Method for removing metallic foreign matter from fluororesin and method for producing fluororesin with reduced metallic foreign matter

Abstract

Provided are: a method for suitably removing metal contaminants in a fluorine resin; and a method for producing a fluorine resin having a reduced amount of metal contaminants, the production method having the method for removing metal contaminants in a fluorine resin as one step. The method for removing metal contaminants from a fluorine resin involves applying a magnetic field using an electromagnet while allowing the fluorine resin to drop due to gravity, thereby removing metals.

Description

[Technical field]

[0001] The present disclosure relates to a method for removing metallic foreign matter from a fluororesin and a method for producing a fluororesin with reduced metallic foreign matter. [Background technology]

[0002] Fluoropolymers are used in a wide variety of applications. Metallic contaminants may be mixed into fluoropolymers due to friction or corrosion of manufacturing equipment. Therefore, the removal of metallic contaminants from fluoropolymers containing metallic contaminants is an important issue.

[0003] Patent Documents 1 and 2 disclose the use of a magnet to remove trace amounts of metallic foreign matter from resin. Patent Document 3 discloses a method for separating and collecting a fluororesin powder by using a liquid medium consisting of a fluorinated alkane and an aqueous liquid medium. Patent Document 4 discloses the use of a solvent to remove foreign matter from a fluororesin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-263985 A [Patent Document 2] JP 2005-21761 A [Patent Document 3] Japanese Patent Application Publication No. 54-071155 [Patent Document 4] International Publication No. 2004 / 009653 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a method for suitably removing metallic foreign matter from a fluororesin, and a method for producing a fluororesin with reduced metallic foreign matter, the method including, as one step, the method for removing metallic foreign matter from the fluororesin. [Means for solving the problem]

[0006] The present disclosure relates to This is a method for removing metallic foreign matter from fluororesin, characterized in that the metal is removed by applying a magnetic field using a magnet while allowing the fluororesin to fall by gravity. The above-mentioned method for removing metallic foreign matter preferably comprises providing a screen made of a magnetic material in a flow path through which the fluororesin falls by gravity. The magnet is preferably an electromagnet. The fluororesin is preferably in the form of a powder, pellets or granules. In the above-mentioned method for removing metallic foreign matter from a fluororesin, it is preferable that the screen is not vibrated when the fluororesin is passed through the screen.

[0007] The present disclosure also relates to a method for producing a fluororesin with reduced metallic foreign matter, which comprises a step of removing metal by applying a magnetic field by an electromagnet while allowing the fluororesin to fall by gravity. In the above-mentioned method for producing a fluororesin, a screen made of a magnetic material is preferably provided in a flow path through which the fluororesin falls by gravity. The magnet is preferably an electromagnet. The fluororesin is preferably in the form of a powder, pellets or granules. In the above-mentioned method for producing a fluororesin, it is preferable that the screen is not vibrated when the fluororesin is passed through the screen. Effect of the Invention

[0008] The method for removing metallic foreign matter from a fluororesin according to the present disclosure can remove metallic foreign matter efficiently, at low cost, and with high accuracy, thereby reducing the amount of resin that is lot-out when checking for metallic foreign matter, and efficiently providing a fluororesin with low metallic foreign matter. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of an apparatus used in the present invention. [Diagram 2] FIG. 1 is a diagram showing an example of an apparatus used in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present disclosure will be described in detail below. The present disclosure relates to a method for removing metals from fluororesins. The fluororesins used herein are not particularly limited. Specific examples include PTFE resin, PFA resin, FEP resin, ETFE resin, PCTFE resin, and PVDF resin. Among these, PTFE resin is particularly preferred. The fluororesin is preferably solid, and can be applied to any shape such as powder, granules, and pellets.

[0011] In these fluororesins, the metal may exist alone in the form of metal powder or the like, or may be integrated with the fluororesin. In the present disclosure, since the foreign matter removal is performed by magnetic force, even the integrated metal and fluororesin, which are more difficult to remove, can be suitably removed. Examples of metals present as foreign matter include stainless steel, iron, and metals mixed with these and other elements.

[0012] In the present disclosure, metals in fluororesin are mainly caused by foreign metals being mixed in due to rubbing or corrosion of manufacturing equipment, and the occurrence rate is not particularly high. However, when this occurs, it can cause defective products in various applications, so it is preferable to be able to remove it with as high a precision as possible.

[0013] The present disclosure is characterized in that the metal is removed by applying a magnetic field using a magnet while the fluororesin is allowed to fall by gravity. If a metallic foreign body is surrounded by a large amount of fluororesin, the magnetic force is impeded by the surrounding fluororesin, and the metallic foreign body may not be sufficiently removed. For example, when a magnetic force is applied to a fluororesin while it is being moved horizontally using rollers or a conveyor, if a metallic foreign object is placed on the fluororesin, the magnetic force may not be sufficient to remove it. Since a certain amount of the fluororesin is also removed along with the foreign object, there is also the problem of a constant rate of loss during operation.

[0014] In contrast, when a magnetic field is applied while the material is falling by gravity, the magnetic field is applied in a state where the fluororesin is dispersed in the air. When a magnetic field is applied while the material is falling by gravity, the magnetic field reaches the metal sufficiently, and the metal can be suitably removed by the action of the magnetic field. This is also preferable in that continuous processing can be performed. Furthermore, this method has the advantage that the loss of fluororesin is not as large as when rollers or conveyors are used. That is, according to the method disclosed herein, the loss of fluororesin is small, and is limited to the amount of fluororesin that is removed when the screen used as a filter is washed during inspection, etc.

[0015] The magnets used in this disclosure may be electromagnets or permanent magnets. The use of electromagnets is more preferable because it can apply a stronger magnetic field. It is also preferable because metal foreign matter can be easily removed during cleaning by turning off the power. Permanent magnets can also be used, but the magnetic force is low, the intervals between magnets that can be installed are large, and it is difficult to remove foreign matter that has adhered during cleaning. From the perspective of foreign matter removal efficiency, the use of electromagnets is more preferable.

[0016] The magnetic force applied to the fluororesin is preferably 0.8 Tesla or more, and more preferably 1.2 Tesla or more. In particular, treatment in such a high magnetic force range is preferable because fine metal can be removed.

[0017] Furthermore, a screen made of a magnetic material may be set in the space into which the fluororesin falls. When such a screen is installed, the screen becomes magnetic due to the electromagnet, and this plays a role in removing metallic foreign matter. This is also preferable in that metallic foreign matter adhering to the screen can be easily removed by stopping the electromagnet during cleaning.

[0018] Furthermore, the screen may be made of a permanent magnet, and since such a screen has magnetism due to the permanent magnet, the same effect can be obtained.

[0019] The shape of the screen is not particularly limited, and examples thereof include a 5 mm mesh screen, a honeycomb screen, and a micro pitch screen.

[0020] The method for removing metallic foreign matter according to the present disclosure will be described in further detail below with reference to FIG. In the removal method of the present disclosure, several metal screens may be placed on the path along which the fluororesin falls due to gravity.

[0021] 1 shows the screen set in the electromagnetic separator, in which one or more screens 1 made of a magnetic material are held in multiple layers in the vertical direction by holding rods 3 in the hollow space of a cylinder 2 that is open at the top and bottom. The cylinder 2 is placed at the center of an electromagnet 4, and a vibrator 5 may be attached to the bottom of the cylinder 2. Note that the vibrator 5 is an optional requirement, and the machine may not be provided.

[0022] In particular, when powdered fluororesin is used, it is preferable not to use the vibrator 5. If a vibrator is used, the fluororesin may get into gaps and generate flaky or aggregated resin, or new metal pieces may be generated due to friction caused by vibration, so it is preferable not to use a vibrator.

[0023] A product discharge port and a magnetic foreign matter discharge port may be connected to the bottom of the cylinder. In this case, the product discharge port and the magnetic foreign matter discharge port can be switched by rotating a damper with a cylinder.

[0024] Fluororesin containing magnetic foreign matter is fed into the interior of the cylinder 2 from the top in the direction shown by the arrow in Figure 1 and is allowed to fall. It is magnetically attracted to a screen magnetized by magnet 4. The product from which the magnetic foreign matter has been removed passes through the screen and is discharged from the bottom of the cylinder 2. During cleaning, if the magnet is an electromagnet, the electromagnet can be turned off to demagnetize the screen and remove the magnetic foreign matter adhering to the screen. If necessary, the screen 1 can be removed with a holding rod and cleaned to remove the magnetic foreign matter. The cleaned screen can be inserted back into the cylinder.

[0025] An embodiment in FIG. 2 will also be described as an embodiment different from that in FIG. FIG. 2 shows an apparatus for removing magnetic foreign matter by bringing a teardrop-shaped magnet into contact with fluororesin containing the magnetic foreign matter. 2, teardrop-shaped magnet 11 has a semicircular arc portion at the bottom and a triangular portion at the top. As the foreign matter falls along the slope of the triangular portion, it is removed by the magnet. Furthermore, it is preferable that a plurality of teardrop-shaped magnets are arranged via a yoke. Magnetic foreign matter can also be removed by the device shown in FIG.

[0026] The present disclosure relates to a method for removing metallic foreign matter from a fluororesin as described above, and also to a method for producing a fluororesin with reduced metallic foreign matter, which includes a step of removing such metallic foreign matter. That is, there are various methods for attempting to obtain a "fluororesin with reduced metallic foreign matter". The present disclosure also provides a novel method for obtaining a "fluororesin with reduced metallic foreign matter."

[0027] The method for producing a fluororesin with reduced metallic foreign matter according to the present disclosure includes a step of removing metallic foreign matter from the fluororesin by the above-mentioned method. The "step of removing metallic foreign matter" here can be as described above.

[0028] The method for producing a fluororesin with reduced metallic foreign matter according to the present disclosure may further include a step of removing metallic foreign matter in addition to the steps described above.

[0029] In the method for removing metallic foreign matter of the present disclosure, a slow processing speed is more preferable. In other words, processing a large amount of fluororesin in a short time is not preferable because it becomes difficult to sufficiently remove metallic foreign matter. EXAMPLES

[0030] The present disclosure will now be described in detail with reference to examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by weight" and "% by weight", respectively.

[0031] Examples 1 to 3 The sample was prepared by adding 500 ppm of stainless steel 316L powder (Kojundo Chemical, SUS316L powder 150 μm pass) to PTFE granulated powder (Daikin Industries, Polyflon PTFE M-392). 5 kg of PTFE granulated powder containing stainless steel powder was prepared and used for each test. The device used was an electromagnetic separator (CG-180X-1 type) manufactured by Nippon Magnetics Co., Ltd. An electromagnet was used as the magnet. Furthermore, in this device, the screen was made of a magnetic material.

[0032] In each example, the tests were performed while changing conditions such as the processing speed and whether or not a vibrator was used, as shown in Table 1 below. Furthermore, the results in Table 1 make it clear that no vibration provides better results.

[0033] (Method for measuring stainless steel remaining rate) Wrap the drug packing paper tightly around a 15,000G bar magnet and secure it with tape. Fix this bar magnet in place with a clamp. Pour the powder to be measured over the bar magnet. The target processing speed is 4 kg / hour. Once the powder has been poured, pour the collected powder over the bar magnet again. This process causes the metal in the powder to adhere to the magnet. Then, a bar magnet is placed on top of the heat-resistant metal container, the tape that is holding the medicine paper in place is removed, and the medicine paper is removed from the bar magnet, causing the metal adhering to fall into the heat-resistant metal container. Such a heat-resistant metal container was placed in an electric furnace at 600°C and removed after two hours. After cooling in air, the container was weighed and the weight of the empty container was subtracted from this value to determine the metal content. The amount of metal thus measured was calculated as a ratio to the amount of stainless steel powder added to the sample, and the ratio is shown in Table 1 as the stainless steel remaining rate.

[0034] [Table 1]

[0035] From the results of the above examples, it is clear that the method for removing metallic foreign matter of the present disclosure can effectively remove foreign matter in fluororesin.

[0036] (Manufacturing method of PFA powder) 26.6 kg of pure water was charged into a glass-lined autoclave (volume 174 L) equipped with a stirrer. After thoroughly replacing the inside of the autoclave with N2, it was evacuated and 30.4 kg of perfluorocyclobutane [C-318], 0.8 kg of methanol, and 1.6 kg of perfluoro(propyl vinyl ether) [PPVE] were charged. Next, while stirring, the inside of the autoclave was kept at 35°C, and tetrafluoroethylene [TFE] was pressed in to set the internal pressure to 0.58 MPaG. Polymerization was started by adding 0.028 kg of a 50% methanol solution of di-n-propyl peroxydicarbonate [NPP] as a polymerization initiator. As the pressure decreased with the progress of polymerization, TFE and PPVE were continuously added at a ratio that would result in the desired polymer composition.

[0037] After 33 hours from the start of polymerization, the stirring was stopped and the unreacted monomers and C-318 were discharged to terminate the polymerization. The white powder in the autoclave was washed with water and dried at 150°C for 12 hours to obtain a polymer product.

[0038] (Examples 4 and 5) A sample was prepared by adding 500 ppm of stainless steel 316L powder (manufactured by Kojundo Chemical Co., Ltd., SUS316L powder 150 μm pass) to the PFA powder obtained by the above-mentioned method. 1 kg of PFA powder containing stainless steel powder was prepared and used for each test. The device used was a lattice magnet with a housing manufactured by Magnetec Japan Co., Ltd. (neodymium rare earth magnet; the magnet is a permanent magnet).

[0039] [Table 2]

[0040] From the results of the above examples, it is clear that the method for removing metallic foreign matter of the present disclosure can effectively remove foreign matter in fluororesin. [Industrial Applicability]

[0041] The removal method of the present disclosure makes it possible to effectively remove metallic foreign matter from fluororesin. [Explanation of symbols]

[0042] 1: Screen 2: Tube 3: Holding rod 4: Electromagnet 5: Vibrator 6:Product outlet 7: Iron powder outlet 8: Cylinder 9: Damper 11: Teardrop magnet

Claims

1. This is a method to remove metal by applying a magnetic field to the fluororesin while allowing it to fall by gravity. A magnetic screen is provided in the space into which the fluororesin falls. A method for removing metallic foreign matter from a fluororesin, characterized in that vibration from a vibrator is not applied to the screen when the fluororesin is passed through the screen.

2. 2. The method for removing metallic foreign matter from fluororesin according to claim 1, wherein the magnet is an electromagnet.

3. 3. The method for removing metallic foreign matter from a fluororesin according to claim 1, wherein the fluororesin is in the form of a powder, pellet or granules.

4. The method includes a step of removing metal by applying a magnetic field to the fluororesin by gravity, A magnetic screen is provided in the space into which the fluororesin falls. A method for producing a fluororesin with reduced metallic foreign matter, characterized in that vibration from a vibrator is not applied to the screen when the fluororesin is passed through the screen.

5. 5. The method for producing a fluororesin according to claim 4, wherein the magnet is an electromagnet.

6. 6. The method for producing a fluororesin according to claim 4 or 5, wherein the fluororesin is in the form of a powder, pellets or granules.

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