All about transparent, colorless polyimide filmJohn Moot
Polyimide film is an electrical insulating material with very special properties and can therefore be used in a variety of ways. Polyimide (short: PI) is a thermoplastic synthetic substance for high-temperature applications.
Polyimide foil is dimensionally stable, has a very high dielectric strength and is also HF-compatible as an adhesive-free foil. The polyimide foil is often made self-adhesive.
We would like to provide you the most important information about polyimide foil.
What is a polyimide?
A polyimide is a class of polymers and can be used in many different ways. Good examples are thin foils that are used for flexible cable insulation and also for printed circuits. They are also used as fibers for fire protection clothing or in the form of rigid foams for the insulation of aircraft and ships.
Polyimides have practical electrical properties, are chemically very stable and retain their mechanical characteristics even at high temperatures.
Typically, polyimides have a characteristic orange-brown color. This can be seen very well, for example, in rigid printed circuits, for instance in televisions, radios, cell phones and other electronic devices. Since the parts made of polyimide cannot be seen here, the color does not matter in contrast to visible displays.
Which are the components of the polyimides?
In principle, polyimides consist of two essential building blocks. These are diamines and dianhydrides. Diamines are organic compounds and have two amino groups. Dianhydrides have two double carboxylic acid anhydride groups.
Both ingredients tend to be very aromatic. In addition, they have a strong absorption in the UV range, which goes into the visible part of the spectrum. This gives the polyimides their characteristic color.
The aim of research in recent years has been to investigate the combination of the two components in order to determine their advantages for creating a colorless polyimide. Ultimately, the goal was achieved, and colorless polyimides were created.
What is meant by colorless?
First of all, you have to be aware that “colorless” can mean different things and that there are actually two different factors that can explain colorlessness:
- Definition by the so-called Yellowness Index (YI). It is a scale on which e.g. a normal drinking glass has a YI of zero. A typical polycarbonate foil would have a YI of 0.5 and a normal polyimide foil would be around 90. Currently, the goal for so-called colorless polyimides is around 2.
- The second option is transparency. This physical property provides information about how much light is transmitted through a material without being scattered. On the one hand, transparency is defined by the permeability, i.e. how much light of a certain wavelength passes through the material without it being scattered. On the other hand, the haze defines the amount of light scattered in the material. Scotch tape, for example, is colorless, but has a clear cloudiness. The polyimide foil is orange, but still transparent. The drinking glass is both colorless and transparent.
What are the advantages of colorless polyimides?
The advantages of the colorless polyimide foil are very versatile, which is why the material offers important possible uses:
- high light transmission
- high temperature stability
- excellent surface hardness
- smooth surface
- Resistance to acids and bases
- moisture barrier
- Resistance to radiation
- easy further processing
Where are colorless polyimides used??
As already indicated, polyimides are versatile due to the excellent combination of useful properties. Polyimides are particularly often used in the electronic field in aerospace, in automobile construction, in consumer electronics and in other high-technology areas. As far as the colorless variant is concerned, it is predicted that it will be used primarily in the high-tech sector. It is important that the correct combination of the blocks is achieved in order to get an optimal result. The main application areas are according to experts:
- photovoltaic cells
- medical applications
Smartphones are simply indispensable in our lives. The glass displays in particular often cause headaches because they are still quite prone to breakage, or at least are at risk of cracks and chipping. In addition, the glass of the display brings with it quite some weight, which has a negative effect on the total weight of the cell phone. With smartphones, the tendency is rather that the phone is large, since it is not only used for making calls, but also for googling, for all kinds of apps and so on. Therefore, the weight issue is crucial.
A smartphone that is significantly lighter with the same size and functionality has a clear competitive advantage. This can be achieved by completely or partially replacing the glass display with foil. The haptic is also tactile, the display of high quality, of course completely colorless. The additional advantage is that the display does not break even with heavy impacts and when falling.
Glass cover plates are often used together with photovoltaic cells to protect the sensitive circuits inside. Here, too, the weight of the glass is a negative factor, since this requires a more complex attachment, or possibly exceeds the load-bearing capacity of the roof on which the photovoltaic cells are to be installed. In addition, there is of course also a risk of breakage, especially if there are tall trees nearby, the branches of which could fall onto the solar system in stronger winds. The new polyimide technology is also an excellent option here, since it effectively protects photovoltaics – and with significantly less weight and without the risk of glass breakage.
There are also many possible applications in the medical field. For example, one has to think of tubes for the administration of medication, since these require excellent optical quality, should be light in weight, must offer thermal stability and, moreover, must meet high hygiene standards.
Is polyimide foil currently being produced from colorless, transparent polyimide?
Nowadays, transparent polyimide foil can also be produced from the commercially available polyimide. This is available in different thicknesses:
- 0,025 mm
- 0,05 mm
- 0,075 mm
Is it possible to die cut the transparent polyimide film?
All common processing methods for foils can also be used for the colorless polyimide foil. In any case, this also includes punching the foil.
Can a coating be applied to the transparent polyimide foil?
The polyimide foil can be processed so that it is self-adhesive. It can therefore be provided with different coatings depending on the different requirements of the customers. There are different adhesive systems to choose from.
Why is the market potential for transparent polyimide foil so big?
Colorless polyimides are a breakthrough technology and are being discussed for use in numerous modern consumer and communication electronics products. Virtually all major electronics manufacturers are currently working on folding displays. Samsung and Huawei even have devices on the market and Apple is working intensively on the project.
Another promising area of application for transparent polyimide foil is as flexible substrates for optoelectrical components. In this context, for example, flexible organic light-emitting display devices with active matrix (AMOLEDs), flexible printed circuit boards (FPCBs) and flexible solar cells should be considered.
The great advantage is that the displays made possible by the colorless polyimide foil can be rolled up and transported easily. They are light, space-saving, robust and have tactile properties.
Is transparent polyimide foil commercially available?
More and more companies are interested in the commercial production of practical, polyimide-based displays. In the meantime, some companies have established secure supply chains and the scale-up of production is managed while ensuring sustainability. It can be expected that the number of companies will increase significantly due to the innovative product, for which there is clear demand.
However, it must also be pointed out that – as with any new technology – the initial costs will be high, which is why it is likely that high-end products will be equipped with the new technology in a first stage.
Dr. Dietrich Müller GmbH supplies transparent polyimide film Flexiso PI FI 16075 in the thickness of 0,013, 0,025 and 0,050 mm.