JPH0676264A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the dispersibility of magnetic powder into a binder and to improve crosslinking efficiency so as to improve magnetic characteristics, electromagnetic conversion characteristics and durability by using a polyurethane resin contg. ternary amine as a binder. CONSTITUTION:This magnetic recording medium consists of a nonmagnetic base 1 and a magnetic layer 2 which is formed thereon and consists essentially of the magnetic powder and the binder. The magnetic layer 2 is formed by coating the base 1 with a magnetic coating material prepd., for example, by dispersing the magnetic powder into the binder and kneading the binder together with an org. solvent selected according to the kind of the binder. The binder is the polyurethane resin contg. the ternary amine at 80 to 250 equiv. per 10<6>g polyurethane resin. A polyisocyanate compd. is incorporated as a crosslinking agent into the magnetic coating material. Further, the glass transition point of the polyurethane resin is >=60 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is formed on a non-magnetic support, and more particularly to the composition of the binder. .

[0002]

2. Description of the Related Art In a so-called coating type magnetic recording medium, a magnetic paint prepared by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant, a cross-linking agent and the like in an organic solvent is supported by a non-magnetic support such as a polyester film. The magnetic layer is formed by applying it on the body.

The above-mentioned binder is arranged to keep the ferromagnetic powder bound in the magnetic layer. The binder has good dispersibility of the magnetic powder in the binder, and Properties such as the ability to form a magnetic layer having good characteristics and electromagnetic conversion characteristics and the ability to form a magnetic layer having good durability and heat resistance are required.

So far, vinyl chloride-vinyl acetate copolymers, vinyl chloride-propionic acid copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, etc. have been used as binders having relatively excellent properties as described above. Of these, vinyl chloride resins, nitrocellulose, polyurethane resins, etc. are often used. In these resins, it is general to use two or more kinds in combination so as to achieve the required physical properties. For example, nitrocellulose, which has high rigidity in order to balance rigidity and flexibility, is used. And a polyurethane resin having a low glass transition point Tg and high flexibility are used in combination.

[0005]

On the other hand, in recent years, there has been an increasing demand for high density recording, and the particle size of the magnetic powder used in the magnetic layer is becoming smaller. However, the above-mentioned binder in which nitrocellulose and a polyurethane resin are combined causes a problem that the dispersibility of the magnetic powder is not good.

Further, a vinyl chloride resin is used in place of nitrocellulose, and the vinyl chloride resin and the glass transition point T are used.
Although a binder in which a polyurethane resin having a low g and a high flexibility is combined has been proposed, although the dispersibility is improved,
There is a problem that the rigidity of the vinyl chloride resin is not sufficient and the durability of the obtained magnetic layer is not good.

Therefore, a binder has been proposed in which a polyurethane resin having a high glass transition point Tg is used in place of the polyurethane resin having a low glass transition point Tg and a polyurethane resin having a high glass transition point and a vinyl chloride resin are combined. The binder has excellent rigidity and flexibility, and can form a magnetic layer having good dispersibility and durability.
The polyurethane resin having a high glass transition point Tg is
It has a glass transition point Tg of 70 ° C. or higher, and has a higher flexibility than a vinyl chloride resin having the same glass transition point Tg due to its structure.

The above polyurethane resin is synthesized by combining a polyol component having an ester bond or a carbonate bond and a glycol with a bifunctional isocyanate to increase the molecular weight. Further, a functional group may be introduced into such a polyurethane resin in an appropriate ratio for the purpose of improving the resin adsorption property to the magnetic powder and the dispersibility of the magnetic powder. 58-41
Examples thereof include metal sulfonate bases shown in No. 565.

At this time, as described above, a crosslinking agent such as polyisocyanate may be added to the magnetic paint to crosslink the magnetic layer to improve the strength of the magnetic layer. In the polyurethane resin having, the glass transition point Tg is higher than the curing temperature, so the degree of freedom in the magnetic layer is remarkably impaired, the reaction with the polyisocyanate as the crosslinking agent is not promoted, and the crosslinking is promoted. No sufficient crosslinking is achieved. When the curing temperature is not less than the glass transition point Tg of the polyurethane resin, the degree of freedom of the polyurethane resin is secured, but the flow of the non-magnetic support such as polyester causes the shape to change, resulting in magnetic recording. The electromagnetic conversion characteristics of the medium deteriorate. Therefore, when a combination of a urethane resin having a high glass transition point Tg and vinyl chloride is used as the binder, it is impossible to impart further durability to the obtained magnetic layer.

Therefore, the present invention provides a binder having good dispersibility of the magnetic powder in the binder and good cross-linking efficiency, good magnetic properties and electromagnetic conversion properties, and good durability magnetic properties. The purpose is to provide a recording medium.

[0011]

In order to achieve the above object, the present invention provides a magnetic recording medium comprising a nonmagnetic support and a magnetic layer formed of a magnetic paint mainly containing magnetic powder and a binder. In the above, the binder is polyurethane resin 10
It is a polyurethane resin containing 80 to 250 equivalents of a tertiary amine per ⁶ g.

In the above magnetic recording medium of the present invention, the magnetic coating material contains a polyisocyanate compound as a cross-linking agent, and the polyurethane resin as a binder has a glass transition point of 60 ° C. or higher. It is characterized by.

As shown in FIG. 1, the magnetic recording medium of the present invention comprises a non-magnetic support 1, a magnetic powder formed on the non-magnetic support 1, and a magnetic layer 2 mainly containing a binder.

In the magnetic layer 2, in addition to the magnetic powder and the binder, a cross-linking agent such as polyisocyanate, and a dispersant or a lubricant which can be used as an additive usually constituting the magnetic layer of the magnetic recording medium, a lubricant. Agents, abrasives, antistatic agents, rust preventives and the like can be added.

In the magnetic layer 2, for example, magnetic powder is dispersed in a binder, and ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons,
It can be formed by coating the non-magnetic support 1 with a magnetic paint prepared by kneading with an organic solvent selected from chlorinated hydrocarbons and the like.

As the magnetic powder forming the magnetic layer of the magnetic recording medium, any magnetic powder that is usually used as the magnetic powder of this type of magnetic recording medium can be used. Examples of such magnetic powder include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, and iron nitride.

The above-mentioned ferromagnetic iron oxide particles have the general formula F
When expressed as eO _x , the value of X is 1.33 ≦ X ≦ 1.50
In the range of, ie, maghemite (γ-Fe ₂
O ₃ , X = 1.50, magnetite (Fe ₃ O ₄ , X
= 1.33), and solid solutions of these (FeO _x , 1.3
3 <X <1.50). Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing the coercive force. Cobalt-containing iron oxide is roughly classified into two types: dove type and adhered type.

The above-mentioned ferromagnetic chromium dioxide is Cr
O, or Ru, Sn, for the purpose of improving coercive force
It is possible to use a material obtained by adding at least one kind of Te, Sb, Fe, Ti, V, Mn and the like to CrO.

As the ferromagnetic alloy powder, Fe alloy powder,
Co alloy powder, Ni alloy powder, and Fe-Co, F
e-Ni, Fe-Co-Ni, Co-Ni, Fe-Co
-Cr-B, Mn-Bi, Mn-Al, Fe-Co-V
And the like, or alloy powders which are compounds of these alloys and other elements (for example, carbon, oxygen, etc.) can be used. Further, for the purpose of improving various characteristics of these ferromagnetic alloy powders, Al, Si, Ti, Cr, M
A metal component such as n, Cu or Zn can be added.

The polyurethane resin used as the binder for forming the magnetic layer is obtained by reacting a polyhydroxy compound with a polyisocyanate. As the polyhydroxy compound, polyester polyol,
Polyol compounds such as polyether polyol and polycarbonate polyol, and glycols such as ethylene glycol, propylene glycol and 1,4-butanediol are used. Further, examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate.

The content of the tertiary amine contained in the polyurethane resin is preferably 80 to 250 equivalents per 10 ⁶ g of the polyurethane resin. When the content of the tertiary amine is less than 80 equivalents, the dispersibility of the magnetic powder in the binder is poor, the magnetic properties and electromagnetic conversion properties of the formed magnetic layer are not good, and the tertiary amine If the content of is more than 250 equivalents, the fluidity of the binder obtained by the interaction of the tertiary amine is reduced, and the dispersibility of the magnetic powder in the binder is reduced. To introduce the tertiary amine into the polyurethane resin, a glycol having a tertiary amine, such as N-methyldiethanolamine, may be added to the above-mentioned glycol in a predetermined amount.

At this time, the polyurethane resin has a glass transition point Tg of 60 ° C. or higher, preferably 70 ° C. or higher. When polyisocyanate is used as the crosslinking agent as described above, when the glass transition point Tg of the polyurethane resin is 60 ° C. or higher, the tertiary amine effectively acts as a catalyst for the crosslinking reaction between the polyisocyanate and the polyurethane resin. However, high-density crosslinking is performed, and a magnetic layer having good durability can be formed. Further, if the glass transition point Tg of the polyurethane resin is less than 60 ° C., the rigidity is not sufficient, and a magnetic layer having good durability cannot be obtained.

The shape of the magnetic recording medium of the present invention is not limited to the above-mentioned one in which a magnetic layer is formed on the non-magnetic support, and if necessary, one surface of the non-magnetic support 11 as shown in FIG. A magnetic layer 12 is formed on the other side and a nonmagnetic powder made of, for example, carbon black and a backcoat layer 13 mainly composed of a binder are provided on the other side, or both sides of a nonmagnetic support 21 as shown in FIG. The magnetic layers 22 and 23 are formed on the magnetic layer.

[0024]

According to the present invention, in a magnetic recording medium comprising a non-magnetic support and a magnetic layer made of a magnetic coating material containing a magnetic powder and a binder as the main component, the binder is contained in an amount of 10 ⁶ g per 10 ⁶ g of polyurethane resin. Since it is a polyurethane resin containing 80 to 250 equivalents of a tertiary amine, the dispersibility of the magnetic powder in the binder is good even if a polyurethane resin having a relatively high glass transition point Tg is used.

Further, in the above magnetic recording medium of the present invention, since the magnetic coating contains a polyisocyanate compound as a crosslinking agent, a crosslinking reaction occurs between the polyisocyanate compound and the polyurethane resin, and the polyurethane resin is used. Since the tertiary amine contained therein acts as a catalyst for the above-mentioned crosslinking reaction, the crosslinking reaction is promoted.

Further, in the above-mentioned magnetic recording medium of the present invention, the glass transition point of the polyurethane resin as a binder is 60 ° C. or higher, so that the durability of the obtained magnetic layer is good and the magnetic properties formed are high. When the coating contains a polyisocyanate compound as a cross-linking agent, the tertiary amine contained in the polyurethane resin effectively acts as a catalyst to accelerate the cross-linking reaction between the polyisocyanate compound and the polyurethane resin. To be done.

[0027]

EXAMPLES Specific examples to which the present invention is applied will be described below. First, a polyester polyol, N-methyldiethanolamine, glycol and diphenylmethane diisocyanate were reacted at a predetermined ratio under conditions to prepare a binder made of a polyester polyurethane resin. Using this binder, a magnetic paint was prepared with the following compounding ratio. Upon preparation, the materials excluding the cross-linking agent were dispersed in a sand mill, and then a polyisocyanate compound was added as a cross-linking agent and mixed.

<Magnetic coating compounding ratio> Metal magnetic powder (specific surface area 50 m ² / g) 100 parts by weight Binder (A to F) 10 parts by weight Vinyl chloride copolymer 10 parts by weight Carbon black 5 parts by weight Alumina 6 parts by weight Parts Butyl stearate 1 part by weight Myristic acid 1 part by weight Methyl ethyl ketone 125 parts by weight Toluene 70 parts by weight Cyclohexanone 50 parts by weight Polyisocyanate compound (trade name: Coronate L) 4 parts by weight

The content of the tertiary amine in the polyester polyurethane resin, which is the above-mentioned binder, depends on the polyurethane resin 1
0 ⁶ g a per 101 equivalents, the weight average molecular weight measured by GPC method 48000, a magnetic coating material using the binder A glass transition point Tg of 81 ° C. as Example 1, the tertiary amine Polyurethane resin content is 10 ⁶ g
200 equivalents per weight, the weight average molecular weight measured by GPC method is 49000, and the glass transition point Tg is 76 ° C.
Example 2 was a magnetic paint using the binder B which was For comparison, the content of the tertiary amine in the binder is 50 equivalents per 10 ⁶ g of the polyurethane resin, and G
The weight average molecular weight measured by the PC method is 48,000,
A magnetic coating material using a binder C having a glass transition point Tg of 78 ° C. was used as Comparative Example 1, the content of the tertiary amine was 300 equivalents per 10 ⁶ g of the polyurethane resin, and the weight average molecular weight measured by GPC method. Is 48500 and the glass transition temperature Tg is 80 ° C., the magnetic coating material using the binder D is Comparative Example 2, and the content of the tertiary amine is 104 equivalents per 10 ⁶ g of the polyurethane resin, which is measured by the GPC method. The measured weight average molecular weight is 50,000 and the glass transition point Tg
Comparative Example 3 was a magnetic paint using the binder E having a temperature of 52 ° C. Further, polyester polyol having a metal sulfonate group, glycol (glycol such as N-methyldiethanolamine is not included), and diphenylmethane diisocyanate are reacted under predetermined conditions to prepare a binder F made of a polyester polyurethane resin, A magnetic paint using this was set as Comparative Example 4. Binder F
No tertiary amine was contained in the binder F, and the content of the metal sulfonate group in the binder F was 10%.
The amount is 162 equivalents per ⁶ g, the weight average molecular weight measured by GPC method is 47500, and the glass transition point Tg is 7
It was 6 ° C.

The magnetic paints of Examples 1 and 2 and Comparative Examples 1 to 4 were applied on a polyethylene terephthalate film having a thickness of 10 μm, which is a non-magnetic support, so that the thickness after drying would be 3 μm, and a magnetic field was applied. Alignment, drying, and super calendar were performed in this order, and the magnetic layer was formed by curing at 70 ° C. for a predetermined time. Further, after providing a back coat layer having a thickness of 0.8 μm, it was cut into a width of 8 mm to obtain sample tapes Examples 1 and 2 and Comparative Examples 1 to 4.

The magnetic properties, electromagnetic conversion properties, and durability of each of the above-described sample tapes thus formed were evaluated. To evaluate the magnetic characteristics, the residual magnetic flux density T,
The squareness ratio was measured, and the electromagnetic conversion characteristics were evaluated by recording a 7 MHz signal on each sample tape and comparing the reproduction output and Y-C / N of the signal with the in-house standard magnetic tape. As the evaluation of durability, the still characteristics and the amount of powder falling were evaluated. Still characteristics are 7M for each sample tape
A Hz signal was recorded, and the reproduction output of this signal was evaluated by the time (unit: minutes) until the output was attenuated to 50%. The amount of powder fall is to visually observe the amount of powder drop on the head drum, guide pin, etc. after 120 minutes of shuttle travel, and the one with almost no powder drop is 0 point, and the amount of powder drop is very large. The item was evaluated as 5 points. The measurement results were obtained by evaluating 10 tapes with respect to one type of sample tape and expressing the average point. The results are shown in Table 1.

[0032]

[Table 1]

As can be seen from the results shown in Table 1, the sample tapes of Examples 1 and 2 to which the present invention was applied obtained good results in magnetic characteristics, electromagnetic conversion characteristics, and durability.
This is because the dispersibility of the magnetic powder in the binder was improved by containing a proper amount of tertiary amine in the binder polyester polyurethane resin, and the magnetic characteristics and electromagnetic conversion characteristics of the obtained magnetic layer were improved. In addition, the tertiary amine contained in the polyester polyurethane resin acted as a catalyst for the cross-linking reaction between the polyisocyanate compound used as the cross-linking agent and the polyester polyurethane resin to accelerate the high-density cross-linking reaction. This is probably because the durability of the layer is improved. This is Example 1,
This is also confirmed by the fact that the amount of powder falling in No. 2 is very small.

On the other hand, when the amount of the tertiary amine contained in the binder is too small or too large as in Comparative Examples 1 and 2, good results are obtained in magnetic properties, electromagnetic conversion properties and durability. Can't get Therefore, it was also confirmed that the amount of the tertiary amine contained in the binder polyester polyurethane resin was 80 to 250 equivalents per 10 ⁶ g of the binder. Further, when the glass transition point Tg is lower than 60 ° C. (50 ° C. in this case) as in Comparative Example 3, magnetic properties and electromagnetic conversion properties are good, but sufficient strength is imparted to the magnetic layer. It is not possible and durability is not good. This is also confirmed by the fact that the amount of powder falling in Comparative Example 3 is very large. When a binder containing no tertiary amine in the binder and having a metal sulfonate group introduced as a polar group as in Comparative Example 4 was used, the magnetic properties,
The electromagnetic conversion characteristics are good, but the durability is not good. It is considered that this is because the metal sulfonate base does not function as a catalyst during the crosslinking between the polyisocyanate compound and the polyester polyurethane resin, and the high-density crosslinking reaction is not promoted. This is also confirmed by the fact that the amount of powder falling in Comparative Example 4 is very large.

[0035]

As is apparent from the above description, in the present invention, in a magnetic recording medium in which a magnetic layer made of a magnetic paint mainly composed of magnetic powder and a binder is formed on a non-magnetic support. The above binder is polyurethane resin 10
^Since it is a polyurethane resin containing 80 to 250 equivalents of tertiary amine per ⁶ g, it has a relatively high glass transition point T.
Even if a polyurethane resin having g is used, the dispersibility of the magnetic powder is good, a magnetic paint having an appropriate fluidity can be obtained, the magnetic characteristics and electromagnetic conversion characteristics are good, and the magnetic material has good durability. A recording medium can be obtained.

Further, in the magnetic recording medium of the present invention, since the binder contains a polyisocyanate compound as a crosslinking agent, a crosslinking reaction occurs between the polyisocyanate compound and the polyurethane resin, and the polyurethane resin is contained in the polyurethane resin. Since the contained tertiary amine acts as a catalyst for the above crosslinking reaction, the crosslinking reaction is promoted, magnetic properties and electromagnetic conversion characteristics are excellent, and a magnetic recording medium having good durability can be obtained.

Further, in the magnetic recording medium of the present invention, the glass transition point of the polyurethane resin in the binder is 60.
Since the temperature is at least ℃, the durability of the obtained magnetic layer is good, and when the magnetic coating to be formed contains a polyisocyanate compound as a cross-linking agent, it is a tertiary resin contained in the polyurethane resin. The amine acts effectively as a catalyst, accelerates the cross-linking reaction between the polyisocyanate compound and the polyurethane resin, forms a magnetic layer with better durability, has good magnetic characteristics and electromagnetic conversion characteristics, and A good magnetic recording medium can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a sectional view showing another structural example of a magnetic recording medium to which the present invention is applied.

FIG. 3 is a cross-sectional view showing still another configuration example of the magnetic recording medium to which the present invention is applied.

[Explanation of symbols]

 1,11,21 ... Nonmagnetic support 2,12,22,23 Magnetic layer 13 ... Backcoat layer

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising a magnetic coating mainly composed of magnetic powder and a binder, wherein the binder is a tertiary amine per 10 ⁶ g of polyurethane resin. A magnetic recording medium comprising a polyurethane resin containing 80 to 250 equivalents of 2. A magnetic coating material containing a polyisocyanate compound as a cross-linking agent.
The magnetic recording medium described. 3. The magnetic recording medium according to claim 1, wherein the polyurethane resin as a binder has a glass transition point of 60 ° C. or higher.