JPS5851327B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium with improved Young's modulus.
In particular, the present invention relates to a thin magnetic recording tape in which a reinforcing layer is formed on a nonmagnetic film.

Generally, magnetic recording tapes are obtained by coating a non-magnetic film with a magnetic paint containing magnetic powder and a binder as main components.

Magnetic powders include r-Fe203, Fe3O4, intermediates thereof, and those to which co is added, as well as ferromagnetic chromium dioxide, Fe-Co, Fe-Co, etc.
-Alloy powder such as Ni, metal powder, etc. can be used.

Thermoplastic resins, thermosetting resins or reactive resins can be used as binders.

As thermoplastic resins, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, butadiene-
Acrylonitrile copolymers, polyamide resins, cellulose derivatives, polyester resins, etc. can be used.

As the thermosetting resin or reactive resin, epoxy resin, urea resin, melamine resin, silicone resin, polyurethane curable resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, etc. can be used. It is.

As the non-magnetic film, polyesters such as polyethylene terephthalate, polyolefin films such as polypropylene, vinyl chloride films, polyamide films, polyimide films, acetate films, etc. are used.

The value of magnetic tape has been increasing in recent years,
In particular, as video cassettes progress, longer recording times are required, and it is desired to increase the amount of magnetic tape that can be stored in the cassette.

However, increasing the capacity of the cassette itself would increase the size of the VTR (video tape recorder), so it is not practical to make it that thick.

Therefore, it is desired to increase the storage capacity by reducing the thickness of the magnetic tape.

For this reason, it is necessary to make the non-magnetic film used for magnetic tape as thin as possible, but as it becomes thinner, the Young's modulus decreases, the stiffness becomes weaker, and the mechanical strength decreases. For example, when a considerable amount of force is momentarily applied during loading (or unloading), or after repeated use, wrinkles may appear, edges may break, making the product unusable, or skewing may occur. It becomes difficult to record and play back high-quality images.

Regarding the relationship between the thickness and strength of a magnetic tape, as discussed in JP-A-50-30503 filed by the present applicant, the tensile strength is proportional to Young's modulus and its thickness;
The bending strength is proportional to Young's modulus and proportional to the cube of the thickness, so if the thickness of the non-magnetic film becomes 1/2, the tensile strength of the tape becomes 1/2, and the bending strength becomes 1/8. decreases to

Therefore, in order to make the magnetic tape thinner, it is necessary to secure a film that has a sufficient puffiness ratio even if it is thin and has high mechanical strength.

In view of the above points, it is an object of the present invention to provide a magnetic tape that has a high Young's modulus and high mechanical strength even if the nonmagnetic film is thin.

Another object of the present invention is to provide an improved magnetic tape that exhibits significantly less wrinkles and edge folding even under severe use.

Furthermore, the present invention aims to provide a magnetic tape with improved reinforcing effect at an industrially low cost.

That is, in the present invention, in a magnetic recording body in which a magnetic recording layer is provided on a non-magnetic film, a reinforcing layer containing acicular oxalate is provided on at least one surface of the non-magnetic film. It is.

The reinforcing layer in the present invention includes an antistatic layer coated with carbon black or the like on the back side of the magnetic tape, a slippery layer coated with graphite etc. on the back side of the magnetic tape, and a writable layer coated with white pigment on the back side of the magnetic tape. It is essentially different from the above, and the Young's modulus does not actually improve due to the above.

In addition, glass fiber, carbon fiber, etc. are known as reinforcing materials for plastics, but because the particle size is relatively large (minor axis 6 to 9 μm), it is difficult to use them as reinforcing materials for the base of magnetic tape. There are limits due to gender, etc.

Metal and oxide whiskers are also known, but
It is not practical as it is very expensive.

In the above-mentioned Japanese Patent Laid-Open No. 50-30503, the present applicant proposed forming a reinforcing layer of acicular potassium titanate in order to realize a thin magnetic tape.

According to this method, a magnetic tape with a sufficient puffer ratio and improved mechanical strength can be obtained, but on the other hand, acicular potassium titanate is expensive, leading to an increase in the cost of the magnetic tape. The problem is that the manufacturing method is difficult and it is difficult to obtain.

The acicular crystal oxalate used in the present invention has mechanical strength and Young's modulus comparable to those of the acicular potassium titanate, and is extremely inexpensive and easily available. The above-mentioned difficulties can be fully overcome.

The acicular crystal oxalate used in the present invention can be obtained by the following method.

First, an aqueous solution of oxalic acid is adjusted to a predetermined concentration, and an aqueous solution of water-soluble metal salts of a predetermined concentration is added thereto and thoroughly stirred to obtain oxalate.

The chemical formula of oxalate is M (COO)2 ・2H20,M
: Co, Fe, Mn, etc.

In our experiments, we found that cobalt oxalate, iron oxalate, and manganese oxalate can produce materials with excellent needle-like properties.

Further, when the acicular ratio of oxalate is 5 or more, preferably 10 or more, even more excellent effects are exhibited.

Figure 1 is a characteristic curve diagram showing the relationship between the acicular ratio of cobalt oxalate fibers and the Young's modulus of the coating film.It is also recognized from this curve (■) that as the acicular ratio increases, the Young's modulus of the coating film increases. It will be done.

Further, Fig. 2 shows an electron micrograph of the cobalt oxalate fiber (3000x magnification).

The reinforcing material thus obtained is treated with a predetermined binder and, if necessary, with a dispersant or surfactant.
It is applied onto a non-magnetic film, and the coating thickness is set so as to impart a predetermined Young's modulus or mechanical strength depending on the thickness of the film used.

The diameter (minor axis) of the acicular oxalate as a reinforcing agent is preferably at most 1 μm or less, preferably 0.5 μm or less, in order to maintain good smoothness on the surface of the reinforcing layer.

Next, the present invention will be explained according to examples.

Example 1 Acicular cobalt oxalate as a reinforcing agent is obtained by the following method.

First, commercially available primary oxalic acid is dissolved in water and adjusted to a concentration of 7%.

Next, a 1% aqueous solution of commercially available primary cobalt chloride is added to this solution and stirred to react and grow cobalt oxalate.

The reaction time was 30 minutes, and the reaction temperature was room temperature.

After the reaction is completed, filtration and water washing are repeated until the pH is around 7.

Thereafter, it was taken out and dried (80° C.) to obtain cobalt oxalate having an acicular ratio of 30 and a long axis of 22 μm (average).

Next, as shown in FIG. 3, a magnetic recording layer 2 is formed by coating one side of a polyethylene terephthalate film 1 with a thickness of 8 μm with magnetic paint for video, manufactured by Sony, so that the thickness after drying is 3 μm. Then, a reinforcing paint having the composition shown below is applied to the other side to form a reinforcing layer 3.

Composition Acicular cobalt oxalate 0150.100°200
．． 300゜400.500 parts (weight) Composition Vinyl chloride-vinyl acetate copolymer [co-electrolytic polymer of vinyl chloride-vinyl acetate-vinyl alcohol, manufactured by Union Carbide Co., Ltd. Product name: Vinylite VAGH1 copolymerization ratio (weight) Ratio) is vinyl chloride: vinyl acetate: vinyl alcohol -91:3:6,1 60 parts (weight) Polyester resin [trade name: Vylon 200 manufactured by Toyobo Co., Ltd.] 40 parts (weight) Lecithin PHR Solvent [methyl ethyl ketone-methyl Isobutylketone-toluene (1:1:1 weight ratio)] However, the amount of the solvent used is twice the total amount (parts by weight) of the acicular cobalt oxalate powder and the binder.

After mixing the above raw materials in a ball mill for 20 hours, 20 PHR of incyanate compound (Desmodur L: trade name manufactured by Bayer AG) was added immediately before coating, stirred for 30 minutes, taken out through a filter, and coated with a thickness of 3μ. A reinforcing layer 3 was formed.

Thereafter, it was calendered and cut into 1/2 inch width to make a videotape.

FIG. 4 shows the results of measuring the Young's modulus of each tape.

In the figure, the vertical axis shows the tape elastic modulus (kg/mA), and the horizontal axis shows the added amount parts (weight) of cobalt oxalate.

From the curve (■) in FIG. 4, it is recognized that the Young's modulus increases with the amount of cobalt oxalate added. Ratio of cobalt 0 to binder (B) 0/
It was confirmed that when B was 0/B=0.5, the improvement was 27% or more, when 0/B=1, it was about 50% or more, and when 0/B=2 or more, the improvement was more than double.

However, when the amount added exceeds 0/B=5, the effect reaches a saturated state, so there is little economical advantage, and adhesiveness decreases and powder falling easily occurs.

Therefore, the range of addition amount is preferably 0/B from 0.5 to 5.

Example ■ A reinforcing layer obtained in Example ■ (composition: 0/B=
3) was applied at a thickness of tR = 3.5μ) and the stiffness when the thickness tR was changed using only polyethylene terephthalate film. The results are shown in Figure 5.

The method for measuring hip O strength is as follows.

Generally, the resistance to deformation when a film is bent is called the stiffness of the film, and there is a relationship between the thickness of the film and the stiffness, which is proportional to the cube of the film thickness.

In order to quantitatively measure this, one end of the sample tape cut to a certain length is attached to a sample support stand, and the support stand is rotated slowly and at a constant speed.

This rotation brings the free end of the sample tape into contact with the tip of the detector (strain gauge), and as the support rotates, the sample tape is bent.

This bending (deformation resistance) is detected by a detector and the strength of the waist is measured.

In Figure 5, curve 4 is the stiffness when only polyethylene terephthalate film is used, and point a is the stiffness when a 3.5μ thick reinforcing layer is formed on one side of an 8μ thick polyethylene terephthalate film, making the total thickness 11.5μ. shows.

From Figure 5, the thickness of the non-magnetic film is constant (i.e. 8μ).
When comparing the two, it can be seen that the one with the reinforcing layer has significantly greater waist strength.

In order to obtain the same stiffness using only a non-magnetic film without providing a reinforcing layer, it is necessary to use a film with a thickness of about 14.7 μm, and according to this example, the thickness is 14.7 μm and 11.5 μm.
It becomes possible to reduce the thickness by 3.3 μm.

Example ■ A magnetic layer with a thickness of 2μ was formed on a polyethylene terephthalate film with a thickness of 8μ, and the thickness of the reinforcing layer containing cobalt oxalate was changed to a coating thickness of 1 using the composition (0/B = 3) method of Example ■.
Changes in hip strength were measured when changing μ, 2μ, 3μ, 4μ, and 5μ.

The measurement results are shown in FIG.

In Figure 6, the vertical axis shows the stiffness of the tape (m9), and the horizontal axis shows the thickness of the reinforcing layer in the tape of the present invention, and the thickness of the tape without the reinforcing layer (only the magnetic layer and polyethylene terephthalate film). The total thickness is shown.

Curve 5 is a tape of the present invention with different reinforcing layer thicknesses, and curve 6 is a tape without a reinforcing layer.

In addition, curve 60 point A forms a 4μ thick magnetic layer on one side of a 10μ thick polyethylene terephthalate film, and the total thickness is 1.
Indicates the stiffness of tape without a reinforcing layer of 2μ, and the opening is 8μ.
2μ on one side of thick polyethylene terephthalate film
This shows the stiffness of a tape that forms a thick magnetic layer and has a total thickness of 10 μm without a reinforcing layer.

In addition, the state of the tapes when the above-mentioned tapes with various reinforcing layer thicknesses were incorporated into cassettes and used was investigated, and the results are shown in curve (2) in FIG.

The measurement method was to use the Sony Betamax 5L cassette.
-7100 and repeated loading and unloading at the same location 50 times, and visually evaluated the occurrence of so-called scratches such as wrinkles and folds on the tape.

Items with no scratches were given a score of 0, and were graded from 1 to 50 according to the degree of scratches.

A passing score is a score of 0 or higher with no scratches at all.

Note that point A in the figure indicates tape without reinforcement (film thickness 1
0μ, magnetic layer thickness 4μ, total thickness 12μ).

From the above measurement results, that is, from Figure 6, it is clear that the reinforcing layer is 1μ
It can be seen that the stiffness of the tape coated with ~5μ becomes much greater as the thickness increases compared to the tape without the reinforcing layer.

By the way, when comparing a tape with a reinforcing layer with a total thickness of 14μ and a tape without a reinforcing layer with a total thickness of 14μ (A in the figure), the tape with a reinforcement layer has better stiffness. 25■ was also improved, and it can be seen that the effect is very large.

Moreover, from FIG. 7, the tape having a reinforcing layer has a better loading property, and the thicker the reinforcing layer, the better the tape loading property.

Example ■ Acicular crystal oxalate as a reinforcing agent is obtained by the following method.

Dissolve IJium (commercially available first grade oxalic acid) and adjust the concentration to 7%.

Next, a 1% aqueous solution of commercially available primary ferrous chloride was added to the solution,
Stir to react and grow iron oxalate.

Reaction time was 30 minutes. After the reaction, filter and wash with water to adjust pH to 7.

Then dry. The iron oxalate thus obtained has an acicular ratio of 20
, the long axis was 10μ (average).

In the same manner as in Example (2), it was coated on a polyethylene terephthalate film and the stiffness was measured, and the results are shown in the dotted lines in Figure 5.

Example ■ Acicular manganese oxalate is used as a reinforcing agent.

The main manufacturing method is the same as the previous one, but MnCl2
The concentration was 10%.

Other reaction conditions were the same.

As a result, the needle ratio is 30. Manganese oxalate fibers with a long axis of 10 μm (on average) were obtained.

Using this manganese oxalate fiber, we made it into a tape in the same manner as in Example ① and measured its Young's modulus, and it was confirmed that the Young's modulus was almost the same as that of cobalt oxalate fiber, indicating that the reinforcing effect was strong. did.

In addition, in the above examples, as divalent metal ions of oxalate, in addition to the above-mentioned Co2+, Fe2+, and Mn'', M
Partial substitution with g 2 +, Ni2+, Zn2+, Cd2+Cu2+, etc. is also possible.

Furthermore, in the above embodiments, the reinforcing layer was formed on the back surface opposite to the magnetic surface, but the reinforcing layer may be formed on both sides of the non-magnetic film, or furthermore, the reinforcing layer may be formed on one side of the non-magnetic film. However, it is also possible to form a magnetic layer on the reinforcing layer.

As described above, according to the present invention, a sufficiently strong magnetic tape can be obtained even if the non-magnetic film is made extremely thin in the thinning of the magnetic tape, and it can be obtained at low cost, especially for video cassettes. It is suitable to use.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the acicular ratio of cobalt oxalate fibers and the Young's modulus of the coating film, Figure 2 is an enlarged microscope photograph of cobalt oxalate fibers, and Figure 3 is a magnetic field with a reinforcing layer according to an embodiment of the present invention. A cross-sectional view of the tape, Figure 4 is a characteristic diagram showing the relationship between the amount of reinforcing agent added and the tape elastic modulus, Figure 5 is a characteristic diagram showing the relationship between tape stiffness and tape thickness, and Figure 6 is a characteristic diagram showing the relationship between the stiffness of the tape and the tape thickness. Characteristic diagram showing the relationship between layer thickness and tape stiffness strength,
FIG. 7 is a characteristic diagram showing the relationship between the thickness of the reinforcing layer and the loading property of the tape. 1 is a nonmagnetic film, 2 is a magnetic recording layer, and 3 is a reinforcing layer of acicular oxalate.

Claims (1)

[Claims] 1. A magnetic recording body comprising a magnetic recording layer provided on a non-magnetic film, characterized in that a reinforcing layer containing acicular oxalate is provided on at least 10,000 surfaces of the non-magnetic film.