Labeling Glass vs. Plastic Containers: What You Need to Know Before You Switch
Glass is growing in popularity as companies look for more eco-friendly packaging alternatives to avoid filling up landfills. Some have even developed a mixed-use, such as putting a plastic lid on a glass jar. However, glass is heavy and prone to breakage, increasing costs from product loss and transport.
Should you make the switch, or is plastic a better fit for your business? What challenges can you expect when you label containers made from these materials? Let’s take a look at labeling glass vs. plastic containers.
Types of Glass Used in Packaging
While glass is made with a variety of materials, it’s divided into categories based on its performance. Most manufacturers follow United States Pharmacopeia (USP) guidelines, which divide glass into three main categories. The differentiation between the three types takes into account the strength of the glass and its corrosion resistance.
Type I: Borosilicate
Borosilicate glass is mixed with boric oxide, aluminum oxide, alkali, or an alkali oxide. The result is a glass that is ten times as strong as soda-lime glass., Most of us are familiar with this glass’s functionality in cookware, but its strength and chemical resistance also make it a great choice for packaging chemicals and medicines.
Type II: Treated Soda-Lime
By treating soda-lime glass with sulfur during annealing, the resulting glass is more alkali resistant. Some bottles in this class have outer surface treatments to make them more heavy-duty. Type II glass can package neutral or acidic products.
Type III: Soda-Lime and Soda-Lime-Silica
Soda-lime and soda-lime-silica glass are cheap and chemically stable, making them the top choice for beverage bottles and mason jars. Brown-tinted bottles shield the contents from UV light, protecting medicines and beer. These bottles sterilize with dry heat, but they will corrode if autoclaved. Type I and II glasses have better water resistance.
Unlike plastics, all glass types have similar surfaces, so they’re compatible with the same adhesives. The material you choose for labeling glass containers depends on the container’s use and storage conditions.
Types of Plastics Used in Packaging
There are five major types of plastics used for containers. Each type of plastic has unique characteristics, including whether or not they contain bisphenol a (BPA), but they are all semi-permeable. Over long storage periods, gasses can pass through the plastic. (This leads to carbonated beverages going flat or contaminates entering the bottle over long storage periods.)
The adhesives you choose for labeling plastic packaging change depending on the type of plastic used. Here’s a list of the five types of plastics, along with their abbreviations, recycling category, and common uses:
Polyethylene Terephthalate – PET or PETE, Recycling #1
Polyethylene terephthalate is the easiest plastic to recycle. It can go into a variety of products, including carpet, sailcloth, and insulation layers for clothing. It’s commonly used to make food storage containers, soda bottles, peanut butter jars, and medicine bottles. PET is a BPA-free plastic.
High-Density Polyethylene – HDPE, Recycling #2
High-density polyethylene plastic has high chemical resistance and is a great choice for moisture protection. HDPE plastic can be leakproof and is used in containers for cosmetics, bleach, motor oil, milk, and margarine. This plastic is recycled to make sturdy products like plastic lumber and fencing. Low-density polyethylene, on the other hand, is more flexible than HDPE and freezer-safe. HDPE is a BPA-free plastic.
Polypropylene – PP, Recycling #5
Polypropylene plastic is chemical and temperature resistant, making it a great choice for hot liquids. Thanks to its food-safety qualities, PP is used for a wide range of food products, including storing leftovers, condiment bottles, yogurt tubs, lunch boxes, and bottle caps. It’s also popular for lab equipment, including bottles, jars, and test tubes. PP is a BPA-free plastic.
Polystyrene – PS, Recycling #6
While air injection turns polystyrene plastic into Styrofoam, solid PS is easy to shape. This makes it a popular choice for food trays. Recycled PS is mostly used in insulation.
Polylactide – PLA, Recycling #7
Made from natural products, including corn starch and sugarcane, PLA is biodegradable and compostable. The availability of PLA containers is increasing to meet the demands of companies looking for a greener alternative to petroleum-derived plastics. However, PLA is in the “other” recycling category, so it can’t be taken by most recycling services. Polylactide plastic products are not BPA-free.
Labels for plastic bottles can also be plastic. Whether you choose a glass or plastic bottle, the label is either removed or burned off as part of the recycling process.
Product Handling: Breakage and Deformation
Glass containers are fragile, so labeling requires extra care. Steps must be taken to keep bottles steady on the labeling machine and to prevent overflow that could lead to containers spilling over the conveyor belt.
While plastic bottles are more resilient to drops, their flexibility also causes them to deform under pressure. Labeling plastic containers requires a different approach than glass. With glass bottles, it’s possible to use softer rollers and more pressure to help the label conform to the surface. Plastic bottles require less pressure and harder rollers to reduce the chance of warping.
Shape Issues: Manufacturing Inconsistencies, Pitch Lengths, Mold-Friendly Shapes, and Deformation
Even the “flat” sides of a container aren’t always flat. Plastic containers are cast with a slight taper to help them release from molds, and surface inconsistencies are common on low-cost glass bottles. Thin plastic containers, like drink bottles and trays, also bulge slightly when filled. This has to be taken into account when designing your product labels and setting up your labeling equipment.
At CTM Labeling Systems, we do our best to overcome the challenges presented by differences and imperfections of various containers. Our automatic label applicators can store multiple label formats, allowing the operator to easily switch between production runs. Prospective customers should provide product and label samples before purchasing a solution to determine the best approach to compensate for the physics involved.
Static electricity is caused by the transfer of positive or negative electrical charges from one object to another. This transfer happens in production as containers and labels move against rollers, conveyor belts, and other components in the system. If both the label and the container have the same charge, they will repel each other. If they have opposing charges, they will attract each other. This can keep the label from laying flat during the application, leading to bubbles and flagging.
While this is mostly a problem while labeling plastic containers, it can happen to glass under the right conditions.
Static electricity problems may not be apparent when you first go into production. Humid air acts as a natural conductor, letting the static electricity discharge. However, when temperatures drop in the winter, so does humidity, allowing bottles and labels to hold their charge.
Static electricity can be neutralized with an eliminator or ionizer. These devices send an opposing electric current through the container or label, balancing the electrical charge. They take several forms, including ionizing air knives. This is a simple upgrade If you’re already using an air knife for clean up to remove condensation before labeling.
Off-Gassing and Bubbling Labels
Even if you are labeling plastic containers perfectly, off-gassing can ruin labels during the product’s life. With off-gassing, the plastic releases gasses after manufacturing, letting the gas inside the bottle escape over time.
These gasses can form bubbles underneath the label. To solve this problem, you can use permeable labels that let gasses pass through without building up underneath.
No Matter What You’re Packaging, We Can Help You With Your Labels
Trusted by big names like Amazon, CTM Labeling Systems makes a wide range of customizable labeling machines that work with a host of various containers.
If you need a better solution for labeling glass vs. plastic containers, email or give us a call. We’ll get you in touch with one of our local distributors who will work with you to create a labeling system that fits your exact production requirements.