CA1162788A - Aluminum lithographic plate with visible image and process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure describes a lithographic printing plate comprising an aluminum surface which has been treated to render it hydrophilic and negatively charged coated simultaneously or sequentially with a light sensitive, cationic, positively charged diazonium material and a cationic dye. The coated surface is capable of having its solubility altered upon exposure to actinic light and there-after developed to produce a visible, dyed image and a hydrophilic background free of the diazonium material and dye. Also described is a process which comprises coating an aluminum surface which has been treated to render it hydrophilic and negatively charged, simultaneously or sequentially, with a light sensitive, cationic, positively charged diazonium material and a cationic dye, selectively exposing the coated surface to actinic light to alter the solubility of the diazonium material, and developing the exposed coated surface to produce a visible, dyed image and a hydrophilic background free of the diazonium material and dye.

Description

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This application is a division of application No. 362,530, filed October 24, 1980.
This invention relates to lithographic printing plates with visible images and to a process for ma~in~ such plates.
Lithographic printing techniques, using, for example, anodized and silicated aluminum base plates such as described in Fromson us patent No. 3,1~.1,461 issued May 4, 1965, have come into widespread use in the printing industry and especially in offset printing and direct lithographic printing by newspapers using converted letterpress printing presses.
A conventional negative working lithographic printing plate of this type has a coating of a light sensitive sub-stance that is adherent to the aluminum hase sheet for ex-posure. If the light sensitive coating is applied to the base sheet by the manufacturer, the sheet is referrcd to as a "presensiti7ed plate". If the ligh~ sensitive substance is applied to the base by the litho~rapher or trade plate maker, the plate is referred to as a "~ipe-on plate". Dependin~ on the nature of the photosensitive coatin~, employed, a coated plate r,lay be utilized to reproduce directly the i~age to which it is exposcd, in which case it is termed a positive-acting plate, or to produce an ima~e complementary to the one to which it is exposed, in which case it is termed a ne~ative actin~ plate. In either case, the image area o~ the developed plate is oleophilic and the non-image area is hydrophilic.
In the case of negative working pla~e, the surface is coated with an aqueous solution of a conventional diazo resin. The plate is dried and exposed ti-rougll a negative.

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The exposed image areas become water insoluble and the un-exposed non-image areas remain water soluble. The plate is conventionally developed with a lithographic lacquer which consists of a two-phase system, one phase containing an oleophilic resin in a solvent and the other phase a hydrophilic gum. Upon application, the oleophilic resin adheres to and makes visible the exposed insoluble areas, while the hydrophilic phase dissolves away the unexposed soluble non-image or background areas. In this way, the visible image is made oleophilic or ink receptive and the background is made hydrophilic or ink repellent.
In the present invention we provide a lithographic substrate and plate that produces a visible image upon development without relying on a component of the developer to become adhered to the image area.

SUMM~RY

The present invention provides an aluminum litho-graphic substrate which has been treated to render the sur-face hydrophilic and negatively charged and thereafter ionically colored with a cationic dye.
The invention further provides an aluminum printing plate the surface of which has been treated to render it hydrophilic and negatively charged and then coated simultan-eously or sequentially with a light sensitive, cationic, ~osi~i~ely cllar~e~ ~ia~onium ma~c~ i al~l .I caLiollic dye. 'l'hc coated surface is capa~le oE llavin~ its solul)ility al~ered upon exposure to actinie li~llt an~ tllere~fter develope~ to produce a visible, dyed ima~,e an~ a l~y~ro~hilic ~aelc~round free of the diazoniur,l material an~ ~ye. ,' . This invention urther ~rovide~ ~ dye(l anodized aluminum ar~icle. Normally, ano~ized ~lulninum is dyed using anionic and non-ionic dyes. U~ to llOW, cationic'dyes could not be used because ~lle surface.of ~no~ .ed aluminuln is either neutral.or aeid. It ha~ now l~een t3i~covcre~ tllat anodized aluminum can be effeetively ~ye~ or color~ with a cationic dye by first treatin~, the ~nodize~ luminum to r~nder the;surface thereof anionic. This mal<e~ it now po~si~le ~o color code products,and Drovi~lc a visible ima~,e:on a lithogra~llic ~late withou~ i.n~~erEerill~ wich ~he ~Ieveiopin~
pr~ce~ or altering the litllo~r~llic properties oE a plate.
It has been proposed to use an anionic dye on an anodized aluminum substrate for lithographic purposes ~U.S. Patent Number 3~280~734).
However, this was not commercially successful because the dye remained in the background after developing which caused scumming and tonlng during printing.
The present invention employs a cationic dye for anodi~ed aluminum which is ionically removed from the background during develop-ment of the plate,while the color remains permanently in the image area after exposure and development, without undergoing any change during either process. This results in a visible image, with the substrate ionically colored in the image area, and a suitable lithographic background (hydrophylic and o1eophobic) which has been ionically cleared of the cationic dye~

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DESCRIPTION

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Cationic dyes used in the invention can be ap?lied to the negatively charged substrate or incorporated in'the ligh.t sensitive material.to provide a visible image' on the '' plate. Suitable dyes include basic cationic dyes such as 'Victoria Green, Rhodamine B, Rhodamine 5GLD, crystal violet, extra pure APN, Paper Bl'ue R and.the like, Cationic light sensitive materials that can be used in the invention are dia~onium materials'having reactive site's capable of being chemically altered by light or che~ically reacted with an anionic material. For example, 4-diazo diphenylamine condensed with a carbonyl compound such as formaldehyde has the needed multiplicity of reactive sites each having the desir~d dual.functionality. ,Preferred are water soluble diazonium com~ounds but water ins.oluble.cornpounds can also be uscd. Suitable diazonium compounds are described in U.S. 3,849,392 to Steppan and U.S. 3,311,065 to Steppan.
' Suitable anionic materials are wate~ soluble and include the alkali metal salts of alkylaryl sulfonates having 1 to 20 carbon atoms in the alkyl portion and.6 to 14 carbon' atoms in~the aryl portion, alkali metal salts of alkyl sulfonates having 12 to 20 carbon atoms and am~onium and alkali metal salts of sulfated hi~her fatty alcohols having 10.
to 20 carbon atoms. Anionic materials are dissolved .in an ionizing reaction medium (usually water) and the concentration of the anionic material is sufficient to couple with the light sensitive material and to dissolve the coupled reaction product from the unexposed areas.
5pecific exam?les of anionic surfactants are given herein together ~7itll a test to determine sui.tability.

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The aluminum substrate is treated to render the surface hydrophilic and anionically charged. The preferred lithographic substrate is anodized aluminum which may be pretreated before anodizing to roughen or grain the surface, for example using mechanical, chemical or electrochemical techniques as are well known in the art and it may be post-treated after anodizing. It is preferred to impart hydrophilicity and a negative charge by silicating as des-cribed in Fromson U.S. patent ~o. 3,181,461.
After treatment with the anionic mate-ial, the image can be reinforced with an oleophilic W curable material which can be coated on and then cured.
Suitable W curable materials are commercially available from a number of sources in the form of W curable inks, coatings, oligomers and monomers. Such commercially available materials can be obtained from the following companies: Inmont Corporation, Sinclair & Valentine, Celanese Chemical Company, 3-M Company, Desoto Chemical Company, Paulimer Industries, Shell Chemical, Mobile Chemical, W.R. Grace, Design Coat Company, and Ware Chemical Corpora-tion.
W curable materials including monomers and oligomers are described in the following patents:
U.S. 3,297,745 1967 U.S. 3,380,381 1968 U.S. 3,673,140 1972 U.S. 3,770,643 1972 U.S. 3,712,871 1973 U.S. 3,804,736 1974 There are also materials that will cure upon exposure to other sources of radiation~ for example an electron beam.

I ~2'7~8 These curable materials can be used in special apylications in place of the W material and are commercially available.
Electron beam curable compositions are described in U S. pa~ents

3,586,526-30, 1971.
Producing a visible image by chemical a~plification after exposure to actinic radiation ma~es it possible to sub-stantially reduce exposure times normally re~uired with diazoniurll compounds. This can be expressed empirically as simply the amount of actlnic light necessary to produce an -ima~e capable of running on a litho~raphic press. Chemical amplification ma~es it possible to reduce the amount of light needed to attain this by a factor of from 2 to lO or more.
This means that a diazo sensitized plate that normally re~uired 1 or 2 minutes to image can be imaged in a matter of seconds.
~he amount of diazo on the plate can also be reduced.
The amount of light necessary to produce an image capable of running on a lithographic press can also be expressed in terms of millijoules per square centimeter. The amount of actinic light can be from less thatl about lO0 to as little as 5 millijoules/c~2 at UV wave len~ths of 300-400 namometers. This means that plates can be exposed with low power lasers such as are marketed by EOCOM Inc. and developed to produce a visible image.
~fter treatment with the preferred anionic material, the developed amplified image can be blanket exposed ~o actinic li~ht to photo react any remainin~ ,ht sensitive sites in the ima~e area. lhis includes coupled dia~onium an(l anionic materials which re~ain ligllt scnsitivc a~er couplin~.
~ tcst to determinc whether a par~icular anionic material is suitable is as follows:

~ ~2'7~8 A 57~ aqueous solution of the anionic material is prepared. An aluminum litho~raphic plate grained, anodized, ~ .
and silicated is coated with a 1% solution of a li~ht sensitive dlazo condensat;on product (such as ~airmont's Chemical Diazo #4). The coated plate is exposed -to a Stouffer Graphic Arts Guide for a relatively short period of time -- 5 to 10 secolids.
The exposed plate is irnmersed in the 5% solution of anionic material for 10 seconds. The plate is then rinsed and lacquered wlth a standard lithographic lac~uer (such as Fairrnont`s ~lacl~ Lacquer). Another plate, i~e~tically pre-pared and exposed, is treated with the Black Lacquer only.
This is the control. The two plates are compared. IE the anionic material ls effective, the post-treated plate will show significant difference in light sersitivity versus the control.
The effectiveness of certain anionic materials can be enhanced by either a pH adjustment and/or the use of a co-solvent. The optimum p~l for rllost anionic materials useful in this invention is in the range of ~ 2-1~ Suitable co-solvents are alcohols such as ethanol, butanol and the like and glycols.
Many different salts of anionic materials are suit-able; thcse include sodium, lithiurl, ammonium, or triethanol amine salts and the like. Examplcs of suitable anionic surfactants (and their commercial sources) are as ~ollows:
1. Sodium lauryl sulfate (Pr~ctor & Gamble, E~ucx S.
E~uex SP; Alcolac, Inc. Sipex SB).
2. Ammonium lauryl sul~ate (Alcolac, Inc., Sipon L-2Z).

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1! 162788 3. Sodium lauryl etl1er sulfa~e (Alcolae, Inc., - ~ipon ~S).

4. Sodium dodecyl ~enzene sulfonate (Aleolae, Ine. Siponate DS-XO~. . -

5. Ammonium lauryl ether sulfonate (Aleolae, Inc.
S ipon EA) .

6. Triethanola1nine lauryl sulfate (~lcolae, ~ne.
Sipon LT-6).
. . 7. Sodium aikyl- sulfate (Aleolae, Inc., Sipex OLS).
10 - ~. Sodium stearate (Emery Inds.).
9. Sodium palmitate (Emery Inds.).
lO~ Sodium ole~te (~1atlerson, Coleman & Bell).
ll. Dioetyl sodium sulfosuccina~e (Cy~nami~, -~erosol OT).
12. Tetrasodium N-Cl, 2 dicarboxyç~hyl l) - N -oetadeeyl sulfosueeina~e (Cya11amid, Aerosol 22).
13. Sodium X~lene sul~onate (Wi~co Cl1.emieal, Ultra SXS).
14. Sodium toluene sul~onate (Witeo C11emieal, Ultra STS).
15. Sodi~l~ cumene sul~onate (Witco Chemical, Vltra SCS hydrotrope).
16. Sodium dihexyl sul~osuceinate (Cyanamide Aerosol ~Y-65) 17. Sodium diamyl sulfosuccillate (Cyanamide Aerosol l~Y- 65) .
ionie phospl1ate su~f~eLant (l~ol1n~ a.~s Co., Triton QS-30).
. l9. So~ium al~ylaryl polyetl~er sul~e (Rol1m &
ll~s Co., TriLon ~-30 Co11C.).

20. Phosphate surfactallt, l~otassium salt (l~ollr,l &
llaas Co., Triton ~1-66).
21, Sodiurn alkylaryl polyether sulfon~e (Roh~ &
.Haas Co., 'rriton X-200).

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Sodium lauryl sulfate is prefer~-ed ~ecause of Lts availa~ility and cost.

EXAMPLE'l (control) ', ' ' ~ ' ' . '. ' ' A l,' solution of tlle formaldehyde condensation product of a diphenvlamine - 4 - ~iazonium zinc ch~oride double salt (Fairmont Diazo ]lesln '14) is prepared in water. The solution is placcd in'a two roll coatin~ machille. A brushed ~rained, anodizcd and silicated pla~e, lO x 16 x 0.12 (~no-Co'il DeLta Plate) is coated'face down throu~ll the machine. Tlle coa~ed plate is dried and placed in a l~u ~rc Platc ~1aker exposure unit, 24 inches from the source (4 lcw lamp). A Stouffer Graphic Arts Step scale is step exposed'on the Illate ~or the following tir~es: 1 sccond, 5 seconds, lO seconds, 15 seconds, 30 seconds, and 60 seconds. Thc exposed plate is then developed with ~airmont's l)lack lacquer -for wipe-on plates. After developmcnt, 'rinsin~, and dryin~ the solid step exposure l'evel is read for each exposure time: 1 second - no ima~c, 5 scconds - no ima~,e, lO seconds - a ~host ima~c, 15 seco-lds - a solid 1, 30 seconds -a solid 3, and 60 seconds - a solid 5 -- normal for tllis typc of platc .systcm.

EX~1PL~ ~ ' , ~ ~6~8 A brush grained, anodized silicated aluminum plate (Alloy 1100) is immersed in a dye bath of a 1,' solution of a basic (cationic) dye such as DuPont's Victoria Green Liqui Rhodamine B Liquid, Rhodamine 5 GLD, crystal violet extra' pure AP~ or Paper Blue R Liq-lid. The dyed plate is then coated as in Example 1. The coated plate is then exposed in a 4 Nu Arc flip top exposure unit for 5 seconds to a newspaper pa~e ne~ative. The exposed, dyed plate is immersed in a 5%
solution of sodium lauryl sulfate. Immediately upon removal from the bath a strong visible image is seen on the plate.

EYI~L~ 3 A brushed ~rained, silicated, and anodized plate ('Ano-Coil's Delta Plate) is coated with a l% diazo coatin~
(Fairmont nesin #4) containing 1/2% Victoria Green Liquid dye (DuPont). The plate is dryed and ex~osed for 5 seconds on a Nu Arc as in ~xample 7. The plate is developed in a 5%
solution o~ am~onium lauryl sulfa~e. ~pon application of the developer with a sponge, a visible ima~e becomes immediately apparent.

~xam~le 4 A litho~,raphic plate (Ano-Coil's Delta plate) is dyed in a 1% solution of Victoria Green Liquid. The plate is coated with a 1% solution of ~airmont dia70 resin ~4 exposed to a newspaper ne~ative for 10 seconds and im~ersed in a 5/~
solution of sodium lauryl sulfate. I~ne~iately an ima~e becomes visiblc. The plate is rinsed in tap watcr and dryed. Tlle plate is placed on a Goss ~1etro ~rcss and 50,000 ~ood ima~cs are obtained.

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E~A~L~ S
A plate is prepa~ed as in Exa~le 2 but after dev'el-opment it is rubbed wi~h a UV curable emulsion (Lxample 6) rinsed, dryed, and re-ex~osed throu~h a P~G W processor at 2S ft./minute. The plate is placed on a Goss I~etro newspaper .press and 250,000 impressions are obtained , E ~ ~L~ 6 A brush grained, anodized, silicated, aluminum plate is coated with a 1% solution of water soluble polyfunctional diazo resin (Fairmont's dia~o resin ~) containing 1/2%
Victoria Green liquid dye as' ~n'Example 2 and dryed. The sensi-ti;zed plate is then placed in an ~ocom Laserite Platemaker and scanned with an'ion argon laser. A scanning time of 1 minute is necessary to scan a plate approximately 23 x 14. The approximate laser power at tlle plate surface is 8 mj/cm2 After scanning, the plate is developed with a 5% solution of sodium lauryl sulfate as in Examyle 2 to produce a stron~
quality visible image.

' E~AMPLE 7 A plate was coated, laser exposed and develo~ed as in ~xample 5 usin~ 10 mj/cm2 laser power. This ~ime after development, the plate was rubbed with the followin~ UV
curable emulsion:
(A) 30 grms Inmont W Blue In~
12.5 cc Span ~0 (I.C.I.) 120 mls Cellosolve Acetate (n) 250 mils ~ Be Gum Arabic 12.5 grms Pluronic ~38 (B~SF) J ~ 7~

Mix by adding (B) to (A) while stirring The emulsion can be applied with sponge, cloth, or brush. After treatment with the W emulsion the plate is re-exposed in a high inten-sity W processor such as a PPG Industries, Model PC2502A at 25 ft~minute. A tough and abrasion resistant visible image is produced EXA P~E 8 A plate as described in Example 8 was dyed with a cationic water soluble dye, 1% Victoria Green (DuPont). The plate was coated with a 1% solution of diazo resin and dried. This plate was laser exposed as in Example 5 with laser power of 4 mj/cm2.
After exposure to the laser, the plate is developed by hand with sodium lauryl sulfa-te (5% solution). The thus treated plate is then lacquered with a black lacquer from Western Litho Company (Jet Black). A dense black image results . .
An aluminum sheet (Alloy llO0) is degreased using a commercially formulated degreasing compound such as Aldet (Wyandotte Chemical Company). The plate is degreased at 180 to 185F for 30 seconds at a concentration of 6 to 8 ounces/
gallon. Next the plate is rinsed and anodized for 50 AMP -minutes using sulfuric acid (280 grams/liter at 90F), rinsed and silicated with sodium silicate (3%), rinsed and finally ~-dyed with a cationic dye such as Rodamine 5 GLD (DuPont) at 4 grams/liter. The dyed sheet is rinsed in tap water for several minutes and then dried. A brightly colored aluminum sheet results. The dye can be easily discharged using an anionic surfactant (5%) such as sodium lauryl sulfate.
EXAMPLE lO

An aluminum sheet is degreased, rinsed and silicated as in Example 9 but not anodized- The anionically charged surface isthen - 1 1;6~ 788 '~ed with a cat;onic dye such as Dupont's Paper Blue R Liquid 5 cc/liter at room temperature for one minute. A blue sheet results. The dye is resistant to rinse water but is easily d1scharged by immersion in a 5%
solution of sodium lauryl sulfate.

EXAMPLE ll A sheet of aluminum is degreased and anodized as In Example 9 but not silicated and a second sheet is degreased, anodized,-and sili-cated as in Example 9. Both sheets are then immersed for 30 seconds in a 1% solution of copper BF, an anionic dye? (Sandoz) at 160 F and-a pH
of 5.5. The first sheet which is not silicated and therefore cationically charged takes the dye readily. The second sheet which is silicated will not dye. The first sheet is immersed in 5% anionic surfactant to see if the d~e can be removed. It will not discharge w1th this treatment.

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Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Lithographic printing plate comprising an aluminum surface which has been treated to render it hydrophilic and negatively charged coated simultaneously or sequentially with a light sensitive, cationic, positively charged diazonium material and a cationic dye, said coated surface being capable of having its solubility altered upon exposure to actinic light and thereafter developed to produce a visible, dyed image and a hydrophilic background free of the diazonium material and dye.

2. Lithographic plate of claim 1 developed with an anionic material in an ionizing medium.

3. Lithographic plate of claim 2 wherein the anionic material is a surfactant selected from the group of alkali metal salts of alkylaryl sulfonates, alkali metal salts of alkyl sulfonates and alkali metal and ammonium salts of sulfated higher fatty alcohols.

4. Process for making a lithographic printing plate with a visible image which comprises:
(a) coating an aluminum surface which has been treated to render it hydrophilic and negatively charged, simultaneously or sequentially, with a light sensitive, cationic, positively charged diazonium material and a cationic dye, (b) selectively exposing the coated surface to actinic light to alter the solubility of the diazonium material, and (c) developing the exposed coated surface to produce a visible, dyed image and a hydrophilic background free of the diazonium material and dye.

5. Process of claim 4 wherein the developing step is carried out with an anionic material in an ionizing medium.

6. Process of claim 4 wherein the anionic material is a surfactant selected from the group of alkali metal salts of alkylaryl sulfonates, alkali metal salts of alkyl sulfo-nates and alkali metal and ammonium salts of sulfated higher fatty alcohols.