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WVTR and OTR Test for the paper based coated material June 23,2022.

     Ⅰ. Food packaging needs

      As the global retail food customer base grows, food packaging must increasingly meet international food quality and safety standards. This also means that a longer shelf life is necessary. At the same time, the increasing awareness of environmental protection among consumers around the world has led to a dramatic increase in the demand for barrier coatings for sustainable paper packaging. This trend has put enormous pressure on paper and board packaging manufacturers to phase out barrier coatings using polyethylene, paraffin, silicone and fluoride in favor of more environmentally friendly barrier coatings, especially in food and in beverage packaging applications.
     The portfolio of barrier coatings for paper and board includes a range of products for water vapor, hot and cold liquids, and oils and greases. These barrier coatings are available as water-based polymer emulsions or solid biowaxes and are produced with the highest levels of renewable feedstock content currently available. Most importantly, paper-based coating materials using these barrier coatings are often repulpable, recyclable, compostable and biodegradable, providing not only a way for paper and board packaging manufacturers to provide retailers and Basis for sustainable use by consumers. At the same time, it also creates a demand for safe and full consumption of convenience food and longer preservation time. Therefore, protective economical food packaging needs to have a high barrier to oxygen and water vapor.

      Ⅱ. What is paper based coated material

Paper based coated material are various minerals which are used to coat a base paper, in order to enhance its properties. These paper coating materials bring certain properties to the paper such as brightness, gloss, smoothness, etc.

Paper coating materials can be classified into nine types, namely, GCC, PCC, Kaolin Clay, Talc, Starch, SB latex, Titanium Dioxide, Wax, and others. GCC constitutes the major share in the global paper coating materials market. These are widely used as pigments and therefore, are expected to grow aggressively in the next five years. Kaolin clay and talc are widely used as fillers in coating.

The demand for these paper coating materials is influenced by the growing demand in end-user industries, especially the manufacturers of binding covers and corrugated boxes. Paper coating materials are application specific and are available globally.

Its main uses are: printing magazines, books and other publishing paper and trademarks, packaging, catalogues and other printing paper, the ratio of the two is about 1:3. Coated paper can be divided into: coated paper, lightweight coated paper, in addition to special coated paper such as iron coated paper.

Ⅲ .Effective Food Barrier Coatings

WVTR and OTR of environmentally friendly barrier material and other functional coatings include materials is applied to substrates to provide a barrier, as well as packaging used to protect selected packaged goods. Barrier coatings provide barrier to food packaging requirements, which can include protection from oxygen and flavor, liquid water and water vapor, oil and grease. The traditional disposable paper packaging will be covered with a layer of PE coating to achieve the effect of water and oil resistance. The PE coating is difficult to separate from the paper substrate, making the paper products difficult to return.

Paper based coated material In the application field of food contact materials, paper based coated material can be replaced by paper, including two types:
One is the coating of paper products before molding, which has a similar process route to the traditional PE lamination post-processing and molding; the other is the spraying after pulp molding, which is different from the traditional adding in pulp; The process problems to be solved are more complicated.
Food-grade paper product packaging, its key application performance and process performance are mainly waterproof and oil-proof performance, heat sealing and anti-stick performance. "Paper instead of plastic" water-based barrier coating not only takes into account the performance of the original PE coated paper, but also realizes the recyclability of disposable paper packaging and re-slurry recycling: at the same time in application performance (waterproof, oil-proof) and process performance (Heat sealability, anti-adhesion) and other breakthroughs have been made, which will help paper packaging materials become environmentally friendly barrier materials.

      Ⅳ. Manufacturing Principle

The manufacturing of coated paper simply means that the coating is applied on top of the base paper, and after drying, the surface is smoothed by a calender, so the base paper and the coating are important factors that affect the quality of coated paper.

Taking a coating layer with a coating volume of 20g/m2 as an example, assuming that the dry specific gravity of the coating is 1.5, the thickness of the coating layer is only about 0.0013cm, and with such a thin thickness, the quality of the original paper really plays an important role.

If the coating speed is slow, the strength of wet paper must be maintained with moderate gluing because the original paper cannot lose its strength after absorbing water and reaching the drying department. Conversely, when the coating speed is fast, the paper must have a certain strength to resist the mechanical force brought about by high-speed coating, while the uniform water absorption is also very important. Therefore, the water vapor transmission rate test(WVTR) of coated paper is a very important performance test step.The main test methods for the transmittance of coated paper packaging materials are introduced below.

Ⅴ. permeability test method for paper based coated material

Water Vapor Permeability Test:

The water vapor transmission rate (WVTR) of coated paper is calculated from the amount of water vapor per unit area (m 2 ) per unit time (24 h/d) at a certain temperature and relative humidity by testing the material (RH). In this work, the MVTR is evaluated by the weight method, which is based on the ASTM E96 and ASTM D1653-2003 standards.

By testing the water barrier properties on the coating step, it is possible to give manufacturers the specific parameters of the material to manufacture non-toxic and environmentally friendly paper-based packaging materials with high barrier properties.

Oxygen Permeability Test:

The GBPI series Oxygen Permeability Analyzer has a test range of 0.05 to 10,000 g/(m2-24h) , It can be applied to low, medium and high barrier materials. The method used is based on ASTM D3985's Coulomb Electricity Method.

Oxygen Transmission Rate Scope:

Determine oxygen transmission rate (OTR) of flexible barrier materials used in packaging or industrial applications. Key factors to understand material permeation include thickness of the material and environmental factors such as relative humidity and temperature.

ASTM D3985 Test Procedure:
At a selected temperature and humidity, a barrier film is sealed between a chamber containing oxygen and a chamber void of oxygen. A coulometric sensor measures the oxygen that is transmitted through the material.

Typical Test Area: 50cm2

Data:Oxygen Transmission Rate (OTR) mol/(m2•s)

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