Idea Transcript
TECHNOLOGIES & TECHNIQUES FLEXIBLE PACKAGING
Four-roll solventless coating head.
Typical gravure coating head.
Chart 1. Energy LCI for lamination adhesives.
Chart 2. Cure rate of some solventless adhesives.
Solventless Laminating Adhesives Poised for continued growth By Michael Leib and Larry Jopko
I
n the 1970s, one of the first 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 finished and safe laminate in ever shorter 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 COSTS The adhesive is the least costly part of the lamination construction, 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 Solventless • General Purpose and Medium Performance • High / Special Performance Solvent Base • General Purpose and Medium Performance • High / Special Performance Water Base • General Purpose and Medium Performance 32
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As Supplied (based on solids)
As Applied Solids + diluent and coreactant (If needed)
1
1
2.2
2.2
1.7 – 1.9
1.9 – 2.1
2.8 - 3
3.2 – 3.4
1.3
1.5
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TECHNOLOGIES & TECHNIQUES Table 1. Adhesive System 1-part 2-part High Performance
Coating Weight (Pounds/ream) 100% Solids Solvent Based Water Based 0.8-1.2 1.25-1.5 1.0-1.25 0.8-1.2 1.25-1.5 1.0-1.25 1.25-1.5 2.0-3.0 -
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 REQUIREMENTS Solventless adhesives require a dedicated coating head, consisting of three or four smooth application rolls for the adhesive. A conventional gravure, offset gravure, or flexographic coating system cannot be used effectively. In addition, superior tension control 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).
Chart 1 compares the energy LCI of the various adhesive 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 CATEGORIES Adhesives encompass the categories of general purpose (low demand/low performance), medium performance (demanding bonds and performance) and high performance (elevated temperature and specialty/aggressive content performance). Current solventless 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 REGULATIONS
ENERGY EFFICIENCY Over the last five 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 delivered 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 associated with manufacture and use of an adhesive.
For food packaging adhesives, there are very specific regulations 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 3.
Table 2. Machine Characteristic
Solventless
Solvent
Water
Use existing laminator
No – need function specific 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 – high
Medium - high
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
Tension control
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Solvent Base
Water Base
+/-
Fresh Produce
Medical
Hot Fill and Boilable
+/-
Retort
no
Agricultural Chemicals
+/-
End Use
Solventless
Snack Food Confectionery Meat and Cheese Stand Up Pouch All Plastic Lamination Barrier Plastic Lamination Metal Lamination
TECHNOLOGIES & TECHNIQUES Table 4. Availability for Use FDA Regulation 175.105 177.1390 177.1395
Solventless
Water Base
X
Solvent Base
A reputable solventless adhesive supplier will list the FDA Regulations to which the adhesive complies, as well as appropriate recommendations for intended use to ensure safety in the packaging for food supply (Table 4).
CURE BY TECHNOLOGY One of the advantages of current solventless adhesives is that the chemistry is well known and has been in use for decades, based on urethane chemistry developed first as solvent-based adhesives. The history of performance is known and generates confidence in use. With new advancements in chemistry, the same approach of urethane chemistry is now much safer for the workers and can cure in a very fast time to produce fit-for-use packaging in a relatively short time. Many current solventless adhesives now cure as fast, if not faster than, their solvent-born analogues.
FUTURE DIRECTIONS The progress of the solventless adhesive technology continues. Various new approaches and cure mechanisms are being explored, including: • Bio-based raw materials, which reduce 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 efficiency 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 lamination 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 coatings, 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.