JP3196987B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a novel magnetic recording medium in which a coating liquid such as a magnetic liquid and a surface protection liquid is applied to a flexible support made of plastic film, paper, metal or the like. About the method.

[0002]

2. Description of the Related Art Conventionally, in a method of manufacturing a magnetic recording medium, a coating method for applying a coating solution to a flexible support (hereinafter referred to as a web) has been known as a roll coating method, a bead coating method, a curtain coating method, and an extrusion method. Coating methods and the like are known. In any of these application methods, the width of the application portion to which the application liquid is applied is applied to be narrower than the finite width of the web. The application part is left.

[0003] For this reason, for example, Japanese Patent Laid-Open No. 57-84771
JP-A-58-104666 and JP-A-58-109666
162, 58-18069 and 58-1
Nos. 8070 and 60-78664, Japanese Patent Application No. 5
As shown in the extrusion type coating apparatus disclosed in JP-A-9-94657, JP-A-61-230173 and JP-B-49-1459, etc., the web where the coating head is running continuously is applied to the web. When the coating liquid is applied while being pressed, the web, which has been tensioned, is bent so that its widthwise edge warps toward the head, and is in contact with the coating head.

[0004] As a result of contact with the coating head, the web is shaved off to generate powdered shavings, and the scattered shavings mainly cause a loss of a reproduced signal.
Also, shavings deposited on the contact part of the coating head, etc.
By changing the distance between the web and the coating head, there was a case where the film thickness of the coating liquid at the edge portion became uneven or the coating could not be performed. The same operation as the coating head is described in, for example, JP-A-51-140703,
JP-A-52-84242, JP-A-54-8646,
It is also known that this occurs in doctor bars and smoothers disclosed in Japanese Patent Publication Nos. 48-11336 and 60-53674.

Therefore, in order to solve the above-mentioned problems, for example, Japanese Patent Application Laid-Open No. 61-257268,
As disclosed in Japanese Unexamined Patent Publication No. 2736, before application of the coating liquid on the web, a solvent is previously applied to a non-application portion of the coating liquid existing on an edge of the web and lubricated, whereby the coating head is coated. And a method of performing liquid lubrication between them. On the other hand, for example, Japanese Patent Laid-Open No. 61-257263
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-214, a method has been proposed in which a portion of the coating head or the like corresponding to the edge is cut away so as to keep a distance from the web.

[0006] Further, at least the ear portion of the polymer,
As a solution to the edge shaving in the extrusion coating method by applying a monomer, a UV resin or another material having an appropriate lubricating property, for example, JP-A-3-116524
A method found in the Japanese Patent Publication was proposed. That is, by applying and drying a fluorine-based lubricant or a polymer, a monomer, a UV resin, or the like, "at least at the ears in the width direction of the web", the contact force between the extruder blade tip and the web during application of the magnetic liquid is reduced, The purpose is to prevent scraping. With this method, the problem of scraping could be solved very effectively.

However, according to this method, the polymer or the like applied to the ears remains exposed on the surface of the support after drying. This has caused a new problem in the post-process. The magnetic recording medium is subjected to a calendering treatment after the application, and then subjected to a heat treatment in a roll state in order to cure the coating film and remove the thermal stress of the web. Here, the coating of the polymer or the like, which is applied to the above-mentioned ears and is exposed on the outer side of the edge of the magnetic layer on the web, softens or further melts, and adheres to the back of the web. by this,
There was a phenomenon in which the coating surface near the web ears peeled off. It has been found that an increase in this peeling causes an increase in dropout. In recent years, particularly in recent years, with the thinning of magnetic recording media, the web has become thinner,
It has been found that a breakage of the web also occurs because the polymer or the like melts out and adheres to the back of the web.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to eliminate the drawbacks described above, and it is an object of the present invention to eliminate a failure caused by shaving of an ear in an extrusion type coating of a magnetic recording medium. Another object of the present invention is to provide a coating method which does not cause a failure such as adhesion even by a heat treatment in a later step.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coating apparatus having a continuously moving flexible support having a widthwise edge portion on a surface of the flexible support and a tip of a slot of a coating head. When applying a coating solution while pressing to form a magnetic layer,
In a method for manufacturing a magnetic recording medium, wherein an undercoat layer is provided before forming the magnetic layer, at least a portion corresponding to the edge of the flexible support is wider than a width of the magnetic coating layer in advance. A method of manufacturing a magnetic recording medium, comprising applying a polymer solution having a glass transition point (Tg) higher than a heat treatment temperature to the undercoat layer and drying the polymer solution to form at least a part of the undercoat layer. be able to.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a coating apparatus according to the present invention will be described with reference to the drawings. FIG. 2 is a schematic configuration diagram of a magnetic recording medium manufacturing facility to which the manufacturing method of the present invention is applied. First, FIG.
As shown in (1), the continuously running web 1 is supplied from a delivery roller 2 and sent to a coating section 4 for an undercoat layer in a state where the web 1 is maintained at an appropriate tension via an appropriately installed tension roll 3. The undercoat layer 5 is applied leaving both edges 9 (see FIG. 3) in the width direction of the web 1, and the width of the undercoat layer 5 is smaller than the width of the magnetic layer 20, In the treatment zone 6, a polymer solution having a glass transition point (Tg) higher than the temperature of the heat treatment (curing treatment of the synthetic resin) in the subsequent step is applied to the edge 9 to form the protective undercoat layer 13, The width of the protective undercoat layer 13 plus the undercoat layer 5 is naturally larger than the width of the magnetic layer. The coating liquid for forming the undercoat layer 5 may be, for example, an organic solvent solution of a polyester resin or a polyurethane resin, and is not particularly limited. As the polymer solution for forming the protective undercoat layer 13, a solution of a polyester resin can be used. This polyester resin is synthesized from an alcohol component and a dibasic acid. The alcohol component is selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like. As the dibasic acid, a polar group can be contained by using a mixture of an aromatic dicarboxylic acid such as orthoterephthalic acid, isophthalic acid and terephthalic acid and a phthalic acid containing a polar group.

The polar groups include -SO ₃ M, -OSO ₃
M, shown -COOM, -OPO ₃ M ₂ (wherein M represents a hydrogen atom, an alkali metal atom or an ammonium salt.
When there are two Ms, they may be the same or different. ) Is at least one polar group. The polymer solution used in the present invention includes, for example, a solution of a polyurethane resin. The polyurethane resin is synthesized by a reaction between a polyisocyanate compound and a polyol component. As the polyol component, a polyester polyol obtained by reacting a polyol with a polybasic acid is used. Using a polybasic acid having a polar group or a polyol having a polar group as a part of the polybasic acid or a part of the polyol, a polar group is introduced into the polyester polyol, and the polyester polyol is reacted with the polyisocyanate compound. By doing so, a polyurethane resin can be obtained.

Examples of the polybasic acid having a polar group and the polyol having a polar group include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfophthalic acid,
-Sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfophthalate, alkyl 4-sulfophthalate, alkyl 3-sulfophthalate and their sodium or potassium salts, and dimethylolpropionic acid and their sodium or potassium salts. Can be mentioned. The preferred amount of the polar group in both the polyester resin and the polyurethane resin is 0.1.
It is 1 meq / g or more and 3 meq / g or less. The preferred molecular weight is 10,000 to 100,000 by weight average molecular weight, and more preferably 30,000 to 60,000. If the amount of the polar group or the molecular weight is too high, the solubility in a solvent is undesirably deteriorated. The glass transition temperature (Tg) can be controlled by the ratio of the alcohol component to the dibasic acid component.
The temperature can be adjusted in the range of ℃ to 80 ℃.

After the undercoat layer 5 has been applied, the web 1 is sent to an edge treatment zone 6 where
In the above, the protective undercoat layer 13 is formed. After the protective undercoat layer 13 is formed, the protective undercoat layer 13 is further sent to the undercoat layer drying zone 7, where the undercoat layer 5 and the protective undercoat layer 13 are dried. And then sent to a coating step of coating the magnetic dispersion.

FIG. 3 is a perspective view of the coating apparatus 10 constituting the edge processing zone 6. The coating device 10 is provided on both sides of the web 1 on the side where the magnetic dispersion is coated.
This is a configuration in which two reverse rolls 11 are provided in coating liquid pans 12 arranged corresponding to (parts substantially corresponding to parts where no magnetic dispersion is formed). With this configuration, when the reverse roll 11 rotates, the polymer solution having a glass transition point (Tg) higher or higher than the heat treatment temperature in the coating liquid pan 12 or stored therein is applied to the edge 9 of the web 1. Can be applied. Incidentally, when applying the coating to said polymer solution, to the solution is prevented wrap the web back surface side, and slightly inside side of the side edge of the web 1 the outermost end of the coating section It is desirable to be.

The web 1 applied to a magnetic recording medium for a VTR is a general polyethylene terephthalate film (PET base).
In the above, when the magnetic recording medium runs on a magnetic recording / reproducing apparatus, the contact resistance at a contact portion such as a guide pole of the recording / reproducing apparatus is drastically reduced, and a very small amount is applied to the back surface of the web so as to stabilize the tape running. Due to the addition of the filler for providing the unevenness, the shavings adhered to the coating head and the like are removed by the filler (CaCO 2).
₃ , TiO ₂ ) as a main component.

As described above, when the polymer solution has a glass transition point (Tg) higher than the heat treatment temperature, after the application of the magnetic dispersion, curing of the coating film and thermal stress of the web occur. Heat treatment in a rolled state for removal (eg, 24 hours at 65 ° C., 24 hours at 60 ° C.)
(For 48 hours at 55 ° C.), the protective layer exposed outside the edge of the magnetic layer does not melt, so that the phenomenon of adhesion between webs can be avoided. Further, according to the present embodiment, the protective undercoat layer 1 is provided on the edge 9 of the web 1.
When the undercoat layer 3 is formed, the undercoat layer 13 has good slidability and excellent durability, so that, for example, contact between the extrusion type coating head for applying the magnetic dispersion and the edge is avoided. In addition, unnecessary contact between the smoother and the edge portion 9 is avoided, generation of shavings on the edge portion 9 is effectively prevented, dropout of the filler is also avoided, and dropout can be reduced. Further, the protective undercoat layer 1
No. 3 has high lubricity, so that the frictional resistance of the edge portion 9 is smaller than in the prior art, and the web running performance can be improved. The protective undercoat layer 13 may be applied to the coating portion 4 over substantially the entire width of the web 1, or may be applied while leaving a non-application portion of a coating solution applied in a later step as in the present embodiment. You may. Further, the undercoat layer 5 may be omitted, and all functions may be replaced by the undercoat layer 13. In the present embodiment, the edge treatment zone 6 does not need to be located after the undercoat layer coating section 4 as shown in FIG. 2, and is in front of another undercoat layer coating section 4. If the polymer solution is applied to a desired width in the application section 4 as described above, the end processing zone 6 becomes unnecessary. Further, the formation of the undercoat layer may not be continuous with the step of the magnetic dispersion as shown in FIG. 2, and may be formed in a single web manufacturing step before the step of applying the magnetic dispersion. Good. The coating apparatus for carrying out the production method of the present invention is not limited to the apparatuses shown in FIGS. 2 and 3 at all, and it is needless to say that various conventionally known coating apparatuses can be used. is there.

[0017]

As described above, according to the method of the present invention,
For example, before the magnetic dispersion is applied to the web, at the end of the web where the dispersion is not applied, when the magnetic dispersion is applied, a protective layer of the already dried polymer solution is formed,
For example, the contact between the end portion and the extrusion type coating head for applying the magnetic dispersion is avoided, no bleeding of the magnetic dispersion is performed, and unnecessary contact between the smoother and the end portion is avoided. Not only is the generation of shavings at the edges effectively prevented, but in addition to this effect, since the polymer solution is composed of a glass transition point (Tg) higher than the heat treatment temperature, Even after the application of the magnetic dispersion liquid, even if a heat treatment in a rolled state is performed for curing the coating film and removing the thermal stress of the web, the protective layer exposed outside the edge of the magnetic layer is melted. Therefore, the phenomenon of adhesion between webs can be avoided.

[0018]

EXAMPLES The effects of the method for manufacturing a magnetic recording medium of the present invention can be further clarified by examples. Next, in this example, the components of the composition were sufficiently mixed and dispersed in a ball mill, and then 30 parts by weight of an epoxy resin (epoxy equivalent: 500) was added and uniformly mixed to obtain a magnetic dispersion. Hereinafter, the composition will be described.

[0019]

[Table 1]

Further, the coating apparatus and the coating conditions used in the method of the present invention are shown below. Web material: Polyethylene terephthalate Thickness: 9 μm Coating speed: 600 m / min Tension: 20 kg / m Coating thickness: Dry film thickness 3.0 μm (coating amount 15
cc / m ² or equivalent) extruder (extrusion type coating head):
* The specifications are shown below. * Coating width: 500 mm Slit gap: 0.3 mm Slit length: 80 mm on the liquid supply side 77 mm on the non-liquid supply side Liquid reservoir inner diameter: 15 mm

Prior to the application of the magnetic dispersion, the undercoating liquid was applied over substantially the entire width of the web at the coating section 4 in FIG. 1 and dried. Table 2 shows the properties of the undercoat liquid.

[0022]

[Table 2]

The Tg is measured using a Leo Vibron manufactured by Orientec Co., Ltd. Tg is changed by changing the molecular weight or the functional group. This measuring instrument measures the temperature dependency of the loss elastic modulus at a frequency of 110 Hz, and sets the maximum temperature to Tg.
To evaluate the result of the coating, the thickness of the undercoat layer was changed, the coating was performed for 10 minutes (6000 m) under the above-described conditions, and evaluated by visual observation. In addition, as a heat treatment condition after the application, treatment was carried out at 65 ° C. for 24 hours in a constant temperature room, and ear adhesion was evaluated (Table 3). In addition, room temperature (25
° C) for 48 hours (Table 4). Furthermore, it processed at 60 degreeC in a constant temperature room for 24 hours, and evaluated the ear adhesion (Table 5). Moreover, it processed at 55 degreeC for 48 hours in a constant temperature room, and evaluated the ear adhesion (Table 6). In addition, the width of the exposed undercoat layer is 3 mm. Tables 3, 4 and 5 show the results.
And Table 6.

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

According to Tables 3, 4, 5 and 6, the Tg
Is determined to be equal to or higher than the heat treatment temperature, the peeling failure in the post-process can be solved not only at the time of heat treatment but also at room temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a magnetic recording medium manufactured by a method for manufacturing a magnetic recording medium according to the present invention.

FIG. 2 is a schematic configuration diagram of a manufacturing facility to which the method for manufacturing a magnetic recording medium of the present invention is applied.

FIG. 3 is a main part perspective view for illustrating a step of applying a polymer solution in the production method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 web 2 delivery roller 3 tension roll 4 coating section for undercoat layer 5 undercoat layer 6 edge treatment zone 7 undercoat layer drying zone 8 tension roll 9 edge 10 coating apparatus 11 reverse roll 12 coating liquid pan 13 protection Undercoat layer 20 Magnetic layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 5/855 G11B 5/842

Claims (1)

(57) [Claims] 1. A magnetic layer is formed by applying a coating liquid to a surface of a flexible support which is continuously running while pressing the coating solution against the end of a slot of a coating head while leaving an edge in a width direction of the flexible support. In the method for manufacturing a magnetic recording medium, wherein the undercoat layer is provided before the formation of the magnetic layer, the width of the magnetic coating layer is preferably set at least at a portion corresponding to the edge of the flexible support. Glass transition point (T
g) applying a polymer solution having a temperature higher than the heat treatment temperature and drying the polymer solution to form at least a part of the undercoat layer.