JPH0142963B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyvinyl alcohol (hereinafter referred to as PVA) film, and in particular provides a method for producing an ultra-thin film, which has been impossible with conventional techniques. PVA membranes have excellent properties such as high transparency, oxygen impermeability, liquid mixed component separation permeability, and cryogenic electrical insulation properties, so they can be used as packaging materials, gas barrier materials, separation membranes, and electrical insulation. It has traditionally been used as a material, or has recently started to attract attention. In general, the thinner the membrane material is, the more functionally it can be used, and its applications are expected to expand. However, PVA is generally non-thermoplastic, and in film formation, it is necessary to form an independent thin film (i.e., a thin film that maintains the film structure with the PVA film itself, rather than a thin film formed on another film surface such as coating on a support film). ) was extremely difficult to manufacture. To explain in more detail, in order to produce a thin film with a thickness of 2000 Å or less, which is much thinner than the 5 to 50 μm thickness of a normal independent polymer film, PVA in a PVA solution as a film forming stock solution is required.
It is necessary to keep the concentration very low, for example, below 5 g/dl. When using such a low-concentration film-forming stock solution, the stock solution has almost no film-forming ability, so it is very difficult to independently spread the stock solution discharged from the extrusion port (die or nozzle) into a film. Therefore, it was virtually impossible to form a film. The present invention solves this problem or drawback and is a PVA membrane made of PVA with a syndiotact content of 50-65%. According to the invention, the syndiotact content is 50-65%
Since PVA is used, it is possible to obtain an independent thin film with excellent elasticity and an extremely thin film thickness, for example, 10,000 Å or less, or even 5,000 Å or less. It is also possible to obtain ultra-thin films of 2000 Å or less, and even ultra-thin films of 1000 Å or less. Furthermore, by stretching the obtained thin film,
In some cases, the thickness can be set to 300 Å or less. The PVA membrane of the present invention has a syndiotact content of 50 to 65%, preferably 52 to 60% as a membrane forming stock solution.
It can be obtained by using an aqueous solution with a PVA concentration of 1 g/dl or more and a gelation concentration or less. Here, the membrane forming stock solution is the stock solution almost immediately before being discharged, and is an aqueous solution mainly consisting of PVA and water, but it also contains a small amount of solvents such as ethylene glycol and dimethyl sulfoxide (for example, compared to PVA).
20% by weight). The syndiotact content of PVA in the film forming stock solution is 50
It needs to be ~65%; if it is less than 50%, the discharged stock solution will become droplets and no film will be formed, and if it is more than 65%, the film-forming stock solution will gel and cannot be discharged at a uniform speed. In addition, the concentration of PVA in the membrane forming stock solution is extremely important, and in the present invention, it is necessary that the aqueous solution has a concentration of 1 g/dl or more and a gel concentration or less. 1g/
If it is less than dl, it will be difficult to discharge in the form of a film, and conversely, the concentration will become high, and if it exceeds the gel concentration, it will be difficult to discharge and it will not be possible to obtain the desired thin film. The gel concentration varies depending on the temperature of the membrane forming solution, the degree of polymerization of PVA, etc., but it is approximately 3.5 at room temperature.
g/dl. Next, as the method for forming the PVA film of the present invention, any film forming method that can obtain an independent thin film may be used, but from an industrial standpoint, extrusion molding is preferred because it has high molding efficiency. Extrusion molding involves extruding the film-forming stock solution into a pipe shape, blowing compressed air into the pipe before solidification progresses, and expanding the pipe to form a thin cylindrical film, using inflation molding or a T-die. Sheet extrusion molding, in which a film-forming stock solution is directly extruded into a thin, wide sheet, is preferably used. The film was formed in this way
The PVA membrane can be used as is or stretched (e.g. 1.5
~10 times), heat treated (for example, at 100 to 230°C), or stacked on a support (for example, a film, plate, or piece), and then rolled up or cut. In the present invention, the syndiotact content is 50-65%
PVA is typically obtained by polymerizing vinyl trifluoroacetate using an ordinary radical polymerization catalyst such as azobisisobutyronitrile or benzoyl peroxide, and then saponifying the polymer. Furthermore, vinyl trifluoroacetate is copolymerized with a small amount of other vinyl ester, such as vinyl acetate,
It can also be obtained by saponifying it.
The degree of polymerization of the obtained PVA is 900 or more, preferably
1500 or more. If the degree of polymerization is too low, e.g.
If it is less than 900, it becomes difficult to discharge it in a film form.
The degree of saponification of the obtained PVA is not particularly limited as long as it is water-soluble, but it is 80 mol% or more, preferably 90 mol% or more. In the present invention, in addition to such PVA with a syndiotact content of 50 to 65%, ordinary PVA, PVA modified with anionic groups, cationic groups, etc., and other water-soluble film-forming resins, Further, various additives such as surfactants necessary for film formation may be used in combination within the range that does not impede the purpose of the present invention. In the present invention, the film is highly elastic and extremely thin.
A PVA membrane can be obtained, but when forming a film-forming stock solution consisting of PVA with a syndiotact content of 50 to 65%, syndiotact is formed at the interface with air.
It is presumed that the cause is the adsorption and concentration of PVA. In this way, in the present invention, a thin or ultra-thin PVA film that is highly elastic and has a thickness of 10,000 Å or less, further 5,000 Å or less, in some cases 2,000 Å or less or 1,000 Å or less, and furthermore 500 Å or less or 300 Å or less by stretching etc. These membranes can be effectively used as organic derivative capacitors, semiconductor insulating sealing layers, and separation membranes (ultrafiltration membranes, reverse osmosis membranes, gas separation membranes, liquid-liquid separation membranes). In addition, it can be effectively used as a packaging material, a gas barrier material, an electrical insulating material, and an optical film (polarizing film, infrared shielding film). Next, the present invention will be further explained with reference to Examples.
The present invention is not limited in any way by the examples. Example 1 Bulk polymerization using benzoyl peroxide with vinyl trifluoroacetate as catalyst, followed by saponification in diethylenetriamine to reduce PVA
1570, a saponification degree of about 100 mol%, and a syndiotact content of 55% (the syndiotact content was measured by Murahashi's method). A model experiment of inflation film formation was conducted using a 1 to 3.5 g/dl aqueous solution of this PVA. That is, suck up about 0.02 cc of the solution into a thin glass tube,
The material was gently blown to examine the ability to form a balloon film. As a result, large balloon films were formed in the concentration range of 1 to 3.5 g/dl, but especially 3 g/dl
A very stable balloon film was formed even in an aqueous solution of . When the entire film became colored (due to light interference), the blowing was stopped and the film was left to stand at room temperature for about 20 minutes to evaporate water and obtain a dry film. The shape of this dried film was as shown in the table below. The dried film obtained was iridescent, transparent, and elastic.

[Table] Only a slight absorption of the crystallization band at 1140 cm ^-1 was observed in the infrared absorption spectrum of this dry film, but when it was heat-treated at 200°C, clear absorption was observed at 1140 cm ^-1 . This is considered to indicate that the unheated film is almost amorphous with only slight crystallization. Further, when the unheated dried film was observed using a polarizing microscope, no orientation was clearly observed. Comparative Example 1 Vinyl acetate was solution polymerized in methanol using azobisisobutyronitrile as a catalyst,
Next, it was saponified in methanol using caustic soda as a catalyst to obtain PVA (polymerization degree 1700, saponification degree
98.5 mol%, syndiotact content 45%). Thereafter, the formation of a balloon film was examined by blowing in the same manner as in Example 1, but no balloon film was formed, and only water droplets fell from the thin tube.

Claims (1)

[Scope of Claims] 1. A polyvinyl alcohol membrane made of polyvinyl alcohol with a syndiotact content of 50 to 65%. 2. The polyvinyl alcohol membrane according to claim 1, which is polyvinyl alcohol having a syndiotact content of 52 to 60%. 3 When producing a polyvinyl alcohol membrane, the syndiotact content of the membrane forming stock solution is 50 to 65.
% polyvinyl alcohol concentration 1 g/dl or more,
A method for producing a polyvinyl alcohol film, characterized in that an aqueous solution having a gelling concentration or lower is used. 4. The method for producing a polyvinyl alcohol film according to claim 3, wherein the polyvinyl alcohol has a syndiotact content of 52 to 60%.