2009年4月7日星期二

Adhesives

Adhesives
There are mainly three different types of adhesives to select from, depending on the application and on the surface substrates:
Rubber
Acrylic
Silicone
Rubber adhesives can be divided into two main groups: Natural and Synthetic.
1. Natural rubber These adhesive have good tack and shear but limited UV resistance. Such adhesives is mainly used for duct, masking and surface protection tapes.
2. Synthetic rubber Synthetic rubber can be divided in 3 sub categories:
a) Hot-melt rubber which are mainly used for packaging, fixing and carpet tapes. These tapes have lower temperature, UV resistance and ageing performance
b) Solvent rubber based which are mainly used for electrical and foam tapes. These tapes have better temperature and ageing performance but poor UV resistance
c) Butyl rubber tapes are mainly used for sealing applications in the building and construction industry. These tapes have excellent UV and ageing resistance but lower mechanical strength.
Acrylic adhesives can be divided into two main groups: Pure and Modified
1. Pure acrylic These adhesive have excellent bonding, ageing, temperature performance and UV resistance. The main limitations are the adhesion strength on low surface energy substrates and the lower tack than rubber or modified acrylic adhesives. Mainly used for bonding, sealing and protection tapes
2. Modified acrylic These adhesive with good bonding, ageing, temperature performance and UV resistance as well as haveing much better adhesion than pure acrylics on low surface energy substrates (e.g. plastics such as polyethylene and prolypropylene). Mainly used for bonding, lamination and splicing tapes
Acrylic adhesives can be either water (also called emulsion or dispersion) or solvent based. Generally speaking, but not always, solvent based acrylic systems have better resistance to solvents, chemicals and water but are more expensive than water based systems.
Silicone adhesives
Silicone adhesives have excellent temperature, ageing and UV resistance but are significantly more expensive than rubber and acrylic adhesives. Due to the high temperature performance they are mainly used for splicing and masking tapes.

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