A method for preparing high-efficiency filter paper for masks

Abstract

The present invention provides a method for preparing a high-efficiency filter paper for a mask, comprising the following steps: (1) adding soft water to cellulose pulp to prepare a cellulose pulp suspension having a solid content of 5 to 15%, fibrillating the cellulose pulp suspension, and controlling the beating degree to be 40 to 90°SR; (2) preparing a mixed slurry, wherein the mass of cellulose pulp accounts for 35% to 70%, the mass of nanocellulose accounts for 0.1% to 5%, and the mass of polyester fiber accounts for 25% to 64.9%; (3) placing the mixed slurry obtained in step (2) into a debonding machine for debonding for 1-3 minutes, and molding the debonded mixed slurry; (4) freeze-drying the molded paper. The high-efficiency filter paper for a mask provided by the method of the present invention does not need to add auxiliary agents such as a retention agent, a filler, and a sizing agent, further reduces the respiratory resistance of the material, and makes the product completely degradable, thereby reducing the difficulty of recycling and processing discarded masks.

Description

Technical Field

[0001] The invention belongs to the field of air filtration protection and relates to a method for preparing high-efficiency filter paper for a mask. Background Art

[0002] At present, masks that have a protective filtering effect against dust, bacteria, and viruses are mainly composed of three layers, namely the surface layer, the middle filter layer, and the bottom layer. The middle filter layer is the core component of the mask's filtering effect. Its material is basically non-degradable polymer materials such as polypropylene and polytetrafluoroethylene, which has caused certain harm to the ecological environment.

[0003] Chinese patent document CN104872865A (CN201510300144.3) discloses the use of electrospinning to prepare biodegradable mask filters. In this preparation method, polybutylene succinate is dissolved in hexafluoroisopropanol, and a spinning solution is prepared according to a mass fraction of 20%-35%. However, this electrospinning method for preparing nanofilter paper is not only expensive, but also requires the use of solvents in the process and is not easy to recycle. The production process has serious environmental problems and is not efficient. Cellulose is an abundant natural renewable and degradable biopolymer material. It is widely distributed in higher plants. In addition, it also exists in marine animals, algae, bacteria, fungi and invertebrates.

[0004] Chinese patent document CN108187407A (CN201810042956.6) provides a method for preparing an air filter material, which comprises the following steps: weighing 20 parts by weight of softwood fiber cellulose, deflaking it with a deflaking machine to obtain a fiber suspension with a mass concentration of 10% for standby use, and preparing the air filter material according to the target quantitative 150g / m 2and the diameter of the obtained air filter material: weigh 1.695 to 2.495 parts by weight of the fiber suspension in a beaker, add 100 parts by weight of deionized water to dilute, mechanically stir at 300 rpm for 5 minutes to evenly disperse the fibers, then add 2.12 parts by weight of polyethylene terephthalate, mix evenly, pour the fiber suspension into a culture dish with an inner diameter of 130 mm, drop 0.522 parts by weight of dichloromethane and 1.02 to 2.02 parts by weight of ZIF-8 nanocrystals at -4°C, finally add 2.48 to 12.48 parts by weight of cobalt-based porous MOFs material, place the culture dish in a freezing environment and freeze for 2 to 4 hours to complete the molding of the air filter material, and then place it in a freeze dryer and dry it at -64°C, 10Pa for 48 to 72 hours to obtain the cellulose air filter material. However, the patent uses toxic solvents such as polyethylene terephthalate and methylene chloride, and the production process is not environmentally friendly. After freeze-drying, there are residual solvents in the filter material, which may cause harm to the environment and human body. The preparation process is relatively complicated, and the cost of the raw materials used is high, and most of the materials are non-degradable materials. In addition, the paper quantity of this product is large, which increases the weight of the mask and reduces the wearing comfort.

[0005] Chinese patent document CN 106978767 A (201610034279.4) discloses a method for preparing filter paper for PM2.5 protective masks, comprising the steps of pulping, papermaking, calendering, acid treatment and re-drying; characterized in that the pulped Tencel pulp is used as the main raw material to paper a filter paper substrate with a dense structure; the filter paper substrate is then re-moistened and then put into a super calender to increase the compactness to 0.7-0.8g / cm 3 ; The filter paper substrate after calendering is first treated with dilute acid impregnation, and then deacidified by water immersion, dried and shaped to make filter paper. However, the method adds non-degradable raw materials such as polyamide polyamine epichlorohydrin resin, binary retention system (including cationic polymer and anionic polymer), calcium carbonate filler and PET fiber, which affects the degradability of the filter paper. At the same time, it is a filter paper for PM2.5 protective mask, and the filtration efficiency and filtration resistance of the filter paper prepared by it cannot meet the requirements of relevant performance in "GB2626-2006 Respiratory Protection Products". And its preparation principle is to add calcium carbonate to paper, and use acid to consume calcium carbonate reaction after paper is formed, leaving micropores, and a large amount of acid is used in the process. The sewage generated in the preparation process is more, which is not conducive to the sustainable development of the ecological environment. And due to the lack of thermoplastic materials, the filter paper is used to make masks, and it cannot be heat-sealed or difficult, which is inconvenient to make masks.

[0006] It can be seen that although cellulose is used to make filter materials for masks, which are green and degradable, the current cellulose-based air filter paper still has problems such as low filtration efficiency and high resistance, which cannot meet the standards for use of medical and civilian masks; and the addition of various additives to achieve the filtering effect affects the degradation rate. Summary of the invention

[0007] In order to solve the problems of low degradation rate and filtration efficiency and high breathing resistance of cellulose-based air filter paper in the prior art, a method for preparing high-efficiency filter paper for masks is provided. The high-efficiency filter paper of the present invention can take into account both degradation performance and filtration performance.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a high-efficiency filter paper for a mask comprises the following steps:

[0010] (1) adding soft water to cellulose pulp to prepare a cellulose pulp suspension having a solid content of 5-15%, fibrillating the cellulose pulp suspension, and controlling the beating degree to be 40-90°SR;

[0011] (2) mixing the fibrillated cellulose pulp suspension obtained in step (1) with nanocellulose and polyester fibers to obtain a mixed slurry, wherein the weight of the cellulose pulp, the weight of the nanocellulose, and the weight of the polyester fibers in the mixed slurry solids are controlled to be 35% to 70%, 0.1% to 5%, and 25% to 64.9% respectively;

[0012] (3) placing the mixed slurry obtained in step (2) into a debonding machine for debonding for 1-3 minutes, and subjecting the debonded mixed slurry to molding;

[0013] Preferably, the relief speed in step (3) is 500 r / min.

[0014] Preferably, the molding process in step (3) is to pour the dissolved mixed slurry into a paper sheet former for molding, or to use a paper machine or a rotary screen paper machine for molding.

[0015] (4) The formed paper is freeze-dried at a drying temperature of -55 to -35°C.

[0016] The soft water mentioned in the present invention refers to water containing no or less soluble calcium and magnesium compounds, that is, water with a hardness of less than 8.

[0017] Preferably, the cellulose pulp in step (1) can be one or more of coniferous wood pulp, broadleaf wood pulp, bamboo pulp, tencel fluff pulp, and mercerized pulp, preferably tencel fluff pulp.

[0018] More preferably, the specification of the Tencel staple fiber pulp is 2.5 to 0.1 dtex, and the length is 3 to 49 mm. More preferably, the specification of the Tencel staple fiber is 0.9 dtex, and the length is 5 mm.

[0019] Preferably, the fibrillation treatment in step (1) can be carried out using a PFI beater, a disc mill, a sand mill, a colloid mill, a homogenizer, etc., preferably a PFI beater.

[0020] Preferably, the fibrillated cellulose pulp suspension obtained in step (1) may be a mixture of fibrillated pulps with different beating degrees.

[0021] Preferably, the polyester fiber in step (2) is a biodegradable polyester fiber, which can be one of polylactic acid (PLA) ultrafine fiber, polybutylene adipate and polybutylene terephthalate (PBAT) ultrafine fiber, polycaprolactone (PCL) ultrafine fiber, etc., preferably PLA ultrafine fiber.

[0022] Further preferably, the specification of the polyester fiber in step (2) is 0.1-1.7 dtex, preferably 0.3 dtex.

[0023] Preferably, the nanocellulose in step (2) has a diameter of 2 to 100 nm and an aspect ratio of 100 to 500; preferably 50 to 60 nm and an aspect ratio of 200 to 300.

[0024] Preferably, in step (4), the freeze-drying temperature is -53°C; the pressure is 13-50 Pa, and the drying time is 24-48 hours.

[0025] The present invention also provides filter paper for masks prepared by the above method, wherein the filter paper comprises the following components in mass fractions: 35% to 70% of cellulose pulp, 0.1% to 5% of nanocellulose, and 25% to 64.9% of polyester fibers.

[0026] The mask filter paper is tested for filtration efficiency and resistance of particles with a diameter of 0.3 μm according to GB 2626-2006 Respiratory Protective Equipment, and the filtration efficiency is 90-95%, and the breathing resistance is 121-130 Pa; according to GB / T22927-2008 Mask Paper, the longitudinal wet tensile strength (10 min) is 0.10-0.15 kN / m. The quantitative weight of the mask filter paper in the present invention is 31-32 g / m 2 .

[0027] Beneficial effects of the present invention:

[0028] The method for preparing high-efficiency filter paper for masks provided by the method of the present invention, the usage ratio of the three materials of Tencel fluff pulp, nanocellulose and ester fiber of the present invention makes the filter paper of the present invention still have good strength after moisture absorption. It has the same or similar filtration efficiency and resistance as the melt-blown cloth filter layer conventionally used in the market. At the same time, the filter layer completely filters dust and the like through physical barriers, and will not cause static electricity attenuation due to moisture like the melt-blown cloth filter layer, thereby causing a decrease in filtration efficiency and resistance. Since the present invention has no electrostatic adsorption, it has lower requirements for the storage environment and a longer service life.

[0029] The method of the present invention provides a high-efficiency filter paper for masks, which uses a certain proportion of pulp cellulose and degradable polyester as raw materials, and obtains a mixed slurry by adding a certain amount of nanocellulose. The mixed slurry is directly formed using a former, and no auxiliary agents such as a retention agent, a filler, and a sizing agent need to be added, which further reduces the respiratory resistance of the material, and makes the product completely degradable, reducing the difficulty of recycling and processing discarded masks. The method of the present invention further improves the degradation rate through a freeze-drying treatment method; the freeze-drying conditions of the present invention weaken the fiber displacement, increase the distance between fibers, reduce the bonding points and bonding strength between fibers, and are conducive to maintaining the fluffiness of the structure, thereby facilitating the reproduction of aerobic bacteria and improving the degradation efficiency.

[0030] The high-efficiency filter paper for masks provided by the method of the present invention uses an existing papermaking process for its preparation. The process has high production efficiency and large output, which makes up for the shortcoming of low production efficiency of melt-blown filter layers or electrostatic spinning filter layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a polarizing microscope photograph of the filter material obtained in Example 1.

[0032] Figure 2 This is a polarizing microscope photograph of the filter material obtained in Comparative Example 6. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention is further described below in conjunction with the examples. The materials involved in the following examples can all be obtained from commercial channels. The fibrillation treatment, deflaking, molding treatment and other unrecorded parameters are all conventional operations in the art.

[0034] Example 1

[0035] A method for preparing a high-efficiency filter paper for a mask comprises the following steps:

[0036] (1) Pulp fibrillation treatment

[0037] Weigh 25 g of Tencel short fiber pulp with a specification of 1.7 dtex and a length of 6 mm, add an appropriate amount of soft water, and prepare a pulp mixture with a total solid content of 10%; put the pulp mixture into a PFI refiner for refining and fibrillation treatment to prepare a fibrillated pulp with a beating degree of 60° SR;

[0038] (2) Preparation of mixed slurry:

[0039] Take 5g of the above-mentioned fibrillated pulp with a beating degree of 60°SR, 0.02g of nanocellulose, and 0.48g of ultrafine degradable polyester fiber (polylactic acid (PLA), 0.3dtex), mix them, and put them into a decompressor for decompression for 2 minutes to obtain a mixed slurry; in the solid matter of the mixed slurry, the mass fractions of each are: Tencel staple fiber pulp accounts for 50%, nanocellulose accounts for 2%, and degradable polyester fiber accounts for 48%.

[0040] (3) Molding: Pour the relieved slurry into a molding machine for molding;

[0041] (4) Drying treatment: The formed paper is placed in a freeze dryer at a drying temperature of -53°C and a pressure of 20 Pa for 36 hours to obtain a high-efficiency filter membrane paper for masks.

[0042] Example 2 and Example 3

[0043] A method for preparing a high-efficiency filter paper for a mask, compared with Example 1, the difference is that the beating degree of the pulp fibrillation treatment is changed, and the mass fractions of tencel fluff pulp, nanocellulose, and degradable polyester fiber, as well as the freeze-drying temperature are changed. The specific parameters and the properties of the obtained filter paper are shown in Table 1.

[0044] Example 4

[0045] A method for preparing filter paper for masks, which differs from Example 1 in that the type of cellulose is changed to coniferous wood pulp. The specific parameters and properties of the obtained filter paper are shown in Table 1.

[0046] Example 5

[0047] A method for preparing filter paper for a mask, which differs from Example 1 in that the type of degradable polyester fiber is changed to polycaprolactone (PCL) ultrafine fiber. The specific parameters and properties of the obtained filter paper are shown in Table 1.

[0048] Comparative Example 1

[0049] A method for preparing filter paper for a mask comprises the following steps:

[0050] (1) Pulp fibrillation treatment

[0051] Weigh 50 g of Tencel short fiber pulp with a specification of 1.7 dtex and a length of 6 mm, add an appropriate amount of soft water, and prepare a pulp mixture with a solid content of 10%; put the pulp mixture into a PFI refiner twice by weight for refining and fibrillation treatment, and prepare fibrillated pulps with beating degrees of 40°SR and 60°SR respectively;

[0052] (2) Pulp Forming

[0053] Take 5g of the fibrillated pulp with a beating degree of 60°SR and 5g of the fibrillated pulp with a beating degree of 40°SR, mix them and put them into a debonding machine for debonding for 2 minutes; pour the debonded pulp into a molding machine for molding;

[0054] (3) Drying treatment: The formed paper is placed in a freeze dryer at a drying temperature of -53°C and a pressure of 20 Pa; dried for 36 hours to obtain filter membrane paper for masks.

[0055] Comparative Example 2

[0056] A method for preparing filter paper for a mask comprises the following steps:

[0057] (1) Pulp fibrillation treatment

[0058] Weigh 25 g of Tencel short fiber pulp with a specification of 1.7 dtex and a length of 6 mm, add an appropriate amount of soft water, and prepare a pulp mixture with a total solid content of 10%; put the pulp mixture into a PFI refiner for refining and fibrillation treatment to prepare a pulp with a beating degree of 60° SR;

[0059] (2) Preparation of mixed slurry

[0060] 5 g of the fibrillated pulp with a beating degree of 60° SR and 0.5 g of ultrafine degradable polyester fiber (polylactic acid (PLA), 0.3 dtex) were mixed and put into a debonding machine for debonding for 2 minutes; the mass fractions of the solid matter in the mixed pulp were: 50% of Tencel staple fiber pulp and 50% of degradable polyester fiber;

[0061] (3) Molding: Pour the relieved slurry into a molding machine for molding;

[0062] (4) Drying treatment: The formed paper is placed in a freeze dryer at a drying temperature of -53°C and a pressure of 20 Pa; and dried for 36 hours to obtain a high-efficiency filter membrane paper for masks.

[0063] Comparative Example 3

[0064] A method for preparing filter paper for a mask comprises the following steps:

[0065] (1) Pulp fibrillation treatment

[0066] 2. Weigh 25 g of Tencel short fiber pulp with a specification of 1.7 dtex and a length of 6 mm, add an appropriate amount of soft water, and prepare a pulp mixture with a total solid content of 10%; 2. Put the pulp mixture into a PFI refiner for refining and fibrillation treatment to prepare a pulp with a beating degree of 60° SR;

[0067] (2) Pulp Forming

[0068] 10g of the fibrillated pulp with a beating degree of 60°SR and 1g of ultrafine degradable polyester fiber (polylactic acid (PLA), 0.3dtex) were mixed and put into a debonding machine for debonding for 2 minutes; among the solid matter of the mixed pulp, 50% of the Tencel staple fiber pulp and 50% of the degradable polyester fiber;

[0069] (3) Molding: Pour the relieved slurry into a molding machine for molding;

[0070] (4) Drying treatment: The formed paper is placed in a freeze dryer at a drying temperature of -53°C and a pressure of 20 Pa for 36 hours.

[0071] Comparative Examples 4 to 6

[0072] A method for preparing filter paper for masks, which differs from Example 1 in that the mass fractions of tencel fluff pulp, nanocellulose, and degradable polyester fiber, as well as the freeze-drying temperature are changed. Specific parameters and properties of the obtained filter paper are shown in Table 1.

[0073] Performance Testing

[0074] The prepared filter paper was tested for filtration efficiency and resistance according to GB 2626-2006 Respiratory Protective Equipment. The filtration efficiency refers to the filtration effect on particles with a diameter of 0.3 μm. The longitudinal wet tensile strength (10 min) was tested according to GB / T22927-2008 Mask Paper, ≥0.1 kN / m.

[0075] The test results are shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] As can be seen from Table 1, the freeze-drying conditions selected by the present invention can reduce respiratory resistance and improve filtration efficiency. The plastic biodegradation standard EN13432:2002 meets the requirements of packaging recycling through composting and biodegradation treatment processes. The final acceptance test plan and evaluation criteria of the filter paper of the present invention refer to ISO14855:1999. The final aerobic biodegradability and disintegration capacity of the material under controlled composting conditions are determined by a method of measuring the released carbon dioxide. After 90 days of composting degradation, the relative biodegradability of Example 1 is 94.5%, and the relative biodegradability of Comparative Example 6 is 91.8%. It can be seen from the degradation results of the filter paper obtained by the technical solutions of Example 1 and Comparative Example 6 that the freeze-drying conditions of the present invention can also improve the degradation efficiency. This may be because the freeze-drying conditions of the present invention weaken the fiber displacement, increase the distance between fibers, reduce the bonding points and bonding strength between fibers, and are beneficial to the structure to maintain the fluffiness (attached Figure 1 , Attachment Figure 2 ), which is conducive to the reproduction of aerobic bacteria and improves the degradation efficiency.

[0080] It can be seen from Examples 1 to 5 and Comparative Examples 1 to 5 in Table 1 that the Tencel staple fibers, nanocellulose and polylactic acid fibers of the present invention can improve filtration efficiency and reduce breathing resistance through specific types and ratios. The reasons may be: by fibrillating Tencel, the fiber diameter can reach the micro-nano level, and by adding a certain amount of nanocellulose, micro-nano pores with micro-nano sizes can be prepared; after adding a certain amount of polylactic acid polyester fibers, the bonding points between cellulose fibers are reduced, thereby reducing the filtration resistance.

[0081] In addition, it can be seen from Examples 1 to 5 and Comparative Examples 1 to 5 that the usage ratio of the three materials of the tencel fluff pulp, nanocellulose and ester fiber of the present invention enables the filter paper of the present invention to still have good strength after absorbing moisture.

Claims

1. A method for preparing a high-efficiency filter paper for a mask, characterized in that: The following steps are involved: (1) adding soft water to cellulose pulp to prepare a cellulose pulp suspension having a solid content of 5-15%, fibrillating the cellulose pulp suspension, and controlling the beating degree to be 40-90°SR; (2) mixing the fibrillated cellulose pulp suspension obtained in step (1) with nanocellulose and polylactic acid ultrafine fibers to obtain a mixed slurry, wherein the weight of the cellulose pulp, the weight of the nanocellulose, and the weight of the polylactic acid ultrafine fibers in the mixed slurry are controlled to account for 35% to 70% of the solid matter, 0.1% to 5% of the solid matter, and 25% to 64.9% of the solid matter; (3) placing the mixed slurry obtained in step (2) into a dissolving machine for dissolving for 1-3 minutes, and subjecting the mixed slurry to forming treatment after dissolving; (4) Freeze-dry the formed paper at a drying temperature of -55~-35℃.

2. The method according to claim 1, characterized in that: The soft water in step (1) refers to water with a hardness of less than 8.

3. The method according to claim 1, characterized in that The cellulose pulp in step (1) is one or more of coniferous wood pulp, broadleaf wood pulp, bamboo pulp, tencel short fiber pulp, and mercerized pulp.

4. The method according to claim 3, characterized in that The cellulose pulp in step (1) is tencel fluff pulp.

5. The method according to claim 4, characterized in that The tencel staple fiber pulp in step (1) has a specification of 2.5-0.1 dtex and a length of 3-49 mm.

6. The method according to claim 5, characterized in that The tencel staple fiber in step (1) has a specification of 0.9 dtex and a length of 5 mm.

7. The method according to claim 1, characterized in that The fibrillation treatment in step (1) adopts a PFI beater, a disc mill, a sand mill, a colloid mill, and a homogenizer.

8. The method according to claim 1, characterized in that The fibrillation treatment in step (1) adopts a PFI beater.

9. The method according to claim 1, characterized in that: The fibrillated cellulose pulp suspension obtained in step (1) is a mixture of fibrillated pulps with different beating degrees.

10. The method according to claim 1, characterized in that The specification of the polylactic acid ultrafine fiber in step (2) is 0.1~1.7dtex.

11. The method according to claim 10, characterized in that The specification of the polylactic acid ultrafine fiber in step (2) is 0.3 dtex.

12. The method according to claim 1, characterized in that The nanocellulose in step (2) has a diameter of 2-100 nm and an aspect ratio of 100-500.

13. The method according to claim 1, characterized in that The nanocellulose in step (2) has a diameter of 50-60 nm and an aspect ratio of 200-300.

14. The method according to claim 1, characterized in that The release speed in step (3) is 500 r / min; The molding process in step (3) is to pour the dissolved mixed slurry into a paper sheet former for molding, or to use a paper machine or a rotary screen paper machine for molding.

15. The method according to claim 1, characterized in that In step (4), the freeze-drying temperature is -53°C; the pressure is 13~50Pa, and the drying time is 24~48 hours.

16. A filter paper for a mask prepared by the method according to any one of claims 1 to 15.

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