阅读说明：本技术 经涂覆的与食品接触的容器 (Coated food-contact container ) 是由 K·卡利姆 Y·穆萨 于 2015-10-19 设计创作，主要内容包括：公开了一种容器,其包含与食品接触的表面和其上的涂层。该涂层包含得自苯二甲醇的聚合物,该聚合物具有权利要求1中所示的结构的链段,其中R-(1)为亚苯基和R-(2)为二价有机基团和n＝5至50。(A container is disclosed that includes a food-contacting surface and a coating thereon. The coating comprises a polymer derived from benzenedimethanol,the polymer has a segment of the structure shown in claim 1, wherein R 1 Is phenylene and R 2 Is a divalent organic group and n is 5 to 50.)

1. A container comprising a food-contacting surface, wherein at least a portion of the food-contacting surface is coated with a water-based coating composition comprising a polymer derived from benzenedimethanol, the polymer having segments of the structure:

wherein R is₁Is phenylene and R₂Is a divalent organic group and n ═ 5 to 50, wherein the polymer is grafted to a water-dispersible (meth) acrylic functional monomer to form a graft copolymer.

2. The container of claim 1, wherein R₂Comprising arylene radicals containing 6 to 12 carbon atomsAt least one of a radical or a saturated (cyclo) aliphatic radical containing from 4 to 12 carbon atoms.

3. The container of claim 1, wherein R₂Including straight chain alkylene groups.

4. The container of claim 1, wherein the polymer has a number average molecular weight of 2,000 to 25,000 g/mol.

5. The container of claim 1, wherein the composition comprises a (meth) acrylic functional monomer in an amount of 5 wt.% to 40 wt.% based on the weight of the acrylic grafted polyester.

6. The container of claim 1, wherein the composition is substantially free of bisphenol a and derivatives or residues thereof.

7. The container of claim 1, wherein the polymer is grafted to the water-dispersible (meth) acrylic functional monomer via deprotonation.

8. The container of claim 1 wherein the polymer is grafted with a (meth) acrylic functional monomer containing a double bond and polymerizable by a free radical mechanism.

9. The container of claim 1, wherein the (meth) acrylic functional monomer comprises (meth) acrylic acid, (meth) acrylate and/or styrene.

10. The container of claim 1, wherein the water-based coating composition is generally 20 to 50 weight percent resin solids, based on the total weight of the coating composition.

11. The container of claim 1, wherein the container is a metal can.

12. The container of claim 1, wherein the container is metal.

Technical Field

The present invention relates to coated containers, such as coated metal cans, that come into contact with food and beverages.

Background

A wide variety of coatings have been used to coat the surfaces of food and beverage containers. For example, metal cans are sometimes coated using coil coating or sheet coating operations, i.e., a coil or sheet of steel or aluminum is coated with a suitable composition and cured. The coated substrate is then formed into a can body or can lid (can end). Alternatively, the coating composition may be applied to the forming can, for example, by spraying and dipping, and then cured. Coatings for food and beverage containers should preferably be capable of high speed application to a substrate and provide the necessary properties when cured for use in harsh end use environments. For example, the coating should be safe for food contact and have excellent adhesion to the substrate.

Many coating compositions for food and beverage containers are based on polyether resins based on polyglycidyl ethers of bisphenol a. Bisphenol a in container coatings, whether as bisphenol a itself (BPA) or a derivative thereof, such as diglycidyl ether of Bisphenol A (BADGE), epoxy novolac resins and polyols made with bisphenol a and bisphenol F, are problematic. Although balancing the scientific evidence available to date suggests that small trace amounts of BPA or BADGE that may be released from existing coatings do not pose a health risk to humans, these compounds may still be considered by some as being harmful to human health. Therefore, there is a strong desire to eliminate these compounds from coatings for food and beverage containers. Accordingly, what is desired is a container coating composition for food and beverage containers that does not contain extractable amounts of BPA, BADGE or other derivatives of BPA and yet has commercially acceptable properties.

Disclosure of Invention

The present invention provides a container comprising a food-contacting surface, wherein at least a portion of the food-contacting surface is coated with a composition comprising a polymer derived from benzenedimethanol, the polymer having segments of the structure:

wherein R is₁Is phenylene and R₂Is a divalent organic group and n is 5 to 50.

Detailed Description

As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word "about", even if the term does not expressly appear. Furthermore, it should be noted that a plurality of terms and/or phrases encompass the singular equivalent thereof, and vice versa. For example, "a" polymer, "a" crosslinker, and any other components refer to one or more of these components.

When referring to any numerical range of values, such range is understood to include each and every number and/or fraction between the stated range minimum and maximum.

As used herein, the term "polyol" or variants thereof broadly refers to a material having an average of two or more hydroxyl groups per molecule. The term "polycarboxylic acid" refers to acids and functional derivatives thereof, including anhydride derivatives (if present) and lower alkyl esters having 1 to 4 carbon atoms.

As used herein, the term "polymer" broadly refers to prepolymers, oligomers, and both homopolymers and copolymers. The term "resin" is used interchangeably with "polymer".

The terms "acrylic" and "acrylate" are used interchangeably (unless the meaning intended is changed by doing so) and include acrylic acid, anhydrides, and derivatives thereof, such as their C₁-C₅Alkyl esters, lower alkyl-substituted acrylic acids, e.g. C₁-C₂Substituted acrylic acids, e.g. methacrylic acid, ethacrylic acid, etc., and C thereof₁-C₅Alkyl esters, unless expressly indicated otherwise. The term "(meth) acrylic" or "(meth) acrylate" is intended to cover both acrylic/acrylate and methacrylic/methacrylate forms of the indicated material, e.g., (meth) acrylate monomers. The term "(meth) propeneBy "acrylic polymer" is meant a polymer prepared from one or more (meth) acrylic monomers.

(Cyclo) aliphatic refers to both cyclic and linear aliphatic compounds, particularly wherein aliphatic is alkylene.

As used herein, "a" and "at least one" and "one or more" are used interchangeably. Thus, for example, a coating composition comprising "a" polymer can be interpreted to mean that the coating composition includes "one or more" polymers.

As used herein, molecular weight is determined by gel permeation chromatography using polystyrene standards. Unless otherwise indicated, molecular weights are based on number average (Mn).

The term "food" in "surface in contact with food" is meant to include solid foods as well as beverages.

The compositions of the present invention comprise a polyester polymer derived from benzenedimethanol, the polyester polymer having segments with the following structure:

wherein R is₁Is phenylene and R₂Is a divalent organic group and n is 5 to 50.

Polyesters can be prepared by reacting benzenedimethanol with polycarboxylic acids, especially dicarboxylic acids. R₂And may also be an arylene group such as arylene derived from phthalic acid, isophthalic acid, terephthalic acid, and naphthalene dicarboxylic acid. R₂And also saturated (cyclo) aliphatic groups such as (cyclo) alkylene groups containing 4 to 12 carbon atoms, such as adipic acid, sebacic acid, and cyclohexanedicarboxylic acid. R₂From mixtures of the above-mentioned dicarboxylic acids.

In addition to benzenedimethanol, other polyols may be used with benzenedimethanol to make the polyesters. Examples include (cyclo) aliphatic diols such as those containing 2 to 12 carbon atoms, such as ethylene glycol, 1, 4-butanediol, 2-butyl-2-ethyl-1, 3-propanediol and cyclohexanedimethanol. In addition, higher functional polyols may be used in combination with diols. Examples are triols such as trimethylolpropane.

The moles of dicarboxylic acid and polyol are generally adjusted so that the number average molecular weight is 2,000 to 25,000. Polyesters are typically hydroxy-functional with a hydroxyl number of 5 to 15. By a method such as is known in the art and described by Zeno Wicks, Jr. et al, in Organic Coatings; the condensation polymerization conditions described in Science and Technology, Vol.1, pp.122-132 (John Wiley & Sons; New York,1992) for preparing polyesters.

The polyester of the present invention is applied to a substrate as a component in a coating composition comprising a liquid carrier. The liquid carrier can be water, an organic solvent, or a mixture thereof. Thus, the liquid coating composition of the present invention may be water-based (containing water and optionally some water-miscible organic solvent) or organic solvent-based, i.e., substantially free of water (i.e., less than 2 weight percent water based on the total weight of the coating composition). Examples of suitable organic solvents are glycol ethers, alcohols, aromatic or aliphatic hydrocarbons, ketones, esters and mixtures thereof. The liquid carrier is selected to provide a dispersion or solution of the polyester for further coating formulation.

The polyesters of the invention may be dissolved or dispersed in a liquid carrier and formulated with cross-linking agents such as aminoplast or phenoplast curing agents (as described below) and common additives known in coatings for food-contact surfaces of containers. Typically, coating compositions based on the polyesters of the present invention have a resin solids content of from 20 to 50 weight percent, based on the total weight of the coating composition.

Due to the activated methylene groups in the benzenedimethanol, the polyester can be grafted to the water-dispersible (meth) acrylic polymer via deprotonation, such as by grafting with a double bond containing (meth) acrylic functional monomer that can polymerize by a free radical mechanism. Examples of such monomers are (meth) acrylic acid and ethylenically unsaturated monomers containing no acid groups, such as (meth) acrylates, styrene, and the like. The resulting graft copolymer can then be at least partially neutralized with a base such as a tertiary amine. The resin solids content of the water-based coating composition is typically from 20 to 50 weight percent resin solids, based on the total weight of the coating composition.

The acrylic portion of the polyester-epoxy-acrylic graft copolymer comprises polymerized ethylenically unsaturated monomers including a carboxyl functional monomer, such as (meth) acrylic acid, and an unsaturated dicarboxylic acid, such as maleic acid or fumaric acid, to provide carboxyl functionality for dispersing the graft copolymer into water. The remaining monomers are preferably non-functional under the polymerization conditions contemplated, but small amounts of other reactive monomers may be used, such as hydroxyl monomers exemplified by 2-hydroxyethyl (meth) acrylate, amide monomers exemplified by (meth) acrylamide, or N-methylol monomers exemplified by N-methylol (meth) acrylamide. The remaining monomers, other than the copolymerizable olefinic monomers exemplified by: (meth) acrylic esters having 1 to 10 carbon atoms in the ester group such as ethyl (meth) acrylate, methyl (meth) acrylate, isobutyl (meth) acrylate and 2-ethylhexyl (meth) acrylate; aromatic vinyl monomers such as styrene and vinyl toluene; vinyl monomers such as vinyl acetate, vinyl chloride, vinylidene chloride, and other ethylenically unsaturated monomers such as butadiene and acrylonitrile. The (meth) acrylic polymer segment preferably comprises about 5 to 40 weight percent based on the weight of the acrylic grafted polyester.

The polyester acrylic graft copolymer mixture may be prepared by in situ non-aqueous polymerization of olefinic monomers with a polyester resin. The polyester resin may be heated in a reactor, wherein the polymerizable monomer along with the solvent and free radical initiator may be slowly added over a period of at least two or three hours. Although the reaction can be carried out in the absence of a solvent, some solvents are desirable for monomer polymerization in the presence of polyester resins. Solvents such as xylene, benzene, ethylbenzene, toluene and alkoxy alkanols are satisfactory. Alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol monoethyl ether and butanol are preferred. For subsequent dispersion into water, the solvent of choice is typically a water-soluble material such as butanol, propanol, ethylene glycol monoethyl ether, and the like, although small amounts of water-immiscible solvents such as mineral spirits, hexane, and similar aliphatic compounds may be used.

As mentioned above, the coating composition of the present invention contains a crosslinking agent. Examples of crosslinking agents are phenolics and aminoplasts.

Suitable phenoplast resins include condensation products of aldehydes with phenols. Formaldehyde and acetaldehyde are preferred aldehydes. Different phenols may be employed such as phenol, cresol, p-phenylphenol, p-tert-butylphenol, p-tert-amylphenol and cyclopentylphenol.

Suitable aminoplast resins are condensation products of aldehydes, such as formaldehyde, acetaldehyde, crotonaldehyde, and benzaldehyde, with amino-or amido-containing materials, such as urea, melamine, and benzoguanamine. Examples of suitable aminoplast crosslinking resins include, but are not limited to, benzoguanamine-formaldehyde resins, melamine-formaldehyde resins, etherified melamine-formaldehyde and urea-formaldehyde resins.

The amount of curing agent (e.g., crosslinker) used will generally depend on the type of curing agent, the time and temperature of baking, the molecular weight of the binder polymer, and the desired coating characteristics. If used, the crosslinking agent is generally present in an amount of up to 50% by weight, preferably up to 30% by weight, and more preferably up to 15% by weight. If used, the crosslinking agent is preferably present in an amount of at least 0.1 wt.%, more preferably at least 1 wt.%, and even more preferably at least 1.5 wt.%. These weight percentages are based on the total weight of resin solids in the coating composition.

The coating compositions of the present invention may also include other optional polymers that do not adversely affect the coating composition or the cured coating composition resulting therefrom. Such optional polymers are typically included in the coating composition as filler materials, but they may also be included, for example, as binder polymers, crosslinking materials, or to provide desired properties. One or more optional polymers (e.g., filler polymers) can be included in an amount sufficient to meet the intended purpose, but not in an amount to adversely affect the coating composition or a cured coating composition resulting therefrom.

Such additional polymeric materials may be non-reactive and therefore act only as fillers. Such optional non-reactive filler polymers include, for example, polyesters and (meth) acrylic polymers. Alternatively, such additional polymeric materials or monomers may be reactive with other components of the composition. If desired, reactive polymers may be incorporated into the compositions of the present invention to provide additional functionality for different purposes, including crosslinking or dispersing the polymers of the present invention into water. Examples of such reactive polymers include, for example, functionalized polyesters and functionalized (meth) acrylic polymers.

Another optional ingredient is a catalyst for increasing the rate of cure. Examples of catalysts include, but are not limited to, strong acids such as phosphoric acid, dodecylbenzene sulfonic acid (DDBSA) (available as CYCAT 600 from Cytec), methanesulfonic acid (MSA), p-toluenesulfonic acid (pTSA), dinonylnaphthalene disulfonic acid (DNNDSA). If used, the catalyst is preferably present in an amount of at least 0.01 wt-%, such as at least 0.1 wt-%, based on the weight of nonvolatile material in the coating composition. If used, the catalyst is preferably present in an amount no greater than 3 wt-%, such as no greater than 1 wt-%, based on the weight of nonvolatile material in the coating composition.

Another optional ingredient that may be used is a lubricant (e.g., wax) that aids in the manufacture of metal fabricated articles, such as closure caps (closures) and food or beverage can ends, by imparting lubricity to the coated metal substrate sheet. Non-limiting examples of suitable lubricants include, for example, natural waxes such as carnauba wax or lanolin wax, Polytetrafluoroethylene (PTFE), and polyethylene-based lubricants. If used, the lubricant is preferably present in the coating composition in an amount of at least 0.1 wt.%, such as no greater than 2 wt.%, and typically no greater than 1 wt.%, based on the total weight of non-volatile materials in the coating composition.

Another optional ingredient that may be used is a pigment, such as titanium dioxide. If used, the pigment is preferably present in the coating composition in an amount of no greater than 70 weight percent, such as no greater than 50 weight percent, and typically no greater than 40 weight percent, based on the total weight of solids in the coating composition.

Surfactants may optionally be added to the coating composition, for example to aid in the flow and wetting of the substrate. Examples of surfactants include, but are not limited to, nonylphenol polyethers and salts and similar surfactants known to those skilled in the art. If used, the surfactant is preferably present in an amount of at least 0.01 weight percent, such as at least 0.1 weight percent, based on the weight of resin solids. If used, the surfactant is typically present in an amount no greater than 10 weight percent, and typically no greater than 5 weight percent, based on the weight of resin solids.

The coating compositions used in the practice of the present invention are substantially free, may be substantially free and/or may be completely free of bisphenol a and derivatives or residues thereof, including bisphenol a and bisphenol a diglycidyl ether ("BADGE"). Reaction products and/or coatings that are substantially free of bisphenol a are sometimes referred to as "unintended BPA" because BPA, including derivatives or residues thereof, is not intentionally added, but may be present in trace amounts, such as due to impurities or inevitable contamination from the environment. The reaction products and/or coatings of the present invention may also be substantially free, and/or completely free of bisphenol F and its derivatives or residues, including bisphenol F and bisphenol F diglycidyl ether ("BPFDG"). As used in this context, the term "substantially free" means that the reaction product and/or the coating composition contains less than 1000 parts per million (1000ppm) of any of the above compounds or derivatives or residues thereof, "substantially free" means less than 100ppm of any of the above compounds or derivatives or residues thereof and "completely free" means less than 20 parts per billion (20ppb) of any of the above compounds or derivatives or residues thereof.

The coating compositions of the present invention may be present as a layer of a single layer coating system or as one or more layers of a multi-layer coating system. The coating composition can be used as a primer coat, a midcoat, a topcoat, or a combination thereof. The coating thickness of a particular layer and the overall coating system will vary depending on the coating material used, the substrate, the coating application method, and the end use of the coated article. Single or multi-layer coating systems comprising one or more layers formed from the coating compositions of the present invention can have any suitable total coating thickness, but typically have a total average dry coating thickness of from about 1 micron to about 60 microns and thicker, typically from about 2 microns to about 15 microns. Typically, rigid metal food or beverage can applications have an average total coating thickness of about 3 microns to about 10 microns. The coating system for the seal cap application may have an average total coating thickness of up to about 15 microns. In certain embodiments in which the coating composition is used as an inner coating on a cylinder (drum), such as a cylinder used with food or beverage products, the total coating thickness can be about 25 microns.

The coating composition of the present invention can be applied to a substrate before or after the substrate is formed into an article, such as a food or beverage container or portion thereof. In one embodiment, a method is provided comprising: the coating compositions described herein are applied to a metal substrate (e.g., the composition is applied to a metal substrate in the form of a planar coil or sheet), the composition is cured, and the substrate is formed (e.g., via stamping) into a packaging container or portion thereof (e.g., a food or beverage can or portion thereof). For example, a riveted beverage can end having a cured coating of the invention on the surface of the can end can be formed in such a process. In another embodiment, the coating composition is applied to a preformed metal food or beverage can or portion thereof. For example, in some embodiments, the coating composition is sprayed onto the interior surface of a preformed food or beverage can (e.g., as commonly occurs with "two-piece" food or beverage cans). After the coating composition is applied to the substrate, the composition can be cured using various methods, including, for example, oven baking by conventional or convective methods, or any other method that provides an elevated temperature suitable for curing the coating. The curing process may be performed in discrete or combined steps. For example, the substrate may be dried at ambient temperature to maintain the coating composition in a substantially uncrosslinked state. The coated substrate can then be heated to fully cure the composition. In some cases, the coating composition of the present invention may be dried and cured in one step.

The curing conditions will vary depending on the application method and the intended end use. The curing process may be carried out at any suitable temperature, including, for example, oven temperatures in the range of from about 100 ℃ to about 300 ℃, and more typically from about 177 ℃ to about 250 ℃. If the metal coil is the substrate to be coated, the applied coating composition may be cured, for example, by heating the coated metal substrate to a peak metal temperature ("PMT") preferably greater than about 350 ° F (177 ℃) over a suitable period of time. More preferably, the coated metal coil is heated to a PMT of at least about 425 ° F (218 ℃) over a suitable period of time (e.g., about 5 to 900 seconds, more typically about 5 to 30 seconds).

The coating compositions of the present invention are particularly useful for coating metal substrates. The coating composition may be used to coat a packaging article, such as a food or beverage container or a portion thereof. In a preferred embodiment, the container is a food or beverage can and the surface of the container is a surface of a metal substrate. The polymer may be applied to the metal substrate before or after the substrate is formed into a can (such as a two-piece can, a three-piece can) or a portion thereof (whether it be a can lid or a can body). The polymers of the present invention are suitable for use in food contact situations and can be used on the inside of such cans. They are particularly useful on the interior of two-piece or three-piece can ends or bodies.

The metal substrate used to form the rigid food or beverage can or portion thereof typically has a thickness in the range of about 0.005 inch to about 0.025 inch. As metal substrates for food or beverage cans or parts thereof, electrically tinned steel, cold rolled steel and aluminum are commonly used. In embodiments where a metal foil substrate is employed to form, for example, a packaging article, the metal foil substrate may be even thinner in thickness than the substrates described above.

The coating compositions of the present invention may be suitable, for example, for spray coating, coil coating, wash coating, sheet coating, and side seam coating (e.g., food can side seam coating). Further discussion of such application methods is provided below. It is contemplated that the coating compositions of the present invention may be suitable for use in each of these application methods, including end uses associated therewith, discussed further below.

Spraying involves introducing the coating composition to the inside of a preformed packaging container. Typical preformed packaging containers suitable for spray coating include food cans, beer containers, beverage containers, and the like. The spray coating method preferably utilizes a spray nozzle capable of uniformly coating the inside of the preformed packaging container. The sprayed preformed container is then subjected to heat to remove any residual carrier (e.g., water or solvent) and harden the coating.

Coil coating is described as coating a continuous coil comprising a metal, such as steel or aluminum. Once coated, the coated web is subjected to a short thermal curing cycle for hardening (e.g., drying and curing) the coating. Coil coating provides a coated metal (e.g., steel and/or aluminum) substrate that can be fabricated into shaped articles, such as two-piece drawn food cans (two-piece drawn food cans), three-piece food cans, food can lids, thin-walled drawn cans, beverage can lids, and the like.

Wash coating is commercially described as coating the exterior of two thin-walled drawn ("D & I") cans with a thin layer of protectant coating. The exterior of these D & I cans were "wash-coated" by passing a preformed two-piece D & I can under a curtain of coating composition. The can is inverted, i.e., the open end of the can is in a "down" position when fed through the screen. This curtain of coating composition presents a "waterfall" appearance. Once the cans pass under this curtain of coating composition, the liquid coating material effectively coats the exterior of each can. An "air knife" was used to remove excess coating. Once the desired amount of coating is applied to the exterior of each can, each can is passed through a thermal, uv, and/or electromagnetic curing oven to harden (e.g., dry and cure) the coating. The residence time of the coated can in the curing oven is typically 1 minute to 5 minutes. The curing temperature in this furnace is typically 150-220 ℃.

Sheet coating is described as coating separate pieces of a variety of materials (e.g., steel or aluminum) that have been pre-cut into square or rectangular "sheets". Typical dimensions for these sheets are about 1 square meter. Once coated, the coating hardens (e.g., dries and cures) and the coated sheet is collected and ready for subsequent manufacture. Sheet coating provides a coated metal (e.g., steel or aluminum) substrate that can be successfully fabricated into shaped articles, such as two-piece drawn food cans, three-piece food cans, food can ends, thin-walled drawn cans, beverage can ends (including, for example, riveted beverage can ends with rivets for attaching tabs to the can ends), and the like.

Side seam coating is described as applying a powder coating or spraying a liquid coating over the welded area of a formed three-piece food can. When three-piece food cans are made, a rectangular piece of coated substrate is formed into a cylinder. The formation of the cylinder is permanent due to the welding of each side of the rectangle via thermal welding. Once welded, each can typically requires a coating layer that protects the exposed "weld (weld)" from subsequent corrosion or other effects of the contained food. The coating that performs this function is called a "side seam strip". Typical side seam strips are sprayed and, in addition to being slightly heat cured in an oven, quickly cure via residual heat from the welding operation.

Examples

The following examples are provided to aid in the understanding of the present invention and are not to be construed as limiting the scope thereof. All parts and percentages are by weight unless otherwise indicated.

Example I

Preparation of polyesters with benzenedimethanol

A4-neck flask equipped with a stirrer, thermometer, packed column with overhead temperature (head temperature), water condenser, and nitrogen inlet was charged with 139.6 grams of trimethylolpropane, 613.1 grams of phthalic anhydride, 204.9 grams of adipic acid, and 784.8 grams of 1, 4-benzenedimethanol. 1.53 g of FASCAT 9201 catalyst was added to carry out the condensation. The mixture was slowly heated to 160 ℃ (320 ° F). When distillate collection began, the batch temperature was increased to maintain a reactor temperature of 220 ℃ (428 ° F) and the column temperature did not exceed 95 ℃ (205 ° F). Distillation was maintained to continuously remove water. The reaction was continued until a target acid number of less than 9 was obtained. The batch was cooled to room temperature and 400 grams of 2-butoxyethanol and 76.7 grams of Aromatic 100 solvent were added to dissolve the polyester.

Example II

Preparation of polyester grafted acrylic copolymer

A4-necked flask equipped with a stirrer, a thermometer and a water condenser was charged with 175 g of the polyester of example I and 95 g of 2-butoxyethanol. The mixture was heated to 120 ℃. A mixture of 32.5 grams of methacrylic acid, 22.3 grams of ethyl acrylate, and 20.2 grams of styrene monomer was charged to the flask over a period of 120 minutes. At the same time, 6.3 grams of dibenzoyl peroxide initiator dissolved in 14.5 grams of methyl ethyl ketone was charged to the flask over a 120 minute period. The reaction mixture was held at 120 ℃ for a further 15 minutes, followed by the addition of one gram of chaser initiator. The batch was then held for an additional hour to complete the monomer conversion. The resulting graft copolymer was cooled to less than 105 ℃, followed by the addition of 27 grams of dimethylethanolamine, followed by the addition of 400 grams of water to disperse the graft copolymer. The dispersion was cooled to room temperature with stirring and was found to be stable, indicating the formation of a graft copolymer.

While specific embodiments of the invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Although various embodiments of the present invention have been described in terms of "comprising," embodiments that consist essentially of, or consist of,. are also within the scope of the present invention.