JPH0330487B2 - - 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 properties and uniform thickness. Films of acrylonitrile polymers, particularly high nitrile-containing polymers, are difficult to orient, and biaxially stretched films thereof are not easy to produce. The manufacturing method has been published in Tokoku No. 38-26582, Tokoku No. 7458, No. 46-7458,
Although it is stated in Japanese Patent Application Laid-Open No. 50-142673,
There were problems with residual solvent in the stretched film and instability of stretching conditions, and it was difficult to put it into practical use in terms of hygienic physical properties and thickness uniformity. The present inventors focused on the plasticizing effect of water on acrylonitrile-based polymers at high temperatures, and created biaxial sheets (hereinafter referred to as hydrated original fabrics) obtained by film-coagulation of a solution of acrylonitrile-based polymers. After many studies on the stretching method, we found that the stretching of a water-containing raw fabric under contact heating with a metal plate or metal roll has particularly low stretching stress, and that even raw fabrics with relatively low moisture content can be easily stretched, and that sequential biaxial stretching is possible. Furthermore, using a general-purpose roll tenter sequential biaxial stretching device, the water-containing raw fabric was stabilized by horizontal tenter stretching under specific temperature conditions, and then longitudinal roll stretching under specific temperature conditions. Perform biaxial stretching,
It was possible to obtain a stretched film with excellent mechanical strength, transparency, and uniformity of original size. That is, the present invention provides a water-containing coagulated film of an acrylonitrile polymer with a water content of 10 to 50% by weight.
(relative to dry polymer weight), tenter transverse stretching at an ambient temperature of 100 to 180°C, and then at a surface temperature of 70°C with a lower water content (relative to dry polymer weight) than that during transverse stretching of 5 to 40% by weight. The present invention relates to the manufacturability of a biaxially stretched film of an acrylonitrile polymer, which is longitudinally stretched using rolls at a temperature of ~150°C. The present invention will be explained in detail below. The acrylonitrile polymer used in the present invention is
An acrylonitrile polymer or homopolymer containing 60% 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, vinylidene fluoride etc., vinylamides such as acrylamide, methacrylamide, N-methylacrylamide, N-vinylpyrrolidone, etc., vinyl esters such as vinyl acetate, vinyl propionate, vinyl lactate, etc., vinyl aromatic compounds such as styrene, vinylnaphthalene, vinylpyridine, etc.
Vinyl carboxylic acids such as acrylic acid, methacrylic acid, unsaturated dicarboxylic acids such as itaconic acid, maleic acid, furalic acid, etc., unsaturated dicarboxylic acid anhydrides such as itaconic anhydride, maleic anhydride, etc., arylsulfonic acids or methacrylic acids. Lylsulfonic acid or a salt thereof, methacrylonitrile, olefin such as ethylene, propylene, etc., and a polymer in which two or more of these heavy substances are copolymerized with acrylonitrile, or a mixture of these polymers. It is also possible that there is. If the acrylonitrile content of the copolymer is 60% 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, when the acrylonitrile content approaches 100%, that is, close to a homopolymer, the stretching stress increases and uniform stretching becomes difficult. It is possible to perform uniform stretching without compensating for The upper limit of the acrylonitrile content that allows uniform stretching without such auxiliary means is 98%. The water-containing raw material of the acrylonitrile polymer referred to in the present invention is generally conveniently produced by the so-called wet coagulation method as described below. That is, a coagulated film is obtained by casting an acrylonitrile polymer solution onto the surface of a belt or drum, or extruding it into a sheet or tube using a slit die, and coagulating and forming the solution in an aqueous coagulating 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 polymer concentration in the polymer solution is preferably 10% by weight or more in order to produce a dense stretched film, but conversely, the higher the concentration, the higher the viscosity of the solution, making defoaming, filtration, etc. difficult. 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 solvent 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, the concentration tends to be higher in organic solvents than inorganic solvents; for example, nitric acid is preferably 20 to 40% by weight, and dimethylformamide is preferably 30 to 60%. 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 warm water can be used to remove the solvent in the coagulated film. Although it is more convenient for the degree of solvent removal to be incomplete in view of the plasticizing effect of residual solvent during stretching, it is preferable to remove the solvent sufficiently in view of the physical properties and uses of the resulting film. 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 is employed in which a volatile organic solvent is used to form a film by casting, the solvent is evaporated to some extent with hot air, and then the remaining solvent is replaced and removed with water or hot water, or JP-A-48 As described in Japanese Patent No. 49839, it can also be produced by hydrating the nitrile group of an acrylonitrile polymer with water to make it into a semi-molten state, and extruding it under high temperature and high pressure steam, for example. 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 water-containing raw fabric, drying methods such as hot air, infrared rays, far infrared rays, steam, hot plates, hot rolls, etc. can be used, but in any case, rapid drying will damage the raw fabric. It is preferable to avoid it because it tends to cause devitrification and porosity. Among these, drying with hot air has a relatively low drying efficiency, but 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 a high moisture content. For example, by immersing a raw fabric with a moisture content of 250% in hot water at 80°C for about 30 seconds, it can be uniformly dehydrated. It can be dehydrated and dried to a moisture content of about 80% by weight.
If the temperature of the hot water is higher than 90°C, the raw film will become highly 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 film properties, especially mechanical strength. Furthermore, if the temperature is lower than 50°C, the effect of dehydration and drying is small. Roll tenter sequential stretching can be performed under the following conditions. That is, the moisture content is adjusted in advance by the method described above, and the original fabric is first horizontally stretched with a tenter at a moisture content of 10 to 50% by weight and an ambient temperature of 100 to 180°C, followed by horizontal stretching of 5 to 40% by weight. Longitudinal stretching is performed using rolls with a surface temperature of 70 to 150°C and a lower water content than that during stretching. Regarding tenter stretching, if the moisture content of the original fabric is lower than 10% by weight or the ambient temperature is lower than 100° C., stretching stress is high and stretching breaks are likely to occur. On the other hand, the moisture content of the raw fabric is
If it exceeds 50% by weight, the stretching stress becomes high and the stretched film becomes porous (devitrification), and it is difficult to devitrify the film even during subsequent heating or stretching, which is not preferable. Furthermore, when the ambient temperature exceeds 180°C, it becomes difficult to adjust the moisture content uniformly. Generally, the most preferable raw fabric moisture content for tenter stretching is 15 to 35% by weight.
The ambient temperature is 110-150°C. Regarding roll stretching, if the moisture content is lower than 5% by weight or the roll surface temperature is lower than 70° C., stretching stress is high and stretch breakage is likely to occur. If the water content exceeds 40% by weight, thin devitrification occurs in the stretched film and the mechanical strength of the film also decreases. Furthermore, when the roll surface temperature exceeds 150° C., uneven (scale-like) devitrification tends to occur in the stretched film, and the stability of stretching decreases. Generally, the most preferable conditions for roll rolling are moisture content of 10
~30% by weight, roll surface temperature 80~120℃. Note that general-purpose roll tenter sequential biaxial stretching equipment is usually provided with a preheating section at the front of each stretching zone of the rolls and tenter, and this can be used to adjust the moisture content and preheat. I can do it. The stretching ratio is at least 1.5 times in both the vertical and horizontal directions,
Preferably, it is necessary to increase the amount by 2.0 to 4.0 times in order to obtain a stretched film with good mechanical properties. After stretching, heat setting may be performed as necessary to improve thermal dimensional stability and mechanical properties.
It is also possible to perform surface treatment to prevent static electricity, improve adhesion, printability, etc. Examples are shown below. Note that % and parts in the examples are based on weight unless otherwise specified. Example 1 Acrylonitrile 96%, methyl acrylate 4%
16 parts of acrylonitrile polymer consisting of 70% nitric acid was dissolved in 84 parts of 70% nitric acid at 0℃ with stirring, and after defoaming under reduced pressure, it was heated at 0℃ using a T-die with a slit width of 300 mm and a slit gap of 1.5 mm.
It was extruded into a 30% nitric acid coagulation bath and taken up at a speed of 1 m/min, and then the solvent was removed by water washing in a water washing bath. The resulting water-containing raw fabric with a thickness of 400 μm and a water content of 200% was passed through a tunnel-type hot air drying oven at 80° C. to adjust the water content, and first subjected to transverse stretching with a tenter and then longitudinal stretching with rolls. The stretching was performed at a magnification of 3.2 times in width and 2.5 times in length with respect to the length of the original fabric. Table 1 shows the stretching conditions, stretching state, thickness uniformity and physical properties of the stretched film. Since the tenter-stretched film is easily split, the edges were not trimmed and roll-stretched as it was, and then tensioned and heat-set using hot rolls.

[Table] Nos. 1 to 3 are examples, and Nos. 4 to 6 are comparative examples. *The upper row is an example in the MD direction, and the lower row is an example in the TD direction. 2 The water-containing raw fabric obtained in Example 1 was soaked in hot water at 65°C. Immerse it in water for 60 seconds, dehydrate and dry it to a moisture content of 130%,
Thereafter, the moisture content was adjusted to 55% in a tunnel-type hot air drying oven at 80°C, and transverse tenter stretching and then longitudinal roll stretching were performed. Tenter stretching was carried out at a ratio of 2.8 times with the original film moisture content at the time of stretching being 32% and a hot air temperature of 125°C in the stretching machine.Next, roll stretching was carried out with the moisture content of the uniaxially stretched film being 18% at the time of stretching and the roll stretching. The surface temperature was 95°C and 2.5x magnification was performed. Furthermore, after that, tension heat fixation was performed at 180°C for 20 seconds. As shown below, the obtained film was transparent with good thickness uniformity and had excellent mechanical strength. Thickness uniformity (R/): 7 [%] Transparency (haze): 0.8 [%] Tensile strength: 13.6 (MD), 12.8 (TD) [Kg/mm ² ] Tensile elongation: 18 (MD), 28 (TD) [%] In addition, the water content was 72 [%] by immersing it in hot water at 95℃.
The material that was dehydrated and dried, then similarly dried with hot air, and successively biaxially stretched with tenter rolls was inferior in transparency and physical properties as shown below. Transparency (haze): 2.4 [%] Tensile strength: 10.6 (MD), 10.2 (TD) [Kg/mm ² ] Tensile elongation: 12 (MD), 16 (TD) [%] Example 3 Acrylonitrile 88% , 60 parts of acrylonitrile polymer consisting of 12% vinyl acetate and ethylene carbonate.
40 parts were uniformly kneaded at 30°C using a Henschel mixer, extruded into a strand at 150°C using a single screw extruder, and pelletized using a pelletizer. The pellets were extruded into a sheet through a T-die at 155°C using a twin-screw extruder.
A raw fabric with a thickness of 140 μm was obtained. Next, this original fabric is 80
It was immersed in hot water at a temperature of 0.degree. C. to remove the solvent from ethylene carbonate to 3%, thereby obtaining a devitrified water-containing raw fabric with a moisture content of 48%. This water-containing raw fabric was heated using a hot air dryer at 120°C to adjust the water content and thermally densified (devitrification recovery), and then stretched using a tenter stretching machine at a temperature of 105°C and a water content of 32%. The film was stretched horizontally at a magnification of 3.0 times, and then longitudinally stretched at a magnification of 2.5 times using roll stretching at a roll surface temperature of 120° C. and a water content of 10%. The stretching was stable and uniform, and a transparent film of 12 μm with good thickness uniformity was obtained. The physical properties of the film heat-set to a fixed length with hot air at 180° were as follows. In addition, the residual amount of solvent and water in the heat-set film was 0.5% or less. Transparency (haze): 1.6 [%] Tensile strength: 15.2 (MD), 16.0 (TD) [Kg/
mm ² ] Tensile elongation: 38 (MD), 45 (TD) [%]

Claims (1)

[Claims] 1. A water-containing coagulated film of an acrylonitrile polymer is laterally stretched in a tenter under conditions of a water content of 10 to 50% by weight (based on dry polymer weight) and an ambient temperature of 100 to 180°C, and then Surface temperature at lower moisture content (relative to dry polymer weight) than that during transverse stretching of ~40% by weight
A method for producing a biaxially stretched film of an acrylonitrile polymer, which comprises longitudinally stretching using rolls at a temperature of 70 to 150°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, which is carried out by dehydration by immersion in hot water, or a combination thereof with hot air drying.