Do Thermal Labels Turn Black? Understanding the Science and How to Prevent It

Thermal labels are widely used in a range of industries due to their efficiency, reliability, and ease of use. From shipping labels and product barcodes to receipts and packaging labels, thermal labels play a critical role in everyday business operations. However, one concern that often arises when using these labels is whether or not they turn black over time.

Thermal labels can turn black due to heat exposure, sunlight, chemicals, or improper storage. The heat-sensitive coating reacts to temperature changes, leading to discolouration. However, by storing labels properly, avoiding direct sunlight, and choosing the right label type, you can prevent this issue and keep labels legible.

In this blog, we will delve into the science behind this phenomenon and offer tips on how to prevent it, ensuring that your labels remain clear and legible for as long as possible.

What Are Thermal Labels?

The history of thermal printing dates back to 1965 when Texas Instruments invented the thermal print head. This innovation paved the way for the development of thermal printing technology. In 1969, Texas Instruments released the Silent 700, a computer terminal that featured a thermal printer. The Silent 700 was the first thermal print system capable of printing on thermal paper, revolutionising printing in various industries.

Thermal labels are a type of label that uses heat to create an image or text on the surface of the material. These labels are typically used in thermal printers, which use heat instead of ink or toner to print. There are two main types of thermal printing technologies: direct thermal and thermal transfer.

• Direct Thermal Printing: This method uses a heat-sensitive coating on the label material that darkens when exposed to heat. When the print head of the thermal printer applies heat, the image or text appears.
  
  

• Thermal Transfer Printing: In contrast, thermal transfer printing involves the use of a ribbon that melts onto the label surface when heated, transferring the ink to the label.
  
  

Thermal labels are commonly used in industries such as retail, logistics, manufacturing, healthcare, and food services. They are used for barcodes, price tags, inventory labels, shipping labels, and even receipts, thanks to their fast printing speeds and durability.

What Causes Thermal Labels to Turn Black?

The turning of thermal labels to black is caused by a chemical reaction triggered by heat. The heat-sensitive coating on direct thermal labels contains a special material that reacts when exposed to heat from the print head of the thermal printer. When the heat is applied to certain areas of the label, the material darkens, creating the print.

However, under certain conditions, thermal labels can turn black or discolour, even when not in use. This happens due to the following factors:

• Heat Exposure: If thermal labels are exposed to excessive heat, the chemical reaction in the coating can be triggered, causing the entire label to turn black. This is especially common if the labels are stored near heat sources or placed in hot environments.
  
  

• Sunlight: Exposure to direct sunlight can also affect the labels. The UV rays in sunlight can degrade the chemical composition of the coating, leading to blackening or fading.
  
  

• Chemical Exposure: Certain chemicals, such as oils or solvents, can react with the label’s heat-sensitive coating, causing discolouration.
  
  

• Aging of the Label: Over time, thermal labels naturally degrade. The coating may lose its ability to react correctly to heat, causing the label to turn black prematurely.
  
  

Factors That Affect the Colour Change

There are several external factors that can contribute to thermal labels turning black. Understanding these factors will help you take the necessary steps to ensure your labels remain in optimal condition for as long as possible.

1. Exposure to Heat: Thermal labels are designed to react to heat, but excessive heat can cause them to darken or even become unreadable. High temperatures from storing labels near heat sources or placing them in a warm environment can cause the heat-sensitive coating to activate, turning the label black. This is a significant concern for industries that require long-term label storage.
   
   

2. Sunlight Exposure: The ultraviolet (UV) rays from the sun can break down the chemical structure of the heat-sensitive coating. If thermal labels are exposed to direct sunlight for extended periods, they may lose their readability or darken prematurely. This is particularly important for labels used outdoors or in areas where sunlight exposure is unavoidable.
   
   

3. Chemical Exposure: Exposure to certain chemicals or solvents can damage the thermal label’s coating, causing it to turn black or fade. For example, oils or cleaning products used in warehouses, manufacturing plants, or healthcare facilities can come into contact with thermal labels, leading to discolouration.
   
   

4. Humidity and Moisture: Moisture and humidity can also affect the performance of thermal labels. High levels of moisture can degrade the label's surface, resulting in fading or blackening of the printed image. This can be a particular concern for labels used in refrigerated environments or damp conditions.
   
   

5. Storage Conditions: The lifespan of thermal labels depends heavily on how they are stored. Proper storage conditions play a critical role in maintaining the integrity of the labels. Incorrect storage, such as exposure to heat, sunlight, or humidity, can lead to labels deteriorating and turning black.
   
   

How to Prevent Thermal Labels from Turning Black

While it is impossible to completely eliminate the possibility of thermal labels turning black due to their heat-sensitive nature, there are several best practises you can follow to minimise the risk. Here are some essential tips to help you keep your thermal labels in optimal condition:

1. Store Labels Properly: Always store your thermal labels in a cool, dry place away from direct sunlight and heat sources. The ideal temperature for storing thermal labels is between 5°C and 25°C (41°F and 77°F), and the relative humidity should be between 40% and 60%. Make sure that the labels are kept in their original packaging until ready for use.
   
   

2. Avoid Direct Sunlight: When using thermal labels outdoors, try to avoid exposing them to direct sunlight for prolonged periods. If this is not possible, consider using protective covers or storing the labels in shaded areas to reduce UV exposure.
   
   

3. Handle with Care: Be mindful when handling thermal labels, especially when they come into contact with oils, solvents, or chemicals. Always ensure that the surfaces are clean and free from contaminants before applying the labels.
   
   

4. Choose the Right Type of Label: There are different types of thermal labels available, each suited to specific applications. If your labels are exposed to high temperatures or chemicals, opt for a thermal transfer label, which tends to be more durable than direct thermal labels. Thermal transfer labels use ink ribbons that are more resistant to fading or discolouration than direct thermal labels.
   
   

5. Use in Appropriate Environments: Avoid using thermal labels in extreme environments where temperatures, humidity, or exposure to chemicals could damage the label. If labels must be used in such environments, consider selecting a more durable label type, such as those designed for outdoor use.
   
   

6. Regular Inspection: Regularly check the condition of your thermal labels, especially if they have been stored for an extended period. Ensure that they have not been exposed to any adverse conditions that could cause the print to fade or turn black.
   
   

Keep Your Thermal Labels in Perfect Condition

Thermal labels do indeed have the potential to turn black, primarily due to the heat-sensitive coating that reacts to heat exposure. Factors such as excessive heat, sunlight, chemicals, and improper storage can all contribute to this issue. However, by following the proper storage guidelines, handling the labels with care, and selecting the appropriate type of label for your needs, you can significantly reduce the likelihood of your thermal labels turning black.

By following the best practises and choosing the right labels from Label Metrics, you can ensure your thermal labels stay clear, legible, and durable for all your business needs.