JP2000303058A - Gasket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasket for a sanitary pipe, having excellent chemical resistance, undergoing such little stress denaturation even after a long-time use as to exhibit persistent airtightness and sanitariness, being safe because of the absence of the tendency of its constituents to be eluted into the product, and having excellent productivity. SOLUTION: A fluororesin having a melt viscosity of at most 108 P at 230-380 deg.C is melt-molded. It is desirable that the fluororesin is one selected from the group consisting of polyfluoroalkoxyethylene(PFA), fluorinated ethylene/propylene(FEP), poly(chlorotrifluoroethylene)(PCTFE), and an ethylene/ tetrafluoroethylene resin(ETFE).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a seal member for sanitary piping. More specifically, the present invention relates to a seal member for sanitary piping obtained by melt-molding a fluororesin having specific properties.

[0002]

2. Description of the Related Art The material of seal members such as gaskets and O-rings at joints for sanitary piping used in production equipment for pharmaceuticals, foods, drinking water, ultrapure water, etc. is more severe than ordinary piping. Exposed to various conditions. In other words, in the production of pharmaceuticals, impurities do not elute in the product,
In order to remove pyrogen as a pyrogen, it is required to withstand alkali cleaning and cleaning with saturated steam.
In addition, when used for the production of food, drinking water and ultrapure water, of course, impurities do not elute in the product,
It is required to withstand high temperature and high pressure steam sterilization.

[0003] In such a production apparatus for pharmaceuticals, foods, drinking water, ultrapure water, etc., a gasket made of ethylene propylene rubber (hereinafter referred to as EPDM) or a silicone plastic is used as a gasket for sanitary piping. . However, these EPDMs and silicone plastics deteriorate over time when washing is repeated using saturated vapor, alkaline solution, etc. in the pipes, and the deteriorated parts fall off in the pipes and mix as foreign substances in the liquid. In addition, there is a problem that the plasticizer contained in these materials elutes due to long-term use. In addition, silicone plastics
Since alkali resistance is inferior, if a small amount of an alkali component remains after washing, there is a defect such as sticking to the flange metal surface when steam sterilized.

In order to solve this drawback, a seal member made of polytetrafluoroethylene (hereinafter referred to as PTFE) resin which is a fluororesin is used. Although PTFE resin is excellent in heat resistance and chemical resistance, it has a drawback in that it undergoes large stress denaturation with time and is inferior in elastic recovery power. For this reason, the gasket protrudes to the inner diameter side of the pipe, causing a pool of liquid, causing an opportunity for propagation of various germs, and the cleanliness cannot be maintained. In addition, since the hardness of PTFE resin is high, gas leakage such as steam cannot be prevented unless the tightening pressure of the flange portion is increased, and it is difficult to recover elasticity once retightened, and gas leakage is prevented after the second time. There is a drawback that you can not. Furthermore, the sealing member made of PTFE resin is manufactured by compression molding, and the surface treatment must rely on cutting, which is not efficient in terms of productivity and material yield, and it is difficult to smooth the surface. Therefore, there is also a disadvantage that due to the unevenness of the surface, the ability to maintain the cleanliness in the pipe is lacking, and the adhesion of the liquid and the aroma occur.

In order to eliminate the disadvantages of the gasket made of PTFE resin, a gasket for sanitary piping using porous PTFE resin and having a characteristic shape has been proposed (JP-A-5-99343). This gasket is
Because of the porous structure, the sealed fluid comes into contact with the inner periphery of the gasket, and the sealed fluid may penetrate from the inner periphery, so-called permeation leakage may occur. In particular, when used as a gas seal, permeation leakage may be a serious problem, and an attempt has been made to use a non-porous, melt-solidified layer on the inner peripheral surface of a porous PTFE resin gasket. Japanese Unexamined Patent Publication No. Hei 8-121599), which is reaching a use level.

However, a gasket made of PTFE resin in which non-porous material is melted and solidified on the inner peripheral surface has a problem that the production cost is further increased. Thus, PTFE
A sealing member using a resin has a drawback that hardness is high and stress change with time is large, and there is a problem that manufacturing cost is required to cover it.

Therefore, sanitary products which are excellent in chemical resistance, can maintain airtightness and cleanliness without causing stress denaturation even when used for a long time, are safe without elution of component materials in products, and have excellent productivity. A piping member is desired.

[0008]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies on sealing members, particularly sanitary piping members, in order to solve the above-mentioned problems. As a result, they have excellent chemical resistance and can be used for a long time. The present invention has also found a seal member which is small in stress denaturation, can maintain airtightness and cleanliness, does not elute component materials in a product, is safe, and has excellent productivity, and has completed the present invention. According to the present invention, the above problems are solved.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for producing an object at 230.degree.
The fluororesin melt viscosity of 10 ⁸ poises at 80 ° C. relates gasket formed by melting.

In a preferred embodiment, the gasket is made of fluorinated alkoxyethylene resin (PFA), fluorinated ethylene propylene (FEP), chlorotrifluoroethylene resin (PCTFE) and ethylene-tetrafluoroethylene resin (ETFE). It is melt molded from a fluororesin selected from the group consisting of:

[0011] In a preferred embodiment, the fluorine resin is 230 ° C. to 380 melt viscosity at ° C. is 10 ⁶ poises fluororesin.

In a preferred embodiment, the inner peripheral surface of the gasket which is a liquid contact surface has a surface roughness of Rz 0.4 μm or less.

In a further preferred embodiment, the gasket of the present invention comprises a fluorinated alkoxyethylene resin (PFA)
Is obtained by melt molding.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that a fluororesin having a specific melt viscosity is melt-molded.
By adopting such a configuration, the stress relaxation rate and the inner diameter dimensional change rate are small (that is, over a long time,
(Small change with respect to stress and stable in stress) occurs, and even if the tightening pressure of the flange increases, gas leakage does not occur and reuse is possible. Since the surface roughness can be made as small as possible, an effect of maintaining cleanliness in combination with the stress stability is produced. Specific effects include:
In particular, it appears remarkably in sanitary piping. That is,
Even if the gasket does not protrude into the pipe, it is minimized, so it does not hinder the flow of liquid in the pipe, and the roughness of the liquid contact part is extremely small, so that the liquid stays This prevents the growth of various bacteria in the piping.

When a melt-moldable fluororesin is melt-molded into a gasket shape, the gasket exhibits the characteristics of stress stability and good elastic recovery, and even if the tightening pressure of the flange is increased, gas leakage occurs. It is not known that there is no such effect and that the effect of reducing the roughness of the liquid contact surface occurs. In particular, the fluororesin generally has a high hardness, and many fluororesins that can be melt-molded have the same or higher hardness as the PTFE resin. By melt molding such a fluororesin,
The fact that the PTFE resin was able to improve stress instability (difficulty of elastic recovery) and the like was a finding discovered by the present inventors for the first time.

The melt viscosity of the fluororesin used in the present invention is at 230 ° C. to 380 ° C., is less than or equal to about 10 ⁸ poises. More than 10 ⁸ poises, tends to be difficult to melt molding.

The fluororesin used in the present invention includes:
For example, fluorinated alkoxyethylene resin (PFA), fluorinated ethylene propylene (FEP), chlorotrifluoroethylene resin (PCTFE), ethylene-tetrafluoroethylene resin (ETFE) and the like are used. From the viewpoint of handling, stress relaxation, and reducing surface roughness, PFA, FE
P and ETFE are preferred.

Among the above fluororesins, 230 ° C to 3 ° C
Melt viscosity at 80 ° C. and more preferably 10 ⁶ poises fluororesin. If the melt viscosity exceeds 10 ⁶ poise, the fluidity is slightly reduced in order to inject the resin into every corner of the mold while maintaining the molten state at a high temperature, so the molten state must be maintained for a long time. This is because, as a result, the cutting of the molecular chains of the resin by thermal energy proceeds, and the mechanical strength of the solidified product tends to decrease. Examples of the resin satisfying such conditions include fluorinated alkoxyethylene resin (PFA), fluorinated ethylene propylene (FEP), and ethylene-tetrafluoroethylene resin (ETFE).

The term "melt molding" is a general term for a method of heating a fluororesin into a fluidized state, injecting it into a mold, and solidifying the same, and includes injection molding, extrusion molding, blow molding and the like. These methods may be appropriately selected depending on the fluororesin used. For example, when PFA or PCTFE is used, extrusion molding and injection molding are preferable, and when FEP or ETFE is used, extrusion molding, blow molding and injection molding are used.

The melt molding such as injection molding, extrusion molding, blow molding and the like may be performed by a person skilled in the art selecting an appropriate apparatus according to each form and setting appropriate conditions.

The gasket obtained by melt-molding the fusible fluororesin of the present invention (hereinafter referred to as the gasket of the present invention) has a surface roughness Rz of about 0.
It is preferably 4 μm or less. Rz is preferably about 0.2 μm or less, and more preferably about 0.15 μm or less. A desired value (Rz of about 0.15 μm to about 0.2 μm) can be obtained by melt-molding the surface roughness of the gasket of the present invention, and there is almost no need to perform a cutting process unless a minute adjustment is required. . Considering that the surface roughness of the gasket obtained by compression molding of the conventionally used PTFE and then cutting is approximately Rz 5 μm, and Rz about 0.6 μm even when using a cutting tool that cuts well, The present invention has an even more excellent effect that a gasket that does not require cutting and has a smooth liquid contact surface can be obtained. That is, a gasket that is more efficient and has higher performance than the conventional gasket can be provided at low cost.

The surface roughness of the inner peripheral surface (that is, the liquid contact surface) of the gasket may be about Rz of about 0,0 depending on the melt molding conditions and the like.
Although it may exceed 4 μm, in this case, Rz can be reduced to about 0.4 μm or less by heat-treating the inner peripheral surface side. As a method of heat treatment, 300 ° C to 500 ° C
A method of contacting the surface of the heating element with the temperature for a predetermined time.

The surface roughness Rz means a ten-point average roughness, and 0.8 mm was extracted from the roughness curve in the direction of the average line, and was measured in the direction of the longitudinal magnification from the average line of the extracted portion. The sum of the average of the absolute values of the altitudes of the valley bottoms from the highest to the fifth and the average of the absolute values of the valleys of the lowest valley from the fifth to the fifth is expressed in μm. Say.

Further, the shape of the gasket is not specified.
FIG. 1 is a schematic sectional view showing the shape of the gasket of the present invention. FIG. 1 (1) shows a smooth sealing surface, FIGS. 1 (2) and (3) show a sealing surface taper shape, and FIG. 1 (4) shows a relationship between (1) and (2). Combination
(5) and (6) of FIG. 1 are gaskets having a convex shape on the sealing surface.

Hereinafter, characteristics of the gasket of the present invention will be described. The gasket of the present invention was used for 60 kgf / cm ²
When treated at 130 ° C for 24 hours with the tightening surface pressure of
The stress relaxation rate is preferably about 15% or less, more preferably about 10% or less, and even more preferably about 5% or less. If the stress relaxation rate exceeds about 15%, it is difficult to recover elasticity, and gas leakage may occur. In particular, PFA
Is preferably in the above range.

Further, when the gasket of the present invention, for example, a gasket made of PFA, is treated at 130 ° C. for 48 hours with a tightening surface pressure of 60 kgf / cm ² , the stress relaxation rate is about 5%.
% Or less, preferably about 2% or less, whereas the conventional PTFE exceeds 20%, and the gasket made of PFA has excellent stress resistance, low deformation and excellent elastic recovery. Understand. The stress relaxation rate is obtained by the following equation.

[0027]

(Equation 1)

The rate of change in the inner diameter of the gasket of the present invention is extremely small. 30 to 90 kgf / cm ² at room temperature
Even if a load is applied for 24 hours to 48 hours at a tightening surface pressure of about, preferably about -0.2% to about 0.5%, preferably about -0.1% to about 0.2%. is there. 130
Even when a load is applied at 24 ° C. for 24 to 48 hours, it is preferably about −0.1% to about 0.5%, and preferably about 0% to about 0.5%.
% To about 0.3%. The inner diameter dimensional change rate is obtained by the following equation.

[0029]

(Equation 2)

In particular, the rate of change in the inner diameter of the gasket made of PFA is about-when the load is applied for 24 to 48 hours at room temperature with a tightening surface pressure of 30 to 90 kgf / cm ^2.
While it is about 0.1% to about 0.2%, the conventional PT
The inner diameter dimensional change rate of the FE gasket is about -0.3% ~
About -0.9%. This indicates that the PTFE gasket protrudes into the pipe by about 0.3% to 0.9% of the inner diameter, but the gasket of the present invention hardly protrudes. Is shown.

Also, the gasket of the present invention is
When treated at 130 ° C. for 48 hours at a clamping surface pressure of / cm ^2, the rate of change in inner diameter is preferably about 0.5% to about −0.5%, more preferably about 0.4% to about 0%. %, More preferably from about 0.3% to about 0%. If it exceeds about 0.5%, the inner diameter of the gasket increases, and a stagnant portion is formed between the pipe and the liquid contact surface of the gasket, which is not preferable. If it is less than about -0.5%, the inner diameter of the gasket decreases. In addition, the gasket protrudes into the pipe, causing stagnation and contamination of the gasket, which is undesirable because it causes a reaction delay, a side reaction, and a contamination.

The gasket made of PFA of the present invention is 60 kg.
When treated at 130 ° C. for 48 hours with a tightening surface pressure of f / cm ^2, the rate of change in inner diameter is about 0.33%, while the rate of change in inner diameter of a PTFE gasket is about the same under the same conditions. Since it is -5%, the superiority of the present invention becomes clearer.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments, but it goes without saying that the present invention is not limited to these embodiments.

Example 1 PFA (manufactured by Daikin Industries, Ltd.) was heated at 370 ° C. using an injection molding machine (manufactured by Meiki Seisakusho).
Injection molding with a thickness of 3 m having the shape of (6) in FIG.
m, an outer diameter of 65 mm, an inner diameter of 35 mm, and an area of 23.56 cm ² were prepared.

Similarly, as a comparative example, PTFE (manufactured by DuPont) was cut using a cutting machine to a thickness of 3 mm and an outer diameter of 65 mm.
A gasket having a diameter of 35 mm, an inner diameter of 35 mm and an area of 23.56 cm ² was prepared.

The performance of the obtained gasket was examined. Table 1 shows the results.

[0037]

[Table 1]

The results in Table 1 are shown in FIG. 2 and FIG. FIG. 2 is a diagram showing the relationship between the tightening surface pressure and the stress relaxation rate, and FIG. 3 is a diagram showing the relationship between the tightening surface pressure and the rate of change in the inner diameter of the gasket. FIG. 2 shows that the gasket made of PFA of the present invention has a smaller stress relaxation rate at room temperature and 130 ° C. than the gasket made of PTFE of the comparative example, and has a higher elasticity. In addition, from FIG. 3, the PFA has an inner diameter dimensional change rate of almost zero, whereas the PTFE of the comparative example
Is from -1% to -4%, and it is apparent that it largely protrudes into the piping.

The surface roughness Rz of the inner peripheral surface (liquid contact surface) of the obtained gasket made of PFA and PTFE is 0.2 μm and 0.6 μm, respectively.
The gasket made from A was smoother. The electron micrographs are shown in FIGS. FIG. 4 and FIG.
FIGS. 6 and 7 are photographs at magnifications of 100 times and 10,000 times of the inner peripheral surface of the gasket obtained by melt-molding PFA. FIGS. 6 and 7 show the gasket obtained by cutting PTFE, respectively. Peripheral magnification of 100x and 10,000
It is a photograph of 0 times. 4 and 6 and FIGS. 5 and 7 at the same magnification, the difference in surface smoothness is obvious. As described above, the inner peripheral surface of the gasket obtained by the melt molding of PFA is clearly formed of the PTF obtained by cutting.
It turns out that it is smoother than the inner peripheral surface of E.

From the above results, it can be seen that the gasket of the present invention has better stress resistance, less deformation, and better elastic recovery than the conventional PTFE gasket. In addition, the gasket of the present invention can be easily manufactured and has a very smooth surface.

(Example 2) The gasket prepared in Example 1 was used to measure the amount of gasket compression and the amount of gas leakage in a heat cycle test. Test flange of the present invention
Wearing the PTFE gasket A gasket or Comparative Example N ₂ gas ^{(0.392Mpa (4.0kgf / cm 2)} ) to tighten the tightening nut until it sealed and left in a hot air oven at 130 ° C., predetermined heating Removed after a lapse of time. After the heated pressure vessel was cooled to room temperature, the sealed pressure vessel was filled with N ₂ gas, and the gas leaking from the gasket portion by the underwater replacement method was collected for a predetermined time to be leaked.
After the measurement of gas leakage, the nut was retightened until the test gas could be sealed again, and heating and measurement were repeated until the desired cumulative heating time. Table 2 shows the results.

[0042]

[Table 2]

The results in Table 2 show that the PTFE gasket of the comparative example has a large amount of leakage even when the compression ratio is increased, whereas the PFA gasket of the present invention has a small amount of leakage despite the small compression ratio. There were few. This indicates that the gasket of the present invention is excellent in heat resistance and stress resistance.

[0044]

The gasket obtained by melt-molding a fluororesin having a specific melt viscosity is excellent in chemical resistance, has small stress denaturation even after long-term use, has excellent airtightness, and has high productivity. Is also excellent. In addition, since the roughness of the liquid contact surface of the gasket can be minimized, in combination with the above-mentioned stress stability, the accumulation of liquid is prevented, and the propagation of various bacteria in the piping is suppressed, so that the cleanliness is maintained. Is done.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a shape of a gasket of the present invention.

FIG. 2 is a diagram showing a relationship between a tightening surface pressure and a stress relaxation rate.

FIG. 3 is a diagram illustrating a relationship between a tightening surface pressure and a rate of change in an inner diameter dimension of a gasket.

FIG. 4 is an electron micrograph of the inner peripheral surface of a gasket obtained by melt-molding PFA at a magnification of 100 times.

FIG. 5 is an electron micrograph of the inner peripheral surface of a gasket obtained by melt-molding PFA at a magnification of 10,000 times.

FIG. 6 is an electron micrograph of the inner peripheral surface of a gasket obtained by cutting PTFE, which is magnified 100 times.

FIG. 7 is an electron micrograph of the inner peripheral surface of a gasket obtained by cutting PTFE, which is magnified 10,000 times.

[Explanation of symbols]

 1 Sealed surface tapered shape 2 Sealed surface convex shape

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[Procedure amendment]

[Submission date] January 31, 2000 (200.1.3
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (5)

[Claims] 1. A melt viscosity at 230 ° C. to 380 ° C. is formed by melting the fluororesin is 10 ⁸ poises, gaskets. 2. The method according to claim 2, wherein the fluororesin is a fluoroalkoxyethylene resin (PFA), a fluoroethylenepropylene (F)
The gasket according to claim 1, wherein the gasket is a fluororesin selected from the group consisting of EP), ethylene trifluorochloride resin (PCTFE), and ethylene-tetrafluoroethylene resin (ETFE). 3. The method according to claim 1, wherein the fluororesin is 230 to 380 ° C.
The gasket of claim 1 or 2 melt viscosity of less fluororesin 10 ⁶ poise at. 4. The gasket according to claim 1, wherein a surface roughness of an inner peripheral surface of the gasket serving as a liquid contact surface is Rz 0.4 μm or less. 5. The gasket according to claim 1, wherein the gasket is a gasket obtained by melt-molding a fluorinated alkoxyethylene resin (PFA).