JPH0215413A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve adhesive strength without hindering the coatability of a magnetic coating compd. by a incorporating an isocyanate compd. into a magnetic layer and constituting an adhesion reinforcing layer of a radiation curing resin which reacts with isocyanate as an essential component. CONSTITUTION:The isocyanate compd. is incorporated into the magnetic layer and the adhesion reinforcing layer is essentially composed of the radiation curing resin which cures by reacting with the isocyanate compd. This adhesion reinforcing layer is rapidly curved by irradiation of radiations such as electron rays. The swelling and partial dissolution of the adhesion reinforcing layer do not arise and the coatability of the magnetic coating compd. is not hindered even if the magnetic layer contg. the isocyanate compd. is formed in superposition thereon. Since the group which reacts with the isocyanate is incorporated into the resin component, a powerful bond is generated with the magnetic layer by thermal curing, by which the adhesive strength is increased.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to magnetic recording media, and in particular, in improving the adhesive strength between a substrate and a magnetic layer through an adhesive reinforcing layer mainly composed of resin. The present invention relates to a magnetic recording medium with improved adhesive strength between magnetic layers.

(Prior art and its problems) Conventionally, in magnetic recording media of the type in which a magnetic paint in which ferromagnetic powder is dispersed in a resin binder is coated on a substrate such as polyester, the adhesive strength between the magnetic layer and the substrate is This has a significant effect on both the mechanical strength and electrical properties of the medium, and various measures have been studied to improve the adhesive strength.

As one of these measures, it is well known to improve adhesive strength by coating a resin film on a substrate as an adhesion reinforcing layer and interposing it between the substrate and the magnetic layer.

(Problems with the prior art) However, magnetic paint generally contains a large amount of organic solvent, so if the reinforcing adhesive layer is applied and then the magnetic paint is applied on top of it, the resin of the reinforcing adhesive layer is Since the resin is not cured, it swells or partially dissolves in the organic solvent, which impairs the coating properties of the magnetic coating layer, making it impossible to obtain a magnetic layer with a uniform coating thickness. This problem can be solved by applying magnetic paint after sufficiently curing the resin in the adhesive reinforcing layer, but in this case not only does the adhesive effect of the adhesive reinforcing layer tend to decrease, but it also takes time to cure. This impedes workability.

(Objective of the Invention) An object of the present invention is to increase the adhesion strength of the magnetic layer to the substrate without impeding the above-mentioned applicability of the magnetic paint to the adhesion reinforcing layer.

(Summary of the Invention) As a result of various studies on ways to increase the adhesive strength of the magnetic layer to the substrate without impairing the applicability of the magnetic paint to the adhesive reinforcing layer, the inventor discovered that the adhesive reinforcing layer could be replaced with a radiation-cured resin. By forming this as the main component and chemically bonding each layer through a crosslinking reaction using an isocyanate compound, we succeeded in dramatically improving the adhesive strength between the two layers.

Since the radiation-curable resin has a fast curing speed, the adhesive reinforcing layer is rapidly cured by irradiation with radiation such as an electron beam. Therefore, even if a magnetic layer is immediately applied thereon, the conventional problems of swelling and partial dissolution of the adhesive reinforcing layer can be completely prevented. Moreover, since the resin component of the adhesive reinforcing layer of the present invention also contains a thermosetting group that can be cured by reacting with isocyanate, a strong bond can be formed with the magnetic layer by thermosetting. .

(Detailed Description of the Invention) In the present invention, the substrate is polyester resin or other conventionally used plastic films, disks, etc.

The intermediate layer, that is, the adhesive reinforcing layer used in the present invention is mainly composed of a conventionally known radiation-curable resin into which a group capable of reacting and bonding with isocyanate is introduced. Radiation-curable resins are resins that have unsaturated double bonds in their molecular chains and are cured by crosslinking or polymerization generated by radicals generated by radiation, particularly electron irradiation. For example, resins having acrylic double bonds such as acrylic acid, methacrylic acid, and esters thereof, unsaturated double bonds such as maleic acid and maleic acid derivatives, and allylic type 2 bonds. Groups that can react with isocyanates include those having active hydrogen groups such as hydroxyl groups, acid groups, epoxy groups, and amino groups. From the viewpoint of reactivity with isocyanates, hydroxyl groups and amine groups are particularly desirable. Note that an inorganic pigment such as carbon may be added to the intermediate layer as necessary.

The following resins can be used not only for the adhesive reinforcing layer but also for the magnetic layer if desired.

(1) Vinyl chloride/vinyl acetate-based vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinyl alcohol copolymer, vinyl chloride-
Acrylic double bonds, maleic double bonds, and allylic double bonds were added to vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-terminated OH side chain alkyl group copolymer by the method described later. It has been modified to be radiation curable by introducing it.

(I I) Saturated polyester resin phthalic acid, isophthalic acid, terephthalic acid, maleic acid,
Saturated polybasic acids such as maleic acid derivatives, succinic acid, adipic acid, sebacic acid, ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2 propylene glycol, 1,3 butanediol, dipropylene glycol, 1. 4 butanediol, 1
, 6-hexanediol, pentaerythritol, sorbitol, glycerin, neobenluglycol, 1.4-cyclohexane dimetatool, and other polyhydric alcohols in non-stoichiometric ratios. A resin modified to be radiation-curable.

(III) A polyester compound containing a radiation-curable unsaturated double bond in the unsaturated polyester resin molecular chain. For example, a saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol described as a thermoplastic resin in Section (II), containing a radiation-curable unsaturated double bond in which part of the polybasic acid is maleic acid. Examples include unsaturated polyester resins, prepolymers, and oligomers.

Examples of the polybasic acid and polyhydric alcohol components of the saturated polyester resin include the compounds listed in item (I), and examples of the radiation-curable unsaturated double bond include maleic acid,
Examples include fumaric acid.

The radiation-curable unsaturated polyethyl resin is produced by a conventional method, that is, by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohol components, that is, in the presence of a catalyst.
After dehydration or dealcoholization under a nitrogen atmosphere at ~200°C, the temperature is raised to 240-280°C and the temperature is 0.5-1 mm.
A polyester resin can be obtained by a condensation reaction of Hg under reduced pressure. The content of maleic acid, fumaric acid, etc. is 1 to 40 mol% in the acid component due to crosslinking during manufacturing, radiation curability, etc.
It is preferably 10 to 30 mol%.

(rv) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and a copolymer of these components, in which a portion of the hydroxyl groups have been modified to be radiation-sensitized and curable by the method described later.

(■) Epoxy resin, phenoxy resin Epoxy resin produced by the reaction of bisphenol A, epichlorohydrin, and methyl epichlorohydrin - manufactured by Ciel Chemical (Epicote 1)
52.154.828.1001.1004.1007
) Manufactured by Dow Chemical (DEN431, DER732, DE
R511, DER331) manufactured by Dainippon Ink (Evicron 400, Evicron 800), and phenoxy resin manufactured by UCC (PKHA), which is a high polymerization degree resin of the above epoxy.
, PKHC, PKHH) A copolymer of brominated bisphenol A and epichlorohydrin, a product in which a part of the epoxy group has been modified to be radiation curable, such as manufactured by Dainippon Ink Chemical Industry Co., Ltd. (Evicron 145.152.153.1120).

(VI) Cellulose Derivatives Cellulose derivatives of various molecular weights are also effective as thermoplastic components. Among them, particularly effective ones include nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, and acetyl cellulose.

Also, some of the hydroxyl groups in the resin are modified to be radiation curable by a method described later.

On the other hand, the magnetic layer contains an isocyanate compound. Any known curing agent can be used as this material. Furthermore, the adhesive reinforcing layer contains a radiation-curable resin,
This contains groups reactive with isocyanate compounds.

The adhesive reinforcing layer (and optionally the magnetic layer) is cured by radiation. The active energy rays used include electron beams using a radiation accelerator as a source, γ-rays using Co Bo as a source, β-rays using 5r96 as a source, and X-rays using an X-ray generator as a source. - lines etc. are used.

In particular, as an irradiation source, it is advantageous to use an electron beam from a radiation accelerator from the viewpoint of controlling the absorbed dose, introducing it into the manufacturing process line, and shielding ionizing radiation.

As for the radiation characteristics, from the perspective of penetrating power, the acceleration voltage is 100~
It is convenient to use a radiation accelerator of 750 kV, preferably 150 to 300 kV, and irradiate at an absorbed dose of 0.5 to 20 megarats. In particular, a low-dose type radiation accelerator (electrocurtain system) manufactured by Energy Sciences, Inc. in the United States is extremely advantageous for introducing tape coating lines and shielding secondary X-rays inside the accelerator.

Of course, a van de Graaf type accelerator, which has been widely used as an electron beam accelerator, may also be used. In addition, since the coating thickness of the back layer is thin, the curing reaction can be sufficiently performed even by ultraviolet rays, making it possible to obtain the required characteristics.

Examples of the present invention will be shown below, but first a synthesis example of a radiation-curable resin will be presented.

1. 5 The resins used in the following examples are as follows.

(a) Polyester polyurethane resin having an acrylic double bond and a hydroxyl group (M n = 20. Polyester polyurethane resin containing sebacic acid, isophthalic acid, and butanediol as main components having 5 hydroxyl groups) (b,) Polyester polyurethane resin containing no hydroxyl groups of resin (a) (C) Vinyl chloride/vinyl acetate/vinyl alcohol 2HEMA adduct of copolymer VAGH (d) Boisester resin whose main component is adipic acid-butanediol M n = 3.000 2HEMA adduct hydroxyl groups Average 2/molecule (e) Hydroxyl groups of resin (d) are replaced with amino groups changed to .

Jitsu 1 Eko A Adhesive Reinforcement Layer Paint Adjustment Conductive carbon powder (Columbia Carbon, Contactex 301 particle size 20 mμ) 40 parts by weight Polyester polyester polyurethane resin having a 7'llJ double bond and a hydroxyl group (a) 60 parts by weight Methyl ethyl ketone 200 parts by weight Toluene 200 parts by weight The above compositions were mixed and dispersed.

B Magnetic paint preparation Co-γ iron oxide magnetic powder (particle size 0.2μ, Hc740
0e) 100 parts by weight A1□0. Fine powder (particle size 0.2μ) 10 parts by weight Conductive carbon powder (Columbia Carbon, Conductex SC
1 particle size 20 mμ) 5 parts by weight Polyester resin with acrylic double bond 1-golden resin (b)
1 0 parts by weight Vinyl chloride/vinyl acetate/vinyl alcohol copolymer (c) with acrylic double bonds 20 parts by weight Lubricant 3 parts MEK 200 parts by weight Toluene
After 150 parts by weight of the above composition was mixed and dispersed, 5 parts by weight of an isocyanate compound (Japan Polyurethane Coronate L) was mixed immediately before coating.

Composition A was applied to a thickness of 0.3 μm on a 75 μm PET film and cured by irradiation with an electron beam of 4 Mrad.

Next, Composition B was applied to a thickness of 1 μm and cured by irradiation with an electron beam of 5 Mrad. The resulting sheet was heat treated at 70°C for 24 hours.

K plate ■Meng Resin (a) in Example 1 was changed to resin (d).

The hydroxyl group in Resin (d) of Example 2 was changed to an amino group (Resin (e)).

A sheet was prepared in the same manner as in Example 2 without providing the adhesive reinforcing layer.

A sheet was prepared in the same manner as in Example 2 without heat treatment.

Example 2 except that the ratio 1 skin and the adhesive reinforcing layer were not subjected to electron beam curing.
I created a sheet in the same way.

Concealment 1 - Magnetism A sheet was prepared in the same manner as in Example 2 except that the incyanate compound was not added.

Comparison 2 A sheet was prepared in the same manner as in Example 2 except that the resin (d) of Example 2 from which the hydroxyl groups were removed was used.

The properties of the obtained sheet were measured to obtain the results of the vestibule.

The characteristics shown in the table were measured by the following method.

, Adhesive substrate grid test; slits at 1 mm intervals that penetrate the magnetic film of the medium but do not penetrate the non-magnetic support are provided in the grid pattern, and a peel test is performed using adhesive tape, and the number of squares remaining is displayed.

Comparative Example 1: Reflectance of surface gloss (2) 60° incident light (60')
Relative table based on .

Crab MF2HD drive for playback (1,6M BMFD)
G::Measure the 2f playback output (250kHz) and
Compare with the value of f DISK.

Tap test: Repeat the head loading and unloading operations at the same location on the medium, and measure the number of times the playback output becomes 8% or less of the initial value.

(Function and Effect) As is clear from the above, the present invention includes an isocyanate compound in the magnetic layer and a radiation-curable resin having a group reactive with isocyanate in the adhesive reinforcing layer as a main component. An excellent recording medium with improved gloss, reproduction output, and durability could be provided.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing magnetic powder and a resin binder is provided on a substrate via an adhesive reinforcing layer, the magnetic layer contains an isocyanate compound, and the adhesive reinforcing layer is reactive with the isocyanate. 1. A magnetic recording medium characterized in that the main component is a radiation-curable resin having a certain group. (2) The magnetic recording medium according to item 1, wherein the radiation-curable resin has a group selected from -OH and -NH, and is selected from the group consisting of radiation-curable polyurethane resins and radiation-curable polyester resins.