JPH0619823B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk.

2. Conventional Technology Generally, a magnetic recording medium is manufactured by applying a magnetic coating material containing magnetic powder, a binder resin and the like on a support and drying it.

In such a magnetic recording medium, urethane resin is generally used as a binder resin for the magnetic layer and the like. A conventionally known urethane resin is synthesized from a polymeric diol, a diisocyanate, a chain extender, and a crosslinking agent (which is used as necessary). Examples of the polymer diol include polyester diol obtained from adipic acid and butane diol, polyether diol and polycarbonate diol, and diphenylmethane diisocyanate and the like can be used as the diisocyanate. The chain extender may be ethylene glycol, butanediol or the like, and the crosslinking agent may be polyols, polyamines or the like.

However, even though such a general urethane resin is excellent in flexibility, it lacks in hardness, so that the mechanical strength of the magnetic recording medium is poor against sliding contact with a guide pin or a magnetic head. Becomes Moreover, since the urethane resin tends to have adhesiveness, unstable running called stick-slip is likely to occur in the case of a video tape, and as shown in FIG. 1, the average surface roughness (Ra- mag) is especially 0.014μ
If it is less than m, jitter increases and running anxiety becomes remarkable. Therefore, the surface of the magnetic layer may be roughened for the sake of running stability, but this is rather inconvenient because the output is rather lowered.

3. Object of the Invention The object of the present invention is to provide a magnetic layer with appropriate flexibility, sufficient mechanical strength and durability, and further running stability, high output and excellent S / N ratio. To provide.

4. Structure of the Invention and Its Effect: That is, the magnetic recording medium according to the present invention is characterized in that a urethane resin having a yield point is contained in the magnetic layer, and the average surface roughness of the magnetic layer is 0.02 μm or less. It is what

According to the present invention, it is extremely important that the layer contains a urethane resin having a yield point, which is fundamentally different from the conventional urethane resin. That is, a general urethane resin has physical properties shown by a curve a in FIG. 2 and is excellent in flexibility, but lacks in hardness, so that it is not slidably contacted with a guide pin or a magnetic head. On the other hand, the mechanical strength of the magnetic recording medium is liable to be poor, and problems are likely to occur in terms of running property and powder falling. On the other hand, the urethane resin used in the present invention has a yield point Y as illustrated by the curve b in FIG.
Since it is a urethane resin having P, the elongation is very small even when stress is applied up to the yield point YP, which gives the urethane resin appropriate hardness and the yield point YP.
After P, it shows the property of expanding with stress without breaking, and it can be appropriately provided with flexibility and binding force as a binder resin. As a result, the mechanical strength of the magnetic recording medium is improved, the damage such as abrasion during sliding contact, the powder falling, etc. are significantly reduced, and the running property is also significantly improved. In particular, the magnetic tape for VTR has no edge breakage and the like, and it is possible to hold the control track near the edge and to exert its function well. The above-mentioned yield point YP is important for the performance of urethane resin, and is 50 to 600 kg / c.
m ^2, preferably it is desirable to present the yield point stress range of 100~560kg / cm ² (in the example of FIG. 1 about 290kg / cm ^2). If the yield point is in the range of 50 kg / cm ² or more, the resin will not be too soft, and if it is 600 kg / cm ² or less, the resin will not be brittle even if it becomes hard.

Here, the measurement conditions of the yield point are, for example, JISK-6301.
In detail. The measuring method will be described below.

A urethane resin film with a thickness of 100 μm at 80 ° C
Heat treatment for 10 minutes, then at 120 ° C. for 10 minutes, then leave it in an atmosphere of 25 ° C. and 55% RH (relative humidity) for 3 days, and then use No. 2 dumbbell according to JIS K-6301 under the same conditions. It is measured at a pulling speed of 200 mm / min.

The urethane resin having a yield point preferably has a cyclic hydrocarbon residue in the molecule in order to exhibit the above excellent performance. The cyclic hydrocarbon residue is preferably a saturated cyclic hydrocarbon residue, which includes a divalent or monovalent cyclopentyl group, a cyclohexyl group or the like, or a derivative thereof (for example, a substituted alkyl group such as a methyl group, And a halogen substitution product such as a chlorine atom). These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting an appropriate hardness to the urethane resin and the availability of raw materials. Further, the bonding position of this cyclic hydrocarbon residue is preferably in the main chain of the urethane resin molecule, but it may be bonded to its side chain. Further, by changing the amount of the constituent component having a cyclic hydrocarbon residue in the urethane resin,
A urethane resin having an arbitrary glass transition point (Tg) can be obtained, and Tg is -30 ° C to 100 ° C, preferably 0 ° C to 9 ° C.
It is 0 ° C. When Tg is -30 ° C or higher, the film strength is prevented from lowering due to the resin being soft (Tg <-30 ° C), and when it is 100 ° C or lower, the film becomes too hard and brittle. It can be prevented.

Furthermore, according to the present invention, the average surface roughness (Ra
-Mag) and, for example, chroma S / N are confirmed to have a strong correlation as shown in FIG. 3 (however, the data in FIG. 3 shows that the chroma S of the medium with Ra-mag of 0.020 μm is / N is expressed as a relative value when 0 dB). According to this, by setting Ra-mag to 0.020 μm or less according to the present invention, the chroma S / N becomes large, and the chroma S / N changes in inverse proportion to the value of Ra-mag. Therefore,
Ra-mag should be 0.020 μm or less, preferably 0.016 μm or less, and if it is 0.014 μm or less, high quality is required for haafai, high grade, high resolution,
It is suitable as a master tape. Ra-mag
If the value is too small, running characteristics tend to become unstable, such as causing image shake, so the lower limit is preferably set to 0.005 μm.

In order to realize the Ra-mag in the above range according to the present invention, the amount of the dispersant used when forming the magnetic layer is preferably 0.5 to 6% by weight. If the amount of the dispersant is out of this range and the amount of the dispersant is too small, it becomes difficult to reduce the surface roughness of the magnetic layer to Ra-mag ≤ 0.020 μm, which is a small value within a predetermined range, as described above, due to poor dispersion. If it is too much, the dispersant is likely to bleed out from the magnetic layer.

Further, since the urethane resin used in the present invention has a lower adhesiveness than the conventional urethane resin, for example, in the case of a video tape, the running becomes stable, and the jitter value can be suppressed to be smaller than that of the conventional one. Therefore, Ra of the magnetic layer
Even if −mag is set to 0.014 μm or less, there is an advantage that the running property does not become unstable and high output can be maintained.

The above-mentioned "average surface roughness" is measured as follows. That is, using the measurement value at the center line roughness of the cut-off value of 0.25 mm of the roughness curve shown in JIS-B0601 item 5, the measuring device is made by Kosaka Laboratory, three-dimensional roughness measuring instrument SE-3FK
Was used.

Next, the magnetic recording medium according to the present invention will be described in more detail.

The urethane resin used as the binder resin can be synthesized by reacting a polyol with a polyisocyanate. At this time, in order to introduce the cyclic hydrocarbon residue, the following methods (1) to (4) can be adopted.

(1), a method in which a polyhydric alcohol having a cyclic hydrocarbon residue in advance is used as the polyhydric alcohol as a raw material for a polyol (for example, a polymer diol).

(2) A method in which a dicarboxylic acid having a cyclic hydrocarbon residue in advance is used as the organic dibasic acid (dicarboxylic acid) that is a raw material of the polyol.

(3) A method of using the polyhydric alcohol and dicarboxylic acid according to the above (1) and (2) as a raw material for the polyol.

(4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any one of the above (1) to (3) or alone.

For example, as a synthetic method for obtaining the urethane resin, 1,
4-di-hydroxymethylcyclohexane And adipic acid (HOOC- (CH ₂ ) ₄ -COOH) are used as methylene-bis-phenyl isocyanate. There is a method of urethane-forming with. In this case, the chain extender is 1,4-di-hydroxymethylcyclohexane or another diol (for example, butane-1,4-diol).
May be

As the polyhydric alcohol which may have a cyclic hydrocarbon residue in advance, it is possible to use one having a cyclohexyl group in the molecular chain of the ethylene glycol structure as described above.
In addition to such structures, glycols such as propylene glycol, butylene glycol, diethylene glycol, etc. or polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol or their glycols, or a cyclic in its structure Those having a hydrocarbon residue can be used. Examples of the dibasic acid that can be used include phthalic acid, dimerized linoleic acid, maleic acid, and the like, or those having a cyclic hydrocarbon residue in the molecule thereof.
Instead of the above polyol, s-caprolactam, α-
Lactone-based polyester polyols synthesized from lactams such as methyl-1-caprolactam, s-methyl-s-caprolactam, γ-butyrolactam; and polyether polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. May be used.

These polyols are reacted with an isocyanate compound such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc., and thereby a urethane urethane polyester polyurethane and polyether polyurethane are synthesized, according to the present invention. Urethane resins are usually produced primarily by the reaction of polyisocyanates and polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and / or hydroxy groups, or do not contain these reactive end groups. It may be in the form of a urethane elastomer, for example.

The chain extender that can be used may be the polyhydric alcohol exemplified above (which may or may not have a cyclic hydrocarbon residue in the molecule).

If a phenoxy resin and / or a vinyl chloride-based copolymer is contained as the binder resin together with the above urethane resin, the dispersibility of the magnetic powder when applied to the magnetic layer is improved, and its mechanical strength is increased. To do. However, the layer becomes too hard only with the phenoxy resin and / or the vinyl chloride copolymer, but this can be prevented by the inclusion of polyurethane, and the adhesion to the support or the underlayer becomes good.

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

(However, n82 to 13) For example, PKHC and PKH manufactured by Union Carbide
H, PKHT, etc.

Further, as the above-mentioned vinyl chloride-based copolymer that can be used, a compound represented by the general formula: Some are represented by. in this case, The molar ratios derived from 1 and m in the above are 95 to 50 mol% for the former unit and 5 to 50 mol% for the latter unit.

X represents a monomer residue capable of copolymerizing with vinyl chloride, and represents at least one selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride and the like. (L
The degree of polymerization represented by + m) is preferably 100 to 600, and when the degree of polymerization is less than 100, the magnetic layer or the like tends to be tacky, and when it exceeds 600, the dispersibility deteriorates. The vinyl chloride copolymer may be partially hydrolyzed. The vinyl chloride-based copolymer is preferably a vinyl chloride-vinyl acetate-containing copolymer (hereinafter referred to as "vinyl chloride-vinyl acetate copolymer"). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, and the like.
Among the vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferable. Specific examples of the above vinyl chloride-vinyl acetate copolymer include "VAGH", "VYHH", and "VMC" manufactured by Union Carbide Corporation.
H ", Sekisui Chemical Co., Ltd." ESREC A "," ESREC A-5 "," ESREC C "," ESREC M ", Denki Kagaku Co., Ltd." Denka Vinyl 1000G "," Denka Vinyl 1000W ", etc. Can be used.

In addition to the above, a fibrin resin can be used as the binder resin, and a cellulose ether, a cellulose inorganic acid ester, a cellulose organic acid ester, or the like can be used as the binder resin. As the cellulose ether, methyl cellulose, ethyl cellulose or the like can be used. As the cellulose inorganic acid ester, nitrocellulose,
Cellulose sulfate, cellulose phosphate and the like can be used.

As the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, butyryl cellulose or the like can be used. Of these fibrin-based resins, nitrocellulose is preferred.

Further, regarding the entire binder composition, the ratio of the above urethane resin and the total amount of the other resin (phenoxy resin) and the vinyl chloride-based copolymer) is 90/10 by weight.
It has been confirmed that it is preferably -40/60, and more preferably 85 / 15-45 / 55. If the amount of the urethane resin is out of this range, the dispersion tends to be poor, and if the amount of other resins is large, the surface properties are likely to be poor. Particularly, when the amount exceeds 60% by weight, the physical properties of the coating film are generally unpreferable. In the case of vinyl chloride-vinyl acetate, it can be mixed with urethane resin with a considerable degree of freedom.
~ 75% by weight.

As the binder resin of the magnetic layer constituting the magnetic recording medium of the present invention, in addition to the above-mentioned ones, a thermoplastic resin, a thermosetting resin, a reactive resin and an electron beam irradiation curable resin may be used.

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

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and has an infinite molecular weight due to reactions such as condensation and addition after coating and drying.
Further, among these resins, those which are not softened or melted before the resin is thermally decomposed are preferable. In particular,
For example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin and the like.

As the electron beam irradiation curable resin, an unsaturated prepolymer,
Examples thereof include maleic anhydride type, urethane acrylic type, polyester acrylic type and the like.

In the magnetic recording medium of the present invention, carbon black may be further added to the magnetic layer containing the urethane resin. It is desirable that the carbon black has conductivity, but carbon black having light shielding property may be added. As such conductive carbon black, for example, Conductex 975 (specific surface area 250 m ² / g, particle size 24 mμ) manufactured by Columbia Carbon Co., Ltd., Conductex 900
(Specific surface area 125 m ² / g, particle size 27 mμ), Cabot Vulcan (Cabot Vulcan) XC-72 (specific surface area 254 m ² /
g, particle size 30 mμ), Raven 1040, 420, # 44 manufactured by Mitsubishi Kasei. Examples of the carbon black for shading include Raven 2000 (specific surface area) manufactured by Columbia Carbon Co., Ltd.
190 m ² / g, particle size 18 mμ), 2100, 1170, 1000, and Mitsubishi Kasei's # 100, # 75, # 40, # 35, # 30, etc. can be used. Carbon black is 20 to 30 mμ, preferably 21
It should have a particle size of ~ 29mμ, but its oil absorption is
90 ml (DBP) / 100 g or more is desirable in that a structure structure is easily formed and higher conductivity is exhibited.

The layer containing the urethane resin or the like having a cyclic hydrocarbon residue as the binder resin is the magnetic layer 2 of the support 1 as shown in FIG. 4, for example. The BC layer 3 is provided on the surface opposite to the magnetic layer 2. The BC layer is provided as needed, but it is preferable to provide it in order to improve the running property and S / N. Magnetic powder used for the magnetic layer 2,
In particular, as the ferromagnetic powder, γ-Fe ₂ O ₃ , Co-containing γ-Fe
₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O _4, etc. iron oxide magnetic powder; Fe, N
i, Co, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-Ni alloy, etc. F
Examples include various ferromagnetic powders such as metal magnetic powders containing e, Ni, Co, etc. as main components.

The magnetic layer 2 also contains 0.5% of a dispersant (eg, lecithin powder).
-6% by weight, for example 2% by weight, and a lubricant (for example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic resin acid having 12 to 20 carbon atoms (for example, stearic acid), carbon atom) Number 12 to 20 monobasic fatty acids (eg stearic acid) and 4 to 4 carbon atoms
Fatty acid ester consisting of 26 monohydric alcohols),
Abrasives (eg alumina), antistatic agents (eg graphite) etc. may be added.

The BC layer 3 may contain the urethane resin having the above-mentioned yield point as a binder resin, or a general urethane resin may be used. The non-magnetic powder contained in the BC layer 3 is made of carbon black, silicon oxide, titanium oxide, aluminum oxide, or the like.
Preferably, carbon black (particularly conductive carbon black) and / or titanium oxide is used. Further, as the above-mentioned non-magnetic powder, organic powder, for example, benzoguanamine resin, melamine resin, phthalocyanine pigment, etc. may be added.

The magnetic recording medium of FIG. 14 may have an undercoat layer (not shown) provided between the magnetic layer 2 and the support 1, or may not have the undercoat layer ( The same applies below).

As the material of the support 1, polyethylene terephthalate, plastics such as polypropylene, metals such as Al and Zn, glass, BN, Si carbide, porcelain, ceramics such as pottery, etc. are used.

It is desirable that a predetermined amount of polyfunctional isocyanate as a cross-linking agent be added to the coating material when the magnetic layer is formed by coating. Examples of such a cross-linking agent include triphenylmethane triisocyanate and tris- (p-isocyanatophenyl), in addition to the polyfunctional polyisocyanate described above.
Examples thereof include thiophosphite and polymethylene polyphenyl isocyanate, but methylene diisocyanate type and tolylene diisocyanate type are preferable.

FIG. 5 shows another magnetic recording medium.
An OC layer 4 is provided on the magnetic layer 2 of the medium shown. As the binder resin for the OC layer 4, the urethane resin having the above-mentioned yield point can be used. This OC layer 4
Is provided to protect the magnetic layer 2 from damage and the like, and for that reason, it is necessary that the lubricity is sufficient. OC layer 4
Surface roughness is Ra ≦ 0.01μ especially in relation to color S / N
m, Rmax ≦ 0.13 μm is preferable. In this case, it is desirable that the surface roughness of the support 1 is Ra ≦ 0.01 μm and Rmax ≦ 0.13 μm, and the support 1 is smooth.

FIG. 6 shows a magnetic recording medium configured as a magnetic disk, in which the same magnetic layer 2 and OC as those described above are formed on both surfaces of the support 1.
Layers 4 are provided respectively.

5. Examples Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention.

The components shown in Table 1 below were charged in a ball mill and dispersed, and then this magnetic paint was filtered through a 1 μm filter, 5 parts of a polyfunctional isocyanate was added, and a reverse roll coater was applied to a thickness of 5 μm on the support. Then, a super calendar was applied and slit into a width of 1/2 inch to obtain a video tape (corresponding to the numbers of Examples and Comparative Examples). However, the numbers after the second column in Table 1 represent parts by weight, "actual" after the second column represents the example, and "ratio" represents the comparative column.

The following measurements were made on the videotapes according to the above examples.

Chroma S / N: Color video noise meter "Shibasoku 925D / 1"
It was measured by.

Lumi S / N: Same as above RF output: The RF output at 4 MHz was measured using a VTR deck for measuring RF output, and a value was shown that was lower than the original output after 100 times of reproduction.

(Unit: dB).

The performance of the video tape of each example is shown in Table 2.

From the above results, the tape performance is remarkably improved by containing the urethane resin having the yield point in the magnetic layer according to the present invention and controlling the surface roughness of the magnetic layer by appropriately adjusting the dispersant amount. I understand.

[Brief description of drawings]

FIG. 1 is a graph showing changes in the jitter value depending on the average surface roughness of the magnetic layer. 2 to 6 show an embodiment of the present invention, FIG. 2 is a graph showing the relationship between stress and elongation of urethane resin, and FIG. 3 is a chroma according to the average surface roughness of the magnetic layer. Graphs showing changes in S / N, FIGS. 4, 5, and 6 are enlarged cross-sectional views of a part of the magnetic recording medium according to each example. In the reference numerals used in the drawings, 2 ... magnetic layer 3 ... backcoat layer (BC layer) 4 ... overcoat layer (OC layer).

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-57-30718 (JP, A) JP-A-58-63759 (JP, A) JP-A-55-122234 (JP, A) JP-A-58- 130435 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium, wherein a urethane resin having a yield point is contained in a magnetic layer, and the average surface roughness of the magnetic layer is 0.02 μm or less.