Development and Application Exploration of Easy-tear Lid Heat-sealing Adhesive Technology

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With the continuous development of the social economy, consumers have put forward higher requirements for the convenience, safety and aesthetics of food packaging, which makes the application of new packaging including easy-tear covers increasingly widespread.

Development and Application Exploration of Easy-tear Lid Heat-sealing Adhesive Technology

As a new type of cover film packaging, the easy-tear cover has the advantages of safety and hygiene, beautiful appearance and easy opening. It is mainly used in food packaging and has now become a standard cover type of international food metal cans. In addition, it is notable for its environmental friendliness – the wafers left by the punching process of the base cover can be recycled and reused; the food-grade composite film on the cover is smaller in thickness and mass, saving natural resources, even if it is opened by consumers Discarded after use will also degrade naturally without causing environmental pollution.

As far as easy-tear lid heat-sealing materials are concerned, as a solution to overcome the problem of “easy rust in the incision” caused by the easy-tear lid sealing film, domestic easy-tear lid heat-sealing materials have achieved great results in product development and application exploration. Significant progress has been made, and it is expected to help industry users improve economic benefits through import substitution.

Easy-tear cover processing technology

Easy-tear cover is a new composite technology that is bonded by aluminum foil and tinplate or coated metal substrate. It has the characteristics of high sealing and certain pressure resistance. Its processing technology includes: using tinplate or aluminum as the basic material, after punching, stretching, and rounding, shaping treatment, so as to achieve the purpose of being safe and not hurting hands after opening; covered with metal composite film or ultra-high temperature resistant The sterilized composite plastic film is then processed by handle making and embossing for a beautiful appearance and easy opening.

Types and application characteristics of easy-tear lid sealing film

Most of the heat-sealed easy-tear covers use the aluminum-plastic lamination process, and the materials used to achieve the bonding properties are modified polyolefins or polyvinyl acetates. After heating, the film layer melts and is bonded to the substrate.

Polyolefin-based film Polyolefin-based film has excellent water resistance due to its low polarity, no hydrophilic group, and is often used in the easy-tear-cover packaging of yogurt, lunch boxes, hot pot takeaway and other products. But it is also because of the low polarity that modified polyolefins are usually pre-coated with film glue on the aluminum foil, and the film can be well adhered to the aluminum foil substrate through the glue.

Polyvinyl acetate film Polyvinyl acetate film has a high content of ester bonds in the molecular structure, and its water resistance is weakened, so it is often used in the easy-tear cover packaging of dried fruits, tea leaves and nuts.

After long-term research and development, the application of coated iron or coated aluminum easy-tear cover products has gradually matured. However, since the metal substrate at the incision is directly exposed after the lamination product is formed, it is easy to corrode, which affects the food safety and the adaptability of the product. Therefore, how to effectively avoid or reduce the corrosion of the incision has become the current lamination and easy-tear cover industry. a major problem.

Types and application characteristics of easy-tear cover heat sealant (roller hot melt adhesive)

At present, in addition to film-coated easy-tear cover products, there are also some easy-tear covers that use a roll-coating hot-melt adhesive process, and the film thickness is relatively thin (about 10 μm). Compared with the lamination products obtained by extrusion coating, cast film, blown film and other production methods, the use of roll coating hot melt adhesive technology can not only improve production efficiency, save material costs, but also obtain higher product quality stability. More importantly, due to the strong adhesion between the coating and the substrate, the degree of notch corrosion is reduced to a certain extent.

The hot melt adhesives involved in the roll coating process of the easy-tear cover are currently concentrated on materials such as modified saturated polyester, ethylene acrylate copolymer, and modified polyacrylate. , the market scale is gradually expanding, and the application prospect is broad.

Saturated polyester resins Saturated polyester resins are prepared from different polyacids and polyols. By controlling the structure of the monomers used, two different structures, Linear and Branched, can be obtained (Figure 4). If a linear structure of polyols and polyacids is used, the synthesized resin has a linear structure and is very flexible. If a polybasic acid and polyol containing a benzene ring are used, the synthesized resin contains a benzene ring structure. The rigidity of the benzene ring can give the resin hardness, and the stable structure of the benzene ring can give the resin chemical resistance. Because the main chain of the polyester resin contains more ester bonds, the molecular chain has good flexibility, and the terminal or side chain contains polar carboxyl or hydroxyl groups (that is, the acid value or hydroxyl value we often say), they can either As a heat sealant itself, it can also be cured into a film by cross-linking with isocyanate, amino resin and other resins to improve the chemical resistance of the adhesive layer.

Formula developers can screen resins according to product requirements, select appropriate curing agents for product design, and related easy-tear lid product applications include takeaway lunch boxes, dried fruit cans, milk powder cans, etc.

Ethylene acrylate copolymer Ethylene acrylate copolymer is a polymer based on acrylate monomers, by introducing ethylene or vinyl monomers for copolymerization, and using oxygen or peroxide as initiators through free radical polymerization. Its structure is shown in Figure 5(A). The introduction of vinyl monomers endows polymers with adhesiveness and film-forming properties; acrylate monomers provide polymers with good substrate adhesion properties. As the content of vinyl monomers increases, the properties of such polymers will gradually approach those of vinyl polymers—chemical resistance increases, but their stability in solution may decrease to a large extent, so it is necessary to adjust the two The proportion of class monomers to achieve the desired product performance. At present, this kind of polymer has oily and water-based systems, and the oil-based system is widely used. Because vinyl monomer is difficult to disperse in aqueous solution, its application is limited to a certain extent. At present, the vinyl content of water-based ethylene acrylate copolymer on the market is less than 20%. Milk cans, etc.

Modified polyacrylate polymer, modified polyacrylate polymer refers to the polymer obtained by repolymerization or graft modification of polyacrylate through chemical reaction between macromolecules after the completion of polymerization. Modified polyacrylate polymers include polyurethane-modified polyacrylates, polyester-modified polyacrylates, silicone-modified polyacrylates, etc., all of which have the advantages of both modified polymers and polyacrylates. Polyacrylate has the flexibility of the polymer chain, its glass transition temperature (Tg) is low, and the temperature varies with the number of carbon atoms in the ester group and its branching, and it will form a glossy paint film after coating. , strong adhesion, not easy to peel off, can be used in adhesives in different occasions, including easy-tear cover products.

Formula developers can screen resins according to product requirements and select suitable curing agents for product design. The application of related easy-tear lid products covers takeaway lunch boxes, dried fruit cans, milk powder cans, etc.

The localization of easy-tear cover hot melt adhesive will help users reduce costs

At present, most suppliers of easy-tear cover materials are foreign manufacturers, with high prices and relatively limited supply. Therefore, realizing the localization of easy-tear cover materials is a direction for material people.

The Ultimate Recycling of Tin Cans

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In the past few months, thyssenkrupp Rasselstein, a subsidiary of Germany’s thyssenkrupp Steel Europe and one of the three major steel production giants in Europe, and Swiss packaging supplier Hoffmann Neopac have successively released news, as two As a result of a pilot project jointly carried out by the authors, the tin-plated iron used in the Recyclan (recycled cans) is all recycled iron from household packaging, and the packaging can also be recycled an unlimited number of times. This not only pushes the recycling and regeneration of iron cans to the extreme, saving valuable basic resources and energy consumption such as iron ore, coking coal, limestone, etc., but also marks the iron cans with the organic food green packaging credit label, making the strict requirements and sales Customers of organic products get their wish.

According to thyssenkrupp Rasselstein’s official website, the company has a history of more than 250 years, producing cold-rolled tin-plated or chrome-plated steel sheets with a thickness of 0.100~0.499mm. The annual output of packaging steel is about 1.5 million tons, and its applications include food cans, beverages Cans, aerosol cans, paint cans, and various metal cap products like crown caps and screw caps.

Tin Plated Iron Packaging: One of the Most Environmentally Friendly Sustainable Packaging

For many years, tin-plated iron has been regarded as an excellent packaging material for organic food, coffee, tea, candy, dry or paste cosmetics and other care products due to its good content protection properties. At the same time, one of the biggest advantages of tin-plated iron packaging is that it can be recycled indefinitely without loss of quality such as strength, making it more common than other packaging materials.
Can Recycling: Closed Material Cycle Globally, packaging iron is typically made from natural raw materials such as iron ore, coking coal, limestone, and recycled scrap iron. One of the properties of steel is that it can be melted repeatedly and processed into new steel products. Another feature is that iron is magnetic, and once collected for recycling, magnets can be used to separate steel packaging from other waste very easily and quickly during picking.

Therefore, it can be said that if iron cans are well classified and processed today and enter the recycling system, they may become parts of bicycles tomorrow, and may also become part of automobiles the day after tomorrow. Even tin-plated iron produced decades ago, if it has been in a closed material cycle, will still appear on newly produced steel products. According to WV Stahl calculations, 84% of the previously produced steel is still being recycled.
In addition to being used as a component of the aforementioned automobiles and rails, the iron cans can also be made into iron cans after regeneration. The concept of Recycan is said to have been conceived by Hoffmann Neopac in response to a customer request, through cooperation with supplier partner thyssenkrupp Rasselstein, and finally proposed a “recycling of tin-plated iron waste from household packaging, such as metal cans, crown caps, claw type screw caps to make new food jars” idea. Mark Aegler, CEO of Hoffmann Neopac, said that in Europe, North America and other developed markets, tin-plated iron cans are synonymous with “environmentally sustainable” due to their ability to regenerate in a well-established recirculation stream.

Domestic and foreign situation of tin-plated iron packaging recovery rate Data from the British Metal Packaging Manufacturers Association (MPMA) shows that metal packaging is the most recycled packaging material in Europe, with a recycling rate of 82.5% for steel packaging. In Germany, the recycling rate of tinned iron packaging has exceeded this level for ten consecutive years, and even reached 90.4% in 2018 (data from GVM).

In my country, household tin-plated iron packaging has been facing the dilemma of “rejection by scavengers and low recovery rate” for a long time. Only in 2019, the two milk powder giants, Mead Johnson and Nestlé, successively launched milk powder can recycling programs, aiming to help the circular economy and eliminate the potential safety hazards caused by the recycling of waste cans by informal channels. The driving effect of tin-plated iron packaging recycling remains to be seen.

RecyCan: From household waste tin-plated iron packaging to new tin cans for new purposes, pushing the recycling of tin-plated iron packaging to the extreme

Generally speaking, all tinplate cans contain some amount of recycled iron. Made from 100% recycled tin-plated iron, the RecyCan product line takes tin-plated can recycling to the extreme, a way to maximize the recycling of consumer steel packaging without compromising the appearance and contents of the packaging. A full-cycle way to protect performance, while packaging can be recycled almost infinitely, the label effect of green packaging goes without saying.

Seven steps of the full cycle method for tinned iron packaging In a nutshell, RecyCan’s idea is to remelt steel packaging waste from households into molten steel, which is then processed through a complex system to produce new food cans tin plate, and finally into new food cans.

Take a milk powder can as an example, its original role was to protect infant formula. After the milk powder is used up, the milk powder can is collected along with other household recycling items. At the picking station, it can be easily separated from plastics and other metals with magnets, entering the recycling system along with other discarded household steel packaging such as lids, crown caps, etc. Then through the processes of chopping, pressing, cleaning, detinning, burning, melting, pouring, etc., it becomes a well-formed thick steel plate. It is then hot-rolled into coils, cold-rolled, tinned, cut into sheets, printed, and finally made into new consumer packaging cans, such as high-end organic coffee, so the new function allows the packaging to open a new life journey.

The first step is to collect waste cans, screw caps and crown caps from the household.

The second step is to separate the tinned iron packaging from the aluminum and plastic packaging with a magnet and chop.

The third step is to detin the scrap iron and then press it into squares.

The fourth step is to melt the iron block into molten steel, and then pour it into a thick iron plate.

The fifth step is to hot-roll, cold-roll, tin-plate, and cut the thick plate to become a tin-plated sheet for packaging.

The sixth step is to print on recycled tinplate, which is then made into a new tin can.

The seventh step is the retail and consumption of the canned product.

The above seven steps allow tin-plated iron packaging to be fully reused for packaging production, thus forming a closed journey of consumer packaging.

Advantages of RecyCan

According to the data, RecyCan’s cans are divided into three-piece, two-piece shallow-drawing or deep-drawing cans. It is said to have good light, air/oxygen and moisture barrier properties, which can preserve the flavor, nutrition and appearance of food; at the same time, it has obvious ecological advantages – not only saves the use of basic resources, but also consumes more energy than basic resources Production of new cans has been reduced by 60%; in addition, it meets EU food regulatory standards.