Coating processes – Measuring – testing – or indicating
Reexamination Certificate
1999-05-05
2001-01-23
Bareford, Katherine A. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S240000, C427S402000, C427S420000
Reexamination Certificate
active
06177128
ABSTRACT:
The invention relates to a coating method and particularly to a coating method for photographic films and papers. More particularly, the invention addresses the optimization of a coating method whereby the time and cost for formulating and manufacturing products is reduced.
BACKGROUND OF THE INVENTION
Coated photographic products normally comprise one or more layers of a hydrophilic colloidal composition. The vehicle for these compositions is usually gelatin and the layers are coated onto substrates including paper and acetate and polyester films. The substrates may possess a thin subbing layer to promote adhesion of the layers. The subbing layer is typically a hydrophilic colloidal composition comprising gelatin and other addenda including a cross-linking agent, other polymers, matte particles, and surfactants.
Sometimes multilayer photographic products are coated in four or more stages that may follow in one continuous manufacturing line. The second and later stages are coated onto product layers that have been coated and dried; only the first stage is coated directly on an original receiving surface of paper or plastic that may be subbed. The product layers are typically dispersions and emulsions in a gelatin vehicle. The compositions typically contain surfactants as dispersing aids. The compositions are chemically complex.
Economical and reliable manufacturing requires high speeds of coating and a robust coating process. Indeed, it is desirable that manufacturing processes be so reliable that the numerous inspection, sorting, disposition, rework steps, and large inventories characteristic of past manufacturing processes be eliminated to reduce cost. At the same time, it is desirable to reduce greatly the time it takes to formulate new products and bring them to market. Reduced cycle time, as it is called, can make the difference between success and failure in the highly competitive global marketplace. As coating speeds have increased for economic reasons, significant differences in coating latitude among receiving surfaces have become apparent. Manufacturing photographic products may involve several coating operations with as many different receiving surfaces, any one of which may limit productivity. So, it is important that all receiving surfaces be conducive to coating.
The importance of the surface properties of the receiving surface to coating performance has been largely unrecognized in public technical literature; for example, Buonopane R A, Gutoff E B, & Rinmore MMTR, 1986
, AIChE J
., 32, p. 682, and Burley, R., 1992, JOCCA., 5, p. 192. However, in formulating and coating photographic products, large differences among receiving surfaces are observed. For example, the limit of coating speed, usually marked by the entrainment of air between the coating compositions and the receiving surface, can vary by an order of magnitude. A receiving surface with poor properties can severely restrict manufacturing performance. Thus, the ability to predict coating performance on various receiving surfaces quickly and inexpensively can be useful and valuable.
Although coating performance cannot be left to chance, methods to predict performance quickly and inexpensively are virtually nonexistent. Past experience with compositions can be helpful, but it is difficult to recognize when a significant change has been made given the chemical complexity of photographic compositions. Predictions based on scientific and engineering models and principles are not possible because much of coating mechanics, and particularly the high speed wetting of a receiving surface that is the heart of coating, remains an enigma (for example, Shikhmurzaev, Y. D.,
J Fluid Mech
., 334, 1997). As a result, in the prior art coating performance is evaluated empirically on pilot coating machines. These coating machines are called pilot machines because they are much narrower than production coating machines, but they must otherwise duplicate manufacturing conditions such as speed. Such pilot machines are therefore expensive to build, operate, and maintain. Thus, the predictive step of pilot coating practiced in prior art is costly and time consuming and at odds with the modern manufacturing objectives already recited. What may be an even worse drawback is that materials being evaluated for new product formulations may not be readily available in the quantities required for high speed pilot coating. So, costly delays in product programs or compromised formulations can result.
One useful method for characterizing the coating latitude of receiving surfaces and maximizing coating speeds based on the results has been disclosed in European Patent Application EP 0 769 717 A1. The method involves measuring the free energy components of receiving surfaces and ensuring through materials selection that these components lie within specified ranges. Specifically, static advancing contact angles of suitably chosen test liquids (water, 1-bromonaphthalene, and 2,2′-thiodiethanol) on the receiving surface are measured, and the method of Fowkes (1962
, J. Phys. Chem
., 66, p. 382) is employed to determine the free energy components of the receiving surface.
This method for evaluating receiving surfaces for coating speed is useful but has some drawbacks and limitations. The method has proven most reliable for predominantly gelatin/surfactant receiving surfaces, as subbed film is likely to be. Suitable test liquids cannot be found in all cases. The reliable measurement of static advancing contact angles requires considerable skill and experience. Phenomena that occur over the relatively long time of a contact angle measurement but do not occur to a meaningful extent in a coating process can invalidate a measurement. For instance, the test liquid may be adsorbed by the receiving surface, or components of the receiving surface may dissolve or leech into the test liquid, thereby rendering the data questionable. In addition, the time it takes for the test liquid to equilibrate severely limits the capability of the test. So, for some receiving surfaces the method cannot be carried out or the prediction is uncertain.
It would be advantageous to devise a method for evaluating the coatability of substrates for various coating and the appropriate coating temperatures for coating operations for photographic film and paper without having to use a pilot plant operation to determine each situation individually and to avoid the time-consuming process described in European Patent Application 0 769 717 A1.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an improved coating method for which coating performance can be reliably, rapidly, and inexpensively ensured even when only small amounts of materials are available.
French patent FR 2721399 discloses an instrument for studying the entrainment of air when a liquid flows onto a moving receiving surface. The instrument is referred to as the rotating disk coater, or RDC. This device comprises a disk rotating at constant angular speed on which a sample of a receiving surface is placed and a nozzle immediately above the receiving surface for flowing a test liquid onto the receiving surface. To prevent coating over previously applied liquid, the nozzle translates radially inward at a steady speed. This inward translation also has the effect of decreasing coating speed with time. This general type of coating device is used, for example, to supply an excess of coating composition to a receiving surface in preparation for a spin coating process.
Typically, using the method of European Patent 0 769 717 A1, 25 receiving surfaces can be evaluated per day. The proposed method herein disclosed can easily evaluate 50 such receiving surfaces per day.
It has been found unexpectedly that the RDC has predictive value for the coating processes used in the manufacture of photographic products. These coating methods are, specifically, multilayer slide bead coating as described in U.S. Pat. No. 2,716,419 and multilayer slide curtain coating as described in U.S. Pat. No. 3,508,947. Sp
Goppert-Berarducci Kim E.
Higgins Eugene P.
Bareford Katherine A.
Bocchetti Mark G.
Eastman Kodak Company
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