JPH05220438A - Coating device - Google Patents

Abstract

PURPOSE:To stably produce a magnetic recording medium having uniform coating thickness even when a support is not uniform in its lateral direction, free from trouble such as streak and having good electromagnetic conversion characteristics. CONSTITUTION:A coating solution is applied to a support by an extrusion type head having a front edge 2 positioned on the upstream side of a slit emitting a coating solution with respect to the moving direction of the support 1 and a back edge 3 having a sharp tip part positioned on the downstream side of the slit with respect to the moving direction of the support so that the tip thereof retreats in the direction opposite to the support so as to provide difference in level from the front edge 2. The surface center line average roughness Ra of the slit inner surface 4, front edge surface 5 and back edge surface 6 of the leading end part of the coating head forming a coating layer in such a state that the gap between the coating surface of the support and the front edge is sealed with the low viscosity liquid applied to the coating surface of the support is set to 1.0mum or less and the breakage of the corner parts of the above-mentioned edges is set to 10mum or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating device, and in particular,
The present invention relates to an extrusion type coating apparatus for coating a coating liquid continuously extruded onto a moving support surface with a high-speed thin layer on the support surface.

[0002]

2. Description of the Related Art Extrusion type coating apparatuses for coating a coating solution continuously extruded onto a moving support surface with a uniform thickness at a high speed have been studied variously. As a method of blocking the air entrainment in the coating layer by liquid-sealing the upstream edge of the precoat layer,
A method of pre-coating with a liquid having the same composition (JP-A-58-20)
No. 5561), a method of applying a solvent as a precoat on a support (see JP-A-61-139929), and the like. With these coating methods,
It is possible to realize thin layer coating at high speed. However, this coating apparatus is an extrusion type coating apparatus, in which a pressure is applied between the downstream edge and the support, and the coating layer is smoothed. Also becomes non-uniform in the width direction. Further, when foreign matter is mixed on the support or in the precoat coating solution or the coating layer coating solution, the foreign matter is likely to be trapped on the downstream side edge, whereby streaks are likely to occur. The coating liquid mentioned here is, for example, a photographic photosensitive coating liquid, a magnetic coating liquid, a coating liquid for surface protection / antistatic or lubricity, and its typical products are various photographic films and photographic papers. , Magnetic recording media, etc.

The applicant of the present invention has previously improved these characteristics to avoid streak failure and fluctuations in the coating film thickness due to nonuniformity of the thickness of the support, Young's modulus, etc. Further, when the coating solution passes through the slot. As a coating apparatus capable of reducing pressure loss, the coating apparatus described in Japanese Patent Application Laid-Open No. 63-20069 was filed. In Japanese Patent Laid-Open No. 63-20069, as shown in FIG. 3, a liquid is sealed by an organic solvent 11 previously applied to the coating surface of the support 1 and is positioned upstream in the moving direction of the support. Front edge 2 and a back edge 3 located on the downstream side with respect to the moving direction of the support and having a tip stepped back from the front edge in the direction opposite to the support and having a sharp tip. A coating device for forming a coating layer on a support by using the extrusion type head has been disclosed. On the coated surface of the support, first, an organic solvent is coated by a commonly used known coating apparatus such as a gravure coater, a roll coater, a blade coater, and an extrusion coater. It is possible to prevent entrainment of entrained air into the coating layer, maintain a defect-free coating state, and improve high-speed coating characteristics. The front edge 2 is located on the upstream side of the support 1 from the exit of the slit 8 and is formed so that the entire edge surface facing the support 1 bulges toward the support. A curved surface having a curvature is generally used as a form of bulging toward the support side, but the shape is not limited to this as long as entrainment of entrained air can be prevented. The front edge of the back edge 3 is positioned so as to recede in the direction opposite to the support body with respect to the tangent at the exit of the slit 8 of the front edge 2. As a result, no pressing force is applied between the back edge portion 3 and the support 1 during coating, trapping of foreign matter at the same portion can be prevented, and failure of the coating surface due to the foreign matter can be reduced. It was

[0004]

However, the inner surface 4 and the front edge surface 5 and the back edge surface 6 of the slit at the tip of the extrusion type coating head shown in FIG.
Depending on the surface roughness and the state of the edge corners 9 and 10,
It has become clear that vertical stripes occur more frequently than the conventional pressure type extrusion type coating head. this is,
Inner surface 4 of the slit of the extrusion type coating head
The front edge surface 5 and the back edge surface 6 are highly precisely polished into a required shape by a grinder. Depending on the polishing conditions such as feed rate, cutting depth, selection of grindstone, etc., and the material of the tip of the coating head, the surface roughness and the state of the edge corners 9 and 10 become unfavorable, and this state appears directly on the coating surface. It means an easy tendency. That is, for example, a doctor edge known in Japanese Patent Laid-Open No. 60-238179 is smoothed at the doctor edge (back edge), so that the inner surface 4 of the slit and the front edge surface 5 also have a rough surface. Even if the condition of the chipping is a little bad, not only the doctor edge (back edge) surface with smoothing action is required not to have surface roughness or chipping, but in the case of this pressure type extrusion type coating head ,
Due to the internal stress based on the pressure applied to the coating liquid, the flow action of the coating liquid immediately after coating is enhanced, and as a result, the surface roughness of each of the edge surfaces may be increased depending on the liquid behavior of the discharged coating liquid. It can be presumed that it was possible to offset the above, but the coating head of the illustrated type that does not apply the above pressing force to the coating liquid is more likely to have streaks than before,
This will lead to deterioration of the quality of the coated surface. As described above, in the coating apparatus according to the present invention, since smoothing by the doctor edge is not performed, if the surface roughness of the inner surface of the slit and the front edge surface or the state of chipping is bad, streaks or the like will be directly caused. Therefore, it is required that the inner surface of the slit and the front edge surface have neither surface roughness nor chipping like the back edge surface. However, since it is impossible to enhance the polishing or surface finishing state of the coating head endlessly, in the past, how much the finishing state of the coating head should be configured is a trade-off with cost. The current situation is that it depends on empirical skill.

The object of the present invention is to solve the above-mentioned conventional problems and to suppress the variation in coating film thickness in the width direction and the generation of streaks due to the non-uniformity of the support in the width direction so that the coating thickness is uniform and there are no defects such as streaks. An object of the present invention is to provide a thin-layer coating product, particularly, in the case of a magnetic recording medium, a coating apparatus capable of stably producing a magnetic recording medium having excellent electromagnetic conversion characteristics at high speed.

[0006]

The object of the present invention is to provide a front edge located upstream of a slit for discharging a coating liquid in the moving direction of a support, and a slit of the slit in the moving direction of the support. An extrusion type head having a back edge located on the downstream side and having a step different from the front edge and receding in the direction opposite to the support, and a tip portion having an acute-angled back edge is used to apply at least one or more kinds of coating liquids. In a coating apparatus for coating, the tip of the coating head for forming the coating layer in a state where the coating surface and the front edge are liquid-sealed by a low-viscosity liquid coated on the coating surface of the support. The center line average roughness of the inner surface of the slit and the surfaces of the front edge surface and the back edge surface is 1.0 μmRa or less, and the chipping of the corner portion of the edge is 10 μm or less. It is achieved by a coating device characterized in that

The low-viscosity liquid containing an organic solvent as a main component (pre-coat liquid 11 to be described later) in the present invention means a liquid in which an organic solvent such as toluene, methyl ethyl ketone, butyl acetate or cyclohexanone is used alone or in combination, or a binder thereof. It is a liquid dissolved in a liquid and has a viscosity of 20 cp or less, more preferably 5 cp or less. As the binder, the binder used in the coating liquid described later is used. In the present invention, a low-viscosity liquid (precoat liquid 11) is previously applied to the coated surface of the support by a commonly used known coating device such as a gravure coater, a roll coater, a blade coater, and an extrusion coater. To be done. The pre-applied low-viscosity liquid prevents entrainment of entrained air on the upstream side of the front edge when the coating liquid is applied, and maintains a suitable coating state. In the present invention, at least one or more coating layers means, in a magnetic recording medium, at least a magnetic layer, a magnetic layer having a multilayer structure, and a combination of a magnetic layer and a non-magnetic layer. It includes a structure including one layer.
Further, the same layer structure can be applied to other than the magnetic recording medium.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. The shape of the coating head in FIG. 1 shows the case of single layer coating, and the case of FIG. 2 shows the case of double layer coating. As shown in both figures, the front edge 2 is located on the upstream side of the support 1 from the exit of the slit 8 (8a, 8b), and is closer to the support than the tip end of the back edge 3 arranged on the downstream side. It is protruding. Then, the low-viscosity precoat liquid 11 applied to the application surface of the support 1 is liquid-sealed between the application surface and the front edge 2. That is, in both the embodiments, the precoat liquid 11 is liquid-sealed while being appropriately scraped off on the upstream side of the front edge 2. Further, in both figures, the front edge 2 is formed such that the entire edge surface facing the support 1 bulges toward the support. A curved surface having a curvature is generally used as a form of bulging toward the support side, but is not limited to this as long as entrainment of entrained air can be prevented. The tip portion of the back edge 3 has an acute shape and is located away from the tangent line (substantially the passing line of the support 1) at the exit portion of the slit 8 (8a) of the front edge 2. In FIG. 2, the tip portion of the intermediate block 3a is connected to the back edge 3
It has almost the same configuration as. As described above, since the back edge 3 has a sharp edge shape which is closest to the support at the exit of the slit 8 (8b), the coating liquid 7a discharged from the slit 8 (8a, 8b), 7
b is separated at the tip of the sharp edge and is not smoothed downstream of this. In the case of this configuration, if the coating liquid overflows on the downstream slope of the back edge 3, the overflowing coating liquid may be solidified and a coating failure such as streaks may occur.

In this embodiment, as shown in FIGS. 1 and 2, the slit inner surface 4 (intermediate block 3 at the tip of the coating head).
It is preferable that the surface roughness of the front edge surface 5 and the back edge surface 6 including the inner surface 4 which constitutes the slit in a) and the front edge surface 5 and the back edge surface 6 are small. As a result of overlapping, it was surprisingly found that when the center line average roughness (Ra) is 1.0 μm or less and the thickness is less than the boundary, it is extremely difficult to generate streaks. Furthermore, 0.4 μmRa or less is more preferable, and streaks hardly occur. The surface roughness is based on the Japanese Industrial Standard JIS-B0601, and is represented by the commonly used center line average roughness. The cutoff value (λc) is 0.25 mm. Further, it is desired that the front edge corner portion 9 and the back edge corner portion 10 at the tip of the coating head are not chipped at all, but in reality, minute chipping occurs in the polishing process. Therefore, when studies were repeated focusing on the streak generation state due to the agglomeration of the coating liquid and the foreign substance trap, when the existing chippings of 10 μm or less over the entire width of the tip of the coating head, streaks that would affect the quality are less likely to occur. It has been found. 5.0
If it is less than or equal to μm, it is more preferable. It should be noted that the chipping occurs at the front edge corner portion 9 and the back edge corner portion 10 at the tip of the coating head, in which some of the particles forming the tip member are dropped off during the polishing process or during the material sintering process. The fine voids appearing at the edge corners. The size of one chip can be expressed in the width direction and the depth direction of the support, but here, the larger one of the width direction and the depth direction of the support is expressed. The size of is the maximum chipping when the entire width is inspected in the width direction. In the present embodiment, the material of the head tip of the coating head is preferably cemented carbide or ceramic.

Although the coating head is installed between the two guide rollers, the coating head for the precoat liquid 11 may be installed between the guide roller and the guide roller on the upstream side of the coating head. The wrap angle in the coating liquid coating head is 2 ° to 6
It is about 0 °. Further, the span of the guide roller for forming the wrap in this coating head is generally 5
Although it is 0 to 3000 mm, it is not limited to this. The liquid feeding system is not particularly limited, and a known technique according to the properties of the coating liquid can be used. In particular, in the case of a magnetic coating liquid, it generally has a cohesive property, and therefore, it is preferable to give shearing to the extent that it does not coagulate.
Specifically, Japanese Patent Application No. 63-63601 and Japanese Patent Laid-Open No. 62-63
95174, etc. Japanese Patent Application No. 63-63601
In the case where there is no rotor as disclosed in Japanese Patent Laid-Open Publication No. JP-A-2003-242, the pipe diameter of the pump to the coating head is 50 mm or less, the pocket diameter of the magnetic liquid coating head is 2 to 20 mm, and the slit width of the magnetic liquid coating head is 0.05 mm to 1 mm. The slit length is 5
It is suitable that the thickness is in the range of mm to 150 mm, but it is not limited to this.

Further, ferromagnetic fine powder is used in the magnetic layer of the magnetic recording medium of the present invention. As the ferromagnetic fine powder, γ-
Fe ₂ O ₃ , Co-containing γ-Fo ₂ O ₃ , Fe ₃ O ₄ ,
Co-containing Fe ₃ O ₄ , γ-FeOx, Co-containing γ-
FeOx (X = 1.33~1.50), CrO 2, Co
-Ni-P alloy, Co-Ni-Fe-B alloy, Fe-N
Known ferromagnetic fine powders such as i-Zn alloy, Ni-Co alloy and Co-Ni-Fe alloy can be used. The particle size of these ferromagnetic fine powders is about 0.005 to 1 micron, The ratio of length / axis width is about 1/1 to 50/1.
The specific surface area of these ferromagnetic fine powders is 1 m ² / g
It is about 70 m ² / g. Also, as ferromagnetic fine powder,
Plate-like hexagonal barium ferrite can also be used. The particle size of barium ferrite is about 0.001 to 1 micron in diameter and the thickness is 1/2 to 1/20 of the diameter. Barium ferrite has a specific gravity of 4 to 6 g / cc and a specific surface of 1
m is ² / ^{g~70m 2} / g.

In the present invention, a binder is used in the magnetic layer together with the ferromagnetic fine powder. Examples of the binder used include conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. The thermoplastic resin has a softening temperature of 150 ° C. or lower and an average molecular weight of 10,0.
Those having a degree of polymerization of about 00 to 300,000 and about 50 to 2,000, for example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer Combined, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, nylon-
Silicone resin, nitrocellulose-polyamide resin,
Polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene diacrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene A butadiene resin, a polyester resin, a chlorovinyl ether acrylate copolymer, an amino resin, various synthetic rubber type thermoplastic resins, and mixtures thereof are used.

As the thermosetting resin or the reactive resin,
The coating liquid has a molecular weight of 200,000 or less, and when the magnetic layer-forming composition is applied, dried and then heated, these resins undergo reactions such as condensation and addition to give an infinite molecular weight. It can be great. Further, among these resins, it is desirable that the resin does not soften or melt until the resin is thermally decomposed. Specifically, for example, phenol resin, epoxy resin, curable polyurethane resin, urea resin, melamine resin, alkyd resin, silicone resin, reactive acrylic resin, epoxy polyamide resin, nitrocellulose melamine resin, high molecular weight polyester resin and isocyanate. Prepolymer mixture, methacrylate copolymer and diisocyanate prepolymer mixture, polyester polyol and polyisocyanate mixture, urea formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixture, polyamide resin and There is a mixture of these.

The ferromagnetic fine powder dispersed in the binder, the solvent, the dispersant as an additive, the lubricant, the abrasive, the antistatic agent, the non-magnetic support and the like are the same as those conventionally used. To be done. Examples of the dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and stearolic acid having 12 to 18 carbon atoms (R ₁ COOH, R ₁ is an alkyl or alkenyl group having 11 to 17 carbon atoms): Alkali metal (Li, Na, K, etc.) or alkaline earth metal (M) of the above fatty acid
g, Ca, Ba) metal soap: Fluorine-containing compound of the above fatty acid ester: Amide of the above fatty acid:
Polyalkylene oxide alkyl phosphate ester: Resinine: Trialkylpolyolefinoxy quaternary ammonium salt (alkyl has 1 to 5 carbon atoms, olefin has ethylene, propylene, etc.): etc. are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfuric acid ester and the like can be used. As the lubricant, the above-mentioned dispersant is also effective, but dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy poly Silicone oil such as siloxane (alkyl has 1 to 5 carbons, alkoxy has 1 to 4 carbons), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbons), and conductive fine particles such as graphite. Powder: Inorganic fine powder such as molybdenum disulfide, tungsten dioxide: Plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene: α-
Olefin polymer: unsaturated aliphatic hydrocarbon that is liquid at room temperature (α-olefin in which a double bond is bonded to the terminal carbon, about 20 carbon atoms): monobasic fatty acid having 12 to 20 carbon atoms and 3 carbon atoms Fatty acid esters, fluorocarbons and the like composed of 12 monohydric alcohols can be used.

As the abrasive, fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet,
Emery (main component: corundum and magnetite) is used. Electrostatic fine powder such as carbon black and carbon black graft polymer as an antistatic agent: Natural surfactant such as saponin: Nonionic surfactant such as alkylene oxide type, glycerin type and glycidol type:
Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfoniums: acidic such as carboxylic acid group, sulfonic acid group, phosphoric acid group, sulfuric acid ester group, phosphoric acid ester group Group-containing anionic surfactants: amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. As the organic solvent used as the coating solvent, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones: methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether and other ester systems: benzene, toluene, Tar-based (aromatic hydrocarbons) such as xylene: chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene.

The amount of solvent is 2-3 times that of the magnetic fine powder.
The dispersant is 0.5 to 2 with respect to 100 parts by weight of the binder.
0 parts by weight, the lubricant is 0.2 to 20 parts by weight, and the abrasive is 0.
5 to 20 parts by weight, 0.2 to 20 parts by weight of conductive fine powder used as an antistatic agent, and 0.1 to 10 parts by weight of a surfactant similarly used as an antistatic agent. The magnetic powder and the above-mentioned binder, dispersant, lubricant, abrasive, antistatic agent, solvent and the like are kneaded to form a magnetic paint.

Examples of the material for the support on which these magnetic layers are provided are polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and vinyls such as polyvinyl chloride. Resin, polycarbonate, polyamide resin,
Examples include plastic films such as polysulfone, metal materials such as aluminum and copper, and ceramics such as glass. These supports may be previously subjected to pretreatments such as corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, metal vapor deposition treatment and alkali treatment.
The support may be of any desired shape.

[0018]

As described above, according to the coating apparatus of the present invention, the center line average roughness of the inner surface of the slit and the front edge surface and the back edge surface of the extruding type coating head forming the coating layer. Sa (Ra) is 1.0
Since the thickness is not more than μm, the flow of the coating liquid is less likely to be disturbed even when the coating liquid is not pressed during coating, and a coating layer having an excellent surface property can be formed. Further, since the coating liquid is applied without pressurization, the liquid hardly agglomerates due to the coating liquid squeezing out, and it is possible to stably manufacture a product having a good surface property with less streaks and the like due to foreign matter traps. it can. Further, since the corners of the front edge and the back edge of the extrusion type coating head tip portion forming the coating layer are 10 μm or less, the coating solution is applied to the tip portion of the coating head even when the coating solution is not pressurized during coating. It is possible to stably produce a product having a good surface property, in which the flow of the meniscus away from the turbulence does not easily occur, and there are few streaks due to liquid aggregation and foreign material trapping.

[0019]

EXAMPLES Next, the novel effects of the device of the present invention can be further clarified by examples. After putting each component of the coating liquid composition shown below in a ball mill and thoroughly mixing and dispersing, 30 parts by weight of an epoxy resin (epoxy equivalent of 500) was added and uniformly mixed and dispersed to obtain a magnetic coating liquid (magnetic dispersion liquid). did. When the viscosity of the magnetic coating liquid thus obtained was measured with a Rotovisco viscometer, it showed thixotropic viscosity characteristics at each shear rate as shown in FIG. Composition of coating liquid: γ-Fe ₂ O ₃ powder (acicular particles having an average particle size in the major axis direction of 0.5 μ, coercive force of 320 oersted) ... 300 parts by weight Vinyl chloride-vinyl acetate copolymer (copolymerization ratio 87 : 13, polymerization degree 400) ・ ・ ・ 30 parts by weight Conductive carbon ・ ・ ・ 20 parts by weight Polyamide resin (amine value 300) ・ ・ ・ 15 parts by weight Lecithin ・ ・ ・ 6 parts by weight Silicone oil (dimethylpolysiloxane) ・··· 3 parts by weight Xylol ・ ・ ・ 300 parts by weight Methyl isobutyl ketone ・ ・ ・ 300 parts by weight n-butanol ・ ・ ・ 100 parts by weight Further, the pre-coat liquid uses methyl isobutyl ketone and has a thickness of 2.0 μm by a bar coating method. (Wet state). The coating film thickness was 15 μm (wet state).
A polyethylene terephthalate film having a thickness of 15 μm and a width of 500 mm was used as a support, and the film was run at a tension of 10 kg / full width and a coating speed of 600 m / min. Centerline average roughness of surface 6 (μ
mRa) was changed to three levels of 0.4 μm, 1.0 μm and 2.0 μm, and the chipping (maximum value of μm) of the front edge corner 9 and the back edge corner 10 was 5 μm, 10 μm, 2
Comparison was made on the occurrence of streaks by combining the three levels of 0 μm. The results are shown in Table 1.

[0020]

[Table 1]

As shown in Table 1, surface roughness Ra (μm)
Is 2.0 μm in any of the slit inner surface 4, the front edge surface 5, and the back edge surface 6, that is, the extruder No. In the case of ,,, 10 or more streaks were generated in each case, and the number of streaks was considerable when including those that did not cause a problem in terms of characteristics, the quality was significantly deteriorated, and the product was not preferable. In addition, before the product is completed, it may cause a large trouble in the post-application process such as winding failure or cutting due to wrinkles, which may damage the equipment. The cutoff value (λc) is 0.
It is 25 mm. Notch (μm) is the front edge corner 9,
In the case of 20 μm in any of the back edge corner portions 10, that is, in the extruder No.・ Even if
The number of lines is considerable, including those that are markedly streaked and do not pose a problem in terms of characteristics. The quality has dropped significantly,
It is not desirable as a product. In addition, before the product is completed, in the post-coating step, it causes a large trouble that may damage the equipment such as winding failure or cutting due to wrinkles. The streak that causes a particular problem almost coincides with the chipping occurrence position of the extruder (larger than 10 μm). On the other hand, the extruder No.
.., a good magnetic recording medium was obtained without the occurrence of streaks that would cause problems in product quality and subsequent processes. In particular, no coating streak was observed in the extruder having a surface roughness of 0.4 μm and a chipping of 5 μm, and a very good magnetic recording medium could be stably obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of an essential part of an embodiment of a coating apparatus of the present invention.

FIG. 2 is a side sectional view of a main part of another embodiment of the coating apparatus of the present invention.

FIG. 3 is a side sectional view of a conventional coating device.

[Explanation of symbols]

 1 Support 2 Front Edge 3 Back Edge 3a Intermediate Block 4 Inside Slit 5 Front Edge Surface 6 Back Edge Surface 7a, 7b Coating Liquid 8, 8a, 8b Slit 9 Front Edge Corner 10, 10a Back Edge Corner 10b Back Edge Corner Part 11 Precoat liquid

[Procedure amendment]

[Submission date] April 24, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

[0004]

However, the inner surface 4 and the front edge surface 5 and the back edge surface 6 of the slit at the tip of the extrusion type coating head shown in FIG.
Depending on the surface roughness and the state of the edge corners 9 and 10,
It has become clear that vertical stripes occur more frequently than the conventional pressure type extrusion type coating head. this is,
The slit inner surface 4 and the front edge of the coating head are
Edge surface 5 and back edge surface 6 are the shapes required for a grinding machine.
It is ground with high accuracy, but the feed rate during this processing is
And polishing conditions such as cutting depth and selection of grindstone and coating head
Depending on the material of the tip, surface roughness and edge corners
The state of 9 and 10 is not preferable, and this state
It means that it tends to appear directly on the coated surface. You
That is, up to now, for example, JP-A-60-238179
If there is a doctor edge known in the news, etc.
Smoothing of coating liquid at the edge (back edge)
Therefore, the inner surface 4 of the slit and the front edge are
The surface 5 also has a surface roughness or chipping of the back edge surface 6.
Even if the coating quality is a little poor, the smoothing effect of the coating solution
The internal stress generated by the pressure applied to the coating
The liquid may enhance the flow action immediately after its application,
Depending on the liquid behavior of the coating liquid discharged from the slit,
As a result, the finish condition of the surface roughness of the edge surface can be canceled out.
It can be presumed that it was possible to do so, but the so-called coating shown in FIG.
Type of application head that does not apply high pressure to the application liquid
Is easier to produce coating stripes and uneven thickness than the pressure type
Therefore, the quality of the coated surface may deteriorate.
Be done. As described above, in the coating apparatus according to the present invention, since smoothing by the doctor edge is not performed, if the surface roughness of the inner surface of the slit and the front edge surface and the state of chipping are bad, streaks or the like will be directly caused. Therefore, it is required that the inner surface of the slit and the front edge surface have neither surface roughness nor chipping like the back edge surface. However, since it is impossible to enhance the polishing and surface finishing states of the coating head endlessly, in the past, how much the finishing state of the coating head should be configured depends on the cost. The current situation is that it depends on empirical skill.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Further, ferromagnetic fine powder is used in the magnetic layer of the magnetic recording medium of the present invention. As the ferromagnetic fine powder, γ-
Fe ₂ O ₃ , Co-containing γ- Fe ₂ O ₃ , Fe ₃ O ₄ ,
Co-containing Fe ₃ O ₄ , γ-FeOx, Co-containing γ-
FeOx (X = 1.33~1.50), CrO 2, Co
-Ni-P alloy, Co-Ni-Fe-B alloy, Fe-N
Known ferromagnetic fine powders such as i-Zn alloy, Ni-Co alloy and Co-Ni-Fe alloy can be used. The particle size of these ferromagnetic fine powders is about 0.005 to 1 micron, The ratio of length / axis width is about 1/1 to 50/1.
The specific surface area of these ferromagnetic fine powders is 1 m ² / g
It is about 70 m ² / g. Also, as ferromagnetic fine powder,
Plate-like hexagonal barium ferrite can also be used. The particle size of barium ferrite is about 0.001 to 1 micron in diameter and the thickness is 1/2 to 1/20 of the diameter. Barium ferrite has a specific gravity of 4 to 6 g / cc and a specific surface of 1
m is ² / ^{g~70m 2} / g.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

[0019]

EXAMPLES Next, the novel effects of the device of the present invention can be further clarified by examples. After putting each component of the coating liquid composition shown below in a ball mill and thoroughly mixing and dispersing, 30 parts by weight of an epoxy resin (epoxy equivalent of 500) was added and uniformly mixed and dispersed to obtain a magnetic coating liquid (magnetic dispersion liquid). did. The viscosity of the magnetic coating liquid thus obtained was measured with a Rotovisco viscometer.
And showed a thixotropic viscosity characteristic. Composition of coating liquid: γ-Fe ₂ O ₃ powder (acicular particles having an average particle size in the major axis direction of 0.5 μ, coercive force of 320 oersted) ... 300 parts by weight Vinyl chloride-vinyl acetate copolymer (copolymerization ratio 87 : 13, polymerization degree 400) ・ ・ ・ 30 parts by weight Conductive carbon ・ ・ ・ 20 parts by weight Polyamide resin (amine value 300) ・ ・ ・ 15 parts by weight Lecithin ・ ・ ・ 6 parts by weight Silicone oil (dimethylpolysiloxane) ・··· 3 parts by weight Xylol ・ ・ ・ 300 parts by weight Methyl isobutyl ketone ・ ・ ・ 300 parts by weight n-butanol ・ ・ ・ 100 parts by weight Further, the pre-coat liquid uses methyl isobutyl ketone and has a thickness of 2.0 μm by a bar coating method. (Wet state). The coating film thickness was 15 μm (wet state).
A polyethylene terephthalate film having a thickness of 15 μm and a width of 500 mm is used as a support, and the film is run at a tension of 10 kg / full width and a coating speed of 600 m / min, and the inside surface of the slit 4, the front edge surface 5, and the back edge of the extrusion type head shown in FIG. Centerline average roughness of surface 6 (μ
mRa) was changed to three levels of 0.4 μm, 1.0 μm and 2.0 μm, and the chipping (maximum value of μm) of the front edge corner 9 and the back edge corner 10 was 5 μm, 10 μm, 2
Comparison was made on the occurrence of streaks by combining the three levels of 0 μm. The results are shown in Table 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Tomaru 2-12-1, Ogimachi, Odawara City, Kanagawa Fuji Photo Film Co., Ltd.

Claims (1)

[Claims] 1. A front edge located upstream of a slit for discharging a coating liquid with respect to a moving direction of a support, and a front edge located downstream of the slit with respect to the moving direction of the support and having a front edge thereof. In a coating apparatus for coating at least one or more coating liquids by an extrusion type head having a back edge that is stepped more than stepwise and recedes in the direction opposite to the support, and the front end has an acute-angled back edge. The inner surface of the slit at the tip of the coating head and the front edge surface and the back edge surface forming the coating layer in a state where the coating surface and the front edge are liquid-sealed by a low-viscosity liquid coated on the surface. The center line average roughness of the surface is 1.0 μmRa or less, and the chipping of the corner portion of the edge is 10 μm or less.