Note: Descriptions are shown in the official language in which they were submitted.
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1 B~CKG~GUMD OF THE INVENTION
For a number of years the coating industry has been engaged in sub-
3 stantial developmental programs in the quest for procedures which would allow
4 the coating of substrates at high production rates with the coating being
cured to a tack-free condition at a speed ccmmensurate with the contiguous
6 processing steps. The industry has desired to eliminate the volatile solvents
7 required in many of the well kncwn coating processes because of potential
8 1 hazards or because of the cost of equipment to handle the evolved solvent
9 ¦ vapors. In addition, the industry has been seeking coating formulations which
¦ would produee coatings which were durable and which would permit substantial
11 ¦ additional processing of the workpieee, such as metal forming operations where
12 I the substrate is metal strip and container bodies, blanks and closures.
~ I Epoxy eoating formulations have long been recognized as affording !
14 ¦ desirable properties in the finished coating, especially the toughness to
~ I withstand further processing. Hcwever, the problem has remained to develop a
16 ¦ low cost epoxy coating formulation which ~uld ccmbi~e the desired rheologieal
17 I properties for the coatin~ application with both reasonable pot life and rapid
18 ¦ curing in the prcduetion line.
19 I In ~att United States Letters Patent No. 3,794;576 granted February
26, 1974, there are described desirable epoxy formulations whieh ccmbine the
21 I desired rheological properties with s~1itable pot life and rapid curing. me
22 ¦ formulations contain a Lewis acid precursor catalyst whic~ is decomp~sed upon
23 ¦ irradia~ion by ultraviolet light to pro~uoe rapid curing of the coating to a
24 I tack free condition. H~Yever, to achieve the desired rapid curing, the epox-
~5 ¦ ide ormulati~s .herein contain at least about 15 per cent by ~eight of an
~6 ¦ epoxidic ester havi~g t~o epoxycycloalkyl groups; such esters materially in-
2~ ¦ crease the cost of the formulation as ~ pared with the more conventional
28 ¦ epoxide prepol~ er materials.
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.. 1 Since the disclosure of ~latt, a number of patents an~ publicat.ions
2 have appeared proposing various catalyst precursors for the epoxy formulations
3 which could replace the diazonium catalysts speci~ically described in the Watt
~:~ 4 Patent. ~mcng these are the onium cata.lysts disclosed in Barton Unitecl States
:, 5 Letters Patent No. 4,0~0,936 granted May 23t 1978; Crivello United States
Letters Patent Nos. 4,069,055 granted January 17, 1978 and No. 4,058,401
~ 7 granted November 15, 1977. Hc~ever, the search has continued for lc~ cost
i ~ formulations which would cure rapidly, i.e., formulations which ~uld not re-
quire even ~c~all amounts of special components such as the epoxidic esters of
the Watt Patent.
11 Although it has long been knYwn that heat will accelerate the reac-
12 tion rate of polymerization following irradiatlon to effect co~plete curing,
1~ generally in accordance with the Arrhenius equation, and has long ~een sug~
14 gested to augment the irradiation treatment (see, for example, the aforemen-
: 15 tioned Watt Patent at Col~n 6, lines 1-16~, such heating has also been recog-
16 nized to introduoe other problems in the form of production requirements and
17 possible adverse ef~ects upcn the polymer properties since la.~ molecular
18 weight polymers may result. ~Some researchers have evaluated various factors
.- 19 a~fecti.ng cure rate in such irradiated epoxide formulations and have proposed
7 20 substantially elevated temperatures to increase the cure rate while avoiding
21 ¦volatilization of the monomer (See, Crivello et al, "Triaryl Sulfor.ium Salts:
22 ¦A New Class of Photoinitiators for Cationic Polymerization", JOURNPL OF
~ ¦R~D~ArION CU~ING, Volume 5, pages 2, 10-11, January lg78).
.~ ¦ Although elevated temperatures of loo&. and above ~uld appear to .
¦be advantageous in terms of acceleration of reaction rate, such temperatures
¦ 26 ¦have been found to substantially affe~ct the quality of the polymeric coatinq
.~ 2~ ¦although no monaner or volatile con~3Onent may be driven off during the pro-
2~ ~cess. ~oreover, levati~l of the c ~tin to s~rl~ te eratu~es and r~intenalloe
3 ~ 3~
3Z
thereat for any appreciable length of time presents substantial
production problems when high speed processing is involved.
Accordingly, it is an object of the present invention
to provide a process for coating substrates with relatively
low cost epoxy prepolymer formulations which are activated by
irradiation and which will produce a tack free surface condition
rapidly for use on high speed production equipment.
It is also an object to provide such a process which
permits the utilization of relatively low cost epoxy prepoly-
mers and a wi~e range of ultraviolet sensitive catalyst pre-
cursors.
Another object is to provide such a process which
may be adapted to a wide variety of high speed coating lines
and which does not require extensive or expensive equipment.
SUMM~RY OF THE INVENTION
It has now been found that the foregoing and related
objects may be readily attained in a method in which there is
applied to the substrate a fluid coating of polymerizable
composition comprising at least one epoxidic prepolymer
material polymerizable to a higher molecular weight at which it
is tack-free and up to 5 percent by weight of a radiation-
sensitive catalyst precursor which decomposes upon exposure to
electromagnetic radiation to provide a Lewis acid effective to
initiate ~olymerization of the epoxidic prepolymer material.
The catalyst precursor is ineffective to cure the epo~idic
prepolymer material to a tack-free surface condition at ambient
temperatures in a period of two minutes following exposure to
radiation to effect its decomposition. The epoxidic prepolymer
Inaterial contains less than about 15 percent by weight thereof
of epoxidic prepolymer material having two epoxycycloalkyl
groups per molecule.
The coating is exposed to electromagnetic radiation to
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effect decomposition of the catalyst precursor to thereby gener-
ate a Lewis acid, and the
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1 COAting is maintained at a temperature of about 50-90 C. for a period of at
~ least 0.5 second and less than about 2 minutes following initiation of expc-
3 sure to radiation. As a result, the polymerizable composition of the coating
4 is polymerized to a substantially tack-free surface condition in a period of
less than 30 seconds follcwing the cc~bination of exposure to radiation and
6 ~aintenance of the coatirg at the prescribed temperature.
7 The preferred coating compos1tions are substantially free fro~ pre-
8 1 polymer material having t~o epoxyc~cloalkyl groups per molecule and such pre-
¦ polymer materials are conveniently glycidyl ethers of various aromatic alco-
¦ hols. Conveniently, the propolymer is the reaction product of bis-phenol A
11 1 and epichlorohydrin.
1~ ¦ The catalyst precursor economically comprises less than 3 perc~nt by
1~ ¦ ~eight of the polymerizable oo~positic~ and is an aromatic diazonium salt or
1~ 1 an aromatic onium salt selected from the group consisting of onium salts of
group Va elements, onium salts of ~roup VIa elements and halonium salts.
lG ¦ me substrate may be metallic and heating the coating to t~ desired
17 I temperature may be effected by induction heating of the metallic substrate.
18 ¦ Alternatively, conduction, infrared radiation and convection may be used to
¦ heat-any type of substrate anc3/or the coating to the desired temperature. The
~ I coating should be maintained at the prescribed t~ erature for a period of at
l least about ~ seconcls, but less than about 2 minutes. Care mllst be taken to
~2 avoid overheating the coating since this may effect a reduction in the desired
23 properties of the polymer.
24 The most convenient form of radiation to effect catalyst prepolymer
de~ompositon is ultraviolet radiation.
26 DETAILED DF~CRIPTION OF THE PREFERRED E~oDL~Nrs
.. ~
27 As previously indicated, the coating oompositions utilized in the
28 present invention essentially cornprise a mixture of an e~oxidic prepolymer
material and a radiation-sensitive catalyst precursor Other
components such as pigments, dyes, fillers and diluents may be
incorporated if so desired.
The epo~idic prepolymer materials which may be used
herein comprise any monomeric or oligomeric material containing
at least one fuctional epoxy group or oxirane ring so that they
may be polymerized upon opening of the oxirane ring. In
addition, polymeric epoxy materials may be empl~yed if they may
be dispersed in a fluid coating composition and are capable of
10 undergoing further polymerization to produce a solid polymer
coating. ~he epoxy compounds may be aliphatic, cycloaliphatic,
aromatic or heterocyclic.
The epoxidic prepolymer should contain no functional
groups more basic than the oxirane ring and should be a
solvent for the catalyst precursor. Most desirably, the pre-
polymer should contain a reasonablepercentage of epoxy compounds
containing two or more epoxy groups per molecule.
mhe polymerizable material will be epoxide resins used
; either singly or in combination and will have an average epoxide
value of about 0.1 -1Ø The carbon chains having the epoxy
groups may include additional substituents including ethers,
esters, halogens, phosphates, and the like, and the compounds
may include other polymerizable functional groups such as
acrylates and silicones.
Typical epoxy materials are readily available
commercially, the most common being those which are the product
of bis-phenol A with epicholorohydrin or those resulting from
the reaction of epichlorohydrin with a phenol formaldehyde
resin of relatively low molecular weight. Reference May be made
to the HANDBOOK OF EPOXY RESINS by H. Lee and K. Neville
(McGraw-Hill 1967) for various epoxides. In addition, the
technical literature and patent literature both contain extensive
discussions of various epoxidic prepolymer materials which are
useful in the compositions of the present invention as will be
demonstrated hereinafter.
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1 ¦ In W.R. Watt United States Letters Patent 3,794,576, granted February
~ ¦ 26, 1974, there are described radiation-sensitive epoxidic blends containing
3 ¦ at least about 15 percent by ~eight of an epoxidic ester having at least two
4 1 epoxycycloalkyl groups per molecule in order to achieve polymerization ~nd5 I curing of the ccmposition rapidly upon exposure to ultraviolet radiation or
the like. me compositions of the present invention do not require the pres-
¦ enoe of such epoxy cycloalkyl esters for polymerization and curing, and
~ ¦ accordingly will contain less than 15 percent by ~ieight thereof and may be
9 ¦ totally free therefrom.
¦ Although not essential and sometimes undesirable, the polymerizable
11 ¦ composition may contain diluents to improve viscosity, and these diluents may
12 I be reactive such as those prcduced by reaction of an alcohol or a phenol with
i 13 ¦ ~picholorohydrin. Exemplary of reactive diluents is the reaction product of
14 ¦ nonylphenol with epicholorohydrin. q~le amount of diluent may vary from zero
I to as much as 45 percent of the ccmposition if a reactive diluent is employed
16 ¦ and is preferably less than 15 percent if nonreactive diluents such as di-
¦ butylphthalate are employed.
18 ¦ For many applicationsr the composition will contain an inert pigment
19 ¦ or dye to provide a desired coloration. Generally, such pigments and dyes
I will comprise less than about 40 percent by ~eight of the cGmposition. For
21 ¦ certain applications, it may be desired to include an inert filler, but such
2~ ¦ fillers may be deleterious to the desired properties for the coating and will
~3 ¦ normally comprise less than 40 percent by weight and preferably less than 15
24 ¦ peroe nt by ~ight of the polymerizable oomposition.
¦ T~ secon~ essential component of the polymerizable C~llpOSitiOIl iS
26 ¦ the radiatio~-sensitive catalyst precursor which will decompose ~xon exposure
27 to electromagnetic radiation above the visible light spectr~ so as to provide ¦
~8 ! a e~is acid whi is eEEeetive to int~ ~ polymerizeti~ oE the epoxidie pre-
polymer material~ Various compounds exhibiting the desired
photoinitiation characteristics have been discovered and are
known to be effective at the present time, including the aro-
matic diazonium salts of complex halogenides which decompose
to release a halîde Lewis acid described in detail in the
aforementioned Watt United States Letters Patent No. 3,794,576;
the diaryliodonium salts described by Crivello et al in JOURNAL
OE RADIATION CURING, Vol. 4, page 2 (1977); the triarylsulfonium
salts described by Crivello et al in JOURNAL OF RADIATION
CURING, Vol. 5, page 2, (Janua y 1978); the aromatic iodonium
and aromatic sulfoni~ complex salts speci~ically described in
Barton United States Letters Patent No. 4,090,936 granted May
23, 1978; the aromatic onium salts of group Va elements des-
cribed in Crivello United States Letters Patent No. 4,069,055
granted Januray 17, 1978; and the aromatic onium salts of
Group VIa elemènts described in Crivello United States Letters
Patent No. 4,058,401 granted November 15, 1977. Moreover, the
compounds may be the bis- or tris- variants thereof. An
extensive discussion of triarylsulfonium salts useful for the
present invention appears in UV CURING: SCIENCE AND ^ECHNOLOGY
by S.P. Pappas, Technology Marketing Corporation, Stamford,
Connecticut, at pages 5~ et_seq.
The term "Lewis acid precursor" as used herein is
intended to encompass compounds which will directly generate a
Lewis acid or which will indirectly generate a Lewis acid, the
Lewis acid receiving an electron pair from the oxygen of the
oxirane ring to open the oxirane ring and produce a cationic
site for polymerization.
Exemplary of a classic Lewis acid is phorphorus
pentafluoride (PF5) which will complex an electron pair, and
which may be generated by a diaæonium catalyst in the following
reaction:
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Ar - N = N] PF6 ~ Ar F + N2 ~ PF5
PF5 (monomer) - ~ M PF5
This mechanism is described in detail in the aforementioned
Watt Patent No. 3,794,576.
Exemplary of an indirectly formed Lewis acid is the
mechanism postulated by Crivello et al in "Triarylsulfonium
Salts: A New Class of Photoinitiators for Cationic Polymeriæa-
tion" in JOURNAL OF R~DIATION CURING, Vol 5, page 2 (January
1978). The authors postulate that the decomposition of the
diaryl- and triaryl- sulfonium salts produce a 8roensted acid
which in turn provides a proton which will function as the Lewis
acid to accept electrons from ~he oxygen of the oxirane ring
and initiate polymerization in accordance with the following
; mechanism:
6 SOlvent~HAr F + Ar. + Solvent. + HPF6
HPF6~ M(mOnomer) ~ HM PF6
Regardless of the theory o:f the action embraced, it
is apparent that the photoinitiator is decomposing to generate
in the reaction medium an electron acceptor acting as a Lewis
acid to open the oxirane ring and thereby initiate cationic
polymerization of the epoxidic prepolymer material. The
reaction then proceeds as additional oxirane rings are opened
until all of the monomer has been polymerized or until impurities
interfere with the reaction mechanism.
Specific examples of the various classes of photo-
initiators usable in the present invention are the following:
diphenyliodonium tetrafluoroborate; dit2,4-dichlorophenyl)
iodonium hexafluorophosphate; diphenyliodonium hexafluorophosphate;
diphenyliodonium hexafluoroarsenate; triphenylsulfonium
tetrafluoroborate; triphenylsulfonium hexafluorophosphate; tris
(4-phenoxy-phenyl)sulfonium hexafluorophosphate; trifluoromethyl-
diphenylsulfonium tetrafluoroborate; p-chlorobenzenediazonium
., . _ g _
32
hexafluorophosphate; 2,4-dichlorobenzendiazonium tetrafluoro-
borate; and p-methoxybenzenediazoniom hexafluorophosphate.
The amount of the catalyst precursor may vary from
as little as 0.5 precent by weight of the polymerizable com-
position to as much as 5.0 precent by weight thereof and is
preferably on the order of 1.0-3.0 percent~ If so desired,
combinations of the catalyst precursor may be employed.
As indicated, the photoinitiator is decomposed into
a Lewis acid by exposure to electromagnetic radiation. Although
electron beam bombardment, X-ray radiation, and other similar
forms of high energy radiation may be employed for this purpose,
exposure to ultraviolet radiation has been found highly satis-
factory and is desirable for commercial applications. The
exposure to radiation normally required may be of extremely
short duration, periods of about one-half to three seconds being
normally adequate for most compositions depending upon the in-
tensity of the radiation at the surface. However, for relatively
thick coatings of the com~osition, it may be desirable to extend
the period of exposure to four seconds or even more, to ensure
adequate penetration of the radiation through the depth of the
coating.
The coating must be maintained within a relatively
narrow elevated temperature range for a period of 0.5-5.0
seconds following initiation of exposure to the electromagnetic
radiation in order to achieve the desired rapid polymerization
of the epoxidic prepolymer material to a tack-free surface
condition within a period of less than 30 seconds. Although
this elevated temperature range may extend from 50C. to as high
as 90C., it is generally held within the range of 55-75C.
to obtain the desired rate of polymerization while avoiding
adverse effects on the resulting polymer and the desired
physical properties of the coating.
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The temperature of the coating may be elevated to the
desired temperature range by any suitable means including in-
duction heating when a metallic
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1 substrate is employed, conductive heating by passing or placing the coated
2 substrate over a heated element or a source of heat to heat the substrate
3 directly on its opposed surface; convection heating b~ passage of the coated
4 strip through a heated chamber; and radiation heating by exposure of the
¦ coated strip to a source of suitable radiant heat such as infrared lamps. For
6 ¦ convenience and for minimization of the equipment requirements, infrared radi-
7 1 ation provided by suitable lamps is most desirably employed in conjunction
with a source of~ultraviolet radiation~to produce decomposition of the cata-
9 I lyst precursor.
¦ It has been found that the coating may be elevated to the de~ired
11 ¦ temperature range either before or after exposure to the source of electrc~ag-
12 ¦ netic radiation. Moreover, the time period preceding or follc~ing exposure to
13 ¦ the source o~ electrcmagnetic radiation is not critical so long as there is
14 ¦ concurrently obtained activation o~ the catalyst precursor and maintenance of
1 the coating within the desired temperature range for only a limited period of
16 ¦ time, generally less than about two minutes and preferably less than about ten
17 ¦ seconds. It is likely that a protracted period of delay foll~Ying exposure to
18 the ultraviolet radiation before bringing the coating to the desired tempera-
i~ 19 ture might reduce the efectiveness of the method so that desirabl~ the two
steps occur within reasonably short periods of time, i.e., one minute or less.
~1 ¦ It has been found that the method of the present invention will
22 ¦ effect curing of the coating to a tack-free surface condition within a period
23 ¦ of less than 30 seconds and most generally within a period of less than 5
24 ¦ seconds foll~Ying the occurrence of both radiation exposure and maintenance
¦ within the temperature range. This is particularly significant for high speed
26 ¦ ~roduction lines where curing to a tack-free condition desirably oocurs within
27 ¦ t~ seconds or less. Full curing of the coating throughout its entire depth
m y o ntinue aft r the time period descri d, particu]rr1y in the cvellt of
A C~ 0 4 9 Z
1 thicker coating deposits since the tack-free surface condition permits handl-
ing and further processing of the coated substrate.
3 The substrates which may be utilized in the present invention include
4 metallic substrates such as metal strip, formed container bodies, an~ the
like, synthetic resin substrates such as polypropylene, polyvinyl chloride
6 strip and container bodies; fibrous substrates such as nonwoven materials
7 formed from natural fibers, synthetic fibers or mixtures of natural fibers and
8 1 synthetic fibers woven fabrics of natural and synthetic fibers, and mixtures
9 ¦ thereof; and laminates o the various oregoing materials. In additionj cera-
¦ mic substrates such as glass may also be employed.
11 ¦ The method of coating will normally depend upon the nature and shape
12 ¦ of the substrate and the preceding and ~oLlowing production steps. Knife
13 ¦ coating, gravure coating, spray coating, dipping and the like are all useful,
~4 ¦ depending upon the particular product involved.
¦ The me~hods of the present invention are particularly applicable to
- 16 ¦ various processes wherein durable coatings are desired for either aesthetic or
17 ¦ protective purposes. They find particular advantage in the field of graphic
18 ¦ arts because o~ the resistance of the coating to solvents and chemicals as
19 1 well as to abrasion, because of the excellent adhesion to various surfaces
~0 I including metals and because of the ability to withstand drawing and forming
operations. E'or example, metal strip and container blanks, bodies and clos-
22 ¦ ures may be coated and then formed without rupturing the continuity of the
~3 ¦ coating. With some ~onmetallic substrates such as synthetic resins, it may be
2~ 1 desirable to apply a primer to improve adhesion.
¦ Illustrative of the various aspects of the present invention are the
~6 ¦ foll~ing speci~ic examples wherein alI examples are parts by t~ight unless
27 otlr ise 1Idi~ted.
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~X~MPIE ONE
2 A coating formulation is prepared having the follGwing composition:
3 ~ç~ Parts
__
4 Bis-phenol A/epichlorohydrin epoxy prepolymer material (sold
by ~ow Chemical under the designation DER 332) 100.0
6 N-butanol 10.0
7 Fluorocarbon surfactant (sold by Minnesota Mining ~ Manu-
8 ¦ facturing under the designation FC-430) 0.5
9 ¦ Photoinitiator solution (33% by weight p~nethoxybenzene
lO ¦ diazonium hexafluorophosphate in sulfolane) 4.0
11 1 114.5
12 ¦ Electrolytic tinplate is used as the substrate and is coated with a
13 ¦ No. ~ draw bar to provide a coating of about 0.36 mil thickn~ss. Specimens of
14 ¦ the coated substrate are placed upon a heated stage held at a constant temper-
¦ ature until temperature equilibrium is obtained throughout the specimen and
Vl~ ¦ then the coating is exposed to ultraviolet radiation e6~ e~ ~ a 360 watt
17 I General Electric UA3 mercury arc lamp for a period of 4 seconds at a distance
18 ¦ of 4 1/2 inches.
19 ¦ The time period for the surface of the coating to become tack--free is
: ~n noted and, at least one hour after exposure of the coating to the ultraviolet
~1 ¦ radiati~n, the coating is subjected to two separate tests to determine thQ
2~ ¦ mechanical properties of the polymer prcduced thereby.
~3 ¦ In one test, a paper tissue saturated with methylethylketone ~MEK) is
2~ ¦ wrapped arolmd the index finger and rubbed across the coating us;ng m~derate
~5 ¦ fin~er pressure; one complete stroke back and forth is considered "one rub".
2~ ¦ ~ny break or erosion of t~e surface of the coating is considered to represel~t
27 1 a failure.
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In the second test, the needle of a thermal mechanical
analyzer is placed upon the surface of the coating and the tem-
perature elevated until the needle penetrates the coating.
The temperature of penetration is indicative of the degree of-
cross linking and the quality of the polymeric coating.
The results of the series of tests on the afore-
mentioned specimens are set forth in the following table:
Tack-free Time,
Softening
Cure Temp., C. _conds MEK Rubs Point, C
*60+ 13 66
18 66
-50 5 25 68
1 55 66
1 *100+ 66
1 *100-~ 63
1 52 56
100 1 10 52
110 1 4 ~2
120 1 1 35
130 no cure 1 5
* Maximum time of observation and maximum number of rubs,
respectively.
As can be seen from the foregoing test dat~, the
coating will polymerize to a tack-free surface state within 5
seconds after irradiation at 50C. but curing and cross linking
below the surface of the coating apparently requires a more
extended period based upon the low resistance to surface
abrasion with ~EK. At 60C., the cure rate of the surface is
still further materially improved and the resistance to surface
abrasion is significantly benefitted. Within the optimum
temperature range of 65-80C., the surface properties are very
greatly improved. However, if the temperature increases above
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about 85C, deterioration in properties is observable, both
on the ~EK rub test and on the sQftening point test. At 130 C,
curing fails to take place. This is indicative of the criti-
cality of the elevated temperature range at which the coating
is maintained following irradiation.
EXAMPLE TWO
To evaluate the effect of substituting different
epoxy monomers, a series of test formulations II-VI is pre-
pared and tested under conditions simulating a relatively high
speed production line. The substrates again comprise panels
with electrolytic tinplate and the formulations are applied
with a No. 5 wire rod to provide a coating equal to 95 lbs.
per thousand square feet of su~strate surface. The coated
face of the panels is preheated to 150F. by infrared radia-
tion as determined by a thermal paint indicator and then
irradiated with two 200 watt/inch ultraviolet lamps while the
panels are being advanced at a line speed of 110 feet per
minute. The time for the surface of the coating to become
tack-free is noted.
Component Parts
FORMULATION II
Low molecular weight bis-phenol A-based epoxy resin
(sold under the trademark ARALDITE 6004 by 63.7
Ciba-Geigy)
Aliphatic diglycidyl ether (sold under the
designation RD 2 by Ciba-Geigy~ 27.2
n-butanol 3.8
Silicone resin flow agent (sold under the
mark SR 82 by General Electric) 1.9
Photoinitiator solution (33~ by weight of
p-methoxybenzenediazonium hexafluorophosphate 3.4
solution in sulfolane~
la0.0
Time to tack-free surface 5 seconds
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FORMULATION III
Low molecular weight bis-phenol A-based epxoy
resin (sold by Ciba-Geigy under the designa- 47.6
tion ARALDITE 6004~
Tetrafunctional aromatic epoxy resin (sold
by Shell Chemicals under the designation 17.2
EPON 1031~
Aliphatic diglycidyl ether (sold by Ciba-
Geigy under the designation RD-2~ 15.2
Aliphatic mono~lycidyl ether ~sold by Procter
& Gamble under the designation EPOXIDE-7~ 15.2
Silicone resin flow agent ~sold by General
Electric under the designation SR-82~ 1.9
Photoinitiator solution ~33~ by weight
p-methoxybenzenediazonium hexafluorophosphate 2.9
in sulfolane)
100. 0
Time to tack-free surface 2 seconds
FO~MULATION IV
Monomeric diglycidyl ether of bis-phenol A
(sold by Celanese Corporation under the 62.9
designation JD-508~
Cresyl glycidyl ether (sold by Celanese
Corporation under the designation 28.6
EPIREZ 5011)
n-butanol 3.8
20 Silicone resin flow agent (sold by General
Electric under the designation SR-82) 1.9
Photoinitiator solution (33% ~y wei~ht
p-me~hoxybenzenediazonium hexafluorophosphate 2.0
in sulfolane~
100. 0
Time to tack-free sur~ace - 5 seconds
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4~2
FORMUL'ATIaN V
Monomeric diglycidyl ether of ~is-phenol A
(sold by Celanese Corporation under the 31.3
designation JD-508~
Epoxidized linseed oil ~sold by Viking Chemical
Co. under the designation VIKO~LEX 7190~ 62.5
Silicone resin flo~ agent ~sold by General
Electric under the desi~nation SR-82~ 2.3
Photoinitiator solution (33% by weight
p-methoxybenzenediazonium hexafluorophosphate 3.9
in sulfolane) 100.~
Time to tack-free surface 3 seconds
FORMULATION VI
Monomeric diglycidyl ether a~ bis-phenol A
(sold by Celanese Corporation under the 53.6
designation JD-508)
Aliphatic diglycidyl ether (.sold by Ciba-
Geigy under the designation RD-2) 26.8
Cumphenyl glycidyl ether tsold by Kenrich
Chemical Company;under.~.the designation CPE) 14.3
Silicone resin flow agent tSold hy General
Electric under the designation SR-82~ 1.9
Photoinitiator solution (33% by weight
p-methoxybenzenediazonium hexafluorophosphate 3.4
in sulfolane~
100.O
20 Time to tack-free surface 2 seconds
EXAMPLE THREE
To evaluate the efficacy of the method of the present
invention with different catalysts, a series of different
test formulations VII-X are prepared and specimens are coated
and subjects to the same conditions as set forth in Example
Two. Again, the time for the surface of the coating to cure
to a tack-free condition is no~ed.
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Component
FORMULATION VII Parts
Aliphatic diglycidyl ether (sold by Ciba-
Geigy under the designation RD-2) 44.4
Monomeric diglycidyl ether of bis-phenol A
tsold by Celanese Corporation under the 44.4
designation JD-5Q8¦
Silicone resin flow agent (sold by General
Electric under the designation SR-82) 1.9
Photoinitiator ~sold by 3M Company under
the designation FC-503~ 9.3
lQO.O
10 Time to tack-free surface 2 seconds
FORMULATION VIII
Aliphatic diglycidyl ether (sold by Ciba-
Geigy under the designation RD-2) 47.1
Monomeric diglycidal ether of bis-phenol A
(sold by Celanese Corporation under the 47.1
designation JD-5Q8~
Silicone resin flow agent (sold by General
Electric under the designation SR-82) 1.
Photoinitiator (sold by General Electric
Company under the designation UV Cat-14) 3.9
100. 0 '
; Time to tack-free surface 2 seconds
- 18 -
49Z
FORMULATION IX
Aliphatic diglycidyl ether (sold b~ Ciba-
Geigy under the designat~on R~-2~ 46.2
Monomeric diglycidyl ether of bis-phenol A
(sold by Celanese Corporation under the 46.2
designation JD-508~
Silicone resin flo~ agent Csold by General
Electric under th.e dèsignation SR-82~ 1.9
Bis-4tdiphenylsulfonio~phenyl sulfide
bis-hexa~luorophosphate ~Technical Grade) 5~.7
10~. ~
Time to tack-free surface 2 seconds
lQ FORMULATION X
Aliphatic diglycidyl ether (sold by Ciba-
Geigy under the designation RD-2~ 47~2
Monomeric diglycidyl ether of bis-phenol A
(sold by Celanese Corporation under the ~7.2
designation JD-508~
Silicone resin flo~ agent ~sold by General
Electric under the designation SR-82~ 2.0
Photoinitiator solution (33% by weight
p-methoxybenzenediazonium hexafluorophosphate 3.6
in sulfolane1 100.0
Time to tack-free surface 2 seconds
Thus, it can be seen from the above test data that
2Q the method of the present invention is applicable to composi-
tions using diazonium catalyst precursors which are believed
to function to generate directly Lewis acids as well as those
using the sulfonium catalyst precursors which are postulated
to generate first Broensted acids and then an active hydrogen
ion as the Lewis acid.
EXA~IPLE F~UR
To evaluate the effectiveness of the method of the
present inVention with coatings of different thicknesses, a
standard formulation is p~epared aS follows:
3Q
Component Parts
Monomeric di~l~cidyl ether of bis-phenol A
(sold by Celanese ~orporation under the 47.2
designation JD-5Q8~
Aliphatic diglycidyl ether (sold b~ Ciba-
Geigy under the designation RD-2~ 47.2
Silicone resin flow agent Csold hy General
Electric under the designation SR-82~2.0
Photoinitiator solution ~33% by weight
p-methoxybenzenediazonium hexafluorophosphate 3.6
in sulfolane~ 100.0
Test panels are prepared and treated substantially
in accordance with the procedure described in Example Two
except that varying amounts of the coating formulation are
applied to provide different depths o~ coatings. The results
of the tests are set forth in the following table.
Applied Film W2eight, Tack-free time, sec
Mg. per 4 in. -
32 2
57 2
137 2
The first three specimens are found to be cured
through immediately, but the last specimen continues to cure
slowly over the next several minutes until cured through.
- 2Q -
1 1~4V49Z
1 ¦ EXAMPLE FIVE
¦ To evaluate the effect of first effecting photoinitiation of the cat-3 ¦ alyst precursor and of interposing tLme delays before ~ringin~ the coating to
4 ¦ the desired temperature of 65~., a æries of test panels are prepared usiny
¦ the follcwing coating formulation:
6 Component Parts
7 ¦ Low molecular weight bis-phenol A-based epox~ resin (sold
8 ¦ by Ciba-Geigy under the designation A~ALDITE 6004) 56.8
9 ¦ Aliphatic diglycidyl ether (sol~ by Ciba-Gei~y under
10 ¦ the designation gD-2) 37.9
11 I Silico~e rsin flGw agent (sold by General Electric
l~ ¦ under the designation SR-82) 1.9
13 ¦ Photoinitiator solution (33~ by weight p-methoxybenzene
14 ¦ diazonium hexafluoroposphate in solEolane) 3.4
15 1 lO0.0
16 ¦ Follcwing coating, the panels are placed on a belt moving at a line
17 1 speed of llO feet per munute ~nder a pair of 200 watt/inch ultraviolet la~s
18 ¦ to irradiate the coatin~. Following irradiation, the panels are then heated
19 ¦ to 65C. after varying time delays, and the time to cure to a tack free sur-
~0 1 faoe condition is again noted. l'he results are set forth in the following
~l ¦ table.
TLme Delay, Tack-Free
23 ¦ Seconds Time, Sec.
~6 1 20 ` 2
27 1 30 2
2S 60 2
Il ' ~~1,_ '
` ~ 45~
1 ¦ It can be seen from the foregoing results that the sequence of
¦ irradiation and temperature elevation can be reversed and that the time frame
3 ¦ between irradiaticn and temperature elevation is not critical within reason-
4 ¦ able limits for production equipment.
¦ From the foregoing detailed specification and examples, it is appar-
6 1 ent that significant advantages in accelerated cure rate to a tack-free sur-
7 ¦ face condition can be readily attained without excessive loss in polymer prop-
8 ¦ erties by a closely controlled and limited exposure to a 1aw elevated tempera-
9 ¦ ture. As a result, relatively lcw cost epoxide formulations may be used in
¦ high speed coating applications where a tack free surface condition must be
11 ¦ attained rapidly to permit further processing. Where the coatings are of nor-
12 1 mal thickness, curing throughout occurs substantially instantaneously; with
1~ ¦ relatively thick coatings, curing below the surface may continue as the coated
~ workpiece undergoes further processing.
17
18
19
21
~2
'~ I
~ I
` 25
227
