GB2202837A - Process for recovering magnetic powder from a bound magnetic recording material - Google Patents

Abstract

Process for recovering magnetic powder (e.g. Fe2O3, CrO2) from a bound magnetic recording material, e.g. magnetic recording tape, comprises treating the recording material at least once in a solution, preferably boiling, comprising an organic solvent (e.g. a ketone, an ester, an halogenated hydrocarbon or a S-compound such as DMSO) capable of partially dissolving or swelling the binder in the magnetic material, water and/or an alcohol, and an alkali. The solid product of the treatment may be subjected to a further treatment at least once in an aqueous alkali solution.

Description

PROCESS FOR RECOVERING MAGNETIC POWDER FROM MAGNETIC RECORDING MATERIAL The present invention relates to a process for recovering magnetic powder from a magnetic recording material such as a magnetic tape or a magnetic disk.

A coated-type magnetic tape comprises a base film and a magnetic layer formed by applying a uniform magnetic coating which is prepared by kneading magnetic powder, a binder and an organic solvent together, and drying it.

The base film may comprise polyester, polypropylene or polycarbonate.

Magnetic powder may be of metal oxide such as #-Fe203 Co-containing -Fe203 or Cr02, or a powder of metal such as Fe and Fe-Co-Ni. Typically the binder may be polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyurethane resin, polyester resin, epoxy resin or nitrocellulose.

Binders are broadly classified into thermpolastic and theremosetting types. In the field of magnetic tapes, a thermosetting binder is generally selected from the viewpoint of strength and durability. Such a thermosetting binder is minimally soluble in a solvent due to its three-dimensional structure.

Studies have been conducted into processes for recovering base film and magnetic powder from waste coated-type magnetic tape which is inevitably produced when manufacturing such tape. Examples of such processes include one comprising a treatment with an aqueous or alcoholic solution of an alkali (Japanese Patent First Publication Nos. 66985/1979, 70404/1978, and 112979/1978), one comprising a treatment with an alkaline glycol (U.K. Patent No. 1134967), one comprising a treatment with an alkaline glycol and a treatment with a liquid halogenated hydrocarbon (Japanese Patent First Publication No. 94381/1978), and one comprising a treatment with an alkaline glycol and a treatment with an organic solvent having at least one group selected from among ketone, ester, and ether groups (Japanese Patent Second Publication No.

23134/1985).

However, these processes are directed primarily to recovering the base film. Magnetic powder particles separated from the base film are bound to each other by the remaining binder which is in most cases barely soluble in the solvents described above, so that it is not possible to form a uniform dispersion even if the recovered magnetic powder is kneaded with a fresh binder in an organic solvent.

When simultaneously recovering base film and magnetic powder, it is generally essential that the tape be first cut, broken and stirred. Thus, part of the base film is inevitably incorporated into the separated magnetic powder in the form of particles or powder, even though the majority of the base film is recovered.

Utilization of such magnetic powder as a raw material in the product of magnetic tape merely results in a valueless magnetic tape.

It is theoretically possible to separate the magnetic powder from the base film by utilizing the differing specific gravities or magnetic properties thereof. However, from the viewpoint of yield and cost, it is extremely difficult to completely separate them from each other on an industrial scale.

Accordingly, the use of the magnetic powder recovered by the above-mentioned process is limited to those areas in which there is only a small value added, such as toys and magnetic rubber.

The cost of the magnetic powder used in magnetic tape is considerably higher than that of the base film.

It is, therefore, desirable to be able to re-use recovered magnetic powder as a raw material for magnetic tape from the point of view of both economics and conservation and re-utilization of resources.

In order to be able to re-use recovered magnetic powder in recording media, the amount of binder remaining in the recovered magnetic powder must be minimized so that it can be uniformly dispersed in a magnetic layer.

It is an object of the present invention to recover magnetic powder from magnetic recording media without detriment to the characteristics thereof while substantially completely removing the binder, so that the recovered magnetic powder can be used in magnetic tape in which the uniformity of dispersion of the magnetic powder is of critical importance.

According to the present invention, a process for recovering magnetic powder from a bound magnetic recording material comprises treating the recording material at least once in a solution comprising an organic solvent capable of partially disolving or swelling the binder in recording material, water and/or an alcohol and an alkali.

The solution may comprise no alcohol or no water or it may comprise both alcohol and water. In all cases, it is preferred that there is 60 to 95 (V/V)% of the organic solvent and 40 to 45 (V/V)% of the water or alcohol or water and alcohol mixture. If water is present, it may be added before or during the treatment.

After the said treatment has been performed one or more times, it may be desirable to conduct a further treatment in which the solid product of the first treatment is treated at least once in a aqueous alkali solution of a concentration of at least 0.5 (W/V)%.

Any organic solvent may be used in the present invention in so far as it can satisfy the following two requisites: (1) It partially dissolves or swells the binder; and (2) It does not react with the alkali under the conditions of use so as not to inactivate the same, or the reaction, if any, proceeds very slowly.

Such an organic solvent may be, for example, a ketone such as acetone, methyl ethyl ketone or cyclohexanone; an ester such as ethyl acetate; a halogenated hydrocarbon such as chloroform; or a sulphur compound such as dimethyl sulphoxide. A mixed solvent partially containing a solvent not satisfying the above-mentioned requisites may be used in so far as the mixed solvent can satisfy them as a whole.

Common alkalis such as caustic soda and caustic potash may be used as the alkali.

Any alcohol may be used in so far as it has a dissolving capacity for the required amount of alkali and is soluble in the organic solvent and water. Such an alcohol may be, for example, methanol, ethanol, or isopropyl alcohol. Inexpensive alcohols are desirable.

The addition of water at the beginning of the treatment is expedient when consideration is given to the fact that, when it is necessary to recover the solvent or the like from the solution used in the treatment, complete separation of water is not preferable from the economical veiwpoint. The best effect can be attained when the water is added during the treatment.

The alkali is preferably added in such an amount that the solution shows a strong alkalinity even after completion of the reaction. When the amount of the alkali is too small, the reaction rate is slow. In the extreme case, the alkali disappears in the course of treatment and the decomposition reaction no longer proceeds. Although the required amount of alkali varies depending on the amount of binder and the incorporated base film in the magnetic layer, it is usually 5 to 20 (W/W)% with respect to the amount of the magnetic layer.

The amount of alcohol and/or water required is such that it can dissolve the required amount of alkali as well as the decomposed binder and the base film.

When the amount of alcohol and/or water is too large, the proportion of the organic solvent is too low, thus detracting from the effect of the present invention attained by the use of an organic solvent. Therefore, the proportion of the alcohol and/or water in the solution is preferably 5 to 40 (V/V)%.

The higher the treatment temperature, the faster the reaction. When a high temperature cannot be employed due to other factors, treatment at a lower temperature for a longer period of time will suffice.

Although it may be possible to conduct the treatment and the further treatment at a temperature above the boiling point under pressure, the temperature is, in general, merely above ambient temperature, e.g. above 800C or at the boiling point of the solution being employed.

The aqueous alkali solution is suitably of caustic soda, caustic potash or the like, as mentioned above.

A concentration of 0.5 (W/V)% or higher will suffice.

The treatment temperature is in a range from ordinary temperature to the boiling point of the aqueous alkali solution. The higher the treatment temperature, the faster the reaction. When a high temperature cannot be employed due to other factors, treatment at a lower temperature for a longer period of time will suffice.

The step of treatment with a solution of organic solvent - alcohol and/or water - alkali (step I) is conducted at least once, and may be repeated twice or more. The step of treatment with an aqueous solution of alkali (step II) may be conducted at least once after the above-mentioned treatment step I. The sequence of treatment may be, for example step I - step II, step I - step I - step II, or step I - step II step I - step II.

The present invention is particularly applicable to the recovery of magnetic powder from magnetic recording tape comprising a base film carrying bound magnetic recording material and in this case not only the binder binding the magnetic powder together, but also the base film is decomposed to give a matter soluble in water or organic solvents. The magnetic powder can thus be recovered with a high purity. The process of the present invention is thus fundamentally different from the conventional processes.

More specifically, where both the base film and the magnetic powder are to be recovered, the base film and the magnetic layer are separated from each other in a pretreatment step by a known method to recover the base film. Subsequently, the binder binding the magnetic powder together and the base film partially incorporated in the magnetic layer are decomposed and dissolved in the post-treatment step by the process of the present invention to remove the same.

Further features and details of the invention will be apparent from the following examples in accordance with the invention and comparative examples.

Prior to the process in accordance with the invention a pretreatment was effected. A Co-containing #-Fe203 type video tape was physically separated into two components, namely a base film and a magnetic layer.

The obtained magnetic layer (hereinafter referred to as "peeled magnetic layer") contained 23 to 24 (W/W)% of the binder and the base film (hereinafter referred to collectively as "impurities"). It was black and contained the magnetic powder completely bound together.

Example 1: 100g of the peeled magnetic layer was stirred in a solution composed of 1000ml of methyl ethyl ketone, 100ml of water, and 10g of caustic soda at the boiling point thereof for 3 hours, followed by filtration.

Thereafter, the same treatment was repeated, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 1.3 (W/W)% and the recovered magnetic powder assumed a reddish colour.

Example 2 and Comparative Example 1: 10g of the peeled magnetic layer was stirred in a solution composed of 100ml of (1) dimethyl sulphoxide (Example 2), (2) methyl ethyl ketone (Example 2), (3) acetone (Example 2) or (4) methanol (Comparative Example 1) and 10ml of a 10 (W/V)% solution of caustic soda-methanol at 550C for 5 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 2.2 (W/W)% for (1), 1.8 (W/W)% for (2), 1.8 (W/W)% for (3) and 3.9 (W/W)% for (4). The recovered magnetic powder assumed a reddish colour close to the original colour of the Co-containing #-Fe203 in cases (1) to (3) while it assumed a blackish colour in case (4). This may be attributed to a considerable reduction in the proportion of magnetic powder bound together by the binder in cases (1) to (3).

Example 3 100g of the peeled magnetic layer was stirred in solution composed of 1000ml of methyl ethyl ketone, 100ml of methanol and 10g of caustic soda at the boiling point thereof for 3 hours, followed by filtration. Thereafter, the same treatment was repeated, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 1.2 (W/W)96 and the recovered magnetic powder assumed a reddish colour.

Example 4: 100g of the peeled magnetic layer was stirred in solution composed of 1000ml of methyl ethyl ketone, 300ml of methanol and 10g of caustic soda at 550C for hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 2.2 (W/W)% and the recovered magnetic powder assumed a reddish colour.

Example 5: 100g of the peeled magnetic layer was stirred in a solution composed of 1000ml of methyl ethyl ketone, 600ml of methanol, and 9g of caustic soda at the boiling point thereof for 3 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 1.9 (W/W)% and the gloss value of the same was 59.

Gloss value serves to evaluate the dispersibility of magnetic powder. The recovered magnetic powder was kneaded together with the same binder and organic solvent as is used in the production of video tape, and applied to a base film. The lustre of the surface of the resulting film was measured with a gloss meter.

The obtained value was divided by the surface lustre in the case of unused magnetic powder and multiplied by 100 to obtain a gloss value as in the following equation: lustre of recovered magnetic powder gloss value = - ----------------------------- x 100 lustre of unused magnetic powder Example 6 The magnetic powder obtained in Example 5 was further stirred in a 12 (W/V)% aqueous solution of caustic soda (600ml) at 900C for 3 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 1.7 (W/W)% and the gloss value of the same was 78.

Example 7 A treatment was conducted according to the procedure of Example 5, using a solution composed of 600ml of methyl ethyl ketone, 90ml of methanol, 60ml of water and 9g of caustic soda.

The content of the impurities in the recovered magnetic powder was 1.6 (W/W)% and the gloss value of the same was 72.

Example 8 The magnetic powder obtained in Example 7 was further stirred in a 12 (W/V)% aqueous solution of caustic soda (600ml) at 900C for 3 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 1.3 (W/W)% and the gloss value of the same was 87.

Example 9 100g of the peeled magnetic layer was stirred in the same solution as used in Example 5 at 900C for 1 hour, followd by addition of 60ml of water.

Thereafter, the mixture was re-stirred at 900C for 2 hours, followed by filtration, water washing and drying. The content of the impurities in the recovered magnetic powder was 1.2 (W/W)% and the gloss value of the same was 81.

Example 10 The magnetic powder obtained in Example 9 was further stirred in a 12 (W/V)% aqueous solution of caustic soda (600ml) at 900C for 3 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 0.9 (W/W)% and the gloss value of the same was 94.

Example 11 100g of the peeled magnetic layer was stirred in solution (1), (2), (3) or (4) described below at the boiling point thereof for 2.5 hours, followed by filtration and water washing: (1) 600ml of methyl ethyl ketone, 50ml of methanol, 30ml of water and 9g of caustic soda (2) 600ml of methyl ethyl ketone, 90ml of methanol, 60ml of water and 9g of caustic soda (3) 600ml of methyl ethyl ketone, 120ml of methanol, 120ml of water and 9g of caustic soda (4) 600ml of methyl ethyl ketone, 160ml of methanol, 160ml of water and 9g of caustic soda The material produced was further stirred in a 12 (w/v)% aqueous solution of caustic soda (600ml) at 800C for 2.5 hours, followed by filtration, water washing and drying.

The gloss value of the recovered magnetic powder was 86 for (1), 88 for (2), 82 for (3) and 75 for (4).

Example 12 100g of the peeled magnetic layer was stirred in a solution composed of 600ml of methyl ethyl ketone, 90ml of methanol, 60ml of water and 9g of caustic soda at the boiling point thereof for 2 hours, followed by filtration. Thereafter, the filtered matter was further stirred in a solution with the same composition as above at the boiling point thereof for 1 hour, followed by filtration and water washing to produce magnetic powder (1).

10g of the magnetic powder (1) was stirred in 60ml of solution (2), (3), (4) or (5) described below at 900C for 2 hours, followed by filtration, water washing and drying: (2) water (3) a 4% aqueous solution of caustic soda (4) a 12% aqueous solution of caustic soda (5) a 24% aqueous solution of caustic soda The gloss value of the recovered magnetic powder was 89 for (1) and (2), 96 for (3), 94 for (4) and 91 for (5).

Example 13 100g of the peeled magnetic layer was stirred in a solution composed of 600ml of methyl ethyl ketone, 90ml of methanol, 60ml of water and 9g of caustic soda at the boiling point thereof for 2 hours, followed by filtration. Thereafter, the filtered matter was further stirred in a solution with the same composition as above, followed by filtration and water washing.

The material produced was stirred in a 1% aqueous solution of caustic soda (450ml) at 900C for 6 hours, followed by filtration. Then, the filtered matter was stirred in a 1% aqueous solution of caustic soda (450ml) at 900C for 2 hours, followed by filtration, water washing and drying.

The gloss value of the recovered magnetic powder was 95.

Example 14 6kg of the peeled magnetic layer was stirred in a solution composed of 36 1 of methyl ethyl ketone, 5.4 1 of methanol, 3.6 1 of water and 540g of caustic soda at the boiling point thereof for 2 hours, followed by filtration. Thereafter, the same treatment was repeated, followed by removal of supernatant, addition of 30 1 of water, filtration and water washing.

The resulting matter was stirred in a solution composed of 36 1 of water and 1440g of caustic soda at 900C for 6 hours, followed by filtration, water washing and drying.

The content of the impurities in the recovered magnetic powder was 0.8 (W/W)% and the gloss value of the same was 98. A video tape actually manufactured using the recovered magnetic powder was confirmed to have qualities substantially the same as those using virgin magnetic powder.

Comparative Example 2 100g of video tape was stirred in a 6 (W/V)% aqueous solution of caustic soda (5 1) at 900C for 1 hour, followed by filtration and water washing, thereby producing separation into the magnetic layer and the base film.

The recovered base film was transparent while the recovered magnetic powder had 6.6 (W/W)% impurities and assumed a blackish colour. The gloss value of the same was less than 30.

Comparative Example 3 100g of the peeled magnetic layer was stirred in a 12 (W/V)% aqueous solution of caustic soda (1000ml) at 900C for (1) 5 hours, (2) 10 hours or (3) 20 hours, followed by filtration, water washing for reduction to a pH less than 9 and drying at 800C.

The recovered magnetic powder had 4.7 (W/W)% impurities for (1), 4.1 (W/W)% impurities for (2) and 3.1 (W/W)% impurities for (3) and assumed a blackish colour. The gloss value of each magnetic powder was less than 30.

The magnetic powder recovered in method (3) was subjected to the same treatment again, resulting in no change of impurities or colour.

Comparative Example 4 lOg of the magnetic powder recovered in (3) of Comparative Example 3 was stirred in 1000ml of (1) dimethylformamide, (2) ethanol or (3) acetone at 800C (or at the boiling point when it is below 800C) for 30 minutes, followed by filtration. Thereafter, the same treatment was repeated, followed by drying.

The recovered magnetic powder had 3.1 (W/V)% impurities for (1), 3.5 (W/V)% impurities for (2) and 3.3 (W/V)% impurities for (3) and assumed a blackish colour. The gloss value of each magnetic powder was less than 30.

The above examples relate to the recovery of magnetic powder from waste magnetic tape. The process of the present invention is however also applicable to the recovery of magnetic powder from waste magnetic coating or waste cleaning liquid generated in producing a magnetic recording tape.

As described above, in the process for recovering magnetic powder according to the present invention, the binder is partially dissolved or swollen by an organic solvent and is decomposed and dissolved by an alkali and thus rendered soluble in water and/or an organic solvent. Thus, the binder and pieces of base film contained in a magnetic layer peeled from the base film by one of various methods can be almost completely removed. Therefore, high-purity magnetic powder can be easily recovered with a high efficiency. The dispersibility of the recovered magnetic powder is substantially improved, and hence it can be re-used in the production of magnetic tape.

The addition of water during the treatment can increase the purity of the magnetic powder. Further, the use of an aqueous alkali solution in a subsequent treatment step can further increase the purity of the magnetic powder, thus allowing the performance of a magnetic tape incorporating the recovered magnetic powder to be competitive with that of a tape incorporating unused magnetic powder.

Claims (14)

1. A process for recovering magnetic powder from a bound magnetic recording material which comprises treating the recording material at least once in a solution comprising an organic solvent capable of partially dissolving or swelling the binder in the recording material, water and/or an alcohol and an alkali.

2. A process as claimed in claim 1 in which the said solution comprises no alcohol and 60 to 95 (V/V)% of the organic solvent and 40 to 5 (V/V)% of water.

3. A process as claimed in claim 1 in which the said solution comprises no water and 60 to 95 (V/V)% of the organic solvent and 40 to 5 (V/V)% of alcohol.

4. A process as claimed in claim 1 in which the said solution comprises water and alcohol and 60 to 95 (V/V)% of the organic solvent and 40 to 5 (V/V)% of water and alcohol.

5. A process as claimed in any one of the preceding claims in which the said treatment is conducted at a temperature above ambient temperature.

6. A process as claimed in any one of the preceding claims in which the said treatment is conducted at the boiling point of the solution.

7. A process as claimed in any one of claims 1,3 and 4 in which the solid product of the said treatment is subjected to a further treatment at least once in an aqueous alkali solution of a concentration of at least 0.5 (W/V)%.

8. A process as claimed in claim 7 in which the further treatment is conducted at a temperature above ambient temperature.

9. A process as claimed in claim 8 in which the further treatment is conducted substantially at the boiling point of the aqueous alkali solution.

10. A process as claimed in any one of claims 1,2 and 4 in which water is added to the solution during the said treatment.

11. A process as claimed in claim 1 or claim 4 in which water is added to the solution during the said treatment and the solid product of the said treatment is subjected to a further treatment at least once in an aqueous alkali solution of a concentration of at least 0.5 (W/V)%.

12. A process as claimed in any one of the preceding claims of recovering magnetic powder from magnetic recording tape comprising a base film carrying a layer of bound magnetic powder.

13. A process as claimed in claim 12 which includes the preliminary step of separating the bound magnetic powder from the base film.

14. A process for recovering magnetic powder from a bound magnetic recording material substantially as described in any one of Examples 1 to 14.