JPS61177631A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title magnetic recording medium with reduced abrasion by a head and less damage by friction and having excellent S/N, a high output and a good traveling property by providing a magnetic layer obtained by incorporating carbon black into magnetic powder having more than a specified specific surface by the BET method using liquefied nitrogen in a specified ratio. CONSTITUTION:0.2-2pts.wt. carbon black is mixed into 100pts.wt. magnetic powder having >=30m<2>/gr specific surface by the BET method using liquefied nitrogen, and the mixture is coated on a carrier 1 along with a binder and a phonoxy resin contg. at least polyurethane or preferably polyurethane and the phenoxy resin or a vinyl chloride copolymer resin to form a magnetic layer 2. A backcoat layer 3 obtained by dispersing carbon black, nonmagnetic powder of SiO2, etc. in a binder can be formed on the surface of the carrier opposite to the layer 2, and an overcoat layer 4 can be formed on the surface of the layer 2 as a protective layer. Consequently, a magnetic recording medium having excellent S/N, a high output and excellent traveling property and durability is obtained.

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.

Conventional technology Generally speaking, magnetic recording media such as magnetic tapes are produced by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it! = Manufactured accordingly.

As such a magnetic recording medium,
As seen in the publication, 5+-1 at least surface active fine powder carbon black was added at 30 PHR (binder resin 10
A magnetic recording medium is known in which a magnetic layer is coated on a non-magnetic support, and a magnetic layer is formed by dispersing magnetic powder in a binder resin containing a reinforcing binder made of a resin filled with 0 parts by weight or more. There is.

Although the presence of such a magnetic layer is said to reduce wear on the magnetic head and frictional damage on the surface of the medium, and is also effective in preventing static electricity, the following problems remain.

That is, as the demand for higher density increases, especially magnetic powder with a BET value (specific surface area: described below) of 30 W? /f
More than r, further ζ2 is 31 w? / f When using more than r, if there is a large amount of carbon black in the magnetic layer, S/
N or output becomes insufficient. For example, the inventor found that when using magnetic powder of 31 vpl/f r or higher, which is used in high-quality video tapes, the amount of carbon black is an important factor. .

That is, the present inventor discovered for the first time a particularly suitable amount of carbon black in the above case, and achieved the present invention.

8. Purpose of the Invention The purpose of the present invention is to reduce head wear and friction damage on the media surface by setting the amount of carbon black, and not only improve antistatic properties but also provide excellent SA and high output. The object of the present invention is to provide a magnetic recording medium that also has excellent running properties.

2. Structure of the invention and its effects, that is, the present invention relates to a magnetic edge medium with a BET value of 30-/fr or more.

According to the present invention, the BIT value of the magnetic powder is 30 w? / f
r or more, it is possible to achieve higher recording density and higher quality media, and at the same time, while maintaining this high performance, the amount of carbon black can be selected within a specific range of 0.2 to 2 parts. Therefore, it is possible to provide a medium that can obtain high S/N and high output, and has excellent antistatic ability, runnability, durability, etc.

In particular, the amount of carbon black is such that the BET value of magnetic powder is 31
It is important when the ratio is more than i/lr, and even more so when it is 35m''/7r7 parts, and when it is more than 40nl/lr, it becomes a very large factor that significantly influences the properties.The amount of carbon black is On the other hand, if it is 0 part, the running performance becomes extremely unstable, but as shown in Figs. 1 and 2,
If at least 0.2 part is not included as in the present invention, the S/N will be very poor, and if it is more than 2 parts, the S/N will be very poor.
Otherwise, the N or output will become defective. Therefore, it is essential that the amount of carbon black be 0.2 to 2 parts per 100 parts of magnetic powder, more preferably 0.5 to 2 parts, and 1
~1.8 parts is more desirable. In addition, in the present invention, the magnetic powder is used in an amount of 25 to 20 parts per 100 parts of the binder resin (described later).
00 parts may be included. In the above, the BIT value of the magnetic powder of the magnetic layer is 30 n? / f r or more (preferably, the particle size is further reduced), the reproduction output and S/N ratio of the medium can be significantly improved, and the output can be stably obtained.

If the specific surface area of this magnetic powder is made larger than necessary, poor dispersion will occur, so the upper limit is set to 100 n? , 4 r
It is desirable to do so. In addition, in the above, “BIT
"value" refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle size. For example, even if the average particle size is the same, there are some particles with a large specific surface area and others with a small specific surface area. do.

To measure the specific surface area, for example, first, magnetic powder is degassed while being heat-treated at around 250°C for 30 to 60 minutes to remove what is adsorbed to the powder, and then measuring device C: is introduced. , the initial pressure of nitrogen is set at 0.5 Vi, and the adsorption measurement is carried out at the liquid nitrogen temperature (-195°C) (generally referred to as the B, E, T method). For details, please contact J, Ame.

Chem, Soc, 60309 (1938)). As a device for measuring the specific surface area (BET value), it is possible to use the "powder measuring device (Cantersoap)" manufactured by ζ2, which is jointly manufactured by Yuasa Battery (1) and Yuasa Ionics (2). A general explanation of the specific surface area and its measurement method can be found in "Measurement of Powders" (J.

M, DALLAVALLE, CLYDEORR Jr.
Co-authored, translated by others; published by Sangyo Toshosha).
Page, Nippon Kagaku Yoshin, Maruzen ■ Published April 1966) (In addition, in the above-mentioned ``Chemistry Handbook'', specific surface area is simply written as surface area (m''/fr). However, it is the same as the specific surface area in this specification.)
.

At least polyurethane can be used as the binder resin for the magnetic layer in the magnetic recording medium of the present invention, and this can be synthesized by reacting polyol and polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid, adipic acid, azelaic acid, trimerized luruic acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane. , hexanetriol, glycerin, trimethylolethane, pentaerythritol and other polyhydric alcohols, or any two or more polyols selected from these glycols and polyhydric alcohols (synthesized by polyester polyol;
Or, a polyester polyol composed of lactams such as 3-cabrolactam, α-methyl-1-caprolactam, S-methyl-6-caprolactam, T-butyrolactam; or ethylene oxide, propylene oxide, butylene oxide, etc. Examples include synthesized polyether polyols.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene 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 only the phenoxy resin and/or the vinyl chloride copolymer is used, the layer becomes too hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved.

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

(However, n mi 82-13) For example, PKHC manufactured by Union Carbide.

There are PKHHlPKHT, etc.

In addition, as for the vinyl chloride copolymer that can be used, the molar ratio derived from t and m is 95 to 50 mol% for the former unit, and 5 to 50 mol% for the latter unit. It is.

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. (t
The degree of polymerization expressed as +m) is preferably from 100 to 6
00, and the degree of polymerization is less than 100 (if it is 2, the magnetic layer etc. tends to become sticky).

If it exceeds this, the dispersibility will deteriorate. The vinyl chloride copolymer described above may be partially ζ-dihydrolyzed. As the vinyl chloride copolymer, a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymer") is preferably used. Examples of vinyl chloride-acetic acid and dihydropolymers include vinyl chloride-acetic acid and dihydropolymers.
Examples include vinyl acetate-vinyl alcohol and vinyl chloride-vinyl acetate-maleic anhydride copolymers, and among the vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include (7) rVAGHJ, rVYHHJ, rVMcHJ, manufactured by Union Carbide;
“S-LEC A” and “S-LEK A-5” manufactured by Tanemizu Kagaku ■
, "Eslec C", "Eslec M", "Denkabinir 1000 G J", "Denkabinir 1000 W J" manufactured by Denki Kagaku Kogyo ■, etc. can be used.

In addition to the above, cellulose resins can be used as the binder resin, but cellulose ether, cellulose inorganic acid esters, cellulose organic acid esters, etc. can be used as the binder resin. As 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 /
10~40/60 is desirable, 85715~
It has been confirmed that 45155 is even more desirable. Outside this range, if the amount of urethane resin is large, dispersion tends to be poor, and if the amount of other resins is too large, the surface properties tend to be poor.In particular, if the amount exceeds 60% by weight, the overall physical properties of the coating film become worse. . In the case of vinyl chloride-vinyl acetate, it can be mixed with urethane resin with a considerable degree of freedom.
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 degree of polymerization of about 2.
For example, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 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 until the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, etc. are used.

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

In the magnetic recording medium of the present invention, 0.2 to 2 parts of carbon black per 100 parts of magnetic powder, preferably carbon black having an average particle diameter of lO to 30IIIμ, is added to the magnetic layer. The particle size of this carbon black is preferably 10 μm or more in terms of dispersibility. Further, it is desirable that the carbon black has electrical conductivity in order to stabilize the running of the medium, but carbon black having light-shielding properties may also be added.

Examples of such conductive carbon black include Conductex (Condu) manufactured by Columbia Carbon Co., Ltd.
ctax) 975 (specific surface area 250 J/g, particle size 24
m1μ), Conductex 900 (specific surface area 125
j/gs particle size 27 μ), Conductex ao-22
0 (particle size 2oI11μ), Conductex SC (particle size 20-μ), Cabot V
urean) X C-72 (specific surface area 254-/g1
Particle size: 30μ), Palcan P (particle size: 2oμ), Rapen 1G40. 420, Black Pearls 2000 (
Particle size: 15ssμ), manufactured by Mitsubishi Kasei ■. As the light-shielding carbon black, for example, Rapen 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area t9oz/g
.

Particle size 18 times μ), 2100.1170.1000, $100 manufactured by Mitsubishi Kasei ■, ≠75, ≠40. fathom 35, sub 30
etc. are available. It is preferable that carbon black has an oil absorption of 90 d(DBP)/100 g or more because it tends to form a striated structure and exhibits higher conductivity. The "average defective particle size" herein may be measured by directly selectively counting with an electron microscope, or may be measured from particle size distribution. It can also be calculated as a sphere from the specific surface area. Other known methods can also be used. For more information r CARBON BLACK
Yearbook 1984J (Carbon Black Association column), “Carbon Black Handbook” (Carbon Black Association Line), and “
You can refer to "New Experimental Chemistry Course Volume 18" (Nihon Kagaku Complete Edition, 1978, published by Maruzen Co., Ltd.).

The magnetic recording medium of the present invention has, for example, as shown in FIG.
A magnetic layer 2 is provided on a support 1.

Further, the surface opposite to the magnetic layer 2 (a second BC layer 3 is provided. This BC layer may be provided, but it is not necessary to provide it. The ferromagnetic powder used for the magnetic layer 2 is as follows: 1
-Fe203, Co-containing 1-Fe10B, FeSO
4. Co-containing iron oxide magnetic powder such as Fe3O4; Fe.

Ni, Co, Fe-Ni-Co, Fe-Mn-Z
n%Fe-Ni-Zn%Fe-Co-Ni-Cr, F
e-Co-N1-P, Co-Ni etc. Fe, Ni%C
Examples include metal magnetic powders whose main components are O and the like. In this case, the iron particles may be doped with nicobalt or may be coated on the surface. The magnetic layer 2 also contains a lubricant such as glycerin ester (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, etc.), an abrasive (for example, fused alumina), and an antistatic agent (
For example, graphite) may be added.

The non-magnetic powder contained in the BC layer 3 includes carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide,
α-Fs103. Talc, kaolin, calcium sulfate,
Boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (
In particular, those made of conductive carbon black) and/or titanium oxide may be mentioned. According to the present invention, the magnetic layer has zero
．． Since 2 to 2 parts of carbon black is contained, B
The nonmagnetic powder used for the C layer is preferably carbon black.

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

Furthermore, the magnetic recording medium shown in FIG. 3 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.

In addition, the material of the support body 1 includes plastics such as polyethylene terephthalate and polypropylene, At, and Zn.
Metals such as glass, BN, St carbide, ceramics such as porcelain and earthenware, etc. are used.

When forming the above-mentioned magnetic layer, etc., it is desirable to add a predetermined amount of polyfunctional isocyanate as a crosslinking agent to the coating material in order to strengthen the magnetic layer. In addition to polyfunctional polyisocyanate, triphenylmethane triisocyanate, tris-
(p-isocyanate phenyl) thiophosphite, polymethylene polyphenylisocyanate, etc., methylene diisocyanate type and tolylene diisocyanate type are preferable. Note that when the magnetic layer is cured by electron beam irradiation or the like, the addition of the isocyanate compound may be omitted, but it may be added.

Figure 4 shows another magnetic recording medium.
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 therefore needs to have sufficient ζ: 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 0CJI4 is particularly high in color 8/
In relation to N, Ra≦o, otμs+t, Rmax≦0.
It is preferable to use 13μ dew. In this case, the surface roughness of the support 1 is Ra≦0.0IJ111, Rmax≦0.134
It is preferable to use m1 and a smooth support l.

FIG. 5 shows a magnetic recording medium configured as a magnetic disk, with magnetic layers 2.00 similar to those described above on both sides of the support l.
Layers 4 are provided, and the 00 layer 4 may contain a binder resin containing the above-mentioned urethane resin as a main component.

E, Example Hereinafter, the present invention will be explained with reference to a specific example.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

After dispersing the ingredients shown in Table 1, apply 1μ of this magnetic paint.
After filtration, 5 parts of polyfunctional isocyanate was added, coated on a support to a thickness of 5 μm, supercalendered, 1 part was slit into 2-inch widths, and videotape was added (each example, comparative number). corresponding). However, the numbers after the second column of Table 1 represent parts by weight, and "actual" after the second column represents examples, and "ratio" represents comparative examples.

Table-1 However, the numbers in the column of Act-5 indicate the composition of the BC layer, and the medium of Act-5 has the above-mentioned BC layer in addition to the magnetic layer having the same composition as Act-3. .

The following measurements were made for each tape.

Chroma S/N: Color video noise meter r 5hibasoku9
Measurements were taken from the 25" mouth.

Lumi S/N: Measure the RF specific output at 4 MHz using the V'l'R deck for measuring RF output, and after 100 playbacks, calculate the value that has decreased from the initial output. (unit: dB).

Jitter value: Using a VTR jitter meter rMK-612AJ manufactured by Meguchi Electronics Co., Ltd., each jitter was measured after 0 and 100 runs at 30° C. and 80% RH under high temperature and humidity.

The performance of each example videotape is shown in Table 2 (however,
The relative value is shown when the ratio -1 is set to 0).

(Margin continues on next page) Table 2 The above results show that the tape performance is significantly improved by configuring the magnetic layer based on the present invention.

[Brief explanation of drawings]

The drawings show examples of the present invention, and FIGS. 1 and 2 are graphs showing changes in characteristics due to carbon black thickness, and FIGS. 3, 4, and 5 are graphs showing changes in characteristics depending on each side FIG. 3 is an enlarged cross-sectional view of a portion of a magnetic recording medium. In addition, in the symbols used in the drawings, 2...
...Magnetic layer 3... Back coat layer (BC layer) 4...
...Overcoat layer (00 layer). Agent Patent Attorney Hiroshi Aisaka Figure 2

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer contains magnetic powder having a BET value of 30 m^2/gr or more and 0.2 to 2 parts by weight of carbon black per 100 parts by weight of this magnetic powder.