Spin Coating Nozzle Distance for Bubble Prevention
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Solution Overview
Problem
The spin coating method for forming a photochromic layer on eyeglass lenses often incorporates bubbles due to high discharging velocities of photochromic coating agents with high viscosity, which reduces the commercial value and adhesion of the coating film.
Innovation Solution
A spin coating method involving a nozzle with a diameter of 3.0 mm or less, discharging the coating liquid at a distance of 2.5 mm or less from the substrate surface, and maintaining a linear velocity of 1 cm/sec or more, with a viscosity range of 50 cP to 500 cP, ensures uniform film formation and prevents bubble incorporation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the discharging velocity of the coating liquid is increased to drop a predetermined amount within a predetermined period of time, then the productivity is improved, but bubbles are incorporated into the coating film
Solution Approach 1:
The patent applies parameter changes by optimizing the nozzle diameter to 3.0 mm or less and controlling the distance between the nozzle tip and substrate surface to 2.5 mm or less. These parameter adjustments enable the coating liquid to be discharged at high velocity (1 cm/sec or more) while preventing bubble incorporation, thus resolving the contradiction between productivity and manufacturing precision.
2Manufacturing precision
If a nozzle with smaller diameter is used to prevent dripping, then the manufacturing precision is improved, but the discharging velocity must be increased which causes bubble incorporation
Solution Approach 1:
The patent resolves this contradiction by introducing a new dimensional parameter: the distance between the nozzle tip and substrate surface (controlled to 2.5 mm or less). This additional spatial dimension allows the system to use small nozzle diameters for dripping prevention while maintaining high discharging velocities without bubble incorporation, as the short distance prevents bubbles from forming during the discharge process.
3Strength
If the photochromic coating agent contacts the primer layer for a long period, then the adhesion is improved, but the primer layer uniformity is impaired
Solution Approach 1:
The patent applies preliminary action by pre-forming the primer layer with uniform thickness and properties before applying the photochromic coating agent. The controlled discharge process ensures that the coating agent is applied quickly (within 10-120 seconds), limiting the contact time to prevent excessive dissolution of the primer layer while still achieving adequate adhesion through the controlled interaction period.
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 method effectively prevents bubble incorporation into the photochromic layer, enhancing the uniformity and adhesion of the coating film on eyeglass lenses, thus improving the commercial value and productivity of photochromic eyeglasses.
Implementation Method 1
by dropping a coating liquid onto a surface of a lens substrate while the substrate is rotated along the central axis, the coating liquid is developed by centrifugal force during the rotation to form a uniform coating film
Data Source
Figure 1
AI summary
It is an objective of the present invention.to reduce or prevent incorporation of bubbles into a coating film formed by spin coating a surface of a substrate with a coating liquid having a high viscosity at a relatively high discharging velocity. The spin coating method relating to the present invention comprises the steps of discharging a coating liquid from the tip of a nozzle and dropping onto a surface of a rotating substrate to form a uniform coating film on the surface of the substrate, characterized in that the distance between the tip of the nozzle and the surface of the substrate during discharging the coating liquid is 2.5 mm or less.