JPH01220122A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having excellent durability without losing dispersion stability and boundary face reinforcing characteristic by incorporating a silane coupling agent having an alkoxyl group and carboxyl group into a magnetic layer formed on the nonmagnetic base of the magnetic recording medium so that said coupling agent well bonds the magnetic layer and a binder. CONSTITUTION:The magnetic layer essentially consisting of magnetic powder and the binder is formed on the nonmagnetic base 1 of the magnetic recording medium and the magnetic layer 2 contains the silane coupling agent having the alkoxyl group and the carboxyl group. The silane coupling agent bonds well to the magnetic layer 2 and the binder to prevent the bonding of additives such as lubricating agent and dispersant to the magnetic powder. The durability of the magnetic recording medium is thus improved without losing the dispersion stability and boundary face reinforcing characteristic.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks, and particularly relates to improving the dispersibility of magnetic powder mixed in a magnetic layer. be.

[Summary of the invention]

The present invention provides a magnetic recording medium having a magnetic layer mainly composed of magnetic powder and a binder, by incorporating a silane coupling agent having an alkoxyl group and a carboxyl group into the magnetic layer, thereby improving the dispersibility of the magnetic powder. The aim is to improve the deterioration of electromagnetic conversion characteristics and improve the durability of the coating film.

[Conventional technology]

Magnetic recording media are moving toward higher density recording year by year. Under these circumstances, in the magnetic layer, magnetic powder with an extremely fine particle size is highly dispersed in the binder resin, making the surface of the magnetic layer mirror-finished, improving the electromagnetic conversion characteristics, and at the same time improving the magnetic properties. There is a need to improve the durability of paint films.

That is, in the above magnetic recording medium, how well the magnetic powder contained in the magnetic layer is dispersed in the paint;
Furthermore, it is a very important issue how well the magnetic powder contained in the magnetic layer can be bonded to the binder.

Conventionally, as a method to satisfy the above requirements, a so-called dispersant (for example, a surfactant) is added to the magnetic paint to bond the hydrophilic groups of the surfactant with the hydrophilic groups of the magnetic powder, and then It has been proposed to bond the magnetic powder and the binder by bonding the lipophilic group of the activator and the lipophilic group in the binder, thereby improving the durability and dispersibility of the magnetic powder. ing. However, in this method, since the lipophilic group of the dispersant has no polarity, the bonding force with the binder is very weak, and the interface reinforcing function is not fully exhibited. Additionally, if an excessive amount of dispersant is added in order to exert its interface reinforcing function, the binder may become plasticized or the dispersant may precipitate on the surface of the coating film, resulting in a significant lack of durability of the coating film. There is.

In response to this, in recent years, a method of introducing a polar group into a binder has been proposed, and a technique has been proposed in which the binder has both the functions of a polymer, a dispersant, and an interface reinforcing agent. However, when attempting to introduce a polar group into the binder to strengthen the interface with the magnetic powder as described above, the hydrophilic group of the polar group causes steric hindrance due to the function of the binder as a polymer. In addition, compounds with long-chain alkyl groups and fatty acids added to paints for the purpose of improving durability may not be able to sufficiently adsorb to the hydrophilic groups on the surface of the magnetic powder, resulting in deterioration of dispersibility. If agents, dispersants, etc. are present, they will preferentially be adsorbed to the magnetic powder, which will hinder the adsorption of the binder that has a dispersion function, resulting in problems such as deterioration of the dispersibility of the magnetic powder.

[Problem to be solved by the invention]

As mentioned above, in the field of magnetic recording media, there are various practical characteristics due to insufficient capacity of the binder used and the polar group added to it, and the relationship between the polar group and the surface characteristics of the powder. remains dissatisfied with.

Therefore, the present invention was proposed in view of the above-mentioned conventional situation, and aims to prevent the adsorption of lubricant to magnetic powder, improve the dispersibility of magnetic powder, reduce falling off, and improve electromagnetic conversion. The purpose is to provide a magnetic recording medium with excellent characteristics and durability.

[Means to solve the problem]

As a result of intensive research, the inventor of the present invention found that, in order to achieve the above object, instead of making the magnetic powder and the binder interact directly,
We have come to the knowledge that by bonding via a silane coupling agent containing an alkoxyl group and a carboxyl group, the affinity between the magnetic powder and the binder is significantly improved, and the dispersibility of the magnetic powder is dramatically improved. Ta.

The present invention has been made based on the above findings, and the present invention is based on the above findings.
As shown in the figure, in a magnetic recording medium having a magnetic layer (2) mainly composed of magnetic powder and a binder on a non-magnetic support (1), the magnetic layer (2) contains an alkoxyl group and a carboxyl group. It is characterized by containing a silane coupling agent having the following properties.

The present invention also provides a non-magnetic support (1
Applicable to a magnetic recording medium in which a magnetic layer (12) having the above-mentioned structure is formed on one surface of 1), and a back coat layer (13) mainly composed of non-magnetic powder and lubricant, etc. is formed on the other surface. You may.

The magnetic layer of the magnetic recording medium contains a silane coupling agent having an alkoxyl group and a carboxyl group as described above. The purpose of this silane coupling agent is to bond with the surface of the magnetic powder blended into the magnetic layer, thereby changing the apparent surface condition of the magnetic powder.

The above-mentioned silane coupling agent having an alkoxyl group and a carboxyl group contained in the magnetic layer means that -OR (R represents an alkyl group) in the silane coupling agent. is preferable, and if the carbon chain is long, hydrolysis will not be carried out well and it will not be possible to form a good chemical bond with the surface of the magnetic powder. It includes.

As such a silane coupling agent, ■(CLO)
*SiCtllJHCJaNHCLCOOHN-(3-
()suI toxysilyl)propyl] Phthal 7miFN
-()rimethoxysilylbu I'3) ethylenediaminetriacetic acid and the like.

In order to cause the silane coupling agent and the magnetic powder to react, for example, (a) a method of adding the silane coupling agent and the magnetic powder at the same time during the preparation of the magnetic coating film, (b) a method of adding the silane coupling agent and the magnetic powder at the same time in water; (c) A method in which magnetic powder is treated with a silane coupling agent in an organic solvent and then the organic solvent is dried; (d) [
There is a method in which a silane coupling agent is spray-mixed with a synthetic powder and then dried.

The amount of the silane cuff pulling agent containing alkoxyl groups and carboxyl groups added to the magnetic layer is 0.3 to 5 parts by weight (0.3 to 5 parts by weight) per 100 parts by weight of the 6n powder.
It is expressed as PHP. ) is preferably within the range. If the amount added is less than this range, the effect of adding a silane coupling agent containing alkoxyl groups and carboxyl groups cannot be expected, and if the amount added is increased, the coating film will tend to be acidic. , this leads to deterioration of the corrosion resistance of the magnetic recording medium.

By reacting the magnetic powder with the silane coupling agent by the method described above, the alkoxyl groups present in the silane coupling agent molecules are hydrolyzed to form -5i-0-, which forms the magnetic powder. chemically bonds well with the surface of As a result, the carboxyl group, which is the other polar group present in the silane coupling agent molecule, covers the surface of the magnetic powder, and the magnetic powder appears to be in an acidic state (a state in which there are sufficient protons). .

This makes it possible to prevent adsorption of fatty acids added to the magnetic powder, for example, to impart lubricity to the magnetic layer, and also to bring out an excellent lubricating effect even when a small amount of the fatty acids is added.

Furthermore, the carboxyl groups that give the surface of the magnetic powder an apparently earthy acidic state bond well and firmly to the binder resin constituting the magnetic layer, making it possible to form a coating film with excellent durability. Therefore, the magnetic powder does not come off even when the magnetic recording medium slides, and durability can be improved. Note that since the surface of the magnetic powder is in an acidic state as described above, it is more preferable to use a binder resin with a basic polar group introduced therein, which is highly effective in improving durability.

Examples of the magnetic powder whose surface is covered with the silane cuff pulling agent include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, macrogonal barium ferrite fine particles, iron nitride, and the like.

The above-mentioned ferromagnetic iron oxide particles are those whose value of X is in the range of 1.33≦X≦1.50 when expressed by the general formula FeOx, that is, magnetite (γ-Fe2oz 1X=1.
50), magnetite (PesOn, X = 1
．． 33) and their solid solutions (FeOx, 1.33<X
<1.50). Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.
There are different types.

The above-mentioned ferromagnetic chromium dioxide may include CrO2 or Ru for the purpose of improving the coercive force thereof.

A material to which at least one of Sn, Te, Sb, Fa, Ti, V, Mn, etc. is added can be used.

Examples of the ferromagnetic alloy powder include Fe, Co, and Ni.

Fe-Co, Fe-Ni, Fe-Co-Ni, C.

-Ni, Fe-Co-B, Fe-Co-Cr-B.

Mn-B i, Mn-Al1. Fe-Co-V, etc. can be used, and Aj! can be used to improve various properties of these materials. , Si, Ti, Cr, Mn, Cu, Zn, and other metal components may be added.

In addition to the above-mentioned magnetic powder, various powders such as abrasives, inorganic pigments, and carbon may be added to the magnetic layer, and in this case, due to the action of the silane coupling agent contained in the binder, As in the case of magnetic powder, the alkoxyl groups present in the silane coupling agent molecules are hydrolyzed to form -5i-0-, which forms a good chemical bond with the surface of the powder. As a result, the carboxyl group, which is the other polar group present in the silane coupling agent molecule, covers the surface of the powder, giving the powder an earthy acidic appearance. Therefore, a good and strong bond is formed with the binder constituting the magnetic layer, improving the dispersibility of the powder and reducing the amount of powder falling off.

In the magnetic recording medium of the present invention, the magnetic layer may be formed, for example, by dispersing the above-mentioned magnetic powder in a binder and dissolving it in an organic solvent, and applying a magnetic paint to the surface of the non-magnetic support.

Here, as the binder for dispersing the magnetic powder, any resin that is normally used as a binder for this type of magnetic recording medium can be used, but if the surface of the magnetic powder is Considering that the coating creates an acidic state, it is desirable to use a binder with a basic polar group introduced therein in order to maximize its effect.

As the binder, a commonly used binder without a polar group introduced therein as described above may be used alone, or a resin into which a basic polar group is introduced may be used alone. Furthermore,
A combination of a binder with a basic polar group introduced and a binder with no polar group introduced, a combination of different resins with a basic polar group introduced, and a binder with a basic polar group introduced. Any combination with a binder into which other polar groups (acidic polar groups or neutral polar groups) have been introduced can be used. In addition, in the combination of a resin into which a basic polar group has been introduced and a resin into which no polar group has been introduced,
It is necessary that resins into which basic polar groups have been introduced are combined in a proportion of at least 10% or more.

Examples of such resins include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, and vinyl chloride. −
Acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin, polyfluoride vinyl chloride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative.

Examples include binder resins such as styrene-butadiene copolymers, polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, or mixtures thereof.

In addition, when a basic polar group is introduced into these resins, the basic polar group to be introduced is (a) -C1l
z-9H-NH.

(b) Primary amines (-NH2), secondary amines (-NRH), and tertiary amines (-NRz) introduced in the form of -NHCH, CH, -, etc.,
It may be introduced in the form of a quaternary ammonium salt (NR4.X).

Alternatively, it may be introduced in the form of a heterocycle such as the following.

Furthermore, it may be introduced in the form of a Schiff base (:C=N-) as shown in the following, or it may be introduced in the form of a diazo group (-N, N-). . That is, any binder may be used as long as it has a nitrogen atom having an unpaired electron as a polar group.

Any conventionally known method can be used to introduce the above-mentioned basic polar group. For example, a typical basic polar group such as tertiary amine or quaternary ammonium may be introduced into a condensation resin (for example, polyurethane). For introduction, (i) method using basic polar group-containing polyol, polyisocyanate, etc. as part of the chain extender, (ii) wi
A method that utilizes active hydrogen, etc. (e.g., hydroxyl group) remaining in the side chains or terminals of the synthetic resin and modifies it with a compound that has both a group that can react with active hydrogen and a basic polar group in the molecule, etc. Bye.

In addition, in order to introduce these polar groups into a copolymer resin such as a vinyl chloride resin, (iii) a basic polar group having a double bond that can be copolymerized with a vinyl monomer such as vinyl chloride, and an equal molecule of (iv) A method of introducing active hydrogen in advance and modifying it with a compound having both a group capable of reacting with active hydrogen and a basic polar group in the molecule, etc. In addition, other basic polar groups can also be introduced by the same method.

Note that the content of basic polar groups contained in the binder is 0. OO1m mol/g ~1.0 m +ao
It is preferably within the range of l/g.

Further, various additives that are normally added to the magnetic layer of this type of magnetic recording medium may be added to the magnetic layer. However, it is preferable to add various additives to an extent that does not interfere with the effect of adding the silane coupling agent containing an alkoxyl group and a carboxyl group.

As mentioned above, magnetic powder, a silane coupling agent containing an alkoxyl group and a carboxyl group added to make the surface of the magnetic powder acidic, and various other additives normally used in the magnetic layer of a magnetic recording medium. When forming a magnetic layer by coating a paint consisting of a binder and a binder for dispersing these, it is sufficient to dissolve the coating material in a 81 solvent and then coat it on a non-magnetic support.

Examples of the organic solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, methyl acetate, and ethyl acetate.

Ester systems such as butyl acetate, ethyl lactate, glycol acetate monoethyl ether, glycol dimethyl ether,
Glycol monoethyl ether, glycol ethers such as dioxane, benzene.

Examples include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, and chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. .

On the other hand, the surface opposite to the magnetic layer forming surface formed as described above has an antistatic function and a friction image fJ1. A back coat layer may be formed for the purpose of improving performance, and further, preventing scratches (improving durability).

The above-mentioned back coat layer is formed by dispersing non-magnetic powder in a binder, dissolving it in a ferromagnetic solvent to prepare a coating material, and coating it on the surface opposite to the surface on which the magnetic layer is formed. It is formed.

As the non-magnetic powder constituting the back coat layer, any powder commonly used as non-magnetic powder for this type of magnetic recording medium can be used, such as contact black, channel black, roll black, disk black, All kinds of carbon black such as furnace black, thermal black, lamp black, CaC01 powder, B a S Oa powder, ZnO powder,
a-Fe20 powder, Tie, powder, A It t O
Examples include non-magnetic powders such as x powder and crzoz powder.

Further, in the back coat layer, as well as in the magnetic layer, any of the various additives that are commonly added can be used.

In addition, the back coat layer also contains alkoxyl groups and carboxyl groups in the same manner as the magnetic layer in order to improve the dispersibility of the non-magnetic powder used in the back coat layer and to prevent the non-magnetic powder from separating. A silane cuffing agent may also be added.

The materials for the non-magnetic support constituting the magnetic recording medium according to the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, and cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate. , polyvinyl chloride, vinyl resins such as polyvinylidene chloride, polycarbonate polyimide.

Examples include plastics such as polyamideimide, light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass. The nonmagnetic support may be in any form such as a film, sheet, disk, card, or drum.

[Effect]

The silane cuffing agent containing an alkoxyl group and a carboxyl group used in the present invention has a strong bond with the magnetic powder, and a carboxyl group that bonds well with the binder. It has a remarkable effect on powder dispersibility and interface reinforcement.

Further, since the surface of the magnetic powder is covered with the carboxyl group of the silane coupling agent containing an alkoxyl group and a carboxyl group, the surface of the magnetic powder appears to be in an earthy acid state. This prevents adsorption of additives with oxygen-donating atomic groups such as fatty acids to the magnetic powder, and as a result, the coating film is completed without losing the dispersion stability of the magnetic powder or interfacial reinforcement, and has high magnetic properties. , a coating film with excellent durability is completed.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Co T -FezOs 1 on blood removal team
2 parts by weight Cr, 030
．． 6 parts by weight carbon 0.6
Part by weight Stearic acid 0.06 part by weight Butyl stearate 0.12 part by weight Silane cuff pulling agent 0.24 part by weight ((CH30) 5sicJJHcJaNHcHzcO
OH) Vinyl chloride Vinyl acetate resin 1 part by weight Urethane resin 2 parts by weight (contains 0.3 nmol/g of tertiary amine group) Methyl ethyl ketone 30 parts by weight The above composition was mixed in a ball mill for 48 hours and then taken out through a filter.
This magnetic layer paint was applied to the back side of a polyethylene terephthalate film having a thickness of 12 μm so that the thickness after drying would be 5 μm, and after magnetic field orientation, the film was wound up. This was calendered and then cut to a width of 172 inches to produce a sample tape.

Disaster Management Team 1 The silane coupling agent used in Example 1 was
A resample tape was prepared in the same manner as in Example 1, except that (3-()rimethoxysilyl)propyl]phthalamide was used.

The silane coupling agent used in Sotabienyu Example 1 was N-
A sample tape was prepared in the same manner as in Example 1 except that (trimethoxysilylpropyl)ethylenediaminetriacetic acid was used.

A sample tape was prepared in the same manner as in Example 1, except that the silane coupling agent used in Comparative Tsubagi Example 1 was not used.

For each sample tape produced as described above, gloss, powder removal, friction coefficient, magnetic flux density Bm, squareness ratio Rs
, the coercive force Hc was measured.

The above gloss was measured using a gloss meter with an incident angle of 75° and a reflection angle of 75°.
The reflectance at 100°C was measured. In addition, for powder falling, visually observe the amount of powder falling on the head drum, guide pin, etc. after running the shuttle 100 times for 60 minutes, and give θ points for those with almost no powder falling off, and 15 points for those with a large amount of falling powder. evaluated.

Furthermore, the friction coefficient is
The friction coefficient (load W = 50 g>) between the magnetic layer surface and the IS stainless steel in e) was measured.Furthermore, the magnetic properties were measured in a magnetic field of 2500 Gauss.

These results are shown in Table 1.

Table 1 As is clear from Table 1, the examples containing a silane cuff-pulling agent in the magnetic layer were compared with the comparative examples not containing the silane coupling agent in terms of gloss, powder dropout, and coefficient of friction. Very good results were obtained for both magnetic properties.

〔Effect of the invention〕

As is clear from the above explanation, in a magnetic layer containing a silane coupling agent containing an alkoxyl group and a carboxyl group, the coupling agent bonds well with the magnetic layer and the binder, so lubricants and dispersants are used. It is possible to prevent additives such as the like from binding to the magnetic powder, and to complete a coating film with excellent durability without losing dispersion stability and interfacial reinforcing properties.

Therefore, by using this as the magnetic layer of a magnetic recording medium, it is possible to provide a magnetic recording medium with excellent electromagnetic conversion characteristics, coating durability, etc.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part showing an example of the structure of a magnetic recording medium to which the present invention is applied. FIG. 2 is an enlarged sectional view of a main part showing another example of the configuration of a magnetic recording medium to which the present invention is applied. ■, 11...Nonmagnetic support 2.12...Magnetic layer 13...Back coat layer Patent applicant Sony Corporation representative Patent attorney Akioka Kowa, Sakae Tamura - Masaru Sato Figure 1, Figure 2 (Departed from Tushuan Fuzheng Shue) June 23, 1986

Claims (1)

[Claims] A magnetic recording medium having a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, characterized in that the magnetic layer contains a silane coupling agent having an alkoxyl group and a carboxyl group. magnetic recording medium.