Adhesive for Anti-corrosion polyethylene composite tape for pipe bend, preparation method therefor, and polyethylene composite tape

Abstract

The present application relates to the technical field of adhesives, in particular to an adhesive for an anti-corrosion polyethylene composite tape for a pipe bend, a preparation method therefor, and a polyethylene composite tape. The adhesive for an anti-corrosion polyethylene composite tape for a pipe bend comprises the following components in parts by weight: 5-20 parts of a maleic anhydride grafted polyethylene wax, 60-90 parts of a polyethylene matrix resin, 5-20 parts of a polyurethane elastomer, 2-6 parts of an epoxy resin, and 0.1-0.5 parts of an antioxidant. In the maleic anhydride grafted polyethylene wax, the maleic anhydride grafting rate is 2%-8%. The present application uses a maleic anhydride grafted polyethylene wax in combination with a polyurethane elastomer and an epoxy resin. This improves both the heat resistance and adhesive strength of the material while ensuring the mechanical properties of the material, allowing the adhesive meet to technical requirements and have good adhesion with the cured epoxy coating.

Description

Adhesive for anti-corrosion polyethylene composite tape for bent pipes and its preparation method; polyethylene composite tape Technical Field

[0001] This application relates to the field of adhesive technology, and in particular to an adhesive for anti-corrosion polyethylene composite tape for bent pipes, its preparation method, and the polyethylene composite tape itself. Background Technology

[0002] The 3PE anti-corrosion coating for steel pipes consists of a fusion-bonded epoxy powder base layer, an adhesive intermediate layer, and an outer polyethylene anti-corrosion layer. Its significant advantages stem from the organic integration of these three layers into a unified whole, with the bottom epoxy powder layer firmly bonded to the steel pipe substrate. This combination gives the coating the advantages of both fusion-bonded epoxy powder coatings and polyethylene coatings. The fusion-bonded epoxy powder adheres firmly to the metal surface primarily through the interaction of its active groups with activated ions on the steel pipe surface, forming ionic bonds and physical interlocking forces. The adhesive intermediate layer organically bonds the bottom fusion-bonded epoxy layer and the outer polyethylene layer, protecting the bottom fusion-bonded epoxy layer from external corrosion.

[0003] However, due to limitations in the 3PE anti-corrosion coating processing technology, it can only be used for straight pipe anti-corrosion production. Continuous 3PE anti-corrosion cannot be applied to bends and joints. Currently, anti-corrosion for bends and joints mainly uses heat-shrinkable tape coatings, liquid coatings, polymer adhesive tape coatings, viscoelastic tape coatings, FBE powder coatings, and modified polyolefin coatings. However, these types of anti-corrosion coatings all have certain shortcomings compared to 3PE coatings. For example, heat-shrinkable tapes and liquid coatings require high-level construction techniques and are easily affected by the external environment and the operator's skill level. Heat-shrinkable tapes also carry the risk of poor adhesion between layers. FBE powder coatings offer good anti-corrosion performance, but require high standards for the production line and transportation. The outer anti-corrosion layer is easily damaged during transportation and handling, increasing the workload for repairs. Modified polyolefin coatings have strict process requirements, high material performance requirements, low production efficiency, and high overall production costs.

[0004] A new type of product for pipe bending corrosion protection and steel pipe joint repair has emerged on the market: polyethylene composite tape. This tape consists of a two-layer structure: a high-density polyolefin substrate layer that has undergone radiation cross-linking, and a polyolefin adhesive layer. Conventional 3PE adhesives cannot be used on this type of polyethylene composite tape for two main reasons: First, during the production process, the adhesive is coated onto the already irradiated and cross-linked polyethylene tape. To prevent deformation of the polyethylene tape, the coating temperature is relatively low, and conventional adhesives cannot bond with polyethylene at such low temperatures. Second, due to the special processing characteristics, the inner epoxy powder layer of the polyethylene composite tape is already cured during use, and the bonding temperature between the adhesive and the epoxy coating is low. Conventional adhesives require the epoxy powder to be in a gelled state and at higher temperatures to achieve adhesion, resulting in lower adhesion to a cured epoxy coating. Furthermore, there are specific technical requirements for the adhesives used in polyethylene composite tapes. Currently, there are no adhesives for polyethylene composite tapes that meet these requirements. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0006] One objective of this application is to provide an adhesive for anti-corrosion polyethylene composite tape for bent pipes, which meets various performance requirements and has good adhesion to cured epoxy powder.

[0007] Another objective of this application is to provide a method for preparing an adhesive for a bend-corrosion-resistant polyethylene composite tape.

[0008] Another object of this application is to provide a polyethylene composite tape.

[0009] In a first aspect, this application provides an adhesive for anti-corrosion polyethylene composite tape for bent pipes, comprising the following components in parts by weight:

[0010] The mixture consists of 5-20 parts of polyethylene wax grafted with maleic anhydride, 60-90 parts of polyethylene matrix resin, 5-20 parts of polyurethane elastomer, 2-6 parts of epoxy resin, and 0.1-0.5 parts of antioxidant.

[0011] In the polyethylene wax grafted maleic anhydride, the grafting rate of maleic anhydride is 2% to 8%.

[0012] In one specific embodiment of this application, the polyethylene wax grafted with maleic anhydride has a weight-average molecular weight of 5,000 to 50,000, a softening point of 80 to 120°C, a melting point of 90 to 130°C, and a viscosity of 100 to 5,000 mPa·s at 150°C.

[0013] In one specific embodiment of this application, the polyethylene wax grafted with maleic anhydride is mainly prepared by reacting polyethylene wax, maleic anhydride, and an initiator. Further, the amount of maleic anhydride used is 3 wt% to 10 wt% of the polyethylene wax; the initiator is a peroxide-based initiator, and the amount of the initiator used is 0.2 wt% to 1.5 wt% of the polyethylene wax; the reaction temperature is 140 to 180°C, and the reaction time is 2 to 3 hours.

[0014] In one specific embodiment of this application, the polyethylene matrix resin includes at least one of high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and low-density polyethylene (LDPE). Further, the melt flow rate of the polyethylene matrix resin at 190°C / 2.16 kg is 0.5–20 g / 10 min.

[0015] In one specific embodiment of this application, the polyurethane elastomer is at least one of polyether-type polyurethane elastomer and polyester-type polyurethane elastomer. Further, the polyurethane elastomer has a melting point of 90–140°C, a melt flow rate of 1–5 g / 10 min at 150°C / 2.16 kg, and a Shore A hardness of 50–80.

[0016] In one specific embodiment of this application, the epoxy resin has an epoxy equivalent of 150–250 g / eq and a softening point of 50–80°C. Further, the epoxy resin is a phenolic epoxy resin.

[0017] In one specific embodiment of this application, the mass ratio of the polyethylene wax grafted with maleic anhydride to the epoxy resin is 1:(0.3-0.5).

[0018] In one specific embodiment of this application, the mass ratio of the polyurethane elastomer to the polyethylene matrix resin is 1:(3-8).

[0019] In one specific embodiment of this application, the antioxidant includes at least one of antioxidant 1010, antioxidant 168, and antioxidant 245.

[0020] In one specific embodiment of this application, the adhesive for the bent pipe anti-corrosion polyethylene composite tape satisfies at least one of the following conditions:

[0021] (1) The melt flow rate at 190℃ / 2.16kg is 1~3g / 10min;

[0022] (2) Density is 0.920~0.950g / cm³ 3 ;

[0023] (3) The Vicat softening point at 9.8N / A50 is 90-100℃;

[0024] (4) Embrittlement temperature ≤ -50℃;

[0025] (5) Oxidation induction period at 200℃ ≥ 20 min;

[0026] (6) Moisture content ≤ 0.1%;

[0027] (7) Tensile strength at a tensile speed of 50 mm / min ≥ 18 MPa;

[0028] (8) The nominal strain at break when the tensile speed is 50 mm / min is ≥600%;

[0029] (9) Peel strength at 20℃ ≥150N / cm;

[0030] (10) Peel strength at 60℃ ≥100N / cm.

[0031] Secondly, this application provides a method for preparing the adhesive for the anti-corrosion polyethylene composite belt for bent pipes as described above, which includes the following steps: mixing the components in proportion and then extruding and granulating at 160-200°C.

[0032] Thirdly, this application provides a polyethylene composite tape, which includes a polyolefin substrate layer and an adhesive layer disposed on the surface of the polyolefin substrate layer; the adhesive layer is mainly made of any of the adhesives described above.

[0033] Compared with related technologies, the beneficial effects of this application are as follows:

[0034] (1) The adhesive for the anti-corrosion polyethylene composite tape for bent pipes of this application is made of polyethylene wax grafted with maleic anhydride, polyurethane elastomer and epoxy resin. The high grafting rate of polyethylene wax grafted with maleic anhydride can effectively improve the reactivity of polar groups. At the same time, the epoxy resin improves the adhesion to epoxy powder. The use of polyurethane elastomer can improve the heat resistance and adhesion of the material as well as ensure the mechanical properties of the material, so that the adhesive can meet the technical requirements.

[0035] (2) The adhesive of this application has good adhesion to the cured epoxy coating and can bond with the cured epoxy coating at temperatures below 150°C. At the same time, it has good adhesion to polyethylene at temperatures below 150°C, ensuring that the polyethylene composite tape will not shrink due to excessive temperature during the preparation process, thus meeting the production and use requirements of the polyethylene composite tape.

[0036] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0037] The technical solution of this application will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0038] In a first aspect, this application provides an adhesive for anti-corrosion polyethylene composite tape for bent pipes, comprising the following components in parts by weight:

[0039] The mixture consists of 5-20 parts of polyethylene wax grafted with maleic anhydride, 60-90 parts of polyethylene matrix resin, 5-20 parts of polyurethane elastomer, 2-6 parts of epoxy resin, and 0.1-0.5 parts of antioxidant.

[0040] In the grafting of maleic anhydride onto polyethylene wax, the grafting rate of maleic anhydride is 2% to 8%.

[0041] The adhesive for the anti-corrosion polyethylene composite tape for bent pipes in this application employs a high-grafting-rate polyethylene wax grafted with maleic anhydride. On one hand, polyethylene wax has a lower molecular weight than ordinary polyethylene, resulting in significantly higher reactivity of the maleic anhydride grafted onto the polyethylene wax compared to that grafted onto the polyethylene itself (the reactivity of the maleic anhydride groups in the polyethylene grafted with maleic anhydride is limited by the molecular chain segments, leading to low reactivity and poor adhesion to the cured epoxy powder). Simultaneously, the high grafting rate of maleic anhydride in the polyethylene wax-grafted maleic anhydride allows for effective adhesion to the cured epoxy powder with only a small amount added, in combination with other components. Furthermore, the use of polyurethane elastomer leverages its polarity to enhance the adhesion between the adhesive and epoxy while maintaining compatibility and mechanical properties with polyethylene. Combined with epoxy resin to further improve adhesion to the epoxy powder, the overall adhesive strength is increased, lowering the reaction temperature and enabling adhesion to the cured epoxy powder at low temperatures. At the same time, ensure that the remaining properties of the adhesive meet the technical specifications.

[0042] In different implementation methods, the amounts of each component in the adhesive for the anti-corrosion polyethylene composite tape for bent pipes can be as follows, by weight:

[0043] The amount of polyethylene wax grafted with maleic anhydride can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or any combination thereof.

[0044] The amount of polyethylene matrix resin can be 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, or any combination thereof.

[0045] The amount of polyurethane elastomer can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or any combination thereof;

[0046] The amount of epoxy resin can be 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, or any combination thereof;

[0047] The amount of antioxidant can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, or any combination thereof.

[0048] In different embodiments, the grafting rate of maleic anhydride in polyethylene wax grafted with maleic anhydride can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any combination thereof. By using polyethylene wax grafted with maleic anhydride at a high grafting rate, the adhesive properties can be modified with a smaller amount of maleic anhydride, avoiding excessive dosage which would cause the adhesive to become brittle, affecting the impact performance and environmental stress cracking resistance of the final anti-corrosion layer. Excessive dosage would also lead to an increase in melt index, which is difficult to control during the preparation of polyethylene composite tapes.

[0049] In one specific embodiment of this application, in the polyethylene wax grafted with maleic anhydride, the polyethylene wax has a weight-average molecular weight of 5000-50000, a softening point of 80-120°C, a melting point of 90-130°C, and a viscosity of 100-5000 mPa·s at 150°C.

[0050] In various embodiments, in the grafting of maleic anhydride onto polyethylene wax, the weight-average molecular weight of the polyethylene wax can be within the range of 5000, 8000, 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, or any combination thereof, and the softening point can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, or any combination thereof. The range of any two of these conditions may be used, and the melting point may be 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃ or any two of these conditions may be used. The viscosity at 150℃ may be 100mpa·s, 500mpa·s, 1000mpa·s, 2000mpa·s, 3000mpa·s, 4000mpa·s, 5000mpa·s or any two of these conditions may be used.

[0051] In one specific embodiment of this application, the grafting of maleic anhydride onto polyethylene wax is mainly prepared by reacting polyethylene wax, maleic anhydride, and an initiator. Further, the amount of maleic anhydride used is 3 wt% to 10 wt% of the polyethylene wax; the initiator is a peroxide-based initiator, and the amount of the initiator used is 0.2 wt% to 1.5 wt% of the polyethylene wax; the reaction temperature is 140 to 180°C, and the reaction time is 2 to 3 hours.

[0052] In various embodiments, in the preparation of maleic anhydride grafted onto polyethylene wax, polyethylene wax is used as the matrix. The amount of maleic anhydride can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any combination thereof of the polyethylene wax. The amount of initiator can be 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, or any combination thereof of the polyethylene wax. Peroxide initiators may include, but are not limited to, at least one of di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane, bis(tert-butylperoxide isopropyl)benzene, and tert-butylisopropylphenyl peroxide.

[0053] In different embodiments, the reaction temperature in the preparation of polyethylene wax grafted with maleic anhydride can be a range of 140°C, 150°C, 160°C, 170°C, 180°C or any combination thereof, and the reaction time can be a range of 2h, 2.5h, 3h or any combination thereof.

[0054] In practice, the preparation of polyethylene wax grafted maleic anhydride may include: adding polyethylene wax, maleic anhydride and initiator to a reaction vessel in proportion, stirring and reacting at 140-180°C for 2-3 hours under nitrogen protection; after the reaction is complete, reducing the pressure for 0.5-1 hours to remove unreacted maleic anhydride monomers; then washing the product in methanol while maintaining high-speed stirring, so that the polyethylene wax grafted maleic anhydride forms micro-particles distributed in the solvent, and filtering and drying to obtain polyethylene wax grafted maleic anhydride.

[0055] In one specific embodiment of this application, the polyethylene matrix resin includes at least one of high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and low-density polyethylene (LDPE). Further, the melt flow rate of the polyethylene matrix resin at 190°C / 2.16 kg is 0.5–20 g / 10 min.

[0056] In various embodiments, the melt flow rate of the polyethylene matrix resin at 190°C / 2.16 kg can be a range of 0.5 g / 10 min, 1 g / 10 min, 5 g / 10 min, 8 g / 10 min, 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, 20 g / 10 min, or any combination thereof. The polyethylene matrix resin can guarantee or improve mechanical and processing properties.

[0057] In a specific embodiment of this application, the polyethylene matrix resin includes high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). Further, the mass ratio of high-density polyethylene (HDPE) to linear low-density polyethylene (LLDPE) is 1:(1.4 to 2.5).

[0058] In specific embodiments of this application, the polyurethane elastomer is at least one of polyether-type polyurethane elastomer and polyester-type polyurethane elastomer. Further, the polyurethane elastomer has a melting point of 90–140°C, a melt flow rate of 1–5 g / 10 min at 150°C / 2.16 kg, and a Shore A hardness of 50–80.

[0059] Polyurethane elastomers have high polarity, which can improve the adhesion between adhesives and epoxy resins. For example, in different embodiments, the melting point of the polyurethane elastomer can be 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or any combination thereof; the melt flow rate at 150°C / 2.16 kg can be 1 g / 10 min, 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, or any combination thereof; and the Shore A hardness can be 50, 55, 60, 65, 70, 75, 80, or any combination thereof.

[0060] In a specific embodiment of this application, the epoxy resin has an epoxy equivalent of 150–250 g / eq and a softening point of 50–80°C. Further, the epoxy resin is a phenolic epoxy resin.

[0061] The addition of a small amount of epoxy resin can improve the adhesion between the adhesive and the epoxy powder. This is mainly because, firstly, the epoxy groups in the epoxy resin are highly reactive and can quickly react with the polar groups in the epoxy powder; secondly, the epoxy groups have high polarity, resulting in high intermolecular bond energy with the epoxy powder, thus leading to strong adhesion. In different embodiments, the epoxy equivalent of the epoxy resin can be in the range of 150 g / eq, 180 g / eq, 200 g / eq, 220 g / eq, 250 g / eq, or any combination thereof, and the softening point of the epoxy resin can be in the range of 50°C, 60°C, 70°C, 80°C, or any combination thereof.

[0062] In a specific embodiment of this application, the mass ratio of polyethylene wax grafted with maleic anhydride to epoxy resin is 1:(0.3 to 0.5).

[0063] In different embodiments, the mass ratio of polyethylene wax grafted maleic anhydride to epoxy resin can be 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, or any combination thereof.

[0064] Grafting maleic anhydride onto polyethylene wax in adhesives can improve reactivity, but excessive use can lead to brittleness and affect performance. Conversely, insufficient use can result in weak adhesion to epoxy powder, failing to provide adequate protection. Introducing epoxy resin can further enhance adhesion to the epoxy powder, but excessive addition can negatively impact the basic properties of polyethylene. In this application, the two are mixed in a specific ratio, ensuring both strong adhesion to the epoxy powder and optimal processing, mechanical, and performance characteristics of the polyethylene.

[0065] In one specific embodiment of this application, the mass ratio of polyurethane elastomer to polyethylene matrix resin is 1:(3-8).

[0066] In different embodiments, the mass ratio of polyurethane elastomer to polyethylene matrix resin can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8 or any combination thereof, preferably 1:(4 to 8), such as 1:(4 to 5).

[0067] The addition of polyurethane elastomers can improve adhesion, but the compatibility between polyurethane elastomers and polyethylene is relatively poor. When the amount added is too much, it will lead to low mechanical properties of the material, while when the amount added is too little, it cannot effectively improve adhesion.

[0068] The antioxidants in this application may include thermal oxidation stabilizers, UV absorbers, light stabilizers, etc., such as at least one of antioxidant 1010, antioxidant 168, or antioxidant 245. Adding various antioxidants can reduce material degradation during processing and increase the oxidation induction period and thermal aging performance of the material, effectively extending the service life of corrosion-resistant pipelines.

[0069] In a specific embodiment of this application, the adhesive for the anti-corrosion polyethylene composite tape for bent pipes satisfies at least one of the following conditions:

[0070] (1) The melt flow rate at 190℃ / 2.16kg is 1~3g / 10min;

[0071] (2) Density is 0.920~0.950g / cm³3 ;

[0072] (3) The Vicat softening point at 9.8N / A50 is 90-100℃;

[0073] (4) Embrittlement temperature ≤ -50℃;

[0074] (5) Oxidation induction period at 200℃ ≥ 20 min; such as 25 min, 30 min, 35 min, 40 min, 42 min, etc.;

[0075] (6) Moisture content ≤ 0.1%;

[0076] (7) Tensile strength at a tensile speed of 50 mm / min ≥ 18 MPa; such as 20 MPa, 22 MPa, 23 MPa, etc.

[0077] (8) The nominal strain at break when the tensile speed is 50 mm / min is ≥600%; such as 650%, 700%, 750%, 800%, 820%, etc.

[0078] (9) Peel strength at 20℃ ≥150N / cm; such as 170N / cm, 200N / cm, 220N / cm, 250N / cm, 280N / cm, 300N / cm, etc.

[0079] (10) Peel strength at 60℃ ≥100N / cm; such as 120N / cm, 130N / cm, 150N / cm, 180N / cm, 200N / cm, etc.

[0080] The technical requirements for adhesives in polyethylene composite tapes issued by China Oil & Gas Pipeline Network Corporation are detailed in Table 1.

[0081] Table 1 Technical Specifications of Adhesives in Polyethylene Composite Tapes

[0082] The adhesive for polyethylene composite tape of this application fully meets the above technical requirements and exhibits good cohesive failure.

[0083] Secondly, this application provides a method for preparing any of the above-mentioned adhesives for anti-corrosion polyethylene composite belts for bent pipes, which includes the following steps: mixing the components in proportion and then extruding and granulating at 160-200°C.

[0084] In the preparation of adhesives for anti-corrosion polyethylene composite belts for bent pipes, mixing can be carried out using a high-speed mixer, and extrusion granulation can be carried out using a twin-screw extruder.

[0085] Thirdly, this application provides a polyethylene composite tape, which includes a polyolefin substrate layer and an adhesive layer disposed on the surface of the polyolefin substrate layer; the adhesive layer is mainly made of any of the above-mentioned adhesives.

[0086] The polyolefin substrate layer can be the radiation-crosslinked high-density polyolefin substrate layer used in existing polyethylene composite tapes.

[0087] In practice, the preparation of polyethylene composite tape includes: applying an adhesive to the surface of a radiation-crosslinked high-density polyolefin substrate layer through a flat die at a temperature of 120-140°C using a single-screw extruder; then calendering the two together using a shaping roller; cooling and shaping; cutting, traction, and length setting; and finally winding to form a polyethylene composite tape.

[0088] Example 1

[0089] This embodiment provides an adhesive for anti-corrosion polyethylene composite tape for bent pipes, comprising the following components by weight:

[0090] The composition consists of 10 parts polyethylene wax grafted with maleic anhydride, 27 parts HDPE, 50 parts LLDPE, 10 parts polyurethane elastomer, 3 parts epoxy resin, and 0.5 parts antioxidant.

[0091] The preparation method of polyethylene wax grafted with maleic anhydride includes: taking polyethylene wax with a weight average molecular weight of 10,000 (softening point of 100℃, melting point of 110℃, and viscosity of 3000 mPa·s at 150℃), adding it, maleic anhydride, and di-tert-butyl peroxide into a reaction vessel, and stirring at 160℃ for 3 hours to ensure complete reaction, under nitrogen protection throughout the process. After the reaction is complete, the pressure is reduced for 1 hour to remove unreacted monomers. Then, the reaction product is washed in methanol solvent while maintaining high-speed stirring, so that the polyethylene wax grafted with maleic anhydride forms microparticles distributed in the solvent. Then, the mixture is filtered and dried to obtain polyethylene wax grafted with maleic anhydride, with a grafting rate of 3.8%. The amounts of maleic anhydride and di-tert-butyl peroxide used are 5% and 1% of the mass of polyethylene wax, respectively.

[0092] The melt flow rate of high-density polyethylene (HDPE) at 190℃ / 2.16kg is 8g / 10min;

[0093] The melt flow rate of linear low-density polyethylene (LLDPE) at 190℃ / 2.16kg is 20g / 10min;

[0094] The polyurethane elastomer is a polyether-type polyurethane elastomer with a melting point of 95℃, a melt flow rate of 2g / 10min at 150℃ / 2.16kg, and a Shore A hardness of 60.

[0095] The epoxy resin is a commercially available phenolic epoxy resin with an epoxy equivalent of 200 g / eq and a softening point of 73℃.

[0096] The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0097] The preparation method of the adhesive for the anti-corrosion polyethylene composite tape for bent pipes includes the following steps:

[0098] The components are mixed evenly in a high-speed mixer according to the proportion, and then extruded and granulated through a twin-screw extruder to obtain adhesive granules; wherein the temperature of each zone of the twin-screw extruder is set to 160℃, 180℃, 200℃, 200℃, 200℃, 200℃, 200℃, 200℃ and 190℃.

[0099] Example 2

[0100] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 1, the only difference being the amount of raw material components used.

[0101] In this embodiment, the adhesive comprises the following components by weight: 10 parts polyethylene wax grafted with maleic anhydride, 25 parts HDPE, 50 parts LLDPE, 10 parts polyurethane elastomer, 5 parts epoxy resin, and 0.5 parts antioxidant.

[0102] Example 3

[0103] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 1, the only difference being the amount of raw material components used.

[0104] In this embodiment, the adhesive comprises the following components by weight: 10 parts polyethylene wax grafted with maleic anhydride, 20 parts HDPE, 50 parts LLDPE, 15 parts polyurethane elastomer, 5 parts epoxy resin, and 0.5 parts antioxidant.

[0105] Example 4

[0106] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 1, the only difference being the amount of raw material components used.

[0107] In this embodiment, the adhesive comprises the following components by weight: 15 parts polyethylene wax grafted with maleic anhydride, 20 parts HDPE, 45 parts LLDPE, 15 parts polyurethane elastomer, 5 parts epoxy resin, and 0.5 parts antioxidant.

[0108] Example 5

[0109] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 1, the only difference being the amount of raw material components used.

[0110] In this embodiment, the adhesive comprises the following components by weight: 18 parts polyethylene wax grafted with maleic anhydride, 20 parts HDPE, 45 parts LLDPE, 15 parts polyurethane elastomer, 2 parts epoxy resin, and 0.5 parts antioxidant.

[0111] Example 6

[0112] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 1, the only difference being the amount of raw material components used.

[0113] In this embodiment, the adhesive comprises the following components by weight: 15 parts polyethylene wax grafted with maleic anhydride, 18 parts HDPE, 42 parts LLDPE, 20 parts polyurethane elastomer, 5 parts epoxy resin, and 0.5 parts antioxidant.

[0114] Example 7

[0115] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 4, the only difference being that the polyethylene wax is grafted with maleic anhydride.

[0116] In this embodiment, the preparation method of polyethylene wax grafted with maleic anhydride includes: taking polyethylene wax with a weight average molecular weight of 10,000 (softening point of 100℃, melting point of 110℃, and viscosity of 3000 mPa·s at 150℃), adding it to a reaction vessel along with maleic anhydride and di-tert-butyl peroxide, and stirring at 160℃ for 3 hours to ensure complete reaction, under nitrogen protection throughout the process. After the reaction is complete, the pressure is reduced for 1 hour to remove unreacted monomers. Then, the reaction product is washed in methanol solvent while maintaining high-speed stirring, so that the polyethylene wax grafted with maleic anhydride forms microparticles distributed in the solvent. The mixture is then filtered and dried to obtain polyethylene wax grafted with maleic anhydride, with a grafting rate of 2%. The amounts of maleic anhydride and di-tert-butyl peroxide used are 3% and 0.3% of the mass of polyethylene wax, respectively.

[0117] Example 8

[0118] This embodiment refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Embodiment 4, the only difference being that the polyethylene wax is grafted with maleic anhydride.

[0119] In this embodiment, the preparation method of polyethylene wax grafted with maleic anhydride includes: taking polyethylene wax with a weight average molecular weight of 10,000 (softening point of 100℃, melting point of 110℃, and viscosity of 3000 mPa·s at 150℃), adding it to a reaction vessel along with maleic anhydride and di-tert-butyl peroxide, and stirring at 160℃ for 3 hours to ensure complete reaction, under nitrogen protection throughout the process. After the reaction is complete, the pressure is reduced for 1 hour to remove unreacted monomers. Then, the reaction product is washed in methanol solvent while maintaining high-speed stirring, so that the polyethylene wax grafted with maleic anhydride forms microparticles distributed in the solvent. The mixture is then filtered and dried to obtain polyethylene wax grafted with maleic anhydride, with a grafting rate of 8%. The amounts of maleic anhydride and di-tert-butyl peroxide used are 10% and 1.2% of the mass of polyethylene wax, respectively.

[0120] Comparative Example 1

[0121] Comparative Example 1 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 1, the only difference being the amount of raw material components used.

[0122] In Comparative Example 1, the adhesive comprises the following components by weight: 15 parts polyethylene wax grafted with maleic anhydride, 35 parts HDPE, 50 parts LLDPE, and 0.5 parts antioxidant.

[0123] Comparative Example 2

[0124] Comparative Example 2 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 4, the only difference being that the polyethylene wax grafted with maleic anhydride is replaced with an equal weight of polyethylene grafted with maleic anhydride.

[0125] In Comparative Example 2, polyethylene-grafted maleic anhydride was obtained by using polyethylene as the matrix resin, 2.5 wt% maleic anhydride as the grafting monomer, and 0.5 wt% dicumyl peroxide as the initiator through reactive extrusion process. The grafting rate of maleic anhydride was 2%.

[0126] Comparative Example 3

[0127] Comparative Example 3 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 1, the only difference being the amount of raw material components used.

[0128] In Comparative Example 3, the adhesive comprised the following components by weight: 30 parts of polyethylene grafted maleic anhydride (same as Example 2), 15 parts of HDPE, 35 parts of LLDPE, 10 parts of POE, 10 parts of EVA, and 0.5 parts of antioxidant. The POE had a melt flow rate of 1.2 g / 10 min (190°C, 2.16 kg) and a melting point of 35°C; the EVA had a melt flow rate of 7 g / 10 min (190°C, 2.16 kg) and a melting point of 70°C; and contained 28% VA.

[0129] Comparative Example 4

[0130] Comparative Example 4 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 4, the only difference being that the polyethylene wax is grafted with maleic anhydride.

[0131] In Comparative Example 4, the preparation method of polyethylene wax grafted with maleic anhydride included: taking polyethylene wax with a weight-average molecular weight of 10,000 (softening point of 100℃, melting point of 110℃, and viscosity of 3000 mPa·s at 150℃), adding it to a reaction vessel along with maleic anhydride and di-tert-butyl peroxide, and stirring at 160℃ for 3 hours to ensure complete reaction, under nitrogen protection throughout. After complete reaction, the pressure was reduced for 1 hour to remove unreacted monomers. The reaction product was then washed in methanol solvent while maintaining high-speed stirring, causing the polyethylene wax grafted with maleic anhydride to form microparticles distributed in the solvent. The mixture was then filtered and dried to obtain polyethylene wax grafted with maleic anhydride, with a grafting rate of 1.5%. The amounts of maleic anhydride and di-tert-butyl peroxide used were 2% and 0.25% of the mass of polyethylene wax, respectively.

[0132] Comparative Example 5

[0133] Comparative Example 5 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 4, the only difference being the amount of raw material components used.

[0134] In Comparative Example 5, the adhesive comprises the following components by weight: 15 parts polyethylene wax grafted with maleic anhydride, 17 parts HDPE, 38 parts LLDPE, 25 parts polyurethane elastomer, 5 parts epoxy resin, and 0.5 parts antioxidant.

[0135] Comparative Example 6

[0136] Comparative Example 6 refers to the adhesive for the anti-corrosion polyethylene composite tape for bent pipes and its preparation method in Example 4, the only difference being the amount of raw material components used.

[0137] In Comparative Example 6, the adhesive comprises the following components by weight: 10 parts polyethylene wax grafted with maleic anhydride, 20 parts HDPE, 45 parts LLDPE, 15 parts polyurethane elastomer, 10 parts epoxy resin, and 0.5 parts antioxidant.

[0138] Experimental Example

[0139] The performance parameters of the adhesives prepared in different embodiments and comparative examples were tested, and the test results are shown in Table 2.

[0140] The peel strength test measures the peel strength of the adhesive bonded to the cured epoxy coating. The test method is based on GB / T23257-2017. The adhesive and the cured epoxy coating are bonded together at 150℃.

[0141] Table 2 Performance test results of different adhesives

[0142] The test results above show that the adhesive for the bend-type anti-corrosion polyethylene composite tape of this application, by combining polyethylene wax grafted with maleic anhydride, polyurethane elastomer, and epoxy resin, effectively improves the material's heat resistance and adhesion while ensuring its mechanical properties, thus meeting the technical requirements. Furthermore, the adhesive exhibits good adhesion to the cured epoxy powder, achieving bonding at temperatures below 150°C. It also demonstrates good adhesion to polyethylene at temperatures below 150°C, ensuring that the polyethylene composite tape will not shrink due to excessively high temperatures during its preparation, thus meeting the production and usage requirements of the polyethylene composite tape.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An adhesive for a corrosion-resistant polyethylene composite tape for a bent pipe, comprising, by weight parts: polyethylene wax grafted maleic anhydride 5-20 parts, polyethylene matrix resin 60-90 parts, polyurethane elastomer 5-20 parts, epoxy resin 2-6 parts, and antioxidant 0.1-0.5 parts. In the polyethylene wax grafted maleic anhydride, the grafting rate of maleic anhydride is 2-8%. In the polyethylene wax grafted maleic anhydride, the weight average molecular weight of the polyethylene wax is 5,000-50,000, the softening point is 80-120°C, the melting point is 90-130°C, and the viscosity at 150°C is 100-5,000 mpa·s.

2. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein The polyethylene wax grafted maleic anhydride is mainly prepared by the reaction of polyethylene wax, maleic anhydride, and an initiator.

3. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein Preferably, the amount of maleic anhydride is 3-10 wt% of the polyethylene wax. Preferably, the initiator is a peroxide initiator, and the amount of the initiator is 0.2-1.5 wt% of the polyethylene wax. Preferably, the reaction temperature is 140-180°C, and the reaction time is 2-3 hours. The polyethylene matrix resin includes at least one of high-density polyethylene, linear low-density polyethylene, and low-density polyethylene.

4. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein Preferably, the melt flow rate of the polyethylene matrix resin at 190°C / 2.16 kg is 0.5-20 g / 10 min. The polyurethane elastomer is at least one of a polyether type polyurethane elastomer and a polyester type polyurethane elastomer.

5. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein Preferably, the melting point of the polyurethane elastomer is 90-140°C, the melt flow rate at 150°C / 2.16 kg is 1-5 g / 10 min, and the Shore A hardness is 50-80. The epoxy resin has an epoxy equivalent weight of 150-250 g / eq and a softening point of 50-80°C.

6. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein Preferably, the epoxy resin is a phenolic epoxy resin. The mass ratio of the polyethylene wax grafted maleic anhydride to the epoxy resin is 1:(0.3-0.5).

7. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein And / or, the mass ratio of the polyurethane elastomer to the polyethylene matrix resin is 1:(3-8). The antioxidant includes at least one of antioxidant 1010, antioxidant 168, and antioxidant 245.

8. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to claim 1, wherein The adhesive for a corrosion-resistant polyethylene composite tape for a bent pipe satisfies at least one of the following conditions:

9. The adhesive for a corrosion-proof polyethylene composite tape for a bent pipe according to Claim 1, wherein (1) The melt flow rate at 190°C / 2.16 kg is 1-3 g / 10 min; (2) The density is 0.920-0.950 g / cm3; (3) The Vicat softening point at 9.8 N / A50 is 90-100°C; (4) The embrittlement temperature is ≤-50°C; (5) The oxidation induction time at 200°C is ≥20 min; (6) The water content is ≤0.1%; (7) The tensile strength at a tensile speed of 50 mm / min is ≥18 MPa; (8) The breaking nominal strain at a tensile speed of 50 mm / min is ≥600%; (9) The peel strength at 20°C is ≥150 N / cm; (10) The peel strength at 60°C is ≥100 N / cm. ​ 10. A method of preparing the adhesive for a corrosion-protective polyethylene composite tape according to any one of claims 1 to 9, which comprises the step of extrusion granulation at 160 to 200°C after mixing the components in a predetermined ratio.

11. A polyethylene composite tape, which comprises a polyolefin base layer and an adhesive layer provided on the surface of the polyolefin base layer; the adhesive layer is prepared mainly from the adhesive for a corrosion-protective polyethylene composite tape according to any one of claims 1 to 9 or the adhesive for a corrosion-protective polyethylene composite tape prepared by the method according to claim 10.

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