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Release Liners: Not just trash you throw away (Part I)


Release liners are being used in so many different products and often we are asked – “what exactly do you make”.    As a supplier in this industry, over the years the best answer I have come up with is – we sell Performance. 
Performance:
Why Performance?  We spend a lot of time finding the right adhesive and substrate for a given application.  Release liners are often the last part of the total product design.  But so much is riding on making sure the correct adhesive is delivered to the end user.   And unless it is a self-wound tape, the release liner usually finds its way to its final destination – A Dumpster..
Not to think of our industry or products as “trash”, but some of the best products are at their best when the customer doesn’t even notice it, the release liner that is.
The Top Five Variables
All though there are several variables that can impact the performance of a release chemistry, we often are dealing with the following 5 variables.  These 5 variables will affect how your tape removes from the release liner.  We have written this paper as somewhat a basic introduction on how things work.  We do get somewhat technical, but we wanted to start with the core facts and basics presently available to most end users.  Further detail on each on these variables can be found at the TAPPI web site or searching these topics on the Internet.
  1. Cure Type
  2. Additives and Cross-linkers
  3. Peel Speed
  4. Aging Time
  5. Aging Temperature
We will explore these variables using components that are typical in the tape industry and see the results in a typical tape application.

The Basics of a Silicone Release
So if you don’t read anything else in this white paper, reading this page is key.  This is where everything starts and you need to know the tools or options you have available.
The two tables below show the Different Methods of Silicone Release Manufacturing and Components in Silicone Release Coatings.
 
Table 1 – Different Methods of Silicone Release Manufacture
Energy Cure Thermal Cure
   
Electron Beam (EB) Ultraviolet (UV) Solventless Solvent Emulsion
Cationic Free Radical Cationic Free Radical Platinum Catalyst Rhodium
Catalyst		 Platinum Catalyst Tin Catalyst Platinum Catalyst Tin Catalyst
                   
The table above provides the variables to consider when choosing a release chemistry.  We explain the use of each variable later in the paper.
 
Table 2 – Components in Silicone Release Coatings
COMPONENT FUNCTION
Base Polymer Primary release component
CRA+ Polymer Additive to increase release value
Cross-linker Links polymer chains (Thermal systems only)
Catalyst Initiates cross-linking reaction
Additives Provide other characteristics
 
With these tables you can quickly release you have several options to choose.  You need define the cure method, and a catalyst to work with the cure method. 
We will start to review these variables and the 5 Variables in Part II of this paper.

Release Liners: Not just trash you throw away (Part II)

  1. Cure Type
A “premium” or “Easy” release is a common request in the release line industry.  Meaning it is easy to peel off.  Where a “tight” release is hard to “peel” off, more on the peel test later in the paper.  Using the chart in Part I of this series as a reference, here are some guidelines for finding the correct cure type.  These are based on using a common industry standard of solvent acrylic adhesive.
  • Under an Energy Cure, EB(Electron Beam) has the tightest release cure type. 
  • Under the Thermal Cure, Solventless Platinum blends have the lowest release or “easy” release.
  • EB and Tin are not good choices when you are looking for a “premium” or easy release
 
  1. Additives and Crosslinkers
Control release additives are often used on their own to create single sided tapes, they are commonly used in conjunction with a premium release blend to create differential tapes.   Mixing reactive silicone polymers, catalysts and cross-linkers together therefor initiates the curing process.  Functional groups are usually incorporate into the polymer for chemical reactivity reasons (e.g., crosslinking).  This type of chemical reaction is desired to minimize the adhesives film’s thermoplastic response and maximize its tensile properties.  As an example, the bond strength and other properties can be modified and improved by adding multivalent metal ions in a suitable form to promote ionic crosslinking.
  • The selection of cross-linkers in Solventless platinum systems can play a major role in determining how your adhesive releases.
  • Additives influence the chemistry and physical interaction of the formulation components.  They affect the base polymer (e.g., initiators, crosslinker, filler) or the dispersed polymeric system.
 
  1. Peel Speed
When discussing applications, there are two general categories: machine dispensed and hand dispensed.   You will come across this reference in a lot of spec sheets regarding a release level.
In the release liner industry, a typical peel speed referenced for hand dispensed products is 300 ipm (inch per minute held at 180 degree peel angle).
  • How a release chemistry performs with a given adhesive can be greatly impacted by the speed at which the adhesive is removed. 
  • It is important that the test method used will simulate as closely as possible the dispensing conditions.
 
  1. Aging Time
Often it is difficult to predict when the tape you’ve made will be consumed.   This is why it is critical to understand how it will behave over time. 
Will the tape see regular turnover?  Will it sit on a shelf at room temperature or high humidity etc.?  Could it be there for 6 months or longer? 
Simulating these conditions can be challenging, but depending on the end use of your product, this type of testing should be performed.  Something as simple as subjecting the release liner or tape to an enclosed heated area will predict results.
 
  1. Aging Temperature
This is the case where the product is made indoors at room temperature and then shipped via truck, train or plane, in cold weather.  Or the reverse, shipped in high heat.    This can have an impact on the tape by the time it reaches your customer.
 
SUMMARY
 
There have been some general guidelines that have come from this paper, in summary here are the key takeaways.
  1. Even if the cure method, adhesive, and release polymer type are the same, one can’t assume identical performance
  2. In looking for an “easy’ or “premium” release, starting with a UV free radical or Platinum thermal system is a good starting point.
  3. Products stored at higher temperatures may have a shorter shelf-life, so and understanding of storage conditions important
  4. Understanding how a differential tape behaves under end use production conditions is critical in avoiding adhesion confusion or too tight of a release.
  5. Release values will rise over time, but tend to plateau if there is no chemical interaction between the adhesive and release chemistry.
You always need to keep in mind and give extra time to the Release Liner part of your project – it can save you from putting your whole project in the Dumpster!!.