Note: Descriptions are shown in the official language in which they were submitted.
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
7B6
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
86
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~
B6
11
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~
12
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
12
13
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
14
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
14
'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.
16
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
17
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
86
18
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
18
't'~
19
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
19
~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
21
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
21
3786
22
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
23
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.
23
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
-
.
24
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
26
B'786
27
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
27
8~Jt~
28
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
28
~trcld~lc~fk
8~36
29
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
29
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
31
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
32
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
33
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
34
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
34
,'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
35-
'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
36
tracler~laf ~<
~1~8'786
37
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.
37
786
_ 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
38
8~7~36
39
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
36
~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
41
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
42
- 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
42
,
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
44-
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
44
'7~3~
- 45
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.
786
46
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.
