What is the chemical solvent resistance of unidirectional polyimide film
Unidirectional polyimide (PI) films are prepared by uniaxial stretching process, with molecular chains mainly oriented along the stretching direction, and the binding force between transverse molecular chains is relatively weak. The overall chemical stability of polyimide material is inherent, but its anisotropy results in significant differences in solvent resistance in different directions, whic
Unidirectional polyimide (PI) films are prepared by uniaxial stretching process, with molecular chains mainly oriented along the stretching direction, and the binding force between transverse molecular chains is relatively weak. The overall chemical stability of polyimide material is inherent, but its anisotropy results in significant differences in solvent resistance in different directions, which is distinct from biaxially oriented PI films.
Stable tolerance (short-term/long-term exposure at room temperature)
1. Various hydrocarbons, mineral oils, silicone oils, and lubricants;
2. Conventional organic solvents such as ethanol, isopropanol, and acetone;
3. Ordinary soldering flux and electronic cleaning agent;
4. Weakly acidic and weakly alkaline aqueous solutions.
At room temperature, the film will not dissolve or swell significantly when in contact with the above medium, and its size and mechanical properties remain stable, meeting the requirements of conventional processes such as electronic process cleaning and welding.
Use with caution, long-term or high temperature exposure may cause damage
1. Strong polar amide solvents: DMF, DMAc, NMP, etc., soaking at room temperature for a long time will slowly swell, and even dissolve the film at high temperatures;
2. Strong inorganic acids such as concentrated sulfuric acid and concentrated nitric acid can corrode and damage the molecular structure of polyimide;
3. High temperature strong alkaline solution: It is easy to cause hydrolysis of polyimide, resulting in a decrease in film toughness, brittleness, and a decline in mechanical strength.
Unique characteristics brought by uniaxial stretching (emphasis)
The solvent resistance of unidirectional PI film has directionality: the longitudinal direction (stretching orientation direction) has better solvent resistance, while the transverse direction is relatively weaker.
When the solvent penetrates into the interior of the film, the transverse molecular chain gaps are more easily stretched and swelling occurs; Under stress, it is easy to produce transverse microcracks, or even direct cracking.
In addition, the edge of the film after slitting is a weak position, and the solvent is prone to penetrate inward from the edge of the incision, accelerating lateral cracking. Bidirectional orientation of polyimide film molecules eliminates this shortcoming, resulting in stronger resistance to solvent cracking.
Suggestions for actual selection and use
1. Under normal temperature and short-term exposure to conventional media such as alcohol, acetone, and soldering flux, unidirectional PI film can fully meet the requirements for use;
If the process involves prolonged immersion and high-temperature chemical treatment conditions, it is not recommended to use unidirectional PI, and bidirectional polyimide film should be prioritized for evaluation;
3. During the processing and cutting process, edge protection should be done well to reduce burrs and minimize the risk of failure caused by solvent intrusion from the edges;
If the product needs to continuously withstand external forces in a chemical medium environment, it is necessary to conduct immersion verification testing in advance to assess the risk of lateral cracking.
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