JP7597439B2 - Waste plastic sorting device and waste plastic sorting method - Google Patents

Description

This disclosure relates to a waste plastic sorting device and a waste plastic sorting method.

Material recycling, in which new materials or products are produced using waste plastics, is known as the main method for reusing waste plastics derived from discarded home appliances, discarded automobiles, etc. Since collected waste plastics usually contain various types (materials) of plastics, in material recycling, the waste plastics must be sorted by material according to the recycled products to be produced.

One known method for sorting waste plastics is to irradiate pieces of waste plastic with light such as infrared light and use the spectrum of the reflected light obtained by the irradiation to determine the material of the plastic (for example, Patent Document 1).

JP 2018-100903 A

In order to produce high-quality products in material recycling, waste plastics need to be sorted with high precision. However, in conventional waste plastic sorting using the reflection of infrared light or other light, halation can occur depending on the intensity of the irradiated light, the irradiation distance, etc., and there are cases where it is not possible to obtain sufficient reflected light to generate a reflection spectrum that is effective for determining the material. Therefore, there is a demand for improved sorting precision in waste plastic sorting devices or methods that use light reflection.

Therefore, one aspect of the present invention aims to provide a sorting device that can sort waste plastic by material with high accuracy.

The waste plastic sorting device according to one aspect of the present invention includes a surface treatment section that treats the surfaces of waste plastic pieces, including black waste plastic pieces; an irradiation section that irradiates the surface-treated waste plastic pieces with light; a reflection spectrum detection section that receives reflected light of the light irradiated by the irradiation section and detects the spectrum of the reflected light; a determination section that determines the material of the waste plastic pieces based on the spectrum of the reflected light; and a sorting section that sorts at least the black waste plastic pieces by material based on the result of the determination.

This disclosure provides a sorting device that can sort waste plastic by material with high accuracy.

FIG. 1 is a perspective view showing a schematic configuration of a waste plastic sorting device according to an embodiment; FIG. 2 is a side view of the waste plastic sorting device shown in FIG. FIG. 2 is a plan view of the waste plastic sorting device shown in FIG. Schematic diagram showing an example of a surface treatment section Functional block diagram of the sorting device Flowchart of waste plastic material discrimination process according to the embodiment Diagram showing the method of extracting spectra for correction FIG. 13 is a diagram showing an example of a process for extracting a characteristic wavelength region from a reflected wave spectrum. A diagram showing an example of extracted feature data An example of material discrimination using a decision tree FIG. 2 is a plan view showing a first material sorting method using the sorting device of the present embodiment; FIG. 4 is a plan view showing a second material sorting method using the sorting device of the present embodiment; FIG. 11 is a plan view showing a third material sorting method using the sorting device of the present embodiment; FIG. 11 is a plan view showing a fourth material sorting method using the sorting device of the present embodiment. FIG. 11 is a plan view showing a fifth material sorting method using the sorting device of the present embodiment. FIG. 13 is a diagram showing an example of an operation screen of the sorting device.

The following describes the embodiments with reference to the attached drawings. To facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicate descriptions are omitted.

In the following description, the x, y, and z directions are perpendicular to each other. The x and y directions are horizontal, and the z direction is vertical. The x direction is the conveying direction of the conveying path 3 of the conveyor 2. The y direction is the width direction of the conveying path 3 of the conveyor 2. For ease of explanation, the positive z direction side may be referred to as the upper side, and the negative z direction side as the lower side. Additionally, the negative x direction side may be referred to as the upstream side, and the positive x direction side as the downstream side.

The schematic configuration of a waste plastic sorting device 1 according to one embodiment of the present invention will be described with reference to Figures 1 to 3. Figure 1 is a perspective view showing the schematic configuration of the waste plastic sorting device 1 according to this embodiment. Figure 2 is a side view of the waste plastic sorting device 1 shown in Figure 1. Figure 3 is a plan view of the waste plastic sorting device 1 shown in Figure 1. As shown in Figures 1 to 3, the waste plastic sorting device 1 is equipped with a surface treatment unit 20 upstream of the device.

The waste plastics sorted by the sorting device 1 according to the present embodiment are aggregates of waste plastic pieces (waste plastic piece group) obtained from waste home appliances, waste automobiles, etc., and formed by crushing. One waste plastic piece may have a plate-like or layer-like shape, and may have an average maximum length of 5 to 50 mm and an average area of 20 to 2500 ^mm2 in plan view. In this embodiment, waste plastic pieces of a predetermined material are sorted from an aggregate of waste plastic pieces (waste plastic piece group) including black waste plastic pieces, preferably from an aggregate of black waste plastic pieces (black waste plastic piece group). In addition, the waste plastic pieces sorted by this embodiment may contain colored waste plastic pieces of another color, such as blue or red, in addition to the black waste plastic pieces.

In this specification, black refers to a color with a brightness of 6 or less, as expressed in Munsell notation according to JIS 8721. The black color of black waste plastic pieces usually comes from the carbon black (carbon filler) contained in the black waste plastic pieces.

1 to 3 show, as an example, an apparatus for determining and separating waste plastic pieces of one material from a group of waste plastic pieces S1 made of one type of material and waste plastic pieces S2 made of a different type of material from the waste plastic pieces S1. In the following, the waste plastic pieces S1 and S2 may be collectively represented by the symbol S. The number of materials (types) of the waste plastic pieces separated from the group of waste plastic pieces is not particularly limited, and may be 2 to 10 types. Specific examples of plastic materials include polyethylene (PE), polypropylene (PP), polycarbonate/acrylonitrile-butadiene-styrene (PCABS), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polyphenylene ether/polystyrene (PPEPS), polyamide (PA), polycarbonate (PC), polyacetal (POM), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), etc.

In the waste plastic sorting device 1 according to this embodiment, the material of the waste plastic is determined based on the reflection spectrum detected from the reflected light obtained by irradiating the waste plastic with infrared light or the like, and the material is identified (details on the determination will be described later). Here, in the conventional configuration, when light is applied, depending on the intensity of the irradiated light, the irradiation distance, etc., strong regular reflection (specular reflection) occurs, and there are cases where the reflected light (diffuse reflected light) effective for determining the material is not obtained sufficiently. In contrast, the sorting device 1 according to this embodiment has a surface treatment unit 20, which processes the surface of the waste plastic pieces, making it possible to obtain appropriate reflected light.

In particular, black plastic has a weaker level (strength) of the material-specific absorption region compared to plastics of other colors, and is therefore more affected by the surface condition. In particular, when the gloss of the plastic surface is relatively high, the influence of infrared reflection from the plastic surface, particularly the influence of regular reflection (specular reflection), becomes greater, making it difficult to see the absorption level and distinguish the material. Therefore, by roughening the surface to a specified roughness through surface treatment, the influence of regular reflection of infrared rays from the plastic surface can be suppressed, and the spectral intensity of the reflected light spectrum can be increased, allowing the differences in reflection spectrum intensity due to material to be properly observed. As a result, the accuracy of sorting black plastic pieces can be improved.

The surface treatment by the surface treatment section 20 may be a treatment that, when irradiated with light, results in a surface state that allows a reflection spectrum effective for identifying the material to be obtained. For example, the surface treatment according to this embodiment may be a treatment that changes the surface state of the waste plastic pieces so that the glossiness (specular glossiness) (Gs60 (%)) at an incident angle of 60° measured in accordance with JIS Z 8741 is 10 or less. The glossiness at an incident angle of 60° may be preferably 8 or less, more preferably 6 or less, and even more preferably 1.5 or less. The glossiness at an incident angle of 60° may be 0.1 or more. Furthermore, the surface treatment according to this embodiment may be a treatment that changes the surface state so that the glossiness (specular glossiness) (Gs75 (%)) at an incident angle of 75° measured in accordance with JIS Z 8741 is 25 or less. The glossiness at an incident angle of 75° may be preferably 15 or less, more preferably 10 or less, and even more preferably 5 or less. The glossiness at an incidence angle of 75° may be 0.1 or more. The surface treatment in this embodiment is preferably performed so that the glossiness at an incidence angle of 60° falls within the above range, and the glossiness at an incidence angle of 75° falls within the above range. By having the above glossiness, particularly the glossiness at an incidence angle of 60° and/or the glossiness at an incidence angle of 75°, it is possible to impart an appropriate roughness to the surface of the plastic, thereby improving the sorting accuracy even when the waste plastic pieces are black plastic pieces.

The surface treatment according to this embodiment may be a treatment to change the surface condition of the waste plastic pieces so that the surface roughness mean deviation (SMD) is 1 μm or more. The surface roughness mean deviation may be preferably 1.1 μm or more, more preferably 1.2 μm or more. The surface roughness mean deviation may be preferably 6 μm or less, preferably 3 μm or less, more preferably 2.5 μm or less. By performing surface treatment to have a surface roughness mean deviation (SMD) in the above range, an appropriate rough surface condition can be imparted to the plastic surface. Therefore, even if the waste plastic pieces are black plastic pieces, an appropriate reflection spectrum can be obtained, and sorting accuracy can be improved.

In addition, by making 50% or more, and preferably 80% or more, of the total surface area of the waste plastic pieces satisfy one or more of the following conditions: gloss (specular gloss (%)) at an incident angle of 60° measured in accordance with JIS Z 8741 is 10 or less, gloss (specular gloss (%)) at an incident angle of 75° measured in accordance with JIS Z 8741 is 25 or less, and the surface roughness mean deviation (SMD) is 1 μm or more, the sorting accuracy of the waste plastic pieces using infrared rays can be improved.

The surface treatment in this embodiment may be a roughening treatment or a smoothening treatment depending on the surface condition of the original waste plastic pieces. The surface treatment may be a wet treatment using a liquid, or a dry treatment not using a liquid. Specific examples of surface treatment include polishing (or grinding) using an abrasive tool such as a wire brush or sandpaper and/or an abrasive, and surface treatment using chemicals. Of these, polishing is preferred because it generates relatively little waste and is easy to dispose of.

Figure 4 is a schematic diagram of an example of the surface treatment section 20. The surface treatment section 20 shown in Figure 4 is equipped with multiple rollers with rough surfaces. By passing the waste plastic pieces S' before surface treatment between the multiple rollers, the surface of the waste plastic pieces S' is scraped, forming fine irregularities and/or eliminating excessively large irregularities, thereby obtaining waste plastic pieces S with appropriately sized irregularities. The surface of the waste plastic pieces with appropriately sized irregularities has the above-mentioned specified glossiness, and the plastic type can be determined with higher accuracy by using light irradiation in the sorting device 1.

In the surface treatment section 20 shown in FIG. 4, a large roller 21 that rotates in the direction of transport of the waste plastic pieces and small-diameter rough-surface rollers 23, 23, 23 that face the large roller 21 and rotate in the opposite direction to the large roller 21 are arranged. Brushes or sandpaper are attached to the surfaces of the rough rollers 23, 23, 23. The waste plastic pieces S' before surface treatment supplied from the supply section 28 are supplied between the large roller 21 and the rough rollers 23, 23, 23, and are transported in the transport direction, while the surface facing the rough rollers 23, 23, 23 is roughened. In the surface treatment section 20, downstream of the large roller 21 and the rough rollers 23, 23, 23, another large roller 22 that rotates in the direction of transport of the waste plastic pieces and small-diameter rough-surface rollers 25, 25, 25 that face the large roller 22 and rotate at high speed in the opposite direction to the large roller 22 are arranged. The rough-surface rollers 25, 25, 25 are fitted with brushes or sandpaper, similar to the rough-surface rollers 23, 23, 23. The large roller 22 and the rough-surface rollers 25, 25, 25 are arranged so that the surface of the waste plastic pieces S' opposite to the surface roughened by the rough-surface rollers 23, 23, 23 is roughened. With this configuration, both sides of the waste plastic pieces S' have an appropriate surface condition for the material judgment in the sorting device 1, and sorting by material can be performed with high accuracy. The rotation speeds of the rough-surface rollers 23, 23, 23 and the rough-surface rollers 25, 25, 25 can be set according to the desired surface condition of the waste plastic pieces. The appropriate surface condition can be one that satisfies one or more of the following conditions: gloss (specular gloss (%)) at an incident angle of 60° measured in accordance with JIS Z 8741 is 10 or less, gloss (specular gloss (%)) at an incident angle of 75° measured in accordance with JIS Z 8741 is 25 or less, and the surface roughness mean deviation (SMD) is 1 μm or more. In the case of waste plastic pieces that contain or consist of black plastic pieces, the above surface condition can improve sorting accuracy.

The waste plastic pieces are obtained by removing plastic parts from discarded home appliances, discarded automobiles, etc., and then crushing them to reduce their size to make them easier to reuse. The surface treatment in this embodiment may be incorporated into the crushing process.

Referring again to Figures 1 to 3, the processing of the waste plastic pieces S after surface treatment in the sorting device 1 will be described. The main components include a vibrating feeder 8 as an example of a supply unit that sequentially supplies the waste plastic pieces S1 and S2 after surface treatment obtained from the surface treatment unit 20, and a conveyor 2 as an example of a transport unit that transports the waste plastic pieces S1 and S2 supplied by the vibrating feeder 8. The crushed (surface-treated) waste plastic pieces S1 and S2 are supplied to the vibrating feeder 8, for example, via an input hopper or the like. The vibrating feeder 8 vibrates the loading surface on which the waste plastic pieces S1 and S2 are placed, thereby supplying the waste plastic pieces S1 and S2 to the conveyor 2 while preventing them from overlapping with each other. The conveyor 2 has a transport path 3 on its upper surface, and transports the waste plastic pieces S1 and S2 on the transport path 3 in a direction away from the vibrating feeder 8.

The sorting device 1 also includes a light 10 as an example of an irradiation unit that irradiates the waste plastic pieces S1 and S2 with infrared rays, a mid-infrared camera 4 as an example of a reflection spectrum detection unit that detects the reflection spectrum from the waste plastic pieces S1 and S2, and a discrimination device 5 that determines or identifies the material of the waste plastic pieces S1 and S2 based on the reflection spectrum detected by the mid-infrared camera 4.

The lighting 10 has a lamp 10A (see FIG. 7) that is an infrared light source such as a halogen tungsten lamp, and emits infrared rays from the lamp 10A toward the waste plastic pieces S1 and S2. The lighting 10 is also installed so that reflected light from the waste plastic pieces S1 and S2 enters the mid-infrared camera 4, and is installed on both upper sides (or one upper side) of the conveyor 2 in the flow direction relative to the mid-infrared camera 4.

The light irradiated onto the waste plastic pieces may include infrared light of 2 to 8 μm, preferably mid-infrared light of more than 3 μm, more specifically infrared light of more than 3 μm and 8 μm or less. The mid-infrared light in the above wavelength range includes a region where the light absorption rate of black plastic is relatively low, so even for black waste plastic, it is possible to obtain a reflected light spectrum that is effective for determining the plastic material (a reflected light spectrum in which significant differences can be observed depending on the material).

As shown in FIG. 1, for example, one mid-infrared camera 4 can measure the entire width direction (y direction) of the conveyor 2, divide the conveyor 2 into multiple (e.g., 318) regions along the width direction, receive near-infrared reflected light from the black waste plastic pieces S1 and S2, and measure the spectrum of the reflected light for each region. The mid-infrared camera 4 may be, for example, a camera equipped with a spectrometer in the infrared wavelength range of 3 μm or more or more than 3 μm. The mid-infrared camera 4 performs measurements at a scan frequency of, for example, 230 Hz, and transmits 318 pieces of spectral data to the discrimination device 5 for each scan. The discrimination device 5 outputs the material judgment results for each of the 318 regions based on the 318 pieces of spectral data received from the mid-infrared camera 4 to the injection control unit 6 described below.

The reflected light received by the mid-infrared camera 4 may preferably include infrared rays in a wavelength range of more than 3 μm, more preferably more than 3 μm and 8 μm or less, and even more preferably more than 3 μm and 5 μm or less. By receiving reflected light in the above wavelength range, data useful for determining the material of black waste plastic can be obtained. In other words, significant differences due to material can be observed in the spectral intensity of reflected light in the above wavelength range.

Furthermore, the sorting device 1 is equipped with an injection nozzle row 7 that injects air horizontally or obliquely in a direction intersecting the conveying direction (x direction) downstream of the conveying direction of the conveyor 2. The injection nozzle row 7 is composed of a plurality of injection nozzles (e.g., 318) arranged in the width direction (y direction) of the conveyor 2, and the operation of each injection nozzle is controlled by the injection control unit 6. The injection control unit 6 can inject air from the injection nozzles of the injection nozzle row 7 or not inject air according to the material judgment result received from the discrimination device 5. That is, it is possible to select the target waste plastic pieces and blow air onto them (selective blowing). Then, for example, the black waste plastic pieces S1 and S2 are sorted and dropped into a plurality of areas (e.g., a collection hopper or container) divided by a partition plate 9 (Figure 2), and the waste plastic of the desired material is separated and collected. In other words, in this embodiment, the injection control unit 6 and the injection nozzle row 7 function as a sorting unit 12 that collects pieces of the desired material from the waste plastic pieces flowing along the transport path 3 of the conveyor 2 based on the material determination results from the discrimination device 5.

In the example shown in Figures 1 to 3, the sorting unit 12 uses a jet of air or a specified gas to selectively blow or not blow away the waste plastic pieces S on the conveyor 2, but the sorting method is not limited to that shown in the figure. For example, information on the material determination results by the discrimination device 5 may be sent to a robot arm, and the robot arm may sort the waste plastic pieces by their material, separating the waste plastic pieces.

The operation of the sorting device 1, i.e., the processing of waste plastic pieces supplied from the surface treatment unit 20, will be described below. For example, when the crushed waste plastic pieces S1 and S2 are supplied to the vibrating feeder 8 via an input hopper or the like, the vibrating feeder 8 vibrates the supplied waste plastic pieces S1 and S2, transporting them downstream while preventing them from overlapping, and supplies them to the conveyor 2.

The waste plastic pieces S1 and S2 supplied to the conveying path 3 on the upper surface of the conveyor 2 are conveyed in the conveying direction in the positive x direction, and infrared light is irradiated from the lighting 10 at a position where the mid-infrared camera 4 can capture the images. The mid-infrared camera 4 receives the infrared light emitted from the lighting 10 and reflected by the waste plastic pieces S1 and S2, and outputs the light reception result (received light spectrum data) to the discrimination device 5.

The discrimination device 5 identifies the material of the waste plastic pieces S1 and S2 based on the light reception results input from the mid-infrared camera 4. Details of the material determination method used by the discrimination device 5 will be described later with reference to Figures 5 to 10. The discrimination device 5 outputs the material identification results to the injection control unit 6.

The injection control unit 6 selects an injection nozzle corresponding to the material from among the multiple injection nozzles arranged in the injection nozzle row 7, and transmits a control signal at the appropriate timing. Each injection nozzle in the injection nozzle row 7 that receives the control signal opens its nozzle opening and injects air. By injecting air from the injection nozzle at an appropriate timing based on the discrimination result of the discrimination device 5, the material to be sorted can be separated from other materials and recovered.

In the example shown in Figures 1 to 3, the waste plastic pieces S1 on the conveyor 2 receive air from the air injection nozzle that has received the control signal, are blown away, fall, and are collected in a collection container or the like. Also, the black waste plastic pieces S2 on the conveyor 2 do not receive air from the injection nozzle, so are collected in a collection container or the like different from the black waste plastic pieces S1. In this way, by individually injecting and stopping the multiple injection nozzles included in the injection nozzle row 7, it is possible to sort and collect waste plastic pieces of a specific material from a group of waste plastic pieces of multiple materials.

In addition, according to this embodiment, the waste plastic pieces to be sorted are surface-treated and have a predetermined surface roughness, preferably on both sides, so that they have an appropriate coefficient of friction with the conveyor 2. Therefore, in the sorting section 12, the targeted waste plastic pieces are reliably blown away, and the non-targeted waste plastic pieces are reliably not blown away, which also contributes to improving sorting accuracy.

Next, the material determination and discrimination of waste plastics by the discrimination device 5 will be described with reference to Figures 5 to 10. Figure 5 is a functional block diagram of the discrimination device 5.

As shown in FIG. 5, the discrimination device 5 has a preprocessing unit 51, and further has a first judgment unit 52, a second judgment unit 53, and a third judgment unit 54 (collectively referred to as the judgment units).

The pre-processing unit 51 performs pre-processing such as correcting and processing the reflection spectrum of the black waste plastic pieces S1 and S2 detected by the mid-infrared camera 4. For example, the pre-processing unit 51 corrects the detected reflection spectrum using a spectrum measured under conditions where the reflected light is bright and a spectrum measured under conditions where the reflected light is dark. "Dark conditions (dark conditions)" refers to conditions that are relatively darker than the above-mentioned "bright conditions (light conditions)." In addition, the pre-processing unit 51 performs processing to extract a specified frequency range from the corrected reflection spectrum.

The first determination unit 52 determines whether the spectrum detected by the mid-infrared camera 4 is from the waste plastic pieces S1, S2, or the conveying path 3 of the conveyor 2. The first determination unit 52 makes the determination using a trained One Class SVM (Support Vector Machine).

One Class SVM is a type of SVM, which is a type of machine learning classification algorithm. In SVM, the support vector of each class (the one closest to other classes in the training data) is used as the basis, and the classification boundary is set so that the Euclidean distance between them is maximized. In addition, if the features are nonlinear, a kernel is used to map the data into the feature space. By appropriately selecting the kernel, it is possible to draw the classification boundary even with a complex data arrangement.

In One Class SVM, a method called the kernel trick is used for one type of training data to map the data into a high-dimensional feature space. At this time, the training data is mapped so that it is placed far away from the origin, so data that is not similar to the original training data is gathered near the origin. This property is used to distinguish between normal data (conveyor 2) and abnormal data (objects (waste plastic pieces S1, S2)).

By using a One Class SVM with excellent pattern recognition capabilities in the first judgment unit 52, it is possible to accurately identify whether the reflection spectrum is reflected by the waste plastic pieces S1 and S2 or the conveying path 3 of the conveyor 2. Note that a supervised learning classification method of machine learning other than the One Class SVM may be applied to the first judgment unit 52.

The second determination unit 53 extracts feature data Score1 and Score2 (feature amounts) from the spectrum determined to be a waste plastic piece by the first determination unit 52. The feature amount may be, for example, the maximum value, average value, or integral value of the spectral intensity in a specified wavelength region, but it is preferable to extract the feature amount using a trained PLS (Partial Least Squares) method.

PLS is a type of regression algorithm for supervised learning in machine learning, and performs regression analysis between only a small number of principal components calculated from explanatory variables and the objective variable. In PLS, the principal components are calculated so that their covariance with the objective variable is large. In this embodiment, two types of feature data, Score1 and Score2, are calculated using PLS based on the explanatory variables of the reflection spectra determined to be reflected by the waste plastic pieces S1 and S2.

By using PLS in the second judgment unit 53, the multidimensional explanatory variables of the reflectance spectrum can be reduced to a small number of feature quantities, so that appropriate feature data Score1 and Score2 that are easier to distinguish can be extracted. Note that the second judgment unit 53 may also use a machine learning multivariate analysis method other than PLS.

The third judgment unit 54 judges the material of the waste plastic pieces S1, S2 corresponding to the reflection spectrum based on the two feature values Score1, Score2 extracted by the second judgment unit 53. The third judgment unit 54 makes the judgment using a trained decision tree. A decision tree is a type of classification algorithm for supervised learning. A decision tree represents the rules for classifying the objective variable in a tree structure, and is frequently used in classification problems.

By using a decision tree in the third judgment unit 54, the material of the waste plastic pieces S1 and S2 can be accurately determined from the two feature amounts Score1 and Score2 of the reflection spectrum. Note that a supervised learning classification method of machine learning other than the decision tree may also be applied to the third judgment unit 54.

The discrimination device 5 can be physically configured as a computer system including a CPU (Central Processing Unit), a RAM (Random Access Memory) and a ROM (Read Only Memory) as main storage devices, a communication module, an auxiliary storage device, and the like. Each function of the discrimination device 5 shown in FIG. 5 is realized by loading a specific computer software (material determination program) into the CPU, RAM, etc., and operating various hardware under the control of the CPU and reading and writing data in the RAM. That is, by executing the material determination program according to this embodiment on a computer, the discrimination device 5 functions as the preprocessing unit 51, the first determination unit 52, the second determination unit 53, and the third determination unit 54 of FIG. 5.

The material discrimination program of this embodiment is stored, for example, in a storage device provided in a computer. Note that the material discrimination program may be configured so that a part or all of it is transmitted via a transmission medium such as a communication line, and is received and recorded (including installed) by a communication module or the like provided in the computer. Also, the material discrimination program may be configured so that a part or all of it is recorded (including installed) in the computer from a state in which it is stored in a portable storage medium such as a CD-ROM, DVD-ROM, or flash memory.

The discrimination device 5 may be a circuit configured with an analog circuit, a digital circuit, or an analog-digital mixed circuit. It may also be equipped with a control circuit that controls each function of the discrimination device 5. Each circuit may be implemented using an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), etc.

Similarly, the injection control unit 6 can also be physically configured as a computer system including a CPU, RAM, ROM, a communication module, an auxiliary storage device, etc., and its functions are realized by loading specific computer software into the CPU, RAM, etc.

Figure 6 is a flowchart of the process for determining the material of waste plastic according to the embodiment. Each process in the flowchart shown in Figure 6 is executed by the determination device 5.

In step S01, the pre-processing unit 51 acquires a spectrum S _org (n, w) by the mid-infrared camera 4. Here, n is the number of sensors (the number of spectrum detection regions divided in the width direction of the conveyor 2 by the mid-infrared camera 4), and when the number of sensors is 318, an integer from 0 to 317 corresponding to each detection region is used. w is the wavelength of the spectrum, and in this embodiment, a total of 131 wavelengths are set in increments of 20 (nm) between 2700 (nm) and 5300 (nm), and an integer from 0 to 130 corresponding to each wavelength is used. In other words, S _org (n, w) represents the numerical value of the spectrum intensity of wavelength w in the n-th spectrum detection region along the width direction of the conveyor 2.

In step S02, the pre-processing unit 51 corrects the spectrum _Sorg (n,w) acquired in step S01 to calculate a corrected spectrum _Scor (n,w). This correction absorbs differences in the characteristics of the spectral intensity due to the influence of changes in the concentrations of water vapor and carbon dioxide in the measurement space, the temperatures of the black waste plastic pieces S1 and S2 to be measured, deterioration of the lighting 10 and the mid-infrared camera 4 over time, the position on the conveyor 2, etc. The corrected spectrum _Scor (n,w) can be calculated, for example, by the following formula (1).

上式中、W_ref（ｎ，ｗ）は、反射光が明るい条件で計測した第１の補正用スペクトルである。D_ref（ｎ，ｗ）は、反射光が上記の明るい条件よりも暗い条件で計測した第２の補正用スペクトルである。これらの補正用スペクトルW_ref（ｎ，ｗ）、D_ref（ｎ，ｗ）は、例えば、材質判別処理を実行する前に中赤外線カメラ４の校正を行うときに抽出できる。

In the above formula, _Wref (n,w) is a first correction spectrum measured under conditions where the reflected light is bright. _Dref (n,w) is a second correction spectrum measured under conditions where the reflected light is darker than the above-mentioned bright conditions. These correction spectra _Wref (n,w) and _Dref (n,w) can be extracted, for example, when calibrating the mid-infrared camera 4 before executing the material discrimination process.

Fig. 7 is a diagram showing a method for extracting the correction spectra W _ref (n, w) and D _ref (n, w). As shown in Fig. 7, a calibration plate 11 for acquiring the correction spectra is placed in the imaging area of the mid-infrared camera 4 on the transport path 3 of the conveyor 2, and the spectrum of reflected light is detected by the mid-infrared camera 4, whereby the correction spectra W _ref (n, w) and D _ref (n, w) can be acquired.

In the case of the first correction spectrum W _ref (n, w) measured under conditions of bright reflected light, a calibration plate 11 (aluminum, stainless steel, etc.) that reflects all wavelengths in the mid-infrared region is placed, and with the light 10 turned on, data is obtained for all wavelengths (w = 0 (2700), 2 (2720), ..., 130 (5300)) for all sensors (n = 0, 1, 2, ..., 317).

In the case of the second correction spectrum D _ref (n, w) measured under conditions of low reflected light, a calibration plate 11 (aluminum, stainless steel, etc.) that reflects all wavelengths in the mid-infrared region is placed, and data for all wavelengths (w = 0 (2700), 2 (2720), ..., 130 (5300)) is acquired for all sensors (n = 0, 1, 2, ..., 317) with the illumination 10 turned off (or the camera shutter closed).

The calibration plate 11 is preferably installed so as to be movable between the position of the imaging area of the mid-infrared camera 4 on the conveying path 3 of the conveyor 2, where the calibration plate 11 is placed when acquiring the correction spectra W _ref (n, w) and D _ref (n, w), as shown by the dotted arrow in FIG. 7, and a standby position outside the imaging area of the mid-infrared camera 4 and the irradiation range of the illumination 10. In other words, the calibration plate 11 is preferably fixable to a predetermined position within the field of view of the mid-infrared camera 4 and a predetermined position outside the field of view, and is preferably movable between both predetermined positions. The calibration plate 11 is preferably processed so that the main surface that receives the light from the illumination 10 has a large surface roughness and is a rough surface. This makes it possible to suppress the occurrence of halation of reflected light on the calibration plate 11.

The conveyor 2 may be stopped when the correction spectrum is acquired. In this case, if the calibration plate 11 is not correctly positioned in the imaging area of the mid-infrared camera 4 due to some malfunction in the operation of the calibration plate 11, the temperature of the portion of the conveyor 2's transport path 3 irradiated with infrared rays from the lighting 10 will rise, which may cause burning or fire. For this reason, if the calibration plate 11 is not fixed within the field of view of the mid-infrared camera 4, it is preferable to provide an interlock so that infrared rays are not irradiated from the lighting 10.

As shown in FIG. 7, the lighting 10 has a lamp 10A (sheath heater, carbon lamp, Kanthal lamp, etc.) that is an infrared light source, and a reflector 10B that collects heat from the lamp 10A. The lamp 10A is formed to extend along the width direction (y direction) of the conveyor 2, and is arranged to radiate infrared rays in all directions around the axis along the y axis. The reflector 10B is arranged on the opposite side of the conveyor 2 from the conveying path 3 with respect to the lamp 10A, and is curved along the circumferential direction around the axis of the lamp 10A, so that it can collect infrared rays radiated from the lamp 10A to the opposite side of the conveyor 2 and reflect them to the conveyor 2 side. The reflector 10B is made of a material such as aluminum, stainless steel, or aluminum-plated material.

Returning to FIG. 6, in step S03, the preprocessing unit 51 extracts a characteristic wavelength region from the corrected spectrum S _cor (n, w). FIG. 8 is a diagram showing an example of a process for extracting a characteristic wavelength region from a reflected wave spectrum obtained when infrared rays are irradiated onto black waste plastic pieces. The horizontal axis of FIG. 8 indicates the wavelength (nm) of the spectrum, and the vertical axis indicates the intensity of the spectrum at each wavelength. FIG. 8 shows an example of the spectrum of each material, acrylonitrile-butadiene-styrene (ABS), high impact polystyrene (HIPS), polypropylene (PP), and polyethylene (PE). In the example of FIG. 8, the spectra of the wavelength regions of 3250 to 3750 (nm) and 4400 to 4600 (nm) are extracted. Therefore, when sorting black plastics by material, the spectrum of at least one of the wavelength regions in the above ranges can be used.

Returning to FIG. 6, in step S04, the first judgment unit 52 uses the spectrum corrected in step S02 and from which characteristic wavelength regions have been extracted in step S03 to judge whether each spectrum is the belt of the conveyor 2 (the conveying path 3) or an object on the conveying path 3 (waste plastic). In this embodiment, the first judgment unit 52 makes the judgment using a trained One Class SVM.

In step S05, the second judgment unit 53 extracts two types of feature data Score1 and Score2 from the spectrum judged to be an object (waste plastic) in step S04 using the trained PLS. FIG. 9 is a diagram showing an example of extracted feature data. The horizontal axis of FIG. 9 indicates the first feature data (Score1), and the vertical axis indicates the second feature data (Score2). FIG. 9 shows an example of extraction of four types of materials, ABS, HIPS, PP, and PE, as exemplified in FIG. 8. As shown in FIG. 9, it can be seen that the areas plotted for each material can be divided in a two-dimensional space using the two feature data Score1 and Score2. The number of types of feature data may be other than two.

Returning to FIG. 6, in step S06, the third judgment unit 54 uses a learned decision tree to determine the material based on the two types of feature data Score1 and Score2 extracted in step S5. FIG. 10 is a diagram showing an example of material determination using a decision tree. In this embodiment, in order to ultimately identify four types of materials (PE, PP, ABS, HIPS), the decision tree has two levels of conditional branching as shown in FIG. 10. In the first level, the set of feature data Score1 and Score2 is divided into two groups G1 and G2 using the conditional branching function f1 (Score1, Score2). In the second level, the group G1 is further divided into two groups G11 and G12 using the conditional branching function f2 (Score1, Score2). The other group G2 is further divided into two groups G21 and G22 using the conditional branch function f3 (Score1, Score2) in the second layer. As a result, the set of feature data Score1 and Score2 is classified into four groups G11, G12, G21, and G22, and the materials of each group are determined to be PE, PP, ABS, and HIPS, respectively.

Thus, the discrimination device 5 of the waste plastic material discrimination/sorting device 1 according to this embodiment includes a first discrimination unit 52 that discriminates whether the spectrum of the reflected light of the light irradiated by the light 10 onto the conveyor 2's transport path 3, detected by the mid-infrared camera 4, is that of the waste plastic piece S or the transport path 3, a second discrimination unit 53 that extracts two types of characteristic data Score 1 and Score 2 from the spectrum that has been determined to be that of the waste plastic piece S by the first discrimination unit 52, and a third discrimination unit 54 that discriminates the materials S1 and S2 of the waste plastic piece S based on the characteristic data Score 1 and Score 2 extracted by the second discrimination unit 53.

With this configuration, output information on the material of the waste plastic can be obtained through three stages of judgment processing and data narrowing: narrowing down the spectrum of black waste plastic pieces S by object discrimination in the first judgment unit 52, dimensional compression from the spectrum information to feature data by feature extraction in the second judgment unit 53, and classification processing in the third judgment unit 54. Therefore, the waste plastic sorting device 1 of this embodiment can judge the material of the waste plastic taking into account various conditions, and can perform detailed judgment over multiple stages, improving the accuracy of the judgment of the material of the waste plastic.

In addition, the discrimination device 5 of the waste plastic sorting device 1 in this embodiment is equipped with a pre-processing unit 51 that corrects the reflection spectrum S _org (n, w) detected by the mid-infrared camera 4 using a first correction spectrum W _ref (n, w) measured under conditions where the reflected light is bright, and a second correction spectrum D _ref (n, w) measured under conditions that are relatively darker than these bright conditions.

In this way, by correcting the reflection spectrum _Sorg (n,w) using the correction spectra _Wref (n,w) and _Dref (n,w) using, for example, equation (1), it is possible to suppress differences in the characteristics of the spectral intensity due to the influences of the temperature of the black waste plastic pieces S1 and S2 to be measured, the deterioration of the mid-infrared camera 4 over time, the position on the conveyor 2, etc. Therefore, by using the corrected spectrum _Scor (n,w) to perform learning and judgment in the first judgment unit 52, the second judgment unit 53, and the third judgment unit 54, the accuracy of judgment of the material of the waste plastic can be further improved.

The pre-processing unit 51 further processes the corrected spectrum S _cor (n, w) by extracting a predetermined frequency range from the spectrum, and outputs the processed spectrum to the first determination unit 52 .

This configuration allows the parts of the spectrum that are closely related to the material of the waste plastic to be extracted and used for learning and judgment by the first judgment unit 52, the second judgment unit 53, and the third judgment unit 54, thereby reducing the inclusion of noise that impedes learning and judgment, and further improving the accuracy of judging the material of the waste plastic.

In this embodiment, the pre-processing unit 51 performs two processes, namely, a process of correcting the reflection spectrum S _org (n, w) and a process of extracting a predetermined frequency range, but may be configured to perform only one of the two processes.

Furthermore, with reference to Figures 11 to 15, a method for sorting waste plastics of a desired material using the sorting device 1 of this embodiment will be described. Figure 11 is a plan view showing a first material sorting method using the sorting device 1 of this embodiment. Figure 11 shows a simplified diagram corresponding to the plan view of the sorting device 1 shown in Figure 3. Figures 11 and onwards will explain an example of a sorting method in which a plastic mix containing waste plastic pieces of five different materials (1), (2), (3), (4), and (5) is to be sorted.

In the example of FIG. 11, a configuration is illustrated in which the conveyor 2 and the sorting section 12 form a single transport path that is not divided in the width direction (y direction) of the conveyor 2. In the sorting section 12, the waste plastic is separated into two major types by the jetting and stopping of each jet nozzle of the jet nozzle row 7, with the partition plate 9 shown in FIG. 2 as the boundary. Therefore, in order to separate the plastic mix containing five types of materials to be sorted into each individual material, it is necessary to repeat the process of separating each type into one of the sorting sections 12-1 (for example, a device that collects waste plastics sprayed with air from the jet nozzle 7) of the sorting section 12. In other words, as shown in FIG. 11, first, only waste plastic pieces of material (1) are selected from the plastic mix and collected in the sorting section 12-1. At this time, the remaining plastic mix collected in the other sorting section 12-2 contains the other four types of materials (2) to (5). Next, the remaining plastic mix containing the four types is again fed into the sorting device 1, and one of the materials (2) to (5) is selected. By repeating this procedure four times, the five types of waste plastic pieces (1) to (5) can be separated by material.

Figure 12 is a plan view showing the second material sorting method by the sorting device 1A of this embodiment. From Figure 12 onwards, the transport path 3 of the conveyor 2 is divided into two systems, a first system and a second system, in the width direction. More specifically, the inlet (vibration feeder 8), the conveyor 2, and the sorting section 12 are each divided into two systems in the width direction. Note that the inlet 8 and the conveyor 2 are not divided into two components, but rather a single element is provided with a partition or the like to prevent mixing between the systems. For example, the transport path 3 of the conveyor 2 can be divided into two systems by providing a partition wall along the transport direction at approximately the center position in the width direction.

In the following description, the first system is denoted with the suffix A, and the second system is denoted with the suffix B. Additionally, elements corresponding to sorting unit 12-1 in FIG. 11 are denoted as "sorting unit A1" and "sorting unit B1," and elements corresponding to sorting unit 12-2 in FIG. 11 are denoted as "sorting unit A2" and "sorting unit B2."

In the example of Figure 12, waste plastic pieces of the same material are collected in the first and second systems. For example, as shown in Figure 12, a plastic mix containing waste plastic pieces of five different materials (1) to (5) is supplied to the inlets A and B of the first and second systems, respectively, and material determination is performed in each system, and waste plastic pieces of the same material (1) are collected in sorting sections A1 and B1. In addition, waste plastic pieces containing the remaining materials (2) to (5) other than material (1) are collected in sorting sections A2 and B2.

Figure 13 is a plan view showing a third material sorting method using the sorting device 1B of this embodiment. In the example of Figure 13, the first system collects waste plastic pieces of a first material and supplies the remaining waste plastic pieces to the second system, which collects waste plastic pieces of a second material from among the remaining waste plastic pieces. In the example of Figure 13, multiple types of mixed materials can be separated into three types: the first material, the second material, and other materials.

In the example of Figure 13, a plastic mix containing waste plastic pieces of five different materials (1) to (5) is supplied to the inlet A of the first system, the material is determined by the conveyor A of the first system, and the waste plastic pieces of material (1) are collected in the sorting section A1. In addition, the remaining waste plastic pieces containing materials (2) to (5) are collected in the sorting section A2.

Next, the remaining waste plastic mixed with materials (2) to (5) collected in sorting section A2 is transported by conveying device 13 to inlet B of the second system and supplied to inlet B. Material determination is performed on the second system conveyor B, and waste plastic pieces of material (2) are collected in sorting section B1. In sorting section B2, the remaining waste plastic pieces mixed with materials (3) to (5) are collected.

Figure 14 is a plan view showing a fourth material sorting method using the sorting device 1C of this embodiment. In the example of Figure 14, the first system collects waste plastic pieces of a first material and trace amounts of other materials, and supplies the collected waste plastic pieces to the second system, which collects waste plastic pieces of the first material from the waste plastic pieces of the first material and trace amounts of other materials. In the example of Figure 14, plastic pieces of a specific type of material can be sorted to a high purity.

In the example of Figure 14, a plastic mix containing five types of materials (1) to (5) is supplied to the first system's inlet A, the materials are determined on the first system's conveyor A, and the waste plastic pieces of material (1) and trace amounts of materials (2) to (5) are collected in the sorting section A1. In addition, the remaining waste plastics containing materials (2) to (5) and trace amounts of material (1) are collected in the sorting section A2.

Next, the waste plastics collected in sorting section A1, which are a mixture of material (1) and trace amounts of (2) to (5), are transported by conveying device 13 to inlet B of the second system and supplied to inlet B. The material is determined by conveyor B of the second system, and material (1) is sorted again in sorting section B1, and waste plastic pieces of material (1) are collected. The material (1) collected in sorting section B1 has a higher purity of material (1) than the material collected in sorting section A1. In sorting section B2, the remaining waste plastics mixed with materials (1) to (5) are collected.

Figure 15 is a plan view showing a fifth material sorting method using the sorting device 1D of this embodiment. In the example of Figure 15, in the first system, waste plastic pieces of the first material and trace amounts of other materials are removed, and the remaining removed waste plastic pieces are supplied to the second system, and in the second system, waste plastic pieces of the first material and trace amounts of other materials are further removed from the other waste plastic pieces, and waste plastic pieces not containing the first material are collected. In the example of Figure 15, plastic pieces of a specific type of material can be more reliably sorted from mixed materials.

In the example of Figure 15, a plastic mix containing five types of materials (1) to (5) is supplied to the first system's inlet A, the materials are determined on the first system's conveyor A, and waste plastic pieces of material (1) and small amounts of materials (2) to (5) are collected in sorting section A1. In addition, waste plastics containing the remaining materials (2) to (5) and a small amount of (1) are collected in sorting section A2.

The waste plastic collected in sorting section A2, which is a mixture of materials (2) to (5) and a small amount of (1), is then transported by conveying device 13 to inlet B of the second system and supplied to inlet B. The material is determined by conveyor B of the second system, and material (1) is again sorted in sorting section B1, and waste plastic pieces containing a mixture of material (1) and traces of materials (2) to (5) are collected. In sorting section B2, the remaining waste plastic containing a mixture of materials (2) to (5) and a trace amount of (1) is collected.

Figure 16 is a diagram showing an example of the operation screen of the sorting device 1. The operation screen shown in Figure 16 is displayed, for example, on a display device installed in the material sorting device 1. As shown in Figure 16, the operation screen lists the names of the plastic materials to be sorted, and the materials to be sprayed and sorted for each of the first system ("primary" in Figure 16 and the second system ("secondary" in Figure 15) can be individually selected. The display device on which the operation screen is displayed is, for example, a touch panel, and by switching the "OFF" display in the "Spray selection" column to "ON" by pressing the "OFF" display, it is possible to set the injection nozzles of the injection nozzle row 7 to inject air and separate the material in the sorting section in the case of the material (ABS in Figure 16). In addition, the operation screen also has a "Raw material input area ratio" column, which can display the ratio of each material to be mixed into the material depending on the result of the material judgment process.

In the above, the waste plastic sorting device has been mainly described as including a surface treatment section 20 that treats the surface of the waste plastic pieces, but the sorting device may be in a form that does not include the surface treatment section 20. That is, another embodiment of the present invention is a waste plastic sorting device that includes an irradiation section that irradiates light onto waste plastic pieces including black waste plastic pieces that have been surface-treated, a reflection spectrum detection section that receives reflected light of the light irradiated by the irradiation section and detects the spectrum of the reflected light, a judgment section that judges the material of the waste plastic pieces based on the spectrum of the reflected light, and a sorting section that sorts at least the black waste plastic pieces by material based on the result of the judgment. That is, the sorting device may be in a form that allows the input of waste plastic pieces that have already been surface-treated. In this case, the surface-treated waste plastic pieces may be treated so that their surfaces satisfy one or more of the following conditions: a glossiness (specular glossiness (%)) at an incident angle of 60° measured in accordance with JIS Z 8741 is 10 or less, a glossiness (specular glossiness (%)) at an incident angle of 75° measured in accordance with JIS Z 8741 is 25 or less, and a surface roughness mean deviation (SMD) is 1 μm or more.

Another embodiment of the present invention may be a method for sorting waste plastics, the method including an irradiation step of irradiating light onto surface-treated waste plastic pieces, including black waste plastic pieces; a determination step of receiving reflected light from the light irradiated by the irradiation unit, detecting the spectrum of the reflected light, and determining the material of the waste plastic pieces based on the spectrum of the reflected light; and a sorting step of sorting at least the black waste plastic pieces by material based on the result of the determination.

(Example 1)
In this embodiment, a group of black waste plastic pieces (plastic mix) was used as the target of sorting. The size of each plastic piece was about 5 to 30 mm in average diameter in plan view. The group of black waste plastic pieces used was a group of plastic pieces containing at least seven types of plastic pieces, namely polyethylene (PE), polypropylene (PP), polycarbonate/acrylonitrile-butadiene-styrene (PCABS), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polyphenylene ether/polystyrene (PPEPS), and polyamide (PA), but also contained plastics other than the above seven types of plastics. Such a group of black waste plastic pieces was sorted by material using a sorting device similar to the sorting device 1 shown in Figures 1 to 3. The weight of the group of black waste plastic pieces used in one trial was 2.35 kg. The conveyor speed of the sorting device was 120 to 150 m/min.

The sorting device irradiated the samples with infrared light of 3 to 5 μm and detected the spectrum of the reflected light. From the reflected light spectrum obtained, spectra in the wavelength ranges of 3250 to 3750 nm and 4400 to 4600 nm were then extracted, and characteristic quantities were calculated. Based on these characteristic quantities, the plastic material was determined.

The sorting device used in this embodiment was provided with a nozzle row of 318 nozzles arranged in a direction perpendicular to the conveying direction. The discrimination device in the sorting device was capable of registering seven types of plastics: polyethylene (PE), polypropylene (PP), polycarbonate/acrylonitrile-butadiene-styrene (PCABS), acrylonitrile-butadiene-styrene (ABS), polystyrene (PS), polyphenylene ether/polystyrene (PPEPS), and polyamide (PA). For each trial, it was possible to select one or more types of plastic to be blown away by spraying air from the spray nozzle (selectively sprayed).

Waste plastic was sorted by selective spraying using Trials 1-A and 1-1 to 1-7 shown below.

Trial 1-A: All seven types of plastics were selected and sprayed. Trial 1-1: Only PE was selected and sprayed. Trial 1-2: Only PP was selected and sprayed. Trial 1-3: Only PCABS was selected and sprayed. Trial 1-4: Only ABS was selected and sprayed. Trial 1-5: Only PS was selected and sprayed. Trial 1-6: Only PPEPs was selected and sprayed. Trial 1-7: Only PA was selected and sprayed.

<Measurement and Evaluation>
To evaluate the sorting accuracy, the recovery rates R _A (%) of all seven types of plastics in the recovered material obtained in Trial 1-A, the recovery rates R _PE , R _PP , ... (%) of various plastics in the recovered material obtained in Trials 1-1 to 1-7, and the purities R _PE , R _PP , ... (%) of various plastics in the recovered material obtained in Trials 1-1 to 1-7 were determined. The results are shown in Table 1.

(Calculation of recovery rate _RA )
The recovery rates R _A (%) of all seven types of plastics in Trial 1-A were calculated as follows.

R _A (%)=W _A /W _L ×100
W _L (kg): Input amount of waste plastic pieces (plastic mix) W _A (kg): Recovery amount of all 7 types of waste plastic pieces (recovery amount of plastic pieces blown away by selective spraying)

(Calculation of recovery rates R _PE , R _PP , ...)
The recovery rates R _PE , R _PP , ... (%) of various plastics in Trials 1-1 to 1-7 were determined as follows: First, a group of waste plastic pieces having the content ratio and amount of each material shown in Table 2 was prepared and each trial was performed, and the recovery rate for each type of plastic was determined based on the actually obtained recovery amount.

For example, R _PE in trial 1-1 was calculated using the following formula:
R _PE (%) = W1 _PE /sWA _PE ×100
W1 _PE (kg): Actual recovery amount of PE from Trial 1-1 sWA _PE (kg): PE content (Table 2)
The recovery rates of the other plastics in Trials 1-2 to 1-7 were similarly determined.

(Purity R _PE , R _PP ,...)
The purities P _PE , P _PP , ... (%) of the collected materials from Trials 1-1 to 1-7 are the content ratios of various plastics in each collected material from each trial. The plastic pieces collected in each trial of the device were fed back into the sorting device, and the plastic ratio determination function of the sorting device was used to obtain the purity PPE in trial 1-1. For example, the purity _PPE in trial 1-1 was calculated by dividing the plastic ratio by the plastic ratio. The PE content was measured by the judgment function. The same was true for the other plastics in Trials 1-2 to 1-7.

(Measurement of surface properties)
As the surface characteristics of the plastic pieces after the surface treatment, the glossiness (specular glossiness (%)) according to JIS Z 8741 was measured. For the measurement, a glossmeter "VG 7000" manufactured by Nippon Denshoku Industries Co., Ltd. was used to measure the glossiness (specular glossiness (%)) at an incidence angle of 60° and an incidence angle of 75°. Furthermore, the mean deviation (SMD) of the surface roughness of the plastic pieces after the surface treatment was measured using an automated surface tester "KES-FB4-A" manufactured by Kato Tech Co., Ltd. The measurement results of the surface characteristics of PCABS and PS as representative examples are shown in Table 3.

(Example 2)
Except for not carrying out surface treatment, the plastic pieces were sorted according to their material in the same manner as in Example 1. As in Example 1, selective spraying was carried out according to Trials 2-A and 2-1 to 2-7 shown below.

Trial 2-A: Selected and sprayed all seven types of plastic Trial 2-1: Selected and sprayed only PE Trial 2-2: Selected and sprayed only PP Trial 2-3: Selected and sprayed only PCABS Trial 2-4: Selected and sprayed only ABS Trial 2-5: Selected and sprayed only PS Trial 2-6: Selected and sprayed only PPEPs Trial 2-7: Selected and sprayed only PA

The content ratio, content, recovery rate, and purity were determined in the same manner as in Example 1. The results are shown in Tables 1 and 2. The surface characteristics of the plastic pieces before sorting were also determined in the same manner as in Example 1. The results are shown in Table 3.

Table 1 shows the results of the selective spraying trials of all seven types of plastics (Trial 1-A of Example 1 and Trial 2-A of Example 2) and the selective spraying trials of various representative plastics (Trials 1-3 to 1-6 of Example 1 and Trials 2-3 to 2-6 of Example 2), comparing Example 1 (with surface treatment) with Example 2 (without surface treatment). These results show that the recovery rate and purity of the plastic pieces can be improved by performing surface treatment before sorting the waste plastic pieces. In particular, it was found that the recovery rate and purity of the plastic pieces can be improved by performing surface treatment so that the gloss (specular gloss (%)) at an incident angle of 60° measured in accordance with JIS Z 8741 is 10 or less, the gloss (specular gloss (%)) at an incident angle of 75° measured in accordance with JIS Z 8741 is 25 or less, or the surface roughness mean deviation (SMD) is 1 μm or more.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of each of the above-mentioned specific examples can be combined in different ways as appropriate, as long as no technical contradictions arise.

1, 1A, 1B, 1C, 1D Waste plastic sorting device 2 Conveyor 3 Transport path 4 Mid-infrared camera (reflection spectrum detection unit)
5 Discrimination device 6 Injection control unit 7 Injection nozzle row 8 Vibration feeder 12, 12-1, 12-2, A1, A2, B1, B2 Sorting unit 20 Surface treatment unit 21, 22 Large roller 23, 25 Rough surface roller 28 Supply unit 51 Pretreatment unit 52 First judgment unit 53 Second judgment unit 54 Third judgment unit S, S1, S2 Waste plastic pieces (black waste plastic pieces)
S' Waste plastic pieces before surface treatment

Claims (14)

A waste plastic sorting device, comprising:
A surface treatment section for treating the surfaces of the waste plastic pieces including the black waste plastic pieces;
An irradiation unit that irradiates the surface-treated waste plastic pieces with light;
a reflection spectrum detection unit that receives reflected light of the irradiated light and detects a spectrum of the reflected light;
a pre-processing unit that corrects the spectrum of the detected reflected light using a first correction spectrum and a second correction spectrum obtained by measuring a calibration plate that is irradiated with light from the irradiation unit , the first correction spectrum being obtained by measuring reflected light of light irradiated onto the calibration plate under bright conditions, and the second correction spectrum being obtained by measuring under dark conditions that are darker than the bright conditions;
A determination unit that determines the material of the waste plastic pieces based on the corrected spectrum of the reflected light;
A waste plastic sorting device comprising a sorting section that sorts at least black waste plastic pieces by material based on the results of the judgment. A waste plastic sorting device, comprising:
A surface treatment section for treating the surfaces of the waste plastic pieces including the black waste plastic pieces;
An irradiation unit that irradiates the surface-treated waste plastic pieces with light;
a reflection spectrum detection unit that receives reflected light of the irradiated light and detects a spectrum of the reflected light;
A determination unit for determining the material of the waste plastic pieces based on the spectrum of the reflected light;
A sorting unit that sorts at least black waste plastic pieces by material based on the result of the judgment ,
In the surface treatment section, the surface of the waste plastic pieces is
(a) A specular gloss at an incident angle of 60° measured in accordance with JIS Z 8741 is 10% or less;
(b) A specular gloss at an incident angle of 75° measured in accordance with JIS Z 8741 is 25% or less; and
(c) Surface roughness mean deviation (SMD) is 1 μm or more
A waste plastic sorting device that processes the waste plastic so as to satisfy one or more of the above conditions . The waste plastic sorting device according to claim 1 or 2, wherein the irradiated light includes mid-infrared light with a wavelength of more than 3 μm. The waste plastic pieces are transported on a transport path,
The determination unit is
A first determination unit that determines whether the spectrum of the reflected light is the spectrum of the waste plastic pieces or the spectrum of the transport path;
A second determination unit that extracts a feature amount from the spectrum determined to be the spectrum of the waste plastic pieces;
A third determination unit that determines the material of the waste plastic pieces based on the feature amount;
The waste plastic sorting device according to any one of claims 1 to 3, further comprising a sorting section that sorts at least black waste plastic pieces by material based on the results obtained in the third judgment section. The pre-processing unit performs processing to extract a predetermined frequency range from the corrected spectrum,
The waste plastic sorting device according to claim 4 , which cites claim 1 , wherein the first determination unit determines the material of the waste plastic pieces using the extracted spectrum. The waste plastic pieces are transported on a transport path,
The waste plastic sorting device according to claim 1 , wherein the transport path is divided into two systems, a first system and a second system, in a width direction of the transport path. The waste plastic sorting device according to claim 6, wherein the first and second systems collect waste plastic pieces of the same material. In the first system, waste plastic pieces of a first material are collected, and the remaining waste plastic pieces are supplied to the second system;
The waste plastic sorting device according to claim 6, wherein in the second system, waste plastic pieces of a second material are collected from the remaining waste plastic pieces. In the first system, waste plastic pieces of a first material and a small amount of other materials are collected, and the collected waste plastic pieces are supplied to the second system;
7. The waste plastic sorting device according to claim 6, wherein in the second system, waste plastic pieces of a first material are collected from among the first material and trace amounts of waste plastic pieces of other materials. In the first system, the first material and a small amount of other waste plastic pieces are removed, and the remaining waste plastic pieces are supplied to the second system.
The waste plastic sorting device described in claim 6, wherein in the second system, waste plastic pieces containing the first material and trace amounts of other materials are further removed from the remaining waste plastic pieces, and waste plastic pieces not containing the first material are collected. A method for sorting waste plastics, comprising the steps of:
A surface treatment step of treating the surfaces of the waste plastic pieces including black waste plastic pieces;
An irradiation step of irradiating the surface-treated waste plastic pieces with light from an irradiation unit ;
a reflection spectrum detection step of receiving reflected light of the irradiated light and detecting a spectrum of the reflected light;
a pre-processing step of correcting the spectrum of the detected reflected light using a first correction spectrum and a second correction spectrum obtained by measuring a calibration plate on which light from the irradiation unit is irradiated , the first correction spectrum being obtained by measuring reflected light of light irradiated onto the calibration plate under bright conditions, and the second correction spectrum being obtained by measuring under dark conditions that are darker than the bright conditions;
A determination step of determining the material of the waste plastic pieces based on the corrected spectrum of the reflected light;
A method for sorting waste plastic, comprising a sorting step of sorting at least black waste plastic pieces by material based on the results of the judgment. A waste plastic sorting device, comprising:
An irradiation unit that irradiates light onto the surface-treated waste plastic pieces, including the black waste plastic pieces;
a reflection spectrum detection unit that receives reflected light of the light irradiated by the irradiation unit and detects a spectrum of the reflected light;
a pre-processing unit that corrects the spectrum of the detected reflected light using a first correction spectrum and a second correction spectrum obtained by measuring a calibration plate that is irradiated with light from the irradiation unit , the first correction spectrum being obtained by measuring reflected light of light irradiated onto the calibration plate under bright conditions, and the second correction spectrum being obtained by measuring under dark conditions that are darker than the bright conditions;
A determination unit that determines the material of the waste plastic pieces based on the corrected spectrum of the reflected light;
A waste plastic sorting device comprising a sorting section that sorts at least black waste plastic pieces by material based on the results of the judgment. A waste plastic sorting device, comprising:
An irradiation unit that irradiates light onto the surface-treated waste plastic pieces, including the black waste plastic pieces;
a reflection spectrum detection unit that receives reflected light of the light irradiated by the irradiation unit and detects a spectrum of the reflected light;
A determination unit for determining the material of the waste plastic pieces based on the spectrum of the reflected light;
A sorting unit that sorts at least black waste plastic pieces by material based on the result of the judgment ,
The surface of the waste plastic piece is
(a) A specular gloss at an incident angle of 60° measured in accordance with JIS Z 8741 is 10% or less;
(b) A specular gloss at an incident angle of 75° measured in accordance with JIS Z 8741 is 25% or less; and
(c) Surface roughness mean deviation (SMD) is 1 μm or more
A waste plastic sorting device that is processed to meet one or more of the above conditions . A method for sorting waste plastics, comprising the steps of:
An irradiation step of irradiating light from an irradiation unit onto the surface-treated waste plastic pieces including the black waste plastic pieces;
a reflection spectrum detection step of receiving reflected light of the irradiated light and detecting a spectrum of the reflected light;
a pre-processing step of correcting the spectrum of the detected reflected light using a first correction spectrum and a second correction spectrum obtained by measuring a calibration plate on which light from the irradiation unit is irradiated , the first correction spectrum being obtained by measuring reflected light of light irradiated onto the calibration plate under bright conditions, and the second correction spectrum being obtained by measuring under dark conditions that are darker than the bright conditions;
A determination step of determining the material of the waste plastic pieces based on the corrected spectrum of the reflected light;
A method for sorting waste plastic, comprising a sorting step of sorting at least black waste plastic pieces by material based on the results of the judgment.

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