Patent Application
20120077929
The present invention relates to polyurethane ionomers based on polytrimethylene ether glycol (“PO3G”), aqueous dispersions of such polyurethanes, and their manufacture and use.
Polyurethanes are materials with a substantial range of physical and chemical properties, and are widely used in a variety of applications such as coatings, adhesives, fibers, foams and elastomers. For many of these applications, the polyurethanes are used as organic solvent-based solutions; however, recently environmental concerns have caused solvent-based polyurethanes to be replaced by aqueous dispersions in many applications.
Polyurethane polymers are, for the purposes of the present disclosure, polymers wherein the polymer backbone contains urethane linkage derived from the reaction of an isocyanate group (from, e.g., a di- or higher-functional monomeric, oligomeric and/or polymeric polyisocyante) with a hydroxyl group (from, e.g., a di- or higher-functional monomeric, oligomeric and/or polymeric polyol). Such polymers may, in addition to the urethane linkage, also contain other isocyanate-derived linkages such as urea, as well as other types of linkages present in the polyisocyanate components and/or polyol components (such as, for example, ester and ether linkage).
Polyurethane polymers can be manufactured by a variety of well-known methods, but are often prepared by first making an isocyanate-terminated “prepolymer” from polyols, polyisocyanates and other optional compounds, then chain-extending and/or chain-terminating this prepolymer to obtain a polymer possessing an appropriate molecular weight and other properties for a desired end use. Tri- and higher-functional starting components can be utilized to impart some level of branching and/or crosslinking to the polymer structure (as opposed to simple chain extension).
Polyurethanes have been prepared using PO3G-based homo and copolymers, as disclosed in U.S. Pat. No. 6,852,823, U.S. Pat. No. 6,946,539, US2005/0176921A1, US2007/0129524A1, and Conjeevaram et al. (J Polym Sci, 23, 429, (1985)). These publications, however, do not disclose PO3G-based polyurethane ionomer compositions and aqueous dispersions thereof.
Aqueous dispersions of polyurethanes are in a generic sense well known in the art. The polyurethanes can be stably dispersed in the aqueous medium by one or a combination of mechanisms, including external emulsifiers/surfactants and/or hydrophilic stabilizing groups (ionic and/or non-ionic) present as part of the polyurethane polymer.
Aqueous dispersions of self-dispersing, ionic polyurethanes are disclosed, for example, in U.S. Pat. No. 3,412,054 and U.S. Pat. No. 3,479,310. In these disclosures, ionic or potentially ionic diols are incorporated into the polyurethane polymer and, following neutralization, these polyurethane ionomers can be stably dispersed in water. The polyurethane dispersion process and chemistry has been reviewed by Dieterich, Prog. Org. Coat. 9, 1981, 281, and in Industrial Polymers Handbook 2001, 1, 419-502.
Polyurethane dispersions have been made using a wide range of polymeric and low molecular weight diols, diisocyanates and hydrophilic species. The dispersion process may involve synthesis and inversion from volatile solvent such as acetone, followed by distillation to remove organic solvent components. Polyurethanes may also be synthesized in the melt phase with or without inert, non-volatile solvents such as NMP (N-methylpyrrolidone). In this case, the solvent remains in the polyurethane dispersion. Added emulsifiers/surfactants may also be beneficial to dispersion stability.
Recently, polyurethane dispersions have been extended to acrylic/polyurethane hybrids and alloys, such as disclosed in U.S. Pat. No. 5,173,526, U.S. Pat. No. 4,644,030, U.S. Pat. No. 5,488,383 and U.S. Pat. No. 5,569,705. This process typically involves synthesis of polyurethanes in the presence of vinylic monomers (acrylates and/or styrene) as the solvent. Following inversion to form a polyurethane dispersion, the acrylic or styrenic monomers are polymerized by addition of free radical initiator(s). Variations on this process are known in the art. Acrylic/urethane hybrid dispersions offer potential advantages to coatings and other end products, including enhanced hardness, adhesion and nearly Newtonian rheology along with lower cost, low VOC and improved manufacturing.
Aqueous polyurethane dispersions have found application in numerous end uses, including but not limited to pigmented and clear coatings, textile treatments, paints, printing inks, adhesives and surface finishes. In general these polyurethane dispersions are added to the formulations as a freely added material and as such behave as non-interacting resins in the formulation. Thus there is a need for aqueous based polyurethane dispersions with good hydrophilic/hydrophobic balance and low viscosity.
One aspect of the present invention is an aqueous polyurethane dispersion comprising a polyurethane having a polymeric backbone having ionic and/or ionizable functionality incorporated into, pendant from and/or terminating the polymeric backbone. The polymeric backbone consists essentially of one or more non-ionic segments derived from a reaction product of polytrimethylene ether glycol and a diisocyanate. The polyurethane can be obtained from combination of: (a) a polyol component consisting of polytrimethylene ether glycol having a number average molecular weight from 250 to about 2000; (b) a diisocyanate; and (c) a hydrophilic reactant comprising a compound selected from the group consisting of (i) mono or diisocyanate containing an ionic and/or ionizable group, and (ii) an isocyanate reactive ingredient containing an ionic and/or ionizable group, wherein the aqueous polyurethane dispersion has a viscosity of less than 30 cP at 25° C. and the surface tension of at least 39 dynes/cm.
Another aspect of the present invention is a method of preparing an aqueous dispersion of a water-dispersible polyurethane ionomer comprising the steps:
(a) providing reactants comprising (i) a polyol component consisting essentially of polytrimethylene ether glycol having a number average molecular weight from 250 to about 2000, (ii) a diisocyanate, and (iii) a hydrophilic reactant comprising a compound selected from the group consisting of (1) mono or diisocyanate containing an ionic and/or ionizable group, (2) an isocyanate reactive ingredient containing an ionic and/or ionizable group and (3) mixtures thereof;
(b) reacting (i), (ii) and (iii) in the presence of a polymerizable acrylic compound to form a polyurethane/acrylic hybrid dispersion; and
(c) adding water to form an aqueous dispersion.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.
Except where expressly noted, trademarks are shown in upper case.
Unless stated otherwise, all percentages, parts, ratios, etc., are by weight.
When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.
When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or endpoint referred to.
As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
Use of “a” or “an” are employed to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.
The materials, methods, and examples herein are illustrative only and, except as specifically stated, are not intended to be limiting. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.
The polyurethane is preferably prepared from ingredients comprising (a) a polyol component comprising at least about 40 wt % PO3G (based on the total weight of polyol); (b) a polyisocyanate component comprising a diisocyanate; and (c) an ionic and/or ionizable functional group-containing component, wherein the an ionic and/or ionizable functional group-containing component comprises isocyanate and/or isocyanate-reactive functionality. Such a polyurethane with ionic and/or ionizable functional group(s) is a preferred example of a polyurethane “ionomer”.
As indicated above, the polyol component comprises at least about 40 wt % PO3G, more preferably at least about 50 wt % PO3G, still more preferably at least about 75 wt % PO3G, and even still more preferably at least about 90 wt % PO3G, based on the weight of the polyol component.
In one embodiment, the PO3G may be blended with other oligomeric and/or polymer polyfunctional isocyanate-reactive compounds such as, for example, polyols, polyamines, polythiols, polythioamines, polyhydroxythiols and polyhydroxylamines. When blended, it is preferred to use difunctional components and, more preferably, one or more diols including, for example, polyether diols, polyester diols, polycarbonate diols, polyacrylate diols, polyolefin diols and silicone diols.
In this embodiment, the PO3G is preferably blended with about 60 wt % or less, more preferably about 50 wt % or less, still more preferably about 25 wt % or less, and even still more preferably about 10 wt % or less, of the other isocyanate-reactive compounds.
PO3Gs for the purposes of the present disclosure are oligomers and polymers in which at least about 50% of the repeating units are trimethylene ether units. More preferably from about 75% to 100%, still more preferably from about 90% to 100%, and even more preferably from about 99% to 100%, of the repeating units are trimethylene ether units.
PO3Gs are preferably prepared by polycondensation of monomers comprising 1,3-propanediol, thus resulting in polymers or copolymers containing —(CH2CH2CH2O)— linkage (e.g, trimethylene ether repeating units). As indicated above, at least about 50% of the repeating units are trimethylene ether units.
In addition to the trimethylene ether units, lesser amounts of other units, such as other polyalkylene ether repeating units, may be present. In the context of this disclosure, the term “polytrimethylene ether glycol, PO3G” encompasses PO3G made from essentially pure 1,3-propanediol, as well as those oligomers and polymers (including those described below) containing up to about 50% by weight of comonomers.
The 1,3-propanediol employed for preparing the PO3G may be obtained by any of the various well known chemical routes or by biochemical transformation routes. Preferred routes are described in, for example, U.S. Pat. No. 5,015,789, U.S. Pat. No. 5,276,201, U.S. Pat. No. 5,284,979, U.S. Pat. No. 5,334,778, U.S. Pat. No. 5,364,984, U.S. Pat. No. 5,364,987, U.S. Pat. No. 5,633,362, U.S. Pat. No. 5,686,276, U.S. Pat. No. 5,821,092, U.S. Pat. No. 5,962,745, U.S. Pat. No. 6,140,543, U.S. Pat. No. 6,232,511, U.S. Pat. No. 6,235,948, U.S. Pat. No. 6,277,289, U.S. Pat. No. 6,297,408, U.S. Pat. No. 6,331,264, U.S. Pat. No. 6,342,646, U.S. Pat. No. 7,038,092, US20040225161A1, US20040260125A1, US20040225162A1 and US20050069997A1.
Preferably, the 1,3-propanediol is obtained biochemically from a renewable source (“biologically-derived” 1,3-propanediol). A particularly preferred source of 1,3-propanediol is via a fermentation process using a renewable biological source. As an illustrative example of a starting material from a renewable source, biochemical routes to 1,3-propanediol (PDO) have been described that utilize feedstocks produced from biological and renewable resources such as corn feed stock. For example, bacterial strains able to convert glycerol into 1,3-propanediol are found in the species Klebsiella, Citrobacter, Clostridium, and Lactobacillus. The technique is disclosed in several publications, including U.S. Pat. No. 5,633,362, U.S. Pat. No. 5,686,276 and U.S. Pat. No. 5,821,092. U.S. Pat. No. 5,821,092 discloses, inter alia, a process for the biological production of 1,3-propanediol from glycerol using recombinant organisms. The process incorporates E. coli bacteria, transformed with a heterologous pdu diol dehydratase gene, having specificity for 1,2propanediol. The transformed E. coli is grown in the presence of glycerol as a carbon source and 1,3-propanediol is isolated from the growth media. Since both bacteria and yeasts can convert glucose (e.g., corn sugar) or other carbohydrates to glycerol, the processes disclosed in these publications provide an alternative to conventional sources of 1,3-propanediol monomer.
The biologically-derived 1,3-propanediol, such as produced by the processes described and referenced above, contains carbon from the atmospheric carbon dioxide incorporated by plants, which compose the feedstock for the production of the 1,3-propanediol. In this way, the preferred biologically-derived 1,3-propanediol contains only renewable carbon, and not fossil fuel-based or petroleum-based carbon. The PO3G, and polyurethane ionomers and aqueous polyurethane dispersions utilizing the biologically-derived 1,3-propanediol, therefore, can have less impact on the environment as the 1,3-propanediol used in the compositions does not deplete diminishing fossil fuels and, upon degradation, releases carbon back to the atmosphere for use by plants once again.
The biologically-derived 1,3-propanediol, and PO3G and polyurethanes based thereon, may be distinguished from similar compounds produced from a petrochemical source or from fossil fuel carbon by dual carbon-isotopic finger printing. This method usefully distinguishes chemically-identical materials, and apportions carbon in the copolymer by source (and possibly year) of growth of the biospheric (plant) component. The isotopes, 14C and 13C, bring complementary information to this problem. The radiocarbon dating isotope (14C), with its nuclear half life of 5730 years, clearly allows one to apportion specimen carbon between fossil (“dead”) and biospheric (“alive”) feedstocks (Currie, L. A. “Source Apportionment of Atmospheric Particles,” Characterization of Environmental Particles, J. Buffle and H. P. van Leeuwen, Eds., 1 of Vol. I of the IUPAC Environmental Analytical Chemistry Series (Lewis Publishers, Inc) (1992) 3-74). The basic assumption in radiocarbon dating is that the constancy of 14C concentration in the atmosphere leads to the constancy of 14C in living organisms. When dealing with an isolated sample, the age of a sample can be deduced approximately by the relationship:
t=(−5730/0.693)In(A/A0)
wherein t=age, 5730 years is the half-life of radiocarbon, and A and A0 are the specific 14C activity of the sample and of the modern standard, respectively (Hsieh, Y., Soil Sci. Soc. Am J., 56, 460, (1992)). However, because of atmospheric nuclear testing since 1950 and the burning of fossil fuel since 1850, 14C has acquired a second, geochemical time characteristic. Its concentration in atmospheric CO2, and hence in the living biosphere, approximately doubled at the peak of nuclear testing, in the mid-1960s. It has since been gradually returning to the steady-state cosmogenic (atmospheric) baseline isotope rate (14C/12C) of ca. 1.2×10−12, with an approximate relaxation “half-life” of 7-10 years. (This latter half-life must not be taken literally; rather, one must use the detailed atmospheric nuclear input/decay function to trace the variation of atmospheric and biospheric 14C since the onset of the nuclear age.) It is this latter biospheric 14C time characteristic that holds out the promise of annual dating of recent biospheric carbon. 14C can be measured by accelerator mass spectrometry (AMS), with results given in units of “fraction of modern carbon” (fM). fM is defined by National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) 4990B and 4990C, known as oxalic acids standards HOxI and HOxII, respectively. The fundamental definition relates to 0.95 times the 14C/12C isotope ratio HOxI (referenced to AD 1950). This is roughly equivalent to decay-corrected pre-Industrial Revolution wood. For the current living biosphere (plant material), fM≈1.1.
The stable carbon isotope ratio (13C/12C) provides a complementary route to source discrimination and apportionment. The 13C/12C ratio in a given biosourced material is a consequence of the 13C/12C ratio in atmospheric carbon dioxide at the time the carbon dioxide is fixed and also reflects the precise metabolic pathway. Regional variations also occur. Petroleum, C3 plants (the broadleaf), C4 plants (the grasses), and marine carbonates all show significant differences in 13C/12C and the corresponding δ13C values. Furthermore, lipid matter of C3 and C4 plants analyze differently than materials derived from the carbohydrate components of the same plants as a consequence of the metabolic pathway. Within the precision of measurement, 13C shows large variations due to isotopic fractionation effects, the most significant of which is the photosynthetic mechanism. The major cause of differences in the carbon isotope ratio in plants is closely associated with differences in the pathway of photosynthetic carbon metabolism in the plants, particularly the reaction occurring during the primary carboxylation, i.e., the initial fixation of atmospheric CO2. Two large classes of vegetation are those that incorporate the “C3” (or Calvin-Benson) photosynthetic cycle and those that incorporate the “C4” (or Hatch-Slack) photosynthetic cycle. C3 plants, such as hardwoods and conifers, are dominant in the temperate climate zones. In C3 plants, the primary CO2 fixation or carboxylation reaction involves the enzyme ribulose-1,5-diphosphate carboxylase and the first stable product is a 3-carbon compound. C4 plants, on the other hand, include such plants as tropical grasses, corn and sugar cane. In C4 plants, an additional carboxylation reaction involving another enzyme, phosphoenolpyruvate carboxylase, is the primary carboxylation reaction. The first stable carbon compound is a 4-carbon acid, which is subsequently decarboxylated. The CO2 thus released is refixed by the C3 cycle.
Both C4 and C3 plants exhibit a range of 13C/12C isotopic ratios, but typical values are ca. −10 to −14 per mil (C4) and −21 to −26 per mil (C3) (Weber et al., J. Agric. Food Chem., 45, 2942 (1997)). Coal and petroleum fall generally in this latter range. The 13C measurement scale was originally defined by a zero set by pee dee belemnite (PDB) limestone, where values are given in parts per thousand deviations from this material. The “δ13C” values are in parts per thousand (per mil), abbreviated % o, and are calculated as follows:
Since the PDB reference material (RM) has been exhausted, a series of alternative RMs have been developed in cooperation with the IAEA, USGS, NIST, and other selected international isotope laboratories. Notations for the per mil deviations from PDB is δ13C. Measurements are made on CO2 by high precision stable ratio mass spectrometry (IRMS) on molecular ions of masses 44, 45 and 46.
Biologically-derived 1,3-propanediol, and compositions comprising biologically-derived 1,3-propanediol, therefore, may be completely distinguished from their petrochemical derived counterparts on the basis of 14C (fM) and dual carbon-isotopic fingerprinting, indicating new compositions of matter. The ability to distinguish these products is beneficial in tracking these materials in commerce. For example, products comprising both “new” and “old” carbon isotope profiles may be distinguished from products made only of “old” materials. Hence, the materials can be followed in commerce on the basis of their unique profile and for the purposes of defining competition, for determining shelf life, and for assessing environmental impact.
Preferably the 1,3-propanediol used as the reactant or as a component of the reactant will have a purity of greater than about 99%, and more preferably greater than about 99.9%, by weight as determined by gas chromatographic analysis. Particularly preferred are the purified 1,3-propanediols as disclosed in U.S. Pat. No. 7,038,092, US20040260125A1, U520040225161A1 and US20050069997A1, as well as PO3G made therefrom as disclosed in US20050020805A1.
The purified 1,3-propanediol preferably has the following characteristics:
(1) an ultraviolet absorption at 220 nm of less than about 0.200, and at 250 nm of less than about 0.075, and at 275 nm of less than about 0.075; and/or
(2) a composition having L*a*b* “b*” color value of less than about 0.15 (ASTM D6290), and an absorbance at 270 nm of less than about 0.075; and/or
(3) a peroxide composition of less than about 10 ppm; and/or
(4) a concentration of total organic impurities (organic compounds other than 1,3-propanediol) of less than about 400 ppm, more preferably less than about 300 ppm, and still more preferably less than about 150 ppm, as measured by gas chromatography.
The starting material for making PO3G will depend on the desired PO3G, availability of starting materials, catalysts, equipment, etc., and comprises “1,3-propanediol reactant.” By “1,3-propanediol reactant” is meant 1,3-propanediol, and oligomers and prepolymers of 1,3-propanediol preferably having a degree of polymerization of 2 to 9, and mixtures thereof. In some instances, it may be desirable to use up to 10% or more of low molecular weight oligomers where they are available. Thus, preferably the starting material comprises 1,3-propanediol and the dimer and trimer thereof. A particularly preferred starting material is comprised of about 90% by weight or more 1,3-propanediol, and more preferably 99% by weight or more 1,3-propanediol, based on the weight of the 1,3-propanediol reactant.
PO3G can be made via a number of processes known in the art, such as disclosed in U.S. Pat. No. 6,977,291 and U.S. Pat. No. 6,720,459. A preferred process is as set forth in US20050020805A1.
As indicated above, PO3G may contain lesser amounts of other polyalkylene ether repeating units in addition to the trimethylene ether units. The monomers for use in preparing polytrimethylene ether glycol can, therefore, contain up to 50% by weight (preferably about 20 wt % or less, more preferably about 10 wt % or less, and still more preferably about 2 wt % or less), of comonomer polyols in addition to the 1,3-propanediol reactant. Comonomer polyols that are suitable for use in the process include aliphatic diols, for example, ethylene glycol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 3,3,4,4,5,5-hexafluro-1,5-pentanediol, 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol, and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10-hexadecafluoro-1,12-dodecanediol; cycloaliphatic diols, for example, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and isosorbide; and polyhydroxy compounds, for example, glycerol, trimethylolpropane, and pentaerythritol. A preferred group of comonomer diols is selected from the group consisting of ethylene glycol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, C6-C10 diols (such as 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol) and isosorbide, and mixtures thereof. A particularly preferred diol other than 1,3-propanediol is ethylene glycol, and C6-C10 diols can be particularly useful as well.
One preferred PO3G containing comonomers is poly(trimethyleneethylene ether) glycol such as described in US2004/0030095A1. Preferred poly(trimethylene-ethylene ether) glycols are prepared by acid catalyzed polycondensation of from 50 to about 99 mole % (preferably from about 60 to about 98 mole %, and more preferably from about 70 to about 98 mole %) 1,3-propanediol and up to 50 to about 1 mole % (preferably from about 40 to about 2 mole %, and more preferably from about 30 to about 2 mole %) ethylene glycol.
Suitable PO3Gs useful can contain small amounts of other repeat units, for example, from aliphatic or aromatic diacids or diesters, such as described in U.S. Pat. No. 6,608,168. This type of PO3G can also be called a “random polytrimethylene ether ester”, and can be prepared by polycondensation of 1,3-propanediol reactant and about 10 to about 0.1 mole % of aliphatic or aromatic diacid or esters thereof, such as terephthalic acid, isophthalic acid, bibenzoic acid, naphthalic acid, bis(p-carboxyphenyl)methane, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 4,4′-sulfonyl dibenzoic acid, p-(hydroxyethoxy)benzoic acid, and combinations thereof, and dimethyl terephthalate, bibenzoate, isophthlate, naphthalate and phthalate; and combinations thereof. Of these, terephthalic acid, dimethyl terephthalate and dimethyl isophthalate are preferred.
Preferably, the PO3G after purification has essentially no acid catalyst end groups, but may contain very low levels of unsaturated end groups, predominately allyl end groups, in the range of from about 0.003 to about 0.03 meq/g. A preferred PO3G can be considered to comprise (consist essentially of) the compounds having the following formulae (II) and (III):
HO—((CH2)3O)m—H (II)
HO—((CH2)3—O)mCH2CH═CH2 (III)
wherein m is in a range such that the Mn, the number average molecular weight, is within the range of from about 200 to about 5,000, with compounds of formula (III) being present in an amount such that the allyl end groups (preferably all unsaturation ends or end groups) are present in the range of from about 0.003 to about 0.03 meq/g. The small number of allyl end groups in the polytrimethylene ether glycols are useful to control polyurethane molecular weight, while not unduly restricting it, so that compositions ideally suited for particular end-uses can be prepared.
The preferred PO3Gs have a number average molecular weight (Mn) in the range of about 200 to about 5000, and more preferably from about 200 to about 3000. More preferred PO3Gs have a Mn in the range of about 250 to 2000. The PO3Gs preferred for use herein are typically polydisperse polymers having a polydispersity (i.e. Mw/Mn) of preferably from about 1.1 to about 2.2, more preferably from about 1.2 to about 2.2, and still more preferably from about 1.5 to about 2.1. The polydispersity can be adjusted by using blends of PO3Gs.
The PO3Gs preferably have a surface tension in the range of 40-43 dynes/cm at ambient temperature. The surface tension is a measure of the inward force acting on the surface of a liquid due to the attraction of molecules in the liquid. The surface tension decreases slightly with increase in molecular weight of polytrimethylene ether glycol. The surface tension of the polytrimethylene ether glycol affects the surface tension of the aqueous polyurethane dispersions.
The PO3Gs preferably have viscosity in the range of 30-2000 cP at 40° C. The PO3Gs preferably have a color value of less than about 100 APHA, and more preferably less than about 50 APHA.
As indicated above, the PO3G may be blended with other polyfunctional isocyanate-reactive components, preferably up to about 60 wt %, most notably oligomeric and/or polymeric polyols.
Suitable polyols contain at least two hydroxyl groups, and preferably have a molecular weight of from about 60 to about 6000. Of these, the polymeric polyols are best defined by the number average molecular weight, and can range from about 200 to about 6000, preferably from about 300 to about 3000, and more preferably from about 500 to about 2500. The molecular weights can be determined by hydroxyl group analysis (OH number).
Examples of polymeric polyols include polyesters, polyethers, polycarbonates, polyacetals, poly(meth)acrylates, polyester amides, polythioethers, and mixed polymers such as a polyester-polycarbonates where both ester and carbonate linkages are found in the same polymer. Also included are vegetable-based polyols. A combination of these polymers can also be used. For examples, a polyester polyol and a poly(meth)acrylate polyol may be used in the same polyurethane synthesis.
Suitable polyester polyols include reaction products of polyhydric, preferably dihydric alcohols to which trihydric alcohols may optionally be added, and polybasic (preferably dibasic) carboxylic acids. Instead of these polycarboxylic acids, the corresponding carboxylic acid anhydrides or polycarboxylic acid esters of lower alcohols or mixtures thereof may be used for preparing the polyesters.
The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic or mixtures thereof and they may be substituted, for example, by halogen atoms, and/or unsaturated. The following are mentioned as examples: succinic acid; adipic acid; suberic acid; azelaic acid; sebacic acid; 1,12-dodecyldioic acid; phthalic acid; isophthalic acid; trimellitic acid; phthalic acid anhydride; tetrahydrophthalic acid anhydride; hexahydrophthalic acid anhydride; tetrachlorophthalic acid anhydride; endomethylene tetrahydrophthalic acid anhydride; glutaric acid anhydride; maleic acid; maleic acid anhydride; fumaric acid; dimeric and trimeric fatty acids such as oleic acid, which may be mixed with monomeric fatty acids; dimethyl terephthalates and bis-glycol terephthalate.
Suitable polyhydric alcohols include, e.g., ethylene glycol; propylene glycol-(1,2) and -(1,3); butylene glycol-(1,4) and -(1,3); hexanediol-(1,6); octanediol-(1,8); neopentyl glycol; cyclohexanedimethanol (1,4-bis-hydroxymethyl-cyclohexane); 2-methyl-1,3-propanediol; 2,2,4-trimethyl-1,3-pentanediol; diethylene glycol, triethylene glycol; tetraethylene glycol; polyethylene glycol; dipropylene glycol; polypropylene glycol; dibutylene glycol and polybutylene glycol; glycerine; trimethylolpropane; ether glycols thereof; and mixtures thereof. The polyester polyols may also contain a portion of carboxyl end groups. Polyesters of lactones, for example, epsilon-caprolactone, or hydroxycarboxylic acids, for example, omega-hydroxycaproic acid, may also be used.
Preferable polyester diols for blending with PO3G are hydroxyl-terminated poly(butylene adipate), poly(butylene succinate), poly(ethylene adipate), poly(1,2-proylene adipate), poly(trimethylene adipate), poly(trimethylene succinate), polylactic acid ester diol and polycaprolactone diol. Other hydroxyl terminated polyester diols are copolyethers comprising repeat units derived from a diol and a sulfonated dicarboxylic acid and prepared as described in U.S. Pat. No. 6,316,586. The preferred sulfonated dicarboxylic acid is 5-sulfo-isophthalic acid, and the preferred diol is 1,3-propanediol.
Suitable polyether polyols are obtained in a known manner by the reaction of starting compounds that contain reactive hydrogen atoms with alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide, epichlorohydrin or mixtures of these. Suitable starting compounds containing reactive hydrogen atoms include the polyhydric alcohols set forth above and, in addition, water, methanol, ethanol, 1,2,6-hexane triol, 1,2,4-butane triol, trimethylol ethane, pentaerythritol, mannitol, sorbitol, methyl glycoside, sucrose, phenol, isononyl phenol, resorcinol, hydroquinone, 1,1,1- and 1,1,2-tris-(hydroxylphenyl)-ethane, dimethylolpropionic acid or dimethylolbutanoic acid.
Polyethers that have been obtained by the reaction of starting compounds containing amine compounds can also be used. Examples of these polyethers as well as suitable polyhydroxy polyacetals, polyhydroxy polyacrylates, polyhydroxy polyester amides, polyhydroxy polyamides and polyhydroxy polythioethers, are disclosed in U.S. Pat. No. 4,701,480.
Preferred polyether diols for blending with PO3G are polyethylene glycol, poly(1,2-propylene glycol), polytetramethylene ether glycol, copolyethers such as tetrahydrofuran/ethylene oxide and tetrahydrofuran/propylene oxide copolymers, and mixtures thereof.
Polycarbonates containing hydroxyl groups include those known, per se, such as the products obtained from the reaction of diols such as propanediol(1,3), butanediol-(1,4) and/or hexanediol-(1,6), diethylene glycol, triethylene glycol or tetraethylene glycol, higher polyether diols with phosgene, diarylcarbonates such as diphenylcarbonate, dialkylcarbonates such as diethylcarbonate or with cyclic carbonates such as ethylene or propylene carbonate. Also suitable are polyester carbonates obtained from the above-mentioned polyesters or polylactones with phosgene, diaryl carbonates, dialkyl carbonates or cyclic carbonates.
Polycarbonate diols for blending are preferably selected from the group consisting of polyethylene carbonate diol, polytrimethylene carbonate diol, polybutylene carbonate diol and polyhexylene carbonate diol.
Poly(meth)acrylates containing hydroxyl groups include those common in the art of addition polymerization such as cationic, anionic and radical polymerization and the like. Examples are alpha-omega diols. An example of these type of diols are those which are prepared by a “living” or “control” or chain transfer polymerization processes which enables the placement of one hydroxyl group at or near the termini of the polymer. U.S. Pat. No. 6,248,839 and U.S. Pat. No. 5,990,245 have examples of protocol for making terminal diols. Other di-NCO reactive poly(meth)acrylate terminal polymers can be used. An example would be end groups other than hydroxyl such as amino or thiol, and may also include mixed end groups with hydroxyl.
Polyolefin diols are available from Shell as KRATON LIQUID L and Mitsubishi Chemical as POLYTAIL H.
Silicone glycols are well known, and representative examples are described in U.S. Pat. No. 4,647,643.
In some instances, vegetable oils may be the preferred blending component because of their biological origin and biodegradability. Examples of vegetable oils include but are not limited to sunflower oil, canola oil, rapeseed oil, corn oil, olive oil, soybean oil, castor oil and mixtures thereof. These oils are either partial or fully hydrogenated. Commercially available examples of such vegetable oils include Soyol R2-052-G (Urethane Soy Systems) and Pripol 2033 (Uniqema).
Other optional compounds for preparing the NCO-functional prepolymer include lower molecular weight, at least difunctional NCO-reactive compounds having an average molecular weight of up to about 400. Examples include the dihydric and higher functional alcohols, which have previously been described for the preparation of the polyester polyols and polyether polyols.
In addition to the above-mentioned components, which are preferably difunctional in the isocyanate polyaddition reaction, mono-functional and even small portions of trifunctional and higher functional components generally known in polyurethane chemistry, such as trimethylolpropane or 4-isocyanantomethyl-1,8-octamethylene diisocyanate, may be used in cases in which branching of the NCO prepolymer or polyurethane is desired.
It is, however, preferred that the NCO-functional prepolymers should be substantially linear, and this may be achieved by maintaining the average functionality of the prepolymer starting components at or below 2:1.
Similar NCO reactive materials can be used as described for hydroxy containing compounds and polymers, but which contain other NCO reactive groups. Examples would be dithiols, diamines, thioamines, and even hydroxythiols and hydroxylamines. These can either be compounds or polymers with the molecular weights or number average molecular weights as described for the polyols.
Other optional compounds include isocyanate-reactive compounds containing self-condensing moieties. The content of these compounds are dependent upon the desired level of self-condensation necessary to provide the desirable resin properties. 3-amino-1-triethoxysilyl-propane is an example of a compound that will react with isocyanates through the amino group and yet self-condense through the silyl group when inverted into water.
Other optional compounds include isocyanate-reactive compounds containing non-condensable silanes and/or fluorocarbons with isocyanate reactive groups, which can be used in place of or in conjunction with the isocyanate-reactive compounds. U.S. Pat. No. 5,760,123 and U.S. Pat. No. 6,046,295 list examples of methods for use of these optional silane/fluoro-containing compounds.
Suitable polyisocyanates are those that contain aromatic, cycloaliphatic and/or aliphatic groups bound to the isocyanate groups. Mixtures of these compounds may also be used. Preferred are compounds with isocyanates bound to a cycloaliphatic or aliphatic moieties. If aromatic isocyanates are used, cycloaliphatic or aliphatic isocyanates are preferably present as well.
Diisocyanates are preferred, and any diisocyanate useful in preparing polyurethanes and/or polyurethane-ureas from polyether glycols, diols and/or amines can be used
Examples of suitable diisocyanates include, but are not limited to, 2,4-toluene diisocyanate (TDI); 2,6-toluene diisocyanate; trimethyl hexamethylene diisocyanate (TMDI); 4,4′-diphenylmethane diisocyanate (MDI); 4,4′-dicyclohexylmethane diisocyanate (H12MDI); 3,3′-dimethyl-4,4′-biphenyl diisocyanate (TODI); Dodecane diisocyanate (C12DI); m-tetramethylene xylylene diisocyanate (TMXDI); 1,4-benzene diisocyanate; trans-cyclohexane-1,4-diisocyanate; 1,5-naphthalene diisocyanate (NDI); 1,6-hexamethylene diisocyanate (HDI); 4,6-xylyene diisocyanate; isophorone diisocyanate (IPDI); and combinations thereof. IPDI and TMXDI are preferred.
Small amounts, preferably less than about 10 wt % based on the weight of the diisocyanate, of monoisocyanates or polyisocyanates can be used in mixture with the diisocyanate. Examples of useful monoisocyanates include alkyl isocyanates such as octadecyl isocyanate and aryl isocyanates such as phenyl isocyanate. An example of a polyisocyanate is triisocyanatotoluene HDI trimer (Desmodur 3300), and polymeric MDI (Mondur MR and MRS).
The hydrophilic reactant contains ionic and/or ionizable groups (potentially ionic groups). Preferably, these reactants will contain one or two, more preferably two, isocyanate reactive groups, as well as at least one ionic or ionizable group.
Examples of ionic dispersing groups include carboxylate groups (COOM), phosphate groups (—OPO3 M2), phosphonate groups (—PO3 M2), sulfonate groups (—SO3 M), quaternary ammonium groups (—NR3 Y, wherein Y is a monovalent anion such as chlorine or hydroxyl), or any other effective ionic group. M is a cation such as a monovalent metal ion (e.g., Na+, K+, Li+, etc.), H+, NR4+, and each R can be independently an alkyl, aralkyl, aryl, or hydrogen. These ionic dispersing groups are typically located pendant from the polyurethane backbone.
The ionizable groups in general correspond to the ionic groups, except they are in the acid (such as carboxyl —COOH) or base (such as primary, secondary or tertiary amine —NH2, —NRH, or —NR2) form. The ionizable groups are such that they are readily converted to their ionic form during the dispersion/polymer preparation process as discussed below.
The ionic or potentially ionic groups are chemically incorporated into the polyurethane in an amount to provide an ionic group content (with neutralization as needed) sufficient to render the polyurethane dispersible in the aqueous medium of the dispersion. Typical ionic group content will range from about 5 up to about 210 milliequivalents (meq), preferably from about 10 to about 140 meq, more preferably from about 20 to about 120 meq, and still more preferably from about 30 to about 90 meq, per 100 g of polyurethane.
Suitable compounds for incorporating these groups include (1) monoisocyanates or diisocyanates which contain ionic and/or ionizable groups, and (2) compounds which contain both isocyanate reactive groups and ionic and/or ionizable groups. In the context of this disclosure, the term “isocyanate reactive groups” is taken to include groups well known to those of ordinary skill in the relevant art to react with isocyanates, and preferably hydroxyl, primary amino and secondary amino groups.
Examples of isocyanates that contain ionic or potentially ionic groups are sulfonated toluene diisocyanate and sulfonated diphenylmethanediisocyanate.
With respect to compounds which contain isocyanate reactive groups and ionic or potentially ionic groups, the isocyanate reactive groups are typically amino and hydroxyl groups. The potentially ionic groups or their corresponding ionic groups may be cationic or anionic, although the anionic groups are preferred. Preferred examples of anionic groups include carboxylate and sulfonate groups. Preferred examples of cationic groups include quaternary ammonium groups and sulfonium groups.
The neutralizing agents for converting the ionizable groups to ionic groups are described in the publications cited hereinabove, and are also discussed hereinafter. As used herein, the term “neutralizing agents” is meant to embrace all types of agents that are useful for converting ionizable groups to the more hydrophilic ionic (salt) groups.
Suitable compounds for incorporating the previously discussed carboxylate, sulfonate and quaternary nitrogen groups are described in U.S. Pat. No. 3,479,310, U.S. Pat. No. 4,303,774, U.S. Pat. No. 4,108,814 and U.S. Pat. No. 4,408,008.
Suitable compounds for incorporating tertiary sulfonium groups are described in U.S. Pat. No. 3,419,533.
Sulfonate groups for incorporation into the polyurethanes preferably are the diol sulfonates as disclosed in U.S. Pat. No. 4,108,814. Suitable diol sulfonate compounds also include hydroxyl terminated copolyethers comprising repeat units derived from a diol and a sulfonated dicarboxylic acid and prepared as described in U.S. Pat. No. 6,316,586. The preferred sulfonated dicarboxylic acid is 5-sulfoisophthalic acid, and the preferred diol is 1,3-propanediol. Suitable sulfonates also include H2N—CH2—CH2—NH—(CH2)r—SO3Na, where r=2 or 3; and HO—CH2—CH2—C(SO3Na)—CH2—OH.
Examples of carboxylic group-containing compounds are the hydroxycarboxylic acids corresponding to the formula (HO)xQ(COOH)y wherein Q represents a straight or branched, hydrocarbon radical containing 1 to 12 carbon atoms, x is 1 or 2 (preferably 2), and y is 1 to 3 (preferably 1 or 2).
Examples of these hydroxy-carboxylic acids include citric acid, tartaric acid and hydroxypivalic acid.
The preferred acids are those of the above-mentioned formula wherein x=2 and y=1. These dihydroxy alkanoic acids are described in U.S. Pat. No. 3,412,054. The preferred group of dihydroxy alkanoic acids are the α,α-dimethylol alkanoic acids represented by the structural formula R2—C—(CH2OH)2—COOH, wherein R2 is hydrogen or an alkyl group containing 1 to 8 carbon atoms. Examples of these ionizable diols include but are not limited to dimethylolacetic acid, 2,2′-dimethylolbutanoic acid, 2,2′-dimethylolpropionic acid, and 2,2′-dimethylolbutyric acid. The most preferred dihydroxy alkanoic acids is 2,2′-dimethylolpropionic acid (“DMPA”).
When the ionic stabilizing groups are acids, the acid groups are incorporated in an amount sufficient to provide an acid group content, known by those skilled in the art as acid number (mg KOH per gram solid polymer), of at least about 5, preferably at least about 10 milligrams KOH per 1.0 gram of polyurethane. The upper limit for the acid number is about 90, and preferably about 60.
Suitable carboxylates also include H2N—(CH2)4—CH(CO2H)—NH2, and H2N—CH2—CH2—NH—CH2—CH2—CO2Na.
In addition to the foregoing, cationic centers such as tertiary amines with one alkyl and two alkylol groups may also be used as the ionic or ionizable group.
The process of preparing the dispersions begins with preparation of the polyurethane, which can be prepared by mixture or stepwise methods.
In the mixture process, an isocyanate-terminated polyurethane prepolymer is prepared by mixing the polyol component, the ionic reactants and solvent, and then adding polyisocyanate component to the mixture. This reaction is conducted at from about 40° C. to about 100° C., and more preferably from about 50° C. to about 90° C. The preferred ratio of isocyanate to isocyanate reactive groups is from about 1.3:1 to about 1.05:1, and more preferably from about 1.25:1 to about 1.1:1. When the targeted percent isocyanate is reached (typically an isocyanate content of about 1 to about 20%, preferably about 1 to about 10% by weight, based on the weight of prepolymer solids), then the optional chain terminator can be added, as well as a base or acid to neutralize ionizable groups incorporated from the ionic reactant.
If some cases, addition of neutralization agent, preferably tertiary amines, may be beneficial during early stages of the polyurethane synthesis. Alternately, advantages may be achieved via the addition of the neutralization agent, preferably alkali base, simultaneously along with the water of inversion at high shear.
In the stepwise method, an isocyanate-terminated polyurethane prepolymer is prepared by dissolving the ionic reactant in solvent, and then adding the polyisocyanate component to the mixture. Once the initial percent isocyanate target is reached, the polyol component is added. This reaction is conducted at from about 40° C. to about 100° C., and more preferably from about 50° C. to about 90° C. The preferred ratio of isocyanate to isocyanate reactive groups is from about 1.3:1 to about 1.05:1, and more preferably from about 1.25:1 to about 1.1:1. Alternately, the polyol component may be reacted in the first step, and the ionic reactant may be added after the initial percent isocyanate target is reached. When the final targeted percent isocyanate is reached (typically an isocyanate content of about 1 to about 20%, preferably about 1 to about 10% by weight, based on the weight of prepolymer solids), then the optional chain terminator may be added, as well as a base or acid to neutralize ionizable groups incorporated from the ionic reactant.
The resulting polyurethane solution is then converted to an aqueous polyurethane dispersion via the addition of water under shear, as discussed in further detail below. The optional chain extender is added at this point, if the chain terminator is omitted or reduced to leave sufficient isocyanate functionality. Chain extension is typically performed at 30° C. to 60° C. under aqueous conditions. If present, the volatile solvent is distilled under reduced pressure.
Catalysts are often necessary to prepare the polyurethanes, and may provide advantages in their manufacture. The catalysts most widely used are tertiary amines such as tertiary ethylamine, organo-tin compounds such as stannous octoate, dibutyltin dioctoate, dibutyltin dilaurate, organo-titanates such as TYZOR TPT or TYZOR TBT, organo-zirconates, and mixtures thereof.
Preparation of the polyurethane for subsequent conversion to a dispersion is facilitated by using solvent. Suitable solvents are those that are miscible with water and inert to isocyanates and other reactants utilized in forming the polyurethanes. If it is desired to prepare a solvent-free dispersion, then it is preferable to use a solvent with a high enough volatility to allow removal by distillation. Typical suitable solvents are acetone, methyl ethyl ketone, toluene, and N-methyl pyrollidone. Preferably the amount of solvent used in the reaction will be from about 10% to about 50%, more preferably from about 20% to about 40% of the weight.
Polymerizable vinyl compounds may also be used as solvents, followed by free radical polymerization after inversion, thus forming a polyurethane/acrylic hybrid dispersion, as disclosed in U.S. Pat. No. 5,173,526, U.S. Pat. No. 4,644,030, U.S. Pat. No. 5,488,383 and U.S. Pat. No. 5,569,705.
The polyurethanes are typical prepared by chain extending the NCO-containing prepolymers. The function of a chain extender is to increase the molecular weight of the polyurethanes. Chain extension can take place prior to addition of water in the process, but typically takes place by combining the NCO-containing prepolymer, chain extender, water and other optional components under agitation.
The reactants used to prepare the polyurethanes may contain a chain extender, which is typically a polyol, polyamine or aminoalcohol. When polyol chain extenders are used, urethane linkages form as the hydroxyl groups of the polyol react with isocyanates. When polyamine chain extenders are used, urea linkages are formed as the amine groups react with the isocyanates. Both structural types are included within the meaning of “polyurethanes”.
Preferably, the optional chain extender will be polyamine. Suitable polyamines for preparing the at least partially blocked polyamines have an average functionality, i.e., the number of amine nitrogens per molecule, of 2 to 6, preferably 2 to 4 and more preferably 2 to 3. The desired functionalities can be obtained by using mixtures of polyamines containing primary or secondary amino groups. The polyamines are generally aromatic, aliphatic or alicyclic amines and contain between 1 to 30, preferably 2 to 15 and more preferably 2 to 10 carbon atoms. These polyamines may contain additional substituents provided that they are not as reactive with isocyanate groups as the primary or secondary amines. These same polyamines can be partially or wholly blocked polyamines.
Diamine chain extenders useful in making the polyurethanes include 1,2-ethylenediamine; 1,6-hexanediamine; 1,2-propanediamine; 4,4′-methylene-bis(3-chloroaniline) (also known as 3,3′-dichloro-4,4′-diaminodiphenylmethane) (MOCA or Mboca); isophorone diamine; dimethylthiotoluenediamine (DMTDA); 4,4′-diaminodiphenylmethane (DDM); 1,3-diaminobenzene; 1,4-diaminobenzene; 3,3′-dimethoxy-4,4′-diamino biphenyl; 3,3′-dimethyl-4,4′-diamino biphenyl; 4,4′-diamino biphenyl; 3,3′-dichloro-4,4′-diamino biphenyl; hydrazine; and combinations thereof. Polyamines such as diethylene triamine (DETA), triethylene tetraamine (TETA), tetraethylene pentamine and pentaethylene hexamine are also useful.
Suitable polyamine chain extenders can optionally be partially or wholly blocked as disclosed in U.S. Pat. No. 4,269,748 and U.S. Pat. No. 4,829,122. These publications disclose the preparation of aqueous polyurethane dispersions by mixing NCO-containing prepolymers with at least partially blocked, diamine or hydrazine chain extenders in the absence of water and then adding the mixture to water. Upon contact with water the blocking agent is released and the resulting unblocked polyamine reacts with the NCO containing prepolymer to form the polyurethane.
Suitable blocked amines and hydrazines include the reaction products of polyamines with ketones and aldehydes to form ketimines and aldimines, and the reaction of hydrazine with ketones and aldehydes to form ketazines, aldazines, ketone hydrazones and aldehyde hydrazones. The at least partially blocked polyamines contain at most one primary or secondary amino group and at least one blocked primary or secondary amino group which releases a free primary or secondary amino group in the presence of water.
Water may also be employed as a chain extender. In this case, water will be present in a gross excess relative to the free isocyanate groups, and these ratios are not applicable since water functions as both dispersing medium and chain extender.
The reactants used to prepare the polyurethanes of the aqueous dispersions may also contain a chain terminator. The optional chain terminators control the molecular weight of the polyurethanes, and can be added before, during or after inversion of the pre-polymer.
Suitable chain terminators include amines or alcohols having an average functionality per molecule of 1, i.e., the number of primary or secondary amine nitrogens or alcohol oxygens would average 1 per molecule. The desired functionalities can be obtained by using primary or secondary amino groups. The amines or alcohols are generally aromatic, aliphatic or alicyclic and contain between 1 to 30, preferably 2 to 15 and more preferably 2 to 10 carbon atoms.
Preferred monoalcohols for use as chain terminators include C1-C18 alkyl alcohols such as n-butanol, n-octanol, and n-decanol, n-dodecanol, stearyl alcohol and C2-C12 fluorinated alcohols, and more preferably C1-C6 alkyl alcohols such as n-propanol, ethanol, and methanol.
Any primary or secondary monoamines reactive with isocyanates may be used as chain terminators. Aliphatic primary or secondary monoamines are preferred. Example of monoamines useful as chain terminators include but are not restricted to butylamine, hexylamine, 2-ethylhexyl amine, dodecyl amine, diisopropanol amine, stearyl amine, dibutyl amine, dinonyl amine, bis(2-ethylhexyl) amine, diethylamine, bis(methoxyethyl)amine, N-methylstearyl amine and N-methyl aniline. A more preferred isocyanate reactive chain terminator is bis(methoxyethyl)amine.
Urethane end groups are formed when alcohol chain terminators are used; urea end groups are formed when amine chain terminators are used. Both structural types are referred to herein as “polyurethanes”.
Chain terminators and chain extenders can be used together, either as mixtures or as sequential additions to the NCO-prepolymer.
The amount of chain extender/terminator employed should be approximately equivalent to the free isocyanate groups in the prepolymer, the ratio of active hydrogens in the chain extender to isocyanate groups in the prepolymer preferably being in the range from about 0.6:1 to about 1.3:1, more preferably from about 0.6:1 to about 1.1:1, and still more preferably from about 0.7:1 to about 1.1:1, and even more preferably from about 0.9:1 to about 1.1:1, on an equivalent basis. Any isocyanate groups that are not chain extended/terminated with an amine or alcohol will react with water which, as indicated above, functions as a chain extender.
When the potential cationic or anionic groups of the polyurethane are neutralized, they provide hydrophilicity to the polymer and better enable it to be stably dispersed in water. The neutralization steps may be conducted (1) prior to polyurethane formation by treating the component containing the potentially ionic group(s), or (2) after polyurethane formation, but prior to dispersing the polyurethane, or (3) concurrently with the dispersion preparation. The reaction between the neutralizing agent and the potentially ionic groups may be conducted between about 20° C. and about 150° C., but is normally conducted at temperatures below about 100° C., preferably between about 30° C. and about 80° C., and more preferably between about 50° C. and about 70° C., with agitation of the reaction mixture.
In order to have a stable dispersion, a sufficient amount of the ionic groups (e.g., neutralized ionizable groups) must be present so that the resulting polyurethane will remain stably dispersed in the aqueous medium. Generally, at least about 70%, preferably at least about 80%, of the acid groups are neutralized to the corresponding carboxylate salt groups. Alternatively, cationic groups in the polyurethane can be quaternary ammonium groups (—NR3Y, wherein Y is a monovalent anion such as chlorine or hydroxyl).
Suitable neutralizing agents for converting the acid groups to salt groups include tertiary amines, alkali metal cations and ammonia. Examples of these neutralizing agents are disclosed in U.S. Pat. No. 4,701,480, as well as U.S. Pat. No. 4,501,852. Preferred neutralizing agents are the trialkyl-substituted tertiary amines, such as triethyl amine, tripropyl amine, dimethylcyclohexyl amine, and dimethylethyl amine and alkali metal cations such as sodium or potassium. Substituted amines are also useful neutralizing groups such as diethyl ethanol amine or diethanol methyl amine.
Neutralization may take place at any point in the process. Typical procedures include at least some neutralization of the prepolymer, which is then chain extended/terminated in water in the presence of additional neutralizing agent.
The final product is a stable aqueous dispersion of polyurethane particles having a solids content of up to about 60% by weight, preferably from about 15 to about 60% by weight, and more preferably from about 20 to about 40% by weight. However, it is always possible to dilute the dispersions to any minimum solids content desired.
As used herein, the term “aqueous polyurethane dispersion” refers to aqueous dispersions of polymers containing urethane groups, as that term is understood by those of ordinary skill in the art. These polymers also incorporate hydrophilic functionality to the extent required to maintain a stable dispersion of the polymer in water. The compositions are aqueous dispersions that comprise a continuous phase comprising water, and a dispersed phase comprising polyurethane.
Following formation of the desired polyurethane, preferably in the presence of solvent as discussed above, the pH may be adjusted, if necessary, to insure conversion of ionizable groups to ionic groups (neutralization). For example, if the preferred dimethylolpropionic acid is the ionic or ionizable ingredient used in making the polyurethane, then sufficient aqueous base is added to convert the carboxyl groups to carboxylate anions.
Conversion to the aqueous dispersion is completed by addition of water. If desired, solvent can then be removed partially or substantially completely by distillation under reduced pressure. The total solids level of the aqueous dispersions are preferably in the range of from about 5 wt % to about 70 wt %, and more preferably from about 20 wt % to about 40 wt %, based on the total weight of the dispersion. The d50, or median particle size, is variable and dependent on ingredients and method of preparation but generally varies from about 1.0 to about 200 nanometers.
If desired, surfactant may be added to the dispersion to improve stability. The surfactant may be anionic, cationic or nonionic. If used, the preferred amount of surfactant is from about 0.1 wt % to about 2 wt %. Examples of preferred surfactants are dodecylbenzenesulfonate or TRITON X (Dow Chemical Co., Midland, Mich.).
The final product is a stable, aqueous polyurethane dispersion having a solids content of up to about 70% by weight, preferably from about 10% to about 60% by weight, and more preferably from about 20% to about 45% by weight. However, it is always possible to dilute the dispersions to any minimum solids content desired. The solids content of the resulting dispersion may be determined by drying the sample in an oven at 150° C. for 2 hours and comparing the weights before and after drying. The particle size is generally below about 1000 nanometer, and preferably between about 0.01 to about 300 nanometer. The average particle size should be less than about 500 nanometer, and preferably between about 100 to about 300 nanometer. The small particle size enhances the stability of the dispersed particles.
Flow properties of aqueous polyurethane dispersions are critical for certain applications. Low viscosity usually gives easy processability and better flow characteristics. The viscosity of the aqueous polyurethane dispersion is less than 50 cPs, preferably less than 35 cPs and more preferably less than 20 cPs at 25 ° C.
The surface tension is a measure of the inward force acting on the surface of a liquid due to the attraction of molecules in the liquid. When the surface tension of PEG (mol wt 300, 45.9 dynes/cm) is compared with PPG (mol. Wt 425, 32.9 dynes/cm), it is clear that the intermolecular forces are high for polyethylene glycol which is why these molecules are crystalline, viscous and polar (hydrophilic) in nature where as PPG is a low viscosity liquid, amorphous and non-polar (hydrophobic) in nature. On the other hand, the surface tension value for PO3G (mol wt 650, 40.7 dynes/cm) is significantly higher than its isomer, PPG, in spite of having same number of carbon and oxygen atoms in the backbone. Thus the surface tension of polytrimethylene ether glycol was in between PEG and PPG suggesting that the molecules of polytrimethylene ether glycol are neither too hydrophilic like polyethylene glycol nor too hydrophobic like PPG.
The surface tension of the aqueous polyurethane dispersion is preferably in the range from about 39 to 43, more preferably from about 40 to 43 dynes/cm.
The number average molecular weight of the dried polyurethane polymers is preferably below 30,000, preferably below 20,000 and more preferably below 10,000 g/mole.
Fillers, plasticizers, pigments, carbon black, silica sols, other polymer dispersions and the known leveling agents, wetting agents, antifoaming agents, stabilizers, and other additives known for the desired end use, may also be incorporated into the dispersions.
It is within the scope of the present invention to have some crosslinking in the polyurethane.
The means to achieve the crosslinking of the polyurethane generally relies on at least one component of the polyurethane (starting material and/or intermediate) having 3 or more functional reaction sites. Reaction of each of the 3 (or more) reaction sites will produce a crosslinked polyurethane (3-dimensional matrix). When only two reactive sites are available on each reactive components, only linear (albeit possibly high molecular weight) polyurethanes can be produced. Examples of crosslinking techniques include but are not limited to the following:
the isocyanate-reactive moiety has at least 3 reactive groups, for example polyfunctional amines or polyol;
the isocyanate has at least 3 isocyanate groups;
the prepolymer chain has at least 3 reactive sites that can react via reactions other than the isocyanate reaction, for example with amino trialkoxysilanes;
addition of a reactive component with at least 3 reactive sites to the polyurethane prior to its use, for example tri-functional epoxy crosslinkers;
addition of a water-dispersible crosslinker with oxazoline functionality;
synthesis of a polyurethane with carbonyl functionality, followed by addition of a dihydrazide compound;
and any combination of the these crosslinking methods and other crosslinking means known to those of ordinary skill in the relevant art.
Also, it is understood that these crosslinking components may only be a (small) fraction of the total reactive functionality added to the polyurethane. For example, when polyfunctional amines are added, mono- and difunctional amines may also be present for reaction with the isocyanates. The polyfunctional amine may be a minor portion of the amines.
The emulsion/dispersion stability of the crosslinked polyurethane can if needed be improved by added dispersants or emulsifiers.
When crosslinking is desired, the lower limit of crosslinking in the polyurethane is about 1% or greater, preferably about 4% or greater, and more preferably about 10% or greater, as measured by the THF insolubles test.
The amount of crosslinking can be measured by a standard tetrahydrofuran (THF) insolubles test. For the purposes of definition herein, the tetrahydrofuran insolubles of the polyurethane dispersoid is measured by mixing 1 gram of the polyurethane dispersoid with 30 grams of THF in a pre-weighed centrifuge tube. After the solution is centrifuged for 2 hours at 17,000 rpm, the top liquid layer is poured out and the non-dissolved gel in the bottom is left. The centrifuge tube with the non-dissolved gel is re-weighed after the tube is put in the oven and dried for 2 hours at 110° C.
% THF insolubles of polyurethane=(weight of tube and non-dissolved gel−weight of tube)/(sample weight*polyurethane solid %)
An alternative way to achieve an effective amount of crosslinking in the polyurethane is to choose a polyurethane that has crosslinkable sites, then crosslink those sites via self-crosslinking and/or added crosslinking agents. Examples of self-crosslinking functionality includes, for example, silyl functionality (self-condensing) available from certain starting materials as indicated above, as well as combinations of reactive functionalities incorporated into the polyurethanes, such as epoxy/hydroxyl, epoxy/acid and isocyanate/hydroxyl. Examples of polyurethanes and complementary crosslinking agents include: (1) a polyurethane with isocyanate reactive sites (such as hydroxyl and/or amine groups) and an isocyanate crosslinking reactant, and 2) a polyurethane with unreacted isocyanate groups and an isocyanate-reactive crosslinking reactant (containing, for example, hydroxyl and/or amine groups). The complementary reactant can be added to the polyurethane, such that crosslinking can be done prior to its incorporation into a formulation.
Further details on crosslinked polyurethanes can be found, for example, in US20050215663A1.
The aqueous polyurethane dispersions have low viscosities with a good hydrophilic and hydrophobic balance and therefore could be used in applications where these properties are critical. The aqueous polyurethane ionomers and dispersions have utility in a wide variety of fields, including but not limited to golf balls, coatings, wire enamel, textile treatments, inkjets, adhesives and personal care products, among other applications, where they may replace some solvent-based counterparts.
The following examples are presented for the purpose of illustrating the invention and are not intended to be limiting. All parts, percentages, etc., are by weight unless otherwise indicated.
The dispersions whose preparation is described in the examples below were characterized in terms of their particle size and particle size distribution.
Particle sizes were determined using a Microtrac® UPA150 model analyzer manufactured by Honeywell. Viscosity was determined using a Brookfield viscometer with a UL adapter from Brookfield Instruments. All molecular weights disclosed herein are determined by GPC (gel permeation chromatography) using poly(methyl methacrylate) standards. The reaction progress was followed as a function of percent isocyanate as determined using the standard dibutyl amine back-titration method (ASTM D1738).
All of the aqueous polyurethane dispersions prepared from PO3G polymer (Examples 1-3 and 5) below had an average particle size less than 300 nanometers. The small particle size of the dispersions indicates enhanced stability of the dispersions.
The 1,3-propanediol utilized in the examples was prepared by biological methods as described above and had a purity of >99.8%.
Surface tension for various low molecular weight polyether glycols used in preparing aqueous polyurethane dispersion was measured by ring (DuNouy) method using Cahn dynamic contact angle analyzer (model DCA-312).
This example illustrates preparation of an essentially organic solvent-free polyurethane dispersion from PO3G, isophorone diisocyanate and dimethylolpropionic acid ionic reactant, which was chain extended after inversion with a combination of diamine and polyamine.
A 2L reactor was loaded with 201.11 g PO3G (Mn of 2000, prepared as described in U.S. Pat. No. 6,977,291) and heated to 100° C. under vacuum until the contents had less than 500 ppm water. The reactor was cooled to 40° C., and acetone (99 g) and 0.13 g dibutyltin dilaurate catalyst were added. 53.01 g isophorone diisocyanate was added over 1 hr, and rinsed in with 2.6 g dry acetone. The reaction was allowed to continue at 50° C. for 2.5 hr, and then the wt % NCO was determined to be below 3.5%. Dimethylol proprionic acid (12.98 g) and triethyl amine (8.82 g) were added, followed by a rinse with dry acetone (3.16 g). The reaction was held at 50° C. for 2 hrs, and the wt % NCO was determined to be below 0.6%. The resulting polyurethane solution was inverted under high speed mixing while adding 575 g water immediately followed by ethylene diamine (7.52 g) and triethylene tetraamine (36.6 g). The acetone was distilled off under reduced pressure at 70° C.
The resulting PO3G-based polyurethane dispersion had a viscosity of 13.4 cPs, 30.2 wt % solids, a titrated acid number of 17.6 mg KOH/g solids, and an average particle size of 37 nanometer with 95% below 63 nanometer.
This example illustrates preparation of an organic solvent-containing aqueous polyurethane dispersion from PO3G, isophorone diisocyanate, dimethylolpropionic acid ionic reactant and bis(methoxyethyl)amine chain terminator.
A 2L reactor was loaded with 214.0 g PO3G (Mn of 545), 149.5 g tetraethylene glycol dimethyl ether, and 18.0 g dimethylol proprionic acid. The mixture was heated to 110° C. under vacuum until contents had less than 500 ppm water. The reactor was cooled to 50° C., and 0.24 g dibutyl tin dilaurate was added. 128.9 g isophorone diisocyanate was added over thirty minutes, followed by 21.2 g tetraethylene glycol dimethyl ether. The reaction was held at 80° C. for 3 hrs, and the wt % NCO was determined to be below 1.1%. The reaction was cooled to 50° C., then 14.1 g bis(2-methoxyethyl) amine was added over 5 minutes. After 1 hr at 60° C., the polyurethane solution was inverted under high speed mixing by adding a mixture of 45% KOH (15.1 g) and 211.2 g water, followed by additional 727.8 g water.
The resulting polyurethane had an acid number of 20 mg KOH/g solids, and the polyurethane dispersion had a viscosity of 7.86 cPs, 25.5 wt % solids, and a particle size of d50=47 nanometer and d95=72 nanometer.
This example illustrates preparation of an organic solvent-containing, aqueous polyurethane dispersion from PO3G, toluene diisocyanate, dimethylolpropionic acid ionic reactant and bis(2-methoxy ethyl)amine chain terminator.
A 2L reactor was charged with 166.4 g of PO3G (Mn of 545), 95.8 g tetraethylene glycol dimethyl ether and 21.2 g dimethylol propionic acid. The mixture was heated to 110° C. under vacuum until the contents had less than 400 ppm water. This required approximately 3.5 hrs. Then the reaction was cooled to 70° C. and, over 30 minutes, 89.7 g of toluene diisocyanate was added followed by 15.8 g of tetraethylene glycol dimethyl ether. The resulting reaction mixture was held at 80° C. for 2 hrs at the end of which time the wt % NCO was determined to be below 1.5%. Then, 12.4 g bis(2-methoxy ethyl)amine was added over 5 minutes. After stirring for 1 hour at 60° C., 50 g was removed for analysis. The remaining polyurethane solution was inverted under high speed mixing by adding a mixture of 45% aqueous KOH (15.5 g) and 218.0 g water followed by additional 464 g water.
The resulting polyurethane had an acid number of 30 mg KOH/g solids, and the polyurethane dispersion had a viscosity of 17.6 cPs, 22.9% solids, and an average particle size of 16 nanometer, with 95% below 35 nanometer. A sample dried for analysis had a molecular weight by GPC of Mn 7465 and Mw 15,500.
This example illustrates preparation of a polyurethane/acrylic hybrid dispersion. The polyurethane component was prepared from tetramethylene xylylene diisocyanate, dimethylolpropionic acid ionic ingredient, and a mixture of PO3G, a polyester/carbonate diol, 1,4-butane diol and trimethylol propane.
A 2L reactor was charged with 135.4 g of PO3G (Mn of 1,217), 222.9 g VPLS2391 polyester/polycarbonate diol (Bayer), and 12.8 g dimethylolpropionic acid. The resulting mixture was dried by heating to 110° C. under vacuum for 1 hour. The reactor was then cooled to 85° C. and, over a period of 10 minutes, 53.6 g of m-tetramethylene xylylene diisocyanate was added followed by 6.8 g of 1-methyl-2-pyrrolidinone. The reaction mixture was stirred at 85° C. for 1 hour at which time the wt % NCO was determined to be below 0.3%. Then a mixture of the following ingredients was added over 10 minutes: 10.64 g of 1,4-butane diol, 2.87 g of trimethylol propane, 8.33 g of hydroxy ethyl methacrylate, 0.59 g of dibutyl tin dilaurate, 0.23 g of di-t-butyl-4-methylphenol, 35.7 g of butyl acrylate and 35.7 g isobornyl methacrylate. Over 10 minutes, an additional 82.01 g of m-tetramethylene xylylene diisocyanate was added followed by 6.3 g of 1methyl-2-pyrrolidinone. The resulting reaction mixture was held at 80° C. for 2 hrs, at which time the wt % NCO was determined to be below 0.5%. Diethanol amine (16.7 g) and 6.5 g water were then added, followed by 6.32 g dimethyl ethanol amine. After 10 min, the polyurethane solution was inverted under high speed mixing with the addition of 1028 g water.
A solution of 1.29 g of ammonium persulfate (free radical initiator) in 60 g water was added over 30 minutes for the acrylates and methacrylates, and the resulting reaction mixture was held at 80° C. for 2 hours. The dispersion was cooled and filtered.
The resulting hybrid polymer had an acid number of 9 mg KOH/g solids, and the dispersion had a viscosity of 7.2 cPs, 34.5% solids, a pH of 6.4, and an average particle size of 106 nanometer with 95% below 268 nanometer.
Aqueous polyurethane dispersion was prepared as described in Example 3, using PO3G, except that the amount of dimethylolproprionic acid was increased to adjust the polyurethane acid number to 45 mg KOG/g solids while maintaining the NCO/OH ratio. The number average molecular weight of PO3G used was 650. The resulting polyurethane had an acid number of 45 mg KOH/g solids, and the polyurethane dispersion had a viscosity of 16.8 cPs, 25.9% solids, pH of 7.37, surface tension of 41.47 dynes/cm and an average particle size of 195 nanometer. A sample dried for analysis had a molecular weight by GPC of Mn 7903 and Mw 18,019.
The polyurethane dispersion was prepared as described in Example 5 with polyethylene ether glycol having a number average molecular weight of 600 (Carbowax PEG-12 from Dow Chemicals). The resulting polyurethane had an acid number of 45 mg KOH/g solids, and the polyurethane dispersion had a viscosity of 37.7 cPs, 24.95% solids, pH of 6.87, and an average particle size of 17.1 nanometer. A sample dried for analysis had a molecular weight by GPC of Mn 5576.
The polyurethane dispersion was prepared as described in Example 5 with poly(1,2-propylene) glycol having a number average molecular weight of 650 (Poly G 55-173 ethylene oxide capped polypropylene glycol from Arch Chemicals). The resulting polyurethane had an acid number of 45 mg KOH/g solids, and the polyurethane dispersion had a viscosity of 128 cPs, 21.7% solids, pH of 7.39, and an average of 122 nanometer. A sample dried for analysis had a molecular weight by GPC of Mn 5576.
The polyurethane dispersion was prepared as described in Example 5 with poly(1,2-propylene) glycol having a number average molecular weight of 440 (Poly G 20-265 polypropylene glycol from Arch Chemicals). The resulting polyurethane had an acid number of 45 mg KOH/g solids, and the polyurethane dispersion had a viscosity greater than 1000 cPs, 25.0% solids, pH of 9.98, and a surface tension of 25.17 dynes/cm. A sample dried for analysis had a molecular weight by GPC of Mn 19306.
As shown in comparative example 1-3, the aqueous polyurethane dispersions prepared from low molecular weight PEG and PPG demonstrated much higher viscosities in spite of the lower percent solids than the aqueous polyurethane dispersion prepared from PO3G (Example 3). In addition, the surface tension of aqueous polyurethane dispersion prepared from PO3G (Example 5) is significantly higher from the surface tension of aqueous polyurethane dispersion prepared from PPG (comparative example 3) which is an isomer of PO3G indicating the PO3G based polyurethane dispersion is unique and is useful in applications where low viscosity and a good balance of hydrophilic/hydrophobic are critical. The aqueous polyurethane dispersion prepared from PO3G can be used as a dispersant to disperse certain pigments in coatings and inks formulations by taking advantage of its higher surface tension value to improve properties such as gloss, distinctness of image and adhesion.
This continuation in part application claims priority under 35 U.S.C. §119 from Provisional Application No. 60/834,014 (filed Jul. 28, 2006), and application Ser. No. 11/782,098 (filed Jul. 24, 2007).
| Number | Date | Country | |
|---|---|---|---|
| 60834014 | Jul 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11782098 | Jul 2007 | US |
| Child | 13080818 | US |
