JPS62185225A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve tape runnability and durability and to improve the dispersion of a filler with a binder by forming a back coat layer into which specific materials are incorporated. CONSTITUTION:This recording medium is constituted by providing the back coat layer contg. the filler dispersed into the binder on the surface of a nonmagnetic base on the side opposite from the magnetic layer formed thereon. A polyurethane resin contg. a hydroxyl group and metallic base of sulfonic acid and vinyl chloride copolymer contg. a hydroxyl group, the metallic base of sulfonic acid and epoxy group are incorporated as the binder component into the back coat layer. The dispersion of the filler to be incorporated into the back coat layer is thereby made extremely easier than heretofore and not only the formation of the back layer having the excellent smoothness is executed but also the back coat layer having a low coefft. of friction and excellent durability is obtd. The recording medium having the excellent running stability and durability is obtd. without spoiling the S/N characteristic of the magnetic layer medium.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks used in audio and video equipment, computers, and the like.

BACKGROUND OF THE INVENTION In recent years, each of these magnetic recording media has become suitable for high-density recording, and for this purpose, the trend has been to shorten the recording wavelength, narrow the recording track width, and reduce the thickness of the recording medium.

As a result, the S/N ratio and sensitivity 1-frequency characteristics are generally disadvantageous, but as a countermeasure, the surface properties of the magnetic layer can be further improved by making the magnetic powder finer and using a highly smooth non-magnetic support. This method is adopted. However, if the above measures are taken alone, the surface properties of both the front and back sides of the recording medium will increase, resulting in an increase in the coefficient of friction on both sides, which will be disadvantageous in terms of running performance and durability. It is known to provide a back coat layer (hereinafter abbreviated as back layer) on the opposite surface of the support from the magnetic layer surface.

Problems to be Solved by the Invention These back layers generally have fillers and binders as their main constituents, but back layers that use binders that have been used in the past suffer from abrasion and a decrease in the coefficient of friction. In addition to easily causing the tape to fold and bend, it was also difficult to sufficiently disperse the filler, and as a result, the surface condition of the backing layer became too rough, causing it to be rolled into a roll like a magnetic tape. In magnetic recording media stacked in sheet form, the unevenness of the bank layer is reflected on the surface of the magnetic layer. The problem of deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the so-called show-through phenomenon was also likely to occur. The present invention aims to provide a magnetic recording medium that can solve this problem.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a back layer containing a filler dispersed in a bonding layer on a surface of a non-magnetic support opposite to the magnetic layer surface. In magnetic recording media,
By containing a polyurethane resin containing a hydroxyl group and a sulfonic acid metal base and a vinyl chloride copolymer resin containing a hydroxyl group, a sulfonic acid metal base, and an epoxy group as binder components for the back layer, S/ of the magnetic layer medium can be improved. A magnetic recording medium having excellent running stability and durability without impairing the N characteristics is obtained.

By combining a specific polyurethane resin and a vinyl chloride copolymer resin as a binder for the bank layer, it becomes extremely easy to disperse the filler contained in the bank layer compared to conventional methods, and the smoothness is reduced. Not only is it possible to form a back layer with a high friction coefficient, but also a back layer with a low coefficient of friction and excellent durability can be obtained. In other words, the sulfonic acid metal base and hydroxyl group in both of the resins greatly contribute to improving the dispersibility of the filler, and furthermore, the presence of the epoxy group in the vinyl chloride copolymer resin improves the thermal stability of this resin. There are two things that can be mentioned: In other words, conventional polyurethane resin,
When using a combination of vinyl chloride copolymer resin, the dispersibility of the filler was opaque, and the stability of the vinyl chloride copolymer resin itself was not sufficient, so relatively low molecular weight dispersants and The use of heat stabilizers could be avoided, and as a result, various problems such as softening of the coating film and extrusion of additives were likely to occur.However, in the combination of binders for the back layer according to the present invention, For the above reasons, it is not necessary to use such additives at all. It is thought that

Examples Polyurethane resins containing hydroxyl groups and sulfonic acid metal groups used in the present invention are basically polyesters obtained by polycondensation of dicarboxylic acids and polyhydric alcohols, or polycondensation of polyhydric alcohols together. In the synthesis step of the polyether obtained by using a sulfonic acid metal base-containing polyester or polyether obtained by partially using a dicarboxylic acid or polyhydric alcohol containing a sulfonic acid metal base, various incyanates are added. Compounds such as toluene diisocyanate (TDI), diphenylmethane4.
It can be obtained by reacting 4' diisocyanate (CMDI), inphorone diisocyanate (IPDI), hexamethylene diisocyanate (HMDI), or a condensate of trimethylolpropane and TDI to form a urethane.

The metal element of the sulfonic acid metal base is generally sodium or potassium, which is suitable for improving dispersibility.

The vinyl chloride copolymer resin containing a hydroxyl group, a sulfonic acid metal base, and an epoxy group used in the present invention can be easily obtained as follows.

For example, a vinyl chloride monomer and glycidyl (meth)acrylate can be copolymerized, and then a portion of the glycidyl group (epoxy group) can be cleaved with hydrogen sulfite ions, and then a desired metal salt can be obtained. Expressed as a reaction formula, it is as follows.

(Left below) Rollo! In the synthesis example of the vinyl chloride copolymer resin described above, an example of the use of a binary system was shown, but as a method for introducing a hydroxyl group into the resin, a hydroxyl group such as 2-hydroxyethyl (meth)acrylate can also be used. It is also possible to copolymerize the containing acrylic monomer as a third component. This copolymerization reaction can be carried out by any conventionally known method such as bulk polymerization, suspension polymerization, emulsion polymerization, or solution polymerization.

The polyurethane resin and vinyl chloride copolymer resin used in the present invention both contain hydroxyl groups, and by reacting these resins with a polyisocyanate compound, VC1lIi' can be made with excellent heat resistance and abrasion resistance. Moreover, it becomes possible to form a coating film with a low coefficient of friction.

In the back layer, a filler is usually dispersed in a binder in order to adjust the strength, surface roughness, surface electrical resistance, etc. of the coating film. These fillers include carbon black, graphite, CaCO3, BaSO4゜ZnO,
0s, TlO2, etc., and they can be used alone or in combination of two or more, but in the back layer of the present invention, it is particularly preferable to use carbon black. Carbon black is suitable as a filler that imparts conductivity, slipperiness, and light-shielding properties to coating films, but on the other hand, it has a drawback in terms of dispersibility. It became possible to form a back layer with excellent properties, conductivity, and light-shielding properties. Furthermore, in order to improve the abrasion resistance of the coating film, K120.
It is also possible to use a high hardness fine powder such as , TlO2, etc., but in order to take advantage of the good characteristics of carbon black, it is desirable that 90% by weight or more of the filler in the back layer be carbon black.

Examples of the present invention will be specifically described below. Note that all parts of components mentioned in the examples indicate parts by weight.

Polyurethane resin containing hydroxyl groups and sulfonic acid metal bases and hydroxyl groups used in Examples of the present invention.

Vinyl chloride copolymer resins containing a sulfonic acid metal base and an epoxy group are shown below.

(Polyurethane resin) (Vinyl chloride copolymer resin) (Example 1) A magnetic paint and a back layer paint were prepared as follows.

0 Preparation of magnetic paint Ferromagnetic Go gold-containing Fe 205 Polyurethane resin [manufactured by Nippon Polyurethane Co., Ltd., N-2304] 10 parts Nitrocellulose resin [manufactured by Asahi Kasei Co., Ltd., Seltsuba BTH 1/4]...10 parts α-AE203 [Average particle size = 0.3 μm] 4
1 part carbon black [average particle size = 50 mμ] 3 parts soybean oil lecithin 1 part myristic acid 1 part butyl stearate 1 part Methyl ethyl ketone 120 parts Toluene River 120 parts Cyclohexanone So part The above composition was mixed and dispersed using a pressure kneader and a sand grinder to prepare a magnetic coating material.

To the obtained magnetic paint was added 15 parts of Coronate L', a polyisone anate compound manufactured by Ishihon Polyurethane Co., Ltd., thoroughly mixed and stirred, and then filtered through a filter with an average pore size of 1 μm to prepare a magnetic paint.

0 Adjustment of paint for back layer Polyurethane resin [1] 25 parts Vinyl chloride copolymer resin C4pO”J 2
5 parts carbon black [average particle size = 90 mμ] 50 parts γ
-Aβ205 [average particle size = 0.2 μm]...
2 parts Methyl ethyl ketone...1
50 parts toluene ・・・・・・16
0 parts cyclohexanone...5
0 parts The above composition was mixed and dispersed in a ball mill for 48 hours to remove the contaminants, then 8 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added, and after thorough mixing and stirring, the mixture was mixed and dispersed using a filter with an average pore size of 1 μm. After filtration, a paint for the back layer was prepared.

Next, the above-mentioned magnetic paint was applied onto a 14 μm thick polyester film, subjected to magnetic field orientation and drying treatment, followed by mirror polishing treatment using a super calender roll and then heat treatment to form a raw fabric roll having a 5 μm thick magnetic layer. Obtained. The above-mentioned back layer paint is applied to the opposite side of the raw roll from the magnetic layer.

After drying and then heat treatment, a back layer with a thickness of O.S.mu.m was formed. This was cut to a width of about an inch to prepare a videotape sample (2tsom length).

(Comparative Example 1) Polyurethane resin (+1) and vinyl chloride copolymer resin (≠
C) and a polyurethane resin containing no sulfonic acid metal base (Mw=15000, hydroxyl value=14.
ts') and sulfonic acid metal base, a vinyl chloride copolymer resin containing no epoxy group (Mw = 31000. Hydroxyl value = 5.1), and further dispersion of filler (carbon black, γ-k120.') A videotape sample was prepared in exactly the same manner as in Example 1, except that one part of lecithin was used as the agent.

(Example 2) Adjustment of O-back layer paint polyurethane resin (4P3) 20
Part vinyl chloride copolymer resin (≠mu) 20
Carbon black (average particle size = 50 mμ)...68
Part Ti02 (average particle size = 0.3 μm) - mark・
2 parts methyl ethyl ketone...15
0 parts toluene...15
0 parts cyclohexanone...5
0 parts The above composition was mixed and dispersed in a ball mill for 48 hours to remove the contaminants, then 8 parts of a polyiso/anate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added, and after thorough mixing and stirring, a filter with an average pore size of 1 μm was added. A paint for the back layer was prepared by filtration.

Videotape samples were prepared in exactly the same manner as in Example 1 using the magnetic layer paint and the back layer paint used in Example 1.

(Comparative Example 2) The polyurethane resin (+3) as a binder in the back layer paint of Example 2 was replaced with a polyurethane resin containing no sulfonic acid metal base (Mw = 64000, hydroxyl value =
A videotape sample was prepared in exactly the same manner as in Example 2, except that 2.4) was replaced.

(Example 3) Ferromagnetic (We, Co, Ni) alloy polyurethane resin (4=2) 12 parts Vinyl chloride copolymer resin (+A) 8 parts α-person 71
203 (average particle size = o, 2 μm) 6
1 part carbon black (average particle size = 20 mμ) 2 parts ethyl stearate 1 part palmitic acid 1 part methyl ethyl ketone
・・・・・・ 100 parts toluene
・・・・・・ 100 parts cyclohexanone
609 The above composition was cross-dispersed using a pressurized knee gun and a sand grinder to prepare a magnetic paint.

Part a of a polyisocyanate compound (manufactured by Bayer AG, Desmodur L) was added to the obtained magnetic paint, thoroughly mixed and stirred with a high-speed stirrer, and then filtered through a filter with an average pore size of 1 μm to prepare a magnetic paint.

0 Adjustment of back layer paint Polyurethane resin (+2) 25 parts Vinyl chloride copolymer resin (4PB) 20 parts Carbon black (average particle size = 9Qmμ) 46 parts Carbon black (average particle size Diameter = 30 mμ) 10 parts Methyl ethyl ketone 150 parts Toluene
...... 150 parts Cyclohexanone ...... 60 parts The above composition was mixed and dispersed in a ball mill for 48 hours to remove the contaminants, and then a polyisocyanate compound (manufactured by Nippon Polyurethane Co., Ltd.,
8 parts of Coronate L) were added, thoroughly mixed and stirred, and filtered through a filter with an average pore size of 1 μm to prepare a paint for the back layer.

Next, the above-mentioned magnetic paint was applied onto a 10 μm thick polyester film, subjected to magnetic field orientation and drying treatment, followed by mirror polishing treatment using a super calendar roll, followed by heat treatment. Got the roll.

The above-mentioned back layer paint is applied to the opposite side of the raw roll from the magnetic layer.

Drying and then heat treatment were performed to form a back layer with a thickness of 0.7 μm. This was cut into inch-wide pieces to prepare videotape samples (250 m long).

(Comparative Example 3) The vinyl chloride copolymer resin (4PR) as the binder in the back layer paint of Example 3 was replaced with a vinyl chloride/glycidyl methacrylate copolymer resin (Mw= A videotape sample was prepared in exactly the same manner as in Example 3, except that 25,000 and epoxy value = 6.5) were used.

(Comparative Example 4) The vinyl chloride copolymer resin (≠B) used as the binder in the back layer paint of Example 3 was replaced with vinyl chloride, vinyl acetate, and vinyl alcohol copolymer resins that do not contain sulfonic acid metal bases or epoxy groups. A videotape sample was prepared in exactly the same manner as in Example 3, except that the polymer resin (kW = 27,000, hydroxyl value = 7.0%'l) was used.

The videotape samples obtained in each of the above Examples and Comparative Examples were subjected to the evaluation tests shown below.

(1) Surface roughness The surface roughness of the magnetic layer and back layer was measured using a Talystep type surface roughness meter manufactured by Taylor Hopson. The value was determined by calculating the root mean square of the peak height in the roughness chart.

(References; National Technical
Report Vol, 28 No. 3 June
1982 pp, 520) [210/N Wind each sample tape into a cassette half and
c7n in z was measured. As a videotape recorder (VTR) for C/N measurement, a VH8 type VTR (Matsushita Electric Industrial Co., Ltd., NY-88OO) was used. however,
Regarding sample tapes (Example 3, Comparative Example 3, and Comparative Example 4) using ferromagnetic alloy powder, measurements were performed by replacing the recording/reproducing head of the VTR with Sendust alloy. Super HG videotape (made by Matsushita Electric Industrial Co., Ltd., NVT120HG) was used as the standard tape, and its C/N
was defined as OdB.

(3) Running durability Using the same VTR as in (1), each sample tape was heated at 40°C for 80 minutes.
After running the bus 200 times in an environment of 0% RH, the number of dropouts (*) was measured and the condition of the sample tape was observed.

(*); Using the same VTR as t21, momentary dropouts in the video signal were observed using a dropout counter.

(4) Prevention of irregular winding (2) Using the same VTR, each sample tape was fast-forwarded and rewound over its entire length, and then the winding appearance of the tape rewound onto the reel was observed.

The evaluation test results for each sample tape are shown in the table below.

(Margins below) In the above embodiments, a coated magnetic tape was explained, but the present invention also describes a back coat of a vapor-deposited magnetic tape,
It goes without saying that the present invention can be applied not only to magnetic tapes but also to magnetic recording media such as magnetic disks and magnetic cards having back coats.

Effects of the Invention As is clear from the above, according to the present invention, a polyurethane resin containing a hydroxyl group and a metal sulfonate group and a vinyl chloride copolymer resin containing a hydroxyl group, a metal sulfonate group and an epoxy group are used as main binders. The back coat layer not only provides smooth tape running properties but also has good durability, and the binder has extremely good dispersibility with the filler, resulting in a coating film with good surface properties. Therefore, the surface properties of the magnetic layer are not impaired and good electromagnetic conversion characteristics can be obtained.

Claims (3)

[Claims] (1) A magnetic recording medium in which a magnetic layer is provided on one main surface of a non-magnetic support, and a back code layer containing a filler dispersed in a binder is provided on the other main surface. hand,
A magnetic recording medium characterized in that the binder for the back coat layer is a polyurethane resin containing a hydroxyl group and a metal sulfonate base, and a vinyl chloride copolymer resin containing a hydroxyl group, a metal sulfonate base, and an epoxy group. (2) The magnetic recording medium according to claim 1, wherein 90% by weight or more of the filler in the back coat layer is carbon black. (3) The magnetic recording medium according to claim 1, characterized in that a low molecular weight polyisocyanate compound is contained as a binder component for the back coat layer.