JPS58161132A - Magnetic coating composition for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a well-balanced magnetic recording medium having superior bonding strength to the support and undergoing no reduction in the magnetic characteristics, by using modified cellulose nitrate as a component of a binder forming a magnetic layer. CONSTITUTION:A linear urethane prepolymer having isocyanate groups at both terminals is dissolved in a solvent, and after partially extending the chain with an active hydrogen compound, the residual isocyanate groups are reacted with cellulose nitrate at a relatively low temp. to soften the cellulose nitrate while leaving most of the hydroxyl groups in the cellulose nitrate. This modified cellulose nitrate is used as a binder together with other resin such as polyurethane, and magnetic powder is dispersed in the binders to prepare a magnetic coating for a magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic coating composition for magnetic recording media that has improved adhesion to plastics, particularly polyester films, and has good dispersibility of magnetic powder and the like. Currently, the magnetic coating composition for recording media with 1% FP is composed of a mixture of magnetic powder such as Fe, O, etc., a binder, a dispersant, a lubricant, a solvent, etc.The binder is vinyl chloride/acetic acid. Two or more types selected from vinyl copolymer resin, vinyl chloride/vinyl acetate/vinyl alcohol copolymer resin, butyral resin, Evokin resin, polyurethane resin, phenoxy resin, isocyanate group-containing resin, amino resin, nitrification width, etc. Only a combination of these can be mentioned.

Among these, nitrified cotton is used in combination with other resins. When nitrated cotton is used, magnetic powder is better dispersed, and the surface hardness, abrasion resistance, and slipperiness of the binder are improved. Ru.

For example, polyurethane resin/isoanate group-containing resin/
The main binder formulation is nitrified cotton or a combination of polyurethane resin/vinyl chloride, vinyl acetate copolymer resin/isocyanate group-containing resin/nitrified cotton.

However, since nitrified cotton has a low elongation and a high Young's modulus, when a coating solution containing nitrated cotton is applied and formed into a coating, there is a problem in that large internal stress is generated in the coating during the drying process. It has the disadvantage of poor adhesion to the substrate, and if the substrate is soft, the paint film may peel or crack.

In particular, poor adhesion between the binder and the substrate is noticeable when applied to chemically inert, highly crystalline plastics, plastic films, and especially polyethylene terephthalate films.

Conventionally, in order to make up for this lack of nitrified cotton, plasticizers were used or resin from ponds was mixed in, but this resulted in problems such as it becoming too soft. Particularly when a paint containing nitrified cotton is used as a magnetic paint for magnetic recording media, the use of plasticizers is not preferable because it has a strong influence on magnetic properties.

In addition, as a modification of nitrified cotton, there are graft copolymers grafted with acrylic resin, etc., but the reaction conditions for this are relatively high temperatures, and decomposition of nitrified cotton occurs. Esterification of nitrified cotton using acid chloride, acid anhydride, etc., which can be carried out at low temperatures, is a complex process such as the need for purification of the reactant to remove unreacted substances and by-product oxides after the reaction, resulting in a core doorknob.

Compared to these, when modifying nitrified cotton with an isone anate compound, there is an advantage that it reacts quantitatively at low temperature and can be used as it is without purifying the reactant, but as an isone anate compound, tolylene diisonoanate etc. If a low molecular weight diisocyanate is used, the crosslinking density will be high and the coating film will be too hard. In addition, even when using a relatively flexible urethane prepolymer made by reacting low-molecular-weight diisocyanate at both ends of polyester polyol or polyether polyol, if it is mixed with nitrified cotton to improve the adhesion of the coating film, it can be applied for 1 u. Unless mixed beforehand, gelation occurs and long-term storage is difficult, which poses a practical problem.

As a result of repeated research to improve this drawback, the present inventor dissolved a cotton-like urethane prepolymer having isocyanate groups at both ends in a solvent, partially extended the chain with an active hydrogen compound, and then By adding modified nitrified cotton, which softens the nitrified cotton while leaving most of the hydroxyl groups in the nitrified cotton, by reacting the 7-anate groups with the nitrified cotton at a relatively low temperature, it can be applied to polyester films, etc. The inventors have discovered that it is possible to obtain a magnetic coating composition for magnetic recording media that can improve adhesion and also have good dispersibility of magnetic powder, etc., and have completed the present invention.

That is, the present invention uses a Neuson ane7 compound in which two isocyanate groups in the molecule are separated by an atomic chain containing at least a linear alkylene group having at least 2 carbon atoms as a binder for a magnetic coating composition for magnetic recording media. This is a magnetic coating composition for a magnetic recording medium, characterized in that modified nitrified cotton is added with a reaction product of an active hydrogen compound in an amount equal to or less than 7 seconds.

The diisocyanate compound used in the present invention in which two isocyanate groups in the molecule are separated by an atomic chain containing at least 2 or more carbon atoms [U-chain alkylene group] has two hydroxyl groups in the molecule. has a molecular weight of 1000-2
000, a relatively low molecular weight compound, and a diisocyanate, a low molecular weight compound having two isocyanate groups in the molecule, under conditions of stoichiometric excess of incyanate groups. Polyol components include, for example, linear polyethylene adipate, polyethylene propylene, polyester diols such as polycarrolactone, polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether, etc. Examples include polyether di-p such as glycol. Further, as the diisocyanate component, for example, 24-
Examples include tolylene diisonoanate, 26-tolylene diisonoanate, 4-4'-nophenylmethane diisocyanate, 1,3-xylene diisocyanate, and the like.

The active hydrogen compounds used in the present invention include ethylene glycol% L3-propylene glycol, L4-butanediol, L6-hexamethylene diamine, ethylene diamine, propylene diamine, 1,6-hexamethylene diamine, tanolamine, , water, polyester polyol, polyether polyol, and the like.

In the present invention, a catalyst can also be used in the reaction between the diisocyanate compound and the active hydrogen compound. As the catalyst, known catalysts such as tin compounds such as tin octylate and diptyltin dilaurate, and amines such as triethylenediamine and N-ethylmorpholine may be used.

The amount added is from 0.01 to the diisocyanate.
Preferably, LO weight percent is added. Although these reactions can be carried out under known conditions, they are preferably carried out in an isocyanate inert solvent.

The nitrogen content (N%) of the nitrified cotton used in the present invention is
) is 10 to 13%, and it is necessary to use one with a viscosity of 7 seconds or less, and it is desirable that the nitrified cotton used here does not contain water or alcohol.

The method for producing the modified nitrified cotton used in the present invention is to dissolve the nitrified cotton in an isone anate non-talking bath agent, and to mix this solution and the two isone anate groups in the molecule with at least 2 carbon atoms or more. A diiso/anate compound separated by an atomic chain containing two linear akylene chains is mixed with a compound obtained by reacting an isocyanate group with less than the same mole of an active hydrogen compound in an isocyanate inert solvent. The reaction temperature obtained by this is 30 to s o 'c, and the reaction time is 2 to 40
It is best to do it in time.

As for the mixed a ratio, nitrification is the above-mentioned incyanate active V1-
The amount ranges from 10 to 90% by weight based on the total weight of the hydrogen reaction product and nitrified cotton. Further, the isonanate group content of the isocyanate active hydrogen reaction product at this time is preferably in the range of 1/20 to 1/100 of the number of moles of hydroxyl groups in the nitrified cotton used.

The magnetic coating composition for magnetic recording media of the present invention includes magnetic powder, a binder containing the above-mentioned nitrified cotton, a dispersant, a wetting agent,
Consists of solvent etc. The magnetic powder may be anything that is normally used for magnetic media, such as l -F e, O,, F
e,O,,C,O,,CoO−F e,O,,C1,=
f-Fe, 0. and mixtures thereof, branch axis 1
It is preferable to have an acicular shape with a diameter of ~0.2μ and a minor axis of 0.2~005P. As a binder, a reaction product of a diisocyanate compound in which two isone anate groups in the molecule are separated by an atomic chain containing at least a straight chain alkylene group with a diuretic prime number of 2 or more and an active hydrogen compound of equal mole or less is used as a binder. Copolymerization of nitric alcohol in 7 seconds or less m fat, butyral resin, epoxy resin 1. Examples include combinations of one or more selected from polyurethane resins, phenoxy resins, incyanate group-containing resins, amino resins, and the like.

The method for producing the magnetic coating composition of the present invention can be used by a conventional LM production method for magnetic coating compositions.

For example, it can be obtained by mixing magnetic powder, binder, solvent, and the modified nitrification width in a kneader, ball mill, sand mill, attritor, or the like.

This will be explained in detail in Examples below.

Example 28 Nitrified fed SS% (manufactured by Daicel Chemical Industries, Ltd.) was dried to remove isopropyl alcohol, and dissolved in methyl isobutyl ketone to form a 30% by weight liquid.

On the other hand, tolylene diisocyanate adduct of polytetramethylene ether-glycol (isocyanate content 3
Weight %) 712F and 16-hexamethylene diol L2t were dissolved in 2682 toluene, 0.12% of dibutyltin dilaurate was added, and the mixture was stirred and reacted at 60°C for 2 hours. This solution and the above-mentioned nitrified cotton solutions 333 and 32 were mixed and stirred at 30C for 48 hours to produce modified nitrified cotton.

Example 1 Modified nitrified Ml obtained in Reference Example 58.61 (solid content 25
6%), polyurethane 100F (11 pieces made of polyurethane ■, Niboran 2304. Solid content 35%) Methyl ethyl ketone 232F, magnetic powder Co-rFe, ql 17
9 into a ball mill, mixed and dispersed for 10 hours, and then coated with a bar coater with a clearance of 75 to a thickness of 25μ.
The magnetic flux density is 18 immediately after coating on a polyester film.
A magnetic coating film was prepared by passing through a 0.00 Gauss orientation tube and drying at 80° C. for 4 minutes.

The magnetic powder dispersibility in the magnetic coating film was evaluated by measuring the magnetic hysteresis curve using a magnetic hysteresis measuring device manufactured by Yokogawa Electric Corporation and calculating the squareness ratio from this curve.

The adhesion strength of the magnetic coating film was determined by applying a magnetic coating composition to a polyester film, drying it, and then fixing the coated surface to a metal plate with an epoxy-based solvent-free mold adhesive. /ff by the 180° peeling method.

The results are shown in the table.

Comparative Example 1> Nitrification 1/il 15 F, polyurethane 100F (Ninoboran 2304 manufactured by Nippon Polyurethane ■ solid content 35%)
, Methyl Ethyl Ketone 2852, C.

Magnetic Powder 4HD-FFE, 1 1 7
After mixing and dispersing 2 for 10 hours in a poll mill, it was coated on a polyester film with a thickness of 25 PT using a bar coater with a clearance of 75 μm, and immediately passed through a magnetic medium density 1800 gas oriented film. 80℃ after
A magnetic coating film was prepared by drying for 4 minutes.

The magnetic coating film was evaluated in the same manner as in Example 1.

The results are shown in the table.

<Example 2> Modified nitrified cotton 992 obtained in Reference Example (solid content 236%, solid content raw nitrified cotton 60%) Vinyl chloride 7U/viny acetate - copolymer (manufactured by Denki Kagaku Kogyo Co., Ltd. 10000KT) 142 ．． Polyurethane resin 80p (35% solids, Daicel Chemical M)
EA1422) Methyl ethyl ketone 1316 F,
Methyl isobutyl ketone 202.0 Kami-FFe, 0.106 F was placed in a ball mill, mixed and dispersed for 8 hours, and Coronate HL2F (solid content 70%, manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed and dispersed for 1 hour, after which the clearance was 75μ. 25μ thick with 11 bar coater
801:10 after coating on a polyester film of n1 and immediately passing through an orientation tube with a magnetic flux density of 1800 Gauss.
Dry for a minute to prepare a magnetic coating film. It was further heated at 60° C. for 12 hours and evaluated. The results are shown in the table [.

Ta.

Comparative Example 2 Nitrified cotton MEK solution i' [56F (solid content 25%) Vinyl chloride/vinyl acetate copolymer (Denki Kagaku Kogyo Co., Ltd. 10
00GK'l') 14F, polyurethane resin 80F (solid content 35%, manufactured by Daicel Chemical Industries, Ltd. EA1422), methyl ethyl ketone 40? , methyl isobutyl ketone 60
C.

? , ) le x y 689 , dadh-IFe, 0
．． 1 (16 t was placed in a ball mill, mixed and dispersed for 8 hours, and 2 t of Coronet-1-HL (solid content 70%, 11 bottles manufactured by Polyurethane Co., Ltd.) was added and mixed and dispersed for another 1 hour. A bar coater with a clearance of 75 Pm was used to coat the ball to a thickness of 25 μm. Immediately after coating on a polyester film, the magnetic flux density is 1800.
After passing through a Gaussian orientation chamber, the magnetic coating was dried at 80°C for 10 minutes to prepare a magnetic coating.1, and further heated at 60°C for 12 hours for evaluation. The results are shown in the table.

As seen in the examples, by adding modified nitrified cotton to the binder, it is possible to form a magnetic recording medium with excellent adhesion to the support and with good balance without deteriorating the magnetic properties.

Claims (1)

[Claims] As a binder for a magnetic coating composition for magnetic recording media, a diisocyanate compound in which two isocyanate groups in the molecule are separated by an atomic chain containing at least a linear alkylene group having 2 or more carbon atoms, and a diisocyanate compound with an equimolar or less activity. A magnetic coating composition for mK recording media, characterized in that it is made by adding modified nitrified cotton, which is obtained by adding a reaction product with a hydrogen compound to nitrified cotton having a viscosity of 7 seconds or less.