GB791064A - Method and apparatus for examining sheet materials - Google Patents

Abstract

791.064. Polarizing apparatus. BRITISH CELANESE, Ltd. July 27, 1956 [July 29, 1955], No. 21980/55. Class 97(1) [Also in Group XL(b)] A method of testing the anisotropy of transparent sheet material having a basis if high polymer comprises passing through the sheet normally thereto a test-beam and a control-beam both of the same intensity and both plane-polarized, the test-beam in a plane at 45 degrees to the optic axis of the sheet and the control beam in a plane at 45 degrees to the plane of polarization of the test-beam' and then passing the beams through analysers to fall side by side on a screen, the optic axis of the analyser for the test beam being at 45 degrees to the optic axis of the specimen, the analyser in the control beam being rotated to equalize the intensities of the two images on the screen and the degree of anisotropy being indicated by the angular adjustment of the analyser. The point of matching may be determined photoelectrically and the rotation of the analyser may be controlled by servo mechanism operated by the photoelectric control and servo mechanism may be provided to control either temperature, screw speed, relative rates of casting roll and screw and relative rates of casting roll and draw-off means in the hot-extrusion and casting of film. As shown light from a sodium lamp 11 passes via a condenser 12 and a stop 13 to a frame 15 containing sheets 16, 17 of polarizing material the sheet 17 having its optic axis vertical and producing the control beam and the sheet 16 having its optic axis at 45 degrees to the vertical and providing the test-beam. The two plane-polarized beams pass to the specimen 27 under test mounted in a frame 18 slidable in a holder 28 rotatable about the axis of the beam to orient the optic axis of the specimen 27 at right angles to the optic axis of the polarizer 17. The two beams after passage through the specimen are focused by a lens 19 on a screen 22 having D-shaped windows 23, 24. The window 23, receiving light from the polarizer 16, has fixed to it an analyser 21 with its optic axis perpendicular to that of the polarizer 16, while the window 24, receiving light from the polarizer 17 carries a rotatable analyser 20 the angular position of which is indicated on a scale 33. The rotation of the analyser 20 to produce matching of the fields gives a measure of the anisotropy of the specimen 27 and may be correlated with certain physical properties thereof. Alternative relative arrangements of the various optic axes are also described.