JPS5928219A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium contg. a binder having superior dispersing power by using a cross-linked product prepared by cross-linking a copolymer consisting of polycaprolactone polyol, diamine and isocyanate with a curing agent as the principal component of a binder component for ferromagnetic powder. CONSTITUTION:Polycaprolactone polyol (PC), diamine (DI) and isocyanate (IS) are used as starting materials for manufacturing a copolymer. The mol.wt. of said PC and the number of terminal hydroxyl groups are not especially restricted, and commercially available PC may be used as it is. Said DI is required only to have one or two primary amino groups or two secondary amino groups, and phenylenediamine or alkylenediamine is preferably used. A general isocyanate compound such as tolylene diisocyanate or diphenylmethane diisocyanate is used as said IS. The preferred amount of PC is 20-80wt% of the total amount of PC, DA and IS, that of DA is 10-40wt%, and that of IS is 10-40wt%. The kind of ferromagnetic powder is not especially restricted, and powder of gamma-Fe2O3, Co-gamma-Fe2O3, CrO2, Cu or the like is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and an object thereof is to provide a magnetic recording medium with excellent dispersibility of ferromagnetic powder.

Magnetic recording bodies are usually made by applying a magnetic paint consisting of ferromagnetic powder, a binder, a solvent, and optionally other additives to a non-magnetic substrate such as a polyester film.

Examples of ferromagnetic powder include iron oxide fine powder, which has traditionally been used, and metal powder, which has recently begun to be used to improve magnetic recording density and reproduction output due to its high saturation magnetization and coercive force. etc. As the solvent, 1-toluene, 1-methyl ethyl ketone (MBK), methyl isobuterketone (MI'BK), isopropyl alcohol, cyclohe++/-fi, etc. (7) -fi, or a mixture of two or more are generally used. . As other additives, dispersants, abrasives/fillers, antistatic agents, rust preventives, etc. may be used as necessary. The dispersant may be used by coating ferromagnetic powder. The binder plays an extremely important role in terms of the dispersibility of the ferromagnetic powder and the characteristics of the magnetic recording medium. Therefore, it is necessary to select a ferromagnetic powder that has good dispersibility and can impart excellent electromagnetic properties such as high sensitivity and high S/N ratio to the magnetic recording medium. Based on these backgrounds, there are two types of binders currently in actual use: vinyl chloride copolymer resins and polyurethane resins.

However, in the case of vinyl chloride copolymer resin, although it is relatively hard, its ability to disperse ferromagnetic powder is still insufficient. On the other hand, polyurethane resins are excellent in terms of strike characteristics and durability, but have poor dispersibility with respect to ferromagnetic powder, resulting in deterioration of electromagnetic properties such as sensitivity and 8N ratio.

The present invention was made to overcome these drawbacks that occur when conventional resins are used, and an object of the present invention is to provide a magnetic recording medium containing a binder with excellent dispersibility.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder printed on a nonmagnetic substrate, in which the binder component cures a coelectric material consisting of a polycaprolactone polyol, a diamine, and an incyanate. The main component is a crosslinked product formed by crosslinking with an agent.

The polycaprolactone polyol (hereinafter abbreviated as "PC"), which is a raw material for producing the copolymer used in the present invention.
There are no particular restrictions on the molecular weight or the number of terminal hydroxyl groups, and commercially available products can be used as they are. Examples include Placcel (trademark) manufactured by Dial Corporation and NIAXPCP (trademark) manufactured by UCC Corporation.

The diamine (hereinafter abbreviated as "DI") includes:
Any compound having one or two -class amino groups or two secondary amino groups may be used, and among them, phenylene diamine, alkylene diamine, etc. are preferable.

As the incyanate (hereinafter abbreviated as "IS"), common insinate compounds such as tolylene diisocyanate, diphenylmethane diisonanate, hexamethene diisonanate, etc. can be used.

Specific examples of the method for producing the copolymer are shown in Examples,
There are no particular limitations, and known methods such as solution polymerization and emulsion polymerization can be employed.

PCIDA and I used in the production of the copolymer
The ratio of s is 20 to 80 PC for these total amounts.
It is preferable that DA be 10 to 40% by weight and Is be 10 to 40% by weight.

Examples of materials that are mixed with the ferromagnetic powder together with the copolymer and serve as a curing agent for the copolymer include polyisocyanate (hereinafter abbreviated as 1'-PI 8J) and epoxy resin. . The former is preferred because the curing reaction is quick.

Examples of FIS include a trifunctional low molecular weight isocyanate compound which is a reaction product of 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate. The reactant is available from Bayer under the trade name "Desmodur L".
'' and is commercially available from Nippon Polyurethane Industry ■ under the trade name ``Corone 5-Ito L''.

The amount of PI8 mixed into the copolymer is 5 to 5 parts by weight per 100 parts by weight of the copolymer, because if it is too large, the final coating film will become brittle, and if it is too small, problems will arise in solvent resistance, etc.
30 parts by weight is suitable.

The ferromagnetic powder in the present invention is particularly li, l.
For example, 1-Fe2O3, Co-1-Fe2
Examples include iron alloys such as 0B, CrO2, metallic iron, cobalt, nickel, copper, chromium, and silicon.

A magnetic paint is obtained by dissolving a binder in a solvent, adding ferromagnetic powder thereto, mixing and dispersing it, but there are no limitations on the order of addition of the binder and ferromagnetic powder, the dispersion means, etc. Next 1″
-1 The present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these.

EXAMPLE A reaction vessel equipped with a stirring bar, a condenser, a dropping device, a nitrogen blowing tube, and a thermometer is used.

First, the reactor was heated to 50°C, purged with nitrogen, and 10 parts by weight of 6-diphenylmethane diisocyanate and 2 parts of polycaprolactone diol with an average molecular weight of 1250 were added.
5 parts by weight was added, and the contents were heated for 8 hours under a nitrogen atmosphere while stirring.
The reaction is carried out at 0°C for 4 hours. After the reaction was completed, the mixture was cooled to 50°C, and 28 parts of dimethylformamide was added.
Stir for a minute to dissolve uniformly. On the other hand, prepare a solution of 9 parts by weight of pinuaminoprobyl biperazine in 28 parts by weight of dimethylformamide, add it to the reaction product, and react at 50°C for 2 hours under a nitrogen atmosphere with stirring,
After the reaction, the chamber is cooled down. The resin concentration of the resulting reaction product was 44% by weight. Using this reaction product, as shown in Table 1, using a ball mill, 4
The mixture was mixed and dispersed for 8 hours to prepare a magnetic paint. This paint was applied to a 12μ thick polyester film base by a known method, dried and cured at 80°C for 30 minutes to form a 4μ thick magnetic layer, and cut into 10μ width pieces. and made magnetic tape.

Comparative Examples Among the blended compositions of Examples, vinyl chloride, vinyl acetate, and vinyl alcohol copolymer (manufactured by UCC; trade name: VAGH; resin content: 10 CI) was used instead of the binder in the present invention.
) or polyurethane resin (manufactured by Nippon Polyurethane Industries ■;
Magnetic tapes were produced in exactly the same manner as in the examples, except that each product had a product name: Niraporan 2304 (resin content: 35% mold weight).

The formulation table is summarized in Table 2. However, for comparison with Examples, the amounts of binder and solvent are the same.

Table 3 summarizes data on the magnetic properties and glossiness of the magnetic tapes obtained in Examples and Comparative Examples. From this table, as magnetic powder, 1 Fe2O3, Co 1 Fe
Both when using 20B and Fa gold alloys, the magnetic properties (residual magnetic flux density (Br), squareness ratio (Br / B
The superiority of the magnetic tape according to the invention as a highly dispersive recording medium is evident in terms of m)) and surface gloss.

Table 3 that's all

Claims (3)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing ferromagnetic powder and a binder is provided on a nonmagnetic substrate, the binder component crosslinks a copolymer consisting of polycaprolactone polyol, diamine, and isocyanate with its curing agent. The magnetic recording medium is characterized in that the main component is a crosslinked body consisting of: (2) The magnetic recording medium according to item (1), wherein the crosslinked body uses polyisocyanate as the curing agent. (3) The magnetic recording medium according to item +11, wherein the crosslinked body uses an Epoquine resin as the curing agent.