JPH0684011B2 - Plastic pellet manufacturing method and granulating equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing plastic pellets and a granulating apparatus.

[Background technology]

It is well known that mainly thermoplastic plastics such as film flakes and fibers made of polypropylene, polyester, nylon, polyethylene, etc. are once granulated for recycling. ing. As the granulation method, there are cases in which various types such as a screw type or a roll type are used, but basically, by using a die having a die hole, a plastic material material finely divided into this die is pressed. ,
This pressing forces the material out of the die hole,
After that, the extruded product is sequentially cut and granulated. During the process from pressing to extruding (processing system), mainly at the time when the material pieces pass through the die hole, the material pieces are rubbed against the pressing means (for example, a roll) by being pressed against the die, or the material pieces are rubbed against each other. It fits. The frictional heat generated at this time causes the material piece to have a considerably high temperature, so that a plastic material piece having a low melting point (low softening point) often melts. When the material piece melts during pressing in this way, the pressing means cannot capture the material, so it cannot be extruded through the die hole, making granulation impossible and also increasing the heat of the material piece. As a result, it was affected by excessive heat, resulting in deterioration of physical properties.

Therefore, in the past, the die or pressing means were water-cooled jacket type or air-cooled type to cool the material pieces and prevent melting.However, if the water cooling jacket type is used, the device is complicated. Therefore, the cost was increased, and the cooling effect of the air-cooled type was extremely low and was not suitable for adoption. There is also a method to suppress the melting of the material pieces by supplying to the granulating apparatus a material piece that has been moistened in advance before pressing to the material piece, but in this method, the added water is difficult to evaporate sufficiently. However, since water remains in the pellets, bubbles are generated due to the dissolution of the water when it is reused, which is one of the causes of defective plastic products.

[Object of the Invention]

In view of the above problems, the present invention is capable of always granulating even a plastic material piece having a low melting point, no deterioration in physical properties is observed after granulation, and moreover, residual moisture in the pellets remains. It is an object of the present invention to provide a method for producing a plastic pellet and an apparatus for the same, in which no defective plastic product is generated.

[Disclosure of Invention]

In order to achieve the above-mentioned object, a method for producing a plastic pellet according to the first invention is such that a fine plastic material piece is supplied to a granulator and pressed against an inner surface of a die having a die hole to pass through the die hole to outside the die. In the method of producing a plastic pellet in which pellets are obtained by extruding into, and then granulating by cutting it, the temperature of the atmosphere is adjusted at an appropriate stage from the time of extrusion with the die to immediately after the granulation. Detecting, based on this ambient temperature, spraying a fine cooling liquid to the plastics material piece before extruding from the die hole to evaporate, and melt the plastics material piece at a temperature rise during granulation It is characterized by being cooled to a temperature at which there is no A granulating apparatus according to a second invention is a die having a die hole, a material supply system for supplying a fine plastic material piece to the die, and a fine plastic material piece supplied to the die. In a device for manufacturing plastic pellets, which comprises a pressing means for pressing against the inner surface, and a cutter for cutting and granulating an extruded product of a plastics material piece that is provided outside the die and is extruded from a die hole, in the die, The temperature sensor that detects the temperature between the pressing of the plastics material piece and the time immediately after granulation at a specific point, and the temperature sensor is linked with this temperature sensor. When the temperature that is judged to melt by raising the temperature is detected, the finely divided cold pieces of plastics material before pressing with the die are Liquid is sprayed transpired,
It is characterized in that it comprises a cooling liquid spraying means for cooling the plastics material piece to a temperature at which it does not melt due to a temperature rise during granulation, and a pellet collecting container for receiving granulated pellets. .

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof.

FIG. 1 and FIG. 2 show a roll type cylindrical die vertical type (or horizontal type) as an example of the granulating apparatus according to the present invention. In these drawings, the die 1 has a cylindrical shape, and the die 1 is provided with a large number of die holes 2 in a radial pattern. The die hole 2 does not need to be provided over the entire circumference of the cylindrical die. The die 1 rotates so that a pair of rollers (extruding means) 3 provided in contact with the inner circumference of the die 1 rotate in the same direction. This roller 3 is always in a fixed position. A cutter 4 is provided on the outer periphery of the die 1 so as to be in a fixed position. The plastic material piece (polymer material piece) 5 is placed in the material piece supply space 6 formed by the die 1 and the roller 3 in a screw type material supply system A.
This material supply system A, which is adapted to be continuously supplied through, has a vertically oriented supply chute 31 and a horizontal screw housing 32 as a case body. The supply sheet 31 is supplied with a miniaturized piece of plastics material 5. A screw conveyor 33 is provided in the screw housing 32 so as to transfer the plastics material piece 5 to the right, and the conveyor 33 is rotated by an external motor 34. . At the end of the screw housing 32 in the material transfer direction, a cover 35 having a U-shaped cross section is provided so as to cover the die 1. A pellet drop chute 36 is formed in the lower portion of the cover 35 so as to correspond to the die hole 2. cover
A conical material supply guide 37 that expands in the direction of the die 1 is provided between the base of the die 35 and the die 1.
The piece of plastic material 5 is sandwiched between the die 1 and the roller 3 as they rotate. As a result, the plastic material piece 5 is pushed out of the die 1 through the die hole 2 and then cut by the cutter 4 to be granulated and molded into pellets 7. This granulator has
A pellet temporary collection container 8 for receiving the molded pellets 7 is installed, and the pellet temporary collection container 8 is provided.
Is a small container having an opening / closing plate 8a on its bottom surface. A temperature sensor 9 is attached to one side of the pellet temporary collection container 8 and a sensing piece 9a thereof faces the container 8. The temperature sensor 9 is connected to a control unit 10, and a valve opening / closing mechanism 11 is connected to the control unit 10 so as to work together. The valve opening / closing mechanism 11 is adapted to open / close the flow control valve 12.
The flow control valve 12 is provided on the water supply pipe 13, and the water supply pipe 13 is divided into two routes.
Each path is connected to a cooling liquid spraying means 14 attached to the screw housing 32. A compressed gas source (not shown) is connected to one end of an air supply pipe 15 which is another pipe, and the other end thereof is divided into two paths and connected to the cooling liquid spraying means 14. Coolant spraying means
For example, 14 is provided with a nozzle and a resonance box attached slightly away from this tip. As shown in FIG. 2, each of the cooling liquid spraying means 14 sprays while dispersing a finely divided cooling liquid (for example, an ultrafinely atomized one) in the screw housing 32,
These are designed to be sprayed into the screw housing 32.

The granulated pellets 7 are put into a pellet temporary collection container 8. At that time, the temperature held by the pellet 7 is increased due to the friction, and the temperature is detected by the temperature sensor 9 when the pellet 7 contacts the sensing piece 9a. The detected signal is sent to the temperature control unit 10, and when it is confirmed by the temperature control unit 10 that the temperature is a certain temperature or higher, that is, the temperature at which the low-melting point material melts, the valve opening / closing mechanism 11 An opening command is sent to open the flow control valve 12. The opening of the flow rate control valve 12 is controlled to be large or small depending on the temperature of the pellet 7.
That is, when the temperature of the pellet 7 is high, the opening is large,
When the temperature of the pellet 7 is low, the opening is controlled so as to be small, so that the material piece 5 having a low softening point always has a temperature slightly lower than the softening point.
Compressed gas is constantly flowing from the air supply pipe 15 (or may be controlled by opening / closing by the temperature control unit 10), whereby the compressed gas is transferred from the nozzle tip to a resonance box provided at the tip. Are violently ejected to generate a strong sonic energy field between the nozzle and the resonance box. When the cooling liquid (water) is supplied from the water supply pipe 13 to such a strong sonic energy field (the cooling liquid may be supplied from the nozzle or from another), the cooling liquid (water) is All are atomized into ultrafine particles of 5 to 20 microns. The ultrafine particles have a uniform particle size, a small mass, and a low speed, and not only extend to the material transferred into the die 1 by the screw conveyor 33, but also extend to the plastics material piece 5. As a result, the plastic material piece 5 is effectively subjected to precooling. Since the finely atomized cooling liquid (water droplets) is sprayed on the plastics material piece 5,
The cooling liquid is not effectively evaporated by the generated heat and remains in the plastic material piece 5. From the standpoint of the residual cooling liquid, it is preferable that the means for spraying the cooling liquid is adapted to make the cooling liquid finer to a smaller level.

As described above, according to the present invention, the temperature rise due to granulation is detected and the temperature rise is suppressed so that the plastic material piece 5 is extruded. However, it does not lead to melting, so that even a material piece having a low melting point can always be reliably granulated. Moreover, since the low-melting-point material is not excessively affected by heat, it is possible to obtain good quality pellets 7 without lowering the physical properties, and to mix with the pellets 7 when molding a plastic product. The quality is as good as the new pellets used. As a result, good quality plastic products can be obtained. As described above, the finely atomized cooling liquid (water) is sprayed on the plastic material pieces in advance, so that the evaporation is very active and the moisture remains in the pellets 7 after granulation. Nothing.
As a result, no bubbles are generated when the plastic product is molded, so that it is possible to always obtain a good-quality plastic product without bubbles.

The temperature sensor 9 may be installed at any position near the die hole 2 of the die 1, the roller 3, and the roller connecting plate 22, as indicated by the double circle mark in FIG. In the above embodiments, the roll type cylindrical die vertical (or horizontal) type is used, but generally well-known screw type, blade type, self-forming type (using a gear or cylinder as a pressing means). The present invention can also be applied to the granulating machine. A screw type granulator uses what is called a screen as an alternative to a die, and this screen is also called a die in the present invention. The rotation speed of the die and the shape of the die hole are selected so as to be optimum for the target material piece.

The temperature control unit 10 is described as controlling a low melting point material, but for melting point materials higher than that, rather than always cooling, when reaching an excessive temperature, that is, It is assumed that the control unit applies cooling only when the temperature reaches a temperature at which melting must be suppressed.

In order to select the die rotation speed and the die hole shape so as to be optimum for the material piece, for example, the following is performed. Assuming that the material feed rate, die hole shape, and material pieces are constant, the higher the die rotation speed, the greater the friction and the greater the amount of heat generation. The die rotation speed should be controlled to be smaller and smaller as it is made of a high melting point material. Assuming that the material feed rate, the die rotation speed, and the piece of material are constant, the more friction the die hole shape is, the more frictional heat is generated. Select materials that are as loose as possible and materials that are tight as the material becomes a high melting point. Also, the larger the piece of material, the more difficult it is to pass through the die hole,
The lower the melting point material, the larger the die hole, and the higher the melting point material, the smaller the die hole. As a result, not only pellets having a low air content and a small volume and high bulk density can be obtained, but also pellets that are not easily broken even by pneumatic transportation can be obtained.

Moreover, if the scraps of those products generated during the production of films, fibers, and threads of polymer materials are used as fine plastics material pieces, they will not have excessive heat history and will have the same physical properties as the new material. It is possible to obtain pellets having The fine plastics material pieces are not limited to the above-mentioned ones, and waste materials of polymer materials and other materials can also be used.

The cooling liquid may be liquid nitrogen or liquid carbon dioxide gas. The cooling liquid that evaporates is discharged to the outside of the processing system by suction so as to be released into the atmosphere. In addition, the gas to be discharged such as the evaporated (evaporated) cooling liquid is used to prevent pollution.
If it is necessary to treat it, it must be treated, but if it is not necessary, it can be released into the atmosphere as it is. As shown in FIG. 3, the cooling liquid spraying means 14 may be installed so as to look into the die 1. In this case, the axial position of the driven rollers 3, 3 is always a fixed position and does not move. For this reason, it is not necessary to rotate the portion of the cooling liquid spraying means 14 desired in the die 1. The cooling liquid spraying means is not limited to ultrasonic waves.

〔The invention's effect〕

As described above, according to the present invention, even in the case of a plastic material piece having a low melting point, granulation is always performed reliably, physical properties are not deteriorated after granulation, and the moisture content in the pellets is not increased. It is now possible to obtain excellent plastic products with no residue.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing an example of a plastic pelletizing apparatus according to the present invention, FIG. 2 is a central sectional view thereof, and FIG. 3 is a sectional view showing another embodiment. 1 ... Die, 2 ... Die hole, 4 ... Cutter, 5 ...
… Plastic material pieces, 7 …… Pellet, 8 …… Pellet temporary collection container, 9 …… Temperature sensor, 14 …… Cooling liquid spraying means

Claims (5)

[Claims] 1. A fine plastic material piece is fed to a granulator and pressed against the inner surface of a die having a die hole to be extruded to the outside of the die through the die hole, and then cut and granulated. In the method for producing plastic pellets to obtain pellets, the temperature of the atmosphere is detected at an appropriate stage from the pressing of the plastic material piece in the die to immediately after granulation, and based on the ambient temperature, , Characterized by spraying a fine cooling liquid on the plastic material piece before pressing with a die to evaporate it, and cooling the plastic material piece to a temperature at which it does not melt due to the temperature rise during granulation The method of manufacturing plastic pellets. 2. The method for producing a plastic pellet according to claim 1, wherein the ambient temperature is a temperature held by the pellet immediately after being granulated. 3. A plastic material piece is extruded from a die hole by a relative rotational movement of a cylindrical die and a roller inscribed therein, and a cooling liquid is preliminarily supplied in a material supply system provided at a stage prior to the die. The method for producing a plastic pellet according to claim 1 or 2, wherein the plastic pellet is sprayed. 4. A die having a die hole, a material supply system for supplying a minute plastic material piece to the die, and a pressing means for pressing the minute plastic material piece supplied to the die against the inner surface of the die. , A plastic pellet manufacturing apparatus comprising a cutter for cutting and granulating an extruded product of a plastics material piece extruded from a die hole and provided outside the die, in a plastics material piece in the die, A temperature sensor that detects the temperature between pressing and immediately after granulation at a specific point, and in conjunction with this temperature sensor, the temperature sensor determines that the plastic material piece melts due to the temperature rise during granulation. When the temperature being detected is detected, a fine cooling liquid is sprayed onto the plastic material piece before being pressed by the die to evaporate. Then, a plastics material piece,
A granulating apparatus comprising: a cooling liquid spraying means for cooling to a temperature at which the temperature does not melt due to a temperature rise during granulation; and a pellet collecting container for receiving granulated pellets. 5. The granulating apparatus according to claim 4, wherein the temperature sensor is installed in the pellet collecting container.