Note: Descriptions are shown in the official language in which they were submitted.
AZ-743
~057105
DEVELOPING AND STRIPPING OF BINDER-CONTAINING,
PRESENSITIZED COATINGS
Background of the Invention
This invention relates to presensitized litho-
graphic plates. More specifically, the present invention
relates to the removal of photosensitive, binder-containing
coatings used in the manufacture of said plates.
In the present day art, many of the commercially
available presensitized, offset lithographic plates consist
of an aluminum plate or foil coated with a water-insoluble,
light-sensitive compound, SUch as a diazo compound, contain-
ed in a resinous binder.
In practical use, the light-sensitive coating is
exposed to light under a master and the image is developed
by utilizing a developer WhiCh removes the exposed, coated
area, when light exposure is made through a negative master.
After development, in accordance with known pro-
cedures, the printing image is prepared for receiving a
greasy ink and the non-image areas are made hydrophilic by
such known operations as rinsing and acid and salt fixing.
An imaged planographic printing plate prepared in such a
manner will effectively maintain a good diferentiation
between the hydrophilic metal surface and the oleophilic
image, during offset printing.
Photosensitive, binder-containing plates came
into existence as an advance over the practice of lacquer-
ing plates to put a protective cap over the image (U. S.
Patent 3,136,637, Larson; U. S. Patent 3,679,419, Gillich).
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Current plates are, in effect, pre-lacquered, and uniform
factory coating insures higher quality and more consistent,
longer runs with less effort than was possible with previous
post-lacquered plates.
The commercial developers used for development of
the imagedphotosensitive coatings, particularly of those
sensitive to light exposure through a negative master, are
composed of solvents which soften and dissolve the unexposed
resinous areas, so that these areas can be cleaned by mechani-
cal and water rinsing action. Examples of such developers
are given in the U. S. Patents just referred to above.
The metallic surface is thus exposed and then de-
sensitized, following any of the known procedures to make
these metallic surfaces more hydrophilic. The main disad-
vantage in using present developers, espe~ially with current
negative-working developers (using negative image masters),
is that these developers are composed of volatile solvents
such as alcohols, esters, and ethers. Usually, the volatil-
ity of the solvent i9 9uch as to create formulation diffi-
culties, necessitating adjustments in order to minimize
flammability and combustion hazards. The use of volatile
solvents also necessitates that room areas where the plate
development is performed be well ventilated, to protect per-
sonnel from toxic effects. Furthermore, the direct washing
of such solvents into sanitary sewers creates environmental,
ecological problems which require that such disposal in sew-
erage systems be monitored to meet locally acceptable pollu-
tion standards.
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It is therefore an object of this invention to
provide non-toxic developers of very low volatility so that
the image development of the lithographic plates can be
accomplished without hazard to human health and with a mini-
mum deleterious effect on the environment.
Another object of this invention is to economi-
cally reclaim photosensitive-coated aluminum or other metal-
lic foils, which have been rejected for commercial use be-
cause the coatings do not meet quality assurance, specifica-
tion standards. The rejected metal foils can be in the form
of webs or sheets.
Still another object of this invention is to use
the principle described below to provide economical litha-
graphic plate developing processors. The mechanism for such
development is simple, since only a very brief (seconds)
immersion of the imaged plate is required, followed by a
spray rinse with water under pressure, with or without
slight mechanical action.
~rief Summary of Invention
In order to strip unwanted coating, a simple pro-
cessing machine is used. The operation of the process is
best understood by reference to Fig. 1, which shows the pro-
cess utilized for stripping coating. This machine provides
means for transporting a web or plate of coated metal through
a chamber kept filled with the novel developer composition
of the present invention, which is maintained at an elevated
temperature. The coating comes in contact with the develop-
ing solution, absorbs a portion of it and swells. Further,
Aæ-743
`` 1057105
the adhesion of the coated layer to the carrier metal, which
it is desired to strip, weakens materially (deadhesion~. Sur-
plus developer is returned to the chamber by squeegee rollers,
although other means may be used for this purpose. ~o more
developer is needed than the amount which will be absorbed
and swell the coating, there being no benefit in permitting
"drag-out". The total dwell time may be measured in seconds.
After the web has passed the squeegee, it is led to a zone,
in which it is subjected to the action of a high pressure
water spray (with or without brushing action), to flush off
the swelled coating. By simple filtration, the rinse water
may be made reusable or the water slurry of coating particles
may be disposed of in the drain.
When it is desired to develop an exposed plate, the
apparatus of Fig. 2 will be found more useful. This apparatus
provides means for transporting an exposed, cut plate through
the developing bath, squeegee rollers, and, finally, a high
intensity water spray, with or without brushing action.
The developer in the chamber consists principally of:
a. a high boiling glycol or glycol ether, or
ethoxylated or propoxylated alcohol.
b. a non-ionic or anionic surfactant.
c. optionally, a high boiling solvent, and
d. optionally, a small amount of acid.
Brief Description of the Drawings
Figure 1 of the drawings is a perspective view of
apparatus for stripping a presensitized coating from a web of
lithographic plate substrate,and
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~057105 AZ-743
Figure 2 is a perspective view of apparatus for
developing, an exposed, presensitized lithographic plate.
Detailed Description of the Invention
For stripplng coating from a presensitized web of
lithographic substrate, the device of Fig. 1 is employed.
In Fig. 1, a metal roll of coated substrate 1 is disposed on
an unwind stand 2. Guide rollers 3 and 4 lead the web of
coated metal into developing or stripping chamber 5. Follow-
ing immersion in the developing chamber, the web passes
through a set of squeegee rollers 6 which squeegee off excess
decoating solution and return the surplus to the developing
chamber 5. The web is then led into rinse section 11 of the
apparatus. Here, a set of high pressure sprays 7, one on
each side of the web, impinge upon it to remove the coating
(if on both sides). If only one side is coated, one spray
may be dispensed with but it will normally remove residual
developer from the uncoated side. Tha brushes 8, and addi-
tional sprays 9, are optional and may be used when the action
of sprays 7 i9 not complete. The axe~ of guide rollers 10
are tilted away from the horizontal to permit rapid flow of
rinse fluid from the web. Following the final rinse, the
web passes through squeegee rollers 12 and drying zone 13,
and is then recoiled at rewind station 14.
For developing or stripping coated, cut sheets of
lithographic substrate, on a continuous basis, the apparatus
of Fig. 2 is employed. Inasmuch as a continuous web of metal
is not available to be pulled through the various stations of
the apparatus, driven pinch rollers, at suitable intervals,
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1057105 AZ-743
are relied on to grip the leading edge of the sheet and keep
it in continuous motion until it leaves the exit end of the
machine. The cut sheet 15 is carried by rollers 16, 17 and
18 through developing chamber 19. Upon leaving chamber 19,
the sheet passes through squeegee rollers 20 and then through
the pressure spray rinse means 21. As before, optional brush-
es 22 and a second spray rinse 23 may be used. Pinch rollers
24 pull the plate through and propel it into drying zone 25.
Pinch rollers 26 pull the plate out of the machine.
A simple device for developing or stripping cut sh-
eets consists of a heated tank, containing suitable developer,
in which the plates are immersed. After removal from the
tank, they are spray rinsed.
The compositions of stripper or developer consist,
as noted above, of high boiling glycol, surfactant, and op-
tionally, a high boiling water miscible solvent and/or a
small amount of acid.
GlYcol
The glycol portion can be as high as 95% of the
total compo9ition with the other ingredient9 forming the re-
mainder of the composition. As examples of the type of gly-
cols which can be used in this invention, it has been found
that ethylene glycol is satisfactory as well as the ethylene
oxide condensates of ethylene glycol. Such glycols as die-
thylene glycol, triethylene glycol and the higher ethoxylated
and propoxylated polymers can be used. I prefer to select
those glycols of a non-toxic nature, such as diethylene gly-
col. of course, propylene glycol ~an be used as well as its
AZ-743
~057105
derivatives. In the selection of the high boiling component,
the controlling factors o~ selection are non-toxicity and
cost of materials.
Surfactants
Non-ionics: Ethylene oxide condensates of:
Trade Name Manufacturer
Nonylphenol "Igapal CO" GAF Corporation
"Triton" . Rohm & Haas
Iso-octyl cresols "Triton X-100" Rohm & Haas
"Igepal CA" GAF Corporation
Tridecyl alcohol "Emulphogenes" GAF Corporation
Sorbitol "Spans, Tweens" Atlas
Sec. Alcohols "Tergitols" UCC
Fatty acid "Emulphors" GAF Corporation
Alkylamides "Ethomides" Armour
Alkylamines "Ethomeens" Armour
Modified linear aliphatic
polyeth~r "Antarox BL 240" GAF Corporation
Phosphate esters o~
above: "Gafac" GAF Corporation
"Tryfac" Trylon Chemical9
Anionics:
Fatty acid taurates "Igepon T" GAF Corporation
Alkyl naphthalene
sulfonates "Nekal BX, A" GAF Corporation
Alkyl benzene sulfonates "Nacconol" Allied Chemical
Corporation
~ci~
Citric Phosphoric
Glycollic Nitric
Acetic Other mineral acids
Other organic acids
AZ-743
1057105
Solvents
Gamma-butyrolactone
N-methyl pyrrolidone
Dimethyl formamide
Ethylene carbonate
The surfactants, acids and solvents enumerated
above are merely examples, not intended to restrict the
scope of the invention.
The compositions which are useful, according to
the present invention, include from 95% glycol to as low as
25% glycol, with the balance surfactant. It is preferred,
however, to use compositions in which the glycol ranges from
95% to 85% of the total composition, with the balance surfac-
tant. The optional solvent, when added, may constitute up to
60% of the composition. The optional acid similarly may be
added in amounts up to 10% of the composition.
The principle described in this invention has been
found particularly applicable to commercial, negative-working,
presensitized, lithographic plates manufactured by such com-
panies as Azoplate - Division of American Hoechst Corporation,
DuPont, Polychrome, Eastman Kodak, and Minnesota Mining and
Manufacturing Company.
The boiling point of the glycol and the temperature
of treatment with the glycol-containing solution are interrela-
ted to the extent that the boiling point of the glycol should
be above the treatment temperature. The boiling point of the
high boiling solvent should likewise be above the treatment
temperature.
AZ 743
1057105
The treatment temperatures, with glycol-containing solution,
which are most effective depend upon whether stripping or develop-
ing operations are being conducted, upon whether the treating
solution contains solvent, upon the temperature employed in the
rinsing step and upon the nature and thickness of the coating.
Considering all these factors, the treatment temperature may vary
between about 60 and 110 C. The following discussion and
examples illustrate these relatlonships as they affect the treating
temperature .
When decoating ENCO N-50 plates (products of Azo-
plate - Division of American Hoechst Corporation), with or without
added solvent, a temperature ranglng from approxlmately 65 C to
95 C ls suitable . Below the lower temperature the coating is not
sufficiently removed after rinsing. Above the upper temperature,
the coating is removed, but begins to come off in the treatment
solution, which results ln premature depletlon of the treatlng solu-
tlon. The preferred temperature range, for the most effectlve
cleanlng in most cases, ls approxlmately 80 C to 100 C .
When uslng the treatlng solutlon as a developer tto remove
unwanted non-lmage areas) for Enco N-50 plates, the addltlon of
solvent ls preferable. If 25% of butyrolactone ls added, a tem-
perature range from approximately 75 C to 95 C ls sultable, but
best results are obtained at the upper end of this range. Agaln,
hlgher temperatures provlde good development, but are less economl-
cal because removal of non-lmage areas occurs ln the treatlng
solutlon, resultlng in lts premature depletlon. Thls composltlon
w111 not satlsfactorily develop Enco N-100 and N-200 plates
(products of Azoplate - Dlvlsion of American Hoechst
~L057105 AZ-743
Corporation) which have thicker coatings
and progressively longer press lives than ENCO N-50
plates. The addition of butyrolactone to the level of about
6~/o is necessary to accomplish this purpose, (although the 25%
level is sufficient to strip Enco N-100 and N-200 plates). When
developing with the 6~/o butyrolactone-containing solution, the
Enco N-50 plate can be developed at temperatures ranging from
approximately 65C to 85C with the upper end of the range pre-
ferred. Enco N-100 and N-200 plates can be developed within a
temperature range of approximately 85C to 105C.
In general, it has been found that elevation of the
temperature or an increase of solvent concentration, with conse-
quent lowering of the glycol level, for a given operation with
a given plate, shortens the time required for treatment. The
water wash may be carried out at ambient temperature but is
also preferably above ambient temperature. However, it need
not be as high as the treating temperature and is preferably
above about 50C and in the range of about 50 to 60C.
It is further evident that, in view of the numerous
factors of composition and proce9s alr~ady discussed and the
following examples, together with a correct and proper under-
standing of them, with ordinary skill in their application, a
very wide range of commercially available presensitized litho-
graphic plates may be successfully treated and are within the
scope of this invention.
The following examples serve to illustrate the
principle of this invention:
ExamPle 1
A solution, of the following composition:
Diethylene Glycol 57%
~B~ -lo-
~057105 AZ 743
Triton X-100 10%
Gamma Butyrolactone 25%
Phosphoric Acid (85%) 8%,
was heated to 70 - 80 C and a negative-working, presensitized
plate was subjected to a dwell time in the solution of approximately
30 seconds, then removed from the solution, squeegeed and sprayed
for about 3 minutes with water at 50 - 60 C, with and without
slight brushing action .
This solution was found effective for Enco N -5 0, Kodak
LN-M , and Kodak LN-L presensitized and exposed sub-
strates. Full development of the image was obtained, with the
background satisfactorlly desensltized.
Example 2
Following the procedure of Example 1, a solutlon of:
Diethylene Gl,y~ol 85%
Triton X-100 5%
Phosphoric Acid (85%) 10%
was used to completely decoat an exposed Enco N-50 lithographlc
plate .
Example 3
Similarly, a compositlon of:
Dlethylene Glycol50%
~ .
Antarox BL 240 45%
Phosphorlc Ac1d (85%) 5%
completely decoated an unexposed Enco N-50 negative-working,
presensitized lithographic plate, following the procedure of Example
1 above.
Example 4
In a composition of:
...~ .i~,
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1057105 AZ 743
Diethylene Glycol 45%
Igepon T-77 7%
Phosphoric Acid (85%) 8%
Enco N-50 , Lydel I , Lydel II--', and Polychrome LS II
presensitized substrates were decoated, at 70 - 90C, after a
dwell time of approximately 30 seconds and washing, while brush-
ing, with a spray of water at 50 - 60 C.
Examples_5 to 8
An unexposed Enco N-5 0 plate was divided into four por-
tions and immersed in a solution composed of:
Diethylene glycol 9 0%
Triton X-100 10%
for varying lengths of time at progressively higher temperatures to
determine stripping actlvity. Following immersion, a water rlnse
was applied for 60 seconds at 30 psi and at 55 - 60 C.
Example No. Solution Tem. C Dwell Time, Sec. Strlppinç~
80 30 - 60 none
6 90 30 complete
7 100 30 complete
8 110 30 complete, with
coating dissolv-
ed before rlnsing
Example 9
Following the procedure of Example 1 above, a compositlon
of:
Dlethylene Glycol 82%
Igepal DM 970 10%
Phosphoric Acld 8%
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~05710~ AZ-743
was used to decoat an Enco N-50 lithographic plate after a
30 second dwell time at 70-90C and a water (50-60C) spray,
with slight brushing action.
The above experiments serve to illustrate the
applicability of the novel principle used for the develop-
ment of imaged presensitized lithographic plates.
As shown in Examples 5 to 8, the same principle
can be applied to the decoating of metallic webs or plates
which, during their production, are found unacceptable for
market release because standards of quality are not met.
This method permits the reclaiming of such substrates which
can be made into acceptable products by further processing
Thus, economies can be realized.
Example 10
A solution of the composition of Example 1 was
heated to 90C and an Enco ~-100 plate was subjected to a
dwell time of 30 seconds, removed from the solution, squee-
geed and then sprayed with water for about one minute at 30
psi and 55C. The coating survived the immersion in the
treatment bath but was completely flushed off in the rinse.
When the temperature was lowered to 70C and the dwell time
increased to 60 seconds, the coating was only incompletely
removed. By raising the temperature to ilOC, the coating
was removed in the treatment bath, without need for rinse;
thus a temperature of 110C is too high, as it results in
undue contamination of the treatment bath.
Example 11
A solution of the composition:
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105710S AZ-743
Diethylene Glycol 22%
Triton X-100 l~/o
H3Po4 (85%) 8/~
Gamma Butyrolactone 6~/o
was heated to 90C, and imagewise exposed Enco N-100 and Enco
~-200 plates were immersed in it for 30 seconds, squeegeed af-
ter removal and rinsed with water for 120 seconds at 55C and
30 psi with slight brushing action. Both plates were found to
be properly developed. In contrast, use of the solution of
Example 10 at temperatures ranging from 60C to 110C was unsat-
isfactory, due to incomplete development up to 100C and re-
moval of imageareas at 110C.
ExamPle 12
Three solutions of the formula of Example 1 were
r made up, in which ethylene glycol, hexylene glycol and poly-
ethylene glycol (average molecular weight 380-420), respect-
ively, replaced diethylene glycol. Each of these solutions
was used to decoat Enco N-50 and N-100 plates by immersion for
30 seconds at 80C followed by squeegeeing and rinsing with
water at 60C. for two to three minutes. The samples were
evaluated for completeness of decoating and the results are
summarized in the following table:
EncoEthylene Hexylene Polyethylene*
PlateGlYCol Glycol GlY
N-50 Good Good Good
N-100Incomplete Good Good
*Decoating temperature 90C.
Example 13
The solutions of Example 12 were used to develop
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1057105 AZ-743
imagewise exposed Enco ~-50, N-100, and N-200 plates at 80C
for 30 seconds followed by squeegeeing and rinsing as in
Example 12. The samples were evaluated for completeness of
development and the results are sùmmarized in the following
table:
Enco Ethylene Hexylene Polyethylene
Plate Glycol GlYcol Glycol
~~50 Good Incomplete Undeveloped
N-100 Good Good at 95C Good at 95C
for 60 seconds. for 60 seconds.
Some coating Some coating
attack. attack.
N-200 Good at Incomplete Incomplete
90C
(30 sec.)
In the above examples, there was no image area
attack, except as noted.
The above cited experiments also illustrate the
non-polluting, non-toxic and non-hazard composition of the
developer media used.
It will be obvious to those skilled in the art
that many modifications may be made within the ~cope o~
the present invention without departing from the spirit
thereof and the invention includes all such modifications.
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