A non-plastie and biodegradable aqueous natural oil based lacquer for food grade flexible packaging.

FIELD OF THE INVENTION

This invention relates to an aqueous natural oil based lacquer for food grade flexible packaging, developed by using a carrier comprising of the combination of non-plastic substrate and paper, and coated with a natural oil based poly-urethane dispersion disclosed herein.

This packaging material is non-plastic and biodegradable, and possesses properties such as moisture resistance, heat sealability and durability. Such properties make the packaging material waterproof, long lasting, environment friendly, user friendly and widely applicable in industry.

Due to the fundamental nature of this invention, the flexible packaging material can be used for various goods, without any restriction/limitation of shape, size or nature of the goods.

BACKGROUND OF THE INVENTION Commonly known packaging materials use materials which are plastic in nature and non- biodegradable.

The most common substrate/carrier used for producing packaging materials is VMCH resin, aluminum or any other conventional plastics/plastic polymers to achieve properties of moisture barrier, heat sealing and other chemical properties. Amongst the coating used for bonding with the substrate, it is generally known that water-based anionic polyurethane-urea polymers are useful. References describing such include the following: 1. UK Pat. No. 1 ,128,568 (Farbenfabriken Bayer Aktiengesellschaft) discloses a laminating adhesive wherein anionic polyesteramide polyols are used in the preparation of water-based sulfonated/carboxylated polyurethane-urea polymers. The NCO-terminated prepolymers are processed with acetone. 2. U.S. Pat. No. 5,334,690 (Hoechst Aktiengesellschaft, Fed.) discloses a water- based sulfonated/carboxylated polyurethane-urea adhesive, wherein the anionic groups are present in the polyol segment. The solvent-less prepolymers are processed at temperatures greater than 120° C. C. 3. U.S. Pat No. 4,851,459 and U.S. Pat No. 4,883,694 (Century Adhesives Corp) disclose high performance water dispersible polyurethane laminating adhesives wherein the NCO-terminated prepolymers are dispersed in water and chain extended with peroxides containing hydrogen active atoms. In the preferred method of the invention, a tertiary amine is added to neutralize the anionic prepolymer.

The prior art teachings disclose water-based anionic polyurethane-urea laminating adhesives processed with volatile and/or leachable contaminants. Contaminants such as cosolvents, urethane catalysts and Organic chain terminators can be detrimental.

Another disadvantage associated with the prior ait teachings relates to processing temperatures and polymer composition. Elevated temperatures can increase the prepolymer's crosslink density through uncontrolled isocyartate side reactions. For example, as described in the "Encyclopedia of Polymer Science and Engineering," Vol. 13, page 252, isocyanates react with the NH group of urethanes, ureas and amides at 100°C to 140°C to form allophanates, biurets and acyl ureas, respectively. Polymer composition can also increase the adhesive's heat activation temperature. To meet FDA requirements as stated in 21 CFR .sctn.175.300, there remains a need for heat sealable aqueous dispersions, which are substantially free of volatile and/or leachable contaminants and have reduced heat activation temperatures.

AIMS AND OBJECTIVES OF THE INVENTION

The fundamental objective of this invention is to disclose a nori-plastic and biodegradable aqueous natural oil based lacquer for food grade flexible packaging material, which can be widely used in industry due to the materials used to produce it and its superior properties/characteristics.

Yet another objective of this invention is to produce a packaging material, which uses a carrier comprising of the combination of 100% viscose non woven and paper rather than the conventional plastics/plastic polymers and other substrates used in prior art.

Consequently, another objective of this invention is to produce a packaging material, in which, no VMCH resin, aluminum or any other conventional plastics/plastic polymers is used to achieve properties of moisture barrier, heat sealing and other chemical properties.

Another objective of this invention is to produce an aqueous natural oil based lacquer for food grade flexible packaging that is coated with a natural oil based poly-urethane dispersion disclosed herein, which is substantially free of volatile organic chemicals and/or leachable contaminants, to achieve bonding with the substrate/carrier. Yet another objective of this invention is to produce a packaging material, which is non-plastic and biodegradable. Yet another objective of this invention is to produce a packaging material, in which, both the substrate/carrier and the coating disclosed herein, are individually non plastic and biodegradable in nature.

Yet another objective of this invention is to disclose a packaging material, which can be produced in an efficient and economical manner.

Consequently, another objective of this invention is to disclose a packaging material, which can be widely used in industry. Additionally, the objective of this invention is to disclose a packaging material, which possesses properties of being waterproof, durable, long lasting, environment friendly, user friendly and capable of sealing heat.

Additional objects and advantages of the invention will become apparent to those skilled in the art

DESCRIPTION OF THE INVENTION The packaging material disclosed herein uses a substrate/carrier, which is a combination of 100% viscose non woven and paper.

The 100% viscose non woven and paper, used in this invention as substrate/carrier, has a thickness of around 25 grams per square meter to 75 grams per square meter. The coating used to achieve bonding with the substrate/carrier is a natural oil

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based poly-urethane dispersion of water-based anionic polyurethane/urea polymer of high molecular weight, processed at reduced temperatures. The natural oil based poly-urethane dispersion is produced as a result of a reaction product of a polyol component and a polyisocyanate component, at a reduced temperature, which is then dispersed in solvent-free water after applying a neutralizing agent, and then reacted with a chain extender, iii the manner described below.

The polymer-polyol blend used in the natural oil based poly-urethane dispersion includes a mixture of ricinoleated natural ester based mono blocked polyol and a carboxylic group-containing polyols.

Ricinoleated natural ester based mono blocked polyol is prepared by way of a multi-step process, without using the system of alcoholysis for deriving the blocked natural ester oil. Examples of natural oils used include plant-based oils (e.g., vegetable oils) and animal fats. Useful natural oil sources include canola oil, tall oil, soybean oil, safflower oil, linseed oil, Castor oil, corn oil, sunflower oil, olive oil, canola oil, sesame oil, cottonseed oil, palm-based oils, rapeseed oil, tung oil, peanut oil, jatropha oil, and combinations thereof. Animal fats may also be used, for example, fish oil, lard, and tallow. The plant-based oils may be natural or genetically modified vegetable oils, for example, high oleic safflower oil, high oleic soybean oil, high oleic canola oil, high oleic peanut oil, high oleic sunflower oil, and high erucic rapeseed oil (crafnbe oil). Also included are microbial oils, such as algal oil, including those that are genetically modified to increase yields and/or to obtain selective fatty acid distributions.

In the preferred embodiment of the invention, the ricinoleated natural ester based mono blocked polyol constitutes up to about 95% by weight of the total weight of the polyol formulation of the natural oil based poly-urethane dispersion.

' The carboxylic group-containing polyols used in the natural oil based poly- urethane dispersion are advantageously dihydroxy materials. The carboxylic group-containing polyol can be reacted, without any significant reaction between the carboxylic groups and the diisocyanate component. Among the polyols which may be employed are those which have relatively unreactive free carboxylic acid groups, for instance, the alkanoic acids having one or two substituents on the alpha carbon atom. The substituent may be, for example, a hydroxyl or alkyl group, for example, an alkylol group. This component of the polyol composition has at least one carboxylic group, and generally has 1 to about 3 carboxylic groups, per molecule. The polyols which may conveniently be employed in accordance with this invention frequently have about 2 to 20, or more, preferably about 2 to 10, carbon atoms such as tartaric acid, the α,α-dialkylol alkanoic acids, e.g., having alkylol groups of about 1 to 3 carbon atoms, and the like. A preferred group are the α,α-dimethylol alkanoic acids. The α,α-dimethylol alkanoic acids which may be employed in accordance with this invention include 2,2-dimethylol acetic acid, 2,2-dimethylol propionic acid, 2,2-dimethylol butyric acid, 2,2- dimethylol pentanoic acid, and the like. The carboxylic group-containing polyol may frequently provide about 5% to 50% b weight of the total polyol component in the prepolymer.

The polyisocyante component used in the preparation of the Water dispersible NCO-terminated polyurethane prepolymer is an isomer of toluene diisocyanate and methylene diphenyl diisocyanate. The ratio of the polyisocyanate component to the polyol component can be 1 :4, and is most preferably 1 :2.

To reduce the risk of worker exposure to inhalation, it is important not to exceed a temperature of 100°C. during the prepolymer synthesis reaction of the natural oil based poly-urethane dispersion.

The NCO-terminated prepolymer of the natural oil based poly-ur ethane dispersion is prepared by reacting a stoichiometric excess of the said polyisocyante component with the said polyol component. The materials are processed at temperatures ranging from about 10°C to about 100°C, and preferably from about 40° C. to about 100° C. The reactants are in such proportions that the resulting percent isocyanate is in a range from about 20% to 40% by weight of the total prepolymer solids.

Although, the presence of a solvent for the prepolymer or the polyurethane-urea of the natural oil based poly-urethane dispersion is not necessary to provide a stable dispersion, the prepolymer may be optionally prepared in the presence of solvent, provided that the solvent is substantially non-reactive in the context of the isocyanate-polyol reaction. The solvents are preferably organic and may be comprised essentially of carbon and hydrogen with or without other elements such as oxygen or nitrogen. Solvents which may be employed include dimethylformamide, esters, ethers, ketoesters, ketones, e.g., methyl ethyl ketone and acetone, glycolether-esters, chlorinated hydrocarbons, aliphatic and alicyclic hydrocarbon-substituted pyrrolidinbnes, e.g., N-methyl-2-pyrrolidinone, hydrogenated furans, aromatic hydrocarbons, and the like, and mixtures thereof.

The amount of solvent employed should be sufficient to provide a prepolymer solution, which has a sufficiently low viscosity to enhance the formation of the polyurethane-urea dispersion of this invention. However, the solutions may be successfully employed in forming the dispersion of this invention, even though the viscosity of the solution is relatively high at the temperature of dispersion. Often about 0.01 to 10 parts by weight of solvent per part by weight of the prepolymer can be used.

Often, when solvent is employed during the preparation of the isocyanate- terminated prepolymer and/or the polyurethane-urea of the natural oil based poly- urethane dispersion, it is desirable to remove atleast a portion of the solvent from the dispersion. Advantageously, the solvent, which is to be removed from the dispersion, has a lower boiling point than water. Thus the solvent can be removed from the dispersion by, for example, distillation. The removal of the low boiling solvent is desirably conducted under conditions which are not deleterious to .the polyurethane-urea such as by vacuum distillation or thin film evaporation. A solvent, having a higher boiling point than water, such as dimethyl formamide, N- methyl-2-pyrrolidinone, and the like, may be employed. In such a case, the higher boiling solvent is generally retained in the polyurethane-urea dispersion polymer to enhance the coalescence of the polyurethane-urea particles.

In order to render this prepolymer 'water-dispersible', the potential anionic groups must be neutralized before, during, or after their incorporation into the polyurethane-ureas, with the help of suitable neutralizing agents or mixtures thereof. Suitable compounds for neutralizing the potential anionic groups are the primary, secondary, or tertiary amines. Of these the trialkyl-substituted tertiary amines are preferred. Examples of these amines are trimethyl amine, triethyl amine, triisopropyl amine, tributyl amine, Ν,Ν-dimethyl-cyclohexyl amine, N,N- dimethylstearyl amine, Ν,Ν-dimethylaniline, N-methylmorpholine, N- ethylmorpholine, N-methylpiperazine, N-methylpyrrolidine, N-methylpiperidine, Ν,Ν-dimethyl-ethanol amine, N,N-diethyl-ethanol amine, triethanol amine, N- methyl-diethanol amine, dimethylaminopropanol, 2-rnethoxyethyldirnethyl amine, N-hydroXyethylpiperazine, 2-(2-diriiethylaminoethOxy)-ethanol and 5- diethylamino-2-pentanone. The most preferred tertiary amines are those which do not contain active hydrogen(s) as determined by the ZereWitihoff test since they are capable of reacting with the isocyanate groups of the prepolymers which can cause gelation, the formation of insoluble particles or chain termination.

The tertiary amines are especially advantageous since the salts formed from these amines are capable of decomposing under ambient conditions With volatilization of the tertiary amine. Another advantage of these tertiary amines is that they do not take part in the isocyahate-polyol reaction. For example, when isocyanate-

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terminated prepolymers containing potential anionic groups are formed, it would be difficult to neutralize these groups prior to dispersion in water with primary or secondary amines due to the fact that these amines may react with the free isocyanate groups of the prepolymer. In this context, these primary or secondary amines act more like chain terminators or chain extenders than neutralizing agents, and make the subsequent high molecular weight build-up during the aqueous chain extension step more difficult and less predictable. Thus, if primary and secondary amines are used, they should preferably be used only as neutralizing agents prior to the formation of the prepolymer, i.e., when the potential anionic groups are converted to anionic groups prior to their incorporation into the prepolymer. However, the tertiary amines are preferred even when neutralization is conducted in this manner.

When the potential anionic groups of this prepolymer are neutralized, they provide hydrophilicity to the prepolymer and better enable it to be stably dispersed in water. The potential, or unneutralized, anionic groups do not provide this degree of hydrophilicity. Accordingly, a sufficient amount of the potential ionic groups must be neutralized so that when combined with the optional hydrophilic ethylene oxide units, the polyurethane-urea final product will be a stable dispersion.

Generally, at least about 75%, preferably atleast about 90%, of the potential anionic groups are neutralized to the corresponding anionic groups. Larger amounts of potential ionic groups may remain Unneutralized. However, there are no advantages to be gained from large quantities of unneutralized potential anionic groups and their presence could be detrimental as they would minimize the improvements in hydrolytic stability, which is obtained in accordance with this invention. When smaller amounts of potential ionic groups are incorporated, it may be necessary to neutralize substantially all of these groups to obtain the desired amount of hydrophilicity.

No firm guidelines can be given as to the amount of anionic groups needed, since the dispersibility of the polyurethane-urea depends on many factors including, but not limited to, the amount of hydrophilicity required, the desired particle size and the application requirements.

The neutralization steps may be conducted:

1 . prior to prepolymer formation by treating the component containing the potential ionic groups(s);

2. after prepolymer formation, but prior to dispersing the prepolymer; or

3. by adding the neutralizing agent to all or a portion of the dispersing water.

The reaction between the neutralizing agent and the potential anionic groups may be conducted at temperatures below about 90° C, preferably between about 30° and 80° C, with agitation of the reaction mixture.

Once the NCO-terminated prepolymer of the natural oil based poly-urethane dispersion has been formed, it is dispersed in distilled/de-ionized water with mild agitation. The water temperature before dispersing is in a range from about 5°C to about 0°C, and preferably from about 25° C to about 85° C.

This dispersed NCO-terminated prepolymer is then chain extended with a polyamine. The polyamine component is a polyamine or a mixture of polyamines having an (average) amine functionality of 2 to 3 and an (average) molecular weight of from 50 to about 2000, preferably 50 to about 300. The presence of primary and/or secondary amino groups in the polyamines mentioned is crucial.

Suitable polyamines include ethylenediamine, 1 ,2- and 1 ,3-diaminopropane, 1,4- diaminobutane, 1 ,6-diaminohexane, isophoronediamine, isomer mixture of 2,2,4- and 2,4,4-trimethylhexa-methylenediamine, 2-methyl-pentamethylenediamine, diethylene-triamine, 1.3- and 1 ,4-xylylenediamine, a, a, a', a'-tetrarhethyl-l ,3- and -1 ,4-xylylenediamine and 4,4-diaminodicyclohexylmethane. Suitable diamines in the context of the invention are also hydrazine; hydrazine hydrate and substituted hydrazines, such as, for example, N-methylhydrazine, Ν,Ν'- dimethylhydrazine and their homologues and acid dihydrazides, adipic acid, β- methyladipic acid, sebacic acid, hydracrylic acid and terephthalic acid, semicarbazidoalkylene hydrazides, such as, for example, β- semicarbazidopropionic acid hydrazide (e.g. DE-A 17 70 591 ), semicarbazidoalkylene-carbazine esters, such as, for example, 2- semicarbazidoethylcarbazine ester (e.g. DE-A 19 18 504), or aminosemicarbazide compounds, such as, for example, β-aminoethyl semicarbazido-carbonate (e.g. DE-A 19 02 931 ).

In addition to these low molecular weight polyamines having a molecular weight of up to 300, it is also possible, in principle, to use polyamines of relatively high molecular weight, so that the polyamine component has an average molecular weight of up to 2000. Suitable relatively high molecular weight polyamines of this type include the known polyether polyamines obtained by conversion of the hydroxyl groups of above-mentioned polyether polyols into primary amino groups.

The particle size (mean diameter) of the fully reacted water based anionic polyurethane-urea polymers of this natural oil based poly-urethane dispersion are in a range of about 30 nanometer to about 500 nanometer, and preferably from about 40 rim to about 100 nfn. The water-based dispersions of the inventive polyurethane-urea polymers haVe solids content in a range from about 20% by weight to about 45% by weight, and preferably from about 30% by weight to about 40% by wei ght. In order to prepare the packaging material, both sides of the substrate/carrier, disclosed above, are coated with the natural oil based poly-urethane dispersion disclosed herein and the said composition is joined with heat and pressure.

One side of this substrate/carrier, disclosed above, is coated with a layer of atleast 10 grams per square meter to 50 grams per square meter of the above-referred natural oil based poly-urethane dispersion. This layer of coating is cured at a temperature range of 125°C to 170°C. This helps achieve waterproofing and moisture barrier properties for the packaging material. It is pertinent to note that there is no use of aluminum to achieve waterproofing and moisture barrier properties in this packaging material.

The other side of the substrate/carrier, disclosed above, is coated with a layer of atleast 05 grams per square meter to 25 grams per square meter of the above- referred natural oil based poly-ufethane dispersion. This layer of coating is dried at a temperature range of 90°C to 170°C. It helps achieve heat scalable properties for the packaging material.

The packaging material thus produced is non-plaStic and bio degradable in nature.

The packaging material, as disclosed, is efficient in terms of cost as well as the materials used.

The packaging material, as disclosed, is printable, thereby making it useful in industry. The packaging material, as disclosed, is multi-purpose and can be widely used in the industry due to its superior properties/characteristics.

The packaging material disclosed in this invention is specifically suitable for, amongst others, direct food contact applications.

Due to the fundamental nature of this invention, the packaging material, as disclosed, can be used for Various goods, without any restriction/limitation of shape, size or nature of the goods. All percentages, preferred amounts or measurements, ranges and endpoints thereof herein are inclusive. Numbers herein have no more precision than stated. All amounts, ratios, proportions and other measurements are by weight unless

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stated otherwise. All percentages refer to weight percent based on total composition according to the practice of the invention unless stated otherwise. Except in the examples, or where otherwise indicated, all numbers expressing quantities, percentages, OH numbers, functionalities and so forth in the specification are to be understood as being modified in all instances by the term "about." Unless stated otherwise or recognized by those skilled in the art as otherwise impossible, steps of processes described herein are optionally carried out in sequences different from the sequence in which the steps are discussed herein. Furthermore, steps optionally occur separately, simultaneously or with overlap in timing. Unless stated otherwise, when an element, material, or step capable of causing undesirable effects is present in amounts or in a form such that it does not cause the effect to an unacceptable degree it is considered substantially absent for the practice of this invention. Those skilled in the art recognize that acceptable limits Vary with equipment, conditions, applications, and other variables but can be determined without undue experimentation in each situation where they are applicable. In some instances, variation of deviation in one parameter may be acceptable to achieve another desirable end. The foregoing description will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge will be able to modify and/or adapt, for various applications, such an invention without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to this invention. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not for limitation. It will also be apparent to those skilled in the art that other

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embodiments, improvements, details and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent.