Glassware has been used for drinking, eating and general use since the Stone Age, UV printing on glass takes modern glassware to the next level. Although the glass we use today is the same or a variation of the “liquid sand” invented many years ago, glass decoration techniques have evolved over time with advances in technology. Although a naturally occurring substance, glass was first produced by humans accidentally in the form of beads in the mid-third millennium BC. For many years after that, glass was recognized as a luxury. Just like there are many ways to make glass, there are also many ways to decorate glass.
Have you ever sat down at a formal business event or fancy dinner and been served your drink from a plastic or Styrofoam cup? Chances are, you haven’t. There’s a reason you’re given a plastic cup at a fast food restaurant and a fancy wine glass at a formal dinner. Glassware has and still to this day shows status. It can be cut and molded into virtually any design and can be beautifully decorated in many ways. In addition to its ability to show status, glass is also a sustainable product. First, glass is not a product you would toss unless it is broken. You can constantly use glass or sell it. Second, glass will not pollute the environment. Unlike plastic or Styrofoam, you can melt glass and recycle it back into glass. There are thousands of applications for glass such as tableware, windows, phone screens and packaging.
In general, glass is made up of a combination of soda lime and sand, but the three most common types are soda lime, borosilicate and tempered.
1. Soda Lime:
Soda lime is the most common type of glass, accounting for about 90% of glass products in the market. It typically makes windowpanes (flat glass) and glass containers for food and the like (container glass). Soda lime is a mixture of soda lime and sand.
Borosilicate is another type of glass made up of soda lime, sand and boron. This type of glass has excellent heat resistance so items that are constantly sitting over a fire or in an oven will not melt or crack. Items that are borosilicate glass range from test tubes or beakers to Pyrex.
Tempered glass is unique in that when broken, it shatters without making shards. Certain countries require establishments to use this type of glass as a safety precaution. Some common applications include vehicle windows, shower doors, screen protectors and even bullet proof glass.
There are two popular methods of coating that manufacturers will apply either before and/or after the annealing process to ensure the glassware is protected. Annealing refers to the slow cooling of the glass. The two methods are hot end coating and cold end coating.
Hot End Coating
Hot end coating is used on all bottles including wine, soda, spirit and even beer bottles before the annealing process. Once the glass is formed, a thin tin-chloride film is applied onto the glass making the surface more resistant to breakage. This coating is sprayed onto the inside and outside of the bottle. Hot end coating protects consumers from the glass shattering, which may occur because of a buildup of pressure due to carbonation.
Cold End Coating
For all other types of glass, manufacturers use a cold end coat to protect items from scratching and scuffing during shipping. This type of coating is either a spray or a vapor that is applied after the annealing process. There are multiple types of cold end coatings including water soluble, water insoluble, polyethylene or fatty acid types.
Before UV printing on glass, the surface must be properly pre-treated. Although glass is ideal for printing, partly due to its high surface free energy, it is susceptible to absorbing debris or other coatings which may inhibit adhesion. The most common pre-treatment machines for industrial applications include flame treating, Pyrosil®, and plasma. All three methods and combinations of each have a goal of improving the strength of adhesion, and in turn, improving product quality. The purpose of the flame treatment is to burn off the cold end coating. Inkcups has created their own 3-part pre-treatment solution called MagiCoat®. MagiCoat® acts as the anchor after flame-treating. The water-based primer spray adds a new coating to the glass which promotes adhesion between the ink and glass. Unlike other methods on the market, MagiCoat® is completely safe to use and has been FDA approved. Learn more about the differences between a few pretreatment methods for glass.
Once the glass has been made and coated, many glassware companies will seek to decorate these items. The four most popular methods for decorating glass are using printed decals, pad printing, screen printing and UV printing.
Depending on the purpose of decorating glass and the volume of products, the method that is right for you will vary. Decals are popular for their easy application – the process is as simple as sticking the design onto the glass and applying pressure. Although most decals are manually applied, advances in technology such as heat transfer labeling machines have automated the process. This ensures the decals are uniform and adhered properly. One major downside to decals is the inability to personalize each object as well as the overall quality they produce. Depending on the type of decals, consumers can easily see the adhesive edging and peel them off. Decals as a method of decorating glass for mass production are losing popularity to more efficient, higher quality techniques that are faster and more affordable than ever before.
Pad printing allows you to choose up to 6 colors to print with. Depending on the artwork you wish to transfer, this may be limiting. However, many logos and designs use fewer colors, sometimes even just 1 or 2. The method you choose must align with your production and design goals. Because of the low cost per print, pad printing typically leads to a high return on investment. Pad printing can be done on glass (or any other substrate) of even the most irregular shapes. The set-up costs to begin pad printing are low compared to other methods, and the process is relatively easy to learn. Once you buy the pad printing machine, you will also need a pad, ink cup (with ink) and etched plate to begin printing. This type of printing works best for low-mid sized volume production and promotional products with simple designs, such as logos that do not require a full wrap.
Screen printing can print up to 10 colors. Again, this may be limiting, but it depends on the production goals of the manufacturer. This process is the most time-consuming of the methods in terms of printing, but also when it comes to setting-up and cleaning the parts involved. To begin screen printing, you need inks, a squeegee, multiple screens, and an emulsion stencil. Screen printing is best for large designs without intricate detail, whereas pad printing works best for detailed designs on smaller products. However, there are options to buy finer screens with a higher mesh count for more detailed designs. Not only does screen printing require the most consumables, it also requires the most space. There must be enough room to properly wash the screen with water and screen wash solution, as well as the squeegee and stencils. Unlike pad printing, screen printing can achieve a 360-degree print, however, it will produce a seam.
Digital or inkjet printing utilizes UV ink to print full color onto cylindrical and tapered items. Once a graphic is created using the respective software, the UV printer will transfer a high resolution, picture-perfect image onto almost any surface at the click of a button. One of the greatest benefits of inkjet printing is that the finished products are high-quality and uniform in appearance. In this process, the machine jets the ink to the glass. UV digital printing on glass is a revolutionary technology which leads to quick, professional results at a low cost per print. Just like with decals, there is no drying necessary, which means products are immediately ready for shipping. For companies looking to produce multi-color designs for large volume industrial use, inkjet printing is the optimal method of glass decoration. In addition to its full-color production, digital UV printing allows companies to produce a 360-degree image without registration marks or a seam.
After a graphic has been UV digitally printed onto the glass, some adhesion testing may be necessary. In order to assure that the ink has properly adhered to the glass, industry standard tests such as the scratch, tape, crosshatch, and dishwasher test can be performed. The first three tests ensure that the edges of the cuts are completely smooth and the surface stays fully intact after being scratched and crosshatched. The dishwasher test validates resistance properties of the ink and pre-treatment solutions together. Depending on the application and customer requests, a residential dishwasher test and/or commercial dishwasher test can be performed. Taking testing a step further, some require an ice bucket test which involves immersing the finished glass products in a bucket of ice for 24 hours, then applying firm thumb pressure and evaluating any degradation of the image. All methods are part of the ASTM guidelines. To learn more about adhesion testing on glass and to see them in action, check out our blog post.
Listen to our experts discuss ink adhesion testing methods for digital printing.
Glassware continues to be the material of choice, especially with the rise of plastic pollutants. Its inherent versatility makes it the perfect substrate to decorate and to personalize. Although it does provide a clear surface, it is important to note that printing directly onto glassware items will require pre-treatment as noted above. Each decorating method has its own pros and cons, but these are specific to what each company would like to accomplish. In any case, when choosing which decorating method is right for your needs, always remember to note printing capabilities (number of colors, speed, etc.), the cost per print, and the pre-treatment methods needed. For further questions, the Inkcups Team is always available to help.