Date: 31 March 2023
Author: Luc Moeyersons
This information corresponds to our current knowledge on this subject. It is offered solely to provide possible suggestions for your own experimentations. It is not intended, however, to substitute for any testing you may need to conduct to determine for yourself the suitability of our advice for your particular purposes.
This information may be subject to revision as new knowledge and experience become available. Since we cannot anticipate all variations in actual end-use conditions, LAMI-Solutions makes no warranties and assumes no liability in connection with any use of this information.
Nothing in this publication is to be considered as a license to operate under or a recommendation to infringe any patent right.
TABLE OF CONTENTS
1. Introduction1.1. Stages of production1.2. Comments
2. Preparation of glass2.1. Stages of production2.2. The glass2.3. Unloading the glass2.4. Cutting the glass2.5. Breaking out of the glass2.6. Seaming2.7. Washing2.8. Separating Agent2.9. Ceramic band2.10. Coated glass
3. Bending the glass3.1. Sag bending3.2. Press bending3.3. Press assisted bending
4. PVB Preparation4.1. Stages of preparation4.2. Interleaved – Refrigerated4.3. Packaging4.4. Unwinding the roll4.5. Adhesion & Moisture control4.6. Stretching
5. Assembly5.1. Preparation of glass5.2. Assembly room
6. Prepressing6.1. A look at different processes6.2. vacuum ring process6.3. vacuum bag process6.4. Roller process6.5. Ovens in use6.6. Edge sealants6.7. Use of clips6.8. Windscreen stacking
7. Autoclaving7.1. A look at different autoclaves7.2. The purpose of autoclaving7.3. Operational parameters7.4. Risk of volatiles evaporation & autoclave fires7.5. The ideal “practical” autoclave cycle7.6. Possible autoclave cycle improvements7.7. Recommended precautions
8. Windscreen finishing8.1. Encapsulation8.2. Trimming of excess PVB
9. Inspection9.1. Defects in the glass9.2. Defects in the PVB9.3. Defects in the laminated glass9.4. the shape of the windscreen9.5. Laboratory testing
10. Lamination Defects10.1. Bubbles10.2. Bubbles: Rule of thumb on root cause10.3 Delamination
4.1. Stages of preparation
4.2. Interleaved – Refrigerated
Refrigerated PVB needs to be stored/transported between 4 and 10 °C. The higher temperature limit is to prevent the PVB to stick to itself creating blocked rolls.
If stored at lower than 4°C temperature, there is the risk of dew formation even in (30 % ) RH controlled clean rooms.
Interleaved PVB needs to be stored/transported, by preference below 25 °C to prevent surface roughness deformation.
If stored at higher temperature, it is advisable to store the rolls (for minimum 24 hours) prior to usage, at 20 °C.
In former times, Sodium bicarbonate (NaHCO 3 ) powder was used for non refrigerated rolls. This had to be washed/rinsed off and afterwards the PVB film had to be reconditioned.
The rolls are packed in OPA bags or double PE bags and sealed with plastic end-caps, to prevent moisture pick up by the hygroscopic PVB. The OPA (Oriented Polyamide) bags are barriers against moisture penetration, at least the central aluminium film is. The aluminium foil is protected from oxidation by a Poly Ethylene film (inside) and on the outside an “Oriented Poly Amide” film to reduce the risk of tearing of the bag. Most commercial PVB’s are delivered with a moisture content between 0.35 and 0.55 % ; this to ensure a stable adhesion between the PVB and the glass. The use of OPA bags is recommended (+ plastic end caps), as protection against moisture, even for partially used rolls. Recommended temperature for storage of refrigerated PVB’s : 7 °C. The PVB is wound on plastic cores (PolyEthylene, PolyPropylene or ABS polymer) in order to ensure:- The elimination of static electricity- A PVB which is not contaminated (provided that the core is not damaged) Plastic cores are part of the industry packaging waste reduction program. Suppliers take back all plastic packaging components, except stretch wrap and protective bags.
4.4. Unwinding the roll
◦ Risk of blocking (store below 10 °C)◦ Recommendations:
- After unwinding and cutting the PVB film, allow the blanks to rest for 16 to 24 hours before use.- This will allow relaxation from eventual stretching during unwinding.
- Store a maximum of cut blanks equal to a roll of 250 meters in a pile.
4.5. Adhesion & Moisture control
(Adhesion is influenced by the moisture content).
The relation between the moisture content of the PVB and the relative humidity.
The fractional approach to moisture equilibrium (0.76mm PVB thickness) at ambient temperature.
The fractional approach to moisture equilibrium (0.76mm PVB thickness) at different temperatures
The moisture pick-up during short exposures to 50% relative humidity.
The relation between the adhesion and the moisture content of the PVB.
The relation between the adhesion and the moisture content of the PVB for different thicknesses and water content.
CSS correlation to Moisture Content and PVB Thickness (B5)
Doubling the PVB thickness reduces the CSS adhesion result to app. 66 % of the original value.
Other factors:(influencing level of adhesion)◦ The cleanliness of the glass surfaces (wash water quality and drying method)◦ The tin content of the ‘float’ glass.
The relation between the adhesion and the impact of the 2.27kg ball (5 pound).
ECE R43/Temperature:23 deg.C
- Cosmetic. (The shade band should follow the roof line of the windscreen, avoiding a “frowny appearance of the shade band”, once installed in the car)
◦ Saving in PVB loss (trimmings).
If the blank is shaped correctly the surface area gain can be up to 15%
Both the thickness and the ball drop performance will be variable from (originally) non-stretched PVB.
4.6.2. Warping of the blanks:
- Low investments.- Possible with refrigerated PVB.
The thickness is not significantly affected
- Slow and labour intensive.- Conditioning of the PVB required after stretching.- High risk of defects (wrinkling).
4.6.3. Expandable mandrels:
The PVB is wound hot, expanded, heated, etc.
Interleaved PVB is necessary(the stretchability of interlayer and interleaving film is important)Stretching cycle of 60 min. at 100 deg. C
- Conditioning necessary.- The surface pattern is altered.
4.6.4. Stretching on a fixed cone:
◦ The interleaved PVB is wounded under high tension onto a fixed pitch cone.
- Conditioning necessary- The surface pattern is altered.
4.6.5. Continuous stretching:
- The PVB is continuously stretched over a single variable pitch cone.
- Process is limited to 10 meters/min.- Temperature required is approximately 100 deg. C(to avoid shrinkage of the stretched PVB-blanks)
- Speed- Can be used for clear PVB and PVB with shaded band.- No further conditioning necessary (if correctly set).- A change in bending radius is easily achieved.
- Dimensional stability is reduced.- Variation in thickness.- High investment.- Risk of PVB drying.
4.6.5. Continuous stretching:
- The PVB is continuously stretched over a fixed-pitch cone array. Some of the cones are used for cooling.- A change in radius is achieved by changing the position of the film on the cone.
- Very high investment.- No significant advantage over the Ford Type A.
4.6.5. Continuous stretching:
- The PVB is continuously stretched over a system with variable heat and uniform stretching.- Mirror image of variable stretching with uniform heat.
Cut from PVB roll With Shade band
The blanks are cut afterwards from the wound-up roll in a rectangular shape but due to the shrinkage variability, the blanks change (over time) into an arc form.Author: Luc MoeyersonsTABLE OF CONTENTS4. PVB Preparation4.1. Stages of preparation4.2. Interleaved – Refrigerated4.3. Packaging4.4. Unwinding the roll4.5. Adhesion & Moisture controlCSS correlation to Moisture Content and PVB Thickness (B5)Remark:4.6. StretchingCut from PVB roll With Shade band