Thin Coating Thermal Inkjet Printhead Heater Elements

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Solution Overview

Problem

Inkjet printheads face challenges with nozzle clogging due to dried ink, oxidation and corrosion of heater elements, and limitations in nozzle density and firing rate caused by thick protective layers and inefficient heat dissipation.

Innovation Solution

The design includes a heater element with a protective surface coating less than 0.1 μm thick, allowing for efficient energy transfer and reduced thermal insulation, along with a MEMS fluid sensor for ink detection and a print engine controller to manage actuation energy and prevent nozzle clogging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If thick protective layers are used on heater elements, then oxidation and corrosion resistance is improved, but heat transfer efficiency deteriorates and thermal insulation increases

Engineering Contradiction:

Improveoxidation and corrosion resistanceVSAvoidheat transfer efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent changes the thickness parameter of the protective coating from conventional thick layers to an ultra-thin layer less than 0.1 μm. This parameter change allows the coating to provide oxidation and corrosion protection while minimizing thermal insulation effects, thereby maintaining high heat transfer efficiency for bubble formation.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If thick protective layers are used on heater elements, then oxidation and corrosion resistance is improved, but nozzle density and firing rate are limited

Engineering Contradiction:

Improveoxidation and corrosion resistanceVSAvoidnozzle density and firing rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

By changing the protective coating thickness parameter to less than 0.1 μm, the patent reduces thermal insulation and enables faster heating rates. This allows for higher nozzle density and increased firing rates while maintaining adequate protection against oxidation and corrosion in the harsh inkjet environment.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If heater elements are exposed without protective coatings, then heat transfer efficiency is improved, but oxidation and corrosion resistance deteriorates

Engineering Contradiction:

Improveheat transfer efficiencyVSAvoidoxidation and corrosion resistance

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies an ultra-thin protective coating with thickness less than 0.1 μm, which is thin enough to maintain high heat transfer efficiency but sufficient to provide oxidation and corrosion resistance. This optimized thickness parameter resolves the contradiction between needing protection and requiring efficient heat transfer.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses composite material structures combining the heater element with an ultra-thin protective coating layer. This composite structure provides both the thermal conductivity needed for efficient heating and the chemical resistance required to withstand oxidation and corrosion from ink components and dissolved oxygen.

Inventive Principle:

Principle #40Composite materials

4Reliability

If conventional protective layers are used, then heater protection is improved, but actuation energy requirements increase

Engineering Contradiction:

Improveheater protectionVSAvoidactuation energy

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

By reducing the protective coating thickness to less than 0.1 μm, the patent minimizes the thermal mass that must be heated during each actuation cycle. This parameter change reduces the energy required to heat the coating to bubble formation temperature, thereby lowering overall actuation energy requirements while maintaining heater protection.

Inventive Principle:

Principle #35Parameter changes

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 configuration enables the printhead to eject more than one billion drops with improved efficiency, reduced risk of oxidation and corrosion, and increased nozzle density and firing rate, while maintaining self-cooling capabilities.

Implementation Method 1

heating the heater element to a temperature above the boiling point of the ejectable liquid forms a gas bubble

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

The gas bubbles generate pressures in the ink causing ink drops to be ejected through the nozzles

Methodology Applied

Scientific EffectPressure generation through phase change: Phase Change

Implementation Method 3

Dissolved oxygen in the ink can attack the heater surface and oxidise the heater material

Methodology Applied

Scientific EffectOxidation resistance: Oxidation

Data Source

PatentUS7448729B2Inkjet printhead heater elements with thin or non-existent coatings

Publication Date: 2008.11.11 MEMJET TECH LTD

AI summary

A thermal inkjet printhead with a heater element disposed in each of the bubble forming chambers wherein, the heater element has a protective surface coating that is less than 0.1 μm thick while still being capable of ejecting more than 1 billion drops without failure. Removing most or all of the protective coatings from the heater reduces or eliminates the thermal insulation between the heater and the ink. Nucleating a bubble in the ink chamber requires a much shorter pulse of less energy thereby improving printhead efficiency.