Analyse Bubbles of Laminated Glass with EVA Film Interlayer
By peter shin
cnc@cncnext.com/ benext77@gmail.com
What People May Think, When They Face Bubbles
When some customers processing laminated glass with EVA FILM, bubbles appear inside the laminated glass, People would always think is this way:
1.The EVA Film I ordered last time, didn't have bubbles problem, why this time the bubbles is coming out, that's definitely the reason of the quality of EVA Film.
2. Some customers face this situation. Maybe they don't use EVA Film very much, so they don't finish the one roll of EVA FILM in a short period. They used two thirds of the roll of EVA film, and after several weeks, they go back to use the left part of the roll. But this time the bubbles coming out, they are very confused. How come the same roll has different quality?
3. Some customer may just change the new EVA FILM supplier and the bubbles comes out. Even their new supplyer tell them it's all about the processing , they would not believe him, they would think it's of course the problem of the quality of your EVA film, because my older supplier don't have this bubbles problem.
General Reasons for Bubbles
Many Laminated glass producer have misconception of the reasons of the bubbles problems. Here is the real why:
1. First situation: the temperature is too high, maybe more than 180 degree, which will cause the compound to break down and create gas. In this way, it's just reducing your temperature, and everything would just be fine.
2. Second situation: the temperature in the oven is not average, which means some part of the glass, is hotter than others. So some part of the EVA film will melt and finish the crosslink reaction while other parts of EVA Film is still not melted, which will interrupt the vacuuming and cause the bubbles. For this situation, we suggest you modified the lamination machine.
3. Third situation: the Vacuum machine is old or the vacuum ability is not good enough. If the vacuum machine is old, renew it. If the vacuum ability is not powerful enough, try to buy a new one.
4. Four situation: the air moisture is high. The moisture in the air in your region is changed, which will easily cause the EVA film wet when it exposes in the air. Moisture in the EVA FILM would cause the bubbles. Although the EVA FILM is less sensitive to moisture compared with PVB FILM. But if the moisture is too high, the bubbles will also come out.
Some customer open the packaged of one roll, and don't use it up at one time. And the left part of the EVA film will absorb the moisture in the air and cause the bubbles.
5. Five Situation: Different EVA FILM supplier has different formula for EVA FILM, so if you change the EVA FILM supplier, you need to adjusting the processing parameters according to the supplier's EVA FILM property.
Micro Reasons for Bubbles:
I wrote an article Bubbles Solution for Laminated Class with EVA Film, talked about the situations that bubbles come out the laminated glass. It is macro views. Today I like to talk about the other reasons in micro views that cause the bubbles in laminating glass with EVA Film.
1. The plainness of the tempered glass is bad.
+As you known, tempered glass is less plain than the flat glass. So you should choose a company that produce better tempered glass.
+ Since the tempered glass's plainness is worse than flat glass, you should use thicker EVA FILM interlayer for the tempered glass. Generally speaking, the tempered glass should be laminated with at least 0.8 mm thickness EVA Film Interlayer.
+ Laminate Less layers "pre- laminated glass" in a silicon bag at one time. If you laminate too many layers "pre-laminated glass" in a silicon bag at one time, the vacuuming would not work perfect and cause the bubbles.
+If you laminated small pieces "pre-laminated glasses" at the same time, put the "pre –laminated glasses" on the fabric, which will help vacuum, and the fabric should cover the vacuum hole to make sure the vacuum hole is not sealed by the silicone bag itself.
2. Check if the silicon bag is leaking.
1) Averagely speaking, a silicon bag can be used for several years. But check the silicon bag if your laminated glasses have bubbles.
2) Check the concavo convex of the edge of the silicon bag is sealed perfectly when processing laminated glass with EVA Film.
3. It's too early to put the laminating glass out of the oven,
The temperature of laminated glass is still very high and the EVA FILM is still melting and reacting. When the laminated glass is getting cold, the melted EVA FILM is contracting, and the EVA Film can't fully fill the gap between two glasses, so bubbles come out.
4.It's too early to stop the vacuuming.
And the cross link reaction of the EVA film is not totally finished and stable. And also the silicon bag would suck same air back in to the bag, which cause the bubbles. So generally speaking, don't stop vacuuming until the temperature of the laminated glass is lower than 45 degrees.
Notes:Always remember you put the wire net on the vacuuming hole to make sure the vacuuming is not stop by the laminated glass on the hole. To be more perfect, also can use wire net over the laminated glass.
Case Study: Bubbles of Laminated Glass with EVA Film Interlayer
We have seen a situation in this way: Bubbles comes out in the Laminated Glass. And we checks all the details of vacuuming and vacuuming is definitely no problem.
But the bubbles still comes out in the laminated glass. And the bubbles are regular and on lines.
Finally we realized that the bubble lines are right upon the heating pipes.
So we reduced the temperatures and did the test. Then no bubbles comes out, but some part of laminated glass is not very transparent.
So we know the reason:
Because the heating pipes are under silicon bag, when laminating glass, the part of laminated glass right upon the heating pipes are in higher temperature. And the temperature inside the oven is not in average.
Remember that when the temperature is too high, the copolymer will be breaking up and produce gas which would cause bubbles inside laminated glass.
So It's better of you can talk to the EVA Glass Lamination Oven producer to modify the oven.
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Safety Architectural Laminated Glass, Smart Glass, Privacy Glass, LED Glass etc.
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