Method for producing aqueous dispersion

Abstract

A method for producing an aqueous dispersion of a polymer includes forming an aqueous medium that is an aqueous emulsion or suspension of a water-insoluble plasticizer containing a dispersant, forming a polymer melt, and mixing the aqueous medium with the polymer melt to form the aqueous dispersion. By providing an aqueous medium containing a combination of a water-insoluble plasticizer and a dispersant, it is possible to produce an aqueous dispersion of the polymer without using an organic solvent or applying pressure to the aqueous medium or the polymer melt. Methods for producing a coated substrate using the aqueous dispersion, and uses of the aqueous dispersion and the aqueous medium are also provided.

Description

[Background technology]

[0001] Plastic packaging is widely used to package food and beverages. Plastic is inexpensive to produce and transport, and it provides an effective barrier against moisture and grease. However, plastics have significant environmental impacts. For example, most plastics are produced from non-renewable resources, are not biodegradable, and are difficult to recycle. There is a growing desire to reduce the amount of plastic waste.

[0002] Glass and metal packaging materials can be used as alternatives to plastics. These materials have excellent barrier properties and are easily recyclable. However, glass and metal have the drawback of being expensive to manufacture and transport.

[0003] Cellulosic materials such as cardboard are attractive from an environmental perspective because they are made from renewable sources and are biodegradable, but they are often porous and hygroscopic and typically do not provide sufficient moisture and grease barrier properties.

[0004] Coating cellulosic materials with polymers can improve their moisture and oil barrier properties. The polymers can be applied as dispersions of polymer particles in a liquid phase. Existing technologies for producing such dispersions require the use of large amounts of organic solvents and / or energy-intensive processing conditions, such as high temperatures and pressures. It would be desirable to provide a method for producing coating compositions with less environmental impact. Summary of the Invention

[0005] In one embodiment, a method for producing an aqueous dispersion of a polymer is provided. The method includes forming an aqueous medium that is an aqueous emulsion or suspension of a water-insoluble plasticizer containing a dispersant, forming a polymer melt, and mixing the aqueous medium with the polymer melt to form the aqueous dispersion. Surprisingly, it has been found that by providing an aqueous medium that is an aqueous emulsion or suspension containing both the water-insoluble plasticizer and the dispersant, it is possible to produce an aqueous dispersion of the polymer without using organic solvents or processing pressures above 1 atmosphere.

[0006] The aqueous medium may be an aqueous emulsion of a water-insoluble plasticizer.

[0007] The dispersant may comprise a non-ionic surfactant. The dispersant may comprise a polymeric surfactant. The dispersant may comprise a non-ionic polymeric surfactant.

[0008] The nonionic polymeric surfactant may include polyvinyl alcohol or its analogs. The nonionic polymeric surfactant may include partially hydrolyzed polyvinyl alcohol or its analogs having a degree of hydrolysis of 98% or less, optionally 80% or less. The degree of hydrolysis of the partially hydrolyzed polyvinyl alcohol or its analogs may range from 50% to 98%, optionally 75% to 85%. For example, the degree of hydrolysis of the partially hydrolyzed polyvinyl alcohol or its analogs may be about 80%. General structural formulas of partially hydrolyzed polyvinyl alcohol and its analogs are shown in the detailed description.

[0009] The water-insoluble plasticizer may comprise a fatty acid ester. For example, the water-insoluble plasticizer may comprise a compound of Formula 1: [ka] formula 1 In Equation 1 n is 2 to 26; R1 and R2 are each independently selected from an alkyl group having 2 to 10 carbon atoms, an alkene group having 2 to 10 carbon atoms, a benzyl group, and a phenyl group.

[0010] For example, the water-insoluble plasticizer may include dibutyl sebacate.

[0011] The aqueous medium may contain less than 5% by weight of the organic solvent. It has been found that the use of organic solvents is not necessary to produce aqueous dispersions of the polymer. Avoiding the use of organic solvents may reduce the environmental impact of this process.

[0012] The polymer melt may include a water-insoluble plasticizer. In such embodiments, the water-insoluble plasticizer of the polymer melt may be the same as or different from the water-insoluble plasticizer of the aqueous medium.

[0013] The polymer may comprise a bio-based polymer. For example, the polymer may comprise a cellulose ester, such as cellulose acetate butyrate. Alternatively or additionally, the polymer may comprise a polyhydroxyalkanoate.

[0014] Mixing the aqueous medium and the polymer melt may include adding the polymer melt to the aqueous medium. During mixing, the aqueous medium may have a temperature of less than 100°C and a pressure in the range of 0.9 to 1.1 atmospheres. Many polymers have melting points higher than 100°C. Adding the polymer melt to the aqueous medium may avoid pressurizing the aqueous medium.

[0015] The median particle size d(0.5) of the aqueous dispersion, measured by laser diffraction, may be in the range of 0.1 μm to 15 μm, optionally 0.3 μm to 10 μm, and further optionally 0.5 μm to 3 μm.

[0016] The 90th percentile particle size d(0.9) may be less than or equal to 30 μm, optionally less than or equal to 20 μm, for example, the 90th percentile particle size d(0.9) may be in the range of 15 μm to 30 μm.

[0017] In another aspect, a method for producing a coated substrate is provided. The method includes producing an aqueous dispersion of a polymer according to the methods described herein, applying the aqueous dispersion to a substrate, and drying the aqueous dispersion to form a coating on the substrate. The aqueous dispersions provided herein are useful for forming coatings. Such coatings can, for example, improve the barrier properties of the substrate.

[0018] The substrate may be in sheet form. Alternatively, the substrate may be in fibrous form. For example, the aqueous dispersion may be used for sizing paper.

[0019] The substrate may comprise a cellulosic material. By forming a coating on the cellulosic substrate, a renewable, recyclable, and repulpable packaging material can be obtained. Such packaging materials are useful for packaging food, beverages, and the like.

[0020] According to yet another aspect, there is provided an aqueous dispersion of a polymer suitable for forming a coating on a substrate. The dispersion comprises water, dispersed particles of a polymer, a water-insoluble plasticizer, and a dispersant. The median particle size d(0.5) of the dispersed particles of the polymer, as measured by laser diffraction, is in the range of 0.1 μm to 15 μm. The aqueous dispersion has a solids content of at least 20% by weight of the aqueous dispersion. The aqueous dispersion can be obtained by the method presented herein. This method allows for the production of an aqueous dispersion having a high solids content and a desirable particle size distribution.

[0021] It will be understood that the descriptions of various materials presented herein in relation to the method embodiments are equally applicable to the aqueous dispersion embodiments. For example, the polymer may be a cellulose ester, optionally cellulose acetate butyrate, the water-insoluble plasticizer may be a fatty acid ester, optionally a fatty acid ester of Formula 1, further optionally dibutyl sebacate, and / or the dispersant may be partially hydrolyzed polyvinyl alcohol having a degree of hydrolysis of 98% or less, optionally between 50% and 90%, further optionally between 75% and 85%.

[0022] According to yet another aspect, there is provided a use of an aqueous medium in producing an aqueous dispersion of a polymer, the aqueous medium comprising water, a water-insoluble plasticizer, and a dispersant, the water-insoluble plasticizer being dispersed in water, the use comprising the step of mixing the aqueous medium with a polymer melt to form an aqueous dispersion of the polymer. It has been found that by providing an aqueous medium that is an emulsion or suspension containing both the water-insoluble plasticizer and the dispersant, and then adding the polymer melt to the aqueous medium, a dispersion of the polymer can be obtained without heating the aqueous medium to 100°C or above and without applying pressure to prevent the aqueous medium from boiling.

[0023] The descriptions of the various components of the aqueous medium presented herein in relation to the method embodiment are equally applicable to the use embodiment.

[0024] For example, the water-insoluble plasticizer may be a fatty acid ester. The dispersant may be a partially hydrolyzed polyvinyl alcohol or its analogues having a degree of hydrolysis (DH) of 98% or less. The general structural formula of partially hydrolyzed polyvinyl alcohol and its analogues is shown below: [Brief explanation of the drawings]

[0025] To facilitate an understanding of embodiments of the present disclosure and to show how such embodiments may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0026] [Figure 1] 1 is a flow chart outlining an exemplary method for producing an aqueous dispersion of a polymer. [Figure 2] 1 is a flowchart outlining an exemplary method for producing a coated substrate. [Figure 3] FIG. 3 is a schematic cross-sectional view of a coated substrate obtained by the method of FIG. 2. [Figure 4] 1 is a graph showing the particle size distribution of an aqueous dispersion of a polymer obtained according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] The verb "comprise" is used herein as shorthand for "include" or "consist of." In other words, although the verb "comprise" is intended to be an open term, particularly when used in connection with chemical compositions, it is expressly contemplated that this term be replaced by the closed term "consist of."

[0028] A "bio-based" material contains carbon, where at least 30%, preferably at least 50%, and most preferably all of the carbon in the material is derived from renewable sources. Carbon from renewable sources can be distinguished from carbon from fossil fuel sources by isotopic analysis. Fossil fuel sources are mostly 14 Renewable resources contain approximately the same proportion of carbon atoms as are present in the atmosphere, i.e., 10 12 1-2 pieces per piece 14 C. Therefore, bio-based materials contain 10 carbon atoms. 12 At least 0.3 per piece 14 C atoms, preferably 1 to 2 14 Contains C atoms.

[0029] "Ambient pressure" is a pressure of approximately 1 atmosphere (101 kPa).

[0030] All particle sizes described herein are measured by laser diffraction using the method described in Example 1.

[0031] The solids content of a composition is determined by determining the change in mass that occurs when the composition is dried. Solids content can be conveniently measured using a commercially available moisture / solids analyzer, such as the "SMART6" available from CEM Corporation.

[0032] As used herein, the term "water-insoluble" refers to a compound that has an intrinsic solubility of 0.1 g / L or less in 0.15 M aqueous KCL at 25° C. "Intrinsic solubility" is measured under equilibrium conditions and at a pH selected such that the compound does not ionize. For compounds that do not have ionizable groups, solubility can be measured at any pH.

[0033] Unless otherwise stated, all particle sizes set forth herein are measured by laser diffraction and all melting points set forth herein are measured at ambient pressure.

[0034] Viscosity is measured at 20°C using a Brookfield LVDV viscometer with a small volume sample adapter with spindle 18.

[0035] An exemplary method for measuring aqueous dispersions of polymers is described with reference to Figure 1, which is a flow chart outlining the method.

[0036] In block 101, an aqueous medium is prepared. The aqueous medium is an aqueous suspension or emulsion containing a water-insoluble plasticizer and a dispersant. Preparing the aqueous medium may involve dissolving a dispersant in water and then adding a water-insoluble plasticizer. Heat and / or stirring may be used to facilitate the formation of the suspension or emulsion.

[0037] The aqueous medium may be a suspension or emulsion of the water-insoluble plasticizer, depending on the melting point of the water-insoluble plasticizer. Preferably, the aqueous medium is an aqueous emulsion. The continuous phase comprises water, and the dispersed phase comprises the water-insoluble plasticizer.

[0038] The nature of the water-insoluble plasticizer is not particularly limited, as long as an aqueous emulsion or suspension of the plasticizer is obtained. The water-insoluble plasticizer can be appropriately selected based on the nature of the polymer contained in the dispersion.

[0039] The water-insoluble plasticizer may be a fatty acid ester, which may be derived from bio-based materials and may have a lower environmental impact than other water-insoluble plasticizers, such as phthalate derivatives.

[0040] Examples of fatty acid esters include those of Formula 1: [ka] formula 1 In Equation 1, n is 2 to 26; R1 and R2 are each independently selected from an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a benzyl group, and a phenyl group.

[0041] n may optionally range from 4 to 10, and even from 6 to 9. For example, the fatty acid ester may be an adipate (n=4) or a sebacate (n=8), preferably a sebacate (n=8).

[0042] R1 and R2 may each be selected from alkyl groups having carbon atoms of 2 to 10. Furthermore, both R1 and R2 may be butyl groups.

[0043] Particularly preferably, the water-insoluble plasticizer may be dibutyl sebacate (n=8, R1=linear alkyl having 4 carbon atoms, R2=linear alkyl having 4 carbon atoms).

[0044] The fatty acid esters of Formula 1 may be particularly suitable for embodiments in which the dispersed polymer is a cellulose ester, such as cellulose acetate butyrate.

[0045] Other examples of water-insoluble plasticizers include water-insoluble citrate esters. Citrate esters useful as plasticizers include, for example, those of Formula 2: [ka] formula 2 In Equation 2, R1, R2, and R3 are each independently selected from an alkyl group having 2 to 6 carbon atoms, an alkenyl group having 3 to 6 carbon atoms, a benzyl group, and a phenyl group; R4 is selected from H, an alkyl group having 2 to 6 carbon atoms, an alkenyl group having 3 to 6 carbon atoms, a benzyl group, a phenyl group, and an acyl group having 2 to 6 carbon atoms.

[0046] R1, R2, and R3 may each independently be selected from alkyl groups having 3 to 5 carbon atoms.

[0047] R4 may be an acetyl group (ie, an acyl group having two carbon atoms).

[0048] An example of a water-insoluble citrate ester of Formula 2 is acetyltributyl citrate.

[0049] Water-insoluble triglycerides are yet another type of useful plasticizer. For example, a triglyceride plasticizer of formula 3 can be used: [ka] formula 3 In Equation 3, R1, R2, and R3 are each independently selected from an alkyl group having 1 to 14 carbon atoms, an alkenyl group having 3 to 14 carbon atoms, a benzyl group, and a phenyl group.

[0050] Exemplary compounds of Formula 3 include triacetin (R1=C1 alkyl, R2=C1 alkyl, R3=C1 alkyl), tributyrin (R1=C3 alkyl, R2=C3 alkyl, R3=C3 alkyl), and trilaurin (R1=C11 alkyl, R2=C11 alkyl, and R3=C11 alkyl).

[0051] Further examples of water-insoluble plasticizers include glycerol esters of fatty acids (eg, glycerol monostearate) and alkyl esters of fatty acids (eg, methyl oleate).

[0052] The aqueous medium contains an amount of a water-insoluble plasticizer effective to obtain an aqueous dispersion of the polymer when the aqueous medium is mixed with the polymer melt, as described below in connection with block 103 .

[0053] The aqueous medium further comprises a dispersant, which allows for the formation of a dispersion (i.e., emulsion or suspension) of the water-insoluble plasticizer. Dispersants are sometimes called surfactants or emulsifiers.

[0054] The dispersant may comprise a non-ionic surfactant. The dispersant may comprise a polymeric surfactant. The dispersant may comprise a non-ionic polymeric surfactant.

[0055] Examples of non-ionic polymeric surfactants include polyvinyl alcohol, polyvinyl alcohol copolymers (e.g., polyacrylic acid-polyvinyl alcohol block copolymers and ethylene vinyl alcohol copolymers), polysorbates, poloxamers, and alkyl polyglycosides.

[0056] Water-soluble nonionic polysaccharides such as hydroxyalkyl celluloses and gums such as xanthan gum are also useful as nonionic polymer surfactants. Specifically, the water-soluble nonionic polysaccharide may be a hydroxyalkyl cellulose. For example, the water-soluble polysaccharide may include a hydroxyalkyl cellulose ether having a hydroxyalkyl group selected from hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, and combinations thereof.

[0057] Depending on the method of producing water-soluble polysaccharides, the presence of a small number of carboxylic acid groups may result in products with a small negative charge.These water-soluble polysaccharides are considered to be nonionic surfactants as long as the negative charge does not substantially change the surfactant properties of the water-soluble polysaccharides.For example, hydroxyalkyl cellulose ethers with a negative group substitution degree of less than 0.03 can be considered to be nonionic.

[0058] Other examples of non-ionic surfactants include lignin and polyol fatty acid esters.

[0059] The non-ionic surfactant may be a partially hydrolyzed polyvinyl alcohol, a partially hydrolyzed polyvinyl alcohol copolymer, or the like. Such non-ionic surfactants include: Hydrophobic unit of formula 4A [ka] formula 4A In Equation 4A, R1 is a methyl, ethyl, or propyl group; R2 is absent, a methylene group, or an ethylene group; R3 is absent, a methylene group, or an ethylene group. Hydrophilic Unit of Formula 4B [ka] formula 4B In Equation 4B, R4 is absent, a methylene group, or an ethylene group; R5 is absent, a methylene group, or an ethylene group; R6 is absent or a methylene group. It may also include a hydrophobic linker of formula 4C. [ka] formula 4c In Formula 4C, R7 is an alkyl group having 1 to 4 carbon atoms.

[0060] The proportion of hydrophilic units present in the polymer of the above structural formula can be expressed as the degree of hydrolysis DH, which is expressed in units of mol % and is defined by Equation 1:

number

[0061] The degree of hydrolysis is usually 98% or less, preferably 80% or less, and may be in the range of 50% to 98%, 50% to 80%, 75% to 98%, or 75% to 85%.

[0062] Because commercial polyvinyl alcohol is typically produced by the hydrolysis of polyvinyl acetate, the term "degree of hydrolysis" is adopted to refer to the parameter defined by Equation 1. The use of this term does not imply any limitation on how the nonionic surfactant is synthesized.

[0063] The copolymers of the above general formula may be random copolymers or block copolymers, and are most typically random copolymers.

[0064] The molecular weight of the copolymer of the above general formula is not particularly limited as long as the copolymer is water-soluble and a dispersion of the water-insoluble plasticizer can be obtained. The molecular weight of the copolymer may be selected so that a 4 wt % solution of the copolymer has a viscosity of 150 mPa·s or less at 20°C.

[0065] Preferably, only one of R2 and R3 is absent, only one of R4 and R5 is absent, and R6 is absent.

[0066] The hydrophobic linker of formula 4C may be absent, ie, p may be 0. When the hydrophobic linker of formula 4C is present, R7 is preferably an ethylene group.

[0067] Most preferably, the dispersant comprises polyvinyl alcohol having a degree of hydrolysis of 98% or less, optionally 80% or less. The degree of hydrolysis may range from 50% to 98%, optionally from 75% to 98%, and even more optionally from 75% to 85%. Polyvinyl alcohol is biodegradable.

[0068] The dispersant may comprise a non-ionic small molecule surfactant, i.e., a non-polymeric non-ionic surfactant. Examples of non-ionic small molecule surfactants include fatty alcohols such as oleyl alcohol, cetyl alcohol, and cetostearyl alcohol, and mixtures thereof, ethanolamines such as cocamide monoethanolamine and cocamide diethanolamine, glucosides such as octyl glucoside, lauryl glucoside, and decyl glucoside, and sorbitan esters.

[0069] Combinations of two or more surfactants may be used. For example, the dispersant may include a nonionic polymeric surfactant and a nonionic small molecule surfactant. In such embodiments, the nonionic small molecule surfactant may be referred to as a co-surfactant.

[0070] The dispersant is present in the aqueous medium in an amount effective to obtain a dispersion of the water-insoluble plasticizer. The amount of the dispersant can be appropriately selected based on the properties and amount of the water-insoluble plasticizer contained in the aqueous medium.

[0071] On an anhydrous basis, the weight ratio of water-insoluble plasticizer to dispersant may range from 1:99 to 50:50, optionally from 5:95 to 50:50.

[0072] The solids content of the aqueous medium is typically at least 1% by weight, and may be, for example, in the range of 5% to 50%, or 20% to 50%, based on the total weight of the aqueous medium. Higher solids contents may also be employed.

[0073] The aqueous medium may further comprise one or more additional components, such as an acid, a base, or a buffer system to adjust the pH of the aqueous phase of the aqueous medium. An example of a useful acid is acetic acid.

[0074] The method described herein does not require the use of an organic solvent. The aqueous medium is preferably substantially free of organic solvents. For example, the aqueous medium may contain 5% or less, optionally 0.5% or less, and even optionally 0.05% of organic solvent by weight of the aqueous medium.

[0075] The aqueous medium is typically produced at atmospheric pressure (i.e., a pressure of about 1 atmosphere) and at a temperature below the boiling point of water. The aqueous medium may be produced at a temperature ranging from 15°C to 95°C, for example. Avoiding the use of high pressures and temperatures can reduce energy consumption.

[0076] A polymer melt is produced in block 102. The operations in this block involve heating the polymer above its melting point using a suitable device such as an extruder or melt kneader.

[0077] The nature of the polymer can be selected appropriately depending on the application of the polymer dispersion. The polymer is typically a water-insoluble polymer. In embodiments where the polymer dispersion is used to form a coating on a substrate, the polymer is preferably a film-forming polymer. The polymer is preferably bio-based.

[0078] The bio-based film-forming polymer may be selected from carbohydrates and their derivatives, where a "derivative" is a polymer that has been chemically modified to include additional substituents.

[0079] Examples of film-forming polymers include polyacrylates, polyphenols, polyureas, polyisocyanates, polyolefins such as polyethylene or polypropylene, polyesters (especially bio-based polyesters such as poly(lactic acid)), polyamides, epoxy polymers, and polyvinyl acetate. Bio-based polyesters are sometimes called polyhydroxyalkanoates.

[0080] The polymer may comprise a water-insoluble α-glucan or β-glucan.

[0081] Examples of water-insoluble α-glucans include glycogen, amylose, amylopectin, starch, and cyclodextrin.

[0082] Examples of β-glucans include cellulose and cellulose derivatives, the term "cellulose derivatives" specifically referring to cellulose esters.

[0083] The polymer preferably comprises a cellulose ester, particularly a cellulose ester in which the ester groups are each independently selected from alkyl ester groups having 1 to 18 carbon atoms, and optionally alkyl ester groups having 1 to 6 carbon atoms. The cellulose ester may contain free hydroxyl groups and ester substituents.

[0084] The alkyl ester groups having 1 to 6 carbon atoms are preferably each independently selected from an acetate ester group, a propionate ester group, and a butyrate ester group.

[0085] The cellulose ester may contain one type of alkyl ester group, i.e., each of the alkyl ester groups may contain the same group. For example, the cellulose ester may be cellulose acetate. Alternatively, the cellulose ester may contain two or more different types of alkyl ester groups. Examples of such cellulose esters include cellulose acetate propionate and cellulose acetate butyrate.

[0086] Particularly preferably, the polymer may comprise cellulose acetate butyrate.

[0087] The polymer melt may comprise a single polymer or a mixture of two or more different polymers.

[0088] Specifically, mixtures containing cellulose esters and one or more compatible polymers are contemplated. Most cellulose esters are compatible with most polyacrylates, polyesters such as polyhydroxyalkanoates, polyphenols, polyureas, and polyisocyanates. Other examples of compatible polymers include polyolefins such as polyethylene or polypropylene, poly(lactic acid), cellulose esters such as cellulose acetate, regenerated cellulose ("cellophane"), polyamides such as polyamide 11, epoxies, polyvinyl acetate, and lignin.

[0089] A water-insoluble plasticizer may optionally be included in the polymer melt, which may be the same as or different from the water-insoluble plasticizer included in the aqueous medium described with reference to block 101. Any of the water-insoluble plasticizers described above may be used, for example, dibutyl sebacate.

[0090] In embodiments in which the polymer melt includes a water-insoluble plasticizer, the water-insoluble plasticizer may be present in an amount of up to 50% by weight of the polymer melt.

[0091] After forming the aqueous medium and the polymer melt, the method proceeds to block 103 where the aqueous medium and the polymer melt are mixed to form an aqueous dispersion of the polymer.

[0092] The polymer melt may be added to the aqueous medium, for example, the polymer melt may be formed in the barrel of an extrusion apparatus and then extruded from the barrel into a vessel containing the aqueous medium.

[0093] By adding the polymer melt to the aqueous medium, the polymer melt and the aqueous medium can be mixed at atmospheric pressure even when the melting point of the polymer exceeds 100° C. Mixing the aqueous medium and the polymer melt at atmospheric pressure allows for the use of simpler equipment and / or reduces energy consumption.

[0094] The temperature of the aqueous medium is maintained below the boiling point of water and may not exceed 95° C. For example, the weight ratio of the polymer melt to the aqueous medium and / or the addition rate of the polymer melt to the aqueous medium may be adjusted so that the temperature of the aqueous medium does not exceed the boiling point of water.

[0095] The aqueous medium may optionally be heated before adding the polymer melt. For example, the aqueous medium may be heated to a temperature of up to 85°C, optionally to a temperature in the range of 70°C to 85°C. Varying the temperature of the aqueous medium may alter the particle size distribution of the dispersion obtained by this method. To reduce energy consumption, it may be desirable to minimize the amount of heating.

[0096] Generally, the aqueous medium is agitated, e.g., stirred, as the polymer melt is added. The rate of addition of the polymer melt and the amount of agitation are selected to obtain a dispersion of the polymer in water. As the rate of addition increases, the level of agitation also increases.

[0097] The weight ratio of the polymer melt to the aqueous medium can be appropriately selected. The polymer dispersion can have, for example, a solids content of at least 20 wt %, optionally in the range of 20 wt % to 70 wt %, based on the total weight of the polymer dispersion. A high solids content can form a continuous film or coating in a single coating operation.

[0098] The polymer melt may provide a solids content of from 10% to 80% by weight, optionally from 20% to 75% by weight, and further optionally from 30% to 75% by weight.

[0099] It has been found that mixing a polymer melt with an aqueous medium containing both a water-insoluble plasticizer and a dispersant can result in a polymer dispersion without pressurizing the aqueous medium or heating the aqueous medium to a temperature above 100°C.

[0100] The aqueous dispersion of the polymer can have a viscosity of 4,000 mPa·s or less, optionally 2,500 mPa·s or less. For example, the viscosity of the aqueous dispersion of the polymer can be in the range of 5 mPa·s to 2,000 mPa·s, or 1,000 mPa·s to 2,000 mPa·s.

[0101] Various variations on the exemplary method may be made.

[0102] Figure 1 shows a method in which the aqueous medium is produced before the polymer melt. These two operations may be carried out in any order or simultaneously.

[0103] The method may be carried out as a batch process or as a continuous process.

[0104] In this example, the polymer melt is added to an aqueous medium. Adding the polymer melt to an aqueous medium may be preferred if the polymer has a melting point of 100° C. or higher. In another embodiment, the aqueous medium may be added to the polymer melt, especially if the polymer has a melting point below 100° C.

[0105] The aqueous dispersions obtained by the methods described herein can be used to form barrier layers or coatings on substrates. An exemplary method for producing a coated substrate will now be described with reference to Figure 2. An exemplary product 300 obtained by this method is shown in Figure 3.

[0106] First, in block 201, an aqueous dispersion of a polymer is prepared according to the method of FIG.

[0107] Optionally, one or more additional ingredients may be mixed with the aqueous dispersion, examples of which include pigments, cobinders, and rheology modifiers.

[0108] The dispersion is then applied to the surface of the substrate 310 in block 202. Any suitable coating technique may be utilized to apply the dispersion to the surface. Examples of coating techniques include casting, rod coating, curtain coating, and spraying.

[0109] Finally, in block 203, the dispersion is dried to form a coating 320 on the substrate 310. The thickness of the coating 320 depends on the amount of dispersion applied to the substrate and the solids content of the dispersion. The amount of dispersion applied to the substrate is typically selected to form a continuous film on the surface of the substrate 310.

[0110] The nature of the substrate 310 is not particularly limited. The substrate may be a cellulosic substrate, particularly a bio-based cellulosic substrate. Cellulosic substrates may include, for example, paper, paperboard, fiberboard, or textiles such as cotton fabrics. In embodiments where the cellulosic substrate includes paper or paperboard, the material may be used as packaging for food or beverages.

[0111] Coating 320 may improve the barrier performance of the substrate, ie, may improve the resistance of substrate 310 to one or more of water vapor, liquid water, oil, and grease.

[0112] In the illustrated example, coating 320 is applied to only one surface of substrate 310. In other embodiments, both surfaces of substrate 310 may be coated.

[0113] In this example, one layer of coating 320 is included, although in variations, two or more layers may be applied.

[0114] The substrate 310 is in the form of a single sheet. Alternatively, the substrate may be a multi-layer sheet.

[0115] The substrate need not be in sheet form. Alternatively, the substrate may be in fibrous form. The fibers may be bio-based fibers, such as cellulose fibers. Coated fibers may be useful in sheet production. [Example]

[0116] Example 1 To 20 mL of a 10 wt % aqueous solution of partially hydrolyzed polyvinyl alcohol, 1 mL of dibutyl sebacate was added to form an aqueous medium, and the mixture was stirred at room temperature until a white emulsion was formed.

[0117] The emulsion was placed under a melt flow indexer and heated to 80°C with stirring.

[0118] A polymer blend was prepared by mixing 4 g of cellulose acetate butyrate with 3 ml of dibutyl sebacate. The polymer blend was placed in a melt flow indexer and heated to 220°C until melted. The resulting polymer melt was added dropwise to the emulsion, which was then stirred while maintaining the emulsion temperature at 80°C.

[0119] An aqueous dispersion of the polymer was obtained. Stirring was stopped and the dispersion was allowed to cool to room temperature. The emulsion was observed to be stable. The particle size distribution of this emulsion was measured by laser diffraction using a Malvern Mastersizer 2000. The results are shown in Figure 4 and in the table below. [Table 1]

[0120] d(0.1), d(0.5), and d(0.9) are the 10%, 50%, and 90% volume percentiles, respectively. That is, for example, 10% of the particles by volume are smaller than a given value d(0.1) in μm. d(0.5) is the median particle size. Comparative Example

[0121] The process described in Example 1 was repeated, omitting dibutyl sebacate from the aqueous medium. No dispersion was formed: the polymer separated from the aqueous phase.

Claims

1. A method for producing an aqueous dispersion of a polymer, comprising the steps of: forming an aqueous medium that includes a dispersant and is an aqueous emulsion or suspension of a water-insoluble plasticizer; forming a polymer melt; mixing said aqueous medium with said polymer melt to form said aqueous dispersion.

2. The method of claim 1 , wherein the aqueous medium is an aqueous emulsion of the water-insoluble plasticizer.

3. The method of claim 1 or claim 2, wherein the dispersing agent comprises a non-ionic polymeric surfactant.

4. The method of claim 3 , wherein the nonionic polymeric surfactant comprises polyvinyl alcohol.

5. 5. The method of claim 4, wherein the polyvinyl alcohol is a partially hydrolyzed polyvinyl alcohol having a degree of hydrolysis of 98% or less.

6. 10. The method of any preceding claim, wherein the water-insoluble plasticizer comprises a fatty acid ester.

7. The fatty acid ester comprises a compound of Formula 1: 【Chemistry 1】 Formula 1 In the formula 1 n is 2 to 26; 7. The method according to claim 6, wherein R1 and R2 are each independently selected from an alkyl group having 2 to 10 carbon atoms, an alkene group having 2 to 10 carbon atoms, a benzyl group, and a phenyl group.

8. The method of claim 7 , wherein the water-insoluble plasticizer comprises dibutyl sebacate.

9. 10. The method of any of the preceding claims, wherein the aqueous medium comprises less than 5% organic solvent by weight of the aqueous medium.

10. 10. The method of any preceding claim, wherein the polymer melt comprises a water-insoluble plasticizer.

11. 10. The method of any preceding claim, wherein the polymer comprises a bio-based polymer.

12. The method of claim 11 , wherein the polymer comprises a cellulose ester.

13. The method of claim 12 , wherein the cellulose ester comprises cellulose acetate butyrate.

14. 10. The method of any preceding claim, wherein mixing the aqueous medium and the polymer melt comprises adding the polymer melt to the aqueous medium.

15. The method according to claim 14, wherein the aqueous medium has a temperature of less than 100°C and a pressure in the range of 0.9 atmospheres to 1.1 atmospheres during the mixing.

16. 10. The method of any of the preceding claims, wherein the median particle size d(0.5) of the aqueous dispersion, as measured by laser diffraction, is in the range of 0.1 μm to 15 μm.

17. 1. A method for producing a coated substrate, comprising:

10. Producing an aqueous dispersion of a polymer by a method according to any of the preceding claims, applying the aqueous dispersion to a substrate; drying the aqueous dispersion to form a coating on the substrate.

18. The method of claim 17 , wherein the substrate comprises a cellulosic material.

19. 1. An aqueous dispersion of a polymer suitable for forming a coating on a substrate, comprising: a continuous phase comprising water; dispersed particles of the polymer; a water-insoluble plasticizer; a dispersant, the median particle size d(0.5) of the dispersed particles of the polymer, as measured by laser diffraction, is in the range of 0.1 μm to 15 μm; The aqueous dispersion has a solids content of at least 20% by weight of the aqueous dispersion.

20. 20. The aqueous dispersion according to claim 19, the polymer is cellulose acetate butyrate; the water-insoluble plasticizer is a fatty acid ester; The dispersant is a partially hydrolyzed polyvinyl alcohol having a degree of hydrolysis of 80% or less.

21. Use of an aqueous medium in the production of an aqueous dispersion of a polymer, the aqueous medium comprising: Water and a water-insoluble plasticizer; a dispersant, the water-insoluble plasticizer is dispersed in the water; The use includes mixing the aqueous medium with a polymer melt to form an aqueous dispersion of the polymer.

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