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Title:
PRECAST LIQUID PHOTOPOLYMERIC PLATE
Document Type and Number:
WIPO Patent Application WO/2019/009695
Kind Code:
A1
Abstract:
This invention relates to a precast liquid photopolymeric plate, a flexible relief plate derived therefrom and a method for producing the precast liquid photopolymeric plate. Particularly, a flexible container having a top layer, a bottom layer, and a photosensitive layer defined by a continuous frame having planar surfaces, the frame comprising a cured photopolymer preparation, the top and bottom layer being adhered to each side of the photosensitive layer so as to seal the container, in which the top and bottom layer are sheets being transparent to photo irradiation used in curing the photopolymer and being inert to the photopolymer; and an uncured photopolymer preparation contained within the container.

Inventors:
RIPAMONTI, Matteo (15-1, Jalan PJU 3/34Parkville Townhouse Sunway Damansara, Petaling Jaya, Selangor, 47810, MY)
WONG, Kim Sau (26 Jalan PJU 10/16D, Sutera Damansara, Petaling Jaya, Selangor, 47830, MY)
Application Number:
MY2018/050014
Publication Date:
January 10, 2019
Filing Date:
March 30, 2018
Export Citation:
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Assignee:
POLYFABER SDN BHD (5 Jalan PJU 3/46, Sunway Damansara Technology Park Petaling Jaya, Selangor, 47810, MY)
International Classes:
G03F7/20; B41M1/04; B41N1/12; C08G18/00; G03C1/00; G03F7/09; G03F7/26
Domestic Patent References:
WO2001044874A12001-06-21
Foreign References:
US20040219458A12004-11-04
EP0084851B11986-12-03
US6403269B12002-06-11
EP0691357A11996-01-10
Attorney, Agent or Firm:
LOK, Choon Hong (Pintas Consulting Group Sdn Bhd, No. 19, Jalan SS 1/36, Petaling Jaya, Selangor, 47300, MY)
Download PDF:
Claims:
CLAIMS

1. A precast liquid photopolymeric plate comprising:

a flexible container having a top layer (11), a bottom layer (12), and a photosensitive layer defined by a continuous frame (13) having planar surfaces, the frame comprising a cured photopolymer preparation, the top (11) and bottom layer (12) being adhered to each side of the photosensitive layer so as to seal the container, in which the top (11) and bottom layer (12) are sheets being transparent to photo irradiation used in curing the photopolymer and being inert to the photopolymer; and

an uncured photopolymer preparation contained within the container.

2. A plate according to claim 1, wherein the photopolymer preparation of the frame is the same as the polymer preparation contained within the container.

3. A plate according to claim 1 or 2, wherein an adhesive composition is applied on the frame so as to adhere the top (11) and the bottom layer (12).

4. A plate according to claim 4, wherein the adhesive composition comprises 15 to 17 wt % of hydroxyl modified vinyl chloride or vinyl acetate copolymer, 0.4 to 0.5 wt % of hydroxyl ethyl methacrylate, 0.4 to 0.5 wt % of trimethylolpropane trimethacrylate, 0.4 to 0.6 wt % of 2,2-dimethoxy-l,2-diphenylethan-l-one, 2.5 to 3 wt % of silica powder and 70 to 80 wt % of ethyl acetate. 5. A plate according to any one of the preceding claims, wherein the photopolymer preparation comprises a polyurethane prepolymer present in an amount of 50 to 80 wt% of the preparation, a urethane acrylate oligomer present in an amount of 10 to 30 wt% of the preparation, an acrylate monomer present in an amount of 1 to 15 wt% of the preparation and a photoinitiator.

6. A plate according to any one of the preceding claims, wherein the bottom layer is a surface treated polyethylene terephthalate (PET) film.

7. A plate according to claim 6, wherein the bottom layer has a thickness of 100 to 250 μπι.

8. A plate according to claim 6 or 7, wherein one side of the bottom layer is coated with vinyl acetate copolymer. 9. A plate according to any one of the preceding claims, wherein the top layer is a polyethylene terephthalate (PET) film, a surface treated PET film, or a biaxially oriented polypropylene (BoPP) film.

10. A plate according to any one of the preceding claims, wherein the top layer has a thickness of 19 to 75 μιη.

11. A plate according to any one of the preceding claims, wherein the top layer (11) is surface treated using trichloroacetic acid (TCA). 12. A plate according to any one of the preceding claims has a maximum width of 50 inches and a maximum length of 80 inches.

13. A plate according to any one of the preceding claims has a thickness of 2.8 mm to 7 mm.

14. A liquid photopolymer plate produced using the precast photopolymer plate according to any one of the preceding claims. A flexible relief plate produced using the precast photopolymer plate according to one of the preceding claims.

Description:
PRECAST LIQUID PHOTOPOLYMERIC PLATE FIELD OF TECHNOLOGY

The present invention relates generally to the field of photopolymer platemaking technology. More particularly, it relates to a precast liquid photopolymeric plate which can be readily used for curing and plate imaging.

BACKGROUND OF THE INVENTION

Flexible relief plate used in flexography can be used for printing on various substrate, including plastic, metallic films, cellophane and paper. It is basically a sheet of solid (or liquid) material which is chemically altered using ultraviolet (UV) irradiation, followed by removal of undesired areas, leaving a desired image used as a template during the printing process. Particularly, the material is made from polyurethane prepolymer, acrylate monomers and UV initiators that, when exposed to UV light, experience a chemical reaction to make the monomers join together and become a solid mass of polymers. As the polyurethane prepolymer and the acrylate monomer used are generally a photopolymer, such a plate is generally known as photopolymer or photopolymeric plate in related art.

A photo-polymeric plate can be sold as a liquid photopolymer. Example of such technology can be found in United States Patent No. US 5006447 A and a method of producing relief image from a liquid photopolymer resin can be found in United States Patent No. US 8476000 B2. Generally, a liquid photopolymer is provided to the plate- maker as a viscous liquid, and thus requires that the plate-maker create the plate at the dimension of their specification. Particularly, the plate-maker needs to cast the liquid photopolymer onto a protective film covering a negative mask bearing the desired image. Vacuum is often applied to pull the film close to the mask for a perfect casting. The casted photopolymer layer is then exposed to UV irradiation. As setting forth, the process of plate-making is laborious, requires skilful workers as well as a specialized equipment. Therefore, it is desired to develop a way to simplify the above plate-making process. This invention provides a precast liquid photopolymeric plate which can be readily used for imaging and curing.

SUMMARY OF THE INVENTION One object of the present invention is to provide a precast liquid photopolymeric plate which can be readily processed into a flexible relief plate.

The term 'flexible' used herein defines bendability or deformability of the plate which allows it to be sufficiently wrapped around a rotary printing cylinder without difficulty.

Another object of the present invention is to provide a precast liquid photopolymeric plate with reduced leaking issue.

Another object of the present invention is to provide a precast liquid photopolymeric plate which, after processing, provides a flexible relief plate with reduced scattering issue.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which one of the embodiments of the present invention is a precast liquid photopolymeric plate comprising: a flexible container having a top layer, a bottom layer, and a photosensitive layer defined by a continuous frame having planar surfaces, the frame comprising a cured photopolymer preparation, the top and bottom layer being adhered to each side of the photosensitive layer so as to seal the container, in which the top and bottom layer are sheets being transparent to photo irradiation used in curing the photopolymer and being inert to the photopolymer; and an uncured photopolymer preparation contained within the container.

In the preferred embodiment, the photopolymer preparation of the frame is the same as the polymer preparation contained within the container.

Preferably, an adhesive composition is applied on the frame so as to adhere the top and the bottom layer. In the preferred embodiment, the adhesive composition comprises 15 to 17 wt % of hydroxyl modified vinyl chloride or vinyl acetate copolymer, 0.4 to 0.5 wt % of hydroxyl ethyl methacrylate, 0.4 to 0.5 wt % of trimethylolpropane trimethacrylate, 0.4 to 0.6 wt % of 2,2-dimethoxy-l,2-diphenylethan-l-one, 2.5 to 3 wt % of silica powder and 70 to 80 wt % of ethyl acetate.

In the preferred embodiment, the photopolymer preparation comprises a polyurethane prepolymer present in an amount of 50 to 80 wt% of the preparation, a urethane acrylate oligomer present in an amount of 10 to 30 wt% of the preparation, an acrylate monomer present in an amount of 1 to 15 wt% of the preparation and a photo initiator.

Preferably, the bottom layer is a surface treated polyethylene terephthalate (PET) film.

Advantageously, the bottom layer has a thickness of 100 to 250 μιη. Preferably, one side of the bottom layer is coated with vinyl acetate copolymer.

Preferably, the top layer is a polyethylene terephthalate (PET) film, a surface treated PET film, or a biaxially oriented polypropylene (BoPP) film. Advantageously, the top layer has a thickness of 19 to 75 μηι.

Preferably, the top layer is surface treated using trichloroacetic acid (TCA). In the present invention, the plate can achieve a maximum width of 50 inches and a maximum length of 80 inches. Further, the plate can achieve a thickness of 2.8 mm to 7 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

Fig. 1 shows an exploded view of one preferred embodiment of this invention (not to scale).

Fig. 2 shows optical microscopic images of imprinted images (magnified by 40 times) on one preferred embodiment of the invention, in which the images are derived from a negative film having lines with width of 1.0 mm, 0.50 mm, 0.30 mm and 0.25 mm. The exposure time for all samples are 300s under UV intensity of 60 W. (A) denotes cross- section images of printed lines obtained from exposing a photosensitive layer through a PET film explained in Example 3; and (B) denotes cross-section images of printed lines obtained from exposing a photosensitive layer through a general TCA-treated PET with silica particles. (A)(i) to (iv) denote lines derived from a negative film having lines with width of 1.0 mm, 0.50 mm, 0.30 mm and 0.25 mm, respectively. (B)(i) to (iv) denote lines derived from a negative film having lines with width of 1.0 mm, 0.50 mm, 0.30 mm and 0.25 mm, respectively. BRIEF DESCRIPTION OF THE INVENTION This invention relates to a precast liquid photopolymer plate which can be readily cured and further imaged into a flexible relief plate. Such precast plate can be transported and stored in proper condition until further use. Further, such precast plate is suitable for user which do not have casting or platemaking device equipped with automatic polymer- pouring system. For the convenience of a user, the precast plate can be used without the need to spend time and effort in producing a suitable plate, i.e. without bubbles, no scattering issue, etcetera.

Exemplary, non-limiting embodiments of the precast liquid photopolymeric plate and a method of producing thereof will be disclosed with reference made to Fig. 1. However, it is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim. According to Fig. 1, the precast liquid photopolymer plate comprises a flexible container having a top layer (11), a bottom layer (12) and a photosensitive layer defined by a continuous frame (13) having planar surfaces, the frame (13) comprising a cured liquid photopolymer preparation, the top layer (11) and the bottom layer (12) being adhered one on each side of the frame (13), the top layer (11) and the bottom layer (12) being formed from a material which is transparent to photo irradiation used in curing the photopolymer and being chemically inert to the photopolymer; and an uncured liquid photopolymer preparation (not shown) contained within the container. It shall be noted that the top layer (11) refers to the side of the precast plate where relief images are formed in the end. More particularly, the top layer (11) is removable to expose the relief images after curing of the entire precast plate. On the other hand, the bottom layer (12) refers to the supporting side of the precast plate, sometimes known as backing layer. More particularly, the bottom layer (12) acts as a permanent support where photopolymer preparation of the photosensitive layer adheres thereto.

In the preferred embodiment, the container and its content are basically cured and uncured version of one liquid photopolymer preparation. In the present invention, the frame is rendered gel-like after curing, while the uncured version remains in liquid form for further processing. Such arrangement provides a user with freedom to determine degree of curing for a plate.

According to Fig. 1, the photosensitive layer is defined by a continuous four-sided frame (13) having a sufficient depth to allow bordering and filling of a pool of uncured liquid photopolymer preparation. The frame should not comprised of any porous material such that no uncured liquid photopolymer preparation can seep there through. More particularly, the frame itself is derived from curing a liquid photopolymer preparation by ultraviolet (UV) light, in which the degree of curing and the composition of the liquid photopolymer preparation determine the physical and mechanical properties of the frame.

As used herein, the term 'cure' is intended to encompass the meaning of polymerize, crosslinking, or both. In the present invention, the photopolymer preparation is formed of a composition comprising at least one monomer, a photoinitiator and a binder. Suitable liquid photopolymer preparations are described in European Patent Application Publication No. EP 0691357 Al and United States Patent No. US 6773859. In the preferred embodiment, the liquid photopolymer preparation comprises a polyurethane prepolymer present in an amount of 50 to 80 wt% of the preparation, a urethane acrylate oligomer present in an amount of 10 to 30 wt% of the preparation, an acrylate monomer present in an amount of 1 to 15 wt% of the preparation and a photoinitiator. More preferably, the acrylate monomer used is lauryl methacrylate. Optionally, the liquid polymer preparation may further comprises additives such as, but not limited to, UV radiation absorbers, pigment, filler, deformer, flatting agent, wetting agent and/or slip agent. Preferably, the slip agent is a polymer which can be dissolved or swelled in the liquid photopolymer preparation thereby forming a slip layer on the photosensitive layer. The slip agent can be selected from organic carbonyl compound, polyamide resin, urea resin, urethane resin, melamine resin, acrylamide resin, vinyl acetate copolymer, vinyl copolymer, epoxy resin, cellulosic resin, butyral resin, acetal resin, acrylic resin and the like, but not limited thereto. Suitable organic carbonyl compounds are described in United States Patent No. US 4202696 A. Amongst them, myristic acid is preferred in the present invention. Preferably, the photoinitiator is selected from benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, -methylbenzoin, 2-methylanthraquinone, 9- fluorenone, benzyl, benzyl methyl ketal, acetophenone, 2,2' dimethoxy-2-phenyl acetophenone benzophenone, phenyl-2-thienyl ketone, p-dimethylaminobenzophenone, ρ,ρ'-tetramethyldiaminobenzo-phenone, and the like; and those having a substituent such as cyano, nitro, methoxy, sulfonic acid, phosphinic acid or a salt thereof, ester thereof, for example, 2,6-dimethoxybenzoyl diphenylphosphinoxide, 2,4,6-trimethylbenzoyl- diphenyl-phosphinoxide, 2,4,6-trimethyl-benzoyl-phenylphosphinic acid ethyl ester, sodium 2,4,6-trimethylbenzoyl phenyl-phosphinate) and the like. Amongst them, 2,2' dimethoxy-2-phenyl acetophenone is most preferred. Photoinitiator is generally present in amount from 0.2 wt % to 1 wt % of the photopolymer preparation.

Accordingly, the material used as the top layer (11) and bottom layer (12) are preferably chemically inert to the photopolymer preparation used, such that they do not somehow react with the liquid photopolymer in the container or the frame during storage or during any step of plate-processing.

It is known that inking is made directly on the photosensitive layer during a printing process. Therefore, the top layer (11) is preferably peel-able from a cured precast plate. In view of the above, a suitable adhesive is required to ensure sealing of the uncured liquid photopolymer within the container, without compromising the peel-ability of the top layer (11) therefrom after plate-processing. In the preferred embodiment, an adhesive composition is provided along borders of the plate so as to adhere the frame (13) to the bottom layer (12) on one side and with the top layer (11) on the other side. In the preferred embodiment, the adhesive composition comprises 15 to 17 wt% of hydroxyl modified vinyl chloride or vinyl acetate copolymer, 0.4 to 0.5 wt % of hydroxyl ethyl methacrylate, 0.4 to 0.5 wt % of trimethylolpropane trimethacrylate, 0.4 to 0.6 wt % of 2,2-dimethoxy-l,2-diphenylethan-l-one, 2.5 to 3 wt % of silica powder and 70 to 80 wt % of ethyl acetate. It is preferred that the silica powder used has a particle size distribution between 200 to 400 mesh. More preferably, 350 mesh. In accordance to the preceding description, the bottom layer (12) and the top layer (11) are preferably sheet material which are transparent, particularly being transparent to ultraviolet irradiation, so as to allow irradiation there through. Accordingly, the bottom layer (12) and the top layer (11) ought to have a dimension sufficient for covering the frame (13). Further, adhesion of the top layer (11) and bottom layer (12) to the photosensitive layer should not reduce its flexibility. Further, it is preferred that the bottom layer (12) is relatively less stiff than the top layer (11), such that bending can be achieved without breaking seal between dissimilar layers. In the preferred embodiment, the top layer (11) is a polyethylene terephthalate (PET) film, a surface treated PET film, or a biaxially oriented polypropylene (BoPP) film. Preferably, the top layer (11) has a thickness of 19 to 75 μηι, more particularly, 36 μπι. Further, the bottom layer (12) is a surface treated polyethylene terephthalate (PET) film. Advantageously, the bottom layer (12) has a thickness of 100 to 250 μηι, more particularly, 125 μηι. More preferably, one side of the bottom layer (12) is coated with vinyl acetate copolymer to enhance adhesion to the photosensitive layer.

More preferably, one side of the top layer (11) and one side of the bottom layer (12) are surface treated, chemically or mechanically, to enhance adhesion. For example, one side of the top layer (11) is preferably treated using trichloroacetic acid (TCA). More particularly, the treated side is preferably placed in contact with the liquid photopolymer preparation during production. It is known that PET film used in similar art generally contains silica particles which causes light scattering issue during flexography printing. In the present invention, it is preferred that the PET film used has a reduced content of silica particles, or even do not contain silica particles, to avoid the light scattering issue. As described in preceding description, silica particles are made present in the adhesive composition instead.

In the present invention, the precast plate has a gel-like frame (13) filled with liquid photopolymer therein. It shall be noted that the size and depth of the frame can be customized. As set forth in foregoing description, the frame can achieve a maximum width of approximately 50 inches (approximately 1270 mm) and a maximum length of approximately 80 inches (approximately 2032 mm). Thickness of the frame border can be approximately 0.1 inches to 0.3 inches (2.54 mm to 7.62 mm). The irradiation intensity used depends on the dimension of the frame.

EXAMPLE EXAMPLE 1

Photopolymer Preparation

To a 1L glass kettle were charged 0.6g of butylated hydroxy toluene, 351.2g of an propylene oxide block polyether diol (Arcol Polyol 1021, Covestro Co.) having a number average molecular weight of 2000 and 349.5g of of an ethylene oxide-propylene oxide block polyether triol (Voranol CP6055, Dow Chemical Co.) having a number average molecular weight of 6000 and about 10% by weight of ethylene oxide terminated unit. The two polyols were reacted with 54.97g of a mixture of 2,4-tolylene diisocyanate/2,6- tolylene diisocyanate (TDI 80/20 by weight) in the presence of 3 drops dibutyl tin dilaurate at 70°C for 2-3 hours.

1.5g of butylated hydroxy toluene (BHT) stabilizer was added. The resulting polymer was reacted with 52.5g polypropyleneglycol monomethacrylate (PPGMMA) which has a number average molecular weight of 350-380, in the presence of 4 drops dibutyl tin dilaurate, at 70°C until all of the isocyanate was consumed as determined by IR spectroscopy by the disappearance of the peak at 2600 cm -1 . A photosensitive resin is formed and the PPGMMA is present in an excess. The photosensitive resin were further added with 2.43g of 2,2'-dimethoxy-2-phenyl acetophenone (Ircacure 651, BASF) and diluted using liquid having lOg of lauryl methacrylate ( Bisomer LMA, Geo Specialty Chemicals).

EXAMPLE 2

Adhesive Composition

To a 1L glass beaker were charged 135g of of hydroxyl modified vinyl chloride/vinyl acetate copolymer ( UAGH-1, Univar SPA), 3.6g of hydroxyl ethyl methacrylate ( Visomer HEMA, Evonic Co), 3.6g of trimethylolpropane trimethacrylate ( Visomer TMPTMA, Evonik Co), 24g of silica with 350 mesh and 632g of ethylacetate ( Durochimia sdn bhd). The resulting mixture was stirred for 6 hours under presence of nitrogen blanket. EXAMPLE 3

Formation of Precast Liquid Photopolymeric Plate

The precast plate having features as mentioned in the foregoing description can be made from a platemaking machine (tradename "AGT 3050, Flecomac Sdn Bhd") according to the following steps, but not limited thereto. It shall be noted that process parameters may vary according to different machine used to provide satisfactory result. In the present invention, the precast plate was made by:

1. covering at least a part of a planar working surface with a light impenetrable material, such as a negative film (such as a silver halide-based sheet);

2. covering the surface with a PET film (36 μπι), in which vacuum can be applied to ensure tight surface between the working surface and the film (minimum or no air bubbles);

3. applying adhesive composition as prepared according to Example 2 at perimeter of the working surface to define a border;

4. applying foam tape surrounding the border to define a dented area;

5. pouring and spreading the liquid photopolymer preparation as shown in Example 1 into the dented area, wherein the liquid photopolymer spreads to the border and adheres thereto;

6. covering the working surface with a vinyl acetate-coated PET film (125 μιη) (trade name "COVEME KFC6"), including the border and the dented area;

7. exposing only the border to UV radiation, in which the UV radiation comes from UV light beneath the working surface, also known as 'backflashing', such that light does not penetrate through the negative film hence only curing the liquid photopolymer at the border. The border can be exposed for 1 to 3 cycles. In this way, a gel-like frame is formed while the uncured area remains in liquid state; and

8. lifting the entire plate from the working surface by activating blower equipped in the platemaking machine. EXAMPLE 4

A precast liquid photopolymeric plate produced according to description as set forth in Examples 1-4 has a frame dimension of width in 508 mm, depth in 762 mm and border thickness of 3.96 mm. Such dimension is derived from 1.6 L of the liquid photopolymer preparation. When cured under UV intensity of 60 W for 5 mins, the frame achieves a 36 shore hardness A. Adhesion force between the top and bottom layer with the frame border is between 6 to 125 N/cm 2 , no leaking issue.

EXAMPLE 5

The precast plate can be made into a flexible relief plate with reversed image. As set forth in the foregoing description, reverse images on the plate can be observed via microscopic images as shown in Fig. 2. Apparently, a relief plate having the aforementioned elements provides improved image quality.