WO1998013540A1

WO1998013540A1 - Automotive acoustical insulator

Info

Publication number: WO1998013540A1
Application number: PCT/US1997/017291
Authority: WO
Inventors: David J. Keough; Kirit Patel
Original assignee: Wwj, Llc
Priority date: 1996-09-27
Filing date: 1997-09-26
Publication date: 1998-04-02
Also published as: AU4652597A

Abstract

An acoustical insulator for use in a vehicle body is provided, comprising a flexible, non-woven fiber material, the material comprising about 60 % to about 90 % by weight of a natural fiber and about 10 % to about 40 % of a synthetic binder fiber. The acoustical insulator material has a density of less than about 1.5 pounds per cubic foot and recovers at least about 80 % of its precompression volume within one minute after a compressive force is removed. Preferably, the natural fiber component of the material is cotton. Optionally, the acoustical insulator material may be encapsulated in plastic. A method for acoustically insulating a vehicle body is also provided, the method comprising the steps of providing a flexible, non-woven fiber material, the material comprising about 60 % to about 90 % by weight of a natural fiber, and about 10 % to about 40 % of a synthetic binder fiber; and installing the material into a void of the vehicle body. The method may further comprise the steps of compressing the material to less than its original volume prior to installing the material and releasing the material from compression following the installing step, allowing the material to recover and fill the void. The non-woven material has a surprisingly good ability to insulate against sound over a broad range of frequencies. By compressing the material and installing it into a vehicle body void and allowing it to recover its initial volume, the insulator fills the body with a light-weight, effective acoustical insulator.

Description

AUTOMOTIVE ACOUSTICAL INSULATOR

TECHNICAL FIELD

This invention relates generally to an acoustical insulator, and more particularly

concerns an acoustical insulator formed from a low density, flexible sound absorbing batt of

non-woven fibers for use in a vehicle body.

BACKGROUND ART

During the construction of a vehicle body numerous irregularly-shaped voids and

other spaces are created. For example, in a car there are substantially hollow structural pillars behind and in front of the doors and, in a two-door car, between the doors. Spaces

are also created between the door panels, in the wheelhouses, cowl sides, roof rails and

quarter trim panels. Acoustical insulators are used to fill these voids and spaces in the

body in order to absorb low and high frequency sounds. Therefore, engine and wheel noise and other sounds are significantly attenuated before they reach the passenger compartment, thereby providing a quiet interior environment for the rider.

The ability of an acoustical insulator to absorb sound is attributed to the properties

of the material comprising the insulator as well as the method of making the insulator. Generally, acoustical insulation efficiency increases with mass. Separation within the material without undue increase of mass (i.e., decreased density) further improves acoustical

efficiencies. Also, acoustical insulator materials increase the reduction of sound

transmission by dampening sheet metals and/or restricting or absorbing sound waves. In addition to having good sound absorption efficiencies, automotive acoustical insulators should also be as light as possible so as not to substantially contribute to the overall weight of the vehicle. They should also completely fill the voids and spaces in the

vehicle body. Any gaps between the insulator and the automobile body or neighboring

insulator material reduces sound absorption. To improve fit and reduce gaps,

manufacturers must custom-make, or the user must cut, the insulator to fit the voids and

spaces. Of course, this increases the cost and time required to insulate the vehicle. An

alternative is to make acoustical insulators from compressible material and force the material into the voids and spaces. When the insulator returns to its original volume after

compression it fills the voids.

Automotive acoustical insulators are made from various types of sound absorbing

materials. One such material is polyurethane foam which has been molded or die cut to conform to the vehicle body. Alternatively, the liquid components of the urethane foam

can be poured directly into the automobile body and hardened in place. However, foam

acoustical insulators are expensive and the latter process can produce toxic gasses and

therefore require both air ventilation and protective clothing. Occasionally, the foam will fail to completely fill the void and the defective product will need to be reworked.

Non-woven fibrous materials also find use as automotive acoustical insulators.

The fiber materials may include cellulose, glass, polyethylene and polypropylene. The fibers are mechanically or chemically bound to form a blanket or batt often using conventional textile processing techniques. The drawbacks inherent in many of the

conventional non-woven products are that they are typically heavy, dense, or expensive materials and thus add to the weight or cost of the automobile. Some products are not

flexible enough to conform to the abnormal spaces or voids into which they are installed. Some are also harder to install because they are difficult to compress to accommodate small openings and often lack the ability to recover well from compression when installed

into a void. Moreover, some of the materials, particularly fiberglass, present

environmental and handling concerns.

For the foregoing reasons, there is a need for an improved, low density acoustical

insulator for use in the automotive industry. Ideally the insulator should show good

absorption of low and high frequency sounds as well as being a flexible structure which

conforms to abnormal voids and spaces in vehicle bodies. The insulator should recover quickly from compression, be easy to install quickly in an assembly line and be environmentally safe and economical to produce.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to provide a new acoustical

insulator, for use in a vehicle body, having one or more of the novel features of this

invention as hereinafter shown and described.

Further, it is an object of the present invention to provide a new method for installing an acoustical insulator in a vehicle body having one or more of the novel

features of this invention as hereinafter shown and described. Another object of the present invention is to provide an acoustical insulator for use

in the voids and other spaces of a vehicle wherein the insulator exhibits a high degree of

sound absorption over a broad range of frequencies.

A further object of the present invention is to provide an improved acoustical insulator which conforms to the voids and other spaces in a vehicle body.

Another object of the present invention is to provide an acoustical insulator which

is easy to make and simple and convenient to install.

A related object of the present invention is to provide an environmentally safe and recyclable acoustical insulator.

The present invention is directed to a device that meets these objectives and

satisfies the needs in the art. An acoustical insulator for use in a vehicle body having features of the present invention comprises a flexible, non-woven fiber material, the material comprising about 60% to about 90% by weight of a natural fiber and about 10% to about 40% of a synthetic fiber. The acoustical insulator material has a density of less

than about 1.5 pounds per cubic foot and recovers at least about 80% of its precompression volume after a compressive force is removed. In a preferred embodiment of the insulator, the natural fiber is cotton. Optionally, the acoustical insulator material may be

encapsulated.

Further in accordance with the present invention, a method for acoustically

insulating a vehicle body is provided, the method comprising the steps of providing a

flexible, non-woven fiber material, the material comprising about 60% to about 90% by

weight of a natural fiber, and about 10 % to about 40% of a synthetic fiber; and installing the material into a void of the vehicle body. The method may further comprise the steps of compressing the material to less than its precompression volume prior to installing the

material and releasing the material from compression following the installing step

allowing the material to decompress and fill the void.

It has thus been discovered that the combination of certain ratios of natural and

other fibers produces a high-loft, non-woven batt that has a surprisingly good ability to insulate against sound. The material is of low density, flexible and quickly returns to it

original volume following compression which makes it very effective as an automotive acoustical insulator.

Using the low density acoustical insulator of the present invention reduces the weight of the vehicle and offers a significant cost savings in materials. By compressing

the material and installing it into a body void and allowing it to recover its initial volume, the insulator fills the body with a light-weight, effective acoustical insulator. The

acoustical insulator expands and conforms its shape into areas into which it has been

installed. Moreover, the insulator lends itself to economical and efficient modes of

production and installation.

BRIEF DESCRIPTION OF DRAWINGS

For a more complete understanding of this invention reference should now be had to the accompanying drawings and the embodiments described below.

Fig. 1 shows the results of measurement of the acoustical absorption coefficient for a

2-inch thick flexible, non-woven batt having features of the present invention; and Figs. 2 and 3 show the results of measurement of the acoustical absorption coefficient

for a 5-inch thick flexible, non-woven batt having features of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with the present invention, an acoustical insulator is provided

generally comprising a natural fiber and formed as a flexible, non-woven batt. The batt is a predetermined thickness and is characteristically of low density and recovers quickly

following compression. Optionally, the batt may be encapsulated to protect the batt from

the environment. The present invention further provides a method of using the batt as an

automotive acoustical insulator by installing the insulator in the voids and other spaces of a automobile body.

The non-woven batt for use in the present invention is available from Greenwood

Cotton Insulation Products, Inc. of Greenwood, South Carolina, U.S.A. While the process

used for making the batt is proprietary, the process is similar to that described in U.S. Patent No. 5,057,168, granted on October 15, 1991, to Paul M. Muncrief, and owned by

Greenwood, the contents of which are hereby incorporated by reference. However, the

material used for the acoustical insulator of the present invention is made to different thicknesses and densities than the product described in the ' 168 patent. The method for

making the batt generally comprises the steps of forming a batt from insulative fibers.

Binder fibers are blended with the insulative fibers or added to a web of insulative fibers

during the batt forming step. Alternatively," stilt" fibers can be spread between lapped layers which function to spread apart and maintain a space between adjacent lapped web layers comprising the batt. Subsequently, the batt is heated to a temperature sufficient to cause the

binder fibers to soften and adhere to the insulative fibers to connect insulative fibers to one

another. The batt is cooled to harden the softened binder fibers, thus forming the batt

structure.

The predominant fibers in the batt are preferably natural fibers and preferably cotton.

However, wool, flax, jute, mohair, silk, ramie, hemp, asbestos or mixtures thereof, might be

suitable in appropriate circumstances. Natural fiber seconds which have been separated into

individual fibers or small groups of fibers can be used, especially those from denim and other garments. Preferably, the natural fiber is cotton from waste cotton material, which is

sometimes referred to as "cotton shoddy." To the extent that synthetic fibers are used, they

may be selected from rayon, acetate, nylon, polyester, polyenes, acrylics, vinyons, kevlar or

mixtures thereof. Any synthetic or natural fiber can be utilized as a binder fiber. The preferred binder fiber is a polyester fiber.

The proportion of fibers can vary as desired. The amount of natural fibers is

typically in the range of from about 60% to about 90% by weight of the batt, and preferably form about 80% to about 90%. Binder fibers are combined with the natural fibers in the

range of about 10% to about 40% by weight of the batt, and preferably about 10% to about 20%. These fibers, when bonded together in a batt, result in an acoustic insulator which is

economical to produce, since it can be formed of waste cloth and other waste materials and

which has excellent acoustical insulating properties.

Preferably, the non-woven batt for use in the acoustical insulator of the present invention has a bulk density of less than about 1.5 pounds per cubic foot, more preferably less than about 1.2 pounds per cubic foot. While batts having a density over 1.5 pounds per

cubic foot will perform well, the material is cost inefficient to produce because the return on

performance does not justify the increased manufacturing cost for using more fiber. Also,

the heavier material without a commensurate performance enhancement becomes a distinct

disadvantage to automotive manufacturers, who are always conscious of overall vehicle

weight.

At the preferred densities, the batts preferably have a thickness in the range of from

about 1 inch to about 6 inches. Batts above six inches are generally too thick and cannot

easily be compressed to fit the voids in a vehicle body and are difficult to encapsulate. At a thickness of under about one inch, the material is too flimsy.

Important features of the batt are its unique combination of flexibility and

compressibility. More importantly, the batt has good recovery from compression, rapidly

returning to its original, precompression volume when the compressive forces are released. The batt recovers at least about 80% of its precompression volume immediately after the

compressive forces are removed and more preferably about 95%. This property is tested by

compressing or squeezing the material to as though the compressed material were about to be

inserted into a representative void in an automobile and then releaseing the material. The thickness of the recovered material is then measured, and the thickness of the recovered material is compared with the thickness of the precompressed materiial.

In addition to the above properties, the batt material is resistant to mildew, staining,

bleeding and water wicking. There is no disagreeable odor associated with the material, wet or dry. Since the material should have a certain amount of resistance to combustion when used in certain parts of an automobile, the batt material is preferably chemically treated during the manufacturing process to render the material flame resistant, vermin

resistant and non-corrosive.

The sound absorption properties of the batt were tested in accordance with ASTM El 050 {Impedance and Absorption of Acoustical Materials Using a Tube, Two

Microphones and a Digital Frequency Analysis System). Specifically, Briiel & Kjer 4206

two microphone impedance measurement tubes were used to measure the normal incidence sound absoφtion coefficient of the batt. One measurement tube had a diameter of 100 mm with a measurement range of 100 hertz to 1600 hertz and the other tube had a

diameter of 29 mm and a measurement range of 1000 hertz to 6300 hertz. The tests were

conducted with plane waves generated in each tube by a random noise source. The standing waves in the tube were measured at two fixed locations using wall mounted microphones. Signals from the microphones were sent to a Bruel & Kjer type 2032 dual

channel signal analyzer to determine the complex acoustic transfer function and ultimately

to compute the sound absoφtion coefficient using a Bruel & Kjer type BC 5050 software package. Absoφtion coefficients were computed using a finite frequency bandwidth of 2 hertz over the measurement ranges of the tubes.

Samples of two and five-inch thick pads were evaluated. Initially, the samples

were conditioned for a minimum of 24 hours at standard laboratory conditions of 23 ° C,

plus or minus 2°C, and 50% relative humidity, plus or minus 5% relative humidity. Two samples of each pad were dye cut to fit the tubes' sample holders with no air space

between the sample and backplate of the sample holder. The absoφtion coefficients for each of the batt samples over the testing range is shown in Figs. 1-3. The graphs show the normal incidence of sound absoφtion at each of the finite bandwidths for the large and small tube samples. In each graph, the data for the 100 mm tube follows the curve denoted by "1" and the data for the 29 mm tube follows the curve denoted by "2." All of the

samples performed equally well showing excellent absoφtion efficiencies over a wide range of frequencies.

The acoustic insulator material is typically produced in 8" to 36" wide by 30' to 150'

long rolls. The material may be slit and/or cut into individual pieces of any desired size and

shape. An exterior cover may be added to one or more surfaces of the pieces. The exterior cover may be, for example, plastics, such as polyethylene, polypropylene; self reacting coatings or cross-linked polymers; metallized films; craft paper; non-woven materials; or

combinations thereof. Preferably, the batt pieces are sealed loosely in plastic, ideally polyethylene, with a thickness of less than 1.5 mils (thousandths of an inch) and more preferably between 1.0 mils and 1.5 mils. Loosely sealing the pieces in plastic does not

restrict movement of the batt relative to the exterior layer.

Natural fibers, such as cotton, sometimes compact and loose insulating properties when they becomes wet and can exhibit an odor when exposed to moisture. By encapsulating the batt in plastic, the structure becomes air-impermeable and the entry of

dirt and moisture can be substantially prevented without any reduction of the sound

absoφtivity. This arrangement has the advantage of providing permanent assurance of good use properties in the spaces of a vehicle. While the cutting and encapsulating operations can be done any number of ways

using conventional machinery, or even by hand, the preferred automated method is to use an

"L-sealer" for both cutting and encapsulating the material. An L-sealer is a common type of

packaging machine which wraps or encapsulates various products. An L-sealer suitable for use in the present invention is available from a company by the name of "Hayssen" located in Spartanburg, South Carolina. L-sealers can also be obtained from Weldotron Coφoration,

1532 S. Washington Avenue, Piscataway, New Jersey, 08855.

The present invention provides a superior acoustical insulator which may be installed in any desired vehicle body void location or other spaces during assembly to absorb low and

high frequency sound. The product may be used in the pillars, wheelhouses, cowl sides,

roof rails and quarter trim panels and other locations. As the vehicle moves by on the assembly line, the user compresses the insulator and places the compressed insulator in the desired location. When the user releases the insulator, the insulator expands and fills and

conforms to the area into which it is installed. This expansion and resultant filling of the

space enhances the overall acoustical performance of the insulator.

The automotive acoustic insulator of the present invention has many advantages, including excellent sound absoφtivity, including attenuation of a particularly wide

spectrum of sound of different wavelengths. The efficiency of the insulator along with the

low density of the material is an advantage in view of the weight concerns of automobile manufacturers. This advantage meets the desire of the automobile industry to save weight. Particularly advantageous is the flexibility and compression recovery of the material. The advantages of the conformable insulation are realized in the vehicle body void. The batt

expands quickly and conforms to the shape of the area available to it. The conformable

insulation needs no cutting to be shaped to fit around or in obstacles in the installation area.

Recovery from compression is also important in shipping since the insulator may be tightly compressed and packaged to minimize shipping volume. Once removed from packaging the insulator quickly returns to its original precompressed volume. The batt does not collapse over time thus retaining its bulk, structural integrity and insulating properties.

Moreover, the insulator is convenient and easy to install. Using a low-density material significantly reduces the cost of producing the batt. A low-density insulation batt

requires less material to manufacture. The acoustic insulator is able to use waste, second

grade, or recycled fibers, reducing the cost of raw materials.

Claims

CLAIMSWe claim:

1. An acoustical insulator for use in a vehicle body, the acoustical insulator comprising: a flexible, non-woven fiber material, the material comprising about 60% to about 90 % by weight of a natural fiber, and

about 10% to about 40% by weight of a synthetic fiber.

2. An acoustical insulator as recited in claim 1, wherein the natural fiber is cotton.

3. An acoustical insulator as recited in claim 2, wherein the synthetic fiber is a polyester

binder fiber.

4. An acoustical insulator as recited in claim 1 , wherein the synthetic fiber is a polyester

binder fiber.

5. An acoustical insulator as recited in claim 1 , wherein the density of the material is less

than about 1.5 pounds per cubic foot.

6. An acoustical insulator as recited in claim 1 , wherein the material recovers at least about 80 % of the precompression volume of the material after a compressive force is

removed.

7. An acoustical insulator as recited in claim 1, wherein the material is encapsulated.

8. An acoustical insulator as recited in claim 7, wherein said material is encapsulated in plastic.

9. An acoustical insulator as recited in claim 8, wherein said plastic is polyethylene.

10. A method for acoustically insulating a vehicle body, the method comprising the steps

of:

providing a flexible, non-woven fiber material, the material comprising about 60%

to about 90% by weight of a natural fiber, and about 10 % to about 40% by weight of a synthetic fiber; and

installing the material a void of a vehicle body.

1 1. A method for acoustically insulating a vehicle body as recited in claim 10, the method further comprising the steps of compressing the material to less than the volume the

material occupied before compression prior to installing the material and releasing the

material from compression following the installing step for allowing the material to recover to fill the void.