By Liz White, UT editor
Sowerby Bridge, UK- Rosehill Polymers has developed a semi-continuous reaction process to make polyurethane hot melt reactive adhesives which it claims is "set to replace the outdated and inadequate techniques which have so far limited growth in the sector."
The UK-based prepolymer manufacturer has introduced the "unique semi-continuous method in its West Yorkshire plant, to make its Fleximelt range, aimed at a wide range of industrial applications, said a Rosehill statement.
"PU hot melt adhesives have been developed through much formulating expertise and the use of high quality raw materials, but manufacturing methods have hindered their exploitation, said Rosehill's Dr Colin Reed, in the company's announcement. "We believe that a semi-continuous reaction process is the best way to drive developments within this exciting and growing area."
Rosehill says the latest version of its reactor for liquid products can produce prepolymers at a rate of 1000 kg in 13 minutes, with only one operator.
The reactor has brought "significant environmental benefits," improved manufacturing flexibility and efficiency, and also raised product quality and consistency, said Rosehill's statement.
Rosehill is now applying the same technology to making PU adhesives. And the continuous process is bringing Rosehill more export opportunities, the group added. European countries, notably Holland, Belgium and Germany, are anxious to replace solvent-based adhesives, with hot melts for example, said the firm.
Process flexibility allows Rosehill to meet customer requirements faster, "even where a large number of small batches are needed," the company added.
PU hot-melt adhesives are moisture curing. This means they are thermoplastic when uncured, and can be melted and applied, to form a bond when they solidify. They can be re-melted to break the bond or reposition joints as necesssary. But the difference from conventional thermoplastic hot-melts is that, after reacting with atmospheric moisture, they becomes thermosets and cannot be re-melted.
Rosehill claims that continuous manufacturing is also in more environmentally friendly: "The process generates less waste than other PU manufacturing systems, while cleaning requirements - and the use of the necessary solvents - is much reduced."
"In all aspects of our business we are looking to adopt a 'lean manufacturing' approach and this continuous manufacturing process is making a substantial contribution," said Reed. "There is a tremendous space-saving compared with batch reactors, production speed is much higher, there are no limits on batch size and we can switch between products very easily."
Rosehill claims to be a technology leader in continuously manufactured urethane polymers. Its efficient flow reactor takes products straight from bulk storage and mixes them under intense conditions, ensuring that the reaction runs with the correct excess of isocyanate groups. This in turn provides better 'capping' of the polyols, tighter molecular weight distribution, lower melt viscosity and better crystallisation rates, the firm explains.
Rosehill currently offer three Fleximelt types:
Fleximelt 7100, fast setting with high bond strength and most suited to automated factory processes such as profile wrapping and edge banding;
Fleximelt 7200, a range of multi-purpose reactive hot melt adhesives. They are medium to high viscosity with long open times and high uncured strength. Suitable for semi-manual assembly processes with excellent adhesion to plastics, metals, wood and MDF; and
Fleximelt 7300, for flexible laminating applications, for example with fabrics, membranes and foams. Flexible, heat and chemical resistant.
The versatility of the Fleximelt range is opening up new markets for Rosehill and the company has just taken its first orders from the bookbinding industry.
Pic: Rosehill's Fleximelt 7301 is applied to fabric using a slot coater.
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