A polyvinyl alcohol dustproof film, its preparation method and application

Abstract

This invention provides a polyvinyl alcohol (PVA) dustproof film, its preparation method, and its applications. The PVA dustproof film comprises a PVA base film and dustproof functional molecules grafted onto the surface of the PVA base film via ultraviolet light initiation. The PVA base film has a crystallinity of ≥20%, a haze of 0.1-10%, and a light transmittance of ≥85%. This invention connects the dustproof functional molecules to the film surface through chemical bonds, resulting in a longer effective period. Compared with existing technologies, the dustproof film of this invention simultaneously possesses high light transmittance, low haze, and excellent dustproof performance, and can be used as a greenhouse film with high light transmittance and excellent dustproof performance.

Description

Technical Field

[0001] This invention relates to the field of photocuring, and more specifically, to a polyvinyl alcohol dustproof film, its preparation method, and its application. Background Technology

[0002] In the application of agricultural greenhouse films, polyethylene (PE) film remains the most widely used type of greenhouse film in my country. However, it still has certain shortcomings. One prominent issue is the low light transmittance of PE film. Furthermore, due to its low polarity, PE film easily generates and accumulates static electricity, attracting dust from the environment to its surface. This reduces light transmittance and light intensity inside the greenhouse, affecting crop growth and reducing yield. This effect accumulates over time. my country experiences frequent and high-concentration dust storms, making it particularly vulnerable to this problem. Therefore, developing a new type of greenhouse film with high light transmittance, high polarity, and long-lasting dustproof function is of paramount importance.

[0003] Polyvinyl alcohol (PVA) is a general-purpose functional polymer material obtained by saponification and alcoholysis of polyvinyl acetate, which is produced by the polymerization of vinyl acetate. Due to its excellent optical properties, PVA is used in polarizing films and high-transparency packaging films. Furthermore, biaxial stretching can significantly improve the barrier properties and light transmittance of PVA films. Biaxial stretching offers advantages such as high stretch ratio (transverse stretch ratio can reach over 10 times), fast forming speed (maximum winding speed can reach hundreds of meters per minute), high production efficiency, and the resulting films possess high mechanical strength and high transparency.

[0004] To achieve long-lasting dustproof properties on greenhouse film surfaces, silicon- or fluorine-containing materials can be grafted onto polyolefin materials through a chemical reaction. Because the dust-repellent molecules containing silicon or fluorine have low surface energy, the grafted film surface exhibits stain resistance and a "self-cleaning" effect. Chinese patent CN111098576A describes using reactive extrusion to graft dust-repellent molecules onto polyethylene material, followed by single-screw blow molding to obtain a polyethylene dustproof greenhouse film with the grafted dust-repellent molecules. However, this patent uses reactive extrusion for chemical grafting, resulting in a significant portion of the dust-repellent molecules being distributed within the polyethylene film rather than on the surface, requiring a relatively large molecular weight of dust-repellent molecules. Furthermore, the haze of the grafted dustproof greenhouse film in this patent remains relatively high, between 10-15%. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a highly transparent polyvinyl alcohol (PVA) dustproof film with excellent dustproof performance, its preparation method, and its applications. The dustproof functional monomers are grafted onto the surface of the PVA-based film via chemical bonds using ultraviolet light initiation. Simultaneously, the high transparency of the biaxially oriented PVA film is utilized, resulting in a film that possesses both excellent dustproof performance and high transparency.

[0006] One objective of this invention is to provide a polyvinyl alcohol dustproof film, comprising a polyvinyl alcohol base film and dustproof functional molecules grafted onto the surface of the polyvinyl alcohol base film by ultraviolet light initiation; wherein, the polyvinyl alcohol base film has a crystallinity of more than 20%, a haze of 0.1-10%, and a light transmittance of more than 85%.

[0007] The dust-proof molecule has the structure shown in formula (I):

[0008]

[0009] In formula (I), X is a low surface energy group, preferably selected from silyl or siloxane, more preferably selected from methylsiloxane;

[0010] Y is a radical reactive group, preferably having the structures shown in formulas (II) and (III):

[0011]

[0012] In formulas (II) and (III), R1-R5 may be the same or different, and each is independently selected from hydrogen or C1-C2. 10 The alkyl group is preferably selected from hydrogen or C1-C6 alkyl groups, more preferably from hydrogen, methyl, ethyl, propyl or butyl; Z is O or NH;

[0013] R is H or OH;

[0014] p and q may be the same or different, and each is an independent integer between 0 and 6;

[0015] n is an integer from 0 to 20, preferably an integer from 0 to 5.

[0016] The polyvinyl alcohol-based film of the present invention has high crystallinity and excellent light transmittance. Its crystallinity is not less than 20%, preferably 25%-30%; its haze is 0.1-10%, preferably 0.1-8%; and its light transmittance is above 85%, preferably above 88%.

[0017] This invention utilizes biaxially oriented thermoplastic polyvinyl alcohol film as the base film (BOTPVA). Compared to traditional polyvinyl alcohol film (PVA) which cannot be thermoplastically processed, the BOTPVA film used in this invention can be prepared by a low-energy, more environmentally friendly thermoplastic processing method, and has the characteristics of high transparency, water resistance, and high strength.

[0018] The contact angle of the polyvinyl alcohol dustproof film of the present invention is 10° or more, preferably 15° or more.

[0019] The haze of the polyvinyl alcohol dustproof film of the present invention is 0.1-15%, preferably 1-10%.

[0020] A second objective of this invention is to provide a method for preparing the polyvinyl alcohol dustproof film, comprising the following steps:

[0021] a) Prepare thin films by extruding blown film or extrusion casting of thermoplastic polyvinyl alcohol, and then perform biaxial stretching to obtain biaxially stretched polyvinyl alcohol-based films;

[0022] b) Dissolve the initiator in the dust-proof functional molecules to obtain a photocurable dust-proof functional molecule solution;

[0023] c) The photocurable dustproof functional molecular solution is coated onto a polyvinyl alcohol base film, and a release liner is then placed on top of it.

[0024] d) The polyvinyl alcohol-based film obtained in step c) is subjected to ultraviolet light irradiation. After curing for a certain period of time, the covered substrate is removed to obtain the polyvinyl alcohol dustproof film.

[0025] This invention uses unsaturated siloxane monomers with the structure shown in formula (I) as dust-proof functional molecules and thermoplastic polyvinyl alcohol film as base film; under the action of photoinitiator, ultraviolet light irradiation is used to graft the dust-proof functional molecules onto the surface of BOTPVA film in the form of chemical bonds.

[0026] This invention uses a highly transparent polyvinyl alcohol (BOTPVA) base film as the base film.

[0027] The thermoplastic polyvinyl alcohol resin constituting the polyvinyl alcohol film is obtained by homopolymerization or copolymerization of polyvinyl acetate monomers, and modified to achieve thermoplasticity through melt thermoplasticization. Examples of thermoplastic modification include polyvinyl alcohol homopolymers such as vinyl alcohol, as well as other comonomers that can copolymerize with vinyl alcohol. These comonomers can be unsaturated or hydroxyl-unsaturated monomers containing hydroxyl, carboxyl, or sulfonic acid groups, such as allyl alcohol, butenol, acrylic acid, methacrylic acid, butenoic acid, hydroxyethyl methacrylate, vinyl sulfonic acid or its salts, and allyl sulfonic acid or its salts. There are no particular limitations on the melt thermoplasticization modification method; methods commonly used in the art are acceptable.

[0028] The dust-repellent functional molecule has the structure shown in formula (I), and the dust-repellent functional molecule may be, for example, acrylate oxypropyl bis(trimethylsiloxy)methylsilane, methacryloxypropyl tri(trimethylsiloxane)silane, or a dust-repellent monomer with the structure shown in formula (IV).

[0029]

[0030] The photoinitiator is a photoinitiator well known to those skilled in the art and is not particularly limited. In this invention, it is preferably one or more of the following photoinitiators: ketal, α-hydroxy ketone, α-amino ketone, aryl iodomonium salt type photoinitiator, acylphosphine oxide, benzoin ether, acetophenone, aromatic sulfonyl chloride, photoactive oxime, benzoin, benzoyl, thioxanone, or benzophenone, more preferably acetophenone and / or benzophenone.

[0031] In step a) of the above preparation method, extrusion blowing or extrusion casting is performed on an extruder. Preferably, the temperature from the feed inlet to the outlet is 170℃-210℃, and the screw speed is 10-150 rpm. A single-screw extruder, such as HAAKE, can be used. TM Rheomex OS single-screw extruder.

[0032] In step a) of the above preparation method, the film obtained by extrusion blown film or the sheet obtained by extrusion casting is subjected to biaxial stretching. The preheating temperature is preferably 170-210℃, the longitudinal stretching ratio is preferably 3-5 times, and the transverse stretching ratio is preferably 3-5 times; the annealing temperature is preferably 50-160℃. There are no particular limitations on the equipment used for biaxial stretching; it can be performed on a biaxial stretching testing machine, such as the Karo IV biaxial stretching testing machine manufactured by Brückner GmbH, Germany, or an industrial-scale continuous biaxial stretching film production line. The polyvinyl alcohol-based film obtained after biaxial stretching exhibits high crystallinity and excellent light transmittance.

[0033] In step b) of the above preparation method, the initiator is dissolved in the dustproof functional molecule and stirred at room temperature. The stirring method is a common stirring method, such as mechanical stirring, magnetic stirring, or ultrasonic dispersion.

[0034] In step b) of the above preparation method, the initiator is 0.01-10 parts by mass, and the dust-proof functional molecule is 50-100 parts. For example, the initiator can be 0.01 parts, 0.1 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.; the dust-proof functional molecule can be 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, etc.

[0035] In step c) of the above preparation method, the photocurable dustproof functional molecular solution is coated on one or both surfaces of the polyvinyl alcohol base film, and then a release light-transmitting plate is covered on it.

[0036] In step c) of the above preparation method, the material of the release liner is a common high-transmittance resin or quartz substrate, such as polyethylene film, polypropylene film, glass, quartz, etc.

[0037] In step d) of the above preparation method, the ultraviolet light can be provided by various light sources, as long as they can output ultraviolet light with a wavelength of 200-500nm. Suitable light sources include carbon arc lamps, mercury vapor lamps, xenon lamps, metal halide lamps, and lasers of specific wavelengths. Preferably, high-pressure or medium-pressure mercury lamps commonly used in industry are preferred, with an output power of 100-2000W.

[0038] In step d) of the above preparation method, the ultraviolet light source can irradiate either the side of the sample without the high-transmittance release liner covering the polyvinyl alcohol film or the side covered by the high-transmittance release liner, depending on the requirements for the contact angle and dustproof performance. It is preferable to place the ultraviolet lamp on the side of the high-transmittance release liner, so that the dustproof film obtained has better light transmittance and dustproof effect, but the contact angle is small.

[0039] Similarly, there are no specific requirements for the illumination time and the distance between the light source and the sample. It depends on the requirements for the light energy of photocuring and the properties of the substrate. The closer the distance, the stronger the ultraviolet radiation energy and the shorter the time required, but the material is easily deformed by heat and the curing may be uneven. The farther the distance, the weaker the ultraviolet radiation energy and the longer the time required.

[0040] Covering with a release liner serves two purposes: firstly, it prevents the monomers from volatilizing during the polymerization process, and secondly, it prevents the photocuring agent from coming into contact with oxygen during the reaction, thus affecting the free radical reaction.

[0041] In step d) of the above preparation method, the covered substrate is removed, and the obtained polyvinyl alcohol dustproof film is soaked in a solvent to remove monomers that have not been grafted onto the base film. The solvent can be a solvent commonly used in the art.

[0042] According to some embodiments of the present invention, the contact angle of the dustproof film is 10° or more, preferably 15° or more, and more preferably 25° or more.

[0043] According to some embodiments of the present invention, the haze of the dustproof film is 0.1-15%, more preferably 1-10%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0044] According to some embodiments of the present invention, the dustproof film has an elongation at break greater than 200% and a tensile strength greater than 15 MPa; more preferably, the elongation at break is greater than 350% and the tensile strength is greater than 20 MPa.

[0045] If ultraviolet light initiation is used, dust-repellent functional monomers can be directly grafted onto the surface of polyvinyl alcohol (PVA)-based films. This allows the dust-repellent molecules to be primarily grafted onto the film surface without affecting the overall haze, significantly improving grafting efficiency, reducing the amount of dust-repellent monomers required, and resulting in better dust-repellent performance. Furthermore, utilizing the high transparency of biaxially stretched PVA films, highly transparent greenhouse film outer layers with excellent dust-repellent properties can be prepared.

[0046] A third objective of this invention is to provide the application of the polyvinyl alcohol dustproof film or the polyvinyl alcohol dustproof film obtained by the preparation method in greenhouse films.

[0047] The dustproof greenhouse film provided by this invention has a dustproof effect that is more than 15% better than that of the internally added dustproof greenhouse film in the prior art.

[0048] This invention selects unsaturated monomers containing silicon-oxygen bonds as dust-proof functional molecules and a highly transparent polyvinyl alcohol film as the base film, grafting the dust-proof functional molecules onto the surface of a polar BOTPVA film via chemical bonds.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. Compared with traditional internally added dustproof greenhouse films, this invention uses ultraviolet light grafting to graft a layer of dustproof functional molecules only onto the surface of the base film, requiring less dustproof functional molecules. Furthermore, it achieves better dustproof performance.

[0051] 2. Compared with traditional polyethylene greenhouse film, the present invention uses biaxially stretched thermoplastic polyvinyl alcohol film, which has better transparency and lower haze.

[0052] 3. Compared with traditional internally added dustproof greenhouse films, the present invention connects dustproof functional molecules to the surface of the base film through chemical bonds, resulting in a longer effective period. Attached Figure Description

[0053] Figure 1 The contact angles are those of the dustproof polyvinyl alcohol grafted films prepared in Examples 2-4.

[0054] Figure 2 The haze and light transmittance of the BOTPVA film grafted with trisilicon dustproof monomer in Example 2 are shown after dustproof testing.

[0055] Figure 3 The haze and light transmittance of the grafted BOTPVA film with altered illumination method in Example 3 are shown after a dustproof test. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0057] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified were either readily available for purchase or prepared using methods disclosed in the prior art.

[0058] Test materials:

[0059] The polyvinyl alcohol used in this invention has a degree of polymerization of about 1100 and a degree of alcoholysis of about 95%.

[0060] Acryloxypropylbis(trimethylsiloxy)methylsilane (containing trisilicone dust suppressant monomer) and methacryloyloxypropyltri(trimethylsiloxane)silane (containing tetrasilicone dust suppressant monomer) were selected from Maclean's reagents and were of analytical grade.

[0061] n=2 dustproof monomer: According to the structure of formula (I), the dustproof monomer with the chemical structure shown in formula (IV) (referred to as n=2 dustproof monomer) is selected and provided by Sinopec Shanghai Petrochemical Research Institute:

[0062]

[0063] The photoinitiator benzophenone (BP) was selected from Bailingwei Technology and was of analytical grade purity.

[0064] The quartz plate measures 80mm x 80mm x 1mm and is sourced from Shanghai Heqi Glass Instruments.

[0065] Test methods and equipment:

[0066] Contact angle test: The test is conducted on a German KRUSS DSA100 contact angle measuring instrument. The test procedure is usually as follows: the sample is laid flat on the sample stage, a suitable liquid is selected, and a small droplet of about 5μL is squeezed out through a fine needle and hung on the needle tip. The sample stage is moved to gently stick the small droplet onto the sample. After a set time, a picture is taken. The angle between the tangent of the contact edge between the droplet and the sample and the sample plane in the picture is analyzed by the software. This angle is the measured contact angle.

[0067] Transmittance and haze testing: The tests were conducted on a Haze Gardi transmission haze meter from BYK GmbH, Germany. The test was performed in transmission mode, and each sample was usually measured at least 5 times, and the average value was taken.

[0068] Dustproof test: The overall test process is briefly described as follows: a. Prepare quartz sand with a particle size of 20-80 mesh, place it in a dust generator, and the mass ratio of quartz sand to the volume of the dust generator is 5 kg / m³. 3 b. Take the membrane sample to be tested, perform a transmittance test and record the results; c. Seal the inner layer of the membrane sample to be tested, exposing only the outer layer, and fix it vertically in the dust-generating machine; d. Close the dust-generating machine cover, start the machine, and continuously generate dust for 30 seconds; e. Turn off the dust-generating machine and wait 120 seconds to ensure that the dust has basically settled completely; f. Open the dust-generating machine, remove the membrane sample, remove the inner sealing layer, perform a transmittance test and record the results; g. Repeat steps cf above to obtain the relationship between the number of cycles and transmittance of the tested membrane, thus enabling the simulation and comparison of the dustproof performance period. The above process is easily affected by the environment and has a large systematic error. Therefore, it is best to process and test the membrane samples to be compared together to obtain more reliable results. Currently, there is no clear definition in the industry regarding the failure of greenhouse film to prevent dust. However, based on practice, when the light transmittance of the greenhouse film is below 70%, crop yield will be significantly affected. Therefore, the point at which the light transmittance is below 70% due to dust adsorption is defined as the critical point of failure of greenhouse film to prevent dust. The time from the start of use to the critical point is the dust prevention period of the greenhouse film.

[0069] Example:

[0070] [Example 1] Preparation of biaxially oriented polyvinyl alcohol film (BOTPVA)

[0071] The polyvinyl alcohol used has a degree of polymerization of approximately 1100 and a degree of alcoholysis of approximately 95%, and uses PolyLab HAAKE from ThermoFisher Technologies, Inc. TM The Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16mm, L / D = 40) performs thermoplasticization, extrusion, and granulation. This extruder has 11 sections from the feed inlet to the die, numbered 1-11. Section 1 only serves as the feeding section and cannot be heated. Polyvinyl alcohol (PVA) raw material is fed into the twin screws via a powder feeder at a rate of 820 g / h. Thermoplasticizer (by mass fraction, a mixture containing 86% glycerol, 7% xylitol, and 7% tripropylene glycol) is added to the extruder through the feed inlet at a feeding rate of 180 g / h. The temperatures of sections 2-11 of the extruder are 180℃, 190℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃, and 190℃, respectively, with the screw speed set at 250 rpm. The extruder is equipped with a 3mm diameter circular die. After the sample is extruded from the die and cooled by air, it is cut into thermoplastic polyvinyl alcohol (TPVA) particles of about 3mm in diameter by a pelletizer. The particles are collected and packaged for later use.

[0072] The aforementioned TPVA particles are placed in the HAAKE mentioned above. TM TPVA sheets are produced by extrusion casting on a Rheomex OS single-screw extruder. The extruder has three heating sections with temperatures of 190°C, 200°C, and 200°C from the inlet to the outlet, respectively. The TPVA melt is extruded through a flat die, drawn by a series of rollers at the front end, cooled, and then wound up. The average thickness of the TPVA-based sheet is approximately 375 μm.

[0073] The aforementioned thin films were subjected to biaxial stretching on a Karo IV biaxial stretching testing machine manufactured by Brückner GmbH, Germany. This equipment has three modular sections; in this invention, only the first two sections are used. The first section is the preheating and stretching section, with a preheating temperature of 185°C, a longitudinal stretching ratio of 3.5 times, and a transverse stretching ratio of 3.5 times. The second section is the annealing and setting section, with an annealing temperature of 75°C. The biaxially stretched monolayer BOTPVA film has an average thickness of 15 μm, a haze of 2.4%, a light transmittance of 91.3%, and a crystallinity of 27%.

[0074] [Example 2] Dustproof polyvinyl alcohol film grafted with trisilicone dustproof monomer

[0075] Different amounts of benzophenone (BP) were dissolved in 10g of 3-methacryloyloxypropylbis(trimethylsiloxy)methylsilane containing three silicon atoms to prepare solutions with BP concentrations of 0%, 1%, 5%, 7.5%, and 10% by mass. The solutions were thoroughly stirred and dissolved in a 45°C water bath to obtain a photocurable dust-repellent molecular solution. A biaxially stretched thermoplastic modified polyvinyl alcohol (BOTPVA) film from Example 1 was cut into 8cm x 8cm shapes, and a certain amount of the dust-repellent molecular solution was coated on one side. A quartz release sheet of the same size (80mm x 80mm x 1mm) was placed on the coated film and pressed firmly to ensure full contact. A 200W high-pressure mercury lamp (wavelength 360nm) was used to irradiate and photocur the quartz sheet, with a distance of 3cm between the lamp and the film. The reaction was allowed to proceed for 20 minutes, after which the release sheet was removed from the film. The obtained dustproof film was soaked in 400 mL of acetone for 4 hours, and magnetic stirring was turned on to remove monomers that were not grafted onto the base film, thus obtaining a dustproof polyvinyl alcohol film containing trisilicon dustproof functional molecules. (Named according to different initiation doses: Example 2-0%, Example 2-1%, Example 2-5%, Example 2-7.5%, Example 2-10%).

[0076] [Example 3] Grafting a dustproof polyvinyl alcohol film containing trisilicone dustproof monomer by changing the lighting method

[0077] Different amounts of benzophenone (BP) were dissolved in 10g of 3-methacryloyloxypropylbis(trimethylsiloxy)methylsilane containing three silicon atoms to prepare solutions with BP concentrations of 1%, 5%, 7.5%, and 10% by mass. The solutions were thoroughly stirred and dissolved in a 45°C water bath to obtain a photocurable dust-repellent molecular solution. The biaxially stretched thermoplastic modified polyvinyl alcohol (BOTPVA) film from Example 1 was cut into 8cm x 8cm shapes, and a certain amount of the dust-repellent molecular solution was coated on one side. A quartz release sheet of the same size (80mm x 80mm x 1mm) was placed on the coated film and pressed firmly to ensure full contact. A 200W high-pressure mercury lamp (wavelength 360nm) was used to irradiate and photocur the BOTPVA film on one side, with a distance of 3cm between the high-pressure mercury lamp and the film. The reaction was allowed to proceed for 20 minutes, and then the release sheet covering the film was removed. The obtained dustproof film was soaked in 400 mL of acetone for 4 hours, and magnetic stirring was turned on to remove monomers that were not grafted onto the base film, thus obtaining dustproof polyvinyl alcohol containing trisilicone dustproof functional molecules. (Named according to different initiation doses: Example 3-0%, Example 3-1%, Example 3-5%, Example 3-7.5%, Example 3-10%)

[0078] [Example 4] Dustproof polyvinyl alcohol film grafted with tetrasilicone dustproof monomer

[0079] Different amounts of benzophenone (BP) were dissolved in 10g of methacryloyloxypropyltris(trimethylsiloxane)silane containing four silicon atoms to prepare solutions with BP concentrations of 1%, 5%, 7.5%, and 10% by mass. The solutions were thoroughly stirred and dissolved in a 45°C water bath to obtain a photocurable dust-repellent molecular solution. The biaxially stretched thermoplastic modified polyvinyl alcohol (BOTPVA) film from Example 1 was cut into 8cm x 8cm shapes, and a certain amount of the dust-repellent molecular solution was coated on one side. A quartz release sheet of the same size (80mm x 8mm x 1mm) was placed on the coated film and pressed firmly to ensure full contact. A 200W high-pressure mercury lamp (wavelength 360nm) was used to irradiate and photocur the quartz sheet, with a distance of 3cm between the lamp and the film. The reaction was allowed to proceed for 20 minutes, and then the release sheet was removed from the film. The obtained dustproof film was soaked in 400 mL of acetone for 4 hours, and magnetic stirring was turned on to remove monomers that were not grafted onto the base film, yielding dustproof polyvinyl alcohol containing tetrasilicon dustproof functional molecules. (Named according to different initiation doses: Example 4-1%, Example 4-5%, Example 4-7.5%, Example 4-10%)

[0080] [Example 5] Grafting n=2 dustproof monomers

[0081] Benzophenone (BP) was dissolved in 10g of an n=2 dust-repellent monomer (formula (IV)) containing three silicon atoms within its molecule. The solution was thoroughly stirred and dissolved in a 45°C water bath to obtain a photocurable dust-repellent functional molecular solution with a 5% BP concentration. The biaxially stretched thermoplastic modified polyvinyl alcohol (BOTPVA) film from Example 1 was cut into an 8cm x 8cm shape, and a certain amount of the n=2 dust-repellent monomer solution was coated onto one side. A quartz release sheet of the same size (80mm x 8mm x 1mm) was placed on top of the coated film and pressed firmly to ensure full contact. A 200W high-pressure mercury lamp (wavelength 360nm) was used to irradiate and photocur the quartz sheet, with a distance of 3cm between the lamp and the film. The reaction was allowed to proceed for 20 minutes, and then the release sheet covering the film was removed. The obtained dustproof film was soaked in 400 mL of acetone for 4 hours, and magnetic stirring was turned on to remove monomers that were not grafted onto the base film, yielding dustproof polyvinyl alcohol containing 3 silicon n=2 dustproof functional molecules. (Named: Example 5-5%)

[0082] [Example 6] Haze and transmittance test

[0083] The transmittance and haze of the 14 types of films in Examples 2-5 were measured respectively, and the results are shown in Table 1.

[0084] Table 1. Transmittance and haze of different samples

[0085]

[0086] As shown in Table 1, comparing Examples 2, 4 and 3, changing the illumination method affects the light transmittance of the final grafted film in this invention. In Example 2, when ultraviolet light is irradiated from one side of the quartz substrate, the haze is only 4.3%-9.4% (far lower than the haze of traditional polyolefin greenhouse film). The light transmittance of the resulting grafted film is significantly better than that of the grafted film irradiated from the polyvinyl alcohol film side in Example 3, and the haze is significantly lower.

[0087] [Example 7] Contact Angle Test

[0088] The 13 types of membranes from Examples 2-4 were subjected to contact angle tests, and the results are as follows: Figure 1 As shown, the contact angle can reflect the degree of grafting of dust-repellent molecules; the larger the contact angle, the greater the amount of grafted dust-repellent molecules.

[0089] Contact angle testing confirmed the effective grafting of dust-repellent molecules onto the membrane surface. Figure 2As shown, the unmodified BOTPVA film, due to its rich hydroxyl content, exhibits hydrophilic properties, with a contact angle of only about 17°. In Examples 2 and 4, however, by photoinitiating grafting on one side of the quartz plate, the contact angle of the resulting dustproof BOTPVA film slowly increased with increasing initiator content, eventually reaching 40°-50°. In contrast, in Example 3, when photoinitiation was performed on one side of the BOTPVA film, the contact angle of the resulting grafted BOTPVA film increased dramatically, achieving a larger contact angle with the same initiator content. When the initiator content was 10%, the contact angle reached 82°, demonstrating hydrophobic properties.

[0090]

Example 8

[0091] Six types of membranes from Examples 2 and 3, with initiator contents of 0%, 5%, and 7.5%, were subjected to dustproof tests. The transmittance and haze of the membranes were measured for each cycle. The results are as follows: Figures 2-3 As shown.

[0092] like Figure 2 As shown, the dust-resistant BOTPVA film prepared by photoinitiation on one side of the quartz plate in Example 2 exhibits significantly better dust-resistant performance compared to the ungrafted BOTPVA film. After the fifth cycle, the dust-resistant grafted film with 5% initiator showed a light transmittance of approximately 81% and a haze of 42%, significantly higher than the ungrafted BOTPVA film (76% transmittance) under the same cycle conditions, and significantly lower haze (61%). Notably, after one cycle, the haze of the grafted dust-resistant BOTPVA film was only 30%, while the haze of the ungrafted BOTPVA film had increased dramatically to 55%. This demonstrates that the dust-resistant BOTPVA film prepared using the dust-resistant functional molecules of this invention, when initiated on one side of the quartz plate, possesses excellent dust-resistant performance. Furthermore, when using n=2 dust-resistant monomers for grafting, the light transmittance was 77% and the haze 54% after the fifth cycle. Its light transmittance is slightly better than that of the ungrafted membrane under the same conditions, and its haze is significantly better than that of the ungrafted BOTPVA membrane under the same conditions.

[0093] In comparison, Figure 3 In Example 3, when photoinitiation was performed on one side of the film, the resulting grafted BOTPVA film exhibited weaker dustproof performance than the ungrafted BOTPVA film. Under the same fifth cycle, the grafted BOTPVA film with 7.5% initiator had a transmittance of approximately 72% and a haze of 69%, which was weaker than the ungrafted BOTPVA (76% transmittance and 61% haze).

[0094] This indicates that the initiation method significantly affects the final dustproof effect. Although the contact angle test showed that the grafting and curing reaction of the dustproof functional molecules in Example 3 was more complete, the stronger light intensity and higher film surface temperature may have promoted the grafting and hydrolytic cross-linking of the dustproof functional molecules on the film surface, resulting in a certain degree of adhesion to the film surface, which is detrimental to the dustproof performance of the grafted film. However, when initiation was performed on one side of the quartz sheet, the reaction conditions were milder, and the resulting film exhibited better dustproof performance.

[0095]

Comparative Example 1

[0096] In Chinese patent CN111098576A, the dustproof performance of a traditional internally added PE film and a PE film grafted with reactive extrusion dustproof functional molecules were tested using the same method. After three cycles, the light transmittance of the traditional internally added PE film and the PE film grafted with reactive extrusion dustproof functional molecules were 71% and 70.5%, respectively. However, in this invention, the dustproof BOTPVA film of "Example 2-7.5%" still maintained a light transmittance of 83% after the same three cycles, indicating that the high-transmittance dustproof BOTPVA film prepared by photocuring in this invention has better dustproof performance than traditional PE dustproof greenhouse film.

[0097] Furthermore, the haze transmittance tests in the embodiments show that the dustproof BOTPVA films obtained in Examples 2 and 4 exhibit excellent transmittance and haze performance. After grafting with dustproof monomers, the haze is only between 2-9%, which is significantly better than that of dustproof polyethylene greenhouse films (13-15%, CN111098576A).

[0098] Therefore, the dustproof BOTPVA greenhouse film prepared by the method of the present invention grafts a layer of dustproof functional molecules only on the surface of the greenhouse film through ultraviolet light reaction grafting. This requires fewer dustproof functional molecules, has a high content of dustproof functional molecules on the surface, has a longer effective period, and has the characteristics of high light transmittance, low haze, and excellent dustproof performance. It can be used as a high-performance greenhouse film outer layer with high transparency, low haze, and excellent dustproof performance.

Claims

1. A polyvinyl alcohol (PVA) dustproof film, comprising a PVA base film and dustproof functional molecules grafted onto the surface of the PVA base film via ultraviolet light initiation; wherein, The polyvinyl alcohol-based film has a crystallinity of 20%-30%, a haze of 0.1-10%, and a light transmittance of over 85%. The dust-proof molecule has the structure shown in formula (I): （I）， In formula (I), X is a low surface energy group selected from silyl or siloxane; Y is a radical reactive group with the structure shown in formula (II): (II), R1-R3 are each independently selected from hydrogen or C1-C2. 10 Alkyl group; Z is O; R is H or OH; p and q may be the same or different, and each is an independent integer between 0 and 6; n is an integer between 0 and 20.

2. The polyvinyl alcohol dustproof film according to claim 1, characterized in that: R1-R3 are each independently selected from hydrogen or C1-C6 alkyl groups; n is an integer between 0 and 5.

3. The polyvinyl alcohol dustproof film according to claim 1, characterized in that: The polyvinyl alcohol-based film has a crystallinity of 25-30%, a haze of 0.1-8%, and a light transmittance of over 88%.

4. The polyvinyl alcohol dustproof film according to any one of claims 1-3, characterized in that: The contact angle of the dustproof film is 10° or more; and / or, The haze of the dustproof film is 0.1-15%.

5. The polyvinyl alcohol dustproof film according to claim 4, characterized in that: The contact angle of the dustproof film is 15° or more; and / or, The haze of the dustproof film is 1-10%.

6. A method for preparing a polyvinyl alcohol dustproof film according to any one of claims 1-5, comprising the following steps: a) Prepare thin films by extruding or casting thermoplastic polyvinyl alcohol, and then perform biaxial stretching to obtain polyvinyl alcohol-based films; b) Dissolve the initiator in the dust-proof functional molecules to obtain a photocurable dust-proof functional molecule solution; c) The photocurable dustproof functional molecular solution is coated onto a polyvinyl alcohol base film, and a release liner is then placed on top of it. d) The polyvinyl alcohol-based film obtained in step c) is subjected to ultraviolet light irradiation and cured to obtain the polyvinyl alcohol dustproof film.

7. The method for preparing the polyvinyl alcohol dustproof film according to claim 6, characterized in that: The thermoplastic polyvinyl alcohol is obtained by homopolymerization or copolymerization of polyvinyl acetate monomers and modified by melt thermoplasticization; and / or, The initiator is at least one of the following: ketals, α-hydroxy ketals, α-amino ketals, aryl iodonium salts, acylphosphine oxides, benzoin ethers, acetophenones, aromatic sulfonyl chlorides, photoactive oximes, benzoin, benzoyl, benzophenones, thioxanones, and benzophenones.

8. The method for preparing the polyvinyl alcohol dustproof film according to claim 7, characterized in that: The initiator is an acetophenone and / or benzophenone.

9. The method for preparing the polyvinyl alcohol dustproof film according to claim 6, characterized in that... In step a): When extruding blown film or extruding cast film, the temperature is 170-210℃ and the rotation speed is 10-150 rpm; and / or, When performing biaxial stretching, the preheating temperature is 170-210℃, the longitudinal stretching ratio is 3-5 times, the transverse stretching ratio is 3-5 times, and the annealing temperature is 50-160℃.

10. The method for preparing the polyvinyl alcohol dustproof film according to claim 6, characterized in that... In step b): By weight, the initiator is 0.01-10 parts and the dustproof functional molecule is 50-100 parts.

11. The method for preparing the polyvinyl alcohol dustproof film according to claim 6, characterized in that... In step d): The wavelength of ultraviolet light is 200-400 nm; and / or, An ultraviolet light source irradiates the polyvinyl alcohol-based film on one side of a release diaphragm.

12. The application of the polyvinyl alcohol dustproof film according to any one of claims 1-5 or the polyvinyl alcohol dustproof film obtained by the preparation method according to any one of claims 6-11 in greenhouse film.

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