1 is coated with the solution of a polyimide precursor, the core body 1 is heated while being supported at its upper end part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyimide tubular article, and more specifically, a solution of a polyimide precursor is uniformly applied to the outer peripheral surface of a core and the coating film is heated to produce a tubular article. The method for producing a polyimide tubular article having a good appearance without bulging and the like, which prevents the generation of foreign matter and deterioration of the core.

[0002]

2. Description of the Related Art Heat-resistant films are used in various applications such as flexible printed boards, insulators of electric devices, and magnetic tapes. Among these heat resistant films, tubular heat resistant films are used as fixing belts for electrophotographic copying machines, facsimiles, printers and the like. That is, in an electrophotographic copying machine or the like, as a method of heating and melting the toner on the recording paper to fix the toner image on the recording paper, as a method for fixing the toner image on the recording paper with a heater through a film-shaped endless fixing belt (tubular material). There is a method of directly heating the toner. Since the fixing belt is required to have excellent heat resistance, strength, physical properties such as Young's modulus, a polyimide film having excellent heat resistance and mechanical strength is generally used. As a method for producing a tubular product made of a polyimide film, a polyimide precursor solution is applied to the outer peripheral surface of a core such as a cylindrical mold or the inner peripheral surface of a cylindrical mold, and then a liquid coating layer (coating layer) is applied. A method of heating a film to form a cured film of polyimide is known (Japanese Patent Laid-Open No. 3-180309).
No. JP-A-62-19437). Among these methods, the method of immersing the core body in the polyimide precursor solution to form a coating film of the polyimide precursor solution on the outer peripheral surface of the core body is generally used.

Specifically, a columnar core is supported at one end (upper end) thereof, and a portion below the upper end is immersed in a polyimide precursor solution, and the solution is formed on the outer peripheral surface of the core. To form a coating film consisting of. The core body on which the coating film is formed is conveyed into a heating furnace and heated until the coating film can maintain at least the strength as a tubular material. As a method of transporting the core body on which the coating film is formed, a method of supporting the lower end portion of the core body on a gantry is generally adopted. Pins (projections) on the frame
On the other hand, as shown in FIG. 4, a pin hole 5 is formed in the bottom portion of the core for fitting with the pin. The pin hole 5 needs to have a size and a depth enough to stably support the core body. The core body on which the coating film is formed is conveyed to a heating furnace and is heat-treated while being supported by a pedestal through a pin hole at the bottom. By the heat treatment, the polyimide precursor is dehydrated and ring-closed to form a polyimide. However, the polyimide precursor solution has a problem that the coating film drips at the initial stage of the heat treatment, so that the coating film sags, the pin hole is blocked, or the pedestal is soiled.
Furthermore, when the polyimide precursor solution that has blocked the pin holes or soiled the pedestal is heated to be polyimidized and hardened, the core may not be removed from the pedestal.

Therefore, conventionally, after the dipping treatment, as shown in FIG. 4, it was necessary to scrape off the coating film 4 on the lower end portion of the core 1 with a scraper 8 to remove it. However, in the method of scraping off the coating film with the scraper 8, since the residues 6 and 7 of the polyimide precursor solution are generated, it is difficult to reliably prevent the pin hole at the bottom and the mount from being soiled. The polyimide precursor solution 7 adhered around the pin holes 5 may harden between the pin holes, and the core may not come off the pins of the pedestal. Further, since the scraper 8 cannot completely scrape off the coating film on the lower end portion of the core body, the remaining coating film portion becomes a small piece after heat curing and falls off. It causes a defect. Similarly, when the polyimide scraps cured on the pin hole 7 of the core body or the pedestal are peeled off and adhered to another coating film,
It may cause foreign matter defects. Further, when scraped with a scraper 8, a peelable coating layer (glass coating, fluororesin coating layer, etc.) provided on the surface of the core body.
9 is peeled off from the scraped portion 10, the releasability is lowered, and the life of the core is shortened.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to apply a solution of a polyimide precursor uniformly to the outer peripheral surface of a core and heat the coating film to produce a tubular product, and It is an object of the present invention to provide a method for producing a polyimide tubular article which has a good appearance without swelling or the like, which prevents deterioration of the core body. As a result of intensive research to overcome the above-mentioned problems of the prior art, the present inventors did not use the conventional method of supporting the core body on the pedestal through the pin hole at the bottom, but the core body at the upper end thereof. It was conceived to adopt a method of supporting, transporting in a suspended state, and heat treatment. However, when this method is applied to an ordinary cylindrical core, there is no gas vent hole, so that the cured coating film swells during heat treatment. That is, the polyimide precursor undergoes a dehydration reaction and other side reactions during the polyimidization to generate a gas at a high temperature. When this gas accumulates inside the coating film, the resulting cured coating film (polyimide tubular material) swells and the shape is distorted. When a gas vent hole is formed in the coating film by a physical means, the release coating layer on the surface of the core body is likely to be damaged or fall off, and it may cause the generation of curing scraps.
Therefore, as a result of further research, it was found that by devising the shape of the bottom of the core body, a gas vent hole without dropping out of the polyimide pieces can be formed without adopting a means of physical contact. The present invention has been completed based on these findings.

[0006]

According to the present invention, a polyimide precursor solution is applied to the outer peripheral surface of a core, and after heating until the coating film retains at least the strength as a tubular product,
In a method for producing a polyimide tubular product including a step of taking out a tubular product from a core, as a core, a convex shape that is smoothly connected from the outer peripheral surface of the cylindrical body to the bottom is formed,
A core body having a recess formed in the convex center portion, or (B) a core body having a flat or concave bottom portion of a cylindrical body with a sharp edge formed from the outer peripheral surface to the bottom portion of the cylindrical body. A method for producing a polyimide tubular article is provided, which comprises using a body and applying a polyimide precursor solution to an outer peripheral surface of the core body, and then heating the core body while supporting the core body at an upper end thereof. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
A tubular product made of a polyimide film is generally prepared by applying a solution of a polyimide precursor to the outer surface of a core, and then heating until the coating film (coating) has a strength capable of retaining at least the structure of the tubular product. , Manufactured by removing the tubular object from the core. The degree of heating is such that the coating has at least a strength capable of retaining the structure as a tubular article. When the degree of curing (polyimidization) of the removed tubular product is insufficient, heat treatment can be performed separately. Of course, the polyimide precursor can be sufficiently cured on the core. Generally, in the case of heating, the temperature is raised stepwise in a heating furnace and heated up to about 350 ° C. to 450 ° C. to dehydrate and ring the polyimide precursor to form a polyimide. Therefore, in the core,
It is necessary to have heat resistance to withstand a high temperature of at least about 350 to 450 ° C.

As the core body, a metal core body conventionally used such as aluminum or stainless steel can be preferably used. Further, a release coating treatment layer such as a glass coating layer, a ceramic coating layer, a fluororesin coating layer or the like is usually provided on the surface of the metal core. A columnar body is preferably used as the core body, and a columnar body with a groove may be provided depending on the application, and ribs may be provided on the tubular body to be produced. Specific examples of the core of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an example of a core body (A) having a shape in which a convex shape that is smoothly connected from the outer peripheral surface of the cylindrical body to the bottom is formed and a concave portion is provided in the central portion of the convex shape. A disc-shaped support member 2, for example, is attached to the upper end of the core 1. By supporting the core body with the support member 2, the core body can be immersed in the polyimide precursor solution. A convex shape that is smoothly connected to the outer peripheral surface of the core is formed on the bottom that is one end of the core. The convex shape may be various shapes such as a hemispherical shape, a convex lens shape, and a dish shape. It is necessary that the outer peripheral surface of the core body and the convex shape of the bottom portion are smoothly connected. As shown in FIG. 1, a recess 3 is provided in the convex center portion. The cross-sectional shape of the recess 3 may be various shapes such as a hemispherical shape, a disk shape, and a dish shape.

When the core body 1 shown in FIG. 1 is dipped in a polyimide precursor solution to form a coating film 4 on the outer peripheral surface of the core body 1,
The bottom recess 3 is not filled with the polyimide precursor solution. Therefore, the core body 1 on which the coating film 4 is formed
When the sample is conveyed to a heating furnace in a state of being suspended by the support part 2 and subjected to a heat treatment, the gas generated at the time of polyimidization easily escapes to the outside from the concave portion 3 at the bottom of the core body 1, and a cured coating film ( No swelling occurs in the tubular material). As described above, when the core body (A) is used, a gas vent hole is naturally formed in the coating film, so that the treatment by physical contact for forming the gas vent hole is unnecessary, and the life of the core body is shortened. Never shrink. Also, because polyimide curing scraps do not occur,
No foreign matter defect will occur. After forming a cured coating film (tubular material), remove it from the core and cut off the end,
A tubular product having a good appearance can be obtained.

In the core (A), the ratio (b / a) of the projected area b of the recesses to the total projected area a of the bottom of the core is preferably 0.05 to 0.50, more preferably 0.10.
~ 0.40. The ratio of the depth D of the recess to the outer diameter D _A of the core (D / D _A ) is preferably 0.05.
˜0.20, more preferably 0.08 to 0.15 (FIG. 2). The outer diameter of the core is usually about 20 to 60 mm. Depending on the viscosity of the polyimide precursor solution, generally used grades (commercially available polyimide varnish; viscosity at room temperature = 800 to 2000 poise) will naturally degas holes in the coating within the above range. Is formed. If the area and depth of the dent 3 are too small, it is difficult to form natural holes in the coating film. On the other hand, if the dent 3 is too large, the polyimide precursor solution adheres to the inner surface of the dent, which also creates natural holes. It becomes difficult to remove the foreign matter, or the attached dust may cause a defect of the foreign matter.

In the present invention, a core body (B) having a flat or concave bottom as shown in FIG. 3 and having a sharp edge formed from the outer peripheral surface to the bottom of the cylinder is used. You can also The bottom of the core body (B) is flat (smooth surface) or concave. The concave shape is preferably a concave lens shape having a shallow bottom as shown by a dotted line in FIG. Concave depth H with respect to outer diameter D _A of the core
The ratio (H / D _A ) is preferably 1/3 or less, more preferably 1/4 or less. If the depth of the recesses is too large, it is difficult to form a coating film on the bottom portion, and the formed coating film is likely to fall off during the heat treatment.

When the core (B) is dipped in the polyimide precursor solution, a coating film of the solution is formed on the outer peripheral surface and the bottom of the core. The outer peripheral surface and the bottom of the core body (B) form a sharp edge of 90 degrees or less. Therefore, when the core body on which the coating film is formed is heated, the generated gas breaks the sharp edge portion, and the gas is uniformly released from the broken portion. However, since the coating film on the bottom portion is usually partially connected to the coating film on the outer peripheral surface, there is little risk of falling off.
However, in the case of the core body (B), the coating film may be completely broken at the sharp edge portion due to its structure, and the coating film at the bottom portion may drop off. If the bottom coating film falls off and adheres to other coating films, it may cause foreign matter defects. Therefore, it is preferable to use the core body (A) rather than the core body (B).

[0013]

In the present invention, since the core body is of the upper end supporting system, there is a problem such as peeling of the releasable coating layer and mixing of foreign matter in the system of scraping a part of the coating film using a conventional scraper or the like. You can overcome the points. Further, in the present invention, the problem of degassing that occurs when the upper end supporting method is adopted can be solved by devising the shape of the core bottom. According to the production method of the present invention, physical contact between the scraper or the like and the core is not required, and therefore the peelable coating treatment layer of the core is not damaged or peeled. Therefore, according to the manufacturing method of the present invention, a polyimide tubular article having a good appearance can be obtained by a simple operation.

[0014]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Embodiment 1] As a core body, as shown in FIG. 1, a cylindrical aluminum rod is formed with a convex shape which is smoothly connected from the outer peripheral surface to the bottom, and a spherical concave portion is formed in the convex central portion. 3 is provided, and the outer surface of the core body (A ₁ ) having a glass coating treatment (product name Ceramica G-90) is used. As a polyimide precursor solution, a polyimide varnish manufactured by Ube Industries (product name U Varnish-S) is used. I was there. In this core body (A ₁ ), the ratio (b / a) of the projected area b of the recess to the total projected area a of the bottom is 0.36, and the ratio of the depth D of the recess to the outer diameter D _A ( D / D _A ) is 0.
It was 12. When this core body (A ₁ ) was immersed in the polyimide varnish while being supported by the support portion 2 at the upper end to form a coating film, a natural hole was formed in the recess 3 portion of the bottom portion. Then, the core body was conveyed into a heating furnace while being supported by the support portion 2 at the upper end, and was heated stepwise from 150 ° C. to 450 ° C. to perform solvent removal and polyimidization. Did not swell due to the generated gas. Therefore, the generated gas can be considered to have escaped from the hole of the recess at the bottom. After the heat treatment, the cured coating film was removed from the core and the lower end portion was cut off to obtain a polyimide tubular article having a good appearance. This polyimide tubular product had an inner diameter of 25 mm, a thickness of 50 μm, and a length of 300 mm.

After the same core (A ₁ ) was continuously used 800 times, the release coating layer applied to the outer surface of the core was observed and no abnormality was found. On the other hand, when a conventional tubular body as shown in FIG. 4 is used, it is supported on the pedestal by the pin hole 5 at the bottom and the lower part of the coating film is scraped off by the scraper 8 to form a polyimide tubular article. It was necessary to repeat the release coating treatment every 500 times on average.
Even when the shape of the recess was changed from a spherical shape to a disk shape as shown in FIG. 2, a good polyimide tubular article without swelling could be similarly obtained. The ratio (b / a) of the projected area b of the recess to the total projected area a of the bottom of the core is 0.05 to
Change to 0.50, and the depth D of the recess with respect to the outer diameter D _A
When the ratio (D / D _A ) of 0.05 to 0.20 was changed, similarly, a natural hole was formed in the bottom of the coating film, and a good polyimide tubular product without swelling could be obtained. It was
In particular, b / a = 0.10 to 0.40 and D / D _A = 0.
In the range of 08 to 0.15, gas vent holes were stably formed, and the polyimide varnish and the cured polyimide small pieces could be more effectively prevented from falling off. For comparison, when a core body having the shape shown in FIG. 1 and having no recess 3 was used, the cured coating film (tubular material) swelled due to the gas generated during heating.

[Embodiment 2] As a core body, as shown in FIG.
On the outer surface of a cylindrical aluminum rod with a smooth bottom.
Glass coating treatment (product name Ceramica G-90)
What you did (B₁) Is the same as in Example 1 except that
Then, a polyimide tubular article was prepared. As a result, heating
At the time of processing, a sharp edge formed by the outer peripheral surface and the bottom of the core body.
The coating film partially ruptured at the juncture and gas escaped from there.
As a result, it was possible to obtain a tubular product having a good appearance and no blistering.
As shown by the dotted line in FIG. 3, a concave shape (H /
D _A= 1/4) formed core (B₂) Is used
Similarly, it is possible to obtain a tubular product with a good appearance without blistering.
did it. However, these (B) type cores
If used, the coating film will be completely torn at the sharp edge and the bottom
The coating film on the surface may fall off, and the core of the (A) group
The body was preferred.

[0018]

According to the present invention, in a method for producing a polyimide tubular article by applying a solution of a polyimide precursor to the outer surface of a core and heating the coating film, in the heating step, the core is By adopting a supporting method and devising the shape of the bottom of the core body, it is possible to provide a polyimide tubular article having a good appearance without bulging or the like, which prevents the generation of foreign matter and deterioration of the core body.

[Brief description of drawings]

FIG. 1 is a schematic view showing one embodiment of a core body used in the present invention.

FIG. 2 is a schematic view showing one embodiment of a core body used in the present invention.

FIG. 3 is a schematic view showing another embodiment of the core body used in the present invention.

FIG. 4 is a schematic view showing a conventional core body and a scraping operation by a scraper.

[Explanation of symbols]

1: Core body 2: Support part at the upper end 3: Recess 4: Coating film 5: Pin hole 6: Debris of polyimide precursor solution 7: Deposition residue of polyimide precursor solution 8: Scraper 9: Releasable coating layer 10 : scraping by the scraper part D: dent depth D _H: dent diameter D _a: outer diameter of the core

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Goto 1-1-1 Kunyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (2)

[Claims] 1. A polyimide tubular article comprising a step of applying a polyimide precursor solution to the outer peripheral surface of a core and heating the coating until it retains at least the strength of the tubular article, and then taking out the tubular article from the core. In the manufacturing method, as the core body, (A) a core body in which a convex shape that is smoothly connected from the outer peripheral surface of the cylindrical body to the bottom is formed, and a concave portion is provided in the central portion of the convex shape, or (B) the cylindrical body The bottom of the core is flat or concave, using a core body in which a sharp edge is formed from the outer peripheral surface of the cylindrical body to the bottom portion, and, after applying a polyimide precursor solution to the outer peripheral surface of the core body, A method for producing a polyimide tubular article, which comprises heating the core while supporting it at its upper end. 2. The core (A) has a total projected area a of its bottom.
The ratio (b / a) of the projected area b of the depression to the
The manufacturing method according to claim 1, wherein the ratio (D / D _A ) of the depth D of the recess to the outer diameter D _A of the core is 0.05 to 0.20.