Method and system for on-line measurement of thickness and birefringence of thin plastic films
AssigneeHoneywell International Inc.
InventorSebastien Tixier
Life of this patent
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Abstract
A system and method for analyzing the characteristics of a thin film is provided whereby the in-plane birefringence of thin films is determined by measuring the interference fringes in the transmission or reflection spectra using unpolarized light and light linearly polarized along the MD and CD directions. The three spectra can be measured simultaneously or sequentially. The in-plane birefringence data can be used to characterize clear polymer films, which are principally made of biaxial oriented polymer, as the film is being continuously fabricated on a production line.
Claims50
A method of analyzing one or more characteristics of a film, which is moving in a machine direction, said method comprising the steps of:
- (a) providing a broadband source of radiation that creates a probe beam;
- (b) directing the probe beam along a beam path onto or through the film such that the probe beam is reflected from the film to form a first output beam or is transmitted through the film to form a second output beam;
- (c) providing an analyzer to determine the intensity of the first output beam or the second output beam at desired wavelengths or wavelength bands;
- (d) positioning a neutral density filter, a first polarizing filter, or a second polarizing filter in the beam path such that the neutral density filter, the first polarizing filters or the second polarizing filter is located between the broadband source of radiation and the analyzer;
- and
- (e) utilizing differences in the spectral fringes of unpolarized and linearly polarized light to calculate birefringence characteristics of the film.
A system for analyzing one or more characteristics of a film, that is moving in a machine direction, the system comprising:
- (a) a broadband source of radiation that creates a probe beam;
- (b) means for directing the probe beam along a beam path onto the film to form a first output beam or through the film to form a second output beam;
- (c) analyzer means for determining the intensity of the first output beam or the second output beam at desired wavelengths or wavelength bands;
- (d) a first polarizing filter;
- (e) a second polarizing filter wherein the first polarizing filter has a direction of linear polarization that is parallel to the machine direction and the second polarizing filter has a direction of linear polarization that is perpendicular to the machine direction, wherein the first polarizing filter and the second polarizing filter are located between the broadband source of radiation and the analyzer means;
- and
- (f) calculation means for utilizing differences in the spectral fringes of unpolarized and linearly polarized light to calculate birefringence characteristics of the film.
Dependencies are inferred from the claim text.