JP4899291B2 - Coating method - Google Patents

Description

  The present invention relates to a coating method for smoothing a substrate having surface irregularities.

  In recent years, in the field of circuit boards, there has been a demand for manufacturing a product with a smooth surface at a low cost and at a high speed while demands for miniaturization and high functionality have increased. There is a circuit board for a display element as a product with a strong tendency. Display elements that can be directly touched, such as liquid crystal displays, plasma displays, EL displays and the like, which have been used in recent years, use ceramics such as glass plates and plastic sheets.

Conventionally, various techniques have been applied to form a smooth surface. For example, when glass is used for the substrate, an operation of forming a smooth surface by polishing the surface as shown in Patent Document 1 and Patent Document 2 is generally performed. In these polishing processes, it is inevitable that fine scratches are formed on the surface, and there is a possibility that a defective portion is generated by polishing powder or the like.
Moreover, when using a plastic sheet for the base material, a transfer material having a highly smooth surface, for example, a metal foil such as copper foil, a smoothed steel plate or a metal roll, and the smooth surface is used as the base material surface. A pressure molding operation for transferring is performed. Moreover, the smoothing process by coating as described in Patent Document 3 and Patent Document 4 is generally performed. The coating method is roughly divided into two types. In the contour coating method, surface unevenness reflecting the surface unevenness is generated to trace the unevenness of the base substrate, and in the smooth coating method, the unevenness of the base substrate is generated. Due to the resulting film thickness variation, there was a problem that surface irregularities were generated due to the difference in shrinkage during the curing process. The coating method for forming a smooth surface as proposed in Patent Document 3 and Patent Document 4 is a proposal of a system relating to the formation of a smooth surface with a liquid coating film, and refers to the surface smoothness after curing. At present, no proposal has been made.

JP 2001-039737 A JP 07-249710 A JP 2000-349423 JP 2003-80139 A

  In view of the above problems, the present invention provides a coating method for forming a smooth surface on a substrate having surface irregularities, and provides a smoothing sheet, glass, metal plate and the like produced thereby. Furthermore, a display element device using the same is also provided.

  In the coating method in which a coating resin is applied to a substrate having surface irregularities, a smooth surface is formed by leveling by applying a low-viscosity state with high fluidity during coating. The present inventors have found a coating method in which fluidity is suppressed by increasing the resin viscosity of the coating film and curing is performed while maintaining a smooth surface.

That is, the present invention
(1) A method of coating an ultraviolet curable resin composition on a base substrate having surface irregularities, and at the time of coating, a smooth coating surface is formed with the leveling property improved by controlling the temperature of the liquid, After that, a coating method including a cooling step of maintaining the shape of the coated surface and curing.
(2) The coating method according to (1), wherein the viscosity of the resin composition during coating is 50 cPs or less.
(3) The coating method according to (1) or (2), wherein the resin composition after the cooling treatment has a viscosity of 3000 cPs or more.
(4) A smoothing sheet coated by the coating method described in (1) to (3), using a plastic sheet made of a resin composition or a composite base made of an inorganic filler and a resin composition as the base substrate.
(5) The smoothing sheet according to (4), wherein the surface irregularities are 200 nm or less in terms of maximum surface roughness.
(6) The smoothing sheet according to (4) or (5), which is transparent.
(7) Smoothed glass coated by the coating method described in (1) to (3) using glass as the base substrate.
(8) The smoothed glass according to (7), wherein the surface roughness is 200 nm or less in terms of the maximum surface roughness. (9) The smoothed glass according to (7) or (8), which is transparent.
(10) A smoothed metal plate coated with the coating method described in (1) to (3) using a metal plate as the base substrate.
(11) The smoothed metal foil, smoothed metal sheet or smoothed metal plate according to (10), wherein the surface roughness is 200 nm or less in terms of maximum surface roughness.
It is.

  The manufacturing process obtained by the method of the present invention relates to a coating method that enables high smooth surface formation. Furthermore, by using the smooth substrate, a circuit substrate and a display element device having high display performance and low cost can be obtained.

The coating method of the present invention will be described below.
In the coating method of the present invention, the target base substrate is a resin sheet using a thermosetting or ultraviolet curable resin, a composite sheet or glass plate made of an inorganic filler and a resin, and a metal plate. Although these materials meet the requirements for circuit boards, particularly transparent / opaque substrates for various display elements, they have surface irregularities and have not been able to cope with high functionality.
Although the case where a plastic sheet is used as the base substrate is mainly described below, it is not particularly limited, and the same applies to other glass plates, metal plates, and the like. In addition, the circuit board is mainly targeted for use, but there is no problem even if it is applied to other purposes.

The inventive principle of this patent will be described.
A technique for forming a smooth coating surface in view of a leveling effect in a low-viscosity resin having high fluidity is relatively known. As described in Patent Document 3 and Patent Document 4 described above, the method of forming a smooth coating surface is often described as a feature of the coating method, but these evaluation criteria remain on the liquid coating surface, No proposals have been taken into account until after final cure.
The driving force for leveling the coating liquid surface is the surface tension of the liquid and the hydrostatic pressure gradient. When the shearing stress generated in the coating film during leveling exceeds the maximum shearing stress shown in equation (1) Since the resin flow stops, the leveling effect after that cannot be expected. When a low-viscosity coating liquid is used, the generated shear stress is small, so that the maximum shear stress is rarely reached, and a smooth surface can be formed from the high leveling properties obtained thereby. On the other hand, according to the Orchard theory shown in Equation (2), the surface roughness of the substrate, the viscosity of the coating solution,
The temporal change behavior of the coating film surface unevenness in the coating film thickness can be grasped. Even when the shear stress generated in the coating film does not reach the maximum shear stress, it is easily estimated from this theory that leveling time is required as the viscosity increases, and the advantage of low viscosity in smooth surface formation Has been proven.

The high fluidity of the low viscosity has a disadvantage that it easily breaks the formed smooth surface while providing high leveling properties. Until the coated film surface is solidified, it is subject to various disturbances such as vibration and wind pressure generated during conveyance. Therefore, a smooth surface is temporarily formed in a state where the fluidity is high, but it is difficult to finally maintain the smooth surface. In addition, when a smooth coating film is formed on a surface having unevenness due to the leveling effect, the coating film thickness necessarily has a thickness variation due to the base surface unevenness. Since the film thickness variation causes a variation in the curing speed, the amount of shrinkage differs during the curing process, so that irregularities are formed.
In view of these events, by utilizing the thickening effect of the coating film generated by performing a cooling treatment after coating, by controlling the balance between the leveling speed and the thickening speed by performing this at an appropriate timing, High leveling at low viscosity and surface shape retention at high viscosity are compatible, and furthermore, a flat coating film surface is formed by curing by UV irradiation without temperature influence, and a smooth surface is maintained until after curing. It became possible.

  The ultraviolet curable resin composition used as the coating resin of this patent refers to a composition containing a general resin that is three-dimensionally crosslinked and cured by ultraviolet rays, such as an acrylate resin or an epoxy acrylate resin. These may be used alone or in combination. At this time, a substance capable of generating radicals upon irradiation with ultraviolet rays, such as an aryl alkyl ketone, or a substance capable of generating cations upon irradiation with ultraviolet rays, such as an aryldiazonium salt, may be blended as a curing accelerator. Moreover, you may use the composite material which mix | blended the inorganic filler with the said ultraviolet curable resin composition as coating resin.

  This patent forms a smooth surface by coating the coating resin in a highly leveled state, and suppresses the flow until the coating film is made highly viscous and cured by cooling treatment after leveling, thereby smoothing the surface. It is characterized by maintaining. Examples of the coating method include die coating, comma knife, dipping, and gravure coating, but are not particularly limited. However, when using a coating solution that is highly viscous at room temperature with a low viscosity by heating, a coating method with relatively stable temperature control, such as die coating, is desirable. It is not desirable to have a system in which the viscosity changes abruptly from to the workpiece. As the cooling method after leveling, when the coating film is a thin film, a cooling phenomenon is exhibited even in natural cooling, but it is desirable to select a method capable of controlling the cooling rate by forced cooling. Examples of the forced cooling method include, but are not limited to, a direct cooling method in which a cooling roll is wound around a base substrate, a non-contact method in a cooling environment using cooling air, and the like.

  The maximum surface roughness is a numerical value indicating the maximum uneven height difference in the measurement plane. In particular, regarding the surface roughness of 200 nm required for a high-performance display element substrate, it is known that the numerical values shown differ greatly depending on the difference in the method depending on the measuring instrument. Therefore, the numerical value of the surface roughness specified this time is specified as a numerical value by non-contact surface roughness measurement based on the optical principle.

As the plastic sheet used for the base substrate of this patent, for example, a plastic sheet made of the ultraviolet curable resin or the thermosetting resin can be used. Thermosetting resins generally indicate resins that are three-dimensionally crosslinked and cured by heat, such as epoxy resins, phenol resins, melamine resins, and polyester resins. These resins may be used alone or in combination. Moreover, when the hardening | curing agent and hardening accelerator to be used are required, it can be used together. An epoxy resin is most preferably used as the thermosetting resin. In this case, amine-based, particularly dicyandiamide and aromatic amine, tetramethylenehexamine, phenol novolac-based curing agent and acid anhydride-based curing agent are used as the curing agent. As the curing accelerator, organic phosphorus-based curing accelerators such as triphenylphosphine and imidazole-based nitrogen-based curing accelerators are preferably used. The inorganic filler used when the composite sheet of the inorganic filler and the resin composition is used for the base substrate is in the form of powder or sheet. Examples of the powdery inorganic filler used here include a spherical shape, a crushed shape, a scale shape, and a rod shape. Examples of the sheet-like inorganic filler include a glass fiber, a carbon fiber, a metal fiber, and a mineral fiber. Woven fabrics, non-woven fabrics, mats, etc., and paper. These inorganic fillers may be used alone or in combination. The metal plate used for the base substrate is made of various metals such as copper and aluminum, and forms from a metal foil having a thickness of several μm to a metal plate having a thickness of several mm. There is no particular limitation on the production method such as electrolysis and rolling. Glass cloth, glass nonwoven fabric, and paper are most preferably used as the base substrate.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
Example 1
(1) Preparation of varnish 100 parts by weight of an alicyclic epoxy resin (EHPE3150 manufactured by Daicel Chemical Industries), 75 parts by weight of methylhexahydrophthalic anhydride (Riccaside MH-700 manufactured by Shin Nippon Chemical Co., Ltd.), tetraphenylphosphonium bromide (Hokuko Chemical Industries) Varnish A was prepared by mixing 0.5 parts by weight of TPP-PB) with 120 parts by weight of acetone.
(2) Preparation of base substrate A composite sheet was prepared in the following manner.
An 80-μm thick E glass-based glass cloth (Nittobo WEA2319) was impregnated with varnish A by dipping. After immersing the varnish in the glass cloth for a sufficient amount of time,
The resin was applied to both sides while adjusting the pulling speed so that a resin thickness of 2 to 3 μm was applied. Impregnation /
The resin was cured by treatment at 120 ° C. for 5 minutes and further treatment at 200 ° C. for 2 hours in a state where it was suspended in the oven after the application was completed. The maximum surface roughness at that time was 3240 nm.
(3) Preparation of coating resin Coating resin was prepared in the following manner.
50 parts by weight dicyclopentadienyl acrylate (M-203 manufactured by Toagosei Co., Ltd.), 50 parts by weight of bis [4- (acryloyloxyethoxy) phenyl] sulfide (TO-2066 manufactured by Toagosei Co., Ltd.), 1 0.5 part by weight of hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184 manufactured by Ciba Specialty Chemicals) was melt-mixed at 80 ° C. to obtain a coating resin.
The viscosity coefficient of the coating solution was measured while raising the temperature with a parallel plate viscometer. Although it was 3600 cps at room temperature of 25 ° C., it decreased to 30 cps at a temperature of 80 ° C. (4) Coating treatment The coating treatment was performed under the following conditions.
A coating resin was applied to the surface of the base substrate using a direct reverse gravure coater. A gravure roll having a 120 mesh pyramid shape was used, and the temperature of the gravure roll and the bath bat was controlled at 80 ° C. A water-cooled roll installed with a rotary joint was used as a backup roll, and a cooling treatment was performed by winding the substrate immediately after coating around the backup roll. The temperature of the backup roll was controlled by flowing 5 ° C. chiller water, and the ratio between the peripheral speed and the line speed of the gravure roll was 1: 1.5. After coating one side of the base substrate, the coating resin was cured by irradiating with ultraviolet rays (500 mJ / cm 2) using a mercury lamp.
(5) Measurement results
The maximum surface roughness of the coating film surface was measured using a light interference type roughness meter manufactured by zygo. The maximum surface roughness was 127 nm.

(Example 2)
(1) Production of base substrate An unpolished soda lime glass plate produced by a float manufacturing method was used as a base substrate. The maximum surface roughness of the glass plate was 425 nm.
(2) Coating treatment The coating treatment was performed under the following conditions.
Using the direct reverse gravure coater, the same coating resin as in Example 1 was applied to the surface of the base substrate. A gravure roll having a 120 mesh pyramid shape was used, and the temperature of the gravure roll and the bath bat was controlled at 80 ° C. A water-cooled roll installed with a rotary joint was used as a backup roll, and the line was controlled so that the substrate immediately after coating was placed on a temperature-controlled metal plate. The temperature of the backup roll and the metal plate was controlled by flowing chiller water at 5 ° C., and the ratio between the peripheral speed and the line speed of the gravure roll was 1: 1.5. After coating one side of the base substrate, the coating resin was cured by irradiating with ultraviolet rays (500 mJ / cm 2) using a mercury lamp.
(3) Measurement results
The maximum surface roughness of the coating film surface was measured using a light interference type roughness meter manufactured by zygo. The maximum surface roughness was 27 nm.

Example 3
(1) Production of base substrate An electrolytic copper foil having a thickness of 18 μm was used as the base substrate. The maximum surface roughness of the copper foil was 2389 nm.
(2) Coating treatment The coating treatment was performed under the following conditions.
A coating resin was applied to the surface of the base substrate using a direct reverse gravure coater. A gravure roll having a 120 mesh pyramid shape was used, and the temperature of the gravure roll and the bath bat was controlled at 80 ° C. A water-cooled roll installed with a rotary joint was used as a backup roll, and a cooling treatment was performed by winding the substrate immediately after coating around the backup roll. The temperature of the backup roll was controlled by flowing 5 ° C. chiller water, and the ratio between the peripheral speed and the line speed of the gravure roll was 1: 1.5. After coating one side of the base substrate, the coating resin was cured by irradiating with ultraviolet rays (500 mJ / cm 2) using a mercury lamp.
(3) Measurement results
The maximum surface roughness of the coating film surface was measured using a light interference type roughness meter manufactured by zygo. The maximum surface roughness was 89 nm.

(Comparative Example 1)
(1) Production of base substrate A base substrate was produced in the same manner as in Example 1.
(2) Coating treatment The coating treatment was performed under the following conditions.
Using the direct reverse gravure coater, the same coating resin as in the example was applied to the surface of the base substrate. A gravure roll having a 120 mesh pyramid shape was used, and the temperature of the gravure roll and the bath bat was controlled at 80 ° C. A water-cooled roll installed with a rotary joint was used as the backup roll, and the temperature was controlled by winding the substrate immediately after coating around the backup roll. The temperature of the backup roll was controlled by flowing hot water at 80 ° C., and the ratio of the peripheral speed and the line speed of the gravure roll was 1: 1.5. After coating one side of the base substrate, the coating resin was cured by irradiating with ultraviolet rays (500 mJ / cm 2) using a mercury lamp.
(3) Measurement results
The maximum surface roughness of the coating film surface was measured using a light interference type roughness meter manufactured by zygo. The maximum surface roughness was 538 nm.

(Comparative Example 2)
(1) Production of base substrate A base substrate was produced in the same manner as in Example 1.
(2) Coating treatment The coating treatment was performed under the following conditions.
Using the direct reverse gravure coater, the same coating resin as in the example was applied to the surface of the base substrate. A gravure roll having a 120 mesh pyramid shape was used, and the temperature of the gravure roll and the bath bat was controlled at 80 ° C. The ratio between the peripheral speed and the line speed of the gravure roll was 1: 1.5, and temperature control after coating was not particularly performed. After coating one side of the base substrate, the coating resin was cured by irradiating with ultraviolet rays (500 mJ / cm 2) using a mercury lamp.
(3) Measurement results
The maximum surface roughness of the coating film surface was measured using a light interference type roughness meter manufactured by zygo. The maximum surface roughness was 399 nm.

Claims (4)

The base substrate surface having surface irregularities, and step 1 of applying a UV-curable resins composition was heated by a predetermined temperature A
A method for producing a substrate for a display device, comprising: a step 2 of cooling the surface of the base material coated with the resin composition by the step 1 at a predetermined temperature B;
The ultraviolet curable resin composition has a viscosity of 50 cPs or less at the temperature A; and
The method for manufacturing a substrate for a display device, wherein the temperature B is 3000 cPs or more.   2. The method for producing a display device substrate according to claim 1, wherein the base substrate is a plastic sheet made of a resin composition.   The method for producing a substrate for a display device according to claim 2, wherein the resin composition contains a resin and an inorganic filler.   2. The method for producing a substrate for a display device according to claim 1, wherein the base substrate is a glass plate.