Glossary of Terms

LIQUID ADHESIVES

Water-based adhesives use water as the carrier fluid, with the adhesive particles suspended in water, reducing the adhesive’s viscosity so that it can be applied to various substrates at varying thicknesses. Evaporation of the carrier fluid generates the desired bond.

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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 1940s. 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 non-woven binders. Vinyl acetate emulsion adhesives can be broadly classified shoo or copolymer. Each of these two types can be further classified as self-cross-linking or non-cross-linking.

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 “workhorses” of the industry due to their excellent adhesion to a wide variety of substrates, particularly cellulosic-based substrates such as paper and wood.

PVA adhesives have the following characteristics:

• Fast speed of set
• High strength
• Excellent adhesion to celllulosic substrates, ceramics, concrete, and glass
• High molecular weight
• Cost-effective

Compared to PVAc homo-polymers, 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:

• Textiles
• Construction
• Packaging
• Graphic Arts

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 PSA’s 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 is a synthetic polymer derived from isocyanate reactions. Environmentally friendly water-based polyurethane adhesive was developed in the late 1960s. 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.

• Textiles – cloth fibers, backing coats, foam-backed carpets, carpet cushioning
• Construction – windows, cabinet doors, furniture, glass fibers, paint applicators
• Automotive – plastic to glass
• Packaging – film to film, film to foil

Polychloroprene, developed in the 1930s as a substitute for natural rubber, is an extremely versatile synthetic elastomer that offers a unique combination of adhesive properties. Polychloroprene-based adhesives provide outstanding toughness, chemical resistance, weathering resistance, heat resistance, oil and chemical resistance, as well as very rapid bond strength development. In contact adhesive applications, they develop an “instant bond” which allows assembled components to be immediately processed without clamping or fixturing.

Typical applications for polychloroprene-based adhesives include:

• Footwear constructions
• Lamination of furniture, kitchen cabinets and countertops, interior and exterior panels
• Automotive trim attachment
• Aluminum foil laminates for food packaging and HVAC

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:

• An adhesive in construction for wood working applications
• Packaging industries for breweries, wineries and packagers where refrigerated products are packaged
• A binder in paints
• An additive in other 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.

• Is an ancient adhesives
• Became widely used during the industrial revolution

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.

• Corrugated board
• Paper products
• Lamination applications
• Tube winding
• Labeling and envelopes
• Bookbinding

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 front he 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.

• First used in South and Central America
• Today, most comes from the Far East

Natural Latex Applications
• Graphics Arts
• Engineered Systems
• Packaging
• Converting

HOT MELT ADHESIVES

Hot-melt adhesives form the highest volume component of all adhesive systems, primarily due to their extensive use in the packaging and footwear industry. They are easy to apply and can be very low cost with many being derived from mixtures of common bulk polymers in conjunction with additives to impart the necessary adhesive and structural properties.The primary distinguishing factor of a hot melt adhesive over most other adhesive systems is that it is applied in a molten state, which cools to form a solid bond between the two substrates (adherends).

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EVA based adhesives are very versatile adhesives that can be formulated for a wide variety of applications. The type and amount of wax and resin used with the EVA copolymer can control the set time and the residual tack of the adhesive. In some instances, filler may be added to EVA adhesives for special applications, EVA adhesives are widely used in the following industries:

• Bookbinding
• Case and Carton Sealing
• General Packaging
• Appliance
• Doors and Millwork
• Furniture
• Multi-wall and Specialty Bag

Polyethylene adhesives are good, general purpose adhesives. they perform well in moderate temperature ranges and are well suited for porous substrates where flexibility is not required. Polyethylene adhesives have excellent pot life stability, as they are not prone to charring. They also exhibit good resistance to acid, grease, and other oily compounds. PE hot melts are commonly used the following industries:

• Multi-wall and Specialty Bag
• Case and Carton Sealing
• General Packaging
• Appliance
• Doors and Millwork
• Furniture

APAOs are often used when a low cost adhesive with good acid or fuel resistance and moderate heat resistance is needed. These non-crystalline adhesives are soft, tacky, and flexible. This gives them longer open times and good adhesion. APAOs are used in the following industries:

• Appliance
• Doors and Millwork
• Furniture
• Case and Carton Sealing
• General Packaging
• Diaper
• Adult Incontinence
• Feminine Hygiene
• Dress Shoes
• Athletic Shoes

Block copolymer based hot melt adhesives (also known as styrene copolymer adhesives and rubber-based adhesives) are best known for their low temperature flexibility combined with high heat resistance. Most are used for pressure sensitive applications where the substrates can be mated after the adhesive has cooled. However, they are also used in adhesives and sealants that lose their tack when cooled so the substrates must be mated while the adhesive is hot. Industries supplying block copolymer adhesives are:

• Bookbinding
• Diaper
• Adult Incontinence
• Feminine Hygiene
• Appliance
• Doors and Millwork
• Furniture
• Case and Carton Sealing
• General Packaging
• Dress Shoes
• Athletic Shoes

Polyamides are high-performance hot melts that are used when bonds need to resist high temperatures (up to 350°F) and fuels or solvents. They are also among the strongest hot melt adhesives. These can be formulated to be soft and tacky or hard and rigid depending on the polymer and the resin used. Polyamides are used in the following industries:

• Appliance
• Doors and Millwork
• Furniture
• Dress Shoes
• Athletic Shoes

Capital Adhesives provides adhesive solutions for a variety of substrates.

Type of Board
Description
Uses
Solid Bleached Sulphate (SBS)
virgin materials
a high quality board, white throughout with one side coated pharmaceuticals, dry foods, etc. where quality printing and “clean” look is required
Clay Coated Whiteback (CCWB)
100% recycled materials
(78% post consumer)
smooth board with white top and off-white to white back industrial or high-end retail needing slightly less strength with good printing quality
Clay Coated Kraftback (CCKB)
recycled or virgin materials
heavy duty board with white top and brown back heavier products where strength as well as printability are needed
Clay Coated Newsback (CCNB)
100% recycled materials (78% post consumer)
smooth board with white top and manila to gray back dry foods, cosmetics, etc. where high quality printing is needed
Solid Kraft
virgin materials
very strong board, brown throughout, with smoother top automotive, hardware, etc. where extra strength is required, as well as printability
Bending Chip
100% recycled materials
similar to Solid Kraft but with coarser printing surface heavier items needing average strength but not requiring high printing clarity
Poly-Coated Variety of poly coated substrates, including metalized poly Decorative and moisture resistant packaging for food, cosmetic, etc.
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