depth of color, properties not readily obtained in other thermosetting
resins. Being odorless and tasteless and completely resistant to oils
and greases, they are adapted to use in the manufacture of cosmetic
containers. Concentrated acids and alkalies attack the resin. The
electrical properties of the urea resins compare favorably with those of
the tar-acid resins. They have a lower power factor at high-frequencies
than the tar-acid resins, and are replacing, to some extent, established
materials in heavy duty electrical equipment where “tracking” causes
trouble. Molded articles made from urea resins are resilient but not
unbreakable.
[Illustration: THERMOSTAT CASE OF MOLDED UREA RESIN.
Source: Plaskon Company, Inc., 2112 Sylvan Avenue, Toledo, Ohio.]
[Illustration: SCALES CASE OF MOLDED UREA RESIN.
Source: Plaskon Company, Inc., 2112 Sylvan Avenue, Toledo, Ohio.]
The important uses of the urea resins are dictated by their pleasing
color and appearance. In 1935 the largest outlets were in buttons and
buckles, in bottle closures, and in such premium items as biscuit cutters
and cereal bowls distributed by a large food manufacturer. Tableware,
bathroom fixtures, all sorts of containers and closures, housings for
radios, clocks, scales, and other machines for retail stores, and
light-colored wall plates and switches, knobs, handles, and trim on dash
panels of automobiles, and handles and trimming on gas and electric
ranges were among the widespread applications of the urea resins. In
1938 probably the fastest growing outlet for urea resins is in lighting
equipment. Use in packaging, in closures, and in housings, is also
increasing. Tableware, the principal outlet for a number of years, is
declining markedly.
A comparatively new use is in shades and reflectors, replacing opal
glass. The unpigmented resin is highly translucent and gives high
light transmission and an exceptional degree of light diffusion. These
properties, together with low unit manufacturing costs, reduced shipping
costs, and resistance to breakage make the urea resins an ideal material
for all sorts of shades and reflectors for direct and indirect lighting
fixtures. Many of the shades used in railway cars are of this material.
The resin is available in degrees of denseness and opacity to give
particular ratios of reflection and transmission. Reflectors as large as
28 inches in diameter are on the market.
Although molded articles are the large outlets for the urea resins, other
applications are of increasing importance. Sirups used to impregnate
paper and cloth are used in laminating and the resulting materials have
unusual decorative possibilities. The surface is hard and durable and the
wide range of colors possible permits very attractive applications. The
urea resins are used both as the principal binding material for laminated
sheets or on the surface laminae of sheets where tar-acid resins are used
as the chief binder. The latter practice permits a wide color range in
decorative materials without loss of strength or other characteristics
of the tar-acid resins. In 1937 there were seven makers, and their
production of urea resins for laminating accounted for slightly less than
10 percent of the total of all urea resins.
Another application of urea resins which has grown rapidly in the past 2
years is in combination with alkyd resins in surface coatings. In 1937
there were three makers, and their output of urea resins for coatings
amounted to more than 10 percent of the total production of urea. Until
recently the use of urea resins in paints and varnishes was discouraged
by their insolubility in organic solvents and their instability. On the
other hand, their lack of color, their high transparency, their hardness,
and their freedom from after-yellowing were desirable characteristics.
The development of methods for preparing condensates, which overcome the
undesirable properties, has made available resins for this use. They
are marketed as water-white viscous solutions in a mixture of organic
solvents and are intended for use in baking finishes. They cannot be
used alone because the cured resin is extremely hard and brittle and
lacks adhesion. When combined with more elastic film-forming materials
such as drying or nondrying oil alkyd resins, they produce coatings that
are mar-proof, resistant to alcohol, grease, oil, and fruit acids, and
available in a full range of colors. Applications are in metal furniture
finishes, toys, refrigerators, can, and drum coatings.
The value of urea resins as adhesives has been known for many years and
one of the first patents issued for such use was United States Patent
No. 1,355,834 granted in 1920. Commercial development and application,
however, did not take place until the last 2 years. Several brands of
urea adhesives are now on the market. These meet the need for a hot-press
adhesive which is applied in liquid form, cures rapidly at moderate
temperatures, and is economical. For greater economy, the urea adhesive
may be mixed with various proportions of flour (up to 50 percent) without
affecting its water resistance. Diluted thus it comes within the cost
range of animal and vegetable glues and is more durable. At present, it
sells for 18 to 20 cents per pound; mixing it with 50 percent flour gives
an adhesive for plywood, costing about 10 cents per pound. In 1937 three
producers made urea resins for this use.
Other uses are in the treatment of textiles to obtain crease-proof
properties and in the impregnation of wood. United States Patent No.
1,951,994 issued on March 20, 1934, reports the preparation of artificial
silk from urea resins.
Production in the United States.
Commercial production of urea resins in the United States was reported
for the first time in 1929. Early in that year the American Cyanamid Co.
concluded an arrangement with the British Cyanides Co. of England for
the American rights to manufacture and sell in the United States a resin
made from urea, thiourea, and formaldehyde and marketed as Beetle molding
powder. A manufacturing unit was built at Bound Brook, N. J., and in 1930
the output was substantial.
In 1931 another producer, the Toledo Synthetic Products Co., began
manufacture of urea resins. Several years prior to that time the Toledo
Scale Co. started a search for a material light in weight to replace the
heavy porcelain-on-steel used in cases for scales. The search led to the
urea resins and to commercial production by their subsidiary. In 1935 the
Toledo Synthetic Products Company reached an agreement with the Imperial
Chemical Industries of England for the interchange of technical and
commercial information and of free patent licenses on urea molding and
laminating resins. The name of the domestic firm was later changed to the
Plaskon Co.
In 1932 the Unyte Corporation started commercial production of urea
resins at Grasselli, N. J. This firm was affiliated with the American
I. G. Corporation. Late in 1936 the Plaskon Co. took over the Unyte
Corporation.
The output of urea resins increased markedly in 1936 and 1937. Statistics
for those years cannot be published without disclosing operations of
individual firms. It may be stated, however, that the increase in both
years over the previous year was considerably greater than for any
earlier period. Most of the production was used in molded articles
although appreciable quantities were consumed in laminated articles, in
surface coatings, in the impregnation of fabric, and in adhesives.
There were 10 domestic makers of these resins in 1937.
Domestic production and sales of urea resins are shown in table 8.
TABLE 8.—_Urea resins: United States production and sales, 1933-37_
--------+------------+------------------------------------
| | Sales
Year | Production +-----------+------------+-----------
| | Quantity | Value | Unit value
--------+------------+-----------+------------+-----------
| _Pounds_ | _Pounds_ | |
1933 | 3,234,356 | 2,977,791 | $1,422,671 | $0.48
1934 | 3,470,916 | 3,115,608 | 1,290,802 | .41
1935 | 4,202,536 | 4,005,083 | 1,828,565 | .46
1936-37 | ([1]) | ([1]) | ([1]) |
[1] Not publishable; figures would reveal operations of
individual firms.
Source: Dyes and Other Synthetic Organic Chemicals in the United
States, U. S. Tariff Commission.
United States imports and exports.
Resins obtained from urea and thiourea, if imported, would probably be
classified under paragraph 11 of the Tariff Act of 1930. The present rate
of duty under this classification is 4 cents per pound and 30 percent ad
valorem.
There has been no importation of these resins. This is due principally
to the international licensing arrangements which usually include the
allocation of markets.
Exports are not shown separately in official statistics.
6. ACRYLATE RESINS
A new development of widespread importance in the synthetic resin
industry is the commercial production of the polymers of certain
derivatives of acrylic acid. The commercial exploitation of the acrylates
is another example of the belated realization of the value of substances
known for many years. Acrylic acid has been known for about a hundred
years, and the polymer of methyl acrylate was first described in 1880. It
was not until 1927, however, that a suitable method for their commercial
production was developed. The study of the many derivatives of acrylic
and methacrylic acids leads to the conclusion that those of greatest
practical application in the resin field are the lower esters, such as
methyl and ethyl, polymerized separately or together.
Colorless transparency, stability against aging, thermoplasticity, and
chemical resistance to many reagents are the general characteristics
of the acrylate resins. In consistency they range from soft, sticky,
semiliquids to hard, tough, thermoplastic solids. Since these widely
varying properties are obtained by control of manufacturing conditions,
rather than by the use of plasticizers, the resins retain their initial
properties indefinitely. Aging and weathering have no effect as they
are stable under exposure to heat, light, and oxidizing agents. The
methacrylates are harder and tougher but less elastic than the acrylates.
Properties and uses.
The acrylate resins are marketed in a number of forms, such as solutions
in organic solvents, dispersions in water, solid cast sheets, rods and
tubes, and molding powders. All of these are distinguishable from many
other resins by their colorless transparency, adhesive qualities,
great elasticity, and chemical resistance. The brilliant water-white
color makes it possible to secure masses having a high degree of light
transmission and great optical clarity.
The earliest commercial use of the acrylate resins was in laminated
safety glass marketed as Plexigum in the United States and as Luglas and
Sigla in Europe. The extensibility and elasticity of the resin film gives
the laminated glass a flexible or yielding type of break when subjected
to a hard impact. Having excellent adhesion to glass there is no need of
an auxiliary cement to bond the resin to the glass, nor is it necessary
to seal the edges since the resin has good resistance to moisture. The
acrylate resin used for this purpose is in the form of a viscous solution
in an organic solvent. A film is applied to each sheet of glass, the
solvent removed by drying, and the sheets are pressed together.
The harder acrylic resins are used in the form of solid thermoplastics.
Methyl methacrylate is of special interest. As the monomer is a mobile
liquid it can be cast-polymerized to a solid of any desired shape in
predesigned molds or produced in finely divided form for use as molding
powder. The cast resin is marketed in this country as Crystalite,
Plexiglas and Lucite, and in England as Diakon.
The solid acrylate resins are clearer than cast phenolic resins, not as
brittle as the polystyrene resins, and not as tough as cellulose acetate
or nitrocellulose plastics. Their transparency and resistance to aging
and weather permit their use in applications not previously considered
for synthetic resins. Sheets of this resin may be formed or molded
into many useful shapes. The aircraft industry has found them suitable
for windshields and cockpit enclosures to effect streamlining and thus
greatly reduce wind resistance.
Methyl methacrylate is probably the nearest approach to organic glass
thus far developed. Its optical properties make it suitable for spectacle
lenses, camera lenses, magnifying glasses, and protective goggles.
Spectacle lenses are now being made to prescription by molding. It is
estimated that 900 molds will supply the requirements of about 98 percent
of the prescriptions. The excellent light transmitting quality of methyl
methacrylate permits its use in edge lighting, advertising displays, and
instrument dials. It is also used in inspection windows in various types
of machinery where curved sections are necessary and where glass might be
broken.
A synthetic resin combining the properties mentioned, together with high
tensile and impact strength, good dielectric properties, ultraviolet
transmission, and resistance to water, oil, acids, and alkalies is an
important contribution. The acrylates may be colored or have fillers
added to give any desired translucency or opaqueness. They can be sawed,
cut, blanked, turned, drilled, ground, polished, and sanded much the same
as are nitrocellulose plastics.
[Illustration: AIRPLANE COCKPIT ENCLOSURES OF CAST ACRYLATE RESIN.
Source: Rohm & Haas Company, 222 W. Washington Square, Philadelphia, Pa.]
[Illustration: SPECTACLE LENSES MOLDED TO OPTICAL PRESCRIPTION FROM
ACRYLATE RESIN.
Source: Rohm & Haas Company, 222 W. Washington Square, Philadelphia, Pa.]
A new and interesting application of the acrylate resins is as molded
reflectors in a system of indirect highway lighting. The reflectors are
pressed from colorless, transparent methyl methacrylate resin and are
1⅝ inches in diameter. They are assembled in a pressed metal housing to
form a double facing marker which is snap-locked to the top of an angle
iron post. The posts are so located that the reflectors are accurately
aligned 3 feet above the pavement edge. An installation has been made
on U. S. Highway No. 16 between Detroit and Lansing, Mich., at a cost
of about $340 per mile. The motorist provides his own light from his
headlights which strikes the reflectors and is returned as a narrow beam
of brilliant illumination. The chief of the United States Bureau of
Public Roads states that this is a definite contribution to the safety
and utility of the highways at night. The reflector is a group of tiny
cube corners, over 300 in each disk. Each cube corner is a complete
retrodirective optical system; a light ray entering the front surface
is reflected from surface to surface of the cube and after the third
reflection is directed back toward the headlight regardless of the
entrance angle. If the cubes are made with a high degree of dimensional
accuracy, the reflected light has a high candlepower, strong enough to be
seen for a mile.
Other uses for these resins are in sound recording records, dentures,
telephone and radio transmitter diaphragms, novelties, and lighting
fixtures.
The monomer (unpolymerized methyl methacrylate) may be used to impregnate
wood, cloth, wallboard, cork, paper, electrical coils, tile, or stone,
and then polymerized to form the resin. Paper and cloth so treated have
many uses, such as in the electrical and food-packaging industries.
Laminated sheets find wide possibilities for use in the aircraft field,
and for lamp shades. Wood may be impregnated with as much as 60 percent
of the monomer. Solutions of these resins in organic solvents, such as
ethylene dichloride, ethyl acetate, and toluol, are used in surface
coatings, undercoats on difficult adhesion jobs, to impregnate paper and
textiles, and in insulation. These coating solutions are marketed in the
United States under the trade name Acryloids and in Europe under the
trade names, Borron, Plexigum, and Acronol. They may be brushed, sprayed,
dipped, and baked. Baking is recommended to give a higher gloss, better
adhesion, and a harder film. The dried film has an elasticity of 1,000
percent at ordinary room temperature and the light transmission of clear
films is intermediate between ordinary window glass and quartz.
Acrysol is an adhesive consisting of a dispersion of the resin in water
and is recommended for use where adhesion is difficult, as on rubber or
rubberized surfaces.
Production in the United States.
Commercial production of acrylate resins in the United States was started
in 1931 by Rohm and Haas, Philadelphia, Pa., under United States Patents
Nos. 1,388,016 of August 16, 1921, and 1,829,208 of October 27, 1931.
Commercial production of methyl methacrylate resins was started in 1937
by E. I. du Pont de Nemours & Co. This development is under United States
Patent No. 1,980,483, issued in 1934. The liquid monomer is produced at
Belle, W. Va., and shipped to Arlington, N. J., where it is polymerized
by heat to the solid resin.
The output of acrylate resins was hardly more than experimental in 1935
but increased somewhat in 1936 and very appreciably in 1937. Although
statistics of production are not publishable, it can be stated that
in 1937 the output approached that of other synthetic resins made in
commercial quantities. The properties of these resins indicate very
large commercial production in the near future. Prices of the several
types are still high as compared with other resins but should eventually
be somewhat lower than those of cellulose acetate and nitrocellulose
plastics and slightly higher than those of cast phenolic resins.
Imports into and exports from the United States.
There have been no recorded imports of acrylate resins. The two domestic
producers have agreements, licenses, or affiliations with the principal
foreign makers of these products, one in England and one in Germany. Such
arrangements would account for the absence of imports, except for sample
or experimental lots, and might also limit export markets.
7. COUMARONE AND INDENE RESINS
Coumarone and indene are present in appreciable quantities in certain
coal-tar fractions, especially in the solvent naphtha fractions
distilling between 160° and 190° C. No attempt is made to isolate
them from the solvent naphtha. Such a procedure would be difficult
and expensive and, since polymerization readily takes place in dilute
solutions, it is more economical to use fractions of solvent naphtha rich
in these substances. The resins obtained are mixtures of polymerized
coumarone and polymerized indene.
The solvent naphtha must be refined by fractional distillation and
the polymerization very carefully controlled. The polymerizing agent
is usually sulphuric acid although metallic salts, such as aluminum
chloride, are sometimes used. The yield and color of the resin are
affected by temperature and amount of acid used. Light colored resins
are the most desirable. After polymerization the acid or metallic salt
is removed, the product washed and neutralized and finally distilled.
Several byproducts, such as naphtha, paracoumarone soap, and high boiling
oils, are also obtained.
Description and uses.
Coumarone and indene resins are produced and marketed in the United
States under the trade names Cumar and Neville. A number of grades are
available, including the following:
Designation: _Melting point_
Rubber grade, soft 50°- 65° C.
Medium soft 65°- 85° C.
Rubber grade, hard 85°-100° C.
Medium hard 100°-135° C.
Varnish grade 135°-160° C.
In addition to these, certain types are produced for special purposes.
The coumarone and indene resins are used to a large extent in varnishes
for metal and wood. In this application they may be used to replace
all or part of the higher priced natural resins and, to some extent,
ester gum. Their application is somewhat limited by their rather
short durability and elasticity. They are neutral, nonoxidizing and
nonsaponifiable and impart to varnishes greater inertness and adhesion,
fair dielectric strength, and shorter drying time than many of the
natural resins. They cannot be used in nitrocellulose lacquer since they
are not compatible with that plastic.
Another important use of these resins is as an ingredient in mastic
floor tile, in the production of which a thermoplastic binder is
used. Originally, asphalt was used, but demand for light colored tile
necessitated some other binder, the requirements for which were met by
the coumarone and indene resins.
The next largest application of these resins is in rubber compounding,
their effect being to soften the rubber during milling and to facilitate
its handling on rolls. They do not affect the aging qualities of rubber
and are used as a softener for reclaimed as well as for new rubber.
Coumarone and indene resins are used, to some extent, in linoleum, for
impregnating roofing felt, in electrical and friction tapes, paper
and cloth sizing, printing inks, brake linings, adhesives, artificial
leather, oil cloth, and shoe polishes. As a substitute for chicle as
much as 10 percent may be incorporated in the chewing gum mixture.
Their application in molded articles is very limited because of their
brittleness and low tensile strength.
Production in the United States.
There are three domestic makers of these resins. Statistics of production
and sales cannot be published without disclosing the operations of
individual companies. The output, however, has increased appreciably
in recent years and this type of synthetic resin is now among the most
important produced.
Imports into and exports from the United States.
There have been no recorded imports of coumarone and indene resins in
recent years. This is understandable because the duty alone would usually
be more than the domestic price.[4]
Official export statistics do not separately record these resins,
although quantities are exported to nearby countries, including Canada.
8. PETROLEUM RESINS
Considerable research work has been done on the synthesis of resins from
petroleum. It has long been known that cracked petroleum distillates,
when stored for a time, have a tendency to form gums. This tendency is
so pronounced that inhibitors are added to arrest such formation. These
gums are of little value as resins, but it is possible to obtain good
varnish resins by oxidation or controlled polymerization of certain
distillates of petroleum cracking. By carefully controlling operations,
resins of varied properties are obtained and several of them have become
commercially important. The unsaturated compounds, largely olefins
and diolefins, present in highly cracked petroleum distillates can be
polymerized, with certain catalysts. The resin produced depends upon the
types of unsaturated hydrocarbons present and upon the conditions of
polymerization.
Properties and uses.
Several types of petroleum resins are on the market, one made from the
“polymer slop” obtained in the high temperature, vapor-phase cracking
operation, and the other prepared primarily for the production of resin.
The former is marketed under the trade name Petropol and the latter as
Santoresin.
The “Petropol” resins are marketed in two grades, No. 1158 and No. 2138.
The specifications for these are as follows: