Note: Descriptions are shown in the official language in which they were submitted.
1~1554
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The present invention relates to processes
~; ~ and apparatus for curing coatings~ both deooratlve and
;~ protecti~e, secured to unsupported or supported sensi-
: . .
~ tive substrates, which intrinsically limit the dqgree of
: : . .
practlcable thermal or radiation curing and consequently
restrict the possible speed of curing. More particularly,
the invention also embraces the use o~ electron curing
~ . ~
for the high speed trans~er casting of films used for
the forementioned applicatlons. An unexpected benefit
of the process herein dlsclosed, indeed, is the elimina-
tion of damage to the paper or plastic release sheets
~ ~ . . . .
used to impart pattern or special ~inish to the cast
llm, so that these ~ilms can have a greatly increased
lifetime in continuous. transfer casting applicatlons.
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The curlng of protectlve or decorative coatlngs
applied to heat sensitive webs, such as paper or fabrl¢,
is usually accomplished by passing the product through
a drying oven. Typically the coating is applied in a
solvent solution of the coating resin, so that convective
or radiative heating of the coated product in the oven
leads to evolution of the solvent, and curing of the
residual resin. Solvent concentrations may range from
20~ to 60% by weight of the liquid coating, depending
upon the viscosity required for application, flowout of
the coating~ wettability of the substrate surface and
other factors af~ecting ~he c02ting process~ In partl-
cular, for coated fabri applications, it is necessary
to prevent e~cessive strike through of the coating into
the fabric yarn so that a "bsardy" or stiff hand in the
fabric does not result. Complete solvent evaporation
must occur from the coating before the next layer can
be applied, so that a normal sequence is to apply
several light coatings, each of which is fully cured by -
passage through the drying oven before the next appll-
cation occurs.
Two large scale industrial examples of this
.
rather laborious build-up of thermally cured, solvent
bassd coatings are: urethane or vinyl coating of fabrics,
and the (phenolic) lnsulating coating of magnet wire.
Depending upon the thickness of the coatlng needed, four : -
to twentg passes are used to build up to the final coat-
ing wlth oven temperatures limited so that boiling or
bubbling ln the coating will not occur as the volatile
: : :
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lOS54~1
solvent ls removed ~rom the coating~ with concomitant
pln-holing or void creatlon in the rilm. These processes
and related coating appllcations involve relatively thln
coatings. For example, for coated fabrics, dry ~ilm
thicknesses in the range of 25-80 microns (2-50zs. per
54 inch yard) are t~pical; ~or release coatings on paper~
thicknesses o~ only 10 microns are typical; while ~or the
wlre coating application, rilm thicknesses o~ only a rew
microns are normally used.
An object o~ the present invention, accordingly,
is to provide a novel electron-beam curing process which
utili~es all solid (solvent rree) coatings to obviate such
prior art difficulties. In ract, because Or the absence
Or high volatile concentrations in the coating and the
room temperature nature Or the process disclosed, the
danger Or p$n-holing and hence coating ~ailure is eliminated.
A further ob~ect is to provide a new and im-
proved curing process and apparatus utilizing 100% reactive
coating systems of more general applicability than those
currently available. For example, similar coating systems
which are dependent upon free radical-initiated polymeri-
atlon for the cure may be treated with alternat: radia-
tion sources, such as ultraviolet, which, however, ls
unable to handle pigmented coating systems which readily
absorb the ultraviolet at the surface, nor can lt cure at
h$gh speeds on thermolabile substrates due to the low
energy conversion erflc$ency Or industrial ultravlolet
lamps and there~ore a concomitantly high inrrared loading
. ~
o~ the treated product. In addltlon, additives such as
3-
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benzoin e~hers or benzophenone required to sensiti~e the
coating to ultraviolet are not needed with the process
Or the present invention, due to the ability Or the curing
energy (electrons) to create directly free radicals in
the coating. As a consequence, coatings stable against
storage and natural ultraviolet exposure are usable with .
the process of the invention.
Other and ~urther ob~ects are delineated herein-
after and are more particularly set rorth in the appended
claims.
Similar coating systems which are dependent upon
free radical-initiated polymerization and which use other
radiation sources, such as high energy electrons (E>300
keV as from a scanned accelerator) or gamma-rays (E~1 17 or
1.33 MeV as from Cobalt 60 sources), are unable to limit
or restrict the region Or the product arrected by the
ionizing radiation. As a consequence, the substrate may
receive a treatment level equal to or greater than that
of the coating. In the case Or many important polymers
both natural (cellulose) and man~made (terlon, rayon, etc.~,
this may lead to degradation through bond-breakage or
scisslon ln the polymer. This process rOr many degrading
(Group II) polymers, has been discussed in detail by
Chapiro, Radiation Efrects in Polymers of the Degrading
Type, Ch. X, Radiation Chemistry of Polymeric Systems,
Interscience Publishers, N.Y., 1961. In cotton, for
éxample, radlatlon lnduced scission in the 1, 4-glycosidlc
bonds whlch link the anhydroglucose units Or the macro-
molecule,lead to reduced tenslle strength, Discoloratlon
also occurs due to radlolytic effects, largely in the
' . ' .
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5S~l
adsorbed water of this hydrophilic material. As a con-
sequence, radiation curing o~ finishing or coatings on
these materials has been impractical since the degrada-
tlon o~ the substrate and its e~ects on product properties
have not been tolerable. For these materials of the de-
grading type, it is clear that a radiation curing system
must be discriminating in delivering its energy pre~eren-
tially to the coating or finish so that substrate treat-
ment is minimized.
Nor does the process disclosed herein suffer
from the lim~tations o~ alternate all-solid coating pro- -
cess which do not utilize radiation. For example, powdered
coatings (which also involve no solvents) still requlre
a large thermal investment in the substrate to ef~ect a
change in the coating itsel~ during the curing process.
For paper or ~abric coating, particularly with urethane
systems, two-part coatings such as those described by
J. C. Zemlin,i'Development o~ a 100% Solids Urethane Fabric
Coating Process,'Proc. AATCC Symposium on Coated Fabrics
Technology, 101-107, March 28, 1973, are often used, which
.
do eliminate solvent e~luent and a large fractlon of
the waste heat required to cure conventional solvent based
lacquers. Such systems are lnflexlble, however, and do
not permlt Or thin coatings (below 40-50 microns) on light
substrates, nor are they appropriate Por temperature-
aensitive substrates because of the hlgh temperatures
(100C) required ~o effect a cure.
ln summary, from one o~ lts broad aspects, the
invention embra¢es a process for the curlng of surface
coating~ such as aoryllcs, urethanes, epoxles etc. applled
.
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or secured to a sensitive substrate that lnherently limits
the speed Or curing. This comprises applying an electron-
curable coating to the substrate, either by transfer o~
a cast rilm or by direct application, passing the laminate
o~ substrate and uncured coating material past a predetermined
region, directing the electron energy at said predetermlned
region upon the coating, adJusting the electron beam to
produce a dose Or up to 4 megarads Or e~ergy from, prererably,
50-200 keV, and with a line speed o~ passing the predetermined
region preferably Or the order o~ 20-100 meters per minute,
in order to cure the applied coating without arfectlng
thc heat- or radiation-sensitive substrate. At the 4
megarad level, less than 10 calories Or energy per gram
Or coating material are required for a cure, with less
than 20% of this level reaching the substrate under the
conditions outlined above. Assumlng a coating speciric
heat Or 0.3, coating temperature elevations of less than
30C are expected during the curing process, with much ;
lower rigures ror the underlying temperature sensitive
web. With precise control Or the processor energy,
electron induced substrate degradation is minimized in
the same manner. Prererred details are hereinafter set
rorth.
Specl~ically, lt has been discovered that if
an electron beam is produced, as an illustration, by apparatus
or the type described in U. S. Letters Patents 3,702,412,
3,745,396 or 3,769,600, and is critically controlled ln
accordance wlth the invention to direct its energy at a
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`-\ 1055421
predetermined region upon the coated substrate with traject-
ories essentially perpendicular to the coating sur~ace, precise
control of the energy deposition profile is possible. This
con~iguration and the control of energy deposition which it
permits, are not possible with alternate energy sources, such
as those described for example in U.S. Letters Patents 2,602,751
or 3,013,154, wherein the combination of the oblique incidence
. .
of the electrons on the permeable window, and the thick windows
used, lead to very large scatter angles in the emerging electron
distribution. A secondary advantage of the process is taught
in U.S. Letters Patent 3,780,308 in which the high stopping
powers of low energy electrons in the 100-150 keV region are
utilized to increase the curing efficiency of the system at a
given processor power level. It is only through the use of
these electrons, at energies well below those heretofore
available for industrial application, that the penetration of
the curing flux through the coating of the~labile substrate,
.
can be controlled.
Thus, one aspect of the present invention is broadly
defined as a process for electron-beam curing of coatings applied
to substrates comprising accelerating electron-beam raaiation
~; through an electron permeable window at a preselected region of
; ~ a path and causing the radiation to extend over a line along the
path at the region but accelerated in a direction transversely
into the path; adjusting the linearly extending radiation within
; energy limits of from subskantially 50-300 keV and with dose
rates o~ from substantially 0.5 to several megarads. ~
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10554Zl
Another aspect of the present invention is broadly
defined as an apparatus for electron-beam curing of coatings
applied to substrates comprising means for drawing the substrate
carrying an electron-beam-curable coating longitudinally along
a predetermined path; electron-beam generating means disposed
at a preselected region and provided with electron-beam-permeable
window means through which electron radiation may be accelerated
transversely into and longitudinally along the region, the
electron-beam generating means being adjustable to produce
energy within limits of from substantially 50-300 keV and with
dose rates of from substantially 0.5 to several megarads.
The invention will now be described with reference
to the accompanying drawings, Fig. 1 of which is a longitudinal
section illustrating electron-radiation geometries and adjust-
ments for curing coatings on sensitive substrates in accordance
with the invention;
: Fig. 2 is a graph of energy penetrations in
accordance with process controls of the invention;
Figs. 3(a), 3(b) and 4 are views similar to Fig. 1
, 20 of modified irradiation techniques;
Figs. 5 and 6 are schematic process flow system
diagrama;
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10554Z~
Figs. 7(a) and 7(b) are respectively isometrlc
and longitudinal section drawings of the process as applied
to ~ilamentary products and the like and illustrating
the use o~ primary electron back-re~lection; and
Fig. 8 is a graph illustratin~ low electron
energy deposition pro~iles for coatings on steel and wood,
Referring to Fig. 1, the bonding o~ natural
to ~an-made polymer systems is illustrated, uslng a wool
~ace-cloth layer, so-labelled, bonded to d foam substrate
or backing material, which is, in turn, ~aced with a nylon
backing ~abric layer, labelled "Nylon Tricot". Such a
bonded or laminated ~abric is typical of that used ~or
garments and llke applications. For thls system, the
adhesive was ~irst applied with a Coin laminator, manu~ac~ured
by the International Machine Builders Inc. o~ Guil~ord,
Maine. A 625 micron (~) thick urethane ~oam substrate of
density 0.034 gm/cc (i.e. 2.2 mg/cm2) was used, to whlch
a 25 micron film Or Dow XD 7530.01 epoxy (or Hughson Chemi~al
Co. B-2107-30 polyurethane) adhesive was applied. The
7 oz/yd2 (23 mg/cm2)wool face cloth was then padded onto
~: :
the adhesive ~llm and cured at a rate o~ 60 meters per
minute with an appropriately ad~usted and operated Electro-
curtain T~ processor of the type described in the ~irst-
named U. S. patents, above, (Energy Sciences Inc. of Burllngton,
Massachusetts) and in Nablo, S. V. et al, "Electron Beam
Processor Technology", Non~olluting Coatings and Coatin~
Processes, 179-1~3, ed. J. L. Gardon and J. W. Prane,
Plenum Press, New York, 1972. The apparatus was ad~usted
to produce a dose o~ 2 megarads with an electron energy
8-
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l(~S54Zl
of 150 keV, with the curing rlux directed through the
electron-permeable nylon layer and the roam lnto the face
cloth (wool)-urethane in~er~ace as shown ln Fig. 1. The
same adhesive was then applied with a standard 6-inch
laminator to the open surface o~ the ~oam. The nylon
~abric (1 o~/yd2 or 3 mg/cm ) was padded onto the ~oam-
wood laminate, and the adhesive then cure~ at the same
rate with the beam energy adjusted to 100 keV. ~he
process shown in Fig. 1 proved to eliminate any "treatment"
of the wool face cloth, either through heating or bombard-
ment by ionizing radiation as illustrated in the energy
deposition profile of Fig. 2,plotting energy as a function
of depth, wherein lt is shown that the positioning and
adjustments have e~fected a matching such that the princi-
pal energy is concentrated and confined to the adhesive
reglons with minimal energy reacting with the cloth or
other substrate. More general penetration propertles
of these low-energy electrons on steel and substrates are
shown in Fig. 8.
These samples were subJected to standard wash-
.
ability and dry cleanability tests to ascertain that the
laminate integrity was adequate, and that both adhesive
... . .
films had been fully cured by such "rear-surface" treatment
technlque.
As a second example of the process o~ the lnven-
tlon, a pressure-sensltlve adheslve has been applled and
cured on a varlety of heat and radiatlon labile substrates,
in¢ludlng paper, vinyl, vlnyl-asbestos, cork, wood, cotton,
; ~ polystyrene, nylon, urethane ~llm, leather and the llke.
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~0554Z~L
For these applications, a radiation curable pressure-sensitive
adhesive (e.g. W. R. Grace ~ C) is applied with a standard
draw-down bar or kn~fe applicator, to provide a wet ~ilm thick-
ness in the 25-100~ range. This adhesive is then cured at line
speeds o~ 60 meters/minute with such an Electrocurtain source
adjusted to 150 keV by directing its beam onto and through ~
the liquid ~ilm. In the same manner, it has been demonstrated
that such pre~sure-sensitive adhesive coatings may be cured
through a release paper or film layer, i~ necessary. In this
way, as later explained, a coated and adhesive covered web
or tape can be spooled or wound immediately a~ter passage
through the electron curirg ~one. The advantages o~ this
single-pass, fast cure on a sensitive substrate in the pro-
duction Or products such as wall and ~loor coverings or
pressure-sensitive tapes will be obvious to those skilled in this art.
A ~urther example o~ the process ~or the trans~er
casting o~ ~ilms onto fabrics is illustrated in Figs. 3(a~,
3(b~ and 4. As shown in Fig. 3(a), the skin or top coat 1,
typically 1-3 mils (25-75~) thick, is applied dlrectly to a
release paper 2, typically o~ 4-~ mils (100-150~) thickness,
wlth a denlsty o~ 0.9-1.0 gm/oc, the release paper bein6
on the slde remote ~rom the electron beam window. Flexible,
.
elastomeric coatings wlth good wear characterlstics are used
for thls purpose, such as Hughson's RD-2484-18 urethane.
Uslng electron energies of 80-110 keV from the said Eleo-
trocurtainTM processor deiscribed earlier, this skin ¢oat
can be "set" at 0.2-1.0 megarad, or ~ully cured at 2-5 mega-
rads, wlth less than 20~ o~ the curlng energy reaching the
- . :
reIease paper itself. ~his has been con~lrmed experimentally
through measurements o~ the dose delivered at the surrace
1' o~ the skln coat 1 and at the front and rear surfaces 2'and
2" oP ~he release paper 2. ~ypicai treatment ratlos o~ 5:1:0
were respectlvely mea~ured ~or the settlngs already described
.
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t~ith the treatment geometry shown in Flg. 3(a).
As shown in Fig. 3(b), on the other hand, a
thin adhesive or tie coat 6 is now applied to the sur~ace 1'
of the skin coat 1 and the support fabric 7 is napped or rolled
into it. The tie coat 6 is then cured by treatment through
the electron-permeable release paper 2 and skin coat 1, as
shown, with the release paper now adjacent the electron
beam window. Electron energies o~ ~rom 130-180 keV are typi-
cally used here to provide penetration of the release paper 2
and skin coat 1, and delivery o~ adequate energy for curing
of the tie coat 6 at the fabric-adhesive interface. ~or
the example described, where a cotton support fabric was used
with a weight of 12 ozs/yd2 (42 mg/cm2), dose levels measured
at the release paper rear surface 2', tie coat-fabrlc inter-
face 6, and support fabric rear or bottom sur~ace, as shown~
were typically 10:6:0. The process disclosed herein ef~ectively
eliminates the undesirable treatment o~ the supporting web
whlch is, however, intrinsic to all prior processes, using
either heat or radiation sources of curing energy.
It is therefore possible, in accordance with the
lnvention, to cure the tie coat without signi~icantly a~fect-
ing the support web or fabric, and simultaneously to ~ully
cure the tie coat and the skin coat, which had been only
partially cured or "set" by the first treatment. Another
lmportant benefit o~ the process herein described ls the
reduced degradation of the release paper so that lt may be
removed a~ter release of the skin coat, and used again ln the
process. In the ¢onventional thermal curing process, on the
other hand, relea~e papers may only be used 3-5 times be~ore
being discarded due to thermal degradation. At a cost o~
15-2~ ¢ents per square yard, this llmited release paper re-
use i~ o~ eoonomic importanoe, as it represent~ a procesS cost
., ' ' .
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10554~:1
comparable to the coatlng/adhesive costs. The process des~-
cribed hereln perm~ts almost unlimited (typically 50 times)
reuse Or tile release film or paper, determined by the minimal
radiation degradation of the paper by the tie-coat curing pro-
cess o~ Figs. 3(a) and 3(b).
As shown in Fig. 4, furthermore, the ~inal curing
process may also be reversed where thin or loosely woven
support webs or fabrics 7 are used. In this case, the cure
is effected with the energy directly applied from the rear
through the uncoated support fabric surface 1, so that no
substantial energy is delivered to the release coating or
paper 2~ and its unlimited reuse is assured. This technique
has been demonstra~ed wlth a curing electron flux a'~ energles
of 180 keV where a very heavy 10 oz/yd2 (35 mg/cm ) cotton
fabric 1 was used as the backing web. Because o~ the reduced
scattering angles znd normality Or incidence at the product
surface provided by the Electrocurtain processors adJusted
and operated as before explained, good penetrat~on of the woven
backing fabric is possible, even for fabric weights well
. .
; beyond the lntrinsic penetration capability of the lncident
electrons. The process of Fig. 4 is thus particularly useful
for non-degrading supporting webs.
Two main processes flow systems for direot and
transfer castlng ooatingJ made possible with thls lnvention,
; are lllustrated ln Figs. 5 and 6, respeotlvely.
In Flg. 5, the flexlble web or substrate 2 ls
; ; unrolled from drum 12 and ooated wlth an electron ourable
. ~ . .. .
coatlng by ooater 3. The ooated web 1-2 ls then presented
TM
to Eleotrocurtain prooessor 5 or equiralentJvla web handllng
fixture 11, and the oured ooated web is then drawn by oapstan
13 onto take-up roller 14.
-12-
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lOS54~1
In Fig. 6, the trans~er casting process flow
system is illustrated in which the trans~er paper 2 ls
drawn from drum 12 and the skin coa~i 1 is applied at the
coating station 3. The coated paper or film is then intro-
duced to the electron curing station 5 via the web-handling
system 11. A~ter the skin coat set or cure at station 5,
the tie coat 6 is then applied at coater 14 to which the sup-
porting ~abr~c or textile 7 is nipped in, via the padder
station or nip rollers 15. ~he laminate is then cured
through the backing fabric 7 by station5' and laminate-
handling assembly 11' (as described in Fig. 4), or via the
reverse process discussed above and depicted in Fig. 3(b).
The coated product 7-6 is then rewound aPter separatlon or
peeling away at 1~ o~ the paper 2, which is then wound ror
re-use on drum lô.
Still a ~urther example of the ~lexibility o~ the
process Or the invention, by the before-described apparatus
o~ Fig- 5, involving the single-pass curing at high speeds of
binders as used in the manufacture of non-woven rabrics, has
been demonstrated.- In this application, the flexible web
.
2, which is unrolled ~om drum 12, or as taken directly ~rom
the web lay-up line, is bonded at station 3 by means o~ the
appllcation of an adhesive with a gravure type cylinder or
- .
similar printing station. In this case, the patterned adhesive
layer 1 permeates the printed sections Or the non-woven web
and i8 presented to the electron-processor curing station 5.
Arter curlng, the web now has good tensile strength in both
dimensions and i8 ~elP supporting, such that it may be drawn
through nip-rollers 13 to~the rewind cyllnder 14 or to a Pur-
ther finlshlng station.
In suoh operatlon, pure polyester non-woven web
of weight 3.3 mg/cm (.96 oæ/yd ) and pUre rayon non-woren web
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1C~5542~L
2 2
of weight 3.5 mg/cm (1.02 o~/yd ) were printed with electron
curable binders such as; ~eichhold's polyester adhesive
type 31039, C . L. Iiauthaway's urethane adhesive type 139A
or Hughson's urethane adhesive type 2536-30, all o~ these
being 100~ solids. ~hese webs were processed in a CB 150
type Electrocurtain o~ the assignee, Energy Sciences, Inc.,
at line speeds of ~rom 5-50 meters/minute and at dose levels
o~ from 2-5 megarads. ~he electron beam energies used here
were in the range of 100-125 ~eV. The ~ebs so-bonded with
this process, were found to be of good hand and tear strength,
and demonstrated that the print-bonding process could be
performed at high speeds with commercial webs using such
low-energy electron curing technique, and with no measurable
degradation in the physical or cosmetic properties o~ the
cellulosic or man-made web.
Another example o~ the process of the invention
involved the use of a Highson urethane top-coat RD-2536-59
which was rolled on to a heavy (16 oz/yd ) vinyl coated up-
holstery fabric. The protective sealing topcoat was cured
at a line speed o~ 50 meters/minute and at a dose level o~ -
.. .: , .
3 megarads. At lower doses, the trichlorethylene and solvent
resistance were marginal. At levels for rull cure, the sam-
ples passed a 50,000 cycle wear test on a Wyco Wear ~ester,
and 25,000 single ~lexes and 10,000 ~old tests. This topcoat
satls~ied other tests on cold fold, crocking, soll reslstance,
: ~ .
and related requlrements ~or the coated ~abrlc topcoat appli-
catlon.
; Further to show the wide utility of the lnventlon,
the process 18 illustrated ln Fig. 7 as applled to the single
pass curlng at hlgh speeds o~ thin enamel coatlngs of ~ood
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1~:9559~Z~L
dielectric strength on wire; thls being accompllshed with
the use of low energy (~100 keV) from the before-described
processor. Such technique is equall~ appropriate ror the
curing of ~inish coatings on yarn made up o~ natural ~ibers
(wool, cotton), man-made ~ibers (nylon, orlon, dacron~f ~lber
glass, etc.) or blends thereof. As with the coating applica-
tions mentioned earlier~ solvent blow-out o~ the coating
with the conventional thermal process is a severe problem-
As a result, multiple pass coating-curing is necessary so
that 12-24 passes may result in a typical magnet wire enamel- -
ling application (using high solvent concentration phenolic
lacquers). The process o~ the invention applied to such uses
is shown in Fig. 7(a), utilizing a single-pass cure o~ a 100%
solids coating (such as Hughson RD-2536-59 or Cray Valley
Products SF-71475) which can be accomplished at very high
line speeds along the length o~ the electron processors, as
Or the type described in berore-cited U.S. Letters Patents
3,702,412; 3,745,396 or 3,769,600. As shown in Fig. 7(a),
with treatmen~ æones some 15 cm in length, process speeds
of some 1000 meters per minute have been found possible with
these available electron cured coatings. Several coated
ends (yarn, wire, cable, string, ropes, threads, monofila-
ment plastlc, etc.) may be passed simultaneously along the
longltudinal symmetry axes of a pair of successive upper
and lower or opposlte-direction electron processor statlons
5, longltudinally along the space between their electron
windowa and corresponding longltudlnally mounted planar water-
cooled or similar re~lectors R, for returning primary electrons
back to the underside o~ the wlres or other product. The pro-
cessor houslngs serve as a prlmary electron radlation shield,
and the housing into which the wires or fllaments are fed,
,
~e ~ 15-
~ i, ,, ,, ,, .,.. ", .,,",,,,.;,.. . . . . . . ... . . ..... . .
,
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.
from the le~t, and from whlch they exit at 20, serves as a
secondary shleld. Full utilization is thus made of the energy
pattern or curing zone provlded by the processors. For exam-
ple, several levels of many ends are possible to fully
utillze the curlng flux for ~ihe surface finishing o~ yarns.
This process utillzes the ability of high atomic
number materlals to reflect, with high efficiency, low energy
electrons. ~or example, the work of A. Bisi and L. Bralcovich,
Nucl. Phys. 58, 171, 1964, for low energy electrons showed ~ -
that these backscatter coe~ficients could rise to over 50%
at Z=50 ( for tin or above) and reached 70% at Z = 82 (lead).
These backscattered electrons, N, fall lnto a roughly Gaussian
distrlbutlon described by
N - No cos x.e /2 ,
where No ls the incident flux and x = ~ -~, where ~ is the
angle between the backscattered electron and the normal to the
surface of the relector. This distribution of reflected
; energy, coupled with the scatterlng of the primary beam in
the alr path about the coated filament, can provide a highly
- uniform treatment about the periphery of the cylindrical work-
plece with bllateral treatment.
Thls has been demonstrated using the conflguratlon
; ehown ln ~lg. 7(b), ln which a reflecting semi-clrcular or
concavely shaped channel R Or an electron-re~lectlng hi~h
atomic number material, such as tantalum tZ = 73) or lead
tZ ~ 82), 18 used to direct a large percentage of the prlmary
eleotrons ~rom the processor 5 that have gone around or pa~t
the product, baok to the under~lde Or the product, shown as
wlres or strands or rllaments.
:; ~ : . . ,: :
-16- ~
: . . ,.'::
1. ~
"''~' ', ' "i'"' '"'''' ',' '` ''",'' . ,' ;'' ' ' .i' '';''','"'' ,', ' '''~ ,' ' ~ ', .'''',' "; '. "..''"",'` ' '''" ''
.': .. " " ' ' ', '' 1. ' . . ', '.. '. ,'', '' . '. ' " ' '' ' . , ' ': ,. . ', ,: ' . ' , :
11~554;Z1
As ln the case Or the re~lectors R of Fig. 7(a) J the re~lector
R o~ Fig. 7(b) is disposed below or on the opposite side Or
the product from the electron window but in an area in sub- ~-
stantial register therewith. Measurements o~ the deposited
energy distributions about the periphery Or a 1 and 2 mm
diameter workpiece (~18 and #12 AWG wires, respectively),
TM
with a CB 150 Electrocurtain electron processor 5, demon-
strated that single pass treatment uni~ormities oP + 20%
and + 15% were respectively possible with the bilateral back-
scatter technique illustrated in Fig. 7(a).
As a ~urther demonstration o~ the process, tests
using several ends Or cotton perle and wool yarn coated with
adhes~ves (Hughson RD-2526-67) were also per~ormed to demon-
strate single pass uniform curing using the approach illustra-
ted ln Fig. 7(a), as well as to demonstrate the uniform excita-
tion o~ free radicals about the periphery o~ the yarn, as is
used, for example, in the dry or pre-irradiation of textil~s
prlor to grart copolymerization of a subsequently coated -
~ilm. Such graft copolymerization processes have been described,
or exsmple, by Chapiro et al in U.S. Let;ters Patents 3,131,138,
3,298,942; 3,433,724, etc. The tests performed in these
demonstrations also utilized the con~iguration Or Flg. 7(b)
in which adhesive coated yarn (cotton) which had been coated
wlth a rree-radioal curable urethane (l~ughson RD-2536-56) to
a thickness of~ 50~, and then rlocked with 3 denler x 260~
nylon fibers, was given a single-pass cure. This veriried the
ability o~ the unilateral source coupled with the appropriate
backscatter geometry to provide ~ull cures Or thin coatlngs,
lncluding ~look "protected" adhesives, with the single-pasi3
-
,
-17_
~ , .
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'.' '' ' ' ''' ''' ', ''', ',"'': - '.'`~ "' .. ,'':' ", :"', . ' '
. .
.:
: ',' -: ~ '' ; '" '.' ~ .. ' ~ . ' .
~L~5542~L
process, as ~he yarn "texturized" ln this manner showed good
abrasion reslstance and tensile strength. The re~lectlon con-
cept o~ Figs. 7(a) and 7(b) may also be used, where appropriate~
with other work pieces or products such as those Or the
other flgures. ~-
The following Table I presents ~he approximate ranges
o~ energies and do~es Or energetic electron radiation and
corresponding attainable line speeds for various types o
products treated in accordance with the invention:
TABLE_I
50-300 keV range and doses of from 1-5 mega-
rads, for the curing of free-radical initiated
laminating adhesives in the textile field at
line speeds of from 10-100 meters/minute,
particularly for lamination of man-made or ~ -
natural ~abrics to heat-sensltive substrates
such as expanded foams (pvc, urethane, etc.)
or non-woven webs (paper, cotton, polye~terJ
etc.) used as a backing "fabric"; 50-300 keV
range and doses of frOm 0.5-3 megarads for
the curing of free-radical initiated bonding
~: :
agents at line speeds of from 25-200 meters/
minute as used, ~or example, in the manu~acture
of non-woven webs of paper, cotton, polyester,
~: .
rayon and like temperature sensitive ~lbers;
50-300 keV range and doses Or from 1-8 mega-
rads for the curing Or elastomerlc type coatlngs
; on substrate fabrlcs, includlng non-wovens,
at line speeds of from 10-60 meters/mlnute, ln-
cludlng rabrl¢ coatings of free-radloal inltlated
urethanes, vlnyl compounds an~ like flexible
; :
18-
1~554~
skin coats which may be applied by either direct
coa~ng or transfer casting; ~or the curing of
a thin sealing topcoat on coated ~abrics, leather,
leather substitutes, paper, laminates and like
temperature-sensitive matte for plastlcizer sealing,
abrasion resistance, cosmetic improvement, coeff1-
cient o~ friction modirication, including pro-
tective topcoats for upholstery and garment appli-
cations, energetic electrons in the 50-150 keV
range and doses o~ from 0.25-2 megarads at line
speeds o~ ~rom 40-250 meters/minute, 50~300
~eV and doses in the range Or 0.5-S megarads,
for curing pressure sensitive adhesive on tem-
perature-sensitive webs such as paper, plastlc
and the llke, elther directly, through a release
paper, or through the overlying web to whlch it
is applied, and at line speeds of 20-100 meters/
minute; 50-150 keV and doses in the range of -
1-4 megarads for curing coatings on magnet
Yire cylindrically symmetric work pieces, with
the coatings o~ thicknesses ln the range o~ :
5-50 microns and wlth the use of backscatter
refleotor shields to ~latten the curing dose
distribution about the perlphery of the coated
oonductor, at product speeds in the range of
50-1000 meters/minute; 50-300 keV range and
doses of from 0.5-3 megarads at product speeds
of 20-1000 meters/minute, for curing adhesive
and ~lnish coatings on textile flbers and yarn
for flock texturizlng, soil release improvement
and the like; 50-250 keV and doses Or ~rom 0.5-
2.5 megarads at product speeds Or 10-80 meters/
minute for the oure Or pigmented deoorative
19-- , .
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. .
: : . :., .
r~
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105542~
finlshes used in both the pi~ment and dye
printlng of textiles, plastics and ceramics,
including glass; and 50-200 keV and doses in
the range of 1-5 megarads at web speeds of
20-200 meters/minute, to cure release coatings
such as silicones, polyesters and the like on
paper, non-woven webs or similar heat-sensitive
substrates.
While, as above explained, the relatively low energy
energetic electron radiation used in accordance with the in
vention is preferably generated as a linearly extending
~an or curtainj~ a beam of such radiation may be moved or
scanned, or a plurality of contiguous beams used, to provide
extension linearly along the treatment region within the
ad~ustment ranges above presented. : : -
Further ~odifications will also occur to those
skilled in this art, and all such are considered to fall
within the spirit and scope of the invention as defined in
the appended claims. . :: n
: :
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