TW201325695A - Method for fabricating filter material - Google Patents

Abstract

A method for fabricating a filter material includes the following steps. A polyvinyl alcohol solution and a thermal cross-linking agent are provided, wherein the thermal cross-linking agent is a blocked isocyanate. The polyvinyl alcohol solution and the thermal cross-linking agent are evenly mixed to form a mixture solution, and the ratio of the polyvinyl alcohol solution and the thermal cross-linking agent is between 100: 1 and 2: 1. The mixture solution is put into a spinning device to perform an electro-spinning process to form a plurality of nano-fibers. A hot-press treatment process is performed to the nano-fibers so as to form the filter material.

Description

Method for manufacturing filter material

The present invention relates to a method for producing a filter material, and more particularly to a method for producing a high-performance filter material.

In order to improve the quality of people's lives, there are various ways to make air filters. Every technological change brings significant improvements to people's indoor air quality. In general, air filters are classified according to purification techniques: high efficiency Particulate Air Filter (HEPA), activated carbon air filter, negative ion air filter, and the like.

HEPA technology is one of the hottest technologies in air filters. HEPA air filter is mainly used to remove particles with a particle size of 0.3 microns or more, and the filtration efficiency can be as high as 99.97% or more according to the dust counting method. In addition, "pressure loss" (pressure loss) is also an evaluation indicator for filter materials. The definition of pressure loss is that when the airflow passes through the filter, the filter will form a resistance to the airflow and the air volume will decrease. When the pressure loss is larger, the filter needs to input more power to reach the air volume that is scheduled to be delivered, that is, the more energy is consumed.

At present, most of the HEPA filters on the market use glass fiber filter materials made by wet-laid process. However, glass fibers have problems such as high density, high air resistance, poor alkali resistance, brittleness, high melting point, and skin irritation. Therefore, the waste after use is difficult to be treated by combustion, resulting in many environmental problems in recycling.

The invention provides a method for manufacturing a filter material, which is simple in process and suitable for manufacturing a filter material of HEPA grade.

The present invention provides a method of producing a filter material comprising the following steps. First, a polyvinyl alcohol solution and a thermal crosslinking agent are provided, wherein the thermal crosslinking agent is a blocked isocyanate. The polyvinyl alcohol solution is uniformly mixed with the thermal crosslinking agent to form a mixed solution, and the ratio of the polyvinyl alcohol solution to the thermal crosslinking agent is between 100:1 and 2:1. The mixed solution is placed in a spinning device to perform an electrospinning process to form a plurality of nanofibers. These nanofibers were subjected to a hot pressing process to form a filter material.

In an embodiment of the invention, the blocked isocyanate is as shown in formula (1):

Wherein R1 represents a substituent as shown below:

R2 represents a substituent shown below: -CH ₃ , -(CH ₂ )nX, -OCH(CH ₃ )(CH ₂ )nX, -((CH ₂ )nNH ₂ ), -((CH ₂ )nOH) , -((CH ₂ )nC ₆ H ₄ )-X, -((CH ₂ )nC ₆ H ₄ (CH ₂ )y)-X, -((CH ₂ )nNH(CH ₂ )y)-X, -(CH ₂ CH(CH ₃ )-X, -(CH ₂ CH(CH ₃ )CH ₂ -X, -CH ₂ CH ₂ CH(CH ₂ CH ₃ )CH ₂ CH ₂ CH ₂ -X, wherein, n =1~50, y=1~50, X=F, CH ₃ , H.

In an embodiment of the invention, the polyvinyl alcohol in the polyvinyl alcohol solution has a molecular weight of from 15,000 to 120,000.

In an embodiment of the invention, the polyvinyl alcohol in the polyvinyl alcohol solution has a molecular weight of from 75,000 to 80,000.

In an embodiment of the invention, the ratio of the polyvinyl alcohol solution to the thermal crosslinking agent is between 40:1 and 2:1.

In an embodiment of the invention, the polyvinyl alcohol solution has a concentration of from 3% to 30% by weight.

In an embodiment of the invention, the ratio of the above thermal crosslinking agent to the mixed solution is from 0.1% to 30% by weight.

In an embodiment of the invention, the nanofibers have an average diameter of nm1000 nm after the hot pressing procedure described above.

In an embodiment of the invention, the temperature of the hot pressing process is ≦250 °C.

In an embodiment of the invention, the hot pressing process has a time of ≦10 minutes.

Based on the above, the method for producing a filter material of the present invention adds a thermal crosslinking agent to form a nanofiber having excellent hydrolysis resistance. Further, the method for producing a filter material of the present invention further includes a hot pressing process to form a filter material, thereby further providing the filter material with good tensile strength and fit. Further, the above filter material has a good filtration effect and a low pressure loss. As such, the filter material described above will be suitable for use in high efficiency particulate filter (HEPA) filtration materials.

The above described features and advantages of the present invention will be more apparent from the following description.

1 is a schematic view showing a manufacturing process of a filter material according to an embodiment of the present invention. Referring to FIG. 1, first, step S10 is performed to provide a polyvinyl alcohol solution and a thermal crosslinking agent.

The polyvinyl alcohol in the above polyvinyl alcohol solution has a molecular weight of from 15,000 to 120,000. Preferably, the polyvinyl alcohol in the polyvinyl alcohol solution has a molecular weight of from 75,000 to 80,000. Further, the concentration of the polyvinyl alcohol solution is from 3% to 30% by weight. In detail, the polyvinyl alcohol solution includes a polyvinyl alcohol molecule and a solvent. The above concentration refers to the weight percent concentration of the solute in the solution. It is explained here that the polyvinyl alcohol solution is an aqueous phase solution which does not require the use of an organic solvent as a solvent. Further, the filter material made of polyvinyl alcohol molecules can be treated by combustion after use. Therefore, there is no problem that recycling is difficult.

The above thermal crosslinking agent is, for example, a blocked isocyanate. In the present embodiment, the above blocked isocyanate is represented by the formula (1):

R1 represents a substituent as shown below:

Wherein R2 represents a substituent represented below: -CH ₃ , -(CH ₂ )nX, -OCH(CH ₃ )(CH ₂ )nX, -((CH ₂ )nNH ₂ ), -((CH ₂ ) nOH), -((CH ₂ )nC ₆ H ₄ )-X, -((CH ₂ ) nC ₆ H ₄ (CH ₂ )y)-X, -((CH ₂ )nNH(CH ₂ )y)- X, -(CH ₂ CH(CH ₃ ))-X, -(CH ₂ CH(CH ₃ )CH ₂ )-X, -CH ₂ CH ₂ CH(CH ₂ CH ₃ )CH ₂ CH ₂ CH ₂ -X , where n=1~50, y=1~50, X=F, CH ₃ , H. Wherein the R2 substituent is preferably -(CH ₂ )nX or -(CH ₂ CH(CH ₃ ))-X.

Then, in step S20, the polyvinyl alcohol solution and the thermal crosslinking agent are uniformly mixed to form a mixed solution, wherein the weight ratio of the polyvinyl alcohol solution to the thermal crosslinking agent is between 100:1 and 2:1. In a preferred embodiment, the ratio of polyvinyl alcohol solution to thermal crosslinker is between 40:1 and 2:1. According to this embodiment, the proportion of the thermal crosslinking agent in the mixed solution is from 3% to 30% by weight.

Next, in step S30, the mixed solution is placed in a spinning device to perform an electrospinning process to form a plurality of nanofibers. Here, the textile device and the electrospinning program can employ both existing and known textile devices as well as electrospinning parameters.

Finally, in step S40, the nanofibers are subjected to a hot pressing process to form a filter material. It should be noted that, in the present embodiment, after performing the above hot pressing procedure, the average diameter of the nanofibers is ≦1000 nm. These nanofibers are folded and stacked on each other to form a structure having a small pore size, and thus can be used to filter fine particles with a relatively good filtering effect. Further, the hot pressing procedure described above was carried out for 10 minutes, and the temperature of the hot pressing procedure was °250 °C.

It is explained here that the blocked isocyanate is stable at normal temperature. When the blocked isocyanate is heated above 90 ° C, it will begin to be reactive and the nanofibers will be crosslinked together by covalent bonding. In this way, the nanofiber can have hydrolysis resistance. More importantly, when the nanofibers are subjected to hot pressing treatment, the nanofibers are covalently bonded and crosslinked with the crosslinking agent to form a hydrolysis resistance, and the fibers can be bonded to each other in addition to the fibers. The tight bonding between the fibers can also increase the adhesion between the nanofibers and the substrate, and further enhance the tensile strength.

In order to explain in more detail the manufacturing method of the filter material according to the present invention and its advantages, the following will be explained by the production process of the example and the experimental results.

Instance

In this example, the polyvinyl alcohol used has a molecular weight of between 75,000 and 80,000, the polyvinyl alcohol is dissolved in water, and the concentration of the polyvinyl alcohol solution is adjusted to 8% by weight. Further, the thermal crosslinking agent used in this example is a blocked isocyanate represented by the formula (1).

Where R1 is . R2 is -((CH ₂ ) ₃ C ₆ H ₄ H)-.

Next, the above polyvinyl alcohol solution and blocked isocyanate were uniformly mixed into a mixed solution at a room temperature of 20:1. This mixed solution was further subjected to an electrospinning process to form a plurality of nanofibers having an average diameter of ≦250 nm. After collecting the nanofibers, a hot pressing procedure was carried out in which the hot pressing time was 3 minutes and the hot pressing temperature was 250 ° C or less. So far, the production of the filter material of this example was completed.

Further, the filter materials of Comparative Example 1 and Comparative Example 2 were synthesized and described as a control for hydrolysis resistance test. Table 1 shows the synthesis conditions and hydrolysis resistance test results of the examples, Comparative Example 1 and Comparative Example 2.

As can be seen from Table 1, the mixing conditions of the present example did not require heating and did not require additional reaction time compared to the mixing conditions of Comparative Example 1. In addition, the hot pressing procedure in the subsequent processing in this example can be completed in only 3 minutes. More importantly, compared with the process of Comparative Example 2, since the filter material of the present example was added with a thermal crosslinking agent, the hydrolysis resistance was good. In other words, when air passes through the filter material during the use of the filter material, the moisture contained in the air does not cause loss of the filter material. Therefore, the filter material of the present example is suitable for use in an air filter.

The filter efficiency and pressure loss of the filter material of this example were tested in the following. In order to illustrate the advantages of the filter material of this example, the filter material of Comparative Example 3 was additionally used as an alignment. The process conditions of the filter material of Comparative Example 3 were substantially the same as those of the present example, wherein Comparative Example 3 was different from the present example in that the blocked isocyanate was not added in the process of Comparative Example 3, and the polyvinyl alcohol solution was electrospun separately. The procedure formed nanofibers and the nanofibers were not subjected to a hot pressing procedure.

In addition, for the filter effect and pressure loss test of the filter material of the present example, in addition to testing the conditions of the non-immersion water, the filter material after 60 days of water immersion is tested to further understand the filter material of the present example after immersion in water. The effect. Table 2 shows the filtration efficiency and pressure loss test results of the examples and Comparative Example 3.

It can be seen from Table 2 that the filter material of the present example can achieve the filtration efficiency of the HEPA grade filter material after the hot pressing process. Moreover, after the hot pressing, although the pressure loss of the filter material of the present example is slightly improved, it still meets the pressure loss regulation of the HEPA grade filter material. More importantly, the filter material of this example has good hydrolysis resistance, so the same filtration efficiency and pressure loss can be maintained after 60 days of water immersion.

Further, the tensile strength of the filter material of the present invention will be described. In general, nanofibers prepared by electrospinning have low tensile strength, so they are easily broken and cannot be used in the process of air filter. In order to increase the tensile strength, the production method of the present invention enhances the strength of the nanofiber by adding a thermal crosslinking agent. Fig. 2 is a graph showing the relationship between stress and strain of the filter material of Comparative Example 3 and the filter material of the present example. It should be noted that "stress" refers to the amount of force applied to the fiber membrane to pull outward. "Strain" refers to the deformation of the fiber membrane caused by stress. Among them, the direction of the tensile force of the stress is further divided into a longitudinal direction (MD) and a lateral direction (CD). Table 3 shows the longitudinal and transverse tensile strength test results for the examples. It should be noted that "tensile strength" refers to the stress when the fiber membrane is pulled to break.

2 and Table 3, the tensile strength of the filter material to which the thermal crosslinking agent is added has a small difference in strength between the longitudinal direction and the lateral direction. In other words, the filter material of the present example has a uniform tensile effect, so that the filter material is not easily broken in one direction. In addition, the stress of the filter material (example) subjected to the hot pressing procedure was increased by more than three times as compared with the filter material without the hot pressing procedure (Comparative Example 3). Specifically, when the nanofibers are subjected to a hot pressing process, the nanofibers are bonded to each other, thereby forming a denser filter material and thus having a better tensile strength. In this way, the filter material having better tensile strength can be practically applied to the manufacture of the air filter material.

It is worth mentioning that the hot pressing process can increase the fit of the nanofibers to the substrate (for example, non-woven fabric). In general, the filter material that has not been subjected to the hot pressing process has poor adhesion to the non-woven fabric, and therefore is joined by using a press point. However, the way of pressing the dots causes a problem of a reduction in the filtration area. Further, the adhesion between the filter material and the non-woven fabric obtained by the method for producing a filter material according to the present invention is good, and the problem of a reduction in the filtration area due to the pressure point method can be avoided, and the production can be facilitated.

As described above, in the method for producing a filter material of the present invention, a thermal crosslinking agent is added to form a nanofiber having excellent hydrolysis resistance. Further, the method for producing a filter material of the present invention further comprises a hot pressing process of heating the nanofibers to form a filter material. By this hot pressing procedure, the filter material of the present invention has a relatively good tensile strength and good fit, thereby making the filter material of the present invention suitable for practical production applications of air filters. More importantly, the method for producing a filter material according to the present invention is simple, and the filter material produced thereof has a relatively high filtration effect and a low pressure loss. As such, the filter material described above will be suitable for use in high efficiency particulate filter (HEPA) filtration materials.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

S10, S20, S30, S40. . . step

1 is a schematic view showing a manufacturing process of a filter material according to an embodiment of the present invention.

Figure 2 is a graph showing stress versus strain for a comparative example and an example of the present invention.

S10, S20, S30, S40. . . step

Claims (10)

A method for producing a filter material, comprising: providing a polyvinyl alcohol solution and a thermal crosslinking agent, wherein the thermal crosslinking agent is a blocked isocyanate; uniformly mixing the polyvinyl alcohol solution with the thermal crosslinking agent to form a a mixed solution, wherein the ratio of the polyvinyl alcohol solution to the thermal crosslinking agent is between 100:1 and 2:1; the mixed solution is placed in a spinning device to perform an electrospinning process to form a plurality of nanometers Fibers; and subjecting the nanofibers to a hot pressing process to form the filter material. The method for producing a filter material according to claim 1, wherein the blocked isocyanate is represented by the formula (1): Wherein R1 represents a substituent as shown below: R2 represents a substituent shown below: -CH ₃ , -(CH ₂ )nX, -OCH(CH ₃ )(CH ₂ )nX, -((CH ₂ )nNH ₂ ), -((CH ₂ )nOH) , -((CH ₂ )nC ₆ H ₄ )-X, -((CH ₂ )nC ₆ H ₄ (CH ₂ )y)-X, -((CH ₂ )nNH(CH ₂ )y)-X, -(CH ₂ CH(CH ₃ )-X, -(CH ₂ CH(CH ₃ )CH ₂ -X, -CH ₂ CH ₂ CH(CH ₂ CH ₃ )CH ₂ CH ₂ CH ₂ -X, wherein, n =1~50, y=1~50, X=F, CH ₃ , H. The method for producing a filter material according to claim 1, wherein the polyvinyl alcohol in the polyvinyl alcohol solution has a molecular weight of from 15,000 to 120,000. The method for producing a filter material according to claim 3, wherein the polyvinyl alcohol in the polyvinyl alcohol solution has a molecular weight of from 75,000 to 80,000. The method for producing a filter material according to claim 1, wherein the ratio of the polyvinyl alcohol solution to the thermal crosslinking agent is from 40:1 to 2:1. The method for producing a filter material according to claim 1, wherein the polyvinyl alcohol solution has a concentration of from 3% to 30% by weight. The method for producing a filter material according to claim 1, wherein the ratio of the thermal crosslinking agent to the mixed solution is from 0.1% to 30% by weight. The method for producing a filter material according to claim 1, wherein the nanofibers have an average diameter of ≦1000 nm after the hot pressing process. The method for producing a filter material according to claim 1, wherein the hot press program has a temperature of °250 °C. The method for producing a filter material according to claim 1, wherein the hot pressing procedure is performed for 10 minutes.