JP6668839B2 - Pelletizer and method for producing pellets using the same - Google Patents

Description

  The present invention relates to a pelletizer, and a method for producing pellets using the same, and has a low melting point and soft resin, which has conventionally been considered difficult to cut. The present invention relates to a pelletizer that can be manufactured and a method for manufacturing a pellet using the pelletizer.

  A pelletizer for producing resin pellets is provided with a cutter unit having a plurality of cutter blades at the tip, facing a die having a plurality of nozzles provided at the tip of an extruder. The cutter blade rotates while being in contact with the die surface, and cuts the molten resin extruded from the die to produce pellets (for example, Patent Documents 1 to 3).

FIG. 1 shows an outline of a conventional pelletizer device. In this apparatus, an extrusion head 4 is mounted via a breaker plate 3 on the tip side of an extrusion cylinder 2 containing an extrusion screw 1 of an extruder, and a large number of nozzle holes (nozzle openings) are provided at the tip of the extrusion head 4. A die 6 having a portion 5 and a body (cutter box) 7 are mounted. A cutter shaft 8 is coaxially supported by the body 7 and the extrusion screw 1, and a cutter blade 9 disposed close to the tip surface of the die 6 is attached to the cutter shaft 8. ) 10.
A cooling water tank 11 is formed on the inner peripheral surface of the body 7, and the cutter shaft 8 is driven to rotate at a high speed by a motor, and the molten resin extruded from the nozzle hole 5 is cut into pellets by a cutter blade 9. The water is scattered in the radial direction by the centrifugal force of the cutter blade 9, cooled and solidified in the cooling water tank 11, and discharged from the outlet 12 together with the cooling water.

Japanese Utility Model Publication No. 1-1010809 Japanese Utility Model Laid-Open No. 6-24913 JP-A-2003-21442 JP 2008-246854 A JP 2008-307711 A

It is known that cutting of a molten resin having a low melting point and soft properties is difficult, and the pellets contact each other in a cooling water tank before the pellets are completely crystallized. Will produce deformed pellets fused together.
Such deformed pellets may cause troubles due to poor addition and poor plasticization in the weighing machine and the apparatus and process on the consumer side, and may cause troubles. It is desired.

In order to solve the above problems, several methods are conventionally known. For example, Patent Literature 4 discloses a method of adding silicone oil to cooling water to prevent cohesion between pellets. Has been proposed.
However, if additives such as silicone oil and surfactant remain on the surface of the product pellets and are supplied as they are to the user, contamination may occur depending on the application.
As a means for preventing the fusion of the pellets, a method of lowering the temperature of the resin or the temperature of the die heating medium is usually used.
Further, as the most effective countermeasure in the operation of the pelletizer, there is a method of lowering the temperature of the cooling water.
However, an excessively low cooling water temperature causes extremely small pellets due to clogging of the nozzles of the dies, and further, by increasing the local resin linear velocity in nozzles without clogging, large pellets, There is a problem in that rosary pellets that are connected like a rosary via a resin as shown in FIG. 11, that is, deformed pellets different from fused pellets are generated.

  An object of the present invention is to provide a pelletizer that can stably produce pellets without a fused pellet, in view of the above-mentioned current situation, and regarding a resin having a low melting point and softness, which was conventionally considered to be difficult to cut. An object of the present invention is to provide a method for producing pellets using a pelletizer.

  The present inventor has conducted various studies to solve the above-mentioned problems, and as a result, in a pelletizer having a plurality of cutter blades at the tip with respect to a die surface having a plurality of nozzles, the nozzle spacing of the dies is controlled as follows. By doing so, it was found that the fused pellets were significantly reduced, and the present invention was completed.

The pelletizer of the present invention, a polyethylene-based resin or polypropylene-based resin extruded from a nozzle in a die surface attached to the tip of the extrusion cylinder, by a rotary cutter blade disposed close to the tip surface of the die surface. After cutting into pellets, in a pelletizer that is to be water-cooled and solidified,
A plurality of nozzles that are in contact with the blade surface of the same cutter blade are characterized in that they are spaced apart such that the distance (Lz) between adjacent nozzles is 6 mm or more.

In the pelletizer of the present invention, a portion where the maximum value (ΣWn) max of the sum (ΣWn) of the length (Wn) of the opening portion of the nozzle contacting the cutter blade and the die surface including the opening portion overlaps The length (Lx) preferably satisfies the following relational expression.
(ΣWn) max / Lx ≦ 0.2

In the pelletizer of the present invention, for a triangle configured such that the outer peripheral length is minimized by any three nozzle hole center points arranged on the die, the outer peripheral length (Ly) and the nozzle hole diameter (d) Preferably satisfy the following relational expression.
Ly-3 × d ≧ 20.5

  In the pelletizer of the present invention, the temperature of the cooling water injected into the cooling water tank in the water-cooled solidification is preferably higher than 20 ° C. and equal to or lower than 45 ° C.

  The method for producing a pellet according to the present invention is characterized in that the pellet is produced from a polyethylene-based resin or a polypropylene-based resin having a melting point of 110 to 145 ° C and a flexural modulus of 50 to 350 MPa by using the pelletizer.

  According to the pelletizer of the present invention and the method for producing pellets using the same, when the cutter blade cuts the molten resin, the interval between the die nozzles arranged on the cutter blade surface is controlled to be a certain distance or more. Furthermore, the nozzles arranged on the cutter blade surface and the dies having the nozzle arrangement such that the interval between the dice nozzles is equal to or more than a certain distance without considering the cutting of the molten resin discharged from these nozzles are provided. By using a pelletizer, it is possible to produce pellets stably without cutting defects for a resin characterized by a low melting point and softness, which was conventionally considered difficult to cut.

Specifically, the present invention can stably and efficiently perform cutting of a resin having a melting point of 110 to 145 ° C or less and a flexural modulus of 50 to 350 MPa or less.
In the prior art, regarding the granulation of a polyethylene-based resin or a polypropylene-based resin having a low melting point and a soft characteristic as described above, the temperature of the cooling water must be extremely lowered to cope with the problem. Therefore, there is a problem of formation of a deformed pellet having a different form and yield.
On the other hand, according to the present invention, by devising the interval between the die nozzles, it is possible to suppress the generation of the fusion pellet without performing an extreme temperature decrease of the cooling water, and to suppress the generation of the fusion pellet. Granulation can be performed stably while simultaneously suppressing the die clogging.

The pelletizer of the present invention is also suitable for cutting a high-flow resin as described in Patent Document 5.
Further, the present invention can be applied to cutting of a molten resin having a resin characteristic such as low melting point, softness, and high fluidity, which is opposite to the resin characteristics.
Therefore, by adjusting the temperature of the cooling water and other operating conditions as appropriate with one die, various characteristics with a wide range of characteristics from low melting point to high melting point, soft to hard, and low fluidity to high fluidity It is possible to cope with a granulation process of a suitable resin and can be suitably used for these.

  Furthermore, according to the pelletizer of the present invention, pellets can be produced stably without cutting defects, so that the pellets can be produced efficiently at low cost with little breakage of the cutter.

  In addition, according to the present invention, pellets manufactured stably without causing cutting defects, irregular shaped pellets and irregularities in the shape of the pellets fused together are reduced, without reducing the commercial value due to poor appearance, In addition, there is an effect that a trapping in a hopper during extrusion or injection molding and a poor plasticization in a molding machine do not occur.

It is a side sectional view showing the outline of the pelletizer device by one conventional example. FIG. 2 is a schematic view of a representative example of the arrangement of nozzle openings on a die surface in the pelletizer of the present invention, and a die 6 having nozzle openings 5 in FIG. 1 is illustrated in an axial direction (hereinafter also referred to as “X-axis”). ). FIG. 2 is a schematic view of a typical example of a pelletizer of the present invention in which a cutter head including a cutter shaft, a cutter blade, and the like is covered on a die surface, where a cutter shaft 8 and a cutter blade 9 in FIG. 1 are viewed from an X-axis direction. Hit something. FIG. 4 is an enlarged view of a part (a) of FIG. 3. FIG. 4 is an enlarged view of a part (b) of FIG. 3. FIG. 6 is a diagram illustrating an example of a comparative example of FIG. 5. FIG. 6 is a diagram illustrating an example of a comparative example of FIG. 5. This figure illustrates the outer peripheral length of a triangle formed by arbitrary three nozzle hole center points. It is a schematic diagram which shows that when a cutter blade contacts a plurality of nozzle openings, there is a moment when the length of the opening differs for each nozzle. It is a schematic diagram which shows an example of a fusion pellet. It is a schematic diagram which shows an example of a bead pellet.

  Hereinafter, a pelletizer of the present invention and a method for producing a pellet using the pelletizer will be described with reference to the drawings.

1. Pelletizer FIG. 2 shows a representative example of the arrangement of nozzle openings on the die surface in the pelletizer of the present invention.
FIG. 3 shows a representative example of the pelletizer of the present invention in which a die surface is covered with a cutter head including a cutter shaft and a cutter blade.
4 is an enlarged view of the portion (a) of FIG. 3, and FIG. 5 is an enlarged view of the portion (b) of FIG. 6 and 7 are diagrams illustrating an example of the comparative example of FIG.
The die surface of FIG. 2 is obtained by viewing the die 6 having the nozzle opening 5 of FIG. 1 in the axial direction (hereinafter also referred to as “X axis”). The cutter shaft and the cutter blade of FIG. This corresponds to the cutter shaft 8 and the cutter blade 9 in FIG. 1 viewed from the X-axis direction.

The basic structure of the pelletizer of the present invention is the same as that of a conventionally known pelletizer, and mainly includes a cylinder, an extrusion screw, a die, a cutter head, and a cooling water tank.
Specifically, as an example, as shown in FIG. 1, the cutter head includes a plurality of cutter blades 9 radially arranged so as to be orthogonal to the cutter shaft 8, and a cutter for attaching the cutter blade 9 to the cutter shaft 8. The cutter blade 9 has a cutter support for uniformly distributing and positioning the holder 10 and the cutter blade 9 in the circumferential direction and a key for transmitting the rotational force from the cutter shaft 8 to the cutter holder. The cutter holder 10 and the cutter support are fixed to the cutter shaft 8 by bolts. Thus, the cutter head transmits the rotational driving force of the cutter shaft 8 around the X axis and the pressing force in the X axis direction to the cutter blade 9.
The cooling water tank 11 is connected to a cooling water circulating device for cooling and transporting the pellets. A large number of nozzle openings 5 on the surface of the die 6 are formed on the surface (cutting surface) of the surface of the disk-shaped die 6. Be placed. Inside the die 6, a heat medium passage (not shown) for heating the die is provided, and the die is heated to an appropriate temperature as needed.

In the pellet manufacturing process using a pelletizer as described above, a feed device such as a screw extruder (single screw extruder, twin screw kneader, etc.), a gear pump, etc. The above molten resin is supplied, and is continuously extruded into the cooling water tank 11 from the many nozzle openings 5 in the form of strands. The strands continuously extruded into the cooling water tank 11 are cooled at the outlet of the nozzle opening portion 5 by generally contacting cooling water at 60 ° C. to facilitate cutting, and a plurality of rotating cutter blades are rotated by a cutting surface. The strand that comes into contact with the entire width and is continuously discharged from the nozzle opening portion 5 is cut.
The temperature of the cooling water injected into the cooling water tank 11 is not particularly limited, but may be more than 20 ° C. and 45 ° C. or less from the viewpoint of suppressing generation of fused pellets and suppressing die clogging. preferable.

  At the time of cutting, the cutter head holding the cutter blade 9 adjusts the pressing force in the X-axis direction by the pressurizing drive source, is moved back and forth in the axial direction via the cutter shaft 8, and moves the cutter blade 9 to the cutting surface. It is also possible to press without gaps.

  The presence or absence of a gap between the cutting surface and the cutter blade is appropriately selected depending on the resin to be handled. In the case of a polypropylene resin which is difficult to cut, it is required that the parallelism between the cutting surface and the cutter blade be 3/100 mm or less, and therefore it is preferable to employ a contact cut without a gap.

When cutting the resin by sliding the cutter blade on the cutting surface of the die surface, it is important to minimize the wear and reduce maintenance costs. A hard plate made of titanium carbide (TiC), tungsten carbide (WC), or the like is attached to form a cut surface, or the hard metal is bonded by thermal spray overlay or pressure sintering by HIP. There are known methods for improving the wear resistance of the cut surface, and these can be used.
As for the cutter blade, a hard metal such as titanium carbide or tool steel is used as a material for the cutter blade itself, or a blade obtained by joining a blade made of titanium carbide to a base material made of general steel such as stainless steel, or the like. A method for improving the wear resistance of a cutter blade by forming a high-hardness coating layer on the surface of a base material is known, and these can be used.

In the pelletizer of the present invention, when the cutter blade cuts the molten resin discharged from the die nozzle, the distance (Lz) between the adjacent nozzles of the plurality of nozzles in contact with the blade surface of the same cutter blade is 6 mm or more. It is characterized by being arranged at intervals so that
The state of the nozzle in contact with the cutter blade differs at the moment when the cutter blade makes one rotation, but in the present invention, Lz satisfies 6 mm or more in any state in the history of one round. Is preferred.
The distance (Lz) between the adjacent nozzles is, as shown in FIG. 5, that is, the other nozzle hole on the outer periphery of one nozzle hole in the nozzle hole of the adjacent nozzle which is in contact with the blade surface of the same cutter blade. From the position closest to the nozzle hole to the position closest to the one nozzle hole on the outer periphery of the other nozzle hole.
If Lz is less than 6 mm, fused pellets are remarkably generated, resulting in poor cutting, which is not preferable. Therefore, from the viewpoint of enhancing the effect of suppressing the occurrence of cutting defects mainly using fused pellets, Lz is preferably 8 mm or more, more preferably 10 mm or more, and even more preferably 11 mm or more. is there. If Lz is too large, the number of die holes will decrease. Therefore, from the viewpoint of suppressing a decrease in productivity, Lz is preferably 17 mm or less, more preferably 15 mm or less.
In addition, by setting Lz within the above range, it is possible to suppress the occurrence of defective cutting, and also to reduce the load on the cutter blade when cutting the molten resin and to make the load uniform, leading to blade chipping or breakage of the cutter blade. It is possible to perform stable operation without any problem.

In the pelletizer of the present invention, when cutting molten resin, the maximum value (ΣWn) max of the sum (ΣWn) of the lengths (Wn) of the openings of the nozzles in contact with the cutter blade overlaps the die surface with the die surface. The length (Lx) of the portion satisfies the following relational expression. Here, (ΣWn) max means the maximum value when the cutter blade makes one round of the die surface in the sum of the line segments where the nozzle opening and the cutter blade are in contact.
(ΣWn) max / Lx ≦ 0.2

The opening portions of the nozzle that the cutter blade contacts are indicated by W1 to W3 in FIG. 4 and indicated by W1 to W8 in FIG. The molten resin is extruded from the opening of the nozzle, and the extruded resin is cut by a cutter blade.
The sum (ΣWn) of the length (Wn) of the opening portion of the nozzle contacting the cutter blade is the sum of the lengths obtained by W1 + W2 + W3 in FIG. 4 and W1 + W2 + W3 + W4 + W5 + W6 + W7 + W8 in FIG.
Further, the length (Lx) of the portion where the cutter blade and the die surface overlap is the length of the portion where the cutter blade and the die surface including the opening actually overlap. Indicates the indicated length.

In general, if nozzles are efficiently arranged during die production, the number of nozzles and the length of nozzle opening portions that cross one cutter blade at a certain moment vary depending on the angle. For example, the number of nozzles may be three as shown in FIG. 4 or eight as shown in FIG. 6, and as shown in FIG. Wn) may be different.
In the present invention, Wn and Lx need to satisfy the relational expression of ΣWn / Lx ≦ 0.2 at any position when the cutter blade makes one round of the die surface, that is, It is necessary to satisfy the relational expression of (ΣWn) max / Lx ≦ 0.2. Preferably, the relational expression of (ΣWn) max / Lx ≦ 0.17 is satisfied. More preferably, (ΣWn) max / Lx ≦ 0.14.
More specifically, in the present invention, the sum of the length of the opening portion of the nozzle that crosses at a certain moment with respect to the total length of the blade portion of the cutter blade (Lx in FIG. 4) is as shown in FIG. W1 + W2 + W3), and in FIG. 6, (W1 + W2 + W3 + W4 + W5 + W6 + W7 + W8), the ratio is (好 ま し く Wn) max / Lx ≦ 0.2, preferably (ΣWn) at any position on the die surface when the cutter blade makes one round. ) Max / Lx ≦ 0.17, more preferably (ΣWn) max / Lx ≦ 0.14.
By satisfying ΣWn / Lx ≦ 0.2, it is possible to remarkably suppress the occurrence of defective cutting mainly using fused pellets.
The minimum value of ΔWn is 0, which means that the cutter blade does not cross the opening of the nozzle.
Furthermore, the lower limit of (ΣWn) max is also theoretically 0, but 0 means that the nozzle is not open at all, and the productivity tends to decrease as it approaches 0. Therefore, from the viewpoint of suppressing a decrease in productivity, preferably, 0.09 ≦ (ΣWn) max / Lx.

As shown in FIG. 8, the pelletizer according to the present invention is configured such that, for a triangle configured such that the outer peripheral length is minimized by any three nozzle hole center points disposed on the die, the outer peripheral length (Ly) and the nozzle The hole diameter (d) satisfies the following relational expression.
Ly-3 × d ≧ 20.5
If Ly−3 × d <20.5, the effect of suppressing the generation of fused pellets is low, resulting in poor cutting, which is not preferable. Therefore, from the viewpoint of increasing the effect of suppressing the occurrence of cutting defects mainly using fused pellets, preferably Ly-3 × d ≧ 21.0, and more preferably Ly-3 × d ≧ 21.5. It is.
Further, a large value of Ly−3 × d means that the interval between a plurality of adjacent die nozzle openings is large regardless of whether or not the cutter blade cuts the molten resin. Therefore, if the nozzle interval is too large, the number of die nozzle holes decreases. Therefore, from the viewpoint of suppressing a decrease in productivity, preferably, 32 ≧ Ly−3 × d, and more preferably, 28 ≧ Ly−3 × d.
In the present invention, the term “nozzle hole” refers to a hole (opening portion) of a nozzle that is open.
On the other hand, in the present invention, the nozzle opening portion length Wn refers to a distance between two intersections between the cutter blade and a certain nozzle outer periphery at the moment when the cutter blade makes one rotation.

In a preferred embodiment of the present invention, the outer diameter of the die is preferably 200 mm or more. The larger the outer diameter, the higher the productivity. However, if the apparatus is too large, maintenance becomes difficult. In addition, the warpage of the cutter blade causes the alignment with the die surface to be out of order, which tends to cause poor cutting. Therefore, from the viewpoint of suppressing the occurrence of poor cutting, the outer diameter is preferably 1000 mm or less. It is preferable area of the die is 20000~200000mm ^2.
Further, the diameter of the nozzle is 2.0 mm to 4.0 mm, more preferably 2.2 to 3.0 mm, although it depends on the molten resin and the size of the pellet to be produced. The number of nozzles is preferably 300 or more, and more preferably 5000 or less. The area of the opening is preferably 600 to 20000 mm ² .
The nozzle opening ratio determined by “area of nozzle opening portion / die area” is 2.5 to 12%, preferably 3.0 to 10%. By setting the nozzle opening ratio to 2.5% or more, it is possible to suppress a decrease in the extrusion amount and suppress a decrease in productivity. On the other hand, by setting the nozzle opening ratio to 12% or less, a decrease in controllability of the die temperature can be suppressed.
The nozzle opening may be a tapered hole in order to control the extrusion of the molten resin.
Although depending on the size of the die, the number of cutter blades is 10 to 50.
As the material of the cutter, a martensitic stainless steel such as SUS440C, titanium carbide (TiC) or the like is suitably used.

An example in which the pelletizer of the present invention is realized by filling a nozzle opening portion of an existing pelletizer with a pin will be described with reference to the drawings.
In FIG. 6, for example, for a plurality of nozzles that are in contact with the blade surface of the cutter blade, when the distance Lz between the adjacent nozzles is all 4.6 mm, the relationship “the distance Lz between the adjacent nozzles is 6 mm or more” is satisfied. Absent. Further, when the length Wn of the opening portion of the nozzle in contact with the cutter blade is 2.4 mm, and the length Lx where the cutter blade and the die surface overlap is 72 mm, the number of nozzle openings is eight, so that The sum Wn of Wn is 19.2 mm, ΣWn / Lx is 0.27, and does not satisfy the relationship of ΣWn / Lx ≦ 0.2 ”.
For this reason, in FIG. 6, the arrangement of the nozzle holes (nozzle opening portions) is considered in order to satisfy the requirements of the pelletizer of the present invention, or some of the already existing nozzle holes are adapted to meet the conditions. A closing change may be implemented. Here, it is sufficient to perform a change to close every other nozzle hole, and FIG. 5 shows an example in which the nozzle holes are preferably closed. Which nozzle hole is to be closed can be determined as appropriate, but the closing method as shown in FIG. 7 is not preferable because the distance Lz between adjacent nozzles at some locations becomes smaller than 6 mm.
In FIG. 7, since the number of nozzle openings is five, the sum of Wn ΣWn is 12.0 mm and ΣWn / Lx is 0.17, which satisfies the relationship of ｎWn / Lx ≦ 0.2. Since the relationship of “the distance Lz between adjacent nozzles is 6 mm or more” is not satisfied, the requirements of the pelletizer of the present invention are not satisfied, and it is presumed that the effect of suppressing generation of fused pellets is poor.

2. Pellet production method One aspect of the present invention is a pellet production method, which comprises producing a pellet from a low melting point and soft molten resin using the above pelletizer. According to the pellet manufacturing method of the present invention, as described above, a resin having a low melting point and softness, which has conventionally been considered difficult to cut, specifically, a melting point of 110 to 145 ° C and a flexural modulus of 50 to 350 MPa Pellets can be produced using the following resin.

The resin used in the production method of the present invention is a thermoplastic resin, for example, polyethylene resin, polypropylene resin, polyester resin, polyamide resin, polycarbonate resin, polyurethane resin, polyvinyl acetate, ABS resin, or these. Can be used as a material. In particular, it is possible to stably and efficiently produce low-melting-point and soft pellets, which have conventionally been difficult to stably and efficiently pelletize.
Therefore, in the method for producing pellets of the present invention, it is preferable to use a polyethylene-based resin or a polypropylene-based resin having a melting point of 110 to 145 ° C and a flexural modulus of 50 to 350 MPa at which the effects of the invention are remarkably exhibited.

By using the above resin and the pelletizer of the present invention, pellets of the raw material resin can be manufactured stably and efficiently.
The cut resin (pellet) is generally a granular resin. As for the size of the granular resin, preferably, the diameter is 0.1 mm to 3 mm (among others, 0.5 mm to 2 mm, further 1 mm to 2 mm), and the length (length in the extrusion direction) is 0.5 mm to 3 mm. (Especially 1 mm to 2 mm) and are discharged into the cooling water tank.
Since the pellets thus obtained do not contain fused pellets and have a uniform shape, there is an effect that no trouble occurs in the subsequent injection molding or the like.
The produced pellets are transported and cooled by a cooling water circulating device, and finally separated from the cooling water and dried to be packed into a bag to obtain a product.

  Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited by these examples unless departing from the gist of the present invention. In addition, the measuring method of an apparatus and a fusion | melting pellet is as follows.

1. Pelletizer used A pelletizer with the following device specifications was used.
Outer diameter of die: 445mm
Die inner diameter: 315mm
Full length of cutter L: 128mm
Cutter blade length Lx: 72mm
Die nozzle diameter d: 2.4mm

2. Resin used Random block copolymer produced by a gas phase process using a metallocene catalyst and having a melting peak temperature of 132 ° C. by differential scanning calorimetry and a flexural modulus of 280 MPa according to a bending test (ISO 178). It was used.

3. Fusion pellet generation rate The weight fraction of the fusion pellet in which two or more pellets contained in the pellet collected from the sample valve downstream of the pelletizer were fused.

  Table 1 below shows the arrangement conditions of the die nozzles, the temperature of the pellet cooling water, the rate of occurrence of fused pellets, and the clogging state of the die nozzles in Examples 1 and 2 and Comparative Examples 1 and 2.

(Example 1)
In the above pelletizer, the distance Lz between adjacent nozzles that is in contact with the cutter blade when cutting the molten resin is 6 mm or more, that is, 11.6 mm, and the ratio of the total nozzle opening portion length ΣWn to the cutter blade portion length Lx is 0.20 or less, that is, (ΣWn) max / Lx = 0.13, and for a triangle composed of any three nozzle holes so that the outer peripheral length is minimized, the outer peripheral length Ly and the nozzle hole diameter d are equal to each other. The pellet production was performed so that the relationship of Ly-3 × d ≧ 20.5 was satisfied, that is, Ly-3 × d = 21.9, and the cooling water temperature was set to 25 ° C.
As a result, the incidence of fused pellets was 0.45%, which was further reduced from Example 2 described later. Further, since the fusion pellets can be reduced, the temperature of the pellet cooling water does not need to be lowered as in the case of Example 2 described later, and the effect of increasing the cooling water temperature to 25 ° C. The clogging was also greatly improved, and the generation of small pellets and irregular pellet shapes were reduced.

(Example 2)
In the above pelletizer, pellet production was performed by setting Lz to 10.6 mm, (ΣWn) max / Lx = 0.13, Ly-3 × d = 20.1, and setting the cooling water temperature to 25 ° C. .
As a result, the incidence of fused pellets was reduced to 1.20%. In addition, since the fused pellets can be reduced, the temperature of the pellet cooling water does not need to be lowered further, and the effect of increasing the cooling water temperature to 25 ° C. greatly reduces the clogging of the die nozzle, The generation of small pellets and the irregular shape of the pellets were reduced.

(Comparative Example 1)
In the above pelletizer, using a die before improvement, Lz is set to less than 6 mm, that is, 4.1 mm, (ΣWn) max / Lx = 0.23, Ly-3 × d = 20.1, and the cooling water temperature is set. Pellets were produced at 20 ° C.
As a result, the fusion pellet generation rate is as high as 2.00%, and the pellet cooling water temperature is set as low as 20 ° C. in order to reduce the fusion pellets. Remarkably many small pellets smaller than the size of the regular pellets were generated, and irregularities in the pellet shape were also observed.

(Comparative Example 2)
In the above pelletizer, pellet production was performed by setting Lz to 4.1 mm, (ΣWn) max / Lx = 0.13, Ly-3 × d = 20.1, and setting the cooling water temperature to 20 ° C. .
As a result, the fusion pellet generation rate was still as high as 1.90%, and the pellet cooling water temperature was set as low as 20 ° C. in order to reduce the fusion pellets as in Comparative Example 1. Clogging was remarkable, small pellets smaller than the size of regular product pellets were remarkably increased, and irregular pellet shapes were also observed.

(Evaluation)
Comparing the results of the example and the comparative example, the condition that does not satisfy the present invention, especially the condition shown in the comparative example 2, is that the ratio of the total nozzle opening portion length ΣWn to the cutter blade portion length Lx is 0.20 or less. However, fusion pellets could not be suppressed, and pellets could not be produced stably and efficiently.
On the other hand, in addition to the condition shown in Examples 1 and 2 that “the ratio of the total nozzle opening length 部分 Wn to the cutter blade portion length Lx is 0.20 or less”, “the cutter blade is discharged from the die nozzle When cutting the melted resin, the requirement of “the distance Lz between adjacent nozzles in contact with the cutter blade, 6 mm or more” was satisfied, whereby the amount of fused pellets could be reduced. Further, the condition described in the first embodiment is that, for a triangle formed by arbitrary three nozzle holes such that the outer peripheral length is minimized, the outer peripheral length (Ly) and the nozzle hole diameter (d) are Ly− By satisfying the requirement of 3 × d ≧ 20.5, fused pellets could be significantly reduced.
From the results of the examples, it is estimated that cutting with a polyethylene resin or a polypropylene resin having a melting point of 110 to 145 ° C. and a flexural modulus of 50 to 350 MPa can be performed stably and efficiently without clogging of the dies. Is done.
Therefore, according to the present invention, it was found that pellets can be stably and efficiently produced using the above-described low melting point and soft resin.

Reference Signs List 1 extrusion screw 2 extrusion cylinder 3 breaker plate 4 extrusion head 5 nozzle opening (nozzle hole)
6 Dies 7 Body (Cutter box)
8 cutter shaft 9 cutter blade 10 mounting body (cutter holder)
11 Cooling water tank 12 Outlet

Claims (5)

The cooling water tank polyethylene resin or polypropylene resin is extruded to the cooling water tank nozzle in the die surface, which is attached to the distal end of the ejector tube, the rotary cutter blade disposed proximate to the distal end surface of the die surface In a pelletizer that is cut into pellets at the same time and solidifies with water cooling,
A pelletizer characterized in that a plurality of nozzles in contact with the blade surface of the same cutter blade are arranged at intervals so that the distance (Lz) between adjacent nozzles is 6 mm or more. The maximum value (ΣWn) max of the sum (ΣWn) of the lengths (Wn) of the opening portions of the nozzles contacting the cutter blade, and the length (Lx) of the portion where the cutter blade and the die surface including the opening portion overlap. The pelletizer according to claim 1, wherein the following relational expression is satisfied.
(ΣWn) max / Lx ≦ 0.2 With respect to a triangle configured such that the outer peripheral length is minimized by the arbitrary three nozzle hole center points arranged on the die, the outer peripheral length (Ly) and the nozzle hole diameter (d) are expressed by the following relational expression. The pelletizer according to claim 1, wherein the pelletizer satisfies the following.
Ly-3 × d ≧ 20.5 In the water-cooled and solidified, the temperature of the cooling water to be injected into the cooling water bath exceeds 20 ° C., at 45 ° C. or less, pelletizer according to any one of claims 1 to 3.   A pellet made by using the pelletizer according to any one of claims 1 to 4 to produce a pellet from a polyethylene resin or a polypropylene resin having a melting point of 110 to 145 ° C and a flexural modulus of 50 to 350 MPa. Production method.