Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-04-08
2004-03-30
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S412000
Reexamination Certificate
active
06713131
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of coating substrates with a composition comprising a water continuous emulsion of a curable elastomeric polymer, and aqueous polyurethane dispersion, and an optional cure agent. Coated fabrics prepared according to these methods are particularly useful in the construction of automobile protective airbags.
BACKGROUND OF THE INVENTION
The use of airbags in motor vehicles has grown exponentially in recent years. Their use has expanded beyond frontal airbags for protection for the driver and passenger. Side airbags and inflatable curtains are now included in side compartments of vehicles for enhanced protection from side collisions or rollovers. This expanded use has placed new demands on the physical properties attributed to the airbags. In particular, improved air retention performance of airbags are desired to ensure the airbag remains inflated and maintains its integrity for an extended period of time upon deployment.
Typically, airbags are made from synthetic fibers, such as a polyamide (nylon) or polyester and coated with a polymeric film. The most common polymeric materials currently being used to coat airbag fabrics are based on silicones, as described for example in U.S. Pat. No. 6,037,279. The silicone coating primarily provides a thermal barrier on the airbags to protect the fabric from the high temperature burst associated with ignition of the gas upon deployment. The silicone coating also provides some gas retention properties for the deployed airbag. One option to meet the increasing demand for gas retention is to increase the thickness of the silicone coating. However, newer designs for airbags, and in particular side impact airbags and inflatable curtains for side compartments, require airbags to have a more compact design. This results in a need for lower coating weights on the airbag fabrics. Furthermore, next generation side and inflatable curtain airbags have a need to retain pressured air/gas for sufficient time to provide rollover protection for greater than 5 seconds. Current silicone based coatings are too permeable to air/gas, especially at lower coat weights, to provide sufficient gas retention in deployed side and curtain airbags. Thus, there is a need for a fabric coating composition, and methods of application, to provide coated fabrics with sufficient air/gas retention for use in the construction of airbags, and in particular side and curtain airbags.
The current airbag fabrics also requires the removal of unwanted sizing, protective oil after woven steps before application of the coating material. This is done by chemical scouring, washing, then drying of the scoured airbag fabrics. These steps are non-value added, labor-intensive, and costly. Also, residual moisture on the fabric surface can cause imperfections on the coated surface when a non-aqueous coating is applied. Thus, there exsits an additional need to develop a coating composition that can be applied directly over wet fabrics, provides good adhesion to the fabric, and dries to a uniform coating without imprefections.
One technique that has been reported to decrease coating weights and maintain low permeability performance of coated fabrics for use in airbags has been to use a two layered coating system, as disclosed for example in U.S. Pat. No. 6,177,365. The U.S. Pat. No. 6,177,365 patent teaches the application of a first layer to the fabric of a non-silicone material followed by the application of a silicone containing topcoat. U.S. Pat. No. 6,177,366 also teaches a two layer coating system for airbag fabrics where the first layer contains up to 30% of a silicone resin and the topcoat contains a silicone material. U.S. Pat. No. 6,239,046 teaches an airbags having a first coating layer of adhesive polyurethane and a second coating layer of an elastomeric polysiloxane.
Alternative coating compositions have been disclosed based on polyurethanes, such as in U.S. Pat. No. 5,110,666, or on polyurethane/polyacrylate dispersions as found in U.S. Pat. No. 6,169,043.
While the coating systems cited above represents advancements in airbag technology, a need still exists to provide improved compositions and techniques for coating fabrics for use in airbags. In particular, coating compositions that provide similar or improved permeability at lower coating weights and improved aging stability are desired. Furthermore, there is a need to provide coatings that eliminate the need for pre-treatment of the fabrics.
SUMMARY OF THE INVENTION
The present invention is directed to a method for coating a substrate comprising the steps of:
(I) applying a layer on the substrate of a curable composition comprising:
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50° C.,
(B) an aqueous polyurethane dispersion, and optionally
(C) a cure agent
(II) exposing the layer to air for sufficient time to form a cured coating. The present invention further provides a method for forming a cured second coating of a composition comprising a polyorganosiloxane-based elastomeric material upon the first cured coating.
The present invention is also directed to the coated substrates prepared by the methods described herein.
DETAILED DESCRIPTION OF THE INVENTION
Step (I) of the method of the present invention is applying a layer on a substrate of a curable composition comprising:
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50° C.,
(B) an aqueous polyurethane dispersion, and optionally
(C) a cure agent
Component (A) is a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50° C. As used herein, “water-continuous emulsion” refers to an emulsion having water as the continuous phase of the emulsion. Water-continuous emulsions are characterized by their miscibility with water and/or their ability to be diluted by the further addition of water.
The elastomeric polymers that can be used as starting materials to prepare the water continuous emulsion suitable as component (A) in the present invention, are any polymers having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50° C. One skilled in the art recognizes the term elastomeric to describe materials as having rubber-like properties or rubbery characteristics, that is, materials which can be extended to twice its own length at room temperature or having an elongation of 100% or higher at room temperature. When the term “polymer” is used herein, it should be understood to describe polymers that may be homopolymers, copolymers, terpolymers, and mixtures thereof.
For the purpose of this invention, the viscosity of the curable elastomeric polymer is defined as “zero-shear” viscosity at ambient temperature. This is commonly defined as the viscosity of a polymer when approaching zero-shear rate conditions and is regarded as a constant value for a given polymer. The “zero-shear” viscosity is an approximated constant viscosity value derived empirically or from experimentally measured viscosity values.
The curable elastomeric polymers suitable in the present invention can have a viscosity of 0.5 to 1,000,000 KPa-s, preferably the viscosity is 0.5 to 500,000 KPa-s, and most preferable is when the curable elastomeric polymer has a viscosity of 1.0 to 100,000 KPa-s. While the correlation of viscosity and molecular weight will vary depending on the specific type of polymer, generally the number average molecular weights (Mn) of the curable elastomeric polymers that can be typically used in the present invention range from 5,000 to 300,000 g/mole, preferably 5,000 to 200,000 g/mole, and most preferably range from 5,000 to 100,000 g/mole.
For purposes of this invention, the term “glass transition temperature” is the accepted meaning in the art, that is, the temperature at which a polymer changes from
Blackwood William Raye
Lin Shaow Burn
Saxena Anil Kumar
Cameron Erma
Dow Corning Corporation
Zombeck Alan
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