JPS626430A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve durability, magnetic characteristics, electromagnetic conversion characteristic, etc. by using a vinyl chloride copolymer having double bonds sensitive to electron rays and a ternary amine salt of a sulfonic acid or ternary amine salt of sulfate as a polar group in the molecule for a binder constituting a magnetic layer. CONSTITUTION:The vinyl copolymer having the double bonds sensitive to electron rays and further having the ternary amine salt of the sulfonic acid and the ternary amine salt of sulfate as the polar group in the molecule is used as the binder for the magnetic material, by which the high affinity to magnetic powder is exhibited and the good dispersibility is obtd. even with the ultrafinely pulverized magnetic powder or the magnetic powder having a large quantity of magnetization. The durability and surface characteristic of the resulted magnetic recording medium are improved and the electromagnetic conversion characteristic is extremely highly improved as well. Since the binder has the double bonds sensitive to electron rays in the molecule, the magnetic coated film is easily cured by the irradiation of electron rays and the process for production is extremely simplified; in addition, the pot life and solidification of the paint are improved and thus there are many advantages in the process.

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 electron beam sensitive double layer in the molecule. By using a vinyl chloride copolymer having a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt as a bond and a polar group, we aim to improve the solid content of the paint, improve the pot life, and simplify the manufacturing process. The aim is to improve the dispersibility of magnetic powder and the surface properties of the magnetic layer, thereby improving the durability, magnetic properties, electromagnetic conversion properties, etc. of the resulting magnetic recording medium.

[Conventional technology]

In recent years, in magnetic recording media, especially magnetic recording media for VTRs (video tape recorders), there has been a demand for improved magnetic properties and magnetic conversion properties 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.

On the other hand, conventionally used binders for magnetic recording media include vinyl chloride-vinyl acetate copolymer, vinyl chloride-propionic acid copolymer, and vinyl chloride-vinyl acetate copolymer.
Examples include vinyl chloride-based binders such as vinyl alcohol copolymers, among which the hydroxyl groups of vinyl alcohol contribute to the dispersibility of magnetic powder, and the active hydrogen of the hydroxyl groups reacts with isocyanate compounds to form a crosslinked structure. Vinyl chloride-vinyl acetate-vinyl alcohol copolymer is widely used because it increases the mechanical strength of the coating film formed.

Furthermore, it is known that electron beam-curable acrylic double bonds are introduced into these binders, and a magnetic paint made by mixing this with magnetic powder is applied onto a base film and then cured by irradiating it with electron beams. ing. The introduction of this electron beam-curable acrylic double bond is effective in improving the coagulation of the solid content of the paint and pot life, simplifying the manufacturing process, and saving energy.6 However, the above-mentioned magnetic powder Due to the increase in specific surface area due to finer particles and the increase in cohesive force due to higher magnetic force, it is difficult to obtain satisfactory dispersibility and surface properties with the above-mentioned binders, and it is also difficult to increase the backing density of magnetic powder. It has become a thing.

Therefore, the durability, magnetic properties, and electromagnetic conversion properties were also insufficient. Alternatively, methods such as using a surfactant as a dispersant have been considered, but in this case, since the surfactant is a low molecular weight, the presence of this surfactant in the magnetic layer causes the powder to become powdery. Problems have arisen regarding mechanical strength and durability, such as fading and blooming due to changes over time.

Under these circumstances, there is a need for binders that can further improve these properties, such as vinyl chloride-vinyl acetate copolymers with electron beam-sensitive double bonds or vinyl chloride-vinyl acetate-vinyl alcohol copolymers. For the purpose of improving the dispersibility of the combined magnetic powder, polymers with polar groups such as sulfonic acid or its alkali metal salts, a-type sulfuric esters or its alkali metal salts, carboxylic acids or its metal salts introduced into the side chains are used. Techniques for applying it as a binder have been proposed.

However, although the binders produced by these technologies show some effect in improving dispersibility compared to conventional binders in which no polar groups are introduced, The performance against powder was insufficient.

C Problems to be Solved by the Invention] As described above, there is no known binder that exhibits sufficient dispersibility even for ultrafine magnetic powder, and therefore magnetic recording using this ultrafine magnetic powder is not possible. It has been difficult to ensure predetermined durability, magnetic properties, and electromagnetic conversion properties in media.

Therefore, the present invention was proposed in order to eliminate the above-mentioned drawbacks in the technical field, and it significantly improves the dispersibility of magnetic powder and the surface properties of the magnetic layer while maintaining the advantages of electron beam sensitive double bonds. The object of the present invention is to provide a magnetic recording medium that is excellent in durability and has good magnetic properties and electromagnetic conversion properties by providing a binder that can be improved.

[Means for solving problems]

The inventors of the present invention have conducted intensive research over a long period of time in order to achieve the above-mentioned objective, and have found that sulfonic acid tertiary amine salts or sulfuric acid ester tertiary amine salts, which are polar groups, exhibit high affinity for magnetic powder. They discovered this and completed the present invention, which provides a magnetic recording medium in which a magnetic layer mainly consisting of ferromagnetic powder and a binder is formed on a non-magnetic support. It is characterized by containing a vinyl chloride copolymer having an electron beam sensitive double bond and a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt as a polar group.

In the present invention, the vinyl chloride copolymer contained in the binder has a polar group (sulfonic acid tertiary amine salt or sulfuric acid ester tertiary amine salt) on the side chain and an electron beam sensitive double amine salt. It introduces a bond, and has the general formula (CHzCH)+ (Z )j(CLCH)m (C
HzCtl)tl II ce x
y (in the formula, X represents a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt which is a polar group, Y represents a group having an electron beam sensitive double bond, and Z represents a vinyl copolymerizable with vinyl chloride. Each represents a monomer having a group, and i
, j, 1 represents the degree of polymerization, respectively. ) is a compound represented by In addition, in the above general formula,
For convenience, each component of the compound is described as being arranged in a regular order, but in addition to the case shown in the general formula above,
It goes without saying that each component may be regularly and repeatedly arranged in a fixed proportion, or may be arranged randomly.

In the above compound, the polar group X introduced into the side chain is (i) 0 (ii) 0 (iii) 0 (iv) 0 (v) 0 (vi) 0 (However, in any of the above polar groups , R1゜Rz
, R* represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, R4
represents a divalent organic residue represented by -CHz, 0CHzCHtCHz-1). Specific examples include the following.

OS　OHN(CHs)s 0SOHN(CzHs)* 0SOHN(CiHy)t II ■　　　　　0 ■　　　　0 ■　　　　0 ■　　　　0 ■　　　0 ■　　　0 D 0 ■　　　0 ■　　　　　　　0 11 e.

CHz　5OHN(C4Hq)i [Phase] O o 　　　　　0 [Phase] 0 e　　　　　O [Phase] O ■　　　　　cH,0 + 11 Go.

CN HCCHz S OHN (CtHs)*II
I 11OCH,○ OCHi 0 11 1 II OCR,0 0CH30 0CHz CHz CHz S OHN(C*H
,)x The above-mentioned polar group can be introduced into the vinyl chloride polymer by the following synthetic route.

(Left below) A. Acidic sulfate ester group in vinyl chloride-vinyl acetate-polyvinyl alcohol copolymer.

Method 6 of Grafting a Sulfonic Acid Group or a Molecular Residue Containing a Sulfonic Acid Group On the other hand, in addition to the above-mentioned scratching group, the binder used in the present invention includes a group Y having an electron beam sensitive double bond. is introduced into the side chain, and an acrylic double bond such as R6 (in the formula, R4 represents H or CHI) is effective as the electron beam sensitive double bond.

Examples of methods for introducing the acrylic double bond include the following methods.

0. A method in which one functional group of a bifunctional isocyanate compound is reacted with an acrylic or methacrylic compound capable of reacting with an isocyanate group, and then the other isocyanate group is reacted with an OH group of a vinyl alcohol component.

Here, as the above-mentioned bifunctional isocyanate compound, for example, hexamethylene diisocyanate.

Aliphatic diisocyanates such as isophorone diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, m-phenyl diisocyanate, p-phenyl diisocyanate, 2
．． 4-) lylene diisocyanate, 2.6-lylene diisocyanate, 1.3-xylylene diisocyanate, 1.4-xylylene diisocyanate, L5-naphthalene diisocyanate.

4.4'-diphenylmethane diisocyanate, 3,3
Aromatic diisocyanates such as '-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, ditolylene diisocyanate, dianisidine diisocyanate, and the like can be mentioned.

Examples of acrylic or methacrylic compounds that can react with isocyanate groups include acrylic acid, methacrylic acid, hydroxymethyl ester, 2-hydroxyethyl ester, and
Examples include hydroxyalkyl esters such as -hydroxypropyl ester, 4-hydroxybutyl ester, and 8-hydroxyoctyl ester, acrylamide, methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide. These reaction formulas are shown below.

RE-OH+ 0CN-Ra-NHC-0-C-C=C
L00R.

→ R1-0CNH-Ra-NHC-0-C-C1IC
Ht(C-2) R1 OCN-RA-NCO+ HO-Rm-0-C-CII
CI+□(C-3) (However, in the formula, R7 is vinyl chloride into which a polar group has been introduced.
Vinyl acetate copolymer, RA and h represent divalent hydrocarbon groups, R represents H or CH, respectively, )゛D, OH group of polyvinyl alcohol component, epoxy group or aziridinyl group and electron beam A method in which a compound having a functional double bond acts directly on the compound.

As the above-mentioned compound which acts directly, it is preferable to use 2-(1-aziridinyl)ethyl methacrylate, allyl-2-aziridinylpropionate, glycidyl methacrylate and the like. The reaction formula is as follows.

([1-1) R1 → Rt-0-CHzCIIt-NH(C)It),
11-0CC=CH→ Fh-0-CHzCHz-N
H(CHz)--COCHzCH=CHz(D-3) Rz-OH+ CHI CH-(C)It)--
OCC-CHz\0'8 R& (wherein R1 is a vinyl chloride copolymer into which a polar group has been introduced, R1 is H or CH, n is an integer from 1 to 8,
) It is also possible to introduce the vinyl alcohol component by directly reacting the hydroxyl group of the vinyl alcohol component with acrylic acid chloride or methacrylic acid chloride in the presence of a hydrochloric acid scavenger such as triethylamine or pyridine.

As described above, an electron beam sensitive double bond and a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt can be introduced into the vinyl chloride copolymer. In this introduction, an electron beam-sensitive double bond is added to the side chain hydroxyl group, and a sulfonic acid 3
Either the sulfonic acid tertiary amine salt or the sulfuric acid ester tertiary amine salt may be introduced first, but the double bond may be introduced later into the copolymer into which the sulfonic acid tertiary amine salt or the sulfuric acid ester tertiary amine salt has been introduced. In some cases, it may be necessary to subsequently partially saponify the synthesized copolymer to form a vinyl alcohol component, or to simultaneously copolymerize a vinyl monomer having hydroxyl groups.

Furthermore, the vinyl chloride copolymer described above may be copolymerized with a monomer Z having a vinyl group that is copolymerizable with vinyl chloride (such monomers Z include vinyl acetate, vinyl alcohol, maleic acid, etc.). , maleic anhydride, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonide 11, vinylidene chloride, vinyl propionate, etc. Select one or more of these monomers and copolymerize them. This makes it possible to control to some extent the solubility in solvents, the flexibility of coatings, the dispersibility of magnetic powder, etc.

Compound (binder) synthesized by the method described above
The vinyl chloride component contributes to the strength of the coating film and its solubility in solvents. That is, if the polymerization degree i of the vinyl chloride component is less than 100, the desired coating film strength cannot be obtained, and if i is greater than 1000, the solubility in the solvent will be poor. Therefore, it is necessary to set 1=100 to 1000. Furthermore, the vinyl component in which the scratching group X is introduced into the side chain contributes to improving the dispersibility of the magnetic powder due to the polar group in the side chain, but if the degree of polymerization k is less than 0.1, the vinyl component will not be dispersible. If it exceeds 100, problems will arise in terms of moisture resistance, so it is necessary to set it to 0.1 to 100. Furthermore, the vinyl component into which the group Y having an electron beam-sensitive double bond is introduced is important for causing a crosslinking reaction upon electron beam irradiation, but its degree of polymerization is 6 = 2 to 10.
It is preferable to set it to 0. If l is less than 2, crosslinking by electron beam irradiation will be insufficient, and if it exceeds 100, the crosslinking density will become too high, resulting in a coating structure with poor durability.

Further, in the present invention, the equivalent weight of the electron beam-sensitive binder for one polar group, that is, the molecular weight, is 200 to
A value of 100,000 is preferable. The reason is that if the equivalent weight is less than 200, the hydrophilicity of the binder will be too strong, resulting in poor solubility in solvents, compatibility with other binders, and moisture resistance of the magnetic coating; This is because if it is too large, the effect on the dispersibility of the magnetic powder will be insufficient. Similarly, the equivalent weight of the electron beam sensitive double bond is 200 to 1000
00 is better. If this equivalent exceeds 100,000, there will be insufficient crosslinking, while if it is less than 200, the crosslinking density will become too high and durability will deteriorate.

From this point of view, the following compounds are suitable for use as a binder in the present invention.

(Left below) (CHz4)ts CHI The compound represented by the above general formula may be used in combination with other binders. Such binders include those conventionally used as binders for magnetic recording media. Among them, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-acetic acid and maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer , chloride and nyl-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic Polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester Examples include resins, phenolic resins, epoxy 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. Moreover, if a trifunctional isocyanate compound, a reaction product of 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate, etc. are used in combination as a crosslinking agent, durability etc. can be further improved.

In any case, the polar group equivalent (molecular weight per polar group) of the sulfonic acid tertiary amine salt or sulfuric acid ester tertiary amine salt, which is the polar group in these binders, is 1000 to 10.
It is preferable that the polar group equivalent is within the range of 100,000.If the polar group equivalent exceeds 100,000, no effect can be expected;
If it is less than 0, the effect will not change much, but problems will arise in terms of moisture resistance.

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, paper, metals such as aluminum and copper. , 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 71941 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-150), magnetite (Fed, X=1.33)
and solid solutions thereof (FeOx, 1.33<X<1.5
Furthermore, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing iron oxides are roughly divided into two types: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide includes CrO, or Ru, Sn, Te, and Sb for the purpose of improving coercive force.
, Fe, Ti, V, Mn, etc. can be used.

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

Fe-Co, Fe-Ni, Fs-Co-Ni, Co-N
i, Fe-Co-B, Fe-Co-Cr-B, Mn-
B1. Mn-Al1. Fe-Co-V, etc. can be used, and ACSi,
Metal components such as Ti, Cr, Mn, Cu, and Zn may 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,
Rust inhibitors and the like may also be added.

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. Ketones, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, etc.
Aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, methylene chloride and ethylene chloride.

Tetracarbonized carbon L chloroform, ethylene chlorohydrin,
Examples include chlorinated hydrocarbons such as dichlorobenzene.

In addition, the applied magnetic paint is cured by irradiation with electron beams, and the irradiation amount is preferably 1 to 10 Mrad, and 2 to 10 Mrad.
When using a particle accelerator, the irradiation energy (acceleration voltage) is preferably 100 mrad or more. In the present invention, it is preferable to irradiate the magnetic coating film with an electron beam after applying the paint and subjecting it to calender treatment, but it is also possible to irradiate the magnetic coating film with calender treatment after irradiation.

[Effect]

As mentioned above, the sulfonic acid tertiary amine salt or sulfuric acid ester 3 which has an electron beam-sensitive double bond and a polar group in the molecule
By using a vinyl chloride copolymer containing a class amine salt as a binder, the affinity for magnetic powder is greatly improved, and it is suitable even for ultrafine magnetic powder or magnetic powder with a large amount of magnetization. The magnetic layer is easily hardened by electron beam irradiation.

〔Example〕

Ferromagnetic alloy powder (specific surface area 40n?/g) 100
Parts by weight Vinyl chloride-vinyl acetate copolymer 141 parts Polyurethane resin (N-2304) 141
1 part dimethyl silicone oil 1 part lecithin 1 part CrtOs
2 parts by weight Methyl ethyl ketone 100 parts by weight Methyl isobutyl ketone 50 parts by weight Toluene
50 parts by weight The above composition was mixed in a ball mill for 48 hours, filtered with a filter, and then further mixed with 3 parts by weight.
After mixing for 0 minutes, this was applied onto a polyethylene terephthalate film having a thickness of 16 μm so that the film thickness after drying was 6 μm. Next, after performing a magnetic field orientation treatment, the coating film was cured by electron beam irradiation and wound up. This was calendered and then cut to a width of 172 inches to produce a sample tape.

According to the method described above, electron beam sensitive double bonds (acrylic)
and a vinyl chloride-vinyl acetate copolymer into which a polar group 1 to Example 8 were obtained.

Similarly, a sample tape was prepared using a vinyl chloride-vinyl acetate copolymer into which no polar group had been introduced, and this was designated as Comparative Example 1. In addition, as a polar group -OS O!
Sample tapes were prepared using a vinyl chloride-vinyl acetate copolymer into which Na and SOz Na were introduced, and these were used as Comparative Example 2. This was designated as Comparative Example 3.

Surface gloss, powder removal, and still characteristics were measured for each sample tape obtained.

Note that the above surface gloss is based on the glossy needle (GLO3S METE).
R) under the conditions of an incident angle of 75' and a reflection angle of 75°. Further, powder falling was evaluated by visually observing the amount of falling powder on the head drum, guide, etc. after running the shuttle 100 times for 60 minutes, and using a point deduction method (-5 to 0). The still characteristics are
A video signal of 4.2 Mllz was recorded on a sample tape, and the time until the playback output attenuated to 50% was defined as the time. The results are shown in the table below.

(The following is a blank space) From this table, it can be seen that each sample tape according to the present invention not only has excellent surface gloss and powder removal, but also has lower still life compared to tapes in which 13OffNa or 10303N a is introduced as a polar group. 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,
The binder for the magnetic layer is a vinyl chloride copolymer that has an electron beam-sensitive double bond in the molecule and also has a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt as a polar group. Shows high affinity for powder,
Even if the magnetic powder is made into ultrafine particles or has a large amount of magnetization, the dispersibility will be good. therefore,
The durability of the obtained magnetic recording medium 1 The surface properties are improved, and it
The magnetic conversion characteristics are also extremely excellent.

In addition, since the above-mentioned binder has an electron beam-sensitive double bond in its molecule, the magnetic coating film can be easily cured by electron beam irradiation, which greatly simplifies the manufacturing process and reduces the pot life of the paint. There are also great advantages in the process, such as improved coagulation properties.Patent applicant: Sony Corporation Shin-Etsu Chemical Co., Ltd. Agent: Patent attorney: Kodo Kowa Art supplies: Sakae

Claims (1)

[Claims] 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 magnetic layer has electron beam sensitive double bonds and polarity in the molecules. A magnetic recording medium comprising a vinyl chloride copolymer having a sulfonic acid tertiary amine salt or a sulfuric acid ester tertiary amine salt as a binder.