Functional Laminated Glazing of Passenger Vehicle by Advanced PVB Technology
- Multi-Layer Technology for Noise Reduction and More -

Terry Yoshioka, Sekisui Chemical Co., Ltd., Osaka, JAPAN

 
  * Introduction
  * Multi-Layer Technology
  * Sound Reduction
  * Limit of Mono-Layer
  * Multi-Layer Solution
  * Performance Review
Engine Noise
  * Wind Noise
  * Additional Feature
  * Summary
  * About SEKISUI

Introduction

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  Looking at the history of automotive glazing, laminated glass with a PVB interlayer was first introduced in the United States in 1935 and regulated by law in 1938. After that in 1964, HPR (high penetration resistance) laminate was developed to further pursue passenger safety, and now it is used in many countries as a standard. Recently the functions required for automotive glazing are becoming more diverse to meet customer needs such as comfort, security, and environmental issues in addition to safety. Naturally, PVB interlayer for laminated glass is being discussed more as a practical way of adding new functions on the automotive glass system. As a PVB supplier, Sekisui has long been contributing to the automotive glass industry by continually developing new products. The company has a multi-layer extrusion methodology that is one of its core technologies. It is by combining this technology and the gFunction-by-layerh concept (stack of different functional layers) that more benefits are being added to a normal interlayer. These high performance interlayer films that meet various market needs will be very promising in the future.

Multi-Layer Technology

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One example of a multi-layer PVB interlayer is shaded film (film with shade band color). Shaded film has long been produced by a co-extrusion method. In the past, it consisted of 2 layers; one with clear resin and the other with colored. Currently it has 3 layers; 2 outside layers with clear resin and one in the middle with colored resin (Figure 1). In such case, surface quality remains consistent at any location on either sides.

Figure 1 Multi-layer construction of shaded interlayer film

Figure 2 Multi-layer construction of S-LECR Acoustic Film
  Another example of multi-layer production is a PVB interlayer for noise reduction, S-LECR Acoustic Film (SAF). In this case, the whole film consists of 3 layers, having 2 outside layers of normal PVB with a special inside layer (Figure 2). This design significantly enhances acoustic attenuation performance because the acoustic PVB interlayer reduces much more sound transmission than a normal PVB interlayer does. Industry leaders in Architectural and Automotive markets are now adopting this special interlayer film. This paper will present how the multi-layer technology of Sekisui contributes to highly functional PVB film.

Sound Reduction

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  Reducing the noise level of a vehicle cabin is an important factor for passenger comfort. It is also important for safety concerns because noise is believed to reduce driver efficiency over time. Sound transmission loss through a glazing system can be induced by mass, stiffness, and damping. In reality, there is a limit for increasing the mass, or the thickness of glass, and also for controlling stiffness due to the limit of glass design. To increase damping effectively and obtain good sound attenuation, laminated glass is used with a viscoelastic plastic interlayer that changes vibration energy into heat energy. In the architectural area, for example, laminated glass is commonly installed in the buildings near airport to minimize noise pollution.
  Sound arises from vibrating molecules. The human ear can hear sounds in the frequency range from 20 Hz to 20,000 Hz, and it is especially sensitive to sounds in the range of 1,000 Hz to 4,000 Hz. The degree of sound attenuation by glass can be measured by Sound Transmission Loss (STL), and it depends on frequency as shown in Figure 3. Each glass type and thickness has a critical frequency, or coincidence dip, at which its sound reduction value is low. At this frequency, the vibration of the glass matches the sound vibration very closely, and it is very easy for sound to pass without dampening. In case of a 4mm thick single glass plate, the frequency range for it's coincidence dip is around 3,000 Hz.
Figure 3 Sound Transmission Loss of PVB laminate and glass
  Since the range of coincidence dip overlaps what is also the most sensitive range to the human ear, improving the coincidence dip is a key demanded for sound attenuation with glass. Compared with a monolithic glass plate, laminated glass of the same thickness has better acoustic performance to some extent. The coincidence dip still remains however, and therefore normal PVB is not enough if better acoustical performance is required at an ordinary cabin temperature (10 to 25 degree C). This is because elasticity of PVB should be low for better sound attenuation performance and the elasticity of normal PVB at an ordinary cabin temperature is not so low. To increase the acoustic performance of laminated glass, Sekisui designed and examined the prototype of the special PVB interlayer with lower elasticity. Also in the current automotive glass industry, acoustic PVB interlayer is being evaluated and is becoming very appealing to some vehicle manufacturers.

Limit of Mono-Layer

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  This special acoustic interlayer is designed to have a lower elasticity than normal interlayer film. Therefore, it has better sound attenuation performance due to higher damping. During development at Sekisui however, it was found that this acoustic interlayer which was mono-layer (a single layer of special PVB plastic film)was inferior to normal PVB interlayer in terms of mechanical strength and handling due to low elasticity or softness at an ambient temperature range. That is;
 
1. Laminated glass with a monolayer acoustic interlayer has low penetration resistance. A thicker interlayer is needed to pass safety and security codes.
2. Monolayer Interlayer is sticky and difficult to handle during laminating process.
3. Due to the difference of elasticity when the single layer film is heated, prepress conditions may have to be adjusted.
  With the difficulties in real applications to automotive acoustic glazing, maximum sound insulation performance in a single layer interlayer film could never be achieved. The limits of monolayer film became known at this point of development. Through this investigation, researchers at Sekisui found that maximum acoustic performance could only be achieved through a unique 3-layer construction technology.

Multi-Layer Solution

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  In order to overcome the shortcomings of a monolayer film, Sekisui utilized one of its core technologies, multi-layer extrusion. By using a gFunction-by-Layerh concept, a 3-layer construction was adopted. This new make-up has a low elasticity special resin layer as its core for maximum acoustic performance at ordinary temperatures; and normal PVB resin as outer layers for mechanical strength and handling ease like normal PVB film (Figure 2). This patented multi-layer solution gave a new way of achieving higher acoustical performance in automotive glazing. Now vehicle designers are able to choose the best acoustic performance in glazing systems without any risk of safety problems. This new level of noise reduction cannot be achieved by a monolayer acoustic film. In addition the special acoustic PVB layer in the middle can be independently designed, so that sound attenuation performance and its temperature dependency can be controlled without sacrificing the general properties of PVB interlayer. Thus, a whole new acoustic PVB interlayer was born, that gives the best sound-attenuating automotive glass.

Performance Review
Engine Noise

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  Engine noise is the vibration of engine units when the vehicle is running, especially when accelerating. This vibration is transmitted through many parts of the vehicle, including the windshield. As a result, the windshield creates a solid sound that people feel as noise (often called a Booming Effect). This noise includes vibrations that occur mainly at a low frequency range of 100 Hz to 500 Hz.
  Sound (vibration) attenuation of glass at a low frequency range is quantified by the loss factor. The bigger the loss factor, the higher the sound insulation performance. Loss factor is obtained by mechanical impedance method (MIM) in which a continuous subtle vibration is applied on the center of a laminated glass test piece. MIM can measure vibrations at a low frequency range, around 100 Hz to 300 Hz (often most associated with engine noise and the Booming Effect). The Loss Factor from MIM measurement is a good way to evaluate noise from vibration and it can be related to the Sound Transmission Loss (STL) of a glazing system.
Figure 4a Loss factor of acoustic and normal PVB laminates by frequency
Figure 4b Loss factor of acoustic and normal PVB laminates by temperature
  Shown in Figure 4a and 4b are the loss factors of normal PVB laminated glass, a monolayer acoustic film laminate, and a multi-layer acoustic film laminate. Based on these results, the multi-layer acoustic interlayer has vibration reduction performance superior to both normal and monolayer acoustic interlayer at any frequency and also at any temperature within a normal cabin range (10 to 25 degree C). In winter, the interlayer temperature is estimated to be around 10 degrees C (0 C outside, 20 C inside), when multi-layer SAF demonstrates superior sound-attenuating performance. Monolayer acoustic PVB however, has much less performance than multi-layer SAF, and it can no longer be called acoustic PVB. In summer, the interlayer temperature can go up to around 28 C (35 C outside, 20 C inside) in a very hot climate area. Even in such a case, multi-layer SAF has the best performance. By this excellent vibration reduction performance, multi-layer acoustic interlayer effectively reduces engine noise from the windshield.

Wind Noise

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  Wind noise comes from air blowing across the car body and is transmitted through glass parts, which then increase the interior noise level. This noise mainly includes high frequency sounds around 1,000 Hz to 5,000 Hz. To evaluate how much sound (vibration) is attenuated while passing through the glass, Sound Transmission Loss of each glass construction is shown in Figure 5. Multi-layer acoustic PVB interlayer shows the highest STL value over monolayer acoustic PVB and normal PVB interlayer, especially in the coincidence dip range of 1,000 to 4,000 Hz. Therefore, high frequency sounds like wind noise from outside is effectively blocked by a multi-layer acoustic PVB interlayer.
 
Figure 5 Sound transmission loss of different laminated glasses
As discussed above, multi-layer extrusion technology made it possible to choose proper viscoelastic interlayer film and maximize sound-attenuating performance of the automotive glazing system, while retaining safety and security performance. This special acoustic PVB interlayer, S-LECR Acoustic Film, has been adopted by several automobile manufacturers not only for high-end luxury vehicles but also for mid-class passenger cars. It achieves a quieter interior. Because of these acoustic properties, the manufactures can reduce the weight of the vehicle by using thinner (normally acoustically inferior) glass, which in turn results in better fuel efficiency.

Additional Feature

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  Multi-layer extrusion technology is not limited to only our shaded band film or this new acoustic product. For example, a sound acoustic PVB and a solar control PVB can be combined. As consumers' requirements such as safety, security, and comfort, become much more diverse in the future, multi-layer PVB will surely be a key technology to meet such demand.
  Sekisui also has an IR cut-off PVB interlayer as one of its high performance interlayer films. Since its introduction to the market, the automotive industry has shown great interest in this special PVB film because of its solar control performance and electromagnetic transparency. Since 2002, some automobile manufacturers have started using this film in Europe and Japan. It is expected to generate worldwide interests in applying future automobile models. This special interlayer, S-LECR Solar Control Film (SCF), was developed by nano-dispersion technology, and has the following features:
 
1. Low solar transmission with high visible light transmission. Contributes to cooler interior and higher fuel efficiency.
2. Reduces human skin sensation from direct sunlight
3. Allows the transmissions of electromagnetic wave.
  When the solar control function and the acoustic function are combined in a monolayer PVB film, compatibility of the IR cut-off materials with the special acoustic PVB resin has to be carefully examined. However, with multi-layer technology, it is relatively easy to combine these two by having acoustic PVB layer sandwiched with two solar control PVBs outside.

Summary

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  As consumers become more concerned about safety, security, comfort, and environment, more functions are requested from automotive glazing. Considering the possible future growth of laminated side and rear glass, the role of high performance interlayer is increasingly more important. Sekisui is committed to contributing to the automotive glass industry with its high performance PVB interlayer families. Multi-layer interlayer film is one of the company's core technologies and it opens opportunities for further development to meet consumers' ever-increasing demand. Unlike conventional technologies, S-LECR Acoustic Film is designed to have maximum sound-attenuating performance by multi-layer technology and gFunction-by-Layerh concept, which offers excellent noise reduction solution,.

About SEKISUI

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  For over 50 years, Sekisui Chemical Co., Ltd. has made a significant contribution to improve our customers' quality of life and to develop infrastructure of residential area by supplying various range of high quality plastic products including S-LECR Film PVB interlayer. Sekisui S-LECR Film has been used in automotive and architectural laminated glass industries for more than 40 years. S-LECR Acoustic Film and Solar Control Film are among the company's high performance PVB interlayer products. More information about new technologies can be found at http://www.s-lecfilm.com.
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