Mulching paper for greenhouse and preparation method therefor

Abstract

The present invention relates to the technical field of mulching paper. Disclosed are a mulching paper for greenhouse and a preparation method therefor. The method comprises the following steps: beating wheat straw biomechanical pulp with a beating degree of 35-40°SR to obtain a pulp; fully mixing the pulp with a papermaking auxiliary agent, and performing papermaking to obtain a mulching raw paper; uniformly applying gelatinized cationic starch or gelatinized soybean oil modified starch on a single side or front and back sides of the mulching film raw paper, and drying; and then uniformly applying a polyurethane or acrylic resin coating on the single side or the front and back sides, and drying to obtain the product. The mulching paper uses biomechanical pulp as a main raw material, high physical and mechanical properties and high hydrophobicity and moisture resistance of the mulching paper are achieved by means of addition into the pulp and surface coating, and the mulching paper can replace black plastic mulching films to solve the problems of environmental pollution and the like caused by the plastic mulching films.

Description

Greenhouse ground film paper and preparation method thereof

[0001] The present invention claims priority to the Chinese patent application filed with the Patent Office of China on June 2, 2023, with application number 202310661608.8 and invention name “A kind of ground film paper for greenhouse and its preparation method”, the entire contents of which are incorporated into the present invention by reference. Technical Field

[0002] The invention belongs to the technical field of mulch film paper, and particularly relates to mulch film paper for greenhouses and a preparation method thereof. Background Art

[0003] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0004] As a major agricultural country, my country has become the world's largest producer and user of agricultural film. Currently, most mulch films are made from petroleum-based plastics such as polyvinyl chloride (PVC) and polyethylene (PE). These materials remain in the soil and are difficult to fully degrade, causing ecological damage. Black mulch is a type of plastic film commonly used in greenhouses, providing insulation, moisture retention, and weed control. It is often used to improve the growing environment for crops, increase fertilizer utilization, and prevent weeds from affecting crop quality.

[0005] Due to environmental pollution and other issues caused by plastic mulch, biodegradable mulch has become a research focus, with paper-based mulch offering certain advantages. Made from plant fibers, paper-based mulch is mixed with different pulps or proportions using papermaking technology. While it possesses a certain dry strength and light-blocking properties, it lacks the light-blocking properties of black mulch, making it less effective at suppressing weed growth.

[0006] Importantly, traditional plastic-based black mulch films offer excellent moisture retention, effectively preventing soil moisture evaporation. However, paper-based mulch films have poor water vapor barrier properties and cannot match the moisture retention requirements of black plastic mulch films. Furthermore, current paper-based mulch films still lack the high dry and wet strength required for use in greenhouses. Furthermore, the high production cost of current paper-based mulch films poses a significant obstacle to their widespread application.

[0007] Therefore, although the current paper-based film has good biodegradability, it is still difficult to replace black plastic film.

[0008] Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a greenhouse mulch paper and a preparation method thereof. The mulch uses biomechanical pulp as the main raw material, and achieves high physical and mechanical properties and high hydrophobicity and moisture resistance of the mulch paper through the methods of pulp addition and surface coating. It can replace black plastic mulch and solve the problems of environmental pollution caused by plastic mulch.

[0010] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing greenhouse mulch paper, comprising the following steps: beating wheat straw bio-mechanical pulp after debonding, with a beating degree of 35-40° SR, to obtain a slurry;

[0012] After the slurry is fully mixed with the papermaking auxiliary agent, papermaking is performed to obtain the base paper of the ground film;

[0013] Evenly coating one side or both sides of the base paper of the mulch film with gelatinized cationic starch or gelatinized soybean oil-modified starch, and drying; during gelatinization, the mass percentage of the cationic starch aqueous solution is 3-10%; the mass percentage of the starch in the soybean oil-modified starch is 2.5-10%;

[0014] Then evenly apply polyurethane or acrylic resin coating on one side or both sides and dry it.

[0015] In some embodiments, the papermaking aid includes 0.5%-3% of cationic polyacrylamide (CPAM) or cationic starch (CAS) or chitosan by weight of the absolute dry pulp, 1.5%-3% of polyamide polyamine epichlorohydrin by weight of the absolute dry pulp, 0.5%-2% of alkyl ketene dimer (AKD) or aluminum sulfate by weight of the absolute dry pulp, and 0.1%-0.3% of cationic / anionic polyacrylamide or cationic / anionic starch by weight of the absolute dry pulp.

[0016] Biomechanical pulp is first pretreated with bio-enzymes before being mechanically refined. The bio-enzymes are a complex enzyme composed of pectinase, lipase, and xylanase in a specific ratio. Biomechanical pulping shifts from traditional high-temperature, high-alkali pulping to low-temperature, low-alkali, or alkali-free pulping. This technology combines modern biotechnology with mechanical pulping of agricultural straw, replacing traditional chemicals with bio-enzymes. This approach not only addresses the shortage of papermaking raw materials caused by the sharp decline in waste paper imports, but also achieves zero wastewater discharge.

[0017] By adding polyamide polyamine epichlorohydrin (PAE) wet strength agent into the pulp, the paper has obvious wet strength enhancement and surface water resistance. The specific dosage was discussed and the optimal effect was achieved when the addition amount reached 2.5% (see Example 4 for details).

[0018] To achieve less than 800g / m2 The inventors have studied the internal sizing process and the surface coating process. The first layer of the surface coating process is a gelatinized cationic starch layer or a modified starch coating. The gelatinized cationic starch layer or the modified starch layer alone can increase the water vapor permeability of the base paper from 2895 g / m 2 ·24h down to 2100g / m 2 · Less than 24h; The second layer is a hydrophobic moisture barrier coating, which is a coating of polyurethane or acrylic resin. Under the premise of reducing the coating amount as much as possible, the two preferred hydrophobic moisture barrier coatings both make the water vapor permeability of the ground film paper reach 800g / m 2 Less than 24 hours.

[0019] The hydrophobic moisture barrier coating can also enhance the mechanical properties and hydrophobic properties of the paper-based membrane.

[0020] The degradable portion of both natural-color mulch papers, coated with acrylic resin and polyurethane, accounts for over 95% of their total mass, making them essentially fully biodegradable after use. Degradation experiments showed that both mulch papers retained their original appearance after 80 days in soil.

[0021] To reduce visible light transmittance to below 5%, bio-mechanical pulp from wheat straw is used as raw material. This material is environmentally friendly, low-cost, and light-proof. The resulting mulch paper has a low visible light transmittance of 3.6%. The subsequent application of gelatinized cationic starch or modified starch coating further reduces the transmittance, ensuring that the mulch paper consistently maintains a visible light transmittance below 5%.

[0022] Experiments have shown that the gelatinized cationic starch layer or modified starch layer applied in the present invention not only improves the water vapor barrier and visible light barrier properties of paper-based membranes, but also enhances the mechanical strength and smoothness of the paper-based membranes, while reducing their water absorption. Furthermore, the gelatinized cationic starch layer or modified starch layer exhibits excellent pore-filling properties, reducing the amount of coating required for hydrophobic and moisture-blocking coatings such as polyurethane and acrylic resins. This effectively reduces the production cost of mulch paper and facilitates its widespread application.

[0023] When 0.5-3% of the absolute dry pulp mass of a dry strength agent (cationic polyacrylamide (CPAM) or cationic starch (CAS) or chitosan) is added to the biomechanical pulp, the dry strength of the base paper can be increased by about 30% at most.

[0024] When 1.5-3% of the absolute dry pulp mass of a wet strength agent (polyamide polyamine epichlorohydrin) is added to the biomechanical pulp, the wet strength of the base paper can be increased by up to about 369%.

[0025] When 0.5-2% of the absolute dry pulp mass of sizing agent (alkyl ketene dimer (AKD) or aluminum sulfate) is added to biomechanical pulp, the sizing agent works together with the dry strength agent and wet strength agent to increase the dry strength of the base paper by about 46% and its wet strength by about 400%.

[0026] Adding 0.1-0.3% of a retention aid (cationic / anionic polyacrylamide or cationic / anionic starch) to biomechanical pulp, based on the absolute dry pulp weight, effectively improves pulp retention when it is applied to the screen, effectively retains fine fibers, and significantly reduces pulp consumption. Furthermore, this excellent fine fiber retention effectively reduces the light transmittance of the resulting paper-based film, thereby further suppressing weed growth. However, excessive amounts of retention aid can cause sediment to form.

[0027] In some embodiments, the method further comprises adding 0-40% by mass of waste corrugated paper pulp or 0-40% by mass of wheat straw pulp to the wheat straw biomechanical pulp.

[0028] Adding waste corrugated paper pulp or wheat straw pulp to wheat straw bio-mechanical pulp can reduce costs. Experiments have found that when 0-40% by mass of waste corrugated paper pulp or wheat straw pulp is added to wheat straw bio-mechanical pulp, the dry and wet strength of the prepared paper-based film will not be significantly reduced, and dark-colored waste corrugated paper pulp is more conducive to reducing the visible light transmittance of the film paper.

[0029] In some embodiments, the papermaking aid includes 0.5%-2% of the absolute dry pulp mass of cationic polyacrylamide or cationic starch or chitosan, 2%-3% of the absolute dry pulp mass of polyamide polyamine epichlorohydrin, 0.5%-1% of the absolute dry pulp mass of alkyl ketene dimer or aluminum sulfate, and 0.1%-0.2% of the absolute dry pulp mass of cationic / anionic polyacrylamide or cationic / anionic starch.

[0030] Preferably, the papermaking auxiliary agent includes 1%-2% of cationic polyacrylamide by weight of the absolute dry pulp, 2%-3% of polyamide polyamine epichlorohydrin by weight of the absolute dry pulp, and 0.5%-1% of alkyl ketene dimer by weight of the absolute dry pulp.

[0031] In some embodiments, the preparation method of gelatinized cationic starch is as follows: adjust the cationic starch aqueous solution to alkaline, heat it to 40-50° C., and stir it for 20-40 minutes.

[0032] Preferably, the mass percentage of the cationic starch aqueous solution is 3-10%, preferably 7%.

[0033] Preferably, the mass percentage of sodium hydroxide in the cationic starch aqueous solution is 8%-15%.

[0034] In some embodiments, the preparation method of gelatinized soybean oil-modified starch is as follows: soybean oil and sodium carbonate are added to a dimethyl sulfoxide solution of starch to obtain a mixed solution, and the mixture is heated to 110-150° C. for 1-3 hours to hydrophobically modify the starch to obtain modified starch.

[0035] Soybean oil replaces hydroxyl groups and esterifies starch, effectively improving its hydrophobic properties. Sodium carbonate is used as a catalyst to promote the modification reaction.

[0036] Preferably, in the mixed solution, the mass percentage of starch is 2.5-10%; the mass percentage of soybean oil is 8-12%; and the mass percentage of sodium carbonate is 13-17%.

[0037] Preferably, the modified starch undergoes the same gelatinization process as the cationic starch.

[0038] In some embodiments, the gelatinized cationic starch or gelatinized soybean oil-modified starch is coated on the surface of the mulch paper using a 10 μm linear coating rod and dried.

[0039] Preferably, the single-sided coating amount of gelatinized cationic starch or gelatinized soybean oil modified starch is 1.5-2 g / m 2 , double-sided coating amount is 3-4g / m 2 .

[0040] In some embodiments, the hydrophobic moisture barrier coating is coated by using a 4 μm linear coating rod to coat the surface of the gelatinized cationic starch or gelatinized modified starch coating, and then drying the coating.

[0041] Preferably, the single-sided coating amount of polyurethane is 1.5-2 g / m 2 , double-sided coating amount is 3-4g / m 2 .

[0042] Preferably, the single-sided coating amount of acrylic resin is 2.5-3g / m 2 , double-sided coating amount is 5-6g / m 2 .

[0043] Compared to dipping and spraying, the coating method can precisely control the amount of coating, resulting in a uniform coating. The 4μm linear coating rod can minimize the amount of coating.

[0044] In some embodiments, the basis weight of the ground film base paper is 60-70 g / m 2 .

[0045] The drying temperature of polyurethane and acrylic resin coatings is 105-110℃.

[0046] In a second aspect, the present invention provides a mulch paper for greenhouses, which is prepared by the preparation method.

[0047] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0048] 1) Water resistance of mulch paper Cobb 120 ≤20g / m 2 , has certain hydrophobic properties, which is beneficial to prolong the service life of mulch paper in a humid environment.

[0049] 2) Water vapor transmission rate ≤800g / m 2 24h, has strong barrier properties to water vapor and can reduce soil moisture loss.

[0050] 3) Physical strength index: tear index ≥ 2.5mN·m 2 / g, burst resistance index ≥ 2kPa.m 2 / g, wet tensile index ≥ 25% of dry tensile index, so that the mulch paper will not be damaged or rotted during the covering period.

[0051] 4) The light transmittance is ≤5%, which can effectively inhibit the growth of weeds and achieve the purpose of inhibiting weed growth.

[0052] 5) The relative biodegradation rate is ≥90%. After use, it can be completely or mostly degraded into organic matter and enter the land, which is beneficial to improving soil structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0054] Figure 1 is a flow chart for the preparation of natural color biodegradable mulch paper for greenhouses. DETAILED DESCRIPTION

[0055] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0056] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0057] Example 1

[0058] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp and beat it with a Wall-E pulper to obtain biomechanical pulp with beating degrees of about 20°SR, 30°SR, and 40°SR respectively. After beating, use a pulp bag to filter out most of the water, put it in a 5°C low-temperature refrigerator for 24 hours to balance the moisture, and measure the solid content.

[0059] Take 1.88g of absolute dry pulp and a papermaking additive comprising 0.5% CPAM dry strength agent, 2% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention agent by weight of the absolute dry pulp, blend them in a deflaking machine, deflake at 10,000 revolutions to disperse the fibers completely. After deflaking, feed the pulp into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0060] Coating experiment for mulch film base paper: First, prepare a 5wt% cationic starch aqueous solution, then add sodium hydroxide (10% by weight of the starch). Mechanically stir at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch. Fix the mulch film base paper in place, then evenly coat the front surface of the mulch film base paper with the gelatinized cationic starch using a 10μm linear coating rod. Dry at 80°C for 10 minutes. Remove the paper, and continue coating the starch layer on the front surface with polyurethane using a 4μm linear coating rod. Dry at 110°C for 10 minutes.

[0061] The properties of mulch paper prepared with different beating degrees are shown in Table 1.

[0062] Table 1 Properties of mulch paper prepared with different beating degrees

[0063] Example 2

[0064] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp and beat it with a Wall-E pulper to obtain a biomechanical pulp with a beating degree of about 40°SR. After beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24 hours to balance the moisture, and measure the solid content.

[0065] 1.88g and 2.19g of absolute dry pulp and a papermaking additive comprising 0.5% CPAM dry strength agent, 2% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp were mixed in a deflaking machine and deflaked at 10,000 revolutions to completely disperse the fibers. After deflaking, the pulp was fed into a papermaking machine to obtain a basis weight of 60g / m 2 and 70g / m 2 Ground film base paper.

[0066] For the coating experiment on mulch film base paper, a 5 wt% cationic starch aqueous solution was prepared, followed by the addition of sodium hydroxide (10% by weight of the starch mass). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch.

[0067] Fix the mulch base paper and evenly coat the front of the mulch base paper with gelatinized cationic starch using a 10μm linear coating rod. Dry at 80℃ for 10 minutes. Remove the paper and continue coating the starch layer on the front with polyurethane using a 4μm linear coating rod. Dry at 110℃ for 10 minutes.

[0068] The properties of the prepared mulch papers with different weights are shown in Table 2.

[0069] Table 2 Properties of mulch paper prepared with different papermaking weights

[0070] Example 3

[0071] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0072] Take 1.88g of absolute dry pulp and papermaking additives with the absolute dry pulp weight percentage of 0.5%, 1%, 1.5%, 2% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention agent, blend them in a deflaking machine, deflake at 10,000 revolutions to make the fibers completely dispersed. After deflaking, feed the pulp into a papermaking machine to obtain 60g / m 2 Ground film base paper.

[0073] For the coating experiment on mulch film base paper, a 5% cationic starch aqueous solution was prepared, followed by the addition of sodium hydroxide (10% by weight of the starch). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch.

[0074] Fix the mulch film base paper and evenly coat both sides with gelatinized cationic starch using a 10μm linear coating rod. Dry at 80°C for 10 minutes. Remove the paper and continue coating the starch layer on both sides with polyurethane using a 4μm linear coating rod. Dry at 110°C for 10 minutes.

[0075] The properties of mulch paper prepared with different dry strength agent contents are shown in Table 3.

[0076] Table 3 Properties of mulch paper prepared with different dry strength agent contents

[0077] Example 4

[0078] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0079] Take 1.88g of absolute dry pulp and papermaking additives with the absolute dry pulp weight percentage of 1% CPAM dry strength agent, 2%, 2.5%, 3% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention agent, blend them in a deflaking machine, deflake at 10,000 revolutions to make the fibers completely dispersed. After deflaking, feed the pulp into a papermaking machine to obtain 60g / m 2 Ground film base paper.

[0080] For the coating experiment on mulch film base paper, a 5 wt% cationic starch aqueous solution was prepared, followed by the addition of sodium hydroxide (10% by weight of the starch mass). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch.

[0081] Fix the mulch film base paper and evenly coat both sides with gelatinized cationic starch using a 10μm linear coating rod. Dry at 80°C for 10 minutes. Remove the paper and continue coating the starch layer on both sides with polyurethane using a 4μm linear coating rod. Dry at 110°C for 10 minutes.

[0082] The properties of mulch paper prepared with different wet strength agent contents are shown in Table 4.

[0083] Table 4 Properties of mulch paper prepared with different wet strength agent contents

[0084] Example 5

[0085] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0086] 1.88g of absolute dry pulp and papermaking additives, which are 1% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp, are mixed in a deflaking machine and deflaked at 10,000 revolutions to fully disperse the fibers. After deflaking, the pulp is fed into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0087] For the coating experiment on mulch film base paper, 1%, 5%, and 7% cationic starch aqueous solutions were prepared. Then, sodium hydroxide (10% by weight of the starch) was added. The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch.

[0088] Fix the mulch base paper and evenly coat the front of the mulch base paper with gelatinized cationic starch using a 10μm linear coating rod. Dry at 80℃ for 10 minutes. Remove the paper and continue coating the starch layer on the front with acrylic resin using a 4μm linear coating rod. Dry at 110℃ for 10 minutes.

[0089] The properties of mulch paper prepared with different cationic starch concentrations are shown in Table 5.

[0090] Table 5 Properties of mulch paper prepared with different cationic starch concentrations

[0091] As shown in Table 4, different concentrations of gelatinized cationic starch result in different actual coating amounts of starch. When the gelatinized cationic concentration increases, its pore-filling effect on the fiber is improved, which reduces the coating amount of acrylic resin and can also make the relevant properties of the mulch paper meet the requirements.

[0092] Example 6

[0093] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0094] 1.88g of absolute dry pulp and papermaking additives, which are 1% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp, are mixed in a deflaking machine and deflaked at 10,000 revolutions to fully disperse the fibers. After deflaking, the pulp is fed into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0095] Coating experiment for mulch film base paper: First, prepare a 7% cationic starch aqueous solution, then add sodium hydroxide (10% by weight of the starch). Mechanically stir at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch. Fix the mulch film base paper and evenly coat the gelatinized cationic starch on both sides using a 10μm linear coating rod. Dry at 80°C for 10 minutes. Remove the paper and continue coating the starch layers on both sides with polycaprolactone (PCL), polyvinylidene chloride (PVDC), and modified starch using a 4μm linear coating rod. Dry at 30°C for 10 minutes.

[0096] The properties of mulch paper prepared with different hydrophobic and moisture-resistant coatings are shown in Table 6.

[0097] Table 6 Properties of mulch paper prepared with different hydrophobic and moisture-resistant coatings

[0098] During the experiment, the coating effects of PCL and PVDC were compared. Although they have excellent hydrophobicity and water vapor barrier properties, they are relatively difficult to coat and the coating amount is difficult to reduce, resulting in high coating costs.

[0099] Example 7

[0100] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0101] 1.88g of absolute dry pulp and papermaking additives, which are 1% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp, are mixed in a deflaking machine and deflaked at 10,000 revolutions to fully disperse the fibers. After deflaking, the pulp is fed into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0102] A coating experiment for mulch film base paper involved preparing a 7% cationic starch aqueous solution, followed by the addition of sodium hydroxide (10% by weight of the starch). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch. The mulch film base paper was fixed in place and evenly coated with the gelatinized cationic starch on both sides using a 10μm linear coating rod. The paper was then dried at 80°C for 10 minutes. The mulch film base paper was removed and polyurethane was applied to the starch layer on both sides using a 4μm linear coating rod. The paper was then dried at 110°C for 10 minutes to obtain the mulch film. The properties of the prepared mulch film paper are shown in Table 7.

[0103] Table 7 Properties of mulch paper

[0104] Water resistance of mulch paper Cobb 120 8.6g / m 2 , showing excellent hydrophobic properties, which is conducive to the sliding of water droplets on the surface of the mulch paper and extends the service life of the mulch paper.

[0105] The water vapor permeability of the ground film paper is 683g / m 2 · 24 hours, 424% higher than the base paper of mulch film. Through the coating process, the mulch film paper is given excellent water vapor barrier properties, which can effectively prevent water loss in the soil and crops, thereby achieving the effect of increasing production and efficiency.

[0106] Physical strength index of mulch paper: tear index is 8.3mN·m 2 / g, burst resistance index is 2.48kPa.m 2The dry tensile index was 35.6 N·m / g, and the wet tensile index was 26.7 N·m / g. All four test results met the requirements for laying in greenhouses. The wet tensile index reached 75% of the dry tensile index and was 556% higher than the base paper, indicating that the bio-mechanical pulp mulch paper can be used for a long time even in a high humidity environment in a greenhouse.

[0107] The light transmittance of the mulch paper is 3.9%, which can effectively inhibit the growth of weeds, thereby achieving the purpose of inhibiting weed growth in the area covered by the mulch paper.

[0108] Example 8

[0109] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0110] 1.88g of absolute dry pulp and papermaking additives, which are 1% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp, are mixed in a deflaking machine and deflaked at 10,000 revolutions to fully disperse the fibers. After deflaking, the pulp is fed into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0111] For the coating experiment on mulch film base paper, a 7% cationic starch aqueous solution was prepared, followed by the addition of sodium hydroxide (10% by weight of the starch). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch.

[0112] Fix the base paper of the mulch film, and evenly coat the front and back sides of the base paper with gelatinized cationic starch using a 10 μm linear coating rod, and dry at 80°C for 10 minutes.

[0113] Take it out, and continue to coat acrylic resin on the starch layer on both sides with a 4μm linear coating rod, and dry it at 110℃ for 10min.

[0114] The properties of the prepared mulch paper are shown in Table 8.

[0115] Table 8 Properties of mulch paper

[0116] Water resistance of mulch paper Cobb 120 18.7g / m 2 , has certain hydrophobic properties, which is beneficial to prolong the service life of mulch paper in a humid environment.

[0117] The water vapor permeability of the ground film paper is 734g / m2 ·24h, the water vapor barrier performance of the film paper is improved by 394% compared with the base paper. After coating with acrylic resin, the water vapor barrier performance of the film paper is still less than 800g / m 2 24 hours, and the cost is lower than polyurethane.

[0118] Physical strength index of mulch paper: tear index is 7.3mN·m 2 / g, burst resistance index is 2.27kPa.m 2 / g, dry tensile index of 44.7 N·m / g, and wet tensile index of 20.7 N·m / g. All four test results met the requirements for laying in greenhouses, with the wet tensile index reaching 46% of the dry tensile index and a 431% improvement over the base paper. Compared to Example 1, Example 2 exhibited a higher dry tensile index.

[0119] The light transmittance of mulch paper is 4.5%, which can still effectively inhibit the growth and development of weeds and achieve the purpose of inhibiting weed growth.

[0120] Comparative Example 1

[0121] Papermaking of mulch paper: Take about 500g of absolute dry weight of biomechanical pulp, beat it with a Wall-E pulper, the beating time is about 20min, the beating degree is about 40°SR, after beating, use a pulp bag to filter out most of the water, put it in a 5℃ low-temperature refrigerator for 24h to balance the moisture, and measure the solid content.

[0122] 1.88g of absolute dry pulp and papermaking additives, which are 1% CPAM dry strength agent, 2.5% PAE wet strength agent, 0.5% AKD sizing agent and 0.1% retention aid by weight of the absolute dry pulp, are mixed in a deflaking machine and deflaked at 10,000 revolutions to fully disperse the fibers. After deflaking, the pulp is fed into a papermaking machine to obtain a 60g / m 2 Ground film base paper.

[0123] For the coating experiment on mulch film base paper, a 7% cationic starch aqueous solution was prepared, followed by the addition of sodium hydroxide (10% by weight of the starch). The mixture was mechanically stirred at 10,000 rpm for 30 minutes at 40°C to obtain gelatinized cationic starch. The mulch film base paper was then fixed in place and evenly coated on both sides using a 10μm linear coating rod. The mixture was then dried at 80°C for 10 minutes.

[0124] The properties of the prepared mulch paper are shown in Table 9.

[0125] Table 9 Properties of mulch paper

[0126] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing greenhouse mulch paper, characterized in that: The steps include: The biomechanical pulp of wheat straw is debonded and then beaten to obtain a pulp with a beating degree of 35-40°SR; After the slurry is fully mixed with the papermaking auxiliary agent, papermaking is performed to obtain the base paper for ground film; Evenly coating gelatinized cationic starch or gelatinized soybean oil modified starch on one side or both sides of the mulch base paper, and drying; during gelatinization, the mass percentage of the cationic starch aqueous solution is 3-10%; the mass percentage of the starch in the soybean oil modified starch is 2.5-10%; Then evenly apply polyurethane or acrylic resin coating on one side or both sides and dry it.

2. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The method also includes the step of adding 0-40% by mass of waste corrugated paper pulp or 0-40% by mass of wheat straw pulp to the wheat straw biomechanical pulp, wherein the addition ratio of the waste corrugated paper pulp or wheat straw pulp is not zero.

3. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The papermaking auxiliary agent comprises 0.5%-3% of cationic polyacrylamide or cationic starch or chitosan by weight of absolute dry pulp, 1.5%-3% of polyamide polyamine epichlorohydrin by weight of absolute dry pulp, 0.5%-2% of alkyl ketene dimer or aluminum sulfate by weight of absolute dry pulp, and 0.1%-0.3% of cationic / anionic polyacrylamide or cationic / anionic starch by weight of absolute dry pulp; Preferably, the papermaking auxiliary agent comprises 1%-2% of cationic polyacrylamide or cationic starch or chitosan by weight of the absolute dry pulp, 2%-3% of polyamide polyamine epichlorohydrin by weight of the absolute dry pulp, 0.5%-1% of alkyl ketene dimer or aluminum sulfate by weight of the absolute dry pulp, and 0.1%-0.2% of cationic / anionic polyacrylamide or cationic / anionic starch by weight of the absolute dry pulp; Preferably, the papermaking auxiliary agent includes 1%-2% of cationic polyacrylamide by weight of absolute dry pulp, 2%-3% of polyamide polyamine epichlorohydrin by weight of absolute dry pulp, and 0.5%-1% of alkyl ketene dimer by weight of absolute dry pulp.

4. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The preparation method of gelatinized cationic starch is as follows: adjust the cationic starch aqueous solution to alkaline, heat it to 40-50°C, and stir it for 20-40 minutes to obtain; Preferably, the mass percentage of the cationic starch aqueous solution is 3-10%; Preferably, the mass percentage of sodium hydroxide in the cationic starch aqueous solution is 8%-15%.

5. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The preparation method of soybean oil modified starch is as follows: soybean oil and sodium carbonate are added to a dimethyl sulfoxide solution of starch to obtain a mixed solution, and the mixed solution is heated to 110-150° C. for 1-3 hours to hydrophobically modify the starch; Preferably, in the mixed solution, the mass percentage of starch is 2.5-10%; the mass percentage of soybean oil is 8-12%; and the mass percentage of sodium carbonate is 13-17%.

6. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The coating method of gelatinized cationic starch or gelatinized soybean oil modified starch is: use a 10 μm linear coating rod to coat the surface of the mulch base paper, and then dry it; Preferably, the single-sided coating amount of gelatinized cationic starch or gelatinized soybean oil modified starch is 1.5-2 g / m 2 , double-sided coating amount is 3-4g / m 2 .

7. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The coating method of the polyurethane or acrylic resin coating is: coating the surface of the gelatinized cationic starch or gelatinized modified starch coating with a 4 μm linear coating rod, and the coating is obtained after drying.

8. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The single-sided coating amount of polyurethane is 1.5-2g / m 2 , double-sided coating amount is 3-4g / m 2 ; Preferably, the single-sided coating amount of acrylic resin is 2.5-3 g / m 2 , double-sided coating amount is 5-6g / m 2 .

9. The method for preparing greenhouse mulch paper according to claim 1, characterized in that: The basis weight of the base paper is 60-70g / m 2 .

10. A mulch paper for greenhouse, characterized by: Prepared by the preparation method described in any one of claims 1 to 9.

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