JPS58152067A - Magnetic paint - Google Patents

Abstract

PURPOSE:To provide a magnetic paint having excellent dispersibility of the magnetic powder, and containing a polyester resin having a specific molecular weight and a hydroxyl value higher than the acid value, as a binder. CONSTITUTION:The objective magnetic paint contains a binder component composed of a polyester resin having an average molecular weight of 1,000-8,000 and a hydroxyl value higher than the acid value (preferably the product obtained by using fumaric acid or succinic acid as the dibasic acid component and a product obtained by adding 2-4mol of propylene oxide to 1mol of bisphenol A as the diol component) and if necessary, a low molecular weight polyisocyanate. The amount of the binder is preferably 10-50wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic paints. For more details, please refer to the magnetic paint with excellent dispersibility of magnetic powder.

In general, one type of magnetic recording medium is one in which a magnetic layer is formed by coating and drying a magnetic paint containing magnetic powder, a binder component, a solvent, various additives, etc. on a substrate such as a polyester film. Its performance (especially KWLal conversion characteristics) largely depends on the state of dispersion of the magnetic powder in the magnetic layer. Therefore, in order to obtain a high-performance magnetic recording medium by applying a magnetic paint, it is necessary to select a binder component that has excellent dispersibility of magnetic powder.

Conventionally, vinyl chloride and
Although vinyl acetate copolymers (for example, VAGIi (manufactured by Union Carbide)) are widely used, they are not always satisfactory.

In particular, polyurethane resins are often used in combination for the purpose of improving abrasion resistance, but in such cases, even if VAGH, which has relatively good dispersibility, is used, its dispersibility is significantly reduced.

In addition, in order to improve dispersibility, it is possible to use a large amount of commonly known surfactants and dispersants, but such substances generally have a small molecular weight, and even those with a large molecular weight are only a few hundred at most. After molding, K oozes out with such a low molecular weight material, so-called bleed, which deteriorates electromagnetic conversion characteristics with the passage of time and deteriorates runnability.

Therefore, the present inventors conducted extensive research in order to obtain a magnetic paint with excellent dispersibility of magnetic powder and less deterioration of dispersibility due to the pressure of polyurethane resin. It was discovered that when a blend of resin and low molecular weight polyisocyanate is used, the dispersibility of magnetic powder is greatly improved, the electromagnetic properties and runnability are good, and there is little deterioration in dispersibility due to polyurethane resin. 90 years after completing the invention, the present invention is based on a binder component having an average molecular weight of 100.
0 to 8,000 and whose hydroxyl value is larger than the acid value, or a magnetic paint containing such a polyester resin and a low molecular weight polyisocyanate.

The polyester resin according to the present invention is produced by an esterification reaction between a dibasic acid and a diol, but as long as it has a molecular weight of 1,000 to 8,000, a polyfunctional hydroxy compound or an acidic compound may be added to the polyester resin. This does not preclude its use in resin production. Preferable examples of the dibasic acid used in the present invention include fumaric acid and succinic acid, but any carboxylic acid with double blind capacity can be used to produce the polyester resin that achieves the purpose of the present invention. can.

Fumaric acid, succinic acid, maleic acid, itaconic acid, adipic acid, geltaric acid, malonic acid, pimelic acid, speric acid, sepacic acid, phthalic acid, isophthalic acid,
Terephthalic acid and these anhydrides are prized. or,
The diol used in the present invention has the following structural formula (1
) or hydrogenated versions thereof are preferred, and an adduct of bisphenol A with 2 to 4 moles of propylene oxide is most preferred.

(In the formula, R' and R' are equal or different and both are alkylene groups having 2 or 3 carbon atoms.), R2 is an alkylene group having 1 carbon number.
-5 alkylene groups, m and n are integers, and 2≦m+n≦20. ) The polyvarnish and chill resin according to the present invention are preferably solid at normal room temperature. A substance that is liquid at room temperature can also be used as a binder component for magnetic recording media, but in this case, it is necessary to use a chemical substance with multiple reactive groups such as polyisocyanate or polyepoxide! become. Furthermore, for the purpose of improving the abrasion resistance, it is preferable to actively incorporate a low molecular weight polyisocyanate regardless of whether it is in solid or liquid form. That is, by containing the above-mentioned specific polyester resin and a low molecular weight polyisocyanate, the abrasion resistance can be improved without forming grains that impair dispersibility. .

The proportion of low molecular weight polyinocyanate is O
The number of Neo groups per 1 H group is suitably 0.7 or more, preferably 1.0 or more, more preferably 1.5 or more. The blended polyisocyanate reacts with the polyester in the paint to remove the polyurethane resin, but in particular, when a magnetic paint is applied and dried by heating, it converts into urethane to create a urethane resin.

Examples of the low molecular weight polyisocyanate used in the present invention include hexamethylene diisocyanate, 2.4-tolylene diisocyanate, 2.6-tolylene diisocyanate), 1. i%-phenylene diisocyanate $-) 1.1
．． 4-phenylene diisocyanate, isonoropylbenzo-2,4-diisocyanate, 4,4'-diphenylmethane diisocyanate, biphenyl-4,4'-
Diisocyanate or a reaction product of diisocyanate (tolylene diisocyanate, hexamethylene diisocyanate in %) and trimethylolpropane (for example, product name Coronate L), a reaction product of hexamethylene diisocyanate and water (product name Dismodur N), benzene- 1,2,4-) diisocyanate, 2,4.6-
Examples include triisocyanate and toluene.

The solvent used in the present invention is an organic solvent. Preferred are those commonly used for dissolving polyesters, such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, and ethyl acetate.

In carrying out the present invention, all the magnetic powders that are conventionally used in magnetic paints can be used, and the polyester resin as the binder component of the present invention has a solid content of It is usually blended in an amount of 10 to 50% by weight.

Moreover, the addition of various additives such as shavings, dispersants, and others that do not impair the effects of the present invention is not prohibited.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.In the Examples, "parts" means "parts by weight". Production of polyester resin) 104.5 f (0.9 mol) of fumaric acid, 2.2 mol of propylene oxide adduct of bisphenol A ( Hydroxyl value = s19.o)! 552 F (
1.0 mol), hydroquinone 0.05 F was added, and an esterification reaction was carried out at 220°C to 180°C for 6 hours while blowing nitrogen gas, resulting in an acid value of 15.5, a hydroxyl value of 29,
1. Obtain a polyester with an average molecular weight of 2,500.90 This will be referred to as polyester A.

Polyesters B and G shown in Table 1 were also obtained by changing the charging ratio and reaction time.

Example 1 Magnetic powder 49.5 parts (Toda Kogyo)
KM-1500) (15 parts as solid content)
Lecithin 0.2 parts Binder Resin solids (Table 2) s, y 5 parts Methyl ethyl ketone (
MIK) 25.5 parts cyclohexanone
A magnetic paint was obtained by milling a formulation of 2S, 3 parts for 244 hours in a ball building. PE this paint! After coating and drying using a T-film wire coater 20, the gloss of the coating film was measured and the dispersion state of the magnetic powder was observed using a scanning electron microscope. The results are shown in Table 2. The gloss, gloss and dispersibility were measured by the methods shown below.

(Gloss) Using a glossy needle, measure the percentage of reflected light at an incident angle of 40WL.

Gloss has a correlation with dispersibility, and also has a great impact on product value, such as not damaging the head of the playback machine.

(Dispersibility) Electron microscopic observation is performed and relative evaluation is performed on a scale of 5 to 105. 5 is the best dispersibility and 1 is the worst.

As is clear from the table, the paint containing the polyester resin of the present invention has excellent gloss and dispersibility when observed under a microscope, and it can be seen that there is no significant decrease in gloss or deterioration of dispersibility even when used in combination with polyurethane resin. .

Table-2 Umbrella 1 Polyurethane manufactured by Goofl Rich in the United States-2
Vinyl chloride vinyl acetate copolymer umbrella 6 manufactured by UOO, USA Polyester Example 2 manufactured by Toyobo Co., Ltd. Lecithin 0.2 parts MFfK/cyclohexanone = 1/1 20.5 parts Binder resin solids (
Table 3) After milling 4.5 parts of the mixture in a ball mill for 12 hours, 1/110 parts of MEK/cyclohexanone was added and mixed for 1 hour to obtain a magnetic paint.

pH this paint! Wire coater φ on iT film
The coating was coated and dried in Example 2, and the gloss of the coating film and the dispersion state of the magnetic powder were observed, as well as its abrasion resistance was examined in the same manner as in Example 1.

The results are shown in Table 5.

As is clear from the table, the polyester resin urethane paint of the present invention had good gloss, good dispersibility, and VRTC drag resistance equivalent to that of commonly used VAGH/urethane paints.

Claims (1)

[Claims] 1. The binder component has an average molecular weight of 1000 to 8000.
A magnetic paint containing a polyester resin whose hydroxyl value is larger than the acid value. 2 As a binder component, the average molecular weight is 1000 to 800
0), and the magnetic paint contains a polyester whose hydroxyl value is much higher than the acid value and a low molecular weight polyisocyanate.