JPS625044B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a thick film of a 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 thick film from a solution of the mixed solvent by a solution coating method. This is because when a saponified ethylene-vinyl acetate copolymer solution with a high resin content is prepared in order to obtain a thick film, it exhibits significant structural viscosity. This is because if it is coated on top, streaks or die lines will occur and the thickness accuracy will be poor. This kind of trouble is not so noticeable up to a film thickness of about 15μ because a solution with a relatively low concentration can be used, but if you want to obtain a film with a thickness of 17μ or more, it is necessary to use a highly concentrated solution. Trouble quickly becomes apparent. On the other hand, in order to suppress the structural viscosity of an alcohol-water mixed solvent solution, a method has been proposed in which the solution is kept at a temperature of 50°C or higher and applied to a support, and then dried at a temperature of 50°C or higher and below the boiling point. ,
In this case, the initial drying rate becomes excessive, resulting in smoothness of the coated surface and whitening of the coated layer, making it impossible to obtain a thick film of good quality. The inventors of the present invention thought that streaks or die lines would be less likely to occur if the coating speed of the stock solution was lowered, and repeated experiments, but no improvement was observed even when the coating speed was lowered. However, upon further investigation, the present inventors discovered the unexpected fact that streaks or die lines disappear when the coating speed is increased due to an accidental application. Based on this fact, repeated research resulted in the present invention. The invention has been achieved. The method for producing a thick film of the present invention involves using a solution of a saponified ethylene-vinyl acetate copolymer dissolved in a monohydric alcohol (hereinafter simply referred to as alcohol)-water mixed solvent with a resin concentration of 14% by weight or more as a support. To obtain a film with a thickness of 17μ or more by coating and drying, and the shear rate D (sec ^-1 ) at the time of coating, and when the resin concentration of the solution is C (wt%), (41ogC - 3.60 )×10 ² ≦D ≦ (−31ogC+4.45)×10 ₇ . Here, the shear rate D is
When the thickness of the applied solution is d and the coating speed is V, it is determined by the relational expression D=V/d. By the method of the present invention, it is possible to industrially advantageously produce a film with good film thickness accuracy without streaks or die lines. 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,
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, 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 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 applied onto a support. The concentration of the resin in the solution is determined by the following: since the effects of the present invention are more pronounced in the case of thick films,
It is required that the content be 14% by weight or more, and among other things
The content is preferably 21% by weight or more. 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 to which the solution is applied include metal surfaces such as endless belts and drums, resin-coated metal surfaces, as well as plastic films, metal foils, paper, cellophane, and the like. The solution is applied by means such as discharging from a casting head, roll coating, doctor knife coating, doctor roll coating, curtain flow coating, or the like. The shear rate D (sec ^-1 ) when applying the solution is as shown in the above formula: (41ogC-3.60) x 10 ² ≦D ≦ (-31ogC + 4.45) x 10 ⁷ (4logC - 1.60) x 10 ² ≦D ≦(-3logC+
4.45) × 10 ⁶ and adjusted to a fast speed. For example, at a resin concentration of 23% by weight, the shear rate is 1.85×10 ² to 3.5×
10 ⁶ sec ^-1 , especially 3.84×10 ² ~3.5×10 ⁵ sec ^-1
is adjusted to the range of If the shear rate does not reach this range, streaks or die lines are likely to occur, while if it exceeds this range, streaks or die lines are more likely to occur. After coating at the above shearing rate, drying is then performed in a drying step. The temperature conditions for the drying process are room temperature or
The temperature is set at about 140°C, and preferably a method is adopted in which the temperature is increased in stages. The film thickness after drying should be set to 17μ or more, or even 20μ or more, and since the film can be formed from a solution with a low resin content at thin film thicknesses, it is possible to form a film from a solution with a low resin concentration, so streaks can be formed without paying particular attention to the shear rate. Or the die line is not very noticeable. Therefore, it is preferable to control the concentration of the stock solution, the amount of coating, etc. so that the final thickness is 17 μm 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. 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, "parts" and "%" are expressed on a weight basis unless otherwise specified. Note that the temperature condition of the dryer refers to the ambient temperature. Example 1 226 parts of a 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 774 parts of SP=17.7), the mixture was allowed to cool at room temperature overnight. The resin concentration is
It was 22.6% by weight (17.8% by volume). Apply the above solution to a thickness of 100 mm using an applicator.
Coated on μ polyester film. The scale of the applicator was set at 150μ, and the coating speed was varied. After coating, leave it at room temperature for 60 seconds to form a film on the surface of the coating solution, then place it in a dryer at a blow rate of 8.
Drying was performed at a speed of m/sec and a temperature of 105°C. Through the above operations, a film with a thickness of about 22 μm was obtained.
The results are shown in Table 1.

[Table] Example 2 Powder of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 40 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 55:45 mixed solvent (SP=16.9) and then allowed to cool. The resin concentration was set at 23% by weight (18.5% by volume). The above solution was coated onto a polyester film using an applicator. The scale of the applicator was set at 150μ, and the coating speed was varied. After coating, leave it at room temperature for 60 seconds to form a film on the surface of the coating solution, and then put it in a dryer at the air blow rate.
Drying was carried out at a speed of 8 m/sec and a temperature of 100°C. Through the above operations, a film with a thickness of about 24 μm was obtained.
The results are shown in Table 2.

[Table] Example 3 A coating device equipped with a doctor roll coater and a blow dryer was prepared, and a polyester film was supplied to the device, and Example 1 was added to the liquid reservoir.
The room temperature stock solution used in step 1 was charged and film formation was started.
The distance from the coater to the dryer entrance is 4m.
The distance from the dryer inlet to the outlet was 16 m, air was blown inside the dryer at a speed of 10 m/sec, and the drying temperature was 75°C at the dryer inlet and 130°C at the dryer outlet. The film that came out of the dryer was wound up on a winder together with the polyester film. The film was easily peeled from the polyester film. The above operations were repeated while varying the coating thickness and coating speed. The results are shown in Table 3.

[Table] Example 4 The stock solution at room temperature used in Example 2 was discharged from the casting head onto the endless belt surface of a casting film forming apparatus equipped with a casting head and a blower type dryer (the temperature of the belt surface was 40°C). ), film formation was started. The distance from the head to the dryer inlet is 2.5m, and the distance from the dryer inlet to the outlet is
The air was blown at a speed of 12 m/sec inside the dryer, and the drying temperature was 70°C at the dryer entrance and 130°C at the dryer outlet. The film that came out of the dryer peeled off from the belt surface and was wound up on a winder. The above operation was repeated while varying the coating speed. The results are shown in Table 4.

[Table] Example 5 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 37°C. The resin concentration was set at 23.5%. The above solution was coated onto a polyester film using an applicator. The scale of the applicator was set at 150μ, and the coating speed was varied. After coating, it was left at room temperature for 60 seconds, and then dried in a dryer at a blow rate of 8 m/sec and a temperature of 100°C. The results are shown in Table 5.

【table】

Claims (1)

[Claims] 1 ethylene-vinyl acetate copolymer saponified product
Concentration of resin dissolved in alcohol-water mixed solvent
Apply a solution of 14% by weight or more on a support and dry it to obtain a film with a thickness of 17μ or more, and set the shear rate D (sec ^-1 ) at the time of coating, and the resin concentration of the solution to C (weight% ), (41ogC−3.60)×10 ² ≦D≦(−31ogC+4.45)×10 ⁷ . 2. The method according to claim 1, wherein the resin concentration of the solution is 21% by weight or more. 3. The method according to claim 1, characterized in that a film having a thickness of 20 μm or more is obtained. 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 monohydric alcohol-water mixed solvent is -0.12E+19.3≦SP≦-0.12, where E (mol%) is the ethylene content of the saponified ethylene-vinyl acetate copolymer. The method according to claim 1, characterized in that the type of monohydric alcohol and the mixing ratio with water are selected so that E+22.7.