JPH01292620A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain preferable crosslinked structures and to improve durability by incorporating butadiene copolymer having epoxy groups and vinyl chloride copolymer having active hydrogen in a binder of a magnetic layer essentially consisting of ferromagnetic powder and the binder. CONSTITUTION:The butadiene copolymer having epoxy groups to be used for the binder of the magnetic layer essentially consists of butadiene copolymer with which monomers having epoxy groups and double bonds crosslinkable with butadiene compound are copolymerized to form crosslinked structures. The vinyl chloride copolymer having active hydrogen essentially consists of vinyl chloride copolymer with which monomers having active hydrogen and double bonds crosslinkable with vinyl chloride copolymer are copolymerized to form crosslinked structures. Thereby, the binder is not affected by water in the reaction and preferable crosslinked structures can be formed, which improves durability of the medium.

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 more particularly to a binder contained in a magnetic layer formed on a non-magnetic support. This is related to the improvement of.

[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 has an epoxy group as a polar group in the molecule. The present invention attempts to provide a magnetic recording medium with excellent durability by using a butadiene-based copolymer having the above and a vinyl chloride-based copolymer having active hydrogen as binders.

[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. As a countermeasure, efforts have been made to make the magnetic powder particles finer and to increase the magnetic force, and there is a strong tendency to increase the packing density of the magnetic powder in the magnetic layer, the so-called backing density.

Therefore, the proportion of the binder in the magnetic coating film is extremely small. In a magnetic coating film containing such a small amount of binder, there is a risk that the magnetic layer will peel off when used as a magnetic recording medium.In order to prevent such deterioration in strength of the magnetic coating film, it is necessary to It is necessary to improve the strength of To this end, it has been proposed to improve the mechanical strength of the magnetic coating by crosslinking the binder in the magnetic coating.

As mentioned above, binders that increase the mechanical strength of magnetic coatings by forming a crosslinked structure include those that form a crosslinked structure using a compound that has an electron beam-sensitive bond in the molecule, or those that use a compound that uses a hydroxyl group in the molecule to form a crosslinked structure. It has been proposed to form a crosslinked structure by utilizing the reaction between active hydrogen and isocyanate-1-.

However, for example, a binder made of a compound having an electron beam-sensitive bond as described above requires extremely expensive equipment in order to form a crosslinked structure, and is therefore impractical.

On the other hand, in the case of the above-mentioned binder in which the active hydrogen of the hydroxyl group reacts with an isocyanate compound etc. to form a crosslinked structure, the reaction is aimed at -NGO+-OH→ -NGO-, whereas in the actual reaction, -N(
:O+ H2O→ -N)12 +CO□ The isocyanate reacts with water, and the amino group created by this reaction becomes -N11□+ -NCO→ -
It reacts with other isocyanates as NICONH-. Therefore, when an isocyanate compound is reacted with a hydroxyl group, effective -NGO groups are affected by moisture as shown in the above reaction formula, and the amount of -NGO groups that contribute to crosslinking decreases, making it difficult to form a sufficient crosslinked structure. This makes it less durable.

[Problem to be solved by the invention]

As mentioned above, a binder that forms a crosslinked structure through electron beam sensitive bonding and increases the mechanical strength of the coating film, or a binder that uses the reaction between isocyanate and hydroxyl groups to form a crosslinked structure and increase the mechanical strength of the coating film. Binders and the like used as binders lack practicality due to equipment problems, and the reaction itself is susceptible to moisture and does not form a good crosslinked structure. Therefore, magnetic recording media using these binders do not have sufficient durability. The problem is that it is not possible to obtain

Therefore, the present invention was proposed to solve the above-mentioned drawbacks in the technical field, and provides a binder that has a good crosslinked structure without being affected by moisture during the reaction to form a crosslinked structure. The object of the present invention is to provide a magnetic recording medium with excellent durability.

[Means to solve the problem]

As a result of extensive research over a long period of time in order to achieve the above-mentioned object, the present inventor has discovered that a binder consisting of a butadiene copolymer having an epoxy group and a vinyl chloride copolymer having an active hydrogen has excellent durability. The present invention was completed based on the discovery that the present invention exhibits the same properties as above.

That is, the magnetic recording medium of the present invention is 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 binder is a butadiene having an epoxy group. It is characterized by containing a vinyl chloride-based copolymer and a vinyl chloride-based copolymer having active hydrogen.

The butadiene-based copolymer having an epoxy group used as a binder in the present invention is mainly composed of a butadiene-based copolymer. It is made by copolymerizing a monomer having a double bond that can be copolymerized with a compound.

Here, the butadiene compounds constituting the butadiene copolymer include butadiene rubber mainly composed of 1,3-butadiene, butadiene-styrene rubber (SBR) which is a copolymer of 1,3-butadiene and styrene, and 1 .3
-butadiene-acrylonitrile rubber (NBR), which is a copolymer of butadiene and acrylonitrile, and the like. Furthermore, a monomer copolymerizable with a butadiene compound may be included as a third component.

Monomers copolymerizable with the above butadiene compound include vinyl chloride, vinylidene chloride, vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid,
Methacrylic acid, acrylic ester, methacrylic ester, hydroxyacrylate, hydroxymethacrylate, vinyl propionate and acrylamide alkyl sulfonic acid and its salts, phosphoric ester of hydroxyacrylate (methacrylate) and its salt, trialkylammonium alkyl methacrylate halide, Examples include monomers having a hydrophilic group such as acrylic acid dialkylaminoalkyl ester. By selecting and copolymerizing one or more of these monomers, the solubility in solvents, the physical properties of the coating film, the dispersibility of the ferromagnetic powder,
Crosslinkability etc. can be controlled to some extent.

However, in this case, the proportion of butadiene in the copolymer is preferably in the range of 95 to 50% by weight, and if the content of butadiene is less than 50% by weight, the original characteristics of the butadiene copolymer will be lost. For example, the SN ratio deteriorates.

Further, the number average molecular weight is preferably about 5,000 to 100,000.

In addition, examples of monomers having a double bond copolymerizable with the butadiene compound and having an epoxy group introduced to form a crosslinked structure include unsaturated alcohols such as acryl glycidyl ether and methacryl glycidyl ether. glycidyl ethers of unsaturated acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl p-vinyl benzoate, methylglycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiyl esters of unsaturated acids, butadiene monooxide,
Vinylcyclohexene monooxide, 2-methyl-5
, 6-nipoxyhexene and other epoxide olefins.

The amount of epoxy groups contained in the butadiene copolymer is preferably about 0.05 to 2.5 mmol/g. If the amount of this epoxy group is small, durability will deteriorate, and if it is large, it will be difficult to make it into a paint.

The vinyl chloride copolymer having active hydrogen used as a binder in the present invention is mainly composed of a vinyl chloride copolymer, and the active hydrogen and chloride introduced therein to form a crosslinked structure are It is made by copolymerizing a monomer having a double bond that can be copolymerized with a vinyl compound.

Here, the vinyl chloride compounds constituting the vinyl chloride copolymer include a homopolymer obtained mainly by suspension polymerization of vinyl chloride, a binary copolymer of vinyl chloride and vinyl acetate, and a copolymer of vinyl chloride and vinyl acetate. Examples include binary copolymers with higher vinyl ethers, terpolymers of vinyl chloride, vinyl acetate, and maleic acid derivatives, and the like. The colander may contain a monomer copolymerizable with a vinyl chloride compound as another component.

Monomers copolymerizable with the above vinyl chloride compounds include vinyl chloride, vinylidene chloride, vinyl acetate, vinyl alcohol, maleic acid, maleic anhydride, acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, and hydroxyacrylate. , hydroxy methacrylate, vinyl propionate and acrylamide alkyl sulfonic acid and its salts, hydroxy acrylate (
Examples include monomers having a hydrophilic group such as phosphoric acid esters of (methacrylate) and salts thereof, trialkylammonium alkyl methacrylate halides, and dialkylaminoalkyl acrylates. By selecting and copolymerizing one or more of these monomers, the solubility in solvents, the physical properties of the coating film, the dispersibility of the ferromagnetic powder, the crosslinking properties, etc. can be controlled to some extent.

However, in this case, it is preferable that the proportion of vinyl chloride in the copolymer be 50% by weight or more; if the content of vinyl chloride is less than 50% by weight, the original characteristics of the vinyl chloride copolymer will be lost. be exposed. In addition, the average degree of polymerization is 100
It is preferable that it is about 1,000 to 1,000.

In addition, as a monomer having a double bond copolymerizable with the above-mentioned vinyl chloride compound and having active hydrogen introduced to form a crosslinked structure, for example, C1h = CH
0C4HaOIl.

C1l□ -C1l CN11C1120)1
.

CHl2 -- CIl C11□O(C:II
□c)12o-)-7)1゜CH3 CH2= CIl -CI(20(CH3COOh
H.

CH3′CHg=CH-CH20(ClIC1120-)
−r−+CH2Cll0辷=)I, CHI=
CHCO(C)IzC)IzOsu,)I.

CH30 CHz = CCO (CHzCllzO+-TH.

CHz = C to O(CHzCIIO+1r
Compounds having a hydroxyl group such as H- (in the above, m and n represent numbers from 2 to 9); acrylic acid, methacrylic acid,
Maleic acid, fumaric acid, ester of maleic acid and 2-hydroxyethyl methacrylate, ester of maleic acid and 2-hydroxyacrylate, maleic acid and 2-
Compounds with a carboxyl group such as esters with hydroxypropyl acrylate; esters between phosphoric acid and 2-hydroxyethyl methacrylate, esters between phosphoric acid and 2-hydroxyacrylate, esters between phosphoric acid and 2-hydroxypropyl acrylate, etc. Compounds with phosphate groups; CHl. -CI SOJ , CHz = CII
CIIZ 5Q3H.

C11° CL = Cll-C6H4-5O3H, CH2=C-C
H2SOJ, CHl CH2=CH(-Go-NH-C-CHzSOJ.

■ CH3 CH3 CUt SeC-Coo -CZlltSO3H1C
H2=CHCOOCJ4. S.O.J.

Examples include compounds having a sulfonic acid group such as.

The amount of active hydrogen contained in the vinyl chloride copolymer is preferably about 0.05 to 4.0 mmol/g. If the amount of active hydrogen is small (H7), good crosslinking properties cannot be obtained, and if it is large, the viscosity of the paint increases and the properties of the paint deteriorate.

In the present invention, by combining the above-mentioned butadiene-based copolymer having an epoxy group and the above-mentioned vinyl chloride-based copolymer having an active hydrogen, the active hydrogen and the epoxy group react to form a butadiene-based copolymer. A crosslinked structure develops between the vinyl chloride copolymers, resulting in a coating film with excellent durability.

This crosslinking reaction is shown as follows.

(However, Rbuta represents a butadiene copolymer, and R
vi□ represents a vinyl chloride copolymer. ) The ratio of the butadiene copolymer and vinyl chloride copolymer is butadiene copolymer/vinyl chloride copolymer -278
A ratio of ~8/2 is desirable.

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 butadiene-based copolymer can be promoted. For example, it is also possible to form a crosslinked structure between butadiene copolymers by crosslinking them with active hydrogen (eg, hydroxyl group) contained in the butadiene copolymers. Of course, it is also possible to form a similar crosslinked structure with active hydrogen contained in the vinyl chloride copolymer.

By using the crosslinked structure between a butadiene copolymer and a vinyl chloride copolymer as described above, and the crosslinked structure between butadiene copolymers, a magnetic coating film with even greater strength can be obtained.

The above-mentioned epoxy group-containing butadiene copolymer and active hydrogen-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 derivative, styrene-butadiene copolymer, polyester resin, phenolic resin, epoxy Examples include resins, thermosetting polyurethane resins, 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 butadiene copolymer or active hydrogen-containing vinyl chloride copolymer or other binder used in combination for the purpose of further improving dispersibility.

The hydrophilic polar groups include -3OJ group, -0503M
group, -PO(OM')z group, -C00M group, -NG3J
group (where M is a hydrogen atom or an alkali metal atom, M'
is a hydrogen atom, an alkali metal atom or a hydrocarbon atom, G
represents an alkyl group, and J represents a halogen. ) etc.

In the magnetic recording medium of the present invention, the magnetic layer is formed by coating the surface of the non-magnetic support with a magnetic paint prepared by, for example, dispersing ferromagnetic powder in the above-mentioned binder and dissolving it in 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. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum.

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.

The above-mentioned ferromagnetic iron oxide particles are those whose X value is in the range of 1.33≦X≦1.50 when expressed by the general formula FeOx, that is, magnetite (γ-Fed).

x=1.50), magnetite (Fed, x=1.3
3) 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.

The above-mentioned ferromagnetic chromium dioxide includes cro2 or Ru, Sn, Te, and S for the purpose of improving coercive force.
A material to which at least one of b, Fe, Ti, V, Mn, etc. is added can be used.

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

Co-Ni, ,Fe-Co-BXFe-Co-Cr-B
XM n -B i , M n -A R1Fe-
Co-V etc. can be used, and Aj! can be used to improve various properties of these. , S i, Tt, Cr, Mn, , Cu
.

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.

The above-mentioned constituent materials of the magnetic layer are prepared as a magnetic paint by dissolving it in a ta-containing solvent, and are coated on a non-magnetic support.
Solvents for the magnetic paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol acetate monoethyl ether, glycol dimethyl ether, and glycol. Glycol ether solvents such as monoethyl ether and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, aliphatic hydrocarbon solvents such as hexane and heptane, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, Examples include organic chlorine compound solvents such as ethylene chlorohydrin and dichlorobenzene.

〔Example〕

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

The butadiene copolymer used as the binder in this example is shown in Table 1, and the copolymer monomer of the vinyl chloride copolymer is shown in Table 2.

Table 1 Table 2 VC: Vinyl chloride B8: Phyl 7 acrylate 0: 2-hydroxyethyl methacrylate C: Maleic acid P: Ester of 2-hydroxyethyl methacrylate and phosphoric acid S: 2-acrylamide-2-methylpropanesulfone Acid SO: +Na: Sodium 2-acrylamido-2-methylpropanesulfonate NR2 Niacrylamidopropane dimethylamine Vinyl chloride copolymer from a butadiene copolymer shown in Table 1 and a copolymer shown in Table 2 A magnetic recording medium was fabricated using this as a binder.

Examples 1 to 15 Co adhesion r Fe2O3 100 parts by weight Vinyl chloride copolymer 16 parts by weight butadiene copolymer
8 parts by weight carbon blank (antistatic agent)
2 parts by weight Cr z○3 (abrasive)
2 parts by weight dimethyl silicone (lubricant) 1 part by weight butyl stearate (lubricant) 1 part by weight methyl ethyl ketone 100 parts by weight toluene
60 parts by weight cyclohexanone
60 parts by weight 2 parts by weight of dimethylstearylamine was used as a catalyst if necessary.

The above composition was mixed in a ball mill for 24 hours, filtered through a 3 μm filter, and then applied onto a 14 μm thick polyethylene terephthalate film so that the film thickness after drying was 6 μm. After performing magnetic field orientation treatment (next), the film was dried and rolled 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.

Comparative Examples 1 to 5 In the composition of the magnetic paint, the butadiene copolymer was selected from one of the butadiene copolymers shown in Table 1, and the vinyl chloride copolymer was selected from the copolymer monomers shown in Table 2. Sample tapes were prepared in the same manner as in Example 1, except that the type and monomer composition of the vinyl chloride copolymer were changed as shown in Table 3. .

Still characteristics and powder fall-off were measured for each sample tape obtained.

The above still characteristics are based on 4.2M I on the sample tape.
(The video signal of z was recorded, and the time until the playback output attenuated to 50%.
After running 0 times, the amount of powder falling onto the head drum, guide, etc. was visually observed and evaluated using a point deduction method (-5 to 0). The results are shown in Table 3.

(The following margins are continued on the next page.) Table 3 [ [ '' ■ 2 B As is clear from Table 3 above, each sample tape according to the present invention not only has less powder falling, but also It can be seen that the characteristics have been significantly improved.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
By using a butadiene copolymer containing epoxy groups and a vinyl chloride copolymer containing active hydrogen,
The action of active hydrogen in the vinyl chloride copolymer promotes the ring-opening reaction of the epoxy group in the butadiene copolymer.
A crosslinking reaction occurs between the butadiene copolymer and the vinyl chloride copolymer, resulting in a binder with excellent mechanical strength.

Furthermore, since this reaction proceeds almost unaffected by moisture, the binder can have very good durability.

Therefore, by using this binder, a magnetic recording medium with excellent durability can be provided without deteriorating the electromagnetic conversion characteristics.

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer mainly consisting of ferromagnetic powder and a binder is formed on a non-magnetic support, the binder comprises a butadiene copolymer having an epoxy group and an active hydrogen. A magnetic recording medium characterized by containing a vinyl chloride copolymer.