JPH0312818A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having excellent durability and recording and reproducing characteristics by providing a magnetic layer contg. specific magnetic powder and resin on a base. CONSTITUTION:The magnetic layer contg. magnetic powder having 15 to 25dyne/ cm free surface energy and resin having a negative functional group and 30 to 45dyne/cm free surface energy is provided on the base. The free surface energy of the magnetic powder is matched with the level of the free surface energy of the binder resin in such a manner, by which the affinity of both is enhanced and the dispersibility of the magnetic powder is enhanced. The high characteristics with the durability are obtd. in this way and the magnetic recording medium having the excellent electromagnetic conversion characteristics and recording and reproducing characteristics is obtd. in this way.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to magnetic recording media.

[Background of the invention]

It is well known that there is currently a demand for magnetic recording media that can handle high-density recording.

Then, as a means to cope with higher density, a method was proposed that used fine-grained magnetic powder to smooth the surface of the magnetic layer, which made it possible to reduce noise and obtain a high signal-to-noise ratio. .

However, the finer the particles of magnetic powder, the more difficult it is to disperse it, making it difficult to obtain high output, and the strength of the magnetic coating layer often weakens, leading to deterioration in durability.

In other words, with only the technology of making magnetic powder fine particles, an increase in the S/N ratio can be expected due to the smoothness of the surface of the magnetic layer, but it is more difficult to disperse the magnetic powder, and the magnetic powder particles aggregate.
No improvement in output can be expected, and improvement in electromagnetic conversion characteristics is not effective.

In addition, the binding between the magnetic powder and the binder resin is insufficient,
Since the magnetic layer coating itself becomes brittle, running durability deteriorates, dropouts occur, edge damage and running stops, and further disadvantages such as peeling of the magnetic layer occur.

Furthermore, the still durability is greatly reduced.

[Disclosure of the invention]

While conducting research on the above-mentioned problems, the present inventor discovered that these problems are caused by the poor dispersibility of the magnetic powder in the magnetic paint and the insufficient bonding force between the magnetic powder and the binder resin. As a result of further research, we considered the surface free energy of each binder resin such as magnetic powder and polyurethane resin with respect to the liquid, and calculated the surface free energy of the magnetic powder from the surface free energy of the binder resin. It has been found that by adjusting the energy level, it is possible to increase the affinity between the two and to improve the dispersibility of the magnetic powder.

Therefore, an object of the present invention is to improve the dispersibility of magnetic powder, improve the electromagnetic conversion characteristics, have good binding properties between the magnetic powder and binder resin, have excellent durability, and improve recording and reproducing characteristics. The objective is to provide an excellent magnetic recording medium.

The purpose of the present invention is to have a surface free energy of 15 to 25.
dyne/cm of magnetic powder and a resin having a negative functional group and a surface free energy of 30 to 45 dyne/cm, the magnetic recording medium comprising a magnetic layer provided on a support. achieved by.

The surface free energy values of the magnetic powder and the binder resin such as polyurethane resin can be obtained by determining the contact angles (θ) of the magnetic powder and the resin with respect to the liquid.

Calculation of surface free energy (7S) is based on D, Owe
ns ”Estimation of the 5u
rface freeEnergy of Pol
ymers” Journal of Appl
ied Polymer 5science 13 (19
Based on the literature of 69), the following (1
) can be obtained using the formula.

That is, (1) γ, v: surface tension of the liquid γL'': surface tension related to the dispersion force component of the liquid γ, h: surface tension related to the hydrogen bonding force component of the liquid Here, T1.'
+ For the 7th, J, Panzer”Comp
onents of 5solid 5surface f
ree energy from wetting me
asurements” Journal ofCo
lloid and Interface 5cien
ce + vol, 44 No, 1 to γL' r t'' (dyne/cm) H2O
Since it is written as 10,838,46 CHzlz 43.7 2.65, CO3θ, γL″ of H2O and CHzh,
By substituting the known values of γ♂ and γL%l into the above equation (1), T2 and γsh can be obtained.

Note that the sum of T2 and γs'' is r.

The contact angle θ between a binder resin such as polyurethane resin and water or methylene iodide is calculated by forming a 5 μm thick binder resin film on a PET substrate, drying it, and dropping droplets of water or methylene iodide on it. , the contact angle can be determined using a microscope.

However, in the case of powder such as magnetic powder, the contact angle cannot be determined by this measurement method, so the following method is adopted.

First, for example, 15 g of magnetic powder is placed in a cylindrical measuring cell with a diameter of 3.6c+n, and tapped 500 times using a tapping device that operates at a speed of 40 times per minute to maintain a constant porosity of the magnetic powder. make it yours.

Then, the permeation rate of the liquid is determined for the measurement cell thus adjusted using a permeation rate measuring device ``Peneto Analyzer'' manufactured by Hosokawa Micron.

In other words, the depth of this cell placed on the lifter is 6c.
Hang it on the hook of an electronic balance so that it is submerged in the solution placed in a deep petri dish about m in size, and calculate the weight of the liquid that permeates. Note that the weight of the adjusted measurement cell at the time it is attached to the hook of the device is O, and the weight of the solution permeated by raising the lifter is input into the computer along with time.

Once the powder has permeated the solution, the weight will no longer change, so the measurement ends here.

The relationship between the penetration height 2 of the medium that penetrates the powder layer and the time t is W
It can be expressed by the ashburnO formula.

t: Time (sec) γL: Surface tension of liquid (dyne/cm) ηL: Viscosity of liquid (g/cm, 5ec) r: Capillary radius in powder layer (cm) θ: Contact angle or penetration height 2 The relationship between W and penetration weight W is expressed by the following equation (3).

S: cross-sectional area of measurement tube (cm2) ρL: liquid density (g/cm') ε: porosity From (2) and (3), the relationship between the permeation weight WL and the measurement time t is as shown in (4) below.

By the way, the value of W,''/l by the above computer is
- When output to a Y plotter, it becomes a straight line with a constant slope.

Calculating the slope within a certain time, this slope K = (S
・ε・ρL)2 T' 7 tcos/7 So, by substituting each constant, we can find the cos θ of powder and liquid.
is obtained.

This is measured for water and methylene iodide, respectively.

In addition, the value of r・ε2 is carbon tetrachloride, methylene chloride, chloroform, methanol, ethanol, n-butanol, methyl acetate, ethyl acetate, n-butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane. , cyclohexane, n-octane, n-dodecane, Hensen, toluene, tetrahydrofuran, 1,4-dioxane, ion-exchanged water, methylene iodide, and dibenzyl ether. It can be calculated by setting it to θ-1.

When determining cos θ of powder with respect to water r L-72
,75 (dyne/cm) 77L = 1 (g/
cm -5ec) Substitute ρ1° - 1,0 into (4) 2.

CI (for 212, r t =51.Hdyne/c
m), ηL=2.39 (g/cm, 5ec), ρL
By similarly substituting =3.3'l, the contact angle between the magnetic powder and the liquid can be determined.

The surface energy of the binder resin having a negative functional group is more preferably about 35 to 42 dyne/cm, and the ratio of the energy of the hydrogen bond force component to the energy of the dispersion force component is about 0.15 to 0. The surface free energy of the magnetic powder is preferably about 18 to 23 dyne/cm.

In addition, examples of the negative functional groups of the resin serving as the binder include:
-503M, -COOM, -PO(OM')(0M
2) (However, Ml is hydrogen, lithium, potassium,
Alkali metals such as sodium, M2 is hydrogen, lithium,
It is an alkali metal such as potassium or sodium, or a hydrocarbon residue, and M1 and M2 may be the same or different. ), among others, 13O, Na, COON
a is preferred.

And such negative functional group is 0.01~0.10m
o1%, more preferably 0.03 to 0.08 mo1%
It is preferable that there be.

Further, as the resin itself, for example, urethane polymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Boria'amide resins, polyvinyl butyral, cellulose derivatives, styrene-butadiene copolymers, polyester resins, various synthetic rubber binders, phenolic resins, epoxy resins, urea resins, melamine resins, silicone resins,
There are acrylic reactive resins, mixtures of high-molecular polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, mixtures of low-molecular-weight glycols and high-molecular-weight diol compounds, and mixtures thereof, among which urethane polymers, chlorinated Preferred are resins based on vinyl-vinyl acetate copolymers, mixtures of polyester polyols and polyisocyanates, and the like.

Note that it is not necessary to use only resins with the above characteristics as binder resins; ethyl cellulose, nitrocellulose, polyvinylidene chloride, vinyl chloride-vinyl acetate, etc., which have been conventionally used as binders for magnetic recording media, may also be used. Polymers, styrene-butadiene copolymers, polymethyl methacrylates, vinylidene chloride-methacrylic resins, polyester resins, etc. may also be used in combination.

However, in such a case, it is desirable that the binder resin according to the present invention, which has a negative functional group and has a surface free energy of 3'0 to 45 dyne/cm, accounts for about 50% or more of the total binder resin width.

In addition, as magnetic powder, ferromagnetic iron oxide (Cr, Mn.

Co, Ni, Cu, Zn, etc. may be added), ferromagnetic chromium dioxide (Na, K, T
i, V, metals such as MnFe, Co, Ni, P,
ferromagnetic alloy powder, etc. may be used as appropriate.

The magnetic powder is used in an amount of about 500 to 800 parts by weight based on 100 parts by weight of the binder resin according to the present invention, which has the negative functional group and has a surface free energy of 30 to 45 dyne/cm.

Further, as other components added to the magnetic layer as necessary, there are dispersants, lubricants, abrasives, antistatic agents, rust preventives, antifungal agents, etc. As dispersants, for example, carbon Number 12 to 18 fatty acids, alkali metals of the above fatty acids (L
i, Na, K, etc.) or alkaline earth metals (Mg,
Metal soaps consisting of Ca, Ba), fluorine-containing compounds of the aforementioned fatty acid esters, amides of the aforementioned fatty acids, and the like are used. In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters, etc. can also be used.

Examples of lubricants include silicone oils such as dialkylpolysiloxane (alkyl group has 1 to 5 carbon atoms), dialkoxypolysiloxane, monoalkylmonoalkoxypolysiloxane, phenylpolysiloxane, fluoroalkylpolysiloxane, and conductive materials such as graphite. fine powder,
Solid lubricants such as molybdenum disulfide and tungsten disulfide, fine plastic powders such as polyethylene, polypropylene, polyethylene-vinyl chloride copolymer, and polytetrafluoroethylene, monobasic fatty acids with 12 to 20 carbon atoms, and monobasic fatty acids with 3 to 20 carbon atoms. Fatty acid esters consisting of 12 monohydric alcohols, fluorocarbons, etc. can be used.

As the polishing agent, for example, alumina, silicon carbide, chromium oxide (Crz(1+), corundum, artificial corundum, diamond, artificial diamond, emery (main components: corundum and magnetite), etc. are used.

Examples of antistatic agents include conductive fine powder such as carbon black, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin, and glycidol, higher alkylamines, and quaternary ammonium salts. , pyridine and other heterocycles, cationic surfactants such as phosphonium or sulfonium, and other amphoteric surfactants are used.

Examples of rust preventives include volatile rust preventives such as phosphoric acid, sulfamide, guanidine, pyridine, amines, urea, zinc chromate, calcium chromate, strontium chromate, and synchlohexylamine nitride (inorganic acids such as amines, amides, or imides). salts or organic acid salts).

Examples of antifungal agents include salutylanilide, bis(tributyltin) oxide, mercuric phenyloleate, and dihydroacetoic acid.

Examples of organic solvents used in magnetic paints include ketones such as acetate, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl acetate; Chlorination of glycol ethers such as ether and glycol dimethyl ether, cool systems (aromatic hydrocarbons) such as benzene, toluene, and xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. There are hydrocarbons, etc.

Then, the mixture of these magnetic fine powders, binders, dispersants, lubricants, abrasives, antistatic agents, rust preventives, antifungal agents, solvents, etc. is processed using a two-roll mill, a three-roll mill, etc.
Make a magnetic paint using a ball mill, etc., and apply air doctor coat, blade coat, air knife coat, squeeze coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, etc. on a non-magnetic support.
It is applied using cast coat, spin cord, etc.
After the magnetic powder is oriented if necessary, it is dried.

〔Example〕

<Composition of magnetic layer composition> Co-containing r-Fezes (BET value 40 m2/g
r5=15) 100 parts polyurethane resin (γS・
34) 15 parts vinyl chloride-vinyl acetate copolymer 10 parts butyl palmitate
1 part myristic acid
2nd part alumina
4 parts carbon black 1 part lecithin 3 parts cyclohexanone 50 parts methyl ethyl ketone 100 parts toluene
100 parts of these compositions were sufficiently stirred and mixed in a ball mill, and 5 parts of a polyfunctional isocyanate (Coronate L manufactured by Nippon Polyurethane Industries, Ltd.) was added, followed by filtration with a filter having an average pore size of 1 μm.

The magnetic paint obtained in this way was applied to the surface of a polyethylene terephthalate haze with a thickness of 14 μm to a dry thickness of 4 μm, and after heating and drying, the magnetic layer was surface-treated with a super calendar roll to achieve a predetermined thickness. A wide magnetic film having a large magnetic layer was obtained, and this was slit into 1/2 inch width to produce a video magnetic tape.

In addition, the characteristics of the magnetic powder and polyurethane resin used here are as shown below, and Examples 1 to 5 and Comparative Examples 1 to 1
Table 1 shows the combinations of magnetic powder and polyurethane resin in Example 8.

Co-containing 7-Fe20. lMagnetic powder ■BET40m”/g
, Hc7300eCo-containing γ-Fe203 magnetic powder■
BET40m2/g, Hc8500eCo containing 7-
Fe20. , magnetic powder■ BET40m2/g, Hc8
800eCo-containing 1-Fe20. Magnetic powder ■BE749m
2/g,,Hc9000eCo-containing 1-Fe20. Magnetic powder■BET49m2/g, Hc9200eCo containing γ-FezO:+Magnetic powder■BET49m2/g,
) lc9400e polyurethane resin■ 4,4゛-diphenylmethane diisocyanate (M
DI), 1.6 hexanediol (1,6)IG),
Neobentanediol (NPC), adipic acid (AD)
Contains 0.07 m mol/g of sulfonic acid group consisting of A).

■ Same composition as ■, sulfonic acid group 0.05 m mol/
Contains g5.

■ Same composition as ■, but does not contain sulfonic acid groups.

■ Tolylene diisocyanate (TDI), 1611
Composition consisting of G, NPG, and ADA with 0 sulfonic acid groups
．． Containing 05 mmol/g ■ Same composition as ■ without containing sulfonic acid group.

■ Composition consisting of MDI, 1,6HG, NPC, and isophthalic acid, containing 0.05 mmol/g of sulfonic acid group.

■ Same composition as ■, sulfonic acid group 0.02 m mol/
Contains g.

■ Same composition as ■, but does not contain sulfonic acid groups.

■ It has a composition consisting of MDI, 1.48G, and 0.03 mmol/g of sulfonic acid groups.

[Phase] Same composition as ■, but does not contain sulfonic acid groups.

6 The running properties and durability of the magnetic tape obtained as described above were investigated, and the results are shown in Table 2.

<Measurement method> Lum1 SN, RF out, chroma
Out: HR-37000 (manufactured by Victor Japan) recording and reproducing device and Shibaku Noise Meter (9250) were used.

Dropouts, number of dropouts greater than or equal to 15 μS, -12 dB in 1 minute using HR-37000 recording and reproducing equipment.

Squareness ratio: H
Br78m value when m is 5 KOe.

Durability of 400 repeated runs: 20″C165%RH
Below is the state of the magnetic tape after 400 repetitions.

From the results shown in Table 2, it can be seen that the magnetic recording medium according to the present invention has high characteristics in terms of running performance and durability, and has excellent electromagnetic conversion characteristics and excellent recording and reproducing characteristics.

9 hand Continued Supplementary Positive spontaneous writing) June 13, 1989

Claims (1)

[Claims] Magnetic powder with a surface free energy of 15-25 dyne/cm and a negative functional group with a surface free energy of 30-25 dyne/cm
A magnetic recording medium characterized in that a magnetic layer containing a resin of 45 dyne/cm is provided on a support.