GB2263255A - Fount solution for lithographic printing - Google Patents

Abstract

Fount solutions, useful in lithographic printing processes, comprise water and an ester of a monohydric carboxylic acid. The ester serves as an alcohol substitute and/or a hydrotrope and preferably has the general formula: <IMAGE> wherein R1 is a C1, to C4 alkyl or alkenyl group and R2 is a substituted or unsubstituted alkyl, alkenyl, carbocyclic heterocyclic or aralkyl group.

Description

Fount Solutions and Printing Methods Musing the Same The present invention relates to printing processes and in particular to planographic printing processes.

Planographic printing plates, such as lithographic plates, comprise image regions and non-image regions which are essentially co-planar. The image regions are formed from a hydrophobic, oleophilic material. Greasy printing inks are attracted to these regions. The nonimage regions are formed from a hydrophilic, oleophobic material from which the greasy printing ink is repelled. Thus, on application of the greasy printing ink to the printing plate, the ink is attracted to, and retained on, the image areas and repelled from the nonimage areas. The ink can thus be transferred from the printing plate to the printing substrate to produce an image on the printing substrate corresponding to the image areas of the printing plate.

The printing plate may, for example, be provided by photomechanical means wherein a hydrophilic substrate (such as a metal sheet) is coated with a layer of radiation sensitive material. The coating of radiation sensitive material is such that, on imagewise exposure of the coating to radiation, a solubility differential is provided between the exposed and nonexposed areas. Treatment of the coating with a suitable developer solution causes the more soluble areas to be removed to reveal the underlying substrate whilst the less soluble areas of the coating are retained on the substrate Thus, the substrate forms the non-image areas and the exposed and developed coating which remains on the substrate forms the image areas.

A fount solution is conventionally used to assist in maintaining the hydrophilic properties of the nonimage areas of the printing plate and to prevent scumming of the ink into the non-image areas. It is usual to use a polar liquid for this purpose, and water itself may perform satisfactorily as a fount solution for a short time. An aqueous solution including various performance enhancing additives is more commonly used as a fount solution. The performance of the fount solution is optimised to ensure that the solution is repelled by the image areas and is retained on and wets the non-image areas of the plate.

Additives may also be used to control the interaction of the fount solution with the ink and the substrate.

Known additives include aqueous electrolytes, surfactants and water soluble polymers.

Various methods have been employed to apply the fount solution to the printing plate. In many conventional lithographic presses, the means used to apply the fount solution (the dampening system) is entirely separate from the means used to apply the printing ink. In an example of such a method, the fount solution is transferred from a reservoir by a first roller, which is partially immersed in the fount solution, to a second ductor roller. The ductor roller transfers the fount solution (directly or indirectly) to the form rollers which contact the printing plate.

The ductor roller oscillates between the first roller and the form rollers (or their precursors) so that contact with each is intermittent, whereby the amount of fount solution which is applied to the plate can be controlled. In alternative methods which attempt to avoid transfer of ink from the printing plate to the dampening system, the fount solution is transferred from the first roller to a brush roller. When rotating the brush roller "flicks" droplets of the fount solution onto the form rollers or directly onto the printing plate. Similarly, nozzles can be used to spray a fine mist of fount solution onto the plate or the form rollers.

In a further alternative method, the printing plate is contacted only by the inked form rollers. The fount solution must then be transferred from the dampening system to the printing plate via one or more inked rollers.

In particular in the latter method it has been common practice to include in the fount solution as much as 308 by volume of an alcohol, in particular isopropyl alcohol, which is effective to solubilise better the surfactant and to lower the surface tension of the fount solution, thereby to increase its wetting action in the non-image areas. Other advantages of the inclusion of an alcohol in the fount solution may include greater operating latitude of the printing press, brighter ink colour, better image reproduction, better control of emulsification of the ink and fount solution, lower overall damping requirements, improved ink drying, drier stock and more consistent clean-up.

However, health, safety, environmental and cost requirements now determine that the use of such alcohols is unacceptable. It is also known that in some cases the alcohol may attack the printing image areas. Thus, alternatives for the alcohol are sought.

A number of materials have been suggested as replacements for isopropyl alcohol in fount solutions.

However, these can, in general, perform only some of the functions of isopropyl alcohol. Additives such as 2-butoxy ethanol and ethylene glycol have been used.

U.S. Patent 3,877,372 describes a fount solution which includes 2-butoxy ethanol and at least one of hexylene glycol and ethylene glycol, a silicone glycol copolymer and a defoamer type surfactant. U.S. Patent 4,378,467 describes an isopropyl alcohol-free fount solution which includes an additive having a surface tension less than about 0.05 Newton/metre (50 dynes/cm) such as n-hexoxydiethylene glycol (n-hexyl cellosolve), nhexoxydiethylene glycol (n-hexyl carbitol), 2-ethyl1,3-hexanediol, n-butoxyethylene glycolacetate, nbutoxydiethylene-glycolacetate, 3-butoxypropan-2-ol and mixtures thereof. U.S. Patent 4,560,410 describes a fount solution containing a mixture of a polyol and/or glycol ether partially soluble in water with a polyol and/or glycol ether completely soluble in water.

The use of higher boiling solvents such as glycols, glycol ethers and glycol ether acetates as alcohol substitutes in fount solutions has been said to result in a higher dynamic surface tension because of the limited solubility of the surfactants in these systems. The higher dynamic surface tension has been considered to reduce the performance and effectiveness of the fount solution due to decreased wetting action at press speeds. In addition certain fount solution concentrate systems containing alcohol substitute systems cannot be supplied in a one step form because of precipitation of one or more components when mixed with the alcohol substitutes. This type of one-step fount solution concentrate is desirable because of the simplicity of metering it on existing dilution equipment.

Further, known fount solutions commonly contain alcohol and alcohol substitutes in order to dissolve surfactants in an aqueous system. It would be desirable to be able to dissolve surfactants in an aqueous system while eliminating or reducing alcohol or alcohol substitutes to avoid the environmental problems they cause as well as the lithographic problems caused by their evaporation, and to avoid the costs involved in the storage and safe use of such volatile and/or flammable materials.

European patent application No. 0 251 621 teaches that the content of alcohol or alcohol substitutes in fount solutions can be minimised by the inclusion in the fount solution of particular hydrotropes. These hydrotropes are said to increase the solubility of surfactants in the fount solution and this is considered to reduce the dynamic surface tension and to enhance the wetting action of the fount solution. In the corresponding US patent No. 4,854,969 the surfactants are required to have an HLB value (the "hydrophilic-lipophilic balance") within the range of from 1 to 8.

British patent No. 1 492 529 describes a treatment solution for lithographic printing plates which is intended to: a) remove a protective coating from the surface of the plate b) promote ink receptivity in the image areas c) promote water receptivity in the non-image areas The treatment solution is required to include (i) a solvent for removing the protective coating (ii) a desensitising agent for promoting water receptivity in the non-image areas (iii) a humectant for maintaining water receptivity in the non-image areas and (iv) a high boiling point solvent for promoting ink receptivity in the image areas. Ethyl lactate is suggested as a suitable high boiling point solvent.

The treatment solution of GB 1 492 529 is purely concerned with the treatment of lithographic printing plates prepared by inscription with an electrical stylus and is used exclusively immediately after the inscription of the plate. Thus, the treatment solution of GB 1 492 529 does not function as a fount solution, which is continually applied to the plate during printing.

The inventors have found that fount solutions including esters of monohydric carboxylic acids have surprising and unexpected advantages. In particular, the inventors have found that the inclusion of such esters in a fount solution can (a) reduce the surface tension of the solution (b) assist in the control of the ink/water balance (c) reduce or obviate the requirement for an alcohol by, in particular, (i) allowing the non-image to image contrast to be maintained at an acceptable level (ii) allowing faster start-up of the printing press, (iii) allowing greater control of damping.

In suitably formulated fount solutions, such esters can also function as a hydrotrope.

Accordingly, one aspect of the present invention provides a fount solution for a lithographic printing process, comprising in admixture (a) water, and (b) at least one ester having the general formula

wherein R1 is a C1 to C4 alkyl or alkenyl group and R2 is a substituted or unsubstituted alkyl, alkenyl, carboxylic heterocyclic or aralkyl group.

In preferred embodiments of the invention, R1 and R2 are alkyl; particularly preferably R1 represents a C2 alkyl and R2 is methyl ethyl, propyl or butyl. In a particularly preferred embodiment, the ester is ethyl lactate (ethyl 2-hydroxypropanoate). It is, of course essential that the ester is water soluble.

Further aspects of the present invention comprehend methods of lithographic printing employing a fount solution in accordance with the first aspect of the invention as a dampening agent.

Still further aspects of the present invention relate to the use of an ester having the general formula

where R1 and R2 are as hereinabove defined in fount solutions for lithographic printing. Particular embodiments relate to the use of such esters respectively as a hydrotrope or an alcohol substitute.

By the incorporation of various additives, the fount solution of the present invention may be formulated to allow the ester to function as an alcohol substitute, as a hydrotrope, or as both an alcohol substitute and a hydrotrope. Thus, where the ester functions as a hydrotrope, in addition to water (which is preferably demineralised), and the ester, the fount solution will preferably include: i) A corrosion inhibitor; The choice of corrosion inhibitor is not limited, but a preferred material is tolyltriazole in an amount of, for example, up to 10% w/v of the solution ii) Surfactant or Wetting Agent; Various commercial surfactant may be employed, a preferred example being Surfynol 465, in an amount of up to 10%. (Surfynol 465 is an ethylene oxide adduct of 2,4,7,9 tetramethyl-5-decyn -4,9-diol. Surfynol is a trade mark of Air Products and Chemicals Inc.).

iii) Desensitising agent; this additive acts to promote water receptivity in the non-image areas and is preferably present in an amount of from 0.5t to 20%. A preferred desensitising agent is Dextrin, but other suitable agents include sodium carboxymethylcellulose, gum arabic, mesquite gum, guar gum, karaya gum and gum tragacanth.

iv) Film Former; Suitable film formers include glycerine and sorbitol. The film former is preferably present in an amount of up to 20%.

Optionally, where the ester in the fount solutions of the present invention functions as a hydrotrope, the fount solutions may further include: v) A Buffer System; The inclusion of a buffer system is particularly desirable and the system will preferably comprise a salt and an acid. A pH of about 4.9 is preferred and the salt and the acid are preferably each present in an amount of from 1% to 10%. Suitable salts include trisodium citrate, sodium glycolate, sodium lactate, disodium hydrogen phosphate, dipotassium hydrogenphosphate and tripotassium citrate.

Suitable acids include phosphoric acid, lactic acid, acetic acid, nitric acid, glycolic acid and sulphuric acid.

vi) Sequestrant; This acts to sequester any salts which might otherwise build up.

Suitable sequestrants include borax, sodium hexametaphosphate (Calgon R) and salts of EDTA (ethylene diamine tetraacetic acid).

Preferably, the sequestrant is present in an amount of up to 10%.

vii) Bactericide; The choice of bactericide is not particularly limited and an amount of up to 10% may be included. Preferred bactericides include Bacteron B6 and Kathon 886. General preservatives such as dimethoxane, phenol, sodium salicylate and the like can also be used.

Other additives which may usefully be incorporated into these fount solutions include anti-foaming agents and dyes, such as are generally known in the art.

In the above fount solutions, the ester is preferably included in an amount of from 0.05% to 60%.

An amount of about 11% is particularly preferred.

Whilst functioning as a hydrotrope in the fount solutions of the present invention, the ester acts to solubilise the corrosion inhibitor, to give clarity to the solution, to prevent separation of the components of the solution and to increase storage stability.

Furthermore, the cloud point of the surfactant may be increased. Unlike other hydrotropes, the ester used in the fount solutions of the present invention can achieve the above without promoting the generation of foam on the press.

Where the ester functions as an alcohol substitute, in addition to water (preferably demineralised) and the ester, the fount solution will preferably include: i) Desensitising agent; The desensitising agent is preferably present in an amount of from 0.5% to 20% and preferred agents include sodium carboxymethyl cellulose, gum arabic, mesquite gum, guar gum, karaya gum and gum tragacanth.

ii) Surfactant; The choice of surfactant is not limited and the amount of surfactant included is preferably up to 10%. A particularly preferred surfactant comprises a block co-polymer of ethylene oxide and propylene oxide having an HLB value in the range of from 11 to 13. Other suitable surfactants include alkyl phosphates, ethoxylated alcohols, fatty acids, amines, amides, fatty acid esters alkanol amides, glycol esters, sorbitan fatty acid esters, ethoxylated alkylphenols, ethoxylated acetylenic glycols, acetylenic carbinols, ethoxylated acetylenic carbinols, acetylenic glycols, 2,4,7,9-tetramethyl-5 decyne-4,7-diol, 3, 5-dimethyl-1-hexyn-3-ol, block copolymers of propylene oxide, ethylene oxide and ethylenediamine, silicone glycols, silicone alkylene oxide copolymers, although this list is not exhaustive.Mixtures thereof may also be used.

iii) Hydrotrope; the hydrotrope can serve to assist in solubilising the desensitising agent and the surfactant and can help to desensitise the non-image areas.

Preferably the hydrotrope is included in a ratio of approximately 20:1 with regard to the surfactant. Sodium xylene sulphonate is a particularly preferred hydrotrope; other suitable hydrotropes include sodium toluene sulphonate, sodium cumene sulphonate, ammonium xylene sulphonate, tetrabutyl ammonium hydrogen sulphonate, tetraphenyl phosphonium bromide, tetrabutylammonium bromide, cetyl trimethyl ammonium bromide, sodium thiocyanate, sodium terpene sulphonates, ammonium toluene sulphonate, ammonium cumene sulphonate and mixtures thereof.

The ester, functioning as an alcohol substitutelis preferably present in an amount of from 0.05% to 60%. Particularly preferred are the methyl, ethyl, propyl and butyl esters of lactic acid. Aryl, aralkyl and heterocyclic derivatives of lactic acid are also suitable.

Optionally, where the ester in the fount solutions of the present invention functions as an alcohol substitute, the fount solution may further include: iv) A Buffer system; A preferred buffer system includes citric acid as the acid and trisodium citrate as the salt. Such a system is effective to reduce the degree of hydrolysis of the ester of the invention.

Other suitable buffer systems, the preferred pH and the amounts of each component are as specified for the case where the ester of the invention acts as a hydrotrope.

v) Sequestrant; suitable sequestrants include sodium hexametaphosphate (Calgon R), potassium hexametaphosphate, tetrasodium borate, EDTA and diethylene triamine pentaacetic acid.

vi) Bactericide; suitable bactericides and the preferred amounts are as those specified above above for the case where the ester of the present invention acts as a hydrotrope.

vii) A further desensitising agent; suitable examples include polyvinylphosphonic acid and Cyanomer P21 (an acrylic polymer).

Corrosion inhibitors, anti-foaming agents, dyes and the like may also be included.

It will be appreciated that although the fount solutions of the present invention have been described for the cases where the ester acts either as a hydrotrope or as an alcohol substitute, the invention is not limited to such cases. In particular formulations, the ester may act as both an alcohol substitute and a hydrotrope, and one function may, or may not, be dominant.

The fount solutions of the present invention may be used on a wide variety of lithographic printing apparatus. Particular examples include those sold under the trade names Dahlgren, Roland, Miehlematic, Harris Duotron, Komorimatic, Alcolor and Millermatic.

The fount solutions of the present invention may, as is customary in the art, be supplied as a fount solution concentrate which is diluted before use. All quantities in this specification refer to the fount solution concentrates. The concentrates are then diluted with water to form working strength solutions containing from 0.5% to 60t weight/volume of the concentrate.

The following formulations are illustrative of the fount solutions of the present invention: ExamDle 1 In this formulation, the ester (ethyl lactate) acts primarily as a hydrotrope.

Ethyl lactate 11% v/v Surfynol 465 0.5% v/v Dextrin 4% w/v Glycerine 5% v/v Tolyltriazole 1% w/v Trisodium citrate 4% w/v Anhydrous citric acid 3.66% w/v Borax 4% w/v Bacteron B6 3% v/v the remainder being demineralised water and incidental impurities.

Example 2 In this formulation, the ester (ethyl lactate) acts primarily as an alcohol substitute Ethyl lactate 28.5% v/v Demineralised Water 48.9% v/v CMC 397 (carboxymethyl 5.78 w/v cellulose) Cyanomer P21 0.57% w/v Supronic B25 0.5% v/v Sodium Citrate 2.28% w/v Citric Acid 1.14% w/v Sodium Xylene Sulphonate 11.42% w/v (30% in demineralised water) Bacteron B6 0.85% v/v Calgon R 0.14% w/v Supronic B25 is an ethylene oxide/propylene oxide block copolymer with an HLB value greater than 8 (believed to be about 11).

Example 3 In this formulation, the ester (ethyl lactate) acts primarily as a hydrotrope Ethyl lactate 11.5t v/v Surfynol 465 0.5% v/v Sodium carboxymethyl cellulose 2.5 w/v Sorbitol 5% v/v Tolyltriazole 1% w/v Sodium glycolate 4% w/v Lactic acid 3.5% w/v Calgon R 4% w/v Kathon 886 0.5 v/v the remainder being demineralised water and incidental impurities.

Example 4 In this formulation, the ester (propyl lactate) acts primarily as a hydrotrope Propyl lactate 11% v/v Surfynol 465 0.5t v/v Dextrin 4% w/v Sorbitol 5% v/v Tolyltriazole 1% w/v Trisodium citrate 4% w/v Anhydrous citric acid 3.5% w/v Borax 4% Kathon 886 0.5% the remainder being demineralised water and incidental impurities.

Example 5 In this formulation, the ester (ethyl-3hydroxybutyrate) acts primarily as a hydrotrope Ethyl-3-hydroxybutyrate 15% v/v Surfynol 465 1% v/v Dextrin 3.5% w/v Glycerine 4% v/v Tolyltriazole 1% w/v Disodium hydrogen phosphate 4% w/v Phosphoric acid 1.5% v/v Sodium EDTA 3.5 w/v Bacteron B6 3% v/v the remainder being demineralised water and incidental impurities.

Example 6 In this formulation, the ester (ethyl lactate) acts primarily as an alcohol substitute Ethyl lactate 27% v/v Gum arabic 5% w/v Polyvinylphosphonic acid 1% v/v Supronic B25 0.5t v/v Sodium citrate 2.5% w/v Anhydrous citric acid 1% w/v Sodium toluene sulphonate 11% w/v Sodium toluene sulphonate 11% w/v (30% demineralised in water) Kathon 886 0.5% v/v Tetrasodium borate 1% w/v the remainder being demineralised water and incidental impurities.

Example 7 In this formulation, the ester (methyl lactate) acts primarily as an alcohol substitute Methyl lactate 30% v/v CMC 397 6% w/v Cyanomer P21 0.5% w/v Supronic B25 0.5% v/v Di sodium hydrogen phosphate 3% w/v Phosphoric acid 1% v/v Sodium xylene sulphonate 10% w/v (30% demineralised in water) Bacteron B6 1% v/v Calgon R 0.5% w/v the remainder being demineralised water and incidental impurities.

Example 8 In this formulation, the ester (butyl lactate) acts primarily as an alcohol substitute.

Butyl lactate 25% v/v CMC 397 6% w/v Cyanomer P21 0.5% w/v 3,5-Dimethyl-1-hexyn-3-ol 1% v/v Sodium citrate 3% w/v Anhydrous citric acid 1.5% w/v Sodium xylene sulphonate 11.5% w/v (30t demineralised in water) Bacteron B6 1% v/v Calgon R 0.5% w/v the remainder being demineralised water and incidental impurities.

Claims (24)

CLAIMS:

1. A fount solution for a lithographic printing process comprising in admixture a) water and b) at least one ester, having the general formula:

wherein R1 is a C1 to Cq alkyl or alkenyl group and R2 is a substituted or unsubstituted alkyl, alkenyl, carbocyclic, heterocyclic or aralkyl group.

2. A fount solution as claimed in claim 1 wherein groups R1 and R2 are alkyl groups.

3. A fount solution as claimed in claim 1 or 2 wherein R1 is C2 alkyl and R2 is a methyl, ethyl, propyl or butyl group.

4. A fount solution as claimed in any of claims 1 to 3 wherein the ester is present in an amount of from 0.05% to 60t.

5. A fount solution as claimed in any of claims 1 to 4 which further includes a surfactant and/or a desensitising agent.

6. A fount solution as claimed in any of claims 1 to 5 wherein the ester acts as a hydrotrope.

7. A fount solution as claimed in any of claims 1 to 5 wherein the ester acts as an alcohol substitute.

8. A fount solution as claimed in any of claims 1 to 5 wherein the ester acts as both a hydrotrope and an alcohol substitute.

9. A fount solution as claimed in any of claims 1 to 6 which further includes a corrosion inhibitor and/or a film former.

10. A fount solution as claimed in claim 9 wherein the corrosion inhibitor is tolyltriazole.

11. A fount solution as claimed in claim 5 or any of claims 6,9 or 10 when dependent on claim 5 wherein the surfactant is an ethylene oxide adduct of 2,4,7,9tetramethyl-5-decyn-4,9-diol.

12. A fount solution as claimed in claim 5 or any of claims 6,9,10 or 11 when dependent on claim 5 wherein the desensitising agent is dextrin, sodium carboxymethylcellulose, gum arabic, mesquite gum, guar gum, karaya gum or gum tragacanth.

13. A fount solution as claimed in any of claims 9 to 12 wherein the film former is glycerine or sorbitol.

14. A fount solution as claimed in any of claims 6 or 9 to 13 which further includes a buffer system, a sequestrant and a bactericide.

15. A fount solution as claimed in any of claims 1 to 5 or 7 which further includes a hydrotrope.

16. A fount solution as claimed in claim 15 when dependent on claims 7 and 5 wherein the desensitising agent is sodium carboxymethylcellulose, gum arabic, mesquite gum, guar gum, karaya gum or gum tragacanth.

17. A fount solution as claimed in claim 15, when dependent on claims 7 and 5, or 16 wherein the surfactant is a block copolymer of ethylene oxide and propylene oxide having an HLB value in the range of from 11 to 13, an alkyl phosphate, an ethylated alcohol, a fatty acid, an amine, an amide, a fatty acid ester, an alkanolamide, a glycol ester, a sorbitan fatty acid ester, an ethoxylated alkylphhenol, an ethoxylated acetylenic glycol, an acetylenic carbinol, an ethoxylated acetylenic carbinol, an acetylenic glycol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 3,5dimethyl-l-hexyn-3-ol, a block copolymer of propylene oxide, ethylene oxide and ethylenediamine, a silicone glycol, a silicone alkylene oxide copolymer, or a mixture thereof.

18. A fount solution as claimed in claim 15,16 or 17 wherein the hydrotrope is sodium xylene sulphonate, sodium toluene sulphonate, sodium cumene sulphonate, ammonium xylene sulphonate, tetrabutylammonium hydrogen sulphonate, tetraphenylphosphonium bromide, tetrabutylammonium bromide, cetyl trimethylammonium bromide, sodium thiocyanate, sodium terpene sulphonate, ammonium toluene sulphonate, ammonium cumene sulphonate, or a mixture thereof.

19. A fount solution as claimed in any of claims 15 to 18 which further includes one or more of a buffer system, a sequestrant, a bactericide and a further desensitising agent.

20. A fount solution as claimed in any preceding claim wherein the ester is ethyl-2-hydroxypropanoate.

21. A lithographic printing process including the step of applying to a printing plate a fount solution as claimed in any preceding claim.

22. A printed article when produced by the process of claim 21.

23. A fount solution as claimed in claim 1 substantially as herein described with reference to the accompanying examples.

24. Use of a solution comprising, in admixture (a) water, and (b) at least one ester having the general formula

wherein R1 and R2 have the meanings specified in claim 1, as a fount solution in a lithographic printing process.