Acoustically active plastisols

Details Acoustically active plastisols Acoustically active plastisols

1995-12-07

1998-04-21

Cooney, Jr., John M.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

427180, 427195, 427421, 428461, 428500, 521 75, 521146, 521149, C08J 930

Patent

active

057418241

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to the use of sprayable plastisol compositions for soundproofing.
2. Discussion of the Related Art
Nowadays, very thin metal plates are almost exclusively used in the production of vehicles, machines and appliances. Under the effect of mechanically moving parts or running engines, these thin plates are inevitably made to vibrate, generating sound in the process. Another cause of troublesome noise, particularly in travelling motor vehicles, are the particles (stains and chippings, sand, water) which are thrown up by the wheels against the wheel arches and the underbody of the vehicle. This noise is particularly troublesome and unpleasant because it contains a large percentage of relatively high-frequency sound components.
Numerous proposals have been put forward with a view to reducing both types of sound. Accordingly, to reduce sound emission and mechanical vibration, the plates used in particular in automotive construction and in the manufacture of domestic appliances are provided with soundproofing coatings, so-called antivibration coatings.
In the conventional process, mixtures of fillers of high specific gravity and bitumen are extruded to sheets from which the corresponding shapes are then stamped or cut out. They are then bonded to the metal parts in question and may have to be adapted to the shape thereof by heating. Although these bitumen sheets are extremely brittle and tend to flake off the plate, particularly at low temperatures, they are still commonly used by virtue of their low price. Even the frequently proposed additions of elastomers produce only a slight improvement which is inadequate for many applications. In addition, the preformed bitumen shapes are impossible to apply to intricately shaped or awkwardly situated parts of machines or motor vehicles, for example the inner surfaces of the hollow interiors of motor vehicle doors. Another disadvantage is that, in many cases, several different shapes are required for a single vehicle or appliance, so that expensive stock-keeping is necessary.
Accordingly, there has been no shortage of attempts. to eliminate the disadvantages of bitumen sheets by using other polymer systems. For example, filler-containing aqueous polymer dispersions of polyvinyl acetate or ethylene/vinyl acetate copolymers have been developed for spraying onto the metal parts in the necessary layer thickness. Unfortunately, these systems are unsuitable for industrial use for high-volume production because the water present in the layer applied by spraying cannot be removed quickly enough, particularly from relatively thick layers.
The soundproofing properties of polymer coatings are at their best in the vicinity of the glass transition temperature of the polymer system because, at temperatures in this range, the mechanical vibration energy is converted into heat through molecular flow processes by virtue of the viscoelasticity of the polymer. Conventional sprayable coating materials based on PVC plastisols, which are widely used for example for undersealing in the automotive industry, have no significant soundproofing effect in the working temperature range from -20.degree. C. to +60.degree. C. because the maximum glass transition temperature is in the range from about -20.degree. C. to -50.degree. C., depending on the plasticizer content.
Accordingly, attempts have been made to modify these conventional PVC plastisols in such a way that they would have better soundproofing properties in the working temperature range from -20.degree. C. to +60.degree. C. Thus, DE-A-35 14 753 describes coatings which contain polyunsaturated compounds, for example diacrylates or triacrylates, peroxide crosslinkers and inorganic fillers in typical PVC plastisols. However, in their cured state, plastisols such as these are as hard as glass and brittle so that they are unsuitable for use in automobile construction because they lack flexibility, particularly at low temperatures. In addition, these formulations have a ver

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