THE SIPOLPRENE® ENGINEERING POLYMERS ARE MADE THROUGH THE MACROMOLECULAR COMBINATION OF RIGID POLYESTER BLOCKS (CRYSTALLINE SEGMENTS) AND FLEXIBLE LONG-CHAIN POLYETHER BLOCKS (AMORPHOUS SEGMENTS)
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Founded in 1998 by a pool of entrepreneurs active in Northern Italy, SIPOL® is a private company whose core business consists in the polymerisation of specialty copolyesters and copolyamides which are tailor-made for the adhesives and engineering plastics sector. The company currently sells 25 million euro of specialty polymers developed and manufactured at its plant in Mortara (about 40 km west of Milan). Its main activities are the development and manufacturing of thermoplasticether-ester elastomers (TPC-ET), specialty hotmelt adhesives (copolyester and copolyamide based), and biodegradable polymers (copolyester based). Sipol’s business policy is based on marketing its superior competence in polymer chain modification. Depending on application needs, the R&D department creates new copolymers by inserting different blocks (comonomers) into the polymer chain; this produces tailor-made materials designed to match application requirements with the level of business flexibility that only a medium-sized company is able to offer.
A new range of TPEs is born
With regard to engineering polymers, in 2002 the company introduced SIPOLPRENE® as trade brand for its thermoplastic ether ester elastomer range (TPC-ET), to then gain, in over 10 years of activity, an excellent reputation in a niche market, in a field where the number of companies with proprietary chemical know-how is extremely limited worldwide. These engineering polymers are made through the macromolecular combination of rigid polyester blocks (crystalline segments) and flexible long-chain polyether blocks (amorphous segments). This combination grants the polymer a unique behaviour as the rigid part of the molecule develops intermolecular associations with the other rigid segments, providing the dimensional stability and the mechanical properties of a semicrystalline polymer, while the flexible part, with its relatively low glass transition temperature, imparts elastomeric properties to the material. Sipol’s polymerisation know-how in regard to hot melt adhesives and its familiarity with the building of a polymer chain using different comonomers like in toy blocks, enabled the company to develop several SIPOLPRENE® grades through the variation of the macromolecular composition. From the analysis of the structure shown in figure 1, it is possible to modify the rheological, physical or chemical polymer behaviour acting on both the length of monomer components and their combination. In order to have a general understanding of the possible molecular modifications achievable, it should be observed that what is shown as “Rigid part” is practically a PBT chain, while the “Flexible part” is mainly a polyether.
Chemical and physical charateristics
The SIPOLPRENE® standard portfolio of products covers a range in hardness levels going from ShD 25 up to ShD 72 with melting temperatures between 170°C and 220°C, where all grades share a common “polyester” backbone which provides superior chemical and thermal resistance. In addition to the traditional SIPOLPRENE® range, SIPOL® has been continuously adding specialty grades providing a unique performance, like SIPOLPRENE® 35150 (TPC-ET low melting point suitable for PVC modification), SIPOLPRENE® 55211 (TPC-ET with improved rate of hardening for ultra- high-speed injection moulding) and the SIPOLPRENE® B series, showing a moisture absorption value greater than 15% (breathable products). Therefore, the SIPOLPRENE® family offers a good balance of characteristics, which can be briefly summarised as follows:
- performances over a temperature range from -40°C to +120°C;
- excellent flexibility with high-impact strength even at low temperatures;
- high mechanical strength;
- good resilience;
- excellent wear resistance;
- high resistance to chemicals (e.g. organic solvents, gasoline, naphtha, light acids, sea water and zinc chloride solution);
- excellent surface gloss and good paintability;
- easy welding with several techniques (e.g. spin, ultrasonic, and hot-plate);
- printable using sublimation inks, pad printing and silk screening;
- laser markable with the most conventional techniques;
- suitable for sterilisation with gamma radiations, ethylene oxide and steam autoclave (harder types);
- availability of stabilised versions providing an increased resistance to heat, UV, hydrolysis, NOx and copper contact;
- almost all Sipolprene grades are suitable for food contact according to FDA and EN 10/2011 regulations.
The entire SIPOLPRENE® range provides a combination of sharp melting points typical of every single product with an excellent melt stability; this combination allows easy and reliable product processing in various injection moulding techniques, pipe extrusion, film extrusion, monofilament extrusion and rotomoulding (powder). In injection moulding, which is the most common technology used to process SIPOLPRENE®, the rheological behaviour of the polymer shows curves of viscosity vs. nearly flat shear rate (non Newtonian), allowing the stable flow of molten polymer through mould restrictions found in complex moulds and in multi-cavity moulds without the over-heating, and consequent degradation, of the polymer. The products can be injection moulded by means of conventional runners as well as runnerless moulds. When using conventional runners, the use of regrind mixed with the virgin polymer even at high percentages is permitted without a significant loss of performance on the moulded parts. The soft nature of SIPOLPRENE® and its chemical structure, which allows the development of good compatibility with several rigid engineering plastic products, has made SIPOLPRENE® commonly used in 2K moulding applications where a “soft touch” is needed and where other thermoplastic elastomers do not provide sufficient adhesion. Una delle caratteristiche peculiari di tutta la gamma SIPOLPRENE® è, inoltre, l’idoneità al contatto alimentare in accordo alle norme FDA ed EN 10/2011. A livello di lavorabilità, i prodotti della gamma SIPOLPRENE® combinano punti di fusione ben definiti (natura semicristallina) con un’eccellente stabilità del fuso; ciò permette lavorazioni semplici e affidabili secondo varie tecniche di stampaggio a iniezione, estrusione in forma di tubi, film e monofilo e stampaggio rotazionale, previa polverizzazione.
Industrial and consumer application
Besides the easy and economical processing, there are several benefits to choosing SIPOLPRENE® in demanding applications where other TPEs cannot be used because of the high mechanical performance required or because of the working temperature of the parts. SIPOLPRENE® is used in several market fields for industrial applications as well as for consumer goods. Considering its excellent mechanical properties, together with its good thermal and chemical resistance, the automotive segment represents one of the most important areas of application for SIPOLPRENE®, which is used to make gaskets, door latch covers, special connectors, clips, vibration absorbers, thermoplastic hoses, trim rods, monofilaments for seats support and many other types of products. Another important area of application is the industrial segment where SIPOLPRENE® is utilised for making low noise gears, covers, pulleys, distribution valve bodies, and cable jacketing. Its suitability for food contact and the absence of any plasticiser make it an excellent polymer for various applications in the consumer goods markets where SIPOLPRENE® is used to make kitchen tools, toy components, valves for packaging, body-care equipment, and in many other specialised applications. As for hot-melt adhesives, SIPOL® operates with special copolyesters and copolyamides (dimeric acid based) specifically designed for many industrial sectors, like the footwear industry, where the company is a worldwide leader with regard to the production of long-lasting products, and automotive filters, where SIPOL® is one of the best known worldwide players. All the hot-melt adhesives specifically designed for textile lamination are marketed under the trade name SIPOLTEX®, while all the other grades are under the trade name TECHNIPOL®.