JP7518775B2 - How to crush plastic - Google Patents

Description

The present invention relates to a method for crushing plastics using a crusher equipped with a rotating blade and a fixed blade installed inside a container.

Conventionally, dry crushers have been known that have a rotating blade and a fixed blade with their blade surfaces facing each other inside a container, and crush materials to be processed between the opposing blade surfaces. For example, Patent Document 1 describes a crusher in which the rotating blade and the fixed blade have a truncated cone-shaped blade surface with a recessed center and multiple blades arranged in the circumferential direction, and the cutting edges of the blades do not intersect when viewed from the axial direction during crushing processing. For this reason, in the crusher described in Patent Document 1, as the rotating blade rotates, the cutting edge of the rotating blade approaches and passes over the cutting edge of the fixed blade in a state that is approximately parallel to it.

For example, Patent Document 2 describes a crusher in which the cutting edges of the multiple blades on the rotating blade and fixed blade all extend in an inclined direction relative to a straight line passing through the axis, and when viewed from the axial direction during crushing processing, the cutting edges of the rotating blade and the fixed blade intersect. In this case, when the rotating blade rotates, the cutting edge of the rotating blade approaches and passes over the cutting edge of the fixed blade at a certain angle. In other words, both cutting edges act like the blades of scissors.

For example, Patent Document 3 describes a crusher in which the rotating blades and fixed blades are cooled by a cooling medium. Patent Document 3 also describes that, due to the rise in temperature during crushing, if the material to be processed is plastic, the material will melt and crushing will become impossible, and if the material to be processed is food, the material will oxidize and lose its aroma and flavor.

For example, Patent Document 4 describes a grinder in which the rotating blades and fixed blades are each made up of an inner blade arranged radially inward and an outer blade arranged radially outward and surrounding the inner blade, in order to enable finer grinding.

Japanese Patent Application Publication No. 10-28894 JP 2003-80092 A JP 2018-153757 A JP 2019-162615 A

The crushers described in Patent Documents 1 to 4 are all described as being suitable for crushing plastics. However, depending on the type of plastic, there is a problem in that the material melts during the crushing process, making it impossible to obtain plastic with an appropriate particle size.

The present invention was made with the above problem in mind, and aims to provide a method for crushing plastics that can suppress melting of the processed material when crushing granular plastics.

In order to achieve the above object, the present invention provides a method for crushing plastics using a crusher equipped with a rotating blade and a fixed blade installed in a container with their blade surfaces facing each other, the crusher includes a rotating blade attached to a rotating shaft, a rotating side blade member having a plurality of linearly extending cutting edges that are aligned in a circumferential direction about the axis of the rotating shaft when viewed from the axial direction of the rotating shaft, the fixed blade fixed to the container includes a fixed side blade member having a plurality of linearly extending cutting edges that are aligned in a circumferential direction about the axis of the rotating shaft when viewed from the axial direction of the rotating shaft, and a gradually reducing inter-face portion between the rotating side blade member and the fixed side blade member in which the blade surface spacing gradually narrows from the axis side toward the radially outward direction, and the crusher includes a measuring step for measuring the nominal tensile fracture strain of the plastic to be crushed before the crushing process using the crusher, and a selecting step for selecting the rotating side blade member and the fixed side blade member based on the measured value of the nominal tensile fracture strain, and setting the orientation of the cutting edges at the gradually reducing inter-face portion when viewed from the axial direction of the rotating shaft during the crushing process.

As a result, the plastic crushing method of the present invention can suppress melting of the processed material when crushing granular plastic.

1 is an overall system diagram showing a crushing system to which the plastic crushing method of Example 1 is applied. FIG. FIG. 2 is a schematic cross-sectional view showing the pulverizer of the first embodiment. FIG. 2 is a schematic plan view showing the crusher of the first embodiment. 4(a) is a plan view showing a first inner blade member used in the crusher of the first embodiment, and FIG. 4(b) is a cross-sectional view taken along line AA of FIG. 4(a). 5(a) is a plan view showing a second inner blade member used in the crusher of the first embodiment, and FIG. 5(b) is a cross-sectional view taken along line BB of FIG. 5(a). 6(a) is a plan view showing a split blade constituting a second inner blade member, and FIG. 6(b) is a side view of the split blade shown in FIG. 6(a) as viewed from the center side. 7A is a plan view showing a first outer blade member used in the crusher of the first embodiment, and FIG. 7B is a cross-sectional view taken along the line CC of FIG. 8(a) is a plan view showing a second outer blade member used in the crusher of Example 1, and FIG. 8(b) is a cross-sectional view taken along the line DD of FIG. 8(a). 4 is a flowchart showing the procedure of a plastic crushing process performed by the crusher of the first embodiment. FIG. 2 is an explanatory diagram showing a stress/strain curve of a material. This is an explanatory diagram showing that the cutting edges of the rotating blade and fixed blade do not intersect when viewed from the axial direction of the rotating shaft, where (a) shows the cutting edges overlap when viewed from the axial direction, and (b) shows the cutting edges shifted circumferentially when viewed from the axial direction. 1 is an explanatory diagram showing how the cutting edges of a rotary blade and a fixed blade intersect when viewed from the axial direction of a rotary shaft. 1 is a table showing the results of the pulverization process using the plastic pulverization method of Example 1 and the results of the pulverization process using the plastic pulverization method of the comparative example.

Below, the embodiment for carrying out the plastic crushing method of the present invention will be explained based on Example 1 shown in the drawings.

A crushing system 100 using a crusher 10 to which the plastic crushing method of Example 1 is applied will be described with reference to FIG. 1. The crushing system 100 of Example 1 includes the crusher 10, a feeder 20 installed upstream of the crusher 10, and a powder separator 30 installed downstream of the crusher 10.

The feeder 20 is a device that supplies a specified amount of granular plastic (plastic before crushing, hereafter referred to as "granular plastic"), which is the processing product, to the crusher 10. Granular plastic is stored in the feeder 20 in advance, and the amount of granular plastic supplied is adjusted according to commands from a control device (not shown). The feeder 20 and the crusher 10 are connected via a pellet line 21. The granular plastic is continuously supplied to the supply port 12 of the crusher 10 through the pellet line 21 at a specified flow rate.

The crusher 10 is a device that crushes granular plastic supplied from the supply device 20 into fine powder. As shown in FIG. 1, the crusher 10 has a container 11, and a supply port 12 and a discharge port 13 formed in the container 11. A pellet line 21 and an air line 22 are connected to the supply port 12. A transport line 31 is connected to the discharge port 13. The detailed configuration of the crusher 10 will be described later.

The powder separator 30 is a device that collects the finely powdered plastic (plastic after the crushing process, hereinafter referred to as "finely powdered plastic") crushed by the crusher 10. The crusher 10 and the powder separator 30 are connected via a transport line 31. Here, in order to prevent the finely powdered plastic from melting during the crushing process, it is preferable to quickly discharge the finely powdered plastic from the crusher 10, and in particular, it is preferable to discharge it by blowing it away with a large amount of air. For this reason, in the crushing system 100 of Example 1, the finely powdered plastic is discharged from the crusher 10 by air transport.

That is, an intake fan 33 is connected to the powder separator 30 via an exhaust line 32. By suction using the intake fan 33, air is sucked from the air line 22 into the supply port 12 of the pulverizer 10, and the air flows out from the exhaust port 13. As a result, the finely powdered plastic in the pulverizer 10 is pneumatically transported via the transport line 31.

The finely powdered plastic transported by air through the transport line 31 is separated from the air by centrifugal separation inside the funnel-shaped powder separator 30, and is collected in the product tank 35 via the rotary feeder 34. Meanwhile, the air sucked from the powder separator 30 through the exhaust line 32 by the intake fan 33 is released into the atmosphere via the bag filter 36.

Furthermore, in the crusher 10, it is desirable to cool the rotating blade 40 and fixed blade 50 (see FIG. 2) with a cooling medium and maintain them at a low temperature to prevent the plastic from melting. The rotating blade 40 and the like can be cooled by installing a chiller unit 14 near the crusher 10 and circulating a cooling medium through refrigerant lines 15 and 16. Furthermore, keeping the rotating blade 40 and fixed blade 50 at a low temperature reduces the temperature inside the container 11, and the air used for air transport is also cooled. For this reason, it is desirable to use dry air for air transport, as there is a possibility of condensation inside the container 11 and transport line 31 of the crusher 10.

As shown in Figures 2 and 3, the crusher 10 of Example 1 is a dry crusher in which a rotating blade 40 and a fixed blade 50 are arranged in a flat cylindrical container 11 with their blade surfaces facing each other, and the material to be processed (granular plastic) is crushed between the facing blade surfaces.

The container 11 has a lid member 11a attached to one end wall. A cylindrical supply port 12 is formed in the center of the lid member 11a. A through hole 11c is formed in the other end wall 11b of the container 11 at a position opposite the supply port 12. Furthermore, a discharge port 13 is formed in the peripheral wall 11d of the container 11, as shown in FIG. 3.

The rotating shaft 17 is inserted into the through hole 11c, and the rotating blade 40 is fixed to the tip of the rotating shaft 17 inserted into the container 11. The rotating shaft 17 is rotatably supported relative to the container 11 via a bearing unit (not shown). The gap between the through hole 11c and the rotating shaft 17 is sealed by a shaft seal unit (not shown). A driving mechanism (not shown) is connected to the drive side end (base end) of the rotating shaft 17, and rotates the rotating shaft 17 according to commands from a control device (not shown). Here, the center line in the axial direction of the rotating shaft 17 is the axis O1, and the rotating blade 40 rotates around the axis O1. The axis O1 coincides with the center O2 of the supply port 12.

The rotating shaft 17 is further provided with a cooling passage 17a that is connected to the refrigerant lines 15 and 16 and through which the cooling medium flows. Although the cooling passage 17a is simplified as a single passage in FIG. 2, it is actually composed of two passages, one through which the cooling medium flows in and one through which the cooling medium flows out. A rotary joint (not shown) is provided at the drive end of the rotating shaft 17, and it is possible to supply and discharge the cooling medium via the cooling passage 17a.

As shown in FIG. 2, the rotating blade 40 has a rotating side holding member 41 and a rotating side blade member 42. The rotating side holding member 41 is a disk member to which the rotating shaft 17 is fixed in the center and in which a rotating side cooling space 43 is formed. The rotating side cooling space 43 communicates with a cooling passage 17a formed in the rotating shaft 17, and a cooling medium flows through it.

The rotating side blade member 42 fits into a recess formed on the surface of the rotating side holding member 41 and is fixed to the rotating side holding member 41. The rotating side blade member 42 in the first embodiment has a ring-shaped rotating side inner blade 44 centered on the axis O1 of the rotating shaft 17, and a ring-shaped rotating side outer blade 45 surrounding the rotating side inner blade 44.

The rotating inner blade 44 faces the fixed blade 50 and has an inclined blade surface (hereinafter referred to as the "inner rotating blade surface 44a") that is recessed radially inward from the radially outward. The rotating outer blade 45 faces the fixed blade 50 and has a blade surface with a constant height (hereinafter referred to as the "outer rotating blade surface 45a").

The inner rotating blade surface 44a and the outer rotating blade surface 45a are both formed with blades consisting of numerous concaves and convexes with sharp tips. The cutting edges of the blades are aligned in the circumferential direction around the axis O1 of the rotating shaft 17, and extend in a straight line when viewed from the axial direction of the rotating shaft 17. The rotating side inner blade 44 uses either the first inner blade member 110 or the second inner blade member 120 described below, based on the nominal tensile breaking strain of the granular plastic to be processed. The rotating side outer blade 45 uses either the first outer blade member 130 or the second outer blade member 140 described below.

The fixed blade 50 is fixed to the inner surface of the cover member 11a, and has a fixed side holding member 51 and a fixed side blade member 52, as shown in FIG. 2. The fixed side holding member 51 is a ring-shaped member with a supply through hole 53a formed in the center and a fixed side cooling space 53 formed inside. The fixed side holding member 51 is attached to the cover member 11a with the supply through hole 53a facing the supply port 12. Granular plastic supplied from the supply port 12 is supplied between the rotating blade 40 and the fixed blade 50 through the supply through hole 53a. In addition, the cover member 11a and the fixed side holding member 51 are formed with a cooling passage (not shown) connected to the refrigerant lines 15 and 16. The fixed side cooling space 53 is connected to a cooling passage (not shown) through which the cooling medium flows.

The fixed side blade member 52 fits into a recess formed on the surface of the fixed side holding member 51 and is fixed to the fixed side holding member 51. The fixed side blade member 52 in Example 1 has a ring-shaped fixed side inner blade 54 centered on the center O2 of the supply port 12, and a ring-shaped fixed side outer blade 55 surrounding the fixed side inner blade 54.

The fixed side inner blade 54 faces the rotary blade 40 and has an inclined blade surface (hereinafter referred to as the "inner fixed blade surface 54a") that is recessed radially inward from the radially outward. The fixed side outer blade 55 faces the rotary blade 40 and has a blade surface with a constant height (hereinafter referred to as the "outer fixed blade surface 55a").

The inner fixed blade surface 54a and the outer fixed blade surface 55a are both formed with blades consisting of numerous concaves and convexes with sharp tips. The cutting edges of the blades are aligned in the circumferential direction around the center O2 of the supply port 12, and extend in a straight line when viewed from the axial direction of the rotation shaft 17. The fixed side inner blade 54 uses either the first inner blade member 110 or the second inner blade member 120 described below, based on the nominal tensile breaking strain of the granular plastic to be processed. The fixed side outer blade 55 uses either the first outer blade member 130 or the second outer blade member 140 described below.

Furthermore, since both the inner rotating blade surface 44a and the inner fixed blade surface 54a are inclined surfaces that are recessed radially inward from the radially outward, a gradually reducing inter-surface portion 61 is formed between the rotating side inner blade 44 and the fixed side inner blade 54, in which the blade surface spacing G gradually narrows as it moves radially outward from the axis O1 of the rotating shaft 17. In other words, the rotating side inner blade 44 becomes the rotating side blade member 42 that forms the gradually reducing inter-surface portion 61, and the fixed side inner blade 54 becomes the fixed side blade member 52 that forms the gradually reducing inter-surface portion 61.

In addition, because the outer rotating blade surface 45a and the outer fixed blade surface 55a are both set to a constant height, a constant surface spacing portion 62 with a constant blade surface spacing G is formed between the rotating outer cutter 45 and the fixed outer cutter 55. The blade surface spacing G of the constant surface spacing portion 62 is the same size as the minimum blade surface spacing of the gradually decreasing surface spacing portion 61.

The following describes the inner blade members used for the rotating inner blade 44 and the fixed inner blade 54.

The first inner blade member 110 shown in Figs. 4(a) and (b) has a blade surface 111 on which multiple blades are arranged in the circumferential direction, and the blade tip 112 of each blade extends radially through the center O. That is, the blade tip 112 of each blade of the first inner blade member 110 extends in the radial direction passing through the center O. Note that, when the first inner blade member 110 is used as the rotating side inner blade 44 or the fixed side inner blade 54, the center O of the first inner blade member 110 coincides with the axis O1 of the rotating shaft or the center O2 of the supply port 12. In addition, the blade surface 111 is an inclined surface that is recessed more on the radially inner side than on the radially outer side (see Fig. 4(b)).

The second inner blade member 120 shown in Fig. 5(a) and (b) is formed by combining the divided blades 125 shown in Fig. 6(a) into a ring shape surrounding a center O. The center O of the second inner blade member 120 also coincides with the axis O1 of the rotating shaft or the center O2 of the supply port 12 when the second inner blade member 120 is used as the rotating side inner blade 44 or the fixed side inner blade 54.

A plurality of blades are formed on the blade surface 121 of each split blade 125, and the blade tip 122 of each blade extends linearly along a direction inclined with respect to the radial direction passing through the center O of the second inner blade member 120. In other words, the extension direction of the blade tip 122 of each blade of the second inner blade member 120 intersects with the radial direction passing through the center O. In addition, the split blade 125 has a split groove 127 along the split end surface 126. The split groove 127 is a dent formed on the blade surface 121 as shown in FIG. 6(b). As shown in FIG. 5(a), when the split blades 125 are combined, the adjacent split grooves 127 are butted against each other, and a radially extending dent passing through the center O is formed on the blade surface 121. By forming the split groove 127, it is possible to prevent the material to be processed from getting caught on the butted parts of the split end surfaces 126 during the crushing process, making it difficult to flow. Additionally, the blade surface 121 is an inclined surface that is recessed radially inward relative to the radially outward side (see FIG. 5(b)).

The following describes the outer blade members used for the rotating outer blade 45 or the fixed outer blade 55.

The first outer blade member 130 shown in Figs. 7(a) and (b) has a blade surface 131 on which multiple blades are arranged in the circumferential direction, and the blade tip 132 of each blade extends radially through the center O. That is, the blade tip 132 of each blade of the first outer blade member 130 extends along a radial direction passing through the center O. Note that when the first outer blade member 130 is used as the rotating side outer blade 45 or the fixed side outer blade 55, the center O of the first outer blade member 130 also coincides with the axis O1 of the rotating shaft or the center O2 of the supply port 12. In addition, the blade surface 131 is a plane perpendicular to the center O (see Fig. 7(b)).

The second outer blade member 140 shown in Figs. 8(a) and (b) has a blade surface 141 on which multiple blades are arranged in the circumferential direction, and the blade tip 142 of each blade extends linearly in a direction inclined relative to the radial direction passing through the center O. In other words, the extension direction of each blade tip 142 of the second outer blade member 140 intersects with the radial direction passing through the center O. The center O of the second outer blade member 140 also coincides with the axis O1 of the rotating shaft or the center O2 of the supply port 12 when the second outer blade member 140 is used as the rotating side outer blade 45 or the fixed side outer blade 55. The blade surface 141 is a plane perpendicular to the center O (see Fig. 8(b)).

The plastic crushing process of Example 1 using the crusher 10 will be explained below with reference to Figure 9.

In step S1, the nominal tensile strain at break of the granular plastic that is the material to be supplied to the crusher 10 is measured, and then the process proceeds to step S2. That is, step S1 is a measurement step in which the nominal tensile strain at break of the plastic to be crushed (granular plastic) is measured before the crushing process by the crusher 10.

The method for determining the tensile properties of plastics is stipulated by the Japanese Industrial Standards K7161:2014. The tensile properties of a material are shown by the stress/strain curve in Figure 10. That is, the material whose tensile properties are shown by curve a in Figure 10 is a brittle material that does not yield and breaks in the low strain range. The material whose tensile properties are shown by curve d in Figure 10 is a ductile material that does not yield and breaks in the high strain range. Many plastics have tensile properties such as those shown by curves b and c, and are characterized by breaking after yielding. The "nominal tensile strain at break" is the nominal strain just before the stress decreases to 10% or less of the tensile strength when the material breaks after yielding. The "nominal tensile strain" is calculated by dividing the displacement of the crosshead during the tensile test (the increase in the gripper distance) by the initial gripper distance.

In step S2, following the measurement of the nominal tensile breaking strain of the granular plastic in step S1, it is determined whether the measured value of the nominal tensile breaking strain is less than a preset threshold value. If the answer is YES (measured value of the nominal tensile breaking strain < threshold value), proceed to step S3. If the answer is NO (measured value of the nominal tensile breaking strain ≥ threshold value), proceed to step S4.

Here, the "threshold" is set to a value greater than 20% and equal to or less than 400%, and is set to 100% in Example 1. Generally, the smaller the nominal tensile strain at break of a plastic, the less ductile it is, and the larger the nominal tensile strain at break, the more ductile it is. Examples of plastics with nominal tensile strain at break of less than 100% include polypropylene homopolymer, polystyrene (PS), polyphenylene sulfide (PPS), etc. Also, examples of plastics with nominal tensile strain at break of 100% or more include polyethylene (PE), polypropylene random copolymer, ethylene vinyl acetate (EVA), polyamide 12 (PA12), rubber, etc.

In step S3, following the determination in step S2 that the measured value of the nominal tensile fracture strain is less than the threshold value, an inner blade member is selected in which the cutting edges of the rotating side inner blade 44 and the fixed side inner blade 54 do not intersect in the gradually reducing inter-face portion 61 when viewed from the axial direction of the rotating shaft 17 during the crushing process, and the process proceeds to step S5.

Here, "when viewed from the axial direction of the rotating shaft 17 during the crushing process, the cutting edges of the rotating side inner blade 44 and the fixed side inner blade 54 do not intersect in the gradually reducing inter-face portion 61" means that, as shown in Figure 11(a), when the cutting edges α of the multiple blades formed on the inner rotating blade surface 44a of the rotating side inner blade 44 and the cutting edges β of the multiple blades formed on the inner fixed blade surface 54a of the fixed side inner blade 54 are viewed from the axial direction of the rotating shaft 17, the extension direction L1 of the cutting edge α and the extension direction L2 of the cutting edge β intersect at the axis O1, so that even if the cutting edges α and β move relatively in the circumferential direction during the crushing process, the cutting edges α and β do not intersect within the gradually reducing inter-face portion 61, as shown in Figure 11(b). In step S3, specifically, the first inner blade member 110 is selected as the inner blade member to be used for the rotating side inner blade 44, and the first inner blade member 110 is selected as the inner blade member to be used for the fixed side inner blade 54.

In step S4, following the determination in step S2 that the measured value of the nominal tensile fracture strain is equal to or greater than the threshold value, the process selects an inner blade member in which the cutting edges of the rotating inner blade 44 and the fixed inner blade 54 intersect in the gradually reducing inter-face portion 61 when viewed from the axial direction of the rotating shaft 17 during the crushing process, and proceeds to step S5.

Here, "when viewed from the axial direction of the rotating shaft 17 during the crushing process, the cutting edges of the rotating inner blade 44 and the fixed inner blade 54 intersect in the gradually reducing inter-surface portion 61" means that when the cutting edges α of the multiple blades formed on the inner rotating blade surface 44a of the rotating inner blade 44 and the cutting edges β of the multiple blades formed on the inner fixed blade surface 54a of the fixed inner blade 54 are viewed from the axial direction of the rotating shaft 17, the cutting edges α and β intersect in the gradually reducing inter-surface portion 61 as shown in FIG. 12. In other words, in the rotating inner blade 44, the extension direction L1 of the cutting edge α is offset from the radial direction centered on the axis O1, and in the fixed inner blade 54, the extension direction L2 of the cutting edge β is along the radial direction centered on the axis O1. Therefore, when the cutting edges α and β move relatively in the circumferential direction during the crushing process, the cutting edges α and β approach each other at an angle like scissors. In step S4, specifically, the second inner blade member 120 is selected as the inner blade member to be used for the rotating side inner blade 44, and the first inner blade member 110 is selected as the inner blade member to be used for the fixed side inner blade 54.

The first inner blade member 110 may be selected as the inner blade member used for the rotating side inner blade 44, and the second inner blade member 120 may be selected as the inner blade member used for the fixed side inner blade 54. Furthermore, the second inner blade member 120 may be selected as the inner blade member used for the rotating side inner blade 44, and the second inner blade member 120 may be selected as the inner blade member used for the fixed side inner blade 54.

Steps S2 to S4 are selection steps for selecting the rotating blade member 42 and the fixed blade member 52 based on the measured value of the nominal tensile fracture strain of the granular plastic, and for setting the orientation of the blade tips α and β in the gradually reducing inter-face portion 61.

In step S5, following the selection of the inner blade member in step S3 or step S4, the outer blade member to be used for the rotating outer blade 45 and the outer blade member to be used for the fixed outer blade 55 are selected, and the process proceeds to step S6.

In addition, the outer blade member used for the rotating side outer blade 45 is matched in principle to the inner blade member used for the rotating side inner blade 44. In other words, when the first inner blade member 110 is used for the rotating side inner blade 44, the first outer blade member 130 is used, and when the second inner blade member 120 is used for the rotating side inner blade 44, the second outer blade member 140 is used. In addition, the outer blade member used for the fixed side outer blade 55 is matched in principle to the inner blade member used for the fixed side inner blade 54. In other words, when the first inner blade member 110 is used for the fixed side inner blade 54, the first outer blade member 130 is used, and when the second inner blade member 120 is used for the fixed side inner blade 54, the second outer blade member 140 is used. However, the outer blade members used for the rotating outer blade 45 and the fixed outer blade 55 can be selected arbitrarily based on the target flow rate of the material to be processed and the average particle size of the finely powdered plastic, taking into consideration the number of blades on the rotating blade 40, the volume of air flowing through the air line 22, the dimensions of the blade surface spacing G, the depth and spacing of the blade tips 132 and 142, the area of the constant surface spacing portion 62, etc.

In step S6, following the selection of the outer blade member in step S5, the inner blade member selected in step S3 or step S4 is set on the rotating blade 40 of the crusher 10, the outer blade member selected in step S5 is set on the fixed blade 50 of the crusher 10, and the process proceeds to step S7.

In step S7, following the setting of the rotary blade 40 and the fixed blade 50 in step S6, the crushing process is performed in the crushing system 100, and the process proceeds to the end. Here, the crushing process in the crushing system 100 first supplies granular plastic from the feeder 20 to the crusher 10. Next, the crusher 10 is driven to crush the granular plastic. At this time, the granular plastic passes through the supply through hole 53a from the supply port 12 and is supplied between the rotary blade 40 and the fixed blade 50. Then, as the rotary blade 40 rotates, the granular plastic flows from the radially inner side to the radially outer side between the rotary side inner blade 44 and the fixed side inner blade 54. In the gradually reducing inter-face portion 61 formed between the rotary side inner blade 44 and the fixed side inner blade 54, the blade surface interval G gradually narrows as it moves radially outward. Therefore, the granular plastic is successively crushed in the gradually reducing inter-face portion 61 into powder, and gradually changes into fine powder.

The processed material (fine powdered plastic) that has been converted into fine powder in the gradually reducing inter-face area 61 flows into the gap between the rotating outer blade 45 and the fixed outer blade 55. In the constant inter-face area 62 formed between the rotating outer blade 45 and the fixed outer blade 55, the processed material that has been converted into fine powdered plastic is continuously pulverized at a constant blade surface distance G. This causes the processed material to become fine powdered plastic with a uniform particle size.

Below, the results of the plastic crushing process in Example 1 and the results of the plastic crushing process in the Comparative Example will be explained based on Figure 13. Note that the plastic crushing process explained below uses the crusher 10 shown in Figure 1.

In the crushing process of Example 1, the nominal tensile strain at break of the processed granular plastic is first measured (step S1).

Next, based on the measured nominal tensile fracture strain of the granular plastic, the inner blade member to be used for the rotating inner blade 44 and the inner blade member to be used for the fixed inner blade 54 are selected. That is, it is determined whether the measured value of the nominal tensile fracture strain is less than a preset threshold value (here, 100%) (step S2). If the measured value of the nominal tensile fracture strain is less than the threshold value, the process proceeds to step S3 in the flowchart shown in FIG. 9, and an inner blade member in which the cutting edges of the rotating inner blade 44 and the fixed inner blade 54 do not intersect during the crushing process is selected. On the other hand, if the measured value of the nominal tensile fracture strain is equal to or greater than the threshold value, the process proceeds to step S4 in the flowchart shown in FIG. 9, and an inner blade member in which the cutting edges of the rotating inner blade 44 and the fixed inner blade 54 intersect during the crushing process is selected.

Then, the outer blade member to be used for the rotating outer blade 45 and the outer blade member to be used for the fixed outer blade 55 are selected (step S5), and the selected inner blade member and outer blade member are set on the rotating blade 40 and the fixed blade 50, respectively (step S6). Then, the crushing process is carried out by the crusher 10 (step S7).

In the crushing process of the first embodiment 1 shown in FIG. 13, a polypropylene homopolymer with a nominal tensile break strain of 20% is crushed. At this time, since the measured value of the nominal tensile break strain of the granular plastic is less than the threshold value, the process proceeds to step S3 in the flowchart shown in FIG. 9, and an inner blade member in which the cutting edges of the rotating side inner blade 44 and the fixed side inner blade 54 do not intersect during the crushing process is selected. In other words, as shown in FIG. 11, the first inner blade member 110 is selected as the inner blade member to be used for the rotating side inner blade 44, and the first inner blade member 110 is selected as the inner blade member to be used for the fixed side inner blade 54.

The pulverization conditions in the pulverization process in Example 1 were set to a minimum blade surface interval of 0.6 mm, a rotation speed of the rotary blade 40 of 10,000 to 12,000 min ^-1 , and a processing amount of 100 kg/hr. As a result, in the pulverization process in Example 1, fine powdered plastic with an average particle size of 1 mm or less could be obtained.

In contrast, in the pulverization process of Comparative Example 1, a polypropylene homopolymer with a nominal tensile break strain of 20% is pulverized in the same manner as in the pulverization process of the first embodiment. Then, during the pulverization process, an inner blade member is selected in which the blade tips of the rotating inner blade 44 and the fixed inner blade 54 intersect. That is, in the pulverization process of Comparative Example 1, although the measured value of the nominal tensile break strain of the granular plastic is less than the threshold value, as shown in FIG. 12, the second inner blade member 120 is selected as the inner blade member used for the rotating inner blade 44, and the first inner blade member 110 is selected as the inner blade member used for the fixed inner blade 54. The pulverization conditions are set to the same as in the first embodiment, with a minimum blade surface interval of 0.6 mm, a rotation speed of the rotating blade 40 of 10,000 to 12,000 min ^-1 , and a processing amount of 100 kg/hr.

As a result, in the grinding process of Comparative Example 1, the processed product, granular plastic, melted, and fine powdered plastic could not be obtained.

Furthermore, in the pulverization process of Comparative Example 2, similar to the pulverization process of First Example 1 and the pulverization process of Comparative Example 1, granular plastics that are polypropylene homopolymers with a nominal tensile break strain of 20% are pulverized. Also, similar to the pulverization process of Comparative Example 1, an inner blade member is selected in which the blade tips of the rotating side inner blade 44 and the fixed side inner blade 54 intersect during the pulverization process. Then, in the pulverization conditions, the minimum blade surface interval is set to 0.6 mm, the rotation speed of the rotating blade 40 is set to 10,000 to 12,000 min ^-1 , and the processing amount is set to 25 kg/hr, which is reduced from that of the pulverization process of First Example 1 and the pulverization process of Comparative Example 1.

In other words, in the pulverization process of Comparative Example 2, the processing amount was reduced compared to the pulverization process of Comparative Example 1. However, even when the processing amount was reduced, the granular plastic, which was the processed product, melted, and fine powdered plastic could not be obtained.

On the other hand, in the crushing process of the second embodiment 1, polyethylene with a nominal tensile break strain of 400% is crushed. At this time, since the measured value of the nominal tensile break strain of the granular plastic is equal to or greater than the threshold value, the process proceeds to step S4 in the flowchart shown in FIG. 9, and an inner blade member in which the cutting edges of the rotating inner blade 44 and the fixed inner blade 54 intersect during the crushing process is selected. In other words, as shown in FIG. 12, the second inner blade member 120 is selected as the inner blade member to be used for the rotating inner blade 44, and the first inner blade member 110 is selected as the inner blade member to be used for the fixed inner blade 54.

The pulverization conditions in the pulverization process in Example 1 of Second Example were set to a minimum blade face distance of 0.2 mm, a rotation speed of the rotary blade 40 of 8000 min ^-1 , and a processing amount of 70 kg/hr. As a result, in the pulverization process in Example 1 of Second Example, fine powdered plastic with an average particle size of 0.2 mm or less could be obtained.

In contrast, in the crushing process of Comparative Example 3, polyethylene with a nominal tensile break strain of 400% is crushed in the same manner as in the crushing process of Second Example 1. Then, during the crushing process, inner blade members are selected in which the blade tips of the rotating inner blade 44 and the fixed inner blade 54 do not cross. That is, in the crushing process of Comparative Example 3, although the measured value of the nominal tensile break strain of the granular plastic is equal to or greater than the threshold value, the first inner blade member 110 is selected as the inner blade member used for the rotating inner blade 44, and the first inner blade member 110 is selected as the inner blade member used for the fixed inner blade 54, as shown in Fig. 11. The crushing conditions are set to the same as in Second Example 1, with a minimum blade surface interval of 0.2 mm, a rotation speed of the rotating blade 40 of 8000 min ^-1 , and a processing amount of 70 kg/hr.

As a result, in the grinding process of Comparative Example 3, the processed product, granular plastic, melted, and fine powdered plastic could not be obtained.

In this way, in the crushing process of Example 1, the nominal tensile strain at break of the granular plastic to be crushed is measured. Then, based on the measured nominal tensile strain at break, the inner blade members to be used for the rotating blade member 42 and the fixed blade member 52 in the gradually reducing inter-face portion 61 formed on the rotating blade 40 and the fixed blade 50 are selected.

In other words, if the measured value of the nominal tensile strain at break of the granular plastic is less than the threshold value, the rotating side blade member 42 and the fixed side blade member 52 are configured so that their blade tips do not intersect when viewed from the axial direction of the rotating shaft 17 during the crushing process. Also, if the measured value of the nominal tensile strain at break of the granular plastic is equal to or greater than the threshold value, the rotating side blade member 42 and the fixed side blade member 52 are configured so that their blade tips intersect when viewed from the axial direction of the rotating shaft 17 during the crushing process.

As a result, as shown in FIG. 13, when granular plastic is pulverized by the pulverizer 10, melting of the material to be processed is suppressed, and the material can be pulverized appropriately. In addition, one of the setting conditions of the pulverizer 10 (the orientation of the blade tips of the rotary blade 40 and the fixed blade 50) can be easily determined by measuring the nominal tensile break strain, which is one of the physical properties of the granular plastic to be processed. Then, by adjusting the rotation speed of the rotary blade 40 and the minimum blade face spacing, the average particle size of the finely powdered plastic after pulverization can be controlled to an appropriate value, and the amount of material to be pulverized can be increased.

In addition, in Example 1, the threshold value of the nominal tensile breaking strain, which is the criterion for selecting the inner blade member used for the rotating side inner blade 44 and the inner blade member used for the fixed side inner blade 54, is set to a value greater than 20% and less than or equal to 400% (e.g., 100%). This allows the inner blade member to be set appropriately, and melting due to crushing of granular plastics can be suppressed.

The above describes the plastic crushing method of the present invention based on Example 1, but the specific configuration is not limited to Example 1, and design changes and additions are permitted as long as they do not deviate from the gist of the invention as defined by each claim in the scope of the claims.

In the first embodiment, the rotating side blade member 42 is composed of a rotating side inner blade 44 and a rotating side outer blade 45, and the fixed side blade member 52 is composed of a fixed side inner blade 54 and a fixed side outer blade 55. However, this is not limited to the above, and the rotating side inner blade 44 and the rotating side outer blade 45 may be integrally formed, or the fixed side inner blade 54 and the fixed side outer blade 55 may be integrally formed.

For example, the rotating outer blade 45 may be configured with multiple split blades that are divided in the circumferential direction.

In the crusher 10 of Example 1, a gradually reducing inter-face portion 61 and a constant inter-face portion 62 are formed between the rotary blade 40 and the fixed blade 50. However, since it is sufficient to have the gradually reducing inter-face portion 61, the constant inter-face portion 62 does not have to be formed.

In addition, in Example 1, the threshold value of the nominal tensile breaking strain, which is the criterion for selecting the inner blade member to be used for the rotating side inner blade 44 and the inner blade member to be used for the fixed side inner blade 54, is set to 100%. However, it can be set arbitrarily between 20% and 400% depending on the conditions during crushing, such as temperature and humidity. Furthermore, the threshold value may be set to a value outside the range of 20% to 400% as necessary.

REFERENCE SIGNS LIST 10 Grinder 11 Container 12 Supply port 13 Discharge port 17 Rotating shaft 20 Supply device 30 Powder separator 40 Rotating blade 41 Rotating side holding member 42 Rotating side blade member 44 Rotating side inner blade 45 Rotating side outer blade 50 Fixed blade 51 Fixed side holding member 52 Fixed side blade member 54 Fixed side inner blade 55 Fixed side outer blade 61 Gradually reducing inter-face portion
O1 Shaft center
O2 Center

Claims (3)

A method for crushing plastics using a crusher equipped with a rotary blade and a fixed blade, the blade surfaces of which are disposed in a container facing each other, comprising:
In the crusher, the rotating blade attached to the rotating shaft has a rotating side blade member having a plurality of linearly extending cutting edges that are aligned in a circumferential direction about the axis of the rotating shaft when viewed from the axial direction of the rotating shaft, and the fixed blade fixed to the container has a fixed side blade member having a plurality of linearly extending cutting edges that are aligned in a circumferential direction about the axis when viewed from the axial direction of the rotating shaft, and a gradually reducing inter-face portion is provided between the rotating side blade member and the fixed side blade member, in which the blade surface distance gradually decreases from the axis side toward the radially outward direction,
A measuring step of measuring a nominal tensile break strain of the plastic to be crushed before the crushing process by the crusher;
a selection step of selecting the rotating side blade member and the fixed side blade member based on the measured value of the nominal tensile strain at break, and setting the orientation of the blade edges at the gradually reducing inter-face portion when viewed from the axial direction of the rotating shaft during the crushing process. The method for crushing plastics according to claim 1,
the selection step selects the rotating side blade member and the fixed side blade member whose cutting edges do not intersect at the gradually reducing inter-face portion when viewed in the axial direction of the rotating shaft during the crushing process when the measured value of the nominal tensile strain at break is less than a predetermined threshold value, and selects the rotating side blade member and the fixed side blade member whose cutting edges intersect at the gradually reducing inter-face portion when viewed in the axial direction of the rotating shaft during the crushing process when the measured value of the nominal tensile strain at break is equal to or greater than the threshold value. The method for crushing plastics according to claim 2,
A method for crushing plastics, characterized in that the threshold value is set to a value greater than 20% and equal to or less than 400%.