WO2002078966A2

WO2002078966A2 - Prepolymer and screen roller filler for depth-variable laser ablation

Info

Publication number: WO2002078966A2
Application number: PCT/DE2002/001063
Authority: WO
Inventors: Corinna Sieke; Klaus Hanke; Mathias KÖTTER
Original assignee: Michael Huber München Gmbh
Priority date: 2001-03-29
Filing date: 2002-03-22
Publication date: 2002-10-10
Also published as: EP1373335A2; DE10115434A1; AU2002312714A1; WO2002078966A3

Abstract

The invention relates to a prepolymer containing, per molecule, at least one UV photo-cross-linking functional group and at least one thermally labile functional group. The invention also relates to a screen roller filler that comprises the prepolymer.

Description

PREPOLYMER AND GRID ROLL FILLING MATERIAL FOR DEPTH VARIABLE LASER ABLATION

The invention relates to a UV radiation-curing prepolymer and anilox roller filling material for depth-variable laser ablation.

EP 0 730 953 A1 and EP 0 813 957 A1 describe a method for transmitting digital image information by means of an IR laser beam into filled raster structures. It is known under the name DICOWEB-GRAVURE technology. An anilox roller corresponding to an anilox anilox roller whose cups are filled with a hot-melt wax compound softening at 60 ° C. at 140 ° C. serves as the blind form. This filling contains soot. It can be removed by variable-depth laser engraving at the printing points. This creates a gravure form that can be printed with water-based gravure inks.

After printing is complete, the wax compound can be removed using hot high pressure water, i.e. the printing form created is deleted. The cylinder can now be available for refilling with a wax compound and imaging using laser ablation.

The well structure to be filled specified on the anilox rollers or form sleeves consists, for example, of wells with an area of 145 μm ² and 30 μm depth. A YAG-IR laser with a wavelength of 1064 nm and 11 W / cm, 30 μm spot diameter in focus and about 4 joules / cm ² energy density can function as the improvement glaze. However, the wax compound has several disadvantages that make the technical implementation of the DICOWEB-GRAVURE process very difficult. The explosive ejection of the wax compound creates crater rims during laser ablation, which have a restless edge structure and have a disruptive effect on the printed image. Furthermore, the crater edges are sheared off by the doctor blade in the gravure printing process, which leads to grooves in the soft wax compound layer of> 1 μm groove depth. These grooves in the circumferential direction mark themselves in the printed image. Furthermore, the thermoplastic wax compound filling material is mechanically unstable and swellable. It is also considered a disadvantage that only water-based gravure inks can be used.

US Pat. No. 5,324,617 describes a filler material in which ablation is assisted by thermo-explosive additives such as ammonium nitrate. As expected, however, the filling material described there shows no positive effect with regard to the edge structures and the crater rim formation.

The object of the present invention is therefore to provide a filling material for the filling of anilox roller cups or molded sleeves, with which rapid, sharply defined images can be produced without ejection that forms the edge of the crater.

To solve this problem, it was first necessary to provide a prepolymer which is characterized in that it contains at least one UV photocrosslinking functional group and at least one thermally labile functional group in the molecule.

A prepolymer in which the UV photocrosslinking group contains at least one olefinic double bond is preferred. Also preferred is a prepolymer in which the UV photocrosslinking group contains an oxirane function, also called an epoxy function.

Furthermore, a prepolymer is preferred in which the UV photocrosslinking group contains an acrylate and / or methacrylate function.

Also preferred is a prepolymer in which the thermally labile functional group contains one or more of the following atomic groups: -N = N-, -O-O-, -C≡C-.

Alipathic azo compounds and alkynols are particularly preferred.

The prepolymer according to the invention can be prepared by chemical reaction of compounds which contain UV photo-crosslinking functional groups with compounds which contain thermal labile functional groups. Furthermore, so-called spacer molecules can be installed between the UV-photocrosslinking compounds and the thermally unstable connections. The synthesis takes place in bulk as a melt or in solution. Possibly. Existing solvent can be removed by applying high vacuum or freeze drying.

As compounds which contain UV-photocrosslinking groups, for example pentaerythritol (manufactured by UCB; molecular weight 298.30 g / mol) and 2-methacryloyloxyethyl isocyanate abbreviated hereinafter with MOI ^® (made by Showa Denko KK, Japan; molecular weight 155.2 g / mol). Examples of compounds which contain UV photocrosslinking groups include, for example, bisphenol A diglycidyl ether and bis ~ (3,4-epoxycyclohexyl) adipate.

Compounds which contain thermally labile groups are, for example, 4,4'-azobis (4-cyanovaleric acid) (manufacturer: Wako Chemicals GmbH; V-501; molecular weight 280.28 g / mol), 2-butyne-1,4- diol (manufacturer: BASF; molecular weight 86.1 g / mol), 2,2'-azobis [2-methyl-N- (2-hydroxybutyl)] propionamide (manufacturer: Wako Chemicals GmbH; VA-085, molecular weight 344.45 g / mol), 2,2'-azobis [2-methyl-N- (2-hydroxyethyl)] propionamide (manufacturer: Wako Chemicals GmbH; VA-086, molecular weight 288.35 g / mol) and 2,4,7 , 9-tetramethyl-5-decyne-4,7-diol (manufactured by Air Products Surfynol ^® 104, molecular weight 226 g / mol).

A prepolymer is particularly preferred which is characterized in that it has a dynamic viscosity at a shear rate of 50 s ^-1 and a temperature of 60 ° C. of <50 Pa · s

Furthermore, a prepolymer is particularly preferred which is characterized in that the UV photocrosslinking functional group can be crosslinked below a wavelength of 450 nm and the thermally labile functional group can be fragmented above a wavelength of 800 nm.

Filling materials for anilox rollers must have the following properties according to the requirement profile:

suitable rheology (viscosity / flow behavior) for filling the cells by rolling or knife coating, preferably by chamber doctor blade systems, - processability under automated process conditions,

- curing in less than five minutes after filling,

- high abrasion resistance and adhesion of the hardened filling material in the carrier cells, - resistance to swelling or shrinking in contact with water-based, solvent-based and UV radiation-curing gravure inks, i.e. Insolubility in the organic solvents used there,

- after curing and imaging, formation of surface properties that are important for the printing process with regard to ink acceptance /

Wetting and emptying behavior of the well structure created by ablation are suitable,

- Refillability of the cell structure obtained by ablation with filler material for new imaging, - Erasability by complete IR laser ablation of the filler material before refilling and imaging,

- no adverse environmental effects from the fission products during ablation and

- In particular, a quick and sharp imaging without crater-forming ejection.

The object is achieved according to the invention by a filling material for filling the cells of anilox rollers or shaped sleeves, which is characterized in that the filling material comprises a prepolymer which contains at least one UV-photocrosslinking functional group and at least one thermally labile functional group in the molecule. That the The multifunctional anilox roller filling material on which the present invention is based fulfills the above-mentioned requirements to a high degree.

The filling material is applied as a liquid to pasty, multi-function material for filling the well structures of anilox rollers or form sleeves, for example by rolling, preferably by means of a chamber doctor blade. After application, the prepolymer is cured by UV radiation to form a resistant, crosslinked polymer system with high adhesion to the anilox roller / cylinder surface.

In the wells filled with the filler material according to the invention, variable-depth image structures are generated by means of IR laser ablation in that the thermolabile functional groups as predetermined breaking points in the polymers produced are thermally fragmented and lead to an edge-sharp, degree-free ablation. In this way, digital image information is written into the filled cells using an IR laser beam. The cylinder is illustrated in this way.

Fig. 1 shows a laser imaging and full area using the filler material according to the invention according to Example 6. Fig. 1 is the result of a surface scan. It shows the excellent edge sharpness that was achieved by using the filler material according to the invention in the imaging.

2 shows an intaglio printing sleeve with UV-crosslinked, filled cells and ablated, ie illustrated, areas. The gravure printing plate produced in this way can be printed in known gravure printing machine technology by water-based, solvent-based or UV radiation-curing gravure inks.

The image information engraved by means of an IR laser can be deleted after printing and after cleaning the cylinder of printing ink by filling the empty or partially filled cells again with filling material and then UV-curing them.

Another advantage of the invention is that the filling material can also be completely removed from the anilox roller or the form sleeve, for example by laser ablation / infrared radiation. The empty cells can then be filled and the filling material in the cells can be crosslinked by means of UV radiation.

In both cases, the cylinder is available for a new imaging and a new cycle.

According to the invention, a multi-functional prepolymer-containing anilox roller filling material or a reactive mixture of a compound with at least one UV-photocrosslinking oxirane group and a compound with at least one thermally labile functional group-containing anilox roller filling material is provided for a variable-depth laser ablation.

For the UV radiation-induced crosslinking of the multifunctional prepolymer, energetically coordinated photoinitiators are used. The decisive criterion when choosing the prepolymer / photoinitiator combination is that the thermally labile, ablative groups are retained during the photo-crosslinking. The radical photoinitiators can be divided into alpha-splitters and H-abstractors. Alpha splitters break down under UV radiation into two radicals, which trigger the crosslinking reaction. Representatives of this class are, for example, benzoin ethers, alcylphosphine oxides, benzil ketals, α-hydroxyalkylphenones and α-aminoalkylphenones.

H-Abstractors are combined with coinitiators, so-called synergists. C initiators are, for example, amines and alcohols. The radicals are generated in UV radiation via an electron transfer followed by a proton transfer mechanism. Examples of H-abstractors are benzophenones and thioxanthones.

Suitable UV photoinitiators are, for example, Irgacure 819 ^® (bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide), Irgacure 184 ^® (1-hydroxycyclohexylphenyl ketone) (manufacturer: Ciba Specialty Chemicals), Quantacure ^® EPD (ethyl -4-dimethylaminobenzoate) and Quantacure ^® BDK (2,2-dimethoxy-1,2-diphenylethanone) (manufacturer: Great Lakes).

(Great Lakes manufacturers) are used next coactivators for deep drying, such as Quantacure ^® ITX (2-isopropyl-thixoanthon) can.

Advantageously, carbon black is used as a further component of the filling material, such as Elftex ^® 415 (manufactured by Cabot Corporation), and Printex ^® 25 (manufacturer: Degussa) for rapid absorption of high levels of the irradiated for the ablation IR laser energy or to transfer energy to the thermolabile groups of the prepolymer filler base material capable of ablation. Further IR absorbers, such as Epolight ^® types (manufacturer: Epolin) can also be used.

Other ingredients for the filling material may fillers such as CaCO ₃ and fumed silica, such as Aerosil ^® R972 (manufactured by Degussa) be.

To support the ablation, further thermally labile compounds, such as nitrocellulose, can be added to the filler according to the invention.

In individual cases, depending on the type of filler material according to the invention, it is necessary to use elastification components which additionally improve the adhesion in the metal wells. In addition to polymeric plasticizers, epoxidized soybean oil acrylate such as Craynor ^® CN111 (manufacturer: Cray Valley) are particularly suitable.

Depending on the consistency of the prepolymer of the invention or of the filler can even thinner, such as tripropylene glycol diacrylate and hexane diolethoxylatdiacrylat (Photomer 4361, manufactured by Cognis Corporation), surfactants such as Surfynol ^® 104 and polymeric thickeners such as Ethylcelullose (Ethocel ^®, manufacturer Dow Chemical) was added become.

The prepolymers according to the invention, which are reactive acrylates, polymerize initiated by free radicals with a very high reaction rate. However, the polymerization reaction is stopped very quickly when the UV radiation source is switched off or the penetration depth of the radiation is insufficient. The latter is reinforced by highly absorbent pigments such as soot. In order to ensure that the filling material according to the invention is completely crosslinked in the wells of the anilox roller by means of UV radiation, combinations of free-radically and / or ionically, preferably cationically curing, ablative prepolymers or the above-mentioned reactive mixtures are also used.

Cationic radiation-curing substances are, for example, epoxides, especially cycloaliphatic epoxides, which polymerize with the aid of cationic photoinitiators. They continue to react even after the UV source has been removed, so that the filling material in the depths of the cells is fully cured.

Bisphenol-A-diglycidyl ether, 3,4-epoxy-cyclohexylmethyl-3,4-epoxycyclohexane-carboxylate (CER 1) (manufacturer: Union Carbide) and bis- (3,4-epoxycyclohexyl) adipate (CER 2) (Manufacturer: Union Carbide) can be used.

For example, onium salts of very strong acids can be used as cationic photoinitiators.

The invention will now be explained in more detail by means of examples.

Examples of the synthesis of prepolymers:

The prepolymers according to the invention described below were characterized by the thermal decomposition temperature or by the dynamic viscosity using a rotary rheometer. A cone-plate measuring geometry was used for the rotational rheσ meter (manufacturer: Rheometrics). The viscosity was determined at 20 ° C.

The decomposition temperature (peak maximum) was determined by means of differential thermal analysis (DSC) (manufacturer: Mettler), the heating rate being 10 ° C. per minute.

Example 1 :

68.05 g of pentaerythritol acrylate and 31.95 g of ACVS V-501 were dissolved in acetone. Then 0.5 g of p-toluenesulfonic acid was added and the reaction was carried out at 50 ° C. within three hours. The acetone was then removed by applying a vacuum.

A bifunctional acrylate with a thermally labile azo group was formed, the decomposition temperature of the azo group being 84 ° C.

Example 2:

There were 52.60 g of VA-085 and 47.40 g of MOI ^® dissolved in 100 g of methyl ethyl ketone and reacted at 50 ° C within 72 hours. The solvent was then removed at 20 ° C. under a high vacuum.

The result was a bifunctional methacrylate with a thermally labile azo group with a decomposition temperature of 95 ° C. Example 3:

21.72 g of 2-butyne-1,4-diol were melted at 55.degree. Then 78.28 g of ^{MOI® were} added and the two components were stored at 50 ° C. for 72 hours.

A bifunctional methacrylate with ablation-capable alkyne group with a viscosity of 6 Pa • s was formed as the reaction product.

Example 4:

18.08 g of 2-butyne-1,3-diol were melted at 55 ° C. and 6.05 g of VA-086 were dissolved therein. Then 75.57 g of ^{MOI® were} added and the reaction was carried out at 50 ° C. for 72 hours.

The reaction product was a prepolymer mixture of bifunctional acrylates with thermally labile bonds and a viscosity of 10 Pa • s.

Examples for the production of the filling material according to the invention:

Example 5:

There was a filler material from 96.0 g of prepolymer of Example 1, 2.0 g of carbon black Printex ^® 25, and 2.0 g Irgacure ^® 819 manufactured. The components were intimately mixed using a three-roller chair at a temperature of 25 ° C and a pressure of 20 bar. The desired viscosity was adjusted using acetone. Example 6:

It has a filler of 95.0 g of prepolymer of Example 3, 4.0 g Elftex ^® 415, 0.2 g Quantacure ^® ITX, Quantacure ^® EPD 0.4 g and 0.4 g Quantacure ^® BDK prepared. The components were intimately mixed using a three-roller chair at a temperature of 25 ° C and a pressure of 20 bar.

The fillers according to the invention were each applied to the cylinder surface of a DECOWEB gravure anilox roller (gravure Cr sleeve, full-tone engraver, 70 l / cm, 35 μm bowl depth) by means of a chamber chamber. Here, the filling material was applied to the upper doctor blade, roughly stripped off during the cylinder rotation and then scraped cleanly off the lower doctor blade. The cups of the cylinder were filled over the entire surface and seamlessly. The wetting of the cylinder surface is very good and was carried out without any noticeable adhesion problems.

The filling material was cured by means of UV radiation (UV dryer from Hönle with a maximum output of 250 W / cm) and the prepolymer was crosslinked. The cylinder rotation speed was 0.575 or 1.15 cm / s and the UV lamp output was 130 W / cm. The irradiation time per cm was less than two seconds.

The surface quality or roughness is good after curing, it was less than 1 μm.

The abrasion resistance of the hardened filling material was examined automatically using a paper web with impression roller. The discoloration of the paper and the surface properties (smoothness, scratches, tears) of the filling were used as an indicator of the abrasion resistance. The abrasion resistance was assessed as very good.

Imaging tests of the cured filling compound were carried out with a YAG laser at the rotogravure laboratory. The laser power was approx. 10 to 11 watts continuous wave at 1064 nm, the energy density was 8 J / cm ² . The speed was 400 rpm and the spot size was 30 μm.

The shaped sleeve filled with the material according to the invention was imaged with a full-tone test motif by means of a YAG laser, the imaging steps being repeated three times with a precise fit. The results of the laser imaging were evaluated using microscope images and surface scanning (white light interferometer).

The UV-hardened filler material can be engraved with sharp edges without any gradation, i.e. illustrated.

Claims

1. prepolymer, characterized in that it contains at least one UV photocrosslinking functional group and at least one thermally labile functional group in the molecule.

2. Prepolymer according to claim 1, characterized in that the UV photocrosslinking group contains at least one olefinic double bond.

3. Prepolymer according to claim 1 or 2, characterized in that the UV photo-crosslinking group contains an acrylate or methacrylate function.

4. prepolymer according to claim 1, characterized in that the UV photocrosslinking group contains an oxirane / epoxy function.

5. Prepolymer according to one of the preceding claims, characterized in that the thermally labile functional group contains one or more of the following atomic groups: -N = N-, -O-O-, -C≡C-.

6. Prepolymer according to claim 5, characterized in that the thermally labile functional group is an -N = N group or a -C≡C group.

7. prepolymer according to one of the preceding claims, characterized in that it has a dynamic viscosity at a shear rate of 50 s ^"1 and a temperature of 60 ° C of <50 Pa • s.

8. Prepolymer according to one of the preceding claims, characterized in that the UV photo-crosslinking functional group can be crosslinked below a wavelength of 450 nm and the thermally labile functional group can be fragmented above a wavelength of 800 nm.

9. Filling material for filling the cells of anilox rollers or shaped sleeves, characterized in that the filling material comprises at least one prepolymer according to one of claims 1-8.

10. A method for producing a printing form, characterized in that for the production of the printing form, the filling material according to claim 9 or as a filling material, a reactive mixture of at least one compound with at least one UV-photocrosslinking oxirane / epoxy group and at least one compound with at least one thermally labile functional group is used.

11. A method for producing a printing form according to claim 10, characterized in that the filling material is cured by means of UV radiation and then a printing form is produced using IR laser ablation.

12. A method for producing a printing form according to claim 10 or 11, characterized in that the printing form is used in the gravure printing process.

13. A method for generating digital image information, characterized in that it is carried out in the filler material by means of IR laser ablation of the filled wells after the photo-crosslinking of the prepolymer according to one of claims 1-8 or the reactive mixture according to claim 10.