Control system for producing pellet

Abstract

To provide a control system for producing resin pellets with good cuttability, which suppresses variations in size and shape and prevents an occurrence of miscuts, thereby preventing an inclusion of miscuts.SOLUTION: A control system for producing resin pellets having a bending modulus of elasticity of 600 to 1,950 MPa satisfies formulas (1) to (4) when taking up a discharged strand that has been cooled and solidified and cutting the strand with a cutter consisting of a fixed blade and a rotating blade that rotates in a vicinity of the fixed blade. 0.010 g≤M / ncN≤0.050 g formula (1). 4.70 m / s≤2πncR≤19.0 m / s formula (2). 10°≤θ≤25°formula (3). 0.70 g / cm3≤ρ≤1.50 g / cm3 formula (4). Single hole discharge rate: M (g / s), Rotary blade rotation speed: nc (rpm / s), Number of teeth on the rotary blade: N, Rotary blade radius: R (m), Rotary blade rake angle: θ (°), Melted resin density: ρ.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control system for pellet production that suppresses miscutting of strands and improves cuttability. [Background technology]

[0002] When producing pellets (chips), which are the raw material for thermoplastic resin products, the thermoplastic resin is extruded in a molten state from the discharge section and formed into a strand shape, which is then taken up by a take-up roll consisting of a nip roll and a rotating roll, and cut into pellets using a cutter consisting of a fixed blade provided in the fixed section and a rotating blade that protrudes from the outer periphery of the rotating body and rotates with the position close to the fixed blade as its rotational trajectory.

[0003] When cutting a strand made of a resin with a large bending modulus, i.e., a hard resin, into pellets, the strand is less likely to deform between the nip roll and the rotating roll, and can be held by the take-up roll, so the strand is less likely to sway between the discharge hole and the take-up roll. For this reason, the strand is inserted vertically into the cutting section consisting of a fixed blade and a rotating blade, and the strand is cut at regular intervals, making it easy to produce pellets with little variation in size and shape.

[0004] On the other hand, when cutting a strand made of a resin having a small bending modulus, i.e., a flexible resin, into pellets, the strand is crushed between the nip roll and the rotating roll, and the strand cannot be sufficiently gripped, and the strand is prone to lateral shaking. In addition, since the strand itself is flexible and easily bends, the strand is taken up by the take-up roll in a meandering manner and inserted into the cutting section consisting of a fixed blade and a rotating blade. For this reason, the angle at which the strand is inserted into the take-up roll varies, and the angle at which the strand is inserted into the cutting section is not constant, resulting in oblique cutting, and frequently resulting in variations in the pellet shape. In addition, the swinging of the strand between the take-up roll and the cutting section causes the cutting interval of the strand to be not constant, causing variations in the pellet dimensions, and in severe cases, miscut strands occur. As a result, the pellet yield is significantly reduced, and the miscut strands mixed into the pellets cause operational troubles such as winding around the device drive section in downstream processes. For this reason, when producing pellets with little variation in size and shape from strands made of flexible resin, it is necessary to control the operating conditions more precisely than when handling stiff strands.

[0005] Regarding a method for producing pellets with excellent dimensional stability, for example, Patent Documents 1 and 2 propose a strand cooling and cutting device that detects the strand diameter between the discharge section and the take-up roll, measures the obtained pellet dimensions, and adjusts the pellet diameter by controlling the rotation speed of the take-up roll to obtain the desired pellet dimensions.

[0006] Furthermore, Patent Document 3 proposes an extrusion device for producing pellets with little dimensional variation by adjusting the size of the discharge hole with a drive unit provided in the discharge hole to suppress thickening and thinning of the strands.

[0007] However, none of these conventional techniques take into consideration the flexibility of the resin strands, and when producing pellets from flexible resin strands, more advanced control of operating conditions is required, but such control is difficult. In the reality, when control is not good, miscuts occur frequently and miscut strands get mixed in. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 5-345317 [Patent Document 2] Japanese Patent Application Publication No. 5-278027 [Patent Document 3] Patent Publication No. 2021-66035 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, an object of the present invention is to provide a control system for producing resin pellets that suppresses variation in pellet dimensions and shapes, even when cutting flexible thermoplastic resin strands into pellets, and prevents the mixing of miscut strands by suppressing the occurrence of miscutting of the strands, thereby improving cuttability. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention mainly employs the following means.

[0011] That is, this is a control system for use in the production of resin pellets from a resin having a bending modulus of elasticity of 600 to 1950 MPa, in which a strand that is discharged from a hole in a molten state and cooled and solidified is taken up by a take-up roll, and the strand is cut using a cutter consisting of a fixed blade provided in a fixed section and a rotating blade that protrudes from the outer periphery of a rotating body and rotates with the position adjacent to the fixed blade as its rotational trajectory.By satisfying formulas (1) to (4), this is a control system for use in the production of resin pellets that achieves good cutting properties and a good pellet yield.

[0012] 0.010g≦M / n c N≦0.050g...Equation (1) 4.70m / s≦2πRn c ≦19.0m / s...Equation (2) 10°≦θ≦25°...Equation (3) 0.70g / cm 3 ≦ρ≦1.50g / cm 3 ...Equation (4) however, Single hole discharge rate: M(g / s) Rotary blade speed: n c (times / s) Number of teeth on rotary blade: N Radius of the blade: R(m) Rotary blade rake angle: θ(°) Resin melt density: ρ(g / cm 3 ) Effect of the Invention

[0013] The present invention makes it possible to produce pellets with no variation in size or shape even when using flexible thermoplastic resin strands, and by suppressing the occurrence of miscutting of the strands, it is possible to prevent the inclusion of miscut strands, thereby providing a control system for the production of resin pellets that provides good cutting properties and a good pellet yield. [Brief description of the drawings]

[0014] [Figure 1]1 is a schematic diagram of a portion of a rotary blade of a pelletizer used in the present invention and an enlarged view of the blade tip, showing the rake angle (θ). [Diagram 2] FIG. 2 is a schematic diagram of a pelletizer used in the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing the relationship between speed and force when cutting a strand. [Figure 4] This shows the shape of a pellet when viewed from the longitudinal direction of the pellet cut surface and from a direction perpendicular to the uncut surface, and is a schematic diagram showing the relationship between pellet diameter, pellet length, and pellet uncut surface length for normal pellets and diagonally cut pellets in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will be described in detail below.

[0016] First, the control system for producing resin pellets in the present invention is a system that controls various formulas described below to fall within specified ranges when cutting a strand of flexible thermoplastic resin into pellets, in order to produce pellets with no variation in size or shape.

[0017] In this specification, a pelletizer refers to a device that is composed of a take-up roll consisting of a nip roll and a rotating roll, and a cutting section consisting of a fixed blade and a rotating blade, in which a resin strand extruded from a melted thermoplastic resin through a discharge hole is taken up by the take-up roll and sent to the cutting section, where the strand is cut by the fixed blade and the rotating blade to form pellets.

[0018] The control system of the present invention is a control system for use in the production of resin pellets that satisfies all of the formulas (1) to (4).

[0019] First, M / n in the following formula (1) c N is the amount of molten resin discharged from a polymerization tank or extruder in a given time (single-hole discharge rate: M (g / s)), multiplied by the cutting frequency in the same time, that is, the number of rotations of the rotary blade (n cThis formula is calculated by dividing the number of revolutions per second (rpm) by the number of teeth on the rotor blade (N), and represents the theoretical weight of the pellet. 0.010g≦M / n c N≦0.050g...Equation (1) In the control system for producing resin pellets of the present invention, the single hole discharge amount (M (g / s)) and the rotation speed of the rotary blade (n c (rpm / s) and the number of teeth on the rotary blade (N), M / n c It is essential that N is in the range of 0.050g or less and 0.010g or more. When the pellet weight is large, cooling inside the pellet is likely to be insufficient, and in the semi-molten state, the pellet will deform under its own weight, resulting in large variations in pellet dimensions. For this reason, in the control system of the present invention, it is essential that the theoretical pellet weight is 0.050g or less. More preferably, it is 0.046g or less, even more preferably, it is 0.043g or less, and most preferably, it is 0.039g or less. In addition, if the theoretical pellet weight is less than 0.010g, the pellets will fuse together in the subsequent drying process, or the pellets will be poorly bitten in the melt molding process using an extruder, resulting in poor handling. For this reason, it is essential that the pellet weight is 0.010g or more, and more preferably, it is 0.012g or more.

[0020] 2πRn in Equation (2) c is the circumference of the blade (2πR), which is the rotation path of the blade tip, and the number of rotations of the blade (n c ) and represents the peripheral speed of the tip of the rotary blade. 4.70m / s≦2πRn c ≦19.0m / s...Equation (2) In the control system for producing resin pellets of the present invention, the radius of the rotary blade (R) and the number of rotations of the rotary blade (n c) must be 4.70 m / s or more and 19.0 m / s or less. The inventors have thoroughly studied the control system (operation conditions) for producing resin pellets in order to cut flexible resin strands to obtain pellets with little dimensional variation, and have found that keeping the peripheral speed of the rotary blade within a certain range is effective in suppressing the swinging of the strand between the discharge hole and the take-up roll. The reasons for this are considered to be as follows.

[0021] A normal (non-soft) resin strand is taken up by the take-up roll while being held by the nip roll and the rotating roll, and tension is applied to the strand between the discharge hole and the take-up roll to suppress the swinging of the strand. However, in the case of a soft strand, as described above, the strand is deformed as if crushed at the same time as being sandwiched between the nip roll and the rotating roll, weakening the sandwiching of the strand, and the strand is easily deformed in the take-up direction during take-up, so that tension is not easily applied between the discharge hole and the take-up roll. For this reason, when a soft resin strand is taken up by the take-up roll, the strand is more likely to swing compared to a hard resin strand. Therefore, by setting the circumferential speed of the rotary blade within a certain range, sufficient tension can be generated in the strand and the swinging of the strand can be suppressed. For this reason, with respect to the range of the circumferential speed of the rotary blade, from the viewpoint of suppressing the swinging of the strand and improving the pellet yield, it is essential that the value of the circumferential speed of the rotary blade is 4.70 m / s or more. In addition, the pellet yield is preferably 50% or more, more preferably 75% or more, even more preferably 95% or more, and most preferably 98% or more. As for the upper limit of the peripheral speed of the rotary blade, if the peripheral speed of the rotary blade exceeds 19.0 m / s, the motor rotation noise becomes extremely loud, the working environment deteriorates, and the burden on the worker increases. For this reason, it is essential that the peripheral speed of the rotary blade is 19.0 m / s or less. In this case, there is no particular restriction on the radius of the rotary blade used, and a general rotary blade can be used.

[0022] In the control system for producing resin pellets of the present invention, it is essential that the rake angle (θ) of the rotary blade used in the pelletizer is in the range of 10° to 25°. Here, the rake angle refers to the angle between the line passing through the center of the rotary blade and the blade surface of the rotary blade, as shown in Figure 1. 10°≦θ≦25°...Equation (3) If the rake angle is large, the rotary blade is easily worn and the maintenance frequency of the rotary blade increases, which reduces operability and is inefficient. In addition, as described later, in order to suppress the swinging of the strand between the discharge hole and the take-up roll, it is necessary to hold the strand in the direction of the fixed blade with the rotary blade. In this case, if the rake angle is large and sharp, the force holding the strand is weak, and the effect of suppressing the swinging of the strand cannot be exhibited. Therefore, from the viewpoint of reducing the maintenance frequency of the rotary blade and improving operability, and from the viewpoint of being able to efficiently suppress the swinging of the strand, it is essential that the rake angle of the rotary blade is 25° or less. On the other hand, the smaller the rake angle, the less sharp the sharpness is, and the strand is cut as if it is being torn off, and the cut surface of the obtained pellet becomes rough, or the pellet becomes poorly shaped with fuzzing. Therefore, from the viewpoint of obtaining pellets with good shape and excellent quality, the rake angle of the rotary blade of the pelletizer controlled in the present invention must be 10° or more. In this case, there is no particular restriction on the clearance angle, lead angle, or number of blades of the rotary blade used, and any angle within the design range of a typical rotary blade can be used.

[0023] In addition, in the control system for producing resin pellets of the present invention, the melt density (ρ) of the resin used is 0.70 g / cm 3 More than 1.50g / cm 3 The following is the result. 0.70g / cm 3 ≦ρ≦1.50g / cm 3 ...Equation (4) In the control system for producing resin pellets of the present invention, if the melt density of the resin exceeds the above range, the resin strand becomes thin and slips through between the nip roll and the rotating roll, causing a problem of increased strand sway. Also, if the melt density of the resin is below the above range, the strand diameter becomes thick and is not smoothly inserted into the take-up roll consisting of the nip roll and the rotating roll, which may cause the strand to bend and be obliquely cut. Even with the control system for producing resin pellets of the present invention, it becomes difficult to control the pellet dimensions. For this reason, in the control system for producing resin pellets of the present invention, the melt density (ρ) of the resin used is 0.70 g / cm 3 More than 1.50g / cm 3 The upper limit of the melt density is preferably 1.20 g / cm. 3 More preferably, it is 1.15 g / cm or less. 3 or less, and particularly preferably 1.10 g / cm 3 The lower limit of the melt density is more preferably 0.80 g / cm or less. 3 More preferably, it is 0.90 g / cm 3 Here, the melt density (ρ) of the resin refers to a value measured by the method described later in the Examples section.

[0024] In addition, the control system for producing resin pellets of the present invention is particularly effective for resins with a flexural modulus of 1950 MPa or less and 600 MPa or more, and the preferred applicable range is resins with a flexural modulus of 1950 MPa or less and 600 MPa or more. As described above, the control system for producing resin pellets of the present invention is a control system intended to suppress pellet dimensional defects due to strand crushing at the take-up roll and strand shaking between the discharge hole and the take-up roll, and since strand crushing and shaking are unlikely to occur with resins with a flexural modulus of greater than 1950 MPa, the control system of the present invention may not only not work effectively, but may lead to inappropriate operating conditions. In addition, when the flexural modulus of the resin is below 600 MPa, the resin strand is too soft, so even the control system for producing resin pellets of the present invention cannot suppress the shaking of the strand between the discharge hole and the take-up roll, resulting in pellet crushing, oblique cutting, and miscut strands, and sufficient control cannot be achieved. For this reason, the control system for producing resin pellets of the present invention is effective for resins with a flexural modulus of 1950 MPa or less and 600 MPa or more. Regarding the flexural modulus of the resin on which the present control system effectively operates, it is more effective and preferable for the resin to have a flexural modulus of 1800 MPa or less, and even more effective and preferable for the resin to have a flexural modulus of 1600 MPa or less.

[0025] In addition, it is preferable that the theoretical strand diameter (G) satisfies the following formula (5).

[0026]

number

[0027] Here, the ratio of the circumferential speed of the rotary blade to the circumferential speed of the take-up roll is r Regarding the derivation of the theoretical strand diameter (G), assuming that the cross section of the strand is circular and the peripheral speed of the take-up roll (strand take-up speed) is V, the following formula is established. M = π(G / 2) 2 Vρ At this time, since the strand take-up speed is equal to the peripheral speed of the take-up roll, the relationship between the peripheral speed of the take-up roll and the peripheral speed of the rotary blade is expressed by the following formula, where r is the ratio of the peripheral speeds of the take-up roll and the rotary blade. V=2πRn c r From these formulas, the theoretical strand diameter is expressed by the following formula as the relationship between the single hole throughput rate and the rotary blade rotation speed.

[0028]

number

[0029] In the control system for producing resin pellets of the present invention, the theoretical strand diameter (G) is preferably 0.0020 m or more and 0.0046 m or less. As shown in formula (5), the theoretical strand diameter is determined by the single hole discharge rate (M), the resin melt density (ρ), the rotary blade rotation speed (R), and the rotary blade rotation speed (n c), and is determined from the ratio (r) of the peripheral speed of the rotating blade and the take-up roll. If the theoretical strand diameter is smaller than 0.0020 m, the strand becomes thin and stiff, and is likely to meander, and is also likely to slip through the nip roll and the rotating roll without being held, so the strand is likely to sway sideways. The meandering strand is taken up by the take-up roll and inserted into the cutting section consisting of the fixed blade and the rotating blade, and at this time, the angle of insertion of the strand into the take-up roll varies, so the angle of insertion into the cutting section is not constant, and oblique cutting is likely to occur. For this reason, the theoretical strand diameter is preferably 0.0020 m or more. Also, if the theoretical strand diameter value exceeds 0.0046 m, the strand is significantly crushed between the nip roll and the rotating roll, making it difficult to obtain pellets of the desired dimensions. For this reason, the theoretical strand diameter is preferably 0.0020 m or more and 0.0046 m or less. From the viewpoint of suppressing oblique cutting due to meandering of the strand, the theoretical strand diameter is more preferably 0.0022 m or more. Also, from the viewpoint of suppressing variation in pellet dimensions, the theoretical strand diameter is more preferably 0.0044 m or less, even more preferably 0.0042 m or less, and particularly preferably 0.0040 m or less.

[0030] It is also preferable that the force that the rotary blade exerts on the strand in the blade surface direction when cutting the strand satisfies formula (6).

[0031]

number

[0032] The force that the blade exerts on the strand in the blade direction when cutting the strand is calculated as shown in Figure 2. The blade moves at an angular velocity of ω(=2πn c), and when the rotating blade collides with the strand and cuts the pellet of weight: m, if the force exerted in the cutting direction until the cutting is F, the force exerted in the blade plane direction is expressed as Fcosθ. When the pellet moves vertically by the theoretical diameter of the strand: G, it moves in the blade plane direction at the same speed as the blade (2πn c Rcosθ) and then cutting. Regarding this transition, from the relationship between the amount of work and kinetic energy, Fcosθ(G / cosθ)=m(2πn c R cosθ) 2 / 2 It is expressed as F = m(2πRn c cosθ) 2 / (2G) This can be summarized as follows.

[0033] As mentioned above, the theoretical pellet weight (m) is expressed as the output per hole / (number of blades × number of rotations of the rotary blade). m = M / (Nn c ) As mentioned above, the theoretical strand diameter (G) is expressed by the following formula: G = (2M / (π 2 ρRn c r)) 1 / 2 From these three formulas, F = m(2πRn c cosθ) 2 / (2G) =(M / (Nn c ))(2πRn c cosθ) 2 / (2(2M / (π 2 ρRn c r)) 1 / 2 ) =2 1 / 2 π 3 ρ 1 / 2 M 1 / 2 n c 3 / 2 R 5 / 2 r 1 / 2 cos 2 θ / N Therefore, the following formula is derived:

[0034]

number

[0035] where K=2 1 / 2 π 3 Since it is a constant, the force exerted by the blade on the strand in the blade surface direction when cutting the strand is given as a function of the force.

[0036]

number

[0037] It can be expressed as:

[0038] In the control system for the production of resin pellets of the present invention, the value of the force applied to the strand by the rotating blade in the direction of the blade surface when cutting the strand is 1.0 g m 2 / s 2 More than 35.0g m 2 / s 2The present inventors have conducted extensive research into the operating conditions of a control system for producing resin pellets from flexible resin strands that are consistent in size and shape, and have found that controlling the force applied by the rotating blade to the strand in the direction of the fixed blade within an appropriate range suppresses meandering of the strand when the strand is taken up, reduces miscut strands, and improves pellet yield, as well as prevents deterioration of operability due to the inclusion of miscut strands. The reasons for this are considered to be as follows. With normal resin strands, the strands are taken up while being held by the nip roll and the rotating roll when the strands are taken up, so that sufficient tension is applied to the strands between the discharge hole and the take-up roll, and the swinging of the strands is suppressed. However, in the case of flexible strands, the strands are deformed so as to be crushed when sandwiched between the nip roll and the rotating roll, and the strands are not sufficiently held, so that tension is not applied to the strands between the discharge hole and the take-up roll, and the swinging of the strands cannot be suppressed, causing the strands to meander. For this reason, we found that in order to suppress meandering of the strands, it is effective to hold the strands in the direction of the fixed blade with a rotating blade of a cutter that cuts the strands. The inventors found that the value of the force that the rotating blade exerts on the strands in the blade surface direction when cutting the strands is 1.0 g m 2 / s 2 By doing the above, it was found that even with soft resin strands, meandering of the strands during take-off can be suppressed, the occurrence of miscut strands is suppressed, pellet yield is improved, and the variation in pellet shape caused by oblique cutting is improved, making it possible to produce pellets with stable shapes. From the viewpoint of further suppressing meandering of the strands and being able to produce pellets with less variation in shape without oblique cutting, the preferable range of the value of the force that the rotating blade applies to the strands in the blade face direction when cutting the strands is 2.4 g m 2 / s 2 More preferably, it should be 3.2 g m 2 / s 2 More preferably, it should be 3.8 g m 2 / s 2There is no particular upper limit, but from the viewpoint that the impact when the strand comes into contact with the rotary blade is large and extremely large vibration is generated, which deteriorates the working environment and increases the burden on the worker, it is preferable that the force applied to the strand by the rotary blade in the blade surface direction when cutting the strand, expressed by formula (6), is 35.0 g m 2 / s 2 It is preferable that the weight is less than 28.0g·m 2 / s 2 It is more preferable that:

[0039] In the control system for producing resin pellets according to the present invention, the single-hole discharge amount (M) of the discharge device, i.e., the resin supply speed and the rotation speed of the rotary blade (n c ) within a predetermined range, the values ​​of the above-mentioned various formulas can be kept within the specified range.

[0040] There is no particular limit to the single-hole discharge rate (M), and any value can be set according to the capacity of the resin supply device, but from the viewpoint of efficient pellet production, it is preferably 1.0 g / s or more, and more preferably 2.5 g / s or more. There is no particular limit to the upper limit of the single-hole discharge rate, but from the viewpoint of suppressing uneven discharge caused by a drop in the temperature of the discharge hole and the occurrence of thick and thin strands, thereby suppressing variation in chip dimensions, it is preferably 50.0 g / s or less, and more preferably 40.0 g / s or less.

[0041] In addition, the number of rotations of the rotary blade (n c ) is not particularly limited as long as the equation (2) for the peripheral speed of the rotary blade is controlled within a specified range, and any value can be set according to the capacity of the pelletizer. -1 If the rotation speed of the blade exceeds 100s, the motor will generate heat and cause equipment trouble. -1 It is preferable that the rotation speed of the rotary blade is 3 s or less. -1 If the speed is lower than this, miscut strands are likely to occur, so the rotation speed of the rotary blade is set to 3s -1 More preferably, it is equal to or greater than this.

[0042] In the control system for producing resin pellets of the present invention, if the distance between the nip roll and the rotating roll of the take-off roll is 0.0010 m or less, the strand is not smoothly inserted between the nip roll and the rotating roll, and the strand is bent, which may cause oblique cutting. Therefore, from the viewpoint of suppressing oblique cutting, the distance between the nip roll and the rotating roll of the take-off roll is preferably 0.0010 m or more. With regard to the upper limit, from the viewpoint of gripping the strand between the nip roll and the rotating roll and suppressing the swinging of the strand, it is preferably 0.0050 m or less, more preferably 0.045 m or less, and even more preferably 0.0040 m or less.

[0043] In the control system for producing resin pellets of the present invention, the ratio of the peripheral speeds of the take-up roll and the rotary blade can be set before operation if the rotation speeds of the take-up roll and the rotary blade of the pelletizer are linked by gears. Also, if the take-up roll and the rotary blade of the pelletizer are not linked by gears but are determined independently, the ratio of the peripheral speeds of the take-up roll and the rotary blade can be adjusted during operation.

[0044] In the control system for producing resin pellets of the present invention, the peripheral speed of the take-up roll, i.e., the take-up speed of the strand, is not particularly limited and can be set to any value depending on the supply capacity of the molten resin, but from the viewpoint of efficient production of pellets, it is preferably 20 m / min or more, more preferably 50 m / min or more, even more preferably 55 m / min or more, and particularly preferably 60 m / min or more. There is no particular upper limit, but since the molten resin is rapidly stretched immediately after being extruded from the discharge hole, which causes strand breakage, it is preferably 300 m / min or less, more preferably 250 m / min or less, and even more preferably 200 m / min or less.

[0045] The control system for producing resin pellets of the present invention can be used without any particular limitation as long as it is a pelletizer equipped with a mechanism for taking up a strand with a take-up roll and cutting the strand with a rotary blade. The resin is cooled in the form of a strand extruded from a die, and the cooling method for the strand is not particularly limited, and any known method such as water cooling, air cooling, or a combination thereof can be used. In terms of excellent cooling efficiency, it is preferable to provide a water cooling process between the discharge hole and the take-up roll. The control system for producing resin pellets of the present invention is suitably used for a USG cutter that water-cools the strand and cuts it in a semi-molten state.

[0046] In the control system for producing resin pellets of the present invention, the materials for the fixed blade, rotary blade, and take-up roll of the pelletizer are not particularly limited, and any known materials can be used without particular limitation.

[0047] The clearance between the rotary blade and the fixed blade, i.e., the distance between the tip of the rotary blade and the tip of the fixed blade, is preferably 0.015 mm or more, and the upper limit is preferably 0.050 mm or less, and more preferably 0.040 mm or less.

[0048] The above control system makes it possible to easily determine the operating conditions that enable the production of uniform pellets without variation in size and shape even from soft resin strands. This results in excellent pellet quality, good processability and handleability in subsequent processes, as well as a good pellet yield with little miscut strands. EXAMPLES

[0049] The present invention will be described in more detail below with reference to examples. The property values ​​in the examples were determined by the following methods.

[0050] A. Intrinsic viscosity The intrinsic viscosity was measured at 25°C using o-chlorophenol as a solvent.

[0051] B. Melt density Resin density was measured as follows. Approximately 5 g of resin pellets that had been dried to a moisture content of 300 ppm or less were placed in a melt indexer (Toyo Seiki F-F01, cylinder inner diameter: 9.476 mm, orifice inner diameter: 2.09 mm, orifice length: 7.984 mm) and melted at 240°C for 4 minutes, after which extrusion was started with a piston at a load of 1 kg. The weight of the resin extruded while the piston had reached a height displacement of 25.4 mm was measured, and the melt density was calculated using the following formula. Melt density (g / cm 3 ):ρ=resin weight / (π×0.4738 2 ×2.54) The measurement was carried out five times, and the average value was regarded as the melt density.

[0052] C. Flexural modulus The resin composition used in each example was dried to a moisture content of 300 ppm or less. Test pieces (80 mm x 10 mm x 4.0 mm) were molded in accordance with ISO178 using an injection molding machine "SE75DU" manufactured by Sumitomo Heavy Industries under conditions of a cylinder temperature of 260°C and a mold temperature of 80°C. Flexural modulus was measured in accordance with ISO178 using five of the obtained test pieces.

[0053] D. Cutting performance evaluation (1) Pellet yield 1 kg of the obtained pellets was passed through a stainless steel sieve with 5.6 mm mesh twice to remove miscut strands and long pellets that were mixed in the pellets, and the pellet yield was calculated from the weight of the pellets that passed through the sieve.

[0054] (2) Variation in pellet size The variation in pellet size was evaluated according to the following criteria. 100 pellets were randomly selected from the pellets sieved by the method described in (1) above, and the pellet diameter (R p ), the pellet length (L), which is the length perpendicular to the cut surface, and the average pellet diameter (R p,AVE , pellet length average value: (L ,AVEThe pellets whose pellet length and pellet diameter differed by within 10% from the calculated average were counted, and the pellets were rated on a 5-point scale: if the number of pellets in question was 95% or more, it was given an S (4 points), if it was 75% or more but less than 95%, it was given an A (3 points), if it was 50% or more but less than 75%, it was given a B (2 points), if it was 25% or more but less than 50%, it was given a C (1 point), and if it was less than 25%, it was given a D (0 point).

[0055] (3) Evaluation of bevel cutting The bevel cutting was evaluated according to the following criteria. 100 pellets were randomly selected from the pellets sieved by the method described in (1) above, and the uncut surface length (L') of the pellets was measured and the average value (L' ,AVE The average pellet length (L ,AVE ) for L' ,AVE The ratio was graded on a five-point scale: S (4 points) if it was 98% or higher, A (3 points) if it was 94% or higher but less than 98%, B (2 points) if it was 87% or higher but less than 94%, C (1 point) if it was 87% or higher but less than 87%, and D (0 points) if it was less than 87%.

[0056] (4) Cutting ability Cuttability was evaluated according to the following criteria: The pellet size variation evaluation in (2) above and the diagonal cutting evaluation in (3) above were totaled on a 5-point scale, with the maximum score being 8 points. The 6-point scale was used, with 8 points being SS, 7 points being S, 6 points being A, 5 points being B, 4 points being C, 3 points being D, and 2 points or less being E.

[0057] Example 1 A single-screw extruder (screw: φ65 mm, extrusion hole diameter: 8.5 mm) with one extrusion hole was used to extrude polybutylene terephthalate (flexural modulus: 650 MPa, resin density: 1.15 g / cm) copolymerized with 50 wt% polyethylene glycol at a die temperature of 250°C. 3The extrusion of 100% propylene glycol (1,000 g / s) was started, and the single-hole discharge rate was 10 kg / hr (2.8 g / s), and there was no problem with extrusion without pulsation. One strand extruded from the extruder was directly put into a 1.4 m water bath with a water temperature of 20°C to cool it down, and then the strand was inserted into a pelletizer equipped with a rotary blade radius of 0.076 m, number of blades: 28, and a rake angle of 10°, with a fixed blade-rotary blade clearance of 0.02 mm and a nip roll-rotary roll clearance of 1.5 mm. The peripheral speed ratio of the take-up roll and the rotary blade was fixed at 0.177 so that the pellet length was 3 mm, and the rotary blade rotation speed was adjusted. When the rotation speed reached 10 rpm, pellet collection was started. The take-up speed of the strand at this time was 50 m / min. The obtained pellets were passed twice through a stainless steel sieve with 5.6 mm openings to remove miscut strands and long pellets, resulting in a pellet yield of 56%. The shape of the obtained pellets was evaluated, with dimensional variation being A, oblique cutting being C, and cuttability being D. With regard to the cut surfaces of the obtained pellets, approximately 80% of the pellets were obliquely cut. In addition, the pellet dimensions were small, making them difficult to handle.

[0058] Example 2 Pellets were produced in the same manner as in Example 1, except that a rotary blade with a rake angle of 15° was used. The pellet yield was 54%. The shape of the obtained pellets was evaluated, with the dimensional variation being A, the oblique cutting being C, and the cutting ability being D. With regard to the cut surface of the obtained pellets, about 80% of the pellets were obliquely cut. In addition, the pellet dimensions were small, and the handling ability was poor.

[0059] Example 3 Pellets were produced in the same manner as in Example 1, except that a rotary blade with a rake angle of 20° was used. The pellet yield was 52%. The shape of the obtained pellets was evaluated, with the dimensional variation being A, the oblique cutting being C, and the cutting ability being D. With regard to the cut surface of the obtained pellets, about 80% of the pellets were obliquely cut. In addition, the pellet dimensions were small, and the handling ability was poor.

[0060] Example 4 Pellets were produced in the same manner as in Example 1, except that a rotary blade with a rake angle of 25° was used. The pellet yield was 50%. The shape of the obtained pellets was evaluated, with the dimensional variation being A, the oblique cutting being C, and the cuttability being A. With regard to the cut surface of the obtained pellets, about 80% of the pellets were obliquely cut. In addition, the pellet dimensions were small, and the pellets lacked handleability.

[0061] Example 5 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 17.0 kg / h (4.7 g / s) and the rotary blade rotation speed was 14 times / second. The strand take-up speed was 70 m / min, and the pellet yield was 81%. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cutting being B, and the cuttability being A. With respect to the cut surface of the obtained pellets, about 50% of the pellets were obliquely cut.

[0062] Example 6 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 50.0 kg / h (12.8 g / s) and the rotary blade rotation speed was 10 times / second. The strand take-up speed was 50 m / min, and the pellet yield was 82%. The shape of the obtained pellets was evaluated, with the dimensional variation being C, the oblique cutting being B, and the cuttability being D. With respect to the cut surface of the obtained pellets, about 50% of the pellets were obliquely cut.

[0063] Example 7 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 46.0 kg / h (12.8 g / s) and the rotary blade rotation speed was 10 times / second. The strand take-up speed was 50 m / min, and the pellet yield was 80%. The shape of the obtained pellets was evaluated, with the dimensional variation being B, the oblique cutting being B, and the cuttability being C. With respect to the cut surface of the obtained pellets, about 50% of the pellets were obliquely cut.

[0064] Example 8 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 43.0 kg / h (11.9 g / s) and the rotary blade rotation speed was 10 times / second. The strand take-up speed was 50 m / min, and the pellet yield was 80%. The shape of the obtained pellets was evaluated, with the dimensional variation being A, the oblique cutting being B, and the cuttability being B. With respect to the cut surface of the obtained pellets, about 50% of the pellets were obliquely cut.

[0065] Example 9 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 43.0 kg / h (11.9 g / s) and the rotary blade rotation speed was 11 times / second. The strand take-up speed was 55 m / min, and the pellet yield was 86%. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cutting being B, and the cuttability being A. With respect to the cut surface of the obtained pellets, about 50% of the pellets were obliquely cut.

[0066] Example 10 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 43.0 kg / h (11.9 g / s) and the rotary blade rotation speed was 12 times / sec. The strand take-up speed was 60 m / min, and the pellet yield was 86%. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cutting being A, and the cuttability being A. With respect to the cut surface of the obtained pellets, about 10% of the pellets were obliquely cut.

[0067] Example 11 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 40.0 kg / h (11.1 g / s) and the rotary blade rotation speed was 14 times / second. The strand take-up speed was 70 m / min, and the pellet yield was 95%. The shape of the obtained pellets was evaluated, with a dimensional variation of S, a diagonal cut of S, and a cuttability of S. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0068] Example 12 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 40.0 kg / h (11.1 g / s) and the rotary blade rotation speed was 16 times / sec. The strand take-up speed was 80 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0069] Example 13 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 43.0 kg / h (11.9 g / s) and the rotary blade rotation speed was 20 times / second. The strand take-up speed was 100 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0070] Example 14 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 40.0 kg / h (11.1 g / s) and the rotary blade rotation speed was 28 times / second. The strand take-up speed was 140 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0071] Example 15 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 100.0 kg / h (27.8 g / s) and the rotary blade rotation speed was 28 times / second. The strand take-up speed was 140 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0072] Example 16 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 60.0 kg / h (16.7 g / s) and the rotary blade rotation speed was 36 times / second. The strand take-up speed was 180 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0073] (Example 17) Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 120.0 kg / h (33.3 g / s) and the rotary blade rotation speed was 36 times / second. The strand take-up speed was 180 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0074] (Example 18) Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 135.0 kg / h (37.5 g / s) and the rotary blade rotation speed was 40 times / second. The strand take-up speed was 200 m / min, and the pellet yield was 98% or more. The pelletizer was loud and vibrated during operation. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0075] (Example 19) Pellets were produced in the same manner as in Example 1, except that the resin used was polybutylene terephthalate copolymerized with 30 wt% polyethylene glycol, the single hole discharge rate was 40.0 kg / h (11.1 g / s), and the rotary blade rotation speed was 20 times / second. The strand take-up speed was 100 m / min, and the pellet yield was 98% or more. The shape of the obtained pellets was evaluated, with the dimensional variation being S, the oblique cut being S, and the cuttability being SS. Visual inspection of the cut surfaces of the obtained pellets showed that most of the pellets were cut at 90° to the longitudinal direction of the strand.

[0076] Comparative Example 1 Pellets were produced in the same manner as in Example 1, except that the resin used was polybutylene terephthalate copolymerized with 30 wt% polyethylene glycol, the single hole discharge rate was 40.0 kg / h (11.1 g / s), and the rotary blade rotation speed was 20 times / second. The strand take-up speed was 100 m / min, the pellet yield was 40%, and a large amount of long pellets generated by extreme oblique cutting were collected on the sieve. Regarding the shape of the obtained pellets, the dimensional variation was D, the oblique cutting was D, and the cuttability was E. Regarding the cut surface of the obtained pellets, about 80% of the pellets were obliquely cut.

[0077] Comparative Example 2 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 135.0 kg / h (37.5 g / s) and the rotary blade rotation speed was 10 times / sec. The strand take-up speed was 50 m / min, the pellet yield was 40%, and miscut strands were collected on the sieve. The shape of the obtained pellets was evaluated, with the dimensional variation being D, the oblique cutting being B, and the cuttability being E. With respect to the cut surface of the pellets, about 50% were obliquely cut.

[0078] Comparative Example 3 Pellets were produced in the same manner as in Example 1, except that the single-hole discharge rate was 7.0 kg / h (1.9 g / s) and the rotary blade rotation speed was 10 times / sec. The strand take-up speed was 50 m / min, and the pellet yield was 30% while the strand meandered, and a large amount of miscut strands was collected on the sieve. The shape of the obtained pellets was evaluated, with the dimensional variation being B, the oblique cutting being D, and the cuttability being E. With regard to the cut surface of the pellets, most of the pellets were obliquely cut.

[0079] [Table 1]

[0080] [Table 2] [Explanation of symbols]

[0081] 1 Rake angle (θ) 2 Rotary blade 2' Rotary blade surface 3 Fixed blade 4 Nip roll 5 Rotation Roll 6 Strand take-up direction 7 Pelletizer 8 Strand 9 Pellet length (L) 10 Pellet diameter (R p ) 11. Uncut length of pellet (L') 12 Cut surface of pellet a Rotating blade peripheral speed b Blade plane direction speed c Force exerted from the rotating blade to the strand in the direction of the fixed blade d Force exerted on the strand by the rotating blade in the blade plane direction e Strand diameter f Pellet speed in the direction of the blade g Pellet speed in the direction of the blade h Pellet movement distance i Pellet after cutting

Claims

1. A control system for use in the production of resin pellets from a resin having a bending modulus of elasticity of 600 to 1950 MPa, the control system for use in the production of resin pellets being characterized in that when a strand that is discharged from a hole in a molten state and cooled and solidified is taken up by a take-up roll, and the strand is cut using a cutter consisting of a fixed blade provided on a fixed part and a rotary blade that is protruding from the outer periphery of a rotor and rotates with a rotation locus that is a position adjacent to the fixed blade, the system satisfies formulas (1) to (4). 0.010g≦M / n ｃ N ≦ 0.050 g ・・・Formula (1) 4.70m / s≦2πn ｃ R≦19.0m / s ・・・Formula (2) 10°≦θ≦25°...Formula (3) 0.70g / cm ３ ≦ρ≦1.50g / cm ３ ・・・Formula (4) however, Single hole discharge amount: M (g / s) Rotary blade rotation speed: n ｃ (times / s) Radius of the rotary blade: R (m) Rotary blade rake angle: θ (°) Number of blades: N Resin melt density: ρ (g / cm ３ )

2. 2. The control system for producing resin pellets according to claim 1, further comprising: a control system for producing resin pellets, the control system being characterized in that the following formula (5) is satisfied: [0010] however, Ratio of the circumferential speed of the rotary blade to the circumferential speed of the take-up roll: r

3. 3. The control system for producing resin pellets according to claim 1 or 2, further comprising: a control system for producing resin pellets, the control system being characterized in that the following formula (6) is satisfied: [0025]

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