JPH02108226A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics, durability and traveling property by using a binder having epoxy groups and polar groups. CONSTITUTION:The medium has a magnetic layer consisting of ferromagnetic powder and a binder formed on a nonmagnetic supporting substance. The binder contains more than one kind of substituted group selected from -SO3M, -OSO3M, -PO3M2, -OPO3M2, -COOM (wherein M represents H, alkali metal or ammonium) and an epoxy group, both in one molecular thereof. The magnetic layer contains said binder and aliphatic amides having 12 - 26 carbons. Thereby, dispersibility of the ferromagnetic powder is enhanced, so that the obtained recording medium has good durability and traveling porperty with less dropout.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic recording medium having a magnetic layer formed by dispersing ferromagnetic powder in a binder on a non-magnetic support. The present invention relates to a magnetic recording medium with excellent electromagnetic conversion characteristics.

[Prior art]

A magnetic recording medium basically consists of a nonmagnetic support and a magnetic layer provided on the support. Generally, the magnetic layer consists of a binder and ferromagnetic powder dispersed in the binder.

In recent years, due to the demand for higher density recording, γ-Fe20. In place of metal oxide-based ferromagnetic powders such as iron oxide-based ferromagnetic powders containing other components such as cobalt, ferromagnetic metal fine powders have come to be used.

It is known that by pulverizing such ferromagnetic metal fine powder, even higher density recording becomes possible.

On the other hand, the resin component used as a binder to form a magnetic layer by dispersing such fine ferromagnetic metal powder includes vinyl chloride copolymers such as vinyl chloride, vinyl acetate,
(maleic anhydride copolymer) and polyurethane resin are increasingly being used together. By using both in combination, it is possible to form a magnetic layer with improved properties such as strength required for a magnetic recording medium.

However, according to studies conducted by the present inventor, the vinyl chloride copolymer used as the binder can be used at high temperatures (e.g.
When a magnetic recording medium is left under harsh conditions, such as being left unattended for long periods of time (over 0°C) and high humidity, the chlorine bonded to the vinyl chloride copolymer is released as hydrochloric acid gas. It turned out that something happened. The hydrochloric acid gas released in this way can corrode fine ferromagnetic metal powder, and can also corrode metals (e.g., support rods, permalloy heads) inside recording and reproducing devices such as video tape decks. There is.

The applicant has already filed an application regarding the invention of a magnetic recording medium having a magnetic layer using a vinyl chloride copolymer stabilized by introducing a specific polar group and an epoxy group and a polyurethane resin as a binder. (Unexamined Japanese Patent Publication No. 61-25
3627). This magnetic recording medium is a magnetic recording medium because the vinyl chloride resin is stable even if the magnetic recording medium and a recording/reproducing device such as a video tape deck are left in contact with each other for a long time under conditions of high temperature and humidity. It is an excellent magnetic recording medium that hardly corrodes the metal inside the device that it comes into contact with, and does not corrode ferromagnetic metal fine powder when used.

However, as a result of further studies on magnetic recording media using the above-mentioned binder, it has been found that in special cases, such as when extremely finely divided ferromagnetic powder is used, ferromagnetic powder tends to be difficult to disperse. It turns out that there is something. In other words, despite using finely divided ferromagnetic powder,
It was found that the electromagnetic conversion characteristics of the obtained magnetic recording medium were not sufficiently improved.

On the other hand, in order to cope with recent high-density recording, efforts are being made to make the surface of the magnetic layer as smooth as possible to reduce the spacing loss of the magnetic head. It is known that when the surface of the magnetic layer becomes smooth, it comes into contact with magnetic heads, cylinders, guide rollers, etc., increases the coefficient of friction, and deteriorates running performance and durability. Therefore, the use of various lubricants has been proposed to improve the running properties and durability of these vehicles. For example, fatty acids are disclosed in Japanese Patent Publications Nos. 44-18221 and 48-15007, and fatty acid esters are disclosed in Japanese Patent Publications Nos. 43-23889 and 41-18065. -15624, JP-A-5
No. 0-136009, No. 55-139637, No. 54
Publications such as No.-46950 disclose the use of fatty acid amides. A wide variety of other lubricants have been proposed, including fatty acids, silicone oils, and fatty acid-modified silicones, but among these, fatty acids significantly reduce the coefficient of friction and have excellent lubricating performance such as still durability, so fatty acid esters are preferred. It is often used in combination with other substances such as silicone and fatty acid-modified silicone. Therefore, resins containing polar groups such as sulfonic acid and phosphoric acid and epoxy groups (Japanese Unexamined Patent Publication No. 61-123
017, JP-A No. 61-253627) have also been conventionally used in combination with lubricants of fatty acids and fatty acid esters.

However, such a combination of a binder and a lubricant has not been able to achieve particularly excellent lubricant function and dispersibility. Therefore, in order to use the ultrafine ferromagnetic powders of recent years, even better binders and lubricants have been required.

[Problems to be solved by the present invention]

Therefore, the present inventors used ferromagnetic powder with extremely small particle size to disperse the ferromagnetic powder to a high degree to provide a magnetic recording medium that has extremely good electromagnetic conversion characteristics and is both durable and runnable. That is. For this purpose, when the above-disclosed binder having both an epoxy group and a polar group is used, the high degree of dispersibility of the binder is not impaired, and when combined with a specific lubricant, the running properties are dramatically increased. A magnetic recording medium with better durability was replaced. Furthermore, a magnetic recording medium with extremely low dropouts, which is a major quality problem in high-density magnetic recording media, was obtained by combining wood.

Structure of the Invention [Means for Solving the Problems] As a result of intensive studies, the present inventors found that in a magnetic recording medium in which a magnetic layer made of ferromagnetic powder and a binder is provided on a non-magnetic support, -3O,M, -03OJ, -POd
A binder having one or more substituents selected from h, -0PO3M2, -COOM (M is H1 alkali metal or ammonium) and a small number of epoxy groups (both of which have one or more in the same molecule of the binder, and carbon It has been found that the object of the present invention is achieved by a magnetic recording medium characterized in that it contains fatty acid amides of 12 to 26 in number.

In other words, by combining a binder having both an epoxy group and a substituent in the same molecule with a fatty acid amide, the present invention has surprisingly improved the dispersibility of ferromagnetic powder, and has produced a magnetic recording medium with good runnability and durability. A medium was obtained, and as an unexpected effect, a magnetic recording medium with extremely low dropout was obtained. This is because fatty acids are reactive with the epoxy ring of the binder, resulting in the formation of insoluble substances, which can cause dropouts, or because they are highly adsorbent to ferromagnetic powder, inhibiting the adsorption of the binder. or reduce dispersibility. - In the blade wheel invention, it is presumed that this is because fatty acid amide has low reactivity with epoxy groups or low adsorption capacity.

That is, in the past, fatty acids were excellent not only as lubricants but also very effective as dispersants, and were dispersed in the magnetic layer to a large extent. Therefore, the epoxy group of the binder reacts with the fatty acid, and it is thought that the function of the fatty acid as a lubricant is reduced and the excellent dispersibility of the epoxy group is also reduced.

In the present invention, when a binder containing the substituent and an epoxy group in the same molecule is used in combination with a fatty acid amide, there is no interaction with epoxy groups such as fatty acids, and there is also lubricating performance, which improves the dispersion performance of epoxy groups. It seems like it won't hurt. In the present invention, the fatty acid may be completely replaced with a fatty acid amide, but the amount of the fatty acid may be reduced to such an extent that no problem arises in terms of interaction with the epoxy group.

As the ferromagnetic powder used in the present invention, ferromagnetic alloy powder, ferromagnetic iron oxide fine powder, (1'o-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, barium ferrite, etc.) can be used. The acicular ratio of the ferromagnetic alloy powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic iron oxide, and chromium dioxide is about 271 to 20/1, preferably 571 or more, and the average length is 0.2 to 2.0 pm. The present invention is particularly effective when the crystallite size is 500 angstroms or less, and is even more effective when the crystallite size is 40 angstroms or less.
0 angstrom or less, more preferably 25
0 angstrom or less (crystallite size is determined by X-ray diffraction). However, according to the gist of the present invention, effects such as electromagnetic conversion characteristics, runnability, and durability can be achieved by using the technology of the present invention even when the crystallite size is above this size, and it is effective when the crystallite size is below the above-mentioned crystallite size. . The ferromagnetic alloy powder has a metal content of 75 wt% or more, and a metal content of 3 Owt%.
The above are ferromagnetic metals (i.e., Fe).

C01Ni, Fe-N15Co-NiSFe-Co
-Ni) particles.

-503M, -0303M used in the present invention
.

-PO,M2, -0PO3M2, -COOM (M is H
Examples of the binder having at least one epoxy group and one or more substituents selected from the group consisting of alkali metals or ammonium (preferably alkali metals) in the same molecule include vinyl chloride polymers and vinyl chloride-acetic acid. Copolymers such as vinyl copolymers, vinyl chloride-vinyl propionate copolymers, and vinylidene chloride-vinyl acetate copolymers are preferred.

Preferred examples of these substituents are -3O,M.

-[:02M, more preferably -3O,M. The content of these substituents is preferably about 10-' to 10-' equivalent per gram of polymer.
More preferably, it is 10-S to 5X10-' equivalent. If it is outside this range, the dispersibility of the ferromagnetic powder will be poor and the electromagnetic conversion characteristics will also be significantly reduced. These substituents are 1
There may be more than one species, and two or more species may be present.

Furthermore, the presence of an -OH group is effective in further improving dispersibility. The content of epoxy groups is per gram of polymer! JIO-' to 10-2 mol, preferably 5X10-' to 5X10-' mol. Furthermore, the weight average molecular weight of the binder molecules used in the present invention is 2.
0.000-100.000, preferably 30.000
~80,000. Outside this range, dispersibility may become poor or durability may deteriorate.

These binders are synthesized by modifying some of the hydroxyl groups generated by addition reaction to vinyl chloride-glycidyl (meth)acrylate copolymer or by saponifying vinyl chloride-vinyl acetate copolymer. Alternatively, methods described in JP-A-80-238306, JP-A-60-238309, and JP-A-60-238371 may also be used. Also, resins that polymerize and harden by irradiation with radiation such as electron beams, for example, JP-A-61-89207, JP-A-61-106605, JP-A-57-40744, JP-A-59-8126, JP-A-62-1
Those disclosed in No. 12665, No. 62-112668, etc. can also be used.

Furthermore, the fatty acid amide used in the present invention has a total number of carbon atoms of 1.
Those having a number of 2 to 26, particularly those having a number of 14 to 18 are preferred because they are effective in improving running performance and durability. Preferred specific examples of these include lauric acid amide, myristic acid amide,
Palmitic acid amide, stearic acid amide, isostearic acid amide, oleic acid amide, linoleic acid amide,
Fatty acid amides such as linoleic acid amide, eicoic acid amide, elaidic acid amide, and behenic acid amide, as well as N-methylmyristic acid amide, N-ethylmyristic acid amide, which are N-alkinope N-, N-dialkyl derivatives of these, N-methylstearamide, N-, N-
These include dimethylstearamide, N-,N-diethylstearamide, and the like. Particularly effective are those in which the N atom is not substituted with alkyl, and the aliphatic chain has a linear saturated structure.

A preferred method for manufacturing a magnetic recording medium using these ferromagnetic powders, binders, lubricants, etc. will be described below. Since ferromagnetic powder is secondary agglomerated due to its own magnetism, it is preferable to crush it mechanically, and by introducing this step, the time required for the next kneading step can be shortened. The grinding process is carried out by Simpson Mill (
(manufactured by Shinto Kogyo Co., Ltd.), a sand mill (manufactured by Matsumoto Foundry Co., Ltd.), a sand grinder, a two-roll mill, a three-roll mill, an open knee goo, a pressurized knee goo, a continuous kneader-Henschel mixer, and the like can be used.

It is preferable to use the same equipment as that used in the next kneading process, since this eliminates the transfer process. It has been found that omitting this pulverization step is undesirable because it takes a long time for dispersion and causes poor dispersion. In the kneading and dispersing step, the above-mentioned binder and solvent are first kneaded together with the ferromagnetic powder using the above-mentioned roll mill or kneader, and then dispersed. For dispersion, use San Dominope ball mill,
Attritor Henschel mixer etc. can be used. At this time, the binder may be dissolved in a solvent and then added, or the solvent and binder may be added separately. Although it is preferable to add the fatty acid amide after dispersion, it may be added at the same time as the dispersion.

The process is as follows: After preparing the dispersion and immediately before coating,
This can be done using a 2-shaft despa, sand mill, ball minope high-speed mixer, etc. In the present invention, a curing agent can be used as part of the binder, and the curing agent can be added simultaneously with these fatty acid amides.

The amount of fatty acid amide added is 0.05 to ferromagnetic powder.
~2% by weight, particularly preferably 0.1-1.0% by weight, is suitable. If the amount of fatty acid amide added exceeds this range, the lubricant on the surface of the magnetic layer becomes excessive, which may blow out powder on the surface of the magnetic layer or cause malfunctions such as sticking when running on a deck. In addition, there is a problem that the durability is reduced due to the action of plasticizing the magnetic layer binder.

If the amount added is below this range, the running properties will be insufficient and no effect will be obtained.

In the present invention, other lubricants may be mixed. Lubricants that can be used in combination include fatty acids with 12 to 24 carbon atoms, fatty acid esters (including various monoesters, sorbitan, fatty acid esters of polyhydric esters such as glycerin, esters of polybasic acids, etc.), metal soaps, and higher aliphatic alcohols. , monoalkyl phosphates, dialkyl phosphates, trialkyl phosphates, paraffins, silicone oils, fatty acid-modified silicon compounds,
Examples include fluorocarbon oils, esters with perfluoroalkyl groups, perfluoroalkyl silicon compounds, animal and vegetable oils, mineral oils, higher aliphatic amines; and inorganic fine powders such as graphite, silica, molybdenum disulfide, and tungsten disulfide. .

Among these mixed lubricants, those with a carbon number of 14 to
22 fatty acids, fatty acid esters having 22 to 36 carbon atoms, esters having perfluoroalkyl groups having 6 or more carbon atoms,
It is a silicon compound having a perfluoroalkyl group having 6 or more carbon atoms.

Other resins can be added to the binder described above as the binder used in the present invention. For example, vinyl chloride/vinyl acetate copolymer, copolymer of vinyl chloride and vinyl alcohol, maleic acid and/or acrylic acid, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/acryloni copolymer, Examples include ethylene/vinyl acetate copolymers, cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, epoxy resins, phenoxy resins, and polyurethane resins. Among these, the most preferable ones in order to further improve dispersibility and durability are:
In the molecule, there are polar groups (epoxy group, -CO□H1-Ko, -
NH2, -303M, -0303M.

It is a polyurethane resin into which -PO,M, , published PO8M2, where M is hydrogen, alkali metal or ammonium) is introduced. Regarding these urethane resins,
JP 57-165464, JP 5B-41565
No. 62-40615 and JP-A No. 59-30235.

The content of polar groups is 10-5 per gram of polymer.
The preferred range is 10-3 equivalents, and the skeleton may be polyester, polyether, polyester ether, polycarbonate, or the like.

The polymeric binders listed above may be used alone or in combination, and may be cured by adding a known incyanate-based crosslinking agent (for example, tolylene diisocyanate triadduct of trimethylolpropane). Furthermore, a binder system that uses an acrylic acid ester oligomer and a monomer as a binder and is cured by radiation irradiation can also be used.

The total binder content in the magnetic layer of the magnetic recording medium of the present invention is usually 10 to 100 parts by weight per 100 parts by weight of the ferromagnetic powder.
Parts by weight, preferably 20 to 40 parts by weight.

Organic solvents used for kneading, dispersing, and applying the magnetic coating liquid include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and acetic acid glycol monoethyl ether. Ether systems such as ethyl etherenope glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic monohydrocarbons such as benzene, toluene, and xylene nato; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and ethylene chlorhydrocarbons , chlorinated hydrocarbons such as dichlorobenzene, etc. can be selected and used.

Furthermore, additives such as an abrasive, a dispersant, an antistatic agent, and a rust preventive may be added to the magnetic coating liquid of the present invention. The abrasive used is not particularly limited as long as it has a Mohs hardness of 5 or more, preferably 8 or more.

Examples of abrasives with a Mohs hardness of 5 or higher are M2O5 (Mohs hardness 9), Ti0 (6), and TlO□ (6.5).
, 5iO3 (7), SnO, (6.5), Cr2O
, (9), and α-Fe203 (5.5), which can be used alone or in combination. Particularly preferred is an abrasive having a Mohs hardness of 8 or more.

If an abrasive with a Mohs hardness lower than 5 is used, the abrasive easily falls off from the magnetic layer and has almost no abrasive action on the head, resulting in head clogging and poor running durability. Become. The content of the abrasive is usually in the range of 0.1 to 20 parts by weight, preferably in the range of 1 to 10 parts by weight, based on 100 parts by weight of the ferromagnetic powder. As the antistatic agent, it is desirable to include carbon black (particularly one having an average particle size of 10 to 300 nm (nanometers; 10-')).

Materials for the support to which the magnetic coating liquid is applied include polyethylene terephthalate, polyethylene 2. Polyesters such as 6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; plastics such as polycarbonate, polyimide, and polyamideimide; Non-magnetic metals, such as non-magnetic alloys, and plastics on which metals such as aluminum are deposited can also be used.

The thickness of the support is 3 to 100μ, preferably 3 to 20μ for magnetic tape, and 20 to 100μ for magnetic disk.
μ is the commonly used range.

In addition, the forms of non-magnetic supports include films, tapes, sheets,
It may be a disk, card, drum, etc., and various materials are selected depending on the form as necessary.

In addition, the support of the present invention has a so-called so-called A back coat may be provided.

〔Example〕

EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Note that "parts" in the examples indicate "parts by weight."

[Example 1] Ferromagnetic alloy powder (composition: Fe94%, Zn 4%, 1L
+2%, Hc 15000e, crystallite size 200 angstroms) was ground in an oven for 10 minutes, and then hydroxyethyl sulfonate was added to the copolymer of vinyl chloride/vinyl acetate/glycidyl methacrylate = 88/9/5. Compound with added sodium salt (-3O, Na = 6 xio-5eq/g, epoxy group = 10'eq/g, Mw 30.00
0) and 60 parts of methyl ethyl ketone for 60 minutes, and then SO3Na-containing urethane resin 8
(solid content) (rUR8200 manufactured by Toyobo ■) Abrasive (U2OS particle size 0.3-) 5 parts Carbon black (particle size 4Q nm) 2 parts Methyl ethyl ketone/toluene 200 parts-1/1 were added and heated in a sand mill for 120 minutes. Dispersed. To this, 8 parts polyisocyanate (solid content) (Coronate 3041J manufactured by Nippon Polyurethane) stearamide 1 part butyl stearate
2 parts methyl ethyl ketone
After adding 50 parts and stirring and mixing for an additional 20 minutes, the mixture was filtered using a filter having an average pore size of 1- to prepare a magnetic paint. The thickness of the obtained magnetic paint after drying is 3. The coating was applied onto the surface of a 10-thick polyethylene terephthalate support using a reverse roll so that the coating was applied to the surface of the polyethylene terephthalate support.

A non-magnetic support coated with magnetic paint is magnetically aligned with a 3000 Gauss magnet while the magnetic paint is not dry.
After further drying and super calendering, 3
A 3 mm videotape was produced by slitting it into mm widths.

Examples and comparative examples were carried out in the same manner as in Example 1. Table 1 summarizes the differences from Example 1 and the evaluation results of the obtained tape.

Comparative Example 1 In place of the compound in Example 1 in which hydroxyethyl sulfonate sodium salt was added to the copolymer of vinyl chloride/vinyl acetate/glycidyl methacrylate = 86/9/5, vinyl chloride/vinyl acetate/3- Allyloxy-2-hydroxypropanesulfonate (3-a
I Iy Ioxy-2-hydroxypropa
Comparative Example 1 was prepared by using a 1-fonate) copolymer.

Comparative Example 2 Comparative Example 2 was prepared by using the vinyl chloride/vinyl acetate/glycidyl methacrylate-86/9/5 copolymer of Example 1 as it was.

Comparative Example 3 Comparative Example 3 was prepared by adding stearic acid instead of stearamide in Example 1.

Comparative Example 4 In Comparative Example 1, stearic acid was added instead of stearamide.

Example 2 As a compound obtained by adding hydroxyethyl sulfonate sodium salt to the copolymer of vinyl chloride/vinyl acetate/glycidyl methacrylate = 86/9/5 in Example 1, (-3OJa = 4 xto 'eq
/gsx poxy group = 4 xlO-3eq/g SM
w 30.000) was used.

Example 3 In Example 1, as a compound obtained by adding hydroxyethyl sulfonate sodium salt to the copolymer of vinyl chloride/vinyl acetate/glycidyl methacrylate = 86/9/5, (-3OJa = 4 xto-'eq
/g, epoxy group = 8 Xl0-'eq/g,
h 30.000) was used.

Example 4 In Example 1, myristic acid amide was used instead of stearic acid amide.

Example 5 In Example 1, r- coated with Co as ferromagnetic powder
Iron oxide 01c 9000e, crystallite size 280 angstroms) was used.

Comparative Example 5 In Example 5, stearic acid was used instead of stearic acid amide.

"Evaluation method" 1) Electromagnetic conversion characteristics: The video tape obtained as above was tested with a VTR (Fuji Photo Film ■: FUJIX-8).
) was used to record and reproduce a 7 MHz signal. The playback output of 7M) Iz recorded on the reference tape (Comparative Example 1) was set to 0.
(The relative playback output of the videotape was measured when fB was used. However, in Example 5 and Comparative Example 5, the slit was made to a width of 172 inches.
6200) was used.

2) Running properties: The obtained videotape and stainless steel pole were brought into contact with a tension of 50 g (T1) (wrapping angle 180
°), and under these conditions, the videotape was
The tension (T2) required to run at a speed of /s was measured. Based on this measured value, the friction coefficient μ of the videotape was determined using the following calculation formula.

μ=1/π・1n (T2/T1) The friction coefficient test was conducted at 25° C. and 70% R)l.

3) Durability: A test was conducted in a still state using the above-mentioned FUJIX-8, and the time until the playback output reached 50% of the recorded signal was measured. At this time Lln 1oard in
The g function has been canceled. Example 5 and Comparative Example 5 are AG62
00 was used.

4) Do07 Buau): With FUJIX-8, the playback output level is 16dbJ for a period of 1/10H or more.
, J dropout was measured for 1 minute using a dropout counter. Example 5 and Comparative Example 5 are AG
6200 was used.

5) Determination of epoxy group content in binder: 6NHC1
The ring was opened at 40°C for 1 hour, and the remaining HCI was determined by back titration with KOH.

〔Effect of the invention〕

It can be seen that the magnetic recording medium having the combination of the binder and fatty acid amide of the present invention exhibits good electromagnetic characteristics, has a low coefficient of dynamic friction, has excellent still durability, and has extremely low dropout.

Agent Patent attorney (8107) Kiyotaka Sasaki (and 3 others) ,, +:i'=/' ~++/ Procedural amendment January 17, 1990

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer made of ferromagnetic powder and a binder is provided on a non-magnetic support, -SO_
3M, -OSO_3M, -PO_3M_2, -OPO_
A binder having at least one substituent selected from 3M_2, -COOM (M is H, alkali metal or ammonium) and an epoxy group in the same molecule of the binder, and a carbon number of 12 to 26 A magnetic recording medium characterized by containing a fatty acid amide.