Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-30
2004-03-30
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S460000, C528S076000, C528S085000
Reexamination Certificate
active
06713570
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to mixtures of isocyanate-terminated polyurethanes having good adhesion properties.
BACKGROUND OF THE INVENTION
Isocyanate-terminated polyurethane prepolymers (sometimes referred to hereinafter as “polyurethane prepolymers” or “prepolymers”) are desirable in a variety of applications. For example, they can be used in reactive hot melt urethane adhesive, coating and/or sealant systems. Hot melt urethane systems are solid at room temperature, melt to a viscous liquid when heated to moderate temperatures (e.g., 55° C.-121° C.), and are applied in a molten state to an appropriate substrate. They then cool to a solid state to provide an initial bond strength (sometimes referred to as “green strength”), and eventually achieve their ultimate bond strength in a curing reaction with ambient moisture.
An adhesive that can readily bond to polymeric substrates, for example, high impact polystyrene, is useful because such a substrate has previously not been amenable to adhesive bonding. Prior adhesives that have been amenable to bonding have generally required a high energy surface, such as polyvinyl chloride, polycarbonate or acrylonitrile-butadiene-styrene. Plastics with low surface energy, or even high surface energy plastics that are contaminated on the surface with oils, waxes or other release materials have tended to have poor adhesion. What is desired is an adhesive, such as a moisture curing hot-melt adhesive, which has good bonding to low surface energy plastics or plastics contaminated with release materials, for example waxes. Additionally, it is desired to achieve good adhesion to low surface energy plastics at low application temperatures (e.g., 55° C.-90° C.).
SUMMARY OF THE INVENTION
The present invention is directed to a moisture curable, hot melt adhesive coating and/or sealant composition. The composition comprises (a) a first isocyanate-terminated prepolymer comprising the reaction product of an at least essentially semicrystalline hydroxy-functional material (Component A) and a polyisocyanate; (b) a second isocyanate-terminated prepolymer comprising the reaction product of an essentially semicrystalline poly(tetramethylene ether) glycol that has a molecular weight of at least about 1000 (Component B) and a polyisocyanate; and (c) a third isocyanate-terminated prepolymer comprising the reaction product of an essentially amorphous hydroxy-functional material (Component C) and a polyisocyanate, the essentially amorphous hydroxy-functional material having an average functionality less than 2.5 and a Tg≦−20° C. All essentially amorphous hydroxy-functional materials in the composition have a Tg≦−20° C.
DETAILED DESCRIPTION
The present invention relates to a blend or mixture of isocyanate-terminated polyurethane prepolymers useful as an adhesive, coating and/or sealant and having good adhesion to low energy polymeric substrates.
In general, the blend comprises a first isocyanate-terminated polyurethane prepolymer, a second isocyanate-terminated polyurethane prepolymer, and a third isocyanate-terminated polyurethane prepolymer. Each polyurethane prepolymer comprises the reaction product of a hydroxy-functional material, such as a polyester polyol, and a polyisocyanate. “Functionality” is defined generally by the number of reactive groups (e.g., hydroxyl groups) per molecule of the hydroxy-functional material.
First Isocyanate-Terminated Polyurethane Prepolymer
The hydroxy-functional material (Component A) useful in making the first isocyanate-terminated polyurethane prepolymer of the invention is generally an essentially linear, saturated aliphatic material that is at least essentially semicrystalline. By “essentially semicrystalline” it is meant that Component A exhibits both a crystalline melting point (Tm) and a glass transition temperature (Tg), and has a crystallinity index of greater than 0.25. In some embodiments, the crystallinity index is greater than 0.30.
The crystallinity index of a polymer is defined as the fraction of crystalline material present in a sample of the polymer. A value of 1.0 represents 100% crystallinity and a value of zero corresponds to a completely amorphous material. X-ray diffraction data were collected using a Philips vertical diffractometer (available from Philips Analytical, Natick, Mass.), copper K&agr; (“K
alpha
”) radiation, and proportional detector registry of the scattered radiation. The diffractometer was fitted with variable entrance slits, diffracted beam graphite monochromator, and fixed exit slits. The X-ray generator had a sealed tube source, which used a copper target, and was operated at 45 kilovolts (kV) and 30 milliAmperes (mA). Data were collected in a reflection geometry from 5 to 55 degrees (corresponding to an angle of “2 theta”) using a 0.04 degree step size and 8 second dwell time. Samples were prepared as thin smears on zero background specimen holders made of single crystal quartz. The program ORIGIN™ (Version 4.1, available from Microcal Software Incorporated, Northhampton, Mass.) was used to perform the profile fitting and measure peak area values. A Gaussian peak shape model and linear background model were employed to describe the individual crystalline peak and amorphous peak contributions. Crystallinity indices were calculated as the ratio of crystalline peak area to total (crystalline+amorphous) scattered peak area within the 6 to 36 degree (corresponding to an angle of “2 theta”) scattering angle range.
Component A may have a Tm between about 5° C. and 120° C. (generally between about 40° C. and 105° C.) and a Tg below about 0° C. Essentially crystalline materials are included within the scope of “essentially semicrystalline” materials. If Component A is provided in the form of a polyester polyol, it may comprise the reaction product of a polyol, for example, a diol, and a polyacid, for example, a dicarboxylic acid.
Component A typically has a number average molecular weight (Mn) of at least about 2000, generally at least between about 2200 and about 10,000, and in specific embodiments between about 2500 and about 8500. At an Mn below about 2000, the resultant prepolymer is soft and may lack cohesive strength in the uncured state. At an Mn above about 10,000, the resultant prepolymer tends to be viscous which increases the difficulty of depositing acceptably thin lines of adhesive on a substrate.
A suitable diol useful in preparing the hydroxy-functional material Component A include, for example, those having from 2 to 12 methylene groups such as ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol. Cycloaliphatic diols such as, for example, 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol may also be employed.
A suitable dicarboxylic acid useful in preparing the hydroxy-functional material of Component A include, for example, those having from about 2 to 10 methylene groups such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, and 1,12-dodecanedioic acid. Included within the scope of useful acids are acid derivatives such as acid anhydrides, acid halides, and alkyl esters such as, for example, the methyl and ethyl esters.
Certain examples of a suitable Component A of the invention include, for example, polyhexamethylene sebacate, polyhexamethylene adipate, polybutylene adipate, polyhexamethylene dodecanedioate, poly-epsilon-caprolactone, and combinations thereof. In some embodiments, the essentially semicrystalline polyester polyol is polyhexamethylene sebacate or polyhexamethylene adipate. In specific embodiments, the essentially semicrystalline polyester polyol is 1,6-polyhexamethylene sebacate. 1,6-polyhexamethylene sebacate is the reaction product of 1,6-hexanediol and sebacic acid.
Examples of commercially available essentially semicrystalline polyester polyols useful in the invention include, for example, RUCOFLEX S-1074P-30 from Ruco Polymer Corporation, Hicksville, N.Y. and RUCOFLEX S-105P-30 from Ruco Polymer Corporation, Hicksville, N.Y.
Second Isocyanate-Te
3M Innovative Properties Company
Blank Colene H.
Yoon Tae H.
LandOfFree
Moisture curing hot-melt adhesives does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Moisture curing hot-melt adhesives, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Moisture curing hot-melt adhesives will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3278660