JP7774389B2 - Wire manufacturing method - Google Patents

Description

The present invention relates to a cutter blade for a granulator, a granulator, and a method for granulating a resin mixture.

Conventionally, granulation devices that granulate plastics and turn them into pellets are known (see, for example, Patent Document 1). Granulation devices include air-cooled types that use air to cool the pellets obtained by granulation, and water-cooled types that use water. Some plastics, such as soft PVC (polyvinyl chloride), which does not easily adhere to the cutter blade of the granulation device in a molten state and is less likely to adhere to each other (sticking together) or to form multiple pellets into a beaded shape (beaded string), can be granulated using air-cooled granulation devices.

On the other hand, for the granulation of plastics, such as resin mixtures in which at least one of a flame retardant and a filler is added to the resin, where pellets are prone to sticking together during granulation, water-cooled granulation equipment using methods such as strand granulation, underwater granulation, water mist granulation, and watering granulation is used.

Japanese Patent Application Laid-Open No. 2000-176932

Air-cooled granulators are superior to water-cooled granulators in that they do not require a post-process to remove water from the pellets, and they do not require visual inspection of the string-like plastic before pelletization. In order to granulate plastics that have traditionally been granulated using water-cooled granulators using air-cooled granulators, it is necessary to prevent adhesion to the cutter blades during granulation and to prevent the pellets from sticking to each other.

The object of the present invention is to provide an air-cooled granulator that can granulate a resin mixture in which at least one of a flame retardant and a filler has been added to the resin while preventing the pellets from sticking together, a cutter blade for the granulator used in the device, and a method for granulating a resin mixture using the cutter blade for the granulator.

In order to solve the above-mentioned problems, the present invention provides a cutter blade for a granulator, which comprises a cutter blade body having a granulating surface and an amorphous carbon coating covering the granulating surface.

Furthermore, in order to solve the above-mentioned problems, the present invention provides an air-cooled granulator equipped with the above-mentioned cutter blade for a granulator.

Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for granulating a resin mixture, which includes a step of cutting and pelletizing a resin mixture, in which at least one of a flame retardant and a filler has been added to resin extruded from a resin discharge hole of a die, using the cutter blade for the granulation device described above.

The present invention provides an air-cooled granulator that can granulate a resin mixture in which at least one of a flame retardant and a filler has been added to the resin while preventing the pellets from sticking together, a granulator cutter blade used in the granulator, and a method for granulating a resin mixture using the granulator cutter blade.

FIG. 1 is a cross-sectional view schematically showing a part of the configuration of a granulating apparatus according to an embodiment of the present invention. Fig. 2(a) is a perspective view of a cutter blade included in a cutter device according to an embodiment of the present invention, and Fig. 2(b) is a cross-sectional view of the vicinity of the tip of the cutter blade along the length direction. 3(a) and 3(b) are cross-sectional views that schematically show how a cutter blade cuts resin extruded in a string shape from a resin discharge hole of an air-cooled granulation die.

[Embodiment]
(Configuration of Granulation Apparatus)
1 is a cross-sectional view schematically illustrating a portion of the configuration of a granulation apparatus 1 according to an embodiment of the present invention. The granulation apparatus 1 is an air-cooled granulation apparatus that includes an extruder 10 that extrudes a molten resin mixture 50, an air-cooled granulation die 20 that has a plurality of annularly arranged resin discharge holes 21 and is installed at the outlet of a space within a cylinder 11 that is a passage for the resin mixture 50 of the extruder 10, and a cutter device 30 that cuts the resin mixture 50 extruded in a string-like shape from the resin discharge holes 21 of the air-cooled granulation die 20 into pellets.

The extruder 10 includes a cylinder 11 into which the molten resin mixture 50 is supplied, a screw 12 installed inside the cylinder 11 that extrudes the molten resin mixture 50 forward, and a plate-shaped breaker plate 13 installed in front of the screw 12 inside the cylinder 11 and having multiple resin passage holes.

The resin mixture 50 is, for example, a resin mixture containing a base polymer to which at least one of a flame retardant such as magnesium hydroxide, a bromine-based flame retardant, or antimony trioxide and a filler such as calcined clay has been added. The base polymer is, for example, a polyolefin-based resin. Examples of polyolefin-based resins that can be used include polyethylenes such as chlorinated polyethylene (CPE), polypropylene, high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and very low-density polyethylene (VLDPE), as well as ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers (EVA), and ethylene-ethyl acrylate copolymers (EEA), either alone or in combination. The amount of flame retardant or filler added is, for example, 50 to 300 parts by weight per 100 parts by weight of the base polymer.

The cutter device 30 includes a rotary drive source 31 such as an inverter motor, a shaft 32 installed to rotate by the rotary drive source 31, a cutter blade mounting base 33 attached to the shaft 32 so as to rotate around the shaft 32 as the rotation axis, a plurality of cutter blades 34 attached to the cutter blade mounting base 33, and a housing 35 that houses the shaft 32, cutter blade mounting base 33, cutter blades 34, etc. The cutter device 30 is installed, for example, on a movable base (not shown), so that the cutter blades 34 can be separated from the air-cooled granulation die 20 when granulation is not being performed. Note that in the example shown in Figure 1, two cutter blades 34 are attached to the cutter blade mounting base 33, but the number of attached cutter blades 34 is not limited to two and may be, for example, three or four.

The cutter blade 34 is fixed to the cutter blade mounting base 33 so that the distance between its tip and the air-cooled granulation die 20 is approximately 0.01 to 0.1 mm (e.g., 0.02 mm). The cutter blade 34 is fixed to the cutter blade mounting base 33 using, for example, a bolt 331. Then, by rotating the cutter blade mounting base 33 using the rotary drive source 31, the cutter blade 34 rotates over the area on the surface of the air-cooled granulation die 20 where multiple resin discharge holes 21 are arranged in a ring shape.

The molten resin mixture 50 extruded by the screw 12 inside the cylinder 11 of the extruder 10 is extruded in a string-like form from the resin discharge holes 21 of the air-cooled granulation die 20, which is arranged in a ring shape surrounding the torpedo 22, and is cut into pellets by a cutter blade 34 that rotates on the surface of the air-cooled granulation die 20.

(Configuration of cutter blade)
FIG. 2( a) is a perspective view of the cutter blade 34 included in the cutter device 30. FIG. 2( b) is a cross-sectional view of the vicinity of the tip of the cutter blade 34 along the longitudinal direction. The cutter blade 34 comprises a cutter blade body 340 and an amorphous carbon coating 342 covering a granulation surface 341 of the body 340. The granulation surface 341 of the body 340 is the surface that faces away from the air-cooled granulation die 20 when the cutter blade 34 is fixed to the cutter blade mounting base 33, and is the surface that comes into contact with the resin mixture 50 cut and pelletized by the cutter blade 34. The surface 345 of the body 340 opposite the granulation surface 341 has an inclined surface 346 that makes the tip of the body 340 acute-angled in the longitudinal cross section. The cutter blade 34 also has a recess 344 for fixing a bolt, for example, for passing a bolt 331 through it.

Figures 3(a) and (b) are cross-sectional views that schematically show how a cutter blade 34 cuts a resin mixture 50 extruded in a string-like shape from the resin discharge holes 21 of the air-cooled granulation die 20. As shown in Figures 3(a) and (b), the string-like portion 51 of the resin mixture 50 extruded from the resin discharge holes 21 is cut by the tip of the cutter blade 34 moving on the surface of the air-cooled granulation die 20, resulting in pellets 52.

Here, pellets 52 separated from the string-like portion 51 of the resin mixture 50 come into contact with the cutter blade 34. However, because the granulation surface 341, which is the surface facing the cutter blade 34 in the direction of travel, is covered with an amorphous carbon coating 342, adhesion of the pellets 52 to the cutter blade 34 is suppressed, even if the resin mixture 50 is a resin in which pellets tend to stick to each other during granulation, such as a resin mixture in which at least one of a flame retardant and a filler is added to polyethylene or polyolefin. As a result, adhesion of the pellets 52 to each other and beading can be suppressed.

The body 340 of the cutter blade 34 is made of a metal such as SK steel or SKH steel. The amorphous carbon coating 342 is a film made of an amorphous material, primarily composed of carbon and hydrogen, in which the bonding state of these elements is irregular, such as diamond-like carbon (DLC).

To more effectively prevent the pellets 52 from sticking together during granulation, the surface roughness Rz of the granulation surface 341 of the main body 340 is preferably 0.08 μm or more and 3.5 μm or less, and more preferably 0.1 μm or less.

To prevent cracks from occurring in the amorphous carbon coating 342, it is preferable that the granulation surface 341 of the main body 340, which serves as the base surface for the amorphous carbon coating 342, be flat, as shown in Figure 2(a). Furthermore, to more effectively prevent the pellets 52 from adhering to the cutter blade 34, it is preferable that the entire granulation surface 341 be covered with the amorphous carbon coating 342.

The amorphous carbon coating 342 is made of amorphous carbon or carbon in which some of the amorphous carbon has been replaced with other elements such as silicon. The amorphous carbon coating 342 can be formed by, for example, a CVD method such as plasma CVD or plasma ion implantation CVD, or a PVD method such as ionized vapor deposition, arc ion plating, or UBM (Unbalanced Magnetron) sputtering. In particular, it is preferable to form the coating by filtered arc ion plating, in order to more effectively prevent fusion of the workpiece (pellets sticking to each other) and increase the number of times the amorphous carbon coating 342 can be reused.

Using the arc ion plating method makes it possible to form an amorphous carbon coating 342 that is substantially free of hydrogen, has high hardness, and has excellent abrasion resistance. However, using the arc ion plating method, particles (graphite spheres) several micrometers in size called droplets may inevitably become mixed into the amorphous carbon coating 342. If droplets or impurities are present on the surface of the amorphous carbon coating 342, they may become the starting point for fusing the workpiece. Therefore, using the filtered arc ion plating method makes it possible to prevent droplets and impurities from mixing into the amorphous carbon coating, thereby forming an amorphous carbon coating 342 that is high hardness, has excellent abrasion resistance, and has a smooth surface.

Specifically, by using the filtered arc ion plating method, the arithmetic mean roughness Ra (in accordance with JIS-B-0601-2001) of the surface of the amorphous carbon coating 342 can be set to 0.03 μm or less, and the maximum height roughness Rz (in accordance with JIS-B-0601-2001) can be set to 0.5 μm or less. If Ra and Rz are within these ranges, it can be said that the inclusion of droplets, impurities, etc. in the amorphous carbon coating 342 is suppressed to a level that prevents the formed material from fusing. Furthermore, by setting Ra to 0.02 μm or less and Rz to 0.3 μm or less, fusing of the formed material can be more effectively reduced.

Furthermore, by using the filtered arc ion plating method, the nanoindentation hardness measured from the surface of the amorphous carbon coating 342 can be set to 50 GPa or more and 100 GPa or less. By setting the nanoindentation hardness to 50 GPa or more, wear resistance is improved, and the life of the cutter blade 34 can be extended. Furthermore, by setting the nanoindentation hardness to 100 GPa or less, residual stress in the amorphous carbon coating 342 can be suppressed, and adhesion to the main body 340 can be improved.

Here, nanoindentation hardness refers to the plastic hardness when a probe is pressed into a sample (amorphous carbon coating 342) and plastically deformed. Hardness is calculated by determining a load-displacement curve from the indentation load and indentation depth (displacement). Specifically, using a nanoindentation device manufactured by Elionix Co., Ltd., the hardness of the coating surface is measured at 10 points under measurement conditions of an indentation load of 9.8 mN, a maximum load holding time of 1 second, and a removal rate after load application of 0.49 mN/second. The hardness is then calculated as the average of the six points, excluding the two points with the highest and two points with the lowest values.

The thickness of the amorphous carbon coating 342 is preferably 0.2 μm or more and 1 μm or less. By making the thickness of the amorphous carbon coating 342 0.2 μm or more, it is possible to more effectively prevent the pellets from sticking together during granulation, and by making it 1 μm or less, it is possible to increase the number of times the amorphous carbon coating 342 can be reused. In addition, the amorphous carbon coating 342 is required to have heat resistance that can withstand the temperature during granulation (e.g., 190°C), and to further increase heat resistance, a thickness of 0.6 μm or more is preferable.

(Effects of the embodiment)
According to the above embodiment, it is possible to provide an air-cooled granulation device that can granulate a resin mixture in which at least one of a flame retardant and a filler has been added to the resin while suppressing adhesion of the pellets to each other, a cutter blade for the granulation device used in the device, and a method for granulating a resin mixture using the cutter blade for the granulation device.

Several types of cutter blades with different configurations, including the cutter blade 34 according to the above embodiment, were manufactured and their performance was evaluated. Details of the cutter blade configuration, evaluation method, and evaluation results are described below.

(Configuration of cutter blade)
The cutter blade body was prepared with and without buffing on the granulated surface (#300). SK5 or SKH51 material was used for the body material. Three types of coatings (Coatings A to C) were used as the coatings covering the granulated surface of the cutter blade. Table 1 below shows the materials and coating methods for Coatings A to C.

Coating A was obtained by plasma CVD using a silicon-containing hydrocarbon gas as the starting material to form a carbon coating to a thickness of 3.5 μm or less on the granulated surface of the cutter blade body. The "substitution rate" for Coating A in Table 1 refers to the percentage obtained by performing elemental analysis of the surface layer of the coating using X-ray spectroscopy, dividing the resulting nitrogen mass concentration by the unsubstituted carbon concentration.

Coating B was obtained by using a filtered arc ion plating method at a temperature of 473 K or less, using a solid graphite target as the starting material, to coat the granulated surface of the cutter blade body with a diamond-like carbon coating to a thickness of 1.1 μm or less. Coating C was obtained by applying silicone oil to the granulated surface of the cutter blade body with a brush.

Table 2 below shows the configurations of seven types of cutter blades (referred to as samples A to G) equipped with the above-mentioned body and coating. Note that the thickness of coating C on sample F was not measured due to the difficulty of measuring the thickness of the applied silicone oil.

(Evaluation method)
The above-mentioned cutter blade was evaluated by granulating two different types of resin mixtures (resin mixture A and resin mixture B) using a granulating device equipped with a cutter blade.

Resin mixture A is a flame-retardant resin mixture made by adding 80 parts by mass of magnesium hydroxide as a flame retardant to 100 parts by mass of ethylene vinyl acetate copolymer (EVA) as the base polymer, and its tensile elongation value was 450%.

Granulation of resin blend A was carried out by kneading a 6L kneader manufactured by Toshin Corporation at 160°C, and then feeding the kneaded mass of resin blend A into a TEC-7.5 granulating extruder manufactured by Toshin Corporation, equipped with an air-cooled granulating head. A hot-cut die with 28 resin discharge holes with a diameter of 3 mm was used as the air-cooled granulating die. Specific granulation conditions were a granulator cylinder temperature and die temperature of 160°C, a granulator rotation speed (rotation speed of the screw 12 of the extruder 10) of 15 rpm, and a cutter blade rotation speed of 190 rpm.

Resin blend B is a flame-retardant resin blend containing 100 parts by mass of a mixture of high-density polyethylene (HDPE), ethylene-ethyl acrylate copolymer (EEA), and chlorinated polyethylene (CPE) (HDPE/EEA/CPE = 50/40/10) as the base polymer, to which 35 parts by mass of a brominated flame retardant, 35 parts by mass of antimony trioxide, and 20 parts by mass of magnesium hydroxide were added, and its tensile elongation value was 500%.

Granulation of resin mixture B was carried out by kneading a 6L kneader manufactured by Toshin Corporation at 160°C, and then feeding the kneaded mass of resin mixture B into a TEC-7.5 granulating extruder manufactured by Toshin Corporation, equipped with an air-cooled granulating head. A hot-cut die with 28 resin discharge holes with a diameter of 3 mm was used as the air-cooled granulating die. Specific granulation conditions were a granulator cylinder temperature of 165°C and a die temperature of 170°C, respectively, a granulator rotation speed of 15 rpm, and a cutter blade rotation speed of 190 rpm.

200 g of each pellet obtained by granulating the above-mentioned resin blend A and resin blend B was sampled, and the mass of the pellets that were stuck together or linked together was taken as A. Granulation performance was assessed based on the mass-missing pellet rate X, calculated as X = {A/(200 + 200)} x 100 = A/4. Granulation performance was assessed 1 hour and 2 hours after the start of granulation. The granulation of resin blend A and resin blend B and the assessment of their granulation performance were then repeated on different dates and times, a total of 5 times. As an index for evaluating granulation performance, an X value of 10% or less can be assessed as good, and one exceeding 10% can be assessed as poor.

The tensile elongation values for Resin Blend A and Resin Blend B mentioned above are the tensile elongation values of the wire insulators manufactured using pellets granulated from Resin Blend A and Resin Blend B, respectively, and were measured by pulling the conductor out of the manufactured wire, forming each insulator into a tube shape, and conducting a tensile test in accordance with JIS C3005.

(Evaluation results)
Table 3 below shows the X values of the granulation of resin mixture A carried out using samples A to G, and Table 4 shows the X values of the granulation of resin mixture B carried out using samples A to G.

As shown in Tables 3 and 4, good results were obtained in granulation using samples A, B, C, and D, which had coating B for both resin blend A and resin blend B. On the other hand, when granulation was performed using sample E, which had no coating, and sample F, which had coating C, the pellets frequently stuck together and became beaded, so the experiment was discontinued after the third run. Furthermore, when granulation was performed using sample G, which had coating A, the X value increased from the third run onwards, but the X value was able to be kept below 10% until the second run.

These results show that good granulation properties can be achieved by using an amorphous carbon coating as the cutter blade coating. This is thought to be due to the excellent peelability of the amorphous carbon coating and the molten resin mixture under the temperature conditions during granulation.

Furthermore, it was found that forming the amorphous carbon coating on the cutter blade using the filtered arc ion plating method extends the coating's lifespan. This is thought to be due to the fact that hydrogen embrittlement of the coating is less likely to occur under the temperature conditions during granulation, suppressing deterioration, and the coating being formed thinly.

Based on the coating thickness of samples A, B, C, and D, it can be said that the thickness of the cutter blade coating is preferably 0.2 μm or more and 1 μm or less. By making the thickness 0.2 μm or more, the X value can be increased, and by making it 1 μm or less, the number of times the coating can be reused can be increased.

Furthermore, when comparing the X values for granulation using samples A, B, C, and D, the X values for samples A and C are higher than the X values for samples B and D. This is thought to be due to the fact that the granulation surface of the main body of samples A and C is buffed, which reduces the surface roughness Rz of the granulation surface. Since good granulation properties are obtained in all granulations using samples A, B, C, and D, it can be said that good granulation properties are obtained when the surface roughness Rz of the granulation surface of the main body of the cutter blade is 0.08 μm or more and 3.5 μm or less, based on the surface roughness Rz of the granulation surface of the main body of samples A and C. However, it can be said that even better granulation properties are obtained when the surface roughness Rz of the granulation surface of the main body of the cutter blade is 0.1 μm or less, based on the surface roughness Rz of the granulation surface of the main body of samples A and C.

Furthermore, because good results were obtained when granulating both resin blend A and resin blend B using samples A, B, C, and D, which have coating B as a coating, it is possible to suppress the inclusion of air bubbles when molding a resin molded product using the granulated pellets as a raw material, and to obtain a resin molded product with a high tensile elongation value (for example, 400% or more). In other words, resin blends A and B pelletized by granulation using samples A, B, C, and D can be used to mold a resin molded product with a tensile elongation value of 400% or more.

(Summary of the embodiment)
Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[1] A cutter blade (34) for a granulator, comprising a cutter blade body (340) having a granulation surface (341) and an amorphous carbon coating (342) covering the granulation surface (341).

[2] A cutter blade (34) for a granulator described in [1] above, wherein the arithmetic mean roughness Ra of the surface of the amorphous carbon coating (342) is 0.03 μm or less, and the maximum height roughness Rz is 0.5 μm or less.

[3] A cutter blade (34) for a granulator according to [1] or [2] above, wherein the surface roughness Rz of the granulation surface (341) is 0.1 μm or less.

[4] A cutter blade (34) for a granulator described in any one of [1] to [3] above, wherein the thickness of the amorphous carbon coating (342) is 0.2 μm or more and 1 μm or less.

[5] A cutter blade (34) for a granulator described in any one of [1] to [4] above, wherein the amorphous carbon coating (342) does not contain hydrogen.

[6] An air-cooled granulator (1) equipped with a granulator cutter blade (34) described in any one of [1] to [5] above.

[7] A method for granulating a resin mixture, comprising the step of cutting and pelletizing a resin mixture (50) extruded from the resin discharge holes (21) of the die (20) and to which at least one of a flame retardant and a filler has been added using the cutter blade (34) for a granulator described in any one of [1] to [5] above.

[8] A method for granulating a resin mixture described in [7] above, comprising a step of molding a resin molded product having a tensile elongation value of 400% or more using the pelletized resin mixture (50).

Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications are possible within the scope of the gist of the invention. Furthermore, the embodiments and examples described above do not limit the invention as defined by the claims. It should also be noted that not all of the combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

REFERENCE SIGNS LIST 1 Granulation device 10 Extruder 20 Air-cooled granulation die 21 Resin discharge hole 30 Cutter device 34 Cutter blade 340 Main body 341 Granulation surface 342 Amorphous carbon coating

Claims (1)

A method for manufacturing an electric wire having an insulator on a conductor,
a step of cutting a resin mixture, in which at least one of a flame retardant and a filler has been added to a resin extruded from a resin discharge hole of a die, into pellets using a cutter blade for a granulator, the cutter blade having a granulating surface and a hydrogen-free amorphous carbon coating covering the granulating surface ;
forming the insulator on the conductor using the pellet ;
the amorphous carbon coating has a surface with an arithmetic mean roughness Ra of 0.03 μm or less and a maximum height roughness Rz of 0.5 μm or less;
the surface roughness Rz of the granulation surface is 0.1 μm or less,
the amorphous carbon coating has a thickness of 0.2 μm or more and 1 μm or less;
The insulator has a tensile elongation value of 400% or more.
Manufacturing method of electric wire .