JPS625045B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a membrane of saponified ethylene-vinyl acetate copolymer by a solution coating method or a casting method. Saponified ethylene-vinyl acetate copolymer is soluble in an alcohol-water mixed solvent, but insoluble in alcohol or water alone, so a high-quality membrane is manufactured from the mixed solvent solution by solution coating or casting. It's not easy. This is because as the volatile matter evaporates during the drying process, the composition ratio of the remaining mixed solvent changes, and during drying, the film surface loses heat of vaporization to the volatile matter and becomes low temperature, so moisture in the drying atmosphere reaches the surface. This is because the resin condenses, resulting in demixing of the resin, and the resulting film becomes white over the entire surface or becomes white in patches. This whitening phenomenon can be reduced to some extent by increasing the drying temperature, but if the drying temperature is increased, a yuzu skin will appear on the surface, and if it is excessive, air bubbles will be generated. Whether or not problems such as whitening, yuzu skin, and air bubbles occur depends greatly on the film thickness; a thickness of about 10 μm causes almost no problems, and a thickness of about 15 μm does not cause any problems. Although this problem can be overcome, when the thickness exceeds 17 μm, the above-mentioned trouble suddenly becomes noticeable, and it becomes impossible to obtain a film of good quality industrially. However, as a result of intensive research by the present inventors,
When a solution layer formed on a support such as a metal surface or a film surface is first dried virtually without blowing air until the amount of solvent evaporated reaches a certain amount, and then drying with normal air blowing, the above-mentioned problems may occur. The inventors have discovered that this problem can be solved and that high-quality membranes can be manufactured stably on an industrial scale, leading to the completion of the present invention. That is, in the film forming method of the present invention, a layer of a solution of a saponified ethylene-vinyl acetate copolymer dissolved in an alcohol-water mixed solvent is formed on a support and then dried to produce a film. The method is characterized in that drying (A) is carried out substantially without air blowing until the weight loss due to evaporation of the mixed solvent from the layer becomes 0.5 to 30% by weight, and then air drying (B) is carried out. What is saponified ethylene-vinyl acetate copolymer?
It refers to a product obtained by saponifying an ethylene-vinyl acetate copolymer to convert all of the vinyl acetate component or the water portion 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,
This is disadvantageous in terms of solvent resistance, orientation during stretching, etc. The alcohol-water mixed solvent for dissolving the saponified ethylene-vinyl acetate copolymer may be one or more of methanol, n-propanol, isopropanol, ethanol, 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 satisfies -0.12E+19.3≦SP≦-0.12E+22.7. The solubility parameter SP of the mixed solvent is determined by adding the solubility parameter of each solvent, that is, methanol 14.5, ethanol 12.7, n-propanol 11.9, isopropanol 11.5, t-butanol 10.6, and water 23.4, according to the weight ratio of each solvent. can be calculated quantitatively. In addition
Regarding SP values, the SP values of many solvents are listed on pages 345 to 358 of the Polymer Handbook. A solution prepared by dissolving a saponified ethylene-vinyl acetate copolymer in an alcohol-water mixed solvent is coated or cast onto a support to form a solution layer. The concentration of the resin component in the solution is not particularly limited, but since the effect of the present invention is 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. 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. Supports for forming the solution layer include metal surfaces such as endless belts and drums, resin-coated metal surfaces, as well as inorganic materials such as plastic films, plastic sheets or plates, metal foils and plates, glass, plaster, and cement products. Examples include board, paper, wood board, woven/non-woven fabric, and leather. The solution layer is formed by any method such as discharging from a casting head, roll coating, doctor roll coating, doctor knife coating, curtain flow coating, spraying, dipping, or brush coating. After the solution layer is formed on the support, it is not immediately subjected to air drying, but it is first dried substantially without air blowing (A )I do. The purpose of providing this drying step (A) is to form a smooth thin film on the surface of the solution layer in the early stage of drying.The formation of such a thin film on the surface makes it possible to suppress the drying rate, and prevent excessive drying speed. This is thought to be able to eliminate the causes of problems such as → temperature drop in the solution layer due to vaporization of volatile matter → condensation of moisture on the surface → whitening phenomenon. This drying (A) must be done virtually without blowing air; blow drying does not form the desired surface thin film and cannot prevent the whitening phenomenon. In addition, the evaporation loss in this step (A) should be 0.5 to 30% by weight, especially 1 to 20% by weight; if the evaporation loss is less than 0.5% by weight, the whitening phenomenon cannot be prevented; on the other hand, if the evaporation loss is less than 0.5% by weight, If it exceeds 100%, the film formed on the surface becomes too thick, resulting in a disadvantage that the subsequent drying rate is significantly delayed. In addition, "substantially no air blown" in the drying process (A) means not only literally no air blown, but also 5m/
This also includes gentle air blowing conditions of less than sec. The temperature conditions for the drying step (A) can be varied as long as it is about 70°C or less, but it is preferably carried out at 0 to 45°C, particularly around room temperature. Therefore, the temperature of the stock solution is 0 to 45℃,
Normally, it should be kept around room temperature. If the temperature is less than 0°C, it will take a long time to dry, and if it exceeds 45°C, there will be a tendency for the surface smoothness to be disadvantageous. After the drying step (A), blow drying (B) is performed like normal drying. Air blowing speed is 5m/sec or more, and
It is desirable to set it to 7m/sec or more, especially 10m/sec or more. Although various temperature conditions can be selected for the drying step (B), it is usually 50° C. or higher and 140° C. or lower; if it is lower than 50° C., drying takes an extremely long time and becomes unsuitable for industrial use. The same air blowing and temperature conditions may be used throughout the drying process (B), but
is divided into several stages, and the air blowing conditions are changed at each stage.
Temperature conditions may be changed. A membrane is obtained through drying steps (A) and (B). The film thickness can be set arbitrarily from thin to extremely thick, but the thickness must be 17μ or more, and even 20μ.
Since the effects of the present invention are particularly noticeable when the thickness is thicker than 17μ, the effect of the present invention is more pronounced than that of ordinary drying methods, so it is desirable to control the concentration of the stock solution, the amount of application, etc. so that the final thickness is 17μ or more. After film formation, the film is peeled off from the support, but if the support is a base material such as a plastic film, it may be left integral with the base material as it is. 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. "Parts" and "%" below are expressed on a weight basis unless otherwise specified. Note that the temperature condition of the dryer refers to the ambient temperature. Example 1 115 parts of saponified ethylene-vinyl acetate copolymer powder with an ethylene content of 29 mol% and a degree of saponification of the vinyl acetate component of 99 mol% was mixed in a mixed solvent of n-propanol and water at a ratio of 50:50 by weight ( After heating and dissolving 385 parts of SP=17.7), the mixture was allowed to cool at room temperature overnight. The resin concentration is
It was 23%. After applying this solution to a thickness of 120μ on a 100μ thick polyester film using a film applicator, it was left to dry at room temperature 26℃ for 60 seconds to form a film on the surface (evaporation rate of volatile matter 6.2%). Then, it was dried for 90 seconds in a hot air dryer at a temperature of 105° C. while blowing air at a rate of 8 m/sec. This operation increases the thickness
A transparent and smooth film with a diameter of 21μ and a volatile content of 6.8% was obtained. The results are shown in Table 1. Control Example 1 The same procedure as Example 1 was carried out except that after coating, the coating was left to dry overnight at room temperature without blowing air, with a thickness of 20.5μ and a volatile content.
A film of 10.2% was obtained. Control example 2 Immediately after application, it was placed in a hot air dryer at a temperature of 105°C for 8m/
A film having a thickness of 21 μm and a volatile content of 8.5% was obtained in the same manner as in Example 1, except that drying was performed for 120 seconds under air blowing at sec. The results of Control Examples 1 and 2 are also shown in Table 1.

[Table] Uh.
Example 2 A coating device equipped with a doctor coater and a blow dryer was prepared, a 25 μm thick polyester film was supplied to the device, and the stock solution (room temperature) used in Example 1 was charged into the liquid reservoir to form a film. It started. The time from the doctor coater to the dryer inlet was 37 seconds, and the weight loss due to evaporation of the mixed solvent from the coating solution during this time was 4.2%. Air is blown inside the dryer from a direction perpendicular to the membrane surface at a speed of 10 m/sec, and the temperature is 70°C at the dryer entrance and 120°C at the exit.
It was set at ℃. The time required from the entrance to the exit of the dryer was set to 114 seconds. 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 20.5 μm and a volatile content of 4.5% was obtained. The properties of this film are shown in Table 2. Control example 3 The stock solution was heated to 60°C and coated on the surface of a polyester film previously heated to 60°C using a doctor coater installed close to the dryer inlet, and then immediately placed in a blow dryer (blow speed 10 m/sec, temperature
The experiment was carried out in the same manner as in Example 2, except that it was dried at 85℃), and the thickness was 21.5μ, and the volatile content was 18.6%.
A film was obtained. Control example 4 Air blow rate is 10 m/sec, temperature is 70 at the dryer inlet.
Drying was carried out in the same manner as in Control Example 3 except that the temperature was 120°C at the outlet to obtain a film with a thickness of 21 μm and a volatile content of 13.2%. Control example 5 The stock solution was heated to 60°C, and the doctor coater and the dryer inlet were connected so that the evaporation loss of the mixed solution was 35% during the time it reached the dryer inlet after coating on the polyester film surface that had been preheated to 60°C. The distance between them was adjusted, and then they were passed through the dryer. The drying conditions are a blowing speed of 10 m/sec, a temperature of 70°C at the inlet, and 120°C at the outlet.
It was set at ℃. Through this operation, a film with a thickness of 21 μm and a volatile content of 38.6% was obtained. The results of Control Examples 3 to 5 are also shown in Table 2.

[Table] Example 3 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 40 mol% and a saponification degree of vinyl acetate component of 99 mol% was mixed with isopropanol and water by weight.
It was heated and dissolved in a 55:45 mixed solvent (SP=16.9) and then allowed to cool. The resin concentration was set at 23%. The above stock solution at room temperature was discharged from the casting head onto the endless belt surface of a casting film forming apparatus equipped with a casting head and a blow dryer (temperature of the belt surface was 40° C.), and film formation was started. The time from the head to the dryer entrance is 21
The weight loss due to evaporation of the mixed solvent from the casting solution during this period was 8.2%. Air was blown inside the dryer at a speed of 12 m/sec, and the temperature was set at 68°C at the dryer inlet and 122°C at the outlet. The residence time in the dryer was 127 seconds. The film that came out of the dryer was peeled off from the belt surface and wound on a winder. Through the above operations, a film with a thickness of 23 μm and a volatile content of 5.3% was obtained. The properties of the obtained membrane are shown in Table 3. Comparative Example 6 The stock solution was heated to 60°C, discharged onto the belt surface from a casting head installed close to the dryer inlet, and immediately passed through a blower type dryer, resulting in a blowing speed of 12 m/sec and a temperature of 85°C. Drying was carried out under the following conditions. This operation reduced the thickness to 22.5μ and the volatile content.
A 16.5% membrane was obtained. Control Example 7 Drying was carried out in the same manner as in Control Example 6, except that the blow speed was 12 m/sec and the temperature was 70° C. at the inlet and 120° C. at the outlet, to obtain a film with a thickness of 23 μm and a volatile content of 11.7%. Comparative Example 8 In Example 3, a cover was installed from immediately after the casting head to the dryer, and room temperature air was blown at 10 m/sec during this period. The weight loss due to evaporation of the mixed solvent from the casting solution up to the dryer inlet was 21.2%. Other conditions were the same as in Example 3. This operation increases the thickness
A film of 23.5μ and 6.2% volatile content was obtained. The results of Control Examples 6 to 8 are shown in Table 3.

[Table] Example 4 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 20 mol% and a saponification degree of vinyl acetate component of 99 mol% was mixed with ethanol and water at a ratio of 45:55 by weight.
After heating and dissolving in a mixed solvent (SP=18.6), a small amount of dye was added and the temperature was maintained at 30°C. The resin concentration was set at 23%. Casting film formation was performed using this stock solution using the apparatus described in Example 3. The weight loss due to evaporation of the mixed solvent from the head to the dryer inlet is
It was 6.8%. Air was blown inside the dryer at a speed of 12 m/sec, and the temperature was set at 65°C at the dryer inlet and 120°C at the outlet. This operation reduced the thickness to 23.5μ and the volatile content.
A film of 4.8% was obtained. The properties of the obtained membrane are shown in Table 4. Comparative Example 9 The stock solution was heated to 60°C, discharged onto the belt surface from a casting head installed close to the dryer inlet, and immediately passed through a blower type dryer, resulting in a blowing speed of 12 m/sec and a temperature of 80°C. Drying was carried out under the following conditions. This operation reduced the thickness to 24.5μ and the volatile content.
A film of 12.9% was obtained. Control Example 10 Drying was carried out in the same manner as in Control Example 9, except that the air blow rate was 12 m/sec and the temperature was 65° C. at the inlet and 120° C. at the outlet, to obtain a film with a thickness of 24.5 μm and a volatile content of 11.5%. Comparative Example 11 In Example 4, a cover was installed from immediately after the casting head to the dryer, and room temperature air was blown at 10 m/sec during this period. The weight loss due to evaporation of the mixed solvent from the casting solution before reaching the dryer inlet was 27.5%. Other conditions were the same as in Example 4. This operation increases the thickness
A film of 24μ and 6.0% volatile content was obtained. The results of Control Examples 9 to 11 are shown in Table 4.

【table】

Claims (1)

[Scope of Claims] 1. In manufacturing a membrane by forming a layer of a solution of a saponified ethylene-vinyl acetate copolymer dissolved in an alcohol-water mixed solvent on a support and then drying it, first the solution layer is Drying with virtually no air blowing until the weight loss due to evaporation of the mixed solvent is 0.5 to 30% by weight.
A method for forming a film of a saponified ethylene-vinyl acetate copolymer, the method comprising carrying out (A) and then carrying out blow drying (B). 2. The method according to claim 1, characterized in that the drying (A) is carried out substantially without blowing air at a temperature of 0 to 45°C. 3. The method according to claim 1, wherein the blow drying (B) is performed at a temperature of 50°C or higher. 4 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. 5 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. 6. The method according to claim 1, characterized in that the film thickness after drying is set to 17μ or more.