CA1179294A - Aluminum lithographic plate with visible image and process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The disclosure describes an anodized aluminum article having a surface which has been treated to render it anionic and negatively charged and thereafter colored with a cationic dye. A process for producing such article is also disclosed.

Description

Z~

This application is a division of'application No. 362, 530, filed October 24, 1980.
This invention relates to lithograpltic printing plates with visible images and to a process for ma~ing such plates.
Lithographic printing tecllniques, usin~, for example, ano~ized 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 ia offset printing and direct lithographic printing by newspapers using converted letterpress printing presses.
A conventional negative working litho~raphic printing plate of tllis type has a coating of a light sensitive sub-stance that is adherent to the aluminum base sheet for ex-posure. If the light sensit;ve coating is applied to the base sheet by the manufacturer, the shee't is refcrrcd to as a "presensiti7ed plate". If the ligh~ sensitive substance is applied to the base by the litho~rapher or'trade plate maker, the platc is referred to as'a "wipe-on l)late". Dependin~ on the nature of the photosensitive coatin~, employed, a coated plate may be utilized to reproduce directly t'he image to which it is exposed, 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 whicll case it'is termed a negative acting plate. In either case, the image area o~ the developed plate is oleophilic and the non-ima~e area is hydrophilic.
In the case of negative workin~ plate, the surface is coatcd with an aqueous solu~ion of a conventional diazo resin. The plate is dried and exposed ~hrou~ ne~ative.

117~Z9~

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 Z9'~ -?si~ively cl~ar~ed ~ia~oniu~ mate~ l .nll~ a caLionic dye. The coated surface is capa~le of llavin~ its solul)ility altered upon exposure to actinie li~llt all~ there.~Eter develope~ to produce a visible, dyed lma~,e an~ a lly~ro}~hilie ~ckground Eree of the diazonium material an~ ~y~.
This invention ~urther ~rovide~ ~ d~e(l anodized aluminum artiele. Normally, ano~ized ~lu-ninum is dyed using anionic and non-ionic dyes. U~ to TlOW, cati~nic dyes eo~ld not be used because tlle surf,~ce o~ ~no~lized aluminuln is either neutral or aeld. It h~s now l~een ~ covereJ that anodized aluminum can be e~fectively ~ye~ or colored w~th a cationic dye by Eirst treatinp, the ~nodize~ aluminum to render the surface ~hereof anionic This make~ it now po~sible ~o color code products and ~rovi(l~ a visible ima~,e on a litho~rapllic ~late ~ithoùL interreri-lg wiCll tl7e ~lc~elo~in~
pr(7ce~ or alterin~ the litho~ra~)llic prc)perties oE a plate.
It has been proposed to use an anionic dye on an anodized aluminum substrate for lithographic purposes (U.S. Patent Number 3~2807734).
However, this was not conmercially successful because the dye remained in the background after developing which caused scumming and toning during printing.
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 cleared of the cationic dye.

92~ -DESCRIPTION
- . - . .
Cationic dyes used in the invention can be ap?lied to the negatively charged substrate or incorporated in tlle 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 Blue R a~nd the like.
Cationic light sensitive materials that can be used in the invention are dia~onium materials having reactive sites capable of being chemically altered by light or chemically reacted with an anionic material. For example, 4-diazo di~henylamine condensed with a carbonyl compound such as formaldehyde ~as 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 sul~onates 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 higher fatty alcohols havin~ lO
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 tlle light sensitive material and to dissolve the couplcd reaction product from the unexposed areas.
Specific exam~les of anionic surfactants are given herein together ~7itl1 a test to determine sui.tability.

~3 9~

~ 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 exarnple 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 material, 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.

~179;~9~
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 ~.S. patents 3,5~6,526-30, 1971.
- Producing a visible image by chemical amplification after exposure to actinic radiation ma~es it possible to sub-stantially reduce exposure times normally reguired with diazoniu~l compounds. This can be expressed empirically as simply the amount of actinic lir,ht necessary to produce an image capable of running on a lithographic press. Chemical amplifica~ion ma~es it possible to reduce the amount of light needed to attain this by a factor of from 2 to 10 or more.
This means that a diazo sensitized plate that normally re~uired 1 or 2 ~inutes to image can be imaged in a r,latter of seconds.
The 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 than about 100 to as little as 5 millijoules/cm2 at UV wave lenr,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 pro~uce a visible image.
After treatment with the preferred anionic material, the developed amplifie~ imaEe can be blanket exposed to actinic lir~ht to photo react any remaininr, lir,ht sensitive sites in the imar,e area. lhis includes coupled (lia~onium .~n~
anionic materials which remain light scnsitive after couplin~,.
A tcst to determinc whether a particular anionic material is suitable is as follows:

11'79~9~
A 5% aqueous solution of the anionic material is prepared. An aluminum lithographic plate grained, anod.ized, and silicated is coat'ed with a 1% soiution of a light sensitive dlazo condensation product (such as ~airmont's Chemical l)iazo #4). The coated plate is exposed to a Stouffer Gra~hic Arts Guide for a relatively short period of time -- 5 to 10 secolids.
The exposed plate is imm'ersed in the 5%'solution of anionic' material for 10 seconds. The plate is then rinsed and ' lacquered.with a standard lithographic lac~uer (such'as Fairmont's ~lack Lacquer). Another'plate, ide~tically.pre-pared and exposed, is treated Witil the Black Lacquer only.
This is the control. The two plates are compared. 'If the anionic material is 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 pll for most anionic materials useful in this invention.is in the ran~e of ~1 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; these include sodium, lithiu'r.~, ammonium, or triethanol amine salts and tlle like. Examples of suitable anionic surfactants (and their commercial sources) are as follows:
rl~ 1. Sodium lauryl sulfate (Proctor & Gamble, ~quex S.
E~uex SP, Alcolac, Inc. Sipex S~).

2. Ammonium lauryl sulfate (~lcolac, Inc., Sipon L-22).
.

;;r~ R JC f~)b ~ k .

~ ,g2~

3. Sodium lauryl etl~er sulfa~e (Alcolac, Ine,, ' Sipon ~S).

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

5. Ammonium lauryl ether sulfonate (Alcolac, Ine Sipon ~A~. .

6. Triethanolamine lauryl sulfate (~leolae, Ine.
Sipon LT-6).

.. . . ~
. .7. Sodium alkyl sulfate (Aleolae, Inc., Sipex OLS).

3 Sodium stearate (Emery Inds.).

9. Sodium'palmitate (Emery Inds.).

l0. Sodium oleate (~1atlerson, Coleman & Bell).

ll. DioctyL sodium sulfosuccinate (Cyana~i~, -Aerosol OT).

12. Tetrasodium N-Cl, 2 diearboxye~hyl l) - N -oetadeeyl sulfosueeina~e (Cyallamid, Aerosol 22).

13. Sodium X~lene sul~onate (Wi~eo Ch.emieal, Ultra SXS).

14. Sodium toluene sul~onate '(Witco Cllemical, Ultra STS).

15. Sodiur,l eumene sulfonate (Witco Chemieal, Ultra SCS hydrotrope).

16. Sodium dihexyl sul~osuecinaLe (Cyanamide Aerosol AY-65) 17. Sodium diamyl sulfosueeinate (Cyanamide Aerosol AY-65).

18. Anionie pl-osphate surracLan~ ollm ~ l~aas Co., Triton QS-30).

. l9. Sodium al~ylaryl polyetller sulfate (Rollm &

llaas Co., Tri~o~ -30 eone.).

~ ~/-a J~ ~/R,k .
g f 9~94 20. l'l-osptlate sur~actant, potassium salt (l~ohr,l &
l~aas Co., Triton 11-66).
. ;. . :
21. SodiuM alkylaryl polyether sulfonate (Rohm &
- Haas Co., 'rriton X-200).
.
.
Sodium lauryl sulfate is preferl-ed ~ecause of its availa~ilitv and cost.

EXAMPLE 1 (control~

A-1,' solution of~the formaldellyde condensation product of a diphenylamine - 4 - diazonium zinc chloride ~ouble salt (Fairmont Diazo ]aesin ~4) is prepared in water. The solution is placed in a two roll coating machine. A brushed ~rained, anodized ancl silicated plate, 10 x 16 x n. 12 (Ano-Coil Delta Plate) is coated face down through the macl;ine. The coated plate is dried and placed in a l~u ~rc Plate ~lalcer exposure unit, 24 inches from the souree (4 lcw lamp). A Stouffer Graphic Arts Step scale is step exposed on the plate ~or the followin~
ti~es: 1 second, 5 seconds, 10 seconds, 15 seconds, 30 seconds, and 60 seconds. The exposed plate is then developed with ~airmont's l)lack lacquer for wipe-on plates. Af~er development, rinsin~, and dryin~ the solid step exposure level is read fbr each exposure time: 1 second - no ima~e, 5 seconds - no ima~,e, 10 seconds - a ghost imaEe, 15 seconds - a solid 1, 30 seconds -a solid 3, and 60 seconds - a solid 5 -- normal for this type of plate system.

* ~ cl Je ~

.. . _ _ . . , . . . . . .. _ EX~lPL~ 2 li 7~Z~4 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 ~iquid, Rhodamine B Liquid, Rhodamine 5 GLD, crystal violet extra pure APN or Paper Blue R Liqllid. The dyed plate is then coated as in Example 1. The coated pla~e is then ex~osed in a 4 h~
Nu Arc flip top exposure unit for 5 seconds to a newspaper page negative. 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.

-E~V~L~ 3 _ _ .
A brushed grained, silicated, and anodized plate (Ano-Coil's Delta Plate) is coated with a l% diazo coating (Fairmont r~esin #4) containing 1/2% Victoria Green Liquid dye (DuPont). The plate is dryed and exposed for 5 seconds on a Nu Arc as in ~xample 7. The plate is developed in a 5%
solution of am~onium lauryl sulfate. Upon application of the developer with a sponge, a visible ima~e becomes im~ediately apparent.

xam~le 4 A lithographic 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 immersed in a 5%
solution of sodium lauryl sulfate. Il~ncdiately an ima~e becomcs visiblc. The plate is rinsed in tap watcr and drycd. The plate is placed on a Goss l~ctro rress and 50,000 ~ood ima~es are obtained.

~175~Z~
E~AI~PLE 5 A plate is prepared as in E~amnle 2 but after devel-opment it is rubbed with a UV curable emulsion (Example 6) rinsed, dryed, and re-ex~osed tllrou~h a PPG W processor at 25 ft./minute. The plate is placed on a Goss E1etro newspapcr .press and 250,000 impressions are obtained.

.
EX~IPLE 6 - -- ~ brush grained, anodized,-silicated, aluminum plate is coated witll à 1% solution of water soluble polyfunctional diazo resin (Fairmont's diazo resin ~4) containing 1/2%
Victoria Green liq~id dye as' ~n'Example 2 and dryed. The sensi-ti'zed plate is then placed in an Eocom Laserite Platemaker an~ scanned witll an ion argon laser. A scannin~ time of 1 minute is necessary to scan a plate approximately 23 x 14. The approximate laser power at tl~e plate surface is 8 mj/cm2 After scanning, the plate is developed with a 5% solution of sodium lauryl sulfate as in Example 2 to produce a strong quality visi~le image.

E~AMPLE 7 A plate was coated, laser ex~osed and developed as in Example 5 usin~ 10 mj/cm2 laser power. This time after developmcnt, the plate was rubbed with t~le following UV
curable emulsion:
(~) 30 grms Inmont W Blue In~
12.5 cc Span 80 (I.C.I.) 120 ~ls Cellosolve Acctate (n) 250 mils 8 Be Gum Arabic 12.5 grms Pluronic~38 ~BASE) ~r a Je ~ 12-. . _ . . . . . .. .

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.
EXAMP~LE 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/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) 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 usiny sulfuric acid (280 grams/liter at 90F), rinsed and silicated with sodium silicate (3%), rinsed and finally dyed with a cationic dye such as ~odamine 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 is ~n ~r ~J~ r ~ .

~3 Z 9 ~
` ed with a cationic 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 ;s easily discharged by immersion in a 5X
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 lX 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 dye can be removed. It will not discharge with this treatment.

Claims (2)

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

1. Anodized aluminum article having a surface which has been treated to render it anionic and negatively charged and thereafter colored with a cationic dye.

2. Process for coloring an anodized aluminum surface which comprises rendering said surface anionic and negatively charged and thereafter coloring said surface with a cationic dye.