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2022/9/17

Suntory Group, TOYOCHEM develop hot-melt adhesives for roll labels contribute to easy peeling properties and no adhesive residues

Labels for PET bottles are largely divided into two types: a shrink label which is shrunk with heat and a roll label which is rolled by the use of a hot-melt adhesive. Although the type of a roll label which is thinner has been increasing these days, we’ve also heard opinions such as “it is hard to peel off” and “The residue of a hot-melt adhesive is sticky.” Behind this background, a new hot-melt adhesive for roll labels that can solve such problems appeared. It was jointly developed by Suntory Group and TOYOCHEM CO., LTD. and started being adopted to “Suntory Green Tea Iyemon” and “Suntory Tennensui” etc. As it is easy to peel off with less adhesive residue and can enhance efficiency of the recycling process and product quality, both companies are appealing that it is also helpful for parallel (from PET bottles to PET bottles) recycling.

In response to opinions of 'It’s hard to peel off'

Suntory has worked on making roll labels for drinking bottles thinner for years. It developed a roll label of 18μm thick with the use of 60% of recycled PET resin in 2010, and then, a roll label of the world’s thinnest 12μm thick with the use of 80% of recycled PET resin in 2014, promoting to switch from thick shrink films to thin roll labels. Nowadays, shrink labels are used only for some bottles such as carbonated drinks which cannot be rolled with a roll label, and such roll labels account for more than 70% of the share of the whole beverages in the company.

On the other hand, we have heard opinions about the roll labels such as “the label is attached to a bottle so tight that it is hard to peel off” and “the adhesive residue on the surface of a bottle is sticky and uncomfortable.”

Gou Kira, a section chief of the packing material department at Suntory Holdings’ the supply chain headquarters said, “the number of roll labels used are on the increase for sure and we conducted a marketing campaign named “enjoying the green color of inside the bottle of “Suntory Green Tea Iyemon” by peeling off the label”, which brought about many opinions to us in 2020. It all started with the thoughts that we want to respond to such opinions sincerely as we’ve placed a great value on customers’ opinions.

According to our research, we found that there were two types of hot-melt adhesives, a strong adhesive type and a weak adhesive type and adhesive residues were found when a strong adhesive type was used. Mr. Kira said, “Although we have received opinions about adhesive residues on soda products for which the strong adhesive type is used, we also had the similar opinions on adhesive residues of non-soda beverages such as “Iyemon”. The case may be caused by change in the types of the adhesive from weak to strong one at some factories when weak-adhesive labels peeled off at the time of manufacturing there in the past. Then, Suntory jointly invented labels with TOYOCHEM under the conditions that a label has adhesiveness strong enough not to peel off at the time of manufacturing while having easiness for customers to peel off and the setting of our labeler remains the same.”

By the way, a material for roll labels is OPP in many cases. But Suntory also uses recycled PET labels with 12μm thick as I mentioned in the beginning, for many products including “Suntory Green Tea Iyemon.” As for this label, Mr. Kira also said, “Hot-melt adhesives specialized in OPP labels are used quite often, but those for PET labels are rare. We had difficulty in realizing both adhesiveness and peeling-off function for materials and labels both of which are made from PET materials.”

The evaluation method was established Under the experiment for developing a new adhesive, they focused on extra easiness to peel off along with strong adhesiveness by changing components of strong-adhesive type hot-melt adhesives a little and made 2-3 kinds of samples. However, although good results were achieved at an TOYOCHEM laboratory, applying with the labeler used in a Suntory factory generated different results with glue residues on the surface of a bottle.

According to Masanori Nishiyama from the packing material department at the supply chain headquarters, the usage conditions were different between the two. He also said, “In the laboratory experiment in TOYOCHEM, board-type films were used and applying period was also different from the one at an actual factory. Therefore, some changes were added to the ex-periment in the lab by using PET bottles and labels so that the experimental result there would be the same as the one at a Suntory’s factory. This brought about the same results between the experiment at the labo and applying with the labeler at a factory, succeeding in improvement regarding easiness to peel off while conditions on applying with the labeler remained as they were. That was a great achievement.”

Labels with newly-developed hotmelt adhesives can be peeled off smoothly, leaving no glue on a PET bottle, and hot-melt adhesives stay tight on a label.

Yasuhiko Kondo, a manager of ADL-business unit in TOYOCHEM explained it saying, “A hot-melt adhesive is applied at first to a label which is, then, rolled around a PET bottle. A hot-melt adhesive is sprayed from a nozzle at the melted state with a temperature of 150℃, but it started to harden on contact with air. Managing the temperature at the time of spraying enabled us to coordinate the adhesive strength so that a hot-melt adhesive stays on a label but doesn’t transfer to a bottle.

Easier ways to recycle PET bottles

Furthermore, the hot-melt adhesive has a strength in enhancing efficiency of the recycling process and product quality. We understand that those bottles can be easily separated because they can be easily peeled off. But what are other advantages of them? Mr. Kira said, “Used PET bottles are collected, broken into small chips and alkali-cleaned. As hot-melt adhesives attached on a bottle are removed by melting in alkaline water, some residues on PET bottles don’t cause troubles under the current recycling procedure. But labels that are hard to peel off make more burden on customers when they separate bottles. In addition, dust or dirt particles attached to the sticky part remaining on a bottle may worsen the collection quality of used PET bottles. As we ask customers to separate bottles, we think enhancing the easiness of separating bottles is the most important.”

Suntory puts emphasis on such environmental property as well and proceeds to adopt the new adhesive for roll-label products manufactured at all of its factories, including its own and those of its subcontractors. The switchover is proceeding smoothly, and 90% of all factories, including both in-house and outsourced factories, are scheduled to switch by the end of this year.

However, it is not realistic that only Suntory will enhance the quality of recycled PET bottles. Many other beverage manufacturers should adopt easy to-peel hot-melt adhesives as well. Mr. Kira is expecting moves in the industry in the future, saying “We don’t intend to monopolize hot-melt adhesive technology that we developed. We’d like other drink makers to use it if necessary.”

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