GB2436329A - Screenless photolithography ink attracting composition - Google Patents

Abstract

An ink attracting composition for use with a photolithography plate, comprising a black pigment powder admixed with an oil carrier; an asphaltum solution; and a solvent. A method of continuous tone printing is also described in which the ink attracting composition is applied to a developed pre-sensitised printing plate prior to printing.

Description

<p>TITLE: SCREENLESS PHOTOLITHOGRAPHY</p>

<p>DESCRIPTION</p>

<p>The present invention relates to screenless photolithography, and particularly to a priming solution or ::::. tincture used in a screenless photolithography process to S..... enable reproduction of fine detail or micro-imagery' in : *" continuous tone prints. S...</p>

<p>In 1978, Mr. L.E. Lawson published a paper on * screenless photolithography, and included the following S...</p>

<p>brief description of a litho-grained positive method of screenless offset platemaking using (at the time) general purpose commercially available pre-sensitised plates. A film positive is obtained direct from a negative of an original image or indirectly from the original image itself. Quoting from Mr. Lawson's paper: "For some purposes, camera positives can be generated without masking, although masking is to be recommended.</p>

<p>Rather obviously, exposure and processing needs to be carefully carried out to achieve the required densities, if optimum results are required, appropriately monitored auto-film processing being used if possible. The image on the final positive should have the right reading when emulsioned down and, as near as possible, in accordance with predetermined patch density requirements.</p>

<p>A grained and preferably anodised aluminium sheet, factory coated with suitable positive working resinous image material possessing a shelf life of at least several months, is carefully exposed beneath the continuous-tone positive transparency. Any conventional platemaking illuminant is used, preferably in a well designed reflector to maximise the uniformity of the illumination, and the whole operation is carried out in stringent yellow safe- ::::. light conditions (i.e. a room completely devoid of day I...</p>

<p>S..,,' light and illuminated solely by tungsten or gold' : ** fluorescent tubes). Unlike conventional litho platemaking, S...</p>

<p>:, 20 the degree of exposure is critical, needing to be * sufficient to just retain the palest image in the lightest S...</p>

<p>tones after processing. The use of burn-out or similar masking is essential to ensure perfectly clean surrounds." "The exposed plate is developed on a time and temperature basis, similar to that used by photographers.</p>

<p>An appropriate developer is used, preferably adapting extended range chemistry -a typical development time is four minutes at 20 C. The temperature and the duration are critical, and a good degree of agitation is required, particularly during the first minute or two. It is possible to use large photographic dishes for preliminary and exploratory purposes, but for more serious commercial work, the best results have been achieved (for good reasons) while using vertical tanks holding substantial volumes of developer and presenting a small surface to the atmosphere.</p>

<p>It is important for plate-makers to realise fully that the developing operation controls the photographic contrast of the image.</p>

<p>After development, the plate is immediately washed and dried. The image can be examined and assessed, or measured (densitometrically), and, if necessary, additional development given. The use of a complementary filter, coloured in relation to that of the unexposed coating, aids the measuring. At this stage, the traditional lithographic ::::. treatment with polymeric desensitising materials is best S...</p>

<p>avoided, and inking of the image carried out. In the early : *.., days of this process, inking was a problem. Even though S...</p>

<p>manual inking was carried out, the exponents had to depend * on the press to ink the plates fully -an operation which *...</p>

<p>wasted at least 100, if not more, copies, and was not always successful. Research indicated that the problem was to get the ink on to the minute image areas located in the small crevices of the plate. This resulted in the innovation of a two-stage inking procedure employing, at the first stage, a special starting or priming lacquer which was applied to the dry bare imaged plate prior to further treatment and conventional wet inking. The satisfactory inked plate is finally protected with a thin layer of water soluble polymer [Ed. or perhaps more correctly, gum Arabic substitute] and either stored or used immediately.</p>

<p>Although precise control is essential during the platemaking, the basic operation is more simple, if not more reliable, than that of deep-etch methods. However, the need to maintain the correct tone values and plate contrast necessitates the platemaker controlling the developing operation very accurately. it is best dealt with by using appropriate continuous-tone control patches.</p>

<p>Presswise, the successful anodised versions of these plates requires only normal care and are surprisingly rugged. Experience suggests that one can expect to obtain in the region of 50,000 good copies from such a plate, ::::. operating in average printing conditions, and it is this I...</p>

<p>general performance which has convinced several : *.., lithographic printers that the technique is worth serious S...</p>

<p>consideration. it appears that its success is due to the image being located in the recesses of the anodised grain S..</p>

<p>and protected by the peaks of the anodised grain." "Investigation has found that the image elements which form the highlights of a successful screenless' plate rest in the pits of the grained surface and that these elements are close to 14 microns in diameter. Not only are these small elements spaced further apart than occurs with fine screen half-tone, thus contributing to the delicacy and subtlety of the lighter tones, this very small size is known to be readily printable." The present inventor worked with Mr. Lawson but does not know the formulation of Mr. Lawson's printing lacquer mentioned in his paper and it was apparently never made public. Furthermore, it is believed that composition of the printing lacquer can no longer be verified following the cessation of Mr. Lawson's research into continuous tone lithography, with only the present inventor left to persevere with the technique, and adapting it to suit the exacting requirements of the fine art field as opposed to the commercial world. It is within this context that the present inventor has developed the printing solution of the present invention.</p>

<p>In conventional lithography, priming lithographic plates with ink-attracting compositions prior to inking of ::::. the plates is nothing new. For example, in the case of grained zinc plates, asphaltum dissolved in olive oil and : **., turpentine then dried on the plate is used to encourage ink S...</p>

<p>onto the printing plate. However, such known compositions * as well as commercially available lacquers are unsuitable S...</p>

<p>for reproducing finest image information stored in the photolithographic plates, particularly those of anodised aluminium which are commercially available at this time.</p>

<p>In accordance with a first aspect of the present invention, there is provided an ink attracting composition for use with a photolithography plate, comprising: a black pigment powder admixed with an oil carrier; an asphaltum solution; and a solvent.</p>

<p>The present applicant is aware that the viscosity of the ink attracting composition is an important consideration. The ink attracting composition needs to have sufficient fluidity to reach finest image information stored in the photolithographic plate, but without being too fluid as to have insufficient strength to attract ink consistently from the printing rollers (which would give uneven and imprecise results). The presence of the oil carrier and solvent in the ink attracting composition means that care is required to prevent performance degradation with time due to unintentional thickening. For example, the ink attracting solvent should be stored in an airtight container when not in use.</p>

<p>The black pigment powder may be ivory black or equivalent such as bone black, or charcoal black. The ::::. black pigment is used to define tonally the image on the S...</p>

<p>photolithographic plate, acting as an intermediate visual : *** guide. The powder is preferably finely ground. In this S...</p>

<p>:, 20 way, the pigment can be carried to small crevices or pits * in the photolithographic plate. It is believed the black I...</p>

<p>pigment powder is effective with colour printing, not just black and white printing.</p>

<p>The oil carrier may be a natural oil such as linseed oil. Linseed oil is noted as a component binding agent in specialist lithographic inks, where it holds pigment particles in suspension at controllable viscosity (in this case to combine in admixture with the asphaltum solution).</p>

<p>It also has a good quality of adhering to metal surfaces such as aluminium or zinc printing plates. The linseed oil may be pre-boiled. The black pigment is admixed with the oil carrier to form a paste. The paste may comprise about 30 grams of finely ground ivory black pigment per lOOml of boiled linseed oil (or oz per 50m1).</p>

<p>The asphaltum solution comprises powdered asphaltum in a solvent, for example turpentine substitute. The powdered asphaltum is preferably finely ground. Asphaltum solution is a known traditional lithographic product used particularly in aluminium and zinc plate lithography where plates are ball grained. Typically only made by companies specialising in fine art printing products, its components are fine grain asphaltum powder, olive oil and pure spirits of turpentine. The olive oil and the pure turpentine are combined with the asphalum powder to form a liquid solution :.. of approximately 14 Beaume in liquidity. The asphaltum Is..</p>

<p>solution may help to make the printing image on the plate : *. permanently ink receptive and protect the print detail. a...</p>

<p>*, 20 The asphaltum solution may be mixed to a volume ratio of * about 3:1 with the black pigment/oil carrier paste. Thus, I...</p>

<p>ml of asphaltum solution may be blended with SOmi of the paste.</p>

<p>The solvent is used to produce a fluid composition that has the ability to penetrate the bottom of the printing grain of anodised aluminium plates and be able to receive or attract the fluid printing ink during printing, and remain in situ until completion of printing. The solvent may be turpentine substitute, which is neither too volatile nor too greasy. The solvent may be mixed in a volume ratio of about 3:2 with the asphaltum solution and black pigment/oil carrier paste. Thus, 300m1 of turpentine substitute may be blended with a mixture comprising l5Oml of asphaltum solution and 50m1 of the black pigment and oil carrier paste.</p>

<p>In accordance with another aspect of the present invention, there is provided a process for producing a continuous tone print of a continuous tone image, comprising the steps of: providing a continuous tone film positive of the continuous tone image; exposing a pre- sensitised printing plate to light through the continuous film positive to transfer image information to the pre-sensitised printing plate; developing the pre-sensitised printing plate to fix image information transferred thereto :.-. by exposing to light; and lithographically printing the continuous tone print using the developed pre-sensitised :.. printing plate; characterised by applying an ink attracting composition as hereinbefore defined to the developed pre-sensitised printing plate prior to printing.</p>

<p>The ink attracting composition may be applied to the developed pre-sensitised printing plate by rubbing, for example with a lint-free soft cloth using light pressure.</p>

<p>The pre-sensitised printing plate is preferably an anodised aluminium plate.</p>

<p>An embodiment of the invention will now be described with reference to the following example.</p>

<p>An ink-attracting composition was prepared from the following components: finely ground ivory black pigment 14.2g boiled linseed oil 50m1 asphaltum solution (finely ground in pure turpentine) l5Oml The boiled linseed oil and black pigment are mixed together first, and then the asphaltum solution is gradually added. Finally, the turpentine substitute is added to the mixture. The whole mixture is put through a micro-sieve to ensure absence of any course particles and kept in an airtight container in a cool temperature until required.</p>

<p>The resulting composition is rubbed with a lint-free soft cloth, using light pressure in the image areas of an exposed and developed pre-sensitised photolithographic I.e.</p>

<p>plate (in this case, an anodised aluminium plate with a : ** photo-polymer coating). Any volatile residue is driven off I...</p>

<p>by gently heating the plate-surface with an industrial air * drier, and any unwanted composition on the plate is removed with a mixture of gum Arabic substitute solution and water, or other modern substitute gum solution, prior to damping and inking the plate for printing. In this way, a correct replication of the image is obtained. The composition enables exceptional printing of detail and provides excellent longevity of run with edition printing.</p>

Claims (1)

1. <p>CLLIMS</p>

   <p>1. An ink attracting composition for use with a photolithography plate, comprising: a black pigment powder admixed with an oil carrier; an asphaltum solution; and a solvent.</p>

   <p>2. An ink attracting composition according to claim 1, in which the black pigment powder is selected from the group consisting of ivory black, bone black, and charcoal black.</p>

   <p>3. An ink attracting composition according to any : ***. 15 preceding claim, in which the powder is finely ground. S...</p>

   <p>4. An ink attracting composition according to any preceding claim, in which the oil carrier is a natural oil. 5..</p>

   <p>S</p>

   <p>* 20 5. An ink attracting composition according to any S...</p>

   <p>preceding claim, in which the natural oil is linseed oil.</p>

   <p>6. An ink attracting composition according to claim 5, in which the linseed oil is pre-boiled.</p>

   <p>7. An ink attracting composition according to any preceding claim, in which the black pigment is admixed with the oil carrier to form a paste.</p>

   <p>8. An ink attracting composition according to claim 7, in which the paste may comprise about 30 grams of finely ground ivory black pigment per lOOmi of boiled linseed oil.</p>

   <p>9. An ink attracting composition according to any preceding claim, in which the asphaltum solution comprises powdered asphaltum in a solvent.</p>

   <p>10. An ink attracting composition according to claim 9, in which the powdered asphaltum is finely ground.</p>

   <p>11. An ink attracting composition according to any one of claims 9 or 10, in which the solvent is turpentine * S. * . S 55S5 * S I...</p>

   <p>12. An ink attracting composition according to claim 11, in which the turpentine substitute is neither too volatile a..</p>

   <p>nor too greasy. * SI</p>

   <p>* . 20 5..</p>

   <p>13. An ink attracting composition according to claim 10, in which the solvent is pure spirits of turpentine and in which the asphaltum solution further comprises olive oil.</p>

   <p>14. An ink attracting composition according to claim 13, in which the olive oil and the pure turpentine are combined with the asphalum powder to form a liquid solution of approximately 14 Beaume in liquidity.</p>

   <p>15. An ink attracting composition according to any one of claims 7 to 14, in which the asphaltum solution is mixed to a volume ratio of about 3:1 with the black pigment/oil carrier paste.</p>

   <p>16. An ink attracting composition according to claim 15, in which 150m1 of asphaltum solution is blended with 50m1 of the paste.</p>

   <p>17. An ink attracting composition according to any one of claims 7 to 16, in which the solvent may be mixed in a volume ratio of about 3:2 with the asphaltum solution and black pigment/oil carrier paste. * S.</p>

   <p>18. An ink attracting composition according to claim 17, S...</p>

   <p>when dependent on claim 11 via claim 16, in which 300m1 of * S. * a * turpentine substitute may be blended with a mixture S..</p>

   <p>* comprising l5Oml of asphaltum solution and 50m1 of the * . black pigment and oil carrier paste. S. IS * S S * S</p>

   <p>19. A process for producing a continuous tone print of a continuous tone image, comprising the steps of: providing a continuous tone film positive of the continuous tone image; exposing a pre- sensitised printing plate to light through the continuous film positive to transfer image information to the pre-sensitised printing plate; developing the pre-sensitised printing plate to fix image information transferred thereto by exposing to light; and lithographically printing the continuous tone print using the developed pre-sensitised printing plate; characterised by applying an ink attracting composition according to any preceding claim to the developed pre-sensitised printing plate prior to printing.</p>

   <p>20. A process according to claim 19, in which the ink attracting composition is applied to the developed pre-sensitised printing plate by rubbing, for example with a lint-free soft cloth using light pressure.</p>

   <p>21. A process according to any one of claims 19 or 20, in * ** * I S **S* which the pre-sens.tised printing plate is an anodised * * *SSS aluminium plate. * S. * S S S... * *5*</p>

   <p>S S.. * S</p>

   <p>SSS S. SI</p>

   <p>S S S</p>

   <p>S I</p>