KR950013592B1 - Method for bonding a pfa layer on a inner part of metallic container - Google Patents

Abstract

The lining method improves durability and reliability of products by depositing thick seamless PFA polymer layers. The lining method comprises (A) pretreatment process to remove impurities by sand-blasting; (B) forming oxide film as an intermediate layer on the inner wall; (C) forming PFA layer on the oxide film on the inner wall in a rotating container in a furnace;(D) rapid cooling of PFA layers by taking the metal container out of the furnace.

Description

How to bond PFA layer to inner wall of metal container

1 is a longitudinal cross-sectional view of a rotomolded lining apparatus of an inner wall of a metal container according to the method of the present invention.

2 is an enlarged view of portion "A" of FIG.

3 is an enlarged view of portion "B" of FIG.

4 is an enlarged view of portion "C" of FIG.

* Explanation of symbols for main parts of the drawings

1: Metal tank 2: Body

2a: flange 3: cover

3a: flange 4a, 4b: jig

5, 6: nozzle 9: rotating molding machine

11: air outlet 14a, 14b: blemish

L: PFA Resin Layer O: Oxide Film

The present invention relates to a method for adhering a PFA layer to an inner wall of a metal container capable of strongly adhering a fluororesin layer having excellent corrosion resistance and non-adhesive property to an inner wall of a metal container using a rotational molding lining method.

In general, fluorocarbon PFA (copolymer of tetrafluorethy-lene and perfluoro alkoxy) is not only highly corrosion resistant and can be used at high temperatures (up to 260 ° C of continuous use), but also due to its excellent non-adhesive properties. It is widely used as a corrosion-resistant coating material.

However, PFA has a drawback in that it can not be directly adhered to the surface of metal or nonferrous metal because its shrinkage and thermal expansion coefficient are considerably larger than those of other resins.The main characteristics of PFA are shown in Table 1 below. Same as

[Table 1] Comparison of main characteristics of PFA

As can be seen in Table 1, PFA has the advantages of high use temperature and melting point, but has a disadvantage of high coefficient of thermal expansion and molding shrinkage. Thus, it is still possible to form a PFA film with a thickness of 1 mm or more on the inner wall of a metal container. There is no development of technology. On the other hand, the fluorine resin lining method that provides corrosion resistance by lining the inner circumferential surface of valves and pipe fittings including corrosive fluids or high temperature fluid storage tanks using fluorine resins is electrostatic powder lining, sheet lining and Three methods of rotomolding lining are known and these pore methods will be briefly described as follows.

First, electrostatic powder lining is sprayed on the inner wall of the metal container with a spray gun spraying the mixed powder made by adding the chemicals to the fine powder of FEP or PFA, and then repeated several times the heat treatment process to FEP or It is a method to make the adhesion of PFA resin film.

However, in electrostatic powder lining, it is impossible to form the thickness of the film more than 0.8 mm even if the powder spraying and heat treatment processes are repeatedly performed several times. The reason is that when the thickness of the lining film becomes 0.8 mm or more, cracking and peeling occur.

Electrostatic powder lining cannot be used where the antistatic agent added to FEP or PFA powder used in powder coating and the additive for strengthening adhesion act as impurities and the semiconductor manufacturing process or particle generation should be kept in mind.

Next, the sheet lining is made of PTFE resin or PFA resin into a sheet having a thickness of 2 to 3 mm and a width of about 1 m, and heat-sealed glass cloth on the sheet surface to form an inner wall of a metal container requiring lining. It is a method of lining the inner wall of the metal container by cutting along and bonding it to the inner wall of the container using an epoxy-based adhesive or a rubber-based adhesive, and then welding the joint portion with a PFA welding rod.

However, the lining formed by such sheeting is not available at a high temperature of 120 ° C. or higher, and in particular, it cannot be used in a work process in which heating and pressure reduction are repeated.

In addition, since the seam welding part of the sheeting is structurally unstable, problems such as cracking, peeling, and fine particle generation have been pointed out, and the sheeting can only be performed by skilled workers by hand, and thus the reliability of lining is low. In addition to having. However, PFA rotational molding lining puts resin powder inside the metal container, and then heats the metal container while rotating the metal container biaxially to achieve revolution and rotation, thereby melting the resin powder inside the metal container and forming a film on the inner wall of the mold. After this is done, the cooling of the metal container is continued while the rotation of the metal container is completed.

However, in the conventional rotational molding lining, PFA lining products cannot be manufactured because of problems such as bubbles in the resin layer in the lining process or peeling of the resin layer from the metal substrate at a large shrinkage rate during cooling.

As a result, various conventional fluorine resin lining methods have their own characteristics such as limitation of film thickness (electrostatic lining), instability and impurity generation (strain lining) of welding site, and impossibility of direct adhesion of PFA to the substrate to be lined (rotational lining). It can be seen that it has a disadvantage.

Accordingly, the present invention is a metal that can be strongly bonded to the inner wall of the metal container with a thickness of 1mm or more without using a rotatable molding method as a way to solve the problems and disadvantages of the conventional fluorine resin lining method It is an object to provide a method for lining inner walls of a container.

According to the method of the present invention, an oxide film is formed on the inner wall of the metal container to be lined, and then, PAF powder, which is a thermoplastic resin, is charged into the metal container, and the metal container is biaxially rotated while heating and depressurizing the inside of the metal container. When the PFA resin is adhered to the inner wall of the container, it is a series of processes to remove the bubbles in the metal container under reduced pressure and to cool it to room temperature while applying pressure to the entire surface of the lining to make the PFA resin lining to the inner circumferential surface of the metal container. .

Such a method of the present invention will be described in detail for each process as follows.

[Pretreatment Process]

Impurities are removed by sand blasting the inner circumferential surface of the metal container to be lined, and the surface of the inner circumferential surface is formed in an uneven shape to improve adhesion between the oxide film and the PFA film and the substrate.

[Oxide Film Forming Process]

Since the PFA resin cannot adhere PFA directly to the inner circumferential surface of the metal container due to non-adhesion with other materials, the oxide film is formed as an intermediate layer before the PFA film is formed.

This oxide film is obtained by applying a PTFE primer added with metal ions to the PTIFE dispersion on the inner wall of the metal container and drying it, and then heating it to a temperature above the melting point of PTFE in a baking furnace. The oxide film formed on the inner wall of the metal container serves to facilitate the thermal fusion of the PFA in the next step.

[PFA film forming process]

PFA powder is charged into a metal container, the metal container is kept in a sealed state and mounted in a rotating molding machine, and then the metal container is heated and decompressed with heating while rotating the metal container in a baking furnace to melt the PFA powder and to form an inner wall of the container. Make sure that it adheres to At this time, it is to be made to remove the air existing between the base material and the PFA resin by the pressure reduction inside the metal container during the melt bonding.

If bubbles remain between the base material and the resin, the bubbles promote the peeling of the PFA resin coating film in the process of shrinkage and expansion due to temperature change, and thus the bubble removal under reduced pressure should be performed. After the bubble is removed by depressurization, the cooling process is switched to a pressurized state to apply a constant pressure to the surface of the molten resin to prevent shrinkage of the PFA lining, and to smooth the lining surface and uniform the lining thickness.

[Cooling process]

After the formation of the PFA resin film is completed, the metal container itself is taken out of the kiln to perform rapid cooling of the PFA resin. At this time, since the PFA resin has a high molding shrinkage rate, the resin film is formed by shrinking the PFA resin film during the cooling process. In order to prevent the phenomenon of peeling from the present invention, in the present invention, while lowering the crystallinity of the PFA resin by rapid cooling, the PFA resin film by cooling to room temperature while applying a pressure of 0.5 ~ 20Kg / ㎠ to the entire surface of the lining The peeling off is suppressed.

The technical features and specific manufacturing processes of the present invention as described above will be described in detail with reference to the following Examples.

In the present embodiment, as shown in the drawing of FIG. 1, a metal container having a capacity of 20 l is formed using an iron tank having two nozzle portions and a flange portion located between the main body and the lid. PFA resin lining was performed.

The metal container is sand blasted on the inner wall as a pretreatment step prior to mounting on the rotary molding machine to form a roughened surface of the inner wall with the removal of impurities. After drying, the resultant was heated to 380 ° C. in a kiln to form an oxide film. At this time, the application number of the PTFE primer is preferably carried out one to three times depending on the metal material and adhesion conditions.

1 is a cross-sectional view of a small metal tank mounted on a rotating molding machine, and as shown therein, the metal tank 1 is composed of a lid 3 and a main body 2 and includes a lid 3 and a main body 2. The flanges 2a and 3a are connected to each other by the jig 4a, and the nozzles 5 and 6 are formed at each of the cover 3 and the main body 2, respectively. .

The metal tank 1 having such a shape is mounted on the stationary device 10 formed at one end of the rotating shaft 8 of the rotary molding machine 9 provided with the rotating shaft 7 and the rotating shaft 8. Rotating is performed at the same time.

On the other hand, the nozzle 5 is formed in the cover 3 of the metal tank 1, the air inlet and outlet 11 is provided for the pressure control inside the metal tank (1).

Next, after the oxide film formation is completed, 2.5 kg of PFA powder having a size of 170 to 350 µm is filled into the metal tank 1 to close the lid 3, and the flanges 2a and 3a and the nozzles 5 and 6. The part should be kept fully sealed, with the flange 2a shown in FIGS. 2 and 3 for the sealing of the flanges 2a, 3a and the nozzles 5, 6. After the heat-resistant packing 12 and the jig 4a and 4b are provided on the openings of the 3a and the nozzles 5 and 6a, the metal tanks are fixed by fixing bolts 13a and 13b composed of bolts and nuts. While the complete sealing of (1) was maintained, the lining of the flange 2a, 3a part and the nozzle 5, 6 part was made easy. PFA powder is formed in the grooves 14a and 14b at the time of the firing process after the triangular grooves 14a and 14b are formed on the inner surfaces of the outer ends of the flanges 2a, 3a and the nozzles 5, 6, respectively. 14b) was melt-bonded to reduce the occurrence of the peeling phenomenon due to the cooling shrinkage, and to enhance the adhesion of the metal tank (1) inner wall and PFA resin lining.

After the sealing of the metal tank (1) filled with PFA powder was completed, the rotary molding machine (9) was operated so that the speed of revolution of 3 RPM and rotation of 15 RPM was maintained in a kiln preheated to 300 ° C. for 340 over 40 minutes. In heating gradually up to ° C, the vacuum degree inside the metal tank 1 was made to be 400 mmHg or less in absolute pressure from the time of heating (inside of a kiln) of the metal tank 1. The absolute pressure is preferably 200 mmHg-400 mmHg. At this time, the PFA powder is fused to the inner wall of the metal tank (1) and the bubbles present in the fusion resin layer by the pressure reduction is removed to the outside. If no vacuum is applied at this point, bubbles may be trapped in the resin layer. Therefore, vacuum is applied from the point where the powder temperature becomes PFA 300 ° C-305 ° C. According to the experiments of the present inventors, there was no problem in removing bubbles of the molten PFA layer if the degree of vacuum was 400 mmHg or less (Table 2).

Heating condition: 370 ℃ × 1 hour

Vacuum application time: 1 hour

Cooling: take the mold out of the oven and cool it underwater

PFA: TE-9738 (Depont), 0.78 / ㎠ (44g total) powder on the bottom of the mold

On the other hand, the rotation and idle speed of the rotary molding machine (9) should be adjusted so that the PFA powder slides from the inner wall of the cover (3) of the metal tank (1) to the bottom of the opposite side to maintain the original position at each revolution. It is to be noted that the rotation speed of (1) is so high that the PFA powder does not flow by the centrifugal force of the metal tank (1). At 340 ° C, the PFA powder is uniformly fused to the inner wall of the metal tank 1, and then the temperature is raised to 370 ° C over 30 minutes. Rotation conditions are the same as the initial stage, maintaining the absolute pressure of 30 mmHg for 2 hours at 370 degreeC. Here, maintaining the firing temperature at 370 ° C. showed the best results by performing the bubble removal effect of the molten PFA layer. At this time, when the temperature is 350 ° C. or less, the melt viscosity of the PFA is relatively larger than that of 350 ° C. or more, and bubble removal is difficult, and at 380 ° C. or more, there is a high risk of deterioration of PFA. In addition, when rotomolding at 390 ° C. for 90 minutes or less, fine bubbles may remain, and there is a high possibility of deterioration of PFA after 4 hours. Therefore, it was found that the above conditions, that is, rotational molding conditions of 2 hours at 370 ° C., were most suitable.

Then, the cooling process is started after removing the bubbles of the molten PFA layer under reduced pressure of 370 ℃ for 2 hours.

In the cooling step, the metal tank 1 is taken out of the firing furnace and then rapidly cooled using a fan. At the same time, 5 kg / cm 2 of nitrogen gas is introduced into the metal tank 1 through the air inlet 11 to convert the inside of the metal tank ¹ into a pressurized state maintained for about 20 minutes. At this time, the cooling process is performed while maintaining the pressure and rotational speed of 5 kg / cm 2 until it is at room temperature, and as shown in FIG. 4, the PFA resin layer (L) has a strong thickness on the oxide film (O). To obtain a properly bonded lining product.

Here, the nitrogen gas of 5Kg / ㎠ serves to reduce the shrinkage of the lining layer due to the shrinkage of the PFA resin. Ideally, the internal pressure is generally about 7-20Kg / ㎠, which is the design pressure of the lining tank, but it can cause deformation of the tank at high temperature, and the pressure below 1Kg / ㎠ can effectively reduce the shrinkage of PFA resin. Therefore, a pressure of 1-80Kg / cm 2 is suitable, but most preferably a pressure range of 4-6Kg / cm 2 is suitable.

On the other hand, the pressure reduction and pressurization process is an important process having a close relationship with the adhesion of the PFA resin layer (L), PFA resin (L) of the metal tank (1) in the experiment that the high temperature and low temperature for the lining product is repeated The phenomenon of peeling from the inner wall did not occur, and a single-piece lining molded product having a seamless and thick thickness of 3 mm could be formed.

If the method of the present invention is a metal hollow container that can be injected into the PFA powder inside, it can be applied to any shape products, the thickness of the PFA resin layer is much thicker than the existing lining method, the lining itself Since it is molded into a seamless one-piece, there is an advantage that it can be widely melted in the metal hollow body in the semiconductor and chemical fields.

In addition, the products lined by the method of the present invention are excellent in durability and reliability, and in particular, problems such as anxiety in the welding area and accumulation of particles that occur when using the sheeting product in the conventional semiconductor manufacturing process are solved. It can be variously applied to high purity chemical storage containers and chemical reaction tanks for chemical etching process.

Claims (5)

After filling and sealing the PFA powder inside the metal container in which the oxide film was formed on the inner wall, the metal container was mounted in the rotary molding machine, placed in the firing furnace under rotation, and heated and depressurized. When melt-bonded to the inner wall of the metal container, the air bubbles in the PFA resin layer are removed under reduced pressure, and then the metal container is taken out of the firing furnace and rapidly cooled under pressure, thereby reducing the shrinkage of the resin layer. How to glue the layers. The method of claim 1, wherein the oxide film is formed by applying a PTFE primer to a metal container, followed by drying and heating, to bond the PFA layer to the inner wall of the metal container. The method of claim 1, wherein the depressurization step is such that the vacuum degree inside the metal container is set to 400 mmHg or less in absolute pressure from the time when the metal container is introduced into the firing furnace to the start of the cooling process. How to glue. The method of claim 1, wherein the pressurization step is to take out the metal container to the outside of the kiln when the temperature reaches 370 ℃ to stop the decompression when the rapid cooling is carried out by injecting nitrogen or air to 1 ~ 8Kg / ㎠ A method of adhering the PFA layer to the inner wall of the metal container, characterized in that it is kept under pressure for 20 minutes. The method of claim 1, wherein the rapid cooling is applied to the inner wall of the metal container, characterized in that to prevent shrinkage by applying a pressure of 5Kg / ㎠ until the room temperature.