Delivery form and storage
The TROSIFOL film layers stick together on the film roll in spite of the film’s rough surface. This is known as blocking (= sticking together on each other). Various counter-measures can be taken to prevent blocking which, otherwise, would make it impossible to process the PVB film.
One possibility is to wind in an appropriate plastic separating film - in this case preferably a thin embossed PE interleaved film. This process was developed and patented by TROSIFOL and finds widespread use nowadays. Another method is to cool the film down to a temperature of 8°C (46°F) or lower. This greatly diminishes the adhesive (blocking) behaviour of the film for problem-free handling. However, the latter method consumes a great deal of energy and is therefore cost intensive. Both delivery forms are discussed in the following chapters.
TROSIFOL with PE interleaved film
TROSIFOL with PE interlayer For TROSIFOL with PE interlayer, the undesirable adhesion of the film surface to itself is prevented by interleaving the individual TROSIFOL layers with an embossed PE film. In its original packaging, TROSIFOL with PE interlayer can be stored in any normal,dry room. TROSIFOL with PE interlayer in its original heat-sealed PE bags has a usual storage life of at least three years without loss of quality. However, TROSIFOL with PE interlayer in its factory-sealed packaging should not be stored at temperatures in excess of 30°C (86°F). Keeping the product in a refrigerated store at approx. 8°C (46°F) is also possible. Rolls which have been opened and started to use may be stored in a climatized room. This is particularly advantageous when small numbers of windscreens of different types have to be manufactured or when - in the production of flat laminated safety glass for architectural applications - the sizes are such that a full TROSIFOL roll cannot be used at one time. TROSIFOL as refrigerated film When PVB is wound, stored or transported at temperatures below 8°C (46°F), there is no need to use a seperating agent to keep the layers of film apart on the roll. This advantage is available with TROSIFOL refrigerated film, which is transported in special refrigerated trucks and should be stored at temperatures of 8°C. The relative humidity need not generally be controlled with this film type. However, once a roll refrigerated film has been allowed to warm up to a temperature of 12°C (54°F) or more for an extended period of time, it will often be impossible to unroll it without damaging the product. The individual film layers will adhere firmly to each other, even if the film is subsequently cooled down. In the warmer atmosphere of the lay-up room, refrigerated film must be fully unrolled and used, or at least cut into sheets, after no more than 2 to 3 hours.
TROSIFOL as refrigerated film
PVB film is wound into rolls at temperatures of ≤ 8°C (46° F) for storage and transportation. This property is utilized by TROSIFOL refrigerated film that is transported in special refrigerated lorries. TROSIFOL refrigerated film is stored in the original package at ≤ 8°C (≤ 46° F), usually under uncontrolled humidity conditions. Refrigerated film rolls stored for extended periods at temperatures of > 8°C (> 46° F) often cannot be unwound without damaging the film. Even renewed cooling down to lower temperatures still does not ensure damagefree separation of the individual film layers. When stored at >8°C (> 46° F) or higher in the laminating room, the refrigerated film rolls must be completely unwound within 2-3 hours and be used or cut to size.
TROSIFOL with PE interleaved film and TROSIFOL refrigerated film only differ by the delivery form and not by the film composition. Consequently, the operating procedure only differs in the preparation of the film and not in the actual lamination process. Compared with refrigerated film, TROSIFOL with PE interleaved film offers the advantage of being able to store opened rolls in air-conditioned lamination rooms. Refrigerated film rolls have to be unwound and used or cut to size before they warm up, whereas rolls of TROSIFOL with PE refrigerated film can be stored in an air-conditioned room at 18 to 20°C (64 to 68° F) and 25 to 30% relative humidity without the individual film layers adhered together and any change of the previously adjusted film moisture of approx. 0.45%. When a film has become a too high moisture level, it must be reconditioned at 25 to 30% relatively humidity prior to application. Under these conditions the customary conditions of approx. 0.4 to 0.5% for processing are once again regained. The film should be freely suspended for reconditioning, either cut to size or as a film strip. Subsequent reconditioning on the roll or as a film stack is not possible or would take a very long time.
Since TROSIFOL already has the required film moisture prior to delivery, lamination between two glass panes can be carried out directly off the roll in an air-conditioned room (18 to 20°C/25 to 30% relative humidity).
| TROSIFOL | |
|---|---|
with PE interleaved film | as refrigerated film/without PE interleaving |
Storage in a packed state, without air-conditioning at maximum +30°C | Storage and transport refrigerated at ≤ 8°C (≤ 46° F) |
Simple storage of left-over rolls in airconditioned lay-up rooms with frequently changing glass ply sizes | Storage of left-over rolls • Tightly sealed bag at ≤ +8°C (≤ 46° F) without controlled room humidity level • Open bag at ≤ +8°C (≤ 46° F) and 25 to 30% relative humidity |
Blocking not possible | No PE waste |
Film quality is identical for both delivery forms! | |
When unwinding TROSIFOL film, care must be taken to ensure, that a uniform tension is applied over the entire film width, since stretching of the elastic film would lead to subsequent shrinkage. TROSIFOL with PE interlayer can be unwound with a simple mechanical device (see illustration below).
Fully automatic film cutting and stacking machines can be used when larger quantities of TROSIFOL have to be cut to size for the production of windscreens. These machines permit trapezoid cutting pattern to save considerable quantities of film compared with a rectangular cut. The length is merely increased slightly to compensate for the negligible, production-conditioned shrinkage.
For small series the film is drawn manually over a back illuminated screen so that the film can be inspected. The film is cut to size on this glass table with a strong and sharp blade. Coloured adhesive strips underneath the table make it easy to maintain the required cut-off length. Rapid unwinding of the PE interleaved film can result in electrostatic charging of the PE film, causing increased risk of contamination of the PVB film. Consequently absolute cleanliness must be assured in conjunction with air ionisers to prevent electrostatic charging. Contact with earthed metal foil strips will also dissipate electrostatic load.
The glass must be prepared with maximum care since its condition plays a decisive role in the quality of the finished laminate.
The individual glasses are cut to size from the stock glass sheets to produce the laminated safety glass. A clean cut must be produced because even fine micro-cracks at the edges can be the cause of glass breakage when the laminate is produced. In the event that such faults occur more frequently during the production process, it is advisable to check the glass cutting tools and the actual glass quality.
Since the final laminated glass cannot be bent, the required glasses to produced laminated glass must be paired and bent together. Glasses are cut to size from the stock glass sheets. It is necessary to note that the inside and outside glasses have differing formats. After cutting the glasses to size, either on a machine or manually with the help of templates, the glass edges are finished on a grinding machine or with a diamond wheel. Finally, the glasses are cleaned in a flat-glass washing machine. Modern glass washing machines normally operate horizontally, and they are equipped with rotary brushes to produce a perfectly clean glass surface merely with water. Since the quality of the washing water and the cleanliness of the glass surface influences the adhesion of the PVB film on the glass, only fully demineralised water of ≤ 20 µS (if possible ≤ 5 µS) in the last zone of the washing machine should be used. The effect of the conductivity of the washing water on the adhesion of TROSIFOL film on the glass is indicated by the subsequent graph. In this example a conductivity of approx. 150 µS approximately halves the PVB film adhesion to glass.
Water from natural sources usually contain certain quantities of dissolved salts - mainly the so-called hardness-creating alkaline earth ions such as Ca++ and Mg++ plus Na+ and K+ in lower concentrations. The first two seriously diminish glass adhesion already in low concentrations, whereas the alkaline ions have a hardly measurable influence on the adhesion.
In practice, the removal of the ions through complete demineralisation or reverse osmosis is, therefore, imperative. When mixing completely demineralised water with natural water it is essential that the water hardness, or the specific electrical conductivity, are closely checked before and during the washing process.
When detergents are used in the first washing step to clean particularly dirty glass, then it is essential that completely demineralised water is used for the final rinse before the glass is then dried in a powerful stream of filtered hot air. The air-blowing nozzle should be slanted so that any remaining drops on the back edge of the pane are concentrated in one corner so they can be easily removed.
Washed glass sheets cut to size for windscreens pass through another two additional processing operations before the TROSIFOL film is placed between the two glass sheets. When the glasses have left the glass washing machine a thin layer of bending release agent is uniformly applied so that the paired glass sheets do not stick together at a temperature of approx. 630°C (1165°F) in the bending furnace. E.g. talc or sodium sulphate is used as bending release agent. These substances are dusted onto the glass in a dry state or sprayed on in an aqueous suspension (demineralised water) or solution.
Most bending release agents remaining on the glass surface would invariably impair the optical quality of the windscreens and also adversely influence the adhesion of the film on the glass. It is therefore advisable that all traces of bending release agent should be carefully removed before the TROSIFOL film is applied. The bending release agent can be removed with water in an automatic washing machine or manually. Some bending release agents can be readily removed after the bending process with a powerful industrial vacuum cleaner and a brush.
Chemical coating
A metal oxide is coated onto the hot glass surface during the float-glass manufacturing process, thereby establishing a close bond with the glass.
Glass coated in this manner reflects the incoming visible light and can function as heat protection. The surface resistance of this coating is just as high as the actual glass surface.
Physical coating
After the glass has been produced and cut to size, a cathode-ray process (sputtering) coats metal-compounds in various layers onto the glass by vacuum vaporized deposition. The particles are uniformly applied to the glass surface in a continuous process. The coating is more or less durable, depending on the type of metal-compounds used. This type of coating is less durable (corrosion and scratching) than chemical coatings. All these layers can be cleaned by suitable washing machines without fear of damage.
TROSIFOL recommends that the adhesion and competability of the coatings to the PVB has to be checked in advance!
Similar to the production of curved laminated safety glass for automotive glazing direct pressing of the loosely placed sandwich glass/film/glass and other materials for processing into flat and curved laminated glass for architectural applications is not a suitable method to produce laminated glass without air inclusions.
Consequently, a so-called pre-laminate is produced prior to the actual autoclave process. The quality of this pre-lamination is of major importance for the quality of the final laminated glass. A distinction is made in prelamination between rolling press and the vacuum process. The latter is subdivided into the vacuum bag process (analogous to the ASAHI process) and the vacuum-ring process.
Laminated glass can also be produced without the autoclave process. This is known as the autoclave-free laminated glass process with lengthened vacuum deairing process time to compensate for the missing autoclave pressure step.
Laminating room
When different layers of flat and/or curved glass plies - usually in a minimum glass thickness of 3 mm - are laminated with one or more layers of TROSIFOL film, the sheets are almost always cut to size directly from the film roll (except for small formates). For large-formate flat plies up to 3.21 x 6.00 m (so-called jumbo size), sandwich lamination and edge trimming is mainly fully automatic.
Curved glass plies are mainly placed together manually while the actual sandwich is produced by one of the two vacuum processes with a rubber/plastic bag or with rubber ring.
The most common pre-lamination process for flat plies laminated glass plies for buildings is the pre-nip (or calander) process for a high processing speed, particularly with largeformate laminated safety glass. Depending on the given process, squeezeroll heating furnaces with one or two heating zones and one or two roll pairs are used. The heating furnaces can be heated by infra-red radiators or with electricity (hot black tubes) or hot circulating air. The nip rolls usually consist of a solid cylinder or of several assembled individual cylinders (curved glasses). Independent of how the pre-nip process is carried out, the aim is to:
It has proved to be beneficial to produce the pre-laminates with calanders in two steps. The loosely superimposed sandwich of flat plies and film is heated to approx. 35°C (95°F) (measured on the glass surface) in a short heating tunnel with medium-wave infrared radiators. The heated sandwich is then passed through a pair of rubber rolls where most of the trapped air is pressed out. The sandwich is then passed through a second, longer infra-red heating tunnel where it is heated to approx. 60 - 70°C/140 - 158°F, (measured on the glass surface). Any remaining air is then almost completely pressed out by a second pair of calanders and the edges are sealed. The quality of the pre-lamination is indicated by the picture of the pressed sandwich. The laminated glasses should have a slightly striped grey structure distributed uniformly over the entire area. Only a narrow zone around the edge of the ply (edge seal) should be transparent.
The roll gap of the first pair of rolls should be narrower by approx. 1 mm than the overall glass and film thickness, and the gap of the second pair of rolls should be narrower by approx. 2 mm. This spacing may have to be reduced still further for very thick glass/PVB sandwiches when several thick film layers are used. The pneumatic cylinders of the pressing rolls for flat pre-laminations should be operated at 5 to 7 bar. Since the heat transmitted from the glass surface to the TROSIFOL film is primarily responsible for heating the pre-laminates, especially with multi-laminates, a certain amount of time is required to uniformly heat the sandwich. Consequently, the throughput rate and the supplied heating energy must be adapted in such a manner that an optimized pre-laminates is achieved. All temperatures are only indicated values and they depend greatly on the type of laminated glass and the manner of heating in the pre-lamination heating tunnel.
In addition to the above-mentioned process variables, there are also other influencing factors, for instance the flow behaviour of the film (rheology), film’s surface roughness, the waviness of tempered glass and the type of glass coating/colour. The latter changes the heat absorption in the furnace and thus the glass surface temperature of the laminate. Safe and complete deairing is carried out before the glass edges have completely bonded together. Once the edge seal has been produced, any remaining trapped air cannot escape with the result that bubbles are formed in the end product. Consequently, deairing must be carried out at temperatures that are lower than the sealing temperature. On the other hand the temperature must be sufficiently high to ensure that the PVB film securely adheres to the glass surface. Without this the laminate would become prematurely separated and excess air could once again enter into the laminate.
The heating systems can age. With mediumwave radiators that are frequently used it is necessary to note that the radiated light is shifted towards longer wavelengths as a result of burnt-in dust particles. Consequently, in the course of time, heating with light radiators gradually becomes a circulating heating system with correspondingly lengthened cycle times.
The production of pre-laminates by a vacuum process is carried out in an analogous manner. The vacuum-bag and vacuum-ring processes for architectural glass are normally limited to bent glasses and multiple glass/ film make-ups. Large-format glasses are normally not pre-laminated by the vacuum process on account of the handling difficulties. However, the vacuum process can be advantageous for special laminates as well as for the lamination of alternative materials in addition to glass and PVB.
The continuous vacuum process is not customary for architectural glass on account of the lack of uniformity of the curved glass. For all vacuum pre-lamination processes it is necessary to ensure that evacuation of the laminate has ended before heating commences (approx. 10 minutes; longer is even better). This is the only way to prevent premature edge sealing and, thus, incomplete deairing. The vacuum must be maintained throughout the heating time (approx. 20 minutes) and should reach at least 0.1 to 0.2 bar (- 0.8 to - 0.9 bar/approx. 80 to 150 hPA or 1.5 to 3.0 PSI).
The necessary glass surface temperature of 95 to 105°C (203 to 221°F) is reached at an ambient air temperature of approx. 100 to 120°C (212 to 248°F) in the heating tunnel or heating cabinet. The pre-laminates produced by the vacuum process are usually clearer than those produced by calandaring. The favourable processing conditions with regard to temperature and line speed inside the heating tunnel must be established by processing trials depended on the equipment used.
Factors critical for successful vacuum prelamination are:
This is the last step in the process of glass lamination. The quality of this process is determined by the correct selection of temperature, pressure and time to determine the following:
The correct selection of process parameters results in an end product with the required product properties. Thicker, large-format laminates require a different autoclave process compared with thinner laminates such as windscreens. The heating and cooling of the thick glasses must be made at a slower rate to produce laminated glass that is free of tensions. The entire cycle time depends on the equipment and amount of glass and can vary to between 1 and 6 hours, depending on the program for pressure increase, pressure level and curve temperature. The process parameters can be optimised by corresponding in-house tests.
Due to the lower planearity of FTG/HSG, especially less plane than float glass, the lamination of tempered glass with TROSIFOL differs entirely from the previously described process. The subsequently listed rules have proved to be helpful in practice for the production of good quality laminated safety glass:
The finished laminated safety glass plies are removed from the autoclave, checked and packed.
Laminated glass plies for the building industry, also multiple laminates, can then be further processed. They can be drilled, divided into smaller sizes, and the edges can be ground and polished.
Laminated glass consisting of two glasses and one in-between film layer can be divided by cutting them on both sides with a glass cutter. Normally such laminated glasses are broken down in the cutting line after the first and second cut, while the film is separated by heat or with a thin sharp blade. Multiple laminates consisting of three or more layers of glass must be separated with a diamond saw blade.