JPS6214324A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve and electromagnetic conversion characteristic and durability by incorporating specific compds. into a magnetic layer and irradiating radiation thereon. CONSTITUTION:Respectively >=1 kinds of the groups shown by (A) and (B) are incorporated into the magnetic layer and further the radiation is irradiated threon. (A) is a cellulose resin contg. an acryloyl group which is cellulose acetate propionate having an acryloyl group or cellulose acetate butyrate having an acryloyl group and (B) is preferably polyurethane acrylate contg. a COOH group and having 1-10 acid value. The preferable range of the compsn. ratio between the compd. shown by (A) and the compd. shown by (B) is 20-90 pts.wt./80-10pts.wt., more particularly preferably 30-80pts./70-20pts. The good recording medium exhibiting the good electromagnetic conversion characteristic, having a low coefft. of dynamic friction and exhibiting excellent still durability is thus 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, DVD discs, computer tapes, and the like.

[Prior art]

Magnetic recording media that are currently widely used include vinyl chloride acetate resin, vinyl chloride vinylidene chloride resin, and binder.
There is a method of using thermoplastic resins such as cellulose resin, acecool resin, urethane resin, acrylonitrile citadiene resin, etc. singly or in combination, but this method has poor abrasion resistance of the magnetic layer and makes it difficult to control the running path of the magnetic tape. It had the disadvantage of getting dirty.

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 a crosslinking binder is used, 1) there are problems with the storage stability of the liquid in which magnetic particles are dispersed, and it is not possible to maintain the uniformity of the physical properties of the magnetic coating liquid and, by extension, the homogeneity of the magnetic recording medium; 2
) After coating and drying, a heat treatment process is essential for curing the coating film.1
However, it has drawbacks 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 has been proposed in Japanese Patent Publication Nos. 12423-1982 and 1983-1989. No. 13639, JP-A-47-15104, JP-A-50-77433
No. 56-25231, Japanese Unexamined Patent Publication No. 56-25231, and other publications. However, the manufacturing method disclosed in the above-mentioned patent publication could not produce a magnetic recording medium having high electromagnetic conversion characteristics and durability.

[Problem that the invention seeks to solve]

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

For this reason, it is necessary to bring K into 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. On the other hand, 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 produced magnetic recording media that have a smooth surface of the magnetic layer, dispersibility of fine powder, and 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 purpose of the present invention is to achieve characteristics that could not be achieved with conventional magnetic recording media, namely, 1) excellent electromagnetic conversion characteristics, 2) excellent dispersibility of ferromagnetic fine powder, and 2) excellent magnetic properties. The objective is to provide a magnetic recording medium that has good storage stability of the coating liquid, has uniform performance, 4) has excellent running durability, and 5) does not require a heat treatment process for curing the coating film. [Means to solve the problem] The above problem can be solved by the method described below.
Wear.

That is, the present invention provides (1) a magnetic recording medium comprising at least a nonmagnetic support and a magnetic layer, in which the magnetic layer has the following (A
A magnetic recording medium is characterized in that it contains one or more compounds from the groups represented by (B) and (B), and is further irradiated with radiation.

(A) Cellulose resin containing an acryloyl group (B) Polyurethane acrylate In the present invention, in particular, the above (A) is cellulose acetate propionate having an acroyl group or cellulose acetate butyrate having an acroyl group. is preferable, and it is also preferable that the above (B) is a polyurethane acrylate containing a COOH group and having an acid value of 1 to 10.

The present invention will be explained in detail below.

As the cellulose resin (A) containing an acryloyl group used in the present invention, cellulose acetate propionate, cellulose acetate butyrate, cellulose nitrate, cellulose diacetate, etc. each having an acryloyl group are preferable. The preferred range is the degree of polymerization of cellulose "t' 50 to 400, more preferably 80 to 200 mA. Outside this range, the viscosity of the magnetic coating liquid becomes high (resulting in poor dispersibility). From the viewpoint of safety, cellulose acetate propionate and cellulose acetate butyrate are particularly preferred as the cellulose to be used.Acrylate compounds of these celluloses can be prepared, for example, by reacting cellulose with polyisocyanates.
Furthermore, the present invention can be obtained by reacting with an active hydrogen compound (for example, hydroxyacrylates such as β-hydroxyethyl acrylate and 2-hydroxypronolacrylate) to acryloylate the OH group. Polyurethane acrylate used (
As B), the main chain skeleton may be polyester, polyether, or polyester ether, and specific examples of dibasic acids used in these are oxalic acid, malonic acid, succinic acid, glutaric acid, and acetinic acid. Acid sepacic acid,
Dodecanedioic acid 1. maleic acid, fumaric acid, itaconic acid,
Trimethyladipic acid, hexahydrophthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene radical yl? acid, etc. can be used. Examples of dihydric alcohols include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, occumethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 2.2
-dimethyllonozone-1,3-,jol,2,2-・
Quetylprono-1,6-)ol, cyclohexane-1,3-,9ol, cyclohexane-1,4-
Diol, cyclohexane-1,4-dimetatool, cyclohexane-1,ro-, dimetatool, 2,2-bis(4-hydroxyethoxy-cyclohexyl) furo A, 2,2-his(4-hydroxyethoxy-phenyl) furo En, 2,2-bis(4-hydroxyethoxyethoxy-phenyl)prozone, etc. can be used. It is also possible to use a lactone-based polyester skeleton made of γ-butyrolactone, δ-valerolactone, ε-caprolactone, or the like. Isocyanates that form urethane bonds include 2.4-) lylene diisocyanate, 2.6-) lylene diisocyanate, and 1,6-
xylylene diisocyanate, 1,4-xylylene diisocyanate), 1,5-naphthalene, diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 6.5-,) methylphenylene diisocyanate, 4.4-) phenylmethane Polyhydric incyanates such as 25.5-dimethyl-4,4-diphenylmethane, diisocyanate, hexamethylene diisocyanate, incyanate, cyclohexylmethane diisocyanate, and trimethylolpronozone tolylene diisocyanate are used. Wear.

Further, a part of the dibasic acid and dihydric alcohol may be replaced with trivalent or higher acid and alcohol. The acryloyl group may be located at the terminal or side chain of voriclekun.

Methods for introducing these groups include 1) trivalent or higher acid;
2) Incorporating one or more types of alcohol or incyanate into the urethane skeleton and reacting with an acryloyl compound that can react with these groups; or 2) adding one or more acryloyl groups and one OH group to a urethane having an incyanate group at the end.
It can be obtained by reacting active hydrogen compounds having more than one active hydrogen compound.

The polyurethane acrylate that can be used in the present invention has a molecular weight of 1,000 to 100.000.
1, preferably 3,000 to 50,000, particularly preferably 5,000 to ao, ooo. In addition, in the present invention, COOH, OH, 5O5H, 5O5Na, OPO,
Polyurethane acrylates containing polar groups such as HlOP 06 Na are preferred. Particularly preferably CO
There are polyurethane acrylates 1 having an OH group and an acid value of 1 to 10, and a more preferable acid value is 1.5 to 6''1'.The average content of acryloyl groups is 1.5 to 10 per molecule. If the molecular weight is less than 1000, the magnetic layer of the obtained magnetic recording medium will be too strong and may crack when bent, or the magnetic layer may deteriorate due to curing shrinkage after electron beam irradiation. The problem of curling of the recording medium is likely to occur.On the other hand, when the molecular weight is 10
If it exceeds 0,000, the solubility of the polyurethane acrylate in the solvent tends to be poor, which not only makes handling inconvenient, but also deteriorates the dispersibility of the magnetic material and requires a large amount of energy for curing. do not have.

Furthermore, in the present invention, it is necessary to add a vinyl monomer. Vinyl monomers include compounds 1 that can be polymerized by radiation irradiation and have one or more carbon-carbon unsaturated bonds in the molecule, such as acrylic esters, acrylamides, methacrylamides, and methacrylic esters. Examples include allyl compounds, 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 acryloyl groups or methacryloyl groups. Specifically, polyethylene glycol acrylates such as diethylene glycol diacrylate, triethylene glycol diacrylate, and tetraethylene glycol diacrylate, trimethylol protonate acrylate, penquerythritol tetraacrylate, and diine erythritol tetraacrylate1. Diine erythritol hexaacrylate, diethylene glycol diacrylate barreto, tetraethylene glycol, diacrylate, trimethylolpronocentrimethacrylate, pentaerythritol tetramethacrylate, tris(β-acryloyloxyethyl)in cyanurate, bis(β-acryloyloxy) ethyl) in cyanurate, or polyisocyanate (2,4-tolylene di inocyanate,
2.6-) rylene quiisocyanane), 1.5-
xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate,
m-phenylene, diisocyanate, p-phenylene diisocyanate)1. S, 3-dimethylphenylene diisocyanate, 4,4-diphenylmethane, -) incyanate, 5.5-・thumenal-4,4-,:,' phenylmethanoisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, cyclohexylmethane Reaction compounds of diisocyanate, tolylene diinocyanate 3 adduct of trimethylolprozone) and hydroxyacrylate compounds (β-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, etc.), or other compounds with more than 2G ability There are acrylates and methacrylates such as esters of polyols and acrylic acid and methacrylic acid. One type of these monomers may be used, or two or more types may be used.

Preferred range of composition ratio of the compound represented by (A) and the compound represented by (B): 20 to 90 parts by weight/80
~10 parts by weight, particularly preferably 30-80 parts/70-2
It is 0 copies. If the ratio of the compound represented by (A) is less than this ratio or the ratio of the compound represented by (B) 't' is less than this ratio, preferred durability cannot be obtained. Further, the amount of the vinyl monomer added is preferably 50 parts by weight or less based on the total MM parts of the compounds shown in (A) and (B)1. If the ratio exceeds this ratio, the amount of electron beam required for polymerization becomes large, which is 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, nogrium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is approximately 2/1 to 20/1, preferably 5/1 or more, and the average length is effectively within the range of approximately 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., PE, Co
.

There are particles of Ni, Fe-Ni, Co-Ni, Fe-Co-N1) with a major axis of about 1.0 μm or less.

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, vinegar rycol monoethyl ether; ethyl ether, glycol, cumethyl ether, glycol monoethyl ether, dioxane, tetrahydro-7rane, etc. Ethers: Aromatic hydrocarbons such as benzene, toluene, and xylene; Chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene, etc. can be selected and used. .

Further, additives such as a lubricant, an abrasive, a dispersant, 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 having 12 or more carbon atoms, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, fluorine-based f
These compounds may be added when preparing the magnetic coating liquid fJ'J, or they may be dissolved in a certain solvent after drying or irradiation with radiation, or they may be directly applied to the surface of the magnetic layer, or sprayed or sprayed. You may.

Materials for the support to which the magnetic coating liquid is applied include polyethylene terephthalate, polyethylene 2,6, -Nac l/
−) etc. village? Polyesters; polyolefins such as periethylenino and polypropylene, cellulose derivatives such as tenulose triacetate, polycar, Nate,
Boliimi 1″″, Boliami 2 imi 1? In addition, non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these, and plastics made by vaporizing metals such as anosiminium can also be used depending on the usage.

In addition, embossing of non-magnetic supports can be done by films, tapes, sheets, etc.
It may be a disk, Kerr P, Rano, etc., and various materials are selected depending on the form and the heart wall.

In addition, the support of the present invention can be used to prevent static electricity, to prevent transfer, to prevent wow and flutter, to improve the strength of magnetic recording media, and to make the pack surface matte.
The surface may be coated with a so-called ・taku coat.

In the present invention, it is preferable to irradiate radiation after applying magnetic paint and calendering, but it is also possible to irradiate and then calender. Alternatively, it is also possible to irradiate one more time. As the radiation irradiated to the magnetic layer of the present invention, electron beams, gamma rays, beta rays, etc. can be used, but electron beams are preferable. [Scanning method, double scanning method, curtain beam method, broad beam curtain method, etc. are used for the particle accelerator). The electron beam has an accelerating voltage of 100 to 1000 KV, preferably 150 to 300 KV.
The absorbed dose is 1 to 20 Mrad, preferably 3 to 15 Mrad't%. If the accelerating voltage is less than 10KV, the amount of energy transmitted is insufficient and the
If it exceeds V, the efficiency of energy used in polymerization decreases, making it uneconomical. If the absorbed dose is less than IMrad, the curing reaction will be insufficient and the strength of the magnetic layer will not be obtained. If it exceeds 20 Mrad, the energy efficiency used for curing will decrease and the irradiated object will generate heat, especially for plastic supports. It is undesirable for the material to be deformed.

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) The mixture was kneaded for 150 hours using a Seel Mill, a magnetic coating liquid having the following composition.

Fe alloy powder (He: 15000e, BET surface area 50
m71) 400 parts Binder composition 60 parts Urethane acrylate (acid value 6, molecule J1) 0.000
(average acryloyl group content: 4 pieces/molecule) 40 parts stearic acid 4 parts butyl stearate 4 parts Al2O, 4 parts Kazen black 10 parts methyl ethyl ketone 1000 parts After dispersion, use a doctor blade on a polyethylene terephthalate support with a thickness of 10 μm. After applying the film to a dry film thickness of 3 μm and orienting it using a Konogult magnet, the solvent was dried (for 10,001 minutes) and calendering was performed. Then acceleration voltage 165KV beam current 6mA? After irradiating the tape with an electron beam to give an absorbed dose of 7 Mrad, it was slit into 1/2 inch width to obtain a video magnetic tape sample 1.

Magnetic tape samples were obtained in the same manner as in Example 1 except that the binder composition of Example 1 was changed as shown in Table 1. The obtained samples were evaluated by the method shown below and summarized in Table 2.

(Evaluation method) Still durability time: Using a VHS video tape recorder (manufactured by Matsushita Electric Industrial, NV8200),
A constant video signal was recorded for each sample), and the time required for the reproduced stop image to lose its sharpness was shown (the experiment was conducted at 50
Performed at 80% RI-1. ).

Video S/N: Using the above video tape recorder,
Record the gray signal with 50% set-up and use Shibatsu 9
Measure the noise with a 25C type s/N meter and sample A.
It is shown as a relative value when 1 is OdB.

Storage stability: After the magnetic coating liquid was stored at room temperature for 48 hours and stirred for 10 minutes, a magnetic tape was prepared using 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.

Measurement of acid value Sample 1. ! i' was dissolved in tetrahydrofuran and titrated with an ethyl alcohol-water (9515y7y%) solution of potassium hydroxide using phenolphthalene as an indicator, and the genus 9 number of potassium hydroxide required was taken as the acid value.

〔Effect of the invention〕

As is clear from the above results, it can be seen that the magnetic recording medium containing the binder combination of the present invention exhibits good electromagnetic conversion characteristics, has a low coefficient of dynamic friction, and exhibits excellent still durability. Furthermore, it was confirmed that the method for manufacturing a magnetic recording medium of the present invention has excellent storage stability.

Claims (3)

[Claims] (1) In a magnetic recording medium consisting of at least a non-magnetic support and a magnetic layer, the magnetic layer is one of the following (A) and (B).
A magnetic recording medium characterized in that it contains one or more compounds from the group shown as a binder and is further irradiated with radiation (A) A cellulose resin containing an acryloyl group (B) Polyurethane acrylate. (2) Claim 1 provides that (A) the cellulose resin containing an acryloyl group is cellulose acetate propionate having an acryloyl group or cellulose acetate butyrate having an acryloyl group. magnetic recording media. (3) In claim 1, the polyurethane acrylate (B) contains a COOH group and has an acid value of 1 to 1.
A magnetic recording medium characterized in that the magnetic recording medium is 0.