JPH06278252A - Multilayer fluororesin molded product and manufacture of the same - Google Patents

Abstract

PURPOSE:To provide a multilayer fluororesin molded product with a cylindrical or ring shape which hardly causes abnormal abrasion due to thermal expansion, the deterioration in sealing, and other defects even when it is attached on a piston or the like with a relatively smaller axial clearance. CONSTITUTION:In a moled product having a coaxial-multilayer structure, the linear expansion coefficent MD in the axial direction (a) and the linear expansion coefficient CD in the perpendicular direction (b) are in a relationship of MD/CD<=1.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tubular or ring-shaped multilayer fluororesin molding and a method for producing the same.

[0002]

2. Description of the Related Art Fluororesin is excellent in water repellency, non-adhesiveness, low friction, chemical resistance, etc., so it is molded into a predetermined shape and has low friction properties such as a corrosion resistant material for chemical plants and bearings. It is used in a wide range of fields such as required mechanical parts, medical supplies and leisure products.

By the way, in recent years, with the expansion of application fields of fluororesin moldings, use under special conditions has been studied,
For example, there is a demand for a tubular or ring-shaped molded body used as a sliding member of a piston, a piston ring, a seal ring, or the like.

Polytetrafluoroethylene (hereinafter referred to as "PTFE"), which is one of the fluororesins, has a high melt viscosity, so that it is difficult to melt-mold it like a general thermoplastic resin. Is filled with PTFE powder, and the powder is pressed from a direction parallel to the axial direction of the mold to bind the powders together to form a molded body, and then this molded body is heated to a temperature not lower than the melting point of PTFE. It is molded by the method of firing.

In order to obtain a cylindrical molded body by this method, a cylindrical mold is prepared, a core is arranged in the mold so as to be parallel to the axial direction of the mold, and the core and the inside of the mold are arranged. PT in the space between the peripheral surfaces
The FE powder may be filled, the powder may be pressed from a direction parallel to the axial direction of the mold to form a cylindrical molded body, and then the molded body may be fired. A ring-shaped molded body can be obtained by cutting in a direction perpendicular to the direction. The cylindrical or ring-shaped molded body obtained by this method has a cylindrical shaft (that is, a pressing direction during molding).
On the other hand, the linear expansion coefficient in the parallel direction is larger than that in the vertical direction.

[0006]

Then, this conventional molded body is mounted, for example, in a groove provided on the inner peripheral surface of the piston so that the axial direction of the molded body and the axial direction of the piston coincide with each other. When it is used for a long time, the temperature of the molded body greatly expands in the axial direction due to the temperature rise due to the operation of the piston, and the clearance between the molded body and the groove becomes small, which may cause problems such as abnormal wear and deterioration of sealing performance.

In view of such circumstances, the present invention provides a fluororesin molded product which does not cause abnormal wear due to thermal expansion or deterioration of sealing performance even when mounted on a piston or the like having a small axial clearance. It aims at providing the manufacturing method.

[0008]

Means for Solving the Problems As a result of earnest studies to achieve the above object, the present inventor has found that by adopting a specific pressurizing method at the time of molding a fluororesin powder, the direction of the coefficient of linear expansion is different from the conventional one. It was found that moldings having different properties could be obtained, and the present invention was completed.

That is, the tubular or ring-shaped multilayer fluororesin molding according to the present invention has a linear expansion coefficient in the direction parallel to the cylinder axis as MD and a linear expansion coefficient in the vertical direction as CD. , MD / CD ≦ 1.0.

The tubular or ring-shaped fluororesin molding according to the present invention has a multilayer structure. Here, the term "multilayer" means that it is composed of at least two layers adjacent to each other in the direction perpendicular to the axial direction.

From the viewpoint of heat resistance and the like, PTFE is preferable as the fluororesin forming each of these layers, but other fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene- Perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer may be used, and further, two or more kinds of them may be mixed and used. May be.

FIG. 1 shows an example of a tubular multi-layer fluororesin molding according to the present invention. Each of the formed bodies has a cylindrical shape, and has a three-layer structure including an intermediate layer 13, an inner layer 12 adjacent to the inner peripheral surface of the intermediate layer 13, and an outer layer 14 adjacent to the outer peripheral surface of the intermediate layer 13. Have The multilayer fluororesin molding according to the present invention may have a tubular shape other than the cylindrical shape, such as an elliptic tubular shape or a rectangular tubular shape.

If this tubular molded body is cut into a thin plate along a direction (direction of arrow b in FIG. 1) perpendicular to the axial direction of the cylinder (direction of arrow a in FIG. 1), a ring is formed. A multi-layered molded product is obtained.

In these cylindrical or ring-shaped multilayer molded products, the expansion coefficient MD in a direction parallel to the cylindrical axis (direction of arrow a in FIG. 1) and a direction perpendicular to the cylindrical axis (in FIG. 1). The linear expansion coefficient CD (in the direction of arrow b) is MD / CD ≦
1.0 The relationship of 0.85 ≦ MD / CD ≦ 1.0 is particularly preferable.

If the linear expansion coefficients in these two directions in the tubular or ring-shaped multi-layer fluororesin molded product have the above relationship, this is placed in the groove provided on the inner peripheral surface of the piston and the shaft of the molded product is formed. When the piston is mounted so that the direction and the axial direction of the piston coincide with each other, the linear expansion in the axial direction of the molded body is small, so the clearance between the groove and the molded body is secured even if the temperature rises, so abnormal wear occurs. It does not cause deterioration of the sealing property.

The above-mentioned multilayer structure can be formed by changing the components of at least two layers constituting the molded body. As a specific mode of the multilayer structure, for example, a mode in which each layer is formed of different fluororesin, a mode in which one layer is formed only of fluororesin and another layer is formed by mixing a desired filler in fluororesin A mode in which the type of filler added to each layer is changed can be cited.

Examples of the filler used here include glass fiber, carbon fiber, aramid fiber, alumina fiber, boron fiber, glass beads, silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers and the like as reinforcing fillers. , Graphite as a sliding filler, molybdenum disulfide, tungsten disulfide, boron nitride, mica,
Aromatic polyester resin, silicone resin, calcium fluoride, graphite fluoride, glass flakes, carbon black, graphite, bronze and the like, as conductive fillers, metal powder, metal flakes, metal fibers, beryllium oxide, aluminum nitride, alumina, Examples of the adsorptive filler include magnesia, titania, silica gel, zeolite, talc, bentonite, barium titanate, calcium carbonate, barium titanate, kaolin, clay and the like. When these fillers are used, the proportion of the filler in the total weight of the fluororesin and the filler is usually 60% by weight or less, preferably 20% by weight or less. The fluororesin and the filler can be mixed using a known mixer such as a tumbler mixer, a Henschel mixer and a super mixer.

Then, as shown in the following examples, copper powder, glass fiber and carbon fiber were prepared as fillers, and these were respectively mixed with fluororesin to obtain three kinds of mixed powders,
It has been found that a three-layer structure formed by using this is preferable. In this case, the positional relationship between the layers may be arbitrary.

In such a multilayer fluororesin molding, a fluororesin powder for forming a tubular layer is filled between a mold and an elastic mold coaxial with the mold, and the powder is perpendicular to the axial direction of the mold. It can be manufactured by repeating the tubular layer forming step of pressurizing from a different direction through an elastic die to form a tubular shape two or more times.

In this method, first, as shown in FIG. 2, a lower mold 1 is fitted with a cylindrical or rod-shaped mold 2 made of iron or the like and a cylindrical elastic mold 3 coaxial with the mold. , A fluororesin powder 4 for forming a tubular layer in the space between the mold 2 and the elastic mold 3.
Then, the upper mold 5 is fitted and sealed. Elastic type 3
For example, a rubber mold made of natural rubber or synthetic rubber can be used, and the rubber mold has a rubber hardness (Hs) of 50.
It is particularly preferable that the elongation is 100 to 100% or more.

Then, this is placed in a pressurizing device 9 equipped with a pressure-resistant container 6, an upper lid 7 and a lower lid 8 and the powder is pressurized by a fluid 11 (gas or liquid) supplied from an introduction passage 10.

The pressure exerted on the powder by this pressing is applied through the elastic die 3 only from the direction perpendicular to the axial direction because the axial direction of the die 2 is restricted by the die 2 itself. By this application, the powders are bound to each other to form a cylindrical layer (inner layer).

In FIG. 2, the elastic mold is arranged outside the mold and pressure is applied from the outside of the elastic mold. However, the cylindrical elastic mold is arranged inside the cylindrical mold, and the elastic mold and the mold are arranged. A similar cylindrical layer can be formed by filling the space between the molds with fluororesin powder and pressing the powder from the inside of the elastic mold.

After the formation of this first tubular layer, it is taken out from the pressurizing device, the upper die is removed, and the space between the formed tubular inner layer and the elastic die is filled with a fluororesin powder for tubular layer formation. Then
A two-layer structure multilayer fluororesin molded product can be obtained by fitting and sealing the upper mold and then pressing again in the pressure device to form a tubular layer on the inner layer. Further, in order to obtain a multilayer molded body having three or more layers, the formation of the tubular layer may be further repeated. The pressure during this tubular layer formation, when the outermost layer is about 100 to 1000 / cm ^2, when the other layers have been found to be preferable to provide about 1~500kg / cm ^2.

The tubular multi-layer fluororesin molding thus obtained is not yet fired, and in order to improve its strength, it is usually
It is heated to a temperature not lower than the melting point of the fluororesin and fired. The firing may be carried out while being housed in the mold, or may be carried out after detaching from the mold. However, in order to prevent thermal deterioration, it is better to remove the elastic mold when the baking is carried out while being housed in the mold.
The time required for firing may vary depending on the heating temperature, the thickness of the molded body, etc., but is usually about 30 minutes to 20 hours.

Then, the fired tubular multi-layer molded body is subjected to a direction (FIG. 1) perpendicular to the axial direction (direction of arrow a in FIG. 1).
A ring-shaped multilayer molded article can be obtained by cutting along the direction of the arrow b). Further, the unfired cylindrical multilayer molded body may be cut into a ring shape and then fired.

[0027]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 40 parts by weight of PTFE powder were mixed with copper powder (average particle size 20 μm).
m) 60 parts by weight are mixed, and the mixed powder is mixed with an iron rod-shaped mold (outer diameter 30 mm, length 300 mm) as shown in FIG.
Cylindrical rubber mold coaxial with (inner diameter 45 mm, thickness 20 mm,
Fill the space between the length of 350 mm, elongation 500%),
An upper mold and a lower mold form a closed system, which is placed in a pressurizing device, water is used as a pressurizing fluid, and the pressure is 50 kg / cm ^2.
For 1 minute to form a cylindrical inner layer.

Next, this was taken out from the pressurizing device, the upper mold was removed, and the PTF was placed in the space between the cylindrical inner layer and the rubber mold.
Glass fiber (average diameter 10 μm, 85 parts by weight of E powder,
A mixed powder in which 15 parts by weight of an average length of 30 μm) is mixed is filled. Then, a cylindrical intermediate layer is formed by making this a closed system and applying pressure (conditions are the same as when forming the inner layer) in a pressure device.

Then, this was taken out from the pressurizing device, the upper mold was removed, and P was put in the space between the cylindrical intermediate layer and the rubber mold.
90 parts by weight of TFE powder, carbon fiber (average diameter 15μ
m, average length 300 μm) 10 parts by weight are mixed and mixed powder is filled. Then, this is used as a closed system and pressurized at a pressure of 600 kg / cm ² for 5 minutes in a pressure device to form a cylindrical outer layer.

After that, it was taken out from the pressurizing device, the upper mold, the lower mold and the rubber mold were removed, heated and baked at 370 ° C. for 4 hours, and released from the mold to obtain a cylindrical shape similar to that shown in FIG. A three-layer molded body was obtained. This molded product has a length of about 300 mm
The inner layer has an inner diameter of 30 mm and a wall thickness of 2.5 mm, the intermediate layer has an inner diameter of 35 mm and a wall thickness of 2.0 mm, and the outer layer has an inner diameter of 39 mm.
The thickness was 1.5 mm and the wall thickness was 1.5 mm.

With respect to this cylindrical three-layer molded body, the one end side and the other end side in the direction parallel to the cylindrical axis are divided into 15 equal parts, and the linear expansion coefficient of any part in each division is as follows. It was measured by the method. The results are shown in Table 1.

(Measurement of Linear Expansion Coefficient) A sample is cut into a 5 mm square and the linear expansion coefficient MD in the direction parallel to the cylindrical axis of the cylindrical three-layer molded body and the linear expansion coefficient CD in the direction perpendicular to Analyzer (TMA2 manufactured by Seiko Instruments Inc.
0), measurement temperature 30-150 ° C, temperature rising rate 10 ° C
It is measured under the condition of / min, and is calculated by Equation 1. In addition,
When showing MD and CD in Table 1, “× 10 ⁻⁵ /
“° C.” is omitted.

[0034]

[Equation 1]

In the above equation 1, K is a device constant, L is a sample length (5 mm), T is a temperature (° C.), α ₀ is a coefficient of linear expansion of silica glass (10 ⁻⁵ / ° C.), α Is the temperature T ₂
The average linear expansion coefficient in the through T _1, [Delta] L is the temperature T ₂ through T ₁
The amount of displacement of the sample length in each is shown.

[0036]

[Table 1]

Comparative Example A rod-shaped iron shaft core having a diameter of 30 mm and a length of 700 mm was placed in the center of an iron cylindrical mold having an inner diameter of 42 mm and a length of 700 mm, and PTFE powder was placed between the shaft core and the inner peripheral surface of the mold. And is pressurized from the axial direction of the cylinder of the mold at 300 kg / cm ² for 5 minutes.

Then, it was heated at a temperature of 370 for 4 hours, baked, and released from the mold to obtain a cylindrical molded body having an inner diameter of 30 mm, an outer diameter of 42 mm and a length of about 300 mm. Table 2 shows the results obtained by measuring the linear expansion coefficient of this molded article in the same manner as in the examples.

[0039]

[Table 2]

[0040]

Since the present invention is constructed as described above and the fluororesin is molded by a specific pressing method, the fluororesins are adjacent to each other in the direction perpendicular to the axial direction which could not be produced by the conventional method. It is possible to obtain a multilayer molded body having at least two layers, and the multilayer molded body has a direction of linear expansion coefficient different from that of the conventional product. According to this molded body, a piston having a not so large clearance is provided. Even if it is mounted on a machine or the like, it is possible to effectively prevent abnormal wear due to thermal expansion and deterioration of sealing performance.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a cylindrical multilayer fluororesin molding according to the present invention.

FIG. 2 is a cross-sectional view showing an example of an apparatus used in the method for producing a multi-layer fluororesin molding according to the present invention.

[Explanation of symbols]

 12 inner layer 13 middle layer 14 outer layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tsutomu Onoda 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Yasuo Kaneko 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (3)

[Claims] 1. When the linear expansion coefficient in the direction parallel to the cylinder axis is MD and the linear expansion coefficient in the vertical direction is CD, M
A cylindrical or ring-shaped multi-layer fluororesin molded product having a relationship of D / CD ≦ 1.0. 2. A fluororesin powder for forming a tubular layer is filled between a mold and an elastic mold coaxial therewith, and the powder is passed through the elastic mold from a direction perpendicular to the axial direction of the mold. A method for producing a tubular multi-layer fluororesin molded article, which comprises repeating a tubular layer forming step of pressurizing and pressurizing to form a tubular shape two or more times. 3. A fluororesin powder for forming a cylindrical layer is filled between a mold and an elastic mold coaxial therewith, and the powder is passed through the elastic mold from a direction perpendicular to the axial direction of the mold. A cylindrical multilayer molded body is obtained by repeating the cylindrical layer molding step of pressing with pressure to mold into a cylindrical shape two or more times, then the multilayer molded body is fired, and then this multilayer molded body is cut into a ring shape. A method for producing a multi-layer fluororesin molding, which comprises: