US2060210A

US2060210A - Preparation of dispersions

Info

Publication number: US2060210A
Application number: US744256A
Authority: US
Inventors: Heckert Winfield Walter
Original assignee: DuPont Rayon Co
Current assignee: DuPont Rayon Co
Priority date: 1934-09-15
Filing date: 1934-09-15
Publication date: 1936-11-10
Anticipated expiration: 1953-11-10

Description

Patented Nov. 10, 1936 UNITED STATES PATENT OFFICE PREPARATION OF DISPERSIONS No Drawing. Application September 15, 1934, Serial No. 744,256

12 Claims. (Cl- 252-45) This invention relates to the production of finely divided materials and in particular it pertains tothe production of finely divided, organic materials suitable for use in artificial silk spin- 5 ning solutions to produce'low luster yarn.

Grinding methods are known whereby materials may be ground, in part at least, to particles of small dimensions (below 2-4 microns); Thus, a water slurry of the material may be ground in 1 a. pebble milLa ball mill, or a colloid mill such as a Charlotte inill. Extremely long grinding periods are required to grind substantially all of the particles to dimensions below 2-4 microns. A much more eflicient procedure involves grinding 15 for a short period of time, diluting the millbase to a suitable concentration and centrifuging to remove the coarse particles which may then be reground, at a higher grinding rate than before. The product from such a grinding process is a 20 diluteslurry, ill adapted to shipment or storage for long periods of time. The partially ground concentrated slurries cannot be shipped to the a point at which they are to be used and then diluted and centrifuged because in such event 25 large quantities of residues must be returned.

Where grinding methods are used for the production of finely divided, organic materials, for example, organic pigments, it is extremely difficult to obtain suitable sub-division particularly when 30 the materials to be ground are organic compounds of definitely crystalline form and for this and other reasons it is extremely difiicult to obtain them in the form of stable, aqueous dispersions of particles nearly all of which are under 4 microns 35 in size. I V In accordance with the present invention, a method has now been found whereby a concentrated slurry (i. e. a slurry having a concentration above 15% and generally'25.-30% of solid m matter) containing less than 10% of coarse material, that immaterial having a particle size above 4 microns, can be directly produced by a .grinding and classifying process. Such a slurry is economical to ship. It may later be diluted and 45 classified again if so desired. comparatively small amounts of coarse material are then returned for re-grinding.

It is an object of this invention to prepare concentrated slurries, suitable for shipping and 50 storage, of materials with very fine particle size and not more than a few percent of material above 4 microns in diameter. An object is to prepare concentrated slurries and/or dispersions of water-insoluble organic materials suitable for 5 sh pment and storage with fine particle size and not more than a few percent of material above 4 microns in diameter. An object is to prepare concentrated water-dispersions of water-insoluble, poiynuclear organic compounds highly deficient in hydrogen, suitable for shipment and storage, 5 with fine particle size and not more than a few percent of material above 4 microns in diameter. Another object is to eliminate excessively long grinding periods in the preparation of such slurries. Another object is to prepare slurries which are substantially non-foaming so that eflicient grinding and water classification can be achieved. Other objects of the invention will appear hereinafter.

I have found that grinding slurries can be made up at concentrations of 40-50% of solid matter and after grinding, prior to classifying, be diluted with the fines secured from the grinding and classifying of residues from other grinds. The

- resulting slurry may be centrifuged at a concentration of 33-35% which will contain 70% or more of the material as fines. The classified slurry will now have a concentration of -30% with 90% or more of the solid material below 4 microns in diameter.

Another method for increasing the concentration of the final slurry is to reclassify or to regrind and reclassify the residues a second time and to use these fines in diluting one of the first residue grinds prior to classification.

Slurries of fines resulting from the classification of residue grinds can also be used to make up the initial grinding slurries in place of water. Such a practice is not particularly desirable, however, because there is a well known tendency for the presence of fines to reduce the grinding rate.

By the practice of the present invention, it has further been found that concentrated water dispersions containing about 15%, generally 25-30% of solids of solid matter with a particle size distribution 90-100% below 4 microns in diameter and only 0-10'% above 4 microns in diameter can be prepared by grinding water slurries of the material with an agent comprising a substantially non-foaming dispersing agent, adding a preservative as desired, and combining the grinding and classifying steps in such a manner that the fines obtained from the grinding and classifying of nesidues are used in making up and/or diluting the initial grinds prior to centrifuging.

Substantially non-foaming dispersing agents have been found to belong to that class of organic -materials with a molecular weight of about 400 are understood groups which are water-soluble or tend to contribute water-solubility to an organic substance. In general, they are polar 8 1 1 8- or alkylated derivatives thereof in which one or more of the hydrogen atoms attached to the nitrogen atoms are substituted by alkyl or aryl groups, etc.

Materials which we have found to be substantiallynon-foaining include such things as peptized casein, 'alkalimetal salts ofthe formaldehyde condensation product of naphthalene sulfonic acids such as those described in U. 8. Patent No. 1,696,199, starch acetate. starch; cellulose glycolic acid, gelatin, agar-agar, sulphite cellulose and viscose. Such materials have their polar groups substantially symmetrically arranged in contrast once may be illustrated by the tural formulas:

i 11. Structural unit for thesoamm salt of olvcolic' acid omooom n Jolsiooom I n. o'ook K 111. The sodium salt of the formaldehyde W- sation product of naphthalene-beta sulfonic acid.

N08 0 mac j IV. Sodium stearate tfooms severely) o'ouo within the" molecule. By "hydrophylic groups" V. Sodiumsclt of steam! sulfate (foams severely) v1. Isoprml aaphthole'ne sodium silllonate (foams severely) While the exact structure for casein is unlrnown,-it yields many different amino acids on hydrolysis. These are held together by numerous hydrophylic/polypeptide linkages in the casein molecule. .Any sinsle amino acid constitutes but a small proportion of the protein molecule, so that casein contains a plurality of hydrophylic groups.

substantially symmetrically arranged withinthe molecul'e".-

I have found that casein is one of the most satisfactory agents for use in this invention. -'ll'ie foaming of its solutions d as the pH is lowered. 'I prefer to use solutions with a pH between 5 and I. Such a solution is made up by known methods according to the following formula:

Casein Hydrated trisodium phosphate.'... 18 Water 882 The casein should o. added slowly to the grindas needed to secure adequate dispersion. If too large an excess of casein is addedat one time.

considerable foam may be produced. In no case.

however, is the foaming as severe as with'the use of. soap-like agent.

When caseinisusedasadispersingagent,a preservative should beadded to prevent bacterial decomposition. Phenols have been used for this purpose. when preservative materials are added prior to the grinding operation, severe foam of a very permanent nature is produced. If added subsequent to grinding, the dispersion is apt to flocculate-and thicken objectionably. I have found that if a phenolic solution of a soap-like product, such as monopole oil, is added near the end of the grind that severe foaming is avoided. Such foam as may beformed is found to break very quickly on standing and is not ob- :Iectionable. Exceptionally good dispersion is also obtained. A I

A phenolic solution of Monopole oil is made up according to the following formula:

Phenol 49.5 Sodium hydroxide 8.25 Water 1225 Monopole oi 30 I prefer to use about 1% of this solution based on the weight of the'grind. The invention is not limited to these proportions. Other phenols and other types of soapy-like materials may be used.

Grinding may be done in any manner capable of reducins an appreciable portion of the ma- 7 terial to particles below 4 microns in diameter.

1 have used pebble or ball mills and particularly colloid mills.

Classifications of the particles may be brought about in a centrifuge of the rotating, bowl type, or by gravitation.

If a slurry of an organic material with a density of about 1.3 is ground to 60% below 4 microns in diameter, (at which point further grinding generally becomes inefilcient) in a colloid mill, the slurry diluted to 28-30% and centrifuged, it is possible toobtain a slurry with a concentration of 18-20% of solids of which about 95% is fines, i. e. under 4 microns. If the residues from the centrifuging operation are now reground, diluted and centrifuged, it is diflicult to obtain a slurry with a concentration above 13-15% of solids. Such dilute slurries are unsuitable for shipment because of the large amount of water which they contain. They also settle badly on storage. However, by the practice of the present invention, the same material may be ground and classified to yield more highly concentrated, stable slurries having ahighly uniform particle size, as indicated in the following examples Eaample I.-Grinding and dispersing of ethylene glycol di-beta-naphthyl ether Eighty pounds of j ethylene glycol di-betanaphthyl ether are ground with 104 pounds of water and 4 pounds of 10% casein solution'of the type described above, by recirculation through -a colloid mill at the rate of 60 to 250 gallons per hour through a 20 horizontal centrifuge rotating at 1200 R. P. M. The slurry of fines so obtained is of about 15% concentration, and while of suitable fineness, is ill adapted for shipment or storage.

The coarse residues'from the preceding operation are reslurried with one pound of 10% casein -of additional casein is generally sufficient.

solution preparedas described above, and enough water to yield a 40% suspension. This is ground by recirculation through the colloid mill at a rate of about 100 gallons per hour for a period of 3 hours. Additional casein solution is added as required to secure a good dispersion. Three pounds A phenolic solution of Monopole oil, prepared as, described above, is added in an amount which is approximately 1% of the weight of the slurry, the slurry is passed out through the mill into a dilution tank where it is diluted with waterto about 27-30% ether (it may, if desired, be diluted with the fines from the preceding operation) The slurry is passed to a centrifugal separator at a rate of 35 gallons per hour. The slurry of fines is retained, and the coarse material is recrystallized and used over again.

Eighty pounds of ethylene glycol di-b-naphthyl' ether crystals are slurried with 104 pounds of water and 4'pounds of 10% casein solution of the type described above. The slurry is ground for 6 hours by recirculation through a colloid mill and a cooler. Additional casein solution is added as required. Generally 12 pounds more is sumcient. At the end of the grind, 1% by weight (based on the weight of the slurry) of a phenolic solution of Monopole oil, such as has been described above, is added and the slurry is passed out through the mill into a dilution tub. It is diluted with the fines obtained from a preceding operation. The resulting slurry is passed at a rate of about 35 gallons per hour through a 20- inch horizontal centrifime, rotating at about 1200 R. P. M. The slurry .of fines so obtained generally contains between and of the finely divided ether, 95% or more of which is below 4 microns in diameter. It is suitable for shipment or storage. The residues are removed from the centrifuge and may be reground as described in the preceding paragraph.

A solution containing 10% starch acetate and 2.5% methylene-polynuclear sulfonate is made up by warming and stirring the following materials:

Starch acetate 100 30% sodium salt of the formaldehyde condensation product of naphthalene-beta-. sulfonic acid 83 Water 817 Eighty pounds of ethylene glycol di-betanaphthyl ether are ground as described in Example I, using the starch acetate solution described above in place of the casein solution and omitting the addition of the phenolic solution of Monopole oil.

Thecoarse residues from the grinding and centrifuging of the ether are reslurried with 3.2 lbs. of the solution of starch acetate-sodium salt of the formaldehyde condensation product of naphthalene-beta-sulfonic acid together with enough water to yield a 36-38% suspension. The resulting slurry is ground as previously described in Example I. No preservative need be added in this case. The slurry is then diluted to 32% with water and centrifuged as previously desalt of the formaldehyde condensation product of naphthalene-beta-sulfonic acid together with 104 pounds of water. This is ground as described above, without the addition of a preservative agent. This slurry is then diluted with a slurry of fines obtained from a preceding operation, and is'centrifuged as described in Example I. The resulting slurry of fines contains 20-30% solids and 90% or more below 4 microns in diameter, and it is suitable for shipment or storage. The residues may then be again reground as described in the preceding paragraph.

The present invention is particularly applicable to the preparation of finely dividedorganic pigments adapted for use in the delustering of artificial thread such as rayon. The delusterant is introduced into the cellulosic solution prior to extrusion through the spinneret, for example, in the delustering of rayon of the regenerated cellulose type prepared from viscose, the delusterant is introduced into the viscose, the solution then being extruded through the spinneret, coagulated, regenerated, and subsequently processed in the usual fashion. It is essential that the maand a-iplurality of Paving a rialused for delustering be finely. divided; that be uniform in size andhave all but a few pernt of the particles underA microns; and that it a capable of uniform dispersion throughout the llulosic solution. These conditions are necesry in order'that the thread be uniformly destered, that the. treatment be uniformly disibuted throughout the thread so as to produce tread of. uniform strength and in order that the trticles of delusterant' pass througlr'the spin- I eret without dimculty andin order that the deisterant will not seriously abrade the different ements of the spinning machine.

Among the organic delusterants to which the ivention may be applied with great benefit are;

1. Organic ethers,'their -'-8, Se.-. '1'e.

nd NH analoguesjsuch as ethylene glycol l-b-naphthyl ether,- di-benzthiazyl-mercapto thane and N-di-b-naphthyl" diphenylene dimine;

2. Chlorinated ring hydrocarbonssuchas octahloro naphthalene and the other solid highly hlorinated naphthaienes, chlorinated diphenyl' nd the other chlorinateddiphenyls, as 'well as ther solid halogenated ring hydrocarbons;

3. Organic heterocyclic compounds such as nethyl-dinaphtho-xanthene and 'thimthrene.

In addition to those classes oflorganici'deusterants specifically mentioned. other organic ielusterants maybe similarly groundiin accordmcewith the practice of the invention as decribed.

Any variation or modification which conforms ;o the spirit of theinvention isintended to be in- :luded within the scope of the claims.

1. The process of producing slurries of- ;eria .ls having a substantially uniform particle size which comprises grinding said materialsf diluting thegrind, and classifying whereby to remove the this particles from-the coarse particles.-

characterized in that the ground materials prior to classification are diluted with the fine particle slurryremoved during a previous operation.

-2.=The process of producing slurries of waterinsoluble, substantially colorless, poZLvnuclear, aromatic organic .materials, having a substantially uniform particle size which grinding said materials,-diluting=the grind, and classifying whereby to remove the fine P r cles from thecoarse particles, characterised in that the groundmaterials prior-to classification are during a previous operation. I

3. The processof-producing slurries of materials in water-containing a dispersing asent.,, having a substantially vuniform particle which comprises grinding said materiala'diluting the grind, and classifying whereby to remove the fine particles from the coarse particles, characterized in that the ground materials prior-to classificationare-diluted with the fine pprticle slurry. removed during a previousoperation.

dfluted with the fine particle numremoved 4. The process of'producing slurries .of ma- I terialsin water containing. a

, agent. having a molecular weight above four hundred brdrorhrlic smur orm'particle size,

which comprises grinding said materials, dilute ing the grind, and classifying whereby to remove the fine particles from the coarse particles, characterized, in that the ground materials prior 'to classification are diluted with the fine particle slurry removed during a previous operation.

5. The process of producing slurries of materials-in water containing a dispersing agent having amolecular weight above four hundred and having a plurality of hydrophylic groups 10 substantially symmetrically arranged within the molecule, having a substantially uniform particle size, which comprises grinding said materials, dilutingthe grind. and classifying whereby to remove the fine particles from the coarse particles, characterized in that the ground mate-- rials prior to classification are diluted .with the fine particle slurry removed during a previous =operation.

6. The process of producing slurries of rna-v 20 terials in water containing .a dispersing agent having a molecular weight above four hundred and having a plurality of hydrophylic groups substantially symmetrically arranged within the molecule, having a substantiallyuniform par- 25 ticie, size,-which comprises grinding said materials, diluting the grind, and classifyingwhereby to remove the fine particles from the coarse particles, characterized in that the ground materials prior to classification are diluted with the 80 fine particle slurry removed during -a previous operation, said process being further characterized in that a preservative for said 'agent is added.

'i. Theprocess of claim 5 characteriaedinthat B the dispersing agent is peptized casein.

8.1heprocess of claim 6 characterized in that the dispersing agent is ,peptized casein, and thgpreservative is a phenol. the dispersing agent is peptized casein, and the preservative is an aqueous phenolic solution of a water-soluble sulfonate.

- 10. The process of producing a slurry of ethylene glycol-di-beta naphthyl ether having a substantially uniform particle size which comprises grinding said.ether"with a dispersing agent, di luting. the grind with the fine slurry obtained from a previous grinding. operation, and classifying' whereby to remove the fineparticles from 11-."1he of producing a slurry of octaehloro naphthalene having as'ubstantially uni- .formparticle' size which comprises grinding said octachloro naphthalene ,with a agent, diluting the grind withjthe fine slurry obtained from a previous grinding operation, and classifying whereby to remove the fineparticles from -,-12. The process of producingaslurryof dihemso.

thiazyl-mercapto ethane having a substantially uniform particle size which comprises grinding V d dil-mercapto ethane with a. disslurry obtained from a previous grinding operg5 ation, and classifying whereby to remove the fine particles from the coarse particles.

f WALTER The process ofelaim 6 characterized in that do.