JPS61243933A - 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 phosphoric acid group-contg. vinyl monomer as constituting units at wt% of a limited range as an essential resin component. CONSTITUTION:Vinyl chloride is incorporated at 60-95wt% the hydroxyl group- contg. vinyl monomer at 1-30t% and the phosphoric acid group contg. vinyl monomer at 0.05-8wt% respectively into the vinyl chloride copolymer. The hydroxyl group contg. vinyl monomer and the phosphoric acid group contg. vinyl monomer are particularly 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 therefore a magnetic layer having a high squareness ratio is formed. Since the vinyl chloride is incorporated into the copolymer, the adequate hard ness and flexibility are obtd. by the same coupled with the other components. The wear resistance and heat resistance are improved if the binder contains an isocyanate compd. The degree of polymn. of the copolymer is preferably about 150-600 in terms of the strength of the binder and the magnetic paint.

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 silver drawing tapes, magnetic disks, etc. are usually made by coating a substrate with a magnetic paint containing magnetic powder and a binder that adheres 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 sliding contact with a magnetic 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.

American-based vinyl chloride-vinyl acetate-vinyl alcohol polymers are used as having relatively good properties, and when it is particularly necessary to improve the wear resistance of the magnetic layer, the above polymers and isocyanate compounds are included. A binder for magnetic recording media was used.

(c) Problems to be solved by the invention However, recently, with the increase in the density of magnetic recording media, there is a tendency for magnetic powder to become finer particles2.
Therefore, there has been a demand for the development of a binder with even better separation properties.

In view of the current state of binders for magnetic recording media, the present invention has been developed to provide excellent dispersibility of magnetic powder when made into a magnetic coating material, and to provide excellent wear resistance and heat resistance by adding an isocyanate compound as necessary. A binder for magnetic recording material that can form a magnetic layer is
The purpose is to provide the following.

2) Methods to Solve the Problem #I The authors researched a binder for magnetic recording media consisting of a copolymer of a hydroxyl group-containing vinyl monolayer and vinyl chloride, and further developed K IJ phosphoric acid. The present invention was completed based on the discovery that when used as a component of a group-containing vinyl monomer copolymer, the dispersibility of magnetic powder is greatly improved.

That is, the gist of the present invention is that a vinyl chloride copolymer having a hydroxyl group-containing vinyl monomer and a phosphoric acid group-containing vinyl monomer as constituent units is used as the main resin component, and an isocyanate compound is optionally 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 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 60 to 95% by weight.

The hydroxyl group-containing vinyl monomer used as a structural unit of the above copolymer includes those having a structural formula of a reaction product of acrylic acid or methacrylic acid and a polyhydric alcohol, and those having a structural formula of a monomer structure, and those having an acrylic acid group or methacrylic acid group. 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, 3-chloro-2-hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate represented by the following formula CH2= CRCoo +CH2CH20+ nH(n
is 2 to 9 IE&, R is hydrogen or methyl group), polypropylene glycol mono(meth)acrylate 0 CH3 represented by the following formula (n is an integer of 2 to 6, R is hydrogen or methyl M), 2-
Examples include (meth)acrylic acid esters such as hydroxyethyl-2'-acryloyloxy heptalate;
A specific example of the latter is #iN-methylol (meth)acrylamide. These may be used alone or in appropriate combinations as constituent units of the copolymer, and 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate are particularly preferably used.

If the amount of monomers containing these hydroxyl groups is too large, problems such as a decrease in the solvent solubility of the copolymer, a decrease in the surface smoothness of the magnetic recording medium, and a decrease in contamination resistance may occur; If it is too much, the dispersibility of the magnetic powder tends to decrease.
In addition, since the phletane bond is not sufficiently formed by the reaction with the isocyanate compound contained if necessary, the strength of the coating film tends to be weakened and blocking tends to occur. weight%
, more preferably 8 to 20% by weight.

The phosphoric acid group-containing vinyl monomer in the present invention refers to a vinyl polymerizable monomer having a phosphoric acid group in the molecule. Specific examples include acid phosphoxyethyl (meth)acrylate, acid phosphoxypropyl (meth) ) acrylate,
3-Chloro-2-acid phosphoxypropyl (meth)
Acrylates are mentioned as suitable examples.

The phosphoric acid group-containing vinyl monomer greatly contributes to improving the dispersibility of the magnetic powder, but if the amount is too large, the solvent solubility of the copolymer decreases, making it impossible to obtain a transparent solution. When the water resistance deteriorates, side reactions other than the crosslinking reaction with the isocyanate compound contained may occur, so crosslinking effects such as improving abrasion resistance may not be obtained, or the pot life of the magnetic paint may be shortened. This causes the inconvenience of being shortened.

If the amount is too small, the dispersibility of the magnetic powder tends to deteriorate, so it is preferably contained in the copolymer in an amount of 0.05 to 8% by weight, more preferably 11 to 5% 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 the homopolymer or copolymer of these It may also 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, the solubility of the phosphoric acid group-containing vinyl monomer is good, and the resulting polymer is insoluble in methanol or n-hexadiene.

is used as a suitable solvent, but methanol is preferred from the viewpoint of solvent solubility of the produced copolymer and economic efficiency. Incidentally, the copolymer can be obtained as a fine powder regardless of the solvent type. 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 paint, making it less practical, while if it exceeds 600, the paint viscosity will be high, making it difficult to apply a solution. This is because the workability when doing so is poor.

Isocyanate compounds to be mixed 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 1 mole of trinothylolpropane and 3 tolylene diisocyanate
Examples include reactants with mole, such as Nippon Zerikurekune 1! ■It is commercially available as the product name "Coronate LJ.

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 113 to 30 parts by weight per 100 parts by weight of the above copolymer. To prepare a magnetic paint using the binder of the present invention, for example, a magnetic powder material such as Cor-iron oxide is added to a solution of the above copolymer dissolved in a mixed solvent of methyl imptylgetone heptoluene as a surfactant. In addition to additives such as
A magnetic coating material is obtained by mixing an isocyanate compound as necessary, such as by mixing and dispersing the mixture and 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 f (in the present invention f) are not limited at all. Generally, one or a mixture of two or more of toluene, methyl ethyl getone, methyl imptyl getone, cyclohexanone, etc. is used as the copolymer.

Parts by weight are used, and the magnetic paint is usually made to have 5 to 30% 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, a vinyl monomer containing a hydrophilic group is contained in the vinyl chloride copolymer, which is the main component. and a phosphoric acid group-containing vinyl monomer as structural units, the obtained magnetic paint has excellent dispersibility of magnetic powder, and therefore a magnetic layer with a high squareness ratio is formed. Since it contains vinyl chloride, in combination with other components, a magnetic layer with 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 participate in the crosslinking reaction between the copolymer and the isocyanate compound, resulting in improved wear resistance and heat resistance. Forms an excellent magnetic layer.

(f) 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.

The winter physical properties were measured using the following method.

Squareness Ratio Prepare a magnetic recording medium by applying a magnetic paint to which an isocyanate compound is added, if necessary, on a λ5μ thick polyester film to a dry thickness of 6μ, orienting it, drying it, and then measuring the squareness ratio.

The reflectance of the magnetic coating film subjected to the squareness measurement above was measured using a gloss meter at an incident angle of 5 otL.

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 if they would adhere. ), and × indicates adhesion.

Gel fraction A vinyl chloride copolymer film containing no magnetic powder was heated to toluene-methylisobutyltetone (weight ratio 1) at 50°C.
: 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. It is what it is.

Example 1 Internal volume 201 with initial charge agitator! Methanol (reagent-grade) 81002 and α-cumyl peroxyneodecanoate 25f as a polymerization initiator were charged into a stainless steel autoclave, and the autoclave was evacuated for 5 minutes using an aspirator to remove remaining air.

Next, 2600 y of vinyl chloride was charged.

After removing the air from the suspendable stainless steel container (referred to as addition container) of post-addition preparation 31, 259y of 2-hydroxypropyl acrylate dissolved in 500y of methanol and acid phosphoxyethyl methacrylate 152 were added. The mixed solution was sucked, and then vinyl chloride 10451 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 Orpm, and the internal temperature was raised to 43° C. by passing hot water through the diode.

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, 502 of the monomer mixed solution was added from the addition container, and then depending on the progress of the polymerization reaction, 46fX4 times every 5 minutes, 31PXS times every 10 minutes, and 27yX49 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 KIO at the start of the reaction.
Kf/cdG, KHL 8 Kf/cjG at the end of the reaction.

After cooling, unreacted vinyl chloride was exhausted, nitrogen gas was passed through the reactor to sufficiently remove the vinyl chloride, and the methanol slurry of the copolymer was extracted from the autoclave.
After filtration, vacuum drying was performed at 50°C for 24 hours to obtain 1300y of white powdery copolymer A.

The polymerization degree of the resin is 330, and the composition is vinyl chloride 86.5%.
, 2-hydroxypropyl acrylate 119%, acid phosphoxyethyl methacrylate) a 6%.

In addition, the acid phosphoxyethyl methacrylate content was determined by a neutralization titration method using KO)I/MeOH.

A 15% copolymer solution was prepared by dissolving copolymer A in a toluene-methyl isoptyl getoxy (weight ratio 1:1) mixture, and then to this solution, 20 parts by weight of copolymer solids 80 parts by weight of Co-7-iron oxide and 8 times the amount of magnetic powder 1
/8 inch diameter stainless steel pole was added and mixed for 6 hours in a paint conditioner (manufactured by Red Devil) to form a magnetic paint. A magnetic recording medium was prepared and the squareness ratio was measured to be 0.83. A high value was obtained. Also, the gloss level was $197%.

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 amounts of each monomer, methanol, and initiator were varied according to the weight ratios shown in Table 1, and the polymerization was carried out. First, a powdered copolymer B was obtained, the composition of the copolymer was analyzed, and a 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 glossiness exceeded that of O and SO with a high value of 90% or more.

Margin 1 Table Comparative Example 1 Copolymer of hinyl chloride/2-hydroxypropyl acrylate produced in the same manner as Resin A of Example 1 (degree of polymerization 350.2-HP Al: &0% by weight Containing) AS and vinyl chloride/vinyl acetate/vinyl alcohol copolymer (composition ratio in this order: 91/3/6) b For K, a magnetic recording medium was prepared according to the same method as in Example 1, and the squareness ratio was measured. The results were +175 and (L76), respectively. Also, the gloss levels were low at 52% and 54%, 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 a concentration of 15%. The solution was adjusted to

To this hot solution, 80 parts by weight of copolymer solids was added.
Add Co-γ-iron oxide in the weight part and 1/8 inch diameter stainless steel ball in 8 times the amount of magnetic powder and paint conditioner J.
After mixing for 6 hours with
65 parts of the mixture was added and stirred to obtain a magnetic paint, and this paint was applied onto 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 of the magnetic recording bodies were as shown in Table 2. In addition, the gel fraction i! indicates the crosslinking reactivity between each copolymer and isocyanate! It was as shown in Table 2.

Comparative Example 2 A magnetic recording medium was prepared using the copolymer used in Comparative Example 1 in the same manner as in Example 1, and when the heat adhesion was measured, blocking occurred.

Claims (1)

[Claims] 1. The main resin component is a vinyl chloride copolymer having a hydroxyl group-containing vinyl monomer and a phosphoric acid group-containing vinyl monomer as constituent units, and optionally contains an isocyanate compound. 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 vinyl monomer containing a phosphate group has a content of 0.05 to 8% by weight in the vinyl chloride copolymer. 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. Containing vinyl chloride in vinyl chloride copolymer 1
is 60 to 95% by weight, the content of the hydroxyl group-containing vinyl monomer is 1 to 30% by weight, and the content of the phosphoric acid group-containing vinyl monomer is 0.05 to 8% by weight. Or the binder for magnetic recording bodies according to item 4. 6. The binder for a magnetic recording medium according to any one of items 1 to 5, wherein the phosphoric acid group-containing vinyl monomer is acid phosphoxyethyl methacrylate.