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| Polyvinyl Acetates |
| Polyvinyl acetate (PVAc) is a synthetic polymer and a member of the vinyl ester family.
PVAc emulsion adhesives first gained market share by replacing hide glues in the 1940ís.
Today, vinyl acetate adhesives are the most widely used adhesives on the market, but vinyl acetate emulsions are also heavily used in paints, textile sizing and nonwoven binders.
Vinyl acetate emulsion adhesives can be broadly classified as homopolymer or copolymer. Each of these two types can be further classified as self-crosslinking or non-crosslinking. |
| Homopolymer Emulsions |
| PVAc homopolymers were the first polyvinyl acetate emulsions developed.
These polymers are hard and brittle with high molecular weight, high tensile strength and rapid speed of set.
Today these homopolymers are still the ìworkhorsesî of the industry due to their excellent adhesion to a wide variety of ìpolarî substrates,
particularly cellulosic-based substrates such as paper and wood. PVA adhesives have the following characteristics: |
| Copolymer Emulsion (VAE, VAA) |
| Compared to PVAc homopolymers,
vinyl acetate copolymer emulsions offer the advantage of being able to bond difficult-to-bond substrates such as plastic films, coated papers, and metal surfaces.
Vinyl acetate copolymer emulsions are internally flexibilized with a comonomer such as ethylene (VAE) or an acrylate (VAA).
The increased polymer flexibility provides for increased polymer mobility and, therefore, better adhesion. Applications for PVAc copolymers include: |
| Acrylics: Polymers and Copolymers |
| Acrylics are available as emulsions and dispersions as well as liquids containing 100% polymer.
Acrylic emulsions are often used as a multipurpose adhesive. Dispersions provide an excellent paper-to-paper bond and are used in many laminating processes.
A wide variety of acrylic and methacrylic monomers are available for manufacturing specific acrylic adhesives. Acrylic based water-base adhesives are usually used in PSA applications. The heat seal coatings and flame spread resistance of acrylics is very good for PSAís and are used in many UL applications. Most acrylics used in the textile industry are crosslinkable giving the final product weather and aging resistance as well as resistance to water, laundry detergents and solvents. They are FDA approved and are used in some edible oils and milk filters. Some of the largest structural bonding applications for acrylics include medical devices, electrical components, flexible ducts, window seals, and various home uses. They are also used on some private label diapers and other sanitary products. |
| Polyurethane Dispersions |
| Polyurethane is a synthetic polymer derived from isocyanate reactions.
Environmentally friendly water-based polyurethane adhesive was developed in the late 1960ís.
Polyurethanes are polymerized in water to produce a thermoplastic polyurethane emulsion.
It then becomes thermoplastic and crosslinkable.
Polyurethane dispersions are used in some of the most demanding applications because of their weatherability and resistance to plasticizers and solvents. Generally, water-based polyurethane dispersions can be used in most of the same applications in which solvent-based polyurethane is used. Here are the major markets using polyurethane dispersions. |
| Casein |
|
Casein is a natural polymer from skim milk proteins used in some water-based adhesives.
It represents a small but important percentage of all natural polymers used in water-based adhesives.
The casein formulations are highly soluble in alkaline and water, they thus wash very cleanly off of the glass containers.
Casein can be cross-linked to give excellent water resistance which can be required when the glass containers are filled with a product that is chilled by means of soaking in ice-water.
This cross-linking does not interfere with the casein ability to be washed off cleanly in alkaline water. Casein - Common Applications Casein is now used as: |
| Dextrine/Starch-Based Adhesives |
| Starch-based adhesives are made from natural polymers derived from roots,
tubers and seeds of higher plants such as maize, potatoes, wheat, rice and tapioca.
A starch-based adhesive is either cold or warm water-soluble depending on the application specifications.
Starch granules are slurried in water. The mixture is heated until the granules burst.
The granules absorb water and swell increasing in viscosity forming the paste or adhesive.
The starch source depends on performance, machining and economics. There are two types of starches borated and unborated. Dextrin is a type of dry roasted starch. A wide range of gums and pastes can be developed by controlling acidity, moisture content, and roasting temperature, varying levels of solubility and viscosity can be produced: Dextrine/Starch-Based Adhesives Common Applications Common applications for dextrine/starch-based systems include: |
| Natural Rubber Latex |
| Natural rubber latex is a water-based adhesive in which rubber particles are protected or stabilized by proteins and fatty acid soaps.
Natural rubber comes from the sap of the Hevea Brasiliensis tree, collected at 35% solids.
The formulation with natural latex will vary depending on the final application of the adhesive. Natural Latex Applications: |
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