JPH01267827A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of fine ferromagnetic powder and electromagnetic conversion characteristics by constituting a magnetic layer of specific two groups and incorporating compds. of respectively >=1 kinds of the two groups as a binder therein and further subjecting the layer to radiation irradiation. CONSTITUTION:The magnetic layer is constituted to contain the compds. of respectively >=1 kinds of the two groups shown by the group of the compds. obtd. by adding a polybasic unsatd. acid or unsatd. acid and polybasic acid to an epoxy group-contg. vinyl chloride copolymer and the group of (meth) acryloyl group-contg. polyurethane (meth)acrylate contg. 0.05-5mgeq/g metal base of sulfonic acid and is further subjected to the radiation irradiation. The magnetic recording medium having the excellent electromagnetic conversion characteristics and the excellent dispersibility of the fine ferromagnetic powder is thereby obtd.

Description

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

[Conventional technology]

Magnetic recording media that are currently widely used include thermoplastic binders such as vinyl chloride-vinyl acetate resin, vinyl chloride-vinylidene chloride resin, cellulose resin, acetal resin, urethane resin, and acrylonitrile butadiene resin. There is a method of using resins 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, 1) the storage stability of the liquid in which magnetic particles are dispersed is poor, 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 indispensable for curing the coating film after application and drying, and it also has disadvantages such as requiring a long time.

In order to prevent these drawbacks, methods for manufacturing magnetic recording media using acrylic ester oligomers and monomers as binders and curing them by irradiation with radiation after drying have been proposed in Japanese Patent Publication No. 47-12423 and Japanese Patent Application Laid-open No. 47-13639. , JP-A-47-15104, JP-A-50-77433
No., JP-A-56-25231, JP-A-61-8920
No. 7, JP-A-61-106605, and other publications. However, the manufacturing methods disclosed in the above-mentioned publications have not been able to produce magnetic recording media with advanced electromagnetic conversion characteristics and durability.

[Problem to be solved by the 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. The smoother the surface of the unidirectional 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 achieve characteristics that could not be achieved with conventional magnetic recording media, namely: 1) excellent electromagnetic conversion characteristics;
〉 Excellent dispersibility of ferromagnetic fine powder, 3) Good storage stability and homogeneous performance of the magnetic coating liquid, 4) Excellent running durability, 5) Heat treatment process for curing the coating film The aim is to provide a magnetic recording medium that does not require the use of magnetic recording media.

[Means and effects for solving the problem] The above problems can be solved by the method described below. That is, the present invention provides a magnetic recording medium mainly consisting of a non-magnetic support and a magnetic layer, in which the magnetic layer contains one or more compounds from the groups shown below (^) and (B), and further comprises The problem is solved by a magnetic recording medium characterized by being irradiated.

(A) A compound obtained by adding a polybasic unsaturated acid, or an unsaturated acid and a polybasic acid to an epoxy group-containing vinyl chloride copolymer.

(B) 0.005 to 5 lIge of sulfonic acid metal base
q/g.

Polyurethane containing (meth)acryloyl group (meth)
Acrylate.

The epoxy group-containing vinyl chloride copolymer that is the base of the vinyl chloride compound (A) used in the present invention is glycidyl ethers of unsaturated alcohols such as acrylic glycidyl ether, methacryl glycidyl ether, and vinyl glycidyl ether, butadiene monoxide, etc. , vinylcyclohexene monooxide, epoxide olefins such as 2-methyl-5,6-epoxyhexene, and vinyl chloride. - can be obtained by copolymerizing. The synthesis method is disclosed, for example, in JP-A-61-106605.

The epoxy group content of the obtained base polymer was 0.5w
t% or more is preferable. If it is less than 0.5 wt%, the amount of carbon-carbon double bonds introduced by the addition of an acid as described below will be small, resulting in insufficient radiation curability.

Examples of polybasic unsaturated acids used in the present invention include maleic acid, citraconic acid, fumaric acid, mesaconic acid, hymic acid, and itaconic acid, with maleic acid being particularly preferred.

If the unsaturated acid is monobasic, a polybasic acid must be used in combination to impart dispersibility to the ferromagnetic fine powder.

Monobasic unsaturated acids include halogen-substituted (meth)acrylic acids such as (meth)acrylic acid and chloroacrylic acid;
Vinyl sulfonic acid, methylvinyl sulfonic acid, (meth)
Allylsulfonic acid, styrenesulfonic acid, ethyl (meth)acrylic acid-2-sulfonate, 2-acrylamide-
Unsaturated sulfonic acids such as 2-methylpropanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid; unsaturated monomers of sulfuric acid such as ethyl (meth)acrylate-2-sulfate and 3-allyloxy-2-hydroxypropanesulfate Esters: unsaturated diesters of phosphoric acid such as di-2-(meth)acryloxyethyl acid phosphate, and the like.

Furthermore, examples of polybasic saturated acids among polybasic acids include polycarboxylic acids such as malonic acid, succinic acid, phthalic acid, and trimellitic acid; and sulfocarboxylic acids such as sulfobenzoic acid and sulfosalicylic acid. can give.

The compound (A) thus obtained preferably contains -COOHit in terms of acid value of 1 to 100, more preferably 3 to 20, in order to improve the dispersibility of the ferromagnetic fine powder.

The number of carbon-carbon unsaturated bonds per molecule is preferably 1.5 to 20, more preferably 2 to 15. Outside this range, curing properties are poor and durability is poor. The molecular weight is preferably from s,ooo to 100,000, more preferably from 10,000 to 50,000. Below this range, durability will be insufficient, and above this range, the viscosity will be high and the dispersibility of the ferromagnetic fine powder will deteriorate.

The urethane (meth)acrylate i (B) containing a sulfonic acid metal base used in the present invention may have a main chain skeleton of either polyester or polyester ether, and a specific example of the dibasic acid used therein is oxalic acid. , malonic acid, succinic acid, glutaric acid, adipic acid,
Sebacic acid, dodecanedioic 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,
Pentamethylene glycol, hexamethylene glycol, octamethylene glycol, diethylene glycol,
triethylene glycol, tetraethylene glycol,
2.2-dimethylpropane-1,3-diol, 2.2
-diethylpropane-1,3-diol, cyclohexane-1,3-diol, cyclohexane-1゜4-diol, cyclohexane-1,4-dimetatool, cyclohexane-1,3-dimetatool, 2,2-bis(4-
hydroxyethoxy-cyclohexyl)propane, 2,
2-bis(4-hydroxyethoxy-phenyl)propane, 2.2-bis(4-hydroxyethoxyethoxy-
phenyl)propane, etc. can be used. It is also possible to use a lactone-based polyester skeleton made of T-butyrolactone, δ-valerolactone, ε-caprolactone, or the like. Isocyanates that form urethane bonds include 2,4-tolylene diisocyanate, 2,6-
Tolylene diisocyanate, 1.3-xylylene diisocyanate, 1゜4-xylylene diisocyanate, 1
, 5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3
．． 3-dimethylphenylene diisocyanate, 4.4-
Polyvalent isocyanates such as diphenylmethane diisocyanate, 3°3-dimethyl-4,4-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate 3-adduct of trimethylolpropane can be used. Further, a part of the dibasic acid and dihydric alcohol may be replaced with trivalent or higher acid and hyalcohol. The sulfonic acid metal group and the acryloyl group may be located at the terminal or side chain of the polyurethane. As a method for introducing these groups, synthesis can be performed by using a polyester polyol in which part of the polybasic acid is replaced with a polybasic acid containing a sulfonic acid metal base. As polybasic acids containing sulfonic acid metal bases, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfophoterephthalic acid, 2-potassium sulfoterephthalic acid, etc. can be used.

The preferred content of sulfonic acid metal base in the urethane (meth)acrylate used in the present invention is 0.005 to 5 eq per gram of polymer, more preferably 0.0
1 to 2 eq, more preferably 0°03 to 1.5
■It is eq. The molecular weight is 1,000 to 10o,
ooo, preferably 2,000 to 50,000,
Particularly preferably 3,000 to 30,000. If the content of the sulfonic acid metal base is outside this range, the dispersibility of the ferromagnetic fine powder will be poor, leading to a decrease in electromagnetic conversion characteristics,
Durability may deteriorate. Moreover, the average content of (meth)acryloyl groups is 1.5 to 10, preferably 2 to 8, per molecule. When the molecular weight is less than 1000, the magnetic layer of the obtained magnetic recording medium becomes too strong, causing problems such as cracking when bent, and curling of the magnetic recording medium due to curing shrinkage after electron beam irradiation. Cheap.

On the other hand, if the molecular weight exceeds 100,000, the solubility of urethane (meth)acrylate in solvents tends to be poor.
This is not preferred because it is not only inconvenient to handle, but also because the dispersibility of the ferromagnetic fine powder deteriorates and a large amount of energy is required for curing.

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, (meth)acrylic acids, crotonic acids, itaconic acids, and olefins. Among these, preferred are the following compounds containing two or more methacryloyl groups. Specifically, polyethylene glycol (meth)acrylates such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and tetraethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. , pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tris(β-(meth)acryloyloxyethyl)
Isocyanurate, bis(β-(meth)acryloyloxyethyl)isocyanurate, or polyisocyanate (2,4-)lylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4- xylylene diisocyanate, 1.
5-naphthalene diisocyanate, m-phenylene diisocyanate, P-phenylene diisocyanate, 3.
3-dimethylphenylene diisocyanate, 4,4-diphenylmethane diisocyanate, 3,3-dimethyl-
414=diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate triadduct of trimethylolpropane)
and a reaction compound with a hydroxy(meth)acrylate compound (2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, etc.),
Alternatively, there are other poly(meth)acrylates having two or more functionalities. These monomers may be used alone or in combination of two or more.

The preferred composition ratio of the compound represented by (A) and the compound represented by (B) is 20 to 90 parts by weight/8.
0 to 10 parts by weight, particularly preferably 30 to 80 parts/70 to
There are 20 copies. 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 preferably 50 parts by weight or less based on the total parts by weight of the compounds represented by (A) and (B). 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 chromium dioxide fine powder, ferromagnetic alloy powder, barium ferrite, etc. can be used. It is effective that the acicular ratio of ferromagnetic iron oxide and chromium dioxide is about 2/1 to 20/1, preferably 5/1 or more, and the average length is about 0.2 to 2.0 μm.

The ferromagnetic alloy powder has a metal content of 75 wt% or more, and 80 wt% or more of the metal content is a ferromagnetic metal (i.e., Fe, Co,
Ni, Fe-Ni, Co-Ni.

These are Fe-Co-N1) particles with a major axis of about 1.0 pm or less. Particularly effective in the present invention is that it is difficult to disperse the ferromagnetic fine powder and the ET specific surface area is 30, preferably 45rr.
It is a ferromagnetic alloy powder with fine particles of r/g or more.

Organic solvents used for dispersion and application of magnetic coating liquid include acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, acetic acid glycol monoethyl ether; ethyl ether, glycol dimethyl ether, glycol monoethyl ether,
Ethers such as dioxane and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride,
Chlorinated hydrocarbons such as chloroform, ethylene chloride phosphorus, and dichlorobenzene can be selected and used.

Further, additives such as a lubricant, an abrasive, a dispersion agent, an antistatic agent, and a rust preventive may be added to the magnetic coating liquid of the present invention. In particular, lubricants include saturated and unsaturated higher fatty acids with 12 or more carbon atoms, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine compounds, etc., and these are used when preparing magnetic coating liquids. It may be added, or it may be dissolved in an organic solvent after drying or irradiation with radiation, or applied directly to the surface of the magnetic layer, or
May be sprayed.

Materials for the support to which the magnetic coating liquid is applied include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; plastics such as polycarbonate, polyimide, and polyamideimide. In addition, non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these metals, and plastics on which metals such as aluminum are vapor-deposited may also be used, depending on the purpose.

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

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

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, γ
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.

The electron beam has an accelerating voltage of 100 to 1000 KV, preferably 150 to 300 KV, and an absorbed dose of 1
-20 Mrad, preferably 3-15 Mrad. When the accelerating voltage is less than 100 KV, the amount of energy transmitted is insufficient, and when it exceeds 1000 KV, the efficiency of energy used in polymerization decreases, making it uneconomical. If the absorbed dose is less than I Mrad, the curing reaction will be insufficient and the strength of the magnetic layer will not be obtained, and if it is more than 20 Mrad, the energy efficiency used for curing will decrease, the irradiated object will generate heat, especially the plastic support. is undesirable because it deforms.

〔Example〕

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 50 hours.

Fe alloy powder (15000e, BET surface area 50rr
r/g) 400 parts Binder composition Resin made by adding maleic acid to a copolymer of allyl glycidyl ether and vinyl chloride (acid value 10. Number average molecular weight 20,000) 60 parts Urethane acrylate (SOJa group content 0. 0511geq/g molecular weight to
, ooo Average acryloyl group content 3 pieces/molecule) 4
0 parts Stearic acid 4 parts Butyl stearate 4 parts Al2O 34 parts Carbon black 10 parts Methyl ethyl ketone 800 parts After dispersion 1. Coated onto a 10 μm thick polyethylene terephthalate support using a doctor blade so that the dry film was 3 μm. After orienting using one stone, dry the solvent (
After 100' CI minutes), calendering was performed. Then, the acceleration voltage was 165KV, the beam current was 6mA, and the beam was heated to 7Mra.
After irradiating the electron beam to an absorbed dose of d, 1/2
A video magnetic tape sample Nα1 was obtained by slitting it into inch width pieces.

Magnetic tape samples were obtained in the same manner as in Example-1 except that the binder composition in Table 1 was changed.

Example-2...Sample Nα2 A copolymer of allyl glycidyl ether and vinyl chloride to which malonic acid and chloroacrylic acid were added (acid value 8, number average molecular weight 20,000, average acryloyl group content 3. 4 pieces/molecule) 60 parts urethane acrylate (SOsNa group content 0.3
mgeq/g, average molecular weight 10.000, average acryloyl group content 3/molecule) 40 parts Example 3...Sample 3 Citraconic acid was added to a copolymer of butadiene monooxide and vinyl chloride. (acid value 10. number average molecular weight 15,000) 60 parts urethane acrylate (SO2Na group containing 570.
12 mgeq/g, molecular weight 10,000, average acryloyl group content 5/molecule) 40 parts Example-4...4 for sample Same vinyl chloride resin as Example-1 6
0 parts urethane acrylate (SO3Na group-containing iQ
, Q1mgeq/g, molecule 110,000, average acryloyl group content 1.5 pieces/molecule) 40 parts Example-5...Sample 臘5 Same vinyl chloride resin as Example-1 60
Part urethane acrylate (so, 118 group content 5
IIgeq/g, molecular weight 10,000, average acryloyl group content ff10 pieces/molecule
40 parts Comparative Example-1...Sample Nα6 Same as Example-1 Vinyl chloride resin 60
urethane acrylate (SOsNa group-containing 16+
ageq/g, molecule i10. ooO, average content of acryloyl groups 3 pieces/molecule) 40 parts Comparative Example-2...Sample Nα7 Same vinyl chloride resin as Example-1 6
0 parts urethane acrylate (SO3Na group content 0
, molecular weight 10,000, average acryloyl group content 3W
J/molecule) 40 parts Comparative Example-3...Sample Nα8 Same as Example-1 Vinyl chloride resin 6
0 parts Urethane resin (SOJa group content 0.05 mgeq/g, molecule 130,000, average acryloyl group content θ pieces/molecule) 40 parts Comparative Example-4
...Sample Nα9 Vinyl chloride, vinyl acetate copolymer Molecular weight 10.000 60 parts Urethane acrylate (SOJa base content 0.05 mgeq/g, molecular weight 10,000, average acryloyl group content 3 pieces/molecule 40 parts Comparative example-
5...Sample county l.

Copolymer of allyl glycidyl ether and vinyl chloride with only malonic acid added (acid value 15, number average molecular weight ff 120,000) 6
0 parts Same urethane acrylate as in Example-1 40 parts Comparative Example-6...Sample Nα11 Copolymer of allyl glycidyl ether and vinyl chloride with only chloroacrylic acid added (number average molecular weight 20,000. Acryloyl group Table 1 shows the evaluation results for each sample containing 40 parts or more of urethane acrylate (SO, 10.08 mgeq/g, molecular weight 10,000, average acryloyl group content 5 pieces/molecule). show.

(Evaluation method) Still durability time: A constant video signal is recorded on a videotape (each sample) using a VHS videotape recorder (manufactured by Matsushita Electric Industries (■), NV8200), and the reproduced still image loses sharpness. (The experiment was conducted at 5° C. and 80% RH).

Video S/N: Using the above video tape recorder,
Record the gray signal of the 50% set amplifier and use Shibatsu 9
Measure the noise with a 25C type S/N meter and sample N.
It is shown as a relative value when al is OdB.

Storage stability: After the magnetic coating liquid was stored for 24 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 when not stored as OdB.

Dynamic friction coefficient 2 Using the above video tape recorder, set the tape tension on the delivery side of the rotating cylinder to T11.
When the tape tension on the winding side is T2, the dynamic friction coefficient (μ) is defined by the following equation, and the running tension is evaluated using this μ.

Tz / T+ = e x p (μ*π) measurement is 4
0°C165%RH Table 1 [Effects of the Invention] As shown above, the magnetic recording medium of the present invention has excellent dispersibility of ferromagnetic fine powder, exhibits good electromagnetic conversion characteristics, and has a low coefficient of dynamic friction. It can be seen that the still durability is high. Furthermore, it was confirmed that the magnetic paint for the magnetic recording medium of the present invention has excellent storage stability.

(3 others)

Claims (1)

[Claims] (1) A magnetic recording medium mainly consisting of a non-magnetic support and a magnetic layer, wherein the magnetic layer contains one or more compounds each of the groups shown in the following (A) and (B) as a binder, A magnetic recording medium characterized in that it is further irradiated with radiation. (A) A compound obtained by adding a polybasic unsaturated acid, or an unsaturated acid and a polybasic acid to an epoxy group-containing vinyl chloride copolymer. (B) 0.005 to 5 mgeq/sulfonic acid metal base
g, polyurethane (meth)acrylate containing a (meth)acryloyl group.