Method of marking a lithographic printing plate precursor
A method of making a heat-sensitive lithographic printing plate precursor is disclosed which comprises the steps of (i) providing a web of a lithographic support having a hydrophilic surface; (ii) coating a layer comprising a phenolic resin on the hydrophilic surface of the web; (iii) drying the layer; (iv) a heating step wherein the web temperature is maintained above 150° C. during a period of between 0.1 and 60 seconds; (v) winding the coated web on a core or cutting the coated web into sheets. The short on-line heating step provides a significant improvement of the aging behavior of the precursor. A stable sensitivity is obtained shortly after coating.
1 . A method of making a heat-sensitive lithographic printing plate precursor comprising the steps of
(i) providing a web of a lithographic support having a hydrophilic surface;
(ii) applying a coating comprising a phenolic resin on the hydrophilic surface of the web;
(iii) drying the coating;
(iv) a heating step wherein the web temperature is maintained above 150° C. during a period of between 0.1 and 60 seconds; and
(v) winding the precursor on a core or cutting the precursor into sheets.
2 . The method according to claim 1 wherein during the heating step the web temperature is maintained above 170° C. during a period of between 1 and 30 seconds.
3 . The method according to claim 1 wherein the heating step is carried out by blowing hot air or steam onto the precursor.
4 . The method according to claim 1 wherein the heating step is carried out by exposing the precursor to infrared or microwave radiation.
5 . The method according to claim 1 further comprising a cooling step between step (iv) and step (v).
6 . The method according to claim 5 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
7 . The method according to claim 6 wherein said average cooling rate is at least 0.5° C./s.
8 . The method according to claim 5 wherein during the cooling step the web temperature is reduced from T 1 to T 2 , T 1 being higher than Tg and T 2 being lower than Tg, at an average cooling rate which is lower than 10° C./s, Tg being the glass transition temperature of the coating comprising the phenolic resin.
9 . The method according to claim 8 wherein during the cooling step the web temperature is reduced
in a first phase down to T 1 at an average cooling rate of at least 10° C./s;
in a second phase from T 1 to T 2 at an average cooling rage which is lower than 10° C./s; and
in a third phase from T 2 to about ambient temperature at an average cooling rate of at least 10° C./s.
10 . The method according to claim 8 wherein T 1 is Tg+20° C. and T 2 is Tg−20° C.
11 . The method according to claim 2 wherein the heating step is carried out by blowing hot air or steam onto the precursor.
12 . The method according to claim 2 wherein the heating step is carried out by exposing the precursor to infrared or microwave radiation.
13 . The method according to claim 3 wherein the heating step is carried out by blowing hot air or steam onto the precursor.
14 . The method according to claim 3 wherein the heating step is carried out by exposing the precursor to infrared or microwave radiation.
15 . The method of claim 2 further comprising a cooling step between step (iv) and step (v).
16 . The method according to claim 3 further comprising a cooling step between step (iv) and step (v).
17 . The method according to claim 4 further comprising a cooling step between step (iv) and step (v).
18 . The method according to claim 15 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
19 . The method according to claim 16 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
20 . The method according to claim 18 wherein said average cooling rate is at least 0.5° C./s.
21 . The method according to claim 19 wherein said average cooling rate is at least 0.5° C./s.
22 . The method according to claim 17 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
23 . The method according to claim 22 wherein said average cooling rate is at least 0.5° C./s.
24 . The method according to claim 6 wherein during the cooling step the web temperature is reduced from T 1 to T 2 , T 1 being higher than Tg and T 2 being lower than Tg, at an average cooling rate which is lower than 10° C./s, Tg being the glass transition temperature of the coating comprising the phenolic resin.
25 . The method according to claim 7 wherein during the cooling step the web temperature is reduced from T 1 to T 2 , T 1 being higher than Tg and T 2 being lower than Tg, at an average cooling rate which is lower than 10° C./s, Tg being the glass transition temperature of the coating comprising the phenolic resin.
26 . The method according to claim 24 wherein during the cooling step the web temperature is reduced
in a first phase down to T 1 at an average cooling rate of at least 10° C./s;
in a second phase from T 1 to T 2 at an average cooling rage which is lower than 1° C./s; and
in a third phase from T 2 to about ambient temperature at an average cooling rate of at least 10° C./s.
27 . The method according to claim 25 wherein during the cooling step the web temperature is reduced
in a first phase down to T 1 at an average cooling rate of at least 10° C./s;
in a second phase from T 1 to T 2 at an average cooling rage which is lower than 10° C./s; and
in a third phase from T 2 to about ambient temperature at an average cooling rate of at least 10° C./s.
28 . The method according to claim 9 wherein T 1 is Tg+20° C. and T 2 is Tg−20° C.
29 . The method of claim 11 further comprising a cooling step between step (iv) and step (v).
30 . The method of claim 12 further comprising a cooling step between step (iv) and step (v).
31 . The method according to claim 29 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
32 . The method according to claim 30 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
33 . The method according to claim 31 wherein said average cooling rate is at least 0.5° C./s.
34 . The method according to claim 32 wherein said average cooling rate is at least 0.5° C./s.
35 . The method according to claim 13 further comprising a cooling step between step (iv) and step (v).
36 . The method according to claim 35 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
37 . The method according to claim 36 wherein said average cooling rate is at least 0.5° C./s.
38 . The method according to claim 14 further comprising a cooling step between step (iv) and step (v).
39 . The method according to claim 38 wherein during the cooling step the web temperature of the precursor is reduced at an average cooling rate which is higher than if the precursor would be kept under ambient conditions.
40 . The method according to claim 39 wherein said average cooling rate is at least 0.5° C./s.