JP7166641B2 - Method for making pellets of crosslinked resin - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act. Submit a subsidy application form with a document that describes the "method for producing pellets of crosslinked resin" of the present invention (May 8, 2019)

The present invention relates to a method for making pellets of crosslinked resins.

Synthetic resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS) are generally used as resin materials for forming resin molded articles. Resin molded products made of these resin materials are sometimes collected as appropriate after being discarded and recycled as regenerated pellets. Resin pellets including recycled pellets are used as raw materials for molding resin molded products. This type of resin pellets is obtained by pulverizing collected resin molded products, etc., melt-kneading them with an extruder or the like, extruding them into a long string shape, and cooling them in a water tank or the like in which cooling water or the like is stored. It is obtained by cutting into a predetermined size (see, for example, Patent Document 1).

For example, in the case of resin molded products such as trays and packaging bodies that store fruit and vegetables, the stored fruits and vegetables are easily damaged. It is preferably used as a resin material. In the production of this type of resin molded product, a large amount of offcuts is generated. Therefore, from the viewpoint of reducing the environmental burden, it is required to recycle and effectively use these offcuts.

However, crosslinked resins such as crosslinked polyethylene and crosslinked polypropylene have a molecular structure in which polymer molecular chains are bonded in a three-dimensional network. Things tend to stick together. Therefore, even if the molten resin material (molten resin material) is extruded from an extrusion device or the like, the molten resin material itself becomes brittle and cannot maintain its long string-like shape at the time of extrusion. It quickly collapses into irregular shapes and lengths before cooling. Thus, it has been extremely difficult to pelletize a crosslinked resin by a general pellet manufacturing method.

Moreover, as a method for treating the crosslinked resin, there is a method of mixing a supercritical fluid for causing a chemical reaction with the crosslinked resin and pelletizing it (see, for example, Patent Document 2). In this processing method, a resin crosslinked under high temperature and pressure using a supercritical fluid is mixed with the supercritical fluid to destroy the crosslinked structure, and the resulting treated material is cooled, cut, and pelletized. be. However, in the treatment method using a supercritical fluid, since the treatment conditions are high temperature and high pressure, not only is the work process complicated, but also high energy is required, which is disadvantageous in terms of cost and is preferable in terms of environmental load. do not have.

Thus, the crosslinked resin has poor practicality as a material for recycling. Therefore, waste containing crosslinked resins must be treated as industrial waste at great expense. Therefore, there is a demand for a method for producing pellets that can appropriately recycle waste containing crosslinked resins.

JP 2011-140587 A JP 2007-106827 A

The present invention has been devised in view of the above points, and provides a method for appropriately pelletizing a resin material containing a crosslinked resin in a predetermined length while avoiding an increase in cost without requiring complicated work. is to provide a pellet manufacturing method capable of.

That is, in the invention of claim 1, a resin material containing 60% by weight or more of crosslinked polyethylene or crosslinked polypropylene is melt-kneaded, the obtained molten resin material is extruded from a small-hole type discharge port of an extrusion device, and the The molten resin material extruded by the arranged cutting means is cut into pellets having a length of less than 6 mm immediately after extrusion , and the pellets are blown off by an air blower and introduced into an air cooling device for cooling, The present invention relates to a method for producing pellets of a crosslinked resin, characterized in that the pellets are cooled by air cooling .

In the method for producing pellets of crosslinked resin according to the invention of claim 1, a resin material containing 60% by weight or more of crosslinked polyethylene or crosslinked polypropylene is melt-kneaded, and the obtained molten resin material is discharged from a small hole type extruder. The molten resin material extruded by the cutting means arranged in the discharge part is cut into pellets having a length of less than 6 mm immediately after extrusion , and the pellets are blown off by an air blowing means for cooling. Since the pellets are cooled by air cooling , the resin material can be easily obtained as a recycled material and contributes to the reduction of the environmental load, and the pellets can be quickly transferred to the air cooling device. In addition , it can be introduced appropriately, and it can be cooled and solidified so that it does not contain moisture during cooling, so that complicated work is unnecessary and an increase in cost can be avoided. It becomes possible to appropriately pelletize a resin material containing a resin in a predetermined length.

1 is a schematic diagram of an apparatus for producing pellets containing crosslinked resin; FIG. It is a schematic sectional drawing of an extrusion apparatus. It is a schematic front view and a schematic cross-sectional view showing the structure of the discharge part and the cutting member of the extrusion device.

The present invention is a pellet manufacturing method for molding a resin pellet molded product from a resin material containing a crosslinked resin (hereinafter referred to as a crosslinked resin). The extruded molten resin material is extruded from a small-hole type discharge part of the extrusion device, and the extruded molten resin material is cut into pellets having a length of less than 6 mm before cooling and solidification by a cutting means arranged in the discharge part. It will be.

A crosslinked resin is a resin having a molecular structure (crosslinked structure) in which polymer molecular chains are bonded in a three-dimensional network by subjecting a synthetic resin to a crosslinking treatment. The crosslinked resin contained in the resin material used in the pellet production method of the present invention is, for example, waste crosslinked resin molded products, crosslinked resin waste such as mill ends generated during the production of crosslinked resin molded products. and may contain a crosslinked resin other than the discarded crosslinked resin. Examples of crosslinked resins include crosslinked polyethylene and crosslinked polypropylene. Crosslinked polyethylene and crosslinked polypropylene are materials that are often used for crosslinked resin molded articles and the like, and can be easily obtained as recycled materials.

Moreover, it is preferable that the resin material containing the crosslinked resin contains 50% by weight or more of the crosslinked resin from the viewpoint of reducing the environmental load. In particular, if the resin material is composed of only the crosslinked resin (100% by weight), it can greatly contribute to the reduction of the environmental load. When not using only crosslinked resin, non-crosslinked resin is added. When a non-crosslinked resin is added, the same kind of non-crosslinked resin as the crosslinked resin is selected, for example, non-crosslinked polyethylene for crosslinked polyethylene and non-crosslinked polypropylene for crosslinked polypropylene. By adding the non-crosslinked resin to the crosslinked resin, the resin material can be melt-kneaded more appropriately and the shape retention of the resin material is improved.

Here, a preferred embodiment of a method for producing pellets of a crosslinked resin will be specifically described together with a pellet producing apparatus 10 shown in FIG. The pellet manufacturing apparatus 10 includes a crushing means 20 , an extrusion device 30 , a cutting means 40 , an air blowing means 50 and a cooling means 60 . In the pellet manufacturing method of the embodiment, the pellet manufacturing apparatus 10 is used to perform a pulverization process, a melt-kneading process, an extrusion cutting process, and a cooling process. In FIG. 1, reference numeral 70 is a reservoir for molded pellets.

The pulverization step is a step of pulverizing and agitating the raw material, which is the base of the resin material for forming the pellet compact, and is performed by the pulverizing means 20 . For the pulverizing means 20, for example, a known pulverizing device such as a mixer is preferably used. Examples of raw materials include resin waste such as discarded resin molded products and scraps generated during the production of resin molded products, as well as appropriate materials such as resin pellets used as raw materials for molded products. These raw materials are supplied either as a crosslinked resin material alone or as a crosslinked resin material and a non-crosslinked resin material at a predetermined mixing ratio, depending on the target blending ratio of the crosslinked resin. The pulverized raw material is transported to an extruder 30 described below as a resin material for molding a pellet molded body by a transport means 21 such as a known conveyor.

This pulverizing step is an essential process especially when recycling resin moldings and the like. For recycling, it is necessary to melt the resin moldings and the like once. Therefore, by pulverizing the molded article or the like into an appropriate size, it becomes easier to appropriately melt the resin material. The size of the pulverized product (resin material) such as a molded product is appropriate depending on the performance of the pulverizing means 20, and is, for example, about 2 to 5 mm.

The melt-kneading step is a step of melting and kneading the resin material obtained by crushing in the crushing step to obtain a molten resin material, and is performed by the extrusion device 30 . A known device can be suitably used for the extrusion device 30. For example, as shown in FIG. into the body portion 31, a heating portion 33 such as a heater that heats and melts the resin material in the body portion 31, and the introduced resin material is kneaded and transferred to the tip side. a screw 34 for obtaining a molten resin material, a driving means 35 such as a motor for driving the screw 34, and one or a plurality of small-hole discharge parts 36 for discharging the molten resin material obtained by melting and kneading. and

In the extrusion device 30 of the embodiment, the discharge part 36 is composed of a small-diameter opening having a diameter of about 2 to 6 mm. As shown in FIGS. 2 and 3, it is preferable to form a plurality of discharge portions 36 in terms of production efficiency. In the embodiment, for example, as shown in FIG. 3( a ), the plurality of discharge parts 36 are arranged in a circular shape on the tip surface of the extrusion device 30 .

In the melt-kneading process, first, the resin material pulverized from the conveying means 21 of the pulverizing means 20 is introduced into the input portion 32 and introduced into the main body portion 31 of the extrusion device 30 . The resin material introduced into the body portion 31 of the extrusion device 30 is heated and melted by the heating portion 33 at a sufficiently melting temperature corresponding to its melting point, and is melted by the rotation of the screw 34. The resin material is kneaded to obtain a molten resin material. The melting temperature of the resin material is appropriate according to the type of the resin material, but it is preferable to set the melting temperature, for example, about 30 to 80° C. higher than the melting point of the resin material. If the melting temperature is set too low, there is a possibility that the material cannot be sufficiently melted. Further, the molten resin material is transferred to the tip side of the extrusion device 30 while being kneaded by the rotation of the screw 34 . At this time, if necessary, a degassing means such as a vacuum device may be provided in the main body 31 to remove (degas) the air in the molten resin material. Degassing improves the shape retention of the molten resin material.

As described above, the melt-kneading process is performed in the same manner as the melt-kneading process for general resin materials even for a resin material containing a cross-linked resin. Therefore, a special treatment for recycling the crosslinked resin is not required, and complicated work and an increase in cost can be avoided.

The extrusion cutting step is a step of cutting the molten resin material extruded from the discharge section 36 of the extrusion device 30 before cooling and solidifying to obtain pellets having a length of less than 6 mm. This is done by the arranged cutting means 40 . The cutting means 40 has a cutting blade 41 and a rotating means 42 for rotating the cutting blade 41, as shown in FIG. In the cutting means 40 of the embodiment, as shown in FIG. is extended from the rotating means 42 toward the discharge portion 36 so that is arranged close to the discharge portion 36 .

In the extrusion cutting step, the molten resin material extruded at an appropriate extrusion speed from the discharge section 36 according to the rotation speed of the screw 24 of the extrusion device 30 is cut by the cutting blade 41 of the cutting means 40 rotated at a predetermined rotation speed. It is cut to form pellets less than 6 mm in length. If the length of the pellet is 6 mm or more, problems such as difficulty in maintaining the shape of the pellet arise due to the characteristics of the crosslinked resin. The length of the pellets is set by adjusting the extrusion speed of the molten resin material from the discharge part 36 and the rotation speed of the cutting blade 41 . The extrusion speed of the molten resin and the rotation speed of the cutting blade 41 are determined according to the performance and size of the extrusion device 30 and the cutting means 40. For example, the extrusion speed is 200 to 400 rpm, the rotation speed is is about 150 to 450 rpm.

In particular, since the cutting blade 41 is arranged close to the discharge part 36, the molten resin material is cut immediately after being extruded. That is, the molten resin material is cut at a high temperature (at a temperature equal to or higher than the melting point of the resin material) before cooling and solidification, particularly at the time of extrusion. The temperature of the molten resin material during extrusion is substantially the same as the set temperature during melt-kneading (a temperature about 30 to 80° C. higher than the melting point of the resin material). In a high temperature state before being solidified by cooling, the resin material containing the cross-linked resin is relatively easy to retain its shape, and can be easily formed into pellets having a predetermined length. In other words, in the past, the shape could not be maintained before the molten resin material containing the crosslinked resin was cut into a predetermined length, and pelletization itself was impossible. By cutting the molten resin material before it can no longer hold, it is possible to obtain pellets of a predetermined length. In the case of extruding and cutting the molten resin material from a plurality of discharge parts 36, if the obtained pellets are too long (for example, 6 mm or longer), the pellets tend to stick to each other, resulting in defective products. There is a risk that problems such as

The cooling step is a step of cooling and solidifying the pellets obtained by cutting by the cutting means 40 to obtain pellet compacts, and is performed by the cooling means 60 . A known air-cooling device or the like capable of cooling by air-cooling is preferably used as the cooling means 60 . In addition, the pellets obtained by cutting by the cutting means 40 can be transferred to the cooling means 60 by an appropriate method. 60 is preferred.

The air blowing means 50 is a device for blowing compressed air onto the pellets immediately after being cut by the cutting means 40 and introducing them into a cooling means (air cooling device) 60. A known air blowing device such as an air compressor is used. be done. Since the pellets obtained by cutting by the cutting means 40 are relatively small in shape with a length of less than 6 mm, they can be easily blown away by the compressed air of the air blowing means 50 . Moreover, when the pellets are cut continuously, the pellets may come into contact with each other. At that time, since the pellet-like material immediately after being cut is softened at a high temperature, the contacting pellet-like material may adhere to each other. However, by applying the compressed air of the air blowing means 50 to the contacting pellets, the adhered pellets can be separated from each other and appropriately blown away. By blowing off the cut pellets with the compressed air of the air blowing means 50 in this way, the pellets can be quickly and appropriately introduced into the cooling means (air cooling device) 60 . Reference numeral 51 denotes a transport path for communicating the cutting means 40 and the cooling means 60 and transporting the pellets blown off by the air blowing means 50 to the cooling means 60 .

In the cooling step, the pellets are cooled by air cooling, so unlike the conventional water cooling, the pellets do not come into contact with cooling water or the like during cooling. When the pellet-like material is cooled by water cooling, it may be cooled and solidified while containing moisture. If the cooled and solidified pellets contain moisture, there is a risk that problems such as bursting may occur when the pellets are used as a raw material for resin molded articles or the like. Therefore, by air-cooling the pellet-like material, it is possible to obtain a cooled and solidified pellet compact that does not contain moisture during cooling.

In the cooling step, if necessary, the pellets may be cooled while vibrating the inside of the air cooling device. Vibration in the air cooling device can prevent the pellets from sticking to each other during cooling, and the pellets in the air cooling device can be agitated and efficiently cooled. The cooled and solidified pellets are transferred to and stored in the storage section 70 by an appropriate method such as blowing with a blowing device such as an air compressor, suction with a suction device, or transportation with a conveying device such as a conveyor.

[Mixing ratio of pellet compact]
The resin material was blended based on the blending ratio (% by weight) of Prototype Examples 1 to 10 described later, and the resin material was introduced into the extrusion device. Melt and knead at a set temperature of 190° C., extrude the obtained molten resin material from the discharge part, cut it with a rotating blade of a cutting means arranged close to the discharge part, and blow off the obtained pellet-like material with an air blower. After the mixture was transferred to an air-cooling device, it was cooled and solidified by air-cooling at a set temperature of about 7°C to produce a pellet compact. The extruder had 16 outlets with a diameter of 5 mm arranged in a circle, and the extruding speed of the molten resin material was set at 300 rpm. Moreover, the rotating speed of the rotary blade of the cutting means was 400 rpm.

[Prototype example 1]
The mixing ratio of the resin material in Prototype Example 1 was 60% by weight of crosslinked polyethylene (PE) and 40% by weight of non-crosslinked polyethylene.

[Prototype example 2]
The mixing ratio of the resin material in Prototype Example 2 was 70% by weight of crosslinked polyethylene (PE) and 30% by weight of non-crosslinked polyethylene.

[Prototype Example 3]
The mixing ratio of the resin material in Prototype Example 3 was 80% by weight of crosslinked polyethylene (PE) and 20% by weight of non-crosslinked polyethylene.

[Prototype example 4]
The mixing ratio of the resin material in Prototype Example 4 was 90% by weight of crosslinked polyethylene (PE) and 10% by weight of non-crosslinked polyethylene.

[Prototype Example 5]
The mixing ratio of the resin material in Prototype Example 5 was crosslinked polyethylene (PE) alone (100% by weight).

[Prototype Example 6]
The mixing ratio of the resin material in Prototype Example 6 was 60% by weight of crosslinked polypropylene (PP) and 40% by weight of non-crosslinked polypropylene.

[Prototype Example 7]
The mixing ratio of the resin material in Prototype Example 7 was 70% by weight of crosslinked polypropylene (PP) and 30% by weight of non-crosslinked polypropylene.

[Prototype Example 8]
The mixing ratio of the resin material in Prototype Example 8 was 80% by weight of crosslinked polypropylene (PP) and 20% by weight of non-crosslinked polypropylene.

[Prototype Example 9]
The mixing ratio of the resin material in Prototype Example 9 was 90% by weight of crosslinked polypropylene (PP) and 10% by weight of non-crosslinked polypropylene.

[Prototype Example 10]
The mixing ratio of the resin material in Prototype Example 10 was crosslinked polypropylene (PP) alone (100% by weight).

[evaluation]
Regarding Prototype Examples 1 to 10, during the production of the pellet molded product in the type and blending ratio (% by weight) of the crosslinked resin, adhesion of the pellets after cutting, transfer (blowing) of the pellets by air blowing means, pellets The shape retention of the molded body was evaluated. Regarding the adhesion of pellets after cutting, if the pellets are separated during transportation by blowing means, "○", if some of the pellets are adhered, "△", often When the pellets of 1 were adhered to each other, it was marked as "x". When transferring (blowing off) pellets by blowing means, "○" indicates that the pellets can be properly transferred, and "△" indicates that some adhered pellets cannot be transferred. When many pellets could not be transferred (not blown away), it was marked as "X". Regarding the shape retention of pellets, "○" indicates that pellets of an appropriate size were formed, "△" indicates that some of them became larger or lost their shape due to adhesion, and most of them became larger due to adhesion. When the shape was deformed or the shape was lost, it was indicated as “x”. Then, as a comprehensive evaluation, for each item of adhesion, transfer, and shape retention, if all items are "○", "○", even one is "△" and there is no "×", "△", 1 However, if there was "x", it was evaluated as "x". Table 1 shows the results.

As can be seen from Table 1, good results were obtained in all of Prototype Examples 1 to 10. In particular, the results were also good in Prototype Examples 5 and 10, which consisted of the crosslinked resin alone (100% by weight). It is well known that the more non-crosslinked resin is added to the crosslinked resin, the more the stability of the resin material and the molded article is improved. Therefore, it was found that the mixing ratio of the crosslinked resin is preferably 50% or more in consideration of the reduction of the environmental load.

[Length of pellet compact]
Based on the procedure of the pellet manufacturing method, using a resin material blended with 60% by weight of crosslinked polyethylene and 40% by weight of non-crosslinked polyethylene, as in Prototype Examples 11 to 17 described later, the rotation speed of the rotary blade of the cutting means By changing the length of the pellets to be cut, a pellet compact was obtained.

[Prototype Example 11]
Prototype Example 11 is a pellet compact formed to a length of about 1 mm with a cutting blade rotating speed of 400 rpm.

[Prototype Example 12]
Prototype Example 12 is a pellet compact formed to have a length of about 2 mm with a cutting blade rotating speed of 350 rpm.

[Prototype Example 13]
Prototype Example 13 is a pellet compact formed to a length of about 3 mm with a cutting blade rotating speed of 300 rpm.

[Prototype Example 14]
Prototype Example 14 is a pellet compact formed to a length of about 4 mm with a cutting blade rotating speed of 250 rpm.

[Prototype Example 15]
Prototype Example 15 is a pellet compact formed to have a length of about 5 mm with a cutting blade rotating speed of 200 rpm.

[Prototype Example 16]
Prototype Example 16 is a pellet compact formed to a length of about 6 mm with a cutting blade rotating speed of 150 rpm.

[Prototype Example 17]
Prototype Example 17 is a pellet compact formed to a length of about 7 mm with a cutting blade rotating speed of 100 rpm.

[evaluation]
Regarding Prototype Examples 11 to 17, adhesion between pellets after cutting, transfer (blow-off) of pellets by air blowing means, and shape retention of pellets during production of pellets were evaluated. Regarding the adhesion of pellets after cutting, if the pellets are separated during transportation by blowing means, "○", if some of the pellets are adhered, "△", often When the pellets of 1 were adhered to each other, it was marked as "x". When transferring (blowing off) pellets by blowing means, "○" indicates that the pellets can be properly transferred, and "△" indicates that some adhered pellets cannot be transferred. When many pellets could not be transferred (not blown away), it was marked as "X". Regarding the shape retention of pellets, "○" indicates that pellets of an appropriate size were formed, "△" indicates that some of them became larger or lost their shape due to adhesion, and most of them became larger due to adhesion. When the shape was deformed or the shape was lost, it was indicated as “x”. Then, as a comprehensive evaluation, for each item of adhesion, transfer, and shape retention, if all items are "○", "○", even one is "△" and there is no "×", "△", 1 However, if there was "x", it was evaluated as "x". Table 2 shows the results.

As can be seen from Table 2, all of Prototype Examples 11 to 15 (pellet length of about 1 to 5 mm) gave good results. In addition, in Prototype Example 16, in which the length of the pellet molded body was about 6 mm, adhesion between the pellets was partially observed, and the adhered state was maintained without separation, resulting in a small amount of defective products. . On the other hand, in Prototype Example 17, in which the length of the pellet compact was about 7 mm, adhesion between pellets and deformation of the cut pellets were often observed, and a large number of defective products were produced.

From the results shown in Table 2, it was found that it is extremely difficult to obtain pellets of the desired length when the length of cutting the molten resin material is 7 mm or more. Also, when the cutting length was about 6 mm, a small number of defective products were produced, but many good products were obtained. Considering the balance between molding accuracy and cost, it is considered preferable that the length of the pellet-like material to be cut is less than 6 mm.

As illustrated and explained above, the method for producing crosslinked resin pellets of the present invention includes extruding a molten resin material containing a crosslinked resin from a small-hole discharge port of an extruder, and cutting the molten resin by cutting means disposed in the discharge port. Since the material is cut into pellets having a length of less than 6 mm before being solidified by cooling, the molten resin material can be cut to obtain pellets of a predetermined length before it loses its shape. Therefore, it becomes possible to appropriately pelletize a resin material containing a crosslinked resin, which has been extremely difficult to pelletize, in a predetermined length. In addition, complicated work is not required when melting and kneading a resin material containing a crosslinked resin, and an increase in cost can be avoided, and a pellet compact can be produced with workability and cost comparable to those of general pellet production methods. .

As described above, in the method for producing pellets of a crosslinked resin of the present invention, a resin material containing a crosslinked resin is properly produced by cutting a molten resin material containing a crosslinked resin into pellets having a length of less than 6 mm before cooling and solidifying. Can be pelletized. Therefore, it becomes possible to use waste containing crosslinked resin, which was conventionally treated as industrial waste without being able to be pelletized, as a recycled material, and is expected to contribute to reducing the burden on the environment.

REFERENCE SIGNS LIST 10 pellet manufacturing device 20 pulverizing means 21 conveying means 30 extruding device 31 body portion 32 charging portion 33 heating portion 34 screw 35 driving means 36 discharge portion 40 cutting means 41 cutting blade 42 turning means 50 blowing means 51 transfer path 60 cooling means 70 reservoir

Claims (1)

Contains 60% by weight or more of crosslinked polyethylene or crosslinked polypropylene A resin material is melt-kneaded, the obtained molten resin material is extruded from a small-hole type discharge port of an extrusion device, and the extruded molten resin material is cut by a cutting means arranged in the discharge port.Immediately after extrusionCut into pellets less than 6 mm in length, the pellets are blown off by an air blowing means and introduced into an air cooling device for cooling, and the pellets are cooled by air cooling.
A method for manufacturing crosslinked resin pellets, characterized in that:

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