The plaster consists of a drug and a plaster cloth. The skin is used as a drug delivery channel, and the drug is continuously input into the body through the skin, which is a common form of a transdermal drug delivery system. The plaster structure is generally a non-woven fabric, an adhesive (commonly used pressure sensitive adhesive), a drug, and a release paper. The plaster cloth is the carrier of the plaster, and its adhesive property mainly depends on the adhesive, which has an important influence on the use effect of the plaster preparation. Since it takes a certain time for the drug to penetrate into the body percutaneously, the plaster cloth must have sufficient viscosity to ensure the adhesion performance during the plaster application, and to ensure that the drug can continue to be in close contact with the body.
The Pharmacopoeia stipulates that the adhesion (adhesion) of plasters (stickers) mainly includes three indicators: initial adhesion, holding strength and peel strength. These three indicators are closely related to the quality of the adhesive used in the plaster. The quality of the adhesive can be measured by three parameters: initial tack, adhesion and cohesion.
※The initial tack force is used to characterize the contact “adhesive†between the adhesive and the surface of the adherend. It can be tested by the principle of the bevel ball test: when the steel ball and the adhesive surface of the sample are briefly contacted by a slight pressure, the sample is steel. The adhesion of the ball is used to test the initial tack of the sample.
* Adhesion is used to characterize the ability of the adhesive to resist the interface separation of the surface of the adherend. It is related to the quality of the adhesive, the adherend, pressure, time and environmental conditions. It can be evaluated by the peel strength test. Test method: Cut the sample into a certain size and paste it on the test board as required; clamp the free end of the sample and the stainless steel plate on the upper and lower fixtures of the device; start the test, the two chucks do the relative movement, the upper chuck The force value sensor configured on the upper part records the force value generated by the sample during the stripping process in real time, so that the performance index such as the peel strength of the sample is calculated.
※ Cohesive force is used to characterize the internal strength of the adhesive. It is usually measured by the ability of the plaster to resist shear creep and can be determined by the adhesion test. The test method is to vertically hang the test plate with the plaster sample on the test frame, the weight of the specified weight is suspended at the lower end, the displacement of the sample after a certain time, or the time when the sample is completely detached is used to characterize the glue. The ability of the sticky sample to resist pull-off.
Initial adhesion, adhesion and cohesion are independent parameters of the three different aspects of the adhesive. They must not be confused and require reasonable control. Otherwise, various quality problems may occur. If the adhesion is too small, the plaster will lose its pressure-sensitive adhesive properties. The plaster will be poorly attached and easy to loosen, which will affect the drug's medicinal properties. If the cohesive force is too small, it may cause the plaster to separate from the adhesive layer when it is peeled off. Some adhesives are transferred to the surface to be adhered, which brings disadvantages such as difficulty in cleaning.
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