JPH03187016A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durability by incorporating a hardening agent into magnetic layers in such a manner that the proportion of the hardening agent in a binder of a second magnetic layer is equivalent to or larger than that in a first magnetic layer and specifying the winding hardness of the medium after cutting. CONSTITUTION:On a nonmagnetic supporting body 1, the first magnetic layer 2, the second magnetic layer 4 are stacked and the back surface of the supporting body 1 is covered with a back coating layer. The hardening agent is incorporated into the magnetic layers in such a manner that the proportion thereof in the binder of the second magnetic layer 4 is equivalent to or larger than that in the first magnetic layer 2, and the winding hardness of the medium after cutting is specified to Shore D hardness of 35 - 90. With the larger amt. of the hardening agent, the second magnetic layer 4 can be improved in durability and flatness, which avoids degradation of electromagnetic conversion characteristics caused by transferring or intrusion of foreign matter. With the small amt. of the hardening agent in the first magnetic layer 2, the medium has flexibility and scattering of dust in cutting can be suppressed. By specifying the winding hardness to 35 - 90 Shore D hardness, the stability of the pan cake after cut in a stage of reservation or transfer can be improved.

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 In general, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin (binder), 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, relatively fine magnetic powder is used in the upper layer of the magnetic layer, and larger magnetic powder is used in the lower layer, so that the upper layer receives video output and the lower layer receives chroma audio output. It was designed to.

In recent years, magnetic recording media have been increasingly developed for use in a wide variety of fields and products, and are now required to have electromagnetic conversion characteristics, physical properties, and other mutually antagonistic properties that are far superior to those of the past. For this reason, studies have been conducted to improve the magnetic materials themselves, or to consider the formulation of binders, lubricants, etc.
In addition, various improvements and studies have been made regarding process aspects such as kneading techniques and transport of supports.

Conventionally, in order to prevent instantaneous loss of signals in magnetic recording media, so-called dropout (Do), it has been necessary to manufacture original sheets with no coating defects, to produce materials with less powder falling during cutting, and to improve magnetic layers and supports for these media. We have dealt with this by using wiping materials that effectively wipe away the minute dirt and dust generated from the air. In addition, in order to improve electromagnetic conversion characteristics, smoothing the surface of the magnetic layer and smoothing the back surface of the support will prevent show-through (transfer).
We have responded by preventing

However, even with the combination of these technologies, it is possible to improve the surface quality and durability of the coating film in magnetic recording media, or to reduce wear and tear of the magnetic layer due to winding misalignment or wrinkles during the winding stage, as well as the electromagnetic conversion characteristics and low dust generation. The current situation is that these are not satisfied, leading to deterioration in final quality. In particular, these problems become noticeable in media having a plurality of magnetic layers as described above. That is, in such media, it is difficult to properly control the surface properties of the upper magnetic layer because the layer is thin (usually 1.0 μm or less), and as a result, the wear resistance and running properties of the magnetic layer tend to deteriorate. , the electromagnetic conversion characteristics tend to deteriorate. In other words, if the thin upper magnetic layer has poor surface properties (i.e., is too rough or too smooth), the characteristics of the medium, especially in the high frequency range, may deteriorate or become susceptible to damage. . Furthermore, not only the upper layer but also the lower layer tends to generate dust due to cutting in the conventional composition.

C.1 Purpose of the Invention An object of the present invention is to provide a magnetic recording medium that can improve both electromagnetic conversion characteristics and durability.

More specifically, the first object of the present invention is to provide a magnetic recording medium in which the magnetic layers are multilayered to improve the durability and flatness of the surface layer, where the electromagnetic conversion characteristics tend to deteriorate particularly due to transfer or inclusion of foreign matter. Our goal is to provide the following. The second objective is to provide a magnetic recording medium in which the deep layer of the magnetic layer is made flexible and dust generation during cutting is suppressed to an extremely low level. Thirdly, by setting a high winding hardness of the magnetic layer, which became possible for the first time in achieving the first and second objectives, the process suitability of so-called pancakes (P/C) after cutting is improved. We have developed a magnetic recording medium that dramatically improves the stability of pancake storage and transportation processes, and significantly reduces failures such as falling rows, bent edges, and drop-apart (Do). It is about providing. Furthermore, the fourth object is to provide a magnetic recording medium that can stabilize the cutting and winding process and improve the yield.

20 Structure of the Invention That is, the present invention has a structure in which a first magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support, and both the first and second magnetic layers contain magnetic powder in a binder. In the magnetic recording medium comprising a dispersed layer, the proportion of the curing agent in the binder in the second magnetic layer is equal to or higher than the proportion of the curing agent in the binder in the first magnetic layer. The present invention relates to a magnetic recording medium characterized in that the winding hardness after cutting is 35 or more and 90 or less in Shore D hardness.

According to the magnetic recording medium of the present invention, since the magnetic layer is a plurality of layers (multilayer or laminated type), the second magnetic layer has good high-frequency recording and reproduction characteristics such as video output, and the first magnetic layer has good high-frequency recording and reproducing characteristics.
Each layer can be formed so that the magnetic layer has good relatively low-frequency recording and reproduction characteristics such as chroma and audio output. For this purpose, it is generally necessary that the coercive force (Hc) of the second WL layer (especially the top layer) be larger than that of the first magnetic layer, and that the film thickness (or layer thickness) of the second magnetic layer be thin. The thickness of the first magnetic layer adjacent to the second magnetic layer is preferably 0.1 to 4.0 μm.
It is desirable to set it to 0 μm.

In order to achieve the above-mentioned object of the present invention in such a multilayer magnetic layer, attention was paid to the ratio of the hardening agent to the binder in each magnetic layer, and the hardening agent in the second magnetic layer (upper layer) was The ratio of curing agent is made equal to or larger than the ratio of the curing agent in the first magnetic layer (lower layer). That is, the durability and flatness of the second magnetic layer are improved by increasing the amount of curing agent, and thereby the electromagnetic conversion characteristics are prevented from deteriorating due to transfer or inclusion of foreign matter. Moreover, since the first magnetic layer contains a relatively small amount of curing agent to provide flexibility, dust generation during cutting can be suppressed to an extremely low level.

By setting it to a high value, it is possible to improve the stability in the so-called storage and transportation process of pancakes after cutting, and to significantly reduce malfunctions such as missing pancakes, bent edges, and dropouts. At the same time, it is possible to stabilize the cutting and winding process and improve the yield. Here, the "Shore D hardness" in the present invention is based on JISK7215.

In the present invention, the ratio of the amount of curing agent in the second magnetic layer to the amount of curing agent in the first magnetic layer is preferably 1:(0.2 to 1), and 1
: (0,5-1) is more desirable.

In addition, the Shore D hardness (winding hardness in the wound state after cutting) of the magnetic recording medium of the present invention is 35 to 35 on the magnetic layer side.
It should be 90, but if it is less than 35, it will be too soft and cause folded edges, wrinkles, and dropouts.
Moreover, if it exceeds 90, it will be too hard and blocking will occur, resulting in poor running performance.

Such Shore hardness can be obtained by controlling the winding tension. The Shore D hardness is preferably 40 to 85, more preferably 65 to 83.

In the present invention, a plurality of layers (first, second
It is desirable that the magnetic layers (magnetic layers) are adjacent to each other. The first magnetic layer may be one layer, or may be two or more layers. However, in addition to cases where there is substantially a clear boundary between each layer, there may also be a boundary area where magnetic powder from both layers coexist at a certain thickness; The removed upper or lower layer is each of the above layers. In particular, the media of the present invention coat each magnetic layer with wet simultaneous multilayer coating (sv).
It is suitable for coating and forming by et-on-11st) method. Of course, apply the upper layer after drying the lower layer - eto
An n-dry method may also be used.

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, a back coat layer 3 is provided on the support surface opposite to this laminated surface. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into N5 and N6.

In the magnetic recording media shown in FIGS. 1 and 2, the thickness of the first magnetic layer 2 is 1.5 to 4.5 mm. The thickness of the second magnetic layer 4 or the total thickness of the second and third magnetic layers 5.6 is preferably 0.6 μm or less (for example, 0.5 μm).

The magnetic layer 2.4.5.6 may contain magnetic powder, but
Examples of such magnetic powder include 7-Fe and O.

Iron oxide magnetic powder such as Co-containing r-Fet Ox, Fez Oa, Go-containing Fe3O4; Fe, Ni, Co, F
e-Ni-Co alloy, Fe-Ni alloy, Fe-Al! ,
Alloy, Fe-Al2-Ni alloy, Fe-Affi-Co
alloy, Fe-Mn-Zn alloy, Fe-NiZn alloy, F
e-Al1-Ni-Co alloy, Fe-Af-Ni-Cr
Alloy, Fe-Al! -Co-Cr alloy, Fe-Co-N
i-Cr alloy, Fe-C.

-Ni-P alloy, Co-Ni alloy, and various other ferromagnetic powders such as metal magnetic powders containing Fe, Ni, Co, etc. as main components. Based on the present invention, the outermost magnetic layer 4.6 and the other magnetic layers 2.5 (and/or 2) are such that the former 4.6 is the uppermost layer and the latter 2.5 or 5 and 2 are the lower layers. do.

Among these magnetic powders, one suitable for each of the above-mentioned magnetic layers 2, 4, etc. can be selected.

Each magnetic layer also contains lubricants such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 20 carbon atoms (such as stearic acid), and lubricants with a total of 13 to 40 carbon atoms. fatty acid esters, etc.), abrasives (for example, fused alumina), 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 -3O3M, -COOM.

-P○(OM')t (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M' is a hydrocarbon residue or an alkali metal such as hydrogen, lithium, potassium, or sodium), etc. It is preferable that the resin contains the following. 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, can be 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. can.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

Furthermore, the curing agent for the binder that can be used in the present invention is tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, triphenylmethane triisocyanate, tris-(p-isocyanate phenyl) thiophosphite. , polymethylene polyphenylisocyanate, and the like.

Further, when providing the back coat layer 3, the above-described binder contains non-magnetic particles such as calcium carbonate and is coated on the back surface of the support.

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

Next, an example of the above-mentioned medium manufacturing apparatus is shown in FIG.

In this manufacturing apparatus, when manufacturing the medium shown in FIG.
．． After simultaneous multilayer coating of each paint for 4, for example, 2000
Oriented by the Gauss front-stage orientation magnet 33, and furthermore,
For example, it is introduced into a dryer 34 equipped with a 2000 Gauss rear-stage orientation magnet 35, 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 supercalendar 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 extruded and supplied to the coater 10 through an in-line mixer (not shown). In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. Each extrusion coater 10 is provided with a reservoir 13, 14, from which the coating material is deposited 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 prepared.

<Magnetic paint A for upper layer> Co-7-Fe, Os 100 parts (coercive force (Hc) 7100e, specific surface area (BET) 42
Bo/g) 20 parts of vinyl chloride copolymer (containing 0.5% maleic anhydride, S-LEC E manufactured by Block Chemical Co., Ltd.)
) Thermoplastic polyurethane 10 parts (Niraporan N3132 manufactured by Nippon Polyurethane Co., Ltd.) Alumina
Part 5 CAlt O,,
Particle size: 0.2 μm) Stearic acid 2 parts Butyl palmitate 1 part Methyl ethyl ketone 100 parts Methyl isobutyl ketone 100 parts Toluene
100 parts (lower layer magnetic paint B) Co 7 FezO = 100
(coercive force (Hc) 6500e, specific surface area (BET) 2
5rrf/g) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 parts (UCC Co., Ltd. (7) VAGH) Thermoplastic polyurethane 20 parts (Niraporan N3132, Nippon Polyurethane Co., Ltd.) Red iron (
Particle size: 80 mμ) 55 parts stearic acid 3 parts butyl stearate 2 parts methyl ethyl ketone 150 parts methyl isobutyl ketone 150 parts toluene
150 parts of each of the above compositions (paint A
, B) are thoroughly kneaded and mixed, and then 3 is added as a hardening agent.
Various functional isocyanates (Mytic AD30, manufactured by Mitsubishi Kasei Corporation) were added to the upper layer paint and the lower layer paint as shown in Table 1 below, and each was thoroughly stirred and mixed to obtain each magnetic paint. In Table 1, each paint was prepared by varying the amount of curing agent added while keeping the ratio of pigment to binder in the upper and lower magnetic paints the same. At this time, the content ratio of the vinyl chloride copolymer and thermoplastic polyurethane was the same for the upper and lower layer paints.

(Left below) After filtering these paints, 13
．． On a 0 μm polyethylene terephthalate base, simultaneous multilayer coating was performed using a precision extrusion coater (FEC) so that the coating thickness after drying was 3 μm for the upper layer and 2.5 μm for the lower layer, and after orientation drying in a magnetic field. After completely drying, the surface was smoothed using a super calender roll. A back coat layer paint having the following composition was applied to the surface opposite to the magnetic layer of this original film to a dry thickness of 0.
A 7 μm back coat layer was formed.

Carbon black (average particle size 25 mμ) 40 parts Carbon black (average particle size 300 mμ) 5 parts Calcium carbonate powder (average particle size 60 mμ) 5 parts Nitrocellulose 25 parts N-2301 (manufactured by Nippon Polyurethane Co., Ltd.) 27 parts Coroney L (Japanese) Polyurethane Co., Ltd.) 10 parts cyclohexanone
350 parts methyl ethyl ketone 300
Part toluene 260 parts Samples without back coat were also made from the same raw material, and both were slit to A inch width at a line speed of 600 m/sin, and the winding tension was varied to give the results shown in the table below.
Videotapes of samples (Examples 1 to 71, Comparative Examples 1 to 62) having the winding hardness shown in Table 2 were obtained.

Table 2 also shows the presence or absence of cinching (tight winding) and blocking (firmness on the back side).

(Left below) From these results, it can be seen that if the amount of curing agent in each magnetic layer and the Shore D hardness of the magnetic layer are set based on the present invention, curling wrinkles,
It is possible to provide a medium with improved durability, windability, etc., without (or with little) blocking, cinching, or powder shedding. Note that Comparative Example 62 is an example in which a single-layer (no upper layer) magnetic layer was used in Example-1.

Next, we conducted the following performance evaluations for each of the above tapes.
The results are shown in Table 3 below.

(a), Rumi-3/N: Color video noise meter rShibasoku92
Using 5D/IJ, manufactured by Victor Company of Japan (HR-3700
Values relative to the reference tape are expressed with a deck of 0J.

(middle), Transfer: The presence or absence of transfer after winding was observed under a 200x optical microscope and expressed as a rank of A-D.

A: There are no transfer marks at all in 10 visual fields. B: There are an average of 7 to 8 transfer marks in 10 visual fields (C).

(d).

C: Approximately 15 transfer marks on average in 5 visual fields D: Innumerable transfer marks seen in 1 visual field Dropout (D, O,): A 100% white level signal is recorded and when it is played back. Radup output to video attenuation amount is 12dB, duration is 5μs
I saw more dropouts than ec.

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

(The following are blank spaces) Table 3 (1) Table 3 (2) From these results, by configuring the medium based on the present invention, electromagnetic conversion characteristics and durability can be improved, and transfer and dropouts can be reduced. I can do it.

Next, when the magnetic layer is made up of three layers, layers 2, 5, and 6, as shown in Figure 2 (however, the upper layer 6 is the same as 4 in Figure 1, but the film thickness is 0.3 μm, and the intermediate layer 5 is intermediate Hc (-6800e) between 2 and 4 in Fig. 1, the film thickness is 0.3 μm, and the lower layer 2 is the same as 2 in Fig. 1).When the performance was evaluated in the same manner as above, the following was obtained. The results shown in Table 4 were obtained. According to this, 2
As in the case of the layers, it can be seen that the structure of the present invention provides sufficient performance.

(The following is a blank space) Functions and Effects of the Invention As described above, the present invention is characterized in that the ratio of the curing agent in the second magnetic layer (upper layer) is equal to or greater than the ratio of the curing agent in the first magnetic layer (lower layer). As a result, the durability and planarity of the second magnetic layer are improved, and deterioration of electromagnetic conversion characteristics due to transfer or inclusion of foreign matter does not occur. Moreover, since the amount of curing agent in the first magnetic layer is kept small to give it flexibility, dust generation during cutting can be kept to an extremely low level. It improves stability in the process and significantly reduces failures such as broken lines, bent edges, and dropouts. At the same time, it is possible to stabilize the cutting and winding process and improve the yield.

[Brief explanation of drawings]

The drawings are for exemplifying the present invention, and FIGS. 1 and 2 are sectional views of two sides of a magnetic recording medium, and FIG. 3 is a schematic diagram of an apparatus for manufacturing a magnetic recording medium. 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. A magnetic recording in which a first magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support, and the first and second magnetic layers are both layers in which magnetic powder is dispersed in a binder. In the medium, the proportion of the curing agent in the binder in the second magnetic layer is equal to or higher than the proportion of the curing agent in the binder in the first magnetic layer, and the winding hardness after cutting is A magnetic recording medium having a Shore D hardness of 35 or more and 90 or less.