JPH01320629A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To suppress hydrolysis of a binder composing a magnetic layer and to obtain a recording medium excellent in dispersiveness and durability by using polycarbonate polyurethane resin having tertiary amine in its molecule as the binder. CONSTITUTION:A magnetic coating material comprising a binder contg. polycarbonate polyurethane resin having tertiary amine as a polar group and an organic solvent in both of which magnetic powder and nonmagnetic powder are dispersed is applied on a nonmagnetic supporting substance to form the magnetic layer. Since polycarbonate polyurethane resin has good film property and excellent hydrolysis resistance, it shows excellent durability even at high temp. and high humidity. By introducing the tertiary amine as the polar group into the resin, dispersiveness for magnetic powder can be maintained. Thereby, the hydrolysis of the binder can be inhibited and a recording medium excellent in dispersiveness and durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and floppy disks, and particularly relates to improving the durability of magnetic layers.

[Summary of the invention]

The present invention aims to provide a magnetic recording medium with excellent dispersibility and durability by using a polycarbonate polyurethane resin having a tertiary amine as a binder constituting the magnetic layer.

[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 to improve the electromagnetic conversion characteristics and at the same time increase the durability of the magnetic layer. It is required to improve.

For example, a technique is known in which a hydrophilic polar group is introduced into a binder resin in order to improve the dispersibility of magnetic powder and the like. By introducing this hydrophilic polar group, it is possible to strengthen the bond between the magnetic powder and the binder, which is expected to prevent powder falling off and improve durability.

On the other hand, regarding the binder resin itself, attempts have been made to use resins having various crosslinked structures and physical properties, and polyurethane resins having a certain degree of flexibility have come to be used as part of the binder resin. The combined use of this polyurethane resin is thought to be advantageous in ensuring the durability of the magnetic recording medium, as the coating film becomes tough and the physical properties of the coating film are also good.

Problems to be Solved by the Invention] Incidentally, polyester polyurethane having an ester bond in the molecule is generally used as a polyurethane resin used in magnetic recording media.

However, when the above-mentioned polyester polyurethane is used as a binder, the ester bond is easily hydrolyzed, and the expected physical properties of the coating film cannot be obtained, such as powder shedding after aging under high temperature and humidity, and insufficient still properties. The reality is that it is not.

Therefore, the present invention was proposed in view of the above-mentioned conventional situation, and aims to provide a magnetic recording medium with excellent durability by ensuring dispersibility and mechanical strength of the binder at the same time. This is the purpose.

[Means for Solving the Problem] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that polycarbonate polyurethane resin has high hydrolysis resistance and can ensure the durability of the coating film.
Furthermore, it has been found that dispersibility can be improved by introducing a tertiary amine as a polar group into this polycarbonate polyurethane resin.

The present invention has been made based on the above findings, and provides a magnetic recording medium having a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, wherein the magnetic layer has a tertiary amine in its molecules. It is characterized by containing the existing polycarbonate polyurethane resin as a bond 7FIl.

The polycarbonate polyurethane resin used as a binder in the present invention is obtained by condensing a polycarbonate polyol into which a carbonate bond (carbonate bond) has been introduced and a polyisocyanate via a chain extender.

Here, the polycarbonate polyol into which the carbonate bond has been introduced has a molecular weight of 300 to 20,000, a hydroxyl value of 20 to 300, and R in the general formula +1O-R-011 is, for example, polyhydric alcohol, phosgene, chloroacetate, chloroformate. , obtained by condensation with dialkyl carbonate or diallyl carbonate.

For example, the condensation reaction between a polyhydric alcohol and phosgene is represented by the following formula.

n HO-R-OH+ n Cock 2->
tlo −+R-OCO+R-OH+ 2nflCl
Specific examples of the polyhydric alcohol include 1,1o-decanediol, 1,6-hexanediol, 4. Typical examples include butanediol, 1.3-7'tanediol, neopentyl glycol, 1.5-bentanediol, etc., but they are of course not limited to these, and in particular, those represented by the above-mentioned formulas. Preferably.

Furthermore, as the polyisocyanate, any conventionally known polyisocyanate can be used, and examples include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate, tophenylene diisocyanate, and p-phenylene diisocyanate. Diisocyanate, 2.4-)lylene diisocyanate, 2.6-lylene diisocyanate, diphenylmethane diisocyanate, 3.3-dimethoxy-4,4'-diphenylene diisocyanate, 3
．． 3′-dimethyl-4,41″-biphenylene diisocyanate, 4.4°-diisocyanate diphenyl ether, 1.51-7tale diisocyanate, 2.4-
Aromatic diisocyanates such as naphthalene diisocyanate, 1,3-diisocyanatomethylcyclohexane,
1.4-Diisocyanatomethylcyclohexane, 4.
4”-diisocyanatodicyclohexylmethane, 4.
Examples include alicyclic diisocyanates such as 4'-cyclohexyl diisocyanate and isophorone diisocyanate.

As a chain extender, +1O-R-OH (R represents a hydrocarbon group 0, for example, lo-(Cllz)-Oll (n=2~
10) In addition to the polyhydric alcohols represented by ), aliphatic diamines, alicyclic diamines, aromatic diamines, etc. can also be used.

Specifically, ethylene glycol, diethylene glycol, propylene glycol, 1.4-7" ethylene glycol, bisphenol A1 glycerin, 1.3.6-hexandriol, trimethylolpropane, pentaerythritol, sorbitol, sucrose, dipropylene glycol. , methylgetanolamine, ethylbiisopropanolamine, triethanolamine, ethylenediamine, hexamethylenediamine, bis(p-aminocyclohexane), tolylenediamine, diphenylmethanediamine, methylenebis(2-chloroaniline), etc., and these compounds include ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran,
Examples include polyether polyols obtained by adding one or more types of styrene oxide and the like.

In order to introduce a tertiary amine into the above-mentioned polycarbonate polyurethane resin, a tertiary amine-containing diol or the like may be used as part of the chain extender.

Such tertiary amine-containing diols include ■CHs-
NCCHtCHtOH) t■ CJs-N(CHzG
HzOll) t■ (CHs)zc-N(CHtCI
IzOH)z, etc., and furthermore, CaHza++-
Ethylene oxide to a primary amine expressed in NHZ (n=1-20).

Diols obtained by adding 2 to 50 moles of propylene oxide or the like can also be used. This reaction is shown as follows.

The amount of tertiary amine introduced is 0.01 to 1.0 m m
If the amount of the tertiary amine introduced is less than 0.01 ta mol/g, the effect on dispersibility will be insufficient; conversely, if the amount introduced is less than 1.0 s mol/g,
If it exceeds l/g, the solubility in solvents will deteriorate and at the same time the moisture resistance of the coating film will deteriorate.

Moreover, the number average molecular weight of the polycarbonate polyurethane is preferably 5,000 to 100,000. If the molecular weight is less than 5,000, the durability may be insufficient, whereas if it exceeds 100,000, the solubility in solvents will decrease, resulting in poor handling.

The above-mentioned polycarbonate polyurethane resin may be used in combination with other binders used in ordinary magnetic recording media.

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-acetic acid and nyl-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacryl 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 Polymers, 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.

A hydrophilic polar group may be introduced into the polycarbonate polyurethane resin or other binder used in combination for the purpose of further improving dispersibility. Examples of the hydrophilic polar group include -503M group, -0503M group, PO(
OM')z group, -COOMi, -NR3χ group (however,
M represents a hydrogen atom or an alkali metal atom, Mo represents a hydrogen atom, an alkali metal atom or a hydrocarbon atom, R represents an alkyl group, and X represents a halogen atom.

In the magnetic recording medium of the present invention, the magnetic layer is prepared by dispersing magnetic powder, non-magnetic powder, etc. in a binder containing the aforementioned polycarbonate polyurethane resin and an organic solvent, and then coating the surface of the non-magnetic support with a magnetic paint. It is formed by

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 5 cellulose diacetate cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate polyimide,
Brass tink made of polyamide, polyamideimide, etc.
Examples include metals such as aluminum and W4, 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.

It may be a sheet, disk, card, drum, etc.

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.

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.

The constituent materials of the magnetic layer described above are prepared as a magnetic paint by dissolving it in an organic solvent and coated on a non-magnetic support.The solvent for the magnetic paint may be 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 solvents such as glycol dimethyl ether, glycol monoethyl ether, dioxane, etc.
Aromatic hydrocarbon solvents such as benzene, toluene and xylene, aliphatic hydrocarbon solvents such as hexane and heptane, methylene chloride, ethylene chloride, carbon tetrachloride,
Examples include organic chlorine compound solvents such as chloroform, ethylene chlorohydrin, and dichlorobenzene. Furthermore, sulfoxide solvents such as dimethyl sulfoxide, and amide solvents such as dimethylformamide can also be used.

Note that the above-mentioned tertiary amine-containing polycarbonate polyurethane resin may be used not only for the magnetic layer but also for the back coat layer, etc., and in this case as well, effects in terms of durability etc. are expected as in the case of the magnetic layer. can.

[Effect]

Polycarbonate polyurethane resins exhibit good shearing properties and at the same time exhibit excellent hydrolysis resistance.

Therefore, it exhibits excellent durability even when exposed to high temperature and humidity.

In addition, the polycarbonate polyurethane resin includes:
Since a tertiary amine is introduced into the molecule as a polar group, dispersibility in magnetic powder, non-magnetic powder, etc. is also ensured.

〔Example〕

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

Conclusion 1. First, a polyurethane resin as a binder was synthesized. The raw materials, amount of tertiary amine introduced, and number average molecular weight of the synthesized polyurethane are as shown in Table 1. In addition, in Table 1, polyol A to polyol D and polyisocyanate A to polyisocyanate B represent the following compounds, and polyol A and polyol B correspond to polycarbonate polyols.

Polyol A: 1.6-hexane glycol polycarbonate polyol Hydroxyl value 56 (represents one hydroxyl group per molecular weight 1000).

same as below. ) Polyol B Nidichlorohexane dimethylol polycarbonate polyol Hydroxyl value 56 Polyol C: Polybutane adipate polyester polyol Hydroxyl value 56 Polyol D: 1.4-butanediol Polyisocyanate A Nidiphenylmethane diisocyanate Polyisocyanate B: Isophorone diisocyanate These synthesized polyurethane resins (PU-A~・
A magnetic recording medium was manufactured using PU-J), and the manufacturing method was as follows. 1 stone note 1 legal metal magnetic powder 100 parts by weight
I (specific surface area 52M7g) 1 Polyurethane resin 10 parts by weight Vinyl chloride copolymer 10 parts by weight Carbon black (antistatic agent) 2 parts by weight (Cr
, O, (abrasive) 2 parts by weight Stearic acid (Lubricant) 1 part by weight Butyl stearate (Lubricant) 1 part by weight Methyl ethyl ketone 150 parts by weight Toluene
150 parts by weight cyclohexanone
60 parts by weight The above composition was mixed in a ball mill for 24 hours, 4 parts by weight of a curing agent (trade name Coronate L) was added, mixed for 30 minutes, filtered through a 3 μm filter, and mixed with a 14 μm thick polyethylene filter. It was coated onto a terephthalate film so that the film thickness after drying was 4 μm, and then subjected to magnetic field orientation treatment, dried, and wound up. Further, after performing a super calender treatment, a heat treatment was further performed at 75° C. for 24 hours, and a sample tape was produced by cutting into a width of 172 inches.

The vinyl chloride copolymer used was vinyl chloride 8
8% by weight, average degree of polymerization 420. hydroxyl group), 85-
Peng o1/g, polar group (sodium sulfonate) 10
．． 04mmol/g.

According to the above method, various sample tapes were prepared by changing the type of polyurethane resin as shown in Table 2.

For each sample tape obtained (Examples 1 to 7, Comparative Examples 1 to 3), surface gloss, squareness ratio Rs, powder falling, and still time were measured.

The amount of powder falling off was determined by aging for one week at a temperature of 40°C and relative humidity of 80%, and then visually observing the amount of falling powder from the magnetic layer to the head drum after running the shuttle 100 times for 60 minutes. A score of 0 was given for almost no powder, and a score of 15 was given for a very large amount of powder. For the still time, the video signal was recorded after aging for one week under the conditions of a temperature of 40'C and a relative humidity of 80%, and its RF ratio output 2
The time taken for the temperature to drop to The results are shown in Table 2.

(Margins below) Table 2 As is clear from Table 2 above, magnetic recording media using polycarbonate urethane resin with tertiary amine introduced as a binder have high gloss and very little powder falling off. It can be seen that the magnetic properties and still properties are improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since a polycarbonate polyurethane resin having a tertiary amine in the molecule is used as the binder constituting the magnetic layer, the dispersibility of magnetic powder, non-magnetic powder, etc. is improved, and at the same time hydrolysis of the binder is suppressed. , it is possible to provide a magnetic recording medium with excellent durability.

Furthermore, since the dispersibility of magnetic powder and non-magnetic powder is improved, it is possible to eliminate deterioration of electromagnetic conversion characteristics due to drop-off and the like.

Patent applicant: Sony Corporation

Claims (1)

[Claims] A magnetic recording medium having a magnetic layer mainly composed of magnetic powder and a binder on a non-magnetic support, wherein the magnetic layer comprises a polycarbonate polyurethane resin having a tertiary amine in the molecule as a binder. A magnetic recording medium characterized by containing: