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Detection of Surface Asperities on Film Substrates

IP.com Disclosure Number: IPCOM000050186D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Bartkus, EA: AUTHOR [+2]

Abstract

Asperities in biaxially oriented films produce a birefringent strain pattern which is detected by placing the film between crossed polarizing filters in a transmitted light beam. The height of the asperities is sensed by pressing the film against an optical flat glass surface with a reflected monochromatic light source. The number of the interference fringes is directly proportional to asperity height.

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Detection of Surface Asperities on Film Substrates

Asperities in biaxially oriented films produce a birefringent strain pattern which is detected by placing the film between crossed polarizing filters in a transmitted light beam. The height of the asperities is sensed by pressing the film against an optical flat glass surface with a reflected monochromatic light source. The number of the interference fringes is directly proportional to asperity height.

As shown in the figure, a portion of a film substrate 1, such as a length of magnetic tape substrate of a pliable film of polyethylene terephthalate, is placed against an optical flat glass plate 2 using a low air pressure to hold the film substrate 1 against the optical flat 2. Light from a transmitted light source 3 is directed through crossed polarizing filters 4 and 5 to produce a birefringent strain pattern which is readily detectable by a low magnification microscope 6. Interference fringes between the film substrate 1 and the optical flat 2 can be detected by the microscope 6 when light beams 7 from a monochromatic light source are directed to the optical flat 2 and the the film substrate 1.

The two separate phenomena are observed by the placement of the film substrate 1 against the optical flat 2. The birefringent pattern is detected by the use of the transmitted light from the light source 3. The light source 3 is turned off and the light source, producing light beams 7, is activated to direct a reflected ...