JPS5894B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium in which the binder component of the magnetic layer comprises polyvinyl butyral, a urethane prepolymer, and a low molecular weight incyanate compound.

Generally, a magnetic recording medium is manufactured by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other additives as necessary to a substrate such as a polyester film, and drying the coating.

The binder component used in this case has excellent dispersibility of the magnetic powder, can impart excellent electrical properties such as high sensitivity and high S/N ratio to the magnetic recording medium, and has excellent abrasion resistance of the magnetic layer. It is necessary to choose one that can improve the durability of the recording medium.

Among various binders currently used, polyvinylbratyl is known to have particularly excellent dispersibility.

However, magnetic layers containing polyvinyl butyral as a binder component generally lack flexibility, so in magnetic recording tapes, etc., the tape may curl during storage and handling, and may not be easily connected to tape guides or magnetic heads during recording and playback. It has the drawback of being easily scratched and abraded due to sliding contact and having poor durability.

In order to overcome this drawback, attempts have been made to use low-molecular plasticizers such as dioctyl phthalate and dibutyl phthalate in combination, but the use of such plasticizers reduces the heat resistance of the magnetic layer. When stored at high temperatures, plasticizers ooze out onto the tape surface, making it easier for tape layers to stick together.

The present inventors have previously found that the above-mentioned drawbacks can be overcome by using polyvinyl butyral in combination with a urethane prepolymer having incyanate groups at both ends of the linear chain. As a result, the present invention was completed by discovering that the abrasion resistance and heat resistance of the magnetic layer can be further improved when a trifunctional low molecular weight incyanate compound is used in combination with polyvinyl butyral and urethane prepolymer.

That is, the magnetic recording medium of the present invention is characterized by containing polyvinyl butyral, a urethane prepolymer having incyanate groups at both ends of a linear chain, and a trifunctional low molecular weight isocyanate compound as binder components of the magnetic layer. According to the present invention, a magnetic recording medium having excellent electrical properties unique to polyvinyl butyral as well as excellent wear resistance and heat resistance can be obtained.

As the polyvinyl butyral used in the present invention, any currently commercially available polyvinyl butyral can be used, but it has a hydroxyl group content equivalent to 10 to 40 mol% as polyvinyl alcohol, and an average degree of polymerization of about 200 to 1000. Those are preferably used.

Specific examples of commercially available products include Meiko Sletsku BM-8, BL-3, and BL-1 (manufactured by Tanemizu Kagaku Co., Ltd.), and Denka Butyral #3000 (manufactured by Denki Kagaku Kogyo Co., Ltd.).

The amount of polyvinyl butyral used is 40 to 90% by weight, preferably 50 to 70% by weight, based on the total amount of binder components.

The greater the amount of polyvinyl butyral, the better the dispersibility of the magnetic powder, but if it exceeds 90% by weight, there is a tendency for no improvement in wear resistance to be observed.

Moreover, if it is less than 40% by weight, the excellent dispersibility peculiar to polyvinyl butyral cannot be expected.

The urethane prepolymer used in the present invention has an isocyanate group at both linear ends and has a molecular weight of about 100.
0 to 3000 are preferably used, and specific examples include Takenate L-1007, Takenate L-1006, Takenate L-2710, manufactured by Takeda Pharmaceutical Co., Ltd., Coronate #4095, Coronate #4, manufactured by Nippon Polyurethane Industries, Ltd.
090, Coronae H#4048, Pandex P-538, Pandex 305E manufactured by Dainippon Ink Co., Ltd., and the like.

The trifunctional low molecular weight isocyanate compound used in combination with the above-mentioned polyvinyl butyral and urethane prepolymer usually consists of a reaction product of 1 mol of triol and 3 mol of diisocyanate.

Since the trifunctional isocyanate group contained in this incyanate compound reacts with the OH group contained in polyvinyl butyral to form a network crosslink, the strength of the coating film of the magnetic layer is 10,000, and the abrasion resistance and heat resistance are improved. This is expected to improve.

On the other hand, since the isocyanate groups contained in the urethane prepolymer are trifunctional, sufficient steric network cross-linking cannot be obtained, and the addition of only this prepolymer has poor wear resistance and heat resistance. It just wasn't enough.

Specific examples of such low molecular weight isocyanate compounds include Coronate L manufactured by Nippon Polyurethane Industries, Desmodur L manufactured by Bayer, and Takenate D1 manufactured by Takeda Pharmaceutical Co., Ltd.
Examples include 02.

The amount of the trifunctional low molecular weight incyanate compound used is preferably in the range of 1 to 20% by weight based on the total amount of the binder component.

If the amount exceeds 20% by weight, the crosslinking density may increase, making the magnetic layer hard and brittle, and if the amount is less than 1% by weight, the desired effect may not be obtained.

Examples of magnetic powder used in the present invention include 1-Fe2
A wide variety of conventionally known powders are included, such as O3 powder, Fe3O4 powder, Co-containing -Fe203 powder, Co-containing Fe3O4 powder, and CrO2 powder.

The magnetic recording medium of the present invention can be manufactured according to a conventional method. For example, a binder component consisting of magnetic powder, polyvinyl butyral, a polyurethane prepolymer, and a trifunctional low molecular weight incyanate compound is placed on a substrate such as a polyester film. A magnetic paint containing an organic solvent and other additives may be applied by any means such as spraying or roll coating and dried.

Next, the present invention will be explained in more detail with reference to Examples.

In addition, in the following, parts indicate parts by weight.

Example 1 80 parts of γ-Fe203 magnetic powder, Eslec BM-8 (
10 parts of polyvinyl butyral), 8 parts of Takenate L (polyurethane prepolymer), and 2 parts of Coronate L (trifunctional low molecular weight isocyanate compound) were added to 100 parts of a 1:1 mixed solvent of toluene and methyl ethyl ketone, and mixed for 70 hours in a ball mill. A magnetic paint was prepared by dispersing it.

This magnetic paint was applied to a polyester film having a thickness of 21 μm to a dry thickness of 10 μm and dried.

Next, the surface of the magnetic layer was calendered to give a mirror finish, and then cut into a predetermined width to produce a magnetic tape.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that Desmodur L was used instead of Coronate L in Example 1.

Comparative Example A magnetic tape was obtained in the same manner as in Example 1, except that Coronate L of Example 1 was not used, and 10 parts of Eslec BM-8 and 10 parts of Takenate L were used as binder components.

When the SN ratio and abrasion loss of each of the above magnetic tapes were measured, the results shown in Table 1 below were obtained.

However, the abrasion loss is calculated as an index of the abrasion loss after running a fixed length of magnetic tape 300 times using a tape deck while slidingly contacting a magnetic head at a running speed of 76 cm/sec, with the comparative example being 100. This is what is shown.

In addition, in order to examine the heat resistance of each magnetic tape, each magnetic tape was wound around a glass tube with a tension of 1 kg.
Store at 0℃, 80%RH for 24 hours, then store at room temperature for 24 hours.
After leaving the glass tube for a while, it was observed whether there was any adhesion between the layers of the magnetic tape when the magnetic tape was unwound from the glass tube.

The results were as shown in Table 1.

As is clear from the above results, the magnetic tape of the present invention exhibits a high signal-to-noise ratio, and it can be seen that the abrasion resistance and heat resistance are further improved compared to the comparative example.

Claims (1)

[Claims] 1 The binder for the magnetic layer is 40 to 90% by weight of polyvinyl butyral, 1 to 20% by weight of a trifunctional low molecular weight incyanate compound, and the balance is a urethane prepolymer having isocyanate groups at both straight chain ends. A magnetic recording medium comprising 80% by weight or more of magnetic powder based on the total amount of the binder and the magnetic powder.