JP2021183661A - Method for manufacturing polytetrafluoroethylene resin tube - Google Patents

Abstract

To provide a high-yield method for manufacturing a thin-wall polytetrafluoroethylene resin tube.SOLUTION: A method for manufacturing polytetrafluoroethylene resin tube including: extrusion-molding a mixture including polytetrafluoroethylene fine powder to obtain a tube-shaped extrusion-molded article; performing first burning to the extrusion-molded article to obtain a first tube-shaped precursor; applying polytetrafluoroethylne dispersion to the external surface of the first tube-shaped precursor to obtain a second tube-shaped precursor; and performing second burning to the second tube-shaped precursor.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a polytetrafluoroethylene resin tube.

Polytetrafluoroethylene (PTFE) resin tubes are used in a wide range of fields because they are excellent in lubricity, chemical resistance, heat resistance, and the like. With the miniaturization of equipment and the like in which a tube is used, it is required to reduce the outer diameter of the tube and to increase the inner diameter at the same time. Such a request can be answered, for example, by thinning the tube.

Among the methods for producing a PTFE resin tube, the dip coating-firing method using a dispersion of PTFE resin is suitable for producing a thin-walled tube. However, the tube obtained by the manufacturing method tends to lack strength.

On the other hand, although the tube obtained by the extrusion molding method can be expected to have high strength, it is difficult to manufacture a thin-walled tube by extrusion molding. For example, when a tube having a thin wall thickness is manufactured by extrusion molding of a resin paste, pinholes are likely to occur in the obtained tube.

Patent Document 1 (Japanese Unexamined Patent Publication No. 2006-205680) describes that the wall thickness is adjusted to be moderately high in order to improve the strength of the PTFE resin tube obtained by the dip coating-firing method. Although the wall thickness can be adjusted by simply repeating coating and firing alternately, there is a problem that the thermal deterioration of the resin progresses excessively if firing is repeated many times. As a means for solving this problem, Patent Document 1 employs a method of obtaining a PTFE thin-walled tube adjusted to a desired wall thickness while reducing the number of recoating. Specifically, a fired layer of a pure PTFE resin dispersion is formed as an inner layer, and a fired layer of a PTFE resin dispersion containing a thickener is formed as an outer layer. By adjusting the amount of the thickener added to the dispersion liquid used to form the outer layer, the coating thickness of the dispersion liquid on the outer periphery of the inner layer can be adjusted. By increasing the coating thickness at one time, the number of recoating can be reduced.

According to Patent Document 2 (International Publication WO2008 / 102878), when a PTFE molded product is manufactured by extrusion molding, PTFE powder, which is a primary particle instead of a secondary particle, is used as a dispersion liquid to form a molded product having a thickness of 50 μm or less. It describes how to get the goods.

In Patent Document 3 (Japanese Unexamined Patent Publication No. 10-337405), as a method for manufacturing a fluororesin tube in which a porous structural layer and a non-porous structural layer are integrated in the thickness direction, the fluororesin tube is provided in at least one axial direction. It is described that the tube is stretched to form an orientation, an aqueous suspension of a fluororesin is applied to the outer surface or the inner surface of the tube, and the tube is fired in a state of being fixed in the stretching axial direction. The tube obtained by extruding the admixture of the fluororesin material powder and the liquid lubricant into a tube shape and then heating and removing the liquid lubricant is made porous by stretching in at least one axial direction. A non-porous layer is formed by firing the suspension applied to one surface. Since the porous structural layer and the non-porous structural layer are integrated in the thickness direction, when a drug or the like is used as a membrane material in a vacuum degassing device, it exhibits excellent degassing treatment efficiency and treatment. It can prevent the liquid from permeating into the tube. It is expected that the tube needs to have a wall thickness of a certain level or more, for example, a wall thickness of 0.1 mm or more in order to function as a film material for degassing treatment.

Patent Document 4 (Japanese Unexamined Patent Publication No. 2007-237597) describes that a thin PTFE tube having a wall thickness of 7 to 50 μm can be obtained by using a PTFE resin having an absorbed dose of ionizing radiation of 200 to 4000 Gy. Has been done.

Japanese Unexamined Patent Publication No. 2006-205680 International release WO2008 / 102878 Japanese Unexamined Patent Publication No. 10-337405 Japanese Unexamined Patent Publication No. 2007-2357597

An object of the present invention is to provide a method for producing a thin-walled polytetrafluoroethylene resin tube having a high yield.

The method for producing a polytetrafluoroethylene resin tube is as follows: an admixture containing polytetrafluoroethylene fine powder is extruded to obtain a tubular extruded product, and the extruded product is first fired. To obtain a 1-tube precursor, to obtain a second tubular precursor by applying a polytetrafluoroethylene dispersion to the outer surface of the first tubular precursor, and to obtain the second tubular precursor. On the other hand, it includes performing a second firing.

By the above manufacturing method, a thin-walled polytetrafluoroethylene resin tube can be manufactured with a high yield.

FIG. 2 is a cross-sectional view schematically showing an example of a method for manufacturing a fluororesin tube. The perspective view which shows typically the PTFE resin tube of an example. FIG. 2 is a cross-sectional view taken along the virtual surface III-III'shown in FIG. FIG. 2 is a cross-sectional view taken along the virtual surface IV-IV'shown in FIG. FIG. 6 is a cross-sectional view schematically showing an example of a first tubular precursor. Schematic cross-sectional view of an example extruder. Schematic cross-sectional view of another example extruder.

The method for producing a polytetrafluoroethylene resin tube according to an embodiment of the present invention comprises extruding an admixture containing polytetrafluoroethylene fine powder to obtain a tubular extruded product, and the extruded product. 1 Firing is performed to obtain a first tubular precursor, polytetrafluoroethylene dispersion is applied to the outer surface of the first tubular precursor to obtain a second tubular precursor, and a second tube is obtained. It includes performing a second firing on the state precursor.

In the thin-walled tube obtained by extruding a material containing tetrafluoroethylene resin, that is, a polytetrafluoroethylene (PTFE) resin into a thin tube, and firing the obtained extruded product, pinholes are formed. Likely to happen. Pinholes can be filled by applying a dispersion of PTFE to the outer surface of this tube and then firing it. It is desirable to apply the dispersion liquid to the side surface along the length direction of the tube. As a result, high yield production of thin-walled tubes can be achieved.

That is, an admixture containing the first polytetrafluoroethylene powder (first PTFE powder) is extruded to obtain a tubular extruded product, and the extruded product is first fired to perform a first tubular precursor. A body is obtained, and a dispersion containing a second polytetrafluoroethylene powder (second PTFE powder) is applied to the outer surface of the first tubular precursor to obtain a second tubular precursor to obtain a second tubular precursor. By performing the second firing on the body, a thin pinholeless tube can be manufactured with a high yield.

As the PTFE fine powder, a material widely used for extrusion molding of a PTFE molded product can be used. Fine powder is obtained by coagulating and drying an aqueous dispersion obtained by emulsion polymerization. For example, the fine powder may be mainly composed of primary particles produced by polymerization which are aggregated into secondary particles having a particle size of about 100 μm.

The PTFE fine powder is preferably a PTFE-only powder that does not contain fillers or additives. That is, it is desirable that the PTFE fine powder is composed of PTFE. The PTFE fine powder is preferably virgin PTFE powder.

The PTFE fine powder may be irradiated with ionizing radiation having an absorbed dose of 200 Gy or more and 4000 Gy or less. By irradiating the above amount of ionizing radiation, the pressure during extrusion molding can be reduced. With an absorbed dose of 200 Gy or more, the effect of reducing the extrusion pressure can be obtained. If the absorbed dose is 4000 Gy or less, the mechanical strength of the extruded product does not decrease. Ionizing radiation includes X-rays and γ-rays as electromagnetic waves, β-rays as charged particles, positrons, electrons, α-rays, protons, heavy protons, heavy ions, intermediates, and other uncharged elementary particles alone or these. Mixed radiation can be mentioned.

For example, a paste-like admixture can be obtained by mixing an extrusion aid such as a lubricant with PTFE fine powder. By extruding the admixture containing PTFE fine powder into a tube shape, a tube-shaped extruded product can be obtained. By performing firing (first firing) on this extruded product, a PTFE molded product having a single-layer tube shape, that is, a first tubular precursor can be obtained.

Examples of the extrusion aid include general-purpose solvent naphtha (for example, registered trademark: Isoper E, manufactured by Exxon Chemical Co., Ltd.), white oil, and liquid paraffin having 6 to 12 carbon atoms (for example, registered trademark: Cactus normal paraffin N). -10, manufactured by Japan Energy Co., Ltd.).

The admixture obtained by mixing the PTFE fine powder and the extrusion aid may be aged before being subjected to extrusion molding. Further, a compression molded product (billet) may be produced by compressing the aged mixture. By compressing, the air in the PTFE fine powder can be removed and the uniformity of the extruded product can be improved. The shape of the compression molded body is not particularly limited, but may be, for example, a cylindrical shape. The compression molded product is placed in an extruder and extruded.

It is desirable that the extrusion molding is performed under the condition that the wall thickness of the obtained extrusion-molded product is 20 μm or less. The condition that the wall thickness of the extruded product is 15 μm or less is more preferable, and the condition that the wall thickness is 10 μm or less is further preferable. The thinner the wall thickness, the more likely it is that pinholes will occur, but it is possible to fill the pinholes by applying PTFE dispersion in the subsequent stage.

During extrusion molding, heating may be performed. For example, by setting the temperature of a mold (for example, a die or a die) of an extrusion molding machine to 40 ° C. or higher and 95 ° C. or higher, extrusion molding may be performed while heating. It is preferable to heat the mold to 50 ° C. or higher and 60 ° C. or lower.

The firing temperature in firing (first firing) of the extruded product is not particularly limited. It is desirable to bake at a temperature above the melting point of PTFE of 390 ° C, for example, a temperature of 400 ° C or higher.

It is preferable to crystallize the PTFE resin by drying the extruded product prior to firing. Although the auxiliary agent can be removed by drying, a typical extrusion auxiliary agent volatilizes at about 200 ° C., so that it volatilizes during firing even if it is not removed in advance.

A core wire may be used in extrusion molding. By performing extrusion molding so as to cover the outer periphery of the core wire with an admixture containing PTFE fine powder, a tubular extruded product can be formed on the core wire. Further, by subjecting the extruded product on the core wire to firing (first firing) as it is, a first tubular precursor in the form of covering the core wire can be obtained. In the form of covering the core wire, when the PTFE dispersion is applied to the outer surface of the first tubular precursor, it becomes easy to adopt a continuous coating method.

As the core wire, for example, a metal wire made of a metal such as copper or aluminum, or a core material made of a resin can be used. The diameter of the core wire can be appropriately changed according to the desired inner diameter of the tube.

It is desirable to complete the first firing without performing another treatment on the extruded product obtained by using the PTFE fine powder. For example, when an unfired extruded product is stretched, the tube may be torn or further pinholes may be generated starting from the pinholes. In particular, if the tube is stretched in the radial direction so as to increase the diameter of the tube, the tube may be torn along the longitudinal direction. In the tube obtained by extrusion molding, the resin is oriented along the extrusion direction. Even if the tube is thin, the strength in the longitudinal direction is secured by the orientation, but the strength in the direction intersecting the tube is weak. The orientation is irregular in the part where the pinhole is located, and the tube is easily torn by stretching in any direction. Therefore, it is desirable that the extruded product before the first firing is not stretched. Even after the first firing, stretching may cause the above-mentioned problems.

The PTFE dispersion contains a dispersion medium and the PTFE powder in the dispersion medium. As the PTFE dispersion, a material that is widely used in a method of molding a resin tube by coating, such as a dip coating method, can be used. For example, PTFE dispersion is an aqueous dispersion in which PTFE powder is dispersed in an aqueous dispersion medium by emulsion polymerization. The PTFE dispersion can be a suspension containing PTFE powder.

The PTFE powder contained in the PTFE dispersion is preferably a PTFE-only powder that does not contain fillers or additives. That is, it is desirable that the PTFE dispersion is a powder composed of PTFE dispersed in a dispersion medium. The PTFE dispersion is preferably a dispersion of virgin PTFE.

The dispersion medium can be, for example, water or the like. The composition of the PTFE dispersion is not particularly limited, and for example, a dispersion liquid or suspension having a composition generally used in a method such as a dip coating method can be used.

A second tubular precursor is obtained by applying the PTFE dispersion to the outer surface of the first tubular precursor. It is desirable to apply the PTFE dispersion to the entire outer surface of the first tubular precursor. To apply the PTFE dispersion, for example, the first tubular precursor can be immersed in the PTFE dispersion. Specifically, it is preferable to adopt a dip coating method using a first tubular precursor formed on the core wire. In the dip coating method, a uniform coating thickness can be formed by passing the core wire together with the first tubular precursor through the PTFE dispersion and pulling it up at a constant speed.

The PTFE dispersion is applied to the first tubular precursor and the obtained second tubular precursor is calcined. In this way, a pinholeless resin tube in which the pinhole is closed can be obtained. Further, by applying the PTFE dispersion to the entire outer surface of the first tubular precursor and firing the second tubular precursor, a PTFE resin tube having a two-layer structure can be obtained.

After the PTFE dispersion is applied once and then fired, the PTFE dispersion may be further applied to the outer surface of the obtained tube and fired. By alternately repeating the application and firing of the dispersion liquid, the wall thickness of the tube can be adjusted to a desired thickness.

Alternatively, after the PTFE dispersion is applied and fired, a dispersion containing a filler containing a composite material containing the PTFE powder and the filler may be applied and fired (third firing). As a filler, for example, an imide resin powder can be mixed with the PTFE powder. By forming the outer layer using the mixed powder of the PTFE powder and the imide resin powder, the wear resistance of the outer surface of the tube can be improved. Further, by including a conductive material such as a carbon material as the filler, electrical properties can be imparted to the tube. However, the dispersion liquid to be applied directly to the outer surface of the first tubular precursor is a PTFE dispersion containing no filler.

It is desirable to apply the PTFE dispersion to the first tubular precursor after performing the first firing on the extruded product obtained using the PTFE fine powder and without performing another treatment. For example, when the first tubular precursor is stretched, the tube may be torn or further pinholes may be generated starting from the pinholes as in the case of the extruded product before firing. Therefore, it is desirable not to stretch the first tubular precursor.

After the first calcination, it is desirable to only cool the first tubular precursor to a temperature suitable for coating the PTFE dispersion and then apply the PTFE dispersion to the first tubular precursor. For example, an extruded product is formed on the core wire during extrusion molding, and the same core wire is used consistently until the PTFE dispersion is applied, and the core wire on which the first tubular precursor after the first firing is formed is formed. By sending it out as it is and immersing it in the PTFE dispersion, the process from the first firing to the application of the dispersion may be continued. Alternatively, after the first firing, the first tubular precursor may be wound once, for example, on a winding roll. The roll on which the first tubular precursor is wound may be used as a feed roll, and the application of the dispersion liquid may be started again.

A specific example of a method for manufacturing a fluororesin tube will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of a method for manufacturing a fluororesin tube. In this example, after forming the first tubular precursor on the core wire by the extrusion molding method, the process shifts to the application of PTFE dispersion by the dip coating method while keeping the first tubular precursor on the same core wire. do.

The extrusion die 51 included in the extrusion molding machine 50 is filled with the admixture 20 containing PTFE fine powder. The admixture 20 is a mixture of PTFE fine powder and other materials such as an extrusion aid. The admixture 20 can be, for example, a paste containing PTFE fine powder. Alternatively, the admixture 20 may be a compression molded body (billet) containing PTFE fine powder.

The core wire 4 is supplied to the inside of the extrusion die 51. The core wire 4 passes through the inside of the extrusion die 51 and is drawn out from the discharge port 52 of the extrusion die 51.

By moving the extrusion ram 53 toward the discharge port 52, the admixture 20 is compressed and pushed out from the discharge port 52 together with the core wire 4. In this way, a tubular extruded product 21 that covers the outer periphery of the core wire 4 is obtained.

By adjusting the wire diameter of the core wire 4, the inner diameter of the tube of the extruded product 21 can be controlled. When the core wire 4 is not used, for example, a core pin can be installed in the extrusion die 51, and the inner diameter of the tube can be controlled by the diameter of the core pin. By adjusting the diameter of the discharge port 52 of the extruded die 51, the outer diameter of the extruded product 21 can be controlled. Further, in order to control the outer diameter, for example, a sizing die having appropriate dimensions may be used. The wall thickness of the extruded product can be controlled by adjusting the wire diameter (or core pin diameter) of the core wire 4 and the diameter (or die size) of the discharge port 52.

The extruded product 21 on the core wire 4 is supplied to a drying furnace 61, where it is subjected to drying (first drying). By drying the extruded product 21, crystallization of the PTFE resin is promoted. Subsequently, the extruded product 21 is supplied to the heating furnace 62, where it is subjected to the first firing. By the first firing, the first tubular precursor 22 is obtained in the form of covering the core wire 4.

The first tubular precursor 22 on the core wire 4 is supplied to the dispersion liquid 30 in the bathtub 71 via the cooling device 63. The dispersion liquid 30 is a PTFE dispersion. The means of cooling by the cooling device 63 is not particularly limited, and may include, for example, air cooling and water cooling. The cooling device 63 may be omitted, and instead, the arrangement and number of the guide rollers 90 may be set so that the distance from the heating furnace 62 to the bathtub 71 becomes long, and the heat dissipation time may be increased. Further, the arrangement and number of the guide rollers 90 are not limited to those shown in FIG.

The first tubular precursor 22 (and the core wire 4 in it) is immersed in the dispersion liquid 30 and then pulled up. The dispersion liquid 30 is applied to the outer surface of the first tubular precursor 22 via the dip coating, and the second tubular precursor containing the first tubular precursor 22 and the dispersed PTFE coating 31 covering the outer periphery thereof is included. Body 10 is obtained. At this time, a part of the dispersion liquid 30 is filled in the pinholes formed in the first tubular precursor 22.

The second tubular precursor 10 including the first tubular precursor 22 covering the outer periphery of the core wire 4 and the dispersed PTFE coating 31 further covering the outer periphery thereof is a drying furnace 81 and a heating furnace 82. Is sequentially supplied to and subjected to drying (second drying) and second firing. Through the second firing, a PTFE resin tube 1 having a two-layer structure including an inner layer 2 and an outer layer 3 is obtained. The inner layer 2 corresponds to the one in which the first tubular precursor 22 is reheated by the second firing.

The PTFE resin tube 1 on the core wire 4 is supplied to the take-up roll 91 via the cooling device 83. The means of cooling by the cooling device 83 is not particularly limited, and may include, for example, air cooling and water cooling. The cooling device 83 may be omitted, and instead, the arrangement and number of the guide rollers 90 may be set so that the distance from the heating furnace 82 to the take-up roll 91 becomes long, and the heat dissipation time may be increased. Further, the arrangement and number of the guide rollers 90 are not limited to those shown in FIG. The PTFE resin tube 1 is wound around the winding roll 91 while including the core wire 4.

By removing the core wire 4 at the time of use, the PTFE resin tube 1 having a hollow structure can be used. For example, a PTFE resin tube 1 having the structure shown in FIGS. 2 to 4 can be obtained. FIG. 2 is a perspective view schematically showing an example PTFE resin tube. 3 and 4 are cross-sectional views taken along the virtual surfaces III-III'and IV-IV'shown in FIG. 2, respectively.

The PTFE resin tube 1 shown in FIG. 2 has a hollow cylindrical shape. In this example, the PTFE resin tube 1 has a two-layer structure in which the inner layer 2 and the outer layer 3 are laminated in the radial direction of the cylinder. As shown in FIG. 3, the inner layer 2 and the outer layer 3 may each have a circular cross section at a part along the longitudinal direction of the PTFE resin tube 1. On the other hand, as shown in FIG. 4, the cross-sectional shape of the inner layer 2 may not be a perfect circle in other portions. The protrusion 33, which is a part of the outer layer 3, may enter the portion where the inner layer 2 is missing.

The protrusion 33 is formed from the dispersion liquid 30 filled in the pinhole generated in the first tubular precursor 22. FIG. 5 shows a cross-sectional view of the state before applying the dispersion liquid 30 to the first tubular precursor. Specifically, FIG. 5 is a cross-sectional view of the first tubular precursor 22 when passing through the position A shown in FIG. 1, and is a cross-sectional view including a pinhole 23. When the first tubular precursor 22 passes through the dispersion liquid 30 containing the second PTFE powder, the dispersion liquid (PTFE dispersion) adheres to the outer periphery of the first tubular precursor 22 and a part thereof is pinned. Enter the hall 23. The dispersion liquid that has entered the pinhole 23 by the second firing becomes a protrusion 33, and the pinhole 23 is closed.

The above example is an example of manufacturing a PTFE resin tube having a two-layer structure, but the embodiment is not limited to the above example. For example, the number of times of coating with the dispersion liquid 30 and subsequent firing is not limited to once as shown in FIG. 1, and may be performed, for example, twice or more. Further, after the second firing, a dispersion liquid having a composition different from that of the dispersion liquid 30, such as a dispersion liquid containing a filler, is further applied and fired on the outer surface of the outer layer 3, and a PTFE resin tube having a three-layer structure is formed. Can also be manufactured. In addition, after the first firing, the core wire 4 and the first tubular precursor 22 may be wound once on a roll and used as a supply roll to be supplied to the dispersion liquid 30 again. Further, extrusion molding and coating of PTFE dispersion can be performed without using the core wire 4.

When the core wire 4 is not used, for example, an extruder having the structure shown in FIG. 6 can be used. FIG. 6 is a schematic cross-sectional view of an example extruder.

The illustrated extruder has a cylinder 51a and a die 51c located at the bottom of the cylinder 51a via a seal ring 51b. Further, in the lower part of the die 51c, a die 51d in which a band heater 54 is wound is arranged on the outer peripheral portion. A mandrel 55 is arranged inside the cylinder 51a via a ram 53a and a ram head 53b. A core pin 51e is connected to the lower part of the mandrel 55. Generally, the center ring bush 56 is inserted into the tip end portion (lower end portion) of the die 51d.

The tilt angle (θ) of the central portion of the die 51c may be, for example, 30 ° or more and 60 ° or less. In the case of molding with a high drawing ratio (RR: Reduction Ratio), the inclination angle (θ) is preferably 10 ° or more and 20 ° or less. Further, the die portion can be heated to, for example, 50 ° C. or higher and 60 ° C. or lower by a band heater 54 or the like.

In an extruder having such a configuration, as shown in FIG. 6, when the cross-sectional area of the cylinder-mandrel portion is S ₁ and the cross-sectional area of the die-core pin is S ₂ , the above RR becomes S ₁ / S ₂ and the RR becomes S 1 / S 2. The higher the aperture ratio, the larger the aperture ratio.

FIG. 7 is a schematic cross-sectional view of another example extruder. FIG. 7 may correspond to a more detailed view of the extruder 50 shown in FIG. FIG. 7 will be described with the same members as those in FIG. 6 with the same reference numerals. The extruder has no core pins and has a guide tube 57. The core wire 4 is inserted into the guide tube 57. A clearance is provided between the straight portion of the die 51d and the guide tube 57. The extrusion molding machine may further have a cylindrical frame body 58a, 58b divided into two and an annular clamp 59 for fixing the frame bodies 58a, 58b on the outer periphery of the cylinder 51a and the die 51c.

It can be confirmed that a tube having a two-layer structure is obtained as follows. The cross section is exposed by cutting the tube at a cut surface that intersects the spindle of the tube. Observe the cross section of the tube with a light microscope. The inner layer of the tube is formed of PTFE fine powder suitable for extrusion and the outer layer is formed of PTFE powder for PTFE dispersion suitable for coating-baking of dispersions. At least one of the particle size, transparency, molecular weight, etc. may differ between the PTFE fine powder and the PTFE powder for dispersion. In such a case, the inner layer and the outer layer can be distinguished by observing the cross section of the tube.

The tube to be cut and observed may be a tube as it is provided on the core wire, or the tube may be cut and observed after the core wire is pulled out. Since the tube is easily crushed when there is no core wire, it is desirable to cut at least with the core wire inside.

The observed cross section differs depending on the position of the cut surface. When the cut surface intersects the position where the pinhole was generated in the first tubular precursor, the cross section of the inner layer 2 is not a perfect ring as in FIG. 4, and the protrusion 33 is formed on the inner surface of the outer layer 3. A cross section of the formed state can be observed. If the cut surfaces do not intersect at any of the positions where the pinholes have occurred, the tube cross section in which both the inner layer 2 and the outer layer 3 have a perfect ring shape is obtained as in FIG. Can be observed.

The resin material forming each layer of the tube can be confirmed as follows. It is possible to confirm that the resin material is PTFE by measuring the melting point using a differential scanning calorimeter (DSC).

The presence or absence of pinholes in the PTFE resin tube can be confirmed as follows. If the tube is still covered with the core wire, use a spark tester to check whether there is energization between the outer diameter and the core wire. If energization is confirmed, it is determined that there is a pinhole. In the case of a tube alone that does not include the core wire, seal one end of the tube, introduce air from the other end, and then check for leaks in the water. If air leakage is confirmed, it is determined that there is a pinhole.

[Example]
<Manufacturing>
In this example, extrusion molding and first firing were performed with reference to Patent Document 4 (Japanese Unexamined Patent Publication No. 2007-2357597), and the obtained first tubular precursor was coated with PTFE dispersion on the outer surface of the molded product. , The PTFE resin tube was manufactured by performing the second firing. The embodiment is not limited to this embodiment. For example, as a method for obtaining a thin-walled extruded product at the time of extrusion molding, another method such as a method using a resin suitable for thin-walled extrusion instead of irradiating with γ-rays or a method using a fluororesin auxiliary agent may be used.

(Example 1)
A PTFE resin tube was manufactured by the same manufacturing method as described with reference to FIG. 1. The details are as follows.

As the PTFE fine powder, PTFE 640-J manufactured by The Chemours Company was used. This resin was irradiated with γ-rays having a Co60 (ionizing radiation) as a radiation source at an absorbed dose of 3000 Gy.

As the PTFE dispersion, AD-912 manufactured by Asahi Glass Co., Ltd. was used.

Next, 21 parts by mass of naphtha was added to 100 parts by mass of the resin powder (PTFE fine powder) irradiated with ionizing radiation, and then mixed at room temperature using a tubler mixer. Subsequently, this mixture was formed into a cylindrical shape by a preforming machine, and then put into a paste extruder equipped with a φ2.6 (mm) die and a φ2.58 (mm) core pin (chip) for extrusion molding. The obtained extruded product was subjected to first drying at 180 ° C to 200 ° C and first firing at 380 ° C to 400 ° C.

After cooling the first tubular precursor obtained by the first firing, PTFE dispersion was applied to the outer surface thereof by a dip coating method.

For the PTFE dispersion, a surfactant and distilled water were added, and the PTFE component concentration was adjusted to 54 wt%, and the temperature was raised at a constant rate. Then, the obtained second tubular precursor was subjected to second drying at 140 ° C to 180 ° C and second firing at 380 ° C to 400 ° C. The obtained two-layer structure polytetrafluoroethylene resin tube was cooled and then wound on a roll.

(Example 2)
First, as the PTFE fine powder, Teflon (registered trademark) 640-J manufactured by Mitsui-DuPont Fluorochemical Co., Ltd. was used. This resin was irradiated with γ-rays having a Co60 (ionizing radiation) as a radiation source at an absorbed dose of 3000 Gy. Next, 21 parts by mass of naphtha was added to 100 parts by mass of the resin powder irradiated with ionizing radiation, and then mixed at room temperature using a turbobler mixer. Subsequently, after molding this mixture into a cylindrical shape with a preforming machine, it is put into an extruder equipped with a φ2.6 (mm) die and a guide tube (chip), and the outer diameter is φ2 from the inner diameter of the guide tube. A 58 (mm) silver-plated copper wire was passed through as a core material, pulled in synchronization with extrusion, and the extrusion aid was removed in a heating furnace set at 180 ° C to 200 ° C (first drying). Then, it was fired through a heating furnace set at 380 ° C. to 400 ° C. to obtain a molded product in which the PTFE layer was coated on the core wire (first firing). After that, this molded product is cut to a standard length, and the silver-plated copper wire as the core material is pulled from both ends, stretched, and pulled out from the coated PTFE layer to form a tube with an inner diameter of φ2.58 mm and a wall thickness of 7 μm to 8 μm. Obtained.

Next, PTFE dispersion was applied to the outer surface of the obtained tube under the same conditions as in Example 1, and second drying and second firing were performed. The obtained two-layer structure polytetrafluoroethylene resin tube was cooled and then wound on a roll.

(Comparative Example 1)
Only extrusion molding was performed to manufacture a PTFE resin tube. That is, after firing the extruded product, PTFE dispersion was not applied to the obtained tubular molded product. Specifically, an admixture containing PTFE fine powder prepared by the same procedure as in Example 1 was used, and extrusion molding, first drying, and first firing were performed under the same conditions as in Example 1. The tubular molded product obtained by the first firing was directly wound on a roll.

(Comparative Example 2)
Before the first firing, the extruded product was stretched. Specifically, extrusion molding was performed under the same conditions as in Example 1, and the obtained extruded product was first dried and then double-stretched in the axial direction. The procedure after the first firing was performed under the same conditions as in Example 1 except that the extruded product after stretching was used.

Table 1 below summarizes the conditions for producing PTFE resin tubes in Example 1-2 and Comparative Example 1-2. Specifically, the size of the extrusion die, the wire diameter of the core wire, and the presence or absence of the PTFE dispersion are shown. Since the core wire is not used in Example 1 and Comparative Example 1-2, the wire diameter of the core wire is described as “−”. Further, since the core pin is not used in the second embodiment, the size of the core pin is described as “−”.

<Evaluation>
(Check the wall thickness of the tube)
The wall thickness of each tube produced in Example 1-2 and Comparative Example 1-2 was measured as follows. The cross section was exposed by cutting the tube at a cut surface that intersected the spindle of the tube. The cross section was observed with an optical microscope, and the wall thickness was measured.

(Confirmation of pinhole)
The presence or absence of pinholes was confirmed in each of the tubes manufactured in Example 1-2 and Comparative Example 1-2 by the method described above. Specifically, for Example 1 and Comparative Examples 1 and 2, a method of confirming the presence or absence of an air leak in water was adopted, and for Example 2, a method of using a spark tester was adopted.

Table 2 below summarizes the confirmed tube wall thickness and the presence or absence of pinholes.

As shown in Table 4, thin tubes were obtained in Example 1-2 and Comparative Example 1-2. The PTFE resin tube produced in Example 1-2 had no pinholes. On the other hand, the tubes produced in Comparative Example 1 and Comparative Example 2 contained pinholes.

According to the embodiment described above, a method for producing a polytetrafluoroethylene resin tube is provided. In this production method, a tubular extruded product is obtained by extrusion molding of an admixture containing PTFE fine powder, a first firing is performed on the extruded product to obtain a first tubular precursor, and a PTFE dispersion is obtained. It includes applying to the outer surface of the first tubular precursor to obtain a second tubular precursor, and performing a second firing on the second tubular precursor. With this manufacturing method, a thin-walled polytetrafluoroethylene resin tube can be manufactured with a high yield.

The present invention is not limited to the above embodiment, and can be variously modified at the implementation stage without departing from the gist thereof. In addition, each embodiment may be carried out in combination as appropriate, in which case the combined effect can be obtained. Further, the above-described embodiment includes various inventions, and various inventions can be extracted by a combination selected from a plurality of disclosed constituent requirements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, if the problem can be solved and the effect is obtained, the configuration in which the constituent elements are deleted can be extracted as an invention.

1 ... PTFE resin tube, 2 ... inner layer, 3 ... outer layer, 4 ... core wire, 10 ... second tubular precursor, 20 ... admixture, 21 ... extruded product, 22 ... first tubular precursor, 23 ... pin Hole, 30 ... dispersion liquid, 31 ... dispersion PTFE coating, 33 ... protrusion, 50 ... extrusion molding machine, 51 ... extrusion die, 51a ... cylinder, 51b ... seal ring, 51c ... die, 51d ... die, 51e ... core pin, 52 ... Discharge port, 53 ... Extrusion ram, 53a ... Ram, 53b ... Ram head, 54 ... Band heater, 55 ... Mandrel, 56 ... Center ring bush, 57 ... Guide tube, 58a ... Frame, 58b ... Frame, 59 ... Clamp, 61 ... Drying furnace, 62 ... Heating furnace, 63 ... Cooling device, 71 ... Tube, 81 ... Drying furnace, 82 ... Heating furnace, 83 ... Cooling device, 90 ... Guide roller, 91 ... Winding roll.

Claims (2)

A method for manufacturing a polytetrafluoroethylene resin tube.
Extruding an admixture containing polytetrafluoroethylene fine powder to obtain a tubular extruded product,
The extruded product is first fired to obtain a first tubular precursor.
Polytetrafluoroethylene dispersion is applied to the outer surface of the first tubular precursor to obtain a second tubular precursor.
A production method comprising performing a second firing on the second tubular precursor. The manufacturing method according to claim 1, wherein the extruded product has a wall thickness of 20 μm or less.

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