JPH0330486B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a biaxially stretched film of an acrylonitrile polymer having excellent mechanical strength and transparency. Acrylonitrile polymers, especially acrylonitrile polymers with high nitrile content, have poor thermoplasticity, so it is necessary to use the so-called solvent molding method using a solvent or the semi-melt molding method using a plasticizer to mold the film. . Moreover, the film obtained by simply removing the solvent and plasticizer from this molded film does not have sufficient mechanical strength as it is. Compounding, especially biaxial orientation, is required. Various methods have already been proposed for producing an oriented film with excellent mechanical strength and transparency by biaxially stretching the above-mentioned unoriented film. However, acrylonitrile-based polymers are highly oriented even by a small amount of stretching, and are prone to fibrillation. Stretching is also difficult. Japanese Patent Publication No. 38-26582 and Japanese Patent Publication No. 46-4079 describe a method of biaxial stretching with a large amount of solvent remaining in the formed film. It is extremely difficult to completely remove the solvent, and a considerable amount of the solvent tends to remain in the final product, which is unfavorable in terms of physical properties and safety and hygiene. On the other hand, JP-A-50-142673
No. 54-55049, a water-containing coagulated film obtained by coagulating a polymer solution in an aqueous solid bath and then removing the solvent by washing with water is prepared by controlling the water content to a predetermined range. A method of biaxially stretching in a dry heat or wet heat atmosphere while maintaining the same amount of water while making use of the plasticizing effect of water is described. These methods are preferable in terms of physical properties and safety and hygiene because they can minimize the amount of solvent remaining in the stretched film, but the method disclosed in JP-A-50-142673 requires a stretching temperature
The temperature is as high as 100 to 170°C, and it is difficult to adjust the water content of the water-containing coagulated film, especially in sequential biaxial stretching, and stable stretching is not easy. On the other hand, in the method disclosed in JP-A-54-55049, biaxial stretching of a water-containing coagulated film is carried out in high-temperature water or in a humid atmosphere at a relatively low temperature (90°C or lower, preferably 70°C or lower), so that the stretched film is not stretched. The stretched film also contains approximately the same amount of water as the film before stretching, and as a result, the stretched film has a low density, resulting in poor gas barrier properties and transparency. requires densification treatment at high temperature after stretching, but it is not easy to achieve sufficient densification. The present inventors conducted various studies on a stretching method that utilizes the plasticizing effect of water, and as a result, the water-containing solidified film was heated by contact heating with a metal plate or metal roll, and the water content of the film was maintained at a constant level. It has been found that it is extremely effective to stretch the film while holding it within this range. Adoption of contact heating using the metal plate or metal roll allows the temperature to be raised in a short time, and there is little change in the moisture content during the heating process. In addition, films stretched uniaxially using metal plates or metal rolls can also be stretched biaxially at right angles by readjusting the moisture content and stretching temperature. We have developed a metal plate or metal roll that can produce biaxially stretched films of acrylonitrile polymers using a general-purpose roll tenter sequential biaxial stretching device, which has been considered difficult to use for biaxially stretching hydrous coagulated films. It has been found that the film stretched using this method has unexpected effects such as being able to obtain a dense and highly transparent film even when stretched at a relatively low temperature. Based on the above knowledge, the present inventors have conducted extensive studies on the sequential biaxial stretching method using a roll tenter, and have found that by adjusting the water content and temperature of the film during stretching within a certain range, the orientation We have discovered that it is possible to stably produce a biaxially stretched film that is dense, transparent, and has good mechanical strength with good uniformity.
The present invention has now been accomplished. That is, in the present invention, a water-containing coagulated film of an acrylonitrile polymer is prepared, the water content is adjusted to 20 to 100% by weight (based on dry weight), and the surface temperature is adjusted to 65 to 100% by weight.
It is characterized by being longitudinally stretched with rolls at 95°C, and then transversely stretched in a tenter at an ambient temperature of 100 to 180°C with a moisture content (relative to dry polymer weight) lower than that during longitudinal stretching of 10 to 40% by weight. The present invention relates to a biaxial stretching method. The present invention will be explained in detail below. The acrylonitrile polymer used in the present invention is
An acrylonitrile copolymer or homopolymer containing 70% by weight or more of acrylonitrile. Monomers used in the copolymerization include acrylic esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, phenyl acrylate, octyl acrylate, etc. acid esters, such as methyl methacrylate,
Ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, phenyl methacrylate, octyl methacrylate, etc., vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, fluoride vinylamide, such as acrylamide, methacrylamide, N-methylacrylamide, N-vinylpyrrolidone, etc.
vinyl esters, such as vinyl acetate, vinyl propionate, vinyl lactate, vinyl aromatic compounds,
For example, styrene, vinylnaphthalene, vinylpyridine, etc., vinylcarboxylic acids such as acrylic acid,
Methacrylic acid, unsaturated dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid, etc., unsaturated dicarboxylic acid anhydrides such as itaconic anhydride, maleic anhydride, arylsulfonic acids or methallylsulfonic acids, or salts thereof. , methacrylonitrile, olefins such as ethylene, propylene, etc., and it is also possible to be a polymer in which two or more of these monomers are copolymerized with acrylonitrile, or a mixture of these polymers. be. If the acrylonitrile content of the copolymer is 70% by weight or less, depending on the type of copolymer monomer,
The plasticizing effect of water is reduced, making stretching difficult, and the properties expected of an acrylonitrile polymer film, such as gas barrier properties and weather resistance, become insufficient. On the other hand, the acrylonitrile content is 100%,
In other words, when it approaches a homopolymer, the stretching stress increases and uniform stretching becomes difficult, but by incorporating a small amount of plasticizer or solvent into the unstretched film, it is possible to achieve uniform stretching without compensating for the plasticizing effect of water. It is possible to do so. The upper limit of the acrylonitrile content that allows uniform stretching without such auxiliary means is 98% by weight. Water-containing coagulated film of acrylonitrile polymer as used in the present invention (hereinafter sometimes simply referred to as raw film)
It is generally convenient to produce by the so-called wet coagulation method as described below. That is, an acrylonitrile polymer solution is cast onto the belt or drum surface,
Alternatively, a coagulated film can be obtained by extruding the material into a sheet or tube through a slit die and coagulating it in an aqueous coagulation bath. Solvents used to create the polymer solution include dimethylformamide, dimethyl sulfoxide, N-
Dimethylformamide, N-methyl-β-cyanoethylformamide, α-cyanoacetamide,
There are aqueous solutions of inorganic acids and salts such as acetonitrile, γ-butyrolactone, nitric acid, sulfuric acid, zinc chloride, and sodium thiocyanate. The higher the polymer concentration in the polymer solution is, 10% by weight or more, the better in terms of producing a dense stretched film, but conversely, the higher the concentration, the higher the viscosity of the solution, and the more difficult it is to defoam and
It becomes difficult to be generous. Casting or extrusion of the polymer solution may be performed using known methods. As the aqueous coagulation bath used for coagulation, it is convenient to use water or an aqueous solution of the solution used to prepare the solution. In this case, it is advantageous in producing a dense stretched film to increase the solvent concentration of the aqueous solution within a range that causes coagulation. Generally, its concentration tends to be higher in organic solvents than inorganic solvents.
For example, it is preferably 20 to 40% by weight for nitric acid, and 30 to 60% for dimethylformamide. Furthermore, the higher the polymer concentration in the polymer solution, the denser the film can be obtained even if the solvent concentration in the coagulation bath is lowered. Washing with water or hot water can be used to remove the solvent in the coagulated film. The degree of desolvation is
From the perspective of the plasticizing effect of the residual solvent during stretching, it is more convenient to do so incompletely, but from the viewpoint of the physical properties and uses of the resulting film, it is preferable to do so sufficiently. The water-containing raw fabric obtained in this way usually has a
Contains ~400% by weight (based on dry polymer weight) water. The water-containing raw fabric of the acrylonitrile polymer of the present invention can also be produced by the following method. That is, Special Publication No. 7458 of 1984 and Special Publication of Publication No. 49 of 1973
As described in Publication No. 20625, a method of forming a film by casting using a volatile organic solvent, evaporating the solvent to some extent with hot air, and then replacing and removing the residual solvent with water or hot water, or JP-A-48 -As stated in Publication No. 49839,
It can also be produced by hydrating the nitrile group of an acrylonitrile-based polymer with water to make it into a semi-molten state, and extruding it, for example, under high-temperature, high-pressure steam. The biaxial stretching can be carried out by adjusting the moisture content and temperature of the water-containing raw fabric within a certain range, and using a general-purpose roll tenter sequential biaxial stretching apparatus. To adjust the moisture content of the wet web, drying methods such as hot air, infrared rays, far infrared rays, steam, hot plates, hot rolls, etc. can be used, but rapid drying with any method may result in loss of the web. It is desirable to avoid this as it tends to cause transparency and porosity. Among them, drying with hot air has a relatively low drying efficiency, but it can provide a stretched film that is transparent and has excellent mechanical strength. Further, as an efficient and uniform dehydration drying method, a method of immersing a water-containing raw fabric in hot water of 50 to 90°C can be used. This method is particularly effective for dehydrating raw fabrics with high moisture content; for example, raw fabrics with a moisture content of 250% by weight are soaked in hot water at 80°C.
Approximately 80% by weight uniformly by soaking for around 30 seconds
It can be dehydrated and dried to a moisture content of . If the temperature of the hot water is higher than 90℃, the film will become porous (devitrification) due to dehydration, and it will be difficult to restore the film to a dense state even with subsequent heating, resulting in a decrease in the physical properties of the film, especially its mechanical strength. . Moreover, if the temperature is lower than 50°C, the effect of dehydration and drying will be small. Roll tenter sequential stretching can be performed under the following conditions. That is, when the moisture content of the original fabric is 20 to 100% by weight (based on dry polymer weight), the surface temperature is 65%.
Longitudinal stretching with metal rolls at ~95℃, then moisture content 10~
Transverse stretching is performed using a tenter at 40% by weight and at an ambient temperature of 100 to 180°C. Regarding roll stretching, if the moisture content of the raw fabric is lower than 20% by weight, it will be difficult to increase the moisture content to 10% by weight (preferably 15% by weight) or more during tenter stretching in the subsequent step. 80
When it exceeds % by weight, some porosity is observed, but
Up to 100% by weight, it can be made dense by subsequent tenter stretching.
Become transparent. However, if it exceeds 100% by weight, the porosity (devitrification) caused by roll stretching will not be recovered even by subsequent tenter stretching. Generally, it is preferable that the moisture content of the original fabric in roll stretching is 15 to 70% by weight. On the other hand, if the surface temperature of the metal roll is lower than 65℃, the stretching stress will be high and stretch breakage will easily occur.
If the temperature is higher than 0.degree. C., rapid dehydration on the roll surface causes porosity (devitrification), and subsequent tenter stretching does not result in densification and transparency. Therefore, generally the roll surface temperature is most preferably 70 to 90°C. Regarding tenter stretching, if the moisture content is lower than 10% by weight or the ambient temperature is lower than 100° C., stretching stress is high and stretch breakage is likely to occur. Also, the moisture content is 40
If it is higher than % by weight, the stretching stress becomes high and uniform stretching becomes difficult, and the stretched film becomes thin and devitrified, and its mechanical strength also decreases. Also, the ambient temperature
When the temperature exceeds 180°C, it is extremely difficult to adjust the water content uniformly, and neck stretching tends to occur. Generally, the most preferable conditions for tenter stretching are a water content of 15 to 30% by weight and an ambient temperature of 105 to 150°C. In addition, general-purpose roll tenter sequential biaxial stretching equipment is usually provided with a preheating section at the front of each stretching zone of the roll and tenter, and this can be used to adjust the moisture content and preheat. can do. The stretching ratio is at least 1.5 in both longitudinal and transverse directions.
It is necessary to increase the amount by a factor of 2.0 to 4.0 times, preferably from 2.0 to 4.0 times, in order to obtain a stretched film with good mechanical properties. After stretching, heat fixing treatment is performed as necessary to improve thermal dimensional stability and mechanical properties, and surface treatment is performed to improve static prevention, adhesion, printability, etc. It is also possible. Examples are shown below. Note that % and parts in the examples are based on weight unless otherwise specified. Example 1 Acrylonitrile 94%, methyl acrylate 6%
reduced viscosity (dimethylformamide solvent,
Polymer concentration 0.2%, measured at 35°C) 20 parts of acrylonitrile copolymer (1.4) was dissolved in 80 parts of 70% nitric acid, and after vacuum degassing, the slit width was 300 mm and the slit gap was 20 mm.
The film was coagulated by extrusion into a 30% nitric acid coagulation bath at 0°C using a T-die at a take-up speed of 2 m/min.
A transparent coagulated film of 350 μm was obtained. Rinse with water in a countercurrent washing bath to remove residual solvent (nitric acid) and determine the water content.
A raw fabric containing 170% water was obtained. This is dried in a hot air oven at 80℃ to adjust the moisture content, and then
Using an axial stretching device, sequential biaxial stretching was carried out, first by roll longitudinal stretching and then by tenter transverse stretching. In addition,
Stretching was performed at a magnification of 3.0 times vertically and 2.5 times horizontally relative to the length of the original fabric. After stretching, the film is heated to 180℃.
Fixed-length heat fixation was carried out under hot air. Table 1 shows the stretching conditions, stretchability, and physical properties of the stretched film.

【table】

[Table] Nos. 1 to 3 are examples, Nos. 4 to 7 are comparative examples * Upper row is MD direction, lower row is TD direction Example 2 30 parts of the acrylonitrile copolymer of Example 1 was dissolved in 70 parts of dimethylformamide. After defoaming, it was extruded into a 50% dimethylformamide aqueous solution using the T-die of Example 1 to obtain a coagulated film with a thickness of 280 μm. After washing with water and desolventizing in a countercurrent water washing bath, heat again at 60°C.
The solvent was removed by switching to warm water to obtain a water-containing raw fabric containing 3% residual solvent. Similar to Example 1,
After drying with hot air at 120° C. to adjust the moisture content, sequential biaxial stretching was performed, first by roll stretching and then by tenter stretching. For stretching, the moisture content of the original fabric during roll stretching is 20% (a)
and 40% (b), roll surface temperature 80℃, moisture content during tenter stretching 12% (a) and 30% (b), stretching atmosphere temperature
Under both conditions (a) and (b) at 120° C., a stretched film with almost uniformity and good transparency could be obtained at a stretching ratio of 3.0×3.0 times. Example 3 The water-containing raw fabric obtained in Example 1 was immersed in hot water at 40 to 95°C for 60 seconds, and then dried with hot air at 120°C.
Roll surface temperature 80℃, raw fabric moisture content 40%, first 3.0
Roll lengthwise stretching was carried out by 2 times, and then 2.5 times tenter transverse stretching was carried out at a moisture content of 15% and a stretching atmosphere temperature of 130°C.
Table 2 shows the hot water treatment conditions and the physical properties of the stretched film. The physical properties of the film are determined by heat-setting the film at a constant length with hot air at 180°C.

[Table] Example 4 60 parts of acrylonitrile polymer consisting of 88% acrylonitrile and 12% vinyl acetate, ethylene carbonate
40 parts were uniformly kneaded at 30°C using a Henschel mixer to obtain flakes. This was extruded into a strand using a single screw extruder at 150°C, and pelletized using a pelletizer. The pellets were extruded into a sheet through a T-die at 155° C. using a twin-screw extruder to obtain a sheet having a thickness of 140 μm. Next, this raw fabric was immersed in hot water at 80° C. to remove the ethylene carbonate from the solvent until it became 3%, thereby obtaining a devitrified water-containing raw fabric with a water content of 48%. This raw fabric was longitudinally stretched at a magnification of 3.0 times using a roll stretching machine equipped with rolls preheated to 60°C at a roll surface temperature of 80°C and a moisture content of 30% during stretching, followed by a tenter stretching machine. The film was laterally stretched at a stretching ratio of 2.7 times at an atmospheric temperature of 110° C. and a water content of 16%. After stretching, heat fix the length with hot air at 180℃,
A uniform and transparent film having the following physical properties was obtained. Transparency (haze): 2.2 [%] Tensile strength: 16.6 (MD) 15.6 (TD) [Kg/mm ² ] Tensile elongation: 32 (MD) 55 (TD) [%] Thickness uniformity (R/): 7 [%]

Claims (1)

[Claims] 1. A water-containing coagulated film of an acrylonitrile-based polymer is longitudinally stretched with a roll having a surface temperature of 65 to 95°C while the water content is adjusted to 20 to 100% by weight (based on dry polymer weight). and then lower moisture content (relative to dry polymer weight) than that during longitudinal stretching of 10 to 40% by weight.
A method for producing a sequentially biaxially stretched film of an acrylonitrile polymer, which comprises transversely stretching in a tenter at an ambient temperature of 100 to 180°C. 2. The manufacturing method according to claim 1, wherein the water content of the water-containing coagulated film is adjusted by hot air drying. 3 Adjust the moisture content of the water-containing coagulated film at 50 to 90℃
The manufacturing method according to claim 1, wherein dehydration is carried out by immersion in hot water or a combination thereof with hot air drying.