Development of bacteriostatic conformal coating and methods of applicatio

Bland, C.

Le Doux, F. N.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
November %$. 1970 
REPLY TO 
ATTN OF: Gp 
~ ~ ~ / ~ c i e n t i f  i c  P Technical In£ ormation Divioion 
Attentions Miss Winnie M. Morgan 
FROMr 
 office of A s s i q t a ~ t  ~ e n e r a l  Counsel for  
Patent Matters 
SUBJECT:. Annouxicement of NASA-Owned U. 8. Patents i n  STAR 
In accordance with the procedures agreed upon by Code GP 
and Code USX, the attached NASA-owned U. S. Patent is being 
forwarded for  abstracting and announcement . in NASA ST=. 
The following in£ ormation isprovidedl 
U. S.  Patent No. .' t . 2wzm%' 
Government or 
Corporate Employee 
Supplementary Corporate 
Source (if applicable) t A@* 
NASA Patent Case No. 
NOTE - If th i s  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is applicable: 
yes 0 NO (3 
Pursuant t o  Section 305(a) of the National Aeronautics and 
Space Act. the name of the Administrator of NASA appears on 
the f i r s t  page of the patent; however, the name of the actur). 
inventor (author) appears a t  the heading of Column NO. 1 of 
- the Specification, following the words ". . . with teepect to 
Enclosure 9 
Copy of Patent aited above 3 Y
4 - 
=? 
", 
bb71 - 1 p ~ 4  
(A C E S S ~  NUMBER 
I 
(PAGES) 
/' 
(NASA CR OR TMX OR AD NUMBER) 
https://ntrs.nasa.gov/search.jsp?R=19710006571 2020-03-17T02:42:54+00:00Z
3,532,538 
3ACTERi@STATP@ CoNFokak~AL COATING AND 
RTETEIODS OF APPLICATION 
F~'rancis N, Le Daox, Seat Pleasant, and Charles Bland, 
he, Seabrook, Md., assignors to tbe United States of 
Alrlerica as represented by the Administrator of the 
National Aeronautics and Space Administration 
No Drawing. Filed Mar. 30, 1967, Ser. No. 627,599 
lint. Ci. H05k 3/28 
U.S. 61. 111-201 4 Clairn~s 
These compounds can be cured to give a solid therrno- 
set, resiiious material. 
Ordinarily, epoxy resins contain a plurality of ternlinal 
epoxy groups and are of moderately high molecular weight. 
5 containing more than 10, usually more than 20 carbon 
atoms per molecule. 
Epoxy groups can be introduced into organic mole- 
cules, particularly cyclic organic compounds, by treat- 
ment of an aliphatic double bond with an  appropriate 
10 oxidizing agent. However, epoxy resins are typically pre- 
pared by reaction of a polyfunctional epoxy compound 
ABSTRACT OF THE DISCLOSURE with a polyol, that is, a compound containing two or  more 
hydroxy radicals, producing epoxy resins comprising one 
Bacteriostatic electronic components and assemblies or more ether linkages joining organic radicals and termi- having a cured epoxy coating thereon, preferably with a 15 nating in epoxy groups. The epoxy resins used in the manu- 
coating thickiless of from 0.005 to 0.010 inch. factore of materials in accordance with the present proc- 
ess will ordinarily be of this description. 
A preferred class of epoxy resins are the product of 
The invention described herein was made by employees reaction of a polyfunctional compotlnd with an 
of the United States Government and may be manufac- 20 aromatic polyhydric phenolic The polyfunc- 
tured and used by or  for the Government for govern- tional epoxy compound used may be a diepoxide, dis- 
me:~tal purposes without the payllleni of any royalties tinguished froln the ,--lass of epoxy resins by its relatively 
thereon or therefor. low molecular weight, illustrative of which are diepoxy- 
This invention relates to a method for making hacterio- butadiene, his (2,3-epoxy-2-methylpropyl) ether and the 
static electronic components and component assemblies, 25 like. usually, the polyfunctional epoxy is a 
and to the products made by this method. More particu- haloepoxy conlpound such as epichlorohydrin. Reaction of lady; the invention relates to bacteriostatic electronic com- epichlorohydrin, for u,iih an aromatic polyhy.. 
pollent assemblies produced by applying a thin coating of dric phenolic in the formation of a 
a curable epoxy system to  such components and assenl- polymer containing ether linkages between arlllene radi- 
b!ies, then curing the system until the coating sets. 30 cals derived from the initial aromatic polyhydric corn- 
With the advent of travel in space, a need has devel- pound and hy~roxy-alkylene radicals derived from the 
oped to avoid carrying viable bacteria on electronic corn- initial haloepoxy conlpound, the polymers terminating in 
pollent assemblies to other planets to hinder the growth e~o;oxpa~koxy radicals. The =onlatic polyhydric 
and reproduction of both vegetative and sporulative bzc- may conlprise a ~ ~ o l l o c y c ~ i c  phellol such as a resorcinol, 
teria found on such components, and to restrain the cam- 35 a polycyclic phenol such as p,pl-(dihydroxy)-biphenyl, a 
ponet~t and assemblies when they are subjected to high phenolic resin such as a phenolformaldehyde resin, and 
vibration levels. the like. Particularly preferred are epoxy resins derived 
It is an  object of this invention to provide a method for from the reaction of epichlorohJidrin and bisphenols. 
producing electronic co,nlponent asseinblies which are bac- Illustrative of bisphenols which may be employed to 
teriostatic, and thus hinder or  siibstantially prevent the B0 produce resins of this type are, for example, p,p'-oxybis- 
reproduction and growth of vegetative and sporulative bac- pi:enol, p,p'-methylenehisphenol, 2,2-bis(4-hydroxyphen- 
teria. yl) propane, 2,2-bis(4-hydroxy-2 - methylphenyl)pro:,ane, 
Another object is to provide a method for restraining 2.2 - bis(2-t-bu[yl-4-llyd~oxpphenyl)pr0pane, 2,2-bisf 2,s- 
electronic coinpolle~ll assemblies which are to  be sub- 
, 
dilllcthyl - 4 - hydroPhenyl)pl-opane, 2,2 - bis(2-chloro- jected to high vibration levels, such as those encountered ri-' 4-hydroxyphenyl)propane, 2,2-bis(2 - bromo-6-fiuoro-4- 
during flight at  high acceleration in spacecraft. hpdroxyphenyl)propane, 1,l-bis(4-hydroxyphenyl)ethane, 
Stili another object is to provide electronic component I,l-bis(4 - hydrosyphenyl)isobut~e, 1,l-bis(2-isopropyl- 
assemblies having a thin, tough, semi-rigid, bacteriostatic, 4~~ydrosyp~~enol)isobu~ane, 2.2 - bis(4-hydroxyphenyl) 
electrica!ly resistive coating which is readily applied and 50 butane, 4,4-bis(4-hydroxyphenyl)heptane, l,l-bis(4-hy- 
which restrains the components ai high vibration levels. ct~cxyphenyljdodecane, 2,2-bis(4 - hydroxypheny1)hexa- 
Other objects and advantages of the invention are ap- decnne, and the like. 
pa-rent from the disclosure and claims. Another class of epoxy resins useful in the present 
This invention provides a method for producing bnc- process comprises aliphatic epoxy resins. Compounds of 
tcriostalic electronic coillponent assemblies con~prising ap- 5;, this nature for exar,,ple be prepared by a process 
plying a thin coating of an epoxy system to  the Component analogolls to that ill preparing an  epox), resin 
assemblies and curing the coating to a iougE1, semi-rigid from a bispllenol, with the substitution of an aliphatic 
state. The epoxy system used to coal the cunlponents cor-il- pol:lol for the aromatic hydroxy coIl,pctund. Illastrative 
prises: ( 1 )  at least orle pol-m~ric  epoxy comiiol~nd; (2) 
,f of this class are reaction products of an  
at lea~,t one inonon-ieric epoxy compound: ( 3 )  :it lerist one epoxy group source sucli as epich!orohydrin with aliphatic 
pol;,anlide resin; and (4)  zit least one orgitnic an:inr. polyols sirch is iriethyI,rre glycol, 1.4-blitylene glycol, 
E1ectrol;ic con~ponenls s1ir.h as dioclec, tiiocles, l?-ahis-  , 
e,. ,. . 
nexnrncthyiene glycol, r-ctzrethyle~ie g l~co l ,  glycerol, soy- 
iu,i rilucliricr,. etc.. !!ray he uriliie~i c n>z*i:i l ip the nssem- 
. bit01 an6 i k  iike. h!Lcs (1-eat& by the coml:osi!ion of the instr!nt invention. i n  genera?, aliphatic chains produce more flexible 
Such assemblies are generally of rigid printed circuit type o j  resins than aromatic, and mixed aliphatic and aromatic 
aithcugh the coating can also be applied to flexible printed chains mav be inlo an 
circuiis. 
-- 
r-ecin, usin'z the aforedescribed procedures, proclucirlg 
i he polymeric epoxy compounds used in the syste~n are sesins of modified properties. 
characterized by the prcscnce of epoxy which have the As mentioned above, epoxidized cycloaliphatic com- formula ;n pounds such as diepoxide of diethylene glycol bisdihydro- 
disyclopentadienyl ether, are also within the class of 
epoxy resins curable to thermoset resinous products. 
2,532, fl3S 
=; 
b 
4 
f i ~  coi~~meri:i:il epoxy i-e,iil-, th:; riiinlber of ;iirl-s tire 7rIx: cp~ ' ;y  S ~ ~ ~ ~ C I I I  i h  pr~~j:~f':i.! by 111ihiilg I !?( :  foil[ i l l -  
repeated u:lit of the poiymer ckiaiir 1-ect1r.s \.:'ill vary i i o l i~  predients in the iie~,l:.ed projjortions in any i!csircd oi.tier 
n~tslec~rle to rnoieeule. In general, any co!iiinet.cini resin and  is a!7pliect to iht; electi.or~ic con~j>occirts by brushing, 
will represent a ~ f ~ i ~ l ~ t ~ e  of rebills of vcr-yiilg c h : h  ltenz:I~a &?ping or spraying. When Lhe coniponeiils arc coiilpletely 
corresponding to a varying number oi ripc?.ted tiiliti. coatrcl, the excess continz nlziierial is pcirr~ittetl to drain 
Compared to other widely-used resin products, the epoxy of£ before curing is initiated. Depending upon the nsture 
resins are of relatively low molec t~ la~  weight. Such resins oE tile four ingredients heating may or may not be neces- 
are nevertheless designzted as polymeric, however, viiih sary to initiate and/or complete cure. If desii-ed, healing 
reference to the duplication of chain units in the mole- may be employed to accelerate cui-ing provided the conl- 
cule, and to the at  least partial content of polymeric polients can withstand the temperature. 
n~olecules usually present. Furthermore, though ide:+i!y More than one coat can be applied lo an  individual 
the resin molecule contains two epoxy grozps per mole- component or assernbly by repat ing the steps described 
cule, in practice i t  is found that the rejinous products above, but each layer should be only partially cur-ed be- 
have a varying average cumber of epoxy grotips per mole- fore applying the next layer, as described in Example I. 
cule. The epoxy group content of snch resins is conven- 15 The finished product preferably has a coating thickness 
tionally expressed as the epoxide equivalent, which refers, of from 0.005 to 0.010 inch. 
to the grams of resin containing a gram equivalent of As shown in the exan~ples, the electronic cornponent'i 
epoxide. The epoxide equivalent of a commercial resin is are usually cleaned and decontaminated before coating 
generally expressed as a range, such as 125-175, 150-200, with one or more of the following substances: 2-propa- 
etc. Epoxy resins having low epoxide equivalents, below 20 ilol, n-propanol, n-buianol, 2-butanol, amyl alcohol, mix- 
about 250, are preferred because of the lower viscosity tures thereof, and the like. 
of such resins. The following examples indicate the ease of applica- 
The monomeric epoxy compound has a low molecular tion and the durability of the coatings used to  make 
weight and contains a single epoxy group. By using up to bacteriostatic, vibration resistant electronic components. 
about 25% by weight of the monomeric epoxy based on 2.5 EXAMPLE I 
the total weight of the epoxy system, the viscosity of the 
system is reduced but the strength of the thermoset sys- A mixture was prepared containing the following 
tem is not impaired. Examples of such monomeric epoxy COnlPonents: 
are: aliphatic compounds like ally1 glycidyl ether, aro- 64% epoxy resin with epoxide equivalent of 175-195 
matic compounds like phenyl glpcidyl ether, glycidyl- 30 (Epon 815, Shell Chemical Company) 
benzene, and styrene oxide (1,2-epoxyeihylbenzene) hp- 12% polyamide resin (Versamid 125, General Y\.liils, 
droxyalkyl glycidyl ethers such as 2-hydroxyethplglpcidyl Kankakee, 111.) 
ether, and mixtures thereof. 20% ally1 glycidyl ether (as sold by Shell Chemical 
The polyamides used in this composition are condensa- Company) 
tion products of a polj~nierized long chain fatty acid :'' 4% aromatic amine curing agent (Shell "Z" Curing 
con~pound, such as dimerized or  trirnerized vegetable oils Agent, Shell Chemical Company). 
or  unsaturated fatty acids, with an aryl or  alkyl poly- The ingredients were proportional by weight in the 
amine. Illustrative of such materials are the condensation percentages shown and thoroughly mixed together for products of a polymerized (dimerized or  trimerized) fatty 
several minutes or until a was 
acid such as dimerized linoleic acid or polymerized veget- 
obtained. This mixture was employed to coat electronic 
able oil such as dimerized linseed oil with an anline such cords and components used in spacecraft. The electronic 
as ethylene-diamine. When used with organic anlines, componeIlt assemblies were thoroughly cleaned and polyamide curing agents offer several advantages. Greater decontaminated in a bath of 2-propanol and then pre- flexibility and impact resistance can be obtained in the heated to 1150 F.-125e p. prior to applying the coating final product. As the reaction of this invention is exo- The coatjng be applied in several mays, 
thermic, the low volatility of the polyanlide compounds is such as brushing, dipping or spraying, depending on the 
of ereat value. With the exothermic nature of such re- particular electronic assemblies to be coated and con- 
actions, it is possible for the build-LIP of heat in large venience. When the are completely coated the 
masses of reacting inaterials to exceed the decomposi?ion excess coating material is allowed to drain before the 
temperature of one or more of the ingredients, resulting 5U curing is initiated. The cure for the coatiag mate- 
in weak or discolored end product. Becacse the P l y -  rial in this application map be accomplished by hanging 
amides are less highly reactive than organic aniines, the the electronic cards in a forced air circulating ox,en p;c- 
exotherm of the reaction can be partially controlled by heateti to 150 ~ . - 1 2 5 0  F.  hi^ procedLire will curt 
use of increased proportions of polyamides to organic ;;j coatir,g in approximately 2-3 hours. 
amines as the mass of the reaciing resin is increased. A higher curing tenlperature may be employed if the 
 he organic anlines used in the epoxy sjistenl are, for electronic components involved can withstand the higher 
example, selected from polyamines and tertiary amines curing temperaiul-es, ~h~ coating tiljckness achjeT-cd jn 
snch as benzyl dimethyl anline. il!ustrative of polllalnines ;his procedure \vi!l be approxirnaiely 3.005 inch to 0.010 
are N,N-diethylethylenediamine, ethylenediatnine, dieth- c;;, inch. A thicker final coating may be obtained by apply- 
ylenetriarnine, triethylenetetranline. Y\i - (hydrox:lethyl) ing additional coats in the mariner prcviouslg described, 
tlielhyler~etriamine, phen:~lenediarnine and the like. Aii- h i lh l lowir ig  J O  illinlrtes tiille i n  the pl.ioi. 
pllatic potyallline~ of the forlnlila a";if~I?~Cl~-12+,i"d~-Ia, lo each ajlpijcat~on of the material, A fi:?al 
nihei-e .X is a whole number, are przfej.3-ei?. pariic:ilarl;1 ctlre of ;lpiProximately 2 to 3 hours is effcc/i7d svhen :I 
jlreferred heiiig po1yalkyleneroi)-ami~~e,~; as  irieii:y?- (,; cl*sirab!e tliiickncss has keen obtninrtl. 
rnttef:.aiiiine. con-:biriiri:: high rcacfiviiy wi:ii epoxy EXAMPLE 11 
resins with low volatility. 
i n  general, the polyamidc and organic amine shoulc! This exampic clcscribes a system wl~ich \vIil cure at  
conlp:.isc from about 5 to 15% by iveiiflll of the cp0-y ambient o r  room teraperatcre of appro:iirn:itcly 75" F. 
systel?-j htit may broadly vary front j 76 or less to 50r/t or jO if a heat cure is not desirect. A mixiiii.e was pseparcri 
nxose by weigl~t of the epoxy system. Generally, srlficie:lt col~tainling the following ingredients: 
polyamide and organic ami?ze should be used to s!~pply 62% epoxy resin an epoxide of 150-195 
at  least one reactive site for each epoxy group present in (Epon 820. Shell Cherniciil Cony-)any) 
the resin. In practice an ainouitt sornewl~:rt ii; excess of 15% polyainide resin (T/ii.s;inlici 140, Gcncr.nl Mli!lsi 
Iile theoretical rgquirenlent shorlld be used. P. , , - K:in!takee, Ill.) 
;'5,!3:2,538 
5 G 
20% ally1 glyciciyl ether a thickness within the range of Erorxl 0.005 to 0.0iO inch. 
3 %  diethylenetriamine (Shcli Cheniiczii Company). 3. The coating composition of cinirn 4, in a ciired state, 
This nlixture lvas tho,.oughiy mixed app,ied lo being of a thickness of from 0.005 inch to 0.010 inch. 
electronic components as described in Exan-iple 1. The 4. A low viscosity coating composition particrrlarly 
curing cycle for this mixture may be eifected at rcon: adaptable for space application in encapwlatir~g elec- 
temperature (750 F.) for approximately to hours, tronic coi-liponents and assemblies thereof, cliarncteiizeci 
or, in an  oven, at  115" F.-125" F. for 2 hours. in its cured state in possessing bacteriostatic qualities and 
Components coated in the manner described in the forming a strong, semi-rigid system having ihe ability to 
examples showed bacteriostasis (as determined by stand- restrain said electronic components when subjected to 
ard techniques) for: flight vibration, said coating composition made from a 
mixture consisting essentially of: (1 )  a t  least one poly- 
( a )  Bncillis sztbtilis var. rliger meric epoxy compound; (2)  at  least one monomeric 
(b) Stnphylococcw Alrrerts epoxy compound; (3 )  a t  least one polyamide resin; and 
(c)  Pselidornonns alcaligenes (4) at  least one organic anline. 
( d )  coxynebactenium spp. 15 
From the foregoing description it will be evident that References Cited 
numerous variations and modifications can be made in UNITED STATES PATENTS 
the present process without departure from the invention. 3,055,777 91 1962 ~~~d --- --- ---- 117-16 1 XR 
What is claimed is: 3,251,705 5/1966 Schmetterer et al. - 117-161 XR 
1. Method of making bacteriostatic electronic com- 20 
ponents and assemblies comprising coating said compo- WILLIAM L. JARVIS, Primary Examiner 
nents and assemblies with a mixture consisting essentially 
of (1 )  a t  least one polyn~eric epoxy compound; (2 )  a t  U.S. Cl. X.R. 
least one monomeric epoxy compound; (3 )  at  least one 117-161; 260-834 polyamide resin; and (4 )  at  least one organic amine. 25 
2. The method of claim 1 wherein said coating has 


Bacteriostatic conformal coating and methods of application Patent

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server