JPH01112517A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve various characteristics necessary for a recording medium by incorporating specified polyurethane resin into a binder contained in a magnetic layer in combination with magnetic powder. CONSTITUTION:Polyurethane resin having a polysiloxane chain in the side chain is incorporated into a binder in a magnetic layer formed on a nonmagnetic support. Magnetic particles pulverized so as to increase density or S/N can highly be dispersed, filled and oriented in the magnetic layer, the surface of the magnetic layer is highly smoothened and a magnetic recording medium having high characteristics, improved travelling performance and durability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks. More specifically, the present invention relates to a magnetic recording medium using a polyurethane resin having excellent properties as a binder component of a magnetic layer provided on a non-magnetic support L.

(Prior art) Magnetic tapes and magnetic disks, which are general-purpose magnetic recording media, use long-sleeved acicular magnetic particles of 1 μm or less in a binder solution together with appropriate additives (dispersants, lubricants, antistatic agents, etc.). It is manufactured by dispersing it into a magnetic paint and applying it to polyethylene terephthalate film.

The properties that are included in the binder of magnetic recording media include dispersibility, filling properties, orientation of magnetic particles, durability of the magnetic layer, abrasion resistance, heat resistance, smoothness, and contact with non-magnetic supports. rt properties, etc., and the binder plays a very important role. Conventionally used binders include vinyl chloride, vinyl acetate copolymer, vinyl chloride, vinyl acetate, vinyl alcohol copolymer, vinyl chloride, vinylidene chloride copolymer,
Polyurethane resins, polyester resins, acrylonitrile, butadiene copolymers, nitrocellulose, cellulose, acetates, butyrates, epoxy resins, acrylic resins, and the like are used.

Among these resins, polyurethane resins have superior properties such as toughness and abrasion resistance compared to other resins due to intermolecular hydrogen bonding caused by urethane bonds, but the dispersibility of magnetic particles is insufficient. Dispersibility can be improved by introducing a sulfonic acid metal salt or a metal salt of an acidic phosphorus compound into the resin, as the inventors have already discovered (Japanese Patent Publication No. 41585/1983, Japanese Patent Application Laid-Open No. 1983-1999) 128470, Japanese Unexamined Patent Publication No. 17037/1983).

However, in recent years, there has been an increase in recording density in magnetic recording media, and S/
There is ammonium water in which finer magnetic particles are highly dispersed due to the N ratio of 1, etc., and are highly filled in the magnetic layer.

In response to these requirements, the introduction of sulfonic acid metal salts or acidic phosphorus compound metal salts has a remarkable effect. Also, S
A smooth magnetic layer has been required due to the negative /N ratio, but the surface of the magnetic layer is increasingly becoming smoother by highly dispersing finely divided magnetic particles. As a result, it has become difficult to satisfy requirements such as ease of leaving the office and running durability.

As a result of intensive research into a binder that has excellent running properties and running durability for this smoothed magnetic layer, the present inventors found that polyurethane containing a reactive silicone compound at both ends having a polysiloxane skeleton as a starting material. It was discovered that the resin is effective for several pieces of the properties listed in 1- (Japanese Patent Laid-Open No. 81-48
No. 120+%l).

However, when the polyurethane resin is incorporated into the magnetic layer, the degree of freedom of the polysiloxane segment, which was introduced with the aim of improving running properties and running durability, decreases, and the demand for running properties is increasing year by year. At present, it is not always possible to obtain a satisfactory product in terms of performance and running durability.

(Problems to be Solved by the Invention) The present invention is directed to high density or S/
Due to the -L direction of the N ratio, it is possible to achieve high dispersion, high filling, and high orientation of the finer magnetic particles -R, which not only satisfies the high smoothness of the magnetic layer surface but also improves running properties and running durability. The present invention provides an excellent magnetic recording medium.

(Means for Solving the Problems) That is, the present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder, in which the binder includes a polyurethane resin having a polysiloxane chain in a side chain. This is a magnetic recording medium with special characteristics.

The silicone compound used as a raw material for the polyurethane resin used in the present invention preferably has an isocyanate-reactive functional group only at one end represented by the general formula [I].

(R,, R,, 1R4 in the formula is an alkyl group having 1 to 6 carbon atoms and/or a phenyl group.

R2 and R15 are groups represented by general formula (II), the amount -fcH-CH, -Oh R8-(II) R7 is a hydrogen atom or a methyl group, and RR is an alkylene group having 2 to 10 carbon atoms. . R is a functional group that is reactive with an isocyanate group or a branched alkylene group that has a functional group that is reactive with an incyanate group at the end. Also m
is an integer from 0 to 5, and n is an integer from 10 to 100. ) The polyurethane resin used in the present invention has a diisocyanate component (Δ), a long chain diol component ([11, chain extension component 1
c) and the polysiloxane component D+, which are reacted in the ratio shown below.

A/(B+C+D)=110.85~1.2 (11 ratio) B/I)=10010.01~20
(Gravity rli ratio) Examples of the organic diisocyanate (A) used in the present invention include many diisocyanates including 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, and inphorone diisocyanate.

Examples of the long-chain diol component include polyester diol, polyether diol, polycarbonate diol, etc., but polyester diol (B) is preferable because of the toughness of the polyurethane resin.

The polyester diol component (B,) consists of a dicarboxylic acid component and a diol component, and the dicarboxylic acid component includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and orthophthalic acid, and aliphatic acids such as succinic acid, adipic acid, and sebacic acid. Examples include dicarboxylic acids and alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid.

Examples of the diol component include ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol cyclohexanedimethanol, and the like.

Other examples of polyester diols include lactone-based polyester diols obtained by ring-opening polymerization of lactones such as ε-caprolactone.

Chain extension component (as Cl, adjust the urethane group concentration,
Glycols such as ethylene glycol, 1,3-propylene glycol, 1,4-tetramethylene glycol, 1,6-hexanesiol propylene glycol, neopentyl glycol, and monoethanol have the role of imparting toughness unique to polyurethane. Examples include amino alcohols such as amines, and diamines such as ethylene diamine and hexamethylene diamine.

1. In addition to the above, trifunctional components such as trimethylolpropane may be used as long as the performance is not impaired.

Furthermore, the chain extension component (Cl) may be water in place of -1-.

The polysiloxane component [Dl is as described above, and is a silicone compound having a functional group at one end.

The terminal may have any number of functionalities, but in order to introduce a polysiloxane chain into the side chain with monofunctionality, it must first undergo a reaction with a trifunctional or higher functional component, and with a polyfunctional component of trifunctional or higher functionality, In this case, the molecular 11 distribution of the produced polyurethane expands, which is undesirable because it has negative effects such as a decrease in solubility in general-purpose solvents and a decrease in the dispersibility of magnetic particles.

It is preferable to use difunctionality at one end because it can be handled in the same way as other diol components and can be easily introduced as a side chain of the polyurethane resin chain. Specific compounds include the following.

C Ha to H*
n = +u~+uuCH. CH3 etc.

The amount of polysiloxane component + Dl used is in the range of 0.01 to 20% by weight of the polyester diol component, preferably 0.5 to 10% by weight of the mark. Ingredients + [31
If it is less than 0.01'rRii1% of s20 tons r. If it exceeds 1%, the adhesion strength as a binder decreases, the compatibility with other resins deteriorates, and the solubility of the smooth polyurethane resin in general-purpose solvents decreases. Further, the polysiloxane component (Dl) may be introduced during the reaction either during the production of polyester diol or during the production of polyurethane.

In addition to the polyurethane resin of the present invention, which has excellent running properties and running durability, in order to further improve the dispersibility, filling property, and orientation of magnetic particles, the present inventors have found that , it is effective to introduce sulfonic acid metal salts and/or metal salts of acidic phosphorus compounds (Japanese Patent Publication No. 58-41565, JP-A-58-128470,
JP-A-59-17037). This sulfonic acid metal salt and/or acidic phosphorus compound metal salt-containing machine has a total sulfur and phosphorus content of 0.0 in the polyurethane resin.
1-2%, preferably 0.01-1.5%
, particularly preferably in the range of 0.05 to 1.0% by weight. If the total content is 0.01ff<nt%, no effect will be seen, and if it exceeds 1-5%, the viscosity of the solution will increase significantly, the solubility in general-purpose organic solvents will decrease, and the physical properties will depend on humidity. When it exceeds 2% by weight, the solubility decreases.
Physical properties change significantly due to humidity.

When producing the polyurethane resin used in the present invention, the ratio of incyanate groups to hydroxyl groups is in the range of 110.85 to 1.2. If the inocyanate groups are in excess of the hydroxyl groups, the resulting polyurethane resin will have isocyanate groups at the ends, resulting in poor storage stability.On the other hand, if the hydroxyl groups are in excess, the molecular weight of the polyurethane will decrease, which is undesirable.

The ratio of isocyanate groups to hydroxyl groups is 1/1 to 1/1.1
5 is particularly preferred.

The method for producing the polyurethane resin used in the present invention is Wanshi F
Either the l''/t method or the prepolymer method may be used.

Further, the reaction method may be either reaction in a molten reaction solution.

In the magnetic recording medium of the present invention, in addition to the polyurethane resin used in the present invention, other resins may be added for the purpose of adjusting flexibility, improving cold resistance, heat resistance, etc. It is desirable to mix a compound that crosslinks by reacting with the polyurethane resin. Other resins include vinyl chloride resin, polyester resin, cellulose resin,
Examples include epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile-butadiene copolymer, and the like.

On the other hand 1. Compounds that crosslink with polyurethane resin include:
Examples include polyisocyanate compounds, epoxy resins, melamine resins, urea resins, etc. Among these, polyisocyanate compounds are particularly desirable.

The magnetic particles used in the magnetic layer of the magnetic recording medium of the present invention include γ-Fe2O3, γ-Fe*O* and Fe*04.
crystal, cro2, cobalt-doped γ-Fe20
．． or Fe, o4, barium ferrite and Fe-C
Examples include ferromagnetic alloy powder such as o5Fe-Co-Ni.

The magnetic recording medium of the present invention may optionally contain plasticizers such as dibutyl phthalate and triphenyl phosphate, dioctyl sulfonodium succinate, t-butylphenol/polyethylene ether, ethylnaphthalene/sodium sulfonate, dilauryl succinate, and stearin. Lubricants such as acid zinc, soybean oil lecithin, silicone oil, and various antistatic +1- agents can also be added.

(Example) The present invention will be specifically illustrated below with reference to Examples.

In the examples, 91 parts means parts by weight.

Each physical property was evaluated according to the following method.

■゛11pa' (Evaluation of wear resistance and durability):! 2
A magnetic tape prepared using the prepared polyurethane resin as a binder for a magnetic recording medium was run on a video deck, and the state of wear of the magnetic layer was observed after running 100 and 200 times.

L stop Li (evaluation of running stability): The same operation as in 1- was performed and unevenness during running was observed.

Σ[(RV) (Evaluation of filling property): The porosity was determined by the following formula.

RV=1-M5/(111M+1 (MS: l
Saturation magnetization of the magnetic media per t-position volume. Mo：'
Saturation magnetization of magnetic powder only per l'-position volume. q: Volume fraction of magnetic powder in the magnetic coating film. ). The smaller the porosity, the greater the filling property.

Magnetism "k ox Ll - Choice (Evaluation of dispersibility):" - Gloss was measured using a 60mm scale.

The polyester diol component + Bl used in each synthesis example was
It has the composition and molecular weight shown in Table 1.

5-Sodium sulfoisophthalic acid in Table 1, 2゜3-
Sodium dihydroxypropylphenyl phosphonates are a compound containing a sulfonic acid metal salt and a metal salt of an acidic phosphorus compound, respectively.

Table 1: Synthesis Example 1 100 parts of polyester diol A with a molecular weight of 2000 was mixed with 173 parts of toluene in a reaction vessel equipped with a thermometer, a stirrer, and a reflux cooling tube. and 173 parts of methyl ethyl ketone, and after dissolving, 1 part of neopentyl glycol (NPC)
0 parts, 4,4'-difunylmethane diisocyanate) (
36 parts of Ml)I) and 2 parts of the polysiloxane compound (b) (described above) having a molecular weight of 500 were added, and the mixture was heated and stirred at 75°C for 10 hours. The obtained polyurethane resin fAl solution was a pale yellow, transparent, homogeneous solution with a solid content concentration of 30% and a solution viscosity (25° C.) of 20 poise. Further, analysis by gel permeation chromatography showed that the molecule: IX was 26,000 in terms of standard polystyrene. Moreover, the total content of sulfur and phosphorus was 0.18%.

Synthesis Example 2 In the reaction vessel used in Synthesis Example 1, 200 min.
After dissolving 100 parts of polyester diol IcI of 0.0, 173 M< of toluene and 173 parts of methyl ethyl ketone, 38 parts of MDI was added, and after heating and stirring at 75°C for 1 hour, 5 parts of molecule Fit 1000 polysiloxane compound (a) (above) was added. In addition, after further heating at 75℃ for 2 hours,
Seven NPCs were added and the mixture was further heated and stirred at 75°C for 8 hours.

The obtained polyurethane resin 10+ had a solid content concentration of 30%, a solution viscosity of 35 poise, and a molecular h of 128,000, and a sulfur and phosphorus content of 0.20%.

Synthesis Example 3 Polyester diol component (B) with a molecular weight of 1500,
Polyurethane IcI was obtained in exactly the same manner as in Synthesis Example 1 except that the polysiloxane component was replaced with (d) having a J' amount of 1500. Solid content concentration 30% solution viscosity (25°C
) 25 poise molecule kt18. It was ooO.

Comparative Synthesis Example 1 Synthesis Example 1 except that it does not contain the polysiloxane compound (b)
A polyurethane resin (Dl) was obtained in the same reaction F order.

Comparative Synthesis Example 2 Synthesis Example 3 except that it does not contain polysiloxane compound (d)
Polyurethane resin (E) was obtained in the same reaction procedure as above.

Comparative Synthesis Example 3 A polyurethane resin (F) was obtained in the same reaction procedure as in Synthesis Example 1, except that a polysiloxane compound having a general formula with molecule r+k of 1,500 having a general formula reactive at both ends was used in place of the polysiloxane compound (B).

Polyurethane resins obtained in each synthesis example and comparative synthesis example (
The results of A) to (F) are shown in Table 2.

In the following margin Examples 1 to 3 and Comparative Examples 1 to 3 Using the polyurethane resin obtained in each synthesis example and comparative synthesis example, a composition with the blending ratio shown below was placed in a ball mill, dispersed for 48 hours, and then injected. 5 parts of Coronate 2030 (manufactured by Nippon Polyurethane), a cyanate compound, was added as a hardening agent, and the mixture was further mixed for 1 hour to obtain a magnetic material. This was placed on a 12μ thick polyethylene terephthalate film-1-20 so that the thickness after drying would be 5μ.
The coating was carried out while applying a magnetic field of 0.00 glass. After being left at 50°C for 20 minutes, it was slit into 172-inch pieces to obtain a magnetic tape.

Polyurethane resin solution 100 parts (30% solids, MEK/Tolton = 1/1 solution) Cobalt-coated γ-FezO* 120 parts Olive oil
1 part cyclohexanone
50 Saekaku Toluene
100 copies MEK
Table 3 shows the properties of magnetic tapes manufactured using the polyurethane resins obtained in Examples and Comparative Examples in amounts ranging from 50 parts to 1 unit. The binder content M in the magnetic layer is 1/4 of the magnetic powder (weight).

In addition, since it has a polysiloxane chain in its side chain, when it is used as a binder for magnetic particles, even if the base described in [11] is strongly adsorbed to the magnetic particles, the polysiloxane component acts on the if effect, and the obtained magnetic layer has high dispersion, high filling, and high Y.
Despite achieving lubricity, the surface friction resistance is improved, and a magnetic recording medium with extremely excellent wear resistance and running stability can be provided.

Claims (1)

[Claims] (1) A magnetic recording medium having a magnetic layer containing magnetic powder and a binder, wherein the binder contains a polyurethane resin having a polysiloxane chain in a side chain.