JPH0231319A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having a highly durable magnetic layer by incorporating a silane coupling agent having an amino group or mercapto group and a vinyl chloride copolymer having an epoxy group as a binder into the magnetic layer. CONSTITUTION:The silane coupling agent having the amino group or mercapto group adsorbs and bonds magnetic powder and nonmagnetic powder on one hand and generates a crosslinking structure with the epoxy group of the vinyl chloride copolymer which is the binder in the amino group or mercapto group on the other. The reaction to effect crosslinking is progressed by the effect of said epoxy group as well as the amino group or mercapto group with substantially no influence of moisture. The magnetic powder, nonmagnetic powder and the binder are, therefore, eventually coupled securely to each other via the silane coupling agent. The dislodgment of the magnetic powder, etc., are suppressed in this way and the durability of the magnetic layer is assured. The magnetic recording medium having the extremely good durability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, and particularly to improving the durability of a magnetic layer.

[Summary of the invention]

The present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, in which the binder constituting the magnetic layer is a vinyl chloride-based copolymer having an epoxy group. By using a polymer and mixing a silane coupling agent having an amino group or a mercapto group into the magnetic layer, the bond between the magnetic powder, non-magnetic powder, etc. and the binder is strengthened, and the magnetic This is intended to prevent powder from falling off and to improve the durability of the magnetic layer.

[Conventional technology]

In recent years, magnetic recording media, especially magnetic recording media for VTRs (video tape recorders), are required to have improved magnetic properties, electromagnetic conversion properties, etc. in order to obtain high playback output even when recording at short wavelengths. ing. Therefore, efforts have been made to make the magnetic powder particles finer and to increase the magnetic force, and the packing density of the magnetic powder in the magnetic layer has increased.

There is a growing tendency to increase so-called backing density.

By the way, as mentioned above, when the backing density of the magnetic powder increases, the ratio of the binder in the magnetic layer decreases significantly, which may cause problems such as peeling of the magnetic layer when used as a magnetic recording medium. There is a possibility that the strength of the layer may deteriorate. Therefore, in order to prevent such deterioration in the strength of the magnetic layer, it is necessary to improve the strength of the binder constituting the coating film.

Under these circumstances, a method has been proposed to improve the mechanical strength of a magnetic coating film by crosslinking the binder in the magnetic coating film. These include those that form a crosslinked structure using a compound that has a hydroxyl group, or those that form a crosslinked structure using a reaction between an active hydrogen of a hydroxyl group in a molecule and an isocyanate.

[Problem to be solved by the invention]

However, in the above-mentioned method of crosslinking a binder, the binder made of a compound having an electron beam-sensitive bond requires very expensive equipment in order to form a crosslinked structure, and is therefore impractical.

On the other hand, with a binder in which the active hydrogen of the hydroxyl group reacts with an isocyanate compound etc. to form a crosslinked structure, NCO+-OH
→ −N) ICO, whereas in reality NGO+ 1(to −NH! + cot
The isocyanate group preferentially reacts with water, as shown in the following reaction formula, and the produced amino group reacts with other isocyanate groups, as shown in the following equation. arise. In other words, when attempting to form a crosslinked structure by the reaction between an isocyanate compound and a hydroxyl group, the isocyanate group in particular is easily affected by moisture, and the isocyanate group that substantially contributes to crosslinking decreases, resulting in insufficient There is a possibility that a crosslinked structure cannot be formed.

As described above, the mechanical strength of the coating film is increased by forming a crosslinked structure using a binder that forms a crosslinked structure through electron beam sensitive bonding and increases the mechanical strength of the coating film, and by using the reaction between isocyanate and hydroxyl group. However, there are problems with binders and the like that lack practicality due to equipment issues, and the reaction itself is susceptible to moisture and does not form a good crosslinked structure.
Magnetic recording media using these as binders still have some dissatisfaction, such as insufficient durability.

Therefore, the present invention has been proposed in order to eliminate the above-mentioned drawbacks in these technical fields, and provides a binder that exhibits a good crosslinked structure without being affected by moisture when forming a crosslinked structure. Another object of the present invention is to provide a magnetic recording medium having a magnetic layer with excellent durability by ensuring a strong bond between magnetic powder or non-magnetic powder and a binder.

[Means to solve the problem]

The inventors of the present invention have conducted intensive research over a long period of time in order to achieve the above-mentioned objectives, and have found that a binder made of a vinyl chloride copolymer having an epoxy group has excellent crosslinking properties, and that the silane coupling agent described above can be used as a binder. By introducing surface-treated magnetic powder and non-magnetic powder into a vinyl chloride-based copolymer having an epoxy group, these magnetic powder and non-magnetic powder are bonded to a vinyl chloride-based copolymer which is a binder through the silane coupling agent. The present invention was completed based on the discovery that it binds strongly to copolymers and is very effective in improving the durability of coating films.

That is, the present invention provides a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, in which the magnetic layer contains a silane coupling agent having an amino group or a mercapto group. It is characterized by containing a vinyl chloride copolymer having an epoxy group as a binder.

The silane coupling agent used here is a group that can react with the epoxy group introduced into the binder in order to strengthen the bond with the binder described below.

That is, it shall have either an amino group or a mercapto group.

Therefore, usable silane coupling agents include, for example, those represented by the general formula %() (n is an integer of 0 to 2, R represents an alkyl group such as CHs, CHsCHz, etc.). Specifically, γ-aminopropyltriethoxysilane, N-(β-aminoethyl)
-T-aminopropyltrimethoxysilane, N-(β-
(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, etc., manufactured by Toshiba Silicone Co., Ltd., TSL8331. ↑5
L8340. TSL8345 and Nippon Unicar Co., Ltd.
There are A-1100, A-1120, etc.

The amount of the silane coupling agent to be added (or the amount to be treated) may be set appropriately depending on the type of magnetic powder and non-magnetic powder, the amount of epoxy groups introduced into the binder described below, etc., but usually The amount may be 0.2 to 10 parts by weight per 100 parts by weight of magnetic powder (or non-magnetic powder).

These silane coupling agents can be mixed into the magnetic paint when preparing the magnetic paint, but in particular, the magnetic powder and non-magnetic powder (such as abrasives) should be surface-treated with these silane coupling agents in advance. By doing so, even greater effects can be expected.

To treat the surface of magnetic powder or nonmagnetic powder using the above-mentioned silane coupling agent, for example, the following method may be used. That is, first, magnetic powder is dehydrated using a dehydrated solvent under high temperature conditions, and then reflux treatment is performed under high temperature conditions using the above-mentioned amino group- or mercapto group-containing silane coupling agent to surface-treat the magnetic powder. After that, the surface-treated magnetic powder may be washed using a washing solvent and dried by air drying.

Vinyl chloride copolymers with epoxy groups are mainly composed of vinyl chloride compounds, and the epoxy groups and double bonds that can be copolymerized with vinyl chloride compounds are introduced to form a crosslinked structure. It is obtained by copolymerizing a monomer having

Vinyl chloride compounds constituting the vinyl chloride copolymer include vinyl monomers such as vinyl chloride, vinyl acetate, vinyl propionate, vinyl alcohol, methyl vinyl ether, isobutyl vinyl ether, and cetyl vinyl ether, methyl (meth)acrylate, ( meth)ethyl acrylate.

Propyl (meth)acrylate, Isopropyl (meth)acrylate, Butyl (meth)acrylate.

(meth)acrylic acid lauryl, (meth)acrylic acid-2
- Acrylic monomers such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, and acrylic acid ester; vinylidene monomers such as vinylidene chloride and vinylidene fluoride; one or more of these monomers can be copolymerized. are available.

In addition, examples of monomers having a double bond copolymerizable with the vinyl compound and having an epoxy group introduced to form a crosslinked structure include unsaturated monomers such as allyl glycidyl ether and methacryl glycidyl ether. Glycidyl ethers of alcohol, glycidyl acrylate,
Glycidyl esters of unsaturated acids such as glycidyl mequaacrylate, glycidyl-p-vinylbenzoate methylglycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene monooxide, vinylcyclohexene monooxa, ido, 2-methyl-5,
Examples include epoxide olefins such as 6-epoxyhexene.

Further, the vinyl copolymer may be copolymerized with another monomer having a double bond copolymerizable with the vinyl compound in order to improve its properties. Examples of such monomers include butadiene monomers such as 1,3-butadiene, maleic acid anhydride, diethyl maleate, phthylhenzyl maleate, and di-2 maleic acid.
-Hydroxyethyl, dimethyl itaconate, styrene,
Examples include α-methylstyrene, p-methylstyrene, acrylonitrile, ethylene, propylene, and the like.

The amount of epoxy groups contained in the vinyl copolymer is preferably about 0.05 to 2.0 m tsol/g. If the amount of epoxy groups is less than the above range, the crosslinked structure will be insufficient and the durability will deteriorate.
On the other hand, if the amount is too large, problems such as poor handling and difficulty in forming a coating will occur.

By further adding a tertiary amine compound to the binder used in the magnetic recording medium of the present invention, the ring-opening reaction of the epoxy group of the vinyl chloride copolymer can be promoted.
It is also possible to form a crosslinked structure between vinyl chloride copolymers by crosslinking them with active hydrogen (eg, hydroxyl group) contained in the vinyl chloride copolymers by utilizing the ring-opening reaction. Of course, it is also possible to form a similar crosslinked structure with the hydroxyl groups contained in the polyurethane resin. By using the crosslinked structure between the vinyl chloride copolymer and the polyurethane resin in combination with the crosslinked structure between the vinyl chloride copolymers as described above, a magnetic coating film with even greater strength can be obtained.

Furthermore, the binder used in the magnetic recording medium of the present invention includes:
It is also possible to form a crosslinked structure by adding polyisocyanate as a curing agent and utilizing the reaction between this polyisocyanate and the hydroxyl group in the vinyl chloride copolymer or the hydroxyl group in the polyurethane resin. By using it in combination with a crosslinked structure based on mercapto groups, a magnetic coating film with even greater strength can be obtained.

The above-mentioned epoxy group-containing vinyl chloride copolymer may be used in combination with other binders.

As such other binders, those conventionally used as binders for magnetic recording media can be used, such as vinyl chloride-vinyl acetate copolymer.

vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinylacetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer Polyvinyl butyral, cellulose derivatives, styrene-butadiene copolymers, polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins.

Examples include urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof.

Among these, polyurethane resins, polyester resins, acrylonitrile butadiene copolymers, etc., which are said to impart flexibility, are preferred.

A hydrophilic polar group may be introduced into the epoxy group-containing vinyl chloride copolymer or other binder used in combination for the purpose of further improving dispersibility. , -0502M group, PO(
OM')z group, -C00M group, NIhX group (however, M
is a hydrogen atom or an alkali metal atom, M″ is a hydrogen atom,
R represents an alkyl group, and X represents a halogen. ) etc.

In the present invention, by adding magnetic powder or non-magnetic powder surface-treated with the above-mentioned amino group- or mercapto-group-containing silane coupling agent to a binder mainly composed of a vinyl chloride copolymer having an epoxy group, The amino group and mercapto group of the silane coupling agent interact with the epoxy group in the binder, and the method involves graft polymerization of the amino group and mercapto group of the silane coupling agent and the epoxy group of the binder. By doing so, an even stronger bond can be achieved.

In the magnetic recording medium of the present invention, the magnetic layer includes, for example, a magnetic powder surface-treated with a silane coupling agent having an amino group or a mercapto group as described above, a non-magnetic powder, and a vinyl chloride copolymer having an epoxy group. It may be formed by coating the surface of a non-magnetic support with a magnetic paint prepared by dispersing it in a binder and an organic solvent.

Here, the material for the non-magnetic support may be any material that is normally used in this type of magnetic recording medium, such as polyesters such as polyethylene terephthalate, polyolefins such as polyethylene, polypropylene, etc. cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide, and polyamideimide;
Examples include paper, metals such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon. Examples of the forms of this non-magnetic support include film and tape.

Any of sheet disks, cards, drums, etc. may be used.

Moreover, any ordinary ferromagnetic powder can be used as the ferromagnetic powder used in the magnetic layer. Therefore, ferromagnetic powders that can be used include ferromagnetic iron oxide particles,
Examples include ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, iron nitride, and the like.

As the above-mentioned ferromagnetic iron oxide particles, when expressed by the -i formula Fe OX, the value of X is in the range of 1.33≦X≦1.50, that is, maghemite (γ-Fed, x=1. 5
0) ,? Gnetite (Fe○, x=1.33) and their solid solutions (F e O,, 1,33 < x <
1.50).Furthermore, these ferromagnetic iron oxides have
Cobalt may be added for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide may include CrO□ or Ru for the purpose of improving the coercive force thereof.

A material containing at least one of Sn, Te, Sb, Fe, Ti, V, Mn, etc. can be used.

As the ferromagnetic alloy powder, Fe, Co, NiFe-Co
, Fe-Ni, Fe-Co-Ni.

Co-Ni, Fe-Co-B, Fe-Co-C
rB, Mn-B1. Mn-Aj! , Fe-Co-V
Af, Si, Ti, Cr, Mn, Cu, etc. can be used for the purpose of improving various properties.

A metal component such as Zn may also be added.

In addition to the binder and ferromagnetic powder, the magnetic layer also contains additives such as a dispersant, a lubricant, an abrasive, an antistatic agent,
A rust preventive agent or the like may be added. These dispersants, lubricants,
Any conventionally known abrasives, antistatic agents, and rust preventives can be used.

Examples of the dispersant include fatty acids such as phosphoric acid esters and caprylic acid, metal soaps made of alkali metals or alkaline earth metals of the fatty acids, and the like.

Examples of the lubricant include silicone oil such as phenylpolysiloxane, conductive fine powder such as graphite, and plastic fine powder such as polyethylene.

Examples of the abrasive include molten alumina, corundum, silicon carbide, and diamond.

Examples of the antistatic agent include conductive fine powder such as carbon blank, natural surfactants such as saponin, nonionic surfactants such as glycerin, and cationic surfactants such as phosphoniums.

Examples of the rust preventive include phosphoric acid, sulfide, guanidine, pyrimidine, amine, urea, zinc chromate, calcium chromate, strontium chromate, and the like.

The above-mentioned constituent materials of the magnetic layer are prepared as a magnetic paint by dissolving them in a solvent, and are coated on a non-magnetic support. Examples of the solvent for the magnetic paint include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. ketone solvents, methyl acetate, ethyl acetate, butyl acetate,
Ethyl lactate.

Ester solvents such as acetic acid glycol monoethyl ether, glycol ether type t91 such as glycol dimethyl ether, glycol monoethyl ether, dioxane, etc.
F1, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, aliphatic hydrocarbon solvents such as hexane and heptane, and organic solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Examples include chlorine compound solvents.

Note that the vinyl chloride copolymer having an epoxy group and the silane coupling agent having an amino group or a mercapto group may be used not only for the magnetic layer but also for the back coat layer, etc. In this case as well, As with the case, effects can be expected in terms of durability, etc.

The crosslinking reaction due to the action of the to group proceeds almost unaffected by moisture.

Therefore, the magnetic powder, non-magnetic powder, etc. and the binder are firmly bound together via the silane coupling agent.

This prevents the magnetic powder and the like from falling off and ensures the durability of the magnetic layer.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[Effect]

A silane coupling agent having an amino group or a mercapto group adsorbs and bonds with magnetic powder and non-magnetic powder, and also binds the amino group or mercapto group with the epoxy group of the vinyl chloride copolymer that is the binder. A cross-linked structure appears.

First, a vinyl chloride copolymer as a binder was synthesized.

The composition of the synthesized vinyl chloride copolymer and the amount of epoxy group introduced are shown in Table 1.

(Margins below) Table 1 Magnetic recording media were produced using these synthesized vinyl chloride copolymers, and the following two methods were used for processing them.

Kabutojib Kunin magnetic powder (metal magnetic powder, specific surface area 52rrr/g)
100 parts by weight, silane coupling agent (type and amount added are as shown in Table 2) and 200 parts by weight of methyl ethyl ketone
Parts by weight were placed in a flask equipped with a condenser and mixed at 80°C for 1 hour, followed by washing with a large amount of methyl ethyl ketone to obtain treated magnetic powder.

Next, a magnetic paint was prepared by mixing the following composition in a ball mill for 488 hours, and then adding 4.8 parts by weight of a hardening agent (trade name Corone L) and mixing for 30 minutes.
This was applied onto a polyethylene terephthalate film having a thickness of 14 μm so that the film thickness after drying was 6 μm. After magnetic field orientation treatment, drying and winding, and further supercalender treatment,
A sample tape was prepared by heating at 60° C. for 20 hours and cutting into 1/2 inch width. The composition of the magnetic paint is shown below.

Treated magnetic powder Vinyl chloride copolymer 100 parts by weight 18 parts by weight Polyurethane resin A42tOi (abrasive) Carbon black (antistatic agent) Stearic acid (lubricant) Butyl stearate (lubricant) Methyl ethyl ketone Toluene cyclohexanone 6 parts by weight 5 parts by weight Part 3 parts by weight 1 part by weight 1 part by weight 100 parts by weight 60 parts by weight 60 parts by weight The above polyurethane resin is polybutane adipate.
It is an MDI system, and the -3OJa group is Q, 05m mol/
It has an average molecular weight of 24,000.

Sotori law magnetic powder (Co adhesion - F e gos + specific surface area 3
5rrr/g) 100 parts by weight, silane coupling 7PI (type and amount added are shown in Table 2), 0.5 parts by weight myristic acid, 60 parts by weight methyl ethyl ketone, 40 parts by weight toluene and 40 parts by weight cyclohexanone. The mixture was then combined in a ball mill for 4 hours.

Next, this was added to a composition having the following composition, and the mixture was heated in a ball mill for 20 hours.

Vinyl chloride copolymer 18 parts by weight Polyurethane resin 6 parts by weight (manufactured by Nippon Polyurethane Co., Ltd., N-2304) AfzOh (abrasive)
3 parts by weight carbon black (antistatic agent) 2 parts by weight dimethylmyristylamine (
Lubricant) 1 part by weight Butyl stearate (lubricant)
1 part by weight methyl ethyl ketone
40 parts by weight toluene 2
1 part cyclohexanone 20 parts by weight This was coated on a 14 μm thick polyethylene terephthalate film so that the film thickness after drying would be 6 μm, subjected to magnetic field orientation treatment, dried and wound up. After further supercalendering, the tape was heat-treated at 75°C for 20 hours and cut into a 172-inch width to prepare a sample tape.

According to the above method, the type of vinyl chloride copolymer, the treatment method, the type and amount of silane coupling agent are
Various sample tapes were created with the changes shown in the table.

Table 2 shows the type of vinyl chloride copolymer used in each of the sample tapes produced (Examples 1 to 7, Comparative Examples 1 to 4).

In the table, silane coupling agent A is T-aminopropyltriethoxysilane, B is N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, and C is T-mercaptopropyltrimethoxysilane.

(Margin below) Table 2 For each sample tape obtained, Still characteristics and powder drop were measured.

In addition, the above still characteristics are 4.2MHz for the sample tape.
The video signal was recorded, and the time until the playback output attenuated to 50% was taken as the time. Further, powder falling was evaluated by visually observing the amount of falling powder on the head drum, guide, etc. after running the shuttle 100 times for 60 minutes, and using a point deduction method (-5 to 0). 3rd result
Shown in the table.

(The following is a blank space) Table 3 As is clear from the above Table 3, it can be seen that the sample tapes according to the present invention not only had less powder falling, but also had significantly improved still characteristics.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since a silane coupling agent having an amino group or a mercapto group is added to the magnetic layer and a vinyl chloride copolymer having an epoxy group is used as a binder,
A cross-linked structure is developed between the vinyl chloride copolymer and the silane coupling agent, and the magnetic powder, non-magnetic powder, etc. are firmly bonded to the binder via the silane coupling agent, so that the coating film is It is possible to increase the strength and significantly improve the durability of the magnetic recording medium.

In addition, since this reaction proceeds almost unaffected by moisture, the crosslinked structure is reliably achieved and a magnetic coating film with very good durability can be obtained.

Patent applicant: Sony Corporation

Claims (1)

[Scope of Claims] A magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed on a non-magnetic support, wherein the magnetic layer has a silane coupling agent having an amino group or a mercapto group. 1. A magnetic recording medium comprising, as a binder, a vinyl chloride copolymer having an epoxy group and an epoxy group.