JPWO2022004536A5 - - Google Patents

Description

In the small-angle X-ray scattering measurement, when a sample is irradiated with X-rays, the X-rays are scattered or interfered by electrons around atoms, and the diffraction is analyzed. In particular, by analyzing the diffraction that appears in the low-angle region of 2θ<10° or less, it is possible to evaluate the structure of the sample that is the object of measurement. It is said to be possible. For example, it is possible to evaluate the crystal long period (the average value of the inter-crystal distances randomly present in the polymer) of the sample to be measured.

The PVA film has a crystalline portion (lamellar crystal) in which the PVA molecular chains are folded and an amorphous portion in which the PVA molecular chains are unfolded. In the present invention, the crystal long period is defined as the average distance between crystals (lamellar crystals). This crystal long period can be obtained from the diffraction peak of the scattering curve obtained by performing small-angle X-ray scattering measurement on the PVA film. Then, when the PVA film is a raw film for optical film production, the diffraction peak derived from this crystal long period may appear near the scattering vector q(nm ⁻¹ ) of 0.5 nm ⁻¹ . commonly known.

As described above, in the small-angle X-ray scattering measurement of the PVA film, the diffraction peak derived from the crystal long period of the PVA film appears near the scattering vector q (nm ⁻¹ ) of 0.5 nm ⁻¹ in the scattering curve. . In the present invention, the crystal long period Ds and the crystal long period Da were calculated from the value of the scattering vector q (nm ⁻¹ ) at the peak top of this diffraction peak. Here, the peak top is an inflection point at which the scattering curve becomes convex in the range of the scattering vector q(nm ⁻¹ ) from 0.2 to 1.0 (see FIG. 1).

In the present invention, the crystal long period Ds obtained from the small-angle X-ray scattering measurement performed in a water/methanol mixed solvent (volume ratio: 2/8), and the small-angle X-ray scattering measurement performed before immersion in the mixed solvent It is important that the crystal long period D a obtained from the formula satisfies the formula 0.3≦(Ds−Da)/Da<0.5.

The PVA film thus produced is further subjected to humidity control treatment, cutting of both ends (edges) of the film, etc., if necessary, and wound into a roll on a cylindrical core to provide a moisture-proof film. It is packaged and becomes a product.

The maximum stretching stress of the PVA film in uniaxial stretching is preferably 50 N/mm ² or less, more preferably 25 N/mm ² or less, even more preferably 15 N/mm ² or less, and 10 N/mm ^{2 .} The following are particularly preferred. Here, the maximum stretching stress is a value obtained by dividing the stretching tension applied to the PVA film between adjacent rolls in the stretching bath by the cross-sectional area of the PVA film. At this time, the stretching tension of the PVA film can be measured by tension rolls installed between adjacent rolls in the stretching bath, and the maximum value among them when three or more rolls are used in the stretching bath. is used . Also, the cross-sectional area of the PVA film is obtained from the unstretched PVA film before being subjected to the preparation of the polarizing film. A polarizing film with low shrinkage stress can be obtained by reducing the maximum stretching stress. Also, the maximum stretching stress is usually 1 N/mm ² or more.

(6) Shrinkage stress of polarizing film at high temperature Shrinkage stress was measured using an autograph AG-X with a constant temperature bath manufactured by Shimadzu Corporation. For the measurement, a polarizing film (15 cm in the length direction, 1.5 cm in the width direction) that had been conditioned at 20° C./20% RH for 18 hours was attached to a chuck (chuck interval: 5 cm), and at the same time as the start of pulling, it was heated to 80° C. in a constant temperature bath. Heating was started. The polarizing film was pulled at a speed of 1 mm/min, and when the tension reached 2 N, the pulling was stopped, and the tension was measured for 4 hours after that state. At this time, the distance between the chucks changes due to the thermal expansion of the shaft. Measurements were made with the ability to correct for distance. The shrinkage force of the modified film was obtained by subtracting the initial tension of 2 N from the tension measured after 4 hours, and the shrinkage stress (N/mm ² ) was defined as the value obtained by dividing this value by the cross-sectional area of the sample.