GB2130124A

GB2130124A - Method and apparatus for reclamation of raw materials

Info

Publication number: GB2130124A
Application number: GB08330464A
Authority: GB
Inventors: Yasuo Iwata
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-11-17
Filing date: 1983-11-15
Publication date: 1984-05-31
Also published as: DE3341608A1; GB8330464D0; IT1170248B; IT8323757A1; FR2536006A1; NL8303935A; IT8323757A0; KR840006778A; JPS5991028A

Abstract

Raw materials are reclaimed from magnetic tape scrap by cutting the scrap into small pieces; treating the cut scrap with aqueous alkali solution; stirring the alkali-treated scrap at high speed thereby completely separating them into tape substrate and magnetic powder; washing the scrap with water and draining it; stirring only the tape substrate fragments at high speed under vacuum and at a temperature not exceeding the melting point of the material of the tape substrate and thereby drying the fragments and curling them into twisted strings having a moisture content not exceeding 0.01%; and feeding the twisted strings in their unaltered form into an extrusion pelletiser where they are pelletised.

Description

SPECIFICATION Method and apparatus for reclamation of raw materials This invention relates to a method for the reclamation of raw material from scrap tape and to an apparatus to be used for working that method. More particularly, this invention relates, but is not limited, to a method and apparatus for efficient reclamation of polyester and magnetic powder from magnetic tape scrap using a polyester film as its substrate.

In recent years, the rapid growth of the information industry has promoted the extensive use of magnetic recording tapes such as audio recording tapes, computer tapes, and video tapes in huge volumes. Particularly, magnetic tape using a substrate of polyethylene terephthalate possess excellent properties and, accordingly, has come to be produced in gradually increased volumes in recent years.

Magnetic tape scrap is generated in large volumes during the course of production and during the course of actual use by the consumers.

At present, such magnetic tape scrap is disposed of as by burying and by being burnt in incinerators.

From the standpoint of encouraging reclamation of resources, full exploitation of magnetic tape scrap is a prominent desideratum.

It has previously been proposed to reclaim the raw materials of magnetic tape scrap, by immersing the scrap in an aqueous alkali solution to separate the polyester tape substrate from the magnetic powder. When magnetic tape scrap is simply immersed in aqueous alkali solution, the material deposited on the substrate is barely caused to swell and the material cannot be completely separated from the substrate.

The polyester type substrate of magnetic tape scrap which has undergone the treatment with the aqueous alkali solution yields to hydrolysis when it is heated in the presence of water. The conventional method gives no consideration to this fact.

Reclaimed polyester resin has therefore inferior transparency and poor mechanical properties and, as such, is not usable in fibres and films for which polyethylene terephthalate by nature is particularly suitable. It is only barely usable where there is little concern to the question of physical properties and offer little room for changes of added value.

The conventional method described above requires the polyester tape substrate stripped of the magnetic powder to be cut into small pieces preparatory to the subsequent treatment. Since these small pieces are very thin and the transfer of heat between adjacent small pieces occurs at a low speed, the small pieces delivered in their unaltered form to an extrusion pelletiser cannot be smoothly drawn into the machine interior and are extruded through the machine with very poor efficiency and are vulnerable to local thermal degradation. That situation may suggest that the difficulties may be removed by having the small pieces melted under an atmosphere of inert gas in a separate heating device. However, that would require the provision of bulky facilities and the operation of such facilities would entail extra time and labour.In any event, the small pieces would be kept exposed to the danger of sustaining local thermal hysteresis while they are being melted under heat. This phenomenon constitutes itself a cause for further degradation of quality of the resin to be finally reclaimed.

In one aspect, the invention provides a method for the reclamation of raw materials from magnetic tape scrap comprising, in combination: (A) comminuting the magnetic tape scrap. (B) immersing the comminuted magnetic tape in an aqueous alkali solution and thereby swelling the comminuted scrap. (C) stirring the swollen comminuted scrap at high speed in water and thereby separating the scrap into fragments of tape substrate and magnetic powder, (D) washing with water and then dewatering the separated substrate fragments, (E) heating the substrate fragments under vacuum and, at the same time, stirring them at a high speed thereby to curl them into short twisted strings, and drying them until the moisture content thereof decreased below 0.01%, and (F) pelletising the twisted strings of substrate.

The invention also provides apparatus for the reclamation of raw materials from magnetic tape scrap, comprising, in combination, (A) a tape scrap cutting device capable of comminuting a composite tape having a plastic tape substrate and a coating layer and other layers such as of paper or metal superposed thereon, (B) a tank for immersing the comminuted composite tape in an aqueous alkali solution, (C) a stirrer provided with high-speed rotary blades and adapted to stir the alkali-treated comminuted composite tape, to separate the composite tape into fragments of plastic tape substrate and the material of the previously superposed layer or layers, and to wash them with water, (D) a device for separating the washed substrate fragments and the layer material from each other, (E) a vacuum stirring and drying device provided with high-speed rotary blades, a heating device, and an evacuating device and adapted to heat and stir under vacuum the substrate fragments stripped of the layer material, thereby to curl the substrate fragments into twisted strings, and (F) a pelletiser serving to melt the dried twisted strings of substrate under heat and pelletise the resultant melt.

The invention will be more readily understood by way of example from the following description of apparatus and method for reclaiming the raw materials of tape scrap, reference being made to the accompanying drawing which schematically illustrates the apparatus.

As illustrated in the drawing, the apparatus for the reclamation of raw materials from magnetic tape scrap principally comprises, in combination: a tape scrap cutting device 1 capable of comminuting by cutting a composite tape having a coating layer or layers such as of paper or metal interposed on a plastic tape substrate; a tank 2 for immersing the comminuted composite tape in an aqueous alkali solution; a peeling stirrer 3 provided with high-speed rotary blades and adapted to stir the alkali-treated composite tape in water and to separate the material previously deposited on the surface from the sustrate; a separating and washing stirrer 4 provided with high-speed rotary blades and adapted to stir and wash the fragments of substrate treated by the peeling stirrer 3 and the surface-deposited material peeled off the substrate fragments, and to dewater by draining the fragments and material; a vacuum stirring and drying device 5 provided with high-speed rotary blades, a heating device, and a vacuum pump and adapted to stir the washed and drained substrate fragments under vacuum and with the application of heat, and consequently to curl the fragments into twisted strings; and an extrusion pelletising device 6 serving to melt the vacuum dried twisted strings of plastic tape and pelletise the resultant melt.

The apparatus described above is constructed to serve the purpose of reclaiming the raw materials of magnetic tape scrap. When it is partially modified as described hereafter, it serves the purpose of reclaiming from some other type of composite tape the raw materials used in that composite tape.

The tape scrap cutting device 1 cuts magnetic tape scrap into small pieces about 1 to 5 cm in length so as to facilitate the various subsequent treatments such as washing with water, draining, and drying and smoothing the transportation of tape scrap to the subsequent steps and, at the same time, to enable the cut scrap to be curled into twisted strings in the vacuum stirring and drying device 5.

The immersion treatment tank 2 has an opening in the top and holds an aqueous solution containing caustic soda in a concentration of about 5 to 20%.

A conveyor line 7 is laid between the tape scrap cutting device 1 and the tank 2 and transfers small cut pieces of magnetic tape scrap cut in the tape scrap cutting device 1 to the alkali-treating tank 2.

Immersion of the magnetic tape scrap in the alkali-treating tank 2 is effected by placing the comminuted pieces of scrap in a basket made of an alkali proof material and causing the basket containing the scrap to pass through the bath of the aqueous alkali solution in the tank.

Between the tank 2 and the stirrer 3, there is a semi-finished product storage vessel 8 for temporarily accommodating the comminuted pieces of magnetic tape scrap which has been swollen in the alkali-treatment tank 2. The storage vessel 8 has a strainer 9 near the bottom for removing by gravity water adhering to the swollen pieces of scrap.

Between the tank 2 and the semi-finished product storage vessel 8, there is a transfer device capable of lifting by cable the basket which holds the cut scrap in the tank 2, discharging the scrap from the basket in to the semi-finished product storage vessel 8. Alternatively, transfer of the treated scrap may be effected by a raking device 10 having a netlike bottom and adapted to drain water from the wet scrap, rake them and release them into the semi-finished product storage vessel 8.

Between the half-finished product storage vessel 8 and the peeling stirrer 3, a conveyor line 7 is laid to transfer the cut scrap from the former to the latter. Similarly, conveyor lines 7 are arranged between the other parts of the process line.

The peeling stirrer 3 is in the form of a mixing tank provided with a heating device and high speed rotary blades. It receives the comminuted scrap from vessel 3; and water or an aqueous alkali solution, the latter being used for the treatment of magnetic tape scrap which is difficult to separate, heats the scrap to about 900 to 950C and stirs them simultaneously with the rotary blades operated at a rate of about 1200 r.p.m. to effect separation of the tape substrate from the magnetic powder. When aqueous alkali solution is used for this treatment, the solution is recovered after the separation and the separated substrate fragments are washed with water as described afterwards. A commercially available mixer (produced by Mitsui Miike Manufactory and marketed under trademark designation of Henschel Mixer) is advantageously used as the stirrer 3.Other stirrers of comparable performance may be used when desired.

The separating and washing stirrer 4 is constructed similarly to the peeling stirrer 3. In it, the substrate fragments and the separated magnetic powder are stirred at high speed in water of volume of about 1 to 1.5 times the combined volume of the fragment and powder so as to effect thorough separation thereof, wash them and dewater them.

Since the peeling stirrer 3 and the separating and washing stirrer 4 have similar constructions, it is not imperative to use two separate stirrers, one each for the two dissimilar treatments described above, and it is, instead, permissible to use just one such stirrer for one or the other of the two treatments at any one time. The sole use of the peeling stirrer 3, for example, for the two treatments just described is effected specifically by first carrying out the peeling treatment in the stirrer 3, then draining the stirrer while allowing the substrate fragments to remain therein, and thereafter pouring water into the stirrer and giving the fragments the required water wash. Adoption of this method permits omission of one of the two stirrers mentioned above. It is also permissible to use two stirrers alternately so that the two treatments may be carried out independently without any interruption.

Disposed between the separating and washing stirrer 4 and the vacuum stirring and drying device 5 is a small tank 1 1 for the temporary storage of substrate fragments which have been washed and dewatered and which are subsequently fed automatically to the subsequent drying step.

A wet magnetic separator 12, recovers the magnetic powder which has been separated and discharged by the peeling stirrer 3 and the separating and washing stirrer 4. The effluent entraining the magnetic powder is brought into this wet magnetic separator 12 through a cleaning liquid transfer pipe 13 which is connected to the respective outlets of the stirrers 3, 4. This cleaning liquid transfer pipe 13 has a capacity large enough to allow temporary accommodation of the effluents from the stirrers 3, 4. Alternatively, a separate storage tank (not shown) capable of receiving the effluents to regulate the volume of influent to the wet magnetic separator 12 is required. To the cleaning liquid transfer pipe 13 are additionally connected discharge pipes from the immersion treatment tank 2 and the semifinished product storage vessel 8.

The wet magnetic separator 12 consists of a water storage tank incorporating a discharge outlet in the bottom, a permanent magnet disposed on the bottom of the tank, and a filter disposed halfway up the interior of the tank; the filter serves to separate the magnetic powder from the effluents. The magnetic powder thus separated is washed and dewatered with a washing dehydrator (not shown) and then, in a stirring and drying pelletiser 14, is stirred at high speed under application of heat. In this manner, the magnetic powder is dried, pulverised, and sieved. A Henschel mixer described above may be advantageously used as the stirring and drying pelletiser 14. The pellets of the magnetic powder obtained as described above are packaged with a metering packaging device 15.The effluent from the wet magnetic separate 12 is accommodated in a neutralising tank 16, there to be adjusted by addition of a neutralising agent to the quality satisfying the prescribed standard for effluent. The neutralising tank 16 has at its outlet a magnet intended to capture minute amounts of magnetic powder entrained in the effluent.

Instead of the wet magnetic separator 12, a sedimentation tank may be used, wherein the effluent carrying the magnetic powder is subjected repeatedly to decantation and sedimentation until the magnetic powder is cleaned to desired purity.

The vacuum stirring and drying device 5 consists of a mixing tank incorporating a heating device, high speed rotary blades within the tank, and a vacuum pump serving to evacuate the interior of the mixing tank. In this vacuum stirring and drying device 5, the polyester tape substrate fragments are dried under vacuum at temperatures not exceeding the softening point of the polyester resin making up the tape substrate, at 900 to 1 00C for example, until the moisture content thereof decreases below 0.01%, preferably in the range of 0.006% to less than 0.01% and, at the same time, they are curled by the high-speed rotation to form short twisted strings. Again, a Henschel mixer described above may be advantageously used as the vacuum stirring and drying device.

The extrusion pelletising device 6 consists of a melt extruder 6a, a water-cooled transfer device 6b, and a pelletiser 6c. The melt extruder 6a which has an open hopper adjacent the discharge outlet of the vacuum stirring and drying device 5 melts the curled polyester tape substrate fragments received from the vacuum stirring and drying device 5 at a temperature of about 2600C and extrudes the resultant melt as a plurality of cords.

The transfer device 6b cools and transfers the cords of resin to the pelletiser 6c, there to be cut into pellets. The polyester pellets thus produced are allowed to fall into a receptacle box 17 and subsequently packaged by a packaging device 18.

The method of reclaiming from magnetic tape scrap the polyester resin making up the tape substrate and the magnetic powder by the use of the apparatus described above will now be explained.

Magnetic tape scrap is continuously fed into the tape scrap cutting device 1. In the tape scrap cutting device 1 ,they are cut into small pieces about 1 to 5 cm in length. The small cut pieces are then conveyed to the immersion treatment tank 2, there to be kept immersed overnight in an aqueous solution containing about 5 to 20% of caustic soda.

The magnetic powder which is separated from the small cut pieces and sedimented during the immersion is recovered by attraction with a permanent magnet or separated by a filter disposed at the outlet of the tank during the replacement of the alkali solution with a fresh supply.

The magnetic tape scrap, which has been swollen during the immersion, is temporarily held in the semi-finished product storage vessel 8, where it is dewatered, and is then fed to the peeling stirrer 3 holding hot water at 900 to 950C and stirred therein for about 20 minutes. The aqueous caustic soda solution separated from the magnetic tape scrap within the semi-finished product storage vessel 8 is adjusted to an appropriate pH value and returned for reuse to the immersion treatment tank 2. The specific gravity of the magnetic tape scrap supplied to the peeling stirrer 3 is greater than that of the hot water and settles to the bottom of the stirrer and are exposed thoroughly to the stirring action.Where the layers of the magnetic tape, because of the properties of their materials, defy separation by physical stirring, an aqueous alkali solution heated to the same temperature may be used in the place of hot water. By this stirring, the magnetic tape scrap is separated into fragments of transparent polyester tape substrate and a slurry of magnetic powder.

Then, the water in the peeling stirrer 3 is discharged through the cleaning liquid transfer pipe 13, leaving the sediment intact in the stirrer 3. The remaining sediment is conveyed to the separating and washing stirrer 4. The aqueous caustic soda solution held temporarily in the cleaning liquid transfer pipe 1 3 is forwarded to a magnetic powder recovery device in the subsequent step.

The polyester tape substrate fragments which have been washed and dewatered in the separating and cleaning stirrer 4 are forwarded for temporary storage in tank 11 and thence fed automatically to the subsequent step of drying.

The liquid spent in the separating and cleaning stirrer 4 together with the effluent from the peeling stirrer 3, is temporarily stored in the cleaning liquid transfer pipe 13 and then supplied in fixed volume to the wet magnetic separator 12, there to be stripped of the magnetic powder and cleaned.

In the stirring and drying pelletiser 14, the magnetic powder is dried, pulverised, sieved at a temperature not exceeding 4000 C, and preferably near 1 500C, and pelletised to produce the finished product. The magnetic powder, when heated at temperatures not exceeding 4000 C, will not suffer any substantial degradation of its quality.

The effluent from the wet magnetic separator 12 is neutralised in the neutralising tank 16 and then discarded as plant effluent. In the meantime, the polyester tape substrate fragments are supplied from the small cut pieces storage tank 11 to the vacuum stirring and drying device 5, there to be stirred at a high speed at 90 to 1 000C under vacuum. They are then supplied to the hopper of the extrusion pelletising device 6. During the course of the stirring, the substrate fragments are dried under vacuum by the high-speed operation of the rotary blades until the moisture content thereof decreases below 0.01%, preferably in the range of 0.006% to less than 0.01% and, at the same time, curled in the form of twisted strings.

In theory, the extrusion pelletising device 6 is capable of pelletising the substrate fragments even when the fragments have not undergone the treatment with the vacuum stirring and drying device. Unfortunately, the substrate fragments are too thin to transfer heat advantageously, with the result that the efficiency of the operation of the stirrer will be notably impaired. There is also a possibility that the substrate fragments, when suffered to retain a high moisture content, will undergo hydrolysis in the presence of water and suffer from a heavy loss of molecular weight.

The treatment with the vacuum stirring and drying device 5 enables the substrate fragments to be formed in the shape of twisted strings and, at the same time, to be heated uniformly throughout their entire volume. Consequently, the extrusion pelletising device 6 can operate 2.5 to 3 times more efficiently than when it is operated with the fragments supplied thereto in their untwisted form. Since the twisted strings have a water content not exceeding 0.01%, they have substantially no possibility of undergoing hydrolysis and consequently losing molecular weight. Especially, when the moisture content is in the range of 0.006% to less than 0.01% the twisted strings have no possibility of suffering deterioration in quality due to overheating.

The twisted strings are fed in their highly dry state to the hopper of the melting device of the extrusion pelletising device 6, there to be melted and extruded into a plurality of cords under application of heat. The hot cords are then cooled with the water-cooled transfer device 6b and pelletised with the pelletiser 6c.

The method described above permits efficient reclamation of polyester-based resin and magnetic powder, both in high purity, from magnetic tape scrap.

Since the polyester resin from the tape substrate is dried by the vacuum drying until the moisture content thereof decreases below 0.01% and is consequently protected from the phenomenon of hydrolysis which is otherwise liable to occur during the thermal melting step, the method can reclaim polyester resin of higher molecular weight and better quality than the polyester resin reclaimed by the conventional method.

In order to reclaim the magnetic powder separately of the polyester resin, a magnetic separator or a sedimentation tank has been described. Optionally, the reclamation of the magnetic powder may be effected by means of static electricity, or pneumatically, or by the use of a sieve, for example.

In addition to the reclamation of polyester from magnetic tape scrap, the apparatus and method of this invention may be used for reclaiming plastics from various composite tapes having substrate of polyester and other plastic substances and coating layers of silver salts, paper, and metals.

Claims

1. A method for the reclamation of raw materials from magnetic tape scrap, comprising, in combination, (A) comminuting the magnetic tape scrap, (D) immersing the comminuted magnetic tape in an aqueous alkali solution and thereby swelling the comminuted scrap, (C) stirring the swollen comminuted scrap at high speed in water and thereby separating the scrap into fragments of tape substrate and magnetic powder, (D) washing with water and then dewatering the separated substrate fragments, (E) heating the substrate fragments under vacuum and, at the same time, stirring them at a high speed thereby to curl them into short twisted strings, and drying them until the moisture content thereof decreased below 0.01%, and (F) pelletising the twisted strings of substrate.

2. A method according to claim 1, wherein the separation of the swollen comminuted scrap into fragments of plastic tape substrate and magnetic powder is effected by placing the scraps with water or an aqueous alkali solution in a peeling stirrer comprising a mixing tank incorporating therein a heating device and rotary blades disposed within the mixing tank and adapted to be driven at high speed, thereby enabling the comminuted scrap to be heated to about 90 to 950C and, at the same time, stirred at a high speed by the rotation of the rotary blades.

3. A method according to claim 1 or claim 2, wherein the washing and dewatering of the fragments of plastic tape substrate is accomplished by stirring the substrate fragments and magnetic powder at high speed in water of a volume of about 1 to 1.5 times the combined volume of the fragments and magnetic powder to complete the separation of the magnetic powder, then washing the separated fragments and magnetic powder with water, and thereafter dewatering the substrate fragments and magnetic powder.

4. A method according to any one of the preceding claims, wherein the curling of the fragments of plastic tape substrate into twisted strings and, at the same time, drying said twisted strings is accomplished by stirring the fragments of plastic tape substrate at high speed at a temperature of 90 to 11 OOC and under vacuum.

5. A method according to any one of the preceding claims, wherein the tape substrate is made of polyester.

6. A method according to any one of the preceding claims, wherein the moisture content of the substrate fragments after heating under vacuum is in the range of 0.006% to less than 0.01%.

7. Apparatus for the reclamation of raw materials from magnetic tape scrap, comprising, in combination, (A) a tape scrap cutting device capable of comminuting a composite tape having a plastic tape substrate and a coating layer and other layers such as of paper or metal superposed thereon, (B) a tank for immersing the comminuted composite tape in an aqueous alkali solution, (C) a stirrer provided with high-speed rotary blades and adapted to stir the alkali-treated comminuted composite tape, to separate the composite tape into fragments of plastic tape substrate and the material of the previously superposed layer or layers, and to wash them with water, (D) a device for separating the washed substrate fragments and the layer material from each other, (E) a vacuum stirring and drying device provided with high-speed rotary blades, a heating device, and an evacuating device and adapted to heat and stir under vacuum the substrate fragments stripped of the layer material, thereby to curl the substrate fragments into twisted strings, and (F) a pelletiser serving to melt the dried twisted strings of substrate under heat and pelletise the resultant melt.

8. Apparatus according to claim 7, wherein a semi-finished product storage vessel for permitting temporary storage of composite tape scrap treated in the alkali solution tank is disposed between that tank and the stirrer.

9. Apparatus according to claim 8, wherein a transfer device adapted to lift a basket containing the comminuted composite tape scrap immersed in the alkali tank is arranged to transfer the comminuted, scrap from within the basket into the semi-finished product storage vessel or a raking device provided with a netlike bottom and adapted to drain wet comminuted scrap, rake the scrap, and transfer it into the semi-finished product storage vessel is disposed between the alkali tank and the semi-finished product storage vessel.

10. Apparatus according to claim 8 or claim 9, wherein a conveyor line is laid between the semifinished product storage vessel and the peeling stirrer and used for transferring the comminuted composite tape scrap from the semi-finished product storage vessel to the peeling stirrer.

11. Apparatus according to any one of claims 7 to 10, wherein the composite tape scrap is magnetic tape scrap.

12. A method for the reclamation of raw material from magnetic tape scrap, substantially as herein described with reference to the accompanying drawing.

13. Reclaimed material obtained by the method of any one of claims 1 to 6 and 12.

14. Apparatus for the reclamation of raw material from magnetic tape scrap, substantially as herein described with reference to the accompanying drawing.