CA1175384A - Lithographic printing plates - Google Patents
Lithographic printing platesInfo
- Publication number
- CA1175384A CA1175384A CA000396367A CA396367A CA1175384A CA 1175384 A CA1175384 A CA 1175384A CA 000396367 A CA000396367 A CA 000396367A CA 396367 A CA396367 A CA 396367A CA 1175384 A CA1175384 A CA 1175384A
- Authority
- CA
- Canada
- Prior art keywords
- anodising
- electrolyte
- phosphoric acid
- aluminium
- acid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT
Aluminum sheets for lithographic printing plate production are anodised firstly in a phosphoric acid electrolyte and secondly in in electrolyte containing a major amount of phosphoric acid and a minor amount of sulphuric acid.
Aluminum sheets for lithographic printing plate production are anodised firstly in a phosphoric acid electrolyte and secondly in in electrolyte containing a major amount of phosphoric acid and a minor amount of sulphuric acid.
Description
~ ~7538~ 1 "Improvements in or reIating to lithographic printing' n'l'a't'e's'l''''''''''''''''' ' _, .
This invention relates to treating aluminium and alloys thereof, in part'icular for use as substrates ~or lithographic printing plates.
Aluminium and aluminium alloys are the materials most commonly used as substrates for lithographic plates due to their relative'cheapness, ductility, dimensional stability and the ability of the surface to be treated to 10 improve its lithographic properties. Thus, it is common practice to grain the surface'to increase its water holding capacity and improve the adhesion of the radiation sensitive coating used to form the image and to anodise the surface to lncrease its abrasion resistance and hydrophilic na*ure. The most commonly used electrolytes for the anodising p~ocess are phbsphoric acid and sulphuric acid.
The use of phosphoric acid as anodising electrolyte produces an anodic layer which has a maximum thickness of only l micron due to the'fact that the layer dissolves in the electrolyte. Thus, the abrasion resistance is relativeIy low.
The anodic layer produced using sulphuric acid as electrolyte'is thicker, and therefore has better 25 ~abras1on resist~nce,~ but'is'prone to staining and has inadequate adhesion to some types of light sensitive coating. Although'the adhesion can be increased, in a few circumstances, by certain chemical post-anodising treatments both'the'anodising treatments and the chemical treatment have to be'carefully controlled so that a balance between image adhesion and ease of develop~ent of non-image'areas can be maintained conslstently.
The production o~ lmproved aluminium or aluminium alloy substrates for lithographic printing plates has exercised the minds of those in the art for many years and to this end many different types of electroly-tic treatment and many different types of electrolytes based on - ................... . ,,~
3 8 ~ 1 sulphuric acid, phosphoric acid and other conductive li~uids have been tried. Surprisingly, it has now been found that anodic layers having excellent suitability for lithographic printing plates can be readily obtained merely by firstly anodising the aluminium or alloy thereof in phosphoric acid electrolyte and secondly anodising the aluminium or alloy thereof in an electro]yte comprising a mixture containing a major amount of phosphoric acid and a minor amount of sulphuric acid.
In accordance with one embodiment the first anodising is carried out for from 0.25 to 4 minutes using, as electrolyte, an aqueous solution containing 250-400 g/l (preferably 328 to 380 g/l) of phosphoric acid at a voltage of 15 to 35 V and a temperature of 15 -46C and the second anodising is carried out for from 0.25 to 4.0 minutes using, as the electrolyte, an aqueous solution containing 20-150 g/1 (preferably 40 -to 100 g/l) sulphuric acid and 250-380 g/l phosphoric acid at a voltage of 15-35 Y and a temperature of 15-46 deg C.
According to a further preferred feature, the voltage used in the second anodising step is equal to or greater than the voltage used in the first step. Unless the voltages are arranged in this way, there is a delay whilst barrier layer thinning takes place before current can pass in the second anodising step.
The following Examples illustrate the invention.
EXA~LE 1 .
Three sheets of electrochemically grained aluminium were anodised using direct current and respective-ly in phosphoric acid only (sheet 1), sulphuric acidonly (sheet 2), and firstly in phosphoric acid and then in a mixture of phosphoric acid and sulphuric acid (sheet 3) using the following conditions:-. .,,~, . .
Sheet 1 Conc- 3 4 P
~ Temp. 20 deg C.
Electrolyte: aqueous phosphoric acid. ~ Voltage 22 V
~ Time 3 mins.
. .
Sheet 2 ~Conc. 160g H2S04 per litre ~ Temp. 15 degC
Electrolyte aqueous phosphoric acid. ~ ~
Voltage 22 V
~ Time 1 min Sheet 3 .
~Conc. 3~0 H3P04 20 degC
:
1st Electrolyte:
~aqueous phosphoric acid.
Voltage 30 V
Time 3 mins .
f Conc. 340g H3P04 per litre 60 g H2S04 per litre Temp. 20 degC
2nd Electrolyte:
aqueous phosphoric acid/sulphuric acid mixture. Voltage 30 V
Time 3 mins.
I ~ 7538~ , The anodised sheets were coated with a radiation sensitive composition comprising the reaction product of p-diazodiphenylamine/formaldehyde condensate and sodium tri-isopropyl naphthalene sulphonate and Victoria Cyan F5G dye (BAS~) to form radiation sensitive plates which were then exposed to W light beneath a negative transparency and developed with 20% v/v aqueous solution o-~ isopropanol containing 2% anionic surfactant. E~ch o~ the resultant lithographic printing plates was then used to print copies.
The sheet anodised in phosphoric acid only gave a print run of 60,000 copies before scumming due to the anodic layer being worn away in the non-image areas.
The non-image areas of the sheet anodised in sulphuric acid only were dye stained on development and the plate gave a priDt run of 60,000 copies before the image areas became worn due to lack of adhesion to the anodic layer .
The sheet anodised in two-stages in accordance with the present invention developed cleanly with no dye staining and gave a print run of 130,000 copies.
A further electrograined sheet was anodised in sulphuric acid only and then given a post anodic dip in sodium silicate. No improvement in either the degree of staining or the run length was found.
~, An aluminium web was continuously elec$rograined and then anodised using direct current firstly in phosphoric acid electrolyte and then iD an electrolyte comprising a mixture o~ phosphoric and sulphuric acids. The web was theD
I .1 75384 coated with the radiation sensitive composition of Example 1 to form a radiation sensitive plate.
The conditions used ~or the anodising were as follows:-f Conc. 328 g H3P04 per litre~ Temp. 43 deg C.
1st Electrolyte: a~ueous phosphoric acid ¦ Voltage 29-5 V
Time 30 secs.
Conc. 312g H3P04 per litre 77 g H2S04 per li*re 2nd Electrolyte : aqueous ~hos~horic acid/
sulp~uric acid mixture ¦ Temp 40.5 degC
¦ Voltage 29.5 V
Time 30 secs.
A sample of the web was exposed and developed as in Example 1. It developed cleaniy and the resultant lithographic priDting plate gave a print-run of 130, 000 copies.
.
Three aluminium sheets ~ere e]ectrochemically grained and anodised as in Example 1.
..... .. . . . . . . . . . .. . . ...
i 1 ~ 7 5 3 ~
The sheets were coated with a radiation sensitive composition comprising an epoxy resin ester of 4-azido-alpha-cyano-delta-chloro-cinnamylidene acetic acid to form radiation sensitive plates which were then exposed beneath a negative transparency to UV light and developed with a mixture of 2-ethoxy ethanol, 2-ethoxy ethyl acetate and a non-ionic surfactant. The resultant lithographic printing plates were then used for printing.
The sheets anodised in one acid only gave print runs of 60,000 copies whereas the sheet anodised in two stages in accordance with the present invention gave a print run of 120,000 copies.
A further sheet of electrograined aluminium was anodised in sulphuric acid under the above conditions and then given a post anodic treatment with hydrofluoro-silicic acid. A print run of 120,000 copies was obtained, but unless the post anodic treatement was carefully control-led within very tight limits, removal of the non-image areas of the developer was rendered impossible~
EXAMPL~ 4 Three ~urther aluminium sheets were electro-chemically grained and anodised as in Example 1.
The sheets were coated with a radiation sensitive composition comprising a quinone diazide ester, a novolak resin and a crystal violet dye to ~orm radiation sensitive plates which ~ere exposed to ultra-violet light beneath a positive transparency and developed with an aqueous solution containing sodium metasilicate r sodium phosphate and a non-ionic surfactant~ Each of the resultant lithographic printing plates was then used for printing.
9 .11 ~38~1 A print run of 120,000 copies was obtained from the sheet anodised in two stages in accordance with the present invention whereas the sheet anodised in phosphoric acid only gave 80,000 copies and the sheet anodised in sulphuric acid only gave 120,000 copies but had badly stained non-image areas.
Three further aluminium sheets were electro-chemically grained and anodised as in Example 1.
The sheets were coated with a radiation sensitive composition as disclosed in Example 5 of British Patent Application 2,069,997~ in the name of Vickers Limited and published September 3 , 1981, and exposed and developed as in that Example.
Results similar to those of Example 4 were obtained.
:`~
This invention relates to treating aluminium and alloys thereof, in part'icular for use as substrates ~or lithographic printing plates.
Aluminium and aluminium alloys are the materials most commonly used as substrates for lithographic plates due to their relative'cheapness, ductility, dimensional stability and the ability of the surface to be treated to 10 improve its lithographic properties. Thus, it is common practice to grain the surface'to increase its water holding capacity and improve the adhesion of the radiation sensitive coating used to form the image and to anodise the surface to lncrease its abrasion resistance and hydrophilic na*ure. The most commonly used electrolytes for the anodising p~ocess are phbsphoric acid and sulphuric acid.
The use of phosphoric acid as anodising electrolyte produces an anodic layer which has a maximum thickness of only l micron due to the'fact that the layer dissolves in the electrolyte. Thus, the abrasion resistance is relativeIy low.
The anodic layer produced using sulphuric acid as electrolyte'is thicker, and therefore has better 25 ~abras1on resist~nce,~ but'is'prone to staining and has inadequate adhesion to some types of light sensitive coating. Although'the adhesion can be increased, in a few circumstances, by certain chemical post-anodising treatments both'the'anodising treatments and the chemical treatment have to be'carefully controlled so that a balance between image adhesion and ease of develop~ent of non-image'areas can be maintained conslstently.
The production o~ lmproved aluminium or aluminium alloy substrates for lithographic printing plates has exercised the minds of those in the art for many years and to this end many different types of electroly-tic treatment and many different types of electrolytes based on - ................... . ,,~
3 8 ~ 1 sulphuric acid, phosphoric acid and other conductive li~uids have been tried. Surprisingly, it has now been found that anodic layers having excellent suitability for lithographic printing plates can be readily obtained merely by firstly anodising the aluminium or alloy thereof in phosphoric acid electrolyte and secondly anodising the aluminium or alloy thereof in an electro]yte comprising a mixture containing a major amount of phosphoric acid and a minor amount of sulphuric acid.
In accordance with one embodiment the first anodising is carried out for from 0.25 to 4 minutes using, as electrolyte, an aqueous solution containing 250-400 g/l (preferably 328 to 380 g/l) of phosphoric acid at a voltage of 15 to 35 V and a temperature of 15 -46C and the second anodising is carried out for from 0.25 to 4.0 minutes using, as the electrolyte, an aqueous solution containing 20-150 g/1 (preferably 40 -to 100 g/l) sulphuric acid and 250-380 g/l phosphoric acid at a voltage of 15-35 Y and a temperature of 15-46 deg C.
According to a further preferred feature, the voltage used in the second anodising step is equal to or greater than the voltage used in the first step. Unless the voltages are arranged in this way, there is a delay whilst barrier layer thinning takes place before current can pass in the second anodising step.
The following Examples illustrate the invention.
EXA~LE 1 .
Three sheets of electrochemically grained aluminium were anodised using direct current and respective-ly in phosphoric acid only (sheet 1), sulphuric acidonly (sheet 2), and firstly in phosphoric acid and then in a mixture of phosphoric acid and sulphuric acid (sheet 3) using the following conditions:-. .,,~, . .
Sheet 1 Conc- 3 4 P
~ Temp. 20 deg C.
Electrolyte: aqueous phosphoric acid. ~ Voltage 22 V
~ Time 3 mins.
. .
Sheet 2 ~Conc. 160g H2S04 per litre ~ Temp. 15 degC
Electrolyte aqueous phosphoric acid. ~ ~
Voltage 22 V
~ Time 1 min Sheet 3 .
~Conc. 3~0 H3P04 20 degC
:
1st Electrolyte:
~aqueous phosphoric acid.
Voltage 30 V
Time 3 mins .
f Conc. 340g H3P04 per litre 60 g H2S04 per litre Temp. 20 degC
2nd Electrolyte:
aqueous phosphoric acid/sulphuric acid mixture. Voltage 30 V
Time 3 mins.
I ~ 7538~ , The anodised sheets were coated with a radiation sensitive composition comprising the reaction product of p-diazodiphenylamine/formaldehyde condensate and sodium tri-isopropyl naphthalene sulphonate and Victoria Cyan F5G dye (BAS~) to form radiation sensitive plates which were then exposed to W light beneath a negative transparency and developed with 20% v/v aqueous solution o-~ isopropanol containing 2% anionic surfactant. E~ch o~ the resultant lithographic printing plates was then used to print copies.
The sheet anodised in phosphoric acid only gave a print run of 60,000 copies before scumming due to the anodic layer being worn away in the non-image areas.
The non-image areas of the sheet anodised in sulphuric acid only were dye stained on development and the plate gave a priDt run of 60,000 copies before the image areas became worn due to lack of adhesion to the anodic layer .
The sheet anodised in two-stages in accordance with the present invention developed cleanly with no dye staining and gave a print run of 130,000 copies.
A further electrograined sheet was anodised in sulphuric acid only and then given a post anodic dip in sodium silicate. No improvement in either the degree of staining or the run length was found.
~, An aluminium web was continuously elec$rograined and then anodised using direct current firstly in phosphoric acid electrolyte and then iD an electrolyte comprising a mixture o~ phosphoric and sulphuric acids. The web was theD
I .1 75384 coated with the radiation sensitive composition of Example 1 to form a radiation sensitive plate.
The conditions used ~or the anodising were as follows:-f Conc. 328 g H3P04 per litre~ Temp. 43 deg C.
1st Electrolyte: a~ueous phosphoric acid ¦ Voltage 29-5 V
Time 30 secs.
Conc. 312g H3P04 per litre 77 g H2S04 per li*re 2nd Electrolyte : aqueous ~hos~horic acid/
sulp~uric acid mixture ¦ Temp 40.5 degC
¦ Voltage 29.5 V
Time 30 secs.
A sample of the web was exposed and developed as in Example 1. It developed cleaniy and the resultant lithographic priDting plate gave a print-run of 130, 000 copies.
.
Three aluminium sheets ~ere e]ectrochemically grained and anodised as in Example 1.
..... .. . . . . . . . . . .. . . ...
i 1 ~ 7 5 3 ~
The sheets were coated with a radiation sensitive composition comprising an epoxy resin ester of 4-azido-alpha-cyano-delta-chloro-cinnamylidene acetic acid to form radiation sensitive plates which were then exposed beneath a negative transparency to UV light and developed with a mixture of 2-ethoxy ethanol, 2-ethoxy ethyl acetate and a non-ionic surfactant. The resultant lithographic printing plates were then used for printing.
The sheets anodised in one acid only gave print runs of 60,000 copies whereas the sheet anodised in two stages in accordance with the present invention gave a print run of 120,000 copies.
A further sheet of electrograined aluminium was anodised in sulphuric acid under the above conditions and then given a post anodic treatment with hydrofluoro-silicic acid. A print run of 120,000 copies was obtained, but unless the post anodic treatement was carefully control-led within very tight limits, removal of the non-image areas of the developer was rendered impossible~
EXAMPL~ 4 Three ~urther aluminium sheets were electro-chemically grained and anodised as in Example 1.
The sheets were coated with a radiation sensitive composition comprising a quinone diazide ester, a novolak resin and a crystal violet dye to ~orm radiation sensitive plates which ~ere exposed to ultra-violet light beneath a positive transparency and developed with an aqueous solution containing sodium metasilicate r sodium phosphate and a non-ionic surfactant~ Each of the resultant lithographic printing plates was then used for printing.
9 .11 ~38~1 A print run of 120,000 copies was obtained from the sheet anodised in two stages in accordance with the present invention whereas the sheet anodised in phosphoric acid only gave 80,000 copies and the sheet anodised in sulphuric acid only gave 120,000 copies but had badly stained non-image areas.
Three further aluminium sheets were electro-chemically grained and anodised as in Example 1.
The sheets were coated with a radiation sensitive composition as disclosed in Example 5 of British Patent Application 2,069,997~ in the name of Vickers Limited and published September 3 , 1981, and exposed and developed as in that Example.
Results similar to those of Example 4 were obtained.
:`~
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of treating aluminium or an alloy thereof for use as a substrate in lithographic printing plate production which comprises firstly anodising it in phosphoric acid electrolyte and secondly anodising it in an electrolyte comprising a mixture containing a major amount of phosphoric acid and a minor amount of sulphuric acid.
2. A method according to claim 1 wherein the first anodising is carried out for from 0.25 to 4.0 minutes, at a voltage of from 15 to 35 V, at a temperature of from 15 to 46°C, and using an electrolyte containing from 250 to 400 g/l phosphoric acid.
3. A method according to claim 2 wherein the electrolyte used in the first anodising contains from 328 to 380 g/l phosphoric acid.
4. A method according to claim 1 wherein the second anodising is carried out for from 0.25 to 4.0 minutes, at a temperature from 15 to 46°C, and using an electrolyte containing from 20 to 150 g/l sulphuric acid and from 250 to 380 g/l phosphoric acid.
5. A method according to claim 4 wherein the electrolyte used in the second anodising contains at least 40 g/l sulphuric acid.
6. A method according to claim 1 wherein the voltage used in the second anodising is equal to or greater than the voltage used in the first anodising.
7. A method of manufacturing a radiation sensitive plate for lithographic printing plate production which comprises (i) anodising aluminium or aluminium alloy using an electrolyte consisting essentially of aqueous phosphoric acid solution, (ii) anodising the aluminium or aluminium alloy using an electrolyte consisting essentially of a major amount of phosphoric acid, a minor amount of sulphuric acid, and water, and (iii) coating the anodised aluminium or aluminium alloy with a radiation sensitive composition to obtain the desired radiation sensitive plate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000396367A CA1175384A (en) | 1982-02-16 | 1982-02-16 | Lithographic printing plates |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000396367A CA1175384A (en) | 1982-02-16 | 1982-02-16 | Lithographic printing plates |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1175384A true CA1175384A (en) | 1984-10-02 |
Family
ID=4122071
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000396367A Expired CA1175384A (en) | 1982-02-16 | 1982-02-16 | Lithographic printing plates |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1175384A (en) |
-
1982
- 1982-02-16 CA CA000396367A patent/CA1175384A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |