Flexible polyurethane material

Abstract

The present invention provides a flexible two component polyurethane and method for producing the polyurethane. The cured polyurethane is flexible, durable and weather resistant. The polyurethane is suitable for use as a protective layer on various substrates. The flexible polyurethane is the reaction product of solvent-free reaction components. The first component includes one or more polyols, optionally, one or more diols, and a catalyst. The second component includes a primary aliphatic isocyante crosslinker.

Description

[0001]This is a divisional of application Ser. No. 09 / 064,490, filed Apr. 22, 1998 which is now U.S. Pat. No. 6,258,918.FIELD OF THE INVENTION[0002]This invention relates to a flexible, polyurethane material, more particularly, to a solvent free, two-component polyurethane and, even more particularly, to such a polyurethane which is transparent and exhibits improved flexibility, durability and weathering characteristics. The present invention also includes an article utilizing the polyurethane as a top coat, and a method of making such a polyurethane top coat.BACKGROUND OF THE INVENTION[0003]Decorative articles often utilize a polyurethane top coat to cover or protect a base substrate and any indicia or decorative features located on the substrate. The articles may include various substrates upon which printing or profiled graphics have been applied. The polyurethane material is generally clear or optically transparent and functions as a lens in order to display the substrate or any...

AI Technical Summary

Benefits of technology

[0034]Upon curing, the polyurethane of the present invention exhibits desired flexibility, durability, and weather resistant properties. Preferably, the polyether segments, resulting from the use of polyether based polyols and diols in the first component, represent no more than 20 weight percent in the cured polyurethane. More preferably, the polyether segments in the cured polyurethane is about 15 weight percent or less. A polyether content in excess of the noted limitation may adversely impact the clarity and weathering properties of the cured polyurethane.

[0035]The flexibility of the present invention enables use of the polyurethane on various articles. For example, the present invention may be utilized as a protective layer on an adhesive backed substrate. The flexibility of the polyurethane of the present invention enables the application of the coated article on curved or non-planer surfaces. The flexibility significantly reduces the tendency of the polyurethane to spring back to its originally cured form after being bonded to a surface.

[0036]The flexibility of the polyurethane is demonstrated by the Shore A hardness properties, the storage modulus, and the flexural modulus. The Shore A hardness test of the present inventive polyurethane is generally less than 94, and preferably less than 92. Shore A hardness levels in excess of 94 are considered stiff or rigid. The storage modulus indicates the rigidity of the polyurethane under tension. The polyurethanes of the present invention have a storage modulus of 1.0×108 or less. The flexural modulus measures the flexibility of the polyurethane under tortional strain. The polyurethanes of the present invention have a flexural modulus of 1.0×108 or less. Additionally, the flexibility of the polyurethane is often indicated by its self-healing characteristics, or the ability to return to its original shape upon deformation.

[0037]The durability and weathering properties of the present invention are important features which enable the use of the polyurethane in various environments. For applications of the polyurethane in exterior environments, the polyurethane must not yellow or significantly change color when exposed to environmental conditions. The present invention, when subjected to a heat aging test in accordance with ASTM D2244-79, exhibits a color shift within 1 delta E. Other environmental tests utilized to indicate acceptable exterior performance are the salt spray test, the humidity resistance test, and the thermal shock test. A polyurethane should remain clear and not cloudy or opaque upon completion of the noted tests. The durability of the polyurethane top coat is measured by the Hoffman scratch resistance test which indicates the abrasion resistance of the material. The present invention generally has a Hoffman scratch resistance of 2 or less.

[0038]The polyurethane of the present invention may be applied to various substrates to form a layer on the substrate, or a portion of the substrate. The substrate may include wood, polymeric material, fiber reinforced polymers, metal, or combinations thereof. The choice of substrate is dependent upon the desired end use. Some examples of combined substrates would include metal coated polymer films and polymer sealed wood or wood veneer. The polyurethane of the present invention is ideally suited for applications with substrates containing moisture or applications permitting the direct or indirect contact of the isocyanate with carboxyl groups. For example, a porous substrate with an adhesive backing permits the indirect contact of the isocyanate in the polyurethane reaction mass with carboxyl groups in the adhesive.

[0039]The polyurethane of the present invention is ideally suited for use in forming decorative articles requiring a transparent layer. Some decorative articles utilize a substrate with indicia applied onto the substrate. Indicia includes any distinctive marks or representations. In accordance with the present invention, the polyurethane may be applied directly onto the substrate and the indicia.

Problems solved by technology

Rigid polyurethanes are susceptible to abrasion and scratching.

Additionally, the materials do not demonstrate an appropriate level of self-healing.

However, some specific substrates are not suitable for use with conventional polyurethanes.

Some substrates are susceptible to absorbing an amount of moisture which can react with the polyurethane to form bubbles in the cured polyurethane.

This reaction results in the release of carbon dioxide which generally becomes trapped in the polyurethane.

The occurrence of outgassing in a cured polyurethane is aesthetically undesirable.

The solvent based polyurethanes are generally not viscous enough to provide a desired thickness to the polyurethane lens.

Additionally, solvent based polyurethanes, when applied as top coats, do not permit the complete evaporation of the solvent from the polyurethane.

The incomplete evaporation can produce striations, parting lines, or bubbles in the polyurethane and therefore result in an aesthetically unacceptable top coat.

However, they tend to degrade and yellow when exposed to sunlight.

Thus, existing polyurethane compositions, and methods for producing them, often result in undesirable finished properties or are unsuitable for exterior applications.

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