GB2323560A

GB2323560A - Fount solution concentrate

Info

Publication number: GB2323560A
Application number: GB9706041A
Authority: GB
Inventors: Stephen Richard Coals; Susan Elizabeth Scammell
Original assignee: HYDRO DYNAMIC PRODUCTS PLC
Current assignee: HYDRO DYNAMIC PRODUCTS PLC
Priority date: 1997-03-24
Filing date: 1997-03-24
Publication date: 1998-09-30
Also published as: GB9706041D0

Abstract

A fount solution concentrate which is effective in maintaining the required hydrophillic properties of non-image areas of lithographic printing plates and removes the need for separate dosing of isopropyl alcohol (IPA) to aqueous fount solutions, comprising a solution of IPA in which is dissolved quantities of a buffer, a desensitising agent and a biocide, the density of the solution being between 0.7 and 0.9 g/cc.

Description

PRINTING PROCESSES This invention relates to printing processes and more especially to lithographic printing processes.

Printing plates used in lithographic printing processes include generally co-planar image and non-image areas. The image areas are formed from a hydrophobic material to which oil based printing inks are attracted. The non-image areas are formed from a hydrophillic material from which oil based printing inks are repelled. Thus on application of printing ink to a printing plate, the ink is repelled from the non-image areas and attracted to and retained on the image areas. The ink is transferred from the printing plate onto a contacting offset roller or blanket which transfers the image to paper or board.

A water based dampening solution known as a fount solution is employed to assist retention of the hydrophillic properties of the non-image areas to repel ink. The fount solution is normally an aqueous solution which includes various performance enhancing additives to assist repulsion of oil-based ink from the image areas and to ensure that fount solution is retained on and wets the non-image areas of the plate. These additives normally include a desensitising agent to help retention of the fount on the non-image area of a plate, a buffer to maintain the pH of the solution at its optimum level, and a biocide to prevent microbial growth. Surfactants may also be added to reduce the surface tension of the fount to enable a thinner fount to be deposited on the plate. This is particularly the case when a roller not covered with an absorbent material is employed. Such a roller may be of rubber on like material. Solutions of isopropyl alcohol (IPA) or the like are conventionally employed to reduce surface tension. Typically additions of IPA are of the order of 10% by volume. Addition of IPA has the added advantage of reducing emulsification of the ink and improving drying because of the rapid evaporation properties of IPA. To avoid unnecessary evaporation and to provide extra control, IPA containing solutions are usually chilled to below 12"C.

For health and environmental reasons, attempts have been made either to avoid the use of IPA or to minimise such use. For practical reasons, IPA is beneficial and is preferred by many printers.

Various methods are conventionally employed to apply fount solutions to printing plates. In many of these methods, fount solution is transferred from a reservoir by a series of cooperating rollers1 one of which is partially immersed in the fount solution and a second of which is in contact with the printing plate. One or more additional rollers may be positioned between these two rollers1 each transferring fount solution one to another whereby the amount of fount solution which is applied to the plate can be controlled.

In an alternative method, fount solution is transferred by means of a brush roller partially immersed in the fount solution. When rotating, the brush roller flicks droplets of the fount solution onto 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.

Conventionally doses of a concentrate of fount solution are added to a bath of aqueous fount solution present in the reservoir. Typically dosing is controlled to ensure a fount concentration of around 2% to 4% by volume in water. These dosages may be effected by timed injections into the reservoir or, for smaller printing presses, by hand. Similarly the required doses of IPA are made to the fount solution within the reservoir, these doses being separate from the fount concentrate doses and conventionally being made in response to changes in the density of the aqueous fount solution. Typically, conventional fount solutions have a density approximating to lgm/cc.

Hitherto, therefore, additions of IPA and fount concentrate have been made separately to the aqueous fount solution within the reservoir.

The present invention sets out to provide an improved process which removes the need for separate dosing equipment and enables less IPA to be employed.

In one aspect, the invention provides a fount solution concentrate which comprises a solution of isopropyl alcohol in which is dissolved quantities of a buffer1 a desensitising agent and a biocide, the density of the solution being between 0.7 and 0.9 g/cc. Preferably, the density approximates to 0.8g/cc.

A density of this order enables the isopropyl alcohol based fount concentrate solution to be dosed to a water based fount solution in respect to changes in the density of the fount solution.

According to the present invention in another aspect there is provided a fount solution concentrate for a lithographic printing process which comprises a solution of isopropyl alcohol in which is dissolved quantities of a buffer, a desensitising agent, and a biocide, the fount concentrate solution containing between 50% and 98% by volume of isopropyl alcohol.

In a preferred embodiment, the fount solution concentrate contains between 60% and 90% of isopropyl alcohol. Alternatively, the content of isopropyl alcohol may be between 65% and 80% by volume.

The buffer may for example be a mix of an acid and an alkali; for example a mix of citric acid and an amine. The desensitivity agent may for example be a cellulose gum derivative soluble in isopropyl alcohol.

The concentrate fount solution may be added in doses to the aqueous fount solution to achieve in the latter a 2% to 4% concentration by volume.

Wetting agents may be added to the concentrate solution to reduce the amount of additions required from, for existing processes, 10% by volume IPA and 2% to 4% by volume fount solution to a total of concentrate solution of 5% by volume. Thus, the amount of IPA is significantly reduced.

By dissolving the various additives in isopropyl alcohol a fount solution concentrate is produced which is effective in maintaining the required hydrophillic properties of non-image areas of printing plates and removes the need for separate dosing of IPA to aqueous fount solutions.

The density of this IPA based concentrate is typically of the order of 0.8g/cc.

IPA based fount concentrate solutions in accordance with the present invention enable only one does to be made to the fount solution, removing the need for separate dosage of IPA or the like and fount concentrate.

Also, because of the relatively low density of the IPA based fount concentrate solution, dosing can readily be effected in response to variations in density of the fount solution to be dosed. Thus, fount concentrate solution doses can automatically be effected as and when the density of the fount solution increases to a level above a set value. The extant density value of the fount solution may, for example, be measured by conventional systems including floats or the like.

In addition to IPA fount solution concentrates in accordance with the invention include, in solution, a buffer, a desensitising agent and a biocide.

As mentioned the buffer preferably comprises an alkaline and an acid. A pH of about 5.5-6.0 is preferred and the salt and the acid are preferably each present in an amount of from 0.5% to 10% weight/volume.

A suitable acid is citric acid. A preferred buffer is a mix of citric acid and an amine.

The desensitising agent acts to promote water receptivity and to prevent or reduce ink receptivity in the non-image areas and is preferably present in an amount of from 0.5% to 20% weight/volume. A preferred desensitising agent is an IPA soluble cellulose gum derivative.

The biocide is added to prevent biological spoilage in the solution.

Up to 10% volume/volume may be included. Preferred biocides include isothiazolinone derivatives.

Other additives which may usefully be added include wetting agents1 film formers, surfactants, anti-foaming or defoaming agents and dyes.

Wetting agents act to prevent ink receptivity in the non-image areas and typically comprise an alkyl sulphate or alkanol. A wetting agent is typically present in an amount of from 0.001% to 10%, preferably from 0.01% to 8% volume/volume.

Fount solutions in accordance with the present invention may be used on a wide variety of lithographic printing apparatus. The formulations of the present invention are, as is customary in the art, supplied as fount solution concentrates which are diluted before use. All quantities discussed above refer to the fount solution concentrates and are based on the total compositions of the concentrates. The concentrates are diluted with water to form working strength solutions containing from 0.1% to 60% weight/volume of concentrate.

The following is illustrative of a fount solution concentrates of the present invention: Example Citric acid 1% Aminomethylpropanol 1% Propan-2-ol 88% Hydroxypropylcellulose 0.2% Bactron BFI 1% Propylene glycol 4% Methoxypropoxypropanol 4% Antarox B50 0.8% It will be appreciated that the foregoing is merely exemplary of printing processors in accordance with the invention and that various modifications can readily be made thereto without departing from the true scope of the invention.

Claims

1. A fount solution concentrate comprising a solution of isopropyl alcohol in which is dissolved quantities of a buffer, a desensitising agent and a biocide, the density of the solution being between 0.7 and 0.9 g/cc.

2. A fount solution concentrate according to claim 1 wherein the density of the solution approximates to 0.8 g/cc.

3. A fount solution concentrate for a lithographic printing process comprising a solution of isopropyl alcohol in which is dissolved quantities of a buffer, a desensitising agent, and a biocide, the fount concentrate solution including between 50% and 98% by volume of isopropyl alcohol.

4. A fount solution concentrate according to claim 3 which includes between 60% and 90% by volume of isopropyl alcohol.

5. A fount solution concentrate according to claim 3 or claim 4 which includes between 65% and 80% by volume of isopropyl alcohol.

6. A fount solution concentrate according to any one of claims 3 to 5 wherein the buffer maintains the pH at about 5.5-6.0.

7. A fount solution concentrate according to any one of claims 3 to 6 wherein the buffer includes a salt and an acid.

8. A fount solution concentrate according to claim 7 wherein the buffer includes a salt and an acid at between 0.5% to 10% weight/volume.

9. A fount solution concentrate according to claim 7 or claim 8 wherein the buffer includes citric acid and an amine.

10. A fount solution concentrate according to any one of claims 3 to 9 which includes between 0.5% to 20% weight/volume of desensitising agent.

11. A fount solution concentrate according to any one of claims 3 to 10 wherein the desensitising agent is a cellulose gum derivative which is soluble in isopropyl alcohol.

1 2. A fount solution concentrate according to any one of claims 3 to 11 which includes up to 10% volume/volume of biocide.

1 3. A fount solution concentrate according to any one of claims 3 to 1 2 wherein the biocide is an isothiazolinone derivative.

14. A fount solution concentrate according to any one of the preceding claims which further includes wetting agents, film formers, surfactants, anti-foaming and/or defoaming agents and dyes.

1 5. A fount solution concentrate according to claim 14 wherein the fount solution concentrate further includes a wetting agent.

1 6. A fount solution concentrate according to claim 1 5 wherein the wetting agent is an alkyl sulphate or alkanol.

1 7. A fount solution concentrate according to claim 1 5 or claim 1 6 wherein the wetting agent is included at between 0.001% to 10% volume/volume.

18. A fount solution concentrate according to claim 17 wherein the wetting agent is included at between 0.01% to 8% volume/volume.

19. A fount solution concentrate according to any one of the preceding claims including citric acid, aminomethylpropanol, propan-2-ol, hydroxypropylcellulose, propylene glycol, and methoxypropoxypropanol.

20. A fount solution concentrate according to claim 1 9 including citric acid at 1%, aminomethylpropanol at 1%, propan-2-ol at 88%, hydroxypropylcellulose at 0.2%, propylene glycol at 4%, and methoxypropoxypropanol at 4% volume/volume.

21. A fount solution concentrate according to any one of the preceding claims which is effective in maintaining the required hydrophillic properties of non-image areas of printing plates and removes the need for separate dosing of IPA to aqueous fount solutions.

22. A fount solution concentrate as herein described and with reference to the accompanying example.

23. A fount solution obtained by diluting a fount solution concentrate as defined in claim 22.

24. A fount solution according to claim 23 including from 0. 1% to 60% weightivolume of concentrate.