JOY D. Robinson E. I. du Pont de Nernours and Co.
Wilrnington, Delaware 19898
An Optical Partide Detector for Evaluating Film Quality
A new and novel means of observing film imperfections bas been developed using an optical particle detector. The optical particle detector (OPD) is a device incorporating the use of a series of grid lines to optically accentuate the presence of film imperfections, primarily gels. This technique has been useful in objectively evaluating film quality as compared to subjective techniques. The OPD may also be used to evaluate imperfections in mediums other than film. I t has been observed that the gels in a film sample are but only more discernible using the OPD (see Fig. I), not the evaluation may be reproduced by more than
Figure 1. Comparison of the obilily to discern gels in film with and without the "re of the OPD.
one person and over a period of time. The precision a t 1 2 c is 3.8 defects/ftZ a t a 1 4 4 6 defect/ft2 level. A 0.020-in. spacing of 0.020 in. line thickness yielded a sensitivity of approximately 0.020 in. minimum diameter defect discernible. This sensitivity may be adjusted by varying line spacing or thickness. The unit consists of an optical grid, a fluorescent light source, and an enclosure to house these items (see Fig. 2). The grid was prepared by ~hoto~raphing a preprinted line pattern sheet (Jaggers, Chiles, Stovall, Inc., Dallas, Texas, Cat. #307) and enlarging to 175y0 of its original size on Du Pont Ortho-S Litho film. The negative was used as the optical grid. Any transparent material having the r e quired line spacing and , , line thickness would suffice. Figure 2 shows to scale the light source and enclosure used by the author. The only critical dimension is the spacing between the optical grid and the sample support (3/, in.). The enclosure mav be constructed of v i r h l y any materialand Figure 2. Diagram of lhe optical in any convenient size. partide detedor.
Volume
45, Number 3, March 1968
/
205
