Pulsed electron beam curing of polymer coatings
by Richter, Karl Benjamin, Ph.D., UNIVERSITY OF MINNESOTA, 2007, 230 pages; 3279705

Abstract:

Low-voltage electron beam (

EB

) curing is fast, efficient, solvent-free, and consequently environmentally friendly. The goal of this research is to lay the foundation for continued exploration of

EB

curing in general and pulsed electron beam (

PEB

) curing in particular.

PEB

curing considerably expands the capabilities of continuous

EB

curing. It is significantly more versatile and speedy; yet, it requires less energy and, through appropriately timed pulses, polymerizes and crosslinks neat acrylic monomers in a single-step process.

PEB

exploits the inherently heterogeneous nature of energy deposition along electron tracks to spatially separate free radical initiation sites, thereby suppressing second-order termination reactions in favor of first-order propagation. This is, in effect, heterogeneous polymerization in a single phase, which is beyond the capabilities of conventional

EB

. Theoretical computations of conversion kinetics that include the fall of species mobility with rising conversion, which can lead to radical trapping, quantify this view of the process.

To test this model experimentally, a new

PEB

apparatus was constructed. It is unique in its ability to uniformly irradiate an inerted, temperature-controlled 200 cm2 sample chamber at atmospheric pressure with 80-160 kV electrons in pulses of 10-20 μsec duration at frequencies of up to 2 kHz. The flexibility of this design allows for wide-ranging investigations of

PEB

curing, and to ensure reliable experimental results, performance testing of the apparatus before and during experimentation established attainable voltages, pulse characteristics, and dose uniformity.

Conversion kinetics in mono- and multifunctional acrylate systems have been used to benchmark

PEB

curing against continuous

EB

and

UV

curing. The acrylates were converted quickly and more completely by

PEB

, without the need for added crosslinking agents. Observed changes in conversion with changes in operating conditions, including pulse frequency, pulse duration, dose per pulse, and temperature, were explored and are consistent with predictions from the kinetic model. These experimental results and the kinetic modeling can be applied directly to industrial web widths, and equipment design can be readily extended to large facilities.

This work also offers some alternative approaches to investigating

EB

curing that could prove useful. But for its versatility and low energy demand,

PEB

curing should be considered the future radiation curing method of choice.

 
AdvisersA. V. McCormick; L. E. Scriven
SchoolUNIVERSITY OF MINNESOTA
SourceDAI/B 68-08, p. , Nov 2007
Source TypeDissertation
SubjectsChemical engineering
Publication Number3279705
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