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INK

An ink is a liquid containing various pigments and/or dyes used for coloring a surface to produce

an image or text. Ink is used for drawing or writing with a pen or brush or quill. Thicker inks, inpaste form, are used extensively in letterpress and lithographicprinting.

Ink is a complex medium, comprised of solvents, pigments, dyes, resins, lubricants, solubilizers,

particulate matter, fluorescers, and other materials. The components of inks serve manypurposes; the inks vehicle, colorants, and other additives are used to control flow, thickness, andappearance of the ink when dry.

TYPES OF INK

Early varieties include Egyptian ink, various natural dyes made from metals, the husk or outer

covering of beans or seeds, and sea creatures like the squid (known as sepia). India ink is blackand originated in Asia. Walnut ink and iron gall ink are thought to have been used by many of the

old masters for drawing. However, there is no proof of this. Walnut Inks, if they were used, wouldhave faded fairly quickly.

Pigmented inks

Pigmented inks contain other agents that ensure adhesion of the pigment to the surface and

prevent it from being removed by mechanical abrasion. These materials are typically referred toas resins (in solvent-based inks) or binding agents (in water-based inks).

Pigmented inks are advantageous when printing on paper because the pigment stays on thesurface of the paper. This is desirable because more ink on the surface means that less ink needs

to be used to create the same intensity of color.

Pigments are the main components of ink, containing the different colors. The size of the pigment

is very important for the ability to diffuse in the solution inks. Qualities such as hue, saturation,

and brightness or lightness are inherent in the ink, and vary dependent on the source and type ofpigment.

Dyes in inks

Dye-based inks are generally much stronger than pigment-based inks and can produce muchmore color of a given density per unit of mass. However, because dyes are dissolved in the liquid

phase, they have a tendency to soak into paper, thus making the ink less efficient and alsopotentially allowing the ink to bleed at the edges of an image, producing poor quality printing.

To circumvent this problem, dye-based inks are made with solvents that dry rapidly or are usedwith quick-drying methods of printing, such as blowing hot air on the fresh print. Other methods

include harder paper sizing and more specialized paper coatings. The latter is particularly suitedto inks used in non-industrial settings (which must conform to tighter toxicity and emission

controls), such as inkjet printer inks. Another technique involves coating the paper with a chargedcoating. If the dye has the opposite charge, it is attracted to and retained by this coating, while

the solvent soaks into the paper. Cellulose, the material that paper is made of, is naturallycharged, and so a compound that complexes with both the dye and the papers surface will aid

retention at the surface. Such a compound in common use in ink-jet printing inks is polyvinylpyrrolidone.
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An additional advantage of dye-based ink systems is that the dye molecules interact chemicallywith other ink ingredients. This means that they can benefit more than pigmented ink from optical

brighteners and color-enhancing agents designed to increase the intensity and appearance ofdyes. Because dyes get their color from the interaction ofelectrons in their molecules, the way in

which the electrons can move is determined by the charge and extent of electron delocalization inthe other ink ingredients. The color emerges as a function of the light energy that falls on the

dye. Thus, if an optical brightener or color enhancer absorbs light energy and emits it through or

with the dye, the appearance changes, as the spectrum of light re-emitted to the observerchanges.

A disadvantage of dye-based inks is that they can be more susceptible to fading, especially when

exposed to ultraviolet radiation as in sunlight.

History of ink

Approximately 5000 years ago, an ink for blacking the raised surfaces of pictures and textscarved in stone was developed in China. This early ink was a mixture of soot from pine smoke,

lamp oil, and gelatin from animal skins and musk. Other early cultures also developed manycolors of ink from available berries, plants and minerals.

In an article for the Christian Science Monitor, Sharon J. Huntington describes these otherhistorical inks:

About 1,600 years ago, a popular ink recipe was created. The recipe was used forcenturies. Iron salts, such as ferrous sulfate (made by treating iron with sulfuric

acid), was mixed with tannin from gallnuts (they grow on trees) and a thickener.When first put to paper, this ink is bluish-black. Over time it fades to a dull brown.

Scribes in medievalEurope (about AD 800 to 1500) wrote on sheepskin parchment.One 12th century ink recipe called for hawthorn branches to be cut in the spring and

left to dry. Then the bark was pounded from the branches and soaked in water foreight days. The water was boiled until it thickened and turned black. Wine was

added during boiling. The ink was poured into special bags and hung in the sun.Once dried, the mixture was mixed with wine and iron salt over a fire to make the

final ink.

In the 15th century, a new type of ink had to be developed in Europe for the printing press by

Johannes Gutenberg. Two types of ink were prevalent at the time: the Greek and Roman writing

ink (soot, glue, and water) and the 12th century variety composed of ferrous sulfate, gall, gum,and water.[1] Neither of these handwriting inks could adhere to printing surfaces without creating

blurs. Eventually an oily, varnish-like ink made of soot, turpentine, and walnut oil was createdspecifically for the printing press.

Modern ink applications

Up until a few years ago, consumers had very little interest in ink other than refills for their pens.Fountain pens became a novelty as the disposable ball point pen took over the market. The

introduction ofhome computing led to home printing. Today, in developed nations, it is rare tofind a residence or a business that does not have a printing capability. As a result, buying ink in

the form of a cartridge or having that cartridge refilled at an inkjet island in a local mall has onceagain become a part of the day-to-day shopping experience, similar to buying a bottle of ink fifty

years ago.
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Ink refilling services for printer cartridges are offered by large, official printing companies as wellas smaller, unofficial refill companies. Customers can often cut printing costs by using refill

services from a refill company, or buying the new non-OEM brands instead of refilling.

Poisonous ink

There is a misconception that ink isnt harmful even if swallowed, but this is false. Once ingested,

ink can be very hazardous to ones health. Certain inks, such as those used in printers, and eventhose found in a common pen can be harmful. Though ink will not cause death, it can cause sideeffects such as a damaged nervous system and severe headaches. These effects are caused by a

chemical known as p-Anisidine, used in the process of creating the inks color and shine. Thepoison control center has stated that any consumption of ink should be reported to a local

hospital or poison control center.

Writing Inks and Preservation

The two most used black writing inks in history are carbon inks and iron and gall inks. Both typescreate problems for preservationists.

Carbon Inks

Carbon inks were commonly made from lampblack or soot and gum arabic. Gum arabic keeps the

carbon particles in suspension and adhered to paper. The carbon particles do not fade over timeeven when in sunlight or bleached. One benefit of carbon ink is that it is not harmful to the paper.

Over time, the ink is chemically stable and therefore does not threaten the strength of the paper.Despite these benefits, carbon ink is not the ideal ink for permanence and ease of preservation.

The ink has a tendency to smudge in humid environments and can be washed off an item. Thebest method of preserving documents written in carbon ink is to ensure it is stored in a dry

environment (Barrow 1972). Recently, carbon inks made from carbon nanotubes have beensuccessfully created. They are similar in composition to the traditional inks in that they use a

polymer to suspend the carbon nanotubes. These inks can be used in inkjet printers and produceelectrically conductive patterns.[2]

Iron Gall Inks

Iron gall inks became prominent in the early 1100s and were used for centuries and thought tobe the best type of ink. However, iron gall ink is corrosive and damages the paper it is on(Waters

1940). Items containing this ink can become brittle and the writing fades to brown. The original

scores ofJohann Sebastian Bach are threatened by the destructive properties of iron gall ink. Themajority of his works are held by the German State Library, and about 25% of those are in

advanced stages of decay (American Libraries 2000). The rate at which the writing fades is basedon several factors, such as the proportions of the ink ingredients, the amount deposited on the

paper, and the composition of the paper (Barrow 1972:16). The corrosion is caused by twomajor degradation processes: acid catalysed hydrolysis and iron(II)-catalysed oxidation of

cellulose (Rouchon-Quillet 2004:389).

Treatment is a controversial subject. There is no treatment that will undo the damage already

caused by the acidic ink. Deterioration can only be stopped or slowed for a period of time. Thereare some people who think it best not to treat the item at all for fear of the consequences. Others

believe that non-aqueous procedures are the best solution. And then, there are some that believean aqueous procedure may provide the answer for preserving items written with iron gall ink.

Aqueous treatments include distilled water at different temperatures, calcium hydroxide, calciumbircarbonate, magnesium carbonate, magnesium bicarbonate, and calcium phytate. There are

many possible side effects from these treatments. There can be mechanical damage, which would
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further weaken the paper. The color of the paper or ink may change and ink may bleed. Otherconsequences that might arise from aqueous treatment are a change of ink texture or the

formation of on the surface of the ink (Reibland & de Groot 1999).

CLASSIFICATION OF INK

INK USED BY US HAS NOTHING IN COMMON WITH THAT OF THE ANCIENTSMANUFACTURERS

OF THE PRESENT TIME HAVE LARGELY UTILIZED FORMULAS EMPLOYED IN PAST CENTURIESTHE COMMON ACCEPTATION OF THE TERM INKSEVEN DIFFERENT CLASSES OF INKS AND

THEIR COMPOSITION BRIEFLY TOLDFAILURE OF EFFORTS TO SECURE A REAL SAFETY INK.

THE inks used by us have nothing in common with those of the ancients except the color andgum, and mighty little of that.

Those of the gall class employed in the fourteenth, fifteenth, sixteenth, seventeenth andeighteenth centuries, some formulas of which are utilized by the manufacturers of ink in our own

time, consisted generally in combination; infusions of nut-galls, sulphate of copper or iron, orboth, and fish-glue or gum, slightly acidulated. The frequent introduction of the so-called added

color into these inks, time has shown to have been a grave mistake.

The common acceptation of the term ink may be said to characterize an immense number offluid compounds, the function of which in connection with a marking instrument is to delineate

conventional signs, characters and letters as put together and commonly called writing, on paper

or like substances.

To classify them would be impossible; but black writing ink, chemical writing fluid, colored writing

ink, copying ink, India ink, secret or sympathetic ink, and indelible ink make seven classes; theothers may be denominated under the head of miscellaneous inks, and of them all, there is no

single ink answering every requirement and few answer at all times the same requirements. Inkmay be either a clear solution of any coloring matter or of coloring matter held in suspension. It

is a remarkable fact that although most inks are chemical compositions and many times madeafter the same formula, identical results cannot always be calculated or obtained. This is more

particularly to be noted in the case of black writing inks otherwise known as the tanno-gallate ofiron inks [gallic and gallotanic acid obtained from nut-galls, sulphate of iron, (green copperas)

and some gummy vehicle].

The variations would appear to be largely due to the difference in quality of the gall-nuts,

treatment, and temperature of the atmosphere; perhaps, however, not so much to-day as it was

ten or twenty years ago, when to make ink of this character boiling processes were employed.Most of them as already stated are now cold made.

Inks of this class consist of a finely divided insoluble precipitate suspended in water by the use of

gum and possessing a slight acidity.

The requisites of a good black writing ink or black writing fluid require it to flow readily from the

pen, to indicate in a short time a black color and to penetrate the paper to an appreciable degree,and more important than all the rest, to be of great durability. When kept in a closed vessel no

sediment of any account should be precipitated, although such will be the case in open ink-wells,and this the quicker the more the air is permitted to get to it. If it is to be used for record or

documentary purposes it must not be altogether obliterated if brought into contact with water oralcohol, and should depend for permanency on its chemical and not on its pigmentary qualities.

The second class, called for distinction chemical writing fluids, possesses the same essentialingredients to be found in class one, but much less in quantity and with some added colored

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substance which I shall term loading, for its real purpose is to cheapen the cost of productionand not altogether as some manufacturers state simply to give them an agreeable color.

Previous to the discovery of the soluble anilines, logwood, indigo, madder, orchil and other dyeingmaterials were used for a period of some eighty years and vanadium for some twenty years (very

costly at that time), for this purpose, but since 1874, and with frequent changes as the newer

aniline compounds were invented, these by-products of coal-tar, as well as logwood, etc., have

been and are to-day employed for loading, or as the manufacturer expresses, it added color.The chemical writing fluids as now prepared, yield when first written a blue or green color with a

tendency to change to black afterwards. They are not as permanent as those of the first class.

Another black ink not durable, however, is logwood; its extract is combined with a little

chromate of potassium and boiled together in water. It possesses its own gum and containssome tannin. In combination with alum and water, it forms a dark purple ink.

The colored writing inks, of which red is the more important, are in great number and withhardly an exception at the present time, manufactured by adding water and water-glass to a

soluble aniline red color. Cochineal which was used for red ink formerly is now almost obsolete.Nigrosine, one of the best known of them, is much used as a cheap black ink, but as it is blue

black and never becomes black, it really belongs to the family of colored writing inks. Theypossess an undeserved popularity for they flow freely from the pen which they do not corrode,

nor do they thicken or spoil in the inkwell; they are however very fugitive in character andshould not be employed for record, legal, monetary or other documentary purposes. The indigo

and 5russian blue inks are well known, the former under certain conditions a very permanent ink,the latter soon disintegrating.

Copying inks are of two kinds, one dependent on the addition of glycerine, sugar, glucose or likecompounds to the black writing inks or chemical writing fluids heretofore mentioned, which are

thereby kept in a moist offsetting condition; the other due to the solubility of the pigmentary colorwith water, such as the aniline inks which are given more body than those for ordinary purposes

and the logwoods in which the pigment is developed and given copying qualities by chemicals,and hence becomes responsive to the application of a sheet of paper dampened with water.

Copying ink should never be used for record purposes as it is affected by changes of thetemperature.

India ink, sometimes called China ink, or as formerly known by the ancients and in classical andlater times Indian ink, is now used more for drawing and engrossing than it is for commercial

purposes. It belongs to the carbon class and in some form was the first one used in the veryearliest times. In China it is applied with a brush or pith of some reed to the rice paper also

there manufactured. It is easily washed away unless bichromate of ammonium or potassium inminute quantities be added to it, and then if the paper on which it appears be exposed for a short

time to the action of the actinic rays of sunlight, this gummy compound will be rendered insolubleand cannot be removed with any fluid, chemical or otherwise. It possesses also great advantages

in drawing, since it acts as a paint, and will give any degree of blackness according to the

quantity of water mixed with it.

Secret or sympathetic inks are invisible until the writing is subjected to a subsequent operation,such as warming or exposing to sunlight. To further aid the object in view, the paper may be first

steeped in a liquid and the writing only made visible by using another liquid which has somechemical affinity with the previous one. The number of this kind were but few but have multiplied

as chemistry progressed. The ancients were acquainted with several modes. Ovid indiscreetlyadvises the Roman wives and maidens if they intend to make their correspondence unreadable to

the wrong persons to write with new milk, which when dried may be rendered visible by rubbing

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ashes upon it or a hot iron. Pliny suggests milky juices of certain plants of which there are aconsiderable variety.

Indelible ink is not used for writing purposes on paper, but is found best adapted for marking linenand cancellation or endorsing purposes. It is chiefly composed of nitrate of silver preparations, to

which heat must be applied after it has been dried; or a pigment is commingled with the same

vehicles used in making common printing ink and in its use treated as such.

Diamonds, gold, silver, platinum and a host of other materials are manufactured into ink and areto be placed under the head of miscellaneous inks. They are in great number and of no interest in

respect to ink writing except for engrossing or illuminating.

Still another ink once held in much esteem and now almost obsolete is the so-called safety ink.

Manufacturers, chemists and laymen in great number for many years wasted money, time andenergy in diligent worship at a secret shrine which could not give the information they sought. A

summary of the meager and barren results they secured is of little value and unimportant. Hence,there is no REAL safety ink.

It is true that lampblack (carbon) as made into ink, resists any chemical or chemicals, but simplewater applied on a soft sponge will soon remove such ink marks. The reason for this is obvious,the ink does not penetrate the paper.

Safety ink which will not respond to acids may be affected by alkalis, or if resisting them

separately, will yield to them in combination.

THE COMPOSITION OF INK

An aqueous ink composition comprising a water-soluble dye having the formula (I) in an amountsufficient for ink printing and water, ##STR1## wherein R.sup.1 and R.sup.2 each represent

hydrogen, a lower alkyl group, a lower alkoxy group or halogen; R.sup.3 represents hydrogen, a

lower alkyl group, a lower alkoxy group, halogen, a sulfonic acid group or a sulfonate group;Z.sup.1 and Z.sup.2 each represent hydrogen, a lower alkyl group, a phenyl group, an acetylgroup, an alkyl sulfonyl group, a benzoyl group which may have a substituent, a benzenesulfonyl

group which may have a substituent, or a 1,3,5-triazine group which may have a substituent; M

represents hydrogen, an alkali metal or NH.sub.4.sup.+ ; and n is an integer of 1 or 2.

10. An aqueous ink composition comprising (i) a water-soluble dye having the formula (I)

in an amount sufficient for ink printing and (ii) water, ##STR28## wherein R.sup.1and R.sup.2 each represent hydrogen, a lower alkyl group, a lower alkoxy group or

halogen; R.sup.3 represents hydrogen, a lower alkyl group, a lower alkoxy group,halogen, a sulfonic acid group or a sulfonate group; Z.sup.1 and Z.sup.2 each

represent hydrogen, a lower alkyl group, a phenyl group, an acetyl group, an alkylsulfonyl group, a benzoyl group which may have a substitutent selected from the group

consisting of a lower alkyl group, a lower alkoxy group and halogen, a benzenesulfonylgroup which may have a substituent selected from the group consisting of a lower alkylgroup, a lower alkoxy group and halogen, or a 1,3,5-triazine group which may have a

substituent selected from the group consisting of an alkyl group, an alkoxy group, a

hydroxyl group, halogen, a hydroxyalkyl amino group, an alkyl amino group and anaromatic amino group; M represents hydrogen, an alkali metal or NH.sub.4.sup.+ ;

and n is an integer of 1 or 2.

2. The aqueous ink composition as claimed in claim 1, wherein the amount of said dyeis in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of said

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aqueous ink composition.

3. The aqueous ink composition as claimed in claim 1, further comprising a humectantselected from the group consisting of a polyhydric alcohol and an alkyl ether thereof,

and the mount of said humectant is in the range of 5 to 80 parts by weight withrespect to 100 parts by weight of said aqueous ink composition.

4. The aqueous ink composition as claimed in claim 1, further comprising a humectantselected from the group consisting of triethanol amine, dimethylformamide, N-methyl-

2-pyrrolidone, 2-pyrrolidone and 1,3-dimethyl imidazolidinone, dimethylformamide andtriethanolamine and the amount of said humectant is in the range of 5 to 80 parts by

weight with respect to 100 parts by weight of said aqueous ink composition.

5. The aqueous ink composition as claimed in claim 1, further comprising a

preservative and anti-mold agent selected from the group consisting of sodiumdehydroacetate, sodium benzoate, 2-pyridine thiol-1-oxide sodium salt and sodium

pentachlorophenol.

6. The aqueous ink composition as claimed in claim 3, wherein said polyhydric alcoholis selected from the group consisting of ethylene glycol, diethylene glycol, triethylene

glycol, polyethylene glycol, polypropylene glycol and glycerin.

7. The aqueous ink composition as claimed in claim 3, wherein said alkyl ether ofpolyhydric alcohol is selected from the group consisting of ethylene glycol monoethyl

ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol

monomethyl ether and triethylene glycol monoethyl ether.

8. The aqueous ink composition as claimed in claim 1, wherein said water-soluble dyeis selected from the group consisting of: ##STR29##

Description:BACKGROUND OF THE INVENTION

The present invention relates to an aqueous ink composition suitable for use as printing ink and

stamping ink in general use, and for use with writing instruments, recording apparatus or the like.More particularly, it relates to an aqueous magenta ink composition for ink-jet printing, which is

capable of yielding printed images with high quality (i.e., high clearness and sharpness, etc.), and

with excellent resistance to water and light, and which is also capable of providing stable inkejection, without causing the plugging of the nozzles of the ink-jet printing apparatus, even if it is

used continuously for a long period of time or it is used intermittently after a period of non-use of

the ink-jet printing apparatus.

Generally, an aqueous ink for ink jet-recording comprises as the main components a dye, ahumectant such as a polyhydric alcohol or an ether thereof, and water, and when necessary,

additives such as an anti-mold agent.

An aqueous ink for use in ink-jet recording should satisfy the following conditions in order to yieldan excellent print over an extended period of time:

First, in order that the ink be compatible with ink droplet formation and control of the direction of

the ejected ink droplet streams, it is necessary that its viscosity, surface tension, specific electricconductivity, and density each fall within certain appropriate ranges.

Second, it is necessary that no precipitates be separated, due to coagulation, precipitation,

chemical change of slightly soluble components or other causes, from the ink during an extended

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period of continuous use or storage, or during the periods when the apparatus is not in use. Norshould the physical properties of the ink otherwise change during the above-mentioned periods. If

the separated solid components or viscous materials in the ink become affixed around thenozzles, or if the physical properties of the ink change, deviating from the predetermined physical

properties achieved at the time of the preparation, the desired recording quality, the desired inkejection stability, and the desired ink ejection response cannot be obtained.

Third, it is necessary that the ink provide adequately high contrast, clearness and the desiredcolor in the printed image, in particular, for use with full-color printers.

Fourth, it is necessary that the ink for ink-jet recording be such that the printed images are

resistant to water, light and physical wear.

Fifth, it is necessary that the images printed by the ink dry rapidly.

In order to satisfy the above first through fourth conditions, it is preferable that the molecular

extinction coefficient of the dye employed in the ink composition be high and the solubility of thedye in water and the humectant be also high.

In the conventional magenta aqueous ink compositions, for example, direct dyes such as C.I.

Direct Red 1, C.I. Direct Red 11, C.I. Direct Red 37, C.I. Direct Red 62, C.I. Direct Red 75, C.I.Direct Red 87, C.I. Direct Red 89, C.I. Direct Red 95, and C.I. Direct Red 227; and acid dyes such

as C.I. Acid Red 1, C.I. Acid Red 8, C.I. Acid Red 87, C.I. Acid Red 94, C.I. Acid Red 115, C.I. AcidRed 131, C.I. Acid Red 144, C.I. Acid Red 152, C.I. Acid Red 154, C.I. Acid Red 186 and C.I. Acid

Red 245 are employed.

However, the ink compositions comprising the direct dyes, when used in ink jet-printing, have theshortcomings that (a) the plugging of the nozzles is caused in the course of continuous printing or

at the time of intermittent use because of the poor solubility of the direct dyes in water and thehumectant, and that (b) the color reproduction is poor. When the aqueous ink compositions

comprising the acidic dyes are employed, the durability of the printed images is unsatisfactorybecause of the poor resistance to light and water.

So far, many proposals have been made for an ink for ink-jet recording, but from the viewpoint of

practical use, a satisfactory ink composition which is capable of meeting the above-describedrequirements has not been found.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a magenta aqueous ink composition

for ink jet recording from which the above discussed conventional shortcomings have beeneliminated, thereby satisfying the above outlined requirements for ink jet-recording. That is to

say, the object of the present invention is to provide a magenta aqueous ink composition for ink-jet recording which does not result in plugging of the nozzles, does not change in quality or

separate precipitates therefrom with time during storage, but exhibits excellent ink-ejection

stability, and has good ink ejection response, shows slight changes in physical properties, if any,when used for a long period with continuous recirculation, or when used intermittently, and yieldsprinted images which are non-spreading, and have high sharpness, high image density, and high

resistance to water and light.

The above object of the present invention is attained by a magenta aqueous ink compositioncomprising a water-soluble dye having the following formula (I) and water, optionally with

addition of a humectant and other additives thereto: ##STR2## wherein R.sup.1 and R.sup.2each represent hydrogen, a lower alkyl group, a lower alkoxy group or halogen; R.sup.3

represents hydrogen, a lower alkyl group, a lower alkoxy group, halogen, a sulfonic acid group or

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a sulfonate group; Z.sub.1 and Z.sup.2 each represent hydrogen, a lower alkyl group, a phenylgroup, an acetyl group, an alkyl sulfonyl group, a benzoyl group which may have a substitutent

selected from the group consisting of a lower alkyl group, a lower alkoxy group and halogen, abenzenesulfonyl group which may have a substituent selected from the group consisting of a

lower alkyl group, a lower alkoxy group and halogen, or a 1,3,5-triazine group which may have asubstituent selected from the group consisting of an alkyl group, an alkoxy group, a hydroxyl

group, halogen, a hydroxyalkyl amino group, an alkyl amino group and an aromatic amino group;

M represents hydrogen, an alkali metal or NH.sub.4.sup.+ ; and n is an integer of 1 or 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, the dye having the above described formula (I) is contained in theaqueous ink composition in a sufficient amount for ink printing. More specifically, it is preferable

that the dye be contained in an amount of 0.5 to 20 parts by weight, more preferably in an

amount of 1.5 to 6 parts by weight, with respect to 100 parts by weight of the ink compositionaccording to the present invention, in order to obtain sufficient coloring performance of the dye as

a colorant and to avoid the precipitation of the dye during an extended period of continuous useand storage or during the periods when the ink-jet printing apparatus is not in use, thereby

preventing the plugging of the nozzles with the precipitates.

Specific examples of the dyes represented by the formula (I) for use in the present invention areas follows:

TABLE 1##STR3##

No. 1

##STR4##No. 2

##STR5##

No. 3##STR6##

No. 4##STR7##

No. 5##STR8##

No. 6##STR9##

No. 7##STR10##

No. 8##STR11##

No. 9##STR12##

No. 10##STR13##

No. 11##STR14##

No. 12##STR15##

No. 13##STR16##

No. 14##STR17##

No. 15

##STR18##

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No. 16##STR19##

No. 17##STR20##

No. 18##STR21##

No. 19

##STR22##No. 20

##STR23##No. 21

##STR24##No. 22

##STR25##

No. 23##STR26##

No. 24##STR27##

No. 25

The above dyes can be synthesized without difficulty. For example, Dye No. 12 can be synthesized

by subjecting N,N-bis(4-aminobenzoyl)-p-phenylenediamine to tetera-azotization by aconventional method, followed by coupling the tetra-azo product with N-(p-toluenesulfonyl) H acid

in mildly alkaline solution.

In the present invention, water is used as a base solvent of the ink composition. For the purposeof adjusting the physical properties of the ink composition so as to have the desired properties, to

control the drying speed of the ink composition and to increase the solubility of the dye employedin the solvent of the ink composition, the following water-soluble organic solvents (humectants)

can be used together with water:

Polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, poly-propylene glycol and glycerin; alkyl ethers of polyhydric alcohols, such as ethylene

glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol

monomethyl ether and triethylene glycol monoethyl ether; and other compounds such as N-

methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl imidazolidinone, dimethylformamide andtriethanolamine.

Of the above mentioned humectants, the most preferable humectants are diethylene glycol,polyethylene glycol (200 to 600), triethylene glycol, ethylene glycol, glycerin and N-methyl-2-

pyrrolidone, by which the solubility of the employed dye in the solvent of the ink composition canbe increased and the evaporation of water from the ink composition can be appropriately

controlled, so that the initial properties of the ink composition can be maintained even for an

extended period of continuous use or storage, or during the periods when the apparatus is not inuse. Thus reliable ink droplet stability and ink droplet ejection response of the ink composition,particularly after a prolonged period of non-use of the apparatus, are obtained.

In the present invention, it is preferable that the above humectant be contained in an amount of 5

to 80 parts by weight, more preferably 10 to 40 parts by weight, with respect to 100 parts byweight of the ink composition according to the present invention, from the viewpoint of obtaining

an appropriate viscosity and drying speed of the ink composition.

In the present invention, in addition to the above humectants, additives, for instance,

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preservative and anti-mold agents, Ph adjustment agents, specific electric conductivityadjustment agents, chelating agents and anti-rusting agents, can be added to the ink

composition.

As preservative and anti-mold agents, for example, sodium dehydroacetate, sodium sorbate, 2-pyridine thiol-1-oxide sodium salt, sodium benzoate and sodium pentachlorophenol can be

employed.

As Ph adjustment agents, any materials can be used optionally, so long as they do not have any

adverse effect on the ink composition and can control the Ph of the ink composition within therange of Ph 9.0 to 11.0. Specific examples of such Ph adjustment agents are amines, such as

diethanolamine and triethanolamine; hydroxides of alkali metals, such as lithium hydroxide,sodium hydroxide and potassium hydroxide; ammonium hydroxide; and carbonates of alkali

metals, such as lithium carbonate, sodium carbonate and potassium carbonate.

As specific electric conductivity adjustment agents, inorganic salts such as potassium chloride,

ammonium chloride, sodium sulfate and sodium carbonate, and water-soluble amines such astriethanolamine can be employed.

As chelating agents, for example, sodium ethylenediaminetetraacetate, trisodium nitrilotriacetate,

hydroxyethyl ethylenediamine trisodium acetate, diethylene triamino pentasodium acetate anduramil disodium acetate can be employed.

As rust preventing agents for the nozzles, for example, acid sulfites, sodium thiosulfate,

ammonium thioglycolate, diisopropyl ammonium nitrite, pentaerythritol tetranitrate anddicyclohexyl ammonium nitrite can be employed.

Other additives, for example, water-soluble ultra-violet-ray-absorbing agents, water-soluble

infrared-ray-absorbing agents, water-soluble polymeric compounds, solubility increasing agentsfor increasing the solubility of the dye dissolved in the solvent of the ink composition, and

surfactants can be employed as thought necessary in specific embodiments of an aqueous inkcomposition for ink-jet recording according to the present invention.

Preferred embodiments of an aqueous ink composition for ink-jet recording according to the

present invention will now be explained by referring to the following examples:

EXAMPLE 1

A mixture of the following components was heated to about 50.degree. C. and stirred until

completely dissolved. The mixture was then filtered twice through a membrane filter with a 0.22

.mu.m mesh, whereby an aqueous ink composition No. 1 according to the present invention wasprepared:

______________________________________wt. %

______________________________________Dye No. 3 in Table 1

3.0Diethylene glycol 15.0

Glycerin 5.0Sodium dehydroacetate

0.1Ion-exchanged water

76.9

______________________________________

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The properties of the thus prepared aqueous ink composition were asfollows:

______________________________________Ph = 10.1 (25.degree. C.)

Viscosity = 1.95 cp (25.degree. C.)

Surface tension = 56.0 dynes/cm (25.degree. C.)Water resistance = 4.8%

(indicated by fading ratio)Light resistance = 8.5%

(indicated by fading ratio)______________________________________

In the above, the water resistance of the ink composition indicated by fading ratio was measured

as follows:

The aqueous ink composition No. 1 was diluted with ion-exchanged water to the extent that theconcentration of Dye No. 3 contained in the ink composition was 1 wt. %. The thus diluted ink

composition was applied to a sheet of high quality paper by use of a doctor blade and was thendried at room temperature for one day to prepare a test sample. Then the density d.sub.o of the

applied ink composition on the paper was measured by a Macbeth densitometer. This test samplewas immersed in water at a temperature of 30.degree. C. for one minute and was then taken out.

Immediately after this, the density d of the ink composition applied on the immersed paper wasmeasured by the Macbeth densitometer. From the above measured d.sub.0 and d.sub.1, the

resistance to water of the ink composition was determined in accordance with the followingformula: ##EQU1##

The result was that the water resistance of the ink composition No. 1 was 4.8% in terms of the

above defined fading ratio.

Likewise, the light resistance of the ink composition No. 1 was measured as follows:

A test sample having an applied ink density d.sub.0 was prepared in the same manner asdescribed above.

This test sample was exposed to the light of a carbon arc lamp by a fade meter at 63.degree. C.for 3 hours and the density d.sub.2 of the ink composition of the test sample was measured by

the Macbeth densitometer. From the d.sub.0 and d.sub.2, the resistance to light of the ink

composition No. 1 was determined by the following formula: ##EQU2##

The result was that the light resistance of the ink composition No. 1 was 8.5% in terms of theabove defined fading ratio.

The aqueous ink composition No. 1 was then subjected to the following ink-jet performance tests:

(1) Image Clarity and Image Dryness Test The ink composition was caused to issue from a nozzlewith an inner diameter of 30 .mu.m, with vibrations at a frequency of 1100 KHz, by which

vibrations the ink composition was ejected in a stream broken into individual drops, and was thencaused to impinge on a sheet of commercially available high quality paper. As a result, clear

images were obtained on each of the sheet. The time required for drying the printed image wasnot more than 10 seconds at normal room temperature and humidity.

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(2) Preservability Test

Samples of the ink composition were tightly sealed in glass containers and subjected to thefollowing storage tests:

a. Preserved at 20.degree. C. for one month;

b. Preserved at 4.degree. C. for one month;

c. Preserved at 20.degree. C. for one year; and

d. Preserved at 90.degree. C. for one week.

Separation of precipitates from the ink composition was not observed at all in storage. In

addition, no changes were detected in the properties or color of the ink composition.

(3) Ink Droplet Ejection Stability Test

Ink-jet recording as was done in the above-described Image Clarity and Image Dryness Test wascontinuously carried out for 1,000 hours. There was no evidence of either clogging of the nozzle

or change in ejection direction of the ink droplets; rather, stable recording was maintained.

(4) Ink Droplet Ejection Response Test

After ink-jet recording was performed as outlined in (1), the apparatus and ink composition wereallowed to stand at at room temperature and humidity for one month, after which they were used

again to perform ink-jet recording under the same conditions as previously stated in (1). As in (3)above, there was no change in the ink droplet ejection stability.

The above test was repeated in the same manner, except that the apparatus and ink were allowed

to stand at 40.degree. C./30% RH for one week, instead of being allowed to stand at roomtemperature and humidity for one month. The result was that again no change was observed in

the ink droplet ejection stability.

EXAMPLE 2

The procedure for Example 1 was repeated except that the formulation of Example 1 was replaced

by the following formulation, whereby an aqueous ink composition No. 2 according to the presentinvention was prepared:

______________________________________

wt. %______________________________________

Dye No. 9 in Table 13.0

Diethylene glycol 15.0Glycerin 5.0

Sodium dehydroacetate0.1

Ion-exchanged water76.9

______________________________________

EXAMPLE 3

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by the following formulation, whereby an aqueous ink composition No. 3 according to the presentinvention was prepared:

______________________________________wt. %

______________________________________Dye No. 12 in Table 1

3.0Diethylene glycol 15.0



76.9______________________________________

EXAMPLE 4

The procedure for Example 1 was repeated except that the formulation of Example 1 was replacedby the following formulation, whereby an aqueous ink composition No. 4 according to the present

invention was prepared:

______________________________________

wt. %______________________________________

Dye No. 22 in Table 13.0

Triethylene glycol10.0

2,2-thiodiethanol10.0

Sodium benzoate 0.2Ion-exchanged water

76.8______________________________________

EXAMPLE 5


by the following formulation, whereby an aqueous ink composition No. 5 for ink-jet recordingaccording to the present invention was prepared:

______________________________________

wt. %______________________________________

Dye No. 25 in Table 1 3.0Polyethylene glycol 200

5.0Triethylene glycol monomethyl ether

15.0Sodium benzoate 0.2

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Ion-exchanged water 76.8______________________________________

COMPARATIVE EXAMPLE 1


by the following formulation, whereby a comparative aqueous ink composition No. 1 wasprepared:

______________________________________

wt. %______________________________________

C.I. Acid Red 35 3.0Diethylene glycol 15.0



76.9

______________________________________



by the following formulation, whereby a comparative aqueous ink composition No. 2 wasprepared.

______________________________________

wt. %______________________________________

C.I. Acid Red 92 3.0Diethylene glycol 15.0



76.9______________________________________



by the following formulation, whereby a comparative aqueous ink composition No. 3 wasprepared:

______________________________________

wt. %______________________________________

C.I. Direct Red 2273.0

Diethylene glycol 15.0Glycerin 5.0

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Sodium dehydroacetate0.1

Ion-exchanged water76.9

______________________________________

The properties of the ink compositions No. 1 through No. 5 according to the present invention andthe comparative ink compositions No. 1 to No. 3 are summarized in Table 2.

TABLE 2

______________________________________Water Light

Surface ResistanceResistance

Ph ViscosityTension (Fading (Fading

(25.degree.(CP) (dyne/cm) Ratio) Ratio)

10. (25.degree. C.)

(25.degree. C.)(%) (%)

______________________________________

Example10.1 1.95 56.0 4.8 8.5

No. 1

Example10.2 1.99 54.5 6.5 7.2

No. 2

Example9.8 2.05 54.5 5.0 10.4

No. 3Example

10.0 1.95 55.5 6.8 10.1No. 4

Example10.2 1.98 54.0 7.5 5.9

No. 5Compar-

9.8 1.98 55.5 20.0 12.8ative

ExampleNo. 1

Compar-10.2 1.88 50.5 40.0 30.0

ativeExample

No. 2Compar-

10.0 2.20 53.0 5.0 15.0ative

ExampleNo. 3

______________________________________

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Aqueous ink compositions No. 2 through No. 5 according to the present invention andcomparative ink compositions No. 1 through No. 3 were also subjected to the same ink droplet

ejection response tests as were done in Example 1.

With respect to aqueous ink compositions No. 2 through No. 5, the same excellent results were

obtained as in Example 1. However, when comparative ink compositions No. 1 through No. 3 wereemployed, the nozzles became partially clogged when the apparatus and ink composition were

allowed to stand at normal room temperature and humidity for one week, and when theapparatus and ink composition were allowed to stand at 40.degree. C./30% RH for three days,

the direction. Of ejected ink droplets became extremely unstable and normal ink-jet recordingwas impossible.

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Technological University of the Philippines

College of Liberal Arts

Graphic Arts and Printing Technology

RESEARCH IN ECONOMICS

INK CORPORATION

GROUP 9

SUBMITTED BY: SUBMITTED TO:

RENZ L. TUGAY MRS. PURISIMA P. PEREDA

KRISTINE JOYCE M. CAHAPAY

JOAN G. RUEDA

ESY PANGANIBAN

TULIO

ERWIN BERJA

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6823634-ink-corp

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