JPH01158619A - Binder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent wear resistance by using a vinyl chloride copolymer having a hydroxyl group-contg. vinyl monomer and a vinyl monomer constituted by bonding a bulky cyclic group indirectly to a vinyl group as a constituting unit as the essential component of the title binder. CONSTITUTION:The vinyl chloride in the vinyl chloride copolymer imparts adequate hardness and flexibility together with the other constituting units to a magnetic layer. The wear resistance is too low if the ratio thereof is excessively low and the solubility is low if the ratio is excessively high; the more preferable ratio is 60-95wt.%. The amt. of the hydroxyl group-contg. vinyl monomer to be used results in the degraded solubility if said amt. is too large and results in the degraded dispersibility of magnetic layer if said amt. is too small; said monomer is preferably incorporated at 8-20wt.% in the polymer. The vinyl monomer which is formed by bonding the bulky cyclic group indirectly to the vinyl group and is used as the constituting unit of the vinyl chloride copolymer refers to the vinyl monomer formed by bonding the bulky cyclic group to the carbon atom constituting the 'vinyl group' and acrylic acid or methacrylic acid is preferably used. An isocyanate compd. such as tolylene diisocyanate is used at 0.3-30wt.% if there is a need for particularly enhancing the wear resistance and heat resistance of the magnetic layer.

Description

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

(b) Conventional technology Magnetic recording materials used in magnetic recording tapes, magnetic disks, etc. usually contain magnetic paint containing magnetic powder and a binder and solvent to bind the powder to a substrate such as polyester. It is obtained by coating, orienting, and drying on a substrate, and is required to have excellent electrical properties and durability with a magnetic head. Therefore, binders for magnetic recording media are particularly required to have excellent dispersibility of the magnetic powder in the magnetic layer P+, and as a result, to impart a high squareness ratio to the magnetic recording media, as well as abrasion resistance and heat resistance. It is required to be able to form a magnetic layer with excellent properties.

Conventionally, vinyl chloride-vinyl acetate-vinyl alcohol polymers have been used as those with relatively good properties, and when it is necessary to particularly improve the abrasion resistance of the magnetic layer, the above polymer and an isocyanate compound are used. A binder for a magnetic recording medium containing the above was used.

However, in recent years, as the crystal density of magnetic recording media has increased, magnetic powder has tended to become finer and more powdery, so there has been a demand for the development of a binder with even better dispersibility.

(c) Problems to be Solved by the Invention In view of the current state of binders for magnetic recording media, the present invention provides excellent dispersibility of magnetic powder when made into a magnetic paint, and 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 layer with excellent wear resistance and heat resistance.

(d) Means for solving the problem The inventors
A binder for magnetic recording materials whose main resin component is a vinyl chloride copolymer having as constituent units a vinyl monomer containing a hydroxyl group and a vinyl monomer in which a bulky cyclic group is indirectly bonded to the vinyl group. The present invention was completed by discovering that the adhesive has excellent dispersibility of magnetic powder.

That is, the gist of the present invention is that the main resin component is a vinyl chloride copolymer having as constituent units a vinyl monomer containing a hydroxyl group and a vinyl monomer in which a bulky cyclic group is indirectly bonded to the vinyl group. The present invention relates to a binder for a magnetic recording medium, which contains an incyanate compound as required.

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 #4 abrasion resistance of the magnetic recording material will be insufficient. If the amount is too large, the solvent solubility tends to decrease, so the content in the copolymer is preferably 60 to 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-based or methacrylic acid-based amides. A specific example of the former is 2-hydroxyethyl (meth)acrylate (which is 2-hydroxyethyl acrylate and 2-hydroxyethyl meth) k/ -1
− Represents both. (same below), 2-hydroxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (
meth)acrylate, polyethylene glycol mono(meth)acrylate CH2-CRCOO+ CH9CH20+nH (n ke 2
(an integer from 9 to 9, R is hydrogen or methyl group), polypropylene glycol mono(meth)acrylate OCR represented by the following formula.

(n is an integer from 2 to 6, R is hydrogen or methyl group), 2-
Examples include (meth)acrylic acid esters such as hydroxyethyl-2'-acryloyloxy heptalate;
A specific example of the latter is 1-tN-methylol (meth)acrylamide. Further, depending on the case, it may be a vinyl alcohol component obtained by polymerizing vinyl acetate and then converting it into a resin.

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 moisture 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 urethane bonds are not sufficiently formed by reaction with the isocyanate compound that is optionally included, resulting in a weakened coating film strength and a tendency to cause blocking. Therefore, the above-mentioned components (1) are preferably contained in an amount of 1 to 30%, more preferably 8 to 20%.

A vinyl monomer in which a bulky cyclic group is indirectly bonded to a vinyl group, which is used as a constituent unit of a vinyl chloride copolymer, is a vinyl monomer in which a bulky cyclic group is indirectly bonded to a vinyl group. means a vinyl monomer to which is indirectly bonded (that is, bonded via another carbon or oxygen atom or atomic group, etc.), preferably an ester of acrylic acid or methacrylic acid is used. It will be done.

In addition, the above-mentioned "vinyl group" may have hydrogen substituted with other atoms or atomic groups as appropriate.

The bulky cyclic group is preferably composed of a five-membered ring to a twelve-membered ring, regardless of whether it is a monocyclic or polycyclic cyclic group, and examples include alicyclic, aromatic, and heterocyclic groups. Among the alicyclic groups, bornane group and related compounds (derivatives)
A cyclic group having is often used.

More specifically, an example of a vinyl monomer to which the alicyclic group is bonded is inbornyl (meth)acrylate (organizational name, 1°7.7-drimethyl-bicyclo(
:2,2.1:]]hepter-2-yl meth)acrylate).

Examples include cyclohexyl (meth)azilylate, 4-t-butylcyclohexyl (meth)azilylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, 1-methoxyclododecajenyl (meth)acrylate, etc. Examples of vinyl monomers having an aromatic cyclic group bonded to them include benzyl (meth)acrylate, 2-phenoxyethyl (
Examples of the vinyl monomer to which a heterocyclic cyclic group is bonded include tetrahydrofurfuryl (meth)acrylate.

Among these, isotocyl(meth)acrylate is particularly preferred as an example of a vinyl monomer having a cyclic group bonded thereto.

Such a cyclic group-containing vinyl monomer contributes to improving the dispersibility of the magnetic powder, but if the content in the vinyl chloride copolymer is too small, the desired effect will not be achieved, or if the content exceeds a certain level. Since the effect tends to be saturated, usually 1~
It is said to be about 20% by weight.

The binder of the present invention has a vinyl chloride co-assembly having the hydroxyl group-containing vinyl monomer and the bulky cyclic group-containing vinyl monomer as essential constituent units as a main resin component, The vinyl chloride copolymer further contains acid groups such as carboxyl groups, phosphoric acid groups, and sulfo groups (and salts thereof),
Preferably, the constituent unit is a vinyl monomer containing at least one polar group selected from amino groups and ammonium bases.

The carboxyl group-containing vinyl monomer means a vinyl polymerizable monomer having a carboxyl group in the molecule, and specific examples thereof include acrylic acid, methacrylic acid, succinic acid monoacryloyloxyethyl ester, (CH2= CH
-COO(CH2)20CO(CH2), C00H)
1 in the molecule of phthalic acid monoacryloyloxyethyl ester, succinic acid monomethacroyloxyethyl ester, phthalic acid monomethacroyloxyethyl ester, etc.
Preferred examples include those containing one carboxyl group, and those containing a plurality of carboxyl groups in the molecule, such as maleic acid and hexamaric acid. Phosphoric acid group-containing vinyl monomer refers to a vinyl polymerizable monomer that has a phosphoric acid group in its molecule.Specific examples include acid phosphoxyethyl (meth)acrylate and acid phosphoxyethyl (meth)acrylate. , 3-chloro-2-anodophosphoxypropyl (meth)acrylate is mentioned as a suitable example. A vinyl monomer containing a nulpho group is a vinyl monomer having a sulfo group in the molecule, and specific examples include 2-acrylamido-2-methylpropa, sulfonic acid, acrylsulfonic acid, methallylsulfone. Suitable examples include acids, vinylsulfonic acid, styrenesulfonic acid, and the like.

The amino group-containing vinyl monomer in the present invention refers to a vinyl monomer having an amino group in the molecule. Examples include meth)acrylic acid esters, acrylamides such as dimethylacrylamide and dimethylaminopropylacrylamide, and allylamine.

The quaternary ammonium base-containing vinyl monomer in the present invention refers to a vinyl monomer having a quaternary ammonium base in the molecule. Specific examples include 2-hydroxy-3-methacryloyloxypropyl trimethylammonium chloride, methacryloyl Suitable examples include oxyethyltrimethylammonicum chloride and trimethyl-3-methacrylamidoprobyl ammonicum chloride.

If the content of these polar group-containing vinyl monomers is too high, the solvent solubility of the copolymer may decrease, making it impossible to obtain a transparent solution, worsening water resistance, or worsening thermal stability. , side reactions other than the crosslinking reaction with the incyanate compound contained if necessary occur, resulting in inconveniences such as not being able to obtain a crosslinking effect such as improving wear resistance, and shortening the pot life of the magnetic paint. It is contained in the copolymer in an amount of 0 to 10% by weight, and J! KtIT-Masukuke is contained in an amount of 0 to 5% by weight.

The binder of the present invention further includes, if necessary, vinyl ethers such as carboxylic acid vinyl ester dimethyl vinyl ether such as vinyl acetate and vinyl propionate, inftyl vinyl ether, and cetyl vinyl ether; vinylidene chloride;
Vinylidene such as vinylidene fluoride; diethyl maleate,
Unsaturated carboxylic acid alkyl esters such as digtyl maleate, diethyl itaconate, methyl (meth)acrylate, and ethyl (meth)acrylate: Contains olefins such as ethylene and fluoropylene as constituent units of vinyl chloride copolymers. Alternatively, 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, which has good solubility in the quaternary ammonium base-containing vinyl monomer and the acid group-containing vinyl monomer and in which the produced polymer is insoluble, is used as a suitable solvent.

Incidentally, the copolymer is generally obtained as a fine powder. The degree of polymerization of the copolymer is preferably in the range of about 100 to 700 from the viewpoint of the mechanical strength of the binder and the properties of the magnetic coating material. That is, if the average degree of polymerization is less than 100, if it is applied as a magnetic paint to a substrate, the coating surface will be weak, making it less practical, and if it exceeds 700, the viscosity of the paint will be high and a solution must be applied. This is because the workability tends to be poor.

In addition, when it is particularly necessary to enhance the abrasion resistance and heat resistance of the magnetic layer, incyanate compounds that are kneaded with the magnetic powder together with the above copolymer include tridene diisocyanate, diphenylmethane diisocyanate, dianidine diisocyanate, and tridene diisocyanate. , hexamethylene diisocyanate, metaxylylene diisonanate, and a reaction product with 3 moles of trimethylolpropuff 17-tolylene diisocyanate. It is commercially available as Coronate J.

When using an incyanate compound, if it 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. %, usually α3 to 30 parts by weight.

The magnetic layer P)'i-K prepared using the binder of the present invention is:
For example, a magnetic powder material such as Cor-iron oxide is added to the copolymer solution dissolved in a mixed solvent of methyl isobutyl ketone and toluene together with additives such as a surfactant,
A magnetic paint is obtained by kneading and dispersing the mixture, and adding an incyanate compound as necessary, such as when particularly enhancing the abrasion resistance of the magnetic layer.

However, the order of addition, dispersion means, etc. of the copolymer, incyanate 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 lactone, methyl isobutyl ketone xanone, and the like. The above-mentioned copolymer is usually used in an amount of 10 to 100 parts by weight per 100 parts by weight of the magnetic material powder, and the magnetic paint is usually prepared to contain 5 to 30% by weight of the above-mentioned copolymer.

(e) Example 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 performed using the following method.

Magnetic paint to which an isocyanate compound is added as necessary is applied to a 25μ thick polyester film to a dry thickness of 6.A.
A magnetic recording medium was prepared by coating, orienting, and drying so as to have a squareness of t, 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, and calculations were made based on this value. Glossiness indicates the surface smoothness of a coating film and is also a measure of dispersibility.

Heat-adhesive magnetic recording material is heated at 120°C for 15 minutes to see whether the magnetic layers adhere to each other when stacked on top of each other. In the table, O 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: l) at 50°C.
:1) The weight of the film after being immersed in the mixed solvent for a day and night was divided by the weight of the film before immersion (a (wt%)), which determines the reaction efficiency of the crosslinking reaction between the copolymer and the incyanate compound. This is a guideline.

Example 1 After charging 8100 y of methanol (reagent-grade) and 30 y of α-cumyl peroxyneodecanoate as a polymerization initiator into a stainless steel autoclave with an internal volume of 201 mm equipped with an initial charging stirrer, the autoclave was evacuated for 5 minutes using an aspirator. , the remaining air was eliminated.

Next, 2600 y of vinyl chloride was charged.

After removing the air from a stainless steel container (referred to as an addition container) that can be suspended in the post-addition preparation 3j, methanol 500y
The value obtained by immersing a Vc-dissolved 2-hydroxy film in a mixed solvent of toluene-methylisozotylgtone (weight ratio 1:1) at 50°C for one day and night, then dividing the weight of the film by the weight of the film before immersion ( % by weight) and serves as a standard for determining the anti-Ji5 efficiency of the crosslinking reaction between the copolymer and the incyanate compound.

(Left below) Example 1 Methanol (reagent-grade) 81002 and α-cumyl peroxyneodecanoate 30g' as a polymerization initiator were placed in a stainless steel autoclave with an internal volume of 20 tons equipped with an initial charging stirrer.
After charging, the mixture was evacuated using an aspirator for 5 minutes to remove remaining air.

Next, 260CM' of vinyl chloride was charged.

After removing the air from a 3 ton suspendable stainless steel container (referred to as an addition container) for post-addition, add 2-hydroxyglobyl acrylate 2449 dissolved in 500 pl of methanol.
and inbornyl methacrylate 80y1 maleic acid 15
The mixed solution with y is aspirated, and then vinyl chloride 104
52 was press-fitted.

After shaking the container and mixing and dissolving the contents, it was hung on a spring balance, and connected to the addition nozzle of an autoclave using a 7-lexil tube from the bottom valve.

The rotation speed of the stirrer of the polymerization reaction autoclave was set to 38 orpm,
Wet water was passed through the Jahut and the internal temperature was externally heated to 43°C. The polymerization reaction started when the internal temperature reached 43℃, so from now on,
The temperature was adjusted so that the internal temperature was 43°C.

On the other hand, when the temperature reached 43°C, 502 times of the monomer mixture was added from the addition container, and then, depending on the progress of the polymerization reaction, 46yX4 times for every 5, 31PX8 times for every 10+), and every 5 minutes. It was added in 27Px49 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 zO/ctt at the beginning of the anti-ES cycle.
lG, and L 8 Kf/awl G at the end of the reaction.

After cooling, unreacted vinyl chloride was exhausted, nitrogen gas was passed through the reactor to remove the vinyl chloride sufficiently, and then the methanol scree of the copolymer was extracted from the autoclave.
After filtration, vacuum drying was performed at 5°C for 24 hours to obtain 1300y of white powdery copolymer A.

A copolymer solution of 1596 was prepared by dissolving copolymer A in a mixture of toluene and methyl ing thyl ketone (weight ratio 1:1). and 80 parts by weight of C.

-r- Add iron oxide and a 178-inch diameter stainless steel pole that is 8 times the amount of magnetic powder, mix and disperse for 6 hours in a paint container (manufactured by Left Devil Co., Ltd.) to make a magnetic paint, and then apply a magnetic recording medium. The squareness ratio and glossiness were measured.

The results were close to those shown in Table 1.

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, the polymerization was carried out by changing the phase of each monomer, methanol, and IIu initiator. First, a powdered 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 the table. In addition, in the same manner as copolymer B, copolymers C, D% E1F, G, H and
When the magnetic recording materials were obtained and the magnetic recording materials were adjusted, the respective squareness ratios and glossiness were as shown in Table 1.

(Space below) Comparative Example 1 Using the same equipment as used in Example 1 and changing various monomers, a copolymer with the composition ■ shown in the comparative example in Table 1 was produced. and ■ were obtained. A magnetic recording medium was prepared using this resin in the same manner as in Example 1, and the squareness ratio and glossiness were measured, and the results were as shown in Table 2.

Table 2 a': Polyvinyl alcohol component t: Vinyl acetate m: 2-ethylhexyl acrylate Example 3 Copolymer A obtained in Example 1 and copolymer B-K obtained in Example 2. One portion of a mixture of toluene and methyl isobutyl ketone (weight ratio 1:1) was dissolved to prepare a 15% solution.

To this solution, 80 parts by weight of Cor-iron oxide and 1/8-inch diameter stainless steel core, which is 8 times the amount of magnetic powder, were added to 20 parts by weight of the copolymer solid content, and a T-paint conditioner was added. 1
After mixing for 6 hours in a spray bottle, 65 parts of incyanate compound (Coronate, manufactured by Nippon Polyurethane Industries) was added and stirred to make a magnetic paint, and this paint was applied onto a polyester film, oriented, and dried. A magnetic recording material in which the crosslinking reaction was sufficiently advanced was obtained. The squareness ratio, glossiness, and heat adhesion of the magnetic recording bodies were as shown in Table 2.

In addition, the gel fraction indicating the crosslinking reactivity between each copolymer and incyanate was as shown in Table 3. Table 3 Comparative Example 2 Regarding copolymer ■ used in Comparative Example 1, Example A magnetic recording medium was prepared in the same manner as in Example 2, and its heat adhesion was measured, and blocking occurred.

(F) Effects of the Invention The binder for magnetic recording materials of the present invention has the above-mentioned structure. In particular, the main resin component, a vinyl chloride copolymer, contains a hydroxyl group-containing vinyl monomer and a bulk-containing vinyl monomer. Since the vinyl monomer in which a highly cyclic group is indirectly bonded to a vinyl group is contained as a constituent unit, the obtained magnetic paint has excellent number properties of magnetic powder, and therefore has a magnetic layer with a high squareness ratio. Since the copolymer contains vinyl chloride, 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 incyanate compound, the hydroxyl groups introduced into the copolymer contribute to the crosslinking reaction between the copolymer and the incyanate compound, resulting in improved wear resistance and heat resistance. It forms a magnetic layer with excellent properties.

Claims (1)

[Claims] 1. The main resin is a vinyl chloride copolymer having as constituent units a vinyl monomer containing a hydroxyl group and a vinyl monomer in which a bulky cyclic group is indirectly bonded to the vinyl group. 1. A binder for a magnetic recording medium, which contains an isocyanate compound as a component. 2. The binder for a magnetic recording medium according to item 1, wherein the vinyl monomer in which a bulky cyclic group is indirectly bonded to a vinyl group is an ester of acrylic acid or methacrylic acid.