Solvent Composition for Stable Inkjet Organic EL Film Formation

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Solution Overview

Problem

The inkjet method for forming organic EL layers using solvents like diethylbenzene, trimethylbenzene, or nitrobenzene faces issues with nozzle clogging and film flatness due to low boiling points, and the presence of polar solvents with electron-withdrawing groups can affect element characteristics.

Innovation Solution

A functional layer forming composition is developed using a combination of a first aromatic solvent with an electron-withdrawing group, such as nitrobenzene, and a second aromatic solvent with an electron-donating group, like trimethoxytoluene, where the boiling point of the second solvent is higher, ensuring stable film formation and reducing the residual solvent impact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a solvent with low boiling point (e.g., diethylbenzene, trimethylbenzene) is used for inkjet coating, then drying proceeds easily, but nozzle clogging occurs and ejection stability deteriorates

Engineering Contradiction:

Improvedrying speedVSAvoidejection stability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the boiling point parameter of the solvent from low (diethylbenzene: 140°C, trimethylbenzene: 165°C) to high (nitrobenzene: 210°C or higher). This parameter change resolves the contradiction by preventing premature drying in the nozzle (improving ejection stability) while still enabling effective drying during the actual coating process through controlled heating.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If nitrobenzene is used as a solvent, then ejection stability improves, but the electron-withdrawing nitro group may remain in the functional layer and affect element characteristics

Engineering Contradiction:

Improveejection stabilityVSAvoidelement characteristic degradation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent utilizes phase transition (evaporation) of the nitrobenzene solvent through controlled heating during the drying process. The high boiling point of nitrobenzene allows it to remain liquid during ejection (ensuring stability) but then transition to vapor during controlled drying (removing it from the functional layer), thus eliminating the harmful electron-withdrawing nitro groups while maintaining ejection stability.

Inventive Principle:

Principle #36Phase transitions

3Stability of the object's composition

If a solvent with high electron-withdrawing property is used, then dissolution property for solid component is ensured, but residual solvent in functional layer affects element characteristics

Engineering Contradiction:

Improvedissolution propertyVSAvoidelement characteristic degradation

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent employs controlled phase transition from liquid to vapor through heating. The solvent with high electron-withdrawing property (nitrobenzene) is used to ensure good dissolution of the solid component, then removed via controlled evaporation during the drying process, transitioning from liquid state (providing dissolution) to vapor state (eliminating harmful residual effects on element characteristics).

Inventive Principle:

Principle #36Phase transitions

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solvent configuration enhances ejection stability and film flatness in the inkjet method, preventing nozzle clogging and minimizing the impact of electron-withdrawing groups on organic EL element characteristics.

Implementation Method 1

a dissolution property for the solid component is ensured by the first aromatic solvent which is a polar solvent

Methodology Applied

Scientific EffectSolvation: Solvation

Implementation Method 2

drying for removing the solvent from the functional layer forming composition (liquid) proceeds

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentEP3276696B1Functional layer forming composition and method for manufacturing the same

Publication Date: 2023.10.11 SEIKO EPSON CORP

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AI summary

To provide a functional layer forming composition capable of obtaining a stable film forming property when a liquid phase process is used, a method for producing a functional layer forming composition, a method for producing an organic EL element, an organic EL device, and an electronic apparatus. A functional layer forming composition of the invention is used when at least one layer in a functional layer containing an organic material is formed by a liquid phase process, and is characterized in that the composition includes a solid component for forming a functional layer, a first aromatic solvent having an electron withdrawing group, and a second aromatic solvent having an electron donating group, and the boiling point of the second aromatic solvent is higher than the boiling point of the first aromatic solvent.