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Coatings for Tin-plated cans: Introduction & Significance

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A Tinplate is a thin steel sheet with a tin coating. Tinplate is one of the most common materials used for the production of metal cans, which serve the food service industry, and others. Tin-plated cans have been witnessing a steady growth in demand, which is attributed to several features such as an excellent barrier, good mechanical properties, and high moisture resistance, among others. The global push for the use of recyclable packaging solutions is expected to facilitate the growth in preference for packaging solutions such as tin-plated cans. Tin-plated cans are also used for the storage and preservation of food by canning, which is regarded as one of the most efficient methods available. Furthermore, tin-plated cans also find applications in the beverage packaging industry, with cans being one of the most preferred packaging formats for the modern consumer. Therefore cans have witnessed growing usage among consumers across the world.

Why Tin-plated cans

The usage of metal is nowadays declining in the packaging industry with the ongoing trend of lightweight packaging. Many manufacturers are gradually inclining towards tin as these are light in weight and can be made available in a wide range of sizes, styles, and shapes.

Evolving consumer preferences, changing lifestyles, and a surging middle-income group population is some of the vital factors that are anticipated to boost the growth in this market. The increasing demand for petroleum lubricants and chemicals in numerous end-use industries is another significant factor that is likely to propel sales in this market.

In addition to that, the surging demand for sucrose-based juices, health drinks, carbonated soft drinks, and healthy beverages across the globe is projected to influence the market in the forthcoming years. The rising number of grocery stores and superstores in both developed and developing economies is also set to augur well for the global market.

Which prominent drivers are Spearheading Tin Containers Market Growth?

The rising usage of tin containers and tinplate in the pharmaceutical industry for the packaging of capsules, powders, ointments, and pastilles is expected to bode well for the global market. As these containers are highly resistant to microbes, odors, moisture, and gases, their demand is anticipated to surge at a fast pace in future years. These are also robust, opaque, and unbreakable, as compared to other metals.

These containers provide excellent printability which further helps key companies to propel their brand credibility. The easy availability of customized containers as per the requirement of customers is likely to push sales of tin containers during the assessment period. Even though these containers are facing competition owing to the surging sales of glass and plastic containers, their ease of filling and high-speed manufacturing is providing them with a competitive edge. 

How is the Asia Pacific Contributing to the Growth of the Tin Containers Market?

The growing production of tin in India, China, and some of the South East Asian countries is projected to bolster the Asia Pacific tin container market growth in the upcoming years. The rising number of food processing companies in these countries is also set to bode well for the regional market.

The entrance of several international companies into India and China through huge investments in their local manufacturing facilities is another crucial driving factor. The rising focus of multiple beverage companies on the production of mini cans and containers to provide smaller volumes of products at a relatively low cost is also estimated to augment the growth across the Asia Pacific.

Lacquers for Tin Containers

Coatings are applied to the metal and after thermal treatment (cure schedule or stoving) form a dry (final) film on the metal. The major constituents in a can coating as applied to the metal include:

• Resin(s)

• Cross-linking agents

• Additives

• Solvents

The cured film, which is in contact with food, must comply with relevant food regulations. Unlike plastics, coatings form a very thin film of between 1 and 10 μm, about a twentieth of the thickness of a sheet of paper. In some cases, solvent-free coatings (e.g. powder side seam stripes) are used, albeit at higher film weights

Internal coatings for metal packaging are typically applied by either roller coating or spraying before undergoing a cure schedule. The metal to be coated can be shaped as a sheet, coil, or preformed object. As in many cases, the coatings are applied before the deformation of the metal to form the container or cap, and the coating has to withstand severe mechanical deformations (e.g. for lug closures, crowns, ends, and some shallowly drawn cans). In other cases, the coatings are applied after forming the object, but nearly always further deformation is required before the final object is obtained, e.g. necking a DWI can. It is not unusual to apply more than one internal coating or to apply one type of coating several times. Each internal coating would be cured before the application of the next one.

There are a limited number of different chemical functionalities available for direct food contact coatings, resulting in a limited number of different types of resins that can be used for coatings for metal packaging. However, there are many variations of each type. The different resins consist of monomers and starting substances, which have to be approved by regulatory authorities. The resins discussed here are all approved for food contact, albeit with restrictions. The main types of resins are given in Table 1.

Table 1: Types and properties of resins used in internal can coatings

Types and properties of resin used in internal can coatings.

ChemistryNatureFlexibilityPack ResistanceMain end-uses
Epoxy-PhenolicHigh Molecular weight epoxy resin cross-linked with phenolic resolesGoodVery GoodUniversal gold lacquer for three-piece cans shallow drawn cans.
OrganosolPVC is dispersed in an appropriate varnish and conventionally stabilized with a low molecular weight epoxy resin or novolac epoxy resin.
Epoxidized oils can also be used.
Very GoodVery GoodDrawn cans.
Easy-open ends
Often used over epoxy-phenolic basecoat
Epoxy-anhydrideHigh Molecular weight epoxy resin cross-linked with anhydride hardeners.GoodVery GoodInternal white for three-piece cans
Epoxy-AminoHigh Molecular weight epoxy resin cross-linked with amino resin. Also epoxy acrylic water-based spray internals for B&B DWIGoodLimitedUniversal lacquer for beer and beverage cans (water reducible) side seam stripes Some food system.
PolyesterPolyester resin is cross-linked with amino or phenolic resins.
It May contain lower molecular weight epoxy resin
Very GoodPack-dependentMay not be suitable for very acidic and aggressive foods.
PhenolicPhenolic resin(S) which self crosslink (cure)Very poor, but film quality is weight-dependentExcellent, particularly for aggressive foodstuffsDrum and pails where flexibility is not a critical factor
Oleo resinousNaturally occurring oils with synthetic modificationVariablePack-dependentVery limited uses

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