Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2002-09-17
2004-06-15
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S501000, C427S505000, C427S596000, C427S551000
Reexamination Certificate
active
06749903
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for electron beam irradiation of a single layer or multi-layer article, and resulting products. More particularly, the invention is directed to use of a low loss electron beam path to irradiate an electron beam modifiable material coated on an electron beam degradable substrate.
BACKGROUND
In recent years, electron beam radiation has increasingly been used for modifying various materials, including polymerizing, crosslinking, grafting, and curing materials. For example, electron beam processing has been used to polymerize and/or crosslink various pressure-sensitive adhesive formulations coated on film substrates, to graft coatings onto substrates, and to cure various liquid coatings, such as printing inks. Using an electron beam to modify a material avoids the need for coating solutions, including those comprising volatile organic compounds (“VOCs”). This allows for a reduction in VOC emissions, and a concurrent reduction in energy costs and environmental or occupational hazards.
Unlike ultraviolet (“UV”) radiation, which is also used to crosslink, polymerize, graft, and cure various materials, electron beam radiation does not require the use of an initiator. In addition, electron beam radiation is readily absorbed by all organic materials, even those materials that are not readily modified by UV radiation, such as thick, opaque materials and those that resist UV modification, such as allylic, olefinic, and unsaturated compounds. Polyethylene is an exemplary unsaturated compound that cannot readily be cured by UV radiation, but is curable by electron beam radiation.
Although electron beam radiation has many advantages, it does have some limitations. These limitations include the fact that electron beam generating equipment has traditionally been relatively expensive. The high expense is at least partially associated with the need for large power supplies, lead shielding, high voltage components, and safety monitoring equipment. In recent years, manufacturers have been able to build less expensive, more compact, lighter electron beam equipment by lowering the voltage of the electron beam to 125 kilovolts (kV) or less. For example, Energy Sciences, Inc. of Wilmington, Mass.; Advanced Electron Beam Technologies, Wilmington, Mass.; and American International Technologies, Inc. of Torrance, Calif. are manufacturers of compact, low cost electron beam generators. These machines make it possible to lower the purchase and operating costs of electron beam radiation equipment.
Another significant limitation of electron beam radiation is that electrons frequently penetrate too deeply into the material being irradiated. High voltages are frequently used to obtain a reasonably uniform dose over the entire cross-section of an electron beam modifiable coating, but this can result in a significant amount of energetic electrons passing into layers below the electron beam modifiable coating. This becomes a problem in multi-layer materials that comprise a coating of material that is being modified, and a substrate or backing of material that can be damaged by electron beam radiation. Paper, polyvinyl chloride, polypropylene, and TEFLON are all materials that often are used as substrates for adhesives, yet are susceptible to degradation from electron beam radiation. Electron beam radiation can cause the substrate to become brittle or otherwise degraded. The result is a deteriorated substrate that makes the product either lower quality or unusable for its desired application.
SUMMARY OF THE INVENTION
Existing electron beam generation systems do not adequately address the problems of high machine costs and satisfactorily modifying a coating without degrading the substrate. Consequently, a need exists to control electron beam irradiation such that the electron beam penetration is substantially limited to specific layers of the irradiated material, preferably just the electron beam modifiable coating of the material.
The present invention is directed to an apparatus and method for delivering electron beam radiation to a material, particularly a multi-layer material having an electron beam modifiable coating and an electron beam degradable substrate. The invention is also directed to products manufactured using the apparatus and method of the invention. At least one embodiment of the present invention allows one to control the dose (energy deposited per unit mass) delivered to particular depths in an irradiated material.
One aspect of the invention is directed to an electron beam apparatus comprising an electron beam source, a window proximate the electron beam source comprising a polymeric film having at least two surfaces, a protective layer resistant to free radical degradation on at least one surface of the polymeric window, a support proximate the window on which to place materials to be irradiated by the source, and a gap between the window and support.
Another aspect of the invention is directed to a window for use with an electron beam source comprising a polymeric film having at least two surfaces, the film having a protective layer resistant to free radical degradation on at least one surface wherein the film is able to contain an environment having a pressure of less than 10
−4
Torr.
Another aspect of the invention is directed to a method of irradiating an article with an electron beam comprising providing an electron beam source; providing a window for use with the electron beam source, the window comprising a polymeric film having at least two surfaces a protective layer resistant to free radical degradation on at least one surface; and irradiating the article through the window with electrons from the electron beam source.
Another aspect of the invention is directed to a method of modifying the properties of an article having two or more layers comprising providing an article having an electron beam modifiable first layer and an electron beam degradable second layer proximate the first layer; providing an electron beam source for which energy, voltage, and current levels may be adjusted; providing a window between the electron beam source and the article to be irradiated, wherein a gap exists between the window and article, the window having a unit path length of 3 to 50 grams per square meter, setting the electron beam source energy to between 50 and 150 keV; adjusting the electron beam source voltage and current, and adjusting the gap distance between the window and article such that the electron beam can modify the first layer without substantially degrading the second layer, and irradiating the article with an electron beam from the electron beam source.
Another aspect of the invention provides an electron beam modified article comprising an electron beam degradable backing material, and an electron beam modified coating on the backing material, the 30 micrometers of the electron beam degradable backing adjacent the modified coating having absorbed between 0.1 and 40 mJ/cm
2
of energy.
Another aspect of the invention provides an electron beam modified article comprising an electron beam degradable backing material, and an electron beam modified coating on the backing material, the modified coating being free of release material contamination. Because the present invention allows an electron beam modifiable layer to be modified, e.g., cured, directly on an electron beam degradable backing without materially degrading the backing, the modifiable layer is not required to be modified on a release material, such as silicone, then transferred to the backing. This eliminated the possibility of the modifiable layer being contaminated with release material.
In irradiating an electron beam modifiable material coated on an electron beam degradable substrate, it is important to provide a dose to, and through, the irradiated material that will adequately modify the modifiable layer so it will be useful for its intended purpose and so it will adhere to the substrate. However, it is important that the dose is
DiZio James Patrick
Kalweit Harvey William
Schlemmer Roy G.
Sventek Bruce Alan
Weiss Douglas Eugene
3M Innovative Properties Company
Gover Melanie
Little Douglas B.
Padgett Marianne
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