Paint Technology and Tests.

by Henry A. Gardner.

PREFACE

A few years ago the producer and consumer of paints possessed comparatively little knowledge of the relative durability of various pigments and oils. There existed in some cases a prejudice for a few standard products, that often held the user in bondage, discouraging investigation and exciting suspicion whenever discoveries were made, that brought forth new materials. Such conditions indicated to the more progressive, the need of positive information regarding the value of various painting materials, and the advisability of having the questions at issue determined in a practical manner.

The desire that such work should be inst.i.tuted, resulted in the creation of a Scientific Section, the scope of which was to make investigations to determine the relative merits of different types of paint, and to enlighten the industry on various technical problems. Paint exposure tests of an extensive nature were started in various sections of the country where climatic conditions vary. This field work was supplemented in the laboratory by a series of important researches into the properties of pigments, oils, and other raw products entering into the manufacture of protective coatings. The results of the work were published in bulletin form and given wide distribution. The demand for these bulletins early exhausted the original impress, and a general summary therefore forms a part of this volume.

The purpose of the book is primarily to serve as a reference work for grinders, painters, engineers, and students; matter of an important nature to each being presented. Without repet.i.tion of the matter found in other books, two chapters on raw products have been included, and they present in condensed form a summary of information that will prove of aid to one who desires to become conversant with painting materials with a view to continuing tests such as are outlined herein. In other chapters there has been compiled considerable matter from lectures and technical articles presented by the writer before various colleges, engineering societies, and painters' a.s.sociations.

The writer wishes to gratefully acknowledge the untiring efforts of the members of the Educational Bureau of the Paint Manufacturers'

a.s.sociation, whose early endeavors made possible many of the tests described in this volume. Kind acknowledgment is also made to members of the International a.s.sociation of Master House Painters and Decorators of the United States and Canada, who stood always ready to aid in investigations which promised to bring new light into their art and craft.

HENRY A. GARDNER.

WASHINGTON, October, 1911.

CHAPTER I

PAINT OILS AND THINNERS

=Constants and Characteristics of Oils and Their Effect upon Drying.= An attempt has been made to give in this chapter a brief summary of the most important characteristics of those oils finding application in the paint and varnish industry. For methods of oil a.n.a.lysis, the reader is referred to standard works on this subject; the a.n.a.lytical constants herein being given only for comparative purposes.

It is well known that one of the most desirable features of a paint oil is the ability to set up in a short period to a hard surface that will not take dust. This drying property is dependent upon the chemical nature of the oil. If it is an unsaturated compound, like linseed oil, rapid absorption of oxygen will cause the film to dry rapidly and become hard. If the oil be of a fully satisfied nature, like mineral oil, oxygen cannot be taken up to any great extent and drying will not take place. The various animal and vegetable oils differ in their power of oxygen absorption to a lesser or greater extent. This difference is referred to by the chemist in terms of the iodine value. The iodine value of linseed oil is approximately 190, meaning that one gram of the oil will take up 190 centigrams of iodine. Oils with high iodine values have good drying powers, while those with low iodine values are, as a rule, very slow drying in nature.

For a description of the working and drying properties of various oils used in paints, see Chapter XIV. The oxygen absorption of various oils and mixtures is shown in Chapter II.

=Linseed Oil.= The seed of the flax plant which is extensively grown in North Dakota, Argentine Republic and Russia, contains approximately 36% of oil which may be obtained by grinding, heating, and expression. Ripe native seed generally produces a pale oil of little odor; the oil from Argentine seed often having a greenish tint and an odor resembling sorghum. While filtering, pressing and ageing will remove considerable of the ("foots") mucilaginous matter, phosphates, silica, etc., from the oil, the better grades which are intended for varnish making are often refined with sulphuric acid. A light colored oil which may be heated without "breaking" results from this treatment, but such oils are apt to contain considerable free fatty acid, unless they are washed with alkali subsequent to the sulphuric acid treatment. On account of its rapid drying properties and general adaptability for all cla.s.ses of paints and varnishes, linseed oil has never been supplanted by any other oil.

Chemically it consists of the glycerides of linoleic, oleic, and isolinoleic acid, its const.i.tution being responsible for its very high iodine value.

[Ill.u.s.tration: Field of Flax in bloom in North Dakota]

Boiled linseed oil, a heavier and darker product, is made by heating the raw oil in open kettles to high temperatures, generally with the addition of metallic driers such as litharge, and black manganese. The resinates of lead and manganese are often added to oil heated at a lower temperature, to obtain a boiled oil of lighter color.

[Ill.u.s.tration: New type of Flax Harvester which pulls plant up by the roots, thus preventing infection of soil]

[Ill.u.s.tration: Modern Concrete Elevators for storing Flaxseed]

[Ill.u.s.tration: View of Linseed Oil Factory showing hydraulic press, tanks, etc.]

[Ill.u.s.tration: _Photographs courtesy of Spencer Kellogg Sons_

Flaxseed Crushers]

[Ill.u.s.tration: Filter Presses for removing extraneous matter from linseed oil]

[Ill.u.s.tration: Linseed Cake from Oil Press]

[Ill.u.s.tration: Glycine Hispida

Mammoth soya bean plants]

[Ill.u.s.tration: _Photographs courtesy of David Fairchild, Plant Explorer, U. S. Dept. of Agriculture_

Glycine Hispida

Soya bean plants under cultivation at Arlington, Va.]

By blowing air through linseed oil that has been heated to approximately 200 degrees Fahrenheit, either with or without drier, heavy bodied oils are obtained, which find special application in varnishes and technical paints. As the viscosity of these oils increase, the iodine values decrease, and a slight rise in saponification value and specific gravity is observed. The following a.n.a.lyses of various types of linseed oil were recently made by the writer:

===========+========+========+=========+========+=========+========= |Pure Raw| Boiled | Boiled | Blown | Litho. | Old |Linseed | L. O. | L. O. | L. O. | L. O. |Treated | Oil | (Lino- | (Resin- | | | Oil | | leate) | ate) | | | -----------+--------+--------+---------+--------+---------+--------- Color | Amber | Dark | Reddish | Pale | Dark | Amber | Clear | Brown | Brown | | Brown | Clear | | | | | | Sp. Gr. at | .933 | .941 | .930 | .968 | .970 | .943 15 C. | | | | | | |Average | | | | | Iodine No. | 180 | 172 | 176 | 133 | 102 | 172 | | | | | | Saponifi- | 191 | 187 | 186 | 189 | 199 | 197 cation No. | | | | | | | | | | | | Free Fatty | 3.2 | 2.7 | 2.2 | 2.8 | 2.7 | 6.9 Acid | | | | | | | | | | | | Unsaponi- | 1.4 | -- | -- | -- | -- | 1.8 fiable | | | | | | | | | | | | Maumene | 111 | -- | -- | -- | -- | 96 | | | | | | Moisture | .2% | -- | -- | -- | -- | none ===========+========+========+=========+========+=========+=========

[Ill.u.s.tration: Glycine Hispida

Mammoth soya bean plant]

[Ill.u.s.tration: Glycine Hispida

Soya bean plant, showing nitrogen gathering tubercles on roots]

=Soya Bean Oil.= The soya plant which is extensively cultivated in Asia produces a seed bearing up to 22% and over of a golden colored oil having a peculiar leguminous odor. The oil, which probably consists of the glycerides of oleic, linoleic, and palmitic acids, is secured by crushing, steaming and pressing the seed. There are several varieties of the plant, and they are said to be the best annual legume for forage, the straw and fruit being rich in nitrogen and very fattening as a cattle food. Soya may be grown in nearly any country and is a great carrier of nitrogen to land deficient in this element. Although the oil has been used abroad for many years for soap-making purposes, its use as a drying oil is comparatively recent; being introduced into the paint industry of the United States during the year 1909, when linseed oil started on its phenomenal rise in price.

The oil has given fair service in some paints when mixed with upwards of 75% of pure linseed oil. It is of a semi-drying nature, but may be made to dry rapidly when mixed with manganese and lead linoleate driers. By compounding it under heat with tung oil and rosin, a subst.i.tute for linseed oil is produced, which some claim to be quite valuable.

Table I gives the constants of several samples of soya oil examined by the writer. Table II shows the iodine value of mixtures of soya and linseed oils. Table III shows the results of drying experiments on soya oils containing different percentages of lead and manganese driers.

TABLE I

CHEMICAL CHARACTERISTICS OF SOYA BEAN OIL

=======+==========+===========+============+==========+=========== Sample | Specific | Acid No. | Saponifi- | Iodine |Per cent.

No. | gravity | | cation | No. | of foots | | | No. | | -------+----------+-----------+------------+----------+----------- 1 | 0.9233 | 1.87 | 188.4 | 127.8 | 3.81 2 | 0.9240 | 1.92 | 188.3 | 127.2 | -- 3 | 0.9231 | 1.90 | 187.8 | 131.7 | -- 4 | 0.9233 | 1.91 | 188.4 | 129.8 | -- 5 | -- | -- | -- | 130.0 | -- 6 | -- | -- | -- | 132.6 | -- 7 | -- | -- | -- | 136.0 | -- Average| 0.9234 | 1.90 | 188.2 | 130.7 | -- =======+==========+===========+============+==========+===========

TABLE II

IODINE VALUES OF LINSEED OIL AND MIXED OILS

==============+============+============+============+============ | | Soya | Soya | Soya Sample No. | Straight |25 per cent.|50 per cent.|75 per cent.

| linseed | Linseed | Linseed | Linseed | |75 per cent.|50 per cent.|25 per cent.

--------------+------------+------------+------------+------------ 1 | 190.3 | 175.2 | 160.7 | 140.4 2 | 189.5 | 175.9 | 161.7 | 140.8 3 | 188.0 | 175.4 | 160.3 | 139.0 --------------+------------+------------+------------+------------ Average | 189.3 | 175.5 | 160.9 | 140.4 ==============+============+============+============+============