JPS60111331A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable much more suppression of the sagging in the middle of a magnetic tape and prevention of the decrease in output in a high range in such a stage by constituting the magnetic powder for the lower layer of >=2 kinds of magnetic powders having different coercive forces and constituting the magnetic powder for the upper layer of the magnetic powder having the coercive force higher than the coercive forces of the magnetic powder for the lower layer. CONSTITUTION:The magnetic powder of the lower layer 2B on a base 1 consisting of a nonmagnetic material such as a polyester film or the like has the two peak values mu1 and mu2 in the coercive force distribution as shown by the curve-beta for the coercive force distribution and the magnetic powder on the upper layer 2A has one peak value mu3 in the coercive force distribution as shown by the curve-alpha for the coercive force distribution. The value mu3 is made higher than the max. value mu2 of the peak value of the above-mentioned lower layer. More specifically, the respective peak values have the relation mu1<mu2<mu3. The magnetic powder for the upper layer having the above-mentioned one peak value mu3 is constituted of one kind of the magnetic powder having generally the above-mentioned peak value mu3 and on the other hand, the magnetic powder for the lower layer having the two peak values mu1, mu2 is constituted of the mixture composed of two kinds of the magnetic powders having the respective peak values mu1, mu2.

Description

[Detailed description of the invention]

The present invention relates to magnetic tapes and other magnetic recording media that have high output over a wide range of high, middle and low frequencies. In recent years, as the quality of magnetic tapes has improved and higher densities have been demanded, magnetic tapes have appeared in which a two-layer magnetic layer consisting of an upper layer and a lower layer is provided on a base film. However, this type of tape has one problem.
It is known that a decrease in output is observed in the middle frequency range of about 5 KHz, that is, a sagging phenomenon occurs. In order to suppress the sagging phenomenon, the upper layer magnetic powder should have two or more peaks in its coercive force distribution, and the lower layer magnetic powder should have any peak in the coercive force distribution of the upper layer magnetic powder. A magnetic tape using a coercive force distribution having one peak with a coercive force value smaller than the coercive force value, that is, a magnetic tape in which the upper layer magnetic powder has a higher coercive force than the lower layer magnetic powder, and a single layer of magnetic powder. A magnetic tape composed of two or more kinds of magnetic powders having different coercive forces has been proposed in JP-A-54-5705. The inventor discovered that the magnetic tape has a greater effect of suppressing the sagging phenomenon in the middle than the magnetic tape proposed above, and does not cause a decrease in output in the high range when suppressing the sagging phenomenon in the middle. The present invention was completed as a result of extensive research aimed at obtaining a two-layered magnetic tape or other single-layer magnetic tape capable of producing high output. That is, the present invention provides a magnetic recording medium in which upper and lower magnetic layers containing magnetic powder and binder are provided on a base, in which the lower magnetic powder has at least two peaks as a coercive force distribution, and the upper layer's magnetic The powder has at least one peak as a coercive force distribution, and the coercive force value giving the peak in the upper layer is higher than the coercive force value giving any peak in the coercive force distribution of the lower layer magnetic powder. 1, which relates to a magnetic recording medium that
As described above, in this invention, the two-layer magnetic powder has a higher coercive force than the lower layer 6-parallel powder, which is the same as the magnetic tape proposed above, but the lower layer magnetic powder has a higher coercive force. The magnetic tape in the upper layer is composed of at least one kind of magnetic powder having a higher coercive force than the magnetic powder in the lower layer. It has characteristics. It can be seen from Figures 3 and 4 that when the above configuration is adopted, the sagging phenomenon in the middle can be further suppressed compared to the magnetic tape proposed above, and the drop in output in the high range can be prevented at that time. is also clear. FIG. 3 shows the frequency characteristics of a two-layer magnetic tape for normal position produced by the method of Example 1 described later. The coercive force value that gives the peak of the coercive force distribution (hereinafter referred to as the peak value of the coercive force distribution or simply the peak value) is 45
A cobalt-containing T-iron oxide magnetic powder with a coercive force distribution of 350 Oe and a cobalt-containing T-iron oxide magnetic powder with a coercive force distribution of 250 Oe as the lower layer magnetic powder are used. is T
- The present invention relates to a magnetic tape using a magnetic compound with iron oxide magnetic powder. Curve 31) in Figure 3 shows a cobalt-containing T-iron oxide magnetic powder with a coercive force distribution peak value of 450 oersteds and a T-iron oxide magnetic powder with a coercive force distribution peak value of 350 oersteds as the magnetic powder in the upper layer. - A magnetic tape according to the above-mentioned proposal, which uses an equal MP1 compound with iron oxide magnetic powder, and uses T-iron oxide magnetic powder having a peak value of coercive force distribution of 250 oersteds as the lower layer magnetic powder, Curve 30 uses cobalt-containing γ-iron oxide magnetic powder with a coercive force distribution peak value of 450 Oersteds as the upper layer magnetic powder, and uses a cobalt-containing γ-iron oxide magnetic powder with a coercive force distribution peak value of 250 Oersteds as the lower layer magnetic powder. Conventional magnetic tapes made of T-iron oxide magnetic powder are shown for comparison. From the comparison of the curves 3a, 3b, and 3c, it can be seen that the magnetic tape of the present invention is 1 to 5
The sagging phenomenon in the middle of KHz is further suppressed, and there is no decrease in output in the high range of 5 KHz or more, which is the case with the magnetic tape proposed above, and the output is suppressed in the entire high-mid-low range from below IKHz to 10 KHz or more. It can be seen that high output is obtained throughout. Next, FIG. 4 shows the frequency characteristics of a two-layer magnetic tape for chromium positions produced by the method of Example 2, which will be described later. A cobalt-containing T-iron oxide magnetic powder with a peak value of magnetic force distribution of 750 Oersteds is used, and a cobalt-containing T-iron oxide magnetic powder with a peak value of coercive force distribution of 600 Oersteds is used as the lower layer magnetic powder. The present invention relates to a magnetic tape which uses a cobalt-containing T-iron oxide magnetic powder having a magnetic force distribution peak value of 450 oersteds. Curve 4b in Fig. 4 indicates that the magnetic powder in the upper layer is
A cobalt-containing T-iron oxide magnetic powder having a peak value of coercive force distribution of 750 oersteds and a cobalt-containing γ-iron oxide magnetic powder having a peak value of coercive force distribution of 600 oersteds are used; Curve 4c shows the magnetic tape according to the above proposal, which uses a cobalt-containing T-iron oxide magnetic powder having a coercive force distribution peak value of 450 oersteds as the magnetic powder, and curve 4c shows the case where the magnetic tape is kept as the upper layer of the nutritious powder. A cobalt-containing T-iron oxide magnetic powder with a peak value of magnetic force distribution of 750 Oe is used, and a cobalt-containing T-iron oxide magnetic powder with a peak value of coercive force distribution of 450 Oe is used as the lower layer magnetic powder. This figure shows conventional magnetic tapes for comparison. Is it clear from the comparison of the above curve -48 + 4 b + 4 c? J, the same results were obtained with the magnetic tape for the chrome position as with the magnetic tape for the normal position, that is, the sagging phenomenon in the middle was further suppressed compared to the magnetic tape according to the proposal. Moreover, there is no decrease in output in the high range, and high output is obtained throughout the low range in the cylinder. The above effects of this invention are believed to be based on the following reasons. That is, in the magnetic tape of this invention,
The above-mentioned self-demagnetization is reduced by configuring the upper layer on the high coercive force side, which tends to cause self-demagnetization due to oversaturation of the bias current when the magnetic head is close to each other, with magnetic powder with a narrow distribution of coercive force having one peak value. On the other hand, the lower layer on the low coercive force side located far from the magnetic head is made of magnetic powder with a wide coercive force distribution 11 with two peak values, which reduces the coercive force gap with the upper layer. This lower layer is less likely to cause self-demagnetization, and is made thicker than the upper layer or has a higher packing ratio of magnetic powder to increase the residual magnetic flux density.

It is believed that these factors contributed to the effects of the present invention as described above. Hereinafter, the configuration of the present invention will be explained in detail. FIG. 1 shows an example of a lit recording medium of the present invention, in which 1 is a base made of a non-magnetic material such as a polyester film, 2 is a magnetic layer formed on the base, and 2 is a magnetic layer made of magnetic powder. The two layers are horizontally arranged: an upper layer 1ifj 2 A containing a binder and a lower layer 2B. The lower layer 2B (magnetic powder has a coercive force distribution curve −β in FIG.
The peak values of the two coercive force distributions, as shown in )
1+ and /L2, and the magnetic powder of i2i2 A above has one coercive force distribution peak value /''3, as shown by the coercive force distribution curve -〇 in Fig. 2. This peak value μ3 is the highest value P2 of the peak values of the lower layer.
It is more expensive than that. That is, each peak value is 11
The relationship is </12〈ノ13. The upper layer magnetic powder having the above-mentioned one peak value is generally composed of one kind of magnetic powder having the above-mentioned peak value μ3, while the lower layer magnetic powder having two peak values /ll +12 each has the peak value p1. ．． p. It is composed of a mixture of two types of magnetic powders having . The mixing ratio of the magnetic powder having a peak value μm and the magnetic powder having a peak value 12 in the magnetic powder for the lower layer is as follows:
Since it affects the frequency characteristics, it is desirable to set it within an appropriate range. FIG. 5 shows the frequency characteristics when the mixing ratio of the lower layer magnetic powder in the normal position magnetic tape shown in FIG. 3 is changed. Curve 3a is the peak value shown in Figure 3 above,
T-iron oxide magnetic powder with III (250 oersted) and T with peak value μ2 (350 oersted)
- The mixing ratio ()s//12) with iron oxide magnetic powder is 5152 by weight pressure, resulting in a magnetic Kechi blue shape - "4+1+
curve -3 for the magnetic tape with the above mixing ratio of 8/2.
00a indicates a magnetic tape in which the above mixing ratio is 2/8. From the above curves 3a, 30a, and 300a, the peak value μ
The mixing ratio (μ, /) i2) of the magnetic powder having m and the magnetic powder having a peak value of 2 is 2/8 to 8/2 in terms of weight.
2, preferably within the range of 3/7 to 7/3, and by setting within this range stable output can be obtained over the entire frequency range. The magnetic powders having peak values of /11+/'2+μ3 used in the upper layer 2A and lower Jl 2 B do not need to be composed of one type of magnetic powder, and may have approximately the same peak value. - may be composed of a mixture of two or more magnetic powders having different coercive force distributions. It is preferable that the differences and magnitudes of the peak values t+, μ2, and 13 are set within the ranges shown in Table 1 below. Table 1 Note that in the above explanation, the case where the magnetic powder for the lower layer has two peak values of coercive force distribution is taken as an example, but the present invention also includes cases where the above-mentioned peak value is 3 or more. . In such an embodiment, the minimum value (door,
) and the highest value ()12) should just satisfy the above relationship. Further, the main object of the present invention is to provide a magnetic tape or other magnetic recording medium that can exhibit the best performance in the conventional position, that is, the normal position and the chrome position. The effect can also be achieved at other positions, and in this case, the size of each peak value depends on the position. It is possible to change the difference etc. as appropriate. Specific examples of the magnetic powder for the upper layers 2A and 2B include iron oxide magnetic powder having a predetermined peak value of coercive force distribution, cobalt-containing iron oxide magnetic powder, magnetic iron and its alloy powder, chromium oxide powder, and barium ferrite powder. Any of the conventionally known ones can be used. The formation of the magnetic layer 2 consisting of the upper layer 2A and the lower layer 2B can be carried out according to a conventional method. First, a magnetic paint for the lower layer containing a binder and a predetermined magnetic powder is applied onto the base 1 to form the lower layer 2B. Then, an upper layer magnetic paint containing a binder and a predetermined magnetic powder may be further applied thereon to form the upper layer 2A. The binders used here include various conventionally known resins and rubbery polymers such as vinyl chloride-vinyl acetate copolymers, vinylidene chloride resins, polyester resins, cellulose resins, polyurethane resins, and polyacrylic resins. is also available. It goes without saying that conventionally known additives such as dispersants, lubricants, antistatic agents, plasticizers, pigments, etc. can be added to the magnetic coatings for the upper and lower layers. The layer thickness of the upper layer 2A is 1 to 47 m, preferably 15 to 3 μm.
1 lower J! The layer thickness of the upper layer 2B is preferably in the range of 5 to 5) tyn, preferably 2 to 4 μm, and the layer thickness of the upper layer 2A is preferably equal to or less than that of the lower layer 2B. With such a thickness relationship, good sensitivity characteristics can be obtained over the entire frequency range. EXAMPLES Below, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight. Example 1 On a polyester base film with a thickness of 12 pn, the following magnetic paint for lower layer was applied and dried to form a magnetic layer with a thickness of 30 μm. In addition, as magnetic powder, T-iron oxide magnetic powder whose peak value (μ2) of coercive force distribution is 350 oersteds and peak value (μ2) of coercive force distribution is 250 oersteds.
An isotropic compound with Oersted T-iron oxide magnetic powder was used. Magnetic paint for lower layer> Magnetic powder 82 parts Garfuck (dispersant manufactured by Toho Chemical Co., Ltd.) 1 part Methyl isobutyl ketone 50 parts Toluene A magnetic layer with a thickness of 2.5 mm was formed by coating and drying, and then a mirror polishing process and cutting process were carried out according to conventional methods.
A magnetic tape for normal position according to the present invention was produced. As the magnetic powder for the upper layer, a cobalt-containing T-iron oxide magnetic powder having a coercive force distribution peak value (13) of 450 oersteds was used. <Magnetic paint for upper layer> Magnetic powder 80 parts VAGH (mentioned above) 10 parts T-5201 (mentioned above) 8 parts Coronate (mentioned above) 2 parts Garfac (mentioned above) 1 part methyl isobutyl ketone 50 parts Toluene 50 The results of examining the frequency characteristics of the magnetic tape thus produced were as shown by curve 3a in FIGS. 3 and 5. Comparative Example 1 As a magnetic powder for upper layer, the peak value of coercive force distribution is 450
The cobalt-containing T-iron oxide magnetic powder is Oersted and the T-iron oxide magnetic powder has a coercive force distribution peak value of 350 Oersted.
The upper layer and A normal position magnetic tape having the same lower magnetic layer thickness as in Example 1 was produced. The frequency characteristics of this tape were as shown by curve 3b in FIG. Comparative Example 2 A cobalt-containing T-iron oxide magnetic powder having a coercive force distribution peak value of 450 oersteds was used as the upper layer magnetic powder, and a T-iron oxide magnetic powder having a coercive force distribution peak value of 250 oersteds was used as the lower layer magnetic powder. A normal position magnetic tape was produced in the same manner as in Example 1, except that iron oxide magnetic powder was used, and the upper and lower magnetic layers had the same thicknesses as in Example 1. The frequency characteristics of this tape were as shown by curve 3c in FIG. Example 2 As magnetic powder for upper layer, peak value of coercive force distribution ()l,
) is 750 oersted, and cobalt-containing T-iron oxide magnetic powder whose coercive force distribution peak value () (2) is 600 oersted is used as the magnetic powder for the lower layer. Cobalt-containing T- whose peak value (p+) of magnetic force distribution is 450 oersted
A magnetic tape for chromium position was produced in the same manner as in Example 1, except that a homogeneous compound with iron oxide magnetic powder was used, and the thicknesses of the upper and lower magnetic layers were the same as in Example 1. The frequency characteristics of this tape were as shown by curve 4a in FIG. Comparative Example 3 As a magnetic powder for upper layer, the peak value of coercive force distribution is 750
Using an equal MAR compound of cobalt-containing T-iron oxide magnetic powder which is Oersted and cobalt-containing T-iron oxide magnetic powder whose coercive force distribution peak value is 600 Oersted,
And the peak value of the coercive force distribution as the magnetic powder for the lower layer is 45.
An LA magnetic tape for the chromium position was prepared in the same manner as in Example 1, except that a cobalt-containing T-iron oxide magnetic powder of 0 oersted was used, and the upper and lower magnetic layer thicknesses were the same as in Example 1. The frequency characteristics of this tape are
This was as shown by curve-4b in FIG. Comparative Example 4 A cobalt-containing T-iron oxide magnetic powder having a coercive force distribution peak value of 750 oersteds was used as the magnetic powder for the upper layer, and a cobalt-containing T-iron oxide magnetic powder having a coercive force distribution peak value of 450 oersteds was used as the lower layer magnetic powder. -A 611-magnetic tape for chromium position was produced in the same manner as in Example 1 except that iron oxide magnetic powder was used, and the magnetic jζ1 thickness of the two-layer and lower layer was the same as in Example. The frequency characteristics of this tape were "J" as shown by curve 4c in FIG. Example 3 Peak value of coercive force distribution ()11 as magnetic powder for lower layer
) is 250 oersted and T-iron oxide magnetic powder whose coercive force distribution peak value ()t2) is 350 oersted is mixed at a mixing ratio (μm/μ2) of 2/ Two types of normal position magnetic tapes having the same upper and lower magnetic layer thicknesses as in Example 1 were produced in the same manner as in Example 1, except that the thicknesses were changed to 8 and 8/2. The frequency characteristics of the magnetic tape with a weight ratio of 2/8 are shown by curve 300a in Figure 5, and the frequency characteristics of the magnetic tape with a weight ratio of 8/2 are shown by curve 30a in Figure 5. Met.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the magnetic recording medium of the present invention;
Figure 2 is an explanatory diagram showing an example of the coercive force distribution curve of the magnetic powder for the upper layer and the O/lower layer in this invention, Figure 3 is a frequency characteristic diagram of the magnetic tape for the normal position, and Figure 4 is for the chrome position. FIG. 5 is a frequency characteristic diagram of the magnetic tape, in which the mixing ratio of the magnetic powder for the lower layer is used as a parameter in the present invention. 1...base, 2A...upper layer, 2B...lower layer, 2...magnetic layer, μm, μ2. μ3: Coercive force value that gives the peak of coercive force distribution. 3a, 30a, 300a, 4a Characteristic curves showing the magnetic tape of the present invention, 3b, 3c, 4J4c... Characteristic curves showing the magnetic tape for comparison. Patent applicant Hitachi Maxell Co., Ltd. 2F! ! J Ikuishidariki (X-Komata TetP) Figure 3 Figure 4 Figure 5 Fl: iFJIL (KH2)

Claims (1)

[Claims] +1) In a magnetic recording medium in which an upper layer and a lower magnetic layer containing magnetic powder and a binder are provided on a base, the lower layer magnetic powder has at least two peaks in the coercive force distribution, and the upper layer magnetic powder has a coercive force distribution of at least two peaks. A magnetic recording medium having at least one peak in its distribution, and characterized in that the coercive force value giving the peak in the upper layer is higher than the coercive force value giving any peak in the coercive force distribution of the lower layer magnetic powder.