JP2002086050A - Coating method and coated product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of equal-pitch stripes on the surface of a coating layer when the thin coating layer (2 μm or less in a wet state) is formed by multiple-layer coating at a high speed. SOLUTION: In the case of multiple-layer coating of a web 12 with a coating head 14 having a plurality of slits 30, a travelling speed of the web 12, an average high shear viscosity of a plurality of, or one or more coating liquids, and a surface tension of the utmost upper coating layer of multiple coating layers are adjusted in such a way that a cappillary number Ca calculated by an equation Ca=U μ/σ (wherein U [m/sec] is the travelling speed of the web 12; μ [Pa.sec] is the average high shear viscosity of a plurality of, or one or more coating liquids; σ [N/m] is the surface tension of the utmost upper coating layer of the multiple coating layers) is set up to satisfy 0.1<Ca<4, and then the coasting is carried out.

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 method for coating a thin and uniform coating layer on a flexible support (hereinafter referred to as "web") in a multilayered manner at a high speed. The present invention relates to a coating method and a coated product.

[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 to be reduced to 0.2 μm or less (2 μm or less in a wet state), the magnetic recording layer will not be coated. There is a disadvantage that streaks of equal pitch are generated on the surface of the layer. 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. When two or more coating layers are applied in multiple layers, particularly when the thickness of the layers other than the lower layer in a wet state is to be set to 2 μm or less, streaks of a uniform pitch are generated on the surface of the coating layer.

[0008] From such a background, the wet thickness of a plurality of layers coated in a multilayer is set to 2 µm or less, preferably 1 µm or less.
There is a demand for a coating method that does not generate streaks of equal pitch even when the thickness is less than μm.

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 the above, the traveling speed of the flexible support is U [m / sec], the average high shear viscosity of the plurality of coating fluids is μ [Pa · sec], and the uppermost coating fluid of the multi-layered coating is When the surface tension is σ [N /
m], the running speed, the average high shear viscosity, and the surface of the uppermost layer coating solution such that the capillary number Ca calculated by the following formula, Ca = Uμ / σ, satisfies 0.1 <Ca <4. It is characterized in that the application is performed while adjusting the tension.

According to the present invention, when a multi-layer coating is carried out on a flexible support with a coating head having a plurality of slits, or when an excess coating solution for the lower layer is previously applied to the coating surface of the flexible support, When the multi-layer coating is performed while a part of the lower layer is wet while the lower layer is scraped off at the upstream edge portion of the edge surface of the coating head having one or more slits, the flexibility is increased. The traveling speed of the support is U [m / sec], the average high shear viscosity of a plurality or one or more coating solutions is μ [Pa · sec], and the surface tension of the uppermost coating solution of the multilayer coating layer is σ [N / M], the following equation:
The capillary number Ca calculated by Ca = Uμ / σ is 0.
The running speed, the average high shear viscosity, and the surface tension of the uppermost layer coating solution were adjusted so as to satisfy 1 <Ca <4, and coating was performed. Thus, 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, it is possible to suppress the occurrence of uniform pitch streaks on the coating layer surface. Therefore, a coated product manufactured by using the above-mentioned 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.

[0012]

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 the coating method of the present invention is applied. A single coating head having a plurality of (two in FIG. 1) slits applies thixotropic to a web. This is an example in which two types of coating liquids having properties are applied in multiple layers. 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 solution to the web 12, and an upstream side in the web running direction that sandwiches the coating head 14. Provided respectively on the downstream side,
A pair of guide rollers 1 for mounting a continuously running web
8 and 18. 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, two cylindrical pocket portions 22, 2 parallel to the width direction.
2 are formed, and the respective pocket portions 22 and the respective coating liquid tanks 24, 24 for storing the two types of coating liquids 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 the corresponding pocket portion 22 and spread to a width corresponding to the coating width. The two application liquids which have been spread in the pocket portions 22 rise up the respective slits 30 and 30 and respectively form the slit discharge ports 3 formed on the edge surface 16.
Discharge from 0A and 30A.

FIG. 2 is an enlarged view of the tip of the coating head 14. The coating head 14 is composed of three blocks 32, 34, and 36 with two slits 30 interposed therebetween. The front edge surface 32A, the lower layer doctor edge surface 34A, and the upper layer doctor edge surface 36A are sequentially arranged from the running direction of the web 12 for each of the layers 34 and 36.
It consists of. 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. Also, the slit 30 is usually 0.03 to 2 m
The slit width is about m. 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 R2 mm.
This is an example in which the slit width is set to 0.2 mm.

A lower layer liquid (a lower layer coating liquid) is discharged from the slit 30 on the upstream side in the web running direction.
An upper layer liquid (a coating liquid to be an upper layer) is discharged from the slit 30 on the downstream side, and a coating layer A including two layers, an upper layer and a lower layer, is formed on the surface of the web 12. In this case, the web 12
A gap may be formed between the coating head 14 and the front edge surface 32A on the upstream side in the web running direction, and the upper layer liquid may be applied in a state where the lower layer liquid overflows into the gap.
As described above, the advantage of overflowing the lower layer liquid is that when the lower layer liquid is applied very thinly, the entrainment of air entrained by the web 12 can be prevented and the web 12 is scraped due to contact between the front edge and the web 12. That is not to do.

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, as described above, a coating apparatus 10 that discharges different coating liquids from a plurality of slits 30 formed in one coating head 14 and performs multilayer coating (Japanese Patent No. 2581975). In addition to this, as shown in FIG. 4, a plurality of coating heads 14 are used to discharge a coating liquid from respective slits 30 and 30 to apply the coating liquid, as shown in FIG. It is possible to use a coating apparatus 10 (see Japanese Patent No. 2646265) in which the liquid is in a wet state, and the liquid is applied in multiple layers.

Further, as shown in FIG. 5, the lower layer liquid slit 30 located on the upstream side of the continuously running web 12 is provided.
a, a lower layer is formed on the coating surface of the web 12 in advance, and while the lower layer is in a wet state, a part of the lower layer is scraped off by the downstream front edge portion 32a. Slit 30b, middle liquid slit 30
c. A coating apparatus 10 that discharges the middle layer liquid and the upper layer liquid from the lower layer and coats the lower layer with the upper layer liquid (Japanese Patent No. 2684486, Japanese Patent No. 26013).
No. 67) can be used. In this case, it is possible to separately provide the coating head for the lower layer liquid and the coating head for the middle layer liquid and the upper layer liquid. However, if it is integrally configured as one coating head, the apparatus can be made compact and It is suitable for wet-on-wet coating in which the middle layer liquid and the upper layer liquid are coated while the lower layer coating liquid formed is in a wet state. In FIG. 4, the slit width of the lower layer liquid slit 30a is set to 0.3 mm, the taper angle of the edge 17 at the upstream edge of the lower layer liquid slit 30a is set to 20 °, and the intermediate layer liquid and the upper layer liquid are separated. This is an example in which the coating head 14a has a front edge surface with a curvature R3 mm, a middle layer doctor edge surface with a curvature R3 mm, an upper layer doctor edge surface with a curvature R2 mm, and a slit width of 0.1 mm.

However, in any of the above-described coating apparatuses 10, if the coating is performed by the conventional coating method, the thickness of the upper layer and / or the intermediate layer except for the lower layer in the coating layer A composed of multiple layers is reduced. Attempts to apply the coating to a thickness of 0.2 μm or less (2 μm or less in a wet state) have a drawback that streaks 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 the streaks of equal pitch, and found that the streaks of equal pitch are unstable phenomena occurring on the free surface downstream of the coating head 14 in the web running direction. And found that this unstable phenomenon is greatly affected by the number of capillaries in the entire coating solution.

The coating method of the present invention is based on the above-mentioned knowledge, and is used when a coating head having a plurality of slits is used for multi-layer coating on a web, or an excess coating solution for the lower layer is previously applied to the coating surface of the web. To form a lower layer, and while the lower layer coating liquid is in a wet state, a part thereof is scraped off at an upstream edge portion of a front edge surface of a coating head having one or more slits. In the case where one or more coating liquids are applied over the lower layer, the following formula (1)

[0024]

[Formula 1] Ca = Uμ / σ (1) It is configured such that the capillary number Ca calculated by (1) satisfies 0.1 <Ca <4 and is applied.

Here, U: The traveling speed of the web is [m /
Sec] μ: average high shear viscosity [Pa · sec] of a plurality or one or more coating liquids σ: surface tension [N / m] of the uppermost coating liquid of the multi-layer coated layers.

In addition, the average high shear viscosity is defined as
The shear rate of the coating solution forming each layer using a shear viscometer
10000 sec^-1And measure the viscosity at
Calculate the average viscosity by weighting with the thickness to be clothed
It was done. Specifically, for example, wet on
Liquid X with jet_Aμm, B solution to X_Bμm, liquid C _c
Solution A for multi-layer coating with a thickness of μm
The viscosity of μ_A, The viscosity of solution B_B, C viscosity μ_CWhen
Average high shear viscosity μ_AVEIs given by the following equation (2):

[0027]

[Number 2] mu _AVE = to be defined by _{(X A μ A + X B} μ B + X c μ C) / (X A + X B + X c) ... (2).

Further, the surface tension σ [N /
m] was used by measuring the surface tension of a solution containing a polymer binder having a molecular weight of 1,000 or less, a solvent, a lubricant, and a surfactant contained in the coating solution.

Then, the coating apparatus 10 configured as described above
By applying the coating method of the present invention, the thickness of the upper layer and / or the intermediate layer excluding the lower layer is reduced to a thin layer of 2 μm or less in a wet state, and the surface of the coating layer A even when coated at a high speed. Therefore, the occurrence of uniform pitch streaks can be suppressed. Thereby, since the coating performance can be improved, not only can the product quality be improved,
Productivity can be improved.

The coating product manufactured by the wet-on-wet method using the coating method of the present invention, and in particular, at least one layer other than the lower layer among the multilayer coated layers
When the two layers are formed to a thickness of 2 μm or less in a wet state, excellent performance can be exhibited. For example, in the case of a magnetic recording layer, the performance of a product magnetic recording medium can be significantly improved.

The inventor of the present invention has conducted intensive studies on the causes of the occurrence of the uniform pitch streaks. As a result, the occurrence of the uniform pitch streaks was reduced by the coating method for forming adjacent layers among a plurality of layers applied to the web 12 in multiple layers. It was found that the solution strongly depends on the difference in viscosity when high shear was applied between the liquids.

The coating method of the present invention is based on the above-mentioned knowledge, and is used when a plurality of coating solutions having thixotropic properties are coated in a multilayer by a so-called wet-on-wet method from a plurality of slits, or when a web is coated. Apply the excess lower layer coating solution on the surface in advance to form the lower layer,
When the lower layer is in a wet state, a part of the lower layer is scraped off at an upstream edge portion of an edge surface of a coating head having one or more slits, and a multilayer coating is performed by a so-called wet-on-wet method. The composition is such that the respective viscosities of a plurality of coating liquids are adjusted and applied so as to satisfy "the viscosity difference condition of the present invention" described in 3).

[0033]

−15 × 10 ⁻³ [Pa · sec] <μ _n−1 −μ _n <5 × 10 ⁻³ [Pa · sec] (3) In the formula (3), “the viscosity difference condition of the present invention” Μ _n : High shear viscosity [Pa · sec] of the coating liquid forming the n-th (n ≧ 2) layer from the flexible support among a plurality of layers to be multi-layer coated μ _n-1 : It is a high shear viscosity [Pa · sec] of a coating solution for forming a layer adjacent to the web side of the n-th layer.

Further, when the high shear viscosity of the first layer coating solution for forming the first layer closest to the web among a plurality of layers to be applied is represented by μ ₁ [Pa · sec], 4),

[0035]

It is preferable to adjust the viscosity of the first layer coating solution so as to satisfy μ ₁ <20 × 10 ⁻³ [Pa · sec] (4).

Here, the high shear viscosity originally means the viscosity of the coating liquid at the time of applying a high shear applied to the coating liquid between the tip of the coating head 14 and the web 12, but usually the shear rate at this time is Is extremely high, such as tens of thousands to millions of sec ⁻¹ , and in the present invention, the shear rate is 100
The viscosity of the coating liquid at 00 sec ^-1 is defined as the high shear viscosity.

The coating apparatus 10 constructed as described above
By applying the coating method of the present invention, 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 becomes 1 μm or less in a wet state, the surface of the coating layer A has a uniform pitch stripe. Can be suppressed. 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 particular, at least one layer other than the lower layer among the multilayer-coated layers is wet thickness. Formed to a thickness of 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-described coating method of the present invention is generally used at a coating speed of 30 to 1500 m / min, but is not limited thereto. The web 12 is desirably run at 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 web 12 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. In addition, the web 1 having low rigidity
In the case of 2, an expander roll, a crown roll,
It is also preferable to use 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. Yes, but 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. .

[0042]

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

In Examples 1 and 2, the coating stock solution A having the component composition shown in Table 1 was mixed in a kneader, dispersed using a sand mill, and the obtained solution was filtered using a filter having an average pore size of 1 μm. An appropriate amount of methyl ethyl ketone, toluene, butyl acetate, stearic acid, and butyl stearate were added to obtain upper layer solutions A1 to A8. Table 2 shows the high shear viscosity and surface tension of each liquid.

[0044]

[Table 1]

[0045]

[Table 2]

Further, the coating stock solution B having the component composition shown in Table 3 was mixed in a kneader, dispersed using a sand mill, and the obtained solution was filtered using a filter having an average pore size of 1 μm to obtain an appropriate amount of methyl ethyl ketone. Toluene, butyl acetate, stearic acid, and butyl stearate were added to obtain lower layer solutions B1 to B5. Table 4 shows the high shear viscosity of each liquid.

[0047]

[Table 3]

[0048]

[Table 4]

Example 1 Two types of coating solutions were used in which the upper layer solution of Table 2 and the lower layer solution of Table 4 were combined, and one coating head having two slits as shown in FIG. 2 was used. Multilayer coating was performed on a 6 μm-thick polyethylene terephthalate web by changing the coating speed, the type of coating liquid, and the coating conditions of the coating thickness using a coating device. Then, the presence or absence of the occurrence of equal pitch streaks on the coating layer surface at this time was evaluated.

FIG. 6 shows the coating conditions and the evaluation results. FIG.
In terms of the surface properties, ○ is good without occurrence of equal pitch streaks,
X means that there is a uniform pitch streak or unevenness and there is a defect.

As can be seen from FIG. 6, the number of capillaries C
Condition 1 where a is a test group satisfying 0.1 <Ca <4
(Ca number = 1.6), condition 2 (Ca number = 3.1), condition 7 (Ca number = 3.8), condition 8 (Ca number = 3.7), condition 9 (Ca number = 3. 8), condition 11 (Ca number = 0.5)
Regarding the surface properties of the coating layer, good results were obtained without generation of equal pitch streaks.

On the other hand, the condition 12 (the number of Ca = 0.1) in which the capillary number Ca is less than the lower limit of 0.1,
And condition 3 (Ca number = 4.7), condition 4 (Ca number = 6.2), condition 5 (Ca number = 4.6), condition 6 (Ca number) in which the capillary number Ca exceeds the upper limit of 4. Number = 4.2),
Regarding the surface property of the coating layer under the condition 10 (Ca number = 4.3), there were occurrence of uniform pitch streaks and unevenness, resulting in a defective result. (Example 2) In addition to the upper liquid A5 in Table 2 and the lower liquid B1 in Table 4, three coating liquids using A4 in Table 2 as an intermediate liquid were used, and the lower layer was previously formed on the coated surface of the web. Then, while the lower layer is in a wet state, the middle layer liquid and the upper layer liquid are applied while scraping off a part of the lower layer while using the coating apparatus of FIG.
Multilayer coating was performed on a 3.5 μm thick polyamide web by changing the coating speed, the type of coating solution, and the coating conditions of the coating thickness. Then, the presence or absence of the occurrence of equal pitch streaks on the coating layer surface at this time was evaluated.

FIG. 7 shows the coating conditions and the evaluation results. FIG.
In terms of the surface properties, ○ is good without occurrence of equal pitch streaks,
X means that there is a uniform pitch streak or unevenness and there is a defect.

As can be seen from FIG. 7, the number of capillaries C
Condition 1 where a is a test group satisfying 0.1 <Ca <4
3 (Ca number = 1.1), condition 14 (Ca number = 2.2),
Regarding the surface properties of the coating layer under the condition 15 (Ca number = 3.4), good results were obtained without any occurrence of equi-pitch streaks.

On the other hand, the condition 17 where the capillary number Ca is less than the lower limit of 0.1 (Ca number = 0.0)
9), the surface properties of the coating layer under the condition 16 (Ca number = 4.5) in which the capillary number Ca exceeded the upper limit value of 4 were all equal pitch streaks and unevenness, resulting in failure. .

Next, in Examples 3, 4, and 5, the coating stock solution A having the component composition shown in Table 1 was mixed in a kneader and then dispersed using a sand mill, and the obtained solution was filtered using a filter having an average pore size of 1 μm. Then, an appropriate amount of methyl ethyl ketone was added to obtain coating solutions A9 to A21. Table 5 shows the high shear viscosity of each liquid.

[0057]

[Table 5]

Further, the coating stock solution B having the component composition shown in Table 3 was mixed in a kneader, dispersed using a sand mill, and the obtained solution was filtered using a filter having an average pore size of 1 μm to remove an appropriate amount of methyl ethyl ketone. In addition, coating solution B6 ~
B18 was obtained. Table 6 shows the high shear viscosity of each liquid.

[0059]

[Table 6]

(Example 3) Two types of coating using the coating liquid shown in Table 5 and the coating liquid shown in Table 6 in combination using a coating apparatus having one coating head having two slits shown in FIG. The liquid was used, and two layers (lower layer and upper layer) were coated on a 16 μm-thick polyethylene terephthalate web at a coating speed of 600 m / min. Also, the lower layer thickness at this time is 6
The upper layer thickness (wet state), at which equal pitch streaks occur, is fixed at μm (wet state), and the viscosity difference between the coating solutions forming the lower and upper layers when high shear is applied. And examined the relationship.

FIG. 8 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.
0.5 μm (wet state) or less with sufficient margin (wet state), ○: target 1 μm (wet state) possible, ×: target 1 μm (wet state) impossible And ○ or more was regarded as a pass. Also, “0. Means that, when the supply amount of the coating liquid was continuously reduced, no uniform pitch streaks occurred until the moment when the flow rate became zero.

As can be seen from FIG. 8, a lower layer and an upper layer are formed.
The viscosity difference when applying high shear between the coating liquids to be applied,
A test group that satisfies the “viscosity difference condition of the present invention”.
20 (viscosity difference = 3.6 × 10^-3), Condition 21 (viscosity difference =
2.2 × 10^-3), Condition 22 (viscosity difference = 0.9 × 1)
0^-3), Condition 23 (viscosity difference = 0.2 × 10^-3), Condition 2
4 (viscosity difference = −3.9 × 10^-3), Condition 25 (viscosity difference =
−5.1 × 10^-3), Condition 26 (viscosity difference = −7.7 × 1)
0^-3), Condition 27 (viscosity difference = -10.7 × 10^-3), Article
Case 28 (viscosity difference = 14.1 × 10^-3), Condition 31 (viscosity
Difference = −6.0 × 10 ^-3), Condition 32 (viscosity difference = -4.
7 × 10^-3), Condition 33 (viscosity difference = −2.1 × 1)
0^-3), Condition 34 (viscosity difference = −0.2 × 10^-3),conditions
35 (viscosity difference = 1.3 × 10^-3), 38 (viscosity difference =-
2.8 × 10^-3), Condition 39 (viscosity difference = -2.7 × 10
^-3), Condition 40 (viscosity difference = -3.9 x 10)^-3), Condition 4
1 (viscosity difference = −4.3 × 10^-3))
It passed. In particular, all of the conditions except for ○ in conditions 40 and 41
And the upper layer is thinned to an extremely thin layer of 0.5 μm or less.
Could be stratified.

On the other hand, the difference in viscosity between the coating solutions forming the lower layer and the upper layer when high shear is applied is less than −15 × 10 ⁻³ [Pa · sec], which is the lower limit of the “viscosity difference condition of the present invention”. Condition 29 (viscosity difference = −20.4 × 10
^-3 ) and condition 30 (viscosity difference = -26.1 × 10 ^-3 ), the upper layer thickness at which equal pitch streaks are generated is
The thickness was 1.9 μm and 3.6 μm, and the upper layer could not be thinned to 1 μm or less. On the other hand, the viscosity difference when applying high shear between the coating solutions forming the lower layer and the upper layer,
5 × 10 ^-3 [Pa] which is the upper limit of the “viscosity difference condition of the present invention”
[Sec.]] (Condition 18 (viscosity difference = 7.9)
× 10 ⁻³ ), condition 19 (viscosity difference = 6.2 × 10 ⁻³ ), condition 36 (viscosity difference = 5.8 × 10 ⁻³ ), condition 37 (viscosity difference = 7.1 × 10 ⁻³ ). Indicates that the upper layer thicknesses at which critical pitch streaks occur are 5.0 μm, 2.1 μm, and 1 μm, respectively.
The thickness was 9 μm and 3.8 μm, and the upper layer could not be thinned to 1 μm or less in a wet state. Example 4 Using a coating apparatus having one coating head having three slits as shown in FIG. 3, a coating speed of 200 μm was applied to a 5.5 μm thick polyethylene terephthalate web.
Three layers (lower layer, middle layer, upper layer) were applied at m / min. At this time, the thickness was 6 μm using the coating solution B11 as the lower layer.
(Wet state) and the thickness of the upper layer is reduced to 2 μm (wet state) using the coating solution A14 for the middle layer to reduce the thickness of the upper layer. And the viscosity difference between the coating solutions forming the middle layer and the upper layer when high shear was applied.

FIG. 9 shows the coating conditions and the evaluation results. FIG.
In the evaluation of ×, 評 価, × are the same as in FIG.

As can be seen from FIG. 9, the viscosity difference between the coating solutions forming the middle layer and the upper layer when high shear is applied is as follows.
Condition 4 which is a test group that satisfies the “condition of viscosity difference of the present invention”
3 (viscosity difference = 2.2 × 10 ⁻³ ), condition 44 (viscosity difference = −
0.2 × 10 ⁻³ ), condition 45 (viscosity difference = −10.4 × 1)
Coating products 0 ^-3) are both a pass, could be thinned below a very thin layer 0.5μm upper layer even in the case of a three-layer coating.

On the other hand, the viscosity difference between the coating solutions forming the middle layer and the upper layer when high shear is applied is less than −15 × 10 ⁻³ [Pa · sec], which is the lower limit of the “viscosity difference condition of the present invention”. Condition 46 (viscosity difference = 16-1 × 10
^-3 ) The upper layer thickness (wet state) at which equal pitch streaks occur was 2.1 μm, and it could not be reduced to 1 μm or less. On the other hand, the viscosity difference between the coating solutions forming the middle layer and the upper layer when applying high shear is higher than 5 × 10 ⁻³ [Pa · sec], which is the upper limit of the “viscosity difference condition of the present invention”. 42 (viscosity difference = 6.7 × 10 ⁻³ )
The upper layer thickness at which uniform pitch streaks occur was 5.0 μm, and the upper layer could not be thinned to 1 μm or less. Example 5 Three layers (a lower layer, a middle layer, and a middle layer) were applied to a 3.5 μm-thick polyamide web at a coating speed of 100 m / min using a coating apparatus having one coating head having three slits shown in FIG. Upper layer) was applied. At this time, the thickness was fixed at 6 μm (wet state) using the coating solution B11 as the lower layer, and the thickness was 1 μm using the coating solution A17 as the upper layer.
(Wet state), the middle layer thickness is reduced by thinning the middle layer thickness (wet state)
The viscosity difference between the coating solutions forming the lower layer and the middle layer when applying high shear (referred to as first viscosity difference), and the viscosity difference between the coating solutions forming the middle layer and the upper layer when applying high shear (second viscosity) (Referred to as difference).

FIG. 10 shows the coating conditions and the evaluation results. ◎, 、, and × in the evaluation of FIG. 10 are the same as in FIGS. 8 and 9.

As can be seen from FIG. 10, both the first viscosity difference and the second viscosity difference are the test sections satisfying the “viscosity difference condition of the present invention”, and the condition 48 (first viscosity difference = 4.3). × 1
0 ⁻³ , second viscosity difference = −12.0 × 10 ⁻³ ), condition 49
(First viscosity difference = -10.2 × 10 ⁻³ , second viscosity difference =
2.5 × 10 ⁻³ ), condition 53 (first viscosity difference = −6.6)
× 10 ^-3 , the second viscosity difference = 2.5 × 10 ^-3 ) are all acceptable, and the coating method of the present invention is used even when the middle layer is thinned in three-layer coating. By this, 1μ
m or less.

On the other hand, while the second viscosity difference satisfies the “viscosity difference condition of the present invention”, the first viscosity difference is a condition 47 ( First viscosity difference = 6.9 × 10 ⁻³ , second viscosity difference = −14.6 ×
10 ⁻³ ), condition 51 (first viscosity difference = 10.5 × 1)
0 ⁻³ , second viscosity difference = −14.6 × 10 ⁻³ ), condition 52
(First viscosity difference = 7.9 × 10 ⁻³ , second viscosity difference = −
The middle layer thickness (wet state) at which equal pitch streaks of 12.0 × 10 ⁻³ ) are generated is 5.0 μm and 3.8 μm, respectively.
m and 2.4 μm, and the middle layer could not be thinned to 1 μm or less. On the other hand, the first viscosity difference satisfies the “viscosity difference condition of the present invention”, but the second viscosity difference is a test group which does not satisfy the “viscosity difference condition of the present invention”.
Viscosity difference = -12.5 × 10 ⁻³ , second viscosity difference = 8.4
The thickness of the middle layer (wet state) at which critical pitch streaks of (× 10 ⁻³ ) occur was 2.8 μm, and the thickness of the middle layer could not be reduced to 1 μm or less. Furthermore, the first viscosity difference and the second viscosity difference are conditions 50 (first viscosity difference = -16.1) which is a test group that does not satisfy the “viscosity difference conditions of the present invention”.
The middle layer thickness (wet state) at which a uniform pitch streak of × 10 ⁻³ and the second viscosity difference of 8.4 × 10 ⁻³ ) occurs is 3.2 μm.
m, and the thickness of the middle layer could not be reduced to 1 μm or less.

As described above, in the coated product manufactured by the coating method of the present invention, the thickness of at least one layer other than the lower layer in a wet state can be reduced to 1 μm or less.

In the present embodiment, an example in which the coating method of the present invention is performed using a coating apparatus having one coating head having two or three slits has been described. The coating liquid is discharged from each slit using the coating liquid, and the coating liquid is applied in a wet state while the coating liquid is applied in a multi-layer coating.Furthermore, the lower liquid is slit from the lower liquid slit located on the upstream side of the continuously running web. By discharging the liquid, a lower layer is formed in advance on the coating surface of the web, and while the lower layer is in a wet state, a part of the lower layer is scraped off at the front edge on the downstream side, and the slit for the middle liquid, the upper liquid The same effect can be obtained when the coating method of the present invention is performed using a coating apparatus that discharges the middle layer liquid and the upper layer liquid from the slit for application and coats the lower layer with the liquid.

[0072]

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, preferably 1 μm or less in a wet state, is formed by high-speed coating, the coating method can be used. Equal pitch streaks can be suppressed on the surface of the coating layer. 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, at least one layer other than the lower layer of the multi-layer coated layer can be made into a thin layer having a wet thickness of 2 μm or less, preferably 1 μm or less. For example, in the case of a magnetic recording layer, the performance of a product magnetic recording medium 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 of setting up 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 is an explanatory diagram illustrating a result of Example 2.

FIG. 8 is an explanatory diagram for explaining the results of Example 3.

FIG. 9 is an explanatory diagram illustrating a result of Example 4.

FIG. 10 is an explanatory diagram illustrating the results of Example 5.

[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

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hideaki Takekuma 1-2-1, Ogimachi, Odawara-shi, Kanagawa Prefecture F-Film Co., Ltd. F-term (reference) 2H025 AA18 AB14 AB17 EA04 4D075 AC04 AC72 AC94 AC96 AC99 AE23 CA22 CA24 CA47 CB03 DA04 DB06 DB07 DB13 DB14 DB18 DB36 DB38 DB48 DB53 DC16 DC18 DC21 DC24 DC28 EA05 EA10 EA45 EB15 EB35 EB52 EB56 4F041 AA12 AB01 BA05 BA56 CA02 CA12 5D112 AA04 CC02

Claims (1)

[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 in which a plurality of slits are formed in the width direction of the flexible support and the multi-layer coating is performed on the flexible support in a wet-on-wet manner, the traveling speed of the flexible support is set to U [m / Sec], the average high shear viscosity of the plurality of coating liquids is μ [Pa · sec], and the surface tension of the uppermost coating liquid of the multilayer-coated layers is σ.
[N / m], the capillary number Ca calculated by the following equation: Ca = Uμ / σ is equal to 0.
An application method characterized in that application is performed by adjusting so as to satisfy 1 <Ca <4.