Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Utilizing electron arc or electron beam
Reexamination Certificate
1999-05-21
2001-05-08
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Utilizing electron arc or electron beam
C264S495000, C425S174400
Reexamination Certificate
active
06228314
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and process for crosslinking a polymer film. This invention specifically relates to an apparatus for irradiating a polymer film at a level of 500 kV or less wherein the polymer film is treated in two or more passes.
BACKGROUND OF THE INVENTION
The making of polyolefin packaging films is well-known and includes the techniques of casting films as thin sheets through narrow slit dies, and the blownfilm techniques wherein an extruded tube of molten polymer is inflated to the desired “bubble” diameter and/or film thickness. In an exemplary process, the resins and additives are introduced into an extruder where the resins are melt plastified by heating and then transferred to an extrusion die for formation into a film tube. When desired, films may then be crosslinked by various means, with electron beam crosslinking preferred.
In an electron beam processor (EBP), electrons are generated and accelerated in a vacuum then emitted to irradiate an object with electrons. The electron beam processor is used in various applications including curing of coatings and inks, irradiation of foodstuff, sterilization of medical products, as well as crosslinking and grafting of polymeric materials.
An electron beam processor typically comprises: a) a power supply, b) an electron emitter, e.g. a heated cathode, c) an accelerator for shaping the emitted particles into a beam and for directing and accelerating the energized particle beam towards an emissions window, d) a vacuum chamber from which air molecules are removed so air cannot interfere with the generation of the particle beam, e) a support structure which provides a method to seal the vacuum chamber, f) an emissions window, g) a product treatment area where the object being irradiated passes through, and h) an emission collector plate. Electron beam energy is expressed by the acceleration voltage, which is typically in the range of 100 kV to 10,000 kV. A polyethylene crosslinking application typically runs at high energy levels with typical voltages over 500 kV.
The use of multi-pass irradiation to treat polymer films is generally known. Typically this is done by passing the film over a series of rollers and irradiating at a high voltage. U.S. Pat. No.3,126,680, Baird, Jr. et al, discloses such a process, indicating that the voltage should be high, 750 kV or higher, preferably at least 1000 kV. Though this method may be preferred for irradiating polymer films, the electrons must pass through not only two or more thicknesses of the film, but also through the intervening air spaces. This typically has not been an impediment provided the voltage of the machine, or the energy of the electrons, is high enough. (James H. Bly,
Electron Beam Processing
, 106-107 (1988).)
Multi-pass irradiation of polymer films at low voltages requires special considerations. Applicants have designed an apparatus and process to overcome the problems of low voltage, multi-pass irradiation.
SUMMARY OF THE INVENTION
The invention, accordingly, resides in an apparatus for crosslinking a polymer film comprising:
a. a means for irradiating the polymer film at a level of 500 kV or less, such means having an emissions window;
b. a first means for passing the polymer film adjacent to the emissions window for a first-pass film irradiation treatment, wherein the distance between the emissions window and the first-pass film defines a first air gap; and
c. a second and n additional means for passing the polymer film adjacent to the first pass film and opposite the emissions window for a second-pass and n additional-pass film irradiation treatments, where n≧0;
wherein the polymer film may travel either in a direction from the first means to the second means for passing the polymer film, or in the reverse direction, and
wherein the distance between the first-pass film and the second-pass film defines a second air gap, and each distance between each additional pass and the previous pass thereafter defines a corresponding air gap,
each of the air gaps being no more than about 5 inches.
Furthermore, the invention also provides an improved process for crosslinking a polymer film comprising treating the polymer film with electron irradiation to cause cross-linking, wherein the improvement comprises irradiating the polymer film at a level of 500 kV or less, in at least two steps, comprising
(a) passing the polymer film adjacent to an emissions window of an electron irradiation means, wherein the distance between the emissions window and the film defines a first air gap; and
(b) passing the film adjacent to the film pass of step (a) and opposite the emissions window for a second treatment of the film, wherein the distance between the film pass of step (a) and the film pass of step (b) defines a second air gap; and optionally
(c) passing the film adjacent to the film pass of step (b) and opposite the emissions window for additional pass treatments of the film, wherein the distance between each additional pass and the previous pass defines a corresponding air gap,
such that each air gap is no more than about 5 inches.
Steps (a) and (b) of the process may be reversed such that the film initially passes adjacent to the second air gap, and subsequently passes adjacent to the emissions window and first air gap.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention.
REFERENCES:
patent: 3126680 (1964-03-01), Baird, Jr. et al.
patent: 3564238 (1971-02-01), Martin et al.
patent: 3657533 (1972-04-01), Spillers
patent: 3844232 (1989-07-01), None
patent: 0 012 330 (1980-06-01), None
patent: 0 333 492 (1989-09-01), None
James H. Bly, Electron Beam Processing,Electron Beam Processing, 106-107, 1988.
PCT International Search Report, International application No. PCT/US99/11415, dated Sep. 27, 1999.
Kotwis Joseph E.
Parrish Grant Franklin
Trueblood Ricky L.
E. I. Du Pont de Nemours and Company
Tentoni Leo B.
LandOfFree
Multiple-pass irradiation of polyolefin films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multiple-pass irradiation of polyolefin films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiple-pass irradiation of polyolefin films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449964