JPS6013466B2 - How to separate plastic molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating plastic molded products according to their materials, and more specifically to a method for separating waste plastic molded products according to their materials in their original form without crushing them.

At present, the number of plastic pallets and containers used in the distribution system is on the order of several dozen.

Since these pallets and containers are exposed products, they deteriorate due to ultraviolet rays, reduce strength, or fade in color after about 10 days, reducing the product value, and over a million pieces are sold each year. It has been discarded. Therefore, these waste plastics from pallets and containers are being recycled to prevent pollution and to make effective use of petroleum resources.

Incidentally, these waste plastics from pallets and containers may have different materials even if they have the same shape.

For example, beer containers may have the same shape but are made of polyethylene resin or polypropylene resin. If plastics made of different materials are remolded in a mixed state without being separated, the quality of the remolded product may deteriorate.

When performing recycling processing for this purpose, it is necessary to separate waste plastics by material as a pretreatment. Traditionally, the methods of separating waste plastic by material are as follows:
Examples include fluidized air sorting, wet specific gravity sorting, electrostatic sorting, and low-temperature crushing sorting.

The fluidized wind sorting method is a method in which air is blown into a tilted screen from below to separate plastics into upper and lower parts of the screen based on the difference in specific gravity under fluidized conditions.The plastic particle size and shape must be aligned in advance. There is. Wet gravity sorting is a method that uses water or a gravity liquid to separate floating plastic from sinking plastic.
After separation, it is necessary to wash off the specific gravity liquid and dry it. Furthermore, the electrostatic separation method is a method of sorting based on the fact that the amount of static electricity generated varies depending on the material of the plastic, and it is necessary to prepare the particle size and shape of the plastic in advance and to dry it. In addition, the cryogenic crushing and sorting method is
This method involves cooling the plastic to 0°C, crushing it, and sorting the crushed pieces using a sorting device, which takes advantage of the fact that the size of the crushed pieces differs depending on the plastic's arming temperature, but it is necessary to cool the plastic beforehand. There is. However, although the above-mentioned separation method targets various types of waste plastics, when it is applied to waste plastics such as pallets and containers, the following disadvantages occur.

That is, waste plastic must be crushed into appropriate sizes one by one, which complicates the process and increases the cost of sorting. Furthermore, since mixed crushed products are separated, there is a limit to the accuracy of separation. Furthermore, the sorting method differs depending on the material of the plastic, and depending on the material, it is necessary to combine various sorting methods, which requires a long time for sorting. The present invention has been made in view of the above circumstances, and it is possible to maintain the original form of waste plastic molded products without crushing them.
The purpose is to provide a separation method that allows easy separation by material type.

That is, in the present invention, a plastic molded product is supported by a cushioning material and is struck with a constant force by a striking device, and the vibrations generated at that time are detected and converted into electrical signals. In addition to selecting those in a unique vibration band, converting the selected electrical signals into an envelope using an envelope converter, and comparing the wave height and wave width of the envelope with preset reference wave height and reference wave width. This system is characterized by the ability to separate plastic molded products by material. An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, first, the surface of a plastic molded product 3 such as a pallet or container is struck with the hammer 2 of the striking device 1.

Here, the plastic molded product 3 is supported by a cushioning material so that it does not resonate when struck by the hammer 2.

The striking device 1 is constructed using a known piano action as shown in FIG. This striking device 1 is
A solenoid 4 is used in place of the keyboard, and when the solenoid 4 is energized, one end of the wibeso 5 is pushed up and the wibeso 5 is rotated in the opposite direction. As the wiben 5 rotates, the hammer 2 attached to the hammer pad 7 via the hammer shank 8 by the jack 6 strikes the surface of the plastic molded product 3. After the hammer 2 hits the surface of the plastic molded product 3, the hammer 2 immediately returns to its original position due to the elasticity of the hammer spring 9 provided on the hammer pad 7. Note that 10,1 in the figure
1 and 12 are fixed rails. Therefore, the surface of the plastic molded product 3 can always be struck with a constant force.

In addition, the hammer 2 immediately returns to its original position after hitting the surface of the plastic molded product 3, and does not hit the surface of the plastic molded product 3 multiple times in succession (chatter). The vibration generated when struck by the hammer 2 differs depending on the hardness of the plastic molded product 3, that is, it differs depending on the material of the plastic molded product 3.

This vibration is detected by a piezoelectric acceleration detector 14 attached to the plastic molded product 3 and converted into an electrical signal. Here, the acceleration type detector 14 is constructed using an electrical element such as quartz crystal, Rothschel salt, barium titanate, zirconium titanate salt, etc., which generates a potential difference when mechanical strain is applied. The hammer 2 is mounted at a certain distance (usually one specific water level) from the striking position of the hammer 2.

The impact signal (see Fig. 2a) converted into an electric signal by the piezoelectric acceleration type detector 14 is amplified by the amplifier 15 (see Fig. 2b).
), the noise component (signal other than that generated by the impact) is removed by the wave generator 16, and the noise component (signal other than that generated by the impact) is removed by the wave generator 17.
The passing frequency band of is divided into small parts, and after the characteristic natural vibration band is selected by the plastic molded product 3 (see Fig. 2c), it is converted into an envelope by the envelope converter 18 (
(see FIG. 2d), the shape of the signal, that is, the peak value V and the wave width T are determined. The impact signal converted into a comprehensive line is sent to comparators 19, 20, and 21.

The comparator 19 receives the high level set value V set by the peak value setter 24 as a comparison signal, and the high level set value V of the impact signal is inputted as the high level set value V. When the value is higher than , the comparator 19 outputs the material separation code A. Further, the comparator 20 receives as a comparison signal a low level set value V2 set lower than the high level set value V by the peak value setter 25, and the peak value V of the impact signal is set to the low level set value V2. The comparator 20 outputs the material discrimination signal B when the value is lower than . Further, the comparator 21 receives a low/low level setting value V3 which is lower than the low level setting value V2 as a comparison signal by the wave height setting device 26, and the wave height rise V of the impact signal is inputted to the low/low level setting value V3. The signal C is output from the comparator 21 when the signal C is higher than the comparator 22 and 23
It is now entered into Further, the comparator 22 is configured to output the material discrimination signal A2 when the signal C is inputted within the set time information set by the time setter 27. Further, the comparator 23 outputs the material discrimination signal & when the signal C is inputted after the set time L, which is set longer than the set time T by the time setter 28. Note that when the peak value V of the impact signal is in the intermediate range between the high level setting value V and the low level setting value V2, it is assumed that the material is other than the material determined by the comparators 19 and 20, or it is difficult to distinguish. It is now processed. Also, when the time when the peak value V of the impact signal falls to the low/low level setting value V3 is in the intermediate zone between the set time T and T2, the material is other than the material determined by the comparators 22 and 23. Otherwise, it is treated as something difficult to distinguish. Here, the set value V,,V2
, V3, T, , T2 are determined based on the vibration characteristics (wave height, wave width) of the plastic molded products to be separated, for example, if they are molded with polypropylene resin or polyethylene resin. . When the envelope of the impact signal of the plastic molded product 3 is like a shown in FIG. 3, the comparator 19 outputs a material discrimination signal A, and the comparator 22 outputs a material discrimination signal A2. The material of the plastic molded product 3 is determined from these signals A, , A2.

Further, in case b shown in FIG. 3, the comparator 20 outputs the material discrimination signal B, and the comparator 23 outputs the material discrimination signal &, and from these signals B, , B2, the plastic molded product 3 is output. The material of the material is determined. Further, in case c shown in FIG. 4, the comparator 19 outputs the material discrimination signal A, and the comparator 23 outputs the material discrimination signal B2, and from these signals A, Z, the plastic molded product 3 is output. The material of the material is determined. In the case d shown in FIG. 4, the comparator 20 outputs the material discrimination signal B, and the comparator 22 outputs the material discrimination signal A. The material of the material is determined.
As described above, if the material is discriminated from the combination of the two types of material-specific signals, that is, the wave height value and wave width (time until the predetermined low wave height value is reached) of the impact signal, the discrimination accuracy is high and four types of materials can be discriminated. .

Next, specific examples of the present invention will be explained.

A beer container made of polypropylene resin and a beer container made of polyethylene resin are struck with a 30-piece brass hammer attached to a piano action, and the vibrations generated at this time are transferred to a beer container IQ away from the point of impact of the hammer. After detecting it with a tortoise acceleration type detector attached to the surface and converting it into an electrical signal, 7 was intensified with a ratio intensifier and the waveform was measured with an oscilloscope.

Based on this measurement result, the reference signal V, = 155V, V2
=15V, V3=4V, T:8hs, L=67ms were set. Then, the polypropylene resin beer container (8 years old) and the polyethylene resin beer container (1st year old unexposed item) total low hardness were struck and separated as described above. , 98 pieces could be accurately sorted by material. The remaining two containers were difficult to separate, one had a large crack in the container, and the other had a large amount of coal tar attached to it. Although the above embodiment shows a case in which a piano action is used as the striking device 1, the invention is not limited to this, and the point is that any device can be used as long as it can apply a single strike to a plastic molded product with a constant force. good.

In addition, although a piezoelectric acceleration type detector was used to detect the vibration given by the striking device 1, it is not limited to this, and in short, an acoustic/electrical signal converter (microphone) or other sensor that is generated during striking is used. Any material that can convert vibrations into electrical signals may be used. As explained above, according to the present invention, it is possible to easily separate plastic molded products by material without crushing them (in their original form), so the separation cost is low and the separation can be done quickly, especially for pallets and containers. It is effective in separating waste plastics of various kinds, and contributes significantly to the prevention of pollution and the effective use of petroleum resources.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus for carrying out the present invention;
Figures 2a, b, c, and d are waveform diagrams of striking signals, Figures 3 and 4 are explanatory diagrams for explaining the method of the present invention, and Figure 5 is a side view showing an example of a striking device. be. In the figure: 1...impact device, 2...hammer, 14...piezoelectric acceleration type detector, 15...
... Amplifier, 16, 17... Reactor wave generator, 18...
・・・Envelope converter, I9, 20, 21, 22, 23・
... Comparator, 24, 25, 26 ... Peak value setting device, 27, 28 ... Time setting device. Figure 1 Figure 2 Figure 5 Figure 3 Figure 4

Claims (1)

[Claims] 1. A plastic molded product supported by a cushioning material is struck with a constant force by a striking device, the vibrations generated at that time are detected and converted into electrical signals, and among the electrical signals, those in the vibration band specific to the plastic material are detected. In addition to selecting the
The selected electrical signal is converted into an envelope using an envelope converter, and the wave height and width of the envelope are compared with preset reference wave height and wave width to separate plastic molded products by material. A method for separating plastic molded products.