AU608532B2 - Improvements in or relating to printing - Google Patents

Description

TO: The Commissioner of Patents, COMMONWEALTH OF AUSTRALIA.

L S1 SAU-AI7802/87 WORLD INTELLECTUALPROPERTY ORGANIZATION International Bureau

PCI

INTERNATIONAL APPLICATI i% LEL4 ffiEHETENT COOPERATION TREATY (PCT) (51) International Patent Classificatioi i I i ati Publication Number: WO 88/ 00961 C09D 11/10 Al (43) International Publication Date: 11 February 1988 (11.02.88) (21) International Application Number: PCT/GB87/00540 (22) International Filing Date: (31) Priority Application Numbers: 30 July 1987 (30.07.87) 8618596 8619244 8706848 30 July 1986 (30.07.86) 6 August 1986 (06.08.86) 23 March 1987 (23.03.87) Laureston, Park Drive, Harrow Weald, Middlesex PATEL, Dakshesh, Shashikant [GB/GB]; 6 North Avenue, North Harrow, Middlesex HA2 7EA

(GB).

(74) Agent: E. EDER CO.; 39 Cranbrook Road, Ilford, Essex IGI 4NH (GB).

(81) Designated States: AT(Europsi patent), AU, BE (European patent), BR, CH (European patent), DE (European patent), DK, FI, FR (European patent), GB (European patent), IT (European patent), JP, LU (European patent), NL (European patent), NO, SE (European patent), US.

(32) Priority Dates: (33) Priority Country: (71) Applicant (for all designated States except US): SMALL PRODUCTS LIMITED [GB/GB]; Thames House, 566 Cable Street, London El (GB).

(72) Inventors; and Inventors/Applicants (for US only) SMALL, Richard, Frederick [GB/GB]; 29 Bredhurst Road, Wigmore, Gillingham, Kent ME8 OPE BARROW, Lascelle, Augustus [GB/GB]; 44 Gun Wharf, Wapping, London El DIX, Barry, Martin [GB/GB]; Published With international search report.

A.Do.P. 24 MAR S4usrALAN 2 4FE8 1988 PATENT

OFFICV

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1988 (54) Title: IMPROVEMENTS IN OR RELATING TO PRINTING (57) Abstract A water based screen printing ink that is at least partially curable by irradiation and comprises an emulsion of a resin dispersed in water.

WO 880961 PCr/TIGB87/00540 IMPROVEMENTS IN OR RELATING TO PRINTING This invention relates to printing and in particular to screen printing (commonly known as silk screen printing).

As is well known, the silk screen printing process involves the use of a screen of silk, polyester, nylon, metal gauze or any other suitable mesh-like or perforated material. For convenience (and for consistency with the terminology historically employed in this art) the term "silk screen printing" will be used herein and it will be appreciated that no restriction to "silk" material is thereby intended.

Although silk screen printing is a very old technique, it still has numerous problems and/or limitations associated with it. For example, where several large-size multi-colour sheets are to be silk screen printed for, say, a poster to be pasted up on a hoarding, large quantities of specialised, screen printing inks are needed which are expensive.

The printing inks required for screen printing are quite different from those to be used for other forms of printing.

The screen printing inks being generally used at present are organic solvent-based and usually contain ethyl or nitro cellulose resins. They are dried in warm air tunnels by driving off the organic solvents, and are thus potentially hazardous to the printing operatives. Another problem which arises with such organic solvent-based screen printing inks, relates to solvent loss from the ink on the printing screen whereby the ink increases in viscosity and after a certain period of time will not properly pass through the open areas of the printing mesh. This "drying in" results in loss of printed image and is described as screen stability, i.e.

inks with poor screen stability "dry in" rapidly.

Recent developments over the last ten years have seen the introduction of Ultra-Violet-curing screen process inks.

SUBSTrruUT SHET I

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WO 88/00961 PCT/GB87/00540 Here the formulations use raw materials which do not increase in their viscosity on the printing screen but instead dry by exposure to intense Ultra Violet light. This means that this type of ink has almost unlimited screen stability compared to non-UV curing, organic solvent-based, screen printing inks. However, such UV-curing inks are expensive, and leave a very thick print coat on the paper surface particularly where multi-colour, e.g. 4-colour, silk screen printing is effected.

Such thick or heavy print images on the surface of a sheet of poster paper often necessitate that for mounting the poster to its hoarding, a special adhesive which is other than an inexpensive starch-based adhesive must be used if efficient bonding is to be achieved. A similar problem often arises with the older type of organic solvent-based silk screen printing inks. This adhesion problem is common where the individual sheets overlap, e.g. at overlapping marginal edges of adjacent poster sheets. The back of the top sheet does not have sufficient adhesion to the ink surface printed on the sheet beneath. When the poster paste dries out, the top sheet of the overlap often curls up and away from the sheet underneath. The problem is particularly severe when the paper is completely covered with several layers of ink. Posters printed with offset litho inks have less tendency to curl when they dry out compared to those produced with screen printing inks. As the screen printing process achieves its high quality print appearance by a much higher ink deposit, the curl problem is pronounced with screen printing inks. Therefore the adhesives used with screen printed posters need to have better adhesion properties to prevent overlap curl.

Mixtures of one or more starch adhesives and one or more polyvinyl alchol adhesives were investigated by the applicants, and these were found to give a much improved adhesion at the overlapping edges of superimposed sheets as SUBSTITUTE SHrET _L ii .iu i li- compared to a 100% starch-based adhesive product.

However, mixtures of starch and P.V.A. adhesives have the disadvantage of being more expensive and the resultant improved adhesion make the removal of the total poster from the hoarding more difficult. Thus, they are not likely to find favour with bill-posters, ie. those responsible for putting up the posters on the hoardings.

It is therefore considered desirable to reduce, if not wholly obviate, some or all of the above-mentioned and/or other disadvantages associated with or relating to prior art screen printing methods and inks.

According to this invention, there is provided a printing ink for silk screen printing, characterised in that the screen printing ink is a water-based ink that is wholly or partially curable by irradiation and comprises an emulsion of an unsaturated acrylate resin :00: disposed in water, said resin comprising a polyester acrylate resin or an epoxy acrylate resin or a mixture S 20 of said acrylate resins.

The term "irradiation" as used herein in rleation to curing refers to electron beam radiation and to electro- 0000 magnetic radiations having wavelengths shorter than 0000 000 those of the visible spectrum, ie. it includes UV 25 (ultra-violet) radiation.

Preferably, the emulsion has said resin wholly or ooo o substantially in dispersed phase and wholly substantially insoluble in the water, the water being S the continuous phase of the emulsion.

000000 0 :oo Advantageously, said resin comprises 30% to (preferably 50%) of the emulsion.

UAAN

D CT 3 WO 88/00961 PCT/GB87/os05 4 Preferably the water-based screen printing ink has a composition which comprises one or more photoinitiators and is at least partially curable by irradiation comprising electromagnetic radiations in the ultra-violet light waveband.

Alternatively, or additionally, the screen printing ink may be at least partially curable by irradiation with an electron beam.

Where the screen printing ink is curable solely by irradiation with7 an electron beam, then photoinitiator(s) may be omitted from the printing ink composition.

Preferably, and in either case, the water-based printing ink composition is subjected to heat or to thermal radiation, e.g. is subjected to electromagnetic radiations in the infra-red light waveband, prior to curing.

The following relates to the production of individual silk screen printed sheets and their treatment for application onto hoarding sites in accord with embodiments of the present invention. As well as single sheet posters, the embodiments are concerned with the usual combinations of multiple sheet posters "16 sheet", "48 sheet" or "96 sheet" posters) for pasting up onto large hoardings. The screen printing method used in these embodiments may be for the production of four colour halftone prints as well as continuous line and tone colour prints.

The following embodiments of this invention concern the screen printing ink used to print the sheets. The screen printing ink in each of these embodiments comprises an emulsion of a resin dispersed in water, i.e. is water miscible, and dries by exposure to UltraViolet radiation.

The emulsion has said resin wholly (or at least substantially) in dispersed phase and wholly (or at least SUBSTITUTE

SHEET

WO 88/00961 PCT/G87/00540 substantially) insoluble in the water, the water being the continuous phase of the emulsion. Thus the screen printing ink contains water and is water thinnable to a considerable extent, but the water is to be regarded as a carrier or diluent (rendering the ink aqueously reducible in viscosity) rather than as a solvent. Preferably the water-based screen ink contains at least 40% water.

In a first embodiment of this invention the printing ink composition comprises: an Ultra Violet curing resin emulsified with water, e.g. an equal part of water; a photoinitiator and an aqueous pigment dispersion. In the emulsion the water is the continuous phase and the resin (amounting to 50% of the emulsion) is the dispersed phase.

One specific formulation of this is given in Example 1.

Example 1 Parts by weight Emulsion Laromer* PE 55W 1) 95.3 Darocur* 1173( 2 Photoinitiator Aquadisperse* Phthalo Blue GB EP 3 2.7 A composition as formulated in Example 1 was printed through a screen made from 165 threads per cm polyester mesh halfcalendered. The calendered side was positioned face down towards the substrate, ie. M.G. (machine glazed) poster paper. The stencil was made from direct emulsion using a half-tone positive. The print was produced on an S.P.S.

cylinder action screen printing press. The ink was dried through a two lamp S.P.S. U.V. dryer (rated at 300 watt per inch). The resultant dried print was a good half tone image of high definition.

However this initial formulation, when tested, gave poor screen stability. This was improved in a.second embodiment by the addition of n-vinyl pyrrolidone a solvent miscible with water which also takes part in the curing reaction. A SUBSTITUTE SHEET I WO 88/00961 Pcr/GB87/o05 4 specific formulation of this second embodiment, which likewise had water as the continuous phase and had the resin (amounting to 50% of the emulsion) as the dispersed phase, is given in Example 2.

Example 2 Parts by weight Laromer* PE 55W 1 85.3 Darocur* 1173(2) Aquadisperse* Phthalo Blue GB EP 3 2.7 n-vinyl pyrrolidone 4 10.0 A composition as formulated in Example 2 was printed and dried in the same manner as for Example 1. The resultant dried print was a good half tone image of high definition.

Due to the relatively high price of this water-miscible solvent, i.e. the n-vinyl pyrrolidone, compared to the other materials used in the formulation, the final material cost was considered uneconomic. To offset this, a calcium carbonate extender was introduced into the composition to obtain a third embodiment with an acceptable raw material cost. A mixture of photoinitiators was also used in place of the single type. A specific formulation of this third embodiment, which likewise had water as the continuous phase and had the resin (amounting to 50% of the emulsion) as the dispersed phase, is given in Example 3.

Example 3 Parts by weight Emulsion Laromer* PE 55W 63.3 Aquadisperse* Phthalo Blue GB EP 3 2.7 N Vinyl Pyrrolidone 4 Omyalite* 95T Extender 5 20.0 Photoinitiator Irgacure* 651( 6 Photoinitiator Quantacure* ITX 7 SUBSTITUTE

SHEET

i; i, i I U WO 88/00961 PCT/GB87/005 A composition formulated as in Example 3 was printed and dried in the same manner as for Example 1. The resultant dried print was a good half tone image of high definition.

Samples of four colours Trichromatic yellow, magenta, cyan and black were made for container storage stability trials.

After four weeks storage, the magenta and black inks had gelled whereas the yellow and cyan were unchanged.. Further work was carried out to improve storage stability. In order to retain screen stability and an economic raw.-.material cost, a fourth embodiment was devised in which the:' r-vinyLpyrrolidone and the photoinitiator mixture were replaced by a solvent, ethoxy-propanol and a single initiator compound rather than the mixture of photoinitiators. The calcium carbonate extender was also omitted as this was not now required to obtain an acceptable raw material cost. A thickening agent was introduced to maintain the ink at a printable viscosity. Again the emulsion had water as the continuous phase and the resin as the dispersed phase.

Slight improvements in screen stability were obtained with this embodiment by the introduction of small amounts of a humectant/surfactant compound and of a silicone emulsion lubricant. A specific formulation of this fourth embodiment is provided in Example 4.

Example 4 Parts by weight Laromer* PE 55W 75.2 Darocur* 1173 2 2.9 Ethoxy Propanol 8 9.7 Curlout Plus*( 9 5.8 Alcoprint* PTF(10) Alcoprint* PHL 1 1 Alcoprint* PSJ 12 1.9 Aquadisperse* Phthalo Blue GB EP 3 SUBSTITUTE

SHEET

WO 88/00961 PCrT/GB87/f54 -8- A composition formulated as in Example 4 was printed and dried in the same manner as for Example 1. The resultant dried print was a good half tone image of high definition.

The storage stability of trichromatic yellow, magenta, cyan and black printing inks with this latest formulation were then retested and found to be satisfactory.

To provide a completely aqueous-based composition avoiding the use of any inflammable solvents, a fifth embodiment Ras devised in which the ethoxy propanol was replaced by a mixture of water and an acrylic monomer Tripropylene glycol diacrylate for maintaining the appropriate dispersion of the resin solids. A specific formulation of this fifth embodiment is provided in Example Example 5 Parts by deight Laromer* PE 55W 61.6 Darocur* 1173(2) 3.1 Acrylic Monomer T.P.G.D.A. 13 7.7 Water 15.4 Curlout Plus*( 5.7 Alcoprint* PTF 1 0 Alcoprint* PHL 11 Alcoprint* PSJ 12 Aquadisperse* Phthalo Blue GB EP 3 A composition formulated as in Example 5 was printed and dried in the same manner as for Example 1. The resultant dried print was a good half tone image of high definition.

All the above-mentioned tests were carried out using 60" x 40" (1.5m x Im) machine glazed Poster Paper. It gas found that when heavy deposits of colour were used across the whole area of the paper, a high degree of curl at the 8UBSTI'rUr E S9HE .r

II

edges of the paper was experienced. This was overcome (in accord with embodiments of the invention of our Australian Patent Application No AU-B-77804/87 (593938) by providing for the first colour to be printed down onto the paper to be a screen printing ink producing minimal paper curl (eg. enabling the paper sheet to be re-fed through the printing machine), and for the or each subsequent printing thereon to be with a waterbased UV curing ink. The screen printing ink producing minimal curl can be a conventional non-aqueous UV curing ink or a conventional solvent-based printing ink, or an aqueous ink of low water content (eg. less than The above-described water-based inks of Examples 1 to when cured only by UV radiation, were found to have a wet rub-resistance not adequate for all purposes, and to have a variable gloss level. Experiments were carried S: out with infra red heating just before the UV curing was effected. This technique produced prints with good wet goes rub-resistance and with a substantially uniform level of gloss. It is thought that this was due to the removal of excess water by the infra-red heating. It was also found that more efficient water removal could be

V.

achieved by using a jet air dryer to force cold air over the print. It is considered that excess water might be removed, additionally or alternatively, by microwave or radio frequency drying.

SoTests were conducted is pasting up the individual sheets to produce hoarding posters, and starch based pastes S (obtained from Wilsons Adhesives and Morris Greenhaugh) were used for these tests. The surface of the prints produced by the above ink Examples was found to accept the starch pastes used by bill-posters more readily than S prints printed with the solvent-based inks which are currently in general use. Prints produced with the water-based inks of Examples 1 to 5, when dried only by UV radiation, showed excellent adhesion properties with the starch adhesives. These prints WO88/00961 -10- C PCT/GB:97PW54 when dried both by infra-red and by UV radiation showed a reduction in adhesion properties but this was still an improvement on that attainable with multi-colour prints produced with the standard organic solvent based screen printing inks. Never-theless, by subjecting the prints to corona discharge, this reduction in adhesion properties was overcome and prints with good gloss and wet-rub resistance were still obtained. In a preferred example, prints dried by infra-red and UV radiation were treated to 73 dynes/cm using a Sherman Treaters Corona Discharge Machine. These prints showed the same excellent adhesion properties that were obtained by just drying with UV radiation.

Notes means Trade Mark 1. Laromer* PE 55W is a 50% emulsion of a polyester acrylate in water obtainable from B.A.S.F.

2. Darocur* 1173 is a obtainable from E. Merck Hydroxy-2-methyl-l-propan-l-one 3. Aquadisperse* Phthilo Blue GB EP is an aqueous dispersion of pigment Blue 15 obtainable from Tennant-

K.V.K.

4. n-vinyl pyrrolidone is a UV obtainable from B.A.S.F.

reactive solvent Omyalite* 95T is a calcium carbonate obtainable from Croxton Garry.

extender 6. Irgacure* 651 is Benzil Dimethyl Ketal- obtainable from Ciba Geigy.

SUBSTITUTE SHEET j WO 99/00961 PCr/GB87ffl0540 7. Quantacure* ITN is Isopropyithioxanthone obtainable from Ward Blenkinsop.

8. Ethoxy Propylene Glycol Ether obtainable from B.P.

Chemicals.

9. Curlout* Plus is a modified acrylic solution polymer obtainable from American Carbonyl Inc.

Alcoprint* PTF is an acrylic copolymer in mineral oil thickner obtainable from Allied Colloids.

11. Alcoprint* PHL is a humectant and surfactant blend obtainable from Allied Colloids.

12. Alcoprint* PSJ is a silicone emulsion softner/lubricant obtainable from Allied Colloids.

13. T.P.G.D.A. is a Tripropylene Glycol Diacrylate obtainable from Degussa.

Claims (8)

1. A printing ink for silk screen printing, characterised in that the screen printing ink is a water-based ink that is wholly or partially curable by irradiation and comprises an emulsion of an unsaturated acrylate resin disposed in water, said resin comprising a polyester acrylate resin or an epoxy acrylate resin or a mixture of said acrylate resins.

2. A screen printing ink according to Claim 1 characterised in that the emulsion has said resin wholly or substantially in dispersed phase and wholly or substantially insoluble in water, the water being the continuous phase of the emulsion.

3. A screen printing ink according to Claim 1 or Claim 2, characterised in that said resin comprises to 60% of the emulsion.

4. A screen printing ink according to any one of S the preceding Claims, characterised in that said resin is 50% of the emulsion. 20 5. A screen printing ink according to any one of the preceding Claims comprising one or more photoinitiators and being partially curable by irradiation comprising electromagnetic radiations in the ultra-violet light waveband.

6. A screen printing ink according to any one of Claims 1 to 4, characterised in that said ink is curable by irradiation with an electron beam. S7. A printing ink according substantially to that S. of Example 1.

8. A printing ink according substantially to that of Example 2. i ~1 April A 1988 PCT/GB 87/005 -13-

9. A printing ink according substantially to that of Example 3. A printing ink according substantially to that of Example 4.

11. A printing ink according substantially to that of Example IUniedSUBSTT ,;ntE SHEETOfflca SUBSTITUIE SHEET -11=t S-i SMALL106 i-04/88 ,x INTERNATIONAL SEARCH REPORT International Application No PCT/GB 87/00540 1. CLASSIFICATION OF SUBJECT MATTER (it several classification symools Apply, indicate &Ill According to Internationai Patent Classification (IPC) or to both National Classification and IPC 'PC 4: C 09 D 11/10 II. FIELDS SEARCHED Minimum Documentation Searched Classification System I Classification Symbols IPC 4 C09 D B 41 M Documentation Searched other than Minimum Documentation to the Extent that such Documents are Inciuded In the Fields Searched III. DOCUMENTS CONSIDERED TO UE RELE VANT Category I Citation ot Document, 11 with indication, where appropriate, ot the relevant passages Is Reievantt to Claim No. '3 X US, A, 3574617 (MARTIN SKOULTCHI) 13 April 1971 see abstract; claims 1,5; column 5, 1-4,7 lines 36-38; column 6, lines 70-73 X WO, A, 82/02894 (STAYBOND PTY.) 2 September 1982 see abstract; page 2, line 13 end; 1 1,7,8 ps.gOs 18-19, example 13 A EP, A, 0026313 (BAYER) 8 April 1981157 see abstract; page 17, lines 4-81-, A US, A, 4374670 (ROBERT J. SLOCOMBE) 22 February 1983 see claims 1,7 1-4,7 A EP, A, 0111138 (BAYER) 20 June 1984 see abstract; page 12, line 11 end 1-8 A US, A, 4280888 (RICHARD W. BUSH) 28 July 1981 *Speciai categories of cited documents: Is T' later document published after the International filing date document defining the general state of the art which is not or priority date and not in conlict with the application but cosrd tbefpatclreevnecited understand the principle or theory uttoefing the consdere tobe o Paticuar elevnceInventio~n earlier document but published on osr after the International douetopaiclreevneth came ivnin flgdate '*dcmn fPriua r~vne h lie neto cannot be considered novel or cannot be considered to L' document which may throw doubts on prior"tveaimr(s) or involve ant inventive step *hic h is cited to establish the publication date of another document of particular relevance;' the claimed invention Citation or other special reason (as speified) cannot be considered to Involve an Inventive atop when the document referring to an oral disclosure, uea, exhibition or document is combined with one or more other such docu- other means toents, such combination being islivious to a person "iled document published prior to the Intermational fing date but In the art. later than the priority date claimed document member ot the same patent familyi IV. CERTIFICATION Date of the Actual Completion of the International Search Date of Mailing of this International Search Report 28th October 1987 2 4 NOV 1987 International Searching Authority Signature of Authorized o EUROPEANI PATENT' OFFICE H YAN MOL Form PCTIISA1210 (second sheat) (January tIM) "-'AlE LL ~ijSI 0 Pmm -2- Internatina c&.OllcatlifI No. PCT/ GB 87/00540 Ill. DOCUMENTS CONSIDERED 10 SE RELEVANT ICONTINUED FROM THE SE1CONID SHEET) Categiory C'tstoi o, Oowanwit. with wijton. wexats appropiate. of thisele~ivant passaes Relevant to Claim No FR, A, 2124501 (BAYER) 22 September 1972 Form PCT ISA 210 (extra ghost) (j~fiUieY 165) ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL APPLICATION NO. PCT/GB 87/00540 (SA 18128) This Annex lists the patent family members relating to the patent documents cited in the above-mentioned international search report. The members are as contained in the European Patent Office EDP file on 10/11/87 The European Patent Office is in no way liable for these particulars which are merely given for the purpose of information. Patent document Publication Patent family Publication cited in search date member(s) date report US-A- 3574617 13/04/71 US-A- 3429852 25/02/69 GB-A- 1167683 22/10/69 DE-A,B,C 1768083 23/03/72 WO-A- 8202894 02/09/82 None EP-A- 0026313 08/04/81 DE-A- 2936039 02/04/81 JP-A- 56038316 13/04/81 US-A- 4339566 13/07/82 US-A- 4374670 22/02/83 US-A- 4414354 08/11/83 EP-A- 0111138 20/06/84 DE-A- 3241264 10/05/84 US-A- 4280888 28/07/81 None FR-A- 2124501 22/09/72 NL-A- 7201314 08/08/72 DE-A- 2105179 10/08/72 GB-A- 1348951 27/03/74 AT-A,B 313929 15/02/74 CH-A- 572967 27/02/76 BE-A- 778971 04/08/72 For more details about this annex see Official Journal of the European Patent Office, No. 12/82 L