JP7159653B2 - Method for producing fluororesin powder - Google Patents

Description

The present invention relates to a method for producing fluororesin powder.

Conventionally, powdery fluororesin (fluororesin powder) has excellent properties such as low friction properties, non-adhesiveness, heat resistance and chemical resistance. Therefore, it is used for mechanical parts such as sliding bodies.

As a method for producing such a fluororesin powder, for example, Patent Document 1 describes a method of mechanically pulverizing a fluororesin sheet or block to obtain a fluororesin powder having a predetermined particle size. there is

JP-A-10-316761

However, according to the study of the present inventors, even if the pulverization method of the fluororesin is appropriately selected, the average particle diameter of the fluororesin powder is reduced and the particle size distribution of the fluororesin powder is narrowed. found to be difficult to combine.

The present invention has been made in view of the problems described above, and can achieve both a reduction in the average particle diameter of the fluororesin powder and a narrower particle size distribution of the fluororesin powder. An object of the present invention is to provide a method for producing fluororesin powder.

A brief outline of typical inventions disclosed in the present application is as follows.

[1] (a) a step of pulverizing the fluororesin to form pulverized pieces, and (b) after the step (a), heating the pulverized pieces to produce a fluororesin powder, In the step (a), the fluororesin is pulverized by a pulverization method that leaves residual stress in the pulverized pieces, and in the step (b), the pulverized pieces are heated to a temperature equal to or higher than the melting point of the fluororesin. Production method.

[2] In the method for producing fluororesin powder described in [1], the pulverizing method is a method of pulverizing mainly by shearing force.

[3] In the method for producing a fluororesin powder described in [1], the pulverizing method is any one of a mortar method, a roller mill method and a ball mill method.

According to the present invention, it is possible to both reduce the average particle diameter of the fluororesin powder and narrow the particle size distribution of the fluororesin powder.

FIG. 2 is a process flow chart showing steps for producing a fluororesin powder according to one embodiment of the present invention. FIG. 2 is an SEM image of the fluororesin powder after the pulverization process shown in FIG. 1. FIG. FIG. 3 is a graph showing the particle size distribution of the fluororesin powder shown in FIG. 2. FIG. FIG. 2 is an SEM image of the fluororesin powder after the heat treatment process shown in FIG. 1. FIG. 5 is a graph showing the particle size distribution of the fluororesin powder shown in FIG. 4; FIG. 2 is an SEM image of fluororesin powder heat-treated at different temperatures in the heat treatment step shown in FIG. 1 ; FIG. 1 is a schematic diagram showing an example of a protective film using the fluororesin powder obtained by the present invention; FIG. FIG. 3 is a schematic diagram showing an example of a protective film using a conventional fluororesin powder.

(to be considered)
First, before describing the embodiments, the matters studied by the inventors will be described.

FIG. 8 shows a protective film (protective member, coating film) 200 using the conventional fluororesin powder 100 . The protective film 200 is formed on the substrate 1 made of metal or the like. The protective film 200 is composed of the fluororesin powder 100 and the coating agent 2 . This protective film 200 is formed by applying a resin (not shown) having a high affinity with the base material 1 onto the base material 1, then applying a coating agent 2 in which the fluororesin powder 100 is dispersed, and baking the coating. It is formed. By forming the protective film 200 on the base material 1 in this manner, non-adhesion and low friction properties can be imparted compared to the case where only the base material 1 is used.

Although not shown, another example of the protective film formed on the substrate is a plated film (metal plated film). This plated film is formed by coating a base material with a metal plated layer in which fluororesin powder is dispersed. In this case, both the properties of the metal plating layer (eg, corrosion resistance) and the properties of the fluororesin (eg, self-lubricating properties, water repellency, and non-stickiness) can be achieved.

Here, a method for producing the fluororesin powder will be examined. As described above, the fluororesin powder 100 is generally produced by mechanically pulverizing a fluororesin sheet or block. Methods for pulverizing the fluororesin include, for example, pulverization by impact (jet mill method, etc.), pulverization by shearing force (mortar method, roller mill, etc.), or a combination thereof (ball mill method, etc.).

First, the jet mill method is a method in which high-pressure gas is ejected from a nozzle, the raw material is accelerated by the generated jet stream, and the raw material is pulverized by collision between the accelerated particles. The jet mill method is effective when the hardness of the object to be ground is high. However, since fluororesin has high elasticity, when the average particle diameter is less than a certain value (approximately 40 μm or less), the kinetic energy generated when particles collide with each other causes plastic deformation. less than the energy required for Therefore, it is difficult to obtain a fluororesin powder having an average particle size of 40 μm or less by the jet mill method. As shown in FIG. 8, if the protective film 200 containing the fluororesin powder 100 having an average particle size of 40 μm or more is formed on the substrate 1, the protective film 200 has a rough surface. In this case, the coefficient of friction of the protective film 200 increases. Therefore, there is a problem that the fluororesin powder 100 is easily separated from the protective film 200, and the abrasion resistance of the protective film 200 is lowered.

Next, the mortar method is a method in which one of a pair of grindstones arranged vertically is rotated, and the raw material is pulverized by the shear force generated on the raw material as it passes between the pair of grindstones. is. In addition, the roller mill method is a method in which a roller is rotated on an iron plate and the raw material is pulverized by shearing force generated on the raw material when the raw material passes between the iron plate and the roller. In the mortar method and the roller mill method, the material exceeding the plastic deformation region of the raw material is broken and pulverized. At this time, since the material is stretched beyond the elastic deformation region of the raw material, particles with a smaller average particle size (40 μm or less) are likely to be produced compared to, for example, the jet mill method. On the other hand, since the material is stretched beyond the elastic deformation region of the raw material, particles with a large aspect ratio (non-spherical) tend to be generated. A large number of particles with a large aspect ratio widens the particle size distribution (particle size distribution). Therefore, it is difficult to obtain a fluororesin powder having a narrow particle size distribution by the mortar method and the roller mill method. As shown in FIG. 8, when the protective film 200 containing the fluororesin powder 100 having a wide particle size distribution is formed on the substrate 1, the protective film 200 has a rough surface. As described above, in this case, there is a problem that the wear resistance of the protective film 200 is lowered.

Next, the ball mill method is a method in which raw materials and hard balls are placed in a container and the raw materials are ground and pulverized by rotating the container. In this method, pulverization occurs due to both impact and shear, but pulverization due to shear has a large effect, and particles with a large aspect ratio are likely to be produced similarly to the mortar method and roller mill method. Therefore, it is difficult to obtain a fluororesin powder having a narrow particle size distribution by the ball mill method. Therefore, as shown in FIG. 8 described above, if the protective film 200 containing the fluororesin powder 100 having a wide particle size distribution is formed on the substrate 1, the protective film 200 has a rough surface.

From the above, it was found that it is difficult to simultaneously reduce the average particle diameter of the fluororesin powder and narrow the particle size distribution of the fluororesin powder even if the fluororesin pulverization method is appropriately selected. . Therefore, it is desired to reduce the average particle size of the fluororesin powder and narrow the particle size distribution of the fluororesin powder by devising a method for producing the fluororesin powder.

(Embodiment)
An embodiment of the present invention will be described below with reference to the drawings. In each drawing showing the embodiments, the same or similar parts are denoted by the same or similar symbols or reference numbers, and the description will not be repeated in principle.

As shown in FIG. 1, the method for producing a fluororesin powder according to the present embodiment comprises a fluororesin pulverization step (S1), and a fluororesin pulverized in the pulverization step (S1) (hereinafter referred to as pulverized pieces of the fluororesin). ) and a heat treatment step (S2).

The fluororesin is not particularly limited, but examples include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer ( FEP) or the like can be used. Two or more of these fluororesins may be used in combination. Polytetrafluoroethylene is most suitable as the fluororesin powder used for the protective film.

Then, in the pulverization step (S1), the fluororesin is pulverized by a pulverization method that leaves residual stress in the pulverized pieces. Residual stress is the stress that exists in the object even after the external force has been removed. As a pulverization method in which residual stress remains in pulverized pieces, a mortar method, a roller mill method, or a ball mill method, which are pulverization methods mainly using shear force, are preferable. The shape of the pulverized pieces of the fluororesin in which the residual stress remains has a shape with a large aspect ratio, specifically, a scale or twist shape. When the fluororesin is pulverized by the mortar method, it is preferable to grind the fluororesin into a powder having an average particle size of 1 to 2 mm in advance.

Further, in the heat treatment step (S2), the pulverized pieces of the fluororesin are heated to a temperature higher than the melting point of the fluororesin to produce fluororesin powder. For example, when polytetrafluoroethylene (melting point 327°C) is used as the fluororesin, the heating temperature is preferably 340±10°C. Also, the heating time is preferably 15 minutes or more and 60 minutes or less. If the heating time is less than 15 minutes, the temperature may become uneven, and stress release due to heat, which will be described later, may not proceed sufficiently. On the other hand, if the heating time exceeds 60 minutes, a decomposition reaction that cuts the carbon chains constituting the fluororesin proceeds, possibly degrading the properties of the fluororesin. Moreover, the heating atmosphere in the heat treatment step (S2) is not particularly limited, and the heating of the crushed pieces of the fluororesin can be performed, for example, in the atmosphere.

The effects of the method for producing fluororesin powder according to the present embodiment will be described below.

In this embodiment, in the fluororesin pulverization step (S1) shown in FIG. 1, the fluororesin is pulverized by a pulverization method that leaves residual stress in the pulverized pieces. Specifically, in the pulverization method that mainly uses shear force such as the mortar method, the raw material is stretched beyond the elastic deformation range (elastic deformation region), and then the plastic deformation range (plastic deformation region) of the raw material is stretched. Breaks and pulverizes by exceeding. Here, after the raw material is deformed by the external force, the raw material tends to return to its original shape when the external force is removed. However, in the plastically deformed region, the raw material remains deformed and cannot return to its original shape. Therefore, a stress (residual stress) that tends to restore the original shape is generated inside the raw material. As a result, by pulverizing the fluororesin mainly by a pulverization method using a shearing force, it is possible to produce pulverized pieces of the fluororesin having a shape (non-spherical shape) with a large aspect ratio (that is, residual stress remains). can.

Next, in the present embodiment, in the heat treatment step (S2) of the fluororesin shown in FIG. 1, the pulverized pieces are heat-treated to produce fluororesin powder. By heating the crushed pieces of the fluororesin to a temperature higher than the melting point of the fluororesin, the molecular chains constituting the fluororesin are allowed to move, and the residual stress remaining in the crushed pieces of the fluororesin is released. As a result, the non-spherical pulverized pieces of the fluororesin change into a spherical or nearly spherical shape.

Specifically, in the pulverization step (S1), when the fluororesin is pulverized by a pulverization method that mainly uses a shearing force such as a mortar method, the fluororesin is elongated to form pulverized pieces. . Therefore, when the residual stress remaining in the pulverized pieces of the fluororesin is released, the stretched pulverized pieces shrink and become spherical. As a result, it is possible to produce a fluororesin powder having a smaller average particle size and a narrower particle size distribution than the pulverized pieces of the fluororesin.

As described above, in the present embodiment, it is possible to obtain a fluororesin powder having a smaller average particle diameter and a narrower particle size distribution than the fluororesin powder produced only by the pulverization process.

In addition, as shown in the examples below, in the present embodiment, one pulverization step and one heat treatment step are performed without performing the pulverization step multiple times, for example, the average particle diameter obtained by the jet mill method A fluororesin powder having a small average particle size (20 μm or less) and a narrow particle size distribution can be obtained.

<Protective film using fluororesin powder>
FIG. 7 is a schematic diagram showing a protective film (protective member, coating film) using fluororesin powder according to one embodiment of the present invention. As shown in FIG. 7, the protective film 3 is formed on the substrate 1 made of metal or the like. The protective film 3 is composed of the fluororesin powder 10 and the coating agent 2 . This protective film 3 is formed by applying a resin (not shown) having a high affinity with the base material 1 onto the base material 1, then applying a coating agent 2 in which fluororesin powder 10 is dispersed, and baking the coating. It is formed. By forming the protective film 3 on the base material 1 in this way, the abrasion resistance (frictional characteristics) can be improved as compared with the case where the base material 1 is used alone. As a result, the durability of the substrate 1, such as a mechanical component, can be enhanced.

In particular, as shown in FIG. 7, when a protective film 3 containing fluororesin powder 10 having an average particle size of 40 μm or less (more preferably 20 μm or less) and having a narrow particle size distribution is formed on a substrate 1, , a protective film 3 having a smooth surface is obtained. By doing so, the protective film 3 can keep the coefficient of friction small, and can further improve the non-adhesiveness and lubricity of the substrate 1 such as a machine part.

EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

<Configuration of Example 1 and Comparative Examples 1 to 3>
The raw material used in Example 1 and Comparative Examples 1 to 3 is crosslinked fluororesin powder (average particle size: about 1 to 2 mm).

The crosslinked fluororesin powder can be produced, for example, by the following method. First, for a fluororesin molded body (for example, a sheet), in an oxygen-free atmosphere or a low-oxygen atmosphere with a concentration of about 500 ppm or less, and at least the melting point of the fluororesin (preferably 10 to 30 ° C. higher than the melting point) temperature), it is irradiated with ionizing radiation such as an electron beam (irradiation dose: 1 kGy to 10 MGy) to crosslink the fluororesin (crosslinking treatment). Thereafter, the crosslinked fluororesin compact can be mechanically pulverized by a cut mill method or the like to obtain a crosslinked fluororesin powder (average particle diameter 1 to 2 mm). The crosslinked fluororesin powder may be obtained by subjecting the fluororesin powder to a similar cross-linking treatment.

In Example 1, Comparative Example 1, and Comparative Example 2, tetrafluoroethylene (melting point: 327° C.) was used as the fluororesin. In this case, the heating temperature in the cross-linking treatment is 340° C., for example.

In Example 1 and Comparative Examples 1 to 3, a crosslinked fluororesin was used as a raw material, but the raw material is not limited to this, and an uncrosslinked fluororesin may be used.

<Manufacturing methods of Example 1 and Comparative Examples 1 to 3>
Example 1 and Comparative Examples 1 to 3 were produced by the following method. Each condition is an example.

(S1) Pulverization Step A crosslinked fluororesin powder (average particle size: 1 to 2 mm) was pulverized by a mortar method to obtain pulverized pieces of fluororesin. The pulverized pieces of the fluororesin obtained here were designated as Comparative Example 1. The mortar method may be a dry method that does not use water or a wet method that uses water.

(S2) Heat treatment step After the step (S1), the pulverized pieces of the fluororesin were heated for 30 minutes. The heating temperature at this time was 330° C. in Example 1, 300° C. in Comparative Example 2, and 360° C. in Comparative Example 3.

<Results of Example 1 and Comparative Example 1>
The results of Example 1 and Comparative Example 1 are summarized in FIGS. 2 to 5. FIG. FIG. 2 is an SEM image of the pulverized pieces of the fluororesin obtained in the (S1) pulverizing step (Comparative Example 1). FIG. 3 shows the particle size distribution of the pulverized pieces of the fluororesin shown in FIG. 2 (Comparative Example 1). FIG. 4 is an SEM image of the fluororesin powder (Example 1) obtained by the (S2) heat treatment step. FIG. 5 shows the particle size distribution of the fluororesin powder (Example 1) shown in FIG.

First, the shape of the pulverized pieces of the fluororesin of Comparative Example 1 will be described. (S1) The pulverization step is performed using a mortar method, which is a pulverization method that mainly uses shear force. Therefore, as shown in FIG. 2, the pulverized pieces of the fluororesin obtained in the (S1) pulverization step (Comparative Example 1, that is, before the (S2) heat treatment step in Example 1) had a shape with a large aspect ratio (non-spherical , specifically scaly or twisted). As described above, it is considered that residual stress remains in the pulverized pieces of the fluororesin.

Next, the particle size distribution of the pulverized pieces of the fluororesin of Comparative Example 1 will be described. As shown in FIG. 3, in Comparative Example 1, the particle size (D50%) at the point of 50 vol% in the cumulative distribution of particle sizes is 21.8 μm, and the particle size at the point of 90 vol% in the cumulative distribution of particle sizes. (D90%) is 43.4 μm. Here, the average particle size refers to the particle size when the cumulative distribution of particles represents 50 vol %, ie, D50%, and D90% represents approximately the maximum particle size among all particles. The results of Comparative Example 1 correspond to the case where the fluororesin powder was obtained only by the pulverization process by the mortar method, for example. That is, it can be said that the fluororesin powder has an average particle size of 20 μm or more and a relatively wide particle size distribution by the pulverization process alone.

Next, the shape of the fluororesin powder of Example 1 will be described. FIG. 4 shows the result of subjecting the fluororesin pulverized pieces obtained in the (S1) pulverizing step in Example 1 to the (S2) heat treatment step. As shown in FIG. 4, the fluororesin powder after the (S2) heat treatment step has a shape with a small aspect ratio (specifically, a spherical shape). As described above, it is believed that the residual stress was released by the heat treatment and the elongated pulverized pieces contracted and spheroidized.

Next, the particle size distribution of the fluororesin powder of Example 1 will be described. As shown in FIG. 5, in Example 1, the particle size (D50%) at the point of 50 vol% in the cumulative distribution of particle sizes was 17.0 μm, and the particle size at the point of 90 vol% in the cumulative distribution of particle sizes. (D90%) is 36.2 μm. The results of Example 1 show that the (S2) heat treatment step reduced the average particle size to 20 μm or less and narrowed the particle size distribution.

<Comparison results of Example 1 and Comparative Examples 1 to 3>
Comparative results of Example 1 and Comparative Examples 1 to 3 are summarized in FIG. FIG. 6 shows SEM (scanning electron microscope) images of Example 1 and Comparative Examples 1-3. The SEM image of Comparative Example 1 is a in FIG. 6, the SEM image of Comparative Example 2 is b in FIG. 6, the SEM image of Example 1 is c in FIG. 6, and the SEM image of Comparative Example 3 is d in FIG. and

Here, the heating temperature in the (S2) heat treatment step is examined. As described above, Comparative Example 1 is unheated, that is, no heat treatment is performed, Comparative Example 2 is heated at 300 ° C. for 30 minutes, Example 1 is heated at 330 ° C. for 30 minutes, Comparative Example 3 was heated at 360° C. for 30 minutes.

As shown in FIG. 6a, the fluororesin powder (pulverized pieces) of Comparative Example 1 had a scaly shape and an average particle size of 21.8 μm (see FIG. 3). As shown in FIG. 6b, the fluororesin powder of Comparative Example 2 had a scaly shape and an average particle diameter of 21.8 μm. That is, in Comparative Example 2, there is no change compared to Comparative Example 1. As shown in FIG. 6c, the fluororesin powder of Example 1 has a spherical shape and an average particle diameter of 17.0 μm (see FIG. 5). As shown by d in FIG. 6, the fluororesin powder of Comparative Example 3 is clearly melted. Therefore, the fluororesin powder was integrated, and the particle size could not be measured.

As described above, Comparative Example 2 is heated at a temperature about 30° C. lower than the melting point (327° C.) of the fluororesin. Therefore, it is considered that the stress is not released and the shape of the fluororesin powder does not change before and after the heat treatment step (S2). As a result, it was found that even if heat treatment is performed at a temperature sufficiently lower than the melting point of the fluororesin, the average particle diameter does not decrease and the particle size distribution does not narrow.

In Comparative Example 3, heating is performed at a temperature about 30° C. higher than the melting point (327° C.) of the fluororesin. As a result, the fluororesin powder was melted, resulting in a meaningless fluororesin powder.

From the above results, it was found that the heating temperature in the (S2) heat treatment step is preferably 340±10°C.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

1 base material 2 coating agent 3,200 protective film 10,100 fluororesin powder

Claims (3)

(a) pulverizing a fluororesin made of polytetrafluoroethylene to form pulverized pieces of the fluororesin;
(b) after the step (a), heating the pulverized pieces to generate fluororesin powder having an average particle size of 20 μm or less,
In the step (a), the fluororesin is pulverized by any one of a mortar method, a roller mill method, and a ball mill method in which residual stress remains in the pulverized pieces to make the pulverized pieces non-spherical,
In the step (b), the crushed pieces are heated at a heating temperature of 340° C.±10° C., which is equal to or higher than the melting point of the fluororesin , to release the residual stress remaining in the crushed pieces, thereby forming a non-spherical shape. A method for producing a fluororesin powder, wherein the crushed pieces are formed into a shape having an average particle diameter smaller than that of the crushed pieces. In the method for producing the fluororesin powder according to claim 1,
The pulverizing method is a method of pulverizing by shearing force, a method for producing a fluororesin powder. In the method for producing the fluororesin powder according to claim 1 or 2,
In the step (a), the method for producing a fluororesin powder, wherein the crosslinked fluororesin is pulverized.

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