Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
we ~~mo rcric~~roo3si
This inventiaat is directed to a touch-readable product having raised,
printed characters such as Braille dots, and to a sereen~ printing process for
the manufactiwe thereof.
The use of tactile-readable patterns has wide application primarily at
present in the use, by sight impaired or blind people, of Braille characters.
These
characters each comprise a particular arrangement of raised dots, which are
generally imprinted out of a planar paper or cardboard medium by embossment.
The embossing process is both slow and expensive.
As an alternative to cmbossment, the use of thermography, does not
appear to be successful, presumably on a basis of the high costs involved, and
other possible technical problems.
In efforts to achieve lower cost, touch-readable products, many attempts
have been made on the basis of silk-screen printing, without however achieving
at an acceptable cost characters of sufficient prominence to enable tactile
distinction thereof.
In some previous, experimental work in this field in which I participated,
a flat bed screen was used in cooperation with an underlying stationary
planar sheet upon which the ink was deposited. It was found that with this
arrangement the speed of application was insuffcient, leading to slumping so
that
a satisfactory economic result and an acceptable standard of readability could
not
be achieved. Also, in using the flat bed method of screening the maximum
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rate of production that could be achieved was in the range of
150 to 200 sheets per hour, which is highly uneconomical, and
cost inefficient. This method is fully described in PCT
WO/9400301 listed below.
In case of known prior art, this includes the following
patents:
PCT WO 94/00301 published January 6, 1994
PCT Norway No. 8700038, April 20, 1987
PCT Netherlands No. 8200045, December 15, 1982
PCT Europe No. 8800548, June 22, 1988
U.S. Patent No. 2,616,198, H.P. Sewell, November 4, 1952
U.S. Patent No. 3,372,638, K.F. Tripp, March 12, 1968
U.S. Patent No. 3,432,328, Vaurio, March 11, 1969
U.S. Patent No. 3,442,207, W.E. Johnson, May 6, 1969
U.S. Patent No. 3,924,019, Jacob, December 2, 1975
U.S. Patent No. 3,987,725, Scantlin, October 26, 1976
U.S. Patent No. 4,571,190, Zagler et al., February 18, 1986
U.S. Patent No. 5,046,415, Oates, September 10, 1991
British Patent No. 827003, January 3, 1958
Japanese Patent No. 83786929
I have found that a large demand exists for touch
readable texts, such as short communications and labels, at an
economic price.
The invention provides a machine article having a
relatively brief, touch-readable message comprising at
least one Braille pattern of spaced-apart, raised dots
on a surface of said article, the raised dots comprising
a cured ink of a type which remains substantially unshrunk
upon curing and which is substantially colourless and
having a height above said surface of at
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least six points and substantially less than nineteen points
and a dot diameter in excess of 1.45mm (0.057 inches). Spacing
between dots within a given character cell exceeds the United
States Congressional Standard Braille dimension for center to
center intra-cell dot spacing and is at least 2.34 mm (0.092
inch). Center to center spacing between corresponding dots of
adjacent character cells exceeds the United States
Congressional Standard Braille dimension for such intercell
dot spacing and is at least 6.22 mm (0.245 inch). The
relatively brief message formed from these raised, Braille
pattern ink dots is readily readable by a Braille reader of
moderate skill.
Also, I have discovered that the standard for Braille
printing established by American Library of Congress of the
United States is unduly high, particularly with regard to the
height of the dots used in the Braille characters, and that
less prominent dots may be provided, economically, using high
viscosity inks and a machine printer, which are touch
readable.
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WO 96J413Ie PC:TIoCA9610~Ci81
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I have found, by using a rotary machine upon which the paper or other
print medium is carried, in combinati~ with a superposed planar s~
im~nted with the desired cherac~s, that a su~cientiy high viscosity, UN ink
can be applied the saneea in a thickness which is adoquate to achieving
a readable Braille-reading standard, and which can be relatively rapidly
cured.
To achieve a Braille-reading capability requires both height and definition
(i.e. prominence or "sharpness"), while achieving sufficiently high rates of
production to prove economically viable.
The stipul~d standard far Braille cheta~Cters, as defined in the Library of
Congress for the United States of America requires "dots" having a height of
0.019 inches ( 19 Poirds, or 0.4826 mm) and having a diameter at their base of
0.457 inches ( 1.4478 mm).
IS
A hemispherical dot is considered by Braille technicians to be ideal, in
terms of touch-readability.
The associated standard Braille requirements are:
dot spacing, centre to cer~re is 0.092 inches: the space between
dots of adjaaoent "ceps" (characters) is 0.245 inches (centre to dot
centre); the line spacing (between adjacent dots) is 0.4 inches.
While the Library of Congress Braille specification is desirable far
continuous reading so as to minimize strain and fatigue of the reader, I have
found that a reduced standard, as low as 6 points in height may be
successfully
adopted in instances of brief use, where a protracted reading effort is g~
required.
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Thus, in instances such as p veering cards or labels, a reduced height of
Braille is found to be readable. I have found the range 6 Points and above to
be '
readable.
In compensation for the reduced height of these touch-readable patterns,
r have found, in the case of Braille, that increasing the diameter of the
dots, and
increasing both the spacing between individual dots of a Braille character,
and
the distance between adjacent characters and between lines of characters, has
facilitated and enabled the reading of the characters, even by a "learner"
group
of Braille readers.
In the case of a cylinder machine, the cylinder of the machine revolves
about a fixed axis at a predetermined rate, and picks up a blank sheet that is
to be
imprinted, at each half revohrtion. The bed upon which the screen is carried
is located over the cylinder. The bed is substantially planar and oscillates
in
synchronism with the linear speed of the blank sheet, such that the instant
highest
portion, i.e. the line of apogee of the sheet, underlies and is in momentary
synchronism with the travelling screen, which is spaced a predetermined
selected, adjustable distance above the sheet.
A pool of ink located upon the upper surface of the seen ~ ~~
up by a squeegee to form an ink concentration located over the line of apogee,
so that the ink flows down through the interstices of the screen and onto 'the
sheet.
In operation the squeegee deflects the screen
downwardly by up to about 1/8 inch.
WO 961~t1320 PGT~CA96A0381
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I have found with use of this arc~ungement and a high viscosity ink, that
su~cient ink is dtbrougb. the screen onto the paper or other medium to
achieve dots of sufficient height to achieve reliable touch-readability.
By using an inclined somewhat soft squeeg~ atmnged in converging
relation with the direction of screen travel, a downward flow component is
applied to the ink flood, to achieve a high rate of ink displacement through
the
scxeers. An outwardly conve~c radius of the squeegee, at the point of contact
with the screen, appears to enhance the "pumping" effect of the squeegee on
the
ink pool. The effectiveness of the squeegee is also a function of its soRness.
While a screen such as 110 mesh has been used successfully, coarsar mesh
screens in the range 90 mesh and ranging down to 64 mesh appear to be
successful. The coarser mesh screens best suited to rotary presses.
It appears that in operation the sheet apogee zone, in contacting relatims
with the underside of the scr~, is effectively sealed from the atmosphere, by
way of the ink filled open interstice of the screen, and by the adjoining
photo-
emulsion sealed scxeen portions, such that the rotation of the cylinder
creates a
divergent, wedge-shaped zone, and serves to generate a downward inductive
pumping actions so as to supplement the downward flow of the ink from the poo!
onto the print medium.
Rotation of the cylinder moves the sheet downwardly away from the
:25 underface of the screen, possibly drawing down a further amount of the ink
through the related screen interstices. At the same time, the related portions
of
the respective ink colunuss that remain resident in the silk screen at the
time of
separation from the deposited ink column portions exert an upward component
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WO 96/41320 PCT/CA96/00381
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of tensional force on the conjoined ink column portions deposited upon and
adhering to the sheet, due to the surface tension and viscosity effect of the
ink.
The moving sheet with its lines of deposited ink character portions is subject
to
centrifugal force, due to the rotation of the drum, which also tends to limit
or
S preclude slumping of the deposited ink portions that form the characters.
In the case of Braille characters, the individual dots are thus precipitated
approximately as hemispheres, and the U/V drying process is sufficiently rapid
that this condition of the dots is substantially maintained, and made
permanent.
Location of the U/Vcuring station in close proximity to the off going side
of the cylinder serves to shorten the lapsed time in which curing or "drying"
of
the ink is effected, thereby minimizing the time available for adverse
slumping
of the deposited ink to occur.
Thus, the present invention provides a medium imprinted with a raised
pattern of predetermined prominence and definition to provide a desired degree
of tactile recognition, using a high viscosity U/V (ultra-violet) curable ink,
applied to the medium on a rotational machine.
It is contemplated that a rotary press which operates on the same dynamic
principles, with the ink and squeegee located within the perimeter of a
rotatable,
photo imprinted wire screen may also be used in order to achieve readable
Braille
characters.
The subject process may be used to produce Braille characters upon a
substrata, such as paper, mylar etc.
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WO 96/41320 PCT/CA96/00381
It is preferable in carrying out the subject process, that the paper or
' cardboard be of sufficiently high gloss to minimize absorption of the ink
deposits
into the surface of the medium. A paper having a porous surface leads to an
undersireably high level of absorption of the ink therein.
In order to ensure effective ink adherance on the surface of the medium
a corona-treated stock or coated paper may be used.
In the case of the ink, where localized ink depositions such as Braille
"dots" are required, it is believed to be important to avoid the presence of
large
air bubbles in the ink, so that in some instances the use of a defoaming agent
may
promote the quality and density of the final tactile "image". However, the use
of
a puffing agent and the presence of minute bubbles helps maintain the height
of
the dots.
The invention thus provides a printed surface having a precise,
predetermined raised pattern thereon wherein the ink from which the pattern is
formed is a high viscosity ink that is applied by the steps of depositing ink
upon
a screen having an ink permeable pattern in accordance with the aforesaid
pattern; passing a surface medium to be imprinted towards a line of apogee in
predetermined relation beneath the underside of the screen, moving the surface
medium in diverging relation from the screen commencing at about the line of
apogee, the medium and the screen being in substantial speed synchronized
relation at the line of apogee whereby ink passing in discrete columns
downwardly through the screen attaches to the surface and medium, and is drawn
downwardly thereby as the screen and medium diverge. The discrete columns
are then separated into an upper portion carried by the screen and a lower
portion
carried by and attached to the surface of the medium, wherein in parting the
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upper portion exerts an upward attractive tensile force upon
the lower portion. It is surmised that the " necking " taking
place as the ink portions separate promotes the ultimate
formation of the highly desirable hemispherical dot shape.
The extent of deposition of the ink may be increased by
the depth of the flood of ink being increased, and may be
enhanced by the provision of a downward flow component by way
of a convergently inclined squeegee. The effectiveness of the
squeegee may be further enhanced by the provision of an
outwardly convex squeegee surface at or adjacent the point of
contact with the screen. The effectiveness of the squeegee is
also influenced by its softness. Squeegees having a low
durometer of 40 are known, and higher durometers may prove
effective.
The motion of the medium in an arcuate outwardly convex
path can then facilitate formation of the lower ink column
portion into a non-slumping substantially hemispherical dot
form upon the medium. Subsequent timely application of U/V
light can forestall adverse slumping and effect curing of the
deposited ink, to provide readable upstanding protrusions of
readable Braille.
In practice, characters in the form of touch-readable
hemispherical Braille dots have been produced by the present
process. These characters are readable by one accustomed to
reading Braille, and even by trainee Braille readers.
In carrying out the process care must be taken to ensure
that adhesion of the characters to the surface of the medium
is adequate to withstand the wear and tear of normal usage.
WO 96141320 PCT03i1
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Certain embodiments of the invention are described, by way of
illustration, without Iimitatiran of the invention d~ereto, other than as set
forth in
the accompanying claims hereof; reference being had to the accompanying
drawings, wherein:
Figure 1 is a plan view of a schematic representation of a sin and
scxeen-frame combination, shaven with the location of a preliminary ink flood
for
carrying out the pt~t invention;
Figure 2 is a sectional view taken at 2-2 of Figure 1;
Figure 3 is a detail showing deposited hemispherical dots upon a medium
or substrate; and
Figure 4 is a schematic cross-section, looking in the cross-machine
direction, showing a portion of a cylinder machine and the silk screen and
frame.
Referring first to Figure 4, a cylinder printing machine 10 has a rotatable
cylinder 12, illustrated as having an apemurd surfacx to which vacuum is
applied, as indicted by the arrows 13. A planar screen bed 14 is mounted
thereabove, for linear oscillation in synchronized relation with the rotation
of the
cylinder 12.
A ~sc~n 16 is min tensi~ed relation upon the bed I4, having
ink supply means 17 mo~n~ted in superposed relation ~ereaver.
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A squeegee 18 serves to localize an ink pool 20 that is deposits ~m-~r the
screen 16, and to depress the screen downwardly.
The heel 19 of the squeegee 18 is downwardly and outwardly convexly
curved, to assist the downward "pumping" action of the squeegee 18 provided by
the angle of inclination "A" from normal.
The sheet of print medium 22, overlies approximately one half of the
, periphery of the cylinder 12 and, is secured by grippers, (not-shown).
Air suction also may be applied through the cylinder shell, for holding the
print medium to the cylinder, as indicated by the air-flow arrows 13, for air
entering through holes 15 in the cylinder 12.
Ultra-violet (UN) curing lamps 24 located over an adjacent portion of a
run-off belt on which the printed sheet is deposited, serve to cure the ink
after
deposition thereof upon the printed sheet 22.
The grippers operate automatically in kaown fashion to pick up a clean
sheet 22 and retain it upon the cylinder 12 until it rotates through the
printing
zone, after which it is released from the cylinder 12, and passes over a
doctor
blade 26 onto a travelling belt, which carries the imprinted sheet to the
adjacent
curing section, having UN lamps 24, after which it is released for inspection
and
packaging.
wo ~u~o pcricai
_11_
While the aforesaid process has been successfully carried out using a
cylinder printing machine, it is contemplated that a rotary press may be
substituted far the cylinder machine.
It has been found that using a cylinder machine 1200 to 1600 sheets per
hour may be pri~od. This in effect reduces the cost per sheet to approximately
one sixth the cost far that produced by the flat 'bed method.
The effective linear printing speed may vary in accordance with the
stif6iess of the stock being used as the print medium. The use of a stii~er
stock
permits effective printing to be achieved at higher speeds.
At a priming rate of 1600 shtets per hour, e~h sheet being of 28 inches
in length, the linear printing sped is about 62 feet per minute.
Tn the case of rotary pritrting machines significantly higher linear speeds
may be achieved.
The process has been found to be speed sensitive, with requisite speed
required in order to effect adequate ink deposition while affording sufficient
time
in the curing scxtion to effect adequate curing
Figure 1 shows the s~ bed 14 having the screen 16 therein, with
circular interstices 16' for the imprinting of raised Braille dots 21.
Figure 2 shows the elements of Figure 1 in side view.
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Figure 3 shows the hemispherical dots 21, deposited in
adhering relation .upon the medium sheet 22.
Preferably the uncured ink used to form the dots using
the aforementioned printing process has a viscosity greater
than 2000 cps.
In one example, colourless ink, identified as J 9318 DC
U/V Clear (Peace and Stevens) having a viscosity of 4500 cps,
(centipoise) used in combination with a 90 mesh screen having
an emulsion Kiwocol Polyplus (B&H Thompson) applied as second
and fourth coats wet upon wet two coats plus two coats, and
one coat on the reverse face, prior to exposure of the
pattern, resulted in a Braille-readable standard of raised
dots. While short term readability at a dot prominence of 6
Points has been established, the achievement of higher dot
prominence is anticipated, using the present process..
It is contemplated that greater thickness of
photosensitive emulsion may be used, such as increasing the
number of coatings to a reasonable, desired extent that is
found practical.
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