Flexible polyureas for flexible packaging adhesive without aromatic amine migration

Abstract

Provided is an adhesive comprising a reaction product of (A) an aliphatic polyisocyanate having a molecular weight of from 132 to 700; and (B) a polyaspartate comprising a reaction product of (B1) a polyamine having a molecular weight of at least 240, and (B2) a Michael addition receptor, wherein viscosity @23° C. according to ASTM D1084-16, remains below 150 cps after four hours, and wherein the adhesive develops an acceptable bond strength to a substrate, defined as having a minimum of 150 g / in. measured @23° C. according to ASTM D 1876-01 or substrate tear, in less than five days after the substrate is laminated with the adhesive. The inventive flexible packaging adhesives are free of aromatic amines and may find use in multilayer laminates for a variety of industries, including the food processing, cosmetics, and detergents industries.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority under 35 U.S.C. § 119 to U.S. Provisional Patent Application Ser. No. 62 / 884,205, filed Aug. 8, 2019, the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates in general to adhesives, and more specifically to flexibilized polyurea compositions for producing flexible packaging adhesives which do not suffer from aromatic amine migration.BACKGROUND OF THE INVENTION[0003]Flexible packagings intended for the packaging of diverse products, such as those manufactured by the food processing, cosmetics or detergents industries, are usually made of several thin layers (sheets or films). The thickness of these layers is between 5 μm and 150 um and may comprise several different materials, such as paper, metal (e.g., aluminum) or thermoplastic polymers. The corresponding multilayer laminate, which may have a thickness of from 20 μm to 400 μm, ma...

AI Technical Summary

Benefits of technology

The patent allows for various non-limiting and non-exhaustive embodiments to be written. However, there may be additional embodiments that can be created by modifying or combining steps, components, or elements of the existing embodiments. The patent also allows for amendments to be made to the claims during prosecution to add features. These features comply with the requirements of certain sections of the patent.

Problems solved by technology

If this curing step is eliminated, or is of insufficient length, the laminates may suffer from two problems: first, the mechanical strength of the adhesive bond may not be sufficient for further handling and use of the laminated packaging film; and second, unreacted monomeric aromatic polyisocyanates can react with moisture in the product to be packaged, generating monomeric aromatic polyamines, which may migrate into the contents of the package.

This is particularly problematic in high performance packaging systems, which are subjected to elevated temperatures (e.g., 116-130° C.) during sterilization of the packaging material and contents (retort process).

Although this approach eliminates the potential for aromatic amine formation, the lower reactivity observed with the use of aliphatic isocyanates leads to a much slower cure time.

However, these systems when cured with conventional low molecular weight polyisocyanates produce hard, rather inflexible coatings which would be unsuitable for flexible packaging adhesive applications.

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