Phenolic plastics are derived from phenol-formaldehyde resins, which are
made by reacting phenol, (carbolic acid) with formaldehyde, a product of
carbon monoxide and hydrogen. This group of resins may be broadly divided
into a number of distinct categories, moulding resins, casting resins,
adhesives, putties, laminating resins (used in the manufacture of plywood),
and lacquers.
Moulding resins, such as Bakelite, which are designed for compression or
transfer moulding processes, require the addition of a reinforcing filler
material, for example, asbestos, wood flour, cotton flock, paper pulp,
diatomaceous earth, barytes, gypsum or mica. This reinforcing filler is used
to strengthen what would otherwise be a very brittle moulded product.
Cast phenolic resins of this type were, - there is only a limited
production nowadays, primarily for jewellery and billiard ball manufacture -
different, by lacking any form of filler material and by being derived from
mixing phenol with formalin (the formaldehyde derivative, which gave a
higher formaldehyde content than for moulding resins), and heating these
together with a catalyst to accelerate the reaction.
One mol of clear synthetic phenol is mixed with substantially more
than 1.5 mols of formaldehyde supplied commercially as (formalin) a
clear, aqueous solution of 37 percent strength. To accelerate the
reaction or resinification a basic catalyst, usually caustic soda or
caustic potash is introduced and the mixture is heated in a nickel or
stainless steel kettle at 70 to 100 deg. C. for periods varying from 10
minutes to 3 hours. As the chemical combination of phenol with the
formaldehyde takes place the water-clear mixture darkens slightly in
colour and increases in viscosity. This reaction is principally
controlled by temperature, time factors, pH measurements and viscosity
readings to give end products of varying physical and chemical
properties. The alkaline resin at this point is concentrated in the
reaction kettle by heating under vacuum to remove approximately 75
percent of the water. As the elimination of this water takes place the
resin becomes quite syrupy and at the proper end point organic acids are
introduced in sufficient quantity to acidify the mass and clarify the
colour which now ranges from water-clear to amber. The product now has
the consistency of honey. Before the final concentration of the light
resin syrup …. various plasticizers, modifying agents, dyestuffs etc.
are introduced in the reaction kettle. (Kline. 1942: p40).
The resulting syrup was poured into metal moulds and baked in ovens at
150 to 175 deg. F. for up to a week to polymerise or ‘cure’. Being
thermosetting, these resins could not thereafter be changed by the
re-application of heat.
To produce phenolic resin suitable for casting, phenol and
formaldehyde are reacted together in the presence of a catalyst such as
caustic soda. This reaction process takes place in special kettles and
lasts for several hours. After the excess condensation, produced during
the reaction, has been removed, basic colouring dyes are added to the
liquid in the kettles. The phenolic resin is then withdrawn from the
kettles and is ready for use. (Tayler. 1946: p89).
Tayler’s comment on ‘excess condensation’ is interesting as there
developed a certain reliance of the amount of water in cast resins to
enhance their properties.
The latest methods adopted for cast resin manufacture result in resin
that still contains a small proportion of water. But the size of the
particles of this contained water can be so regulated that the final
cured resin can be made either perfectly transparent, because of
extremely small particles of water, or perfectly opaque when the
particles are larger. Intermediate sized particles provide translucency.
(Plastes. 1942: p 21).
Although the manufacture of billiard balls are today one of the main uses
for phenolic resin, as produced by Saluc Ltd. of Belgium from their Aramith
cast resin range, they were also one of the first proposed products. James
Swinburn’s laboratory notes from 1904 show a formula for cast resin and the
note ’suitable for billiard balls’. (Fielding. Undated: p2).
History
Otto Baeyer, in 1872, showed that the reaction of phenol and formaldehyde
produced a hard resinous substance. At the turn of the twentieth century
James Swinburn, seeking a material for electrical insulation purposes,
developed the previous work of Beyer, Smith and the Austrian chemist Luft.
Both Smith and Luft succeeded in obtaining only insoluble, infusible
resinous products which were impossible to mould. (ICI. 1962: p19).
In 1904 Swinburn developed a formula for phenolic resin, whilst in the
same year establishing the Fireproof Celluloid Syndicate Ltd. to
commercialise the product. This commercialisation was not very successful
although a very usable lacquer, for the protection of brass and other metal
surfaces, was produced and sold well. By 1910 this lacquer was the dominant
company product and the name of the firm was changed to the Damard Lacquer
Company.
In parallel to this L.H. Baekeland, working in New York, was also
investigating the phenol formaldehyde reaction in the search for an
electrical insulating material.
Arthur Smith, in England, took out the first patent for the use of
phenolic resins, as they were called, in 1899 (it happened to be for
electrical insulation), and five years later an electrical engineer,
James Swinburne, established the Fireproof Celluloid Syndicate in London
to manufacture and sell the same sort of material. However, neither of
these ventures was technically or commercially successful. Baekeland was
therefore not tilling virgin soil … (Kaufman 1968: p13).
From 1902 onwards, after five years research, and in a masterpiece of
chemical investigation, Baekeland succeeded in producing a synthetic resin
which he called Bakelite, registering his ‘Heat and Pressure’ patent on July
13th 1907. Unfortunately this material did not prove itself to be
easily mouldable and it is his patent of October 1908 that really covers
what is now considered to be a mouldable Bakelite material.
Baekeland was not the first chemist to make a resin …(from phenol and
formaldehyde) ….. but he was the first to make a resin which could be
used to manufacture useful things (Farrell 1955: p14).
In the 1908 patent Baekeland details Bakelite material in three forms
which he calls Bakelite A, B and C according to its differing physical and
chemical properties.
Bakelite A was the initial product of the reaction of phenol and
formaldehyde carried out in the presence of a small amount of ammonia
and made by stopping the reaction at a stage where the resultant product
was liquid while hot, solid when cold, but was still soluble in
solvents. Bakelite B was produced at a further stage of reaction and was
gelatinous when hot, solid when cold, but no longer entirely soluble.
This product has had little commercial value and is really an
intermediate stage between Bakelite A and C. Bakelite C was the name he
applied to the final product in the insoluble and infusible form, which
Baekeland produced free from bubbles and blisters. (Fielding. Undated:
p6).
‘A’ stage resins are known as resol; ‘B’ stage resins are known as
resitol; it is only the ‘C’ stage material that is used to produce cast
phenolic resins.
In the late 1950s Howard Potter, who had worked for Sir James Swinburne’s
Damard Lacquer Company, and who was later to become Managing Director and
Chairman of Bakelite Ltd. made a series of tape recordings documenting his
career in the plastics industry. Percy Reboul uses these recordings to
provide a basis for the history of Bakelite in Rob Perree’s book ‘Bakelite -
the material of a thousand uses’ and states;
By 1916 the demand for Damard lacquers and resins far exceeded the
capacity of (the company’s) Bradford Street branch. At the invitation of
the British Government’s Custodian of Enemy Property, Damard was invited
to run a small purpose built factory at Cowley, Middlesex, which had
previously been run by part of the German Bakelite Organisation … at the
plant the Germans had been making a resin for casting into umbrella
handles, pipe stems and the like. They were cast in lead moulds and the
mould making shop (discontinued during the war) consisted of a container
for melting the lead and solid, polished metal dies which were dipped
into the molten lead to form the mould into which the resin could be
cast. There were a number of these moulds lying about in the shop ….. (Perree
1996: p43)
The ‘German Bakelite Organisation’ is a reference to Bakelite
Gesellschaft, a company part founded in 1909 by Leo Baekeland to produce
phenolic resins to his newly acquired European patents. The factory may have
been relatively small (5000sq ft.) but on inspection it was found to contain
the most advanced resin still in the country.
At the end of the war production by Damard at the Cowley plant was
considerably expanded to meet the increased demand for semi-luxury goods.
Of greater value at that time from the financial point of view was
the production of "C" material, i.e. cast resin. In 1919 production of
cast resin reached half a ton a week. It was used to produce blanks for
cigarette holders and pipe stems, the liquid resin being run off into
lead moulds. Umbrella handles were another important application for
cast resin, the method here being to run the resin into glass moulds
which were broken off after heat treatment to polymerise the resin.
(Fielding. Undated: p16).
In 1921 the Damard Lacquer Company relocated to Birmingham and was
capable of providing good quality phenolic casting resin, and to manufacture
with it using this glass and lead mould technology.
Bakelite Ltd. acquired the Damard Lacquer Company in 1927 along with two
other plastics companies, Mouldensite Ltd. and Redmanol Ltd. In 1928 a
strategic decision was made by Bakelite Ltd to stop all in-house moulding
and casting, (because of growing competition from other manufacturers), and
to concentrate solely on moulding materials production. Bakelite Ltd. ceased
the production of cast resins at this date.
Properties
Cast phenolic resins lack the fillers that are mixed with the moulding
resins used in the compression or transfer moulding processes and which make
the typical Bakelite product brown and opaque. Phenolic resins made for
casting are clear to pale yellow in colour and naturally translucent, or as
James Swinburn famously said ‘like frozen beer’. Mixing pigments into these
resins gives rich, vibrant colours, whilst mixing a number of colours
together would give, for example, the variegated colour effects of quartz,
onyx or jade, giving each piece great individuality.
Imitation of the natural or traditional remained a strong motive for
using plastic. As late as 1933 an advertisement in Plastic Products
proudly declared that "Discriminating manufacturers Insist on Real
Marblette", a cast phenolic illustrated by pictures of three apparently
marble ashtrays. (Mossman&Morris. 1994: p39).
It is the vibrancy of colour of phenolic resins that ‘sells’ the
material. As Kaufman very rightly states;
The great advantage of phenol- formaldehyde resin was its lack of
colour. The gentle conditions of its preparation obviated the darkening
of the resin which occurred in the normal moulding operations. This
meant that at its best phenol-formaldehyde could be made water-white,
and then if necessary treated with a dyestuff or pigment to give any
colour, transparent or opaque. This made a welcome contrast with the
uniformly dark colours which alone are possible in normal
phenol-formaldehyde mouldings. (Kaufman. 1963: p67).
However, cast phenolic resins are not light stable and will react to the
ultra violet in sunlight, which may darken or change their colour over time.
But they do take a very high quality of finish and can be polished to an
almost jewel like quality although, unfortunately, thick sections are not
stable and tend, over the years, to craze internally.
Cast phenolics are hard and rigid, and have high tensile but low impact
strengths. They may have a high degree of transparency, translucency or
opacity and they have good dimensional stability under normal conditions.
They are non-flammable, almost odourless, easily coloured and may be worked
by a wide range of manufacturing methods, including carving. Cast phenolic
objects sometimes have a design carved out on their backs. This is known as
reverse carving, the carved surface generally being painted giving, from the
front side of the object, a highly decorative contrast to the transparent
surface.
Trade names
British: Bakelite Cast Phenolic, Catalin, Erinite, Lorival ‘A’.
American: Bakelite Cast Resinoid, Baker Cast Resin, Catalin (and
its derivatives Catabond, Catacast, Catacol, Catacore, Cataform,
Catalac, Catalure, Catamould,Catamuls, Catanam and Catavar),
Gemstone Marblette, Opalon, Prystal.
German: Dekorit, Leukorit.
Catalin
Perhaps the most commonly known of all cast phenolic resins is the
material Catalin.
Catalin is the common name of cast phenolic and was produced (in
America) after 1928.’ (Mossman 1997: p52).
Catalin is a solid cast phenolic resin and is supplied in standard
rods, tubes, shapes and special profile sections and castings. It is
delivered to the customer in solid form, ready for immediate use, and
this outstanding feature makes it an ideal material for a large variety
of applications. It does not require any curing or seasoning, and is
readily converted into the finished product by the use of standard
machinery, tools and other manufacturing equipment, and does not call
for expensive moulds, presses or dies. (Reilly& Molloy. 1948: p307).
In 1927 the Bakelite patent on phenol-formaldehyde expired and other
manufacturers opened production facilities especially to concentrate on
producing coloured casting resins.
The American Catalin Corporation offered ‘Catalin’, an insoluble,
infusible cast phenolic resin of gem-like beauty and an unlimited colour
range which in the form of rods, tubes, sheets or shapes can be machined
on ordinary shop equipment. Used for toys, costume jewellery, chessmen
and decorative panels, Catalin required no fillers and therefore could
be supplied in any solid, mottled, translucent or transparent colour. (Sparke
1990: p45).
Martin Apley was the first person in England to cast Catalin phenolic
resin in his capacity as head chemist with the English Catalin Company. This
company was started in 1937 at Waltham Abbey, Hertfordshire, to exploit the
technological developments of the American Catalin Corporation, and as
Catalin was selling well in America due to its colourful properties. Apley
made the first batch of Catalin phenolic resin, which he cast into the glass
of a light bulb, in November 1937. The cast is now in the possession of the
British Plastics Historical Society.
The company sold resin castings to fabricators who produced the finished
products, for example, cutlery handles to cutlery manufacturers, and
fulfilled one order from China for a million chopsticks. They also made cast
bowls and billiard balls, although these had to be weighted with barium
sulphate. The Cunard QE2 liner had 2000 solid Catalin toilet seats.
The Catalin Company produced Catcol glue used to make plywood for
mosquito fighters with a 2000lb per sq inch breaking strain. This and other
adhesives were due to research into paratolulin sulphuric acid that cured
the resin quickly and at room temperature. Catcol, loaded with china clay
and taken off a wooden former, was also used to make compression moulds for
sheet metals. It had a 12000lb per square inch compression strength. One
mould was the largest phenolic resin casting ever made in England, 8 x 3ft
and weighing 1200lbs.
Phenolic resin could also be made into an expanded foam by introducing
nitrogen gas pellets. Called Catalex this resin was used to stop Barnes
Wallace’s bouncing bomb from denting.
The post war production of Catalin helped to aid the aesthetic acceptance
of plastics in a period of generally poor quality product, but the company
could not match the demand for low cost, high volume plastic mouldings and
it closed in 1989, although the production of phenolic resins had ceased
some years before this.
Available forms
Between 1920 and 1945, when the use of cast phenolics was at it height,
the material was available in a wide range of polished and unpolished
sheets, clear and opaque casting resins, cast rods, tubes and blocks, liquid
cements, lacquers and laminating resins.
Applications
Cast phenolic resin was used in a very wide range of domestic product
design from buttons, through costume jewellery to cooking utensil handles.
It was also used extensively in the luxury goods market, for example in
clock and radio manufacture, chess pieces, handbag tops and umbrella
handles. The material was commonly found in retail environments as shop
display fittings.
The material also had industrial applications;
… the use of cast phenolics is concerned with a new type of very
fluid low viscosity resin, which can be maintained in its fluid state
over a period of months. This fluidity gives castings which show the
finest detail … The casting moulds used for this resin are usually of
plaster, but wood, lead, nickel, brass, bronze, copper or tin can be
used. Casting is carried out at atmospheric pressure and at
comparatively low temperatures … Originally produced for making moulds
in which to cast certain oil drilling tools, it is now replacing large
quantities of metal dies in aircraft production. (Gloag. 1945: p70).
(cast phenolic resin) is also used for jigs and dies for shaping
light metals such as aluminium and duraluminium. In this cast resin
material, fillers such as asbestos, kieselguhr and ground walnut shell
are mixed with the phenolic resin syrup. A hardening catalyst is added,
the syrup poured into wood or plaster moulds, and baked. The presence of
the filler reduces the shrinkage of the material on hardening and also
it increases the surface hardness of the castings, making them resistant
enough for their use as light metal shaping jigs and dies. (Redfarn.
1959: p23).
Casting
Casting … the pouring of the resinous material in a liquid state into
moulds without the application of pressure. Because no pressure is
applied, the moulds employed are much cheaper, since they can be made of
lead in place of high quality steel. Casting is employed largely for the
production of rods and tubes, and for such objects, buckles and buttons
for instance. (Clair. Undated: p39).
Using steel arbors, dipped into molten lead - which is then allowed to
cool and harden and from which the arbors are withdrawn to make hollow lead
moulds - is the classic way in which phenolic resin is cast. Each dipping of
the arbor would add about 2mm of lead to the surface. An average mould would
be about 8mm thick, so it was a relatively quick process. The arbor had a
rake angle taper of approximately .0015" over its length, which was
necessary to break the hold of the cast resin, reduce the friction and allow
the casting to be finally removed from the mould.
Dipping arbors vary from $90 to $375 depending on the size and
intricacy of the design. (Kline. 1942: p308).
Straight, lead draw moulds of about 14ins in length were very useful for
producing castings that were going to be sliced by manufacturers into, for
example, buttons, or the tubes that were used in box manufacture. But lead
was not the only material used for mould making. Along with rubber, glass
was found to be very effective for complex shapes.
Casting lends itself to the production of unusual or complicated
shapes, which would be difficult to obtain by conventional moulding
techniques. Glass moulds, for example, can be blown into complex shapes
and then filled with liquid plastic and allowed to set. The glass is
then broken away to leave the moulded plastic. Round glass flasks, for
example, have been used in this way for making billiard balls. (Cook.
1964: p165).
Once the moulds were filled the resin had to be baked to cure in
steam-heated hot air ovens, although hardening agents were used to speed
this process. Castings could, dependent on size, spend up to ten days in an
oven at no more than 85 deg. C. Once cured, the lead could be stripped away
from the casting, or the casting driven out by using a pneumatic hammer, and
reused. The physical stripping away of the lead, by hand, allowed undercuts
to be made. Castings required a minimum wall thickness of 4mm, (or they
would break when removing the lead), and most shrank by about 1% in volume
on ageing. Castings could be further enhance by being printed on by roll
leaf blocking or offset printing processes, or by filled engraving – and
very large castings could be produced;
Almost any desired shape ... can be produced very much as are home
made jellies. To what limits this can be actually extended can be
gathered from the statues in "Marblette" which were exhibited at the
World’s Fair in 1939 in New York. These statues are all about 10ft high
and weigh over half a ton; one is built up of five sections and is 30ft
long. The surfaces are in some cases sand blasted to give the appearance
of ground glass, and the transmitted light from internal illumination
gives very pleasing effects. It was stated that these particular statues
were cast in phenolic plastic in reinforced rubber moulds and required
curing for a week at 185 degrees F. (Yarsley & Couzens. 1945: p83).
In general, castings required more finishing processes than mouldings,
often having to be machined and polished. Polishing was known as ashing,
being undertaken using pumice powder.
The method usually recommended is to sand lightly, continue rubbing
down with pumice and water and finally polish on a muslin wheel. (Plastes.
1942: p 212).
The mould making costs for casting were much lower than for producing
compression or transfer moulds, and the quality of the finished product,
because of the inherent nature of the casting resin, was much higher. A
range of mould types was used including split moulds for undercuts, cored
moulds for small hollow items and slush (rotational) moulds for large hollow
items.
Moreover, there are virtually no limits to how large a casting may
be: units 20ins square and 12ins deep are now included in regular
production. Pilasters as long as 36ins and having a periphery of 18ins
are likewise standard production. (Kline. 1942: p308)
Hence this is the way that one of the iconic range of cast products, the
American FADA radios, were made in the 1940s – but they are fragile.
Casting, however, has obvious disadvantages compared with machine
moulding. Besides the time taken, the strength of articles so produced
is necessarily inferior to that of articles produced by high-pressure
moulding. (Kellaway & Meadway. 1945: p43).
It had other disadvantages as well. Even though release agents were used
there were considerable problems of the castings sticking to the lead
moulds, due to the reactivity of the resin and the agent. This may be why
glass, and occasionally rubber moulds were used. And it was very much a hand
made process –
…. marbled effects were made by pouring from several jugs of resins.
Two colour castings were made by pouring and curing one piece and
inserting it into a larger mould and casting a second colour around it.
(Morgan. 1994: p12).
In the end it was probably the inability of the casting process to be a
production method that matched contemporary mass production demands that led
to its demise. It did not lend itself to the high volume mass production
methods that post war industry required.
Casting phenolic resins required unique moulding techniques which ….
were ruled out on economic grounds as more conventional and less
hazardous methods could be employed. (Morgan. 1994: p12).
The material could not keep up with a post war society’s demands for
cheap, injection moulded items, even though the products that were made from
it were infinitely better.
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