CA1055421A - Process and apparatus for the curing of coatings on sensitive substrates by electron irradiation - Google Patents

Abstract

Abstract of Disclosure This disclosure deals with a new process and apparatus for using a critically adjusted electron beam to cure protective and decorative coatings, including opaque, heavily pigmented coatings, on paper, fabric and other thin substrates which are sensitive to heat or various forms of radiation. The process utilizes re-stricted dose, energy and process rates to obviate de-gradation of the substrate during curing and to achieve previously unattainable line speeds in the curing of coatings on products of web, sheet and filamentary geometry.

Description

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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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1~554Zl 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 ,:~: ~ .
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~OSS4; :1 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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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 ,~ ~: ` ' .

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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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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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~OSS~Zl 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 ., ' ' .

,.. ~, -'"'-''1'' ''~ 1 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.

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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 - -, , .. -. ' :,:. ' .,: ~. ' . , .' :,i ' .' .. . .' . , : ~' ' ' .; :

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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 ~: ' -1 ~ ' ' . . ' ~: :: . :.

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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.

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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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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 ; :

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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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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Claims (35)

1. A process for electron-beam curing of coatings applied to substrates, that comprises, passing the coated substrate along a predetermined path, accelerating electron beam radiation through an electron-permeable window at a preselected region of said path and causing the radiation to extend linearly along said path at said region but accelerated in a direction transverse to said path; adjusting the linearly extending radiation within energy limits of from substantially 50 to 300 keV and with dose rates of from substantially 0.5 to several megarads; interposing an electron-permeable layer upon the coated substrate; and positioning the proximity of said path region along which the layered coated substrate is passing to match the adjusting of said energy and dose rate to the thickness and materials of the coating, substrate and interposed layer in order to concentrate the principal amount of the electron beam energy in said coating to cure the same and to insure minimal energy reacting with said substrate.

2. A process as claimed in claim 1 and in which said layer comprises release paper, and, following radiation treat-ment by the electron beam radiation, said release paper is peeled from the cured coated substrate as it passes further along said path.

3. A process as claimed in claim 2 and in which said release paper layer is disposed adjacent said window, with the coated substrate layered therebelow.

4. A process as claimed in claim 2 and in which said release paper is disposed remote from said window with the coated substrate interposed in the path of the electron beam radiation from said window.

5. A process for electron-beam curing of coatings applied to substrates, that comprises, passing the coated substrate along a predetermined path; accelerating electron beam radiation through an electron-permeable window at a preselected region of said path and causing the radiation to extend linearly along said path at said region but accelerated in a direction transverse to said path; adjusting the linearly extending radiation within energy limits of from substantially 50 to 300 keV and with dose rates of from substantially 0.5 to several megarads; positioning the proximity of said path region along which the coated substrate is passing to match the adjusting of said energy and dose rate to the thickness and materials of the coating and substrate in order to con-centrate the principal amount of the electron beam energy in said coating to cure the same and to insure minimal energy reacting with said substrate; and reflecting electron beam energy passing around and past said coated substrate back into the same from an area in substantial register with, but on the opposite side of the substrate from, said window.

6. A process as claimed in claim 5 and in which said coated substrate comprises coated strands, and said reflecting step causes the electron curing of the back surfaces thereof

7. A process as claimed in claim 6 and in which said preselected region comprises a plurality of successive posi-tions along said path at which electron beam radiation is directed upon said substrate passing therethrough.

8. A process as claimed in claim 7 and in which said reflecting step is effected at each of said successive posi-tions.

9. A process as claimed in claim 7 and in which the electron beam radiation is directed in different directions upon said substrate at the successive positions along said path.

10. A process as claimed in claim 9 and in which said different directions are substantially in bilateral opposition to one another, but each substantially transversely normal to the said path.

11. A process for electron-beam curing of coatings applied to strand-like substrates such as wires, cables, filaments, strings, ropes, yarn and threads, that comprises, accelerating electron beam radiation through an electron permeable window at a preselected region of said path and causing the radiation to extend over a line along said path at said region but accelerated in a direction transversely into said path; ad-justing the linearly extending radiation within energy limits of from substantially 50 to 300 keV and with dose rates of from substantially 0.5 to several megarads; and reflecting electron beam energy passing around and past said substrates back into the same from an area in substantial register with, but on the opposite side of the substrates from said window.

12. A process as claimed in claim 11 and in which said preselected region comprises a plurality of successive posi-tions along said path at which electron beam radiation is directed upon said substrates passing therethrough.

13. A process as claimed in claim 12 and in which the electron beam radiation is directed in different directions upon said substrate at the successive positions along said path.

14. A process as claimed in claim 13 and in which said different directions are substantially in opposition to one another, but each substantially normal to the said path.

15. A process as claimed in claim 11 and in which said reflecting is effected by positioning an electron-beam reflector to extend along said region but on the side of said substrates opposite to said window and in substantial transverse register with said window.

16. A process as claimed in claim 15 and in which said reflector is concavely shaped.

17. A process as claimed in claim 15 and in which said reflector is substantially planar, substantially parallel to said path at said region.

18. A process for electron-beam curing of coatings applied to strand-like substrates such as wires, cables, fila-ments, strings, ropes, yarn and threads, that comprises, accelerating electron beam radiation through an electron permeable window at a preselected region of said path and causing the radiation to extend over a line along said path at said region but accelerated in a direction transversely into said path; adjusting the linearly extending radiation within energy limits of from substantially 50 to 300 keV and with dose rates of from substantially 0.5 to several megarads;
said preselected region comprising a plurality of successive positions along said path at which electron beam radiation is directed upon said substrates passing therethrough.

19. A process as claimed in claim 18 and in which the electron beam radiation is directed in different directions upon said substrate at the successive positions along said path.

20. A process as claimed in claim 19 and in which said different directions are substantially in opposition to one another.

21. Apparatus for electron-beam curing of coatings applied to substrates, that comprises, web means and means for drawing the same longitudinally along a path containing guide means at a preselected region thereof, and past said region; electron beam generating means disposed at said guide means and provided with electron-beam-permeable window means through which electron radiation may be accelerated transversely into and longitudinally along said region, said electron beam generating means being adjustable to produce energy within limits of from substantially 50 to 300 keV
and with dose rates of from substantially 0.5 to several megarads; means for placing an electron-curable coating applied to a substrate upon the web means prior to its passage through said preselected region; and means disposed beyond said region for physically separating said web means from the electron-cured coated substrate; and means for receiving the separated electron-cured coated substrate.

22. Apparatus as claimed in claim 21 and in which said web means comprises release paper, and means is provided for supplying the same and recovering the same after the electron-cured coated substrate is separated therefrom.

23. Apparatus as claimed in claim 21 and in which said region comprises a plurality of successively longitudinally disposed positions each provided with a guide and an electron beam generator thereat for producing radiation as the release paper-coated substrate passes along said path.

24. Apparatus as claimed in claim 22 and in which the guide means receives the combined release paper-coated substrate with the release paper facing the said window means.

25. Apparatus as claimed in claim 22 and in which the guide means receives the combined release paper-coated substrate with the coated substrate facing the said window means.

26. Apparatus for electron-beam curing of coatings applied to substrates, that comprises, 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 of said path and provided with electron-beam-permeable window means through which electron radiation may be accelerated transversely into and longitudinally along said region, said electron beam generating means being adjustable to produce energy within limits of from substantially 50 to 300 keV and with dose rates of from substantially 0.5 to several megarads; and electron-beam reflector means positioned to extend along said region but on the side of said coated substrate opposite to said window means and in substantial transverse register with said window means in order to reflect electron energy passing said substrate back into the same.

27. Apparatus as claimed in claim 26 and in which said preselected region comprises a plurality of successively longitudinally disposed positions each provided with an elec-tron beam generator thereat for producing radiation at the plurality of longitudinally separated positions as the coated substrate passes along said path.

28. Apparatus as claimed in claim 27 and in which the electron beam generators are positioned to direct electron beam radiation through their respective window means in dif-ferent directions upon said substrate at the successive longi-tudinal positions along said path.

29. Apparatus as claimed in claim 28 and in which the said different directions are substantially in opposition to one another.

30. Apparatus as claimed in claim 26 and in which said reflector means is substantially planar, substantially parallel to said path at said region.

31. Apparatus as claimed in claim 26 and in which said reflector means is concavely shaped.

32. Apparatus as claimed in claim 26 and in which said reflector means comprises water-cooled electron-beam-imper-meable surfaces.

33. Apparatus as claimed in claim 26 and in which said substrate comprises strand-like elements such as wires, cables, filaments, string, ropes, yarn and threads.

34. A process for electron-beam curing of coatings applied to substrates comprising accelerating electron-beam radiation through an electron permeable window at a preselected region of a path and causing the radiation to extend over a line along said path at said region but accelerated in a direction transversely into said path; adjusting the linearly extending radiation within energy limits of from substantially 50-300 keV and with dose rates of from substantially 0.5 to several megarads.

35. 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 said region, said 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.