JPH01196721A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility of nonmagnetic powder in a back coat layer and to decrease the drop-outs thereof by using a specific resin as the binder of said layer. CONSTITUTION:A magnetic layer 2 is formed on one face of a nonmagnetic base 1 and the back coat layer 3 essentially consisting of the nonmagnetic powder (e.g.: carbon black) and the binder (A) is formed on the other face. A resin having a residual aminocarboxylic acid {e.g.: -NH(CH2)nCOOH} in the molecule is used for the binder A and a residual iminocarboxylic acid group and residual pyridine carboxylic acid group may be used as well. These resins are formed by bringing the compd. having the above-mentioned residual group into reaction with a condensation resin or the components thereof or by copolymerizing a monomer having the above-mentioned residual group with a vinyl monomer.

Description

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

[Summary of the invention]

The present invention achieves the following by introducing aminocarboxylic acid residues into the binder of the hack coat layer that constitutes the magnetic recording medium
The aim is to improve the dispersibility of non-magnetic powder and reduce its shedding, thereby improving the deterioration of electromagnetic conversion characteristics and improving the durability of the coating film.

[Conventional technology]

In the bank coat layer formed on the side opposite to the magnetic layer formation side of the magnetic recording medium, non-magnetic powder such as carbon with a fine particle size is highly dispersed to control the surface roughness of the back side. The aim is to improve the winding properties of magnetic recording media, to improve the durability of the bank surface to reduce dropout and the coefficient of friction, and to prevent charging of non-magnetic supports. There are demands for preventing the adhesion of dust and improving running stability, and for reducing the transfer of lubricant in the magnetic layer.

That is, how well the non-magnetic ↓5) powder contained in the back coat layer in the hack coat layer for magnetic recording media can be dispersed in the paint, and how well can it be mixed with the binder. How to combine them is a very important issue.

Conventionally, as a method to satisfy the above requirements, a so-called dispersant (for example, a surfactant) is added to the back coat layer coating material, and the hydrophilic group of the surfactant and the hydrophilic group of the non-magnetic powder are bonded. Furthermore, by bonding the lipophilic group of the surfactant with the lipophilic group in the binder, the non-magnetic powder and the binder are bonded, improving durability and dispersibility of the non-magnetic powder. It is proposed that 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, and furthermore, the nonmagnetic powder is detached. 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 as described above and thereby reinforcing the interface with the non-magnetic powder, the hydrophilic group of the polar group interferes with the function of the binder as a polymer. Due to steric hindrance, it is not possible to sufficiently adsorb to the hydrophilic groups on the surface of the non-magnetic powder, resulting in deterioration of dispersibility.
Additionally, if there are compounds with long-chain alkyl groups, fatty acids, various lubricants, dispersants, etc. added to the paint for the purpose of improving durability, etc., these will preferentially be adsorbed to the non-magnetic powder. This causes problems such as impeding the adsorption of the binder having a dispersion function and deteriorating the dispersibility of the non-magnetic powder.

Furthermore, there are various types of non-magnetic powder, and each type has different surface properties, so simply introducing a polar group into the binder is not sufficient to handle each type of non-magnetic powder. It is not possible to ensure adequate dispersibility and durability.

[Problem to be solved by the invention]

As mentioned above, in the field of magnetic recording media, there are various practical characteristics due to the lack of ability of the binder used and the polar group added to it, and the relationship between the polar group and the surface characteristics of the non-magnetic 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 non-magnetic powder, improve the dispersibility of non-magnetic powder, and reduce falling off. The purpose is to provide a magnetic recording medium with excellent electromagnetic conversion characteristics and durability.

[Means to solve the problem]

As a result of intensive research to achieve the above object, the present inventors found that by introducing aminocarboxylic acid residues into the binder resin of the back coat layer, the affinity between the nonmagnetic powder and the binder was significantly improved. We have found that the dispersibility of magnetic powder and the durability of coating films are dramatically improved.

The present invention has been made based on the above findings, and as shown in FIG. The magnetic recording medium is formed of a binder (Bassokuko) JW (3), which is characterized in that the binder contains a resin having an aminocarboxylic acid residue in its molecule.

In the case of a coated magnetic recording medium, the magnetic layer may have the above structure, or both the magnetic layer and the back coat layer may have the above structure.

Here, the binder resin constituting the backcoat layer paint of the magnetic recording medium is a resin that is normally used as a binder for this type of magnetic recording medium, and is a resin in which the following aminocarboxylic acid residues are introduced. Any suitable material can be used.

Furthermore, for example, a resin into which an aminocarboxylic acid residue has been introduced may be used alone, a resin into which an aminocarboxylic acid residue has been introduced and a resin into which the aminocarboxylic acid residue has not been introduced, or a combination of a resin into which an aminocarboxylic acid residue has been introduced, or a resin into which an aminocarboxylic acid residue has been introduced may be used. Any combination of different resins into which carboxylic acid residues have been introduced can be used. In addition, in the case of a combination of a resin into which aminocarboxylic acid residues have been introduced and a resin into which aminocarboxylic acid residues have not been introduced, the proportion of the resin into which aminocarboxylic acid residues have been introduced is at least 10%. It is necessary that they be combined.

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 polyurecne resin, polyfluoride Vinyl chloride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose ml.

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.

The aminocarboxylic acid residue introduced into the binder resin includes both a proton-accepting group with a coordinating ability such as nitrogen, and a proton-donating acidic group with a salt-forming ability. It is a compound that simultaneously has in its molecule, for example -Nl
In addition to aminocarboxylic acid residues containing +□ groups and -COO11 groups, it also includes iminocarboxylic acid residues containing -N11 groups and -COOI+ groups, and pyridinecarboxylic acid residues containing N- groups and -COOI+ groups. .

Such aminocarboxylic acid residues include ■-Nll (
Cl z) , 1COOH■ N-(CHz) 7C
Examples include various residues that are introduced into the binder resin in the form of OOII and the like.

As a method for introducing these various residues, any conventionally known method can be used. For example, in order to introduce the above-mentioned various residues into a condensation resin, It(Clh)i (h) C-jjz(: II-N(CIl□C00I
+)2-1-→Polyol 9H.

11N-CIl□C00I+ Su(k) -NGO+1IN(CHzCOOII)
z → −NCON (C)I 2COOI+)
! There are various introduction methods such as

In addition, in order to add the above-mentioned four types of residues to a copolymer resin such as a vinyl chloride resin, for example, U-L, 11tl, ln II! There is a method of constructing a monomer having an aminocarboxylic acid residue and a double bond in the molecule, such as the above, and introducing this monomer each time it is copolymerized with another vinyl resin.

The content of aminocarboxylic acid residues contained in the binder is 0°001 m with tertiary amine as one unit.
mol/g" 1. Om It is preferably within the range of mol/g.

Non-magnetic powders used in the back coat layer of the magnetic recording medium include all kinds of carbon blacks such as contact black, channel black, roll black, disk black, furnace black, thermal black, lamp blank, CaC01 powder, Ba
SO4 powder, ZnO powder, α-FezO, powder, Tie
, powder, Δ1203 powder, Crz○3 powder, and other inorganic pigments. The particle size of the non-magnetic powder contained in the back coat layer is preferably about 0.001 μm to 1 μm, and the surface of the non-magnetic powder has been modified such as by oxidation treatment. It may be.

In the 66-magnetic recording medium of the present invention, the back coat layer is prepared by dispersing the above-mentioned non-magnetic powder in the above-mentioned binder and dissolving it in an organic solvent to prepare a back coat layer paint. It may be formed by coating on the opposite side. When a back coat layer is provided as described above, the magnetic layer may be formed by applying a magnetic paint, or a ferromagnetic material may be formed by vacuum evaporation,
It may be formed on a non-magnetic support by means such as ion blasting, sputtering, plating or the like.

Examples of organic solvents used to form the back coat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and acetic acid glycol monoethyl ether. Ester type, glycol dimethyl ether, glycol monoethyl ether,
Glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, hexane.

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

In addition to the above-mentioned binder and non-magnetic powder, the above-mentioned back coat layer contains a dispersant, a lubricant, a grinding agent,
Antistatic agents, rust inhibitors, etc. may be added. When these substances are added, they are preferably added within a range that does not inhibit the effect of introducing aminocarboxylic acid residues into the binder.

In particular, as the fatty acid used for the purpose of imparting lubricity to the back coat layer and improving the durability of the bank coat layer, a fatty acid having a carbon number of 10 or more is usually used. The fatty acid may be any fatty acid that satisfies the above-mentioned conditions and is normally used in this type of magnetic recording medium, including saturated fatty acids, unsaturated fatty acids, and the like. Specifically, the above fatty acids include capric acid, undecylic acid, lauric acid,
Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, heptaconic acid, montanic acid, melisic acid, lafcelic acid, undecylic acid, oleic acid , elaidic acid, cetoleic acid, erucic acid, brassic acid, linoleic acid, linoleic acid, arachidonic acid, stearolic acid, and the like.

These fatty acids have a non-polar alkyl group in their structure, so they have a weak bonding force with the binder, but if the surface of the non-magnetic powder is basic, for example, they preferentially The fatty acids are adsorbed and the durability of the coating film is significantly deteriorated.

However, in the magnetic recording medium of the present invention, since aminocarboxylic acid is introduced into the binder resin, the aminocarboxylic acid residue is strongly bonded to the nonmagnetic powder containing basic active sites. Therefore, the non-magnetic powder is well bonded to the aminocarboxylic acid residue without adsorption of fatty acids, thereby improving the dispersibility of the non-magnetic powder. Furthermore, since the fatty acid exists alone in the back coat layer, it can exhibit a good lubricating effect.

Note that the aminocarboxylic acid residues bond well with the nonmagnetic powder regardless of whether the surface properties of the nonmagnetic powder are basic, acidic, or neutral.

The material for the nonmagnetic support forming the back coat layer as described above 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 and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, and polyamide.

Examples include plastics such as polyamide-imide, synthetic materials such as aluminum and copper, light alloys such as aluminum alloys and titanium alloys, ceramics, and single crystal silicon. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

[Effect]

The aminocarboxylic acid residues introduced into the binder resin in the present invention have multidentate coordination on the surface of the non-magnetic powder and bond very strongly to the non-magnetic wax powder, thereby improving the dispersibility of the non-magnetic powder. It has a remarkable effect on the reinforcement of the paint film interface.

Therefore, the binder and the like on the bank coat layer side are prevented from migrating to the magnetic layer side, and the electromagnetic conversion characteristics of the magnetic recording medium are improved.

In addition, since the surface of the non-magnetic powder and aminocarboxylic acid residues are strongly adsorbed, it is possible to prevent various additives having oxygen-donating atomic groups such as fatty acids from adsorbing to the non-magnetic powder. Even when the non-magnetic powder is added, a coating film with high surface gloss and excellent durability is completed with little falling off of the non-magnetic powder.

〔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.

Removal carbon for coloring 5 parts by weight (acidic PL+2.5, particle size 23mμ) binder
3.3 parts by weight (urethane resin containing 0.05 m mol/g of iminodicarboxylic acid groups) Solvent (methyl ethyl ketone) 24.9 parts by weight The bank coat layer paint having the above composition was mixed in a ball mill for 24 hours and then taken out through a filter. This was applied to the back side of a 12 μm thick polyethylene terephthalate film on which a magnetic layer had been previously formed so that the thickness after drying would be 2 μm, and the magnetic layer was oriented in a magnetic field and then wound up. This was calendered and cut into 1/2 inch width to produce sample tapes.

Carbon for color 5 parts by weight (neutral pl+6.0, particle size 23mmμ) binder
3.3 parts by weight (vinyl chloride vinyl acetate copolymer resin containing iminodicarboxylic acid group 0.05 m mol/g) Solvent (methyl ethyl ketone) 2
A sample tape was prepared in the same manner as in Example 1 using 4.9 parts by weight of the hack coat layer paint having the above composition.

5 parts by weight of carbon for upper color (acidic PL+2.5, particle size 23mμ) binder
3.3 parts by weight (-5OyNa group 0.0
(Urethane resin containing 5 s mol/g) Solvent (methyl ethyl ketone) 24.9 parts by weight A sample tape was prepared in the same manner as in Example I using a magnetic paint having the above composition.

Carbon for color A 5 parts by weight (neutral pH 6, o, particle size 23 mμ) binder
3.3 parts by weight (-3OJa group 0.05m
A sample tape was prepared in the same manner as in Example 1 using a magnetic material having the above composition.Vinyl chloride/vinyl acetate copolymer resin containing moI/g) Solvent (methyl ethyl ketone) 24.9 parts by weight.

Gloss and fading were measured for each sample tape produced as described above. The reflectance of the above gloss was measured using a glossy needle at an incident angle of 45'' and a reflection angle of 45°.In addition, the amount of powder falling on the head drum, guide bin, etc. after running the shuttle 100 times for 60 minutes was measured. Visual observation was performed, and a score of 0 was given for a sample with almost no amount of powder falling off, and a score of -5 was given for a sample with a very large amount of powder falling off.The measurement results are shown in Table 1.

Table 1 As is clear from Table 1 above, the back coat layer using the binder into which aminocarboxylic acid residues were introduced had high gloss and very little powder falling off.

〔Effect of the invention〕

As is clear from the above explanation, in the magnetic recording medium according to the present invention, aminocarboxylic acid residues are introduced into the binder resin. Coordinating and strongly binding, the coating film is completed without losing the dispersion stability of the non-magnetic powder or the interfacial reinforcing properties of the binder, and a strong coating film with high surface gloss is formed.

Therefore, by using this as the back coat layer of a magnetic recording medium, it is possible to improve the dispersibility of the non-illucent powder and reduce the shedding of the powder, resulting in a magnetic recording medium with excellent electromagnetic conversion characteristics and coating durability. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a magnetic recording medium to which the present invention is applied. 1...Non-magnetic support 2...Magnetic layer 3...Back coat layer Patent applicant Sony Corporation Figure 1 "E+m" 1 (Spontaneous) June 20, 1988

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer is formed on one side of a non-magnetic support and a back coat layer mainly composed of non-magnetic powder and a binder is formed on the other side, the binder has aminocarbon atoms in its molecules. A magnetic recording medium characterized by containing a resin having acid residues.