USRE21402E

USRE21402E - Coixoidized vat dyes

Info

Publication number: USRE21402E
Authority: US
Publication date: 1940-03-19

Description

Reissues] Mar. 19, 1940 UNITED STATES PATENT OFFICE COLLOIDIZED VAT DYES No Drawing. Original No. 2,090,511, dated August 17, 1937, Serial No. 17,130, Apr-i118, 1935. Application for reissue January 6, 1940, Serial 14 Claims.

This invention relates to new highly dispersible vat dye powders. Vat dyes are used both for the dyeing of textiles from a dye bath and also particularly for the printing of textiles and other materials using a printing .gum or paste. Other uses of vat dyes are for coloring of plastics, paper and other material. It has been the practice in the past to use vat dyes primarily in the form of pastes and pastes having a reasonably high dispersibility are known. However, there are many disadvantages in the use of pastes and the tendency in recent years has been to develop powders having the advantages that the dye is in concentrated form and therefore when shipped there is no freight to be paid on water and also there is no tendency to freeze or to change characteristics on storage which renders pastes undesirable. Dye powders also permit a very accurate mixing of colors by the dyer, because there is no change in the concentration of the dye due to alterations in the composition of the pastes on standing.

The production of vat dye powders, however, has raised several problems. In the first place most of the powders have not been as rapidly dispersible as the pastes, that is to say when placed in water they have not shown the properties of almost instantaneous dispersion analogous to a soluble solid. An even'more serious drawback has been the fact that the dye particles have tended to agglomerate, which results in a product of low tinctorial power, because of course the coloring effect of an insoluble pigment is of a surface character, that is to say when a number of particles of pigment are agglomerated into a larger agglomerate the particles in the interior of the agglomerate do not have any effect in coloring the products in which the dye is used. This low tinctorial power therefore requires the use of a large amount of dye and what is even more serious, the intensity of the shade obtained even with a larger amount of dye is not as great and the tone is not as brilliant as when'the dye particles are completely dispersed into minute colloidal particles" of the order of size of only a few microns at most.

The agglomeration of dye powders not only adversely affects the tinctorial power, but it also tends to produce spotting or marbled effects, particularly in printing, which are, of course highly undesirable. countered in printing. When textiles are printed, the dye powder ,is incorporated into a suitable printing gum or printing thickening as it is sometimes referred to in the trade, and this paste.-'

' into the fiber.

Another drawback is enmaterial is then applied to the printing rollers and is printed on to the textiles. Theprinting paste always contains in addition to the materials giving it .the necessary thickness and adhesiveness, a reducing agent such as a hydrosuliite. At ordinary temperatures of course the hydrosulfite will not reduce the vat dye particles in the printing gum, but at elevated temperatures this action begins to take place. Therefore after a piece of textile goods has been printed, it issubjected to heat, usually by means of steam in a so-called ager. The high temperature and moist atmosphere cause the hydrosulfite in the printing gum .to reduce a portion of the vat dye to the leuco form and this leuco form then is capable of attaching itself to the fiber or rather being adsorbed therein, so that when the goods are removed from the ager and subjected to oxidation, usually by air, the portion of the dye which has been reduced to the leuco form and which has been adsorbed on the fiber is transformed again into the insoluble colored dye, in which form it can no longer be removed from the fiber by washing. After oxidizing the dye on the fiber, the printing gum is washed off, carrying with it, of course, all of the dye which was not adsorbed The printing process from the standpoint of dye utilization is very inefficient. Normally only a moderate percentage of the dye is actually fastened on to the fiber. The remainder constitutes waste which is disadvantageous from two standpoints. First, the dye which is not actually applied to the fiber is wasted and, secondly, unless a fairly high percentage of the dye prints on to the fiber it is not possible to obtain strong deep shades. Also, unless the dye is to a large percentage reduced and adsorbed on to the fiber, large variations in the amount of dye aflixed to the fiber may easily take place, which of subdivision or dispersion and therefore aremore readily adsorbed into the fiber, which means that a larger percentage of the reduced dye is actually adsorbed into the fiber. A third advantageof fine dispersion is the uniformity of shade which is obtained; Where large agglomerates arepresentwhichareoniypartlyreduced-bythe hydrosulnte andthereducedportionofwhichis onlypartiallyadsorbedontheiibenmtsorpoor shadesarepresent,givingamottiedeffectinthe flnalgoods. Of coursethe largertheamount of dyeadsorbedontheflberwherethedispersicnis veryflneresuitsinahigherflnctorialpojwerand therefore deeper and more brilliant shades.

Whilesmallerdyeparticlesgivegreatertinctorialstrength,thereisalimittoparticleslae andiftheparticluaremadetoosmalltheywill tendtopenetratetoodeeplyintothefabrlcwhich wiilresult'inthecolorappearingonthewrong side of the goods. Sometimes this eifect is so markedthatthewrongsidewillshowaneven.

sired strength with a considerably shortened ag-' ing time and this is of marked importance.

The powders which have been produced in the prior art show varying degrees of autodispersibility,thatis ofdispersioninwater, and they have all hitherto shown a relatively unsatisfactory total dispersion and particle size, particularly in printing gums. Up to the time of the present invention no powder even approached a good,freshly preparedpasteintinctorlal power, m A of shade and efliciency in utilization of the dye. Moreover, the powders of the prior art,

thosewhich show satisfactory autodispersihilityareaisoopentotheveryserious disadvantage that they are highly hygromopic and therefore if exposed to the atmosphere they tend to adsorb moisture andjof course, the advantage of a powder is then lost. Excss hygroscopicity also tends to cause the dye to blend in printing which results in blurred lines. This advantage is very marked in certain dye powders now on the market where in order to obtain high ty apparently a relatively large amount of very ygroscopic dispersing agents are used. These dye powders, while capable of reasonably rapid aging,-will not give sharp prints. It is a marked advantage of the present invention that high dispersibility is obtained without sacrificing of printing. The present invention produces pastes and particularly powders of higher 'dispersibility and much improved tinctorial power. Moreover, the powders of the present invention show no loss in tinctoriai power, autodispersibility or total dispersibility when compared with the corresponding pastes.

The products of the present invention are obtained by deflocculating the dye in the form of a thin paste in a dough mixer which may be of any suitable type capable of handling stiif pastes, such as for example the Werner and Pfleiderer or Day kneading machines or a Banbury mixer, the paste being sufliciently thick and stiff so that it exerts a shearing action on the dye particles, producing a perfect colloidal dispersion or deflocculation and also preferably coating the particles with a thin him of a protective agent sufliciently elastic so that it does not crack off on drying. The defloccuiated paste which may preferably contain the protective agents and, if desired, wetting agents, is thencarefullydriedatalowtemperatureandcan then be pulverized, producing a powder in which theimividmlparticlesareccatedwithpmtectiveagentanddonotanddisperae eitherinwaterorinaprlntinggum,oompletely andperfectly-givingaasperfectas obtainableintheverybestdyepasteamadeinthe priorartwhcnfreshly prepared.

'Thepastesoftheprumtinventionaremperior tothepasteswhichhavebemmadeinthepast.

' yh v l perfectaaswasever obtainedinafreahlymadepasteandthisperiectionofdlspersionisnotlostonstanding. Of couraethepastessharecertainofthedisadvantags common to all pastes, namely,.the tendency tofreeaeinooldweather,thediiiicultyofshipping and the liability to fermentation on standing where fermentable protective agents or diluting agents are present. They do not, however,

the disadvantaga which are inherent in the pastes produced hitherto, namely, the poor keepingqualitiesandtheeflfectonprintlng gums. Contrarytothepastesofthepriorartthepastes of the present inventiondo notsettleonstanding. Theydonotgelorliverandtheydonot undulyincreasethevbcosityoftheprintinggum or thickening, nor do they have a tendency which isundesirable insomc prior artproducts of first lowering the viscosity of printing gum and then on standing raising the viscosity.

It is, of course, important that the viscosity of printing gum remain constant as the whole mechanismofprintingmachinerydependsona \miform printing paste. 'lhe powdered products of the present invention differ from those of the priorart,flrstinthattheyshowperfect total dispersiomthatistosaythereisnodiiference in the dispersion or particle size of the powder when used over that obtained from the best pastes, so that all of the advantages of a powder 'are obtained without any disadvantages which have beeninherent in vat dye powders in the past. A second characteristic of the powders is that they have a very high autodispersibiiity and this high autodispersibility is obtained without increafing the city of the powder. The high autodispersibility aids in cutting down the time of aging and this advantage is obtained without the use of excessive amoimts of hygroscopic dispersing agents which will result in producing prints with blurred outlines. In more specific embodiments of the invention where antidusting agents are employed, the quality of nondusting is likewise a characteristic of the vat dye powders of the present invention.

The above characteristics of the products of the present invention render them superior to the known products of the prior art both from the standpoint of their use in vat dyeing and in their use in printing. Some of the characteristics are of advantage both in -dyeing and in printing. Other characteristics are of particular importance only in printing and it is in this use that Deflocculatina agents I Protective aaents These agents are primarily colloidal materials which form films around the minute pigment particles which films are sufliclently elastic so that they do not crack off on drying and are preferably soluble in water, or at least take up water to swell. The commercially most attractive class of protecting agents are the carbohydrate colloids such as the dextrins. These agents give very satisfactory films, they are cheap and do not introduce into the pigment any components which would be harmful in the products which are to be colored by the pigment. Anothertypical protective agent is the alkali salt of lignin sulfonic acids which are obtained from the waste liquor of the sulflte process of producing wood pulp. While the above two classes of protective agents are the preferred examples, the invention includes the use of any other protective agent for example, gelatin, albumens, alkali, metal'silicates, pectin, colloidal clays, etc., capable of forming a satisfactory film around the individual pigment particles.

Diluting agents The preferred diluting agents are mainly carbohydrates such as sugar, dextrose, cerelose, xylose and the like. In fact, any of the common soluble carbohydrates are suitable. Other common diluting agents such as salts may also be used in certain cases. It is an advantage of the present invention that it is applicable to pigment pastes and dry powders containing the standard diluents used in the art. The invention is, however, not concerned with the use of any specific diluent and where a pigment in undiluted form is desired, the diluent may of course be eliminated. Cerelose is particularly desirable as it permits producing a product of very low hygroscopicity.

Wetting agents Any of the usual wetting agents can be used which are suitable for the particular conditions.

.The synthetic tanning agents of the disulfodiaryl methane type such as disulfodinaphthylmethane, are also very effective and have the additional desirable feature as referred to above under deflocculating agents, of serving as combined wetting and defiocculating agents. The alkali and alkaline earth metal salts of lignin sulfonic acids form another class of wetting agents which have tion.

the additional advantage of being at the same time protecting agents. Sodium salts of sulfonate lauryl, cetyl and similar high molecular alcohols, are also excellent wetting agents and may be used to advantage in the present inven- Another class of wetting agents are the ethers of polyglycols such as, for example, the ethyl ether of diethylene glycol. These wetting I agents are also anti-dusting agents.

Examples of other compounds which are both wetting agents and anti-dusting agents are certain esters of ethers of simple polyhydric' alcohols such as, for example, the acetates of the methyl, ethyl or butyl ether of ethylene glycol. These esters are in general combined anti-dusting and wetting agents when they are partially miscible with water.

The above enumeration of a few classes of wetting agents is not intended as limiting the invention to these products. They are typical of some of the well known wetting agents which have proven highly successful in "the present invention and which are preferred, but any other wetting agent which does not introduce undesirable components into the final product may be employed.

Antidustinp agents alcohols and other low molecular organic acids may be used. The ethers are condensed polyhydric alcohols such as the ethyl ether of diethylene glycol, are also very eflective and have the additional advantage that they are also wetting agents' It might appear that the use of an antidusting agent which operates by reason of its hygroscopic I properties, would result in producing a very hygroscopic pigment power and would therefore defeat one of the main advantages of the present invention. However, the antidusting agents are present in suchsmall quantities that although they prevent dusting by reason of their high hygroscopicity, they form so minute a fraction of the pigment powder that they do not materially increase the hygroscopicity of the pigment as a whole.

Printing aids It is common to use printing aids in printing gums. These are materials which appear to make for better prints. The exact way in which they improve the results is not entirely understood. When pastes are used liquid printing aids are employed such as alkylol amines, for example triethanol amines, glycerine, ethers of ethylene glycol and polyglycols and their derivatives, glycol, diethylene glycol, etc. Where powders are employed, solid printing aids are necessary and examples of such solids are the hydrochlorides of alkylol amines, such as triethanol amine; sil

ver salt; (sodium anthraquinone' betasulfonate) anthraquinone-and oxalates of metals such as cobalt or iron. The present invention permits using a considerably smaller amount of print- Thevatdyeswhiehcanbemedintheprcsent invention include all of the insoluble dyes oningareafewtyplcalclassa dvatdyeswhlch.

maybeemployedin'thepresmt invention,but itshouldbeundeistoodthatitisnotlimited The abbreviation C. I. refers-to the A. Anthraquinone vat dyes:

1. Anthraflavones;

'Exampleunderthnclasswouldbeanthraflsvone G., C. I. 1095. 2. Pyranthrones;

Example: Indanthrene Golden Orange (3.,

C. I. 1096. 3. Dibenmnthrones and thrones;

Example: Dark Blue B0, C. I. 1099; Vat Black BB, C. I. 1102; Jade Green, no C. 1. number; Indanthrene Violet 28. C. I. 1104; Vat Navy Blue. at 0.1. number. 4. anthraquinone Axines;

IndanthrmeBlue GCD, C. I. 1113; Indanthrene Blue 3G8, C. I. 1114. 5. Flavanthrones;

Example: lndanthrene Yellow 0., C. I.

1118. 6. Benmwl Amino Anthraquinons;

Example: Algol Red 213, C. I. 1133. 7. Di-anthraquinonylamines and ureas;

Example: Algol Orange R, C. I. 1137; Algol Yellow 36, C. I. 1139. 8. Anthrapyridones;

Example: Indanthrene Orange RT, C. I.

1157. 9. Anthraquinone Acridones;

Example: Indanthrene Violet RRN, C. I.

1161. 10. Anthraquinone Thioxanthones;

Example: Indanthrene Yellow. ON, C. I.

1165. ll. Anthraquinone Sulfur Dyes of unknown constitution;

Example: Vat Yellow 56. B. Indigolds and Thioindigoirh:

. Indigo, C. I. 117']. Clba Blue B, C. I. 1183. p Hydrone Pink, C. I. 1211, in which thebroe mine atoms are replaced by chlorine. Hydrone Orange, C. I. 1217. Hydrone Scarlet-a mixture of pink and orange.

While the advantages of the present invention are preeminent in uses of vat dyes, particularly vat dye powders where the dye is reduced and reoxidized as .in vat dyeing or printing, it should be understood that the new products may also be used as pigments, that is to say without reducing and reoxidizing. These mes are largely in coloring of materials where adsorption of the leuco compound cannot or does not need to take place, for example, the coloring of plastics, some processes of coloring paper, and the like, which employ the vat dyes as ordinary pigments, Just as for example inorganic pigments are used. For such purposes the high total dispersion and autodispersibility coupled with the low hygrosooplcity of the powders of the present invention are just as real advantagm as in the p where the dyelsflrstreducedandthenreoxldized. also,

theenhancedkeerdngpowersotthepastesotthe presentinventionarecquallyusefulinprocesses wherethedyeisnotredueedandreofldised. It should be noted, however, that the practically perfect colloidal dlspusion of the products of thepresentinventinnareolevengreaterimportance in procemes where reduction and reoxidationtakeplacebecausethefinenessofdispersioniseifectiveintwofactorsinsuchproc esses,namelycompletenessoireductionandcompleteness of adsorption of the reduced material, sothatwhereasfalrrsultsmaybeobtainedwith someofthebestproductsofthepriorartwhen used as pigments, the improved results obtainable from the products of the pruent invention aremorestrongiymarkedinwhichinvolve reduction and reoxidation. The higher tinctorialpower oftheperfect colloidal dispersion or the products of the present invention is of course equally important in all employingthecoloringmatter.

Hie invention will be described in greater detail in connection withthe following specific exampleswhich illustrate typical products of the prwent invention. It should be understood. of

Example 1 1500 parts by weight of Hydron Orange (C. I. 1217) press cake containing 420 parts of real dyestuif are introduced into a steam jacketed Werner-Pfleiderer mixer together with 10 parts by weight of sodium isopropylnaphthalene sulfonate. After mixing thoroughly a thin slurry forms to which 600 parts by weight of yellow dextrine are slowly added. The entire mixture is worked until uniform and free from lumps whence steam is introduced into the jacket and the mixer heated to evaporate the major portion of the water. The entire mass is then cooled and the thick plastic magma kneaded for six hours, a temperature rise being observed in the Attheendofthisworklnmtlm is poured into aluminum or enamelled trays and V dried in a vacuum oven at a temperature of ap- Example 2 510 parts of Hydron Orange (C. I. 1217) press cake are placed in a Werner-Pfleiderer dough mixer and 3.5 parts of the sodium salt of disulfodlnaphthylmethane added, followed by 20'! parts of yellow dextrine. A thin slurry results which is worked for about six house, then poured into enamel pans and dried, preferably in a vacuum drim'. although a low temperature air oven will suflice. The dried cake is roughly ground and returned to the mixer, adding at the and dried in a vacuum oven at '65 (3., then same time from 20 to 25 percent by weight water. A thick plastic magma results which isworked for 4 to 8 hours, poured into enamelled trays, and vacuum dried at a temperature approximately 65 C. The dried magma is ground to a powder, then transferred to a ball mill or. any other suitable blender. For every 250 parts of the concentrated pulverized color added to the ball mill, there is also added 83 parts ofcerelose and 3.4 parts of the monethyl ether of diethylene glycol. After a homogeneous mixture has been produced, an orange powder results which is stable, of low hygroscopiclty and which readily dis perses in aqueous media. 1

Example 3 434 parts of Hydron Orange press cake containing 132 parts of real dyestufl. and 3.5 parts of sodium isopropylnaphthalene sulionate are placed in a Day dough-mixer together with 175 parts of the sodium salt of the lignin sulfonic acids obtained from the waste liquors of spruce pulp 'manuiacture. A thin slurry results which is worked for about 6 hours, then poured into trays and dried either in a low temperature air or vacuum oven. After drying, the mixture is ground and returned to the mixer. Approximately 25 percent of water is added to form a thick plastic magma which is worked for about six hours. The thick magma is poured'into trays ground. The resulting powder is placed in a ball mill and blended with cerelose and the ethyl ether of diethylene glycol as in Example 2. The product is a powder'of low hygroscopicity, high autodispersibility, which in moderate additions produces little effect on the consistency-of the aqueous media to which it is added.-

Example 4 1500 parts of Hydron Orange press cake, containing 325 parts of real dyestuff, are added to a Werner-Pfleiderer mixer along with 15 parts of sodium isopropylnaphthalene sulfonate and 465 parts of dextrine and worked until a smooth homogeneous slurry results. This slurry is placed in trays,dried in a vacuum oven, and ground to a powder. This powder is again placed in the mixer, along with 22 to 28 percent of water, and the plastic mass resulting, kneaded for 6 hours. It is then transferred to enamelled trays and vacuum dried at about 65 C. After grinding, a powder results which, when all thereof is placed in a' ball mill with 1490 parts of water and 2.5 parts of betanaphthol and milled a short time until homogeneous, yields a. paste wherein the dyestufif is so well dispersed that little or no settling is obtained even after standing for six months.

Example 5 1500 parts of a Hydron Pink (C. I. 1211) press cake, containing 420 parts of real d'yestuff, 15

parts of sodium isopropylnaphthalene sulfonate, and 600 parts of dextrine are placed in a Wemer- Pfieiderer mixer and kneaded for about hours. The resulting thin slurry is poured into suitable pans and dried at a moderate temperature, for example, 70 C. The ground, dried product is then again added to the dough mixer along with about 25 percent of water. and kneaded as a thick plastic for 8 hours. The thick plastic is transferred to suitable trays and dried in a vacuum oven at 65 C. The dried material is then ground to any desired particle size either used as of is or blended in a blender with diluting, wetting,

700 parts of tetrabromindigo, 100 percent powder is placed in a Werner-Pfleiderer mixer along with 17 parts of disodium dinaphthyl methane sulfonate, 1000 parts of dextrine, and 400 parts of water. The thick plastic mass resulting is kneaded for 10 hours, poured into trays, vacuum dried at 65 C., ground, and reintroduced into the mixer. 25 percent of water is added to produce the desired plastic condition for the second working which requires 6 hours. The smooth plastic mass formed is transferred to trays, andvacuum dried at about 65 C. The dried material ispulverized and dry blended in a ball mill or other suitable blending tool with 119 parts of cerelose and 18 parts of the monoethyl ether of diethylene glycol- A powder of low hygroscopicity results which, when added toidueousmedia, disperses therein coloring the media blue.

Example 7 sulting precipitate is filtered by suitable means,

washed free from acid to yield a filter cake of approximately 25 percent solids. This filter cake is placed in a dough mixer, 17 parts of disodium dinaphthyl methane sulfonate and 1000 parts of dextrine added, and then converted into a dried concentrated powder as described in Example 5. 300 parts of the resulting dried concentrated powder, 75 parts of cerelose, and 17 parts of triethanolamine hydrochloride are then placed in a ball mill and blended together to produce a homogeneous mixture. This final mixed powder possesses low hygroscopicity and high dispersive properties.

Example 8 700 parts of Indigo (C. I. 1177) 100% powder, 17 parts of sodium isopropyl naphthalene sulfonate, 1000 parts yellow dextrine, and 400 parts of water are placed in a Wemer-Pfleiderer mixer and kneaded as a thick plastic for 10 hours. The smooth plastic produced is poured into aluminum trays and vacuum dried at 6 5-70 C. The dry material is ground and when 150 parts thereof are blended, in a suitable blender, with 150 parts of xylose and 3 parts of sodiumsecondary butyl naphthalene sulfonate, a powder results which so readily disperses in water that it would appear as if the powder were' going into solution.

Such solutions have merit as vat dyeing baths.

Example 9 6 chaos that the bottom of the depression is approximate 1y linchbelowthetopedgeofthebottle. One gram of the powder to be tested, which has been previously passed through a 140 mesh screen, is

A placedontheclothand25 cc. ofwateriscaused l to flow over it from a 25 cc. pipette, having a graduated column approximately 1 ft. high, at a rate such that it takes approximately 80 seconds for the 25 cc. to flowthrough. The end of the r pipette is held approximately 4 inches over the 10 top of the bottle and the stream from the pipette is played on the surface of the powder by manipulating the end of the pipette in a horizontal plane so as to uniformly wet the powder. The cloth is then carefully removed, dried at 100 deg. 15 C. for 1 hour, cooled, and immediately weighed. Thus the amounts of powder remaining on the cloth and passing through into the bottle are determinedandthepercentagepassingthroughis termed the percentage of autodispersibility. This testisapracticaloneandreallymeasuresspeed and completeness of dispersion as an extremely soluble solid will show approximately 100% autodispersibility. within 2%.theerrornever exceedin 5% r 25 tained repeat the addition of the water and of the dextrine until a total of 300 parts of dextrine has been worked into the mass. Add 50 parts of colloidal clay in water suspension. Mix thoroughly and then add sufiicient dextrine to give a mixture of dough consistency. At this consistency continue kneading until the plastic mass is smooth and free from lumps. Add water andmixthoroughlyuntilthepasteisthinenough to remove from the mixer. Transfer the paste to pans and vacuum dry. When dry, transfer to q a grinder and grind \mtil reduced to a fine powder. 'Ihispowderisstable,dispersesreadilyin water,andismeful for vatdyeingpurposesor similar applications.

sam le 7 Place 1100 parts of Indanthrene Blue 808 (C. I.

Grindtoapowderandaddtheretmbydry mixer along the resulting plastic mass kneaded for 6 hours.

blending, sodimn secondary butyl naphthalene sulfonate in the proportions of 200 parts to 10 parts respectively. The resulting powder, when addedtomintlnggmdispersesthereinproducing little change in the consistencyand showing no speckiness.

l'mmple 11 Place 1400 parts of Vat Yellow G (C. I. 1118), containing 466 parts of real dyestuii', and 650 parts of yellow dextrine in a Werner- Pfleiderer dough mixer and work for 6 hours. Transfer the rather thin slurry to enamel trays anddryeitherinanairorvaeuumoven. After grinding. the matl'ial is returned to the dough was about percent water and The thickmixtureisthenpouredintotraysand driedinavacuumovenat65 C. Grindthe vacuumdriedmaterialandaddtheretmbydry blending in a suitable tool, 10 parts of trlethanoiamine hydrochloride to every 100 parts of the powder. The final powder is very useful for vat dyeing and printing purposes.

Aatodispenibility tests The power of dispersing in water practically instantaneously is of importance in obtaining readily uniform dispersions without excessive stirring. This is particularly of importance where the products are to be employed as pigments, and-is of lesser importance in such uses as the preparation of printing gums where the production of the gum necessary involves thorough steaming. Autodi spersibillty is measured byasimpletestingeneralusebythecalco Chemical Company. A woven bleached cotton cloth of 64x60 mesh per' inch and weighing approximately 2.5 olmces per square yard, such as is used as a container for laundry bluing blocks. is cut into 5 inch squares. One of these squares, after drying in an oven at approximately 100 deg. C. for 10 minutes is weighed and then fastened over the 1.4 inch diameter mouth of an 8 ounce bottle,beingheidinplacebyarubberband. In fastening the square of cloth over the mouth of paste, containing440 parts real Thetestisusuallyaccurateto It has been shown in practice that no distinction in eflectiveness can be noted between a material having 90% autodispersibility and one having 100%. However, when the autodispersibility (11:11: below 75%, the product is distinctly infillvroacopicitil Certain vat powders have appeared on the market since the development of the present invention showing a high autodispersibility. For example, certain competing vat orange powders. show autodispersibility ranging from 30 to 85%. These high autodispersibilities', however, are obtained at the expense of hygroscopicity for these 40 products are highly hygroscopic and cannot be keptforanylengthoftimeexposedtotheatmosphere. It has'been found that a reliable test for hygroscopicity is obtained by exposing the powder in a desiccator at room temperature to an atmosphere having 84.7% humidity, which is maintained by a saturated aqueous solution of potassium chloride in the .daiceator. The amount of moisture absorbed by a product of low hygroscopicity increases fairly rapidly in the first two days and then increases very slowly, reaching a practically complete equilibrium in a week. With more hygroscopic material the absorption continues fairly rapidly during thewhole of the week. For practical purposes one weeks exposure gives a very definite index of hygroscopicity. The products of the present invention all have hygroscopicities well below 25% asmeasm'ed by the above tests and usually range from 18 to 20%,. depending to some extent on p the nature of the diluting agent or protective agent used. Thus products made with a preferred diluting agent, cerelose (dextrose monohydrate), show lmus ua'lly low hygroscopicities. The vat orange powders available in the trade at thepresent time have autodispersibiiities of from 30 to 85%, showing hygromopicities of approximately 40%. They are therefore valueless unless stored in absolutely airtight containers at all times. t For practical purposes a product having more than 25% hygroscopicity can not be stored exposed to the atmosphere without serious eating, or even in some extreme cases reverting to a kind of soupypaste. It is one of the outstanding advantages of the present invention thebottleadepressionismadeinthe clothso thattheproductsdespitetheirenormouslyhigh Viscosity changes in printinggum Another characteristic of the products of the present invention is that they do not result in wide fluctuations in the viscosity of printinggum and particularly thickening thegum. There is a tendency whenever vat dyes. particularly pastes, and the powder is frequently made up into a paste before incorporation with a gum, to thin out the printing gum temporarily, probably by reason of the additional water present. Many products of the prior art, however, have the serious disadvantage that after standing for a while the viscosity of the printing gum which is at first reduced increases rapidly and greatly exceeds that of the printing gum itself. A small fluctuation does not have serious effects and all of the products of the present invention show an effect 'on printing gum viscosity which is so small as not to interfere with full efficiency of the printing process. The products of the present invention will result in a viscosity change of not more than 6-10%. Normally, the viscosity is reduced and then comes back to approximately its original value. Products having a viscosity change of greater than 15% are normally undesirable as it is impossible for the printer to rely on his consistency and obtain uniform prints.

Some of the prior art products are very serious offenders in this respect, for example, pigment powders have been described in the patent ,to Bishop and Thompson, No. 1,659,131. These powders are prepared by dispersing in -a foam of soap or other dispersing agent and then drying and grinding the foam. Pigment powders produced by following the teachings of this patent show very markedly inferior total dispersion to those of the present invention and they exert a very serious eifect on the viscosity of printing gum; The fluctuation is so great that the printing gum could not be used with ordinary machinery without constant adjustment. The products of the present invention on the other hand enjoy all the advantages of practically perfect colloidal dispersion with its high tinctorial power and efl'lciency in printing without exerting any deleterious effect on the viscosity of printing gum and it is a peculiar advantage of the present invention that the desirable features of its products are obtained without corresponding disadvantages which so frequently necessitate a compromise in qualities of coloring matter which have been produced hitherto.

In the claims the term protective agent" is used to define the class of compounds having the physical properties of forming adherent films which are soluble or swell with water, which properties are possessed by the typical materials recited in the specification under the heading Protective agents. It should be understood that the phrase, as used in the claims, has no other meaning. i

We claim:

1. A dispersible vat dye powder having as its major coloring component a vat ,dye, a suflicient proportion .of the individual vat dye particles being individually coated with a hydrophilic autodispersibility producing protective agent" in an amount sumcient so that the powder as a whole possesses an autodispersibility of not less than same vat dye.

75% and is capable of complete colloidal dispersion in 'aqueous media or in printing gum, the completeness of said dispersion equalling that of a dispersion of 'a freshly prepared paste of the 2. A dispersible vat dye powder havingas its major coloring component a vat dye, a sufficient proportion of the individual vat dye particles being individually coated with a hydrophilic autodispersibility producing protective agent in an amount sufflclent so that the powder as a whole possesses an autodispersibility of not less than 85 to 90% and is capable of complete colloidal dispersion in aqueous media or in printing gum, the completeness of said dispersion equalling that of a dispersion of a freshly prepared paste of the same vat dye.

3. A dispersible vat dye powder having as its major coloring component a vat dye, a suflicient proportion "of the individual vat dye particles being individually coated with a hydrophilic autodispersibility producing "protective agent" in an amount suflicient so that the powder as a whole possesses an "autodisper'sibilit f of not less than 75% and is capable of complete colloidal dispersion in aqueous media or in printing gum, the completeness of said dispersion equalling that of a dispersion of a freshly prepared paste of the same vat dye, the product also possessing a hygroscopicity of less than 25%.

4. A dispersibile vat dye powder having as its major coloring component a vat dye, a sufficient proportion of the individual vat dye particles being individually coated with'a hydrophilic autodispersibilityproducing protective agent" in an amount sufficient 50 that the powder as a whole possesses an autodispersibility.of not less than 85 to 90% and is capable of complete colloidal dispersion-in aqueous media or in printing gum, the completeness of said dispersion equalling that of a dispersion of a freshly prepared paste of the same vat dye, the product also possessing a hygroscopicity of less than 25%.

5. A product according to claim 1 in which the protective agent is dextrin.

6. A product according to claim 2 in which the protective agent" is de'xtrin,

'7. A product according to claim 3 in which the protective agent is dextrin.

8. A product according to claim 4 in which the protective agent is dextrin.

' 9. A paste having as its major component a vat dye, a suilicient proportion of the individual particles of the vat dye being individually coated with a hydrophilic auto-dispersibility producing protective agent so that the paste possesses substantially perfect total d-ispersibility and does not settle or liver on standing.

10. A method of producing a dye paste which comprises defiocculating a vat dye powder in thepresence of a hydrophilic auto-dispersibility producing, protective agen by kneading the product in the form of a paste sufliciently stifl to exert a shearing action on thedye particle aggregates and continuing the kneading for a sufllcient pewhich comprises defloccuhting a. vet dyein the presence of: hydrophflic auto-dispersihiiity producing "protective agent" by kneeding in the 'tormotepestesumcientlysflfltoexerta'aheerclemendtrenatormingtheddedmateflelintoe powder, the resulting powder had an "eutodiaperaihility of not is: flun 75%.

13.Amethodecoordingtoclnim loinwhich the protective agent is dextrln. 5 14.Amethodtoclaimi2inwhich the protective agent" ia dextrin.

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