Ecopack Learning: the science behind supercalendered paper

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Calendered paper. How fun, you might say.

But even the most mundane commodity, such as a small muffin cup, can have an interesting history. Chemistry, engineering, physics, mechanics: so many sciences are behind the muffin wrapper we just throw away!

So stay with me, and read until the end for something very curious!

Why a newsletter about calendered paper?

People that work in the bakery industry hear the term greaseproof paper and supercalendered paper every day. But do we really know what it means??

For some, maybe recently moved from another industry, or working in an area that has very little contact with the technical features of a products, it can be difficult to make sense of all the technical terms.

If this is you, no worries: we got you covered.

What is greaseproof paper?

First things first: in this article, we are referring to greaseproof paper used in industrial bakery applications. Not every paper is the same, and in different industries the term greaseproof paper might refer to a paper with different technical properties than the ones discussed here.

Now that we have settled the first distinction, we can look at a general description of greaseproof paper: a specific type of paper, essential in the industrial bakery application due to its unique ability to resist grease and oil. This attribute makes it a fantastic choice for containing or wrapping food products that require a barrier against oils and fats.

The physics of supercalendered paper

One of the most fascinating traits of industrial processes is how they can combine many disciplines, to create one single product: in our first article we delved into the chemistry of PFAS and PFAS-free paper; now, we touch the mechanical properties of paper, to show how greaseproof paper is made (ad-hoc!) to suit the necessities of an industrial production.

Paper can become greaseproof by a chemical or mechanical treatment. In this article we won't explore the chemical process. We will instead focus on the mechanical one, the calendering process.

So, what is calendered paper?

Calendered or supercalendered paper is the paper that had been treated mechanically, to close its fibers enough to to develop a resistance to water, stains and grease.

The calendering process involves passing the paper through a series of highly polished metal rollers at high pressure (and sometimes elevated temperatures).

The calendering process compresses the paper fibers, closing them together and making the paper extremely smooth and significantly reducing its porosity.

It’s this reduction of paper’s porosity that minimizes the ability of grease and oil to penetrate the paper. This critical process ensures the paper has the necessary density and surface finish to provide effective grease resistance.

A little bit of history

In the past, paper was smoothed either with polished hammers or by pressing it between polished metal sheets.

Modern paper machines evolved into rolling the paper continuously between rollers that can be heated, to helps maintain the paper's bulk and stiffness. Rollers are made of cast iron or steel, and are slightly tapered to ensure even pressure distribution, which improves the quality of the finished paper.

Calendered or supercalendered?

When paper is calendered, the paper is pressed between hard rollers, and this step is included in the production line, just like every other step needed to create the final product. This type of paper is usually used in the publishing industry.

Supercalendered paper, instead, undergoes an additional, more intensive calendering process. The material is pressed using alternating hard and soft rollers, usually steel and fiber-covered rollers. This step is added at the end of the production process, in a separate supercalendering unit.

Supercalendering makes the paper shiner, glossier, and greaseproof, making it suitable for the baking industry.

The printing effect is also more precise, because the degree of paper smoothness is higher:

For our paper mould category products, we use supercalendered paper to provide both process performance and application performance due to the correct resistance to food grease.

Importance and Impact on Product Shelf Life

Greaseproof paper plays a vital role in maintaining the quality and shelf life of food products. By providing a barrier against grease and oil, it helps to preserve the freshness and integrity of food items, preventing them from becoming soggy or greasy. This is particularly important for baked goods, fried foods, and other oily products. The use of greaseproof paper in packaging ensures that the food remains appetizing and retains its intended texture and flavour over time.

Curiosity

Did you know that supercalendered paper can be used for electrical insulation? This paper has dielectric properties, meaning it can resist electric current and prevent electrical discharge. This makes it suitable for use as insulation in electrical components. How curious!

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