JPH0827929B2 - Magnetic recording media - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape, a floppy disk, a hard disk used in audio equipment, video equipment, computers and the like.

2. Description of the Related Art In the past, a wide variety of inorganic and organic materials have been studied and used in magnetic recording media, but there were some problems with Na ⁺ remaining in the magnetic coating film. One of them is
This is a so-called "squirting phenomenon", and when PVC resin is used as one of the binders, the liberation that occurs during paint preparation
NaCl on the surface of the magnetic layer due to Cl ⁻ and residual Na ⁺ in the magnetic powder
Precipitation. The second is the problem of "blocking" as described later. Therefore, first, a means for removing Na ⁺ from the magnetic layer will be described. First, from magnetic powder,
A lot of Na ⁺ is brought in. Needless to say, most magnetic powders use a reaction using an alkali (mainly NaOH) as the first step in the synthesis, but NaOH is often used in subsequent steps, and even the final commercially available magnetic powder that has undergone a washing step, Residual
Na ⁺ will remain in the magnetic powder. Further, in recent various binder resins, because of their dispersibility improved, also mixing of Na ⁺ from materials other than the magnetic powder, etc. is actively performed by introducing a -SO ₃ Na group in the polymer the polymer Yes, but this amount is small. Therefore, To reduce the magnetic residual magnetic layer of the recording medium Na ^+, it is important to reduce the residual Na ⁺ in the magnetic powder. As a method therefor, there is a patent that uses crown ether as a substance for capturing Na ⁺ in the step of washing magnetic powder with water (the present application and the present application). On the other hand, although it is possible to reduce the —SO ₃ Na group in the high molecular weight polymer, the dispersibility of the magnetic powder is reduced to that extent. Therefore, in the prior art, there was no good method other than the method described in the present patent by the present inventor and the patent of the same application.

Problems to be Solved by the Invention The problem of reducing residual Na ⁺ in the magnetic layer is
"Blocking", which is one of the quality evaluation items for videotapes (when the videotape is loaded into the VCR under high temperature and high humidity, and the running is stopped due to a power failure, etc., the tape magnetic layer is applied to the upper cylinder of the VCR. It is deeply related to the reduction and elimination of the phenomenon that the magnetic layer remains attached and is partly peeled off. This blocking is thought to be caused by salt damage due to the so-called “squirting phenomenon” of the magnetic layer of the magnetic tape, but it is closely related to the amount of Na ⁺ and Cl ⁻ extracted from the magnetic layer with distilled water. That is, the residual Na ⁺ is large, liberated Cl ^- many, Cl ^- degree of more blocking was found to be poor. (First, second
Figure reference) Thus, the problem the present invention is to provide, to reduce the Na ⁺ in the magnetic layer, and since not embossed on the constraining and the magnetic layer surface of the magnetic layer in the residual Na ⁺ in the magnetic layer It was to apply the means of.

Means for Solving the Problems In order to solve this problem, the present inventor obtained the results of preliminary experiments that it was effective to use a chemical scavenger of Na ⁺ . While several materials considered as a chemical scavenger Na ^+, their chemical when capturing the Na ⁺ (complex)
The surface of which is lipophilic and compatible with the high molecular weight organic binders that compose the magnetic layer, has the property of being hard to stand out on the surface of the magnetic layer, is easy to handle, and forms a stable compound (complex) with Na ^+. There is nothing other than so-called crown ethers. Among these, 15-crown-5 was found to be the most effective in consideration of various points, and experiments have been conducted. This crown ether has the following properties (manufactured by Nippon Soda Co., Ltd.).

Colorless viscous liquid, bp 0.3 = 130 ° C, mp = -24 to -22 ° C Easy to dissolve in all organic solvents, especially stable complexes with Na ⁺ . Structural formula is Incidentally, 18-crown-6 was found to be effective as well.

Action The action of this 15-crown-5 crown ether is
Needless to say, it is necessary to trap Na ⁺ in its own intramolecular vacancy to form a stable complex and to modify the surface of the complex to be lipophilic. The significance of this is
Owing to the inclusion of Na ⁺ in crown ether, lipophilic N
It behaves as a ⁺ , which allows it to be trapped in the organic binder that constitutes the magnetic layer. Therefore, Cl liberated by the thermal decomposition of PVC in the magnetic layer ^- is, Na ⁺ that remain charged - by electrical attraction between the crown ether complex, easily remains in the magnetic layer, and the cylinder on the VCR This has the positive effect of reducing the degree of blocking.

Example A video tape in 1/2 inch was produced under the following conditions. The number of parts of each material indicates the number of parts by weight when the magnetic powder is 100.

Magnetic powder (commercially _{available, Co-r-Fe 2 O} 3) ...... 100 parts polyurethane (Nippon Polyurethane Industry Co., part number R1
01) …… 10 parts Vinyl chloride resin (UCC, product name VAGH) …… 10 parts Carbon black (product number BP-200) …… 4 parts Abrasive (d-Al ₂ O ₃ , Sumitomo Chemical AKP-30)… … 3 parts Dispersant (GAFAC Product No. RE610) …… 4 parts Lubricant Butyl stearate …… 3 parts Organic solvent MEK …… 100 parts Toluene …… 100 parts Cyclohexanone …… 50 parts The above mixture is magnetically coated by a conventional method. Then, add an isocyanate curing agent to the binder by 20 phr and coat it on a 15 μm PET base film with a mini coater so that the magnetic layer thickness is 5 μm, and apply a super calendar.
1/2 inch with a slitter after curing at 60 ℃ for 20 hours
Cut into width.

The thus obtained video tape was evaluated for blocking under the conditions above and below.

Cut the tape to a length of 25 cm, wrap it around the upper cylinder of the VTR deck with the magnetic layer inside, and hang a 60 g weight. In this state, it was brought into a thermo-hygrostat at 40 ° C-80% RH and left for 7 days. After that, the sample tape was peeled off, and the peeling condition of the tape magnetic layer and the adhesion condition of the magnetic layer to the upper cylinder were compared with a limit sample prepared in advance, and five-level indexing by numbers 1 to 5 was performed. I do. In the experiment, when the hardener was added, 15-crown-5 was added to the magnetic coating material in an amount equivalent to 0.003 parts with respect to 100 of the magnetic powder as an example, and one not added was set as a comparative example. The measurement of n = 5 is performed, and the 5-step display is O …… 5, △…
... 3, X ... It corresponds to 1.

As shown in this example, the effect of the addition of crown ether is clearly recognized.

Therefore, it is possible to make a model by inference that Na ⁺ is trapped in the magnetic layer by the addition of crown ether, and thereby Cl ⁻ is suppressed from protruding to the surface of the magnetic layer.

EFFECTS OF THE INVENTION As described above, according to the present invention, the effect of the present invention that only the blocking property can be easily improved by using a small amount of crown ether additive is widely applied to various magnetic recording media. There is a big thing in opening the possibility.

[Brief description of drawings]

Figure 1 shows that the magnetic layer was peeled off on various prototype video tapes, 500 mg of which was shaken with 50 ml of pure water for 5 minutes, and the water-soluble N
FIG. 2 is a characteristic diagram showing the results of measuring the concentrations of a ⁺ and Cl ⁻ by the flame atom absorption method, and FIG. 2 is a characteristic diagram showing the relationship between the concentration of water-soluble Cl ⁻ and the degree of blocking.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing a substance that traps sodium. 2. The magnetic recording medium according to claim 1, wherein the substance that traps sodium is crown ether.