Method of making a relief image
A relief (or flexographic) printing precursor has first and second radiation-sensitive layers, or a plurality of radiation-sensitive layers. The first radiation-sensitive layer is sensitive to a first imaging radiation having a first λ max . The second radiation-sensitive layer is disposed on the first radiation-sensitive layer and is sensitive to a second imaging radiation having a second λ max that differs from the first λ max by at least 25 nm. An infrared radiation ablatable layer can be present and is opaque or insensitive to the first and second imaging radiations and contains an infrared radiation absorbing compound. These relief printing precursors can be used to prepare flexographic printing plates, cylinders, or sleeves where the ablatable layer is used to form an integral mask on the element. Use of the invention provides a relief image without any loss in the strength of the small dots and can be carried out using multiple irradiation steps using the same apparatus.
1. A method of making a relief printing image comprising:
providing a relief printing precursor that is a flexographic printing precursor that is in the form of a flexographic printing plate, sleeve, or cylinder precursor, the relief printing precursor comprising at least:
a first radiation-sensitive layer that comprises a radiation-sensitive composition that is sensitive to and curable by a first imaging radiation comprising a first λ max ,
a second radiation-sensitive layer disposed on said first radiation-sensitive laver, wherein said second radiation-sensitive layer that comprises a radiation-sensitive composition is sensitive to and curable by a second imaging radiation comprising a second λ max that differs from said first λ max by at least 25 nm, wherein the second radiation-sensitive layer is insensitive to the first imaging radiation comprising a first λ max , and
an infrared radiation ablatable layer disposed on said second radiation-sensitive layer, said ablatable layer being opaque to said first and second imaging radiations and comprising an infrared radiation absorbing compound,
imagewise exposing the relief printing precursor to infrared radiation ablative energy to form a mask image in the infrared radiation ablatable layer,
subsequently or simultaneously with the imagewise exposing, exposing the relief printing precursor to a second imaging radiation through the mask image,
modifying the mask image using additional infrared radiation ablative energy to form a modified mask image, and
subsequently exposing the relief printing precursor to a first imaging radiation through the modified mask image.
2. The method of claim 1 wherein the relief printing precursor is self-supporting and wherein one of the radiation-sensitive layers is capable of being cured to provide a substrate.
3. The method of claim 2 wherein the first λ max is from about 250 to about 750 nm, and the second λ max is from about 250 to about 750 nm.
4. The method of claim 1 wherein the first λ max is from about 250 to about 750 nm, and the second λ max is from about 750 to about 1400 nm.
5. The method of claim 1 wherein the first λ max is from about 290 nm to about 400 nm, and the second λ max is from about 290 to about 320 nm.
6. The method of claim 1 wherein the second radiation-sensitive layer is also transparent to the first imaging radiation.
7. The method of claim 2 wherein the relief printing precursor is a flexographic printing sleeve precursor.
8. The method of claim 1 wherein the first radiation-sensitive layer is disposed on a substrate.
9. The method of claim 1 wherein the relief printing precursor is a coated flexographic printing cylinder precursor.
10. The method of claim 1 wherein the relief printing precursor is a self-supporting flexographic printing plate precursor.
11. The method of claim 1 wherein the thickness ratio of the first radiation-sensitive layer to the second radiation-sensitive layer is at least 1:1 and up to 300:1.
12. The method of claim 1 wherein the first radiation-sensitive layer and the second radiation-sensitive layer comprise a UV-curable composition comprising a UV-curable component, a photoinitiator, and an elastomeric resin.
13. The method of claim 1 , wherein:
providing the relief printing precursor is by laminating the first radiation-sensitive layer as a first unit to the second unit comprising the second radiation-sensitive layer and the infrared radiation ablatable layer.
14. The method of claim 13 wherein the second unit further comprises a peelable protective layer that is peeled off before laminating the first and second units.