Paint Technology and Tests Part 2

--+---------+------------+----------------+------ A | .966 | 41 | 27 | 16.7 B | .99 | 48 | 38 | 10.0 ==+=========+============+================+======

=Hydrocarbon Oils.= Several grades of neutral or mineral oils, varying somewhat in gravity, color, and quality, are produced as the last distillate in the refining of petroleum. These oils when mixed with drying oils and strong driers find application in the manufacture of some freight-car, barn, and other paints which sell at a low price. A small percentage of mineral oil is said to be valuable in structural steel paints, acting as a preventative of hard drying and thus keeping the film soft and elastic. Streaking and sweating is apt to ensue if any great quant.i.ty is used. Mineral oils have a characteristic bloom, showing a greenish fluorescence when examined by transmitted light. This bloom is due to the presence of some strongly fluorescent material which is shown up with intensity when mineral oils are exposed to ultraviolet rays such as emanate from an enclosed arc light. Outerbridge[1] first proposed this test for mineral oils, and he has worked out a "fluorescent scale," by which very small percentages of hydrocarbon oils may be detected in other oils. Several types of so-called debloomed oil have been placed upon the market, and although such oils appear under ordinary light conditions to be free from bloom, they fluoresce quite strongly when given the Outerbridge test.

[1] Alexander E. Outerbridge, Jr.: "A Novel Method of Detecting Mineral Oil and Resin Oil in Other Oils." Proc. 14th Annual Meet., Amer. Soc. for Testing Mater., Atlantic City, N.J., June 28, 1911.

[Ill.u.s.tration: View of Stills Where Petroleum Paint Thinners are Manufactured (Waverly)]

a.n.a.lYSIS OF DEBLOOMED MINERAL PAINT OIL[2]

========+============+================+===== Sp. Gr. | Iodine No. | Saponification | Acid | | No. | No.

--------+------------+----------------+----- .92 | 12 | 4 | 0 ========+============+================+=====

[2] Oil of mirbane present, probably as a deblooming agent, or to mask the odor.

=Pine Oil.= This oil is produced by the redistillation of the heavy, high boiling point fractions resulting from the steam distillation of wood turpentine. It is a heavy straw-colored oil, and should be of some use in the paint and varnish industry, where a high boiling point solvent with an oxidizing principle is desired. It will probably find application in the manufacture of Baking j.a.pans, Asphalt Paints and Enamels. Its oxidizing and solvent values are very high. It has a distinctive sweet pine smell, which makes it popular in the manufacture of turpentine subst.i.tutes from petroleum spirits.

The writer has examined samples of this material, and the following appear to be of the best grade:

CONSTANTS OF PINE OILS

==========================+======================+==================== | No. 1 | No. 2 --------------------------+----------------------+-------------------- Color |Straw Color |Light Yellow Specific Gravity at 15 C.|.934 |.936 Boiling Point |192 C. |202 C.

Distillation |95% distils between |95% distils between | 192-270 C. | 202-280 C.

Residue on Evaporation |14.34% |14.60% Polymerization Test |3-2/3% unpolymerized |2-1/2% unpolymerized | at end of 1/2 hour | at end of 1/2 hour Flash-Point |72 C. |76 C.

Spot Test |Leaves no grease spot |Same as Pine Oil No.

|but only evaporates |1.

|completely in 24 hours| ==========================+======================+====================

=Turpentine.= By direct fire or steam distillation of the sap drippings collected in pockets cut into pine trees, there is obtained the turpentine of commerce. It consists largely of pinene and isomeric terpenes, and has the property of attracting oxygen, with the formation of peroxides which stimulate the drying of oils. It is a high-grade solvent for various gums, and is therefore used in the manufacture of many lacquers as well as for thinning down oil-gum varnishes.

REQUISITE CONSTANTS OF PURE GUM TURPENTINE

Color Water White Specific Gravity at 15 C. .862-.875 Boiling Point About 156 C.

Distillation 95% should distil between 153 and 165 C.

Residue on Evaporation Not over 2% Polymerization Not over 5% should remain unpolymerized at end of half hour Flash-Point Over 40.5 C.

Spot Test No grease spot should remain when dropped on paper and allowed to evaporate Water None

=Wood Turpentine.= High-grade wood turpentine is now produced by the steam distillation of finely cut fat pine wood. The lower-grade qualities are often produced from the destructive distillation of sawdust, stumpage, etc., and these products, on account of their content of formaldehyde, are objectionable in odor. In the steam distillation process, however, a high quality product is obtained by cutting out the heavy fractions and redistilling the lower and purer fractions. It has a high oxidizing value, causing the rapid drying of paints and varnishes to which it has been added. Its solvent value is often greater than that of gum turpentine. When properly refined it has a sweet smell and is to be highly recommended.

a.n.a.lyses of samples of pure wood turpentine which have come to the writer for examination follow:

======================+==========================+==================== | No. 1 | No. 2 ----------------------+--------------------------+-------------------- Sp. Gr. at 15 C. |.862 |.862 Boiling Point |158 C. |162 C.

Distillation: 95% | | distils between |158 and 185 C. |162 and 177 C.

Residue on Evaporation|1.03% |3.06% Polymerization Test |4.1% remains unpolymerized|0.1 cc. out of 6 cc.

|at end of 1/2 | unpolymerized = |hour | 1.66% Spot Test |No grease spot on |No grease spot on | evaporation | evaporation Odor |Excellent |Not objectionable Color |Water White |Water White Flash Point | |47.6 C.

=Petroleum Spirits.= There are produced from Texas crude oil which has an asphaltum base, and Pennsylvania crude oil which has a paraffin base, high boiling-point petroleum spirits which have come into wide use as paint and varnish thinners. When such materials have the proper evaporating value, high flash-point and freedom from sulphur, they are to be highly recommended as paint thinners. The following shows the a.n.a.lyses of a few of these materials examined in the writer's laboratory:

PETROLEUM SPIRITS

=======================+=============+============+============== | Texas Base | California | Penna. Base | | Base | -----------------------+-------------+------------+-------------- Color | Water White | White | Water White Specific Gravity | .811 | .79 | .81 Boiling Point | 156 C. | 138 C. | 146 C.

Flash-Point | 44 C. | 40.5 C. | 43 C.

Residue on Evaporation | .2 | .15 | .12 =======================+=============+============+==============

=Benzol.= "Solvent naphtha" or 160-degree benzol is a product obtained from the distillation of coal tar, differing from benzine, a product obtained from the distillation of petroleum. It is a valuable thinner to use in the reduction of paints for the priming of resinous lumber and refractory woods such as cypress and yellow pitch pine. The penetrating and solvent values of benzol are high, and it often furnishes a unison between paint and wood, that is a prime foundation to subsequent coatings, preventing the usual scaling and sap exudations which often appear on a painted surface. Because of the great solvent action of benzol, it should never be used in second and third coatings. The writer has successfully painted inferior grades of cypress with a paint containing benzol in the priming coat.

=Benzine.= Benzine is seldom used in paints on account of its rapid evaporation, which is apt to cause pinholing of films and other surface defects. In paints of the dipping type where rapid evaporation is essential, benzine finds its widest application.

CHAPTER II

A STUDY OF DRIERS AND THEIR EFFECT

The proper drying of oils and their behavior with various siccatives in varying quant.i.ty is an interesting problem, and obviously of considerable importance from a practical standpoint. Unfortunately there is a decided scarcity of reliable literature dealing with the subject for the guidance of those concerned in the manufacture or application of siccative products. Furthermore, when the problem is investigated, it is not difficult to see why this is so.

=Uniform Conditions.= At a glance it is evident that a decided obstacle in experimentation on the drying properties of oils is the difficulty in obtaining identical conditions for comparative purposes. Inasmuch as a mult.i.tude of factors, such as uniformity and h.o.m.ogeneity of the driers and the oils themselves, intensity and source of light, temperature, uniformity of application, and many others, play a decisive part in the siccative tendencies of oils, the resources and ingenuity of the chemist engaged in the research are severely taxed.

=Oxygen Absorption.= It is a well-known fact that linseed oil, when applied to a clean surface, such as a gla.s.s plate, will undergo oxidation and take up oxygen to the extent of about 16%, forming a hard, elastic, non-sticky product which has been called linoxyn. This material, unlike the oil from which it has been formed, is insoluble in most solvents. Other oils, such as cottonseed, hemp, rape, olive, etc., are more fully satisfied in nature and have not the power to absorb the amount of oxygen taken up by linseed oil.

In carrying out the following tests, on the drying of oils, a quant.i.ty of pure linseed oil of the following a.n.a.lysis was secured:

Specific gravity at 15 C. 0.934 Acid number 5 Saponification number 191-1/2 Iodine number 188

This oil was distributed into a number of 8-oz. oil sample bottles, and to a series of these bottles was added varying quant.i.ties of a very concentrated drier made by boiling oil to 400 degrees Fahrenheit in an open kettle, with the subsequent addition of lead oxide. The amount of drier added to each bottle varied according to the percentage desired; being calculated on the lead content of the drier, which was very accurately determined by a.n.a.lysis.

There was secured in this manner a series of oils containing varying amounts of lead oxide, and from this lot was selected a certain number of samples which would be representative and typical of paint vehicles now found in the market.

Another series of tests were made by combining with a large number of samples of pure linseed oil as used above, various percentages of a manganese drier made by boiling oil at 400 F. and incorporating therewith manganese dioxide.

Still another series of tests were made upon a number of oils into which were incorporated various small quant.i.ties of lead oxide and manganese oxide together, using the standard driers made in the above manner, all of which were carefully a.n.a.lyzed to determine their contents.

In view of the errors in manipulation that could occur where so many tests were made, it was not deemed advisable, in carrying out the tests, to use gla.s.s plates on which only a minute quant.i.ty of oil could be maintained. A much better solution of the difficulty presented itself in using a series of small, round, crimped-edge tin plates, about three inches in diameter, such as are used for lids of friction-top cans.

With paints it is impossible to secure films as thin as those presented by layers of oil on gla.s.s, nor would it be desirable to secure films of this same relative thickness. For this reason an endeavor was made to conduct the following tests with films of the same relative thickness as that possessed by the average coating of paint. The drying of the films did not take place in the same short period, nor in the same ratio, as with the thin layer that is secured by flowing oil upon gla.s.s. The results, however, are more practical, and of greater value to the manufacturer.

The cans were carefully numbered in consecutive order, corresponding to the numbers on the various samples of oil. A very small quant.i.ty of oil was placed in each of the can covers, which were previously weighed, and allowed to distribute itself over the bottom surface thereof. Reweighing of the covers gave the amount of oil which was taken for each test. The test samples in the covers were all placed in a large box with gla.s.s sides, having a series of perforated shelves. In the side of this box is an opening through which a tube was pa.s.sed, carrying a continual current of air washed and dried in sulphuric acid. Oxidation of the oil films commenced at once, and the amount of oxygen absorbed was determined at suitable periods by weighing, the increase in weight giving this factor.

This test was kept up for a period of twenty days.

A test was also made in the same manner with a current of damp air pa.s.sing into the box, to observe the relative oxidation under such conditions. A chart of the results obtained has been made (Table VI), to show the effect of the various driers.

=Results of Tests.= The following outline will present to the mind of the reader the most salient points which have been gleaned from these experiments, and which should give the manufacturer definite knowledge as to the best percentage of oxides to use either in boiled oil, paints or varnishes.

In the case of lead oxide, an increase in the percentage of lead oxide in the oil causes a relative increase in the oxygen absorption, but when a very large percentage of lead has been added, the film of oil dries to a leathery skin.

In the case of manganese oxide, the increase in oxygen absorption on the first day is much more p.r.o.nounced than is the case with lead oxides.

Furthermore, the oxidation of manganese oils seems to be relative to the increase in manganese up to a certain period, when the reverse of this law seems to take place, and beyond a certain definite percentage of manganese, added percentages seem to be of no value. It was furthermore observed that the films dry to a more brittle and harder skin than is the case when lead oxide is used. The oxygen absorption with oils high in manganese has been noticed to be excessive, and the film of oil becomes surface-coated, drying beneath in a very slow manner; a condition that often leads to checking. The critical percentage where the amount of manganese appears to give the greatest efficiency seems to be 0.02%. This critical percentage, as it may be termed, should not be exceeded, and any added amount of manganese has the effect of making the film much more brittle and causes the so-called "burning up" of the paint. The loading of paint with drier and the bad result therefrom may be explained to some extent from the above results.