JP2002172362A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide coating method capable of preventing coating defects such as stringing by applying a coating solution in which the concentration of a coagulation core is decreased to a moving film. SOLUTION: In the coating method comprising means of applying a coating solution to at least one face of a moving plastic film and means of supplying a coating solution, at least one means for filtering the coating solution is installed in the coating solution supplying means and the filtering means has a filtration precision of 0.2-3 μm and is capable of suppressing the concentration of a coagulation core of 0.6-5 μm to 6,000,000/ml in the coating solution filtered thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method, and more particularly, to a coating liquid which can be applied to an off-line coating on a running film or an in-line coating in a film production process, wherein the concentration of cohesive nuclei contained in the coating liquid is reduced. The present invention relates to a coating method in which coating defects such as streaks do not occur by coating the film on a running film.

[0002]

2. Description of the Related Art For the purpose of imparting functionalities to plastic films, for example, easy adhesion, lubricity, gas barrier properties, moisture proof properties, antistatic properties, ink receptivity, etc., coatings having these functions are applied to films. Application of a film is widely performed. As a method for coating such a film, a roll coating method represented by a gravure roll method, a reverse roll method, or the like has become mainstream.

However, in these coating methods, since the coating liquid is subjected to severe shear (shear) force between the rolls and between the film and the roll, the dispersing agent in the coating liquid is aggregated, and the aggregation nuclei are formed. It tended to appear as coarse defects on the film. In particular, the need for highly transparent films has increased for optical films, and when aggregated nuclei are densely packed on the film, visible light is partially blocked, which impairs transparency and becomes a fatal defect. Was. In particular, when the defective portion is analyzed, as shown in FIG. 2, about 10 agglomerated nuclei d are densely formed on the film, and this group is scattered in a streak in the running direction of the film. State defects (hereinafter referred to as coating streaks) occurred.

As a method of reducing cohesion nuclei in a roll coater, a method of reducing the amount of pressing between the roll and the film to reduce shear (shear) or a method of forming coagulation nuclei by generating heat by shearing heat by passing cooling water inside the roll. There have been ways to mitigate this. However, in these methods, the circulated coating liquid is subjected to shearing on the rolls many times, and there is a problem that a coating streak is generated over time when coating is performed for several hours. In particular, in the in-line coating in the film forming process, it is necessary to perform stable coating for several days, and these methods are not suitable.

A coating method and an apparatus for reducing solids deposited on a roll and eliminating coating streaks are disclosed in, for example, JP-A-8-71474, in which a coating liquid is applied to a running film in advance by a fountain die. A coating method and apparatus are disclosed. However, this method did not reduce the shear between the roll and the film, and thus could not suppress the occurrence of streaks.

[0006]

The present inventors have conducted intensive studies to improve the coating streaks, and as a result, when the concentration of agglomerates in the coating liquid reaches a certain level, the agglomerates gather on the film,
I noticed that it appeared as a streak.

Accordingly, an object of the present invention is to provide a good coating method which can prevent coating streaks in which cohesive nuclei are densely packed and has no coating defects.

[0008]

An object of the present invention is to provide a coating method comprising a means for applying a coating liquid on at least one surface of a running plastic film and a means for supplying the coating liquid. At least one or more means for filtering the coating liquid, and the filtration accuracy of the filtration means is 0.2 to 3
μm, and the concentration of the aggregated nuclei having a size of 0.6 to 5 μm contained in the coating liquid having passed through the filtration means is 6 million / ml.
It can be achieved by a coating method characterized by the following.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a side view showing a coating apparatus including a gravure coater and a coating liquid supply apparatus according to one embodiment of the present invention.

In FIG. 1, 1 is a gravure roll, 2 is a chamber, 3 is a running film, 4 is a coating liquid tank, 5 is a liquid feed pump, 6 is a pressure gauge, 7 is a filter, 8 is a liquid drain port, and a is The traveling direction of the film, b is the rotation direction of the roll 1, and c is the liquid flow direction.

The coating method according to the present invention uses the coating liquid tank 4
Is supplied to the chamber 2 by the liquid feed pump 5,
Further, while measuring the coating liquid in a cell on the surface of the gravure roll 1, an appropriate amount of the gravure roll is pressed against the running film 3 for transfer coating.

The feature of the present invention is that the coating liquid after filtration by the filter 7 is sampled from the liquid drain port 8, and if the concentration of the cohesion nuclei in the coating liquid is 6,000,000 / ml or less, no coating streaks are generated. And more preferably 3 million pieces / m
1 or less. The filtration accuracy of the filter is preferably from 0.2 to 3 μm, more preferably from 0.5 to 1 μm, in order to reduce the frequency of replacement of the filter element by increasing the pressure of the filter while efficiently capturing the aggregation nuclei. The filter medium of the filter can be exemplified by polypropylene and nylon 6 for a water-based coating liquid, and may be glass fiber, sintered metal, or Teflon (registered trademark).

The gravure roll 1 illustrated in FIG. 1 is a gravure coating system in which a gravure cell is provided by laser engraving on the surface of the ultra-hard sprayed roll, and is transferred and applied to the running film 3 by reverse rotation. In addition to this method, a well-known reverse roll coater, Meyer bar coater, offset gravure coater, or the like can also exhibit the effect of reducing cohesive nuclei and eliminating coating streaks.

As the coating liquid used in the present invention, for example, a film is coated with a functional layer such as an easily adhesive layer, a slippery layer, a gas barrier layer, a moisture proof layer, an antistatic layer, and an ink receiving layer. A coating liquid containing a functional component for setting as a solid content can be given.

The solid content of the coating solution may include a binder component for improving the adhesion between the coating film and the film, in addition to the above-mentioned functional components. As the binder component, for example, a polyester resin, a polyurethane resin, an acrylic resin, an epoxy resin, a vinyl resin, an acryl-modified polyester, a polyether, a water-soluble resin, or the like can be used.

In the present invention, it is particularly preferable to use an aqueous coating solution in which the above functional component and binder component are dissolved and / or dispersed in water. This aqueous coating liquid contains functional components and binder components such as fillers, surfactants, antioxidants, antistatic agents, coloring agents, pigments, fluorescent brighteners, plasticizers, crosslinking agents, lubricants, and ultraviolet absorbers. And other components can be added.

The solid content of the aqueous coating solution is usually 1 to 30 watts.
Although it is t%, it is particularly desirable to be 2 to 20 wt%. The aqueous coating composition may contain a small amount of an organic solvent.

In the present invention, the running film 3 includes
Polyethylene terephthalate, polyethylene-2,6-
Polyester films such as naphthalate and polybutylene terephthalate; polyamide films such as nylon 6, nylon 66 and nylon 12; polyethylene;
Examples thereof include polyolefin films such as polypropylene and polymethylpentene, and films in which respective polymers are blended. Among these films, it is preferable to use a polyester film.

The polyester constituting the polyester film is preferably a crystalline linear polyester comprising a dicarboxylic acid component and a glycol component. As the dicarboxylic acid component, terephthalic acid, isophthalic acid,
Examples thereof include 2,6-naphthalenedicarboxylic acid, hexahydroterephthalic acid, 4,4'-diphenyldicarboxylic acid, adipic acid, sebacic acid and dodecanedicarboxylic acid. Of these, terephthalic acid, 2,6-
Naphthalenedicarboxylic acid is preferred.

The glycol components include ethylene glycol, propylene glycol, 1,3-propanediol, 1,6 hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, bisphenol A, 1,4-cyclohexanedimethanol, and polyethylene glycol. , Polytetramethylene glycol and the like. Of these, ethylene glycol is particularly preferred.

The polyester can be produced by a conventional method, and its average molecular weight is preferably 10,000 or more. The polyester preferably contains fine particles such as silica, alumina, kaolin, calcium carbonate, titanium oxide, graphite, carbon black, crosslinked silicone resin, melamine resin, crosslinked polystyrene, and crosslinked acrylic resin as a lubricant. If desired, an antioxidant, an antistatic agent, a colorant, a pigment, a fluorescent brightener, a plasticizer, a cross-linking agent, a lubricant, an ultraviolet absorber, and the like can be added.

In the present invention, the running film 3 can be manufactured by conventionally known methods and conditions or by methods and conditions accumulated in the art. For example,
The polyester can be produced by melt-extrusion, quenching and solidifying to give an unstretched film, and stretching and heat-setting the obtained unstretched film. The stretching treatment is performed at least in a uniaxial direction, but is preferably performed in a biaxial direction.
Stretching is usually performed at a temperature equal to or higher than the secondary transition point of the polyester.
It is performed at a magnification of 2 times or more, preferably 3 times or more in each direction.

In the present invention, in the process of producing such a plastic film, particularly a polyester film, it is preferable to apply an aqueous coating solution, and then perform drying and stretching treatment. More preferably, an aqueous coating solution is applied to a vertically stretched film, and stretched in the horizontal direction after drying or while drying. If necessary, the film is further stretched in the machine direction or the transverse direction, and further heat-treated to obtain a laminated film. WET coating amount from 1 to 20 g / m ^2, in particular 2~12g / m ² is preferred. After the application, the film is preferably stretched in the horizontal direction while drying, but if necessary, it can be further vertically stretched in the vertical direction and / or the horizontal direction and subjected to heat treatment. The thickness of the coating layer after drying and stretching is 0.005 to 3
μm, particularly preferably 0.015 to 1 μm.

[0025]

The present invention will be further described with reference to the following examples. In addition, the concentration of the aggregation nucleus or the evaluation of the product film was measured by the following method, or the definition was adopted.

(1) Measurement of Coagulation Nucleus Concentration in Coating Liquid The coating liquid filtered by the filter 7 is sampled from the liquid outlet 8. 0.1 ml of the sampled liquid was applied to a polycarbonate New-Crypore filter (filtration area of φ1
(0 mm, pore size of 0.6 μm), trap the aggregated nuclei of 0.6 μm or more, and air-dry the sample at room temperature for about 1 day. Then, SEM was applied to any five points on the sample surface.
Observation (magnification × 3500 times, visual field range 25μm × 2
5 μm), the number of cohesion nuclei having a size of 5 μm or less is counted, and the average value of the number at five locations is defined as X. Using this X,
The concentration of aggregation nuclei (number / ml) in the coating solution was determined by the following equation.

[0027]

[Number 1] aggregation nuclei concentration in the coating solution (number /Ml)=X×1.2×10 ⁶

Incidentally, the observation of the sample surface with the SEM always selected a total of five locations including one location at the center of the sample.

(2) Evaluation of coating streaks of product film After the coating film on the film is dried, the product film is extracted 2 m in the film running direction and the entire width in the width direction. The film was irradiated with halogen light in a dark room, and the number of applied streaks was counted visually. The coating streaks were checked at the start of coating and at the end of coating, and at the timing of rewinding the product film.

(3) Overall Evaluation Based on the number of coating streaks of the product film and the service life of the filter, the evaluation was made by ○, Δ, and ×. ：: The number of applied streaks is 0 and the replacement life of the filter is 24 hours or more. Δ: The number of applied streaks is 0 and the replacement life of the filter is 8 hours or more and less than 24 hours. ×: The number of applied streaks is one or more. Or, the replacement life of the filter is less than 8 hours.

[Examples 1 to 3] Using the coating apparatus shown in FIG. 1, in-line coating was performed in the film manufacturing process. Polyethylene terephthalate (containing a lubricant, Tg = 78 ° C.) having an intrinsic viscosity of 0.61 dl / g (measured at 35 ° C. in an orthochlorophenol solution) was discharged from an extrusion die at 280 to 280 ° C.
It was melt-extruded at a temperature of 300 ° C. and rapidly cooled while applying static electricity on a rotating cooling drum maintained at about 30 ° C. to obtain an unstretched film. Next, this unstretched film is
The film is stretched 3.6 times in the longitudinal direction at
A μm uniaxially stretched film was obtained. On one surface of the product part of the uniaxially stretched film formed at 80 m / min, a coating liquid having the composition described below was applied by a gravure roll rotating in reverse at a peripheral speed of about 1.2 times the film speed. At this time, as a measure against coating streaks, filtration accuracy of 3μ
Was applied while filtering the aggregated nuclei using a polypropylene filter. Next, the uniaxially stretched film coated with the coating solution was stretched 3.8 times in the width direction at 120 ° C., and subjected to tension heat treatment at 220 ° C. with a fixed length to obtain a biaxially oriented polyester film.

By the above-mentioned measures for reducing the cohesion nuclei, a product film could be obtained without the occurrence of coating streaks for 24 hours in a continuous manner and without replacing the filter due to pressurization of the filter. The results are shown in Table 1 as Example 1.

Further, the filtration accuracy of the filter is 1 μm,
The results of coating under the same conditions as in Example 1 were set to 0.2 μm, and the results were shown in Table 1 as Example 2 and Example 3, respectively.
It was shown to. In each case, good products could be obtained without any application streaks for a continuous 24 hours.

Coating liquid: acid component is terephthalic acid (90 mol%), isophthalic acid (6 mol%) and potassium 5-sulfoisophthalate (4 mol%), glycol components are ethylene glycol (95 mol%) and neopentyl Glycol (5 mol%) copolymerized polyester (Tg = 68)
C) is 80% by weight, N, N'-ethylenebiscaprylic amide is 5% by weight, acrylic resin fine particles (average particle size:
An aqueous coating liquid having a solid content of 8%, comprising 10% by weight of 0.03 μm) and 5% by weight of polyoxyethylene nonylphenyl ether.

Comparative Example 1 Coating was started under the same conditions as in Example 1 except that a filter having a filtration accuracy of 5 μm was used. Although there was no streak at the start of coating, the concentration of aggregated nuclei was measured in about 8 hours.
Since the number was more than 100,000 / ml and three streaks were found on the film, commercialization with this filter was abandoned.

Comparative Example 2 Coating was started under the same conditions as in Example 1 except that a filter having a filtration accuracy of 0.1 μm was used. No application streaks were observed during the continuous 24 hours, but the pressure was severely increased due to clogging of the filter, and the filter was replaced approximately every 4 hours. Under these conditions, it was found that unless the filter was replaced frequently, the amount of liquid sent from the pump during production decreased, and the desired amount of application could not be maintained.

[0037]

[Table 1]

[0038]

According to the coating method of the present invention, coagulation nuclei in the coating liquid can be reduced and good coating without coating streaks can be realized.

[Brief description of the drawings]

FIG. 1 is a side view of a coating apparatus according to one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a form of a coating streak.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gravure roll 2 Chamber 3 Running film 4 Coating tank 5 Liquid feed pump 6 Pressure gauge 7 Filter a Film running direction b Roll 1 rotation direction c Flow direction of liquid d Aggregation nucleus

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA07 MC23 PA01 PB70 PC80 4D075 AC25 AC26 AC72 AC84 AC97 BB16X BB91X CA48 DA04 DB36 DB48 DB53 DC27 EA06 EB22 EB35 EB39 EB57

Claims (1)

[Claims] 1. A coating method comprising: means for applying a coating liquid on at least one side of a running plastic film; and means for supplying a coating liquid, wherein said coating liquid supply means includes at least one means for filtering the coating liquid. The filtration accuracy of the filtration means is 0.2 to 3 μm, and the concentration of agglomeration nuclei having a size of 0.6 to 5 μm contained in the coating liquid passing through the filtration means is 6,000,000 / ml or less. A coating method, characterized in that: