JPS5932288B2 - Mixture separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for separating mixtures containing thermoplastics.

Many plastics have similar chemical and physical properties, and conventional methods for separating such plastic mixtures include separation based on size differences, separation based on specific gravity differences, and buoyancy. A separation method based on the difference in

The present invention provides a novel separation method different from the separation methods described above, and an object thereof is to provide a method for efficiently separating a mixture containing a thermoplastic plastic.

As a result of research into a method for separating mixtures containing thermoplastics, the present inventors found that by utilizing the difference in melting point and thermoplasticity of plastics, a part of the surface of thermoplastics was attached to a heated metal plate. I learned that it is possible to separate the

This invention was obtained based on the above findings, and includes supplying a mixture containing a thermoplastic onto a metal plate heated below the melting point of the plastic, and causing the plastic to adhere onto the metal plate. This is a method of separation. The melting point of typical thermoplastics is EVA1
00℃ or less (EVA is a copolymer of low-density polyethylene and vinyl acetate) Low-density polyethylene 105-120℃ High-density polyethylene 130℃ Polypropylene 1700C Hard polyvinyl chloride 200-220℃ Polyvinyl alcohol 250℃ Tetrafluoroethylene resin 320 ~ As per 3300C,
There is a clear difference in melting point depending on the type of plastic, and even within the same type of polyethylene, there is a clear temperature difference between high-density polyethylene and low-density polyethylene.

This type of thermoplastic melts when heated above its melting point, and solidifies as it is when cooled; its properties do not change no matter how many times it is heated and cooled, and its behavior with respect to heat is reversible. It is true. Thermosetting plastics, on the other hand, will burn in their original shape if they are overheated. When thermoplastic plastic is placed on a heated metal plate, the plastic surface softens at a temperature slightly lower than the melting point of the plastic and adheres to the metal plate. When the temperature of the heated metal plate is lowered, the adhesive force disappears and it can be easily peeled off from the metal plate surface. It is best for metal plates to be heated uniformly, so those with high thermal conductivity are selected, such as copper plates, iron plates,
A stainless steel plate or the like is used. When a mixture containing a thermoplastic is supplied onto a heated metal plate, the plastic particles are scattered on the plate in a single layer so that they come into direct contact with the metal surface, and if they are supplied in multiple layers, they come into contact with the metal surface. There are some particles that do not, and in such cases the efficiency of separation decreases. According to experimental results, the temperature of the heated metal plate used in the method of this invention is at or about 10 to 10 degrees below the melting point of the thermoplastic to be deposited.
A temperature lower by 20°C is good.

Furthermore, when the thermoplastic plastic used in the method of this invention is in the form of pellets or granules, the separation accuracy is high, but when it is in the form of a film or sheet, it is difficult to feed it in a single layer, so the separation accuracy is reduced. do. The size of the plastic is 1 to 5 meters and it is easy to process.

The method of this invention can be applied not only to the sorting of thermoplastic plastics with different melting points, but also to the separation of mixtures of thermoplastic plastics, thermosetting plastics, and inorganic substances such as glass, metals, and earth and sand. For continuous separation, a belt conveyor or rotating drum is used.

In the case of a belt conveyor type, the belt material is a stainless steel plate or the like, and the upper surface of the belt is heated on the forward side. A good way to heat the belt is to install an electric heater below the belt surface so that the belt temperature can be adjusted using a slider or the like. The raw material mixture is charged into a hopper and fed in a single layer onto the belt surface using a vibrating feeder. The plastic that has fallen onto the belt surface comes into contact with a metal plate heated to a temperature approximately 10° C. lower than its melting point, and a portion of the plastic surface softens and adheres to the metal surface. Plastics and other inorganic substances with a melting point higher than that of the adhered plastics do not adhere to the plate surface, but fall off the belt at the pulley end on the advancing side of the belt conveyor and are separated from the adhered plastics. The attached plastic gradually cools down on the return side of the bottom of the belt conveyor and solidifies again.
The adhesion to the metal plate becomes weak, and if a brush or scraper is provided on the belt surface, it can be easily peeled off. By stacking heated belt conveyors in multiple tiers, lowering the belt temperature on the top tier and increasing the belt temperature as you go down to the second and third tiers, you can continuously mix two or more types of thermoplastics. can be separated. As described above, the method of the present invention takes advantage of the difference in melting point and thermoplasticity of thermoplastic plastics to adhere thermoplastic plastics onto a metal plate heated below the melting point, and then This is a method of separating plastics or other inorganic substances, and it has great merits in terms of the utilization of waste resources, as it can easily separate mixtures that would have previously been discarded because no separation method was known.

Next, examples will be shown.

EXAMPLE A mixture of pelletized EVAl low-density polyethylene, high-density polyethylene, and polypropylene having a particle size of approximately 3 mm was used as a raw material.

A stainless steel belt conveyor with a width of 500 m, a length of 1 m, and a length of 1 m, which had a built-in electric heater whose temperature could be adjusted with a slider, was used as the metal plate.

First, the temperature of the belt surface was maintained at 80℃, raw materials were supplied, and EVA was attached.The falling objects were then fed to the belt heated to 100℃ and low-density polyethylene was attached. High-density polyethylene was applied to a belt at a temperature of 12°C to obtain polypropylene as falling material.

The raw materials could be identified by the shape and color of the pellets, but the plastics deposited at each temperature and the final droplets were highly purified separation products containing almost no other species.

Claims (1)

[Claims] 1. A mixture containing a thermoplastic plastic is supplied to a metal plate heated to a temperature of 5 to 30 degrees Celsius lower than the melting point of the plastic, and the plastic is adhered to the metal plate and separated. Separation method.