JP2003253007A - Method for producing modified fluororesin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a modified fluororesin which does not cause discoloration on molding. <P>SOLUTION: This method comprises irradiating a fluororesin with a specified dose of radiation, and then subjecting the irradiated fluororesin to heat treatment at a temperature of ≥50°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a modified fluororesin, and more particularly to a method for producing a modified fluororesin that does not cause discoloration during molding.

[0002]

2. Description of the Related Art Polytetrafluoroethylene (PTF
Fluorine resins such as E) have excellent properties such as heat resistance, chemical resistance, and solvent resistance. Therefore, taking advantage of these characteristics, high cleanliness such as chemical, medical, food or semiconductor is required. It is widely used in various fields.

Further, among these applications, the application requiring abrasion resistance is modified by irradiating radiation, and this abrasion resistance modification technique is based on fluororesin. Occupies an important position in expanding the application of.

[0004]

However, according to the conventional method of modifying by radiation, when the modified fluororesin is molded by hot molding, discoloration is likely to occur, so that a clean image of the fluororesin is obtained. Have the problem of damaging.

Therefore, it is an object of the present invention to provide a method for producing a modified fluororesin that does not cause discoloration during molding.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for producing a modified fluororesin in which the abrasion resistance is improved by irradiating the fluororesin with radiation, and the fluororesin has a predetermined content. The present invention provides a method for producing a modified fluororesin, which comprises irradiating a dose of radiation and subjecting the obtained irradiated fluororesin to a heat treatment at 50 ° C. or higher.

The heat treatment for the irradiated fluororesin in the present invention is carried out in order to prevent discoloration of the fluororesin at the time of molding. The reason for setting the temperature to 50 ° C. or higher is that the discoloration by the following mechanism is effective. This is to suppress it.

That is, the cross-linking of the fluororesin progresses efficiently under the conditions of low oxygen concentration and specific temperature, but on the one hand, the characteristics of the radiolytic type of the fluororesin still remain, and therefore, the cross-linking As the reaction progresses, a low molecular weight product will be produced in the resin.

Since this low molecular weight product is a product of a disproportionation reaction or a defluorination reaction at the time of irradiation with radiation, it has an intramolecular double bond and a molecular terminal double bond.
In a sealed mold or the like, fluorine atoms are easily released, which causes discoloration due to carbonization.

The heat treatment in the present invention releases this low molecular weight substance generated in the irradiated fluororesin to the outside, thereby suppressing the occurrence of discoloration, and in order to effectively perform this action. Requires a certain temperature condition, and the temperature setting of 50 ° C. or higher is a prerequisite for this. The heat treatment is often
It is performed at 100 ° C. or higher.

As the radiation irradiation conditions, the oxygen concentration in the irradiation atmosphere is set to 10 torr or less, the fluororesin is heated to the melting point or higher, and the irradiation dose is 1 kG.
It is preferable to set y to 10 MGy.

An oxygen concentration of 10 torr or less is preferable for preventing oxidative deterioration of the fluororesin and ensuring high wear resistance, and heating above the melting point activates the molecular motion of the main chain of the fluororesin. However, this is a preferable condition for achieving highly efficient crosslinking.

Further, the radiation dose of 1 kGy to 10 MGy is suitable for ensuring a sufficient improvement in wear resistance at the lower limit and for preventing the deterioration of elongation properties and the like due to the radiation at the upper limit. It becomes a condition.

However, under the above-mentioned conditions, it is not preferable to raise the temperature of the fluororesin excessively, because it leads to the breakage of the main chain of the molecule.
The temperature is set to 0 ° C higher. The melting point referred to here is a differential scanning calorimeter (D) when the temperature is raised at 20 ° C./min.
It is determined by measuring the endothermic peak by SC), and is specified to be 327 ° C. in the case of PTFE and 310 ° C. and 260 ° C. in the case of PFA and FEP described later, respectively.

The fluorine resin to be modified in the present invention includes PTFE, tetrafluoroethylene-fluoro (alkyl vinyl ether) type copolymer (PF).
A), tetrafluoroethylene-ethylene-based copolymer (FEP), tetrafluoroethylene-ethylene-based copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene-based copolymer or polyvinylfluorine Ride and the like can be mentioned, and these can be used alone or as a mixture with each other.

These fluororesins include, for example, PTFE obtained by copolymerizing perfluoro (alkyl vinyl ether), hexafluoropropylene, (perfluoroalkyl) ethylene or chlorotrifluoroethylene, and the copolymerization thereof is also included. The amount is often
It is set to 1.0 mol% or less. Further, in the case of the copolymer type fluororesins listed above, it is possible to include a small amount of the third component in the molecular constitution.

In the modified fluororesin obtained by the production method of the present invention, in order to further enhance the utility of the modified fluororesin, the heat of crystallization and the melting point of the resin after modification are 40 J / g or less, respectively. And preferably 325 ° C. or lower.

In particular, the amount of heat of crystallization has the property of being inversely proportional to the molecular weight, and when the main chain of the molecule is cleaved by the irradiation of radiation in the resin and the resulting cross-linking reaction is caused, branching of the main chain improves. Therefore, in order to obtain a good degree of crosslinking, it is preferable to suppress it to a certain value or less, and the above-mentioned 40 J / g is a preferable maximum value therefor.

On the other hand, the melting point after the modification tends to decrease as the crystal becomes smaller due to crosslinking, and therefore, in order to secure a predetermined level of wear resistance, the above-mentioned level is required. Is preferable. The amount of heat of crystallization mentioned above is a peak that is determined by connecting a point at which the curve deviates from the baseline and a point at which the curve returns to the baseline with a straight line when the exothermic peak at the time of cooling at 20 ° C./min is measured by DSC. Calculated by area.

In most cases, the irradiation of radiation in the present invention is performed on a powdery fluororesin. Also,
The modified resin obtained may be used alone,
Alternatively, it is possible to use a mixture with an unmodified fluororesin that does not emit radiation. In the latter case, the average particle size of the modified resin is 50 μm or less in order to ensure dispersibility in the unirradiated resin. And the maximum particle size is preferably 150 μm or less. The radiation used in the present invention may be ionizing radiation such as γ-ray, electron beam, X-ray, neutron beam or high energy ion.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the method for producing a modified fluororesin according to the present invention will be described.

Example 1 A PTFE molding powder (G-163 manufactured by Asahi Glass Co., Ltd.) having an average particle size of 25 μm was prepared, and this was subjected to a vacuum with an oxygen concentration of 0.5 torr and 335 ° C.
The electron beam was irradiated so that the absorbed dose would be 100 kGy under the heating temperature. Next, this powder was pulverized with a jet mill until the average particle size became 20 μm, and the heat of crystallization was determined, and a result of 33.1 J / g was obtained.

Next, 50% by weight of this irradiated powder and 50% by weight of the above-mentioned PTFE molding powder (unirradiated powder) were mixed with each other by a Henschel mixer, and this mixed powder was then heated at 50 ° C. × 200 in a thermostat in an air atmosphere. Heat-treated for a certain period of time, which gives the desired molding PTFE
A powder was produced.

[0023]

Example 2 A predetermined PTFE powder for molding was manufactured by setting the heat treatment condition in the constant temperature bath to 100 ° C. × 24 hours in Example 1 and setting the other conditions to the same conditions.

[0024]

[Example 3] In Example 1, a step of granulating a mixed powder of an irradiated powder and an unirradiated powder with isopropyl alcohol (IPA) and water was further added.
A predetermined PTFE powder for molding was manufactured by performing heat treatment at 0 ° C. for 12 hours and setting the other conditions under the same conditions.

[0025]

Example 4 In Example 3, a predetermined PTFE powder for molding was manufactured by setting the heat treatment condition in the constant temperature bath to 330 ° C. × 8 hours and setting the other conditions to the same conditions.

[0026]

[Comparative Example] In Example 1, a predetermined PTFE powder for molding was produced by setting the heat treatment condition in the constant temperature bath to 40 ° C x 200 hours and setting the other conditions to the same conditions.

[0027]

2. Description of the Related Art In Example 1, a predetermined molding PTFE powder was manufactured by not performing heat treatment in a constant temperature bath and setting the other conditions to the same conditions.

Table 1 summarizes the presence or absence of discoloration and the abrasion resistance of the molding PTFE powder obtained by the above examples after molding.

[0029]

[Table 1]

The molding was carried out by filling the molding powder obtained in each example into a cylindrical mold having an inner diameter of 40 mm,
After firing at 50 ° C. for 50 minutes, a hot coining method of applying a pressure of 100 kgf / cm ² and cooling to 100 ° C. was performed.

In the wear resistance test, a 1 mm-thick sheet sample collected from each molded body was adhered to a SUS ring, which was then subjected to a ring-on-disk wear tester in air at room temperature to obtain a surface pressure of 0. 0.25 MPa and speed 1.33
It was carried out by measuring the specific wear amount under the condition of m / s.

According to Table 1, the molded articles using the molding PTFE powders obtained in Examples 1 to 4 all have a good appearance without discoloration, whereas the conventional PT
The molded body using the FE powder turned gray and a clear difference was observed between the two.

This is because the irradiated PTFE powder of the example was subjected to a predetermined heat treatment at a temperature of 50 ° C. or higher before molding,
Therefore, the low molecular weight substance that causes discoloration at the time of molding is not built in, whereas the conventional example that does not undergo heat treatment has a built-in discoloration factor, and this difference is the presence or absence of discoloration. It appeared.

Also, in terms of abrasion resistance, the sheet samples of the examples all show characteristics similar to those of the conventional example, and therefore, according to the present invention, the original clean image of the fluororesin is maintained. As it is, it becomes possible to give the fluororesin a predetermined level of abrasion resistance. In addition, the reason why the molded body using the powder of the comparative example is discolored in spite of being subjected to the heat treatment is that the heat treatment temperature is low.

[0035]

As described above, according to the method for producing a modified fluororesin according to the present invention, since the fluororesin is irradiated with radiation and then heat-treated at 50 ° C. or higher, discoloration occurs during molding. An unmodified fluororesin can be provided.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuaki Yamamoto             1-6-1, Otemachi, Chiyoda-ku, Tokyo             Standing Wire Co., Ltd. F-term (reference) 4F070 AA23 HA03 HA04 HA05 HB14

Claims (4)

[Claims] 1. A method for producing a modified fluororesin for improving abrasion resistance by irradiating a fluororesin with radiation, wherein the fluororesin is irradiated with a predetermined dose of radiation, and the obtained irradiation fluororesin is heated to 50 ° C. A method for producing a modified fluororesin, which comprises performing the above heat treatment. 2. The step of irradiating the radiation is performed under an oxygen concentration of not less than a melting point of the fluororesin and not more than 10 torr, and an irradiation dose of 1 kGy to 10 MGy. Method for producing modified fluororesin. 3. The step of irradiating with radiation is performed such that the heat of crystallization of the irradiated fluorocarbon resin is 40 J / g or less and the melting point is 325 ° C. or less. Method for producing modified fluororesin. 4. The step of irradiating with radiation comprises polytetrafluoroethylene, tetrafluoroethylene-fluoro (alkyl vinyl ether) type copolymer, tetrafluoroethylene-hexafluoropropylene type copolymer, tetrafluoroethylene-ethylene type Copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene-based copolymer, polyvinylfluoride and the fluororesin selected from the mixture thereof, characterized in that it is performed for the fluororesin The method for producing the modified fluororesin according to claim 1.