Transparent acoustical and mechanical barrier

Details Transparent acoustical and mechanical barrier Transparent acoustical and mechanical barrier

1999-06-09

2002-08-13

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S424600, C428S688000

Reexamination Certificate

active

06432522

ABSTRACT:

BACKGROUND OF THE INVENTION
Many polymeric interlayer materials and lamination designs have been described for use in automotive and architectural glazing applications. Industry, government and customer specifications for safety, impact resistance, ultraviolet and infrared light blockage, moisture resistance, haze or optical clarity, sound transmission, weight and thermal transmission direct the selection of materials and designs for particular glazing products. In general, manufacturers require lighter weight, thinner glazing products for automotive assembly than for architectural uses.
Impact resistance and controlled patterns of glass shattering are specified safety parameters for automotive glazing products. To meet these parameters, automotive glazing products are generally constructed of a multi-layer laminate of a glass sandwich containing a polymeric interlayer film. Many automobile-makers require security or anti-theft properties in glazing products in addition to mandatory safety properties. For deterring unauthorized entry into a vehicle, to lessen the likelihood of a person being thrown from a vehicle during an accident and for acceptable security functionality, the glazing products must possess high penetration resistance and high rigidity after glass breakage.
Among the polymeric interlayer materials described as useful in security and safety glass laminations are the high modulus “ionomeric resin” materials used as a film interlayer between two rigid transparent sheets in the manner described in U.S. Pat. No. 4,668,574. In general, an adhesion promoter, e.g., a silane primer, is needed to laminate the ionomeric resin to glass, and the ionomeric resin is preferably cross-linked, e.g., with a diamine, to increase its effective use temperature, to improve glazing clarity and to reduce haze, as described in U.S. Pat. Nos. 4,619,973 and 4,663,228. The mechanical barrier properties of the ionomeric resin laminates are superb. They are used in bullet-proof glazing and other very demanding security applications. As described in U.S. Pat. No. 5,763,062, the superior transparency of the ionomeric resins, particularly newer resins having a higher acid content (e.g., at least 17 wt %), or those resins modified with diamine cross-linking, permits use at a relatively large film thickness, on the order of 1-4 mm, in optically transparent laminates.
While useful as security barriers, the ionomeric resin films and laminates made with such films are poor acoustical barriers.
Ethylene vinyl acetate resin film (EVA film) has been used in optical laminates, both as the sole polymeric film and as a component of a multi-laminate interlayer, but it lacks mechanical strength. Many forms of EVA film have use temperature limitations or poor light stability characteristics, making EVA films fairly undesirable components of glazing products. Cross-linking with peroxide improves temperature stability, but may cause light instability, e.g., in solar cells, in the manner described in U.S. Pat. No. 5,478,402. Impact resistance problems in laminated glass made with EVA film are noted in U.S. Pat. No. 5,759,698.
Glass laminates containing a multi-layer film interlayer made with peroxide cross-linked EVA film are reported in U.S. Pat. No. 4,600,627. These EVA films are used at a thickness of about 0.2-0.4 mm, with a core polymer layer of organic resin film at a thickness of about 50 microns, in a glass laminate of at least 6 mm in total thickness. The U.S. Pat. No. 4,600,627 makes no mention of acoustical properties of the multi-layer laminates, and as described in the patent, the multi-layer resin film glazings would be ineffective security barriers.
Polyvinyl butyral resin interlayer film (PVB film) has been an industry standard for many years in automotive glazing products, particularly in windshield glazing. PVB film offers the benefits of transparency and good adhesion to glass. Glass laminates of PVB film have appropriate glass shattering properties and good mechanical strength. PVB resin also is compatible with additives, such as UV light absorbers and plasticizers. However, the need to moisture-seal PVB laminates contributes significant costs to laminates made with PVB film. When used in a sealed laminate, as in windshield constructions, the tendency of the PVB film to absorb moisture is not a problem. For other vehicular glazings, such as side lights (windows in side doors having no perimeter gasket or seal), conventional PVB film absorbs water too readily to permit acceptable use life. More complex and costly moisture resistant PVB resin formulations, such as those described in U.S. Pat. No. 4,952,457, have been developed for unsealed glazing.
When PVB film is used as the sole interlayer film, glazing laminates do not deliver desirable security performance because they have insufficient rigidity after glass breakage due to the low stiffness of the PVB interlayer. An opening can be made too easily between the glazing and the surrounding body of the vehicle. Neither monolithic glass panes, nor PVB film interlayer laminates, provide an adequate security barrier.
Many different types of polyurethane films have been used in automotive glazings. Some polyurethane films are similar to PVB films in their mechanical properties. In WO 98/50228, certain rigid thermoplastic polyurethanes having a Young's modulus of about 2,000 MPa are suggested interlayer films for glazings characterized by a high intrusion resistance. Many have slightly better acoustical barrier attributes than PVB films, but fail to provide an adequate security barrier. Furthermore, as described in U.S. Pat. No. 5,368,917 the polyurethane films tested yielded inadequate acoustical insulating barriers for automotive glazing products.
Acoustical barrier requirements for glazing products are defined in U.S. Pat. No. 5,368,917 for the range of frequencies detectable by the human ear, i.e., about 400-15,000 Hertz, with the most critical range falling between 500 to 10,000 Hertz. The standards in this patent are based on the performance of either a 10 mm or a 5 mm thick monolithic glass pane.
Thus, an acoustical barrier glazing has been traditionally understood to be a barrier providing a level of acoustic comfort within the vehicle or building comparable to the level of acoustic comfort provided by a conventional monolithic glass barrier for a given intensity and quality of environmental noise.
Glass (e.g., soda-lime-silicate mineral glass) provides a good acoustical barrier and, over a critical frequency range of about 800 to 10,000 Hz, is most effective at a total glazing thickness of at least about 10 mm. Effective glass glazing may be monolithic, or it may be a double glass pane construction having an air space between the panes. In automotive glazing products, a maximum thickness of about 5 mm is desired. Automotive side lights have been made with double glass panes separated by an air space to achieve superior acoustical barrier properties, but such a construction is generally unacceptable in automotive glazing due to mechanical barrier (safety and security) considerations.
Thin glass sheets have been laminated with specified “acoustic resins” to make an acoustical barrier laminate at a maximum total thickness of 5 mm. An “acoustic resin” which is a copolymer of 60-98.5 wt % vinyl chloride, 1-10 wt % glycydyl methacrylate and 0.5-10 wt % ethylene blended with 10-40 wt % plasticizer, and a method for measuring sound transmission in glass laminates containing such modified polyvinyl chloride (PVC) resins, are described in U.S. Pat. Nos. 5,773,102 and 5,368,917. Both vehicular and architectural product applications are described. The acoustic resin is laminated between two transparent, rigid sheets made of glass or polymer. The resultant laminate is characterized by acoustical transmission losses which deviate from a 5 mm tempered glass standard by a maximum of 5 decibels in a frequency range from 800 to 2,000 Hz and a maximum of 3 dB at audible frequencies above 2,000 Hz.
The U.S. Pat. No. 5,773,102 discloses a multi-layer fi

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