Patent Application
20160121578
As automobiles have become lighter for better fuel efficiency, there has developed a need for better acoustics to prevent exterior road noise from penetrating into passenger compartments of vehicles. This is an increasingly difficult problem especially with Sports Utility Vehicles (SUVs) that have drivers wanting the durability of 4-wheel trucks with the luxury of a sedan. The large, nubby tires of the SUVs create significant road noise from the tires on the road as well as tire contact with sand, water, and also wind noise in general.
There are many all fiber versions of nonwovens that have a single layer of fibers blended to give some acoustic qualities and thermo-formable material that use blends of high and low melt fibers. However, these compositions have many drawbacks. For example, such substances tend to be very heavy in overall weight lending themselves to poor gas efficiency as well as overall vehicle stability. In addition, the acoustic noise reduction given by such substances fails to provide the acoustic requirements needed for a luxury sedan. Further, materials that are impervious films do not give good acoustic performance.
Acoustic impedance is an important physical property in substances that determine the substances ability to absorb sound. Specific Acoustic Impedance is the ratio between the sound pressure and the particle velocity produced by a sound wave moving through the substance. When sound waves pass through any physical substance, pressure of the sound waves causes the particles of the substance to move. Specific Acoustic Impedance is also directly related to the resistance of airflow. Specific Acoustic Impedance is measured in RAYLS. The higher number of RAYLS, the lower the velocity of sound transmission through a medium. A fabric is considered to have better acoustic sound absorption with a higher RAYLS number.
Specific acoustic impedance is known as being defined in the following formula:
Where Z is the specific acoustic impedance, p is pressure, v is particle velocity, r is the position, and ω is the frequency. The RAYL number is also used for Characteristic Acoustic Impedance of a substance that is inherent physical property in substances.
Characteristic acoustic impedance is known as being defined in the following formula: Z0=ρ0c0
Here Z0 is the characteristic impedance, and ρ0 is the density and c0 is the speed of sound in the unperturbed substance when no sound waves are travelling through it. In both the Specific Acoustic Impedance and Characteristic Acoustic Impedance, the higher the RAYLS value, the better acoustic sound absorption.
Single layer nonwovens have tried to increase RAYLS by using more fine fibers to create a denser medium to reduce air flow, and hence reduce sound transmission. However this technique has not been achieved at a practical cost or weight.
At the same time, the Automobile Manufacturers have found a need for an Underbody Shield to be moldable, durable and fit under the vehicle to prevent road and wind noise from penetrating upward into the passenger compartment. Further, it has been shown that these composites are weighing close to 2,000 gsm (grams per square meter) to achieve the noise reduction levels desired. This amount of weight is too much for an automobile part due to stability of the vehicle, drag and energy efficiency concerns.
In addition, due to the high heat exposure from engine parts, a need exists for a product that does not exhibit failure during heat aging up to 150° C.; has resistance to water, oil, and engine fluids, has low flame spread and low smoke, and is recyclable back into itself. Further, these moldable products must have excellent abrasion resistance against sand & gravel.
Thus there still exists a need for an acoustic absorber that is thermo-formable, light weight, resistant to water penetration, flame retardant, and has a high RAYLS number.
The invention utilizes a manufacturable composite consisting of at least two layers of moldable nonwoven fabrics. An extruded layer of blown film is used to make the material lighter and provide the necessary acoustic qualities of the material.
The composite material is made from a film such as, but not limited to low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, polyvinyl chloride, polyethylene terephalate, polyethylene terephalate glycol-modified, polyamide, nylon and the like. A polyethylene glycol-modified (PETG) may be used as a binder fiber. Polylactic acid (PLA) may also be used in the composite material. Other binder fibers may be used including Isophthallic modified PET, polyethylene, and polypropylene. A blowing agent such as an inert gas of air, nitrogen, carbon dioxide, helium, argon, oxygen or the like may be used to generate cells within the film. The cells created provide lighter weight and increased acoustic capability for the composite material.
During blending fiber finishes such as Goulston L624 (fluorocarbon) may be applied during blending. Other finishes such as Lurol 14951 may be blended with L624 to achieve heat and/or fire retardant characteristics. Anti-stats such as ASY may be added to improve run ability especially with low humidity conditions.
The nonwoven material may include polyethylene terephthalate glycol-modified (PETG) as a binder. When the PETG is melted it flows uniformly and formed meniscus at the bond points of the high melt fibers. The level of the PETG percentage controls the stiffness and the air flow resistance.
Further the nonwoven may use in addition to or as a replacement binder Polylactic Acid (PLA) such as fibers made from Cargill's PLA Ingeo polymer with a melting point of 140° C. The PLA may or may not be blended with the above PETG fibers.
Nonwoven Network, LLC pioneered a Tri-layer product known as Raptor™ that contains a 500 gsm (grams per square meter) polyester absorber layer, an 150 gsm PP film layer acting as a barrier layer, and a 375 gsm polyester absorber layer. This product provides superior sound attenuation qualities and also has an impervious layer that prevents water from penetrating to the metal frame of the vehicle.
Further, Nonwoven Network LLC has developed a new concept in acoustic noise reduction from the wheel wells, especially in Sport Utility Vehicles. Raptor™ is a tri-laminate composite that incorporates an absorber layer-barrier layer-absorber layer to dramatically reduce the noise in the cabin with vehicles with large tires and aggressive treads. The product is in full production in a recently launched vehicle and has received outstanding reviews for sound and durability.
The Tri-Layer Raptor™ product has the best acoustics for a 1,015 gsm product, however there is a need to improve its performance while keeping the weight at the same level.
The invention utilizes a low melt fiber made from a co-polyester where cyclohexane dimethanol (CHDM) has been substituted for some of the ethylene glycol (EG) normally polymerized with Purified Terephthalic Acid to produce Polyester (PET). The result is a polymer called PETG. The melting point of the polymer can be adjusted from 110° C. to 170° C. by adjusting the ratio of CHDM to EG.
The PETG will be blended with Standard PET fiber that has been heat set to 190° C.
Fibers made from Polylactic Acid (PLA) such as fibers made from Cargill's PLA Ingeo polymer the have been drawn and fully crystallized with a melting point of 140° C. and above are blended with Polyester (PET) fibers that have been heat set at 170° C. or above.
The plastics industry has used Blowing Agents to expand the plastic films and injection molded parts by injecting inert gasses such as N2 (Nitrogen) or CO2 (Carbon Dioxide). The first known use was in 1846 when Hancock received a patent to make synthetic sponges with rubber. Other blowing agents such as Sodium Bi-Carbonate (Commonly known as Baking Powder) have been used in bakery products (cakes) and plastics. Ethylene Carbonate decomposes with heat to produce CO2. Ammonium Nitrate decomposes with heat to produce N2.
Examples of companies that make Blowing agents for plastic extrusion include Techmer, Clariant, Reedy, Kibbechem, Wells, and Beryl for example.
It is also possible to inject inert gasses directly into the extruder as shown by Linde Industrial gasses such as Nitrogen, Argon, Helium, and Carbon Dioxide and the like.
Further blending in a blowing agent at a rate of 0.1 to 3.0% will provide inert gasses to allow a producer to make the film lighter in weight at the same thickness. Alternatively, by maintaining the same film weight, the thickness increases. The additional thickness can increase the flexural modulus, thus producing a stiffer part.
By combining the blown film with 1 or 2 fabric layers, a thermo-formable composite can be made. The blown film is protected by the fabrics. Since the fabrics contain a high percentage of low melt formable fibers, a very stiff and durable composite can be formed.
The following are examples given to illustrate the benefits of the present invention. These examples are in no means meant to limit the invention to these particular embodiments.
In the first example, GA24, the following was used:
Layer 1: 200 gsm 70% Type P110 6d Black Polyester/30% Black 4 denier PETG.
Layer 2: 150 gsm Blown HDPE film with 1.0% Techmer Blowing agent.
Layer 3: 650 gsm 70% Type P110 6d Black Polyester/30% Black 4 denier PETG
Total weight 1,000 gsm
The Extrusion temperature was 210° C. to achieve full blowing potential. The products were molded using a 210° C. oven to preheat the composite assuring that the 165° C. melt point of the PETG fiber was achieved.
The result was a very stiff molded part with excellent flexural modulus.
The molded composite was tested for RAYLS and found to be very high with little porosity, but with some porosity. It was then subjected to Acoustic testing with excellent results.
The molded composite withstood long term heat and environmental aging.
In the second example, GA25 the following was used:
Layer 1: 200 gsm 70% Type P110 6d Black Polyester/30% Black 4 denier PETG
Layer 2: 100 gsm Blown HDPE film with 1.0% Techmer Blowing agent
Layer 3: 700 gsm 70% Type P110 6d Black Polyester/30% Black 4 denier PETG
Total weight 1,000 gsm.
The Extrusion temperature was 210° C. to achieve full blowing potential. The products were molded using a 210° C. oven to preheat the composite assuring that the 165° C. melt point of the PETG fiber was achieved.
The result was a very stiff molded part with excellent flexural modulus.
The molded composite was tested for RAYLS and found to be very high with little porosity, but better than GA24. It was then subjected to Acoustic testing with excellent results.
The molded composite withstood long term heat and environmental aging.
It was determined that the composites could be made with other blends of Polyester, Polypropylene, Nylon, Cotton, or other types of fibers. Other binder fibers could also be used.
The extruded film could be made from any thermoplastic resin such as LDPE, LLDPE, HDPE, Polypropylene, PVC, PET, Polyamide (Nylon), EVA and the like.
Adverting to the drawings,
The extruder 10 has a mixing screw 12 that melts the resin pellets and mixes the blowing agent to generate microscopic voids. The voids are preferably open cell holes for use in acoustic impedance as described herein. An extrusion die 18 sets the film thickness of the polymer. And creates a film 20 with the microscopic voids or holes.
Depending on the implementation of either a bi-layer or tri-layer composite material, a fabric (non-woven) layer 22 is released from roll 23 and may or may not be stretched or worked, depending on the embodiment, for nonwoven fabric 27 to be attached to film 20 by nip rolls 28.
In a tri-layer composite implementation, another fabric (non-woven) layer 24 is released from roll 25. Again the nonwoven layer may or may not be stretched or worked, depending on the embodiment, for nonwoven fabric 26 to be attached to film 20 by nip rolls 28. Nip rolls 28 may or may not be chilled or heated depending on the embodiment. Nip rolls 28 also use mechanical pressure to squeeze the layers together. Nonwoven fabric may be made of any compositions discussed in this specification. PETG, Polyethylene, isophthallic modified PET, and/or PLA may also be used as binders in the non-woven fabric. Examples of non-woven materials include for example, and are not limited to, cellulosic, keratin, wool, cotton, polyesters, fabric, polylactic acids, nylons, rayons, polypropylene, and any combination thereof. In either a bi-layer or tri-layer composite the grams per square meter (gsm) of each layer may be controlled by nips 28 and/rollers 23, 25, and/or the line speed of the extrusion line and/or the amount of blowing agent 16. In a tri-layer composite embodiment 29, for example layer 1 of a nonwoven material may be 1-200 gsm, layer 2 of a blown film may be 1150 gsm, and layer 3 of a nonwoven fabric may be 650 gsm, for example.
Additional materials may also be applied to any fibrous element. For example, the PTEG or PLA fibers or any of the non-woven materials or blown film described above may be treated with a performance enhancing finish, either during fiber formation or fiber blending. The finish types may vary depending on the embodiments. In some embodiments, the finish is comprised of a fluorocarbon, such as the CF fluorocarbon sold by Goulston Technologies as FC-L624. This enhances among other things the durability and moisture resistance of the moldable fabric. In other embodiments, the finish is comprised of an inorganic phosphate salt, such as that sold by Goulston Technologies as L-14951. This enhances additive also enhances the heat resistance and flame retardant and/or durability of the moldable fabric. In either instance, the performance enhancing finish preferably does not exceed 0.05% to 1.0% of the fiber weight. An alternate finish may also be comprised of a combination of a fluorocarbon and an inorganic phosphate salt to achieve fire retardant characteristics. Preferably, this alternate finish does not exceed 0.05% to 2.0% of the fiber weight. An anti-static element, such as ASY, may also be added to improve run ability, especially when the moldable fiber is manufactured within a low humidity environment.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/072,305, filed Oct. 29, 2014, the disclosure of which is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62072305 | Oct 2014 | US |
