Synthesis And Properties Of Optically Clear Adhesives For Folding Screens

The traditional optical transparent adhesive has good optical properties,bonding performance and ageing resistance.Thus it is becoming one of the irreplaceable components in high-tech electronic products such as touch screen mobile phones,tablet PCs,and e-readers.However,due to the continuous progress of science and technology,people’s requirements for existing touch screen mobile phones are increasing.The functions of touch screen mobile phones tend to diversify.The size is gradually becoming less portable.In order to meet the demand for touch screen mobile phones,folding screen mobile phones were born.The optical transparency adhesive as an important part of the touch screen.Its performance needs to be further studied.Existing optically clear adhesives can be broadly classified into polyacrylates,polyurethanes,and silicones.With polyacrylates being the most widely used due to their structural versatility.For application in folding screens,we modify them by adding suitable cross-linking agents to obtain optically transparent adhesives that meet the requirements.In this thesis,we introduce three different macromolecular cross-linking agents to cross-link conventional polyacrylate optically transparent adhesives respectively.The specific studies are divided into three parts as follows.1.Synthesis and properties of polyacrylate optically transparent adhesives based on triisocyanate cross-linkingIn order to solve the problem that the traditional polyacrylate optically transparent adhesive cannot meet the needs of bending and creep resistance of folding screens,we cross-linked it by introducing cross-linking agents.Firstly,we selected isooctyl acrylate and hydroxybutyl acrylate in different ratios to synthesise polyacrylates.A trimer of hexamethylene diisocyanate is used as a cross-linking agent.Synthesis of triisocyanate cross-linked polyacrylate curing compounds.The successful synthesis of the target products was confirmed by structural characterisation of the products by nuclear magnetic resonance spectroscopy(1H NMR)and Fourier transform infrared spectroscopy(FTIR).The effect of the content of hydroxybutyl acrylate on the bonding properties and mechanical properties of the prepared cured compounds was investigated.In the bonding performance tests,the bonding strength gradually decreased with increasing hydroxybutyl acrylate content,with the highest bonding strength of 2.62 MPa at 10%.In the creep resistance test,the creep resistance gradually increases with increasing levels of hydroxybutyl acrylate.In the bending resistance test,a single bending test failed the 200,000 bending resistance test.The results measured in this chapter provide a reference for the next two chapters.2.Synthesis and properties of polyacrylate optically transparent adhesives based on cross-linking of polybutadiene chain segmentDue to the excellent mechanical properties and excellent low temperature resistance of liquid rubber.Hydroxyl-terminated polybutadiene is the most widely used.We have therefore chosen Hydroxyl-terminated poly-butadiene as the macromolecular cross-linker.It was also produced by nucleophilic addition reactions with isophorone diisocyanate to produce end-isocyanate-based polybutadiene.The target products were also structurally characterized by nuclear magnetic resonance spectroscopy(1H NMR),Fourier transform infrared spectroscopy(FTIR)and gel permeation chromatography(GPC).The polyacrylate curing compounds cross-linked with polybutadiene were obtained by reacting the polyacrylate in the optimal proportions from the previous chapter with the macromolecular cross-linker prepared in this chapter.The bonding performance test showed that the highest bond strength of 10.4 MPa was obtained with a cross-linking agent content of 10%,which indicates that the cured products prepared with lower cross-linking agent content have better bonding performance.In tests of creep resistance and bending resistance,The 10%content also showed excellent performance.It has also passed the 300,000-times bending resistance test,which significantly exceeds the 200,000-times requirement for ordinary folding screens.It shows that the introduction of polybutadiene chain segments can effectively enhance the toughness of the material.It is significantly better than the previous chapter in terms of bonding,bending and creep resistance.3.Synthesis and properties of polyacrylate optically transparent adhesives based on cross-linking of silicone chain segmentBased on the excellent mechanical properties of silicone chain segments,we introduced them into the polyacrylate crosslinking network.Firstly,we obtained octa-methylcyclotetra-siloxane as well as 1,3-bis(3-aminopropyl)-1,1,3,3-tetra methyldi-siloxane by ontogenetic polymerisation under the catalysis of tetramethylammonium hydroxide to obtain a terminal amino polysiloxane.The reaction of end-amino polysiloxane,hexamethylene diisocyanate and polyacrylate produces a silicone cross-linked polyacrylate optically clear adhesive.The target products were structurally characterized by nuclear magnetic resonance spectroscopy(1H NMR),Fourier transform infrared spectroscopy(FTIR),and gel permeation chromatography(GPC).In the bonding performance tests,the introduction of silicone chain segments was effective in improving the bonding compared to the triisocyanate system.But it was still lower than the polybutadiene system,indicating that the best bonding properties were obtained with the introduction of polybutadiene chain segments.In the bending resistance test,the 10%content showed better bending resistance and passed the bending resistance test for 300,000 cycles.However,the bending resistance decreases as the content of the end-amino polysiloxane increases.70%content only being able to bend 100,000 times.In the creep resistance test,the 70%content has better creep resistance.In summary,the introduction of silicone chain segments enhances its mechanical properties and provides a reference for the preparation of a high tenacity silicone optical transparent adhesive for folding screen applications.