enamels and varnishes, for both interior and exterior application.
They are also used in the manufacture of linoleum, artificial leather,
adhesives, and printing inks. When incorporated with nitrocellulose
or cellulose acetate lacquers they improve the adhesion, luster, and
resistance to alkalies.
Production in the United States.
In 1937 the output of tar-acid resins for surface coatings exceeded 20
million pounds (net resin). Those from phenol and the substituted phenols
accounted for a very large part of the total. They were followed by
resins from cresylic acids and the xylenols in that order.
In 1937 there were about 20 domestic makers of this type of synthetic
resin, with factories located in California, Connecticut, Illinois,
Indiana, New Jersey, New York, Massachusetts, Michigan, Missouri, Ohio,
Pennsylvania, and Rhode Island.
Imports into and exports from the United States.
Imports of oil-soluble phenolic resins have been negligible. This is due,
in part, to licenses and agreements between certain domestic and foreign
makers, to the remarkable advancement and pioneering work done in this
country, to the holding of many basic patents by Americans, and to the
relatively high duty on imports.
Exports of these products, usually in the form of enamels, varnishes, and
lacquers, have been appreciable and are probably increasing each year.
Official statistics are not reported separately.
TAR-ACID RESINS IN ADHESIVES
A comparatively new use for tar-acid resins is in the manufacture of
wood adhesives. Ordinary vegetable and animal glues have long been used,
although their deficiencies in certain characteristics are well known.
These include (a) their inability to produce uniform products, (b) the
tendency of most alkaline glues to stain wood, (c) the bad effects
of moisture on them, and of bacteria and fungi in the case of animal
glues. The tar-acid resins have none of these objectionable qualities.
Being chemically inert they are free from attack by fungi and bacteria.
Moisture does not affect them, and they do not stain wood.
Three types of resins are used as wood adhesives, principally in bonding
plywoods and veneers: (1) Hot press liquid, (2) cold press liquid, and
(3) resin film. Furniture, radio cabinets, games, and building products
constructed from plywoods bonded with resins can be shipped to tropical
countries, the bond not being affected by extreme climatic conditions.
These resin adhesives are more expensive than the usual animal and
vegetable glues, a factor which has limited their application. Their
advantages may, however, open up to resin bonded plywoods uses in which
the more ordinary types are not satisfactory.
TAR-ACID RESINS FOR OTHER USES
The application of tar-acid resins in casting, molding, laminating,
surface coatings, and adhesives has been described. There are many other
uses, but most of them approach the types of application dealt with.
Impregnation of all sorts of materials with tar-acid resins is an
increasing use; such applications are in fabrics for aircraft, crease
resistant textiles, wood, asbestos, concrete, and electrical coils. Wood
with resin forced into the fiber under pressure is used for furniture,
flooring, heads for golf clubs, and handles for utensils. Resin is used
as a binder in the manufacture of brake linings for automobiles, as well
as in the manufacture of abrasive and grinding wheels.
An interesting application is in the construction of corrosion-resistant
chemical plant equipment. In 1922 the German firm of Saureschutz
Gesellschaft was incorporated to fabricate equipment composed of a
special acid-resisting type of phenolic resin and asbestos. Sometime
later its manufacture was started in the United States. All sorts of
industrial plant equipment is now available, including cylindrical and
rectangular tanks up to 9 feet in diameter and 12 feet high, piping for
corrosive liquids and gases, valves, pumps, fans and ventilators, filter
press plates and frames, buckets, dippers, etc.
Another new use is for making matrices in which to mold rubber printing
plates. Such plates are used at present chiefly in printing cotton and
paper bags but extensive experimentation promises to broaden their use.
The matrix is made of fiber board of very open structure impregnated with
tar-acid resin in the process of manufacture.
4. ALKYD RESINS
Description and uses.
The alkyd resins, used principally in paints, varnishes, and lacquers,
are a group of condensation products synthesized by reacting polyhydric
alcohols, such as glycerin and the glycols, with dibasic organic acids,
such as phthalic, maleic, succinic, and sebacic. The condensation product
is almost always modified to give properties to the resin desirable or
essential to the specific application contemplated. The modifying agent
may be a drying, semidrying, or nondrying oil; the fatty acid of an oil;
a natural resin, such as rosin; a synthetic resin of the tar-acid group
or of the urea-formaldehyde type; or other substance. Up to the present
time unmodified alkyd resins have not been commercially important.
A wide variety of types is obtained by the use of different materials
and different modifiers. The variations begin with the dibasic acid
used, and with the polyhydric alcohol used. The modifications possible
are practically endless, and almost any fixed oil or the corresponding
fatty acid, and most of the natural or synthetic resins may be used. The
importance of the modifier is shown by the proportion used in most alkyd
resins. On the average, approximately 50 percent of the total weight of
the drying and semidrying alkyd resin products is modifier, 30 percent
dibasic acid, and 20 percent polyhydric alcohol. The proportions will, of
course, vary with individual types. Certain types on the market contain
only 25 percent modifier while others have as much as 75 percent.
In a new industry such as this, rapid changes in types and applications
must be expected. Extensive research is being carried on by various
groups. The raw material makers are seeking cheaper products or those
with special properties; the resin makers are investigating an endless
number of modifications, and the makers of surface coatings are testing
most of the new types offered.
Development and patents.
Probably the earliest record of research leading to the development of
the alkyds was that of van Bemmelen, who reported in a German technical
journal in 1856 the sirupy products obtained by heating together succinic
acid and glycerin or citric acid and glycerin. The first investigation
of the phthalic anhydride-glycerin resins was recorded in 1901.[3]
Watson Smith, while engaged in research on phthalein dyes, obtained a
transparent, highly refractive resinlike substance when glycerin and
phthalic anhydride were heated together. Smith recommended the product as
a cement for ceramic wares.
During the period 1910-16 the research laboratories of the General
Electric Co., engaged in research on a synthetic resin from glycerin
and phthalic anhydride. As a result of these studies numerous patents
were granted for this type of resin to which the trade name Glyptal
was applied. Intensive research was carried on by several firms, many
variations were developed, and literally hundreds of patents were granted.
The paint and varnish industry has been undergoing radical readjustment.
Methods and natural products, which for decades or centuries had changed
very little, are giving way to synthetic creations of our laboratories.
The first important departure from the traditional practices was the
development of nitrocellulose lacquers. The commercial application of
the alkyd resins followed, and their use is increasing rapidly. Because
this development is still comparatively young, the large number of
modifications offered has confused the coating manufacturer. It is
probable that many of the synthetic products now being marketed have no
special technical or economic justification and that they will in time
lose out in competition with better products known at present, or still
to be developed.
United States Patent No. 1,893,873, dated January 10, 1933, granted to R.
H. Kienle and assigned to the General Electric Co., was considered one of
the basic patents in this field. Early in 1936 it was declared invalid
in a suit claiming infringement brought against the Paramet Chemical Co.
of Brooklyn, N. Y. The decision in this case seems to have opened the
glycerin-phthalic anhydride resins to a large number of manufacturers.
Among the principal brands of alkyd resins now on the domestic market are
Beckosol, Dulux, Esterol, Glyptal, Rezyl, and Teglac. Each of these trade
names identifies a series of products.
Classification of alkyd resins.
A number of classifications of the alkyd resins are possible and
practical. Since by far the most important applications are in
surface coatings, and their use in molding compositions is relatively
unimportant, it seems advisable at this time to emphasize the
more important use. For the purpose of this survey the following
classification is used:
(1) Drying alkyd resins.
(a) Unmodified.
(b) Modified with natural materials.
(c) Modified with other synthetic resins.
(d) Modified with other synthetic resins and oil extended.
(2) Semidrying alkyd resins.
(3) Nondrying alkyd resins.
(4) Miscellaneous modified alkyd resins.
(5) Alkyd resins in water dispersion.
(6) Alkyd resins in molding compositions.
At least 75 percent of the alkyd resin finishes used at present are of
the drying type and about 15 percent of the nondrying type.
_Unmodified drying alkyd resins._—This class of alkyd resins consists of
a series of compounds made from polyhydric alcohols, polybasic acids, and
fatty acids in chemical combination. The alcohol is usually glycerin, and
the polybasic acid largely phthalic anhydride or acid, although others,
such as maleic anhydride (acid) are increasing rapidly in importance. The
fatty acid or oil used may be linseed, tung, perilla, hempseed, soybean,
sunflower, safflower, or other drying oil. It is believed that tung oil
and perilla oil are the most important at this time.
Unmodified drying alkyd resins are characterized by excellent durability
but limited resistance to water in air-dried finishes. Both in air-dried
and in baked finishes they are outstanding as to flexibility, quick
drying, long luster life, and permanent adhesion. Their principal uses
are in finishes for interior walls and woodwork, automobiles, coatings on
steel such as for refrigerators, railway equipment, bridges, advertising
signs, and lithographed containers. In these applications the products
of this type compete with nitrocellulose lacquers and the older types
of varnishes and paints. While the initial cost is higher, greater
durability is obtained together with faster drying, flexibility, and
hardness.
Probably the largest field for surface coatings is outdoor wood finishes.
Several attempts have been made to adapt pure alkyd finishes to this
use but with limited success because the hard and non-porous finish
does not permit the escape of moisture contained in the wood and the
pressure developed from vaporization of the moisture by the sun’s rays
tends to lift the coating from the wood surface. Recently it has been
found practicable to incorporate from 15 to 20 percent alkyd resins in
conventional types of outdoor paints for wood. Here the use of alkyds has
contributed greater durability and retention of fresh appearance over a
longer period. Paints of this type are now on the retail market.
_Drying alkyd resins modified with natural materials._—This type of
alkyd resin is modified principally with natural resins, such as rosin,
damar, mastic, shellac, or copal. The use of these natural resins imparts
hardness to the resin but shortens its durability. They make the product
less expensive, permit easier incorporation of the drying oil, and in
some instances increase the water resistance.
Their principal application is to modify nitrocellulose lacquers and
lacquer sealers, in order to impart gloss, hardness, and easy sanding. It
has been said that the commercial production of drying alkyds modified
with natural resins was as important a development in the surface coating
industry as the discovery of the alkyds themselves.
_Drying alkyd resins modified with other synthetic resins._—Drying alkyd
resins may be modified with tar-acid formaldehyde resins, tar-acid
furfural resins, urea-formaldehyde resins, petroleum resins, and the
coumarone and indene resins.
Modification with tar-acid resins gives a quicker setting, harder drying
finish with a higher gloss. Alkyd resins so modified are adapted to both
air-drying and baked undercoats and finishes; they have good durability
and adhesion and good resistance to grease, oils, alcohol and abrasion.
For some uses the tar-acid resin modification gives better qualities
than either component possesses alone, but in light colored finishes it
has a tendency to cause the finish to yellow. Coatings made of drying
alkyd resins modified with tar acid resins are widely used on automobile
chassis, fenders, and bodies, machinery coatings, steel fixtures and
toys; they are especially suitable for primers, undercoats, and finishes
on metal.
Modification with urea resins produces baked-finish coatings. As much as
40 percent of the urea resin is incorporated. It makes possible coatings
with a full range of permanent colors and improves their hardness and
mar-proofness, whereas without the ureas the combination of color range
with hardness had been difficult to obtain. The urea resin modified
alkyds find use on metal surfaces of articles which must stand rough
handling, such as toys, furniture, and motors.
Modification with petroleum resins produces air-dried finishes. For
industrial use on metal they give coatings with better adhesion,
dispersion of pigments, and resistance to acids, alkalies, and moisture
at a lower cost than is obtained by ester gum or tar-acid resin
modification. The petroleum resin modification minimizes skinning and
improves the luster and the flow.
_Drying alkyd resins modified with other synthetic resins and oil
extended._—Excellent water resistance and versatility are the
characteristics of finishes made of alkyd resins modified with other
synthetic resins (usually tar-acid) and oil extended. The incorporation
of drying oils gives a low cost finish with better compatibility and
brushing and with the combined properties of a quick-setting varnish
and an alkyd resin. Although not so durable or quick setting as the
unmodified finishes, they have better water resistance. These finishes
may be brushed or sprayed, air-dried or baked. They have wide industrial
and architectural uses.
_Semidrying alkyd resins._—Cottonseed oil is the principal modifier in
semidrying alkyd resins. Alkyd resins of this type are used in finishes
requiring maximum gloss and color retention. When baked on metal at
high temperatures they show no tendency to wrinkle. They are used as
reinforcing agents to increase flexibility and durability, and to
plasticize other finishes.
_Nondrying alkyd resins._—The nondrying or nonoxidizing alkyd resins
are those containing a nondrying oil, such as castor oil or coconut
oil, or the fatty acid of a nondrying oil, such as stearic, palmitic,
or oleic acid. Nondrying oils make the resin less sensitive to heat
hardening and impart greater flexibility. These resins are used
principally as plasticizers in nitrocellulose lacquers. In this use they
have the advantage of better retention of plasticizing efficiency than
other plasticizers, many of which are lost by evaporation, migration,
absorption, or oxidation. These modified nitrocellulose lacquers, either
clear or pigmented, are used for coating wood, composition board, cloth,
paper, rubber, leather, and similar surfaces.
_Miscellaneous modified alkyd resins._—This group includes alkyd resins
modified with materials other than those already discussed. To date
(1938) there has been little, if any, commercial production of such
resins. There are many modifiers which have been suggested and which
might be used but for the fact that they are too expensive. Among these
are butyl alcohol and benzoic acid.
_Alkyd resins in water dispersion._—Emulsions of alkyd resins in water
are now available for use in clear and pigmented coatings. These are sold
in the form of paste containing 40 to 50 percent solids and are diluted
with water at the time of application. They are especially suitable for
coating porous surfaces, such as brick, concrete, plaster, stucco, and
masonry of all kinds. They are applied by brushing or spraying and they
combine the ease of application of water paints with the durability,
washability, and hardness of oil paints. They dry quickly, and the dried
film cannot again be dissolved or suspended in water; the coating can
therefore be washed or, after several weeks, scrubbed with cleansers.
Compared with oil paints, they give better coverage, are easier to apply,
and cost appreciably less. Compared with other types of water paints,
such as kalsomine, they give a glossier coating of greater durability and
superior appearance; they seal porous surfaces better; their covering
capacity is greater; and their applied cost is slightly less per square
yard of surface.
Coatings of this type may be applied directly over fresh plaster without
a sizing coat, since they allow the curing of the plaster to continue.
The usual paint pigments may be incorporated.
A special use of the water dispersed alkyds is on asphalt or tar since
they are nonbleeding in the solvents of these materials. This quality
permits their use for traffic and zone markers on streets.
_Alkyd resins in molding compositions and other uses._—The alkyd resins
are much less important as binders in molded articles than in coatings
and finishes. Conversion of the resin to the insoluble infusible form is
extremely slow, requiring days as compared with minutes for the tar-acid
and urea resins.
The alkyds are used as binders for flake, powder, and split mica to
produce insulation material of high electrical strength. Other uses are
in the production of linoleums; gaskets; brake linings; laminated fabric,
paper, and cardboard sheets; printing inks; and coated paper, textiles,
and leathers.
Pigments and solvents in alkyd finishes.
Since the alkyd resins are largely used in surface coatings and finishes
and since this application in this field is producing great changes in
the industry, it is appropriate to consider the effect of their use on
other materials.
The average alkyd resin consists of 50 percent glycerol phthalate
modified with 50 percent oil, fatty acid, natural resin, or synthetic
resin. The alkyd and modifier are dissolved in a solvent, usually a
coal-tar light oil such as toluol, or xylol, or a petroleum solvent, and
pigmented with titanium dioxide or other pigment. Highly basic pigments
such as zinc oxide, carbonate white lead, whiting and aluminum hydrate
(all important pigments in the conventional types of finishes) are not
used in alkyd finishes.
Production in the United States.
Prior to 1929, the domestic production of resins from phthalic anhydride
was confined largely to one maker. The quantities produced were
relatively small. In 1929 there were three producers, the volume of whose
production exceeded one million pounds for the first time. Beginning with
1933 the Tariff Commission collected and compiled production and sales
statistics for these resins. They are shown in table 7.
TABLE 7.—_Alkyd resins from phthalic and maleic anhydride: United States
production and sales, 1933-37_
--------+-----------+------------+------------------------------------
| | | Sales
Year | Number of | Production +------------+-----------+-----------
| makers | | | |
| | | Quantity | Value | Unit value
--------+-----------+------------+------------+-----------+-----------
| | _Pounds_ | _Pounds_ | |
1933 | 6| 9,930,705| 3,654,854 | $673,890 | $0.18
1934 | 10| 15,219,247 | 7,084,602 | 1,022,436 | .14
1935 | 15| 34,312,713 | 15,836,942 | 3,482,078 | .22
1936[1] | 31| 46,952,452 | 24,252,535 | 5,312,121 | .22
1937[1] | 39| 61,254,019 | 34,738,295 | 6,864,194 | .20
--------+-----------+------------+------------+-----------+-----------
[1] Includes resins from maleic anhydride.
Source: Dyes and Other Synthetic Organic Chemicals in the United
States, U. S. Tariff Commission.
In 1933 there were 6 makers of resins from phthalic anhydride, in 1935
there were 15, and in 1937 there were 35. The 1937 output of alkyd resins
from phthalic anhydride was 58,450,032 pounds net resin, with sales
of 32,583,307 pounds valued at $6,446,011. Producing plants are well
scattered through northern and eastern United States. In 1936 fewer than
one-third of the makers accounted for about 90 percent of the output.
The domestic production of resins from maleic anhydride was reported for
the first time in 1933. The output in that year consisted of experimental
quantities produced by two firms. A small increase in production occurred
in 1934 when another maker began operation. In 1936 there were eight
producers and the output was many times that of 1934. In 1937 there were
12 makers of these resins with an output of 2,803,987 pounds and sales of
2,154,988 pounds, valued at $418,183. It is the opinion of some persons
in the industry that in volume of production and sales the resins from
maleic anhydride will in the near future approach that obtained from
phthalic anhydride.
Imports into and exports from the United States.
No imports of alkyd resins have been recorded in official statistics.
Exports of alkyd resin coatings and finishes are not separately shown,
but data collected from the several producers show that appreciable
quantities were exported in recent years, principally to Central and
South American countries.
5. UREA RESINS
One of the most important series of thermosetting resins is the group
made by condensing urea and formaldehyde. As early as 1897 it was
discovered that an amorphous condensation product was obtained from the
reaction of urea and formaldehyde. The clear glass-like mass obtained led
to considerable research work toward the development of a substitute for
glass. It was found, however, that the resin obtained absorbed moisture,
resulting in a dimming of its luster, and that on standing for a time,
the condensation continued producing cracks, fissures, and disfigurements
in the molded article. In 1926 a successful commercial product was
developed in England by the use of thiourea. Cost of production, however,
was high. The addition of thiourea gave the product greater strength
and water resistance than that obtained with urea alone but retarded
the rate of cure. Also the sulphur present attacked steel molds, which
necessitated the use of expensive chromium plated or stainless steel
molds.
About 1929 the first successful straight urea product was perfected in
the United States. It was found that a filler, such as highly refined
alpha cellulose, minimized the stresses. The filler (as much as 30 to 40
percent is usually incorporated), destroys the transparency but permits
the manufacture of translucent articles in a wide range of color. Many of
the colors possible with the urea resins, particularly the light shades,
cannot at present be obtained in molded tar-acid resins.
An interesting fact concerning these resins is that they are produced
indirectly from four gases: Ammonia, carbon dioxide, hydrogen, and carbon
monoxide. Ammonia and carbon dioxide react to form urea, and hydrogen and
carbon monoxide yield methyl alcohol which is converted to formaldehyde.
Description and uses.