CA1154303A - Aluminum lithographic plate with visible image and process - Google Patents

Abstract

ABSTRACT

Aluminum substrate suitable for making lithographic, plates which has been treated to render the surface hydrophilic and negatively charged and thereafter ionically colored with a cationic dye.

Description

3~3 B~C~GROU~ID

This invention relates to lithograplli.c printing plates with visible images and to a process for making such plates.
Lithographic printing techniques, using, for example, anodized and silicated aluminur,l base plates such as described in Fromsonlpatent llo. 3,1gl,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 ~.he aluminum base slleet for ex-posure. If the light sensitive coating is applied to the base sheet by the manufac~u~er, the sheet is reEerre(l to as a "presensitized plate". If the light sensi.tive substance is applied to the base by the lithograpl~e]^ or trade pla~e mclker, the plate is referred to as a "w.ipe-on plate". Depending on the nature of the photosensitive coatin~, employed, a coated plate may be utilized to reproduce directly the i~age to whicl it is exposed, in which case it is termed a positive-acting plate, or to produce an image cor.~plementary to the one to which it is exposed, in whicll case it is termed a ne~ative acting plate. In either case, the image area of the developed plate is oleophilic and the non-image area is hydrophilic. ! '' In the case of negative worl~ing pla~e, the surface is coated witll an aqueous solution of a col~ventional diazo resin. The plate is dried and exposed ~hrougll a negative.

3~3 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.

SUMMARY

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, 3~3 positiv~ly cl~r~c~ ~ia~oniull m~l~c~ l(l(l (ILiol~ Iy~. .L`h~
coate~ surface is capa~l~ of l~avi.n~ its solul~ility altercd upon exposure ~o ac~inic li~llt all~l tl-lere~lf~:er cl~velope~ to produce a visible, dyed imay~ l a l~y~rol?l~ilic ~.lck~,round free of the cliazoniuM material an~ dye.
This invention :Eurther ~r~vi(~ (lye(l~noclize~l aluminum article. Normally, ~Ino~ize~ ~lull~ um is dyed using anionic and non-ionic dyes. U~ to llow, c.ltionic dycs could not be used ~ecause tl)e surf,~ce o~ ~no~li..(~d a].~minu is ei.~her neutral or acicl. It ha~ lloW l~C~ liscovere~l tllat anodized aluminum can be effectively ~y~ ~r coLor~ witll a cationic dye by first treatinl~ thc ~nodi.7,~ lluminulll to render the surface ~hereof anionic. This makes i~ not~ po~sible to color code products and ~rovi(l~ ~ visibl~ i.mage 011 lithograpllic pla~e withoul: i tl~ erEc~ WiL~ cl~veLo proce~s or alterin~ ~he litho~ ic prop~ ies oF ~I pl.lt~.
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 toning during pr;nting.
The present invention employs a cationic dye for anodized 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 oleophobic) which has been ionically c e red of the cat;onic dye.

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DESCRIPTION

Cationic dyes used in the invention can be ap~lied to the negatively charged substrate or incorporated in the light 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 Blue R and the like. -Cationic light sensitive materials that can be usedin the invention are diazonium materials having reactive sites capable of being chemically altered by light or chemically 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 desired dual functionality. Preferred are water soluble diazonium compounds but water insoluble compounds can also be used. 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 water soluble and include the alkali metal salts of alkylaryl sulfonates havin~
l-~o 20 carbon atoms in the alkyl portion and 6 to 14 carbon atoms in~the aryl portion, alkali me-tal salts of alkyl sulfonates having 12 to 20 carbon atoms and ammonium and alkali metal salts o~ sul-Eated higher fatty alcohols having 10 to 20 carbon a~oms. ~nionic 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 tl-e unexposed areas.
Specific examples of anionic surEàctants are given herein together witll a test to detennine suitability.

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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 No. 3,181,461.
After treatment with the anionic materialS 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 in~s, 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. ~race, 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.

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These curable materials can be used in special applications in place of the W material and are commercially available.
Electron beam curable compositions are described in U.S. patents 3,5~6,526-30, 1971.
Producing a visible image by chemical amplification after exposure to actinic radiation makes it possible to sub-stantially reduce exposure times normally re~luired with diazonium compounds. This can be expressed er,~pirically as simply the amount of actlnic light necessary to produce an image capable of running on a lithograpllic press. Chemical amplification makes it possible to reduce the amount of light needed to attain this by a factor of from 2 ko 10 or more.
This means that a diazo sensitized plate that normally re~uired 1 or ~ minutes to image can be imaged in a matter of seconds.
The amount of diazo on the plate can also be reduced.
The amount of light necessary to produce an image capable o~ 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 than abou~ 100 to as little as 5 millijoules/cm2 at UV wave lengths of 300-400 namometers. This ~eans that plates can be exposed with 10W
power lasers s-uch as àre marketed by EOCOM Inc. and developed to produce a visible image.
~ fter treatment witll the preferred anionic material, the developed amplified image can be blanket exposed to actinic light to photo react any remaining light sensitive sites in tlle image area. Thls includes coupled dia~oniutn and anionic materials which remain light sensitive after coupling.
A test to determine whe~her a particular anionic material is suitable is as ~ollows:

A 5~/~ aqueous solution of ti~e anionic material is prepared. An aluminurn lithograpl~ic plate grained, anodized, and silicated is coated with a 1% solution of a li~ht sensitive diazo condensation product (such as Eairmont 's Chemical Diazo ~4). The coated plate is exposed to a Stouffer Gral~hic Arts Guide for a relatively short period of time -- 5 to 10 secon(ls.
The exposed plate is immersed in the 5% solution of anionic material for 10 seconds. The plate is then rinse~ and lacquered with a standard l:ithographic lac~luer (such as Fairmont ' s Dlack Lacquer) . Another plate, iderltically pre-pared and exposec~, is treated with the Black Lacquer only.
This is the control. The two plates are compared. If the anionic rnaterial is effective, the post-treated plate will show significant difference in ligllt sensitivity versus the con tro l .
The effectiveness of certain anionlc materials can be enhanced by either a pH adjustment and/or the use of a co-solvent. The optimum pll for most anionic materials useful i.n this invention is in the range of F~H 2-1~). Suitable co-solvents are alcohols such as ethanol, butanol and the like ¦
an~l glycols.
~ lany different salts of anionic materials are suit-able; -tllese include sodium, llthiurn, ammonium, or triethanol amine sal ts and tlle like . Exarnples of suitabl e anionic surfactants (and their commercial sources) are as follows: ` !
1. Sodium lauryl sulfate (Proctor & Gamble, Equex S.
E(luex SP; Alcolac, Inc. Sipex SB).

2. Ammonium lauryl sulfate (Alcolac, Inc., Sipon L-22).
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3. Sodium la~lryl etl~er sul~a~e (Alcolac, Inc,, Sipon ~S).
~. Sodium ~odecy] ~enzene sulEollate (~lcolac, Il~c. Siponate DS-XO).
5. Ammonium lauryl ether sulfollate (Alcolac, Inc.
Sipon EA).
6. Triethanolamlne lauryl sulEate (~lcolac, Inc.
Sipon LT-6).
7. Sodium al]cyl sulfate (Alcolac, Inc., Sipex OL.S).
. Sodium stearate (~mery Incls.).
9. Sodium palmitate (Emery Inds.).
10. Sodium oleate (~latlerson~ Coleman & Bel]).
11. Dioctyl sodium sulfosuccinate (Cyanamicr, Aerosol OT).
12. Tetrasodium N-Cl, 2 dicarboxyetllyl 1) - N -octadecyl sul~osuccinate (~yallalnld, ~erosol 22).
13. Sodium Xylelle sul~otlate (Wl~co Cllemical, UItra SXS).
14. Sodium toluene sul~onate (W:itco Cllemical, Ultra STS), 15. Sodium Gumene sulfonate (Witco Chemical, Ultra SCS hydrotrope).
16. Sodium dihexyl sulfosuccinate (Cyanami~e Aerosol AY-65) 17. Sodium diamyl sulfosuccillate (Cyanami~e Aerosol AY-G5).
l~. Atlionic phos~hate surEactallt (Rollm ~ llaas Co , Tri~on QS-30).
19. Sodium al~ylaryl polyetller su]:~atc (Rollm &
llaas Co., Trlton ~-30 COllC. ) .

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20. l'llospilate surfactallt, l~otassiunl salt (l~ohr,l &
llaas Co., Triton ~1-66).
. 21. Sodiurn alkylaryl polyetller sulforlate (Rohm &
llaas Co., Triton X-200).

Sodium lauryl sulfate is preEer~-ed ~ecause of its availa~ilitv and cost.

~XAM ~ 1 (control) ~ , , :

A 1',' solution of tlle formaldellyde condensation product o~ a diphenylamine - 4 - diazonium zinc chloride double salt .¦ ..
(Fairmont Diazo l'esin ~y4) is prepared in water. The solution is placed in a t~o roll coating machine. A brushecl ~rained, anoclized and silicated plate, 10 x 16 ~ 0.1~ no-Coil Delta :
Plate) is coated ace down ~llrougll tlle machine. The coated plate is dried and placed in a I~u ~rc Plate ~1akel- exposure .
unit, 24 inches ~rom tlle source (4 Icw lam~ tou.E:Eer Grapllic Arts Step scale is step exposed on the plate for the i.oll.owin~
times: 1 second, 5 seconds, lO seconds, 15 seconds, 30 seconds, and 60 seconcls. The exposed plate is then developed with ~airmont's black lacquer for ~ipe-on plates. Aiter clevelopment,¦
rinsing, ancl dryin~ the solid step exposure level is read Eor each exposure time: 1 second - no image, 5 seconcls - no image, ¦
10 seconds - a ghost image, lS seconds - a solid 1, 30 seconds -a solid 3, and ~0 seconds - a solid 5 --- normcll for thi.s type of p~ate system.
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EX~ 2 ~ 3~3 A brush grained, anodized silicated aluminum plate (Alloy 1100) is immersed in a dye bath of a 1,' so1ution of a basic (cationic) dye such as DuPont's Victoria Green Liquid, Rhodamine B Liquid, Rhodamine 5 GLD, crystal violet extra pure APN or Paper Blue R Liquid. The dyecl plate is then coated as in Example 1. The coated plate is tllen exposed in a ~ k~ i ~u Arc flip top exposure unit for 5 seconds to a newspaper page negative. The exposed, dyed plate is immersed in a 5C/o solution of sodium lauryl sulfate. Immediately upon removal from the batll a strong visible image is seen on the plateO

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A brushed grained, silicatecl, ancl anodized plate (Ano-Coil's Delta Plate) is coated with a 1% cliazo coating (Fairmont P~esin #4) containing l/2% Victoria Green Liquicl dye (DuPont). The plate is dryed and exposed for 5 seconds on a Nu Arc as in Example 7. The plate is ~leveloped in a 5%
solution of amtnonium lauryl sulfate. Upon application oE the developer with a sponge, a visible image becornes im~ediately apparent.
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Lxam!~le 4 ~ lithographic plate (Ano-Coil's Delta plate) is dyed in a 1% solution of VicT oria Green Liquid. The plate is coated with a 1% solution of ~airmont diazo resin ~4 exposed to a newspaper negative for 10 seconds and immersed in a 5%
solution o:E sodium lauryl sulfate. Immediately an image becomes visible. The plate is rinsed in tap water and dryed. The plate is placed on a Goss Metro rress and 50,000 good images are obtained.
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E,~ PLE 5 . . ._ _ A plate is prepared as in Example 2 but a~ter devel-opment it is rubbed with a UV curable emulsion (~xample 6) rinsed, dryed, and re-exposed tI~rougll a P~G UV processor at 25 ft./minute. The plate is placed on a Goss ~etro newspaper press and 250,000 impressions are obtained.
~ ' ~Xl~IPL~, 6 A brush grai.ned, anodized, silicated, aluminum plate is coated wit'n a l~o solution of water soluble poly~unctional diazo resin (Fairmont's diazo resin #~? containing l/2%
Victoria Green liquid dye as in Example 2 and dryed. The sensi-l tized plate is then placed in an Eocom Laserite Platemaker and scanned witIl an ion argon laser. A scanni.n~ time of 1 ~l rminute is necessary to scan a pla~e approximately 23 x 1~. The approximate laser powe~ at the plate surface is 8 m;j/cm2.
A~ter scannin~, the plate is developed wi.tb a 5% solution of sodium lauryl sulfate as in ~xample 2 to produce a strong quality visible image.
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E~MPL~ 7 . .
A plate was coated, laser exposed and developed as in ~xample 5 using 10 mj/cm2 laser power. Tllis tiné after .dev~lopment, the plate was rubbed with tlle following UV
curable emulsion: , I
(A) 30 grms Inmont UV Blue Inl~ ¦
. 12.5 cc Span ~0 (I.C.I.) 120 mls Cellosolve Acetate (~) 250 mils 8 ~e Gum Arabic 12.5 grms Pluronic .~38 (BASF) -12~

Mix by adding ~B) to (A) ~hile 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.
EXAMP~E 8 ~ 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/cm After exposure to the laser, the plate is developed by hand with sodium lauryl sulfate (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 1100) ;s degreased using a commercially formulated de~reasing compound such as Aldet (Wyandotte Chemical Company). The plate is degreased at 180 to 1~35F for 30 seconds at a concentration o~ 6 to 8 ounces/
gallon. Next the plate is rinced 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.

An aluminum sheet is degreased, rinsed and silicated as in Example 9 but not anodized- The anionically charged surface isthen .

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dyed with a cationic dye such as Dupont's Paper Blue R Liquid 5 cc/liter at room temperature for one minute. A b1ue sheet results. The dye is resistant to rinse water but is easily discharged by immersion in a 5%
solution of sodium lauryl sulfate. ~ -:---- !
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, tSandoz) 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 dye can be removed. It will not discharge w;th this treatment.
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Claims (8)

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

1. Lithographic substrate comprising an aluminum plate having a surface which has been treated to render said sur-face hydrophilic and negatively charged and thereafter ionic-ally colored with a cationic dye.

2. Substrate of claim 1 wherein the plate has a porous anodic oxide surface thereon which has been treated to render it hydrophilic and negatively charged.

3. Substrate of claim 2 wherein the oxide surface has been treated with an alkali metal silicate.

4. Substrate of claim 1 wherein the aluminum plate has been treated with an alkali metal silicate.

5. Substrate of claim 1 coated with a cationic, posi-tively charged light sensitive material.

6. Lithographic plate of claim 1 wherein the substrate is treated with an alkali metal silicate.

7. Lithographic plate of claim 1 wherein the substrate is anodized aluminum treated with an alkali metal silicate.

8. Lithographic plate of claim 6 or 7 wherein the aluminum is grained.