Apparently a minimum of about 4 percent of haze for sheets up to 100 mils thi

Apparently a minimum of about 4 percent of haze for

This preview shows page 7 - 9 out of 56 pages.

Apparently a minimum of about 4 percent of haze for sheets up to 100 mils thi ck is the best that can be done and for thicker sheets this would be somewhat higher. The fog or cloudiness in sheets with haze values of this order is quite easily detected by the naked eye and is a much more serious defect than the lo wering of white-light trans- mission by blue dye. Th e va lu es recorded in table 1 for the materials oth er than cellulose nitrate, cellulose acetate, and acrylate resin, were obtained on experimental samples only, such products not being available in sheet form for aircraft windshields at the present time.
Image of page 7
AxilrOd] [({ine Transparent Plastics jor Aircrajt III. INDEX OF REFRACTION 373 The index of refraction is of inter e st in considering the light-trans- mission characteristics of plastics. This property was measured by means of an Abbe refractometer on the same specimens used in the light-transmission and haze tests. Two contact liquids, alpha- bromonaphthalene and mercuric iodide, were employed in order to guard against incorrect values resulting from reaction between the sample and the contact liquid. The data obtained are presented in table 1. The refractive indices for the materials studied range from 1.47 to 1.58. IV. VISIBILITY DISTORTION TESTS ON PLASTICS Visibility distortion tests were made in accordance with the proce- dure suggested by the American Standards Association for laminated safety glass using sheets 12 inches square. In this test, a line is pro- jected with a lantern so as to fall midway between two parallel lines 1 inch apart marked on a screen. The test specimen is 25 feet from the screen and the lantern is adjusted so that the center 10- by 10 -inch square fills the beam. The sample in a suitable frame is moved across the beam and the movement of the projected line observed; the safety- glass specification requires that the projected line shall not deviate more than }6 inch as the sheet is moved across the beam. Several materials were tested but none failed to meet the specification. Measurements were then made on each sample of the deviation of the projected line as the square was moved an inch at a time across the beam. This measurement was made at the top, center, and bottom of the screen for the sample normal to the incident light; this was repeated just at the center of the screen for angles of 75, 60, 45, and 30°. The data did not prove suitable for giving an estimate of the visibility because a specimen with many relatively small ripples simply causes the projected line to move back and forth rapidly as well as causing it to get out of focus; a sample which is slightly wedge- shaped or one with a large wave in its surface might cause the line to deviate as much or more, yet it would be far superior as regards distortion.
Image of page 8
Image of page 9

You've reached the end of your free preview.

Want to read all 56 pages?

  • Winter '12
  • Light, Cellulose acetate, Journal of Research

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture