WO1993006528A1

WO1993006528A1 - Positive-working coating compositions

Info

Publication number: WO1993006528A1
Application number: PCT/US1992/006936
Authority: WO
Inventors: Shashikant Saraiya; William Rowe; Eugene Golda; Arsene Cirignano
Original assignee: Sun Chemical Corp
Current assignee: Sun Chemical Corp
Priority date: 1991-09-13
Filing date: 1992-08-19
Publication date: 1993-04-01
Anticipated expiration: 1994-03-13

Abstract

The present invention features a printing article comprising an aluminum base with an aluminum oxide layer upon which a silicate interlayer has been formed. Also, a positive working coating containing unique sensitizers is coated on the silicate interlayer. The positive working coating with the unique sensitizers makes possible the use of silicate as an interlayer on an anodized aluminum substrate. The sensitizers derive their properties from functionalities that permit adhesion with the silicate interlayer, whether by reaction or complexing. The coatings containing the sensitizers provides a manufacturing advantage, in that both positive and negative lithographic plates can be fabricated from the same aluminum base, thus allowing a continuous production run without line stoppage. The positive coating is caused to bind with the silicated aluminum base. Negative working coatings of course, already possess the ability to bind with a silicated aluminum base. The silicated aluminum base provides protection for the aluminum base against the deteriorating effects of alkaline developers used to develop the positive coatings. It is possible to manufacture both types of plates in a common production run without line stoppages, as a result of having a common silicated aluminum base that accommodates both positive and negative coatings and which further protects against an alkaline development with actinic radiation of positive working plates.

Description

POSITIVE-WORKING COATING COMPOSITIONS

Field of the Invention

The invention involves a positive-working coating, containing a unique sensitizer, which allows a silicate to be used as an interlayer on an anodized aluminum substrate, and more particularly to positive working coatings having unique properties derived from certain chemical functionalities that permits adhesion, whether by reaction or complexing with the silicate interlayer. The coating containing unique sensitizers provides a manufacturing advantage by allowing the fabrication of both positive and negative lithographic plates from the same aluminum base, thus avoiding production line

stoppages. Background of the Invention

The manufacture of lithographic plates is excessively complicated by current demands of positive-working and negative working coatings and their respective interlayer requirements, and in some cases a lack of interlayer requirements. For example, negative-working coatings are often coated upon aluminum substrates sealed with

silicated interlayers. In contrast, positive working coatings usually utilize interlayers containing

naphthalenesulfonic acid-formaldehyde condensate disposed on an aluminum oxide base, or sometimes the positive working coatings are coated directly on to the aluminum oxide base, without the use of an interlayer, or on to an aluminum oxide base that has been treated with polyvinyl phosphonic acid. Heretofore, positive working coatings have never been coated upon an aluminum base that comprises a silicate interlayer. The purpose of an interlayer in lithographic plate manufacture is to provide adhesion of the coating on the aluminum oxide surface, as well as to provide protection to the aluminum oxide surface against alkaline developers.

It is generally known, that a silicate interlayer could not be employed in the fabrication of positive type plates, because of adhesion loss, i.e. the coating would not properly adhere to the interlayer, thereby curtailing the length of the run. While it may appear possible to adhere the positive coating directly to the aluminum oxide base without the silicate interlayer, this is not always practical. There is a very narrow time constraint placed upon the plate development step. During

development, the alkaline developer will etch the plate surface, and this in turn will undercut the dot patterns that effect resolution. Therefore, it becomes difficult to prepare for press usage, positive type plates without a protective interlayer.

Another useful property of the silicated aluminum substrate is its ability to eliminate non-image area staining. Such staining is usually encountered when non- interlayered substrates are treated with colorants

(dyes/pigments) utilized in the light sensitive,

development compositions to improve image visibility.

The present invention allows for a positive type coating to be coated upon an aluminum web or sheet having an oxide surface and a silicate interlayer disposed thereon. The use of unique sensitizers in the light sensitive coating in accordance with the present

invention, greatly simplifies the manufacturing process for lithographic plates, since now it is possible to utilize the same base or substrate for both positive and negative plate manufacture. The manufacture in

accordance with the present invention allows for ease of switching in a continuous production process, from positive to negative plates, or vice versa, without line shutdown.

It is well known that there are plate manufacturing lines in existence that start with a raw aluminum base, and in one continuous step, grain anodize, desmut and apply the light sensitive coating. The base preparation, however, is different for positive, vis-a-vis negative plates. Therefore, the process cannot be continuous in the sense of this invention, when it is desired to switch between positive and negative plate runs, and vice-versa.

The unique sensitizers employed in the coatings of the present invention allow for the same base preparation with a common silicate interlayer for both positive and negative plates. Other intermediate layers have been developed for fabricating printing plates, specifically because of the previous drawbacks presented by use of silicate as an interlayer. One such system treats the aluminum

substrate with a polyvinyl phosphonic acid, and is the subject of United States Patent No. 4,153,461. The polyvinyl phosphonic acid improves the hydrophilic properties of the aluminum oxide surface of the

substrate, so that positive printing plates can be prepared that will readily reject oleophilic printing inks. The polyvinyl phosphonic acid layer does not significantly interfere with the adhesion of the positive working coating on the aluminum oxide base. However, this interlayer has poor resistance to alkaline etching of the aluminum substrate. In the United States Patent No. 4,446,221, it is taught that a sodium salt of a condensed

naphthalenesulfonic acid can be applied to the aluminum support surface as an intermediate layer for positive- acting and negative-acting coating compositions.

However, this interlayer also has poor resistance to alkaline etching of the aluminum substrate.

It is contemplated by this invention to use a silicate intermediate layer in the fabrication of both negative- and positive-type lithographic printing plates. The advantage of this accomplishment would be the newly-found ability to provide a continuous manufacturing run of both types of plates on the same line without stopping. Both types of printing articles would be fabricated in a continuous process free of costly and time consuming stoppages. Both positive and negative plates would have a common substrate of silicate interlayer, requiring only a change on the continuous production line of the

reproduction coating solutions required to make the printing plates either positive or negative.

The invention reflects the discovery, of a sensitizer having functionality capable of reacting with, or

complexing with, silicate, so that a coating containing such sensitizer will adhere to the silicate interlayer. Such sensitizers with active functionalities includes resins such as epoxies, urethanes, acrylics, etc.

The active functionalities of the sensitizers are believed to be the hydroxy or amino groups of the

urethane; the residual free epoxy groups; or pendent acrylates containing carboxyl, hydroxyl, amino or amide. The active functionalities provide the unique adhesion of the coatings to the silicate interlayer. The most active of the aforementioned functionalities is the epoxy functionality. The epoxy functionality is thought to react with the hydroxy functionality of the silicate interlayer alone, or possibly in combination with

o-quinone diazide. Positive-acting radiation-sensitive components useable in connection with the present

invention, include: diazo-oxides such as: aromatic or heterocyclic esters of amides of naphthaquinone diazide sulfonic or carboxylic acids, for example, those diazooxides described by Kosar, "Light Sensitive Systems", John Wiley & Sons, N. Y., 1965; and in United States Patents 2,797,213; 3,454,400; 3,544,323; 3,573,917;

3,674,495; and 3,785,825. Also of interest are those diazo-oxides described in U.K. Patents 1,227,602;

1,251,345; 1,267,005; 1,329,888 and 1,330,932; as well as German Patent 854,890 and Canadian Patent 602,980. A preferred diazo oxide is the ester of 1,2-naphthoquinone- 2-diazide-4 or -5-sulfonic acid with the product prepared by the condensation of hydroxy bearing resins, either based on acrylics, epoxies or urethanes.

As will be demonstrated, the esters of the present invention differ from the previous utilized esters, in that they are the reaction products of the -4 or

-5-sulfonyl naphthaquinone diazo oxide with alkyl

reactive groups. Heretofore, the esters have been the reaction product of -4 or -5-sulfonyl naphthaquinone diazo oxide with aryl hydroxyl groups, i.e. such as in phenol, cresol, benzophenones, hydroxy-benzophenones, tris-hydroxy benzenes, etc.

Positive working coatings involve resins bearing free hydroxy groups that react completely or partially with quinone diazide compound, such as 1,2 naphthaquinone-2- diazide 4- or 5-sulfonyl chloride, and the resultant product is coated upon the aluminum oxide base with or without a suitable interlayer. Additionally, other resins can be used in the coating formulation. When exposed to UV light, solubilization occurs. The solubilized material can be removed by developer to provide a positive reproduction printing plate.

In United States Patent No. 3,859,099, it is suggested that an acrylate containing a naphthoquinone diazide can be used for fabricating a positive-type coating for printing plates. This patent, however, does not teach or suggest that this type of coating will adhere to an intermediate silicate layer. Moreover, the

aforementioned patent additionally does not teach or suggest the use of the silicate layer as a common or universal support for both positive-type and negative- type coatings in a continuous production run.

Summary of the Invention

In accordance with the present invention, there is provided an aluminum base with an aluminum oxide layer upon which a silicate interlayer has been formed. Also, a positive working coating containing unique sensitizers is coated on the silicate interlayer. The positive working coating with the unique sensitizers makes

possible the use of silicate as an interlayer on an anodized aluminum substrate. The sensitizers derive their properties from functionalities that permit

adhesion with the silicate interlayer, whether by

reaction or complexing. The coatings containing the sensitizers provides a manufacturing advantage, in that both positive-type and negative-type lithographic plates can be fabricated from the same aluminum base, thus allowing a continuous production run without line

stoppage. The positive-type coating is caused to bind with the silicated aluminum base. Negative working coatings of course, already possess the ability to bind with a

silicated aluminum base. The silicated aluminum base provides protection for the aluminum base against the deteriorating effects of alkaline developers used to develop the positive coatings. It is possible to manufacture both types of plates in a common production run without line stoppages, as a result of having a common silicated aluminum base that accommodates both positive-type arid negative-type coatings and which further protects against an alkaline development with actinic radiation of positive-working plates. Description of the Preferred Embodiment

Generally speaking, a positive or negative printing article can be fabricated utilizing a silicated support substrate. The reproduction coating of the printing article utilizes a light-sensitive coating having

sensitizers with a functionality for adherence to the silicated substrate. Epoxies, urethanes, and acrylics are chosen for providing the active functionality, hydroxy or amino of the urethane, or residual free epoxies. Epoxies, urethanes, and acrylics are chosen for their properties to best adhere to the silicated base. A positive coating is fabricated using one of the above resins in reaction with a 1,2-naphthoquinone-2-diazide-5- sulfonyl chloride:

e

+ (C₂H₅)₃N · HC I

unexposed area remaining on plate

exposed area , washed out w/a l k . deve l o p e r

The bonding characteristics of the Positive Diazo Resin (PDR) utilizing an epoxy, coated on a silicated substrate can be attributed to reactions of residual epoxy functionality.

Positive reproduction coatings of the invention, were fabricated according to the following Examples:

EXAMPLE I

Into a 1 liter ground glass, four-necked flask

equipped with a stirrer, inert gas inlet, water cooled condenser and thermometer, were charged 400g diglycidyl ether of Bisphenol A, eq wt. 650, and 291.8g methyl cellosolve acetate.

The contents of the flask were heated to 82-85° C. by means of a heating mantle, while under mechanical

agitation and an inert atmosphere. Upon reaching 82° C., 0.9g benzyl dimethyl amine was added, and the temperature was held at 82-85° C. for 10 to 15 minutes.

36.8g gallic acid were then incrementally added to the flask over 30 to 60 minutes. A mild exotherm was experienced in the first 10 to 15 minutes, and then subsided. The batch temperature was then raised to 100- 105° C., and held there for the duration of the process. The batch was monitored by running acid values

periodically. When the batch reached acid value 7.0 or less, it was cooled to room temperature. The final product had a non-vol. of 60.0 ± 1%, methyl cellosolve acetate viscosity of Z₃ - Z₄ and an acid value of 5.0 ± 2.0. The final product was checked for acid value by using ASTM method number D1639-83.

EXAMPLE II

Into the same flask equipment as in Example I, 96g of the diglycidyl ether of Bisphenol A of 185 to 190 eq wt. and 225 grams of methyl cellosolve acetate were charged. The contents of the flask were heated to 82-85° CC ., under an inert gas atmosphere with agitation. At the

temperature of 82° C., 0.6g benzyl dimethyl amine was added and after 10 to 15 minutes at 82-85° C., 128.5g diphenolic acid were incrementally added over 45 to 60 minutes. The temperature of the batch was raised gradually to 105-110° C., and held there for the

remainder of the process. When the acid value was below 5.0 and the viscosity was L-N, the batch was cooled to room temperature. The final specifications were: non- vol. 50±1%, in methyl cellosolve acetate viscosity L-N, and acid value <5.0. The final product was checked for acid value by using ASTM method number D1639-83.

EXAMPLE III

The following example was achieved utilizing the teachings of Example 2, step 1 of United States Patent No. 4,163,094. Into a 2 liter ground glass, four-necked flask heated by a heating mantle, were charged 770g isophorone diisocyanate, which was heated to 82-85° C., under an inert gas atmosphere with mechanical agitation. In a separate container, 113g of e-caprolaσtam were dissolved in 200g methyl ethyl ketone. This was stirred until a clear solution was obtained. This solution was then gradually added to the flask over a period of 30 to 45 minutes, when the temperature therein reached 82-85° C.

The percentage of free NCO was determined

approximately 30 minutes after completion of the

addition. When 28.0±2% free NCO had been obtained, the batch was cooled to room temperature and held for preparation of the final product.

EXAMPLE IV

The following example was achieved utilizing the teachings of Example 2, step 2 of United States Patent No. 4,163,094, with the substitution of 1,4-butanediol in place of polycaprolactone diol 0200.

To the flask equipment of Example I were charged 22.5g 1,4-butanediol, 33.7g trimethylol propane, 33.5g

dimethylolpropionic acid and 213g methyl ethyl ketone. The contents of the flask were heated to 82-85° C., under inert atmosphere with agitation and held for 5 to 10 minutes. To the flask, 270.8g of the product of Example III were added from a dropping funnel over a period of from 1.5 to 2.0 hours. The percentage of free NCO was determined at hourly intervals until 0.00% was obtained. The flask was then cooled to room temperature. The specifications of the material were: non vol. 55±1% in MEK viscosity U-X, acid value 6.01.5. The final product was checked for acid value using ASTM method D-2572-87. Also, free-NCO groups were analyzed by infra red

spectrophotometry, and no peak for NCO was observed.

EXAMPLE V To a 500 ml ground glass, three-necked flask equipped with mechanical stirrer, inert gas inlet, water cooled condenser, thermometer and dropping funnel, were charged 225g methyl cellosolve acetate. The flask was then heated to 105-110° C., under an inert atmosphere with mechanical agitation. After a few minutes at that temperature, 75.0g hydroxyethyl methacrylate, 30.0g acrylonitrile, 45.0g ethyl methacrylate and 1.5g dicumyl peroxide which had been mixed together, were added to the flask by cylindrical dropping funnel over 2 to 3 hours at 110-120° F. After 1 hour of addition, a second portion of dicumyl peroxide (0.8g) was added to the flask. The reaction was monitored by the percent non-volatiles, which was complete at 40±1% non-volatiles. To complete the reaction, an additional 0.7g dicumyl peroxide had to be added. The batch was then cooled to room temperature. The final non-volatiles were 40±1%, and the viscosity was Z₃ - Z₅.

EXAMPLE VI

To a 500 ml four-necked flask equipped with a stirrer, nitrogen inlet tube, water cooled condenser and glass thermometer, were charged 53.9g of the epoxy oligomer of Example I. Stirring took place at room temperature. To this was added 8.9g triethylamine over 10 minutes.

In a separate container were dissolved 334g methyl cellosolve acetate into 21.52g 1,2-naphthoquinone-2- diazide-5-sulfonyl chloride. The solution was stirred until clear. This mixture was then added to the flask in 10 minutes and a slight exotherm reaction was observed that raised the temperature to the range of 28-29° C.

After the exotherm reaction subsided, the temperature was raised to 43-46° C., and held for four hours. The completion of the reaction was measured by thin-layer chromatography.

The reaction mixture was then filtered, and triethyl amine hydrochloride salt was then removed from the flask. The filtrate (mother liquor) was pH adjusted to 5.9+0.1 with addition of 0.1N KOH. The pH was held constant for 30 minutes. The mother liquor was then added drop-wise into a 2% aqueous NaCl ice/water solution under high agitation to precipitate the product, which was recovered as a powder. The powder product was filtered and dried at room temperature.

EXAMPLE VII

To a 500 ml four-necked flask equipped as described in Example VI, were charged 47.6g of the epoxy oligomer described in Example II. To this flask were then added 7.98g triethylamine at room temperature over a 10 minute period.

In a separate container were dissolved 262.9 grams methyl cellosolve acetate into 18.83 grams 1,2- naphthoquinone-2-diazide-5-sulfonyl chloride. The solution was stirred until clear. This mixture was then added to the flask in 10 minutes and a slight exotherm reaction was observed that raised the temperature to 32° C. After the exotherm reaction subsided, the temperature was raised to 43-46° C., and held for four hours. The completion of the reaction was measured by thin-layer chromatography. The reaction mixture was then filtered, and triethyl amine hydrochloride salt was then removed from the flask. The filtrate (mother liquor) was pH adjusted to 5.9±0.1 with addition of 0.1N KOH. The pH was held constant for 30 minutes. The mother liquor was then added drop-wise into a 2% aqueous NaCl ice/water solution under high agitation to precipitate the product, which was recovered as a powder. The powder product was filtered and dried at room temperature. EXAMPLE VIII

To the 500 ml flask equipped as in Example VI, 43.6g of the urethane oligomer described in Example IV were charged. To the flask, 8.0g triethylamine and 50g methyl cellosolve acetate which had been previously mixed together, were then added in 10 minutes.

In a separate container were dissolved 237.8g methyl cellosolve acetate into 18.83g 1,2-naphthoquinone-2- diazide-5-sulfonyl chloride. The solution was stirred until clear. This mixture was then added to the flask in 10 minutes and a slight exotherm reaction was observed that raised the temperature to a range of 30 to 31° C.

After the exotherm reaction subsided, the temperature was raised to 43-46° C., and held for 4 hours. The

completion of the reaction was measured by thin-layer chromatography.

The reaction mixture was then filtered, and triethyl amine hydrochloride salt was then removed from the flask. The filtrate (mother liquor) was pH adjusted to 5.9±0.1 with addition of 0.1N KOH. The pH was held constant for 30 minutes. The mother liquor was then added drop-wise into a 2% aqueous NaCl ice/water solution under high agitation to precipitate the product, which was recovered as a powder. The powder product was filtered and dried at room temperature. EXAMPLE IX

To the 500 ml flask equipped as described in Example

VI, were added 65. Ig of the acrylic terpolymer described in Example V, while stirring at room temperature. To this were added in 10 minutes at room temperature, 7.98g triethylamine.

In a separate container were dissolved 262g methyl cellosolve acetate into 18.83g 1,2-naphthoquinone-2- diazide-5-sulfonyl chloride. The solution was stirred until clear. This mixture was then added to the flask in 10 minutes. The mixture was held for 30 minutes at room temperature, and then the temperature was raised to 110- 115° F., and held for 4 hours. The completion of the reaction was measured by thin-layer chromatography.

The reaction mixture was then filtered, and triethyl amine hydrochloride salt was then removed from the flask. The filtrate (mother liquor) was pH adjusted to 5.9±0.1 with addition of 0.1N KOH. The pH was held constant for 30 minutes. The mother liquor was then added drop-wise into a 2% aqueous NaCl ice/water solution under high agitation to precipitate the product, which was recovered as a powder. The powder product was filtered and dried at room temperature. EXAMPLE X

To 61.6g methyl cellosolve were dissolved 5.88g of one of the light sensitive compounds obtained in Examples VI,

VII, VIII and IX. The compound of Example VII is

preferred. Then 28.2g methyl ethyl ketone and 4.7g methyl cellosolve acetate were added. Thereafter, 0.04g 2-(p-methoxyphenyl)-4,6-bis(trichoromethyl)-s-triazine was added.

The above mixture was then coated upon treated substrates, such as pumice grained silicate, using a barcoater. The substrates were dried for 5 minutes at 32° C. with an air dryer. The thickness of the coating was applied in a range of approximately 0.8 to 2.0 g/m², with the preferred range being 1.0 to 1.5 g/m². The coated substrates were then image exposed to UV radiation through a positive plate using a 5 kw metal halide source at a distance of 91.44cm for a period of 1.0 to 1.5 minutes. The substrates were developed using an alkaline developer having a ph of approximately 12 to 13, which needed some solvent for better development. EXAMPLE XI

To 30.6g methyl cellosolve were dissolved 2.625g of one of the light sensitive compounds obtained in Examples VI, VII, VIII and IX. The compound of Example VII is preferred. To 0.3g of the reaction product of 1,2- naphthoquinone-2-diazide-5-sulfonyl chloride was added the condensation product of acetone and pyrogallol. Then 14. Ig methyl ethyl ketone and 2.3g methyl cellosolve acetate were added. Then, 0.03g 2-(p-methoxyphenyl)-4,6- bis(trichoro methyl)-s-triazine was added. When the mixture was clear, printout dye was added and the mixture was filtered through a No. 4 Whatman filter paper.

The above mixture was then coated upon treated

substrates, such as pumice grained silicate, using a barcoater. The substrates were dried for 5 minutes at 32° C. with an air dryer. The thickness of the coating was applied in a range of approximately 0.8 to 2.0 g/m², with the preferred range being 1.0 to 1.5 g/m². The coated substrates were then image exposed to UV radiation through a positive plate using a 5 kw metal halide source at a distance of 91.44cm for a period of 1.0 to 1.5 minutes. The substrates were developed using an alkaline developer having a pH of approximately 10 to 11.

EXAMPLE XII

To 30.6g methyl cellosolve were dissolved 1.425g of one of the light sensitive compounds obtained in Examples VI, VII, VIII and IX. The compound of Example VI is preferred. To 0.03g of the reaction product of 1,2- naphthoquinone 2-diazide 5-sulfonyl chloride was added the condensation product of acetone and pyrogallol. Then 14.1g methyl ethyl ketone and 2.3g methyl cellosolve acetate and 0.9g Novalac resin treated with triethylamine (United States Patent No. 4,350,753) were added. When the mixture was clear, printout dye was added and the mixture was filtered through a No. 4 Whatman filter paper.

The above mixture was then coated upon treated

aluminum, such as pumice-grained silicate or Electrograin polyvinyl phosphonic acid, using a bar-coater. The substrates were dried for 5 minutes at 32° C. with an air dryer. The thickness of the coating was applied in a range of approximately 0.8 to 2.0 g/m², with the

preferred range being 1.0 to 1.5 g/m². The coated substrates were then image exposed to UV radiation through a positive plate using a 5 kw metal halide source at a distance of 91.44cm for a period of 1.0 to 1.5 minutes. The substrates were developed using an alkaline developer having a pH of approximately 10 to 11. COMPARISON DATA OF ALUMINUM ETCH RESISTANCE

The data presented below in Table 1, represents aluminum etch resistance to alkali developer when various interlayers are applied to a standard aluminum oxide substrate:

TABLE 1

GRAVIMETRIC LOSS IN G/M₂RELATIVE TO TIME

The loss of the oxide was measured gravimetrically using 6 g./l NaOH solution.

The test indicates that when no interlayer is

utilized, the poorest etch resistance to alkaline

developer is obtained, resulting in the worst image loss. However, a silicated positive plate showed the best resistance to alkaline development and the least image attack, thus maintaining resolution quality.

EXAMPLE XIII

A lithographic plate was prepared utilizing the

teachings in Example 1 of United States Patent No.

4,350,753, as follows: Acid-free Novalac was prepared. To 100g Novalac resin that had been dissolved in 500 ml 2-propanol, were added 200g triethylamine. The resultant mixture was then added to an aqueous solution comprising 1 wt.% NaCl. The precipitated product was removed by filtration, washed, dried and ground.

A radiation-sensitive, positive-working, acid- sensitive composition was prepared by blending the aforementioned: Novalac resin 6.35 g Product of the reaction of 1,2-naphthoquinone- 2-diazide-5-sulfonic acid with the product

of condensation of acetone and pyrogallol 3.30 g 2-(p-methoxyphenyl)-4,6-bis(trichloromethyl)- s-triazine 0.40 g

Bromocresol green, Na+ salt 0.06 g

Calco Oil Blue RA 0.06 g

Bromophenol Blue 0.25 g

The aforementioned radiation sensitive composition was then dissolved in a solvent comprising 32g MEK, 48g MIBK, 48g n-amyl acetate and 37g ethylene glycol monomethyl ether. The resulting solution was then coated on a sheet of aluminum alloy AA1100 which had been mechanically grained and then anodized in an electrolyte comprising 17% wt. aqueous sulfuric acid at 30° C. and 3.2 A/dm² for 1 minute.

After evaporation of the solvents, the resulting coated sheet was exposed by image UV radiation through a positive plate, using a 5 kw metal halide radiation source at a distance of 91.44cm for 1 minute. The exposed sheet was developed using alkaline developer having a pH in the range of 10 to 11. The printing articles prepared in Examples X, XI, and XII were compared with the printing article prepared in Example XIII for an adhesion test, consisting of a ball mill test method described below: 2' x 9" unexposed plates were placed in a rack, which was deposited in an 8.5" x 9" cylinder with 140 ml.

water, 50 ml isopropanol, 10 ml fountain solution, 75g carborundum and various sizes of 10 rubber stoppers. The cylinder was then closed and rolled for 6 hours.

Afterwards, the plates were removed and the remaining coatings were inspected. The plates from Examples X, XI, and XII lost 20 to 30% of the coating and Example XIII lost 80% of the coating. The plates from Examples X, XI, and XII incorporating the sensitizers of the present invention, had the best adhesion and length of run, as shown by the comparative loss results.

PRESS TEST

The positive working coatings of this invention presented in Examples X and/or XI were coated on an aluminum oxide substrate using various interlayers, viz., no-interlayer; Na salt of condensed naphthalenesulfonic and polyvinyl phosphonic acid and silicate. They were then press tested using the following conditions:

- Single color sheet fed 25" press. - Polychrome PR637 (pH 4.5 to 5.5) acid fountain

solution with cobalt drier, containing butyl

cellosolve.

- 12% Isopropyl alcohol with alcohol substitute PR

628. A blue ink was used and printed on 27.26 kg uncoated, offset paper. The press tests were conducted at a press speed of 6,000 sheets per hour. The following Table 2, indicates that the silicate interlayer coated with the coating of the invention containing the sensitizers, provided a better length of run compared with the other interlayers.

TABLE 2

- No-interlayer = 70,000 impressions - Na Salt of a condensed

naphthalenesulfonic salt = 35,000 impressions

- Polyvinyl phosphonic acid = 50,000 impressions

- Silicate = 85,000 impressions

The positive working, photosensitive, compositions in accordance with the present invention can further

comprises in combination with said sensitizers at least one material selected from a group of materials

consisting of: photosensitizers,polymers, monomers, oligomers, film formers, wetting agents, dyes, and pigments, and other materials commonly included in the preparation of reproductive coatings.

The coatings can be applied to silicated base plates of aluminum on steel; chromium on steel; and chromium on aluminum, but a silicated aluminum base with an oxide layer is preferred.

Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. Having thus described the invention, what is desired to be protected by Letters Patent is presented by the subsequently appended claims.

Claims

What is claimed is:

1. A positive-working printing plate comprising a silicated substrate having a coating thereon comprising a photosensitive composition including a sensitizer

comprising a reaction product of quinone diazide with a polymer selected from a group of polymers consisting of acrylics, epoxies, urethanes, and mixtures thereof.

2. The positive-working printing plate of claim 1, wherein said polymer comprises an epoxy polymer.

3. The positive-working printing plate of claim 1, wherein said quinone diazide comprises a 1,2- naphthoquinone-2-diazide-4- or -5-sulfonyl chloride.

4. The positive-working printing plate of claim 1, wherein said silicated substrate comprises a base

selected from a group of materials consisting of:

aluminum on steel, chromium on steel and chromium on aluminum.

5. The positive-working printing plate of claim 1, wherein said silicated substrate comprises an aluminum base.

6. The positive-working printing plate of claim 5, wherein said aluminum base comprises an aluminum oxide layer formed by anodization of said aluminum base.

7. The positive-working printing plate of claim 5, wherein said silicated substrate contains an alkaline- protective silicate interlayer.

8. The positive-working printing plate of claim 1, wherein the composition comprises the reaction product of a diazo ketone with the alkyl-reactive groups of a monomeric, oligomeric or polymeric compound.

9. The positive-working printing plate of claim 7, wherein the ketone comprises an aryl diazo ketone.

10. A method of fabricating both positive-working and negative-working printing plates during the same

continuous manufacturing run, which comprises the steps of: a) manufacturing a silicated substrate; b) during a continuous production run, coating the substrate with a photosensitive composition having a given positive or negative character; and c) during the same continuous production run,

coating the substrate with a photosensitive composition of opposite character to that selected in step (b),

whereby both positive-working and negative-working

printing plates are manufactured in the same continuous production run.

11. The method of claim 10, wherein the

photosensitive composition comprises a sensitizer

comprising a reaction product of a quinone diazide with a polymer selected from a group of polymers consisting of acrylics, epoxies, urethanes and mixtures thereof.

12. The method of claim 11, wherein said polymer comprises an epoxy polymer.

13. The method of claim 11, wherein the quinone diazide comprises a 1,2-naphthoquinone-2-diazide-5- sulfonyl chloride.

14. The method of claim 10, wherein said silicated substrate comprises a base selected from a group of materials consisting of: aluminum on steel, chromium on steel and chromium on aluminum.

15. The method of claim 10, wherein said silicated substrate comprises an aluminum base.

16. The method of claim 15, wherein said aluminum base comprises an aluminum oxide layer formed by

anodization of said aluminum base.

17. The method of claim 16, wherein said aluminum oxide layer contains an alkaline-protective silicate interlayer.

18. The method of claim 10, wherein the composition comprises the reaction product of a diazo ketone with the alkyl-reactive groups of a monomeric, oligomeric or polymeric compound.

19. The method of claim 18, wherein the ketone comprises an aryl diazo ketone.