JP7178671B2 - Manufacturing method for recycled plastic pellets - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing recycled plastic pellets, which makes it possible to reuse defective molded materials, offcuts, crushed products, and the like produced by manufacturers of molded plastic products.

Plastics that are discarded in daily life, as well as plastic products that are discarded without being used as products, such as defective molded products at production sites, runners and spools (hereinafter referred to as "waste plastics"), In recent years, recycling has been promoted from the viewpoint of effective utilization of waste resources and reduction of plastic waste. One of the major recycling methods for waste plastics is material recycling, in which waste plastics are reused as plastic materials. Such material recycling is a highly sustainable recycling method because it directly contributes to resource recycling.

In the current material recycling of waste plastics, in many cases, a process of heating and melting the waste plastics is performed. For example, Patent Document 1 discloses a melt molding step of melt molding a recycled polyolefin-based thermoplastic resin composition to form a molten resin composition, and rapidly cooling the molten resin composition melted in the melt molding step with ice water or the like. A method for regenerating a thermoplastic resin composition has been proposed, which includes a quenching step.

Further, Patent Document 2 proposes a method of recycling waste plastics containing a plastic-based mixture composed of a plurality of types of plastics. That is, it includes at least a sorting step of sorting out the desired plastic from waste plastics by specific gravity separation, and a molding step of heating and melting the plastic sorted out in this sorting step and molding it to obtain a plastic molded product. , The type and amount of additives added to the sorted plastics are changed according to the removal step for removing metals mixed in the sorted plastics and the mesh size of the filter for removing metals. A method for recycling waste plastics has been proposed, which includes a step of adding In this example, too, a method is proposed that includes a melt molding step.

There is also a method of pulverizing plastic at room temperature without heating and melting it for reuse. It is difficult to adopt in practice because there are cases where it is difficult.

Japanese Patent No. 6333674 JP 2010-234812 A

However, the methods of producing recycled plastic pellets by heating and melting disclosed in Patent Documents 1 and 2 above have the following problems. That is, thermal decomposition during heat melting of the plastic tends to cause a decrease in strength and discoloration. In addition, there is a problem that corrosive gas or decomposed gas may be generated depending on the type of plastic, which may promote corrosion of the molding apparatus. Furthermore, plastic molded products often contain additives such as plasticizers and flame retardants, and there is concern that the additives may cause discoloration or gas generation due to thermal decomposition due to heat melting. SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, and to provide a method for producing plastic pellets without heat melting, which causes various problems.

In means 1 for achieving the above object, waste plastics such as polyolefins are treated with cryogens such as liquid nitrogen, mixtures of dry ice and ethanol (dry ice/ethanol), mixtures of dry ice and acetone (dry ice/acetone). or a mixture of dry ice and ethyl ether (dry ice/ethyl ether) for 1-30 minutes . After cooling in this way, while cooling the waste plastic, it is pulverized using, for example, a metal ball , so that a sieve with an opening of 4 mm and a wire length of 1.4 mm specified in JIS Z 8801 is used. It is granulated to a size that does not pass through a sieve with an opening of 250 µm and a wire length of 160 µm . Since it is difficult to solidify the granules of this granulated waste plastic even when tableting pressure is applied, cellulose, rayon, acetate, chitin, chitosan, silk, wool, stearic acid, palmitin After adding one or more selected from the group of acids and aluminum hydroxide and a binder in the range of the same size condition as the granules in the range of 0.5 wt% to 20 wt% , substantially uniformly mixing , For example, it is tableted into an arbitrary shape , such as granules, with a tableting machine or the like under a pressure range of 5 MPa to 60 MPa . Through such a process, waste plastic pellets can be produced. Means 1 is a method having the steps as described above, and the material of the waste plastic can be selected according to the application.

In means 1 of the generic concept described above, the coagulable binder is, for example, one selected from the group consisting of cellulose, rayon, acetate, chitin, chitosan, stearic acid, palmitic acid, silk, wool, and aluminum hydroxide. It has been explained that those containing the above are used. Furthermore, the binder is more preferably cellulose, rayon, acetate, chitin, chitosan, stearic acid, and palmitic acid. This is because the plastics mentioned in means 1 cannot be coagulated by tableting pressure even if they are granulated, but they can be coagulated by adding the binder described above. In addition, although the proportion of waste plastic in the recycled plastic pellets decreases as much as the binder is added, by setting the proportion of the binder in the recycled plastic pellets to 20 wt% or less, it becomes a quasi-rich product of plastic, that is, the main component. It can be put to practical use as a recycled plastic containing 60 wt % or more of plastic as a material, and can contribute to industrial use.

This is a method for producing plastic pellets for recycling , wherein the tableting pressure in the above means 1 is 5 MPa or more and 60 MPa or less. This is because if the pressure is less than 5 MPa, the strength is low even if pelletized by tableting, and the shape may easily collapse during heat treatment. This is because there is no change in strength even when tableting is performed at a pressure exceeding 60 MPa, and the industrial significance is diminished. Furthermore, the tableting pressure is more preferably 25 MPa or more and 50 MPa or less, and further preferably 35 MPa or more and 45 MPa or less. Within such a tableting pressure range, it is possible to provide a method for producing recycled plastic pellets, which can be used as a practical raw material, from waste plastics.

In the above means 1, there is provided a method for producing recycled plastic pellets, wherein the weight ratio of the binder in the recycled plastic pellets is 0.5 wt % to 20 wt %. Here, if the proportion of the binder added is less than 0.5 wt %, there is a high possibility that the shape cannot be maintained even if the product is tableted and pelletized. Also, if the proportion of the binder added exceeds 20 wt %, the amount of the binder in the recycled plastic pellets is large, and there is a high possibility that the applications of the recycled plastic will be limited. The proportion of the binder to be added is preferably 2 wt % or more and 10 wt % or less, and most preferably 4 wt % or more and 8 wt % or less. Even with the above weight ratio, even if it is difficult to make pellets by tableting, by adding a binder and mixing, it is possible to pelletize with an appropriate tableting pressure of a tableting machine. become possible.

According to the above-described method for producing recycled plastic pellets of the present invention, by eliminating the heating step, thermal decomposition of the resin and additives is prevented, the strength of the plastic is reduced, discoloration, and corrosive gas or decomposition gas is generated. can be eliminated. This also enables simplification of manufacturing facilities.
(Other means to solve the problem)

The method as the means 2 of the lower concept in the means 1 of the above-mentioned generic concept is that the waste plastic is polypropylene (PP), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polycarbonate (PC), poly A method for producing recycled plastic pellets containing, as a main component, one or more selected from a group of thermoplastic resins such as oxymethylene (POM). The above-mentioned waste plastic has been converted into recycled plastic pellets by heating and melting until now. It is inevitable that adverse effects such as the occurrence of According to the method shown in means 1, the waste plastic shown in means 2 can be pelletized without being heated and melted. That is, after cooling with a cryogenic agent such as liquid nitrogen, pulverization is performed while cooling to form powder, a binder is added, and the mixture is tableted to form pellets. In addition, although the above-described waste plastic is a material that is difficult to pelletize by tableting, the addition of a binder makes it possible to produce recycled plastic pellets. In addition, the above-mentioned main component means containing 75 wt% or more, and means that if the main component is rich, there is no problem as a raw material. However, there are cases where 90 wt % or more is required, and it can be changed depending on the application. In this way, recycling of waste plastics can be realized.

In the method as the means 3 of the lower concept in the means 1 of the above-mentioned generic concept, the waste plastic is one or more kinds selected from the thermosetting resin group such as phenol resin (PF), epoxy resin (EP), urethane resin, etc. A method for producing recycled plastic pellets containing waste plastic as a main component. In the group of thermosetting plastics shown here, the same method for producing recycled plastic pellets as in the group of thermoplastics is possible. The meaning of the main component is the same as in the thermoplastic resin. In the case of thermosetting resins in particular, it takes time and effort to recycle them, so it is becoming important today when the Sustainable Development Goals (SDGs) are being called out.

Conceptual diagram explaining the process of the present invention FIG. 1 is a conceptual diagram of a partial cross-section of a freezing compartment used in freeze-grinding of the present invention. FIG. 1 is a conceptual diagram of a partial cross section of a tableting machine used in the present invention.

Embodiments of the present invention will be described below. The embodiments described below describe examples of preferred embodiments of the invention, and do not limit the constituent elements of the invention described in the claims.

(Outline of waste plastic pellet manufacturing)
As shown in FIG. 1, the method for producing recycled plastic pellets in the present invention employs, for example, a method of cooling bulk waste plastic using liquid nitrogen as a cryogen, and then pulverizing it while cooling. there is In any case, there is a step of first cooling the bulk plastic with cryogen. Subsequently, there is a step of pulverizing the cooled mass of waste plastic with metal balls into powder. These two steps can be accomplished using a freeze crusher. The freeze grinder is described in detail in Figure 2 below. Appropriate binder is added to the plastic granules thus obtained so that they can be pelletized by compression by tableting, and a mixture of waste plastic granules and binder, that is, waste plastic granules containing a binder is prepared. It is carried out by a combination of a step of adding a binder to be prepared and a tableting step of tableting the binder-containing waste plastic granules.

(Types of plastics targeted by the present invention)
The object of the present invention is plastic, which is relatively difficult to recycle. That is, the main component is waste plastic that does not solidify only by using mechanical tableting pressure. For example, both thermoplastics and thermosets can be selected. It is also possible to target a plurality of different types of plastic mixtures for the same thermoplastic, or to target different types of plastic mixtures for the same thermosetting plastic.

However, mixtures of thermoplastics and thermosets are not covered by the present invention. This is because thermoplastics and thermosetting plastics have completely different molding methods for recycled use. Even a mixture of thermoplastic and thermosetting plastics can be pelletized by adding a binder and compressing. However, such recycled plastic pellets cannot be formed into arbitrary final products by various molding methods such as injection molding, extrusion molding, blow molding, and rotational molding. It should be noted that, depending on the object of the molding, there are cases where the mixed use of thermoplastics or thermosetting plastics is not permitted. In such a case, the present invention can be applied after sufficiently sorting out the waste plastics and narrowing down to one kind of waste plastics.

First, thermosetting waste plastic targets the following materials. For example, one or more selected from polypropylene, polyethylene, polystyrene, polyvinyl chloride, polycarbonate, and polyoxymethylene can be preferably used. Next, for thermosetting waste plastics, one or more selected from phenol resins, epoxy resins, and urethane resins can be preferably used. In the case of thermosetting waste plastics, it has generally been said that they cannot be recycled, but here we have only listed those for which processing methods that allow recycling have been developed. can be added to the target.

Thermoplastic waste plastic obtained by pelletizing recycled plastic according to the present invention can be subjected to various molding such as injection molding, extrusion molding, blow molding, and rotational molding. Further, in the case of thermosetting waste plastics such as phenolic resins, even if recycled plastic pellets are formed according to the present invention, they cannot be used for molding as they are. However, by adding phenol and acid and heating, it becomes thermoset again and can be used for molding. Such an invention is introduced in Japanese Unexamined Patent Application Publication No. 8-269227. Epoxy resins are disclosed in WO2014009229A1, etc., and urethane resins are disclosed in a paper (Toshiba Review Vol.

(freeze pulverization)
Next, a small-scale apparatus for cooling the above-described waste plastic to a temperature below the embrittlement temperature and then pulverizing it will be described with reference to a schematic diagram of FIG. First, the above-described waste plastic material 3 is put into the freeze-grinding container 5 to about one third of the container. Subsequently, the freeze crushing container 5 is put into the dur bottle 2 . In order to freeze the recyclable plastic material 3, a cryogen 1 is placed between the inside of the Dewar bottle 2 and the outer circumference of the freeze-grinding container 5. Hold until frozen at the prescribed temperature. Here, the predetermined temperature is a temperature of about -60° C. or lower, which is lower than the brittle temperature of plastic. While the waste plastic material 3 in the Dewar bottle 2 is frozen, the rod 6 attached to the lid side of the freezing crushing container 5 containing the metal steel balls 4 is reciprocated up and down to reduce the waste plastic to a desired average particle size. Grind to In such a device, the cryogen has a cooling effect even during pulverization, so the pulverization is performed while cooling, and the temperature does not rise due to the cooling effect of the cryogen, which should normally increase due to frictional heat. and pulverization proceeds efficiently.

(Temperature in cooling process and grinding process in freeze grinding)
The temperature in the cooling step and the pulverization step in freeze pulverization must be in the temperature range below the embrittlement temperature of the target waste plastic. More specifically, it is preferable to keep the temperature of the waste plastic below −60° C. using the cryogenic agent 1 . In addition, the lower the temperature, the shorter the time required for pulverization. By maintaining the temperature below the embrittlement temperature even in the pulverization process, it is possible to suppress the temperature rise during pulverization, so pulverization is possible without changing the properties of the waste plastics. For this reason, cooling during milling is also highly preferred.

(Type of cryogen used in cooling process and pulverization process)
In the freeze-grinding process described above, the cryogen 1 used in the cooling process and grinding process of the waste plastic includes liquid nitrogen, a mixture of dry ice and ethanol (dry ice/ethanol), a mixture of dry ice and acetone (dry ice/acetone), and dry ice. Ethyl ether mixtures (dry ice/ethyl ether) are preferred. Furthermore, liquid nitrogen, dry ice/ethanol, dry ice/acetone are more preferred, and liquid nitrogen is most preferred. Liquid nitrogen not only has the lowest temperature among the cryogens, but also can be used simply by opening and closing a valve without requiring mixing.

(Cooling time for cooling process using liquid nitrogen as cryogen)
In the case of the apparatus shown in FIG. 2 described above, the cooling time for freezing with the cryogen 1 is preferably 1 minute or more and 30 minutes or less. 3 minutes or more and 20 minutes or less is more preferable, and considering the thermal conductivity of the recycled plastic, 8 minutes or more and 12 minutes or less is most preferable and efficient. If the cooling time is less than 1 minute, depending on the size of the recycled plastic, the core of the recycled plastic may not be cooled, and the plastic may not be efficiently pulverized in the subsequent pulverization process. It is from. Moreover, even if the cooling time is longer than 30 minutes, no change is observed in the degree of pulverization of the plastic in the subsequent pulverization process, and the industrial significance is diminished.

(Cooling time for cryogens other than liquid nitrogen)
When dry ice/ethanol, dry ice/acetone, or dry ice/ethyl ether is used as the cryogen in the apparatus shown in FIG. 2, the cooling time is preferably 5 minutes or more and 60 minutes or less. Further, it is more preferably 20 minutes or more and 40 minutes or less, and most preferably 25 minutes or more and 35 minutes or less. If the cooling time is less than 5 minutes, the plastic may not be efficiently pulverized in the subsequent pulverization process. This is because the industrial significance is diluted because it cannot be used.

(Pulverization time when liquid nitrogen is used as cryogen)
In a small-scale apparatus as shown in FIG. 2, the pulverization time in the pulverization step is preferably 1 to 30 minutes, more preferably 3 to 20 minutes, and most preferably 8 to 12 minutes. If the pulverization time is less than 1 minute, the particle size of the plastic after pulverization is large, making it difficult to make tablets. This is because the

(Pulverization time when the cryogen is other than liquid nitrogen)
When dry ice ethanol, dry ice/acetone, or dry ice/ethyl ether is used as a cryogen in a small-scale apparatus as shown in FIG. preferable. Furthermore, 50 minutes or more and 70 minutes or less is the most preferable. If the pulverization time is less than 20 minutes, the particle size of the plastic after pulverization is large, making tableting difficult. This is because it has little meaningful meaning.

(The number of vertical reciprocations of the rod in the crushing process)
In a small-scale apparatus as shown in FIG. 2, the number of vertical reciprocations per minute of the rod 6 during pulverization is preferably 800 or more and 1600 or less, more preferably 1000 or more and 1400 or less. Furthermore, 1200 times or more and 1300 times or less is most preferable. If the number of vertical reciprocations per minute of the rod 6 is less than 800 times, the plastic will not be sufficiently pulverized, and if it is more than 1600 times, it will be difficult to control the particle size of the pulverized material after freeze-pulverization. .

(Appropriate size of waste plastic granules obtained in the pulverization process)
Prior to the step of adding a binder and the step of tableting following the pulverization step, it is preferable to sift the waste plastic particles obtained in the pulverization step to make them uniform. The size of the waste plastic is preferably a size that can pass through a sieve with an opening of 4 mm and a wire diameter of 1.4 mm, but does not pass through a sieve with an opening of 250 μm and a wire diameter of 160 m 2 specified in JIS Z8801. A size that passes through a sieve with an opening of 2 mm and a wire diameter of 0.9 mm and does not pass through a sieve with an opening of 500 μm and a wire diameter of 315 μm is more preferable. A size that does not pass through a sieve with an opening of 710 μm and a wire diameter of 450 μm is most preferred. In the case of a size that can pass through a sieve with an opening of 250 μm and a wire diameter of 160 μm, it is difficult to handle because it is easy to scatter. may become. On the other hand, in the case of a size that does not pass through a sieve with an opening of 4 mm and a wire diameter of 1.4 mm, the moldability in the tableting process may deteriorate and the strength of the molded product may become insufficient.

(Type of binder used in binder addition process)
As described above, among the waste plastics, thermoplastic resins targeted are polypropylene, polyethylene, polystyrene, polyvinyl chloride, polycarbonate, and polyoxymethylene. Phenolic resin, novoloid resin, epoxy resin and urethane resin cannot be molded by pressing and tableting by themselves. Such materials require the addition of a binder component. Preferred binder types are cellulose, rayon, acetate, chitin, chitosan, silk, wool, stearic acid, palmitic acid and aluminum hydroxide, and more preferred are cellulose, rayon, acetate, chitin, chitosan, stearic acid and palmitic acid. . Furthermore, cellulose, rayon, acetate, chitin and chitosan are most preferred. In particular, cellulose, rayon, acetate, chitin, and chitosan are discharged as waste, and their use as binders contributes to recycling.

(preferred size of binder)
The binder to be added to the waste plastic particles obtained by freeze-grinding is preferably sieved to have a uniform size. The size of the binder is preferably a size that can pass through a sieve with a mesh size of 4 mm and a wire diameter of 1.4 mm but does not pass through a sieve with a mesh size of 250 μm and a wire diameter of 160 μm as defined in JIS Z8801. Furthermore, a size that passes through a sieve with an opening of 2 mm and a wire diameter of 0.9 mm but does not pass through a sieve with an opening of 500 μm and a wire diameter of 315 μm is more preferable. A size that does not pass through a sieve having an opening of 710 μm and a wire diameter of 450 μm is most preferable. In the case of a size that can pass through a sieve with an opening of 250 μm and a wire diameter of 160 μm, it is difficult to handle because it is easy to scatter. may become. On the other hand, in the case of a size that does not pass through a sieve with an opening of 4 mm and a wire diameter of 1.4 mm, the moldability in the tableting process is lowered, and the strength of the molded product may be insufficient.

(Amount of binder added)
When a binder is added to waste plastic granules that are difficult to coagulate in tableting to prepare recycled plastic pellets as the binder-containing waste plastic granules, the weight ratio of the binder in the recycled plastic pellets is 0.5. 5 wt % or more and 20 wt % or less is preferable, and 2 wt % or more and 10 wt % or less is more preferable. Furthermore, 4 wt % or more and 8 wt % or less is most preferable. The weight ratio of the binder to the waste plastic is . If it is less than 5 wt%, the shape may not be retained even by tableting, and if the binder is added at a rate of more than 20 wt%, the percentage of plastic in the recycled plastic pellets obtained in the subsequent tableting process. This is because the low

(Tabletting process)
The binder-containing waste plastic granules pulverized in the pulverization step as described above and then added with a binder in the binder addition step are tableted by, for example, a press molding machine schematically shown in FIG. That is, a specular plate 9a is placed on a molding die 8 placed on a pedestal 7, and an arbitrary required amount of waste plastic particles 10 containing a binder is put on the specular plate 9a. Next, after placing the specular plate 9b on the pulverized waste plastic granules 10 containing the binder, the metal rod 11 is installed. By raising and lowering the lever 12 of the hydraulic press, the oil in the cylinder 13a is transferred to the cylinder 13b through the hydraulic hose 14, and the ram 15 is pushed down. As a result, the binder-containing waste plastic granules 10 are tableted through the metal rod 11 to obtain the molded product. The tableting pressure is displayed by the pressure gauge 16, and the tableting pressure is applied. Also, the cylinder 13b portion is supported by a metal frame 17. As shown in FIG. In industrial applications, a large amount of tablets can be produced in a short time by using a rotary tablet press.

(Pressure during tableting)
The pressure during tableting is preferably 5 MPa or more and 60 MPa or less. Furthermore, it is more preferably 25 MPa or more and 50 MPa or less, and most preferably 35 MPa or more and 45 MPa or less. If the pressure during tableting is lower than 5 MPa, there is a concern that the shape of the recycled plastic pellets will easily collapse. Moreover, even if tableting is performed at a pressure exceeding 60 MPa, no change in the mechanical strength of the recycled plastic pellets is observed, and the industrial significance is diminished.

(Retention time during tableting)
In the tableting process using the apparatus shown in FIG. 3, the holding time during tableting is preferably 1 minute or longer and 6 minutes or shorter, more preferably 2 minutes or longer and 5 minutes or shorter, and 3 minutes or longer and 4 minutes or shorter. Most preferred. This is because sufficient shape retention is not reliably performed in a short time of less than 1 minute, and even if it exceeds 6 minutes, no difference in shape retention is observed, and the industrial significance becomes weak. be. For example, in the case of rotary tablet presses, the retention time will be much shorter.

It has been explained that according to the embodiment of the method for producing recycled plastic pellets of the present invention, the heating step can be eliminated and pellets that can be used as a material for recycled plastic can be produced. Such a production method prevents thermal decomposition of the waste plastic itself and additives contained in the waste plastic, eliminates deterioration in strength and discoloration of the produced recycled plastic pellets, and eliminates corrosive gas or decomposition generated in the manufacturing process. It becomes possible to eliminate the generation of gas. In addition, as a result, it is possible to simplify equipment related to manufacturing, such as exhaust equipment and air conditioning equipment, compared to the conventional technology that manufactures recycled plastic pellets through heating and melting.

Examples for obtaining preferable recycled plastic pellets are shown below and explained in more detail. The examples are for the purpose of explaining the invention in detail, and are not intended to limit the interpretation of the invention.
[Example 1]

(waste plastic and binder)
The waste plastic used in Example 1 was obtained by cutting a polyethylene sheet having a thickness of 3 mm into a size of 1 cm square with a cutting machine. Waste cotton fibers were used as the binder in Example 1. For use as a binder, waste cotton fibers cut to a length of 1 cm were pulverized using a freeze pulverizer (JFC-300, manufactured by Nippon Analytical Industry Co., Ltd.).

(Waste plastic cooling process and crushing process)
In the cooling process and crushing process of the waste plastic used in this Example 1, freeze crushing 4 as shown in Fig. 2
An apparatus (JFC-300, manufactured by Japan Analytical Industry Co., Ltd.) was used. Liquid nitrogen was used as a coolant in the cooling process and the pulverization process, and the cooling time in the cooling process was set to 10 minutes. Further, the pulverizing time in the pulverizing step was 10 minutes, and the metal ball at the tip of the rod was reciprocated up and down 1250 times/min. The average particle diameter of the waste plastic particles thus obtained was 913 μm.

(Binder addition process and tableting process for waste plastic particles)
In the step of adding the binder in Example 1, the proportion of the binder in the binder-containing waste plastic granules was set to 6 wt %. A hydraulic press (MINILAB PRESS MP-100 manufactured by Labnect) was used for tableting the binder-containing waste plastic granules thus obtained. 0.51 g per piece of plastic containing a binder was placed in the apparatus shown in FIG. 3 and tableted for 3 minutes at a tableting pressure of 40 MPa to obtain 30 waste polyethylene pellets with a diameter of 11 mm and a height of 3 mm. . This was used as the recycled plastic pellet in the present Example 1.

(Appearance evaluation of recycled plastic pellets)
The external appearance of 30 recycled plastic pellets obtained was evaluated based on the 5-grade evaluation shown in Table 1.

(Appearance evaluation and comprehensive evaluation)
Appearance evaluation was performed on the recycled plastic pellets obtained in Example 1, and the evaluation was 5 for all 30 samples. Based on the above results, the overall evaluation was judged to be appropriate because the polyethylene waste material could be tableted satisfactorily in this example.
[Example 2]

(waste plastic and binder)
The waste plastic used in Example 2 was obtained by cutting a rigid polyvinyl chloride pipe having a thickness of 2 mm into squares with an average width of 1 cm using a cutting machine. As the binder in Example 2, waste cotton fibers similar to those in Example 1 were used. In addition, when using the binder, the same operation as in Example 1 was performed to obtain powder.

(Waste plastic cooling process and crushing process)
In Example 2, the waste plastic was pulverized in the same manner as in Example 1, except that the cooling time in the cooling step was set to 3 minutes, and the crushing time in the crushing step was set to 10 minutes. The average particle size of the waste plastic particles thus obtained was 1022 μm.

(Binder addition process to waste plastic granules and tableting process)
In the binder addition step of Example 2, the ratio of the binder to the binder-containing waste plastic granules was set to 0.5 wt %. The binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1 except that the tableting pressure was 40 MPa and the tableting time was 3 minutes. 30 pellets were produced in the same manner as in Example 1 as recycled pellets of waste plastic in .

(Comprehensive Appearance Evaluation of Recycled Plastic Pellets)
The external appearance of 30 recycled plastic pellets obtained was evaluated on the basis of the 5-level evaluation shown in Table 1, and all the evaluations were 5. In addition, from the above results, in the present example, the waste polyvinyl chloride material could be tableted satisfactorily, so the overall evaluation was judged to be appropriate.
[Example 3]

(waste plastic and binder)
As the waste plastic in Example 3, a polystyrene sheet having a thickness of 1 mm was cut into squares with an average width of 1 cm using a cutting machine. Further, stearic acid powder (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the binder in Example 3.

(Waste plastic cooling process and crushing process)
In the cooling process and the crushing process of the third embodiment, dry ice/acetone, which is a mixture of dry ice and acetone at a weight ratio of 1:1, is used as the refrigerant, and the cooling time in the cooling process of the waste plastic is 20 minutes. Granules were obtained in the same manner as in Example 1, except that the pulverization time was changed to 3 minutes. The average particle size of the waste plastic particles thus obtained was 1312 μm.

(Binder addition step and tableting step)
In Example 3, the proportion of the binder in the binder-containing waste plastic granules was set to 10 wt %. Thirty pieces of the binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 50 MPa and the tableting time was 6 minutes. Recycled plastic pellets in Example 3 were obtained.

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
Regarding the appearance of the obtained recycled plastic pellets, all 30 pellets were evaluated on the basis of the 5-level evaluation shown in Table 1, and all the evaluations were 5. Based on the above results, in Example 3, the polystyrene waste material could be tableted satisfactorily.
[Example 4]

(waste plastic and binder)
As the waste plastic in Example 4, a phenolic resin sheet having a thickness of 1 mm was cut into squares with an average width of 1 cm using a cutting machine. As the binder in Example 4, the same cotton fiber waste material as in Example 1 was used. In addition, when using it as a binder, the same operation as in Example 1 was performed to obtain powder.

(Waste plastic cooling process and crushing process)
In Example 4, the powder was granulated in the same manner as in Example 1, except that the cooling time in the cooling step was set to 8 minutes, and the pulverization time in the pulverization step was set to 8 minutes. The average particle size of the waste plastic particles thus obtained was 1182 μm.

(Binder addition step and tableting step)
In this example, the proportion of the binder in the binder-containing waste plastic granules was set to 2 wt %. Thirty pieces of the binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 60 MPa and the tableting time was 4 minutes. was used as the recycled plastic pellet in this example.

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
The appearance of the obtained recycled plastic pellets was evaluated on the basis of the 5-level evaluation shown in Table 1, and all evaluations were 5. Based on the above results, the phenolic resin waste material was able to be tableted satisfactorily in this example, so the overall evaluation was judged to be appropriate.
[Example 5]

(waste plastic and binder)
The waste plastic in Example 5 was obtained by cutting a polypropylene sheet having a thickness of 1 mm into squares with an average width of 1 cm using a cutting machine. As the binder in Example 5, waste rayon fibers were used. In addition, when used as a binder, the same operation as in Example 1 was carried out to form powder.

(Waste plastic cooling process and crushing process)
In the cooling step and the pulverization step of the fifth embodiment, dry ice/ethanol, which is a mixture of dry ice and ethanol at a weight ratio of 1:1, is used as the refrigerant, the cooling time in the cooling step is 10 minutes, and the pulverization step is performed. Granules were produced in the same manner as in Example 1, except that the time was changed to 20 minutes. The average particle diameter of the waste plastic particles thus obtained was 1229 μm.

(Binder addition step and tableting step)
In Example 5, the proportion of the binder in the binder-containing waste plastic granules was set to 2 wt %. Thirty pieces of the binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 25 MPa and the tableting time was 5 minutes. The recycled plastic pellets in Example 5 were obtained.

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
When the appearance of the obtained recycled plastic pellets was evaluated based on the 5-level evaluation shown in Table 1, most of them were evaluated as 4, although some were evaluated as 5. Based on the above results, in Example 5, the polypropylene waste material was able to be tableted satisfactorily, so the overall evaluation was judged to be appropriate.
[Example 6 ]

(waste plastic and binder)
As the waste plastic in Example 6 , a polystyrene sheet having a thickness of 1 mm was cut with a cutting machine into an average size of 1 cm wide square and used. The binder used in Example 7 was acetate fiber waste. In addition, when used as a binder, the same operation as in Example 1 was performed to form granules.

(Waste plastic cooling process and crushing process)
In the cooling step and the pulverization step in the present Example 6 , granules were formed in the same manner as in Example 1 except that the cooling time in the cooling step was set to 30 minutes and the pulverization time in the pulverization step was set to 30 minutes. The average particle diameter of the waste plastic particles thus obtained was 734 μm.

(Binder addition step and tableting step)
In Example 6 , the proportion of the binder in the binder-containing waste plastic granules was set to 20 wt %. The binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 25 MPa and the tableting time was 5 minutes. 7 as recycled plastic pellets.

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
Regarding the appearance of the obtained recycled plastic pellets, 30 pellets were evaluated based on the 5-level evaluation shown in Table 1, and all the evaluations were 5. Based on the above results, in Example 6 , the polystyrene waste material could be tableted satisfactorily.
[Comparative Example 1]

(waste plastic)
As the waste plastic in Comparative Example 1, a polyethylene sheet having a thickness of 1 mm was cut by a cutting machine into a size of 1 cm on average and square.

(Waste plastic cooling process and crushing process)
The cooling step and pulverizing step of the waste plastic were carried out in the same manner as in Example 1. Moreover, the average particle size of the waste plastic particles obtained in Comparative Example 1 was 945 μm. The obtained waste plastic granules were tableted in the same manner as in Example 1.

(Appearance and overall evaluation after tableting waste plastic)
In this Comparative Example 1, the waste plastic granules could not be pelletized. Therefore, based on the 5-level evaluation shown in Table 1, the evaluation was judged to be 1. From the above results, in this comparative example in which no binder was added and only the polyethylene granules were used for tableting, pelletization was not possible.
[Comparative Example 2 ]

(waste plastic and binder)
The waste plastic in Comparative Example 2 was obtained by cutting a polyethylene sheet having a thickness of 1 mm into squares with an average width of 1 cm using a cutting machine. Stearic acid powder was used as the binder in Comparative Example 2 .

(Cooling process and crushing process)
The cooling step and crushing step of the waste plastic were carried out in the same manner as in Example 1. The average particle size of the waste plastic powder obtained in Comparative Example 2 was 956 μm.

(Binder addition step and tableting step)
In Comparative Example 2 , the proportion of the binder in the binder-containing waste plastic granules was set to 5 wt %. Five of the binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 1 MPa and the tableting time was 3 minutes. It was used as a recycled plastic pellet in this example.

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
The appearance of the obtained recycled plastic pellets was evaluated on the basis of the 5-level evaluation shown in Table 1, and all the evaluations were 2. Based on the above results, when the tableting pressure of the waste plastic granules containing a binder in Comparative Example 2 was low, the obtained recycled plastic pellets were easily disintegrated, so the comprehensive evaluation was judged to be inappropriate. .
[Comparative Example 3 ]

(waste plastic and binder)
As the waste plastic in Comparative Example 3 , a polyethylene sheet having a thickness of 1 mm was cut into a size of 1 cm on average with a width of 1 cm using a cutting machine. As the binder in Comparative Example 3 , the same cotton fiber waste material as in Example 1 was used. In addition, when used as a binder, the same operation as in Example 1 was performed to form granules.

(Cooling process and crushing process)
The cooling process and crushing process of the waste plastic were carried out in the same manner as in Example 1. In addition, the average particle size of the waste plastic granules obtained in Comparative Example 3 was 907 μm.

(Binder addition step and tableting step)
In Comparative Example 3 , the proportion of the binder in the binder-containing waste plastic granules was 6 wt.%. Five pieces of the binder-containing waste plastic granules thus obtained were tableted in the same manner as in Example 1, except that the tableting pressure was 40 MPa and the tableting time was 0.5 minutes. was used as the recycled plastic pellet in this Comparative Example 3 .

(Appearance and Comprehensive Evaluation of Recycled Plastic Pellets)
The appearance of the obtained recycled plastic pellets was evaluated on the basis of the 5-grade evaluation shown in Table 1, and all the evaluations were 2. Based on the above results, the recycled plastic pellets obtained easily disintegrated when the tableting time was shortened in the tableting of polyethylene waste material, so the overall evaluation was judged to be inappropriate.

Table 2 shows the recycled plastic pelletizing conditions in Examples 1 to 6 and Comparative Examples 1 to 3 . Appearance evaluation and comprehensive evaluation of the pellets are summarized in Table 3.

From the results shown in Tables 2 and 3 above, it can be seen that the plastic waste material is subjected to 1) cooling with a cryogen, 2) powdering, 3) adding a binder, 4) shaping into an arbitrary shape. It was confirmed that pelletization as a molding material for recycled plastic can be achieved by a combination such as the tableting process. For this reason, since it does not undergo a heat melting process, it can be used as a raw material for recycled plastics free from the harmful effects of thermal decomposition. Moreover, the present invention is very simple, can sufficiently contribute to recycling in a recycling society, and is a highly sustainable technique.

1 Cryogenic agent 2 Dewar bottle 3 Plastic 4 Metal ball 5 Freeze grinding container 6 Rod 7 Pedestal 8 Forming mold 9a, 9b Mirror plate 10 Waste plastic powder containing binder 11 Metal rod 12 Hydraulic press lever 13a, 13b Cylinder 14 Hydraulic hose 15 ram 16 pressure gauge 17 metal frame

Claims (3)

A step of cooling the plastic waste material with a cryogen for 1 to 30 minutes ;
The plastic waste material cooled in the cooling step is passed through a sieve with an opening of 4 mm and a wire length of 1.4 mm specified in JIS Z 8801, and does not pass through a sieve with an opening of 250 μm and a wire length of 160 μm. a step of forming granules of a size ;
0.5 wt of one or more binders selected from the group consisting of cellulose, rayon, acetate, chitin, chitosan, silk, wool, stearic acid, palmitic acid, and aluminum hydroxide are added to the granulated plastic waste material. % to 20 wt% ;
a step of tableting the plastic waste material granules to which the binder has been added into an arbitrary shape under a pressure range of 5 MPa to 60 MPa ;
A method for producing recycled plastic pellets comprising: 2. The method for producing recycled plastic pellets according to claim 1, wherein the plastic waste material is mainly composed of one or more selected from the thermoplastic resin group consisting of polypropylene, polyethylene, polystyrene, polyvinyl chloride, polycarbonate, and polyoxymethylene. . 2. The method for producing recycled plastic pellets according to claim 1, wherein the plastic waste material is mainly composed of one or more types selected from the group consisting of thermosetting resins such as phenol resin, epoxy resin and urethane resin.

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