Hot Melt vs Acrylic Carton Sealing Tape
August 7th, 2009 | 
Author: AMERISOURCE INDUSTRIAL SUPPLY
PACKAGING PRODUCTS MICHIGAN- CARTON SEALING TAPE
HOT MELT (HP SERIES) VS. ACRYLIC CARTON SEALING TAPE
HP Series adhesives are much more aggressive than acrylic.
• HP adhesives have significantly higher adhesion to almost any substrate.
• HP adhesives have much, much greater shear performance.
• HP adhesives have higher quick tack values.
• HP adhesives have greater adhesion to fiberboard.
• Bottom line: acrylics will perform in less demanding applications, but under stressful conditions they will fail long before HP.
HP Series products will perform in more than 95% of applications.
• In less than 2% of these applications acrylic will work better. HP 232 has decreased the applications that HP products in which HP could not compete.
Common Mistakes made while evaluating HP products:
• Assuming all hot melt products are the same. There are dramatic differences.
• Assuming release level is an indication of adhesive strength. The opposite is true. Acrylics don’t need release coats because the adhesive is weaker and less aggressive.
• Assuming finger tack is an indication of adhesive strength. Not true. Adhesives can have no “finger tack” at all, and still have very powerful adhesion and shear properties.
• Performing a cursory fiber pull test and assuming it’s an absolute indication of adhesive performance. HP Series products require wipe-down and a few minutes of dwell time on the substrate to allow the adhesive to flow. This does not mean that the product will fail immediately after application. There is plenty of quick tack to anchor the adhesive while it flows.
• Assuming the opacity of the adhesive is a reflection of the clarity of the product. Actually this is a very positive attribute when properly explained. The high viscosity of the adhesive is related to its high shear strength, and the viscosity causes air entrapment during the coating process. Low viscosity adhesives allow the air to escape rapidly.
HP adhesives are economical
· Hot melt adhesives are coated effectively at much higher speeds than acrylics.
• Hot melt adhesives can be coated easily on wide webs, allowing very high yields. Acrylic adhesive profiles are difficult to maintain over a wide web.
• Most hot melt manufacturers make their own adhesive from raw materials purchased in bulk. Almost all domestic acrylic tape manufacturers purchase their adhesives. Many overseas manufacturers manufacture their own small batches of acrylic. Small batches are hard to control and cause a high degree of variability in the performance of the tape.
HP adhesives perform much better than acrylics in automated carton sealing applications.
• The easier unwind feature of our hot melt machine length rolls offer a demonstrable advantage in automated carton sealing because it prevents the backing from being over-stretched during application. Film backings, when stretched, attempt to return to their original length. Unless the adhesive has sufficient shear strength (and acrylics do not) to hold the film in place, the bond will fail and the tabs will “flag” or pop up on the ends of the box, allowing the flaps to open. Eventually the seal on the major flaps will fail as well. With acrylics the film begins stretching at the point of unwind and it continues through the rollers of the tape head. This requires the user to effectively bypass the tension controls of the tape head – which can cause problems with cut-off and application pressure.
· HP adhesives bond to a wider variety of substrates
good to know information about acrylic construction
Acrylic adhesive performance: smoke and mirrors.
• Users mistake “finger tack” for adhesive power:
The most attractive feature of an acrylic adhesive is its wettability. Acrylic adhesives are very soft. As a result, they flow very quickly over the surface of the substrate and form a quick bond. This makes the adhesive appear to be very tacky and aggressive; however, this initial bond is very weak. In order to form a strong bond, an adhesive must flow deeply into the surface features of the substrate and the adhesive must have a strong polymer “backbone” to support the bonding action. Acrylics have two problems here: 1) because of their chemical properties they flow quickly at the surface, but they require much more time to flow deeply, and 2) the same design features that make them soft also result in a weak polymer backbone. As a result, they flow into and bond quickly only with the uppermost surfaces of the substrate, and they flow out of the substrate just as easily as they flow in. Hot melt adhesives can be designed to mimic acrylics in wettability, but you rarely see this because the modifications diminish the adhesion and shear advantages of the hot melt adhesive. In other words: the modification makes them similar to acrylics in adhesive performance
• Users mistake tighter unwind for adhesive power:
Acrylic adhesives have higher adhesion to backing – only because they don’t require a release coat. Hot melt adhesives are designed to have an easy release because the adhesive bonds to the film much more strongly. Without this release level the user wouldn’t be able to unwind the tape from its backing. This easy unwind feature allows hot melt BOPP tapes to perform better in automated carton sealing applications because the backing is not over-stretched (see below).
• Acrylic adhesive performance is much more sensitive to coating weight than hot melt:
When acrylic adhesive coat weight drops below 0.8 mils, the adhesive performance drops significantly. This is because the adhesive must be present in sufficient quantities to allow it to flow effectively over the substrate. With thin coat weights this flowing action is greatly minimized. An important corollary to this phenomenon is the fact that when comparing hot melts and acrylics of equal thickness, the acrylic will nearly always have a thinner film backing.
Hot melt adhesives are much less sensitive to coat weight.
Bottom line: at equal coat weights, hot melt adhesive significantly outperforms acrylics.
• Acrylic modifications require a trade-off in performance features:
Acrylics can be modified to offer greater shear strength, adhesion, and tack, but these modifications also result in greatly diminished cold temperature performance. Acrylic adhesives must retain a certain amount of moisture or “wetness” in order to perform well at cold temperatures. The increased polymerization required for greater shear properties “exposes” the polymer backbone to drying.
• Caveat emptor: beware of “home-made” acrylic adhesives!
Nearly all of the Asian acrylic adhesives are made in small-batch reactors. These small operations are usually owned or co-owned by the manufacturer, and the technological support in the manufacturing process is minimal. The result is a highly variable process that results in extreme inconsistency. In most cases the adhesives produced by these operations are made to achieve high tack and adhesion, but nearly all have poor or very inconsistent shear and cold temperature performance. Many domestic distributors are seduced by the low price of these Asian products (due only to favorable exchange rates resulting from currency devaluation in Asia), and only later do they find out that the performance is not what they are accustomed to with acrylics. In contrast, Rohm and Haas adhesives, which represent better than 85% of all acrylics sold worldwide, are made in huge batch sizes and are supported by extensive research, proprietary designs, and custom modifications which ensure consistent performance from batch to batch. The standard adhesive performs consistently at cold temperatures.
AP SERIES ACRYLICS VS. OTHER ACRYLICS
When selling AP series acrylic packaging tapes against other acrylics there are many features and benefits to discuss.
• Usage of cast film for even film profile. Cast film (with a 2.5% profile variability) is much ”flatter” than blown film (with a 15-20+% profile variability). By requiring cast film Shurtape ensures that adhesive coats will be consistent, roll after roll.
• Use of Rohm and Haas Adhesive. Mixed in huge batches, extensively researched and produced under very tight controls, R&H produces some of the best acrylic adhesive on the market. By requiring the use of R&H adhesive Shurtape knows that each roll will consistently deliver a high level of performance.
Rohm and Haas has done an admirable job of promoting acrylic adhesives and supporting acrylic manufacturers. Some of the measurable differences between Rohm and Haas acrylics compared to other acrylic adhesives include…
• “Not as sensitive to temperature variations”
• “Superior adhesion over temperature extremes”
• “Excellent clarity”
• “Non-yellowing”
• “Proven long term performance”
Other performance features compared:
• Appearance – UV resistance, aging, and discoloration due to oxidation
• Impact of appearance on retail consumer
• Printability
Advantages of acrylics:
• These boil down to two distinct features: 1) resistance to oxidation – which means resistance to aging, yellowing, and overall improved clarity, and 2) excellent wettability – which allows the adhesive to wet-out and bond rapidly (but weakly).
When to use acrylics:
• When applied at below freezing temperatures (if HP 232 is not an option)
• When used on highly finished graphics and stored or displayed in the box before usage.
• When stored for long periods in the presence of oxidizing light sources (UV, Mercury vapor lamps, sunlight).
• When applied to very smooth surfaces and stored below 20 degrees under stress.
• When rapid initial bonding is an advantage – as with some recycled cartons that will not be subjected to stress. Note limitations.
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