JP2009050746A - Coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating apparatus and a coating method capable of stably carrying out coating for a long time without film thickness fluctuation caused by a change in the property of a coating liquid, without an increase in coating defects resulting from agglomeration or the like of the coating liquid, and without causing a streak and an uneven thickness of a coating film, even if the coating liquid contains particles larger than the thickness of a newly formed undried coating film. <P>SOLUTION: The coating method for coating a moving substrate with a coating liquid containing particles having a diameter larger than the thickness of a newly formed wet coating film is characterized by overlaying a plurality of coating liquids on the substrate, provided that at least one of the coating liquids is free of the particles described above. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating liquid coating apparatus and a coating method including particles having a particle size larger than the wet film thickness immediately after coating.

  Conventionally, a coating liquid containing particles having a particle size larger than the wet film thickness in an undried state immediately after coating, for example, coating of a light diffusion layer of a light diffusion sheet used for a backlight of a liquid crystal display device (practical plan) No. 2539491) has used a known comma roll coating device and reverse roll coating device.

  However, these coating devices apply the coating solution from the open reservoir to the support, and most of the coating solution applied to the roll is collected and reused without being applied. For general use, a highly volatile solvent-based coating solution will evaporate rapidly during coating, causing changes in coating film thickness due to changes in coating solution properties and increased coating failure due to the occurrence of aggregation, etc. Stable application was difficult.

  For this reason, it is necessary to frequently stop the application in a short time and replace it with a new application liquid, perform filtration again to remove foreign matter, or adjust the concentration of the application liquid by adding a solvent. Productivity decreased due to increased losses and increased man-hours.

  As a coating apparatus for solving these problems, an extrusion coating (extrusion coating) apparatus that directly coats a support with a coater die is known (Patent Documents 1 to 3). The following problems have also been known in the system containing.

  When this coating apparatus performs coating using a back roll, it is necessary to accurately set the gap between the support and the coater die (coater gap) to be twice or less the coating film thickness, and the coating film thickness is 30 μm or less. When applied to a thin light diffusion layer, the coater gap must be 60 μm or less, and there is a limit to the gap accuracy in the coating width direction.

  Also, when applying without using a back roll, press the edge part of the coater die against the support, and apply with a balance between the reaction force from the support and the holding power of the coating liquid between the support and the edge, The coater gap is almost the same as the coating film thickness. Coarse particles for diffusing light in the coating solution get caught in the coater gap, causing streak failure, or the coating solution gathers only around the coarse particles and the film thickness increases. A failure occurred that became thicker and the film thickness was uneven.

For these reasons, there has been no practical consideration.
Japanese Patent Laid-Open No. 02-251265 Japanese Patent Laid-Open No. 02-268862 JP 2004-136282 A

  In the present invention, the coating liquid containing particles larger than the film thickness in the undried state immediately after coating does not increase coating film thickness due to changes in coating liquid physical properties, increase in coating failure due to occurrence of aggregation, etc. It is an object of the present invention to provide a coating apparatus that can be applied stably over time and does not cause streak failure or uneven film thickness, and a coating method therefor.

The present invention has been achieved by the following.
1. A coating method for applying a coating liquid containing particles having a particle size larger than the wet film thickness immediately after coating to a traveling support, the coating liquid not containing the particles on at least one side of the coating liquid A coating method, wherein the liquid is layered and applied.
2. An apparatus for performing the coating method includes a front bar having a front edge surface and located upstream with respect to the traveling direction of the support, and a back bar having a back edge surface and downstream with respect to the traveling direction of the support. On the cross section of the apparatus for performing the coating method in the running direction of the support, on the downstream side of the front edge surface. A coating method, wherein a part of the back bar protrudes from the tangent of the front bar at the end, and the shape of the back edge surface satisfies the following condition 1 or condition 2.
(Condition 1)
A straight line passing through the downstream end of the front edge surface and the upstream end of the back edge surface, the X axis with the upstream end of the back edge surface as the origin, and the traveling direction of the support as the positive direction, In the XY plane where the straight line perpendicular to the origin is the Y axis with the direction from the back bar toward the support as the positive direction, the shape of the back edge surface in the plane has the following relationship: Has the formula.
y = a (x / Lb) ⁿ
(However, 0.1 ≦ a ≦ 1.0, 0.1 ≦ n ≦ 0.7,
x is a distance from the origin on the cross section, y is a value in the Y-axis direction on the cross section,
Lb is the distance from the origin of the projection point on the X axis of the back edge surface on the cross section,
It is 0.2 <= Lb <= 5.0 (mm). )
(Condition 2)
The shape of the back edge surface on the cross-section is such that the first arc, the second arc, and the third arc having different radii of curvature each having a center on the back bar side from the upstream end to the downstream end of the back edge surface. The arc is continuous.
3. An apparatus for performing the coating method includes two or three liquid reservoirs therein, slit portions extending from the respective liquid reservoir portions toward the liquid discharge portion, and all slits in the discharge portion. 1 or 2, wherein the single slit portion is a slit portion located between the front bar and the back bar. Application method.

  In the back rollless extrusion coating apparatus of the present invention, it becomes possible to adjust the flow of the coating liquid containing particles having a particle size larger than the wet film thickness immediately after coating from the slit portion to the edge portion, Since the coarse particles in the coating liquid are not caught in the coater gap, the object of the present invention is achieved. This effect is significant when the wet film thickness is 1 to 30 μm or less.

Hereinafter, embodiments of the present invention will be described.
<Coating solution>
The present invention is characterized in that the coating liquid contains particles having a particle size larger than the wet film thickness immediately after coating.

  Here, the wet film thickness immediately after coating refers to the film thickness in a state where the coating liquid is not dried at all immediately after being discharged from the slit portion of the coating apparatus and applied onto the support, and is included in the coating liquid. The particle size of the generated particles is not considered.

  The coating liquid of the present invention is characterized in that a coating liquid not containing particles is applied in multiple layers on at least one side of a main liquid containing particles. Therefore, the coating liquid consists of two or three layers as a whole. In the case of two layers, the upper layer liquid and main liquid, or the main liquid and lower layer liquid, and in the case of three layers, the upper layer liquid, main liquid and lower layer liquid are configured in this order. The upper layer refers to the coating layer farthest from the support to be coated.

  The upper layer liquid and the lower layer liquid do not include particles having a particle size larger than the wet film thickness immediately after coating, and the particles are added to the main liquid.

  The wet film thickness of the upper layer liquid is desirably 1/25 to 1/2 of the wet film thickness of the main liquid.

  If it is thinner than 1/25, the effect of applying the upper layer is reduced, and if it is thicker than 1/2, the projection of coarse particles in the main liquid layer is reduced, and the light diffusion effect is reduced in the light diffusion sheet, and the desired diffusion performance. Becomes lower.

  In the present invention, the upper layer liquid is applied at the same time, and in the portion sandwiched between the support and the edge, there is an upper layer liquid without coarse particles between the main liquid and the edge, so the coarse particles in the main liquid No longer touches the edge directly, causing streak failure due to the catching of coarse particles, and uneven scaly unevenness failure where the coating liquid gathers only around the coarse particles and the film thickness increases. Is considered.

  Although the effect can be obtained even if the viscosity of the upper layer liquid is equal to that of the main liquid, it is preferably higher. If the viscosity is higher than that of the main liquid, the velocity gradient generated by the movement of the support to the coating liquid sandwiched between the support and the edge is reduced in the upper layer portion where the viscosity is high. It is considered that the film thickness is increased, the distance between the support and the edge is increased, and the coarse particles are further hardly caught.

  The wet film thickness of the lower layer liquid is preferably 1/20 to 1/2 of the wet film thickness of the main liquid. If it is thinner than 1/20, the effect of applying the lower layer is reduced, and if it is thicker than 1/2, coarse particles in the main liquid layer bite into the lower layer and the protrusions become smaller. Thus, the desired diffusion performance is lowered.

  In the present invention, the lower layer liquid is applied at the same time, so that there is a lower layer without coarse particles between the main liquid and the support in the portion sandwiched between the support and the edge. Even if it contacts the edge, it is considered that the effect is obtained because the particles are less likely to be caught by moving to the lower layer side.

  Although the effect can be obtained even if the viscosity of the lower layer liquid is equal to the viscosity of the main liquid layer, it is preferably higher. If the viscosity is higher than the main liquid layer, the velocity gradient generated by the movement of the support to the coating liquid sandwiched between the support and the edge becomes smaller in the lower viscosity layer, so the lower layer in this area It is considered that the film thickness of the substrate becomes thick, the distance between the support and the edge increases, and the coarse particles become more difficult to catch.

  The wet film thickness of the coating solution to which the present invention can be preferably applied is 1 to 30 μm, preferably 3 to 25 μm.

  The dry film thickness of the main liquid layer after drying is 0.5 to 25 μm, and the dry film thicknesses of the upper layer and the lower layer are 0.01 to 13 μm.

  The wet film thicknesses of the upper layer liquid and the lower layer liquid can be appropriately determined in relation to the main liquid, and may be the same or different.

  The viscosity of the upper layer liquid, the main liquid and the lower layer liquid is 50 to 5000 cps (measured with a B-type viscometer) as the coating liquid viscosity at the temperature at the time of coating.

  The particles contained in the coating solution may be spherical or non-spherical. In the case of a spherical shape, the particle diameter refers to the diameter. The particle size is 3 to 50 μm, preferably 5 to 45 μm.

  As the particles, polymer particles such as polymethyl methacrylate particles and polystyrene particles, and inorganic particles such as titanium oxide and silica can be used as appropriate.

  The amount of particles contained in the coating solution is 1 to 30% by mass with respect to the entire coating solution, and 3 to 25% by mass as the solid content.

The coating liquid according to the present invention has a high viscosity when receiving a weak force (shear rate of 10 sec-1 or less) from the outside, and has a low viscosity when receiving a strong force (shear rate of 10,000 sec-1 or more). It may have what is called thixotropic property.
<Coating device>
1A is a perspective view of an embodiment of a coater head according to the present invention, FIG. 1B is a side view of FIG. 1A, and FIG. 1C is a cross-sectional view taken along PP of FIG. (D) is an enlarged view of the Q portion of (c), and other drawings in this specification correspond to the enlarged view of the Q portion of (c) unless otherwise specified. It is.

FIG. 2 shows an example of the coating apparatus according to the present invention, that is, the coating apparatus according to the configuration (1) of the present invention. The figure shows the front bar (1) at the downstream end (C) of the front edge surface. A part of the back bar (2) protrudes from the tangent line, and a straight line passing through the downstream end (C) of the front edge surface and the upstream end (A) of the back edge surface is defined on the back edge surface. An X axis with the upstream end (A) as the origin and the traveling direction (R) of the support (W) as the positive direction, and a straight line perpendicular to the X axis at the origin from the back bar (2) to the support In the XY plane when the Y direction is the positive direction, the shape of the back edge surface in the plane has the following relational expression.
y = a (x / Lb) ⁿ
(However, 0.1 ≦ a ≦ 1.0, 0.1 ≦ n ≦ 0.7,
x is a distance from the origin on the cross section, y is a value in the Y-axis direction on the cross section,
Lb is the distance from the origin of the projection point on the X axis of the back edge surface on the cross section,
It is 0.2 <= Lb <= 5.0 (mm). )
When increasing the coating speed, the angle θo formed by the X axis of the back edge surface and the slit (3) located between the front bar (1) and the back bar (2) is actually about −10 degrees to +30 degrees. However, in consideration of maintenance of the processing accuracy of the apparatus and a wide range of application conditions for obtaining good application properties, −10 to +20 degrees is preferable.

  3, 4 and 5 are examples of graphs showing the shape of the back edge surface according to Condition 1 of the present invention (provided that the projection length Lb = 1 on the X axis of the back edge surface).

  FIG. 6 is an example of a coating apparatus according to Condition 2 of the present invention, and a part of the back bar (2) protrudes from the tangent line of the front bar (1) at the downstream end (C) of the front edge surface. The shape of the back edge surface on the cross section is such that the curvature radii having centers at the back bar (2) side from the upstream end (A) to the downstream end (B) of the back edge surface are r1 and r2, respectively. , R3 arcs are continuous.

More specifically, in the coating apparatus according to the present invention, a straight line passing through the downstream end (C) of the front edge surface and the upstream end (A) of the back edge surface is defined as an upstream end (A) of the back edge surface. Is the origin, the running direction (R) of the support (W) is the positive direction, a straight line perpendicular to the X axis at the origin, and the direction from the backbar (2) toward the support is the positive direction In the XY plane when the Y axis is taken, the shape of the back edge surface in the plane satisfies the following relational expression.
0.2 ≦ Lb ≦ 5.0 (mm)
0 ≦ x1 / Lb ≦ 0.5
0.2 ≦ x2 / Lb ≦ 0.8
−0.5 ≦ Hb / Lb ≦ 0.5
0.05 ≦ r1 ≦ 2.0 (mm)
0.5 ≦ r2 ≦ 5.0 (mm)
6.0 ≦ r3 ≦ 30.0 (mm)
(Where x1 <r1, x2-x1 <r2, Lb-x2 <r3, r1 is the radius of curvature of the first arc, r2 is the radius of curvature of the second arc, and r3 is the radius of curvature of the third arc) X1 is the length of projection on the X axis of the connection point between the first arc and the second arc on the cross section, and x2 is the length of the second arc on the cross section. The length of the projection on the X axis of the connection point with the third arc, Lb is the distance from the origin of the projection point on the X axis of the back edge surface on the cross section, Hb is the distance from the origin of the projection point on the Y-axis of the back edge surface on the cross section (however, Hb has a negative sign when located on the negative side of the Y-axis))
In FIG. 7, the angle (θ1) between the tangent line of the first arc and the tangent line of the second arc at the connection point (b1) between the first arc and the second arc is within 5 degrees. And the angle (θ2) formed by the tangent line between the second arc and the third arc at the connection point (b2) between the second arc and the third arc is within 5 degrees. It is.

  It has been known that the shape of the back edge surface having a plurality of curvature radii is effective particularly when the particle size is small (the major axis is 0.15 μm or less) like metal magnetic powder. Application to a coating solution containing particles having a particle size larger than the wet film thickness has become possible as a result of trial and error.

  In particular, it is preferable that the three radii of curvature gradually increase from the upstream end to the downstream end of the back bar (2). That is, the relationship 2 × r1 <r2 <1/2 × r3 is satisfied.

  Further, it is preferable that the length Lb of the back bar projected on the X axis becomes shorter as the coating speed increases. Specifically, 3 mm or less is preferable.

  Hb / Lb, which is a ratio of the distance Lb from the origin of the point projected on the X axis to the downstream end (B) of the back bar and the distance Hb from the origin of the point projected on the Y axis, is −0.5. To 0.5.

  Further, the angle formed by the joint portions having a plurality of radii of curvature is preferably 1 degree or less in consideration of occurrence of coating failure.

  FIG. 8 shows that two or three liquid reservoirs in the present invention, slits extending from the respective liquid reservoirs toward the liquid discharge part, and all slits merge in the vicinity of the discharge part. It is sectional drawing of the coating device which has a single slit part comprised as mentioned above.

  In the extrusion type coating apparatus of the present invention, the angle θ between the slit 6 extending from the liquid reservoir 4 in the direction of the liquid discharger and the slit 7 extending from the liquid reservoir 5 in the direction of the liquid discharger is 5 °. As mentioned above, it is preferable to make it 50 degrees or less, and it is desirable to usually make it 10-45 degrees.

  When the angle θ is 5 ° or less, it is difficult to reveal the processing accuracy of the coating apparatus due to the structure, and thus uneven coating tends to occur, which is not preferable.

  On the other hand, when the angle θ is 50 ° or more, the interface between the two liquids is disturbed, and the upper and lower liquids are likely to be mixed.

  Furthermore, it is preferable that the length L of the slit 3 after the slit 6 and the slit 7 merge to form a single slit is 50 mm or less.

Usually, L is preferably 0 to 30 mm, and exceeding 50 mm is not preferable because the interface between the two liquids is disturbed and the upper and lower liquids are likely to be mixed. A single slit may be formed at the point where L = 0, that is, the slit 6 and the slit 7 just join at the discharge portion 8 of the coating liquid.
<Support>
The coating liquid of the present invention is applied by discharging the coating liquid from a fixed coating device onto a support that runs from the front bar to the back bar.

  As the support, a plastic film can be preferably used. As the plastic film, films of polyethylene terephthalate, polyamide, polyimide, cellulose acetate, polycycloolefin, and the like can be used.

  As a film thickness, a thing of 5-350 micrometers can be used, Preferably, it is 30-200 micrometers.

Before applying the coating solution on the support, surface treatment such as corona discharge may be performed.
<Application method>
In this invention, the coating liquid which concerns on this invention can be favorably apply | coated by using the said coating device.

  As the coating speed, 20 to 300 m / min is applied, and preferably 30 to 200 m / min. As application | coating temperature, it is 10-40 degreeC, Preferably it is 15-30 degreeC.

Hereinafter, the effect of the present invention is illustrated by examples.
Example 1
In a liquid crystal display, a light diffusing layer of a light diffusing sheet material used as a light diffusing plate for uniformly diffusing light of a backlight was produced by the apparatus and method of the present invention.
<Coating solution>
<Main liquid>
・ Coating agent with acrylic beads (particle size 5 to 40 μm) (“RUB coating agent”, manufactured by Dainichi Seika Co., Ltd.) 100 parts by mass ・ Curing agent “PTC LN curing agent” (manufactured by Dainichi Seika Co., Ltd.) 5 parts by mass Methyl ethyl ketone 50 parts by mass The viscosities were 250 cps with a B-type viscometer and 200 cps (1000 1 / sec) and 180 cps (1000000 1 / sec) with a Rotovisco viscometer (manufactured by Harke).
<Upper layer liquid and lower layer liquid>
-Coating agent without acrylic beads ("RUB coating agent", manufactured by Dainichi Seika Co., Ltd.) 100 parts by mass-Methyl ethyl ketone 30 parts by mass The viscosity was 700 cps with a B-type viscometer.

  Using the coating apparatus (coater) described in Table 1, the coating solution was coated at a rate of 50 m / min so that the wet layer thickness of the upper layer solution was 1 μm, the main solution was 10 μm, and the lower layer solution was 5 μm at 25 ° C. On a 175 μm polyethylene terephthalate film, simultaneous multilayer coating was applied with a coating width of 1000 mm and a coating length of 5000 m.

  The dry film thickness after drying was 0.8 μm for the upper layer, 5 μm for the main liquid layer, and 4 μm for the lower layer, respectively.

The results are shown in Table 1. In Examples 1-12 and 1-24 and Comparative Example 1-2, a coating apparatus having a single circular arc back edge with a curvature radius of 7.5 was used.
<Applicability evaluation method>
<Line failure>
All streak failures that occurred during coating were counted and converted to the number of occurrences per 1000 m.
<Square unevenness failure>
Visually observe the entire length of the coating and check whether it occurs. Judged by the criteria of.

A: Not generated B: Partially weak but no problem level C: Partially weak but no problem level D: Full length weak but no problem level E: Partially strong level F: Strongly generated over the entire length <Coating yield>
The film thickness after coating was measured every 100 m, and the part where the film thickness did not enter 8.0 to 10.0 μm was regarded as a defective product, and evaluation was performed with a non-defective product rate (%).

Example 2
Using the coating solution used in Example 1, the same coating test as in Example 1 was performed. The coating apparatus is as described in Table 2. The results are shown in Table 2.

Example 3
Using the coating solution used in Example 1, a three-layer coating test was performed using the coating apparatus shown in FIG. L was 12 mm and θ was 15 °.

  In Example 3-12 and Comparative Example 3-2, a coating apparatus having a single circular arc back edge with a curvature radius of 7.5 was used. The results are shown in Table 3.

(A) The perspective view which cut and showed a part of one embodiment of the extruder concerning this invention, (b) Side view, (c) Sectional drawing, (d) Cross-sectional enlarged view. It is sectional drawing of the coating device concerning this invention. It is a graph showing the shape of the back edge surface concerning this invention. It is a graph showing the shape of the back edge surface concerning this invention. It is a graph showing the shape of the back edge surface concerning this invention. It is an example of sectional drawing of the coating device concerning this invention. It is another example of sectional drawing of the coating device concerning this invention. It is sectional drawing of the coating device which has two liquid storage parts concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front bar 2 Back bar 3 Slit 4, 5 Liquid storage part 6, 7 Internal slit 8 Discharge part r1, r2, r3, r4 Curvature radius showing the shape of bar W Support A, B, C, D Bar surface position

Claims (3)

  A coating method for applying a coating liquid containing particles having a particle size larger than the wet film thickness immediately after coating to a traveling support, the coating liquid not containing the particles on at least one side of the coating liquid A coating method, wherein the liquid is layered and applied. An apparatus for performing the coating method includes a front bar having a front edge surface and located upstream with respect to the traveling direction of the support, and a back bar having a back edge surface and downstream with respect to the traveling direction of the support. On the cross section of the apparatus for carrying out the coating method in the running direction of the support, on the downstream side of the front edge surface, and having a back bar positioned and a slit portion positioned between the front bar and the back bar A coating method, wherein a part of the back bar protrudes from the tangent of the front bar at the end, and the shape of the back edge surface satisfies the following condition 1 or condition 2.
(Condition 1)
A straight line passing through the downstream end of the front edge surface and the upstream end of the back edge surface, the X axis with the upstream end of the back edge surface as the origin, and the traveling direction of the support as the positive direction, In the XY plane where the straight line perpendicular to the origin is the Y axis with the direction from the back bar toward the support as the positive direction, the shape of the back edge surface in the plane has the following relationship: Has the formula.
y = a (x / Lb) ⁿ
(However, 0.1 ≦ a ≦ 1.0, 0.1 ≦ n ≦ 0.7,
x is a distance from the origin on the cross section, y is a value in the Y-axis direction on the cross section,
Lb is the distance from the origin of the projection point on the X axis of the back edge surface on the cross section,
It is 0.2 <= Lb <= 5.0 (mm). )
(Condition 2)
The shape of the back edge surface on the cross-section is such that the first arc, the second arc, and the third arc having different radii of curvature each having a center on the back bar side from the upstream end to the downstream end of the back edge surface. The arc is continuous.   An apparatus for performing the coating method includes two or three liquid reservoirs therein, slit portions extending from the respective liquid reservoir portions toward the liquid discharge portion, and all slits in the discharge portion. 3. The apparatus according to claim 1, further comprising: a single slit portion formed by joining together, wherein the single slit portion is a slit portion positioned between the front bar and the back bar. Application method.

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