JP2002018347A - Coating method and coated product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of uniform pitch stripes on a surface of a coating layer even if the thin coating layer (<=2 μm thickness in wet state) is formed in a high speed multilayer coating. SOLUTION: A binder resin contained in a coating liquid forming the uppermost layer in multiply coated plural layers and having the number average molecular weight of >=5,000 is controlled to have <=5% concentration to a solvent contained in the coating liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method and a coated product, and more particularly to a flexible support (hereinafter referred to as "web").
In addition, the present invention relates to a coating method for applying a thin and uniform coating layer in multiple layers and at a high speed, and a coated product thereof.

[0002]

2. Description of the Related Art In recent years, magnetic recording media, photographic photosensitive materials, electronic materials, coating type batteries, optical films such as antireflection, and polishing tapes have been developed.
With the advancement of functions and performance of paper and information recording paper, there is an increasing demand for applying a thin and uniform coating layer on a web in multiple layers at a high speed.

[0003] For example, in the production of magnetic recording media, thinning and multi-layering of the magnetic recording layer are being studied along with the increase in the density of the medium. In particular, the demand for thinner magnetic recording layers has been rapidly increasing due to the spread of high-sensitivity magnetic heads such as MR heads, and the thickness of the magnetic recording layer is 0.02 to 0.2 μm in a dry state (0.2 to 2 μm in a wet state). And a coating method capable of forming an extremely thin magnetic recording layer. Since the surface of the magnetic layer is required to have extremely high smoothness, the magnetic recording layer has a thickness of 0.2 to 3 as a lower layer (layer in contact with the web).
By providing a non-magnetic coating layer of about μm, the protrusions on the surface of the web are flattened, thereby improving the performance of the magnetic recording layer. Therefore, from the viewpoint of productivity in manufacturing a magnetic recording medium, it is important how thin and uniform a magnetic recording layer and other layers can be multi-layer coated on a web at high speed.

Conventionally, as a method for coating and forming a magnetic recording layer having a thickness of 0.5 μm or less in a dry film state, see Japanese Patent No. 2581
975 and JP-A-6-296917 have been proposed. This coating method and apparatus are
By coating a non-magnetic lower layer in an appropriate amount by applying a suitable coating layer to prevent mixing of air, the upper magnetic recording layer can be thinly coated to about 2 μm in a wet state. .

Japanese Patent No. 2942938 and the like disclose a low-viscosity lower-layer coating solution applied to a web in advance and scrape off a part of the lower-layer coating solution to prevent air from being mixed in with the magnetic recording layer. A method of applying a coating liquid has also been proposed.

[0006]

However, even if the above-mentioned conventional coating method and apparatus are used, if the thickness of the magnetic recording layer is reduced to 2 μm or less in a wet state, the magnetic recording layer cannot be coated. There is a disadvantage that streaks of equal pitch are generated on the surface. The occurrence of the streak has caused the performance of the magnetic recording medium as a product to deteriorate.

[0007] This is not limited to the application of the magnetic recording layer, but also in the application other than the manufacture of the magnetic recording medium, the so-called wet-on-wet method in which the upper layer is applied before the lower layer coating solution dries. In the case where two or more coating layers are applied by multi-layer coating, particularly when the thickness of the layers other than the lower layer in a wet state is reduced to 2 μm or less, stripes at an equal pitch are generated on the surface of the coating layer.

[0008] From such a background, even if the thickness of the layers other than the lower layer in contact with the web in a wet state is made to be 2 µm or less, preferably 1 µm or less, a plurality of layers having a plurality of layers applied thereon have uniform pitches. There is a demand for an application method that does not require the application.

The present invention has been made in view of such circumstances, and even if a thin coating layer, particularly a coating layer of 2 μm or less, preferably 1 μm or less in a wet state, is formed by high-speed coating, the coating can be performed by a multi-layer coating. It is an object of the present invention to provide a coating method capable of suppressing generation of uniform pitch streaks on the surface of a layer and a product thereof.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method in which a continuously moving flexible support and an edge surface of a coating head are pressed relatively to each other and a plurality of flexible supports supplied into the coating head are provided. A coating method in which the coating liquid is discharged from each slit discharge port formed in the width direction of the flexible support on the edge surface through each slit and wet-on-wet multi-layer coating the flexible support. In at least one of the plurality of layers to be multi-layer coated, a binder resin having a number average molecular weight of 5,000 or more contained in a coating liquid forming at least the uppermost layer has a concentration of 5% or less with respect to a solvent contained in the coating liquid. It is characterized by becoming.

Further, in order to achieve the above object, the present invention provides a method for relatively pressing a continuously running flexible support against an edge surface of a coating head, and further comprising one or more coatings supplied into the coating head. A coating method in which a liquid is discharged from each slit discharge port formed on the edge surface through each slit and is applied to the flexible support in a wet-on-wet manner, wherein the coating of the flexible support is performed. A lower layer is formed by applying an excess lower layer coating solution to the surface in advance, and while the lower layer coating solution is in a wet state, a part of the lower layer coating solution is scraped off at the upstream edge portion of the edge surface. In a coating method in which two or more coating liquids are stacked on the lower layer and multilayer coated,
At least the binder resin having a number average molecular weight of 5000 or more contained in the coating liquid forming the uppermost layer among the plurality of layers to be multi-layer coated has a concentration of 5% or less with respect to the solvent contained in the coating liquid. It is characterized by doing so.

Further, in order to achieve the above object, the present invention provides a coated product manufactured by the coating method according to any one of claims 1 to 3.

According to the present invention, when a multi-layer coating is performed on a flexible support with a coating head having a plurality of slits by wet-on-wet, or an excess lower layer coating solution is previously applied to the coating surface of the flexible support. A lower layer is formed by coating, and while the lower layer is in a wet state, a part of the lower layer is wet-on-wet while being scraped off at an upstream edge portion of an edge surface of a coating head having one or more slits. In the case of applying, among a plurality of layers to be multi-layer applied,
At least the binder resin having a number average molecular weight of 5,000 or more contained in the coating liquid for forming the uppermost layer has a concentration of 5% or less with respect to the solvent contained in the coating liquid. Thus, even when a coating layer having a thickness of 2 μm or less is formed by high-speed coating, it is possible to suppress the occurrence of uniform pitch streaks on the coating layer surface. In addition, a coated product manufactured by using the above-described coating method can obtain a coated layer having a thickness of 2 μm or less in a wet state and having no equal pitch streaks. Can significantly improve the performance of the magnetic recording medium.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a coating method and a coated product according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram showing an example of an extrusion type coating apparatus to which a coating method of the present invention is applied. A plurality of types of coating liquids are applied to a web by a single coating head having a plurality of slits. This is an example in which multilayer coating is performed by a so-called wet-on-wet method. In this case, when the coating layer to be formed is a magnetic recording layer, two different magnetic coating solutions may be used, but the lower layer coating solution to be the lower layer (layer in contact with the web) is for non-magnetic undercoating or low-viscosity precoating. May be used.

As shown in FIG. 1, a coating apparatus 10 mainly includes a web 12 that runs continuously, a coating head 14 that applies a coating liquid to the web 12, and an upstream side in the web running direction across the coating head 14. Provided respectively on the downstream side,
It comprises a pair of guide rollers 18, 18 on which the continuously running web 12 is mounted. Then, the coating liquid is applied to the web 12 while the continuously running web 12 and the edge surface 16 of the coating head 14 are relatively pressed against each other.

The coating head 14 has a web 1 inside.
2, a plurality of cylindrical pocket portions 22, 2 parallel to the width direction.
2 are formed, and the respective pocket portions 22 and the respective coating solution tanks 24, 24 for storing the plurality of coating solutions are connected by pipes 28, 28 via fixed-quantity liquid sending pumps 26, 26.
As a result, the coating liquid is supplied from each coating liquid tank 24 to each pocket portion 22 and is expanded to a width corresponding to the coating width. The two coating liquids which have been spread in the pocket portions 22 rise up the respective slits 30 and 30 and respectively form the respective slit discharge ports 30 formed on the edge surface 16.
A and 30A.

FIG. 2 is an enlarged view of the tip of the coating head when one coating head 14 has two slits. The coating head 14 has three slits 30
Edge surface 1
Reference numeral 6 designates a front edge surface 32A, a lower layer doctor edge surface 34A, and an upper layer doctor edge surface 36A for each of the blocks 32, 34, and 36 in order from the distillation side in the running direction of the web 12. The front edge surface 32A is formed to have a length (length in the web running direction) in the range of 0.1 to 30 mm, and the surface shape may be a flat surface or an arc having a certain curvature. You may. Further, the doctor edge surfaces 34A and 36A for the lower layer and the upper layer are formed to have a length (length in the web running direction) of 0.5 to 20 mm, and the surface shape is an arc shape having a certain curvature. Or a combination of an arc and a plane. In addition, the slit 30 is usually 0.03
It is formed with a slit width of about 2 mm. In FIG. 2, the front edge surface 32A has a curvature R1 mm, and the lower and upper doctor edge surfaces 34A and 36A have a curvature R2m.
m and a slit width of 0.2 mm. And the slit 30 on the upstream side in the web running direction
, A lower layer liquid (coating liquid to be a lower layer) is discharged, and an upper layer liquid (coating liquid to be an upper layer) is discharged from the slit 30 on the downstream side. Form A. In this case, a gap may be formed between the web 12 and the front edge surface 32A on the upstream side in the web traveling direction of the coating head 14, and the upper layer liquid may be applied in a state where the lower layer liquid overflows into the gap. .

FIG. 3 shows that one coating head 14
FIG. 4 is an enlarged view of a tip end portion of a coating head having two slits. The coating head 14 includes four blocks 32, 34, 35, and 36 with three slits 30 interposed therebetween.
The edge surface 16 is arranged in order from the running direction of the web 12 for each of the blocks 32, 34, 35, 36 in the order of the front edge surface 3
2A, a lower layer doctor edge surface 34A, a middle layer doctor edge surface 35A, and an upper layer doctor edge surface 36A. The preferred forms of the length, surface shape, and slit width of each edge surface 32A, 34A, 35A, 36A are the same as those in FIG. In FIG. 3, the front edge surface 3
2A has a flat shape, the lower layer doctor edge surface 34A has a curvature R4 mm, and the middle layer and upper layer doctor edge surfaces 35A.
A, 36A is curvature R6mm, slit width is 0.2m
This is an example where m is set.

As a coating apparatus to which the coating method of the present invention is applied, a different coating liquid is discharged from a plurality of slits 30 formed in one coating head 14 as described above to perform a wet-on-wet multi-layer coating. 10 (Patent 2
No. 581975, Japanese Patent Publication No. 6-49171, Patent 293
In addition to this, as shown in FIG. 4, each slit 3 is formed by using a plurality of coating heads 14 and 14.
A coating apparatus 10 that discharges a coating liquid from 0 and 30 and applies the coating liquid while the coating liquid is in a wet state to perform multi-layer coating (Patent 26)
No. 46265) can be used.

Further, as shown in FIG. 5, the lower liquid slit 30 is located on the upstream side of the continuously running web 12.
a, a lower layer liquid is ejected from a, a lower layer is previously formed on the coating surface of the web 12, and while the lower layer is in a wet state, a part of the lower layer liquid is scraped off by the front edge portion 32a on the downstream side while the lower layer liquid is scraped off. A wet-on-wet coating device 10 (see Japanese Patent No. 2684486 and Japanese Patent No. 2601367) in which the upper layer liquid is discharged from the slit 30b for application and is applied over the lower layer. In this case, it is possible to separately provide a lower layer liquid application head and an upper layer liquid application head. However, if they are integrally configured as one application head, the apparatus can be made compact and the lower layer liquid formed in advance can be formed. It is suitable for so-called wet-on-wet coating in which the upper layer liquid is applied while the lower layer coating liquid is in a wet state. In FIG. 5, the lower layer liquid slit 30 is shown.
The slit width of a is 0.3 mm, the lower layer doctor edge surface 31a has a curvature R8 mm, the upper layer front edge surface 32 has a curvature R6 mm, the upper layer doctor edge surface 34 has a curvature R10 mm, and the slit width is 0.2 mm.
This is an example of the configuration.

However, in any of the above-described coating apparatuses 10, if the coating is performed by the conventional coating method, the upper layer and / or the intermediate layer of the multilayer coating layer A excluding the lower layer in contact with the web 12 is used. If the thickness of the layer is to be applied to a thickness of 2 μm or less in a wet state, there is a disadvantage in that stripes of equal pitch are generated on the surface of the coating layer A.

The inventor of the present invention has conducted intensive studies on the causes of the occurrence of streaks of equal pitch, and as a result,
It has been found that the number average molecular weight contained in the coating solution strongly depends on the concentration of the binder resin having a number of 5000 or more with respect to the solvent.

The coating method of the present invention is based on the above-mentioned knowledge, and is applied when a plurality of coating solutions are applied in multiple layers by a so-called wet-on-wet method from a plurality of slits, or an excessively A lower layer is formed by applying a lower layer coating solution, and while the lower layer is in a wet state, a part thereof is scraped off at an upstream edge portion of an edge surface of a coating head having one or more slits. However, in the case of multi-layer coating in a so-called wet-on-wet method, among a plurality of layers to be multi-layer coated, at least a binder resin having a number average molecular weight of 5000 or more contained in a coating liquid forming an uppermost layer is applied to a coating liquid. The coating liquid was constituted so that the concentration with respect to the contained solvent was 5% or less.

In this case, more preferably, for all other coating liquids in the uppermost layer, the concentration of the binder resin having a number average molecular weight of 5,000 or more contained in the coating liquid with respect to the solvent contained in the coating liquid is preferred. It is good to make it 5% or less.

The coating apparatus 10 constructed as described above
Then, by applying the coating method of the present invention, the web 1
Even when high-speed coating is performed so that the thickness of the upper layer and / or the intermediate layer except for the lower layer in contact with 2 is 2 μm or less in a wet state, uniform pitch streaks can be suppressed on the surface of the coating layer A. Thereby, the coating performance can be improved, so that not only can the product quality be improved, but also the productivity can be improved.

A coating product manufactured by a so-called wet-on-wet method using the coating method of the present invention, in which at least one layer other than the lower layer among the multilayer-coated layers is wet thickness. Formed to 2 μm or less, preferably 1 μm or less, can exhibit excellent performance. For example, in the case of a magnetic recording layer, the performance of a product magnetic recording medium can be significantly improved.

The above-mentioned coating method of the present invention is generally used at a coating speed of 30 to 1500 m / min, but is not limited to this. Web 1
2 is preferably run with a tension of 5 to 50 kgf per lm width of the web from the viewpoints of running stability and uniform pressing to the coating head 14, and it is necessary to appropriately adjust the tension according to coating conditions. Further, the distance between the guide roller 18 and the coating head 14 is preferably set to about 50 to 300 mm. It is preferable that the guide roller 18 and / or the coating head 14 be configured to be movable so that the angle of penetration or separation of the web 12 from the coating head 14 can be adjusted according to the coating conditions. Further, in the case of the web 12 having low rigidity, the guide rollers 18 are used to suppress wrinkles.
It is also preferable to use an expander roll, a crown roll, a concave roll, or the like.

As the web 12, polyethylene terephthalate, polyethylene-2,6-naphthalate,
Plastic films such as cellulose diacetate, cellulose triacetate, cellulose acetate propionate, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyimide, polyamide, etc. or paper, laminated paper, metal foils such as aluminum and copper, and glass and ceramics etc. There is, but is not limited to this.

The web 12 has a width of 0.1 to 3 m, a length of 1000 to 100,000 m, and a thickness of 0.5 to 100 μm.
Is common but not limited to this. The web 12 may be provided with an underlayer such as an adhesive layer in advance and dried and cured, or may be provided with another functional layer in advance. . As the binder resin used in the present invention, a vinyl chloride copolymer (for example, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, vinyl chloride / vinyl acetate / acrylic) Acid copolymers, vinyl chloride / vinylidene chloride copolymers, vinyl chloride / acrylonitrile copolymers), ethylene / vinyl acetate copolymers, cellulose derivatives such as nitrocellulose resins, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, Epoxy resins, phenoxy resins, polyurethane resins (for example, polyester polyurethane resins, polyether polyurethane resins, polycarbonate polyurethane resins) and the like can be mentioned.

Particularly preferred among the above binder resins are vinyl chloride copolymers. These vinyl chloride copolymers are used as base polyvinyl chloride copolymers, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl maleate copolymer, Vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinylidene chloride-vinyl acetate-maleic acid copolymer, vinylidene chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid-vinyl alcohol copolymer Vinyl chloride copolymers such as polymers, and these copolymers may be saponified.

Examples of the method of introducing a functional group include
For example, the following method can be used. Above
Hydroxy or carboxy of the copolymer to be the base
Of some of the hydroxyl groups or saponification
A part of the droxyl group is converted to one N
React with the CO groups and convert the remaining NCO groups_TwoH group, SO _Three
M group, OPO_ThreeM_TwoHydroxyl compounds containing groups
And can be obtained by reacting

The method for introducing these groups is not limited to the method described above. Examples of synthesis of these resins are described in JP-A-61-89207, JP-A-61-10660, and JP-A-61-10660.
No. 40744 and No. 59 No. 8126. The resins that can be used in the present invention are not limited to these synthetic examples.

As the polyurethane resin, in the case of a polyester polyurethane resin, the main chain skeleton may be any of polyester, polyether, polyester ether, polycaprolactone, polycarbonate and the like. Most commonly used is polyester. Specific examples of the dibasic acid used for this include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, dodecane diacid, maleic acid, fumaric acid, itaconic acid, trimethyladipate, and hexahydro acid. Examples include phthalic acid, tetrahydrophthalic acid, phthalic acid, isophthalic acid and the like. As a method for introducing a functional group into the polyurethane resin, a method in which a functional group is introduced into these dibasic acids, for example, 5-sodium sulfoisophthalic acid,
-Reacting potassium sulfoisophthalic acid with a polyol.

[0035]

EXAMPLES The preparation method of the coating solution used for the test is as follows.

The compositions shown in Tables 1 to 10 were mixed in a kneader, dispersed using a sand mill, and the obtained liquid was filtered using a filter having an average pore size of 1 μm. Coating solutions A to J were prepared.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

[Table 9]

[0046]

[Table 10]

Example 1 Using a coating apparatus having one coating head having two slits as shown in FIG.
Two layers (lower layer and upper layer) were coated on a μm polyethylene terephthalate web at a coating speed of 400 m / min. At this time, the thickness of the lower layer is fixed at 10 μm or 5 μm (wet state) to reduce the thickness of the upper layer, and the upper layer thickness (wet state) at which equal pitch streak occurs and the coating for forming the lower layer and the upper layer The relationship between the concentration of the binder resin with respect to the solvent contained in the liquid and the number average molecular weight of the binder resin was examined.

Here, with respect to the binder resin having a number average molecular weight of 5,000 or more contained in the coating liquid, the concentration of the binder resin with respect to the solvent contained in the coating liquid is 5% or less. This is referred to as “the coating solution after improvement”, and the coating solution that does not satisfy the conditions is referred to as “the coating solution before improvement”.

FIG. 6 shows the coating conditions and the evaluation results. FIG.
The item “Evaluation” is an evaluation as a coated product, and the symbol ◎ indicates that the upper layer thickness at which equal pitch streaks occur is 1 μm as the target.
(Wet state) with sufficient margin, ○: target 1 μm (wet state) possible, ×: target 1 μm
(Wet state) was not possible, and 以上 or more was considered acceptable.

As can be seen from FIG. 6, condition 2, condition 3, condition 5, condition 6, and condition 10 were such that the upper layer solution was a test section of the "coating solution after improvement" and the lower layer solution was a test section of "coating solution before improvement". , Condition 1
In each of the coated products of No. 2, the upper layer thickness (wet state) of the limit at which equal pitch streaks occur is 2 μm or less, and the target 2
The thickness could be reduced to less than μm.

Further, both the upper layer solution and the lower layer solution are conditions 8, 9 and 14 which are the test sections of the "modified coating solution".
In each of the coated products, the upper layer thickness (wet state) at which uniform pitch streaks were generated was 1 μm or less, and the upper layer could be thinned with a sufficient margin to the target of 12 μm or less.

On the other hand, in the test sections of conditions 1, 4 and 11, which are the test sections of the “coating solution before improvement” for both the upper layer liquid and the lower layer liquid, all of the test sections were at the limit where uniform pitch streaks were generated. The upper layer thickness (wet state) is 5.0 μm and 5, respectively.
The thickness was 2 μm or 4.3 μm, and it could not be thinned to 2 μm or less.

In the test sections of conditions 7 and 13 in which the upper layer liquid is the test liquid of the “coating liquid before improvement” and the lower liquid liquid is the test plot of the “coating liquid after improvement”, uniform pitch streaks are generated. Limit upper layer thickness (wet state) is 3.6 μm and 3.2, respectively.
μm, and could not be thinned to the target of 2 μm or less.

As can be seen from the results, in order to reduce the thickness of the coating layer so as not to generate uniform pitch streaks, at least the uppermost layer (that is, the upper layer) of a plurality of layers to be multilayer-coated is included. The binder resin needs to have a concentration of 5% or less with respect to the solvent contained in the coating liquid for forming the uppermost layer.

Further, under the condition 14, the coating solution J as the upper layer solution contains 4% of a binder resin of a vinyl chloride copolymer having a number average molecular weight of 20,000 with respect to the solvent,
6% of a binder resin of a polyester urethane resin having a number average molecular weight of 3000 is contained in the solvent, and the total concentration of the two binder resins is 10%, which exceeds 5%. However, the upper limit thickness (wet state) at which equal pitch streaks occur was 0.2 μm, which was a good result. This shows that the binder resin having a number average molecular weight of less than 5,000 in the coating liquid does not adversely affect the thickness of the coating layer so as to reduce the thickness of the coating layer so that the pitch streaks do not occur.

From the above, in order to make the layer thin so as not to generate uniform pitch streaks, at least the binder resin having a number average molecular weight of 5,000 or more contained in the coating liquid for forming the uppermost layer should be coated with the coating liquid. It is necessary that the concentration with respect to the solvent contained in the solvent be 5% or less. (Example 2) Using a coating apparatus having one coating head having three slits as shown in FIG. 3, three layers (lower layer, lower layer,
Middle layer, upper layer) Coating is performed, and coating liquid G is used as a lower layer liquid.
(Binder resin concentration: 4%), the thickness was fixed at 5 μm (wet state), and the thickness of the middle layer or the upper layer was changed.

FIG. 7 shows that the thickness of the middle layer liquid is fixed at 3 μm (wet state) and the thickness of the upper layer is made thinner.
The relationship between the concentration of the binder resin and the number average molecular weight of the binder resin with respect to the solvent contained in each of the middle and upper coating liquids was examined.

FIG. 8 shows that the thickness of the upper layer liquid is fixed at 3 μm (wet state) and the thickness of the middle layer is made thinner.
The relationship between the concentration of the binder resin and the number average molecular weight of the binder resin with respect to the solvent contained in each of the middle and upper coating liquids was examined.

◎, 図, × in the evaluation of FIGS. 7 and 8
Are the same as in FIG.

First, as can be seen from FIG. 7 in which the thickness of the upper layer was changed, the upper layer solution and the middle layer solution of condition 15 were the “coating solution before improvement”, and only the lower layer solution was the test solution of “the coating solution after improvement”. In the case of (1), the upper layer thickness (wet state) at which critical pitch streaks occur was 3.0 μm, and the upper layer could not be thinned to the target 2 μm or less.

Conditions 16 and 17 When the upper layer solution and the lower layer solution were the "coating solution after improvement" and the middle layer solution was the test group "the coating solution before improvement", the upper layer thickness at which equal pitch streaks occurred was determined. (Wet state) was 1.2 μm and 1.0 μm, respectively, and the upper layer could be thinned to the target 2 μm or less.

In the case where the middle layer solution and the lower layer solution of the condition 18 are the “coating solution after improvement” and the upper layer solution is the test group of “the coating solution before improvement”, the upper layer thickness (wetting State) was 2.3 μm, and it was not possible to reduce the thickness to a target of 2 μm or less.

Conditions 19 and 20 When the upper layer solution, the middle layer solution, and the lower layer solution were all in the “improved coating solution” test section, the upper layer thickness (wet state) at which equal pitch streaks were generated was 1.0 μm each. , 0.2 μm, and the upper layer
m with a sufficient margin.

Next, as can be seen from FIG. 8 in which the thickness of the middle layer was changed, the upper layer solution and the lower layer solution of the condition 21 were the “coating solution after improvement”, and the middle layer solution was the test solution of “the coating solution before improvement”. In the case of (1), the middle layer thickness (wet state) at which critical pitch streaks occur was 2.0 μm, and the middle layer could be thinned to the target 2 μm or less.

Condition 22 When the upper layer solution, the middle layer solution, and the lower layer solution are all in the “improved coating solution” test section, the middle layer thickness (wet state) at which equal pitch streak occurs is 0.3 μm, Was able to be thinned sufficiently below the target of 2 μm or less. (Example 3) A lower layer was previously formed on the coating surface of the web on the upstream side in the web running direction, and while the lower layer was in a wet state, a part of the lower layer was scraped off by the front edge on the downstream side while the upper layer liquid was scraped off. Using a coating apparatus shown in FIG. 5, two layers (a lower layer and an upper layer) were applied to a 60 μm-thick polyethylene-2,6-naphthalate web at an application speed of 200 m / min. In this case, the thickness of the lower layer is 6 μm or 1 μm.
(Wet state), the upper layer thickness is reduced by thinning the upper layer thickness.
The relationship between the concentration of the binder resin with respect to the solvent contained in the coating solution for forming the lower layer and the upper layer, and the number average molecular weight of the binder resin was examined.

FIG. 9 shows the coating conditions and the evaluation results. FIG.
, ○, and × in the evaluation of are the same as in FIGS. 6, 7, and 8.

As can be seen from FIG. 9, the upper layer liquid of condition 23 is the “coating liquid before improvement” and the lower layer liquid is the “coating liquid after improvement”.
In the case of the test plot, the upper layer thickness (wet state) at which equal pitch streaks occur was 2.2 μm, and the upper layer could not be thinned to the target 2 μm or less.

Conditions 24, 25, and 26 When both the upper layer solution and the lower layer solution were the "improved coating solution" test sections, the middle layer thickness (wet state) at which uniform pitch streaks were generated was 0.1%. The thickness was 9 μm, 0.3 μm, and 0.5 μm, and the upper layer could be made thinner with a sufficient margin below the target of 2 μm or less.

In the present embodiment, an embodiment of a coating apparatus in which a plurality of coating heads are used to discharge a coating liquid from respective slits, and to apply a multi-layer coating while the coating liquid is in a wet state is described. However, similar effects can be obtained when the coating method of the present invention is performed using the coating apparatus.

[0070]

As described above, according to the coating method of the present invention, even when a thin coating layer, particularly a coating layer having a thickness of 2 μm or less in a wet state, is formed by high-speed coating, the surface of the coating layer can be formed. It is possible to suppress the occurrence of equal pitch streaks. Thereby, the coating performance can be improved, so that not only can the product quality be improved, but also the productivity can be improved.

In the coated product of the present invention, the thickness of at least one layer other than the lower layer in the wet state can be made as thin as 2 μm or less out of the multi-layer coated layers. In this case, the performance of the magnetic recording medium as a product can be significantly improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an example of a coating apparatus to which a coating method of the present invention is applied.

FIG. 2 is an explanatory view illustrating a coating apparatus for coating a web with one coating head having two slits.

FIG. 3 is an explanatory view illustrating a coating apparatus for coating a web with one coating head having three slits.

FIG. 4 is an explanatory view illustrating a coating apparatus that performs multi-layer coating using a plurality of coating heads.

FIG. 5 is an explanatory view illustrating a coating apparatus that applies a lower layer liquid to a coating surface of a web in advance and then scrapes off a part of the lower layer liquid to apply a middle layer liquid and an upper layer liquid in a multilayer manner.

FIG. 6 is an explanatory diagram for explaining the results of Example 1.

FIG. 7 shows the result of Example 2, and illustrates the case where the thickness of the upper layer is changed.

FIG. 8 shows the result of Example 2, and illustrates the case where the thickness of the middle layer is changed.

FIG. 9 is an explanatory diagram illustrating a result of Example 3.

[Explanation of symbols]

10: coating device, 12: web, 14: coating head, 1
6 ... Edge surface, 18 ... Guide roller, 22 ... Pocket part, 24 ... Coating liquid tank, 26 ... Material liquid sending pump, 30
... Slit, A ... Coating layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B05C 5/02 B05C 5/02 (72) Inventor Hideaki Takekuma 1-2-1 Ogimachi, Odawara-shi, Kanagawa No. Fuji Photo Film Co., Ltd. F-term (reference) 2H023 EA01 4D075 AC02 AC09 AC92 AC96 AE06 CA48 DA04 DB31 EA05 EB15 EB52 EC30 4F041 AA12 AB01 BA13 CA02 CA12 CA22 5D112 AA05 BB08 BB09 BB13 CC02 CC08

Claims (5)

[Claims] The present invention is characterized in that a continuously running flexible support and an edge surface of a coating head are relatively pressed against each other, and a plurality of coating liquids supplied into the coating head are applied to the edge surface of the coating head through respective slits. In a coating method of discharging from each slit discharge port formed in a width direction of the flexible support and performing wet-on-wet multi-layer coating on the flexible support, at least the A coating method, wherein the concentration of a binder resin having a number average molecular weight of 5000 or more contained in a coating liquid for forming an upper layer with respect to a solvent contained in the coating liquid is 5% or less. 2. The method according to claim 1, wherein said flexible support is continuously pressed against an edge surface of said coating head, and one or more coating liquids supplied into said coating head are supplied to said edge surface through respective slits. A wet-on-wet coating on the flexible support by discharging from each of the slit discharge ports formed on the flexible support, wherein an excess lower layer coating solution is previously applied to the coating surface of the flexible support. And forming a lower layer, and while the lower layer coating solution is in a wet state, a part thereof is scraped off at the upstream edge portion of the edge surface, and the one or more coating solutions are stacked on the lower layer. In the coating method of multilayer coating, among the plurality of layers to be multilayer-coated, at least a binder resin having a number average molecular weight of 5,000 or more contained in a coating liquid for forming an uppermost layer is based on a solvent contained in the coating liquid. A coating method characterized in that the concentration is 5% or less. 3. A binder resin having a number average molecular weight of 5,000 or more contained in the coating liquid of all other coating liquids in the uppermost layer has a concentration of 5% or less with respect to a solvent contained in the coating liquid. 3. The coating method according to claim 1, wherein the coating method is performed. 4. A coated product produced by the coating method according to claim 1. 5. The coated product according to claim 4, wherein at least one layer other than the lower layer in contact with the flexible support in the multi-layer coated layer has a thickness of 2 μm or less in a wet state. To apply products.