JPH01182330A - Cellular film having heat resistance imparted thereto and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title cellular film having excellent heat resistance and applicable to membrane separation uses, such as medical applications, by thermally polymerizing a specific polymerizable monomer and monomers in a state held on the surface of a cellular film made of polyethylene. CONSTITUTION:The aimed cellular film, obtained by thermally polymerizing (B) one or more polymerizable monomers consisting of styrene and alpha- methylstyrene and (C) monomers containing divinylbenzene in a state held on the surface of at least part of (A) a cellular film consisting of polyethylene or polypropylene and holding a crosslinked polymer consisting of the components (B) and (C) on the surface of at least part of the component (A).

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a porous membrane with excellent heat resistance.

Specifically, the present invention relates to a porous membrane in which heat resistance is imparted to a polyethylene or polypropylene fissured porous membrane, and a method for producing the same.

[Conventional technology].

In recent years, with the development of industry, various separation membranes have been used in the water purification field, blood treatment field, air purification field, food industry field, etc. For example, microfiltration membranes are used to obtain highly purified water or highly clean air. Porous membranes made of polyethylene or polypropylene are particularly frequently used as precision filtration membranes because they are inexpensive, have excellent chemical resistance, and have excellent membrane properties such as strength, elongation, and flexibility.

Among these, porous hollow fiber membranes are an extremely desirable membrane form because of their advantage in that a large membrane area can be set per unit volume.

The scope of application of precision filtration membranes is expanding more and more, and use at high temperatures is particularly strongly desired.

On the other hand, depending on the use of the microfiltration membrane, the membrane itself cannot be allowed to be contaminated with microorganisms such as bacteria and mold, and in that case, it is sterilized by some method.

Sterilization methods include drugs such as ethylene oxide, formalin, and hydrogen peroxide, radiation such as R-rays, steam heating, and psychokinesis, but the steam heating method is the most desirable in terms of effectiveness and simplicity. Normally 121℃ by heating method
A condition of approximately 30 minutes is adopted.

[Problem that the invention seeks to solve]

However, porous membranes made of polyethylene and polypropylene undergo significant heat shrinkage, and when these porous membranes are heat-treated or used at high temperatures, their water or air permeability decreases dramatically, making them difficult to function as a separation membrane. decreases.

In view of this situation, the present inventors have conducted research on a porous membrane that can withstand use and heat treatment at such high temperatures while taking advantage of the features of porous membranes made of polyethylene or polypropynon, and have developed the present invention. I hope it's completed.

[Ninth Means for Solving the Problems] The gist of the present invention is that styrene, α
- A porous membrane holding a crosslinked polymer of divinylbenzene and a polymerizable monomer of 1 m or more consisting of methylstyrene, and styrene, A method for producing a porous membrane imparted with heat resistance, characterized by carrying out thermal polymerization in a state in which one or more polymerizable monomers consisting of α-methylstyrene and monomers such as divinylbenzene t-f are retained.

Divinylbenzene used in the present invention refers to divinylbenzene that is normally available industrially, but it may be of higher purity. Examples of industrially available divinylbenzene include divinylbenzene 55-6096. It is a mixture of 35-40% ethylvinylbenzene and 10 qb or less of saturated compounds.

In the present invention, one of the crosslinked polymers used is heat resistance,
This is because the hydrolysis resistance in hot water was considered. Ester-based crosslinked polymers such as acrylic methacrylate crosslinked polymers have poor hydrolysis resistance in hot water, so the porous membrane does not have sufficient heat resistance. cannot be assigned gender.

Hereinafter referred to as divinylbenzene t-ri bridge monomer,
Polymerizable monomers and crosslinking monomers are collectively referred to as "septumers."

In the present invention, the polyethylene or polypropylene porous membrane (hereinafter simply referred to as "porous membrane") includes hollow fiber membranes,
Any form of membrane, such as a flat membrane or a tubular membrane, can be used, and membranes with various pore diameters can be used depending on the application.
00μm, porosity is approximately 20-90m, water permeability by alcohol hydrophilization method is α001-1017m"
shr Working sw+Hg degree, pore diameter 101~5a
Examples include those of about m.

Various pore structures can be used for the porous membrane, but
Among these, a porous membrane obtained by a method of melt shaping and stretching is preferably used because the crosslinked polymer can be easily held and the porosity is large so that there is little performance deterioration due to clogging tb. This porous membrane has a pore structure in which slit-like microspaces (pores) formed by microfibrils and knots communicate with each other in three dimensions. It can be produced by the psychokinetic method described in Publication No. 56-52123, Japanese Patent Application Laid-open No. 57-42919, etc.

Further, as the form of the porous membrane, a hollow fiber type is preferably used because the membrane area per unit volume is large.

In the porous membrane of the present invention, at least a part of the surface of the porous membrane on which the crosslinked polymer is retained refers to a part or all of the pore surface and the outer surface.

That is, it is sufficient that the crosslinked polymer is retained so that the heat resistance is substantially improved, and it is not necessary that the crosslinked polymer be retained on all surfaces.

The f of the crosslinked polymer retained on the surface depends on the porosity and pore diameter of the porous membrane, and can be selected appropriately depending on the balance between the required heat resistance and membrane permeability. The weight ratio may be approximately 1 to 150% by weight, preferably approximately 5 to 120% by weight, and more preferably 10 to 100% by weight relative to the weight of the membrane. 20~ below 121℃
In response to the requirement of suppressing shrinkage during steam heat treatment for about 30 minutes, it is sufficient that the weight ratio is about 1 to 40 per weight of the crosslinked polymer. However, when using a hollow fiber membrane for a long period of time at high temperatures, such as passing hot water over 70°C for a long period of time, especially when using a hollow fiber membrane by the external pressure method, the filtration pressure increases over time. The permeation performance decreases due to the collapse and flattening of the hollow fiber membrane configuration. Therefore, such high temperatures
When used for long periods of time under high overpressure, it is preferred that the crosslinked polymer be retained even more. It should be noted that as the amount of crosslinked polymer retained increases, the permeation performance decreases to some extent due to the decrease in pore volume, but this is outweighed by the advantage of being usable at high temperatures and high filtration pressures.

If the amount of crosslinked polymer retained is less than 1%, the heat resistance of the porous membrane will be insufficient, and if it exceeds 150%, sufficient permeation performance will not be exhibited, so neither is practical.

The composition ratio of the polymerizable heptamer and the crosslinkable monomer constituting the crosslinked polymer is not particularly limited, and is approximately 98/2 to 2/98.
(parts by weight) may be sufficient.

Retained means that it does not easily come off during storage or use.
It means that the cross-linked polymer is tightly bonded to the pore surface to some degree, but the cross-linked polymer may be chemically bonded to the pore surface, or the cross-linked polymer is tightly bonded to the pore surface. They may be closely attached to each other by an anchor effect, or may be held together by a chemical bond or an anchor effect.

In particular, when a porous membrane made porous by the above-mentioned melt-forming and stretching method is used, a crosslinked polymer is formed to wrap around the microfibrils and can be held firmly. It is preferable to use a material made porous by a method of melt-forming and then stretching.

Next, a method for producing a nine-porous membrane imparted with heat resistance according to the present invention will be described.

In the present invention, various methods can be employed to retain the polymer on the pore surface of the porous membrane. If the animal is grown, a solution can be prepared by dissolving monomers or a polymerization initiator if necessary in a suitable solvent, and a porous membrane can be immersed in the solution, or a membrane module can be produced using the porous membrane. After that, a method can be adopted in which the solution is impregnated into the porous membrane by pressurizing the solution into the porous membrane, and then the solvent is removed by volatilization.

By using a solution diluted with a solvent, monomers can be deposited almost uniformly over the entire porous membrane without blocking the pores of the porous membrane. In addition, the amount of the monomers attached can be adjusted by changing the concentration of the monomers in the solution and the peeling rate during immersion.

When preparing the above solution, an organic solvent is used that has a boiling point lower than that of the monomers and is capable of dissolving the heptamers, but when adding a polymerization initiator, the polymerization initiator is It is preferable to use a solvent that can dissolve both.

Such organic solvents include methanol, ethanol,
Examples include alcohols such as propatool and impropatool; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as tetrahydrofuran and dioxa v; ethyl acetate and chloroform.

The boiling point of the organic solvent is not particularly limited, but in view of ease of solvent removal before the polymerization step, it is preferably about 100°C or less, more preferably about 80°C or less.

The composition of the monomers and the solvent in the solution may be selected appropriately taking into consideration the type of solvent and the target amount of crosslinked polymer retained, etc., and the proportion of the solvent is 5 parts by weight per 100 parts by weight of the monomers.
The amount may be about 10,000 to 10,000 parts by weight, and more preferably about 50 to 5,000 parts by weight.

The immersion time or press-fitting time when dipping or press-fitting a porous membrane using these solutions is approximately α5.
It takes about 10 seconds to 30 minutes, and can be carried out in a much shorter time using a seed solution with good wetting properties for the porous membrane.

In this manner, the porous membrane, which retains the monomers and the polymerization initiator on at least a portion of its surface, is subjected to a polymerization step after removal of excess liquid around it. Note that the solvent inside the pores can be removed by evaporation before or during polymerization.

In the present invention, thermal polymerization method, photopolymerization method, radiation polymerization method,
A polymerization method such as a plasma polymerization method can be employed, and a known polymerization initiator can be used.

In the case of a thermal polymerization method, it is desirable that the polymerization temperature is higher than the decomposition temperature of the polymerization initiator and lower than the temperature that does not change the membrane structure of the porous membrane and damage the membrane substrate. A temperature of about 50 to 100°C can be employed. The heating time depends on the type of polymerization initiator and the heating temperature, but in the patch method it is usually about 1 minute to 5 hours, preferably about 15 minutes to 3 hours. Further, since the heat transfer efficiency is high in a continuous method, polymerization can be carried out in a shorter time, and the heating time is usually about 10 seconds to 60 minutes, preferably about 20 seconds to 10 minutes.

In the case of the photopolymerization method, ultraviolet rays or visible light can be used as the light source for light irradiation, and the ultraviolet ray sources include low-pressure mercury lamps,
High-pressure mercury lamps, xenon lamps, arc lamps, etc. can be used.

As for the light irradiation conditions, for example, when using a mercury lamp as a light source, the input should be about 10 to 500 W/cm.
From a distance of ~50 am (by irradiating for about L5~300 seconds, α001 ~ 10 jouie / 51
``It's about 105~1jou'le/c.''
A condition of irradiating energy of about 100 yen (vm) is adopted.

In the case of radiation polymerization, for example, using an electron beam irradiation device, 1
This can be carried out by irradiating with an electron beam f:lo to about 50 Mrad at a temperature of 20° C. or lower, preferably 100° C. or lower.

In addition, during these polymerizations, the presence of oxygen in the atmosphere will significantly inhibit the polymerization reaction, so it is best to carry out the polymerization in an inert gas atmosphere such as a nitrogen atmosphere, or in a state in which oxygen is substantially absent, such as in a vacuum. desirable.

Although various polymerization methods can be employed in accordance with the present invention as described above, a method using thermal energy is most preferred. When using thermal energy, the pores of the porous membrane can be heated to a uniform temperature, so monomers can be uniformly polymerized on all pore surfaces where monomers are held, and the polymerization temperature can be maintained evenly. By appropriately setting , there is an advantage that polymerization can be carried out without changing the structure of the membrane and without causing deterioration of the membrane substrate. On the other hand, when using light energy, there is a problem that light scattering makes it difficult for light to reach the pores of a porous membrane, and that increasing the intensity of light irradiation tends to cause deterioration of the membrane substrate. Furthermore, when using radiation energy, there is a problem in that the membrane substrate tends to deteriorate. Therefore, when employing these polymerization methods, it is necessary to carefully select polymerization conditions that will not deteriorate the membrane substrate.

Since the monomers held on the surface of the porous membrane are polymerized and crosslinked by these polymerization techniques, at least a portion of the surface of the porous membrane is coated with these crosslinked polymers.

After the crosslinked polymer is generated, use an appropriate cleaning solvent as necessary to remove unreacted monomers and free polymers that exist around the pore surface and outer surface of the porous membrane by dipping or press injection. It is desirable to remove the components.

Each step has been explained separately above, but in the present invention, retention of monomers etc. on the surface of the porous membrane, solvent removal, polymerization, washing after polymerization, etc. are carried out continuously in 1-1-1. You can also do that.

〔Example〕

The present invention will be specifically explained below using examples.

In addition, in the examples, slit-like spaces (pores) formed by the microfibrils and knots obtained by a method of melt-forming and then stretching the porous membranes are connected three-dimensionally to form nine pores. A porous membrane is used, and the pore diameter of the porous membrane is expressed by the average width and length of the slit-like spaces.

Also, be sure to use commercial grade divinylbenzene with a purity of about 55 to 60 yen.

The retained amount of the crosslinked polymer was determined by a dissolution fractionation method in which the porous membrane was dissolved under refluxing tetralin, and expressed as the weight relative to the porous membrane. In addition, water permeability and pressure resistance are determined when the effective membrane area is 1
The measurement was carried out by the following method using a 65cym'' test membrane module.

(1) Water permeability: Ethanol from one side of the test membrane module (inside the hollow fiber membrane in the case of a hollow fiber membrane)
/min for 15 minutes to thoroughly wet the inside of the pores of the porous membrane with ethanol, and then add water to 100 ml of water.
d/Win for 15 minutes to replace the ethanol present inside the pores with water. 25℃ from one side of the test membrane module (inside of the hollow fiber in case of hollow fiber)
The permeated water Jllt- was measured at a transmembrane pressure difference of 50-Hg by flowing water, and from that value the water permeability (1/-・hr
・111g).

(2) Only the pressure-resistant hollow fiber porous membrane is measured. By the external pressure method] water at 90°C is permeated while increasing the filtration pressure at a rate of α5 151" per minute, and the point where the dependence of the water permeability on the filtration pressure changes rapidly (point M in Figure 1). Measure the filtration pressure corresponding to F! and take it as the positive pressure withstand pressure.

(3) Pressure resistance properties over time: Measured only for hollow fiber porous membranes. Using the external pressure method, water at 90°C was permeated for t-1 hours at a filtration pressure of 5 kll/cya", and the change in the amount of permeated water over time was measured, and the value was determined based on the water permeability rate CL/m8・hr・-Bg)
Find the change over time.

Example 1 Width of slit-like pores as a porous membrane (L8 μm, length 2.2 μm, porosity 70s, membrane thickness 55 μm, inner diameter 27
0μm1 Water permeability by alcohol hydrophilization method (25℃)
A polyethylene porous hollow fiber membrane having a temperature of 4.617 m"-hr .wHg was used. The hollow fiber [t-styrene 5
0 parts, 25 parts of mixed monomers with a composition ratio of 50 parts of divinylbenzene, benzoyl peroxide (1025 parts, 'acetone 1 part)
After immersing it in a solution consisting of 0.00 parts for 10 seconds, it was taken out from the solution and air-dried for 30 minutes at room temperature to volatilize and remove the acetone. Next, the cymonomers were polymerized by heating at 60° C. for 2 hours in a nitrogen atmosphere.

The amount of crosslinked polymer retained in the porous membrane thus obtained was 258, and the water permeability was 45 L/m"・hr-samH.
g, and the pressure resistance was 55 kg/eta.

When the pressure resistance characteristics of this porous membrane were measured over time, the water permeability tended to decrease slightly (Figure 2). Furthermore, when this porous membrane was heat-treated with steam at 121°C for 30 minutes, there was no change in morphology, and the water permeability after heat treatment was 4.5L/m.
”・hr・−11 g, which was equivalent to the value before heat treatment.

Example 2 A porous membrane was prepared under the same conditions as in Example 1 using a solution consisting of 40 parts of a mixed monomer with a composition ratio of 50 parts of styrene and 50 parts of divinylbenzene, 104 parts of benzoyl peroxide, and 100 parts of acetone. I got it. The retention amount of the porous membrane crosslinked polymer thus obtained was 62.5%, and the water permeability was 4.
．． O1/m" ・hr ・wxHg, pressure resistance frl
4.5 kg 7 cm"] and has good pressure resistance over time.
19 (Figure 2).

Further, when this membrane was heat-treated with steam at 121° C. for 30 minutes, there was no change in morphology and no change in water permeability.

Comparative Example 1 The same polyethylene porous hollow fiber membrane as used in Example 1 was measured for pressure resistance and pressure resistance characteristics over time.

The pressure resistance is extremely low at α5 kg/cra, and the pressure resistance characteristics over time are poor and poor as shown in Figure 2.

Also, when steam heat treated at 121℃, crimp occurs.
The water permeability decreased to 2.8t/-.hr.11g.

[Effects of the Invention] As is clear from the results of the Examples, the porous membrane of the present invention has significantly improved heat resistance as compared to ordinary polyethylene porous membranes and polypropynon porous membranes.

That is, the porous membrane in which the crosslinked polymer of the present invention is retained is 9
It has high pressure resistance in hot water at 0°C, and there is almost no change in form or decrease in water permeability even after steam treatment at 121°C.

Therefore, the porous membrane of the present invention can be applied to membrane separation applications that require steam sterilization in the medical, food, and fermentation industries, as well as in high-temperature water treatment such as polysaccharide purification and condensate treatment in power plants. can be applied.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of pressure resistance measurement, and FIG. 2 is a diagram showing measurement results of pressure resistance characteristics over time. blue 1 mouth

Claims (2)

[Claims] (1) A porous membrane comprising a crosslinked polymer comprising one or more polymerizable monomers such as styrene or α-methylstyrene and divinylbenzene held on at least a portion of the surface of a porous membrane comprising polyethylene or polypropylene. (2) Carrying out thermal polymerization while retaining one or more polymerizable monomers such as styrene and α-methylstyrene and monomers containing divinylbenzene on at least a portion of the surface of a porous membrane made of polyethylene or polypropylene. A method for producing a porous membrane imparted with heat resistance, characterized by: