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