Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-07-08
2004-11-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S021000, C524S022000, C524S027000, C524S035000, C524S047000, C524S055000
Reexamination Certificate
active
06818686
ABSTRACT:
The invention relates to water based resin compositions containing biopolymer, e.g. from starch, in particular in the form of biopolymer nanoparticles having good storage stability. The resins are intended for the production of coatings with fair properties such as adhesion, barrier, solvent and wet resistance, mechanical strength, applicability, durability and film formation when applied to various types of substrates. Along with the introduction of a renewable resource, the presence of a considerable amount of biopolymer leads to an enhanced biodegradable character of the coating.
Various types of polymer coatings containing biopolymers, such as polysaccharides and proteins, are known. For example, starch is utilised in a wide variety of coating applications, whether or not in combination with other polymer resins. For some end-users, it is highly desirable to provide starch compositions in a ready-to-use and coatable form.
Starch dispersions refer to aqueous starch systems where the granular starch structure has partly or totally been disrupted using sufficient work or heat. In excess of water, the process of starch hydration and granule destruction is known as gelatinisation and can be facilitated or impeded by chemical modifications (cf. converted, derivatized or cross-linked starch) (“Starch:Chemsitry and Technology”, R. L. Whistler, J. N. BeMiller, E. F. Paschall Eds., Academic Press, London, 1984). Pregelatinisation and physical treatment (e.g. via extrusion, drum- or spray drying) of starch (and derivatives) yields cold-water dispersible systems. Although there is no need for cooking, pregelatinised starch still requires substantial mechanical energy for dispersion in water. The stability of many starch dispersions over time is an additional problem since the amylose fraction, and to a much lesser extent also the amylopectin fraction, shows a strong tendency towards retrogradation, a process of crystallisation resulting in gel formation or precipitation. U.S. Pat. No. 5,032,683 describes the production of a stable aqueous starch composition having a coatable viscosity, wherein the starch has been gelatinised and reacted at temperatures above 70° C. in the presence of a blocked glyoxal compound. However, converted (thin-boiling) and/or chemically modified starch are the advised starch materials for these compositions. The subject matter of U.S. Pat. No. 5,116,890 comprises the preparation of water-dispersible, self cross-link lattices based on a starch hydrolyzate to produce stable emulsions with low viscosity. The process requires undesirable chemicals and is quite laborious.
Blends of starch and synthetic polymers obtained via thermoplastic processing, are also well-known in the art (“Production of Thermo-Bioplastics and Fibers based mainly on Biological Materials”, H. G. Fritz, T. Seidenstücker, U. Bölz and M. Juza, EU-Study AGRE-0200-DE, 1994). These materials are usually developed for the production of moulded or shaped articles, not for the preparation of latex compositions for coating purposes. Numerous patents describe the destructuration of starch in combination with hydrophilic and hydrophobic synthetic components, such as vinyl alcohol copolymers (EP 327505, EP 408503), polyvinylesters and polyesters (EP 327505, US 5439953), aliphatic polyesters (WO 92/19680), polylolefines (WO 92/20740), ethylene acrylic acid (EAA) copolymer (US 4133784, US 5262458). In U.S. Pat. No. 5,262,458, it is noted that in the starch/EAA blend after processing part of the destructurized starch (<30% of total starch in the mixture) is found as particles with diameter lower than 1 micrometer.
Recently, a new thermo-mechanical process has been proposed for the production of cross-linked biopolymer material, in particular starch (EP 99200203 patent application). The thermo-mechanical process uses an extrusion treatment at raised temperatures and under conditions of high shear and high pressure. A plasticiser is preferably present during the thermo-mechanical treatment. Most importantly, the process is conducted in the presence of a cross-linking agent. The obtained starch material can readily be dispersed in cold water at increased solids content (up to 40 wt. %), and with relatively low viscosity (typically lower than 100 mPa.s at 25° C. and 10 wt. %) as compared to other cold-water dispersible starches. The size of the dispersed starch particles is in the submicron size range, typically less than 200 nm on the average.
However, the limited storage stability of these colloidal starch dispersions makes them unsuitable for practical application. Depending on the nature of the starch used, shelf life may be as low as a few hours at 20 wt. % before the system turns irreversibly to a gel. Moreover, the sensitivity to humidity of starch is often a restrictive factor for coating application where wet resistance, durability, strength, barrier, etc. are required.
It has now been found that the addition of certain synthetic polymers to the colloidal starch dispersions of EP 99200203 patent application not only imparts desired properties to the coating but surprisingly, also stabilises the aqueous formulation over time. This constitutes the main object of the present invention.
It was found that hydrophilic resins and/or resins with a hydrophilic/hydrophobic character can, surprisingly, stabilise these nanoparticles in water. Upon storage, the compositions exhibit constant particle size and viscosity for at least 1 day up to one month or even more.
The present invention therefore provides a water based polymer composition comprising a biopolymer and a synthetic polymer resin, characterised in that the biopolymer results from a mechanical thermoplastic processing of a polysaccharide and/or protein starting material using shear forces in the presence of a crosslinking agent, and the synthetic polymer resin consists of a water based hydrophilic resin and/or hydrophilic/hydrophobic resin.
According to the invention, the water based polymer resin is in the form of a solution, or a dispersion, or an emulsion or a colloid.
According to the invention, the polymer resin can be an anionic, cationic and/or nonionic modified resin.
According to the invention, the polymer resin is composed of a water based resin which has been selected from polyurethanes, polyesters, polyethers, polyesterurethanes, polyacrylates, polyvinylacrylates, polystyreneacrylates, styrene-butadiene, poly(meth)acrylic acid, polyvinylalcohols, polyvinylacetates, polyvinylethers, polyethylenevinylacetates, polyethylenevinylalcohols, epoxy resin, alkyds, epoxy-, urethane-, polyester-, amino-, and amido-(meth)acrylates, or mixtures thereof.
Preferably, the polymer resin is chosen from polyurethanes, polyester-urethanes, epoxy-acrylates, polyester-acrylates, urethane-acrylates, polyacrylates, polystyrene-acrylates, styrene-butadiene and epoxy resin or mixtures thereof.
According to this particular embodiment, the said polymer resin in the composition may comprise functional groups such as hydroxyl, methylol, carbonyl, carboxyl, sulfonyl, amino, epoxy, acetyl acetoxy, (meth)acrylic and/or vinylic groups.
According to EP 99200203 patent application, in the process for producing the biopolymer nanoparticles, the biopolymer is subjected to thermoplastic processing using shear forces, a crosslinking agent being added during the mechanical treatment.
Thermoplastic processing as used in this context means a thermomechanical treatment, which is in particular an extrusion treatment performed at elevated temperature (above 40° C., especially up to 140° C.) under conditions of high shear and high pressure (e.g. between 5 and 150 bar). The shear can be effected by applying at least 500 J of specific mechanical energy (SME) per g of biopolymer. The elevated temperature can be moderated, in case of starch, by using an alkaline medium or by using pregelatinised starch. During the thermomechanical treatment, the biopolymer is present in high concentration, especially a concentration of at least 40, more preferably at least 50 wt. %, in an aqueous solven
Bontinck Dirk
Colpaert Marc
Roose Patrice
Nutter Nathan M.
UCB S.A.
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