A cold-soluble polymer and its preparation method and application

Abstract

The present invention provides a cold-soluble polymer and its preparation method and application. The preparation method comprises: step S1, dispersing the saponified polymer in a good solvent to obtain a polymer dispersion, the polymer is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%; step S2, precipitating the polymer dispersion with a precipitant to obtain a first polymer wet solid, the first polymer wet solid includes liquid molecules entrained in the polymer, and the liquid molecules include a good solvent and a precipitant; step S3, extracting the liquid molecules in the first polymer wet solid with an extractant to obtain an extracted wet solid, the extractant is selected from a precipitant and the volatilization rate is higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a low alkane; step S4, drying the extracted wet solid to obtain a cold-soluble polymer. The above preparation method is efficient and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of cold-soluble polymers, and in particular to a cold-soluble polymer and a preparation method and application thereof. Background Art

[0002] Polyvinyl alcohol (hereinafter sometimes referred to as "PVA") is a crystalline polymer that is water-soluble, has excellent film-forming, laminating and printability. Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH") is currently the most powerful synthetic material with gas barrier capabilities. Together with PVA, it is used as a gas barrier material for gas containers such as hydrogen and oxygen. Commercial EVOH is usually non-water-soluble, and melt processing is generally used in applications. Since the crystallization temperature and decomposition temperature are close, there is a disadvantage of a narrow processing temperature range. EVOH is mainly prepared by melting the polymer at high temperature and preparing the finished product by extrusion molding, injection molding, compression molding or calendering molding.

[0003] Generally, in industry, polyvinyl acetate is obtained by homopolymerization of vinyl acetate, ethylene-vinyl acetate copolymer is prepared by copolymerization of ethylene and vinyl acetate, and polyvinyl acetate and ethylene-vinyl acetate copolymer are saponified to obtain PVA and EVOH. The hydrogen barrier properties of PVA and EVOH are affected by many factors such as molecular weight and saponification degree. The influence of these factors on the hydrogen barrier properties of PVA and EVOH films is the difference in crystallinity. For these two polymers, the higher the saponification degree, the higher the upper limit of crystallinity, the stronger the hydrogen barrier property, and the greater the difficulty of melt processing. In addition to the difficulty of melt processing, polymers with high crystallinity will also be more difficult to dissolve.

[0004] Since the drying temperature of PVA and EVOH with high saponification degree (>94 mol %) is usually over 40°C during the production process, the obtained dry PVA and EVOH products have high crystallinity. PVA and EVOH with high crystallinity need to be heated for a long time to dissolve completely, which limits their application in applications that require cold dissolution and quick dissolution. Some PVA powders with low saponification degree show the characteristics of cold dissolution and quick dissolution, but the physicochemical properties of this type of PVA with low saponification degree are significantly different from those of PVA with high saponification degree, and they cannot replace PVA with high saponification degree. The dispersion of PVA with high saponification degree can be prepared into a low-crystalline or non-crystalline solid product by freeze-drying, but this method is costly and inefficient. Summary of the invention

[0005] The main purpose of the present invention is to provide a cold-soluble polymer and a preparation method and application thereof, so as to solve the problems of high cost and low efficiency of the methods for preparing cold-soluble PVA and EVOH in the prior art.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a cold-soluble polymer is provided, the method comprising: step S1, dispersing a saponified polymer in a good solvent to obtain a polymer dispersion, wherein the polymer is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol %; step S2, precipitating the polymer dispersion with a precipitant to obtain a first polymer wet solid, wherein the first polymer wet solid includes liquid molecules entrained in the polymer, and the liquid molecules include a good solvent and a precipitant; step S3, extracting the liquid molecules in the first polymer wet solid with an extractant to obtain an extracted wet solid, wherein the extractant is selected from a precipitant and has a volatilization rate higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a low-alkanes; step S4, drying the extracted wet solid to obtain a cold-soluble polymer.

[0007] Furthermore, the good solvent is selected from any one or more of the first good solvents, a first mixed solvent composed of any one of the first good solvents and any one of the second good solvents, or a second mixed solvent of two of the second good solvents, the mass content of the second good solvent in the first mixed solvent is 25% to 75%, the first good solvent includes any one or more of polyols, lower fatty acids, phenolic solvents, lower fatty acids and other solvents, the second good solvent includes water and lower fatty monohydric alcohols, and the mass content of water or lower fatty monohydric alcohols in the second mixed solvent is 25% to 75%, wherein the polyol is selected from any one or more of ethylene glycol, propylene glycol, and glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol, and p-cresol; the lower fatty monohydric alcohol is selected from any one or more of methanol, ethanol, n-propanol, and isopropanol; the lower fatty acid is selected from any one or more of formic acid, acetic acid, and propionic acid; and the other solvents are selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0008] Further, the polarity of the above-mentioned precipitant is lower than the polarity of the good solvent. Preferably, the precipitant is selected from any one or more combinations of lower aliphatic alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, low polarity water-soluble solvents, and water. The lower aliphatic alcohols used for the precipitant include methanol, ethanol, isopropanol, and n-propanol. Preferably, the lipid solvents include ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate, and methyl propionate. The chlorinated hydrocarbons include dichloromethane and chloroform. The lower alkanes include C5 alkanes, C6 alkanes, and petroleum ether. The low polarity water-soluble solvent is selected from tetrahydrofuran, acetone, or butanone. Preferably, when the precipitant is a lower aliphatic alcohol, The mass ratio of the precipitant to the good solvent is 4 to 8:1; preferably, when the precipitant is a low-polarity water-soluble solvent, the mass ratio of the precipitant to the good solvent is 2 to 8:1; preferably, when the precipitant is a lipid solvent or a chlorinated hydrocarbon, the mass ratio of the precipitant to the good solvent is 2 to 8:1; preferably, when the precipitant is a lower alkane, the mass ratio of the precipitant to the good solvent is 2 to 8:1; preferably, when the precipitant is water, the mass ratio of the precipitant to the good solvent is 5 to 10:1; preferably, when the good solvent is a second mixed solvent, and the mass contents of water and lower fatty monohydric alcohol in the second mixed solvent are independently 25% to 75%, the precipitant is water.

[0009] Further, the above step S3 comprises: using a first extractant to perform a first extraction on the first polymer wet solid to obtain a first extracted wet solid, preferably the first extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction; using a second extractant to perform a second extraction on the first extracted wet solid to obtain a second extracted wet solid, preferably the second extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction; using a third extractant to perform a third extraction on the second extracted wet solid to obtain an extracted wet solid, preferably the third extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction; the first extractant is miscible with a good solvent, and the second extractant is miscible with a lower alkane, preferably the first extractant, the second extractant and the third extractant are miscible and the volatilization rate gradually increases, preferably the mass ratio of the first extractant to the polymer is 5 to 100:1, preferably the mass ratio of the first extractant to the second extractant is 5 to 1:1, and the mass ratio of the second extractant to the third extractant is 5 to 1:1, and the third extractant is preferably selected from any one or more of the lower alkanes.

[0010] Furthermore, the good solvent is a phenolic solvent, the precipitant does not contain water and methanol, and step S3 uses C5alkane, C6alkane and petroleum ether as extractants to perform extractions for 2 to 4 times.

[0011] Furthermore, the above-mentioned polymer is polyvinyl alcohol, and the mass content of water in the good solvent is less than 5%, the precipitant is a mixed precipitant composed of lower fatty alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, and low-polarity water-soluble solvents, and the mass content of lower alkanes is less than 80%. In step S3, the first extractant does not contain water, and the second extractant does not contain water and methanol.

[0012] Furthermore, the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is not less than 5%; the precipitant is a mixed precipitant composed of lower aliphatic alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, and low-polarity water-soluble solvents, in which the mass content of lower aliphatic alcohols and lipid solvents is not less than 20%, and the mass content of lower alkanes is less than 80%; in step S3, the first extractant does not contain water, and the second extractant does not contain water and methanol.

[0013] Furthermore, the above-mentioned polymer is an ethylene-vinyl alcohol copolymer, and the good solvent contains polyols, lower fatty acids, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide, the first extractant is water, lower fatty alcohols, low polarity water-soluble solvents, chlorinated hydrocarbons or lipid solvents; the second extractant does not contain water and methanol, and the content of ethanol, n-propanol, isopropanol or low polarity water-soluble solvents in the second extractant is not less than 30%.

[0014] Furthermore, the polymer is an ethylene-vinyl alcohol copolymer, and the good solvent is a mixed solvent of water and low-order fatty monohydric alcohol, and the mass content of ethanol, isopropanol, n-propanol or low-polarity water-soluble solvent in the first extractant is not less than 30%.

[0015] Furthermore, in the above step S1, the dispersion temperature is 60°C to 220°C, and the dissolution time is 1 to 72 hours.

[0016] Furthermore, in the above step S4, the drying is carried out under normal pressure or vacuum, the temperature is 0 to 30° C., and the drying time is 0.5 h to 200 h.

[0017] Furthermore, the above-mentioned ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol binary copolymer or an ethylene-vinyl alcohol-vinyl acetate terpolymer; based on mass, the alkaline impurity content in the polymer is preferably less than 0.1%, preferably less than 0.08%, more preferably less than 0.04%, and particularly preferably less than 0.02%.

[0018] According to another aspect of the present invention, a cold-soluble polymer is provided, which is prepared according to any one of the above-mentioned preparation methods; preferably, the cold-soluble polymer is a cold-soluble polyvinyl alcohol or a cold-soluble ethylene-vinyl alcohol copolymer, and preferably, the cold-soluble ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol binary copolymer or an ethylene-vinyl alcohol-vinyl acetate ternary copolymer.

[0019] Furthermore, the saponification degree of the cold-soluble polyvinyl alcohol and the cold-soluble EVOH is 94 to 100 mol %, and preferably the saponification degree of the cold-soluble polyvinyl alcohol and the cold-soluble EVOH is 94.5 to 99.99 mol %.

[0020] Furthermore, the melt index of the above-mentioned cold-soluble polyvinyl alcohol is 2.2 to 15.2 g / 10 min, preferably the melt index of the cold-soluble polyvinyl alcohol is 2.7 to 14.7 g / 10 min, and more preferably the melt index of the cold-soluble polyvinyl alcohol is 2.9 to 13.9 g / 10 min; the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.2 to 15.2 g / 10 min, preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.7 to 14.7 g / 10 min, and more preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.9 to 13.9 g / 10 min.

[0021] Furthermore, the molar content of vinyl alcohol in the above cold-soluble ethylene-vinyl alcohol copolymer is 28% to 94%, preferably 36% to 92%, and more preferably 42% to 84%.

[0022] Furthermore, the molar content of ethylene in the cold-soluble ethylene-vinyl alcohol copolymer is 6% to 72%, preferably 8% to 64%, and more preferably 16% to 58%.

[0023] Furthermore, the molar content of vinyl acetate in the cold-soluble ethylene-vinyl alcohol copolymer is 0% to 6%, preferably 0.01% to 6%, and more preferably 0.01% to 5.5%.

[0024] Furthermore, the yellowness index of the cold-soluble polymer is 40 or less, preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less.

[0025] According to another aspect of the present invention, there is provided an application of a cold-soluble polymer, which is any one of the cold-soluble polymers mentioned above, and the application includes applying the cold-soluble polymer to putty powder, concrete, special mortar, gap filler, cold-soluble adhesive, interface fusion agent or stripping agent.

[0026] By applying the technical scheme of the present invention, the present application prepares a cold-soluble polymer by a solvent replacement method, which has a simple process and low cost; at the same time, the cold-soluble polymer can be purified during the solvent replacement process, effectively reducing the content of transition metal impurities and alkaline impurities in the polymer, improving its hue, and improving its optical properties, which is beneficial for application in optical devices such as polarizers or food, biological packaging materials and other fields. Compared with the cold-soluble polymer in the prior art, the cold-soluble polymer prepared by the preparation method of the present application has a lower crystallinity than the raw material with high crystallinity before treatment, and the polymer dispersion obtained by dissolving the cold-soluble polymer in the solvent has better fluidity and is not easy to form a gel, and the upper limit of the solid content of the polymer is higher, so that the polymer dispersion is easier to process and the processing window is wider; the prepared cold-soluble polymer not only has the characteristics of cold dissolution and quick dissolution, but also maintains a high degree of saponification, even if the low-crystallinity polymer is formed after heat treatment, the crystallinity is improved, the solvent resistance is stronger, the mechanical properties are better, and the barrier property is higher.

[0027] In the above preparation method, a good solvent having good solubility for the polymer is used to dissolve the polymer to form a polymer dispersion; then a precipitant is used to precipitate the polymer dispersion to obtain a first polymer solid, wherein the difference in the dispersion performance of the polymer in different solvents is utilized, and the precipitant is used to change the stable system formed by the polymer dispersion, so that the polymer is precipitated to form a solid, and part of the good solvent and / or the precipitant is simultaneously wrapped and precipitated during the precipitation process; then the first polymer wet solid is extracted with an extractant, and the liquid molecules in the first polymer wet solid are replaced by the extractant by the diffusion and concentration difference of the liquid molecules, such as the good solvent and the precipitant added previously; finally, the extracted wet solid is dried, and the type of the extractant is controlled to be the same as the precipitant, and the volatilization rate is controlled to be higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a lower alkane, so that according to the mutual solubility characteristics of different precipitants, the liquid molecules in the wet solid are replaced by a lower alkane with a low boiling point, fast volatilization and poor adsorption to the polymer. Therefore, the temperature required for drying is lower than the dissolution temperature in step S1, and the low-temperature drying process is lower than the glass transition temperature of the polymer. When the polymer is in a glassy state, the molecular chain is difficult to move and difficult to form crystals, thereby obtaining a cold-soluble polymer. The dissolution process will destroy the crystallization of the polymer, and in the final drying process, due to the low temperature, the polymer will basically not crystallize, maintaining a low degree of crystallinity, that is, maintaining the characteristics of the cold-soluble polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 The DSC curve of cold-melt F171B of Example 4 of the present invention is shown;

[0030] Figure 2 The DSC curve of the hot-melt type F171B of Comparative Example 4 of the present invention is shown. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] As analyzed in the background technology of this application, PVA and EVOH with high saponification degree in the prior art are difficult to be cold-soluble. In order to solve this problem, this application provides a cold-soluble polymer and a preparation method and application thereof.

[0033] In a typical embodiment of the present application, a method for preparing a cold-soluble polymer is provided, and the preparation method comprises: step S1, dissolving a saponified polymer in a good solvent to obtain a polymer dispersion, wherein the polymer is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94 to 100 mol %; step S2, precipitating the polymer dispersion with a precipitant to obtain a first polymer wet solid; step S3, extracting liquid molecules in the first polymer wet solid with an extractant to obtain an extracted wet solid, wherein the extractant comprises a first component and a second component; step S4, drying the extracted wet solid to obtain a cold-soluble polymer.

[0034] The present application prepares a cold-soluble polymer by a solvent replacement method, which has a simple process and low cost; at the same time, the cold-soluble polymer can be purified during the solvent replacement process, effectively reducing the content of transition metal impurities and alkaline impurities in the polymer, improving its hue, and improving its optical properties, which is beneficial for application in optical devices such as polarizers or food, biological packaging materials and other fields. Compared with the cold-soluble polymer in the prior art, the cold-soluble polymer prepared by the preparation method of the present application has a lower crystallinity than the raw material with high crystallinity before treatment, and the polymer dispersion obtained by dissolving the cold-soluble polymer in the solvent has better fluidity and is not easy to form a gel, and the upper limit of the solid content of the polymer is higher, so that the polymer dispersion is easier to process and the processing window is wider; the prepared cold-soluble polymer not only has the characteristics of cold dissolution and quick dissolution, but also maintains a high degree of saponification, even if the low-crystallinity polymer is formed after heat treatment, the crystallinity is improved, the solvent resistance is stronger, the mechanical properties are better, and the barrier property is higher.

[0035] In the above preparation method, a good solvent having good solubility for the polymer is used to dissolve the polymer to form a polymer dispersion; then a precipitant is used to precipitate the polymer dispersion to obtain a first polymer solid, wherein the difference in the dispersion performance of the polymer in different solvents is utilized, and the precipitant is used to change the stable system formed by the polymer dispersion, so that the polymer is precipitated to form a solid, and part of the good solvent and / or the precipitant is simultaneously wrapped and precipitated during the precipitation process; then the first polymer wet solid is extracted with an extractant, and the liquid molecules in the first polymer wet solid are replaced by the extractant by the diffusion and concentration difference of the liquid molecules, such as the good solvent and the precipitant added previously; finally, the extracted wet solid is dried, and the type of the extractant is controlled to be the same as the precipitant, and the volatilization rate is controlled to be higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a lower alkane, so that according to the mutual solubility characteristics of different precipitants, the liquid molecules in the wet solid are replaced by a lower alkane with a low boiling point, fast volatilization and poor adsorption to the polymer. Therefore, the temperature required for drying is lower than the dissolution temperature in step S1, and the low-temperature drying process is lower than the glass transition temperature of the polymer. When the polymer is in a glassy state, the molecular chain is difficult to move and difficult to form crystals, thereby obtaining a cold-soluble polymer. The dissolution process will destroy the crystallization of the polymer, and in the final drying process, due to the low temperature, the polymer will basically not crystallize, maintaining a low degree of crystallinity, that is, maintaining the characteristics of the cold-soluble polymer.

[0036] The selection of the good solvent of the present application can refer to the commonly used solvents for polymer dissolution in the prior art, combined with the properties of polyvinyl alcohol and ethylene-vinyl alcohol copolymer. In some embodiments, the good solvent is selected from any one or more of the first good solvents, a first mixed solvent composed of any one of the first good solvents and any one of the second good solvents, or a second mixed solvent of two of the second good solvents. The mass content of the second good solvent in the first mixed solvent is 25% to 75%. The first good solvent includes any one or more of polyols, lower fatty acids, phenolic solvents, lower fatty acids and other solvents. The second good solvent includes Water and low-fat monohydric alcohol, the mass content of water or low-fat monohydric alcohol in the second mixed solvent is 25% to 75%, wherein the polyhydric alcohol is selected from any one or more of ethylene glycol, propylene glycol, and glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol, and p-cresol; the low-fat monohydric alcohol is selected from any one or more of methanol, ethanol, n-propanol, and isopropanol; the low-fat fatty acid is selected from any one or more of formic acid, acetic acid, and propionic acid; the other solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. The low-fat monohydric alcohol single solvent cannot dissolve polyvinyl alcohol and ethylene-vinyl alcohol copolymer, but the mixed solvent formed by mixing the low-fat monohydric alcohol with the solvent other than the low-fat monohydric alcohol in the good solvent can accelerate the dissolution of the polymer. Preferably, the polymer is polyvinyl alcohol, which is dissolved in a good solvent containing low-fat monohydric alcohol, and the mass content of the low-fat monohydric alcohol in the good solvent is less than 75%; preferably, the polymer is ethylene-vinyl alcohol copolymer, which is dissolved in a good solvent containing water or low-fat monohydric alcohol, and the low-fat monohydric alcohol is selected from n-propanol and isopropanol, and the mass content of the low-fat monohydric alcohol or water in the good solvent is 25% to 75%.

[0037] Good solvents other than water and lower fatty alcohols, whether single solvents or mixed solvents, can dissolve polyvinyl alcohol and ethylene-vinyl alcohol copolymers at a certain temperature. According to the solubility properties of the polymer in different solvents, the mass ratio of the solvent to the polymer is controlled to be 5 to 50:1 to achieve full dissolution of the polymer. For example, a good solvent composed of 25% water and 75% isopropanol / n-propanol can dissolve EVOH, and a good solvent composed of 75% water and 25% isopropanol / n-propanol can also dissolve EVOH. 25% water and 75% DMSO can also dissolve EVOH. Solvent systems that can dissolve EVOH can usually dissolve PVA.

[0038] In order to dissolve the polymer in the good solvent as quickly as possible, in some embodiments, in the above step S1, the dissolution temperature is controlled to be 60° C. to 220° C., and the dissolution time is 1 to 72 hours.

[0039] On the basis of determining the good solvent, the precipitant is selected based on the regulation of polarity and solubility parameters. Polyvinyl alcohol polymer is soluble in water, which has the highest polarity among common solvents, so low-polarity solvents are suitable precipitants. Mixing low-order fatty monohydric alcohols with solvents such as water adjusts the polarity and solubility parameters of the solvent within a suitable content, which helps dissolve the polymer, but excessive low-order fatty monohydric alcohols will cause the solvent polarity to be too low, thereby causing the polymer to precipitate. In some embodiments, the precipitant of the above-mentioned polymer dispersion is selected from any one or more combinations of low-order fatty alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, low-polarity water-soluble solvents, and water. The mutual solubility of the precipitant and the good solvent can change the polarity and solubility parameters of the solvent, thereby causing the polymer to precipitate.

[0040] According to the mutual solubility of the precipitant and the good solvent, there are five kinds of precipitants. The first precipitant is a lower aliphatic alcohol, which is miscible with any good solvent. The first precipitant is selected from methanol, ethanol, isopropanol, and n-propanol, and the mass ratio of the first precipitant to the good solvent is 4 to 8. As the content of the lower aliphatic alcohol increases, the polarity of the solvent system decreases continuously, the solubility parameter changes, and the polyvinyl alcohol polymer and the ethylene-vinyl alcohol copolymer begin to precipitate.

[0041] The second precipitant is a low polarity water-soluble solvent, which is miscible with any good solvent. The low polarity water-soluble solvent is selected from tetrahydrofuran, acetone or butanone, and the mass ratio of the precipitant to the good solvent is 2 to 8. The second precipitant has a low polarity, a large difference in solubility parameter with the polymer, and is miscible with all the above-mentioned good solvents. With the addition of the second precipitant, the polarity of the solvent system decreases, the solubility parameter changes, and the polyvinyl alcohol polymer and the ethylene-vinyl alcohol copolymer are precipitated.

[0042] The third precipitant is a precipitant that is immiscible with water, including chlorinated hydrocarbons and lipid solvents. Considering the drying efficiency and cost of precipitation, the preferred chlorinated hydrocarbon precipitants are dichloromethane and chloroform, and the preferred lipid precipitants are ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate, and methyl propionate. Other chlorinated hydrocarbons and lipid solvents with carbon 1 to carbon 5 can also be used as precipitants, but the higher boiling point will lead to slow volatilization rate, long volatilization time, and low drying efficiency. The third precipitant is immiscible with water and can precipitate a polymer dispersion dissolved in a good solvent other than water. The mass ratio of the third precipitant to the good solvent is 2 to 8. With the addition of the third precipitant, the polarity of the solvent decreases, the solubility parameter changes, and the polymer precipitates.

[0043] The fourth precipitant is a lower alkane precipitant with the lowest polarity, and the lower alkane is selected from C5 alkanes, C6 alkanes and petroleum ether. Alkanes with longer carbon chains can also be used as precipitants, but higher boiling points will lead to slow volatilization rate, long volatilization time and low drying efficiency. Since the fourth precipitant has very low polarity, it is miscible with phenolic solvents, ethanol, isopropanol, n-propanol, the second precipitant and the third precipitant, but is not miscible with good solvents and precipitants. Therefore, the fourth precipitant is used alone as a precipitant, and the good solvent is a phenolic solvent.

[0044] The fifth precipitant is water, which has the highest polarity among commonly used solvents, and can be used for the precipitation of ethylene-vinyl alcohol copolymers in the embodiments of the present invention. Compared with polyvinyl alcohol, the ethylene segment in the ethylene-vinyl alcohol copolymer is a hydrophobic segment and a non-water-soluble polymer. A mixed solvent of water and isopropanol or n-propanol can dissolve ethylene-vinyl alcohol copolymers, but the contents of water and alcohol are both limited to 25% to 75%. If the water content is too much and the solvent polarity is too high, the ethylene-vinyl alcohol copolymer will precipitate, so water can be used as a precipitant for ethylene-vinyl alcohol copolymers. The mass ratio of water to good solvent is 5 to 10, and the system temperature does not exceed 40°C, and the ethylene-vinyl alcohol copolymer will precipitate. If the system temperature is too high, the vinyl alcohol segment and the ethylene segment form a core-shell structure, which is easy to form an emulsion, resulting in the inability of the polymer to precipitate.

[0045] The mixed system of different precipitants also has a good precipitation effect. For the mixed precipitant composed of the first precipitant, the second precipitant, the third precipitant and the fourth precipitant, when the mass content of the first precipitant and the second precipitant in the mixed precipitant exceeds 25%, the mixed precipitant has no restrictions on the composition of the good solvent; when the content of the fourth precipitant in the mixed precipitant is 30% to 80%, the mass of water in the good solvent is less than 1 / 2 of the mass of the first precipitant and the second precipitant, and other good solvents are not restricted. Alternatively, the good solvent and the precipitant are mutually soluble, and there is only one phase of the liquid phase after mixing, and the mass of the second precipitant, the third precipitant and the fourth precipitant in the dispersion is more than twice the mass of other liquid molecules, the polymer precipitates.

[0046] In some embodiments of the present application, in order to replace the liquid molecules in the first polymer wet solid as much as possible, the preferred step S3 includes: using the first extractant to extract the first polymer wet solid for the first time to obtain the first extracted wet solid, preferably the first extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction; using the second extractant to extract the first extracted wet solid for the second time to obtain the second extracted wet solid, preferably the second extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction, and using the third extractant to extract the second extracted wet solid for the third time to obtain the extracted wet solid, preferably the third extraction is a multi-stage extraction, and more preferably 1 to 4 stages of extraction. The above-mentioned first extractant is mutually soluble in the good solvent, and the second extractant is mutually soluble in the lower alkane. In some embodiments, the first extractant, the second extractant and the second extractant are mutually soluble and the volatilization rate gradually increases. Of course, it is also possible to directly use the lower alkane for direct extraction. By using three rounds of extraction steps, the liquid molecules in the first polymer wet solid can be removed as much as possible, and the content of liquids other than the lower alkane can be gradually reduced, the temperature of subsequent drying can be further reduced, and the volatilization rate can be increased.

[0047] Preferably, the mass ratio of the first extractant to the second extractant is 5 to 1:1, and the mass ratio of the second extractant to the third extractant is 5 to 1:1 or more. As the number of extractions increases, the liquid molecules contained in the wet solid continue to decrease, the swelling of the wet solid decreases, the volume decreases, and the amount of the extractant can also be continuously reduced.

[0048] The amount of the extractant used can be referenced by the amount of the polymer used. Different amounts of polymer will produce different liquid molecules in the first polymer wet solid. After experimental verification, the preferred mass ratio of the extractant to the polymer is 5:1 to 100:1, so as to achieve the most thorough removal of the liquid molecules.

[0049] The purpose of extraction is to replace the solvent with high boiling point, strong adsorption and low volatility with low boiling point, weak adsorption and easy volatility of lower alkanes. Therefore, the first extractant is miscible with the good solvent, and the second extractant is miscible with the lower alkanes. The extractant is selected from the precipitant. Except for water and methanol, the extractants are miscible with the lower alkanes and have suitable boiling points and volatility rates. Based on this, it is preferred that the third extractant is selected from any one of the lower alkanes.

[0050] In some embodiments, when the good solvent is a phenolic solvent and the precipitant does not contain water and methanol, in order to simplify the process and reduce costs, five carbon alkanes, six carbon alkanes and petroleum ether are used as extractants for 2 to 4 extractions, and then low-temperature drying is performed to obtain a cold-soluble polymer. The same effect can be achieved by first extracting with a precipitant other than water and methanol and then extracting with a lower alkane, but it will cause unnecessary losses.

[0051] In some embodiments, when the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is less than 5%, the first extractant does not contain water (the meaning of not containing water is any extractant other than water), and the mass content of the fourth precipitant is less than 80%, the second extractant does not contain water and methanol (the meaning of not containing water and methanol is any extractant other than water and methanol), and the mass content of the fourth precipitant is less than 80%.

[0052] In some embodiments, when the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is not less than 5%, the first extractant does not contain water, and the mass content of the first precipitant and the second precipitant is not less than 20%, the second extractant does not contain water and methanol, and the mass content of the fourth precipitant is less than 80%.

[0053] In some embodiments, when the polymer is ethylene-vinyl alcohol copolymer, and the good solvent includes a high boiling point, strong hygroscopic solvent such as polyol, low fatty acid, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide, in order to reduce costs, water is used as the first extractant to remove the high boiling point organic solvent; the second extractant does not contain water and methanol, and the content of ethanol, n-propanol, isopropanol or the second precipitant is not less than 30%. The first extractant using the first precipitant, the second precipitant and the third precipitant can also effectively remove the high boiling point organic solvent, but the cost is higher.

[0054] In some embodiments, when the polymer is an ethylene-vinyl alcohol copolymer and the good solvent is a mixed solvent of water and a lower fatty alcohol, in order to simplify the process and reduce costs, the mass content of ethanol, isopropanol, n-propanol or the second precipitant in the first extractant is not less than 30%, and the second extractant may not be used, and the third extractant may be used directly for subsequent extraction operations, and low-temperature drying may be performed to obtain a cold-soluble polymer.

[0055] In order to accelerate the formation efficiency of the cold-soluble polymer, in some embodiments, in the above step S4, the drying is carried out by normal pressure drying or vacuum drying, the drying temperature is controlled to be 0 to 30° C., and the drying time is 0.5 h to 200 h, so as to remove the solvent in the polymer as completely as possible.

[0056] In another typical embodiment of the present application, a cold-soluble polymer is provided, and the cold-soluble polymer is prepared according to the above-mentioned preparation method. The cold-soluble polymer in the present application not only has the characteristics of cold dissolution and quick dissolution, but also maintains a high degree of saponification, high crystallinity after heat treatment and molding, stronger solvent resistance, better mechanical properties, and higher barrier properties. The above-mentioned cold-soluble polymer can be a cold-soluble polyvinyl alcohol or a cold-soluble ethylene-vinyl alcohol copolymer, and preferably the cold-soluble ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol binary copolymer or an ethylene-vinyl alcohol-vinyl acetate terpolymer.

[0057] Referring to the prior art, the higher the saponification degree of the polymer, the stronger the hydrogen barrier property, and the greater the difficulty of melt processing. The cold-soluble polymer of the present application reduces the difficulty of melt processing while maintaining a high saponification degree. In some embodiments, the saponification degree of cold-soluble polyvinyl alcohol and cold-soluble EVOH is 94 to 100 mol%, preferably 94.5 to 99.99 mol% for cold-soluble polyvinyl alcohol and cold-soluble EVOH. When the saponification degree is less than 94 mol%, the crystallinity of polyvinyl alcohol and EVOH is significantly reduced, and the mechanical strength, barrier properties and other physical properties of the molded body are reduced. The saponification degree is preferably 94 mol% or more, more preferably 94.5 mol% or more; when the saponification degree exceeds 99.99 mol%, there is a tendency that the manufacture of polyvinyl alcohol becomes difficult and the moldability also deteriorates. The melt index of the cold-soluble polyvinyl alcohol is preferably 2.2 to 15.2 g / 10 min, preferably 2.7 to 14.7 g / 10 min, and more preferably 2.9 to 13.9 g / 10 min.

[0058] When the cold-soluble polymer is a cold-soluble ethylene-vinyl alcohol copolymer, the melt index is preferably 2.2 to 15.2 g / 10 min, more preferably 2.7 to 14.7 g / 10 min, and even more preferably 2.9 to 13.9 g / 10 min.

[0059] In some embodiments, the molar content of vinyl alcohol in the cold-soluble ethylene-vinyl alcohol copolymer is 28% to 94%, preferably 36% to 92%, more preferably 42% to 84%; and / or the molar content of ethylene in the cold-soluble ethylene-vinyl alcohol copolymer is 6% to 72%, preferably 8% to 64%, more preferably 16% to 58%; and / or the molar content of vinyl acetate in the cold-soluble ethylene-vinyl alcohol copolymer is 0% to 6%, preferably 0.01% to 6%, more preferably 0.01% to 5.5%. To meet the current needs of industrial applications.

[0060] After multiple extractions, the transition metal impurity content and alkaline impurity content in the polymer are reduced, the hue of the polymer is improved, and the yellowness index of the cold-soluble polymer is 40 or less, preferably the yellowness index of the cold-soluble polymer is 30 or less, more preferably the yellowness index of the cold-soluble polymer is 20 or less, and further preferably the yellowness index of the cold-soluble polymer is 10 or less. In terms of mass, the alkaline impurity content in the polymer is preferably 0.1% or less, preferably 0.08% or less, more preferably 0.04% or less, and particularly preferably 0.02% or less.

[0061] In another typical embodiment of the present application, an application of a cold-soluble polymer is provided, and the cold-soluble polymer is the above-mentioned cold-soluble polymer, and the application includes applying the cold-soluble polymer to putty powder, concrete, special mortar, gap filler, cold-soluble adhesive, interface fusion agent or stripping agent. The above-mentioned cold-soluble polymer can be dissolved below 30°C and can be used in scenarios that are sensitive to dispersion temperature. The cold-soluble PVA prepared in this application can be applied to emulsifiers, suspending agents, surfactants, fiber processing agents, various adhesives, paper processing agents, adhesives, and films like untreated commercial PVA, and is easier to process.

[0062] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0063] PVA and EVOH solid yellowness index test: HunterLab's UltraScan VIS spectrophotometer is used to characterize the yellowness index. The yellowness index is used to evaluate the solid hue of the polymer.

[0064] Optical properties: The optical properties of polymer films were measured using Shanghai Instrument and Electronics Optical Transmittance and Haze Tester WGT-S, and the test was conducted in accordance with GB / T2410-2008 standard. The higher the transmittance and the lower the haze, the better the optical properties.

[0065] Determination of transition metal elements: The content of transition metal elements iron, cobalt and nickel in the polymer was tested using Thermo Fisher's inductively coupled plasma mass spectrometer (ICP-MS).

[0066] DSC: A differential scanning calorimeter (DSC3) from Mettler-Toledo was used to characterize the thermal properties of the polymer. The specific test method is shown in the test curve diagram.

[0067] In the examples, all PVAs were purchased from Sinopharm Reagents; all EVOHs were purchased from Kuraray Co., Ltd.; and other drugs were of analytical grade.

[0068] In order to prevent contamination by metal ion impurities, the high-temperature and high-pressure dissolution process is carried out in a corrosion-resistant high-pressure reactor independently designed by State Power Investment Corporation Hydrogen Energy Technology Development Co., Ltd.

[0069] Example 1: Preparation of cold-soluble PVA1795

[0070] 5 parts by mass of PVA1795 (polymerization degree 1700, saponification degree 95 mol%) were dissolved in 30 parts by mass of dimethyl sulfoxide dispersion at 180°C with stirring for 1 hour to form a PVA dispersion. 100 parts by mass of methanol were added to the PVA dispersion to precipitate a wet polymer solid.

[0071] The wet solid was extracted using 500 parts by mass of ethanol as the first extractant, stirred for 1 hour, and filtered to separate the solid.

[0072] The wet solid was extracted with a mixture of 40 parts by mass of isopropanol and 60 parts by mass of industrial hexane as a second extractant, stirred for 1 hour, and filtered to separate the solid.

[0073] The wet solid was extracted with 20 parts by mass of cyclopentane as the third extractant, stirred for 1 hour, and filtered to separate the solid. The process was repeated 4 times. The wet solid was vacuum dried at 30° C. for 72 hours to obtain a dry cold-soluble PVA1795 solid.

[0074] 1 part by mass of cold-soluble PVA1795 was added to 9 parts by mass of water for dissolution at a dissolution temperature of 30° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 2 minutes.

[0075] 1 part by mass of cold-soluble PVA1795 was added to 2 parts by mass of dimethyl sulfoxide for dissolution at a dissolution temperature of 25° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 5 minutes.

[0076] Example 2: Preparation of cold-soluble PVA1799

[0077] 5 parts by mass of PVA1799 (polymerization degree 1700, saponification degree higher than 99 mol%) were dissolved in 30 parts by mass of N,N-dimethylacetamide dispersion at 90° C. with stirring for 24 h, and a mixed solvent of 100 parts by mass of industrial hexane and 50 parts by mass of ethanol was added for precipitation.

[0078] The wet solid was extracted using 100 parts by mass of ethyl acetate as a first extractant, stirred for 1 hour, and filtered to separate and obtain a solid.

[0079] The wet solid was extracted with a mixture of 20 parts by mass of tetrahydrofuran and 30 parts by mass of industrial hexane as a second extractant, stirred for 1 hour, and filtered to separate the solid. This was repeated twice.

[0080] The wet solid was extracted with 50 parts by mass of industrial hexane, stirred for 1 hour, filtered and separated to obtain a solid, and the process was repeated once. The obtained wet solid was vacuum dried at 30° C. for 12 hours to obtain a dry cold-soluble PVA1799 solid.

[0081] 1 part by mass of cold-soluble PVA1799 was added to 9 parts by mass of water for dissolution, the dissolution temperature was 30°C, the stirring speed was 300 r / min, and the polymer solid was completely dissolved within 5 minutes. The cold-soluble PVA1799 dispersion was cast at 90°C to obtain a film X-1 with a thickness of 100±3μm. The yellowness index of the film X-1 was 2.74, the transmittance was 99.54%, the haze was 0.31%, and the contents of iron, cobalt, and nickel were 1.2ppm, 0ppm, and 2.1ppm, respectively.

[0082] 1 part by mass of cold-soluble PVA1799 was added to 4 parts by mass of dimethyl sulfoxide for dissolution at a dissolution temperature of 25° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 6 minutes.

[0083] Example 3: Preparation of cold-soluble PVA2699

[0084] 5 parts by mass of PVA2699 (polymerization degree 1700, saponification degree higher than 99 mol%) were dissolved in 150 parts by mass of water and 100 parts by mass of isopropanol aqueous dispersion at 220° C. under 20 MPa pressure and stirring for 2 h, and 1500 parts by mass of acetone were added for precipitation.

[0085] The wet solid was extracted with 24 parts by mass of industrial hexane and 1 part by mass of dichloromethane as the first extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration. This was repeated 4 times.

[0086] The wet solid was extracted using 24.9 parts by mass of industrial hexane and 0.1 parts by mass of dichloromethane as a second extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration, and the process was repeated 4 times.

[0087] The wet solid was extracted with 25 parts by mass of n-pentane as the third extractant, stirred for 1 hour, filtered and separated to obtain a solid, and repeated 4 times. The obtained wet solid was vacuum dried at 30° C. for 0.5 hour to obtain a dry cold-soluble PVA2699 solid.

[0088] 1 part by mass of cold-soluble PVA2699 was added to 9 parts by mass of water for dissolution. The dissolution temperature was 30° C. and the stirring speed was 300 r / min. The polymer solid was completely dissolved within 8 minutes.

[0089] 1 part by mass of cold-soluble PVA2699 was added to 4 parts by mass of dimethyl sulfoxide for dissolution at a dissolution temperature of 25° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 9 minutes.

[0090] Example 4: Preparation of cold-soluble fully saponified PVA

[0091] After the saponification or alcoholysis reaction of polyvinyl acetate in methanol under the catalysis of sodium hydroxide, a hot-soluble fully saponified PVA is obtained, and the saponification degree of the fully saponified PVA is not less than 99.99 mol%, and is named PVA-H. 1 part by mass of PVA-H solid is dissolved in 19 parts by mass of dimethyl sulfoxide dispersion at 80° C. with stirring for 72 hours, and precipitated in 100 parts by mass of dichloromethane to obtain a wet solid.

[0092] The wet solid was extracted using 10 parts by mass of dichloromethane as the first extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration.

[0093] The wet solid was extracted using 4.9 parts by mass of n-hexane and 0.1 parts by mass of methanol as a second extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration.

[0094] The wet solid was extracted using 5 parts by mass of isopentane as the third extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration.

[0095] After vacuum drying at 20°C for 72 h, a cold-soluble PVA-H solid was obtained, which was named PVA-HL.

[0096] 1 part by mass of PVA-HL solid was added to 9 parts by mass of water for dissolution. The dissolution temperature was 30° C. and the stirring speed was 300 r / min. The polymer solid was completely dissolved within 30 minutes.

[0097] 1 part by mass of PVA-HL solid was added to 4 parts by mass of dimethyl sulfoxide for dissolution at a dissolution temperature of 25° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 20 minutes.

[0098] Example 5: Preparation of cold-melt E105B, F171B, and L171B

[0099] E105B, F171B and L171B are all EVOH produced by Kuraray, with a saponification degree of not less than 99.9% and an ethylene content of 44 mol%, 32 mol% and 27 mol%, respectively.

[0100] 1 part by mass of F171B was dissolved in 9 parts by mass of N,N-dimethylacetamide dispersion at 150° C. with stirring for 4 hours, and 60 parts by mass of ethanol was added for precipitation to obtain a wet polymer solid.

[0101] The wet solid was extracted using 95 parts by mass of n-hexane and 5 parts by mass of ethanol as a first extractant, stirred for 1 hour, and filtered to separate the solid.

[0102] The wet solid was extracted with 19 parts by mass of n-hexane and 1 part by mass of acetone as a second extractant and stirred for 1 hour, and the solid was separated by filtration.

[0103] The wet solid was extracted using 6 parts by mass of isopentane as the third extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration, and the process was repeated 3 times.

[0104] The mixture was dried under vacuum at 10°C for 144 h to obtain a cold-soluble F171B solid.

[0105] The preparation method of cold-soluble types E105B and L171B is the same as that of F171B.

[0106] 1 part by mass of cold-soluble EVOH solid was added to 4 parts by mass of N,N-dimethylacetamide for dissolution. The dissolution temperature was 25°C and the stirring speed was 300 r / min. Cold-soluble E105B, cold-soluble F171B and cold-soluble L171B were all completely dissolved within 60 seconds.

[0107] 1 part by mass of cold-soluble F171B solid was added to 9 parts by mass of N,N-dimethylacetamide to dissolve, and the obtained dispersion was cast to obtain a film Y-1 with a thickness of 100±3μm. The yellowness index of the film Y-1 was 0.89, the transmittance was 99.32%, the haze was 0.42%, and the contents of iron, cobalt and nickel were 0.2ppm, 1.6ppm and 1.1ppm respectively.

[0108] Example 5: Preparation of cold-soluble fully saponified EVOH

[0109] A hot-soluble fully saponified ethylene-vinyl alcohol copolymer (ethylene content 38 mol %, saponification degree not less than 99.99 mol %) is obtained by saponification or alcoholysis reaction in a methanol dispersion of ethylene-vinyl acetate copolymer under the catalysis of sodium hydroxide, and is named EVOH-H.

[0110] 1 part by mass of EVOH-H solid was dissolved in 7 parts by mass of n-propanol and 3 parts by mass of aqueous dispersion at 70° C., and precipitated in 60 parts by mass of ethanol to obtain a wet solid.

[0111] The wet solid was extracted using 10 parts by mass of dichloromethane and 30 parts by mass of n-hexane as the first extractant, and the mixture was stirred for 1 hour, and the solid was separated by filtration, and the process was repeated twice.

[0112] The wet solid was extracted using 2 parts by mass of dichloromethane and 8 parts by mass of n-hexane as a second extractant, stirred for 1 hour, and filtered to separate the solid.

[0113] The wet solid was extracted with 10 parts by mass of industrial hexane as the third extractant, stirred for 1 hour, filtered and separated to obtain a solid, and repeated 3 times. The solid was vacuum dried at 0°C for 200 hours to obtain a cold-soluble EVOH-H solid, named EVOH-HL.

[0114] 1 part by mass of EVOH-HL solid was added to 4 parts by mass of dimethyl sulfoxide for dissolution at a dissolution temperature of 25° C. and a stirring speed of 300 r / min. The polymer solid was completely dissolved within 2 minutes.

[0115] Comparative Example 1: Dissolution of hot-melt PVA

[0116] Different solvents were used to dissolve the hot-soluble PVA at a stirring rate of 300 r / min. The dissolution conditions are shown in Table 1. The stirring time of PVA in the dispersion at 30°C and 60°C was 48 h.

[0117] Comparative Example 2: Dissolution of hot-melt EVOH

[0118] Different solvents were used to dissolve the hot-soluble EVOH at a stirring rate of 300 r / min. After stirring at 30°C for 48 hours, the hot-soluble EVOH was almost insoluble, and after stirring at 60°C for 48 hours, the hot-soluble EVOH was partially dissolved. The dissolution at 100°C is shown in Table 2.

[0119] Comparative Example 3: Preparation of film using hot-melt PVA1799

[0120] 1 part by mass of hot-melt PVA1799 was added to 9 parts by mass of water and heated to dissolve, and the obtained dispersion was cast at 90°C to obtain a film X-2 with a thickness of 100±3μm. The yellowness index of the film X-2 was 22.74, the transmittance was 95.38%, the haze was 2.11%, and the contents of iron, cobalt, and nickel were 15.2ppm, 0.1ppm, and 9.7ppm, respectively.

[0121] Comparative Example 4: Preparation of film using hot melt type F171B

[0122] 1 part by mass of hot-melt F171B was added to 9 parts by mass of N,N-dimethylformamide and heated to dissolve, and the obtained dispersion was cast at 90°C to obtain a film Y-2 with a thickness of 100±3μm. The yellowness index of the film Y-2 was 3.62, the transmittance was 98.67%, the haze was 0.61%, and the contents of iron, cobalt, and nickel were 1.2ppm, 8.9ppm, and 3.5ppm, respectively.

[0123] Compared with the hot-soluble PVA1795 in Comparative Example 1, the cold-soluble PVA1795 can be dissolved at low temperatures, and the dissolution time is greatly shortened, and it has the characteristics of cold dissolution and fast dissolution.

[0124] Compared with the hot-melt PVA1799 and the hot-melt PVA2699 in Comparative Example 1, the cold-melt PVA1799 and the cold-melt PVA2699 in Example 2-3 can be dissolved at low temperatures, and the dissolution time is greatly shortened, and they have the characteristics of cold dissolution and quick dissolution. Compared with the film prepared from the untreated hot-melt PVA1799 in Comparative Example 3, the film prepared from the cold-melt PVA1799 in Example 2-3 has less metal impurities, higher purity, lower yellowness index, better hue, and significantly improved optical properties.

[0125] Compared with the hot-soluble EVOH in Comparative Example 2, the cold-soluble EVOH can be dissolved at low temperatures, and the dissolution time is greatly shortened, and it has the characteristics of cold dissolution and fast dissolution.

[0126] Compared with the untreated film prepared by hot-melt F171B in Comparative Example 4, the film prepared by cold-melt F171B has less metal impurities, higher purity, lower yellowness index, better hue, and significantly improved optical properties.

[0127] The DSC curve of cold-melting F171B is as follows: Figure 1 As shown, the DSC curve of hot-melt F171B is as follows Figure 2 As shown in Figure 2, compared with the hot melt type F171B, the cold melt type F171B has a lower crystallinity and can be Figure 1 The glass transition phenomenon was observed, and the melting temperature was slightly lower than that of the hot-melt F171B. However, the hot-melt F171B had a higher crystallinity and only the melting peak was observed.

[0128] Table 1

[0129]

[0130]

[0131] Table 2

[0132]

[0133] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0134] The present application prepares a cold-soluble polymer by a solvent replacement method, which has a simple process and low cost; at the same time, the cold-soluble polymer can be purified during the solvent replacement process, effectively reducing the content of transition metal impurities and alkaline impurities in the polymer, improving its hue, and improving its optical properties, which is beneficial for application in optical devices such as polarizers or food, biological packaging materials and other fields. Compared with the cold-soluble polymer in the prior art, the cold-soluble polymer prepared by the preparation method of the present application has a lower crystallinity than the raw material with high crystallinity before treatment, and the polymer dispersion obtained by dissolving the cold-soluble polymer in the solvent has better fluidity and is not easy to form a gel, and the upper limit of the solid content of the polymer is higher, so that the polymer dispersion is easier to process and the processing window is wider; the prepared cold-soluble polymer not only has the characteristics of cold dissolution and quick dissolution, but also maintains a high degree of saponification, even if the low-crystallinity polymer is formed after heat treatment, the crystallinity is improved, the solvent resistance is stronger, the mechanical properties are better, and the barrier property is higher.

[0135] In the above preparation method, a good solvent having good solubility for the polymer is used to dissolve the polymer to form a polymer dispersion; then a precipitant is used to precipitate the polymer dispersion to obtain a first polymer solid, wherein the difference in the dispersion performance of the polymer in different solvents is utilized, and the precipitant is used to change the stable system formed by the polymer dispersion, so that the polymer is precipitated to form a solid, and part of the good solvent and / or the precipitant is simultaneously wrapped and precipitated during the precipitation process; then the first polymer wet solid is extracted with an extractant, and the liquid molecules in the first polymer wet solid are replaced by the extractant by the diffusion and concentration difference of the liquid molecules, such as the good solvent and the precipitant added previously; finally, the extracted wet solid is dried, and the type of the extractant is controlled to be the same as the precipitant, and the volatilization rate is controlled to be higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a lower alkane, so that according to the mutual solubility characteristics of different precipitants, the liquid molecules in the wet solid are replaced by a lower alkane with a low boiling point, fast volatilization and poor adsorption to the polymer. Therefore, the temperature required for drying is lower than the dissolution temperature in step S1, and the low-temperature drying process is lower than the glass transition temperature of the polymer. When the polymer is in a glassy state, the molecular chain is difficult to move and difficult to form crystals, thereby obtaining a cold-soluble polymer. The dissolution process will destroy the crystallization of the polymer, and in the final drying process, due to the low temperature, the polymer will basically not crystallize, maintaining a low degree of crystallinity, that is, maintaining the characteristics of the cold-soluble polymer.

[0136] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a cold-soluble polymer, characterized in that: The preparation method comprises: Step S1, dispersing the saponified polymer in a good solvent to obtain a polymer dispersion, wherein the polymer is polyvinyl alcohol or ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%; Step S2, precipitating the polymer dispersion using a precipitant to obtain a first polymer wet solid, wherein the first polymer wet solid includes liquid molecules entrained in the polymer, and the liquid molecules include the good solvent and the precipitant; Step S3, extracting the liquid molecules in the first polymer wet solid with an extractant to obtain an extracted wet solid, wherein the extractant is selected from the precipitant and has a volatilization rate higher than the volatilization rate of the precipitant used in step S2, and more than 90% of the extractant remaining in the extracted wet solid is a lower alkane; Step S4, drying the extracted wet solid to obtain the cold soluble polymer; In the step S1, the dispersion temperature is 60°C to 220°C, and the dissolution time is 1 to 72 hours; In the step S4, the drying is carried out under normal pressure or vacuum, the temperature is 0-30° C., and the drying time is 0.5 h-200 h.

2. The preparation method according to claim 1, characterized in that: The good solvent is selected from any one or more of the first good solvents, a first mixed solvent composed of any one of the first good solvents and any one of the second good solvents, or a second mixed solvent of two of the second good solvents, the mass content of the second good solvent in the first mixed solvent is 25%~75%, the first good solvent includes any one or more of polyols, lower fatty acids, phenolic solvents and other solvents, the second good solvent includes water and lower fatty monohydric alcohols, and the mass content of the water or the lower fatty monohydric alcohol in the second mixed solvent is 25%~75%, wherein the polyol is selected from any one or more of ethylene glycol, propylene glycol, and glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol, and p-cresol; the lower fatty monohydric alcohol is selected from any one or more of methanol, ethanol, n-propanol and isopropanol; the lower fatty acid is selected from any one or more of formic acid, acetic acid and propionic acid; the other solvents are selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

3. The preparation method according to claim 2, characterized in that: The polarity of the precipitant is lower than the polarity of the good solvent.

4. The preparation method according to claim 3, characterized in that: The precipitant is selected from any one or more combinations of lower aliphatic alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, low polarity water-soluble solvents, and water. The lower aliphatic alcohol used for the precipitant includes methanol, ethanol, isopropanol, and n-propanol. The lipid solvent includes ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate, and methyl propionate. The chlorinated hydrocarbons include dichloromethane and chloroform. The lower alkanes include C5 alkanes, C6 alkanes, and petroleum ether. The low polarity water-soluble solvent is selected from tetrahydrofuran, acetone, or butanone. When the precipitant is the lower aliphatic alcohol, the mass ratio of the precipitant to the good solvent is 4 to 8:

1. When the precipitant is the low-polarity water-soluble solvent, the mass ratio of the precipitant to the good solvent is 2 to 8:1; When the precipitant is the lipid solvent or the chlorinated hydrocarbon, the mass ratio of the precipitant to the good solvent is 2-8:1; When the precipitant is the lower alkane, the mass ratio of the precipitant to the good solvent is 2-8:1; When the precipitant is water, the mass ratio of the precipitant to the good solvent is 5-10:

1.

5. The preparation method according to claim 3, characterized in that: When the good solvent is the second mixed solvent, and the mass contents of the water and the lower aliphatic monohydric alcohol in the second mixed solvent are independently 25% to 75%, the precipitant is water.

6. The preparation method according to claim 2, characterized in that: The step S3 comprises: Performing a first extraction on the first polymer wet solid using a first extractant to obtain a first extracted wet solid; extracting the first extracted wet solid for a second time using a second extractant to obtain a second extracted wet solid; Performing a third extraction on the second extracted wet solid using a third extractant to obtain an extracted wet solid; The first extractant is miscible with the good solvent, and the second extractant is miscible with the lower alkane.

7. The preparation method according to claim 6, characterized in that: The first extraction is a multi-stage extraction; and / or, the second extraction is a multi-stage extraction; and / or, the third extraction is a multi-stage extraction.

8. The preparation method according to claim 6, characterized in that: The first extraction is a 1-4 level extraction; and / or, the second extraction is a 1-4 level extraction; and / or, the third extraction is a 1-4 level extraction.

9. The preparation method according to claim 6, characterized in that: The first extractant, the second extractant and the third extractant are mutually soluble and their volatilization speeds gradually increase.

10. The preparation method according to claim 6, characterized in that: The mass ratio of the first extractant to the polymer is 5-100:1; and / or, the mass ratio of the first extractant to the second extractant is 5-1:1, and the mass ratio of the second extractant to the third extractant is 5-1:1; and / or, the third extractant is selected from any one or more of lower alkanes.

11. The preparation method according to claim 3, characterized in that: The good solvent is a phenolic solvent, the precipitant does not contain water and methanol, and the step S3 uses C5alkane, C6alkane and petroleum ether as extractants to perform extraction 2 to 4 times.

12. The preparation method according to claim 6, characterized in that: The polymer is polyvinyl alcohol, and the mass content of water in the good solvent is less than 5%. The precipitant is a mixed precipitant composed of low-order fatty alcohols, lipid solvents, chlorinated hydrocarbons, low-order alkanes, and low-polarity water-soluble solvents, and the mass content of the low-order alkanes is less than 80%. In step S3, the first extractant does not contain water, and the second extractant does not contain water and methanol.

13. The preparation method according to claim 6, characterized in that: The polymer is polyvinyl alcohol, and the mass content of water in the good solvent is not less than 5%; the precipitant is a mixed precipitant composed of lower fatty alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, and low-polarity water-soluble solvents, in which the mass content of the lower fatty alcohols and the lipid solvents is not less than 20%, and the mass content of the lower alkanes is less than 80%; in step S3, the first extractant does not contain water, and the second extractant does not contain water and methanol.

14. The preparation method according to claim 6, characterized in that: The polymer is an ethylene-vinyl alcohol copolymer, and the good solvent contains polyols, low-level fatty acids, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; the first extractant is water, low-level fatty alcohol, low-polarity water-soluble solvent, chlorinated hydrocarbon or lipid solvent; the second extractant does not contain water and methanol, and the content of ethanol, n-propanol, isopropanol or low-polarity water-soluble solvent in the second extractant is not less than 30%.

15. The preparation method according to claim 6, characterized in that: The polymer is an ethylene-vinyl alcohol copolymer, and the good solvent is a mixed solvent of water and low-order fatty monohydric alcohol. The mass content of ethanol, isopropanol, n-propanol or low-polarity water-soluble solvent in the first extractant is not less than 30%.

16. The preparation method according to claim 1, characterized in that: The ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol binary copolymer or an ethylene-vinyl alcohol-vinyl acetate terpolymer.

17. The preparation method according to claim 16, characterized in that: The content of basic impurities in the polymer is less than 0.1% by mass.

18. The preparation method according to claim 16, characterized in that: The content of basic impurities in the polymer is less than 0.08% by mass.

19. The preparation method according to claim 16, characterized in that: The content of basic impurities in the polymer is less than 0.04% by mass.

20. The preparation method according to claim 16, characterized in that: The content of basic impurities in the polymer is less than 0.02% by mass.

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