Radiant energy – Luminophor irradiation – Methods
Reexamination Certificate
1998-07-15
2001-06-26
Hannaher, Constantine (Department: 2878)
Radiant energy
Luminophor irradiation
Methods
C250S461100, C250S559270
Reexamination Certificate
active
06252237
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for measuring the thickness of a coating on a substrate. More specifically, the invention is directed to a method for measuring the thickness of a coating by directing fluorescent light onto the coated surface and analyzing the intensity of light that is emitted from the coating due to fluorescence at a specific wavelength.
BACKGROUND OF THE INVENTION
Many products are manufactured by processes that include continuous coating of a substrate with a coating composition. For example, functional coating compositions are frequently applied to continuous thin films during the production of adhesive film, tape, etc. These functional coatings add important properties to the finished product. In order to perform properly, functional coatings must be applied in a manner that is predictable, controllable, and measurable. The measurement of the thickness of functional coatings applied to thin films is an important process in the manufacture and production of the products, because it allows for the application of the coatings to be monitored and controlled.
Performance of products containing coating compositions often depends upon the accuracy with which the coating compositions are applied, and the thickness of the coating compositions can be critical to performance and price. Variations in thickness of a coating composition can occur for a number of reasons, including the inherent variability of mechanisms used to apply the coatings, as well as variability of the properties of the coating composition being applied, such as variation in the temperature and the pressure at which the coating compositions are applied.
When a coating is applied in an uneven manner, product uniformity and quality can be detrimentally effected. Such non-uniformity may be experienced, for example, along the length of the web to create streaks along the web. Alternatively, non-uniformity may be experienced across the width of the web to give a banded coating. Manufacturing costs can be detrimentally increased by over-application of the coating, and quality can be affected by over-application, under-application, or uneven application.
While it is possible to measure the thickness of thin film coatings by methods known in the art, many of these methods are inadequate or have significant limitations, such as limited accuracy due to the very low signal levels. Some methods require the removal and analysis of individual samples of the coated substrate from the web. Removal of these samples hinders the manufacturing process by slowing and/or interrupting the continuous coating of the substrate. In addition, these measurement techniques provide only an incremental assessment of coating thickness and do not provide real time measurements of thickness. Other methods allow for less disruptive analysis, but do not provide sufficient indications of the thickness on all parts of the web.
Therefore, a need exists for a system and method to thoroughly, quickly, and precisely measure the thickness of a coating composition, particularly a thin coating composition applied to a film.
SUMMARY OF THE INVENTION
The present invention relates to a method of measuring the thickness of a coated surface and a system for performing such measurements. In one aspect of the present invention, the coated surface has fluorescent properties. A first wavelength of light is directed from a light source onto the coated surface such that the coated surface absorbs the light and fluoresces to emit light of a second wavelength. The intensity of the light of the second wavelength is measured by use of a solid state array of light-sensitive elements. The measured intensity of the light of this second wavelength is used to determine the thickness of the coating, and is substantially proportional to the thickness of the coating on the coated surface.
The coating on the surface is very thick in specific implementations, and may be less than 1 percent of the thickness of the substrate which it coats. In specific implementations, the coating is less than 50 nanometers thick, and in certain implementations is less than 25 nanometers thick.
In order to measure coating thickness, a surface having an unknown coating thickness is provided. In addition, a second reference surface is provided. This second surface has light emitting properties that are the same as a surface having a known coating thickness. This second surface functions as a reference “standard” or “control”. The intensity of light emitted from the surface having an unknown thickness is compared to the measured intensity of light from the second surface in order to determine coating thickness. The comparison is made according to the formula:
Coated_Surface
_Thickness
=
T
S
i
=
(
T
R
i
)
(
I
R
i
-
I
B
i
)
×
(
I
S
i
-
I
B
i
)
wherein
T
S
i
=
thickness of coated surface;
T
R
i
=
thickness of reference;
I
R
i
=
intensity of reference;
I
B
i
=
intensity of backing;
I
S
i
=
intensity of coated surface;
In specific implementations, the first and second wavelengths of light are in the ultraviolet spectrum. The fluorescent properties of the coated surface are developed by either adding a fluorescing material to the coating or by using a coating composition having inherent fluorescent properties. In addition, one or more optical band pass filters may be positioned intermediate the light source and the coated surface, and intermediate the coated surface and the solid state array of light sensitive elements. The optical band pass filters limit the passage to a narrow wavelength of light and allow more accurate measurements.
The above summary of the present invention is not intended to describe each illustrated embodiment of the present invention. The figures and detailed description which follow should make more aspects of the invention apparent.
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patent: 4841156 (1989-06-01), May et al.
patent: 4922112 (1990-05-01), Zierl et al.
patent: 4922113 (1990-05-01), Melancon
patent: 4956558 (1990-09-01), Batishko et al
patent: 5001353 (1991-03-01), Odake et al.
patent: 5281819 (1994-01-01), Keffert et al.
patent: 5310604 (1994-05-01), Melancon et al
patent: 0 806 652 A2 (1997-11-01), None
patent: 08309262 (1996-11-01), None
Abstract of JP-A-08309262.
Floeder Steven P.
Harklau Lanny L.
Kostuch Gregory D.
Lai Jack W.
Manning Arthur T.
3M Innovation Properties Company
Gagliardi Albert
Hannaher Constantine
Szymanski Brian E.
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