Note: Descriptions are shown in the official language in which they were submitted.
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OIL-REPELLENT MICROVOID-IMAGING MATERIAL
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Background of the Invention
This invention relates to sheet material,
especially a base sheet obscured by an opaque but trans-
parentizable microporous, diffusely light-reflec-tive layer.
For centuries paper has been one of the most
versatile substances made by man. Formed from commonly
available cellulosic materials, it can be made stiff or
flexible, rough or smooth, thick or thin, and provided with
any desired color. After it has served its intended
purpose, it can often be repulped and used again. In recent
years, however, the demands for paper have increased to the
extent that it has finally been recognized that the sources
of cellulosic raw materials are not inexhaustible.
Further, the energy required to manufacture paper is a
significant consideration in a world becoming increasingly
aware that supplies of energy are also finite. It has also
become recognized that, where paper is used as a carrier
for indicia, it can generally be used only once, it being
impossible or impractical to remove indicia which are no
longer needed or desired. There has thus arisen a desire
for a substitute for conventional paper, especially one
which can be repeatedly and easily reused; even a
substitute which was more expensive to manufacture would be
less expensive in the long run if i-t could be reused a
sufficient number of times.
Several U.S. Patents (e.g., Nos. 2,299,991,
3,031~328 and 3,508,344) disclose composite sheet material
in which a light-colored opaque blushed lacquer layer is
coated over a base sheet that is either dark-colored or
imprinted with dark-colored indicia. The opacity and light
color of the blushed lacquer coating are due to the
inclusion of numerous microvoids; the local application of
(1) heat or pressure (either of which irreversibly
collapses the microvoids) or (2) a non-solvent liquid
having substantially the same refractive index as the
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lacquer (which fills the microvoids), causes the coating to
become selectively transparent and the underlying dark
backing to become visible. A liquid employed to impart
transparency to the opaque microporous layer can subse-
quently be evaporated to restore the original appearance.
U.S. Patent No. 2,854,350 describes structureswhich are functionally similar to those just described,
except that the blushed lacquer coatings are replaced by a
microporous layer of finely divided calcium carbonate in an
organic binder. Transparency is imparted by locally apply-
ing pressure or treating selected areas with a wax, oil orgrease having a refractive index similar to that of the cal-
cium carbonate; see U.S. Patent 2,854,350. Other pigments
may be incorporated in a microporous highly plasticized
resin binder; see U.S. Patents 2,920,979 and 3,247,006.
It is sometimes desirable to have microvoid-
containing sheet material which can be transparentized by
applying a liquid, but which cannot readily be trans-
parentized by the application of heat or pressure. In
such circumstances, a microvoid-containing layer of the
type described in U.S. Patent 4,299,880, owned by
applicant's assignee, is preferred. This patent discloses
a structure in which the microvoid-containing layer
consists essentially of particles held in pseudo-sintered
juxtaposition by a thermoset binder and has a cohesion
value of at least 400 grams ~orce*.
* The cohesion value is determined by knife-coating a dis-
persion of a putative composition on a cleaned gray cold
rolled steel panel, drying and curing as appropriate for
the composition, to provide a coating 50-60 micrometers
thick. Using a "Balance Beam Scrape-Adhesion and Mar Tester",
sold by Gardner Laboratories, Inc., Bethesda, Maryland, a
sapphire-tipped stylus is lowered into contact with the
test panel and held in fixed position while a ball bearing-
supported platform moves the panel. The minimum grams-
force required to Eorm a 50-micrometer deep scratch in the
coating in a single pass is determined at a magnification
of 40X and reported as cohesion value.
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One important use for the microvoid-containing
sheet materials just described is in the manufacture of
re-usable order blanks for the fast food industry. Order
blanks oE this type are typically printed with a list of
the various products offered for sale, as well as the
number of each type of item which a customer might request.
Upon receiving an order, the serving person utilizes a pen
filled with a volatile clear "ink" to apply markings in the
appropriate places; wherever the "ink" is applied, the
microvoid layer is locally transparentized, allowing the
dark backing to be seen. An order blank marked in this
manner can then be fed into an optical mark recognition
device, which automatically computes ~he total cost of the
merchandise purchased. After a time, the volatile "ink"
evaporates, so that the order blank can be used again.
One problem encountered with order blanks of the
type just described is inadvertent contamination by various
liquids in the area. For example, if cooking oil contacts
the face of the order blank~ it penetrates the microvoids
and imparts local transparency. Since such oil is
essentially non-volatile, a permanent mark may remain,
causing erroneous readings when the order blank is scanned
by the optical mark recognition device. To a lesser
extent, similar problems may be caused by spilling soft -
drinks, coffee, syrup or other water-based liquids on the
surface of the order blank. Even if an oil- or water-
repellent treatment is applied to the surface of the
microvoid layer, the treatment may retard but not
completely prevent penetration of the contaminating liquid,
especially over an extended period of time. When used
blanks are subsequently stacked on top of each other until
the volatile "ink" has evaporated, the weight of the stack
forces contaminating liquids into the microvoid layer,
`~ causing random mar]cs and future erroneous readings by the
optical scanner.
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Detailed Description
The present invention provides improved self-
supporting sheet material of the type which can be provided
with temporary markings by applying a colorless liquid of
predetermined volatility, such sheet material comprising
(a) a self-supporting, oil- and grease-impermeable dark-
colored (preferably infrared-absorbing) base sheet having a
face side and a back side and (b) bonded over each side of
the base sheet, a diffusely reflective opaque white to
pastel microvoid-containing layer comprising an organic
polymer having a refractive index in the range of about 1.3
to 2.2. Present at least at the exposed surface of the
layer on only the face side oE the base sheet is an
oleophobic fluorochemical which prevents the microvoids at
the face side of the sheet material from being readily
penetrated by oil or grease, so that the face side can be
penetrated on transparentized by only a limited number of
liquids. Depending on the specific oleophobic fluoro-
chemical the useful transparentizing liquids have a low
surface tension or are polar. Penetration, oE course,
effects local transparentization of the face side layer to
expose tha dark~colored base. The microvoids at the back
side of the sheet material, however, remain readily
penetrable by almost all liquids, including both polar and
non-polar liquids having either low surface tension or high
surface tension. This construction ensures that
potentially transparentizing contamination of the microvoid
layer on the face side of the sheet material, as might be
caused by contact with vegetable oil or animal fat can be
removed by promptly placing the face side layer in contact
with the back side layer of another portion of the sheet
material, the contaminating liquid thereupon being absorbed
into the adjacent back side layer. (Transparentization of
the back side layer does not affect readings made by the
optical mark reading equipment, which "sees" only the face
side.) Desirably (although less essentially) the face side
also resists penetration by water-based substances.
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Order blanks or other sheet material made in
accordance with the invention, advantageously printed with
permanent indicia on the face side, possess a self-cleaning
property, so that contaminating liquids which contact the
face side and might otherwise lead to erroneous optical
mark recognition device readings, are absorbed into the
back surface. In other words, despite the possibility that
an order blank or other sheet material may be exposed
repeatedly to con-taminants, its useful life is essentially
unaffected by such exposure.
Presently Preferred Embodiments
Understanding of the invention will be furtner
enhanced by referring to the following illustrative but
non-limitative examples, in which all parts, ratios and
percentages are by weight unless otherwise noted.
Self-Cleaning Test
In the examples, various types of sheet material
were prepared, all having a microvoid-containing layer on
both the back and face sides, with an oleophobic fluoro-
chemical treatment on the face side only. The fluoro-
chemical treatment was provided either by applying to the
face side a dilute solution of an oleophobic fluorochemical
and evaporating the solvent or by incorporating the fluoro-
chemical in the microvoid-forming composition before
coating. The product of each example was then evaluated to
determine if either a commercial French fry oil (a
partially hydrogenated soya bean oil having an iodine
number of 102, a density of 0.929, a surface tension of 37
dynes/cm at 23C., containing about 1% polydimethylsiloxane,
available from Procter & Gamble under the trade designation
"FRY MAX") or tap water applied to the treated surface
would cause localize transparentization within 15 minutes.
In each case the oil and water were applied to separate
portions of the test specimen, using a medicine dropper to
form a circular puddle about 3 cm in diameter. Diffuse
reflec-tance of each area was measured both before and 15
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minutes after applying the test liquid. A decrease of 10
or less units (measured on a Hunter color difference meter,
L scale) indicates negligible penetration of the liquid and
acceptable performance.
The product of each such contaminated example was
then evaluated for its self-cleaning properties. The
untreated back side of an 11 x 28 cm sheet of the shee-t
material in contact with a weighed portion of the treated
face side, to which had been applied 10 mg each of French
fry oil and tap water in separate 3-cm diameter areas.
Sufficient weight was then added in the form of additional
sheets to ensure intimate contact; pressures from 0.0013 to
0.5 KPa appeared to be equally effective. After one hour
at room temperature, the previously weighed portion of the
sample was again weighed; a weight gain of less than 1 mg
was considered to indicate satisfactory self-cleaning
properties.
Oleophobic fluorochemical treatment of the face
surface tends to limit the types of clear liquid "ink"
which can be used to impart the desired localized trans-
parentization. Only liquid "inks" having a low surface
tension (i.e., less than about 30 dynes/cm) appear to be
useful where the surface has been treated with fluoro-
chemical which renders it both oleophobic and hydrophobic.
On the other hand, liquid "inks" which either are polar
(e.g., water, glycols, and alcohols) or have a very low
surface tension (i.e., less than about 20 dynes/cm~ are
useful where the fluorochemical has rendered the face side
oleophobic but not hydrophobic. Suitable volatile liquids
for use as clear marking liquids, having a surface tension
of less than about 30 dynes/cm, include perfluorocarbons
and liquid polysiloxanes, as well as certain hydrocarbons
and alcohols.
Many families of fluorochemicals are effective in
imparting the desired oleophobic properties. Because of
the variety of fluorochemicals which are effective, and
because other fluorochemicals are unexplainably not
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suitable for the practice of the invention, it has been
found helpful to employ a physical test to determine
whether a given fluorochemical will be satisEactory, as
will now be explained.
S Contact angle measurement.
-
A strin~ is clipped to one end of a glassmicroscope slide, which is then quickly immersed in a
dilute solution (5% unless solubility is so poor that a
less concentrated solution must be employed) of fluoro-
chemical and withdrawn vertically at the rate of 0.12mm/second, guarding against stray air currents which might
cause movement of the slide or uncontrolled evaporation of
the solvent. The treated slides are dried at room
temperature for 30 minutes, heated 2 minutes at about
120~C. and cooled to room temperature. ~ drop of the
French fry oil previously described is then applied and the
contact angle measured. Fluorochemicals which yield a
contact angle of at least 60 + 2 are found to be
satisfactory for practicing the invention, while fluoro-
chemicals which yield a lower contact angle are found to be
unsatisfactory.
Preferred oleophobic fluorochemicals for surface
treatments include chromium complexes of RfSO2N(R')RCOOH,
wherein Rf is a perfluoroalkyl group containing 4-20 carbon
atoms, R is an alkylene bridging group containing 1-12
carbon atoms, and R' is H or an alkyl group containing 1-6
carbon atoms; U.S. Patent 2,934,350 discloses such
fluorochemicals. Another suitable class of oleophobic
fluorochemicals is defined by the structural formula
[RfSO2N(R)R'0]m PO(OX)3_m~ wherein Rf i5 as just defined,
R is H or an alkyl group having 1-12 carbon atoms, R' is an
alkylene bridging group having 2-12 carbon atoms, X is H,
NH4, Na or NH2(C2H4OH)2, and m is 1 or 2; U.S. Patent
3,094,457 discloses such fluorochemicals. Fluorochemicals
are, of course, well known and have been employed as
surface treatments for imparting oleophobic or oleophobic-
hydrophobic properties to fibrous sheet material; see,
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e.g., U.S. Patent No. 2,~03,615, 2,934,450, 2/950,29g,
3,574,791, 3,916,053, and 2,~03,656.
In each o~ exalnples 1-1~ and comparison examples
A-E:, tabula1;s~d below, one si~e vE 100-lnicromel;er black
greaseproof paper was coated wi th a blend of 77 . 39 parts
toIuene, 11.18 parts diisobutylketone, 22.37 parts
methylisobutyl-ketone, 41.47 parts o~ a 60% solids
OH-~unctional acrylic re~in (Henkel G-Cure 868 RX-60),
0.9 part di(dioctylpyropllosphato) ethylene titanate,
466 parts 0.5-15 micrometer CaCO3 tSylacauga Calcium
Products "Microwhite" 25), and 7.9 parts of a 75~ solution
oE the biuret of 1 ,6~hexalnethylene diisocyanate (Mobay
Chemical Company "Desmodur" N-75). The solvent was then
evaporated and the coating cured, leaving a ~nicrovoid layer
approximately 25 micrometers thick, haviny a void volume o~
35%. The opposi~e side of the greaseproo~ paper was then
provided with a microvoid layer by coating and curing the
sa~ne composition.
To the surEace oE one microvoid layer 5herein-
aEter reEerred to as ~he "~ace" layer) was the~ applied a
dilute (typicaily 1-1/2 - 3~) solution o~ fluoroch mical in
suE~icient guantity to fill the Inicrovoids, a~ter which i~
was evaporated to leave a dry surface. When tested for
self-cleaning propertie.s in accordance with the test
previously described, the Eace side o~ each sample was
readily purged o~ contamination. In each case, a suitable
volatile transparentizing "ink" was available; such inks
are listed in the tabulated examples.
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Substantially the same results are obtained when
the backing sheet is greaseproof plastic or paper which is
both waterproof and greaseproof.
Example 20
Following the general procedure descrihed in U.S.
Patent No. 2,854,350, a control was prepared by placing
39.6 grams of water, 0.4 gram sodium alginate and 5 grams
precipitated calcium carbonate in a 4-ounce (approximately
125-cc) jar and ball milling for several days. The
resulting composition was knife-coated, at a thickness of
approximately 200 micrometers, onto the surface of black
60-micrometer greaseproof paper and allowed to dry at room
temperature overnight; the dried microvoid-containing
coating was approximately 25 micrometers thick. A similar
coating was applied to the opposite face in the same
manner. The face side of a portion of the sheet material
just described was then treated in the same manner as in
Example 6 and subjected to the contamination and self-
cleaning tests described, per~orming successfully in each
case. A suitable marking liquid was polydimethyl siloxane.
Example 21
Example 20 was repeated, substituting the oleo-
phobic fluorochemical of Example 1. Contamination
resistanee and self-cleaning test results were satis-
factory. A suitable marking ink was found to be
perfluorotributylamine O
Example 22
Following the general procedure described in U.S.
Patent No. 3,508,344, a control was prepared by placing
75.1 grams acetone, 6.6 grams polymethyl methacrylate
("Elvaeite" 2041, avaiIable from E.I. duPont de Nemours h
Co.), 1.6 grams diethylphthalate, 1.1 grams polyaerylate ~-
~"Rhoplex" B-15, available from Rohm & Haas Company) and
11.0 grams of water~in an 8-ounce (approximately 250-ec~
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jar and ball milling overnight. The resulting composition
was knife-coa~ed onto the black greaseproof paper used in
Example 1 and allowed to dry at room temperature to leave a
microvoid-containin~ coating approximately 50 micrometers
thick. A similar coating was then applied in the same way
to the opposite side of the sheet material. The face side
of the sheet material just described was coated with the
oleophobic fluorochemical of Example 1 and subjected to the
same types of tests. Results were comparableO sheet
material was conveniently marked, using as a transparent
"ink" polydimethyl siloxane.
Example 23
Sheet material substantially similar to that just
described was prepared and coated with the face side with
the dilute solution of the oleophobic fluorochemical
described in Example 14. When subjected to the tests
previously described, the results were comparable. A
suitable "ink" is dodecane.
Example 2~
Sheet material generally similar to that of
previous examples was prepared using a black greaseproof
60-micrometer paper backing and a microvoid coating of the
type described in U.S. Patent No. 3,247,006. Specifically,
a mixture of 28.5 parts toluene, 6 parts vinyl toluene
butadiene resin (Goodyear "Prolite" VT), 6 parts diphenyl
phthalate, and 18 parts magnesium carbonate was ball milled
overnight, knife coated onto both sides of the backing and
the solvent evaporated to leave a dried 20-micrometer
coating on each face. A portion of the face surface of
this product was treated with the oleophobic Eluorochemical
described in Example 1. Test resul-ts were comparable. A
suitable marking ink for this product was cyclic
hexamethyltrisiloxane.
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Example 25
A portion of the face surface of the sheet
material described in the precediny example was coated
with a dilute solution of the oleophobic fluorochemical
described in connection with Example 14. Test results
were comparable. A suitable markiny ink was found to
be octane.
Example 26
This example illustrates incorporation of the
fluorochemical directly into the microvoid-forming face
layer composition. Accordingly, 40 parts toluene, 2.4
parts diisobutylketone, 7.85 parts of a 60% solution
of hydroxy-functlonal acrylic resin (Henkel G-Cure
867-RX-60), 0.2 part di(dioctylpyrophosphato) ethylene
titanate (Kenrich KR-238s), 100 parts 0.5 - 15 micrometer -
calcium carbonate (Sylacauga Calcium Products "Microwhite"
25), 2.2 parts of a 75% solution of the biuret of 1-6,
hexamethylene diisocyanate (Mobay "Desmodur" N-75) and
8 17 2N(cH3)c2H4ocH2cH(cH2cl)o2ccH2cH ]
were ball milled together. The resultant mixture was
knife-coated onto a 100-micrometer black greaseproof
paper backing and dried and cured at room temperature
to form a 20-micrometer microvoid coating. An identical
coating, except for omission of the fluorochemical, was
coated onto the other side of the backing. The face side
exhibited satisfactory oil and water repellency and was
self-cleaning. A suitable "ink" was polydimethylsiloxane.
It is understood that the following terms,
used herein, are trademarks: "Fry Max", "G-Cure 868 RX-60",
"Microwhite", "Desmodur", "Elvacite", "Rhoplex", and
"Rrolite".
It will be readily appreciated that the foregoing
description is not intended to be exhaustive, and it
is believed that those skilled in the art will readily
devise other products embodying the principles taught
in the invention. Accordingly, what is claimed is as
follows:
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