JPS6284423A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an electromagnetic conversion characteristic, dispersibility of pulverized ferromagnetic powder and shelf life of a magnetic coating compd. by incorporating >=1 kinds of compds. selected from a specific group as a binder into a magnetic layer and irradiating radiation thereto. CONSTITUTION:>=1 kinds of the compds. selected respectively from the group shown by (A) and (B) are incorporated as the binder into the magnetic layer and the radiation is irradiated thereto. (A) is a polyvinyl chloride (meth)acrylate contg. a polar group and (B) is a polyurethane (meth)acrylate contg. an OH group. The preferable hydroxyl value of the urethane (meth)acrylate is 1-50 and the mol.wt. thereof is 1,000-100,000. The average content of the (meth) acryloyl group is 1.5-10, more preferably 2-8 for each one molecule. The preferable range of the compsn. ratio between the compd. shown by (A) and the compd. shown by (B) is 20-90/80-10pts.wt. The medium which exhibits the good electromagnetic conversion characteristic and still durability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as video tapes, audio tapes, computer tapes and the like.

[Prior art]

Magnetic recording media that are currently widely used include thermoplastic resins such as vinyl chloride-vinylidene chloride resin, vinyl chloride vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, acrylonitrile butadiene resin, etc. as a binder. There is a method of using these materials alone or in combination, but this method has the disadvantage that the abrasion resistance of the magnetic layer is poor and the running path of the magnetic tape is contaminated.

Also known are a method using a thermosetting resin such as a melamine resin or a urea resin, or a method in which a crosslinkable binder such as an isocyanate compound or a compound having an epoxy ring is added to the thermoplastic resin through a chemical reaction. However, when the above-mentioned crosslinking binder is used, l) there is a problem in the storage stability of the liquid in which magnetic particles are dispersed, and the uniformity of the physical properties of the magnetic coating liquid and, by extension, the homogeneity of the magnetic recording medium cannot be maintained; 2) A heat treatment step is essential for curing the coating film after coating and drying, and it has disadvantages such as requiring a long time.

In order to prevent these drawbacks, a method for producing magnetic recording media using acrylic acid ester oligomers and monomers as binders and curing them by irradiation with radiation after drying was proposed. Kaisho≠7-136
No. 32, JP-A Sho≠7-/j10μ, JP-A ShojQ-77
4t3.3, Tokukai Akira! It is disclosed in various publications such as No. t--23'23/. However, with the manufacturing method disclosed in the above patent publication, a magnetic recording medium having high electromagnetic conversion characteristics and durability could not be obtained.

[Problems to be solved by the present invention]

In recent years, there has been a demand for higher image quality in magnetic recording media.

This requires closer contact between the magnetic layer surface and the video head and audio head.
It is important to improve the surface smoothness of the magnetic recording medium and to further dramatically improve the dispersibility of the ferromagnetic fine powder. -1 The smoother the surface of the magnetic layer, the greater the friction in the running system inside the video tape recorder.
As running tension increases, magnetic recording media are required to have increasingly severe running durability. For this reason,
Conventional manufacturing methods for magnetic recording media have not yielded magnetic recording media that have the smoothness of the surface of the magnetic layer, the dispersibility of the ferromagnetic fine powder, and the running durability.

The present inventors have proposed a method using a thermoplastic resin, a thermosetting resin, and a method of adding a crosslinking binder through a chemical reaction.
Furthermore, the present invention was achieved as a result of extensive research to improve the drawbacks of conventional techniques, such as methods using radiation-curable binders.

Therefore, the objects of the present invention are to provide characteristics that could not be achieved with conventional magnetic recording media, namely: l) excellent electromagnetic conversion characteristics;
The ferromagnetic fine powder has excellent dispersibility, 3) the magnetic coating liquid has good storage stability and uniform performance, and 4) it has excellent running durability and does not require a heat treatment process to harden the coating film. The purpose of the present invention is to provide a magnetic recording medium that is of high quality.

Composition of the invention [Means to solve problems] The above problem is solved by the method described below.

That is, the present invention provides (1) a magnetic recording medium comprising a magnetic layer provided on a non-magnetic support, in which the magnetic layer comprises one or more compounds selected from the groups shown below (A) and (B). It relates to a magnetic recording medium characterized in that it contains as a binder and is irradiated with radiation.

(A) Polyvinyl chloride (meth)acrylate containing a polar group (B) Polyurethane (meth)acrylate containing an OH group The polyvinyl chloride (meth)acrylate (A) containing a polar group used in the present invention is ( Hereinafter, acryloyl group and methacryloyl group are collectively referred to as (meth)acryloyl group, acrylate, and methacrylate are collectively referred to as (meth)acrylate), and as a polar group, CO2H
,OH.

So B H, SO3N a, OP O3H, OP
Vinyl chloride-vinyl acetate copolymers containing groups such as 03Na, vinyl chloride-vinyl propionate copolymers,
It is a (meth)acrylate of a copolymer such as vinylidene chloride-vinyl acetate copolymer. Preferred polar groups are Co2H,OH groups, most preferably C0
It is a 2H group. When the polar group is a CO2H group, the CO2H content in terms of acid value is preferably 30 to 30, more preferably 3 to 20. When the polar group is an OH group, the hydroxyl value is 7 to 30. Preferably it is 10-30. If it is outside this range, the dispersibility of the ferromagnetic fine powder will be poor and the electromagnetic conversion characteristics will also be significantly reduced. The average content of (meth)acryloyl groups per molecule is /,! r%20, preferably 2-10.

Outside this range, the curing properties may be poor or the durability may be poor.

These compounds are based on polyvinyl chloride polymers such as vinyl chloride-vinyl acetate copolymers,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-Pa vinyl pionate-vinyl maleate Copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-maleic acid copolymer, vinylidene chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid Copolymers, vinyl chloride copolymers such as vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymers, and these copolymers may be used after being saponified.

As a method for introducing (meth)acrylate groups, a part of the OH group or CO2H group of these copolymers or a part of the hydroxyl group generated by saponification is introduced into a polyfunctional isocyanate (for example, 2. -tolylene diisocyanate, 2゜4-) lylene diisocyanate,
l,3-xylylene diisocyanate, 19 μm xylylene diisocyanate, i, s-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, μ, 4C-diphenylmethane diisocyanate, 3,3-dimethyl −μ.

diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane, etc.), and the remaining NGO group is converted into active hydrogen having a (meth)acryloyl group. Compounds (e.g. (meth)acrylic acid, hydroxyalkyl (meth)acrylates such as co-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, co-hydroxybutyl (meth)acrylate, (meth)acrylamide, N- methylol(meth)acrylamide)
It can be obtained by a method of reacting with.

Furthermore, examples of methods for introducing polar groups include the following methods. A part of the OH group or C02H group of the above-mentioned base copolymer, or a part of the OH group generated by saponification, is reacted with one NCO group of the polyfunctional isocyanate, and the remaining NCO group is converted to C02H.
It can be obtained by reacting a hydroxyl compound containing an O2H group, an 803 Na group, an OP Oa Na group, etc. It is also possible to introduce the polar group simultaneously with the (meth)acryloyl group. Alternatively, a compound having both a polar group and a (meth)acryloyl group may be used. The method of introducing these groups is not limited to the above-mentioned method.

The urethane (meth)acrylates (B) containing an OH group used in the present invention may have a main chain skeleton of polyester, polyether, or polyester ether, and specific examples of dibasic acids used therein include Citrus acid, mapric acid, succinic acid, glutaric acid,
Adipic acid, sepacic acid, dodecane λ acid, maleic acid,
Fumaric acid, itaconic acid, trimethyladipic acid, hexahydrophthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, etc. can be used. Examples of dihydric alcohols include ethylene glycol, trimethylene glycol, tetramethylene glycol, -metamethylene glycol, hexamethylene glycol, octamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and co-1,2-dimethylpronomol. Hmm/, :I
-diol, 2. -1 diethylpropane/, J-diol, Schiff's hexane-7,3-diol, cyclohexane-1.

l-diol, cyclohexane-I, dirzimethanol, cyclohexane-/, J-dimethatool, 2,2-bis(4A-human tetraxyethoxycyclohexyl)propane, 2I co-bis(≠-hydroxyethoxyphenyl)propane, λ, 2-bis(hydroxyethoxyethoxyphenyl)propane, etc. can be used. It is also possible to use a lactone-based polyester skeleton made of γ-butyrolactone, δ-valerolactone, C-caprolactone, or the like. Isocyanates that form urethane bonds include co, μ-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, '1≠-xylylene diisocyanate, ``l''l thietalene diisocyanate, m-
Phenylene diincyanate, p-phenylene diincyanate, J,! -Dimethylphenylene diisocyanate, μ, diphenylmethane diisocyanate, 3°3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, inphorone diisocyanate, dicyclohexylmethane diisocyanate, and other polyvalent incyanates can be used. The OH group and (meth)acryloyl group may be located at the terminal or side chain of the polyurethane. The method for introducing these groups is to replace a portion of the dihydric alcohol with a trivalent or higher alcohol, form a urethane oligomer using a polyhydric polyester polyol, and then introduce a portion of the side chain and/or terminal OH group. N reacted with diisocyanates
It can be obtained by reacting a compound having a CO group with hydroxy (meth)acrylates.

The preferred hydroxyl value of the urethane (meth)acrylate used in the present invention is /-jO, more preferably ~4cO, and still more preferably /θ~30.

The molecular weight is /, 000% 10o, ooo, preferably 1. <C2.00OA-10°ooo, particularly preferably 3,000 to 3θ,oo.

It is. If the hydroxyl value is out of this range, the dispersibility of the ferromagnetic fine powder will be poor, leading to a decrease in electromagnetic conversion characteristics and deterioration in durability. The average content of (meth)acryloyl groups is 1 to io per 7 molecules, preferably 1 to t.

When the molecular weight is lOθO, the magnetic layer of the obtained magnetic recording medium becomes too strong (too strong), causing problems such as cracking when bent, and curling of the magnetic recording medium due to curing shrinkage after irradiation. On the other hand, the molecular weight is 10
If it exceeds 0.00θ, the solubility of urethane (meth)acrylate in solvents tends to be poor, which not only makes handling inconvenient (but also causes the dispersibility of the magnetic material to deteriorate and requires a large amount of energy for curing). So I don't like it.

Furthermore, vinyl monomers can be added to the present invention. Vinyl monomers include compounds that can be polymerized by radiation irradiation and have one or more carbon-carbon unsaturated bonds in the molecule, such as (meth)acrylic esters, (meth)acrylamides, allyl Compound,
Examples include vinyl ethers, vinyl esters, vinyl heterocyclic compounds, N-vinyl compounds, styrenes, acrylic acid, methacrylic acid, crotonic acids, itaconic acids, and olefins. Among these, preferred are the following compounds containing two or more (meth)acryloyl groups. Specifically, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,
Polyethylene glycol (meth)acrylates such as meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol is meth(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tris(β-(meth)acryloyloxyethyl)isocyanurate, bis(β-(meth)acryloyloxyethyl)isocyanurate, or polyisocyanate(2, di-lylene diisocyanate 1)
．． 2.4-) lylene diisocyanate, l, 3-xylylene diisocyanate, /, g-xylylene diisocyanate, 1. ! - naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3-dimethylphenylene diisocyanate, μ, l-diphenylene diisocyanate, 3,3-dimethyl-≠,
diphenylmethane diisocyanate, hexamethylene diisocyanate, inphorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpronoξ), and hydroxy (meth)acrylate compounds (2-hydroxyethyl (meth)acrylate, λ-hydroxy and other poly(meth)acrylates having two or more functional groups. These monomers may be used alone or in combination of two types.
More than one species may be used.

The preferable range of the composition ratio of the compound represented by (A) and the compound represented by (B) is 20 to 0 parts by weight/
If O-70 parts by weight, particularly preferably j O to lrO
parts/70 to 20 parts. If the ratio of the compound represented by (A) is less than this ratio or the ratio of the compound represented by (B) is less than this ratio, durability cannot be obtained. Further, the amount of the vinyl monomer added is -7 in total of the compounds represented by (A) and (B) above! - Preferably 10 parts by weight or less based on the total parts by weight. If the ratio is higher than this, the amount of radiation required for polymerization becomes undesirable, and the magnetic recording medium may curl or may not have sufficient durability.

As the ferromagnetic fine powder used in the present invention, ferromagnetic iron oxide fine powder, CO-doped ferromagnetic iron oxide fine powder, ferromagnetic silium dioxide fine powder, ferromagnetic alloy powder, barium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is 1.2//-Jo/1, preferably z/i or more, and the average length is preferably in the range of about 0°2 to J, 0 μm. Ferromagnetic alloy powder has a metal content of 7jwt%
Above, I Ow t% or more of the metal content is ferromagnetic metal (i.e., Fe).

Co, Ni, Fe-Ni, Co-N1. Fe-Co-N
1) is a particle with a major axis of about 2.2 μm or less. The present invention is particularly effective because it is difficult to disperse the ferromagnetic fine powder.
It is a fine particle ferromagnetic alloy powder having a T specific surface area of JO1, preferably uom/I1 or more.

Organic solvents used for dispersion and application of magnetic coating liquids include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methyl acetate,
Ester systems such as ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether; ethyl ether,
Ethers such as I7-comethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, tetrachloride, chloroform, ethylene chlorohydrin,
Chlorinated hydrocarbons such as dichlorobenzene can be selected.

In addition, even if additives such as lubricants, abrasives, dispersants, antistatic agents, and rust preventives are added to the magnetic coating liquid of the present invention, the lubricants may contain saturated or These include unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine compounds, etc. These may be added when preparing the magnetic coating liquid, or they may be added after drying or irradiation. Afterwards, it may be dissolved in an organic solvent and applied or sprayed directly onto the surface of the magnetic layer.

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

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

In addition, the support of the present invention has a so-called so-called pack surface on the side opposite to the side on which the magnetic layer is provided for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, improving the strength of magnetic recording media, and making the back surface matte. A back coat/lf- may be provided.

In the present invention, it is preferable to irradiate radiation after applying a magnetic paint and performing calender treatment, but it is also possible to perform calender treatment after irradiation. Alternatively, it is also possible to irradiate one more time.

The radiation irradiated to the magnetic layer of the present invention includes electron beam, r
Although rays, β rays, ultraviolet rays, etc. can be used, electron beams are preferable. As the electron beam accelerator, a scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. can be adopted.

As for the electron beam, the accelerating voltage is 100-1000 KV, preferably /tO~J00KV tar'), and the absorbed dose is t--20 Mrads, preferably 3 to /1 Mrad. When the accelerating voltage is less than 100 Kv, the amount of energy transmitted is insufficient, i.

If it exceeds 0QKv, the efficiency of energy used for polymerization decreases, making it uneconomical. If the absorbed dose is less than /Mrad, the curing reaction will be insufficient and the strength of the magnetic layer will not be obtained;
If it exceeds ad, the energy efficiency used for curing decreases, the object to be irradiated generates heat, and especially the plastic support deforms, which is not preferable.

The present invention will be explained in more detail below using Examples and Comparative Examples. In the following Examples and Comparative Examples, all "parts" indicate "parts by weight."

Example 1 A magnetic coating liquid having the following composition was kneaded in a ball mill for 10 hours.

Fe alloy powder (/j000e.

BET specific surface area 44/m"/77) 1DO moiety bond composition C0OH group-containing vinyl chloride copolymer based acrylate 60 parts (oxidation 10,
Molecular weight: 20,000, average acryloyl group content: 4 LO parts of OH group-containing urethane acrylate (hydroxyl value: 20, molecular weight: to.

000 Average acryloyl group content 3 pieces/molecule) Stearic acid particulate butyl stearate q part A1□03
Sanbe carbon black
19 parts methyl ethyl ketone
After dispersing 100 parts, 3 parts of the dry film was spread on a polyethylene terephthalate support with a thickness of 10 μm using a doctor blade.
After coating to a thickness of μm and orienting using a cobalt magnet, the solvent was dried (for too'cI minutes) and calendering was performed. Next, the sample was irradiated with an electron beam at an accelerating voltage of 4 jKV and a beam current of A mA to give an absorbed dose of 7 Mrad, and then slit into a width of 172 inches to obtain a magnetic tape sample cliff l for video.

Magnetic tape samples were obtained in the same manner as in Example I except that the binder composition in Example I was changed as shown in Table 1. The evaluation results are summarized in Table 2.

-J/- The evaluation method was as follows.

Measurement of hydroxyl value: Sample 19 was dissolved in tetrahydrofuran, acetylated with acetic anhydride/pyridine, and then back titrated with a solution of potassium hydroxide in ethyl alcohol water (Ri!/NIF volume %) using phenolphthalene as an indicator.

Measurement of oxidation: Dissolve /l/ of the sample in tetrahydrofuran, titrate with a solution of potassium hydroxide in ethyl alcohol/water (volume %) using phenolphthalene as an indicator, and calculate the number of potassium hydroxide required. It was taken as acid value.

Still durability time: Videotape (
A constant video signal is recorded for each sample), and the time taken for the reproduced stop image to lose its sharpness is shown (the experiment was performed at z o
cro%RH).

Video S/N: Using the video tape recorder mentioned above, record the gray signal with a 10% setup, and
Noise was measured using a manufactured JzC type S/N meter and expressed as a relative value when sample A/ was set as OdB.

Storage stability: After the magnetic coating liquid was stored for 21 hours at room temperature and stirred for 10 minutes, a magnetic tape was prepared by the method described in Example 1, and the video S/N was measured. Storage stability was evaluated using the video S/N of each sample as OdB when a magnetic tape was prepared immediately after dispersion of the coating solution.

〔Effect of the invention〕

The magnetic recording medium of the present invention exhibits good electromagnetic conversion characteristics,
It can also be seen that it exhibits excellent still durability. Furthermore, it was confirmed that the magnetic layer composition liquid of the magnetic recording medium of the present invention has excellent storage stability.

Claims (4)

[Claims] (1) In a magnetic recording medium comprising a magnetic layer provided on a non-magnetic support, the magnetic layer contains one or more compounds selected from the groups shown below (A) and (B) as a binder. A magnetic recording medium characterized by being irradiated with radiation. (A) Polyvinyl chloride (meth)acrylate containing a polar group (B) Polyurethane (meth)acrylate containing an OH group (2) Compound (A) is CO with an acid value of 1 to 30 as a polar group
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a polyvinyl chloride (meth)acrylate containing a _2H group, an OH group with a hydroxyl value of 1 to 50, or both. (3) The magnetic recording medium according to claim (1), wherein the compound (B) is a polyurethane (meth)acrylate containing an OH group having a hydroxyl value of 5 to 50. (4) The magnetic recording medium according to claim (1), wherein the ferromagnetic fine powder used in the magnetic layer is a ferromagnetic alloy powder having a BET specific surface area of 30 m^2/g or more. .