WO2002002346A2

WO2002002346A2 - Preparation of printing cylinders using ultra-violet radiation

Info

Publication number: WO2002002346A2
Application number: PCT/IL2001/000541
Authority: WO
Inventors: Hannoch Ron
Original assignee: Kba (Advanced Imaging Technology) (Israel) Limited
Priority date: 2000-07-05
Filing date: 2001-06-12
Publication date: 2002-01-10
Also published as: US6723491B2; EP1299236A2; ATE264191T1; DE60102820D1; EP1299236B1; US20020017211A1; AU2001266281A1; DE60102820T2; WO2002002346A3

Abstract

In one embodiment, the present invention is directed to a method for preparing a printing member by coating a printing cylinder with a layer comprising ultraviolet-curable silicones and curing the layer using ultraviolet radiation.

Description

UTILIZING UV TO FORM AND DECOMPOSE A PRINTING MEMBER

BACKGROUND OF THE INVENTION

Plateless imaging is a method of generating an image directly on a printing cylinder. The coating materials, which form the plateless printing member together with

the cylinder surface, are applied on-press. The coating materials are applied in a liquid state

and then cured. After each printing job, the cured materials are removed and the printing

cylinder is prepared for reuse, either by cleaning the printing cylinder or by replacing a

reusable substrate.

The use of cross-linked poly-dimethyl siloxane (PDMS) is well known in waterless offset printing. In existing plateless printing systems, the PDMS coating is cured by heating

it to a temperature of approximately 120°C to 150°C. In order to prevent toning, the

printing cylinder has to be cooled before printing to a temperature of approximately 20°C.

It would be desirable to use a coating that eliminates the need for heating the

printing press.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed out and

distinctly claimed in the concluding portion of the specification. The invention, however,

both as to organization and method of operation, together with objects, features and

advantages thereof, may best be understood by reference to the following detailed

description when read with the accompanying drawings in which:

Fig. 1 is a schematic illustration of a plateless printing system according to some

embodiments of the present invention;

Fig. 2 is a flow chart diagram of the operation of the system of Fig. 1 according to some embodiments of the present invention;

Fig. 3 is a cross-sectional schematic illustration of a two-coat printing member

according to some embodiments of the present invention;

Fig. 4 is a flow chart diagram of the operation of the system of Fig. 1 according to

some embodiments of the present invention; and

Fig. 5 is a flow chart diagram of the operation of the system of Fig. 1 according to some embodiments of the present invention.

It will be appreciated that for simplicity and clarity of illustration, elements shown

in the figures have not necessarily been drawn to scale. For example, the dimensions of

some of the elements may be exaggerated relative to other elements for clarity. Further,

where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are set forth in order

to provide a thorough understanding of the invention. However, it will be understood by

those of ordinary skill in the art that the present invention may be practiced without these

specific details. In other instances, well-known methods, procedures, components and

circuits have not been described in detail so as not to obscure the present invention.

Various embodiments of the present invention are directed to utilizing ultraviolet

(UV) or visible radiation to form and decompose a printing member for waterless offset

printing. In these embodiments the imaging layer may comprise UV/visible-curable

silicones, which are cross-linking poly-dimethyl siloxane (PDMS) having the ability of being cured by UV or visible radiation.

In some embodiments, which will be described hereinbelow with respect to Fig. 2,

a single ablatable imaging layer comprising UV-curable silicones is formed. A formulation comprising UV-curable silicones may be coated onto a printing cylinder having an

ink-accepting oleophilic surface. The coated layer may be cured by UV radiation and then

may be imaged by selectively ablating the cured layer, thus revealing the ink-accepting

imaged areas.

In other embodiments, which will be described hereinbelow with respect to Figs. 3

and 4, a two-coat ablatable imaging layer comprising UV-curable silicones is formed. In

these embodiments, the cured bottom layer may serve as an ink-accepting agent.

In further embodiments, which will be described herein below with respect to Fig.

5, the imaging layer comprising UV/visible-curable silicones may allow direct imaging. In the direct imaging method, a suitable light source may be used to perform selective UV/visible-curing of the silicone formulation. Non-limiting examples of such a light

source include a laser having a suitable wavelength and a broadband light source having a

suitable filter and a spatial light modulator (SLM). The formulation may be coated onto a

printing cylinder having an ink-accepting oleophilic surface. The coated layer may be

selectively cured in the non-imaged areas. The uncured formulation may then be removed

exposing the ink-accepting imaged areas.

Reference is now made to Fig. 1, which is a schematic illustration of a plateless

printing system 10 according to some embodiments of the present invention. Printing

system 10 may comprise a printing cylinder 12, a blanket cylinder 14, an inking system 16

and an imaging system 18.

Printing cylinder 12 may have an imaging layer, generally designated 100, directly

coated onto cylinder 12. Alternatively, printing cylinder 12 may carry a replaceable

substrate (not shown), either as a sleeve or as a sheet, that may be replaced after a large

number of jobs. This has the advantage of protecting the cylinder from wear. Printing system 10 may further comprise a coating system 20, a cleaning system 22

adapted to clean printing cylinder 12 after imaging and an erasing system 24 adapted to remove the ink leftover and the imaged layer after the printing impressions have been

made. Coating system 20, cleaning system 22 and erasing system 24 may be any suitable

system using any suitable process for coating, cleaning, and erasing, respectively.

Printing system 10 may comprise an UV curing system 25 having at least one UV

lamp 26. UV lamp 26 may be adapted to move parallel to the longitudinal axis of cylinder

12 as it rotates, as indicated by arrows 30 and 32. Alternatively, the length of UV lamp 26 may be approximately the length of cylinder 12. Printing cylinder 12 may comprise an oleophilic surface from a material that is

suitable for receiving and adhesion of the oleophobic coating layer 100. Non-limiting

examples of such a surface include plastics, reinforced plastics, metals such as aluminum

(or anodized aluminum) and copper, ceramics and stones, such as granite.

Imaging layer 100 may comprise UV/visible-curable silicones such as UV 9500 of

GE Bayer silicones, the Netherlands and SILCOLEASE UV POLY 200 of Rhodia

Silicones, Lion, France. It has been found that in order to obtain good coating for a variety

of substrates together with good adhesion to said substrates and good release properties of the layer formed and good scratch resistance, the following components of the coating may

be present in the following parts by weight:

UV-curable silicone ~50%-90%

Photo-initiator ~1%-10%

Photo-sensitizer ~1%-10%

Infrared absorber ~l%-20%

Vinyl ether such as those manufactured by BASF, Germany, by ISP, USA or by

Morflex Inc. NC, USA may be added to the formulation described hereinabove. The

properties of the coating formulation may be modified by vinyl ether monomers. The

addition of vinyl ether to the above formulation may increase the adhesion of the layer to the surface, may reduce the viscosity of the formulation, and may improve flow properties.

Additionally, the incorporation of infrared (IR) absorbing materials, such as carbon black

may be easier in a mixture comprising vinyl ethers.

Reference is now made to Fig. 2, which is a flow chart diagram of the operation of system 10 according to some embodiments of the present invention. Optionally, prior to

coating, printing cylinder 12 may be irradiated using UV lamp 26 in order to clean its surface (step 200). The UV radiation of the surface prior to coating may increase the

adhesion of coating layer 100 to printing cylinder 12. Short UV radiation (either UVB or UVC) may activate certain surfaces by the oxidation of polymers having carbonyl and/or

carboxyl groups, which are attached to the surface. As a result, the surface energy may be

increased and the adhesion of the coating to the surface may be improved.

UV-curable silicones may have a long shelf life and/or pot life compared to other

curable silicones used in existing printing systems. Therefore, the mixture for coating may

be prepared off-press. The mixture may then be coated onto the surface of printing cylinder

12 using coating system 20 (step 202).

Next, UV lamp 26 may be turned on and may traverse the cylindrical surface as it

rotates to allow the curing of layer 100 (step 204). Compared to other curing methods (e.g. heat energy), the use of UV and visible radiation for curing may be more efficient.

The radiation may be directly focused on the surface with only relatively minor losses to

the ambience. Additionally, UV lamps 26 may be turned on and off instantaneously and

the duration of radiation may be shorter.

Imaging system 18 may then selectively expose the imaging layer during multiple

rotations of printing cylinder 12 (step 206). During further rotations of cylinder 12,

cleaning system 22 may be operated (step 208). At this stage, system 10 is ready to print

and the appropriate ink may be applied to printing cylinder 12 by inking system 16.

Printing cylinder 12 may be cooled if necessary to control the temperature of the ink during printing, for example in waterless printing. After the required number of impressions have been printed (step 210), the remainders of layer 100 and ink may be

removed by erasing system 22 (step 212). It is known that in the presence of UV radiation and nitrate (NO₃ ^") ions may

decompose PDMS. In order to facilitate the post-printing cleaning, an aqueous solution

comprising NO₃ ^" ions may be applied to the remainders of layer 100. UV lamp 26 may

be turned on and cylinder 12 may be irradiated as it rotates to allow the decomposition of

the cured layer 100.

Reference is now made to Fig. 3, which is a cross-sectional schematic illustration

of a two-coat imaging layer coated on a metal cylinder surface according to some

embodiments of the present invention. Printing member 110 may comprise a metal surface

112, a first ink-accepting and heat-isolation layer 114, and a top IR ablateable oleophobic

layer 116.

First layer 114 may be of thickness between approximately 10-50μm and may

comprise a radiation-curable resin or a heat-curable resin. Layer 114 may comprise

UV-curable acrylates with a low resistance to aqueous solutions. Non-limiting examples of

such acrylates include polyether acrylate, polyethylene glycol based acrylates and acrylates with high acid value.

After curing, first layer 114 may be able to serve as an ink-accepting agent and as

an isolating material for the IR imaging laser. It may eliminate the need for a polyester film and a clamping system to mount the film onto the cylinder. As a result, printing cylinder 12 may become a seamless cylinder having a printing member around its entire surface.

First layer 114 may be at least partially water-soluble or water sensitive and may be

easily removed. Since no water is present during the waterless printing process, layer 114

may be removed in an easy and controlled manner. Top IR ablateable oleophobic layer 116

may be applied on top of cured layer 114 and may comprise the UV-curable silicone formulation described hereinabove in relation to Fig. 2. Reference is now made to Fig. 4, which is a flow chart diagram of the operation of

system 10 when applying the two-coat imaging layer on the printing cylinder according to

some embodiments of the present invention. Optionally, prior to coating, printing cylinder

12 may be irradiated using UV lamp 26 for cleaning purposes (step 400). Then a

formulation comprising curable resin may be applied to the surface of cylinder 12 forming

first layer 114 (step 402). First layer 114 may then be cured using UV lamp 26 (step 404).

It should be noted that other curing methods like heat might be suitable for curing first

layer 114.

A second formulation comprising UV-curable silicones is then applied on top of

layer 114 to form top layer 116 (step 406). Top layer 116 may be cured using UV lamp 26 (step 408). Imaging system 18 may then selectively expose the imaging layer during

multiple rotations of printing cylinder 12 (step 408). During further rotation of cylinder 12,

cleaning system 22 may be operated (step 410). At this stage, system 10 is ready to print

and the appropriate ink may be applied to printing cylinder 12 by inking system 16. After

the required number of impressions have been printed (step 412), the remainders of layer

100 and ink may be removed by erasing system 22 (step 414).

It should be noted that some of the processes described hereinabove might be performed concurrently. For example, removing the remainders of the printed layer (step

414) and cleaning the cylinder with UV radiation before coating it for another printing job. Another example may be coating the cylinder while curing the coating layer. It should be noted that also more than two processes might be performed concurrently.

Reference is now made to Fig. 5, which is a flow chart diagram of a direct imaging operation of system 10 according to some embodiments of the present invention. The term

direct imaging refers to selective hardening of the non-imaged area of the imaging layer. In the method of ablation imaging described previously in relation to Fig. 2, the entire coating

layer coated onto an ink-accepting substrate is first cured and then imaged by ablating, thus

exposing the ink-accepting areas.

In contrast, in the method of direct imaging, only the non-imaged areas are selectively cured by radiation from a suitable light source, which emits in the visible or UV

region. Non-limiting examples of a suitable light source include a laser having a suitable

wavelength and a broadband light source having a suitable filter and an SLM. The imaging

layer may be coated onto a printing cylinder having an ink-accepting oleophilic surface.

After selectively curing the imaging layer to form the non-imaged areas, the ink-accepting

imaged areas are exposed by removing the uncured formulation and exposing the cylinder.

In these embodiments, the imaging system and the curing system are integrated,

eliminating the need for two distinct units and speeding up the process of printing.

In the direct image process, printing cylinder 12 may be coated by a formulation comprising suitable photo-sensitizers and/or photo-initiators (step 500). Example II, which

is given below, describes a non-limiting example of such a formulation. The formulation

may be applied directly onto the metal surface of cylinder 12, which may serve as the

ink-accepting agent. Unlike the method of IR ablation, there is no need for thermal

isolation achieved by a polyester film, therefore the printing member is mounted

seamlessly on cylinder 12.

The non-image areas may be cured and imaged by a suitable radiation source (step

502). The uncured silicone, which is in a liquid state, is then removed (step 504). It should be noted that to remove the uncured silicone in this process is much easier than to remove the cured siiicone in the ablation process. At this stage, system 10 is ready to print and the appropriate ink may be applied to printing cylinder 12 by inking system 16. After the required number of impressions have been printed (step 506), the remainders of layer 100

and ink may be removed (step 508).

The following examples are now given, though by way of illustration only, to show

certain aspects of some formulations according to some embodiments of the present invention without limiting its scope.

Example I - Top ablatable layer

This is an example illustrating the preparation of the formulation for a top

IR ablatable layer. The following formulation was prepared as a mixture (all numbers

designating parts in the formulation are in parts by weight of the entire formulation).

UV9400 (GE Bayer Silicones, the Netherlands) 16

SILCOLEASE UV (Rhodia, Lion, France) 5 RCA 200

SILQUEST A- 186 (Witco, USA) 10

UV9380C (GE Bayer Silicones, the Netherlands) 2

DAROCUR 1173 (Ciba-geigy, Switzerland) 1

SPEEDCURE-ITX (Lambson Limited, UK) 1 SPECIAL BLACK 250 (Degussa, Germany) 5

The mixture was applied to a polymeric surface of a printing cylinder to a wet

thickness of approximately 3μ and then was irradiated by UV lamp, which emits mainly

in the UV region. The layer was then imaged with infrared imaging system. Example II - Direct imaging layer

This is an example illustrating the production of the formulation for a direct imaging layer. The following formulation was prepared as a mixture (the percentages are

by weight of the entire formulation).

Name Producer %

Methyl en chloride Aldrich Sigma 50

UV 9500 GE Bayer silicones 47

UV 9380c GE Bayer silicones 1.5

Dye Green 471151 Aldrich-Sigma 1.5

While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the

invention.

Claims

What is claimed is:

1. A method for preparing a printing member comprising:

coating a printing cylinder with layer comprising ultraviolet-curable

silicones; and

curing said layer using ultraviolet radiation.

2. The method of claim 1, further comprising:

attaching an image bearing substrate to said printing cylinder, prior to

coating.

3. The method of claim 1, wherein said layer further comprises photo-initiators,

photo-sensitizers and infrared absorbing materials.

4. The method of claim 1 , wherein said layer further comprises vinyl ethers.

5. A method comprising: applying water and nitrate ions to a layer comprising cured silicones, said

layer coated onto a printing cylinder; and

irradiating said layer with ultraviolet radiation to decompose at least a

portion of said layer.

6. The method of claim 5 further comprising:

removing said at least partially decomposed layer from said printing

cylinder.

7. A method comprising:

coating a printing cylinder having a first layer thereon with a second layer comprising ultraviolet-curable silicones and infrared absorbing materials; and curing said second layer using ultraviolet radiation.

8. The method of claim 7, wherein said coating and said curing are performed in

parallel.

9. The method of claim 7 further comprising:

curing said first layer prior to coating said second layer.

10. The method of claim 7, wherein said first layer is at least partially water-soluble.

11. The method of claim 7, wherein said first layer is water sensitive.

12. The method of claim 7, wherein said first layer comprise ultraviolet-curable

acrylates with low resistance to aqueous solutions.

13. The method of claim 12, wherein said acrylates comprise polyether acrylates.

14. The method of claim 12, wherein said acrylates comprise polyethylene glycol.

15. The method of claim 12, wherein said acrylates comprise acrylates with high acid

value.

16. The method of claim 7, wherein said second layer further comprises

photo-initiators and photo-sensitizers.

17. The method of claim 7, wherein said second layer further comprises vinyl ethers.

18. A method comprising :

coating a cylinder surface with a layer comprising ultraviolet-curable silicones;

imaging said layer by applying any one of visible and ultraviolet radiation

to non-imaged areas thereon; and

removing said layer from imaged areas.

19. A method for promoting adhesion of a coating to a printing cylinder, wherein

said coating is coated on-press, comprising : irradiating said printing cylinder with ultraviolet radiation prior to said

coating.

20. A printing member comprising:

a printing cylinder; and

an imaging layer coated on said printing cylinder, said imaging layer

comprising ultraviolet-curable silicones.

21. The printing member of claim 20, wherein said printing member is configured

such that after ultraviolet-curing and selective ablation of said imaging layer,

selective areas of said imaging layer are removed thereby exposing said cylinder.

22. The printing member of claim 20, wherein said imaging layer further comprises photo-initiators, photo-sensitizers and infrared absorbers.

23. The printing member of claim 22, wherein said imaging layer further comprises

vinyl ethers.

24. A printing member comprising:

a printing cylinder;

an image bearing substrate attached to said printing cylinder; and

an imaging layer coated on said substrate on-press, said imaging layer

comprising ultraviolet-curable silicones.

25. The printing member of claim 24, wherein said printing cylinder is a seamless machined cylinder.

26. The printing member of claim 24, wherein said printing member is configured

such that after ultraviolet-curing and selective ablation of said imaging layer, selective areas of said imaging layer are removed thereby exposing said image

bearing substrate.

27. The printing member of claim 24, wherein said imaging layer further comprises

photo-initiators, photo-sensitizers and infrared absorbers.

28. The printing member of claim 27, wherein said imaging layer further comprises

vinyl ethers.

29. A printing member comprising:

a printing cylinder;

a first layer coated thereon, said first layer comprising curable resin; and

an imaging layer coated on said first layer, said imaging layer comprising

ultraviolet-curable silicones.

30. The printing member of claim 29, wherein said printing cylinder is a seamless

machined cylinder.

31. The printing member of claim 29, wherein said printing member is configured such that after ultraviolet-curing and selective ablation of said imaging layer,

selective areas of said imaging layer are removed thereby exposing said first

layer.

32. The printing member of claim 29, wherein said imaging layer further comprising

photo-initiators and photo-sensitizers.

33. The printing member of claim 32, wherein said imaging layer further comprising

vinyl ethers.

34. The printing member of claim 29, wherein said first layer is at least partially

water-soluble.

35. The printing member of claim 29, wherein said first layer is water sensitive.

36. The printing member of claim 29, wherein said curable resin comprises ultraviolet-curable acrylates having low resistance to aqueous solutions.

37. The printing member of claim 36, wherein said acrylates comprise polyether

acrylates.

38. The printing member of claim 36, wherein said acrylates comprise polyethylene

glycol.

39. The printing member of claim 36, wherein said acrylates comprise acrylates with

high acid value.

40. A printing system comprising:

a printing member comprising an imaging layer having ultraviolet-curable silicones and coated on a printing cylinder or a replaceable substrate attached to

said printing cylinder; an imaging system adapted to place an image on said printing cylinder or

said substrate; and

an ultraviolet radiation system.

41. The printing system of claim 40, wherein said imaging system and said

ultraviolet radiation system are integrated into a single system.

42. The printing system of claim 40 further comprising an erasing unit adapted to remove at least a portion of said imaging layer.

43. The printing system of claim 40 further comprising a cleaning system adapted to

clean said image placed on said printing member or said substrate.

44. The printing system of claim 40, wherein said printing member is configured

selective areas of said imaging layer are removed thereby exposing said cylinder

or said substrate.

45. The printing system of claim 40, wherein said imaging layer further comprises

photo-initiators, photo-sensitizers and infrared absorbers.

46. The printing system of claim 45, wherein said imaging layer further comprises

vinyl ethers.

47. A printing system comprising:

a printing member comprising a printing cylinder, a first layer coated

thereon and an imaging layer coated on said first layer, said first layer comprising

curable resin, said imaging layer comprising ultraviolet-curable silicones;

an imaging system adapted to place an image on said printing member; and

an ultraviolet radiation system.

48. The printing system of claim 47 further comprising an erasing unit adapted to remove at least a portion of said printing member.

49. The printing system of claim 47 further comprising a cleaning system adapted to

clean said image placed on said printing member.

50. The printing system of claim 47, wherein said printing member is configured

selective areas of said imaging layer are removed thereby exposing said first layer.

51. The printing system of claim 47, wherein said imaging layer further comprising photo-initiators and photo-sensitizers.

52. The printing system of claim 51, wherein said imaging layer further comprising vinyl ethers.

53. The printing system of claim 47, wherein said first layer is at least partially

water-soluble.

54. The printing system of claim 47, wherein said first layer is water sensitive.

55. The printing system of claim 47, wherein said curable resin comprises

ultraviolet-curable acrylates having low resistance to aqueous solutions.

56. The printing system of claim 55, wherein said acrylates comprise polyether

acrylates.

57. The printing member of claim 55, wherein said acrylates comprise polyethylene

glycol.

58. The printing member of claim 55, wherein said acrylates comprise acrylates with

high acid value.

59. A formulation for a printing member, said formulation comprising a mixture including an ultraviolet-curable silicone, a photo-initiator, a photo-sensitizer and an infrared absorber.

60. The formulation ofclaim 59 further comprising vinyl ether.