This invention pertains to asphaltic sheet sound deadener for use as a vibration damping medium, which can be bonded in place without excessive sag or flow by subjecting the material to 250.degree.-400.degree. F. The main use of this material is in the automotive field, but may be used in other areas such as the appliance and furniture industries. The melt flow properties of the deadener are controlled by the use of ground mica.

BACKGROUND OF THE INVENTION 
For the last few years both domestic and foreign automobile manufacturers 
have been using heat bondable sheet sound deadeners which are placed in 
the car body prior to the final paint oven. In the oven the sound deadener 
sheet softens, conforms to the contours of the body and bonds without 
excessive sag or flow from the sloped or vertical areas. This type of 
material is also being used in areas where high inservice temperatures 
(190-400.degree. F.) would result in flowing of standard asphaltic 
deadeners. 
The majority of the heat bondable sound deadener sheets used domestically 
contain asbestos to control the melt flow properties of the asphalt at 
elevated temperatures, however, asbestos being a known carcinogen requires 
special handling thereby complicating the manufacture of the product. 
A typical asbestos-containing formula would be: 
5% 7R Asbestos 
67% Ground Limestone Filler 
28% Asphalt 
Other heat bondable sound deadeners which are available are based on 
thermoplastic resins such as butadiene-styrene, coumarone-indene, 
styrene-indene, such as disclosed in British Pat. No. 1,039,711 and 
Canadian Pat. Nos. 721.237 and 784.029. These compositions, however, tend 
to be more expensive and more difficult to manufacture than the 
asbestos-containing sound deadening material. 
The main object of the invention is to provide a heat bondable sound 
deadener sheet which is asbestos-free, inexpensive and can be manufactured 
using the same equipment as the present asbestos compositions. 
SUMMARY OF THE INVENTION 
A bituminous sound deadening material which can be bonded in place without 
excessive sag or flow by subjecting it to temperatures between 
250.degree.-400.degree. F. The melt flow properties of the bituminous 
material are controlled by ground mica mixed into the bituminous material. 
The bituminous material need not be, but may be covered on one side or 
both sides with a release paper or preferably a thermoplastic film such as 
polyethylene to facilitate stacking and shipping of the material by 
eliminating the possibility of sticking.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The sound-deadening material includes an inner layer 1 of sound-deadening 
material capable of being softened by heat and melt flowing into 
conformity with a metal panel. A preferred inner layer composition 
comprises ground mica, which is ideally suited to this application due to 
its large surface area per unit size, ground lime stone filler and asphalt 
in the following quantities, 20%, 50% and 30%, respectively. 
Wherein the mica has a screen grading of: 
0-5% retained on U.S. #60 mesh 
5-15% retained on U.S. #80 mesh 
10-20% retained on U.S. #100 mesh 
30-45% retained on U.S. #200 mesh 
25-40% passing a U.S. #200 mesh 
The ground limestone has a screen grading of: 
2% max. retained on U.S. #60 mesh 
20% max. retained on U.S. #100 mesh 
5-50% retained on U.S. #200 mesh 
95% max. passing a U.S. #200 mesh 
The asphalt has: 
Softening Point (R&B)--180.degree.-195.degree. F. (ASTM D36-70) 
Penetration @77.degree. F.--50-65 (ASTM D5-73) 
Without deviating from the spirit of this invention the formula of this 
composition could be varied as follows, depending on the grades of 
material used: 
(by wt.) Mica 5-50% 
(by wt.) Inert Filler 0-80% 
(by wt.) Asphalt 20-80% 
Grades of ground mica or mica schist other than #160 could be used, but 
would require adjustment of the formula within the above limits. The #160 
grade was found to be the most effective. 
Fillers other than limestone could be used such as ground stone dust, sand, 
clay, silt, chopped fiber glass, etc. Material of a screen grading other 
than that given in the limestone example could be used, but to maintain a 
smooth appearance of the product the majority of the material should pass 
a U.S. #60 mesh sieve. 
Asphalt within a softening point of 85.degree.-260.degree. F. and 
penetration @77.degree. F. of 5-300 could be used, but to give the optimum 
product an asphalt with a softening point of 180.degree.-195.degree. F. 
and penetration @77.degree. F. of 50-65 has been found to be the most 
suitable. 
The inner layer 1 carries on at least one side, a sheet of polyethylene 2, 
preferably resistant to hydrocarbon solvents and non-tacky so that it does 
not readily adhere at normal atmospheric temperatures to other surfaces. 
The polyethylene, however, adheres to the inner layer 1. 
When a film 2 of polyethylene or other film-forming resinous material is 
employed to cover one or two faces of the sound-deadening inner layer 1 it 
is preferably applied to the sound-deadening sheet as a preformed film or 
sheet which is laid down on a face of the sound-deadening layer and 
secured to the sheet by passing the assembly between rollers which press 
the sheet and layer gently together. Such film may, however, be applied in 
suitable instances by spray or other coating technique. 
In carrying out a procedure illustrative of the invention in its method 
aspects, a metal panel 3 of a car body is covered by bituminous sheet 4 to 
reduce its tendency to vibrate, by laying sheet material 4 with either 
side down, as shown in broken lines in FIG. 2 on an upwardly facing 
surface of the metal panel 3. The metal panel 3 and sheet material 4 are 
heated in an oven wherein the sheet material 4 melt flows into close 
conformity with the surface of the metal panel 3 as shown in solid lines 
in FIG. 2. If air is trapped between the sheet material 4 and the metal 
panel 3 it is allowed to escape through optional holes 5 in the sheet 4. 
At the temperature reached in automobile paint ovens the sheet 2 of 
polyethylene composition allows the inner layer 1 to flow onto the panel 3 
through the polyethylene sheet 2 which has melted and both the melted 
polyethylene sheet 2 and inner layer 1 fuses with the surface of the metal 
panel 3, whereupon cooling, the sheet material 4 is firmly bonded with 
uniform thickness to the surface of the metal panel 3. 
The minimum fusion conditions to give a good bond to clean or painted metal 
is fifteen minutes in an air convection oven at 250.degree. F. At higher 
temperatures a good bond is obtainable more rapidly. Fusion temperatures 
of up to 400.degree. F. are satisfactory, but above this figure 
degradation of the sound deadening compound can occur. 
In applications where an irregular metal surface is used the fusion 
conditions have to be selected to enable the sound deadening material to 
droop and make 100% contact. In these cases temperatures in excess of 
250.degree. F. may be necessary. 
The illustrative material when covered on both sides with a sheet of 
polyethylene 3, can be provided as pieces of suitable shape and size and 
stacked for storage and transport without any additional interleaved 
release paper, and the pieces can readily be separated one from another 
when they come to be used in a car factory. 
When sound-deadening material in accordance with the invention comprises a 
perforate sheet the holes in the perforate sheet are preferably 1/16" to 
1/8" in diameter at centers 1/4" to 1" apart (the larger the hole the 
larger the spacing), but may, if desired, be larger and more widely 
spaced. When the sound-deadening material is to have a covering of 
polyethylene sheet 3 and is to comprise a perforate sheet, the sheet is 
preferably perforated before, but may be perforated after laminating with 
polyethylene sheet. The polyethylene sheet 3 may, if desired, be provided 
with narrow, shallow, intersecting grooves (not shown) so that, when that 
side is laid against a metal panel, air may escape along the grooves. The 
polyethylene sheet 3 is usually 0.0005 to 0.0020 inches thick with an 
overall weight of sheet 4 being 0.5 lbs. to 2 lbs. per sq. ft. 
In carrying out the illustrative method of treating metal panels 3 of car 
bodies in a car factory, the pieces of sound-deadening material 4 are 
taken one by one and laid on upwardly-facing surfaces of metal panels 
passing along a conveyor to an oven heated to 250.degree.-400.degree. F. 
On emerging from the oven, the pieces of material 4 are found to conform to 
the contour of the panels 3 and to be firmly bonded in place with little 
or no evidence of degradation.