Note: Descriptions are shown in the official language in which they were submitted.
~8~
Related Application
I'his application is related to copending,
commonly assigned Canadian application serial no. 41~,431,
filed ~ctober 28, 19~2.
Background of the ~nvention
Screen printing is a well established and sub-
stantial industry. Essentially, printin~ screens are im-
parted with various designs, art work or printed indicia
by rather permanent emulslons on the screen for locali~ed
appllcation oE dye pastes or inks used in reproducing the
image from the screen. The emulsions surroundin~ the image
areas of the printed screens are resistant to inks so that
they resist removal during the printin~ process when ink is
applied through the screen for reproduction of the images
therefrom. The same quali~ies which make emulsions resis-
tant to ink and cleaning solvents can make them more diffi-
cult to be removed Erom a printed screen. Printing screens
are usually made from silk, synthetic fabric or metal
materials and, in the practice oE screen printing, it is
common to reuse them. This involves a cleaning process
whereby ink residue ~rom one printing operation will be
removed and cleaned from the screens which permits their
storage and later reuse. In the removal of ink, it is
sometimes important not to affect the emulsion area which
has been imparted to the sreen. Modern day screen printing
has evolved rather complex ink or dye formulations which are
sometimes very difficult to remove. Agents which may be
suitable to clean inks from the screens may also affect the
underlying emulsion. Therefore, screen printing lnvolves a
balance~ variety of chemical processes in which ~creens are
prepared from artwork with semi- to fully-permanent emulsions
for reproducinq ink images in a manner such tha-t the emulsion
areas resist ink attack. In such operations, the screen is
repeatedly clear)ed For filinc~ an~/or subse(luent reuse. It is
mab/ . ~
also important that the screen be capable of reclamation when
ink image and/or emulsion areas are removed with different
types of screen reclaiming solu~ions or agents.
Commercial screen printing shops usually clean or
reclaim many screens daily and, for this purpose, employ screen
cleaning machines or reclaiming systems. Such cleaning
machines or recl~;~;ng systems usually employ recirculating
solvents which allow the synthetic or metal screens to be
introduced and either cleaned or reclaimed, depending upon
production requirements. In addition, other commercial
operations involve hand cleaning or recl~;m;ng with various
solvents or corrosive agents. During the course o cleaning or
recla;~;ng, the screen printer is often in intimate contact
with the chemicals or solvents. There are many solvents or
agents used in screen cleaning and reclama~ion. The three mos~
c~ orly used agents may be classified as aliphatic
hydrocarbons, aromatic hydrocarbons and oxygenated solvents,
and less frequently, chlorinated solvents~ Aliphatic
hydrocarbons are commonly referred to as "mineral spirits" bu~
more accurately these aliphatic solvents are composed of
mixtures of straight-chain and/or branched-chain saturated
hydrocarbons. The higher the molecular weight or the number of
carbon atoms, the higher the boiling point of the solvent. The!
higher the boiling point, the slower the solvent will
evaporate, hence, usually the higher boiling aliphatic
hydrocarbons are desirable for use in screen cleaning. The
aromatic hydrocarbon solvents include cyclic hydrocarbons
containing the benzene ring. These aromatic hydrocarbons are
usually more flammable but much stronger in solvation power
than the aliphatic type solvents and, similarly, the higher the
~9~
molecular weight for the aromatic hydrocarbon, the higher the
boiling range. In contrast to the rather non-polar
hydrocarbons, oxygenated solvents are more polar compounds.
Typically, oxygenated solven~s are those having hydroxyl or
carbonyl groups, and many of them have considerable solubility
in water. Other solvents include chlorinated solvents which
are fully~ or semi-chloxinated hydrocarhons and the rarely used
fluorinated hydrocarbons of the Freon types.
Today's screen printer thus routineLy deals with a
multiplicity of solvents which are used for screen cleaning and
reclamation. In the past, when there was perhaps little
understanding of the health and safety hazards which printers
or wo~kers were exposed to, such solvents were used with
impunity. More recently, in view of Federal and State legis-
lation, solvents must meet material safety standards. Pro-
longed ox repeated sol~ent contact with the skin is generally
avoided and, in most instances, because of fl ohility,
solvents must be kept away from e~L~ c heat or open flame, and
frequently fire departments request their s~orage outside.
Occupational Safe~y and Health ptlm;ni~trations at both Federal
and State levels have also placed various restrictions upon the
use of solvents and, many may no longer be used. Furthermore,
in known processes, hot reclamation systems have been requlred
in order to clean or reclaim printing screens, but such systems
crsate pollution and hazards which are no longer tolerable. In
the search for suitable screen cleaning and reclamation sol-
vents or agents, it would be desirable to be able to el;m;n~te
the DOT (Department of Transportation) red label which warns of
hazardous, fl~ -hle solvents. It would also be desirable to
offer cleaning and reclamation composi~ions which are either
completely or essentially biodegradable. Another highly
desirable objective would be to make available to the industry
cleaning and reclamation products having a high threshold limit
values (TLV) which means that the amount of aixborne matter
provided by such products offers greater safety in breathing.
The above background provides a practical overview of
the screen printing industry from the standpoint of the
cleaning and reclamation processes to a person of ordinary
skill in this art. In addition, in the preparation of this
application, patents have been loca~ed which may be considered
to relate to the subject matter of this invention. The
following is a list of prior patents which may be helpful in
understanding this invention without leaving the impression
that it is exhaustive or that there may not be more relevant
patent art or literature: U.S. Patent Nos. 2,780rl68;
3,459,594; 3,511,657; 3,615,827; 3,642,537; 3,673,099;
3,679,479; 3,706,691; 3,737,38~; 3,764,384; 3,78~,007;
3,796,602; 3,928,065; 3,953,352; 4,024,085; 4,055,515 and
4,070,203. It must be mentioned that these patents have been
listed with the knowledge of this invention and even have been
obtained from non-analogous arts. Ther~fore, it is not to be
in any way inferred that their listing here rapresents the
state of the printing screen cleaning or reclamation art.
It is submitted that there is a need for printing
screen cleaning and reclamation compositions which are effec-
tive in a wide variety of applications. Moreover, it is highly
desirable that such compositions, while effective, ~everthe-
less, meet environmental health and safety standards~
.,
Sur~ary of the Invention
~ 'his invention :l~ directed to p~intincJ screen
cleaning or reclaiming methods which are generally efEec-
tive in solvating or degradiny inks used in the printiny
industry. 'rhe methods furlction witll ink cleanirlcJ composi-
tions which not only solubili~e or degrade broad classes
oE printing inks, but also possess high or no ~lash points,
excellent bioclegradabilities and high threshold limit
values. Thus, the health and safety of the screen printer
or worker in the industry is exceedingly enhanced by this
method. In addition, this invention provides for methods
of cleaning and reclaiming printing screens which are
syner~istically operative whereby inks can be removed and
the printed emulsion on the screen may be sensitized for
effective removal. In addition, in another of its general
aspects, this invention involves a method Eor cleaning or
cleanin~ and reclaiming printing screens made of silk,
textile, metal or other types, without damaging the screen
and to place it in an immediate condition for either
stora~e or reuse.
The method o this invention employs the
unique compositions disclosed in said copendin~ application
serial no. 414,431, which consist essentially of N-methyl-
2~pyrrolidone (herein simply sometimes "N~lP"), an oxygenated
solvent and a surfactant. ~s reported therein, a non-
aqueous system of these essential components will solubilize
and degrade a wide variety of polymeric or other inks
currently being employed in the modern screen printin~
industry. The composition has been found to penetrate,
emulsify and prevent redeposition of inks during their
-- 5 ~
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removal from a variety of common printing screens. It has also
been discovered that the NMP, oxygenated solvent and surfactant
composition must be non-aqueous in order to e~fectively clean
screens or to sensitize the cleaned printed screen for subse-
quent emulsion removal, if desired.
In this invention, a screen cleaning or reclamation
method is provided b~ spra~ing a concentrate of NMP, oxygenated
solvent and surfactan~ system (herein sometimes simply "NMP
concentrate") onto a screen surface for a sufficient dwell time
to enable solubiliæation or degradation of the ink. Then, the
ink may be rinsed with water to remove it from the screen. By
this method, the ink is degraded to a point whereby a medlum to
high pressuxe, low-volume water spray will permit the complete
removal of ink. According to the method of this invention, the
NMP concentrate is sprayed onto the screen ink surface.
Spraying a coherent spray of the Nl~P concentrate enables
extremely low amounts to be used and degradation may still
surprisingly be achieved. It has also been found that, after
the ink cleaning step with the N~ concentrate, the printed
emulsion is in a sensitized state for r~ val from the screen
with a periodate containing emulsion remover. The screen may
thus be totally recl~; m~ . Therea~ter, i~ further desired, any
image ink residue or "ghost" as the term is used in the trade,
may be removed with a caustic solution containing oxygenatçd
solvents. By the above sequence, this invention also providas
for an overall screen cleaning and reclamation process.
As developed in the background of this invention, hot
solvent and alkaline techniques have been employed in the prior
art screen cleaning and reclamation. This invention avoids the
need for such hot cleaning techniques and ~he associatPd health
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hazards created by such techniques. In another of its aspects,
the invention is capable of performance at ambient or room
temperature conditions. In this essential respect, it is
considered highly unexpected and unobvious that a cleaning and
reclamation process could operate at such low or ambient
temperatures and be as effective in removing a wide variety of
ink compositions. Furthermore, whereas it has been disclosed
in prior patents to employ derivatives of pyrrolidone including
alkyl pyrrolidones, in cleaning compositions, it has not
heretofore been suggested that any such pyrrolidone derivative
may be employed in a composition or me~hod for the L~- - val of
screen printing ink compositions. Fur~hermore, even where
pyrrot;~o~es have been suggested in non-analogous arts, they
generally are en~ployed in aqueous systems in contrast to the
essentially non-aqu~ous concentrates of this invention. Also~
for purposes of this invention, N-methyl-2 p~L r olidone is
essentially required to operate in combination with oxygenated
solvents and surfactants in order to achieve the most optimum
desired results. In substance, in the screen printiny
industry, it has not been heretofore suggested that a
non-toxic, biodegradable and very safe cleaning composition may
be provided, and still achieve highly desirable cleaning and
synergistic reclamation ef~ects, as has been provided by the
methods of this invention.
SB
Detailed Description of the Invention
As delineated above, the method o this invention
employs compositions of N-methyl-2-pyrrolidone~ an oxygena~ed
solvent and a surfactant~ In a preferred composition, the
oxygenated solvents are a co~bination of butyl cellosolve and
cyclohexanone. These preferred oxygenated solvents are from
the class of glycol ethers, alcohols and ketones, respectively.
Other classes of applicable oxygenated solvents include esters
and ethers, and mixed classes thereof. The surfactant is
preferably from the group consisting of nonionic or anionic
surfactants, or mixtures'thereof, and a specific example of
nonionic surfactant is octyl phenoxy (polyethoxy) ethanol of
Rohm & Haas, sold under the trademark TRITON X-114 and an
organic phosphate ester sold under the trademark GAFAC RP-710
by General ~n~ 1; ne and Film Corporation. Fuxther Pxamples o~
oxygenated solvents from the class of glycol ethers which may
be used include methyl cellosoIve, hexyl cellosolve, cellosolve
solvent, methyl carbitol, carbitol solvent, butyl carbitol,
hexyl carbitol, and the liXe. Other examples of ketones
include methyl ethyl ketone, methyl isobutyl ketone, methyl
isoamyl ketone, ethyl butyl ketone, isobutyl heptyl ketone,
isophorone, diacetone alcohol, acetone, and the like. O~her
examples of ethers include butyrolactone, die~hyl carbitol and
dibutyl carbitol, and others. Examples of esters include butyl
lactate, butyl acetate, butyl carbitol aceta~e, carbitol
acetate, butyl cellosolve acetate, cellosolve acetate, 2-ethyl
hexyl acetate, amyl ace~ate, methyl cellosolve acetate,
formates, and others. Examples of alcohols include amyl
alcohol, butyl alcohol, furfurol alcohol, 2~butyne 1,4,diol,
, ~_
tetrahydrofurfurol alcohol, and others. Therefore, in
accordance with the broader principles o this invention,-
oxygenated solvents from the above mentioned classes are
suitable for use, dependlng upon the required solvating
capacities of the oxygenated solvents in order to obtàin the
most desired biodegradability, least flammability and highest
threshold limit values to meet or exceed health and safety
standards. In accordance with the preferred principles of this
invention, however, as mentioned above, there are specific
e~amples which meet all of these criteria in the mos~ preferred
aspects o this invention. In a generic aspect, the oxygenated
solvent facilitates the low viscosity solvating character of
the NMP and helps disperse it ~o solubilize or degrade the ink
compositions. The NMP is also water active when needed. Thus,
the combination of the NMP and the oxygenated solvent provide a
coaction between organic co-solvents along with a unique water
activity to provide a synergistic action in solvating or
degrading of ink compositions on ~creens for removal with
water. Yet, it is imperative tha~ the NMP concentrates be
essentially non-aqueous during solvation or degradation of ink
because any significant water will destroy the effectiveness of
NMP in its cleaning power as i~ is used in this invention.
However, the solvated or degraded ink must then be in a state
for removal with a low-volume, pressurized stream of water.
In addition to the surfactants mentioned above, other
nonionic, anionic, cationic and amphoteric surfactants may be
used, as listed primarily in McCutcheon's Detergents and
Emulsifiers, 1980 ~dition, MC Publishing Company, Glenrock/ New
Jersey. The surfactants aid in the dispexsion and degradation
l of the inks for aqueous removal. Surfactants of the anionic
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type may be (1~ of the group of saponified fatty acids or
soaps, or ~2~ of saponified petroleum oil such as sodium salts
or organic sulfonates ox sulates or (3) of saponified esters,
alcohols or glycols, with the latter being well known as
anionic synthetic surfactants. Examples of these anionic
surfactants include the alkaryl sulfonates or amine salts
thereof such as sulfonates o dodecyl benzene or diethanolamine
saLt o dodecyl benzene sulfonic acid. Most of these
sulfonates contain many chemical species. The class name given
to most of them is "alkylaryl sulfonate". Simply, this means
that a paraffinic hydrocarbon is bonded to an aromatic or
benzene nucleus and the aromatic portion has been sulfonated.
Examples of saponified fatty acids (C6-C24) are the sodium or
potassium salts of myristic, palmitic, stearic, oleic or
linoleic acids or mixtures thereof. Also in this class of
anionic surfactants are organic phosphate esters including
alkali and alkaline earth metal salts of neutral phosphoric
acid esters o~ oxylalkylated higher alkyl phenols or aliphatic
monohydric alcohols. Aerosol OT is a dioctyl alkali metal
sulfosuccinate anionic surfactant made by Cyanamide. The
nonionic surfactants suitable for use commonly ha~e hydrophylic
portions or side chains usually of the polyoxyalkylene type.
The oil soluble or dispersible part of the molecule i5 derived
from either fatty acids~ alcohols, amides or amines. By
suitable choice of starting materials and regulation of the
length of the polyoxyalkylene chain, the surfactant parts o~
the nonionic detergents may be varied as is well known.
Suitable examples of nonionic surfactants include alkylphenoxy
polyoxyethylene glycol, for example, ethylene oxide adduct o
o either oc~yl-, nonyl- or tridecyl- phenol and the like~ These
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ment~oned nonionic surfactants are usually prepared by~the
reaction of the alkyl phenol with ethylene oxide. Commercial
products are sold under the trademarks "Triton X-100 or
X-114"by Rohm and Haas Co. ox "Tergitol" by Union Carbide and
Carbon Corp. which are alkyl phenyl ethers of polyethylene
glycol. Othex specific examples of nonionic surfactants
include glyceryl monooleate, oleyl monoisopropanolamide
sorbitol dioleate, alkylol amides prepared by reacting
alkanolamides such as monoisopropanolamine, diethanolamine, or
monobutanolamine with fa~ty acids such as oleic, pelargonic,
lauric and the like. The cationic surfactants are also well
developOed and mainly include betaines and quaternar~ n; um
compounds. Some specific examples of be~aines include
imidazoline betaines, aliphatic and carboxycyclic betaines, and
betaines with hetero atoms in the hydrophobic cha;n~s such as
dodecyloxypropyldimethyl aminoacetic acid. Typical of the
quaternary ammonium compounds that may be mentioned are
dimethyl dicoco ammonium chloride, cetyl pyridinium aceta~e,
methyl cetyl pip~xidinium proprionate, N,N dilautyl, N,N
dimethyl ammonium diethophosphate, and the like. Thus, it will
be understood that other anionic, cationic, amphoteric or
nonionic surfactants may be employed in accordance with the
principles of this invention.
The amounts of ingxedients vary over wide ranges,
however, it is preferred to use a significant amount of the
N-methyl-2-pyrrolidone, i~e., about 30-85% by weight. The
oxygenated solvent is usually contained in amount o about
15-35% by weight. The r~m~in~er of the composition comprises a
surfactant or a mixture of surfactants within the range of
about 1 to about 5% by weight. The NMP concentrates m~y aI~o
be supplemented with other organic solvents such as methylene
chloride, trlchloroethane, dimethyl sulfoxide and its deriva-
tives, fluorocarbons, and freons in amounts of about 10-30% by
by weight where additional faster penetrating power may be
desired for ink solubilization. Such organic solvents are
permitted which would not alter the essential characteristics
of the ink cleaning compositions of this invention and may help
to enhance activity of the co-solvents in penetrating,
emulsifying and accelerating the degradation of ~he inks foir
subsequent removal.
In order to fur~her illustrate the invention, refer-
ence is made to the specific operating for~llAq detailed
hereinafter and detailed methods of cleaning and recla;m;ng a
printing screen.
EXAMPLE 1
75.72% N-methyl-2-pyrrolidone
18.52~ Butyl Cellosolve
3.04~ Cyclohexanone
2.62% OctyI Phenoxy IPolyethoxy) Etbanol
(TRITON X-114~
0.10~ Organic Phosphate Ester
tGAFAC RP-710)
I
EXAMPLE 2
37.86% N-methyl~2-pyrrolidone
9~26~ Butyl Cellosolve
1.52% Cyclohexanone
24.00~ Cellosolve Acetate
26.00% MethyLene Chloride
1.31% Octyl Phenoxy (Polyethoxy~ Ethanol
ITRITON X114)
0.05~ Organic Phosphate Ester
(G~FAC RP-710)
In the alternative to the specific ingredients of
Example 2, 50~ o Example 1 may be combined with 26~ of methy
lene chloride and 24% cellosolve acetate. Examples 1 and 2 are
preferred formulas for ~he N~ cleaning concentrates because of
their biodegradability, reduced fl ~hility and low TLV
values.
Before describing in detail the cleaning and re-
claiming of printing screens emloying the methods of this
invention, an unders~n~i ng of certain underlying facts or
terms is impox~ant. First of all, the ink side o~ the printing
screen is alternately c~lled the squeegee side, thQ well side,
or the front side, but for purposes of this description-it will
be called the ink side. The opposite side o the screen is
called the back side, down side or print-contact side. Again,
for purposes of this description, it will be called the print~
contact side. The term "ink" will be the generic term for many
of the compositions that are employed in tha practice of screen
printing including dyes or inks commonly referred to as
flexible enamels, synthetic enamels, fast-dry enamels, flexible
l3
lacquers, industrial lacquers, flat vinyl ink, vinyl half-tone
ink, fluorescent vinyl ink, gloss vinyl ink, satin vinyl ink,
flock adhesive, transparent ink, me~allic powders, acrylic ink,
plastisol ink, mylar ink, textile ink, among many other types
of inks. For general information on ink compositions, refer-
ence may be had to the catalog by KC Graphics, Inc. 1978-1979,
copyright 1978 by KC Graphics, Inc. Reerence may also be had
to "Te~tile Screen Printing" by Albert ~osloff, Second Edition,
International Standard Book Number 0-911380-39~6 (1976). These
sources will also serve as backyround information for the inks
which may b~ cle~n~ with the inventive cleaning compositions.
As developed above, the printing screen may be made from a
number of materials and may have various mesh sizes. A mono-
ilament screen is a single strand of material for example of
polyester, nylon, stainless steel, silk, chrome-plated wire, o~
other things r which is woven into a specific number of squares
per a d; -nsionr i.e., a 230 mesh means 230 open squares per
square inch. A multi-f;1~Qnt screen is comprised of a sexies
of strands of similar materials just mentioned, braided before
weaving into the mesh measurement, i.e., 12xx150 mesh would
mean lZ interwoven strands subsequently woven into 150 open
squares per square inch and, where the cross-over points of
mesh occur, pigment can get into the strands and ma~ become
extremely hard to L~...ove. Thus, it may be determined by this
description of either the mono-filament or the multi-filament
screens that the requirements for complete removal of ink
residue, for instance, may differ due to the construction of
the screen. In particular, that last residue often referred to
in the art as "ghost" or "haze" would be more readily apparent
in the multi-filament screens where pigment can get into the
strands and becomes very hard to remove. There are a number of
classes of emulsions which ini~ially cover the print-contact
side of the screen. For ins~ance, a direct emulsion is a
water-reducible substance which cures to a temporary,
non-removable substance when exposed to specific wavelengths of
light. For instance, the art work can be placed over the fresh
emulsion while it is still reactive to water and exposed to
halide light, at which time the part of the emulsion not
expos~d to the light~ because it is covered with the art, stays
water reactive. After a certain shooting or light exposure
time, the art i5 Le...Oved~ the screen is then flushed with water
and the part that has not been exposed to the light is flushed
out, leaving the emulsion-void image area through which the ink
1OWS through the screen for printing. The measure of
difficulty of emulsion removal also relates to the number o
coats ~hich are put on the mesh, that is, dried and reapplied,
and so orth, until you have between, for instance, 2 to about
5 coats of emulsion. Thus, the degree of dificulty in
removing emulsion depends upon a number of factors including
the number of coats, whether i~ is strongly sensitized, the
exposure time, type of light activa~ion and chemical hardeners
used after emulsion development, among other factors.
In view of the above background, the cleaning
composition of Example 1 is a liquid non-aqueous solvent
con~entrate having a flash point of approximately 200F (95C)
and it is designed to remove a large variety of inks and paints
from screens. In another eature of the method, NMP
concentrate of Example 1 prepares or sensitizes many common
emulsions for subsequent removal with a low-volume, high
pressure water rinsing. It i5 fast, efficient, economical by
1~
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its capability of low-volume usage~ biodegradable and does not
carry the red label (DOT fl~mm~ble~ solven-t designation. It is
also safe on all screens and can be left on screens for
extended periods prior to rinsing for cleaning. In the method
of this invention, the ink side of the screen is sprayed in a
light even pattern with a cohesive spray to prevent
volatilization, followed by a dwell time of about 2-5 minutes.
A pressuriæed unit is operated for example under about 30 to
100 psi (typically 40 psi~ to provide a coheren-t stream of
concentrate from a nozzle about 6" to 12" away rom the screen.
Mists are avoided. After the spray treatment, the degraded
inks are then easily removed by a light to high pressure, i.e.,
approximately 50 to 1000 psi, low-volume ~ater rinse.
Lo~-volume means 2 - 4 gallons per minute. A an spray has
been found preferred to provide a balance of force and
quantity. A suitablè fan spray nozzle is the UniJet 65/01
manufactured by Spraying Systems Company of Wheaton, Illirois.
It is important, as developed above, that the screens on which
the ink will be solubilized or degraded are free fxom water
'0 prior to cleaning. The presence of water either in khe N~
concentrate or on the screen greatly destroys the effectiveness
of the composition.
It has been found that tAe most preferred cleaning
technique for achieving the advantages of the invention is the
method ~hereby the cleaning concentrate is sprayed onto the ink
side of the screen in a light even pattern and allo~ed to dwell
for a short period of time, i.e., several minu~es up to several
hours~ depending upon the factors involved in the cleaning
system, composikion of the inks, production timing, and so
forth. During the dwell time, the liquid cleaning concentrate
- lfi -
*trade mark
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penetrates, emulsifies and solubilizes the ink. The ihk stays
on the screen, but its ormer ink character is destroyed.
During the dwell ~ime, the co-solvent actions of N-methyl-2-
pyrrolidone and the oxygenated solvent are at work. Further-
more, the surfactant is penetrating the ink composition for
dispersion and to aid in later ink removal by water. The
coaction of all three ingredients permits the solubilization or
degxadation of the ink permitting it ~o be dispersed easily for
removal. The ~-methyl-2-pyrrolidone provides water activity to
the composition for removal with water~ however, water must be
under pressurized conditions such that the ink composition may
be blown out, i.e., blo~n away from the screen. Thus, the
composition is a delicate balance of ingredients whereby
organic c~mronents of the ink may be solubilized or degraded by
both the N-methyl-2-pyrrolidone and oxygenated solvents.
Furthermore, even though water during the presence of the
soluhilization and degradation of the ink would be detrimental
to the activity of N-methyl-2-pyrrolidone, nevertheless, the
degraded ink in the presence of the NMP and cosolvent is
water-active and may be L~.~.ov~d from the screen with a pres-
surized fan of low-volume water rinse. In this connection it
is preferred to employ a slicing fan or stream of water and
sweeping it across the screen rom the bottom upwards in a
~nner such that the ink may be removed without redeposition.
The composition of ~xample 2 above is employed in the
same manner for cleaning as the li~uid solvent concentrate of
Example 1. However, the presence of methylene chloride tends
to enhance the penetration of the entire composition and
cellosolve ace~ate enhances the wa~er solubility of the
composition. Other organic solvents which may be substituted
~&-
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for ~he methylene chloride include other chlorinated solvents
like l,l,l-trichloroethane, dimethyl sulfoxide, its derivatives
and fluorocarbons ox Freons, In either case, the addition of
such an organic solvent which enhances penetration, may also
tend to evaporate and, therefore, has a much shorter wet life
or dwell time on the screen. For instance, whereas the
composition of Claim 1 may be left on the screen surface for a
number of hours, the composition of Example 2 i5 usually
employed for several minu~es, i.e., between 2-5 minutes for
example. It is to be further understood that the ink
solubilizer of Example 1 may be sequentially used in
combination with the cleaning concentrate of Example 2. For
instance, during the course of a cleaning operation, the ink
may be solubilized with the Example 1 concentrate where~an
operation may require screens to be left from production for a
period of time up to several hours prior to the rinse .~ val
of the ink. In such a case, the dwell time may be followed by
a fresh degrading concentrate of Example 2 so that the residue
may be activated for subsequent removal with a low-volume, high
pressure water rinse. Furthermore, the amounts of the mate
xials sprayed onto the substrate vary but normally they are
withLn the range of several ounces per several ~quare ~eet, for
example, 2-4 ounces per 6 foot square of screen.
Thus, in a preferred aspect, the me~hod of this
invention involves spraying of the conc~ntrates of either of
the Examples 1-2 onto a screen. The spray is an economieal and
low volume usage followed by dwell time to solubilize and/or
degrade the ink. Thereafter, a low-vol~me, high pressure water
stream is directed at the substrate, preferably a fan spray is
employed to slice through and help remove the destroyed ink
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composition. If the solubilized and degraded screen were
simply dipped in water, the inks would set up and the screen
would not be efectively cleaned. There is a balance between
the force and the quantity of the water which is employed which
will be understood by the person of ordinary skill in the art
in view of this description.
It has been observed in connection with the method of
cleaning the screens with a low area coverage spray, that a
light mist may tend to settle on o~her remaining areas of
degraded inks. It has been found th~t this problem can be
alleviated or overcome by the addition of another component
into the concentrate. That COmpQnent may be characterized as a
hydrophobic additive and in particular it has been found that
synthetic water soluble oils sold under the trademark UCON are
satisfactory. Depending upon the amount of water mist or
back-lash that is to be expected from the water rinse out, par~
of the surfactant package or liquid NMP concentrake may contain
a water dispexsible oil which functions initially as a water
repellant to a ligh~ water spray or mist, but readily allows a
low volume, pressurized stream of water to removs the ink
compositions previously degraded and solubilized by the NMP
concentrate. Such water soluble oils are of the class ~f
polyalkylene glycols, commonly known as UCON lubricants
manufactured by Union Carbide Corporation, but other types and
mixtures thereo could be used of dif~ering water solubility.
A preferred high molecular weight one is UCON 50-HB5100~
Specific compounds include polyalkylene gly501s, i.e~, an
oxirane polymer, CAS Registration No. 9038-95-3 or ethoxylatecl
lanolin or ethoxylated castor oil. However, it is preferred
Jq
that the oils of the types described herein do not leave a
residue on the screen after an adequate water rinse.
When the printing screen is to be ~otally reclaimed,
that is, cleaned and the emulsion removed completely, the
process is as follows. When the process of printing is com-
pleted~ the operator cards or squeegees off any xesidual ink
that is on the ink side of the screen, as well as any ink from
the print-contact side. From a very prac~ical standpoint, inks
are ~p~n~ive and an attempt is made to return as much of the
ink as possible. From a standpoint of cleaning, more excess
ink requires more cleaning concentrate in order to remove the
ink and reclaim the screen without haæe o~ ghost residue.
After the screen is well carded, either before or after L~l,.oval
from the press, and the cleaning process begins. If the
process is to be an ;mme~;~te reclaim, either the co~centrate
of Example l or 2 may be used, generally speaking, depending on
ink type. Bither concentrate is sprayed on the ink s~de of the
screen and then moved to the reclaim area. In the process of
; d;~te recl~;m;ng, within about 5-10 minutes after the
application of either of the compositions of ~rl es 1 or 2,
immediate recl ~;m; ng should be ~ -nc~d. After spraying with
either concentrate, the image is flushed out from the
print-contact side of the screen with high pressure water, as
developed above, and this clears all or practically all of the
ink. At the same time, the entire surface of the emulsion is
wetted with water to prepare it for the application o a
periodate-containing emulsion L~ ver. It has been found that
there is a synergistic action resulting from use of the
non-aqueous concentrate of Example 1 or 2 whose residue ~ jn!~
even after the watex spray such that the emulsion is sensitized
,~o
~--
for faster removal. It is theorized, however, that in the
immediate reclaim process, the emulsion is somehow softened or
made more permeable for the treatment with a
periodate-containing emulsion remover. A suitable example of
an emulsion remover is exemplified by Example 3.
EXAMPLE 3
94.096~ Water
2.880% Sodium Meta Periodate
3.000~ Monosodium Phosphate~ Anhydrous
110 grams/1000 pounds water of an Anionic Surfa~tant
Package of Equal Amounts
of GAFAC RP-710, identif.ied
above and CALSOFT F-90 Isodium
dodecylbenzene sulfonate)
The above periodate cont~;~;ng remover is then
sprayed onto the screen surface on the print side and is per-
mitted to dwell there anywhere from about 15 seconds to several
minutes. This is generally an adequate time for degradation ~of
the emulsion. Again a high pressure spray is employed to clean
the emulsion from the screen. As developed above, it is
important that residual effect of the concentrate of Examples 1
or ~ after the water spray be utilized immediately by following
with an application of the periodate-containing emulsion re-
mover. It has been proven that when more time elapses, for
instance one-half hour, the emulsion will be taken off with
greater difficultv. Accordingly, there is a synergism between
the residual effect of the cleaning compositions of this
invention insofar as they coact with such periodate con~ining
emulsion removers and provide the complete xemoval o~ the
emulsion.
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*trade mark
Finally, in the event that there is a residual ghost
image as explained above, especially in connection with a
multi-filament screen, a ghost or image remover may be
employed. It is to be noted, however, that although there are
at some time residual images, they are not necessarily a
hindrance to further use of the screen and some screen printers
axe not particular where there is a tinge of residue as long as
the mesh squares themsel~es are no~ blocked in the screen. If
a ghost or haze remover is used, it is typically a caustic
solution of oxygenated solvents. The reason for such usage is
that they are water rinsable or soluble and leave no residue to
cause emulsion pro~lems later. In the case of the ghost or
haze removers o~ this type it is necessary to brush, roll or
card them on as opposed to spraying because Qf the enhanced
viscosity. A typical composition is as follows:
31.64~ Cyclohexanone
19.40% Cellosolve Acetate
38.83~ 50dium Hydroxide 50
9.61~ DOWFAX 2Al Solution
(sodium Didodecylphenoxy-
benzenedisulfonate 70%,
sodium dodecylphenoxy-
benzenedisul~onate 30%)
0.01% Brilliant Milling Red Dye
O.51~ GAFAC RP-710 ~identified above)
For screens which will be delayed in processing but
which will be totally reclaimed, it is important to destroy the
ink so that at some time thereafter, that is in a matter of
hours, the screen may be treated. For instance, the compo-
sition of Example 1 is sprayed onto the ink side and, again~
this is a cohesive spray of the type referred to above without
- 22 -
*traae mark
~,'
!
5~
mist so as to reduce volatilization. The screen is thus wet
and the ink tends to stay wet for a period of time. However,
if there is a lapse of time before it goes to the screen shop
for complete removal of the emulsion, there will be some
~endency for drying and possibly some run-down on the print
side of the screen. I this develops, then the print side of
the screen may be resprayed with a composition of Example 2
which acts to freshen up the solubilized residue after treat-
ment with the composition of Example 1 to degrade the ink upon
~eing contacted with the water spray. At this poin~, upon
respraying the print-contac~ side of the screen with a concen-
trate of Example 2, the emulsion is sensit.ized or conditioned
~or the subsequent action with the emulsion cleaner as men-
tioned above. Again, if a ghost or haze occurs, the ghost
remover may be employed as set forth above.
One of the very significant aspects of the cleaning
and reclAim;ng procedures i5 that no urther screen degreasing
is required as is required when products typically availabie i~
the prior art have been used on screens to remove the inks and
emulsions. In the past, toluene, acetone, bleach, trisodium
phosphate, and other solvents or cl~n; n~ agents of the type
indicated in the background of this invention have been
employed in order to ~1 im- n~te screen oily residue at the end
of processing. Accordingly, this invention o~fers a highly
advantageous system for the complete cleaning of inks and
emulsions from printing screens in a manner heretofore
n~chi eved.
In view of the above detailed descrip~ion, printing
screen cleaning and reClA;mlng methods are provided with
distinct advantages over the methods now available. In
~3
5~
addition, methods of employing the compositions of this inven-
tion have been provided which are unique and operate syner-
gistically with other compositions in the process of cleaning
and reclaiming screens. In view of the above detailed descrip-
tion, it will be apparent to a person of ordinary skil1 in the
art that deviations may be made from the specific examples and
methods of operation without departing from the spirit and
scope of this invention.
What is claimed is:
;2 't
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