Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Weight per unit area specified
Reexamination Certificate
1998-06-04
2001-05-22
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Weight per unit area specified
C428S423100, C428S423500, C428S423700, C428S424200, C428S424800
Reexamination Certificate
active
06235384
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an aqueous laminating adhesive composition and a method of using thereof in adhesives for manufacturing laminate structures. More particularly, the invention is directed to an aqueous laminating adhesive composition comprising a stabilized polyurethane dispersion to which are added crosslinking agents at the time of use. One particularly important application of such dispersions is as adhesives in the manufacture of laminates from thin flexible sheet substrates.
BACKGROUND OF THE INVENTION
In general, the function of a laminating adhesive is to join together different or similar substrates, e.g., polyethylene, polypropylene, polyester, polyamides, metal, paper or cellophane to form composite films used for many different purposes. A suitable laminating adhesive is expected to provide excellent bonds on numerous substrates with only a small application of adhesives. Large amounts of such laminates are used in the packaging industry, especially in making food packaging. Due to environmental, health and safety reasons, it is preferred that the adhesives be solvent free.
Aqueous linear or crosslinked aqueous polyurethane dispersions may be used in a wide range of commercial applications such as coatings and adhesives as shown in several patents including U.S. Pat. Nos. 5,147,926, 5,610,232, 5,637,639, 5,608,000 and 5,334,690.
U.S. Pat. No. 5,147,926 disclose crosslinkable aqueous polyurethane dispersion having long shelf life and containing polyurethanes which have carbonyl and polyhydrazides and their use for the preparation of printing inks.
U.S. Pat. No. 5,01,881 is directed to aqueous coating composition comprising aqueous acrylic resin and urethane resin emulsion in the absence of a crosslinking agent. The coatings are used for plastic substrates.
U.S. Pat. No. 5,281,655 is directed to aqueous coating composition for metallic and plastic substrates. The composition comprising a urethane resin emulsion, a resin for use in aqueous coating composition and a hydrophobic melamine resin as a crosslinking agent. There is no disclosure regarding the use of the composition as a laminating adhesive.
U.S. Pat. No. 5,281,655 is directed to an aqueous polyurethane dispersion and its use in the manufacturing of laminate structures. The adhesive comprises a prepolymer comprising a reaction product of an aliphatic polyfunctional isocyanate compound, and an acid functional polyol component, wherein said prepolymer is dispersed in water in the presence of a dispersion stabilizing amount of a tertiary amine.
The present inventors have found an alternate stabilizer for use in dispersing a polyurethane prepolymer in water that is surprisingly effective while not adding to VOCs (volatile organic contents) of the dispersion.
SUMMARY OF THE INVENTION
The present invention is generally directed to an aqueous laminating adhesive composition and its use in adhesives for manufacturing laminate structures. It has been discovered that improved bonded properties of dry laminated flexible film substrates, such as laminates comprising films of thermoplastics, such as polyolefin, polyesters and polyamides as well as paper, cellophane, and metals particularly after exposure to boiling water, are obtained with polyurethane dispersion adhesives when a polyfunctional aziridine, a carbodiimide compound or mixtures thereof is employed as the crosslinker of the adhesive system.
The invention comprises a polyurethane polymer dispersed in an aqueous vehicle, the polymer having a plurality of carboxyl or sulfonic groups thereon which are stabilized with ammonia to result in a clear, stable aqueous dispersion, which can further be chained extended and crosslinked. Surprisingly, ammonia effectively neutralizes the acid groups, is volatile enough to be driven off during any drying step without leaving an unwelcome odor. It also does not contribute to the VOC of the adhesive system, thus making it even more environmentally friendly than the adhesives disclosed in U.S. Pat. No. 5,532,058, which uses tertiary amines as stabilizers.
Another aspect of the present invention is a dry bonded laminate comprising a pair of flexible film substrates bonded with an adhesive, the laminating adhesive composition comprising a polyurethane polymer having carboxylic or sulfonic acid groups thereon which are stabilized with ammonia, and a crosslinker comprising a polyfunctional aziridine, a carbodiimide compound or mixtures thereof, wherein said ammonia stabilizer is easily driven off during the drying step without leaving an unwelcome odor.
A further aspect of the invention is a curable adhesive prepared by blending the two parts at the time of use, the first part comprising a polyurethane polymer having carboxylic or sulfonic acid groups thereon which are stabilized with ammonia, and the second part is a crosslinker comprising a polyfunctional aziridine, a carbodiimide compound or mixtures thereof. Surprisingly, the ammonia stabilized system can be crosslinked without encountering any problem, to produce an effective laminating adhesive.
A still further aspect of the invention comprises a method of manufacturing a flexible film laminate comprising applying to a first flexible film substrate an aqueous adhesive composition comprising an aqueous dispersion of polyurethane polymer having plural carboxylic or sulfonic acid groups thereon which are stabilized with ammonia, and a crosslinking agent, drying the adhesive, and then applying a second flexible film substrate to the dried substrate.
The adhesive exhibits excellent adhesion in a variety of film/film and film/foil, etc. lamination applications. As mentioned before, large amounts of laminating adhesives are used in the packaging industry, especially in making food packaging.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane polymer dispersion employed in the present invention have carboxylic or sulfonic acid groups on the polyurethane polymer molecule which are neutralized with ammonia. Such dispersion may be prepared by well known procedures involving the following steps:
i) reacting a mixture of a) an aliphatic polyfunctional isocyanate compound, and b) an acid functional polyol component to form a polyurethane prepolymer; and then
ii) dispersing the resulting polyurethane prepolymer in water in the presence of a dispersion stabilizing amount of ammonia.
Suitably, the prepolymer is left with a residual level (typically 2.0-3.0%) of isocyanate groups which can be reacted with chain extenders and chain terminators after dispersion so as to increase the molecular weight of the dispersed polymer and provide pendant reactive crosslinkable groups. The final polyurethane polymer is substantially free (<0.5%) of isocyanate groups.
Particularly preferred polyurethane polymer dispersions are prepared from aliphatic polyisocyanate which are characterized by median particle sizes of about 80 nm or less, typically about 30-80 nm, preferably about 70 nm or less. Median particle sizes are determined conventionally, for instance by the use of a BI-90 particle sizer sold by Brookhaven Instruments. The small particle size dispersion of the invention are almost clear and have improved application properties, especially using rotogravure application machinery.
In the preferred embodiments, the aliphatic isocyanate is a hindered isocyanate compound. The use of a hindered isocyanate helps prevent isocyanurate trimer formation during polymer manufacture and reduces the reactivity of residual isocyanate groups on the prepolymer. The hindered isocyanate can be any di-, tri- or polyfunctional isocyanate having tertiary aliphatic isocyanate functionality. Representative non-limiting examples of such isocyanates include m-tetramethylxylene diisocyanate and p-tetramethylxylene diisocyanate. Other polyisocyanate containing at least one sterically hindered group such as isophorone diisocyanate (IPDI) are usually employed in the preferred embodiments.
The plural isocyanate compound is reacted with polyol component providing acid functionality
Rolando Thomas E.
Voss Peter A.
Ahmed Sheeba
H. B. Fuller Licensing & Financing Inc.
Thibodeau Paul
LandOfFree
Aqueous laminating adhesive composition and a method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous laminating adhesive composition and a method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous laminating adhesive composition and a method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2562409