FIELD OF THE INVENTION
The present invention relates to tissue paper having printed indicia
BACKGROUND OF THE INVENTION
Tissue paper is well known in the art. Tissue paper is used as facial
tissue, bath tissue, paper toweling, napkins, place mats, etc. The tissue paper
may be provided with indicia for either aesthetic or functional purposes. Indicia
may also be applied to paper plates. Typically the indicia are printed.
Consumers react positively to aesthetically pleasing indicia. Printed
indicia have evolved from line printing to process printing, evoking positive consumer
response. However, current process printing, without more, is not, sufficient to
render high fidelity indicia on tissue substrates. High fidelity printing is necessary
to reproduce, with fidelity, indicia corresponding to the source of the indicia.
In the prior art, the source of the indicia has typically been artwork. Artwork
is authored by an artist, may optionally correspond to a theme which is desirable
to the consumer, and is commercially available from several vendors.
More recently photographs have been used as the source of the indicia.
Photographs may be taken of landscapes, scenery, or even of artwork. Photographic
sources of indicia comprising individual elements such as animals, flowers, etc.
may be particularly desirable to consumers. Photographs comprise images which are
reproduced digitally, including scanning, otherwise electronically, or chemically
onto a film. It is not critical how the photograph is reproduced, only that it be
reproducible to a tangible medium of expression.
However, high fidelity printing of indicia taken from a photographic
source presents special challenges. If several parameters are not properly adjusted,
the indicia will not have enough fidelity to appear realistic.
Recently, one vendor of commercial printing equipment executed quality
printing on a tissue substrate. However, the substrate was apparently conventionally
dried on a press felt. Printing high fidelity indicia on a conventionally dried
substrate is relatively easy task because such a substrate is smooth. But consumers
often desire through air dried substrates, which are textured. However, printing
high fidelity indicia on a textured substrate is more difficult due to the rugosities
and asperities inherent in the substrate.
Successful printing of high fidelity indicia on a textured substrate
does not directly translate from experiences printing such indicia on a smooth substrate.
Several complications occur. For example, textured through air dried substrates
are typically more absorbent. This increased absorbency results in dot gain, causing
dots of ink to run together, blurring the image represented by the indicia. The
dot gain may be accommodated by decreasing the amount of ink used to print the indicia.
However, a uniform downward adjustment of all colors will result in indicia having
a muddy appearance or even a faded and washed out appearance, if enough color is
removed. Such adjustments can either be done electronically with software or by
adding less ink to the printing roll.
Compensating for dot gain on a tissue paper substrate is made particularly
difficult by the nonlinear response of the dot gain as a function of the amount
of area collectively covered by the dots. Referring to Fig. 1, it is seen that the
dot gain increases as less area of the tissue paper is desired to be covered. However,
the nonlinear response does not permit easy compensation for the dot gain by decreasing
the amount of ink alone.
Another approach to compensating for the increased absorbency of a
textured substrate is to try color purification. Color purification results from
using fewer primary colors to achieve the desired shade. For example, four color
printing may use magenta, yellow, cyan, and black to produce a spectrum of colors.
Alternatively, four color printing may utilize brown, green, blue and black, provided
red and orange shades are not desired. If one used an evenly reduced mix of the
four process colors to achieve the same shades as was produced using more colors,
less total ink could be applied to the textured substrate. However, color purification,
without more, results in indicia having a faded and washed out appearance.
In yet another approach, one could increase the resolution and decrease
the volume of the anilox roll used to print the indicia if flexographic printing
is used. However, this approach has been shown to result in less than full coverage
of ink occurring where the indicia is desired, and requires higher pigment concentrations
in the ink.
It is clear that there is a need in the art for an improved printing
process, particularly one which yields high fidelity printed indicia on a textured
substrate. There is further a need for such a process which can be used with photographically
sourced indicia. Such a process, and the printed tissue paper produced thereby are
described and claimed below.
The present invention is also applicable to printing on other textured
substrates. For example, textured substrates may be used in packaging to provide
surfaces which are easily gripped by the user. Further, the substrate need not be
cellulosic, if other material properties are desired.
SUMMARY OF THE INVENTION
The invention comprises a process for printing indicia on a textured
substrate and a tissue according to the claims. The indicia have high fidelity to
the original from which they were taken. The process comprises the steps of providing
a textured substrate. The substrate has first and second opposed faces, at least
one of which is textured. A photograph is also provided. The photograph has a first
resolution. A printing roll is provided. The printing roll has a second resolution
which is less than the first resolution. The printing roll has an image thereon.
The image is taken from the photograph. The resolution of the photograph is greater
than or equal to the resolution of the printing roll. Ink is applied to the printing
roll, and then transferred from the printing roll to the substrate. Indicia representative
of the photograph are formed on the substrate and have a specified black level.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- Fig. 1 is a graphical representation of dot gain as a function of the amount
of ink covered by the dots.
- Fig. 2 is a print of a butterfly and flowers according to the present invention,
the print being decomposed into the four colors used for the flexographic printing
process used to make the print.
- Fig. 3 is a print of a butterfly and flowers according to the prior art, the
print being decomposed into the four colors used for the flexographic printing process
used to make the print.
- Figs. 4-5 are flexographically printed indicia according to the present invention
as represented in Examples 1 and 2, respectively.
The present invention comprises tissue paper having high fidelity
indicia printed thereon. The tissue paper is textured, and suitable for a variety
of household tasks, as noted above. The printed indicia are visible to the consumer
and may be provided for aesthetic purposes, whereby the tissue provides a visually
pleasing appearance. Alternatively, the indicia may be functional wherein they provide
instructions for use of the product, relevant data, etc.
Examining the tissue substrate in more detail, the tissue substrate
is textured. By textured, it is meant that the tissue substrate has a physiological
surface smoothness greater than 800 µm, preferably greater than 850 µm, more preferably
greater than 900 µm, and most preferably greater than 1000 µm.
The tissue paper according to the present invention has first and
second opposed surfaces. The tissue paper is considered to meet the limitations
set forth above if either the first, the second, or both of the opposed faces meets
the aforementioned texture values for physiological surface smoothness and has indicia
disposed on at least its face which meets the aforementioned physiological surface
smoothness. It is to be recognized that indicia may also be disposed on the opposite
face of the tissue paper, without regard to whether or not that face meets the aforementioned
physiological surface smoothness limitations.
The tissue according to the present invention preferably has micropeaks,
typically occurring in the machine direction as a result of an optional foreshortening
operation. Foreshortening may be accomplished by wet microcontraction, rush transfer,
or preferably creping. However, it is to be recognized that foreshortening is an
optional operation and need not be performed at all.
A plurality of the micropeaks may have a micropeak height of at least
0.3 and preferably at least 0.6 millimeters. Micropeak height is the amplitude of
the undulations in the tissue taken normal to the base plane of the tissue. Micropeak
height is measured as the distance from the base plane of the tissue to the top
of the micropeak of the tissue. The measurements may be made from digitized images
as is known in the art and illustrated in commonly assigned U.S. Patent No. 5,855,738
and issued Jan. 5, 1999 to Weisman et al. Micropeak width is orthogonal to micropeak
height and represents the lateral extent of the micropeak. Micropeak width is measured
at an elevation coincident one-half of the micropeak height.
The tissue according to the present invention may have a micropeak
frequency of about 3 to 10 micropeaks per centimeter. Micropeak frequency is measured
from digitized images as set forth above and known in the art. A digitized cross-sectional
image of about 40X may be suitably utilized for the aforementioned measurements.
Typically the image covers about 2.0 to 2.8 millimeters of tissue.
For the physiological surface smoothness measurement, a sample of
the tissue paper is selected which avoids wrinkles, tears, perforations, or gross
deviations from macroscopic monoplanarity. The tissue paper, a portion of the sample
on or equivalent to that having printed indicia thereon is tested. The tissue paper
according to the present invention is considered to be textured if either side of
any portion of the tissue paper having printing thereon meets the textured criterion
set forth above, or if a like portion of the same sample juxtaposed with near, adjacent,
or between printed elements meets the textured limitation set forth above. The sample
is conditioned at 22 to 24°C and 48 to 52% relative humidity for at least two hours
prior to testing. The sample is placed on a motorized table and magnetically secured
in place. Either face of the sample may be selected for the measurement, provided
all traces are taken from the same face.
Physiological surface smoothness is obtained by scanning the tissue
paper sample in any direction with a profilometer to obtain the Z-direction displacement
as a function of distance. The Z-direction displacement is converted to an amplitude
versus frequency spectrum by a Fourier Transform. The spectrum is then adjusted
for human tactile response using a series of filters. The peak heights of the filtered
amplitude frequency curve are summed from 0 to 10 cycles per millimeter to give
The tissue paper sample is approximately 100 millimeters x 100 millimeters
in size and mounted on a motorized table. While any suitable table will suffice,
a table with surface tester model KES-FB-4NKES-SE, available from Kato Tech Company
Limited of Koyota, Japan, or a CP3-22-01 DCI Mini Precision table using a NuStep
2C NuLogic Two Axis Stepper Motor Controller in the closed loop control mode have
been found suitable. The table has a constant drive motor which travels at the rate
of 1 millimeter per second. The sample is scanned 30 millimeters in the forward
direction transversely indexed one millimeter, then reversed. Data are collected
from the center 26 millimeters of the scan in both the forward and reverse directions.
The first and last 2 millimeters of each scan are ignored and not used in the calculations.
The profilometer has a probe with a tip radius of 2.54 µm and an applied
force of 0.20 grams. The gauge range is calibrated for a total Z-direction displacement
of 3.5 millimeters. Over the scan distance of the sample, the profilometer senses
the Z-direction displacement of the stylus in millimeters. The output voltage from
the gauge controller is digitized at a rate of at least 20 points per second. Over
the entire 26 millimeter scan range, 512 pairs of time surface height data points
are obtained for both the forward and reverse directions of a scan. The profilometer
is mounted above the sample table such that the surface topography can be measured.
A suitable profilometer is a EMD 4320 WI Vertical Displacement Transducer, having
an EPT 010409 stylus tip, and an EAS 2351 Analog Amplifier. This equipment is obtainable
from Federal Products of Providence, Rhode Island.
The digitized data pairs are imported into a standard statistical
analysis package for further analysis. Suitable software analysis packages included
SAS of Cary, North Carolina, and preferably LabVIEW Instrument Control Software
3.1 available from National Instruments of Austin, Texas. When using the LabVIEW
software, raw data pairs linking surface height and time from the individual scans
are centered about the mean using the Mean.vi analysis tool in the LabVIEW software.
The 512 data points from each of the 16 traces are converted to 16 amplitude spectra
using the Amplitude and Phase Spectrum.vi tool. Each spectrum is then smoothed using
the method described by the PROC Spectra Method of the SAS software. LabVIEW smoothing
filter values of 0.000246, 0.000485, 0.00756, 0.062997, 0.00756, 0.000485, 0.000246
are utilized. The output from this tool is taken as the Amp Spectrum Mag (vrms).
The amplitude data are then adjusted for human tactile response using a series
of frequency filters designed from Verrillo's data on vibrotactile thresholds as
a function of vibration frequency as set forth in the Journal of Acoustical Society
of America, in the article entitled "Effect Of Contactor Area On The Vibrotactile
Threshold", Vol. 35, 1962 (1963). The aforementioned data are reported in a time
domain as cycles per second and converted to the spatial domain in cycles per millimeter.
The conversion factor and filter values are found in the procedure set forth in
the 1991 International Paper Physics Conference, TAPPI Book 1, more particularly
the article entitled "Methods For The Measurement Of The Mechanical Properties Of
Tissue Paper" by Ampulski, et al., and found at page 19, utilizing the specific
procedure set forth at page 22 entitled "Physiological Surface Smoothness". The
response from the filters are set at 0 below the minimum threshold and above the
maximum response frequencies and varies from 0 to 1 therebetween as described by
the aforementioned Ampulski et al. article.
The physiologically adjusted frequency amplitude data are obtained
by multiplying the amplitude spectra described above by the appropriate filter value
at each frequency. A typical amplitude spectrum and filtered amplitude spectrum
are illustrated in Fig. 5 of the aforementioned Ampulski et al. article. The Verrillo-adjusted
frequency amplitude curve is summed point by point between 0 and 10 cycles per millimeter.
This summation is considered to be the physiological surface smoothness. The eight
forward and eight reverse physiological surface smoothness values thus obtained
are then averaged and reported in microns.
Physiological surface smoothness measurements using the SAS software
is described in commonly assigned U.S. Pat Nos. 4,959,125, issued Sept. 25, 1990
to Spendel; 5,059,282, issued Oct. 22, 1991 to Ampulski et al.; 5,855,738, issued
Jan. 5, 1999 to Weisman et al., and 5,980,691, issued Nov. 9, 1999 to Weisman et
The textured tissue paper has first and second opposed surfaces as
noted above. To obtain the texture on either, or both, of the first and second opposed
surfaces, the tissue may be through air dried. Through air dried tissue is disclosed
in commonly assigned U.S. Patent Nos. 4,529,480, issued July 16, 1985 to Trokhan;
4,637,859, issued Jan. 20, 1987 to Trokhan; 5,364,504, issued Nov. 15, 1994 to Smurkoski
et al.; 5,529,664, issued June 25, 1996 to Trokhan et al.; 5,679,222 issued Oct.
21, 1997 to Rasch et al.; 5,714,041 issued Feb. 3, 1998 to Ayers et al.; 5,906,710,
issued May 25, 1999 to Trokhan. Alternatively, the tissue paper may be through air
dried and made as disclosed in U.S. Patent Nos. 5,429,686 issued July 4, 1995 to
Chiu et al. and 5,672,248 issued Sept. 30, 1997 to Wendt et al.
Alternatively, the tissue paper may be textured by providing various
regions of differing basis weights, so that a multi-basis weight tissue paper and
even an apertured tissue paper is presented. Multi-basis weight tissue paper is
disclosed in commonly assigned U.S. Patents Nos. 5,245,025, issued Sept. 14, 1993
to Trokhan et al.; 5,527,428 issued June 18, 1996 to Trokhan et al.; 5,534,326 issued
July 9, 1996 to Trokhan et al.; 5,654,076, issued Aug. 5, 1997 to Trokhan et al.;
5,820,730, issued Oct. 13, 1998 to Phan et al.; 5,277,761, issued Jan. 11, 1994
to Phan et al.; 5,443,691, issued Aug. 22, 1995 to Phan et al.; 5,804,036 issued
Sept. 8, 1998 to Phan et al.; 5,503,715, issued Apr. 2, 1996 to Trokhan et al.;
5,614,061, issued March 25, 1997 to Phan et al.; 5,804,281 issued Sept. 8, 1998
to Phan et al.; and 5,900,122 issued May 4, 1999 to Huston. A nonwoven and apertured
material may be utilized for the substrate as illustrated by commonly assigned U.S.
Pat. No. 5,895,623 iss. Apr. 20, 1999 to Trokhan et al.
Alternatively, the paper may be conventionally dried with a texture
according to commonly assigned U.S. Patent Nos. 5,549,790, issued Aug. 27, 1996
to Phan; 5,556,509, issued Sept. 17, 1996 to Trokhan et al.; 5,580,423, issued Dec.
3, 1996 to Ampulski et al.; 5,609,725, issued Mar. 11, 1997 to Phan; 5,629,052 issued
May 13, 1997 to Trokhan et al.; 5,637,194, issued June 10, 1997 to Ampulski et al.;
5,674,663, issued Oct. 7, 1997 to McFarland et al.; 5,693,187 issued Dec. 2, 1997
to Ampulski et al.; 5,709,775 issued Jan. 20, 1998 to Trokhan et al.; 5,776,307
issued Jul. 7, 1998 to Ampulski et al.; 5,795,440 issued Aug. 18, 1998 to Ampulski
et al.; 5,814,190 issued Sept. 29, 1998 to Phan; 5,817,377 issued October 6, 1998
to Trokhan et al.; 5,846,379 issued Dec. 8, 1998 to Ampulski et al.; 5,855,739 issued
Jan. 5, 1999 to Ampulski et al.; 5,861,082 issued Jan. 19, 1999 to Ampulski et al.,
5,871,887 issued Feb. 16, 1999 to Trokhan et al.; 5,897,745 issued April 27, 1999
to Ampulski, et al.; and 5,904,811 issued May 18, 1999 to Ampulski et al..
Alternatively, after the indicia are applied to the tissue paper,
the texture may be imparted to the tissue paper by embossing. Knob to knob embossing
is well known in the art as illustrated by commonly assigned U.S. Patent No. 3,414,459,
issued Dec. 3, 1968 to Wells. The texture may also be imparted to the tissue paper
by nested embossing as illustrated by U.S. Patent No. 4,320,162, issued Mar. 16,
1982 to Schulz et al.. Alternatively, the texture may be imparted to the tissue
paper by dual ply lamination embossing as illustrated by commonly assigned U.S.
Patent No. 5,468,323, issued Nov. 21, 1995 to McNeil and incorporated herein by
reference. It is to be recognized that the process of printing tissue paper which
is smooth, rather than textured as defined herein, and embossing such tissue paper
after printing, and the tissue paper made thereby, is outside the scope of the present
invention. The process according to the present invention of printing the tissue
paper after embossing provides the benefit that the print more closely follows the
embossment pattern. If the tissue paper is embossed after printing, the indicia
are distorted by the embossing process resulting in more of the unprinted substrate
showing through as the tissue paper is stretched upon embossment. One of ordinary
skill will recognize that the amount of distortion, and hence the amount of substrate
not having indicia and visible to the user is dependent upon the emboss design and
emboss depth. Textured paper may be embossed after printing, as is known in the
art. Any suitable process for applying the ink to the roll, and even for applying
the ink directly to the substrate, may be utilized. Suitable processes for applying
the ink to a roll and then from the roll to the tissue paper by printing include,
but are not limited to lithography, letter press, gravure, screen printing, intaglio,
and preferably flexography. Flexographic printing is preferred because a removable
covering is provided for the roll. Coverings include both plates and sleeves as
are known in the art. Alternatively, the ink may be sprayed onto or otherwise applied
directly to the substrate by ink jet printing as is known in the art.
The raw ink composition used in the present invention may have a Shell
Cup viscosity at a temperature of 20°C of preferably about 200 centipoises or less,
more preferably about 70 centipoises or less, and most preferably about 25 centipoises
or less, although viscosities ranging from 5 centipoise to a pasty consistency can
be utilized. As used herein, "raw ink" refers to the ink composition prior to the
application process in which it is applied to the substrate. As is well known in
the art, a #1 Shell Cup is used to measure viscosities which range from about 1
centipoise to 10 centipoise. A #2 Shell Cup is used to measure viscosities which
range from about 7.5 centipoise to 30 centipoise. A #3 Shell Cup is used to measure
viscosities which range from about 25 centipoise to 80 centipoise and a #4 Shell
Cup is used to measure viscosities which range from about 60 centipoise to 200 centipoise.
The ink compositions used in the present invention have a pH in the
range of about 2 - 11 and preferably about 7 - 10. A surfactant(s) or dispersant(s)
may be added to the ink composition to disperse the binder and pigment.
To improve ink rub-off resistance, the ink composition of this invention
may contain a wax. A wax suitable for this invention includes but is not limited
to a polyethylene wax emulsion. Addition of a wax to the ink composition of the
present invention enhances rub resistance by setting up a barrier which inhibits
the physical disruption of the ink film after application of the ink to the fibrous
sheet. Based on weight percent solids of the total ink composition, suitable addition
ranges for the wax are from about 0.5 % solids to 10 % solids. An example of a suitable
polyethylene wax emulsion is JONWAX 26 supplied by S.C. Johnson & Sons, Inc.
of Racine, Wisconsin.
Glycerin may also be added to the ink composition used in the present
invention in order to improve rub-off resistance. Based upon weight percent of the
total ink composition, suitable addition ranges for the glycerin range from about
0.5% to 20%, preferably from about 3% to 15%, and more preferably from about 8%
Methods of curing the inks used in the present invention include but
are not limited to thermally curing, electron beam curing, photon curing (for example
ultraviolet light, x-ray, and gamma ray), and combinations thereof.
Crosslinking agents are generally added to the finished ink composition
or to a pigment dispersion. As used herein, "finished ink composition" refers to
an ink composition that contains the key components such as a vehicle, pigment,
and binder so as to render the ink composition ready to use. As used herein, "pigment
dispersion" refers to a composition comprised of pigment solids, surfactant, and
a vehicle such as water or oil to which a binder is added.
Crosslinking agents are believed to enhance the rub-off resistance
of the ink by crosslinking with the ink. A non-limiting example of a suitable crosslinking
agent, is a solution polymer of a cationic polyamine-epichlorohydrin polymer. Based
upon weight percent of the total ink composition, suitable addition ranges for the
crosslinking agent are from about 3% to 15 %, and preferably from about 4 % to 8%
(based on the solids content of the crosslinking agent). A preferred crosslinking
agent is KYMENE PLUS available from Hercules Inc. of Wilmington, Delaware.
It is well known in the art that the final ink density is a function
of several variables, such as substrate texture, dot area, anilox cell volume, anilox
geometry, pigment concentration, and pigment efficiency. Numerous methods can be
used to deliver a given density by changing the relationships between the aforementioned
variables. Most important, however, is the mass of pigment deposited on the sheet
as the density is proportional to the mass of pigment. While not wishing to be bound
by theory, the mass of pigment on the sheet can be roughly estimated by the following
transfer efficiency * pigment concentration * anilox cell volume * print area
= mass of pigment on sheet
Therefore, if one wishes to achieve a higher ink density, one may increase the
pigment concentration, or increase the anilox cell volume. In one preferred execution,
an anilox roll with a 4 billion cubic µm cell volume per 6.45 square centimeters
(per square inch), 157 lines per centimeter (400 lines per inch), and a 60 degree
cell angle is used to deliver an ink density of 0.65. Suitable inks are commonly
available from Sun Chemical Corp. of Northlake, Illinois as : 16966651 or WKIFW2618324
for yellow, 16966652 or WKIFW4618325 for magenta, 16966653 or WKIFW5618326 for cyan,
and 16966654 or WKIFW9618327 for black.
The color density of the indicia may be measured with a densitometer.
Color density, a dimensionless measurement, refers to the density of the color produced
by the ink or dye. The higher the color density, the greater the intensity or strength
of the color. As color density increases, the densitometer measurements also increase.
The densitometer measures the color density of the dominant primary color present
in the image. The densitometer then displays the color density of the dominant primary
color. As used herein, "process color" refers to one of the four colors of yellow,
magenta, cyan, and black, which colors are typically disposed on the tissue paper
in that order.
A non-limiting list of optional additives which may be added to the
finished ink compositions of the present invention include crosslinking agents,
printing press hygiene control agents, humectants, corrosion control agents, pH
control agents, viscosity modifiers, preservatives, and defoamers.
The printed image produced on the paper can be line work, halftoning,
preferably a process print, or a combination of these. As used herein, "line work"
refers to a printed image composed of solids and lines. As used herein, "process
print" refers to a halftone color print created by the color separation process
whereby an image composed of two or more transparent inks is broken down into halftone
dots which can be recombined to produce the complete range of colors of the original
The advantage of a process printed image over a line work printed
image is that the process printed image enables many colors and shades of those
colors to be produced with a few inks. For example, a human image may be comprised
of ten or more colors. This image can be reproduced by process printing utilizing
as few as three colors. The same image reproduced by line work would typically require
ten or more inks each with a corresponding printing station on the printing press.
Though the preferred ink compositions used in the present invention are pigment-based
process inks, dyes, and other types of pigment-based inks can be used in this invention.
Coloration in a process print image is produced by varying the area
of ink deposition in a given image area, frequency of ink deposition, and the number
of inks in the image area. Ink deposition area may be varied by adjusting the frequency,
size, or combination thereof of halftone dots. Suitable inks are described in commonly
assigned Application Serial No. 09/130,615, filed Aug. 7, 1998, in the names of
McFarland et al..
Preferably, the ink used in the present invention has a color density
of at least about 0.50, more preferably at least about 0.55 and is suitable for
color densities ranging as high as 1.0 or greater. More particularly, the ink used
in the present invention has a color density of at least about 0.55 and preferably
0.70 for yellow and black, and a color density of at least about 0.65 and preferably
at least about 0.80 for cyan and magenta. The color density may be measured on any
individual color, or upon any element comprising two or more colors.
The color density of indicia applied to tissue paper may be measured
using a reflectance densitometer. The densitometer setting is adjusted to read the
dominant primary color present in the image. The sample to be measured is placed
on top of four unprinted sheets of the tissue paper. The four unprinted sheets are
used in order to eliminate any influence of background from a colored surface. Four
sheets of a white substrate having a L*a*b* values of about 91.17, 0.64, and 4.29,
respectively, wherein the L*a*b* values are measured by a spectrocolorimeter set
to A10° observer angle with an A2 illuminant in the CIELAB L*a*b* mode.
Three color density measurements are made within a given color, or
within a given color of a particular element, of an indicium using the reflectance
densitometer. The average of the three measurements is recorded.
Color density measurements may be measured on any ink or dye applied
to any substrate. Preferably color density is measured with a white background,
although the color density is measured on a substrate beginning with the white background
having the aforementioned L*a*b* values.
One suitable white background is found in Bounty® paper towels
marketed by the instant assignee. A suitable densitometer for measuring color density
is the X-RITE® 418 Reflectance Densitometer and a suitable colorimeter is the
X-Rite 928 Spectrocolorimeter, both commercially available from X-Rite Inc. of Grandville,
Michigan. From the L*a*b* values, a dimensionless difference is obtained by subtracting
the L*a*b* values of the unprinted background from the average L*a*b* measurement
found in the indicia. The greater this difference, the greater the color density
provided by the ink.
High fidelity printing requires a relatively high degree of color
purification. However, a uniform color purification will not suffice. The color
purification herein requires a threshold level of the black color in order to reproduce
indicia with the requisite fidelity. The requisite fidelity is deemed to be achieved
when the indicia subjectively resemble photographs -- given the limitations of printing
on a textured and/or tissue paper substrate.
For the embodiments described and claimed herein, the indicia have
a mean black level of less than to 245, preferably less than or equal to 235, more
preferably less than or equal to 225, and most preferably less than or equal to
215. Further, the indicia may have a median black level of less than or equal to
235, and more preferably less than or equal to 225. Black level is measured according
to the following procedure.
The black level measurement is an image analysis method useful for
quantifying the amount of shadow present, and the average brightness of, the indicia.
A scanner is also provided. The scanner should have a resolution of
approximately 59 dots per centimeter (150 dots per inch) and be usable with the
image editing and manipulation software.
An AGFA Arcus II scanner and corresponding AGFA Fotolook 32 v3.00.00
software (® of Agfa-Gevaert AG ) are suitable. Additionally, a visually distinctive
12 Step Opaque Gray Scale is provided. Image editing and manipulation software,
such as Adobe® Photoshop® 4.0 software, and a calibrated, X-Rite® 418
Densitometer from the X-Rite Corporation are used. The image editing and manipulation
software should provide an RGB to CMYK conversion formula equivalent to the default
method of Adobe® Photoshop® 4.0. The Arcus II scanner should be a choice
for twain in the Photoshop® software.
The following list is an appropriate output of Densitometer Readings
from the grayscale standard:
measured luminosity: 215-220
measured luminosity: 27-32
If the variation in densitometer readings is greater than +/-0.02,
the densitometer should be recalibrated.
The grayscale set forth above is scanned and the optical densities
at 0.19 and 1.74 are verified to have the luminosities set forth above as measured
in the Photoshop® software using the Histogram tool.
The scanner and software are set as follows:
The histogram boundaries are set as follows:
Bits per color
A sample of the tissue paper or other substrate is provided. The sample
should be at least 12.7 x 12.7 centimeters (5" x 5") in size. The histogram boundaries
and setup of the Fotolook software are confirmed. The grayscale and sample are placed
on the scanner. The grayscale should not cover any indicia, and preferably the sample
overlays the grayscale.
The sample and grayscale are scanned into Photoshop® in 24 bit
RGB format. Using the marquee tool an area of the sample not having indicia is selected.
Preferably the area is as large as possible. If the entire sample has indicia this
step maybe omitted.
The histogram is viewed, selecting the luminosity channel. This allows
one to see information for the unprinted regions of the sample.
If a non-zero pixel count at 255 occurs, the scanner is unsuitable
and a new scanner should be selected.
Using the crop tool, the sample is selected to exclude any non indicia
area of the background. The selected image is converted into the CMYK mode. A noise-median
filter, radius of 5, is selected. The grayscale strip is selected with the marquee
tool and inverted with the inverse function. A tolerance of 35 with the anti-aliased
selection is set using the magic wand tool. This step is repeated until only the
indicia are selected. If some elements of the indicia contain white areas these
are included in the selection process.
The black (K) channel is selected from the pallet menu. The mean and
median values are then recorded from the Histogram function.
For the invention described herein, a three to ten-color printing
process is envisioned, with a preferred process having from four to six colors.
Assuming a preferred four-color printing process is selected, the principal color
may comprise 29 to 46% of the shade making of a particular element of the indicium.
The secondary color may be applied at a level of 14 to 29%, the tertiary color -
11 to 14%, and the fourth color - 0-11%. The above percent figures represent the
amount of ink coverage on the printed area of the tissue paper. Black is often the
third most dominant color in the printing process according to the present invention
and may be used to outline, by shading, a particular element of the indicia. Black
was to be used to increase shading, contrast and depth in the indicia.
The indicia, as seen upon the substrate, preferably has an overall
color curve with an output value of 3 to 75%. For CMYK indicia, the color curve
represents the percentage of color within the total range available to reproduce
the indicia. Color curve may be determined multiple ways. One suitable way is to
use the PhotoShop 4.0 software distributed by the Adobe Systems Inc. of San Jose,
California. Preferably the color curve does not exceed 75%, otherwise the indicia
may look muddy, rather than sharp.
Preferably, the high fidelity printed indicia according to the present
invention displays color gradations, i.e., the blending of one color into an adjacent
color, so that a wide range of colors are printed within the indicia. The high fidelity
printed indicia according to the present invention has subtle variations in tone
as the shades smoothly blend from one shade to the next. Shading is related to color
gradations and is accomplished by having gradual transitions from the main part
of an element of the indicia into the peripheral regions. Shading provides a shadow
or highlight to give the element a more realistic appearance. The high fidelity
prints according to the present invention typically utilize a high proportion of
dark colors, including black, to create shadows and contrast. In contrast, typical
artwork prints use black or dark colors as an abrupt border for the elements of
One convenient way to adjust contrast is to utilize the Contrast tool
in the aforementioned Photoshop® software. The printed indicia according to
the present invention have a contrast of 50 to 70%.
The intensity within a given element of the indicia is adjusted to
increase the apparent depth of that element. The range of intensity is adjusted
by increasing the contrast of that shade within the element. For example, the lightest
color of the element may remain unprinted, i.e. generally white in order to enhance
the realistic appearance by providing the perception of roundness, highlights, and
glare. Preferably, the photographic source is provided with a color density of less
than about 0.05.
The high fidelity print is taken from a photograph, as noted above.
The photograph should have a minimum resolution of at least 39 dots per centimeter
(100 dots per inch) and more preferably at least 240 dots per centimeter (600 dots
per inch). Preferably, the photograph does not have a solid background, such as
a sky or thick forest. If the photograph contains too much background imagery, the
amount of ink necessary to reproduce the background will overwhelm one's ability
to adjust the other colors making up the elements of primary interest.
The indicia may be printed using a flexographic printing process,
although prophetically gravure, ink jet, or lithographic printing may be utilized.
If a flexographic printing process is utilized according to the present invention,
preferably the process utilizes a printing roll having a line screen resolution
between 24 to 41 (60 to 105), preferably a resolution of 26 to 39 (65 to 100), and
more preferably 26 to 33 lines per centimeter (65 to 85 lines per inch).
Ink may be supplied to the flexographic printing roll by an anilox
roll as is known in the art. To assure proper resolution of the ink applied to the
printing roll, the anilox roll may have from 78.7 to 394 lines per centimeter (200
to 1000 lines per inch) and a volume of 1 to 10 billion cubic µm per 6.45 square
centimeters (per square inch). One suitable anilox roll has been found to have 157
lines per centimeter (400 lines per inch) and a volume of 4 billion cubic µm per
6.45 square centimeters (per square inch). The cells have a cell depth to cell opening
ratio of 0.28 ± 5% using a 65 line screen anilox roll. Ink is applied by the print
roll to the tissue paper, or other substrate using the print roll. Preferably the
print roll has a line screen to anilox cell resolution of not less than 5:1 and
preferably not less than 6:1.
In addition to meeting the minimum resolution requirements, the registration
of the print must be controlled as well. Preferably the registration is held to
a tolerance of 1.6 millimeters (0.063 inches) in each of two perpendicular directions.
More preferably, registration is held to at least 0.8 millimeters (0.032 inches).
Registration is defined as the offset between the desired and actual placement of
the dots. It is preferred to use a printing process having a central impression
cylinder and multiple printing stations engaging the central impression cylinder.
Utilizing a central impression cylinder reduces occurrences of misregistration of
the various colors of the indicia on the substrate. Such misregistration occurs
more commonly with the low basis weight, high extensibility substrates common to
tissue papers, nonwoven materials, and the like, usable for but not required by
the present invention.
It is desirable that each element of the high fidelity indicia have
a threshold dimension of at least about 1 centimeter, more preferably 2.5 centimeters,
and most preferably 5.0 centimeters, depending upon the level of detail in the elements.
The threshold dimension is the largest linear dimension measured in any single direction.
Larger elements tend to have a more lifelike and realistic appearance when printed
as described herein. Printing resolution and the texture of the tissue paper limit
the visual acuity when one views smaller sized elements in the indicia.
Utilizing textured substrates according to the present invention,
it is particularly critical, and difficult, to obtain the desired registration.
The registration is maintained in the printing process as described below.
Example #1: Christmas Wreath
Example #2: Pink Rose
- Image Selection: Referring to Fig. 4, for this image, a clip-art electronic
file of a high resolution photograph was selected of a Christmas wreath hanging
on a door. This image was opened in Adobe® Photoshop® for manipulation.
- Background Removal: All of the background elements were selected and
removed from the image, leaving only the wreath itself.
- Purification: In order to maintain a high fidelity to the original, the
majority of the Magenta was removed to maintain an Evergreen color. The primary
colors left in the wreath were Yellow and cyan. Black was left in to create the
appearance of depth and realism.
- Color curve alteration: The color curve output value was reduced to 70%
by dragging the output point down the right axis of the color curve until the output
level read 70%..
- Contrast: The contrast was adjusted to 55%. The brightness was left at
- Printing: This sample was printed using the following inks: 16966651,
16966652, 16966653, 16966654, commonly available from Sun Chemical Corp. of Northlake,
IL. Target intensities were Y/K = 0.55 and M/C = 0.65. The press consisted of four
stations with the inks in the YMCK order. Anilox roll specifications were 4.0 BCM
at 157 lines per centimeter (400 lines per inch).
While the intensities listed in the examples above are the targets, it should be
understood that minor adjustments may need to be made to the inks to achieve the
appropriate intensity levels due to substrate variations, equipment variations,
anilox plugging, nip settings, etc. If the ink intensity is substantially different
than the targets, it is recommended that water or toner additions be made according
to recommendations of the ink supplier.
- Image Selection: Referring to Fig. 5 for this image, a clip-art electronic
file of a high resolution photograph was selected of several roses in a garden.
This image was opened in Adobe® Photoshop® for manipulation.
- Background Removal: All of the background elements including two of the
original roses were selected and removed from the image, leaving only one pink rose.
- Purification: In order to maintain a high fidelity to the original, the
majority of the Cyan and some of the Yellow was removed to maintain a pink color.
Black was left in to create the appearance of depth and realism.
- Color curve alteration: The color curve output value was reduced to 70%
by dragging the output point down the right axis of the color curve until the output
level read 70.
- Contrast: The contrast was adjusted to 55%. The brightness was left at
zero. In order to create the appearance of realism, the existing veins in one of
the leaves was further manipulated with a sponge tool set to "desaturate" at a 50%
pressure. Additionally, Magenta was removed from the lightest parts of the image
(e.g., the tips of the petals) to create a greater appearance of depth and glare.
This manipulation was accomplished using the erasure tool.
- Printing: This sample was printed using the following inks: WKIFW2618324,
WKIFW4618325, WKIFW5618326, WKIFW9618327, commonly available from Sun Chemical Corp.
of Northlake, IL. Target intensities were YMCK = 0.8. The press consisted of four
stations with the inks in the YMCK order. Anilox roll specifications were 4.0 BCM
at 400 lines per inch.
Referring to Figs. 2-3, two prints are shown. The print of Fig. 2
is in accordance with the present invention and, taken from a photographic source,
and is subjectively realistic. The print according to Fig. 2 has a mean black level
of 206 and a median black level of 221. The print of Fig. 3 is taken from hand drawn
artwork, and is not subjectively realistic. The print according to Fig. 3 has a
mean black level of 244 and a median black level of 255.