DE2719285A1 - Magnetic recording medium prodn. - from nitrocellulose compsn. in which a polymer replaces isopropanol - Google Patents

Abstract

In prodn. of a magnetic recording medium, the magnetic layer is formed by a nitrocellulose compsn. in which isopropyl alcohol has been replaced by a polymer. The squeak caused by increased resistance when the tape is run on a video-tape recorder is avoided. Blistering of the magnetic coating by the recording head under severe friction conditions is prevented. The polymer is esp. PVC or a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Other suitable polymers are polyurethane, polybutadiene, butadiene-acrylonitrile copolymers, epoxides, polyvinyl-butyral or -formal, and polyesters.

Description

Magnetic recording medium

Summary A magnetic recording medium is provided which with a magnetic coating comprising a nitrocellulose composition which was obtained by replacing the isopropyl alcohol with a resin and in which the Nitrocellulose is crosslinked with the isocyanate groups of a urethane compound.

The invention relates to a magnetic recording medium.

Magnetic recording media are made by coating a substrate, e.g. B. a plastic film, in particular a polyester film or an aluminum plate with a mass containing a magnetic powder and a binder includes. A wide variety of binders have already been used for the magnetic recording media suggested. However, it has heretofore been a satisfactory binder in all respects not found. In general, nitrocellulose compounds have hitherto been used as binders, because they have excellent wetting properties and excellent flow properties have in the manufacture of the magnetic recording medium. Nitrocellulose compositions however, have the disadvantage that they are self-igniting and therefore increased care to prevent inflammation in the andhabun of the masses is required. For this reason, 30 to 35% by weight of isopropyl alcohol was used incorporated onto the nitrocellulose.

This is to prevent it from becoming too dusty Air explodes through dry, fine particles of nitrocellulose. By The incorporation of the isopropyl alcohol will ensure storage and safety Handling of the masses increased.

On the other hand, nitrocellulose is combined with polyurethane so that the hydroxyl groups of the cellulose chain of the nitrocellulose crosslinking points with form the isocyanate groups of the urethane compound. This creates the affinity of the magnetic powder is increased and the mechanical properties are improved by networking improves. In particular, this also gives those for magnetic tapes required electromagnetic characteristics and wear resistance values or abrasion resistance values. When using isopropyl alcohol additives now, however, the disadvantage that there is a reaction between the isocyanate groups the urethane compound and the hydroxyl groups of the isopropyl alcohol of the nitrocellulose composition comes so that the degree of crosslinking is decreased and the effect of improvement the abrasion resistance or scuff resistance of the magnetic recording medium and the running wear characteristics are lowered. These problems are in the U.S. Patents 3,808,136 and 3,810,840 are discussed.

To overcome these drawbacks, it has been suggested the physical To improve properties by the fact that the nitrocellulose composition with about 15 % By weight of a plasticizer, e.g. B. dibutyl phthalate, dioctyl phthalate, based on the Solid components are mixed and kneaded in a kneader and then that of the mass Incorporated isopropyl alcohol evaporated on a hot two-roller mill. Included solid particles of the nitrocellulose mass are obtained, the isopropyl alcohol is replaced by a plasticizer. A crosslinking agent is then mixed in active isocyanate groups to the nitrocellulose mass pieces, as well as a polyurethane, the isocyanate groups reacting with the main binder components.

However, the video tapes obtained with such a binder have various disadvantages. In particular, there are running problems or squeaking Noise due to increased friction when running the belt in the case of application in conjunction with a video recording device.

Furthermore, one observed in drastic test attempts to examine the Friction of the magnetic coating causes the magnetic coating to peel off through the recording head. This phenomenon is particularly observed in the still image reproduction test to reproduce the same track to obtain a stationary illustration. The running belt is stopped. This works the plasticizer incorporated into the magnetic coating, e.g. B. the dibutyl phthalate, disadvantageous.

It is therefore an object of the present invention to provide a magnetic To provide recording medium which does not have the above-mentioned disadvantages. According to the invention, this object is achieved by a magnetic recording medium, which has an iniagnetic coating comprising a nitrocellulose composition, which was obtained by replacing the isopropyl alcohol with a resin and wherein the nitrocellulose is crosslinked with isocyanate groups of a urethane compound.

The nitrocellulose composition containing the isopropyl alcohol is mixed with mixed and kneaded a resin suitable for magnetic coating is. Then the isopropyl alcohol is removed and replaced with the resin.

The nitrocellulose composition formed comprises nitrocellulose and the resin. It is preferable to use a vinyl chloride type resin in order to reduce the risk of fire to meet. The nitrocellulose composition is usually dissolved in a solvent, e.g. B.

in methyl ethyl ketone or methyl isobutyl ketone together with a suspending agent, z. B. lecithin, dissolved and then a magnetic powder, -z. B. needle-shaped (aciculares) t-Fe203 or Co-containing iron oxide powder and carbon black therein by kneading dispersed.

The mass content of magnet powder and carbon black can be the same as with conventional recording media.

The mixture obtained is then mixed with a polyurethane solution. The polyurethane solution comprises a polyurethane resin and a solvent and can contain suitable additives. An abrasive powder, e.g. B. CrO2, Cr203, ZrO2, Cm203, SiC, «-Fe203, A1203 and TiO2 can be added to improve the characteristics. The mixture is a urethane compound with two to crosslink the nitrocellulose or more isocyanate groups added. The amount of the urethane compound becomes such chosen that the crosslinking of the nitrocellulose is brought about. With the received Magnetic recording material is coated on a tape or a disk or plate, whereby the magnetic recording medium is obtained.

Preparation of the nitrocellulose mass: Nitrocellulose chips 10 kg (H-1/2 sec) (isopropyl alcohol content 30%) vinyl chloride-vinyl acetate copolymer 3 kg (VAGH; manufactured d. VCC) methyl ethyl ketone 2 kg.

The components are in a kneader at room temperature during Kneaded for 30 min, the nitrocellulose and the vinyl chloride-vinyl acetate copolymers be mixed.

The mixture obtained in the kneader is then processed on a hot two-roll mill kneaded at 40 0C by running through several times, the nitrocellulose and the vinyl chloride-vinyl acetate copolymer is completely mixed and the isopropyl alcohol and the methyl ethyl ketone will be evaporated. A plate or film is obtained in this way the crowd.

The residual solvents in the bulk are measured. The solids content is 87.5% by weight. The composition also contains 6.5% by weight isopropyl alcohol and 6 Wt .-% methyl ethyl ketone.

The plate or film is blown with air at room temperature dried for 10 days to evaporate the remaining solvents. the Plate contains 96.5% by weight of solids, 2% by weight of isopropyl alcohol and 1% by weight of methyl ethyl ketone.

The plate or film obtained is then crushed into chips and The chips are used as a binder for making the magnetic recording medium used.

From the point of view of security and prevention of one Inflammation when kneading in the roller mill should preferably contain nitrocellulose be less than 80% and the content of vinyl chlorine-vinyl acetate copolymer should preferably be more than 20% by weight.

In the above example, the isopropyl alcohol was replaced by the yinyl chloride-vinyl acetate copolymer replaced. However, the same results are achieved if other resins are used, which are commonly used in the field of magnetic recording media, z. B. a polyurethane resin; a polybutadiene resin; a butadiene-acrylonitrile copolymer; a vinyl chloride-vinyl acetate-vinyl alcohol copolymer; a vinyl chloride-vinyl acetate copolymer; a vinyl chloride-vinylidene chloride copolymer; a vinylidene chloride-acrylonitrile copolymer; a vinyl acetate resin, an epoxy resin, a phenoxy resin, a polyvinyl butyral resin Polyvinyl formaldehyde resin or a polyester resin.

It is particularly preferred to use vinyl chloride type resins, from the point of view of processing - and handling safety. Incorporation of the vinyl chloride type resin increases the flammability the nitrocellulose is further reduced.

A magnetic tape is produced in each of the following examples using the respective nitrocellulose chips obtained by Replacement of the isopropyl alcohol with the respective resin or the respective plasticizer or when using untreated nitrocellulose and the characteristics of the obtained magnetic tapes are compared.

Comparative Example 1 <r-Fe 2 O 3 (0.8 to 0.2) 120 parts by weight of carbon black Lecithin 2 n nitrocellulose (h-1/2 sec) 22 n (isopropyl alcohol content 30%) methyl ethyl ketone 50 "methyl isobutyl ketone 50 N nitrocellulose, lecithin, methyl ethyl ketone, methyl isobutyl ketone are carefully mixed in a mixer to dissolve the solid components. The paste obtained is placed in a ball mill together with t-Fe 2 O 3 and carbon black and mixed there carefully for 3 hours to wet the particles.

Polyurethane resin (solids content 33 parts by weight 45% by weight) methyl ethyl ketone 200 ~ methyl isobutyl ketone 100 ~ lubricant (silicone oil) 3 ".

The components are carefully mixed to form the solid components dissolve and the paste obtained is placed in a ball mill containing T -Fe203 and the others Contains components and then carefully during Mixed for 42 hours to disperse the particles. After dispersing, 5 parts by weight an isocyanate compound which is associated with the functional groups, e.g. B. the hydroxyl groups of the binder of the magnetic recording material can react with crosslinking, the The mass is added in the ball mill and the mixture is continued for a further 20 minutes. The magnetic recording material obtained is used to coat a polyester film used. A magnetic recording tape is thereby obtained. After surface treatment of the magnetic tape undergoes the thermosetting reaction of the magnetic coating Heating to 80 ° C. carried out for 48 h. The magnetic tape obtained is made into individual tapes cut to a width of 1.25 cm to obtain video tapes. the Characteristics of the video tape obtained are shown in Figures 1 and 2, represented by the sample labeled n j # ".

The video tape is used to record a signal.

For this purpose, a video tape recorder (VTR) (EIAJ -I type; standard) (NV-3120, manufactured by Matsushita Denki) was used. The signal will then reproduced in the steady state, under a voltage of 200 on the winding side, determined by spring measurement. Fig. 1 shows the relationship between the attenuation of the reproduced signal and the time. One recognizes from Fig. 1 that the attenuation of the reproduced signal is extremely large, since the isocyanate, which is to give the magnetic coating a higher strength, with reacts with the isopropyl alcohol used to plasticize the nitrocellulose. For this reason, a satisfactory crosslinking structure of the magnetic coating cannot be achieved and the magnetic coating is not resistant to extreme wear and tear, how they z. B. occur in the playback of idle images. The magnetic coating on which the signal was recorded is caused by wear and tear by the head a speed of 11 m / sec scratched or scraped off.

The magnetic tape obtained is stored for 5 days with 5 cycles from 0% relative humidity to -100C and 80 X relative humidity at 60 OC Furthermore, the tape is stored at room temperature for a further 24 hours.

Then run the magnetic tape through a video recorder, to measure the signal attenuation. The stress analyzer (1 VA-500; manufactured by Nippon Jidoseigyo) is placed between the Xopftrommel and the Ankleirunrolle, to measure the variation in tension on the take-up side during the run. Fig. 2 shows the relationship between the variation or fluctuation in voltage and the running time. It can be seen clearly from Fig. 2 that the friction with a longer running time is increased dramatically.

Comparative Example 2 Co-containing iron oxide (0.6 P; 0, Q6 p) 120 parts by weight Carbon black 6 "lecithin 2 n nitrocellulose pellets (H-1/2 sec) (12% isopropyl alcohol replaced by 12% dibutyl phthalate) 18.3 "(pellet form) methyl ethyl ketone 50" methyl isobutyl ketone 50 ".

The nitrocellulose pellets, lecithin, methyl ethyl ketone and methyl isobutyl ketone are carefully mixed in a mixer to dissolve the solid components. The paste is then placed in a ball mill along with the Co-containing iron oxide and carbon black are added and the mixture is carefully prepared for the purpose of utilizing the particles mixed.

Polyurethane resin 15 parts by weight of methyl ethyl ketone 200N tetrahydrofuran 100 n lubricant (butyl myristate) 3 ", The Xo components will be mixed to dissolve the solid components and the paste obtained is in given the ball mill containing the Co-containing iron oxide, etc. and the mixture is mixed thoroughly for 42 hours to disperse the particles. After this Dispersion process are 5 parts by weight of isocyanate, which with the functional groups, z. B. the hydroxyl groups, the binder of the magnetic mass can react in the Added ball mill and the mixture is mixed for 20 minutes. The received magnetic mass is used to coat a polyester film, with a Magnetic tape is obtained. After the surface treatment of the magnetic tape, the magnetic coating thermoset by heating for 48 h to 80 Or The magnetic tape is cut into tapes with a width of 1.25 cm, which are used as video tapes. The characteristics of the video tape obtained are shown in Figures 1 and 2, represented by the curves "# 2 ". It can be seen from FIG. 1 that the signal attenuation is particularly important with increased running time is large because the dibutyl phthalate used as a plasticizer deteriorates the sliding effect, in particular with the high relative speed of the rest image reproduction, although the nitrocellulose composition contains dibutyl phthalate instead of isopropyl alcohol and although crosslinking of the magnetic coating composition by reaction of the isocyanate is effected with the achievement of high strength of the magnetic coating. It can be seen in particular from Fig. 2 that the tendency to increase the friction at longer runtime is extremely high.

Example 1 Co-containing iron oxide (0.6 u; 0.06 u) 120 parts by weight of carbon black 6 "Lecithin 2" nitrocellulose chips (H-1/2 sec) (30 0 isopropyl alcohol replaced by 30 £ ## vinyl chloride-vinyl acetate copolymer; 70% nitrocellulose) 15 n Ethyl ethyl ketone 50 parts by weight of methyl isobutyl ketone 50 #.

The nitrocellulose chips, lecithin, ethyl ethyl ketone and methyl isobutyl ketone are carefully mixed in a mixer and the solid components become thereby resolved. The resulting mass is placed in a ball mill, together with the Co-containing iron oxide and the soot and the whole is carefully put to use the wetting of the particles.

Polyurethane resin 15 parts by weight of methyl ethyl ketone 200 N tetrahydrofuran 100 # ~ lubricant (butyl myristate) 3 ".

The components are mixed for the purpose of dissolving the solid components and the paste obtained is put in the ball mill, which contains the Co-containing iron oxide etc. and the mixture obtained is carefully mixed for 42 hours, to disperse the particles.

After the particles have been dispersed, 5 parts by weight of isocyanate are added in the ball mill, which with the functional groups, z. B. the hydroxyl groups, of the binder of the magnetic recording material reacts. The mixture obtained is then kneaded for another 20 minutes. With the magnetic recording media obtained a polyester film is coated to obtain a magnetic tape.

The surface of the magnetic tape is processed and the magnetic one Coating material is subjected to a thermosetting treatment by heating for 48 h on SO OC. Then the magnetic tape is made into tapes with a width of 1.25 cm cut. This is how you get a videoban. The characteristic Properties of the video tape are shown in Figures 1 and 2, namely using the curve "f 3".

It can be seen from Fig. 1 that the signal attenuation even with longer running times is low and that the abrasion resistance or wear resistance of the magnetic Coating is improved compared to Comparative Example 2 (Sample 82) because in this case the isopropyl alcohol in the nitrocellulose component has been removed and das.Isocyanat effectively with the urethane resin in the crosslinking reaction reacts to form a high strength magnetic coating.

From Fig. 2, it can be seen that the magnetic tape has stable running properties shows even when the test was performed on a video tape recorder after storage under drastic conditions. This fact shows that the Binder leads to a magnetic tape with high reliability.

In general, the polyurethane resin should have an average molecular weight from 103 to 106 from the point of view of solubility and the physical properties.

Example 2 Co-containing iron oxide (0.6; 0.06 r # 12 parts by weight of rut3 ' Lecithin 2 "nitro cellulose pellets (E-1/2 sec) (Nitrocelluse: vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VYNC) - 60:40) (made from 30% isopropyl alcohol contain tenbr nitrocellulose and 40% of a charge of VYNC in isopropyl acetate) 15 "methyl ethyl ketone 50" methyl isobutyl ketone 50 " The nitrocellulose pellets, lecithin, methyl ethyl ketone and Methyl isobutylene are carefully mixed in a mixer to get the solid components dissolve. The paste obtained is placed in a ball mill, together with the Co-containing iron oxide and soot and the mixture is carefully mixed, to wet the particles.

Polyurethane resin 33 parts by weight of methyl ethyl ketone 200 "methyl isobutyl ketone 100 n fine particles of Cr203 (0.8) (abrasion) 4 n.

The components are mixed in order to dissolve the solid constituents and the paste is put in the ball mill, which removes the Co-containing iron oxide, etc. contains. The mixture is mixed thoroughly for 42 hours to close the particles disperse. After dispersing, 5 parts by weight of isocyanate are added, which with the functional groups, especially the hydroxyl groups of the binder, the magnetic mass can react in the ball mill and is mixture is still during Mix for 20 min. The magnetic mass obtained is used to coat a Polyester film is used to obtain a magnetic tape. After editing the surface of the magnetic tape undergoes heat curing of the coating material 80 ° C. carried out for 48 h. The magnetic tape becomes tapes with a width cut by 1.25 cm. Receives. man videotapes. The characteristic Properties of the video tape are shown in Figures 1 and 2, and that is illustrated by the curves 84. It can be seen from FIG. 1 that the sealing properties are essential are improved because the strength of the magnetic coating by adding the fine Abrasion particles is improved. The abrasion resistance or wear resistance of the Magnetic coating is made by adding the fine abrasive particles of high hardness improved. It can be seen from Fig. 2 that the Magnetic tape even more stable Has running properties than the sample jr 3.

In the above example, Cr203 was used as an abrasive. You can replace this abrasive with other abrasives, e.g. B. by ZrO2, Co203, Al203, Ti02 or the like. The desired effect is achieved in particular, when considering abrasive particles with an average particle diameter of 5 to 0.05 u added (general). If in general the content of the abrasive is less than 0.5% by weight based on the magnet powder, the effect of the abrasive becomes not achieved, while with a content of the abrasive of more than 15 wt .-> disadvantageously strong wear occurs. A content of the abrasive in the range from 0.5 to 15% by weight, based on the magnet powder, is therefore preferred.

Example 3 titanium works according to the procedure of Example 2. Here a magnetic tape is produced with the addition of 1% by weight butyl myristate as a lubricant when mixing the polyurethane resin and the abrasive. The characteristic Properties of the video tape are shown in Figures 1 and 2, namely by the curve n 8 5 ". It can be seen from Fig. 1 that the signal attenuation is less than 1 db is, in fact with a rest image playback for more than 24 hours, since the Lubricant effect or lubricant effect is the relative friction between the belt and the head moving at high speed. This is done by Addition of the butyl myristate. Furthermore, a magnetic coating of high strength is obtained and high abrasion resistance due to the addition of the abrasive. From Fig. 2 it can be seen that the magnetic tape has stable running properties, just like the tape ß 3.

In the example above, butyl myristate was added as a lubricant. However, it is also possible to use other lubricants. Generally suitable straight-chain saturated esters of aliphatic acids of the formula CnH2nCOOCmH2m + i (n = 12 up to 22 and m = 1 to 8).

The content of the lubricant should be in the range of 0.5 to 20 parts by weight per 100 parts by weight of the binder, from the point of view of Abrasion resistance.

The nitrocellulose composition and the magnetic recording media that can be produced therewith are significantly superior to conventional products.

Urethane compounds can be used as crosslinking agents, which lead to isocyanate compounds with two or more isocyanate groups when heated. These isocyanate compounds can be aliphatic or aromatic isocyanate compounds be.

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Claims (8)

P A T E N T A N S P R Ü C H z # magnetic recording medium, characterized by a magnetic coating made using a nitrocellulose composition, which replaces the isopropyl alcohol with a Resin was obtained. 2. Magnetic recording medium according to claim 1, characterized in that that the resin is a vinyl chloride type resin; and that a nitrocellulose composition is used in the preparation of the nitrocellulose composition containing the isopropyl alcohol and a solvent has been added to the vinyl chloride type resin, and the Solvent and isopropyl alcohol have evaporated. 3. A magnetic recording medium according to any one of claims 1 or 1 2, characterized in that the resin is a vinyl chloride-vinyl acetate-vinyl alcohol resin is, 4. Magnetic recording medium according to one of claims 1 to 3, characterized by crosslinking the nitrocellulose with two or more isocyanate groups supplying urethane compound. 5. A magnetic recording medium according to any one of claims 1 to 4, characterized by a nitrocellulose mass, in the production of which after replacement of isopropyl alcohol through the resin is a polyurethane resin with an average Molecular weight of 103 to 106 and a magnetic powder were mixed. 6. A magnetic recording medium according to any one of claims 1 to 5, characterized by a nitrocellulose mass, in the production of which after replacement of isopropyl alcohol through the resin a polyurethane resin with a average molecular weight of 103 to 106 and a magnetic powder, as well an abrasive powder having an average particle diameter of 5 to 0.05 / u were mixed in an amount of 0.5 to 15 wt .-% based on the magnet powder. 7. A magnetic recording medium according to any one of claims 1 to 6, characterized in that the nitrocellulose composition is a straight-chain saturated aliphatic ester of the formula CnH2n + lCooCmH2m + (n - 12 to 22; m P 1 to 8) in in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the total amount of the nitrocellulose and the polyurethane. 8. A magnetic recording medium according to any one of claims 1 to 7, characterized in that the resin is a vinyl chloride-vinyl acetate type resin is.