JPH07171487A - Strip coating method - Google Patents

Abstract

PURPOSE:To eliminate the nonuniform film thickness due to longitudinal streaks at the time of simultaneously coating a strip with plural coating solns. by a head having >=2 coating soln. passage outlets by specifying an edge gap and the value for the viscosity of the solns. over the straight length of a die part. CONSTITUTION:A coating head 1 contains the coating soln. feed passages 2a and 2b formed in parallel in the width direction of a strip F and the slit coating soln. passages 3a and 3b communicating with the former passages. The die parts 4e and 4f parallel to the strip F are formed close to the front edges 4c and 4d of the outlets of the passages 3a and 3b. In this case, the ratio of the gap DELTA formed between the edgy rear ends 4a and 4b and/or the lower edge 5 of the head 1 and the surface of the strip F on the head side to the straight length L of the die part satisfies log mu>2.4-(1/1250)X(L/DELTA), where mu is the viscosity at the coating soln. temp. of 25 deg.C and at the shear rate of 1 sec<-1> and coating is carried out under such conditions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously coating and laminating a plurality of layers on one surface of a strip. In particular, the present invention relates to a coating method for coating a multilayer recording medium at the same time, in which each layer is coated on the surface of the belt-shaped material with a uniform film thickness.

[0002]

2. Description of the Related Art In recent years, various recording media have become more sophisticated,
Along with this, what has conventionally been made to express various functions by a single layer is being shifted to the direction of further improving the function as a recording medium by separating each function by making a thin film multilayer. In order to achieve these multi-layers, a sequential coating method in which one layer of a coating solution having various functions is coated, dried, and then repeated is adopted. In this method, the coating and drying steps are repeated. Therefore, the productivity is poor, and if it is attempted to complete the multi-layer coating in one step in one line, the apparatus becomes large and the equipment cost becomes high.
Therefore, a method of simultaneously forming multiple layers in one coating and drying step has been desired.

As this method, as shown in FIG. 11, the coating solution flowing out in multiple stages along the inclined slide surface 10 of the slide hopper 9 having a plurality of coating solution flow path outlets is transferred to the surface of the strip in a laminated state, The slide application method to apply,
As shown in FIG. 12, a method of applying a plurality of coating liquids simultaneously by running a strip along the coating liquid flow path outlet of a coating head having a plurality of coating liquid flow channels 11 and a plurality of doctor edge portions 12 is provided. Was proposed.

However, in the method of transferring and coating the coating liquid onto the surface of the strip along the inclined slide surface, the fluidity of the coating liquid becomes unstable on the inclined slide surface because the coating liquid has a high viscosity. It is easy to cause unevenness of the coating film and unevenness of the film thickness, and the coating liquid contains an organic solvent so that it is easy to dry, and it is difficult to maintain the smoothness of the inclined surface. Was not suitable for multi-layer coating due to reasons such as unsuitability.

On the other hand, in a system in which a strip is made to travel along the coating solution outflow surface of a coating head having a coating solution flow path and a doctor edge, and multiple layers are simultaneously coated, a fine swing occurs in the traveling strip. Therefore, there were many problems such that the uniformity of the film thickness of each layer, the smoothness of the layer interface and the coating film surface were not ensured, and the coating unevenness occurred when the width of the strip was wide. .

Therefore, as an epoch-making device for solving these problems, a coating device as shown in FIGS. 1 and 2 has been proposed. In FIG. 1, the coating head 1 arranged and fixed above the strip F has coating liquid supply passages 2a and 2b formed inside the strip F parallel to the width direction of the strip F and a slit-shaped coating liquid connected to the coating liquid supply passages 2a and 2b. It has channels 3a and 3b. The coating liquid flow paths 3a and 3b are opened on the surface of the coating head 1 facing the strip F and form the coating liquid flow path outlet.

The rear end edges 4a, 4b of each coating solution flow path outlet are formed in the shape of a right angle, and the front end edge 4 of the flow path is formed.
c and 4d are formed in an arc shape having a predetermined curvature.
Further, the front lower edge 5 of the coating head 1 in the running direction of the strip is also formed in an edge shape like the rear edges 4a and 4b of the coating liquid flow path outlets. Moreover, between the front end edge 4c of the outlet of the first flow path 3a and the rear end 4b of the outlet of the second flow path 3b, and the front end edge 4d of the exit of the second flow path 3b and the strip running direction of the coating head 1. The surface facing the strip-shaped article between the front lower edge 5 is the die sections 4e and 4f parallel to the strip-shaped article, and the straight lengths of the die sections are La and Lb, respectively.

A plurality (two in the illustrated example) of rotating rolls 6a and 6b are arranged on the facing surfaces of the coating head 1 with the strip F interposed therebetween, and the coating head 1 is provided near the inlet and outlet of the strip. On the belt running path of the free rotation guide roll 7a,
7b is provided. Two rotating rolls 6 of this embodiment
As shown in FIGS. 1 and 2, a and 6b are edge-shaped rear end edges 4 of the coating liquid flow path outlet opening forward in the belt running direction.
b and the edge-shaped lower end edge 5 on the front surface of the coating head 1 in the traveling direction of the belt-like material, the center lines thereof are located respectively. By providing the rotating rolls 6a and 6b, the distance Δ between the edge-shaped rear end edge and the upper surface of the belt-like material can be precisely controlled, and the coating film Ta having the predetermined wet thick films t ₁ and t ₂ can be obtained. , Tb are formed.

[0009]

However, it is still difficult to say that the film thickness is uniform and the smoothness is not sufficient. Particularly, in the case of applying a dispersion solution containing inorganic fine particles, as shown in FIGS. As shown, the coating film becomes uneven,
Problems such as vertical stripe-shaped unevenness in film thickness occur when they are stacked in multiple layers.

Therefore, according to the present invention, not only in the case of wide width and high speed but also in the case of applying any dispersion solution, there is no vertical stripe-like thickness unevenness, and each layer is applied smoothly and uniformly at the same time. It is an object of the present invention to propose a method for applying a band-shaped material that can be formed.

[0011]

In order to solve these problems, the present invention provides a plurality of coating liquids on one surface of a belt running along a head having two or more slit-shaped coating liquid flow path outlets. Is applied at the same time, and a plurality of layers are laminated.
Alternatively, a gap Δ formed between the lower edge of the front surface of the coating head and the surface of the belt-shaped coating head on the side of the coating head, a ratio L / Δ of the straight length L of the die portion to the gap Δ, a temperature of the coating liquid of 25 ° C., and a shear rate. The main constitution is a coating method for a strip-shaped article, which is characterized in that the viscosity μ at 1 sec ⁻¹ satisfies 1 og μ> 2.4− (1/1250) × (L / Δ).

[0012]

The strip-shaped material is guided with a predetermined gap from the coating head by free-rotating guide rolls provided on the strip-shaped material supply side and the discharge side of the coating head, and the coating liquid of the coating head is sandwiched by the strip-shaped material. It travels while being contacted and supported by the surface of each rotating roll arranged opposite to the flow path outlet.

The coating liquid flowing out from each coating liquid flow path is sequentially applied to the surface of the strip-shaped material from the strip-shaped material supply side in the strip-shaped material traveling direction,
Stacked. First, the first coating film flows out from the gap between the edge-like rear end edge of the coating liquid flow path outlet at the tail end of the coating head and the surface of the strip-shaped material. By setting the value for the viscosity μ in the range according to the present invention, the first coating film Ta is formed while gradually reducing the wet film thickness, that is, while causing a contraction flow.

Next, the second coating film which is applied and laminated on the first coating film also has the next leading edge-like rear edge and the first coating film applied on the surface of the strip in the same manner. Although it flows out from the gap of the second coating liquid by setting the value of the gap and the straight length of the die portion with respect to the viscosity μ of the second coating liquid within the range according to the present invention, the second coating liquid is compressed while the second coating liquid is generated. Coating film Tb is formed. In this manner, the film thickness of each layer is determined and smoothed, and the multi-layer coating is sequentially performed.

[0015]

The details of how the method of the present invention was derived will be described below. When the dispersion solution containing the inorganic fine particle pigment and the like was applied by the above-mentioned apparatus, a non-uniform coating film as shown in FIGS. 3 and 4 was formed.

In the case of FIG. 3, the cause is the second
It is presumed that the reverse flow of the coating liquid occurs and the coating liquid is turbulent, which causes a plurality of vertical stripes and impairs the uniformity of the coating film. In addition, in the case of FIG. 4, since the first coating liquid does not contract, a stagnation portion of the coating liquid is formed in the vicinity of the trailing edge 4b of the edge strip, and the turbulence of the coating liquid due to the occurrence of overflow in this portion causes It is presumed that the uniformity was impaired.

The major factors underlying these are:
It is considered that smooth contraction does not occur, or that even if the contraction occurs, the ratio of the gap Δ to the wet film thickness t, that is, the contraction ratio t / Δ is increased.

Therefore, based on the above consideration, the gap formed between the trailing edge 4b of the edge of the coating liquid flow path and the surface of the strip coating head is Δa, and the straight length of the die is L. Using a head, a coating liquid having a viscosity (hereinafter abbreviated as viscosity) μ at a coating liquid temperature of 25 ° C. and a shear rate of 1 sec ⁻¹ is discharged at an outflow pressure P, and a wet film thickness on the upper surface of a belt running at a velocity V. After forming t ₁ , the factors related to the formation of the coating film were examined.

As a result, the factors for reducing the contraction ratio t ₁ / Δ and obtaining a uniform coating film without generation of vertical stripes are as follows.
In addition to the outflow pressure P, the viscosity μ of the coating liquid, the gap Δ, the straight length L of the die portion, and the traveling speed V of the belt-like material are clarified. As Δ and P increase, the contraction ratio also increases, and It was confirmed that the uniformity of the coating film when coated and laminated on the substrate was impaired, while if the values of μ, V and L were increased, a uniform multilayer film surface could be obtained by reducing the contraction ratio. It was

From the above, the following is considered. That is, the wet film thickness t at the time of application is determined by the discharge amount flowing out from the gap Δ, and thus the contraction ratio t / Δ is determined. Gap outflow amount Q from the delta is runoff Qa (Qa = b · Δ · V / 2) and the outflow amount by outflow pressure P Qb (Qb = b · Δ 3 · P / 12 · caused by the travel movement of the web μ
-It is given as the sum of L) and is estimated from these, which is in good agreement with the above-mentioned examination results.

When the contraction ratio is large, that is, when it exceeds 0.8, as shown in FIGS. 3 and 4, a throat portion or a retention portion is formed in the flow path of the second coating liquid, and inversion occurs at these portions. Disturbance of the coating liquid occurs due to the flow or vortex, and the uniformity is impaired. On the other hand, when the contraction ratio is in the range of 0.5 to 0.8, the flow path of the second coating solution is formed smoothly, the disturbance of the coating solution is prevented, and a uniform coating film is obtained. .

From the above, it can be understood that it is extremely important to suppress the contraction ratio to be low, in other words, to increase the viscosity μ of the coating liquid in order to form a multilayer coating film. However, the coating liquid used for the recording material and the like is inorganic fine particles,
Since it is a dispersion liquid containing an inorganic pigment, the viscosity is remarkably reduced as the shear rate increases. However, the shear rate inside the die shown in FIG. 2 is estimated to be about 1000 to 10000.
It is as large as sec ^-1, and this value becomes even larger under high-speed thin film. Therefore, the coating liquid containing the inorganic pigment is a solution whose viscosity change does not depend on the shear rate (Newtonian flow solution).
It is extremely difficult to reduce the contraction ratio as compared with.

However, in addition to the viscosity μ, the gap Δ and the die portion straight length L are considered as factors affecting the contraction ratio, and therefore the relationship between these and the coating state was examined.

As a result, the graph shown in FIG. 5 was obtained.
This is a graph showing the results of multi-layer coating as a model with the viscosity of the coating liquid μ on the vertical axis (logarithmic axis) and the L / Δ ratio on the horizontal axis. The ratio is small, and it shows the range where a coating layer with good uniformity without vertical stripes during multi-layer coating can be obtained. In zone II, the contraction ratio exceeds 0.8, and a uniform multi-layer coating film can be obtained. The range is not shown.

From this graph, the straight line A = log μ> 2.
It becomes clear that the coating film is divided into a good coating film region and a non-uniform coating film region at the boundary of 4- (1/1250) × (L / Δ). It can be seen that by setting the part straight length L, it becomes possible to apply a dispersion liquid containing inorganic fine particles or the like, the viscosity of which significantly decreases when the shear rate increases.

In addition to the dispersion liquid containing the above-mentioned inorganic fine particles, as a coating liquid suitable for the method of the present invention, each layer is
A system containing a polymer and a solvent in which the polymer is soluble,
Further, there are systems containing a monomer, a system containing an additive for imparting functionality to these systems, and a system in which inorganic fine particles or organic fine particles, pigments, dyes, etc. are added to these solutions. Although its viscosity can be used in a wide range as shown in FIG. 5, it is 1000 cps to 1000 cps.
It is particularly effective in the range of 00 cps. In addition, the film thickness after drying of the coating film by the method of the present invention is 1 to
It is effective for forming a relatively thin film of 30 μm, but especially 2 to
10 μm is preferred. As the belt-like material, a sheet or film of synthetic resin having good surface smoothness, or synthetic paper can be used, and specific examples thereof include synthetic resin sheets such as polyester, polycarbonate, polyethylene teflate, and synthetic paper. Furthermore, a laminated paper in which these are laminated can also be used.

Experimental examples are shown in Table 1 below to support the above-mentioned examination results.

[0028]

[Table 1]

As a first coating liquid, a coating liquid in which polymethylmethacrylate resin was dissolved in methylethylkent, and calcium oxide as an inorganic pigment was added in the same amount as that of the resin to change the solid content concentration variously. Prepared. As the second coating liquid, a polyester resin was dissolved in methyl ethyl kent to prepare a solution having a solid content concentration of 20%. A transparent polyester film was used for the belt-like material, coating was performed at a film running speed of 5 m / min, and the coating was dried to obtain a two-layer coating film having a thickness of 10 μm. The viscosity of the coating liquid is a value measured by a rotational viscometer at 25 ° C. and a shear rate of 1 sec ⁻¹ .

From this table and the graph in FIG. 5, the viscosity μ and L /
In Examples 1 to 7 in which the Δ ratio is included in the range of I zone in the graph, a uniform coating film was obtained, and in Comparative Examples 1 to 5 in which the Δ ratio was not included in the range of I zone, vertical stripes were generated in the second layer. However, it can be seen that a good coating film could not be obtained. That is, from these results, it was confirmed that the set value of the relationship between the viscosity of the coating liquid and the contraction ratio in the coating method of the present invention was appropriate.

The coating apparatus described above employs a coating head 1 as shown in FIG. 1, which is a typical embodiment, disposed above the strip F. It is also possible to install the coating bed 1 as shown in FIG. 6 below the strip F, and as shown in FIGS. 7 and 8, the strip F is caused to run vertically upward or downward and the coating head 1 It is also possible to install on the side of the strip.

Further, in the above coating apparatus, the rotating rolls are arranged so that the edge portions are opposed to each other with the strip-shaped material sandwiched therebetween. However, this rotating roll is not essential and does not have the rotating roll as shown in FIG. A coating device can also be used. Further, the shape of the surface of the coating head 1 facing the belt-like object is not only the secondary plane shape as shown in FIG. 1, but also a shape having a curved surface bulging toward the belt-like object F or the whole as shown in FIG. It is also possible to have a shape having a circular vertical cross section.

[0033]

As described above in detail, by setting the values of the viscosity and the contraction ratio of the coating liquid within the ranges disclosed in the method of the present invention, a wide width can be obtained when a multilayer thin film is coated on a strip. Not only in the case of high speed but also in the case of applying any dispersion solution, there is no vertical stripe-shaped film thickness unevenness, and each layer can be coated and formed smoothly and uniformly at the same time.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a typical coating device used for multilayer coating in the method of the present invention.

FIG. 2 is an enlarged view of the vicinity of the outlet of the coating liquid flow path in FIG. 1 when the multilayer thin film is favorably formed with a uniform film thickness.

FIG. 3 is an enlarged view of the vicinity of the outlet of the coating liquid flow path in FIG. 1 when the multilayer thin film is formed with a non-uniform film thickness.

FIG. 4 is an enlarged view of the vicinity of the outlet of the coating liquid flow path in FIG. 1 when the multilayer thin film is formed with a non-uniform film thickness.

FIG. 5 is a graph showing a model of an operation region for favorably performing multi-layer coating.

FIG. 6 is a vertical cross-sectional view showing another coating apparatus used for multilayer coating in the method of the present invention.

FIG. 7 is a vertical sectional view showing still another coating apparatus used for multi-layer coating in the method of the present invention.

FIG. 8 is a vertical sectional view showing still another coating apparatus used for multilayer coating in the method of the present invention.

FIG. 9 is a vertical sectional view showing still another coating apparatus used for multilayer coating in the method of the present invention.

FIG. 10 is a vertical sectional view showing still another coating apparatus used for multilayer coating in the method of the present invention.

FIG. 11 is a schematic view showing an example of a conventional coating device.

FIG. 12 is a schematic view showing an example of a conventional coating device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Coating head 2 Coating liquid supply path 3 Coating liquid flow path 4a, 4b Edge-shaped rear end edge 4c, 4d Exit part 4e, 4f Die part 5 Edge-shaped lower end edge 6a, 6b Rotating roll 7a, 7b Free rotation guide roll F Band-shaped Material Ta, Tb Coating film Δa, Δb Gap t ₁ , t ₂ Wet film thickness La, Lb Die part straight length Pa, Pb Outflow pressure

Claims (1)

[Claims] 1. A method for simultaneously coating a plurality of coating liquids on one surface of a strip running along a head having two or more slit-shaped coating liquid flow path outlets to laminate a plurality of layers. , A gap Δ formed between the edge-shaped rear end edge of each coating liquid flow path outlet and / or the front lower end edge of the coating head and the coating head side surface of the belt-shaped member, and the die portion straight length L with respect to the gap Δ. Ratio L / Δ, coating liquid temperature 25 ° C and shear rate 1s
A method for applying a belt-like material, characterized in that the application is performed under the condition that the viscosity μ at ec ^-1 satisfies the following formula. 1 ogμ> 2.4- (1/1250) × (L / Δ)