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Description  |
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FIELD OF THE INVENTION
The present invention relates to record material sheets bearing a coating
which contains a phenolic resin which acts as a co-reactant for colorless
chromogenic dye precursor material to develop a useful color thereon, and
more particularly to such record sheets which provide excellent imaging
with smaller amounts of phenolic resin. The present invention also relates
to the ink composition which is applied to the paper to make such record
material sheets and the method of application of such ink composition.
BACKGROUND OF THE INVENTION
In the manufacture of pressure-sensitive recording papers, better known as
carbonless copy papers, a layer of pressure-rupturable microcapsules
containing a solution of colorless dyestuff precursor is normally coated
on the back side of the front sheet of paper of a carbonless copy paper
set. This coated backside is known as the CB coating. In order to develop
an image or copy, the CB coating must be mated with a paper containing a
coating of suitable color developer, also known as dyestuff acceptor, on
its front. This coated front color developer coating is called the CF
coating. The color developer is a material, usually acidic, capable of
forming the color of the dyestuff by reaction with the dyestuff precursor.
Marking of the pressure-sensitive recording papers is effected by
rupturing the capsules in the CB coating by means of pressure to cause the
dyestuff precursor solution to be exuded onto the front of the mated sheet
below it. The colorless or slightly colored dyestuff, or dyestuff
precursor, then reacts with the color developer in the areas at which
pressure was applied, thereby affecting the colored marking. Such
mechanism or the producing technique of pressure-sensitive recording
papers is well known.
Among the well known color developers used on CF record sheets are
phenolic-type resins, such as acetylated phenolic resins, salicylic acid
modified phenolics and, particularly, novolac type phenolic resins.
Among the well known basic, reactive, colorless, chromogenic dye-precursors
useful for developing colored marks when and where applied to a receiving
sheet coated with such color developers are Crystal Violet Lactone (CVL),
the p-toluenesulfinate salt of Michler's Hydrol or
4,4'bis(diethylamino)benzhydrol, Benzoyl Leuco Methylene Blue (BLMB),
Indolyl Red, Malachite Green Lactone, 8'-methoxybenzoindoline spiro-pyran,
Rhodamine Lactone, and mixtures thereof.
Acid sensitized record receiving sheets have previously been prepared by
application of an aqueous slurry of finely ground resin to a paper
substrate, as is disclosed, for example, in U.S. Pat. No. 3,672,935. It is
also known to apply the resin to the substrate paper sheet as a solution
in a volatile organic solvent which evaporates completely after
application to leave a thin film of solid resin on the sheet. The latter
method is taught in U.S. Pat. Nos. 3,466,184 and 3,466,185. The
consistency of these solid solutions and the necessarily volatile solvents
used therein give rise to printing problems, causing swelling of rubber
plates and rolls. Furthermore they have high energy requirements and
environmental contamination problems. The above discussed aqueous slurry
application has high energy requirements in grinding the resin and in
drying the applied slurry. Such slurries are also not adaptable to
printing techniques. Very often, the film of phenolic resin which has been
applied to the paper does not adhere firmly to the paper which can cause
dusting and offsetting during printing operations.
One previous solution to the problem of standard printing operation
adaptability is illustrated in U.S. Pat. No. 4,060,262. The present
invention, by the same inventor, is essentially an improvement over said
patent.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to eliminate the
deficiencies of the prior art, such as those set forth hereinabove.
It is a further object of the present invention to provide an improvement
in the ink used for printing CF coatings in carbonless copy paper sets.
It is another object of the present invention to provide an improved record
sheet coated with color developer.
It is yet another object of the present invention to provide a record sheet
having a very thin film of color developer which still has excellent
imaging and image retention properties.
It is still a further object of the present invention to provide a record
sheet having a very thin film of color developer which has properties
which are superior to record sheets having larger amounts of resin
deposited by prior art processes.
It is yet a further object of the present invention to provide a record
sheet having a thin film of color developer having excellent adhesion,
substantially eliminating dusting and minimizing offsetting.
It is still another object of the present invention to provide a color
developer composition which can be applied to paper using standard
unmodified printing presses without affecting any of the rollers used on
conventional presses therefore being equally adaptive to both selective
and general coating.
It is still another object of the present invention to provide an ink
composition containing color developer which can be applied on
conventional printing presses at high speeds in excess of 1,000 ft./min.
without objectionable misting or the requirement of special venting.
It is yet another object of the present invention to provide a method of
applying phenolic-resin coatings on paper by standard printing processes.
These and other objects of the present invention are obtained by means of
the present invention in which a very thin film having a substantially
spongy nature is firmly adhered to the paper without diffusing thereinto.
The three critical ingredients of the film in order to obtain a film with
the appropriate properties are a phenolic resin, amorphous lipophilic
silica and a fatty alcohol, particularly cetyl alcohol.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The outstanding properties of the present invention occur because of the
spongy type porous structure of the film which is obtained by use of the
composition of the present invention. The porous structure of the film
serves as a capillary type attractive film which helps to absorb and hold
the color forming reactants and solvent, and thus provides a greater color
producing ability with a smaller amount of reactants. This film is
obtained when using a composition comprising a phenolic resin, a fatty
alcohol such as cetyl alcohol, amorphous lipophilic silica, and a solvent.
Other additives may also be present.
Any type of phenolic-type resin which is organic solvent soluble and serves
as an acidic image former when in combination with a dye precursor may be
used in accordance with the present invention. These include acetylated
phenolic resins, salicylic acid modified phenolics and, particularly,
novolac type phenolic resins.
It is known that with phenolic resin type acid reactive components it is
very difficult to obtain a gel because of the fact that this component is
so highly aromatic in nature. In view of this highly aromatic nature, it
is difficult to obtain a gel structure which holds and retains the product
and prevents diffusion into the paper. This problem is solved by means of
the other components of the composition of the present invention.
The preferred phenolic resin for use in the present invention is a phenol
formaldehyde novolac resin. Either what is termed normal novolac resins or
zinc reacted novolac resins can be used. Resins reacted with other
appropriate cations to enhance reactivity may also be used. Examples of
zinc reacted novolac resins and other metal cations which can be used to
enhance the reactivity of novolac resins are disclosed, for example, in
U.S. Pat. No. 3,732,120. Rather than being zinc-reacted, the novolac resin
may be present with a separate zinc salt, as disclosed in U.S. Pat. No.
3,723,156.
Another known problem with phenolic resins is the fact that they are
particularly tacky and therefore create great problems in their use on
letterpress-type printing processes at the required concentration levels.
This is another of the problems which is solved by the present invention.
The other components of the present composition serve to detackify the
phenolic resins and permit use of the compositions on standard printing
presses.
The second critical component of the present composition is a fatty
alcohol, preferably cetyl alcohol which is a C.sub.16 saturated alcohol.
This component has a dual function. First, it serves as an adjunct to the
structure in order to get the spongy film which is important to the
present invention. The spongy structure of the film which is obtained is a
very significant feature of the present invention because the porous
structure of the film serves as a capillary type attractive film which
helps to absorb and hold the color forming reactants and solvent and thus
provide a greater color producing ability with a smaller amount of
reactants. The second function of the fatty alcohol is to serve as an
internal lubricant in order to reduce the tackiness of the remaining
components of the ink, particularly of the phenolic resin. Thus, it serves
not only to obtain the particularly novel film which is involved but also
for the secondary purpose of making this particular ink not only a better
product when on the paper but also a better product because it is easier
to apply to the paper.
While cetyl alcohol is the most preferred fatty alcohol, it is possible to
use other fatty alcohols if variation of certain ancillary properties due
to such substitution are acceptable. For example, it is known that stearyl
alcohol will provide similar advantages with respect to acting as an
adjunct to the structure in order to get the spongy film and will serve as
an internal lubricant to reduce tackiness. However, stearyl alcohol has
the disadvantage of affecting ultraviolet stability of the formed image.
Stearyl alcohol substantially affects the image forming potential as well
as the image stability of the ink. Nevertheless, for some applications
this might not be objectionable.
While solid fatty alcohols, such as cety alcohol, are preferred, it is
possible that liquid fatty alcohols could be used although it is expected
that liquids would give poorer diffusibility. In other words, the spongy
structure of the film would not be the same with the use of a liquid fatty
alcohol and the capillary action would be different thus causing a
difference in the image definition. Furthermore, the more liquid the film,
the more likely under elevated temperature conditions that the film will
become diffused into the paper thus decreasing the image forming potential
as well as the image retention at elevated temperature. Again, however,
this may not be a problem in particular applications, such as where denser
paper structures are to be used, and in such case liquid fatty alcohols
would also be usable.
Other fatty alcohols such as saturated or unsaturated fatty alcohols having
even numbers of carbon atoms between 10 and 22, as, for example, oleyl
alcohol, myristyl alcohol, lauryl alcohol, and palmitoleyl alcohol are
also usable under certain circumstances. However, the product which gives
the best all around results is cetyl alcohol.
The third critical ingredient is the silica. This compound actually is a
structural adjunct in the composition and is an active ingredient as it
chemically forms a skeletal structure in the system. It must be lipophilic
in order to be mutually compatible with all of the components in the
system. It must also be amorphous and have a stable size not exceeding 50
millimicrons.
The preferred silica is pyrogenic silica. Pyrogenic hydrophilic silicas
exist which are lipophilic to some extent and it is possible to use such
substances, as, for example, when a polar solvent is used. In general,
however, polar solvents, such as glycols and diacetone alcohol, have a
deteriorative effect on imageability. Furthermore, a much larger amount of
hydrophilic silica must be used in order to compound it into the system.
The most preferred product is a pyrogenic hydrophobic silica.
It is the combined use of the pyrogenic lipophilic silica with the fatty
alcohol, preferably cetyl alcohol, which achieves the structural formation
of the present invention which is critical to the results. Specific
examples of silicas usable in the present invention are those commercially
known as Aerosil R 972, manufactured by Degussa or Tullanox 500,
manufactured by Tolco, Inc. The former is preferred.
A solvent must also be present in the composition in order to dissolve the
phenolic resin and the fatty alcohol. Theoretically, any solvent can be
used in which the phenolic resin and the fatty alcohol are soluble, as
long as it does not unduly interfere with the dye-resin reaction. Even
volatile solvents can be used to lay down a film which will have the
properties which are essential to the present invention. However, the
preferred solvents are those which are substantially non-evaporative,
i.e., having a boiling point above 175.degree. C., preferably 275.degree.
C. Using such a non-volatile solvent improves the characteristics of the
coated film because there will be a residue of solvent in the solidified
gel structure of the spongy film. This high boiling point solvent, as
retained in the deposited film, tends to act as a plasticizer and give
flexibility to the deposited film, preventing excess dusting at a future
time. Having the solvent in small quantities in the deposited film acts in
a way to attract the lipophilic components normally found in conventional
CB coated systems. Thus, at the instant of impact, the liquid oranophilic
nature of the CB dye system is more readily attracted into the slightly
wetted highly organophilic surface.
Eligible preferred plasticizing solvent which are compatible with the other
components of the formulation and with the chromogenic dye-precursor
materials, which are compatible with printing press elements, including
rubber plates and rolls, and which show the proper tendency to evaporate
in part, include a mixture of alkyl and aromatic hydrocarbons, alkyl
esters, aromatic acids, and aryl ethers. Particularly useful is a mixture
of monoisopropyl biphenyl and diisopropyl biphenyl, preferably in about a
65:35 percent weight ratio; a similar ratio mixture of monoisopropyl
naphthalene and diisopropylnaphthalene, mineral seal oil, as well as
mixtures selected from the following: butyl benzoate, methyl isopropyl
biphenyl, biphenyl oxide, dimethyl phthalate and benzyl benzoate.
Preferred is mineral seal oil, a commercially available hydrocarbon
solvent known as Mentor 28 solvent which is likewise a mixture of
petroleum fractions containing 25-60% paraffins, 25-60% naphthenics, and
5-20% aromatics (percents by volume). The mineral seal oil may also
contain a minor amount (0.5 to 2% by volume) of olefinics. Commercial
mineral seal oils have a boiling range of about 260.degree. to 370.degree.
C. In use about 50% of the applied mineral seal oil will evaporate from
the paper substrate surface, leaving the residue to serve as a film
plasticizer and chromogenic reaction solvent.
As disclosed hereinabove, it is also possible to use volatile solvents,
such as toluene, xylene, benzene, cyclohexane, hexane, heptane,
diethylbenzene, butyl alcohol and ethyl acetate. However, most of these in
practice would not be used as they would ruin the rubber rolls of the
printing press or would be environmentally offensive.
Whatever solvent is used, it should be present in amounts sufficient to
dissolve the phenolic resin and the fatty alcohol. Beyond this, the
specific amount of solvent will depend on the particular properties of the
composition desirable for use on the printing press, or the particular
properties of the obtained film which are desired, all within the confines
of the present invention.
Besides the phenolic resin, fatty alcohol, amorphous lipophilic silica and
solvent, all of which are necessary, a number of optional additives may
also be present to improve the composition or the final film. For example,
as a performance additive, there may be added an extremely low volatility
oil which will be certain to remain in the film even if the conditions are
such as to cause evaporation of the solvent. Preferably, such an oil would
have a volatility of no more than 7% weight loss when measured over a 22
hour period at 225.degree. F. Naphthenic oils are exemplary such as
Sunthene 410, a product of Sun Petroleum Products Co.
Another additive which improves the properties of the obtained film is
polyethylene. Granular polyethylene dissolves in the system at elevated
temperatures and provides mechanical rigidity to the structure and serves
to prevent syneresis. The preferred polyethylene to be used is oxidized
polyethylene because of its imagibility and image stability properties. It
is very difficult to find a polymeric additive which will have suitable
imagibility and image stability properties in view of the fact that most
polymers are either non-compatible with the chemistry of image formation,
or they affect the stability of storage, that is, they promote syneretic
separation. The preferred polyethylene product for use in the present
invention is produced by Allied Chemical Company under the name AC
Polyethylene 655.
As stated hereinabove, the color-producing functionality of the phenolic
resin is greatly improved when it is present either in conjunction with a
zinc salt or in a form which is actually reacted with a zinc compound in
order to produce a zincated resin as, for example, in U.S. Pat. No.
3,732,120. While the term zinc is being used, because this is the
preferred cation, other metal cations may also be used, such as cadmium
(III), zirconium (II), vanadium (II), manganese (II), calcium (II), nickel
(II), cobalt (II), strontium (II), aluminum (III), copper (III), and tin
(II).
When a metal salt is used as an additive along with the phenolic resin, it
is important that it be a zinc salt which is soluble in the system. Liquid
zinc salts which are soluble in the system are preferable to solid zinc
salts, such as zinc abietate, because the liquid salt will also provide
performance characteristics for the ink, such as reducing tack, which are
desirable when using letterpress printing, therefore improving press
performance. Furthermore, they remain liquid on the paper to contribute to
the plasticity of the resin film and promote ready contact of the
color-producing reagents. Zinc abietate is operable as far as its color
producing functionality, but adds no appreciable properties with respect
to improving press performance. Zinc salts which are not organic solvent
soluble, such as zinc acetyl acetonate, should not be used as they cannot
be compounded into the system. The preferred compounds are liquid zinc
alkyl-carboxylate salts, preferable zinc octoate. Also useful is zinc
neodecanoate.
It should be understood that the present invention is not meant to exclude
other additives for the purpose of further modifying the physical
properties of the ink or effecting economy, as long as the imaging and
image durability properties of the coating and the spongy nature of the
coating, are not unduly affected.
When a volatile solvent is used, an amount of solvent sufficient to
dissolve both the phenolic resin and the fatty alcohol is used and the
remaining ingredients are present in the following ranges:
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Phenolic resin 54-95%
Fatty alcohol 2-40%
Lipophilic silica 0.5-6%
______________________________________
When a non-volatile solvent is used, the following relative proportions of
ingredients are contemplated within the ambit of the present invention:
______________________________________
Preferred
Range % Range %
______________________________________
Phenolic Resin 10-70% 20-50%
Fatty alcohol 2-20% 2-15%
Lipophilic silica
.5-6% .5-5%
Non-volatile solvent
18-82% 35-69.5%
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With respect to the additives, the polyethylene may be added in the range
of 1-6% of the total formulation, preferably 2-4%. The plasticizing oil,
such as a naphthenic oil, is added in an amount of 5-20%, preferably
5-15%. When a liquid zinc salt is used, it is added in a range of 2-15%,
preferably 5-10%. It should be understood, however, that the liquid zinc
salt also functions as a plasticizing oil, therefore the combined amount
of naphthenic oil and liquid zinc salt should not exceed 20% in the
formulation, and preferably should not exceed 15%. When a solid zinc salt
is used, such as zinc abietate, it is added in the amount of 5-15% and
preferably 7-10%.
The fully stabilized functional coating weight of the coating composition
in accordance with the present invention is preferably 0.4-1.4 g/m.sup.2,
preferably 0.7-1.1 g/m.sup.2.
In preparing the formulation, the liquid ingredients are first mixed and
then heated to 90.degree.-110.degree. C. Then the solid components are
added, preferably in the order: polyethylene, cetyl alcohol, pyrogenic
silica, zinc abietate, phenolic resin.
The following examples will better illustrate the invention:
EXAMPLE 1
Ink Formulation.
With heating (90.degree.-110.degree. C.) and stirring the following
materials are combined, conveniently in the order shown:
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Range % Preferred %
______________________________________
Mineral seal oil 25-32 29.5
Sunthene 410 5-9 7
Zinc octoate 4-8 6
AC Polyethylene 655
2-4 3.5
Aerosil R 972 2-4 4
Cetyl alcohol 5-10 8
Polytack 100 (zinc abietate)
5-12 8 Novolac
HRJ 1216 (zincated
novolac resin) 30-40 34
100%
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The ink so produced is ready for use. Novolac HRJ 1216 is available from
Schenectady Chemicals, Inc. The preferred non-zincated novolac resin is
HRJ 426, also available from the same source.
EXAMPLE 2
CF Record Sheet.
A letterpress printing press was loaded with the ink of example 1 and
adjusted to apply the equivalent of 0.15-0.35 (and preferably 0.2-0.3)
lbs. of ink per ream of 17.times.22 inch paper. This proportionate weight
of application is used regardless of whether the press is web-fed or
sheet-fed. A solvent loss (by evaporation) on the paper of 20-30%
sufficient to immobilize the ink to leave it in a plastic state, was
observed to have occurred in 1-4 hours. Evaporation and diffusion continue
in the roll, but appear to be essentially complete to give a stable
product within 48 hours after application. A high speed press, having
speeds in excess of 1,000 ft./minute may be used without objectionable
misting.
A commercial CB sheet, having a coating of CVL-mono-isopropyl biphenyl
droplets in microcapsules thereon, when mated with the sensitized record
sheet of this example, gave dark blue to blue-black marks on the
sensitized record sheet at points corresponding to positions marked on the
upper surface of the CB sheet.
The final results of the present process is substantially superior to all
other CF coatings, particularly in view of the fact that only a very thin
film is necessary. Despite the fact that a very thin film is used, the
properties of the record sheets are actually superior than when larger
amounts of resin are deposited by prior art processes. Furthermore, the
adhesion of the thin film of the present invention through the paper is
extremely good, substantially eliminating dusting and minimizing
offsetting. The entire coating remains on the surface of the paper and
does not unduly diffuse itself within the fibers, thus leaving the entire
reactive body of the coating on the surface of the paper, and yet highly
adhesively bonded thereto.
The preferred composition of the present invention is also extremely
important in that it can use standard printing presses unmodified without
affecting any of the rollers used on conventional presses. Therefore, it
can be easily used with conventional presses to place discontinuous
portions of CF coatings on portions of the paper in the midst of the
regular printing process which is otherwise printing the forms. In other
words, it is equally adapted to both selective and general coating.
Discontinuous printing with screening effects on the print surface may
also be used.
Another desirable property of the composition of the present invention is
its functionality at high speeds in excess of 1,000 ft./min. without
objectionable misting. Special venting is not required. Water evaporation
is not necessary, thus resulting in energy savings, and the dimensional
stability of the paper is retained. Furthermore, this is a pumpable system
which can be automatically fed to the press; therefore, the entire ink may
be formulated and stored before use. No storage limitation conditions have
yet been ascertained. Because the tack and the body of the resin are
controllable in accordance with the present invention, any type of
conventional printing press may be used including letterpress,
flexographic gravure, offset, etc.
Although preferred embodiments of the composition coated sheet and process
of the present invention has been described, it will be understood that
within the purview of this invention various changes may be made in the
form, proportion and ingredients and the combination thereof, which
generally stated consists in a method and a composition capable of
carrying out the object set forth, as disclosed and defined in the
appended claims.
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