High-barrier direct plating paper and preparation method thereof

Abstract

The application discloses a kind of high-barrier straight plating paper and preparation method thereof, it is related to packaging material technical field.The preparation method of a kind of high-barrier straight plating paper of the application includes the following steps: paper surface is coated with primer, and pretreated substrate is obtained;Pretreatment coating surface is coated with moisture and oxygen barrier coating, and substrate with moisture and oxygen barrier coating on surface is obtained;Moisture and oxygen barrier coating surface is plated with aluminum, and high-barrier straight plating paper is obtained;Primer includes the following raw materials: montmorillonite modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, curing agent, crosslinking agent, tackifier, dispersant, wetting agent;The paper is treated before plating with aluminum in the application, not only improves the barrier property of straight plating paper to water vapor, oxygen and grease, but also improves the adhesion of paper and plated aluminum layer and the smoothness of plated aluminum layer, ensures the integrity of plated aluminum layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of packaging materials, in particular to a high-barrier direct plating paper and a preparation method thereof. BACKGROUND

[0002] With the development of science and technology and the improvement of people's living standards, people pay more and more attention to the sustainable development of resources and the protection of the living environment, and require green production and green consumption. Food packaging paper is a packaging material mainly made of paper and paperboard, which can effectively prevent food from being damaged by external oxygen, water vapor, potential harmful migration, oil and other substances during storage and transportation, and plays a role in delaying food deterioration and protecting food quality and safety. Paper material is interwoven by fibers, and the hydrophilicity and capillary action of the fibers make the water absorption of the paper strong. The porous structure also exacerbates the penetration of oil and grease, so untreated paper does not have any water and oil barrier ability. In order to meet the needs of high barrier and functional transformation of food packaging paper, direct plating paper (also known as direct vacuum aluminum plating paper) is mainly composed of base paper, aluminum layer and coating layer. It is obtained by pre-coating the paper surface to improve the surface smoothness and brightness of the paper, and then placing the paper in a vacuum aluminum plating machine to directly plate aluminum on its surface. The direct plating paper has the advantages of good gloss and smoothness, good flexibility, beauty and environmental protection, and also has good printing performance and mechanical processing performance, so it is widely used in the packaging of cigarettes, wine, tea, food, cosmetics and other products.

[0003] However, in order to enhance its barrier performance (such as water resistance, gas resistance, oil resistance, etc.), the formula and preparation process of its surface coating need to be optimized. The common paper barrier coating materials are mainly divided into two categories. One is natural biopolymer, such as cellulose, starch, chitosan and sodium alginate, which forms a dense film through the molecular structure characteristics of the polymer itself, thereby playing a barrier role. However, these materials are mostly hydrophilic substances, which have the disadvantages of poor water resistance, strong crystallinity, large brittleness and poor melt stability, and are not easy to realize industrialized production and application. The other is artificially synthesized high molecular polymer, such as polyvinyl alcohol (PVA), polylactic acid (PLA), polyhydroxybutyrate (PHB) and acrylate copolymer. Among them, polyvinyl alcohol has regular molecular chain stacking, high crystallinity and good film forming property, and excellent oxygen barrier performance, which is suitable for soft packaging coating. However, due to the presence of hydrophilic hydroxyl groups in polyvinyl alcohol, polyvinyl alcohol will absorb environmental moisture when exposed to humid conditions, and the water molecules will enter the interior of the molecule to swell and dissolve the intermolecular hydrogen bonds, greatly damaging its barrier capacity. SUMMARY

[0004] The purpose of the present application is to provide a high-barrier direct plating paper and a preparation method thereof, which solves the following technical problems:

[0005] Existing barrier coatings use hydrophilic polyvinyl alcohol as a base material. Polyvinyl alcohol absorbs moisture from the environment in humid conditions, which greatly reduces the barrier coating's ability to block moisture.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing high-barrier direct-coated paper includes the following steps:

[0008] S1: A base coating and a moisture- and oxygen-barrier layer are sequentially coated on the paper surface to obtain a pretreated substrate;

[0009] S2: Aluminum is plated on the surface of the moisture-proof and oxygen-proof layer of the pretreated substrate to obtain high-barrier straight-coated paper;

[0010] The base coating comprises the following raw materials in parts by weight: 75-85% montmorillonite-modified polyvinyl alcohol, 10-15% ethylene-vinyl alcohol copolymer, 1-3% curing agent, 2-4% crosslinking agent, 2-4% tackifier, 0.1-0.3% dispersant, and 0.3-0.5% wetting agent;

[0011] The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0012] A1: Add acidified montmorillonite, anhydrous ethanol, deionized water, and N,N-diethyl-3-aminopropyltrimethoxysilane to a reaction vessel and disperse evenly. Control the temperature at 60-80℃ and keep the reaction at this temperature for 2-4 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0013] A2: In a nitrogen atmosphere, organic montmorillonite and methanol are added to a reaction vessel and dispersed evenly. The temperature is controlled at 45-55℃. Epichlorohydrin is added, and the reaction is maintained at this temperature for 3-6 hours. The mixture is then cooled to room temperature, filtered, washed, and dried to obtain modified montmorillonite.

[0014] A3: Polyvinyl alcohol and dimethyl sulfoxide are added to a reaction vessel and dispersed evenly. The temperature is controlled at 85-95℃, and the mixture is stirred to dissolve. The temperature is controlled at 55-65℃, and modified montmorillonite and sodium hydroxide solution are added. The mixture is kept at this temperature for 3-6 hours, filtered, washed, and dried to obtain montmorillonite-modified polyvinyl alcohol.

[0015] As a further embodiment of the present invention: the addition ratio of acidified montmorillonite, anhydrous ethanol, deionized water and N,N-diethyl-3-aminopropyltrimethoxysilane in A1 is 10g: 20-40mL: 80-160mL: 4-8g.

[0016] As a further aspect of the present invention: the addition ratio of organo-modified montmorillonite, methanol, and epichlorohydrin in A2 is 10g: 50-100mL: 1.5-3g.

[0017] As a further aspect of the present invention: the sodium hydroxide solution in A3 is a 10-15wt% sodium hydroxide solution; the addition ratio of polyvinyl alcohol, dimethyl sulfoxide, modified montmorillonite, and sodium hydroxide solution is 10g:100-150mL:1-2g:10-20mL.

[0018] As a further aspect of the present invention: acidified montmorillonite is obtained by washing montmorillonite with water and then treating it with hydrochloric acid.

[0019] As a further aspect of the present invention: the curing agent is a polyamide-epoxy resin copolymer; the crosslinking agent is melamine-formaldehyde resin; the tackifier is carboxymethyl cellulose; the dispersant is ammonium polyacrylate dispersant; and the wetting agent is sodium dodecyl sulfate.

[0020] As a further aspect of the present invention: the ethylene-vinyl alcohol copolymer has a molar fraction of ethylene of 20-40% and a molar fraction of vinyl alcohol of 60-80%.

[0021] As a further aspect of the present invention: the specific method for aluminum plating in S2 is: physical vapor deposition of aluminum in a vacuum environment, with an aluminum plating thickness of 200-400 Å.

[0022] As a further aspect of the present invention: the water vapor permeability of the moisture-barrier and oxygen-barrier layer is 0.5-1.5 g / m². 2 • 24h, oxygen permeability is 0.8-1.2 cm 3 / (m 2 (24h, 0.1MPa).

[0023] As a further aspect of the present invention: the base coating is obtained by dry molding. The specific steps of the dry molding method are: applying a pre-treatment coating on the surface of the film carrier, laminating the film carrier with paper, then peeling the film carrier from the paper and drying it to form a base coating on the surface of the paper; the film carrier is BOPP or PET film.

[0024] As a further aspect of the present invention: the dry weight of the pretreatment coating is 1.5-2.5 g / m². 2 The solid content of the pretreatment coating is 35-50%.

[0025] A method for preparing high-barrier direct-coated paper, which is made by any of the above preparation methods.

[0026] The beneficial effects of this invention are:

[0027] (1) This application utilizes hydrochloric acid to acidify montmorillonite to obtain acidified montmorillonite; and uses N,N-diethyl-3-aminopropyltrimethoxysilane to organically treat the acidified montmorillonite. The alkoxy group of N,N-diethyl-3-aminopropyltrimethoxysilane is hydrolyzed in an aqueous alcohol solution to generate silanol, which then reacts with the silanol on the end face of the acidified montmorillonite and is dehydrated at high temperature to obtain organic montmorillonite. Utilizing the Si-O-Si bond in its main chain, the water absorption and swelling properties of montmorillonite are effectively reduced; this application further utilizes epichlorohydrin to react with the tertiary amine between the organic montmorillonite layers to obtain modified montmorillonite. Modified montmorillonite; the modified montmorillonite prepared in this application not only has antibacterial groups and epoxy groups, but also further improves the interlayer spacing and reduces the polarity of montmorillonite through modification with epichlorohydrin; this application utilizes the epoxy groups of modified montmorillonite to react with the hydroxyl groups of polyvinyl alcohol to obtain montmorillonite-modified polyvinyl alcohol; this application crosslinks polyvinyl alcohol and modified montmorillonite, introducing montmorillonite to effectively inhibit the swelling of the coating after contact with water and improve the density of the coating; the addition of montmorillonite makes the molecular diffusion channels more tortuous, prolongs the diffusion distance of molecules per unit time, and the permeation flux of the coating decreases accordingly.

[0028] This application utilizes montmorillonite-modified polyvinyl alcohol as a base material. Polyvinyl alcohol has excellent oxygen barrier properties. Modifying montmorillonite increases the interlayer spacing, which helps polyvinyl alcohol molecular chains penetrate and form tighter intermolecular forces. Montmorillonite fills the micro-gaps in the coating, reducing air permeability. After treating polyvinyl alcohol with modified montmorillonite, the oxygen permeability and water vapor permeability of the coating are significantly reduced, and the mechanical properties, thermal stability, and surface smoothness are significantly improved, effectively enhancing the barrier properties of direct-coated paper and the smoothness of subsequent aluminum plating.

[0029] (2) This application sets a base coating and a moisture- and oxygen-barrier layer between the paper and the aluminum plating layer, effectively improving the barrier properties of the material. The prepared direct-coated paper has good barrier properties against water vapor, oxygen, and grease, which can extend the shelf life of the contents. This application uses montmorillonite-modified polyvinyl alcohol as the base material for the base coating, which effectively improves the adhesion and smoothness of the coating and ensures the integrity of the subsequent aluminum plating layer. The direct-coated paper prepared by this application can be more widely used in food, pharmaceutical, and industrial packaging, and meets the demand for high-barrier materials.

[0030] (3) This application utilizes the synergistic effect of montmorillonite-modified polyvinyl alcohol and EVOH (ethylene-vinyl alcohol copolymer) and polyamide-epoxy resin copolymer to impart excellent gas barrier properties, water vapor barrier properties and moisture resistance to the base coating. This application adds melamine-formaldehyde resin as a crosslinking agent to improve the mechanical strength and moisture resistance of the coating; adds carboxymethyl cellulose as a tackifier to improve the adhesion of the coating; adds ammonium polyacrylate as a dispersant to ensure uniform dispersion of the barrier material; and adds sodium dodecyl sulfate as a wetting agent to enhance the uniformity of the coating application. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0033] A1: Disperse 10g of sodium montmorillonite in 50mL of deionized water, centrifuge and wash, add 10mL of 1mol / L hydrochloric acid solution to acidify, wash with water to obtain acidified montmorillonite;

[0034] A2: Add 10g of acidified montmorillonite, 20mL of anhydrous ethanol, 80mL of deionized water, and 4g of N,N-diethyl-3-aminopropyltrimethoxysilane (CAS: 41051-80-3) to a reaction vessel and disperse evenly. Control the temperature at 60℃ and keep the reaction at this temperature for 2 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0035] A3: In a nitrogen atmosphere, 10g of organomodified montmorillonite and 50mL of methanol were added to the reaction vessel and dispersed evenly. The temperature was controlled at 45℃. 1.5g of epichlorohydrin was added and the reaction was maintained at this temperature for 3h. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain modified montmorillonite.

[0036] A4: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 100mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 85℃, stir to dissolve, control the temperature at 55℃, add 1g of modified montmorillonite and 10mL of 10wt% sodium hydroxide solution, keep the temperature for 3h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0037] Example 2: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0038] A1: Disperse 10g of sodium montmorillonite in 50mL of deionized water, centrifuge and wash, add 10mL of 1mol / L hydrochloric acid solution to acidify, wash with water to obtain acidified montmorillonite;

[0039] A2: Add 10g of acidified montmorillonite, 30mL of anhydrous ethanol, 120mL of deionized water, and 6g of N,N-diethyl-3-aminopropyltrimethoxysilane (CAS: 41051-80-3) to a reaction vessel and disperse evenly. Control the temperature at 70℃ and keep the reaction at this temperature for 3 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0040] A3: In a nitrogen atmosphere, 10g of organomodified montmorillonite and 70mL of methanol were added to the reaction vessel and dispersed evenly. The temperature was controlled at 50℃, and 2g of epichlorohydrin was added. The reaction was kept at this temperature for 4 hours, then cooled to room temperature. The mixture was then filtered, washed, and dried to obtain modified montmorillonite.

[0041] A4: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 120mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 90℃, stir to dissolve, control the temperature at 60℃, add 1.5g of modified montmorillonite and 15mL of 10wt% sodium hydroxide solution, keep the reaction at this temperature for 4h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0042] Example 3: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0043] A1: Disperse 10g of sodium montmorillonite in 50mL of deionized water, centrifuge and wash, add 10mL of 1mol / L hydrochloric acid solution to acidify, wash with water to obtain acidified montmorillonite;

[0044] A2: Add 10g of acidified montmorillonite, 40mL of anhydrous ethanol, 160mL of deionized water, and 8g of N,N-diethyl-3-aminopropyltrimethoxysilane (CAS: 41051-80-3) to a reaction vessel and disperse evenly. Control the temperature at 80℃ and keep the reaction at this temperature for 4 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0045] A3: In a nitrogen atmosphere, 10g of organomodified montmorillonite and 100mL of methanol were added to the reaction vessel and dispersed evenly. The temperature was controlled at 55℃, and 3g of epichlorohydrin was added. The reaction was kept at this temperature for 6 hours, then cooled to room temperature. The mixture was then filtered, washed, and dried to obtain modified montmorillonite.

[0046] A4: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 150mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 95℃, stir to dissolve, control the temperature at 65℃, add 2g of modified montmorillonite and 20mL of 10wt% sodium hydroxide solution, keep the temperature for 6h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0047] Example 4: The preparation method of melamine-formaldehyde resin includes the following steps:

[0048] 60 mL of 37 wt% formaldehyde aqueous solution and 0.15 g of hexamethylenetetramine (also known as thiamethylenetetramine) were added to a reaction flask and dispersed evenly. 35 g of melamine was added, the temperature was controlled at 80 ℃, and the mixture was stirred to dissolve. The reaction was kept at this temperature until the precipitation ratio reached 2:2. Triethanolamine was added to adjust the pH to 8 to obtain melamine-formaldehyde resin.

[0049] Example 5: A method for preparing high-barrier direct-coated paper, comprising the following steps:

[0050] S1: 78.1g of montmorillonite-modified polyvinyl alcohol prepared in Example 1, and 12g of ethylene-vinyl alcohol copolymer (ethylene molar fraction 32%, density 1.19g / cm³) 3 3g of polyamide epoxy curing agent NP-650, 3g of melamine-formaldehyde resin prepared in Example 4, 3.2g of carboxymethyl cellulose, 0.3g of ammonium polyacrylate dispersant, 0.4g of sodium dodecyl sulfate, and deionized water were blended to obtain a pre-treated coating with a solid content of 40%. After coating the PET film with the pre-treated coating, it was mixed with paper (inner liner paper 60g / m²). 2 The dry coating weight of the composite and pretreated coating is 2 g / m². 2 Then, the film carrier is peeled off from the paper and dried to form a base coating on the paper surface;

[0051] S2: Apply a moisture- and oxygen-barrier layer to the surface of the primer layer. The moisture- and oxygen-barrier layer is TAKELAC WPB-341 manufactured by Mitsui Chemicals Co., Ltd., and the water vapor permeability of the moisture- and oxygen-barrier layer is 1 g / m³. 2 24h, oxygen permeability is 1cm 3 / (m 2 (24h, 0.1MPa) to obtain a pretreated substrate;

[0052] S3: The surface of the moisture- and oxygen-barrier layer of the pretreated substrate is coated with aluminum by physical vapor deposition under vacuum conditions, with an aluminum coating thickness of 200 Å, to obtain high-barrier straight-coated paper.

[0053] Example 6 A method for preparing high-barrier direct-coated paper, comprising the following steps:

[0054] S1: 78.1g of montmorillonite-modified polyvinyl alcohol prepared in Example 2, and 12g of ethylene-vinyl alcohol copolymer (ethylene molar fraction 32%, density 1.19g / cm³) 3 3g of polyamide epoxy curing agent NP-650, 3g of melamine-formaldehyde resin prepared in Example 4, 3.2g of carboxymethyl cellulose, 0.3g of ammonium polyacrylate dispersant, 0.4g of sodium dodecyl sulfate, and deionized water were blended to obtain a pre-treated coating with a solid content of 40%. After coating the PET film with the pre-treated coating, it was mixed with paper (inner liner paper 60g / m²). 2 The dry coating weight of the composite and pretreated coating is 2 g / m². 2 Then, the film carrier is peeled off from the paper and dried to form a base coating on the paper surface;

[0055] S2: Apply a moisture- and oxygen-barrier layer to the surface of the primer layer. The moisture- and oxygen-barrier layer is TAKELAC WPB-341 manufactured by Mitsui Chemicals Co., Ltd., and the water vapor permeability of the moisture- and oxygen-barrier layer is 1 g / m³. 2 24h, oxygen permeability is 1cm3 / (m 2 (24h, 0.1MPa) to obtain a pretreated substrate;

[0056] S3: The surface of the moisture- and oxygen-barrier layer of the pretreated substrate is coated with aluminum by physical vapor deposition under vacuum conditions, with an aluminum coating thickness of 200 Å, to obtain high-barrier straight-coated paper.

[0057] Example 7 A method for preparing high-barrier direct-coated paper, comprising the following steps:

[0058] S1: 78.1g of montmorillonite-modified polyvinyl alcohol prepared in Example 3, and 12g of ethylene-vinyl alcohol copolymer (ethylene molar fraction 32%, density 1.19g / cm³) 3 3g of polyamide epoxy curing agent NP-650, 3g of melamine-formaldehyde resin prepared in Example 4, 3.2g of carboxymethyl cellulose, 0.3g of ammonium polyacrylate dispersant, 0.4g of sodium dodecyl sulfate, and deionized water were blended to obtain a pre-treated coating with a solid content of 40%. After coating the PET film with the pre-treated coating, it was mixed with paper (inner liner paper 60g / m²). 2 The dry coating weight of the composite and pretreated coating is 2 g / m². 2 Then, the film carrier is peeled off from the paper and dried to form a base coating on the paper surface;

[0059] S2: Apply a moisture- and oxygen-barrier layer to the surface of the primer layer. The moisture- and oxygen-barrier layer is TAKELAC WPB-341 manufactured by Mitsui Chemicals Co., Ltd., and the water vapor permeability of the moisture- and oxygen-barrier layer is 1 g / m³. 2 24h, oxygen permeability is 1cm 3 / (m 2 (24h, 0.1MPa) to obtain a pretreated substrate;

[0060] S3: The surface of the moisture- and oxygen-barrier layer of the pretreated substrate is coated with aluminum by physical vapor deposition under vacuum conditions, with an aluminum coating thickness of 200 Å, to obtain high-barrier straight-coated paper.

[0061] Comparative Example 1: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0062] A1: Disperse 10g of sodium montmorillonite in 50mL of deionized water, centrifuge and wash, add 10mL of 1mol / L hydrochloric acid solution to acidify, wash with water to obtain acidified montmorillonite;

[0063] A2: Add 10g of acidified montmorillonite, 20mL of anhydrous ethanol, 80mL of deionized water, and 4g of γ-glycidyl etheroxypropyltrimethoxysilane to a reaction vessel and disperse evenly. Control the temperature at 60℃ and keep the reaction at this temperature for 2 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0064] A3: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 100mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 85℃, stir to dissolve, control the temperature at 55℃, add 1g of organomodified montmorillonite and 10mL of 10wt% sodium hydroxide solution, keep the temperature for 3h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0065] Comparative Example 2: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0066] A1: 10g of montmorillonite, 20mL of anhydrous ethanol, 80mL of deionized water, and 4g of N,N-diethyl-3-aminopropyltrimethoxysilane (CAS: 41051-80-3) were added to a reaction vessel and dispersed evenly. The temperature was controlled at 60℃ and the reaction was maintained for 2 hours. The mixture was then washed with water and dried to obtain organo-modified montmorillonite.

[0067] A2: In a nitrogen atmosphere, 10g of organomodified montmorillonite and 50mL of methanol were added to the reaction vessel and dispersed evenly. The temperature was controlled at 45℃. 1.5g of epichlorohydrin was added and the reaction was maintained at this temperature for 3h. The mixture was then cooled to room temperature, filtered, washed, and dried to obtain modified montmorillonite.

[0068] A3: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 100mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 85℃, stir to dissolve, control the temperature at 55℃, add 1g of modified montmorillonite and 10mL of 10wt% sodium hydroxide solution, keep the temperature for 3h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0069] Comparative Example 3: The preparation method of montmorillonite-modified polyvinyl alcohol includes the following steps:

[0070] A1: Disperse 10g of sodium montmorillonite in 50mL of deionized water, centrifuge and wash, add 10mL of 1mol / L hydrochloric acid solution to acidify, wash with water to obtain acidified montmorillonite;

[0071] A2: Add 10g of acidified montmorillonite, 20mL of anhydrous ethanol, 80mL of deionized water, and 4g of N,N-diethyl-3-aminopropyltrimethoxysilane (CAS: 41051-80-3) to a reaction vessel and disperse evenly. Control the temperature at 60℃ and keep the reaction at this temperature for 2 hours. Wash with water and dry to obtain organo-modified montmorillonite.

[0072] A3: Add 10g of polyvinyl alcohol (88% degree of alcoholysis) and 100mL of dimethyl sulfoxide to a reaction vessel and disperse evenly. Control the temperature at 85℃, stir to dissolve, control the temperature at 55℃, add 1g of organomodified montmorillonite and 10mL of 10wt% sodium hydroxide solution, keep the temperature for 3h, filter, wash and dry to obtain montmorillonite-modified polyvinyl alcohol.

[0073] Compared with Example 6, Comparative Example 4 only replaced the montmorillonite-modified polyvinyl alcohol prepared in Example 2 with the montmorillonite-modified polyvinyl alcohol prepared in Comparative Example 1 in an equal amount. The remaining components and preparation methods were completely the same as those in Example 6.

[0074] Compared with Example 6, Comparative Example 5 only replaced the montmorillonite-modified polyvinyl alcohol prepared in Example 2 with an equal amount of the montmorillonite-modified polyvinyl alcohol prepared in Comparative Example 2. The remaining components and preparation methods were completely the same as those in Example 6.

[0075] Compared with Example 6, Comparative Example 6 only replaced the montmorillonite-modified polyvinyl alcohol prepared in Example 2 with the montmorillonite-modified polyvinyl alcohol prepared in Comparative Example 3 in an equal amount. The remaining components and preparation methods were completely the same as those in Example 6.

[0076] Performance testing

[0077] (1) Barrier performance: According to BB / T 0030-2019 "Aluminized film for packaging", the base coatings prepared in Examples 5-7 and Comparative Examples 4-6 were tested using a W3 / 060 water vapor transmission rate tester and a VAC-V1 differential pressure gas permeation tester. The water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) were measured. The test results are shown in Table 1.

[0078] Table 1: Statistical Table of Barrier Performance Test Data for Examples 5-7 and Comparative Examples 4-6

[0079]

[0080] As shown in Table 1, the base coating prepared using the pretreatment coating of this application as raw material has excellent water vapor and oxygen barrier properties, effectively improving the problem of easy swelling when exposed to water in existing coatings based on polyvinyl alcohol.

[0081] (2) Oil resistance: The oil barrier effect was tested by the penetration method according to Q / HYG 002-2019 "Oilproof Paper". The test results are shown in Table 2.

[0082] Table 2: Statistical Table of Oil Resistance Test Data for Examples 5-7 and Comparative Examples 4-6

[0083]

[0084] As shown in Table 2, the base coating prepared in this application has excellent oil and water resistance.

[0085] (3) Mechanical properties:

[0086] ① Smoothness: The base coating was tested according to GB / T 456-2002 "Determination of smoothness of paper and paperboard (Beck method)", and the test results are shown in Table 3;

[0087] ② Interlayer adhesion: The adhesion between the base coat and the paper was tested according to the ASTM D3359-02 scratch test. The test results are shown in Table 3.

[0088] ③ Antibacterial properties: The antibacterial properties of the primers prepared in Examples 5-7 and Comparative Examples 4-6 against Escherichia coli and Staphylococcus aureus were tested using the agar plate diffusion method. The primers were cut into 8mm round pieces, sterilized by UV irradiation, and coated with a concentration of 1.0 × 10⁻⁶. 8 CFU / mL bacterial suspension was incubated at 37℃ for 24 hours, and the diameter of the inhibition zone was measured. The results are shown in Table 3.

[0089] Table 3: Statistical Table of Physicochemical Properties Test Data of Examples 5-7 and Comparative Examples 4-6

[0090]

[0091] The base coating prepared in this application has good surface smoothness and strong adhesion to paper, which facilitates subsequent aluminum plating. Moreover, the base coating has excellent antibacterial properties. The packaging paper prepared in this application, as food packaging paper, has water and oil barrier properties and antibacterial and freshness preservation capabilities.

[0092] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing high-barrier direct-coated paper, characterized in that, Includes the following steps: S1: A base coating and a moisture- and oxygen-barrier layer are sequentially coated on the paper surface to obtain a pretreated substrate; S2: Aluminum is plated on the surface of the moisture-proof and oxygen-proof layer of the pretreated substrate to obtain high-barrier straight-coated paper; The base coating comprises the following raw materials in parts by weight: 75-85% montmorillonite-modified polyvinyl alcohol, 10-15% ethylene-vinyl alcohol copolymer, 1-3% curing agent, 2-4% crosslinking agent, 2-4% tackifier, 0.1-0.3% dispersant, and 0.3-0.5% wetting agent; The preparation method of the montmorillonite-modified polyvinyl alcohol includes the following steps: A1: Add acidified montmorillonite, anhydrous ethanol, deionized water, and N,N-diethyl-3-aminopropyltrimethoxysilane to a reaction vessel and disperse evenly. Control the temperature at 60-80℃ and keep the reaction at this temperature for 2-4 hours. Wash with water and dry to obtain organo-modified montmorillonite. A2: In a nitrogen atmosphere, organic montmorillonite and methanol are added to a reaction vessel and dispersed evenly. The temperature is controlled at 45-55℃. Epichlorohydrin is added, and the reaction is maintained at this temperature for 3-6 hours. The mixture is then cooled to room temperature, filtered, washed, and dried to obtain modified montmorillonite. A3: Polyvinyl alcohol and dimethyl sulfoxide are added to a reaction vessel and dispersed evenly. The temperature is controlled at 85-95℃. The mixture is stirred and dissolved. The temperature is controlled at 55-65℃. Modified montmorillonite and sodium hydroxide solution are added. The mixture is kept at the temperature for 3-6 hours. The mixture is then filtered, washed, and dried to obtain montmorillonite-modified polyvinyl alcohol. The curing agent is a polyamide-epoxy resin copolymer; the crosslinking agent is melamine-formaldehyde resin; the tackifier is carboxymethyl cellulose; the dispersant is ammonium polyacrylate dispersant; and the wetting agent is sodium dodecyl sulfate.

2. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The addition ratio of acidified montmorillonite, anhydrous ethanol, deionized water, and N,N-diethyl-3-aminopropyltrimethoxysilane in A1 is 10g: 20-40mL: 80-160mL: 4-8g.

3. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The addition ratio of organo-modified montmorillonite, methanol, and epichlorohydrin in A2 is 10g: 50-100mL: 1.5-3g.

4. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The sodium hydroxide solution in A3 is a 10-15 wt% sodium hydroxide solution; The addition ratio of polyvinyl alcohol, dimethyl sulfoxide, modified montmorillonite, and sodium hydroxide solution is 10g: 100-150mL: 1-2g: 10-20mL.

5. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The specific method for aluminum plating in S2 is as follows: physical vapor deposition of aluminum in a vacuum environment, with an aluminum plating thickness of 200-400 Å.

6. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The water vapor permeability of the moisture-barrier and oxygen-barrier layer is 0.5-1.5 g / m³. 2 • 24h, oxygen permeability is 0.8-1.2 cm 3 / (m 2 (24h, 0.1MPa).

7. The method for preparing a high-barrier direct-coated paper according to claim 1, characterized in that, The base coating is obtained by dry molding. The specific steps of the dry molding method are as follows: applying a pre-treatment coating to the surface of the membrane carrier, laminating the membrane carrier with paper, peeling the membrane carrier from the paper and drying it to form a base coating on the surface of the paper; the membrane carrier is a BOPP or PET film.

8. The method for preparing a high-barrier direct-coated paper according to claim 7, characterized in that, The dry weight of the pretreatment coating is 1.5-2.5 g / m². 2 The solid content of the pretreatment coating is 35-50%.

9. A high-barrier direct-coating paper, characterized in that, It is prepared by any one of the preparation methods described in claims 1-8.

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