In the plastic mold manufacturing industry, in order to facilitate demolding, improve efficiency, extend mold life, and make the product surface smooth, size qualified, and reduce waste during the molding and manufacturing of plastic products, demolding agents are needed.
Release agents can be roughly divided into two categories: external coating and internal addition:
1. External coating release agent is sprayed on the surface of the mold to prevent adhesion between the product and the mold;
2. Internal release agent is a type of substance added to the molding material. During the vulcanization molding process, it migrates to the surface of the product, thereby playing a role in isolating it from the mold.
1、 Demolding process
After spraying release agent on the surface of the mold, the actual interface during vulcanization molding is that the contact surface between the rubber material and the release agent is surface A, the release agent surface is surface B, and the contact surface between the release agent and the mold shell is surface C; The release agent layer is a cohesive layer. When demolding, it is called interface peeling when peeling off on the A and C surfaces; When peeling off on the B-side, it is called condensed layer failure.
1. The transfer rate of release agent refers to the percentage of release agent transferred to the formed product during the demolding process.
(1) Peel off the mold from surface A without transferring the mold release agent;
(2) A small amount of transfer (about 22%) of the release agent occurred due to the peeling off of surface A and the breakdown of the condensed layer on surface B during demolding
(3) Demoulding only occurs due to the destruction of the cohesive layer, with a significant transfer of release agent (approximately 44% -70%)
(4) Demolding caused by detachment of B and C surfaces and damage to the cohesive layer, resulting in a significant transfer of release agent (approximately 93%)
(5) The molded product comes into contact with the release agent, causing mixing and adhesion. When forced to demold, it will cause damage to the surface and interface of some molded products, leading to demolding.
The commonly used release agent requires peeling and demolding on the B side or A and B sides. The demolding effect caused by the cohesive layer is the best.
2. Surface tension of release agent
The isolation of release agents depends on their surface properties, and the physical properties of non wetting substances on the surface are derived from the concept of their critical surface tension (RC).
The method for measuring Rc is to drop droplets of several substances with different surface tensions onto the surface of the substance being tested, and measure their contact anglesθ。 Using the surface tension of the tested substance and its contact angleθ Plot the cosine value cos to obtain a straight line. Extend this line and intersect it with the vertical axis. The horizontal axis value corresponding to the intersection point is the surface tension value of the measured substance, also known as the critical surface tension RC of the substance.
This value indicates that when the surface tension of the liquid on the surface of a substance is greater than the critical surface tension R of the substance, the liquid does not wet the surface of the substance;
Therefore, substances with low critical surface tension are the best release agents for isolation.
2、 Usage and precautions of silicone free release agent for plastic molds
1. The concentration of demoulding agent should not be too high, and the coating should not be too thick.
2. Choosing the appropriate release agent based on the type of formed polymer can achieve better results.
3. The water used for preparing the release agent should be pure water (ion exchange water or distilled water), and tap water should not be used.
4. When using, it is necessary to distinguish between external coating, internal addition, one-time, multiple use, and semi permanent release agents, and different application processes should be used.
5. Before spraying the mold release agent, the mold should be cleaned thoroughly and there should be no impurities such as rust, oil stains, carbon particles, or organic matter present, otherwise it will reduce the demolding effect.
