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Патент USA US3089961

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May 14, 1963
T. G. WARTMAN ETAL
3,089,952
METHOD AND MEANS FOR THERMOGRAPHIC REPRODUCTION
Filed Jan. 21. 1960
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3,689,952
Patented May 14, 1963
1
2
3,089,952
original and copy-paper but without making any visible
change in the heat-sensitive layer. The composite is then
allowed to pass before the lamp 12, here shown to com
prise a coiled ?lament 17 located along the interior focal
METHUD AND MEANS FOR TI-ERMOGRAPHIQJ
REPRGDUCTIGN
Thomas G. Wartman, Mendota Heights, and Edward A.
G’Mara, Mapiewood, Minn, assignors to Minnesota
Mining and Manufacturing Company, St. Paul, Minn,
a corporation of Delaware
Fiied .Ian. 21, 1960, Ser. No. 3,755
7 Claims. (Cl. 250-65)
This invention relates to the thermographic reproduc
tion on heat-sensitive copy-paper of differentially radia
tion-absorptive graphic originals.
Thermographic reproduction processes are known in
which a differentially radiation-absorptive graphic orig
inal, such for example as a printed page, is brie?y in
tensely irradiated While in heat-conductive pressure-con
tact with a heat-sensitive copy-sheet. The selective ab
sorption of radiant energy at the inked image areas re
sults in the establishing of a corresponding heat-pattern
at the graphic surface which, transmitted to the heat
sensitive layer, produces a visible change.
The required pressure-contact between printed original
and heat-sensitive copy-sheet may be provided by press
ing the two together, for example between a transparent
line of a re?ector 18 having a truncated elliptical cross
sectiou. A suitable lamp having a ?lament ten inches in
length may draw 1350 watts at 280 volts and provide a
color temperature of about 2800° K. The composite
is so guided that the exterior focal line of the re?ector
10 falls at the printed surface of ‘the original, which is there
fore brie?y intensely irradiated as the composite passes
the lamp 12. The thus treated composite 19 is then di
rected by guide 20 to a receptacle 21. After cooling, the
copy is separated from the original by hand stripping.
The copy-sheet separates cleanly, leaving no observable
deposit on the surface of the original. The copy is a
direct positive reproduction of the graphic original.
The same effect is obtainable by ?rst combining the
original and copy-sheet, and then separately irradiating
the composite. Typical procedures involve ?rst pressing
the two sheets together between heated metal plates, or
between a heated smooth metal roll and a compressible
roll pressed thereagainst, and thereafter exposing the ad
herently held composite to brief intense irradiation from
a progressively advancing linear source or a wide-area
panel and a resilient compression cover or between a
?ash source or otherwise.
transparent ?exible carrier belt and a revolving smooth
copy-sheet and original during irradiation is held ?rmly
together, with the elements in heat-conductive contact,
rigid roll, during irradiation. The radiation must then
pass through the transparent panel or belt in order to
impinge on the inked surface of the original. High unit
pressure during irradiation is required in order to assure
uniform transfer of heat from inked image areas to the
heat-sensitive layer, particularly at fold or crease lines.
The necessity for transparent panels or belts which ade
quately transmit the high intensity irradiation While effec
tively resisting the severe stresses occasioned by the high
In all cases the composite of
by internal adhesion rather than by externally applied
pressure.
Clear distinct copies are obtained by using a light
source of adequate intensity and applying the radiation
for a sufficiently brief interval. The requirements vary
with the weight of paper, the ambient temperature, and
various other factors. In general, best results are at
tained in the copying of originals typewritten on bond
contact pressures has, prior to the present invention,
severely restricted the ‘designer of therrnographic copy
ing apparatus.
The present invention avoids the just-described restric
tions and provides improved methods for accomplishing
effective thermographic reproduction of typewritten,
printed and other graphic originals with simpli?ed appa
paper by employing a high intensity gas ?ash lamp rather
ratus and employing novel heat-sensitive copy-paper, all
extremely brief high intensity ?ash obtained from such
as hereinafter described and illustrated.
than a hot ?lament source as heerinbefore described.
Such a lamp may consist of a glass tube about ten inches
long ?lled with xenon or other inert gas under reduced
pressure and having an electrode at each end connected
across an energy storage bank providing a 500 watt
second discharge at a potential of 2600 volts DC. The
45 a lamp minimizes or eliminates the small amount of
In the drawing,
blurring obtained on copies of such originals prepared
FIGURE 1 is a schematic representation of one illus
using a hot ?lament source of radiation, the latter being
better adapted for copying from originals or on copy
sheets having a heavier weight base stock.
trative form of copying apparatus as applied to the
thermographic reproduction of graphic originals, and
FIGURE 2 represents a type of heat-sensitive copy
FIGURE 2 is a sectional representation of a typical 50
sheet which has been found particularly effective in the
sheet of heat-sensitive copy-paper as employed with the
procedures here described. It consists of a transparent
apparatus of FIGURE 1.
carrier or backing web 22, a heat-sensitive layer 23 con
The apparatus of FIGURE 1 consists essentially of
taining at least two visibly interreactive components 24
a roll It) and a heated pressure platen II, in combination
with a lamp source 12 of intense radiant energy, and 55 and 25 in uniformly dispersed- state, and a thin, opaque,
along with suitable frame, power supply, control, and
normally tack-free, heat-activata‘ble surface coating 26.
As a speci?c illustrative example, the copy-sheet of
other elements as required. An ordinary household
FIGURE 2 is prepared with map overlay tracing paper,
mangle or ironing machine provides an effective combi
having a basis Weight of 25 lbs. per ream, as the carrier
nation of roll and platen.
In operation, a heat-sensitive copy-sheet 13 and a 60 web 22. The heat-sensitive layer contains ferric stearate
graphic original 14 are congruently assembled, for ex
particles and methyl gallate particles uniformly distributed
ample on a work-table 15, and are then passed between
the roll 10 and the heated shoe 11 under pressure sup
inert ?lm-forming binder. The combination forms a visi
plied by spring 16. Temperature and pressure are suf?
bly heat-sensitive coating which undergoes a distinct and
in a minor proportion of polyvinyl bu-tyral resin as an
cient to cause close smooth adherent contact between 65 immediate change in color when momentarily heated to
3
temperatures of about 200—250° F., e.g. by pressing the
sheet brie?y against a heated metal test bar. The opaque
surface coating contains titanium dioxide pigment in an
ethyl cellulose binder. Structures as thus de?ned have
previously been described; see Clark Patent No. 2,813,043.
In the present structure, however, the ethyl cellulose
binder of the opaque surface coating is signi?cantly modi
(3.
are suitable. Dioctyl phthalate or other suitable plasti
cizers may replace the triphenyl phosphate. The weight
ratios of ?lm-forming binder, plasticizer, and additives
may be varied widely, in accordance with known princi
ples, in obtaining the desired properties. In all cases there
is provided a thin, normally strongly coherent and tack
free, temporary bonding layer which, at an elevated tem
perature somewhat below the copying temperature of the
?ed by the incorporation therein of just su?icient plasti
heat-sensitive copy-sheet, is activated to a pressure-tacky
cizer material, for example triphenyl phosphate, to render
the coating moderately tacky at temperatures slightly be 10 condition in which it readily lightly adheres under mod
low the temperature at which visible reaction occurs while
still being completely non-tacky at normal room tempera
ture. Thus, a speci?c coating contains 166 parts by
weight of titanium dioxide, 100 parts of ethyl cellulose,
and 134 parts of triphenyl phosphate.
The thin surface coating just described is adequately
tacky at temperatures of the order of 150° F. to pro
vide an effective adherent bond to paper surfaces pressed
thereagainst; and this bond is maintained as the com
posite is cooled. Separation of the sheets of the com
posite at the higher temperature results in splitting of
the tacky layer and leaves a residue on the surface of
the original. However it is found that, on ?rst cooling
to normal room temperature, the material increases suffi
ciently in cohesive strength so that the original and copy 25
sheet may be stripped apart without any splitting or
transfer of the resinous layer and without any degrada
tion of the printed surface.
The incorporation of the heat-activatable layer as a
component of the copy-sheet itself, as just described in
connection with FZGURE 2, is preferred, particularly
in connection with front-printing techniques employing
radiation-transmissive heat-i ensitive copy-paper having a
visibly opaque protective surface coating. The surface
coating itself serves as the heat-aetivatable layer. The
coating may be held at minimum thickness. However it
is possible to obtain effective copies by applying the thin
heat-activatable coating to the graphic original and then
temporarily adherently attaching thereto a heat-sensitive
copy-sheet free of such coating. With the coating ap
plied over the printed surface, and used with radiation
transmissive copy-sheets, the system is suitable for mul
tiple copying by front-printing. The invention is also
applicable to back-printing, in which the heat-sensitive
erate pressure to paper and analogous surfaces.
With
such component the temporary assembling of the copy
sheet and graphic original in close heat-conductive asso
ciation in a self-bonded composite becomes possible; and
thermographic reproduction of the original on the copy~
sheet is then easily achieved in the absence of continuous
mechanically induced pressure-contact.
What is claimed is as follows:
1. Method for the thermographic reproduction of a
graphic original, differentially absorptive of radiant
energy, on a heat-sensitive copy-sheet, comprising: releas
ably adherently bonding together said copy-sheet and
said original as a multi-ply composite; irradiating said
composite with said radiant energy for a time and at an
intensity su?icient to cause reproduction of said original
on said copy-sheet; and stripping said copy-sheet from
said original.
2. Method for the thermographic reproduction on a
heat-sensitive copy-sheet of a graphic original having
image and background areas differentially absorptive of
radiant energy, comprising: releasably adherently bond
ing said copy-sheet and said original together in heat
condnctive contact with a heat-activatable thin bonding
layer non-tacky at room temperature and with said image
and background areas in position for irradiation; irradi
ating said areas with said radiant energy for a time and
at an intensity su?icient to cause reproduction of said
original on said copy—sheet; and stripping said copy
sheet from said original.
3. Method for the therrnographic reproduction on a
heat-sensitive copy-sheet of a graphic original, said copy
sheet including a visibly heat-sensitive layer and a heat
activa-table surface coating non-tacky at normal room tem
perature and said original having image and background
areas differentially absorptive of radiant energy, said
copy-sheet is temporarily adhered to the rear surface of
a thin printed original during brief intense irradiation of
the printed front surface. Tissue ‘paper or other thin
web impregnated or coated on both surfaces with the heat
method comprising: placing said copy-sheet with its said
coating in contact with said graphic original and brie?y
activatable material is useful in providing the required
temporary adherence between copy-sheet and original in
either the front-printing or the back~printing position; but
to a lightly tacky condition but insufficient to cause a
visible change in said heat-sensitive layer; irradiating said
the use of such tissues involves additional time and ex
original with said radiant energy for a time and at an
pressing the two into close heat-conductive contact at an
elevated temperature sui?cient ‘to activate said coating
pense in preparing the composite for copying, and has a
intensity suf?cient to cause reproduction of said original
tendency to cause blurring of image areas in the copy,
on said copy-sheet; and stripping said copy-sheet from
and accordingly is not preferred.
said original.
Partially or fully radiation-absorptive copy-sheets ap 55
4. The method of claim 3 in which the copy-sheet is
propriately releasably adherently bonded to differentially
radiation-transmissive or -re?ective graphic originals like
wise provide useful composites for copying by shadow
releasably adherently bonded to the rear surface of a
thin graphic original having said image and background
areas on the front surface.
or re?ex techniques using gas ?ash radiation somewhat
5. The method of claim 3 in which the copy-sheet is
60
as described in Miller et al. US. 2,844,733 and in Kuhr
transmissive of said radiant energy and is releasably ad
meyer et al. US. 2,919,349. However these techniques
herently bonded to the front surface of said graphic
do not ordinarily have the same rigid requirements of
original.
close contact between copy-sheet and original as do the
6. A heat-sensitive copy-sheet useful in the thermo
more conventional front-printing or back-printing proc 65
esses.
graphic reproduction of graphic originals by the method
herein described and including a chemically reactive,
visibly heat-sensitive layer, the chemical reaction occur
ring within said layer on heating said sheet being respon
sible
for the visible change, and a heat-activatable surface
omitted where desired, or may be replaced by other suit 70
coating non-tacky and highly internally cohesive at nor
able pigments, ?llers, or other additives. Likewise the
mal room temperature while being sufficiently tacky, at an
speci?c binder and plasticizer components may be widely
elevated temperature insufficient to cause said visible
varied so long as the resultant blend meets the require
The speci?c heat-activatable coating or ‘layer hereinbe
fore described contains a large proportion of pigment to
provide opacity and contrast, but this component may be
ments herein set forth. Other cellulose ethers and esters,
various vinyl polymers, and many natural gums or resins
change, to form a releasable adherent bond with a ?rm
paper surface on brief pressure-contact therewith, and
3,089,952
5
6
said coating comprising an ‘organic polymer and a plasti
cizer therefor.
References Cited in the ?le of this patent
UNITED STATES PATENTS
7. A heat~sensitive copy-sheet including a thin ?exible
carrier web, a visibly heat-sensitive layer capable of un
dergoing a rapid permanent visible change on heating to a
minimum conversion temperature, and a plasticized or
ganic polymer surface coating non-tacky and highly in
ternally cohesive at normal room temperature and heat
activatable at an elevated temperature less than said mini
mum conversion temperature to a degree of tackiness 10
sufficient to form a releasable adherent bond with a ?rm
paper surface ‘on brief pressure-contact therewith.
2,503,758
2,616,961
2,663,654
2,813,043
2,891,165
2,927,210
Murray _____________ __ Apr. 11, 1950
Groak ______________ .._ Nov. 4, 1952
Miller et a1. _________ __ Dec. 22, 1953
Clark ______________ __ Nov. 12, 1957
Kuhrmeyer et a1. _____ __ June 16, 1959
O’Mara ____________ __ Mar.
1,
1960
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