JPS647575B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for orienting a film made of polyvinyl alcohol or its derivatives. The oriented film obtained by the method of the present invention is useful for producing polarizing films. Polarizing films are used in a variety of fields, including liquid crystal display devices, various optical devices, photographic filters, sunglasses, and building windows.Generally, polarizing films are made by adsorbing polarizing iodine and dyes onto polyvinyl alcohol-based films. The film is then stretched several times. Polyvinyl alcohol films are generally stretched using a wet method, but moisture breaks the hydrogen bonds between molecules and increases the mobility of molecules, so the moisture content of the film has a large effect on stretchability. Moreover, stable processing is not easy and uneven stretching tends to occur. The secondary transition point of polyvinyl alcohol decreases as the moisture content increases, and in particular it decreases rapidly from around 5% moisture content, so stretching is carried out at moisture contents of 5% or higher, and below 5%. It is considered difficult to stretch. Note that the moisture content referred to here refers to absolute dry PVA.
It is defined as the ratio of water weight to weight. A first object of the present invention is to provide a method for stably orienting a film made of polyvinyl alcohol or a derivative thereof at high magnification, evenly, and stably. As a result of intensive studies for this purpose, the present inventors have determined that the moisture content of the film is 8% or less, that the film is given a rear tension of at least 50 kg/cm ² or more, and that At least 100Kg/cm by paired pressure rolls in a temperature range below 130℃
The inventors have discovered that by rolling at the above line pressure, it is possible to continuously produce an evenly oriented film at a high magnification in an extremely stable manner, leading to the present invention. That is, one of the features of the present invention is that orientation can be performed by a dry method, and therefore, there is no need for a hydrous process or a drying process accompanying it. Another feature is that it is possible to continuously produce a homogeneous oriented film with high magnification and almost no unevenness in quality in an extremely stable manner. Here, high magnification means at least twice or more. Polyvinyl alcohol or its derivatives used in the present invention include polyvinyl alcohol,
In addition to polyvinyl formal and polyvinyl acetal, they are also modified with olefins such as ethylene and propylene, unsaturated carboxylic acids such as crotonic acid, acrylic acid, methacrylic acid, and maleic acid, or their alkyl esters, acrylamide, etc. Can be used. Further, in addition to the above, a plasticizer or the like may be added.
When rolling, the moisture content must be 8% or less; if it exceeds 8%, it is not suitable because it will cause sticking to the pressure roll during rolling. On the other hand, if the water content is 8% or less, orientation in a water content range of 5% or less, which is considered difficult with conventional stretching, can be easily performed without any problem. Also,
A rear tension of at least 50 kg/cm ² must be applied on the entry side of the pressure roll. Here, the backward tension is also called the extending force, and is a force that acts in the opposite direction to the film's traveling direction.
If it is lower than Kg/cm ² , the neutral point (highest pressure point) of the pressure roll will shift to the roll entry side, making it more likely that defects will occur and stable machining will become difficult. Therefore, it is necessary to apply a rear tension of 50 kg/cm ² or more. Next, regarding the rolling temperature, set the pressure roll to 20℃ or higher.
It can be set arbitrarily within a wide temperature range of 130℃ or less. If the temperature is lower than this temperature range, a large number of pressure roll groups are required to obtain the desired rolling ratio,
A very large force is required to apply pressure between the rolls, which causes problems with the equipment and also makes the equipment expensive, making it inappropriate as a rolling condition. On the other hand, if the temperature is higher than this temperature range, the film will stick to the pressure roll and it will be impossible to produce a good orientation effect. Furthermore, the linear pressure applied to the film by the pressure roll is
It is necessary to make it more than 100Kg/cm.
If it is lower than cm, sufficient orientation cannot be achieved. In addition, during rolling, in order to reduce the stiffness coefficient between the pressure roll and the film, an appropriate liquid lubricant may be used at the rolling point, or the film may be heated in advance by infrared heating, far infrared heating, or high frequency heating. Preheating may be performed using a heating method such as heating, hot air heating, steam heating, bath heating, etc., but none of them is a necessary condition. The rolled film made of polyvinyl alcohol or its derivatives obtained as described above has extremely excellent properties as a polarizing film. That is, conventionally, stretched films of polyvinyl alcohol have been mainly used as polarizing films, but as mentioned above, stretching of polyvinyl alcohol is carried out by a wet method, and hydrogen bonds between molecules are formed by moisture. Stable processing is not easy because the moisture content of the film has a large effect on stretchability, as the film is cut and molecular mobility increases.
It has the disadvantage that stretching unevenness tends to occur. Therefore, the quality of polarizing films made from such films is naturally uneven and cannot be said to be sufficient. However, the rolled film made of polyvinyl alcohol or its derivatives according to the present invention
Since the film is homogeneous with almost no unevenness in orientation due to rolling, it has extremely good quality characteristics even when made into a polarizing film. In order to impart polarizing properties, it is necessary to dye the film with iodine, a dichroic dye, etc., but the dyeing agent is not particularly limited in the present invention. Further, dyeing may be carried out before rolling, during rolling, or after rolling. The quality of the polarizing film referred to here mainly refers to the optical properties (single transmittance, orthogonal transmittance, degree of polarization, etc.) in addition to the film appearance. Note that the single transmittance τ _M is defined by the ratio of the light flux F ₁ before the light passes through one polarizing film to the light flux F ₂ after the light passes through it. (...τ _M = F ₂ / F ₁ ) The orthogonal transmittance τ ₁ is the difference between the luminous flux F ₁ before light passes through two polarizing films whose absorption axes are orthogonally combined and the luminous flux F ₃ after passing through. defined by the ratio. (...τ ₁ =
F ₃ /F ₁ ) Also, the degree of polarization V is the speed of light Fu (natural light component) when the vibrations of the polarized light flux F in two directions, vertical and horizontal, are equal.
It is defined by the ratio of F and Fp when the speed of light is separated into Fp (linearly polarized component) of vibration in one direction, either vertical or horizontal. (...V=Fp/F) The values of these optical properties generally required for a polarizing film are: Single transmittance...43±2.5% Orthogonal transmittance...7% or less Polarization degree...85% or more The polarizing film according to the present invention can fully satisfy these required values. EXAMPLES Hereinafter, the present invention will be specifically illustrated with reference to Examples, but the present invention is not limited to these in any way. Example 1 A polyvinyl alcohol film (Kuraray Vinylon Film 7500) with a thickness of 75μ was rolled using a pair of pressure rolls with a diameter of 260φ and a surface length of 700mm under three types of conditions, and a rolled film with a good appearance was continuously stabilized. I was able to get it. The results are shown in Table 1. The moisture content of the film used was 2.5%. Comparative Example 1 The same raw material as in Example 1 was rolled using the same equipment under three types of conditions outside the scope of the claims.
Problems occurred in either the film appearance or the processing stability at rolling magnification (2 times or more). The results are shown in Table 1. Comparative Example 2 The same raw material as in Example 1 was stretched in a wet state under three conditions using roll groups with different take-up speeds, and a film with a relatively good appearance was obtained, but stable continuous processing was difficult. It was hot. Table 2 shows the moisture content and results at that time. Comparative Example 3 The same original fabric as in Example 1 was stretched under three conditions using rolls with different take-up speeds, but slipping occurred between the rolls and the film, causing scratches on the film surface and wrinkles. This was observed, and under some conditions, film breakage was observed. The results are shown in Table 2. Example 2 The rolled film obtained in Example 1 was dyed at 35°C with a dye solution prepared by dissolving 5 g of Sumilite Sprablue FBGL and 0.5 g of a nonionic surfactant in 1 part of water, and then dyed with 5 g of anhydrous sodium sulfate and boric acid. 20 g of nonionic surfactant was washed with a solution of 0.1 g of nonionic surfactant dissolved in 1 part of water, dried at 70°C for 20 minutes, and the single transmittance, cross transmittance, and degree of polarization were measured at a wavelength of 600 m. The results are shown in Table 1. Comparative Example 4 Among the stretched films obtained in Comparative Example 2, a film with good appearance was dyed, washed, and dried in the same manner as in Example 2, and the single transmittance and cross transmittance were also measured at a wavelength of 600 mμ. , the degree of polarization was measured. The results are shown in Table 2.

【table】

[Table] Example 3 Using the same original fabric and the same rolling roll as in Example 1, the moisture content was 2.5%, the temperature was 105°C, the linear pressure was 350 kg/cm,
Rolling was carried out under the conditions of a rear tension of 250 Kg/cm ² , and a rolled film with a stretching ratio of 4.0 times, no stretching unevenness, and a good appearance could be continuously and stably obtained. The rolled film was immersed in a 20° C. solution containing 10 g of iodine, 150 g of potassium iodide, and 3,300 g of water for about 60 seconds while keeping it under tension. Further, the film was immersed in a solution of 150 g of boric acid and 2000 g of water at 65°C for about 300 seconds, and then washed with water at 20°C for 1 minute to obtain a polarizing film. This polarizing film had an average single transmittance of 43.3% in the visible light wavelength range of 400 to 700 mμ, a polarization degree of 97.2%, and a good film appearance.

Claims (1)

[Claims] 1. When orienting a film made of polyvinyl alcohol or its derivatives, the moisture content of the film is set to 5% or less, a backward tension of at least 50 kg/cm ² or more is applied to the film, and the film is heated at 20°C or higher,
1. A method for orienting a film made of polyvinyl alcohol or a derivative thereof, which comprises rolling at a linear pressure of at least 100 kg/cm or more using a pair of pressure rolls in a temperature range of 130° C. or less.