JPS6183272A - Binder for magnetic recording material - Google Patents

Abstract

PURPOSE:The titled binder comprising a specified vinyl chloride-base copolymer contg. a functional monomer unit as a component. CONSTITUTION:A copolymer constituted of about 1-30wt% unit of a hydroxyl group-contg. vinyl monomer such as 2-hydroxyethyl (meth)acrylate, about 0.05-5wt% unit of a sulfo group-contg. vinyl monomer such as 2-acrylamido-2- methylpropnesulfonic acid and the balance of a vinyl chloride monomer unit. About 0.3-30pts.wt. isocyanate compd. may be compounded together for 100pts. wt. said copolymer. About 10-100pts.wt. said copolymer (compsn.) per 100pts.wt. magnetic material powder is added and mixed as a binder, which makes it possible to form a magnetic layer excellent in wearing properties, heat resistance and magnetic powder-dispersing properties.

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 materials used in magnetic recording tapes, magnetic disks, etc. are usually made by coating a substrate with a magnetic paint containing magnetic powder and a binder that binds the powder to a substrate such as polyester.
It is obtained by orientation and drying, and is required to have excellent electrical properties and durability such as resistance to contact with the aX head. Therefore, binders for magnetic recording media are particularly required to have excellent dispersibility of magnetic powder in magnetic coatings, and as a result, to impart a high squareness ratio to magnetic recording media. It is required to be able to form an excellent magnetic layer.

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

(c) Problems to be solved by the invention However, as the density of magnetic recording media has increased recently, magnetic powder has tended 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 state of binders for magnetic recording media, the present invention provides a magnetic layer that has excellent dispersibility of magnetic powder when made into a magnetic coating material, and has excellent abrasion resistance and heat resistance by adding an isocyanate compound if necessary. An object of the present invention is to provide a binder for a magnetic recording body that can form a magnetic recording material.

) Means for solving the problem The inventor'I! We researched a binder for magnetic recording media made of a copolymer of vinyl hydroxyl group-containing vinyl #4i-mer and vinyl chloride, and found that when a sulfo group-containing monomer was used as a component of the copolymer, magnetic powder The present invention was completed by discovering that the dispersibility was greatly improved.

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 sulfo group-containing vinyl monomer as constituent units, and if necessary, an isocyanate compound is contained. The present invention is characterized by a binder for magnetic recording media.

Vinyl chloride in the vinyl chloride copolymer of the present invention, together with other constituents at position 91, imparts appropriate hardness and flexibility to the magnetic layer, and if too little, the abrasion resistance of the magnetic recording medium will be insufficient. If the amount is too large, the solvent solubility tends to decrease, so the content in the copolymer is preferably t/iao ~
It is assumed to be 95% by weight.

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, and acrylic acid group- or methacrylic acid-based amides. Specific examples of the former include 2-hydroxyethyl (meth)acrylate (this represents both 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; the same applies hereinafter), 2-hydroxypropyl (meth)acrylate, -Chloro-2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate CM2= CR-COO+CHICH, 0-3-nH(
n is an integer from 2 to 9, R#'i hydrogen or methyl group), polypropylene glycol mono(meth) represented by the following formula
acrylate (an integer of 6, R is hydrogen or a methyl group), (meth)acrylic esters such as 2-hydroxyethyl-2'-acryloyloxyphthalate,
A specific example of the latter is N-methylol (meth)acrylamide.

These are used alone or in appropriate combinations as constituent units of copolymers, especially 2-hydroxyethyl (meth)
Acrylate, 2-hydroxypropyl (meth)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 solvent solubility of the copolymer, a decrease in surface smoothness of the magnetic recording medium, and a decrease in mixing resistance are likely to occur.
On the other hand, if the amount is too small, the dispersibility of the magnetic powder tends to decrease, and phletane bonds are not sufficiently formed due to the reaction with the isocyanate compound that is optionally contained.6 This may result in weakening of the coating film strength or blocking. During the above copolymerization, preferably 1 to 30
The content is preferably V12 to 20% by weight.

The sulfo group-containing vinyl monomer in the present invention refers to a vinyl monomer having a sulfo group in the molecule, specifically 2
-Acrylamide-2-methylpropanesulfonic acid, acrylsulfonic acid, methallylsulfonic acid, vinylsulfonic acid, styrenesulfonic acid, etc. are mentioned as suitable examples, and 2-acrylamide F- 2
-/flupronosulfonic acid is preferred.

Moreover, these may have hydrogen in the sulfo group substituted with sodium, caritum, or the like.

The sulfo group-containing vinyl monomer greatly contributes to improving the dispersibility of magnetic powder, but if the amount is too large, the solvent solubility of the copolymer may decrease and a transparent solution may not be obtained. If the amount is too low, the dispersibility of the magnetic powder tends to be poor. Therefore, α is preferably incorporated in the copolymer in an amount of 5 to 5% by weight, and more preferably Ql to 3% by weight.

The binder of the present invention may further contain ethylene, propylene, vinyl acetate, etc. as a constituent unit of the vinyl chloride copolymer, if necessary, and if these homopolymers or copolymers are chlorinated. It may also be used together with a vinyl 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, suspension polymerization, and emulsion polymerization. In the case of precipitation polymerization, methanol 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 a magnetic paint with an average degree of polymerization of less than 150 is applied to a substrate as a magnetic paint, the coated film surface will be weak, making it less practical.If the average degree of polymerization exceeds 600, the viscosity of the paint will increase, making it difficult to apply the solution. This is because the workability 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,
Examples include toridane diisocyanate, hexamethylene diisocyanate, metaxylylene diisocyanate *-), 7i, and a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate. -Product name [Coronet] LJ
It is commercially available as.

If the amount of the isocyanate compound used is too large, the crosslinking density will be high and the final coating film will be hard and brittle, and if it is too small, the desired effect will not be obtained. In contrast, it is usually t-j (13 to 30 jushabu).

To prepare a magnetic paint using the binder of the present invention, for example, Co-
A magnetic powder material such as γ-iron acetate is added together with additives such as a surfactant, kneaded and dispersed, and an isocyanate compound is mixed in as necessary, such as when particularly increasing the corrosion resistance of the magnetic layer. This is how we obtain magnetic paint.

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. Incidentally, as a solvent used when dissolving the above copolymer to prepare the binder of the present invention, one or a mixture of two or more of the following is generally used: toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like. Regarding the magnetic material powder 100, the above copolymer usually has the following properties:
lO~100ffi parts are used, and the magnetic paint is
Usually, it is prepared to have 5 to 3 o polymers of 196 of the above copolymer.

=10- (E) Effects of the Invention The binder for a magnetic recording medium of the present invention has the above-mentioned structure, and in particular contains a hydroxyl group-containing vinyl monomer and a vinyl chloride copolymer as the main resin component. Since the sulfo group-containing vinyl monomer is contained as a structural unit, the resulting magnetic paint has excellent dispersibility of magnetic powder, and a magnetic layer with a high squareness ratio is formed. Since it contains, 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 the crosslinking reaction between the copolymer and the isocyanate compound, resulting in excellent wear resistance and heat resistance. forming a magnetic layer.

(F) Example The zero-shot 8A will be explained below with reference to an example. 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: Magnetic coating with isocyanate compound added as required. Dry thickness is 6μ on a total 2.5μ thick polyester film.
A magnetic recording medium is prepared by coating, orienting, and drying so that
Squareness ratio was measured.

Heat-adhesive magnetic recording material is heated at a temperature of 120°C for 15 minutes to see if it adheres when the magnetic layers are stacked on top of each other. No adhesion (no blocking occurs) on the front side. , casing, x indicates to be glued.

Gel fraction A vinyl chloride copolymer film containing no magnetic powder was heated to toluene-methyl isobutyl ketone (weight ratio 1) at 50°C.
:l) It is the value (wt%) 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 Internal volume 201 with initial charge agitator! 8000y of methanol (reagent grade) and 20f5 of α-cumyl peroxyneodecanoate as a polymerization initiator were placed in a stainless steel autoclave.
After charging, it was evacuated using an aspirator for 5 minutes to remove remaining air.

Next, 2600 p of vinyl chloride was charged.

After removing the air from a stainless steel container (referred to as addition container) containing 3 g of post-addition preparation, 2-hydroxypropyl acrylate 259f, 2-acrylamide-2-methylpronosulfonic acid (manufactured by Nitto Kagaku Co., Ltd., AMPS) was added. 15
5,002 F of methanol was suctioned, and then 1.045 F of vinyl chloride 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 nozzle of the polymerization reactor using a flexible tube from the valve at the bottom.

Polymerization reaction operation The rotational speed of the stirrer of the polymerization reactor was set to 38 Orpm, 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 to keep the internal temperature at 43°C.

On the other hand, when the temperature reached 43°C, add the monomer mixed solution sap from the addition container, and then, depending on the progress of the polymerization reaction, add 46 y x 4 times every 5 minutes, 31 p x 8 times every 10 minutes, and increase the concentration to 5 min. It was added in 27f×49 portions.

Ten minutes after the last addition was completed, the polymerization reaction was stopped by cooling to 25°C. The internal pressure of the polymerization reactor is l OK at the start of the reaction.
? / x”G, and at the end of the reaction it was L8/cJiG.

After cooling, unreacted vinyl chloride was vented, nitrogen gas was passed through to thoroughly remove the vinyl chloride, and the methanol slurry of the copolymer was extracted from the polymerization reactor, filtered, and vacuum dried at 50°C for 24 hours. #! 1370y of white powdery copolymer A was obtained.

The degree of polymerization of this resin is 350, and the composition is 87.1% vinyl chloride.
, 2-hydroxypropyl acrylate] 2.0%, 2
-acrylamido-2-methylpropanesulfonic acid a9
%Met.

A 15% copolymer solution was prepared by dissolving copolymer A in a toluene-methyl isobutyl ketone (weight ratio 1:l) mixture, and then 24 times the amount (by weight) of the copolymer was added to this solution. Co
-7- After adding iron oxide and simultaneously mixing and dispersing it in a paint conditioner (manufactured by Red Devil) to make a magnetic paint, a magnetic recording medium was prepared and the squareness ratio was measured.
A high value of 84 was obtained.

Example 2 Polymerization was carried out according to Example 1 using the same equipment and the same monomers as those used in Example 1. However, polymerization was carried out while varying the amount of each monomer charged.

First, a powdered copolymer B was obtained, the composition of the copolymer was analyzed, and a magnetic recording medium was prepared in the same manner as in Example 1 and the squareness ratio was measured. J! i; 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. was also a high value exceeding αδ.

Comparative Example 1 Vinyl chloride produced in the same manner as Resin A of Example 1/
Copolymer of 2-hydroxypropyl acrylate (degree of polymerization: 280.2 - containing 19.0% by weight of HPA) aX and vinyl/vinyl acetate/vinyl alcohol copolymer (composition ratio in this order: 91/3/6) b A magnetic recording medium was prepared according to the same method as in Example 1, and the squareness ratio was measured to be α78 and 0.76, respectively.

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 give a concentration of 15%. The solution was adjusted to

Add to this solution 2.4 times the amount (weight) of the copolymer C〇-T-
After adding iron oxide and mixing and dispersing it in a ball mill for 20 hours, Q65 parts of an isocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industries Co., Ltd.) was added and stirred to make a magnetic paint, and this paint was applied onto a polyester film, oriented and
After drying, a magnetic recording material in which the crosslinking reaction had sufficiently progressed was obtained.

The squareness ratio and heat adhesion of this magnetic recording body were as shown in Table 2. Further, the gel content wI, which indicates the crosslinking reactivity between each copolymer and isocyanate, was as shown in Table 2.

Comparative Example 2 Magnetic recording bodies were prepared using copolymers a and b used in Comparative Example 1 in the same manner as in Example 2, and their heat adhesion was measured. Blocking occurred in both.

Comparative Example 3 Copolymer c having the composition shown in Table 3 in the same manner as Example 2,
d and e were obtained, a magnetic paint and a magnetic stirrup body were prepared in the same manner as in Example 3, and the squareness ratio and heat adhesion were measured to be 1.7. In addition, the gel fraction, which indicates the crosslinking reactivity between the copolymer and isocyanate, was measured. These results are shown in Table 3.

Claims (1)

[Claims] 1. The main resin component is a vinyl chloride copolymer having a hydroxyl group-containing vinyl monomer and a sulfo group-containing vinyl monomer as constituent units, and an isocyanate compound is contained as necessary. 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. Item 1 or 2, wherein the content of the sulfo group-containing vinyl monomer in the vinyl chloride copolymer is 0.05 to 5% by weight.
A binder for a magnetic recording medium as described in 1. 4. The average degree of polymerization of the vinyl chloride copolymer is 150 to 60
0. The binder for a magnetic recording medium according to any one of the first to third items. 5. The content of vinyl chloride in the vinyl chloride copolymer is 60 to 95% by weight, the content of hydroxyl group-containing vinyl monomer is 1 to 30% by weight, and the content of sulfo group-containing vinyl monomer is 0. 5. The binder for a magnetic recording medium according to claim 1 or 4, wherein the binder is 05 to 5% by weight. 6. Sulfo group-containing vinyl monomer is 2-acrylamide-
The binder for a magnetic recording medium according to any one of items 1 to 5, which is 2-methylpropanesulfonic acid.