Electricity: measuring and testing – A material property using electrostatic phenomenon – In a liquid
Reexamination Certificate
2001-04-30
2003-02-18
Oda, Christine (Department: 2858)
Electricity: measuring and testing
A material property using electrostatic phenomenon
In a liquid
C209S011000, C209S127100
Reexamination Certificate
active
06522149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for identifying plastics of unknown materials.
2. Description of the Related Art
To identify materials of unknown objects in the art, JP 7-111397(B2) and JP 8-300354(A) publications describe methods of applying infrared rays on objects to identify them on the basis of differences, for example, in absorption spectrum, and amount of transmitted and reflected infrared rays.
To classify waste plastics into their types, JP 7-124053 application describes a method and apparatus for classifying plastics, which heats plastic fragments with microwaves and using a temperature difference between plastics. This classifying apparatus comprises: a crushing device for crushing waste plastics into a given size; a heating furnace for preheating crushed plastic fragments; a microwave oven for heating the preheated plastic fragments with microwaves; a radiation thermometer for measuring temperatures of the plastic fragments; and a classifying section for classifying the plastics on the basis of the results of measured temperatures. In the microwave heating, heat efficiency depends on permittivity. Therefore, the apparatus measures temperatures of plastic fragments after microwave heating and uses airflow to blow away only such plastic fragments for classification that are heated up to a temperature within a given range. In this apparatus, the heating furnace for preheating is used to enlarge differences in temperatures of plastics.
JP 8-113391 application describes a method and an apparatus for classifying plastics, which heats plastics with infrared rays and uses the temperature difference between plastics. This method and apparatus demonstrates examples identified through the use of temperature differences resulting from amounts of infrared rays absorbed by polyethylene terephthalate (hereinafter referred to as “PET”) and polyvinyl chloride (hereinafter referred to as “PVC”).
JP8-122868 application describes a method and an apparatus for classifying plastics, which frictionally electrifies plastic fragments in an electrifying container and uses differences in polarity and charged amount between the plastic fragments. When plastics of different types are frictionally contacted with each other, their electrostatic properties and charged amounts tend to differ in accordance with materials. In this apparatus, the plastic fragments are frictionally contacted with a frictional medium in the electrifying container. Then, the charged plastic fragments are supplied through electrodes that have a high potential therebetween to classify them for collection into one that adheres on one electrode, one that does not adhere on electrodes, and one that is attracted to the other electrode. A classifying apparatus using this method includes an electrostatic plastic separation device available from Hitachi Zosen Inc.
The conventional method, which uses differences in absorption, transmission and reflection properties for infrared rays, has a disadvantage because it fundamentally uses a ray of light and can not identify materials of colored objects. In particular, in wastes, objects are hardly identified because they are in various forms and mixed.
The method, which uses temperature differences resulting from heating with microwaves, has an extremely high possibility to generate discharges (sparks) when a metal is mixed in objects to be heated and a risk to fire plastics. In addition, JP 7-124053 preheats plastics at 80° C. for increasing an identification rate but temperatures of the plastics finally elevate near to or over 100° C. occasionally. In such a case, there is a risk to melt or decompose the plastics partly, which gives a large disadvantage for safety. Furthermore, even if identifying of plastics succeeds, it is difficult to blow plastic fragments in order to efficiently identify because they do not have a constant weight. Accordingly, this method is not possible to identify the plastic products that are not crashed. Further, the microwave oven has a large size and requires microwave shields in consideration of influences on human beings. As obvious from the forgoing, the apparatus, which uses microwave heating, is hardly applicable to a waste processing system that requires a high identification rate, a low cost and high safety.
The method and apparatus for identifying plastics, which heats plastics with infrared rays and uses the temperature difference between plastics, cannot identify PVC from other plastics. In consideration of a period of time from heating to measurement, a measured error and stability of the heating device, about 5 degrees of Centigrade is an enough temperature difference to identify temperatures by this method. Polymethyl methacrylate (Methacrylic resin; hereinafter referred to as “PMMA”) and polystyrene (hereinafter referred to as “PS”), however, cannot be identified from PVC. The apparatus described in JP 8-113391 demonstrates examples identifying PVC bottles from PET bottles. Its identification rate is extremely lowered when plastics of other types than the above and plastics of other forms than bottles are mixed.
The method and apparatus for classifying plastics, which frictionally electrifies plastic fragments in the electrifying container and uses differences in polarity and charged amount between the plastic fragments, is difficult to perform identification efficiently. For example, in identifying a mixture of PVC fragments and polyethylene (hereinafter referred to as “PE”) fragments, when PVC fragments contact PE fragments in the electrifying container, PE fragments tend to be charged positively and PVC fragments, negatively. When PE fragments contact with each other or when PVC fragments contact with each other, electrostatic polarity and charged amounts greatly vary in accordance with frictional situations. Even if PE fragments are charged positively and PVC fragments, negatively, when weights and sizes of plastic fragments are different, electrostatic force and gravity imparted on plastic fragments may differ. Therefore, the method of identifying, depending on electrostatic force as described in JP 8-122868, is difficult to perform identification efficiently. Thus, a crushing step is essentially required to equate sizes of plastics. It is extremely difficult, however, to crush all waste plastics in various forms into a given particle diameter and greatly increases the cost. Furthermore, an increased number of plastic fragment types make it more difficult to control charged amounts and impossible to identify general waste plastics.
On the other hand, in appropriately processing and recycling wastes, there is a high possibility to generate toxic substances on burning and heating the wastes if PVC is mixed therein, and a technique is needed to identify and remove PVC from the wastes. It is very difficult, however, for the conventional method to identify and remove only PVC. If the wastes with PVC mixed therein are burned easily, toxic substances, represented by dioxin, are possibly generated due to chlorine derived from PVC. A proposed method can make toxic substances harmless just when they are generated, but it requires an extremely expensive chemical facility and is not practical.
In reusing collected plastics as a refuse derived fuel (hereinafter referred to as “RDF”) or a raw material for a blast furnace, it is very important to increase qualities of the collected plastics. For example, an RDF is required to have a high calorific value and a constant amount of heat. If a high exothermic plastic and a low exothermic plastic are mixed, such an RDF cannot be obtained. In particular, for a power generation system that uses an RDF, a high-quality RDF is requested. Currently, the high-quality RDF is not developed progressively, and there is a disadvantage in that an efficiency of power generation is extremely low. In the raw material for the blast furnace, it is required to mix high exothermic plastics and low exothermic plastics in a constant mixing amount in
Matsushima Takaaki
Yokoyama Sadahiko
LeRoux Etienne
NEC Corporation
Oda Christine
Sughrue & Mion, PLLC
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