JPH0376022A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve outputs, such as video output, chroma and audio output, with good balance and to obtain sufficient output characteristics by incorporating magnetic powder contg. silicon and aluminum into a magnetic layer and specifying the ratio of the silicon to the aluminum in the magnetic powder. CONSTITUTION:This recording medium consists of a nonmagnetic base 1, the lower magnetic layer 2, a back coat layer 3, and the upper magnetic layer 4. The silicon and the aluminum at >=3 ratio by weight of the silicon/aluminum are incorporated into the magnetic powder to be added to the uppermost layer 4 of the magnetic layers and at least one layer exclusive of this uppermost layer. Namely, the silicon is effectual to enhance the dispersibility of the magnetic powder and the aluminum is effectual to improve the durability as the medium. The weight ratio of the silicon/the aluminum is specified to >=3 ratio by weight in order to simultaneously exhibit the effect of the respective elements. The outputs, such as video output, chroma and audio output, are improved with the good balance and the sufficient output characteristics are obtd.

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. Since conventional magnetic recording media have only one magnetic layer, it is necessary to cover a wide frequency band from low to high frequencies with one type of magnetic powder.

In particular, with the recent trend toward higher recording densities, magnetic powders with high Hc and high BET values are used because recording characteristics in high frequencies are improved and low noise is required.

However, since magnetic recording media are composed of a single type of magnetic powder (magnetic layer), high-H
c. Since it is necessary to use magnetic powder with a high BET value, the low-frequency characteristics become insufficient.

On the other hand, in magnetic recording media for video, media having multiple magnetic layers have been proposed in order to increase the magnetic recording capacity or to improve and balance the magnetic recording characteristics of the medium in both the high frequency region and the low frequency region. (Unexamined Japanese Patent Publication No. 48-9
No. 8803, Japanese Patent Publication No. 172142/1983, Special Publication No. 172142
-2218, JP-A-51-64901, JP-A-56
-12937, JP-A No. 58-56228, JP-A No. 6
3-146211, etc.).

According to these known techniques, the upper and lower layers of the magnetic layer are designed to separate functions, with the upper layer responsible for video output and the lower layer responsible for chroma and audio output. Since the product (without surface treatment) was used as is, there was a limit to its dispersibility, and sufficient output could not be obtained.

C.1 Objective of the Invention An object of the present invention is to provide a magnetic recording medium that can improve outputs such as video output, chroma output, audio output, etc. in a well-balanced manner, and can obtain sufficient output characteristics.

20 Structure of the invention and its effects, that is, in the present invention, the magnetic layer provided on the non-magnetic support is composed of at least two layers, the uppermost layer of these layers and at least the lower layer other than the uppermost layer. The present invention relates to a magnetic recording medium that contains magnetic powder containing silicon and aluminum, respectively, and in which the ratio of silicon to aluminum in the magnetic powder is 3 or more by weight.

According to the present invention, since the magnetic layer is composed of multiple layers, the upper layer has good high-frequency recording and playback characteristics such as video output, and the lower layer has relatively low chroma and audio output characteristics. Each layer can be formed to improve the recording and reproducing characteristics of the area. For this purpose, the upper layer (
In particular, it is necessary that the coercive force (Hc) of the uppermost layer (N) be larger than that of the lower layer, and that the film thickness (or layer thickness) of the upper layer be thin, especially preferably 0.6 μm or less. The thickness of the lower layer adjacent to is preferably 1.5 to 4.0 μm.

What should be noted in the present invention is that silicon and aluminum are contained in the upper (weight ratio) of the magnetic layer. In other words, silicon has the effect of increasing the dispersibility of magnetic powder, and aluminum has the effect of improving the durability as a medium, but in order to exhibit the effects of these elements at the same time, the silicon/aluminum weight ratio must be adjusted. If the weight ratio is less than 3, the amount of silicon is insufficient,
The dispersibility of the magnetic powder will deteriorate, and in order to improve the video output, the upper layer preferably contains BET (!
! Fine particle magnetic powder with a large particle size (particularly 30 rrf/g or more) is used, and as the particles become finer, it is important to proportionately increase the silicon content in order to ensure dispersibility. In this respect as well, based on the present invention, it is necessary to set the above weight ratio to 3 or more to ensure a sufficient amount of silicon. At the same time, it is necessary to ensure durability, so a certain amount of aluminum must be included, and the upper limit of the above weight ratio is preferably 2Q, the weight ratio is preferably 3 to 20, and even 3 to 10. More preferred.

Further, in the present invention, it is desirable that the silicon content of the ferromagnetic powder contained in the uppermost layer of the magnetic layer is higher than the silicon content of the ferromagnetic powder of other layers other than the uppermost layer. Since the dispersibility of the magnetic powder in the top layer is improved by the large amount of silicon in the top layer, the magnetic powder that is thin and has a large BET value (that is, difficult to disperse) should be sufficiently dispersed in the upper layer. I can do it.

In the above, the silicon content in the magnetic powder is preferably 2.0% by weight or less, and more preferably 0.1-1.2% by weight. Even if the silicon content exceeds 2.0% by weight, the effect commensurate with the increase in silicon content may not be achieved, and the magnetic properties may deteriorate on the contrary. The content of aluminum is preferably 0.7% by weight or less of the magnetic powder within the range that satisfies the above weight ratio, and 0.7% by weight or less of the magnetic powder.
0.005 to 0.4% by weight is more preferable. In addition, in the above, "containing" silicon and aluminum also means when they are attached to the surface of the core of magnetic powder or when they are mixed inside the core.

The attachment of silicon and aluminum to the magnetic powder can also be carried out quantitatively, for example, by adding a soluble silicon compound or aluminum compound to a dispersion prepared by dispersing the magnetic powder in an alkaline aqueous solution. Usable silicon compounds include, for example, orthosilicic acid (H4SiO
4), metasilicate (+1 t S + 03 ), metatrisilicate (II!St!o), metatrisilicate (H4Si
30t), silicic acid such as metatetrasilicic acid (LSLOz);-
Silicon oxide, silicon dioxide; sodium orthosilicate (
NanSi04), sodium metasilicate (NaSiO
s), potassium metasilicate (LSi03), calcium orthosilicate (Ca4sta4), calcium metasilicate (CazSiOs), barium metasilicate (BazS)
iOz), silicate metal salts such as cobalt metasilicate (COtSiOz), and the like. These silicon compounds may be used alone or in combination of two or more.

In addition, examples of aluminum compounds that can be used to attach aluminum to magnetic powder include aluminum oxide (A f , o3) and aluminum fluoride (Alh).
, aluminum chloride (AlCl2), aluminum bromide”F
aluminum (A 42 Brz), aluminum iodide (A
j! I,) Aluminum hydroxide (A 1 (OH),
), aluminum sulfate (Al t (S04) z)
, aluminum nitrate (A 1 (N(h) z), aluminum phosphate (^f PO4), aluminum carbide (
A II! 4C3), aluminum nitride (A f N
), aluminum sulfide (Al zss), and the like. These may be used alone or in combination of two or more.

By using magnetic powder surface-treated with silicon and aluminum in this way, the dispersibility of the magnetic powder is improved, the output is improved, and the durability of the medium is maintained well.

Further, in order to quantitatively mix silicon and aluminum into the magnetic powder, a method of bringing the magnetic powder into contact with a gas containing silicon and aluminum can be adopted.

Further, in the case of magnetic powder obtained by thermal reduction of goethite, the treatment with aluminum and silicon may be performed in the production or treatment stage of the raw goethite, and then this may be reduced.

In the above, silicon and aluminum are preferably present in the form of an oxide or a hydrous oxide in the surface region of the magnetic powder.

In the present invention, it is desirable that the plurality of layers (the top layer and the other N layers) constituting the magnetic layer are adjacent to each other, and the other layers mentioned above may be IN, or may be 2N or more. However, at least one of these should contain magnetic powder with a specified ratio of silicon and aluminum, similar to the top layer. However, in addition to cases in which there is substantially a clear boundary between each layer, there may be a case in which there is a boundary area in which magnetic powder from both layers coexists at a certain thickness.
, the upper or lower layer excluding these boundary areas is referred to as each of the above layers. In particular, the medium of the present invention is suitable when each magnetic layer is coated and formed by a wet-on-net coating method. Of course, an et-on-dry method may be used in which the upper layer is applied after drying the lower layer.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
Non-magnetic support 1 made of polyethylene terephthalate etc.
A first magnetic layer 2 and a second magnetic layer 4 are laminated thereon in this order. Further, although a back coat layer 3 is provided on the support surface opposite to the laminated surface, this need not necessarily be provided. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into layers 5 and 6.

In the magnetic recording media of FIGS. 1 and 2, the thickness of the first magnetic layer 2 is preferably 1.5 to 4.0 μm,
Thickness of the second magnetic layer 4 or the second and third magnetic layers 5.6
It is preferable that the total film thickness is 0.6 μm or less (for example, 0.5 μm).

The magnetic layer 2.4.5.6 may contain magnetic powder, but
Such magnetic powders include γ-Fe, O, Go-containing r
-Few 03 , Fe, 04 , Co-containing Fe, Oa
Iron oxide magnetic powder such as; Fe, Ni, Co, Fe-Ni-C
o alloy, Fe-Ni alloy, Fe-A1 alloy, Fe-Al
-Ni alloy, Fe-Al2-Co alloy, Fe-Mn-Z
n alloy, Fe-Ni-Zn alloy, Fe-Al2-Ni-
Co alloy, Fe-Al-Ni-Cr alloy, Fe-AJ!
-Co-Cr alloy, Fe-Co-Ni-Cr alloy, Fe
'-C.

-Ni-P alloy, Co-Ni alloy, etc. Fe, Ni.

Examples include various ferromagnetic powders such as metal magnetic powders containing Co or the like as a main component. The outermost magnetic layer 4.6 and other magnetic NZ, 5
(and/or 2) contains magnetic powder containing silicon and aluminum in a weight ratio of 3 or more based on the present invention.

Among these magnetic powders, one suitable for each of the above-mentioned magnetic layers 2.4 can be selected based on the present invention.

For example, if the upper layer 4 has a higher coercive force (Hc) than the lower layer 2, a higher output medium can be obtained.

Each magnetic layer also contains lubricants such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 20 carbon atoms (such as stearic acid), and lubricants having a total of 13 to 40 carbon atoms. Abrasives (for example, molten aluminum), antistatic agents (for example, carbon black, graphite), etc. may be added.

The binder that can be used for the magnetic layer 2.4.5.6 preferably has an average molecular weight of about 10,000 to 200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, etc. , vinyl chloride-acrylonitrile copolymer, polyvinyl chloride, urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate,
cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction Examples include resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -3o, M, -COOM.

-PO(OM')t (where M is hydrogen or an alkali metal such as lithium, potassium, and sodium; M' is a hydrocarbon residue or an alkali metal such as hydrogen, lithium, potassium, and sodium); It is preferable that the resin contains In other words, the polar groups in the molecules of these resins improve their compatibility with the magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid. This can also improve the durability of the medium.

Such a binder, especially a vinyl chloride copolymer, is obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and, if necessary, other copolymerizable monomers. be able to.

This copolymer is easy to synthesize because it is based on a vinyl base, and the metal of the salts such as sulfonic acid or phosphoric acid mentioned above is an alkali metal (especially sodium, potassium, and lithium), and potassium is particularly soluble. , reactivity, yield, etc.

Further, when providing the back coat layer 3, the above-described binder contains non-magnetic particles such as barium sulfate, and is applied to the back surface of the support.

Further, as the material of the support 1, plastics such as polyethylene terephthalate and polypropylene, An
Metals such as SZn, glass, BN, St carbide, ceramics such as porcelain, and earthenware are used.

Next, FIG. 3 shows an example of the above-mentioned medium manufacturing apparatus.

In this manufacturing apparatus, when manufacturing the medium shown in FIG. 1, the film-like support 1 fed out from the supply roll 32 is oriented by an extrusion coater 10, and a rear-stage orientation magnet 35 of, for example, 2000 Gauss is arranged. The paper is introduced into a dryer 34, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coated layer is led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered and then wound onto a winding roll 39. Each paint may be supplied to the extrusion coater 10.11 through an in-line or kisser (not shown). In the figure, the arrow O indicates the conveyance direction of the non-magnetic base film. , reservoirs 13,14 are provided to deposit the paint from each coater in a wet-on-wet manner. To produce the media of FIG. 2, one more extrusion coater in FIG. 3 may be added.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

First, the following compositions were kneaded and dispersed in a sand mill,
Each magnetic paint was prepared.

<Magnetic paint A for upper layer> Co 7 FezOz 100
parts (silicon and aluminum content are in Table 1 below,
Hc=9000e, BET straight 50r+f/g, average major axis length 0.16 μm) 10 parts of PVC resin containing potassium sulfonate (MR
IIO1 Nippon Zeon ■) Polyurethane resin 5 parts a-A
nt○, (average particle size 0.2μm) 6 parts carbon black 1 part myristic acid
1 part stearic acid
1 part butyl stearate
Part 1 Coronate L
5 parts (manufactured by Nippon Polyurethane Industries) Magnetic paint B for lower layer Co 7 FezO 1100 parts (silicon and aluminum content are in Table 1 below, H
c=7000e, BET value 38rd/g, average major axis length 0
．． 24 μm) 10 parts of PVC resin containing potassium sulfonate (MR
llo, manufactured by Nippon Zeon ■) Polyurethane resin 5 parts myristic acid 1 part stearic acid
1 part butyl stearate
Part 1 Coronate L
5 parts (manufactured by Nippon Polyurethane Industries ■) Next, various types of lower layer magnetic paint B and upper layer magnetic paint A were sequentially applied onto the polyethylene terephthalate base film with a thickness of 14.5 μm using the apparatus shown in Figure 3, and oriented. After drying, calendering was performed. In this case, the upper layer is 0.5e
m, and the lower layer had a dry film thickness of 2.5 μm.

Thereafter, a paint for the BC layer having the following composition was applied to the surface opposite to the magnetic layer to a dry thickness of 0.8 μm.

Carbon black (Raven1035)
40 parts barium sulfate (average particle size 300mm)
10 parts Nitrocellulose 25 parts N-2301 (made by Nippon Polyurethane) 25 parts Coronet)
L(〃) 10 parts cyclohexanone
400 parts methyl ethyl ketone
250 parts toluene
250 copies of a wide magnetic film was thus obtained and wound up. This film was cut to a width of A inch to produce video tapes shown in Table 1 below.

The magnetic powder used above is as follows.

That is, untreated Co-containing 7 FezO5M1 powder (
Co content 2.5% by weight, needle ratio 9) was suspended in NaOH aqueous solution, and Na4SiO4 and Na2A10s
An aqueous solution of was added thereto, and while stirring well, carbon dioxide gas was blown into the suspension to neutralize it, thereby forming a film consisting of silicon oxide and aluminum oxide on the surface of the magnetic powder.

After washing this magnetic powder with water, it was dried at a predetermined drying temperature for a predetermined time.

As magnetic powder, Na4SiO4 and Na, /M! O.

St and AI shown in Table 1 by changing the concentration and amount of aqueous solution
! , each magnetic powder having a content of .

Then, the following performance evaluations were performed on each of the above tapes, and the results are shown in Table 1 below.

(a), RF-output, Lumi-3/N, Chroma-3/N.

Chroma output crab color video noise meter rshtbasoku92
Using 5D/IJ, "HR-5700" manufactured by Victor Japan Co., Ltd.
Value for reference tape (dB) with 0J deck
It was expressed as

The frequencies of each signal are as follows.

4-)/N: (b).

(C).

(d).

(e).

HiFi-audio output using the rBR-3711J deck manufactured by Victor Japan Co., Ltd.
Expressed as a value (dB) relative to a reference tape.

The frequency of this output signal was 1.7 MHz.

Using the deck of Linear Audio Output Japan Victor Co., Ltd. rBR-3711J,
Expressed as a value (dB) relative to a reference tape.

The frequency of this output signal was IKHz.

Still durability: Indicates the time in minutes until the reproduction output of a still image decreases by 2 dB.

Edge bending in Runnability test: 4
Observe the edge condition after running the tape for 100 hours at 0'C and 80% temperature and humidity.

○ No edge bending Δ Partial edge bending x Edge bending over the entire length Next, in the above, St/A of the upper layer and lower layer of Example 1
FIG. 4 shows the RF output and chroma output obtained by varying j2 (weight ratio). According to this, it can be seen that the output is greatly improved when the St/Af ratio is 3 or more (particularly 5 or more) in both the upper and lower layers. Further, the characteristics are further improved when the amount of St is increased in the upper layer (see Example 6).

In addition, when the above-mentioned magnetic layer is formed in three layers as shown in Table 2 below (the film thickness is 0.3 μm for the top layer and 0.3 μm for the middle layer),
μm, lower layer 2.4 μm), St/Af of at least the upper layer and the middle layer based on the present invention! It was also found that by setting the ratio to 3 or more, the output can be improved.

(Margin below)

[Brief explanation of drawings]

The drawings are for illustratively explaining the present invention, and FIGS. 1 and 2 are cross-sectional views of an example of a magnetic recording medium, FIG. 3 is a schematic diagram of a magnetic recording medium manufacturing apparatus, and FIG. Magnetic powder St/
l! It is a graph showing changes in characteristics when changing the ratio. In addition, in the reference numerals shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 3...Back coat layer 4. 6... Upper magnetic layer 5... Intermediate magnetic layer.

Claims (1)

[Claims] 1. The magnetic layer provided on the non-magnetic support has at least two
The top layer of these layers and at least one layer other than the top layer each contain magnetic powder containing silicon and aluminum, and the ratio of silicon to aluminum in the magnetic powder is in a weight ratio. A magnetic recording medium with a value of 3 or more.