Some Modern Inks

Pro­gress in the improve­ment of print­ers’ mater­i­als is nowadays so rap­id that it is highly import­ant for the print­er to keep in touch with mod­ern devel­op­ments in the basic mater­i­als of the trade. The main advances in print­ing ink tech­no­logy have been the pro­gress­ive improve­ment of col­ours, var­nishes, grind­ing meth­ods, etc.; the intro­duc­tion of out­stand­ing prop­er­ties in com­monly used inks; and the dis­cov­ery of entirely new types of inks. These notes are inten­ded to give a few mod­ern lines.

Blacks

The aim of the ink maker is to pro­duce inks which can be used straight from the tin without hav­ing to be doped by the addi­tion of boiled oil, driers or sim­il­ar mater­i­als. A first-class black should, without incor­por­a­tion of any oth­er mater­i­al, pos­sess the fol­low­ing properties:

• High dens­ity and bril­liance of colour.
• Suf­fi­cient soft­ness and free­dom from tack to pre­vent pluck­ing and pick­ing of the paper.
• Rap­id dry­ing on the paper but slow dry­ing on the machine, so that the ink remains wet for 24 hours, or prefer­ably 50 hours, on the rollers.
• Such con­sist­ency and tex­ture that it feeds well without hanging back in the duct, and does not fill up half-tones.
• Speed of pen­et­ra­tion so that the print does not set-off, even under the pres­sure of a con­sid­er­able pile of super­im­posed sheets.
• Quick hard set­ting, enabling back­ing up to be done soon after printing.
• Free­dom from spray, even on high-speed presses.
• Applic­ab­il­ity to a wide vari­ety of dif­fer­ent papers.

With regard to the last point, we all know that dif­fer­ent classes of paper behave dif­fer­ently with the same ink. It is easy to for­mu­late an ink which does not set off on one paper yet sets off markedly on anoth­er. Real­iz­ing that the print­er­’s choice of paper is often lim­ited by prac­tic­al con­sid­er­a­tions, the ink maker so for­mu­lates his stand­ard lines that they are usable on as many dif­fer­ent papers as possible.

The mod­ern intro­duc­tion of high-speed presses has led to the mak­ing of spe­cial inks for these machines. An ink which has giv­en excel­lent res­ults on a com­par­at­ively slow machine may spray badly when it is tried out on a fast-run­ning one.

Dur­ing the past year or two, much atten­tion has been paid to improv­ing the set­ting of blacks and pre­vent­ing set-off. There are now obtain­able some new blacks, the phys­ic­al prop­er­ties of which are such that there is a very rap­id and firm set on the paper, allow­ing of quick back­ing up, while set-off* is eliminated.

Non-skinning Bronze Blues

It is rarely indeed that the ink maker puts into his bronze blue inks any driers such as cobalt, man­ganese or lead. This is because the bronze blue pig­ment is itself a power­ful drier, and being, of course, present in very high pro­por­tion, causes rap­id dry­ing and skinning.

Expressed dif­fer­ently, bronze blue, like cobalt, man­ganese and lead driers, is a cata­lyst for the reac­tion between lin­seed oil var­nish and oxygen—that is, bronze blue is a sub­stance which increases the rate at which the lin­seed oil var­nish, which is present in the ink, com­bines with the oxy­gen in the air to pro­duce a dry film. Cata­lysts are used for quick­en­ing up many chem­ic­al processes.

When the print­er requires a bronze blue ink which will not skin on the rollers in, say, two days, the ink maker is faced with a prob­lem of a dif­fer­ent type from the usu­al prob­lem of driers. It is, of course, impossible to reduce effect­ively the bronze blue which is at once the pig­ment and the drier. Tiie prob­lem is best solved by using a sub­stance, known as a “neg­at­ive cata­lyst,” which behaves in the oppos­ite way to an ordin­ary cata­lyst; the neg­at­ive cata­lyst reduces the rate at which the ink skins. By using the right neg­at­ive cata­lyst in suit­able pro­por­tion (only a very little is required), it is pos­sible to pro­duce a bronze blue of bril­liant lustre which will not skin or dry on the rollers even in two days and yet will dry sat­is­fact­or­ily on the paper.

Col­oured News Inks Although col­oured news inks are by no means new, it is only in recent times that they have been used to any large extent for advert­ising pur­poses. Good qual­ity col­oured news inks, which work well and do not fill up even on long runs, are now obtain­able at a price suited to news­pa­per work, and it is prob­able that the near future will see a con­sid­er­able increase in the amount of col­oured advertisements.

Aniline Inks and Syrups

Anil­ine inks are being widely employed nowadays with good res­ults. These inks con­sist essen­tially of dyes dis­solved in methyl­ated spir­it, while oth­er ingredi­ents are added to impart fast­ness to water, bright­ness, etc., and to pre­vent excess­ive dry­ing on the rollers.

Anil­ine inks are much used in paper bag and sim­il­ar man­u­fac­ture. The dry­ing of the inks is mainly depend­ent on the rate of absorp­tion and evap­or­a­tion of the volat­ile spir­it, and since this is very fast, the prin­ted sheet can pass dir­ectly from the rub­ber ste­reo to be pro­cessed into the com­pleted bag.

Gen­er­ally, a good anil­ine ink will be found suit­able for most papers, but there are a few excep­tions. For print­ing on kraft paper, for instance, spe­cial anilines are gen­er­ally required in order to obtain the max­im­um bright­ness of col­our. Spe­cial sur­faces like tin­foil and cel­lo­phane also require spe­cial inks for best results.

Where trans­port charges become con­sid­er­able, as is the case with expor­ted inks, anil­ine syr­ups may be used instead of anil­ine inks. These syr­ups are so made that when one part of the syr­up is mixed with two (some­times three) parts of methyl­ated spir­it, the res­ult­is an anil­ine ink. The stronger syr­ups (those to be mixed with three parts of spir­it per one part syr­up) are so con­cen­trated that, in the case of some (not all) col­ours, the syr­up may be rather too vis­cous and may not imme­di­ately mix with the spir­it. It is, there­fore, recom­men­ded that those syr­ups, which are con­vert­ible by adding two parts of spir­it to one of syr­up, should be used, as these nev­er give trouble on mix­ing. These lat­ter syr­ups are of course cheaper.

Spe­cial syr­ups are obtain­able for use on kraft papers.

Letterpress Inks for Non-absorbent Surfaces

A little may per­haps be said about let­ter­press print­ing of black and col­oured inks on sur­faces such as cel­lo­phane, cel­lu­loid and glassine. Inks for these mater­i­als dry almost entirely by oxidation—there is prac­tic­ally no dry­ing by absorp­tion or evap­or­a­tion. Con­sequently spe­cial quick-dry­ing var­nishes are used.

The print­er should care­fully avoid the intro­duc­tion of any non-dry­ing ingredi­ents into such inks. For instance, in wash­ing up pre­vi­ous to a run, par­tic­u­lar .care should be taken to remove traces of wash-up liquid from the rollers and the forme. If the print­ing were done on ordin­ary papers, the pres­ence of a little non-dry­ing liquid would not mat­ter so much— although here, too, there is an ele­ment of danger. On non-absorb­ent papers, how­ever, the danger is con­sid­er­ably increased, because the non-dry­ing liquid remains with the ink on the sur­face and may ser­i­ously hamper the harden­ing of the print.

Gold and Silver Letterpress and Photogravure Inks

When the first exper­i­ments were made towards pro­du­cing metal­lic let­ter­press inks, the main dif­fi­culty was to com­bine the desir­able prop­er­ties of res­ist­ance to rub­bing, extremely high lustre, and non-dry­ing on the machine dur­ing print­ing. A very large amount of work was in fact done on this prob­lem, with the res­ult that excep­tion­ally bril­liant inks which do not wipe off, or oth­er­wise mis­be­have, are on the market.

More recently, metal­lic pho­to­grav­ures have been intro­duced, and the efforts of ink makers’ labor­at­or­ies have res­ul­ted in the avail­ab­il­ity of very bright, firmly-adher­ing metal­lic grav­ures which work well on the machine.

Overprinting Varnishes

As is well known, there are two main types of over­print­ing var­nishes, one con­tain­ing a pro­por­tion of volat­ile liquid such as methyl­ated spir­it or tur­pen­tine, and the oth­er com­posed entirely of non-volat­ile ingredi­ents. Although the former type is excel­lent as far as it goes, it is prob­able that it will be increas­ingly dis­placed by the non-volat­ile var­nishes. These lat­ter are easy of applic­a­tion, being print­able in much the same way as ordin­ary let­ter­press inks; they can also be safely used to over­print many col­ours which would bleed in a methyl­ated spir­it varnish.

Research has been in the dir­ec­tion of increas­ing the gloss and improv­ing the work­ing qual­it­ies of the over­print­ing var­nish. Some mod­ern pre­par­a­tions are quite soft and eas­ily work­able, and yield a hard, smooth film of extremely high gloss, not only when applied to a dry non-absorb­ent ink lay­er, but also when prin­ted dir­ectly on to the paper. Col­oured over­print­ing var­nishes are also available.

Odourless Inks and Varnishes

For some pur­poses, par­tic­u­larly for print­ing on food wrap­pers, it is some­times advis­able to use an ink hav­ing as little odour as pos­sible. Var­nishes made in the ordin­ary way pos­sess a slight smell which is impar­ted to inks made from them.

There are two meth­ods of pro­du­cing an ink which does not pos­sess the smell of ordin­ary var­nish. Either there can be incor­por­ated with the ink a small quant­ity of a per­fume which sat­is­fact­or­ily masks the oth­er smells, or odour­less var­nishes (made by spe­cial pro­cesses) can be used. Both meth­ods can be combined.

Offset and Litho Inks

Improve­ments in off­set and litho inks have included the increas­ing of the water res­ist­ance and the strength of col­our. For—good qual­ity off­set work, par­tic­u­larly where in com­pet­i­tion with pho­to­grav­ure pro­cesses, great col­our intens­ity of the ink is, of course, highly desir­able, since the film of ink in the off­set print is so thin.

One type of mod­ern off­set ink con­tains spe­cial water-insol­uble dyestuffs in addi­tion to the usu­al pig­ments, a device which res­ults in great col­our strength and quite sat­is­fact­ory res­ist­ance to water.

Washing Up—Ink Removers

A vari­ety of good ink removers have been in use for a long time and are well known, but a point of which many are unaware is that there are spe­cial removers for dry ink. A roller or type face which con­tains patches of dry ink will require a con­sid­er­able amount of labor­i­ous scrub­bing with an ordin­ary ink remover before it is clean, but with spe­cial solvents or solvent mix­tures, it is only neces­sary to moisten the sur­face. After a few minutes the power­ful action of the solvent uproots the dry film. Some­times it may be prefer­able to remove the worst of the dry film with the spe­cial solvent and then to fin­ish off with an ordin­ary ink remover. In this way, the clean­ing of dry ink can be done in a tenth of the time usu­ally employed. Of course, the solvent does not injure the roller or type face in any way.

With regard to the clean­ing of ordin­ary anil­ine inks from the machine, methyl­ated spir­it is the stand­ard medi­um for this pur­pose. The best anilines do not dry on the rollers too quickly, but if the rollers or oth­er parts have been left inky overnight, it may be desir­able to wet the sur­face with a spe­cial anil­ine ink remover before fin­ish­ing off the clean­ing with methyl­ated spirit.

This art­icle from the Brit­ish Print­er, 1934 and writ­ten by J. D. Cohen, BSc, AIC