LABORATORY EXPERIMENTS DEALING WITH THE MANUFACTURE OF PAINTS F. S. BOIG Northeastern University, Boston, Massachusetts
INTRODUCTION
As a result of World War 11, interest in science and engineering has been strongly developed and today a large number of students has become interested in the industrial phases of chemistry. Ret,urning veterans seem to have shown a greater preference for scientific and engineering education than formerly. The paint industry has been steadily growing in importance and volume for many years, and an even greater growth is now expected due to reconstruction after the war. To quote some of the inevitable statistics1-in the year 1939, there were 1166 paint establishments with 38,154 workers employed and the value of paint products amounted to $434,960,890 of the total figure of $56,843,024,800 for all industry combined. The estimated figure for 19442was $700,000,000. It would seem logical that some information about a 500-million-dollar industry could be included in the general chemistry course. There is at least one college which includes the topic of paint in a chemistry coursea -Adrian College (Adrian, Michigan) gives a nonprofessional course in the second semester which includes as one of the topics "Surface Protection," including "paints." No doubt there are others and will he more in the future. The following experiments have been written with the idea of using easily obtained apparatus and reagents, and also involving as little time and wasted effort as possible. They have actually been tried and it would seem from the results obtained by the students that there is ample justification for the inclusion of a discussion of paint manufacture in the general chemistry course. EXPERIMENT I.
PREPARATION OF PIGMENTS
There are four essential parts to an ordinary paint: (1) pigment, (2) vehicle, (3) thinner, and (4) drier. The pigmnt is usually an insoluble colored substance, some examples of which will he prepared in this experiment. The vehicle is a liquid, such as linseed oil, soybean oil, etc., or a varnish, which serves as a means of dispersing the finely ground pigment. The thinner serves to dilute the paint to a point where it can be easily applied to a surface by means of brush, spray, or dipping. Common thinners are turpentine, mineral s~irits.na~hthas.etc. The drier is usuallv a
complex organic compound of cobalt, lead, or manganese; these are catalysts which speed up oxidation of the vehicle and hasten the "drying time." In this experiment some of the more common pigments will be prepared. Materials: Normal solutions of the following: Fe(NOJZ KBe(CN)a Pb(NOa)* K,CrxOl SbCls Na2S10s KICrOl NaOH NHdOH
Ferric nitrate Potassium ferrocyanide Lesd nitrate Potassium dichromate Antimony trichloride Sodium thihsulfate Potassium chromate Sodium hydraliide Ammonium hydroxide
Preparation of Pigments Blue (Prussian Blue). To 10 cc. of 1N ferric nitrate solution in a 100-cc. beaker, add 10 cc. of 1 N potassium ferrocyanide solution. Filter. Carefully remove the filter paper from funnel and scrape off the wet precipitate with a spatula, putting the precipitate on a watch glass, which is placed in an oven to dry. When dry it can be ground in a mortar and pestle. Save the finely ground precipitate for later use. (Dilute ammonium hydroxide may be used for cleaning mortar and pestle.) 4Fe(NO&
+ 3ECFe(CN).
-
FedFe(CN)&
+ 12KNOa
Yellow (Chrome Yellow). To 10 cc. of 1 N lead nitrate or lead acetate solution in a 100-cc. beaker add 10 cc. of a 1 N potassium dichromate solution. Filter and wash precipitate, then place in an oven to dry. Grind to a fine powder in a mortar and pestle and save. 2Pb(NOa)*
+ K&nO, + Hz0
-
2PbCrOl
+ 2KNOa + 2HNOa
Red (Antimony Red). To 30 cc. of 1 N antimony trichloride solution add 40 cc. of saturated sodium thiosulfate solution and heat gently for several minutes until a red precipitate forms. Filter and wash precipitate with dilute HC1. (Why?) Transfer precipitate to a watch glass, dry in oven, and save.
Green (Bmnswick Green). I n a 400-cc. beaker, place 25 cc. each of ferric nitrate and lead nitrate. I n a 100-cc. graduate or beaker mix 20 cc. potassium dichromate and 20 cc. potassium ferrocyanide. Pour 1 16th Census of the United States, Vol. 1,pp. 32-3 (1940). this with stirring into the contents of the larger beaker. MORW,D. P. m~ F. TALBOT, Chem. and Eng. News, 23, What is the result? Filter with gentle suction, wash, Jan. 25, 1945. and dry. (Use of nitrates prevents formation of a 8 SCHROPER. J. B.. J. CEEM.EDUC., 22, 197 (1945).
DECEMBER, 1947
595
precipitate that is too colloidal for easy filtration; however, the filtration is slow.) Explain the color.
Color Combilaatias. Tell what colors you would mix to make: (a) Gray (light and dark) (6) Green (light and dark) (c) Oranze id) purpie (e) Brown (light and dark) (f) Army Olive Drab
Orange (Basic Lead Chromate, Chrome Orange). Pour 10 cc. of 1 N lead nitrate solution into a 150-cc. beaker and add 5 cc. of 1 N potassium chromate solution. What happens? In a second small beaker or test tube, place 10 cc. of 1 N lead nitrate solution and Justify your predictions by mixing the colors with add 4 cc. of 1 N sodium hydroxide. What happens? linseed oil as above and determine whether or not you Transfer the contents of the second beaker or tegt tube were correct. to the first beaker. Add a small amount of water and By the method employed in this experiment apheat gently for several minutes. Describe the changes proximations in color can be made to correspond with that take place. Filter, dry the precipitate in an oven, a given sample of a colored paint and then can be made and save. . up and tinted more accurately. EXPERIMENT 111. PREPARATION OF A PAINT
White (to be used in case a Titanox pigment is not available for Experiment 11). To 20 cc. of 1 N lead nitrate solution add dilute ammonium hydroxide until precipitation is complete. Filter. Place filter paper and precipitate on a watch glass, dry in oven, and save. (A lead hydroxide precipitate works better with linseed oil than does a zinc hydroxide.) Pb(NO&
+ 2NHhOH
-
Pb(OH)*
+ 2NH4NOs
These pigments will be used in the next experiment. EXPERIMENT 11.
PREPARATION OF COLORS
Formula ,
17.0 g. TiOl (Titanox A) 19.0 g. Prussian Blue 40.0 g. L i e d oil 100.0 g. Mineral Spirite (or turpentine) 4 . 0 g. Lead drier
-
180.0 g. (makes about ' / r pint)
Procedure: Weigh out 17.0 g. of Titanox A and 19.0 g. of Prussian ~ l u i . Grind the pigments carefully in a mortar, grinding small amounts a t a time to obtain best results. When the n i m e n t is nround as finelv as possil;le, place in a 500-cc. beaker. To the ground pigment in the beaker add 40 g. of linseed oil (vehicle) and mix intimately with a glass stirring rod or spatula to a homogeneous workable paste. Notice the adsorption of oil by the pigment. After a homogeneous paste has been obtained, add the mineral spirits or turpentine (thinner) in small amounts of 20 cc. a t a time. After the first addition of 20 cc., stir thoroughly, noting the viscosity (or "thickness") of the paint. Repeat this procedure twice, with 20 cc. of thinner each time, and after stirring thoroughly, note the thinning down of the paint. After the third addition of thinner, the paint may be thin enough for general use, although more thinner is usually required for the market product since the pigments are more finely ground and consequently adsorb more thinner. In order to speed and facilitate the drying of the paint upon application to a surface a drier must be added. Add 4.0 g. (about 3.5 cc.) of lead drier or a prepared drier. (A "prepared drier" is a composition drier, usually available in paint stores with full directions as to quantity to he added to the paint.) With the exception of some of the t h i i e r which may have been withheld, and the fact that the pigment particles have not been as finely ground, this paint is approximately what you would buy in the market for a blue house paint.
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Materials: White (Titanox C, or White from Expt. I) Yellow (Lead Chromate) Blue (Pmsian Blue) .Red (Antimony Red) Linseed oil
Part A, Preparation of Blue Paint,
Orange (Basic lead chromate) Green (Brunswick Green) Black (Animal cbarcod, lampblack, boneblaok, or carbonblack)
Preparation of the Paste. On a flat, glazed, white porcelain plate place a small amount of solid Titanox C or White from Expt. I. Add linseed oil dropwise from a medicine dropper, and with a flat spatula mix the oil and pigment intimately, keeping the paste which is formed in as small an area as possible. Add more linseed oil if necessary to keep a workable paste. Note the color. (NOTE:~ e f d r eadding a new colored pigment, put aside with the spatula into a corner of the plate a small sample of the pasteto which the new color is to be added. Then a comparison can be easily drawn between the old and new colors and the effect of the color added.) As soon as the pigment and oil are intimately mixed and the color noted add small amounts of yellow, with drops of linseed oil as necessary to maintain a workable paste. Note the progressive changes of color. When several small additions of yellow have been made add in very small amounts some Prnssian Blue pigment. Note the progressive changes of color. Does the resulting color correspond with that which you would have predicted from your general knowledge of elementary colors?
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(Cmtinud on pwe 600)
DECEMBER, 1941 LABORATORY EXPERIMENTS DEALING WITH THE MANUFACTURE OF PAINTS (Catinwed from page 696)
Part B.. Preparation of a Light
en Paint.
Follow same procedure as in Part A. SUGGESTIONS
Fanula 53.0 g. Titanium Calcium (Titanox C) 11.5 g. Calcium carbonate. 7.5 g. Chrome Yellow Light 0.8 g. Prussian Blue 40.0 g. Linseed oil 30.0 g. Mineral Spirits (or Turpentine) 4.5 g. Lead drier
.
Follow same procedure as in Part A. Part C. Preparation of a Red Paint. Fanulo 13.5 g. Toluidime Toner 10.5 g. Calcium carbonate 40.0 g. Linseed oil 112.0 g. Mineral Spirits (or Turpentine) 4.0 g. Lead drier
-
180.og.
'
1. It would be advisable to obtain the required dry pigments a t a hardware or paint store, rather than to take the time necessary t o make them in the laboratory. Average time consumed when pigments are supplied (Expt. 111) is one and one-half hours for each part. 2. Should it be necessary to make the pigments in the laboratory, use the pigments referred to in the p r e vious experiments, omitting the red. Quantities necessary are as follows: 20 g. Prussian Blue.. . . . . . . . ,260 cc. 1 NK4Fe(CN)s 250 cc. 1 N Fe(N03.
7.5 g. Chrome Yellow Light.
. 26 cc. 1 N K~c~o;'50 cc. 1 NPb(NO.),
22 g.,Caleium carbonate.
. ... .5M) cc. 1 N Ca(N03, 5M) cc. (NH4),C08
55
a. Lead white.. . . . . . . . . . ,360 cc. 1 N Pb(NO& completely precipitated with dil. NHIOH
