A composite membrane preparation process and the product obtained therefrom

Abstract

This application relates to the field of composite membrane processing technology, and more specifically, to a composite diaphragm preparation process and the resulting product, comprising the following preparation steps: S1, applying a primer coating to the kraft paper surface of the composite membrane to form a primer coating layer, thereby obtaining a kraft paper composite layer; S2, printing a surface coating onto the substrate using a gravure printing method to form a discontinuous surface coating layer, thereby obtaining a composite substrate layer; S3, bonding the kraft paper composite layer to the composite substrate layer using a wet lamination process, and then bonding the primer coating layer and the surface coating layer together using a pressure roller to obtain the composite diaphragm. This process results in a smooth and flat surface on the kraft paper, making it less prone to adhering putty powder, thus ensuring stable sealing of the putty powder packaging bag, preventing moisture and air from entering, and extending the shelf life of the putty powder.

Description

Technical Field

[0001] This application relates to the field of composite membrane processing technology, and more specifically, to a composite membrane preparation process and the product obtained therefrom. Background Technology

[0002] Putty powder packaging bags prevent putty powder from getting damp or contaminated, keeping it dry and pure. Putty powder packaging bags are typically made of multiple layers, mainly including an outer layer, an inner layer, and a middle insulating layer. The outer and inner layers are usually kraft paper, while the middle layer is usually a PE film. This composite film effectively prevents the putty powder from getting damp or contaminated. The inner kraft paper, combined with the PE film, forms a highly airtight packaging structure, helping to isolate air and moisture and maintain the quality and stability of the putty powder.

[0003] In actual use, it may be observed that the putty will discolor, harden, or clump. The main reason for this is poor sealing of the putty packaging bag during packaging. Traditional putty packaging bags rely mainly on sewing for sealing, using high-strength fiber thread to sew the bottom or sides of the bag. This allows moisture and air to enter the bag through the seal, causing the putty to deteriorate.

[0004] To prevent moisture and air from entering the packaging, hot melt adhesive or other sealant is used. During the sealing process, putty powder is typically added first, followed by bonding. However, some putty powder adheres to the kraft paper surface, affecting the bonding stability of the hot melt adhesive and other sealant. Over time, moisture and air can still enter the packaging, affecting the quality of the putty. Secondly, the surface of kraft paper is uneven. Adhesives and heat sealants cannot completely fill the pores on the kraft paper surface, leading to unstable bonding. As storage time increases, moisture and air can still enter the packaging through these pores, affecting the quality of the putty powder. Summary of the Invention

[0005] To address the issue of moisture and air entering through the seal during the packaging of putty bags, this application provides a composite diaphragm preparation process and the resulting product.

[0006] In a first aspect, this application provides a composite membrane preparation process, which adopts the following technical solution:

[0007] A composite membrane preparation process includes the following steps:

[0008] S1. Apply a primer coating to the kraft paper surface of the composite film to form a primer coating layer, thus obtaining the kraft paper composite layer;

[0009] S2. A discontinuous surface coating is formed by gravure printing on the substrate to create a composite substrate layer.

[0010] S3. The kraft paper composite layer is laminated with the composite substrate layer by a wet process, and then the base coating and the top coating are bonded together by a pressure roller to obtain a composite diaphragm. The wet process means that the base coating and the top coating are bonded together while they are not fully cured. The base coating is prepared by polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, castor oil polyol, curing agent and diluent.

[0011] The topcoat is prepared from polylactic acid emulsion, methylcellulose, glycidyl ester type epoxy resin, nano-sized rubber powder, curing agent and diluent.

[0012] By adopting the above technical solution, the surface of kraft paper becomes smooth and flat, making it less prone to adhering putty powder. This ensures a stable seal on the putty powder packaging bag, preventing moisture and air from entering and extending the shelf life of the putty powder.

[0013] First, the primer is applied using a reverse coating method, allowing it to penetrate the interior of the kraft paper, filling its pores and preventing air and moisture from entering the putty packaging bag. This also prevents putty powder from adhering to the primer surface during filling, improving the stability of the subsequent sealing of the putty packaging bag. The glycidyl ester epoxy resin in the primer, upon curing, combines with the hydroxyl groups on the kraft paper, ensuring a stable adhesion between the primer and the kraft paper. This also facilitates bonding with the topcoat, enhancing the stability of the composite membrane. Methylcellulose improves the primer's fluidity, making it easier to penetrate the kraft paper and fill its pores, while also creating a smoother surface that resists putty powder adhesion. Castor oil polyol helps improve the flexibility and adhesion of the glycidyl ester epoxy resin, further enhancing the primer's adhesion to the kraft paper and improving the structural stability of the primer layer, making it less prone to damage during use.

[0014] Both the topcoat and primer contain polylactic acid emulsion, methylcellulose, and glycidyl ester epoxy resin, which facilitates bonding with the topcoat and primer, resulting in a strong bond between the two layers and preventing delamination. This is because the topcoat and primer are bonded together before complete curing. After pressing, their components fuse, and a curing reaction occurs during subsequent curing, forming a stable network structure. This ensures a stable bond between the primer and topcoat, preventing separation.

[0015] The topcoat layer is in direct contact with the putty. It must provide excellent airtightness and waterproofing while also exhibiting good chemical resistance to prevent corrosion from the putty. The short lifespan of most traditional putty packaging bags is primarily due to the corrosion of the putty powder, leading to internal aging and leakage. This application addresses this issue by preparing a topcoat layer using polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, nano-sized rubber powder, a curing agent, and a diluent. This comprehensively improves the topcoat's airtightness, waterproofing, chemical resistance, and corrosion resistance, thus protecting the putty from environmental erosion and damage. The nano-sized rubber powder acts as a filler, toughener, and corrosion protectant in the coating. Its tiny particle size allows for uniform distribution within the coating, forming an effective reinforcing phase and further enhancing the topcoat's airtightness, waterproofing, chemical resistance, and corrosion resistance. The putty powder packaging bags described in this application can be reused multiple times.

[0016] In step S2, gravure printing is used to prevent the substrate layer from forming a discontinuous and smooth surface coating, which is beneficial for subsequent transfer printing.

[0017] In step S3, the kraft paper composite layer is first wet-laid and then pressed together, so that the top coating layer is transferred to the bottom coating layer. When in use, the substrate layer can be peeled off.

[0018] Preferably, the substrate is an OPP film or a PE film.

[0019] By adopting the above technical solution, it is beneficial for subsequent peeling. Both OPP film and PE film are materials with smooth surfaces, low lint and stickiness, and are easy to peel off as substrates.

[0020] Preferably, the primer is prepared from the following raw materials by weight percentage:

[0021] Polylactic acid emulsion 20-30%

[0022] 4-6% methylcellulose

[0023] 10-15% glycidyl ester type epoxy resin

[0024] Castor oil polyols 6-10%

[0025] 1-2% of curing agent

[0026] The remainder is dilution.

[0027] By adopting the above technical solution, the amount of raw materials for preparing the primer is optimized, which further increases the wettability and fluidity of the primer, which is conducive to filling the interior of the kraft paper, preventing moisture and air from entering the packaging bag, and at the same time can fully combine with the topcoat to form a stable bonding layer, and will not stick to the putty powder after drying.

[0028] Preferably, the topcoat is prepared from the following raw materials by weight percentage:

[0029] Polylactic acid emulsion 20-30%

[0030] 4-6% methylcellulose

[0031] 10-15% glycidyl ester type epoxy resin

[0032] Nano-grade rubber powder 5-8%

[0033] 1-2% of curing agent

[0034] The remainder is diluent.

[0035] By adopting the above technical solution, the weight ratio of the topcoat raw materials is optimized, the chemical resistance of the topcoat is improved, the putty powder leakage is prevented, and it can fully bond with the base coat to form a stable bonding layer, thereby improving the durability of the composite membrane.

[0036] Preferably, the glycidyl ester type epoxy resin has a functionality of 2-4 and an epoxy value of 0.5-0.9.

[0037] By adopting the above technical solutions, the adhesion stability between the base coating and the kraft paper layer is improved, while the base coating becomes denser, reducing the entry of moisture and air into the putty powder packaging bag. Furthermore, a proper balance of functionality and epoxy value ensures that the coating maintains a certain level of hardness and strength while also possessing good flexibility and crack resistance, adapting to the folding and bending requirements of the kraft paper and facilitating packaging.

[0038] Preferably, the polylactic acid emulsion is prepared by the following method:

[0039] 1) Dissolve 20-30 parts of polylactic acid in 60-70 parts of solvent according to weight to obtain a clear solution;

[0040] 2) According to the weight, add 2-3 parts of water-soluble emulsifier to 30-40 parts of deionized water, stir until dissolved, and then add 5-10 parts of water-soluble chitosan to obtain a mixture.

[0041] 3) Stir the clarified solution and the mixture at a high speed of 1000-1500 r / min to obtain polylactic acid emulsion.

[0042] By adopting the above technical solution, the dispersibility of polylactic acid is further improved, so that polylactic acid can be fully and evenly mixed with glycidyl ester epoxy resin in the primer system and topcoat system to form a more uniform and stable system, which is beneficial to the application of primer and topcoat.

[0043] The clarified polylactic acid solution obtained in step 1 is slowly added to the mixture obtained in step 2. During the addition process, the mixture is stirred at a speed of 1000-1500 rpm using a high-speed stirrer. High-speed stirring helps to disperse the polylactic acid solution into tiny droplets, which are stably dispersed in the aqueous phase under the action of the emulsifier and aqueous chitosan, thereby forming a polylactic acid emulsion. This polylactic acid emulsion has good fluidity, which is beneficial for thorough mixing with glycidyl ester type epoxy resin.

[0044] Preferably, the average particle size of the nanoscale rubber powder is 50-300 nm.

[0045] By adopting the above technical solution, the particle size of the nano rubber powder is optimized, so that the nano rubber powder is evenly distributed in the topcoat system, thereby enhancing the chemical resistance and water and gas barrier properties of the topcoat.

[0046] Preferably, the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 55-60 mg KOH / g, castor oil polyol with a hydroxyl value of 70-100 mg KOH / g, and castor oil polyol with a hydroxyl value of 100-150 mg KOH / g in a weight ratio of (8-10):(4-6):3.

[0047] By adopting the above technical solutions, the wetting and adhesion properties of the base coating are improved, while the crosslinking density and toughness of the coating are also increased, which is beneficial to improving the impact resistance of the composite diaphragm. Castor oil polyols with lower hydroxyl values ​​(55-60 mg KOH / g) typically contain longer fatty acid chains, which helps to increase the flexibility of the coating. Castor oil polyols with higher hydroxyl values ​​(70-100 mg KOH / g and 100-150 mg KOH / g) contain more hydroxyl groups, which can undergo more crosslinking reactions with the curing agent during the curing process, thereby increasing the crosslinking density of the coating and reducing the intrusion of moisture and air.

[0048] Preferably, the coating speed in step S1 is 40-60 m / min and the pressure is 20-25 MPa.

[0049] By employing the above technical solution, the primer coating can be stably and evenly applied to kraft paper, while simultaneously improving the density and adhesion of the primer coating. Insufficient pressure will result in uneven distribution of the primer coating and a rough surface; excessive pressure may cause the primer coating to splatter, leading to waste and affecting the quality of the primer coating.

[0050] Preferably, in step S3, the temperature of the pressure roller is 110-120℃, the pressure of the pressure roller is 15-20MPa, and the speed of the pressure roller is 20-25m / min.

[0051] By adopting the above technical solution, a stable connection between the topcoat and the basecoat is achieved, realizing the transfer of the topcoat. Excessive temperature of the pressure roller accelerates the curing of the basecoat and topcoat, causing them to solidify before they are fully fused, which affects the stability of the connection between the basecoat and topcoat. Insufficient temperature results in an unstable connection between the topcoat and basecoat. Appropriate pressure ensures that the topcoat and basecoat are fully compacted, improving the product's density and strength. Excessive pressure may cause material cracking or deformation, while insufficient pressure may lead to inadequate compaction.

[0052] Secondly, this application provides a composite diaphragm, which adopts the following technical solution:

[0053] A composite separator includes a composite membrane, a base coating, and a top coating. The base coating is attached to the surface of a kraft paper layer. The top coating includes a first top coating and a second top coating, and the first top coating and the second top coating are symmetrically disposed on the surface of the base coating. The edges of the first top coating and the second top coating do not overlap with the edge of the base coating.

[0054] The composite diaphragm is prepared by the composite diaphragm preparation process described in the first aspect. By adopting the above technical solution, the bottom coating of the prepared composite diaphragm does not adhere to the putty powder and does not affect the subsequent sealing. At the same time, the composite diaphragm has a stable structure, good barrier performance, good chemical resistance, and is impact resistant, making it easy to package the putty powder and greatly extending the packaging time of the putty powder. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the structure of a composite diaphragm in Example 1.

[0056] Reference numerals: 1. Composite film; 2. Primer coating; 3. Topcoat coating.

[0057] In summary, this application has the following beneficial effects:

[0058] 1. Applying a primer to the kraft paper surface of the composite film via reverse coating helps the primer penetrate deep into the kraft paper, filling its pores and improving its density and barrier properties. The primer is prepared by combining polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, castor oil polyol, curing agent, and diluent. This ensures the primer layer does not adhere to the putty, facilitating subsequent sealing of the packaging bag. The topcoat is prepared by combining polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, nano-grade rubber powder, curing agent, and diluent. This improves the topcoat's airtightness, waterproofing, chemical resistance, and corrosion resistance, protecting the putty from environmental erosion and damage. Simultaneously, the primer and topcoat layers are bonded together using a wet process, forming a strong bond layer that effectively prevents air and moisture from entering through the packaging bag, improving the structural stability of the composite membrane and resulting in excellent airtightness and waterproofing performance, thus extending the shelf life of the putty powder. Detailed Implementation

[0059] Preparation Example

[0060] The water-soluble chitosan was purchased as carboxylated chitosan with a carboxylation degree of 80%.

[0061] Preparation Example 1

[0062] A polylactic acid emulsion is prepared by the following method:

[0063] 1) Dissolve 200g of polylactic acid in 600g of solvent (dimethylamide) to obtain a clear solution;

[0064] 2) Add 20g of water-soluble emulsifier (glyceryl monostearate) to 300g of deionized water and stir until dissolved. Then add 50g of water-soluble chitosan to obtain a mixture.

[0065] 3) Stir the clarified solution and the mixture at a high speed of 1000 r / min to obtain polylactic acid emulsion.

[0066] The difference between Preparation Examples 2-3 and Preparation Example 1 lies in the types and amounts of some raw materials used in preparing the polylactic acid emulsion, as well as the experimental parameters. Specific differences are shown in Table 1.

[0067] Table 1 Experimental data for preparation examples 1-3

[0068]

[0069] Example

[0070] Example 1

[0071] A composite membrane, such as Figure 1As shown, the composite film includes a composite film 1, a base coating layer 2, and a top coating layer 3. The base coating layer 2 is connected to the surface of the kraft paper layer of the composite film 1. The top coating layer 3 includes a first top coating layer and a second top coating layer, which are symmetrically arranged on the surface of the base coating layer 2. The edges of the first and second top coating layers do not overlap with the edges of the base coating layer 2. The areas of the first and second top coating layers are 10cm*20cm, and the area of ​​the base coating layer 2 is 14*50cm. The first and second top coating layers are 5cm apart. The distance between the long edge of the first and second top coating layers and the long edge of the base coating layer 2 is 2cm, and the distance between the long and wide edges of the first and second top coating layers and the wide edge of the base coating layer 2 is 2.5cm.

[0072] The composite membrane is prepared by the following method:

[0073] S1. A primer coating is applied to the kraft paper surface of the composite film to form a primer coating layer. The coating speed is 40 m / min, the coating pressure is 20 MPa, and the coating wet weight is 6 g / m2 to obtain the kraft paper composite layer.

[0074] S2. A discontinuous surface coating is formed by gravure printing on the substrate to create a composite substrate layer.

[0075] S3. The kraft paper composite layer is laminated with the composite substrate layer by wet lamination, and then passed through a pressure roller at a speed of 20m / min and a pressure of 15MPa. The wet coating amount is 10g / m2, so that the base coating and the top coating are bonded together to obtain a composite membrane. Wet lamination means that the base coating and the top coating are bonded together when they are not fully cured.

[0076] The primer was prepared from 200g of polylactic acid emulsion (from Preparation Example 1), 40g of methylcellulose, 100g of glycidyl ester type epoxy resin, 60g of castor oil polyol, 10g of curing agent (triglycidyl isocyanurate) and 300g of diluent (alkylene glycidyl ether).

[0077] The topcoat was prepared from 200g of polylactic acid emulsion (from Preparation Example 1), 40g of methylcellulose, 100g of glycidyl ester type epoxy resin, 50g of nano-grade rubber powder, 10g of curing agent (triglycidyl isocyanurate) and 300g of diluent (alkylene glycidyl ether).

[0078] The glycidyl ester type epoxy resin is an adipic acid diglycidyl ester type epoxy resin with a functionality of 2 and an epoxy value of 0.5.

[0079] The hydroxyl value of castor oil polyol is 55 mg KOH / g.

[0080] The nano-grade rubber powder has an average particle size of 50nm, is nitrile rubber, is branded by Kaiming Plastics, and has the model number SH-830.

[0081] The substrate is a PE film.

[0082] The difference between Examples 2-3 and Example 1 lies in the types and amounts of some raw materials used in the preparation of the composite membrane, as well as the experimental parameters. Specific differences are shown in Table 2.

[0083] Table 2 Experimental data for Examples 1-3

[0084]

[0085]

[0086] Example 4

[0087] A composite membrane, the difference between this embodiment and Embodiment 1 is that: the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 55 mg KOH / g, castor oil polyol with a hydroxyl value of 70 mg KOH / g and castor oil polyol with a hydroxyl value of 100 mg KOH / g in a weight ratio of 8:4:3.

[0088] Example 5

[0089] A composite membrane, the difference between this embodiment and Embodiment 1 is that: the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 60 mg KOH / g, castor oil polyol with a hydroxyl value of 100 mg KOH / g and castor oil polyol with a hydroxyl value of 150 mg KOH / g in a weight ratio of 10:6:3.

[0090] Example 6

[0091] A composite membrane, the difference between this embodiment and Embodiment 1 is that: the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 55 mg KOH / g and castor oil polyol with a hydroxyl value of 70 mg KOH / g in a weight ratio of 8:7.

[0092] Example 7

[0093] A composite membrane, the difference between this embodiment and Embodiment 1 is that: the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 55 mg KOH / g and castor oil polyol with a hydroxyl value of 100 mg KOH / g in a weight ratio of 8:7.

[0094] Example 8

[0095] A composite membrane, the difference between this embodiment and Embodiment 1 is that: the castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 70 mg KOH / g and castor oil polyol with a hydroxyl value of 100 mg KOH / g in a weight ratio of 4:11.

[0096] Example 9

[0097] A composite diaphragm, the difference between this embodiment and embodiment 1 is that the coating speed in step S1 is 40m / min and the pressure is 15MPa.

[0098] Example 10

[0099] A composite diaphragm, the difference between this embodiment and embodiment 1 is that in step S3, the temperature of the pressure roller is 130°C, the pressure of the pressure roller is 15MPa, and the speed of the pressure roller is 20m / min.

[0100] Example 11

[0101] A composite diaphragm, the difference between this embodiment and embodiment 1 is that in step S3, the temperature of the pressure roller is 110°C, the pressure of the pressure roller is 10MPa, and the speed of the pressure roller is 20m / min.

[0102] Comparative Example

[0103] Comparative Example 1

[0104] A composite membrane, which differs from Example 1 in that it has no base coating.

[0105] Comparative Example 2

[0106] A composite membrane, the difference between this comparative example and Example 1 is that a unidirectional coating method is used in step S1.

[0107] Comparative Example 3

[0108] A composite diaphragm, the difference between this comparative example and Example 1 is that screen printing is used in step S2.

[0109] Comparative Example 4

[0110] A composite membrane, the difference between this comparative example and Example 1 is that in step S3, both the base coating and the top coating are fully cured.

[0111] Comparative Example 5

[0112] A composite membrane, which differs from Example 1 in that an acrylic polymer emulsion is used instead of a polylactic acid emulsion in the primer coating.

[0113] Dow acrylic polymer emulsion PRIMAL NW-5118 acrylic emulsion.

[0114] Comparative Example 6

[0115] A composite diaphragm, the difference between this comparative example and Example 1 is that an aliphatic epoxy resin is used instead of a glycidyl ester type epoxy resin in the primer coating.

[0116] The aliphatic epoxy resin is Dow's aliphatic flexible epoxy resin DER732.

[0117] Comparative Example 7

[0118] A composite membrane, which differs from Example 1 in that carboxymethyl cellulose is used instead of methyl cellulose in the primer coating.

[0119] Comparative Example 8

[0120] A composite membrane, which differs from Example 1 in that a polyether polyol is used instead of castor oil polyol in the primer coating.

[0121] The molecular weight of the polyether polyol is 5000.

[0122] Comparative Example 9

[0123] A composite diaphragm, the difference between this comparative example and Example 1 is that silica is used instead of nano-sized rubber powder in the topcoat.

[0124] Comparative Example 10

[0125] A composite diaphragm, the difference between this comparative example and Example 1 is that the rubber powder has a particle size of 1 micrometer.

[0126] Comparative Example 11

[0127] A composite membrane, which differs from Example 1 in that an acrylic polymer emulsion is used instead of a polylactic acid emulsion in the topcoat.

[0128] Dow acrylic polymer emulsion PRIMAL NW-5118 acrylic emulsion.

[0129] Comparative Example 12

[0130] A composite diaphragm, the difference between this comparative example and Example 1 is that an aliphatic epoxy resin is used instead of a glycidyl ester type epoxy resin in the primer coating.

[0131] The aliphatic epoxy resin is Dow's aliphatic flexible epoxy resin DER732.

[0132] Comparative Example 13

[0133] A composite membrane, which differs from Example 1 in that BASF joncryl HPB is used instead of the primer.

[0134] Test method / test method Adhesion of putty powder test: The composite membranes prepared in Examples 1-11 and Comparative Examples 1-13 were peeled off, and each membrane was submerged in putty powder for 1 minute. After that, the membranes were removed, shaken, and the surface of the base layer was observed to see if putty powder adhered. If putty powder adhered, no further test was performed.

[0135] Sealing test: If no putty powder residue is found in the putty powder adhesion test, continue with the sealing test. Apply adhesive to the primer surface, leaving one side uncoated. Fold along the center line of the primer layer, pinch to form a packaging bag, leaving one side uncoated to form a seal. Then add 15g of putty powder, apply the adhesive to the seal, seal, weigh, and then immerse in 80℃ water for 20 days. Remove, wipe dry, weigh, and calculate the increased weight.

[0136] Adhesion stability test of kraft paper layer, base coating and top coating: The composite membranes prepared in Examples 1-11 and Comparative Examples 1-13 were peeled off, soaked in 15% hydrogen peroxide for 5 days, taken out, wiped dry and fixed, and then blown along the side with a hair dryer at a speed of 50m / s for 1 hour. The separation between the layers was observed.

[0137] Chemical resistance test: Peel off the substrate layer, apply adhesive to the primer surface, leaving one side uncoated. Fold along the center line of the primer layer, pinch to form a packaging bag, leaving one side uncoated to form a seal. Then add half the volume of 20% sodium hydroxide solution, then apply adhesive to the primer surface, seal the opening, and place in an environment with 90% humidity and 80℃. Record the leakage time of the packaging bag. If no leakage is recorded after 1000 hours, the test is stopped and recorded as no leakage.

[0138] Drop resistance test: Leave one side uncoated with adhesive, fold the bag along the center line of the base coat, pinch it closed to form a packaging bag, leaving one side uncoated to form a seal, then add half the volume of putty powder, and then apply the adhesive to seal the opening, obtaining the sample. Select a smooth cement surface and drop the sample freely from a height of 3m, observing whether the packaging bag is damaged. The experimental data are shown in Table 3:

[0139] Table 3 Experimental data of Examples 1-11 and Comparative Examples 1-13

[0140]

[0141]

[0142] Comparing Example 1 and Comparative Examples 1-4, Comparative Example 1 showed putty adhesion in the putty powder adhesion test; in the sealing test, the weight increase of Comparative Examples 2-4 was much greater than that of Example 1, especially Comparative Example 2; in the kraft paper layer, primer layer, and topcoat layer adhesion stability test, Comparative Examples 2-3 showed kraft paper separation from the primer layer, and Comparative Example 4 showed primer layer separation from the topcoat layer; in the chemical resistance test, the leakage time of Comparative Examples 2-4 was significantly shorter. Based on the results of Comparative Examples 1-4 and Example 1, the composite diaphragm prepared by the process described in this application is non-sticky to putty powder, easy to seal, and also possesses good structural stability, barrier properties, chemical resistance, and impact resistance.

[0143] Comparing Example 1 and Comparative Examples 5-8, Comparative Example 5 showed putty adhesion in the putty powder adhesion test; in the sealing test, the weight increase of Comparative Examples 6-8 was much greater than that of Example 1; in the kraft paper layer, primer layer, and topcoat layer adhesion stability test, Comparative Examples 6 and 8 showed separation of the kraft paper, primer layer, and topcoat layer; in the chemical resistance test, the leakage time of Comparative Examples 6-8 was significantly shorter; and in the impact resistance test, Comparative Example 6 showed damage. The results of Comparative Examples 5-8 and Example 1 indicate that preparing the primer coating using polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, and castor oil polyol can effectively prevent putty adhesion to the primer surface, while effectively improving the structural stability, barrier properties, chemical resistance, and impact resistance of the composite diaphragm.

[0144] Comparing Example 1 and Comparative Examples 9-12, in the adhesion stability test of the kraft paper layer, base coating, and top coating, Comparative Examples 11-12 showed separation of the kraft paper, base coating, and top coating; in the chemical resistance test, Comparative Examples 9-12 showed a significantly shorter leakage time; and in the drop resistance test, Comparative Examples 9-10 and 12 showed damage. The results of Comparative Examples 9-12 and Example 1 demonstrate that preparing the top coating using polylactic acid emulsion, methylcellulose, glycidyl ester epoxy resin, and nano-sized rubber powder can effectively improve the structural stability, barrier properties, chemical resistance, and drop resistance of the composite diaphragm.

[0145] Comparing Example 1 and Comparative Example 13, Comparative Example 13 showed that putty adhered in the putty powder adhesion test, indicating that the base coating of this application does not adhere to putty powder.

[0146] Comparing Examples 1 and 4-8, in the sealing test, the weight of Examples 4-5 was basically not increased, while the weight of Examples 5-8 increased more than that of Example 1. In the chemical resistance test, no leakage occurred in Examples 4-5, while the leakage time in Examples 6-8 was shorter than that in Example 1. This indicates that using a mixture of castor oil and polyester polyols with different hydroxyl values ​​can effectively improve the barrier properties and chemical resistance of the composite membrane.

[0147] Comparing Examples 1 and 9-11, in the sealing test, the weight increase of Examples 9-11 was greater than that of Example 1; in the adhesion stability test of the kraft paper layer, base coating, and top coating, separation of the base coating and top coating occurred in Example 9; in the chemical resistance test, the leakage time of Examples 9-11 was shorter than that of Example 1. From the experimental results of Examples 1 and 9-11, it can be seen that optimizing the speed of the base coating and the temperature of the pressure roller can effectively improve the barrier properties, chemical resistance, and structural stability of the composite diaphragm.

[0148] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for preparing a composite diaphragm, characterized in that, The preparation steps include the following: S1. Apply a primer coating to the kraft paper surface of the composite film to form a primer coating layer, thus obtaining the kraft paper composite layer; S2. A discontinuous surface coating is formed by gravure printing on the substrate to create a composite substrate layer. S3. The kraft paper composite layer is laminated with the composite substrate layer by wet lamination, and then the bottom coating layer and the top coating layer are bonded together by pressure rollers to obtain a composite diaphragm. Wet lamination means that the bottom coating layer and the top coating layer are bonded together while they are not fully cured. The primer is prepared from polylactic acid emulsion, methylcellulose, glycidyl ester type epoxy resin, castor oil polyol, curing agent and diluent; The topcoat is prepared from polylactic acid emulsion, methylcellulose, glycidyl ester type epoxy resin, nano-sized rubber powder, curing agent and diluent.

2. The process for preparing a composite separator according to claim 1, wherein The primer coating is prepared from the following raw materials by weight percentage: Polylactic acid emulsion 20-30% Methylcellulose 4-6% Glycidyl ester type epoxy resin 10-15% Castor oil polyols 6-10% 1-2% of curing agent The remainder is diluent.

3. The process for preparing a composite separator according to claim 2, wherein The topcoat is prepared from the following raw materials by weight percentage: Polylactic acid emulsion 20-30% Methylcellulose 4-6% Glycidyl ester type epoxy resin 10-15% Nano-grade rubber powder 5-8% 1-2% of curing agent The remainder is diluent.

4. The process for preparing a composite separator according to claim 1, wherein: The glycidyl ester type epoxy resin has a functionality of 2-4 and an epoxy value of 0.5-0.9 mol / 100g.

5. The process for preparing a composite separator according to claim 1, wherein The polylactic acid emulsion is prepared by the following method: 1) Dissolve 20-30 parts of polylactic acid in 60-70 parts of solvent according to weight to obtain a clear solution; 2) According to the weight, add 2-3 parts of water-soluble emulsifier to 30-40 parts of deionized water, stir until dissolved, and then add 5-10 parts of water-soluble chitosan to obtain a mixture; 3) Stir the clarified solution and the mixture at a high speed of 1000-1500 r / min to obtain polylactic acid emulsion.

6. The process for preparing a composite separator according to claim 4, wherein: The average particle size of the nanoscale rubber powder is 50-300 nm.

7. The process of claim 1, wherein: The castor oil polyol is obtained by mixing castor oil polyol with a hydroxyl value of 55-60 mgKOH / g, castor oil polyol with a hydroxyl value of 70-100 mgKOH / g, and castor oil polyol with a hydroxyl value of 100-150 mgKOH / g in a weight ratio of (8-10):(4-6):

3.

8. The process of claim 1, wherein: The coating speed in step S1 is 40-60 m / min, and the pressure is 20-25 MPa.

9. The process of claim 1, wherein: In step S3, the temperature of the pressure roller is 110-120℃, the pressure of the pressure roller is 15-20MPa, and the speed of the pressure roller is 20-25m / min.

10. A composite diaphragm, characterized in that: The composite diaphragm includes a composite membrane, a base coating, and a top coating. The base coating is attached to the surface of the kraft paper layer. The top coating includes a first top coating and a second top coating, and the first top coating and the second top coating are symmetrically disposed on the surface of the base coating. The edges of the first top coating and the second top coating do not overlap with the edge of the base coating. The composite diaphragm is prepared by the composite diaphragm preparation process according to any one of claims 1-9.

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