Glass fragment recovering method

Abstract

 Foreign-substance-attached glass fragments with a printed dark color layer are separated from a group of glass fragments in first and second separating processes CS1 and CS2 for separating dark colored glass fragments, and foreign-substance-attached glass fragments with a printed electroconductive layer are separated in a separating process ES for separating electroconductive glass fragments, whereby recyclable glass fragments are recovered from scrapped glass sheets. Glass fragments usable as a recyclable material for glass sheets are recovered from scrapped glass at a large throughput capacity without sacrifying recovery percentage.

Description

[0001] The present invention relates to a glass fragment recovering method capable of regenerating glass sheets from scrapped glass sheets and a glass sheet producing method using recovered glass fragments.

[0002] A glass sheet fitted to a window of an automobile or a railway car is generally fixed by adhesion to the window by interposing an adhesive agent between the glass sheet and the car body. Practically, a printed dark color layer is provided at the circumference of the glass sheet in order to prevent the deterioration of the adhesive agent by UV rays irradiated through the glass sheet. The printed dark color layer is generally made of a sintered product of a dark-colored ceramic paste.

[0003] Further, a glass sheet for a window for an automobile or a railway car is, in some cases, provided with a printed electroconductive layer in order to impart a defogging function to the window. The printed electroconductive layer is in particular formed to have a shape of thin lines over the almost entire region of a glass sheet for a rear window of automobile. The printed electroconductive layer is usually made of a sintered product of ceramic paste containing an electroconductive material such as silver. Further, the printed electroconductive layer in a shape of thin lines is usable as antenna lines.

[0004] In a window glass for an automobile in particular, it is often the case that the printed electroconductive layer is formed in a rear window or a side window of automobile. For a glass sheet for a rear window or a side window, a tempered glass subjected to a tempering treatment is usually used. When a strong impact is applied to the tempered glass, it is broken into fine fragments.

[0005] In recent years, there is discussion to establish law on recycling of scrapped automobiles. If glass sheets removed from scrapped automobiles can be used as a recyclable material, it is desirable in the standpoint of keeping good global environment. By putting the glass sheets removed from the scrapped automobiles into a glass tank for producing glass sheets, the scrapped glass sheets can be used as recycled material for fresh glass sheets. However, as described above, glass sheets for windows for an automobile or a railway car have various. kinds of printed layers. When a glass sheet with a printed layer is used as a recycled material to produce a fresh glass sheet, the quality of the produced glass sheet is poor. Specifically, a printed dark color layer has normally a black color and a printed electroconductive layer containing silver has normally a brown color. Accordingly, when glass sheets with these printed layers are used, colored glass sheets are produced.

[0006] There are also glass sheets having a green, brown or gray color. A glass sheet takes on a color depending on metallic components which are mixed in a glass frit in certain proportions. In this case, the color tone or transmissivity is determined depending on proportions of mixed metallic components. Accordingly, when a glass sheet with a printed layer is used as a recycled material, it is difficult to adjust the color tone or transmissivity of the glass sheet to a predetermined color tone or transmissivity because it is difficult to measure amounts of the metallic components in the printed layer. Further, the mixing of components of the printed layer causes distortion of a produced glass sheet.

[0007] As described above, when any glass sheet attached with a printed layer is used as a recycled material for a fresh glass sheet, the quality of a produced glass sheet is reduced. Accordingly, it is necessary to remove components of printed layer in order to use a scrapped glass sheet as a recycled material for a fresh glass sheet.

[0008] As an actual method for removing components of printed layer, there is a method as described below. Before putting a glass sheet removed from a scrapped automobile or railway car, as a glass frit, into a glass tank for producing glass sheets, the glass sheet is broken into fine glass fragments. In a group of glass fragments obtained by breaking the glass sheet, foreign-substance-attached glass fragments with a printed layer and glass fragments without the printed layer exist in a mixed state. Since the glass fragments without the printed layer can be used as a glass frit, the foreign-substance-attached glass fragments should be removed from the group of glass fragments.

[0009] In the foreign-substance-attached glass fragments, glass fragments with a printed dark color layer (hereinbelow, referred to as dark-colored glass fragments) can be separated and removed from the group of glass fragments by using an optical technique, and glass fragments having a printed electroconductive layer (hereinbelow, referred to as electroconductive glass fragments) can be removed from the group of glass fragments by using a metal detector. In more detail, glass fragments without the printed layer (hereinbelow, referred to as clear glass fragments) can transmit light and the dark-colored glass fragments cannot transmit light. Accordingly, a technique is used wherein a stream of particles consisting of a group of glass fragments is formed; the dark-colored glass fragments are detected optically from the stream, and the detected dark-colored glass fragments are eliminated from the stream. Similarly, a stream of particles consisting of a group of glass fragments is formed; the electroconductive glass fragments are detected by using the metal detector from the stream, and the detected electroconductive glass fragments are eliminated from the stream. Thus, foreign-substance-attached glass fragments can be removed from the group of glass fragments.

[0010] It is reported that the number of scrapped automobiles in Japan is around 3,000,000 or 4,000,000 per year. Thinking that glass sheets are removed from such a large number of scrapped automobiles, collectable glass fragments exceed 100,000 tons per year. Namely, it is necessary to treat at least 100,000 tons of glass fragments in a year in order to recycle, in an industrial scale, window glass sheets of scrapped automobiles from the viewpoint of recycling resources. It is needless to say that 100,000 tons of glass fragments would not be treated in a single equipment at a single place. However, it is not realistic that many equipments are located to cover the whole area of Japan if an equipment itself is large-sized. Accordingly, in order to use actually the window glass sheets from scrapped automobiles as a recycled material for producing glass sheets, the throughput capacity for removing printed layers should be increased remarkably in comparison with that of laboratory level.

[0011] It is an object of the present invention to solve the above-mentioned problems in conventional techniques, and to provide a new glass fragment recovering method capable of increasing recovery percentage and throughput capacity and a glass sheet producing method.

[0012] In accordance with the present invention, there is provided a glass fragment recovering method wherein recyclable glass fragments and foreign-substance-attached glass fragments are separated from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments with a printed dark color layer and a printed electroconductive layer exist in a mixed state so that the recyclable glass fragments are recovered, the glass fragment recovering method being characterized in that foreign-substance-attached glass fragments with a printed dark color layer are separated from the group of glass fragments; foreign-substance-attached glass fragments with a printed electroconductive layer are separated from the group of glass fragments from which the foreign-substance-attached glass fragments with a printed dark color layer are separated, and recyclable glass fragments are recovered.

[0013] Generally, a magnetic detector or an electronic detector is used as the metal detector. As an electroconductive material attached to electroconductive glass fragments, silver is generally used. Since silver is not a magnetic material, it is preferable to use an electrically detecting technique for the metal detector so that the electroconductive glass fragments are detected.

[0014] However, it is impossible for the electronically detecting technique to increase the flow rate of glass fragments in a case of detecting metal in a stream of electroconductive glass fragments. Accordingly, there 3 takes place the following disadvantage. The basic principle of the electronically detecting technique is that a high-frequency current by self-excited oscillation is supplied to a detection coil to form a magnetic field in the coil. When a group of glass fragments is fed into the magnetic field, an eddy current loss takes place when electroconduccive glass fragments in the group of glass fragments pass therethrough. By detecting the eddy current loss, detection is made as to whether or not electroconductive glass fragments pass. In this case, by determining the threshold value of the eddy current loss, separation percentage to the electroconductive glass fragments can be determined.

[0015] For example, a glass sheet for a rear window of an automobile has a printed layer as shown in Fig. 4. Fig. 4 is a front view of a typical glass sheet 90 for a rear window viewed from a car interior side. At the entire periphery of a tempered glass 91, a printed dark color layer 92 is formed. On the printed dark color layer 92 at both sides of the tempered glass 91, printed electroconductive layers 93a having a predetermined width, which is called bus bars, are laminated. Further, a plurality of thin-line like printed electroconductive layers 93b are formed to connect the printed electroconductive layers 93a at both sides.

[0016] When the tempered glass 91 is broken, glass fragments having a size of about 2 to 10 mm square are generally produced. Further, the width of the printed electroconductive layers 93a is about from 10 to 20 mm, and the width of the printed electroconductive layers 93b is about 1 mm or less. Accordingly, there is a large difference between an amount of silver existing on glass fragment portions corresponding to the printed electroconductive layers 93a and an amount of silver existing on glass fragment portion corresponding to the printed electroconductive layers 93b.

[0017] The eddy current loss is in proportion to the second power of a size of metal, transmissivity or oscillation frequency. If the amount of silver is uniform to a certain extent, the presence or absence of silver can be detected stably by measuring the eddy current loss. Glass fragments obtained from the glass sheet 90 for a rear window show a large fluctuation in the amount of silver as described above. Accordingly, in the use of a typical electronic metal detector, when the oscillation frequency is adjusted based on glass fragments corresponding to portions of the printed electroconductive layers 93a which are rich in the amount of silver, and the threshold value of the eddy current loss is determined, it is impossible to detect glass fragments corresponding to portions of the printed electroconductive layers 93b which are poor in the amount of silver. On the contrary, when sensitivity for detection is widened so that glass fragments corresponding to portions of the printed electroconductive layers 93b which are poor in the amount of silver can be detected while glass fragments corresponding to portions of the printed electroconductive layers 93a which are rich in the amount of silver can also be detected, a large amount of clear glass fragments are separated along with electroconductive glass fragments. Accordingly, in order to detect stably electroconductive glass fragments, it is necessary to control occasionally oscillation frequency while the amount of silver contained in supplied electroconductive glass fragments is estimated or detected. Such occasional delicate control would make it difficult to treat 100,000 tons of glass fragments in a year.

[0018] In view of the above-mentioned circumstances, the inventors of the present application have come to an idea that the dark-colored glass fragments are first separated before electroconductive glass fragments are separated. As shown in Fig. 4, the most printed electroconductive layers 93a exist in areas where the printed dark color layer 92 is formed. Namely, electroconductive glass fragments having the printed electroconductive layer of large surface are dark-colored glass fragments themselves. Accordingly, when the dark-colored glass fragments are separated from glass fragments with any kind of printed layer are separated, electroconductive glass fragments with the printed electroconductive layer of large surface area can be separated resultingly. A group of remaining glass fragments includes electroconductive glass fragments having the printed electroconductive layer of smaller surface area, such as glass fragments with a printed electroconductive layer 93b in a shape of thin line. Thus, amounts of silver to be detected can be uniformized to a certain extent in a metal detecting process after the process for separating dark-colored glass fragments. In this case, the detecting sensitivity should be increased so that clear glass fragments can be discriminated from electroconductive glass fragments with the printed electroconductive layer of smaller surface area, such as glass fragments with the printed electroconductive layer 93b in a shape of thin line. Thus, electroconductive glass fragments can be detected stably in the process for separating the electroconductive glass fragments whereby the electroconductive glass fragments can be separated from clear glass fragments which can be recycled.

[0019] Glass fragments with the printed electroconductive layer 93a are also glass fragments with the printed dark color layer 92. Accordingly, the former can be considered as a kind of glass fragments with the printed dark color layer and the printed electroconductive layer. Namely, the glass fragments with the printed electroconductive layer 93a belong to the dark-colored glass fragments in terms of two kinds of glass fragments: the dark-colored glass fragments and the electroconductive glass fragments, and they are also considered as the electroconductive glass fragments. In consideration of the order of separating steps in the present invention wherein the process for separating the electroconductive glass fragments is carried out after the process for separating the dark-colored glass fragments, the glass fragments with a printed electroconductive layer 93a belong the dark-colored glass fragments in the present specification, and when it is required to classify the electroconductive glass fragments into either kind of glass fragments, they can be classified to be the dark-colored glass fragments.

[0020] Further, the present invention is to provide a glass fragment recovering method wherein recyclable glass fragments and foreign-substance-attached glass fragments are separated from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments with a printed dark color layer exist in a mixed state so that the recyclable glass fragments are recovered, the glass fragment recovering method being characterized in that a process for separating the foreign-substance-attached glass fragments from the group of glass fragments is repeated plural times.

[0021] The method for repeating the process for separating the foreign-substance-attached glass fragments plural times according to the above-mentioned invention is advantageous on the point as follows. In order to establish in an industrial scale that scrapped glass is recovered to use it for recycling, it is necessary to recover a large amount of scrapped glass efficiently. Namely, it is necessary to increase recovery percentage expressed by a percentage of an amount of recovered clear glass fragments to an amount of scrapped glass, without reducing a throughput capacity per unit time (hereinbelow, referred to simply as the throughput capacity). An attempt of increasing the throughput capacity may result such a disadvantage that foreign-substance-attached glass fragments cannot sufficiently be removed, or a certain amount of clear glass fragments are removed together with the foreign-substance-attached glass fragments. An attempt of increasing detection sensitivity in order to increase recovery percentage would cause a reduction of throughput capacity.

[0022] Specifically, in recovering a recyclable material for glass sheets from scrapped glass, a throughput capacity of about 1000 kg/hr is required in a single equipment. The reason is as follows. Assuming an operation rate of 8 hr/day and an operation rate of 200 days/year, the throughput capacity of 1000 kg/hr corresponds to a throughput capacity of 1600 tons/year. When 100,000 tons of scrapped glass per year in Japan is assumed, 100 equipments each having a throughput capacity of 1000 kg/hr are needed. Assuming that the throughput capacity is small by one digit, 1000 equipments having the same capacity are needed in Japan. Accordingly, the throughput capacity of about 1000 kg/hr is required for each equipment in which a recyclable material for glass sheets is recovered from scrapped glass.

[0023] The inventors have a test result in which dark-colored glass fragments are separated from a group of glass fragments by using a dark-colored glass fragment separating device which will be described later. Tests were conducted on a group of glass fragments having a uniformalized glass fragment size so that glass fragments of not more than 4.0 mm (the maximum length) and glass fragments of at least 11.2 mm (the minimum length) were removed. In Table 1, "flow rate" represents an amount per unit time (unit: kg/hr) of a group of glass fragments introduced into the dark-colored glass fragment separating device; "B₀/M₀" represents a proportion (unit: %) of an amount (B₀) of dark-colored glass fragments remaining in the group of glass fragments to the total amount (M₀) of the group of glass fragments from which the dark-colored glass fragments are separated by the dark-colored glass fragment separating device; "C₀/M'₀" represents a proportion (unit: %) of an amount (C₀) of clear glass fragments to the sum (M'₀) of the amount (C₀) of the clear glass fragments existing in a mixed state in the group of dark-colored glass fragments separated by the dark-colored glass fragment separating device and an amount of separated dark-colored glass fragments, and "recovery percentage" represents the total amount (M₀) of recovered glass fragments to the total amount (M) of the originally prepared glass fragments. In this specification, "proportion", "%" indicating "a proportion of content" and "ppm" are all calculated based on mass.

Table 1

Flow rate	B0/M0	C0/M'0	Recovery percentage
1234	11	36	69
1148	10	45	76

[0024] When the value of B₀/M₀ is tried to reduce to 5% or less from the result in Table 1, the amount (C₀) of clear glass fragments mixed in the group of dark-colored glass fragments separated by the dark-colored glass fragment separating device is increased whereby the recovery percentage decreases. On the contrary, when the recovery percentage is tried to increase to 80% or more, the value of E₀/M₀ increases. Namely, it is impossible to satisfy both the recovery percentage and the separating performance of dark-colored glass fragments in the case of a throughput capacity of 1000 kg/hr or more. Accordingly, it is understood that an increase of the throughput capacity without sacrificing the recovery percentage is generally difficult.

[0025] There has been known that foreign-substance-attached glass fragments do not influence the color tone or distortion in a glass sheet to be produced even when they are mixed in a recycled material for glass sheets if they are contained in a slight amount. No problem will be caused in the quality of a glass sheet to be produced if an amount of foreign-substance-attached glass fragments is about 1% or less to the amount of ordinarily used glass materials such as clear glass fragments, soda ash, siliceous sand etc. It is considered that the content of foreign-substance-attached glass fragments in recovered glass fragments in the present invention is about 5%.

[0026] Accordingly, it is unnecessary to separate and remove all foreign-substance-attached glass fragments from the group of glass fragments. Taking this into account, a satisfactory recovery percentage is obtainable without reduction of the throughput capacity by dividing the process for separating foreign-substance-attached glass fragments into plural stages. Namely, the process for separating foreign-substance-attached glass fragments is divided into, for example, two stages. Then, in a first stage of process, a certain amount of dark-colored glass fragments remains in a group of glass fragments from which the dark-colored glass fragments are separated, so as to keep a relatively large amount to be treated. Then, in the same amount of treating as in the first stage of process, the remained dark-colored glass fragments are separated in a second stage of process so that dark-colored glass fragments remain at an allowable proportion, whereby the group of glass fragments after the second stage of process can be used as a recycled material for glass sheets. If the separation is conducted again in order to reduce further the proportion of remained dark-colored glass fragments, a certain amount of clear glass fragments is included in separated dark-colored glass fragments, and an amount of recovered glass fragments in the total amount of scrapped glass is reduced. Thus, it is preferable that the process for separating dark-colored glass fragments be divided into two stages. Specifically, it is preferable that the proportion of the dark-colored glass fragments remaining in the group of glass fragments from which a certain amount of dark-colored glass fragments are separated in the first stage, is about 10% or less, and the proportion of the dark-colored glass fragments remaining in the group of glass fragments from which a certain amount of dark-colored glass fragments are separated in the second stage, is about 5%. Thus, a satisfactory recovery percentage can be obtained without reducing the throughput capacity.

[0027] As described above, the existence of several% of foreign-substance-attached glass fragments in glass fragments to be recovered at the final recovering stage is allowable as a recyclable material for glass sheets. In this specification, accordingly, the separation or removal of recyclable glass fragments and foreign-substance-attached glass fragments from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state, means that at least a part of foreign-substance-attached glass fragments is separated from the group of glass fragments. The separated foreign-substance-attached glass fragments can be used for purposes other than the recycled material for glass sheets, such as a material for paved road. The glass fragments used for such purpose are not always necessary to be the foreign-substance-attached glass fragments. In the present application, accordingly, the separation or removal of recyclable glass fragments and foreign-substance-attached glass fragments from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state, means that a certain amount of clear glass fragments may exist in a group of foreign-substance-attached glass fragments separated from the group of glass fragments.

[0028] In drawings:

Fig. 1 is a diagrammatical side view showing an embodiment of the entire structure for performing the glass fragment recovering method according to the present invention;

Fig. 2 is a diagrammatical side view showing an embodiment of a dark-colored glass fragment separating device;

Fig. 3 is a diagrammatical side view showing an embodiment of an electroconductive glass fragment separating device; and

Fig. 4 is a front view of a typical glass sheet for a rear window of automobile viewed from a car interior side.

[0029] In the following, the present invention will be described in detail with reference to drawings.

[0030] In Fig. 1 showing an embodiment of the entire structure for performing the glass fragment recovering method of the present invention, wherein a symbol G designates the ground level for an equipment, and a direction perpendicular (in parallel to the paper plane) to the ground level G indicates a vertical direction. In the glass fragment recovering method to be performed using this, operations are conducted in the sequence of a process U for uniformizing the size of glass fragments, a first dark-colored glass fragment separating process CS1, a second dark-colored glass fragment separating process CS2, and an electroconductive glass fragment separating process ES.

[0031] The uniformizing process U is conducted as follows. Glass sheets conveyed without being broken from, for example, an automobile wrecker or the like, are broken into glass fragments. The obtained glass fragments (or glass fragments conveyed in a state as they are) are put into a hopper 11 and conveyed upward by means of a conveyor 12. A group of glass fragments conveyed upward is received by a sifter 13 in which excessively large glass fragments and excessively small glass fragments are removed to uniformize the size of glass fragments. The glass fragments having an excessively large size are difficult to eliminate in a separating process conducted later, such glass fragments having a length of, for example, not less than 15 mm long. The excessively small glass fragments imply very fine glass fragments difficult to be detected by an optical detector, which may cause generation of bubbles in a glass tank when they are put into the tank as a raw material for glass sheets, such glass fragments having the maximum length of, for example, 2 mm or less.

[0032] Subsequent to the uniformizing process U, the first dark-colored glass fragment separating process CS1 is conducted. A group of glass fragments from which the excessively large glass fragments and the excessively small glass fragments are removed, is put in a hopper 21 through a declining guide 14, and is conveyed upward again by means of a conveyor 22a. The glass fragments conveyed upward are put into a dark-colored glass fragment separating device 24a through a vibrating feeder 23a which has a width in a perpendicular direction with respect to the paper surface, and is inclined downward. In this case, a stream of the group of glass fragments dispersed uniformly on the surface of the vibrating feeder 23a, is formed by the operation of the vibrating feeder 23a. Thus, the group of glass fragments is dropped in a shape of stream from the vibrating feeder 23a onto the dark-colored glass fragment separating device 24a. The group of glass fragments on the dark-colored glass fragment separating device 24a is irradiated with light as described later so that dark-colored glass fragments are detected optically from the group of glass fragments. The detected dark-colored glass fragments are separated from the stream of glass fragments and are received by a dark-colored glass fragment recovering box 25a.

[0033] The second dark-colored glass fragment separating process CS2 is conducted in the same manner as the above-mentioned first dark-colored glass fragment separating process CS1 in principle. The group of glass fragments from which the dark-colored glass fragments are separated in the first dark-colored glass fragment separating process CS1 is conveyed again upward by means of a conveyor 22b. The glass fragments conveyed upward are put into a dark-colored glass fragment separating device 24b through a vibrating feeder 23b which has a width in a direction perpendicular to the paper surface, and is inclined downward. In this case, a stream of glass fragments dispersed uniformly on the surface of the vibrating feeder 23b, is formed by the operation of the vibrating feeder 23b. Thus, the group of glass fragments is dropped in a shape of stream from the vibrating feeder 23b onto a dark-colored glass fragment separating device 24b. The group of glass fragments on the dark-colored glass fragment separating device 24b is irradiated with light as described later so that dark-colored glass fragments are detected optically from the group of glass fragments. The detected dark-colored glass fragments are separated from the stream of the glass fragments and are received by a dark-colored glass fragment recovering box 25b.

[0034] Then, the electroconductive glass fragment separating process ES is conducted. A group of glass fragments from which the dark-colored glass fragments are separated in the second dark-colored glass fragment separating process CS2, is conveyed upward by means of a conveyor 31. The glass fragments conveyed upward are dropped by gravitation so as to form a stream of glass fragments, and the stream of glass fragments is introduced into electroconductive glass fragment separating devices 32 which are arranged in parallel in a direction perpendicular to the paper surface. A metal detector, which is described later, is used to detect electroconductive glass fragments from the group of glass fragments dropped on the electroconductive glass fragment separating devices 32. The detected electroconductive glass fragments are separated from the stream of glass fragments and are received by an electroconductive glass fragment recovering box 33. Glass fragments which are not separated from the stream of glass fragments are recovered by a clear glass fragment recovering box 34 to be used as a recycled material for glass sheets.

[0035] Next, description will be made as to dark-colored glass fragment separating devices used in first and second dark-colored glass fragment separating processes. Fig. 2 is a diagrammatical side view showing an embodiment of a dark-colored glass fragment separating device 24. Vibration feeders 23 have downwardly declining planes each having a width in a direction perpendicular to the paper surface. When the downwardly declining planes are vibrated, glass fragments are dispersed uniformly on the downwardly declining planes so that streams of glass fragments are formed as if waterfalls each having a width in a direction perpendicular to the paper surface are formed. At an inlet port of each of the dark-colored glass fragment separating devices 24, plural pairs of optical detectors 241a, 241b are arranged in parallel in a direction perpendicular to the paper surface to detect dark-colored glass fragments B from the stream of glass fragments dropping from each vibrating feeder 23.

[0036] When the dark-colored glass fragments B pass through the optical detectors 241a, 241b, light irradiated from a light emitter 241a is interrupted by the dark portion of dark-colored glass fragments B, and light cannot be received by a light receiver 241b. When light is not detected by the light receiver 241b, the dark-colored glass fragments B are recognized as having passed. A detection signal indicating that the dark-colored glass fragments B have passed, is supplied to a gas blower 242. Upon the supply of the detection signal, gas (air) is blown out from the gas blower 242 after a time during which the dark-colored glass fragments B move from the position of the optical detectors 241a, 241b to the gas blower 242, the moving time being previously inputted to a controlling device. By an air pressure of blown-out gas, the direction of movement of the dark-colored glass fragments B is deflected toward a dark-colored glass fragment separating path 243, and thus, the dark-colored glass fragments are separated from the stream of glass fragments.

[0037] When clear glass fragments C pass between the optical detectors 241a and 241b, light emitted from the light emitter 241a transmits through clear glass fragments to be received by the light receiver 241b. In this case, any detection signal is not transmitted to the gas blower 242. Accordingly, the gas blower 242 is not operated, and clear glass fragments C are fed to a recovering path 244 or the next process, without deflection.

[0038] Next, description will be made as to the electroconductive glass fragment separating devices used in the electroconductive glass fragment separating process. Fig. 3 is a diagrammatical side view showing an embodiment of an electroconductive glass fragment separating devices 32. A detection coil which is included in a detector 322 is wound around a pipe 321. A magnetic field is formed in the detection coil by supplying a high frequency current caused by a self-excited oscillation. When a group of glass fragments is fed into the magnetic field, an eddy current loss is generated only when electroconductive glass fragments in the group of glass fragments pass therethrough. By detecting an eddy current loss by the detector 322, detection is made whether or not the electroconductive glass fragments pass.

[0039] A signal indicating that the electroconductive glass fragments A detected by the detector 322 have passed, is supplied to a gas blower 325. Upon the supply of the signal, gas (or air) is blown out from the gas blower 325 after a time during which the electroconductive glass fragments A move from the position of the detection coils to the gas blower 325, which is previously inputted. By a pressure of blowing-out gas, the direction of movement of the electroconductive glass fragments A dropping vertically through the pipe 321 is deflected from the vertical direction to a slantwise direction, whereby the direction of movement of the electroconductive glass fragments A is changed. Thus, the electroconductive glass fragments A are separated from the stream of glass fragments. When clear glass fragments C pass through the magnetic field in the detection coil, any detection signal from the detector 322 is not supplied to the gas blower 325. Accordingly, the gas blower 325 does not operate whereby the clear glass fragments C can maintain the straight path.

[0040] As described above, the electroconductive glass fragments can be detected by examining an eddy current loss caused when the electroconductive glass fragments are passed through magnetic field in the coil. However, when the flow rate of glass fragments passing through the pipe per unit time is increased, the recovery percentage of clear glass fragments is reduced. For this, it is preferable that a plurality of electroconductive glass fragment separating devices are used to as to be in parallel in the electroconductive glass fragment separating process, whereby the throughput capacity can be increased. On the other hand, there is a limit in the flow rate of glass fragments. Accordingly, the maximum throughput capacity in the electroconductive glass fragment separating process is smaller than the throughput capacity in the dark-colored glass fragment separating process. In this sense, it is possible to treat efficiently a huge amount scrapped glass by conducting the electroconductive glass fragment separating process after the dark-colored glass fragment separating process as in the present invention.

[0041] The glass fragment recovering method of the present invention is, however, not limited to the above-mentioned. For example, the dark-colored glass fragment separating process may be a single stage or more than three stages depending on required treating efficiency and throughput capacity. However, the process comprising two stages is preferable from the viewpoint of being capable of providing easy control at the time of increasing the throughput capacity without sacrificing treating efficiency. Other than the above-mentioned technique of separating optically dark-colored glass fragments or the technique of separating electroconductive glass fragments with a metal detector, there can be used a technique of utilizing a difference of density of foreign-substance-attached glass fragments and clear glass fragments, or another technique. However, the optical technique or the metal-detecting technique utilizing a stream of glass fragments as described above is preferred because a large throughput capacity can be obtained. It is not always necessary to convey a group of glass fragments upward and drop downward in each process. It can be considered to perform a series of uniformizing process-dark-colored glass fragment separating process-electroconductive glass fragment separating process so as to step down in positional level in this order. However, it is preferable that a group of glass fragments is moved up and down for each process when a series of such treatments is conducted in a building because it is unnecessary to increase the ceiling level. Further, the structure of the separating device used in each process may be an appropriate structure depending on required treating efficiency and throughput capacity.

[0042] Now, the present invention will be described in detail with reference to Examples. However, it should be understood that the present invention is by no means restricted to such specific examples.

EXAMPLE

[0043] According to processes shown in Fig. 1, a test for separating foreign-substance-attached glass fragments from a group of glass fragments in which the foreign-substance-attached glass fragments exist in a mixed state, was conducted. As the dark-colored glass fragment separating device 24a or 24b in Fig. 1, the dark-colored glass fragment separating device 24 shown in Fig. 2 was used. As the electroconductive glass fragment separating device 32 in Fig. 1, the electroconductive glass fragment separating device 32 shown in Fig. 3 was used. In the dark-colored glass fragment separating device 24, the distance from the optical detectors 241a, 241b to the gas blower 242 was determined to be 15 cm, the time from the detection of dark-colored glass fragments A by the optical detectors 241a, 241b to the operation of the gas blower 242 was 44 milliseconds, and the time period of blowing-out of air from the gas blower 242 was 3 milliseconds respectively. The width (in a direction perpendicular to the paper surface in Fig. 1) of the vibrating feeder 23 is 1.2 m. 128 gas blowers 242 are arranged at equivalent intervals so as to correspond to vibrating feeders 23 in their width direction. 256 pairs of optical detectors 241a, 241b are arranged at equivalent intervals in a width direction of the vibrating feeders 23 so that two pairs of optical detectors are corresponded to a single gas blower 242.

[0044] In each of the electroconductive glass fragment separating devices 32, the inner diameter of the pipe 321 around which the detection coil 322 was wound was determined to be 20 mm, the distance between the detection coil 322 and the gas blower 325 was 30 cm, the time period requiring from the detection of electroconductive glass fragments A by the detection coil 322 to the operation of the gas blower 325 was 55 milliseconds, and the blowing-out time of air from the gas blower 325 was 2 milliseconds, respectively. In the electroconductive glass fragment separating device, a plurality of pipes are arranged in parallel in a direction perpendicular to the paper surface in Fig. 1, and the gas blower 325 etc. are arranged so as to correspond to each pipe. In this Example, the electroconductive glass fragment separating device provided with 6 pipes and gas blowers in the number corresponding to the pipes, was used.

[0045] In the uniformizing process, the size of glass fragments was uniformized so that glass fragments of 3.5 mm (the maximum length) or less and glass fragments of 11.2 mm (the minimum length) or more are removed. Specifically, a shifter having a screen size of 3.5-11.2 mm square was used for the shifter 13. For the dark-colored glass fragment separating process, a test was conducted by changing the flow rate. For the electroconductive glass fragment separating process too, a test was conducted by changing the flow rate. In first and second dark-colored glass fragments separating processes, flow rates were made to be the same. A result is shown in Tables 2 and 3.

[0046] In Table 2, "flow rate" indicates an amount of a group of glass fragments per unit time (unit: kg/hr), flowing from a vibration feeder to a dark-colored glass fragment separating device in a first or second dark-colored glass fragment separating process; "B/M" indicates a proportion (unit: %) of an amount of dark-colored glass fragments (B) to the total amount (M) of a group of prepared glass fragments; "B_u/M_u" indicates a proportion (unit: %) of an amount of dark-colored glass fragments (B_u) to the total amount (M_u) of the group of glass fragments after the uniformizing process (before the first process); "B₁/M₁" in Column (a) indicates a proportion (unit: %) of an amount (B₁) of dark-colored glass fragments in a group of glass fragments after the first process to the total amount (M₁) of the glass fragment group after the first process (before the second process); "B₂/M₂" in Column (a) indicates a proportion (unit: %) of an amount (B₂) of dark-colored glass fragments in the glass fragment group after the second process to the total amount (M₂) of the group of glass fragments after the second process; "C₁/M'₁" in Column (b) indicates a proportion (unit: %) of an amount (C₁) of clear glass fragments to the sum (M'₁) of the amount (C₁) of clear glass fragments mixed in the group of dark-colored glass fragments separated in the first process (before the second process) and an amount of the separated dark-colored glass fragments; "C₂/M'₂ in Column (b) indicates a proportion (unit: %) of an amount (C₂) of clear glass fragments to the sum (M'₂) of the amount (C₂) of clear glass fragments mixed in the group of dark-colored glass fragments separated in the second process and an amount (B'₂) of the separated dark-colored glass fragments; and "recovery percentage" indicates a proportion (unit: %) of the total amount (M₂) of the group of glass fragments to be supplied to the next electroconductive glass fragment separating process after the second process to the total amount (M) of the prepared group of glass fragments.

[0047] In Table 3, "flow rate" indicates a charged amount (unit: kg/hr) of glass fragments charged into six electroconductive glass fragment separating devices per hour; "content of printed electroconductive layer before treatment (or at the initial stage)" indicates a content (unit: ppm) of printed electroconductive layer components to the total amount of the group of glass fragments after the second dark-colored glass fragment separating process (before the electroconductive glass fragment separating process); "content of printed electroconductive layer after treatment" indicates a content (unit: ppm) of printed electroconductive layer components to the total amount of recovered glass fragments after the electroconductive glass fragment separating process; "content of printed electroconductive layer after separation" indicates a content (unit: ppm) of printed electroconductive layer components to the total amount of glass fragments in the electroconductive glass fragments separated in the electroconductive glass fragment separating process; and "recovery percentage" indicates a proportion (unit: %) of the total amount of the group of glass fragments recovered in the electroconductive glass fragment separating process to the total amount of the glass fragment group after the second dark-colored glass fragment separating process (before the electroconductive glass fragment separating process).

[0048] Contents of printed electroconductive layer components shown in Table 3 are all estimated values which are obtained by the following manner.

[0049] First, a predetermined amount of glass fragments is extracted from a group of glass fragments as a mother body. The extracted glass fragments are dispersed on a plane so as not to cause an overlapping state, and a photograph of the glass fragments in a dispersed state is taken by a CCD camera. The total surface area of the glass fragments and the total surface area of the printed electroconductive layer portion are determined based on a picture image taken by the camera. The proportion of the total surface area of the printed electroconductive layer portion to the total surface area of the glass fragments is calculated. A calculated value of the proportion is multiplied with a coefficient (i.e., the ratio of the thickness of the printed electroconductive layer portion to the thickness of the glass fragment: for example, when the thickness of the glass fragments is 3.5 mm and the thickness of the printed electroconductive layer portion is 7 µm, it is 0.002) to obtain a value as the content of printed electroconductive layer components. The reason why the content is referred to as an estimated value is that a predetermined amount of glass fragments is extracted from a group of glass fragments as a mother. body.

Table 2

Flow rate	B/M	Bu/Mu	(a)		(b)		Recovery percentage
			B1/M1	B2/M2	C1/M1	C2/M2
632	17	15	7	6	29	40	83
697	16	15	6	4	28	41	82
731	18	17	8	6	32	41	80
788	18	18	8	6	34	51	79
888	15	18	7	5	47	49	79
908	15	17	6	3	37	56	79

Table 3

Flow rate	Content of printed electroconductive layer before treatment	Content of printed electroconductive layer after treatment	Content of printed electroconductive layer after separation	Recovery percentage
241	139	90	284	75
181	100	80	197	83
175	104	74	58	84

[0050] In Table 2, it is understood that in a case of a flow rate of 888 kg/hr or a flow rate of 908 kg/hr, the content of mixed dark-colored glass fragments in a recovery percentage of about 80% can be made 5% or less by dividing the dark-colored glass fragment separating process into two stages. Accordingly, it is understood that use of a flow rate of 800 kg/hr is preferred. In a case of a flow rate of 908 kg/hr, the value of C₂/M'₂ exceeds 50% which appears to be a large value. However, the value of M'₂ is very smaller than the value of M (M'₂ + M₂ = M₁, M'₁+ M₁ = M_u, M'_u + M_u = M or M'_u is an amount of glass fragments removed in the uniformizing process U). Accordingly, a value indicating the ratio of an amount of clear glass fragments mixed in the group of glass fragments (the group of separated dark-colored glass fragments) which is not usable as recyclable glass fragments, is very small in comparison with the total amount of the group of prepared glass fragments.

[0051] In this sense, the fact that C₂/M'₂ is about 40% shows that determination has been made so as not to contain clear glass fragments as possible in a group of glass fragments which is not usable as recycled glass fragments. Such condition of determination corresponds to a test under a smaller flow rate among actually conducted tests. On the contrary, in such condition of determination, the proportion of dark-colored glass fragments in the group of recovered glass fragments is slightly larger than 5%. In the case of a smaller flow rate in the conducted tests, it is estimated that the proportion of dark-colored glass fragments in a group of recovered glass fragments can be less than 5% by increasing slightly in a permissible range the proportion of an amount of clear glass fragments in a group of glass fragments which cannot be used as recyclable glass fragments.In order to determine the proportion of the amount of clear glass fragments to be slightly larger in a permissible range, it can be considered that for example, the width of the vibrating feeders is narrowed slightly to increase the density of glass fragments on the vibrating feeders.

[0052] When an operation rate of 8 hours per day, i.e., 200 days per year is assumed, a flow rate of 900 kg/hr means a throughput capacity of 1440 ton/year. Accordingly, it is understood from the result in Table 1 that in the glass fragment recovering method suitable for recycling glass sheets wherein the content of mixed dark-colored glass fragments can be 5% or less while a recovery percentage of about 80% is maintained, the separation of dark-colored glass fragments can be achieved for scrapped glass of more than 1000 tons per year.

[0053] Further, it is understood from the result in Table 3 that the content of printed electroconductive layer components mixed in recovered glass fragments can be 100 ppm or less in a recovery percentage of about 80%. In the conducted tests, six electroconductive glass fragment separating devices are used. When the number of electroconductive glass fragment separating devices is made, for example, 2-3 times as much as the number of the devices used in the tests in order to meet an amount of treatment in the dark-colored glass fragment separating process, a glass fragment recovering method suitable for recycling glass sheets, which can treat scrapped glass of about 1000 tons per year can be provided.

[0054] Thus obtained recyclable glass fragments in which the content of dark-colored glass fragments was 5% or less and the content of printed electroconductive layer components was 100 ppm or less, glass fragments recovered from scrapped glass without containing foreign-substance-attached glass fragments to be separated and/or glass fragments recovered from defect glass sheets generated in a glass sheet plant, and a raw material used usually for manufacturing glass sheets, such as soda ash, silica sand, feldspar, potassium carbonate, lime etc., and coloring components and auxiliary agents added according to need were charged in a proportion of 2:6:2 into a glass tank for producing glass sheets, and glass sheets were produced by a float process. Glass sheets having a predetermined color tone and transmissivity without any distortion could be obtained.

[0055] According to the present invention, a process for separating foreign-substance-attached glass fragments with a printed dark color layer from a group of glass fragments is repeated plural times whereby foreign-substance-actached glass fragments with a printed electroconductive layer are separated. Accordingly, glass fragments usable as recyclable glass sheets can be recovered from scrapped glass at a large throughput capacity without sacrificing recovery percentage.

[0056] The entire disclosures of Japanese Patent Application No. 2002-164992 filed on June 5, 2002, Japanese Patent Application No. 2002-164993 filed on June 5, 2002, Japanese Patent Application No. 2002-224856 filed on August 1, 2002 and Japanese Patent Application No. 2002-224857 filed on August 1, 2002 including specifications, claims, drawings and summaries are incorporated herein by reference in their entireties.

Claims

1. In a glass fragment recovering method wherein recyclable glass fragments and foreign-substance-attached glass fragments are separated from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments with a printed dark color layer and a printed electroconductive layer exist in a mixed state so that the recyclable glass fragments are recovered, the glass fragment recovering method being characterized in that foreign-substance-attached glass fragments with a printed dark color layer are separated from the group of glass fragments; foreign-substance-attached glass fragments with a printed electroconductive layer are separated from the group of glass fragments from which the foreign-substance-attached glass fragments with a printed dark color layer are separated, and recyclable glass fragments are recovered.

2. The glass fragment recovering method according to Claim 1, wherein a stream of the group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state, is formed; light is irradiated to the stream of the group of glass fragments to detect the foreign-substance-attached glass fragments with a printed dark color layer; the detected foreign-substance-attached glass fragments are separated from the stream of the group of glass fragments; a metal detector is operated for the group of glass fragments from which the foreign-substance-attached glass fragments with a printed dark color layer are separated, to detect the foreign-substance-attached glass fragments with a printed electroconductive layer, and the detected foreign-substance-attached glass fragments are separated from a stream of glass fragments from which the foreign-substance-attached glass fragments with a printed dark color layer are separated.

3. The glass fragment recovering method according to Claim 2, wherein the metal detector used is an electronic metal detector.

4. The glass fragment recovering method according to Claim 2 or 3, wherein the group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state is conveyed upward; the conveyed group of glass fragments is caused to drop by gravitation to form a stream of the group of glass fragments whereby the foreign-substance-attached glass fragments with a printed dark color layer are separated; the group of glass fragments from which the foreign-substance-attached glass fragments with a printed dark color layer are separated, is again conveyed upward; the conveyed group of glass fragments is caused to drop by gravitation to form a stream of the group of glass fragments.

5. The glass fragment recovering method according to any one of Claims 1 to 4, wherein a process for separating the foreign-substance-attached glass fragments with a printed dark color layer from the group of glass fragments is divided into plural times of processes to be conducted consecutively whereby the foreign-substance-attached glass fragments with a printed dark color layer are separated.

6. In a glass fragment recovering method wherein recyclable glass fragments and foreign-substance-attached glass fragments are separated from a group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments with a printed dark color layer exist in a mixed state so that the recyclable glass fragments are recovered, the glass fragment recovering method being characterized in that a process for separating the foreign-substance-attached glass fragments from the group of glass fragments is repeated plural times.

7. The glass fragment recovering method according to Claim 6, wherein a process for forming a stream of the group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state; detecting the foreign-substance-attached glass fragments by irradiating light to the stream of the group of glass fragments, and separating the detected foreign-substance-attached glass fragments from the group of glass fragments, is repeated plural times.

8. The glass fragment recovering method according to Claim 7, wherein a process for conveying upward the group of glass fragments in which the recyclable glass fragments and the foreign-substance-attached glass fragments exist in a mixed state; causing the conveyed group of glass fragments to drop by gravitation to form a stream of the group of glass fragments, and separating the foreign-substance-attached glass fragments from the group of glass fragments, is repeated plural times.

9. The glass fragment recovering method according to any one of Claims 5 to 8, wherein a process for separating the foreign-substance-attached glass fragments-with a printed dark color layer is conducted two times.

10. A glass sheet producing method characterized in that glass fragments recovered by a glass fragment recovering method described in any one of Claims 1 to 9 are put in a glass tank, and a glass sheet is formed by a float process.

11. The glass sheet producing method according to Claim 10, wherein the recovered glass fragments are put into the glass tank together with a raw material for a glass sheet, and a glass sheet is formed by a float process.

Drawing