Strand cutting method

Abstract

To provide a strand cutting method capable of solving a problem such that a pellet obtained by cutting a strand is attached to a valley portion of a rotary blade to rotate once, and to return to a position where a fixed blade is located, and a resulting material is cut again to produce a double-cut pellet, thereby deteriorating a quality of the pellet delivered as a product.SOLUTION: There is provided a strand cutting method using a pelletizer 20 that cuts a strand 10 sent from a take-up roll 23 through a strand receiving chute 22 between a rotary blade 25B and a fixed blade 25A. The method is configured in that: a pelletizer having the rotary blade 25B having a range of 0.85≤D / L≤1.4, and a range of 160 mm≤D≤300 mm and 150 mm≤L≤500 mm when a diameter of the rotary blade 25B is deemed as D and a horizontal length of the rotary blade 25B is deemed as L, is used; and the strand is cut by setting a rotation speed V of a blade tip, which is defined as a peripheral speed of the rotary blade 25B, to 100 m / min to 1,000 m / min.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a strand cutting method using a pelletizer that cuts a strand between a rotary blade and a fixed blade.

Background Art

[0002] Generally, in order to facilitate the supply to a molding machine, a thermoplastic resin material is blended with a colorant and various additives, kneaded, extruded in a strand shape from a porous die, the strand is cooled by water or air, and then cut by a pelletizer to form pellets having a length of about 2 to 5 mm and sold on the market.

[0003] The pelletizer for forming the above pellets sandwiches one or more cooled strands between two take-up rolls, continuously feeds the strands onto a strand receiving chute and / or a strand running surface, and cuts them between a fixed blade and a rotary blade attached to the tip thereof to produce pellets (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The pellets produced by the pelletizer described in the above-mentioned Patent Document 1 are discharged from the discharge chute of the pelletizer. However, some pellets remain attached to the valleys of the rotating blades and rotate once, then return to the position where the stationary blades are located and are cut again (so-called double cutting), resulting in chipped pellets that are unsuitable as products. Also, usually, the pellets discharged from the pelletizer, including the chipped pellets, are sieved in the downstream process, and most of the chipped pellets contained in the pellets are removed. However, when there are many chipped pellets contained in the pellets, there is a problem that chipped pellets that pass through without falling from the sieve are generated, deteriorating the quality of the pellets delivered as products. When the inventors of the present invention earnestly studied the above-mentioned problems, it was found that chipped pellets are generated by the following mechanism.

[0006] Figures 3(a) and (b) show the mode in which the strand 110 is cut by a general pelletizer 100 (only a part is shown), and Figure 4 shows a schematic perspective view of the rotating blade 120 constituting the pelletizer 100. The following explanation will be made with the distance D / 2 from the rotation axis O to the cutting edge 122 of the rotating blade 120 being the radius of the rotating blade 120 (that is, D is the diameter of the rotating blade 120), the lateral length of the rotating blade 120 being L, and the diameter of the strand 110 being d. The pelletizer 100 shown in Figure 3(a) includes a rotating blade 120, a stationary blade 130, and a take-up roll (not shown). By the action of the take-up roll, the strand 110 is fed from the direction indicated by the arrow R0 and is pinched and cut between the cutting edge 132 of the stationary blade 130 and the cutting edge 122 of the rotating blade 120. As shown in Figure 3(a), taking the horizontal line passing through the rotation axis O where the cutting edge 122 of the rotating blade 120 hits and the cut into the strand 110 starts at the position where the cut of the strand 110 starts as the reference line C1 (shown by the broken line), then, as shown in Figure 3(b), by rotating by the angle θ, the cutting edge 122 of the rotating blade 120 reaches the cutting edge 132 of the stationary blade 130 (shown by the broken line C2), and the cut of the strand 110 is completed. The angle θ is θ = sin with respect to the above-mentioned reference line C1 -1It is a position rotated by an angle θ calculated by (2d / D). Note that FIGS. 3(a), (b), and 4 are schematic diagrams drawn for explanation, and the diameter D and the lateral length L of the illustrated rotary blade 120, the diameter d of the strand 110, and the angle θ do not conform to the actual dimensions and angles.

[0007] And since the cross-section of the rotary blade 120 is circular as a whole, if the peripheral speed of the rotary blade 120, that is, the rotational speed of the tip 122 portion of the rotary blade 120 is V, then as shown in FIG. 3(b), a speed V0 = Vsinθ directed toward the axis O of the rotary blade 120 is generated in the cut pellet 112. When the speed V0 is large, due to the action of the speed V0, the pellet 112 enters the back surface, that is, the valley portion of the rotary blade 120, rotates once with the rotary blade 120, and becomes one of the factors for cutting the pellet 112 twice. Therefore, in order to reduce the double cutting of the pellet 112, it has been found that it is necessary to configure the strand cutting method in consideration of at least the speed V0 directed toward the rotation axis O of the pellet 112. Furthermore, when cutting the strand 110 with the rotary blade 120 to produce the pellet 112, it has also been found that it is difficult to appropriately cut to a desired size while eliminating double cutting unless the lateral length L related to the weight of the rotary blade 120 is appropriately set.

[0008] The present invention has been made in view of the above facts, and its main technical problem is to solve the problem that the pellet obtained by cutting the strand in the valley portion of the rotary blade adheres and rotates once, returns to the position with the fixed blade, and is cut again to produce a double-cut pellet, which deteriorates the quality of the pellet incorporated as a product, and to provide a strand cutting method.

Means for Solving the Problem

[0009] To solve the above main technical problem, according to the present invention, in a strand cutting method using a pelletizer that cuts a strand sent out from a take-up roll between a rotating blade and a fixed blade through a strand receiving chute, when the diameter of the rotating blade is D and the lateral length of the rotating blade is L as described above, it is in the range of 0.85 ≦ D / L ≦ 1.4, and in the range of 160 mm ≦ D ≦ 300 mm and 150 mm ≦ L ≦ 500 mm. A strand cutting method is provided in which a strand is cut using a pelletizer having a rotating blade, and the rotational speed of the tip portion defined as the peripheral speed of the rotating blade is set from 100 m / min to 1000 m / min.

[0010] It is preferable that the number of blades of the rotating blade is 15 or more and 40 or less.

Advantages of the Invention

[0011] The strand cutting method of the present invention is a strand cutting method using a pelletizer that cuts a strand sent out from a take-up roll between a rotating blade and a fixed blade through a strand receiving chute. When the diameter of the rotating blade is D and the lateral length of the rotating blade is L, it is in the range of 0.85 ≦ D / L ≦ 1.4, and in the range of 160 mm ≦ D ≦ 300 mm and 150 mm ≦ L ≦ 500 mm. A pelletizer having a rotating blade is used, and the rotational speed of the tip portion defined as the peripheral speed of the rotating blade is set from 100 m / min to 1000 m / min to cut the strand. Therefore, the pellets obtained by cutting the strand at the trough portion of the rotating blade adhere and rotate one week, and are prevented from returning to the position where the fixed blade is located, so that there is no so-called double-cut pellets, and the problem of reducing the quality of the pellets delivered as products can be solved.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of a strand cutting method configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0014] As a result of intensive studies by the inventors of the present invention to solve the above problems, in a pelletizer that cuts a strand sent out from a take-up roll through a strand receiving chute between a rotary blade and a fixed blade, when the diameter of the rotary blade is D and the lateral (axial) length of the rotary blade is L, in the range of 0.85 ≤ D / L ≤ 1.4, a rotary blade with 160 mm ≤ D ≤ 300 mm and 150 mm ≤ L ≤ 500 mm is used, and the rotational speed V of the tip portion of the rotary blade is set from 100 m / min to 1000 m / min to cut the strand, and it was discovered that the generation of double-cut pellets can be extremely reduced.

[0015] Conventionally, the diameter D of the rotary blade was less than 0.85 of the lateral length L. That is, the diameter D of the rotary blade was smaller than that of the present invention. Also, as understood from the explanation based on FIG. 3(b), the angle θ through which the rotary blade rotates from the start to the completion of cutting the strand tends to increase as the diameter D of the rotary blade decreases, which has been a factor in increasing the speed (V0 = Vsinθ) of the pellet in the rotational axis direction of the rotary blade. And when the diameter D of the rotary blade was less than 160 mm, it became difficult to make the speed (V0 = Vsinθ) of the pellet in the rotational axis direction of the rotary blade a sufficiently small value, and a large number of double-cut pellets were generated. Therefore, it was found that the diameter D of the rotary blade should be 160 mm or more.

[0016] Here, if the value of D / L is made greater than 1.4, or the diameter D of the rotary blade is made greater than 300 mm, or the lateral length L of the rotary blade is made greater than 500 mm, the rotary blade will become extremely heavy and require huge power to drive. Furthermore, the inertial force of the rotary blade will also increase, taking time to change the rotational speed V, taking time to adjust the size of the discharged pellets, and reducing the product yield. Also, when the length of L is less than 150 mm, when cutting many strands, the strands overlap, the rotary blade does not enter parallel to the strands, and diagonal-cut pellets are generated.

[0017] The inventors have found that it is necessary to implement a strand cutting method based on the above conditions in order to efficiently cut pellets while suppressing the generation of the above-mentioned double-cut pellets and diagonal-cut pellets and maintaining a high product yield. For the above conditions, the range of D / L is more preferably 0.9 ≦ D / L ≦ 1.3, and even more preferably 0.95 ≦ D / L ≦ 1.2. Also, it has been found that the range of D is more preferably 190 mm ≦ D ≦ 280 mm, and even more preferably 200 mm ≦ D ≦ 260 mm.

[0018] The rotational speed V of the tip portion defined as the peripheral speed of the rotary blade must be from 100 m / min to 1000 m / min. If it is slower or faster than this range, the generation rate of double-cut pellets will increase. The reason for this is considered as follows.

[0019] Normally, in the case of cutting with a blade, on the side to be cut, there are a cut surface (a surface like being cut by scissors) and a fracture surface (a surface torn off) due to the cutting action of the blade. When the blade is sharp and the cutting speed of the blade is fast, the fracture surface is small and almost only the cut surface remains. However, when the speed of the blade for cutting is slow, the fracture surface becomes large. Since this fracture surface is generated by tearing, it is likely to remain on the back side of the rotary blade. Therefore, it is presumed that the generation rate of double-cut pellets increases for the above reasons.

[0020] When the speed of the rotating blade is high, it becomes almost a cutting surface and cuts sharply, so it is assumed that the number of double-cut pellets decreases. However, when the rotational speed of the rotating blade is too high, the generation rate of double-cut pellets also increases. The reason is thought to involve gravity. In addition to the initial velocity at the time of cutting, the gravitational acceleration g is applied to the cut pellets. That is, after the pellet is cut, after time t, downward, V1 = 1 / 2gt 2 the velocity is added. This makes it easier for the pellet to move downward and less likely to remain behind the rotating blade. However, if the velocity V of the cutting edge of the rotating blade is too fast relative to the above-mentioned velocity V1, the ratio of the influence of gravity g relatively decreases. Even if the diameter D of the rotating blade is appropriate, when the strand 110 is cut and the pellet scatters, the velocity V0 = Vsinθ in the rotational axis direction of the rotating blade increases, making it easier for the pellet to remain behind the rotating blade and increasing the generation rate of double-cut pellets. For these reasons, the rotational speed V of the cutting edge portion of the rotating blade must be between 100 m / min and 1000 m / min.

[0021] Also, in the present invention, it is preferable that the number of blades of the rotating blade is 15 or more and 40 or less. If it is less than 15, the interval between each blade becomes longer, and since it is necessary to rotate the rotating blade at high speed, the probability that the pellet enters behind the rotating blade increases. Since the strand is water-cooled, a certain amount of moisture adheres to the surface of the rotating blade. The probability that the cut pellet adheres to the moisture on the back surface of the blade increases, and the pellet adhering to the rotating blade makes one revolution and becomes a double-cut pellet when it contacts the next fixed blade. Furthermore, when the number of blades of the rotating blade is 40 or more, it becomes necessary to relatively reduce the rotational speed of the rotating blade with respect to the strand extruded from the extruder die at a constant speed, and the strand does not cut sharply, and defective cut pellets are likely to occur. The number of blades of the rotating blade is more preferably 18 or more, even more preferably 20 or more, more preferably 35 or less, and even more preferably 30 or less.

[0022] Incidentally, the pellets cut by the pelletizer are sorted by a vibrating sieve or the like downstream thereof, and although the number of double-cut pellets is reduced to some extent, it is difficult to remove the entire amount. The double-cut pellets contained in the product pellets not only deteriorate the design quality of the product pellets, but also, if minute chips generated by double-cutting are present in the product pellets, they will fly into the air during pellet transportation during injection molding and adhere to the surface of the injection molding die, sometimes causing molding transfer defects. Therefore, the amount of double-cut pellets after cutting by the pelletizer is preferably 200 mass ppm or less, more preferably 150 mass ppm or less, and even more preferably 100 mass ppm or less of the total amount of the cut pellets.

[0023] Hereinafter, embodiments of implementing the strand cutting method according to the present invention will be described more specifically with reference to FIGS. 1 and 2. When implementing the strand cutting method of this embodiment, a pellet production line 1 whose schematic is shown in FIG. 1 is used. The pellet production line 1 includes an extruder 2, a cooling water tank 3, a draining means 4, and a pelletizer 20. The resin melt-kneaded by the extruder 2 is extruded from a porous die 2a into a plurality of strands 10 and conveyed in the direction indicated by arrow R1. The strands 10 are cooled by the cooling water tank 3, the draining means 4 drains the water from the cooled strands 10, and the strands are fed into the pelletizer 20 for cutting to produce pellets.

[0024] FIG. 2 shows a longitudinal sectional schematic view showing an outline of the pelletizer 20 disposed in the above-described pellet production line 1 and a mode in which the strands 10 are cut by the pelletizer 20. In FIG. 2, the plurality of strands 10 extruded from the above-described extruder 2 advance in the direction indicated by arrow R1 by the guide roll 21 and are guided to the strand receiving chute 22. The strands 10 passing through the strand receiving chute 22 are pulled by the rotation of the take-up roll 23 composed of the upper roll 23a and the lower roll 23b, and the strands 10 sent out from the take-up roll 23 are sent to a cutting portion 25 composed of a fixed blade 25A and a rotating blade 25B from a strand inlet 24.

[0025] The rotary blade 25B has a plurality of blade tips 25Ba in a gear shape and rotates in the direction indicated by the arrow R2 (clockwise) in the figure. Above the take-up roll 23, a roll cover 27 that covers the upper roll 23a is provided, and above the cutting section 25, a cutting section cover 28 is provided. The cutting section cover 28 is configured to open upward for maintenance inspection, cleaning of the rotary blade 25B, adjustment of the clearance between the blade tip 25Aa of the fixed blade 25A and the blade tip 25Ba of the rotary blade 25B, and the like. The strand 10 sent from the take-up roll 23 toward the cutting section 25 is cut between the blade tip 25Aa of the fixed blade 25A and the blade tip 25Ba of the rotary blade 25B to become pellets P of a desired length and is guided to the discharge chute 26.

[0026] The appropriate pellet cutting amount (processing amount) in the above-described pelletizer 20 is 100 kg / h or more and 1200 kg / h or less. If it is less than 100 kg / h, the number of strands to be processed decreases, it is difficult for the strands to become uniform in the lateral direction, and the strands tend to concentrate only in a partial region in the longitudinal direction of the rotary blade 25B. Therefore, the wear of the blade in that part progresses easily. If it is more than 1200 kg / h, that is, if the number of strands 10 sent to the pelletizer 20 increases, strands 10 that overlap during cutting are generated. Therefore, diagonal cutting and cutting defects are likely to occur. A more preferable processing amount is 150 kg / h or more and 1000 kg / h or less. More preferably, it is 200 kg / h or more and 800 kg / h or less. For the above reasons, the preferable number of strands 10 is 5 or more and 40 or less. More preferably, it is 8 or more and 30 or less, and even more preferably, it is 10 or more and 25 or less.

[0027] Examples and comparative examples of the strand cutting method of the present invention by the pelletizer 20 disposed on the above-described production line 1 will be described in detail by production examples of polycarbonate pellets. The extruder 2 disposed on the above-described production line 1 for carrying out the present examples and comparative examples is a twin-screw extruder (manufactured by Nippon Steel Works, Ltd., TEX44αIII), and as the resin for generating the strand 10, polycarbonate resin "S3000F" (manufactured by Mitsubishi Engineering Plastics Corporation, trade name, viscosity average molecular weight Mv: 21500) was used.

[0028] (Example 1) The above-described polycarbonate resin "S3000F" was supplied to the extruder 2 at 200 kg / hr (discharge rate), melt-kneaded, and extruded from a porous die 2a equipped with a die plate having 13 holes and a diameter of 3.5 mm. Then, the above-described 13 strands 10 were taken up by the pelletizer 20 at a speed of 47 m / min to obtain pellets P having an average diameter of 2.4 mm and a length of 2.8 mm. In Example 1, the diameter D of the rotary blade 25B of the pelletizer 20 was 200 mm, the lateral length L of the rotary blade 25B was 200 mm (D / L = 1), the number of blades of the blade tip 25Ba of the rotary blade 25B was 24, and the rotational speed V of the blade tip defined as the peripheral speed of the rotary blade 25B was 440 m / min.

[0029] After cutting with the pelletizer 20 for 5 minutes, it was confirmed that the cutting in the pelletizer 20 was stable, and 5 kg of pellets P were collected. The pellets P were visually inspected, and the number of double-cut pellets was determined. The weight of the pellets P formed into the desired shape was 0.0152 g, and the number of pellets P contained in 5 kg was approximately 330,000. On the other hand, the number of discovered double-cut pellets was 25, and when the total weight of the double-cut pellets was measured, it was 0.38 g. That is, it was confirmed that it was 76 mass ppm in 5 kg and was below 100 mass ppm, which is the most preferable standard.

[0030] (Example 2) The discharge rate of the polycarbonate supplied to the extruder 2 was set at 300 kg / h, the take-up speed of the strand 10 was set at 71 m / min, and the rotational speed V of the cutting edge 25Ba of the rotary blade 25B of the pelletizer 20 was set at 662 m / min. Experiments were conducted in the same manner as in Example 1 except for these settings. The obtained pellets P had an average diameter of 2.4 mm and a length of 2.8 mm. After cutting with the pelletizer 20 for 5 minutes, 5 kg of the pellets P were collected. The pellets P were visually inspected, and the number of double-cut pellets was determined. As a result, 29 double-cut pellets were found. The total weight of the double-cut pellets was measured to be 0.44 g. That is, it was confirmed that this was 88 mass ppm in 5 kg, which is below the most preferable standard of 100 mass ppm or less.

[0031] (Comparative Example 1) A pelletizer 20 was used in which the diameter of the rotary blade 25B of the pelletizer 20 was 145 mm, the lateral length L of the rotary blade 25B was 200 mm (i.e., D / L = 0.725), and the number of blades was 24. Other conditions were experimented with in the same manner as in Example 1. Similar to Example 1, these 13 strands 10 were taken up at a speed of 47 m / min, the rotational speed V of the cutting edge 25Ba of the rotary blade 25B was set at 440 m / min, and pellets P with an average diameter of 2.4 mm and a length of 2.8 mm were obtained. After cutting with the pelletizer 20 for 5 minutes, 5 kg of the pellets P were collected. The pellets P were visually inspected, and the number of double-cut pellets was determined. As a result, 72 double-cut pellets were found. The total weight of the double-cut pellets was measured to be 1.09 g. That is, it was confirmed that the double-cut pellets were 218 mass ppm in 5 kg, and did not meet the preferable standard of 200 mass ppm or less of the total amount of pellets.

[0032] (Comparative Example 2) The discharge rate of the polycarbonate supplied to the extruder 2 was set at 300 kg / h, the take-up speed of the strand 10 was set at 71 m / min, and the rotational speed V of the blade tip 25Ba of the rotary blade 25B of the pelletizer 20 was set at 662 m / min. The experiment was conducted in the same manner as in Comparative Example 1 except for these settings. The obtained pellets P had an average diameter of 2.4 mm and a length of 2.8 mm. After cutting with the pelletizer 20 for 5 minutes, 5 kg of the pellets P were collected. The pellets P were visually inspected, and the number of double-cut pellets was determined. As a result, 88 double-cut pellets were found. When the total weight of the double-cut pellets was measured, it was 1.33 g. That is, the double-cut pellets were 266 mass ppm in 5 kg, and it was confirmed that they did not meet the preferable standard of 200 mass ppm or less of the total amount of the pellets.

[0033] (Comparative Example 3) The discharge rate of the polycarbonate supplied to the extruder 2 was set at 40 kg / hr, the take-up speed of the strand 10 was set at 9.4 m / min, and the rotational speed V of the blade tip 25Ba of the rotary blade 25B was set at 88 m / min. The experiment was conducted in the same manner as in Example 1 except for these settings. The obtained pellets P were pellets with an average diameter of 2.4 mm and a length of 2.8 mm. After cutting with the pelletizer 20 for 5 minutes, 5 kg were collected. As a result, 77 double-cut pellets were found. When the total weight of the double-cut pellets was measured, it was 1.17 g. That is, it was 234 mass ppm in 5 kg, and it was confirmed that they did not meet the preferable standard of 200 mass ppm or less of the total amount of the cut pellets.

[0034] (Comparative Example 4) The discharge rate of the polycarbonate supplied to the extruder 2 was set at 400 kg / hr, three of the 13 holes were blocked with brass to make 10 holes, and the 10 strands 10 were taken up by the pelletizer 20 at a speed of 122 m / min. The experiment was conducted in the same manner as in Example 1 except that the rotational speed V of the blade tip of the rotary blade 25B was set at 1140 m / min. The obtained pellets P were pellets with an average diameter of 2.4 mm and a length of 2.8 mm. After cutting with the pelletizer 20 for 5 minutes, 5 kg of the pellets P were collected. The pellets P were visually inspected, and the number of double-cut pellets was determined. As a result, 82 double-cut pellets were found. When the total weight of the double-cut pellets was measured, it was 1.24 g. That is, it was 248 mass ppm in 5 kg, and it was confirmed that it did not satisfy the preferred standard of 200 mass ppm or less of the total amount of pellets.

[0035] In the above-described examples, an example in which a polycarbonate resin was employed as the resin for generating the strands 10 was described. However, the present invention is not limited thereto, and similar results can be obtained even if other resins are selected as the resin for generating the strands 10. Examples of other resins include thermoplastic polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate; styrene resins such as polystyrene resin, high-impact polystyrene resin (HIPS), acrylonitrile-butadiene-styrene copolymer (ABS resin), and acrylonitrile-styrene copolymer (AS resin); polyolefin resins such as polyethylene resin and polypropylene resin; polyamide resin; polyimide resin; polyetherimide resin; polyurethane resin; polyphenylene ether resin; polyacetal resin; polyphenylene sulfide resin; polysulfone resin; polymethacrylate resin, and the like.

Explanation of Symbols

[0036] 1: Production line 2: Extruder 3: Cooling water tank 4: Drainage means 10: Strand 20: Pelletizer 21: Guide roll 22: Strand receiving chute 23: Take-up roll 23a: Upper roll 23b: Lower roll 24: Strand inlet 25: Cutting part 25A: Fixed blade 25Aa: Blade tip 25B: Rotating blade 25Ba: Blade tip 26: Discharge chute 27: Roll cover 28: Cutting part cover 100: Pelletizer 110: Strand 120: Rotating blade 122: Blade tip 130: Fixed blade 132: Blade tip

Claims

1. In a strand cutting method using a pelletizer that cuts a strand fed from a take-up roll through a strand receiving chute between a rotating blade and a fixed blade, when the diameter of the rotating blade is D and the lateral length of the rotating blade is L, a pelletizer having a rotating blade in the range of 0.85 ≦ D / L ≦ 1.4, and 160 mm ≦ D ≦ 300 mm, and 150 mm ≦ L ≦ 500 mm is used, and the strand is cut with the rotational speed of the tip portion defined as the peripheral speed of the rotating blade being from 100 m / min to 1000 m / min.

2. The strand cutting method according to claim 1, wherein the number of blades of the rotating blade is 15 or more and 40 or less.

Images