Ethylene-vinyl alcohol copolymer film and method for producing the same

Abstract

To provide an ethylene-vinyl alcoholic copolymer film with improved film performance and a method for producing the same.SOLUTION: An ethylene-vinyl alcoholic copolymer film has a filtration resistance of less than 3×1010 m-1. Also provided is a method for producing an ethylene-vinyl alcoholic copolymer film with a filtration resistance of less than 3×1010 m-1, including the step of preparing an ethylene-vinyl alcoholic copolymer solution that contains an ethylene-vinyl alcoholic copolymer and a surfactant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ethylene-vinyl alcohol copolymer membrane and a method for producing the same, and more particularly to an ethylene-vinyl alcohol copolymer membrane with improved membrane performance and a method for producing the same. [Background technology]

[0002] Membranes formed from ethylene-vinyl alcohol copolymers (sometimes referred to as "EVOH") have excellent hydrophilicity and are widely used in various separation membrane applications, including industrial and medical uses.

[0003] For example, Patent Document 1 discloses an EVOH film composed of EVOH, having a dense layer on the film surface and an asymmetric structure comprising a porous layer in the parts other than the dense layer where defects of 5 μm or more are substantially absent, and having a porosity of 50 to 90%, in order to obtain an EVOH film without defects such as voids. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2001-79371 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional EVOH membranes have high filtration resistance, and there is room for improvement in membrane performance. Therefore, there is a need to improve the membrane performance of EVOH membranes (i.e., reduce filtration resistance). [Means for solving the problem]

[0006] In view of these circumstances, the inventors conducted extensive research and, as a result, discovered that an EVOH membrane with improved membrane performance can be obtained by reducing the filtration resistance of the EVOH membrane, thus completing the present invention.

[0007] That is, the present invention provides the following [1] to [5]. [1] An ethylene-vinyl alcohol copolymer membrane having a filtration resistance of less than 3 × 10 10 m -1 . [2] The ethylene-vinyl alcohol copolymer membrane according to [1], further containing a surfactant. [3] The ethylene-vinyl alcohol copolymer membrane according to [1], which is an asymmetric membrane. [4] The ethylene-vinyl alcohol copolymer membrane according to [1], which is for fine particles. [5] A method for producing an ethylene-vinyl alcohol copolymer membrane according to any one of [1] to [4], including a step of preparing an ethylene-vinyl alcohol copolymer solution containing an ethylene-vinyl alcohol copolymer and a surfactant. [Advantages of the Invention]

[0008] The EVOH membrane of the present invention has a low filtration resistance and excellent membrane performance. [Modes for Carrying Out the Invention]

[0009] Hereinafter, the present invention will be described in detail, but these are examples of preferred embodiments.

[0010] [EVOH Membrane] The EVOH membrane, which is an embodiment of the present invention, is a membrane formed from EVOH and has a filtration resistance of less than 3 × 10 10 m -1 . The filtration resistance is preferably less than 2.5 × 10 10 m -1 , more preferably less than 2 × 10 10 m -1 , and particularly preferably less than 1 × 10 10 m -1 . The lower limit of the filtration resistance is not particularly limited, but is usually 3 × 10 4 m ―1This is the case. By having the filtration resistance within the above range, a membrane with high filtration efficiency is obtained where the porosity of the voids forming the membrane is less likely to decrease, and an EVOH membrane with high membrane performance can be obtained. Note that the filtration resistance in the present invention refers to the value measured under the following conditions. Using a dead-end filtration device with a filtration area of 4.1 cm 2 , place a circular EVOH membrane with a diameter of 25 mm on a stainless steel perforated plate, apply a pressure of 10 kPa with nitrogen gas, and perform filtration of 10 mL of water at 25°C. Then, calculate the filtration resistance R of the membrane using the following formula. m [m -1 . v = V / A R m =(ΔPt) / (μv) Here, v [m] is the filtrate volume per unit filtration area, V [m 3 is the filtrate volume, A [m 2 is the filtration area, ΔP [Pa] is the filtration pressure, t [s] is the filtration time, and μ [Pa·s] represents the viscosity of water. The viscosity of water at 25°C is 8.9×10 -4 Pa·s.

[0011] The EVOH membrane of the present invention may be a symmetric membrane or an asymmetric membrane, but an asymmetric membrane with different pore diameters in the thickness direction is preferred. Such an asymmetric membrane has a dense layer (also referred to as a skin layer) with a smaller pore diameter than the following support layer and a support layer (also referred to as a porous layer) with a larger pore diameter than the above dense layer. In such an asymmetric membrane, the pore diameter gradually changes in the thickness direction (towards the support layer) from the dense layer on the surface side of the EVOH membrane. Since the pores present in the dense layer cannot be clearly measured with an electron microscope, they cannot be clearly confirmed. However, since the EVOH membrane of the present invention blocks the permeation of polystyrene latex beads (LB3, manufactured by Sigma-Aldrich) with a particle diameter of 0.3 μm while allowing the permeation of bovine serum albumin (BSA), it is considered that pores on the order of 10 to 100 nm exist.

[0012] The EVOH film of the present invention preferably has EVOH as the main component. Here, the main component refers to a content of 50% by weight or more of the present EVOH film. The content of EVOH is preferably 60% by weight or more, more preferably 70% by weight, particularly preferably 80% by weight or more, and most preferably 90% by weight or more.

[0013] [Method for producing EVOH film] The EVOH film of the present invention is produced, for example, through a process of preparing an EVOH solution and a process of obtaining an EVOH film from the EVOH solution. The method for producing the EVOH film of the present invention preferably includes means for reducing the filtration resistance of the EVOH film. Examples of means for reducing the filtration resistance of the EVOH film include using a surfactant and using a pore-forming agent during the production of the EVOH film. Among these, from the viewpoint of more easily producing the EVOH film of the present invention, a production method using a surfactant is preferred.

[0014] The method for producing the EVOH film of the present invention preferably includes a process of preparing an EVOH solution containing EVOH and a surfactant, and a process of obtaining an EVOH film from the EVOH solution.

[0015] The EVOH solution is prepared by mixing EVOH, a surfactant, and a solvent (hereinafter referred to as a good solvent). The mixing order, mixing method, and mixing temperature are not particularly limited. Any good solvent that can dissolve EVOH (has a high solubility) can be used. Specifically, examples include DMSO, N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), NMP (N-methyl-2-pyrrolidone), N-methylmorpholine-n-oxide (N-MMO) hydrate, a mixture of a water-soluble solvent such as alcohol and water, alcohol such as diacetone alcohol, or a mixture thereof. DMSO is preferred in terms of being inexpensive and having excellent handleability. The concentration of EVOH in the EVOH solution is not particularly limited, but is preferably 1 to 50% by weight, more preferably 3 to 40% by weight, and most preferably 5 to 30% by weight, from the standpoint of ease of handling. The concentration of the surfactant in the EVOH solution is not particularly limited, but from the standpoint of more easily obtaining the EVOH film of the present invention, it is preferably 1 to less than 30% by weight, more preferably 3 to 25% by weight, and most preferably 5 to 20% by weight. Most preferably it is 5 to 10% by weight. The addition of the surfactant to the EVOH solution is intended to suppress the extraction rate of the poor solvent and increase the diffusion rate to the good solvent.

[0016] When an EVOH solution is brought into contact with a poor solvent, the good solvent in the EVOH solution is extracted into the poor solvent, and the poor solvent diffuses into the EVOH solution. This causes phase separation, and the EVOH in the EVOH solution solidifies, forming an EVOH film. Any poor solvent can be used as long as it can cause layer separation and precipitate an EVOH film when brought into contact with the EVOH solution. Specifically, examples include water, paraffinic hydrocarbons such as hexane, naphthenic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as toluene and styrene, aromatic compounds such as xylene, esters such as ethyl acetate, ethers such as diethyl ether, and ketones such as acetone. Water is preferred due to its low cost, safety, and ease of handling. The method for bringing the EVOH solution into contact with the poor solvent is not particularly limited; for example, a method of immersing the EVOH solution in a container in the poor solvent can be used. Furthermore, the contact time and contact temperature between the EVOH solution and the poor solvent are not particularly limited, as long as the conditions are met for the EVOH to solidify and form an EVOH film. For example, the contact time is 1 second to 360 minutes, preferably 3 seconds to 180 minutes, more preferably 5 seconds to 60 minutes, and the contact temperature is -10 to 120°C, preferably 0 to 100°C, more preferably 15 to 90°C.

[0017] The poor solvent may contain a surfactant, but it is preferable that it does not. If a surfactant is included, the surfactant content is preferably 50% by weight or less.

[0018] The present invention's method for producing an EVOH film may include steps such as washing the EVOH film with a cleaning solution like water, or drying it under normal or reduced pressure to remove any remaining solvent from the EVOH film.

[0019] [Applications of EVOH film] Because the EVOH membrane of the present invention is hydrophilic, it helps prevent fouling, a phenomenon in which substances to be separated, present in the membrane supply water such as raw water, adhere to and accumulate on the membrane surface or inside the pores, and can therefore be used mainly for particle removal applications.

[0020] [EVOH] The EVOH used in the EVOH film of the present invention is a resin obtained by saponifying an ethylene-vinyl ester copolymer, which is typically a copolymer of ethylene and a vinyl ester monomer, and is a water-insoluble thermoplastic resin. From an economic standpoint, vinyl acetate is generally used as the vinyl ester monomer.

[0021] Copolymerization of ethylene and vinyl ester monomers can be carried out using any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, and generally, solution polymerization using methanol as the solvent is used. Saponification of the obtained ethylene-vinyl ester copolymer can also be carried out by known methods.

[0022] The EVOH produced in this manner mainly consists of ethylene structural units and vinyl alcohol structural units, and when the degree of saponification is less than 100 mol%, it contains a small amount of vinyl ester structural units remaining as unsaponified portions.

[0023] Vinyl acetate is generally used as the vinyl ester monomer due to its economic advantages and the efficiency of impurity treatment during manufacturing. Other vinyl ester monomers include, for example, aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate, and aromatic vinyl esters such as vinyl benzoate. These can be used individually or in combination of two or more. Among these, aliphatic vinyl esters having 3 to 20 carbon atoms are preferred, more preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms.

[0024] The ethylene structural unit content of EVOH, as measured according to ISO 14663, is typically 20 to 60 mol%, preferably 25 to 55 mol%, and particularly preferably 30 to 50 mol%. By having such a content within the above range, the effects of the present invention can be further enhanced. The content of such ethylene structural units can be controlled by the pressure of the ethylene during copolymerization of the vinyl ester monomer and ethylene.

[0025] The degree of saponification of EVOH, as measured according to JIS K6726 (where EVOH(A) is a solution uniformly dissolved in water / methanol solvent), is typically 90-100 mol%, preferably 95-100 mol%, and particularly preferably 99-100 mol%. Having such a degree of saponification within this range enhances the effects of the present invention. This degree of saponification can be controlled by the amount of saponification catalyst (usually an alkaline catalyst such as sodium hydroxide is used) used to saponify the ethylene-vinyl ester copolymer, as well as by temperature, time, etc.

[0026] The melt flow rate (MFR) of EVOH (at 210°C and 2160g load) is typically 0.5 to 100g / 10min, preferably 1 to 50g / 10min, and particularly preferably 3 to 35g / 10min. If the MFR is too high, the viscosity of the EVOH solution becomes too low, making continuous film formation difficult. If the MFR is too low, the viscosity of the EVOH solution becomes too high, impairing film-forming properties and making handling difficult during film preparation.

[0027] Such MFR serves as an indicator of the degree of polymerization of EVOH and can be adjusted by the amount of polymerization initiator and solvent used when copolymerizing ethylene and vinyl ester monomers.

[0028] Furthermore, EVOH may also contain structural units derived from the following comonomers, within a range that does not inhibit the effects of the present invention (for example, 10 mol% or less of EVOH).

[0029] Comonomers include olefins such as propylene, 1-butene, and isobutene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 3-buten-1,2-diol, 4-penten-1-ol, and 5-hexen-1,2-diol, and their esterified and acylated derivatives; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyryloxy-2 - Hydroxyalkylvinylidene diacetates such as methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydride) phthalic acid, (anhydride) maleic acid, (anhydride) itaconic acid, or their salts, or mono or dialkyl esters with 1 to 18 carbon atoms in the alkyl group; acrylamide, N-alkylacrylamide with 1 to 18 carbon atoms in the alkyl group, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its salts or its quaternary salts, etc. Acrylamides; methacrylamide, N-alkylmethacrylamide with 1 to 18 carbon atoms in the alkyl group, N,N-dimethylmethacrylamide, 2-methacrylamidepropanesulfonic acid or its salts, methacrylamidopropyldimethylamine or its salts or its quaternary salts, and other methacrylamides; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; vinyl cyanides such as acrylonitrile, methacrylnitrile; alkyl vinyl ethers with 1 to 18 carbon atoms in the alkyl group, hydro Examples include vinyl ethers such as xyalkyl vinyl ethers and alkoxyalkyl vinyl ethers; vinyl halogenated compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; allyl halogenated compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamide-2-methylpropanesulfonic acid.These can be used individually or in combination of two or more types.

[0030] In particular, EVOH copolymerized with hydroxyl group-containing α-olefins, i.e., EVOH having a hydroxyl group in the side chain, is preferred, more preferably EVOH having a primary hydroxyl group in the side chain, and especially preferably EVOH having a 1,2-diol structure in the side chain.

[0031] As for EVOH having a primary hydroxyl group in its side chain, it is preferable that the content of structural units derived from monomers having the primary hydroxyl group is typically 0.1 to 20 mol%, more preferably 0.5 to 15 mol%, and particularly preferably 1 to 10 mol% of the EVOH.

[0032] Furthermore, EVOH may be a "post-modified" product, such as urethane, acetal, cyanoethylated, or oxyalkyleneated.

[0033] Furthermore, the EVOH used in the EVOH film of the present invention may be a mixture of two or more types of EVOH, for example, those with different degrees of saponification, different degrees of polymerization, or different copolymer components.

[0034] [Surfactants] The surfactant used in the production of the EVOH film of the present invention is an amphiphilic molecule having both hydrophilic and hydrophobic groups in its molecule. Examples of surfactants include anionic surfactants, cationic surfactants, twin surfactants, nonionic surfactants, amphoteric surfactants, which exhibit anionic surfactant properties in alkaline conditions and cationic surfactant properties in acidic conditions when dissolved in water, polymeric surfactants with molecular weights of several thousand or more that have surfactant function, fluorinated surfactants in which the hydrocarbons of the hydrophobic groups of the surfactant are replaced with fluorine, silicon-based surfactants in which the hydrocarbons of the hydrophobic groups of the surfactant are replaced with silicon, and biosurfactants, which are substances with surfactant function produced inside and outside of cells by living organisms (generally referring to surfactants produced outside of the cellular cells by microorganisms).

[0035] More specifically, examples of anionic surfactants include fatty acid salts, higher alcohol sulfate salts, liquid fatty oil sulfate salts, sulfates of aliphatic amines and aliphatic amides, fatty alcohol phosphate salts, sulfonates of dibasic fatty acid esters, fatty acid amide sulfonates, alkylallyl sulfonates, and formalin condensate naphthalene sulfonates. Cationic surfactants include fatty amine salts, quaternary ammonium salts, and alkylpyridium salts. Nonionic surfactants include cationic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, and polyoxyethylene sorbitan alkyl esters. Examples of amphoteric surfactants include alkyl betaine type, aliphatic amidopropyl betaine type, derivatives of 2-alkylimidazolidine, glycine type, amidic acid type, and amine oxide type. Examples of polymeric surfactants include homopolymer type, random copolymer type, alternating copolymer type, block copolymer type, graft copolymer type, and comb type polymeric surfactants. Examples of fluorinated surfactants include perfluoroalkyl sulfonic acid, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylic acid, and fluorinated telomer alcohol. Examples of silicone-based surfactants include side-chain modified type, both-end modified type, one-end modified type, and both-end side-chain modified type. Examples of biosurfactants include sugar-type, amino acid-type, organic acid-type, and polymer-type biosurfactants.

[0036] The EVOH film of the present invention may contain a surfactant. The surfactant content in the EVOH film is not particularly limited, but is, for example, 0.001 to 30% by weight, preferably 0.005 to 10% by weight, and more preferably 0.01 to 3% by weight. [Examples]

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0038] Prior to the examples, the following components were prepared.

[0039] EVOH(A): Ethylene structural unit content 44 mol%, MFR 12 g / 10 min (210°C, load 2160 g, 210°C), degree of saponification 99.8 mol% • Surfactant (B1): Polyoxyethylene (10) oleyl ether • Surfactant (B2): Oleyl alcohol • Surfactant (B3): Isopropyl alcohol

[0040] <Example 1> (Fabrication of EVOH film) An EVOH solution containing 5% by weight of surfactant (B1) was prepared by dissolving EVOH(A) in DMSO (60°C) containing surfactant (B1) so that the solid content of EVOH(A) was 7%. After cooling the EVOH solution to 25°C, the EVOH solution was poured into a mold (80mm x 80mm) made by attaching a polytetrafluoroethylene spacer to a glass plate with double-sided tape. The EVOH solution was leveled to a thickness of 0.5mm, and the mold containing the EVOH solution was immersed in a bath of non-solvent (water) and left to stand for 1 hour to prepare an EVOH film. The prepared EVOH film was washed with water to remove the solvent.

[0041] <Examples 2-4, Comparative Examples 1-3> The EVOH film was prepared in the same manner as in Example 1, except that the type and amount of surfactant were changed as shown in Table 1.

[0042] The filtration resistance of the EVOH membranes prepared in the above examples and comparative examples was evaluated by the following method. <Evaluation of filtration resistance> Filtration area 4.1cm 2Using a dead-end type filtration apparatus, an EVOH membrane was cut into a 25 mm diameter circle, mounted on a stainless steel perforated plate, and filtered through 10 mL of water at 25°C under a pressure of 10 kPa using nitrogen gas. From the results of the water filtration experiment, the membrane filtration resistance R was calculated using the following formula. m [m -1 ] was sought. v=V / A R m =(ΔPt) / (μv) Here, v[m] is the volume of filtrate per unit filtration area, V[m 3 ] is the filtrate volume, A[m 2 ] represents the filtration area, ΔP[Pa] represents the filtration pressure, t[s] represents the filtration time, and μ[Pa·s] represents the viscosity of water. The viscosity of water at 25℃ is 8.9 × 10⁻⁶. -4 It is Pa.s.

[0043] [Table 1]

[0044] Table 1 shows that the EVOH membranes in Examples 1-4, which used a specific amount of surfactant, had lower filtration resistance than Comparative Example 1, which did not use a surfactant. Furthermore, too much surfactant made membrane formation difficult (Comparative Example 2). In Comparative Example 3, which used isopropyl alcohol, the filtration resistance was higher than in the Examples, indicating inferior membrane performance compared to the Examples. Therefore, it can be seen that by using a specific amount of surfactant, it is possible to produce EVOH membranes with low filtration resistance and excellent membrane performance. [Industrial applicability]

[0045] The EVOH membrane of the present invention has low filtration resistance and excellent membrane performance, which helps prevent fouling, a phenomenon in which substances to be separated, present in the membrane-supplied water such as raw water, adhere to and accumulate on the membrane surface or inside the pores. It is therefore particularly useful as a filtration membrane for various applications, mainly particle removal.

Claims

1. An ethylene-vinyl alcohol copolymer film comprising a surfactant, The filtration resistance of the ethylene-vinyl alcohol copolymer membrane is 3 × 10 １０ I understand －１ It is less than, An ethylene-vinyl alcohol copolymer film comprising the surfactant polyoxyethylene (10) oleyl ether and / or oleyl alcohol.

2. The ethylene-vinyl alcohol copolymer film according to claim 1, which is an asymmetric film.

3. An ethylene-vinyl alcohol copolymer film according to claim 1, for use with particle removal.

4. A method for producing an ethylene-vinyl alcohol copolymer film according to any one of claims 1 to 3, comprising the step of preparing an ethylene-vinyl alcohol copolymer solution containing an ethylene-vinyl alcohol copolymer and a surfactant.

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