CA1148786A - Magnetic resist printing process - Google Patents

Abstract

TITLE
MAGNETIC RESIST PRINTING PROCESS, COMPOSITION, AND APPARATUS

ABSTRACT OF THE DISCLOSURE
A process of forming an image of toner on a latent magnetic image in a magnetic member followed by direct transfer to and coalescence on a surface to form a resist is disclosed. The surface portion not protected by the transferred resist toner image is then permanently modified by etching or plating. Chemically milled shapes are prepared as well as printed circuits and printing plates. The printed circuits may be formed by (1) etching away areas of a metal surface not protected by the resist, (2) electroless plating on areas not protected by the resist or (3) electroplating areas of a metal surface not protected by the resist, removing the resist, and in the case of (2) and (3), etching away the metal previously covered by the resist. An especially useful toner which forms a resist composition comprises a binder of thermoplastic resin and plasticizer and magnetic material present in the binder, compounded to have a tack transfer temperature of no greater than 110°C.

DE-0204Al

Description

Title Magnetic Resist Printing Process, Composition, and Apparatus Technical Field The present invention is a process of thermally transferring magnetically-held toner from a magnetic member to a substrate with coalescence of the toner on the substrate and a composition for use as a toner in such process. The transferred toner is cap-10 able of serving as a resist in making printed circuit boards, printing plates, or in chemical milling.
Background Art Printed circuits are commonly made by depositing a resist on a substrate either in the form 15 of the desired pattern or as an overall covering followed by removal of some resist to form the desired pattern, followed by modification of the bare adjacent areas of the substrate through etching or plating.
Conventional printing methods such as 20 letterpress, lithography, and gravure printin~ have been found to be deficient for resist printing, how-ever, because they ar~ only capable of printing a thin resist. Thin resist patterns tend to be full of pin-holes which lead to unacceptable quality upon subsequent 25 etching or plating. This is a particularly severe problem in plating because of the formation of plating DE-0204Al nodules over pinholes in the resist. Use of liquid photoresists presents the same problem.
Two methods are now in commercial use --screen printing and photoprinting -- because they are able to deposit pinhole-free resist patterns. Photo-5 printing, as described in Celeste U.S. 3,469,982,requires the lamination and subsequent exposure and development of each substrate with a suitable photo-polymer. While this process provides the highest quality resists and has many advantages, the expense lO of the materials and exposure and development steps detract from low cost rapid reproduction. Screen printing is low in ink cost but it requires a costly set-up for the master; furthermore, it has only been implemented as a flat-~ed process requiring extensive 15 operator interaction to maintain registration and cor-rect ink viscosity. The screening also limits edge definition. Further, the process requires post-curing.
Attempts have been made to apply xerography (electrophotographic printing or imaging by electro-20 statically-held toner) to the resist art. By way of background in the xerography art, thermal transfer of electrostatic toner to paper has been practiced in the past__ Generally, the heat was applied aftex the trans-fer of the toner, as described in U.S. Patents 2,990,278;
25 3,013,027; 3,762,944; 3,851,964 and 4,015,027. Simul-taneous heating and transfer of electrostatic toner to paper is disclosed in U.S. Patent 3,592,642. U.S.
Patent 2,917,460 discloses the melting of the electro-static toner on the paper surface so that the molten --3~ droplets so formed may be absor~ed in the interstices of the paper to make a permanent image on the paper.
As applied to the resist art, however, xero-graphy has taken a different approach. U.S. Patent

2,947,625 discloses formation of an electrostatically-3s held image of toner, transfer of this image to a wet '7~36 3gelatin-coated paper using pressure which imbeds the toner in the gelatin coating, and exposing the toner image to the softening action of solvent vapors, and pressing the solvent vapor-softened toner image against S a printed circuit board to transfer a stratum of ~he resultant tacky image to the board, and finally sub-jecting the trans~erred image to more solvent vapors or heat to coalesce the image, which is then purportedly available as an etching resist. U.S. Patent 3,061,911 discloses a similar process except that the image is transferred from the transfer paper to the circuit board by electrical charging and the resultant transferred image is fused by exposure to solvent vapor. A trans-fer process has been commercialized, with only limited lS success, involving electrostatic transfer of an image of electrostatically held toner to a tissue, electro-statically transferring the image from this tissue to a circuit board, and fusing the image with solvent vapor.
In the magnetic printing art, U.S. Patent

3,965,478 discloses preheating of paper to which an image of magnetic toner is transferred under pressure, followed by additional heating to melt the toner and cause it to become impregnated into the paper surface.
U.S. Patent 4,067,018 discloses that in order to get a high quality image on unheated paper, free of smearing or smudging, that one or at most 1-1/2 layers of mag-netic toner particles should be adhered to the magnetic imaging member.
As applied ~o the circuit making art, U.S.
Patent 3,880,689 discloses the magnetic printing of catalyst-sensitized toner particles in a circuit pattern onto an adhesively-coated film, followed by electroless plating of the circuit pattern to form a printed circuit.
This patent also discloses that the imase can be printed onto a circuit board, but this would have the 7~3~

disadvantage of the existence of a toner layer between the electroless plating and the circuit board. U.S.
Patent 3,120,806 discloses the use of a magnetic pattern placed beneath a circuit board to attract fusible metal S toner to the circuit board in the pattern of the mag-netic pattern, to form the circuit directly therefrom.
As applied to the resist art, U.S. Patent 3,650,860 discloses a process for using magnetic toner to make a resist image. In this process, a magnetizable layer is deposited on the conductive metal substrate and this layer is imagewise heated above its Curie temperature to form a latent magnetiG image in the layer. This is followed by applying a dispersion of a magnetic toner, made of ferromagnetic material dis~ersed in binder,in a solvent for the binder to the latent magnetic image and drying tbe dispersion, which thereby forms a resist image corresponding to the latent mag-netic image. The bare portion of the magnetizable layer and corresponding underlying conductive metal substrate can then be etched away to form a printed circuit of the remaining conductive metal substrate. Among the disadvantages of this process is the consumption of the magnetizable layer for each printed circuit made and the necessity to use solvent to convert the magnetic toner to a llquid medium and subsequent evaporation of the solvent.
Disclosure of the Invention .
The present invention provides a resist pro-cess involving magnetic imaging which overcomes shortcomings of the resist art, in having the advantage of a quick set-up time for the image master (magnetic member) which is not consumed in the process, providing thick, pinhole-free resist images, 2roviding a high rate of forming such images, such as in a rotary press with-out requiring the use of solvent, utilizing a stable material reauiring no performance monitoring by anoperator and providin~ high auality r~sist images with excellent edge definition. The present invention also provides resist compositions and apparatus which 5 are especially useful in the process of this lnvention.
The process of the present invention involves forming a ~agnetically held image of toner and trans-ferring this image to a s~bstrate by means of heat and pressure. The heat is supplied to the process by pre-10 heating the substrate receiving the toner. Surpris-ingly, the transferred toner forms an image on said sub-strate which is useful as a resist in such processes as making printed circuit boards, printing plates, or in chemical milling, i.e., the process can in~ol~e the 15 steps of (a) transferring a magnetically held image of coalescible magnetic partlcles from a magnetic member to a suit~ble surface to form a coalesced resist image, (b) modifying the exposed areas of the surface which are unprotected by the resist image, and (c) optionally 20 removing the resist image from the surface-modified product. The modification can be to make tne exposed surface hydrophilic or hydrophobic, opposite to the characteristic of the resist image, in which case the resultant product could be used as a lithographic 25 printing plate. The modification can be to ~tch or deposit a metal on the exposed surface o~ the substrate to form the desired electrical circuit as a network of metallic conductors on an insulating background of suitable dimensions. In chemical milling (etching), 30 the interconnecting metallic network is either self-supporting or it may be attached to a suitable substrate.
The resist aomposition of the present inven-tion, which is useful as the toner ln the proc~ss of 35 the present invention, can be described as follows: a dry particulate resist composition of particles having S

8't ~36 an average size up to 30 ~m for substantially instan-taneous application to a heated surface of metal or the like to form resist image capable of withstanding liquid treatment media for said surface, comprising S a) binder consisting essentially of a thermo-plastic resin and up to 40% based on the weight of said binder of plasticizer for said resin, and b) magnetic material in particulate form present in said binder rendering the particles of said compo-10 sition magnetically attractible, the combination of said binder and said magnetic material being substantially non-blocking at 20C and being adherent to said sur-face upon said application to said metal surface and coalescible thereon to form said resist image, said 15 magnetic material constituting from 40 to 80% by weight of the combination of a) plus b) and said binder constituting the remainder.
The apparatus of the present invention can be described as follows:
Apparatus for forming a resist image onto a circuit board comprising means for defining a movable magnetic member for incorporating a latent magnetic image for developme~t by toner, means for heating the surface of a circuit board, means for moving the 25 heated circuit board and magnetic member together and pressing the heated surface of said circuit board against the developed latent magnetic lmage during said movement to transfer said image to said heated surface to form a resist image on said heated surface, 30 said heating means being positioned just upstream of said moving and pressing means.
Brief Description of the Drawings Fig. 1 is a schematic side view of the appa-ratus used for forming a resist image according to the 35 present invention.

8~7~36 Fig. 2 is a schematic side view of the dec-orator used to apply toner to the magnetic member used in the present invention.
Detailed Description of Invention and Best Mode The steps in the process of the invention may be understood by referring to the attached Figures 1 and ~ which illustrate schematically the magnetic printing and thermal transfer machine used in most examples of the invention.
Referring now to Fig. 1, two rolls, 11 and 12, each ~ive inches (12.7 cm) ln width and in diameter are mounted one above the other in a metallic frame, _. The lower roll, 11, is referred to as the printing roll, and it can be rotated by means of a variable 15 speed drive motor, _. The printing roll is surfaced with magnetic me~ber 15 which is a film consisting of a layer of hard (permanent) magnetic material such as discussed below on a polyethylene terephthalate film support and is backed with a thin layer of 20 resilient material such as neoprene. The upper roll, 12, is referred to as the pressure roll. It is movable and is fitted with a pis~on device, 16, which controls the pressure exerted by roll 12 on the printing roll, 11, and forms the nip, 17, in operation.
The desired circuit design is imaged to form a magnetic image in magnetic member 1;. The imaged film ~ can also be referred to as the movable printing member.
Alternatively, the printing may be carried out with an endless belt of the magnetic member material adapted to be pressed against the printed circuit board by a roll similar to roll _, which endless belt would be kept taut about roll _ by one or more additional rolls.
Below the printing roll, a toner applicator, 18, is attached which is used to form a fluidized bed 35 of dry magnetic toner. The position of 18 is adjustabie to permit the fluidized toner to be brought into contact with the lower surface of the printing roll, 11, bearing the printing member. Referring now to Flgure 2, the toner applicator, 18, consists of a revolving roll 5 having a magnetic surface 31, which dips into the toner reservoir, _. Toner 33 is carried upward to a doctor k~ife, 34, which engages toner loosely held by revolving roll 31 and forms a standins wave of toner which comes into contact with magnetic member 15. At 10 a roll surface speed of 40-100 ft/min (20.3-50.8 cm/sec) and a roll-to-blade spacing of 2 to 5 mils (0.051 to 0.127 mm), the toner is doctored ~rom the roll and forms a fluidized standing wave, 35, 30-300 mils (0.762-7.62 mm) deep before it drops back to the roll. When this 15 applicator 18 is brought up to the rotating printing roll, 11, bearing the magnetic member, the fluidized toner impinges on it and tones it, i.e., the magnetic member becomes decorated with the toner in the magne-tized area of the magnetic member.
An AC corona static discharge unit, 19, is located near the magnetic member 15. The function is to dissipate static charge on the toner particles on magnetic member 15 ater toning. Another unit 19 (not shown) can be located upstream of applicator 18 to 25 eliminate static charge on the surface of the magnetic member before toning. This double action can be accomplished with a single unit by operating the machine in stepwise fashion instead of the con-tinuous operation permitted by using two units 19 30 as described above.
A combination of air knife - vacuum knife 20, located after the toner applicator 18, cleans the toned film of background toner before thermal transfer. In the embodiment shown, the toner image is rotated past 35 the knife 20 before the transfer step. For continuous 8'~ 86 operation this combination air knife - vacuum knife 20 can be located between the toner applicator and the nip 17. The air knife blows air vertically at the film through a 10-mil (0.254 ~m) slot while the vacuum 5 knife causes a shearing air flow at the surface of the CrO2 film thereby dislodging background toner. The clearance between the knife and the film controls the air dynamics at the film surface. A clearance of 25-50 mils (0.635-1.27 mm) is very effective. Background 10 toner is that which is adhering to the demagnetized areas of the CrO2 film. An air knife alone, or a vacuum knife alone or in combination with these two elements can be used for this purpose. The vigor of the cleaning process is controlled by the magnitude of 15 air velocity, vacuum, proximity of the knife to the film and the film speed.
A 3" x 6" (7.62 cm x 15.24 cm) circuit board composite, 21, is preheated between hot plates, 22 and 23, just upstream from the nip between the rolls in 20 the diagram. The hot board is pushed into the nip, _, between rolls 11 and 12. The board is rolled_ through the nip so that it comes into momentary contact with and moves together with the decorated magnetic member, so that toner is pressed against the board and 25 is adhesively transferred to the board and simultan-eously fixed thereon. The printed board emerges to the right of the nip, as indicated by 24.
~agnetic Member and I:aging Thereof A printing member such as an endless belt, 30 flexible film or platen is provided with a surface cap-able of containing a magnetic image. The magnetic material forming the surface generally will be a ?arti-culate hard magnetic material in a binder. Suitable hard magnetic materials include the permanent magnetic 35 materials such as the "Alnicos", the "Lodexes" (acicu-lar iron-cobalt alloys encased in lead or plastic;
~ t ~~o~ r k manufactured by General Electric Company), the "Indox"~
barium ferrite compositions, and materials used in tape recording, magnetic discs, and magnetic printing inks. These latter materials include y-iron oxide (Fe2O3), magnetite (black Fe304), x-iron carbide and chromium dioxide. Acicular chromium dioxide is gen-erally preferred because of its magnetic properties.
The magnetic member preferably is a drum in which case the Lmaging surface may be an integral part of the 10 drum or it may be a flexible film coated with the mag-netic material and mounted on the drum.
Any method for forming a latent magnetic image in the magnetic member is useful in the present inven-tion. The image is latent in the sense that it is not 15 visible to the naked eye until decorated with magnetic toner which develops the image.
When using thermal imaging to create the latent magnetic image, the surface is magnetically structured by one of several methods with from about 100 20-to 1000 magnetic lines per inch (39.4 to 393.7 per cm) and preferably from 150 to 600 magnetic lines per inch (59.1 to 236.2 per cm). As used herein, a magnetic line contains one north pole and one south pole. The t-ech--~~
nique of roll-in magnetization can be used to structure the surface of the magnetic member, wherein a high 25 permeability material such as nickel, which has been physically discretely structured to the desired width is placed in contact with the surface of the magnetic member, which previously has been magnetized in one direction by a permanent magnet or a DC electromagnet, 30 and a DC electromagnet or permanent magnet with the polarity reversed is placed on the backside of the permeable material. As the structured high permeability material is brought into contact with the masnetic mem-ber, the nickel or other permeable material concentrates 35 the magnetic flux lines at the points of contact causing ~tr~e~

polarity reversal at these points and resulting in a structured magnetization of the magnetic member.
The surface of the magnetic member can also be thermoremanently structured by placing the magnetic S member having a continuously coated surface of mag-netic material on top of a magnetic master recording of the desired periodic pattern. An external energy source then heats the surface of the magnetic member above its Curie temperature. As the surface of the 10 magnetic member cools below its Curie temperature, the periodic magnetic signal from the magnetic master recording thermoremanently magnetizes it. When acicular chromium dioxide is used as the magnetic material in the surface of the magnetic member, as 15 little as 20 oersteds can be used to structure the surface of the magnetic member when passing through the Curie temperature whereas over 200 oersteds are needed to apply aetectable magnetism to acicular chromium dioxide at room temperature.
Alternatively the latent magnetic image can be created in the magnetic member by means of a mag-netic write head. The magnetic write head can provide the re~uisite magnetic structuring in the latent magnetic image directly.
The magnetic member used in the Examples is a layer of ac:icular chromium dioxide particles in a binder coated on a polyester film which may, or may not be aluminum-backed or aluminized.
The thickness of the CrO2 layer on the film 30 is limited only by the ability of the layer to absorb sufficient thermal energy to effectively demagnetize the CrO2 layer by raising a given thickness of the said layer above the Curie point of 118C during the thermal imaging process. Thicker layers are preferred to 35 enhance magnetic field strength. Practically, the '78~

thickness of the CrO2 layer on the imaging member is from 50 to 2000 microinches (1.27 to 50.8 micrometers), and is preferably from 150 to 500 microinches (3.81 to 12.7 micrometers).
S The magnetic member can be used either mounted in the form of an endless belt supported by a plurality of rolls or mounted to the curved printing roll 11. The imagi~g and toning steps are separate entities which do not need to be done consecutively in predetermined ~o sequential fashion. For instance, it may be desired to mount a preLmaged magnetic member on the printing roll.
The magnetic member can be imaged in a variety of ways, either held flat or attached to the curved 15 printing roll. One form of the master image is a silver photographic image transparency of a printed circuit diagram. This is held in contact with a prestructured magnetic member and flashed with a Xenon flash tube.
The energy transmitted through the transparent parts of 20 the master raises the CrO2 above its Curie temperature~ ~~~~~
of 118C and demagnetizes it; the opaque parts of the design minimize energy transmission and the design remains as a latent image on the CrO2 film if excessive ~lash energy is avoided. Alternative procedures are to 25 scan the desired circuit designs onto the printing member having no prestructure with electromagnetic recording heads, or to selectively demagnetize pre-structured areas of the magnetic member with point sources of radiation, e.g., lasers, which heat selected 30 areas of the magnetic member to above the Curie tempera-ture of the magnetic material in the magnetic member.
These devices may be designed to respond in an on-off fashion to a computer-stored or computer-aided design.
Precise image registration is important when -- 35 the process of the present invention is used to form both single-sided and double-sided circuit boards or to chemically mill double-sided patterns or shapes on metal.
Decoration and Transfer Rotation of the drum past a toner reservoir decorates the latent magnetic image with a magnetic toner to form a toner image which consists of multiple layers of toner. By multiple layers of toner we mean that at least two layers of toner particles are applied to the latent magnetic image in the magnetic member on the surface of the drum. This is necessary so that sufficient toner is available in the transferred image to form a coalesced (hole-free) resist image on the substrate surface. Multiple layers of toner particles on the latent magnetic image are achieved by control of toner particle size so that excessively large particles are not present and by having sufficient field strength of the magnetic member and sufficient concentration of magnetizable material in the toner. A dry toner is preferred which consists of coalescible magnetic parti-cles composed of magnetic and resin binder components.
Background toner is removed from non-magnetized back-ground areas by means of a vacuum knife, air knife, or a combination vacuum knife and air knife.
A substrate which, unlike ordinary paper, is free of interstices, such as a circuit board composite blank of suitable material is uniformly preheated to a suitable temperature. The substrate not only has the capability of being uniformly preheated but has sufficient heat capacity to retain this uniformity of heating sufficiently to make the toner uniformly adhere to the substrate in the transfer step.
Rotation of the drum decorated with multiple layers of toner in rolling contact with the preheated blank using a pressure roll surprisingly effects simultaneous transfer and adhesion of virtually all of /

8~786 the multiple layers of the toner image to the interstice-free surface of the blank in an adhesive transfer step and this is accomplished withou~ loss of image fidelity. The transferred image may be 5 either a positive or a negative resist, depending upon the master design and provides high fidelity repro-duction of this design. Post-transfer heating may im-prove the coalescence ~f tne image ir necessary. --An important feature of the decoration process 10 and subsequent transfer are the properties of the toner used. Preferred toners of the present invention will be described in a later section of this specification. The simultaneous adhesion of the pol~mer component of the toner and transfer of the toner to the circuit board 15 composite to form a resist without loss of image defini-tion demands a narrow and specific set of process condi-tions for the successful transfer of a particular toner.
Imaging, decoration and transfer are separate operations which may be, but are not necessarily imme-20 diately consecutive reactions. In magnetic printing ofcircuit boards, the magnetic image of a particular design can ordinarily be preserved after preparation and used any number of times to prepare multiple copies of identical circuit boards, either in a single run or 25 intermittently. More importantly, the distinguishing feature of the present invention is simultaneous tac~ifying of the toner particles and transfer to the circuit board with adhesion to form a cohered coating on the circuit board without free particles falling off 30 the boards.
An important feature of this invention is that successful transfer and faithful reproduction of the desired image is accomplished without adhesion of softened toner to the magnetic member.
Adhesion of toner particles can be accom-plished by a combination of heat and pressure. The 'J'~36 simultaneous apolication of heat and pressure is the preferred method of adhesive transfer in this invention.
An essential characteristic of the transfer process is that application of heat to the toner particles is from the circuit board which causes the toner to adhere to the circuit board, but not to the magnetic member while the transfer step is carried out. Under one set of preferred operating conditions the combination of heat and pressure causes the adhesive transfer to form thick 10 pinhole-free resists. Under another set of preferred operating conditions, the toner is tackified sufficient-ly to adhere to the substrate but without complete coalescence of the toner particles and the adhered image of toner particles is further treated in a post-transfer lS stage such as by heating to achieve additional adhesion - and coalescence.
. . _ , . . .
Binder components of toners have a tempera-ture region over which they tackiy, i.e., soften and adhere to the substrate (circuit board) sufic-20 iently to be pulled away from the gripping force ofthe latent magnetic image, but do not adhere to the magnetic member under the conditions of transfer. If the resin component becomes truly fluid, loss of image definition occurs by smearing of the transferred 25 image and/or by a portion of the toner remaining ad-hered to the magnetic member. It is essential that the toner resin be solid before transfer, rap~dly become tacky at the transfer nip because pressure at the nip is applied only for a moment (substantially 30 instantaneous tack), and maintain image definition.
For the toner of Example 1, the following chart shows the effect of different heating temperatures for the circuit board at constant pressure and speed for the toner transfer step.

Transfer Temperature Obser~ations on Toner and Resist 125C less than 90~ transferred to boar~, small ~ permanently S adhered to CrO2 image ~ ._ . . _ 120C more than 90% transferred to ~ board; shiny (coalesced) image.
PREFE~*ED RANGE more than 90% transferred to board;
l adhered but not fully coalesced.
112C more than 90~ transferred to board adhered very lightly.

110C less than 90% trans erred to board;
partly adhered.

100C - no toner transferred to-board.
For this chart, the board temperatures of 120 to 112C represent the transfer "window", i.e. the tem-20- perature range at which the process is successfully carried out using the toner and transfer conditions of Exampie 1. From the results shown or temperatures above and below this window, it can be seen that the "window" is quite narrow insofar as temperature range is concerned Transfer by tackifying, or adhesive transfer, - is subject to the important variables of temperature, printing (transfer) speed, s~tored heat and nip pressure.
Adhesive transfer temperature is critical since this is 3~ a dynamic physical process. It is related to the physi-cal properties of the toner resin. In general, the transfer temperature may be from about 40C to 150C
depending on the melting point and melt viscosity of the resin binder and nip pressure. This is illustrated 35 for specific cases in the examples which follow; these '7t~6 examples are non-limiting with respect to the transfer conditions. The lower operating limit is based solely on the necessity of having a non-tacky fluidizable toner at room temperature. Although a lower temperature might be operable, ambient storage temperatures might rise sufficiently to cause such toner to block or coalesce into large particles on standing. The upper limit is also related to the Curie temperature of the magnetic material in the magnetic member. In the case of GrO2, the Curie temperature is about 118C but a transfer temperature somewhat above this value can be employed since the process is dynamic and the momentary heating of the magnetic member by the heated substrate at the pressure nip coupled with the insulating effect of the toner can effectively prevent the surface of the mag-netic member from reaching the Curie temperature. Of course, when using magnetic materials having higher Curie temperatures, higher temperatures may be used.
Generally speaking, the shorter the contact time, the higher the temperature that should be used.
Conversely, increasing contact time by decreasing printing speed can result in lowering the transfer temperature. Depending on the temperature range, the printing speed generally is moré than 1 ft/min (.5 cm/
sec) preferably from 5 to 150 ft/min (2.54 to 76.20 cm/sec) and more preferably from 10 to 120 ft/min (5.08 to 60.96 cm/sec).
Contact pressure may vary considerably.
Generally when using a roll, a pressure of from 5-100 pounds per linear inch (pli) (0.89-17.8 kg/cm) will be used. Highér pressures may be used but transfer pres-sure is eventually limited by the danger of embossing of the magnetic member. Pressure serves to ensure firm contact and to enhance consolidation of the coalescing ,5 toner. The multiple layers of toner particles neces-sary for this consolidation and coalescence to a resist image presents the problem of achieving this result without also losing image fidelity.
The time of application of pressure to trans-fer the toner to the substrate should be momentary in 5 order to achieve the highest fidelity resist image.
Preferably, this time is no greater than one second and more preferably no greater than 0.1 second.
A key feature for the successful operation of the printing machine is the existence of a temperature lO differential between the surface or the circuit board and the magnetic member since the temperature of the surface of the magnetic member should not reach the point at which the toner will tackify and stick to the magnetic member. The precise temperature, of course, lS is related to the toner resin itself and the operating conditions. Some resistance to sticking can be obtained by optional application of release agents such as "Slipspray Dry Lubricant"(Du Pont) or'~TV"Silicone rubber (GE) to the surface of the magnetic member with-20 out destroying the ability of the latent magnetic image to pic~ up toner particles.
The present invention provides a sharp,well defined thick layer of toner in the form of a coalesced resist image on the heated substrate surface receiving the toner from the magnetic imaging member. The success of the present invention is surprising for several reasons, among them being the following. First, the surface of the substrate, e.g. metal or plastic, is smooth relative to the surface or paper, i.e., no inter-30 stices are present, and the toner adheres sufficientlyto the surface to withstand subsequent modification of the surface such as by etching. Second, the resist image is a high fidelity reproduction of the original or desired image despite having been formed under heat 35 and pressure from m~ltiple layers of toner on the * +r~clemav^k 't'~

latent image of the magnetic member. Third, all of the multiple layers of toner, as required to avoid discontinuities in the resist image, are transferred to the substrate upon only momentary application of 5 pressure on toner particles just then being subjected to heat by the substrate. Fourth, the image of toner particles can be transferred from the magnetic member directly to the substrate surface, e.g., printed cir-cuit board, on which the image is to serve as a resist.
The resist image formed of coalesced toner protects the underlying areas of the substrate surface according to the master design. The unprotected areas are then modified,preferably permanently, by such pro-cesses as etching, electroplating or electrolessly 15 plating. In the print and etch mode of manufacture, the unprotected areas are etched away and the resist image is subsequently stripped to expose the under-lying metal, e.g. printed circuitry, if desired.
In another embodiment of the present inven-20 tion, the circuit board substrate onto which the mag-netically held image is transferred is capable of being selectively plated with elec~rically conducting material.
The resist image must be thick enough to minimize pin-hole formation and preferably should be thick enough to 25 provide channels deep enough to contain the thickness of the plating. Significant overplating (mushroom effect) of plated metal beyond the circuit lines onto the resist Lmage is generally prevented when a 0.4 mil (0.0102 mm) or more thic~ness of resist is present.
Either a negative or a positive image may be printed onto a circuit board composite for subsequent conventional circuit board preparation. A positive resist image is defined as one which leaves the circuit lines exposed. The product may be subse~uently treated 3~ by optionally plating the exposed lines with copper and then plating with a material such as solder which is resistant to etchants such as ferric chloride. ~he ~a resist may be removed and the newly exposed substrate removed by etchants to form the printed circuit. Copper is conveniently etched with ferric chloride.
Ferric chloride or other etchants may be used for chemical milling; this is a deep etching method which avoids the strPsses of mechanical milling. If a negative resist image is defined as one which covers the circuit lines with resist, the treatment consists of etching or chemically removing the exposed substrate and, if desired, removing the resist image, and if desired thickening the exposed circuit lines by plating may subsequently be done.
Product The above process forms a printed circuit board, which is an electrical circuit in the form of a network of metallic conductors on an insulating background of suitable dimensions.
The conductive layer may be mounted on inert nonconductive base materials and the toner resist defining the circuit lines printed magnetically on one side only, or a circuit board having a conductive layer on both sides may be printed with complimentary designs which require accurate registration of the toner resist on both sides. In both cases, undesired material in the conductive layex may be removed by etching.
Chemical milling by etching is an alternative process to mechanically milling a desired pattern since mechanical milling tends to leave strains in the metal.
Suitable materials, including alloys, for mag-netic printing substrates are the structural metals which include but are not limited to copper, silver, aluminum, stainless steel, magnesium, dura~uminum, tin, lead, nickel, chromium, iron-nic~el-cobalt alloys such as"Rovar"and"Alloy 42~, and beryllium copper, which may ~t~ad~ k or may not be supported on a suitable electrically insulating base material, depending upon the desired application of the end product. Chemically milled samples are unsupported, whereas printed circuit boards S are usually used in supported form. Providing a support allows the use of a thinner layer of electricallv con-ducting material.
Copper is the preferred metal for the elec-trically conductlng material for printed circuit boards because of its good thermal and electrical conductivity in relation to cost. Iron-nickel-cobalt alloys such as "Xovar"and"Alloy 42', beryllium copper, duraluminum, aluminum and stainless steel are preferred substrates for chemical milling applications.
For circuit boards in which a metal layer is laminated to an insulating base, suitable insulating base materials include vulcanized fiber, mica, glass, asbestos, cotton, glass fiber, polyester, aromatic poly-amide, cellulose, aromatic polyimide_and mixtures of these with one another, preferably bonded into a lam-inata with a thermosetting phenolic resi~ or a~ epoxy r-~si~ OE mixtures thereof.
.
Advantage~ ~ rinting Over Other Methods of PreParing Printed Circuit Boards (1) Magnetic printing provides a better quality resis~ on metallic substrates than is possible with electrophotographic printing. This is because all of the toner in the electrophotographic process has the same electrical charge (either positive or negative) 30 which causes the toner particles to tend to repel each other even though they are attracted to the metallic substrate. This has a tendency to cause pinholes which is a particularly serious problem when plating on the metallic substrate to form a printed circuit board.
35 Magnetic printing can be used to print directly and repetitively on metallic substrates with sharp-edged definition. Electrophotographic systems also require constant reforming of the latent electrostatic image after transfer to the substrate. The electrophoto-graphic process, therefore, is time-consuming and the product circuit boards are typically of low quality.
(2) Magnetic printing does not s~lffer from the distortion of image dimensions observed with screen printing. In screen printin~, the design is prepared on screens of stainless steel wire, nylon, polyester or metallized polyester fibers held in a steel frame.
10 Repetitive off-contact printing with these screens causes screen distortion with every pass of the squeegee. Eventually, the registration of the design is lost and the screen must be prepared again. This is costly in terms of time and materials, particularly 15 since screen preparation is time-consuming.
~ 3) Magnetic printing overcomes the dis-advantage of offset lithography, namely, thin coatings full of pinholes which require more than one pass.
Offset lithography also requires a careful balance to 20 be maintained between the emulsified ink resist and water and drying of the printed resist image which could entrap dust during drying.
~ 4) Thick, well defined (sharp break between resist and substrate surface), dense, uniform coatings 25 of resist of up to 2.0 mils (0.0508 mm) and pre~erabl~
0.3 to 0.8 mil ~0.0076 to 0.0203 mm) can be deposited by magnetic printing. This thickness is sufficient to avoid pinholing and prevent conductor spreading by most overplating.
~5) Simultaneous transfer and adhesion with-out significant loss of definition of the transferred image provide a distinct advantage over t~e magnetic resist-forming process as disclosed in U.S. 3,650,860.
The process of the present invention has the 35 capability of preparing printed circuit boards having 8'786 both conductor area uniformity and conductor line edge quality much superior to those previously prepared by direct printing using fusible dust or adhesive and metal dust or elec~rostatic or xerographic printing.
5 The process of the present invention also has the capability of preparing printed circuit boards having conductor line edge quality superior to those pre-viously prepared by screening, in that the conductor lines do not have undesired "necks" in them as often 10 occurs in screening. O~fset printing is capable of printing sharp lines but canno~ produce the pinhole-free resist needed for etching or plating.
The process of this-invention-can also be used to prepare printing plates for both planographic and re-lS lief printing. ~he use of an oleophilic toner trans-ferred to a hydrophilic support, e.g., aluminum litho-graphic printing plate, will produce directly a litho-graphic plate which will accept ink in the toned areas.
Alternativeiy, the use of a hydrophilic toner applied 20 to a hydrophobic plastic or metallic, e.g., copper, support, will provide a lithographic plate which will accept ink in the areas free of toner. A wide variety of plate making procedures may be employed by depending on the Use of the coalesced toner image as a resist.
25 For example, a hydrophobic coalesced toner image may b~ used for'the manufacture of deep etch as well as bimetallic and trimetallic planographic plates.
Further, coalesced toner images can be used in all the conventional methods of preparing letterpress plates 30 by photoengraving, e.g., etching zinc, copper, or magnesium with powdering or powderless etching methods, and duplicates can be made in the orm of stereotypes, electrotypes, plastic, or rubher plates.
In addition, coalesced toner images made by the process 35 can be used to prepare gravure printing plates wi~
wells of variable area and constant depth.

8~6 _ 24 Specif lC Embodiments of the Invention The ollowing illustrative examples demon-strate ways of carrying out the invention. The inven-tion is not restrictive or limited to these ~pecific 5 examples. All parts and percentages are by weight, and all temperatures are Centigrade, unless otherwise noted.
Example 1 This example embodies a preferred method for printing resists on copper circuit board blanks. The 10 steps in preparing the resist are (1~ mounting a pre-imaged magnetically active film on the print roll and rotating it past the corona unit, (2) toning the imaged film with a finely divided magnetic toner, (3) passing the toned image near an AC corona discharge device to 15 reduce static electricity, (4) passing the toned image under a combination air knife/vacuum knife to remove background toner from the demagnetized areas of the imaged magnetic film, and (5) contacting the toned image momentarily with a preheated circuit board blank to 20 ~ackify, transfer and adhere the toner to the copper surface simultaneously.
The steps described above were carried out on the printing machine described hereinbefore with refer-ence to Figs. 1 and 2.
The toner consisted of 50 parts by weight Atlac'!382ES polyester resin purchasable from ICI, Ltd., (a propoxylated bisphenol-A, fumaric acid polyester having a tack point of 70C and a liquid pointof100C), molecular weight of 2500-3000 and Tg of 58C., and 30 50 parts by weight magnetic iron oxide, MO 7029, (Pfizer) having a~ average particle size of 0.5 ~,lm.
Tack point and liquid point are manufacturer's tests involving temperature at which resin particles will stick to a heated bar and the temperature measured 35 in a meltins point tube, respectively. The average -.

8~786 particle size of this toner was 8.5 ~m. The toner was placed in the toner applicator, 18. The applica-tor, 18, was activated and moved close to the printing roll so that fluidized toner contacted printing 5 roll, 11. The printing roll drive was activated to move the pre-imaged magnetic film 15 through the standing wave of toner and cause magnetic toner to adhere to the magnetic parts of the image. The ~oned film was then rotated past the corona discharge, 10 19, and the combination air knife/vacu~m knife, 20.
The knife, 20, was placed approximately 35 mils (0.89 mm) from the film surface. The air pressure was 3.8 inches (9.65 cm) of water and the vacuum was 0.30 inch (0.76 cm of water).
To effect transfer of the toned image, the film was rotated into position. The circuit board blank, 21, preheated to 116C by hot plates 22 and 23 was pushed into the nip, 17, and contacted with the toned image rotating through the nip at a speed of 26 20 linear feet per minute (13.2 cm/sec) and a pressure of 40 pounds per linear inch (7.15 kg/cm). The circuit board with the printed resist was deposited beyond the nip and no toner was detectable by rubbing with the fingers on the latent magnetic image.
_ ~ 25 Examination of the printed resist by micro- ~ _ scope showed few residual unwanted particles in the circuit lines and very few pinholes in the resist which showed that the melted resist had had good melt cohe-sion. Several circuit boards were prepared ln this 30 manner. Some were post-print heated for 2 minutes in an oven at 125C to cause additional consolidation of the resist. ~he thickness of the resist was measured and found to be 0.6 mil (0.015 mm). 30ards of both ty~es were subsequently processed by standard circuit board electroplating methods, consisting of the steps 7~36 _ 26 of preplating cleaning, electroplating in copper salt baths, additional plating in lead/tin protective plat-ing baths, stripping the resist from the circuit board in methylene chloride, and etching the exposed copper 5 to leave circuit lines. Good circuit boards were obtained. This means that the boards reproduced the original image and acceptable boards were formed~
Reproducibility was demonstrated.
This example illustrates the use of all 10 essential parts of the magnetic printing apparatus.
Example 2 a. The process of Example 1 was repeated using another toner prepared from 50 parts of'Atlac 580 resin, purchasable from ICI, Ltd., having a mole-15 cular weight of 1450 and Tg of 43C., and 50 parts ofmagnetic iron oxide. "Atlac'580 is a bisphenol-A, fumaric acid polyester with terminal vinyl groups modified by inclusion of a urethane moiety. The a~erage par~icle size of this toner was 9.9 ~m. Very 20 good resists with few pinholes and low bac~ground were obtained. The thickness of the resist was measured and found to be 0.8 mil (0.02 mm).
b. Ten g of a toner prepared from 50 parts ~Atla~'580 resi.n, available from ICI, Ltd., and 50 25 parts magnetic iron oxide were mixed in 500 cc of water containing 2 y of "Fluorad" FC128 wetting agent avail-able from the 3M Co. The mixture was used to tone a 47.2 lines/cm halfto~e image on a ~rO2 layer on Mylar~.
The toned magnetic image was rinsed in 2g 30 "Fluorad" FC128 in 500 cc of water and dried.
The toned image was mounted on the printing roll of the apparatus described in Example 1.
To effect transfer of the toned image, a 305 ~m sheet of anodized aluminum lithoplate base 35 was preheated to 120~C by hot plates and was pushed h t~ade~k B'786 into nip 17 and contacted with the toned image rotating through the nip at a speed of 55 linear feet per minute (28 cm/sec) and a pressure of 40 pounds per linear inch (7.15 Rg/cm).
This gave an excellent transfer o~ the toner image to the lithoplate base.
Example 3 In this example a toner was prepared consist-ing of 45 parts by weight"Atlac"382ES, 5 parts triphenyl 10 phosphate and S0 parts magnetic iron oxide of the type used in Example 1. The average particle size of this toner was 19 ~m and it had a melt index of 26 and Tg of 30C. This toner was applied to the CrO2 magnetic film and transferred to a circuit board blank 15 as also described in Example 1. In this case, the board temperature was approximately 85C; the ~ransfer rate through the nip, 39 linear feet per minute (19.8 cm/sec); and the nip pressure, 40 pounds per linear inch (7.15 kg/cm). Under these conditions, the toner 20 transferred to the circuit board but was incompletely coalesced so that individual toner particles and numbers of tiny pinholes could be seen by microscope.! When the board was subse~uently briefly post heated to 120C, the toner particles coalesced fully an~ the previously 25 observed pinholes had disappeared. The thickness of the resist was measured and found to be 0.7 mil (0.018 mm). Post heating can be omitted at a higher board temperature at the transfer step, such as 105~C.
The board was cleaned briefly in a sulfuric 30 acid/ammonium persulfate bath and plated in a copper.
sulfate bath. Good copper deposition occurred on the circuit lines but virtually no plating nodules typical of deposition at pinholes could be found.
Example 4 -~35 This example illustrates wet ton ng and trans-fcr with a nand roll. Image~ CrO2 film ~a-s toned by 8~Jt~

agitation in a slurry of the toner in an Igepal C0710 (nonionic surfactant, ~eneral Dyestuffs Corp.) solution.
The toner composition was a 50:25:25 mixture of low molecular weight polystyrene (Hercules XPS 276) havir.g 5 a Tg of 48C, magnetic iron oxide (Colum`bia,"Mapico Blac~")and carbonyl iron GS-6~(GA~- Co.) having an aver-age particle size of 5 ~m. The average par~icle size of the toner was about 18 ~m and the range of toner particle size was about 8-25 ~m. Surplus toner was 10 rinsed from the film with clean wash water containing "Igepal". The film was dried and mounted on the thermal transfer machine. Circuit board blanks were printed by a hand-operated roll, similar to the one shown in Flgure 1 but without automatic drive and pressure 15 control device (pressure estimated as 0.36-1.8 kg/cm), at a circuit board temperature of 114C and a roll transfer speed of 1 inch/sec (2.54 cm/sec). Clean transfer of the toner to the board was observed. The measured thickness of this resist was from 0.35 to 0.60 20 mil (0.009 to 0.015 mm). The bare surfaces of the circuit board blank can be etched or plated.
Example 5 A 5-mil (0.127 mm) aluminized L~ylar~ polyester film with a topcoat of 0.16 mil (0.00406 mm) of CrO2 25 was prestructured magnetically with a 197 cycles/cm signal. The film was thermally imaged using a 65 line per inch (25.6 line pér cm) halftone image with a xenon flash lamp operating at 2200 volts and 240 microfarads.
After exposure the imaged film was dipped for 15 sec 30 in a toner mixture composed of 7 g of a polystyrene toner (50% by wt. polystyrene, 25~ by ~t. Fe304 and 25% by wt. carbonyl iron) and 2 g of a dispersins agent in 400 g of water. The toned film was then rinsed in a dispersion of 1 g of dispersing agent 35 in 500 cc of water.
Tne toned image was transferred by placing the toned CrO2 film in contact with an anodized ~trcld~lc~fk 8~36 aluminum surface using a ~ytar3 cover sheet in a ~acuurn frame at 28" mercury (71 cm Hg) vacuum to obtain in-timate contact. The surface of the L~qylar~ cover sheet was heated to various temperatures depending on 5 the toner and melt-transferred to the aluminum surface.
The printing quality obtained using a vacuum frame was not as good as when the transfer step involved momentary application of pressure such as by using the apparatus of Pigs. 1 and 2.
1~ In this manner, a polyamide/Fe/Fe304 toner was transferred at 150C, another polyamide (45%)/Fe (27%)/Fe304(27%)/1%C toner was transferred at 120S:, an epoxy (40%)/Fe304(29~)/Pe(30%)/1%C toner was transfer-red at 110C, a poly(styrene)/Fe304 toner was transfer-red at 110C and a poly(styrene/acrylate) (50~)/Fe304 (50%) toner was transferred at 150C. Following trans-fer, the plates were post heated to 200C for about 5 sec.
Lithoplates prepared as above were made using the epoxy/Pe304 and polyamide/Fe/Fe304 toners.
The plate was then coated with a hydrophilic printing ~~
gum. The plate was then placed on a multilith press, and using a multilit~l offset ink, a total of 5~,000 copies were run off with no wear of the image noted.
By a manner indicated in preceding experi-mental sections, a deep etch lithographic printing plate can be prepared by subsequently removing adjacent areas of metal from the resist-printed plate.
Similarly, by transferring the resist to a 30 copper gravure cylinder and etching the remaining exposed surface, a gravure printing surface can be produced.
A letter press printing plate can be pro-duced on metal or plastic by making a resist on the 35 surface of the plate as described above and subse-quently etching or dissolving adjacent metal or 7~6 plastic surfaces.
Resist Compositions of the PreseDt~ Inv~entlcn The process of the present invention places an unusual set of requirements on the magnetic toner.
S The toner has to have a substantial proportion of magnetic material in the particles so as to be attrac-ted to the latent magnetic image in the magnetic member in order to decorate it with the desired image of toner particles. The particles of coalescible lO resin in which particles of this magnetic material are embedded must form the coalesced resist image adherent to the heated surface. The magnetic material detracts from the flowability and coalescibility of the par-ticles into the resist image and the coalescible resin 15 detracts from the ability of the toner particles to decorate the latent magnetic image with fidelity.
The toner particles also have to transfer from the magnetic member to the heated surface in the brief moment of application of pressure of the 20 heated surface and the toner particles against each other. In other words, the adhesion of the particles to the heated smooth surface has to be practically instantaneous, without exceeding the Curie temper-ature of the magnetic member or causing particles 25 to adhere to it. The coalescence of the particles on the surface has to be complete, or made complete later if necessary, because of the resist image utility which cannot tolerate holes, e.g., pin holes, in the resist image which would lead to undesirable 30 etching or plating of the surface. In addition, the instant adhesion of the particles to the surface has to be sufficient to obtain release of the par-ticles from the latent magnetic image in the magnetic member, and sufficient adhesion to the surface has to 35 be obtained for the resist image to withstand such subse~uent modifications of the surface as etcbing or plating of the surface.

~1~8786 The prior art does not disclose toner compo-sitions to be able to meet the requirements set forth above. U. S. Patent 3,650,860 discloses a toner com-position of ferromagnetic materials dispersed in an 5 etch-resistant binder such as polyvinyl chloride.
The toner is not used for image development in the dry ~tate, but instead, is added to solvent for the binder and flowed onto a magnetized surface to adhere only to the magnetized portion thereof. Upon drying, 10 the resultant ilm acts as an etching resist. U.S.
Batent 4,099,186 discloses a ferromagnetic toner for printing onto textiles, in which the toner com-position comprises a ferromagnetic component, a dye and/or chemical treating agent, and a water-15 soluble or water solubilizable, preferably thermo-plastic, resin which encapsulates the other components.
U.S. Patent 3,681,106 discloses electrostatic compo-sitions for electrostatic image reproduction, com-prising pigment and a specific class of polyester resin 20 binders. Additi~es to the composition, such as dye, plasticizers and resin fillers are disclosed to improve the handling properties of the toner or adapt the toner for a particular electrostatic printing process.. The patent also discloses the composition to have both 25 electrostatic and magnetic properties by using up to 50~ by weight of magnetic powdered pigment, such as iron oxide or similar materials, as the pigment.
As mentioned hereinbefore, the dry par-tic~late resist compositions of the present invention 30 comprise three essential ingredients, thermoplastic resin binder, plasticizer for the resin present as part of the binder and magnetic material present in the binder. Each of these ingredients has preferred characteristics and their combination produces a 3S composition having unexpected temperature sensitiv-ity and other preferred characteristics as will '7~36 be described hereinafter.
The plasticizer reduces the temperature at which the ~agnetic particles will tack transfer.
!'Tack transfer" temperature is the preheated substrate surface tempera~ure at which at least 90~ by wt. of the particles will adhere to the substrate surface under a pressure of about 40 pli (7.15 kg/cm) without coalescence of the particles to an impervious image which is a resist image. This temperature is determined using the rolls 11 and 12 of Fig. 1 at a speed of 25 cm/sec, in which the neoprene backing sheet is 0.6 cm thick and has a durometer of 50 and the composite 21 is 0.08 cm thick and has copper cladding (on an insulating base) on the surface being imaged. At t~is temperature, essentially no particles adhere to the magnetic member by virtue of tackiness or melting of the particles. The image at tack transfer consists of particles agglomerated together, whereby the original particles prior to transfer have lost some of their identity, but are not entirely coalesced. The agglomerated particles are bound together and adhered to the substrate surface so that loose "original" particles are not present.
Surprisingly, the reduction in tack transfer temperature through plasticization widens the tem-perature window at which the transfer of toner from the magnetic member to the heated substrate surface, whether by tack transfer or tack transfer and simul-30 taneous coalescence, can be carried out. To illus-trate, the chart contained earlier i-n this specifica-tion shows a temperature of from 112 to 120C for a particular toner in which the binder is thermo-plastic resin only. A small amount of plasticizer, 35 e.g., 5% based on total weisht of the composition can lower the tack transfer temperature to as low as about 65C for the same resin and at the same time 8'~ ~6 enables the transfer to ~e carried out at temper-atures as hish as 110C,without the toner particles sticking to the magnetic member. Thus, the transfer window for the plasticized toner is about 45C
S instead of 8C for the unplasticized toner. This has the advantage that some latitude is available in the process which enables it to have commer-cial utility. Also, less heating is required,thus lowering cost.
The widening of the transfer window provided by resist compositions of this invention also enables the process to be conducted in two steps. The first step is to heat the substrate surface sufficiently so that the composition will tack transfer to it. The 15 second step is to heat the tack-transferred image further at another location in order to coalesce the image to a resist image on the surface. The advantage of this is that it minimizes the amount of preheating of the substrate in order to get the toner particles 20 to transfer to it. It is desirable to minimize pre-heating of the substrate so as to minimize its thermal expansion which detracts from re~istration of the board with the image. Also, infrared heating is the most economical preheat method and it is difficult 25 to preheat the shiny (copper) surface of the sub-strate by radiant heat. As for post heating to coalesce the transferred image, the transferred image is a "black-body" which is o smaller area and absorbs radiant heat more efficiently than the sub-30 strate surface. Thus, relatively little post heatingsuch as by radiant heating is required to coalesce the mage .
The resist composition of the present in-vention is "dry" in the sense that it is powdery and 35 does not appear to have any liquid present.

~1~8'~6 The thermoplastic resin together with the plastici~er for the binder component of the compo-sition of the present invention provides a substan-tially non-blocking composition at ordinary room tem-5 perature (20C) and adhesion to the metal surfaceto which the composition is transferred under heat and pressure. The binder is selected so as to be adherent to the particular substrate under transfer conditions. The binder also supplies strength to 10 the resist image so that it does not smear and can withstand reasonable handling and is not displaced by the usual treatments, e.g., spray of aqueous FeC13 involved in etching. I~ the case of plating, the binder also withstands the chemical action of 15 the plating bath so that the resist image can function as such.
The thermoplastic resin is selected with these criteria in mind. Preferably, the resin is water insoluble at ordinary room temperature so as 20 to be able to withstand aqueous treatments such as etching or plating, although solubility in aqueous alkali solution, e.g., 2% KOH, may be desired.
Preferably, the resin has a weight average molecular weight of at least 1000 and less than 50,000, and 25 more preferably, less than 25,000. Typically, resins used for xerographic toners have a higher molecular weight in order to avoid fracturing during tribo-electric charging which involves tumblinq of toner particles with carrier beads. Such higher molecular 30 weights should not be used in compositions of th_s invention because they decrease the speed at which the resin becomes tacky, there~y detracting from instant adhesion at the ti~e of tack transfer.
Most preferably, the thermoplastic resin has a 35 molecular weight at which the resin has Newtonian ,'l .~8~786 viscosity character, i.e., flow property increases substantially linearly with increasing shear,or which can be made to have Newtonian viscosity charac-ter upon the addition of plasticizer to form the S binder component.
Examples of polymers meeting these criteria are as follows: acrylic polymer in which at least 40% of the polymer is derived from one or more acrylic units, e.g., acrylic acid, methacrylic acid, and 10 esters and nitriles thereof, such as polymethyl-methacrylate and copolymers and terpolymers thereof with Cl-C8 alkyl acrylates, C2-C8 alkyl methacrylates, styrene, and acrylonitrile; styrene copolymers such as with maleic anhydride, acrylonitrile or butadiene;
15 polyvinylacetate; polyesters, especially those prepared by reaction of a dicarboxylic acid with a polyhydroxy compound such as described in U.S. Patent 3,681,106, examples of such acid being as follows:
aromatic ~cids and aliphatic acids, saturated or 20 unsaturated, such as maleic acid~ fumaric acid, glutaric acid, terephthalic acid, and polyhydroxy compounds such as bisphenol A and alkylene diols;
cellulose esters such as cellulose acetate butyrate;
and polyamides such as those formed from diacid 25 chlorides and diamines, e.g., hexamethylene-l, 6-diamine and sebacyl chloride, the N-alkylated polyamides and polyamides described in U.S. Patent 3,778,394.
Particulate compositions of the present 30 invention which are to be soluble or at lPast swollen by aqueous alkali solution, e.g., in order to be strip-pable from the substrate surface after having served as a resist, face the additional problem that they tend to be hygroscopic, which leads to bloc~ing 35 of the particles at ordinary room temperature. As '7~6 _ 36 part of the present invention, it has been discovered that acrylic and styrene copolymers such as described above, which have an acid number of at least 25, and preferably at least 50, and molecular weight low 5 enough to provide transfer, will not be excessively hygroscopic in compositions.o~.the.~resent invention.
In order to avoid excessive sensitivity to humidity, the acid content should not be too high. Thus, an acid number for the polymer of no greater than 125 10 is preferred and no greater than 100 is even more preferred.
Selection of the plasticizer component will generally depend on the particular thermoplastic resin used so as to be compatible therewith, i.e., not 15 form a separate phase. Preferably, the plasticizer has a boiling point above 200C and does not detract from the adhesion capability of the thermoplastic resin for the particular substrate intended and has a lower molecular weight than the thermoplastic 20 resin with which it is used. Examples of plasticizers are the aromatic phosphates such as triphenylphosphate and the phthalates such as dioctyl phthalate, the adipates such as dioctyl adipate, the sulfonamides such as toluene sulfonamide, and polymeric plasti-25 cizers such as low molecular weight acrylic resinssuch as ethyl..acrylate/methyl methacrylate/acrylic acid copolymer("Carboset"515) and ethylene/vinyl acetate copolymer.
The amount of plasticizer is selected to 30 lower the temperature and broaden the temperature range preferably to a range of at least 20C at which the particulate composition will transfer from the magnetic member to the heated surface substantially instan-taneously, with image fidelity whether by tack transfer 35 alone or tack transfer and simultaneous coalesc~nce to produce a tough coalesced resist image on the heated surface. This effect is to-be accomplished tracler~laf ~<

~1~8'786 without causing the particulate compositlon to block at ordinary room temperature. The plasticizer also reduces the brittleness of tne thermoplastic resin, thereby increasing the toughness of the resist 5 image. While lowering the tacX trans~er temperature of the composition, however, the plasticizer should not make the resist image deformably soft. ~Jenerally, no more than 40% based on the weight of the binder is necessary, and as little as 2% by wt. can give 10 significant ~eneficial effect, depending on the thermo-plastic resin and plasticizer involved. Preferably, -the amount of plasticizer will be from 5 to 15% based on the weight of the binder.
The magnetic material component of the compo-15 sition is readily magnetizable, and preferably has a coercivity of less than 400 oersteds. To be useful in electropla~ing, the magnetic material is preferably a dielectric material as well. Preferably, the magnetic material is substantially non-porous and substantially 20 isometric so as to minimize its surface area to be substantially encapsulated by binder. By "substantially non-porous" is meant that the particles of magnetic material are solid instead of fibrous or porous and by "substantially isometric" is meant that the particles 25 are faIrly uniform in shape with all dimensions of each particle being within about a factor of three of each other. Examples of magnetic materials are as follows: Fe304, Fe, CrO2, and ferrites.
The magnetic material preferably has an 30 average particle size of less than 6~m and m~re pref~r-ably from 0.1 to l~m. "Average particle size" disclosed herein can be measured optically by measuring each particle of a sample using an electron microscope or for the larger size toner particles, a coulter counter 35 can conveniently be used for particle size measurement.

_ 38 The proportion of magnetic material in the composition is from 40 to 80~ by wt. and the binder com-ponent from 20 to 60% by wt. to total lO0~ of the total weight of these components in the composition.
S A smaller proportion detracts from the ability of the particles of composition to be attracted sufficiently to the latent image in the magnetic member. A larger proportion detracts from the coalescence and adhesion of the resist image formed from the composition.
10 Preferably, the proportion of magnetic material is from 45 to 65% based on the combined weight of the magnetic material and binder component.
The resist compositio~s of the present inven-tion preferably have a melt index of from l to 100, as 15 measured at 125C and 325g load according to ASTM
procedure Dl238-73. Above 100, the resis~ image is too brittle for most applications and below 1, the toner does not have sufficiently quic~ response to become tacky at the instant the composition is brought 20 into contact with the heated substrate surface under pressure. Preferably, the composition has a melt index of from 1 to 50 and more preferably from 4 to 40 so that the composition will have "quick tac~", and the - resist image will be tough and coalescible.
The presence of the large amount of magnetic material in the composition a~fects the melt index.
For example, a thermoplastic resin having a melt index of 25 has its melt index increased to 56 when lO~ by wt. of plasticizer based on the total amount of resin 30 is mixed with it, but when an equal weight of magnetic material, based on the weight of resin plus plasticizer then is added, the melt index of the resultant composi-tion is 20.
The resist composition (binder component) 35 preferably has a glass transition temperature (Tg) of 8~7~36 no greater than 110C, and more preferably no greater than 80C, obtained by the plasticizer lowering the original Tg of the thermoplastic resin. These low glass transition temperatures permit the composition 5 to have tack and flow and desired transfer temperatures.
The glass transition temperature of the composition should be greater than 2S~ and preferably greater than 40C to insure that the particles of the compo-sition do not block during storage and normal lO handling.
The composition of the present invention can be made by melt blending the thermoplastic resin, plasticizer, and magnetic material, which disperses the magnetic material in the binder, cooling the blend 15 and chopping it into chips in the Abbey Cutter or Micropulverizer (U.S. Filter Corp.) to pass a 20 mesh screen. The chips can then be passed through a micronizer (Sturdevant~ to get the desired particle size. The magnetic material is present in the particle 20 as a dispersed phase in a binder matrix.
The resist composition is also resistant to the particular modification to be practiced on the un-covered substrate surface. Preferably, the composition is at least resistant to aqueous FeC13 etchant.
P~eferably, the particles of the composition of this invention have an average particle size of up to 30~m, usually at least l~m, and more prefera~ly in the range of 5 to 30~m. Greater than 30~m detracts from the coalescibility of the particles. ~espite the 3Q presence of the large proportion of magnetic material in particles of the composition, sufficient binder is present at the surface of each par~icle to obtain the desired coalescence and adhesion.
The particulate compositions of the present 35 invention have a high transfer efficiency at a ~ ~r~d ~a~ 39 ~ransfer ~emperature in the range of 50-120C and tack transfer temperature in the range of 50-110C.
Generally, at least 90~ of the particulate composition will transfer from the magnetic member containing the 5 latent image by tack transfer alone or simultaneous with coalescence to the heated substrate surface on which the composition is to serve as a resist.
Example 3 is a composition of the present in-vention. Further examples (6-8 and 10-14) of particu-10 late resist compositions of the present invention ~ are as follows:
Example 6. A toner was prepared in the followingmanner. Forty-five parts by weight of a low molecular-weight polyester resin (Atlac~ 382ES, purchasable from ICI) was blended with 5 parts triphenyl phosphate in a 70/30 (by weight) mixture of acetone and toluene and 50 parts by weight Fe304 having an average particle size of 0.5 ~m was added to it. The mixture was placed in a ball mill and milled 20 hours after which it was diluted witn additional solvent and spray dried into a drying tower to form a particulate resist composition, having a melt index of 26 and Tg of 30~, that was collected at the bottom of the chamber. The resulting powder was treated with 0.25 parts per hundred by weight with Tullanox~ 500 silica purchased from Tulco, Inc. The toner has an average particle size of 19 microns and was a free flowing powder.
The toner powder was placed in the toning box of the printing apparatus of Figs. 1 and 2 and used according to that process to prepare printed resists on copper circuit board substrates. ~he temperature required to transfer the toner satis-factorily was determined by maklng successive trials 3S at increasing temperature settings. Two temperatures were determined - the value at which essentially com-plete tac.~ transfer was achieved and the value for ~1~8~7~36 full melt coalescence transfer. The tack transrer was about 85C and the melt transfer about 105C.
In contrast, the melt transfer temperature for a toner made from unplasticized Atlac~ 38~ES is about 120C.
5 The resist thickness of a resist of the plasticized toner transferred at 95C was determined to be 0.7 mil. One of the resists that was tack transferred at 85C was reheated at 120C to achieve full coalescence.
The board was electroplated in an acid copper sulfate 10 bath for an hour after being cleaned in an acid ammonium persulfate solution. The resist remained intact throughout this treatment and had essentially no copper nodules indicative of pinholes.
Example 7. A toner sample was prepared by the same 15 procedure as in Example 6 except that the parts by weight of Atlac~ 382ES and triphenyl phosphate were 42.5 and 7.5 respectively and the solvent was acetone alone to reduce the heating temperature required to blow the solvent ~rom the toner particles in the drying 20 chamber. The resulting toner was subsequently treated with 0.25 part/hundred of toner with Tullanox~ 500 as in Example 1 to yield a good, free flowing powder.
Average particle size was measured as about 14.5 -_ micrometers.
The toning and printing characteristics of this toner were determined as in Example 6. Greater than 90% tack transfer occurred at 70C and melt transfer at about 95C. This result is about 25C
lower than that for pure Atlac~ and 10C lower than 30 ~hat-o~ the toner of--Example 6. ~ _ _ ExamPle 8. A toner ~ased on Atlac~ 382ES resin was prepared in the same manner as in Example 6 but the plasticizer was dioctyl phthalate. The composition was 46 parts resin, 4 parts dioctyl phthalate and 50 35 parts Fe304 and had a melt index of about 28 and Tg of about 33C. This toner was applied to the magnetlc 8t7~6 - master film by the wet slurry procedure of Example 4 and test printed as described in the previous examples.
Good tack transfer was achieved at 105-110C in agree-ment with the results obtained with triphenyl phosphate.
5 The transfer temperature was slightly higher ~ecause of the lower plasticizer concentration. A printed resist was subjected to the same plating procedure as in Example 6. ~he resist retained its excellent adhesion, permitting plating to occur only on the 10 exposed circuit lines.
Example 9(Control). A toner was formed by the procedure of Example 7 using cellulose acetate butyrate, type 55i-02, having a molecular weight of 25,000 and Tg of 101C, purchasable from Eastman Kodak. The compo-15 sition was 50 parts resin and 50 parts Fe304. Thistoner was used in the manner of Example 8 and test printing was undertaken at successively higher temper-atures, but even at 13SC only a portion of the toner transferred to the circuit board and this material was 20 dusty and had little or no tack. Temperatures above 135C are higher than desired for economy reasons and also present a r~sk of demagnetizing the latent magnetic image if CrO2 magnetic film is used.
Some higher board temperature can be used since the 25 toner acts as a slight thermal shield and will prevent overheating of the film if the contact time is momentary and the temperature differential is low. Thus, toners with resins such as unmodified cellulose acetate butyrate which have high softening 30 points are difficult to print into satisfactory resists.
Example 10. A cellulose acetate butyrate-based toner was formed as in Example 7 using dioctyl phthalate plasticizer to have a Tg of about 70C and melt lndex 35 increased to be greater than 1. The proportions were , 8'786 43 parts cellulose butyrate, grade 551-02, 7 parts dioctyl phthalate and 50 parts Fe304. 2rinting tests showed good tack transfer at 100-105C and melt transfer at 120-127C. Thus, transfer temperatures 5 were greatly reduced from those of Example 9 in which no useful printing was obtained with unplasticized toner.
One of the boards tack-transferred at 115C was post-print consolidated by reheating and both it and a board melt transfer-printed at 125C were plated 10 as in Example 1. Both boards showed excellent resistance to plating baths and very few copper nodules.
Example 11. A toner similar to that of Example 10 was prepared with triphenyl phosphate as plasticizer to have a Tg and melt index similar to that of Example 15 10. The formulation was 42 parts cellulose acetate butyrate, type 551-02, 8 parts triphenyl phosphate and 50 parts Fe304. This toner was test printed after toning the Cr02 film by the wet slurry procedure as previously described. Excellent tack transfer occurred 20 a~ 110C and the melt transfer point was 120-125C, in agreement with the results of Example 10. A circuit board formed by tack transfer at 110C and consolidated by reheating 2 min at 135C and a board formed by melt transfer printing at 125C were copper plated as pre-25 viously described. The resist had excellent adhesionretention and very few pinholes as judged by copper nodules. --Example 12. This example is illustrative of the effect of plasticizer on the transfer window of a toner. Two 30 toners were prepared using the resin described in Example 2. The first consisted of 50 parts resin/50 parts Fe304. The second was 45 parts resin/5 parts triphenyl phosphate/50 parts Fe304. Transfer tests were carried out using the printing system described in 35 Example 1 and heating the circuit board substrates to 8~786 successively higher temperatures. The transferred images were studied for tack and melt transfer character-istics. In this experiment,the unplastlcized toner was judged to ha~e an acceptable degree of tack transfer S temperature at 112-115C and a melt transfer temperature of about 12Q-123C. At 125C, some sticking of toner to the printing member was occurring. Thus, the transfer window was approximately 10C.
In tests with the plasticized toner sample under similar test conditions, tack transfer was occur-ring at 70-75C and melt transfer at 90-100C. Thus, the transfer window had widened to about 20C or more and the useful temperature range was lowered by 20-30C.
Example 13. A toner was prepared from a mixture of an lS acrylic resin, plasticizer and iron oxide in the fol-lowing manner. The acrylic resin was first prepared by copolymerizing a mixture of methyl methacrylate, ethyl acrylate and methacrylic acid in the ratio of S9, 35, 6 parts by weight. Three parts n-octyl thiol were added to control molecular weight. The monomer solution was added over a 1 hr period to a stirred aqueous polymerization medium containing a surfactant (Duponol~ C "Lorol" sulfate) and ammonium persulfate initiator at 85-90C to yield an acrylic hydrosol which was then partially neutralized with ammonium hydroxide to ~tabilize it. The finished hydrosol contained about 35 parts by weight acrylic resin.
A portion of the acrylic hydrosol was mixed with magnetic iron oxide (grade ~O 7029 purchased from Pfizer Chem. Co.) and aromatic sulfonamide plasticizer (Santicize~ 8) so that the ratio of resin, plasticizer and Fe304 was in the proportion 45, i, iO parts by weight. Additional water was added to make a fluid slurry and the entire mixture was bail-milled o~ernight to ensure a smooth slurry. Following final adjustment tf~ d e,~orlC

'7~3~

of slurry viscosity, the material was spray dried into a drying chamber to yield a toner similar to that of Example 6 in particle size and having a melt index of 7.7 and Tg of 21C. The fluid powder was stabilized S by dry-mixins it wi-th 0.3 part by weight of powdered silica (Tullanox3 500).
This toner was tested for resist printing as in the previous examples. Excellent tack transfer occurred at 80-90C. In other tests, substantial 10 coalescence during printing occurred at 100-110C.
Example 14. A toner was prepared by plasticizing a styrene-maleic anhydride resin (SMA~ 1440, purchased from Ar~o Chem. Co.) having a molecular weight of 1450 with acrylic resins and cinnamic acid and com-lS bining the mixture with iron oxide. The proportionsof materials by weight were: SMA~ 1440, 32 parts;
Carboset~ 514 (Goodrich) styrene/acrylic acid copolymer having a molecular weight of about 30,000 as thermoplastic resins, 8 parts; Carboset~ 515 20 (Goodrich) styrene/acrylic acid copolymer as the plasticizer--rIlquldl~, 8 parts;-~innamic acid, 2 parts;
Fe304, 50 parts. The materials were combined and milled on a 2-roll mill to achieve uniform mixing.
This blend was subsequently powdered by chopping and 25 then passing it through an air micronizer to achieve a small particle size. Finally, the powder was blown into a spray-drying chamber at a temperature designed just to melt and spherudize the particles. The resultant material was a toner that had a Tg of about 30 30C and, when combined with Tullanox~ 500, was a free-flowing powder at room temperature.
In test printing, this toner showed good tac~ transfer at 85-90C with coalescence becoming evident by 100-115C. In contrast, unplasticized 35 toner from S~A~ 1440 and Fe304 did not exhibit any tac~-trans~er characteristics below 130-135C.

The resist com?ositions or ~xamples 13 ~nd 14 a-e ~oth soiuDle in dilute aqueous ammonia (about 2% concentration) at ordinary room temperature.
As many apF2rently -~idely di~ erent em-; hodiments of this invention m2y ~e made withoutdeparting from the s?irit and sco?e thereof, it is to be understood that this invention is not limited to the specific embodlments thereo except as de-fined in the appended claims.
This application is a division of copending Canadian Application Serial No. 324 358, filed March 28, 1979.

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A dry particulate resist composition of particles having an average size of 1 to 30 µm, a melt index of from 1 to 100 and a glass transition tempera-ture from 25°C to 100°C, for substantially instantaneous application to a heated surface to form a resist image capable of withstanding modification of an exposed area of said surface, comprising (a) a coalescible binder consisting essentially of a thermoplastic resin having a weight average molecular weight of at least 1,000 and less than 50,000 and 2 to 40% of plasticizer based on the weight of said binder, said plasticizer having a boiling point above 200°C, and (b) magnetic material having an average particle size of less than 6 µm present in said binder rendering the particles of said composition magnetically attract-able, said magnetic material constituting from 40 to 80%
by weight of the combination of (a) plus (b) and said binder constituting the remainder, the combination of said binder and said magnetic material in said particles rendering them substantially non-blocking at ordinary room temperature and adherent to said surface and coalescible thereon upon said application to said surface to form a resist image.

2. The resist composition of Claim 1 having a transfer temperature in the range of 50 to 120°C.

3. The resist composition of Claim 1 having a melt index of from 1 to 50.

4. The resist composition of Claim 1 having a glass transition temperature of from 25 to 80°C.

5. The resist composition of Claim 1 wherein said binder is soluble or swellable in methylene chloride or aqueous alkali at ordinary room temperature.

6. The resist composition of Claim 1 wherein said magnetic material is substantially non-porous and isometric in particle shape having an average particle size of 0.1 to 1 µm.

7. The resist composition of Claim 1 wherein said magnetic material is a non-conductor of electricity.

8. The resist composition of Claim 1 wherein said thermoplastic resin has a molecular weight which gives it Newtonian flow character.

9. The resist composition of Claim 1 wherein said thermoplastic resin is polyester.

10. The resist composition of Claim 1 wherein said thermoplastic resin is an acrylic polymer.

11. The resist composition of Claim 10 wherein said resin has an acid number of at least 25.

12. A dry resist composition of particles having an average particle size of 1 to 30 µm, and comprising 35 to 65% by weight of coalescible binder component and 45 to 65% by weight based on the weight of the composition of magnetic material having an aver-age particle size up to 6 µm present in said particles, said binder component composed of thermoplastic poly-ester resin and 5 to 15% by weight of plasticizer for said resin based on the total weight of said binder com-ponent, said composition being non-blocking at ordinary room temperature and resistant to aqueous FeC13 etchant and having a melt index of 2 to 100, glass transition temperature of 25 to 110°C and tack transfer temperature of 50 to 110°C and tack transfer window of at least 20°C
said resin having a weight average molecular weight of 1,000 to 50,000 and being adherent to copper at said tack transfer temperature.