Method for making film negative

Abstract

The present invention provides a method for preparing a film negative, the method comprising the steps of: dispersing a UV ink in a desired pattern on a UV printing substrate; and curing the UV ink using an actinic radiation source to crosslink and cure the UV ink and form a UV printing polymer layer in the desired pattern. The UV ink is at least substantially solvent-free, and the printing substrate does not contain an adhesive layer or an ink-receiving layer and has not been modified to be ink-receiving. The film negative can be used in a process for making a flexographic printing element.

Description

Technical Field

[0001] The present invention generally relates to an improved photopolymer platemaking process. Background Art

[0002] Flexographic printing is a printing method that is typically used for high-volume runs. Flexographic printing plates are employed to print on a variety of substrates such as paper, paperboard stock, corrugated board, films, foils, and laminates. Newspapers and grocery bags are prominent examples. Rough surfaces and stretch films can only be economically printed by flexographic printing.

[0003] Flexographic printing elements typically include a support layer, one or more photosensitive layers, an optional slip film peel layer, and an optional protective cover sheet. The protective cover sheet is formed of plastic or any other removable material that protects the plate or photocurable element from damage until it is ready for use. If used, the slip film peel layer may be disposed between the protective cover sheet and the photocurable layer to protect the plate from contamination, increase ease of handling, and serve as an ink receiving layer. After exposure and development, the photopolymer flexographic printing plate consists of various image elements supported by the bottom layer and anchored to the backing substrate.

[0004] It is highly desirable that flexographic printing elements function well under a wide variety of conditions. Thus, the printing element should be able to impart its relief image to a wide variety of substrates, including cardboard, coated paper, newspaper, calendered paper, and polymer films such as polypropylene. Importantly, the image should be transferred quickly and with fidelity in order to obtain as many prints as the printing press is expected to make.

[0005] Flexographic relief image printing elements can be made in a variety of ways, including by imaging and exposing a solid photocurable or photopolymerizable layer (i.e., sheet polymer), and by processing a liquid photopolymer resin. Flexographic printing elements made from liquid photopolymer resins have the advantage that uncured resin can be recovered from the non-image areas of the printing element and used to make additional printing plates. Liquid photopolymer resins have the additional advantage of flexibility over sheet polymers, which enables any desired plate gauge to be produced simply by changing the machine settings.

[0006] A negative of the image can be used to form a relief image for flexographic printing to mask non-image areas on the photosensitive or photocurable layer.The image areas of the photosensitive or photocurable layer can be cured by crosslinking under exposure to ultraviolet (UV) light.

[0007] Flexographic printing plates can be imaged digitally (also called computer to plate or CTP) or by an analog process of exposing and developing conventional films that are processed into negatives via an image setting.

[0008] Negatives can also be prepared using inkjet printers to print UV blocking inks onto light-transmitting plastic (e.g., polyester) materials. The surface of the plastic material must be ink-receptive or made to be ink-receptive. That is, the surface must be able to form an acceptable stable and detailed image, i.e., an image that adheres to the plastic and dries quickly without migration. The plastic material can be made ink-receptive by coating it with an ink-receptive coating (e.g., a microporous coating or an ink-receptive polymer coating), or the material can be treated in some other way (such as acid etching, etc.) to produce a surface that allows the ink to adhere to the film and dry quickly without migration. The use of ink-receptive plastic materials is disclosed, for example, in U.S. Patent No. 9,726,971 to Maneira, the subject matter of which is incorporated herein by reference in its entirety.

[0009] Various methods of making printing plates with liquid photopolymer resins have been developed, as described, for example, in U.S. Patent Application No. 5,213,949 to Kojima et al., U.S. Patent Application No. 5,813,342 to Strong et al., U.S. Patent Publication No. 2008 / 0107908 to Long et al., and U.S. Patent Application No. 3,597,080 to Gush, the subject matter of each of which is incorporated herein by reference in its entirety.

[0010] Typical steps in the liquid platemaking process include:

[0011] (1) Casting and exposure;

[0012] (2) Recycling;

[0013] (3) Flushing;

[0014] (4) post-exposure;

[0015] (5) drying; and

[0016] (6) Remove adhesiveness.

[0017] During the casting and exposure steps, the photographic negative is placed on a bottom glass platen and a cover film is placed over the negative in an exposure unit. The exposure unit typically comprises a bottom glass platen with a UV light source below it (lower light) and a cover with a flat top glass platen with a UV light source (upper light) above it.

[0018] The accurate duplication of the negative image details onto the photopolymer requires that the negative be placed as close to the photopolymer layer as possible. All air is removed by vacuum so that any wrinkles in the negative and / or cover film can be eliminated. In addition, the bottom glass platen may be grooved to further facilitate the removal of any air between the cover film and the negative. The liquid photopolymer layer and backing sheet (i.e., a thin layer of polyester or polyethylene terephthalate) are then cast on top of the cover film and negative to a predetermined thickness. A backing sheet, which may be coated on one side to bond with the liquid photopolymer, is laminated over the cast liquid photopolymer layer to serve as the back side of the plate after exposure.

[0019] An upper and / or lower source of actinic radiation (i.e., upper light and lower light) is used to expose the photopolymer to actinic radiation to selectively crosslink and cure the liquid photopolymer layer in areas not covered by the negative. The top source of actinic radiation is used to form the bottom layer of the printing plate (i.e., back exposure), while the bottom source of actinic radiation is used to expose the photopolymer to actinic radiation through the negative to form a relief image (i.e., front exposure). After dispensing the liquid photopolymer on the protected bottom exposure glass, the plate gauge can be adjusted and / or set by positioning the top exposure glass at a desired distance from the bottom exposure glass.

[0020] The upper light source is turned on for a prescribed amount of time to uniformly crosslink the photopolymer adjacent to the substrate over the entire surface of the plate, thereby forming the bottom layer. Thereafter, the areas to be imaged are exposed to actinic radiation from the lower light source (i.e., through the bottom glass platen). The actinic radiation shines through the light-transmitting areas of the negative, which causes the photopolymer to crosslink in those areas, thereby forming a relief image that is bonded to the bottom layer. The liquid photopolymer that is not exposed to the lower light source (i.e., uncured photopolymer) remains in a liquid state and can be recovered and reused.

[0021] The type of radiation used depends in part on the type of photoinitiator in the photopolymerizable layer. The digitally imaged mask or photographic negative protects the underlying material from exposure to actinic radiation, so those areas covered by the mask do not polymerize, while areas not covered by the mask are exposed to actinic radiation and polymerize. Any conventional source of actinic radiation may be used for this exposure step, including, for example, visible and UV sources such as carbon arc lamps, mercury vapor arc lamps, fluorescent lamps, electron flash units, electron beam units, photographic floodlights, and light emitting diodes (LEDs), and the like, and wherein the wavelength of the emitted light depends in part on the specific type of photoinitiator.

[0022] After exposure is complete, the printing plate is removed from the exposure unit, and the photopolymer not exposed to actinic radiation (i.e., the photopolymer covered by the negative) remains liquid and can be recovered for further use. In liquid platemaking, resin recovery is an important factor associated with producing photopolymerizable resin printing plates, and in all areas not exposed to UV radiation, the resin remains liquid after exposure and can be recovered. In a typical process, the uncured resin is physically removed in a "recovery" step, which generally involves scraping, vacuuming, or otherwise removing the liquid photopolymer remaining on the surface of the printing plate. Using a recovery step not only saves on the material cost of the photopolymerizable resin, but also reduces the use and cost of development chemistry, and makes for lighter plates that are safer and easier to handle.

[0023] Residual traces of liquid resin remaining after the recovery step can then be removed by washing with a nozzle or brush using a washing solution to obtain a washed board, leaving behind a cured relief image. Typically, the board is placed in a washing unit where an aqueous solution containing soap and / or detergent is used to wash away any remaining unexposed photopolymer. The board is then rinsed with water to remove any residual solution.

[0024] The cured areas of the printing element are insoluble in the washout (or developing) solution, and thus after washout a relief image formed of the cured photopolymerizable resin is obtained.The cured resin is also insoluble in certain inks, and thus can be used in flexographic printing.

[0025] The printing plate is then subjected to various post-exposure and detackification steps. Post-exposure may involve immersing the plate in water and saline solutions, and additional exposure of the printing plate to actinic radiation (UV light) is performed to fully cure the printing plate and increase the plate strength. If used, the detackification step may involve the use of a sterilization unit (i.e., a light finisher) to ensure a completely tack-free plate surface. This step is not required for all plates, as some resins may be tack-free and therefore the printing press can be used without the detackification step. The printing plate may then be rinsed and dried.

[0026] Typically, the floor area of ​​a flexographic printing element prepared from a liquid photopolymer comprises at least about half of the thickness of the plate, with the remainder of the plate thickness comprising the relief area. The floor provides dimensional stability to the plate and supports the relief area.

[0027] This process variation minimizes the floor area and significantly increases the amount of liquid photopolymer that can be recycled to reduce the amount of photopolymer used in making the floor that will cover the entire sheet. These printing plates are often referred to as "spliced ​​plates," "island plates," or "I-plates."

[0028] I-type plates add another step to the liquid platemaking process. That is, instead of making a base plate that extends across the entire plate, a second photographic negative is placed on top of the photopolymer layer. This negative (also called a masking film) outlines the image area on the negative. First, the plate is exposed to upper UV light through the masking film, resulting in the formation of islands of cured polymer in the photosensitive layer adjacent to the substrate. The timing and intensity of the exposure are limited to prevent polymerization from extending all the way from the substrate through the photopolymer layer. A second, lower UV exposure from below the relief image negative causes a cured detail relief image to form on top of the islands thus formed. This process is described in, for example, U.S. Patent Application No. 2012 / 0082932 to Battisti et al. and U.S. Patent Application No. 9,726,971 to Maneira, the subject matter of each of which is incorporated herein by reference in its entirety. The relief image negative and the masking film are aligned (i.e., registered) so that each image area of ​​the relief image negative is roughly in the middle of each light-transmitting area of ​​the masking film.

[0029] One of the difficulties in producing I-type plates is that during the setup process, the masking film is registered with the negative film so that the islands formed in the floor area will be aligned (i.e., registered) with the desired relief image. The masking film is usually applied to the surface of the substrate and can slide, causing the masking film to misregister. U.S. Patent Application No. 2012 / 0082932 to Battisti et al. attempts to solve this problem by using a substrate that has been printed with a digital representation of the island image and is then adhered to the liquid photopolymer layer. However, this requires additional steps, further extending the platemaking process.

[0030] U.S. Patent No. 9,703,201 to Vest et al., the subject matter of which is incorporated herein by reference, describes another method of producing an I-type plate in which a liquid photopolymer print blank is selectively exposed to actinic radiation to form a relief image printing plate by scanning a light bar comprising a plurality of UV LEDs across a backing sheet over an upper surface of the liquid photopolymer print blank to cure the liquid photopolymer layer in selected areas to form islands of cured polymer adjacent to the backing sheet. The light bar comprises a plurality of UV LEDs arranged across the width of the light bar such that as the light bar is scanned over the surface of the liquid photopolymer print blank, the surface of the liquid photopolymer print blank can undergo crosslinking and curing to form cured islands therein.

[0031] A time consuming step in the platemaking process is the formation of a film negative or other masking layer used therein. There remains a need in the art for an improved method of forming a film negative or other masking layer in an efficient manner, preferably for use in a liquid platemaking process. Summary of the invention

[0032] It is an object of the present invention to provide an improved liquid photopolymer platemaking process.

[0033] It is another object of the present invention to provide an improved method of forming a film negative or other masking layer, preferably for use in a liquid platemaking process.

[0034] It is yet another object of the present invention to provide a method of forming a film negative or other masking layer which eliminates the need for the inkjet printing substrate (film base) to be ink receptive or to be modified to be ink receptive.

[0035] It is a further object of the present invention to provide an improved method of forming a film negative or other masking layer that can be used in a liquid platemaking process and exhibits a surface morphology that is configured to improve air removal under vacuum during the imaging step of the platemaking process.

[0036] To this end, in one embodiment, the present invention generally relates to methods of producing film negatives or other mask layers using inkjet printing methods. The disclosed film negatives or mask layers including printed polymer layers can be used to make liquid flexographic printing plates. In some embodiments, a UV printed polymer layer (e.g., a UV printed polymer layer mask) having a desired UV light blocking density can be used in the manufacture or imaging of flexographic printing plates.

[0037] The process of producing a film negative or other mask layer using the inkjet printing method described herein produces a UV printing polymer layer, which includes providing a non-absorbent transparent surface (i.e., an inkjet printing substrate) to print ink thereon. The inkjet printing substrate can be positioned to contact with a transparent support surface (e.g., a glass surface), which is configured to allow exposure (e.g., UV exposure) therethrough. The glass surface can be substantially planar, and the inkjet printing substrate can be positioned thereon. The stagnant air between the inkjet printing substrate and the glass surface is removed to ensure that the surface is wrinkle-free, thereby receiving one or more UV inks. Then, the UV ink can be transferred to the inkjet printing substrate with a desired pattern. In a preferred embodiment, the UV ink forming the negative is ejected from the UV inkjet printing head. Based on the desired pattern, the UV printing polymer layer is preferably computer-generated and communicates with the UV inkjet printing head.

[0038] In one embodiment, a UV inkjet printing process may be configured to create a masking layer to produce a reduced floor area for making liquid flexographic printing plates, including, for example, splice plates, island plates, and I-plates.

[0039] In one embodiment, the UV printed polymer layer may include a surface morphology defining one or more microchannels configured in part to improve air removal under vacuum during the photopolymer imaging process.

[0040] The methods described herein can substantially improve, among other enhancements, (i) printing equipment reliability; (ii) technical support; (iii) waste costs; (iv) labor costs; (v) liquid platemaking process; (vi) mask production speed; and (vii) finished product production and quality.

[0041] Note that because the UV inks described herein do not require removal of volatile compounds and / or water, the imaging step can be simplified. More preferably, the UV inks useful in the practice of the present invention are at least substantially solvent-free.

[0042] The disclosed method is capable of producing image negatives in about 15 minutes or less, compared to conventional production times which typically require at least about 60 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Features and aspects of embodiments of the invention are described below with reference to the drawings, in which elements are not necessarily drawn to scale.

[0044] Exemplary embodiments of the present disclosure are further described with reference to the following drawings. It should be noted that various features, steps and combinations of features / steps described below and shown in the drawings can be arranged and organized in different ways to produce embodiments that are still within the scope of the present disclosure.

[0045] Reference is made to the accompanying drawings to assist one of ordinary skill in the art in making and using the disclosed components, systems, and methods, wherein:

[0046] Figure 1 A conventional liquid photopolymer platemaking process according to the prior art is schematically depicted;

[0047] Figure 2 A conventional inkjet film technique according to the prior art is schematically depicted;

[0048] Figure 3 schematically depicts a simulated platemaking process with a UV polymer layer mask according to the present disclosure; and

[0049] Figure 4 The UV inkjet film technology according to the present disclosure is schematically depicted.

[0050] Additionally, although not all elements may be labeled in every drawing, all elements having the same reference number indicate similar or identical parts. DETAILED DESCRIPTION

[0051] The present invention provides a method for preparing a film negative or other masking layer, preferably for use in a liquid platemaking process, wherein the process for preparing the resulting UV-printed polymer layer eliminates the need for a film substrate that is ink-receptive or modified to be ink-receptive. The resulting UV-printed polymer layer can be used as a film negative or other masking layer during a liquid platemaking process.

[0052] The present invention produces a film negative or other masking layer comprising an improved UV printing polymer layer including a surface morphology configured to improve air removal under vacuum during a subsequent imaging process.

[0053] As used herein, "a," "an," and "the" refer to both the singular and the plural, unless the context clearly indicates otherwise.

[0054] As used herein, the term "about" refers to a measurable value, such as a parameter, amount, duration, etc., and is intended to include variations of + / -15% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less relative to the specifically stated value, as long as such variations are suitable for performing in the invention described herein. In addition, it should also be understood that the value to which the modifier "about" refers is itself specifically disclosed herein.

[0055] As used herein, for ease of description, spatially relative terms such as "below," "beneath," "lower," "above," "upper," "front," "rear," etc. are used to describe the relationship of one element or feature structure to another or more elements or features. It should also be understood that the terms "front" and "rear" are not intended to be limiting and are intended to be interchangeable where appropriate.

[0056] As used herein, the terms “include” and / or “comprises” specify the presence of stated features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0057] As used herein, the terms "printed polymer layer" and "UV printed polymer layer" may refer to an image negative, a back mask, or the like.

[0058] As used herein, if not otherwise defined herein for a particular element or compound, the term "substantially free" or "substantially free" means that the given element or compound cannot be detected by ordinary analytical means well known to those skilled in the art of flexographic printing.

[0059] As used herein, unless otherwise defined herein, the term "substantially planar" means that substrates or components are approximately on the same plane.

[0060] With reference to the accompanying drawings, Figure 1 A conventional liquid photopolymer platemaking system of the prior art is depicted, and Figure 2 The conventional inkjet film technology of the prior art is depicted. Figure 1 As shown, a conventional liquid photopolymer plate system 10 includes several layers in a stacked configuration. Each layer positioned on the layer before it includes a lower glass platen 12, an imaging film layer 14, a cover film layer 16, a liquid photopolymer layer 18 cast on or otherwise disposed on the cover film layer 16, a carrier sheet / base film layer 20, a back mask film layer 22, and an upper glass platen 24. A lower UV lamp 26 is positioned below the lower glass platen 12, and an upper UV lamp 28 is positioned above the upper glass platen 24, so that the UV lamps 26, 28 project light toward the upper and lower surfaces of the liquid photopolymer layer 18.

[0061] like Figure 2 As shown, a conventional inkjet film process 50 requires a receiving ink layer 54 to be placed in contact with a film substrate 52 in order to form an acceptable detail image when UV inks 56, 58, 60, 62 are used. The detail image can be formed using UV ink colors including cyan 56 (depicted with diagonal lines), magenta 58 (depicted with cross-diagonal lines), yellow 60 (depicted with vertical lines), and black 62 (depicted as a solid color). An example of this conventional process is described in U.S. Pat. No. 9,726,971 to Maneira, the subject matter of which is incorporated herein by reference in its entirety. The disclosed UV-printed polymer layer (e.g., a UV-printed polymer layer mask) having a desired UV light blocking density can be used in the manufacture or imaging of liquid flexographic printing plates.

[0062] Figure 3 A platemaking process according to the present invention is depicted, the platemaking process utilizing a UV polymer layer mask 100 prepared according to the method as further described herein.

[0063] The liquid platemaking process according to the present invention includes the use of a UV polymer layer mask and includes the following layers each positioned on the previous layer: a lower glass platen 102, an imaging film 104, a cover film layer 106, a liquid photopolymer layer 108, a carrier sheet / base film layer 110, a UV polymer layer mask layer 112, and an upper glass platen 114. A lower UV lamp 116 may be positioned below the lower glass platen 102, and an upper UV lamp 118 may be positioned above the upper glass platen 114, such that the UV lamps 116, 118 project light toward the liquid photopolymer layer 108.

[0064] like Figure 4 shown, and with Figure 2 In contrast to the prior art process shown in , the UV inkjet film system 150 described herein applies UV inks 56, 58, 60, 62 directly to the inkjet printing substrate 152. That is, the inkjet printing substrate 152 does not contain an ink receiving layer and has not been modified to be ink-receptive. The UV ink colors include cyan 56 (depicted with diagonal lines), magenta 58 (depicted with cross-diagonal lines), yellow 60 (depicted with vertical lines), and black 62 (depicted as a solid color). Compared to the prior art methods, the film substrate of the present invention does not contain and does not require any ink receiving layer or modification of the film substrate, which would make the inkjet printing substrate ink-receptive.

[0065] The UV inkjet printing process described herein includes inkjet printing a substrate (eg, film substrate) 152, which is a non-absorbent transparent substrate to print UV inks thereon, which may be four colors 56, 58, 60, 62 or a single color.

[0066] In another preferred embodiment, a single color is used, most preferably and most commonly black. This eliminates the need to use cyan, magenta, and yellow inks and makes the method more efficient. However, other single-color inks will also be useful in the practice of the present invention and will be known to those skilled in the art.

[0067] The inventors of the present invention have discovered that by installing black ink on all the different color channels of the printhead, equipment maintenance and calibration are reduced, ink loss is minimized, and equipment output speed is increased. Therefore, instead of using the typical four-color system, black ink is used to prepare the film negative. This also results in the lowest ink loss possible, making the process more efficient and cost-effective.

[0068] The inkjet printing substrate is positioned in contact with a substantially planar transparent support surface (e.g., a glass surface) that is configured to allow exposure (e.g., UV exposure) therethrough. In one embodiment, air trapped between the inkjet printing substrate and the support surface is removed to eliminate or at least reduce wrinkles in the inkjet printing substrate. Prior to printing the UV ink on the inkjet printing substrate, removal of trapped air is preferably performed (usually by vacuum). Thereafter, the UV ink is printed onto the inkjet printing substrate in a consistent desired pattern, which may be a series of printed dots or other printed features or islands.

[0069] The UV ink is ejected from a UV inkjet print head that is configured to receive (i.e., communicate with) a computer-generated image. The UV ink is then exposed to actinic radiation from at least one UV light, wherein at least one UV light is disposed in an exposure unit. The at least one UV light may be positioned below the glass surface, above the glass surface, and / or at a position therebetween. In one embodiment, the second UV light is positioned opposite the first UV light. Exposure of the UV ink to the UV light promotes crosslinking and curing of the UV ink to form a negative or mask layer on the inkjet printing substrate, thereby producing a UV printed polymer layer in a desired pattern.

[0070] The inkjet printing substrate may include any transparent plastic material that does not contain any UV blocker or inhibitor. Preferably, the inkjet printing substrate is not ink-receptive and / or is not modified to be ink-receptive, and more preferably, the inkjet printing substrate does not include an ink-receptive layer and is not modified to be ink-receptive. In one embodiment, the inkjet printing substrate is a transparent material selected from the group consisting of polyethylene terephthalate (PET), polycarbonate (PC) and polyethylene naphthalate (PEN).

[0071] In one embodiment, the inkjet printed substrate does not contain an adhesive or an ink receiving layer. Therefore, in a preferred embodiment, the UV ink is printed directly onto the inkjet printed substrate, and the UV ink is printed directly onto the surface of the inkjet printed substrate without an adhesive being disposed on the surface.

[0072] In another embodiment, the inkjet printing substrate comprises an adhesive layer but does not comprise an ink receiving layer.Based on the above, the inkjet printing substrate comprises an adhesive layer having a release liner, and the adhesive layer is provided on the surface of the inkjet printing substrate.

[0073] In one embodiment, the inkjet printing substrate is a multilayer structure including a pressure-sensitive adhesive liner integral with the substrate and a release liner mounted thereon to be printed. During the platemaking process, the pressure-sensitive adhesive liner is usually applied to the back of the finished printing plate so that the plate can be adhered to the printing press mounting frame. The process described herein eliminates the need for such additional steps and personnel to adhere the pressure-sensitive adhesive layer to the printing plate. Therefore, the release liner is the surface on which the UV ink is printed, and the release liner is a thin polyester or polyethylene terephthalate film that protects the pressure-sensitive adhesive. The UV ink can be printed on a separate printing liner disposed on the release liner of the adhesive layer.

[0074] The inkjet printing substrate described in the present invention is configured to work with various UV inks, which include one or more photoinitiators, monomers and binders. The UV inks that can be used in the practice of the present invention are those UV inks that are at least substantially solvent-free. As used herein, the term "solvent-free" refers to UV inks that contain a solvent with a detection limit of less than 1% by weight, preferably a detection limit of less than 0.1% by weight.

[0075] The one or more UV inks may be selected by way of example and not limitation from the group consisting of SPC-0371, F-200, LH-100, MUH-100-Si, LF-140, LF-200, LUS-120, LU-125, LUS-150, LUS-170, LUS-175, LUS-200, LUS-350, MH-100, PR-100, PR-200, SW-100, each of which is Engineering Co., Ltd. (Nagano, Japan). Other solvent-free UV inks will also be known to those skilled in the art and can be applied to the present invention. In a preferred embodiment, the solvent-free UV ink has sufficient opacity to limit (or prevent) UV curing of the unexposed photopolymer portions covered by the masked portions of the film negative during the manufacture of the simulated liquid flexographic printing plate. Suitable black inks for monochrome systems include the UV inks listed above.

[0076] The process of making the UV printed polymer layer of the present invention generally comprises the following steps:

[0077] (1) providing an inkjet printing substrate, wherein the inkjet printing substrate does not comprise an ink receiving layer and / or wherein the inkjet printing substrate has not been modified to be ink receiving;

[0078] (2) printing a UV ink in a desired pattern on an inkjet printing substrate, wherein the UV ink is at least substantially solvent-free; and

[0079] (3) Curing the UV printing ink by exposing the UV ink to a UV light source.

[0080] In one embodiment, the UV light source may include at least one UV light configured to produce a wavelength output in the range of about 365 nm to about 405 nm. In one embodiment, the UV light source is mounted so that it can scan across the width of the inkjet printing substrate.

[0081] In one embodiment, the inkjet printing substrate moves relative to the inkjet printer to selectively crosslink and cure the UV ink distributed thereon. In a preferred embodiment, the inkjet printing substrate advances by the inkjet printer to print the UV ink on the inkjet printing substrate with a desired pattern, which is generally a series of printed dots, printed features and / or islands. The inkjet printer may also include a UV light source installed therein to immediately crosslink and cure the UV ink while the ink printing substrate advances by the inkjet printer, which helps eliminate the need for additional coatings. Other configurations will also be known to those skilled in the art.

[0082] In an embodiment of an all-black ink delivery configuration, the inventors have discovered that it is possible to increase device reliability and have faster technical response support by remotely redirecting failed nozzles or channels. The use of black ink ensures that all ink tank losses are equal across all channels and nozzles, thereby eliminating uneven ink volume usage in each respective channel as can occur in a four-color configuration.

[0083] Due to the pigment loading of the black ink, both UV and transmitted light blocking is achieved with minimal ink loss during liquid photopolymer plate exposure. In addition, by ensuring minimum light transmittance, light refraction between different light waves is minimized, providing the highest exposure fidelity.

[0084] In a preferred embodiment, photopolymer crosslinking can be achieved with a light transmittance of less than 2.0 as measured using a transmission densitometer for a single or four color system such as an X-Rite 361T or Macbeth Td-929 Photographic Color Densitometer.

[0085] The curing time of UV ink may depend on and be combined with other parameters, including, for example, printing speed, layer handling, and surface morphology requirements. Printing speed and exposure duration promote the curing of UV ink (e.g., curing to touch). In some cases, the curing time of the polymer layer UV ink can be achieved by advancing the UV ink printing substrate relative to the UV light source at a speed between about 16 inches per minute and about 3 inches per minute. The curing of UV ink can occur at a temperature ranging from about 60°F to about 90°F. Specifically, UV ink curing can occur at a temperature range of about 70°F to about 80°F. More preferably, UV curing can occur at room temperature. However, it should be understood that "room temperature" may be different based on individuals, seasons, and / or countries, and therefore, the present disclosure does not seek to limit a single interpretation of "room temperature". Nevertheless, it should be understood that curing performed at room temperature does not require additional local heat to achieve good adhesion between the UV ink and the substrate, which is a common shortcoming of current UV ink curing methods.

[0086] Compared to the film negatives prepared by the process of the present invention, the UV inks of the prior art are solvent-based inks that require additional steps of heating and drying to produce the film negatives. In this case, insufficient heat can cause smearing and transfer of the mask, making production difficult. On the other hand, too much heat may deform the substrate, resulting in registration problems for the imaging film. Therefore, in a preferred embodiment, the present invention does not require any heating or drying steps to produce the film negatives of the present invention.

[0087] In some embodiments, the disclosed UV printed polymer layer can be utilized during exposure of the "bottom plate". For example, to produce a bottom plate that is similar to the desired pattern but slightly larger in size. For example, the size of the bottom plate that is similar to the desired pattern can be about one-quarter inch to about one-half inch larger than the desired pattern. This method of printing plates is often referred to as "spliced ​​plates", "island plates" or "I-type plates". By utilizing this method, less liquid photopolymer is used to form the bottom plate.

[0088] Thus, in one embodiment, the present invention is generally directed to a method for preparing an I-type plate using a liquid photopolymer resin, the method comprising the steps of:

[0089] (a) positioning a first film negative on a substantially planar transparent support surface, wherein the first film negative is configured in a first desired pattern;

[0090] (b) casting a liquid photopolymer layer in direct or indirect contact with the first film negative;

[0091] (c) positioning a second film negative in alignment with and opposite the first film negative, the second film negative in direct or indirect contact with the liquid photopolymer layer, wherein the second film negative is configured to have a second desired pattern that is aligned with the first desired pattern; and

[0092] (d) exposing actinic radiation through the first UV printed polymer layer and the second UV printed polymer layer to selectively crosslink and cure the liquid photopolymer layer according to the first desired pattern and the second desired pattern,

[0093] wherein the first and second film negatives are produced according to the methods described herein.

[0094] In some embodiments, the disclosed UV ink, when printed to form a UV printed polymer layer, may include a surface morphology that is configured in part to improve air removal under vacuum. Specifically, the UV ink may have a surface morphology that defines one or more microchannels when cured. The one or more microchannels may be positioned in a predetermined pattern, a random pattern, or a partially predetermined pattern and a partially random pattern. The disclosed air removal may facilitate the removal of air trapped between the disclosed UV printed polymer layer and an adjacent surface through a process of mechanical vacuum suction. For example, the disclosed air removal may facilitate the removal of air trapped between the disclosed UV printed polymer layer and the upper glass. Air trapped between the disclosed UV printed polymer layer and the upper glass may cause the upper glass to wrinkle, which may have a negative impact on the quality of the liquid photopolymer sheet.

[0095] Although the present disclosure has been described with reference to exemplary embodiments, the present disclosure is not limited to such exemplary embodiments. Instead, various modifications, improvements and / or alternative embodiments may be adopted without departing from the spirit or scope of the present disclosure.

Claims

1. A method for preparing a film negative for forming a relief image for flexographic printing, the method comprising the following steps: (a) dispersing UV ink on a UV printing substrate in a desired pattern; as well as (b) curing the UV ink using an actinic radiation source to crosslink and cure the UV ink and form a UV printed polymer layer in the desired pattern, wherein the UV ink is at least substantially solvent-free, and wherein the printed substrate does not comprise one or more of an adhesive layer and an ink receptive layer, and the printed substrate has not been modified to be ink receptive.

2. The method of claim 1, wherein the printed substrate comprises a transparent material selected from the group consisting of polyethylene terephthalate, polycarbonate, and polyethylene naphthalate.

3. The method of claim 1, wherein the UV ink is cured by exposure to at least one UV light source with a wavelength output in the range of 365 nm to 405 nm.

4. The method of claim 3, wherein the step of curing the UV ink is accomplished by advancing the printed substrate relative to the at least one UV light source at a speed in the range of 16 inches per minute to 3 inches per minute.

5. The method according to claim 1, wherein the printed substrate comprises an adhesive layer disposed on the printed substrate, wherein the adhesive layer is covered with a release liner, and wherein the UV ink is printed on a surface of the release liner.

6. The method of claim 1, wherein the UV ink is cured at a temperature in the range of 60°F to 90°F.

7. The method of claim 6, wherein the UV ink is cured at a temperature in the range of 70°F to 80°F.

8. The method of claim 1, wherein the UV ink comprises one or more of a photoinitiator, a monomer, and a binder.

9. The method of claim 1, wherein the UV ink comprises a four-color system including cyan, magenta, yellow, and black.

10. The method according to claim 1, wherein the UV ink is a single-color ink, wherein the single-color ink is black.

11. The method of claim 1 , wherein curing of the UV ink produces a surface topography configured to improve air removal under vacuum, wherein the surface topography defines microchannels.

12. The method of claim 1, wherein the UV ink is not subjected to a heating or drying step.

13. A film negative capable of being used in a process for imaging a flexographic printing element, wherein the film negative is produced according to the method of claim 1.

14. A method for preparing an I-type plate using a liquid photopolymer resin, the method comprising the following steps: (a) positioning a first film negative on a substantially planar transparent support surface, wherein the first film negative is configured in a first desired pattern; (b) casting a liquid photopolymer layer in direct or indirect contact with said first film negative; (c) positioning a second film negative in alignment with and opposite the first film negative, the second film negative in direct or indirect contact with the liquid photopolymer layer, wherein the second film negative is configured to have a second desired pattern aligned with the first desired pattern; as well as (d) exposing the first film negative comprising a first UV printed polymer layer having the first desired pattern and the second film negative comprising a second UV printed polymer layer having the second desired pattern to actinic radiation to selectively crosslink and cure the liquid photopolymer layer according to the first desired pattern and the second desired pattern, wherein the first film negative and the second film negative are produced according to the method of claim 1.

15. The method of claim 14, wherein the size of the second desired pattern is larger than the size of the first desired pattern, thereby creating islands surrounding the first desired pattern.

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