Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2000-05-19
2002-06-04
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S261000, C427S322000, C427S402000, C427S569000
Reexamination Certificate
active
06399159
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the manufacture of polyolefin imaging supports and supports having polyolefins at the surface thereof and, more particularly, to a method and apparatus for obtaining the proper surface characteristics to promote adhesion of photosensitive coating materials and/or layers typically coated thereon.
BACKGROUND OF THE INVENTION
Electrical discharge treatments are widely used-o promote adhesion of a variety of organic and inorganic layers to organic polymer substrates. Examples of the use of electrical discharge treatments are found in U.S. Pat. No. 5,538,841 and references cited therein. Additional examples are found in European Pat. Application EP 0 758 687 A1 and references cited therein, as well as well as World Pat. WO 97/42257. A variety of treatment geometries (i.e. positioning of the article to be treated relative to the discharge electrodes, shape of the electrodes, and shape of the article to be treated) are possible (see, for example U.S. Pat. Nos. 3,288,638 and 3,309,299).
The need to treat continuous sheets or rolls of polymeric support material (i.e., webs) has generally led to treatment apparatus design for the purposes of conveying a web through an electrical discharge zone. This purpose has been achieved either by suspending the polymer article in a free span between conveyance rollers, as disclosed in U.S. Pat. No. 5,493,117 or on a drum, as disclosed in U.S. Pat. No. 4,451,497 and U.S. Pat. No. 5,224,441. U.S. Pat. Nos. 4,451,497 and 5,493,117, as well as U.S. Pat. No. 5,538,841, all intend to provide surface treatments for use in the manufacture of photographic imaging elements on polyester supports. Dolazalek et al. (U.S. Pat. No. 4,451,497) disclose an apparatus for conveying a polymer web material into a vacuum chamber, through a treatment zone, and out of the vacuum chamber. The treatment configuration taught is essentially a corona treatment geometry wherein the web travels along a rotating drum that is surrounded by a plurality of discharge electrodes. The objective is to prepare a substrate to be coated with photographic emulsion.
Tamaki et al. (U.S. Pat. No. 5,493,117) disclose an apparatus similar to that of Dolazalek et al. having the similar purpose of providing a support useable for a photosensitive material. However, Tamaki et al. suspend the web in free span between conveyance rollers and have a plurality of treatment electrodes located on either side of the free span in order to treat both sides of the web simultaneously.
Felts et al. (U.S. Pat. No. 5,224,441) disclose a plasma treatment and coating apparatus wherein the web is conveyed over the surface of an electrified drum, facing a grounded counter electrode.
Grace et al. (U.S. Pat. No. 5,538,841) disclose nitrogen-based and oxygen-based surface chemistries that promote adhesion of gelatin-containing layers to respective nitrogen-plasma-treated and oxygen-plasma-treated polyester webs, also for the manufacture of supports usable for photosensitive materials.
A common technique in the industry for treatment of paper surfaces at atmospheric pressures is corona discharge treatment (CDT) (R. H. Cramm and D. V. Bibee, Tappi, 65 (8), pp.75-8, 1982; and W. J. Ambusk, U.S. Pat No. 3,549,406, 1970). As typically practiced, this treatment is more accurately described as a dielectric barrier discharge treatment. As mentioned above, a typical geometry consists of a drum with a series of electrodes placed at a specified radius from the center of the drum. Furthermore, a dielectric layer of insulating material having suitable thickness so that it does not break down at the applied voltages is placed on either the drum or the electrodes. This layer is called the dielectric barrier. At the pressures typically used (i.e. 1 atmosphere) the treatments are generally carried out in air, and efforts to change the dominant treatment chemistry from oxygen to something other than oxygen are not successful. Although air is composed of 80% nitrogen, oxygen is much more reactive than nitrogen, therefore, oxygen present in the discharge treatment zone dominates the gas-phase chemistry. Furthermore, entrained air (present as a layer of gas carried on the moving web surface as it enters the treatment device) provides a considerable source of oxygen, even when the treatment zone is enclosed and purged with an oxygen-free gas.
The typical gas-phase chemistry in a dielectric barrier discharge in air also produces unwanted species such as ozone and oxides of nitrogen, (NOx) both of which must be eliminated from the work environment with pollution abatement technology. These species, in particular the oxides of nitrogen, can also have undesirable effects on the treated surfaces, as they may interact with coatings applied to the treated surfaces. In addition, the use of dielectric barrier discharges to treat polyolefins has been demonstrated to produce a water washable treated layer (M. Strobel, C. Dunatov, J. M. Strobel, C. S. Lyons, S. J. Perron and M. C. Morgen,
J. Adhesion Sci. Technol
. 3 (5), p326, 1989). This washable layer can have adverse consequences for adhesion of applied layers subsequently coated from a solution in water.
Better control of the treatment gas environment can be achieved at reduced pressures (i.e., using a vacuum process). At reduced pressures, the method of conveyance of the web material through the treatment zone has an important effect on the nature of the plasma treatment. In the case of Tamaki et al., the polymer surface to be treated is electrically floating in the discharge zone and moves past one or more powered discharge electrodes. In the case of Dolazalek et al., if the drum is electrically isolated from the walls of the apparatus, the article also is electrically floating in the discharge zone and moves past one or more powered discharge electrodes. If the drum is electrically grounded, however, the surface potential of the polymer article is determined by several factors. These factors include thickness and dielectric properties of the article, the driving frequency of the discharge, the electron density and plasma potential of the discharge, and the relative areas of the discharge electrode and the combination of the drum surface and the grounded inner walls of the apparatus. At a sufficiently low driving frequency (the upper limit being determined by the aforementioned characteristics of the article and plasma), the article surface will charge to the floating potential and the situation will be similar to that of an electrically isolated drum. At a sufficiently high driving frequency (the lower limit being determined by aforementioned characteristics of the article and plasma) the surface of the article will remain near ground potential. Consequently, if the effective grounded surface area in the discharge zone is significantly larger than that of the powered electrode(s), the surface of the article to be treated is generally bombarded by ions having a bombardment energy that is largely determined by the difference between a plasma potential of some tens of volts and a ground potential.
In contrast, if the areas of the powered electrode(s) and the effective grounded electrode are comparable, the ion bombardment of the polymer article will be largely determined by the potential applied to the powered electrode and can have a peak value of several hundred volts or more. In this case, the ion bombardment energies are more characteristic of an etch process. The etching character of the process can be further enhanced by reducing the area of the polymer article, supporting electrode (e.g., drum), and effective grounded surface area relative to that of the driven electrode(s), or by electrically isolating the supporting electrode of reduced area and applying the driving voltage thereto. The effect of the relative areas of driven and grounded electrodes on the effective bombarding potentials at their respective surfaces is well known to those skilled in the art of plasma processing for microelectronics. In that art it is known that alt
Freeman Dennis R.
Gerenser Louis J.
Grace Jeremy M.
Heinsler Michael J.
Romach Mark M.
Bocchetti Mark G.
Pianalto Bernard
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