Photosensitive filler is added to curable epoxy resins to minimize stress from internal shrinkage during curing or polymerization. Cinnamic acid resins and cinnamal ketones may be added in the amount of 1 to 3 percent by weight of the resin mixture

Dillon, J. N.

English

NASA Technical Reports Server

July 1967	 Brief 67-10227 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Photosensitive Filler Minimizes Internal Stresses in Epoxy Resins 
The problem: 
Most cured high-heat, distortion epoxy resins are 
in a stressed condition, which reduces their strength 
and causes deterioration of related physical properties. 
The stress is caused by internal shrinkage during cur-
ing or polymerization. Normal techniques to mini-
mize detrimental high shrinkage include curing at 
relatively low temperatures and adding inert fillers to 
decrease the exothermic heat of reaction. These tech-
niques have their inherent disadvantages which make 
their use under certain conditions unsatisfactory. 
The solution: 
Add a photosensitive filler, such as cinnamic acid 
resins and cinnamal ketones, to a curable epoxy resin 
mixture in the amount of 1% to 3% by weight of the 
resin mixture. 
How it's done: 
The addition of the fillers before cure does not 
inhibit the curing or polymerization of the epoxy 
system since the volumetric addition of the filler is 
minute. The resultant mixture is then cured in the con-
ventional fashion, as by the addition of heat or a 
catalyst. After curing, the epoxy resin, if clear, displays 
internal isoclinic stress lines when viewed under 
polarized light. The epoxy resin is then exposed to a 
strong ultraviolet light source. Such exposure is for a 
time sufficient to allow the photosensitive filler to 
polymerize and relieve the internal stresses. When the 
epoxy resin is again viewed under polarized light, it 
is observed that the internal stress lines have disap-
peared. This indicates an epoxy resin that has high 
resistance to thermal shock and conditioning.
Notes: 
I. This method to relieve internal stress eliminates the 
use of inert fillers. They frequently tend to settle 
out of solution before curing thus producing a 
nonuniform and weakened structural system. 
Inert fillers invariably lower the continuous 
service temperature or heat distortion point of an 
epoxy system. 
2. The epoxy system currently used as an adhesive for 
the ULD ceramic module can be modified to 
utilize a photosensitive additive. Removal of the 
carbon-black additive (for detection of misplaced 
epoxy) would allow the use of a photosensitive 
additive, producing a higher thermal shock prop-
erty. 
3. This epoxy system could be used to produce stor-
age lightweight epoxy tools which would have a 
longer life span in the high ultraviolet radiation 
environment of outer space. 
4. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10227 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by 
NASA, Code GP, Washington, D.C. 20546. 
Source: J. N. Dillon
of IBM
under contract to
Marshall Space Flight Center
(M-FS-1 880)
Category 03 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000227 2020-03-11T20:29:57+00:00Z


Photosensitive filler minimizes internal stresses in epoxy resins

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