Foldable Glass, Transparent Film Opens Future of Foldable Phones

- Increase in Patent Applications for Essential Display Material, Polyimide (PI) Film

■ Global companies such as Samsung Electronics, LG Electronics, Apple, etc. are accelerating technical development of foldable

smartphones, so market interest regarding ‘Polyimide (PI) film’, sometimes called “foldable glass”, as a next generation display material is also increasing.


  • A foldable phone is, as indicated by the word itself, a smartphone on which a foldable display is mounted. Market investigation firm Strategy Analytics forecasts that demand for foldable phones will grow from 3.2 million in 2019 up to 50.1 million in 2022.


  • Due to the characteristic that a foldable phone must fold and unfold, new materials for the cover window, TFT substrate and base film are required. Since transparent PI films have excellent mechanical, electrical and chemical properties in comparison with other materials, they are considered substitutional goods for glass. Accordingly, despite folding and unfolding hundreds of thousands of times, these PI films are light and flexible while being resistant to scratching, so they can also be used in notebooks, etc. as well as smart phones. [Attachment 1]



■ According to KIPO, patent applications in the PI Film field have been continuously increasing over the last 5 years.

  • Even though there were 60 cases in 2014, for the most recent 2 years (‘17~’18), there has been an annual average increase in cases of approximately 37%, and applications dramatically increased to 150 cases in 2018.


  • Not only the number of applications has increased, but for advance occupation or early securing of patent rights in accordance with the fast changing technology, the ratio of requesting preferential examination is also on an upward trend. [Attachment 2]


  • Looking at types of applicants, applications by Korean companies comprised the highest percentage, being 60.9% of the whole, and coming in second place, applications by Japanese companies comprised 25.3%. [Attachment 3]


  • Reviewing targeted subjects, the large majority, 116 cases (24.9%), were for display cover windows, while 276 cases (59.2%) were for use as thin film transistor (TFT) substrate/base film. Cover window use also increased more than 4 times since 2016, keeping pace with the overall development of foldable phones. This activity is due to the main domestic and international companies putting in a great deal of effort to secure essential patents in order to take leadership in this new market. Also, this trend is anticipated to continue going forward. [Attachment 4]


  • Ban Youngbyoung, Fine Chemistry Examination Manager at KIPO, said, “Considering that the next generation display market stream is fast evolving to be foldable, rollable and stretchable, etc., it is considered that demand for PI films will be continuously increasing going forward” and, accordingly, “since competition among companies will be fierce in order to occupy market predominance, the proactive securing of essential patents related to this material field is very important.”

[Source: KIPO]

<Attachment 1: Basic Structure of Display Panels >

  • A smartphone display largely comprises ‘base film*’, thin film transistor (TFT) substrate**’ and a ‘cover window***’. Existing planar smartphones are constituted by both cover window and TFT substrate with glass, but PI film is substituted for these elements in current foldable phones.

*Base film: supports and protects the bottom part of a display

** TFT (Thin Film Transistor): switches light on and off by controlling electrical signals

*** Cover window: protects the surface of a display

<Attachment 2: Number of Patent Applications for PI Film Over The Last 5 Years >

※ Preferential Examination System: System to examine a patent application (that meets certain qualifying conditions) earlier than other applications (Article 61 of the Patent Act)

<Attachment 3: PI Film Patent Application Trend Per Domestic and International Applicants>

<Attachment 4: Trend of PI Film Applications Per Targeted Subject>

(Unit: Cases)

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