Polyvinyl alcohol coated cellulose products

Abstract

The present invention relates to a method for producing a coated material, the method comprising providing a cellulosic substrate, melting a polyvinyl alcohol polymer having a degree of hydrolysis of 90% by weight or more and a melting point in the range of 200°C to 225°C, extruding the molten polyvinyl alcohol polymer to form a molten polyvinyl alcohol polymer film, applying the molten film directly to a substrate surface, and solidifying the film on the surface to form a coated material. The present invention also relates to a coated material prepared by the method.

Description

[Technical Field]

[0001] The present invention relates to coated cellulosic substrates, particularly, but not exclusively, coated paper, and articles made from coated paper, wherein the coating comprises polyvinyl alcohol. The coating can be applied to paper, board, cardboard, molded packaging, containers and cartons, and other cellulosic products. [Background technology]

[0002] The difficulty or inability to recycle packaging, containers, and the like made from traditional polymers, such as polyolefins, has raised environmental concerns. For example, magazines enclosed in polyethylene packaging are often discarded or recycled as waste paper. This has the disadvantage that the polymer packaging can clog equipment in paper mills. This has led to a desire to use paper and other cellulose materials. However, due to the relative lack of mechanical strength and the difficulty of high-speed sealing of paper, paper cannot be used in commercial production lines for form-fill-seal packaging.

[0003] Polyvinyl alcohol has been applied to paper substrates from solution or as an emulsion. However, the properties of the resulting coating limit its use to a few applications. Also, relatively high coating weights may be required.

[0004] WO 2017 / 046361 discloses a method for producing plasticized polyvinyl alcohol having a degree of hydrolysis of 98% by weight or more.

[0005] JP 08-112884 A discloses the production of a polyvinyl alcohol laminate by applying molten polyvinyl alcohol having a degree of saponification of 20% to 80% to a moisture-permeable substrate under pressure.

[0006] Japanese Patent Application Laid-Open No. 02-191799 discloses the production of water-dispersible resin laminated paper by melt extrusion of polyvinyl alcohol resin onto water-dispersible paper. Summary of the Invention

[0007] According to a first aspect of the present invention there is provided a method for producing a coated material, the method comprising: providing a cellulosic substrate; Melting a polyvinyl alcohol polymer having a degree of hydrolysis of 90% or more and a melting point of 180 to 225°C; extruding a molten polyvinyl alcohol polymer to form a molten polyvinyl alcohol polymer film; Applying the molten film directly to the substrate surface and allowing the film to solidify on the surface to form the coated material.

[0008] The molten film may be applied directly to the surface of a substrate without the use of an adhesive or intermediate tie layer. The plasticized polyvinyl alcohol coating may exhibit natural adhesive strength while avoiding the need for the use of adhesives to form bonds between adjacent sheets or to seal containers. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing details of the extrusion head of an extrusion coating apparatus according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The polymers used in the present invention exhibit advantageous properties that facilitate the formation of stable molten films with sufficient melt strength for direct application to cellulosic substrates. Polyvinyl alcohol crystallizes rapidly. The melting point of the polymer is selected so that the temperature of the molten polymer when it contacts the substrate is above its glass transition temperature (Tg). The glass transition temperature of polyvinyl alcohol polymers is in the range of 70°C. Using conventional coating equipment, the temperature during extrusion and up to the point of contact with the cellulosic substrate surface is appropriately controlled. The films of the present invention do not form holes under the stress of extrusion conditions and are thermally stable, so they do not deteriorate. Without wishing to be bound by theory, it is believed that the plasticizer and stabilizer enable the polymer to maintain a stable viscosity even above the glass transition temperature.

[0011] When conventional polyvinyl alcohol is melted and subjected to shear, the viscosity initially decreases but increases after a short period of time, typically 5-10 minutes, and eventually the polymer decomposes, which can be attributed to entanglement of the polymer chains.

[0012] When the plasticized polyvinyl alcohol polymer of the present invention is melted and subjected to shear, the viscosity decreases continuously as the shear rate increases. When a shear rate is applied to the molten polymer, the reduced viscosity is maintained for a period of one hour or more. This characteristic is important for enabling the molten polymer to be maintained in a molten state under shear in conventional equipment before extrusion onto a cellulosic substrate. This allows for commercial production over conventional processing times. Homopolymer polyvinyl alcohol with a high degree of hydrolysis (HD) can be used for high-performance applications not previously available using known polyvinyl alcohol polymer coatings.

[0013] In embodiments, the viscosity of the molten polymer under steady state conditions decreases with shear rate to 1,000 1 / s or greater.

[0014] In embodiments, the reduced viscosity is achieved when shear is applied to the molten polymer, and the reduced viscosity is maintained for an extended period of time, for example, up to 1 hour, when shear is applied.

[0015] In embodiments, when the viscosity of a molten polymer is measured under steady state shear for up to 1 hour, the viscosity decreases with increasing shear rate, from a viscosity at a shear rate of 800 1 / s to a viscosity at a shear rate of 1000 1 / s.

[0016] The molten polymeric material may be pseudoplastic and may exhibit shear thinning behavior that fits the Carreau-WLF viscosity model with 97% or greater accuracy.

[0017] Applying molten polyvinyl alcohol film directly to a substrate has the advantage of eliminating the need for a two-step process: solidifying the film to form a solid film, then applying it to the substrate with an adhesive. The use of adhesives is undesirable because it adds cost and can contaminate water streams during recycling, for example in paper mills.

[0018] In embodiments, the melting point of the polyvinyl alcohol polymer may be from about 190°C to about 210°C, for example, from about 195°C to about 205°C, for example, about 200°C.

[0019] The polyvinyl alcohol is preferably a homopolymer and may be formed by hydrolysis of a polyvinyl acetate homopolymer. The polyvinyl alcohol may have a high degree of hydrolysis (HD) of 90% by weight or more, e.g., 93% by weight or more, 95% by weight or more, or 98% by weight or more. A preferred degree of hydrolysis is in the range of 93% to 96% by weight.

[0020] The use of polyvinyl alcohol homopolymers is particularly advantageous. The coating applied to the substrate can exhibit high transparency, high tensile strength, and excellent barrier properties against oil, grease, and fat. Excellent barrier properties against oxygen can also be achieved.

[0021] Polyvinyl alcohol with a high degree of hydrolysis is difficult to process by previously known methods.

[0022] The polyvinyl alcohol may be a blend of high and low molecular weight polyvinyl alcohols, preferably having the same degree of hydrolysis.

[0023] The polyvinyl alcohol polymer may contain one or more plasticizers, which may be selected from the group consisting of polyhydric alcohols, polyethylene glycols, glycerol, diols or triols such as propylene glycol, ethylene glycol, polyethylene glycol, glycerol, mannitol, erythritol, pentaerythritol, sorbitol, trimethylolpropane, and mixtures thereof.

[0024] Exemplary plasticizers can be selected from the following compounds and mixtures thereof: (a) sugar alcohols selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, and mixtures thereof; (b) polyols selected from the group consisting of pentaerythritol, dipentaerythritol, and mixtures thereof; (c) diols selected from the group consisting of methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, and mixtures thereof; (d) glycols selected from the group consisting of polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, and mixtures thereof; (e) Caprolactam, cyclic trimethylolpropane formal, rosin esters, euricamide, and mixtures thereof.

[0025] The water content of the molten polymer may be less than 0.5% w / w, for example less than 0.1% w / w.

[0026] The cellulosic substrate may be paper, board or card. The cellulosic substrate comprises cellulose fibers.

[0027] The method of the present invention arises from the discovery that molten polyvinyl alcohol film has inherent adhesive properties when coated onto a cellulosic substrate. In contrast, the solidified polyvinyl alcohol film used in prior art methods does not exhibit these inherently advantageous adhesive properties and requires the use of additional adhesive. However, the additional adhesive contaminates the water stream in the paper recycling mill.

[0028] The polyvinyl alcohol coatings of the present invention are capable of strong adhesion to cellulosic substrates and offer improved mechanical properties, including flexibility and resistance to delamination.

[0029] The molten polyvinyl alcohol film can be applied to a substrate using standard equipment, such as that used to coat polyethylene glycol onto a substrate. No specialized equipment is required, which was not previously possible with HD polyvinyl alcohol.

[0030] A particular advantage is that the polyvinyl alcohol-coated paper, board, or other cellulose materials of the present invention can be recycled in conventional paper mills. During recycling in paper mills, the cellulose fibers must be released from the composite product. HD polyvinyl alcohol is soluble in cold water, but may be selected to dissolve in water at temperatures of, for example, about 60°C, the temperature used in the processing of recycled paper and card. The polyvinyl alcohol can be separated by precipitation from the water stream and recovered for reprocessing and further use.

[0031] The polyvinyl alcohol polymers of the present invention are preferably free of starch, dextrin or other polysaccharides.

[0032] Traditionally, paper and board have been coated with polyethylene glycol, which prevents the polymer from being recycled and makes it difficult for paper mills to recycle cellulose materials. The coated materials of the present invention have better barrier properties than previously known polyethylene-coated cellulose materials. Greater mechanical strength and elasticity can be achieved.

[0033] According to one embodiment of the present invention, the coated material comprises a cellulosic substrate and a coating of polyvinyl alcohol polymer applied directly to the substrate in the absence of an adhesive, wherein the polyvinyl alcohol polymer is capable of dissolving in water having a temperature of about 30°C to about 60°C within 10 minutes to allow for the release of 100% of the cellulosic fibers from the coated substrate.

[0034] The polymer may be a plasticized polyvinyl alcohol homopolymer having a high degree of hydrolysis (HD), as disclosed according to the first aspect of the present invention.

[0035] The water temperature may be about 35° C. to about 45° C., for example about 40° C. Excess water may be used. The substrate and polymer may be pulverized before dissolution.

[0036] The solubility of the polyvinyl alcohol coating in water at temperatures of about 30°C to about 60°C, preferably about 35°C to about 45°C, e.g., about 40°C, allows the coated material to be reused in paper mills operating at that temperature without the risk of clogging due to the presence of insoluble polymeric material.

[0037] This allows conventional recycling plants to be used without modification, such as the installation of filtration or separation equipment to remove insoluble polymeric material. Polyvinyl alcohol can be recovered, for example, using the methods disclosed in WO 2016 / 046520.

[0038] The extrusion coating of the present invention may be applied using equipment manufactured by, for example, Davis-Standard, SAM, DaeKang, or Bandera.

[0039] A wide range of papers, boards and fibreboards can be used: offset or printing paper, coated paper, tissue paper, newsprint, cardboard, paperboard, fine art paper, kraft paper, acid-free paper, cellophane.

[0040] Plasticized polyvinyl alcohol coatings can be applied to cellulose films, such as cellulose acetate film manufactured by Celanese Corp. Coatings can also be applied to precipitated cellulose films, such as Natureflex manufactured by Futamura Corp.

[0041] The extrudable compositions and films of the present invention have unexpectedly been found to provide superior properties compared to previously used stock polyvinyl alcohol materials made by precipitation from solution, flocculation, or deposition from emulsion.

[0042] The advantage of the present invention is that it can be used with low-grade paper such as newsprint, but also with high-grade printing paper and kraft paper, particularly in applications where recycling was previously not possible, such as high-grade cosmetics and food packaging.

[0043] An advantage of the present invention is that low cost, low grade paper can be used in applications such as sandwich or food packaging, magazine packaging and paper bags, for example, pet food and other products that have high oil or fat levels that have resulted in difficulty in recycling.

[0044] Paper or other cellulosic materials coated in accordance with the present invention exhibit greater strength and tear resistance, facilitating their use in conventional high-speed manufacturing equipment.

[0045] The coated paper, board, or other cellulose materials of the present invention can be processed using conventional production lines or other equipment designed to handle polyolefin or other polymer sheet materials, such as form, fill, and seal production lines. Conventional polymer sheet production lines operate at speeds much faster than those possible for paper, sheet, or board materials, e.g., 200-800 m / min. Until now, paper has not been able to run on commercial form, fill, and seal lines. Paper tends to tear under high-speed processing conditions. The coated paper of the present invention can be run on high-speed lines, such as those used for polyolefin-coated sheet materials.

[0046] Coating paper according to the invention can provide excellent moisture and oil resistance, for example for the manufacture of packaging for oily products (e.g., fatty foods such as pet food).Unexpectedly, it has been found that coated paper according to the invention, having half the coating weight compared to conventional polyethylene-coated paper, can exhibit up to six times the strength of conventional materials.

[0047] The coated paper composite of the present invention provides superior properties compared to paper sized with a polyvinyl alcohol solution.

[0048] Multiple layers may be used, for example, a layer of polyvinyl alcohol coating may be applied between two layers of paper or other cellulosic material. Such multi-layer laminates have good oil, grease, and fat barrier properties and can be used in the manufacture of paperboard, boxes, trays, and similar products.

[0049] The coated paper composites can be used to produce heat-soluble bags or films for packaging, containment, or protection for a variety of applications, including cytotoxicity bags, electrostatic discharge (ESD) bags, anaerobic digestion (AD) bags, and garment bags. Bags or other films according to the present invention have the advantage of allowing organic waste to be transported to anaerobic digestion facilities without the need to remove the waste from the bags prior to processing. Such bags avoid the need for environmentally friendly cleaning of recycling containers.

[0050] The bags of the present invention can be used in many applications for which starch-based bags are not suitable, as they are weaker, have lower tensile strength and poorer barrier properties compared to bags made in accordance with the present invention.

[0051] The polymer composition can be produced using the methods disclosed in EP20184345 or WO2017 / 046361, the disclosures of which are incorporated herein by reference for all purposes.

[0052] An exemplary method for making a plasticized polyvinyl alcohol polymer mixture includes the following steps: introducing a polyvinyl alcohol polymer, including polyvinyl alcohol having a degree of hydrolysis ranging from 93% to 98% by weight or a blend thereof, into a mixing reactor; Here, the mixing reactor is a blending chamber having a first inlet, a first outlet, and at least two interengaging components extending between the first inlet and the first outlet, the components being positioned to apply a shear force to a polymer as it is conveyed by the components from the inlet through a reaction zone to the outlet; one or more second inlets located downstream of the first inlet for introducing reactants, including processing aids and plasticizers, into the chamber to form a reaction mixture; And the mixing chamber a plurality of heating zones arranged to expose the mixture to a temperature profile that increases in temperature from the inlet to the outlet; a second outlet disposed between the reaction region and the first outlet to allow removal of a processing aid from the chamber; reacting the processing aid, plasticizer, and polymer in a reaction zone to form a plasticized polymer; and Passing the plasticized polymer mixture through a first outlet.

[0053] By using reactive blending, processing aids and plasticizers can be reacted with the polyvinyl alcohol or blend thereof, followed by removal of all or most of the processing aids through a second outlet to provide a plasticized polyvinyl alcohol or blend thereof.

[0054] The total amount of plasticizer or plasticizers may be up to 10% by weight.

[0055] Blends of two or more polyvinyl alcohol polymers can be used, for example, a blend of two polyvinyl alcohol polymers having the same HD value and having high and low molecular weights, respectively.

[0056] For example, the blend may include a low viscosity grade having a molecular weight in the range of 13,000 to 27,000 and a degree of polymerization of 300 to 600, and a medium to high viscosity grade having a molecular weight in the range of 107,000 to 120,000 and a degree of polymerization of 2,400 to 2,600.

[0057] The use of a blend can allow for control of the viscosity of the polymer. The selection of a stabilizer as disclosed herein allows for the use of a blend with a desired viscosity without losing other properties. Alternatively, the use of a blend can allow for the use of polyvinyl alcohol containing one or more stabilizers while maintaining viscosity or other properties to allow for the production of pellets or films.

[0058] In a particularly advantageous embodiment, the polyvinyl alcohol comprises a blend of two or more polyvinyl alcohol polymers, each having a degree of hydrolysis of 93% to 98%, preferably one high molecular weight polyvinyl alcohol and at least one low molecular weight polyvinyl alcohol. In a preferred embodiment, the polymer comprises 80% high molecular weight polyvinyl alcohol and 20% low molecular weight polyvinyl alcohol. The ratio of high molecular weight polyvinyl alcohol to low molecular weight polyvinyl alcohol can be 2:1 to 10:1, preferably 3:1 to 7:1, more preferably 6:1 to 4:1, and most preferably about 5:1.

[0059] The high molecular weight polymer can have a molecular weight of 60,000 to 120,000.

[0060] The low molecular weight polymer may have a molecular weight of 5,000 to 30,000.

[0061] The blend of different molecular weight polymers used is selected according to the physical properties required for the final product. These may require different molecular weight materials to be used. The use of more than two different molecular weight polymers may be advantageous. The use of a single molecular weight polymer is not excluded.

[0062] One or more reactive stabilizers may be included in the polymer composition.

[0063] Exemplary reaction stabilizers may be selected from the group consisting of calcium stearate, stearic acid, sodium stearate, potassium oleate, potassium sorbate, sodium benzoate, and mixtures thereof. Amounts of less than 1% by weight may be used.

[0064] The use of one or more reaction stabilizers can advantageously reduce the degree of decomposition during melt processing. Sodium benzoate has been found to be particularly effective.

[0065] Additional additives may be used, including antioxidants, dyes and pigments.

[0066] The repulpability of cellulosic substrates such as polyvinyl alcohol coated paperboard can be measured in comparison to polyethylene coated paperboard using the Italian National Recyclability Standard: UNII 1743 "Paper and Board: Determination of Recyclability of Cellulose-Based Materials and Products".

[0067] Macrostickiness can be measured by British Standard ISO 15360. Stickies are a diverse group of materials that, when held on a slotted laboratory screen, adhere to objects they come into contact with. Stickies can adhere to objects at ambient temperature, or may exhibit adhesive properties when exposed to elevated temperatures, pressures, or changes in pH.

[0068] As used herein, percentages or other amounts are by weight unless otherwise indicated. Amounts are selected from any range given to add up to 100%.

[0069] The invention will be further illustrated by way of example and not by way of limitation in connection with the accompanying drawings, in which Figure 1 is a schematic diagram showing details of the extrusion head of an extrusion coating apparatus according to the invention. [Example]

[0070] Example 1 - Polymer Composition The formulation used in the extrusion coating run contained a blend of two polyvinyl alcohol (PVOH) polymers with different degrees of hydrolysis and viscosities. PVOH Grade 1: 14.31% (HD 91-93% by weight, viscosity in 4% by weight aqueous solution at 20°C 14.5-19.5 cP) PVOH Grade 2: 57.26% (HD 87-89% by weight, viscosity in a 4% by weight aqueous solution at 20°C: 3.5-4.5 cP)

[0071] The composition comprises: dipentaerythritol 6-9%, preferably 7.5%; Caprolactam 2-3%, preferably 2.5%; sodium benzoate 0.25%; Balance to 100% polyvinyl alcohol.

[0072] The extruder used to prepare the polymer blends was a Zeppelin RHC25 twin-screw extruder with an L:D ratio of 56:1 and venting in zones 7 and 10. The total feed rate to the extruder was 5.0 kg / hand and the torque generated was 19±4.0%. The extruder was equipped with a strand pelletizer at the die exit. The extrusion temperature profile settings were as follows:

[0073] [Table 1]

[0074] Samples of the pellets produced in the above runs were characterized by DSC, TGA, capillary rheometry, and other laboratory methods. The key test was that the pellets produced good coatings using standard commercial extrusion coating methods.

[0075] The viscosity of the polymeric materials was measured at three temperatures and different shear rates using a Dynisco LRC7000 series capillary rheometer. Before measuring the viscosity, the polymers were allowed to equilibrate for 1 hour to reach a steady state at a particular shear rate.

[0076] Table 1 - Viscosity ranges [Table 2]

[0077] Table 2 - Viscosity values [Table 3]

[0078] Example 2 - Properties of molten polymer Melt strength testing of polyvinyl alcohol polymers was performed using a RHEOTENS 71.97 extensional rheometer coupled with a Goettfert Rheograph Model 20 capillary rheometer using a 2000 bar oscillator. The material was allowed to equilibrate in the test barrel for 2 minutes before testing began.

[0079] Tests were performed using a die 30 mm long and 2 mm diameter with entrance angles of 180° and 210°.

[0080] Table 3 - Melt Strength Test Results [Table 4]

[0081] Example 3 - Coating of Substrate The apparatus includes a drive unit arranged to drive a single-screw extruder, the screw having a diameter of 25 mm and a length / diameter (L / D) ratio of 30. A gravity-fed hopper serves as the inlet for pellets of polyvinyl alcohol feedstock into the extruder. A slot die (4) provides a 200 mm wide film of molten polymer. A web path is provided by roll (5), which supports the cellulosic substrate during application of the polyvinyl alcohol coating. Uncoated substrate (6) is fed from unwind roll (9) and passes over an idler roll to the nip roll assembly (5) at the coating station. The coated substrate (7) passes over an idler roll to the unwind roll.

[0082] Figure 1 is an enlarged partial view showing details of the extrusion head (4) and nip roll assembly (5). The uncoated substrate passes over an intermediate roll below a slot in the die (4). A curtain of molten polyvinyl alcohol polymer (13) passes vertically from the die and contacts the surface of the substrate, forming the coated substrate (7). The temperature of the molten polymer (13) as it exits the die can range from 180°C to 225°C, and the temperature exceeds 70°C when the polymer contacts the substrate (6).

[0083] The extruder barrel has five heated zones and a heated adapter nozzle through which the polymer is transported by back pressure from the screw to the back of the coating die.

[0084] The temperature profile of the extruder was as follows:

[0085] [Table 5]

[0086] The coating die has four heating zones, top, bottom and side, with the following temperature settings:

[0087] [Table 6]

[0088] The cellulose substrate is 45 g / m 2 The paper was a clay-coated kraft paper having a basis weight of 20 g / m. 2 The polymer melt temperature was 202°C, the screw speed was 30 rpm, and the pressure was 5,000-8,000 kPa (50-80 bar). The line speed was set at 10 m / min.

[0089] The polymer pellets were fed into the extruder via a gravity-fed hopper. The polymer material was fed directly into the screw and transported down the length of the barrel where it was subjected to heat and pressure to form a molten polymer.

[0090] The molten polyvinyl alcohol was then forced by the extruder screw through a narrow, straight slit in the extrusion coating die, where it emerged as a thin, molten film.

[0091] A variety of coating dies with different internal geometries can be used. The die used in this example has a so-called "coat hanger" geometry. The coat hanger name refers to the internal geometry of the channels that allow the polymer to enter at a single point and then distribute evenly along the width of the die. The die shape and profile depth are varied to maintain a uniform parallel flow of material.

[0092] The thickness of the molten polymer resin was reduced from the die gap thickness (details) to the coating thickness (details) by a nip roll assembly.

[0093] At the point of coating, the polymer was dropped vertically into the nip between the chill roll and the backing or pressure roll. The paper substrate was fed over the backing roll and around the underside of the chill roll. Upon contact with the paper, the polymer bonded due to the heat and pressure applied by the nip. The chill roll ensured that the polymer crystallized without adhering to any rolls or itself when it reached the unwind roll where the composite polyvinyl alcohol-coated paper was collected.

[0094] Example 4 - Solubility Test The solubility of a film or coating of a polyvinyl alcohol composition can be measured by the following method.

[0095] The glass beaker was placed on a stirring hotplate with a calibrated thermometer.

[0096] Six slide frames were divided into upper and lower halves. One was used as a template to cut six replicate samples from a sample of polymer composition film with a thickness of 25-30 microns. The samples were sealed between the upper and lower slide frames, and the frames were snapped shut.

[0097] Water (400 g) was placed in a beaker with a magnetic stir bar and placed on a hot plate. The stirring speed was adjusted to give an 80% vortex and the water was heated to the required temperature.

[0098] The framed sample was clamped and placed in heated water, a timer was started, and the time to failure of the film was recorded.

[0099] The framed film sample was left in the water until the film was completely dissolved with no visible particles remaining. The time was recorded.

[0100] The measurements were repeated with two other replicate samples and fresh water.

[0101] To determine the time and temperature at which the film ceased to dissolve, the framed film sample was clamped below the water line and observed for any change in the structure of the film. The time of film failure was recorded.

[0102] Measurements were repeated with two replicate samples and fresh water. [Explanation of symbols]

[0103] 4 slot die 5 Nip Roll Assembly 6 Uncoated substrate 7 Coated substrate 13 Molten polyvinyl alcohol polymer

Claims

1. A method for producing a coated material, comprising: providing a cellulosic substrate; melting a polyvinyl alcohol polymer composition comprising a polyvinyl alcohol polymer and one or more plasticizers; wherein the plasticizer is selected from the group consisting of triglycerol, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, and caprolactam; the polyvinyl alcohol polymer is a blend of two or more homopolymer polyvinyl alcohol polymers, each having a high or low molecular weight, each having a degree of hydrolysis of 90% by weight or greater, and a melting point in the range of 200°C to 225°C; extruding the molten composition to form a film of the molten composition; applying the film directly to a substrate surface; and solidifying the film onto a surface to form a coated material.

2. 2. The method of claim 1, wherein the plasticizer is selected from the group consisting of triglycerol, xylose, D-mannitol, triacetin, pentaerythritol, and dipentaerythritol.

3. A method according to claim 1 or 2, wherein the film is applied directly to the surface of the substrate without the use of an adhesive or intermediate bonding layer.

4. The method of any one of claims 1 to 3, wherein the polyvinyl alcohol polymer is formed by hydrolysis of a polyvinyl acetate homopolymer.

5. 5. The method of claim 1, wherein the polyvinyl alcohol polymer has a degree of hydrolysis of 93% by weight or greater.

6. 6. The method of any one of claims 1 to 5, wherein the polyvinyl alcohol polymer composition comprises a reaction stabilizer selected from the group consisting of calcium stearate, stearic acid, sodium stearate, potassium oleate, potassium sorbate, sodium benzoate, and mixtures thereof.

7. 7. The method of claim 6, wherein the reaction stabilizer is sodium benzoate.

8. A method according to any one of claims 1 to 7, wherein the cellulosic substrate is paper, board or card.

9. 9. The method of any one of claims 1 to 8, comprising applying shear to the molten composition for one hour or more to reduce the viscosity of the molten composition.

10. The method of any one of claims 1 to 9, wherein the two or more homopolymer polyvinyl alcohol polymers have the same degree of hydrolysis (HD) value.

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