JPS625046B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a film of saponified ethylene-vinyl acetate copolymer by a solution coating method. Saponified ethylene-vinyl acetate copolymer is soluble in an alcohol-water mixed solvent, but it is not easy to produce a high-quality film from a solution of the mixed solvent by a solution coating method. This is because when a membrane is manufactured by spreading the solution from an alcohol-water mixed solvent solution of the saponified product onto a suitable support by a casting method or a conventional coating method, and then subjecting it to a drying process, the resulting membrane This is because streaks (coater lines), pinholes, and air bubbles are noticeable. These problems also depend on the film thickness;
The above disadvantage is not particularly large up to about 15μ, but
When the film thickness becomes 17 μm or more, the above-mentioned disadvantages tend to suddenly become noticeable. However, as a result of intensive research by the present inventors,
A solution prepared by dissolving saponified ethylene-vinyl acetate copolymer in an alcohol-water mixed solvent is applied onto a support such as an endless belt, a drum, or a plastic film and then dried to produce a membrane. We discovered that when coating onto a support using a special doctor roll with a comma-shaped cross section, a high-quality film with excellent film thickness accuracy and no streaks, pinholes, or bubbles could be obtained smoothly. The invention was completed. In the present invention, it is important to use a doctor roll with a comma-shaped cross section as shown in the cross-sectional view in Figure 1. Even with the same doctor method, it is important to use a doctor roll with a circular cross section or a doctor knife with a blade shape. Unable to achieve period objectives. Further, even if dip coating, direct gravure coating, offset gravure coating, air knife coating, reverse roll coating, or cast coating methods are employed, the effects as excellent as those of the present invention cannot be achieved. What is saponified ethylene-vinyl acetate copolymer?
It refers to an ethylene-vinyl acetate copolymer that has been saponified to convert all or most of the vinyl acetate component into a vinyl alcohol component. The ethylene-vinyl acetate copolymer used has an ethylene content of 15 to 55 mol% and a vinyl acetate content of 85 to 45 mol%, and also contains propylene, isobutene,
Comonomers such as α-olefins such as α-octene, α-dodecene, α-octadecene, unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides, unsaturated sulfonic acids or their salts May contain small amounts of. Saponification of vinyl acetate component depends on the degree of saponification.
This is carried out until the concentration is 90 mol% or more, preferably 95 mol% or more. Saponified ethylene-vinyl acetate copolymers with other compositions have moisture resistance, water resistance, oxygen barrier properties,
It is disadvantageous in terms of solvent resistance and orientation during stretching. The alcohol-water mixed solvent for dissolving the saponified ethylene-vinyl acetate copolymer may be one or more of methanol, ethanol, n-propanol, isopropanol, isobutanol, sec-butanol, t-butanol, etc. and water. The ratio of alcohol and water in this mixed solvent is, when the ethylene content of the saponified ethylene-vinyl acetate copolymer used is E (mol%),
It is preferable to select the type of alcohol and the mixing ratio with water so that the solubility parameter SP of the mixed solvent is −0.12E+19.3≦SP≦−0.12E+22.7. The solubility parameter SP of the mixed solvent is calculated according to the weight ratio of the solvents from the solubility parameters of each solvent, namely methanol 14.5, ethanol 12.7, n-propanol 11.9, isopropanol 11.5, t-butanol 10.6, and water 23.4. It can be calculated accurately. Furthermore, SP
For values, see Polymer Handbook (Polymer
SP of many solvents on pages 345-358 of Handbook)
Values are listed. The solution contains plasticizers (polyhydric alcohols, etc.), fillers, reinforcing materials (glass fibers, etc.), colorants, polarizing elements, ultraviolet absorbers, surfactants, modifying resins, thickeners, soluble inorganic salts, Boric acid or borax may also be added. A solution of saponified ethylene-vinyl acetate copolymer dissolved in an alcohol-water mixed solvent can be applied to metal surfaces such as endless belts and drums, resin-coated metal surfaces, plastic films, metal foils, paper, cellophane, and other supports. It is applied using a doctor roll. The concentration of the resin component in the solution is not particularly limited, but since the effects of the present invention are significantly exhibited in the case of a thick film, it is preferable to set the resin concentration to 14% by weight, especially 21% by weight or more. preferable. As the doctor roll, a doctor roll having a comma-shaped cross section as shown in FIG. 1 is used as described above. As an example, as shown in FIG. 2, which is an explanatory diagram of a film forming method using the coating method, the stock solution charged in the liquid reservoir 2 is transferred by a doctor roll 1 having a comma-shaped cross section as the base film 3 travels. It is applied to a certain thickness. After passing through the doctor roll 1, it is dried by passing through dryers 4, 4', and then peeled off from the base film. The temperature conditions for the drying process are room temperature to about 140°C, and preferably a method is adopted in which the temperature is increased in stages. The film thickness can be arbitrarily set from thin to extremely thick, but the effects of the present invention are particularly pronounced compared to conventional methods when the film is thick, such as 17μ or more, or even 20μ or more. Final thickness is 17
It is desirable to control the concentration of the stock solution, the amount of application, etc. so that it is at least μ. After film formation, the film is peeled off from the endless belt surface or drum surface, but if the flat surface is a base material surface such as a plastic film, it may be left integral with the base material. The film obtained by the method of the present invention is of extremely high quality and is useful as a membrane, packaging film, raw film for polarizing film, etc., or a composite material using the film as a coating layer. Next, the method of the present invention will be further explained with reference to Examples. Hereinafter, the term "%" refers to % by weight unless otherwise specified. Note that the temperature condition of the dryer refers to the ambient temperature. Example 1 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 30 mol% and a saponification degree of vinyl acetate component of 99 mol% was mixed with n-propanol and water by weight.
The mixture was heated and dissolved in a 50:50 mixed solvent (SP=17.7) and then allowed to cool at room temperature overnight. The resin concentration was set at 22%. A coating device equipped with a coater and a blow dryer was prepared, a polyester film was supplied to the device, and a stock solution at room temperature was charged into the coater to start film formation. The coater is a roll with a diameter of 200 m/m as shown in Figure 1, and a depth of 10 m/m at the bottom.
A doctor roll with a comma-shaped cross section and a notch of m was used, and the clearance was adjusted to 120μ. The time required from the coater to the entrance of the dryer was 2 minutes, and in the dryer the temperature was 80°C in the first stage for 1 minute, and the second stage was 105°C for 2 minutes. The film that came out of the dryer was wound up on a winder together with the polyester film. The film was extremely easy to peel off from the polyester film. Through the above operations, a film with a thickness of 20 μm was obtained. The properties of this film are shown in Table 1. Comparative Examples 1 to 7 Films were formed in the same manner as in Example 1, except that the following coating method was employed. The results are also shown in Table 1. Control example 1 Dip coating Single-sided coating by line contact between applicator roll and coating liquid, no squeeze roll Control example 2 Direct gravure roll coating Gravure roll (diameter 300 m/m) and back up roll (diameter 300 m/m) in the same direction Rotation coating control example 3 Offset gravure roll coating Combination control example 4 of gravure roll, rubber-covered offset roll and back-up roll Air knife coating Applicator using kiss roll and metal back-up roll with air doctor (dia.
300m/m) Combination Control Example 5 Reverse roll coating 4-roll type using pick-up rolls (each diameter 250m/m) Control Example 6 Doctor blade coating The distance between the knife and the base film is 120μ Control Example 7 Cast coating Cast Coater lip width 150μ

[Table] Example 2 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 41 mol% and a degree of saponification of vinyl acetate component of 99 mol% was mixed with isopropanol and water by weight.
It was heated and dissolved in a 60:40 mixed solvent (SP=16.3) and then allowed to cool. The resin concentration was set at 21.5%. An endless belt type film forming apparatus equipped with a coater and a blow dryer was prepared, and film forming was started by charging the stock solution at room temperature into the coater. The coater used was a doctor roll with a comma-shaped cross section having the same dimensions as that used in the examples, and the clearance was adjusted to 160μ. The time required from the coater to the dryer entrance is 1.5 minutes, and the temperature at the front stage of the dryer is 80°C.
The time required is 45 seconds, and the time required at the second stage is 110℃, and the time required is 1.5 seconds.
Dry with air for minutes. The film that came out of the dryer peeled off from the belt surface and was wound up on a winder. Through the above operations, a film with a thickness of 26 μm was obtained. The properties of this film are shown in Table 2. Control Examples 8 to 11 Films were formed in the same manner as in Example 2, except that the following coating method was employed. The results are also shown in Table 2. Control example 8 Direct gravure roll coating Control example 9 Offset gravure roll coating Control example 10 Reverse roll coating Control example 11 Doctor blade coating

[Table] Example 3 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 24.5 mol% and a saponification degree of vinyl acetate component of 99.5 mol% was mixed with ethanol and water by weight.
After heating and dissolving in a 40:60 mixed solvent (SP=19.1), a small amount of dye was added and the temperature was maintained at 37°C. The resin concentration was set at 24%. Using this stock solution, film formation was performed using the apparatus described in Example 2. The time required from the coater to the entrance of the dryer was 2 minutes, and in the dryer, air blow drying was carried out under the conditions that the first stage was at a temperature of 70°C for 1 minute, and the second stage was at a temperature of 115°C for 2 minutes. The film that came out of the dryer peeled off from the belt surface and was wound up on a winder. Through the above operations, a film with a thickness of 29 μm was obtained. The properties of this film are shown in Table 3. Comparative Examples 12 to 15 Films were formed in the same manner as in Example 3, except that the following coating method was used. The results are also shown in Table 3. Control example 12 Direct gravure roll coating control example 13 Offset gravure roll coating control example 14 Reverse roll coating control example 15 Doctor blade coating

【table】 [Brief explanation of the drawing]

FIG. 1 is a sectional view of a doctor roll used in the present invention, and FIG. 2 is an explanatory diagram showing an example of the film forming method of the present invention. 1...Doctor roll with a comma-shaped cross section, 2...
...Liquid reservoir, 3...Base film, 4, 4'...Dryer.

Claims (1)

[Claims] 1. When producing a membrane by coating a solution of a saponified ethylene-vinyl acetate copolymer dissolved in an alcohol-water mixed solvent on a support and drying it, the solution is coated with a comma-shaped cross section. 1. A method for forming a film of a saponified ethylene-vinyl acetate copolymer, the method comprising coating the saponified ethylene-vinyl acetate copolymer onto a support using a doctor roll. 2 The saponified ethylene-vinyl acetate copolymer is
The method according to claim 1, wherein the resin has a copolymerization composition with an ethylene content of 15 to 55 mol% and a degree of saponification of the vinyl acetate component of 90 mol% or more. 3. The method according to claim 1, characterized in that the film thickness after drying is set to 17μ or more. 4 The solubility parameter (SP) of the alcohol-water mixed solvent is -0.12E+19.3≦SP≦-0.12E+22, where E (mol%) is the ethylene content of the saponified ethylene-vinyl acetate copolymer. 7. The method according to claim 1, wherein the type of alcohol and the mixing ratio with water are selected so that the alcohol content is 7.