JPS63112820A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder in a magnetic coating liquid and to improve the electromagnetic conversion characteristic and durability of the titled medium by incorporating an active group such as hydroxyl group or carboxyl group into a vinylidene chloride copolymer to be used as a binder. CONSTITUTION:This recording medium has a magnetic layer formed by coating the magnetic coating liquid contg. the ferromagnetic powder and binder on a nonmagnetic substrate. The vinylidene chloride copolymer consisting of 55-95wt% vinylidene chloride, 5-45wt% acrylonitrile, 1-12wt% acrylic acid and 1-20wt% hydroxyalkylacrylate is used as the binder. The dispersibility of the magnetic powder is thereby improved and the durability of the recording medium together with the electromagnetic conversion characteristic are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to magnetic recording media, and particularly to magnetic recording media such as magnetic tapes and floppy disks that have excellent electromagnetic conversion and durability. .

(Prior Art and its Problems) The density of magnetic recording media is increasing year by year, and the highly abrasive powder used is being developed into a finer powder. The magnetic powder in these magnetic recording media is required to have a high degree of dispersibility.

In general, magnetic recording media are produced by uniformly applying a magnetic coating liquid obtained by kneading magnetic powder, a binder 9 filler, various additives such as #lubricant, and a bath agent onto a non-magnetic substrate such as a plastic film or sheet. After drying, the surface of the magnetic layer is mirror-finished by calendering. W
Ii powder.

Although it is of course necessary to remove foreign matter and aggregated particles from the magnetic coating liquid consisting of an inder and the like, a homogeneous magnetic layer cannot be obtained unless the magnetic powder is sufficiently dispersed in the abrasive coating liquid. Such non-uniformity in the magnetic layer impairs the electromagnetic properties of magnetic tapes and floppy disks. For example:
These include a decrease in output, an increase in noise, and the occurrence of dropouts.

In addition, if the magnetic powder is not sufficiently dispersed in the 1 m magnetic powder binder, the binding force (adhesive force) between the a-type powder and the binder in the magnetic layer is weak, and when the magnetic recording medium is driven in contact with the magnetic head, Separation of magnetic powder from the surface of the magnetic layer (powder drop phenomenon) is likely to occur, resulting in damage to the medium surface and reduced durability.

As described above, the dispersion of the magnetic powder in the magnetic coating liquid and the adhesion between the magnetic powder and the binder are extremely beneficial for improving the basic performance of the magnetic recording medium, such as the 'flL@ conversion characteristics and durability.

As a result of the inventors' intensive study on the problem of
It was discovered that the dispersibility of magnetic powder in magnetic coating liquids could be greatly improved by introducing active groups such as hydroxyl groups and carbonic acid groups into the vinylitine chloride copolymer as a binder, which led to the invention.

(Object of the Invention) The first object of the present invention is to provide a novel magnetic recording medium.

Second, by improving the dispersibility of magnetic powder, 1! The object of the present invention is to provide a magnetic recording medium with superior magnetic conversion characteristics.

The third objective is to provide a magnetic recording medium with the highest durability.

(Inventor) The above object of the present invention is to provide a magnetic recording medium having a magnetic layer formed by applying a magnetic coating liquid containing ferromagnetic powder, a binder, and t on a non-in substrate, in which vinyl chloride is used as the binder. 55-951 Doku, Acrylonitrile 5-4
5% by weight.

This can be achieved by a magnetic recording medium using a vinylidene chloride copolymer containing 1 to 12N% (meth)acrylic acid and 1 to 2031i% hydroxyalkyl (meth)7 acrylate.

The invention will now be explained.

The preferable composition of the vinylitine chloride copolymer used in the present invention is 70 to 901 hiniritene chloride9, 10 to 30]1jii% of acrylonitrile (meth)acrylic t11
2 to 8*3% and 2 to 15% of hydroxyfurkyl (meth)acrylate. Particularly preferred group & is vinylitine chloride 80-90 N:I!
t5X, a Naro copolymer of 10 to 20% by weight of acrylonitrile, 2 to 61% by weight of (meth)acrylic acid, and 3 to 101% by weight of hydroxyalkyl (meth)acrylate.

In the present invention, if the acrylonitrile content is less than 51% by weight, the thermal stability of the comonomer will be poor.

Moreover, if it exceeds 45 NM%, the dispersibility of the magnetic powder in the i-type layer after coating will decrease, which is not preferable.

If the amount of (meth)acrylic acid is less than the amount of 123i, the dispersibility of the magnetic powder will be insufficient, and if the amount of 123i exceeds 9, the solubility of the copolymer in the bath agent will decrease, which is not preferable.

Furthermore, hydroxyalkyl (meth)acrylate is 1
If the hit is less than 3'6, the dispersibility of the magnetic powder will be insufficient, and if the amount exceeds 20, the solubility of the copolymer in the solvent will decrease, and if the magnetic coating is cross-linked, the property will deteriorate. This is not preferable because it tends to have physically brittle properties.

= 5- The (meth)acrylic acid used in the comonomer of the present invention includes methacrylic acid and acrylic acid.

Also, what is hydroxyalkyl (meth)acrylate?
Contains methacrylic acid and terminal hydroxyalkyl esters of acrylic acid.

Representative examples of hydroxyalkyl (meth)acrylates include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl methacrylate.

Examples include 2,-hydroxypropyl acrylate.

When a vinylidene chloride/acrynitrile/hydroxyalkyl (meth)acrylate copolymer that does not contain a (meth)acrylic acid component is used as the vinylitine chloride copolymer of the present invention, the four-component copolymer of the present invention In comparison, not only the dispersibility of the magnetic powder is insufficient, resulting in poor electromagnetic conversion characteristics, but also the bonding force between the magnetic powder and the binder is reduced, resulting in poor durability as a magnetic recording medium.

Furthermore, when a vinylidene chloride/acrylonitrile copolymer that does not contain both (meth)acrylic acid and hydroquine alkyl (meth)acrylate is used, an improvement in electromagnetic conversion ratio is obtained due to insufficient dispersibility of the magnetic powder. Furthermore, the physical properties of the coating film (tensile strength, initial Young's modulus, etc.) are inferior, and as a result, the durability tends to decrease, which is not preferable.

Furthermore, when a vinylidene chloride/acrylonitrile/(meth)acrylic acid group polymer containing no hydroxyalkyl (meth)acrylate is used, the dispersibility of the magnetic powder is lower than that of the four-component copolymer of the present invention. However, it is inferior to the present invention in terms of coating film W properties and durability.

In this way, the four-component combination of the present invention is characterized by an electromagnetic change based on the dispersibility of the magnetic powder. # The magnetic recording medium has extremely excellent performance not only in terms of characteristics but also in terms of the durability of the recording medium itself.

In the present invention, the degree of polymerization of the vinylitine chloride copolymer is 1
00 to 1500 is preferable, and a particularly preferable range is 200.
~800. If the degree of polymerization is less than 100, the physical properties of the copolymer will be poor (and if the degree of polymerization is greater than 1,500, the solubility of the copolymer in a solvent will be extremely poor, which is not preferred from a practical standpoint.

The ratio of the vinylidene chloride comonomer of the present invention in the binder composition used for forming the magnetic layer is small (at least 5 wt%, preferably 10 wt% or more, particularly preferably 15 wt%).
wt% or more. If the amount of this copolymer is less than 5 wtX, the magnetic powder will not be sufficiently dispersed.

The vinylitine chloride copolymer of the present invention may be used alone, but if necessary, it may be used in combination with other polymer binders.

Examples of these polymer binders include the following.

Polyurethane resin, polycarbonate resin.

These include phenoxy resins, epoxy resins, cellulose polymers such as cellulose nitrate, polybutyral resins, rubber resins such as NBR, vinyl chloride/vinyl acetate copolymers, and polyester resins.

Furthermore, polyisocyanate-based crosslinking agents can be used in combination.

The following examples can be given as these polyincyanate crosslinking agents.

・Tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate), 4.4
Diincyanate such as '-diphenylmethane diisocyanate, or addition product of trimethylolpropane and 3 moles of tolylene diincyanate! fC products (such as "Fronate L" manufactured by Nippon Polyurethane Resin Co., Ltd.), etc.

The proportion of the polyincyanate used in the present invention is preferably 1, less than 9 K 40 wt% in the binder composition, particularly preferably 30 wt% or less, 40 wt% or less.
If the amount is more than t%, the magnetic layer becomes rigid and brittle, and the adhesion between the magnetic layer and the substrate (film) decreases, which is not preferable.

In addition to the above, the present invention uses lubricants, fillers, and stabilizers! A plasticizer etc. can be used together.

Typical lubricants include higher fatty acid esters, silicone, and fluorine-based lubricants. Examples include compounds.

Typical examples of fillers include various ceramics such as α-iron oxide, α-7 lumina, 5to1*5i-C, and TiO2.

The magnetic recording medium of the present invention is a magnetic coating liquid obtained by dispersing the binder composition of the present invention, magnetic powder and various additives in an organic solvent, which is coated onto a non-magnetic substrate, dried, and then subjected to a calendar treatment. It can be obtained by applying a mirror finish.

Representative magnetic powders include rF820B + Co-enclosed γ-Fe20B + hexagonal barium ferrite, and fine alloy powder containing iron as a main component. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

In addition, "peeling" in an Example shows "11 parts."

Examples 1 to 3 A mixture having the following composition was mixed with 16 Rftil using a continuous wet dispersion machine (Ashizawa, Tong Isvaal Mill P to 11), and it was confirmed that the mixture had a good dispersion state.

lecithin 3
．． 2 types α-alumina (average particle size 0.8μm)
s, o part carbon black
7. Exposed vinylidene chloride copolymer (each composition is shown in Table 1) 5.0 Part urethane resin (
Dainippon Ink, Crispon 4216) 9. "Salt vinyl acetate co-N combination (UCC, VAGH)"
6. Os*1 solvent (MEK/CycloNon-3
0/70) 150.0 parts of the obtained dispersion was diluted with a binder and lubricant solution having the following composition to give a viscosity in mg suitable for coating.

Polyisocyanate compound (Japan Polyurethane, Colloid) 6, os” lubricant (butoxyethyl stearate))
4.0 parts solvent (MEK/cyclohexanone-30/70
) 30.0 parts *1 The proportion of vinylidene chloride copolymer in the binder is 5.0/(5,0+9.0+6.0+6.0)XI00
=5.0/26.0
Apply it evenly.

After drying, the surface of the magnetic layer was smoothed by calendering. After curing at room temperature and heating, a 5.25-inch disk was punched out and placed in a polyvinyl chloride jacket with a liner to obtain a floppy disk.

Comparative Examples 1 to 3 Comparative examples 1 to 3 were carried out in exactly the same manner as in Example 1, except that a copolymer not containing the following components (each composition is shown in Table 1) was used as the vinylitine chloride copolymer used in Example 1. A 5.25 inch floppy disk was obtained.

Examples 4-5 All of Examples 1-3 were used except that a magnetic coating liquid with the following composition was used.
Similarly, a 5.25 inch floppy disk was obtained.

Acicular ratio 8/lulecithin
3.8 parts α-alumina (average particle size 0.5 μtn)
4.2 parts carbon black
5.0 parts vinylidene chloride copolymer (
Each composition is shown in Table 2) 8.0 parts *1 Urethane resin (Dainippon Ink, Crispon 4216) 7
．． 5iB*1 phenoxy resin (UCC, PKHJ)
4. s@”, polyisocyanate compound (Japan Polyurethane, Coronate L) 4.0
Part *1 Lubricant (butoxyethyl stearate))
3.6 parts solvent (MEK/cyclohexanone = 3
0/70) 180.0 parts*1 Proportion of vinylidene chloride copolymer in binder 33.3% Comparative example 4 As the vinylidene chloride IJ dene copolymer used in Example 1, a copolymer containing no methacrylic acid component was used. 5.2 was carried out in exactly the same manner as in Example 1, except that 1 coalescence (the composition is shown in Table 2) was used.
5 inch Fronbie disc? :Obtained.

Comparative Example 5 Instead of the vinylitine chloride copolymer used in Example 1, a salt-vinyl acetate copolymer having the following composition (all the same as Example 1 except that C0OH groups and Of (containing groups) are used in the polymer) (Similarly, a 5.25-inch 7P disk was obtained.

Copolymerization composition Weight nine Vinyl chloride 92 Vinyl acetate 2 Maleic anhydride 1 Vinyl alcohol 5 Examples 6 to 7 Magnetic application g was prepared in exactly the same manner as in Example 1 using a mixture having the following composition.

r-Fete, Hc300oe+ys74.5
gmu/j' 65.0 parts Specific surface area 13.4 m"/
1/ Lecithin
2.0 parts α-alumina (average particle size 0.5μsn)
4.0 parts carbon black
5.5 parts vinylidene chloride combined (
Each composition is shown in Table 3) 3.0s*1 Urethane iIk fat (Goodrich+ Nissan 5701)
s, ss” salt vinyl acetate copolymer (8 Shin Chemical + TA)
s, 5g" polyisocyanate compound (Japan Polyurethane! Coronate L) 3, #" lubricant (butoxyethyl stearate))
4.1 part bath additive (MEK/cyclohexane/30
/70) 150.0 parts*1 Proportion of vinylidene chloride copolymer in binder 15. o (X) The obtained magnetic dosing liquid was applied to both sides of a polyethylene terephthalate film with a thickness of 75 μm, so that the film thickness after IE drying was 2 m.
．． It was applied evenly to form a 7μ mesh. After drying the coating layer, the surface of the magnetic layer was smoothed by calendering.

After curing at room temperature and heating, a 5.25-inch floppy disk was obtained.

Comparative Example 6 As the vinylitine chloride co-monomer used in Example 6, a co-monomer containing no methacrylic acid component and 2-hydroxyethyl methacrylate)X component (composition is shown in Table 1g3)
A 5.25-inch floppy disk was obtained in the same manner as in Example 6, except that the following procedure was performed.

Measurement of electric a conversion characteristics Measurements were made using a commercially available floppy disk device YD-380 or YD-274 manufactured by YE Data.

1) 2F output (316) The output level of the innermost circumference was compared and expressed as a percentage (%) with the reference level (comparative example) as 100.

2) Resolution (316) Compare the 2F output of the innermost circumference and the IF ratio output ratio, and It is expressed as a percentage with the reference level (comparative example) as 100.

3) Override difference Overwrite the 1F signal with 1 2F signal, display the IF multiplied signal survival rate in decibels (dB), and set the reference level (comparative example) to ±0
The difference (dB) is shown.

The results of 1) to 3) are shown in Tables 1 to 3.

Durability evaluation: Using a commercially available 5.25-inch floppy disk device,
The head was loaded with a head tension of 20 g, the head was rotated continuously on the same track, and the durability time was defined as the time until peeling occurred on the -1@ side of the coating surface.

The atmospheric conditions for carrying out the durability evaluation were the following temperature and humidity cycle conditions. That is, recycling was repeated every 24 hours.

The trial sales conditions are more severe than the continuous durability test. The results of the durability evaluation are shown in Tables 1 to 3.

Magnetic coating samples were prepared by applying each coating solution using an applicator so that the film thickness after drying would be approximately 40 μm, and drying.

After heat curing, use a tensile tester (*Yo Bold Line Co., Ltd.,
Tensile strength and elongation and initial Young's modulus were measured using Tensilon RTM-100>.

The results of tensile properties are shown in Table 3.

Table 1 Notes 1) 2-Hydroxyethyl methacrylate Notes
2) YD-380ff floppy disk am Table 2 1) 2-Hydroxyethyl methacrylate 2) YD
-380 type floppy disk device 120- #I3 Table 1) 2-Hydroxyethyl methacrylate 2) YD
-274 Floppy Disk Device (Effects of the Invention) The following is clear from the above examples and comparative examples.

fi+ As shown in Examples 1 to 5, vinylidene chloride/acrylonitrile/(meth)acrylic i! of the present invention!
! The 12/2-hydroxyethyl methacrylate copolymer was a vinylidene chloride copolymer containing no (meth)acrylic acid and 2-hydroxyethyl methacrylate shown in Comparative Example 1, and (meth) shown in Comparative Examples 2 and 4. ) Vinylidene chloride copolymer containing no acrylic acid, violet or vinylidene chloride copolymer containing no 2-hydroxyethyl methacrylate shown in Comparative Example 3, and further Comparative Example 5
Maleic anhydride (C0OH
) and vinyl alcohol (OH).

That is, the 2F output and resolution are high, and the override characteristics are excellent.

This is because the dispersibility of the magnetic powder and the binder is good in the magnetic coating film, and the dispersion of the magnetic powder is excellent in the resulting magnetic layer.

Regarding Examples 6 and 7, when the vinylidene chloride copolymer of the present invention was used, the electromagnetic conversion characteristics were superior compared to Comparative Example 6.
It has become something like this.

(21 Durability evaluation results As shown in Examples 1 to 5, when the vinyl chloride=lldene copolymer of the present invention was used, compared to the results of Comparative Examples 1 to 5,
Both have high durability.

This is because the magnetic powder in the magnetic coating liquid is well-dispersed with the binder and has magnetic properties, so the magnetic powder is strongly bonded (adhered) to the binder in the resulting magnetic layer. be.

Furthermore, from the viewpoint of coating film properties, Example 6.7 and Comparative Example 6
As can be seen from the comparison, the copolymer composition of the present invention has high tensile strength and initial Young's modulus (and improved durability as a magnetic recording medium).

The binder composition according to the present invention using vinylidene chloride/acrylonitrile/(meth)afryl/hydroxyalkyl(meth)acrylate copolymer has excellent electromagnetic conversion characteristics as a result of improved dispersibility of magnetic powder.
Furthermore, there is an advantage that a magnetic recording medium with durability of 4&n can be obtained.

Claims (1)

[Claims] In a magnetic recording medium having a magnetic layer formed by coating a magnetic coating liquid containing ferromagnetic powder and a binder on a non-magnetic substrate,
55 to 95% by weight of vinylidene chloride as the binder
, 5-45% by weight of acrylonitrile, 1-12% by weight of acrylic acid or methacrylic acid, and 1-2% of hydroxyalkyl acrylate or hydroxyalkyl methacrylate.
A magnetic recording medium characterized by using a vinylidene chloride copolymer containing 0% by weight as a component.