JPH0312820A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium having a good traveling property and excellent durability by providing a magnetic layer on one surface of a base and providing a layer contg. a specific resin and nonmagnetic powder on the other surface. CONSTITUTION:The magnetic layer is provided on one surface of the base and the layer contg. the resin having 35 to 50dyne/cm free surface energy and 0.15 to 0.30 ratio of the energy of the hydrogen bonding strength component to the energy of the dispersing force component thereof and having a negative functional group and the nonmagnetic powder having >=15dyne/cm free surface energy is provided on the other surface. The bonding strength of a carbon black and the binder is increased in this way and the high characteristics with the traveling property and durability are obtd.

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.

By the way, in general, in magnetic recording media that can handle high-density recording, ferromagnetic powder with a small particle size is used as the ferromagnetic powder contained in the magnetic layer, so the surface of the magnetic layer tends to be smooth, so Improvements in running performance are desired. As a means of improving the running properties of such magnetic recording media, it is necessary to not only consider the surface condition of the magnetic layer provided on one side of the non-magnetic support, but also to consider the surface condition of the magnetic layer provided on one side of the non-magnetic support. Since the surface condition of the other side (back side) has a large effect, it has been proposed to provide a so-called back coat layer on the back side.

This back coat layer is usually formed from non-magnetic powder and a binder, and has a moderately rough surface to reduce the contact area and lower the coefficient of friction. Providing the coat layer improves the running properties of the magnetic recording medium.

However, if, for example, non-magnetic powder in the back coat layer aggregates, the surface roughness of the back coat layer becomes larger than necessary, causing unevenness, which is transferred to the magnetic layer, causing electromagnetic problems such as noise generation. This leads to a decrease in the conversion characteristics (this is a disadvantage).Also, the back coat layer becomes easily scraped, and the scraped powder adheres to the magnetic layer and magnetic head, leading to a decrease in the electromagnetic conversion characteristics. may become unstable.

[Disclosure of the invention]

While conducting research on the above-mentioned problems, the present inventor discovered that these problems were caused by the poor dispersibility of the non-magnetic powder in the bank coat layer and the insufficient bonding force between the non-magnetic powder and the binder. The present invention was achieved based on this suggestion.

That is, for example, carbon black has a low surface energy, so in order to impart activity due to hydrogen bonding force to the surface, a resin with a hydrogen bonding force within a certain range was used, and the dispersibility was improved by using a resin with a similar energy strength. Therefore, it was found that the bonding strength between the carbon black and the binder was increased, and the magnetic recording medium had high properties in terms of runnability and durability.

Therefore, it is an object of the present invention to have good dispersion of non-magnetic powder in a back coat layer, sufficient bonding force between the non-magnetic powder and binder, good runnability, and excellent durability. An object of the present invention is to provide a magnetic recording medium with excellent recording and reproducing characteristics.

The object of the present invention is to provide a magnetic layer on one side of the support, and to provide a surface free energy of 35 to 50 d on the other side.
yne/cm, and the ratio of the energy of the hydrogen bond force component to the energy of the dispersion force component is 0.15 to
0.30, and is achieved by a magnetic recording medium characterized by being provided with a layer containing a resin having a negative functional group and a nonmagnetic powder having a surface free energy of 15 dyne/cm or more.

Note that the values of the surface free energy of a nonmagnetic powder such as carbon black and a binder resin such as a polyurethane resin can be obtained by determining the contact angle (θ) of each of the nonmagnetic powder and the resin with respect to a liquid.

Calculation of surface free energy (γS) 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) γLv: Surface tension of the liquid TL': Surface tension related to the dispersion force component of the liquid TLh; Surface tension related to the hydrogen bonding force component of the liquid Here, TL'l
For 'r-, J.PanzerIIComp
onents of 5solid 5surface f
ree energy from wetting me
asurements” Journal ofCo
lloid and Interface 5cien
ce + vol, 44 No, 1? ) γLd γt' (dyne/cm)1120
10.8 38.46CHzh 43
．． 7 2.65, so by substituting the known values of cos θ, γId1 γLh and γLv of ■2o and CH2I2 into the above equation (1), γ, ' and r
sh is required.

Note that the sum of γS6 and γ- is I5.

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 carbon black, the contact angle cannot be determined by this measurement method, so the following method is adopted.

First, for example, 15g of carbon black is 3°6cm in diameter.
The carbon black was placed in a cylindrical measuring cell and tapped 500 times using a tapping device operating at a rate of 40 times per minute to keep the porosity of the carbon black constant.

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 Hoso Kawa 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 sufficiently permeated the solution, the weight will no longer change, so the measurement ends here.

Penetration height of the medium that penetrates the powder layer! The relationship between time and time is W
It can be expressed by the ashburn equation.

t: Time (see) TL: 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! The relationship between the permeation weight WL and the permeation weight WL is expressed by the following equation (3).

S: cross-sectional area of measurement tube (0 m2) ρL = liquid density (g/cm3) ε: porosity From (2) and (3), the relationship between permeation weight WL and measurement time t is as shown in (4) below.

By the way, the value of WL2/l determined by the above computer is
- When output to a Y plotter, it becomes a straight line with a constant slope.

When calculating the slope within a certain time, this slope K is T 1
γLCO5θ K = (S・ε・ρL)2 p, −1 Therefore, by substituting each constant, the cos θ of powder and liquid is obtained.
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, Select the most easily wetted solvent from among the solvents such as cyclohexane, n-octane, n-dodecane, benzene, toluene, tetrahydrofuran, 1,4-dioxane, ion-exchanged water, methylene iodide, and dibenzyl ether, and in this case cos θ It can be calculated by setting it to -1.

When determining cos θ of powder with respect to water, r L =
72.75 (dyne/cm) 1L= 1 (g/c
Substitute ρL = 1.0 into equation (4).

For CTolt, r t =51. Hdyne/cm
), ηL=2.39 (g/cm, 5ec), ρ, 3
．． By similarly substituting 31, the contact angle between the carbon black and the liquid can be determined.

In addition, the surface free energy of the resin having a negative functional group is more preferably about 38 to 45 dyne/cI11,
The ratio of the energy of the hydrogen bond force component to the energy of the dispersion force component is preferably about 0.18 to 0.27 degrees, and the surface free energy of nonmagnetic powder, such as carbon black, is about 17 to 22 dyne. /
Preferably, it is cm.

In addition, examples of the negative functional groups of the resin serving as the binder include:
-503M, -COOM, -PO(OM')(OM
”) (However, M' 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 Ml and Mt may be the same or different. ), among others, 15O, Na, COON
a is preferred.

And, such a negative functional group is 0.01~0.10+
l1oI%, more preferably 0.03-0.08 mo
Preferably it is 1%.

Further, as the resin itself, for example, urethane polymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Polyamide resin, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, various synthetic rubber binders, phenol resin, epoxy resin, urea resin, melamine resin, silicone resin, acrylic reaction resin, polymeric polyester resin 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, vinyl chloride-
Preferred are resins based on vinyl acetate copolymers, cellulose derivatives, mixtures of polyester polyols and polyisocyanates, and the like.

In the magnetic recording medium according to the present invention, the magnetic layer provided on one side of the non-magnetic support may include, for example, magnetic powder,
In addition to the binder resin, various other additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, and a fungicide are included as necessary.

Here, as the magnetic powder, ferromagnetic iron oxide (Cr.

Mn, Go, Ni Cu, Zn, etc. may be added), ferromagnetic chromium dioxide (Na, K
, ferromagnetic alloy powder, etc. may be used as appropriate.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms, metal soaps made of alkali metals (Li, Na, K, etc.) or alkaline earth metals (Mg, Ca, Ba) of the above-mentioned fatty acids, and the above-mentioned fatty acid esters. Compounds containing fluorine, amides of the aforementioned fatty acids, etc. 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 carbon atoms 3
fatty acid esters consisting of ~12 monohydric alcohols,
Fluorocarbons etc. can be used.

As the abrasive, for example, alumina, silicon carbide, chromium oxide (Crz(h), 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 20 mate, calcium chromate, strontium chromate, and synchrohexylamine nitride (amine, amide, or imide). (inorganic acid salts or organic acid salts).

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

Organic solvents used in magnetic paints include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol acetate monoethyl ether, ether, and glycol dimethyl ether. Glycol ethers such as benzene, toluene, xylene, tars (aromatic hydrocarbons), chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. be.

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.

In addition, the manufacturing method and coating method of the coating material containing a carboxylic acid group/ink with a surface free energy of 15 dyne/cm or more provided on the other side of the non-magnetic support are the same as the manufacturing method and coating method of the magnetic coating material. Good.

〔Example〕

Composition of magnetic layer composition> Go-containing 7-FezO+ polyurethane vinyl chloride-vinyl acetate copolymer stearate butyl myristic acid 100 parts 8 parts 12 parts 0.8 parts 0.5 parts stearic acid 0.5 parts alumina 5 parts Carbon black 0.5 parts Lecithin
4-part cyclohexanone
40 parts methyl ethyl ketone
60 parts toluene
60 parts These compositions were sufficiently stirred and mixed in a ball mill, and after adding 5 parts of a polyfunctional isocyanate (Coronate L manufactured by Nippon Polyurethane Industries, Ltd.), the average pore size was 1.
It was filtered with a μm filter.

The magnetic paint obtained in this way was applied to the surface of a polyethylene terephthalate base with a thickness of 14 μm to a dry thickness of 4 μm, and after being heated and dried, the magnetic layer was surface-treated with a super calendar roll to achieve a predetermined thickness. A wide magnetic film was obtained having a magnetic layer of .

Next, a back coat layer composition having the following composition was dispersed for 24 hours using a ball mill to prepare a back coat paint.

5 The back coat paint thus obtained has a dry thickness of 1.0
It was coated on the other side of the polyethylene ticrate film to a thickness of μm, heated and dried, and then slit into 1/2 inch width to obtain a magnetic recording medium having a back coat layer.

<Composition of back coat paint> Carbon black 100 parts Nitrocellulose 40 parts Polyurethane resin 50 parts Toluene
750 parts methyl ethyl ketone
1000 parts Polyisocyanate (Coronet) L) 10 parts The characteristics of the carbon black and polyurethane resin used here are as shown below, and the characteristics of the carbon black and polyurethane resin in Examples 1 to 5 and Comparative Examples 1 to 17 The combinations are shown in Table 1.

Carbon Black■BET value 33m2/g Carbon Black■BET value 25m"/g Carbon Black■BET
Value 33m"/g6 Carbon black ■BET value 25m"/g Carbon black■BET value 33m"/g Part Polyurethane resin Tolylene diisocyanate (TDI), 1.6 hexanediol (1,6HG), neobentanediol (NPC) , containing 0.03 mmol/g of sulfonic acid group consisting of adipic acid (ADA).

■ Same composition as ■ with carboxylic acid group 0.01 m mol/
Contains g.

■4.4-diphenylmethane diisocyanate (M Roe), 1,4-butanediol (1,48G), ADA
Made of polyurethane. No negative functional groups.

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

■Polyurethane consisting of MDI, 1.6HG, NPG, and ADA.

■ Same composition as ■ with carboxylic acid group 0.01 m mol/
Contains g.

■ Same composition as ■ with carboxylic acid group 0.06 m mol/
Contains g.

■ Contains 0.04 mmol/g of sulfonic acid groups consisting of MDI, 1,6HG, NPC, and isophthalic acid.

■ Same composition as ■, no negative functional group.

[Phase] Same composition as ■, sulfonic acid group 0.07m mo
Contains l/g.

, ■ Isophorone diisocyanate (IPDI), L6
11G, 0 sulfonic acid groups consisting of NPG 5ADA
．． Contains 0.3m mol/g.

@ Same composition as ■, 0.01 m mol of sulfonic acid group
/gi&existence.

@ Same composition as ■, carboxylic acid group 0.02 m mol
/Contains.

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

9 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> Output variation range: The range of RF ratio output variation during playback after 400 repetitions at 20°C and 165% RH.

Dynamic friction coefficient μ: Using a runability tester (TDT-3000) manufactured by Yokohama System Co., Ltd. at 20°C and 165% RH, the inlet tension was set to 20g, and the magnetic tape was attached to a stainless steel pin with a diameter of 3.8mm at 180 degrees. Wrapping, 3.3c
Run at m/sec, measure the exit tension after 4 minutes,
It was calculated from the following formula.

It was measured.

Glabella adhesive 2172 inches wide magnetic tape is wound with a pressure of IKg, left at 60°C, 280% R11 for 20 hours, left at room temperature for another 24 hours, then rewound. Those who did not have it were evaluated as glabellar adhesive fever.

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.

Skew: The video recording of the color par signal is
Using Tekki (HR6500JVC), 40°C18
After 400 repeated runs under 0% RH conditions, the image distortion at the switching point was displayed on the monitor screen in 88 seconds.

Claims (2)

[Claims] (1) A magnetic layer is provided on one side of the support, and the other side has a surface free energy of 35 to 50 dyne/cm,
and the ratio of the energy of the hydrogen bond force component to the energy of the dispersion force component is 0.15 to 0.30, and the surface free energy of the resin having a negative functional group is 1.
A magnetic recording medium comprising a layer containing non-magnetic powder of 5 dyne/cm or more. (2) The magnetic recording medium according to claim 1, wherein the non-magnetic powder is carbon black.