JPS63146211A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic, runnability and durability by using a noncurable binder in a lower magnetic layer. CONSTITUTION:The binder of the lower magnetic layer of a magnetic recording medium having the plural magnetic layers formed by dispersing ferromagnetic powder into the binder on a nonmagnetic base is a noncurable binder and the binder of the upper magnetic layer is a curable binder. Since the lower magnetic layer formed by using the noncurable binder has no shrinkage and has adequate softness, said layer has good compatibility with the nonmagnetic base and improved adhesive power. Since said layers are formed by a wet on wet system, the surface characteristic and glossiness are improved. The electromagnetic conversion characteristic and further the runnability are accordingly improved. On the other hand, the durability is greatly improved by using the curable binder in the upper magnetic layer.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a magnetic recording medium having a plurality of magnetic layers.

In particular, the present invention relates to a novel magnetic recording medium that has improved electromagnetic characteristics, runnability, and durability, and has improved adhesion to a nonmagnetic support.

[Future technology]

In recent years, there has been a demand for compact cassette tapes that have better saturation characteristics in both bass and treble. For this reason, attempts have been made to improve the characteristics by changing the magnetic layer from a single layer to a multilayer.

For example, a ferromagnetic powder with low coercive force (Ilc) is used in the lower magnetic layer to provide low-frequency characteristics, and a ferromagnetic powder with high coercive force (Hc) is used in the upper magnetic layer to achieve high-frequency characteristics. Coarse particles (low 517
) ferromagnetic powder is used to achieve low frequency characteristics and transfer characteristics with high filling, and fine-grained (high S IF7) ferromagnetic powder is used in the upper magnetic layer to obtain bias noise. It is being done.

This is not only limited to compact cassette tapes, but also video tapes, Freonbie disks, etc., and it is known that a plurality of magnetic layers are provided in order to provide multifunctional and wide-ranging electromagnetic conversion characteristics.

(Problem to be solved by the invention) However, since conventional multilayer magnetic tape uses a so-called wet-on-dry coating method in which layers are stacked one by one through a coating and drying process, the lower magnetic layer is necessarily a hardened layer. A binder was used.

The reason for this is that if the lower magnetic layer is coated with a non-curing binder and dried, and then the upper magnetic layer is provided, the lower magnetic layer swells due to the solvent during coating, causing the interface to become disordered. This is because normal application cannot be performed because of the flow.

When a curable binder is used in the lower magnetic layer, shrinkage occurs during drying, which often results in poor adhesion to the non-magnetic support and insufficient electromagnetic conversion properties. Further, it is necessary to carry out bulk thermo-treatment to harden the lower magnetic layer, and as a result, the bulk near the winding core becomes unusable due to tight winding, resulting in a loss of disposal.

In this way, in conventional multilayer magnetic tapes, the lower magnetic layer is made of a curable binder and the upper magnetic layer is made of a curable binder or a non-curable binder. When both of the lower layers are made of a curable binder, there is a problem in that the adhesion to the non-magnetic support is poor and they tend to peel off easily.

Furthermore, the stability of electromagnetic conversion characteristics (output fluctuation) after storage at a high temperature of about 60° C. or higher often deteriorated.

The reason for this is that the upper magnetic layer is made of a non-hardening binder.
This is thought to be because the unevenness on the surface of the support is transferred at high temperatures, deteriorating the surface properties of the magnetic layer.

On the other hand, when the lower magnetic layer uses a hardening binder and the upper magnetic layer uses a non-hardening binder, audio tapes have problems with durability when used for long periods of time, and video tapes have problems with still life. There was a problem of insufficient durability.

An object of the present invention is to provide a novel magnetic recording medium having a plurality of magnetic layers, which has improved electromagnetic conversion characteristics, runnability, and durability, and has improved adhesion to a non-magnetic support. It is in.

[Means for solving problems]

The present inventors wanted to break away from the conventional fixed idea that the lower magnetic layer uses a curing binder, but instead of using simultaneous or sequential wet coating (hereinafter referred to as wet-on-wake), which has already been proposed. / If you use the (referred to as the coating method), it will be possible to apply the
No. 92) It is possible to use a non-hardening binder for the lower magnetic layer, and when we investigated the use of a hardening binder for the upper magnetic layer, we unexpectedly found that the number of m that achieved the above objective was found. It was found that a magnetic recording medium having a magnetic layer of 100 to 100% can be obtained, leading to the present invention.

That is, the present invention provides a magnetic recording medium having a plurality of magnetic layers formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, in which the binder in the lower magnetic layer is a non-hardening binder. , a magnetic recording medium characterized in that the binder of the upper magnetic layer is a curable binder.

In the present invention, by using a non-hardening binder in the lower magnetic layer, there is no shrinkage and the layer has appropriate softness, so it is compatible with a non-magnetic support and improves adhesion. Since it is a wet-on-wet method, the surface quality is good, the gloss is increased, and the electromagnetic conversion characteristics are improved accordingly.
Furthermore, running performance is also improved.

On the other hand, by using a hardening type binder in the upper magnetic layer, durability is significantly improved.

The binder for the lower magnetic layer used in the present invention is a non-curing binder, which is one in which the binder itself does not undergo a curing reaction, such as a thermoplastic resin, and other than that. It does not contain a curing reaction component such as a curing agent (for example, polyisocyanate, etc.).

The thermoplastic resin that is the non-hardening binder used in the lower magnetic layer of the present invention has a softening temperature of 150°C or less and an average molecular weight of 10,000 to 300,000. Degree of polymerization is about 50~
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer, acrylic ester vinylidene chloride copolymer, acrylic ester styrene copolymer,
Methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer,
Nylon-silicon resin, nitrocellulose-polyamide resin, polyfukkavinyl, vinylidene chloride acrylonitrile copolymer, 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, chlorovinyl ether acrylic acid ester comonomer, amino resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof. be done.

Particularly preferred are 13O,M groups and -〇〇M groups in the molecule.
i, -0M group, OS 03 M group, nil-based copolymer,
Polyurethane resins and polyester resins are preferred.

In particular, hydrophilic groups are preferred.

Here, M is hydrogen or an alkali metal (Li.

(Na, etc.), M' is hydrogen, alkali metal (Li, Na, etc.)
, etc.) or a hydrocarbon group.

Regarding resins having these functional groups, Japanese Patent Application Laid-Open No. 59-8
No. 127, No. 57-44227, No. 924 of 1982
No. 22, No. 57-92423, No. 4030 of No. 59-Sho.
Those listed in No. 2 etc. can be used.

A vinyl chloride copolymer containing an epoxy group in addition to the above functional groups can also be used (Japanese Patent Application No. 6O-288935).

A preferred combination of binders is a combination of a vinyl chloride copolymer having the above functional group and polyurethane. As the polyurethane, polyester polyurethane, polyether polyurethane, polyester ether polyurethane, polycaprolactone polyurethane, and polycarbonate polyurethane are preferable.
Il! Particular preference is given to polyurethanes containing groups.

A specific example of the hydrophilic group-containing binder is 1000H group-containing polyurethane (r TIM-3005 manufactured by Sanyo Chemical Co., Ltd.).
J) -S O3N a-containing polyurethane (Toyobo ■
Manufactured by rUR-8300J, [JR-8600J) -
Co.

H group-containing vinyl chloride vinyl acetate copolymer (Nippon Zeon ■
400xllOA), 5OsNa-containing polyester (Vylon 530J manufactured by Toyobo) S OzN
Vinyl chloride vinyl acetate copolymer (Nippon Zeon ■
rMR-110J), etc. The hydrophilicity is preferably in the range of 1 to 10,000 equivalent ft/10'gr, and the molecular weight is preferably in the range of 3,000 to 200,000.

These binders may be used alone or in combination, and the mixing ratio of the ferromagnetic powder and the binder is in the range of 5 to 300 parts by weight per 100 parts by weight of the ferromagnetic powder. Ru.

The coating thickness of the lower magnetic layer is thicker than that of the upper magnetic layer, and is 0.5
The thickness is preferably 1 μm or more, particularly 1 μm or more.

The curable binder used in the upper magnetic layer refers to the combination of the above thermoplastic resin and curing agent (2), thermosetting resin or reactive resin f31 +11, and (2), that is, the magnetic layer. A combination with a binder or curing agent that further causes a curing reaction by applying heat after coating.

The thermoplastic resin is the same as that used in the uncured binder.

As the curing agent, epoxy-polyamide, epoxy-polycarboxylic acid, polyimine, polyisocyanate is used. Particularly preferred is polyisocyanate, which contains -N=C in the molecule.
These include di-, tri-, and tetra-isocyanates selected from aliphatic, aromatic, or alicyclic compounds having two or more =O groups.

These isocyanates include ethane diisocyanate, butane diisocyanate, hexane diisocyanate, 2,2-dimethylpencune diisocyanate, 2.
．． 2. '4-) Limethylbentai diisocyanate,
Decane diisocyanate, ω, ω° -diisocyanate-1,3-dimethylpenzole, ω, ω” -diisocyanate-1,2-dimethylcyclohexane, ω, ω
” diisocyanate)-1,4-diethylpenzole,
ω,ω°-diisocyanate-1゜5-dimethylnaphthalene, ω,ω゛-diisocyanate-)-n-propylbiphenyl, 1,3-phenylene diisocyanate,
1-methylbenzo-2,4-diisocyanate, 1
．． 3-dimethylbenzo-2,6-diisocyanate, naphthalene-1,4-diisocyanate, 1,1°-
dinaphthyl-2,2' diisocyanate, biphenyl-
2,4°-diisocyanate, 3,3′-dimethylbiphenyl-4,4′-diisocyanate, diphenylmethane-4,4′-diisocyanate, 2.2°-dimethyldiphenylmethane-4,4′-diisocyanate, 3,
3′-dimethoxydiphenylmethane-4,4°-diisocyanate, 4.4°-dimethoxydiphenylmethane-
4,4°-diisocyanate, 1-methylbenzo-2.4.6-triisocyanate, 1,3.5-trimethylbenzo-2.4.6-triisocyanate,
diphenylmethane-2,4,4'-) diisocyanate, triphenylmethane-4,4',4"-) diisocyanate, tolylene diisocyanate, 1,5-naphthylene diisocyanate, etc.; dimer or 31-mer of these isocyanates , or addition products of these isocyanates and divalent or trivalent polyalcohols.These are, for example, addition products of trimethylpropane and tolylene diisocyanate or hexamethylene diisocyanate.

These curing agents are used in an amount of 10 to 100 parts by weight of the binder.
It is used in an amount within the range of 60 vignettes.

Commercially available trade names of these polyisocyanates M include Coronate, Coronate H, Coronate 2
030, Coronate 2031, Millionate MR, Millionate MTL (Japan Polyurethane side type), Takene)
D-102, Takene) D-11ON.

There are Takenate D-200, Takenate D-202 (manufactured by Takeda Pharmaceutical ■), Desmodur® L1, Desmodur N, Desmodur HL (manufactured by Sumitomo Bayer), etc., and these can be used alone or with different curing reactivity. They can be used in combination of two or more.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and when heated after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and Mixtures of diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, small molecules! These include mixtures of glycol/high molecular weight diol/triphenylmethane triisocyanate, polyamine resins, and mixtures thereof.

These binders may be used alone or in combination;
Other additives may be added. The mixing ratio of the ferromagnetic fine powder and the binder is in the range of 5 to 300 parts by weight based on 100 parts by weight of the ferromagnetic fine powder.

The binders for the upper and lower magnetic layers preferably have good compatibility. If the compatibility is poor, the adhesion between the upper layer and the lower layer may deteriorate, or the interface may be disturbed, resulting in poor surface properties, which is not preferable.

The coating thickness of the upper layer should be 2.5 μm or less, 0.1 to 2.0
The thickness is preferably 0.1 to 1.0 μm.

If it is thicker than 2.5 μm, it is not preferable because the output in the short wavelength range decreases due to thickness loss.

If it is thinner than 0.1μ, the effect of the multilayer becomes small and the noise improvement effect disappears, which is not preferable.

The plurality of magnetic layers of the present invention may be two layers, an upper layer and a lower layer, or may be three layers, an upper layer, a middle layer, and a lower layer, or may be more than three layers, and may further include a nonmagnetic intermediate layer between the upper layer and the lower layer. good.

Examples of materials forming the non-magnetic support include polyester resins, polyolefin resins, cellulose derivatives,
Examples include polycarbonate resins, polyimide resins, and polyamideimide resins. In addition, depending on the purpose, non-magnetic metals such as aluminum, copper, tin and zinc, or non-magnetic metals containing these, plastics with vapor-deposited metals such as aluminum, and paper coated with or laminated with metals such as aluminum and polio are also available. Paper such as can also be used. Although there is no particular restriction on the form of the nonmagnetic support, a sheet-like support is usually used. However, the nonmagnetic support may be in the form of a film, tape, disk, card, or drum.

When a sheet-like nonmagnetic support is used, the nonmagnetic support generally has a thickness in the range of 5 to 50 μm.

The nonmagnetic support may be provided with a back coat layer on the side on which the magnetic layer is not attached.

Examples of ferromagnetic powders include cobalt-coated ferromagnetic iron oxide powder, fine ferromagnetic chromium dioxide powder, ferromagnetic metal powder and barium ferrite.

The ferromagnetic powder is usually acicular, and the acicular ratio is preferably 2/1 to 20/1 (particularly preferably 571
~20/1) and an average length (major axis length) of 0.1 to 2.0 μm.

The shape of the ferromagnetic powder is not limited to a needle shape, and commonly used shapes such as a rice grain shape and a plate shape can be used.

As the ferromagnetic powder, it is particularly preferable to use a ferromagnetic powder with a long axis length of 0.3 μm or less and a crystallite size of 300 A or less by X-ray diffraction (preferably a long axis length of 0.2 μm or less and a crystallite size of 20 OA or less). preferable.

When using ferromagnetic metal powder, 75% by weight or more (preferably 80% by weight or more) of the metal content of the ferromagnetic metal powder is a ferromagnetic metal or alloy (e.g., Fes Co5).
Ni, Fe-C0% Fe-N'5Co-Ni, Fe-
The particles are preferably Co--N1) and have a major axis of 1.0 μm or less.

The coercive force (Hc) of these ferromagnetic powders is 350 to 5000
Oe is preferred, 600 to 25,000 β is more preferred, and 800 to 20,000 β is particularly preferred. 350O
If it is smaller than e, the output in the short wavelength range will decrease;
If it is larger than 0 e, it is not preferable because recording cannot be performed using a normal head.

The upper magnetic layer and the lower magnetic layer may contain commonly used additives such as lubricants, abrasives, dispersants, antistatic agents, and rust preventives.

For example, examples of substances that can be used as lubricants include saturated or unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils and fluorinated compounds, as well as solid lubricants such as graphite. Agents can be mentioned.

Ferromagnetic powder, a binder, and, if necessary, an abrasive or a filler are kneaded with a solvent to prepare the upper and lower magnetic coatings. As the solvent used during kneading, solvents commonly used in the preparation of magnetic paints can be used.

There is no particular restriction on the kneading method, and the order of addition of each component can be set as appropriate.

When preparing a magnetic paint, known additives such as dispersants, antistatic agents, and lubricants may also be used.

The magnetic paint thus prepared is applied onto the aforementioned non-magnetic support.

A method of applying magnetic paint in a wet state in a superimposed manner according to the present invention,
That is, the wet-on-wet coating method is a so-called sequential coating method in which one layer is first coated and then the next layer is coated on top of it as soon as possible in a wet state, and the extrusion coating method is in which multiple layers are simultaneously coated. Refers to methods, etc.

The wet-on-wet coating method was developed in a patent application filed in 1983.
The magnetic recording medium coating method shown in No. 259941 can be used.

First, the coating method will be explained using No. 11N. Coating liquid (a) 2 is pre-coated on a continuously running flexible support 1 of polyethylene terephthalate using a coating machine (A) 3, and immediately after that, the coated surface is smoothed using a smoothing roll 4,
A method can be used in which the next coating liquid (b) 5 is applied by another extrusion coating II (B) 6 while the coating liquid 2 is in a wet state at t17. Furthermore, the wet-on-wet coating method of the present invention is not limited to this method;
For example, an extrusion type simultaneous multilayer coating method shown in FIG. 2 may be used. Figure 2 shows coating liquid (a) 2 and coating liquid (b) on a flexible support 1 using a liquid injection device 8 for simultaneous multilayer coating.
5 is applied at the same time.

A magnetic layer coated on a non-magnetic support is usually subjected to a treatment for orienting the ferromagnetic powder in the magnetic layer, that is, a magnetic field orientation treatment, and then dried. Furthermore, after the resin component is cured to form a cured product, usually by heating or the like, a surface smoothing treatment can be performed if necessary. The magnetic recording medium that has been subjected to surface smoothing treatment is then subjected to plate treatment as desired, and then cut into a predetermined shape.

【Example〕

The present invention will be specifically explained below with reference to Examples.

All references to "parts" refer to "parts by weight."

Example (wet-on-wet method) % Formula % Crystallite size 400A, Hc 00Oe Ferromagnetic powder 1 for upper layer: Cor-FeOX, X(
-1,45, major axis length 0.2.
crm, crystallite size 300A, Hc 50Oe Upper layer ferromagnetic powder 2: Fe-Zn-Ni alloy, (
(Used in Example 2) Long axis length 0.2 μm 1 Crystallite size 200 A, Hc 1500 Oe Prescription a (Non-curing bonding side - Prescription) Prescription B (Curing bonding agent - Prescription) I Industrial use, 1,8 care acid 1 A magnetic paint is created by combining the above ferromagnetic powder and the recipe, and simultaneously multi-layer coated using an extrusion type coating head (Figure 2) with two slits in one head so that the bottom layer has a thickness of 4μ and the top layer has a thickness of 2μ. The film was subjected to orientation, drying, calendering, bulk thermosetting using a prescribed thermosetting binder, and slit into 2-inch pieces to obtain a VH3 type videotape.

The combination of ferromagnetic powder and formulation and the obtained results were
Shown in the table.

Comparative example (wet-on-dry method) A magnetic paint was created using the combination of the above ferromagnetic powder and prescription, and a lower layer of 4μ was coated using a gravure coater, smoothed, oriented, dried, calendered, and the prescribed curing system was combined. The side formulation was subjected to bulk thermo treatment to obtain a roll coated with the lower layer.

Using the obtained coated roll, use a gravure coating machine,
The upper layer was coated to a thickness of 2μ, smoothed, oriented, and dried.

When Formulation A (non-curing binder, formulation) was used for the lower layer formulation, some of the lower layer mixed with the upper layer during smoothing the application of the upper layer, resulting in very poor surface properties and uneven coating thickness. I couldn't get what I wanted.

■Glossiness Glossiness measured at an incident angle of 45° and a reflection angle of 45° in the coating direction on the surface of the magnetic layer.

Measuring machine: Suga Test Instruments KK GK-45D used A 718
0% or more B: 160-179% C: 130-159% D 7100-129% E: 99% or less ■Adhesion Peel strength of magnetic layer of 1/2 inch wide tape.

A: 80 g or more B: 50 to 79 g C: 30 to 49 g D: 10 to 29 g E: 9 g or less ■V, S, (video sensitivity) The output of 5 MHz was compared with the SHG tape manufactured by Fuji Photo Film KK as OdB.

Measuring device: HR-D555 type deck made by Victor KK Japan A: 2. OdB~2.9dB B: 1. OdB~1.9dB ■Y S/N S/N ratio at 5 MHz, Fuji Photo Film KK S
The HG tape was compared in OdB.

Measuring device: Uses HR-0555 deck made by Victor KK Japan The severity was evaluated according to the criteria described below.

Good with A rainbow ivy and skinny.

B: There is an increase in both jitter and/or skew, although this is not a problem in actual use.

C There are a lot of lids and/or skews, which poses a problem in actual use.

■Durability Durability was examined in still mode.

A: 120 minutes or more B: 60 to 119 minutes C: 30 to 59 minutes D: 10 to 29 minutes E: 9 minutes or less The multilayer tape 11kL1, which uses a curable binder in the upper magnetic layer, has a high degree of gloss, which is an index of the surface properties of the magnetic layer (it can be seen that the surface properties are good).

In addition, it has good adhesion, good electromagnetic conversion characteristics indicated by v, s, and ys, and excellent running properties and durability.

On the other hand, multilayer tapes C-15O-2 and C-5 in which a non-hardening binder is used in the upper layer have significantly poor durability and are not preferred.

Both the lower and upper magnetic layers are made of MC using a hardening binder.
-3 and C-7 have particularly poor adhesion, and also do not have particularly excellent phase conversion properties.

Wet-on-dry coated products NaC-4 and C-6, in which a non-hardening binder was used for the lower magnetic layer, could not be used as magnetic recording media because the upper magnetic layer could not be coated properly.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a sequential coating method, which is an example of a wet-on-wet coating method for carrying out the coating of the present invention;
FIG. 2 is also an explanatory diagram of the simultaneous multilayer coating method. DESCRIPTION OF SYMBOLS 1... Flexible support, 2... Coating liquid (a), 3...
... Coating 8 (A), 4... Smoothing roll, 5... Coating liquid (b), 6... Coating machine (B), 7
... Backup roll, 8... Simultaneous multilayer coating liquid device. Patent applicant Fuji Photo Film Co., Ltd. Figure 1 Figure 2 1986/Month? sunset

Claims (8)

[Claims] (1) In a magnetic recording medium having a plurality of magnetic layers formed by dispersing ferromagnetic powder in a binder on a non-magnetic support,
A magnetic recording medium characterized in that the binder in the lower magnetic layer is a non-hardening binder, and the binder in the upper magnetic layer is a hardening binder. (2) The magnetic recording medium according to claim 1, characterized in that the upper magnetic layer contains a polyisocyanate compound as a curing component of the curing binder. (3) The magnetic recording medium according to claim 1, wherein the coating thickness of the upper magnetic layer is 0.1 to 2 μm. (4) The magnetic recording medium according to claim 1, wherein the coating thickness of the upper magnetic layer is 0.1 to 1 μm. (5) The magnetic recording medium according to claim 1, wherein the thickness of the upper magnetic layer is thinner than the thickness of the lower magnetic layer. (6) The coercivity (Hc) of the upper magnetic layer is 600 to 250
2. The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium is 0 Oe. (7) The coercive force (Hc) of the upper magnetic layer is 800 to 200
2. The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium is 0 Oe. (8) Claim 1, characterized in that a plurality of magnetic layers are coated simultaneously or sequentially by a wet coating method.
Magnetic recording medium described in Section 1.