Cast Phenolic Resin
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).
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).
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).
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).
The Development of the Material
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 Baeyer, 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).
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).
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).
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).
‘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)
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).
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.
The Properties of a cast material
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).
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).
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.
Common Trade Names
British: Bakelite Cast Phenolic, Catalin, Erinite, Lorival ‘A’.
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.
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).
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).
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).
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.
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.
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).
(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
Sawing Catalin cast resin sheet using a power fret saw.
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).
Casting Phenolic Resin
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).
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 I ntricacy of the design. (Kline. 1942).
Pouring liquid phenolic resin into lead moulds.
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.
Catalin cast phenolic rods being driven out of a lead mould by the use of a pneumatic hammer.
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).
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).
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)
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).
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).
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).
In the end 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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