DD269035A1 - METHOD FOR PRODUCING MAGNETIC RECORDING MATERIALS - Google Patents

Abstract

Process for the preparation of magnetic recording media from a dispersion of finely divided magnetically anisotropic material by using the dispersion aids according to the invention. These are a binary mixture of various phosphoric acid esters and are suitable for audio, video and computer tape dispersions. The mixture consists of a Phosphorsaeuremono- or -dialkylester and a Phosphorsaeuremono- or -dialkylphenylethoxyester. The use of the mixture improves the utility properties by good wetting of the pigment surface and incorporation of the pigments into the binder matrix.

Description

wherein

R ₁ = alkylphenylethoxy radical of the formula (2)

CMCH ₂ - CH ₂ - 0> _n

With

m = 4 to 21 η = 3 to 20 R ₂ = RiOderHund

B: a phosphoric acid ester of formula (1), wherein

R ₁ = branched or unbranched, saturated-unsaturated-alkyl with 1 to

22 carbon atoms R ₂ = R ₁ or H is.

2. The method according to claim 1, characterized in that the phosphoric acid esters A and B are used as a mixture in Verhältr.is 15: 1 to 1: 5, preferably 10: 1 to 1: 1.

3. The method according to claim 1 and 2, characterized in that the dispersing agents in a total amount of 0.2 to 10 wt .-%, preferably 3.0 to 7.0 wt .-%, based on the amount of pigment used in the magnetic tape formulation are used.

4. The method according to claim 1-3, characterized in that the magnetic pigment is dispersed with the total amount of dispersing aid in an organic solvent with the addition of polymer binder in an amount of 0-20 wt .-% of the total amount of binder provided and then with the addition of the residual binder and the additives, such as lubricants and antistatic agents dispersed to cndkorngröße and the resulting dispersion is applied to a support.

Field of application of the invention

The invention relates to a process for the production of magnetic recording media by dispersing finely divided magnetically anisotropic material and conventional additives in a polymer binder solution, coating the dispersion on a non-magnetizable substrate, aligning the magnetizable particles with the aid of a magnetic field, removing the solvent from the applied layer and a suitable surface treatment of the magnetic layer.

For modern magnetic data carriers, which are used in audio, video and computer technology, increasing the quality requirements. Particular attention is paid to the tear strength, abrasion resistance, elasticity, surface quality and above all to the electroacoustic or memory and video technical values. This not only requires an improvement of the magnetizable materials used such as chromium dioxide, cobalt-doped iron oxide, metal pigments and Bariutnferriten, but it must also the possibilities of effect dot auxiliaries, coupled with an improvement in the processability of the mixtures, paid more attention.

Characteristic of the known technical solutions

In the existing literature, three main directions crystallize out in the dispersion auxiliaries. There is the lecithin on the one hand. This natural substance with its high content of non-surfactant impurities is not suitable for high-quality recording media. Reinlecithin, which is used in more recent publications, is only available at great expense. An overview of such a cleaning process is DE OS 272I3O87.

The second group of dispersing aids includes the organometallic compounds (DE AS 1195810, DE OS 3123012, DE OS 3138278, DE OS 3139297, DE OS 3314301, DE OS 3339244). These compounds, which are already complexed by the synthesis of alkynes, also impose special, mostly steric requirements on the adsorption sites of the pigment surface. This reduces their adsorption capacity and also their effectiveness. The phosphorus-containing dispersants represent the third group. They are usually as phosphoric acid esters, which are used alone or in admixture with other surfactants. (DE OS 1 234234, DE OS 2250384, DE OS 2754883, DE OS 3044770, DE OS 3418673). It is not taken into account that phosphates with iron oxide surfaces sometimes produce the most stable bonds and therefore mixtures of phosphoric acid esters and other types of surfactants are less effective.

Object of the invention

With the invention, a more effective dispersion of the magnetic pigments and a stronger hydrophobing of the pigment surface should be achieved. The tendency to reagglomeration should be reduced. This results, on the one hand, in a reduction of the grinding work to be introduced into the system and, on the other hand, for the magnetic tapes, an increase in quality through better use of the properties inherent in the magnetic pigment. This is reflected in technical terms by a better pitch uniformity and lower pitch fluctuations. Furthermore, lower layer thicknesses are possible with constant ribbon flow and the adhesion to the carrier layer is improved.

Explanation of the essence of the invention

For the achievement of good mechanical and storage properties, it is essential that the magnetic layer has sufficient adhesion to the support and high mechanical integrity of the layer, combined with a high packing density of the magnetic pigment. From the high packing densities and with the particle sizes used, preferably with a length between 0.1 and 5.0μπι, resulting permanent magnetic Einomänenteilchen, between which therefore always magnetic attraction forces, arise on the one hand for the embedding of the pigments in the binder matrix and on the other hand for the dispersion ei.io series of problems. They can be solved with reasonable effort by using suitable, specially modified dispersing aids, sometimes with the addition of an optimized amount of polymer binder. During the; Dispergierprozesses the dispersant to reduce the magnetic and Van der Waals forces between the individual particles by electrostatic surface potentials and / or steric adsorption as far as possible in their effect and stabilize the coating coatings in the time between production and processing.

Furthermore, the effect of the dispersing aids is to minimize the grinding work to be applied in order to reduce the destruction of the pigment needles, as well as to make the needles movable so that they can be rotated in the wet layer by a magnetic field in a desired direction.

This object is achieved by dispersants having a stable bond between the pigment surface and the dispersing assistant molecule, as well as an organic molecule, which guarantees a complete coating of the pigment particle and thus good hydrophobization.

For the firm embedding of the wetted pigments in the binder matrix, there must be sufficiently strong bonding possibilities between the two partners. The main part a, i these bonds usually carry the hydrogen bonds. From these considerations results the use of suitable surfactants as dispersing aids. Their type and amount must be optimized in each case, on the one hand to cover the surface of the magnetic pigments as much as possible, which promotes good dispersibility and embedding, and on the other hand to prevent overdose resulting from softening of the polymer matrix and efflorescence of low molecular weight Formulation ingredients on the magnetic tape surface and reduced adhesion to the support base wüi de.

It has now surprisingly been found that it is possible to produce magnetic recording materials with higher quality, if according to the invention in dispersing a mixture of different phosphoric acid esters of the formula

^Ί ; p «ο πι

R ₂ - 0 _0H is added as Dispurgierhilfsmittel. This is a binary mixture of the following types of phosphoric esters:

Ri = alkylphenylethoxy radical of the formula

CH, - (CH _o ) _m - / "V- ° -tr GH ₀ - GH ₀ - 0 ->-" ₍₂₎

η = 3 to 20

R ₂ = R ₁ or H

Type II

Rt = branched or unbranched, saturated or unsaturated alkyl radical having 1 to 22 carbon atoms

R ₂ = R ₁ or H

This dispersing agent mixture according to the invention is in the suspension to be dispersed in an amount of 0.2 to

10.0Gew .-%, preferably 3.0 to 7.0Gew .-%, based on the amount of magnetic pigment used. The quality-enhancing effect of the mixture according to the invention remains even when using the usual additives, such as

Lubricants and antistatic agents obtained. In this case, the dispersants used according to type I and II according to the Application in the ratio of 15: 1 to 1: 5, preferably 10: 1 to 1: 1, can be varied. In the process according to the invention, in particular for type I phosphoric acid esters of the formula are suitable

3 ₃ - (CH ₂ ) ₈ -Q> - 0 -4 · CH ₂ - GH ₂ - O) ₁ A - P (0H) _{y (3} )

-4 Λ

η = 3 to 20

>, y = 1 to 2

and for type II phosphoric acid esters of the forms'

- (CH ₂ ) _n - 0

x, y = 1 to 2

For the composition of the dispersion were the commercial products of the magnetic tape industry and for the Processing the usual methods used. As a magnetically anisotropic material are preferably finely divided acicular y-Fc ₂ O 3 pigments, cobalt-doped iron oxides, Barium ferrites and metal pigments related. As binders for the magnetic layers, the usual polymers, such as polyurethane elastomers, hydroxylgruppenheltige Mischpclymerisate (polyvinyl formal), chlorinated polymers, nitrocellulose, vinyl chloride-vinyl acetate copolymers and Blends of the polymers used. Suitable organic solvents for the preparation of the dispersions are the known solvents, such as cyclic Ketones (cyclohexanone), aromatics (benzene, toluene, xylene), linear ketones (acetone, methyl ethyl ketone), cyclic ethers

(Tetrahydrofuran, dioxane), esters (ethyl acetate, ethyl acetate) and chlorinated hydrocarbons (dichloromethane,

Dichloroethane) as well as solvent mixtures. The dispersions to be prepared can be further customary additives for Improvement of the utility properties, such as carbon black or graphite as antistatics or silicone oils, vegetable oils, Carboxylic acids and / or their esters are added as lubricants. The magnetic recording materials produced by the process according to the invention are characterized

in particular by improving the level uniformity (m _lia ), the rectangular _factor (I * ^RS /! * ^S ), the

Alignment coefficients (I * ^RS Iängs / I * ^RS transverse), the adhesion (F _H ) and reduced level drop (Δρ _ι00 ). For the purpose of evaluating the level drop and the level uniformity is on a defined piece of tape to

evaluating a cassette using a generator recorded a 10 kHz tone.

After 100 passes of tape piece through a Sony cassette deck at a speed of 4.75cm / s Level drop and level uniformity are evaluated for origin recording (auto-rewind test). The test data are in Table 1

summarized.

To determine the orientation coefficient and the rectangular factor, corresponding web samples were obtained Measure test casts on a sample vibrating magnetometer. The data compiled from these measurements is

together with the size of the adhesion between the magnetic layer and the backing in Table 2.

embodiment

In a predispersing unit, the following mixture is homogenised for 2 hours:

parts by weight ^ Fe ₂ O ₃ 1000 Phosphoric acid esters of formula (3) 44.5 Phosphoric acid esters of formula (4) 5.5 Copolymer of vinyl acetate, Vinyl alcohol and vinyl formal 21.7 1,2-dichloroethane 1672 cyclohexanone 318.5

After this predispersion phase, the further dispersion takes place in a stirred ball mill over a period of 3.5 hours at a throughput of 1.5 l / min. The further dispersion takes place with the addition of the remaining prescription ingredients:

parts by weight polyester urethane 140.5 Copolymer of vinyl acetate, Vinyl alcohol and vinyl formal 54.3 silicone oil 6.5 alkylbenzene 4.3 1,2-dichloroethane 1028 cyclohexanone 196 1.4! lydroxybenzen 3

When the desired final grain size is reached, the dispersity pq is terminated and the resulting mixture is filtered several times and applied to an 11 μm thick polyester layer. The magnetic layer passes through a magnetic field in which it is still wet, in which the pigment particles are aligned according to the field lines. After drying and calendering, a layer thickness of 4.5 pm is achieved. The calibrated maglev is cut to the desired 3.81 rim range.

Depending on the used Polyesterure'han and to improve the hydrolytic stability of the magnetic layer, a polysocyanate may be added to the dispersion prior to its application to the Folyesterunxerlage.

Comparative Example 1

In The same manner as in the embodiment except that the 50 parts by weight of dispersing aid (phosphoric acid ester) of the formula (3) and (4) was replaced by 20 parts by weight of the phosphoric acid ester of the formula (4), a recording material was prepared.

Comparative Example 2

In the same manner as in the embodiment except that the 50 parts by weight of the dispersing aid (phosphoric acid ester) of the formula (3) and (4) was replaced by 50 parts by weight of the phosphoric acid ester of the formula (3), a recording material was prepared.

Table 1

ν L ₁ .1.DL [dB] m _L "100 DL. [DB] Ap, oo 0.80 0.87 0.89 Comparative Example 1 Comparative Example 2 Embodiment 0.5 0.6 0.15 0.8 tip 1.15 -1.4 0.8 tip 1.3 -0.8 0.2 tip 0.25 ± 0 Table 2 FhIpI i * ^RS along / l * ^RS across I * " ⁸ /! * ⁸ Comparative Example 1 Comparative Example 2 Embodiment Example about 20 about 16 about 25 1.7 2.5 2.7

Claims (1)

1. A process for the preparation of magnetic recording media from a dispersion of finely divided magnetically anisotropic material in a solution of organic solvent, polymer binders and conventional additives, such as lubricants, dispersants and antistatic agents, layered application of the dispersion on a non-magnetizable pad, alignment of the magnetizable particles by a Magnetic field and removal of the solvent from the layer, characterized in that is used for dispersing the magnetic pigment as a dispersing agent 6in binary mixture of different phosphoric acid esters, consisting of
A: a phosphoric acid ester of the formula (1) ^R 1 - °> P - OH ...