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TECHNOLOGIES & TECHNIQUESFLE

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Solventless Laminating Adhesives Poised for continued growth

By Michael Leib and Larry Jopko

In the 1970s, one of the fi rst major energy crunches occurred, spurring the development of solventless adhesive technology for packaging to replace the commonly used solvent-based

adhesives. The same issues exist today: high energy costs, high raw material costs, higher labor costs, environmental concerns and the need to supply fi nished and safe laminate in ever short-er time. The current state of solventless adhesive development favors all of these issues. While converters are paying more for energy and raw materials, retailers and consumer product goods manufacturers are trying to drive prices down.There are many advantages to using solventless adhesives today, based upon the current economic and reglulatory conditions.

RELATIVE COSTSThe adhesive is the least costly part of the lamination con-

struction, between 1 percent and 5 percent of raw material cost (substrates, inks, coatings) but involves the most costly waste—poor adhesion, or lack of performance in the intended use, and usually results in total scrap of the construction. When the cost of the competing adhesive types, solvent-based, water-based and solventless, are compared, there is a clear advantage for solventless.

Relative Cost Normalized to Solventless Adhesives—Average Pricing by class

Adhesive Type/Class As Supplied (based on solids)

As Applied Solids + diluent and coreactant (If needed)

SolventlessGeneral Purpose and Medium Performance• High / Special Performance•

1 1

2.2 2.2

Solvent BaseGeneral Purpose and Medium Performance• High / Special Performance•

1.7 – 1.9 1.9 – 2.1

2.8 - 3 3.2 – 3.4

Water BaseGeneral Purpose and Medium Performance• 1.3 1.5

Four-roll solventless

coating head.

Typical gravure coating head.

Chart 1. Energy LCI for lamination adhesives. Chart 2. Cure rate of some solventless adhesives.

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TECHNOLOGIES & TECHNIQUES

The solventless adhesive also has some cost advantage simply due to applied weight. Solventless adhesive is generally applied at lower weight on average (Table 1).

MACHINE REQUIREMENTSSolventless adhesives require a dedicated coating head, consist-

ing of three or four smooth application rolls for the adhesive. A conventional gravure, offset gravure, or fl exographic coating sys-tem cannot be used effectively. In addition, superior tension con-trol of the substrates is required due to low bond and low shear of the solventless adhesive. Current dedicated solventless machines cost much less than similar laminators dedicated to water- or solvent-based adhesives, or a combination of solventless/water/solvent-based with interchangeable coating heads (Table 2).

ENERGY EFFICIENCYOver the last fi ve years, the cost of natural gas has increased

50 percent and the cost of crude oil has increased by more than 246 percent (U.S. Energy Information Administration). In today’s economy, there is more to the cost of an adhesive than just the de-livered cost to the converter or energy consumed to use it. There is also the need to consider the Life Cycle Inventory (LCI). This is an analysis of the energy required to make and use an adhesive, as well as water consumption and carbon dioxide emissions associ-ated with manufacture and use of an adhesive.

Chart 1 compares the energy LCI of the various adhe-sive types and shows much lower energy consumption for solventless adhesives. Note that energy used for transportation is much lower for solventless because fewer drums are shipped. This also means the converter uses less warehouse space, and has fewer drums to handle/dispose of/recycle.

PRODUCT CATEGORIESAdhesives encompass the categories of general purpose (low

demand/low performance), medium performance (demanding bonds and performance) and high performance (elevated tempera-ture and specialty/aggressive content performance). Current sol-ventless adhesives cover the full range of lamination use, having the capability to be used in place of water-based and solvent-based adhesives. Solventless adhesives can be used across all the current substrates commonly used in packaging (Table 3).

Currently, available solventless adhesives cure more quickly than older versions without the need for energy cure assist, extended hot room acceleration cure, special handling and equipment.

FDA REGULATIONSFor food packaging adhesives, there are very specifi c regula-

tions in Title 21 of the Code of Federal Regulations (CFR) under parts 170 to 199, under the Food and Drug Administration (FDA). Of the many parts, the three that are most pertinent are:

Part 175.105 - Adhesives (for use up to 120 F).• Part 177-1390 - Laminate structures for use at temperatures • of 250 F and above.

Part 177.1395 - Laminate structures for use at temperatures • between 120 F and 250 F.

Table 1.

Adhesive SystemCoating Weight (Pounds/ream)

100% Solids Solvent Based Water Based1-part 0.8-1.2 1.25-1.5 1.0-1.252-part 0.8-1.2 1.25-1.5 1.0-1.25

High Performance 1.25-1.5 2.0-3.0 -

Table 2.Machine

Characteristic Solventless Solvent Water

Use existing laminator

No – need func-tion specifi c coating

method

Yes – can use conventional

laminator

Yes – can use conventional

laminator

Coating head 3 or 4 smooth roll application

Flexo, gravure, offset gravure

Flexo, gravure

Drying None Yes Yes

Typical Line speed (feet/

minute)700-1500 300-1000 500-1200

Relative machine cost (dedicated) Low Medium

– highMedium

- high

Tension control Superior Average to good

Average to good

Factory footprint Low to medium Medium to high

Medium to high

Meter/mix/pump Needed Not needed Not needed

Adhesive waste Low High Medium - high

Heated rolls Application rolls, nip Nip nip

Table 3.

End Use Solventless Solvent Base

Water Base

Snack Food

Confectionery

Meat and Cheese

Stand Up Pouch + / -

All Plastic Lamination

Barrier Plastic Lamination

Metal Lamination

Fresh Produce

Medical

Hot Fill and Boilable + / -

Retort no

Agricultural Chemicals + / -

TECHNOLOGIES & TECHNIQUESTable 4.

FDA RegulationAvailability for Use

Solventless Water Base Solvent Base

175.105

177.1390 X

177.1395

A reputable solventless adhesive supplier will list the FDA Regulations to which the adhesive complies, as well as appropri-ate recommendations for intended use to ensure safety in the packaging for food supply (Table 4).

CURE BY TECHNOLOGYOne of the advantages of current sol-

ventless adhesives is that the chemistry is well known and has been in use for decades, based on urethane chemistry developed fi rst as solvent-based adhesives. The history of performance is known and generates confi dence in use. With new advancements in chemistry, the same ap-proach of urethane chemistry is now much safer for the workers and can cure in a very fast time to produce fi t-for-use packaging in a relatively short time. Many current sol-ventless adhesives now cure as fast, if not faster than, their solvent-born analogues.

FUTURE DIRECTIONSThe progress of the solventless adhe-

sive technology continues. Various new approaches and cure mechanisms are being explored, including:

Bio-based raw materials, which re-• duce petroleum-based materials.

Non-isocyanate curing, which further • enhances safety.

Energy-assist curing (electron beam • or UV light), which cure faster.

Faster-cure mechanisms that retain • ease of use.

Given the current state of solventless adhesives, there are clear advantages in economy, energy use and effi ciency compared to conventional solvent- and water-based adhesives. Solventless now covers all of the foreseen applications for lamination of packaging, from simple snack laminations to the very demanding medical, high-heat sterilizable and retort packaging. For new installations of lami-nation capacity, solventless adhesive use should be considered as one of the prime approaches. ■

ABOUT THE AUTHOR: Larry Jopko is technical service manager, North America Region, Packaging and Industrial Adhesives, Specialty Materials Group. He has 10 years of experience in converting and 24 years on the supply side, mainly in adhesives, coatings, heat seal coat-ings, barrier, functional coatings. Michael Leib has been with Rohm and Haas for 23 years. In his tenure he has held positions such as R&D chemist, technical service chemist and is currently a technical service manager in the Flexible Packaging Group.