used in large volume in this way. An article produced in large quantity
is more likely to be made of molded resin. The cost of the mold, which
may amount to several thousand dollars, then becomes very small per unit
produced. If the article is of such a shape that it would require a great
deal of labor to produce in metal or wood, it may be produced in quantity
much more cheaply from resin, since it will come from the mold almost in
finished form.
A few of the large molders find it economical to make their own
resins when they use one type in large volume or desire some special
modification. Most of the molders buy resins for molding in the form of
either powder or pre-formed pellets ready for use.
Molding powders and pellets.
Molding powder is made from B-stage resin (see p. 13), a filler, a
pigment, a lubricant, and a plasticizer. These materials are mixed and
put through rolls at a moderate heat and pressure. The resin softens
and amalgamates with the other materials. It hardens upon cooling and
is ground to powder. A pre-formed pellet may be made from the powder by
pressure; use in this form saves the time of the molder when filling the
mold, since he is not required to measure the powder.
The proper selection of the filler in a molding powder is important in
influencing the quality of the molded article. Fibrous fillers improve
the mechanical strength and shock resistance of the finished article.
Wood flour is the most widely used filler in tar-acid resins as well as
in other thermosetting resins. Pine, spruce, and fir are the principal
kinds used, and consideration must be given to the bulk, gum content,
color, and the size and shape of the wood particles. Color is the least
important since most of the tar-acid resins give brown or black moldings.
When the molding must withstand high temperatures, asbestos fiber is
used as a filler. In articles requiring high shock resistance, such as
golf club heads, a filler of paper pulp is used. Where high electrical
insulation and dielectric properties are required, ground mica is used
as the filler. Certain inorganic fillers such as powdered slate, gypsum,
barium sulphate, calcium sulphate, china clay, zinc oxide, and infusorial
earths, are sometimes used. Large proportions of these may be used where
hardness is more important than strength, as in phonograph records. Other
materials used include rubber, graphite, horn, bone, starch, pumice, and
cork.
Coloring matter used may be coal-tar dyes or pigments such as bone black,
carbon black, and iron oxides. Pigments are usually more satisfactory,
although dyes are sometimes preferred in articles for insulation.
A lubricant is added to the molding mixture to overcome the tendency to
stick in the mold. Metallic soaps, stearates, and stearic acid are those
most commonly used.
Sometimes a plasticizer is included, its function being to act as a
solvent for the resin, thus increasing the flow of the material in the
mold. The plasticizer should be one which will become infusible or at
least remain solid in the molded article.
[Illustration: PREFORM PRESS MAKING PELLETS FOR USE IN MOLDING.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
[Illustration: VACUUM CLEANER PARTS OF TAR-ACID RESIN ILLUSTRATING THE
INTRICATE MOLDED SHAPES POSSIBLE.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
[Illustration: RADIO CABINET AND TELEPHONE SET OF MOLDED TAR-ACID RESIN.
Source: Bakelite Corporation, 217 Park Avenue, New York, N. Y.]
A typical molding powder or pre-form pellet will contain by weight:
Resin 40 to 50 percent
Filler 35 to 50 percent
Plasticizer 5 percent
Lubricant 1 percent
Pigment 1 percent
The molding of tar-acid resins.
Ordinarily the molds used are made of hardened steel, highly polished.
They must stand working pressures of several thousand pounds per
square inch. The mold is placed in a hydraulic press, heated by steam,
electricity, or gas, and the molding material is placed in the mold. The
press is closed and heat and pressure are applied. The temperatures used
range between 250° F. and 365° F., and the pressures between 1,000 and
8,000 pounds per square inch. The molding time depends on the shape and
size of the article and on the composition of the molding material. As
little as one-half minute is required for small objects and as long as 10
minutes for large objects. Average molding time is about 3 minutes. The
article is removed from the mold, allowed to cool, and is then trimmed,
sanded, filed, or polished. Since the mold is highly polished, the
finishing operation is usually needed only to remove the flash. Inserts,
such as metal parts (binding posts, electrical contacts, etc.), or inlays
of polished metal in name plates, and signs, are often molded in; gear
shift knobs are molded over a hollow metal core; rubber inserts are used
in castors, electrical plugs, and similar objects.
The molding operation is an art, and has made remarkable progress in
recent years. Many articles molded of tar-acid resins are well-known to
the public. The automotive industry is the best customer, using such
molded parts as gear shift knobs, horn buttons, accelerator pedals,
light switches, ignition parts, and distributor heads. Other well-known
applications are builders’ hardware, electrical switch plates, switches
and fixtures, fountain pens, radio parts, telephone parts, handles for
stoves, vacuum cleaners, and other appliances, buttons, buckles, costume
jewelry, camera cases, radio cabinets, small containers, and hundreds of
others.
The importance of tar-acid resins in molded articles is shown by the fact
that more than 75 percent of all synthetic resin molded articles made in
1937 used this type of resin as a binder.
Production of tar-acid molding resins.
Domestic production of tar-acid molding powders and pellets was reported
to the Tariff Commission by 15 makers in 1937. Most of these firms have
specialized in resin development and manufacture. Among the well-known
brands are Bakelite, Durez, Durite, Resinox, Indur, and others (see p.
153 for list of trade names).
Statistics of production and sales of tar-acid resins used in molding
were collected separately for the first time in 1935. They show a net
resin output of about 21,000,000 pounds, with sales of 18,000,000 pounds
or about 40 percent of the total tar-acid resins. The average unit value
was 17 cents per pound. In 1937 the production of tar-acid resins for
molding exceeded 32,000,000 pounds, again about 40 percent of the total.
These statistics are based on net resin and do not include fillers,
modifiers, pigments, or inert material of any kind.
CAST PHENOLIC RESINS
Process of manufacture.
The production of cast phenolic resins requires pure materials, expensive
equipment, and extreme care in the control of the operation. A mixture
of phenol and formaldehyde and a catalyst (usually sodium or potassium
hydroxide) is charged into a nickel-lined reaction kettle and heated
until the water separates and is removed. The reaction is then allowed
to proceed to the desired point. Glycerin is added to aid in forming a
transparent product. All equipment, including pipe lines, valves, and
pumps, is nickel or nickel lined except that used for formaldehyde, which
is made of aluminum.
The resin is usually made in 1,000 pound batches, and the reaction cycle
ranges from 6 to 18 hours. It is colored with soluble coal-tar dyes and
cast into lead molds. These are placed in a heated room and allowed
to cure for 3 to 6 days. The resin is removed from the mold with air
hammers, and the lead molds are melted.
The appearance of the resin may be changed by varying its water content,
by the addition of dyes and fillers, and by the addition of other
substances to produce some desired effect, such as imitation ivory or
marble. The clarity of the resin depends upon its water content—the
greater the degree of dehydration the clearer the product. Range of
colors is complete, from crystal clear to the darker shades, with any
degree of transparency, translucency, or opaqueness.
Casting is in the form of sheets, rods, tubes, or special forms suitable
for the production of buckles, jewelry, and other small products. Molds
of complicated shape cannot be used, which means that most articles
if produced of cast resin must be produced from standard shapes by
subsequent working. Recently small radio cabinets have been cast.
Uses.
Cast phenolic resin can be machined in the same manner as hard wood. It
must be polished after machining, usually by tumbling with shoe pegs and
pumice or with muslin wheels. The smooth finish and low degree of heat
conduction give the material a pleasant feel, not cold to the touch as
is metal. The coloring is not superficial and therefore does not chip
or wear off. Electrical properties are excellent. A slow polymerization
continues for some time after fabrication, resulting in slight shrinkage.
Cast phenolic resins are marketed by the producers as rods, sheets,
cylinders, and special castings. Standard round rods range from ⅜ inch to
more than 5 inches in diameter. Special rods are available in such forms
as square, hexagon, octagon, and fluted. Standard sheets are in sizes
from 12 by 24 inches to 36 by 72 inches, and from ⅛ to 1 inch thick.
Stock cylinders are available in a wide range of inside and outside
diameters.
[Illustration: CAST PHENOLIC RESINS, STANDARD SHAPES AND SMALL ARTICLES
FABRICATED FROM THEM.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
Stock material is fabricated by a number of firms into an endless variety
of articles. Among these are toilet articles such as combs, backs for
brushes, cosmetic containers, and trinkets; fittings for automobiles,
electrical appliances, furniture, and display fixtures; jewelry, dress
ornaments, clock cases, handbag frames, vanity cases, smokers’ articles,
signs and advertising specialties, picture frames, handles for cutlery,
chessmen, pens, desk penholders, pencils, and many others. Probably the
largest consumption is in the making of buttons and buckles.
The cast phenolic resins are odorless, tasteless, nonflammable, resistant
to oils and greases, and practically nonbreakable.
Patents and licensing.
The basic patent covering the manufacture of cast phenolic resins is
United States Patent No. 1,854,600, issued April 19, 1932, to F. Poliak
and A. Ostersetzer, of Vienna, and assigned to Pollopas, Ltd., of London.
Many other patents have been granted on variations and modifications of
this one. The basic process is also patented in England, France, Germany,
and other countries.
United States and Canadian patent rights were purchased by the American
Catalin Corporation; German rights by the Interessen Gemeinschaft
Industrie A. G. (German I. G.); French rights by Kuhlmann Co., and
British rights by the Imperial Chemical Industries. These licensing
arrangements limited the licensee to sales in his own and, in some
instances, nearby countries.
The American Catalin Corporation has successfully defended the validity
of this patent and has licensed a number of domestic manufacturers to
produce cast phenolic resins on a royalty basis.
In 1937 there were seven domestic makers of cast phenolic resins located
in New Jersey, New York, Massachusetts, and Pennsylvania. These firms
produce and market resins under the following trade names: Catalin,
Prystal, Joanite, Fiberlon, Phenolin, and Marblette.
Production of cast phenolic resins.
Production was initiated about 1929 by the American Catalin Corporation.
The output increased substantially every year from that year through
1933. Statistics of production and sales are not publishable for
the years prior to 1934 because they would reveal the operations of
individual firms; they are given in table 6 for subsequent years.
TABLE 6.—_Cast phenolic resins: United States production and sales,
1934-37_
------+-------------+---------------------------------------
| | Sales
Year | Production +------------+-------------+------------
| | Quantity | Value | Unit value
------+-------------+------------+-------------+------------
| _Pounds_ | _Pounds_ | |
1934 | 4,968,445 | 4,793,658 | $2,099,035 | $0.44
1935 | 5,566,621 | 5,454,490 | 2,205,879 | .40
1936 | 6,111,632 | 6,013,855 | 2,476,619 | .41
1937 | 5,459,654 | 5,335,746 | 2,180,620 | .41
------+-------------+------------+-------------+------------
Source: Dyes and Other Synthetic Organic Chemicals in the
United States, U. S. Tariff Commission.
Imports and exports.
The licensing agreements, as outlined above, provide for the allocation
of markets for cast phenolic resins. Because of this arrangement there
are little or no imports and exports of this material.
TAR-ACID RESINS FOR LAMINATING
By laminating is meant the impregnation of sheets of paper, fiber, or
cloth with a solution of synthetic resin and the building up of these
layers into sheets of reinforced synthetic resin of various thicknesses.
When a tar-acid resin is used the paper or cloth is immersed in or coated
with a solution of the B-stage resin, dried, and layers of the material
are compressed and consolidated, under heat and pressure to form sheets,
rods, tubes, blocks, and other forms, in the infusible C-stage.
The coating of sheets of paper with solutions of natural resin and the
compacting of these sheets by heat and pressure is an old practice,
especially for electrical uses. Shellac and copal have been widely used
and yield a laminated board of good electrical and mechanical properties
when used at temperatures under 70° C. Above 70° C. the resin softens and
the desirable properties are lost. Since temperatures above 70° C. are
not uncommon in electrical equipment, the limitations of these natural
resins in this use can readily be seen. The use of tar-acid resins to
impregnate insulation material removes the temperature limitation and
otherwise improves the product; insulators so made are widely used in all
sorts of electrical and radio equipment.
Uses of tar-acid resin laminated products.
Laminated sheets of tar-acid resin are made with paper, canvas, duck,
linen, pulpboard, vulcanized fiber, plywood, and other materials. Paper
is the material generally used for electrical insulation, although cloth
is sometimes used when greater strength is needed. Canvas is used where
maximum strength is required, as in gears for automobiles and industrial
machinery. Impregnated linen is adapted to punched parts and small gears.
These laminated materials are uniformly dense, tough, resilient and light
in weight. They are nonabsorptive, have low thermal conductivity, and a
low coefficient of expansion. Their dielectric strength is excellent and
chemically they are inert to oils, brine, most acids, weak alkalies, and
many solvents. Structurally they are strong under tension, compression,
flexion, or impact; they are easy to machine and are sound absorbing.
Gears made of laminated canvas are widely used; they are silent and
outwear those made of metal. The development of such gears was brought
about by the demand for a positive drive without the clash and clatter
resulting from metal to metal contact. The laminated gear absorbs
vibrations, eliminates noise, and reduces wear. The laminated material is
one-seventh the weight of brass, one-sixth the weight of steel, one-fifth
the weight of cast iron and one-half the weight of aluminum. Laminated
gear blanks may be cut on automatic machines into helical, spur, bevel,
or worm gears.
Timing gears in automobiles are frequently of this type; they require no
adjustment and seldom need replacement during the life of the motor. The
light weight of the material reduces to a minimum flywheel effect on the
camshaft. Where lubrication is difficult a graphite impregnated blank may
be used.
Bearings made from laminated fabric are successfully used in heavy
rolling mills where they reduce replacement costs and decrease power
consumption. The laminated material possesses strength, smooth surface,
density, good load carrying capacity, high impact resistance, nonscoring
properties, and is practically frictionless. Power consumption is said to
be reduced as much as 40 to 60 percent of that of metal bearings and the
life of the laminated bearing has been as much as 10 times that of the
metal ones. It replaces Babbitt metal, brass, bronze, white metal, gun
metal, or lignum vitae in this application.
[Illustration: LAMINATING SHEET PRESS.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
[Illustration: GEARS MADE OF LAMINATED TAR-ACID RESIN.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
[Illustration: COCKTAIL LOUNGE USING TAR-ACID LAMINATED DECORATIVE
MATERIAL.
Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]
In decorative uses, laminated materials have made remarkable progress
in recent years. In this application the material made from laminated
paper is veneered on wood or fiber board, and the surface is so durable
that refinishing is probably not necessary during the life of the
equipment. Table tops for public rooms such as restaurants, cafeterias,
and bars are widely used because of the beautiful designs obtainable and
because the material is not discolored by lighted cigarettes, alcohol
or other liquids, and does not chip or crack. Laminated sheets are used
for bathroom and kitchen walls, doors, window sills, store and theater
fronts, lobby walls in hotel and office buildings, and counter tops in
banks and post offices. The liner _Queen Mary_ is equipped with panels
of this material as is also the new Library of Congress Annex. Most of
the leading hotels have installed bar and cocktail lounges of laminated
materials because of the range of color and the ease with which novel
designs may be carried out.
Almost any solid color, design, or imitation of another material may be
given the laminated sheet simply by printing it upon the top sheet of
paper used in the impregnated assembly. Thus a beautiful piece of walnut
or mahogany may be photographed, inexpensively reproduced upon paper, and
the finished laminated sheet will closely imitate the polished wood. The
combination of beauty with long life should permit the widespread use of
this type of material in all sorts of building and equipment. It has been
suggested as a possibility in automobile body construction.
Other important uses are in trim and door strips for mechanical
refrigerators, in cafeteria trays, buckets and special containers, tires
for factory trucks, textile spools, miners’ safety helmets, gaskets,
valve discs and rings for pumps, pulleys, besides many others.
Production of tar-acid resins for laminating.
Statistics of production and sales of synthetic resins for laminating
were not separately compiled prior to 1935. Since that year the resins
made from cresylic acid have been used to the greatest extent in
laminating, followed by those made from phenol. Tar-acid resins reported
as “used in paints, varnishes, and lacquers” may include appreciable
quantities of resin varnishes used for laminating. The total production
and sale in 1937 of tar-acid resins used in laminating, therefore, would
be the sum of the 20 percent of the total (see table 3) reported for
laminating plus some part of the 25 percent reported for surface coatings.
Domestic producers of tar-acid resins for laminating are located
in Delaware, New Jersey, New York, Illinois, Massachusetts, and
Pennsylvania. The makers of the laminated materials are located in
Delaware, New Jersey, New York, Ohio, Illinois, Pennsylvania, Indiana,
and Connecticut. Their products are marketed under a number of trade
names, including Micarta, Dilecto, Celoron, Formica, Textolite,
Phenolite, Insurok, Spauldite, Synthane and Phenol Fibre.
Imports into the United States.
There has been practically no importation of synthetic resins for
laminating. Imports of laminated products (rods, tubes, blocks, strips,
blanks, or other forms) of which synthetic resin is the chief binding
agent totaled only 215 pounds, valued at $612 in 1931 (principally from
the United Kingdom); 13 pounds, valued at $71 in 1932; none in 1933 and
1934; 609 pounds, valued at $579 in 1935 from Canada, Germany, and the
Netherlands; and 3,260 pounds, valued at $9,468 in 1936 from Austria,
Germany, and the United Kingdom.
Exports from the United States.
Exports of phenolic or other synthetic resins for laminating and of
laminated articles are not separately recorded in official statistics. It
is known that appreciable quantities of laminated articles are exported
to Canada, England, and other countries.
TAR-ACID RESINS FOR SURFACE COATINGS
Synthetic resins are widely used for surface coatings, chiefly because
of the ease with which new types can be produced to meet special
requirements and because of their uniformity. Tar-acid resin coatings may
be varied in composition and properties to meet a particular purpose.
Possible variations depend on the type or mixture of tar acid used
(phenol, cresols, xylenols, tertiary amyl phenol, tertiary butyl phenol,
phenyl phenol), whether the condensation takes place in the presence of
an acid or an alkali, and on the proportion of formaldehyde used. The
resin so formed may be modified with natural resins, synthetic resins
of the alkyd type, fatty acids, or other materials. The almost endless
opportunities for different types can, therefore, readily be appreciated.
Types of resin used and the resultant coatings.
The tar-acid resins used in varnishes and other surface coatings are
usually oil-soluble types. They may be divided into three general
classes: (1) Phenol-formaldehyde condensation products rendered
oil-soluble by chemical combination or physical dispersion in other
materials, such as rosin and copal; (2) condensation products made
from tar acids other than simple phenol, which are themselves soluble
in drying oils and thinners; and (3) products from the condensation
of the substituted phenols and formaldehyde. These three classes of
oil-soluble tar-acid resins differ widely in their chemical and physical
properties and in their functions. The first group are usually called
modified phenolic resins, the second group are referred to as unmodified
or 100-percent soluble, and the third group are known as substituted
phenolic resins.
The unmodified resins are extensively used in long-oil tung varnishes,
to which they impart greater drying speed, durability, and resistance
to alkalis and gases. The modified types impart the same properties to
tung oil varnishes but to a lesser extent. In addition the modified
types possess considerable hardness so that greater gloss and fullness
are obtained. Modifiers are either drying oils or natural resins; tung
oil is the most widely used oil and rosin the principal natural resin.
Substituted phenols such as para tertiary amyl phenol and para tertiary
butyl phenol may be used in place of simple phenol; while these are
relatively high priced components, the resins made therefrom have
increased in recent years to an appreciable volume because of their
improved properties.
Other synthetic resins, such as those of the alkyd, petroleum, urea,
and vinyl types, are sometimes incorporated with the phenolics in the
same surface coating to obtain some desired property. The addition of a
plasticizer, such as tricresyl phosphate or dibutyl phthalate, improves
the flexibility of the film.
Spirit varnishes, in which the synthetic resin is dissolved in a solvent,
are also available. In this type the soluble fusible resin (form A) is
dissolved in an organic solvent such as acetone or the various alcohols,
and conversion of the resin to the insoluble, infusible state (form C) is
effected by baking the film.