A water repellent composition for surface coating of paperboard

Abstract

The application discloses a waterproof composition for paperboard surface coating, which is composed of the following components in percentage by weight: 79.5-89.5% paraffin wax, 5-8% plasticizer, 1-3% tackifier, 3-5% flexibilizer, 1-2% penetration accelerator and 0.5-2.5% other additives; the flexibilizer is polyolefin containing unsaturated double bonds; and the penetration accelerator is modified polyisobutylene, which is maleic anhydride grafted polyisobutylene. The waterproof composition is prepared by using paraffin wax as the main component and adding the plasticizer, the tackifier, the flexibilizer and other additives in a specific proportion range, and under the joint action of the above-mentioned additives, the waterproof composition is facilitated to penetrate into the fiber pores of the paperboard, and a moderate thickness is obtained by one-time coating; during the solidification process of the waterproof composition, cross-linking occurs, a stable cross-linking network is formed, and the waterproof layer obtained after cooling has excellent waterproof function and good anti-brittle cracking performance.

Description

Technical Field

[0001] This invention relates to the technical field of packaging products, and more specifically, to a waterproof composition for coating cardboard surfaces. Background Technology

[0002] Paperboard has the advantages of being biodegradable, widely available, low in production cost, and easy to process. However, the main material of paperboard is plant fiber, and there are many pores between the fibers. When paperboard comes into contact with liquids such as water, it is prone to capillary action, and the liquid penetrates into the interior of the paperboard, which reduces the strength of the paperboard and makes it easy to break. This limits the scope of use of paper packaging products.

[0003] Currently, there are two main methods for waterproofing and oil-proofing paperboard. One method involves adding a waterproofing and oil-proofing agent to the pulp to reduce the surface free energy of the paper, preventing grease and water from wetting it. The other method involves forming a continuous barrier layer on the surface of the paperboard to prevent grease and water from contacting it, thus achieving an oil-repellent and waterproof effect. The barrier layer uses mineral wax as the main raw material, mixed with reagents such as magnesium hydroxide, glycerin-butadiene silicone, and polyethylene glycol, and is applied to the surface of the paperboard to reduce its surface tension. For example, Chinese patent CN104005305B discloses a method for preparing oil-proof paper, which uses paraffin wax, stearic acid, ammonia, water, and an anti-mildew composition in a specific ratio to prepare an oil-proofing agent. However, paraffin wax and water have poor compatibility, making it difficult for the oil-proofing agent to be evenly applied to the paperboard surface. The wax layer formed on the paperboard surface is prone to crystallization and dewaxing, resulting in poor water resistance. Summary of the Invention

[0004] To address the problem of poor water resistance in cardboard, this application provides a waterproof composition for coating cardboard surfaces.

[0005] This application provides a waterproof composition for coating paperboard surfaces, employing the following technical solution: A waterproof composition for coating cardboard surfaces, comprising, by weight percentage, the following components: 79.5-89.5% paraffin wax, 5-8% plasticizer, 1-3% tackifier, 3-5% softener, 1-2% penetration enhancer, 0.5-2.5% other additives; The flexible agent is a polyolefin containing unsaturated double bonds; the penetration enhancer is modified polyisobutylene, which is maleic anhydride-grafted polyisobutylene.

[0006] By adopting the above technical solution, paraffin is used as the main component, and additives with different functions are added to the paraffin. Under the combined effect of the additives, the waterproof composition can stably penetrate into the pores of the cardboard fibers and solidify to form a highly tough waterproof layer.

[0007] Plasticizers are added to paraffin wax. Plasticizers can improve the uniformity of paraffin wax flow, making paraffin wax more fluid at lower temperatures, which helps paraffin wax penetrate into the fiber pores on the surface of paperboard. Tackifiers help control the viscosity of the waterproof composition, allowing the coating amount of the waterproof composition to be controlled within a moderate range, resulting in a high unit coating amount of the waterproof composition on the paperboard surface and good film-forming properties. The flexible agent is a multi-branched polyolefin containing unsaturated bonds. During the curing process of the waterproof composition, the unsaturated bonds of the flexible agent break and cross-link, forming a network cross-linked structure. At the same time, the chain segments of the flexible agent are prone to entanglement, which further enhances the stability of the network cross-linked structure and improves the problem that the addition of plasticizers and tackifiers can easily lead to increased paraffin brittleness. After modification with maleic anhydride, polyisobutylene contains multiple active functional groups such as hydroxyl and carboxyl groups in its structure. The active functional groups of modified polyisobutylene can easily combine with the fibers of paperboard, promoting the penetration of the waterproof composition on the surface of the paperboard. At the same time, the unsaturated double bonds and active functional groups in modified polyisobutylene can also crosslink with polyolefins, enhancing the crosslinking density of the waterproof composition. The wax layer formed by the waterproof composition curing on the surface of the paperboard has good toughness, strength and adhesion. Due to the high cross-linking density inside the waterproof layer, the interaction between polymer chain segments and water molecules is reduced. The polar groups contained in the modified polyisobutylene can hardly play a hydrophilic role. The waterproof layer has a large contact angle with water, which can give the cardboard surface a better waterproof effect. The additives used in the waterproof layer have good miscibility within this percentage range, are not prone to crystallization, and increase the melting point and heat resistance of the waterproof layer.

[0008] Furthermore, the paraffin wax is one or more of the following: No. 52 semi-refined paraffin wax, No. 58 semi-refined paraffin wax, No. 60 semi-refined paraffin wax, No. 62 semi-refined paraffin wax, No. 52 fully refined paraffin wax, No. 58 fully refined paraffin wax, No. 60 fully refined paraffin wax, and No. 62 fully refined paraffin wax.

[0009] By adopting the above technical solution, the paraffin wax is food-grade paraffin wax. The oil content of fully refined paraffin wax is higher than that of semi-refined paraffin wax, but the cost is higher. By selecting fully refined paraffin wax and semi-refined paraffin wax of the same grade for compounding, it is possible to achieve better waterproof performance while reducing the production cost of the waterproof composition.

[0010] Furthermore, the paraffin wax is a compound of No. 58 semi-refined paraffin wax and No. 58 fully refined paraffin wax in a weight ratio of 1:(2-3).

[0011] Furthermore, the plasticizer is a fatty acid.

[0012] By adopting the above technical solutions, fatty acid plasticizers include, but are not limited to, stearic acid, linoleic acid, and oleic acid. Compared with dicarboxylic acid plasticizers, dimethyl phthalate plasticizers, and phosphate plasticizers, fatty acid plasticizers are safer and can stably play a toughening role.

[0013] Furthermore, the plasticizer is a compound of stearic acid and linoleic acid in a weight ratio of 2:(1-2).

[0014] By adopting the above technical solution, this application uses a blend of stearic acid and linoleic acid, which have a synergistic effect in plasticizing. This ratio effectively improves the hardness of paraffin wax, thereby enhancing its resistance to temperature changes and ensuring good adhesion to the cardboard surface even under high and low temperature cycling. Simultaneously, linoleic acid, being an unsaturated fatty acid containing double bonds, can co-crosslink with flexibility agents and penetration enhancers, further improving the crosslinking stability of the waterproof layer.

[0015] Furthermore, the thickener is microcrystalline wax, carnauba wax, or polyethylene wax.

[0016] By adopting the above technical solutions, the palm wax includes, but is not limited to, Brazilian palm wax and Malaysian palm wax, and the polyethylene wax is low molecular weight polyethylene wax; the interaction between the tackifier and the paraffin molecules enhances the viscosity of the paraffin.

[0017] Furthermore, the flexible agent is one or more of the following: ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylate copolymer, polyethylene, polypropylene, polybutene, poly4-methyl-1-pentene, and cycloolefin.

[0018] By adopting the above technical solution, the above polyolefins are all copolymerized from olefins or olefin derivatives containing unsaturated double bonds. During the polymerization process, the olefins or olefin derivatives do not react 100%, and some olefins and olefin derivatives remain inside. The polyolefins can retain large molecular chain segments and undergo good physical entanglement, and can also retain a small amount of olefin or olefin derivative monomers and undergo chemical cross-linking, forming a good cross-linked network structure as a whole. The waterproof layer can be stably attached to the surface of the paperboard for a long time.

[0019] Furthermore, the flexible agent uses an ethylene-vinyl acetate copolymer with a number average molecular weight of 1800-2400.

[0020] By adopting the above technical solution, the ethylene-vinyl acetate copolymer has a low molecular weight and a high ethylene segment content, which ensures the compatibility between the ethylene-vinyl acetate copolymer and paraffin. Within this number average molecular weight range, the ethylene-vinyl acetate copolymer can be well miscible with other components in the waterproof composition, thereby giving the waterproof layer excellent waterproof and adhesion properties, and enabling it to be stably adhered to the surface of the cardboard.

[0021] Furthermore, the modified polyisobutylene is prepared according to the following method: Low molecular weight polyisobutylene, maleic anhydride, and benzoyl peroxide are placed in a reaction vessel at a weight ratio of 100:(4.5-30):(0.1-1). A solvent is added to the reaction vessel, and the temperature is raised to 80-160°C. The reaction is maintained at this temperature for 3-6 hours. After the reaction is completed, the mixture is cooled, purified, and dried to obtain modified polyisobutylene. The number average molecular weight of the low molecular weight polyisobutylene is 2000-4000.

[0022] By adopting the above technical solution, controlling the reaction parameters of modified polyisobutylene and the grafting rate of maleic anhydride on polyisobutylene, the penetration effect of the waterproof composition on the paperboard surface can be significantly improved while ensuring that the modified polyisobutylene has little impact on the kinematic viscosity of the waterproof composition. The waterproof composition gives the paperboard better water-proof function.

[0023] Furthermore, the other additives include crosslinking agents and antioxidants.

[0024] By adopting the above technical solution, the crosslinking agent includes, but is not limited to, peroxide crosslinking agents. The crosslinking agent is controlled within a moderate range so that the active functional groups contained in the flexible agent and the penetration promoter can fully react. In addition, with the addition of antioxidants, the aging of the waterproof layer is delayed. Attached Figure Description

[0025] Figure 1 These are test images of Example 1 and Comparative Example 1 during the waterproofing test.

[0026] Figure 2 These are the detection images of Example 1 and Comparative Example 1 in mechanical property testing.

[0027] Figure 3 These are the detection images of Example 1 and Comparative Example 1 in toughness testing. Detailed Implementation

[0028] Unless otherwise specified, the sources of raw materials involved in the following preparation examples, embodiments, and comparative examples are as follows: paraffin: No. 58 semi-refined paraffin wax, food grade, sourced from Beijing Likang Weiye Technology Co., Ltd. No. 58 fully refined paraffin wax, food grade, sourced from Henan Hengcheng Chemical Products Co., Ltd. Plasticizer: Stearic acid, food grade, brand name: Sven 1801; Linoleic acid, analytical grade, sourced from Jinlai Chemical. Tackifier: No. 70 microcrystalline wax, food grade, sourced from Jingmen Weijia Industrial Co., Ltd. Softener: Ethylene-vinyl acetate copolymer: food grade, custom-made product, with number average molecular weights of 1800, 2200, and 2400 respectively; Polyethylene: Food grade, custom-made product, number average molecular weight 3000; Polyisobutylene: food grade, custom-made product, with number average molecular weights of 2000, 3000, and 4000 respectively; Crosslinking agent: dicumyl peroxide, analytical grade; Antioxidant: Brand No. 264, sourced from BASF; Polyalphaolefin: Grade PAO2; Hydrogenated petroleum resin: Grade DF-A1000.

[0029] Preparation example of modified polyisobutylene

[0030] Preparation example a Modified polyisobutylene was prepared as follows: 10 kg of polyisobutylene with a number average molecular weight of 3000, 1 kg of maleic anhydride, and 0.05 kg of benzoyl peroxide were dissolved in toluene. The polyisobutylene, maleic anhydride, and benzoyl peroxide were transferred to a reaction vessel, which was then sealed. The temperature inside the reaction vessel was raised to 100°C and maintained for 5 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction product was purified with acetone to remove unreacted monomers and dried in a vacuum drying oven at 60°C to constant weight to obtain modified polyisobutylene.

[0031] Preparation example bc The modified polyisobutylene differs from that in preparation example a in that the weight ratio of polyisobutylene, maleic anhydride, and benzoyl peroxide is different, as detailed below: In preparation example b, polyisobutylene, maleic anhydride, and benzoyl peroxide were prepared in a weight ratio of 100:4.5:0.1. In preparation example c, polyisobutylene, maleic anhydride, and benzoyl peroxide were prepared in a weight ratio of 100:30:1.

[0032] Preparation example de The modified polyisobutylene differs from that in preparation example a in that the number-average molecular weight of the polyisobutylene is different, as detailed below: In preparation example d, polyisobutylene with a number average molecular weight of 2000 was used in place of polyisobutylene with a number average molecular weight of 3000 by weight. In preparation example e, polyisobutylene with a number average molecular weight of 4000 was used in place of polyisobutylene with a number average molecular weight of 3000 by weight.

[0033] Preparation example fg The modified polyisobutylene differs from that in preparation example a in that the reaction temperature and reaction time are different, as detailed below: In preparation example f, the reaction temperature was 80℃ and the reaction time was 6h; In preparation example g, the reaction temperature was 160℃ and the reaction time was 3h.

[0034] Comparative preparation example a A modified polyethylene is prepared according to the following method: 10 kg of polyethylene with a number average molecular weight of 3000, 1 kg of maleic anhydride, and 0.05 kg of benzoyl peroxide were dissolved in toluene. The polyethylene, maleic anhydride, and benzoyl peroxide were transferred to a reaction vessel, which was then sealed. The temperature inside the reaction vessel was raised to 100°C and maintained for 5 hours. After the reaction was completed, the mixture was cooled to room temperature. The reaction product was purified with acetone to remove unreacted monomers and dried in a vacuum drying oven at 60°C to constant weight to obtain modified polyethylene. Example

[0035] Examples 1-10 A waterproof composition for coating cardboard surfaces is prepared according to the following method: Paraffin wax, plasticizer, tackifier, flexibilizer, and penetration enhancer are heated to a molten state and mixed together. Then, crosslinking agent and antioxidant are added in sequence, and after mixing, the mixture is coated onto the surface of the cardboard. Examples 1-10 were all prepared in the manner described above, and their compositions are shown in Table 1: Table 1. Weight percentage of each component in Examples 1-10

[0036] Note: The modified polyisobutylene is derived from preparation example a.

[0037] Examples 11-16 A waterproof composition for coating cardboard surfaces differs from Example 1 in that the source of the modified polyisobutylene is different, as detailed below: In Example 11, modified polyisobutylene derived from Preparation Example b was used in place of modified polyisobutylene derived from Preparation Example a by an equal weight percentage. In Example 12, the modified polyisobutylene derived from Preparation Example c was used in place of the modified polyisobutylene derived from Preparation Example a by an equal weight percentage. In Example 13, the modified polyisobutylene derived from Preparation Example d was used in place of the modified polyisobutylene derived from Preparation Example a by an equal weight percentage. In Example 14, the modified polyisobutylene derived from Preparation Example e was used in place of the modified polyisobutylene derived from Preparation Example a by an equal weight percentage. In Example 15, the modified polyisobutylene derived from Preparation Example f was used in place of the modified polyisobutylene derived from Preparation Example a by an equal weight percentage. In Example 16, the modified polyisobutylene derived from Preparation Example g was used in place of the modified polyisobutylene derived from Preparation Example a by an equal weight percentage.

[0038] Comparative Example Comparative Example 1 A waterproof composition for cardboard surfaces, by weight percentage, comprises the following: 21% semi-refined paraffin wax No. 58, 63% fully refined paraffin wax No. 58, 4% polyalphaolefin, 2% microcrystalline wax, 3% polyethylene wax (Mn2000), 3% hydrogenated petroleum resin, and 2% antioxidant (brand name: 264); the above substances are heated and blended to obtain the waterproof composition.

[0039] Comparative Example 2 A waterproof composition for cardboard surfaces differs from Example 1 in that it uses 0.8% sorbitan monooleate polyoxyethylene ether (Tween-80), 0.8% sorbitan fatty acid ester (S-20), and 0.4% sodium stearate in equal weight percentages instead of modified polyisobutylene.

[0040] Comparative Example 3 A waterproof composition for cardboard surfaces, differing from Example 1 in that it uses an equal weight percentage of modified polyethylene prepared in Comparative Preparation Example a instead of modified polyisobutylene prepared in Preparation Example a.

[0041] Performance testing

[0042] The waterproof compositions of Examples 1-16 and Comparative Examples 1-3 were coated on the surface of cardboard boxes to prepare test samples, wherein the amount of waterproof compositions of Examples 1-16 and Comparative Examples 1-3 was controlled to be the same, and the weight and size of the cardboard boxes were the same.

[0043] 1. Waterproofing test: Measure the initial weight of the test sample; Place the same batch and weight of absorbent paper into the test sample, pour the same weight of water into the test sample, cover the test sample with the lid, and leave it for 24 hours. Observe whether the bottom of the test sample absorbs water and becomes soft. Remove the absorbent paper and wipe the surface of the test sample dry. Weigh the sample and calculate the weight difference before and after the waterproof test, which is the absorbency value.

[0044] 2. Mechanical properties: A hydraulic press was used to conduct a compressive strength test on the test samples after the waterproofing test, and the compressive strength at which the test samples deformed was recorded.

[0045] 3. Toughness testing: Fold the lid of the test sample 180° and observe whether a crack appears at the fold.

[0046] 4. Temperature cycling detection: The test sample was placed in a temperature cycling test chamber, with the temperature controlled between -20 and 60°C and the relative humidity controlled at 80%RH. Within this temperature range, the temperature was gradually increased and then decreased at a rate of 1°C / min, which constituted one temperature cycle. This temperature cycle was repeated until 5000 cycles were completed, and then the test sample was removed. The percentage of the surface of the test sample with defects such as blistering and dewaxing was counted. The smaller the percentage, the better the waterproof layer could withstand the thermal cycling shock in a humid environment and adhere stably to the cardboard surface.

[0047] Table 2. Performance test data of Examples 1-16 and Comparative Examples 1-3

[0048] in conclusion

[0049] The test data shows that: First, Example 1 and Comparative Example 1 form a single comparison. In Comparative Example 1, no penetration enhancer was added; paraffin was blended with conventional additives such as polyalphaolefins, microcrystalline wax, polyethylene wax, hydrogenated petroleum resins, and antioxidants. (See [link to relevant documentation]). Figure 1 The experiment showed that the six components had poor miscibility and poor penetration effect, and the resulting waterproof layer was difficult to adhere evenly and stably to the surface of the cardboard, especially at the bends, where dewaxing was prone to occur, leading to water penetration. Meanwhile, due to the absorption of some moisture in Comparative Example 1, the mechanical strength of the cardboard box decreased, and its compressive strength dropped to 290 kgf / cm². 2 See Figure 2 In contrast, Comparative Example 1 showed obvious deformation and box collapse.

[0050] In addition, the physical entanglement between polyalphaolefins, microcrystalline waxes, polyethylene waxes, and hydrogenated petroleum resins is relatively weak; see [link to relevant documentation]. Figure 3 The toughness decreased, and obvious cracks appeared after being folded 180°; in the high and low temperature cycling test, large areas of hollowing and dewaxing occurred.

[0051] Second, Example 1 and Comparative Example 2 form a single comparison. Comparative Example 2 added a conventional surfactant as a penetration enhancer. The surfactant selected was sorbitan monooleate polyoxyethylene ether (Tween-80), sorbitan fatty acid ester (S-20), and sodium stearate as the main components. Tween-80, S-20, and sodium stearate were compounded in a weight ratio of 2:2:1. However, this surfactant has poor miscibility with paraffin wax, resulting in partial crystallization of the waterproof composition during the coating process. The surfactant is unable to play a penetration-enhancing role and instead easily leads to uneven coating of the waterproof composition, reducing the adhesion stability and water-proof effect of the waterproof layer formed by the waterproof composition. At the same time, since the surfactant does not contain functional groups that can react with polyolefins, the stability of the cross-linked network formed by the waterproof layer decreases, and the cold and heat resistance is poor. Problems such as blistering and dewaxing are prone to occur during high and low temperature cycling. Toughness is reduced, and obvious cracks appear after folding at 180°.

[0052] Third, Example 1 and Comparative Example 3 form a single comparison. In Comparative Example 3, maleic anhydride-grafted polyethylene was added instead of maleic anhydride-grafted polyisobutylene. The experiment showed that maleic anhydride-grafted polyethylene could not effectively promote penetration. The reason may be that: the molecular weight of polyethylene is relatively large. After modification, the molecular weight of maleic anhydride-grafted polyethylene further increases. The miscibility between maleic anhydride-grafted polyethylene and paraffin wax decreases. Maleic anhydride-grafted polyethylene is difficult to distribute evenly in the waterproof composition, resulting in poor penetration promotion effect. After the waterproof composition is cured into a film, the formed waterproof layer is easy to fall off.

[0053] Examples 1-3 provide a single comparison. While the proportions of the components in the waterproof compositions differ, all achieve good water-proofing. However, based on the water absorption values, the proportion in Example 1 allows for better mutual solubility of the components, resulting in uniform curing of the waterproof composition and excellent water-proofing performance on the cardboard surface. Conversely, while excessive paraffin content achieves good waterproofing, it reduces toughness and can easily lead to delamination and cracking during high and low temperature cycling tests.

[0054] Examples 1 and 4-5 form a single comparison. The ratio of No. 58 semi-refined paraffin wax to No. 58 fully refined paraffin wax in the waterproof composition was adjusted. It can be seen that increasing the proportion of fully refined paraffin wax helps to improve the waterproof effect, but the cost also increases significantly. Therefore, controlling the ratio of No. 58 semi-refined paraffin wax to No. 58 fully refined paraffin wax within a moderate range can balance the waterproof performance and cost of the waterproof composition.

[0055] Examples 1 and 6-7 form a single comparison. The ratio of stearic acid and linoleic acid in the waterproof composition was adjusted. It can be seen that when only stearic acid is used in the waterproof composition, its waterproof effect decreases.

[0056] Examples 1 and 8-10 form a single comparison. The type of flexible agent and the molecular weight of the ethylene-vinyl acetate copolymer used in the waterproof composition were adjusted. It can be seen that, under the same number average molecular weight, the number of unsaturated double bonds in polyisobutylene is less, and the density of physical and chemical cross-linking with other components in the waterproof composition is reduced. In high and low temperature cycling tests, cracking and delamination problems are more likely to occur.

[0057] Examples 1 and 11-16 provide a single comparison, showing different grafting rates of modified polyisobutylene in the waterproof compositions. This indicates that it is necessary to control the reaction-related parameters of modified polyisobutylene to control the content of active functional groups contained in the modified polyisobutylene. This ensures that the modified polyisobutylene exhibits better compatibility with other components in the waterproof composition. At the same time, it can also enhance the stability of the waterproof layer and reduce the possibility of blistering and cracking under high and low temperature cycling tests.

[0058] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] Furthermore, the above-described embodiments merely illustrate several implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A waterproof composition for coating paperboard surfaces, characterized in that: By weight percentage, it consists of the following components composition: 79.5-89.5% paraffin wax, 5-8% plasticizer, 1-3% tackifier, 3-5% flexible agent, 1-2% penetration enhancer, 0.5-2.5% other additives; the flexible agent is a polyolefin containing unsaturated double bonds; the penetration enhancer is modified polyisobutylene, wherein the modified polyisobutylene is maleic anhydride-grafted polyisobutylene; the flexible agent is one or more of ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylate copolymer, polyethylene, polypropylene, polybutene, poly4-methyl-1-pentene, and cycloolefins; the flexible agent The modified polyisobutylene is prepared by using an ethylene-vinyl acetate copolymer with a number average molecular weight of 1800-2400. The modified polyisobutylene is prepared as follows: low molecular weight polyisobutylene, maleic anhydride, and benzoyl peroxide are placed in a reaction vessel at a weight ratio of 100:(4.5-30):(0.1-1). A solvent is added to the reaction vessel, and the temperature is raised to 80-160°C. The reaction is maintained at this temperature for 3-6 hours. After the reaction is complete, the mixture is cooled, purified, and dried to obtain the modified polyisobutylene. The number average molecular weight of the low molecular weight polyisobutylene is 2000-4000.

2. The waterproof composition for coating paperboard surfaces as described in claim 1, characterized in that: The paraffin wax is a compound made of No. 58 semi-refined paraffin wax and No. 58 fully refined paraffin wax in a weight ratio of 1:(2-3).

3. The waterproof composition for coating paperboard surfaces as described in claim 1, characterized in that: The plasticizer is a fatty acid.

4. The waterproof composition for coating paperboard surfaces as described in claim 3, characterized in that: The plasticizer is a compound of stearic acid and linoleic acid in a weight ratio of 2:(1-2).

5. The waterproof composition for coating paperboard surfaces as described in claim 1, characterized in that: The thickener is microcrystalline wax, carnauba wax, or polyethylene wax.

6. The waterproof composition for coating paperboard surfaces as described in claim 1, characterized in that: The other additives include crosslinking agents and antioxidants.

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