JPS60111326A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having good dispersibility of magnetic powder, good surface smoothness of a magnetic layer, excellent electromagnetic conversion characteristic, high modulus of elasticity and excellent mechanical strength. CONSTITUTION:A magnetic paint contg. magnetic metallic powder, a vinyl chloride/vinyl acetate copolymer or copolymeric polyester resin contg. a sulfonic acid metallic base, low mol.wt. polyol and isophorone diisocyanate polyisocyanate compd. is coated on a base body. A three-dimensional crosslinking reaction is thereby thoroughly caused, by which the strong and tough magnetic layer is formed and mechanical strength is much improved. The magnetic layer has good compatibility with the vinyl chloride/vinyl acetate copolymer or the copolymerized polyester resin contg. sulfonic acid metallic base and the low mol.wt. polyol to be used and therefore the magnetic layer having good surface smoothness without staining a head and without spoiling the dispersibility of the magnetic metallic powder is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium that uses metal magnetic powder as the magnetic powder, and aims to provide good dispersibility of the magnetic powder, good surface smoothness of the magnetic layer, and electromagnetic conversion characteristics. It is an object of the present invention to provide a magnetic recording medium that has excellent elasticity, high elastic modulus, and mechanical strength.

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
If high performance is required, Fes Fe-Ni
Metal magnetic powders such as are used. However, since these metal magnetic powders have a very large magnetic moment, large interactions between particles tend to occur, causing particle aggregation and making it difficult to disperse well in the binder resin. Therefore, as a binder component used together with metal magnetic powder, it has particularly good dispersibility for metal magnetic powder, improves the smoothness of the magnetic layer surface, and can impart excellent electromagnetic characteristics such as high sensitivity to magnetic recording media. Especially in the case of magnetic tapes, which are becoming more dense and thinner in recent years, it is possible to make the surface smoothness of the magnetic layer sufficiently good, as well as having high elasticity and mechanical strength. It is desirable to use a binder component that is capable of providing good properties.

For this reason, various research and developments have been conducted on binder resins.
Vinyl chloride-vinyl acetate copolymers or copolyester resins containing sulfonic acid metal bases are used as binder resins that have excellent dispersibility for metal magnetic powders. Although the dispersibility of the magnetic layer is improved, the elastic modulus of the magnetic layer cannot be sufficiently improved, and sufficient mechanical strength cannot be obtained. Therefore, in order to improve the mechanical strength, a curing agent such as a low molecular weight polyol and a trifunctional low molecular weight isocyanate compound is used in combination with a vinyl chloride-vinyl acetate copolymer or a copolyester resin containing a sulfonic acid metal base. However, conventionally commonly used trifunctional low molecular weight isocyanate compounds are used together with these vinyl chloride-vinyl acetate copolymers or copolyester resins containing sulfonic acid metal bases and low molecular weight polyols. When used together, the compatibility with the binder resin used in combination is poor, resulting in head stains, etc., and the dispersibility of the metal magnetic powder is adversely affected by the influence of the binder resin with poor compatibility. There was a problem.

The inventors conducted various studies in view of the current situation, and found that isophorone diisocyanate-based polyisocyanate compounds are used as the binder component of the magnetic layer, and vinyl chloride-vinyl acetate-based copolymers or copolymerized polyesters containing sulfonic acid metal bases are used. When used in combination with resins and low molecular weight polyols (-1), the isophorone diisocyanate-based polyisocyanate compound has good compatibility with these binder resins, so head stains etc. do not occur and the dispersibility of metal magnetic powder is improved. It is possible to obtain a magnetic recording medium in which the elastic modulus of the magnetic layer is sufficiently improved without impairing the magnetic properties, the surface smoothness of the magnetic layer is good, the electromagnetic conversion characteristics are excellent, and the magnetic recording medium has high elasticity and further excellent mechanical strength. They discovered this and came up with this invention.

The isophorone diisocyanate-based polyisocyanate compound used in this invention is an adduct obtained by reacting isophorone diisocyanate with an active hydrogen-containing compound such as trimethylolpropane, trimethylolethane, hexanetriol, or glycerin. Isophorone diisocyanate monomers with a number of NGO groups greater than 2 (more than 11 J) and significantly reduced toxicity are preferably used.
-315 and the like. This type of isophorone diisocyanate-based polyisocyanate compound is a product obtained by trimerizing and trifunctionalizing isophorone diisocyanate in this way, so it can be combined with a vinyl chloride-vinyl acetate-based copolymer or a copolymer containing a sulfonic acid metal base. When used in combination with a polymerized polyester resin and a low molecular weight polyol, a three-dimensional crosslinking reaction is sufficiently carried out to form a strong magnetic layer, and the mechanical strength is further improved.

In addition, since it has good compatibility with the vinyl chloride-vinyl acetate copolymer or copolyester resin containing a sulfonic acid metal base, and low molecular weight polyol, it does not cause head stains and is highly compatible with metal magnetic powder. A magnetic layer with good surface smoothness can be obtained without impairing the dispersibility.

Furthermore, the low molecular weight polyols used in this invention include acrylic polyols, polyester polyols, polyether polyols, etc., all of which are preferably used, but those having an average molecular weight within the range of 200 to 1000 and a hydroxyl value It is preferably within the range of 200 to 800. If the average molecular weight exceeds 1000 or the hydroxyl value is less than 200, the elastic modulus of the magnetic layer will decrease; When the molecular weight is higher than 800, the solubility in organic solvents becomes poor. Here, the hydroxyl value refers to the number of potassium hydroxides required to neutralize the acetic acid bound to the acetylated product obtained from 1 g of sample. Specific examples of such low molecular weight polyols include Olestar Q-161 (acrylic polyol) manufactured by Mitsui Toatsu Chemical Co., Ltd.;
Adeka New Ace YT-400 manufactured by Asahi Denka Co., Ltd., Desmohen 800, Desmohen 1100 manufactured by Nippon Polyurethane Co., Ltd.
Desmohen 220'O (polyester polyol)
, Sunnisox TP-400, Sunnisox GP-3000, Sanx FA-908 (all polyether polyols) manufactured by Sanyo Chemical Co., Ltd., and the like. The usage ratio of such a low molecular weight polyol and the isophorone diisocyanate-based polyisocyanate compound differs depending on the hydroxyl value of the low molecular weight polyol and the isocyanate group content of the isophorone diisocyanate-based polyisocyanate compound. It is preferable to use the ratio so that it is within the range of 0.7 to 1.3. If the ratio is outside this range, a large amount of the components added in excess will exist as unreacted substances in the magnetic layer, causing head stains and eyesight. This may cause undesirable phenomena such as clogging.

Furthermore, the vinyl chloride-vinyl acetate copolymer used in this invention has good affinity with the metal magnetic powder and has excellent dispersibility of the metal magnetic powder. When used in combination, the dispersibility of the metal magnetic powder is improved and the surface smoothness of the magnetic layer is also improved. As such a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer is preferably used. Examples include S-LEC A manufactured by Sekisui Chemical Co., Ltd.

In addition, copolyester resins containing sulfonate metal bases have very low porosity and have good affinity with metal magnetic powders, so copolyester resins containing this type of sulfonate metal bases are used. When used in combination, the metal magnetic powder can be dispersed well and packed at high density, and the dispersibility and filling properties of the metal magnetic powder are improved. As a specific example of such a copolyester resin containing a sulfonic acid metal base, for example, ET-1 manufactured by Toyobo Co., Ltd.
095 etc. are mentioned.

The usage ratio of these vinyl chloride-vinyl acetate copolymers or copolymerized polyester resins containing sulfonic acid metal bases is based on the total amount of binder components when used in combination with the above-mentioned low molecular weight polyol and isophorone diisocyanate-based polyisocyanate compound. On the other hand, it is preferably within the range of 20 to 80% by weight; if it is too small, the dispersibility of the metal magnetic powder may be impaired, and if it is too large, the elastic modulus of the magnetic layer will not be sufficiently improved.

Examples of the metal magnetic powder used in this invention include:
Fe powder, CO powder, Ni powder, various alloy powders thereof, or these powders are mixed with AI, Cr, Mn, Si,
Various conventionally known metal magnetic powders such as alloy powders containing elements such as Zn are widely included.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, dimethylformamide, etc. are used alone or in combination of two or more.

The magnetic recording medium of the present invention may be manufactured according to a conventional method, for example, by disposing a metal magnetic powder, a vinyl chloride-vinyl acetate copolymer, or a sulfonic acid metal base on a substrate such as a polyester film. A magnetic paint containing a copolymerized polyester resin, a binder component containing a low molecular weight polyol and an isophorone diisocyanate-based polyisocyanate compound, an organic solvent, and other additives is applied by any method such as spraying or roll coating, and then dried. do it.

Next, embodiments of the invention will be described.

Example 1 α-Fe magnetic powder 500 parts by weight VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer manufactured by U, C, C, USA) Adeka New Ace YT-40014 (polyester polyol manufactured by Asahi Denka Co., Ltd.) Average molecular weight 400, hydroxyl value 580) Mytic NY-315 (Mitsubishi 66 isoborone diisocyanate-based polyisocyanate compound manufactured by Kasei Chemical Co., Ltd.) Methyl isobutyl ketone 350 Cyclohexanone 350 Toluene 350 Each of the above compositions except Mytic NY-315 The ingredients were placed in a ball mill, mixed and dispersed for 48 hours, then Mite'Tsuku NY-315 was added, mixed and dispersed for an additional hour, and then taken out to form a magnetic paint. This magnetic paint was applied onto a polyester film having a thickness of 15 μm to a dry thickness of 5 μm, oriented in a direct current magnetic field of 30.00 oersteds, and then dried by heating to perform surface treatment. After that, they were cut to the specified width and made into video tapes.

Example 2 In the composition of the magnetic paint in Example 1, VA G
I (instead of ET-1095 (manufactured by Toyobo Co., Ltd. 503N)
A videotape was produced in the same manner as in Example 1, except that the same amount of the a group-containing copolymerized polyester resin) was used.

Comparative Example 1 In the composition of the magnetic paint in Example 1, Niraporan 3023 was used instead of Adeka New Ace YT-400.
(Polyester polyol manufactured by Nippon Polyurethane Co., Ltd., average molecular weight 2600, hydroxyl value 170) was used, and the amount of Mytic NY-315 was changed from 66 parts by weight to 4 parts by weight.
A videotape was made in the same manner as in Example 1 except that the amount was changed to 3 parts by weight.

Comparative Example 2 In the composition of the magnetic paint in Comparative Example 1, VA G
Instead of H, ET-1095 (S'03 manufactured by Toyobo Co., Ltd.
A videotape was produced in the same manner as in Comparative Example 1 except that the same amount of Na group-containing copolyester resin) was used.

Comparative Example 3 In the composition of the magnetic paint in Example 1, 57 parts by weight of Desmodular trifunctional low molecular weight isocyanate compound (manufactured by Bayer AG) was used in place of 66 parts by weight of Mytic NY-315, and Adeka New Ace YT was used. -40
A videotape was produced in the same manner as in Example 1 except that the amount of 0 used was changed from 14 parts by weight to 17 parts by weight.

Comparative Example 4 Video was produced in the same manner as in Comparative Example 3, except that in the composition of the magnetic paint in Comparative Example 3, the same amount of ET-1095 (SO3Na group-containing copolyester resin manufactured by Toyobo Co., Ltd.) was used in place of AGH. I made a tape.

The surface smoothness, elastic modulus, sensitivity (output of 5 MHz), and head contamination of the magnetic layer were investigated using the methods described below for each videotape obtained in each example and each comparative example. The results are shown in the table below. That's right. Note that the ratio of the low molecular weight polyol to the isophorone diisocyanate-based polyisocyanate compound in each of the Examples and Comparative Examples is such that the ratio of hydroxyl group to isocyanate group is 1.0.
(equivalent weight).

Surface smoothness> Use a stylus type roughness needle, stylus speed 0.06C+n/sec,
The surface average roughness (C,1,,^) of the magnetic layer was measured under the condition of a cutoff of 0.08 m1, and the quality of the surface smoothness was determined by the relative value calculated according to the following formula with reference to that of Example 1. judged.

18th item ZJL;, L, C 1111 Elastic modulus of magnetic layer> The elastic modulus of the entire tape was measured under the conditions of sample length LoCm and pulling speed of 20 m/min, while the elastic modulus of only the polyester base film was measured. The elastic modulus of only the magnetic layer was determined from the constant values on both sides according to the formula below.

0 yen dM: Thickness of magnetic layer (cm) dB: Thickness of polyester base film (cm)
) ET: Elastic modulus of the entire tape EB: Elastic modulus of the polyester base film From the elastic modulus of the magnetic layer of each sample calculated from the above formula, Example 1
Calculate the relative value using the following formula as a reference,
Based on this relative value, it was determined whether the elastic modulus of the magnetic layer was large.

Sensitivity> The output (dB) of 5 MIIz of each sample was calculated using the one of Example 1 as the reference (OdB).

Head dirt> 5M was applied to the video tapes obtained in each example and comparative example.
Record a Hz signal and run it on a video deck, and the playback signal output level may drop to 3 due to head dirt or clogging.
Measure the time it takes for the output level to decrease by dB, and if the output level does not decrease even after 60 minutes (○), if the output level decreases after 30 minutes or more but less than 60 minutes (△), if the output level decreases in less than 30 minutes. Those that decreased were evaluated as (x).

As is clear from the table above, head stains were observed in the videotapes obtained in Comparative Examples 1 to 4, whereas head stains were not observed in the videotapes obtained in Examples 1 and 2. The surface smoothness, elastic modulus, and sensitivity are the same or higher, and this means that the magnetic recording medium obtained by this invention has good dispersibility of metal magnetic powder and excellent surface smoothness, as well as high elasticity and good sensitivity characteristics. I understand.

Claims (1)

[Claims] 1. A magnetic paint containing a metal magnetic powder, a copolymerized polyester resin containing a vinyl chloride-vinyl acetate copolymer or a sulfonic acid metal base, a low molecular weight polyol, and an isophorone diisocyanate-based polyisocyanate compound is applied onto a substrate. Magnetic recording media made by coating