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Introduction of Polyurethane Elastomer and Non-reactive Polyurethane Adhesive

Polyurethane Elastomer

There are majorly two types of polyurethanes: foamed and solid. Although foamed urethane materials account for a huge proportion of the world-wide polyurethanes market, polyurethane elastomer is used in many diverse applications. The various polyurethane elastomers offer a broad range of hardness and processing characteristics.

        Cast polyurethane elastomers, for example, are simply made by low-pressure mixing and pouring a degassed reactive liquid polyurethane resin into a mold, and the entire process can be done by casting machine. These urethane materials have excellent abrasion resistance, and also have decent resistance to be attacked by oil, petrol and many common non-polar solvents. In general, only strong based and acids, oxidizing agents and a few strong polar solvents affect completely-cured cast polyurethane elastomers. Common finished polyurethane products made by casting polyurethane resin are printing rollers (滾輪), industrial off-road tires (橡膠內胎填充), fork-lift tires, press-on tires (堆高機輪), and skate board wheels (滑板輪)etc.

Another type of urethane materials that are commonly used as elastomer is thermoplastic polyurethane elastomers, which are supplied as pellets or granules for processing by conventional thermoplastic processing techniques such as extrusion molding, injection molding and calendering molding. These urethane materials have excellent combination of high elongation and tensile strength with high abrasion and environmental resistance, and the products can be mass-produced in precise dimensions. Depending on the formulation, thermoplastic polyurethane elastomers can also have excellent resistance to oils, fuels, solvents and chemicals. Applications of thermoplastic polyurethane elastomers include many PU products, such as industrial hose, pneumatic tube, high-wear resistant engineering parts and footwear componentsetc.

 

Non-reactive Polyurethane Adhesive

Polyurethane adhesives can be divided into two main classes: non-reactive and reactive. The major application of polyurethane adhesives is to put a thin layer of high molecular weight polyurethane between the two surfaces to be joined and bonded. While reactive polyurethane adhesives are usually supplied as one- or two-components polyurethane resin system, non-reactive polyurethane adhesives are based on high molecular weight polymers, which are applied as solvent-borne, water-borne or as hot-melts.

Firstly, solvent-borne polyurethane adhesives:

1.   By dissolving high molecular weight thermoplastic polyurethanes in solvents, solvent-borne

     polyurethane adhesives are produced.

2.   To improve the bonding strength and heat resistance, solvent-borne cross-linkers are

     frequently added to solvent-borne thermoplastic polyurethane adhesives; however this

     process turns a one-component non-reactive polyurethane adhesive into a two-part reactive

     adhesive with limited pot-life. Therefore, adding cross-linkers is only necessary in certain

     applications.

3.   During the process of preparing solvent-borne polyurethane adhesives, typically, about 50% of

     the solvent required for the final adhesive solution is charged in a closed mixer and

     thermoplastic polyurethane granules are added in stages, to avoid coagulation, to the stirred

     mixture. Since the shear forces generated can raise the temperature as high as the boiling

     point of the solvent, rest of the solvent is added over time to control the viscosity and

     temperature of the mixture. The dissolution time depends on the process conditions and can

     be 24 hours using low-temperature equipment or two hours for reflux conditions.

Secondly, for polyurethane hot-melt adhesives:

1.   Polyurethane hot-melt adhesives are also supplied as thermoplastic granules, which can be

     extruded or melted by heat in holding tanks to form, for examples, glue sticks for hot-melt

     gun or adhesive films for industrial heat press machine.

2.   Polyurethane hot-melt adhesives can be used to bond paper, board, wood, metals, plastics,

     and for laminating fabrics to foams.

3.   One of the common ways to use polyurethane hot-melt adhesives is placing polyurethane hot-

     melt adhesives between substrates, then activating the laminate heat at temperature above

     the melting point, and then simply giving pressure to the substrates to bond layers together.

Lastly, for water-borne adhesives:

1.   Water-borne polyurethane adhesives are fully reacted, high molecular weight polyurethane

     dispersed in water that only contains minor amounts of solvent and thus have a very low

     emission of volatile organic compounds.

2.   The main applications for water-borne polyurethane dispersions, known as PUDs, adhesives

     are in the construction and packaging industries, footwear industry and in the manufacture

     of foils and textile laminates. While water-borne polyurethane adhesives have good bonding

     performance with many materials, including PVC substrates, their adhesion to rubber, or

     certain surface-treated, or high oil content materials is poor.

3.   Water-borne polyurethane are normally applied by roller or sprayer, and heating is required to

     speed up the drying process.

Although solvent-borne thermoplastic polyurethane adhesives are easily operated and highly used in the footwear industry, the products are under increasing pressure due to the fact that evaporating solvent and releasing volatile organic compounds into the atmosphere may potentially damage the environment. Therefore, more and more water-borne polyurethane adhesives are used. More information about water-borne polyurethane dispersion can be found on http://www.taiwanpu.com/faq_detail.asp?seq=7

 

Link to TPUCO products:

Casting Polyurethane Resin:

http://www.taiwanpu.com/products_list.asp?title_seq=249

Thermoplastic Polyurethane Elastomer Granules:

http://www.taiwanpu.com/products_list.asp?title_seq=269

Thermoplastic Polyurethane for Solvent-borne Adhesive:

http://www.taiwanpu.com/products_list.asp?title_seq=288

Hot-Melt Thermoplastic Polyurethane:

http://www.taiwanpu.com/products_list.asp?title_seq=290

Water-borne Polyurethane Adhesive:

http://www.taiwanpu.com/products_list.asp?title_seq=292

Polyurethane Adhesive and Hot-melt:

http://www.taiwanpu.com/products_list.asp?title_seq=287

 

Reference:

Sonnenschein, Mark. Polyurethanes Science, Technology, Markets, and Trends. John Wiley & Sons, Inc. Hoboken, New Jersey. 2015.

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