Where is the chemical stability of bidirectional polyimide film reflected
The chemical stability of Bidirectional Polyimide (BPI) films is mainly attributed to the high stability of the aromatic imide ring (- CO-NH-CO -) in their molecular structure and the dense crystal structure formed by the biaxial stretching process. This is reflected in their resistance to various chemical media, degradation resistance, and environmental stability, which can be analyzed in detail
The chemical stability of Bidirectional Polyimide (BPI) films is mainly attributed to the high stability of the aromatic imide ring (- CO-NH-CO -) in their molecular structure and the dense crystal structure formed by the biaxial stretching process. This is reflected in their resistance to various chemical media, degradation resistance, and environmental stability, which can be analyzed in detail from the following dimensions:
1、 Excellent tolerance to acidic and alkaline media
One of the key characteristics that distinguishes bidirectional polyimide films from ordinary polymer films (such as PET and PI single films) is their ability to maintain structural integrity in a wide range of acidic and alkaline environments, with almost no dissolution, hydrolysis, or chemical corrosion
1. Acid resistance
It exhibits high stability towards common inorganic acids (such as hydrochloric acid, sulfuric acid, nitric acid, concentration ≤ 50%) and organic acids (such as acetic acid, citric acid, formic acid). Even under acidic conditions ranging from room temperature to 80 ℃, the film neither dissolves nor undergoes molecular chain breakage due to protonation of the acid - this is because the nitrogen atom (N) in the imide ring has formed a conjugated double bond (conjugated with adjacent carbonyl and aromatic rings), resulting in a low electron cloud density that is difficult to be attacked by protons, avoiding hydrolysis reactions similar to amide bonds (- CONH -).
Example: In the electronics industry, BPI films are commonly used as insulation layers for flexible circuit boards (FPCs) that require contact with acidic etching solutions. After long-term use, there is no significant decrease in insulation performance and mechanical strength.
2. Alkali resistance
The tolerance to low to medium concentration strong bases (such as sodium hydroxide, potassium hydroxide, concentration ≤ 20%) and weak bases (such as ammonia water, sodium carbonate solution) is better than most polymer materials. At room temperature, strong bases are difficult to destroy its imide ring structure; Only under extreme conditions of high temperature (>100 ℃) and high concentration of strong alkali (such as 50% NaOH), can slow imide ring opening reaction (formation of carboxylate) occur, but the reaction rate is much lower than that of ordinary PI single film or polyester film.
Comparison: PET film will experience surface swelling and strength reduction due to ester bond hydrolysis within one week in a 20% NaOH solution at room temperature, while BPI film shows no significant change within one month under the same conditions.
2、 Resistant to organic solvents and oils, insoluble and non swelling
Bidirectional polyimide films exhibit "insolubility and low swelling" characteristics towards the vast majority of organic solvents, oils, and chemical reagents, which is closely related to their high crystallinity of molecular chains and strong intermolecular forces
Non polar/weakly polar solvents: Fully tolerant to alkanes (such as n-hexane and cyclohexane), aromatic hydrocarbons (such as benzene, toluene, and xylene), and halogenated hydrocarbons (such as chloroform and carbon tetrachloride), without dissolution or swelling, and without performance degradation caused by solvent permeation.
Polar solvents: They only exhibit very slight swelling (swelling rate<1%, at room temperature) for alcohols (methanol, ethanol, ethylene glycol), ketones (acetone, butanone), esters (ethyl acetate, dibutyl phthalate), and ethers (ether, tetrahydrofuran), and the swelling is reversible - after removing the solvent, the film can recover its original size and properties without structural damage.
Oils and lubricants: In the fields of machinery and automobiles, BPI films often come into contact with lubricating oils, hydraulic oils, animal and vegetable oils, etc. The hydrophobic aromatic rings in their molecular structure can effectively resist the penetration of oils and fats, and will not cause a decrease in strength or size deformation due to swelling, making them suitable for insulation and sealing needs in long-term lubrication environments.
3、 High temperature oxidation resistance and aging resistance, strong long-term stability
The chemical stability of BPI films is not only reflected in their static resistance to media, but also in their ability to resist degradation in dynamic high-temperature environments. The core of this stability comes from the antioxidant properties of the imide ring and the dense structure formed by biaxial stretching
High temperature oxidation resistance
The C-N and C=O bonds in the imide ring have high bond energies (approximately 305 kJ/mol and 745 kJ/mol, respectively), and the molecular chain forms a rigid skeleton through aromatic ring conjugation, making it difficult to be broken by oxygen and ozone attacks at high temperatures. Even if used for a long time in an air environment of 200-300 ℃ (such as high-temperature insulation components of aerospace equipment), the film will not undergo oxidative degradation (such as no weight loss, no brittleness, and no small molecule volatiles), far superior to PET (temperature upper limit<150 ℃) and PI single film (temperature upper limit ≈ 250 ℃).
Anti UV and weather aging
The biaxial stretching process makes the molecular chain arrangement of BPI thin films more regular, and the crystallinity is increased to 60% -70% (about 40% for ordinary PI single films). The dense crystal structure can effectively block the penetration of ultraviolet light (especially UV-B and UV-C bands), avoiding free radical breakage reactions of molecular chains caused by ultraviolet light. In outdoor exposure to sunlight or strong ultraviolet environments (such as the insulation layer of photovoltaic modules), the yellowing index (Δ YI) of BPI film is much lower than that of other polymer films, and the mechanical strength and insulation performance degradation rate after long-term use is less than 10%.
4、 Chemical resistance, no ion precipitation
In fields such as electronics and semiconductors that require high levels of "chemical cleanliness", the "ion free precipitation" characteristic of BPI thin films is an important manifestation of their chemical stability
Thin films will not precipitate mobile ions such as sodium ions, chloride ions, and potassium ions in water, organic solvents, or high-temperature and humid environments, nor will they release small organic molecules (such as plasticizers and residual monomers) - this is because there are no additives such as plasticizers or stabilizers added during their preparation process, and the molecular chain structure is stable, without easily hydrolyzed or dissociated side groups (such as ester groups, ether bonds, amino groups).
This feature makes it suitable for packaging insulation layers in semiconductor chips and flexible substrates in liquid crystal displays, avoiding circuit short circuits or device performance degradation caused by ion precipitation.
WeChat number：
Home
Product
Wechat
Telephone