Polypropylene grafted maleic anhydride material, its preparation method and application

Abstract

The application provides a polypropylene grafted maleic anhydride material, a preparation method and application thereof, and raw materials of the polypropylene grafted maleic anhydride material, which comprise the following components: 100 parts of polypropylene, 0.5-4 parts of maleic anhydride, 0.1-3 parts of a grafting monomer, 0.02-0.3 parts of a free radical initiator, and 0.05-0.5 parts of an antioxidant; the grafting monomer comprises an oligomerized aliphatic polyester type polyallyl compound, and the preparation raw materials of the oligomerized aliphatic polyester type polyallyl compound comprise the following components: a dibasic acid, a dibasic alcohol, a branched alcohol and an allyl alcohol. The polypropylene grafted maleic anhydride material provided by the application can improve the MAH grafting level by introducing a specific grafting monomer, reduce the degradation risk caused by simply increasing the MAH and the free radical initiator, and improve the peeling strength of polypropylene and a metal base material, increase the lap shear strength, and improve the bonding retention rate after bending.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a polypropylene grafted with maleic anhydride material, its preparation method and application. Background Technology

[0002] Polypropylene (PP) is a commonly used polyolefin material, used in packaging, automobiles, home appliances, and building materials, with advantages in cost and processability. However, PP has low molecular chain polarity, resulting in weak interfacial forces when directly laminated with metal substrates such as aluminum plates and foils. This can easily lead to problems such as low peel strength and interfacial cracking after bending after hot pressing.

[0003] Currently, in industry, polypropylene grafted with maleic anhydride (PP-g-MAH) is commonly used as an adhesive or compatibility layer between PP and metals, polar coatings, or other polar resins. After MAH grafting, anhydride or carboxylic acid polar groups can be introduced onto the PP chain, thereby improving the wetting and adhesion ability of PP to metal substrates.

[0004] However, the existing PP / MAH / peroxide melt grafting system still has the following problems: (1) The effective grafting rate of MAH is low: When MAH is grafted onto PP by conventional melt grafting, the actual grafting rate is usually not high. The common grafting rate is about 0.3% to 0.5%. Too much unreacted MAH needs to be removed by subsequent devolatilization or extraction.

[0005] (2) Increasing the amount of MAH and initiator can easily lead to PP degradation: In order to improve the grafting rate, the amount of MAH or peroxide is usually increased, but PP free radicals are prone to β-cleavage, resulting in a decrease in molecular weight, an increase in MFR (melt mass flow rate), and a decrease in melt strength.

[0006] (3) The adhesive layer is prone to hardening or brittleness: Some double bond additives such as TAIC (tracene propyl isocyanurate) can improve the efficiency of free radical reaction, but small molecule double bond additives have a high double bond density, which can easily cause local bridging, resulting in insufficient flexibility of the adhesive layer and affecting the adhesion retention rate after bending.

[0007] (4) PP / aluminum composites not only need polarity, but also stress buffering capacity: aluminum has high rigidity, while PP is relatively soft. The two have large differences in modulus and thermal expansion. The intermediate adhesive layer must have polar groups, as well as a certain degree of flexibility and interfacial stress release capacity.

[0008] Therefore, in this field, it is desirable to develop a polypropylene-grafted maleic anhydride material that not only has a high MAH grafting rate, but also improves the flexibility and interfacial stability of the adhesive layer when used as an adhesive layer between polypropylene and a metal substrate. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a polypropylene-grafted maleic anhydride material, its preparation method, and its application.

[0010] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a polypropylene-grafted maleic anhydride material, wherein the raw materials for preparing the polypropylene-grafted maleic anhydride material comprise, by weight, the following components: 100 parts of polypropylene; 0.5 to 4 parts of maleic anhydride; 0.1 to 3 parts of grafting agent monomer; 0.02–0.3 parts of free radical initiator; Antioxidant 0.05–0.5 parts; The grafting monomers include oligoaliphatic polyester polyallyl compounds. The raw materials for preparing the oligomeric aliphatic polyester polyallylic compound include the following components: dicarboxylic acid, diol, branched alcohol and allyl alcohol.

[0011] This invention adds an oligomeric aliphatic polyester polyallyl compound as a grafting monomer to the raw materials for preparing polypropylene grafted maleic anhydride materials. This grafting monomer provides polyallyl reaction sites, which helps to improve the MAH grafting level. On the other hand, it introduces flexible polyester segments. When this polypropylene grafted maleic anhydride material is used as an adhesive layer between polypropylene and a metal substrate, it can improve the flexibility of the adhesive layer and the interfacial stability after bending.

[0012] In this invention, the raw materials for preparing the polypropylene-grafted maleic anhydride material are, by weight, based on the amount of polypropylene (100 parts), and the amount of maleic anhydride can be 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, etc.

[0013] In this invention, the raw materials for preparing the polypropylene-grafted maleic anhydride material are, by weight, based on the amount of polypropylene (100 parts), the amount of grafting monomer can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3 parts, etc.

[0014] In this invention, the raw materials for preparing the polypropylene-grafted maleic anhydride material are, by weight, based on the amount of polypropylene (100 parts), and the amount of free radical initiator can be 0.02 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.08 parts, 0.1 parts, 0.12 parts, 0.14 parts, 0.15 parts, 0.16 parts, 0.18 parts, 0.2 parts, 0.22 parts, 0.24 parts, 0.25 parts, 0.26 parts, 0.28 parts, 0.3 parts, etc.

[0015] In this invention, the raw materials for preparing the polypropylene-grafted maleic anhydride material are, by weight, based on the amount of polypropylene (100 parts), and the amount of antioxidant can be 0.05 parts, 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, 0.5 parts, etc.

[0016] Preferably, the dicarboxylic acid includes any one or a combination of at least two of adipic acid, sebacic acid, azelaic acid, and dodecanoic acid, preferably a combination of adipic acid and sebacic acid, and more preferably a combination of adipic acid and sebacic acid in a molar ratio of (6-9):(1-4). For example, 6-9 can be 6, 6.5, 7, 7.5, 8, 8.5, 9, etc., and 1-4 can be 1, 1.5, 2, 2.5, 3, 3.5, 4, etc.

[0017] Preferably, the diol includes any one or a combination of at least two of 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and diethylene glycol, preferably a combination of 1,4-butanediol and neopentyl glycol, and more preferably a combination of 1,4-butanediol and neopentyl glycol in a molar ratio of (5-8):(2-5). For example, 5-8 can be 5, 5.5, 6, 6.5, 7, 7.5, 8, etc., and 2-5 can be 2, 2.5, 3, 3.5, 4, 4.5, 5, etc.

[0018] Preferably, the molar ratio of the dicarboxylic acid to the diol is (1.3 to 4.2):1, for example, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.5:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.5:1, 3.6:1, 3.8:1, 4:1, 4.2:1, etc., and more preferably (1.5 to 2.8):1.

[0019] Preferably, the branched alcohol comprises trimethylolpropane and / or pentaerythritol.

[0020] Preferably, based on the total molar amount of the diol, branched alcohol, and allyl alcohol being 100%, the molar amount of the branched alcohol is 5% to 25%, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, etc.

[0021] Preferably, based on the total molar amount of the diol, branched alcohol, and allyl alcohol being 100%, the molar amount of allyl alcohol is 25% to 60%, for example, 25%, 30%, 33%, 35%, 40%, 45%, 50%, 54%, 55%, 60%, etc., and more preferably 30% to 55%. Allyl alcohol acts as a capping agent, allowing the allyl group to be incorporated into the polyester chain segment as an allyl ester structure.

[0022] Preferably, the raw materials for preparing the oligomeric aliphatic polyester polyallylic compound also include an esterification catalyst.

[0023] Preferably, the esterification catalyst comprises tetrabutyl titanate.

[0024] Preferably, the amount of the esterification catalyst is 0.03% to 0.1%, for example, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, etc., based on the total mass of the dicarboxylic acid, diol, branched alcohol, and allyl alcohol as 100%.

[0025] Preferably, the oligomeric aliphatic polyester polyallylic compound is prepared by the following method: A diacid, a diol, and a branched alcohol are mixed, and then an optional esterification catalyst is added to carry out an esterification reaction to obtain an oligo-aliphatic polyester intermediate containing multiple end groups or branching sites. Then, the temperature is lowered, allyl alcohol is added, and the reaction continues to allow allyl groups to be incorporated into the polyester chain segment in the form of allyl esters. After the reaction continues until the acid value of the product reaches the target range, unreacted small molecules are removed under reduced pressure to obtain the oligo-aliphatic polyester polyallyl compound.

[0026] Preferably, the esterification reaction is carried out under the protection of an inert gas.

[0027] Preferably, the inert gas includes nitrogen.

[0028] Preferably, the temperature of the esterification reaction is 170 to 220°C, such as 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, etc.

[0029] Preferably, the esterification reaction takes 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and more preferably 3 to 5 hours.

[0030] Preferably, the cooling is to a temperature of 140-180°C, such as 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, etc.

[0031] Preferably, the acid value of the product after the reaction reaches the target range, specifically: the acid value of the product after the reaction is 2 to 20 mg KOH / g, for example, 2 mg KOH / g, 4 mg KOH / g, 5 mg KOH / g, 6 mg KOH / g, 8 mg KOH / g, 10 mg KOH / g, 12 mg KOH / g, 14 mg KOH / g, 15 mg KOH / g, 16 mg KOH / g, 18 mg KOH / g, 20 mg KOH / g, etc.

[0032] In this invention, the acid value of the grafting monomer can be tested with reference to GB / T 2895.

[0033] Preferably, the average number of allyl groups in the oligoaliphatic polyester polyallyl compound is 2 to 4 per molecule, for example, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.1, 3.2, 3.4, 3.5, 3.6, 3.8, or 4 per molecule. Furthermore, the oligoaliphatic polyester polyallyl compound also possesses flexible aliphatic polyester segments. The polyallyl groups provide free radical reaction sites, while the polyester segments provide flexibility and polarity, enabling the oligoaliphatic polyester polyallyl compound to simultaneously aid grafting and improve the flexibility of the adhesive layer.

[0034] Preferably, the number average molecular weight (Mn) of the oligomeric aliphatic polyester polyallyl compound is 500 to 3000, such as 500, 600, 800, 1000, 1200, 1400, 1500, 1600, 1800, 2000, 2200, 2400, 2500, 2600, 2800, 3000, etc., and more preferably 800 to 2000.

[0035] Preferably, the acid value of the oligomeric aliphatic polyester polyallyl compound is 2 to 20 mg KOH / g, such as 2 mg KOH / g, 4 mg KOH / g, 5 mg KOH / g, 6 mg KOH / g, 8 mg KOH / g, 10 mg KOH / g, 12 mg KOH / g, 14 mg KOH / g, 15 mg KOH / g, 16 mg KOH / g, 18 mg KOH / g, 20 mg KOH / g, etc., and more preferably 5 to 15 mg KOH / g.

[0036] Preferably, the glass transition temperature (Tg) of the oligomeric aliphatic polyester polyallyl compound is -50℃ to 20℃, for example -50℃, -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, 20℃, etc.

[0037] Preferably, the free radical initiator comprises dicumyl peroxide (DCP).

[0038] Preferably, the antioxidant includes hindered phenolic antioxidants and / or phosphite antioxidants, and more preferably a combination of the two, such as a 1010 / 168 combination system.

[0039] In a second aspect, the present invention provides a method for preparing a polypropylene-grafted maleic anhydride material as described in the first aspect, the method comprising the following steps: (1) Polypropylene, maleic anhydride, free radical initiator and antioxidant are mixed to obtain a premix; (2) The premix is ​​added to a twin-screw extruder, and then the grafting monomer is added. The material completes melt mixing, free radical grafting reaction and devolatilization in the twin screw. It is then extruded, cooled and pelletized to obtain the polypropylene grafted maleic anhydride material.

[0040] Preferably, the mixing in step (1) is carried out in a high-speed mixer.

[0041] Preferably, step (2) of adding the premix to the twin-screw extruder specifically includes: adding the premix to the twin-screw extruder through the main feed port.

[0042] Preferably, the method of adding the grafting monomer in step (2) includes adding it via a liquid metering pump. This is because the grafting monomer has a high viscosity, so adding it to the system via a liquid metering pump after the PP has basically melted is beneficial for dispersion and reaction.

[0043] Preferably, the parameters of the twin-screw extruder are set as follows: the temperature of zone 15 is set to: 0℃ / 40℃ / 80℃ / 160℃ / 180℃ / 180℃ / 180℃ / 190℃ / 190℃ / 190℃ / 195℃ / 195℃ / 190℃ / 190℃; the screw speed is 200~300rpm; a bipolar vacuum devolatilization is set in the rear section to remove unreacted MAH, small molecule by-products and volatiles; and the length-to-diameter ratio of the screw L / D is ≥48, for example, 48, 50, 52, etc.

[0044] Thirdly, the present invention provides the application of the polypropylene grafted maleic anhydride material as described in the first aspect in a composite structure formed by polypropylene and any one of a metal substrate, a metal oxide layer, a polar coating, and a polar resin.

[0045] Preferably, the metal substrate includes an aluminum plate or aluminum foil.

[0046] Preferably, the polypropylene grafted maleic anhydride material serves as a bonding layer or compatibility layer in the composite structure.

[0047] That is, the polypropylene-grafted maleic anhydride material provided by the present invention can be used as an adhesive layer or a compatibility layer in the following composite structures: PP / aluminum composite structure; PP / aluminum foil composite film; PP / metal oxide layer composite structure; Composite bonding between PP and polar coatings or polar resins.

[0048] The aforementioned composite structures are used in fields such as packaging, building materials, automotive lightweighting, and home appliance composite panels.

[0049] Preferably, the polypropylene-grafted maleic anhydride material is used as an adhesive layer between the polypropylene and the aluminum substrate.

[0050] Compared with the prior art, the present invention has the following beneficial effects: The polypropylene-grafted maleic anhydride material provided by this invention improves the MAH grafting level (MAH grafting rate: 0.58%~0.93%) by introducing specific grafting aid monomers, reducing the degradation risk caused by simply increasing MAH and free radical initiators. Furthermore, when this polypropylene-grafted maleic anhydride material is used in the bonding layer between polypropylene and metal substrate, it can improve the peel strength between polypropylene and metal substrate, increase the lap shear strength, and improve the adhesion retention rate after bending. Detailed Implementation

[0051] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0052] Preparation Example 1 This preparation example provides an oligomeric aliphatic polyester-type polyallylic compound, and the preparation method includes the following steps: Weigh out 8936.75 g (61 mol) of adipic acid, 5300.57 g (26 mol) of sebacic acid, 3028.03 g (34 mol) of 1,4-butanediol, 1499.76 g (14 mol) of neopentyl glycol, 1610.16 g (12 mol) of trimethylolpropane, and 2323.20 g (40 mol) of allyl alcohol. That is, in this preparation example, the molar ratio of dicarboxylic acid to diol is 1.82:1; based on the total molar amount of diol, branched alcohol, and allyl alcohol being 100%, the molar amount of branched alcohol is 12%, and the molar amount of allyl alcohol is 40%. Adipic acid, sebacic acid, 1,4-butanediol, neopentyl glycol, and trimethylolpropane were sequentially added to a reaction vessel. The mixture was stirred and heated under nitrogen protection to ensure that the materials in the vessel were fully melted and mixed evenly. Subsequently, an esterification catalyst (tetrabutyl titanate) was added. The amount of the esterification catalyst added was 0.05% of the total mass of the diacid, diol, trimethylolpropane, and allyl alcohol, i.e., 11.35 g. The temperature was raised to 210℃ to carry out the esterification reaction, and the water generated by the reaction was continuously collected through a condenser. At this point, the acid value was 135 mg KOH / g.

[0053] (2) Cool the system to 165°C, add allyl alcohol, and continue the reaction until the acid value drops to 9 mg KOH / g. Remove the volatiles under reduced pressure to obtain the oligomeric aliphatic polyester polyallylic compound, which is designated as grafting monomer G-1.

[0054] Preparation Example 2 The only difference between this preparation example and Preparation Example 1 is that the molar ratio of adipic acid to sebacic acid is 6:4, the molar ratio of dicarboxylic acid to diol is 1.66:1, and the acid value of the intermediate in step (1) is 107 mg KOH / g. Based on a total molar amount of 100% for diol, branched alcohol, and allyl alcohol, the molar amount of branched alcohol is 12%, and the molar amount of allyl alcohol is 33%. The total amount of alcohol in this preparation example is 100 mol.

[0055] The product obtained in this preparation example is denoted as grafting monomer G-2.

[0056] Preparation Example 3 The only difference between this preparation example and Preparation Example 1 is that the molar ratio of the dicarboxylic acid to the diol is 3.93:1, and the acid value of the intermediate in step (1) is 188 mg KOH / g; based on the total molar amount of diol, branched alcohol, and allyl alcohol being 100%, the molar amount of branched alcohol is 24%, and the molar amount of allyl alcohol is 54%. The total amount of alcohol in this preparation example is 100 mol.

[0057] The product obtained in this preparation example is denoted as grafting monomer G-3.

[0058] Comparative Preparation Example 1 The only difference between this comparative preparation example and preparation example 1 is that branched alcohol (trimethylolpropane) is not added, the molar ratio of dicarboxylic acid to diol is 1.14:1, and the acid value of the intermediate in step (1) is 66 mg KOH / g; correspondingly, based on the total molar amount of diol and allyl alcohol being 100%, the molar amount of allyl alcohol is 19%. The total amount of alcohol in this comparative preparation example is 100 mol.

[0059] The product obtained in this comparative preparation example is a linear oligoaliphatic polyester allyl ester, denoted as grafting monomer G-C1.

[0060] The products obtained from the above preparation examples and comparative preparation examples were tested using the following methods: (1) Number-average molecular weight Mn: tested using GPC; (2) Average number of allyl groups: The above content of allyl unsaturated structures is a theoretical value based on calculations, which are as follows: N db Theoretically, the number of carbon-carbon double bonds in each oligoaliphatic polyester polyallyl compound molecule, expressed in terms of bonds per molecule. M n Number-average molecular weight of oligomeric aliphatic polyester polyallyl compounds, expressed in g / mol. n A : Molar number of allyl alcohols added; n d Total molar number of diols fed; n t : Number of moles of branched alcohols added; r: molar ratio of dicarboxylic acid to diol; n w The theoretical number of moles of water produced in a condensation polymerization reaction; M a : Average molar mass of the mixed dicarboxylic acids, in g / mol; M d : Average molar mass of the mixed diols, in g / mol; M t Molar mass of branched alcohols, in g / mol; M A Molar mass of allyl alcohol, in g / mol; x i : The mole fraction of the i-th dicarboxylic acid in the mixed dicarboxylic acids; M i : The molar mass of the i-th dicarboxylic acid; y j: The mole fraction of the j-th diol in the mixed diols; M j : The molar mass of the j-th diol; Taking Preparation Example 1 as an example, the calculation method is as follows: 1. Calculate the amount of each substance based on the weight of the input materials. Total amount of diols: n d = m BDO / M BDO + m NPG / M NPG n d = 3028.032 / 90.12 + 1499.760 / 104.15 n d = 33.6 + 14.4 = 48 mol Amount of branched alcohol (trimethylolpropane): n t = m TMP / M TMP = 1610.16 / 134.18 = 12 mol Molecular weight of allyl alcohol: n A = m A / M A = 2323.20 / 58.08 = 40 mol Total amount of dicarboxylic acid: n acid = m AA / M AA + m SA / M SA n acid = 8936.753 / 146.14 + 5300.568 / 202.25 n acid = 61.152 + 26.208 = 87.36 mol Molar ratio of dicarboxylic acid to diol: r = n acid / n d = 87.36 / 48 = 1.82 II. Calculation of the min term 2rn d = 2 × 1.82 × 48 = 174.72 2n d + 3n t + n A = 2 × 48 + 3 × 12 + 40 = 172 min(2rn d ,2n d + 3n t + n A = min(174.72, 172) = 172 III. N db calculate N db = [n A M n ] / [rn d M a + n d M d + n t M t + n A M A - 18.015 × min(2rn d ,2n d + 3n t + n A )] N db = [40 × 1180] / [1.82 × 48 × 162.973 + 48 × 94.329 + 12 ×134.18 + 40 × 58.08 - 18.015 × 172] N db = 47200 / 19599.89 = 2.41 Conclusion: N db ≈ 2.4 double bonds / molecule. This result is the theoretical average calculated based on the feed rate, theoretical water loss, and number-average molecular weight.

[0061] (3) Tg: Differential scanning calorimetry (DSC) was used for testing. The test was conducted under nitrogen atmosphere at a heating and cooling rate of 10℃ / min. The glass transition temperature Tg was determined by taking the second heating curve.

[0062] The test results are shown in Table 1.

[0063] Table 1 Unless otherwise specified, the information on some raw materials used in the following embodiments and comparative examples of the present invention is shown in Table 2 below: Table 2 Example 1 This embodiment provides a polypropylene-grafted maleic anhydride material. The specific raw materials and amounts (parts by weight) used in the preparation of the polypropylene-grafted maleic anhydride material are shown in Table 3.

[0064] The polypropylene-grafted maleic anhydride material is prepared by melt grafting using a twin-screw extruder, specifically including the following steps: (1) PP, MAH, DCP and antioxidant are premixed evenly in a high-speed mixer to obtain a premix; (2) The premix is ​​fed into the twin-screw extruder through the main feed port; (3) After the PP has basically melted, the grafting monomer is added through a liquid metering pump; (4) The material undergoes melt mixing, free radical grafting reaction and devolatilization in a twin-screw extruder, followed by extrusion; (5) The extrudate is cooled and pelletized to obtain the polypropylene grafted maleic anhydride material.

[0065] The parameters of the twin-screw extruder are set as follows: the temperature of zone 15 is set to 0℃ / 40℃ / 80℃ / 160℃ / 180℃ / 180℃ / 180℃ / 190℃ / 190℃ / 190℃ / 195℃ / 195℃ / 190℃ / 190℃, the screw speed is set to 250 rpm, and the rear section is equipped with bipolar vacuum devolatilization to remove unreacted MAH, small molecule by-products and volatiles.

[0066] Examples 2-7, Comparative Examples 1-4 The only difference from Example 1 is that the specific raw materials and / or amounts (parts by weight) used are different, as shown in Table 3.

[0067] Table 3 The performance of the polypropylene grafted maleic anhydride materials provided in the embodiments and comparative examples of the present invention was tested using the following methods: (1) MAH grafting rate: The solvent extraction-acid-base titration method was used for testing; before the test, the product was fully purified, for example, by dissolving in hot xylene or by extraction with acetone, to remove free MAH, unreacted auxiliaries and oligomers; (2) MFR: Refer to GB / T 3682 for testing to determine the change in PP molecular weight before and after the reaction.

[0068] The polypropylene grafted maleic anhydride materials provided in the embodiments and comparative examples of the present invention were used to prepare PP film / adhesive layer / aluminum foil composite samples and PP board / adhesive layer / aluminum board composite samples, as detailed below: A polypropylene grafted with maleic anhydride material was placed between a PP film and an aluminum foil, and then pressed at 200℃ and 0.5MPa for 60s to obtain a PP film / adhesive layer / aluminum foil composite sample with a width of 15mm, wherein the thickness of the adhesive layer is about 100μm. Polypropylene grafted with maleic anhydride was placed between a PP plate and an aluminum plate, and then pressed at 200℃ and 0.5MPa for 60s to obtain a PP plate / adhesive layer / aluminum plate composite sample, wherein the thickness of the adhesive layer is about 100μm.

[0069] The composite sample prepared above was then tested using the following methods: (1) 180° peel strength: The PP film / adhesive layer / aluminum foil composite sample was tested according to GB / T 2790; (2) Overlap shear strength: The composite specimens of PP board / adhesive layer / aluminum plate were tested in accordance with GB / T 7124; (3) Peel strength retention rate after bending: The PP film / adhesive layer / aluminum foil composite sample was tested for 180° peel strength according to GB / T 2790. Then, the PP film / adhesive layer / aluminum foil composite sample was bent at 180° 5 times and its 180° peel strength was tested again, and the retention rate was calculated. Peel strength retention rate after bending = peel strength after bending / initial peel strength × 100%.

[0070] The performance test results are shown in Table 4.

[0071] Table 4 As can be seen from Table 4, the polypropylene grafted maleic anhydride materials provided in the embodiments of the present invention all have high MAH grafting rates (0.58% to 0.93%) and suitable MFRs (21 to 34 g / 10 min). Furthermore, when used as an adhesive layer for PP and aluminum, the composite samples obtained all have high 180° peel strength (9.5 to 14.6 N / 15 mm), lap shear strength (2 to 3.2 MPa), and high peel retention rate after bending (55% to 84%, preferably 70% to 84%).

[0072] In Example 6, a higher amount of G-3 allyl groups was used, resulting in a higher grafting rate of the polypropylene-grafted maleic anhydride material. However, the retention rate of the peel strength after bending of the composite sample was lower than that of the examples using the G-1 and G-2 systems (specifically Examples 2 and 3). In Example 7, after further increasing the amount of G-3, the grafting rate reached 0.93%, but the 180° peel strength and the retention rate of the peel strength after bending of the composite sample decreased. In other words, this invention achieves a balance between grafting rate, flowability, and adhesive properties by controlling the amount of allyl groups, the molecular weight of the grafting monomer, and its addition.

[0073] Compared with Example 2, Comparative Example 1 did not add grafting aid monomers, and the MAH grafting rate was significantly reduced. This indicates that the allyl structure in the grafting aid monomers of the present invention has a promoting effect on the grafting reaction.

[0074] The peel strength of the composite sample made from the polypropylene-grafted maleic anhydride material provided in Comparative Example 1 was 5.2 N / 15 mm, while the peel strength of the composite sample made from the polypropylene-grafted maleic anhydride material provided in Example 2 was increased to 12.2 N / 15 mm. This indicates that the introduction of MAH polar groups and polyester ester groups in this invention is beneficial to enhancing the wetting and interfacial interaction of the adhesive layer on the aluminum surface oxide layer.

[0075] The lap shear strength of the composite sample made from the polypropylene-grafted maleic anhydride material provided in Comparative Example 1 was 1.2 MPa, while the lap shear strength of the composite sample made from the polypropylene-grafted maleic anhydride material provided in Example 2 was increased to 2.6 MPa. This indicates that the adhesive layer obtained by the present invention has both polarity and flexibility, which is beneficial to improving the shear bearing capacity of the PP / aluminum composite structure.

[0076] Comparative Example 2 increased the grafting rate to 0.51% by increasing the dosage of MAH and DCP, but the MFR increased to 48 g / 10 min, indicating significant PP degradation. In contrast, Example 2 of this invention, under conditions of milder MAH and DCP dosages, achieved a grafting rate of 0.72% and an MFR of 25 g / 10 min, demonstrating that the grafting aid monomers of this invention improve the grafting rate while better maintaining melt properties.

[0077] Compared with Examples 2 and 3, Comparative Example 3, which uses TAIC as the grafting monomer, showed a post-bending peel strength retention rate of only 48%, while the post-bending peel strength retention rate of the composite sample in Example 2 was 80%, and the post-bending peel strength retention rate of the composite sample in Example 3 was 84%. This indicates that the polyester segments in the grafting monomer provided by the present invention are flexible, which can alleviate the stress concentration at the PP / aluminum interface and improve the interface stability after bending.

[0078] Compared with Example 2, Comparative Example 4 used G-C1 as the grafting monomer, and the grafting rate of polypropylene grafted with maleic anhydride material decreased significantly. In addition, the 180° peel strength, lap shear strength and peel retention rate after bending of the composite sample all decreased.

[0079] The applicant declares that this invention illustrates the polypropylene-grafted maleic anhydride material, its preparation method, and its application through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A polypropylene-grafted maleic anhydride material, characterized in that, The raw materials for preparing the polypropylene-grafted maleic anhydride material include the following components by weight: 100 parts of polypropylene; 0.5 to 4 parts of maleic anhydride; 0.1–3 parts of grafting agent monomer; 0.02–0.3 parts of free radical initiator; Antioxidant 0.05–0.5 parts; The grafting monomers include oligoaliphatic polyester polyallyl compounds. The raw materials for preparing the oligomeric aliphatic polyester polyallylic compound include the following components: dicarboxylic acid, diol, branched alcohol and allyl alcohol.

2. The polypropylene-grafted maleic anhydride material according to claim 1, characterized in that, The dicarboxylic acid includes any one or a combination of at least two of adipic acid, sebacic acid, azelaic acid, and dodecanoic acid, preferably a combination of adipic acid and sebacic acid, and more preferably a combination of adipic acid and sebacic acid in a molar ratio of (6-9):(1-4). Preferably, the diol comprises any one or a combination of at least two of 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and diethylene glycol, preferably a combination of 1,4-butanediol and neopentyl glycol, and more preferably a combination of 1,4-butanediol and neopentyl glycol in a molar ratio of (5-8):(2-5). Preferably, the molar ratio of the dicarboxylic acid to the diol is (1.3–4.2):1, more preferably (1.5–2.8):1; Preferably, the branched alcohol comprises trimethylolpropane and / or pentaerythritol; Preferably, based on the total molar amount of the diol, branched alcohol, and allyl alcohol being 100%, the molar amount of the branched alcohol is 5% to 25%, more preferably 8% to 18%; Preferably, based on the total molar amount of the diol, branched alcohol, and allyl alcohol being 100%, the molar amount of allyl alcohol is 25% to 60%, more preferably 30% to 55%.

3. The polypropylene-grafted maleic anhydride material according to claim 1 or 2, characterized in that, The raw materials for preparing the oligo-aliphatic polyester polyallylic compound also include an esterification catalyst; Preferably, the esterification catalyst comprises tetrabutyl titanate; Preferably, the amount of the esterification catalyst is 0.03% to 0.1% based on the total mass of the dicarboxylic acid, diol, branched alcohol, and allyl alcohol as 100%.

4. The polypropylene-grafted maleic anhydride material according to any one of claims 1-3, characterized in that, The oligomeric aliphatic polyester polyallyl compound was prepared by the following method: A dicarboxylic acid, a diol, and a branched alcohol are mixed, and then an optional esterification catalyst is added to carry out an esterification reaction. After cooling, allyl alcohol is added, and the reaction continues until the acid value of the product reaches the target range. Unreacted small molecules are removed under reduced pressure to obtain the oligomeric aliphatic polyester polyallylic compound.

5. The polypropylene-grafted maleic anhydride material according to claim 4, characterized in that, The esterification reaction was carried out under inert gas protection; Preferably, the inert gas includes nitrogen; Preferably, the temperature of the esterification reaction is 170–220°C; Preferably, the esterification reaction takes 2 to 6 hours, more preferably 3 to 5 hours; Preferably, the cooling is to reduce the temperature to 140–180°C; Preferably, the acid value of the product after the reaction reaches the target range, specifically: the acid value of the product after the reaction is 2-20 mg KOH / g.

6. The polypropylene-grafted maleic anhydride material according to any one of claims 1-5, characterized in that, The average number of allyl groups in the oligomeric aliphatic polyester polyallylic compound is 2 to 4 per molecule; Preferably, the number average molecular weight of the oligomeric aliphatic polyester polyallyl compound is 500-3000, more preferably 800-2000; Preferably, the acid value of the oligomeric aliphatic polyester polyallyl compound is 2-20 mg KOH / g, more preferably 5-15 mg KOH / g; Preferably, the glass transition temperature of the oligomeric aliphatic polyester polyallylic compound is -50°C to 20°C.

7. The polypropylene-grafted maleic anhydride material according to any one of claims 1-6, characterized in that, The free radical initiator includes dicumyl peroxide; Preferably, the antioxidant includes hindered phenolic antioxidants and / or phosphite antioxidants.

8. A method for preparing a polypropylene-grafted maleic anhydride material as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Polypropylene, maleic anhydride, free radical initiator and antioxidant are mixed to obtain a premix; (2) The premix is ​​added to a twin-screw extruder, then the grafting monomer is added, and the mixture is extruded, cooled, and pelletized to obtain the polypropylene grafted maleic anhydride material.

9. The preparation method according to claim 8, characterized in that, The mixing in step (1) is carried out in a high-speed mixer; Preferably, step (2) of adding the premix to the twin-screw extruder specifically includes: adding the premix to the twin-screw extruder through the main feed port; Preferably, the method of adding the grafting agent monomer in step (2) includes adding it by means of a liquid metering pump.

10. The application of a polypropylene grafted maleic anhydride material as described in any one of claims 1-7 in a composite structure formed by polypropylene with any one of a metal substrate, a metal oxide layer, a polar coating, and a polar resin; Preferably, the metal substrate comprises an aluminum plate or aluminum foil; Preferably, the polypropylene grafted maleic anhydride material serves as a bonding layer or compatibility layer in the composite structure. Preferably, the polypropylene-grafted maleic anhydride material is used as an adhesive layer between the polypropylene and the aluminum substrate.

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