Water-Based Adhesives

VAM-Based Emulsion Adhesives

There are two primary types of VAM-based emulsions. The first is polyvinyl acetate (PVA) adhesives. They are aliphatic, rubbery synthetic polymers and are considered a type of thermoplastic. PVAs are designed for use on porous materials, particularly paper, wood, tissue, nonwovens, cloth, and some stone materials. Paper applications, such as corrugated board, bookbinding, envelopes and labelling are the most common uses.

The second is Vinyl Acetate Ethylene (VAE) adhesives. They offer considerable performance advantages over PVA adhesives. VAE adhesives offer comparable machining properties to PVAs with improved adhesion to non-porous surfaces. VAE adhesives have better flexibility and water resistance with superior bonding properties.

Flexible packaging is the biggest application type for VAE adhesives. Another large category is laminating applications due to their flexibility, moisture resistance, and superior substrate adhesion. VAEs are widely used in furniture, bookbinding, and textiles applications. VAEs are also popular in the fabrication of nonwoven products, such as personal hygiene applications.

Acrylic-based Emulsion Adhesives

Acrylic-based emulsion adhesives are made by homogeneously emulsifying vinyl acetate, EVA, or acrylic synthetic resin polymers in water. These adhesives provide a balance between:

• Peel – the strength between the adhesive and the substrate, increasing over time during the curing process
• Shear – the ability for the product to adhere to itself
• Tack – the speed the adhesive bonds immediately to the substrate

Many acrylic polymers are crosslinked, which improves the weather and aging resistance, as well as preventing breakdown by other solvents. Some common acrylic adhesives include pressure-sensitive adhesives and paper laminating adhesives. Acrylic-based emulsion adhesive is commonly used to manufacture packaging, particularly paperboard boxes.

Natural-based or Bio-based Adhesives

Natural-based polymers are developed from organic materials. Some of the most popular are derived from vegetable sources, such as starches and dextrins, or protein sources, such as soybeans, casein, and milk albumen. Natural-based adhesives with caseins have relatively long drying times, form very strong bonds, and are resistant to water. Dextrins are commonly used in the paper industry and very durable with specific materials. However, they are susceptible to breakdown when exposed to water.

Natural-based or bio-based adhesives are supplied in 2 forms – liquid solutions or as dry powders – both are mixed with water prior to application. Adhesive strength results when water evaporates or absorbs into the substrate. Common applications involve a permeable substrate; however, there are other methods involving dry time before the adhesive can be activated with a “quick tack” joining two non-permeable substrates. Many natural-based adhesives are perishable and extended storage is not possible.

Natural Rubber and Polychloride Adhesives

Natural rubber adhesive is one of the earliest substances used to bind materials. Because of its capacity to become elastic when heated, it is one of the most popular adhesives on the market and is typically used in bonding organic and porous materials such as leather, paper, fabrics, as well as other rubber products. 

Natural rubber adhesives offer aggressive and instantaneous tack and have a lower toxicity level. For these chemistries, tackifiers must be added to achieve different levels of adhesion. Rubber-based adhesives offer water-resistant properties, flexibility, and versatility, making it a good choice for use in clothing and footwear manufacturing, as well as for reinforcing the backing of carpets and floor rugs.

Liquid Polyurethane Adhesives

Designed for use in extreme environmental conditions, liquid polyurethane (PUR) adhesives are reactive moisture curing. The chemistry enables the adhesive to bond with low, surface energy substrates which are difficult to bond. Their attributes include strong bonding and exceptional cold, heat and moisture resistance. These adhesives are commonly found in flexible packaging applications.

Liquid polyurethane adhesives produce extremely durable, highly elastic bonds. Reacting to the moisture in the environment, these adhesives form a cross-linked, thermoset bond. They have short open times, are easy to apply, and are simple to clean-up. These chemistries are designed for adhering materials such as – carpet, wood, foam, metal, and most plastics to each other. They are not recommended for vinyl (PVC), polypropylene, polyethylene, and polyolefins.

Additives for Water-Based Applications

Some water-based adhesives contain additives such as surfactants and emulsifiers to stabilize the chemistry. Other ingredients are sometimes added include defoamers, biocides, pigments, flame retardants, anti-static, and wetting agents to support different performance needs of the adhesive.

Commonly part of water-based adhesive formulations with paper packaging applications, additives play an important role in the various paper application process. The most common additive is water resistant resin. These formulations render the formula moisture resistant or waterproof. These additives crosslink with starch molecules making it more difficult for water to dissolve the mix.

Adhesive with water-resistant additives (WRA) should be used within a certain timeframe after the crosslinking agent is added. In many cases, a dye is incorporated into the formulation to give operators a visual cure the additive was added to the adhesive. When working with additives, manufacturers should consideration the following:

• Using fresh adhesive (less than 4 hours after adding resin)
• Targeting a viscosity between 32–38 seconds
• Achieving higher solids (26% +) gives better results

Merlin Dilution System

Concentrated water-based adhesives are used in various markets. There is not an industry standard for diluting the adhesives to the desired percent solids or viscosity, which can cause variations in the performance and use. The Merlin Dilution System is an on-line adhesive dilution system for concentrated adhesives which provides a completely automated process and replaces the current manual practice of dilution. Adhesive is supplied “On Demand” from storage tanks. It eliminates heavy lifting and dumping pails, which keeps line operators from chemical exposure.

Primarily used by tissue and towel manufacturers, the Merlin Dilution System:

• Eliminates risk of contamination
• Controls/adjusts adhesive concentration
• Matches percent solids to processing requirements
• Reduces variability in adhesive concentration

Extrusion Transfer System

Softness and absorbency are important consumer demands for tissue and towel products. Achieving quality is often sacrificed with efficiency on tissue and towel production lines. Open-pot operations face challenges of slinging and maintaining the adhesive properties. The extrusion transfer system is a popular investment supporting a cleaner and more efficient production line.

Installing an extrusion transfer system eliminates the need to clean/remove the pot and reduces safety risks associated with equipment cleaning. Another benefit is manufacturers can utilize higher performance adhesives tailored for specific production needs. Results from numerous system installations include:

• Improved run time 5 – 22 minutes per 12-hour shift
• Reduced add-on rates 15 -50%
• Reduced waste 35 - 50%
• Improved operator safety from reduced clean up

Water-Based Adhesive Monitoring Systems

Understanding the adhesive usage – application levels and environmental factors – provides operational insights for water-based adhesive applications. Designed with a series of sensors feeding real-time data to a dashboard which enables optimization of adhesive consumption and reduction of downtime on the production line. The system can also notify operators of any failure or malfunction of the water-based adhesive equipment.

When an active batch is currently on the production line – running or not – basic information is displayed. This data includes start time, end time, if the batch is finished and general information on the water-based adhesives (e.g., brand, adhesive name and identifying numbers). This provides the operator with pertinent details and allows recognition any discrepancies with the factory condition. Henkel’s monitoring systems perform:

• Environmental condition to assure optimal adhesion
• Consumption details to assure application amounts are within range
• Data on the affixing process to identify interruptions and track efficiency

AEROBOND Foaming Technology

Laminating and corrugating adhesive applications require a precise balance of moisture in the adhesives used.  If the density is off – the result is either warped corrugate or layer curl. The AEROBOND Foaming technology injects air into the adhesive stream to reduce the density, which in turn reduces the amount applied.  Additionally, the rheology is improved and assures the adhesive remains where applied.

Foaming is a key component for thin-film metering systems used in litho-laminating applications. To maintain the highest possible operating speed, the adhesive needs a “high wet tack” to prevent edge lift. Reducing the adhesive density allows manufacturers to operate at the highest possible machine speed with little or no delamination or edge lift. Foaming also enables 100% fiber tear.

Contact us to find out more about any of our equipment or get industry-specific information on our water-based adhesives, contact a member of our team.