JPS623429A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled magnetic recording medium having excellent dispersion stability, coating property, stationary stability and sensitivity by providing a backcoat layer having specified surface roughness on the opposite side of a magnetic layer contg. an org. dye or pigment having a carbonyl group and/or a sulfonic group. CONSTITUTION:A magnetic layer 2 contg. 1-10wt%, based on magnetic powder, org. dye or pigment having a carbonyl group and/or a sulfonic group and contg. a polyurethane resin and a phenoxy resin and/or a vinyl chloride resin as the binder resin is formed on the surface of a substrate 1. A backcoat layer 3 contg. carbon black, silicon oxide and other nonmagnetic powder is formed on the rear surface of the substrate 1 and the surface roughness of the layer is regulated to <=0.07mum.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

Conventionally, in these magnetic recording media, various dispersants and surfactants have been used to disperse fine particulate magnetic powder in an organic solvent together with a binder resin when preparing a coating solution for manufacturing the media. . Examples of dispersants include oily lecithin or powdered lecithin, saturated or unsaturated fatty acids and their salts, hydrocarbons having polyoxyethylene chains, and sulfuric acid esters and phosphoric acid esters of higher alcohols. These dispersants are added in an amount of 0.01 to 20 parts by weight per 100 parts by weight of the magnetic powder.

In recent years, in order to manufacture high-performance magnetic tapes, it is essential to make magnetic particles ultra-fine and increase BET, but it is difficult to obtain a magnetic recording layer with desired characteristics using conventional additives. In addition, even if a prototype in a laboratory has excellent properties, it may not be put into practical use due to mass production or production technology considerations.

Furthermore, in the prior art, dispersion into a binder solution by surface modification of magnetic powder is considered as the primary objective, and consideration is not given to the stability and applicability of the produced paint. In addition, many conventional dispersants have surface-active properties that cause deterioration of the dispersant in the coated magnetic layer, seep onto the tape surface, adversely affect running properties, and degrade electromagnetic characteristics. However, it is overlooked that factors other than surface activity may be involved in surface modification of magnetic powder by adsorption to magnetic powder.

Furthermore, there are no conventional types of additives that have both dispersibility and thermal and chemical stability and are suitable for production.

In addition, as the tape performance improves, the surface properties of the magnetic layer become better (the surface becomes smoother), and the running properties of the tape decrease. It is necessary to provide a coating layer (hereinafter abbreviated as BC layer).

The first object of the present invention is to provide a magnetic recording medium with improved dispersion stability using a new additive for the magnetic layer; second, to improve coating properties and stagnation stability. Thirdly, in conjunction with the first and second objectives, the objective is to provide a magnetic recording medium with good sensitivity; fourthly, the objective is to provide a magnetic recording medium with good sensitivity; The object of the present invention is to provide a magnetic recording medium with good layer durability; and fifth, to provide a magnetic recording medium with good running properties.

20 Structure and Effects of the Invention In other words, in the present invention, an organic dye or pigment having a carboxyl group and/or a sulfo group is contained in a magnetic layer, and the surface roughness is 0. The present invention relates to a magnetic recording medium provided with a back coat layer (BC layer) having a thickness of 0.07 μm or less.

According to the present invention, since the magnetic layer contains the above-mentioned organic dye or pigment (i.e., an organic dye compound: hereinafter referred to as the "compound of the present invention"), the dispersion of the magnetic particles is stabilized, and the coating The electromagnetic conversion characteristics such as S/N ratio and RF/output are greatly improved.

Moreover, since the BC layer is provided, the running properties of the medium are improved, and the surface roughness of the BC layer is equal to the average surface roughness R.
a (cutoff value 0.08 mm) Since the range is below 0.07 μm, the roughness of the BC layer is transferred to the surface of the magnetic layer due to Ra≦0.07 μm, which affects the electromagnetic characteristics of the medium, especially Lumi S/ N is not damaged. however,
If it is less than 0.005 μl, the frictional resistance on the back side will increase, and the running performance of the tape in a deck, for example, will be poor. Therefore, the lower limit of Ra is preferably set to 0.005 μl. In particular, Ra should be 0.005 μl. It is desirable that the thickness be 0.006 to 0.06 μm.

It is desirable that the compound (organic dye or organic pigment) of the present invention satisfies at least one of the following four conditions.

1. Must be an Ab-based compound.

2. It must be in the form of salt. As salt, NH.

(ammonium salts), alkali metal salts, alkaline earth metal salts, and organic amine salts are preferred.

3. The general formula must have the following skeleton.

Rl and RZ are hydrocarbon residues, and at least one of them has a carboxyl group or a sulfo group.

More preferably, Y has the following basic structural formula:
Cl, NO2, -0CH5, CH3, -C2H5
, OCzHs , CON HR' , -H, -
Either OH.

R:l: C11No! , OCH3, CH:I,
CtHs, 0CzHs, -HlCOOH.

A phenyl ring having either -3O or H or a fused ring such as a naphthalene, indole, or quinoline ring.

Z: -COOH or -SO, H or salts thereof (
Salts include ammonium salts, alkali metal salts, alkaline earth metal salts, and organic amine salts).

゛−′ Represents a fused ring such as a ring or a Kihan ring.

X: C1, NOz, OCHs, CH3
, CzHs, -0CtHs, H, COOH.

-503H.

Note that R', -COOH, -3o, and H of X may also form a salt as with Z.

4. Must be of red color.

Examples of these organic dyes or organic pigments are listed below. Other examples that can be used are:

O -CON H (CHz) + oCOOH l Cz Hs H5 The amount of the compound of the present invention added to the magnetic layer has an appropriate range, and the total amount is preferably 1 to 10 parts by weight per 100 parts by weight of magnetic powder. 2 to 7 parts by weight is even better.

By adding 1 part by weight or more, the dispersibility, durability, etc. are sufficient and the surface properties of the layer are improved, and by adding 10 parts by weight or less, the viscosity of the paint is sufficient and the film thickness can be controlled. It becomes easier.

The compound of the present invention may be added at the premix stage, kneaded with the magnetic powder using a kneader or the like, or the magnetic powder may be subjected to a dispersant solution as a pretreatment.

At least polyurethane is used as the pi-resin in the magnetic layer in the magnetic recording media of the 1990s, which can be synthesized by the reaction of polyol and polyisocyanene. Poles that can be used include phthalic acid, adipic acid, azenoic acid, trimerized lyluic acid, maleic acid, and basic acids.
Glycols such as ethylene glycol, probidericol, butylene glycol, diethylene glycol, polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or among these glycols and polyhydric alcohols Polyester polyol synthesized by reaction with two or more selected polyols; or from lactams such as S-caprolactam, α-methyl-1-caprolactam, S-methyl-3-caprolactam, and γ-butyrolactam. and polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, and the like.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamyl diisocyanate, methylene diisocyanate, mexylylene diisocyanate, etc., resulting in urethanized polyester polyurethanes, polyether polyurethanes, and polycarbonates carbonated with phosgene or diphenyl carbonate. Polyurethane is synthesized.

These polyurethanes are usually produced primarily by the reaction of polyisocyanates with polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. (for example, in the form of a urethane elastomer).

Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted.

In addition, in the present invention, if a phenoxy resin and/or a vinyl chloride copolymer is contained in addition to the above-mentioned polyurethane as a binder resin, the dispersibility of the magnetic powder will be improved when applied to the magnetic layer, and its mechanical properties will be improved. Strength increases. However, if the phenoxy resin and/or vinyl chloride copolymer is used alone, the layer will become too hard (too hard), but this can be prevented by containing polyurethane, and the adhesion to the support or base layer will be improved.

The phenoxy resin that can be used is a polymer obtained by polymerizing bisphenol A and epichlorohydrin, and is represented by the following general formula.

(However, nλ82 to 13) For example, PKHClPKHH manufactured by Union Carbide
, PKHT, etc.

Further, as the above-mentioned vinyl chloride copolymers that can be used, there are those represented by the general formula 2: In this case, the molar ratio derived from l and m in is 95-50 mol% for the former unit and 5-50 mol% for the latter unit. Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one member selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like. The degree of polymerization expressed as (j!+m) is preferably 100 to 600,
When the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and when it exceeds 600, the dispersibility becomes poor. The vinyl chloride copolymer described above may be partially hydrolyzed.

As the vinyl chloride copolymer, preferably vinyl chloride-
Examples include copolymers containing vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymers"). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, and vinyl chloride-vinyl acetate copolymers. Among these, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include rVAGHJ rVYHHJ, rVMcHJ manufactured by Union Carbide,
“Suresoku A” and “Suresoku A-5” manufactured by Building Blocks Chemical ■
", "Esure 7ri C", "Esresoku M", "Denkabinyl 100OGJ", "Denkabinyl 100OWJ" manufactured by Denki Kagaku Kogyo ■, etc. can be used. In addition to the above, cellulose resin can also be used as a binder resin. However, these include cellulose ether,
Cellulose inorganic acid esters, cellulose organic acid esters, etc. can be used. As the cellulose ether, methyl cellulose, ethyl cellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred.

In addition, regarding the entire binder composition, the ratio of the above-mentioned urethane resin to other resins (total amount of phenoxy resin, vinyl chloride copolymer, etc.) is 90/1 by weight.
Desirably 0 to 40/60, 85/15 to 45
155 has been found to be even more desirable. If the amount of urethane resin is outside this range, dispersion tends to be poor.
Also, if there is a large amount of other resins, surface properties tend to be poor (,
In particular, if it exceeds 60% by weight, the physical properties of the coating film become less favorable overall. In the case of vinyl chloride-vinyl acetate,
It can be mixed with the urethane resin with a considerable degree of freedom, and preferably the urethane resin is 15 to 75% by weight.

In addition to the binder resins mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used as binder resins for the layers constituting the magnetic recording medium of the present invention.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of 10,000 to 200,000, and a polymerization degree of about 200 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic acid Ester-vinylidene chloride copolymers, acrylic ester-styrene copolymers, etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 20 (j, ooo or less) in the state of a coating liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred.Specifically, such resins include phenol resins, epoxy resins, urea resins, melamine resins, and alkyd resins.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
Examples include maleic anhydride type, urethane acrylic type, and polyester acrylic type.

In the magnetic recording medium of the present invention, carbon black may be further added to the magnetic layer. It is desirable that this carbon black has electrical conductivity, but carbon black with light-shielding properties may also be added. As such conductive carbon black, for example, Conductex 975 manufactured by Columbia Carbon Co., Ltd. (specific surface area 250 m2/
g, particle size 24 μμ), Conductex 900 (specific surface area 125 m2/g, particle size 27 μμ), Cabot Vulean XC-7
2' (specific surface area 254 m''/g, particle size 30 mμ),
There are Raven 1040.420, Mitsubishi Kasei side type #44, etc. As a light-shielding carbon blank, for example, Raben 2000 (specific surface area: 19
0 m”/g, particle size 18 mμ>, 2100.1
170.1000゜Mitsubishi Kasei side type #100, #75
, #40, #35, #3°, etc. can be used. The carbon blank has an oil absorption of 90m1 (DBP)/1
00 g or more, it is easy to form a stracture structure,
It is desirable because it exhibits higher conductivity.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
A magnetic layer 2 is provided on the support IS. Further, a BCC 84 is provided on the surface opposite to the magnetic N2. The magnetic powder used for the magnetic layer 2, especially the ferromagnetic powder, is γ-Fe.
z○1, CO-containing-Fe20i, F1330a,
Co-containing iron oxide magnetic powder such as Fe50; Fe, Ni
5Co-, Fe-Ni-C.

Alloy, Fe-Mn, -Zn alloy, Fe-Ni-Zn
alloy, Fe-Co-Ni-Cr alloy, Fe-C.

-Ni-P alloy, Co-Ni alloy, etc. Fe % N t
Examples include various ferromagnetic powders such as metal magnetic powders containing Co as a main component. Among these, Co-containing iron oxide and metal magnetic powder are preferable.

Further, it is desirable that the BET value of the magnetic powder is 30 m''/gg or more.The magnetic layer 2 also contains a lubricant (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, - Basic fatty acids (
For example, fatty acid esters consisting of stearic acid) and monohydric alcohols having 13 to 26 carbon atoms), abrasives (
For example, fused alumina), antistatic agents (for example, graphite), etc. may be added.

Non-magnetic powders containing BCC20 include carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide,
α-FetO8, talc, kaolin, calcium sulfate,
Examples include those made of nitrogen boron, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black and/or titanium oxide.

Further, as the non-magnetic powder, organic powder such as benzoguanamine resin, melamine resin, phthalocyanine pigment, etc. may be added.

Further, the magnetic recording medium shown in FIG. 1 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may not be provided with an undercoat layer (not shown). Same below). The support may also be subjected to corona discharge treatment. Also,
BCC20 may also contain a compound according to the present invention.

In addition, the material of the support 1 is plastic such as polyethylene terephthalate, polypropylene, etc.
Metals such as Zn, glass, ceramics such as BN, SL tsukaite, porcelain, and earthenware are used.

Incidentally, when forming the magnetic layer by coating, a predetermined amount of polyfunctional isocyanate as a crosslinking agent is added to the coating material.

FIG. 2 shows other magnetic recording media.
A 00 layer 4 is provided on the magnetic layer 2 of the illustrated medium. This 00 layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness.

Therefore, as the binder resin for the 00 layer 4, the urethane resin used for the magnetic layer 2 described above is used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). The surface roughness of the 00 layer 4 is Ra≦0-01μm, Rmax≦0.13trm, especially in relation to color S/N.
It is better to

E. Examples Hereinafter, the present invention will be explained with reference to specific examples and comparative examples. The ingredients, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. , “
"Parts" means parts by weight.

<Example 1> A magnetic paint having the following composition was prepared.

Co-containing r FezOz 100
1 part Urethane elastomer (Nistan 5701, Goodlynch Co., Ltd.) 9 parts Vinyl chloride vinyl acetate copolymer (V, C, C, VAG H) 6 parts Exemplary compound of organic dye compound (1) 4 parts Myristic acid
2 parts butyl palmitate 1 part alumina
4-part methyl ethyl ketone
50 parts cyclohexanone 1
00 parts carbon blank 3 parts This composition was sufficiently stirred and mixed in a ball mill, and then a polyfunctional isocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added.
) was added thereto, and then filtered through a filter with an average pore size of 1 μm. The obtained magnetic paint was applied to the surface of a polyethylene terephthalate base having a thickness of 14 μm to a dry thickness of 4 μm.

Thereafter, the surface of the magnetic layer was treated using a super calendar roll to obtain a wide magnetic film having a magnetic layer of a predetermined thickness.

Next, a back coat layer paint having the following composition was prepared.

Carbon black (Columbia Carbon Co., Ltd. Conductex 975)
11 parts Urethane elastomer (Nistan 5701, Gutdrich) 6 parts Nitrocellulose (Seltsuba BTHI/2, Asahi Kasei Corporation) 4 parts Methyl ethyl ketone 80 parts Toluene
60 parts The above composition was sufficiently stirred and mixed in a ball mill, and further 5 parts of polyfunctional isocyanate (Coronate L) were added, and the average particle size was 1.5.
It was filtered through a μ filter. The obtained back coat layer paint was applied to the back side of a wide magnetic film to a dry thickness of 1.1 μm.
It was applied so that This film was cut to a width of 1 inch to create a magnetic tape for video. At this time, the surface roughness of the bank layer was 0.021 μm.

Comparative Example 1> A magnetic tape was prepared in the same manner as in Example 1 except that the same amount of lecithin was used in place of Exemplified Compound (1) in Example 1.

<Example 2> Titanium oxide powder (average particle size 0.4 μ) 1 was used instead of carbon black in the back coat composition of the example work.
One copy was used.

<Example 3> In place of carbon black in the back coat composition of Example 1, calcium carbonate powder (average particle size 0.07μ
) 6 parts were used.

<Comparative Example 2> The titanium oxide powder having the bank coat composition of Example 2 was replaced with one having an average particle diameter of 1.0 μm.

Comparative Example 3> Calcium carbonate powder with the back coat composition of Example 3 was
I used it after reducing it to 30%.

<Example 4> In the magnetic powder of Example 1, metal magnetic powder was used in place of Co-containing r-Fe, 03.

Comparative Example 4> In place of the exemplified compound (1) of Example 4, 4 parts of stearylamine was used.

<Examples 5 to 21> Instead of exemplified compound (1) of Example 1, exemplified compound (
2) to (18) were used, respectively.

<Example 22> The amount of Exemplified Compound (1) in Example 1 was reduced to 2 parts, and 2 parts of lecithin was added.

According to each column above, the following measurements were made on the Deotabe.

Chroma S/N: Color Video Noise Meter
Measured using 925D/IJ.

Rumi S/N: Same as above.

Jifuku: Using VTR sintermeter rMK-612AJ manufactured by Meguchi Electronics, 30°C, 80% RH.
Each jitter was measured after 0 and 100 runs under high temperature and high humidity conditions.

Winding appearance: When the appearance of the winding after fast forwarding and unwinding is neatly wound, it is rated ◎, when the winding is good, it is rated ○, and when there are many steps in the winding, it is rated ×.

The performance of each example videotape is shown in the table below.

(See margin below, continued on next page) It can be seen that tape performance is significantly improved by configuring the tape body.

[Brief explanation of drawings]

The drawings illustrate an embodiment of the invention, and FIGS. 1 and 2 are enlarged cross-sectional views of a portion of a magnetic recording medium from each side. In addition, in the symbols used in the drawings, 2----
1.-Magnetic layer 3--Back coat layer (BC layer) 4--
...overcoat layer<00 layer). Agent: Patent Attorney Hiroshi AisakaFigure 1Figure 2

Claims (1)

[Claims] 1. Magnetic recording in which a magnetic layer contains an organic dye or pigment having a carboxyl group and/or a sulfo group, and a back coat layer with a surface roughness of 0.07 μm or less is provided on the opposite side of the magnetic layer. Medium.