FLEXO-PLATEMAKER AND METHOD OF MAKING A FLEXO-PLATE

Abstract

A flexo-plate maker uses two different curable liquids. After curing, the curable liquids result in different physical properties. Optionally, the system also uses two illumination subsystems preferably with a different resolution.

Claims

1-15. (canceled)

16. A flexo-plate maker comprising: a vat having a transparent bottom; a first valve that fills the vat with a first curable liquid from a first tank, the first curable liquid having a first set of physical characteristics after being cured; a second valve that fills the vat with a second curable liquid from a second tank, the second curable liquid having a second set of physical characteristics after being cured; a manufacturing platform; an illuminator located underneath the transparent bottom of the vat to expose a layer of the first curable liquid or the second curable liquid disposed between the transparent bottom and the manufacturing platform; a purge valve that purges the first curable liquid and/or the second curable liquid in the vat to one of a waste tank, the first tank, or the second tank; wherein the first set of physical characteristics and the second set of physical characteristics are different; the first curable liquid after being cured defines an elastomeric floor of a flexographic printing plate, a mesa relief layer on an elastomeric floor of a flexographic printing plate, or a relief layer on a mesa relief layer or on an elastomeric floor of a flexographic printing plate.

17. The flexo-plate maker according to claim 16, wherein an elasticity of the first curable liquid after being cured is higher than an elasticity of the second curable liquid after being cured.

18. The flexo-plate maker according to claim 16, wherein a hardness of the first curable liquid after being cured is lower than a hardness of the second curable liquid after being cured.

19. The flexo-plate maker according to claim 16, wherein the illuminator includes a matrix of addressable pixels and is selected from the group consisting of a transparent OLED illuminator, an LCD illuminator, and a digital micromirror illuminator.

20. The flexo-plate maker according to claim 16, wherein the illuminator emits a scanning light beam.

21. The flexo-plate maker according to claim 16, wherein the illuminator includes a two-photon polymerizator.

22. The flexo-plate maker according to claim 16, wherein the illuminator includes: a first illuminator including a matrix of addressable pixels and selected from the group consisting of a transparent OLED illuminator, an LCD illuminator, and a digital micromirror illuminator; and a second illuminator that emits a scanning light beam; wherein a resolution in an X-dimension and a resolution in a Y dimension of the second illuminator are higher than a resolution of the first illuminator.

23. The flexo-plate maker according to claim 22, wherein a first layer of the first curable liquid disposed between the transparent bottom and the manufacturing platform is exposed by the first illuminator; a second layer of the second curable liquid disposed between the transparent bottom and the manufacturing platform is exposed by the second illuminator through the first illuminator which includes a controller to make the matrix of addressable pixels transparent.

24. A flexo-plate manufacturing method comprising the steps of: filling a vat having a transparent bottom with a first curable liquid, which is stored in a first tank, by opening a first valve, the first curable liquid having a first set of physical characteristics after being cured; moving a manufacturing platform a first vertical distance to create a first layer of the first curable liquid between the manufacturing platform and the transparent bottom of the vat; exposing the first layer from underneath the vat to cure the first layer; purging the first curable liquid in the vat through a purge valve to either a waste tank or to the first tank; filling the vat with a second curable liquid, which is stored in a second tank, by opening a second valve, the second curable liquid having a second set of physical characteristics after being cured that is different than the first set of physical characteristics; moving the manufacturing platform a second vertical distance to create a second layer of the second curable liquid between the manufacturing platform and the transparent bottom of the vat; and exposing the second layer from underneath the vat to cure the second layer; wherein the first curable liquid after being cured defines an elastomeric floor of a flexographic printing plate, a mesa relief layer on an elastomeric floor of a flexographic printing plate, or a relief layer on a mesa relief layer or on an elastomeric floor of a flexographic printing plate.

25. The flexo-plate manufacturing method according to claim 24, wherein an elasticity of the first curable liquid after being cured is higher than an elasticity of the second curable liquid after being cured.

26. The flexo-plate manufacturing method according to claim 24, wherein a hardness of the first curable liquid after being cured is lower than a hardness of the second curable liquid after being cured.

27. The flexo-plate manufacturing method according to claim 24, further comprising: exposing one or both of the first layer and the second layer using a first illuminator that includes a matrix of addressable pixels and is selected from the group consisting of a transparent OLED illuminator, an LCD illuminator, and a digital micromirror illuminator; and exposing one or both of the first layer and the second layer using a second illuminator that includes a scanning light beam or a two-photon polymerizator.

28. The flexo-plate manufacturing method according to claim 24, wherein the first curable liquid and/or the second curable liquid includes one or more radically polymerizable groups selected from the group consisting of acrylamide, (meth)acryloylmorpholine, isobornyl(meth)acrylamide, isobornyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, vinylcaprolactam, N-vinylpyrrolidone, phenoxyethyl(meth)acrylate, polyethylene glycol mono(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol mono(meth)acrylate, polypropylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, neopentyl glycol di(meth)acrylate, polyester di(meth)acrylate, urethane di(meth)acrylate, epoxy di(meth)acrylate, (meth)acrylate of phenol novolac polyglycidyl ether, and (meth)(acryloxymethyl)isocyanurate or (meth)(acryloxymethyl)hydroxymethisocyanurate derivatives; and the first curable liquid and/or the second curable liquid includes one or more elastomeric compounds selected from the group consisting of copolymers of butadiene and styrene, copolymers of isoprene and styrene, styrene-diene-styrene triblock copolymers, polybutadiene, polyisoprene, nitrile elastomers, polyisobutylene and other butyl elastomers, polyalkyleneoxides, polyphosphazenes, elastomeric polyurethanes and polyesters, elastomeric polymers and copolymers of (meth)acrylates, elastomeric polymers and copolymers of olefins, and elastomeric copolymers of vinylacetate and partially hydrogenated derivatives thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] FIG. 1 shows examples of images having different image features.

[0080] FIG. 2 shows a rendering of a relief print master for printing images having different image features.

[0081] FIG. 3 shows a preferred embodiment of a flexo-platemaker according to the current invention.

[0082] FIG. 4 shows a cross section in the X-Z plane of a relief print master that is constructed by stacking layers on top of each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] A manufacturing platform (300) resides in a vat (301) with a transparent bottom (302). The vat (301) is filled with a photocurable liquid (341 or 351). The level (304) of the photocurable liquid (341 or 351) is kept constant by means of a sensor (305), a valve (306) that connects the vat (501) to a supply tank (507) filled with photocurable liquid and a control system (307) to control the valve in order to keep the level (304) in the vat (301) constant.

[0084] The manufacturing platform (300) is connected by means of a lever (310) to a motor (311) and a worm drive that is capable to move the platform upwards or downwards in the direction of the Z-dimension. The motor (311) is controlled by a computing device (312).

[0085] Below the transparent bottom (302) of the vat (301) is an illumination system that projects a two-dimensional image on the photocurable liquid layer (313) underneath the manufacturing platform (300).

The Illumination System Comprises Two Illumination Systems

[0086] A first subsystem is an illumination system that that has a low resolution. It could be, for example, a self-illuminating transparent display panel (320) such as a transparent OLED panel. In the off condition such a panel is substantially transparent. When the panel is driven, the pixels (321) of the panel will image-wise light up and expose the layer (313) of curable liquid between the manufacturing platform (300) and the transparent bottom (302). The driving of the pixels (321) of the panel (320) is preferably under the control of the computer (312) or another computing device.

[0087] The low resolution illumination can also be an LCD panel that acts as a matrix of light valves and that is exposed from underneath by an external light source. In a first condition, the light valves are substantially transparent. In a second condition, the transparency of the light valves is image-wise controlled by an LCD driver that is commanded by the computer (312) or another computing device.

[0088] The low resolution illumination system can also be a digital micromirror system. In that case a digital micromirror device is illuminated by an external light source and the reflected and modulated beam is projected onto the bottom 302 of the vat (301).

[0089] A second subsystem of the illumination system may be a high resolution illumination system. A good example is a laser scanning illumination system. In FIG. 3 a laser (530) beams onto a rotating multifaceted mirror (531). The beam is reflected by the rotating multifaceted mirror and is deflected by a cylindrical projection lens system (532), passes through the transparent display panel through which it exposes the curable liquid layer. The rotation of the multifaceted mirror causes a scanning sweep of the laser beam in the fast scan X dimension onto the layer (513) with curable liquid. A slow scan motion in the Y dimension is obtained by having the laser, the rotating multifaceted mirror and the cylindrical projecting lens system mounted on a carriage (533) that can be moved along the Y dimension. During the scanning motion, the intensity of the laser is modulated by a computing device (512) according to information in the image that is to be projected.

[0090] The first illumination system (320) has a first pixel resolution resolution_1 and the second illumination system has a second pixel resolution resolution_2 that has a higher value than resolution_1.

[0091] The apparatus in FIG. 3 comprises two or more tanks of curable liquid. A first tank (340) contains a first curable liquid (341) that is dispensed to the vat (301) through an electronically controlled valve (342). A second tank (350) contains a second curable liquid (551) that is dispensed to the vat (301) through an electronically controlled valve (352). The composition of the curable liquids (341) and (351) is different.

[0092] The vat is also connected to a drainpipe for draining the curable liquid (341 or 351) in the tank (301) in to a waste tank (360). Draining is controlled by means of a valve (362).

[0093] The electronically controlled valves (342, 352 and 362) are driven by a computing device such as for example the computer (312).

Three-Dimensional Modelling of the Flexographic Print Master

[0094] FIG. 1 shows a two-dimensional image in the X-Y dimensions of which a relief print master is to be created. It comprises a halftone part (100) for rendering a picture, a geometrical shape (101) and a text part (102). FIG. 2 shows a rendering of the relief print master in which the halftone part (200), the geometrical shape part (201) and the text part (202) are raised in the Z dimension.

[0095] FIG. 4 shows a three-dimensional model of an exemplary flexographic print master according to a preferred embodiment of the current invention. The print master consists of a set of stacked layers (400) on top of each other that together define the shape of the flexographic print master. As the figure shows, the bottom layers (402), which comprises the elastomeric floor, are thicker in the Z dimension than the top layers (401). Moreover, the bottom layers 402 are represented with a coarser resolution in the X and Y dimensions.

[0096] According to a preferred embodiment of the current invention, the physical characteristics, such as elasticity, plasticity, specific weight, hardness etc . . . of the layers 402 and 401 are preferably different.

Calculation of the Three-Dimensional Model

[0097] A preliminary step in a method according to the current invention comprises preferably the conversion of a binary two-dimensional source image into a three-dimensional model of the relief print plate that is to be created. Such a three-dimensional representation consists of voxels the value of which indicate where during the physical reconstruction of the relief print master material is preserved and where not.

[0098] The patent EP 1437882 B1 assigned to Agfa Graphics NV and having a priority date of 2002 Dec. 11, discloses a first method to obtain such a representation. It makes use of a topographic operator to convert the binary two-dimensional source image representing the image features including, text, graphics and images into a three-dimensional image of a flexographic print master that is suitable for physical reconstruction.

[0099] The original method uses the following steps: [0100] providing a two-dimensional binary source image comprising a plurality of image pixels; [0101] generating a filtered image by replacing every image pixel from the binary source file by a pixel profile spread out over neighbouring image pixels, the pixel profile corresponding to pixel heights; [0102] taking an envelope of the pixel profiles spread from neighbouring image pixels for defining a three-dimensional print structure which is to be formed by three-dimensional printing; [0103] slicing the envelope to form image layers for printing in the three-dimensional printing system to thereby generate definitions of a plurality of image layers from the filtered image for printing using the three-dimensional printing system; [0104] whereby any cross-section through a solid section of a three-dimensional structure at a second level in the three-dimensional print structure which is closer to the substrate than a first level has an area which is equal to or larger than the area of the cross-section of the three-dimensional structure at the first level.

[0105] According to a preferred embodiment of the current invention, the slicing step is adapted so that it discriminates between lower layers (402) and upper layers (401). The lower layers (402) are sliced with a lower resolution in the Z-dimension and result in layers having a value for their thickness distance_1. The upper layers (401) are sliced with a higher resolution in the Z-dimension result in layers having a value for their thickness distance_2 that is smaller than distance_1.

[0106] Additionally the resolution of the pixels in the X-Y planes of the layers (401, 402) can be changed. For example, the lower image layers (402) can be resampled so that the resolution in the X-Y dimensions has a value resolution_1, and the upper image layers (401) can be resampled so that the resolution in the X-Y dimensions has a value resolution_2 that is higher than resolution_1. The value resolution_1 preferably corresponds with the resolution of the first illumination system (320) and the value resolution_2 with the resolution of the second illumination system (330, 331, 332, 333).

[0107] The patent EP 2199065 B assigned to Agfa Graphics NV and having a priority date of 2008 Dec. 19 discloses an alternative technique for the same purpose. It equally starts from the binary two-dimensional source image that corresponds to the top layer of the flexographic print master and next uses an approximate circular spread function for calculating subsequently lower layers. The same adaptation is made to this method to accommodate for the different resolutions of the upper and lower layer stacks in the X, Y and Z dimensions.

[0108] In both techniques, the result is an ordered stack of binary two-dimensional images that together define a three-dimensional representation of the print master that is suitable for physical reconstruction by a three-dimensional printer. During the physical reconstruction of the relief print master, each one of the ordered stack of two-dimensional layers will be converted into a layer of cured photocurable liquid. When these layers (400) are stacked (FIG. 4) in the same order as the two-dimensional images in the three-dimensional model, they together constitute the relief print master.

Operation of the Flexo-Platemaker

[0109] According to a preferred embodiment, the operation of the flexo-platemaker in FIG. 3 for making a flexographic print master is as follows.

[0110] The manufacturing process is subdivided into two stages: one stage for exposing a curable liquid with a first illumination system (320) at a first resolution having a value resolution_1, and a second stage for exposing a curable liquid with a second illumination system at a second resolution having a value resolution_2 that is higher than the value of the first resolution.

[0111] In the initial condition the valves (342, 352) and (362) are closed and the vat is (301) is empty. The manufacturing platform is at its lowest position leaving a space (313) between the platform and the transparent bottom of the vat (301).

[0112] In a first step, the valve (342) is opened under control of a computer (312), and the curable liquid (341) flows into the vat (301). The level of the first curable liquid is controlled by the sensor (305), the control system (307) and the valve (306).

[0113] When the level of the curable liquid (341) has reached an equilibrium level (304), a first exposure takes place of the lowest binary two-dimensional image that is part of the stack (402) of binary two-dimensional images. This exposure is preferably made by the first illumination system (320). For that purpose, pixels of the first illumination system (320) are image-wise controlled by a computing device, for example the computer (312). The image-wise exposure causes curing of the corresponding locations in the intermediate layer (313). The time of the exposure has to be sufficiently long to obtain the desired degree of curing of the intermediate layer (313). When the intermediate layer (313) is locally sufficiently cured, the worm drive (311) is rotated by the motor (310) under control of a computing device (312) to move up the working platform (300) in the Z-dimension over a distance having a value distance_1. The result of the above steps is that a first solidified layer of the three-dimensional object that is to be created, adheres to the manufacturing platform.

[0114] Moving upward the manufacturing platform (300), causes the level of the first curable liquid (341) to drop. This drop is compensated by the opening the valve (306) under control of the sensor (305) and the control system (307) until the equilibrium level (304) of the first curable liquid (304) is reached again.

[0115] At that point a second exposure takes place by the first illumination system (320) of the next binary two-dimensional image that is part of the stack (402) of binary two-dimensional images. The exposure selectively cures locations of the intermediate layer (313) of the curable liquid, thereby creating a second solidified layer of the three-dimensional object that is to be created. The exposure is followed by moving up the manufacturing platform upwards over a distance distance_1, much like in the previous step. The result is that a second solidified layer of the three-dimensional object that is to be created adheres to the manufacturing platform underneath the previously created solidified layer.

[0116] The above steps are repeated a number of times until all layers of the stack (402) have been exposed and physically reconstructed.

[0117] Because the first illumination system (320) exposes all the pixels of a layer of the simultaneously, the process allows for an efficient and rapid physical reconstruction of the three-dimensional flexographic print master.

[0118] As mentioned earlier in this document, the resolution of the self-illuminating transparent display panel can be relatively low. This means that it is sufficient to define the lower layers of the three-dimensional flexographic print master, but not for the upper layers since these carry fine image detail such as halftone dots, text and edges of graphic objects.

[0119] In order to physically reconstruct the stack (401) carrying the fine image detail, the following steps are made in a second stage of the manufacturing process.

[0120] In a next step an exposure takes place with a second illumination system (330, 331, 332, 333).

[0121] To enable this effect, the first illumination system (320) has to be switched off or made transparent. If the first illumination system is a transparent self-illuminating OLED panel, all that is needed is to switch off all the pixels. If it is an LCD panel, the pixels have to be brought in a transparent condition and the external illumination needs to be switched off or removed. If it is a digital micromirror device, the external light source needs to be switched off or shielded.

[0122] Next a series of exposures takes place with the second illumination system of image layers in the stack (401). According to a preferred embodiment, a laser (330) beam scans at a resolution having a value resolution_2 by means of deflection system in the X dimension (331) and the movement of the carriage (333) in the Y dimension the intermediate layer (313) of curable liquid. The intensity of the laser (330) beam is modulated in response to the pixel values in a binary two-dimensional image that is part of the stack of binary two-dimensional images (401). The scanning laser (330) beam selectively solidifies the curable liquid (351) in response to the pixel values of the image layer.

[0123] After this exposure step, the manufacturing platform is raised in the vertical Z-dimension over a second distance having a value distance_2. The value of the second distance distance_2 is smaller than the value of the first distance distance_1 to reflect that the resolution in the Z-dimension of the image layers in stack (401) is higher than the resolution of the image layers in stack (402).

[0124] A second exposure takes place of a second image layer in the stack (401) and the above steps are repeated until all the image layers of the stack (401) have been exposed.

[0125] At that point the physical reconstruction of the three-dimensional print master is finished. The valve (342) is closed and the curable liquid (341) in the vat 301 can be purged into the waste tank (360) by opening the valve (362).

[0126] The finished print master can be removed from the manufacturing plateau and is ready for use on a flexographic printing press or can receive an additional post-fabrication curing step to increase the conversion degree of the object.

Additional Embodiments

[0127] According to a preferred embodiment, a method in the current invention uses not just one, but two or more types of curable liquid. Such an approach enables to target different physical properties of the different layers (401, 402) that make up the flexographic print master such as flexibility, resilience, hardness, adhesion to the substrate and ink transfer during printing. By using curable liquids with different sensitizing dyes, it is possible to accommodate for the case that the two illumination systems used to expose the photocurable liquid emit radiation with a different electromagnetic spectrum.

[0128] A system according to such an embodiment comprises at least one additional tank (351) that contains a second curable liquid (351) that is different from the first curable liquid (341) in the first tank (340).

[0129] The operation is as follows:

[0130] After in first step the curable liquid (341) in the vat (340) has been used to expose a first set of layers (402) of the flexographic print master, the valve (342) is closed under control of a computing device (312) and the valve (362) is opened. As a result, the curable liquid (341) pours through a drainpipe into the waste tank (360), after which the valve (362) is closed. An alternative solution that the first curable liquid (341) is recycled through the valve (362) into the first tank (340).

[0131] A following step involves filling the vat (301) with the second curable liquid (351) that is stored in a tank (350). This is achieved by opening the valve (352) under control of a computing device (312). The sensor (305), the control system (307) and the valve (306) ensure that the filling of the tank (301) until a reference level (304) is reached. After the vat (301) has been filled with the second curable liquid (351) from the tank (350), the exposure of a second set of layers (401) van commence.

[0132] Optionally the second curable liquid (341) is purged back through the valve (362) into the waste tank (360) or alternatively recycled into second tank (350).

[0133] It is not necessary in this embodiment that the layers (402) and (401) have to be exposed by the different illumination systems. For example, both curable liquids (341) and (351) can be either exposed by the first illumination system (320), the second illumination system (330, 331, 332, 333) or a combination of both.

Composition and Characteristics of Curable Liquids

[0134] The curable liquid is preferably a curable resin compositions for flexo-plate creation. The curable liquid comprise at least one polymerizable compound and at least one initiator. Optionally, other compounds such as polymers, fillers, inhibitors, plasticizers, and colorants can be present.

Polymerizable Compounds

[0135] The curable resin composition comprises one or more polymerizable compounds. These polymerizable compounds may comprise one or more polymerizable groups, preferably radically polymerizable groups.

[0136] Any polymerizable mono- or oligofunctional monomer or oligomer commonly known in the art may be employed. The polymerizable component is an compound which causes a polymerization reaction and crosslinking reaction by being irradiated with light energy in the presence of an initiating system. Suitable materials include epoxy compounds, oxetane compounds, oxorane compounds, cyclic acetal compounds, vinyl compounds, ethylenically unsaturated compounds, vinyl ether compounds, thiirane compounds, cyclic lactone compounds, thiethane compounds, cyclic ether compounds, cyclic thioether compounds, and the like.

[0137] Preferred radically polymerizable compounds suitable for use are described are described in the patent EP 1 637 322 B1 (having a priority date of 2004 Sep. 16 and being assigned to Agfa Graphics NV) paragraph [[054] to [0057] and paragraphs to [0064], the patent EP 1 936 438 B1 (having a priority date of 2006-12-20 and being assigned to Agfa Graphics NV) paragraph [0024] and the patent U.S. Pat. No. 8,980,971 B2 (having a priority date of 2007-03-20 and being assigned to Dsm Ip Assets BV) paragraph component D.

[0138] Examples of the monomers suitably used are acrylamide, (meth) acryloylmorpholine, isobornyl(meth)acrylamide, isobornyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, vinylcaprolactam, N-vinylpyrrolidone, phenoxyethyl(meth)acrylate, polyethylene glycol mono(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol mono(meth)acrylate, polypropylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, neopentyl glycol di(meth)acrylate, polyester di(meth)acrylate, urethane di(meth)acrylate, epoxy di(meth)acrylate, (meth)acrylate of phenol novolac polyglycidyl ether, (meth) (acryloxymethyl)isocyanurate, (meth) (acryloxymethyl)hydroxymethisocyanurate derivatives of these compounds and the like.

[0139] Commercially available products include SR344, a polyethyleneglycol (400) diacrylate; SR604, a polypropylene monoacrylate; SR9003, a popoxylated neopentyl glycol diacrylate; SR610, a polyethyleneglycol (600) diacrylate; SR531, a cyclic trimethylolpropane formal acrylate; SR340, a 2-phenoxyethyl methacrylate; 2-phenoxyethylacrylate; tetrahydrofurfuryl acrylate; all from SARTOMER; caprolactone acrylate and Genomer 1122, a monofunctional urethane acrylate from RAHN; Bisomer PEA6, a polyethyleneglycol monoacrylate from COGNIS; Ebecryl 1039, an urethane monoacrylate from CYTEC and CN137, an aromatic acrylate oligomer from CRAYNOR, and the like.

[0140] Preferred cationically polymerizable compounds suitable for use are described in U.S. Pat. No. 8,980,971 (having a priority date of 2007 Mar. 20 and being assigned to Dsm Ip Assets BV) paragraph component B.

[0141] Examples of the monomers suitably used are bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, epoxy novolac resin, trimethylene oxide, epoxidated soybean oil, butyl epoxystearate, epoxidated polybutadiene, tetrahydrofurfuran, trioxane, 1,3-dioxolane, vinyl cyclohexane, isobutylene, polybutadiene, derivatives of these compounds and the like.

[0142] Commercially available products include UVR-6100, UVR-6105, UVR-6110 from Union Carbide Corp, Celoxide 2021, Celoxide 2083, Glycidole, OAEX 24, Cyclomer M100, Epolead GT-301, from Daicel Chemical Industries Ltd., Vectomer 2010, 2020,4010 from Allied Signal, and the like.

Elastomers

[0143] To further optimize the properties of the flexographic printing forme precursor the curable composition may further comprise one or more elastomeric compounds. Suitable elastomeric compounds include copolymers of butadiene and styrene, copolymers of isoprene and styrene, styrene-diene-styrene triblock copolymers, polybutadiene, polyisoprene, nitrile elastomers, polyisobutylene and other butyl elastomers, polyalkyleneoxides, polyphosphazenes, elastomeric polyurethanes and polyesters, elastomeric polymers and copolymers of (meth)acrylates, elastomeric polymers and copolymers of olefins, elastomeric copolymers of vinylacetate and its partially hydrogenated derivatives.

Initiators

[0144] The curable resin compositions according to the present invention may comprise one or more initiator(s). The initiator typically initiates the polymerization reaction. The initiator(s) are preferably photoinitiator(s) but can also include thermal initiator(s). Curing may be realized by more than one type of radiation with different wavelength.

[0145] Examples of thermal initiators suitable for use in a curable resin composition include tert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid), 1,1-azobis(cyclohexanecarbonitrile), 2,2-azobisisobutyronitrile (AIBN), benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-Bis(tert-butylperoxy) cyclohexane, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne, bis(1-(tert-butylperoxy)-1-methylethyl)benzene, 1,1-bis(tert-butylperoxy) 3,3,5trimethylcyclohexane, tert-butyl hydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butyl peroxy benzoate, tert-butylperoxy isopropyl carbonate, cumene hydro peroxide, cyclohexanone peroxide, dicumyl peroxide, lauroyl peroxide, 2,4-pentanedione peroxide, peracetic acid and potassium persulfate.

[0146] A photoinitiator produces initiating species, preferably free radicals, upon absorption of actinic radiation. A photoinitiator system may also be used. In said photoinitiator system, a photoinitiator becomes activated upon absorption of actinic radiation and forms free radicals by hydrogen or electron abstraction from a second compound. Said second compound, usually called the co-initiator, becomes then the initiating free radical. Free radicals are high-energy species inducing polymerization of monomers or oligomers. When polyfunctional monomers and oligomers are present in the curable resin composition, said free radicals can also induce cross-linking.

[0147] Examples of suitable photoinitiators are disclosed in e.g. J. V. Crivello et al. in Photoinitiators for Free Radical, Cationic & Anionic Photopolymerisation 2nd edition, Volume III of the Wiley/_SITA Series In Surface Coatings Technology, edited by G. Bradley and published in 1998 by John Wiley and Sons Ltd London, pages 276 to 294.

[0148] Specific examples of photoinitiators may include, but are not limited to, the following compounds or combinations thereof: quinones, benzophenone and substituted benzophenones, hydroxy alkyl phenyl acetophenones, dialkoxy acetophenones, a-halogeno-acetophenones, aryl ketones such as 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl propan-1-one, 2-benzyl-2-dimethylamino-(4-morpholinophenyl)butan-1-one, thioxanthones such as isopropylthioxanthone, benzil dimethylketal, bis(2,6-dimethyl benzoyl)-2,4,4-trimethylpentylphosphine oxide, trimethylbenzoyl phosphine oxide derivatives such as 2,4,6 trimethylbenzoyl diphenylphosphine oxide, methyl thio phenyl morpholine ketones such as 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, morpholino phenyl amino ketones,2,2-dimethoxy-1,2-diphenylethan-1-one, 5,7-diiodo-3-butoxy-6-fluorone, diphenyliodonium fluoride and triphenylsulfonium hexafluophosphate, benzoin ethers, peroxides, biimidazoles, aminoketones, benzoyl oxime esters, camphorquinones, ketocoumarins and Michler's ketone.

[0149] Suitable commercial photoinitiators include Irgacure 127, Irgacure 184, Irgacure 500, Irgacure 907, Irgacure 369, Irgacure 1700, Irgacure 651, Irgacure 819, Irgacure 1000, Irgacure 1300, Irgacure 1800, Irgacure 1870, Darocur 1173, Darocur 2959, Darocur 4265 and Darocur ITX available from CIBA SPECIALTY CHEMICALS, Lucerin TPO available from BASF AG, Esacure KK, Esacure KT046, Esacure KT055, Esacure KIP150, Esacure KT37 and Esacure EDB available from LAMBERTI, H-Nu 470 and H-Nu 470X available from SPECTRA GROUP Ltd., Genocure EHA and Genocure EPD from RAHN.

[0150] Suitable cationic photoinitiators include compounds, which form aprotic acids or Bronstead acids upon exposure sufficient to initiate polymerization. The photoinitiator used may be a single compound, a mixture of two or more active compounds, or a combination of two or more different compounds, i.e. co-initiators. Non-limiting examples of suitable cationic photoinitiators are aryldiazonium salts, diaryliodonium salts, triarylsulphonium salts, triarylselenonium salts and the like.

[0151] Sensitizing agents may also be used in combination with the initiators described above. In general, sensitizing agents absorb radiation at a wavelength different then the photoinitiator and are capable of transferring the absorbed energy to that initiator, resulting in the formation of e.g. free radicals.

[0152] Preferably, the initiator mixture or initiator system of a first curable liquid is capable of absorbing and transferring energy at a wavelength range according to the first illumination system of the present invention and a second curable liquid is capable of absorbing and transferring energy at a wavelength corresponding to the second illumination system of the present invention.

[0153] The amount of initiators in the curable resin composition of the present invention is preferably from 1 to 20% by weight, more preferably from 4 to 10% by weight, relative to the total weight of the curable resin composition.

Inhibitors

[0154] In order to prevent premature polymerization, the curable resin composition may contain a polymerization inhibitor. Suitable polymerization inhibitors include phenol type antioxidants, hindered amine light stabilizers, phosphor type antioxidants, hydroquinone monomethyl ether, hydroquinone, t-butyl-catechol or pyrogallol. Suitable commercial inhibitors are, for example, Sumilizer GA-80, Sumilizer GM and Sumilizer GS produced by Sumimoto Chemical Co. Ltd.; Genorad 16, Genorad 18 and Genorad 20 from Rahn; Irgastab UV10 and Irgastab UV22, Tinuvin 460 and CGS20 from Ciba Specialty Chemicals; Floorstab UV range (UV-1, UV-2 UV-5 and UV-8) from Kromachem Ltd, Additol S range (S 100, S120, S130) from Cytec Surface Specialties. The amount is preferably lower than 2% by weight relative to the total weight of the curable resin composition.

[0155] The type and amount of monomers and/or oligomers and optionally the elastomeric compounds are selected to realize optimal properties of the printing form precursor such as flexibility, resilience, hardness, adhesion to the substrate and ink transfer during printing.

[0156] The hardness of a flexographic printing forme precursor is typically expressed as Shore A Hardness. The Shore A hardness of a flexographic printing forme according to the present invention is typically between 30 and 75. According to present invention the Shore A hardness of a second curable liquid can be significantly different from the Shore A hardness of a first curable liquid. This could, for instance, improve image resolution during ink transfer.

Plasticizers

[0157] Plasticizers are typically used to improve the plasticity or to reduce the hardness of the flexographic printing form precursor. Plasticizers are liquid or solid, generally inert organic substances of low vapor pressure. Suitable plasticizers include modified and unmodified natural oils and resins, alkyl, alkenyl, arylalkyl or arylalkenyl esters of acids, such as alkanoic acids, arylcarboxylic acids or phosphoric acid; synthetic oligomers or resins such as oligostyrene, oligomeric styrene-butadiene copolymers, oligomeric a-methylstyrene-p-methylstyrene copolymers, liquid oligobutadienes, or liquid oligomeric acrylonitrile-butadiene copolymers; and also polyterpenes, polyacrylates, polyesters or polyurethanes, polyethylene, ethylene-propylene-diene rubbers, a-methyloligo (methylene oxide), aliphatic hydrocarbon oils, e.g., naphthenic and paraffinic oils; liquid polydienes and liquid polyisoprene.

[0158] Examples of particularly suitable plasticizers are paraffinic mineral oils; esters of dicarboxylic acids, such as dioctyl adipate or dioctyl terephthalate; naphthenic plasticizers or polybutadienes having a molar weight of between 500 and 5000 g/mol, Hordaflex LC50 available from HOECHST, Santicizer 278 available from MONSANTO, TMPME available from PERSTORP AB, and Plasthall 4141 available from C. P. Hall Co.

Colorants

[0159] Colorants, dyes and/or pigments, may also be added to the curable composition to enable a visual inspection of the image on the flexographic printing form.

EXAMPLE

List of Ingredients

[0160] KRATON D1163NS a SIS thermoplastic elastomer from SHELL [0161] SR339C a 2-phenoxyethyl acrylate monomer from SARTOMER [0162] SR351 a trimethylolpropane triacrylate from SARTOMER [0163] SR531 a cyclic trimethylolpropane formal acrylate from SARTOMER [0164] SR9035 an ethoxylated trimethylolpropane triacrylate from SARTOMER [0165] OMNIMER ACMO a acryloyl morpholine from IGM RESINS [0166] CD278 2-(2-butoxyethoxy)ethyl acrylate from SARTOMER [0167] Ebecryl 1360 a polysiloxane hexa-acrylate from ALLNEX [0168] Genomer 1122 a monofunctional urethane acrylate from RAHN AG [0169] BYK UV 3510 a polyether modified polydimethylsiloxane from BYK [0170] VERBATIM HR50 a liquid photopolymer from CHEMENCE [0171] BHT=2,6-di-t-butyl-4-methylphenol, an inhibitor from ALDRICH [0172] Lucerin TPO-L a photo-initiator from BASF [0173] IRGACURE 127 a photo-initiator from CIBA-GEIGY [0174] IRGACURE 819 a photo-initiator from CIBA-GEIGY

[0175] The following example illustrates the change in hardness that can be observed when altering the curable liquid compositions.

[0176] Curable resin compositions were prepared by mixing the ingredients as listed in TABLE 1 until complete dissolution:

TABLE-US-00001 TABLE 1 Composition (g) Component COMP-1 COMP-2 COMP-3 COMP-4 5.59 5.59 5.59 ACMD SR339C 31.74 31.74 31.74 SR531 7.95 7.95 7.95 CD278 1.49 1.49 1.49 5R9035 2.75 2.75 2.75 0.24 0.24 0.24 UV3510 2.11 2.11 2.11 819 TPO-L 2.11 2.11 2.11 3 127 BHT 0.04 Verbatim HR50 60 3.28 3.28 1360 SR351 2.69 5.97 1122 2.69 D1163NS

Shore A Hardness Measurement Sample Preparation

[0177] A low wall height crystal-grade polystyrene petri dish is filled with 5 g of curable liquid (Biosciences Labwarecatalog no 35100650 mm9 mm bottom dish with tight-fit top (3.27 mm internal wall height). The sample is placed in a quartz box filled with nitrogen gas before curing.

[0178] UV-A curing was carried out from the backside in a UV-A light box equipped with 8 Philips TL 20 W/10 UVA (max=370 nm) lamps for 10 minutes followed by curing for 10 minutes from the front side with the same exposing device. The distance between the lamps and the sample was approximately 10 cm.

[0179] The Shore A hardness was measured according to ASTM D-2240-05 with an Elcometer 3120 Shore Durometer, employing a sharp indentor point with a load of 12.5 N. The scale readings range from 0 (0.1 penetration) to 100 (zero penetration). Shore A scale is used for soft rubbery materials. Commercial flexo-plates have a Shore A hardness between 30 and 80 Shore A. The shore A hardness obtained with the cured compositions are shown in Table 2.

Flexibility Measurement Sample Preparation

[0180] A silicon spacer (3 mm thickness) was stuck to a polyester support in a rectangular shape of 34 cm. Next, the formed reservoir was filled with the liquid curable formulations from Table 1. Excess liquid was removed by a clean cut metal blade. The coated layer was covered by a polyester/Silicone protective layer of 23 m and introduced in a quartz glass box filled with nitrogen. UV-A curing was carried according to previous description

[0181] The flexibility level of the samples was determined by bending the samples 180 and given a rating number from 0 to 3 (0 meaning no bending, 3 meaning very flexible). The flexibility level obtained with the cured compositions are shown in Table 2.

TABLE-US-00002 TABLE 2 Sample Shore A Flexibility COMP-1 74 1 COMP-2 63 2 COMP-3 64 2 COMP-4 48 3

INDUSTRIAL APPLICABILITY

[0182] The above system and method from the present invention, including the preferred embodiments, are for creating a flexographic print master.