Characteristics of dual-curable blocked isocyanate with thermal radical initiator for low-temperature curing of automotive coatings

Jung, Kevin Injoe,Kim, Beomjin,Lee, Dong Geun,Lee, Tae-Hee,Choi, Seo Yeon,Kim, Jin Chul,Noh, Seung Man,Park, Young Il,Jung, Hyun Wook Elsevier 2018 Progress in organic coatings Vol.125 No.-

<P><B>Abstract</B></P> <P>Dual-curable blocked isocyanate with a thermal radical initiator (BL-Tri-cHD) was designed and synthesized to perform low-temperature curing of automotive coatings. BL-Tri-cHD can simultaneously react with both unsaturated CC double bonds for free-radical polymerization and hydroxyl groups for the urethane reaction in hydroxyl-functionalized urethane methacrylate oligomers (HFUMO) under mild thermal curing conditions. The dual crosslinking behavior and mechanical properties of HFUMO-based coatings using BL-Tri-cHD were compared with those of a commercial blocked isocyanate thermal crosslinker (Desmodur® BL-PL350). The onset temperature for initiating cured by BL-Tri-cHD was about 68 °C, confirming faster crosslinking at relatively lower temperature than BL-PL350, which initiated curing at 140 °C. To quantitatively evaluate the properties of cured coatings, a nano-indentation was made in the surfaces of clearcoat films cured at 150 °C, 130 °C, and 120 °C. Films cured using BL-Tri-cHD and BL-PL350 at 150 °C exhibited similar indentation patterns. The indentation curves for the films with BL-Tri-cHD cured at lower curing temperatures such as 130 °C and 120 °C showed favorable penetration depth profiles similar to the sample cured at 150 °C, whereas the films with BL-PL350 cured below 150 °C had a less dense network structure, resulting in a deeper penetration depth than the sample cured at 150 °C. Therefore, we report that dual-curable BL-Tri-cHD demonstrates promising performance in automotive coating applications and possesses the ability to form highly crosslinked networks, even at low curing temperatures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dual-curable blocked isocyanate with a thermal radical initiator was synthesized. </LI> <LI> New crosslinker assists the crosslinked network in coatings at lower temperature. </LI> <LI> New crosslinker can be usefully applied in low-temperature curing technologies. </LI> </UL> </P>

Effect of methacryloxypropyl and phenyl functional groups on crosslinking and rheological and mechanical properties of ladder-like polysilsesquioxane hard coatings

Jung, Kevin Injoe,Hwang, Seon Oh,Kim, Na Hee,Lee, Dong Geun,Lee, Jung-Hyun,Jung, Hyun Wook Elsevier 2018 Progress in organic coatings Vol.124 No.-

<P><B>Abstract</B></P> <P>The rheological and mechanical properties of photocurable ladder-like polysilsesquioxanes containing phenyl and methacryloxypropyl groups (LPMA) were investigated. LPMAs with various ratios of the two functional groups were synthesized through the hydrolysis and condensation reactions. The chemical structures of the synthesized LPMAs were confirmed using H<SUP>1</SUP> NMR and FT-IR spectroscopy. The basic rheological properties of the LPMA solutions provided information about their flow properties prior to the curing stage, which was relevant for their application as a hard coating. The curing behaviors of the LPMA solutions under UV irradiation were scrutinized using real-time rheological measurements and rigid-body pendulum tests. These results were well correlated with the surface mechanical properties of the final cured LPMA films measured via nano indentation and scratch tests. The phenyl group was found to play a role in providing rigidity to the cured films, and the methacryloxypropyl group affected crosslinking performance. The physical properties of LPMA samples could be improved for application as a promising inorganic-organic hybrid coating by tuning the ratio of two functional groups.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ladder-like polysilsesquioxanes with different functional groups were synthesized. </LI> <LI> Role of methacryloxypropyl and phenyl groups for coating application was elucidated. </LI> <LI> Physical properties of LPMAs can be favorably tuned by the ratio of two groups. </LI> </UL> </P>

Effect of particle shape on drying dynamics in suspension drops using multi-speckle diffusing wave spectroscopy

Park, Baek Sung,Jung, Kevin Injoe,Lee, Seong Jae,Lee, Kwan-Young,Jung, Hyun Wook Springer-Verlag 2018 Colloid and Polymer Science Vol.296 No.5

광개시제 종류에 따른 유기 박막의 경화 특성과 플렉서블 디스플레이 봉지 소재로의 적용성 분석

오준기(Junki Oh),김소현(So Hyun Kim),정인조(Kevin Injoe Jung),허준(June Huh),정현욱(Hyun Wook Jung),방준하(Joona Bang) 한국고분자학회 2020 폴리머 Vol.44 No.6

플렉서블 디스플레이에 적용할 수 있는 유기 박막 개발을 위해 광경화성 소재에 대한 특성화를 진행하였다. 광경화에 필수적인 요소인 광개시제는 광 조사 시 분해되며 라디칼을 생성하는 Type-1 개시제와 분해없이 라디칼을 생성하는 Type-2 개시제 유형으로 구분된다. Type-2 개시제는 미반응물에 의한 아웃가스 배출이 거의 없는 특성으로 인해 디스플레이 봉지 유기층 제조에 결정적인 역할을 할 수 있다. 본 연구에서는 봉지층에 사용될 유기 코팅액의 경화물성을 최적화하기 위해 Type-1, Type-2 개시제에 의한 실시간 가교 물성을 비교 분석하였다. 잉크젯 코팅공정으로의 적용 가능성을 평가하기 위하여 경화 이전 코팅액의 점도와 표면 장력 등과 같은 기본 유동 물성을 측정하였다. 또한 경화된 박막 필름의 투과율, 굴절률 등과 같은 광학적 물성들을 분석하였다. 다양한 실험 결과로부터 아웃가스 저배출 성능이 뛰어난 Type-2 개시제가 유기막의 핵심 성분으로 디스플레이 봉지 기술을 개발하는데 매우 유용함을 확인하였다. In this work, we examined photocurable materials for organic layers that can be used as an encapsulation layer in flexible displays. Photo-initiators, which are essential for UV-crosslinking, can be classified into two categories: Type-1 initiators that produce free radicals through the cleavage reaction caused by UV irradiation and Type-2 initiators that generate free radicals without the cleavage reaction. Type-2 initiators are more desirable for the encapsulation organic layer of the flexible display due to the low outgassing of unreacted components. To optimize the curing properties of organic coatings, the effect of initiator type on the real-time crosslinking behaviors were mainly scrutinized. The flow properties of pre-cured coatings such as shear viscosity and surface tension were also measured to evaluate the applicability in the inkjet coating process, and transmittance and refractive index were analyzed for the optical properties of cured thin films. As a result, it was found that Type-2 initiators, exerting the intrinsic low outgassing performance, are more advantageous in developing the display encapsulation technology as a key component in the organic layer.

Mechanical properties of ladder-like polysilsesquioxane-based hard coating films containing different organic functional groups

Hwang, Seon Oh,Lee, Albert S.,Lee, Ju Yeon,Park, Sang-Hee,Jung, Kevin Injoe,Jung, Hyun Wook,Lee, Jung-Hyun Elsevier 2018 Progress in organic coatings Vol.121 No.-

<P><B>Abstract</B></P> <P>A series of ladder-like polysilsesquioxanes (LPSQs) containing the UV-curable methacryoxypropyl (MA) and different organic functional (R) groups (propyl, hexyl, cyclohexyl, phenyl or naphthyl) at the fixed MA/R molar ratio were synthesized as hard coating materials. The LPSQ hard coating films prepared by a simple UV curing process exhibited excellent optical transparency in the visible light range. X-ray diffraction analysis of the LPSQ films characterized how their intermolecular chain-to-chain distance and thus chain packing density varied according to the organic functional group. In addition, the hardness, elastic modulus and scratch resistance of the LPSQ films were evaluated by nanoindentation and nanoscratch tests. Although the mechanical properties of the LPSQ films were affected by both the chain rigidity of the organic functional group and the chain packing density of the siloxane backbones, chain rigidity played the dominant role in determining their mechanical robustness. Hence, despite its lowest chain packing density, the LPSQ film with the naphthyl group exhibited the best mechanical properties due to its high chain rigidity derived from the increased aromaticity of the naphthyl group. This study suggests the key factor when designing mechanically durable, scratch resistant hard coating films is the chain rigidity of the film network.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ladder-like polysilsesquioxanes (LPSQs) with different functional groups were made. </LI> <LI> The UV-cured LPSQ films have excellent optical transparency in visible light range. </LI> <LI> The chain rigidity dominantly governs the mechanical properties of the LPSQ film. </LI> <LI> The LPSQ film having the naphthyl group exhibits the highest mechanical robustness. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>