Method for producing a water-soluble polymer composition

Abstract

A method for creating a processable water-soluble polymer is disclosed. [Solution] This method consists of the following steps: extruding a water-soluble polymer composition from an extruder barrel without using a die to produce an irregularly shaped polymer extruder (where the extruder barrel is not ventilated except through its extruder outlet); guiding the irregularly shaped polymer extruder to a chilled conveyor to cool it to 60 degrees Celsius or below; and granulating the amorphous polymer extruder to form granular material.

Description

Technical Field

[0001] The present invention relates to polymer compositions (particularly, but not limited to, polyvinyl alcohol polymers), and methods for producing the same.

Background Art

[0002] Currently, the demand for water-soluble biodegradable polymers is increasing to replace non-biodegradable polymers that are currently available in a significant amount on the market. Non-biodegradable polymers require landfill disposal or incineration, consuming a large amount of resources.

[0003] Polyvinyl alcohol (PVA) is one of the few vinyl polymers that dissolve in water and is recognized as being ultimately biodegradable in the presence of appropriately acclimated microorganisms. Therefore, attention has been focused on the preparation of highly environmentally compatible PVA-based materials for various applications. PVA has excellent moldability for films and thin-walled containers and exhibits high impermeability to many gases, making it very suitable for packaging products handled in a water-rich environment. It is also characterized by high adhesiveness and harmlessness. However, when the polymer absorbs water, its tensile strength decreases while its elongation and tear strength increase, so these characteristics are humidity-dependent. In addition, PVA and PVA-containing compositions are difficult to extrude mold well, further limiting their applications. In particular, there is currently no formulation that can be easily molded to the minimum thickness (200 micrometers or less) required for use in products at low water temperatures (typically 5 degrees Celsius or less within 2 minutes). Such films are preferred for applications such as packaging of laundry products that need to release laundry detergents in short washing cycles at low temperatures.

[0004] One polymer property that is expected to be improved is the melt flow index (MFI). This value represents the flowability of the polymer molten material and is defined as the mass (in grams) of polymer that flows through a capillary of a given diameter and length in 10 minutes when pressurized with a given weight at various given temperatures. One such method is specified in the ISO 1133 standard. A higher MFI is required to provide thin-walled molded parts.

[0005] It is known in the art that internal lubricants are used within PVA to increase the melt flow index of PVA. For example, EP1112316 B1 (PVAXX Technologies Limited) discloses the inclusion of up to 5 weight percent of fatty acid amides. Fatty acids provide lubrication between polymer chains and increase the melt flow of the polymer. However, they are insoluble and can dissolve during processing, coating the polymer and inhibiting its dissolution. Furthermore, excess lubricant (generally more than 5 weight percent of PVA) separates from the mixture, limiting the amount of lubricant that can be used and thus limiting its ability to improve the MFI of the polymer.

[0006] Polymers are produced by polymerizing vinyl acetate and then hydrolyzing the resulting polyvinyl acetate (PVAc). Polymers derived from PVA and PVA are readily soluble in water, and their solubility is determined by the molecular weight of the polymer and the degree of hydrolysis (the percentage of acetate groups in the starting polymer (PVAc) that are replaced by OH groups). Higher degrees of hydrolysis result in lower solubility and a slower dissolution rate. This difference is more pronounced at lower dissolution temperatures than at higher temperatures, due to the formation of crystalline zones within the polymer.

[0007] Furthermore, it is known to those skilled in the art that volatile components must be removed from the composition before melting the PVA. This is because failure to do so would make processing difficult due to the formation of vapors and subsequent foaming of the polymer. Drying is generally carried out using a standard drying apparatus at a temperature of 90 degrees Celsius for 4 to 9 hours, although this varies depending on the manufacturer, model, and formulation.

[0008] Despite attempts to mold articles from PVA or PVA-derived compositions, the desired solubility characteristics have not been achieved due to the lack of melt fluidity necessary to mold thin-walled articles that dissolve in aqueous solutions within the desired time frame.

[0009] The object of the present invention is to provide a water-soluble polymer composition (in particular a polyvinyl alcohol composition, but not limited thereto) that addresses, or at least mitigates, the aforementioned problems experienced with prior art polymer compositions.

[0010] A further object of the present invention is to provide a method for producing a water-soluble polymer composition, and a method for extrusion molding and molding. [Overview of the Initiative]

[0011] The present invention provides a method for producing a water-soluble polymer, the method comprising the following steps: extruding a water-soluble polymer composition from an extruder barrel without the use of a die (where the extruder barrel is not aerated except through its extruder outlet) to produce a polymer extruder of an irregular shape; guiding the amorphous polymer extruder onto a chilled conveyor and quenching the amorphous polymer extruder to 60 degrees Celsius; and granulating the amorphous polymer extruder to form granular material.

[0012] Optionally, granulation of amorphous polymer extruders may be performed immediately after the chilled conveyor without a further drying step.

[0013] Preferably, the method may further include a step of forming the granules into a water-soluble polymer product.

[0014] Preferably, the water-soluble polymer may consist of a water-soluble polymer composition having a solvent polymer plasticizer, comprising at least 15 weight percent of the total weight of the composition a hygroscopic salt that acts as a lubricant to make the polymer extrudeable, where the solvent polymer plasticizer is monopropylene glycol or dipropylene glycol, and the water content of the composition is less than 10 weight percent of the total weight of the composition.

[0015] Preferably, the hygroscopic salt may be provided in a higher weight than the solvent polymer plasticizer.

[0016] Preferably, the hygroscopic salt may be an anhydrous or hydrated salt selected from the group consisting of: sodium chloride, sodium citrate, magnesium chloride, calcium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium carbonate, and ammonium carbonate.

[0017] Preferably, the hygroscopic salt may be a water-soluble salt that dissolves in water at 90 degrees Celsius in 10 minutes at a rate of at least 10% by weight.

[0018] Preferably, the hygroscopic salt may have a moisture content of less than 10% by weight relative to the total weight of the composition.

[0019] Preferably, the hygroscopic salt may be included in an amount of at least 25 weight percent of the total weight of the composition.

[0020] Preferably, the hygroscopic salt may be included in an amount of at least 30 weight percent of the total weight of the composition.

[0021] Preferably, the hygroscopic salt may be in an anhydrous form.

[0022] Preferably, the water-soluble polymer and the hygroscopic salt may be provided in solid form.

[0023] Preferably, the polymer may contain a polyvinyl alcohol polymer.

[0024] Preferably, the method may further include a step of extruding the water-soluble polymer composition without using a die.

[0025] Preferably, the method may further include a step of extruding the water-soluble polymer composition onto a chilled conveyor.

[0026] Preferably, the chilled conveyor may be at a temperature above 10°C and below 30°C.

[0027] Preferably, the method may further include a step of granulating the water-soluble polymer composition immediately after the chilled conveyor without performing a further drying step.

[0028] Preferably, the water-soluble polymer may contain wax in order to improve moisture resistance.

[0029] Therefore, the present invention provides a melt-processable water-soluble polymer composition having a water content of less than 10% by weight, which is formed by blending at least 15% by weight of a hygroscopic salt acting as a lubricant for making the water-soluble polymer extrudable, moldable, or both, based on the total weight of the composition.

[0030] Preferably, at least 20% by weight of the hygroscopic salt is provided based on the total weight of the composition. Further, the water-soluble polymer may be solid at room temperature. More preferably, the polymer consists of a polyvinyl alcohol (PVA)-based polymer. The degree of hydrolysis of PVA used in the present invention is not particularly limited. In the present invention, partially hydrolyzed or fully hydrolyzed PVA can be used. Similarly, PVA is not limited to a specific molecular weight. PVA may have a relatively low molecular weight ranging from around 20,000 to 150,000.

[0031] The PVA preferably has a maximum water content of 5 weight percent. Remarkably, the hygroscopic salt not only removes moisture from the PVA but also acts as an internal lubricant, increasing the melt flow index.

[0032] Preferably, the hygroscopic salt is an anhydrous or hydrated salt selected from alkali metal salts or alkaline earth metal salts. Depending on the final use of the composition, it may be beneficial to use salts approved for food or pharmaceutical use, salts with other properties that can impart further advantages to the final product, such as water softeners, or both. More preferably, the salt is selected from the group consisting of sodium chloride, sodium citrate, magnesium chloride, calcium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium carbonate, and ammonium carbonate, and in particular sodium chloride or sodium citrate.

[0033] A preferred embodiment of the first aspect of the present invention comprises a blend of a water-soluble polymer and an amount of sodium chloride effective in making the blend extrudeable.

[0034] The salt has a moisture content of 10% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly 0.2% by weight or less. Ideally, the salt is anhydrous. The salt may be pulverized, for example, into particles having an average size of less than 100 micrometers, with sizes preferably ranging from 0.03 to 75 micrometers, and particularly from 60 to 70 micrometers. The salt may also be coated to improve its properties. For example, it may be coated with sodium aluminosilicate, silicon dioxide, sodium hexacyanoferrate, or a combination thereof. An example of such is a sodium chloride salt coated with 0.5% sodium aluminosilicate (E554), 0.75% silicon dioxide (E551), and sodium hexacyanoferrate (E535) as a caking inhibitor, available from Custom Powders (www.custompowders.co.uk).

[0035] Salt may be included in the composition in an amount up to 75% by weight of the total weight of the composition. Salt is included in an amount of at least 15% by weight, preferably at least 20% by weight, more preferably at least 25% by weight, more preferably at least 30% by weight, more preferably at least 35% by weight, more preferably at least 40% by weight, more preferably at least 45% by weight, and particularly at least 50% by weight of the total weight of the composition.

[0036] To improve the processability of the composition, optional additives may be included, such as plasticizers to increase flexibility and lower the melting temperature of the polymer during extrusion molding, stabilizers to improve heat resistance, and pigments to add color. Preferably, a heat stabilizer such as a metal stearate is included in an amount of up to 0.5% by weight, preferably up to 0.3% by weight. However, it is preferable that the composition does not contain fatty acid amides or esters.

[0037] In one aspect of the present invention, a salt is used to allow inbound water (water flowing inward from other components within the composition surface, such as the polymer itself) to act as an internal lubricant. This "internal" lubricant has the function of improving the lubricity between polymer chains. By using a salt as a lubricant, the need for other conventional internal lubricants, such as fatty acid amides or esters, is eliminated.

[0038] Examples of compositions that do not contain solvent-based plasticizers include: Polyvinyl alcohol (PVOH) (80% hydrolysis) 69.7% Sorbitol 10.0% Sodium chloride 20.0% Heat stabilizer 0.3% Total 100% The melt flow index = 21.5 was tested at 190 degrees Celsius with a 2.16 kg gram weight for 10 minutes. Sodium chloride is more soluble in water than polymers, but it is not a thermoplastic resin. Therefore, it would be expected that the angular crystalline structure of the salt would not mix with the polymer and would instead inhibit melt flow. However, surprisingly, this has been found not to be the case.

[0039] Preferably, the salt is provided in a higher weight percentage than the solvent polymer plasticizer. More preferably, the ratio of salt to solvent polymer plasticizer is 1.25 to 12:1, particularly 1.25 to 7:1, and ideally 4 to 5:1.

[0040] Alternatively, the composition may contain a solvent polymer plasticizer. The solvent polymer plasticizer is preferably a hygroscopic organic solvent, more preferably selected from glycerin (also known as glycerol) and propylene glycol. Preferably, the solvent polymer plasticizer is monopropylene glycol, and in a more preferred embodiment, the solvent polymer plasticizer is dipropylene glycol.

[0041] The present invention provides a melt-processable water-soluble polymer composition comprising a water-soluble polymer and at least 15% by weight of a hygroscopic salt that acts as a lubricant to make the polymer extrudeable and moldable.

[0042] According to another aspect of the present invention, a soluble polymer internal lubricant is provided, comprising a blend of a hygroscopic salt and a solvent polymer plasticizer of that salt.

[0043] The lubricant according to the present invention may be formulated with a water-soluble polymer for processing. In this regard, a further aspect of the present invention provides a melt-processable water-soluble polymer composition comprising a blend of a water-soluble polymer and an internal lubricant for making the polymer extrudeable or moldable. Here, the lubricant comprises a hygroscopic salt, preferably an anhydrous metal salt or a hydrated metal salt, blended with a solvent polymer plasticizer. Preferably, the lubricant is according to the aforementioned aspect of the present invention.

[0044] The moisture content of the salt is preferably minimal, and a salt having a moisture content of less than 10% by weight is preferred. Here, the salt constitutes at least 15% by weight, more preferably at least 40% by weight, and particularly preferably at least 50% by weight of the total weight of the composition.

[0045] The lubricant according to the present invention, when mixed with a water-soluble polymer, preferably has a melt flow index of at least 20 g (10 mins / 190°C / 2.16 kg, compliant with ISO 1133), more preferably at least 40 g, and particularly 60 g.

[0046] The compositions according to the present invention can be used in food and pharmaceuticals. Therefore, it should be understood that, where possible, the components of the compositions, such as lubricants, are approved for use in food and pharmaceuticals.

[0047] The compositions according to the present invention may be provided in any suitable form for further processing, but preferably, extrusions such as extruded filaments containing soluble polymers or extruded molded articles may be provided in the form of powders, tablets, or pellets for use in molding. The compositions can be manufactured by any conventional method, such as melt kneading or cold working. This may include calendering, adaptive calendering, compression, or one or more thereof. Cold pressing, more preferably adaptive calendering, may be selected as preferred methods.

[0048] The composition of the present invention may further contain a plasticizer for lowering the melting temperature of the polymer under extrusion or molding conditions. The plasticizer may be selected from the group consisting of glycerin, ethylene glycol, triethylene glycol, low molecular weight polyethylene glycol, and low molecular weight amide. A preferred plasticizer is glycerin, more preferably monopropylene glycol, and most preferably dipropylene glycol. The plasticizer may also function as a solvent polymer plasticizer for salt-based internal lubricants.

[0049] A further aspect of the present invention provides a method for producing a water-soluble polymer composition, comprising incorporating a water-soluble polymer with a hygroscopic salt that acts as a lubricant to make the polymer extrudeable or moldable in at least 15 weight percent of the total weight of the composition, wherein the water content of the composition is less than 10 weight percent, and the method optionally includes the addition of a solvent polymer plasticizer.

[0050] A further aspect of the present invention provides an extrusion, molding, or both method for a water-soluble polymer composition, comprising softening the composition according to the preceding aspects of the present invention to form a molten flow. Preferably, the composition is softened by heat or pressure to generate a molten flow.

[0051] Regarding melt flow, the melt flow index is preferably 20 g or more (10 mins / 190°C / 2.16 kg, based on ISO 1133), more preferably 40 g or more, and particularly preferably 60 g or more. Preferably, the polymer composition is molded into a form having a thickness of less than 200 micrometers, preferably less than 100 micrometers, thereby enabling the form to dissolve in an aqueous solution at 5 degrees Celsius within 80 seconds. The molded body may be any thin-walled molded body such as a container or a film. Extrusion molding is also possible, but the composition of the present invention is particularly advantageous for molded articles (moulding).

[0052] Further aspects of the present invention provide water-soluble polymer products formed according to earlier aspects of the present invention.

[0053] A further aspect of the present invention provides a melt-processable water-soluble polymer composition comprising: a water-soluble polymer; a mixture of a hygroscopic salt acting as a lubricant to make the polymer extrudeable; a solvent polymer plasticizer; and a wax. Herein, the wax content of the composition is at least 0.3 weight percent of the total weight of the composition; the water content of the composition is less than 10 weight percent of the total weight of the composition; and the hygroscopic salt is included in the composition in an amount of at least 15 weight percent of the total weight of the composition.

[0054] Preferably, the melt-processable water-soluble polymer composition may have a wax content of at least 1.0 weight percent of the total weight of the composition.

[0055] Preferably, the wax may be glycerol monostearate. [Modes for carrying out the invention]

[0056] The melt-processable composition of the present invention can be processed by any known heat treatment method (including, but not limited to, injection molding, compression molding, rotational molding, and film extrusion molding). The composition is particularly suitable for thin-walled molded products.

[0057] The melt-processable composition according to the present invention is suitable for the manufacture of any article currently made from extrudeable polymers, moldable polymers, or both, such as films, containers, and bottles. This composition is suitable for the manufacture of spunbond, nonwoven fabrics, filaments and fibers used in melt-blown applications. It is also suitable for the manufacture of detergent and pesticide pouches and containers, mulch films, flower pots, household bags, diapers, straws, nursing care products, hangers, urine pads, pouches, six-pack rings, disposable clothing, foams, gloves, film containers, golf tees, shotgun cartridges, bedpans, bottles, bowls, cotton swabs, hospital curtains, disposable sterile products, packaging materials, and the like.

[0058] Generally, PVA contains up to 5% by weight of moisture. To avoid processing problems in standard thermoplastic equipment, such as the generation of volatile substances that cause foaming, this value needs to be reduced to less than 1%. Traditionally, polymers were dried at 90 degrees Celsius for 4 to 8 hours using a general polymer dryer. It has been found that moisture can be removed from the surrounding PVA by adding a specific amount of hygroscopic salt, preferably with low moisture content or anhydrous. Even more surprisingly, as the salt absorbs water, a self-lubricating coating forms on the salt, which then acts as an internal lubricant for the PVA. The drying effect of the salt reduces drying time to 2 to 4 hours, enabling significant energy savings in polymer production. Furthermore, the lubrication provided by the salt greatly increases the melt flow index of the composition, making it easier to extrude and mold the PVA for products. It is particularly suitable for thin shapes of 200 micrometers or less and is suitable for applications that require the melting or molding of films at low temperatures of around 5 degrees Celsius in a short time (less than 2 minutes). The self-lubricating effect is effective even at low moisture levels of less than 1% (i.e., even during the drying process). It is also possible to lower the temperature further, bringing it closer to 0 degrees Celsius, and to shorten the time required.

[0059] It has been found that hygroscopic salts such as sodium chloride have a lubricating effect when the composition includes a hygroscopic salt solvent containing glycerin or propylene glycol, particularly a polymer plasticizer such as monopropylene glycol, or most preferably dipropylene glycol. The absorption of water by the salt acts as a surface treatment, and if necessary, a non-solvent plasticizer can be added. Anhydrous salts are generally not considered suitable for internal lubrication of water-soluble polymers. In this regard, small amounts (2-3%) of precipitated calcium carbonate (PCC) have been used. Alcohol-based plasticizers are not solvents for PCC, and because PVA is encapsulated around the PCC particles, they provide a high melt flow, and high addition amounts are required to obtain a very ductile product. The melt flow index is also undesirable. In contrast, the present invention uses glycerin, monopropylene glycol, and dipropylene glycol as solvents for anhydrous sodium chloride to partially dissolve the outer surface of the sodium chloride, thereby providing lubricity within the polymer chain. This results in a relatively high MFI (melt flow index), increasing the solubility of the polymer while reducing ductility (which is a desirable property).

[0060] Sodium chloride is a possible hygroscopic salt. In addition, sodium citrate, magnesium chloride, calcium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium carbonate, and ammonium carbonate can be considered as alternatives. The necessary properties of the hygroscopic salt used in this invention are that it is water-soluble, has the ability to absorb moisture from the atmosphere, and has a solubility of 10% by weight or more in water at 90 degrees Celsius in 10 minutes, or a combination of these.

[0061] It should be understood that even when using hygroscopic salts, the advantages of the present invention cannot be achieved if the composition contains high levels of water (either as a plasticizer or binder). This water will cause some or all of the present salt to reversibly dissolve. Furthermore, reducing the water content to ensure successful processing removes the self-lubricating layer and leads to the formation of salt crystals of unpredictable size and shape. This hinders the melt flow and prolongs the drying time. Therefore, it is a preferred embodiment of the present invention not to add water to the formulation beyond the low water content present in the various components of the composition, such as PVA.

[0062] Next, the present invention will be described with reference to the following non-limiting examples. The examples illustrate the high melt flow index achieved by compositions according to the present invention and the reduction in their drying time, and compare these properties with compositions that fall outside the protected range.

[0063] (Manufacturing method) PVA (polymer), sodium chloride (lubricant), glycerin (plasticizer), and thermoplasticizer were mixed for 3 minutes in a Velbus, low-shear mixer. This mixture was fed into a compounder via a screw and formed into pellets through a suitable calendering process. The suitable calendering process causes the PVA to partially or completely melt as a result of frictional shear as it passes between the rollers and the die, causing agglomeration before being extruded through the die. The temperature of the pre-extruded material was between 110°C and 140°C, and the formed pellets were then placed in a tray-type polymer dryer at 90°C for 3 hours.

[0064] (Melt flow analysis) A 5-gram sample of the formulation prepared according to the present invention was tested for MFI at 190 degrees Celsius using a 2.16-kilogram weight. Each sample was tested for MFI according to ISO 1133 and compared. The test was repeated several tens of times, and the average result was recorded.

[0065] The samples were formed using a mold equipped with a hot runner system, with a 50-ton forming press in automatic mode, at temperatures ranging from 180 to 200 degrees Celsius, and with cycle times of 7 to 10 seconds. The screw temperature profiles (in degrees Celsius) from the hopper to the tip were 160, 170, 180, and 180-190. The cross-sectional area of ​​the part wall was measured at 600-350 micrometers.

[0066] (Example 1) The components shown in Table 1 below were mixed in the specified weight ratios, and formulations were prepared according to the method described above. Each formulation contained 88 percent hydrolyzed PVA, and the heat stabilizer was calcium stearate. The melt flow index (MFI) was determined according to the analysis described above. [Table 1] Formulation 2 shown in Table 1 above is white / cream-colored and was found to have the following characteristics: Density 1.68g / cm Melt density: 1.52 g / cm³ (at 200 degrees Celsius) (according to ISO 1183)

[0067] These results demonstrate the importance of increasing the salt-to-plasticizer ratio in the formulation to achieve the desired high MFI, and explain that the peak MFI value is obtained in the above formulations where the salt-to-plasticizer ratio is 3.5-5:1, more preferably 4-4.4:1.

[0068] Example 2 The components shown in Table 2 below were mixed in predetermined weight ratios, and the formulations were prepared according to the method described above. 88 percent hydrolyzed PVA was used in each formulation. The melt flow index (MFI) was determined according to the analysis described above. The outer wall thickness of the molded parts was measured between 600 micrometers and 100 micrometers. [Table 2] Table 2 shows that the type of plasticizer does not have a significant impact on the achieved MFI.

[0069] (Example 3) Compounds having the raw materials shown in Table 3 were prepared by mixing them in given weight percentages according to the method described above. Compounds 10 to 13 used 98 percent hydrolyzed PVA, and compounds 14 to 16 used 80 percent hydrolyzed PVA. The compound was molded using a Boy 50-ton molding process in automatic mode with a cycle time of 20 seconds, using a mold with a cold runner system. The screw temperature profiles (Celsius) from the hopper to the tip were 160, 170, 180, 180, and 220. The outer wall thickness of the part was measured from 600 to 2000 micrometers. [Table 3]

[0070] (Example 4) Formulation 17 was prepared as a blend similar to Formulation 2 of Example 1, but with sodium citrate instead of sodium chloride, as follows: PVA (88% hydrolysis) 39.0% by weight Sodium citrate 51.0% by weight Glycerol 9.70% by weight Calcium stearate 0.3% by weight This compound was found to have the following properties: Density 1.67 g / cm Melt density: 1.40–1.42 g / cm³ (at 190°C) (ISO 1183) MFI 38g. The processing temperature was 190-200 degrees Celsius with a maximum residence time of 30 minutes. The drying time was 4 hours at 90 degrees Celsius. Again, the MFI is substantially higher when salt is included in the composition.

[0071] This formulation and formulation 2 were tested for extrudeability in injection molding machines manufactured by Boy, Demag, and Arburg. Extrusion was performed using a single-screw full-flight type screw with a constant pitch. The barrel temperature had a profile of 160-200 degrees Celsius, and the screw speed was varied between 20-150 rpm. Equipment shutdown was performed by stopping the screw rotation and maintaining the temperature at 100 degrees Celsius. A complete shutdown was then performed by switching off the machine.

[0072] Formulations 2 and 17 could be molded into containers of various dimensions and colors and were suitable for injection molding. The use of sodium citrate as a polymer lubricant provides an additional benefit, as it acts as a water softener when used to package laundry products.

[0073] (Example 5) Tests were conducted to examine the requirement of low moisture content in the formulation according to the present invention. Table 4 below shows the relationship between the composition of the formulation, MFI (Metal Injection Factor), and drying time. [Table 4] Table 4 clearly shows the importance of the amounts of salt and water in the formulations on drying time and MFI. In this formulation, the proportion of salt is high (at least 15 percent, preferably at least 20 percent, more preferably at least 40 percent), and the water content is minimal or zero. Formulations C and D contain 13 percent and 17 percent water, respectively, and are very sticky, non-flowing, and unsuitable for formulation. Furthermore, excessively long drying times are undesirable in terms of glycerin evaporation.

[0074] (Example 6) Relative humidity (RH) is the ratio (usually expressed as a percentage) of the partial pressure of water vapor in the environment to the equilibrium vapor pressure of pure water. The RH at which a material begins to deliquesce, that is, when water adsorbed on the material begins to dissolve the material's molecules, is called the deliquescence point (RHo) of the material (also called the critical relative humidity). This is an important parameter that characterizes the structural stability of polymer materials. RHo is temperature-dependent and is usually expressed as the RHo value at a given temperature. For example, the RHo of crystalline NaCl at 20 degrees Celsius is approximately 77% RH. This is because, at an ambient temperature of 20 degrees Celsius, if the ambient RH is 77 percent or higher, water vapor in the atmosphere will spontaneously adsorb to the NaCl crystals and solvate them.

[0075] Materials with low RHo values ​​are more hygroscopic and can therefore act as desiccants. On the other hand, materials with high RHo values ​​tend to absorb less moisture. In the case of polymer compositions, the advantages of having a high RHo value include a reduced need for secondary packaging and the provision of a more structurally stable product when opened in an unprotected environment.

[0076] Products made from water-soluble polymers have the challenge of being hygroscopic and prone to structural instability in environments with high relative humidity (RH). For example, at an ambient temperature of 20 degrees Celsius, PVA begins to deliquesce when the RH exceeds 50 percent.

[0077] As mentioned above, while the compound consisting of PVA, sodium chloride, and glycerin facilitates melt processing due to the lubricating effect of the glycerin and salt combination, it presents a challenge in that the molded product easily absorbs moisture, requiring secondary packaging with high resistance to moisture and gases.

[0078] Using three solvent polymer plasticizers—glycerin, monopropylene glycol, and dipropylene glycol—various water-soluble polymer compositions consisting of 88% hydrolyzed polyvinyl alcohol (PVA) and NaCl were prepared. Table 5 below shows the formulations of nine different compositions. Compositions 1-3 contain glycerin, compositions 4-6 contain monopropylene glycol, and compositions 7-9 contain dipropylene glycol. [Table 5] As shown in Table 5, it was surprisingly found that using propylene glycol as a solvent polymer plasticizer resulted in lower water absorption and, therefore, more stable PVA-based polymer products compared to comparative formulations using glycerin as the solvent polymer plasticizer. While formulations 7 to 9 using glycerin had an RHo of 62-66 percent at 2 degrees Celsius, all formulations using propylene glycol had a significantly higher RHo of 76-83 percent at 20 degrees Celsius.

[0079] Furthermore, formulations using dipropylene glycol were found to be even more stable than equivalent formulations using monopropylene glycol. The RHo values ​​at 20 degrees Celsius for formulations 1 to 3 using dipropylene glycol were 80 to 83 percent, while the RHo values ​​at 20 degrees Celsius for formulations 4 to 6 using monopropylene glycol were lower, at 76 to 77 percent.

[0080] The deliquescence point of sodium chloride is approximately 77 percent RHo at 20 degrees Celsius, but molded products made with formulations containing PVA, sodium chloride, and glycerin tend to deliquify to over 60 RHo at 20 degrees Celsius.

[0081] A remarkable effect of replacing dipropylene glycol with glycerin is that the deliquescence point of sodium chloride rises above 20 degrees Celsius (82 RHo). This reduces the specifications requirements for secondary packaging and improves dimensional stability when opened unprotected.

[0082] (Example 7) The melt flow indices of formulations containing dipropylene glycol and sodium chloride were compared. [Table 6] It was demonstrated that the melt flow index significantly improved as the concentration of hygroscopic salts increased.

[0083] (Further manufacturing methods) Conventionally, in this field, PVA resins have been manufactured by extrusion molding via slot dies or strand dies. Both slot dies and strand dies provide sufficient back pressure to ensure a uniform flow of polymer melt from the extruder to the cooling area of ​​the extruded material. This is typically achieved by immersion in water or cooling at room temperature or with cold air.

[0084] The problem with water immersion is that, because PVA is water-soluble, it needs to be dried further after immersion.

[0085] When cooling with ambient air, a problem arises because plasticizers are lost from the formulation until the extruded product cools to below 60 degrees Celsius.

[0086] PVA containing a hygroscopic lubricating salt produced according to the method of the present invention is highly soluble and brittle, making it unsuitable for strand extrusion and water cooling. When cooled in water, the pellets become slimy due to dissolution and stick together, requiring further drying. In addition, the strands become brittle due to polymer reduction, high salt content, and plasticizer loss during air cooling (up to 0.75%). Strand breakage and material loss can lead to process instability and process downtime. Volatilization loss of plasticizers negatively affects product consistency, depending on ambient conditions and cooling time. The melt flow index may also change significantly.

[0087] Slot dies are used to produce tapes for extrusion, not pellets for reprocessing.

[0088] As mentioned above, air cooling is preferable to conventional water baths. However, it is also possible to cool the extruded material with air assisted by a fan supported by a moving conveyor. The extruded strands leave the strand die at 165 to 200 degrees Celsius and reach the stand pelletizer at a maximum temperature of 60 degrees Celsius. On this moving conveyor, the aforementioned evaporation of plasticizer occurs. This mass loss not only negatively affects the melt flow index but also leads to economic losses.

[0089] Therefore, to accommodate the improved polymer composition, a new cooling method for extruded products was developed. For convenience of labeling, this new method is sometimes called the chilled roller method.

[0090] The chilled roller method allows polymers to be extruded without the need for additional vents in the barrel or the use of slot dies or strand dies. In the absence of back pressure, the barrel releases steam, producing an extruded material that is (1) irregular, with inconsistent size and shape, and (2) has a very low moisture content, preferably less than 1 percent (v / v). This is a significant difference from conventional processes in which polymers are extruded through slot or strand dies. Slot die and strand die methods cannot operate unless the extruded material is regular and of consistent size and shape. Because the presence of steam in the barrel causes inconsistencies, slot die and strand die methods require additional venting of the barrel.

[0091] When the irregular extruded material is allowed to fall onto a cooling roller or conveyor, it is rapidly cooled there to a temperature below 100 degrees Celsius, above 10 degrees Celsius, preferably below 60 degrees Celsius. The cooling process is almost instantaneous, taking less than 30 seconds, more preferably less than 20 seconds, even more preferably less than 10 seconds, and generally less than 5 seconds. The chilled rollers are set to cool instantaneously to prevent plasticizer loss. In practice, if the extruded material is cooled instantaneously, it will not have enough plasticity to pass through the cooling rollers, so it is necessary to cool it slightly beforehand. In practice, if the extruded product is cooled slightly before instantaneous cooling, it will not have enough plasticity to pass through the cooled rollers. It needs to pass through immediately to maintain sufficient malleability for rolling. The cooled irregular extruded material is led to a commercially available polymer grinder and granulated. This can then be stored, usually sealed in vacuum bags, in preparation for the next processing.

[0092] To address the unevenness of the extruded material, applying a calendering process, preferably using a water-cooled chilled roller, allows for rapid cooling of the extruded material to below 60 degrees Celsius. Furthermore, the high thermal conductivity of PVA containing 15% or more by weight of hygroscopic salts further improves the cooling through this system.

[0093] If salt is not included, a lower temperature roller is required. Specifically, to achieve the same cooling rate while preventing plasticizer loss, the temperature must be below 10 degrees Celsius. This can cause condensation on the cooled roller, leading to process problems and material adhesion. This makes the entire process inefficient. A water temperature between 10 and 30 degrees Celsius is found to be optimal for PVA and salt compositions. On the other hand, compositions without salt require temperatures below 10 degrees Celsius, but in this case, condensation becomes a problem.

[0094] Below 60 degrees Celsius, the plasticizer is fixed to the polymer composition, below the plasticizer evaporation temperature, and the loss of total weight of the polymer composition due to evaporation is prevented to a range of 0.75 to 1.25 percent. Furthermore, the resulting polymer has a very low moisture content, as most of the present water is lost as water vapor during the extrusion process. The moisture content can be maintained at less than 1 weight percent, which is the maximum possible moisture content required for successful reprocessing of irregularly extruded materials. This eliminates the need for further drying of the polymer.

[0095] Tables 7 and 8 below show a comparison between the product produced by the above-described chilled roller method and the product produced by the conventional chilled air stand line process (a process in which the extruded material is directly extruded into strands and then air-cooled). (Chilled roller manufacturing method) [Table 7] (Extruder and stand line) [Table 8] Thus, it can be seen that the chilled roller method yields extruded products with a higher melt flow index, even under the same conditions. Furthermore, in the chilled roller method embodiment, the extruded product temperature is always low when it reaches the granulator, suppressing the evaporation of plasticizer.

[0096] The cooled, irregular extruded material may be guided to a commercially available polymer grinder or granulator. There, the polymer is ground, the particles pass through a sieve, and the maximum particle size is determined. However, due to the irregularity of the extruded product, the polymer particle size typically varies in the range of 2 to 4 millimeters.

[0097] Surprisingly, this specific size non-uniformity aids polymer melting during subsequent reprocessing. This makes the chilled roller method very suitable for use with granulators. Smaller particles melt faster, resulting in lower energy consumption. Compared to the strand-die-pellet process, the barrel zone temperature has been observed to be 10 degrees Celsius lower. Lower processing temperatures also result in a lower plasticizer loss rate. Plasticizers can typically gasify and generate gas during reprocessing by injection molding or extrusion molding. Since gas generation can cause scorching during molding, part defects during processing, and mold contamination, suppressing gas generation is a significant improvement.

[0098] Generally, vegetable waxes are used to impart moisture resistance to polymers. Typically, 0.3 to 1.0 percent of glycerol monostearate or stearic acid amide would be used as the vegetable wax. However, using vegetable wax during melting also has the drawback of causing "screw slip." Screw slip occurs when, during the melting process, the vegetable wax applied to the barrel acts as a lubricant, making the polymer melt slippery and preventing the extruder or injection molding machine from transporting the molten material.

[0099] In salt-free PVA, the maximum permissible wax content is typically 0.3 percent due to screw lubrication requirements. However, with a small amount of salt, a higher wax content of 2 to 3 percent is possible. The addition of these vegetable waxes has been shown to reduce the water absorption rate of PVOH formulations containing mono and dipropylene glycol by up to 50 percent compared to salt-free formulations.

[0100] Surprisingly, the irregularity of the particulate shape also benefits the formulation of polymer compositions containing amounts of vegetable wax that would typically be expected to result in screw slip, thus reducing screw slip.

[0101] The irregular size and shape of the granules before melting allow for a more gradual formation of the mixture in this invention, resulting in better adhesion during polymer transfer via the screw. This allows for the addition of a larger amount of wax component.

[0102] Accordingly, the compositions according to the present invention provide melt-workable PVA-containing polymers that typically have a flexural modulus similar to that of other extrudeable polymers. This makes it possible to use soluble and biodegradable polymers in the processing of a wide variety of articles without the processing problems experienced in the prior art, such as thermal degradation and crosslinking at high temperatures. The known advantageous properties of PVA, such as its high tensile strength and good barrier properties, are maintained in the melt-workable compositions, and they can be directly extruded using existing extrusion lines, blow molding machines, and injection molding machines.

Claims

1. A step of extruding a water-soluble polymer composition from an extruder barrel without using a slot die or strand die to produce an amorphous polymer extruder with non-uniform size and shape, The steps include: guiding the amorphous polymer extruded material onto a chilled conveyor and rapidly cooling the amorphous polymer extruded material to 60 degrees Celsius or below; The steps include granulating the amorphous polymer extruder to form granular material, The extruder barrel from which the water-soluble polymer composition is extruded is sealed in other parts to prevent the discharge of vapor. Methods for creating water-soluble polymers.

2. The granulation of the aforementioned amorphous polymer extruded material is carried out immediately after the preceding chilled conveyor and does not involve any further drying process. The method according to claim 1.

3. Furthermore, the step includes forming the granules into a water-soluble polymer product, The method according to claim 1.

4. The water-soluble polymer composition comprises a water-soluble polymer, a hygroscopic salt acting as a lubricant to make the polymer extrudeable and / or moldable in at least 15% by weight of the total weight of the composition, and a solvent polymer plasticizer. The solvent polymer plasticizer is monopropylene glycol or dipropylene glycol. The water content of the aforementioned water-soluble polymer composition is less than 10% by weight relative to the total weight of the composition. The method according to any one of claims 1 to 3.

5. The hygroscopic salt is provided in an amount greater than that of the solvent polymer plasticizer. The method according to claim 4.

6. The hygroscopic salt is an anhydrous or hydrated salt selected from the group consisting of sodium chloride, sodium citrate, magnesium chloride, calcium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium carbonate, and ammonium carbonate. The method according to claim 4 or claim 5.

7. The hygroscopic salt is a water-soluble salt that dissolves in water at 90 degrees Celsius in 10 minutes at a rate of 10% or more by weight. The method according to any one of claims 4 to 6.

8. The hygroscopic salt has a water content of less than 10% by weight relative to the total weight of the water-soluble polymer composition. The method according to any one of claims 4 to 7.

9. The hygroscopic salt is present in an amount of at least 25 weight percent of the total weight of the water-soluble polymer composition. The method according to claim 8.

10. The hygroscopic salt is in an anhydrous state. The method according to any one of claims 4 to 9.

11. The water-soluble polymer and the hygroscopic salt are provided in solid form. The method according to any one of claims 4 to 10.

12. The aforementioned polymer includes a polyvinyl alcohol polymer. The method according to any one of claims 1 to 11.

13. The chilled conveyor has a temperature of 10 degrees Celsius or higher and 30 degrees Celsius or lower. The method according to any one of claims 1 to 12.

14. The water-soluble polymer composition includes a wax for improving moisture resistance. The method according to any one of claims 1 to 13.

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