Hot Melt Pressure Sensitive Adhesives (HMPSAs) have been widely used for making medical pads and tapes in the past couple decades. Prior to introducing HMPSAs to this industry, both calendared and solvent-borne natural rubber (NR) based PSAs dominated this market. NR PSA is normally tackified by rosin or its derivatives. This type of PSA generates very good adhesion to human skin because of its high acidity or polarity.
Beginning in 1990, HMPSA and Acrylic water-borne PSA were introduced to skin contact applications. Disregarding those common adhesion performances, three major requirements must be met for medical pad and tape applications.
- No irritation. No rosin and rosin derivates are allowed to be used in the formulation. Some research reports suspect that the irritation that occurred on human skin primarily resulted from those acidic ingredients.
- No maceration. Medical pads and tapes should be breathable. Otherwise, body fluid or sweat will be trapped in between adhesive film and skin, which will cause maceration and adhesion failure.
- Conformability. Medical pads and tapes should impart very good affinity to skin instead of very high adhesion to skin; that often results in some uncomfortable feeling.
It is known that a HMPSA containing acidic or more polar ingredients will adhere to skin better. That is the major reason why rosin and its derivatives are always used in the skin contact adhesive formulations historically. However, due to the great concern of irritation to skin, these types of acidic and polar materials are strictly banned by many brand name medical pads and tapes manufacturers. Without incorporation of rosin and its derivatives in a HMPSA formulation, the adhesion to skin is difficult.
How to select an appropriate SBC and hydrocarbon tackifiers for skin contact application becomes a challenge for most hot melt formulators.
HMPSA is a hydrophobic material and is not water absorbable. To effectively diffuse body fluid and sweat, many adhesive pads and tapes are needle punched. Another technique is to select an appropriate spray gun or patterned roller to form an adhesive film without a full coverage.
HMPSA has higher pressure sensitive adhesion and is more rubbery than Acrylic-based PSAs. It is less flexible or yielding on a moving body. As a result, to attach HMPSA-based pads and tapes on skin is not quite pleasant. How to select an appropriate SBC and tackifier to improve the conformability to skin and minimize the uncomfortable feeling is also a challenge for most hot melt formulators.
For more information call or email Pierce Covert,
海角大神 Corporation
1(888)202-2468