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The variability of Materials, Shapes and Configurations that are used in the construction of laminates are generally the main cause of the problems that affect them. That is for example the case of the semi-flexible Photovoltaic modules and also the case of many BRG structures. These structures, made from the combination of layers of different materials, are very sensitive to the internal tensions that are generated inside the structures during the lamination processes.

This article is intended to analyze, by trying to separate the threads from the ball, why and when these tensions are generated. It is our aim to driving towards some clues to mitigate or avoid such tensions. These tensions are in general the responsible of the durability and consistency of the laminates, being the driving force in favor of the main causes of the laminations failure, that is the layers de-laminations.

 

Many lamination structures are based on: 

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Some considerations about the combination of different Materials:

It is a common idea that by combining different materials, it is posible to produce new products with the added advantages of each of their individual elements on it. But, this is not exactly true. Moving forward it is easy to realize that this is a simplistic approach, and there is the need to take into account the “devil details” (we should not forget that the “devil always is in the details”). Problems derived from the details are not detected easily most of the times. These “subtle details” are undervalued, overpassed and sometimes completely forgotten. We usually notice them later, normally when the product is finished.

And what is described above is a common situation in the case of laminates, in which different layers are assembled. That is the case, for example, of semi-flexible photovoltaic modules manufacturing. As it can be seen in the picture below, the different type of materials used to construct them can generate big tensions inside the laminated structure forcing them to bend.

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Something similar also happens to BRG structures. BRG structures show bending, but in their case in less extent than in the PV semi-flexible modules. That is because the structures are thicker and made of stiffer materials like glass and PC.  Regardless of the type of structure, the planarity loss is mainly due to the physical differences that exist between the different material layers.

The tensions that force the structure deformations might come from the individual tensions that each one of the layers may introduce individually, also added to the ones that can be generated during the assembly because of their physical materials differences.

 

The regular lamination deformation types (warpings): Bending and Curling

The most usual type of deformation is the bending of the structure. This type of deformation takes place because of layers integration, as a compendium of individual layers tensions.

But, how does this happen?.

 

If there is good integration between them, the tensions are re-arranged and re-distributed inside the structure. The layer with higher dilatation coefficient (the PC) tends to expand at the time that the more rigid one (the Glass) does it, but not in the same extension. The temperature differences generate internal stress inside the structure in the form of a perpendicular force that makes the structure to get curved, as it is represented in the drawing below

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Why this happens?  Where the sources of tensions come from?

To understand Why the warping happens? and Where the bending comes from?

First we should have a look at the structure and the materials used to build that:

  • the number of layers and dimensions of the stack
  • the type of materials and thickness of each layer, and 
  • the way and order they are arranged in the stack

 

And Secondly have a look to the way they are assembled together. The process conditions and how these conditions might affect to their integration.

  • All layers, when they are heated suffer different morphological and even chemical changes.
  • If there is no bonding between the different layers, each one changes its own dimensions without any constraint. Each layer can move and change freely without many limitations. The changes on each layer depend on themselves, that is, of its particular physical and chemical material characteristics.
  • During the lamination or layers bonding process, all of them start to behave as a monolithic heterogeneous block of materials, that is as a “single” piece.
  • But inside each type of monolithic block, each one of the layers shows its “personality” and wants to have its “own life”. Looking for its freedom, it gets affected and conditioned by all the rest at the “neighborhood”. At the end, and depending of how they have been accommodated during the assembly process, they might fit more or less comfortably inside the block. If they are not completely relaxed, the block might end up with a non-balanced force inside the structure. This force in laminates is normally translated into structure irregularities such as bending, curling or warping.

 

 

The layers and how they are assembled are the causes of lamination tensions

When the structure is submitted to high temperatures then:

  • the different dilatation coefficients between Glass, TPU and PC show up.
  • also all internal tensions of each one of the layers might play an important role.

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How they show up and how they can look like?

If there is no adhesion between the different layers, each one extends differently  when the layers are submitted to temperature.

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If there is good integration between them, forces are re-arranged and re-distributed inside the structure, forcing the structure to suffer from different type of deformations.

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Which are the BRG components’ role and how they contribute to the Bending?

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  • The Glass layer is the more rigid of the three. That one is also the layer with the lower dilatation coefficient of the three. It is consequently the layer that resists better the temperature stress.  It might bring tensions by itself depending on their manufacturing. Due to lamination temperatures is difficult that lamination tensions are added to the glass layer.

 

  • The TPU layer transfers the tensions from the PC to the Glass “helping” the Bending. The higher the strength of the TPU, the better the tension transference. It might bring tensions by itself, depending on their manufacturing process. During lamination some tensions can be added to the TPU layer.

 

  • The PC layer, being the rigid organic layer, is the one that “catalyzes” the mechanical stress inside the structure. This layer is the one that is highly affected by the temperatures. The PC layer, with its higher dilatation coefficient expands as much as possible being sustained by the Glass layer. It might provide tensions by itself to the structure. During lamination some new tensions might be added.

 

Scheme of Laminate Tensions formation during lamination

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How we can help you ?

If you are interested to know how you can control Bending, specially in the case of BRG structures, you can get in contact with us. We can help find answers to some of your questions. We can assist you answering questions as:

      • How the different type of materials behave during the lamination process ?
      • How different they are and behave? Why?
      • How to minimize their differences?
      • How the TPU can help you match all these differences?
      • How to improve their adhesion?
      • How to reduce structures tensions?
      • How to minimize warping?
      • How to construct stronger and more durable structures?

Let’s work together to reach excellence 🙂