JPS61243934A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the performance of a magnetic layer by using a vinyl chloride copolymer contg. respectively a hydroxyl group-contg. vinyl monomer and carboxyl group-contg. monomer as a constituting unit at wt% of a limited range as an essential resin component. CONSTITUTION:The vinyl chloride copolymer contains respectively 60-95wt% vinyl chloride, 1-30wt% hydroxyl group-contg. vinyl monomer and 0.05-5wt% carboxyl group-contg. monomer. The hydroxyl group-contg. vinyl monomer and carboxyl group-contg. monomer are incorporated as the constituting unit into the vinyl chloride copolymer which is the essential resin component and therefore the resultant magnetic paint is improved in the dispersibility of the magnetic powder and the magnetic layer having a high squarenness ratio is thus formed. Since the vinyl chloride is incorporated into the copolymer, the magnetic layer having the adequate hardness and flexibility is formed by said vinyl chloride coupled with the other components. The magnetic layer having the high wear resistance and heat resistance is formed if the binder contains an isocynate compd.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a binder for magnetic recording materials that provides excellent dispersibility of magnetic powder and provides a magnetic layer with excellent wear resistance and heat resistance.

(b) Conventional technology Magnetic recording tape or magnetic disk#? The magnetic recording material used for this purpose is usually obtained by coating, orienting, and drying a magnetic paint containing magnetic powder and a binder that binds the powder to a substrate such as polyester, and has excellent electrical properties. Additionally, durability such as resistance to sliding contact with the magnetic head is required. Therefore, binders for magnetic recording media are particularly required to have excellent dispersibility of magnetic powder in magnetic paints, and as a result, to impart a high angular expansion ratio to magnetic recording media, as well as abrasion resistance and heat resistance. It is required to form a magnetic layer with excellent properties.

Conventionally, hinyl chloride-hinyl acetate-vinyl alcohol polymers have been used as having relatively good properties, and when it is necessary to particularly improve the abrasion resistance of the magnetic layer, magnetic materials containing the above polymers and isocyanate compounds have been used. A binder for recording bodies was used.

E→ Problems to be solved by the invention However, as the density of magnetic recording media increases, magnetic powder tends to become finer particles, so there is a demand for the development of a binder with even better dispersibility. It had been.

In view of the current status of binders for magnetic recording media, the present invention has been developed to provide a magnetic layer with excellent dispersibility of magnetic powder when made into a magnetic coating material, and with excellent abrasion resistance and heat resistance by adding an isocyanate compound if necessary. The object of the present invention is to provide a binder for a magnetic recording medium that can form a magnetic recording material.

2) Means for Solving the Problems The present inventors have conducted research on a binder for magnetic recording media consisting of a copolymer of a vinyl monomer containing a hydroxyl group and vinyl chloride, and further developed The present invention was completed based on the discovery that the dispersibility of magnetic powder is greatly improved when used as a component of a copolymer.

That is, the gist of the present invention is that the main resin component is a vinyl chloride copolymer having a hydroxyl group-containing vinyl monomer and a carboxyl group-containing monomer as constituent units, and an isocyanate compound is contained as necessary. It consists in a binder for magnetic recording media.

Vinyl chloride in the vinyl chloride copolymer of the present invention, together with other structural units, imparts appropriate hardness and flexibility to the magnetic layer, and if it is too small, the abrasion resistance of the magnetic recording medium may be insufficient. If too much, the solvent solubility tends to decrease, so the content in the copolymer is preferably Fi60-95.
It is said to be Juho%.

Examples of the hydroxyl group-containing vinyl monomer used as a structural unit of the above copolymer include those having a structural formula as a reaction product of acrylic acid or methacrylic acid and a polyhydric alcohol, acrylic acid groups or methacrylic acid-based amides, etc. A specific example of the former is 2-hydroxyethyl (meth)? r acrylate (this represents both 2-hydroxyethyl acrylate and 2-hydroxyethyl meth), 2-hydroxypropyl (meth)
Acrylate, 3-chloro-2-hydroxypropyl (
meth)acrylate, polyethylene glycol mono(meth)acrylate CH2=CR-coo+ctt2cn2o-)-n represented by the following formula.

(n is a regular drink of 2 to 9, Re: hydrogen or methyl group),
Examples include (meth)acrylic acid esters such as polypropylene glycol mono(meth)acrylate (n-2 to 6, 91Elk, Rti hydrogen or methyl group), 2-hydroxyethyl-2'-acryloyloxy 7-talate, etc., represented by the following formula: I can do it,
A specific example of the latter is #-jN-methylol (meth)acrylamide.

These are used alone or in appropriate combinations as constituent units of copolymers, especially 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.
Acrylate and the like are preferably used.

If the amount of these vinyl monomers containing hydroxyl groups is too large, disadvantages such as a decrease in the solvent solubility of the copolymer, a decrease in surface smoothness of the magnetic recording medium, and a decrease in resistance to contamination tend to occur.
-1 If it is a little too much, the dispersibility of the magnetic powder tends to decrease, and the reaction with the necessary isocyanate compound will not form sufficient phletane bonds, and the strength of the coating will become weaker and blocking may occur. Therefore, it is preferably contained in the above copolymerization in an amount of 1 to 30% by weight, more preferably 8 to 20% by weight.

The carboxyl group-containing monomer in the present invention means a vinyl polymerizable monomer having a carboxyl group in the molecule,
Specific examples include molecules such as acrylic acid, methacrylic acid, succinic acid monoacryloyloxyethyl ester, heptatalic acid monoacryloyloxyethyl ester, succinic acid monomethacroyloxyethyl ester, and heptadalic acid monomethacroyloxyethyl ester. Suitable examples include those with one carboxyl group in the VC, and those with multiple carboxyl groups in the molecule such as maleic acid and fumaric acid, but maleic acid is particularly preferred in terms of the dispersibility of the magnetic powder. preferable.

The carboxyl group-containing monomer lamp greatly contributes to improving the dispersibility of magnetic powder, but if this amount is too large, the solvent solubility of the copolymer will decrease and a transparent FJ solution may not be obtained. , water resistance may deteriorate, side reactions other than the crosslinking reaction with the isocyanate compound contained may occur if necessary, so crosslinking effects such as improved wear resistance may not be obtained, and the pot life of the magnetic paint may be shortened. This inconvenience arises. Furthermore, if the amount is too small, the dispersibility of the magnetic powder tends to deteriorate. Therefore, the copolymer preferably contains α05 to 5% by weight, and more preferably 0.1% by weight.
Contains ~3% by weight.

The binder of the present invention may also contain ethylene, propylene, vinyl acetate, etc. as a constituent unit of a vinyl chloride copolymer, or a homopolymer or copolymer of these , may be used together with a vinyl chloride copolymer.

In particular, it is preferable to use ethylene as a constituent unit of the vinyl chloride copolymer from the viewpoint of improving solvent solubility.

The above-mentioned vinyl chloride copolymer can be obtained by known polymerization methods such as precipitation polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.

In the case of precipitation polymerization, methanol, in which the carboxyl group-containing monomer has good solubility and the resulting polymer is insoluble, is used as a suitable solvent, and the copolymer is obtained as a fine powder. The copolymerization degree is preferably in the range of about 150 to 600 from the viewpoint of the mechanical strength of the binder and the properties of the magnetic coating material. In other words, if the average degree of polymerization is less than 150, the coating surface will be weak when applied to a substrate as a magnetic coating, making it less practical. This is because the workability when doing so is poor.

Isocyanate compounds to be kneaded with the magnetic powder together with the above copolymer when particularly enhancing the abrasion resistance and heat resistance of the magnetic layer include (c) tolylene diisocyanate, diphenylmethane diisocyanate, dianisidine diisocyanate,
Tridene diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate, and hydrimethylolpropane 1 mol tolylene diisocyanate 3
For example, the reactant is commercially available from Nippon Polyurethane Industries under the trade name "Coronate".

If the amount of isocyanate compound used is too large, the crosslinking density will increase and the final coating film will become hard and brittle.
If the amount is too small, the desired effect cannot be obtained, so the amount is usually 3 to 30 parts by weight per 100 parts by weight of the copolymer.

A magnetic coating material is prepared using the binder of the present invention. For example, a magnetic powder material such as a solution of the above copolymer KCo-γ-iron oxide dissolved in a mixed solvent of methyl isobutyl ketone and toluene is added with a surfactant, etc. A magnetic coating material is obtained by adding an isocyanate compound together with an agent, kneading and dispersing it, and mixing an isocyanate compound as necessary, such as when particularly increasing the abrasion resistance of the magnetic layer.

However, the order of addition, dispersion means, etc. of the copolymer, isocyanate compound, and magnetic material powder in the present invention are not limited at all.

The solvent used to dissolve the copolymer to form the binder of the present invention is generally one or a mixture of two or more of toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like. The above copolymer is usually 10 to 10 parts by weight per 100 parts by weight of the magnetic material powder.
0 parts by weight is used, and the magnetic paint is usually 5 to 30 parts by weight.
% by weight of the above copolymer.

(E) Effects of the Invention The binder for magnetic recording materials of the present invention has the above-mentioned structure, and in particular contains a hydroxyl group-containing vinyl monomer and a carboxyl group-containing vinyl monomer in the vinyl chloride copolymer which is the main resin component. Since the monomer is contained as a structural unit, the resulting magnetic paint has excellent dispersibility of the magnetic powder, so a magnetic layer with a high squareness ratio is formed, and the copolymer does not contain vinyl chloride. Therefore, in combination with other components, a magnetic layer having appropriate hardness and flexibility is formed.

Furthermore, when the binder of the present invention contains an isocyanate compound, the hydroxyl groups introduced into the copolymer contribute to crosslinking between the copolymer and the isocyanate compound, thereby improving wear resistance, heat resistance, and heat resistance. Forms an excellent magnetic layer.

(f) Examples The present invention will be explained below with reference to Examples. In the following, "parts" and "%" indicate parts by weight and % by weight, respectively.

In addition, measurements of each property were conducted using the following method.

Squareness Ratio A magnetic coating material to which an isocyanate compound was added as necessary was coated on a 25μ thick polyester film to a dry thickness of 6μ, oriented and dried to prepare a magnetic recording medium, and the squareness ratio was measured.

Glossiness The reflectance of the magnetic coating film subjected to the above squareness measurement was measured using a glossmeter at an incident angle of 60 degrees. A gloss meter indicates the surface smoothness of a coating film and at the same time serves as a measure of dispersibility.

The heat-adhesive magnetic recording material was heated at a temperature of 120°C for 15 minutes, and the magnetic layers were stacked on top of each other to see whether they adhered or not. In the table, ○ indicates no adhesion (blocking does not occur). ), and × indicates adhesion.

Gel fraction A vinyl chloride copolymer film containing no magnetic powder was heated to toluene-methyl isobutyl ketone (weight ratio 1) at 50°C.
:1) It is the value (% by weight) obtained by dividing the weight of the film after being immersed in a mixed solvent for one day and night by the weight of the film before immersion,
This serves as a guideline for determining the reaction efficiency of the crosslinking reaction between the copolymer and the isocyanate compound.

Example 1 Into a stainless steel autoclave with an internal volume of 20 mm equipped with an initial charging stirrer, methanol lK reagent-&) 8100F and α-cumyl peroxyneodecanoate 259 as a polymerization initiator were charged, and the mixture was evacuated for 5 minutes using an aspirator. to remove any remaining air.

Next, vinyl chloride 2600F was charged.

Post addition preparation 31! After removing the air from a suspended stainless steel container (referred to as the addition container), methanol 500 PK
Dissolved 2-hydroxyglobil acrylate 2599
A mixed solution of , and maleic acid (reagent grade) 152 was suctioned, and then vinyl chloride 1045F was injected under pressure.

After shaking the container to mix and dissolve the contents, it was hung on a spring balance, and connected to the addition nozzle of an autoclave using a flexible tube from the valve at the bottom.

Polymerization reaction operation The rotation speed of the stirrer of the autoclave was set to 38 rpm, and warm water was passed through the jacket to raise the internal temperature to 43°C.

Since the polymerization reaction started when the internal temperature reached 43°C, the temperature was thereafter adjusted so that the internal temperature reached 43°C.

On the other hand, when the temperature reached 43°C, 509 % of the monomer mixed solution was added from the addition container, and then depending on the progress of the polymerization reaction, 461 F x 4 times every 5 minutes, 319 x 8 times every 10 minutes, and 27 P x 49 every 5 minutes. It was added in portions.

Ten minutes after the last addition was completed, the polymerization reaction was stopped by cooling to 25°C. The internal pressure of the autoclave is 2. at the start of the reaction.
．． At the end of the 0th floor/-G1 reaction, 9/, m G to L8
Met.

After cooling, unreacted vinyl chloride was exhausted, nitrogen gas was passed through the reactor to sufficiently remove the vinyl chloride, and the copolymer slurry was extracted from the autoclave.
After filtration, vacuum drying was performed at 50° C. for 24 hours to obtain 12901 white powdery copolymer A.

The polymerization degree of the resin is 1j320, and the composition is vinyl chloride 86.9.
96.2- and droxyglovir acrylate 115%,
Maleic acid α was 6%.

The maleic acid content tf was determined by a neutralization titration method using KOH/MeOH.

Copolymer A was dissolved in a toluene-methyl isobutyl ketone (weight ratio 1:1) mixture to prepare a 15% copolymer solution, and then added to this solution based on 20 parts by weight of copolymer solids. , 80 parts by weight of Co-γ-iron oxide and 8 times the amount of magnetic powder were processed into a 178-inch diameter stainless steel pole, mixed and dispersed for 6 hours using paint conditioner (manufactured by Red Devil Co., Ltd.) to form a magnetic paint. When a magnetic recording medium was prepared and the squareness ratio was measured, a high value of 82 was obtained. Moreover, the glossiness was 93%.

Example 2 Polymerization was carried out according to Example IK using the same equipment and the same monomers as those used in Example 1.

However, the polymerization was carried out by changing the phase of each monomer, methanol, and initiator as shown in the weight ratio shown in Table 1. The first powder of copolymer B was obtained, the composition of the copolymer was analyzed, and the magnetic recording medium was adjusted in the same manner as in Example 1 to measure the squareness ratio. It was as shown in Table 1.

In addition, in the same manner as copolymer B, copolymers C, D, E, and F having the compositions shown in Table 1 were obtained, and magnetic recording bodies were prepared. The gloss exceeded α80 and the gloss was a high value of 90% or more.

Comparative Example 1 Vinyl chloride 7 produced in the same manner as Resin A of Example 1
2-Hydroxypropyl acrylate copolymer (polymerization degree 350.2-HPA 13.0% by weight content) a, and vinyl chloride/vinyl acetate/vinyl alcohol copolymer (composition ratio Kono+c91/3/6) bK- ) Magnetic recording bodies were prepared according to the same method as in the example, and the squareness ratios were measured to be α75 and α76, respectively. Furthermore, the gloss levels were low at around 52% and 54%.

Example 3 Copolymer A obtained in Example 1 and copolymer B-F obtained in Example 2 were each dissolved in a toluene-methyl isobutyl ketone (weight ratio 1:1) mixture to a concentration of 15%. solution of KH
I made 2 adjustments.

To this solution, 80 parts by weight of Co-γ-iron oxide and 178-inch diameter stainless steel pole, which is 8 times the amount of magnetic powder, were mixed and separated for 6 hours using a processed paint conditioner, based on 20 parts by weight of copolymer solid content. After that, an isocyanate compound (manufactured by Nippon Polyurethane Industries Co., Ltd., Coronat) was added to Q,
65 parts of the mixture was added and stirred to form a magnetic coating, and this coating was spread on a polyester film, oriented, and dried to obtain a magnetic recording medium in which the crosslinking reaction had sufficiently progressed. The squareness ratio, glossiness, and heat adhesion Fi of the magnetic recording medium were as shown in Table 2. The gel fraction #'1vJ2 table shows the crosslinking reactivity between each copolymer and isocyanate.

Comparative Example 2 When the copolymer used in Comparative Example 1 was pressed in the same manner as in Example 1 to create a magnetic recording medium and the heat adhesion was measured, blocking occurred.

Claims (1)

[Scope of Claims] 1. The main resin component is a vinyl chloride copolymer having a hydroxyl group-containing vinyl monomer and a carboxyl group-containing monomer as constituent units, and if necessary, an isocyanate compound is contained. A binder for magnetic recording media characterized by: 2. The binder for a magnetic recording medium according to item 1, wherein the content of the hydroxyl group-containing vinyl monomer in the vinyl chloride copolymer is 1 to 30% by weight. 3. The binder for a magnetic recording medium according to item 1 or 2, wherein the content of the carboxyl group-containing monomer in the vinyl chloride copolymer is 0.05 to 5% by weight. 4. The average degree of polymerization of the vinyl chloride copolymer is 150 to 6
00. The binder for a magnetic recording body according to any one of items 1 to 3, which is 00. 5. The vinyl chloride content in the vinyl chloride copolymer is 60 to 95% by weight, the hydroxyl group-containing vinyl monomer content is 1 to 30% by weight, and the carboxyl group-containing monomer content is The binder for a magnetic recording medium according to item 1 or 4, which contains 0.05 to 5% by weight. 6. The binder for a magnetic recording medium according to any one of items 1 to 5, wherein the carboxyl group-containing monomer is maleic acid.