JPH022850A - Narrowly fractionated molecular weight polyvinylformal film for ultrafiltration and its production - Google Patents

Abstract

PURPOSE:To obtain a film for ultrafiltration without the adsorption of material to be treated, having excellent antibacterial property by using a polymer film mixed with 2 kinds of polyvinylformal resin having different mol.wt. and repetitive unit of fixed formula in ultrafiltration an aq. soln. of hydrophobic protein milk, etc. CONSTITUTION:The 2 kinds of resin having the repetitive unit of formula I, and having 550-650 and 700-800 degree of polymerization n are dissolved in a solvent to prepare a dope. The dope is applied to polyester non-woven fabric and then, immersed in a coagulation bath to produce the film by wet film- forming method. The film is highly hydrophilic and has the scare adsorption of the material to be treated. Besides, it has excellent decomposability of bacteria. Therefore, the film can be used for manufacturing process of pharmaceuticals, foodstuffs, etc., and treatment of waste water.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a hydrophilic ultrafiltration membrane made of polyvinyl formal resin, particularly a hydrophilic ultrafiltration membrane having a small molecular weight cut-off of 100,000 or less. This invention relates to an ultrafiltration membrane and its manufacturing method.

[Conventional technology] Conventionally, polysulfone, polyethersulfone.

Various trees 11' such as acetyl cellulose and cellulose,
A method of obtaining an ultrafiltration membrane from t by a wet membrane forming method is known. However, ultrafiltration membranes made of hydrophobic resins such as polysulfone and polyethersulfone cannot handle highly hydrophobic aqueous solutions such as hydrophobic protein aqueous solutions, oil emulsions, milk, citrus fiber bundles 11-1 plasma, and serum. When used as a treatment target, since the membrane is hydrophobic, the target substances are adsorbed to the membrane surface, which contaminates the membrane itself, and the amount of permeated water decreases over time. are doing. In addition, membranes made of cellulose are extremely hydrophilic, and although they solve the problems that occur with hydrophobic membranes, such as membrane contamination due to adsorption of hydrophobic substances and a decrease in the permeation port, they are not acid resistant. It has been pointed out that cellulose has poor alkali resistance, and that cellulose has extremely low bacterial resistance.

In addition, films made of polyvinyl alcohol resin have been known for some time (for example, Japanese Patent Laid-Open No. 49-53'155
Since polyvinyl alcohol is a water-soluble polymer, formaldehyde or gel tar is added to an aqueous solution of polyvinyl alcohol in order to form a film and impart water resistance. The film was formed by adding an acetalizing agent such as dialdehyde such as aldehyde and a crosslinking agent, and heating the water-soluble polymer aqueous solution to advance the acetalization reaction of polyvinyl alcohol.

[Problems to be Solved by the Invention] The drawbacks of ultrafiltration membranes made of polysulfone and cellulose resins that are currently mainly used are summarized above.

1) Polysulfone membranes significantly adsorb hydrophobic substances.

2) Cellulose membranes have extremely low bacterial resistance.

In addition, the manufacturing process for conventional ultrafiltration membranes made of polyvinyl alcohol resin is water-based and involves a homogeneous reaction in an aqueous solution. requires the addition of a pore-forming agent. Furthermore, it is difficult to control the temperature for uniform acetalization, and the reactivity is not uniform depending on the scale of film formation.

[Means for Solving the Problems] The present inventors aimed to solve the above-mentioned problems, reduce the adsorption of hydrophobic substances to be treated, and obtain an ultrafiltration membrane having bacteria resistance. As a result of intensive research, an ultrafiltration membrane was manufactured using a wet membrane forming method using polyvinyl formal resin (general formula (I) below), which is a hydrophilic resin.

The present invention has been achieved, which allows the desired ultrafiltration membrane to be obtained without adding a pore-forming agent or the like.

That is, the present invention provides the repetition 111 shown in the above general formula (1).
The present invention provides an ultrafiltration membrane made of a polymer made by blending two types of resins, which are polyvinyl formal resins with a − position and differing degrees of polymerization, and a method for producing a bacterial membrane using a wet membrane forming method. be.

The present invention will be explained in detail below.

The raw material resin for the membrane is polyvinyl formal resin, and this polyvinyl formal resin is derived from polyvinyl alcohol. This polyvinyl alcohol is a saponified product of vinyl acetate homopolymer, and its degree of saponification is 70%.
Above, 80% or more is particularly preferable. This polyvinyl alcohol is treated with formaldehyde according to a conventional method to obtain an intramolecularly formalized polyvinyl formal resin. If the degree of polymerization of this polyvinyl formal resin is lower than 600, the stability of the membrane performance will be poor, and if it is higher than 950, the viscosity of the dope will be high, and the viscosity will change greatly due to temperature changes, so the degree of polymerization is usually Those in the range of 600 to 950 are used for making ultrafiltration membranes.

However, when a resin having a degree of polymerization lower than the above range is used, the molecular weight cutoff of the ultrafiltration membrane can be reduced, although the membrane strength is reduced.

Therefore, we created a film by blending a resin with a degree of polymerization in a range suitable for film formation and a polyvinyl formal resin with a low degree of polymerization. It has become possible to form polyvinyl formal resin into an ultrafiltration membrane having sufficient membrane strength. The two types of polyvinyl formal resins used here each have a polymerization degree of nl-550 to 650.
゜n2 - Desirably within the range of 700 to 800, and the blend ratio of both is low polymerization degree: high polymerization degree - 10:90
The range is preferably 85:15 (weight ratio).

If the resin has a low degree of polymerization of 10% or less, an ultrafiltration membrane having a small molecular weight cut-off of 1'' cannot be produced, and if the resin has a low degree of polymerization of 85% or more, the membrane does not have sufficient strength.

Solvents used in the production of dopes for producing ultrafiltration membranes with a small molecular weight cut-off of 100,000 or less by dissolving resins within the above-mentioned range suitable for film production include: , polar solvents that are compatible with water can be used, and particularly preferred solvents include single solvents such as N-methyl-2-pyrrolidone and N,N-dimethylformamide, or solvents that have a slow diffusion rate in water and that are contained within the molecule. 1,4-dioxane, tetrahydrofuran, which is a polar solvent having an oxygen atom,
It is a mixed solvent of 13-dioxolane, etc. and N-methyl-2-pyrrolidone or NN-dimethylformamide, which has a moderately fast diffusion rate in water, and the mixing ratio is 1:9 to 9.
:1 (weight ratio), or acetone, which is a solvent with a fast vaporization rate, relative to the total weight of the above mixed solvent,
A mixed solvent system in which the solvent is added in an amount ranging from 1 to 20% of the total solvent weight is preferred.

The polyvinyl formal resin is dissolved using the above solvent to prepare a film-forming dope, and the total polymer concentration at this time is preferably 10 to 30 weight percent. 10
When attempting to produce an ultrafiltration membrane with a concentration of less than weight percent, it is difficult to produce an ultrafiltration membrane with a desired small molecular weight cutoff because the concentration of the polymer in the dope is dilute. In addition, dopes with a concentration of more than 30% by weight have too high a viscosity and are not substantially suitable for film formation.
The film is formed by phase conversion method). The wet film forming method referred to in the present invention is a method in which the atmosphere for gelling the dope is maintained in a wet state (in the liquid phase), that is, the solvent in the dope is transferred to the liquid phase in a coagulation bath, and the dope is gelled. It refers to the method of

For the coagulation bath used at this time, water having a temperature range of 0°C to 45°C is preferably used. At temperatures above 45° C., the dope undergoes rapid shrinkage and gels, resulting in lack of uniformity in film performance.

[Effects of the Invention] A polyvinyl formal ultrafiltration membrane can be obtained through the above steps, and since the wave membrane is highly hydrophilic, the adsorption of hydrophobic substances is extremely low and the membrane has excellent bacterial decomposition resistance.

Therefore, the obtained ultrafiltration membrane can be used in fields such as the manufacturing process of pharmaceutical products, foodstuffs, etc., and wastewater treatment. Filtration and purification of vaccines, depyrogenization, filtration of oil emulsions, concentration of milk, and fruit juice.

Suitable for removing COD from wastewater, treating activated sludge, etc.

Moreover, the corrugated membrane retains its membrane properties even after drying, and has the advantage that the membrane can be handled in a dry state.

[Examples] The present invention will be explained in more detail with reference to Examples and Comparative Examples below, but the present invention is not limited to these Examples.

Example I Using N-methyl-2-pyrrolidone as a solvent, a polyvinyl formal resin with an average degree of polymerization of 550 (formalization rate of 8
0%) and polyvinyl formal resin with an average degree of polymerization of 750 (formalization rate 80%), 15% by weight and 10% by weight, respectively.
A dope was prepared by dissolving it in a proportion of % by weight. This dope was evenly applied onto a polyester nonwoven fabric, and then the water temperature was increased to 5°C.
It was introduced into a coagulation bath filled with pure water at ℃, and a film was formed by a wet film forming method. The obtained flat membrane has a separation membrane layer thickness of 230 μm.
and pure water permeation rate 4001/d-hr-kgf/c
It was i. In addition, as a result of determining the fractional molecular weight by 4?1 depending on the rejection rate of globular proteins, the wave membrane has a fractional molecular weight of fii30.
,000 performance. In addition, the contact angle of the wave membrane with pure water was approximately 50° immediately after the water droplet was dropped, but it completely spread in approximately 1 minute, indicating that the resulting membrane was highly hydrophilic. .

Example 2 Using a mixture of 1,4-dioxane and N,N-dimethylformamide at a ratio of 723 (weight ratio) as a solvent, a polyvinyl formal resin with an average degree of polymerization of 550 (formalization rate 80%) was prepared. 15% each of polyvinyl formal resin with an average degree of polymerization of 750 (formalization rate 80%)
A dope was prepared by dissolving it in a proportion of 10% by weight. Using the dope, by the same operation as in Example 1,
A film was formed at a water temperature of 5°C. The obtained flat membrane has a separation membrane layer thickness of 230 μm and a pure water permeation rate of 100 g/trr-
It was hr·kgf/c-. Furthermore, as a result of measuring the molecular weight cut-off based on the rejection rate of globular proteins, the wave membrane had a performance with a cut-off molecular weight of 10,000.

In addition, when the contact angle of the wave film with pure water was measured, the water droplets completely wetted and spread within one minute.

Comparative Example 1 A polyvinyl formal resin having an average degree of polymerization of 500 (formalization rate: 80%) was prepared into a 20% by weight dope using N-methyl-2-pyrrolidone as a solvent. Using this dope, an ultrafiltration membrane was produced in the same manner as in Example 1. However, with this resin, it was not possible to obtain an ultrafiltration membrane having a molecular weight cut off of 100,000 or less and having substantially sufficient membrane strength.

Comparative Example 2 A polyvinyl formal resin with an average degree of polymerization of 970 (formalization rate 80%) was mixed with a solvent of 1,4-dioxane and N,N-dimethylformamide at a ratio of 7:3 (ffl ratio). A dope of 17% by weight was prepared. When an attempt was made to form a film using this dope in the same manner as in Example 1, it was not possible to form a film due to the high viscosity of the dope.

Claims (1)

[Claims] (1) A polyvinyl formal resin having a repeating unit represented by the general formula (I), characterized in that it is made of a polymer obtained by blending two types of resins with different degrees of polymerization. Ultrafiltration membrane. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) (2) Degree of polymerization is n1 = 550 to 650, n2 = respectively
The ultrafiltration membrane according to claim 1, characterized in that two types of resins having a molecular weight of 700 to 800 are used. (3) 2 represented by the following general formula (I) and having different degrees of polymerization
A method for producing an ultrafiltration membrane according to claim 1 or 2, characterized in that a polyvinyl formal resin blended with different types of resins is formed into a film by a wet film forming method. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(2)