~ Rotten Squeegee ~
One day, I received a call asking for advice because the print was rubbing.
The first thing that comes to mind when you hear the word "print rubbing" is clogged screen plates.
When I asked him to check the condition of the screen, he said that even the new version was scratched. The next possible cause is the viscosity of the ink, but even new ink rubbed off.
Even though neither the squeegee nor the printing conditions were changed, the print was rubbing 100%.
Since it was not possible to fully grasp the printing status over the phone, I visited the point of contact to confirm the printing status. As a result, a strange phenomenon was observed.
Even if the printing pressure is steadily increased, the rubbing does not disappear. Normally, if you increase the printing pressure, the rubbing phenomenon will change little by little.
But nothing changed. Even after replacing the screen version with another one, there is no change.
No change even after adjusting other conditions such as print speed and clearance. No change even if the work material is changed to PET or paper.
But nothing changed. Even after replacing the screen version with another one, there is no change.
No change even after adjusting other conditions such as print speed and clearance. No change even if the work material is changed to PET or paper.
When I was at a loss, I happened to look at the squeegee and it seemed that the color had changed a little.
When I asked a local person, "Since when have you been using this squeegee?", the answer was, "I have been using this squeegee for printing for a long time. I have been able to print with this squeegee until now."
I think it's a well-used squeegee, and when I tried to bend the squeegee, there was no stiffness!!
Perhaps the squeegee is hydrolyzing?
So, when I replaced it with a new squeegee...I was able to print beautifully without any problems.
This example shows that the quality of screen printing is affected not only by the hardness of the rubber, but also by the elasticity of the rubber itself.
Urethane rubber, which is the raw material of squeegees, is hydrolyzed by moisture in the air. As the molecular bonds of urethane rubber are broken by this, rubber elasticity deteriorates. Then the rubber will look like a caramel candy. When printing pressure is applied to the squeegee that has become like this, the squeegee deforms and becomes unable to transmit the printing pressure to the screen plate.
This is the cause of the print rubbing this time.
Urethane rubber, which is the raw material of squeegees, is hydrolyzed by moisture in the air. As the molecular bonds of urethane rubber are broken by this, rubber elasticity deteriorates. Then the rubber will look like a caramel candy. When printing pressure is applied to the squeegee that has become like this, the squeegee deforms and becomes unable to transmit the printing pressure to the screen plate.
This is the cause of the print rubbing this time.
When evaluating a squeegee, it is necessary to consider not only the rubber hardness but also the deterioration of the rubber.
Hydrolysis of urethane rubber proceeds slowly. Note that squeegees that have been manufactured for more than one year may be hydrolyzed.
Hydrolysis of urethane rubber proceeds slowly. Note that squeegees that have been manufactured for more than one year may be hydrolyzed.
