JP6027809B2 - Coating method using slot die and method for producing functional film - Google Patents

Description

  The present invention relates to a coating method using a slot die for applying a low-viscosity coating agent onto a base film while reducing the pressure on the upstream side of the base film of the bead formed at the lip end of the slot die, and The present invention relates to a method for producing a functional film.

  Conventionally, as a method of forming a coating film on a base film, a slot die is brought close to the base film, and a coating agent is discharged from the tip of the slot die to apply the coating agent onto the base film. A coating method for a coating film is known.

  Since the coating method of the coating film by this slot die is suitable for high-precision coating, it is widely used for applications in which a coating agent is continuously applied to a base film with a uniform thickness. In order to stably form a coating film with a good appearance on the base film, depending on the properties of the coating agent such as the viscosity of the coating agent, static surface tension and the coating film thickness (wet film thickness) It is necessary to select optimum conditions such as the coating speed, the distance between the tip of the slot die and the base film (hereinafter sometimes referred to as a coating gap), the thickness and shape of the tip of the die lip. Is a coating having a specific relationship between the capillary number Ca calculated from the viscosity, static surface tension and coating speed of the coating agent and the value H / h obtained by dividing the coating gap H by the coating film thickness h. There has been proposed a coating method for applying a coating film under which the coating film having a uniform film thickness can be obtained with extremely little generation of streaks and unevenness by coating under the working conditions. Further, Non-Patent Document 1 examines the low flow rate limit due to the slot die using the film shape formula model (FPE model) and the finite element method model (FEM model) using the Navier-Stokes formula, It is described that a coating film having a good appearance can be obtained by coating under a coating condition in which the capillary number Ca and H / h are in a specific relationship. That is, when the number of capillaries Ca is on the vertical axis and H / h is on the horizontal axis, the boundary line between the stable region and the unstable region of the bead becomes a downwardly convex curve. It is described that a coating film with a stable appearance and a good appearance can be obtained. Here, the capillary number Ca is expressed by Ca = μ · V / σ. Μ represents the viscosity of the coating agent, σ represents the static surface tension of the coating agent, and V represents the coating speed.

However, if a low-viscosity coating agent is applied thinly to form a thin film on the base film, the bead volume is reduced, so that the stability of the bead tends to be impaired, and stable coating becomes difficult. As a method for solving this, the bead is kept stable and coated by reducing the pressure on the upstream side of the bead (upstream side in the conveyance direction of the base film). The coating conditions in the coating method for reducing the pressure on the upstream side of the bead are greatly different from the conventional coating method for coating film in which no pressure difference is provided between the upstream side and the downstream side of the conventional bead. Patent Document 2 describes that high-speed coating is possible and a thinner coating can be formed by simultaneously pressurizing the downstream side of the bead while reducing the pressure on the upstream side of the bead. Patent Documents 3 and 4 also subtract the pressure upstream of the bead and the lower pressure reduction degree (theoretical lower limit vacuum pressure) from the pressure downstream of the bead in order to obtain a coating having a uniform thickness and less appearance defects. It is described that a coating film having a good appearance can be formed when coating is performed under coating conditions in which the value falls within a specific range.

  On the other hand, in Patent Document 5, the viscosity of the coating agent is used in order to make the film thickness in the width direction uniform, suppress the occurrence of streaky unevenness due to fluctuations in the hydraulic pressure of the coating agent, and maintain stable coating. A method has been proposed in which coating is performed under conditions in which a value calculated from μ, coating speed V, coating film thickness h, slot length, and lip gap falls within a specific range. However, in the coating method in which the upstream side of the bead is depressurized, not only the viscosity μ of the coating agent but also the static surface tension σ is an important factor that enables stable coating. Sometimes the coating speed V, the coating film thickness h, the lip gap as well as the pressure reduction degree P upstream of the bead, the coating gap H, and the die lip thickness are important factors that enable stable coating. It was difficult to stably realize a thin film coating having a good appearance and a uniform film thickness only by satisfying the coating conditions described in No. 5.

JP 2004-66232 A Japanese Patent Laid-Open No. 10-118560 JP 2006-95454 A JP 2007-225839 A JP 2006-95491 A

Edited by Processing Technology Research Co., Ltd., “All about New Coating”, Processing Technology Study Group, published on October 4, 2009, P38-P44

  The present invention has been made in view of such a situation, and is accompanied by high-speed coating even when a low-viscosity coating agent is applied thinly (for example, a coating film thickness of 30 μm or less). It is an object of the present invention to provide a coating film coating method and a functional film manufacturing method capable of suppressing the occurrence of streaky unevenness due to air entrainment and stably coating a thin film having a good appearance and a uniform film thickness.

(1) A slot die is brought close to the base film, and a coating agent is discharged from the tip of the slot die to form a bead with the base film, and the upstream side of the base film of the bead is reduced in pressure. While in the coating method of the coating film by the slot die to apply the coating agent on the substrate film surface,
The viscosity of the coating agent is μ, the static surface tension of the coating agent is σ, the relative speed between the base film and the tip of the slot die is V, the outlet end of the upstream die lip and the contact line When the distance is L, the downstream die lip thickness is L ₁ , the coating gap is H, the coating film thickness is h, and the number of capillaries is Ca (Ca = μ · V / σ), the formula (2) is satisfied. A coating method of a coating film by a slot die, characterized in that coating is performed in a range of coating conditions and a degree of vacuum of 0.1 to 1.0 kPa ,
Ca / (L / L1) ≦ 0.1149e− ^{0.2857 (H / h)} (2)
(2) The method for coating a coating film according to (1), wherein the viscosity of the coating agent is 20 mP · s or less, is provided.
(3) The coating film coating method according to (1) or (2), wherein the coating film thickness is 5 μm to 30 μm,
(4) A method for producing a functional film including the coating method using the slot die according to any one of (1) to (3) is provided.

  According to the coating method of the coating film by the slot die of the present invention, conventionally, even when thinly applying a low-viscosity coating agent that is likely to cause poor appearance, it is caused by air entrainment accompanying high-speed coating. It is possible to suppress the occurrence of streak-like unevenness, and to stably apply a coating film having a uniform film thickness and a good appearance. In addition, by a method for producing a functional film that coats a functional coating agent on a base film by a method including the coating method, antireflection performance, antiglare performance, scratch resistance performance, antifouling performance, A functional film having retardation performance, conductive performance, and the like can be obtained.

It is a schematic sectional drawing which shows an example of the coating method of the coating film by the slot die which provided the decompression chamber of this invention. It is an expansion schematic sectional drawing of the bead part in a slot die. Is a graph showing the relationship between the appearance of the coating conditions and coating using a parameter (H / h and Ca / (L / L ₁₎ in the coating method of the coating film of the present invention. It is the graph which showed the relationship between coating conditions and the external appearance of a coating film using the parameters (H / h and capillary number Ca) described in the nonpatent literature 1.

  Hereinafter, the coating method by the slot die which concerns on this invention, and the manufacturing method of a functional film using the same are demonstrated.

  As described above, in the case of coating with a slot die that is applied at normal pressure without controlling the pressure upstream and downstream of the normal bead, the shape of the bead formed between the tip of the slot die and the substrate film surface It is known that streak-like unevenness due to air entrainment associated with high-speed coating can be significantly reduced by stabilizing.

The inventors focused on the fact that streaky irregularities due to air entrainment caused by high-speed coating generated on the coating surface can be greatly reduced by stabilizing the above-described bead, and a slot die having a decompression chamber is used. In the coating method using a slot die for applying a low-viscosity coating agent onto the base film while reducing the pressure on the upstream side of the bead, studies were made to stabilize the bead. As a result, the coating gap H, which is the distance between the die tip and the base film, the coating thickness h, the relative speed between the base film and the slot die tip (hereinafter sometimes referred to as coating speed) V, The bead is stable if the parameters calculated from the viscosity μ of the coating agent, the static surface tension σ of the coating agent, the lip thickness L ₁ on the downstream side of the slot die and the degree of pressure reduction P on the upstream side of the bead are below a predetermined value. As a result, the present inventors have found that streak-like unevenness due to air entrainment accompanying high-speed coating can be greatly reduced, and the present invention has been completed.

Appearance defects due to high-speed coating are too large in the coating gap H, which is the distance between the tip of the slot die and the base film, the viscosity μ of the coating agent, the downstream lip thickness L ₁ and / or the coating speed V. Or a phenomenon that occurs when the coating film thickness h, the static surface tension σ of the coating agent, the distance L between the discharge port of the upstream die lip and the contact line and / or the pressure reduction degree P upstream of the bead are too small, Striped unevenness occurs due to air entrainment.

Next, the coating method of the coating film by the slot die of this invention is demonstrated in detail using FIG. 1 and FIG.
FIG. 1 and FIG. 2 show an example of a method of coating a coating film with a slot die 8 provided with a decompression chamber 7 according to the present invention, and the slot die 8 provided with a slit 3 for discharging a coating agent is used. The state where the coating film 12 is formed on the base film 9 stretched around the backup roll 6 and traveling is shown. As shown in these drawings, when the coating film is formed, a bead 11 made of a coating agent supplied from the slit 3 is formed between the lip tip 5 and the surface of the base film 9. By running the base film 9 in this state, the coating film 12 is formed on the surface of the base film 9, but when the shape of the bead 11 is unstable when the coating film 12 is formed, The film thickness of the formed coating film 12 becomes nonuniform. For this reason, if the coating gap H, which is the distance between the die tip and the substrate film, is too wide or the coating speed V is too fast, streaky unevenness due to air entrainment occurs, and a coating film with a good appearance is obtained. It becomes impossible. Therefore, it is important to stabilize the shape of the bead 11.

  The viscosity of the coating agent suitable for the present invention is 20 mPa · s or less, preferably 10 mPa · s or less, and preferably 1 mPa · s or more. When the viscosity of the coating agent is too high, the pressure loss inside the die increases and the burden on the liquid feeding system increases, which is not preferable. On the other hand, if it is too low, the pressure inside the die is insufficient and the film thickness accuracy in the width direction becomes unstable. The static surface tension of the coating agent is preferably 10 mN / m to 40 mN / m or less, and more preferably 15 mN / m to 35 mN / m. A coating agent having a static surface tension outside this range makes it difficult to form a bead when the distance H between the die lip tip and the substrate film is wide.

  The base film used in the present invention is particularly preferably an optical film composed of a polyester resin, an acrylic resin, a cellulose resin, a polycarbonate resin, a cyclic olefin resin, an olefin resin, etc., and its thickness is 15 μm to 200 μm. Is preferred. Moreover, in order to improve the coating suitability, surface treatment such as corona discharge treatment or excimer laser treatment may be performed to improve the wettability of the base film.

  The pressure in the decompression chamber provided on the upstream side of the slot die is preferably reduced in the range of 0.05 kPa to 2.0 kPa from atmospheric pressure. If the degree of vacuum is less than 0.05 kPa, there is almost no effect of reducing the upstream side of the bead, and increasing the coating speed is undesirable because streaky unevenness due to air entrainment tends to occur, and conversely, the pressure exceeding 2.0 kPa If the pressure is too high, the degree of vacuum in the vacuum chamber is too large, and the bead is pulled upstream, making it difficult to form a stable bead.

  The coating gap H, which is the distance between the tip of the slot die of the present invention and the base film, is preferably 50 μm to 200 μm, and more preferably 70 μm to 150 μm. If the coating gap is less than 50 μm, the coating gap is too narrow, which is not preferable because the tip of the slot die may hit the substrate film. Conversely, if the coating gap exceeds 200 μm, the coating gap becomes large and the bead becomes Since it becomes difficult to stabilize, it is not preferable.

On the other hand, the coating film thickness (wet film thickness) is preferably 5 μm to 30 μm, and more preferably 7 μm to 20 μm. When the coating film thickness is less than 5 μm, the bead thickness becomes thin, so even if a slight force is applied to the bead, the bead is easily affected and difficult to stabilize, while when the coating film thickness exceeds 30 μm, The processed coating agent is not preferred because it tends to flow down.
The coating speed is preferably 3 m / min to 60 m / min, and more preferably 5 m / min to 50 m / min. If the coating speed is less than 3 m / min, the coating speed is slow and the productivity is poor, which is not preferable. If the coating speed exceeds 60 m / min, air entrainment is likely to occur due to high-speed coating, and streaky unevenness is likely to occur. .

  Normally, the slot die slit is used by being installed so that the coating agent is discharged in the horizontal direction or the vertical direction, but the slot die slit of the present invention is installed inclined and applied from the installation direction. You can also.

In the present invention, attention was paid to appearance defects due to high-speed coating, and coating conditions for stabilizing beads and causing no streaky unevenness due to air entrainment were examined.
As described above, streaky unevenness due to air entrainment is caused by the coating gap H, which is the distance between the tip of the slot die and the base film, the viscosity μ of the coating agent, the downstream lip thickness L ₁ and / or the coating speed V. If too large, or if the coating film thickness h, the static surface tension σ of the coating agent, the distance L between the discharge port end of the upstream die lip and the contact line and / or the pressure reduction P upstream of the bead are too small If the coating is performed under such conditions, a part of the bead shown in FIG. 1 is cut, streaky unevenness is generated, and finally a portion that is not applied is generated. The present inventors examined these coating conditions, and quantified the results to clarify the range of coating conditions that are uniform and free of streak-like unevenness. The coating method of the coating film by the slot die which can be obtained was established.

<Test 1>
Using three types of slot dies shown in Table 1, a coating agent having a viscosity of 1.9 mPa · s and a static surface tension of 26.8 mN / m was applied to a polyethylene terephthalate film having a thickness of 50 μm. And the coating gap H was changed in the range shown in Table 1, it applied to the coating film thickness (wet film thickness) 10 micrometers, and the external appearance of the coating film was observed.

  As described above, when coating with a slot die is represented in the figure with the capillary number Ca as the vertical axis and the dimensionless film thickness H / h as the horizontal axis, the region where the number of capillaries is small and the dimensionless film thickness is small is a bead. It is known to be a stable region. Also in the present invention, the test results were analyzed focusing on the number of capillaries Ca and the dimensionless film thickness H / h as parameters for stabilizing the beads.

  Generally, from the standpoint of bead stabilization, in order to reduce the number of capillaries, the lower the viscosity μ of the coating agent and the higher the static surface tension σ of the coating agent, the more stable the bead shape. It is preferable when maintaining it. Further, a lower coating speed V is preferable in terms of bead stabilization.

  On the other hand, in order to stabilize the bead, it is preferable that the dimensionless film thickness H / h is small. The dimensionless film thickness is the ratio of the coating gap (distance between the slot die tip and the base film) H and the coating film thickness h, and the smaller the ratio, the fewer the appearance defects such as streak-like unevenness, And it is preferable when maintaining a bead stably.

  From the above, FIG. 4 shows the results obtained in Test 1 with the number of capillaries Ca on the vertical axis and the dimensionless film thickness H / h on the horizontal axis. In FIG. 4, a circle mark indicates that no streak-like unevenness has occurred, and a cross mark indicates that a streak-like unevenness has occurred. The presence or absence of streak-like unevenness was observed by observing the reflected light by irradiating the coating surface with an explosion-proof fluorescent lamp.

  As apparent from FIG. 4, in the method of the present invention in which coating is performed with the pressure upstream of the bead being reduced, the circle mark and the x mark are mixed in all regions, and the capillary number Ca and the dimensionless film thickness H / It is clear that the suitability of the coating conditions cannot be clearly determined only by h.

In view of the above results, the inventors of the present invention have a bead stability in which the pressure reduction degree P on the upstream side of the bead, the coating gap H, the distance L between the upstream end of the die lip discharge port and the contact line, and the downstream side of the die lip. thought to give a thickness L ₁ influence, these conditions also considered parameter Ca / a (L / L ₁₎ on the vertical axis plots the results of tests 1 dimensionless thickness H / h on the horizontal axis Figure 3 was obtained. In FIG. 3, a circle mark indicates that a coating film having a good appearance was obtained without causing stripe-shaped unevenness, and a mark X indicates that stripe-shaped unevenness occurred.

Since the coating agent used in the present invention is considered to be a Newtonian fluid, the distance L between the discharge port end of the upstream lip and the contact line can be calculated using the following equation.
L = H ² (P−ΔP) / 6 μV
here,
ΔP = 12 μL ₁ V (h−H / 2) / H ³

As is clear from FIG. 3, in the coating method of coating with the bead upstream side being decompressed, Ca / (L / L ₁ ) is on the vertical axis and dimensionless film thickness H / h is on the horizontal axis. As a result, the region where the circles (coating having a good appearance) are plotted and the region where xs (coating where streaky unevenness is generated) are plotted are clearly separated, and are indicated by a solid line in FIG. It became clear that the lower side of the straight line is a suitable coating region. This is expressed in the formula (1), and the stripe-shaped unevenness can be greatly reduced by coating under the condition satisfying the formula. In addition, the value converted into the unit shown below was used for the numerical value used for calculation.

Ca / (L / L ₁ ) ≦ 0.1309e ^{−0.2212 (H / h)} (1)

However, Ca is the number of capillaries: μV / σ
L = H ² (P−ΔP) / 6 μV
ΔP = 12 μL ₁ V (h−H / 2) / H ³
ΔP: Bead downstream pressure loss (kPa)
μ: Viscosity (Pa · s)
σ: Static surface tension (N / m)
P: Decompression degree (Pa)
V: Relative speed between base film and slot die tip (m / s)
H: Coating gap (m)
h: Coating film thickness (wet thickness) (m)
L ₁ : downstream die lip thickness (m)
L: Distance between upstream die lip outlet end and contact line (m)

Furthermore, the region below the straight line indicated by the broken line in FIG. 3 is a more preferable coating region. This is expressed in the formula (2). By coating under the coating conditions that satisfy this formula, the stripe-like unevenness can be completely eliminated.

Ca / (L / L ₁ ) ≦ 0.1149e− ^{0.2857 (H / h)} (2)

  Although the viscosity and static surface tension of the coating agent applicable to the present invention have been described above, the types of coating agent include antireflection properties, antiglare properties, scratch resistance, antifouling properties, retardation properties, self Coating agents that can provide restorability, conductivity, etc. can be used, and by applying them to the base film, antireflection performance, antiglare performance, scratch resistance performance, antifouling performance, etc. A functional film having phase difference performance, self-healing performance, conductive performance and the like can be obtained.

Next, measurement methods for various parameters used in the present invention will be described.
<Μ: viscosity of coating agent>
The viscosity of the coating agent was measured at 23 ° C. and a liquid volume of 0.6 mL using a viscometer TVE-22L (manufactured by Toki Sangyo Co., Ltd.).

<Σ: Static surface tension of coating agent>
The static surface tension σ of the coating agent was measured by a Wilhlmy method using a surface tension meter CBVP-A3 (manufactured by Kyowa Interface Science Co., Ltd.).

<H: coating thickness>
The coating thickness (wet film thickness) h was calculated by dividing the discharge amount of the coating agent coated on the base film by the coating area.

<Examples 1-4>
Using a slot die shown in Table 2, a coating agent having a viscosity of 1.9 mPa · s and a static surface tension of 26.8 mN / m is applied to a polyethylene terephthalate film having a thickness of 50 μm. The film was coated at a degree, a coating gap, and a coating film thickness (wet thickness), and the appearance of the coating film was observed. As a result, as shown in Table 2, the coating conditions of each example satisfy the coating conditions of the present invention (the value of Ca / (L / L ₁ ) is calculated on the right side of the equation (1). No streak-like unevenness was observed, and a coating film having a good appearance was obtained.

<Comparative Examples 1-3>
Using a slot die having a lip thickness shown in Table 2, a coating agent having a viscosity of 1.9 mPa · s and a static surface tension of 26.8 mN / m is applied onto a 50 μm thick polyethylene terephthalate film. Coating was carried out at a work speed, a reduced pressure degree, a coating gap, and a coating film thickness (wet thickness), and the appearance of the coating film was observed. As a result, as shown in Table 2, the coating conditions of each comparative example do not satisfy the coating conditions of the present invention (the value of Ca / (L / L ₁ ) is calculated on the right side of the formula (1). In both cases, streaky unevenness occurred in part and the appearance was poor.

As described above, according to the present invention, it is possible to manufacture a coating film by a slot die in which a coating agent is applied to the surface of a base film while reducing the pressure on the upstream side of the base film of the bead. By coating under the working conditions, it is possible to obtain a coating film having no streak-like unevenness, uniform film thickness and good appearance. Furthermore, by a method for producing a functional film that coats a coating agent having functionality on a base film by a method including a coating method of a coating film by the slot die of the present invention, antireflection performance, antiglare performance, It is possible to obtain a functional film provided with performance with scratch resistance, antifouling performance, retardation performance, self-healing performance, conductive performance, and the like.

1. 1. Upstream lip 2. Downstream lip Slit 4. Manifold 5. Lip tip (slot die tip)
6). 6. Backup roll Decompression chamber 8. Slot die 9. Base film 11. Bead 12. Coating film H: Coating gap h: Coating film thickness L ₁ : Downstream die lip thickness L: Distance between upstream die lip outlet and contact line

Claims (4)

A slot die is brought close to the base film, and a coating agent is discharged from the tip of the slot die to form a bead between the base film and the upstream side of the base film of the bead while reducing the pressure. In the coating method of the coating film by the slot die that coats the coating agent on the material film surface,
The viscosity of the coating agent is μ, the static surface tension of the coating agent is σ, the relative speed between the base film and the tip of the slot die is V, the outlet end of the upstream die lip and the contact line When the distance is L, the downstream die lip thickness is L ₁ , the coating gap is H, the coating film thickness is h, and the number of capillaries is Ca (Ca = μ · V / σ), the formula (2) is satisfied. A coating method using a slot die, characterized in that coating is performed in a coating condition and a degree of reduced pressure in the range of 0.1 to 1.0 kPa .
Ca / (L / L1) ≦ 0.1149e− ^{0.2857 (H / h)} (2) The coating method of a coating film according to claim 1, wherein the coating agent has a viscosity of 20 mP · s or less. The coating film coating method according to claim 1, wherein the coating film thickness is 5 μm to 30 μm. The manufacturing method of the functional film characterized by including the coating method by the slot die in any one of Claims 1 thru | or 3.

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